Inhibition of choline kinase as an antiamoebic approach in Entamoeba histolytica infection

Entamoeba histolytica is the parasite responsible for amoebiasis, which can result in amoebic colitis or amoebic liver abscess. Metronidazole has been the conventional treatment for intestinal amoebiasis, but concerns regarding resistance have emerged due to the identification of resistance pathways in E. histolytica. This study investigates a novel anti-amoebic approach targeting the CDP-choline pathway. Inhibition studies were conducted using potential choline kinase (CK) inhibitors to inhibit the EhCK enzyme, and RNA interference was employed to knock down the EhCK gene. Km and Vmax of purified EhCK and hCKa2 proteins were determined by pyruvate kinase-lactate dehydrogenase (PK-LDH) coupled assay. The IC50 values for EhCK and hCKa2 were determined with several commercial CK inhibitors. Selected inhibitors were incubated with E. histolytica trophozoites for 48 hours to determine the EC50 for each inhibitor. Silencing of gene encoding EhCK was carried out using duplex siRNA and the gene expression level was measured by real-time qPCR. Based on the IC50 values, three of the inhibitors, namely CK37, flavopiridol and H-89 were more potent against EhCK than hCKa2. Trophozoites growth inhibition showed that only HDTAB, H-89 and control drug metronidazole could penetrate and induce cell death after 48-hour incubation. siRNA concentration of 10 µg/mL was used for the transfection of positive control GAPDH, EhCK, and non-targeting GFP siRNAs. RNAi experiment concluded with positive control GAPDH downregulated by 99% while the level of EhCK mRNA was downregulated by 47%. In this study, potential inhibitors of EhCK and siRNA have been identified, paving the way for further refinement and testing to enhance their potency against EhCK while sparing hCK. The utilization of these specific inhibitors and siRNA targeting EhCK represents a novel approach to impede the growth of E. histolytica by disrupting its phospholipid synthesis pathway.

Entamoeba histolytica induced NETosis and the dual role of NETs in amoebiasis

Entamoeba histolytica (Eh), a microaerophilic parasite, causes deadly enteric infections that result in Amoebiasis. Every year, the count of invasive infections reaches 50 million approximately and 40,000 to 1,00,000 deaths occurring due to amoebiasis are reported globally. Profound inflammation is the hallmark of severe amoebiasis which is facilitated by immune first defenders, neutrophils. Due to size incompatibility, neutrophils are unable to phagocytose Eh and thus, came up with the miraculous antiparasitic mechanism of neutrophil extracellular traps (NETs). This review provides an in-depth analysis of NETosis induced by Eh including the antigens involved in the recognition of Eh and the biochemistry of NET formation. Additionally, it underscores its novelty by describing the dual role of NETs in amoebiasis where it acts as a double-edged sword in terms of both clearing and exacerbating amoebiasis. It also provides a comprehensive account of the virulence factors discovered to date that are implicated directly and indirectly in the pathophysiology of Eh infections through the lens of NETs and can be interesting drug targets.

Case report: multiple and atypical amoebic cerebral abscesses resistant to treatment

BACKGROUND

The parasite Entamoeba histolytica is the causal agent of amoebiasis, a worldwide emerging disease. Amebic brain abscess is a form of invasive amebiasis that is both rare and frequently lethal. This condition always begins with the infection of the colon by E. histolytica trophozoites, which subsequently travel through the bloodstream to extraintestinal tissues.

CASE PRESENTATION

We report a case of a 71-year-old female who reported an altered state of consciousness, disorientation, sleepiness and memory loss. She had no history of hepatic or intestinal amoebiasis. A preliminary diagnosis of colloidal vesicular phase neurocysticercosis was made based on nuclear magnetic resonance imaging (NMRI). A postsurgery immunofluorescence study was positive for the 140 kDa fibronectin receptor of E. histolytica, although a serum analysis by ELISA was negative for IgG antibodies against this parasite. A specific E. histolytica 128 bp rRNA gene was identified by PCR in biopsy tissue. The final diagnosis was cerebral amoebiasis. The patient underwent neurosurgery to eliminate amoebic abscesses and was then given a regimen of metronidazole, ceftriaxone and dexamethasone for 4 weeks after the neurosurgery. However, a rapid decline in her condition led to death.

