Molecular biology research to benefit patients with Entamoeba histolytica infection

Characterization of Entamoeba fatty acid elongases; validation as targets and provision of promising leads for new drugs against amebiasis

Entamoeba histolytica is a protozoan parasite belonging to the phylum Amoebozoa that causes amebiasis, a global public health problem. E. histolytica alternates its form between a proliferative trophozoite and a dormant cyst. Trophozoite proliferation is closely associated with amebiasis symptoms and pathogenesis whereas cysts transmit the disease. Drugs are available for clinical use; however, they have issues of adverse effects and dual targeting of disease symptoms and transmission remains to be improved. Development of new drugs is therefore urgently needed. An untargeted lipidomics analysis recently revealed structural uniqueness of the Entamoeba lipidome at different stages of the parasite's life cycle involving very long (26-30 carbons) and/or medium (8-12 carbons) acyl chains linked to glycerophospholipids and sphingolipids. Here, we investigated the physiology of this unique acyl chain diversity in Entamoeba, a non-photosynthetic protist. We characterized E. histolytica fatty acid elongases (EhFAEs), which are typically components of the fatty acid elongation cycle of photosynthetic protists and plants. An approach combining genetics and lipidomics revealed that EhFAEs are involved in the production of medium and very long acyl chains in E. histolytica. This approach also showed that the K3 group herbicides, flufenacet, cafenstrole, and fenoxasulfone, inhibited the production of very long acyl chains, thereby impairing Entamoeba trophozoite proliferation and cyst formation. Importantly, none of these three compounds showed toxicity to a human cell line; therefore, EhFAEs are reasonable targets for developing new anti-amebiasis drugs and these compounds are promising leads for such drugs. Interestingly, in the Amoebazoan lineage, gain and loss of the genes encoding two different types of fatty acid elongase have occurred during evolution, which may be relevant to parasite adaptation. Acyl chain diversity in lipids is therefore a unique and indispensable feature for parasitic adaptation of Entamoeba.

Links between cholesteryl sulfate-dependent and -independent processes in the morphological and physiological changes of Entamoeba encystation

The protozoan parasite Entamoeba histolytica causes amoebiasis, a global public health problem. Amoebiasis is solely transmitted by cysts that are produced from proliferative trophozoites by encystation in the large intestine of humans. During encystation, various metabolites, pathways, and cascades sequentially orchestrate the morphological and physiological changes required to produce cysts. Cholesteryl sulfate (CS) has recently been revealed to be among the key molecules that control the morphological and physiological changes of encystation by exerting pleiotropic effects. CS promotes the rounding of encysting Entamoeba cells and maintains this spherical morphology as encysting cells are surrounded by the cyst wall, a prerequisite for resistance against environmental stresses. CS is also involved in the development of membrane impermeability, another prerequisite for resistance. The initiation of cyst wall formation is, however, CS-independent. Here, we overview CS-dependent and -independent processes during encystation and discuss their functional linkage. We also discuss a potential transcriptional cascade that controls the processes necessary to produce dormant Entamoeba cysts.

Unique features of Entamoeba histolytica glycerophospholipid metabolism; has the E. histolytica lipid metabolism network evolved through gene loss and gain to enable parasitic life cycle adaptation?

Entamoeba histolytica, a protozoan parasite, causes amoebiasis, which is a global public health problem. During the life cycle of this parasite, the properties of the cell membrane are changed markedly. To clarify the mechanism of membrane lipid changes, we exploited state-of-the-art untargeted lipidomic analysis, and atypical features of glycerophospholipids, lysoglycerophospholipids, and sphingolipids were observed compared with human equivalents. Here, we overview an entire E. histolytica glycerophospholipid metabolic pathway based on re-evaluated whole lipidome and genome along with the results of metabolic labeling experiments. We also discuss whether the E. histolytica lipid metabolism network, including the glycerophospholipid metabolic pathway, has unique features necessary for parasitic life cycle adaptation through gene loss and/or gain, and raise important questions involving biochemistry, molecular cell biology, and physiology underlying this network. Answering these questions will advance the understanding of Entamoeba physiology and will provide potential targets to develop new anti-amoebiasis drugs.

