INVOLVEMENT OF CYTOCHROME-P450 3A4 IN N-DEALKYLATION OF BUPRENORPHINEIN HUMAN LIVER-MICROSOMES

Buprenorphine is a long acting analgesic of the opiate family. Recentl y, it has been proposed for the opioid dependency treatment at a large scale. The drug is extensively metabolized by the hepatic cytochrome P450 in man, yielding a N-dealkylated metabolite, norbuprenorphine. Th e specific forms of P450 involved in this oxidative N-demethylation we re examined in a panel of 18 human liver microsomal preparations previ ously characterized with respect to their P450 contents. Buprenorphine was N-dealkylated with an apparent Km of 89 +/- 45 mu M (n = 3). The metabolic rates were 3.46 +/- 0.43 nmol/(min x mg of protein). This me tabolic pathway was strongly correlated with 6 catalytic activities sp ecific to P450 3A4 and with the immunodetectable P450 3A content of li ver microsomal samples (r = 0.87). Buprenorphine metabolism was 62-71% inhibited by three mechanism-based inhibitors (TAO, erythralosamine, gestodene), by nifedipine as competitive inhibitor (Ki = 129 mu M) and by ketoconazole 0.6 mu M (25% residual activity), all these inhibitor s specific to P450 3A. Among 10 heterologously expressed P450s tested, only P450 3A4 was able to dealkylate buprenorphine with a turnover nu mber of 9.6 min(-1). Morever, this catalytic activity was inhibited up to 80% (vs control) by anti-rat P450 3A antibody. Taken together, all these data demonstrate that P450 3A4 is the major enzyme involved in hepatic buprenorphine N-dealkylation.