M K Reddy

Induction of Hamster Hepatic Peroxisomal β-oxidation and Peroxisome Proliferation-associated 80000 mol. wt. Polypeptide by Hypolipidemic Drugs

1 The effects of hypolipidemic drugs fenofibrate (isopropyl[4-(p-chlorobenzoyl)-2-phenoxy-2-methyl]propionate), pyrinixil (BR-931; [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio(N-β-hydroxyethyl) acetamide]), methyl clofenapate (2-methyl-2[4-(p-chlorophenyl)phenoxy]2-methyl-propionate), and clofibrate (ethyl α-p-chloro-phenoxyisobutyrate) on plasma triglyceride levels, hepatic peroxisome proliferation and peroxisome-associated enzymes in hamsters were investigated. 2 Fenofibrate, pyrinixil and methyl clofenapate were administered in the diet at 0.2% level (w/w) for 6 weeks. Clofibrate was fed at 0.5% level. 3 Fenofibrate, pyrinixil and methyl clofenapate induced a marked proliferation of peroxisomes in hamster liver cells which was comparable to that observed in the rat and mouse liver, whereas the peroxisome proliferative effect of clofibrate was less pronounced. Peroxisomal fatty acid β-oxidation system was found in the hamster liver and its activity was enhanced significantly by hypolipidemic drugs. The magnitude of induction of [1-14C]palmitoyl CoA oxidation, heat-labile enoyl-CoA hydratase and peroxisome proliferation-associated 80000 mol. wt. polypeptide in the hamster appeared to parallel the extent of peroxisome proliferation. 4 All four hypolipidemic compounds increased hepatic catalase and carnitine acetyltransferase activities and decreased plasma triglyceride levels in the hamster. The observed hepatic effects of hypolipidemic drugs in hamster are identical to those induced by peroxisome proliferators in the rat and mouse. 5 These observations suggest that hypolipidemic agents identified as peroxisome proliferators in rats, mice and now hamsters would very likely enhance the peroxisomal enzyme system in other species. Additional information on the interspecies responses to peroxisome proliferators, however, is necessary to assess the role of peroxisome proliferation in carcinogenesis.

Comparison of the peroxisome proliferator-induced pleiotropic response in the liver of nine strains of mice.

We have investigated the hepatic effect of ciprofibrate, a potent peroxisomal proliferator, in 9 strains of mice to ascertain whether all strains show similar peroxisome proliferation or if there are any that are resistant to the induction of peroxisome proliferation. Dietary feeding of ciprofibrate at 2 concentrations (0.0125% or 0.025% w/w) for 2 weeks resulted in a significant increase in liver weight (170 to 200%) and a 7- to 11-fold increase in volume density of peroxisomes. Catalase and peroxisomal β-oxidation enzymes increased by 1.7- to 2.7- and 1.9- to 9.3-fold, respectively, over the controls. SDS-polyacrylamide slab gel electrophoresis of post-nuclear fractions of livers showed a marked increase in 80,000-mol. wt. polypeptide. Immunocytochemical studies, as expected, revealed higher levels of PBE. Ciprofibrate treatment also induced hepatic DNA synthesis in all strains as determined by [3H]thymidine incorporation and autoradiography. Dot blot analysis of total RNA from livers of ciprofibrate-treated mice (5 strains) showed a significant increase in peroxisomal enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase bifunctional enzyme (PBE) mRNA. When the 9 strains were ranked for each parameter, CBA/Ca was the least responsive mouse strain and the B6C3F1 was the most responsive. However, the results of this study indicate that there is no significant interstrain difference in rankings across strains to ciprofibrate-induced hepatic pleiotropic response.