Tissue destruction and invasion by Entamoeba histolytica

Multi-locus sequence analysis reveals phylogenetically segregated Entamoeba histolytica population

Amoebiasis, caused by the enteric parasite, Entamoeba histolytica, is one of the major food- and water-borne parasitic diseases in developing countries with improper sanitation and poor hygiene. Infection with E. histolytica has diverse disease outcomes, which are determined by the genetic diversity of the infecting strains. Comparative genetic analysis of infecting E. histolytica strains associated with differential disease outcomes from different geographical regions of the world is important to identify the specific genetic patterns of the pathogen that trigger certain disease outcomes of Amoebiasis. The strategy is able to elucidate the genealogical relation and population structure of infecting E. histolytica strains from different geographical regions. In the present study, we have performed a comparative genetic analysis of circulating E. histolytica strains identified from different parts of the world, including our study region, based on five tRNA-linked short tandem repeat (STR) loci (i.e., D-A, NK2, R-R, STGA-D and A-L) and evaluated their potential associations with differential disease outcomes of Amoebiasis. A number of regional-specific, emerging haplotypes of E. histolytica, significantly associated with specific disease outcomes have been identified. Haplotypes, which have a significant positive association with asymptomatic and amoebic liver abscess outcomes, showed a significant negative association with diarrheal outcome, or vice versa. Comparative multi-locus analysis revealed that E. histolytica isolates from our study region are phylogenetically segregated from the isolates of other geographical regions. This study provides a crucial overview of the population structure and emerging pattern of the enteric parasite, E. histolytica.

Advances in Protozoan Epigenetic Targets and Their Inhibitors for the Development of New Potential Drugs

Protozoan parasite diseases cause significant mortality and morbidity worldwide. Factors such as climate change, extreme poverty, migration, and a lack of life opportunities lead to the propagation of diseases classified as tropical or non-endemic. Although there are several drugs to combat parasitic diseases, strains resistant to routinely used drugs have been reported. In addition, many first-line drugs have adverse effects ranging from mild to severe, including potential carcinogenic effects. Therefore, new lead compounds are needed to combat these parasites. Although little has been studied regarding the epigenetic mechanisms in lower eukaryotes, it is believed that epigenetics plays an essential role in vital aspects of the organism, from controlling the life cycle to the expression of genes involved in pathogenicity. Therefore, using epigenetic targets to combat these parasites is foreseen as an area with great potential for development. This review summarizes the main known epigenetic mechanisms and their potential as therapeutics for a group of medically important protozoal parasites. Different epigenetic mechanisms are discussed, highlighting those that can be used for drug repositioning, such as histone post-translational modifications (HPTMs). Exclusive parasite targets are also emphasized, including the base J and DNA 6 mA. These two categories have the greatest potential for developing drugs to treat or eradicate these diseases.

High-throughput phenotypic screen identifies a new family of potent anti-amoebic compounds

Entamoeba histolytica is a disease-causing parasitic amoeba which affects an estimated 50 million people worldwide, particularly in socioeconomically vulnerable populations experiencing water sanitation issues. Infection with E. histolytica is referred to as amoebiasis, and can cause symptoms such as colitis, dysentery, and even death in extreme cases. Drugs exist that are capable of killing this parasite, but they are hampered by downsides such as significant adverse effects at therapeutic concentrations, issues with patient compliance, the need for additional drugs to kill the transmissible cyst stage, and potential development of resistance. Past screens of small and medium sized chemical libraries have yielded anti-amoebic candidates, thus rendering high-throughput screening a promising direction for new drug discovery in this area. In this study, we screened a curated 81,664 compound library from Janssen pharmaceuticals against E. histolytica trophozoites in vitro, and from it identified a highly potent new inhibitor compound. The best compound in this series, JNJ001, showed excellent inhibition activity against E. histolytica trophozoites with EC50 values at 0.29 μM, which is better than the current approved treatment, metronidazole. Further experimentation confirmed the activity of this compound, as well as that of several structurally related compounds, originating from both the Janssen Jump-stARter library, and from chemical vendors, thus highlighting a new structure-activity relationship (SAR). In addition, we confirmed that the compound inhibited E. histolytica survival as rapidly as the current standard of care and inhibited transmissible cysts of the related model organism Entamoeba invadens. Together these results constitute the discovery of a novel class of chemicals with favorable in vitro pharmacological properties. The discovery may lead to an improved therapy against this parasite and in all of its life stages.

Alcohol Abuse Drug Disulfiram Is Effective against Cyst Stages of Entamoeba histolytica Parasite

New anti-Entamoeba histolytica multistage drugs are needed because only one drug class, nitroimidazoles, is available for treating invasive disease, and it does not effectively eradicate the infective cyst stage. Zinc ditiocarb (ZnDTC), a main metabolite of the FDA-approved drug disulfiram, was recently shown to be highly effective against the invasive trophozoite stage. In this brief report, we show that ZnDTC is active against cysts, with similar potency to first-line cysticidal drug paromomycin.

Comparative Surfaceome Analysis of Clonal Histomonas meleagridis Strains with Different Pathogenicity Reveals Strain-Dependent Profiles

Histomonas meleagridis, a poultry-specific intestinal protozoan parasite, is histomonosis’s etiological agent. Since treatment or prophylaxis options are no longer available in various countries, histomonosis can lead to significant production losses in chickens and mortality in turkeys. The surfaceome of microbial pathogens is a crucial component of host–pathogen interactions. Recent proteome and exoproteome studies on H. meleagridis produced molecular data associated with virulence and in vitro attenuation, yet the information on proteins exposed on the cell surface is currently unknown. Thus, in the present study, we identified 1485 proteins and quantified 22 and 45 upregulated proteins in the virulent and attenuated strains, respectively, by applying cell surface biotinylation in association with high-throughput proteomic analysis. The virulent strain displayed upregulated proteins that could be linked to putative virulence factors involved in the colonization and establishment of infection, with the upregulation of two candidates being confirmed by expression analysis. In the attenuated strain, structural, transport and energy production proteins were upregulated, supporting the protozoan’s adaptation to the in vitro environment. These results provide a better understanding of the surface molecules involved in the pathogenesis of histomonosis, while highlighting the pathogen’s in vitro adaptation processes.

Gasdermins in Innate Host Defense Against Entamoeba histolytica and Other Protozoan Parasites

Gasdermins (GSDMs) are a group of proteins that are cleaved by inflammatory caspases to induce pore formation in the plasma membrane to cause membrane permeabilization and lytic cell death or pyroptosis. All GSDMs share a conserved structure, containing a cytotoxic N-terminal (NT) pore-forming domain and a C-terminal (CT) repressor domain. Entamoeba histolytica (Eh) in contact with macrophages, triggers outside-in signaling to activate inflammatory caspase-4/1 via the noncanonical and canonical pathway to promote cleavage of gasdermin D (GSDMD). Cleavage of GSDMD removes the auto-inhibition that masks the active pore-forming NT domain in the full-length protein by interactions with GSDM-CT. The cleaved NT-GSDMD monomers then oligomerize to form pores in the plasma membrane to facilitate the release of IL-1β and IL-18 with a measured amount of pyroptosis. Pyroptosis is an effective way to counteract intracellular parasites, which exploit replicative niche to avoid killing. To date, most GSDMs have been verified to perform pore-forming activity and GSDMD-induced pyroptosis is rapidly emerging as a mechanism of anti-microbial host defence. Here, we review our comprehensive and current knowledge on the expression, activation, biological functions, and regulation of GSDMD cleavage with emphases on physiological scenario and related dysfunctions of each GSDM member as executioner of cell death, cytokine secretion and inflammation against Eh and other protozoan parasitic infections.