Diversity and Plasticity of Virulent Characteristics of Entamoeba histolytica

The complexity of clinical syndromes of amebiasis, caused by the parasite Entamoeba histolytica, stems from the intricate interplay between the host immune system, the virulence of the invading parasite, and the surrounding environment. Although there is still a relative paucity of information about the precise relationship between virulence factors and the pathogenesis of Entamoeba histolytica, by accumulating data from clinical and basic research, researchers have identified essential pathogenic factors that play a critical role in the pathogenesis of amebiasis, providing important insights into disease development through animal models. Moreover, the parasite's genetic variability has been associated with differences in virulence and disease outcomes, making it important to fully understand the epidemiology and pathogenesis of amebiasis. Deciphering the true mechanism of disease progression in humans caused by this parasite is made more difficult through its ability to demonstrate both genomic and pathological plasticity. The objective of this article is to underscore the heterogeneous nature of disease states and the malleable virulence characteristics in experimental models, while also identifying persistent scientific issues that need to be addressed.

Gene expression of axenically-isolated clinical Entamoeba histolytica strains and its impact on disease severity of amebiasis

The severity of Entamoeba histolytica infection is determined by host immunology, pathogen virulence, and the intestinal environment. Conventional research for assessing pathogen virulence has been mainly performed using laboratory strains, such as a virulent HM-1: IMSS (HM-1) and an avirulent Rahman, under various artificial environmental conditions because of the difficulties of axenic isolation of the clinical strains. However, it is still unclear whether scientific knowledge based on laboratory strains are universally applicable to the true pathogenesis. Hereby, we performed transcriptomic analysis of clinical strains from patients with different degrees of disease severity, as well as HM-1 under different conditions. Even after several months of axenization, Clinical strains show the distinct profile in gene expression during in vitro passage, moreover, difference between any 2 of these strains was much greater than the changes on the liver challenge. Interestingly, 26 DEGs, which were closely related to the biological functions, were oppositely up- or down regulated between virulent Ax 19 (liver abscess) and avirulent Ax 11 (asymptomatic carrier). Additionally, RNAseq using laboratory strain (HM1) showed more than half of genes were differently expressed between continuously in vitro passaged HM1 (in vitro HM1) and periodically liver passaged HM1 (virulent HM1), which was much greater than the changes on the liver passage of virulent HM1. Also, transcriptomic analysis of a laboratory strain revealed that continuous environmental stress enhances its virulence via a shift in its gene expression profile. Changes in gene expression patterns on liver abscess formation were not consistent between clinical and laboratory strains.

Various genotypes of Entamoeba histolytica are prevalent in the field. Some papers suggest the association between genotypes and disease severity. However, most studies for assessing pathogen virulence were performed using laboratory strains, such as virulent HM1: IMSS (HM1) and avirulent Rahman, because axenic isolation from clinical specimen is technically complex and time consuming. This transcriptomic analysis using clinical strains from the patients with different clinical severity, as well as the laboratory strain HM1 under different conditions showed unique gene expression patterns. Following things were confirmed; 1. Virulent clinical strain maintains its virulence with unique gene expression pattern after axenic isolation, 2. Continuous environmental stress enhances its virulence via the accumulation of altered gene expressions, and 3. Changes in gene expression on the liver abscess formation are not always the same amongst strains. For an accurate understanding the pathogenesis, comprehensive analyses of various clinical strains under different environmental conditions should be promoted.

Pleiotropic Roles of Cholesteryl Sulfate during Entamoeba Encystation: Involvement in Cell Rounding and Development of Membrane Impermeability

