RT Journal Article SR Electronic T1 CYP3A4 and CYP3A7-Mediated Carbamazepine 10,11-Epoxidation Are Activated by Differential Endogenous Steroids JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 432 OP 438 DO 10.1124/dmd.31.4.432 VO 31 IS 4 A1 Hiroyoshi Nakamura A1 Nao Torimoto A1 Itsuko Ishii A1 Noritaka Ariyoshi A1 Hiromitsu Nakasa A1 Shigeru Ohmori A1 Mitsukazu Kitada YR 2003 UL http://dmd.aspetjournals.org/content/31/4/432.abstract AB Recently, we reported that several endogenous steroids affect CYP3A4-mediated drug metabolism, using human adult liver microsomes as an enzyme source. Especially, carbamazepine (CBZ) 10,11-epoxidation is activated by androstenedione (AND). In the present studies, we investigated the effects of endogenous steroids on the activity of CBZ 10,11-epoxidation by expressed CYP3A4 and CYP3A7. When expressed CYP3A4 was used as an enzyme source, the addition of AND to the reaction mixture also caused a drastic increase in the activity of CBZ 10,11-epoxidase, and resulted in a change in the kinetics from sigmoid to Michaelis-Menten type. On the other hand, expressed CYP3A7-mediated CBZ 10,11-epoxidation was activated by sulfate conjugate steroids, such as pregnenolone 3-sulfate, 17α-hydroxypregnenolone 3-sulfate, and dehydroepiandrosterone 3-sulfate (DHEA-S), whereas the unconjugated form corresponding to these three steroids did not activate the reaction. Especially, DHEA-S was found to be a potent activator of CBZ 10,11-epoxidation by expressed CYP3A7. The kinetic character of CBZ 10,11-epoxidation by CYP3A7 is Michaelis-Menten type regardless of the presence of DHEA-S. The presence of DHEA-S caused a decrease inKm and increase inVmax for CYP3A7-mediated CBZ 10,11-epoxidation, whereas DHEA-S 16α-hydroxylation was not affected by the coexistence of CBZ. In conclusion, CYP3A4 and CYP3A7-mediated CBZ 10,11-epoxidations are activated by different types of endogenous steroids. This is the first report regarding CYP3A7 cooperativity. The American Society for Pharmacology and Experimental Therapeutics