nitrophenols and Chemical-and-Drug-Induced-Liver-Injury

Certain drugs containing a nitroaromatic moiety (e.g., tolcapone, nimesulide, nilutamide, flutamide, nitrofurantoin) have been associated with organ-selective toxicity including rare cases of idiosyncratic liver injury. What they have in common is the potential for multistep nitroreductive bioactivation (6-electron transfer) that produces the potentially hazardous nitroanion radical, nitroso intermediate, and N-hydroxy derivative. These intermediates have been associated with increased oxidant stress and targeting of nucleophilic residues on proteins and nucleic acids. However, other mechanisms including the formation of oxidative metabolites and mitochondrial liability, as well as inherent toxicokinetic properties, also determine the drugs' overall potency. Therefore, structural modification not only of the nitro moiety but also of ring substituents can greatly reduce toxicity. Novel concepts have revealed that, besides the classical microsomal nitroreductases, cytosolic and mitochondrial enzymes including nitric oxide synthase can also bioactivate certain nitroarenes (nilutamide). Furthermore, animal models of silent mitochondrial dysfunction have demonstrated that a mitochondrial oxidant stress posed by certain nitroaromatic drugs (nimesulide) can produce significant mitochondrial injury if superimposed on a genetic mitochondrial abnormality. Finally, there may be mechanisms for all nitroaromatic drugs that do not involve bioactivation of the nitro group, e.g., AHR interactions with flutamide. Taken together, the focus of research on the hepatic toxicity of nitroarene-containing drugs has shifted over the past years from the identification of the reactive intermediates generated during the bioreductive pathway to the underlying biomechanisms of liver injury. Most likely one of the next paradigm shifts will include the identification of determinants of susceptibility to nitroaromatic drug-induced hepatotoxicity.

Topics: Benzophenones; Biotransformation; Chemical and Drug Induced Liver Injury; Flutamide; Imidazolidines; Nifedipine; Nitro Compounds; Nitrofurantoin; Nitrophenols; Sulfonamides; Tolcapone

Parkinson's disease patients treated with a combination of levodopa and an aromatic L-amino acid decarboxylase inhibitor usually develop motor complications after some years. To minimise this problem, selective catechol-O-methyltransferase (COMT) inhibitors were developed in order to improve the poor pharmacokinetic profile of levodopa. Tolcapone and entacapone are the two marketed drugs in this class, and both increase the half-life of levodopa and improve clinical parameters, such as the increase in the duration of 'on' and decrease of 'off' time. Soon after its release, tolcapone was suspended in the EU due to it's implication in the deaths of three Parkinsonian patients. The cause of death in these patients was fulminant hepatitis. The mechanism by which tolcapone induces liver damage has been studied. Results show that this drug induces uncoupling of oxidative phosphorylation in mitochondria, thus significantly reducing the cell's capacity to generate ATP. This toxic effect was demonstrated both in vitro and in vivo in several models but the concentrations required to induce it are significantly higher than those needed to inhibit COMT. Inter-individual differences in the capacity to metabolise tolcapone may yield higher plasma levels and may explain its toxic effects in a small sample of patients. Recently, the suspension on tolcapone was lifted, based on new clinical data and ongoing monitoring of its use in other countries. The European Agency for the Evaluation of Medicinal Products concluded that, in some situations, tolcapone has a clinical efficacy that is superior to entacapone and that an adequate level of safety could be achieved with appropriate liver function monitoring and other measures. It is concluded that tolcapone can be safely used in Parkinsonian patients who do not respond or cannot, for other reasons, be prescribed with other COMT inhibitors.

Topics: Adenosine Triphosphate; Antiparkinson Agents; Benzophenones; Catechol O-Methyltransferase Inhibitors; Chemical and Drug Induced Liver Injury; Half-Life; Humans; Levodopa; Liver; Mitochondria; Nitrophenols; Oxidative Stress; Parkinson Disease; Phosphorylation; Safety; Tolcapone

