Iron as a critical determinant for survival, oxidative stress, and infectivity of Leishmania parasites

Iron is an essential for all living organisms, including humans, and is present in RBCs & other iron-binding proteins that play crucial roles in oxygen transport, DNA synthesis & electron transport. Similarly, iron also plays a critical role in parasite biology. The unicellular Leishmania parasites scavenge essential iron inside host macrophages. We investigated the impact of iron on parasite growth, apoptosis, oxidative stress, and the expression of proteins involved in ROS, thiol metabolism, Fe-S clusters, and infectivity in macrophages. Our findings revealed that optimum iron concentrations promote parasite proliferation, whereas higher levels induce toxicity, leading to DNA fragmentation and caspase-like activity. Iron supplementation enhances parasite tolerance to oxidative stress by decreasing intracellular ROS and increasing total intracellular thiol content in a concentration-dependent manner. However, iron depletion increases ROS levels and decreases total thiol content in a concentration-dependent manner, which disrupts redox homeostasis. To support our finding, we further exposed these treated parasites to menadione, which supports that iron-supplemented cells can better survive under oxidative stress than the depleted cells. Furthermore, extra iron availability increases the expression of key metabolic proteins, Fe-S clusters (Nbp35, Frataxin, IScU) and thiol metabolism (TryS, TryR, CS, SAT, cTXN, cTXNPx), while under iron-depleted conditions these proteins were downregulated except frataxin. In vitro infectivity demonstrated that iron supplementation enhances parasite infectivity, while iron depletion impairs percentage infectivity. Our study demonstrates the roles of iron in the survival, redox regulation, and virulence of L. donovani , which can correlate with the role of cellular iron homeostasis in VL pathogenesis.