Involvement of human cytochrome P450 2B6 in the ω- and 4-hydroxylation of the anesthetic agent propofol

Abstract

Human liver microsomal cytochrome P450s (P450s or CYP) involved in the oxidative biotransformation of the anesthetic agent propofol were investigated. Of six cDNA-expressed human P450 enzymes tested, CYP2B6 and CYP1A2, followed by CYP3A4, had high catalytic activities at a 20 µM propofol concentration, corresponding to clinical plasma levels. Km and kcat values for propofol ω- and 4-hydroxyation were 27 µM and 21 nmol ω-hydroxypropofol formed/min/nmol CYP2B6 and 30 µM and 42 nmol 4-hydroxypropofol formed/min/nmol CYP2B6, respectively. CYP2B6 expressed in HepG2 cells also effectively catalyzed propofol ω- and 4-hydroxylation. In a panel of individual human liver microsomes, propofol ω- and 4-hydroxylation activities (at the substrate concentration of 20 µM) were highly correlated with CYP2B6 contents, and moderately with CYP3A4 contents. Anti-CYP2B6 antibody inhibited both ω- and 4-hydroxylation activities in human liver samples that contained relatively high levels of CYP2B6, whereas α-naphthoflavone and an anti-CYP1A2 antibody showed inhibitory effects on the 4-hydroxylation activity in a liver microsomal sample in which the CYP1A2 level was relatively high. These results suggest that CYP2B6 has an important role in propofol ω- and 4-hydroxylation in human livers and that the hepatic contents of CYP2B6, CYP3A4, and CYP1A2 determine which P450 enzymes play major roles in propofol oxidation in individual humans.