Entamoeba histolytica, a protozoan parasite, causes amoebiasis, which is a global public health problem. The major route of infection is oral ingestion of cysts, the only form that is able to transmit to a new host. Cysts are produced by cell differentiation from proliferative trophozoites in a process termed "encystation." During encystation, cell morphology is markedly changed; motile amoeboid cells become rounded, nonmotile cells. Concomitantly, cell components change and significant fluctuations of metabolites occur. Cholesteryl sulfate (CS) is a crucial metabolite for encystation. However, its precise role remains uncertain. To address this issue, we used in vitro culture of Entamoeba invadens as the model system for the E. histolytica encystation study and identified serum-free culture conditions with CS supplementation at concentrations similar to intracellular CS concentrations during natural encystation. Using this culture system, we show that CS exerts pleiotropic effects during Entamoeba encystation, affecting cell rounding and development of membrane impermeability. CS dose dependently induced and maintained encysting cells as spherical maturing cysts with almost no phagocytosis activity. Consequently, the percentage of mature cysts was increased. CS treatment also caused time- and dose-dependent development of membrane impermeability in encysting cells via induction of de novo synthesis of dihydroceramides containing very long N-acyl chains (≥26 carbons). These results indicate that CS-mediated morphological and physiological changes are necessary for the formation of mature cysts and the maintenance of the Entamoeba life cycle. Our findings also reveal important morphological aspects of the process of dormancy and the control of membrane structure. IMPORTANCE Entamoeba histolytica causes a parasitic infectious disease, amoebiasis. Amoebiasis is a global public health problem with a high occurrence of infection and inadequate clinical options. The parasite alternates its form between a proliferative trophozoite and a dormant cyst that enables the parasite to adapt to new environments. The transition stage in which trophozoites differentiate into cysts is termed "encystation." Cholesteryl sulfate is essential for encystation; however, its precise role remains to be determined. Here, we show that cholesteryl sulfate is a multifunctional metabolite exerting pleiotropic roles during Entamoeba encystation, including the rounding of cells and the development of membrane impermeability. Such morphological and physiological changes are required for Entamoeba to produce cysts that are transmissible to a new host, which is essential for maintenance of the Entamoeba life cycle. Our findings are therefore relevant not only to Entamoeba biology but also to general cell and lipid biology.

Effect of Caging on Cryptosporidium parvum Proliferation in Mice

Cryptosporidiosis is an enteric infection caused by several protozoan species in the genus Cryptosporidium (phylum Apicomplexa). Immunosuppressed mice are commonly used to model this infection. Surprisingly, for a pathogen like Cryptosporidium parvum, which is readily transmitted fecal-orally, mice housed in the same cage can develop vastly different levels of infection, ranging from undetectable to lethal. The motivation for this study was to investigate this phenomenon and assess the association between the severity of cryptosporidiosis and the fecal microbiota. To this aim, the association between severity of cryptosporidiosis and caging (group caged vs. individually caged) and between the microbiota taxonomy and the course of the infection was examined. In contrast to mice caged in groups of four, a majority of mice caged individually did not excrete a detectable level of oocysts. Microbiota α diversity in samples collected between three days prior to infection and one day post-infection was negatively correlated with the severity of cryptosporidiosis, suggesting a causal negative relationship between microbiota diversity and susceptibility to C. parvum.

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.

A RETROSPECTIVE ANALYSIS OF AMOEBIASIS IN REPTILES IN A ZOOLOGICAL INSTITUTION

Amoebiasis is a significant protozoal disease of reptiles causing nonspecific clinical signs including diarrhea, anorexia, and lethargy. It frequently results in acute death. Investigation of the pathophysiology of amoebiasis in reptiles has been hampered by the inability to accurately identify amoeba to the species level using conventional techniques. This study reviewed reptile medical records from the Wildlife Conservation Society's archives from 1998 to 2017. Amoebae were identified histologically in 54 cases in 31 different species. Of these, amoebiasis was the cause of death in 32 (18 chelonians, 7 lizards, and 7 snakes), a significant co-morbidity in 14 (six chelonians, two lizards, and six snakes), and seen incidentally in eight cases (one chelonian, six lizards, and one snake). Relocation from one enclosure to another was also evaluated and 65% of cases had been moved within 180 days of death (median 46 days). Frozen tissue samples from 19 of these cases were tested via an Entamoeba (genus-specific) polymerase chain reaction (PCR) assay. PCR products were sequenced and Entamoeba species were identified. Six individuals were positive for Entamoeba invadens (three chelonians, two snakes, one lizard), two for Entamoeba ranarum (both snakes), and one for Entamoeba terrapinae (chelonian); the other 10 cases were negative via PCR. Entamoeba ranarum has typically been considered a disease of amphibians with only one report of disease in a snake. Entamoeba terrapinae has only been reported without associated disease in chelonians. These results suggest that amoebiasis is a complicated and nuanced disease of reptiles, and warrants additional study.

