Abstract 1716 Importance for Polyamines for Metabolic Activity in Leishmania Parasites

The protozoan parasite, Leishmania, causes the neglected tropical disease leishmaniasis, which among parasitic diseases, is the 2nd leading cause of mortality. The parasite is transmitted by the bite of a sand fly. Currently, the limited treatment options for leishmaniasis cause side effects and drug resistance is emerging. Thus, there is an urgent need to identify new therapeutic targets. Recent research has emphasized the importance of polyamines for Leishmania parasites, and our investigation is centered on unraveling their functions for parasite growth and survival. The primary polyamine biosynthetic enzymes in Leishmania are ornithine decarboxylase (ODC) and spermidine synthase (SPDSYN), which sequentially convert ornithine to the polyamines, putrescine and spermidine. The gene deletion mutants, Δodc and Δspdsyn, show significantly reduced infectivity phenotypes in mice, validating this pathway as a potential therapeutic target. The goal of my research is to determine the function of polyamines for mitochondrial metabolism. Unlike mammalian cells, which have up to thousands of mitochondria, Leishmania parasites only have one mitochondrion, making them uniquely vulnerable to mitochondrial dysfunction. Our method is centered on measuring the conversion of resazurin (a blue non-fluorescent dye) to resorufin (red and fluorescent), which depends on mitochondrial dehydrogenases, as a tool to assess mitochondrial metabolism. We found that putrescine-depleted Δodc parasites do not proliferate and show profoundly reduced mitochondrial activity. Surprisingly, Δspdsyn parasites supplemented with spermidine may have an improved metabolic rate compared to wild type parasites. Previous research has shown that supplemented Δspdsyn parasites contain higher amounts of spermidine compared to wild type parasites (likely due to increased transport to compensate for the lack of biosynthesis). Thus, we speculate that spermidine may stimulate mitochondrial metabolism. The addition of putrescine and/or spermidine does not affect mitochondrial metabolism in wild type cells, but this could be due to lack of uptake. Together, these experiments suggest that polyamines are important for mitochondrial function. Because putrescine is especially important for cell proliferation and mitochondrial metabolism, inhibiting ornithine decarboxylase could be a promising strategy for drug development. Research reported in this poster was supported by NIAID of the National Institutes of Health under award number R15AI151980.