CONCLUSIONS

The present case of an individual with a rare form of cerebral amoebiasis highlights the importance of performing immunofluorescence, NMRI and PCR if a patient has brain abscess and a poorly defined diagnosis. Moreover, the administration of corticosteroids to such patients can often lead to a rapid decline in their condition.

Intestinal parasites including Cryptosporidium, Cyclospora, Giardia, and Microsporidia, Entamoeba histolytica, Strongyloides, Schistosomiasis, and Echinococcus: Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice

These updated guidelines from the Infectious Diseases Community of Practice of the American Society of Transplantation review the diagnosis, prevention, and management of intestinal parasites in the pre- and post-transplant period. Intestinal parasites are prevalent in the developing regions of the world. With increasing travel to and from endemic regions, changing immigration patterns, and the expansion of transplant medicine in developing countries, they are increasingly recognized as a source of morbidity and mortality in solid-organ transplant recipients. Parasitic infections may be acquired from the donor allograft, from reactivation, or from de novo acquisition post-transplantation. Gastrointestinal multiplex assays have been developed; some of the panels include testing for Cryptosporidium, Cyclospora, Entamoeba histolytica, and Giardia, and the performance is comparable to conventional methods. A polymerase chain reaction test, not yet widely available, has also been developed to detect Strongyloides in stool samples. New recommendations have been developed to minimize the risk of Strongyloides donor-derived events. Deceased donors with epidemiological risk factors should be screened for Strongyloides and recipients treated if positive as soon as the results are available. New therapeutic agents and studies addressing the optimal treatment regimen for solid-organ transplant recipients are unmet needs.

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.

Escherichia coli mediated resistance of Entamoeba histolytica to oxidative stress is triggered by oxaloacetate

Amebiasis, a global intestinal parasitic disease, is due to Entamoeba histolytica. This parasite, which feeds on bacteria in the large intestine of its human host, can trigger a strong inflammatory response upon invasion of the colonic mucosa. Whereas information about the mechanisms which are used by the parasite to cope with oxidative and nitrosative stresses during infection is available, knowledge about the contribution of bacteria to these mechanisms is lacking. In a recent study, we demonstrated that enteropathogenic Escherichia coli O55 protects E. histolytica against oxidative stress. Resin-assisted capture (RAC) of oxidized (OX) proteins coupled to mass spectrometry (OX-RAC) was used to investigate the oxidation status of cysteine residues in proteins present in E. histolytica trophozoites incubated with live or heat-killed E. coli O55 and then exposed to H2O2-mediated oxidative stress. We found that the redox proteome of E. histolytica exposed to heat-killed E. coli O55 is enriched with proteins involved in redox homeostasis, lipid metabolism, small molecule metabolism, carbohydrate derivative metabolism, and organonitrogen compound biosynthesis. In contrast, we found that proteins associated with redox homeostasis were the only OX-proteins that were enriched in E. histolytica trophozoites which were incubated with live E. coli O55. These data indicate that E. coli has a profound impact on the redox proteome of E. histolytica. Unexpectedly, some E. coli proteins were also co-identified with E. histolytica proteins by OX-RAC. We demonstrated that one of these proteins, E. coli malate dehydrogenase (EcMDH) and its product, oxaloacetate, are key elements of E. coli-mediated resistance of E. histolytica to oxidative stress and that oxaloacetate helps the parasite survive in the large intestine. We also provide evidence that the protective effect of oxaloacetate against oxidative stress extends to Caenorhabditis elegans.