PTEN differentially regulates endocytosis, migration, and proliferation in the enteric protozoan parasite Entamoeba histolytica

PTEN is a lipid phosphatase that is highly conserved and involved in a broad range of biological processes including cytoskeletal reorganization, endocytosis, signal transduction, and cell migration in all eukaryotes. Although regulation of phosphatidylinositol (3,4,5)-trisphosphate [PtdIns(3,4,5)P3] signaling via PTEN has been well established in model organisms and mammals, it remains elusive in the parasitic protist E. histolytica, which heavily relies on PtdIns phosphate(s)-dependent membrane traffic, migration, and phago- and trogocytosis for its pathogenesis. In this study, we characterized the major PTEN from E. histolytica, EhPTEN1, which shows the highest expression at the transcript level in the trophozoite stage among 6 possible PTENs, to understand the significance of PtdIns(3,4,5)P3 signaling in this parasite. Live imaging of GFP-EhPTEN1 expressing amebic trophozoites showed localization mainly in the cytosol with a higher concentration at pseudopods and the extending edge of the phago- and trogocytic cups. Furthermore, quantitative analysis of phago- and trogocytosis using a confocal image cytometer showed that overexpression of EhPTEN1 caused reduction in trogo- and phagocytosis while transcriptional gene silencing of EhPTEN1 gene caused opposite phenotypes. These data suggest that EhPTEN1 has an inhibitory role in these biological processes. Conversely, EhPTEN1 acts as a positive regulator for fluid-phase and receptor-mediated endocytosis in E. histolytica trophozoites. Moreover, we showed that EhPTEN1 was required for optimal growth and migration of this parasite. Finally, the phosphatase activity of EhPTEN1 towards PtdIns(3,4,5)P3 was demonstrated, suggesting that the biological roles of EhPTEN1 are likely linked to its catalytic function. Taken together, these results indicate that EhPTEN1 differentially regulates multiple cellular activities essential for proliferation and pathogenesis of the organism, via PtdIns(3,4,5)P3 signaling. Elucidation of biological roles of PTEN and PtdIns(3,4,5)P3 signaling at the molecular levels promotes our understanding of the pathogenesis of this parasite.

In Vitro and In Vivo Antiamebic Activity of Iron-Targeting Polypyridine Compounds against Enteric Protozoan Parasite Entamoeba histolytica

The infectious protozoan parasite Entamoeba histolytica is responsible for amebiasis causing colitis and liver abscesses, which is an epidemic in developing countries. To develop a drug discovery strategy targeting the iron source required for the proliferation of E. histolytica, an untapped chemical group consisting of low-molecular-weight compounds with metal-binding affinity was investigated. Electrochemically neutral polypyridine compounds, PHN-R₂, that showed specific Fe(II)-binding affinity and growth inhibitory ability against E. histolytica were identified. Furthermore, the iron-dependent IC₅₀ values of PHN-R₂ and the spectrometric analytical data of their iron complexes clarified the relationship between the antiamebic activity and the iron-targeting specificity. Notably, when PHN-H₂ was administrated to E. histolytica-infected hamsters as an animal model of amebiasis, it exhibited a prominent therapeutic efficacy to completely cure liver abscesses without serious side effects. Deciphering the antiamebic activity of iron-targeting compounds in vitro and in vivo provides valuable insights into the development of a next-generation drug against amebiasis.

Parasites in surgically removed appendices as a neglected public health concern: a systematic review and meta-analysis

The role of various parasitic infections in the occurrence of appendicitis is illustrated through cases recorded all over the world. The purpose of the current study was to estimate the global prevalence of parasite infestation (other than E. vermicularis) in appendectomy specimens.In the setting of the PRISMA guidelines, multiple databases (Science Direct, Scopus, Web of Science, PubMed, and Google Scholar) were explored in articles published until 28 September 2020. Totally, 62 studies (106 datasets) with 77, 619 participants were included in the analysis.The pooled prevalence of parasites in appendectomy samples was as follows; 0.012% (95% CI; 0.004-0.025) for Ascaris lumbricoides, 0.004% (95% CI; 0.001-0.009) for Trichuris trichiura, 0.025% (95% CI; 0.007-0.052) for Schistosoma mansoni, 0.002% (95% CI; 0.001-0.005) for Taenia spp., 0.061% (95% CI; 0.020-0.122) for Entamoeba histolytica and 0.034% (95% CI; 0.018-0.056) for Giardia lamblia.Our results demonstrated that the risk of appendicitis may increase in the presence of helminth and protozoan infections. As such, the most cases of parasites in appendectomy specimens were reported in developing countries. Regular screening plans for diagnosis, treatment and prevention are needed for prevention of parasitic infection as well as parasitic associated appendicitis, especially in endemic regions of the world.

Protein Phosphatase PP2C Identification in Entamoeba spp

Entamoeba histolytica is the causative agent of amoebiasis, and Entamoeba dispar is its noninvasive morphological twin. Entamoeba invadens is a reptilian parasite. In the present study, Western blot, phosphatase activity, immunofluorescence, and bioinformatic analyses were used to identify PP2C phosphatases of E. histolytica, E. dispar, and E. invadens. PP2C was identified in trophozoites of all Entamoeba species and cysts of E. invadens. Immunoblotting using a Leishmania mexicana anti-PP2C antibody recognized a 45.2 kDa PP2C in all species. In E. histolytica and E. invadens, a high molecular weight element PP2C at 75 kDa was recognized, mainly in cysts of E. invadens. Immunofluorescence demonstrated the presence of PP2C in membrane and vesicular structures in the cytosol of all species analyzed. The ~75 kDa PP2C of Entamoeba spp. shows the conserved domain characteristic of phosphatase enzymes (according to in silico analysis). Possible PP2C participation in the encystation process was discussed.

The flip side of reactive oxygen species in the tropical disease-Amoebiasis

Entamoeba histolytica is the conductive agent of amoebiasis. Upon the parasite's infection, macrophages and neutrophils are activated by interferon γ, IL-13 and tumour necrosis factor. These immune cells then carry out the amoebicidal activity by releasing nitric oxide synthase and reactive oxygen species (ROS). This review talks about the protective and destructive role of ROS in Eh. E. histolytica has defence strategies against oxidative stress which is a result of excess ROS production. They possess antioxidants for their defence such as L-Cysteine, flavodiiron proteins, peroxiredoxin and trichostatin A, which contribute to the parasite's virulence. The ROS are harmful to the host cells as excess ROS production stimulates cell death by mechanisms like apoptosis and necroptosis. NADPH oxidase (NOX) is a key source of ROS in mammalian cells and causes apoptosis of host cells via the protein kinase transduction pathway. This review provides insights into why NOX inhibitors that could be a potent antiparasitic drug, is not effective for in vivo purposes. This paper also gives an insight into a solution that could be a potent source in generating new treatment and vaccines for amoebiasis by targeting parasite development.

Revisiting the Mechanisms of Immune Evasion Employed by Human Parasites

For the establishment of a successful infection, i.e., long-term parasitism and a complete life cycle, parasites use various diverse mechanisms and factors, which they may be inherently bestowed with, or may acquire from the natural vector biting the host at the infection prelude, or may take over from the infecting host, to outmaneuver, evade, overcome, and/or suppress the host immunity, both innately and adaptively. This narrative review summarizes the up-to-date strategies exploited by a number of representative human parasites (protozoa and helminths) to counteract the target host immune defense. The revisited information should be useful for designing diagnostics and therapeutics as well as vaccines against the respective parasitic infections.

