Clofibrate-Induced in Vitro Hepatoprotection against Acetaminophen Is Not Due to Altered Glutathione Homeostasis

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Abstract
Prior induction of peroxisome proliferation protects mice against the in vivo hepatotoxicity of acetaminophen and various other bioactivation-dependent toxicants. The mechanisms underlying such chemoresistance are poorly understood, although they have been suggested to involve alterations in glutathione homeostasis. To clarify the role of glutathione in this phenomenon, we isolated hepatocytes from mice in which hepatic peroxisome proliferation had been induced with clofibrate. The cells were incubated with a range of acetaminophen concentrations and the extent of cell killing after up to 8 h was assessed by measuring lactate dehydrogenase leakage from the cells. Hepatocytes from clofibrate-pretreated mice were much less susceptible to acetaminophen than cells from vehicle-treated controls. However, the extent of glutathione depletion during exposure to acetaminophen was similar in both cell types, as were rates of excretion of the product of glutathione-mediated detoxication of acetaminophen's quinoneimine metabolite, 3-glutathionyl-acetaminophen. The glutathione-replenishing ability of clofibrate-pretreated cells after a brief exposure to diethyl maleate also resembled that of control cells. More importantly, prior depletion of glutathione by diethyl maleate did not abolish the resistance of clofibrate-pretreated cells to acetaminophen. Taken together, these findings indicate that although glutathione-dependent pathways may contribute to hepatoprotection during peroxisome proliferation, the resistance phenomenon is not due exclusively to this mechanism.

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