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-γ (LPS/IFN-γ)-induced NO production and inducible NOS (iNOS) gene expression is still undefined. Here, nicotine alone did not affect the NO and PGE 2 production in RAW264.7 and primary peritoneal macrophages. Interestingly, nicotine showed the dose-dependent stimulatory effect on LPS (20 ng/ml)/IFN-γ (10 ng/ml)-induced NO but not PGE2 production in both cells. Although nicotine stimulates NO production in the presence of LPS/IFN-γ, 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-γ (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-γ (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-γ treatment. These data indicates that nicotine may potentiate LPS/IFN-γ-induced cytotoxic effects by enhancing NO production; enhancing iNOS gene expression induced by LPS/IFN-γ is involved. A cross-talk between inflammation and smoking was proposed in the present study.
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