Immune Response to the Enteric Parasite Entamoeba histolytica

Entamoeba histolytica is a protozoan parasite responsible for amoebiasis, a disease with a high prevalence in developing countries. Establishing an amoebic infection involves interplay between pathogenic factors for invasion and tissue damage, and immune responses for protecting the host. Here, we review the pathogenicity of E. histolytica and summarize the latest knowledge on immune response and immune evasion mechanisms during amoebiasis.

Differential Exoproteome and Biochemical Characterisation of Neoparamoeba perurans

Infection with the protozoan ectoparasite Neoparamoeba perurans, the causative agent of AGD, remains a global threat to salmonid farming. This study aimed to analyse the exoproteome of both an attenuated and virulent N. perurans isolate using proteomics and cytotoxicity testing. A disproportionate presence of proteins from the co-cultured microbiota of N. perurans was revealed on searching an amalgamated database of bacterial, N. perurans and Amoebozoa proteins. LC-MS/MS identified 33 differentially expressed proteins, the majority of which were upregulated in the attenuated exoproteome. Proteins of putative interest found in both exoproteomes were maltoporin, ferrichrome-iron receptor, and putative ferric enterobactin receptor. Protease activity remained significantly elevated in the attenuated exoproteome compared with the virulent exoproteome. Similarly, the attenuated exoproteome had a significantly higher cytotoxic effect on rainbow trout gill cell line (RTgill W1) cells compared with the virulent exoproteome. The presence of a phosphatase and serine protease in the virulent exoproteome may facilitate AGD infection but do not appear to be key players in causing cytotoxicity. Altogether, this study reveals prolonged culture of N. perurans affects the exoproteome composition in favour of nutritional acquisition, and that the current culturing protocol for virulent N. perurans does not facilitate the secretion of virulence factors.

Neutrophils vs. amoebas: Immunity against the protozoan parasite Entamoeba histolytica

Entamoeba histolytica is a protozoan parasite with high prevalence in developing countries, and causes amoebiasis. This disease affects the intestine and the liver, and is the third leading cause of human deaths among parasite infections. E. histolytica infection of the intestine or liver is associated with a strong inflammation characterized by a large number of infiltrating neutrophils. Consequently, several reports suggest that neutrophils play a protective role in amoebiasis. However, other reports indicate that amoebas making direct contact with neutrophils provoke lysis of these leukocytes, resulting in the release of their lytic enzymes, which in turn provoke tissue damage. Therefore, the role of neutrophils in this parasitic infection remains controversial. Neutrophils migrate from the circulation to sites of infection, where they display several antimicrobial functions, including phagocytosis, degranulation, and formation of neutrophil extracellular traps (NET). Recently, it was found that E. histolytica trophozoites are capable of inducing NET formation. Neutrophils in touch with amoebas launched NET in an explosive manner around the amoebas and completely covered them in nebulous DNA and cell aggregates where parasites got immobilized and killed. In addition, the phenotype of neutrophils can be modified by the microbiome resulting in protection against amoebas. This review describes the mechanisms of E. histolytica infection and discusses the novel view of how neutrophils are involved in innate immunity defense against amoebiasis. Also, the mechanisms on how the microbiome modulates neutrophil function are described.

Entamoeba gingivalis Exerts Severe Pathogenic Effects on the Oral Mucosa

The protozoan Entamoeba gingivalis colonizes the healthy oral mucosa with a prevalence of 15%. Colonization can be asymptomatic, and it is considered not pathogenic. However, it is able to invade lacerated oral mucosa, where it ingests fragments of live cells, suggesting pathogenous potential. Here, we characterized the transcriptomes of gingival cells after infection with E. gingivalis using RNA sequencing and observed pathogen interaction with the epithelial monolayer barrier by scanning electron microscopy. In epithelial and fibroblast cells, strongest differential expression showed gene set “chemokines and inflammatory molecules in myeloid cells” (area under the curve [AUC] = 0.9, effect size 5.15, adjusted P = 3.1 × 10⁻¹⁹) and “cell cycle and growth arrest” (AUC = 0.91, effect size = 4.56, adjusted P = 4.8 × 10⁻⁹), respectively. The most upregulated genes were TNF (fold change 430) and IL8 (fold change 359) in epithelial cells and ZN331 (fold change 18) in fibroblasts. We showed that E. gingivalis killed live epithelial cells by trogocytosis, demonstrating strong pathogenic potential.

Evaluation of the PEΔIII-LC3-KDEL3 Chimeric Protein of Entamoeba histolytica-Lectin as a Vaccine Candidate against Amebic Liver Abscess

Entamoeba histolytica is an intestinal parasite that causes dysentery and amebic liver abscess. E. histolytica has the capability to invade host tissue by union of virulence factor Gal/GalNAc lectin; this molecule induces an adherence-inhibitory antibody response as well as to protect against amebic liver abscess (ALA). The present work showed the effect of the immunization with PEΔIII-LC3-KDEL3 recombinant protein. In vitro, this candidate vaccine inhibited adherence of E. histolytica trophozoites to HepG2 cell monolayer, avoiding the cytolysis, and in a hamster model, we observed a vaccine-induced protection against the damage to tissue liver and the inhibition of uncontrolled inflammation. PEΔIII-LC3-KDEL3 reduced the expression of TNF-α, IL-1β, and NF-κB in all immunized groups at 4- and 7-day postinfection. The levels of IL-10, FOXP3, and IFN-γ were elevated at 7 days. The immunohistochemistry assay confirmed this result, revealing an elevated quantity of +IFN-γ cells in the liver tissue. ALA formation in hamsters immunized was minimal, and few trophozoites were identified. Hence, immunization with PEΔIII-LC3-KDEL3 herein prevented invasive amebiasis, avoided an acute proinflammatory response, and activated a protective response within a short time. Finally, this recombinant protein induced an increase of serum IgG.

Antineoplastic kinase inhibitors: A new class of potent anti-amoebic compounds

Entamoeba histolytica is a protozoan parasite which infects approximately 50 million people worldwide, resulting in an estimated 70,000 deaths every year. Since the 1960s E. histolytica infection has been successfully treated with metronidazole. However, drawbacks to metronidazole therapy exist, including adverse effects, a long treatment course, and the need for an additional drug to prevent cyst-mediated transmission. E. histolytica possesses a kinome with approximately 300–400 members, some of which have been previously studied as potential targets for the development of amoebicidal drug candidates. However, while these efforts have uncovered novel potent inhibitors of E. histolytica kinases, none have resulted in approved drugs. In this study we took the alternative approach of testing a set of twelve previously FDA-approved antineoplastic kinase inhibitors against E. histolytica trophozoites in vitro. This resulted in the identification of dasatinib, bosutinib, and ibrutinib as amoebicidal agents at low-micromolar concentrations. Next, we utilized a recently developed computational tool to identify twelve additional drugs with human protein target profiles similar to the three initial hits. Testing of these additional twelve drugs led to the identification of ponatinib, neratinib, and olmutinib were identified as highly potent, with EC₅₀ values in the sub-micromolar range. All of these six drugs were found to kill E. histolytica trophozoites as rapidly as metronidazole. Furthermore, ibrutinib was found to kill the transmissible cyst stage of the model organism E. invadens. Ibrutinib thus possesses both amoebicidal and cysticidal properties, in contrast to all drugs used in the current therapeutic strategy. These findings together reveal antineoplastic kinase inhibitors as a highly promising class of potent drugs against this widespread and devastating disease.

