entacapone and 3-methoxytyrosine

Catechol-O-methyltransferase inhibitors may be used to decrease levodopa requirement. The objective was to investigate whether the levodopa/carbidopa intestinal gel infusion dose can be reduced by 20% without worsening of motor fluctuations and levodopa concentration stability when oral catechol-O-methyltransferase inhibitors are added.. A short-term, randomized, partly blinded, crossover, investigator-initiated clinical trial was performed, with levodopa/carbidopa intestinal gel combined with oral entacapone and tolcapone on two different days in 10 patients. The primary outcome measure was difference in coefficient of variation of levodopa in plasma between levodopa/carbidopa, levodopa/carbidopa/entacapone, and levodopa/carbidopa/tolcapone. The secondary outcome measures other pharmacokinetic variables, patient-reported outcome, and blinded analysis of motor performance.. Variation of plasma levodopa concentrations did not differ significantly between the treatments. The treatments did not differ regarding motor performance. Levodopa concentrations were significantly higher using tolcapone. Concentrations of the metabolite 3-O-methyldopa decreased gradually during catechol-O-methyltransferase inhibition.. According to this small, short-term pilot study, oral catechol-O-methyltransferase inhibitors administered in 5-h intervals may be useful in cases where levodopa/carbidopa intestinal gel dose reduction is wanted. Stability of plasma levodopa levels is not significantly altered, and off-time is not increased when decreasing the levodopa/carbidopa intestinal gel dose by 20%. Rather, the dose should probably be decreased more than 20%, especially under tolcapone co-treatment, to avoid increased dyskinesias with time.

Topics: Adult; Aged; Aged, 80 and over; Antiparkinson Agents; Benzophenones; Catechols; Cross-Over Studies; Drug Therapy, Combination; Female; Humans; Levodopa; Male; Middle Aged; Nitriles; Nitrophenols; Parkinson Disease; Pilot Projects; Self Report; Single-Blind Method; Sweden; Tolcapone; Tyrosine

Elevation of plasma total homocysteine concentrations were observed in levodopa/dopa decarboxylase inhibitor (DDI)-treated patients with Parkinson's disease (PD). Degradation of levodopa to 3-O-methyldopa via the enzyme catechol-O-methyltransferase (COMT) is a methyl group demanding reaction. It generates homocysteine from the methyl group donor methionine. But there are inconsistent outcomes, as most investigators determined homocysteine after an overnight washout of levodopa. They did not consider the acute effects of levodopa/DDI intake in relation with COMT inhibition on homocysteine bioavailability. The purpose of this study is to measure levels of homocysteine, levodopa, and its metabolite 3-O-methyldopa in plasma after reiterated oral levodopa/DDI administration with and without the COMT-inhibitor entacapone (EN). Sixteen PD patients received 100 mg levodopa/carbidopa three times on day 1 and with EN on day 2 under standardized conditions. Homocysteine concentrations increased on day 1 and generally over the whole interval. No significant ascent of homocysteine appeared on day 2 only. Levodopa bioavailability was higher on day 2 due to the COMT inhibition. No change of 3-O-methyldopa appeared between both days. The correlation coefficients between homocysteine, levodopa, and 3-O-methyldopa were higher on day 1 than on day 2. Rise of homocysteine does not only depend on the oral levodopa dose, but also on the acute intake of levodopa/DDI with or without COMT inhibition. Measurements of homocysteine should consider acute repeated levodopa/DDI applications, as homocysteine and metabolically related 3-O-methyldopa accumulate due to their long plasma half-life in contrast to short-living levodopa.

