A series of pyrazolo(dihydro)pyridines was synthesized and evaluated for antileishmanial efficacy against experimental visceral leishmaniasis (VL). Among all compounds, 6d and 6j exhibited better activity than miltefosine against intracellular amastigotes. Compound 6j (50 mg/kg/day) was further studied against Leishmania donovani/BALB/c mice via the intraperitoneal route for 5 days and displayed >91 and >93% clearance of splenic and liver parasitic burden, respectively. Combination treatment of 6j with a subcurative dose of miltefosine (5 mg/kg) in BALB/c mice almost completely ameliorated the disease (>97% inhibition) by augmenting nitric oxide generation and shifting the immune response toward Th1. Furthermore, investigating the effect of 6j on Leishmania promastigotes revealed that it induced molecular events, such as a loss in mitochondrial membrane potential, externalization of phosphatidylserine, and DNA fragmentation, that ultimately resulted in the programmed cell death of the parasite. These results along with pharmacokinetic studies suggest that 6j could be a promising lead for treating VL as an adjunct therapy with miltefosine.
Innate lymphoid cells (ILCs) are critical mediators of immunological and physiological responses at mucosal barrier sites. Whereas neurotransmitters can stimulate ILCs, the synthesis of small-molecule neurotransmitters by these cells has only recently been appreciated. Group 2 ILCs (ILC2s) are shown here to synthesize and release acetylcholine (ACh) during parasitic nematode infection. The cholinergic phenotype of pulmonary ILC2s was associated with their activation state, could be induced by in vivo exposure to extracts of Alternaria alternata or the alarmin cytokines interleukin-33 (IL-33) and IL-25, and was augmented by IL-2 in vitro. Genetic disruption of ACh synthesis by murine ILC2s resulted in increased parasite burdens, lower numbers of ILC2s, and reduced lung and gut barrier responses to Nippostrongylus brasiliensis infection. These data demonstrate a functional role for ILC2-derived ACh in the expansion of ILC2s for maximal induction of type 2 immunity.
Immuno-modulators in combination with antileishmanial drug miltefosine is a better therapeutic approach for treatment of Visceral Leishmaniasis (VL) as it not only reduces the dose of miltefosine but also shortens the treatment regimen. However, immunological mechanisms behind the perceived benefits of this combination therapy have not been investigated in detail. In the present study, we hypothesized that potential use of drugs that target the host in addition to the parasite might represent an alternative strategy for combination therapy. We investigated immune responses generated in Leishmania donovani infected animals (hamsters and mice) treated with combination of CpG-ODN-2006 and miltefosine at short dose regimen. Infected animals were administered CpG-ODN-2006 (0.4 mg/kg, single dose), as free and liposomal form, either alone or in combination with miltefosine for 5 consecutive days and parasite clearance was evaluated at day 4 and 7 post treatment. Animals that received liposomal CpG-ODN-2006 (lipo-CpG-ODN-2006) and sub-curative miltefosine (5 mg/kg) showed the best inhibition of parasite multiplication (∼97%) which was associated with a biased Th1 immune response in. Moreover, compared to all the other treated groups, we observed increased mRNA expression levels of pro-inflammatory cytokines (IFN-γ, TNF-α and IL-12) and significantly suppressed levels of Th2 cytokines (IL-10 and TGF-β) on day 4 post treatment in animals that underwent combination therapy with lipo-CpG-ODN-2006 and sub-curative miltefosine. Additionally, same therapy also induced heightened iNOS mRNA levels and NO generation, increased IgG2 antibody level and strong T-cell response in these hamsters compared with all the other treated groups. Collectively, our results suggest that combination of lipo-CpG-ODN-2006 and sub-curative miltefosine generates protective T-cell response in an animal model of visceral leishmaniasis which is characterized by strong Th1 biased immune response thereby underlining our hypothesis that combination therapy, at short dose regimen can be used as a novel way of treating visceral leishmaniasis.
Reciprocal changes in histone lysine methylation/demethylation of M(LPS + IFN-g)/M(IL-10) genes is one of the factors that direct macrophage polarization and contribute to host defense/susceptibility toward infection. Although, histone lysine methyltransferases and lysine demethylases orchestrate these events, their role remains elusive in visceral leishmaniasis, a disease associated with macrophage M(IL-10) polarization. In this study, we observed that L. donovani induced the expression of histone lysine methyltransferases Ash1l, Smyd2, and Ezh2 and histone lysine demethylases Kdm5b and Kdm6b in J774 macrophages and BALB/c mice. Chromatin immunoprecipitation analysis revealed that L. donovani facilitated H3K36 dimethylation at TNF-a promoter by Smyd2 and H3K27 trimethylation at inducible NO synthase promoter by Ezh2 to suppress their expression in macrophages. Furthermore, infection-induced Kdm5b and Kdm6b modulated H3K4 and H3K27 trimethylation at IL-12, TNF-a, and arginase-1 promoters, respectively, whereas H3K4 trimethylation by Ash1l at IL-10 promoter induced its expression. Analysis of transductional events revealed that HIF-1a upregulated Kdm5b and Kdm6b expression, whereas Ash1l and Ezh2 expression were induced by transcription factor MeCP2. Additionally, Smyd2 was induced by c-Myc in infected macrophages. Knockdown of Ash1l, Ezh2, Kdm5b, and Kdm6b by specific small interfering RNA and Vivo-Morpholino, as well as inhibition of Smyd2 by its specific inhibitor, AZ505, led to increased protective proinflammatory response and inhibited amastigote multiplication in infected J774 macrophages and BALB/c mice, respectively. Collectively, our findings demonstrate that L. donovani exploits specific histone lysine methyltransferases/demethylases to redirect epigenetic programming of M(LPS + IFN-g)/M(IL-10) genes for its successful establishment within the host.
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