Every year, nearly a hundred thousand people worldwide die from infection by the intestinal parasite Entamoeba histolytica, despite the widespread availability of metronidazole as a treatment. Here we report that six anticancer drugs of the kinase inhibitor class possess potent anti-amoebic properties, with one of them killing both actively dividing parasite and its transmissible cysts. These anticancer kinase inhibitors, including the dual-purpose drug with both amoebicidal and cysticidal activities may be used to treat amoebiasis, especially in cancer patients or in life-threatening brain- and liver-infecting forms of the disease.

An encapsulated bulky abdominal abscess due to amoeba

We report a rare case of amebiasis associated with an intraabdominal abscess without colitis, an intestinal perforation, or other extraintestinal amebiasis. A patient was admitted with cirrhosis and a history of spontaneous bacterial peritonitis (SBP) and was found to have a high C-reactive protein (CRP) level. Dynamic CT and ultrasound echo findings showed an intraabdominal abscess. No intestinal lesions or extraintestinal lesions other than the intraabdominal abscess were observed. Blood cultures and puncture fluid cultures were negative for bacteria. However, microscopic examination of the puncture fluid showed a cystic form of amoeba, leading to a diagnosis of an amoeba abscess. The abscess disappeared after 10 days of oral treatment with metronidazole. When an abdominal abscess is seen in an immunocompromised patient such as a cirrhotic patient, amoeba infection should be considered as a possible diagnosis.

Low molecular weight protein tyrosine phosphatase (LMW-PTP2) protein can potentially modulate virulence of the parasite Entamoeba histolytica

The Entamoeba histolytica parasite is the causative agent of amebiasis, infecting approximately 1% of the world population and causing 100,000 deaths per year. It binds to Fibronectin (FN), activating signaling pathways regulated by kinases and phosphatases. EhLMW-PTPs genes from E. histolytica encode for Low Molecular Weight Tyrosine Phosphatases expressed in trophozoites and amoebic cysts. The role of these phosphatases in the virulence of the parasite has not yet been well characterized. Our results showed a differential expression of the EhLMW-PTPs, at the mRNA and protein levels, in an asynchronous trophozoites culture. Furthermore, we observed that trophozoites transfected that overexpressed EhLMW-PTP2 phagocytized fewer erythrocytes, possibly due to decreased phagocytic cups, and showed deficiencies in adherence to FN and less cytopathic effect. These analyzes suggest that the parasite's EhLMW-PTPs have an essential role in the mechanisms of proliferation, adhesion, and phagocytosis, regulating its pathogenicity.

Solution structure of the inhibitor of cysteine proteases 1 from Entamoeba histolytica reveals a possible auto regulatory mechanism

The genome of Entamoeba histolytica encodes approximately 50 Cysteine Proteases (CPs) whose activity is regulated by two Inhibitors of Cysteine Proteases (ICPs), EhICP1 and EhICP2. The main difference between both EhICPs is the acquisition of a 17 N-terminal targeting signal in EhICP2 and three exposed cysteine residues in EhICP1. The three exposed cysteines in EhICP1 potentiate the formation of cross-linking species that drive heterogeneity. Here we solved the NMR structure of EhICP1 using a mutant protein without accessible cysteines. Our structural data shows that EhICP1 adopts an immunoglobulin fold composed of seven β-strands, and three solvent exposed loops that resemble the structures of EhICP2 and chagasin. EhICP1 and EhICP2 are able to inhibit the archetypical cysteine protease papain by intercalating their BC loops into the protease active site independently of the character of the residue (serine or threonine) responsible to interact with the active site of papain. EhICP1 and EhICP2 present signals of functional divergence as they clustered in different clades. Two of the three exposed cysteines in EhICP1 are located at the DE loop that intercalates into the CP substrate-binding cleft. We propose that the solvent exposed cysteines of EhICP1 play a role in regulating its inhibitory activity and that in oxidative conditions, the cysteines of EhICP1 react to form intra and intermolecular disulfide bonds that render an inactive inhibitor. EhICP2 is not subject to redox regulation, as this inhibitor does not contain a single cysteine residue. This proposed redox regulation may be related to the differential cellular localization between EhICP1 and EhICP2.

Direct and high-throughput assays for human cell killing through trogocytosis by Entamoeba histolytica

Entamoeba histolytica is the causative agent of amoebiasis. Pathogenesis is associated with profound damage to human tissues. We previously showed that amoebae kill human cells through trogocytosis. Trogocytosis is likely to underlie tissue damage during infection, although the mechanism is still unknown. Trogocytosis is difficult to assay quantitatively, which makes it difficult to study. Here, we developed two new, complementary assays to measure trogocytosis by quantifying human cell death. One assay uses CellTiterGlo, a luminescent readout for ATP, as a proxy for cell death. We found that the CellTiterGlo could be used to detect death of human cells after co-incubation with amoebae, and that it was sensitive to inhibition of actin or the amoeba surface Gal/GalNAc lectin, two conditions that are known to inhibit amoebic trogocytosis. The other assay uses two fluorescent nuclear stains to directly differentiate live and dead human cells by microscopy, and is also sensitive to inhibition of amoebic trogocytosis through interference with actin. Both assays are simple and inexpensive, can be used with suspension and adherent human cell types, and are amenable to high-throughput approaches. These new assays are tools to improve understanding of trogocytosis and amoebiasis pathogenesis.

Role of inflammasomes in innate host defense against Entamoeba histolytica

Intestinal amebiasis is the disease caused by the extracellular protozoan parasite Entamoeba histolytica (Eh) that induces a dynamic and heterogeneous interaction profile with the host immune system during disease pathogenesis. In 90% of asymptomatic infection, Eh resides with indigenous microbiota in the outer mucus layer of the colon without prompting an immune response. However, for reasons that remain unclear, in a minority of the Eh-infected individuals, this fine tolerated relationship is switched to a pathogenic phenotype and advanced to an increasingly complex host-parasite interaction. Eh disease susceptibility depends on parasite virulence factors and their interactions with indigenous bacteria, disruption of the mucus bilayers, and adherence to the epithelium provoking host immune cells to evoke a robust pro-inflammatory response mediated by inflammatory caspases and inflammasome activation. To understand Eh pathogenicity and innate host immune responses, this review highlights recent advances in our understanding of how Eh induces outside-in signaling via Mϕs to activate inflammatory caspases and inflammasome to regulate pro-inflammatory responses.

EhC2B, a C2 domain-containing protein, promotes erythrophagocytosis in Entamoeba histolytica via actin nucleation

Remodelling of the actin cytoskeleton in response to external stimuli is obligatory for many cellular processes in the amoebic cell. A rapid and local rearrangement of the actin cytoskeleton is required for the development of the cellular protrusions during phagocytosis, trogocytosis, migration, and invasion. Here, we demonstrated that EhC2B, a C2 domain-containing protein, is an actin modulator. EhC2B was first identified as an effector of EhRab21 from E. histolytica. In vitro interaction studies including GST pull-down, fluorescence-based assay and ITC also corroborated with our observation. In the amoebic trophozoites, EhC2B accumulates at the pseudopods and the tips of phagocytic cups. FRAP based studies confirmed the recruitment and dynamics of EhC2B at the phagocytic cup. Moreover, we have shown the role of EhC2B in erythrophagocytosis. It is well known that calcium-dependent signal transduction is essential for the cytoskeletal dynamics during phagocytosis in the amoebic parasite. Using liposome pelleting assay, we demonstrated that EhC2B preferentially binds to the phosphatidylserine in the presence of calcium. The EhC2B mutants defective in calcium or lipid-binding failed to localise beneath the plasma membrane. The cells overexpressing these mutants have also shown a significant reduction in erythrophagocytosis. The role of EhC2B in erythrophagocytosis and pseudopod formation was also validated by siRNA-based gene knockdown approach. Finally, with the help of in vitro nucleation assay using fluorescence spectroscopy and total internal reflection fluorescence microscopy, we have established that EhC2B is an actin nucleator. Collectively, based on the results from the study, we propose that EhC2B acts like a molecular bridge which promotes membrane deformation via its actin nucleation activity during the progression of the phagocytic cup in a calcium-dependent manner.

