DEHYDROEPIANDROSTERONE 3-BETA-SULFATE IS AN ENDOGENOUS ACTIVATOR OF THE PEROXISOME-PROLIFERATION PATHWAY - INDUCTION OF CYTOCHROME-P-450 4A AND ACYL-COA OXIDASE MESSENGER-RNAS IN PRIMARY RAT HEPATOCYTE CULTURE AND INHIBITORY EFFECTS OF CA2+-CHANNEL BLOCKERS

The role of steroids related to the adrenal androgen dehydroepiandrosterone (5-androstene-3 beta-ol-17-one; DHEA) in regulating the expression of peroxisomal and cytochrome P-450 4A (CYP4A) enzymes active in fatty acid metabolism was assessed using a primary rat hepatocyte culture system. Exposure of hepatocytes to the peroxisome proliferator, clofibric acid (10-250 mu M), for 48-96 h led to substantial increases in CYP4A protein, CYP4A1, CYP4A2 and CYP4A3 mRNAs, and the mRNAs encoding both forms of peroxisomal acyl-CoA oxidase (ACOX-I and ACOX-II), as judged by Northern-blot analysis using gene-specific oligonucleotide probes. Although DHEA treatment in vivo is effective in inducing these mRNAs in rat liver, it had no effect in the cultured hepatocytes. In contrast, treatment of the cells with DHEA 3 beta-sulphate (DHEA-S; 10-250 mu M) stimulated major increases in CYP4A and ACOX mRNA levels. Examination of several analogues indicated a preference for 3 beta-sulphate over 17 beta-sulphated steroids and the (i)nactivity of a 3 alpha-hydroxy-17 beta-sulphate derivative (DHEA-S > 5-androstene-3 beta,17 beta-diol 3-sulphate similar to 5 alpha-androstene-3 beta-ol-17-one 3-sulphate > 5-androstene-3 beta, 17 beta-diol 17-sulphate similar to 5 beta androstane-3 alpha-ol-17-one 3-sulphate much greater than 5 alpha-androstane-3 alpha,17 beta-diol 17-sulphate). Induction of CYP4A mRNAs by either DHEA-S or clofibric acid was partially blocked by structurally diverse Ca2+-channel antagonists (nicardipine nifedipine and diltiazem; 50 mu M), suggesting that both the steroidal and fibrate classes of CYP4A inducers stimulate peroxisomal-proliferative responses via a Ca2+-dependent pathway. Retinoic acid alone slightly induced CYP4A mRNAs but did not enhance the induction by clofibrate or DHEA-S. As DHEA-S corresponds to a physiologically important major circulating androgen, these findings suggest that it may serve as an endogenous regulator of hepatic peroxisome enzyme levels, They further suggest that Ca2+-channel blockers may be useful pharmacological tools for the further study of the underlying cellular mechanisms whereby endogenous steroids and fibrate drugs induce peroxisome proliferation, and the relationship of these events to activation of the peroxisome proliferator-activated receptor.