Entacapone and tolcapone are selective catechol-O-methyltransferase (COMT) inhibitors developed recently as adjuncts to levodopa for the treatment of Parkinson's disease (PD). They extend the duration of action of levodopa. As a result, they increase 'on' time, decrease 'off' time and improve motor scores in patients with motor fluctuations. Both benefits and main side effects are related to increased dopaminergic activity. This paper reviews the use of those COMT inhibitors in PD with particular focus on the issue of hepatotoxicity. Neither tolcapone nor entacapone caused hepatotoxicity in preclinical studies. However, in 1998, four patients who were using tolcapone presented with serious liver dysfunction; three of them died due to acute liver failure. Tolcapone is now known to have the potential to cause hepatotoxicity in clinical use and experimental studies. It is now recommended that tolcapone be administered only in patients with motor fluctuations who are no longer satisfactorily treated with other medications for PD. Routine liver monitoring is now mandatory with this agent. Entacapone has been described as a well-tolerated and safe drug in recent experimental studies, human clinical trials and postmarketing surveillance. It can be offered to any patient with motor fluctuations and routine liver monitoring is not required.

Topics: Antiparkinson Agents; Benzophenones; Catechol O-Methyltransferase Inhibitors; Catechols; Chemical and Drug Induced Liver Injury; Chemical and Drug Induced Liver Injury, Chronic; Enzyme Inhibitors; Humans; Levodopa; Nitriles; Nitrophenols; Parkinson Disease; Tolcapone

Levodopa is the cornerstone of idiopathic Parkinson's disease (PD) treatment. However, after long-term use of levodopa, a significant percentage of patients experience motor fluctuations, which worsen their quality of life. Catechol-O-methyltransferase (COMT) inhibitors reduce levodopa metabolism and enhance the respective plasma levels, resulting in improvements in symptoms and overall quality of life. Tolcapone was the first drug of this class to be marketed, but was withdrawn in the European Union due to its implication in the deaths of three PD patients due to hepatic failure. Three deaths from fulminant hepatic failure in 40000 patient-years is a number that is 10-100 times higher than the expected incidence in the general population and, according to the manufacturer's own information, the number is probably underestimated due to under-reporting of cases. In the US, tolcapone was not withdrawn, but restrictive liver enzyme monitoring measures were issued by authorities, which severely limited its use. No further deaths from hepatic failure were reported since these measures were implemented. The mechanisms by which tolcapone may induce liver toxicity are still under debate. It was thought that mitochondrial uncoupling of oxidative phosphorylation by tolcapone, and consequent impairment of energy production by hepatocytes, could be responsible for the observed effects. Some experts consider that the restrictive guidelines issued in the US regarding tolcapone use may be loosened with no consequential reductions in safety. It was suggested that ongoing clinical information about safety should be considered and periodical revisions of the restrictions made accordingly. The identification of the molecular and biochemical basis of tolcapone hepatotoxicity, when completed, should also provide important indications for the clinical use of this drug. In conclusion, appropriate monitoring of liver function can ensure adequate safety in PD patients receiving tolcapone, who can therefore benefit from the symptomatic improvements obtained with this drug.

Topics: Antiparkinson Agents; Benzophenones; Catechol O-Methyltransferase Inhibitors; Chemical and Drug Induced Liver Injury; Humans; Liver Function Tests; Nitrophenols; Parkinson Disease; Tolcapone

Topics: Adverse Drug Reaction Reporting Systems; Antiparkinson Agents; Benzophenones; Chemical and Drug Induced Liver Injury; Drug-Related Side Effects and Adverse Reactions; European Union; Humans; Legislation, Drug; Nitrophenols; Parkinson Disease; Tolcapone

Topics: Antiparkinson Agents; Benzophenones; Chemical and Drug Induced Liver Injury; Enzyme Inhibitors; Humans; Liver Failure; Neurology; Nitrophenols; Tolcapone; United States; United States Food and Drug Administration

