18β-Glycyrrhetinic Acid Triggers Curative Th1 Response and Nitric Oxide Up-Regulation in Experimental Visceral Leishmaniasis Associated with the Activation of NF-κB

Abstract

The efficacy of 18β-glycyrrhetinic acid (GRA), a pentacyclic triterpene belonging to the β-amyrin series of plant origin, was evaluated in experimental visceral leishmaniasis. GRA is reported to have antitumor and immunoregulatory activities, which may be attributable in part to the induction of NO. Indeed, an 11-fold increase in NO production was observed with 20 μM GRA in mouse peritoneal macrophages infected with Leishmania donovani promastigotes. In addition to having appreciable inhibitory effects on amastigote multiplication within macrophages (IC50, 4.6 μg/ml), complete elimination of liver and spleen parasite burden was achieved by GRA at a dose of 50 mg/kg/day, given three times, 5 days apart, in a 45-day mouse model of visceral leishmaniasis. GRA treatment resulted in reduced levels of IL-10 and IL-4, but increased levels of IL-12, IFN-γ, TNF-α, and inducible NO synthase, reflecting a switch of CD4+ differentiation from Th2 to Th1. This treatment is likely to activate immunity, thereby imparting resistance to reinfection. GRA induced NF-κB migration into the nucleus of parasite-infected cells and caused a diminishing presence of IκB in the cytoplasm. The lower level of cytoplasmic IκBα in GRA-treated cells resulted from increased phosphorylation of IκBα and higher activity of IκB kinase (IKK). Additional experiments demonstrated that GRA does not directly affect IKK activity. These results suggest that GRA exerts its effects at some level upstream of IKK in the signaling pathway and induces the production of proinflammatory mediators through a mechanism that, at least in part, involves induction of NF-κB activation.

Bioactive Component of Licorice as an Antileishmanial Agent

“…GRA exhibited potent in vitro activity against intracellular L. donovani amastigotes (IC 50 , 4.3 μg/ml); it was devoid of any obvious cytotoxicity on macrophage host cells, because the cytotoxic concentration causing 50% cell death was ~100 μg/ml [19]. The infected mice treated with GRA were completely cured.…”

“…Moreover, this therapy was seen to be effective in mice with established disease-progressive Th2 response. After treatment and resolution of parasitism, the cytokine profile indicated a switch to a protective Th1 pattern associated with upregulation of NO [19].…”

“…Upon pathogenic challenge, the large multisubunit protein kinase, inhibitor of nuclear factor kappa-B kinase subunit beta(IKK) causes rapid proteasomal degradation of IκBα, thereby releasing NFκB and allowing its nuclear translocation. This event is inhibited in Leishmania donovani infection thereby promoting parasite survival [19] (Figure 4). GRA, on the other hand, activates NF-κB through the regulation of genes essentially involved in encoding proinflammatory cytokines and inflammatory mediators such as NO.…”

“…This in turn was achieved by modulating the upstream signal leading to IKK (inhibitor of nuclear factor kappa-B kinase subunit beta) activation, that is, without directly interfering with IKK (inhibitor of nuclear factor kappa-B kinase subunit beta). Overall this signaling activation by GRA led to degradation of IκBα leading to the translocation of NF-κB in the nucleus and transcriptional activation of iNOS and proinflammatory cytokines [19] (Figure 4). The antileishmanial activity of GRA was dependent on the iNOS activity and NO production was further justified by addition of a specific NOS inhibitor, N G -monomethyl-L-arginine (NMMA).…”

Assessment of β-lapachone loaded in lecithin-chitosan nanoparticles for the topical treatment of cutaneous leishmaniasis in L. major infected BALB/c mice

“…I.e. berberine [32] and 18b-glycyrrhetinic acid [33] had antileishmanial activity via MAPKinases, iNOS induction and NO up-regulation. However, they showed inhibitory effects on LPS-iNOS in macrophages [34,35].…”