Learning points from a case of severe amoebic colitis

A case of amoebic colitis and liver abscess is described in a previously fit 59-year old man who had been given the incorrect diagnosis of ulcerative colitis. His symptoms were so severe that a colectomy was being considered. The patient had a significant travel history including trips to Morocco, the Gambia and Cape Verde, putting him at risk of acquiring amoebic disease. However, this history was not ascertained until much later on in the disease process. The case highlighted crucial learning points including the importance of taking a lifelong travel history, the difficulties in telling ulcerative colitis and amoebic colitis apart both clinically and histopathologically, and the importance of sending multiple stool samples for parasitological microscopy analysis in patients being investigated for inflammatory bowel disease.

All that glitters is not gold. A different cause for an "ulcerative colitis"

The authors present the case of a 32-year-old Caucasian male, engineer, who was submitted to a colonoscopy after a presumptive diagnosis of ulcerative colitis. The patient referred an acute bloody and mucous diarrhea, lasting for three weeks, with no fever or rectal tenesmus. Stool studies were negative. During the procedure, colonic segments with continuous hyperemic and exudative mucosa, with small papules with apical ulcers and erosions, were observed.

Effect of Mass Stool Examination and Mass Treatment For Decreasing Intestinal Helminth and Protozoan Infection Rates in Bolivian Children: A Cross-Sectional Study

Bolivia is one of the countries with a high intestinal helminth and protozoan infection rate. Despite the high prevalence of the parasitic infection, nationwide preventive measures for Bolivian children have not yet been implemented. We evaluated the effect of mass stool examination and treatment as a strategy for decreasing the infection rate. This study was conducted between 2013 and 2015 in children aged 2–18 years. A total of 2,033 stool samples (575 in 2013, 815 in 2014 and 642 in 2015) were collected and examined using the formalin-ether medical sedimentation method. As an anthelminthic medicine, nitazoxanide was given to all infected children within 2 months post-examination, each year. The effect of mass stool examination and treatment was evaluated based on the changes in the overall or individual parasitic infection rates during the study period. The overall parasitic infection rate decreased significantly from 65.2% in 2013 to 43.0% in 2015; a 22.2 percentage point decrease (P<0.001). Protozoan infection accounted for a large portion of the parasitic infections, in the following rates: 62.4% in 2013, 49.3% in 2014, and 41.0% in 2015. The rate of the most common helminth infection, Hymenolepis nana, decreased significantly from 9.0% in 2013 to 6.4% in 2014 to 3.4% in 2015 (P<0.001). Prevalence of the most common pathogenic protozoan infection, Entamoeba histolytica, decreased significantly from 19.0% in 2013 to 3.0% in 2015 (P<0.001). Conversely, the rate of Giardia intestinalis increased significantly from 16.5% in 2013 to 21.2% in 2015 (P<0.01). Mass stool examination and treatment for intestinal helminth and protozoan infections was effective for decreasing the overall parasitic infection rate in the study population, excluding Giardia intestinalis. Further studies on the long-term effect of mass stool examination and treatment for decreasing all intestinal parasitic infection rates in Bolivian children are needed.

Intestinal helminth and protozoan (parasitic) infections are found mainly in areas with warm, humid climates and in many developing countries. Bolivia currently has high parasite infection rates, including intestinal helminth and protozoan infections. Despite the high prevalence of parasitic infections, nationwide preventive measures for Bolivian children have not yet been implemented. Soil-transmitted helminth infection rates in Japan decreased sharply through practice of health education, mass stool examination and treatment. We investigated the effects of mass stool examination and treatment on parasitic infection rates in Bolivian children. Mass stool examination was performed using the formalin-ether medical sedimentation method between 2013 and 2015, and all infected children were administrated anthelminthic medicine within 2 months post-examination. During the study period, the overall infection rate decreased significantly, but Giardia intestinalis infection rate increased. This may have been related to the interval between treatment and examination. To decrease infection rates for all parasites, the treatment should be performed once or twice a year. Our results suggest that a program of mass stool examination and treatment could effectively reduce the overall parasite-infection rate in Bolivian children.

