Entamoeba histolytica: Oxygen resistance and virulence

Entamoeba histolytica virulence has been attributed to several amoebic molecules Such as adhesins, amoebapores and cysteine proteinases, but supporting evidence is either partial or indirect. In this work we compared several in vitro and in vivo features of both virulent E. histolytica (vEh) and non-virulent E. histolytica (nvEh) axenic HM-1 IMSS strains, such as complement resistance, proteinase activity, haemolytic, phagocytic and cytotoxic capacities, survival in mice caecum, and susceptibility to O-2. The only difference observed was a higher in vitro susceptibility of nvEh to O-2. The molecular mechanism of that difference was analyzed in both groups of amoebae after high O-2 exposure. vEh O-2 resistance correlated with: (i) higher O-2 reduction (O-2(center dot-) and H2O2 production); (ii) increased H2O2 resistance and thiol peroxidase activity, and (iii) reversible pyruvate: ferredoxin oxidoreductase (PFOR) inhibition. Despite the high level of carbonylated proteins in nvEh after O-2 exposure, membrane oxidation by reactive oxygen species was not observed. These results suggest that the virulent phenotype of E. histolytica is related to the greater ability to reduce O-2 and H2O2 as well as PFOR reactivation, whereas nvEh undergoes irreversible PFOR inhibition resulting in metabolic failure and amoebic death. (C) 2008 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.