The 29-Kilodalton Thiol-Dependent Peroxidase of Entamoeba histolytica Is a Factor Involved in Pathogenesis and Survival of the Parasite during Oxidative Stress

Abstract

The 29-kDa surface antigen (thiol-dependent peroxidase; Eh29) of Entamoeba histolytica exhibits peroxidative and protective antioxidant activities. During tissue invasion, the trophozoites are exposed to oxidative stress and need to deal with highly toxic reactive oxygen species (ROS). In this investigation, attempts have been made to understand the role of the 29-kDa peroxidase gene in parasite survival and pathogenesis. Inhibition of eh29 gene expression by antisense RNA technology has shown approximately 55% inhibition in eh29 expression, maximum ROS accumulation, and significantly lower viability in 29-kDa downregulated trophozoites during oxidative stress. The cytopathic and cytotoxic activities were also found to decrease effectively in the 29-kDa downregulated trophozoites. Size of liver abscesses was substantially lower in hamsters inoculated with 29-kDa downregulated trophozoites compared to the normal HM1:IMSS. These findings clearly suggest that the 29-kDa protein of E. histolytica has a role in both survival of trophozoites in the presence of ROS and pathogenesis of amoebiasis.Entamoeba histolytica, the enteric protozoa, is a well-established causative agent of amoebic dysentery and liver abscesses in humans (37). E. histolytica is well known for its high potential for invading and destroying human tissue, leading to diseases such as hemorrhagic colitis and extraintestinal abscesses (30). The parasite usually lives and multiplies within the human gut, which constitutes an environment of reduced oxygen pressure. During tissue invasion, E. histolytica is exposed to elevated amounts of exogenous reactive oxygen species (ROS), such as superoxide radical anions (O 2 ⅐ Ϫ ) and hydrogen peroxide (H 2 O 2 ) (14, 26). These highly toxic molecules cause severe damage to biological macromolecules, leading to metabolic malfunctions. In addition, E. histolytica has to inactivate the ROS produced by endogenous enzymes for its survival. Several defense mechanisms exist in which a wide array of enzymatic and nonenzymatic antioxidants, including superoxide dismutase (SOD), glutathione peroxidase, catalase, and glutathione, play an active role in cell survival during oxidative stress. E. histolytica produces an iron-containing SOD that is induced by superoxide anions to produce H 2 O 2 (9). Hydroperoxides produced during oxidative stress could be detoxified by a bifunctional NADPH:flavin oxidoreductase containing NADPH-dependent disulfide reductase and a H 2 O 2 -forming NADPH oxidase activity (10, 12). Catalase and glutathione reductase systems are absent in E. histolytica, but it encodes a 29-kDa cysteine-rich antigen (thiol-dependent peroxiredoxin) located on the surface of the trophozoites (8). The 29-kDa thiol-dependent peroxiredoxin of E. histolytica (Eh29) is homologous to AhpC (alkyl hydroperoxide C-22 protein) of Salmonella enterica serovar Typhimurium and Saccharomyces cerevisiae thiol-specific antioxidant protein (17). In our previous study it was clearly demonstrated that the enzymes SOD and Eh29 increased...

Hydrogen peroxide induces apoptosis-like death in Entamoeba histolytica trophozoites

“…Our positive results could be due to the longer annexin V reaction period used. Our lab had previously shown that after 6 h exposure to oxidative stress, E. histolytica shows annexin-positive staining (Sen et al, 2007).…”

“…In addition, direct divalent reduction of O 2 to H 2 O 2 is catalysed by an NADPH : flavin oxidoreductase (Bruchhaus et al, 1998). Catalase and glutathione reductase systems are absent in E. histolytica (Sen et al, 2007), but the H 2 O 2 generated by both pathways can be further transformed to H 2 O by the action of peroxiredoxin (eh29) (Bruchhaus et al, 1997). The mRNA level of SOD and eh29 was found to decrease gradually with the increase in duration of exposure to oxidative stress.…”

A proteome reference map of Trichomonas vaginalis

“…During tissue invasion, the trophozoites are exposed to oxidative stress and need to deal with highly toxic reactive oxygen species (Coombs et al 2004;Sen et al 2007). Toxic molecules such as superoxide (O 2 · − ) and hydrogen peroxide (H 2 O 2 ) can alter membrane properties and disrupt membrane-bound proteins and biological macromolecules, leading to cell death (Sen et al 2007). Therefore T. vaginalis has to maintain its redox homeostasis for survival.…”

Identification of an Entamoeba histolytica Serine-, Threonine-, and Isoleucine-Rich Protein with Roles in Adhesion and Cytotoxicity

“…The cytotoxicity data are a significant finding, as the relative difficulty in manipulating gene expression in E. histolytica has limited the ability to associate particular genes with pathogenicity. To date, only a few amebic genes have been genetically shown to be involved in cytotoxicity (3,11,16,25,29,43,47).…”