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Alcohol Use Disorder (AUD) is characterized by loss of control over drinking. Behavioral control is mediated, in part, by cortical dopamine signaling. Inhibition of catechol-O-methyltransferase (COMT), the enzyme primarily responsible for cortical dopamine inactivation, may increase cortical dopamine, especially among individuals with genetically mediated lower dopaminergic tone, such as COMT rs4680 (val158met) val-allele homozygotes. This study was a randomized, placebo-controlled, pharmacogenetic trial of the COMT inhibitor tolcapone. Ninety non-treatment-seeking AUD individuals were prospectively genotyped for rs4680 and randomized to tolcapone (200 mg t.i.d.) or placebo for 8 days. At baseline and on day 7, peripheral COMT activity was assayed, and participants completed an fMRI alcohol cue-reactivity task; on day 8, they completed a bar-lab paradigm. Primary outcomes were: (1) natural drinking during the medication period; (2) alcohol self-administration in the bar lab; and (3) alcohol cue-elicited cortical (right inferior frontal gyrus [rIFG]) and ventral striatal activation. At baseline, the rs4680 val-allele had an additive effect on COMT activity. Tolcapone, relative to placebo, reduced COMT activity in all genotype groups. COMT genotype moderated tolcapone’s effect on drinking during the medication period and in the bar lab, such that tolcapone, relative to placebo, reduced drinking only among val-allele homozygotes. Tolcapone did not affect cue-elicited ventral striatal activation but reduced rIFG activation; less rIFG activation on day 7 was associated with less drinking during the medication period. Taken together, these data suggest that COMT inhibition may reduce drinking specifically among individuals genetically predisposed to excessive COMT activity and potentially low cortical dopamine tone.ClinicalTrials.gov identifier: NCT02949934 https://clinicaltrials.gov/ct2/show/NCT02949934

Whether to continue to exploit a source of reward, or to search for a new one of potentially greater value, is a fundamental and underconstrained decision. Recent computational studies of this exploration-exploitation tradeoff have found that variability in exploration across individuals is influenced by a functional polymorphism (Val158Met) in the catechol-O-methyltransferase (COMT) gene, whose protein product degrades synaptically released dopamine. However, these and other genotype-phenotype associations have rarely been causally tested. To directly test this association and to evaluate additional behavioral characteristics, including perceived locus of control (LOC), here we used the COMT inhibitor tolcapone in a randomized, double-blind, counterbalanced, within-subject study of 66 subjects genotyped for the Val158Met allele to assess the hypothesis that reducing COMT enzymatic activity interacts with genotype to increase uncertainty-driven exploration. In keeping with our initial hypothesis, tolcapone led to an increase in exploratory, but not exploitative, behavior in Met/Met rather than Val/Val subjects. Independent of genotype, those subjects with a more external LOC also showed increases in uncertainty-driven exploration on tolcapone relative to placebo. However, we did not replicate our previous finding that Met/Met subjects show greater exploration at baseline. Together these findings support a model in which exploration is hypothesized to have a dopaminergic basis. Moreover, in keeping with findings in other behavioral and cognitive domains, the response to an increase in presumptively frontal dopamine is dependent upon baseline dopamine tone.

