In alcoholic liver disease, tumor necrosis factor-a (TNFa) is a critical effector molecule, and abnormal methionine metabolism is a fundamental aquired metabolic abnormality. Although hepatocytes are resistant to TNFa-induced killing under normal circumstances, previous studies have shown that primary hepatocytes from rats chronically fed alcohol have increased TNFa cytotoxicity. Therefore, there must be mechanisms by which chronic alcohol exposure "sensitizes" to TNFa hepatotoxicity. S-adenosylhomocysteine (SAH) is product of methionine in transsulfuration pathway and a potent competitive inhibitor of most methyltransferases. In this study, we investigated the effects of increased SAH levels on TNFa hepatotoxicity. Our results demonstrated that chronic alcohol consumption in mice not only decreased hepatic S-adenosylmethionine levels but also increased hepatic SAH levels, which resulted in a significantly decreased S-adenosylmethionine-to-SAH ratio. This was associated with signscant increases in hepatic TNFa levels, caspase-8 activity, and cell death. In vitro studies demonstrated that SAHenhancing agents sensitized hepatocytes to TNFa killing, and the death was associated with increased caspase-8 activity, which was blocked by a caspase-8 inhibitor. In addition, increased intracellular SAH levels had no effect on nuclear factor KB activity induced by TNFa. In conclusion, these results provide a new link between abnormal methionine metabolism and abnormal TNFa metabolism in alcoholic liver disease. Increased SAH is a potent and clinically relevant sensitizer to TNFa hepatotoxicity. These data further support improving the S-adenosylmethionine-to-SAH ratio and removal of intracellular SAH as potential therapeutic options in alcoholic liver disease. Supplemmtury muteriulfbr thb article can be found on the HEPATOLOGY website (http://int~s~ce.wiley.com/jpages/O2~O-~~3~/suppmat/index.h~~. (HEPATOLOGY 20O4;4O:989 -997.) lcoholic liver disease (ALD) continues to be an important health problem in the United States.
A,, though much progress has been made over the past decade, we still do not have a complete understand-