A landscape of gene regulation in the parasitic amoebozoa Entamoeba spp

Entamoeba are amoeboid extracellular parasites that represent an important group of organisms for which the regulatory networks must be examined to better understand how genes and functional processes are interrelated. In this work, we inferred the gene regulatory networks (GRNs) in four Entamoeba species, E. histolytica, E. dispar, E. nuttalli, and E. invadens, and the GRN topological properties and the corresponding biological functions were evaluated. From these analyses, we determined that transcription factors (TFs) of E. histolytica, E. dispar, and E. nuttalli are associated mainly with the LIM family, while the TFs in E. invadens are associated with the RRM_1 family. In addition, we identified that EHI_044890 regulates 121 genes in E. histolytica, EDI_297980 regulates 284 genes in E. dispar, ENU1_120230 regulates 195 genes in E. nuttalli, and EIN_249270 regulates 257 genes in E. invadens. Finally, we identified that three types of processes, Macromolecule metabolic process, Cellular macromolecule metabolic process, and Cellular nitrogen compound metabolic process, are the main biological processes for each network. The results described in this work can be used as a basis for the study of gene regulation in these organisms.

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.

The non-LTR retrotransposons of Entamoeba histolytica: genomic organization and biology

Genome sequence analysis of Entamoeba species revealed various classes of transposable elements. While E. histolytica and E. dispar are rich in non-long terminal repeat (LTR) retrotransposons, E. invadens contains predominantly DNA transposons. Non-LTR retrotransposons of E. histolytica constitute three families of long interspersed nuclear elements (LINEs), and their short, nonautonomous partners, SINEs. They occupy ~ 11% of the genome. The EhLINE1/EhSINE1 family is the most abundant and best studied. EhLINE1 is 4.8 kb, with two ORFs that encode functions needed for retrotransposition. ORF1 codes for the nucleic acid-binding protein, and ORF2 has domains for reverse transcriptase (RT) and endonuclease (EN). Most copies of EhLINEs lack complete ORFs. ORF1p is expressed constitutively, but ORF2p is not detected. Retrotransposition could be demonstrated upon ectopic over expression of ORF2p, showing that retrotransposition machinery is functional. The newly retrotransposed sequences showed a high degree of recombination. In transcriptomic analysis, RNA-Seq reads were mapped to individual EhLINE1 copies. Although full-length copies were transcribed, no full-length 4.8 kb transcripts were seen. Rather, sense transcripts mapped to ORF1, RT and EN domains. Intriguingly, there was strong antisense transcription almost exclusively from the RT domain. These unique features of EhLINE1 could serve to attenuate retrotransposition in E. histolytica.

Entamoeba histolytica Trophozoites Interact with the c-Met Receptor at the Surface of Liver Origin Cells through the Gal/GalNAc Amoebic Lectin

Amoebiasis in humans is caused by the protozoan parasite Entamoeba histolytica, which cytotoxic activity has been demonstrated on a wide variety of target cells. The process involves the adherence of the parasite to the cell, and such adherence is mediated by an amoebic surface lectin, known as Gal/GalNAc lectin. It is composed of heavy, intermediate, and light subunits. The carbohydrate recognition domain (CRD) has been identified within a cysteine-rich region in the lectin heavy subunit and has an amino acid sequence identity to the receptor-binding domain of hepatocyte growth factor (HGF). Recombinant CRD has been previously shown to compete with HGF for binding to the c-Met receptor IgG fusion protein. In the present study, we searched for evidence of interaction between the Gal/GalNAc lectin at the surface of trophozoites with the c-Met receptor expressed at the surface of HepG2 in coculture assays. Immunoprecipitation of the coculture lysate indicated interaction of the c-Met with a 60 kDa peptide recognized by antiamoebic lectin antibody. Colocalization of both molecules was detected by fluorescence confocal microscopy. Incubation of HepG2 cells with HGF before coculture with trophozoites prevents the cytotoxic effect caused by the parasites but not their adherence to the cells. Our results point to Gal/GalNAc lectin as a ligand of the c-Met receptor at the surface of HepG2 cells.

