Assessing the effect of antimony pressure on trypanothione reductase activity in Leishmania (Viannia) braziliensis.

Leishmania parasites have an oxidative and chemical defense mechanism called trypanothione system (T[SH]2), the most abundant thiol system in trypanosomatids. This system has a central role in processing pentavalent antimony and resistance has been related to a better capacity to metabolize it through the activation of T[SH]2 enzymatic cascade. A biochemical approach was applied to assess the effect of trivalent (SbIII) and pentavalent antimony (SbV) on Trypanothione Reductase (TR) activity of two Leishmania (Viannia) braziliensis clinical isolates, which were labeled as responder (R) and non-responder (NR) after patient treatment with Glucantime®. Both isolates were characterized based on in vitro susceptibility to SbIII and SbV and trypanothione reductase (TR) activity. SbIII and SbV discriminated susceptibility profiles in all parasite forms, since isolate NR had significantly higher EC50 values than isolate R. Differences were observed in TR activity between promastigotes, axenic amastigotes and intracellular amastigotes: R (0.439 ± 0.009, 0.103 ± 0.01 and 0.185 ± 0.01AU.min-1.µg of protein-1) and NR (1.083 ± 0.04, 0.914 ± 0.04 and 0.343 ± 0.04 AU. min-1.µg of protein-1), respectively. Incubation with SbIII and SbV using each form EC50 value caused a time-dependent differential effect on TR activity suggesting that oxidative defense is related to the antimony susceptibility phenotype. Data gathered here shows a biochemical approach able to discriminate two L. (V.) braziliensis clinical isolates measurements TR activity of promastigotes, axenic amastigotes and intracellular amastigotes.