Vol. 285, Issue 3, 1096-1103, June 1998

Activation of Human Liver 3-Hydroxysteroid Dehydrogenase by Clofibrate Derivatives¹

Kazuya Matsuura, Akira Hara, Makiko Kato, Yoshihiro Deyashiki, Yoshiyuki Miyabe, Syuhei Ishikura, Tadashi Sugiyama and Yoshihiro Katagiri

Laboratory of Biochemistry (K.M., A.H., M.K., Y.D., Y.M., S.I.), Gifu Pharmaceutical University, Mitahora-higashi, Gifu, 502-8585 Japan, and Department of Pharmacy (T.S., Y.K.), Gifu University Hospital, Tsukasa-machi, Gifu, 500-8705 Japan

The NADP⁺-dependent dehydrogenase activity of a predominant isoenzyme of human liver 3-hydroxysteroid dehydrogenase was activated by antihyperlipidemic drugs, such as bezafibrate and clinofibrate, and by clofibric acid and fenofibric acid (active metabolites of clofibrate and fenofibrate, respectively). The optimal pH of the activation by the drugs was about 7.5, and the concentrations giving maximum stimulation (1.8- to 2.4-fold) were 100, 50, 400 and 50 µM for bezafibrate, clinofibrate, clofibric acid and fenofibric acid, respectively. Clofibrate and fenofibrate acted as weak inhibitors, and the clofibric acid derivatives that lack the chloro group, methyl group on the -carbon or carboxyl group greatly decreased the stimulatory effects. The activation by the drugs increased both K_m and kcat (turnover number) values for the coenzyme and substrates. Kinetic analysis with respect to NADP⁺ showed that bezafibrate, clinofibrate, clofibric acid and fenofibric acid were nonessential activators showing dissociation constants of 32, 6, 103 and 11 µM, respectively. The combined activators experiments with one of the above drugs and sulfobromophthalein, a known activator specific for this enzyme, and comparison of their effects on the activities of mutant enzymes (with Met replacing Lys-270 or Arg-276) indicated that sulfobromophthalein and the drugs bind to an identical site on the enzyme. These results suggest that the long-term therapy with the antihyperlipidemic drugs influences the metabolism of steroid hormones, bile acids and several ketone-containing drugs mediated by the enzyme.