Entamoeba thiol-based redox metabolism: A potential target for drug development

Amebiasis is an intestinal infection widespread throughout the world caused by the human pathogen Entamoeba histolytica. Metronidazole has been a drug of choice against amebiasis for decades despite its low efficacy against asymptomatic cyst carriers and emergence of resistance in other protozoa with similar anaerobic metabolism. Therefore, identification and characterization of specific targets is urgently needed to design new therapeutics for improved treatment against amebiasis. Toward this goal, thiol-dependent redox metabolism is of particular interest. The thiol-dependent redox metabolism in E. histolytica consists of proteins including peroxiredoxin, rubrerythrin, Fe-superoxide dismutase, flavodiiron proteins, NADPH: flavin oxidoreductase, and amino acids including l-cysteine, S-methyl-l-cysteine, and thioprolines (thiazolidine-4-carboxylic acids). E. histolytica completely lacks glutathione and its metabolism, and l-cysteine is the major intracellular low molecular mass thiol. Moreover, this parasite possesses a functional thioredoxin system consisting of thioredoxin and thioredoxin reductase, which is a ubiquitous oxidoreductase system with antioxidant and redox regulatory roles. In this review, we summarize and highlight the thiol-based redox metabolism and its control mechanisms in E. histolytica, in particular, the features of the system unique to E. histolytica, and its potential use for drug development against amebiasis.

[Coecum amoebiasis can be a rare manifestation of Entamoeba histolytica infection]

A 58-year-old Danish male was admitted to hospital with acute abdominal pain. Laparoscopy showed a normal appendix. However, a tumour in the ascending colon was found and hemicolectomy was performed. Pathological examination showed deep ulcerations with undermined edges and massive inflammation and necrosis. Periodic acid Schiff (PAS)-positive amoebae trophozoites were identified, and the patient was diagnosed with and treated for amoebiasis. The patient had not been abroad for 14 years but he worked with sewage. Patients in developed countries working with sewage should be considered at risk of developing amoebiasis.

A rare case of multilocus brain abscess due to Entamoeba histolytica infection in a child

Brain abscess due to Entamoeba histolytica (E. histolytica) may pose a diagnostic problem or a therapeutic challenge, as evidenced by the paucity of papers reporting complete recovery after treatment. An 11-year-old girl presented with progressive drowsiness, diminished movements of the left upper limb, and swallowing problems. Cranial MRI showed multiple, contrast-dense masses with fluid content. She was started on meropenem. Surgical drainage was performed. No bacterial or fungal growth was observed in drainage samples. Entamoeba histolytica trophozoites were detected in the tissue sample. Intravenous metronidazole was started and continued for 6 weeks, at the end of which abscesses were found and to have shrunk considerably. Intravenous therapy was switched to oral metronidazole, which was continued for 2 weeks. She regained all her preexisting abilities. Multiple brain abscesses due to E. histolytica is a very rare occurrence, and histopathologic evaluation is important in diagnosis.

Parasitic causes of prolonged diarrhoea in travellers - diagnosis and management

BACKGROUND

Prolonged infectious diarrhoea in the returning traveller is generally caused by protozoal and occasionally by helminth parasites.

OBJECTIVE

This article provides a framework for the diagnosis, management and prevention of the diseases that cause persistent diarrhoea in the traveller.

DISCUSSION

A large proportion of disease is caused by Giardia lamblia, Cryptosporidium parvum and Entamoeba histolytica. However, given the ease of travel with comorbid conditions such as human immunodeficiency virus, there is an expanding list of organisms that can cause persistent diarrhoea. An awareness of the likely aetiological agents and their clinical features enables a more effective diagnosis and management of the patient's condition using an appropriate antiparasitic agent. Prevention strategies need to be initiated before travel and should consist of simple but memorable advice. Noninfectious causes of diarrhoea should be considered as diarrhoea can be a prominent feature of conditions such as hyperthyroidism or coeliac disease.

