HUMAN BUPRENORPHINE N-DEALKYLATION IS CATALYZED BY CYTOCHROME-P450 3A4

Buprenorphine (BN) is a thebaine derivative with analgesic properties. To identify and characterize the cytochrome P450 (CYP) enzyme(s) invo lved in BN N-dealkylation, in vitro studies using human liver microsom es and recombinant human CYP enzymes were performed. Norbuprenorphine formation from BN was measured by a simple HPLC-UV assay method, witho ut extraction. The BN N-dealkylation activities in 10 human liver micr osomal preparations were strongly correlated with microsomal CYP3A-spe cific metabolic reactions, i.e. triazolam 1'-hydroxylation (r = 0.954) , midazolam 1'-hydroxylation (r = 0.928), and testosterone 6 beta-hydr oxylation (r = 0.897). Among the eight recombinant CYP enzymes studied (CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4) , only CYP3A4 could catalyze BN N-dealkylation. The apparent K-M value for recombinant CYP3A4 was similar to that for human liver microsomes (23.7 vs. 39.3 +/- 9.2 mu M). The demonstration of BN N-dealkylation by recombinant CYP3A4 and the agreement in the affinities (apparent K- M values) of human liver microsomes and recombinant CYP3A4 provide the most supportive evidence for BN N-dealkylation being catalyzed by CYP 3A4.