gamma-Glutamyl transpeptidase: a novel biochemical marker in inflammation

gamma-Glutamyl transpeptidase (gamma-GT) plays an important role in the turnover of glutathione and protein biosynthesis. Because in inflammation both catabolic and anabolic steps are activated together with migration of cells, an alteration in gamma-GT activity was postulated to occur at the site of inflammation with the development of the inflammatory process. We discovered that gamma-GT activity was increased markedly at sites of inflammation produced in several ways in rats. A significant increase in enzyme activity appeared soon after the induction of inflammation. In carrageenin-induced acute inflammation, the paw tissue attained a 3- to 4-fold increase in enzyme activity within 4 hr; in established adjuvant arthritis, a 20- to 24-fold increase over its basal activity occurred in the rat paw tissue. The specific enzyme activity was 20-22 nmoles/min/mg protein in the cellular sediment of carrageenin-induced pleural exudate. In cotton granulomatous tissue it was 5- to 6-fold higher compared to the enzyme activity of the skeletal muscles. The in vivo increase in gamma-GT activity was prevented from occurring in proportion to the anti-inflammatory potencies of the test drugs given orally. The prevention of enzyme activity was observed with indomethacin in carrageenin-induced edematous paw tissue and with phenylbutazone in both adjuvant arthritis and carrageenin-induced pleural exudate. Prednisolone was observed to be the most potent drug against cotton granuloma. Nonsteroidal anti-inflammatory drugs (NSAIDs) were not found to affect enzyme activity in vitro when incubated with cellular infiltrate from a cotton pellet granuloma. Differences in certain physico-chemical characteristics, viz. stability at 50 degrees, pH dependency and effects of solvents, were not discernible in between the enzyme activities of the untreated and edematous paw tissues. The studies thus suggest that measurement of gamma-GT in inflammation may prove to be a valuable biochemical marker for the assessment of anti-inflammatory activity of drugs in vivo.