Platelet-Activating Factor Receptor Contributes to Antileishmanial Function of Miltefosine

Abstract

Miltefosine [hexadecylphosphocholine (HPC)] is the only orally bioavailable drug for the disease visceral leishmaniasis, which is caused by the protozoan parasite Leishmania donovani. Although miltefosine has direct leishmanicidal effects, evidence is mounting for its immune system–dependent effects. The mechanism of such indirect antileishmanial effects of miltefosine remains to be discovered. As platelet-activating factor and HPC share structural semblances and both induce killing of intracellular Leishmania, we surmised that platelet-activating factor (PAF) receptor had a significant role in the antileishmanial function of miltefosine. The proposition was supported by molecular dynamic simulation of HPC docking into PAF receptor and by comparison of its leishmanicidal function on PAF receptor–deficient macrophages and mice under HPC treatment. We observed that compared with wild-type macrophages, the PAF receptor–deficient macrophages showed 1) reduced binding of a fluorescent analog of HPC, 2) decreased TNF-α production, and 3) lower miltefosine-induced killing of L. donovani. Miltefosine exhibited significantly compromised leishmanicidal function in PAF receptor–deficient mice. An anti-PAF receptor Ab led to a significant decrease in miltefosine-induced intracellular Leishmania killing and IFN-γ production in a macrophage–T cell coculture system. These results indicate significant roles for PAF receptor in the leishmanicidal activity of HPC. The findings open new avenues for a more rational understanding of the mechanism of action of this drug as well as for improved therapeutic strategies.

Systematic Review of Host-Mediated Activity of Miltefosine in Leishmaniasis through Immunomodulation

“…donovani are known to suppress the activation of p38 mitogen-activated protein kinases (p38MAPK), which is required for the production of proinflammatory Th1 cytokines (36). Miltefosine was able to increase the levels of p38MAPK activation in BALB/c-derived peritoneal macrophages, which in turn increased IL-12 levels in a dose-dependent manner within 48 h posttreatment (19, 29, 30). Moreover, miltefosine treatment of isolated peripheral blood mononuclear cells (PBMCs) derived from monocytes of VL patients resulted in an 8-fold rise in IL-12 levels (37).…”

“…In vitro studies (Table 1) were the first to propose and demonstrate that miltefosine induces a Th1 response via various immunological pathways. Applying miltefosine to Leishmania -infected splenocytes resulted in an induction of a Th1 response shown primarily by increased IFN-γ (19, 29–31). IFN-γ enables class switching from immunoglobulin G1 (IgG1) to IgG2.…”

“…Also, PBMCs isolated from patients with advanced VL showed increased Th1 cytokines after ex vivo miltefosine treatment, further illustrating miltefosine-driven immunomodulation (38). Additionally, a functional role of miltefosine in the synthesis of TNF-α has been shown in vitro (29, 39, 40). BALB/c mouse-derived macrophages with a knockout platelet aggregation factor (PAF) receptor function displayed a complete lack of response to miltefosine, indicated by diminished miltefosine-induced parasite killing (29).…”

“…Additionally, a functional role of miltefosine in the synthesis of TNF-α has been shown in vitro (29, 39, 40). BALB/c mouse-derived macrophages with a knockout platelet aggregation factor (PAF) receptor function displayed a complete lack of response to miltefosine, indicated by diminished miltefosine-induced parasite killing (29). Downregulation of the PAF receptor was also found to enhance IL-4 production, and suppress IFN-γ levels, resulting in progressive VL infection (29).…”

“…BALB/c mouse-derived macrophages with a knockout platelet aggregation factor (PAF) receptor function displayed a complete lack of response to miltefosine, indicated by diminished miltefosine-induced parasite killing (29). Downregulation of the PAF receptor was also found to enhance IL-4 production, and suppress IFN-γ levels, resulting in progressive VL infection (29). Miltefosine is a structural analogue of PAF, and it was found that miltefosine activation of the PAF receptor led to increased IL-12 and TNF-α, while no effect was observed for PAF receptor-deficient macrophages (29, 41).…”