Stage-Specific De Novo Synthesis of Very-Long-Chain Dihydroceramides Confers Dormancy to Entamoeba Parasites

Amoebiasis is a parasitic disease caused by Entamoeba histolytica infection and is a serious public health problem worldwide due to ill-prepared preventive measures as well as its high morbidity and mortality rates. Amoebiasis transmission is solely mediated by cysts. Cysts are produced by the differentiation of proliferative trophozoites in a process termed "encystation." Entamoeba encystation is a fundamental cell differentiation process and proceeds with substantial changes in cell metabolites, components, and morphology, which occur sequentially in an orchestrated manner. Lipids are plausibly among these metabolites that function as key factors for encystation. However, a comprehensive lipid analysis has not been reported, and the involved lipid metabolic pathways remain largely unknown. Here, we exploited the state-of-the-art untargeted lipidomics and characterized 339 molecules of 17 lipid subclasses. Of these, dihydroceramide (Cer-NDS) was found to be among the most induced lipid species during encystation. Notably, in encysting cells, amounts of Cer-NDS containing very long N-acyl chains (≥26 carbon) were more than 30-fold induced as the terminal product of a de novo metabolic pathway. We also identified three ceramide synthase genes responsible for producing the very-long-chain Cer-NDS molecules. These genes were upregulated during encystation. Furthermore, these ceramide species were shown to be indispensable for generating membrane impermeability, a prerequisite for becoming dormant cyst that shows resistance to environmental assault inside and outside the host for transmission. Hence, the lipid subclass of Cer-NDS plays a crucial role for Entamoeba cell differentiation and morphogenesis by alternating the membrane properties.IMPORTANCE Entamoeba is a protozoan parasite that thrives in its niche by alternating its two forms between a proliferative trophozoite and dormant cyst. Cysts are the only form able to transmit to a new host and are differentiated from trophozoites in a process termed "encystation." During Entamoeba encystation, cell metabolites, components, and morphology drastically change, which occur sequentially in an orchestrated manner. Lipids are plausibly among these metabolites. However, the involved lipid species and their metabolic pathways remain largely unknown. Here, we identified dihydroceramides (Cer-NDSs) containing very long N-acyl chains (C₂₆ to C₃₀) as a key metabolite for Entamoeba encystation by our state-of-the-art untargeted lipidomics. We also showed that these Cer-NDSs are critical to generate the membrane impermeability, a prerequisite for this parasite to show dormancy as a cyst that repels substances and prevents water loss. Hence, ceramide metabolism is essential for Entamoeba to maintain the parasitic lifestyle.

Unveiling the role of EVs in anaerobic parasitic protozoa

The anaerobic or microaerophilic protozoan parasites such as the enteric human pathogens Entamoeba histolytica, Giardia intestinalis, Cryptosporidium parvum, Blastocystis hominis and urogenital tract parasites Trichomonas vaginalis are able to survival in an environment with oxygen deprivation. Despite living in hostile environments these pathogens adopted different strategies to survive within the hosts. Among them, the release of extracellular vesicles (EVs) has become an active endeavor in the study of pathogenesis for these parasites. EVs are heterogenous, membrane-limited structures that have played important roles in cellular communication, transferring information through cargo and modulating the immune system of the host. In this review, we described several aspects of the recently characterized EVs of the anaerobic protozoa, including their role in adhesion, modulation of the immune response and omics analysis to understand the potential of these EVs in the pathogenesis of these diseases caused by anaerobic parasites.

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.

Differential detection of Entamoeba histolytica, Entamoeba dispar and Entamoeba moshkovskii in faecal samples using nested multiplex PCR in west of Iran

This study aimed to determine the prevalence of Entamoeba histolytica, Entamoeba dispar and Entamoeba moshkovskii (collectively referred to as Entamoeba complex), using microscopic and molecular methods in Kurdistan Province, northwest of Iran. The relationship between positive Entamoeba species and clinical symptoms was also investigated. Eight positive Entamoeba complex, as well as four Entamoeba complex-like isolates, were detected by microscopic stool examination. DNA was extracted from all positive and from 55 randomly selected negative stool samples. PCR was performed using species-specific 18S rRNA primers for the Entamoeba complex. All positive PCR samples were sequenced. In total, 14 (1.01%) out of 1383 isolates, i.e. 12 microscopy-positive and Entamoeba complex-like isolates and two out of 55 microscopy-negative isolates, were identified via PCR and sequencing. Overall, 0.58% (8/1383) of the isolates were E. dispar, 0.14% (2/1383) E. histolytica, 0.07% (1/1383) E. moshkovskii and 0.22% (3/1383) were mixed of E. histolytica and E. dispar. Based on our findings, the prevalence of E. dispar is greater than that of E. histoltyica. On the other hand, a case of E. moshkovskii was reported for the first time in this region. It seems that some gastrointestinal symptoms may be attributed to Entamoeba species.