Entamoeba Chitinase is Required for Mature Round Cyst Formation

Entamoeba histolytica, a protozoan parasite, causes amoebiasis in humans. Amoebiasis transmission is solely mediated by chitin-walled cysts, which are produced in the large intestine of humans from proliferative trophozoites by a cell differentiation process called encystation. Resistance to environmental stresses, an essential characteristic for transmission, is attributed to the cyst wall, which is constructed from chitin and several protein components, including chitinase. Chitinase may play a key role in cyst wall formation; however, this has not been confirmed. Here, to elucidate the physiological role of chitinase during Entamoeba encystation, we identified a new chitinase inhibitor, 2,6-dichloro-4-[2-(1-piperazinyl)-4-pyridinyl]-N-(1,3,5-trimethyl-1H-pyrazol-4-yl)-benzenesulfonamide, by recombinant-Entamoeba chitinase-based screening of 400 Pathogen Box chemicals. This compound dose dependently inhibited native chitinase associated with Entamoeba invadens encystation, a model for E. histolytica encystation, with an 50% inhibitory concentration (IC₅₀) of ∼0.6 μM, which is comparable to the IC₅₀s (0.2 to 2.5 μM) for recombinant E. histolytica and E. invadens chitinases. Furthermore, the addition of this compound to E. invadens encystation-inducing cultures increased the generation of cyst walls with an abnormal shape, the most characteristic of which was a "pot-like structure." A similar structure also appeared in standard culture, but at a far lower frequency. These results indicate that chitinase inhibition increases the number of abnormal encysting cells, thereby significantly reducing the efficiency of cyst formation. Transmission electron microscopy showed that compound-treated encysting cells formed an abnormally loose cyst wall and an unusual gap between the cyst wall and cell membrane. Hence, Entamoeba chitinase is required for the formation of mature round cysts. IMPORTANCE Amoebiasis is caused by Entamoeba histolytica infection and is transmitted by dormant Entamoeba cells or cysts. Cysts need to be tolerant to severe environmental stresses faced outside and inside a human host. To confer this resistance, Entamoeba parasites synthesize a wall structure around the cell during cyst formation. This cyst wall consists of chitin and several protein components, including chitinase. The physiological roles of these components are not fully understood. Here, to elucidate the role of chitinase during cyst formation, we identified a new chitinase inhibitor by screening a library of 400 compounds. Using this inhibitor, we showed that chitinase inhibition causes the formation of abnormal cyst walls, the most characteristic of which is a "pot-like structure." This results in decreased production of mature cysts. Chitinase is therefore required for Entamoeba to produce mature cysts for transmission to a new host.

Cysteine proteases: Battling pathogenic parasitic protozoans with omnipresent enzymes

Millions of people worldwide lie at the risk of parasitic protozoic infections that kill over a million people each year. The rising inefficacy of conventional therapeutics to combat these diseases, mainly due to the development of drug resistance to a handful of available licensed options contributes substantially to the rising burden of these ailments. Cysteine proteases are omnipresent enzymes that are critically implicated in the pathogenesis of protozoic infections. Despite their significance and druggability, cysteine proteases as therapeutic targets have not yet been translated into the clinic. The review presents the significance of cysteine proteases of members of the genera Plasmodium, Entamoeba, and Leishmania, known to cause Malaria, Amoebiasis, and Leishmaniasis, respectively, the protozoic diseases with the highest morbidity and mortality. Further, projecting them as targets for molecular tools like the CRISPR-Cas technology for favorable manipulation, exploration of obscure genomes, and achieving a better insight into protozoic functioning. Overcoming the hurdles that prevent us from gaining a better insight into the functioning of these enzymes in protozoic systems is a necessity. Managing the burden of parasitic protozoic infections pivotally depends upon the betterment of molecular tools and therapeutic concepts that will pave the path to an array of diagnostic and therapeutic applications.

Structural analysis of EhPSP in complex with 3-phosphoglyceric acid from Entamoeba histolytica reveals a basis for its lack of phosphoglycerate mutase activity

Entamoeba histolytica phosphoserine phosphatase (EhPSP), a regulatory enzyme in the serine biosynthetic pathway, is also a structural homolog of cofactor-dependent phosphoglycerate mutase (dPGM). However, despite sharing many of its catalytic residues with dPGM, EhPSP displays no significant mutase activity. In the current work, we determined a crystal structure of EhPSP in complex with 3-PGA to 2.5 Å resolution and observed striking differences between the orientation of 3-PGA bound to EhPSP and that to its other homologous structures. We also performed computational modeling and simulations of the intermediate 2,3-bisphosphoglyceric acid into the active site of EhPSP to better understand its mechanistic details. Based on these results and those of a similar study with the dPGMs from E. coli and B. pseudomallei, the affinity of EhPSP for 2,3-BPG was concluded to be lower than those of the other proteins. Moreover, a different set of 2,3-BPG interacting residues was observed in EhPSP compared to dPGMs, with all of the crucial interacting residues of dPGMs either missing or substituted with weakly interacting residues. This study has expanded our understanding, at the structural level, of the inability of EhPSP to catalyze the mutase reaction and has strengthened earlier conclusions indicating it to be a true phosphatase.

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.