Opicapone is a novel, once-daily, potent third-generation catechol-O-methyltransferase inhibitor. We aimed to assess the safety and efficacy of opicapone as an adjunct to levodopa compared with placebo or entacapone in patients with Parkinson's disease and motor fluctuations. We did a randomised, double-blind, placebo-controlled and active-controlled trial of opicapone as an adjunct to levodopa in patients with Parkinson's disease with end-of-dose motor fluctuations. Patients aged 30–83 years were enrolled at 106 specialist centres across 19 European countries and Russia and were randomly assigned (1:1:1:1:1) by a proprietary computer-generated sequence to oral treatment with opicapone (5 mg, 25 mg, or 50 mg once daily), placebo, or entacapone (200 mg with every levodopa intake) for 14–15 weeks. Patients and investigators (ie, outcome assessors) were masked to treatment allocation. The primary endpoint was the change from baseline to end of study treatment in absolute time in the off state, as assessed by daily paper patient diaries; the primary analysis followed a hierarchical procedure for each opicapone dose in which superiority compared with placebo in the full analysis set was first tested and then, if positive, non-inferiority to entacapone was tested in the per-protocol set with a margin of 30 min. This trial is registered with EudraCT, 2010-021860-13, and ClinicalTrials.gov, NCT01568073. Between March 31, 2011, and Nov 30, 2013, of 679 patients screened, 600 were randomly assigned. 590 patients were included in the full analysis set (120 in the placebo group, 120 in the entacapone group, 119 in the opicapone 5 mg group, 116 in the opicapone 25 mg group, and 115 in the opicapone 50 mg group) and 537 in the per-protocol set (112 in the placebo group, 104 in the entacapone group, 110 in the opicapone 5 mg group, 105 in the opicapone 25 mg group, and 106 in the opicapone 50 mg group). The mean change in time in the off state was −56·0 min (SE 13·4; 95% CI −82·3 to −29·7) for placebo, −96·3 min (13·4; −122·6 to −70·0) for entacapone, −91·3 min (13·5; −117·7 to −64·8) for opicapone 5 mg, −85·9 min (13·7; −112·8 to −59·1) for opicapone 25 mg, and −116·8 min (14·0; −144·2 to −89·4) for opicapone 50 mg. Treatment with opicapone 50 mg was superior to placebo (mean difference in change from baseline −60·8 min, 95% CI −97·2 to −24·4; p=0·0015) and non-inferior to entacapone (−26·2 min, −63·8 to 11·4; p=0·0051). Treatment with opicapone 5 mg (p=0·056) or 25 mg (p=0·080) was not significantly different from treatment with placebo. Treatment-emergent adverse events were reported in 60 (50%) of 121 patients in the placebo group, 69 (57%) of 122 in the entacapone group, 63 (52%) of 122 in the opicapone 5 mg group, 65 (55%) of 119 in the opicapone 25 mg group, and 62 (54%) of 115 in the opicapone 50 mg group. The most common adverse events were dyskinesia (in five patients in the placebo group, ten in the entacapone group, 17 in the opicapone 5 mg group, nine in the opicapone 25 mg group, and 18 in the opicapone 50 mg group), insomnia (in one, seven, two, seven, and seven patients, respectively), and constipation (in three, five, four, none, and seven patients, respectively). Serious adverse events were reported in six patients in the placebo group, eight in the entacapone group, four each in the opicapone 5 mg and opicapone 50 mg groups, and one in the opicapone 25 mg group. The addition of opicapone 50 mg to levodopa treatment in patients with Parkinson's disease and end-of-dose motor fluctuations could enable a simplified drug regimen that allows physicians to individually tailor the existing levodopa daily regimen, by potentially reducing the total daily levodopa dose, increasing the dosing interval, and ultimately reducing the number of intakes, thereby maximising its benefit. BIAL.

Rationale Impairment in time perception, a critical component of decision-making, represents a risk factor for psychiatric conditions including substance abuse. A therapeutic that ameliorates this impairment could be advantageous in the treatment of impulsivity and decision-making disorders. Objectives Here we hypothesize that the catechol- O -methyltransferase (COMT) inhibitor tolcapone, which increases dopamine tone in frontal cortex (Ceravolo et al Synapse 43:201–207, 2002 ), improves time perception, with predictive behavioral, genetic, and neurobiological components. Methods Subjects ( n  = 66) completed a duration estimation task and other behavioral testing in each of two sessions after receiving a single oral dose of tolcapone (200 mg) or placebo in randomized, double-blind, counterbalanced, crossover fashion. Resting state fMRI data were obtained in a subset of subjects ( n  = 40). Subjects were also genotyped for the COMT (rs4680) polymorphism. Results Time perception was significantly improved across four proximal time points ranging from 5 to 60 s ( T (524) = 2.04, p  = 0.042). The degree of this improvement positively correlated with subjective measures of stress, depression, and alcohol consumption and was most robust in carriers of the COMT Val158 allele. Using seed regions defined by a previous meta-analysis (Wiener et al Neuroimage 49:1728–1740, 2010 ), we found not only that a connection from right inferior frontal gyrus (RIFG) to right putamen decreases in strength on tolcapone versus placebo ( p  < 0.05, corrected), but also that the strength of this decrease correlates inversely with the increase in duration estimation on tolcapone versus placebo ( r  = − 0.37, p  = 0.02). Conclusions Compressed time perception can be ameliorated by administration of tolcapone. Additional studies should be conducted to determine whether COMT inhibitors may be effective in treating decision-making disorders and addictive behaviors.

Caffeic acid O-methyltransferase (COMT) methylates N-acetylserotonin into melatonin; that is, it has N-acetylserotonin O-methyltransferase (ASMT) activity. The ASMT activity of COMT was first detected in Arabidopsis thaliana COMT (AtCOMT). To confirm the involvement of COMT on melatonin synthesis in other plant species, the ASMT activity of a COMT from rice (Oryza sativa) (OsCOMT) was evaluated. Purified recombinant OsCOMT protein from Escherichia coli was used to validate the high ASMT activity of OsCOMT, similar to that of AtCOMT. The K m and V max values for the ASMT activity of OsCOMT were 243 μM and 2400 pmol min−1 mg protein−1, which were similar to those of AtCOMT. Similar to AtCOMT, OsCOMT was localized in the cytoplasm. In vitro ASMT activity was significantly inhibited by either caffeic acid or quercetin in a dose-dependent manner. Analogously, in vivo production of melatonin was significantly inhibited by quercetin in 4-week-old detached rice leaves. Lastly, the transgenic rice plants overexpressing rice COMT showed an increase in melatonin levels whereas transgenic rice plants suppressing the rice COMT had a significant decrease on melatonin levels, suggestive of the direct role of COMT in melatonin biosynthesis in plants.

