Mecanismos moleculares de toxicidade do ditelureto de difenila em cepas de Escherichia coli e efeito antimicrobiano em Drosophila melanogaster

Abstract

Diphenyl ditelluride (PhTe)2 is a dose-dependent organic tellurium compound with antiand pro-oxidant properties. Studies have demonstrated its cytotoxic, mutagenic, genotoxic, neurotoxic and teratogenic potential, in different models, with the toxicological mechanism of action associated with the ability to react with thiol groups of biologically relevant molecules. Tellurium compounds are harmful to microorganisms, due to the generation of reactive oxygen species, which lead to oxidative stress. In microorganisms such as Escherichia coli, the increase in reactive oxygen species (ROS) trigger responses to oxidative stress that activate antioxidant defense systems regulated by transcriptional agents OxyR, which regulates the expression of genes inducible by hydrogen peroxide H2O2 and SoxS o which regulates the transcriptional system that responds to superoxide-generating species. The aim of this study was to evaluate the molecular mechanisms of (PhTe)2 toxicity in Escherichia coli (DE3)RIL cells, and to investigate the antimicrobial effect of (PhTe)2 through an alternative model of bacterial infection by Escherichia coli in Drosophila melanogaster. In article 1, we demonstrated that the exposure of Escherichia coli strains to (PhTe)2 caused toxicological effects, increasing the levels of reactive species, lipid peroxidation and protein carbonylation and the reduction of non-protein thiols levels, in concentrations of 6, 12 and 24µg/ml. The activity of antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) were increased at concentrations of 12 and 24µg/ml, while at a concentration of 6µg/ml, only the SOD enzyme had an alteration in its activity. Gene expression analysis demonstrated positive activation of the oxidative stress response regulators soxS and oxyR and the antioxidant response genes gnd, katG, sodA and sodB, occurring at the highest concentration (24µg/ml), already at concentrations of 6 and 12µg/ml expression was suppressed or remained at baseline. We associate its toxicological potential, or part of it, to the oxidation of thiol groups and the formation of reactive species, demonstrating through the modulation of the soxS and oxyR regulators and the antioxidant response genes gnd, katG, sodA and sodB, the response to the stress caused for its exposure. In view of the toxicological potential of 9 (PhTe)2 in Escherichia coli strains, in manuscript 1, we sought to evaluate the antimicrobial effect of the compound (PhTe)2, using a model of oral infection by Escherichia coli in Drosophila melanogaster. Our findings demonstrated that (PhTe)2 is safe for use in an infection model. Of the flies through the negative geotaxis test and open fields, as a result we observed that (PhTe)2 did not change the behavior of the flies. After evaluating the safety of the compound in the model, we determined the concentration of 10 µM, as the concentration to be used in the microbiological evaluation, and the maximum exposure of 48 hours. To determine the antimicrobial potential of the compound in a bacterial infection model, we used the oral infection model, where axenic flies were reared in an aseptic environment, and exposed for a period of 18-24 hours. Exposure to the bacteria was given orally, after a starvation period, the flies were offered only a bacterial solution as a food source for 24 hours, after which the treatment groups were exposed to the compound. The results of the microbiological evaluation were obtained after the times of 0, 3, 6, 12, 24 and 48 hours, these results demonstrated that the compound is able to significantly reduce the rates of bacterial contamination, when compared with the flies that were only exposed to oral infection. This study elucidated the toxicological mechanism of (PhTe)2 in Escherichia coli strains, and demonstrated its antimicrobial potential of the compound against an alternative model of oral infection of Drosophila melanogaster by Escherichia coli.