The dynamics of ultrastructural changes during Entamoeba invadens encystation

Entamoeba histolytica infection causes amoebiasis, which is a global public health problem. The major route of infection is oral ingestion of E. histolytica cysts, cysts being the sole form responsible for host-to-host transmission. Cysts are produced by cell differentiation from proliferative trophozoites in a process termed ‘encystation’. Therefore, encystation is an important process from a medical as well as a biological perspective. Previous electron microscopy studies have shown the ultrastructure of precysts and mature cysts; however, the dynamics of ultrastructural changes during encystation were ambiguous. Here, we analysed a series of Entamoeba invadens encysting cells by transmission electron microscopy. Entamoeba invadens is a model for encystation and the cells were prepared by short interval time course sampling from in vitro encystation-inducing cultures. We related sampled cells to stage conversion, which was monitored in the overall population by flow cytometry. The present approach revealed the dynamics of ultrastructure changes during E. invadens encystation. Importantly, the results indicate a functional linkage of processes that are crucial in encystation, such as glycogen accumulation and cyst wall formation. Hence, this study provides a reference for studying sequential molecular events during Entamoeba encystation.

Averting transmission: A pivotal target to manage amoebiasis

Amoebiasis is a parasitic infectious disease caused by the enteric protozoan Entamoeba histolytica, a leading basis of deaths accounted to parasites, succeeding malaria and schistosomiasis. Conventional treatment methodologies used to deal with amoebiasis mainly rely on the administration of anti-amoebic compounds and vaccines but are often linked with substantial side-effects on the patient. Besides, cases of development of drug resistance in protozoans have been recorded, contributing further to the reduction in the efficiency of the treatment. Loopholes in the efficacious management of the disease call for the development of novel methodologies to manage amoebiasis. A way to achieve this is by targeting the essential metabolic processes of 'encystation' and 'excystation', and the associated biomolecules, thus interrupting the biphasic life cycle of the parasite. Technologies like the CRISPR-Cas9 system can efficiently be exploited to discover novel and essential molecules that regulate the protozoan's metabolism, while efficiently manipulating and managing the known drug targets, leading to an effective halt and forestall to the enteric infection. This review presents a perspective on these essential metabolic processes and the associated molecules that can be targeted efficaciously to prevent the transmission of amoebiasis, thus managing the disease and proving to be a fruitful endeavour.

NOX4 activation is involved in ROS-dependent Jurkat T-cell death induced by Entamoeba histolytica

AIMS

Entamoeba histolytica can induce host cell death through induction of various intracellular signalling pathways. The responses triggered by E. histolytica are closely associated with tissue pathogenesis and immune evasion. Although E. histolytica can induce reactive oxygen species (ROS) in host cells, which NADPH oxidase (NOX) isoform contributes to amoeba-triggered Jurkat T-cell death is unclear. In this study, we investigated the signalling role of NOX4-derived ROS in E. histolytica-induced Jurkat T-cell death process.

METHODS AND RESULTS

In resting-state Jurkat T cells, NOX4 is strongly expressed. When Jurkat T cells were incubated with live E. histolytica trophozoites, intracellular ROS was significantly increased compared to cells incubated with medium alone. E. histolytica-induced ROS production was inhibited by pretreating Jurkat T cells with a NOX inhibitor. In addition, pretreating Jurkat T cells with a NOX inhibitor (Diphenyleneiodonium chloride) effectively blocked E. histolytica-induced phosphatidylserine (PS) exposure and DNA fragmentation of host cells. Moreover, siRNA-mediated knockdown of NOX4 protein expression in Jurkat T cells prevented E. histolytica-induced ROS generation and DNA fragmentation.

CONCLUSION

These results suggest that NOX4 has a critical role in ROS-dependent cell death process in Jurkat T cells induced by E. histolytica.

Host Invasion by Pathogenic Amoebae: Epithelial Disruption by Parasite Proteins

The epithelium represents the first and most extensive line of defence against pathogens, toxins and pollutant agents in humans. In general, pathogens have developed strategies to overcome this barrier and use it as an entrance to the organism. Entamoeba histolytica, Naegleriafowleri and Acanthamoeba spp. are amoebae mainly responsible for intestinal dysentery, meningoencephalitis and keratitis, respectively. These amoebae cause significant morbidity and mortality rates. Thus, the identification, characterization and validation of molecules participating in host-parasite interactions can provide attractive targets to timely intervene disease progress. In this work, we present a compendium of the parasite adhesins, lectins, proteases, hydrolases, kinases, and others, that participate in key pathogenic events. Special focus is made for the analysis of assorted molecules and mechanisms involved in the interaction of the parasites with epithelial surface receptors, changes in epithelial junctional markers, implications on the barrier function, among others. This review allows the assessment of initial host-pathogen interaction, to correlate it to the potential of parasite invasion.

