Cytoplasmic Fine Granular Expression of 8-hydroxydeoxyguanosine Reflects Early Mitochondrial Oxidative DNA Damage in Nonalcoholic Fatty Liver Disease

To clarify the possible role of oxidative stress in hepatocytes in nonalcoholic fatty liver disease, the hepatic expression of 8-hydroxydeoxyguanosine (8-OHdG), a good marker of oxidative DNA damage, was immunohistochemically investigated in nonalcoholic steatohepatitis (NASH) and steatosis. In double immunostaining, the cytoplasmic fine granular 8-OHdG expression was considered to reflect 8-OHdG-positive mitochondrial DNA affecting oxidation stress. In steatosis, 4 of 8 cases showed cytoplasmic 8-OHdG, 1 case showed nuclear 8-OHdG and 1 case showed both cytoplasmic and nuclear 8-OHdG. In contrast, 8-OHdG expression was more frequently detected in NASH (12 of 13 cases, 92%). Immunoreactivity for 8-OHdG was observed only in the cytoplasm with a fine granular pattern (1 of 13 cases, 8%), only in the nucleus (6 of 13 cases, 46%), and in both the cytoplasm and the nucleus (5 of 13 cases, 38%). Megamitochondria also exhibited 8-OHdG intensely. We indicate that 8-OHdG expression in the cytoplasm with a fine granular pattern reflects oxidative damage to the mitochondrial DNA of hepatocytes in both NASH and steatosis. We propose herein that the evaluation of cytoplasmic 8-OHdG may be a sensitive diagnostic marker of early nonalcoholic fatty liver disease events.