Antimony resistance and trypanothione in experimentally selected and clinical strains of Leishmania panamensis

Abstract

The participation of trypanothione in clinical and experimental antimony (Sb) resistance in Leishmania panamensis was examined by using specific inhibitors. Buthionine sulfoximine (BSO) significantly reversed the resistance to trivalent Sb (Sb(III)) of promastigotes of experimentally derived Sb-resistant lines, supporting the participation of a trypanothione-mediated mechanism of resistance. In contrast, promastigotes of strains isolated at the time of clinical treatment failure and resistant to pentavalent Sb (Sb(V)) as intracellular amastigotes were not cross resistant to Sb(III), and BSO had little or no effect on susceptibility. Difluoromethylornithine did not alter the Sb(III) susceptibilities of experimentally selected lines or clinical strains. The mechanisms of acquired resistance emerging in clinical settings may differ from those selected by in vitro exposure to Sb.

FIG. 1.

Effects of inhibitors of T(SH)₂ synthesis on the susceptibility of the cloned parental 1166 WT, Sb-resistant lines generated by experimental selection in vitro, and U937 macrophages. (A) ED₅₀s of Sb^III for promastigotes of lines selected as promastigotes by using Sb^III (error bars correspond to the mean ± 2 standard errors); (B) dose-response to Sb^III of line SRA898, selected as amastigotes with Sb^V; (C) sensitivity of human U937 macrophages to Sb^V. alone and with different concentrations of BSO (the results of one representative experiment of three independent experiments performed are shown). The results of the statistical analyses are as follows: *, ANOVA, Duncan, P < 0.05 for Sb^III versus BSO-Sb^III (a) and Sb^III versus BSO-DFMO-Sb^III (b); **, Kruskal-Wallis, P = 0.026 for differences between Sb^III versus BSO-Sb^III and Sb^III versus BSO-DFMO-Sb^III.