Showing papers on "Catechol-O-methyl transferase published in 1996"

Human catechol-O-methyltransferase pharmacogenetics: description of a functional polymorphism and its potential application to neuropsychiatric disorders.

Abstract: Catechol-O-methyltransferase (COMT) inactivates catecholamines and catechol drugs such as L-DOPA. A common genetic polymorphism in humans is associated with a three-to-four-fold variation in COMT enzyme activity and is also associated with individual variation in COMT thermal instability. We now show that this is due to G-->A transition at codon 158 of the COMT gene that results in a valine to methionine substitution. The two alleles can be identified with a PCR-based restriction fragment length polymorphism analysis using the restriction enzyme Nla III. The identification of a gentic marker associated with significant alterations in enzyme activity will facilitate the analysis of a possible role for the COMT gene in neuropsychiatric conditions in which abnormalities in catecholamine neurotransmission are believed to occur, including mood disorders, schizophrenia, obsessive compulsive disorder, alcohol and substance abuse, and attention deficit hyperactivity disorder. In addition, this polymorphism may have pharmacogenetic significance in that it will help make it possible to identify patients who display altered metabolism of catechol drugs.

No evidence for allelic association between schizophrenia and a polymorphism determining high or low catechol O-methyltransferase activity

Abstract: OBJECTIVE: Catechol O-methyltransferase (COMT) inactivates catecholamines by methylating their m-hydroxy group. Some previous studies using biochemical methods have found higher levels of COMT activity in schizophrenic patients. Recently, the genetic polymorphism that underlies variation in COMT activity, which results in the creation of a NlaIII restriction site in the low-activity allele, has been elucidated. METHOD: This study investigated this polymorphism in 78 unrelated schizophrenic patients and 78 comparison subjects matched for age and ethnicity. High-molecular-weight DNA was isolated from lymphocytes with routine procedures, and each individual was typed for high and low COMT activity. RESULTS: The frequency of the NlaIII polymorphism was 0.51 in the schizophrenic patients and 0.53 in the comparison subjects, and no significant allelic or genotypic associations were observed. CONCLUSIONS: There was no evidence for variation in COMT activity between a group of schizophrenic patients and matched comparison subjects.

Preferential transmission of the high activity allele of COMT in schizophrenia.

Abstract: Catechol-O-methyl transferase (COMT) metabolizes a variety of catecholamines such as dopamine, adrenaline and noradrenaline. It exists in common high and low activity forms. The low activity form is the result of an amino acid substitution (val-108-met) which reduces the thermostability of the enzyme [Lotta et al. (1994) Biochemistry, 34, 4202-4210]. We have genotyped this polymorphism in 178 trios consisting of Han Chinese schizophrenic subjects and their parents in order to test the hypothesis that the high activity allele is transmitted more often to affected subjects. The data were analysed using the transmission disequilibrium test (TDT), a robust method of detecting linkage in the presence of allelic associations. Of the 131 parents heterozygous at this locus, 80 transmitted the high activity allele (val-108) to affected offspring, while the remaining 51 transmitted the low activity allele (p = 0.005, one-tailed). Combining this result with that of a previous TDT study of the same polymorphism in familial schizophrenia [Kunugi et al. (1996) submitted] gives significant evidence for linkage disequilibrium (p = 0.0015). However, val-108 is frequent in the Han Chinese population, and in the present sample, 239 of the 350 non-transmitted parental alleles were val-108 (68%). It is therefore unlikely that val-108 allele of COMT has a major effect on susceptibility to schizophrenia. Our results suggest that either val-108 is a minor risk factor for schizophrenia, that the COMT gene has additional polymorphisms with greater effect on risk, or that this region of chromosome 22 contains a susceptibility gene which is in linkage disequilibrium with the COMT gene.

Effect of one month's treatment with peripherally acting catechol-O-methyltransferase inhibitor, entacapone, on pharmacokinetics and motor response to levodopa in advanced parkinsonian patients.

Abstract: Summary: 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.