Glycans in the roles of parasitological diagnosis and host-parasite interplay

The investigation of the glycan repertoire of several organisms has revealed a wide variation in terms of structures and abundance of glycan moieties. Among the parasites, it is possible to observe different sets of glycoconjugates across taxa and developmental stages within a species. The presence of distinct glycoconjugates throughout the life cycle of a parasite could relate to the ability of that organism to adapt and survive in different hosts and environments. Carbohydrates on the surface, and in excretory-secretory products of parasites, play essential roles in host-parasite interactions. Carbohydrate portions of complex molecules of parasites stimulate and modulate host immune responses, mainly through interactions with specific receptors on the surface of dendritic cells, leading to the generation of a pattern of response that may benefit parasite survival. Available data reviewed here also show the frequent aspect of parasite immunomodulation of mammalian responses through specific glycan interactions, which ultimately makes these molecules promising in the fields of diagnostics and vaccinology.

A Flow Cytometry Method for Dissecting the Cell Differentiation Process of Entamoeba Encystation

Amoebiasis is caused by Entamoeba histolytica infection, a protozoan parasite belonging to the phylum Amoebozoa. This parasite undergoes a fundamental cell differentiation process from proliferative trophozoite to dormant cyst, termed “encystation.” The cysts formed by encystation are solely responsible for the transmission of amoebiasis; therefore, Entamoeba encystation is an important subject from both biological and medical perspectives. Here, we have established a flow cytometry strategy for not only determining the percentage of formed cysts but also for monitoring changes in cell populations during encystation. This strategy together with fluorescence microscopy enables visualization of the cell differentiation process of Entamoeba encystation. We also standardized another flow cytometry protocol for counting live trophozoites. These two different flow cytometry techniques could be integrated into 96-well plate-based bioassays for monitoring the processes of cyst formation and trophozoite proliferation, which are crucial to maintain the Entamoeba life cycle. The combined two systems enabled us to screen a chemical library, the Pathogen Box of the Medicine for Malaria Venture, to obtain compounds that inhibit either the formation of cysts or the proliferation of trophozoites, or both. This is a prerequisite for the development of new drugs against amoebiasis, a global public health problem. Collectively, the two different 96-well plate-based Entamoeba bioassay and flow cytometry analysis systems (cyst formation and trophozoite proliferation) provide a methodology that can not only overcome the limitations of standard microscopic counting but also is effective in applied as well as basic Entamoeba biology.

Characterization and validation of Entamoeba histolytica pantothenate kinase as a novel anti-amebic drug target

The Coenzyme A (CoA), as a cofactor involved in >100 metabolic reactions, is essential to the basic biochemistry of life. Here, we investigated the CoA biosynthetic pathway of Entamoeba histolytica (E. histolytica), an enteric protozoan parasite responsible for human amebiasis. We identified four key enzymes involved in the CoA pathway: pantothenate kinase (PanK, EC 2.7.1.33), bifunctional phosphopantothenate-cysteine ligase/decarboxylase (PPCS-PPCDC), phosphopantetheine adenylyltransferase (PPAT) and dephospho-CoA kinase (DPCK). Cytosolic enzyme PanK, was selected for further biochemical, genetic, and phylogenetic characterization. Since E. histolytica PanK (EhPanK) is physiologically important and sufficiently divergent from its human orthologs, this enzyme represents an attractive target for the development of novel anti-amebic chemotherapies. Epigenetic gene silencing of PanK resulted in a significant reduction of PanK activity, intracellular CoA concentrations, and growth retardation in vitro, reinforcing the importance of this gene in E. histolytica. Furthermore, we screened the Kitasato Natural Products Library for inhibitors of recombinant EhPanK, and identified 14 such compounds. One compound demonstrated moderate inhibition of PanK activity and cell growth at a low concentration, as well as differential toxicity towards E. histolytica and human cells.

Structural and thermodynamic characterization of metal binding in Vps29 from Entamoeba histolytica: implication in retromer function

Vps29 is the smallest subunit of retromer complex with metallo-phosphatase fold. Although the role of metal in Vps29 is in quest, its metal binding mutants has been reported to affect the localization of the retromer complex in human cells. In this study, we report the structural and thermodynamic consequences of these mutations in Vps29 from the protozoan parasite, Entamoeba histolytica (EhVps29). EhVps29 is a zinc binding protein as revealed by X-ray crystallography and isothermal titration calorimetry. The metal binding pocket of EhVps29 exhibits marked differences in its 3-dimensional architecture and metal coordination in comparison to its human homologs and other metallo-phosphatases. Alanine substitutions of the metal-coordinating residues showed significant alteration in the binding affinity of EhVps29 for zinc. We also determined the crystal structures of metal binding defective mutants (D62A and D62A/H86A) of EhVps29. Based on our results, we propose that the metal atoms or the bound water molecules in the metal binding site are important for maintaining the structural integrity of the protein. Further cellular studies in the amoebic trophozoites showed that the overexpression of wild type EhVps29 leads to reduction in intracellular cysteine protease activity suggesting its crucial role in secretion of the proteases.

