Identification of Glutathione S–Transferase Isozymes and γ–Glutamylcysteine Synthetase As Negative Acute–Phase Proteins in Rat Liver

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Abstract
Because acute infection and inflammation affect drug metabolism and drug–metabolizing enzymes, the effect of the acute–phase response on the expression of glutathione S–transferase (GST) isoenzymes, glutathione synthesis, and several antioxidant enzymes was investigated. Hepatic expression of GST isozymes, positive and negative acute–phase reactants, and antioxidant enzymes were determined by Northern blotting and hybridization with gene–specific oligonucleotide probes after lipopolysaccharide treatment of rats. Lipopolysaccharide caused the expected acute–phase response as judged by the increased expression of positive and decreased expression of negative acute–phase proteins. The messenger RNA (mRNA) expression of the major hepatic rat GST isozymes A1, A2, A3, M1, and M2 was decreased 50% to 90%. Total hepatic GST activity toward 1–chloro–2,4–dinitrobenzene was also significantly decreased. mRNA expression of γ–glutamylcysteine synthetase (GCS) large subunit and catalase was reduced by approximately 60%. GCS enzyme activity was also decreased, resulting in a 35% decrease in the hepatic content of reduced glutathione 4 days after lipopolysaccharide challenge. Mn–Superoxide dismutase expression was increased 13–fold, and thioredoxin level was elevated 3–fold after lipopolysaccharide challenge. The expression of all parameters determined returned to near control levels 7 days after treatment. Together, these data show that GSTs and GCS are negative acute–phase proteins and that decreased GCS activity results in a decrease in hepatic glutathione content. Thus, in addition to the phase I drug–metabolizing enzymes known to be decreased during the acute–phase response, some phase II enzymes involved in the elimination of xenobiotics and carcinogens are also decreased.