Efeito de bioisósteros do resveratrol complexados a metal em espécies de Leishmania associadas à leishmaniose cutânea e estudo do mecanismo de morte do parasito

Abstract

Leishmaniasis is diseases caused by protozoa of the genus Leishmania, causing significant impact on global public health. The treatment is limited by a number of factors, and the need for alternatives to chemotherapy is urgent. Thus, this study aimed to evaluate the leishmanicidal activity of bioisosters of resveratrol and its metal complexes and to study the mechanism of parasite death associated with the treatment. Twelve biosósteros of resveratrol were tested, five not complexed to metals, four complexed to gold and three complexed to vanadium, in promastigotes and amastigotes of L. amazonensis, L. braziliensis and L. major and in peritoneal macrophages. In promastigotes and peritoneal macrophages, the cell viability was assessed by the MTT colorimetric method, while in amastigotes, the effect of the compounds was evaluated by counting the intracellular forms. It was also assessed the selectivity and specificity of the compounds, by calculating the selectivity index and the specificity index of each compound. The compounds complexed to metals, compared to non-complexed, showed a significant effect on promastigotes and amastigotes of Leishmania sp., and were further selective to the parasite compared to the host cell. Subsequently, based on the synthesis, effectiveness and selectivity, the compound 11 (VOSalophen), a vanadium complex, was selected for studies on the mechanisms of death and activity in the murine model of cutaneous leishmaniasis. L. amazonensis promastigotes treated with VOSalophen exhibit mitochondrial alterations, which was observed by JC-1, Mitotracker® Red CMH2XROS e rhodamina 123 staining and transmission electronic microscopy (TEM); increased ROS production (using H2DCFDA); accumulate lipid bodies (Nile Red staining), exhibit morphological changes, but did not alter the integrity of the plasma membrane since no staining with propidium iodide. In addition, the parasites had a reduction in cell volume and size; phosphatidylserine externalization on the outer face of parasite's plasma membrane (annexin V-FITC staining) and using the TUNEL technique, DNA fragmentation was observed. In L. amazonensis intracellular amastigotes, DNA fragmentation was also observed (TUNEL technique). This set of results suggests death by apoptosis-like. Furthermore, there was an increase of autophagic vacuole formation in L. amazonensis promastigotes treated with VOSalophen (MDC staining and TEM), suggesting the occurrence of autophagy. In macrophages infected with L. amazonensis, VOSalophen induces an increase of nitric oxide and reactive oxygen species production, indicating a modulatory effect in infected cells. In the murine model of cutaneous leishmaniasis, the treatment with VOSalophen caused a significant reduction in the parasite load in the paws of BALB/c mice infected with L. amazonensis, when compared to control and furthermore not showed renal and hepatic toxicity to the treated animals, which was evaluated by the AST, ALT, GGT and creatinine dosages. These results, taken together, show the significant effect of bioisosters of resveratrol complexed to metals.