Myxozoan Adhesion and Virulence: Ceratonova shasta on the Move

Motility factors are fundamental for parasite invasion, migration, proliferation and immune evasion and thus can influence parasitic disease pathogenesis and virulence. Salmonid enteronecrosis is caused by a myxozoan (Phylum Cnidarian) parasite, Ceratonova shasta. Three parasite genotypes (0, I, II) occur, with varying degrees of virulence in its host, making it a good model for examining the role of motility in virulence. We compare C. shasta cell motility between genotypes and describe how the cellular protrusions interact with the host. We support these observations with motility gene expression analyses. C. shasta stages can move by single or combined used of filopodia, lamellipodia and blebs, with different behaviors such as static adhesion, crawling or blebbing, some previously unobserved in myxozoans. C. shasta stages showed high flexibility of switching between different morphotypes, suggesting a high capacity to adapt to their microenvironment. Exposure to fibronectin showed that C. shasta stages have extraordinary adhesive affinities to glycoprotein components of the extracellular matrix (ECM). When comparing C. shasta genotypes 0 (low virulence, no mortality) and IIR (high virulence, high mortality) infections in rainbow trout, major differences were observed with regard to their migration to the target organ, gene expression patterns and proliferation rate in the host. IIR is characterized by rapid multiplication and fast amoeboid bleb-based migration to the gut, where adhesion (mediated by integrin-β and talin), ECM disruption and virulent systemic dispersion of the parasite causes massive pathology. Genotype 0 is characterized by low proliferation rates, slow directional and early adhesive migration and localized, non-destructive development in the gut. We conclude that parasite adhesion drives virulence in C. shasta and that effectors, such as integrins, reveal themselves as attractive therapeutic targets in a group of parasites for which no effective treatments are known.

Unique Features of Entamoeba Sulfur Metabolism; Compartmentalization, Physiological Roles of Terminal Products, Evolution and Pharmaceutical Exploitation

Sulfur metabolism is essential for all living organisms. Recently, unique features of the Entamoeba metabolic pathway for sulfated biomolecules have been described. Entamoeba is a genus in the phylum Amoebozoa and includes the causative agent for amoebiasis, a global public health problem. This review gives an overview of the general features of the synthesis and degradation of sulfated biomolecules, and then highlights the characteristics that are unique to Entamoeba. Future biological and pharmaceutical perspectives are also discussed.

Advances in Entamoeba histolytica Biology Through Transcriptomic Analysis

A large number of transcriptome-level studies in Entamoeba histolytica, the protozoan parasite that causes amoebiasis, have investigated gene expression patterns to help understand the pathology and biology of the organism. They have compared virulent and avirulent strains in lab culture and after tissue invasion, cells grown under different stress conditions, response to anti-amoebic drug treatments, and gene expression changes during the process of encystation. These studies have revealed interesting molecules/pathways that will help increase our mechanistic understanding of differentially expressed genes during growth perturbations and tissue invasion. Some of the important insights obtained from transcriptome studies include the observations that regulation of carbohydrate metabolism may be an important determinant for tissue invasion, while the novel up-regulated genes during encystation include phospholipase D, and meiotic genes, suggesting the possibility of meiosis during the process. Classification of genes according to expression levels showed that amongst the highly transcribed genes in cultured E. histolytica trophozoites were some virulence factors, raising the question of the role of these factors in normal parasite growth. Promoter motifs associated with differential gene expression and regulation were identified. Some of these motifs associated with high gene expression were located downstream of start codon, and were required for efficient transcription. The listing of E. histolytica genes according to transcript expression levels will help us determine the scale of post-transcriptional regulation, and the possible roles of predicted promoter motifs. The small RNA transcriptome is a valuable resource for detailed structural and functional analysis of these molecules and their regulatory roles. These studies provide new drug targets and enhance our understanding of gene regulation in E. histolytica.

Characterization of Entamoeba histolytica adenosine 5'-phosphosulfate (APS) kinase; validation as a target and provision of leads for the development of new drugs against amoebiasis

Background

Amoebiasis, caused by Entamoeba histolytica infection, is a global public health problem. However, available drugs to treat amoebiasis are currently limited, and no effective vaccine exists. Therefore, development of new preventive measures against amoebiasis is urgently needed.

