N-ACETYL CYSTEINE INHIBITS INDUCTION OF NO PRODUCTION BY ENDOTOXIN ORCYTOKINE-STIMULATED RAT PERITONEAL-MACROPHAGES, C-6 GLIAL-CELLS AND ASTROCYTES

The present study underscores the importance of N-acetyl cysteine (NAC ), a potent antioxidant, in inhibiting the induction of NO production by lipopolysaccharides (LPS) and cytokines in peritoneal macrophages, C-6 glial cells and primary astrocytes. LPS, interleukin-1 beta (IL-1 beta), interferon-gama (IFN-gamma) and tumor necrosis factor-alpha (TN F-) alone or in combinations induced the production of NO to different degrees. NAC when added 2 h earlier to the addition of these stimuli potentially blocked the increase in NO production in macrophages, astr ocytes and C-6 glial cells. The decrease in NO production by NAC was a ccompanied by a decrease in inducible nitric oxide synthase (iNOS) act ivity, in iNOS protein detected by immunoblot analysis with antibodies against iNOS, and in iNOS mRNA determined by reverse transcriptase co upled polymerase chain reaction (RT-PCR). Time course studies show tha t inhibition was maximum when NAC was added 2 h prior to the addition of LPS and the degree of inhibition decreased progressively with the i ncrease in time interval when NAC was added after the addition of LPS. In addition to NAC, another antioxidant pyrrolidine dithiocarbamate ( PDTC) was also found to inhibit the induction of NO production effecti vely. Since activation of NF-kappa B is necessary for the induction of iNOS, we examined the effect of NAC on the activation of hTF-kappa B. Inhibition of LPS-induced activation of NF-kappa B by NAC in rat peri toneal macrophages suggests that the inhibitory effect of NAC on the i nduction of iNOS is due to the inhibition of NF-kappa B. Besides NO, N AC also blocked the production of TNF-alpha in rat peritoneal macropha ges activated with endotoxin. These results suggest that expression of iNOS and TNF-alpha in macrophages do involve oxygen radicals. The imp ortance of these results in relation to controlling various harmful ef fects of cytokines released by activated macrophages and glial cells i s discussed. (C) 1997 Elsevier Science Inc.