DNA damage related to increased hydrogen peroxide generation by hypolipidemic drug-induced liver peroxisomes.

Abstract

Several hypolipidemic drugs and certain industrial plasticizers induce proliferation of peroxisomes, enhance the activity of peroxisome-associated (-oxidation of fatty acids, and produce hepatocellular carcinomas in the livers of rodents. Because these chemicals themselves are not mutagens and do not covalently modify DNA, unlike the majority of chemical carcinogens, we proposed that the persistent proliferation of peroxisomes, and the induction of associated peroxisomal oxidases, caused a sustained increase in intracellular H202 or other reduced oxygen species, which would then introduce mutagenic DNA damage. In the present study, we investigated the ability of peroxisomes purified from the livers of normal and hypolipidemic drug-treated rats to induce DNA strand scission in vitro. Gradient-purified peroxisomes from livers of hypolipidemic drug-treated rats produced a 30-to 70-fold increase in H202 generation when compared to controls. The levels of H202 generated in incubations containing control or hypolipidemic drug-induced peroxisomes correlated well with the induction of single strand breaks in supercoiled simian virus 40 DNA molecules that were included in these reconstituted peroxisome incubations. Addition of excess catalase to peroxisome incubations failed to prevent strand breaks, suggesting that other reduced oxygen species may be rapidly generated from H202. These experimental results are consistent with a mechanism of hepatocarcinogenesis in which hepatocellular genetic damage is introduced by the by-products of peroxisomal fatty acid ,8-oxidation, an oxidative pathway that is dramatically increased in hypolipidemic drug-treated livers.Several drugs, including clofibrate, are now used for the treatment of hyperlipidemias in humans. Clofibrate, as well as other potent hypolipidemic agents, causes massive hepatomegaly when administered to rodents, chickens, and monkeys (1)(2)(3)(4). This hepatomegaly is characteristically associated with a marked increase in the numerical, as well as volume, densities of peroxisomes in the liver cells of several species tested (1-4). Peroxisomes contain catalase, carnitine acetyltransferase, and five hydrogen peroxide (H202)-generating enzymes, including the enzyme system involved in the ,3oxidation of long-chain fatty acids (5, 6). The activities of these enzymes in liver, including their messenger RNA species, are increased in association with peroxisome proliferation (5-9). Several studies have now established that peroxisome proliferators [i.e., certain hypolipidemic drugs such as clofibrate, Wy-14643 ([4-chloro-6-(2,3-xylidino)2-pyrimidinylthio]acetic acid), nafenopin, BR-931, methyl clofenapate, ciprofibrate, and the industrial plasticizer di(2-ethylhexyl)phthalate] induce hepatocellular tumors in both mice and rats when chronically administered in the diet (6, 10). None of these carcinogenic peroxisome proliferators has been shown to be mutagenic in bacterial assays (11,12); furthermore, they displayed no capacity to covalently modify cellular DNA eith...

Changes in expression of cellular oncogenes and endogenous retrovirus-like sequences during hepatocarcinogenesis induced by a peroxisome proliferator

“…The ability of this compound to induce peroxisome proliferation has been implicated in its carcinogenicity, presumably through the production of oxygen radicals by these organelles (Reddy et al, 1980;Fahl et al, 1984). However, recent studies indicate that the ability of these compounds to induce sustained enhancement of liver cell proliferation, and not the degree of peroxisome proliferation, correlates with the degree of tumour response (Marsman et al, 1988).…”

Liver gene expression in rats in response to the peroxisome proliferator-activated receptor-α agonist ciprofibrate

“…Several genes that appear to be related to stress responses were differentially regulated in the present study (Table 2). Fibrates and other PPs are known to increase H 2 O 2 levels, leading to oxidative stress (21). It is therefore interesting to note that several genes known to be involved in the cell response to oxidative stress are upregulated in ciprofibrate-dosed rats [e.g., superoxide dismutase 3 (Sod3), copper-zinc-containing superoxide dismutase (Sod1), glutathione peroxidase 4 (Gpx4), and glutathione Stransferase, mu type 3 (Gstm3)] (Table 2).…”

Antioxidant Potential of Asparagus adscendens

“…Microsomes release H2O2 which contributes to more than 80% of H2O2 produced in the cell (Stohs and Baghchi 1995). The process of oxidation of fatty acid is also a source of H2O2 (Fahl et al, 1984). The production of H2O2 also takes place in peroxisomes (Valko et al, 2004).…”