Aloe vera leaf exudate induces a caspase-independent cell death in Leishmania donovani promastigotes

Abstract

Leishmaniasis constitutes a complex of diseases with clinical and epidemiological diversity and includes visceral leishmaniasis, a disease that is fatal when left untreated. In earlier studies, the authors reported thatAloe veraleaf exudate (AVL) is a potent antileishmanial agent effective in promastigotes ofLeishmania braziliensis,Leishmania mexicana,Leishmania tropica,Leishmania majorandLeishmania infantumand also in axenic amastigotes ofLeishmania donovani. In the present study, it has been demonstrated that, in promastigotes ofL. donovani(IC50=110 μg ml−1), AVL mediates this leishmanicidal effect by triggering a programmed cell death. Incubation of promastigotes with AVL caused translocation of phosphatidylserine to the outer leaflet of the plasma membrane as measured by annexin V binding, which was accompanied by loss of mitochondrial membrane potential, release of cytochromecinto the cytosol and concomitant nuclear alterations that included chromatin condensation, deoxynucleotidyltransferase-mediated dUTP end labelling and DNA laddering. As this AVL-induced leishmanicidal effect could not be inhibited by protease inhibitors including Z-Val-Ala-dl-Asp (methoxy)-fluoromethylketone, a broad-spectrum caspase inhibitor, non-involvement of caspases and major proteases was suggested. Additionally, AVL treatment caused no increase in cytosolic Ca2+or generation of reactive oxygen species, indicating that although promastigote death was induced by an apoptotic-like mechanism similar to metazoan apoptosis, the pathways of induction and/or execution differed at the molecular level.