Virtual screening, identification and in vitro testing of novel inhibitors of O-acetyl-L-serine sulfhydrylase of Entamoeba histolytica

The explosive epidemicity of amoebiasis caused by the facultative gastrointestinal protozoan parasite Entamoeba histolytica is a major public health problem in developing countries. Multidrug resistance and side effects of various available antiamoebic drugs necessitate the design of novel antiamobeic agents. The cysteine biosynthetic pathway is the critical target for drug design due to its significance in the growth, survival and other cellular activities of E. histolytica. Here, we have screened 0.15 million natural compounds from the ZINC database against the active site of the EhOASS enzyme (PDB ID. 3BM5, 2PQM), whose structure we previously determined to 2.4 Å and 1.86 Å resolution. For this purpose, the incremental construction algorithm of GLIDE and the genetic algorithm of GOLD were used. We analyzed docking results for top ranking compounds using a consensus scoring function of X-Score to calculate the binding affinity and using ligplot to measure protein-ligand interactions. Fifteen compounds that possess good inhibitory activity against EhOASS active site were identified that may act as potential high affinity inhibitors. In vitro screening of a few commercially available compounds established their biological activity. The first ranked compound ZINC08931589 had a binding affinity of ∼8.05 µM and inhibited about 73% activity at 0.1 mM concentration, indicating good correlation between in silico prediction and in vitro inhibition studies. This compound is thus a good starting point for further development of strong inhibitors.

Entamoeba histolytica/Entamoeba dispar infection in chronic hemodialysis patients

To determine the prevalence of Entamoeba histolytica/E. dispar (Eh/Ed) in chronic hemodialysis (HD) patients, we collected 330 samples of feces from 110 patients, and nine individuals were found to be positive for Eh/Ed. We compared the infected patients with a group of 14 uninfected HD patients. Both groups were analyzed for their signs, symptoms and socio-economic characteristics using questionnaires. Blood tests were also performed in both the groups. Although both groups did not differ statistically with respect to their signs, symptoms and socio-economic conditions, there was a trend toward a greater number of individuals with diarrhea in the Eh/Ed infected group. In conclusion, we suggest that a parasitological examination of the patient's stool to detect the Eh/Ed complex should be included with the routine tests so that those patients with a positive fecal test could be initiated on appropriate anti-Eh/Ed therapy.

[Amebiasis: implications of the recognition of Entamoeba dispar and the identification of Entamoeba moshkovskii in humans]

The history of Entamoeba histolytica is very confuse and shows several wrong concepts about the parasite and its relationship with the host. The poor correlation between the prevalence of asymptomatic and symptomatic amebiasis originated the proposal of three explicative hypothesis, among them was the concept of Brumpt that E. histolytica comprised two morphologically identical species, E. dysenteriae and E. dispar. The application of modern molecular techniques irrefutably proved that E. histolytica was really a complex of two species, confirming the concept of Brumpt almost 7 decades later. Recent studies have identified in humans E. moshkovskii, morphologically indistinguishable from E. histolytica and E. dispar, a great genetic diversity within each of these species, and heterogeneity in virulence among E. histolytica strains. The redescription of E. dispar, and the recovery of E. moshkovskii from humans have had a major impact in our understanding of E. histolytica and amebiasis with important clinical and epidemiologic implications. This has led to the need of a reevaluation of the infection in terms of prevalence and morbidity in the global population and to study the geographic distribution, prevalence, and transmission pattern of E. histolytica strains in order to detect those with epidemiologic relevance and predict the risk of amebic disease in a population.

[Tinidazole: a classical anaerobical drug with multiple potential uses nowadays]

Tinidazole is a 5-nitroimidazole active in vitro against a wide variety of anaerobic bacteria and protozoa. Tinidazole is an effective treatment against anaerobic microorganisms based on its pharmacokinetic characteristics (C(max) 51 microg/ml, t(1/2) 12.5 h) and its excellent in vitro activity. Its long half-life allows once a day regimens. Tinidazole is as effective as metronidazole in the treatment of infections caused by T. vaginalis, giardiasis and amebiasis and bacterial vaginosis, malaria, odontogenic infections, anaerobic bacterial infections (pelvic inflammatory disease, diabetic foot), surgical prophylaxis (abdominal and hysterectomy) and Helicobacter pylori eradication. Tinidazole was recently approved by the Food and Drug Administration (FDA) for the treatment of infections caused by Trichomonas vaginalis, Entamoeba histolytica and Giardia lamblia.