Insights into amebiasis using a human 3D-intestinal model

Entamoeba histolytica is the causative agent of amebiasis, an infectious disease targeting the intestine and the liver in humans. Two types of intestinal infection are caused by this parasite: silent infection, which occurs in the majority of cases, and invasive disease, which affects 10% of infected persons. To understand the intestinal pathogenic process, several in vitro models, such as cell cultures, human tissue explants or human intestine xenografts in mice, have been employed. Nevertheless, our knowledge on the early steps of amebic intestinal infection and the molecules involved during human-parasite interaction is scarce, in part due to limitations in the experimental settings. In the present work, we took advantage of tissue engineering approaches to build a three-dimensional (3D)-intestinal model that is able to replicate the general characteristics of the human colon. This system consists of an epithelial layer that develops tight and adherens junctions, a mucus layer and a lamina propria-like compartment made up of collagen containing macrophages and fibroblast. By means of microscopy imaging, omics assays and the evaluation of immune responses, we show a very dynamic interaction between E. histolytica and the 3D-intestinal model. Our data highlight the importance of several virulence markers occurring in patients or in experimental models, but they also demonstrate the involvement of under described molecules and regulatory factors in the amoebic invasive process.

Lipids in Entamoeba histolytica: Host-Dependence and Virulence Factors

Lipids are essential players in parasites pathogenesis. In particular, the highly phagocytic trophozoites of Entamoeba histolytica, the causative agent of amoebiasis, exhibit a dynamic membrane fusion and fission, in which lipids strongly participate; particularly during the overstated motility of the parasite to reach and attack the epithelia and ingest target cells. Synthesis and metabolism of lipids in this protozoan present remarkable difference with those performed by other eukaryotes. Here, we reviewed the current knowledge on lipids in E. histolytica. Trophozoites synthesize phosphatidylcholine and phosphatidylethanolamine by the Kennedy pathway; and sphingolipids, phosphatidylserine, and phosphatidylinositol, by processes similar to those used by other eukaryotes. However, trophozoites lack enzymes for cholesterol and fatty acids synthesis, which are scavenged from the host or culture medium by specific mechanisms. Cholesterol, a fundamental molecule for the expression of virulence, is transported from the medium into the trophozoites by EhNPC1 and EhNPC2 proteins. Inside cells, lipids are distributed by different pathways, including by the participation of the endosomal sorting complex required for transport (ESCRT), involved in vesicle fusion and fission. Cholesterol interacts with the phospholipid lysobisphosphatidic acid (LBPA) and EhADH, an ALIX family protein, also involved in phagocytosis. In this review, we summarize the known information on phospholipids synthesis and cholesterol transport as well as their metabolic pathways in E. histolytica; highlighting the mechanisms used by trophozoites to dispose lipids involved in the virulence processes.

Decreasing trend of seroprevalence of hepatic amoebiasis in tertiary care hospital of North India: 2010-2015

BACKGROUND:

Globally, amoebic liver abscess, a common extraintestinal complication of intestinal amoebiasis. Diagnosis of hepatic amoebiasis is based on the detection of anti-Entamoeba histolytica immunoglobulin G (IgG) antibody using enzyme-linked immunosorbent assay (ELISA), because of its technique's relatively higher sensitivity and specificity (90%).

AIM:

The aim of the present study was to determine the seroprevalence of hepatic amoebiasis in a referral tertiary care hospital in North India.

MATERIALS AND METHODS:

The blood samples were tested specifically for anti-E. histolytica IgG antibody using commercially available ELISA kit (RIDASCREEN^®E. histolytica IgG [K1721] kit).

RESULTS:

A total of 879 patients (n = 879) were evaluated, of which 78.49% (690/879) were positive for anti-E. histolytica IgG antibody. The seroprevalence rates showed a declining trend from 2010 to 2015 with rates falling from 91.4% to 66.7%. He present a study showed the decreasing trend of seroprevalence of hepatic amoebiasis from 2010 to 2015.

CONCLUSIONS:

This decrease may be attributed to several factors such as increase in awareness, improved hygienic practices, use of safe drinking water, better socioeconomic condition, and perhaps early treatment sought for intestinal amoebiasis.

Entamoeba histolytica and amoebic liver abscess in northern Sri Lanka: a public health problem

Entamoeba histolytica (E. histolytica) is a facultative protozoan parasite implicated in amoebic liver abscesses (ALA), the most common extraintestinal manifestation of this infection. E. histolytica is endemic to sub-tropical and tropical countries and has been a major public health concern in northern Sri Lanka (SLK) for the last three decades. This has been attributed to a multitude of factors such as poor sanitation, hygiene, male sex, middle age, overcrowding, unsanitary practices in the production of indigenous alcoholic beverages, and alcohol consumption. Additionally, while rates of E. histolytica have declined substantially throughout the rest of the island, largely due to better infrastructure, it remains pervasive in the northern peninsula, which is generally less developed. Infection arises primarily from fecal-oral transmission through the consumption of contaminated drinking water containing cysts. Upon ingestion, cysts multiply into trophozoites and colonize the host colonic mucosa using lectin and cysteine proteases as virulence factors, leading to host invasion. Symptoms occur along a spectrum, from asymptomatology, to pyrexia, abdominal cramping, and amoebic dysentery. Colonization of the colon results in the formation of distinct flask-shaped ulcers along the epithelium, and eventual penetration of the lamina propria via the production of matrix metalloproteinases. ALA then develops through trophozoite migration via the mesenteric hepatic portal circulation, where microabscesses coalesce to form a single, large right-lobe abscess, commonly on the posterior aspect. The progression of infection to invasive disease is contingent on the unique interplay between host and pathogen factors, such as the strength of host-immunity to overcome infection and inherent pathogenicity of the Entamoeba species. As a preventable illness, E. histolytica complications such as ALA impose a significant burden on the healthcare system. This mini-review highlights epidemiological trends, risk factors, diagnostic modalities, treatment approaches, and opportunities for prevention of E. histolytica-induced ALA, to help address this endemic problem on the island of SLK.