p-Nitrophenol (PNP) is the main end product of organophosphorus insecticides and a derivative of diesel exhaust particles. In addition to its unfavorable impact on reproductive functions in both genders, it also has various harmful physiological effects including lung cancer and allergic rhinitis. The identification of the cellular readout that functions in metabolic pathway perpetuation is still far from clear. This research aimed to study the impact of chronic PNP exposure on the health condition of the liver in Japanese quails. Quails were exposed to different concentrations of PNP as follows: 0.0 (control), 0.01mg (PNP/0.01), 0.1mg (PNP/0.1), and 1mg (PNP/1) per kg of body weight for 2.5 months through oral administration. Liver and plasma samples were collected at 1.5, 2, and 2.5 months post-treatment for biochemical, histopathology, and immunohistochemistry assessment. The plasma aspartate aminotransferase (AST) level was assessed enzymatically. The livers were collected for histopathology, glycogen accumulation, proliferating cell nuclear antigen (PCNA), and apoptosis assessment. Our results revealed an irregularity in body weight due to the long-term exposure of PNP with a significant reduction in liver weight. PNP treatment caused histopathological alterations in the hepatic tissues which increased in severity by the long-term exposure. The low dose led to mild degeneration with lymphocytic infiltration, while the moderate dose has a congestion effect with some necrosis; meanwhile severe hepatocyte degeneration and RBCs hemolysis were noticed due to high dose of PNP. Glycogen accumulation increased in hepatocytes by prolonged exposure to p-Nitrophenol with the highest intensity in the group treated by the high dose. Moderate and high doses of PNP resulted in a significant increase in apoptosis and hepatocytes' proliferation at the different time points after treatment. This increase is markedly notable and maximized at 2.5 months post-treatment. The damage occurred in a time-dependent manner. These changes reflected on the plasma hepatic enzyme AST that was clearly increased at 2.5 months of exposure. Therefore, it could be concluded that PNP has profound toxic effects on the liver in cellular level. Taking into consideration the time and dose factors, both have a synergistic effect on the accumulation of glycogen, apoptosis, and cellular proliferation, highlighting the power of cellular investigation which will potentially open the door for earl

Topics: Animals; Apoptosis; Chemical and Drug Induced Liver Injury; Coturnix; Female; Glycogen; Humans; Liver; Male; Nitrophenols

We investigated the effect of phytosterol (PS) in regard to liver damage induced by 4-nitrophenol (PNP). Twenty rats were randomly divided into four groups (Control, PS, PNP, and PNP+PS). The PS and PNP+PS groups were pretreated with PS for one week. The PNP and PNP+PS groups were injected subcutaneously with PNP for 28 days. The control group received a basal diet and was injected with vehicle alone. Treatment with PS prevented the elevation of the total bilirubin levels, as well as an increase in serum alkaline transaminase and aspartate transaminase, which are typically caused by PNP-induced liver damage. Histopathologically showed that liver damage was significantly mitigated by PS treatment. However, there was no significant change in antioxidant enzyme activities, and the Nrf2-antioxidant system was not activated after treatment with PS. These results suggest that PS could mitigate liver damage induced by PNP, but does not enhance antioxidant capacity.

Topics: Animals; Bilirubin; Chemical and Drug Induced Liver Injury; Gene Expression Regulation, Enzymologic; Injections, Subcutaneous; Male; NF-E2-Related Factor 2; Nitrophenols; Phytosterols; Rats; Rats, Sprague-Dawley; Transaminases

The Liver Toxicity Biomarker Study is a systems toxicology approach to discover biomarkers that are indicative of a drug's potential to cause human idiosyncratic drug-induced liver injury. In phase I, the molecular effects in rat liver and blood plasma induced by tolcapone (a "toxic" drug) were compared with the molecular effects in the same tissues by dosing with entacapone (a "clean" drug, similar to tolcapone in chemical structure and primary pharmacological mechanism). Two durations of drug exposure, 3 and 28 days, were employed. Comprehensive molecular analysis of rat liver and plasma samples yielded marker analytes for various drug-vehicle or drug-drug comparisons. An important finding was that the marker analytes associated with tolcapone only partially overlapped with marker analytes associated with entacapone, despite the fact that both drugs have similar chemical structures and the same primary pharmacological mechanism of action. This result indicates that the molecular analyses employed in the study are detecting substantial "off-target" markers for the two drugs. An additional interesting finding was the modest overlap of the marker data sets for 3-day exposure and 28-day exposure, indicating that the molecular changes in liver and plasma caused by short- and long-term drug treatments do not share common characteristics.

