piperidines and Long-QT-Syndrome

The human ether-à-go-go related gene (HERG) encodes the alpha subunit of Kv11.1, which is a voltage-gated K

Topics: Antineoplastic Agents; Apoptosis; Benzimidazoles; Carcinogenesis; Cell Movement; Cell Proliferation; Epigenesis, Genetic; ERG1 Potassium Channel; Fluoxetine; Gene Expression Regulation, Neoplastic; Humans; Integrin beta1; Long QT Syndrome; Membrane Potentials; Molecular Docking Simulation; Mutation; Myocytes, Cardiac; Neoplasms; Piperidines; Protein Conformation, alpha-Helical; Protein Interaction Mapping; Protein Structure, Quaternary; Pyridines; Signal Transduction; STAT1 Transcription Factor; Sulfanilamides

A meta-analysis of published data was conducted to investigate the overall risks of hypertension and QTc prolongation in patients with advanced non-small cell lung cancer (NSCLC) who were receiving vandetanib.. A computerized search through electronic databases, including PubMed and Embase (until Dec 2014), was performed to obtain eligible randomized controlled trials (RCTs) that compared hypertension and/or QTc prolongation profile of vandetanib alone or plus chemotherapy with control groups (placebo, single targeted therapy, chemotherapy, or a combination of them) in patients with advanced NSCLC. The outcome measures were the overall risks of hypertension and QTc prolongation. Relative risk (RR) and 95% confidence interval (CI) were calculated and pooled using a random effects model.. A total of nine RCTs, which involved 4813 patients, were enrolled in the present study. A significant increase in risk was observed for all-grade hypertension (RR 5.58; 95% CI 4.16 to 7.48; P < 0.00001) and grade ≥3 hypertension (RR 4.79; 95% CI 2.31 to 9.93; P < 0.0001) in advanced NSCLC patients who were receiving vandetanib compared with the controls. Moreover, vandetanib significantly prolonged all-grade QTc interval (RR 7.90; 95% CI 4.03 to 15.50; P < 0.00001) and grade ≥3 QTc interval (RR 3.12; 95% CI 1.01 to 9.63; P = 0.05).. Current evidence showed that significant risks in developing hypertension and QTc prolongation exist in advanced NSCLC patients who were receiving vandetanib. Thus, appropriate monitoring and management of these events are recommended.

Topics: Antineoplastic Agents; Carcinoma, Non-Small-Cell Lung; Humans; Hypertension; Long QT Syndrome; Lung Neoplasms; Piperidines; Quinazolines; Randomized Controlled Trials as Topic; Risk

Iloperidone is a new second-generation (atypical) antipsychotic medication approved for the treatment of schizophrenia in adults. The target dose of 6 mg bid can be achieved in 4 days, with titration recommended to minimize postural hypotension. The maximum recommended dose is 12 mg bid. The tolerability profile of iloperidone is noteworthy in terms of modest weight gain, no medically important changes in lipid and glucose levels, little in the way of prolactin elevation, and absence of extrapyramidal side effects, including akathisia. However, iloperidone can prolong the QTc interval on electrocardiogram. Iloperidone may be best suited for patients who are sensitive to akathisia or who are unable to tolerate the sedation and weight gain that can occur more frequently with other antipsychotics.

Topics: Antipsychotic Agents; Electrocardiography; Heart Rate; Humans; Isoxazoles; Long QT Syndrome; Piperidines; Schizophrenia; Treatment Outcome; Weight Gain

Iloperidone, a mixed D2/5-HT2 antagonist, is currently in clinical development for the treatment of schizophrenia. This article assesses the short-term safety of iloperidone using a pooled analysis of 3 phase 2, short-term acute schizophrenia studies conducted between 1998 and 2002 (N = 1943). Patients exposed to 3 dose ranges of iloperidone, another antipsychotic, or placebo were compared on rates of serious adverse events (SAEs), adverse events (AEs), extrapyramidal symptoms, akathisia, prolactin, weight and metabolic parameters, QTc, and other standard safety parameters. The most common treatment-related AEs observed with iloperidone were dizziness, headache, dry mouth, nausea, and insomnia. Discontinuation due to AEs was 4.8% for iloperidone, 7.6% for haloperidol, 6.2% for risperidone, and 4.8% for placebo. Iloperidone groups showed better overall performance on the Extrapyramidal Symptom Rating Scale and Barnes Akathisia Scale than risperidone or haloperidol groups. Patients taking iloperidone experienced a mild weight increase (range, 1.5-2.1 kg) similar to that of risperidone (1.5 kg), whereas those on haloperidol and placebo showed mean weight loss (-0.1 kg and -0.3 kg, respectively). QTc interval significantly increased across all iloperidone groups (least squares mean change from baseline to end point, 2.9-9.1 msec) and for haloperidol (5.0 msec). No significant QTc changes occurred in the risperidone or placebo groups. Iloperidone was associated with no change from baseline in total cholesterol, mild elevation in serum glucose, and slight decrease in triglycerides. Prolactin levels decreased with iloperidone and increased significantly with risperidone and haloperidol. These short-term trials suggest that iloperidone has a reassuring safety profile in many of the areas that are of potential concern, including relatively low dropout rates because of AEs, low extrapyramidal symptoms, akathisia, and prolactin elevation, and a modest short-term effect on weight gain.

Topics: Adolescent; Adult; Aged; Akathisia, Drug-Induced; Antipsychotic Agents; Basal Ganglia Diseases; Double-Blind Method; Female; Humans; Isoxazoles; Long QT Syndrome; Male; Middle Aged; Patient Dropouts; Piperidines; Prospective Studies; Psychotic Disorders; Randomized Controlled Trials as Topic; Schizophrenia; Weight Gain

Topics: Animals; Butyrophenones; Histamine H1 Antagonists; Humans; Long QT Syndrome; Piperidines; Torsades de Pointes

Topics: Anti-Ulcer Agents; Arrhythmias, Cardiac; Cisapride; Humans; Long QT Syndrome; Piperidines; Risk Factors

Topics: Administration, Oral; Animals; Dose-Response Relationship, Drug; Double-Blind Method; Female; Healthy Volunteers; Humans; Long QT Syndrome; Male; Mice; Mice, Inbred DBA; Oxazoles; Piperidines; Receptors, CXCR; Sex Characteristics

Atogepant is a selective, oral calcitonin gene-related peptide receptor antagonist in development for preventive treatment of migraine. This randomized, double-blind, phase 1 crossover study evaluated the cardiac repolarization effect of a single supratherapeutic (300 mg) atogepant dose vs placebo in healthy adults. Moxifloxacin 400 mg was the open-label active control. The primary end point was a change from baseline in Fridericia-corrected QT intervals (ΔQTcF). Sixty participants were randomized to atogepant 300 mg, placebo, and moxifloxacin; 59 (98.3%) completed all interventions. Assay sensitivity was confirmed: lower 90% confidence interval limit for QTcF interval change from baseline (ΔΔQTcF) for moxifloxacin was >5 millisecond vs placebo at prespecified 2-, 3-, and 4-hour time points. Following single-dose atogepant 300 mg, mean atogepant ΔΔQTcF and upper 90% confidence interval limits were lower than the 10-millisecond threshold at all time points. Atogepant mean peak plasma concentration was 3197 ng/mL, area under the concentration-time curve from time 0 to time t was 16 640 ng • h/mL, area under the concentration-time curve from time 0 to 24 hours was 16 607 ng • h/mL, and median time to peak plasma concentration was 2.1 hours. The incidence of adverse events was low; no serious adverse events or elevations of liver enzymes were reported. Overall, a single supratherapeutic dose of atogepant was safe and did not impact cardiac repolarization in healthy participants.

Topics: Adolescent; Adult; Area Under Curve; Calcitonin Gene-Related Peptide Receptor Antagonists; Cross-Over Studies; Double-Blind Method; Electrocardiography; Female; Humans; Long QT Syndrome; Male; Moxifloxacin; Piperidines; Pyridines; Pyrroles; Spiro Compounds; Young Adult

Topics: Administration, Oral; Adolescent; Adult; Agammaglobulinaemia Tyrosine Kinase; Dose-Response Relationship, Drug; Double-Blind Method; Electrocardiography; Female; Half-Life; Healthy Volunteers; Heart Rate; Humans; Long QT Syndrome; Male; Middle Aged; Piperidines; Pyrimidines; Young Adult

Topics: Administration, Oral; Adult; Anti-Bacterial Agents; Arrhythmias, Cardiac; Asian People; Benzamides; Case-Control Studies; Cisapride; Cross-Over Studies; Double-Blind Method; Electrocardiography; Female; Humans; Indoles; Irritable Bowel Syndrome; Long QT Syndrome; Male; Morpholines; Moxifloxacin; Piperidines; Placebos; Serotonin 5-HT4 Receptor Agonists; Serotonin Receptor Agonists

This thorough QT (TQT) study evaluated the effect of zanubrutinib on electrocardiogram (ECG) parameters by using concentration-QTc (C-QTc) analysis as the primary analysis for this study. Part A of the study determined the safety and tolerability of a single supratherapeutic dose of zanubrutinib (480 mg) in healthy volunteers. Part B was a randomized, blinded, placebo-controlled and positive-controlled, four-way crossover, TQT study of single therapeutic (160 mg) and supratherapeutic (480 mg) doses of zanubrutinib, placebo, and open-label moxifloxacin 400 mg. Thirty-two participants received at least 1 dose of zanubrutinib, and 26 participants completed all 4 periods. Zanubrutinib did not have any effect on heart rate or cardiac conduction (pulse rate, QRS interval, or T-wave morphology) and was generally well-tolerated. Using C-QTc analysis, the predicted placebo-corrected change-from-baseline QT interval using Fridericia's formula (ΔΔQTcF) was -3.4 msec (90% confidence interval: -4.9 to -1.9 msec) at peak concentrations of the 480 mg dose. A QT effect (ΔΔQTcF) exceeding 10 msec could be excluded within the observed concentration range at 160 and 480 mg doses. Assay sensitivity was established by moxifloxacin with 90% lower bound exceeding 5 msec. Implementing a C-QTc analysis prospectively in this TQT study resulted in a substantially smaller sample size to maintain a similar study power as shown in the traditional time-point analysis. A single 160-mg or 480-mg zanubrutinib dose did not prolong the QTc interval or have any other clinically relevant effects on ECG parameters.

Topics: Adolescent; Adult; Agammaglobulinaemia Tyrosine Kinase; Cross-Over Studies; Dose-Response Relationship, Drug; Double-Blind Method; Electrocardiography; Female; Healthy Volunteers; Heart Rate; Humans; Long QT Syndrome; Male; Middle Aged; Piperidines; Protein Kinase Inhibitors; Pyrazoles; Pyrimidines; Young Adult

Anticancer drugs may cause cardiovascular toxicities, including QT interval prolongation. Niraparib, a potent and selective once-daily oral poly (ADP-ribose) polymerase inhibitor, is approved as a maintenance therapy in platinum-sensitive recurrent epithelial ovarian, fallopian tube, and primary peritoneal cancer (EOC). Here, we present the effects of niraparib on cardiac repolarization, and the correlation between changes in baseline QT interval corrected by Fridericia's formula (ΔQTcF) and niraparib plasma concentrations.. Patients with EOC from the NOVA study (subset of n = 15), the food effect NOVA substudy (n = 17), and a QTc substudy (n = 26) underwent intensive electrocardiographic (ECG) monitoring that included triplicate ECG testing on Day 1 at baseline (predose) and at 1, 1.5, 2, 3, 4, 6, and 8 h postdose concurrent with time-matched blood sampling for determination of niraparib plasma concentrations. All patients received once-daily 300-mg niraparib until disease progression or toxicity.. Across the 3 substudies, the upper limit of the two-sided 90% confidence interval (CI) of ΔQTcF was ≤ 10 ms at every postdose timepoint, with a maximum upper limit of 4.3 ms, which indicates no clinically meaningful effect on QTc prolongation. No statistically significant relationship between ΔQTcF and niraparib plasma concentration was observed (estimated slope: 0.0049; 95% CI: - 0.0020, 0.0117; P = 0.164). There were no clinically relevant changes in other ECG parameters that could be attributable to niraparib.. Niraparib administration at the recommended daily dose of 300 mg for EOC is not associated with clinically relevant alteration of ECGs, including QTc prolongation.

Topics: Aged; Carcinoma, Ovarian Epithelial; Cardiotoxicity; Double-Blind Method; Electrocardiography; Fallopian Tube Neoplasms; Female; Humans; Indazoles; Long QT Syndrome; Middle Aged; Peritoneal Neoplasms; Piperidines; Poly(ADP-ribose) Polymerase Inhibitors

Alectinib, a central nervous system (CNS)-active ALK inhibitor, has demonstrated efficacy and safety in ALK+ non-small-cell lung cancer that has progressed following crizotinib treatment. Other ALK inhibitors have shown concentration-dependent QTc prolongation and treatment-related bradycardia. Therefore, this analysis evaluated alectinib safety in terms of electrophysiologic parameters.. Intensive triplicate centrally read electrocardiogram (ECG) and matched pharmacokinetic data were collected across two alectinib single-arm trials. Analysis of QTcF included central tendency analysis [mean changes from baseline with one-sided upper 95% confidence intervals (CIs)], categorical analyses, and relationship between change in QTcF and alectinib plasma concentrations. Alectinib effects on other ECG parameters (heart rate, PR interval and QRS duration) were also evaluated.. Alectinib did not cause a clinically relevant change in QTcF. The maximum mean QTcF change from baseline was 5.3 ms observed pre-dose at week 2. The upper one-sided 95% CI was <10 ms at all time points. There was no relevant relationship between change in QTcF and alectinib plasma concentrations. Alectinib treatment resulted in a generally asymptomatic exposure-dependent decrease in mean heart rate of ~11 to 13 beats per minute at week 2. No clinically relevant effects were seen on other ECG parameters. Approximately 5% of patients reported cardiac adverse events of bradycardia or sinus bradycardia; however, these were all grade 1-2.. Alectinib does not prolong the QTc interval or cause changes in cardiac function to a clinically relevant extent, with the exception of a decrease in heart rate which was generally asymptomatic.

Topics: Algorithms; Anaplastic Lymphoma Kinase; Bradycardia; Carbazoles; Carcinoma, Non-Small-Cell Lung; Dose-Response Relationship, Drug; Electrocardiography; Heart Function Tests; Heart Rate; Humans; Long QT Syndrome; Lung Neoplasms; Monitoring, Physiologic; Piperidines; Receptor Protein-Tyrosine Kinases

The objective of the present study was to compare the effects of pitolisant on QTcF interval in a single ascending dose (SAD) study and a thorough QT (TQT) study.. The SAD study at three dose levels of pitolisant enrolled 24 males and the TQT study at two dose levels 25 males. Both studies intensively monitored ECGs and pitolisant exposure. Effect on QTcF interval was analysed by Intersection Union Test (IUT) and by exposure-response (ER) analysis. Results from the two studies were compared.. In both studies, moxifloxacin effect established assay sensitivity. IUT analysis revealed comparable pitolisant-induced maximum mean (90 % confidence interval (CI)) placebo-corrected increase from baseline (ΔΔQTcF) in both the studies, being 13.3 (8.1; 18.5) ms at 200-mg and 9.9 (4.7; 15.1) ms at 240-mg doses in SAD study and 5.27 (2.35; 8.20) ms at 120-mg dose in TQT study. ER analysis revealed that ER slopes in SAD and TQT studies were comparable and significantly positive (0.031 vs 0.027 ms/ng/mL, respectively). At geometric mean concentrations, bootstrap predicted ΔΔQTcF (90 % CI) were 9.23 (4.68; 14.4) ms at 279 ng/mL (240-mg dose) in the SAD study and 4.97 (3.42; 8.19) ms at 156 ng/mL (120-mg dose) in the TQT study.. Pitolisant lacked an effect of regulatory concern on QTc interval in both the studies, however analysed, suggesting that the results from the SAD study could have mitigated the need for a TQT study. Our findings add to the growing evidence that intensive ECG monitoring in early phase clinical studies can replace a TQT study.

Topics: Adult; Clinical Studies as Topic; Cross-Over Studies; Dose-Response Relationship, Drug; Double-Blind Method; Electrocardiography; Female; Heart Rate; Histamine Agonists; Histamine H3 Antagonists; Humans; Long QT Syndrome; Male; Middle Aged; Piperidines; Young Adult

Topics: Adolescent; Adult; Aged; Analgesics, Opioid; Anesthesia; Anesthetics, Inhalation; Arrhythmias, Cardiac; Double-Blind Method; Electrocardiography; Female; Humans; Hypotension, Controlled; Long QT Syndrome; Male; Methyl Ethers; Middle Aged; Nitroglycerin; Piperidines; Prospective Studies; Remifentanil; Rhinoplasty; Sevoflurane; Vasodilator Agents; Young Adult

The potential for iloperidone, a D2/5-HT2A antipsychotic, to affect the heart rate-corrected QT interval (QTc) was assessed in the absence and presence of metabolic inhibitors in a randomized, open-label, multicenter study. QT interval prolongation by medications, including both conventional and atypical antipsychotic drugs, can predispose patients to cardiac arrhythmias and result in sudden death. Adults with schizophrenia or schizoaffective disorder and normal electrocardiograms at baseline (N = 188) were randomized 1:1:1:1:1 to iloperidone, 8 mg twice daily (BID), 12 mg BID, 24 mg once daily (QD); quetiapine, 375 mg BID; or ziprasidone, 80 mg BID during period 1 (no metabolic inhibitors present). Iloperidone BID produced mean changes in QTc Fridericia correction (QTcF) interval (8.5-9.0 milliseconds [ms]) similar to those produced by ziprasidone (9.6 ms) and higher than those produced by quetiapine (1.3 ms). Iloperidone, 24 mg QD, produced a mean QTcF change of 15.4 ms. Coadministration of metabolic inhibitors with iloperidone during periods 2 (paroxetine) and 3 (paroxetine and ketoconazole) resulted in greater increases in the QTc interval. Increased QTc was observed in individuals with specific cytochrome P450 2D6 polymorphisms. Up to 10% of patients on iloperidone experienced QTc intervals of 60 ms or longer in the presence of metabolic inhibition and QD dosing. However, no patients experienced QTc changes of clinical concern (QTc ≥ 500 ms). The most common adverse events with iloperidone were headache, anxiety, and dyspepsia. The only cardiovascular adverse events with iloperidone were non-concentration-dependent tachycardia that was mild in most patients and did not lead to further sequelae. Pharmacogenetics and recommendations are discussed.

