Protection of Hepatocytes with Hyperoxia against Carbon Tetrachloride-induced Injury

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Abstract
Hyperbaric oxygen (HPO) was administered to rats (100% O2 at 2.8 atm for 90 min) immediately or 1 hr after severe carbon tetrachloride (CCl4) intoxication in order to study the mechanisms of protection against hepatocellular injury by hyperoxia. Slight to moderate hepatocellular injury was observed, particularly by morphologic criteria, 4 hr after CCl4 intoxication. Little cell death was observed; 24 hr after CCl4, 20% of the untreated animals died. In the survivors, the following typical changes occurred in the liver: extensive hepatocellular swelling, vacuolization and necrosis; severe ultrastructural alterations; binding of CCl4 to microsomal lipids; elevation of lipid peroxidation products (conjugated dienes); little decrease in cytochrome b5 and severe decrease in cytochrome P-450 levels. Serum (ransaminase (alanine aminotransferase and aspar-tate aminotransferase) levels were elevated. Immediate treatment with HPO prevented the mortality and markedly decreased the hepatocellular necrosis 24 hr after intoxication. Immediate HPO treatment did not lower the levels of free CCl4 in the liver. However, the rise in lipid peroxidation products caused by CCl4 intoxication at 4 hr was reduced. Delayed treatment with HPO (1 hr after CCl4) prevented the mortality but was less effective in preventing necrosis. Some hepatocellular protection was still demonstrable. In particular, the rise in lipid peroxidation products was reduced. Hyperoxia protects hepatocytes against CCl4 toxicity. The rapid decline in protective effect within 60 min of intoxication suggests that hyperoxia inhibits CCl4 activation and/or damage from molecular intermediates. Hyperoxia has little effect on the progression of sublethal injury to cell death in the livers of CCl4-intoxicated rats.