Topics: Aged; Antiparkinson Agents; Aromatic Amino Acid Decarboxylase Inhibitors; Biological Availability; Carbidopa; Catechol O-Methyltransferase Inhibitors; Catechols; Drug Combinations; Drug Therapy, Combination; Female; Half-Life; Homocysteine; Humans; Levodopa; Male; Middle Aged; Nitriles; Parkinson Disease; Tyrosine

The interval of line tracing performance is more associated to basal ganglia function due to the dependence on bradykinesia and rigidity. The other component of this task, the precision of execution of complex movement sequences, is more related to attention. We compared the motor response after once dosing of 200 mg retarded release LD (levodopa)/CD (carbidopa) and of 150 mg LD/CD/EN (entacapone) by rating of motor symptoms, by measurement of LD- and 3-O-methyldopa (3-OMD) plasma concentrations and by the outcomes of a line tracing task. Thirteen treated patients with Parkinson's disease (PD) took one of the two tested LD formulations on two consecutive days under randomised, double blind, identical standardised conditions. No significant differences appeared regarding rated motor response and LD plasma concentrations, but 3-OMD only significantly went up after LD/CD intake. LD/CD/EN was superior to LD/CD regarding the attention related components of line tracing probably due to a hypothetically increased dopamine occurrence at the prefrontal cortex, which guides human behaviour.

Topics: Adult; Aged; Antiparkinson Agents; Carbidopa; Catechols; Delayed-Action Preparations; Double-Blind Method; Drug Combinations; Female; Humans; Levodopa; Male; Middle Aged; Nitriles; Parkinson Disease; Tyrosine

Addition of the catechol-O-methyltransferase (COMT) inhibitor entacapone (EN) prolongs plasma metabolism of levodopa (LD). Objectives were to determine the clinical response after EN addition and the plasma degradation of LD and 3-O-methyldopa [3-OMD]. Not optimum treated hospitalised patients with Parkinson's disease received the same LD dosage on the first day only with carbidopa (CD) and on the second day with CD and EN (t.i.d.) within a standardised setting. We scored motor symptoms and measured LD- and 3-OMD levels on both days at fixed moments. Motor impairment significant better improved probably due to significant higher maximum concentrations [C(max)] and computed area under the curve values of LD levels during the LD/CD/EN condition. Time to C(max) of LD was significantly delayed after the first two LD/CD/EN intakes. An impact of EN on 3-OMD levels appeared. A possibly augmented LD absorption and a prolonged LD metabolism after EN supplementation may contribute to a more continuous LD delivery to the brain.

Topics: Adult; Aged; Antiparkinson Agents; Area Under Curve; Carbidopa; Catechols; Chromatography, High Pressure Liquid; Female; Humans; Levodopa; Male; Middle Aged; Motor Activity; Nitriles; Parkinson Disease; Tyrosine

Twelve parkinsonian patients with levodopa-related end-of-dose fluctuations in disability were studied in an open-label trial to examine the effects of peripheral catechol-O-methyltransferase (COMT) inhibition with entacapone on pharmacokinetics and metabolism of levodopa and on clinical response to levodopa after a single dose and after 4 weeks' medication with entacapone. The clinical response was assessed with continuous monitoring using the motor part of Unified Parkinson's Disease Rating Scale. Entacapone increased statistically significantly the mean area under the plasma concentration-time curve (AUC) of levodopa by 29% after a single dose and by 21% after 4 weeks' administration, without affecting other pharmacokinetic parameters of levodopa. The AUC of 3-O-methyldopa decreased by 45% and AUC of homovanillic acid by 21% after 4 weeks' dosing with entacapone. The duration of motor response to levodopa increased significantly from 2.3 h to 3.2 h (i.e., by 39%) after a single dose and to 3.4 h (i.e., by 48%) after 4 weeks' medication with entacapone. The magnitude of clinical response remained unchanged, but peak latency of motor response was prolonged after 4 weeks' medication. The duration and magnitude of dyskinesias also increased. Peripheral COMT inhibition with entacapone increased significantly the bioavailability of levodopa and prolonged its antiparkinsonian effect after a single dose and after repeated dosing for 4 weeks. Thus entacapone seems to be a valuable adjuvant to levodopa treatment in parkinsonian patients with end-of-dose failure.

