Authors

Discussion

Visceral Leishmaniasis is a neglected tropical disease, caused by parasitic protozoa of the Leishmania genus. In recent years, the polyene amphotericin B (AmB) has emerged as a treatment of choice against the disease. The drug acts by binding ergosterol in the parasite membrane, leading to cell lysis.  L. Infantum promastigotes were selected for resistance to AmB. Sterol analysis of the resistant line identified a loss of ergosterol and an increase in 5,7, 24(28)-ergostatrienol.  Genome sequence analysis revealed mutations in sterol C22 desaturase which converts 5,7, 24(28)-ergostatrienol to ergostatetraenol. The mutation comprises a 21 base pair deletion corresponding to a 7 amino-acid hydrophobic patch at the periphery of the enzyme. Over-expression of this mutant allele in WT parasites also yielded amphotericin B resistance while over-expression of the WT allele in the mutant cell line restored sensitivity. Moreover, the resistant parasites retained virulence in mice and the resistant line was not cleared by amphotericin B whereas WT were in treated mice. The data indicate that amphotericin B resistance in Leishmania infantum can come about through changes to the sterol pathway, as previously indicated in other amphotericin B resistance leishmania lines where mutations to different enzymes in the sterol pathway were noted.  Interestingly, the L. infantum AmB resistant line described here is hypersensitise to nitric oxide inducing agents and also to pentamidine, as has been described for other AmB resistant lines, offering a potential route to treatment of resistant cases should their emergence become problematic in the field.