Methodology/Principal findings

Here, to develop new drugs against amoebiasis, we focused on E. histolytica adenosine 5′-phosphosulfate kinase (EhAPSK), an essential enzyme in Entamoeba sulfolipid metabolism. Fatty alcohol disulfates and cholesteryl sulfate, sulfolipids synthesized in Entamoeba, play important roles in trophozoite proliferation and cyst formation. These processes are closely associated with clinical manifestation and severe pathogenesis of amoebiasis and with disease transmission, respectively. We validated a combination approach of in silico molecular docking analysis and an in vitro enzyme activity assay for large scale screening. Docking simulation ranked the binding free energy between a homology modeling structure of EhAPSK and 400 compounds. The 400 compounds were also screened by a 96-well plate-based in vitro APSK activity assay. Among fifteen compounds identified as EhAPSK inhibitors by the in vitro system, six were ranked by the in silico analysis as having high affinity toward EhAPSK. Furthermore, 2-(3-fluorophenoxy)-N-[4-(2-pyridyl)thiazol-2-yl]-acetamide, 3-phenyl-N-[4-(2-pyridyl)thiazol-2-yl]-imidazole-4-carboxamide, and auranofin, which were identified as EhAPSK inhibitors by both in silico and in vitro analyses, halted not only Entamoeba trophozoite proliferation but also cyst formation. These three compounds also dose-dependently impaired the synthesis of sulfolipids in E. histolytica.

Conclusions/Significance

Hence, the combined approach of in silico and in vitro-based EhAPSK analyses identified compounds that can be evaluated for their effects on Entamoeba. This can provide leads for the development of new anti-amoebic and amoebiasis transmission-blocking drugs. This strategy can also be applied to identify specific APSK inhibitors, which will benefit research into sulfur metabolism and the ubiquitous pathway terminally synthesizing essential sulfur-containing biomolecules.

Amoebiasis is a parasitic disease caused by Entamoeba histolytica that is an important health problem worldwide because of high morbidity and mortality rates. However, clinical options are inadequate; therefore, developing new preventive measures, such as anti-amoebic drugs, is urgently needed. In general, for the development of new drugs, the identification of appropriate leads and targets is a prerequisite. Here, to develop new drugs against amoebiasis, we focused on E. histolytica adenosine 5′-phosphosulfate kinase (EhAPSK), an essential enzyme in sulfur metabolism. An EhAPSK-based combination approach of computer-based in silico and laboratory-based in vitro analyses enabled us to screen 400 chemicals, from which we identified 15 that inhibit EhAPSK activity. Furthermore, among them, three compounds halted biological processes in Entamoeba that are closely associated with the clinical manifestation and pathogenesis of amoebiasis and with disease transmission. Hence, this study provides leads as well as a target for the development of new drugs against amoebiasis. This study also provides a basis to identify inhibitors for use in the study of sulfur metabolism, an important topic in general biochemistry and physiology.

Bioactivity of Farnesyltransferase Inhibitors Against Entamoeba histolytica and Schistosoma mansoni

The protozoan parasite Entamoeba histolytica can induce amebic colitis and amebic liver abscess. First-line drugs for the treatment of amebiasis are nitroimidazoles, particularly metronidazole. Metronidazole has side effects and potential drug resistance is a concern. Schistosomiasis, a chronic and painful infection, is caused by various species of the Schistosoma flatworm. There is only one partially effective drug, praziquantel, a worrisome situation should drug resistance emerge. As many essential metabolic pathways and enzymes are shared between eukaryotic organisms, it is possible to conceive of small molecule interventions that target more than one organism or target, particularly when chemical matter is already available. Farnesyltransferase (FT), the last common enzyme for products derived from the mevalonate pathway, is vital for diverse functions, including cell differentiation and growth. Both E. histolytica and Schistosoma mansoni genomes encode FT genes. In this study, we phenotypically screened E. histolytica and S. mansoni in vitro with the established FT inhibitors, lonafarnib and tipifarnib, and with 125 tipifarnib analogs previously screened against both the whole organism and/or the FT of Trypanosoma brucei and Trypanosoma cruzi. For E. histolytica, we also explored whether synergy arises by combining lonafarnib and metronidazole or lonafarnib with statins that modulate protein prenylation. We demonstrate the anti-amebic and anti-schistosomal activities of lonafarnib and tipifarnib, and identify 17 tipifarnib analogs with more than 75% growth inhibition at 50 μM against E. histolytica. Apart from five analogs of tipifarnib exhibiting activity against both E. histolytica and S. mansoni, 10 additional analogs demonstrated anti-schistosomal activity (severe degenerative changes at 10 μM after 24 h). Analysis of the structure-activity relationship available for the T. brucei FT suggests that FT may not be the relevant target in E. histolytica and S. mansoni. For E. histolytica, combination of metronidazole and lonafarnib resulted in synergism for growth inhibition. Also, of a number of statins tested, simvastatin exhibited moderate anti-amebic activity which, when combined with lonafarnib, resulted in slight synergism. Even in the absence of a definitive molecular target, identification of potent anti-parasitic tipifarnib analogs encourages further exploration while the synergistic combination of metronidazole and lonafarnib offers a promising treatment strategy for amebiasis.

