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. K_m and k_cat 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.

Key Words::

• CYP2B6
• CYP3A4
• CYP1A2
• 2,6-diisopropylphenol
• propofol hydroxylation

Acknowledgements

We thank Dr Satoru Asahi of Takeda Pharmaceutical Company, Osaka, Japan, and AstraZeneca, UK for supplying human P450 cDNAs and 4-hydroxypropofol, respectively. This work was supported in part by the Ministry of Education, Science, Sports and Culture of Japan, the Research Foundation for Pharmaceutical Sciences, the Japan Research Foundation for Clinical Pharmacology, and United States Public Health Service Grants R37 CA090426.