Topics: Animals; Benzophenones; Biomarkers; Blood Proteins; Catechols; Chemical and Drug Induced Liver Injury; Female; Gene Expression Profiling; Liver; Male; Metabolome; Metabolomics; Nitriles; Nitrophenols; Proteome; Proteomics; Rats; Research Design; Tolcapone; Toxicity Tests, Acute; Toxicity Tests, Chronic

A quantitative high-content screening (HCS) was suggested for the real-time monitoring of drug-induced mitochondrial dysfunction-mediated hepatotoxicity. This HCS is very advantageous in that it allows simultaneous observation of drug-induced activations of hepatotoxic pathways using hypermulticolor cellular imaging. The mitochondrial permeability transition (MPT), cytosolic calcium, and caspase-3 were selected as functional markers to verify drug-induced hepatotoxicity and were concurrently monitored in HepG2 cells in a real-time manner. Nefazodone, tolcapone, and troglitazone caused mitochondrial dysfunction and subsequent apoptotic HepG2 cell death in addition to marked cytosolic calcium increase. On the other hand, extrinsic pathway-mediated apoptotic cell death was monitored when HepG2 cells were treated with piroxicam. It was found that piroxicam-treated HepG2 cells showed apoptotic cell death without the MPT formation, while a cytosolic calcium increase was clearly observed. This finding was confirmed by the caspase-8 inhibition assay. These results demonstrated the unique potential of real-time hypermulticolor HCS to screen hepatotoxic drugs at the in vitro stage rather than the later in vivo stage based on an animal model and to ultimately reduce the probability of drug failure.

Topics: Apoptosis; Benzophenones; Calcium; Caspase 3; Chemical and Drug Induced Liver Injury; Chromans; Hep G2 Cells; Humans; Image Processing, Computer-Assisted; Imidazoles; Liver; Microscopy, Fluorescence; Mitochondria, Liver; Mitochondrial Membrane Transport Proteins; Mitochondrial Permeability Transition Pore; Nitrophenols; Piperazines; Thiazolidinediones; Tolcapone; Triazoles; Troglitazone

Drug-induced liver injury (DILI) is the primary adverse event that results in the withdrawal of drugs from the market and a frequent reason for the failure of drug candidates in the pre-clinical or clinical phases of drug development. This paper presents an approach for identifying potential liver toxicity genomic biomarkers from a liver toxicity biomarker study involving the paired compounds entacapone ("non-liver toxic drug") and tolcapone ("hepatotoxic drug"). Molecular analysis of the rat liver and plasma samples, combined with statistical analysis, revealed many similarities and differences between the in vivo biochemical effects of the two drugs. Six hundred and ninety-five genes and 61 pathways were selected based on the classification scheme. Of the 61 pathways, 5 were specific to treatment with tolcapone. Two of the 12 animals in the tolcapone group were found to have high ALT, AST, or TBIL levels. The gene Vars2 (valyl-tRNA synthetase 2) was identified in both animals and the pathway to which it belongs, the aminoacyl-tRNA biosynthesis pathway, was one of the three most significant tolcapone-specific pathways identified.

Topics: Alanine Transaminase; Animals; Aspartate Aminotransferases; Benzophenones; Bilirubin; Biomarkers; Catechols; Chemical and Drug Induced Liver Injury; Gene Regulatory Networks; Liver; Male; Nitriles; Nitrophenols; Rats; RNA, Transfer, Amino Acyl; Tolcapone

Capture compound mass spectrometry (CCMS) is a novel technology that helps understand the molecular mechanism of the mode of action of small molecules. The Capture Compounds are trifunctional probes: A selectivity function (the drug) interacts with the proteins in a biological sample, a reactivity function (phenylazide) irreversibly forms a covalent bond, and a sorting function (biotin) allows the captured protein(s) to be isolated for mass spectrometric analysis. Tolcapone and entacapone are potent inhibitors of catechol-O-methyltransferase (COMT) for the treatment of Parkinson's disease. We aimed to understand the molecular basis of the difference of both drugs with respect to side effects. Using Capture Compounds with these drugs as selectivity functions, we were able to unambiguously and reproducibly isolate and identify their known target COMT. Tolcapone Capture Compounds captured five times more proteins than entacapone Capture Compounds. Moreover, tolcapone Capture Compounds isolated mitochondrial and peroxisomal proteins. The major tolcapone-protein interactions occurred with components of the respiratory chain and of the fatty acid beta-oxidation. Previously reported symptoms in tolcapone-treated rats suggested that tolcapone might act as decoupling reagent of the respiratory chain (Haasio et al., 2002b). Our results demonstrate that CCMS is an effective tool for the identification of a drug's potential off targets. It fills a gap in currently used in vitro screens for drug profiling that do not contain all the toxicologically relevant proteins. Thereby, CCMS has the potential to fill a technological need in drug safety assessment and helps reengineer or to reject drugs at an early preclinical stage.