Dopamine is an essential neurotransmitter found in both vertebrates and invertebrates which regulates motor coordination, cognition, emotional processing, and autonomic functions. Dopamine is biosynthesized from L-tyrosine and is primarily metabolized by catechol-O-methyltransferase (COMT), which regulates its concentration and ensures proper synaptic signalling within the basal ganglia. Dopamine deficiency, the hallmark of Parkinson’s disease, is a progressive neurodegenerative disorder caused by the loss of dopaminergic neurons in the substantia nigra pars compacta. To alleviate dopamine deficiency, current therapeutic strategies include administration of the dopamine precursor levodopa in combination with COMT inhibitors, which enhance levodopa bioavailability and prolong its therapeutic effect. However, the clinical utility of synthetic COMT inhibitors is often limited by hepatotoxicity and other adverse effects, underscoring the need for safer alternatives. In this context, plant-derived bioactive compounds are being increasingly investigated as potential inhibitors of COMT activity. Our study evaluated the affinity of 170 phytochemicals from Tamarindus indica against COMT utilizing computational strategies. Gallacetophenone, an aromatic ketone, was identified as a promising candidate that met the requirements for drug-likeness. Molecular dynamics (MD) simulations, supported by post-MDS analyses, principal component analysis, and free energy landscape analyses, demonstrated that gallacetophenone binding enhances the conformational stability of 3BWY compared to the control. These findings suggest that gallacetophenone may serve as a potential therapeutic phytochemical; however, its efficacy remains computationally predicted and requires validation through targeted in vitro and in vivo studies.

Background and Objectives The treatment of Parkinson’s disease (PD) is still symptomatic since disease-modifying treatments for PD are not available. Oral levodopa is the gold standard for the treatment of PD motor symptoms. However, incomplete and fluctuating plasma exposure of levodopa leads to suboptimal treatment of the symptoms. The main objective of this study was to investigate to what extent increased carbidopa doses (50 and 100 mg) increase the plasma levels of 100-mg immediate-release (IR) levodopa compared to a 25-mg carbidopa dose with and without co-administration of 200 mg entacapone. Methods A double-blind, placebo-controlled, randomized, crossover, phase I, pharmacokinetic study with 25 healthy volunteers was conducted. In addition, a semi-mechanistic pharmacokinetic model was built to theoretically evaluate the effect of inhibiting aromatic amino acid decarboxylase (AADC) and catechol- O -methyltransferase (COMT) mediated metabolism of levodopa on the exposure of levodopa. Results The effect of increased carbidopa doses 50 and 100 mg on the total exposure (AUC) of 100 mg IR levodopa was +29% and +36%, respectively, when entacapone was co-administered. Without entacapone, the corresponding increases were +13% and +17%. With entacapone co-administration, the increased carbidopa dose also clearly increased levodopa trough concentration. There was no significant effect on the peak concentrations of levodopa. Conclusions Increasing carbidopa doses significantly increased the exposure and reduced the fluctuation of IR levodopa in plasma during simultaneous COMT inhibition with entacapone. Theoretical pharmacokinetic simulations suggested that the plasma profile of oral IR levodopa can be even further improved by optimizing AADC and COMT inhibition.