Intestinal amoebiasis: 160 years of its first detection and still remains as a health problem in developing countries

Amoebiasis is a parasitic disease caused by Entamoeba histolytica (E. histolytica), an extracellular enteric protozoan. This infection mainly affects people from developing countries with limited hygiene conditions, where it is endemic. Infective cysts are transmitted by the fecal-oral route, excysting in the terminal ileum and producing invasive trophozoites (amoebae). E. histolytica mainly lives in the large intestine without causing symptoms; however, possibly as a result of so far unknown signals, the amoebae invade the mucosa and epithelium causing intestinal amoebiasis. E. histolytica possesses different mechanisms of pathogenicity for the adherence to the intestinal epithelium and for degrading extracellular matrix proteins, producing tissue lesions that progress to abscesses and a host acute inflammatory response. Much information has been obtained regarding the virulence factors, metabolism, mechanisms of pathogenicity, and the host immune response against this parasite; in addition, alternative treatments to metronidazole are continually emerging. An accesible and low-cost diagnostic method that can distinguish E. histolytica from the most nonpathogenic amoebae and an effective vaccine are necessary for protecting against amoebiasis. However, research about the disease and its prevention has been a challenge due to the relationship between E. histolytica and the host during the distinct stages of the disease is multifaceted. In this review, we analyze the interaction between the parasite, the human host, and the colon microbiota or pathogenic microorganisms, which together give rise to intestinal amoebiasis.

Pathology Associated With an Outbreak of Entamoebiasis in Wild Cane Toads (Rhinella marina) in Tropical Australia

Infection due to Entamoeba spp. is known to cause serious disease in primates (Entamoeba histolytica) and snakes (Entamoeba invadens), but there are no detailed descriptions of the pathology associated with Entamoeba spp. infection in amphibians. In 2014, an outbreak of entamoebiasis associated with a novel species of Entamoeba induced clinical illness and poor body condition in free-ranging cane toads in Australia's Northern Territory. Here, we describe the gross pathology, histology, and clinical pathology linked to the outbreak. The study compared 25 toads with invasive entamoebiasis, defined as histologically visible amoebas within tissue, and 12 toads without invasive entamoebiasis. Grossly, affected toads had mild to marked congestion of colonic serosal vasculature, with variable thickening of the intestinal wall and serosanguineous to hemorrhagic colonic content. Histologically, invasive entamoebiasis manifested primarily as moderate to severe, variably hyperplastic to ulcerative colitis. The small intestine was affected in 10 of 25 toads, and 5 of 25 toads also had gastric lesions. Amoebas consistent in morphology with Entamoeba sp. were commonly intermingled with mucosal epithelium, frequently along the basement membrane, with deeper invasion into the superficial lamina propria in only 5 toads. Toads with invasive entamoebiasis had neutrophilia, monocytosis, and lymphopenia, and thus elevated neutrophil to lymphocyte ratios, suggestive of an inflammatory and/or stress leukogram.

Plasma membrane damage repair is mediated by an acid sphingomyelinase in Entamoeba histolytica

Entamoeba histolytica is a pathogen that during its infective process confronts the host defenses, which damages the amoebic plasma membrane (PM), resulting in the loss of viability. However, it is unknown whether amoebic trophozoites are able to repair their PM when it is damaged. Acid sphingomyelinases (aSMases) have been reported in mammalian cells to promote endocytosis and removal of PM lesions. In this work, six predicted amoebic genes encoding for aSMases were found to be transcribed in the HM1:IMSS strain, finding that the EhaSM6 gene is the most transcribed in basal growth conditions and rendered a functional protein. The secreted aSMase activity detected was stimulated by Mg⁺² and inhibited by Co⁺². Trophozoites that overexpress the EhaSM6 gene (HM1-SM6HA) exhibit an increase of 2-fold in the secreted aSMase activity. This transfectant trophozoites exposed to pore-forming molecules (SLO, Magainin, β-Defensin 2 and human complement) exhibited an increase from 6 to 25-fold in the secreted aSMase activity which correlated with higher amoebic viability in a Ca⁺² dependent process. However, other agents that affect the PM such as hydrogen peroxide also induced an increase of secreted aSMase, but to a lesser extent. The aSMase6 enzyme is N- and C-terminal processed. Confocal and transmission electron microscopy showed that trophozoites treated with SLO presented a migration of lysosomes containing the aSMase towards the PM, inducing the formation of membrane patches and endosomes in the control strain. These cellular structures were increased in the overexpressing strain, indicating the involvement of the aSMase6 in the PM injury repair. The pore-forming molecules induced an increase in the expression of EhaSM1, 2, 5 and 6 genes, meanwhile, hydrogen peroxide induced an increase in all of them. In all the conditions evaluated, the EhaSM6 gene exhibited the highest levels of induction. Overall, these novel findings show that the aSMase6 enzyme from E. histolytica promotes the repair of the PM damaged with pore-forming molecules to prevent losing cell integrity. This novel system could act when encountered with the lytic defense systems of the host.

The host-amoeba relationship is based on a series of interplays between host defense mechanisms and parasite survival strategies. While host cells elaborate diverse mechanisms for pathogen elimination, Entamoeba histolytica trophozoites have also developed complex strategies to counteract host immune response and facilitate its own survival while confronting host defenses. E. histolytica exposed to pore-forming proteins such as β-Defensin 2, human complement and Streptolysin O (SLO), increases the activity of secreted aSMase, which is related to greater amoebic viability. Other agents that affect plasma membrane (PM) may also increase secreted aSMase but to a lesser extent. SLO form pores in the PM of E. histolytica trophozoites that initiates the uncontrolled entry of Ca²⁺, recognized as the primary trigger for cell responses which favors the migration of the lysosomes to the periphery of the cell, fuses with the PM and release their content, including aSMase to the external side of the cell. The secreted aSMase favoring the internalization of the lesion for its degradation in phagolysosomes. During the early stages of PM damage, the pores are rapidly blocked by patch-like structures that prevent the lysis of the trophozoite and immediately begin internalizing the lesion. The aSMase6 overexpression favors the repair of the lesion and the survival of E. histolytica trophozoites. Pore-forming proteins induced an increase in the expression of EhaSM1, 2, 5 and 6 genes, meanwhile oxidative stress induced an increase in all of them. Here we report, for the first time, that E. histolytica possess a mechanism for PM damage repair mediated by aSMase similar to the system described in mammalian cells.

Multiple colonic and ileal perforations due to unsuspected intestinal amoebiasis-Case report and review

Amoebiasis, caused by the intestinal protozoan Entamoeba histolytica, though a relatively common parasitic disease in the tropical and subtropical regions, is uncommon in the developed countries. In these countries, as amoebic colitis shares similar clinical symptoms and endoscopic features with inflammatory bowel disease (IBD), these cases can be easily unrecognized and misdiagnosed. In this case report, we discuss the case of an adult patient with invasive intestinal amoebiasis, who was initially managed as Crohn's disease on corticosteroid treatment and subsequently rapidly deteriorated and developed multiple perforations in the colon and ileum. Despite total colectomy followed by resection of the small bowel, he died of multiple organ failure and sepsis within two months of his initial clinical presentation of diarrhea with abdominal pain. The learning point of this case is that invasive intestinal amoebiasis should be considered as a differential diagnosis at the first clinical adult presentation of IBD-like symptoms despite suggestive endoscopic findings of Crohn's like ulcers. Regardless of negative endoscopic biopsies, due to the low sensitivity of microscopic examination, serology test for antibody and molecular test for Entamoeba DNA are recommended for accurate detection and identification of Entamoeba species, especially in the high risk populations with recent travel to endemic zones and for patients with immunosuppression and comorbidities such as diabetes mellitus, tuberculosis, alcoholism, HIV/AIDS and in pregnant women. Amoebiasis should be completely ruled out prior to corticosteroid administration, to avoid severe complications such as fulminant intestinal amoebiasis which is associated with an inherently high mortality.