Topics: Animals; Antiparkinson Agents; Benzophenones; Catechol O-Methyltransferase; Catechol O-Methyltransferase Inhibitors; Catechols; Chemical and Drug Induced Liver Injury; Computer-Aided Design; Electron Transport; Enzyme Inhibitors; Fatty Acids; Hep G2 Cells; Humans; Liver; Mass Spectrometry; Microsomes, Liver; Mitochondria, Liver; Mitochondrial Proteins; Models, Molecular; Molecular Structure; Nitriles; Nitrophenols; Oxidation-Reduction; Oxidative Phosphorylation; Peroxisomes; Rats; Reproducibility of Results; Tolcapone; Toxicity Tests

Drug-induced liver injury (DILI) is the primary adverse event that results in withdrawal of drugs from the market and a frequent reason for the failure of drug candidates in development. The Liver Toxicity Biomarker Study (LTBS) is an innovative approach to investigate DILI because it compares molecular events produced in vivo by compound pairs that (a) are similar in structure and mechanism of action, (b) are associated with few or no signs of liver toxicity in preclinical studies, and (c) show marked differences in hepatotoxic potential. The LTBS is a collaborative preclinical research effort in molecular systems toxicology between the National Center for Toxicological Research and BG Medicine, Inc., and is supported by seven pharmaceutical companies and three technology providers. In phase I of the LTBS, entacapone and tolcapone were studied in rats to provide results and information that will form the foundation for the design and implementation of phase II. Molecular analysis of the rat liver and plasma samples combined with statistical analyses of the resulting datasets yielded marker analytes, illustrating the value of the broad-spectrum, molecular systems analysis approach to studying pharmacological or toxicological effects.

Topics: Animals; Antiparkinson Agents; Benzophenones; Biomarkers; Catechols; Chemical and Drug Induced Liver Injury; Dose-Response Relationship, Drug; Female; Gene Expression; Liver; Male; Metabolomics; Nitriles; Nitrophenols; Oligonucleotide Array Sequence Analysis; Proteomics; Rats; Rats, Sprague-Dawley; Tolcapone

Topics: Benzophenones; Catechol O-Methyltransferase Inhibitors; Chemical and Drug Induced Liver Injury; Humans; Male; Middle Aged; Nitrophenols; Severity of Illness Index; Time Factors; Tolcapone

The authors report two cases of catechol-O-methyltransferase (COMT) inhibitor-induced asymptomatic hepatic dysfunction in women with Parkinson disease. The patients were genotyped for the UDP-glucuronosyltransferase (UGT) 1A9 gene (which encodes the main COMT inhibitor-metabolizing enzyme), and found to carry mutations leading to defective glucuronidation activity. This suggests that UGT1A9 poor metabolizer genotype(s) may be a predisposing factor for COMT inhibitor-induced hepatotoxicity.

Topics: Adult; Aged; Antiparkinson Agents; Benzophenones; Catechol O-Methyltransferase; Catechol O-Methyltransferase Inhibitors; Catechols; Chemical and Drug Induced Liver Injury; DNA Mutational Analysis; Enzyme Inhibitors; Female; Genotype; Glucuronates; Glucuronosyltransferase; Humans; Liver; Liver Diseases; Middle Aged; Mutation; Nitriles; Nitrophenols; Parkinson Disease; Polymorphism, Genetic; Tolcapone; UDP-Glucuronosyltransferase 1A9