Topics: Adolescent; Adult; Aged; Antipsychotic Agents; Cytochrome P-450 CYP2D6; Cytochrome P-450 CYP2D6 Inhibitors; Cytochrome P-450 CYP3A; Cytochrome P-450 CYP3A Inhibitors; Dibenzothiazepines; Drug Administration Schedule; Drug Interactions; Drug Monitoring; Electrocardiography; Enzyme Inhibitors; Female; Genotype; Heart Rate; Humans; Isoxazoles; Ketoconazole; Linear Models; Long QT Syndrome; Male; Middle Aged; Paroxetine; Pharmacogenetics; Phenotype; Piperazines; Piperidines; Quetiapine Fumarate; Thiazoles; United States; Young Adult

The International Conference of Harmonisation (ICH) E14 guideline for thorough QT studies requires assessing the propensity of new non-antiarrhythmic drugs to affect cardiac repolarization. The present study investigates whether a composite ECG measure of T-wave morphology (Morphology Combination Score [MCS]) can be used together with the heart rate corrected QT interval (QTc) in a fully ICH E14-compliant thorough QT study to exclude clinically relevant repolarization effects of bilastine, a novel antihistamine.. Thirty participants in this crossover study were randomly assigned to receive placebo, moxifloxacin 400 mg, bilastine at therapeutic and supratherapeutic doses (20 and 100 mg) and bilastine 20 mg co-administered with ketoconazole 400 mg. Resting ECGs recorded at 12 nominal time points before and after treatments were used to determine Fridericia corrected QTc (QTcF) and MCS from the T-wave characteristics: asymmetry, flatness and notching.. There were no effects of bilastine monotherapy (20 and 100 mg) on MCS or QTcF at those study times where the bilastine plasma concentrations were highest. MCS changes for bilastine monotherapy did not exceed the normal intrasubject variance of T-wave shapes for triplicate ECG recordings. Maximum QTcF prolongation for bilastine monotherapy was 5 ms or less: 3.8 ms (90% CI 0.3, 7.3 ms) for bilastine 20 mg and 5.0 ms (90% CI 2.0, 8.0 ms) for bilastine 100 mg. There were no indications of bilastine inducing larger repolarization effects on T-wave morphology as compared with the QTcF interval, as evidenced by the similarity of z-score equivalents for placebo-corrected changes in MCS and QTcF values.. This study shows that bilastine, at therapeutic and supratherapeutic dosages, does not induce any effects on T-wave morphology or QTcF. These results confirm the absence of an effect for bilastine on cardiac repolarization.

Topics: Adult; Aza Compounds; Benzimidazoles; Cross-Over Studies; Double-Blind Method; Electrocardiography; Female; Fluoroquinolones; Guidelines as Topic; Histamine Antagonists; Humans; Long QT Syndrome; Male; Moxifloxacin; Piperidines; Quinolines; Time Factors; Young Adult

Tasocitinib (CP-690,550), a selective inhibitor of the Janus kinase (JAK) family, is being developed for the treatment of several autoimmune diseases and prevention of allograft rejection. The aim of this study was to characterize the effect of tasocitinib on QT interval. Sixty male and female healthy adults were enrolled in a single-dose, randomized, 3-period, crossover study of a supratherapeutic dose of tasocitinib (100 mg), placebo, and moxifloxacin 400 mg. Triplicate electrocardiograms were performed at predose baseline and serially over 24 hours postdose in each treatment period. The upper limits of the 2-sided 90% confidence intervals (CIs) for the difference in QTc interval, corrected using Fridericia correction (QTcF), between tasocitinib and placebo were less than 5 ms at all time points. Concentration-QTcF analysis showed that the predicted mean change (90% CI) in QTcF at the observed mean C(max) was -0.12 (-1.18, 0.94) ms. For moxifloxacin, mean (90% CI) estimates of the change in QTcF from placebo were 11.3 (9.4, 13.1) and 12.5 (10.7, 14.4) ms at 2 and 4 hours, respectively, thereby establishing study sensitivity. A single supratherapeutic dose of tasocitinib 100 mg was well tolerated and not associated with QTc prolongation.

Topics: Adult; Cross-Over Studies; Double-Blind Method; Female; Follow-Up Studies; Heart Rate; Humans; Janus Kinase 3; Long QT Syndrome; Male; Middle Aged; Piperidines; Pyrimidines; Pyrroles; Systole; Young Adult

The aim of this paper was to determine if there were any significant differences between the effects of fentanyl delivered as a bolus or remifentanil delivered as a continuous infusion on the QT interval and QT dispersion (QTD) during the induction of anesthesia and tracheal intubation.. This was a prospective, randomized and single blind study. A total of 50 ASA I-II patients scheduled to undergo elective minor abdominal surgery were divided into two groups. In the remifentanil group (N=25), patients received a continuous infusion (c.i.) of remifentanil (0.25 mcg/kg · min). In the fentanyl group (N=25), a bolus dose of fentanyl (2.0 mcg/kg) was administered. The QT interval, the difference between QTmax and QTmin (QTD), the heart rate-corrected QT (QTc) and the QT dispersion (QTcD) were calculated using a 12-lead computerized electrocardiogram (ECG).. In both groups, there was no significant change in QT or QTc intervals during the study period. In the remifentanil group, a significant decrease in QTD and QTcD was observed during induction compared with baseline values (P<0.05). There was a significant increase in QTD at 1 min and in QTcD at 1 and 3 min after intubation in the fentanyl group (P<0.05).. Both remifentanil and fentanyl did not prolong the QT interval. QTD decreased after the induction of anesthesia and did not increase after tracheal intubation in patients receiving c.i. remifentanil in comparison with fentanyl. Overall, remifentanil infusion may be the opioid-based treatment regimen of choice in patients at risk of dysrhythmias.

Topics: Adult; Anesthesia, Intravenous; Anesthetics, Intravenous; Blood Pressure; Electrocardiography; Female; Fentanyl; Heart Rate; Humans; Long QT Syndrome; Male; Middle Aged; Piperidines; Prospective Studies; Remifentanil

Administration of certain drugs (for example, antiarrhythmics, antihistamines, antibiotics, antipsychotics) may occasionally affect myocardial repolarization and cause prolongation of the QT interval. We performed a whole genome association study of drug-induced QT prolongation after 14 days of treatment in a phase 3 clinical trial evaluating the efficacy, safety and tolerability of a novel atypical antipsychotic, iloperidone, in patients with schizophrenia. We identified DNA polymorphisms associated with QT prolongation in six loci, including the CERKL and SLCO3A1 genes. Each single nucleotide polymorphism (SNP) defined two genotype groups associated with a low mean QT change (ranging from -0.69 to 5.67 ms depending on the SNP) or a higher mean QT prolongation (ranging from 14.16 to 17.81 ms). The CERKL protein is thought to be part of the ceramide pathway, which regulates currents conducted by various potassium channels, including the hERG channel. It is well established that inhibition of the hERG channel can prolong the QT interval. SLCO3A1 is thought to play a role in the translocation of prostaglandins, which have known cardioprotective properties, including the prevention of torsades de pointes. Our findings also point to genes involved in myocardial infarction (PALLD), cardiac structure and function (BRUNOL4) and cardiac development (NRG3). Results of this pharmacogenomic study provide new insight into the clinical response to iloperidone, developed with the goal of directing therapy to those patients with the optimal benefit/risk ratio.

Topics: Adolescent; Adult; Aged; Antipsychotic Agents; Carrier Proteins; CELF Proteins; Cytoskeletal Proteins; Double-Blind Method; Electrocardiography; Female; Follow-Up Studies; Gene Frequency; Genome-Wide Association Study; Genotype; Humans; Intracellular Signaling Peptides and Proteins; Isoxazoles; Linear Models; Linkage Disequilibrium; Long QT Syndrome; Male; Middle Aged; Neuregulins; Organic Anion Transporters; Pharmacogenetics; Phosphoproteins; Phosphotransferases (Alcohol Group Acceptor); Piperazines; Piperidines; Polymorphism, Single Nucleotide; RNA-Binding Proteins; Schizophrenia; Thiazoles; Young Adult

Stimulation of the sympathetic nervous system associated with tracheal intubation causes corrected QT (QTc) interval prolongation. We postulated that the use of remifentanil during induction of anaesthesia might prevent this. Sixty unpremedicated, ASA grade 1 patients were selected and randomly allocated to receive either saline (group S), remifentanil 0.5 microg x kg(-1) (group R 0.5) or remifentanil 1.0 microg x kg(-1) (group R1.0) 1 min before laryngoscopy. The QTc interval was significantly prolonged immediately following intubation in group S and group R0.5, but it remained stable in group R1.0, compared with the QTc interval just before laryngoscopy. It is concluded that the administration of remifentanil 1.0 microg x kg(-1) before intubation can prevent the prolongation of the QTc interval associated with tracheal intubation during induction of anaesthesia with sevoflurane.

Topics: Adult; Analgesics, Opioid; Anesthetics, Inhalation; Blood Pressure; Dose-Response Relationship, Drug; Drug Administration Schedule; Female; Heart Rate; Humans; Intubation, Intratracheal; Laryngoscopy; Long QT Syndrome; Male; Methyl Ethers; Middle Aged; Piperidines; Remifentanil; Sevoflurane

Estimation of QT interval prolongation belongs to safety assessment of every drug. Among unresolved issues, heart rate correction of the QT interval may be problematic. This article proposes a strategy for heart rate correction in drug safety studies and demonstrates the strategy using a study of ebastine, a nonsedating antihistamine.. Four-way cross-over Phase I study investigated 32 subjects on placebo, ebastine 60 mg once a day, 100 mg once a day, and terfenadine 180 mg twice a day. Repeated ECGs were obtained before each arm and after 7 days of treatment. The changes in heart rate-corrected QTc interval were investigated using (A) 20 published heart rate correction formulas, (B) a correction formula optimized by QT/RR regression modeling in all baseline data, and (C) individual corrections optimized for each subject by drug-free QT/RR regression modeling. (A) Previously published correction formulas found QTc interval increases on terfenadine. The results with ebastine were inconsistent. For instance, Bazett's and Lecocq's correction found significant QTc increase and decrease on ebastine, respectively. The results were related (absolute value(r) > 0.95) to the success of each formula (independence of drug-free QTc and RR intervals). (B) The pooled drug-free QT/RR regression found an optimized correction QTc = QT/RR(0.314). QTc interval changes on placebo, ebastine 60 mg, ebastine 100 mg, and terfenadine were -1.95 +/- 6.87 msec (P = 0.18), -3.91 +/- 9.38 msec (P = 0.053), 0.75 +/- 8.23 msec (P = 0.66), and 12.95 +/- 14.64 msec (P = 0.00025), respectively. (C) Individual QT/RR regressions were significantly different between subjects and found optimized corrections QTc = QT/RR(alpha) with alpha = 0.161 to 0.417. Individualized QTc interval changes on placebo, ebastine 60 mg, ebastine 100 mg, and terfenadine were -2.76 +/- 5.51 msec (P = 0.022), -3.15 +/- 9.17 msec (P = 0.11), -2.61 +/- 9.55 msec (P = 0.19), and 12.43 +/- 15.25 msec (P = 0.00057, respectively. Drug-unrelated QTc changes up to 4.70 +/- 8.92 msec reflected measurement variability.. Use of published heart rate correction formulas in the assessment of drug-induced QTc prolongation is inappropriate, especially when the drug might induce heart rate changes. Correction formulas optimized for pooled drug-free data are inferior to the formulas individualized for each subject. Measurement imprecision and natural variability can lead to mean QTc interval changes of 4 to 5 msec in the absence of drug treatment.

Topics: Butyrophenones; Cross-Over Studies; Drug Evaluation; Electrocardiography; Heart Rate; Histamine H1 Antagonists; Humans; Long QT Syndrome; Models, Cardiovascular; Piperidines; Regression Analysis

Cisapride is a prokinetic agent that facilitates gastrointestinal motility and is widely used for the treatment of gastroesophageal reflux disease (GERD) in adults and children. However, reports of ventricular proarrhythmia have been noted in patients taking cisapride, particularly in conjunction with other drugs that may inhibit hepatic metabolism of cisapride via the cytochrome P450 3A4 system.. We designed a prospective, blinded study to evaluate the effect of cisapride on ventricular repolarization in children with GERD.. We analyzed the electrocardiograms (ECGs) from 35 children (age 0.4 to 18 years, mean 5.2 years) including measurement of the resting QT interval (QTc), JT interval (JTc), as well as QT and JT interlead dispersion markers. Data from these patients were compared with ECGs from a control group of 1000 normal children.. Eleven (31%) of 35 patients receiving cisapride had a prolonged QTc (> or = 450 ms). The JTc was prolonged > or = 360 ms in 16 of 35 patients (46%). The mean QTc in the cisapride group was 428 +/- 35 ms and mean JTc was 336 +/- 35 ms. An increased QT or JT dispersion (> 70 ms) was seen in only 3 of 35 children. Of the 11 children with QTc prolongation, 2 had documented torsades de pointes ventricular tachycardia. Both patients were taking cisapride concomitantly with a macrolide antibiotic. All other patients were treated with either cisapride alone or in conjunction with other GERD agents, such as ranitidine or omeprazole.. Cisapride may cause prolongation of ventricular repolarization in children. There does not appear to be increased heterogeneity of repolarization or delayed depolarization in this small sample. The proarrhythmia may be exacerbated by medications that inhibit cytochrome P450 3A4 hepatic metabolism, overdosage, or mechanisms that result in decreased serum clearance. ECG intervals should be monitored in children maintained on cisapride, particularly when used in combination with other known QT-prolonging medications.

Topics: Adolescent; Child; Child, Preschool; Cisapride; Electrocardiography; Gastroesophageal Reflux; Gastrointestinal Agents; Humans; Infant; Long QT Syndrome; Piperidines; Prospective Studies; Single-Blind Method

Recent reports of torsade de pointes and heart block associated with prolonged QT interval in children receiving cisapride raise questions about its safety. We prospectively examined the effects of cisapride on the QT interval in children. Electrocardiography was performed on 30 children before and after cisapride was administered. An additional 71 children underwent electrocardiography only after starting cisapride. The incidence of a corrected QT (QTc) interval > 440 msec or a marked abnormality in T wave morphology was determined in all 101 children. Cisapride significantly lengthened the QTc with a mean increase of 15.5 +/- 4.6 msec (mean +/- SEM, p = 0.002 in the 30 children with baseline electrocardiographs. Twelve of the 101 patients were found to have a QTc > 440 msec, and one had a new prominent notched T wave in all leads. In these 13 (13%) patients with repolarization abnormalities, other factors that might contribute to a long QT were noted in 11 (85%) patients. We conclude that cisapride use in children is associated with a modest increase in QT interval. The incidence of QTc > 440 msec is low. Most children with long QTc have other factors that could compound the effects of cisapride.

Topics: Child; Cisapride; Electrocardiography; Female; Gastrointestinal Agents; Humans; Infant; Long QT Syndrome; Male; Piperidines; Risk Factors

This clinical study was designed to compare rate-dependent effects of class III agents on QT prolongation.. Clinical data that compare the electrophysiologic differences among class III agents with different selectivity for potassium channels are still lacking.. QT intervals were measured over a wide range of preceding RR intervals during sinus rhythm by 24-h Holter electrocardiography before and after oral administration of four class III agents: E4031, dofetilide, MS551 and d-sotalol. Rate-dependent changes in the QT interval were assessed by the slope of the linear regression line estimating the QT-square root of RR relation.. All agents significantly increased the mean slope: E4031 increased the mean [+/- SD] value from 0.32 +/- 0.05 to 0.42 +/- 0.13 (p < 0.01), dofetilide from 0.32 +/- 0.03 to 0.50 +/- 0.12 (p < 0.03), MS551 from 0.35 +/- 0.06 to 0.45 +/- 0.10 (p < 0.02) and d-sotalol from 0.31 +/- 0.05 to 0.33 +/- 0.04 (p < 0.05). However, in those patients given either E4031, dofetilide or MS551, the degree of QT prolongation was smaller at shorter square root of RR intervals and was better preserved at shorter square root of RR intervals by d-sotalol, with a smaller increase in slope (p < 0.02 vs. dofetilide and MS551).. On ambulatory electrocardiography, reverse use dependence in QT prolongation was least prominent with d-sotalol among the four study drugs. In the range of physiologic heart rates, class III agents could manifest different profiles of rate dependence in their QT-prolonging effect.

Topics: Adult; Aged; Analysis of Variance; Anti-Arrhythmia Agents; Electrocardiography, Ambulatory; Female; Humans; Long QT Syndrome; Male; Middle Aged; Phenethylamines; Piperidines; Pyridines; Pyrimidinones; Regression Analysis; Sotalol; Statistics, Nonparametric; Sulfonamides

Antihistamines are among the most widely used medications in the world. Ebastine is an antihistaminic which is long-acting, second-generation, and selective H1-receptor inverse agonist. I report a twelve-year-and-six-month-old girl with temporary prolongation of the QTc interval caused by acute ebastine intoxication due to TikTok challenge. Initial electrocardiogram showed sinus arrhythmia (72 beats/min) and prolongation of the QTc interval (QTc 482 milliseconds). Gastric lavage was performed. Intravenous fluid was administered, and activated charcoal (1 g/kg/per dose) was given. Electrocardiogram 9 h after drug ingestion showed sinus rhythm and normal QTc interval (QTc 414milliseconds). During follow-up, no electrocardiogram abnormalities were detected with electrocardiogram monitoring. She was discharged on day 2 without any complications. This case report is the first in the literature to show acute intoxication with ebastine due to challenge video on TikTok, which leads to a temporary prolongation of the QTc interval. Also, with this case report, I assert the fact that it is important to properly supervise the use of social media, such as TikTok and to review the content of TikTok videos.

