Target identification and intervention strategies against amebiasis

A case report of refractory amebic colitis and literature review

RATIONALE

Amebic colitis has been less prevalent in recent times in China, and the similarity of its symptoms to those of inflammatory bowel disease (IBD) results in the difficulty of early identification and diagnosis.

PATIENT CONCERNS

A 31-year-old male who exhibited intermittent diarrhea and hematochezia was highly suspected as IBD initially. Despite the partial relief of symptoms following the administration of mesalamine, the endoscopic ulcers remained largely unchanged.

DIAGNOSES

Two years after the onset of mesalamine therapy, amebic cysts were detected in stool microscopy and trophozoites were found on the surface of cecal ulcers. The patient was then diagnosed with amebic colitis.

INTERVENTIONS

After 2 rounds of standardized metronidazole treatment, amebic colitis remained refractory until diloxanide was administered.

OUTCOMES

The patient remained asymptomatic, and the mucosa of colon was normal during the annual follow-up.

LESSONS

Individuals newly diagnosed with IBD should undergo essential screening for amebiasis. And the use of steroids should be taken with caution, especially in cases where the effect of mesalamine is limited. For symptomatic intestinal amebiasis, even after the administration of tissue amebicides, the continued use of luminal amebicides is necessary to prevent recurrence.

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.

The Amoebicidal Activity of Diferrocenyl Derivatives: A Significant Dependence on the Electronic Environment

Amoebiasis is the second leading cause of death worldwide associated with parasitic disease and is becoming a critical health problem in low-income countries, urging new treatment alternatives. One of the most promising strategies is enhancing the redox imbalance within these susceptible parasites related to their limited antioxidant defense system. Metal-based drugs represent a perfect option due to their extraordinary capacity to stabilize different oxidation states and adopt diverse geometries, allowing their interaction with several molecular targets. This work describes the amoebicidal activity of five 2-(Z-2,3-diferrocenylvinyl)-4X-4,5-dihydrooxazole derivatives (X = H (3a), Me (3b), iPr (3c), Ph (3d), and benzyl (3e)) on Entamoeba histolytica trophozoites and the physicochemical, experimental, and theoretical properties that can be used to describe the antiproliferative activity. The growth inhibition capacity of these organometallic compounds is strongly related to a fine balance between the compounds' redox potential and hydrophilic character. The antiproliferative activity of diferrocenyl derivatives studied herein could be described either with the redox potential, the energy of electronic transitions, logP, or the calculated HOMO-LUMO values. Compound 3d presents the highest antiproliferative activity of the series with an IC50 of 23 µM. However, the results of this work provide a pipeline to improve the amoebicidal activity of these compounds through the directed modification of their electronic environment.

Amoebiasis: Advances in Diagnosis, Treatment, Immunology Features and the Interaction with the Intestinal Ecosystem

This review of human amoebiasis is based on the most current knowledge of pathogenesis, diagnosis, treatment, and Entamoeba/microbiota interactions. The most relevant findings during this last decade about the Entamoeba parasite and the disease are related to the possibility of culturing trophozoites of different isolates from infected individuals that allowed the characterization of the multiple pathogenic mechanisms of the parasite and the understanding of the host-parasite relationship in the human. Second, the considerable advances in molecular biology and genetics help us to analyze the genome of Entamoeba, their genetic diversity, and the association of specific genotypes with the different amoebic forms of human amoebiasis. Based on this knowledge, culture and/or molecular diagnostic strategies are now available to determine the Entamoeba species and genotype responsible for invasive intestinal or extraintestinal amoebiasis cases. Likewise, the extensive knowledge of the immune response in amoebiasis with the appearance of new technologies made it possible to design diagnostic tools now available worldwide. Finally, the understanding of the interaction between the Entamoeba species and the intestinal microbiota aids the understanding of the ecology of this parasite in the human environment. These relevant findings will be discussed in this review.

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

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

An Unusual U2AF2 Inhibits Splicing and Attenuates the Virulence of the Human Protozoan Parasite Entamoeba histolytica

