THE ROLE OF CYSTEINE IN THE REGULATION OF BLOOD GLUTATHIONE-PROTEIN MIXED DISULFIDES IN RATS TREATED WITH DIAMIDE

The kinetics of GSH, GSSG, and thiol-protein mixed disulfides (RS-SP) of GSH (GS-SP) and cysteine (CYS-SP) were studied in rat blood and liv er in the time range 0-120 min after treatment with 100 and 200 mg/kg ip of diamide, Total consumption (10 min) and regeneration (120 min) o f blood GSH, matched by parallel increases and decreases in RS-SP, wer e observed. GSSG did not change appreciably. No dose-effect relationsh ip was obtained with either treatment. On the contrary, in vitro treat ment of blood with 0.75 mM diamide provoked the same trends of GSH and RS-SP as in vivo (e.g., reversible modifications), whereas treatment with 1.5 mM caused drops and rises in GSH and RS-SP, respectively, wit hout any subsequent return to control values, The presence of a hemati c factor responsible for RS-SP regulation is hypothesized in the in vi vo experiment. Successive experiments involving in vitro pretreatment with 2 mM diamide and treatment with 0.5 mM of various thiols indicate d that cysteine (CYS)? but not GSH or N-acetylcysteine, rapidly restor ed erthyrocyte GSH and RS-SP to their basal levels, No evident sign of hemolysis was observed in these experiments. These results indicate t hat CYS is a diffusible thiol important for RS-SP regulation, Analysis of whole blood of rats treated with 100 mg/kg ip diamide and the pres ence of two reversible peaks (about 10 times the corresponding control level) of CYS-SP and free CYS confirmed the plausible role of CYS in maintaining the reversibility of the process, Preliminary results in l iver of rats treated with 100 mg/kg diamide indicated that CYS may act by metabolic cooperation between organs. We suggest that CYS may have a role in the regulation of the intracellular redox state of rat eryt hrocytes during oxidative stress. (C) 1998 Academic Press.