Topics: Arrhythmias, Cardiac; Drug Inverse Agonism; Electrocardiography; Female; Histamine H1 Antagonists; Humans; Infant; Long QT Syndrome; Piperidines; Social Media

Topics: Animals; KCNQ1 Potassium Channel; Long QT Syndrome; Mutation; Piperidines; Thiazoles; Tosyl Compounds; Xenopus

Human Ether-à-go-go (hERG) channels contribute to cardiac repolarization, and inherited variants or drug block are associated with long QT syndrome type 2 (LQTS2) and arrhythmia. Therefore, hERG activator compounds present a therapeutic opportunity for targeted treatment of LQTS. However, a limiting concern is over-activation of hERG resurgent current during the action potential and abbreviated repolarization. Activators that slow deactivation gating (type I), such as RPR260243, may enhance repolarizing hERG current during the refractory period, thus ameliorating arrhythmogenicity with reduced early repolarization risk. Here, we show that, at physiological temperature, RPR260243 enhances hERG channel repolarizing currents conducted in the refractory period in response to premature depolarizations. This occurs with little effect on the resurgent hERG current during the action potential. The effects of RPR260243 were particularly evident in LQTS2-associated R56Q mutant channels, whereby RPR260243 restored WT-like repolarizing drive in the early refractory period and diastolic interval, combating attenuated protective currents. In silico kinetic modeling of channel gating predicted little effect of the R56Q mutation on hERG current conducted during the action potential and a reduced repolarizing protection against afterdepolarizations in the refractory period and diastolic interval, particularly at higher pacing rates. These simulations predicted partial rescue from the arrhythmic effects of R56Q by RPR260243 without risk of early repolarization. Our findings demonstrate that the pathogenicity of some hERG variants may result from reduced repolarizing protection during the refractory period and diastolic interval with limited effect on action potential duration, and that the hERG channel activator RPR260243 may provide targeted antiarrhythmic potential in these cases.

Topics: Arrhythmias, Cardiac; ERG1 Potassium Channel; Ether; Ether-A-Go-Go Potassium Channels; Humans; Long QT Syndrome; Piperidines; Quinolines

Torsade de pointes (TdP) occurred in a long QT syndrome type 3 (LQT3) patient after switching perospirone to blonanserin. We studied how their electropharmacological effects had induced TdP in the LQT3 patient. Perospirone hydrochloride (n = 4) or blonanserin (n = 4) of 0.01, 0.1, and 1 mg/kg, i.v. was cumulatively administered to the halothane-anesthetized dogs over 10 min. The low dose of perospirone decreased total peripheral vascular resistance, but increased heart rate and cardiac output, facilitated atrioventricular conduction, and prolonged J-T

Topics: Action Potentials; Anesthetics, Inhalation; Animals; Calcium Channel Agonists; Cardiac Conduction System Disease; Delirium; Dogs; Dopamine Antagonists; Dose-Response Relationship, Drug; Electrocardiography; Female; Halothane; Heart Conduction System; Humans; Isoindoles; Long QT Syndrome; Middle Aged; Models, Animal; Piperazines; Piperidines; Potassium Channel Blockers; Serotonin Antagonists; Sleep Initiation and Maintenance Disorders; Thiazoles; Torsades de Pointes

I

Topics: Action Potentials; Anti-Arrhythmia Agents; Calcium; Calcium Channels; Cell Differentiation; ERG1 Potassium Channel; HEK293 Cells; Humans; Induced Pluripotent Stem Cells; Ion Transport; Long QT Syndrome; Models, Biological; Myocytes, Cardiac; Patch-Clamp Techniques; Phenethylamines; Piperidines; Potassium; Potassium Channel Blockers; Pyridines; Scorpion Venoms; Sulfonamides

Mutations in KCNH2 can lead to long QT syndrome type 2. Variable disease manifestation observed with this channelopathy is associated with the location and type of mutation within the protein, complicating efforts to predict patient risk. Here, we demonstrated phenotypic differences in cardiomyocytes derived from isogenic human induced pluripotent stem cells (hiPSC-CMs) genetically edited to harbor mutations either within the pore or tail region of the ion channel. Electrophysiological analysis confirmed that the mutations prolonged repolarization of the hiPSC-CMs, with differences between the mutations evident in monolayer cultures. Blocking the hERG channel revealed that the pore-loop mutation conferred greater susceptibility to arrhythmic events. These findings showed that subtle phenotypic differences related to KCNH2 mutations could be captured by hiPSC-CMs under genetically matched conditions. Moreover, the results support hiPSC-CMs as strong candidates for evaluating the underlying severity of individual KCNH2 mutations in humans, which could facilitate patient risk stratification.

Topics: Arrhythmias, Cardiac; Cell Line; Electrophysiology; ERG1 Potassium Channel; Gene Editing; Genetic Predisposition to Disease; Humans; Induced Pluripotent Stem Cells; Long QT Syndrome; Models, Biological; Mutation; Myocytes, Cardiac; Patch-Clamp Techniques; Piperidines; Pyridines

Upon membrane depolarization, the KCNQ1 potassium channel opens at the intermediate (IO) and activated (AO) states of the stepwise voltage-sensing domain (VSD) activation. In the heart, KCNQ1 associates with KCNE1 subunits to form I

Topics: Animals; Cell Membrane; Cell Polarity; Humans; KCNQ1 Potassium Channel; Long QT Syndrome; Oocytes; Piperidines; Potassium; Potassium Channels, Voltage-Gated; Thiazoles; Tosyl Compounds; Xenopus

Missense mutations in KCNH2, a gene encoding the Kv11.1 channel, cause long QT syndrome (LQTS) type 2 primarily by disrupting the intracellular transport of Kv11.1 to the plasma membrane. The present study aimed to clarify the functional changes by two novel KCNH2 missense mutations.. We performed genetic screening of three unrelated symptomatic LQTS probands with family histories of cardiac symptoms. Chinese hamster ovary cells were transfected with wild-type (WT) and/or mutant KCNH2 plasmid and examined by patch-clamp technique. Immunostaining and confocal microscopy were performed to evaluate the intracellular localization of WT and homozygous mutant Kv11.1 in human embryonic kidney cells. For the study of trafficking rescue, we used low-temperature incubation (30°C). We also examined pharmacological rescue of homozygous mutant Kv11.1 current in cells treated with E-4031 or dofetilide.. We identified two novel KCNH2 missense mutations, G785D and T826I. Electrophysiological study showed that both mutant channels were nonfunctional in homozygous condition and reduced current densities by half in heterozygous condition compared with WT Kv11.1. Heterozygous Kv11.1-G785D produced a significant positive shift in activation and a significant negative shift in inactivation, whereas heterozygous Kv11.1-T826I caused no kinetic changes. Immunostaining revealed that both were transport-refractory mutations. Incubation at 30°C rescued plasma membrane expression of Kv11.1-T826I but not G785D. We confirmed low-temperature-induced restoration of homozygous Kv11.1-T826I transport by functional current measurements. In contrast, incubation with E-4031 or dofetilide failed to produce measurable currents in both homozygous mutant channels.. Two novel KCNH2 mutations disrupted the intracellular transport of Kv11.1. Low-temperature incubation rescued plasma membrane expression of Kv11.1-T826I but not G785D. Both mutations exerted loss-of-function effects on Kv11.1 and explained the phenotypes of the mutation carriers.

Topics: Adult; Animals; CHO Cells; Cricetinae; Cricetulus; ERG1 Potassium Channel; Female; Humans; Kv1.1 Potassium Channel; Long QT Syndrome; Loss of Function Mutation; Mutation, Missense; Patch-Clamp Techniques; Phenotype; Piperidines; Protein Transport; Pyridines

Healthy human heart rate fluctuates overtime showing long-range fractal correlations. In contrast, various cardiac diseases and normal aging show the breakdown of fractal complexity. Recently, it was shown that human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) intrinsically exhibit fractal behavior as in humans. Here, we investigated the fractal complexity of hiPSC-derived long QT-cardiomyocytes (LQT-CMs). We recorded extracellular field potentials from hiPSC-CMs at baseline and under the effect of various compounds including β-blocker bisoprolol, ML277, a specific and potent I

Topics: Adrenergic beta-1 Receptor Antagonists; Adult; Bisoprolol; Cells, Cultured; Dose-Response Relationship, Drug; Female; Fractals; Heart Conduction System; Heart Rate; Humans; Induced Pluripotent Stem Cells; Long QT Syndrome; Myocytes, Cardiac; Piperidines; Thiazoles; Time Factors; Tosyl Compounds

Topics: Adult; Antipsychotic Agents; Female; Humans; Long QT Syndrome; Piperazines; Piperidines; Risperidone; Schizophrenia

An 80-year-old woman with Alzheimer's dementia presented with diarrhoea, vomiting and worsening confusion following an increase in donepezil dose from 5 to 10 mg. The ECG revealed prolongation of QTc interval. Soon after admission, she became unresponsive with polymorphic ventricular tachycardia (VT). Cardiopulmonary resuscitation with a 200 J shock was successful in establishing cardiac output. Following the discontinuation of donepezil, the QTc interval normalised and no further arrhythmias were recorded. Treatment with anticholinesterase inhibitors may result in life-threatening VT. Vigilance is required for the identification of this condition in patients presenting with presyncope, syncope or seizures.

Topics: Aged, 80 and over; Alzheimer Disease; Cardiopulmonary Resuscitation; Donepezil; Electrocardiography; Female; Humans; Indans; Long QT Syndrome; Nootropic Agents; Piperidines; Seizures; Syncope; Torsades de Pointes

Clinical indications for the perioperative use of dexmedetomidine in pediatric anesthesia are accumulating. However, in 2013, dexmedetomidine was added to the list of medications with possible risk of prolonging the QT interval and/or inducing Torsades de Pointes. Unfortunately, current evidence for dexmedetomidine-induced QT prolongation is sparse and somewhat contradictory.. The purpose of this study was to evaluate temporal changes in corrected QT interval (QTc) after a rapid bolus administration of dexmedetomidine under total intravenous anesthesia (TIVA) with a standardized propofol and remifentanil administration.. Electrocardiography (ECG) and corresponding trend data were extracted from automated electronic data capture of physiological monitoring. Ten-second epochs of ECG data were extracted in 1-min intervals for 12 min, starting 1 min before dexmedetomidine bolus administration, and ending 10 min after. QT intervals were extracted using an automated routine in MATLAB, and corrected for heart rate (HR) using Bazett's (QTcB) and Fridericia's formulas (QTcF). QTcB and QTcF were compared using Wilcoxon signed-rank test between baseline measurements and the subsequent four interval values.. Data from 21 subjects (17 male) with median (range) age 7.1 (5.4-9.5) yr, weight 23.6 (16.2-36.7) kg, and height 121 (103-140) cm were analyzed. Bolus administration of dexmedetomidine reduced HR in all subjects (median 22%), and caused transient reduction of QT interval, with its peak at 1-min postbolus administration: QTcB (median reduction 30.7 ms, P < 0.001) or QTcF (median reduction 15.4 ms, P = 0.001); QT shortening became statistically insignificant 4 min following dexmedetomidine bolus administration for QTcB and 2 min for QTcF.. In this study, a rapid bolus of dexmedetomidine transiently shortened corrected QT intervals. However, these effects are confounded by dexmedetomidine-induced bradycardia. These findings should be confirmed in pediatric studies without concomitant TIVA administration and with optimized correction of baseline HR.

Topics: Administration, Intravenous; Anesthesia, Intravenous; Anesthetics, Intravenous; Child; Child, Preschool; Dexmedetomidine; Electrocardiography; Female; Heart Rate; Humans; Long QT Syndrome; Male; Monitoring, Intraoperative; Piperidines; Propofol; Remifentanil; Retrospective Studies

Prolongation of action potential duration (APD), increased spatial APD dispersion, and triangulation are major factors promoting drug-induced ventricular arrhythmia. Preclinical identification of HERG/IKr-blocking drugs and their pro-arrhythmic potential, however, remains a challenge. We hypothesize that transgenic long-QT type 1 (LQT1) rabbits lacking repolarizing IKs current may help to sensitively detect HERG/IKr-blocking properties of drugs.. Hearts of adult female transgenic LQT1 and wild type littermate control (LMC) rabbits were Langendorff-perfused with increasing concentrations of HERG/IKr-blockers E-4031 (0.001-0.1 µM, n=9/7) or erythromycin (1-300 µM, n=9/7) and APD, APD dispersion, and triangulation were analyzed.. At baseline, APD was longer in LQT1 than in LMC rabbits in LV apex and RV mid. Erythromycin and E-4031 prolonged APD in LQT1 and LMC rabbits in all positions. However, erythromycin-induced percentaged APD prolongation related to baseline (%APD) was more pronounced in LQT1 at LV base-lateral and RV mid positions (100 µM, LQT1, +40.6 ± 9.7% vs. LMC, +24.1 ± 10.0%, p<0.05) and E-4031-induced %APD prolongation was more pronounced in LQT1 at LV base-lateral (0.01 µM, LQT1, +29.6 ± 10.6% vs. LMC, +19.1 ± 3.8%, p<0.05) and LV base-septal positions. Moreover, erythromycin significantly increased spatial APD dispersion only in LQT1 and increased triangulation only in LQT1 in LV base-septal and RV mid positions. Similarly, E-4031 increased triangulation only in LQT1 in LV apex and base-septal positions.. E-4031 and erythromycin prolonged APD and increased triangulation more pronouncedly in LQT1 than in LMC rabbits. Moreover, erythromycin increased APD dispersion only in LQT1, indicating that transgenic LQT1 rabbits could serve as sensitive model to detect HERG/IKr-blocking properties of drugs.

Topics: Action Potentials; Animals; Animals, Genetically Modified; Erythromycin; Female; Heart; Long QT Syndrome; Piperidines; Pyridines; Rabbits

KCNH2 encodes Kv11.1 and underlies the rapidly activating delayed rectifier K(+) current (IKr) in the heart. Loss-of-function KCNH2 mutations cause the type 2 long QT syndrome (LQT2), and most LQT2-linked missense mutations inhibit the trafficking of Kv11.1 channels. Drugs that bind to Kv11.1 and block IKr (e.g., E-4031) can act as pharmacological chaperones to increase the trafficking and functional expression for most LQT2 channels (pharmacological correction). We previously showed that LQT2 channels are selectively stored in a microtubule-dependent compartment within the endoplasmic reticulum (ER). We tested the hypothesis that pharmacological correction promotes the trafficking of LQT2 channels stored in this compartment. Confocal analyses of cells expressing the trafficking-deficient LQT2 channel G601S showed that the microtubule-dependent ER compartment is the transitional ER. Experiments with E-4031 and the protein synthesis inhibitor cycloheximide suggested that pharmacological correction promotes the trafficking of G601S stored in this compartment. Treating cells in E-4031 or ranolazine (a drug that blocks IKr and has a short half-life) for 30 min was sufficient to cause pharmacological correction. Moreover, the increased functional expression of G601S persisted 4-5 h after drug washout. Coexpression studies with a dominant-negative form of Rab11B, a small GTPase that regulates Kv11.1 trafficking, prevented the pharmacological correction of G601S trafficking from the transitional ER. These data suggest that pharmacological correction quickly increases the trafficking of LQT2 channels stored in the transitional ER via a Rab11B-dependent pathway, and we conclude that the pharmacological chaperone activity of drugs like ranolazine might have therapeutic potential.

Topics: Adolescent; Adult; Aged; Anti-Arrhythmia Agents; Endoplasmic Reticulum; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Female; HEK293 Cells; Humans; Long QT Syndrome; Male; Middle Aged; Mutation, Missense; Piperidines; Potassium Channel Blockers; Protein Transport; Pyridines; Young Adult

Enhanced dispersion of action potential duration (APD) is a major contributor to long QT syndrome (LQTS)-related arrhythmias.. To investigate spatial correlations of regional heterogeneities in cardiac repolarization and mechanical function in LQTS.. Female transgenic LQTS type 2 (LQT2; n = 11) and wild-type littermate control (LMC) rabbits (n = 9 without E4031 and n = 10 with E4031) were subjected to phase contrast magnetic resonance imaging to assess regional myocardial velocities. In the same rabbits' hearts, monophasic APDs were assessed in corresponding segments.. In LQT2 and E4031-treated rabbits, APD was longer in all left ventricular segments (P < .01) and APD dispersion was greater than that in LMC rabbits (P < .01). In diastole, peak radial velocities (Vr) were reduced in LQT2 and E4031-treated compared to LMC rabbits in LV base and mid (LQT2: -3.36 ± 0.4 cm/s, P < .01; E4031-treated: -3.24 ± 0.6 cm/s, P < .0001; LMC: -4.42 ± 0.5 cm/s), indicating an impaired diastolic function. Regionally heterogeneous diastolic Vr correlated with APD (LQT2: correlation coefficient [CC] 0.38, P = .01; E4031-treated: CC 0.42, P < .05). Time-to-diastolic peak Vr were prolonged in LQT2 rabbits (LQT2: 196.8 ± 2.9 ms, P < .001; E4031-treated: 199.5 ± 2.2 ms, P < .0001, LMC 183.1 ± 1.5), indicating a prolonged contraction duration. Moreover, in transgenic LQT2 rabbits, diastolic time-to-diastolic peak Vr correlated with APD (CC 0.47, P = .001). In systole, peak Vr were reduced in LQT2 and E4031-treated rabbits (P < .01) but longitudinal velocities or ejection fraction did not differ. Finally, random forest machine learning algorithms enabled a differentiation between LQT2, E4031-treated, and LMC rabbits solely based on "mechanical" magnetic resonance imaging data.. The prolongation of APD led to impaired diastolic and systolic function in transgenic and drug-induced LQT2 rabbits. APD correlated with regional diastolic dysfunction, indicating that LQTS is not purely an electrical but an electromechanical disorder.

Topics: Action Potentials; Animals; Animals, Genetically Modified; Anti-Arrhythmia Agents; Arrhythmias, Cardiac; Diastole; Female; Long QT Syndrome; Magnetic Resonance Imaging; Piperidines; Pyridines; Rabbits

Abnormal enhanced transmural dispersion of repolarization (TDR) plays an important role in the maintaining of the severe ventricular arrhythmias such as torsades de pointes (TDP) which can be induced in long-QT (LQT) syndrome. Taking advantage of an in vitro rabbit model of LQT2, we detected the effects of KN-93, a CaM-dependent kinase (CaMK) II inhibitor on repolarization heterogeneity of ventricular myocardium. Using the monophasic action potential recording technique, the action potentials of epicardium and endocardium were recorded in rabbit cardiac wedge infused with hypokalemic, hypomagnesaemic Tyrode's solution. At a basic length (BCL) of 2000 ms, LQT2 model was successfully mimicked with the perfusion of 0.5 μmol/L E-4031, QT intervals and the interval from the peak of T wave to the end of T wave (Tp-e) were prolonged, and Tp-e/QT increased. Besides, TDR was increased and the occurrence rate of arrhythmias like EAD, R-on-T extrasystole, and TDP increased under the above condition. Pretreatment with KN-93 (0.5 μmol/L) could inhibit EAD, R-on-T extrasystole, and TDP induced by E-4031 without affecting QT interval, Tp-e, and Tp-e/QT. This study demonstrated KN-93, a CaMKII inhibitor, can inhibit EADs which are the triggers of TDP, resulting in the suppression of TDP induced by LQT2 without affecting TDR.

