The growth and survival of intracellular parasites depends on the availability of extracellular nutrients. Deprivation of nutrients viz glucose or amino acid alters redox balance in mammalian cells as well as some lower organisms. To further understand the relationship, the mechanistic role of L-arginine in regulation of redox mediated survival of Leishmania donovani promastigotes was investigated. L-arginine deprivation from the culture medium was found to inhibit cell growth, reduce proliferation and increase L-arginine uptake. Relative expression of enzymes, involved in L-arginine metabolism, which leads to polyamine and trypanothione biosynthesis, were downregulated causing decreased production of polyamines in L-arginine deprived parasites and cell death. The resultant increase in reactive oxygen species (ROS), due to L-arginine deprivation, correlated with increased NADP+/NADPH ratio, decreased superoxide dismutase (SOD) level, increased lipid peroxidation and reduced thiol content. A deficiency of L-arginine triggered phosphatidyl serine externalization, a change in mitochondrial membrane potential, release of intracellular calcium and cytochrome-c. This finally led to DNA damage in Leishmania promastigotes. In summary, the growth and survival of Leishmania depends on the availability of extracellular L-arginine. In its absence the parasite undergoes ROS mediated, caspase-independent apoptosis-like cell death. Therefore, L-arginine metabolism pathway could be a probable target for controlling the growth of Leishmania parasites and disease pathogenesis.
Leishmania donovani, the causative agent of Indian Visceral Leishmaniasis, resides in the gut of the insect vector and the macrophages of their mammalian host and avail nutrients for survival. Nutrient deprivation such as glucose or amino acid alters redox balance in mammalian cells as well as some lower organisms. However, the role of L-arginine, in regulation of redox balance and L. donovani survival yet not properly elucidated. In the present study, we found that L-arginine deprivation from the culture medium hinders growth and proliferation of Leishmania promastigotes. Starvation of L-arginine downregulates the expression of polyamine biosynthetic and thiol metabolic pathway enzymes leading to decreased production of polyamines in Leishmania parasites. Moreover, deprivation of L-arginine alters redox balance in Leishmania promastigotes characterized by the concomitant increase in ROS and decreased antioxidant level. Furthermore, L-arginine deprivation triggered phosphatidyl serine externalization, alteration in mitochondrial membrane potential, release of intraellular calcium and cytochrome-c followed by DNA damage. In summary, the growth and survival of Leishmania depends on the availability of extracellular L-arginine, in absence of which the parasite undergoes ROS mediated, caspase-independent apoptosis-like cell death. Therefore, targeting L-arginine metabolism pathway could be an alternative approach for controlling Leishmania growth and hence disease outcome.