Melatonin decreases circulating Trypanosoma cruzi load with no effect on tissue parasite replication.

Cardiac damage during the acute phase of Chagas disease (CD) is associated with an increase in pro-inflammatory markers and oxidative stress. Melatonin (MEL) has emerged as a promising therapy for CD due to its antioxidant and immunomodulatory properties; however, the protective action of MEL in the cardiac tissue, as well as its direct action on the parasite cycle, is not fully understood. We investigated the effects of MEL on heart parasitism in mice infected with Trypanosoma cruzi and also its effects on the parasitic proliferation in vitro. Our in vivo study showed that MEL reduced circulating parasitemia load, but did not control tissue (heart, liver, and spleen) parasitism in mice. MEL did not prevent the redox imbalance in the left ventricle of infected mice. Our in vitro findings showed that MEL did not inhibit parasites replication within cells, but rather increased their release from cells. MEL did not control parasitism load in the heart or prevent the cardiac redox imbalance induced by acute T. cruzi infection. The hormone controlled the circulating parasitic load, but within cells MEL accelerated parasitic release, a response that can be harmful.