Topics: Action Potentials; Animals; Anti-Arrhythmia Agents; Arrhythmias, Cardiac; Benzylamines; Calcium-Calmodulin-Dependent Protein Kinase Type 2; Electrocardiography; Electrophysiologic Techniques, Cardiac; Endocardium; Heart; In Vitro Techniques; Long QT Syndrome; Pericardium; Piperidines; Protein Kinase Inhibitors; Pyridines; Rabbits; Sulfonamides; Torsades de Pointes

Several drugs blocking the rapidly activating potassium (K(r)) channel cause malformations (including cardiac defects) and embryonic death in animal teratology studies. In humans, these drugs have an established risk for acquired long-QT syndrome and arrhythmia. Recently, associations between cardiac defects and spontaneous abortions have been reported for drugs widely used in pregnancy (e.g. antidepressants), with long-QT syndrome risk. To investigate whether a common embryonic adverse-effect mechanism exists in the human, rat, and rabbit embryos, we made a comparative study of embryonic cardiomyocytes from all three species.. Patch-clamp and quantitative-mRNA measurements of K(r) and slowly activating K (K(s)) channels were performed on human, rat, and rabbit primary cardiomyocytes and cardiac samples from different embryo-foetal stages. The K(r) channel was present when the heart started to beat in all species, but was, in contrast to human and rabbit, lost in rats in late organogenesis. The specific K(r)-channel blocker E-4031 prolonged the action potential in a species- and development-dependent fashion, consistent with the observed K(r)-channel expression pattern and reported sensitive periods of developmental toxicity. E-4031 also increased the QT interval and induced 2:1 atrio-ventricular block in multi-electrode array electrographic recordings of rat embryos. The K(s) channel was expressed in human and rat throughout the embryo-foetal period but not in rabbit.. This first comparison of mRNA expression, potassium currents, and action-potential characteristics, with and without a specific K(r)-channel blocker in human, rat, and rabbit embryos provides evidence of K(r)-channel inhibition as a common mechanism for embryonic malformations and death.

Topics: Action Potentials; Animals; Atrioventricular Block; Cells, Cultured; Electrocardiography; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Gene Expression Regulation, Developmental; Gestational Age; Heart Defects, Congenital; Humans; KCNQ1 Potassium Channel; Kinetics; Long QT Syndrome; Myocytes, Cardiac; Organogenesis; Patch-Clamp Techniques; Piperidines; Polymerase Chain Reaction; Potassium Channel Blockers; Potassium Channels, Voltage-Gated; Pyridines; Rabbits; Rats; Rats, Sprague-Dawley; Rats, Wistar; RNA, Messenger; Species Specificity; Teratogens

Torsade de Pointes (TdP) proarrhythmia is a major complication of therapeutic drugs that block the delayed rectifier current. QT interval prolongation, the principal marker used to screen drugs for proarrhythmia, is both insensitive and nonspecific. Consequently, better screening methods are needed. Drug-induced transmural dispersion of repolarization (TDR) is mechanistically linked to TdP. Therefore, we hypothesized that drug-induced enhancement of TDR is more predictive of proarrhythmia than QT interval. High-resolution transmural optical action potential mapping was performed in canine wedge preparations (n = 19) at baseline and after perfusion with 4 different QT prolonging drugs at clinically relevant concentrations. Two proarrhythmic drugs in patients (bepridil and E4031) were compared with 2 nonproarrhythmic drugs (risperidone and verapamil). Both groups prolonged the QT (all P < 0.02), least with the proarrhythmic drug bepridil, reaffirming that QT is a poor predictor of TdP. In contrast, TDR was enhanced only by proarrhythmic drugs (P < 0.03). Increased TDR was due to a preferential prolongation of midmyocardial cell, relative to epicardial cell, APD, whereas nonproarrhythmic drugs similarly prolonged both cell types. In contrast to QT prolongation, augmentation of TDR was induced by proarrhythmic but not nonproarrhythmic drugs, suggesting TDR is a superior preclinical marker of proarrhythmic risk during drug development.

Topics: Action Potentials; Animals; Bepridil; Dogs; Dose-Response Relationship, Drug; Electrocardiography; Ether-A-Go-Go Potassium Channels; Heart Conduction System; Humans; In Vitro Techniques; Long QT Syndrome; Piperidines; Potassium Channel Blockers; Pyridines; Risk Assessment; Risperidone; Time Factors; Torsades de Pointes; Toxicity Tests; Verapamil; Voltage-Sensitive Dye Imaging

Cloperastine is an antitussive drug, which can be received as an over-the-counter cold medicine. The chemical structure of cloperastine is quite similar to that of the antihistamine drug diphenhydramine, which is reported to inhibit hERG K⁺ channels and clinically induce long QT syndrome after overdose. To analyze its proarrhythmic potential, we compared effects of cloperastine and diphenhydramine on the hERG K⁺ channels expressed in HEK293 cells. We further assessed their effects on the halothane-anesthetized guinea-pig heart under the monitoring of monophasic action potential (MAP) of the ventricle. Cloperastine inhibited the hERG K⁺ currents in a concentration-dependent manner with an IC₅₀ value of 0.027 μM, whose potency was 100 times greater than that of diphenhydramine (IC₅₀; 2.7 μM). In the anesthetized guinea pigs, cloperastine at a therapeutic dose of 1 mg/kg prolonged the QT interval and MAP duration without affecting PR interval or QRS width. Diphenhydramine at a therapeutic dose of 10 mg/kg prolonged the QT interval and MAP duration together with increase in PR interval and QRS width. The present results suggest that cloperastine may be categorized as a QT-prolonging drug that possibly induces arrhythmia at overdoses like diphenhydramine does.

Topics: Action Potentials; Amino Alcohols; Animals; Animals, Inbred Strains; Anti-Arrhythmia Agents; Antitussive Agents; Diphenhydramine; Ether-A-Go-Go Potassium Channels; Guinea Pigs; Heart Ventricles; HEK293 Cells; Humans; Long QT Syndrome; Membrane Potentials; Osmolar Concentration; Patch-Clamp Techniques; Piperidines; Potassium Channel Blockers; Recombinant Proteins; Structure-Activity Relationship

The majority of human ether-a-go-go-related gene (hERG) screens aiming to minimize the risk of drug-induced long QT syndrome have been conducted using heterologous systems expressing the hERG 1a subunit, although both hERG 1a and 1b subunits contribute to the K+ channels producing the repolarizing current I(Kr) . We tested a range of compounds selected for their diversity to determine whether hERG 1a and 1a/1b channels exhibit different sensitivities that may influence safety margins or contribute to a stratified risk analysis.. We used the IonWorks™ plate-based electrophysiology device to compare sensitivity of hERG 1a and 1a/1b channels stably expressed in HEK293 cells to 50 compounds previously shown to target hERG channels. Potency was determined as IC₅₀ values (µM) obtained from non-cumulative, eight-point concentration-effect curves of normalized data, fitted to the Hill equation. To minimize possible sources of variability, compound potency was assessed using test plates arranged in alternating columns of cells expressing hERG 1a and 1a/1b.. Although the potency of most compounds was similar for the two targets, some surprising differences were observed. Fluoxetine (Prozac) was more potent at blocking hERG 1a/1b than 1a channels, yielding a corresponding reduction in the safety margin. In contrast, E-4031 was a more potent blocker of hERG 1a compared with 1a/1b channels, as previously reported, as was dofetilide, another high-affinity blocker.. The current assays may underestimate the risk of some drugs to cause torsades de pointes arrhythmia, and overestimate the risk of others.

Topics: Action Potentials; Arrhythmias, Cardiac; Cell Line, Transformed; Drug Evaluation, Preclinical; Ether-A-Go-Go Potassium Channels; Fluoxetine; HEK293 Cells; Humans; Inhibitory Concentration 50; Long QT Syndrome; Piperidines; Protein Subunits; Pyridines; Sensitivity and Specificity; Torsades de Pointes

The reverse rate dependence (RRD) of actions of I(Kr)-blocking drugs to increase the action potential duration (APD) and beat-to-beat variability of repolarization (BVR) of APD is proarrhythmic. We determined whether inhibition of endogenous, physiological late Na(+) current (late I(Na)) attenuates the RRD and proarrhythmic effect of I(Kr) inhibition.. Duration of the monophasic APD (MAPD) was measured from female rabbit hearts paced at cycle lengths from 400 to 2000 milliseconds, and BVR was calculated. In the absence of a drug, duration of monophasic action potential at 90% completion of repolarization (MAPD(90)) and BVR increased as the cycle length was increased from 400 to 2000 milliseconds (n=36 and 26; P<0.01). Both E-4031 (20 nmol/L) and d-sotalol (10 μmol/L) increased MAPD(90) and BVR at all stimulation rates, and the increase was greater at slower than at faster pacing rates (n=19, 11, 12 and 7, respectively; P<0.01). Tetrodotoxin (1 μmol/L) and ranolazine significantly attenuated the RRD of MAPD(90,) reduced BVR (P<0.01), and abolished torsade de pointes in hearts treated with either 20 nmol/L E-4031 or 10 μmol/L d-sotalol. Endogenous late I(Na) in cardiomyocytes stimulated at cycle lengths from 500 to 4000 milliseconds was greater at slower than at faster stimulation rates, and rapidly decreased during the first several beats at faster but not at slower rates (n=8; P<0.01). In a computational model, simulated RRD of APD caused by E-4031 and d-sotalol was attenuated when late I(Na) was inhibited.. Endogenous late I(Na) contributes to the RRD of I(Kr) inhibitor-induced increases in APD and BVR and to bradycardia-related ventricular arrhythmias.

Topics: Acetanilides; Action Potentials; Animals; Anti-Arrhythmia Agents; Bradycardia; Disease Models, Animal; Enzyme Inhibitors; Female; Heart Rate; Long QT Syndrome; Models, Cardiovascular; Myocardial Contraction; Myocytes, Cardiac; Patch-Clamp Techniques; Piperazines; Piperidines; Pyridines; Rabbits; Ranolazine; Sodium; Sodium Channel Blockers; Sodium Channels; Tetrodotoxin; Torsades de Pointes

The Kv11.1 (hERG) K+ channel plays a fundamental role in cardiac repolarization. Missense mutations in KCNH2, the gene encoding Kv11.1, cause long QT syndrome (LQTS) and frequently cause channel trafficking-deficiencies. This study characterized the properties of a novel KCNH2 mutation discovered in a LQT2 patient resuscitated from a ventricular fibrillation arrest. Proband genotyping was performed by SSCP and DNA sequencing. The electrophysiological and biochemical properties of the mutant channel were investigated after expression in HEK293 cells. The proband manifested a QTc of 554 ms prior to electrolyte normalization. Mutation analysis revealed an autosomal dominant frameshift mutation at proline 1086 (P1086fs+32X; 3256InsG). Co-immunoprecipitation demonstrated that wild-type Kv11.1 and mutant channels coassemble. Western blot showed that the mutation did not produce mature complex-glycosylated Kv11.1 channels and coexpression resulted in reduced channel maturation. Electrophysiological recordings revealed mutant channel peak currents to be similar to untransfected cells. Co-expression of channels in a 1∶1 ratio demonstrated dominant negative suppression of peak Kv11.1 currents. Immunocytochemistry confirmed that mutant channels were not present at the plasma membrane. Mutant channel trafficking rescue was attempted by incubation at reduced temperature or with the pharmacological agents E-4031. These treatments did not significantly increase peak mutant currents or induce the formation of mature complex-glycosylated channels. The proteasomal inhibitor lactacystin increased the protein levels of the mutant channels demonstrating proteasomal degradation, but failed to induce mutant Kv11.1 protein trafficking. Our study demonstrates a novel dominant-negative Kv11.1 mutation, which results in degraded non-functional channels leading to a LQT2 phenotype.

Topics: Adult; Blotting, Western; Cell Membrane; Electrophysiology; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Female; Genotype; HEK293 Cells; Humans; Immunohistochemistry; Immunoprecipitation; Long QT Syndrome; Microscopy, Confocal; Models, Biological; Mutation; Piperidines; Proteasome Endopeptidase Complex; Protein Transport; Pyridines

The human ether-a-go-go related gene (hERG) encodes the voltage-gated K(+) channel that underlies the rapidly activating delayed-rectifier current in cardiac myocytes. hERG is synthesized in the endoplasmic reticulum (ER) as an "immature" N-linked glycoprotein and is terminally glycosylated in the Golgi apparatus. Most hERG missense mutations linked to long QT syndrome type 2 (LQT2) reduce the terminal glycosylation and functional expression. We tested the hypothesis that a distinct pre-Golgi compartment negatively regulates the trafficking of some LQT2 mutations to the Golgi apparatus. We found that treating cells in nocodazole, a microtubule depolymerizing agent, altered the subcellular localization, functional expression, and glycosylation of the LQT2 mutation G601S-hERG differently from wild-type hERG (WT-hERG). G601S-hERG quickly redistributed to peripheral compartments that partially colocalized with KDEL (Lys-Asp-Glu-Leu) chaperones but not calnexin, Sec31, or the ER golgi intermediate compartment (ERGIC). Treating cells in E-4031, a drug that increases the functional expression of G601S-hERG, prevented the accumulation of G601S-hERG to the peripheral compartments and increased G601S-hERG colocalization with the ERGIC. Coexpressing the temperature-sensitive mutant G protein from vesicular stomatitis virus, a mutant N-linked glycoprotein that is retained in the ER, showed it was not restricted to the same peripheral compartments as G601S-hERG at nonpermissive temperatures. We conclude that the trafficking of G601S-hERG is negatively regulated by a microtubule-dependent compartment within the ER. Identifying mechanisms that prevent the sorting or promote the release of LQT2 channels from this compartment may represent a novel therapeutic strategy for LQT2.

Topics: Anti-Arrhythmia Agents; Blotting, Western; Endoplasmic Reticulum; Ether-A-Go-Go Potassium Channels; Fluorescent Antibody Technique; Glycosylation; Golgi Apparatus; Green Fluorescent Proteins; HEK293 Cells; Humans; Long QT Syndrome; Microtubules; Mutation; Myocytes, Cardiac; Nocodazole; Patch-Clamp Techniques; Piperidines; Protein Transport; Pyridines; Tubulin Modulators

Droperidol is a highly potent butyrophenone used for the therapy of postoperative nausea and vomiting. Its cardiac safety in cardiovascular-healthy patients and those with long QT (LQT) syndrome is a matter of debate. In this study, we investigated whether droperidol has subtype-specific effects in cellular and computational models of LQT syndrome.. Left ventricular cardiac myocytes were isolated from adult guinea pig hearts. LQT1-like behavior was pharmacologically induced by chromanol 293B (10 micromol/L) and LQT2-like states by E4031 (10 micromol/L). Computational analysis was performed using the Luo-Rudy dynamic model. Data are given as mean + or - SEM.. In control myocytes, droperidol lengthened action potentials in a concentration-dependent manner with a maximal prolongation of 37% + or - 13% (n = 4) at a concentration of 0.6 micromol/L. In LQT1-like myocytes, droperidol (0.6 micromol/L) further prolonged action potentials by 31% + or - 6% (n = 6) but shortened action potentials of LQT2-like myocytes by 11% + or - 2% (n = 8). Computational modeling supported the concept that droperidol, in addition to the rapid component of the delayed K(+) current, blocks depolarizing targets, such as the L-type Ca(2+) current, the Na(+)-Ca(2+) exchanger, and the Na(+)-K(+) adenosine triphosphatase.. Droperidol has more detrimental effects on cardiac repolarization of LQT1-like than of LQT2-like myocytes suggesting subtype-specific cardiotoxic effects in patients with LQT syndrome. The subtype specificity of droperidol seems to be caused by a complex interaction of droperidol with several different molecular targets. This interaction deserves further investigation to establish the feasibility of a subtype-directed approach in the perioperative management of patients with LQT syndrome.

Topics: Action Potentials; Adult; Animals; Anti-Arrhythmia Agents; Antiemetics; Cardioplegic Solutions; Cell Separation; Chromans; Computer Simulation; Data Interpretation, Statistical; Droperidol; Guinea Pigs; Humans; Long QT Syndrome; Models, Statistical; Myocytes, Cardiac; Patch-Clamp Techniques; Piperidines; Potassium Channel Blockers; Pyridines; Sulfonamides

The ionic basis of excitability requires identification and characterisation of expressed channels and their specific roles in native neurons. We have exploited principal neurons of the medial nucleus of the trapezoid body (MNTB) as a model system for examining voltage-gated K(+) channels, because of their known function and simple morphology. Here we show that channels of the ether-à-go-go-related gene family (ERG, Kv11; encoded by kcnh) complement Kv1 channels in regulating neuronal excitability around threshold voltages. Using whole-cell patch clamp from brainstem slices, the selective ERG antagonist E-4031 reduced action potential (AP) threshold and increased firing on depolarisation. In P12 mice, under voltage-clamp with elevated [K(+)](o) (20 mm), a slowly deactivating current was blocked by E-4031 or terfenadine (V(0.5,act) = -58.4 +/- 0.9 mV, V(0.5,inact) = -76.1 +/- 3.6 mV). Deactivation followed a double exponential time course (tau(slow) = 113.8 +/- 6.9 ms, tau(fast) = 33.2 +/- 3.8 ms at -110 mV, tau(fast) 46% peak amplitude). In P25 mice, deactivation was best fitted by a single exponential (tau(fast) = 46.8 +/- 5.8 ms at -110 mV). Quantitative RT-PCR showed that ERG1 and ERG3 were the predominant mRNAs and immunohistochemistry showed expression as somatic plasma membrane puncta on principal neurons. We conclude that ERG currents complement Kv1 currents in limiting AP firing at around threshold; ERG may have a particular role during periods of high activity when [K(+)](o) is elevated. These ERG currents suggest a potential link between auditory hyperexcitability and acoustic startle triggering of cardiac events in familial LQT2.