Discrimination Experiments in Entamoeba and Evidence from Other Protists Suggest Pathogenic Amebas Cooperate with Kin to Colonize Hosts and Deter Rivals

Entamoeba histolytica is one of the least understood protists in terms of taxa, clone, and kin discrimination/recognition ability. However, the capacity to tell apart same or self (clone/kin) from different or nonself (nonclone/nonkin) has long been demonstrated in pathogenic eukaryotes like Trypanosoma and Plasmodium, free-living social amebas (Dictyostelium, Polysphondylium), budding yeast (Saccharomyces), and in numerous bacteria and archaea (prokaryotes). Kin discrimination/recognition is explained under inclusive fitness theory; that is, the reproductive advantage that genetically closely related organisms (kin) can gain by cooperating preferably with one another (rather than with distantly related or unrelated individuals), minimizing antagonism and competition with kin, and excluding genetic strangers (or cheaters = noncooperators that benefit from others' investments in altruistic cooperation). In this review, we rely on the outcomes of in vitro pairwise discrimination/recognition encounters between seven Entamoeba lineages to discuss the biological significance of taxa, clone, and kin discrimination/recognition in a range of generalist and specialist species (close or distantly related phylogenetically). We then focus our discussion on the importance of these laboratory observations for E. histolytica's life cycle, host infestation, and implications of these features of the amebas' natural history for human health (including mitigation of amebiasis).

Genome-Wide Association Study Reveals Genetic Link between Diarrhea-Associated Entamoeba histolytica Infection and Inflammatory Bowel Disease

Entamoeba histolytica is the etiologic agent of amebic dysentery, though clinical manifestation of infection is highly variable ranging from subclinical colonization to invasive disease. We hypothesize that host genetics contribute to the variable outcomes of E. histolytica infection; thus, we conducted a genome-wide association study (GWAS) in two independent birth cohorts of Bangladeshi infants monitored for susceptibility to E. histolytica disease in the first year of life. Children with at least one diarrheal episode positive for E. histolytica (cases) were compared to children with no detectable E. histolytica infection in the same time frame (controls). Meta-analyses under a fixed-effect inverse variance weighting model identified multiple variants in a region of chromosome 10 containing loci associated with symptomatic E. histolytica infection. An intergenic insertion between CREM and CCNY (rs58000832) achieved genome-wide significance (P value from meta-analysis [Pmeta] = 6.05 × 10-9), and each additional risk allele of rs58000832 conferred 2.42 increased odds of a diarrhea-associated E. histolytica infection. The most strongly associated single nucleotide polymorphism (SNP) within a gene was in an intron of CREM (rs58468612; Pmeta = 8.94 × 10-8), which has been implicated as a susceptibility locus for inflammatory bowel disease (IBD). Gene expression resources suggest associated loci are related to the lower expression of CREM Increased CREM expression is also observed in early E. histolytica infection. Further, CREM-/- mice were more susceptible to E. histolytica amebic colitis. These genetic associations reinforce the pathological similarities observed in gut inflammation between E. histolytica infection and IBD.IMPORTANCE Diarrhea is the second leading cause of death for children globally, causing 760,000 deaths each year in children less than 5 years old. Amebic dysentery contributes significantly to this burden, especially in developing countries. The identification of host factors that control or enable enteric pathogens has the potential to transform our understanding of disease predisposition, outcomes, and treatments. Our discovery of the transcriptional regulator cAMP-responsive element modulator (CREM) as a genetic modifier of susceptibility to amebic disease has implications for understanding the pathogenesis of other diarrheal infections. Further, emerging evidence for CREM in IBD susceptibility suggests that CREM is a critical regulator of enteric inflammation and may have broad therapeutic potential as a drug target across intestinal inflammatory diseases.

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.

