Cytokine-induced nitric oxide generation by cultured astrocytoma cells involves Ca(++)-calmodulin-independent NO-synthase.

The effect of several cytokines (IL1 beta and TNF alpha) on the inducible biosynthesis and release of NO by cultured astrocytoma cells was investigated and compared to that observed following pretreatment of cells with LPS. Preincubation for 4, 12, 24 and 48 h of astrocytoma cells with IL1 beta (10 ng ml-1), TNF alpha (500 U ml-1) and LPS (0.5 micrograms ml-1) enhanced their ability to inhibit thrombin-induced platelet aggregation through the release of an NO-like factor and increased nitrite levels in supernatants of stirred cells. The enhancement of NO production induced by cytokines as well as LPS was mediated by a time-dependent increase of NO-synthase activity in cell homogenates being mainly Ca(++)-calmodulin-independent. However, LPS activated earlier than cytokines the inducible NO-synthase and its effect was, at least in part, related to the release of IL1 beta by astrocytoma cells. In conclusion, the present data show, for the first time, that astrocytoma cells possess a cytokine-inducible Ca(++)-calmodulin-independent NO-synthase, whose activation seems to occur with a mechanism different from that described for LPS.