Entamoeba histolytica: ultrastructure of trophozoites recovered from experimental liver lesions

Perils and Promises of Pathogenic Protozoan Extracellular Vesicles

Extracellular vesicles (EVs) are membranous structures formed during biological processes in living organisms. For protozoan parasites, secretion of EVs can occur directly from the parasite organellar compartments and through parasite-infected or antigen-stimulated host cells in response to in vitro and in vivo physiological stressors. These secreted EVs characteristically reflect the biochemical features of their parasitic origin and activating stimuli. Here, we review the species-specific morphology and integrity of parasitic protozoan EVs in concurrence with the origin, functions, and internalization process by recipient cells. The activating stimuli for the secretion of EVs in pathogenic protozoa are discoursed alongside their biomolecules and specific immune cell responses to protozoan parasite-derived EVs. We also present some insights on the intricate functions of EVs in the context of protozoan parasitism.

Morphological Findings in Trophozoites during Amoebic Abscess Development in Misoprostol-Treated BALB/c Mice

During amoebic liver abscess (ALA) formation in susceptible animals, immune response is regulated by prostaglandin E₂ (PGE₂) dependent mechanisms. The aim of this study was to analyze the effect of misoprostol (MPL), a PGE₁ analogue, on ALA formation in BALB/c mice. Male mice from BALB/c strain were intrahepatically infected with 7.5 × 10⁵ trophozoites of E. histolytica strain HM1:IMSS and treated with 10⁻⁴ M of MPL daily until sacrifice at 2, 4, and 7 days postinfection (p.i.). ALA formation was evaluated at 2, 4, and 7 days postinfection; trophozoite morphology was analyzed using immunohistochemistry and image analysis. Results showed an increase in frequency of ALA formation in infected and MPL-treated mice only at 2 days p.i. (P = 0.03). A significant diminution in the size of trophozoites was detected in abscesses from mice independently of MPL treatment (from 5.8 ± 1.1 µm at 2 days p.i. to 2.7 ± 1.9 µm at 7 days p.i.) compared with trophozoites dimensions observed in susceptible hamsters (9.6 ± 2.7 µm) (P < 0.01). These results suggest that MPL treatment may modify the adequate control of inflammatory process to allow the persistence of trophozoites in the liver; however, natural resistance mechanisms cannot be discarded.

Giardia canis: ultrastructural analysis of G. canis trophozoites transfected with full length G. canis virus cDNA transcripts

Giardia canis virus (GCV) is a double-stranded RNA (dsRNA) virus of the family Totiviridae. In this study, the full length cDNA of the G. canis virus was constructed in pPoly2/sfinot vector and RNA was transcribed in vitro. Virus-free G. canis trophozoites were transfected with in vitro transcribed GCV RNA by electroporation. Transfected trophozoites were cultured for 12, 24, 36, 48, 60, or 72h post transfection for analysis. The ultrastructures of the transfected trophozoites were determined by transmission electron microscopy. The viral particles were detectable sporadically in the cytoplasm as early as 24h post transfection, but became evident and wide-spread 36h post transfection. The number of viral particles increased dramatically from 48 to 60h. Viral particles were released into the culture medium starting at about 60h and detectable in nuclei 72h post transfection. Severe vacuolization was seen in transfected G. canis trophozoites as early as 36h post transfection and persisted throughout the course of this study. The results of the present study indicate that in vitro transcribed GCV transcripts were capable of infecting Giardia trophozoites, apparently replicated and packaged into mature infectious viral particles which were released from the host.

Phosphonoxins: rational design and discovery of a potent nucleotide anti-Giardia agent

Phosphonoxins, a new class of synthetic, rationally designed anti-microbial agents, are described. From this class a sub-micromolar inhibitor of Giardia trophozoite growth has been identified.

Rational design and synthesis of novel nucleotide anti-Giardia agents

Design and synthesis of a novel nucleotide anti-Giardia agent that is micromolar inhibitor of Giardia trophozoite growth in culture is described.

Subcellular distribution of theEntamoeba histolytica140 kDa FN-binding molecule during host-parasite interaction

Entamoeba histolyticatrophozoites recovered from the host-parasite interface during abscess development obtain different stimuli compared with long-term cultured cells. In order to have a better understanding about the mechanisms in which the 140 kDa fibronectin (FN)-binding molecule (EhFNR) is involved during the invasive process, we decided to compare the regulation process of this molecule among long-term cultured trophozoites, FN-stimulated trophozoites, and trophozoites recently recovered from a liver abscess. A cDNA clone (5A) containing a fragment of theEhFNR that shows identity to the C-terminal region of the intermediate galactose lectin subunit Igl, was selected with a mAb (3C10). Identity ofEhFNR with Igl was confirmed by immunoprecipitation with 3C10 and EH3015 (against the Gal/GalNAc intermediate subunit) mAbs. The 3C10 mAb was used as a tool to explore the modulation of the amoebic receptor (EhFNR). Our results showed specific regulation of theEhFNR in FN-interacted amoebas, as well as in trophozoites recovered at different stages of abscess development. This regulation involved mobilization of the receptor molecule from internal vesicles to the plasma membrane. Therefore, we suggest that in the host-parasite interface, theEhFNR (Igl) plays an important role in the adhesion process during abscess development.

Secretory organelles of pathogenic protozoa

Secretory processes play an important role on the biology and life cycles of parasitic protozoa. This review focus on basic aspects, from a cell biology perspective, of the secretion of (a) micronemes, rhoptries and dense granules in members of the Apicomplexa group, where these organelles are involved in the process of protozoan penetration into the host cell, survival within the parasitophorous vacuole and subsequent egress from the host cell, (b) the Maurer's cleft in Plasmodium, a structure involved in the secretion of proteins synthesized by the intravacuolar parasite and transported through vesicles to the erythrocyte surface, (c) the secretion of macromolecules into the flagellar pocket of trypanosomatids, and (d) the secretion of proteins which make the cyst wall of Giardia and Entamoeba, with the formation of encystation vesicles.

Cloning and partial characterization of Entamoeba histolytica PTPases

Reversible protein tyrosine phosphorylation is an essential signal transduction mechanism that regulates cell growth, differentiation, mobility, metabolism, and survival. Two genes coding for protein tyrosine phophatases, designed EhPTPA and EhPTPB, were cloned from Entamoeba histolytica. EhPTPA and EhPTPB proteins showed amino acid sequence identity of 37%, both EhPTPases showed similarity with Dictyostelium discoideum and vertebrate trasmembranal PTPases. mRNA levels of EhPTPA gene are up-regulated in trophozoites recovered after 96h of liver abscess development in the hamster model. EhPTPA protein expressed as a glutathione S-transferase fusion protein (GST::EhPTPA) showed enzymatic activity with p-nitrophenylphosphate as a substrate and was inhibited by PTPase inhibitors vanadate and molybdate. GST::EhPTPA protein selectively dephosphorylates a 130kDa phosphotyrosine-containing protein in trophozoite cell lysates. EhPTPA gene codifies for a 43kDa native protein. Up-regulation of EhPTPA expression suggests that EhPTPA may play an important role in the adaptive response of trophozoites during amoebic liver abscess development.