ABSTRACT
Three thioamide-substituted imidazoquinolinone, which possess a heterocyclic center similar to tryptanthrin and are named C1, C2, and C3, were studied regarding (a) their in vitro anti-Trypanosoma cruzi activity, (b) their cytotoxicity and electrochemical behaviour, and (c) their effect on cell viability, redox state, and mitochondrial function. The assayed compounds showed a significant activity against the proliferative forms, but only C1 showed activity on the trypomastigote form (for C1, IC50 epi = 1.49 µM; IC50 amas = 1.74 µM; and IC50 try = 34.89 µM). The presence of an antioxidant compound such as ascorbic acid or dithiotreitol induced a threefold increase in the antiparasitic activity, whereas glutathione had a dual effect depending on its concentration. Our results indicate that these compounds, which exhibited low toxicity to the host cells, can be reduced inside the parasite by means of the pool of low molecular weight thiols, causing oxidative stress and parasite death by apoptosis. The antiparasitic activity of the compounds studied could be explained by a loss of the capacity of the antioxidant defense system of the parasite to keep its intracellular redox state. C1 could be considered a good candidate for in vivo evaluation.
ABSTRACT
A nutritional characteristic of trypanosomatid protozoa is that they need a heme compound as a growth factor. Because of the cytotoxic activity of heme and its structural similarity to cobalamins, we have investigated the in vitro and in vivo effect of vitamin B(12) (or cyanocobalamin) on the different forms of Trypanosoma cruzi. Cyanocobalamin showed a marked antiparasitic activity against epimastigotes (50% inhibitory concentration [IC(50)], 2.42 µM), amastigotes (IC(50), 10.69 µM), and trypomastigotes (IC(50), 9.46 µM). Anti-epimastigote and -trypomastigote values were 1.7 to 4 times lower than those obtained with the reference drug benznidazole (Bnz). We also found that B(12) and hemin do not interact with each other in their modes of action. Our results show that B(12) increases intracellular oxidative activity and stimulates both superoxide dismutase (50%) and ascorbate peroxidase (20%) activities, while the activity of trypanothione reductase was not modified. In addition, we found that the antioxidants dithiothreitol and ascorbic acid increase the susceptibility of the parasite to the cytotoxic action of B(12). We propose that vitamin B(12) exerts its growth-inhibitory effect through the generation of reactive oxygen species. In an in vivo assay, a significant reduction in the number of circulating parasites was found in T. cruzi-infected mice treated with cyanocobalamin and ascorbic acid. The reduction of parasitemia in benznidazole-treated mice was improved by the addition of these vitamins. According to our results, a combination of B(12) and Bnz should be further investigated due to its potential as a new therapeutic modality for the treatment of Chagas' disease.