Multiple-dose clinical pharmacology of the catechol-O-methyl-transferase inhibitor tolcapone in elderly subjects

Abstract: Objective: The purpose of this study was to assess the multiple-dose clinical pharmacology of tolcapone, a novel catechol-O-methyltransferase (COMT) inhibitor, in elderly subjects Methods: The drug was administered orally tid for 7 days to four sequential groups of eight elderly subjects (gender ratio1:1) at doses of 100, 200, 400 and 800 mg in a double-blind, randomised, placebo-controlled, ascending-multiple-dose design On days 2 and 7, a single dose of levodopa/benserazide 100/25 mg was given 1 h after the first intake of tolcapone Plasma concentrations of tolcapone, its metabolite 3-O-methyltolcapone, levodopa and 3-O-methyldopa were determined during the course of the study in conjunction with COMT activity in erythrocytes Results: Tolcapone was well tolerated at all dose levels, with a slight increase in gastrointestinal adverse events in females at higher doses The drug was rapidly absorbed and eliminated and showed no changes in pharmacokinetics with time during multiple doses of 100 and 200 mg tid At doses of 400 and 800 mg tid, tolcapone accumulated moderately as reflected in increased Cmax and AUC values Despite the long half-life of 3-O-methyltolcapone (39 h), only minor accumulation occurred due to suppression of its formation by tolcapone The pharmacodynamics of tolcapone did not change during the week of treatment as reflected in inhibition of COMT activity in erythrocytes, the derived parameters of the plasma concentration-effect relationship (inhibitory Emax model with constant EC50 values) and the effect on levodopa pharmacokinetics (16 to 25-fold increase in bioavailability) This suggests the absence of tolerance development and the insignificance of the altered pharmacokinetics at 400 and 800 mg tid with regard to the pharmacodynamics Conclusion: The results of this study offer promising perspectives for the application of tolcapone as adjunct therapy to levodopa in the treatment of Parkinson’s disease

Ontogenic aspects of liver and kidney catechol-O- methyltransferase sensitivity to tolcapone

Abstract: 1. The present work describes the catechol-O-methyltransferase (COMT) activities in the liver and kidney of developing and adult rats (aged 3, 6, 9, 18, 30 and 60 days; n = 5 per group) and evaluates the enzyme sensitivity to inhibition by tolcapone, a reversible COMT inhibitor. 2. COMT activity, evaluated by the ability to methylate adrenaline to metanephrine, was determined in liver and kidney homogenates prepared in 0.5 mM phosphate buffer (pH = 7.8) containing pargyline (0.1 mM), MgCl2 (0.1 mM), EGTA (1 mM) and S-adenosyl-L-methionine (0.1 mM). Vmax (in nmol mg-1 protein h-1) of liver COMT was found to decrease gradually with age, from 5.3 +/- 0.5 at the age of 3 days up to 2.9 +/- 0.2 at the age of 60 days; for the same age range, Km values (in microM; geometric means with 95% confidence limits) increased from 3.3 (1.0, 7.5) up to 13.1 (2.1, 24.1). At the age of 3 days, Vmax values for kidney COMT (2.6 +/- 0.1) were lower than those for the liver COMT. However, Vmax values for kidney COMT were found to increase up to 6.2 +/- 0.6 at the age of 18 days and then declined by 44% at the age of 30 and 60 days. In kidney, aging was also accompanied by an increase in Km values for COMT (from 2.7 [1.1, 4.3] up to 24.0 [11.7, 36.3]). 3. The sensitivity of liver and renal COMT activity to tolcapone was markedly dependent on the age, 3-days old rats being more sensitive to tolcapone than older animals. The IC50 values (in nM) for inhibition of liver COMT by tolcapone increased gradually with age, from 41 (26, 65) at the age of 3 days up to 720 (640, 800) at the age of 60 days. As was found in the liver, IC50 values (in nM) for inhibition of kidney COMT by tolcapone also increased with age, from 8 (6, 10) at the age of 3 days up to 177 (131, 240) at the age of 60 days. In all experimental groups, the IC50 values for inhibition of liver COMT by tolcapone was higher than those for kidney COMT. 4. In conclusion, these results suggest that aging is accompanied by a decrease in liver and kidney COMT affinity for the substrate (evidenced by the increase in Km values) and a decrease in sensitivity towards inhibition by tolcapone (evidenced by the increase in IC50 values). Furthermore, kidney COMT is shown to be more sensitive to inhibition by tolcapone than liver COMT, irrespective of the age of the animal.

Simultaneous inhibition of catechol-O-methyltransferase and monoamine oxidase A: effects on hemodynamics and catecholamine metabolism in healthy volunteers.