Topics: Action Potentials; Animals; Auditory Pathways; Brain Stem; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Immunohistochemistry; In Vitro Techniques; Kinetics; Long QT Syndrome; Mice; Mice, Inbred CBA; Neurons; Patch-Clamp Techniques; Piperidines; Potassium; Potassium Channel Blockers; Pyridines; Rats; Rats, Wistar; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Sensory Thresholds

Drug-induced long QT syndrome has been principally ascribed to block of the cardiac hERG K(+) channel. Methanesulfonanilides, such as MK-499, E-4031 and dofetilide, are potent hERG antagonists that likely bind along the S6 helix within the inner vestibule of the pore. To further investigate these interactions, we broadly explored the structure-activity relationships of closely related analogs of MK-499 using a high-throughput ion flux assay, and evaluated in greater detail using patch-clamp electrophysiology. We observed that substitutions at the 4-position on the benzopyran ring significantly affected the potency of these analogs with the rank order of unsubstituted approximately ketone>amine>hydroxyl, implicating an important interaction at this position. We also evaluated the potency of these analogs on an S6 mutant of hERG (F656A) previously shown to significantly reduce the affinity for MK-499 and other known hERG antagonists (e.g. cisapride, terfenadine). In contrast to MK-499 (4-hydroxyl) and either the amine or unsubstituted analogs, the potency of the ketone analog was unaffected by this mutation suggesting that a compensatory interaction may be unveiled with the aromatic to apolar substitution, possibly through hydrogen bonding with Ser624 based on molecular modeling. More significantly, we found that this mutation rendered hERG susceptible to block in the closed-state by the smaller, unsubstituted analog, but not by MK-499 or larger analogs. Together these data suggest that interaction with Phe656 is not an absolute requirement for the binding of all methanesulfonanilide compounds, and that this residue may play a broader role in regulating access to the inner vestibule.

Topics: Animals; Benzopyrans; Cell Culture Techniques; Chlorides; CHO Cells; Cricetinae; Cricetulus; Ether-A-Go-Go Potassium Channels; Humans; Ion Channel Gating; Long QT Syndrome; Models, Molecular; Mutation; Patch-Clamp Techniques; Piperidines; Potassium Channel Blockers; Protein Binding; Protein Structure, Tertiary; Rubidium; Structure-Activity Relationship; Transfection

PC-1 (NPP-1) inhibitors may be useful as therapeutics for the treatment of CDDP (calcium pyrophosphate dehydrate) deposition disease and osteoarthritis. We have identified a series of potent quinazolin-4-piperidin-4-ethyl sulfamide PC-1 inhibitors. The series, however, suffers from high affinity binding to hERG potassium channels, which can cause drug-induced QT prolongation. We used a hERG homology model to identify potential key interactions between our compounds and hERG, and the information gained was used to design and prepare a series of quinazolin-4-piperidin-4-methyl sulfamides that retain PC-1 activity but lack binding affinity for hERG.

Topics: Drug Design; Enzyme Inhibitors; Ether-A-Go-Go Potassium Channels; Humans; Long QT Syndrome; Osteoarthritis; Phosphoric Diester Hydrolases; Piperidines; Protein Binding; Pyrophosphatases; Quinazolines; Sulfonamides

An 83-year-old female, who had a history of anterior myocardial infarction, was treated for Alzheimer's disease with donepezil. She suffered from repeated diarrhea and vomiting, and experienced syncope. She was admitted to our hospital and was diagnosed with acute colitis and syncope. On admission, her heart rate was 54 beats/min with regular rhythm. Laboratory data showed a low plasma potassium level. Electrocardiogram (ECG) showed poor R progression, ST elevation, negative T in precordial leads, and marked QT prolongation. Transthoracic echocardiogram showed the enlargement of the left atrium and aneurysmal area at the apex. Torsades de Pointes (TdP) with syncope and convulsion were confirmed on ECG monitoring twice after admission. We treated her with potassium chloride and started magnesium sulfate and lidocaine, and then added isoprenaline injection. After these treatments, her heart rate increased and we did not detect TdP again. With the aging population in Japan, prescriptions for donepezil are increasing. We have to be vigilant for syncope in patients taking donepezil, which is possibly related to QT prolongation and TdP.

Topics: Aged, 80 and over; Alzheimer Disease; Cholinesterase Inhibitors; Colitis; Donepezil; Electrocardiography; Female; Humans; Indans; Isoproterenol; Lidocaine; Long QT Syndrome; Magnesium Sulfate; Nootropic Agents; Piperidines; Potassium Chloride; Syncope; Torsades de Pointes; Treatment Outcome

The long QT syndrome is characterized by a prolongation of the QT interval measured on the surface electrocardiogram. Prolonging the QT interval increases the risk of dangerous ventricular fibrillations, eventually leading to sudden cardiac death. Pharmacologically induced QT interval prolongations are most often caused by antagonizing effects on the repolarizing cardiac current called IKr. In humans IKr is mediated by the human ether-a-go-go related gene (hERG) potassium channel. We recently presented NS3623, a compound that selectively activates this channel. The present study was dedicated to examining the in vivo effects of NS3623. Injection of 30 mg/kg NS3623 shortened the corrected QT interval by 25 +/- 4% in anaesthetized guinea pigs. Accordingly, 50 mg/kg of NS3623 shortened the QT interval by 30 +/- 6% in conscious guinea pigs. Finally, pharmacologically induced QT prolongation by a hERG channel antagonist (0.15 mg/kg E-4031) could be reverted by injection of NS3623 (50 mg/kg) in conscious guinea pigs. In conclusion, the present in vivo study demonstrates that injection of the hERG channel agonist NS3623 results in shortening of the QTc interval as well as reversal of a pharmacologically induced QT prolongation in both anaesthetized and conscious guinea pigs.

Topics: Animals; Anti-Arrhythmia Agents; Consciousness; Delayed Rectifier Potassium Channels; Dose-Response Relationship, Drug; Electrocardiography; Ether-A-Go-Go Potassium Channels; Female; Guinea Pigs; Heart Rate; Humans; Long QT Syndrome; Phenylurea Compounds; Piperidines; Pyridines; Tetrazoles

Cardiac I Kr is a critical repolarizing current in the heart and a target for inherited and acquired long-QT syndrome (LQTS). Biochemical and functional studies have demonstrated that I Kr channels are heteromers composed of both hERG 1a and 1b subunits, yet our current understanding of I Kr functional properties derives primarily from studies of homooligomers of the original hERG 1a isolate. Here, we examine currents produced by hERG 1a and 1a/1b channels expressed in HEK-293 cells at near-physiological temperatures. We find that heteromeric hERG 1a/1b currents are much larger than hERG 1a currents and conduct 80% more charge during an action potential. This surprising difference corresponds to a 2-fold increase in the apparent rates of activation and recovery from inactivation, thus reducing rectification and facilitating current rebound during repolarization. Kinetic modeling shows these gating differences account quantitatively for the differences in current amplitude between the 2 channel types. Drug sensitivity was also different. Compared to homomeric 1a channels, heteromeric 1a/1b channels were inhibited by E-4031 with a slower time course and a corresponding 4-fold shift in the IC50. The importance of hERG 1b in vivo is supported by the identification of a 1b-specific A8V missense mutation in 1/269 unrelated genotype-negative LQTS patients that was absent in 400 control alleles. Mutant 1bA8V expressed alone or with hERG 1a in HEK-293 cells dramatically reduced 1b protein levels. Thus, mutations specifically disrupting hERG 1b function are expected to reduce cardiac I Kr and enhance drug sensitivity, and represent a potential mechanism underlying inherited or acquired LQTS.

Topics: Action Potentials; Amino Acid Substitution; Anti-Arrhythmia Agents; Cell Line; Ether-A-Go-Go Potassium Channels; Humans; Ion Channel Gating; Kinetics; Long QT Syndrome; Models, Biological; Mutation, Missense; Piperidines; Protein Subunits; Pyridines

Pharmacological inhibitors of the human ether-a-go-go (hEAG) potassium channel, astemizole and imipramine, have been used to demonstrate that hEAG plays a role in cancer cell proliferation. Astemizole and imipramine are, however, relatively non-specific ion channel blockers, as astemizole can also block the related potassium channel, human ether-a-go-go-related (hERG). Therefore, we aimed to determine the molecular target of astemizole, in the human mammary carcinoma cell line MCF-7. We initially confirmed the expression of KCNH1 and KCNH2 mRNA and hEAG and hERG channel protein in MCF-7 cells. Using a [3H]-thymidine incorporation assay we determined that astemizole inhibited MCF-7 cell proliferation, whereas the hERG-specific channel blocker E-4031 had no effect. We then determined that E-4031 inhibited the regulatory volume decrease (RVD) observed in these cells following exposure to hypotonic solutions, confirming that functional hERG channels are present and may be important for cell volume regulation in MCF-7 cells. Our results suggest, for the first time, that hERG is involved in cell volume regulation. In addition, the function of hEAG and hERG in MCF-7 cell proliferation can be separated pharmacologically by utilizing the channel inhibitors astemizole and E-4031. The hEAG channel function in MCF-7 cells appears to be involved in the regulation of cell proliferation, whereas hERG is involved in cell volume regulation.

Topics: Adenocarcinoma; Anti-Allergic Agents; Anti-Arrhythmia Agents; Astemizole; Breast Neoplasms; Cell Proliferation; Cell Size; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Humans; Imipramine; Long QT Syndrome; Piperidines; Pyridines; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Tumor Cells, Cultured

Topics: Aged; Dementia; Donepezil; Female; Humans; Indans; Long QT Syndrome; Nootropic Agents; Piperidines; Tachycardia, Ventricular

Torsade de pointes (TdP) can be induced by a reduction in cardiac repolarizing capacity. The aim of this study was to assess whether IKs blockade or enhancement of INa could potentiate TdP induced by IKr blockade and to investigate whether short-term variability (STV) or triangulation of action potentials preceded TdP.. Experiments were performed in open-chest, pentobarbital-anaesthetized, alpha 1-adrenoceptor-stimulated, male New Zealand White rabbits, which received three consecutive i.v. infusions of either the IKr blocker E-4031 (1, 3 and 10 nmol kg(-1) min(-1)), the IKs blocker HMR1556 (25, 75 and 250 nmol kg(-1) min(-1)) or E-4031 and HMR1556 combined. In a second study rabbits received either the same doses of E-4031, the INa enhancer, ATX-II (0.4, 1.2 and 4.0 nmol kg(-1)) or both of these drugs. ECGs and epicardial monophasic action potentials were recorded.. HMR1556 alone did not cause TdP but increased E-4031-induced TdP from 25 to 80%. ATX-II alone caused TdP in 38% of rabbits, as did E-4031; 75% of rabbits receiving both drugs had TdP. QT intervals were prolonged by all drugs but the extent of QT prolongation was not related to the occurrence of TdP. No changes in STV were detected and triangulation was only increased after TdP occurred.. Giving modulators of ion channels in combination substantially increased TdP but, in this model, neither STV nor triangulation of action potentials could predict TdP.

Topics: Action Potentials; Animals; Chromans; Cnidarian Venoms; Delayed Rectifier Potassium Channels; Dose-Response Relationship, Drug; Drug Synergism; Electrocardiography; Electrophysiology; Forecasting; Long QT Syndrome; Male; Piperidines; Potassium Channels, Voltage-Gated; Pyridines; Rabbits; Sodium Channels; Sulfonamides; Torsades de Pointes

The analysis of cardiac electrical restitution (the relationship between an action potential duration and its preceding diastolic interval) has been used to predict arrhythmia liability. However, the procedure to measure restitution is invasive and disrupts normal physiological autonomic balance. Dynamic analysis of sequential beat-to-beat ECG data was used to study restitution under normal sinus rhythm and to quantify changes in temporal hysteresis with heart rate acceleration/deceleration during QT prolongation. Congenital long QT (LQT) 1 and LQT2 syndromes during sympathetic stimulation were modeled because of their association with increased risk of ventricular arrhythmia. Temporal heterogeneity and hysteresis of restitution were examined in the conscious dog under varying conditions of delayed repolarization using either the selective inhibitors of the slowly activating delayed rectifier potassium current (R)-2-(4-trifluoromethyl)-N-[2-oxo-5-phenyl-1-(2,2,2-trifluoroethyl)-2,3-dihydro-1H-benzo[e][1,4]diazepin-3-yl]acetamide (L-768,673); the rapidly activating delayed rectifier potassium current (1-[2-(6-methyl-2-pyridyl)ethyl]-4-methyl-sulfonylaminobenzoyl)-piperidine (E-4031); or a combination of both at rest and during heart rate acceleration with sympathetic stimulation using isoproterenol challenges. Impaired repolarization with the combination of E-4031 and L-768,673 increased heterogeneity of restitution at rest 55 to 91%, increased hysteresis during heart rate acceleration after isoproterenol challenge by approximately 40 to 60%, and dramatically reduced the minimum TQ interval by 72% to only 28 ms. Impaired repolarization alters restitution during normal sinus rhythm and increases hysteresis/heterogeneity during heart rate acceleration following sympathetic stimulation. Thus, dynamic beat-to-beat measurements of restitution could lead to clinically applicable ECG obtained biomarkers for assessment of changes associated with arrhythmogenic risk.

Topics: Acetamides; Action Potentials; Animals; Anti-Arrhythmia Agents; Arrhythmias, Cardiac; Benzodiazepinones; Dogs; Electrocardiography; Female; Heart Rate; Long QT Syndrome; Male; Myocardial Contraction; Piperidines; Potassium Channels, Voltage-Gated; Pyridines

Long QT syndrome type 2 is caused by mutations in the human ether-a-go-go-related gene (hERG). We previously reported that the N470D mutation is retained in the endoplasmic reticulum (ER) but can be rescued to the plasma membrane by hERG channel blocker E-4031. The mechanisms of ER retention and how E-4031 rescues the N470D mutant are poorly understood. In this study, we investigated the interaction of hERG channels with the ER chaperone protein calnexin. Using coimmunoprecipitation, we showed that the immature forms of both wild type hERG and N470D associated with calnexin. The association required N-linked glycosylation of hERG channels. Pulse-chase analysis revealed that N470D had a prolonged association with calnexin compared with wild type hERG and E-4031 shortened the time course of calnexin association with N470D. To test whether the prolonged association of N470D with calnexin is due to defective folding of mutant channels, we studied hERG channel folding using the trypsin digestion method. We found that N470D and the immature form of wild type hERG were more sensitive to trypsin digestion than the mature form of wild type hERG. In the presence of E-4031, N470D became more resistant to trypsin even when its ER-to-Golgi transport was blocked by brefeldin A. These results suggest that defective folding of N470D contributes to its prolonged association with calnexin and ER retention and that E-4031 may restore proper folding of the N470D channel leading to its cell surface expression.

Topics: Calnexin; Detergents; Endoplasmic Reticulum; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Glycosylation; Humans; Long QT Syndrome; Mutation; Piperidines; Protein Folding; Pyridines; Trypsin

Drug-induced block of cardiac hERG K+ channels causes acquired long QT syndrome. Here, we characterized the molecular mechanism of hERG block by two low-potency drugs (Nifekalant and bepridil) and two high-potency drugs 1-[2-(6-methyl-2pyridyl)ethyl]-4-(4-methylsulfonyl aminobenzoyl)piperidine (E-4031) and dofetilide). Channels were expressed in Xenopus laevis oocytes, and currents were measured using the two-microelectrode voltage-clamp technique. All four drugs progressively reduced hERG current during a 20-s depolarization to 0 mV after a 10-min pulse-free period, consistent with the preferential block of open channels. Recovery from block in response to pulses to -160 mV was observed for D540K hERG channels but not for wild-type hERG channels, suggesting that all four drugs are trapped in the central cavity by closure of the activation gate. The molecular determinants of hERG channel block were defined by using a site-directed mutagenesis approach. Mutation to alanine of three residues near the pore helix (Thr623, Ser624, and Val625) and four residues in Ser6 (Gly648, Tyr652, Phe656, and Val659) reduced channel sensitivity to block by dofetilide and E-4031, effects identical with those reported previously for two other methanesulfonanilides, (+)- N -[1' -(6-cyano-1,2,3,4-tetrahydro-2(R)-naphthalenyl)-3,4-dihydro-4(R)-hydroxyspiro(2H -1-benzopyran-2,4' -piperidin)-6-yl]-methanesulfonamide] monohydrochloride (MK-499) and ibutilide. The effect of nifekalant on mutant channels was similar, except that V659A retained normal sensitivity and I655A channels were less sensitive. Finally, mutation of the three residues near the pore helix and Phe656 in the Ser6 domain reduced channel block by bepridil. We conclude that the binding site is not identical for all drugs that preferentially block hERG in the open state.

Topics: DNA Primers; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Humans; Kinetics; Long QT Syndrome; Mutagenesis, Site-Directed; Patch-Clamp Techniques; Phenethylamines; Piperidines; Potassium Channel Blockers; Pyridines; Recombinant Proteins; Sulfonamides

Fluoxetine (Prozac) is a widely prescribed drug in adults and children, and it has an active metabolite, norfluoxetine, with a prolonged elimination time. Although uncommon, Prozac causes QT interval prolongation and arrhythmias; a patient who took an overdose of Prozac exhibited a prolonged QT interval (QTc 625 msec). We looked for possible mechanisms underlying this clinical finding by analysing the effects of fluoxetine and norfluoxetine on ion channels in vitro.. We studied the effects of fluoxetine and norfluoxetine on the electrophysiology and cellular trafficking of hERG K+ and SCN5A Na+ channels heterologously expressed in HEK293 cells.. Voltage clamp analyses employing square pulse or ventricular action potential waveform protocols showed that fluoxetine and norfluoxetine caused direct, concentration-dependent, block of hERG current (IhERG). Biochemical studies showed that both compounds also caused concentration-dependent reductions in the trafficking of hERG channel protein into the cell surface membrane. Fluoxetine had no effect on SCN5A channel or HEK293 cell endogenous current. Mutations in the hERG channel drug binding domain reduced fluoxetine block of IhERG but did not alter fluoxetine's effect on hERG channel protein trafficking.. Our findings show that both fluoxetine and norfluoxetine at similar concentrations selectively reduce IhERG by two mechanisms, (1) direct channel block, and (2) indirectly by disrupting channel protein trafficking. These two effects are not mediated by a single drug binding site. Our findings add complexity to understanding the mechanisms that cause drug-induced long QT syndrome.

