Molecular events leading to death of Leishmania donovani under spermidine starvation after hypericin treatment.

We have previously reported that the hypericin treatment caused spermidine starvation and death of Leishmania parasite. Here, we report different molecular events under spermidine starvation and potential role of spermidine in processes other than redox homeostasis of the parasite. We have analyzed changes in expression of several genes by using quantitative gene expression analysis. Further, these changes at molecular level were also confirmed by using biochemical and cellular studies. Altered expression of several genes involved in redox metabolism, hypusine modification of eIF5A, DNA repair pathway and autophagy was observed. There was decrease in Sir2RP expression after hypericin treatment and this decrease has been found to be associated with induced ROS due to hypericin treatment as it has been rescued by either trypanothione or spermidine supplementation. Translation initiation in the parasite was decreased upon spermidine starvation. We also observed increased AMPK expression upon hypericin treatment. The increase in intracellular ATP and NAD+ levels as well as decrease in Sir2RP expression of the parasite are cytoprotective mechanism towards generated ROS due to hypericin treatment possibly by inducing autophagy as indicated by increase in autophagy related gene expression and acridine orange staining. However, the autophagy needs to be established using more rigorous methodologies.