Uniqueness of Entamoeba sulfur metabolism: sulfolipid metabolism that plays pleiotropic roles in the parasitic life cycle

Sulfur metabolism is ubiquitous and terminally synthesizes various biomolecules that are crucial for organisms, such as sulfur-containing amino acids and co-factors, sulfolipids and sulfated saccharides. Entamoeba histolytica, a protozoan parasite responsible for amoebiasis, possesses the unique sulfur metabolism features of atypical localization and its terminal product being limited to sulfolipids. Here, we present an overall scheme of E. histolytica sulfur metabolism by relating all sulfotransferases and sulfatases to their substrates and products. Furthermore, a novel sulfur metabolite, fatty alcohol disulfates, was identified and shown to play an important role in trophozoite proliferation. Cholesteryl sulfate, another synthesized sulfolipid, was previously demonstrated to play an important role in encystation, a differentiation process from proliferative trophozoite to dormant cyst. Entamoeba survives by alternating between these two distinct forms; therefore, Entamoeba sulfur metabolism contributes to the parasitic life cycle via its terminal products. Interestingly, this unique feature of sulfur metabolism is not conserved in the nonparasitic close relative of Entamoeba, Mastigamoeba, because lateral gene transfer-mediated acquisition of sulfatases and sulfotransferases, critical enzymes conferring this feature, has only occurred in the Entamoeba lineage. Hence, our findings suggest that sulfolipid metabolism has a causal relationship with parasitism.

Entamoeba histolytica Infection in Female Sex Workers: A Matched Case-Control Study in Durango, Mexico

Background

Infection with Entamoeba histolytica (E. histolytica) can be potentially transmitted by sexual contact. The seroepidemiology of E. histolytica in female sex workers has not been studied. The aim of the study was to determine whether E. histolytica is associated with the occupation of female sex work. In addition, the correlates of E. histolytica seroprevalence in female sex workers were also investigated.

Methods

We performed an age- and gender-matched case-control study of 187 female sex workers and 374 women without sex work. Cases and controls were tested for the presence of E. histolytica IgG antibodies using a commercially available enzyme-linked immunoassay. Seroprevalence association with the characteristics of female sex workers was determined by bivariate analysis.

Results

Anti-E. histolytica IgG antibodies were found in five (2.7%) of 187 female sex workers and in 16 (4.3%) of 374 controls (odds ratios (OR) = 0.61; 95% confidence intervals (CI): 0.22 - 1.70; P = 0.34). Mean optical density of the immunoassay in seropositive cases and controls was 1.35 ± 0.93 and 0.73 ± 0.45, respectively (P = 0.05). Seroprevalence of E. histolytica infection did not vary significantly with age, education, socioeconomic level, or health status of sex workers. Seropositivity to E. histolytica did not correlate with work characteristics such as duration in the occupation, condom use, type of sex, or a history of sexually transmitted diseases, or with behavioral variables such as washing hands before eating, or consumption of untreated water.

Conclusions

Results indicate that female sex workers do not have an increased risk for E. histolytica infection in Durango City, Mexico. Further studies to determine the risk of infection with E. histolytica by sexual contact should be conducted.

Detection and differentiation of Entamoeba histolytica and Entamoeba dispar in clinical samples through PCR-denaturing gradient gel electrophoresis

Amebiasis is one of the twenty major causes of disease in Mexico; however, the diagnosis is difficult due to limitations of conventional microscopy-based techniques. In this study, we analyzed stool samples using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) to differentiate between Entamoeba histolytica (pathogenic) and E. dispar (non-pathogenic). The target for the PCR amplification was a small region (228 bp) of the adh112 gene selected to increase the sensitivity of the test. The study involved 62 stool samples that were collected from individuals with complaints of gastrointestinal discomfort. Of the 62 samples, 10 (16.1%) were positive for E. histolytica while 52 (83.9%) were negative. No sample was positive for E. dispar. These results were validated by nested PCR-RFLP (restriction fragment length polymorphism) and suggest that PCR-DGGE is a promising tool to differentiate among Entamoeba infections, contributing to determine the specific treatment for patients infected with E. histolytica, and therefore, avoiding unnecessary treatment of patients infected with the non-pathogenic E. dispar.

