Date Published: April 7, 2015
Publisher: Public Library of Science
Author(s): Raquel García-Hernández, Verónica Gómez-Pérez, Santiago Castanys, Francisco Gamarro, Louis Maes. http://doi.org/10.1371/journal.pntd.0003704
Abstract: Drug resistance represents one of the main problems for the use of chemotherapy to treat leishmaniasis. Additionally, it could provide some advantages to Leishmania parasites, such as a higher capacity to survive in stress conditions. In this work, in mixed populations of Leishmania donovani parasites, we have analyzed whether experimentally resistant lines to one or two combined anti-leishmanial drugs better support the stress conditions than a susceptible line expressing luciferase (Luc line). In the absence of stress, none of the Leishmania lines showed growth advantage relative to the other when mixed at a 1:1 parasite ratio. However, when promastigotes from resistant lines and the Luc line were mixed and exposed to different stresses, we observed that the resistant lines are more tolerant of different stress conditions: nutrient starvation and heat shock-pH stress. Further to this, we observed that intracellular amastigotes from resistant lines present a higher capacity to survive inside the macrophages than those of the control line. These results suggest that resistant parasites acquire an overall fitness increase and that resistance to drug combinations presents significant differences in their fitness capacity versus single-drug resistant parasites, particularly in intracellular amastigotes. These results contribute to the assessment of the possible impact of drug resistance on leishmaniasis control programs.
Partial Text: Leishmaniasis, a neglected tropical parasitic disease that is prevalent in 98 countries spread across three continents, is caused by protozoan parasites belonging to the genus Leishmania ; visceral leishmaniasis (VL), caused by species of the Leishmania donovani complex, is a lethal disease if left untreated. The recommended first-line therapies for VL include: i) pentavalent antimonials (meglumine antimoniate and sodium stibogluconate), except in some regions in the Indian subcontinent where there are significant areas with drug resistance ; ii) the polyene antibiotic amphotericin B or the liposomal amphotericin B formulation AmBisome; iii) the aminoglycoside paromomycin; and iv) the oral drug miltefosine. Although WHO [1, 3] recommended the use of either a single dose of AmBisome or combinations of anti-leishmanial drugs in order to reduce the duration and toxicity of treatment, to prolong the therapeutic life-span of existing drugs and to delay the emergence of resistance, recent experimental findings have demonstrated the ability of Leishmania to develop experimental resistance to different drug combinations . The emergence and spread of Leishmania antimonial-resistant parasites have led to a high rate of antimonial failure in India  and have raised questions about the selection and propagation risk of drug resistant parasites [6, 7]. The spread of drug-resistant parasites in the field probably depends on their transmission potential, which is influenced by, among other factors, the relative fitness of drug-resistant versus drug-susceptible parasites.