Peroxisome Proliferation and Lipid Peroxidation in Rat Liver1

Male F344 rats were fed a diet containing the peroxisome proliferators 2-[4-(2,2-dichlorocyclopropyl)phenoxy]-2-methylpropionic acid [ciprofibrate (0.025%)] or [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio]acetic acid [Wy-14643 (0.1%)] for up to 14 months to determine whether hepatic peroxisome prolifera tion caused by these agents results in the induction of membrane lipid peroxidation in the liver. Peroxidative damage of membrane lipids from whole liver, postnuclear, heavy-particle, microsomal, and nuclear membranes was evaluated by determining the extent of formation of conjugated dienes (ultraviolet absorption, 233 nm). Increased generation of diene conjugates was noted in whole-liver, postnuclear, and heavy-particle membrane lipids of rats fed peroxisome proliferators for 6 months or longer when compared to controls. An additional, more intense absorption profile in the ultraviolet absorption range of ~276 nm was noted in the membrane lipids derived from whole liver, postnuclear, and heavy particle pellets, but not in the nuclear and microsomal membrane lipids of livers with peroxisome proliferation. Although the exact chemical nature of this A276nmpeak is not clear, it is attributed to the formation of ketone dienes and/or conjugated trienes. The excess lipid peroxidation correlates with the pre vious observation of accumulation of abundant quantities of lipofuscin in hepatocytes of rats chronically exposed to peroxi some proliferators. The generation of conjugated dienes and ketone dienes and/or trienes together with increased levels of H2O2generation by peroxisomal enzymes, and decreased levels of hepatic glutathione peroxidase, glutathione reducÃ-ase, and glutathione-S-transferases, enzymes responsible for the defense against H2O2damage, suggest the occurrence of membrane lipid peroxidation and oxidative stress in livers of rats treated with carcinogenic peroxisome proliferators.