Background and objectives Opicapone is a novel third generation catechol- O -methyltransferase (COMT) inhibitor. The purpose of this study was to compare the levodopa pharmacokinetic profile throughout a day driven by the COMT inhibition either following repeated doses of opicapone or concomitant administration with entacapone. Methods A randomized, double-blind, gender-balanced, parallel-group study was performed in 4 groups of 20 healthy subjects each. Four subjects in each group received placebo during the entire study. Sixteen subjects in one group received placebo once daily for 11 days and on day 12, 200 mg entacapone concomitantly with each levodopa/carbidopa dose (three times separated by a 5-h interval). Sixteen subjects in each of the remaining three groups received respectively 25, 50, and 75 mg opicapone once daily for 11 days and on day 12, placebo concomitantly with each levodopa/carbidopa dose. Results Levodopa minimum plasma concentration (C min ) for each levodopa/carbidopa dose and for the mean of all levodopa/carbidopa doses increased substantially with all active treatments (entacapone and opicapone) when compared to the control group (placebo), with values ranging from 1.7-fold (200 mg entacapone) to 3.3-fold (75 mg opicapone). No statistical difference was found for levodopa peak of systemic exposure (as assessed by maximum observed plasma concentration (C max )) between all active treatments and placebo. A significant increase in the levodopa extent of systemic exposure (as assessed by concentration-time curve (AUC)) occurred with all opicapone treatments in relation to placebo. No statistical difference was found for levodopa AUC when entacapone was compared to placebo. When compared to entacapone, both 50 and 75 mg opicapone presented a significant increase for the levodopa AUC. All active treatments significantly inhibited both peak (as assessed by E max ) and extent (as assessed by effect-time curve (AUEC)) of the COMT activity in relation to placebo. When compared to entacapone, all opicapone treatments significantly decreased the extent (AUEC) of the COMT activity due to a long-lasting and sustained effect. The tolerability profile was favorable for all active treatments. Conclusion Opicapone, a novel third generation COMT inhibitor, when compared to entacapone, provides a superior response upon the bioavailability of levodopa associated to more pronounced, long-lasting, and sustained COMT inhibition. The tolerability profile was favorable. On the basis of the results presented in this study and along with the earlier pharmacology studies, it is anticipated that opicapone adjunct therapy at the dosages of 25 and 50 mg will provide an enhancement in levodopa availability that will translate into clinical benefit for Parkinson’s disease patients.

Inhibitors of catechol- O -methyltransferase (COMT) are commonly used as an adjunct to levodopa in patients with Parkinson’s disease (PD) for the amelioration of wearing-off symptoms. This narrative review aims to discuss the role of COMT inhibitors on peripheral levodopa metabolism and continuous brain delivery of levodopa, and to describe their metabolic properties. Oral application of levodopa formulations with a dopa decarboxylase inhibitor (DDI) results in fluctuating levodopa plasma concentrations, predominantly due to the short half-life of levodopa and its slowing of gastric emptying. Following transport across the blood–brain barrier and its metabolic conversion to dopamine, these peripheral ‘ups and downs’ of levodopa are reflected in fluctuating dopamine levels in the synaptic cleft between presynaptic and postsynaptic dopaminergic neurons of the nigrostriatal system. As a result, pulsatile postsynaptic dopaminergic stimulation takes place and results in the occurrence of motor complications, such as wearing-off and dyskinesia. More continuous plasma behaviour was observed after the combination of levodopa/DDI formulations with COMT inhibitors. These compounds also weaken a levodopa/DDI-related homocysteine increase, as biomarker for an impaired methylation capacity, which is involved in an elevated oxidative stress exposure. These findings favour the concept of chronic levodopa/DDI application with concomitant inhibition of COMT and monoamine oxidase, since deamination of dopamine via this enzyme also generates free radicals. This triple combination is suggested as standard levodopa application in patients with PD who need levodopa, if they will tolerate it.

•We examined whether groups that differ in the activity of catechol-O-methyltransferase (COMT), either genetically or as the result of a pharmacological challenge, show differences in regional cerebral blood flow (CBF).•COMT genotype influenced frontal CBF, whilst COMT inhibition altered CBF in parietal and temporal regions.•Our findings demonstrate that both acute and trait differences in dopamine signalling influence regional CBF.•We recommend the inclusion of CBF measures in fMRI studies of the impact of dopaminergic manipulations on BOLD signal. Dopamine has direct and complex vasoactive effects on cerebral circulation. Catechol-O-methyltransferase (COMT) regulates cortical dopamine, and its activity can be influenced both genetically and pharmacologically. COMT activity influences the functional connectivity of the PFC at rest, as well as its activity during task performance, determined using blood oxygen level-dependent (BOLD) fMRI. However, its effects on cerebral perfusion have been relatively unexplored. Here, 76 healthy males, homozygous for the functional COMT Val158Met polymorphism, were administered either the COMT inhibitor tolcapone or placebo in a double-blind, randomised design. We then assessed regional cerebral blood flow at rest using pulsed arterial spin labelling. Perfusion was affected by both genotype and drug. COMT genotype affected frontal regions (Val158 > Met158), whilst tolcapone influenced parietal and temporal regions (placebo > tolcapone). There was no genotype by drug interaction. Our data demonstrate that lower COMT activity is associated with lower cerebral blood flow, although the regions affected differ between those affected by genotype compared with those altered by acute pharmacological inhibition. The results extend the evidence for dopaminergic modulation of cerebral blood flow. Our findings also highlight the importance of considering vascular effects in functional neuroimaging studies, and of exercising caution in ascribing group differences in BOLD signal solely to altered neuronal activity if information about regional perfusion is not available.