Abstract: Objective To evaluate the effects of simultaneous pharmacologic inhibition of catechol-O-methyltransferase (COMT) and monoamine oxidase type A (MAO-A) on hemodynamics and catecholamine metabolism in healthy volunteers at rest and during exercise. Background Entacapone, a COMT inhibitor, is studied as an adjunct to levodopa treatment in patients with Parkinson's disease. Moclobemide, an MAO-A inhibitor, is already in clinical use as an antidepressant. It is likely that entacapone and moclobemide will be used concomitantly in the future in patients who have both Parkinson's disease and depression. It was therefore considered to be important to investigate the tolerability of combined COMT and MAO-A inhibition with entacapone and moclobemide. Design and methods This was a randomized, single-dose, double-blind crossover study of 12 healthy male volunteers. The treatments were either placebo, 200 mg entacapone, 150 mg moclobemide, or the combination of entacapone and moclobemide in single doses. Heart rate, blood pressure, impedance cardiography, and plasma concentrations of catecholamines and their metabolites were measured both at rest and during submaximal standardized bicycle exercise. Results Entacapone and moclobemide (either alone or in combination) did not change heart rate, blood pressure, or any hemodynamic parameter at rest or during exercise compared with placebo. Neither were the concentrations of norepinephrine and epinephrine in plasma influenced. Both drugs had the expected effects on catecholamine metabolite concentrations in plasma. The decrease in the concentration of 3-methoxy-4-hydroxyphenylglycol (MHPG) induced by moclobemide was not potentiated by entacapone. Conclusion The combined use of therapeutic single doses of entacapone and moclobemide in healthy volunteers did not affect the hemodynamics or concentrations of unconjugated norepinephrine and epinephrine in plasma. Other mechanisms are capable of regulating the concentrations of norepinephrine and epinephrine in circulating blood (and apparently also at their receptors in the heart and vascular tissue) when both COMT and MAO-A activity are inhibited to a significant extent. This was also the case during marked sympathetic stimulation. The changes in the catecholamine metabolite concentrations provide evidence of effective COMT and MAO inhibition. Concentrations of MHPG in plasma are determined mainly by MAO-A activity because COMT inhibition did not have an additional effect on the moclobemide-induced decrease in plasma MHPG. Clinical Pharmacology & Therapeutics (1996) 59, 450–457; doi:

Minor effect of tolcapone, a catechol-O-methyltransferase inhibitor, on extracellular dopamine levels modified by amphetamine or pargyline: a microdialysis study in anaesthetized rats.

Abstract: In vivo microdialysis was used to examine the effects of tolcapone (30 mg/kg) on dopamine metabolism in amphetamine (5 mg/kg) and pargyline (75 mg/kg) treated rats. Amphetamine- or pargyline-induced decreases in the extracellular dihydroxyphenyl acetic acid (DOPAC) levels were counteracted by additional tolcapone. Tolcapone also decreased homovanillic acid effluxes below those caused by amphetamine or pargyline. However, dopamine effluxes were not further enhanced by additional tolcapone. These results show that central metabolism of dopamine can be modulated by catechol-O-methyltransferase (COMT) inhibition also without exogenous L-DOPA. However, extracellular dopamine levels are not easily increased.

Simultaneous inhibition of catecholamine-O-methylation by entacapone and neuronal uptake by imipramine: lack of interactions

Abstract: Objective: We have evaluated the effects of simultaneous inhibition of catechol-O-methyltransferase (COMT) by entacapone and of neuronal monoamine reuptake by imipramine on haemodynamics and catecholamine metabolism, and the safety and tolerability of the drug combination in healthy women. Methods: In a randomized, single-dose, single-blind, cross-over study, 12 healthy women were given placebo, entacapone (200 mg), imipramine (75 mg) or entacapone and imipramine in combination. Heart rate, blood pressure, systolic time intervals, and plasma concentrations of catecholamines and their metabolites were measured at rest and during exercise. Results: The only drug-related effect on haemodynamics was an increase in heart rate during exercise after imipramine. The increase in heart rate after the combination of entacapone and imipramine was similar to that after imipramine alone. Entacapone alone had no effects on haemodynamics. Imipramine and entacapone had no significant effects on the plasma concentrations of noradrenaline and adrenaline. No interactions between entacapone and imipramine were detected.

Identification of a BglI polymorphism of catechol-O-methyltransferase (COMT) gene, and association study with schizophrenia.

Abstract: Several linkage studies suggested chromosome 22q11-13 may harbor susceptible genes for schizophrenia. Catechol-O-methyl-transferase (COMT), which is involved in the metabolism of catecholamines, was mapped to 22q11 and is considered a possible candidate gene for schizophrenia. Recently, we identified a polymorphic marker, a single nucleotide C insertion at the 3' untranslated region of the COMT gene, which obliterates a BglI site. Using this BglI polymorphism, we conducted a case-control association study in Chinese patients with schizophrenia. No significant differences of allele and genotype frequencies were noted between patients (N = 177) and controls (N = 99). When patients were subgrouped according to sex, no significant differences of genotype and allele frequencies were noted in either male or female patients compared to normal controls. Our results do not support an association between the BglI polymorphism of COMT gene and schizophrenia.

