Received for publication April 11, 2006.
Revised June 19, 2006.
Accepted for publication June 19, 2006.

Human metabolism of nebicapone (BIA 3-202), a novel COMT inhibitor: characterization of in vitro glucuronidation

Abstract

Nebicapone (BIA 3-202; 1-[3,4-dihydroxy-5-nitropheny]-2-phenyl-ethanone), a novel catechol-O-methyltransferase (COMT) inhibitor, is mainly metabolised by glucuronidation. The purpose of this study was to characterise the major plasma metabolites of nebicapone following oral administration of nebicapone to healthy volunteers and to determine the human UGT enzymes involved in nebicapone glucuronidation. Plasma samples were collected as part of a clinical trial at different time points post-dose and were analysed for nebicapone and its metabolites using a validated method consisting of a solid phase extraction (SPE) followed by high performance liquid chromatography/mass spectrometry (HPLC/MS) detection. The primary metabolic pathways of nebicapone in humans involve mainly 3-O-glucuronidation, the major early metabolite, and 3-O-methylation, the predominant late metabolite. Among nine commercial available recombinant UGT enzymes studied (UGT 1A1, 1A3, 1A6, 1A7, 1A8, 1A9, 1A10, 2B7 and 2B15), only UGT 1A9 exhibited high nebicapone glucuronosyltransferase specific activity (24.3±1.3 nmol mg prot^-1 min^-1). UGTs 1A6, 1A7, 1A8, 1A10, 2B7 and 2B15 exhibited low activity (0.1-1.1 nmol mg prot^-1 min^-1) and 1A1 and 1A3 showed extremely low activities (below 0.03 nmol mg prot^-1 min^-1). The results show that nebicapone is mainly glucuronidated in humans and that multiple UGT enzymes are involved in this reaction.

Key words: drug disposition, metabolite kinetics, methyl transferase, microsomes, phase II drug metabolism, UDP glucuronyltransferases