Amebic colitis in an antigenically and serologically negative patient: usefulness of a small-subunit ribosomal RNA gene-based polymerase chain reaction in diagnosis

Specific identification of Entamoeba histolytica in clinical specimens is an essential confirmatory diagnostic step in the management of amebiasis. Here, we report an unusual case of amebic colitis in a 20-year-old female immigrant from South China. The patient had experienced diarrhea, crampy abdominal pain, and fever for approximately 3 weeks prior to admission to hospital and had treated herself at home with metronidazole. On admission, stool microscopy and serology for E. histolytica were negative. Because the clinical findings raised the suspicion of Clostridium difficile fulminant colitis, she underwent a subtotal colectomy. Histopathology revealed flask-shaped ulcers characteristic of amebic colitis. Consequently, E. histolytica DNA was detected by a sensitive small-subunit rRNA polymerase chain reaction (PCR) from feces, and the patient was successfully treated for amebiasis with metronidazole. This case exemplifies the relative insensitivity of serologic tests for the diagnosis of intestinal amebiasis and the difficulties encountered in detecting the parasite antigen in a patient partially treated with metronidazole. We conclude that when the possibility of invasive intestinal amebiasis is suspected, detecting the parasite DNA directly in the stool sample by PCR using E. histolytica-specific primers may be an alternative, noninvasive, and reliable tool for the specific diagnosis of the disease.

[Amebiasis: importance of the diagnosis and treatment. Minireview]

The protozoa E. histolytica is the etiologic agent of human amebiasis, the identification of its pathogenicity has been of great aid in the search of important antigens for immunodiagnostic and inmunoprofilaxis. In 1995 the isolation and axenization of the first two strains of Venezuelan E. histolytica were described from symptomatic patients, which were denominated: IULA 1092:1 and IULA: 0593:2 These strains have been evaluated through studies of electrophoretic profiles, demonstrating the presence of type II zymodemes, characteristic of pathogenic strains. Also, they have shown to be of high virulence, they present a complex pattern of reactivity and the presence of a marker antigen of pathogenicity. The isoenzymatic analysis has shown correlation with the genotypic analysis, showing a genotypic organization typical of a pathogenic strain. With this strain, it has been possible to evaluate all the amebiasis cases sent to the Institute of Clinical Immunology of Universidad de Los Andes, in Merida, Venezuela. These strains have been useful, here, as well as in other sites, when using their antigens to evaluate urban and even indigenous populations. They can be used, like native strains of reference, in diagnostic tests and prophylaxis for this parasitosis. The limitations of the microscopic analysis, specifically, the false amebiasis diagnosis and its inability to discriminate between infections caused by E. histolytica and E. dispar have led to the development of laboratory procedures that allow for the detection of components of the species present. The success of such procedures would result in a diminution of unnecessary treatments, which could be the cause of antiamoebic drug resistance.

Nitroimidazole action in Entamoeba histolytica: a central role for thioredoxin reductase

