Entamoeba stage conversion: progress and new insights

Serologic diagnosis of Entamoeba histolytica infection based on the gradient-based digital immunoassay

BACKGROUND

Entamoeba histolytica is a parasite that could cause severe amebiasis, an extremely contagious parasitic disease with critical clinical symptoms. Timely diagnosis and treatment of E. histolytica are crucial for preventing complications and fatalities. However, current methods for E. histolytica diagnosis still rely on traditional and laborious methods such as stool examinations and serological immunoassay. Those methods urgently need improved diagnostic sensitivity, diagnostic specificity, detection time, and diagnostic accuracy.

RESULTS

Herein, we developed a rapid and accurate gradient-based digital immunoassay system for diagnosing E. histolytica. This method uses a homemade pre-coated recombinant Igl-C fragment with high binding affinity, designed, recombinantly expressed, and purified by our lab on a one-shot observation microfluidic chip to capture the disease biomarker, specific anti-Igl-C antibodies in the serum. The captured antibodies are detected by anti-human IgG-coated gold nanoparticles, forming a digital binding sandwich immunocomplex. After simple imaging processing, the number of gold nanoparticles bound to the reaction surface within the same field of view of the microscope image was analyzed. Then, it can be easily determined in about 15 min whether specific anti-Igl-C antibodies are in the serum, allowing quicker identification of E. histolytica infection. The detection and diagnosis performance were confirmed by testing 25 clinical serum samples.

SIGNIFICANCE AND NOVELTY

The novel diagnostic method provided a digital immunoassay platform and has a strong potential to be a high-efficiency tool for the clinical diagnosis of E. histolytica infection with heightened diagnostic sensitivity and diagnostic specificity. It offers the potential for rapid point-of-care testing, facilitating prompt treatment initiation and improved patient outcomes in resource-limited healthcare settings, making it a valuable asset in the fight against amebiasis.

First Molecular Identification of Entamoeba spp. in Sheep, Beef Cattle, and Dairy Cattle in Shanxi Province, North China

Entamoeba spp. are common zoonotic intestinal protozoa, which can lead to serious intestinal diseases in both humans and animals through fecal-oral transmission, leading to significant economic losses and public health challenges. To reveal the prevalence of Entamoeba in sheep and cattle in Shanxi Province, North China, fecal samples were collected from 311 sheep, 392 dairy cattle, and 393 beef cattle from three representative counties in the northern, central, and southern regions of Shanxi Province. DNA was extracted from the fecal samples and amplified by PCR with primers targeting the nuclear small subunit ribosomal RNA (SSU rRNA) gene of Entamoeba spp., followed by the sequencing of the positive products. The overall infection rates of Entamoeba were 51.5% (160/311), 82.9% (325/392), and 79.1% (311/393) in sheep, dairy cattle, and beef cattle, respectively. Statistical analysis showed a significant correlation between the infection rate of Entamoeba and the location factor in sheep, dairy cattle, and beef cattle (p < 0.001). According to the obtained SSU rRNA sequences, several Entamoeba species, namely Entamoeba bovis, Entamoeba Ribosomal Lineage (RL) 2, Entamoeba RL4, and Entamoeba RL8, were identified. This study represents the first molecular survey of Entamoeba prevalence in sheep, beef cattle, and dairy cattle in Shanxi Province. The findings extend the geographical distribution of Entamoeba spp. and provide valuable scientific data for the prevention and control of amoebiasis in Shanxi Province.

Amoebae: beyond pathogens- exploring their benefits and future potential

Amoebae, fascinatingly diverse protists, showcase a dual nature that positions them as both friends and foes in our world. These organisms, defined by their distinctive pseudopodia, span a spectrum from harmful to helpful. On the darker side, species like Entamoeba histolytica pose serious health risks, causing intestinal and liver diseases, while the infamous "brain-eating" Naegleria fowleri leads to fatal primary amoebic meningoencephalitis (PAM), with a daunting 97% mortality rate. Other free-living amoebae, including Acanthamoeba castellanii and Balamuthia mandrillaris, also threaten the human central nervous system. Yet, beyond these dangers, amoebae play critical ecological roles. They function as nature's recyclers, decomposing organic material and nourishing aquatic ecosystems, while also serving as food for various organisms. Moreover, certain amoebae help control plant pathogens and offer insight into human disease, proving valuable as model organisms in biomedical research. This review sheds light on the complex, multifaceted world of amoebae, highlighting their dual role as pathogens and as key contributors to vital ecological processes, as well as their significant impact on research and their promising potential for enhancing human well-being.

