The mechanism of alcohol-related liver injury remains uncertain. Chronic ethanol (ETOH) also increases hepatotoxicity of other chemicals, particularly those metabolized to electrophilic intermediates. Since glutathione (GSH) is important in protecting the liver aginst drug-induced injury, effects of ETOH on its metabolism are of interest. Chronic ETOH increases turnover of GSH and requirements for methionine (MET), the principle dietary precursor of GSH. These observations suggest that chronic ETOH may increse transsulfuration of MET to cysteine (CYS) and ultimately to GSH. Our hypothesis is that ETOH increases GSH requirements, perhaps because of the acetaldehyde formed. Thus, the major objective of this study is to determine, in the rat, the effects of both acute and chronic ETOH on metabolism of GSH and its sulfur amino acids precursors, CYS and MET. Attention will be given to whether ETOH or its conversion to acetaldehyde, is responsible for effects on GSH metabolism. The proposed studies will determine the effects of 6-8 weeks of ETOH feeding on content, synthesis, and cellular loss of GSH in intact rats and liver perfusion. To avoid confounding acute effects of ETOH, one group of ETOH fed rats will be studied 24 hrs after withdrawal. Results will be compared to rats pair-fed isocaloric liquid diets and chow-fed rats. Since transsulfuration provides a major source of sulfur for GSH synthesis effects of ETOH on uptake and incorporation of 35S-MET into GSH will be determined in isolated hepatocytes from similar groups and in hepatocyte cultures. Activities of the transsulfuration enzymes will be measured. To determine the mechanism of ETOH-related depletion of GSH, effects of acute ETOH administration on turnover and synthesis of GSH will be determined in intact rats and liver perfusion. Effects of in vitro addition of ETOH or acetaldehyde on incorporation of CYS and MET into GSH will be studied in isolated cells. These studies will improve understanding of how ETOH increases hepatotoxicity of other chemicals, provide clues about ETOH effects on amino acid metabolism and help to define requirements of key nutrients during long-term alcohol consumption.
