Saeed A. Qureshi

Evaluation of Selected Hypolipidemic Agents for the Induction of Peroxisomal Enzymes and Peroxisome Proliferation in the Rat Liver

There is a considerable interest in developing potent and safe hypolipidemic drugs for the prevention and management of coronary heart disease in man. In rodents, many of these hypolipidemic compounds induce hepatomegaly, proliferation of peroxisomes and a polypeptide with an approximate mol. wt. of 80000 in liver cells. In the present study, we have examined 10 hypolipidemic compounds for the induction of peroxisome proliferation associated 80000 mol. wt. polypeptide (polypeptide PPA-80), peroxisomal enzymes and peroxisome proliferation in rat liver, in view of the emerging evidence that hepatic peroxisome proliferators as a class are carcinogenic in rats and mice. All ten compounds, fenofibrate (isopropyl-[4-( p-chlorobenzoyl)2-phenoxy-2-methyl] propionate; LS 2265 (taurine derivative of fenofibrate); bezafibrate (2-{4-(2-[4-chlorobenzamido)ethyl] phenoxy}-methyl propionic acid; gemfibrozil (5-2[2,5-dimethylphenoxy]2-2-dimethylpentanoic acid); methyl clofenapate (methyl-2-[4-(p-chlorophenyl)phenoxy]-2-methyl propionate); DG 5685 (5-[4-phenoxybenzyl]trans-2-(3-pyridyl)1,3-dioxane), DH6463 (5-[4-phenoxybenzyl] trans-2-(3-pyrimidinyl)-1,3-dioxane); tiadenol(bis[hydroxyethylthio]-7, 10-decane); ciprofibrate (2,-[4-{2,2-dichlorocyclopropyl}-phenoxy]2-methyl propionic acid) and RMI-14,514 ([5-tetradecycloxyl-2-furancarboxylic acid), produced a marked but variable increase in the activities of peroxisomal enzymes catalase, carnitine acetyltransferase, heat-labile enoyl-CoA hydratase and the fatty acid β-oxidation system and in the amount of polypeptide PPA-80 as demonstrated by SDS-polyacrylamide gel electrophoresis. The peptide map patterns of polypeptide PPA-80 in liver induced by these compounds were strikingly similar. The ultrastructural studies demonstrate that fenofibrate, ciprofibrate, LS 2265, DG 5685 and DH 6463 can induce proliferation of peroxisomes in liver cells of rats, and further confirm the previous reports of hepatic peroxisome proliferative activity of methyl clofenapate, tiadenol, bezafibrate, gemfibrozil and RMI-14514, as shown morphologically. Whether these structurally unrelated chemicals or their metabolite(s) directly activate the peroxisome specific genes to induce this multi-enzyme system or they exert their action on peroxisomes indirectly by causing fatty acid overload in hepatocytes remains to be elucidated. These chemicals offer a simple and reproducible means of stimulating peroxisomal enzymes in liver and should serve as useful tools, for evaluating the implications of hepatic peroxisome proliferation and in elucidating the mechanism of peroxisome proliferator-induced carcinogenesis.

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.