Functional characterization and subcellular distribution of two recombinant cytosolic HSP70 isoforms from Entamoeba histolytica under normal and stress conditions.

Amoebiasis is a human intestinal disease caused by the parasite Entamoeba histolytica. It has been previously demonstrated that E. histolytica heat shock protein 70 (EhHSP70) plays an important role in amoebic pathogenicity by protecting the parasite from the dangerous effects of oxidative and nitrosative stresses. Despite its relevance, this protein has not yet been characterized. In this study, the EhHSP70 genes were cloned, and the two recombinant EhHSP70 proteins were expressed, purifying and biochemically characterized. Additionally, after being subjected to some host stressors, the intracellular distribution of the proteins in the parasite was documented. Two amoebic HSP70 isoforms, EhHSP70-A and EhHSP70-B, with 637 and 656 amino acids, respectively, were identified. Kinetic parameters of ATP hydrolysis showed low rates, which were in accordance with those of the HSP70 family members. Circular dichroism analysis showed differences in their secondary structures but similarities in their thermal stability. Immunocytochemistry in trophozoites detected EhHSP70 in the nuclei and cytoplasm as well as a slight overexpression when the parasites were subjected to oxidants and heat. The structural differences of amoebic HSP70s with their human counterparts may be used to design specific inhibitors to treat human amoebiasis.

In vitro and in vivo trypanocidal activity of some benzimidazole derivatives against two strains of Trypanosoma cruzi.

The trypanocidal effect of five benzimidazole derivatives (1-5) was determined in vitro and in vivo assays against two strains of Trypanosoma cruzi (NINOA and INC5). The in vitro trypanocidal activity was evaluated by measuring the percentage of lysis of bloodstream trypomastigotes of T. cruzi. Results point to 5-chloro-1H-benzimidazole-2-thiol (1) as the best activity profile compound with a 50% lytic concentration (LC(50)) of 0.014 mM (NINOA strain) and 0.32 mM (INC5 strain). Reference drugs were nifurtimox (Nfx) and benznidazole (Bnz), which on NINOA strain displayed a LC(50)=0.60 mM and LC(50)=0.78 mM, respectively; while on INC5 strain they exhibited LC(50) values of 0.31 mM and 0.69 mM, respectively. The in vivo trypanocidal activity of 1-5 on parasitemia in a murine model acute Chagas' disease indicated that 1 and Nfx showed similar activity on INC5 strain, while 5-chloro-1-methyl-1H-benzimidazole-2-thiol (2) and its regioisomer, 6-chloro-1-methyl-1H-benzimidazole-2-thiol (3), displayed better activity than Nfx and Bnz on NINOA strain. All compounds showed low cytotoxicity against Vero cells, with selective index 38-3000 times higher to the parasite.