DUAL EFFECTS OF ANTIINFLAMMATORY 2-ARYLPROPIONIC ACID-DERIVATIVES ON A MAJOR ISOFORM OF HUMAN LIVER 3-ALPHA-HYDROXYSTEROID DEHYDROGENASE

Nonsteroidal anti-inflammatory drugs have been shown to be potent inhi bitors of mammalian 3 alpha-hydroxysteroid dehydrogenase, Here, we rep ort that the drugs of the 2-arylpropionic acid class act as both activ ators and inhibitors for a predominant isoform of the human liver enzy me which is involved in the metabolism of steroid hormones, bile acids , drug ketones and xenobiotic aromatic hydrocarbons. Flurbiprofen, fen oprofen, ibuprofen, naproxen, ketoprofen and suprofen stimulated the a ctivity of the human enzyme (1.5-2.4-fold) at low concentrations of le ss than 20-100 mu M, whereas at higher concentrations they inhibited t he activity. Comparison of the effects of the structurally related com pounds with the drugs revealed that the essential structure required a s the activator molecule is 2-phenylpropionic acid with a hydrophobic substituent on the aromatic ring. In addition, an R-enantiomer of ibup rofen showed higher activation (3-fold) than its S-enantiomer, Kinetic analysis with respect to NADP(+) concentration indicated that R- and S-ibuprofens are nonessential activators showing binding constants of 23 and 34 mu M, respectively, Neither enantiomers activated, but rathe r inhibited the enzyme, with Met replacing Arg-276 which has been show n to interact with the 2'-phosphate of NADP(+). The inhibitions of the mutant enzyme by R- and S-ibuprofens were competitive with respect to the substrate, giving K-i values of 95 and 18 mu M, respectively. The results suggest that the human liver 3 alpha-hydroxysteroid dehydroge nase isoform possesses the two distinct sites, activator and inhibitor sites, to which anti-inflammatory 2-arylpropionates stereoselectively bind.