E. histolytica is the etiological agent of intestinal amebiasis and liver abscesses, which still poses public health threat globally. Metronidazole is the drug of choice against amebiasis. However, metronidazole-resistant amoebic clinical isolates and strains have been reported recently, challenging the efforts for amebiasis eradication. In search of alternative treatments, E. histolytica transcriptomes have shown the association of genes involved in RNA metabolism with the virulence of the parasite. Among the upregulated genes in amoebic liver abscesses are the splicing factors EhU2AF2 and a paralog of EhSF3B1. For this reason and because EhU2AF2 contains unusual KH-QUA2 (84KQ) motifs in its lengthened C-terminus domain, here we investigated how the role of EhU2AF2 in pre-mRNA processing impacts the virulence of the parasite. We found that 84KQ is involved in splicing inhibition/intron retention of several virulence and non-virulence-related genes. The 84KQ domain interacts with the same domain of the constitutive splicing factor SF1 (SF1KQ), both in solution and when SF1KQ is bound to branchpoint signal RNA probes. The 84KQ–SF1KQ interaction prevents splicing complex E to A transition, thus inhibiting splicing. Surprisingly, the deletion of the 84KQ domain in EhU2AF2 amoeba transformants increased splicing and enhanced the in vitro and in vivo virulence phenotypes. We conclude that the interaction of the 84KQ and SF1KQ domains, probably involving additional factors, tunes down Entamoeba virulence by favoring intron retention.

Are Metabolites From the Gut Microbiota Capable of Regulating Epigenetic Mechanisms in the Human Parasite Entamoeba histolytica?

The unicellular parasite Entamoeba histolytica inhabits the human gut. It has to adapt to a complex environment that consists of the host microbiota, nutritional stress, oxidative stress, and nitrosative stress. Adaptation to this complex environment is vital for the survival of this parasite. Studies have shown that the host microbiota shapes virulence and stress adaptation in E. histolytica. Increasing evidence suggests that metabolites from the microbiota mediate communication between the parasite and microbiota. In this review, we discuss the bacterial metabolites that regulate epigenetic processes in E. histolytica and the implications that this knowledge may have for the development of new anti-amebic strategies.

Foodborne Parasitic Diseases in the Neotropics - A Review

Within the Universal Declaration of Human Rights, it is stated that everyone has the right to an adequate standard of living, which ensures, as well as their family, health and well-being, and food, thereby ensuring adequate nutrition. One of the major threats to overcome this is to ensure food security, which becomes particularly challenging in developing countries due to the high incidence of parasitic diseases. The World Health Organization (WHO), considers it one of the main causes of morbidity, closely linked to poverty and related to inadequate personal hygiene, consumption of raw food, lack of sanitary services, limited access to drinking water and fecal contamination in the environment. It is estimated that more than a fifth of the world’s population is infected by one or several intestinal parasites, and that in many countries of Central and South America the average percentage of infected people is 45%, being Taenia solium, Echinococcus granulosus, Toxoplasma gondii, Cryptosporidium spp, Entamoeba histolytica, Trichinella spiralis, Ascaris spp, Trypanosoma cruzi and Fasciola hepatica some of the most important ones in the neotropics. One of the main reasons why these diseases are diffi cult to control is t he ignorance of their lifecycles, as well as symptoms and current epidemiology of the disease, which contributes to a late or erroneous diagnosis. The present work aims to discuss and make public the current knowledge as well as the general characteristics of these diseases to the general audience.

Derivatisation of metronidazole enhances cytotoxic effect against Acanthamoeba genotype T4 isolates and leads to cytomorphological changes in trophozoites

Amoebae of the genus Acanthamoeba are worldwide distributed causative agents of serious human infections such as granulomatous amoebic encephalitis (GAE) and Acanthamoeba keratitis (AK). To date, treatment of these infections is non-uniform and frequently unsuccessful. Recently, the phosphonium salts were studied for their high levels of antimicrobial activity. This work was aimed to investigate the cytotoxic effect of metronidazole and two phosphonium salts (PS1, PS2) on two clinical Acanthamoeba isolates. The isolates showed distinctly higher susceptibility to both phosphonium salts than to metronidazole. The highest susceptibility was noted to PS1 after 48 h of incubation. Metronidazole derivate PS2 showed higher susceptibility than metronidazole. The values of EC₅₀ of PS2 were approximately twenty times lower than EC₅₀ of metronidazole for Acanthamoeba lugdunensis strain and sixteen times lower for Acanthamoeba quina strain after 48 h. Although the therapeutic effect of metronidazole in Acanthamoeba infections is usually insufficient, its derivatisation can result in a significantly higher amoebicidal effect. Cytomorphological changes of trophozoites after exposure to tested compounds included rounding up of the cells, damage of membrane integrity, presence of pathological protrusions, elongation of the cells or pseudocyst-like stages. Obtained results indicate possible therapeutic potential of studied phosphonium salts.

Entamoeba histolytica-Gut Microbiota Interaction: More Than Meets the Eye

Amebiasis is a disease caused by the unicellular parasite Entamoeba histolytica. In most cases, the infection is asymptomatic but when symptomatic, the infection can cause dysentery and invasive extraintestinal complications. In the gut, E. histolytica feeds on bacteria. Increasing evidences support the role of the gut microbiota in the development of the disease. In this review we will discuss the consequences of E. histolytica infection on the gut microbiota. We will also discuss new evidences about the role of gut microbiota in regulating the resistance of the parasite to oxidative stress and its virulence.