Recent advances in Entamoeba biology: RNA interference, drug discovery, and gut microbiome

In recent years, substantial progress has been made in understanding the molecular and cell biology of the human parasite Entamoeba histolytica, an important pathogen with significant global impact. This review outlines some recent advances in the Entamoeba field in the last five years, focusing on areas that have not recently been discussed in detail: (i) molecular mechanisms regulating parasite gene expression, (ii) new efforts at drug discovery using high-throughput drug screens, and (iii) the effect of gut microbiota on amoebiasis.

Entamoeba Encystation: New Targets to Prevent the Transmission of Amebiasis

Amebiasis is caused by Entamoeba histolytica infection and can produce a broad range of clinical signs, from asymptomatic cases to patients with obvious symptoms. The current epidemiological and clinical statuses of amebiasis make it a serious public health problem worldwide. The Entamoeba life cycle consists of the trophozoite, the causative agent for amebiasis, and the cyst, the form responsible for transmission. These two stages are connected by "encystation" and "excystation." Hence, developing novel strategies to control encystation and excystation will potentially lead to new measures to block the transmission of amebiasis by interrupting the life cycle of the causative agent. Here, we highlight studies investigating encystation using inhibitory chemicals and categorize them based on the molecules inhibited. We also present a perspective on new strategies to prevent the transmission of amebiasis.

Recent progress on the discovery of antiamoebic agents

A large number of protozoans infect humans but Entamoeba histolytica is the only organism responsible for causing amoebiasis, a deadly disease after malaria. Numerous heterocycle-based antiamoebic agents have been previously synthesized as E. histolytica inhibitors and while some of these agents have shown moderate activity, the search for a novel and ideal antiamoebic compound is still ongoing. In this digest Letter, we present the latest data on antiamoebic agents from 2011 to 2016 based on the different classes of heterocyclic agents.

Synthesis, antiamoebic and molecular docking studies of furan-thiazolidinone hybrids

In continuation of our previous work, a series of furan-thiazolidinone hybrids was prepared by Knoevenagel condensation of 3-(furan-2-ylmethyl)-2-(phenylimino)-1, 3-thiazolidin-4-one with different aryl aldehydes in presence of strong base. Some members of the series exhibited remarkable antiamoebic activity and cell viability. Three compounds (3, 6 and 11) showed excellent binding energy for Entamoeba histolytica O-acetyle-l-serine sulfohydrolase and Entamoeba histolytica thioredoxin reductase. These compounds demonstrated significant inhibition of O-acetyle-l-serine sulfohydrolase. The promising antiamoebic activity and enzymatic assay of 3, 6 and 11 make them promising molecules for further lead optimization in the development of novel antiamoebic agents.

A review of the proposed role of neutrophils in rodent amebic liver abscess models

Host invasion by Entamoeba histolytica, the pathogenic agent of amebiasis, can lead to the development of amebic liver abscess (ALA). Due to the difficulty of exploring host and amebic factors involved in the pathogenesis of ALA in humans, most studies have been conducted with animal models (e.g., mice, gerbils, and hamsters). Histopathological findings reveal that the chronic phase of ALA in humans corresponds to lytic or liquefactive necrosis, whereas in rodent models there is granulomatous inflammation. However, the use of animal models has provided important information on molecules and mechanisms of the host/parasite interaction. Hence, the present review discusses the possible role of neutrophils in the effector immune response in ALA in rodents. Properly activated neutrophils are probably successful in eliminating amebas through oxidative and non-oxidative mechanisms, including neutrophil degranulation, the generation of free radicals (O₂⁻, H₂O₂, HOCl) and peroxynitrite, the activation of NADPH-oxidase and myeloperoxidase (MPO) enzymes, and the formation of neutrophil extracellular traps (NETs). On the other hand, if amebas are not eliminated in the early stages of infection, they trigger a prolonged and exaggerated inflammatory response that apparently causes ALAs. Genetic differences in animals and humans are likely to be key to a successful host immune response.