Topics: Adult; Antidepressive Agents, Second-Generation; Blotting, Western; Cell Line; Cell Membrane; Cisapride; Dose-Response Relationship, Drug; Drug Overdose; Ether-A-Go-Go Potassium Channels; Female; Fluoxetine; Humans; Long QT Syndrome; Membrane Potentials; Muscle Proteins; Mutation; NAV1.5 Voltage-Gated Sodium Channel; Patch-Clamp Techniques; Piperidines; Protein Transport; Pyridines; Sodium Channels; Time Factors; Transfection

The long QT syndrome is a rare disease. The prevalence is estimated at 1/5 000 to 1/20,000. Numerous drugs are contra-indicated because they can lengthen the QT interval. A case of pollen allergy in an adolescent with LQTS is described. The possibility to prescribe anti-H1 drugs is reviewed since cases of torsades de pointe and even deaths have been reported for terfenadine and astemizole. Diphenhydramine, orphenadrine and hydroxyzine are contra-indicated. No accidents and no effects on the QT interval have been published for ebastine, fexofenadine, desloratadine and levocetirizine. These anti-H1 drugs could be used with great care, without any association with drugs resulting in low serum potassium level. Azelastine eye drops have been authorized and a routine protection by inhaled corticosteroids during the pollinic period has been advised in this adolescent treated by betablockers.

Topics: Adolescent; Adrenergic beta-Antagonists; Anti-Asthmatic Agents; Butyrophenones; Cetirizine; Conjunctivitis, Allergic; Cromolyn Sodium; Diabetes Mellitus, Type 1; Heart; Histamine H1 Antagonists; Humans; Long QT Syndrome; Male; Piperazines; Piperidines; Rhinitis, Allergic, Seasonal; Terfenadine

Methods to correct the QT interval for heart rate are often in disagreement and may be further confounded by changes in autonomic state. This can be problematic when trying to distinguish the changes in QT interval by either drug-induced delayed repolarization or from autonomic-mediated physiological responses. Assessment of the canine dynamic QT-RR interval relationship was visualized by novel programming of the dynamic beat-to-beat confluence of data or "clouds". To represent the nonuniformity of the clouds, a bootstrap sampling method that computes the mathematical center of the uncorrected beat-to-beat QT value (QTbtb) with upper 95% confidence bounds was adopted and compared with corrected QT (QTc) using standard correction factors. Nitroprusside-induced reflex tachycardia reduced QTbtb by 43 ms, whereas an increase of 55 and 16 ms was obtained using the Bazett (QTcB) and Fridericia (QTcF) formulae, respectively. Phenylephrine-induced reflex bradycardia increased QTbtb by 3 ms but decreased QTcB by 20 ms and QTcF by 12 ms. Delayed repolarization with E-4031 (1-[2-(6-methyl-2-pyridyl)ethyl]-4-methylsulfonylaminobenzoyl)-piperidine), an inhibitor of rectifier potassium current, increased QTbtb by 26 ms but QT prolongation calculations using QTcF and QTcB were between 12 and 52% less, respectively, when small decreases in heart rate (5-8 beats per minute) were apparent. Dynamic assessment of beat-to-beat data, using the bootstrap method, allows quantification of QT interval changes under varying conditions of heart rate, autonomic tone, and direct repolarization that may not be distinguishable with use of standard correction factors.

Topics: Adrenergic beta-Agonists; Animals; Bradycardia; Dogs; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Heart Rate; Humans; Isoproterenol; Long QT Syndrome; Nitroprusside; Phenylephrine; Piperidines; Potassium Channels, Voltage-Gated; Pyridines; Tachycardia

Many drugs inhibit the human ether-a-go-go-related gene (HERG) cardiac K+ channel. This leads to action potential prolongation on the cellular level, a prolongation of the QT interval on the electrocardiogram, and sometimes cardiac arrhythmia. To date, no activators of this channel have been reported. Here, we describe the in vitro electrophysiological effects of (3R,4R)-4-[3-(6-methoxyquinolin-4-yl)-3-oxo-propyl]-1-[3-(2,3,5-trifluoro-phenyl)-prop-2-ynyl]-piperidine-3-carboxylic acid (RPR260243), a novel activator of HERG. Using patch-clamp electrophysiology, we found that RPR260243 dramatically slowed current deactivation when applied to cells stably expressing HERG. The effects of RPR260243 on HERG channel deactivation were temperature- and voltage-dependent and occurred over the concentration range of 1 to 30 microM. RPR260243-modified HERG currents were inhibited by dofetilide (IC50 = 58 nM). RPR260243 had little effect on HERG current amplitude and no significant effects on steady-state activation parameters or on channel inactivation processes. RPR260243 displayed no activator-like effects on other voltage-dependent ion channels, including the closely related erg3 K+ channel. RPR260243 enhanced the delayed rectifier current in guinea pig myocytes but, when administered alone, had little effect on action potential parameters in these cells. However, RPR260243 completely reversed the action potential-prolonging effects of dofetilide in this preparation. Using the Langendorff heart method, we found that 5 microM RPR260243 increased T-wave amplitude, prolonged the PR interval, and shortened the QT interval. We believe RPR260243 represents the first known HERG channel activator and that the drug works primarily by inhibiting channel closure, leading to a persistent HERG channel current upon repolarization. Compounds like RPR260243 will be useful for studying the physiological role of HERG and may one day find use in treating cardiac disease.

Topics: Action Potentials; Animals; CHO Cells; Cricetinae; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Guinea Pigs; Heart; Humans; In Vitro Techniques; Kinetics; Long QT Syndrome; Patch-Clamp Techniques; Piperidines; Potassium Channels, Voltage-Gated; Quinolines

We examined the cellular and ionic mechanism for QT prolongation and subsequent Torsade de Pointes (TdP) and the effect of verapamil under conditions mimicking KCNQ1 (I(Ks) gene) defect linked to acquired long QT syndrome (LQTS).. Agents with an I(Kr)-blocking effect often induce marked QT prolongation in patients with acquired LQTS. Previous reports demonstrated a relationship between subclinical mutations in cardiac K+ channel genes and a risk of drug-induced TdP.. Transmembrane action potentials from epicardial (EPI), midmyocardial (M), and endocardial (ENDO) cells were simultaneously recorded, together with a transmural electrocardiogram, at a basic cycle length of 2,000 ms in arterially perfused feline left ventricular preparations.. The I(Kr) block (E-4031: 1 micromol/l) under control conditions (n = 5) prolonged the QT interval but neither increased transmural dispersion of repolarization (TDR) nor induced arrhythmias. However, the I(Kr) blocker under conditions with I(Ks) suppression by chromanol 293B 10 micromol/l mimicking the KCNQ1 defect (n = 10) preferentially prolonged action potential duration (APD) in EPI rather than M or ENDO, thereby dramatically increasing the QT interval and TDR. Spontaneous or epinephrine-induced early afterdepolarizations (EADs) were observed in EPI, and subsequent TdP occurred only under both I(Ks) and I(Kr) suppression. Verapamil (0.1 to 5.0 micromol/l) dose-dependently abbreviated APD in EPI more than in M and ENDO, thereby significantly decreasing the QT interval, TDR, and suppressing EADs and TdP.. Subclinical I(Ks) dysfunction could be a risk of drug-induced TdP. Verapamil is effective in decreasing the QT interval and TDR and in suppressing EADs, thus preventing TdP in the model of acquired LQTS.

Topics: Action Potentials; Animals; Anti-Arrhythmia Agents; Calcium Channel Blockers; Cats; Chromans; Heart; Long QT Syndrome; Piperidines; Potassium Channel Blockers; Potassium Channels; Pyridines; Sulfonamides; Tissue Culture Techniques; Torsades de Pointes; Verapamil

It has been proposed that the highest risk for cardiac events in patients with long-QT syndrome subtype 2 (LQT2) is related to mutations in the pore region of the KCNH2 channel. It has also been suggested that a subpopulation of LQT2 patients may benefit from pharmacological therapy with modified KCNH2 channel-blocking drugs.. In a large LQT2 family (n=33), we have identified a novel nonpore missense mutation (K28E) in the Per-Arnt-Sim (PAS) domain of the KCNH2 channel associated with a malignant phenotype: One third of the suspected gene carriers experienced a major cardiac event. Wild-type and K28E-KCNH2 channels were transiently transfected in HEK293 cells. For the mutant channel, whole-cell patch-clamp analysis showed a reduced current density, a negative shift of voltage-dependent channel availability, and an increased rate of deactivation. Western blot analysis and confocal imaging revealed a trafficking deficiency for the mutant channel that could be rescued by the K+ channel blocker E-4031. In cells containing both wild-type and mutant channels, deactivation kinetics were normal. In these cells, reduced current density was restored with E-4031.. Our data suggest that besides pore mutations, mutations in the PAS domain may also exhibit a malignant outcome. Pharmacological restoration of current density is promising as a mutation-specific therapy for patients carrying this trafficking-defective mutant.

Topics: Adult; Blotting, Western; Cell Line; Death, Sudden, Cardiac; Electrophysiology; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Female; Glutamic Acid; Humans; Kidney; Long QT Syndrome; Lysine; Male; Microscopy, Confocal; Middle Aged; Mutation, Missense; Patch-Clamp Techniques; Pedigree; Peptides; Phenotype; Piperidines; Potassium Channels, Voltage-Gated; Protein Structure, Tertiary; Proteins; Pyridines

The purpose of this study was to evaluate a telemetry system for examining QT evaluation in the conscious free-moving guinea pig using 10 reference compounds whose effects on human QT interval are well established: 8 positive references (bepridil, terfenadine, cisapride, haloperidol, pimozide, quinidine, E-4031 and thioridazine), and 2 negative references (propranolol and nifedipine). Pharmacokinetic experiments were also performed for the 8 positive references. Telemetry transmitters were implanted subcutaneously in male Hartley guinea pigs, and the RR and QT intervals were measured. All 8 positive references prolonged QTc (QTc = k x QT/RR(1/2)) 10% or more during the 60 min observation period. When the values of the QTc changes were plotted against the serum concentrations, the resulting curves exhibited an anticlockwise hysteresis loop for all 8 references. In guinea pigs treated with haloperidol, changes of the T-wave shape from positive to flat were observed. The 2 negative references did not prolong the QTc. These findings suggest that the present telemetry guinea pig model is useful for QT evaluation in the early stages of drug development, because of the small body size of guinea pigs and their action potential configuration, which is similar to that of humans.

Topics: Animals; Anti-Arrhythmia Agents; Antipsychotic Agents; Bepridil; Cisapride; Disease Models, Animal; Electrocardiography; Guinea Pigs; Haloperidol; Heart; Humans; Injections, Intravenous; Long QT Syndrome; Male; Nifedipine; Pimozide; Piperidines; Pyridines; Quinidine; Reproducibility of Results; Telemetry; Terfenadine; Thioridazine

Mutations in the human ether-a-go-go-related gene (HERG) cause long QT syndrome. We previously showed that the HERG N470D mutation expressed as homotetrameric channels causes a protein trafficking defect, and this can be corrected by the HERG channel blocking drug E-4031. The N470D mutant also has been reported to cause dominant negative suppression of HERG current when coexpressed with wild-type channel subunits. The aims of this study were 1). to investigate the molecular mechanism responsible for the dominant negative effect of the N470D mutant coexpressed with wild-type subunits and 2). to test whether the trafficking defective heteromeric channels could be pharmacologically rescued by E-4031. Using a combination of immunoprecipitation and Western blot methods, we showed that N470D mutant and wild-type HERG subunits were physically associated in the endoplasmic reticulum as heteromeric channels. The coassembly resulted in the retention of both wild-type and N470D subunits in the endoplasmic reticulum. Culturing cells in E-4031 increased the cell surface expression of these channels, although with an altered electrophysiological phenotype. These results suggest that the dominant negative effect of the N470D wild-type coassembled channels is caused by retention of heteromeric channels in the endoplasmic reticulum and that the trafficking defect of these channels can be corrected by specific pharmacological strategies.

Topics: Cation Transport Proteins; Cell Line; Cell Membrane; Endoplasmic Reticulum; Ether-A-Go-Go Potassium Channels; Genes, Dominant; Humans; Long QT Syndrome; Mutation; Patch-Clamp Techniques; Phenotype; Piperidines; Potassium Channels; Potassium Channels, Voltage-Gated; Pyridines

The new anti-anginal drug ranolazine causes a slight (<10 milliseconds) prolongation of the QT interval, raising the concern that its use may be associated with an increased incidence of torsades de pointes ventricular tachyarrhythmias. The goal of this study was to show that ranolazine inhibits the late component of INa and attenuates prolongation of action potential duration when late INa is increased, both in the absence and presence of IK-blocking drugs. Currents and action potentials of guinea pig isolated ventricular myocytes were measured by whole-cell patch clamp. Sea anemone toxin (ATX)-II was used to increase late INa and mimic the effect of an SCN5A gene mutation. ATX-II (3-5 nmol/L) increased late INa by 5-fold; ranolazine attenuated this increase of late INa by up to 61 +/- 8%. ATX-II (10-20 nmol/L) increased action potential duration (APD) by > 1 seconds, and caused early afterdepolarizations; both actions were attenuated by ranolazine (0.1-30 micromol/L). Ranolazine (10 micromol/L) reduced by 89% the 13.6-fold increase in variability of APD caused by 10 nmol/L ATX-II. The effects of ATX-II (3 nmol/L) in combinations with either the IKr blocker E-4031 or the IKs blocker chromanol 293B to increase APD were attenuated 76 +/- 5% and 71 +/- 4%, respectively, by 10 micromol/L ranolazine. The results demonstrate that ranolazine reduces late INa and has an anti-arrhythmic effect when late INa is increased.

Topics: Acetanilides; Action Potentials; Animals; Chromans; Cnidarian Venoms; Delayed Rectifier Potassium Channels; Drug Synergism; Drug Therapy, Combination; Female; Guinea Pigs; Heart Conduction System; Heart Ventricles; Ion Channel Gating; Long QT Syndrome; Male; Myocytes, Cardiac; Piperazines; Piperidines; Potassium Channel Blockers; Potassium Channels, Inwardly Rectifying; Potassium Channels, Voltage-Gated; Pyridines; Ranolazine; Sodium Channels; Sulfonamides; Tetrodotoxin; Time Factors

We have reported identification of the amino acid whose mutation reduces effects of quinidine on the HERG channel. Although the residue (isoleucine at 647) is not in the recently reported methanesulfonanilide binding site, a single concentration of E-4031 (10 microM) was less effective to I647 mutant channels than wild type HERG channel. We designed the present experiment to further investigate influence of mutations at 647 on the effects of methanesulfonanilides.. HERG channels were expressed in Xenopus oocytes and their currents were measured by a two-microelectrode voltage clamp method. Of the two mutations initially studied (I647A and I647F), the I647F had a greater influence and differentially affected the effects of dofetilide and E-4031. The IC(50) for dofetilide of the two mutant channels (I647A and I647F) was increased only 2-fold, but the IC(50) for E-4031 was increased 6-fold (I647A) and 14-fold (I647F). Aromatic residues other than phenylalanine were then substituted for I647, and found to reduce the effects of E-4031. Whereas E-4031 dissociated from the mutant channels during rested state, dofetilide little dissociated. The mutant channels that showed recovery from E-4031 block were inhibited greater at 1 Hz than at 0.1 Hz.. The present results indicate that dissociation of a drug from the HERG channel results in greater block at high frequency. Although the mechanism by which the mutations cause the dissociation of E-4031 is uncertain, it is noteworthy that one methanesulfonanilide dissociates from the channel more easily than another.

Topics: Animals; Anti-Arrhythmia Agents; Cation Transport Proteins; Dose-Response Relationship, Drug; Ether-A-Go-Go Potassium Channels; Isoleucine; Long QT Syndrome; Mutagenesis, Site-Directed; Oocytes; Patch-Clamp Techniques; Phenethylamines; Piperidines; Point Mutation; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Voltage-Gated; Pyridines; Sulfonamides; Xenopus

Budipine is a non-dopaminergic antiparkinsonian drug causing acquired forms of Long QT syndrome (aLQTS). As a consequence, the manufacturer has restricted the use of budipine in patients who exhibit additional risk factors for the development of "Torsades-de-Pointes" tachycardias (TdP). The molecular basis of this serious side effect has not been elucidated yet. Human ether-a-go-go related gene (HERG) channel block being the main cause of drug induced QT prolongation, we investigated the effect of budipine on the rapid component of the delayed-rectifier potassium current (I(K(r))) in guinea pig cardiomyocytes and on HERG potassium channels heterologously expressed in Xenopus oocytes. In guinea pig cardiomyocytes, budipine (10 microM) inhibited I(K(r)) by 86% but was without any effect on calcium currents. In Xenopus oocytes, HERG potassium channels were blocked by budipine with an IC(50) of 10.2 microM. Onset of block was fast and block was only slowly and incompletely reversible upon washout. Budipine blocked HERG channels in the open and inactivated state, but not in the closed states. The half-maximal activation voltage was slightly shifted towards more negative potentials. Steady-state inactivation of HERG was also influenced by budipine. Budipine block was neither voltage- nor frequency-dependent. In HERG channel mutants Y652A and F656A, drug affinity was reduced dramatically. Therefore, these two aromatic residues in the channel pore are likely to form a main part of the binding site for budipine. In summary, this is the first study that provides a molecular basis for the budipine-associated aLQTS observed in clinical practice. Furthermore, these findings underline the importance of the aromatic residues Y652 and F656 in the binding of lipophilic drugs to HERG channels.

Topics: Animals; Antiparkinson Agents; Binding Sites; Calcium Channels; Cation Transport Proteins; Ether-A-Go-Go Potassium Channels; Guinea Pigs; In Vitro Techniques; Long QT Syndrome; Myocytes, Cardiac; Oocytes; Patch-Clamp Techniques; Piperidines; Potassium Channels; Potassium Channels, Voltage-Gated; Time Factors; Xenopus laevis

The aim of this study was to assess the cardiovascular effects of a selective phosphodiesterase 5 inhibitor ER-118585, 4-[(3-chloro-4-methoxybenzyl)amino]-1-(2-hydroxy-7-azaspiro[3.5]non-7-yl)-6-phthalazinecarbonitrile monohydrochloride. The present results indicated that 1) ER-118585 significantly inhibited the human ether-a-go-go related gene (HERG) tail current at 10 nM and above with an IC(50) value of 40.7 nM in human embryonic kidney 293 cells transfected with HERG cDNA; 2) ER-118585 at 100 and 1000 nM significantly increased the action potential duration (APD) at 50% and 90% repolarization in isolated papillary muscles of guinea pig; and 3) intravenous infusion of ER-118585 at 10 microg/kg/min significantly prolonged the QT interval by 10.5+/-1.6% from 281+/-2 ms to 311+/-6 ms in six anesthetized dogs subjected to atrial pacing. In consideration of both the plasma concentration of ER-118585 (984+/-78 nM, n=3) and its protein binding fraction (99.0+/-0.1%, n=5), the free plasma concentration was estimated at 9.8+/-0.8 nM, which is consistent with the minimum concentration of HERG current inhibition. In conclusion, these evaluation methods demonstrated that ER-118585 could prolong the QT interval via APD prolongation, attributable to the inhibition of the HERG potassium current.