Identification of two transcription factors that work coordinately to regulate early development in Entamoeba

The protozoan parasite Entamoeba has a life cycle that switches between infective cysts and invasive trophozoites. Encystation, a crucial process in parasite biology, is controlled by different mechanisms including transcriptional control. We identified two nuclear proteins in Entamoeba invadens, EIN_066100 and EIN_085620, that regulate parasite development by binding to a DNA motif (TCACTTTC) in the promoter regions of genes upregulated in the first 8 h of stage conversion. Overexpression of EIN_066100, a homolog of MAK16 protein, resulted in reduced amoebic proliferation without affecting encystation efficiency. Overexpression of EIN_085620, a protein with an RNA-recognition motif (RRM), led to increased encystation efficiency. Glutathione S-transferase (GST) pull down assays revealed that EIN_066100 interacts with EIN_085620 both in vivo and in vitro, and this interaction is mediated by the EIN_085620 RRM domain. By evaluating truncated proteins with deletions at either the N-terminal or C-terminal regions of EIN_066100, we elucidated the importance of its N-terminal region in proper protein localization, proliferation, encystation, and interaction with EIN_085620. Taken together, these results indicate a coordinated role of EIN_066100 and EIN_085620 in regulating Entamoeba development. This work sheds light on the molecular mechanisms in the earliest stages of Entamoeba encystation.IMPORTANCEAn important biological process in the biology of Entamoeba is stage conversion, which plays a crucial role in disease propagation, facilitating parasite survival outside the host and spreading to new hosts. Multiple mechanisms contribute to controlling the expression of amebic stage-specific genes such as epigenetic and transcriptional control. Identification of early transcriptional control regulators is crucial to understanding the initiation of the encystation cascade. We identified two nuclear proteins, EIN_066100 and EIN_085620, involved in the proliferation and developmental regulation of E. invadens. These proteins work by direct binding to each other and mediating encystation efficiency. Study of new regulators involved in Entamoeba development represents an important advance in a critical aspect of parasite biology.

Role of various virulence factors involved in the pathogenesis of Entamoeba histolytica

Developing countries continuously face challenges to get rid of amoebiasis, a protozoan disease caused by Entamoeba histolytica. Every year around 900 million people get affected by amoebiasis, among them only 10 % of people show the symptoms of the disease while 90 % of people do not show any symptoms but still, serve as carriers of the disease. Asymptomatic persons carry cysts of Entamoeba in their fecal matter, which is carried by house flies to contaminate the food and water. Entamoeba histolytica is a very successful pathogen because it has very well-developed virulence factors that function in infection to host as well as in overcoming the host's immune response. However, researchers have very little information about the clear relationship between virulence factors and the virulence of Entamoeba histolytica, through various research, researchers have been able to identify key pathogenic factors that are crucial to the pathogenesis of amoebiasis and have provided valuable insights into the development of the disease. The objective of this review is to underscore various virulence factors (Monosaccharides, Gal/GalNAc lectin, extracellular vesicles, cysteine proteases, amoeba-pores, and actin microfilament) involved in pathogenesis which may be helpful for designing of future drug or therapy.

Molecular characterization of Giardia duodenalis, Cryptosporidium spp., and Entamoeba spp. infecting domestic and feral/stray cats in Jordan

This study aimed to carry out a molecular screening for the presence of Giardia, Cryptosporidium, and/or Entamoeba in the feces of pet and stray/feral cats in Jordan. G. duodenalis was found in 27.9% (95% CI, 23.2-32.9) of the 348 sampled cats overall; E. histolytica was found in only 0.6% (95% CI, 0.1-2.1) of the cats, while none of the sampled cats had Cryptosporidium infections. The infection rate of G. duodenalis among indoor cats (32.3%) did not differ significantly from that among outdoor cats (24.1%). There were significantly more infections (p = 0.0004) geographically in the cold semiarid areas (67%) than in the cold desert areas (24%). Multilocus sequence typing analysis of amplicons based on the bg, tpi, and gdh genes revealed that the majority of G. duodenalis infections were zoonotic assemblage B (65.9%; 64 of 97 positive samples); followed by feline-specific assemblage F (18.5%, 18/97); cattle-specific assemblage E (5.2%, 5/97); and then assemblage C that was shared with canids (1.0%; 1/97). Within Giardia isolates, a substitution mutation (A/G) was found at position 297 of the complete protein coding sequence (cds) of tpi-assemblage B, which may represent a new spreading mutation within this gene among the cat population in Jordan. The results of the present study suggest that close human-cat interactions could play a role in zoonotic transmission of Giardia, but further research is needed to determine the possible contribution of cats to the transmission of other protozoa to humans.