Thienopyrimidine sulphonamide hybrids: design, synthesis, antiprotozoal activity and molecular docking studies

A series of hybrid compounds containing the thienopyrimidine scaffold with sulphonamide piperazine skeleton were synthesized and evaluated against K1 strain of Plasmodium falciparum and the HM1:1MSS strain of Entamoeba histolytica, respectively

Immune Evasion Mechanisms of Entamoeba histolytica: Progression to Disease

Entamoeba histolytica (Eh) is a protozoan parasite that infects 10% of the world's population and results in 100,000 deaths/year from amebic dysentery and/or liver abscess. In most cases, this extracellular parasite colonizes the colon by high affinity binding to MUC2 mucin without disease symptoms, whereas in some cases, Eh triggers an aggressive inflammatory response upon invasion of the colonic mucosa. The specific host-parasite factors critical for disease pathogenesis are still not well characterized. From the parasite, the signature events that lead to disease progression are cysteine protease cleavage of the C-terminus of MUC2 that dissolves the mucus layer followed by Eh binding and cytotoxicity of the mucosal epithelium. The host mounts an ineffective excessive host pro-inflammatory response following contact with host cells that causes tissue damage and participates in disease pathogenesis as Eh escapes host immune clearance by mechanisms that are not completely understood. Ameba can modulate or destroy effector immune cells by inducing neutrophil apoptosis and suppressing respiratory burst or nitric oxide (NO) production from macrophages. Eh adherence to the host cells also induce multiple cytotoxic effects that can promote cell death through phagocytosis, apoptosis or by trogocytosis (ingestion of living cells) that might play critical roles in immune evasion. This review focuses on the immune evasion mechanisms that Eh uses to survive and induce disease manifestation in the host.

The Transcriptome Sequence of Dientamoeba fragilis Offers New Biological Insights on its Metabolism, Kinome, Degradome and Potential Mechanisms of Pathogenicity

Dientamoeba fragilis is a human bowel parasite with a worldwide distribution. Dientamoeba was once described as a rare and harmless commensal though recent reports suggest it is common and potentially pathogenic. Molecular data on Dientamoeba is scarce which limits our understanding of this parasite. To address this, sequencing of the Dientamoeba transcriptome was performed. Messenger RNA was extracted from cultured Dientamoeba trophozoites originating from clinical stool specimens, and sequenced using Roche GS FLX and Illumina HiSeq technologies. In total 6,595 Dientamoeba transcripts were identified. These sequences were analysed using the BLAST2GO software suite and via BLAST comparisons to sequences available from TrichDB, GenBank, MEROPS and kinase.com. Several novel KEGG pathway maps were generated and gene ontology analysis was also performed. These results are thoroughly discussed guided by knowledge available for other related protozoa. Attention is paid to the novel biological insights afforded by this data including peptidases and kinases of Dientamoeba, as well as its metabolism, novel chemotherapeutics and possible mechanisms of pathogenicity. Currently, this work represents the largest contribution to our understanding of Dientamoeba molecular biology and also represents a major contribution to our understanding of the trichomonads generally, many of which are important pathogens of humans and animals.

Synthesis, characterization and antiamoebic activity of chalcones bearing N-substituted ethanamine tail

A series of chalcones (4-21) possessing N-substituted ethanamine were synthesized by the aldol condensation reaction of 1-(4-(2-substituted ethoxy)phenyl)ethanones with different aldehydes preceded by the reaction of 2-chloro N-substituted ethanamine hydrochloride and 4-hydroxy acetophenone. The structure of all the synthesized compounds was elucidated by various spectral and X-ray diffraction studies. The compounds were screened against HM1: IMSS strain of Entamoeba histolytica and cytotoxicity was performed on A549 (non-small cell lung cancer cell line) cells by MTT assay. Out of eighteen compounds twelve showed better activity then the standard drug metronidazole. The compound 9, 14 and 19 showed good cell viability, hence were least toxic.

Palladium(II) complexes of OS donor N-(di(butyl/phenyl)carbamothioyl)benzamide and their antiamoebic activity

Two promising palladium(II) compounds of general formula, cis-[Pd(L-O,S)2] [where HL-O,S = N-(di(butyl/phenyl)carbamothioyl)benzamide] as metal based antiamoebic drug candidates, have been synthesized. Both complexes are characterized in the solid state by FT-IR spectroscopy, TGA and single crystal X-ray study, as well as in solution by other spectroscopic techniques such as (1)H and (13)C NMR, and UV-visible. All these studies confirm the coordination of ligands through oxygen and sulphur atoms upon thioenolization induced delocalization. Complexes adopt cis-configuration in the solid state. Both the complexes and their respective ligands were screened in vitro for antiamoebic activity against HM1:1MSS strain of Entamoeba histolytica by microdilution method and cell viability in response to drugs was checked by using MTT assay. The IC50 values in the range 0.30-0.80 μM for ligands as well as complexes compared to 1.40 for metronidazole along with their similar inhibitory effect on cell viability of HEK293 cells like metronidazole make them promising future antiamoebic drugs.