The contribution by monoamine oxidase and catechol-O-methyltransferase to the total-body and pulmonary plasma clearance of catecholamines

Abstract: To study the effects of inhibition of catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO) on the removal of circulating catecholamines, anaesthetized rabbits were infused for 120 min with 3H-labelled noradrenaline, adrenaline and dopamine. Total-body plasma clearances (Cltot) and pulmonary fractional extractions (ERP) of the infused amines and the cardiac output of plasma (COP) were determined under steady-state conditions at the end of each of two consecutive 60-min treatment periods. MAO and COMT were inhibited by treatment with pargyline (40 mg/kg)and tolcapone (3 mg/kg followed by 1.5 mg/kg given every 30 min), respectively. Two groups of animals were studied. Group I involved animals treated with tolcapone throughout and given pargyline at the beginning of the second treatment period. In group II, pargyline was given at the beginning of the first, and the treatment with tolcapone was started at the beginning of the second treatment period. As previous experiments had shown that COMT inhibition alone is without any effect on Cltot, of the three catecholamines considered here, the results obtained in the first treatment period of group I can be taken to reflect control results.

COMT inhibition by entacapone does not affect growth hormone or prolactin secretion in healthy volunteers.

Abstract: 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.

Catechol-O-methyltransferase inhibition increases the uptake of 11C-3-(3,4-dihydroxyphenyl)-L-alanine in the rat pancreas.

Abstract: Background: The objective of the present investigation was to evaluate the uptake and metabolism of 3-(3,4-dihydroxyphenyl-L-alanine) (L-DOPA) in the rat pancreas Methods: The procedure included intravenous injection of the positron-emitting radiotracer L-[β-11C]DOPA (DOP) into unanaesthetized male Sprague-Dawley rats and evaluation of uptake of radioactivity in organs in animals only given the tracer and in animals given therapeutic doses of three different catechol-O-methyltransferase (COMT) inhibitors, OR-486, OR-611, or Ro 41–0960 Selected pancreati were homogenized, and the chemical form bearing the radioactivity was analysed with high-performance liquid chromatography (HPLC) Results: The main finding was that the tracer uptake in the pancreas increased fourfold when the rats were pretreated with COMT inhibitors Half maximum effect of OR-486 was found at a dose of 02 mg/kg HPLC analysis showed that with COMT inhibitor, the radioactivity in the pancreas consisted of 90% DOPAC When administering

Nitrocatechol derivatives as inhibitors of catechol-O-methyltransferase.

Abstract: Catechol-0-methyltransferase (EC 2.1.1.6; COMT) catalyses Sadenosylmethionine-dependent methylation of a variety of catechols and plays a role in terminating the activities of the catecholamine neurotransmitters dopamine and noradrenaline. Two isoenzymes, the soluble and membrane-bound forms (S-COMT and MB-COMT) are present in most tissues and although the former is more abundant, their different kinetic parameters suggest that the MB-form may play the dominant role in inactivating the catecholamines [I]. Studies on the inhibition of COMT have been extensive since specific and effective inhibitors could help elucidate the physiological role and properties of the enzyme. Furthermore, development of effective COMT inhibitors could be promising for therapeutic use both in Parkinson's disease and in diseases connected to an aberrant catecholamine metabolism. Early COMT inhibitors, e.g. tropolone, were not suitable for use in vivo (see review [2]). It was observed that catechol compounds with electron withdrawing substituents, particularly NO2 groups, greatly enhanced inhibitory activity [3] and this gave rise to a second generation of potent and selective COMT inhibitors [4,5]. Nitrocatechol was the key structure in the majority of these compounds (see Fig. 1) and these had inhibition constant (Ki) values in the nanomolar range [4,5]. The aims of this work were to study the efficacy of some nitrocatechol derivatives as inhibitors of both forms of COMT, especially the MB-form. Most previous studies have concentrated on the soluble enzyme and since the MB-form may be more important at low, physiological concentrations of substrate, it is possible that this form may have different affinities for inhibitors of the enzyme. Human S-COMT and MB-COMT cloned and expressed in Escherichiu coli [6] were used as enzyme sources. COMT activity was assayed with using a slight modification of a direct solvent-extraction assay which determined the amount of radioactive guaiacol formed 171. A series of fixed inhibitor concentrations was used (see Table l ) , while the concentration of catechol was varied between approximately half to several times the K, concentration for each form of the enzyme and meth~l [~H]labelled AdoMet was held at 390 pM. Representative doublereciprocal plots are also shown in Figs. 2 (a) and (b) for the inhibition of S-COMT and MB-COMT by 4,5-dinitrocatechol with respect to catechol. The Ki values were determined for the nitrocatechol derivatives by plotting slopes of the double reciprocal plots against inhibitor concentration and results for both forms of the enzyme are shown in Table 1. .