The delicate balance between Entamoeba histolytica, mucus and microbiota

Entamoeba histolytica (Eh) is a protozoan parasite of humans that colonizes the outer colonic mucus layer. Under conditions not fully understood, Eh breaches innate host defenses and invades the intestinal mucosa-causing amebic colitis and liver abscess. In asymptomatic infection, Eh interacts with and feeds on resident microbiota that forms biofilms on the outer colonic mucus layer. Despite the close association between Eh and commensal microbiota, we still lack basic knowledge on whether microbiota and/or their metabolites influence Eh virulence traits critical in disease pathogenesis. In the pathogenesis of intestinal amebiasis, Eh overcomes the protective mucus layer using a combination of mucinase/glycosidase and potent mucus secretagogue activity. In this addendum, we discuss the interconnected role of a healthy mucus barrier and the role commensal microbiota play in shaping innate host defense against Eh-induced pro-inflammatory and secretory responses critical in disease pathogenesis.

Trogocytosis by Entamoeba histolytica Mediates Acquisition and Display of Human Cell Membrane Proteins and Evasion of Lysis by Human Serum

Entamoeba histolytica causes amoebiasis, a potentially fatal diarrheal disease. Abscesses in organs such as the liver can occur when amoebae are able to breach the intestinal wall and travel through the bloodstream to other areas of the body. Therefore, understanding how E. histolytica evades immune detection is of great interest. Here, we demonstrate for the first time that E. histolytica acquires and displays human cell membrane proteins by taking “bites” of human cell material in a process named trogocytosis (“trogo-” means “nibble”), and that this allows amoebae to survive in human serum. Display of acquired proteins through trogocytosis has been previously characterized only in mammalian immune cells. Our study suggests that this is a more general feature of trogocytosis not restricted to immune cells and broadens our knowledge of eukaryotic biology. These findings also reveal a novel strategy for immune evasion by a pathogen and may apply to the pathogenesis of other infections.

We previously showed that Entamoeba histolytica kills human cells through a mechanism that we termed trogocytosis (“trogo-” means “nibble”), due to its resemblance to trogocytosis in other organisms. In microbial eukaryotes like E. histolytica, trogocytosis is used to kill host cells. In multicellular eukaryotes, trogocytosis is used for cell killing and cell-cell communication in a variety of contexts. Thus, nibbling is an emerging theme in cell-cell interactions both within and between species. When trogocytosis occurs between mammalian immune cells, cell membrane proteins from the nibbled cell are acquired and displayed by the recipient cell. In this study, we tested the hypothesis that through trogocytosis, amoebae acquire and display human cell membrane proteins. We demonstrate that E. histolytica acquires and displays human cell membrane proteins through trogocytosis and that this leads to protection from lysis by human serum. Protection from human serum occurs only after amoebae have undergone trogocytosis of live cells but not phagocytosis of dead cells. Likewise, mutant amoebae defective in phagocytosis, but unaltered in their capacity to perform trogocytosis, are protected from human serum. Our studies are the first to reveal that amoebae can display human cell membrane proteins and suggest that the acquisition and display of membrane proteins is a general feature of trogocytosis. These studies have major implications for interactions between E. histolytica and the immune system and also reveal a novel strategy for immune evasion by a pathogen. Since other microbial eukaryotes use trogocytosis for cell killing, our findings may apply to the pathogenesis of other infections.

Successful Diagnosis of a Longstanding Giant Amoebic Liver Abscess Using Contrast-Enhanced Ultrasonography (CEUS): A Case Report in a Western Country

BACKGROUND E. histolytica liver abscess results from extra-intestinal diffusion of amebiasis, which is responsible for up 100 000 deaths per annum, placing it second only to malaria in mortality. Currently, the criterion standard for the diagnosis of liver abscesses is ultrasound, but CEUS (contrast-enhanced ultrasound) is emerging as a more accurate method for liver study, and it could be more accurate than ultrasound and non-invasive compared to CT. CASE REPORT A white man (59 years old) with a 2-day history of dyspnea, acute abdominal pain in right upper quadrant, and raised inflammatory markers was admitted to a second-level Emergency Department in Rome (Italy). He reported several trips to tropical areas many years before, during which he ingested non-potable water and became infected with Entamoeba histolytica. This was treated medically with success. After administration of antibiotics (meropenem and metronidazole), a liver CEUS (contrast-enhanced ultrasonography) with administration of SonoVue (sulphur hexafluoride microbubbles) confirmed a giant liver abscess (15×16 cm). One day later, CT-guided drainage was performed without complications and the patient was discharged on the 25th post-procedure day, with improved blood results. CONCLUSIONS Acute abdominal pain can be caused by a variety of diseases, but a diagnosis of parasitic abscess should not be overlooked in non-endemic Western countries. CEUS is a new, promising, and more accurate technique that can be utilized to recognize liver abnormalities, including abscesses; however, retrospective population-wide studies are necessary to define the differential diagnoses.

PtdIns(4,5)P2 is generated by a novel phosphatidylinositol 4-phosphate 5-kinase in the protist parasite Entamoeba histolytica

Entamoeba histolytica is an intestinal protist parasite that causes amoebiasis, a major source of morbidity and mortality in developing countries. Phosphoinositides are involved in signalling systems that have a role in invasion and pathogenesis of this parasite. Phosphatidylinositol 4-phosphate 5-kinase (PIP5K) catalyses the generation of phosphatidylinositol(4,5)bisphosphate (PtdIns(4,5)P₂ ), a key species of phosphoinositide that regulates various cellular processes. However, phosphatidylinositol phosphate kinase (PIPK) family of enzymes have not been characterized in E. histolytica. Here, we report the identification and characterization of type I PIPK (EhPIPKI) of E. histolytica. Computational analysis revealed homologs of type I and III PIPK family in E. histolytica and the absence of type II PIPK. In spite of low overall sequence identity, the kinase domain was found to be highly conserved. Interestingly, a unique insertion of a tandem repeat motif was observed in EhPIPKI distinguishing it from existing PIPKs of other organisms. Substrate profiling showed that EhPIPKI could phosphorylate at third and fifth hydroxyl positions of phosphatidylinositols, though the predominant substrate was phosphatidylinositol 4-phosphate (PtdIns(4)P). Furthermore, EhPIPKI underwent intracellular cleavage close to the amino-terminal, generating two distinct fragments Nter-EhPIPKI (27p) and Cter-EhPIPKI (47p). Immunofluorescence and cellular fractionation revealed that the full-length EhPIPKI and the Cter-EhPIPKI containing carboxyl-terminal activation loop were present in the plasma membrane while the Nter-EhPIPKI was observed in the cytosolic region. In conclusion, E. histolytica has a single EhPIPKI gene that displays novel properties of post-translational processing, the presence of a repeat domain and substrate specificity not observed in any PIPK enzyme so far.

Tissue Destruction Caused by Entamoeba histolytica Parasite: Cell Death, Inflammation, Invasion, and the Gut Microbiome

Purpose of Review

Entamoeba histolytica is a protozoan parasite that causes amebiasis, which remains a significant cause of morbidity and mortality worldwide. E. histolytica causes tissue destruction which leads to clinical disease. This review outlines some of the recent advances that have furthered our understanding of the processes that lead to the tissue damage caused by E. histolytica.

Recent Findings

Recent studies have identified new mechanisms involved in E. histolytica–induced tissue damage. These include (i) new form of contact-dependent killing called trogocytosis; (ii) parasite-produced cytokine, macrophage migration inhibitory factor, that contributes to inflammation; (iii) exploitation of host immune response to promote invasion; and (iv) the contribution of the gut microbiome to clinical disease.

