Glucuronidation of apomorphine

Apomorphine, a dopaminergic receptor agonist, is largely used in the therap y of Parkinson's disease. In this study, we characterized the glucuronidati on of apomorphine and other catechols in rat liver and brain microsomes, us ing UDP-[U-C-14]glucuronic acid and separation of the glucuronides formed b y a thin layer chromatographic method. rat liver microsomes glucuronidate a pomorphine at a significant rate, that was increased in the presence of dit hiothreitol. Two apomorphine glucuronides were separated by high pressure l iquid chromatography. We showed by electrospray mass spectrometry that both products were monoglucuronides. Other catechols were also glucuronidated i n liver microsomes at various rates, and among them, 4-nitrocatechol was th e most efficiently conjugated. in rat brain microsomes, only 4-nitrocatecho l was significantly glucuroni-dated, suggesting that in the liver, several uridine-diphosphate glucuronosyltransferase (UGT) isoforms participate to t he conjugation of catechols. To determine which isoforms catalyze apomorphi ne glucuronidation, two recombinant enzymes expressed in V79 cells were use d. The isoform UCT1A6 was unable to glucuronidate apomorphine, but we obser ved a significant activity catalyzed by the isoform UGT2B1. These results p rovide, to our knowledge, the first demonstration of apomorphine conjugatio n by recombinant UGT2B1, and the first evidence of the lack of apomorphine glucuronidation in the rat brain. (C) 2000 Elsevier Science Inc. All rights reserved.