Tanira Matutino Bastos

Anti-Trypanosoma cruzi activity of nicotinamide

Inhibition of Trypanosoma brucei and Leishmania spp. sirtuins has shown promising antiparasitic activity, indicating that these enzymes may be used as targets for drug discovery against trypanosomatid infections. In the present work we carried out a virtual screening focused on the C pocket of Sir2 from Trypanosoma cruzi. Using this approach, the best ligand found was nicotinamide. In vitro tests confirmed the anti-T. cruzi activity of nicotinamide on epimastigote and trypomastigote forms. Moreover, treatment of T. cruzi-infected macrophages with nicotinamide caused a significant reduction in the number of amastigotes. In addition, alterations in the mitochondria and an increase in the vacuolization in the cytoplasm were observed in epimastigotes treated with nicotinamide. Analysis of the complex of Sir2 and nicotinamide revealed the details of the possible ligand-target interaction. Our data reveal a potential use of TcSir2 as a target for anti-T. cruzi drug discovery.

Nitro/nitrosyl ruthenium complexes are potent and selective anti-Trypanosoma cruzi agents causing autophagy and necrotic parasite death

ABSTRACT cis-[RuCl(NO2)(dppb)(5,5′-mebipy)] (complex 1), cis-[Ru(NO2)2(dppb)(5,5′-mebipy)] (complex 2), ct-[RuCl(NO)(dppb)(5,5′-mebipy)](PF6)2 (complex 3), and cc-[RuCl(NO)(dppb)(5,5′-mebipy)](PF6)2 (complex 4), where 5,5′-mebipy is 5,5′-dimethyl-2,2′-bipyridine and dppb is 1,4-bis(diphenylphosphino)butane, were synthesized and characterized. The structure of complex 2 was determined by X-ray crystallography. These complexes exhibited a higher anti-Trypanosoma cruzi activity than benznidazole, the current antiparasitic drug. Complex 3 was the most potent, displaying a 50% effective concentration (EC50) of 2.1 ± 0.6 μM against trypomastigotes and a 50% inhibitory concentration (IC50) of 1.3 ± 0.2 μM against amastigotes, while it displayed a 50% cytotoxic concentration (CC50) of 51.4 ± 0.2 μM in macrophages. It was observed that the nitrosyl complex 3, but not its analog lacking the nitrosyl group, releases nitric oxide into parasite cells. This release has a diminished effect on the trypanosomal protease cruzain but induces substantial parasite autophagy, which is followed by a series of irreversible morphological impairments to the parasites and finally results in cell death by necrosis. In infected mice, orally administered complex 3 (five times at a dose of 75 μmol/kg of body weight) reduced blood parasitemia and increased the survival rate of the mice. Combination index analysis of complex 3 indicated that its in vitro activity against trypomastigotes is synergic with benznidazole. In addition, drug combination enhanced efficacy in infected mice, suggesting that ruthenium-nitrosyl complexes are potential constituents for drug combinations.

Physalins B and F, seco -steroids isolated from Physalis angulata L., strongly inhibit proliferation, ultrastructure and infectivity of Trypanosoma cruzi

We previously observed that physalins have immunomodulatory properties, as well as antileishmanial and antiplasmodial activities. Here, we investigated the anti-Trypanosoma cruzi activity of physalins B, D, F and G. We found that physalins B and F were the most potent compounds against trypomastigote and epimastigote forms of T. cruzi. Electron microscopy of trypomastigotes incubated with physalin B showed disruption of kinetoplast, alterations in Golgi apparatus and endoplasmic reticulum, followed by the formation of myelin-like figures, which were stained with MDC to confirm their autophagic vacuole identity. Physalin B-mediated alteration in Golgi apparatus was likely due to T. cruzi protease perturbation; however physalins did not inhibit activity of the trypanosomal protease cruzain. Flow cytometry examination showed that cell death is mainly caused by necrosis. Treatment with physalins reduced the invasion process, as well as intracellular parasite development in macrophage cell culture, with a potency similar to benznidazole. We observed that a combination of physalins and benznidazole has a greater anti-T. cruzi activity than when compounds were used alone. These results indicate that physalins, specifically B and F, are potent and selective trypanocidal agents. They cause structural alterations and induce autophagy, which ultimately lead to parasite cell death by a necrotic process.

Structural isomerism of Ru(II)-carbonyl complexes: synthesis, characterization and their antitrypanosomal activities

New complexes with the general formula [RuCl(CO)(dppb)(diimine)]PF6, [dppb = 1,4-bis(diphenylphosphino)butane; diimine = 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen)], were prepared. Thus, the complexes ct-[RuCl(CO)(dppb)(bipy)]PF6 (1), ct-[RuCl(CO)(dppb)(phen)]PF6 (2), tc-[RuCl(CO)(dppb)(bipy)]PF6 (3), tc-[RuCl(CO)(dppb)(phen)]PF6 (4), cc-[RuCl(CO)(dppb)(bipy)]PF6 (5) and cc-[RuCl(CO)(dppb)(phen)]PF6 (6) were obtained and characterized. In this case, the first letter in the prefixes indicates the position of CO with respect to the chlorido ligand and the second one is related to the phosphorus atoms. The compositions of the complexes were confirmed by analytical techniques and an octahedral environment around the ruthenium was confirmed by single-crystal X-ray diffraction of the complexes ct-[RuCl(CO)(dppb)(bipy)]PF6 and cc-[RuCl(CO)(dppb)(phen)]PF6. The oxidation potentials of the complexes were determined by cyclic voltammetry and it was found that they vary according to the CO position in the complexes. In order to obtain information on the stability of the ct, tc and cc-[RuCl(CO)(dppb)(bipy)]PF6 (1), (3) and (5) isomers, computational studies were carried out, and they showed large differences between the HOMO/LUMO energies. As monitored by 13C NMR, the stability of the complexes with respect to CO displacement, for at least 72 h, in DMSO-d6 solution, is independent of the CO position in the complexes. Pharmacological evaluation of the complexes against the Trypanosoma cruzi parasite revealed the structure–activity relationships, showing that the presence and position of the CO ligand in the complexes are relevant for the antiparasitic activity of the compounds. The most active compound, the tc-[RuCl(CO)(dppb)(bipy)]PF6 isomer, presented potent antiparasitic activity, which was achieved by causing oxidative stress followed by parasite cell death through necrosis. Thus, the findings presented here demonstrate that the use of a carbonyl ligand provides stability and pharmacological properties to ruthenium/diphosphine/diimine complexes.