Nicotine enhancement of lipopolysaccharide/interferon-gamma-induced cytotoxicity with elevating nitric oxide production

Nicotine has been shown to induce relaxation via nitric oxide (NO) production with activation of endothelium nitric oxide synthase (eNOS), however the effect of nicotine on lipopolysaccharide/interferon-gamma (LPS/IFN-gamma)-induced NO production and inducible NOS (iNOS) gene expression is still undefined. Here, nicotine alone did not affect the NO and PGE2 production in RAW264.7 and primary peritoneal macrophages. Interestingly, nicotine showed the dose-dependent stimulatory effect on LPS (20 ng/ml)/IFN-gamma (10 ng/ml)-induced NO but not PGE2 production in both cells. Although nicotine stimulates NO production in the presence of LPS/IFN-gamma, LPS at the dose of 20 ng/ml, nicotine showed no obvious inductive effect on the expression of iNOS protein by Western blotting in both cells. However, nicotine significantly stimulates LPS (2.5, 5 ng/ml)/IFN-gamma (10 ng/ml)-induced iNOS expression and NO production in RAW264.7 cells. Cytotoxicity assay showed that nicotine enhanced LPS (20 ng/ml) and IFN-gamma (10 ng/ml)-induced cytotoxicity, which was inhibited by an NOS inhibitor N-nitro-L-arginine (NLA) in RAW264.7 cells. Direct and indirect NOS activity assays indicated that nicotine did not affect NOS activity. And, iNOS protein stability was not changed by nicotine after LPS/IFN-gamma treatment. These data indicates that nicotine may potentiate LPS/IFN-gamma-induced cytotoxic effects by enhancing NO production; enhancing iNOS gene expression induced by LPS/IFN-gamma is involved. A cross-talk between inflammation and smoking was proposed in the present study.