Essential and nonessential metal effects on extracellular Leishmania amazonensis in vitro

Protozoan parasites like Leishmania amazonensis are excellent models to test the effects of new drugs against a functional molecular arsenal used to establish successfully an infection in the vertebrate host, where they invade the cells of the monocytic system. However, little is known about the influence of metal ions on the cellular functionality of the infective forms of L. amazonensis. In the present work, we show that ZnCl₂ (an essential metal to cellular metabolism) did not induce drastic effects on the survival of the promastigote under the conditions tested. However, incubation of ZnCl₂ prior to subsequent treatment with CdCl₂ and HgCl₂ led to a drastic toxic effect on parasite survival in vitro. Nonessential metals such as CdCl₂ and HgCl₂ promoted a drastic effect on parasite survival progressively with increasing dose and time of exposure. Notably, HgCl₂ produced an effective elimination of the parasite in doses/time smaller than the CdCl₂. This toxic action induced in the parasite a high condensation of the nuclear heterochromatin, besides the absence or de-structuring of functional organelles such as glycosomes, acidocalcisomes, and mitochondria in the cytoplasm. Our results suggest that promastigotes of L. amazonensis are sensitive to the toxic activity of nonessential metals, and that this activity increases when parasites are previously exposed to Zn. To summarize, toxic effects of the tested metals are dose and time dependent and can be used as a study model to better understand the functionality of the molecular arsenal responsible for the parasitism.