Peroxisomal participation in the cellular response to the oxidative stress of endotoxin

Exposure to a sublethal dose of endotoxin offers protection against subsequent oxidative stresses. The cellular mechanisms involved in generating this effect are not well understood. We evaluated the effect of endotoxin on antioxidant enzymes in liver peroxisomes. Peroxisomes have recently been shown to contain superoxide dismutase (SOD) and glutathione peroxidase (GPX) in addition to catalase. Peroxisomes were isolated from liver homogenates by differential and density gradient centrifugations. Endotoxin treatment increased the specific activity of SOD and GPX in peroxisomes to 208% and 175% of control activity, respectively. These findings correlated with increases in peroxisomal SOD and GPX proteins observed by immunoblot. Although the quantity of catalase protein was increased when assessed by immunoblot analysis, the specific activity of catalase was decreased to 68% of control activity. Activation of catalase with ethanol only restored catalase activity to control levels suggesting that catalase had undergone irreversible inactivation. The observed increase in GPX activity may represent a compensatory mechanism triggered by accumulating H2O2. The data presented here suggest for the first time that mammalian peroxisomal antioxidant enzymes are altered during the oxidative injury of endotoxin treatment.