Crosstalk between Entamoeba histolytica and the human intestinal tract during amoebiasis

The protozoan parasite Entamoeba histolytica is the microbial agent of amoebiasis - an infection that is endemic worldwide and is associated with high morbidity and mortality rates. As the disease develops, virulent E. histolytica deplete the mucus layer, interact with the intestinal epithelium, and then degrade the colonic mucosa and disrupt the extracellular matrix (ECM). Our research demonstrated that virulent parasites with an invasive phenotype display rapid, highly specific changes in their transcriptome (notably for essential factors involved in carbohydrate metabolism and the processing of glycosylated residues). Moreover, combined activation of parasite and host lytic enzymes leads to the destruction of the intestinal parenchyma. Together, these enzymes degrade the mucus layer and the ECM, and trigger the inflammatory response essential to the development of amoebiasis.

An amebic protein disulfide isomerase (PDI) complements the yeast PDI1 mutation but is unable to support cell viability under ER or thermal stress

In eukaryotic cells, protein disulfide isomerases (PDI) are oxidoreductases that catalyze the proper disulfide bond formation during protein folding. The pathobiology of the protozoan parasite Entamoeba histolytica, the causative agent of human amebiasis, depends on secretion of several virulence factors, such as pore‐forming peptides and cysteine proteinases. Although the native conformation of these factors is stabilized by disulfide bonds, there is little information regarding the molecular machinery involved in the oxidative folding of amebic proteins. Whereas testing gene function in their physiological background would be the most suitable approach, we have taken advantage of the cellular benefits offered by the yeast Saccharomyces cerevisiae (as a model of eukaryotic cell) to examine the functional role of an amebic PDI (EhPDI). As the yeast PDI homolog is essential for cell viability, a functional complementation assay was carried out to test the ability of EhPDI to circumvent the lethal phenotype of a yeast PDI1 mutant. Also, its proficiency under stressful conditions was explored by examining the survival outcome following endoplasmic reticulum (ER) stress induced by a reductant agent (DTT) or thermal stress promoted by a nonpermissive temperature (37 °C). Our results indicate that EhPDI is functionally active when physiological conditions are stable. Nonetheless, when conditions are stressful (e.g., by the accumulation of misfolded proteins in the ER compartment), its functionality is exceeded, suggesting an inability to prevent unfolding, suppress aggregation, or assist refolding of proteins. Despite the latter, our findings constitute the initial step toward determining the participation of EhPDI in cellular mechanisms related to protein homeostasis.

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.

Extensive transcriptome analysis correlates the plasticity of Entamoeba histolytica pathogenesis to rapid phenotype changes depending on the environment

Amoebiasis is a human infectious disease due to the amoeba parasite Entamoeba histolytica. The disease appears in only 20% of the infections. Diversity in phenotypes may occur within the same infectious strain in the gut; for instance, parasites can be commensal (in the intestinal lumen) or pathogenic (inside the tissue). The degree of pathogenesis of clinical isolates varies greatly. These findings raise the hypothesis that genetic derivation may account for amoebic diverse phenotypes. The main goal of this study was to analyse gene expression changes of a single virulent amoebic strain in different environmental contexts where it exhibit different degrees of virulence, namely isolated from humans and maintained through animal liver passages, in contact with the human colon and short or prolonged in vitro culture. The study reveals major transcriptome changes in virulent parasites upon contact with human colon explants, including genes related to sugar metabolism, cytoskeleton rearrangement, stress responses and DNA repair. Furthermore, in long-term cultured parasites, drastic changes in gene expression for proteins with functions for proteasome and tRNA activities were found. Globally we conclude that rapid changes in gene expression rather than genetic derivation can sustain the invasive phenotype of a single virulent isolate of E. histolytica.

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.

The motility of Entamoeba histolytica: finding ways to understand intestinal amoebiasis

The pathogenic amoeba Entamoeba histolytica is able to migrate within various compartments of the human body. The present article reviews progress in understanding the mechanisms of cell motility in E. histolytica during human intestinal invasion and, in particular, how the three-dimensional characteristics of the environment regulate the parasite's behaviour. The amoeboid mode of migration that applies to E. histolytica's displacements on two-dimensional surfaces is also expected to apply to the three-dimensional environment in the human intestine although several unknown, distinct modalities may be involved. Recent advances in the field of tissue engineering have provided clues on how the construction of a human colon model could help us to understand the host's intestinal physiology and its changes following amoebic infection.