DIETARY SULFUR AMINO-ACID ADEQUACY INFLUENCES GLUTATHIONE SYNTHESIS AND GLUTATHIONE-DEPENDENT ENZYMES DURING THE INFLAMMATORY RESPONSE TO ENDOTOXIN AND TUMOR-NECROSIS-FACTOR-ALPHA IN RATS

1. Glutathione concentrations in liver and lung fall when food intake or sulphur amino acid intake is inadequate. However, concentrations ma y be restored during inflammation, despite anorexia, provided that pri or sulphur amino acid intake is adequate. 2. We studied the mechanisms of these changes by measuring the effect of sulphur amino acid and pr otein intake on hepatic glutathione synthesis and gamma-glutamylcystei ne synthetase activity, hepatic and lung glutathione concentrations, g lutathione reductase and glutathione peroxidase activities in young ra ts given an inflammatory challenge by intraperitoneal injection of tum our necrosis factor-alpha or endotoxin (lipopolysaccharide). 3. Diets containing 200 g of casein and 8 g of L-cysteine/kg (normal-protein di et), or 80 g of casein and 8 g of L-cysteine, or isonitrogenous amount s of L-methionine or L-alanine (low-protein diets) were fed ad libitum to young Wistar rats for 8 days. Dietary groups were subdivided into three: one subgroup continued feeding ad libitum, a second was given t umour necrosis factor or lipopolysaccharide and killed 24 h thereafter , while the third was pair-fed to the intakes of the second subgroup f or 24 h before being killed. 4. Glutathione concentrations in liver an d lung were reduced in rats fed the low-protein diet containing alanin e, and in all dietary groups when food intake was restricted. The infl ammatory challenges restored hepatic glutathione concentrations in all groups but the diet supplemented with alanine, which had an inadequat e sulphur amino acid content. In lung, restoration occurred only in an imals fed the normal-protein diet. 5. The activity of gamma-glutamylcy steine synthetase, which is rate limiting for glutathione synthesis, w as unaffected by dietary or sulphur amino acid intake or by the inflam matory response. Substrate supply may therefore be a major determinant in glutathione synthesis in vivo. 6. Total hepatic glutathione synthe sis was affected by food intake, the type and amount of sulphur amino acids in the diet and by inflammation. Total synthesis was 207, 137, 4 21 and 90 mu mol/day for animals fed ad libitum the normal-protein die t, or low-protein diets supplemented with cysteine, methionine or alan ine respectively, ad libitum. Pair-feeding resulted in values of 76, 3 1, 71, and 0 mu mol/day respectively. After lipopolysaccharide injecti on, rates increased to 200, 117, 151 and 56 mu mol/day respectively. 8 . Reductase and peroxidase activities increased in liver and lung, whe n low-protein diets which contained supplemental methionine or alanine were consumed ad libitum. A reduction in food intake resulted in enzy me activity changes, which suggested that recycling of glutathione inc reased in lung and decreased in liver. Injection of tumour necrosis fa ctor reversed this effect. 9. The restoration of glutathione concentra tions in liver after an inflammatory challenge is closely associated w ith an enhanced rate of synthesis and increased recycling. The former is impaired when inadequate sulphur amino acid is consumed before the challenge. In lung, increased recycling of glutathione may help mainta in concentrations when food intake is restricted, but not during infla mmation.