Topics: Aged; Antiparkinson Agents; Catechol O-Methyltransferase Inhibitors; Catechols; Dopamine Agents; Double-Blind Method; Enzyme Inhibitors; Female; Homovanillic Acid; Humans; Levodopa; Male; Middle Aged; Nitriles; Parkinson Disease; Tyrosine

We studied the effects of entacapone, a novel inhibitor of the enzyme catechol-O-methyltransferase (COMT), on spontaneous and levodopa (LD) modulated secretion of growth hormone (GH) and prolactin (PRL) in 12 healthy male volunteers. The study had a double-blind, cross-over design with two experimental settings. In the first setting the subjects received a single oral dose of 400 mg of entacapone or matching placebo in a randomized order. In the second setting, a single oral dose of 300 mg of LD and 75 mg of carbidopa was administered concomitantly with either 400 mg of entacapone or matching placebo in a randomized order. Entacapone had no effect on resting levels of GH, but PRL concentrations in plasma were slightly lower after entacapone than after placebo. As expected, LD/carbidopa increased the concentration of GH and decreased that of PRL. The effects of LD were not influenced by concomitant administration of entacapone. Compared with the administration of LD/carbidopa together with placebo, concomitant administration of entacapone increased the AUC of LD by 29% and reduced the AUC of 3-O-methyldopa (a metabolite of LD produced by COMT) by 69%. Entacapone appears not to enhance the effects of LD on hypothalamic-pituitary function, although the LD dose used may have been bigger than optimal for detection of a small modulatory influence.

Topics: Adult; Antiparkinson Agents; Catechol O-Methyltransferase Inhibitors; Catechols; Cross-Over Studies; Dopamine; Double-Blind Method; Enzyme Inhibitors; Human Growth Hormone; Humans; Levodopa; Male; Nitriles; Placebos; Prolactin; Tyrosine

We evaluated the effects of 3-O-methyldopa (3-OMD), a metabolite of L-DOPA which is formed by catechol-O-methyltransferase (COMT), on the uptake, metabolism, and neuroprotective effects of L-DOPA in striatal astrocytes. We examined changes in the numbers of dopaminergic neurons after treatment with L-DOPA and 3-OMD or entacapone, a peripheral COMT inhibitor, using primary cultured mesencephalic neurons and striatal astrocytes.. The number of tyrosine hydroxylase-positive dopaminergic neurons was not affected by L-DOPA treatment in mesencephalic neurons alone. However, the increase in viability of dopaminergic neurons in the presence of astrocytes was further enhanced after methyl-L-DOPA treatment (25 µM) in mixed cultured mesencephalic neurons and striatal astrocytes. The neuroprotective effect of 25 µM L-DOPA was almost completely inhibited by simultaneous treatment with 3-OMD (10 or 100 µM), and was enhanced by concomitant treatment with entacapone (0.3 µM). The uptake of L-DOPA into and the release of glutathione from striatal astrocytes after L-DOPA treatment (100 µM) were inhibited by simultaneous exposure to 3-OMD (100 µM).. These data suggest that L-DOPA exerts its neuroprotective effect on dopaminergic neurons via astrocytes and that 3-OMD competes with L-DOPA by acting on target molecule(s) (possibly including glutathione) released from astrocytes. Since some amount of entacapone can cross the blood-brain barrier, this reagent may enhance L-DOPA transportation by inhibiting COMT and increase the astrocyte-mediated neuroprotective effects of L-DOPA on dopaminergic neurons.

