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Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.

Context: Opicapone (OPC) is a novel catechol-O-methyltransferase (COMT) inhibitor to be used as adjunctive therapy in levodopa-treated patients with Parkinson's disease. The purpose of this study was to evaluate the effect of moderate liver impairment on the pharmacokinetics (PK) and pharmacodynamics (PD; effect on COMT activity) of OPC. An open-label, parallel-group study in patients (n=8) with moderate liver impairment (Child-Pugh category B, score of 7 to 9) and matched healthy subjects (n=8, control) with normal liver function. All subjects received a single 50-mg oral dose of OPC, with plasma and urine concentrations of opicapone and its metabolites measured up to 72h post-dose, including soluble COMT (S-COMT) activity. A one-way analysis of variance (ANOVA) was used to compare the main PK and PD parameters between groups. Point estimates (PE) of geometric mean ratios (GMR) and corresponding 90% confidence intervals (90%CI) for the ratio hepatic/control subjects of each parameter were calculated and compared with the reference interval (80-125%). Exposure to opicapone (AUC and Cmax) increased significantly in patients with moderate hepatic impairment (PE [90%CI]: AUC0-, 184% [135-250%]; Cmax, 189% [144-249%]). Although apparent total clearance (CL/F) of opicapone was decreased by 35%, similar elimination half-life and unbound/bound fractions of opicapone were observed between the two groups. Both rate and extent of exposure to BIA 9-1103 were higher in the hepatically impaired group, but not statistically significant compared with the control group. Similar to the parent (opicapone), the observed increase in exposure to BIA 9-1106 was statistically significant in the hepatically impaired group over the control group. BIA 9-1106 was the only metabolite detected in urine and its urine PK parameters were in accordance with plasma data. Maximum S-COMT inhibition (Emax) occurred earlier for the hepatically impaired group with values of 100% and 91.2% for the hepatically impaired and control groups respectively. Both Emax and AUEC for the hepatically impaired group reached statistical significance over the control group. OPC was well tolerated in both hepatically impaired and control groups. The bioavailability of an orally administered single dose of 50mg OPC was significantly higher in patients with moderate chronic hepatic impairment, perhaps by a reduced first-pass effect. As the tolerability profile of OPC was favourable under the conditions of this study and its exposure is completely purged from systemic circulation before the subsequent dose administration, no OPC dose adjustment is needed in patients with mild to moderate chronic hepatic impairment. However, as OPC is under clinical development for use as adjunctive therapy in levodopa-treated patients with Parkinson's disease, an adjustment of levodopa and/or OPC regimens in patients should be carefully considered based on a potentially enhanced levodopa dopaminergic response and the associated tolerability.
Question: What enzyme is inhibied by Opicapone?
Output:
catechol-o-methyltransferase