INHIBITION OF NITRIC-OXIDE SYNTHASE EXPRESSION BY PPM-18, A NOVEL ANTIINFLAMMATORY AGENT, IN-VITRO AND IN-VIVO

We studied the effect of PPM-18, a chemically synthesized naphthoquino ne derivative and also an anti-inflammatory agent, on the lipopolysacc haride (LPS)-activated inducible NO synthase (iNOS) expression in rat alveolar macrophages. Pretreatment of macrophages with PPM-18 (0.1-10 mu M) significantly inhibited nitrite production, iNOS protein express ion and iNOS mRNA accumulation. PPM-18 did not directly affect the enz ymic activities of iNOS and other constitutive NOS forms. The LPS-indu ced increase in nuclear transcription factor kappa B (NF-kappa B) p65 and p50 in nucleus was suppressed by PPM-18 (10 mu M). Moreover electr ophoretic mobility-shift assays demonstrated that PPM-18 inhibited DNA binding to NF-kappa B induced by LPS in whole cells but not when adde d in the nuclear extract, suggesting that PPM-18 did not interfere dir ectly with the binding of NF-kappa B to DNA and that some events had t o be processed before NF-kappa B could bind DNA. Examination of NF-kap pa B showed that PPM-18 stabilized the NF-kappa B inhibitor, I kappa B alpha, by preventing its degradation from NF-kappa B. Therefore the s tabilization of I kappa B alpha might have contributed to the inhibiti on of NF-kappa B activation. These results also indicate strongly that NF-kappa B is involved in the production of NO on stimulation by LPS. PPM-18 significantly decreased the production of tumour necrosis fact or cc in response to LPS. PPM-18 protects mice against LPS-induced let hal toxicity. These results also indicate that PPM-18 is a potent inhi bitor of iNOS expression by blocking the binding of NF-kappa B to prom oter and exerts a beneficial effect in the mouse model of sepsis.