Topics: Animals; Astrocytes; Catechol O-Methyltransferase Inhibitors; Catechols; Cells, Cultured; Corpus Striatum; Dihydroxyphenylalanine; Dopamine Agents; Dopaminergic Neurons; Dose-Response Relationship, Drug; Glutathione; Levodopa; Mesencephalon; Neuroprotection; Neuroprotective Agents; Nitriles; Rats, Sprague-Dawley; Tyrosine

In this study, we developed and validated a HPLC-MS/MS method capable of simultaneously determining levodopa, carbidopa, entacapone, tolcapone, 3-O-methyldopa and dopamine in human plasma. RESULTS & METHODOLOGY: Chromatographic separation was achieved using a C8 column with a mobile phase consisting of a gradient of water and acetonitrile:methanol (90:10 v/v), both containing 0.1% formic acid. The developed method was selective, sensitive (LD<7.0 ng ml(-1)), linear (r>0.99), precise (RSD<11.3%), accurate (RE<11.8%) and free of residual and matrix effects. The developed method was successfully applied in plasma patients with Parkinson's disease using Stalevo®.. The new method can be used for the clinical monitoring of these substances and applied to adjustments in drug dosages.

Topics: Benzophenones; Blood Chemical Analysis; Carbidopa; Catechols; Chromatography, High Pressure Liquid; Dihydroxyphenylalanine; Dopamine; Humans; Levodopa; Nitriles; Nitrophenols; Quality Control; Reproducibility of Results; Tandem Mass Spectrometry; Tolcapone; Tyrosine

The aim of this study is to clarify the relationship between serum 3-O-methyldopa (3-OMD) and the clinical effects of entacapone. The 3-OMD and maximum serum concentration (Cmax) of levodopa were measured in 21 Parkinson's Disease patients who took 100 mg levodopa / dopa decarboxylase inhibitor. After the administration of entacapone, the 3-OMD concentration and percentage of "on" time during waking hours (% of "on" time) were studied for 8 weeks. The 3-OMD concentration was reduced by 34%, and the increase in % of "on" time was 28% at the 8th week compared with baseline. We defined the COMT-index as [baseline 3-OMD concentration] / [levodopa Cmax when 100 mg levodopa was administered alone]. The COMT-index was significantly correlated with the increase in % of "on" time at the 8th week. In conclusion, the measurement of baseline 3-OMD and levodopa pharmacokinetics is useful for predicting the clinical effects of entacapone.

Topics: Aged; Aged, 80 and over; Antiparkinson Agents; Aromatic Amino Acid Decarboxylase Inhibitors; Benserazide; Biomarkers; Carbidopa; Catechol O-Methyltransferase; Catechol O-Methyltransferase Inhibitors; Catechols; Disease Progression; Dopa Decarboxylase; Drug Therapy, Combination; Enzyme Inhibitors; Female; Humans; Japan; Levodopa; Male; Middle Aged; Motor Activity; Nitriles; Parkinson Disease; Prospective Studies; Treatment Outcome; Tyrosine

Chronic levodopa (LD)/dopadecarboxylase inhibitor (DDI) increases homocysteine generation as side reaction of O-methylation. Aim was to investigate the impact of the peripheral COMT inhibitor entacapone (EN) on plasma concentrations of homocysteine, LD and 3-O-methyl-dopa (3-OMD). Patients with Parkinson's disease (PD) received on two consecutive days in a standardised fashion one single dose of 200 mg retarded release LD/carbidopa (CD) or of 150 mg LD/CD/EN, since both were shown to have simultaneous pharmacokinetic LD behaviour. Homocysteine increased after retarded release LD/CD application, but not following LD/CD/EN intake. Homocysteine was lower during the LD/CD/EN condition 80 min after baseline when compared with its levels after LD/CD administration. LD levels simultaneously rose on both days. 3-OMD concentrations did not change. Acute LD/CD application caused a rise of homocysteine levels, which was prevented by LD/CD/EN intake. Therefore, peripheral COMT inhibition may have a beneficial effect on putative, controversially debated components of homocysteine-related progression of PD.

