Lipase Precursor-Like Protein Promotes Miltefosine Tolerance in Leishmania donovani by Enhancing Parasite Infectivity and Eliciting Anti-inflammatory Responses in Host Macrophages

The oral drug miltefosine (MIL) was introduced in the Indian subcontinent in the year 2002 for the treatment of visceral leishmaniasis (VL). However, recent reports on its declining efficacy and increasing relapse rates pose a serious concern. An understanding of the factors contributing to MIL tolerance in Leishmania parasites is critical. In the present study, we assessed the role of the lipase precursor-like protein (Lip) in conferring tolerance to miltefosine by episomally overexpressing Lip in Leishmania donovani (LdLip(++)). We observed a significant increase (similar to 3-fold) in the MIL 50% inhibitory concentration (IC50) at both the promastigote (3.90 +/- 0.68 mu M; P < 0.05) and intracellular amastigote (9.10 +/- 0.60 mu M; P < 0.05) stages compared to the wild-type counterpart (LdNeo) (MIL IC(50)s of 1.49 +/- 0.20 mu M at the promastigote stage and 3.95 +/- 0.45 mu M at the amastigote stage). LdLip(++) parasites exhibited significantly (P < 0.05) increased infectivity to host macrophages and increased metacyclogenesis and tolerance to MIL-induced oxidative stress. The susceptibility of LdLip(++) to other antileishmanial drugs (sodium antimony gluconate and amphotericin B) remained unchanged. In comparison to LdNeo, the LdLip(++) parasites elicited high host interleukin-10 (IL-10) cytokine expression levels (1.6-fold; P < 0.05) with reduced expression of the cytokine tumor necrosis factor alpha (TNF-alpha) (1.5-fold; P < 0.05), leading to a significantly (P < 0.01) increased ratio of IL-10/TNF-alpha. The above-described findings suggest a role of lipase precursor-like protein in conferring tolerance to the oral antileishmanial drug MIL in L. donovani parasites.