The macrophage polarization in Entamoeba histolytica infection modulation by the C fragment of the intermediate subunit of Gal/GalNAc-inhibitable lectin

The protozoan parasite Entamoeba histolytica is the causative agent of amebiasis, with clinical outcomes ranging from asymptomatic infections to severe invasive diseases. The innate immune system, particularly macrophages, is of paramount importance in resisting the invasion of host tissues and organs by the trophozoites of E. histolytica. Parasite-derived pathogenic factors, such as lectins, play a pivotal role in the promotion of macrophage polarization phenotypes that have undergone alteration. Nevertheless, the precise mechanisms by which E. histolytica modulates immune polarization remain largely unknown. The current study focused on the immunomodulatory effects of the Igl-C fragment of E. histolytica Gal/GalNAc lectin on macrophage polarization. These results demonstrated that Igl-C could induce the secretion of IL-1β, IL-6, and other cytokines, activating a mixed M1/M2 polarization state. M1 polarization of macrophages occurs in the early stages and gradually transitions to M2 polarization in the later stages, which may contribute to the persistence of the infection. Igl-C induces the macrophage M1 phenotype and causes the release of immune effector molecules, including iNOS and cytokines, by activating the NF-κB p65 and JAK-STAT1 transcription factor signaling pathways. Furthermore, Igl-C supports the macrophage M2 phenotype via JAK-STAT3 and IL-4-STAT6 pathways, which activate arginase expression in later stages, contributing to the tissue regeneration and persistence of the parasite. The involvement of distinct signaling pathways in mediating this response highlights the complex interplay between the parasite and the host immune system. These findings enhance our understanding of the Igl-C-mediated pathogenic mechanisms during E. histolytica infection.

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.

Pathogenicity and virulence of Entamoeba histolytica, the agent of amoebiasis

The amoeba parasite Entamoeba histolytica is the causative agent of human amebiasis, an enteropathic disease affecting millions of people worldwide. This ancient protozoan is an elementary example of how parasites evolve with humans, e.g. taking advantage of multiple mechanisms to evade immune responses, interacting with microbiota for nutritional and protective needs, utilizing host resources for growth, division, and encystation. These skills of E. histolytica perpetuate the species and incidence of infection. However, in 10% of infected cases, the parasite turns into a pathogen; the host-parasite equilibrium is then disorganized, and the simple lifecycle based on two cell forms, trophozoites and cysts, becomes unbalanced. Trophozoites acquire a virulent phenotype which, when non-controlled, leads to intestinal invasion with the onset of amoebiasis symptoms. Virulent E. histolytica must cross mucus, epithelium, connective tissue and possibly blood. This highly mobile parasite faces various stresses and a powerful host immune response, with oxidative stress being a challenge for its survival. New emerging research avenues and omics technologies target gene regulation to determine human or parasitic factors activated upon infection, their role in virulence activation, and in pathogenesis; this research bears in mind that E. histolytica is a resident of the complex intestinal ecosystem. The goal is to eradicate amoebiasis from the planet, but the parasitic life of E. histolytica is ancient and complex and will likely continue to evolve with humans. Advances in these topics are summarized here.

Encystation and Stress Responses under the Control of Ubiquitin-like Proteins in Pathogenic Amoebae

Amoebae found in aquatic and terrestrial environments encompass various pathogenic species, including the parasite Entamoeba histolytica and the free-living Acanthamoeba castellanii. Both microorganisms pose significant threats to public health, capable of inducing life-threatening effects on humans. These amoebae exist in two cellular forms: trophozoites and cysts. The trophozoite stage is the form used for growth and reproduction while the cyst stage is the resistant and disseminating form. Cysts occur after cellular metabolism slowdown due to nutritional deprivation or the appearance of environmental conditions unfavourable to the amoebae's growth and division. The initiation of encystation is accompanied by the activation of stress responses, and scarce data indicate that encystation shares factors and mechanisms identified in stress responses occurring in trophozoites exposed to toxic compounds derived from human immune defence. Although some "omics" analyses have explored how amoebae respond to diverse stresses, these studies remain limited and rarely report post-translational modifications that would provide knowledge on the molecular mechanisms underlying amoebae-specific stress responses. In this review, we discuss ubiquitin-like proteins associated with encystation and cell survival during oxidative damage. We aim to shed light on the signalling pathways involved in amoebic defence mechanisms, with a focus on their potential clinical implications against pathogenic amoebae, addressing the pressing need for effective therapies.

