Chromone linked nitrone derivative induces the expression of iNOS2 and Th1 cytokines but reduces the Th2 response in experimental visceral leishmaniasis.

In our previous work we have shown that the novel synthetic chromone derivative could effectively inhibit the Leishmania donovani replication in vitro and in vivo with less cytotoxicity on murine splenocytes. The aim of the present study is to explore the possible mechanism of anti-leishmanial effect of C-(6-methyl-4-oxo-4H-1-benzopyran-3-yl)-N-(p-tolyl) nitrone (designated as NP1) in vitro and in vivo in experimental visceral leishmaniasis caused by L. donovani. The cytotoxic effect of this derivative was studied in murine peritoneal macrophages by MTT method. NP1 at a dose of 17.06 μM showed 50% inhibition on L. donovani promastigotes but found less cytotoxic to the RAW 264.7 cells. Even the higher concentration of IC50 (up to four fold) did not exert much cytotoxic effect on RAW 264.7. Interestingly, NP1 at lower concentration (8.53 μM) could inhibit 50% of intracellular amastigotes in murine peritoneal macrophages. L. donovani is known to exert its pathogenic effects mainly by the suppression of NO generation and subversion of the cellular inflammatory responses in the macrophages. NP1 was found to induce a potent host-protective immune response by enhancing NO generation and iNOS2 expression at mRNA level and by up-regulating proinflammatory cytokines such as IL-12 and IFN-γ and limiting the expression of IL-10 in vivo. The NO dependent killing was further confirmed in iNOS(-/-) mice compared to wild type. In agreement with the fact, induced synthesis of IL-12 and IFN-γ and associated down-regulation of IL-10 by the treatment of NP1 clearly indicated the possibility of novel strategy of drug development against Leishmania infection.