Effective NADH-dependent oxidation of 7beta-hydroxy-delta8-tetrahydrocannabinol to the corresponding ketone by Japanese monkey hepatic microsomes.
The NADH-dependent activity by hepatic microsomes of Japanese monkeys for 7-oxo-Delta(8)-tetrahydrocannabinol (7-oxo-Delta(8)-THC) formation from 7beta-hydroxy-Delta(8)-THC exhibited about 70% of the NADPH-dependent activity (100%) at the substrate concentration of 72.7 microM, although NADPH was an obligatory cofactor for maximal activity. Both NADH- and NADPH-dependent activities were significantly inhibited by the typical P450 inhibitors, such as SKF525-A and metyrapone. Both activities were almost completely inhibited by the NADPH-P450 reductase inhibitor diphenyliodonium chloride. The ratio of NADH- and NADPH-dependent activities varied significantly according to the substrate concentration. Interestingly, the NADH-dependent activity was higher than that of NADPH at low substrate concentrations of 13-50 microM. The ratio was also affected by the cofactor concentration. In the reconstituted system of CYP3A8 purified from hepatic microsomes of Japanese monkeys as a major enzyme responsible for the NADPH-dependent oxidation, NADH as well as NADPH could sustain the oxidation of 7beta-hydroxy-Delta(8)-THC to the corresponding ketone. The NADH-dependent oxidation of 7beta-hydroxy-Delta(8)-THC by monkey livers is mainly catalyzed by CYP3A8 as well as the NADPH-dependent oxidation. These results indicate that NADH as a cofactor may be also useful for the oxidation of 7beta-hydroxy-Delta(8)-THC, and that the cofactor requirement for the reaction is varied by the concentrations of substrate and/or cofactor.
Matsunaga
Tamihide
T
Division of Pharmacy, Shinshu University Hospital, Matsumoto, Japan. t-matsu@hsp.md.shinshu-u.ac.jp
Higuchi
Shinsuke
S
Watanabe
Kazuhito
K
Kageyama
Takashi
T
Ohmori
Shigeru
S
Yamamoto
Ikuo
I
D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D013759:Dronabinol / Q000031:analogs & derivatives* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008251:Macaca; D008862:Microsomes, Liver / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism*; D015394:Molecular Structure; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D013379:Substrate Specificity
C503071:7beta-hydroxy-delta8-tetrahydrocannabinol; D009243:NAD; D009249:NADP; D013759:Dronabinol; D003577:Cytochrome P-450 Enzyme System