Tolcapone is a catechol-O-methyltransferase (COMT) inhibitor used for control of motor fluctuations in Parkinson's disease (PD). Since its entry onto the market in 1998, tolcapone has been associated with numerous cases of hepatotoxicity, including three cases of fatal fulminant hepatic failure. The cause of this toxicity is not known; however, it does not occur with the use of the structurally similar drug entacapone. It is known that tolcapone is metabolized to amine (M1) and acetylamine (M2) metabolites in humans, but that the analogous metabolites were not detected in a limited human study of entacapone metabolism. We hypothesized that one or both of these tolcapone metabolites could be oxidized to reactive species and that these reactive metabolites might play a role in tolcapone-induced hepatocellular injury. To investigate this possibility, we examined the ability of M1 and M2 to undergo in vitro bioactivation by electrochemical and enzymatic methods. Electrochemical experiments revealed that M1 and M2 are more easily oxidized than the parent compound, in the order M1 > M2 > tolcapone. There was a general correlation between oxidation potential and the half-lives of the compounds in the presence of two oxidizing systems, horseradish peroxidase and myeloperoxidase. These enzymes catalyzed the oxidation of M1 and M2 to reactive species that could be trapped with glutathione (GSH) to form metabolite adducts (C1 and C2). Each metabolite was found to only form one GSH conjugate, and the structures were tentatively identified using LC-MS/MS. Following incubation of M1 and M2 with human liver microsomes in the presence of GSH, the same adducts were observed, and their structures were confirmed using LC-MS/MS and (1)H NMR. Experiments with chemical P450 inhibitors and cDNA-expressed P450 enzymes revealed that this oxidation is catalyzed by several P450s, and that P450 2E1 and 1A2 play the primary role in the formation of C1 while P450 1A2 is most important for the production of C2. Taken together, these data provide evidence that tolcapone-induced hepatotoxicity may be mediated through the oxidation of the known urinary metabolites M1 and M2 to reactive intermediates. These reactive species may form covalent adducts to hepatic proteins, resulting in damage to liver tissues, although this supposition was not investigated in this study.

Topics: Acetylation; Amines; Benzophenones; Catechol O-Methyltransferase Inhibitors; Cells, Cultured; Chemical and Drug Induced Liver Injury; Cytochrome P-450 Enzyme Inhibitors; Cytochrome P-450 Enzyme System; Electrochemistry; Enzyme Inhibitors; Glutathione; Half-Life; Hepatocytes; Horseradish Peroxidase; Humans; Microsomes, Liver; Nitrophenols; Nuclear Magnetic Resonance, Biomolecular; Oxidation-Reduction; Peroxidase; Reactive Oxygen Species; Spectrometry, Mass, Electrospray Ionization; Tolcapone

Topics: Aged; Antiparkinson Agents; Antipsychotic Agents; Benzophenones; Chemical and Drug Induced Liver Injury; Clozapine; Dose-Response Relationship, Drug; Drug Administration Schedule; Drug Therapy, Combination; Female; Humans; Liver Function Tests; Neuroleptic Malignant Syndrome; Neurologic Examination; Nitrophenols; Tolcapone

Four patients with Parkinson disease have recently been described in whom severe hepatic dysfunction developed in association with tolcapone therapy. These reports led to the introduction of a "black box" warning and more intensive monitoring requirements in the United States. A review of these cases and all clinical trials indicates that liver dysfunction did not develop in any patient who had received monitoring of liver function according to the original prescribing information. Virtually all instances of liver enzyme abnormality and clinical liver dysfunction occurred within 6 months of initiating treatment. To assess the current role of tolcapone therapy in Parkinson disease, a panel of neurologists and hepatologists was convened. Consensus was reached with respect to the following: (1) Tolcapone is an effective agent in the treatment of patients with fluctuating Parkinson disease. (2) The risk of developing irreversible liver injury is negligible with appropriate monitoring. (3) It may be possible to reduce the frequency of monitoring after 6 months of treatment. (4) The requirement that tolcapone be withdrawn if liver enzymes are elevated above the upper limit of normal on a single occasion is unnecessarily restrictive. It was concluded that tolcapone, when used as an adjunct to levodopa, is an effective anti-parkinsonian agent and that less frequent monitoring after 6 months, with an action limit of 2 to 3 times the upper limit of normal, is sufficient to ensure safety in patients who are deriving benefit from the drug.

