NITRIC-OXIDE REGULATES INTERLEUKIN-1 BIOACTIVITY RELEASED FROM MURINEMACROPHAGES

The bioactivity of interleukin-1 (IL-1), a major proinflammatory cytok ine, can be modulated by a variety of factors including inhibitors of IL-1 production and release and receptor blockade by IL-1 receptor ant agonist and by binding to nonsignaling soluble receptors. This study d emonstrates that the free radical nitric oxide (NO) is also a regulato r of IL-1 bioactivity. Lipopolysaccharide-activated murine macrophage RAW264.7 cells, and lipopolysaccharide plus interferon-gamma-activated murine peritoneal macrophages release IL-1 bioactivity, which is incr eased 10-fold over control levels by 24 h. N-G-Monomethyl L-arginine ( NMMA), a nitric oxide synthase (NOS) inhibitor, almost completely inhi bits the release of IL-1 bioactivity from activated macrophages in a t ime- and concentration-dependent manner with an IC50 of 50 mu M. IL-1 activity was determined by thymocyte proliferation bioassay and by a n ew spectrophotometric bioassay based on TL-1-specific induction of NOS and NO production by an insulinoma cell Line, RnNm5F. Neither NO nor NOS inhibitors present in the macrophage supernatant interfere with th e bioassays. Aminoguanidine and iodonium diphenyl, mechanistically unr elated NOS inhibitors, also prevent the release of IL-1 activity hom R AW 264.7 cells. The addition of the NO donor S-nitrosoacetylpenicillam ine reconstituted the release of IL-1 bioactivity inhibited by NMMA in a concentration-dependent manner. NO appears to increase the amount o f IL-1 protein released by activated macrophages as determined by enzy me-linked immunosorbent assay, but not by mechanisms involving cell de ath nor modification of IL-1 precursor processing. A cGMP donor, 8-bro mo-cGMP, dose-dependently reverses NMMA inhibition of bioactive IL-1 r elease, suggesting that NO regulates IL-1 release by a cGMP-dependent mechanism, These observations suggest that NO stimulation of the activ ity of IL-1, a key mediator of the immune response, may be a potential ly important mechanism for control of IL-1 activity in vivo.