Drug Repurposing of the Alcohol Abuse Medication Disulfiram as an Anti-Parasitic Agent

Parasitic infections contribute significantly to worldwide morbidity and mortality. Antibiotic treatment is essential for managing patients infected with these parasites since control is otherwise challenging and there are no vaccines available for prevention. However, new antimicrobial therapies are urgently needed as significant problems exist with current treatments such as drug resistance, limited options, poor efficacy, as well as toxicity. This situation is made worse by the challenges of drug discovery and development which is costly especially for non-profitable infectious diseases, time-consuming, and risky with a high failure rate. Drug repurposing which involves finding new use for existing drugs may help to more rapidly identify therapeutic candidates while drastically cutting costs of drug research and development. In this perspective article, we discuss the importance of drug repurposing, review disulfiram pharmacology, and highlight emerging data that supports repurposing disulfiram as an anti-parasitic, exemplified by the major diarrhea-causing parasite Entamoeba histolytica.

Queuine Is a Nutritional Regulator of Entamoeba histolytica Response to Oxidative Stress and a Virulence Attenuator

Entamoeba histolytica is a unicellular parasite that causes amebiasis. The parasite resides in the colon and feeds on the colonic microbiota.

Queuosine is a naturally occurring modified ribonucleoside found in the first position of the anticodon of the transfer RNAs for Asp, Asn, His, and Tyr. Eukaryotes lack pathways to synthesize queuine, the nucleobase precursor to queuosine, and must obtain it from diet or gut microbiota. Here, we describe the effects of queuine on the physiology of the eukaryotic parasite Entamoeba histolytica, the causative agent of amebic dysentery. Queuine is efficiently incorporated into E. histolytica tRNAs by a tRNA-guanine transglycosylase (EhTGT) and this incorporation stimulates the methylation of C38 in tRNAGUCAsp. Queuine protects the parasite against oxidative stress (OS) and antagonizes the negative effect that oxidation has on translation by inducing the expression of genes involved in the OS response, such as heat shock protein 70 (Hsp70), antioxidant enzymes, and enzymes involved in DNA repair. On the other hand, queuine impairs E. histolytica virulence by downregulating the expression of genes previously associated with virulence, including cysteine proteases, cytoskeletal proteins, and small GTPases. Silencing of EhTGT prevents incorporation of queuine into tRNAs and strongly impairs methylation of C38 in tRNAGUCAsp, parasite growth, resistance to OS, and cytopathic activity. Overall, our data reveal that queuine plays a dual role in promoting OS resistance and reducing parasite virulence.

Review of zoonotic amebiasis: Epidemiology, clinical signs, diagnosis, treatment, prevention and control

Amebiasis is a disease caused by the protozoan parasite Entamoeba histolytica, which mainly shows symptoms of acute diarrhea, dysentery, amebic colitis, and amebic liver abscesses. As the fourth leading parasitic cause of human mortality, E. histolytica mainly infect children in developing countries, transmitted by food and water contamination. In the majority of infected individuals, Entamoeba sp. asymptomatically colonizes the large intestine and self-limiting, while in others, the parasite breaches the mucosal epithelial barrier to cause amebic colitis and can disseminate to soft organs to cause abscesses. Metronidazole (MTZ) is the recommended and most widely used drug for treating the invasive amebiasis. No amebiasis vaccine has been approved for human clinical trials to date, but many recent vaccine development studies hold promise. For the prevention and control of amebiasis, improvement of water purification systems and hygiene practices could decrease disease incidence. In this review, we focus on the epidemiology, transmission, clinical signs, pathogenesis, diagnosis, treatment, prevention and control of the zoonotic amebiasis.

Revisiting Drug Development Against the Neglected Tropical Disease, Amebiasis

Amebiasis is a neglected tropical disease which is caused by the protozoan parasite Entamoeba histolytica. This disease is one of the leading causes of diarrhea globally, affecting largely impoverished residents in developing countries. Amebiasis also remains one of the top causes of gastrointestinal diseases in returning international travellers. Despite having many side effects, metronidazole remains the drug of choice as an amebicidal tissue-active agent. However, emergence of metronidazole resistance in pathogens having similar anaerobic metabolism and also in laboratory strains of E. histolytica has necessitated the identification and development of new drug targets and therapeutic strategies against the parasite. Recent research in the field of amebiasis has led to a better understanding of the parasite’s metabolic and cellular pathways and hence has been useful in identifying new drug targets. On the other hand, new molecules effective against amebiasis have been mined by modifying available compounds, thereby increasing their potency and efficacy and also by repurposing existing approved drugs. This review aims at compiling and examining up to date information on promising drug targets and drug molecules for the treatment of amebiasis.