Topics: Adult; Aged; Aged, 80 and over; Antiparkinson Agents; Carbidopa; Catechol O-Methyltransferase Inhibitors; Catechols; Delayed-Action Preparations; Dihydroxyphenylalanine; Enzyme Inhibitors; Female; Homocysteine; Humans; Levodopa; Male; Middle Aged; Nitriles; Parkinson Disease; Time Factors; Tyrosine

We compared--retrospectively--the effects of a 3-month therapy with catechol- O-methyltransferase (COMT) inhibitors tolcapone (100 mg, t.i.d.) and entacapone (200 mg, t.i.d.), on L-DOPA metabolism in two groups of parkinsonian patients with motor fluctuations. Plasma and platelets concentrations of L-DOPA and its direct metabolites, dopamine and 3- O-methyldopa (3-OMD), were measured before starting treatment, after two weeks and at the end of treatment. Patients treated with tolcapone showed significant increases in plasma and platelet L-DOPA levels and marked reduction of plasma and platelet 3-OMD levels, both at short- and long-term. Entacapone did not modify L-DOPA levels, while inducing a less marked reduction of plasma and platelet 3-OMD concentrations, with respect to tolcapone, at both time points. Both drugs were similarly effective in increasing plasma and platelet levels of dopamine. These results confirm the different profiles of activity of the two drugs, with tolcapone proving more effective on both the intra- and extra-cellular levels of L-DOPA and 3-OMD.

Topics: Age Factors; Age of Onset; Aged; Antiparkinson Agents; Benzophenones; Blood Platelets; Catechols; Dopamine; Dose-Response Relationship, Drug; Drug Administration Schedule; Female; Humans; Levodopa; Male; Middle Aged; Nitriles; Nitrophenols; Parkinson Disease; Retrospective Studies; Sex Characteristics; Tolcapone; Tyrosine; Up-Regulation

Flurodopa (FDOPA) is an analogue of L-di-hydroxyphenylalanine (L-dopa) used to assess the nigrostriatal dopamine system in vivo with positron emission tomography (PET). However, FDOPA/PET quantitation is complicated by the presence of the 3-O-methyl-FDOPA (3OMFD) fraction in brain and plasma. Pretreatment with entacapone (OR-611), a peripheral catechol O-methyl-transferase (COMT) inhibitor, greatly reduces the plasma 3OMFD fraction and provides an ideal situation to evaluate the contribution of the plasma 3OMFD fraction in several kinetic models of FDOPA uptake. We performed FDOPA/PET with and without the OR-611 preadministration in six Parkinson's disease (PD) patients. We measured the time-course of the plasma FDOPA and 3OMFD fractions using high-pressure liquid chromatography (HPLC). We calculated striato-occipital ratios (SOR), and estimated the striatal FDOPA uptake rate constant graphically using the plasma FDOPA and occipital tissue time activity curves (KiFD and KiOCC, respectively). We also estimated striatal dopa decarboxylase (DDC) activity (k3D) using a model incorporating independent measurements of 3OMFD transport kinetic rate constants. With the preadministration of OR-611, the pharmacological efficiency in plasma was prolonged significantly (21.1-37.7%; p < 0.01). We also observed significant mean elevations in SOR and KiOCC by 21.8 and 53.5%, respectively (p < 0.05). KiFD and k3D did not show significant change. We conclude that OR-611 prolongs the circulation time of FDOPA in the plasma but does not alter rate constants for striatal FDOPA uptake or decarboxylation.

Topics: Adult; Aged; Catechol O-Methyltransferase Inhibitors; Catechols; Chromatography, High Pressure Liquid; Corpus Striatum; Dihydroxyphenylalanine; Enzyme Inhibitors; Female; Fluorine Radioisotopes; Humans; Kinetics; Male; Middle Aged; Nitriles; Occipital Lobe; Parkinson Disease; Quality Control; Sensitivity and Specificity; Tomography, Emission-Computed; Tyrosine

