The structurally diverse peroxisome proliferators ciprofibrate, clofibrate, and bis(2-ethylhexyl) phthalate [(EtHx)2 greater than Pht] increase the activities of hepatic catalase and peroxisomal fatty acid beta-oxidation enzymes in conjunction with profound proliferation of peroxisomes in hepatocytes. In order to delineate the level at which these enzymes are induced in the liver, the transcriptional activity of specific genes for fatty acyl-CoA oxidase (FAOxase) and enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase bifunctional enzyme (PBE), the first two enzymes of the peroxisomal beta-oxidation system, and for catalase were measured in isolated hepatocyte nuclei obtained from male rats following a single intragastric dose of ciprofibrate, clofibrate, or (EtHx)2 greater than Pht. All three peroxisome proliferators rapidly increased the rate of FAOxase and PBE gene transcription in liver, with near maximal rates (9-15 times control) reached by 1 hr and persisting until at least 16 hr after administration of the compound. FAOxase and PBE mRNA levels, measured by blot-hybridization analysis and FAOxase and PBE protein content, analyzed by immunoblotting, increased concurrently up to at least 16 hr following a single dose of peroxisome proliferator. The catalase mRNA level increased about 1.4-fold, but the transcription rate of the catalase gene was not significantly affected. The results show that the peroxisome proliferators clofibrate, ciprofibrate, and (EtHx)2 greater than Pht selectively increase the rate of transcription of peroxisomal fatty acid beta-oxidation enzyme genes. Whether the transcriptional effects are mediated by peroxisome proliferator-receptor complexes remains to be elucidated.

Transcription regulation of peroxisomal fatty acyl-CoA oxidase and enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase in rat liver by peroxisome proliferators.