In vivo programmed cell death of Entamoeba histolytica trophozoites in a hamster model of amoebic liver abscess

Abstract

Entamoeba histolytica trophozoites can induce host cell apoptosis, which correlates with the virulence of the parasite. This phenomenon has been seen during the resolution of an inflammatory response and the survival of the parasites. Other studies have shown that E. histolytica trophozoites undergo programmed cell death (PCD) in vitro, but how this process occurs within the mammalian host cell remains unclear. Here, we studied the PCD of E. histolytica trophozoites as part of an in vivo event related to the inflammatory reaction and the host-parasite interaction. Morphological study of amoebic liver abscesses showed only a few E. histolytica trophozoites with peroxidase-positive nuclei identified by terminal deoxynucleotidyltransferase enzymemediated dUTP nick end labelling (TUNEL). To better understand PCD following the interaction between amoebae and inflammatory cells, we designed a novel in vivo model using a dialysis bag containing E. histolytica trophozoites, which was surgically placed inside the peritoneal cavity of a hamster and left to interact with the host's exudate components. Amoebae collected from bags were then examined by TUNEL assay, fluorescence-activated cell sorting (FACS) and transmission electron microscopy. Nuclear condensation and DNA fragmentation of E. histolytica trophozoites were observed after exposure to peritoneal exudates, which were mainly composed of neutrophils and macrophages. Our results suggest that production of nitric oxide by inflammatory cells could be involved in PCD of trophozoites. In this modified in vivo system, PCD appears to play a prominent role in the host-parasite interaction and parasite cell death. INTRODUCTIONEntamoeba histolytica is the aetiological agent of amoebic dysentery and its main extra-intestinal complication, amoebic liver abscess (ALA). The infection constitutes an important public health problem worldwide, especially in developing countries. The mechanisms by which this parasite causes intestinal and liver tissue damage have been largely defined using various methods, which have been facilitated by the development of different in vivo experimental models of amoebiasis (Tsutsumi & Shibayama, 2006). In the last two decades, multiple studies have been conducted to understand the molecular basis of host-parasite interactions (Ravdin et al., 1989;Leippe et al., 1991;Que & Reed, 2000). The virulence of E. histolytica trophozoites has been considered a multifactorial process governed by specific interactions at the cellular and molecular levels. These host-parasite interactions take place in a series of sequential steps, including adherence (Petri et al., 1987), contact-dependent cytolysis (Huston et al., 2000) and phagocytosis (Orozco et al., 1983). These steps allow the parasite to invade and damage host tissues, as well as to evade detection by the immune system.Programmed cell death (PCD), or apoptosis, has been reported in all multicellular invertebrate and vertebrate lineages; however, various forms of regulated PCD have now been described in u...

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“…; Villalba‐Magdaleno et al. ). The production of NO in the cerebrovascular endothelium can be induced by the activation of endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) through TLR4 and cytokine receptors (IL‐6R and TNF‐αR) during bacterial or protozoan infections (Ehrchen et al.…”

“…(1) interaction and damage of endothelial cells, (2) secretion of cysteine proteases, (3) disruption of the TJ proteins and actin cytoskeleton, invasion of amoebae, (4) overexpression of endothelial adhesion molecules (VCAM-1 and ICAM-1), (5, 6) pro-inflammatory cytokines and NO production by the endothelial cells, (7) leucocyte recruitment and diapedesis through the endothelial cells to the olfactory bulbs. microorganisms (Marin et al 2001;Minami et al 1998;Shukla et al 1996;Villalba-Magdaleno et al 2011). The production of NO in the cerebrovascular endothelium can be induced by the activation of endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) through TLR4 and cytokine receptors (IL-6R and TNF-aR) during bacterial or protozoan infections (Ehrchen et al 2009;Miller et al 1996;Olefsky and Glass 2010;Shimizu et al 1991;Viswambharan et al 2003).…”

Virulence and virulence factors in Entamoeba histolytica, the agent of human amoebiasis

“…In a pro-inflammatory host environment, trophozoites are exposed to higher NO levels, likely produced by stimulated immune cells (neutrophils, macrophages), and undergo programmed cell death [56]. E. histolytica in turn induces neutrophil and macrophage apoptosis that may contribute to dampen tissue inflammation and damage, highlighting the importance of programmed cell death in ALA pathogenesis.…”

“…Males are highly susceptible and produce large abscesses, with histological features similar to human ALA. Recently, ex vivo infections of precision-cut liver slices have been introduced [60] as well as an approach challenging trophozoites in vivo with peritoneal pro-inflammatory responses prior to testing for ALA formation [56].…”