Giant cells: multiple cells unite to survive

Multinucleated Giant Cells (MGCs) are specialized cells that develop from the fusion of multiple cells, and their presence is commonly observed in human cells during various infections. However, MGC formation is not restricted to infections alone but can also occur through different mechanisms, such as endoreplication and abortive cell cycle. These processes lead to the formation of polyploid cells, eventually resulting in the formation of MGCs. In Entamoeba, a protozoan parasite that causes amoebic dysentery and liver abscesses in humans, the formation of MGCs is a unique phenomenon and not been reported in any other protozoa. This organism is exposed to various hostile environmental conditions, including changes in temperature, pH, and nutrient availability, which can lead to stress and damage to its cells. The formation of MGCs in Entamoeba is thought to be a survival strategy to cope with these adverse conditions. This organism forms MGCs through cell aggregation and fusion in response to osmotic and heat stress. The MGCs in Entamoeba are thought to have increased resistance to various stresses and can survive longer than normal cells under adverse conditions. This increased survival could be due to the presence of multiple nuclei, which could provide redundancy in case of DNA damage or mutations. Additionally, MGCs may play a role in the virulence of Entamoeba as they are found in the inflammatory foci of amoebic liver abscesses and other infections caused by Entamoeba. The presence of MGCs in these infections suggests that they may contribute to the pathogenesis of the disease. Overall, this article offers valuable insights into the intriguing phenomenon of MGC formation in Entamoeba. By unraveling the mechanisms behind this process and examining its implications, researchers can gain a deeper understanding of the complex biology of Entamoeba and potentially identify new targets for therapeutic interventions. The study of MGCs in Entamoeba serves as a gateway to exploring the broader field of cell fusion in various organisms, providing a foundation for future investigations into related cellular processes and their significance in health and disease.

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.

Furanocoumarins from Ruta chalepensis with Amebicide Activity

Entamoeba histolytica (protozoan; family Endomoebidae) is the cause of amoebiasis, a disease related to high morbidity and mortality. Nowadays, this illness is considered a significant public health issue in developing countries. In addition, parasite resistance to conventional medicinal treatment has increased in recent years. Traditional medicine around the world represents a valuable source of alternative treatment for many parasite diseases. In a previous paper, we communicated about the antiprotozoal activity in vitro of the methanolic (MeOH) extract of Ruta chalepensis (Rutaceae) against E. histolytica. The plant is extensively employed in Mexican traditional medicine. The following workup of the MeOH extract of R. chalepensis afforded the furocoumarins rutamarin (1) and chalepin (2), which showed high antiprotozoal activity on Entamoeba histolytica trophozoites employing in vitro tests (IC₅₀ values of 6.52 and 28.95 µg/mL, respectively). Therefore, we offer a full scientific report about the bioguided isolation and the amebicide activity of chalepin and rutamarin.

Signals and signal transduction pathways in Entamoeba histolytica during the life cycle and when interacting with bacteria or human cells

Entamoeba histolytica is the etiological agent of amebiasis in humans. This ameba parasite resides as a commensal in the intestine where it shares intestinal resources with the bacterial microbiome. In the intestinal ecosystem, the ameba encysts and eventually develops disease by invading the tissues. E. histolytica possesses cell surface receptors for the proper sensing of signals involved in encystation or sustaining parasite interaction with bacteria and human cells. Among those receptors are the Gal/GalNAc lectin, G protein-coupled receptors, and transmembrane kinases. In addition there are recently discovered, promising proteins, including orthologs of Toll-type receptors and β trefoil lectins. These proteins trigger a wide variety of signal transduction pathways; however, most of the players involved in the signaling pathways evoked in this parasite are unknown. This review provides an overview of amoebic receptors and their role in encystation, adherence to bacteria or human cells, as well as the reported intracellular signal transduction processes that they can trigger. This knowledge is essential for understanding the lifestyle of E. histolytica and its cytopathic effect on bacteria and human cells that are responsible for infection.