Glycyrrhizic acid suppresses cox2-mediated anti-inflammatory responses during Leishmania donovani infection

Objectives: The aim of the present study was to characterize glycyrrhizic acid (GA) and assess its immunomo-dulatory potential in a model of experimental visceral leishmaniasis. Methods: The antileishmanial activity of GA was tested in an amastigote–macrophage model and its non-cytotoxic dose was measured by a cell viability assay. To understand the effector mechanism of GA-treated macrophages against leishmanial parasites, real-time PCR analysis of inducible nitric oxide synthase 2 (iNOS2) was carried out followed by measurement of nitric oxide generation by Griess reagent. The effect of GA on the production of cytokines, such as interleukin (IL)-12, tumour necrosis factor (TNF)-a, IL-10 and trans-forming growth factor (TGF)-b, was measured by ELISA (protein) and real-time PCR. The expression of iNOS2 and cyclooxygenase-2 (Cox-2) was studied by western blotting. The parasite burden of the liver and spleen following GA treatment was determined by the stamp-smear method, and T cell proliferation was assessed via [3H]thymidine uptake, measured by a liquid scintillation counter. Results: Results showed that GA treatment caused an enhanced expression of iNOS2 along with inhibition of Cox-2 in Leishmania donovani-infected macrophages. GA treatment in infected macrophages enhanced the expression of IL-12 and TNF-a, concomitant with a down-regulation of IL-10 and TGF-b. GA increased macro-phage effector responses via inhibition of Cox-2-mediated prostaglandin E2 release in L. donovani-infecte