Topics: Aged; Antiparkinson Agents; Benzophenones; Chemical and Drug Induced Liver Injury; Clinical Trials as Topic; Drug Prescriptions; Female; Humans; Nitrophenols; Parkinson Disease; Product Surveillance, Postmarketing; Tolcapone; United States; United States Food and Drug Administration

Topics: Benzophenones; Catechol O-Methyltransferase Inhibitors; Chemical and Drug Induced Liver Injury; Depressive Disorder, Major; Enzyme Inhibitors; Humans; Nitrophenols; Tolcapone

Topics: Aged; Antiparkinson Agents; Benzophenones; Catechol O-Methyltransferase Inhibitors; Chemical and Drug Induced Liver Injury; Enzyme Inhibitors; Female; Humans; Liver Failure; Mitochondria, Liver; Nitrophenols; Tolcapone

Topics: Antiparkinson Agents; Benzophenones; Canada; Catechol O-Methyltransferase Inhibitors; Chemical and Drug Induced Liver Injury; Drug Approval; Humans; Nitrophenols; Tolcapone

Isoniazid (INH), a widely used drug in the prophylaxis and treatment of tuberculosis, is associated with a 1 to 2% risk of severe and potentially fatal hepatotoxicity. There is evidence that the INH metabolite hydrazine plays an important role in the mechanism of this toxicity. Metabolism of INH leads to the production of hydrazine via both direct and indirect pathways. In both cases, the activity of an INH amidase is required to hydrolyze an amide bond. In the present study, using a model of INH-induced hepatotoxicity in rabbits, pretreatment of rabbits with the amidase inhibitor bis-p-nitrophenyl phosphate 30 min before injection of INH inhibited the formation of INH-derived hydrazine and decreased measures of hepatocellular damage, hepatic triglyceride accumulation, and hypertriglyceridemia. Bis-p-nitrophenyl phosphate also potently inhibited the production of hydrazine from INH in in vitro microsomal incubations (IC50 2 microM). Although hepatic glutathione stores are decreased, they are not depleted in animals with INH-induced hepatotoxicity. Significant effects on hepatic microsomal cytochrome P-450 1A1/2 and cytochrome P-450 2E1 activities suggest that these isozymes may be involved in the mechanism of the toxicity. In conclusion, this study demonstrates the importance of amidase activity in this rabbit model of hepatotoxicity and provides additional evidence in support of the role of hydrazine in the mechanism of INH-induced hepatotoxicity.

Topics: Amidohydrolases; Animals; Antitubercular Agents; Chemical and Drug Induced Liver Injury; Cytochrome P-450 CYP2E1 Inhibitors; Enzyme Inhibitors; Glutathione; Hydrazines; In Vitro Techniques; Isoniazid; Male; Microsomes, Liver; Nitrophenols; Rabbits; Triglycerides

Topics: Aged; Antiparkinson Agents; Benzophenones; Chemical and Drug Induced Liver Injury; Female; Humans; Liver Failure, Acute; Nitrophenols; Parkinson Disease; Tolcapone

Liver microsomal beta-glucuronidase is stabilized within microsomal vesicles by complexation with the accessory protein, named egasyn. In this study, we showed that egasyn is identical to one of the carboxylesterase isozymes and organophosphorus and carbamate insecticides, acetanilide which is a specific substrate of egasyn and halothane caused a rapid dissociation of the egasyn-microsomal beta-glucuronidase complex when administered in vivo or when added in vitro to isolated hepatocytes. The dissociation was relatively specific to organophosphates, carbamates, but not pyrethroids. Dissociation of the egasyn-beta-glucuronidase complex in vivo by organophosphates was followed by massive and rapid secretion of microsomal beta-glucuronidase into plasma. From these results, we concluded that release of liver microsomal beta-glucuronidase is the most rapid and sensitive marker to organophosphorus or carbamate insecticide-induced intoxication.

Topics: Acetanilides; Amino Acid Sequence; Animals; Carbamates; Carboxylic Ester Hydrolases; Chemical and Drug Induced Liver Injury; Glucuronidase; Halothane; Insecticides; Microsomes, Liver; Molecular Sequence Data; Nitrophenols; Organophosphorus Compounds; Rats; Rats, Inbred Strains