Summary

Targeting these mechanisms that result in tissue injury should be a focus of future research for the development of improved preventive and therapeutic strategies for amebiasis.

Antiamoebic drugs for treating amoebic colitis

BACKGROUND

Infection with the protozoan Entamoeba histolytica is common in low- and middle-income countries, and up to 100,000 people with severe disease die every year. Adequate therapy for amoebic colitis is necessary to reduce illness, prevent development of complicated disease and extraintestinal spread, and decrease transmission.

OBJECTIVES

To evaluate antiamoebic drugs for treating amoebic colitis.

SEARCH METHODS

We searched the available literature up to 22 March 2018. We searched the Cochrane Infectious Diseases Group Specialised Register, CENTRAL, MEDLINE, Embase, LILACS, mRCT, and conference proceedings. We contacted individual researchers, organizations, and pharmaceutical companies, and we checked reference lists.

SELECTION CRITERIA

Randomized controlled trials of antiamoebic drugs given alone or in combination, compared with placebo or another antiamoebic drug, for treating adults and children with a diagnosis of amoebic colitis.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the eligibility and methodological quality of trials and extracted and analysed the data. We calculated clinical and parasitological failure rates and rates of relapse and adverse events as risk ratios (RRs) with 95% confidence intervals (CIs), using a random-effects model. We determined statistical heterogeneity and explored possible sources of heterogeneity using subgroup analyses. We carried out sensitivity analysis by using trial quality to assess the robustness of reported results.

MAIN RESULTS

In total, 41 trials (4999 participants) met the inclusion criteria of this review. In this update, we added four trials to the 37 trials included in the first published review version. Thirty trials were published over 20 years ago. Only one trial used adequate methods of randomization and allocation concealment, was blinded, and analysed all randomized participants. Only one trial used an E histolytica stool antigen test, and two trials used amoebic culture.Tinidazole may be more effective than metronidazole for reducing clinical failure (RR 0.28, 95% CI 0.15 to 0.51; 477 participants, eight trials; low-certainty evidence) and is probably associated with fewer adverse events (RR 0.65, 95% CI 0.46 to 0.92; 477 participants, 8 trials; moderate-certainty evidence). Compared with metronidazole, combination therapy may result in fewer parasitological failures (RR 0.36, 95% CI 0.15 to 0.86; 720 participants, 3 trials; low-certainty evidence), but we are uncertain which combination is more effective than another. Evidence is insufficient to allow conclusions regarding the efficacy of other antiamoebic drugs.

AUTHORS' CONCLUSIONS

Compared with metronidazole, tinidazole may be more effective in reducing clinical failure and may be associated with fewer adverse events. Combination drug therapy may be more effective for reducing parasitological failure compared with metronidazole alone. However, these results are based mostly on small trials conducted over 20 years ago with a variety of poorly defined outcomes. Tests that detect E histolytica more accurately are needed, particularly in countries where concomitant infection with other bacteria and parasites is common.

Rab GTPases take centre stage in understanding Entamoeba histolytica biology

Rab GTPases constitute the largest subgroup in the Ras superfamily of GTPases. It is well established that different Rab GTPases are localized in discrete subcellular localization and regulate the membrane trafficking in nearly all eukaryotic cells. Rab GTPase diversity is often regarded as an expression of vesicular trafficking complexity. The pathogenic amoeba Entamoeba histolytica harbours 91 Rab GTPases which is the highest among the currently available genome sequences from the eukaryotic kingdom. Here, we review the current status of amoebic Rab GTPases diversity, unique biochemical and structural features and summarise their predicted regulators. We discuss how amoebic Rab GTPases are involved in cellular processes such as endocytosis, phagocytosis, and invasion of host cellular components, which are essential for parasite survival and virulence.

Contribution of neutral sphingomyelinases to in vitro virulence of Entamoeba histolytica

Amoebiasis is a worldwide health problem caused by the pathogen Entamoeba histolytica. Several virulence factors have been implicated in host invasion, immune evasion, and tissue damage. There are still new factors that remain to be elucidated and characterized. In this work, we obtained amoebic transfectants overexpressing three of the neutral sphingomyelinase enzymes encoded in the E. histolytica genome. The EhnSM3 overexpression induced an increase in hemolytic and cytotoxic activities, besides an increase in gene expression of amoebapore A, B, and C. Meanwhile the EhnSM1 and EhnSM2 overexpression caused an increase in cytopathic activity. In all the neutral sphingomyelinases overexpressing strains, the gene expression levels for cysteine proteinase 5, adhesin 112 and, heavy and light Gal/GalNAc lectin subunits were not affected. We propose that the increase of cytotoxic and lytic effect of EhnSM3 overexpressed strain can be related to the sum of the effect of EhnSM3 plus amoebapores, in a process cell contact-dependent or as mediator by inducing the gene expression of amoebapores enabling a link between EhnSM3 with the virulence phenotype in E. histolytica. Our results suggest a differential role for neutral sphingomyelinases in E. histolytica virulence.

Epithelial maturity influences EPEC-induced desmosomal alterations

Desmosomes are junctional protein complexes that confer strong adhesive capacity to adjacent host cells. In a recent study, we showed that enteropathogenic Escherichia coli (EPEC) disrupts desmosomes, weakens cell-cell adhesion and perturbs barrier function of intestinal epithelial (C2_BBe) cells. Desmosomal damage was dependent on the EPEC effector protein EspH and its inhibitory effect on Rho GTPases. EspH-mediated Rho inactivation resulted in retraction of keratin intermediate filaments and degradation of desmosomal cadherins. Immunofluorescence studies of EPEC-infected C2_BBe cells revealed keratin retraction towards the nucleus coincident with significant cytoplasmic redistribution of the desmosomal cadherin desmoglein-2 (DSG2). In this addendum, we expand on how EPEC-induced keratin retraction leads to loss of DSG2 anchoring at the junctions, and show that maturity of the epithelial cell monolayer impacts the fate of desmosomes during infection.

Invadosome-Mediated Human Extracellular Matrix Degradation by Entamoeba histolytica

Entamoeba histolytica is a protozoan parasite that causes invasive amoebiasis when it invades the human colon. Tissue invasion requires a shift from an adhesive lifestyle in the colonic lumen to a motile and extracellular matrix (ECM) degradative lifestyle in the colonic tissue layers. How the parasite regulates these two lifestyles is largely unknown. Previously, we showed that silencing the E. histolytica surface metalloprotease EhMSP-1 results in parasites that are hyperadherent and less motile. To better understand the molecular mechanism of this phenotype, we now show that the parasites with EhMSP-1 silenced cannot efficiently form specialized dot-like polymerized actin (F actin) structures upon interaction with the human ECM component fibronectin. We characterized these F actin structures and found that they are very short-lived structures that are the sites of fibronectin degradation. Motile mammalian cells form F actin structures called invadosomes that are similar in stability and function to these amoebic actin dots. Therefore, we propose here that E. histolytica forms amoebic invadosomes to facilitate colonic tissue invasion.

The Differential Diagnosis of Acute Colitis: Clues to a Specific Diagnosis

This review describes a systematic approach to the interpretation of colonic biopsy specimens of patients with acute colitis. Five main histologic patterns are discussed: acute colitis, focal active colitis, pseudomembranous colitis, hemorrhagic colitis, and ischemic colitis. For each pattern, the most common etiologic associations and their differential diagnoses are presented. Strategies based on histologic analysis and clinical considerations to differentiate acute from chronic colitides are discussed.