Nitric oxide at a low concentration protects murine macrophage RAW264 cells against nitric oxide-induced death via cGMP signaling pathway.

1. We investigated the cytoprotective effect of low-dose nitric oxide (NO) on NO-induced cell death in mouse macrophage-like cell line RAW264. 2. Sodium nitroprusside (SNP), an NO donor, at a high concentration (4 mM) released cytochrome c from mitochondria and induced death in RAW264 cells. Acetyl-L-aspartyl-L-glutamyl-L-valyl-L-aspart-1-al (Ac-DEVD-CHO, 100-200 microM), a caspase-3 inhibitor, attenuated the SNP-induced cell death in a concentration-dependent manner. 3. Pretreatment with 100 microM SNP for 24 h, which had no effect on cell viability, attenuated the cell death and reduced cytochrome c release from mitochondria to the cytosol induced by 4 mM SNP. 4. LY83583 (1-3 microM) and 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 30-100 microM), soluble guanylate cyclase inhibitors, negated the protective effect of the 100 microM SNP pretreatment. 5. Pretreatment with 1 mM dibutylyl guanosine-3',5'-cyclic monophosphate (DBcGMP), a cell-permeable guanosine-3',5'-cyclic monophosphate (cGMP) analogue, for 24 h inhibited both cytochrome c release and cell death induced by SNP. 6. Protein kinase G inhibitor KT5823 (10 microM) significantly reduced the cytoprotective effects of low-dose SNP and DBcGMP. 7. These results indicate that low-dose NO protects RAW264 cells from NO-induced apoptosis through cGMP production and activation of protein kinase G.