Mice poisoned with acetaminophen were treated with esterase inhibitors, buthionine sulfoximine, and N-acetyl-L-lysine in experiments designed to explore the mechanism of N-acetylcysteine protection in vivo. Three esterase inhibitors, phenylmethylsulfonyl fluoride, bis-(p-nitrophenyl)-phosphate, and diisopropylfluorophosphate, had no effect on the antidote effectiveness of N-acetylcysteine, although each provided partial protection against acetaminophen poisoning. Buthionine sulfoximine, a specific inhibitor of gamma-glutamyl cysteine synthetase, antagonized the antidote effect of N-acetylcysteine. Acetaminophen-induced hepatotoxicity, as measured by plasma alanine aminotransferase activity, and mortality failed to decline, consistent with stimulation of glutathione synthesis as the primary mechanism of antidote protection. N-Acetyl-L-lysine was given at doses up to ten-fold higher than N-acetylcysteine yet had no effect on acetaminophen hepatotoxicity or its prevention by N-acetylcysteine. These results advance the view that N-acetylcysteine acts primarily as a glutathione precursor. They further suggest the esterase inhibitors limit poisoning by acetaminophen and may be useful agents in antagonizing the toxicity of other metabolically activated drugs.

Topics: Acetaminophen; Acetylcysteine; Animals; Buthionine Sulfoximine; Chemical and Drug Induced Liver Injury; Esterases; Isoflurophate; Lysine; Male; Methionine Sulfoximine; Mice; Mice, Inbred ICR; Nitrophenols; Organophosphorus Compounds; Phenylmethylsulfonyl Fluoride

The relationship between the hepatotoxicity and metabolism of isoniazid and its metabolites, acetylisoniazid and acetylhydrazine, has been investigated. Toxic doses of acetylisoniazid and acetylhydrazine, radiolabeled in the acetyl group, were found to bind covalently to liver protein in vivo. This binding was mediated by the microsomal enzyme system as indicated by the effects of pretreatments altering the activity of these enzymes. Metabolic studies revealed that the pretreatments increased the metabolism of the acetylhydrazine moiety of acetyl-labeled acetylisoniazid and of acetylhydrazine itself by the microsomal enzyme system. Pretreatment with the acyl amidase inhibitor, bis-p-nitrophenyl phosphate, inhibited the hydrolysis of acetylisoniazid to isonicotinic acid plus acetylhydrazine and concomitantly decreased the covalent binding of acetyl-labeled acetylisoniazid. The changes in the metabolism of isoniazid, acetylisoniazid and acetylhydrazine effected by various pretreatments paralleled changes in the severity of the hepatic necrosis caused by the compounds. These results strongly suggest that acetylhydrazine is the metabolite responsible for the hepatic necrosis caused by isoniazid and that mirosomal metabolism of acetylhydrazine in vivo leads to the production of a reactive acylating species capable of reacting covalently with tissue macromolecules.

Topics: Acetylation; Amidohydrolases; Animals; Biotransformation; Carbon Dioxide; Chemical and Drug Induced Liver Injury; Cobalt; Hydrolysis; Isoniazid; Liver; Male; Microsomes, Liver; Nitrophenols; Organophosphorus Compounds; Phenobarbital; Protein Binding; Rats

Topics: Acidosis; Animals; Anthelmintics; Bicarbonates; Body Temperature; Chemical and Drug Induced Liver Injury; Dog Diseases; Dogs; Ethanol; Female; Fever; Ice; Iodine; Lactates; Nephritis; Nitrophenols; Physical Exertion; Temperature

Topics: Abomasum; Aging; Alkaline Phosphatase; Animals; Bone and Bones; Brain; Cattle; Cattle Diseases; Chemical and Drug Induced Liver Injury; Deficiency Diseases; Diarrhea; Duodenum; Female; Hydrogen-Ion Concentration; Isoenzymes; Kidney; Kinetics; Liver; Lung; Mammary Glands, Animal; Nitrophenols; Phenolphthaleins; Phenols; Phenylalanine; Phosphoric Acids; Placenta; Rumen; Spleen; Urea

Topics: Administration, Oral; Alcohol Oxidoreductases; Animals; Anthelmintics; Aspartate Aminotransferases; Carbon Tetrachloride; Chemical and Drug Induced Liver Injury; Chickens; DDT; Fascioliasis; Female; Glutamate Dehydrogenase; Hydrocarbons, Halogenated; Injections, Intraperitoneal; Kidney; Lethal Dose 50; Liver; Male; Muscles; Nitriles; Nitrophenols; Ornithine Carbamoyltransferase; Peritonitis; Phenobarbital; Sheep; Sorbitol