Topics: 3',5'-Cyclic-GMP Phosphodiesterases; Action Potentials; Animals; Cardiac Pacing, Artificial; Cardiovascular Diseases; Cell Line; Cyclic Nucleotide Phosphodiesterases, Type 5; Dogs; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Electrocardiography; Electrophysiology; Guinea Pigs; Humans; Infusions, Intravenous; Kidney; Long QT Syndrome; Male; Papillary Muscles; Patch-Clamp Techniques; Phosphodiesterase Inhibitors; Phosphoric Diester Hydrolases; Phthalazines; Piperidines; Potassium Channels, Voltage-Gated; Protein Binding; Pyridines; Spiro Compounds; Transfection; Ventricular Function; Ventricular Premature Complexes

QT interval prolongation of the electrocardiogram has been associated with the occurrence of life-threatening fatal ventricular arrhythmias. To understand the relationship between preclinical cardiac conduction assessment to clinical outcome, comparisons of free (unbound)-plasma drug concentrations and their associated effects in the conscious mongrel dog were made to the free plasma concentrations in humans reported to produce QT prolongation. E-4031 (an experimental class III antiarrhythmic), cisapride, terfenadine, terodiline, and verapamil all affect cardiac repolarization and can produce QT prolongation in humans. In the conscious dog, the QT interval was assessed on a beat-to-beat basis in relation to each preceding RR interval at concentrations approximating the same unbound human concentrations. E-4031, cisapride and terodiline statistically increased the QT(RR1000) interval [the QT interval at a 60 beats/min (bpm) heart rate] 23, 8, and 9 ms, respectively, at concentrations 0.3 to 15.8 times their relevant clinical level. Increases were not observed for terfenadine or verapamil (p > 0.05 at all doses). Inspection of individual dog QT versus RR interval relationships showed clear QT interval responses specific to each treatment but not readily apparent when data are averaged at a heart rate of 60 bpm. For specific rectifier K(+) current (IKr) blockers, robust effects on mean QT prolongation can be detected. However, for drugs that affect repolarization through multiple channels, the effect on the mean QT interval may be more difficult to detect. Inspection of the beat-to-beat QT-RR interval relationship in an individual animal can increase the sensitivity for more accurate clinical prediction.

Topics: Animals; Anti-Arrhythmia Agents; Butylamines; Cisapride; Disease Models, Animal; Dogs; Female; Heart Rate; Long QT Syndrome; Male; Piperidines; Pyridines; Terfenadine; Verapamil

Endothelin-1 (ET-1) influences the electrical activity of the heart by causing arrhythmias associated with lengthening of the QT interval in the electrocardiogram. Recent results from our laboratory have shown a primary role for a high plasma glucose concentration in determining cardiac QT prolongation. Since high glucose up-regulates the ET-1 system, the aim of the present study was to determine whether the increase of the QT interval and coronary vascular tone induced by high glucose in the heart involves increased activity of the ET system. Perfusion of isolated hearts with a high glucose concentrations (33.3 mM) prolonged the QT interval significantly and increased coronary perfusion pressure (CPP) ( P<0.01). The increases in the QT interval and CPP induced by high glucose were accompanied by increases in cardiac ET-1 levels, and were significantly reduced by an ET-1 antiserum ( P<0.01). Perfusion of the hearts with the selective ET(A) receptor antagonist FR139317 or with the non-selective ET(A)/ET(B) antagonist SB209670, but not with the selective ET(B) receptor antagonist BQ-788, reduced the glucose-induced QT prolongation. In addition, the increase in cardiac vascular tone, as evidenced by the increase in CPP, induced by high glucose was reversed partially by cardiac perfusion with either the non-selective ET(A)/ET(B) receptor antagonist or the ET(B)-selective BQ-788, whereas the ET(A) antagonist was without effect. By increasing the production of ET-1, a high glucose concentration may activate parallel pathways that contribute to a state of increased vasomotor tone and electrical ventricular instability. Antagonism at cardiac ET receptors could be helpful in these cardiovascular complications of diabetes.

Topics: Animals; Azepines; Dose-Response Relationship, Drug; Electrocardiography; Endothelin Receptor Antagonists; Glucose; Heart; Heart Conduction System; In Vitro Techniques; Indans; Indoles; Long QT Syndrome; Male; Oligopeptides; Piperidines; Rats; Receptor, Endothelin A; Receptors, Endothelin

The role of intracellular Ca2+ (Ca2+i) in triggering early afterdepolarizations (EADs), the origins of EADs and the mechanisms underlying Torsade de Pointes (TdP) were investigated in a model of long QT syndrome (Type 2). Perfused rabbit hearts were stained with RH327 and Rhod-2/AM to simultaneously map membrane potential (V(m)) and Ca2+i with two photodiode arrays. The I(Kr) blocker E4031 (0.5 microM) together with 50 % reduction of [K+]o and [Mg2+]o elicited long action potentials (APs), V(m) oscillations on AP plateaux (EADs) then ventricular tachycardia (VT). Cryoablation of both ventricular chambers eliminated Purkinje fibres as sources of EADs. E4031 prolonged APs (0.28 to 2.3 s), reversed repolarization sequences (baseapex) and enhanced repolarization gradients (30 to 230 ms, n = 12) indicating a heterogeneous distribution of I(Kr). At low [K+]o and [Mg2+]o, E4031 elicited spontaneous Ca2+iand V(m) spikes or EADs (3.5 +/- 1.9 Hz) during the AP plateau (n = 6). EADs fired 'out-of-phase' from several sites, propagated, collided then evolved to TdP. Phase maps (Ca2+ivs. V(m)) had counterclockwise trajectories shaped like a 'boomerang' during an AP and like ellipses during EADs, with V(m) preceding Ca2+iby 9.2 +/- 1.4 (n = 6) and 7.2 +/- 0.6 ms (n = 5/6), respectively. After cryoablation, EADs from surviving epicardium (~1 mm) fired at the same frequency (3.4 +/- 0.35 Hz, n = 6) as controls. At the origins of EADs, Ca2+ipreceded V(m) and phase maps traced clockwise ellipses. Away from EAD origins, V(m) coincided with or preceded Ca2+i. In conclusion, overload elicits EADs originating from either ventricular or Purkinje fibres and 'out-of-phase' EAD activity from multiple sites generates TdP, evident in pseudo-ECGs.

Topics: Animals; Anti-Arrhythmia Agents; Artifacts; Calcium; Calcium Signaling; Cryosurgery; Cytosol; Female; Kinetics; Long QT Syndrome; Magnesium; Membrane Potentials; Microscopy, Fluorescence; Movement; Piperidines; Potassium; Pyridines; Rabbits; Torsades de Pointes

The aim of this study was to clarify the ventricular tachyarrhythmia mechanism induced by the I(Kr)-blocking agent E4031, simulating the LQT2 form. Electrophysiologic properties were examined in 13 canines before and after administration of E4031.. Thirty-six needle electrodes were inserted into the anterior left ventricular wall. From each needle, local unipolar electrograms were obtained from four intramural sites. Activation time (AT) and activation-recovery interval (ARI) were measured. To evaluate the susceptibility to ventricular arrhythmia, intramural ARI dispersions and the restitution relationship between ARI and diastolic interval were calculated. After E4031 administration, ARI prolonged uniformly in each myocardial layer. However, ARI dispersion was not augmented compared with control. The slope of the ARI restitution curve after E4031 was significantly steeper than control. A steep slope may result from augmented ARI alternans. In 11 of the 13 canines, ventricular tachyarrhythmia was induced by programmed stimulation after E4031, whereas no arrhythmia was induced by the same protocol in control.. Steepness of electrical restitution may play a major role in arrhythmogenicity in LQT2 hearts.

Topics: Animals; Anti-Arrhythmia Agents; Cardiac Pacing, Artificial; Disease Models, Animal; Disease Susceptibility; Dogs; Electrocardiography; Electrophysiologic Techniques, Cardiac; Heart Conduction System; Heart Ventricles; Long QT Syndrome; Models, Cardiovascular; Piperidines; Pyridines; Tachycardia, Ventricular

Topics: Animals; Anti-Arrhythmia Agents; Cardiac Pacing, Artificial; Electrophysiologic Techniques, Cardiac; Heart Conduction System; Heart Ventricles; Humans; Long QT Syndrome; Piperidines; Pyridines; Ventricular Fibrillation

Mutations in the human ether-a-gogo-related gene (HERG) K(+) channel gene cause chromosome 7-linked long QT syndrome type 2 (LQT2), which is characterized by a prolonged QT interval in the electrocardiogram and an increased susceptibility to life-threatening cardiac arrhythmias. LQT2 mutations produce loss-of-function phenotypes and reduce I(Kr) currents either by the heteromeric assembly of non- or malfunctioning channel subunits with wild type subunits at the cell surface or by retention of misprocessed mutant HERG channels in the endoplasmic reticulum. Misprocessed mutations often encode for channel proteins that are functional upon incorporation into the plasma membrane. As a result the pharmacological correction of folding defects and restoration of protein function are of considerable interest. Here we report that the trafficking-deficient pore mutation HERG G601S was rescued by a series of HERG channel blockers that increased cell surface expression. Rescue by these pharmacological chaperones varied directly with their blocking potency. We used structure-activity relationships and site-directed mutagenesis to define the binding site of the pharmacological chaperones. We found that binding occurred in the inner cavity and correlated with hydrophobicity and cationic charge. Rescue was domain-restricted because the trafficking of two misprocessed mutations in the C terminus, HERG F805C and HERG R823W, was not restored by channel blockers. Our findings represent a first step toward the design of pharmacological chaperones that will rescue HERG K(+) channels without block.

Topics: Anti-Arrhythmia Agents; Astemizole; Benzimidazoles; Binding Sites; Blotting, Western; Cation Transport Proteins; Cell Line; Cell Membrane; Cisapride; DNA-Binding Proteins; Dose-Response Relationship, Drug; Electrophysiology; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Gastrointestinal Agents; Histamine H1 Antagonists; Humans; Inhibitory Concentration 50; Ions; Long QT Syndrome; Models, Chemical; Mutagenesis, Site-Directed; Mutation; Patch-Clamp Techniques; Piperidines; Potassium Channels; Potassium Channels, Voltage-Gated; Protein Folding; Pyridines; Quaternary Ammonium Compounds; Quinidine; Structure-Activity Relationship; Trans-Activators; Transcriptional Regulator ERG

Proper pacemaking of the heart requires a specific organization of the sinoatrial (SA) node. The SA node drives the surrounding atrium but needs to be protected from its hyperpolarizing influence, which tends to suppress pacemaker activity. It has been suggested that the hyperpolarizing atrial influence is minimal at the site of the central nodal area.. Atrio-sinus interaction was assessed by specific depolarization of the SA node by blocking the HERG-encoded rapid delayed rectifier current (I(K,r)) with the drug E-4031. In the SA node, E-4031 (1 micromol/L) changed action potential configuration drastically but never resulted in pacemaker arrest. In the atrium, E-4031 did not affect the membrane resting potential, thereby leaving the normal hyperpolarizing load on the SA node intact. When the SA node was sectioned into strips and subsequently separated from the atrium, spontaneous electrical activity of the strip containing the primary pacemaker ceased on I(K,r) blockade. When not separated from the atrium, I(K,r) blockade never resulted in pacemaker arrest. A similar effective atrio-sinus interaction was demonstrated in computer simulations.. Our results demonstrate that the atrium provides an effective hyperpolarizing load on the central SA nodal area and is at least one of the controlling mechanisms for normal pacemaking function. The present study can be of help in understanding why patients with long-QT2 syndrome secondary to a mutation in HERG do not show sinus arrest.

Topics: Action Potentials; Animals; Anti-Arrhythmia Agents; Biological Clocks; Cation Transport Proteins; Computer Simulation; Electrophysiologic Techniques, Cardiac; Ether-A-Go-Go Potassium Channels; Heart Atria; Heart Conduction System; In Vitro Techniques; Long QT Syndrome; Membrane Potentials; Models, Cardiovascular; Piperidines; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Voltage-Gated; Pyridines; Rabbits; Sinoatrial Block; Sinoatrial Node

In dogs and in humans, potassium channels formed by ether-a-go-go-related gene 1 protein ERG1 (KCNH2) and KCNQ1 alpha-subunits, in association with KCNE beta-subunits, play a role in normal repolarization and may contribute to abnormal repolarization associated with long QT syndrome (LQTS). The molecular basis of repolarization in horse heart is unknown, although horses exhibit common cardiac arrhythmias and may receive drugs that induce LQTS. In horse heart, we have used immunoblotting and immunostaining to demonstrate the expression of ERG1, KCNQ1, KCNE1, and KCNE3 proteins and RT-PCR to detect KCNE2 message. Peptide N-glycosidase F-sensitive forms of horse ERG1 (145 kDa) and KCNQ1 (75 kDa) were detected. Both ERG1 and KCNQ1 coimmunoprecipitated with KCNE1. Cardiac action potential duration was prolonged by antagonists of either ERG1 (MK-499, cisapride) or KCNQ1/KCNE1 (chromanol 293B). Patch-clamp analysis confirmed the presence of a slow delayed rectifier current. These data suggest that repolarizing currents in horses are similar to those of other species, and that horses are therefore at risk for acquired LQTS. The data also provide unique evidence for coassociation between ERG1 and KCNE1 in cardiac tissue.

Topics: Action Potentials; Animals; Anti-Arrhythmia Agents; Benzopyrans; Cell Line; Cisapride; Cricetinae; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Horses; Humans; Immunoblotting; Immunohistochemistry; In Vitro Techniques; KCNQ Potassium Channels; KCNQ1 Potassium Channel; Long QT Syndrome; Myocardium; Patch-Clamp Techniques; Piperidines; Potassium; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Voltage-Gated; Protein Binding; RNA, Messenger; Swine

1. Long OT syndrome has many causes from both acquired and congenital disorders. For the congenital disorders, their presentation and disease course are not identical. We studied two pharmacological models of long QT syndrome (LQT) to identify differences in cellular electrophysiological properties that may account for this. LQT2 was simulated by suppression of the rapidly activating delayed rectifier potassium current (I(Kr)) with the drug E-4031, and LQT3 was simulated by slowing of the sodium current (I(Na)) decay with the toxin ATX II. 2. Single rabbit ventricular cell action potentials were studied using the amphotericin B perforated patch clamp technique. Action potential and early afterdepolarization (EAD) properties were rigorously defined by the frequency power spectra obtained with fast Fourier transforms. 3. The E-4031 (n=43 myocytes) and ATX II (n=50 myocytes) models produced different effects on action potential and EAD properties. The major differences are that ATX II, compared with E-4031, caused greater action potential prolongation, more positive plateau voltages, lower amplitude EADs with less negative take-off potentials, greater time to the EAD peak voltage, and longer duration EADs. Despite causing greater action potential prolongation, the incidence of EAD induction was much less with the ATX II model (28%) than with the E-4031 model (84%). Thus these two pharmacological models have strikingly different cellular electrophysiological properties. 4. Our findings provide cellular mechanisms that may account for some differences in the clinical presentation of LQT2 and LQT3.

Topics: Action Potentials; Animals; Anti-Arrhythmia Agents; Cell Separation; Electric Stimulation; Electrophysiology; Fourier Analysis; Heart; In Vitro Techniques; Long QT Syndrome; Patch-Clamp Techniques; Piperidines; Potassium Channel Blockers; Pyridines; Rabbits; Tetrodotoxin

1. The effects of I(Ks) block by chromanol 293B and L-735,821 on rabbit QT-interval, action potential duration (APD), and membrane current were compared to those of E-4031, a recognized I(Kr) blocker. Measurements were made in rabbit Langendorff-perfused whole hearts, isolated papillary muscle, and single isolated ventricular myocytes. 2. Neither chromanol 293B (10 microM) nor L-735,821 (100 nM) had a significant effect on QTc interval in Langendorff-perfused hearts. E-4031 (100 nM), on the other hand, significantly increased QTc interval (35.6+/-3.9%, n=8, P<0.05). 3. Similarly both chromanol 293B (10 microM) and L-735,821 (100 nM) produced little increase in papillary muscle APD (less than 7%) while pacing at cycle lengths between 300 and 5000 ms. In contrast, E-4031 (100 nM) markedly increased (30 - 60%) APD in a reverse frequency-dependent manner. 4. In ventricular myocytes, the same concentrations of chromanol 293B (10 microM), L-735,821 (100 nM) and E-4031 (1 microM) markedly or totally blocked I(Ks) and I(Kr), respectively. 5. I(Ks) tail currents activated slowly (at +30 mV, tau=888.1+/-48.2 ms, n=21) and deactivated rapidly (at -40 mV, tau=157.1+/-4.7 ms, n=22), while I(Kr) tail currents activated rapidly (at +30 mV, tau=35.5+/-3.1 ms, n=26) and deactivated slowly (at -40 mV, tau(1)=641.5+/-29.0 ms, tau(2)=6531+/-343, n=35). I(Kr) was estimated to contribute substantially more to total current density during normal ventricular muscle action potentials (i.e., after a 150 ms square pulse to +30 mV) than does I(Ks). 6. These findings indicate that block of I(Ks) is not likely to provide antiarrhythmic benefit by lengthening normal ventricular muscle QTc, APD, and refractoriness over a wide range of frequencies.

