Efeito da combinação de isoobtusilactona A e protolimonóides biologicamente ativos sobre epimastigotas de Trypanosoma cruzi

Abstract

Isoobtusilactone A is a butanolide extracted from the xylopodium of Aiouea trinervis which, in previous studies of our research group, has shown excellent activity in the inhibiting the growth of Trypanosoma cruzi. Other molecules, called protolimoids, extracted from the fruits of Guarea kunthiana, also demonstrated reduction in T. cruzi growth. Both compounds have shown a low cytoxicity and became an alternative route for the etiological treatment of Chagas Disease. Chagas Disease is a Neglected Tropical Disease, which is endemic in Latin America. It mainly affects the poorest populations of these countries and still has no cure and an appropriate treatment. Benzonidazole, the current medicine used in the treatment of Chagas Disease, has several side effects and toxicity for the patients, which culminate in the discontinuation of the treatment. In view of the current problem of the Chagas Disease, etiologic treatment and the promising effects of isoobtusilactone A and protolimoids on the delay and induction of parasitic death, the aim of this study will be to evaluate isoobtusilactone A and protolimoids association effect on epimastigotes forms of T. cruzi. For that, a combination assay was done in order to test different proportions of the molecules (to known, 0:4; 1:3; 1:1; 3:1 e 4:0) on the epimastigotes cellular viability. The Combination Index (IC) was calculated for effect’s classification according to Chou (2006) in sinergysm, additive effect and antagonism. As a result, we found that isoobtusylactone A and 3-β-O-tigloylmelianol showed synergism (CI = 0.42), with the former significantly decreasing the concentration of the latter in the combination (DRI = 5.74). On the other hand, the combination between 3-β-O-tigloylmelianol and 3-β-O-tigloylmelianotriol was synergistic only in the 1:3 ratio of IC90 (CI = 0.89), the final effect found was mostly additive (CI = 1), however, with a decrease in the inhibitory concentrations of 3-β-O-tigloylmelianol in all proportions. Furthermore, both combinations, at their highest concentrations, were not cytotoxic. Cell cycle analyzes with propidium iodide showed that treatment for 24 hours with the combinations stagnated most of the epimastigotes in the G1 phase of the cycle, decreasing the population in the S and G2 phases. Finally, analyzes of the effect of the combinations on membrane integrity showed that the compounds are not able to break the integrity of the plasma membrane, however, the combination of isoobtusylactone A and 3-β-O-tigloylmelianol altered the parasite morphology, increasing the cell size.