Authors

M R Simões-Silva¹; J S De Araújo¹; G M Oliveira¹; K C Demarque¹; R B Peres¹; I D'Almeida-Melo¹; D G Batista¹; C F Da Silva¹; C Cardoso-Santos¹; P B Da Silva¹; M M Batista¹; M T BahiaM N Soeiro¹;  ¹ Instituto Oswaldo Cruz, Rio de Janeiro, Brazil;  ² universidade Federal de Ouro Preto, Brazil

Discussion

Chagas disease (CD) is a life-threatening neglected pathology caused by the protozoan Trypanosoma cruzi, mostly asymptomatic in the acute and chronic phases, even though a significant number of patients progress to cardiac and/or digestive forms, that affects the life quality and induce high mortality rates. The treatment demands long periods of administration of nifurtimox or benznidazole (Bz), along with the occurrence of severe side effects, besides both being inactive upon the late chronic stage and the occurrence of naturally resistant parasite strains. The limitations evidence the need of new and alternative treatments for CD. Drug repurposing and combined therapy are strategies applied for other pathologies including the neglected diseases. These approaches are less time-consuming and reduce costs during the drug screening process and may help addressing the issue in a rational way. Metronidazole (Mtz) is a nitroimidazolic derivative in the market with broad-spectrum antimicrobial activity and important safety profile, and thus, represents a reasonable candidate for pre-clinical in vitro tests upon Trypanosoma cruzi, as well as in vivo experimental mice model, in mono- and combined schemes. While Bz is active against intracellular amastigotes and bloodstream trypomastigotes of T. cruzi in a low micromolar range (2.51 and 11.5 mM, respectively), Mtz presents low activity with EC50 > 200mM. Mtz shows no cytotoxicity profile against mammalian host cells up to 200 mM. Its combination with Bz in fixed-ratio proportions although did not provide cell cultures sterile cidality, the potency of Bz was promoted by the addition of Mtz. In vivo toxicity assays confirmed absence of adverse effects since no histopathological neither biochemical alterations were found up to 2000 mg/kg. In vivo studies using Swiss Webster male mice infected with 104 bloodstream forms of Y strain showed that Mtz administered up to 1000 mg/kg in monotherapy scheme did not lead to reduction of the parasitemia while Bz given at its optimal dose (100 mg/kg) completely suppressed the parasite load at the peak. Nevertheless, the doses of 250 and 500 mg/kg of Mtz could prolong animal survival, hence being determined for use in combination with suboptimal dose of Bz (10 mg/kg). These treatments were not able to reduce parasitemia, but 250 mg/kg Mtz + 10 mg/kg Bz prevented mortality in 70% of the animals and protected the cardiac electric alterations induced by the parasite infection, whilst the standard therapy with Bz was not effective in producing the same protection. The present work highlights the importance of the rational, cheap and fast approaches of drug repurposing and combined therapy for CD, aiming to accelerate the search for alternative treatments for this silent pathology. Supported by FAPERJ, CNPq, Fiocruz and STI.