Inhibition of lipopolysaccharide-induced inducible nitric oxide synthase expression by a novel compound, mercaptopyrazine, through suppression of nuclear factor-kappaB binding to DNA

Macrophage cells in response to cytokines and endotoxins produced a large amount of nitric oxide (NO) by expression of inducible nitric oxide synthase (iNOS), resulting in acute or chronic inflammatory disorders including septic hypotension and atherosclerosis. In the present study, we investigated the effect and the mechanism of mercaptopyrazine (MP) in the induction of iNOS and NO production as a culminating factor for several inflammatory disorders. Pretreatment of MP alleviated the mortality of endotoxemic mice receiving a lethal bolus of lipopolysaccharide (LPS), which was associated with the reduced levels of serum nitrite/nitrate and IL-1beta. In RAW264.7 mouse macrophage cells, MP (300microM) inhibited both protein and mRNA levels of iNOS stimulated by LPS/interferon-gamma (IFNgamma) up to 50%. The nuclear factor-kappa B (NF-kappaB)-driven transactivation was also suppressed by MP to the same degree. Treatment of MP reduced the binding of NF-kappaB to the oligonucleotides containing NF-kappaB consensus sequence, while it did not affect the translocation of NF-kappaB to nuclear. Suppression of NF-kappaB activity by MP was completely reversed by a reducing agent, dithiothreitol, implying that MP might oxidize the sulfhydryl group(s) of DNA binding domain of NF-kappaB. In conclusion, MP would be one of interesting candidates or chemical moieties of iNOS expression inhibitor via specific suppression of NF-kappaB binding to DNA, and be useful as a chemopreventive agent or a therapeutic against iNOS-associated inflammatory diseases.