1. Effects of two new inhibitors of catechol O-methylation (CGP 28014 and entacapone; 30 mg kg-1, i.p.) were compared by means of brain microdialysis in rats treated with L-3,4-dihydroxyphenylalanine (L-dopa)/carbidopa (50/50 mg kg-1, i.p., respectively) or saline. 2. In saline-treated rats, CGP 28014 maximally (max) increased striatal dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) effluxes by 41% and 49%, respectively, whereas homovanillic acid (HVA) levels were decreased by 71%. 3. In the presence of L-dopa/carbidopa, a peripherally active inhibitor of catechol O-methyltransferase (COMT) entacapone had a short-lasting increasing effect on L-dopa efflux. Compared to the effects of L-dopa/carbidopa alone 3-O-methyldopa (3-OMD) levels were effectively reduced (max 79%) by entacapone, but not by CGP 28014. 4. Entacapone, in contrast to CGP 28014, increased striatal dopamine efflux (max 492% of that after L-dopa/carbidopa alone). Also DOPAC levels were increased by entacapone (255% at 180 min), but not significantly by CGP 28014 (159% at 180 min). 5. Both compounds initially decreased HVA efflux. The effect of CGP 18014 was longer-lasting. By the end of the measurement, entacapone even increased HVA levels (max 259%). 6. Our results demonstrate that entacapone is a peripheral COMT inhibitor and support the view that CGP 18014 is mainly a centrally acting inhibitor of O-methylation.

Topics: 3,4-Dihydroxyphenylacetic Acid; Amidines; Animals; Biogenic Monoamines; Carbidopa; Catechol O-Methyltransferase Inhibitors; Catechols; Dopamine; Homovanillic Acid; Hydroxyindoleacetic Acid; Levodopa; Male; Microdialysis; Neostriatum; Nitriles; Pyridones; Rats; Rats, Wistar; Stereotaxic Techniques; Tryptophan; Tyrosine

The effects of two new catechol-O-methyltransferase (COMT) inhibitors, OR-611 and Ro 40-7592, in combination with L-3,4-dihydroxyphenylalanine (L-dopa) with or without carbidopa on extracellular levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 3-O-methyldopa (3-OMD), and 5-hydroxyindoleacetic acid in rat striatum were studied. A dose of 10 mg/kg i.p. of Ro 40-7592 alone, in contrast to the same dose of OR-611, decreased the dialysate level of HVA and increased that of DOPAC; this dose was thus used to differentiate between the effects of central and peripheral COMT inhibition. L-Dopa (50 mg/kg i.p.) alone slightly increased extracellular levels of DA, DOPAC, and HVA. The effects of L-dopa were potentiated by carbidopa (50 mg/kg i.p.), and even 3-OMD levels in dialysate samples became detectable. Both OR-611 and Ro 40-7592 significantly further increased the DA and DOPAC efflux from striatum produced by L-dopa. This increase was more pronounced when carbidopa was added to the treatment. OR-611 did not modify the effect of L-dopa or carbidopa/L-dopa on dialysate HVA levels, whereas Ro 40-7592 markedly reduced those levels. Both OR-611 and Ro 40-7592 very clearly suppressed dialysate 3-OMD levels produced by carbidopa/L-dopa. Ro 40-7592 was more effective than OR-611 in potentiating the effects of L-dopa or carbidopa/L-dopa. These in vivo data show that the new COMT inhibitors markedly inhibit the O-methylation of L-dopa and increase its availability to brain, which is reflected as increased DA formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Benzophenones; Carbidopa; Catechol O-Methyltransferase Inhibitors; Catechols; Corpus Striatum; Dihydroxyphenylalanine; Dopamine; Extracellular Space; Male; Nitriles; Nitrophenols; Rats; Rats, Sprague-Dawley; Tolcapone; Tyrosine

