Expression of citrulline-nitric oxide cycle in lipopolysaccharide and cytokine-stimulated rat astroglioma C6 cells

Nitric oxide (NO) is involved in many physiological and pathological proces ses in the brain. NO is synthesized from arginine by nitric oxide synthase (NOS), with citrulline generated as a by-product of the reaction. Thus, cit rulline can by recycled to arginine by argininosuccinate synthetase (AS) an d argininosuccinate lyase (AL) via the citrulline-NO cycle. Rat astroglioma CG cells were treated with bacterial lipopolysaccharide (LPS), interferon- gamma (IFN gamma) and tumor necrosis factor-alpha, and the expression of th e enzymes of the citrulline-NO cycle was investigated by RNA blot and immun oblot analyses. NO production from arginine and citrulline was also assesse d, iNOS mRNA and protein were induced 6-12 h after stimulation with LPS and cytokines and decreased at 24 h. AS mRNA increased up to 12 h and decrease d at 24 h. AS protein increased gradually up to 48 h. On the other hand, AL mRNA remained unchanged by stimulation. NO production from arginine was en hanced by the treatment with LPS and cytokines. NO production was also obse rved when arginine was replaced by citrulline. These results indicate that NO production is enhanced in LPS- and cytokine-stimulated C6 cells due to i nduction of iNOS and that the citrulline-arginine recycling is important fo r NO production. (C) 1999 Elsevier Science B.V. All rights reserved.