Iron enhances generation of free radicals by Artemisinin causing a caspase-independent, apoptotic death in Leishmania donovani promastigotes

Abstract

An increasing incidence of unresponsiveness to antimonials in Leishmaniasis has led to identification of plant-derived anti-leishmanial compounds like Artemisinin. Since iron-mediated generation of free radicals sustains the anti-malarial activity of Artemisinin, this study investigated whether similar mechanisms accounted for its activity in Leishmania promastigotes. Artemisinin effectively disrupted the redox potential via an increased generation of free radicals along with a decrease in levels of non-protein thiols. Attenuation of its IC₅₀ by a free radical scavenger N-acetyl l-cysteine and an iron chelator desferoxamine established the pivotal role of free radicals and of the potentiating effect of iron. An enhanced Fluo-4 fluorescence reflected Artemisinin-induced mobilization of intracellular calcium, which triggered apoptosis. However, the absence of any detectable caspase activity indicated that the leishmanicidal activity of Artemisinin is mediated by an iron-dependent generation of reactive intermediates, terminating in a caspase-independent, apoptotic mode of cell death.