Noninhibitory effect of antioxidants ethoxyquin, 2(3)-7erf-butyl-4-hydroxyanisole and 3,5-di-ferf-butyl-4-hydroxytoluene on hepatic peroxisome proliferation and peroxisomal fatty acid β-oxidation induced by a hypolipidemic agent in rats

6-Ethoxy-1,2-dihydro-2,2,4-trimethylquinoline (ethoxyquin) and the phenolic antioxidants 2(3)-tert-butyl-4-hydroxyanisole and 3,5-di-fert-butyl-4-hydroxytoluene inhibit the development of tumors induced by several chemical carcinogens that are geno-toxic. The antioxidants appear to exert these protective effects by inhibiting metabolic activation and by enhancing enzyme systems that facilitate the detoxification of electrophilic form(s) of carcinogens. Information regarding the protective effects, if any, of antioxidants against carcinogenesis by chemical carcinogens that do not appear to generate electrophilic or mutagenic metabolites is, however, lacking. To examine the proposal that the carcinogenicity of such nonmutagenic compounds is due to their ability to initiate lipid peroxidation chain reactions either directly or indirectly, we plan to systematically investigate the effects of antioxidants on hepatocarcinogenesis by peroxisome proliferators. We have studied the acute effects of antioxidants ethoxyquin, 2(3)-ferf-butyl-4-hydroxyanisole, and 3,5-di-ferf-bu-tyl-4-hydroxytoluene on the induction, in the rat liver, of hepatic peroxisome proliferation and peroxisome-associated enzymes by 2-[4-(2,2-dichlorocyclopropyl)phenoxy]-2-methyl propionic acid (dprofibrate), a potent peroxisome proliferator. Ethoxyquin at 0.5% (w/w) dietary level exerted no inhibitory effect on the induction by dprofibrate (0.1%, w/w) of hepatomegaly, peroxisome proliferation (volume and numerical density), catalase, camitine acetyltransferase, heat-labile peroxisomal enoyl-coen-zyme A hydratase, and peroxisomal fatty acid β-oxidation system. Both 2(3)-ferf-butyl-4-hydroxyanisole (0.7%, w/w) and 3,5-di-fe/f-butyl-4-hydroxytoluene (0.7 or 0.07%) also failed to inhibit the dprofibrate-induced hepatomegaly and hepatic peroxisome proliferation. Additionally, none of these antioxidants altered the dprofibrate-induced increase in M_r80,000 peroxisome proliferation-associated polypeptide in liver as analyzed by sodium dodecyl sulfate:polyacrylamide gel electrophoresis. The similar increases in peroxisome population and elevations of H₂O₂-produdng peroxisomal fatty acid β-oxidation system suggest that excess levels of intracellular H₂O₂ are generated in the livers of rats fed dprofibrate either alone or in combination with a dietary antioxidant. These experiments provide a model system to test.