Heat shock protein 90 inhibitors repurposed against Entamoeba histolytica

Hsp90 is an essential chaperone responsible for trafficking a vast array of client proteins, which are substrates that Hsp90 regulates in eukaryotic cells under stress conditions. The ATP-binding N-terminal domain of Hsp90 (also known as a GHKL type ATPase domain) can serve as a specific drug target, because sufficient structural diversity in the ATP-binding pocket of Hsp90 allows for ortholog selectivity of Hsp90 inhibitors. The primary objective of this study is to identify inhibitors specific for the ATP-binding domain of Entamoeba histolytica Hsp90 (EhHsp90). An additional aim, using a combination of site-directed mutagenesis and a protein in vitro assay, is to show that the antiparasitic activity of Hsp90 inhibitors is dependent on specific residues within the ATP-binding domain. Here, we tested the activity of 43 inhibitors of Hsp90 that we previously identified using a high-throughput screen. Of the 43 compounds tested, 19 competed for binding of the EhHsp90 ATP-binding domain. Five out of the 19 EhHsp90 protein hits demonstrated activity against E. histolytica in vitro culture: rifabutin, rutilantin, cetylpyridinium chloride, pararosaniline pamoate and gentian violet. These five top E. histolytica Hsp90 inhibitors showed 30-100% inhibition of E. histolytica in culture in the micromolar range. These data suggest that E. histolytica-specific Hsp90 inhibitors are possible to identify and provide important lead compounds for the development of novel antiamebic drugs.

Entamoeba histolytica: adhesins and lectins in the trophozoite surface

Entamoeba histolytica is the causative agent of amebiasis in humans and is responsible for 100,000 deaths annually, making it the third leading cause of death due to a protozoan parasite. Pathogenesis appears to result from the potent cytotoxic activity of the parasite, which kills host cells within minutes. Although the mechanism is unknown, it is well established to be contact-dependent. The life cycle of the parasite alternates with two forms: the resistant cyst and the invasive trophozoite. The adhesive interactions between the parasite and surface glycoconjugates of host cells, as well as those lining the epithelia, are determinants for invasion of human tissues, for its cytotoxic activity, and finally for the outcome of the disease. In this review we present an overview of the information available on the amebic lectins and adhesins that are responsible of those adhesive interactions and we also refer to their effect on the host immune response. Finally, we present some concluding remarks and perspectives in the field.

Parasitic diseases of the pleura

Parasitic infections are prevalent in certain parts of the world and may cause pleural involvement, which often goes unrecognized. Common parasites involving the pleura include Entamoeba histolytica, Echinococcus granulosus and Paragonimus westermani. Amebiasis can cause empyema with "anchovy sauce" pus, reactive pleural effusions and bronchopleural fistula with hydropneumothorax. Echinococcosis may result in pleural thickening, pneumothorax, secondary pleural hydatidosis and pleural effusions. Paragonimiasis may cause chylous and cholesterol pleural effusions, pleural thickening and pneumothorax. Less commonly, pulmonary eosinophilia, or Loeffler's syndrome, caused by Ascaris lumbricoides, Ancylostoma duodenale and Necator americanus and tropical pulmonary eosinophilia caused by Wuchereria bancrofti and Brugia malayi may involve the pleura. This article provides a comprehensive review of parasitic infections involving the pleura. A high index of suspicion in the appropriate clinical setting is required to facilitate prompt diagnosis and treatment of these diseases.

Effect of the leptin receptor Q223R polymorphism on the host transcriptome following infection with Entamoeba histolytica

Resistance to amebiasis is associated with a polymorphism in the leptin receptor. Previous studies demonstrated that humans with the ancestral Q223 leptin receptor allele were nearly four times less likely to be infected with Entamoeba histolytica than those carrying the mutant R223 allele. We hypothesized that the Q223 allele protected against E. histolytica via STAT3-mediated transcription of genes required for mucosal immunity. To test this, mice containing the humanized LEPR Q or R allele at codon 223 were intracecally infected with E. histolytica. Susceptibility to amebiasis was assessed, and cecal tissues were analyzed for changes in gene expression. By 72 h postchallenge, all Q223 mice had cleared E. histolytica, whereas 39% of 223R mice were infected. Thirty-seven genes were differentially expressed in response to infection at 72 h, including proinflammatory genes (CXCL2, S100A8/9, PLA2G7, ITBG2, and MMP9) and functions pertaining to the movement and activity of immune cells. A comparison at 12 h postchallenge of infected Q223 versus R223 mice identified a subset of differentially expressed genes, many of which were closely linked to leptin signaling. Further analyses indicated that the Q223 gene expression pattern was consistent with a suppressed apoptotic response to infection, while 223R showed increased cellular proliferation and recruitment. These studies are the first to illuminate the downstream effects of leptin receptor polymorphisms on intestinal infection by E. histolytica. As such, they are important for the insight that they provide into this previously uncharacterized mechanism of mucosal immunity.