We studied the effect of inhibiting the enzyme catechol-O-methyltransferase (COMT) by a novel COMT inhibitor, entacapone, on the pharmacokinetics and metabolism of levodopa in 12 healthy male volunteers. Single increasing oral doses of entacapone (50-400 mg) were administered concomitantly with a single oral dose of levodopa/carbidopa (100/25 mg). The subjects were treated with carbidopa (100 mg t.i.d.) for 1 day prior to the administration of study drugs. Plasma concentrations of levodopa; its metabolites 3-O-methyldopa (3-OMD), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA); as well as carbidopa and entacapone were determined for pharmacokinetic calculations. Entacapone dose-dependently increased the area under the plasma concentration-time curve (AUC) of levodopa; the increase was 65% after the 400 mg dose of entacapone. Neither Cmax nor Tmax of levodopa was statistically significantly influenced by entacapone. Entacapone dose-dependently decreased the AUC of 3-OMD, maximally by 58%. The AUC of DOPAC was statistically significantly increased but no change in the AUC of HVA was observed after entacapone. No drug-related adverse events or hemodynamic effects were observed. The in vivo biochemical effects of entacapone indicate that it is an orally active COMT inhibitor and that it may improve the therapeutic efficacy of levodopa in Parkinson's disease.

Topics: 3,4-Dihydroxyphenylacetic Acid; Adult; Carbidopa; Catechol O-Methyltransferase; Catechol O-Methyltransferase Inhibitors; Catechols; Electrocardiography; Half-Life; Homovanillic Acid; Humans; Levodopa; Male; Nitriles; Reference Values; Tyrosine

Entacapone, OR-611, was found to be a potent peripherally acting inhibitor of catechol-O-methyltransferase (COMT). IC50 values of 10 nmol/l and 160 nmol/l were obtained for rat duodenum and liver-soluble COMT, respectively. There were no effects on other catecholamine metabolizing enzymes. Entacapone showed reversible, tight-binding type of inhibition of soluble rat liver COMT with a Ki-value of 14 nmol/l and it also caused 50% inhibition of rat duodenal, erythrocyte, liver and striatal COMT activity 1 h after oral dosing with 1.1, 5.4, 6.7 and 24.2 mg/kg, respectively. However, penetration of entacapone into the brain was poor, since the formation of homovanillic acid (HVA), the O-methyl metabolite of dopamine in the striatum, was not reduced, even after the highest dose of 30 mg/kg. In rat blood serum, the concentration of 3-O-methyldopa (3OMD), the O-methylated product of L-dopa, was reduced in a dose-dependent manner, and the concentration of L-dopa was increased after the administration of entacapone (3-30 mg/kg p.o.) together with L-dopa + carbidopa. These changes were reflected, in the striatum, by a significant rise in the dopamine concentration and a reduction in the 3OMD concentration. Consequently, when entacapone was added to the treatment with L-dopa + carbidopa, the dose of L-dopa could be lowered from 50 mg/kg to 15 mg/kg in order to produce the same striatal dopamine concentrations as with 50 + 50 mg/kg of L-dopa + carbidopa alone.

Topics: 3,4-Dihydroxyphenylacetic Acid; Animals; Catechol O-Methyltransferase Inhibitors; Catechols; Corpus Striatum; Dihydroxyphenylalanine; Dopamine; Duodenum; Erythrocytes; Homovanillic Acid; In Vitro Techniques; Liver; Male; Nitriles; Rats; Rats, Wistar; Tyrosine

We studied the effectiveness of OR-611 and OR-462, two novel inhibitors of the enzyme catechol-O-methyltransferase (COMT), on 3-O-methyldopa (OMD) formation in cynomolgus monkeys following intravenous levodopa administration. OR-611 dose-dependently reduced the area under the OMD concentration-vs-time curve, reduced maximum plasma OMD concentrations, delayed the time to peak OMD levels, reduced systemic levodopa clearance, and prolonged the elimination half-life of levodopa. Similar effects on peripheral levodopa metabolism were seen with doses of 15 mg/kg of OR-611 and OR-462, its sister compound, which lacks the ability to penetrate the central nervous system (CNS).

Topics: Animals; Catechol O-Methyltransferase Inhibitors; Catechols; Levodopa; Macaca fascicularis; Male; Nitriles; Parkinson Disease; Pentanones; Tyrosine