ROLES OF IL-1 AND TNF-ALPHA IN ENDOTOXIN-INDUCED ACTIVATION OF NITRIC-OXIDE SYNTHASE IN CULTURED RAT-BRAIN CELLS

In astrocytes and microglia, bacterial lipopolysaccharide (LPS) stimul ates production and release of interleukin-1 beta (IL-1 beta), tumor n ecrosis factor-alpha (TNF-alpha), and nitric oxide (NO). Although IL-1 beta and TNF-alpha are themselves capable of inducing NO synthase (NO S) in glia, the specific factors mediating LPS induction of NOS in bra in have not been identified. To determine whether LPS induction of NOS in brain cells is mediated by IL-1 or TNF-alpha, acting alone or in c oncert, the effects of IL-1-receptor antagonist (IL-1Ra) and of TNF-so luble receptor (TNFsRp55), presented individually and in combination, on LPS-induced NOS activity were tested. In glial-enriched mixed prima ry cultures of neonatal rat telencephalic cells, LPS (0.1-100 ng/ml), IL-1 beta (0.01-10 nM), and TNF-alpha (0.1-100 nM) each concentration dependently stimulated accumulation of nitrite, an indicator of NO pro duction. Induction of nitrite accumulation by LPS and by IL-1 was bloc ked by N-omega-nitro-L-arginine methyl ester and N-omega-monomethyl-L- arginine, indicating that it was mediated by NOS. TNF-a alone induced NO production weakly as compared with IL-1, but combined submaximal co ncentrations of IL-1 beta (1 nM) and TNF-alpha (10 nM) induced NOS syn ergistically. Furthermore, TNFsRp55 and IL-1Ra each produced a dose-de pendent partial inhibition of the NO response to LPS, and the effect o f TNFsRp55 was equal to or greater than that of IL-1Ra. TNFsRp55 and I L-1Ra in combination were not significantly more effective than TNFsRp 55 alone. The results indicate that LPS induction of NOS activity in b rain cells is mediated in part by both IL-1 beta and TNF-alpha.