CYP3A4 and CYP3A7-mediated carbamazepine 10,11-epoxidation are activated by differential endogenous steroids.
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, 17alpha-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 in K(m) and increase in V(max) for CYP3A7-mediated CBZ 10,11-epoxidation, whereas DHEA-S 16alpha-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.
Nakamura
Hiroyoshi
H
Division of Pharmacy, Chiba University Hospital Inohana, Chuo-ku, Chiba 260-8677, Japan. hirokun@ho.chiba-u.ac.jp
Torimoto
Nao
N
Ishii
Itsuko
I
Ariyoshi
Noritaka
N
Nakasa
Hiromitsu
H
Ohmori
Shigeru
S
Kitada
Mitsukazu
M
D000818:Animals; D000927:Anticonvulsants / Q000378:metabolism; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D001192:Arylsulfatases / Q000378:metabolism; D001571:Benzoflavones / Q000494:pharmacology; D002220:Carbamazepine / Q000031:analogs & derivatives* / Q000378:metabolism*; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D066298:In Vitro Techniques; D007313:Insecta; D007700:Kinetics; D013250:Steroid Hydroxylases / Q000032:analysis; D013256:Steroids / Q000494:pharmacology*; D043266:Steryl-Sulfatase; D013379:Substrate Specificity
D000927:Anticonvulsants; D001571:Benzoflavones; D013256:Steroids; D002220:Carbamazepine; C011512:alpha-naphthoflavone; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C104464:CYP3A protein, human; C103123:CYP3A7 protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D001192:Arylsulfatases; D043266:Steryl-Sulfatase; C012227:carbamazepine epoxide