Human CYP2B6: expression, inducibility and catalytic activities

Human cytochrome (CYP)2B6 cDNA was cloned and expressed in bacteria and in yeast. Its expression in Saccharomyces cerevisiae enabled us to obtain, at a high level, an active yeast-expressed CYP2B6 protein, so as to assess its role in the metabolism of ethoxyresorufin, pentoxyresorufin, benzyloxyreso rufin, ethoxycoumarin, testosterone and cyclophosphamide, Kinetic analysis showed that human CYP2B6 preferentially metabolized benzyloxyresorufin and pentoxyresorufin, although other CYPs also metabolized these substrates in human liver microsomes. CYP2B6 also manifested a strong 4-hydroxycyclophosp hamide activity. Its expression in Escherichia coli enabled us to produce a very specific anti-human CYP2B6 antibody. No cross reactivity of this anti body was observed with CYPs1A1, 1A2, 3A4, 3A5, 2C8, 2C9, 2C18, 2C19, 2D6 or 2E1. This antibody enabled us to study the hepatic and extrahepatic expres sion of CYP2B6 in man, as well as its expression and inducibility in primar y cultured human hepatocytes and in different human cell lines. Immunoblot analysis revealed that the CYP2B6 protein was expressed in 43 of the 48 hum an liver samples tested, with levels ranging from 0.4 to 8 pmol/mg of micro somal protein with a mean of 1.7 pmol/mg protein, CYP2B was also expressed in human brain, intestine and kidney, and at a lower level in the lung. CYP 2B mRNA was detected in human liver, kidney, lung, trachea and intestine, W e also found that CYP2B6 is induced at protein and mRNA levels by phenobarb ital (2 mM) and cyclophosphamide (1 mM), an anticancer drug known to be met abolized by CYP2B6, No expression or inducibility of CYP2B6 was observed in any of the human cell lines tested, Pharmacogenetics 9:295-306 (C) 1999 Li ppincott Williams & Wilkins.