Topics: Action Potentials; Animals; Anti-Arrhythmia Agents; Benzodiazepines; Cell Separation; Chromans; Colforsin; Electrocardiography; Female; Heart; Heart Ventricles; In Vitro Techniques; Kinetics; Long QT Syndrome; Male; Microelectrodes; Myocardium; Papillary Muscles; Patch-Clamp Techniques; Piperidines; Potassium Channel Blockers; Pyridines; Rabbits; Sulfonamides

The purpose of this study was to investigate the properties of the slow component of the delayed rectifier potassium current (I(Ks)) in myocytes isolated from undiseased human left ventricles.. The whole-cell configuration of the patch-clamp technique was applied in 58 left ventricular myocytes from 15 hearts at 37 degrees C. Nisoldipine (1 microM) was used to block inward calcium current (I(Ca)) and E-4031 (1-5 microM) was applied to inhibit the rapid component of the delayed rectifier potassium current (I(Kr)).. In 31 myocytes, an E-4031 insensitive, but L-735,821 and chromanol 293B sensitive, tail current was identified which was attributed to the slow component of I(K) (I(Ks)). Activation of I(Ks) was slow (tau=903+/-101 ms at 50 mV, n=14), but deactivation of the current was relatively rapid (tau=122.4+/-11.7 ms at -40 mV, n=19). The activation of I(Ks) was voltage independent but its deactivation showed clear voltage dependence. The deactivation was faster at negative voltages (about 100 ms at -50 mV) and slower at depolarized potentials (about 300 ms at 0 mV). In six cells, the reversal potential was -81.6+/-2.8 mV on an average which is close to the K(+) equilibrium potential suggesting K(+) as the main charge carrier.. In undiseased human ventricular myocytes, I(Ks) exhibits slow activation and fast deactivation kinetics. Therefore, in humans I(Ks) differs from that reported in guinea pig, and it best resembles I(Ks) described in dog and rabbit ventricular myocytes.

Topics: Adult; Benzodiazepines; Calcium Channel Blockers; Cell Separation; Chromans; Colforsin; Female; Humans; Ion Channel Gating; Long QT Syndrome; Male; Myocardium; Nisoldipine; Patch-Clamp Techniques; Piperidines; Potassium Channels; Pyridines; Sulfonamides

Potassium homeostasis plays an important role in the control of neuronal excitability, and diminished buffering of extracellular K results in neuronal Hyperexcitability and abnormal synchronization. Astrocytes are the cellular elements primarily involved in this process. Potassium uptake into astrocytes occurs, at least in part, through voltage-dependent channels, but the exact mechanisms involved are not fully understood. Although most glial recordings reveal expression of inward rectifier currents (K(IR)), it is not clear how spatial buffering consisting of accumulation and release of potassium may be mediated by exclusively inward potassium fluxes. We hypothesized that a combination of inward and outward rectifiers cooperate in the process of spatial buffering. Given the pharmacological properties of potassium homeostasis (sensitivity to Cs(+)), members of the ether-a-go-go (ERG) channel family widely expressed in the nervous system could underlie part of the process. We used electrophysiological recordings and pharmacological manipulations to demonstrate the expression of ERG-type currents in cultured and in situ hippocampal astrocytes. Specific ERG blockers (dofetilide and E 4031) inhibited hyperpolarization- and depolarization-activated glial currents, and ERG blockade impaired clearance of extracellular potassium with little direct effect on hippocampal neuron excitability. Immunocytochemical analysis revealed ERG protein mostly confined to astrocytes; ERG immunoreactivity was absent in presynaptic and postsynaptic elements, but pronounced in glia surrounding the synaptic cleft. Oligodendroglia did not reveal ERG immunoreactivity. Intense immunoreactivity was also found in perivascular astrocytic end feet at the blood-brain barrier. cDNA amplification showed that cortical astrocytes selectively express HERG1, but not HERG2-3 genes. This study provides insight into a possible physiological role of hippocampal ERG channels and links activation of ERG to control of potassium homeostasis.

Topics: Animals; Anti-Arrhythmia Agents; Astrocytes; Cation Transport Proteins; Cell Communication; Cesium; Dose-Response Relationship, Drug; Electrophysiology; Epilepsy; Ether-A-Go-Go Potassium Channels; Gene Expression; Heart; Hippocampus; In Vitro Techniques; Long QT Syndrome; Male; Membrane Potentials; Microscopy, Electron; Neurons; Oligonucleotide Probes; Phenethylamines; Piperidines; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Voltage-Gated; Pyridines; Rats; Rats, Wistar; RNA, Messenger; Spinal Cord; Sulfonamides

The chromosome 7-linked form of congenital long QT syndrome (LQT2) is caused by mutations in the human ether-a-go-go-related gene (HERG) that encodes the rapidly activating delayed rectifier potassium channel. One mechanism for the loss of normal channel function in LQT2 is defective protein trafficking, which results in the failure of the channel protein to reach the plasma membrane. Here we show that the N470D LQT2 mutant protein is trafficking-deficient when expressed at 37 degrees C in HEK293 cells, whereas at 27 degrees C its trafficking to the plasma membrane and channel function are markedly improved. We further show that the antiarrhythmic drug E-4031, which selectively blocks HERG channels, also corrects defective protein trafficking of the N470D mutant and can restore the generation of HERG current. Similar findings were obtained with the drugs astemizole and cisapride, as well as with high concentrations of glycerol. The effect of E-4031 on HERG protein trafficking was concentration-dependent and required low drug concentrations (saturation present at 5 microM), developed rapidly with drug exposure, and occurred post-translationally. These findings suggest that protein misfolding leading to defective trafficking of some HERG LQT mutations may be corrected by specific pharmacological strategies.

Topics: Anti-Arrhythmia Agents; Astemizole; Biological Transport; Cation Transport Proteins; Cell Compartmentation; Cisapride; DNA-Binding Proteins; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Glycerol; Humans; Long QT Syndrome; Mutation; Patch-Clamp Techniques; Piperidines; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Voltage-Gated; Protein Folding; Pyridines; Recombinant Proteins; Temperature; Trans-Activators; Transcriptional Regulator ERG

To report a case of QT prolongation and syncopal episodes resulting from concomitant use of cisapride and agents known to inhibit its metabolism.. A 53-year-old white woman was involved in two motor vehicle accidents on the same day after experiencing syncopal episodes. Cardiac and neurologic evaluations were negative; the syncopal episodes were attributed to QT prolongation associated with the concomitant use of cisapride and agents known to inhibit its metabolism.. This is the first case published in the English-language literature describing QT prolongation resulting from the concomitant use of cisapride and agents known to inhibit its metabolism. Clarithromycin inhibits CYP3A4, the isoenzyme responsible for the metabolism of cisapride. Concomitant administration of cisapride with agents known to inhibit CYP3A4 (i.e., azole antifungals, erythromycin, clarithromycin) may result in elevated cisapride concentrations. Elevated cisapride concentrations have been associated with QT prolongation, syncopal episodes, and cardiac dysrhythmias.. Acquired QT prolongation is a well-recognized adverse effect of several drugs. Recognition of newer drugs and drug combinations that place patients at risk for this potentially fatal adverse event is imperative for appropriate monitoring and prevention.

Topics: Accidents, Traffic; Anti-Bacterial Agents; Anti-Ulcer Agents; Cisapride; Clarithromycin; Cytochrome P-450 Enzyme System; Drug Interactions; Electrocardiography; Female; Gastrointestinal Agents; Humans; Long QT Syndrome; Middle Aged; Omeprazole; Piperidines; Syncope

The KCNE1 gene encodes a channel regulator IsK which in association with the KvLQT1 K+ channel protein determines the slow component of the cardiac delayed rectifier current. We have investigated the cellular electrophysiological characteristics of adult KCNE1-knockout mouse hearts by means of the standard microelectrode technique. Action potential parameters from the ventricular endocardium of KCNE1 -/- mice were indistinguishable from those of KCNE1 +/+ animals. In particular, KCNE1 -/- hearts did not exhibit prolonged repolarization. E-4031, a specific blocker of erg K+ channels consistently prolonged repolarization in KCNE1 +/+ but not in KCNE1 -/- hearts. By contrast, the chromanol compound 293B, a specific blocker of KvLQT1 K+ channel produced comparable effects on repolarization in KCNE1 -/- and KCNE1 +/+ mice. We conclude that invalidation of the mouse KCNE1 gene by homologous recombination leads to a mild cardiac phenotype at the cellular level.

Topics: Action Potentials; Animals; Chromans; Electric Conductivity; Electrophysiology; Heart; Homozygote; In Vitro Techniques; KCNQ Potassium Channels; KCNQ1 Potassium Channel; Long QT Syndrome; Mice; Mice, Knockout; Periodicity; Piperidines; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Voltage-Gated; Pyridines; Sulfonamides

Pirmenol hydrochloride is a new orally effective, long-acting antiarrhythmic agent currently used in patients with supraventricular and ventricular tachyarrhythmias. We report on a 56-year-old female who exhibited drug refractory paroxysmal atrial fibrillation, in which marked prolongation of the QT interval and T wave inversion on electrocardiogram was demonstrated reproducibly shortly after the administration of oral pirmenol therapy. The plasma concentration of pirmenol was at a subtherapeutic level and the lymphocyte stimulation test was positive in this patient. Thus, an immunological mechanism might be involved in the mechanism of pirmenol-induced QT prolongation and T wave inversion on the electrocardiogram.

Topics: Anti-Arrhythmia Agents; Atrial Fibrillation; Electrocardiography; Female; Humans; Long QT Syndrome; Middle Aged; Piperidines

Serious undesirable cardiac side effects have been reported with treatment with diphemanil methylsulfate (Prantal) in premature babies or neonates. To understand the origin of this problem, the authors undertook an electrophysiological study of the effects of this product in vitro on rabbit Purkinje fibres. In three separate series (N = 5 to N = 8), the effects of increasing concentrations (0.1 microM-30 microM) of diphemanil methylsulfate, different frequencies of stimulation (0.2 Hz, 1 Hz, 2 Hz) and duration of exposition (60 min followed by 120 min washout) were observed on the properties of the action potential. The results show a clearcut antiarrhythmic Class III type action characterised by a concentration-dependent prolongation of the action potential duration with an inverse frequency dependency without significant changes of the other parameters. During stimulation at 0.2 Hz, early post-depolarizations and induced activity were observed in 3/8 of the fibres exposed to 10 microM and 8/8 fibres exposed to 30 microM. The effect did not attain a steady state after 60 min of exposition. It was not reversed by 120 min of washout of the preparation. These results were compatible with the reported cardiac arrhythmic effects of prolongation of the QT interval and torsades de pointe.

Topics: Action Potentials; Animals; Arrhythmias, Cardiac; Child; Drug Evaluation, Preclinical; Electric Stimulation; Electrocardiography; Humans; Long QT Syndrome; Piperidines; Purkinje Fibers; Rabbits

Topics: Cisapride; Gastroesophageal Reflux; Humans; Infant; Infant, Newborn; Infant, Premature; Infant, Premature, Diseases; Long QT Syndrome; Piperidines

Topics: Cisapride; Drug Overdose; Female; Gastroesophageal Reflux; Humans; Infant; Long QT Syndrome; Piperidines

Topics: Anti-Ulcer Agents; Cisapride; Humans; Infant; Long QT Syndrome; Piperidines; Ranitidine

In the present study the electrophysiological characteristics and the proarrhythmic potential of cisapride and a structurally related drug, mosapride, were compared. In the anesthetized guinea pig, cisapride and d-sotalol (0.01-10 micromol/kg i.v., n = 6) dose-dependently prolonged the duration of the monophasic action potential recorded from the left ventricle. The maximal lengthening was 18 +/- 3.2% at 1.0 micromol/kg (mean +/- S.E.M., P < .01 vs. base line) and 19 +/- 2.5% at 10 micromol/kg (P < .001) for cisapride and d-sotalol, respectively. In contrast, mosapride did not increase this variable. In a rabbit model of the acquired long QT syndrome, infusion of cisapride (0.3 micromol/kg/min for 10 min maximum, n = 6), but not mosapride or vehicle, was associated with a significant lengthening of the QTU interval (43 +/- 3.8 ms, P < .01). Furthermore, torsades de pointes appeared in two of the six rabbits given cisapride. In isolated rabbit Purkinje fibers (PF), cisapride increased the action potential duration (48 +/- 5.6% at 0.1 micromol/l, P < .01 vs. control, n = 4). Mosapride did not significantly influence the action potential duration (3 +/- 2.0% increase at 1.0 micromol/l, n = 6). However, after mosapride was washed out, the addition of cisapride (0.1 micromol/l) caused a 46 +/- 3.2% lengthening of the action potential duration (P < .01 vs. 1.0 micromol/l mosapride). Early afterdepolarizations and triggered activity appeared in four of eight cisapride-superfused PF stimulated at a very low frequency (0.1 Hz). In isolated rabbit cardiomyocytes, cisapride concentration-dependently blocked (IC50 = 9 nmol/l) the rapid component of the delayed rectifying K+ current (I(Kr)). Mosapride was approximately 1000-fold less potent in blocking I(Kr) (IC50 = 4 micromol/l). It is concluded that the electrophysiological characteristics of cisapride may explain the recently reported propensity to prolong the QT interval and to induce torsades de pointes in susceptible patients, although a structurally related benzamide, mosapride, did not appear to have electrophysiological features of relevance for induction of torsades de pointes in common with cisapride.

Topics: Action Potentials; Animals; Arrhythmias, Cardiac; Benzamides; Cisapride; Guinea Pigs; Heart; In Vitro Techniques; Long QT Syndrome; Male; Morpholines; Piperidines; Purkinje Fibers; Rabbits; Structure-Activity Relationship

Cisapride is frequently used in the newborn and infant for treatment of gastroesophageal reflux. Twisting-spikes have been reported in adults due to overdosage or therapeutic interaction. We report seven cases of QT prolongation in infants treated with cisapride.. Seven children (one full-term, two mature preterms, four preterm babies), aged (mean, range) 41.8 +/- 21 days (14-79) weighing 2.1 +/- 1.1 kg (1.2-4), free from any cardiac abnormality, except one patent ductus arteriosus, have been studied by ECG and Holter monitoring. They received cisapride at a mean dose of 1.31 +/- 0.2 mg/kg/d (between 1 and 1.7 mg/kg/d).. The corrected QT (QTc: N < 450 ms) was increased to 486 ms (450-540) with a notched T-wave pattern. No arrhythmia was detected. In five cases, cisapride was stopped and changed to metoclopramide. Cisapride dosage was reduced to 0.8 mg/kg/d in the two others. No other therapeutic modification was done. A control ECG performed 48 hours after therapeutic changes showed a QTc shortening of 74 +/- 18 ms (45-90) and the disappearance of the notches independent of any heart rate changes, leading to normal QTc values: 413 +/- 21 ms (390-440).. High cisapride dosage in preterm, newborns and infants seems to favor QT prolongation which is reversible when dosage is reduced or drug is stopped. The use of cisapride in combination with other drugs known to increase QT should be done with extreme caution.

Topics: Anti-Ulcer Agents; Cisapride; Dose-Response Relationship, Drug; Electrocardiography; Female; Gastroesophageal Reflux; Humans; Infant; Infant, Newborn; Long QT Syndrome; Piperidines; Retrospective Studies

Cardiotoxicity of cisapride may increase when this drug is associated with ranitidine.. A 37-day old term infant, treated with cisapride (1.2 mg/kg/d) and ranitidine for regurgitations, was hospitalized for malaise. A prolonged QT interval (with isolate ventricular extrasystoles), noted at admission, disappeared rapidly after cisapride withdrawal. Linkage to cisapride was probable, promoted by high dosage and cisapride metabolism inhibition by ranitidine, but its plasma concentration was not measured.. This case report stresses the problem of cisapride dosage in infants and the question of an interaction between cisapride and ranitidine.

Topics: Anti-Ulcer Agents; Cisapride; Dose-Response Relationship, Drug; Drug Therapy, Combination; Gastroesophageal Reflux; Histamine H2 Antagonists; Humans; Infant; Long QT Syndrome; Male; Piperidines; Ranitidine; Syncope

Topics: Cisapride; Gastrointestinal Agents; Humans; Hypokalemia; Long QT Syndrome; Piperidines

Cisapride, a gastrointestinal prokinetic agent, is known to cause long Q-T syndrome and ventricular arrhythmias. The cellular mechanism is not known. The human ether-á-go-go-related gene (HERG), which encodes the rapidly activating delayed rectifier K+ current and is important in cardiac repolarization, may serve as a target for the action of cisapride. We tested the hypothesis that cisapride blocks HERG. The whole cell patch-clamp recording technique was used to study HERG channels stably expressed heterologously in HEK293 cells. Under voltage-clamp conditions, cisapride block of HERG is dose dependent with a half-maximal inhibitory concentration of 6.5 nM at 22 degrees C (n = 25 cells). Currents rapidly recovered with drug washout. The onset of block by cisapride required channel activation indicative of open or inactivated state blockage. Block of HERG with cisapride after channel activation was voltage dependent. At -20 mV, 10 nM cisapride reduced HERG tail-current amplitude by 5%, whereas, at + 20 mV, the tail-current amplitude was reduced by 45% (n = 4 cells). At -20 and + 20 mV, 100 nM cisapride reduced tail-current amplitude by 66 and 90%, respectively. We conclude that cisapride is a potent blocker of HERG channels expressed in HEK293 cells. This effect may account for the clinical occurrence of Q-T prolongation and ventricular arrhythmias observed with cisapride.

Topics: Cation Transport Proteins; Cell Line; Cisapride; DNA-Binding Proteins; Dose-Response Relationship, Drug; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Gastrointestinal Agents; Humans; Long QT Syndrome; Membrane Potentials; Patch-Clamp Techniques; Piperidines; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Voltage-Gated; Recombinant Proteins; Trans-Activators; Transcriptional Regulator ERG; Transfection

A 2-month-old infant with gastroesophageal reflux was treated with cisapride. Bradycardia developed and an electrocardiogram revealed 2:1 atrioventricular conduction and a prolonged QT interval. After cessation of cisapride therapy, both the rhythm and the QT interval returned to normal. Prolonged QT interval during treatment with cisapride may occur in children as in adults.

Topics: Adult; Age Factors; Bradycardia; Cisapride; Electrocardiography; Female; Gastroesophageal Reflux; Humans; Infant; Long QT Syndrome; Piperidines

Topics: Anti-Bacterial Agents; Antifungal Agents; Cisapride; Drug Interactions; Drug Labeling; Humans; Imidazoles; Long QT Syndrome; Macrolides; Piperidines; Torsades de Pointes

The gastrointestinal prokinetic drug, cisapride, is widely used for the treatment of diabetic gastroparesis and disorders of gastrointestinal motility. We present a case of acquired QT prolongation, syncope, and nonsustained ventricular tachycardia associated with high doses of cisapride.

Topics: Cisapride; Electrocardiography; Gastrointestinal Agents; Humans; Long QT Syndrome; Male; Middle Aged; Piperidines