Coordinate induction of peroxisomal beta-oxidation activity and cytosolic epoxide hydrolase activity.

The effect of four hypolipidemic compounds (tiadenol, clofibrate, acetylsalicylic acid, 1-benzylimidazole) on the specific activities of peroxisomal beta-oxidation and cytosolic and microsomal epoxide hydrolase of rat liver was investigated. Since specific activity of cytosolic epoxide hydrolase from outbred Sprague-Dawley rats showed large interindividual variations (approximately 38-fold), induction studies were performed with inbred Fischer F-344 rats, which showed only low interindividual variations (approximately 2-fold). Clofibrate, tiadenol and acetylsalicylic acid caused a 8-, 13- and 4.5-fold induction of cEH and a 13-, 19- and 5-fold induction of peroxisomal beta-oxidation activity, respectively. Microsomal epoxide hydrolase activity was only slightly increased (less than 1.5-fold). 1-Benzylimidazole induced both cytosolic epoxide hydrolase and peroxisomal beta-oxidation activity about 2-fold, whereas microsomal epoxide hydrolase activity was increased about 4-fold. Increase in cytosolic epoxide hydrolase activity was not due to enzyme activation as demonstrated by in vitro studies. On the other hand, these in vitro studies showed that the increase in microsomal epoxide hydrolase activity by 1-benzylimidazole may partially be due to activation of the enzyme.