Leishmania major ascorbate peroxidase overexpression protects cells against reactive oxygen species-mediated cardiolipin oxidation

Iron metabolism in trypanosomatids, and its crucial role in infection

Iron is almost ubiquitous in living organisms due to the utility of its redox chemistry. It is also dangerous as it can catalyse the formation of reactive free radicals - a classical double-edged sword. In this review, we examine the uptake and usage of iron by trypanosomatids and discuss how modulation of host iron metabolism plays an important role in the protective response. Trypanosomatids require iron for crucial processes including DNA replication, antioxidant defence, mitochondrial respiration, synthesis of the modified base J and, in African trypanosomes, the alternative oxidase. The source of iron varies between species. Bloodstream-form African trypanosomes acquire iron from their host by uptake of transferrin, and Leishmania amazonensis expresses a ZIP family cation transporter in the plasma membrane. In other trypanosomatids, iron uptake has been poorly characterized. Iron-withholding responses by the host can be a major determinant of disease outcome. Their role in trypanosomatid infections is becoming apparent. For example, the cytosolic sequestration properties of NRAMP1, confer resistance against leishmaniasis. Conversely, cytoplasmic sequestration of iron may be favourable rather than detrimental to Trypanosoma cruzi. The central role of iron in both parasite metabolism and the host response is attracting interest as a possible point of therapeutic intervention.

Overexpression of mitochondrial Leishmania major ascorbate peroxidase enhances tolerance to oxidative stress-induced programmed cell death and protein damage

Ascorbate peroxidase from Leishmania major (LmAPX) is one of the key enzymes for scavenging of reactive oxygen species generated from the mitochondrial respiratory chain. We have investigated whether mitochondrial LmAPX has any role in oxidative stress-induced apoptosis. The measurement of reduced glutathione (GSH) and protein carbonyl contents in cellular homogenates indicates that overexpression of LmAPX protects Leishmania cells against depletion of GSH and oxidative damage of proteins by H(2)O(2) or camptothecin (CPT) treatment. Confocal microscopy and fluorescence spectroscopy data have revealed that the intracellular elevation of Ca(2+) attained by the LmAPX-overexpressing cells was always below that attained in control cells. Flow cytometry assay data and confocal microscopy observation strongly suggest that LmAPX overexpression protects cells from H(2)O(2)-induced mitochondrial membrane depolarization as well as ATP decrease. Western blot data suggest that overexpression of LmAPX shields against H(2)O(2)- or CPT-induced cytochrome c and endonuclease G release from mitochondria and subsequently their accumulation in the cytoplasm. Caspase activity assay by flow cytometry shows a lower level of caspase-like protease activity in LmAPX-overexpressing cells under apoptotic stimuli. The data on phosphatidylserine exposed on the cell surface and DNA fragmentation results show that overexpression of LmAPX renders the Leishmania cells more resistant to apoptosis provoked by H(2)O(2) or CPT treatment. Taken together, these results indicate that constitutive overexpression of LmAPX in the mitochondria of L. major prevents cells from the deleterious effects of oxidative stress, that is, mitochondrial dysfunction and cellular death.