Metronidazole, a 5-nitroimidazole drug, has been the gold standard for several decades in the treatment of infections with microaerophilic protist parasites, including Entamoeba histolytica. For activation, the drug must be chemically reduced, but little is known about the targets of the active metabolites. Applying two-dimensional gel electrophoresis and mass spectrometry, we searched for protein targets in E. histolytica. Of all proteins visualized, only five were found to form adducts with metronidazole metabolites: thioredoxin, thioredoxin reductase, superoxide dismutase, purine nucleoside phosphorylase, and a previously unknown protein. Recombinant thioredoxin reductase carrying the modification displayed reduced enzymatic activity. In treated cells, essential non-protein thiols such as free cysteine were also affected by covalent adduct formation, their levels being drastically reduced. Accordingly, addition of cysteine allowed E. histolytica to survive in the presence of otherwise lethal metronidazole concentrations and reduced protein adduct formation. Finally, we discovered that thioredoxin reductase reduces metronidazole and other nitro compounds, suggesting a new model of metronidazole activation in E. histolytica with a central role for thioredoxin reductase. By reducing metronidazole, the enzyme renders itself and associated thiol-containing proteins vulnerable to adduct formation. Because thioredoxin reductase is a ubiquitous enzyme, similar processes could occur in other eukaryotic or prokaryotic organisms.

The protist parasites Entamoeba histolytica, Trichomonas vaginalis, and Giardia intestinalis grow in environments with low oxygen concentration. Infections with these parasites are commonly treated with metronidazole, a nitroimidazole drug that must be reduced for activation, resulting in several toxic metabolites. We examined the soluble proteome of metronidazole-treated E. histolytica cells for target proteins of these metabolites, applying two-dimensional gel electrophoresis and mass spectrometry. Of about 1,500 proteins visualized, only five formed covalent adducts with metronidazole metabolites, including thioredoxin, thioredoxin reductase, and superoxide dismutase. Metronidazole-bound thioredoxin reductase displayed diminished activity. In addition to these proteins, small thiol molecules, including cysteine, formed adducts with metronidazole. Supplementation with cysteine allowed the cells to survive otherwise lethal metronidazole concentrations. Finally, we discovered that one of the modified proteins, thioredoxin reductase, reduces metronidazole, suggesting a central role for this enzyme with regard to metronidazole toxicity. Taken together, our work reveals a new area of molecular interactions of activated metronidazole with cellular components. Because thioredoxin reductase is a ubiquitous enzyme, similar processes could also occur in other eukaryotic or prokaryotic organisms.

Metronidazole is used for treatment of infections with microaerophilic protist parasites. Here, a new model of metronidazole activation is proposed, with a central role for thioredoxin reductase.

Drug targets from human pathogenic amoebas: Entamoeba histolytica, Acanthamoeba polyphaga and Naegleria fowleri

In this review we present our search for the presence of drug targets in several species of human pathogenic parasites, mainly the amoebas Entamoeba histolytica, Acanthamoeba polyphaga and Naegleria fowleri. We started with an analysis of the concepts of essentiality and validity of the targets and continue with a description of the main characteristics of pathogenicity of these amoebas. We then proceed to evaluate these targets arranged mainly in seven groups corresponding to: a) enzymes which are secreted by these parasites to invade the human host, for example proteinases, phospholipases and pore forming peptides, b) glycolytic enzymes from Entamoeba and Naegleria, like the PPi-dependent phospho-fructokinase that differ from the host enzyme, c) thiols and enzymes of redox metabolism, present only in trypanosomatids, Entamoeba and Naegleria, such as the trypanothione/trypanothione reductase that maintains the reducing environment within the cell, d) antioxidant enzymes to regulate the oxidative stress produced by the phagocytic cells of the host or by the parasite metabolism, like the trypanothione peroxidase in connection with the NADPH-dependent trypanothione/trypanothione reductase which maybe is present in Naegleria fowleri, and peroxiredoxin in E. histolytica, e) enzymes for the synthesis of trypanothione like the ornithine decarboxylase, spermidine synthase and trypanothione synthetase, f) some of the proteins that assemble the secretory vesicles with the cell membrane, like the synaptobrevins and finally, g) encystment pathways and cyst-wall assembly proteins. Some of the above new targets will need to be studied in a more detail, including crystallographic studies of the enzymes for rational drug design. As far as we know there are no advanced crystallographic studies being conducted on targets from these three amoebas, as has been the case for various targets from the trypanosomatids.

Kinetic modeling can describe in vivo glycolysis in Entamoeba histolytica

Glycolysis in the human parasite Entamoeba histolytica is characterized by the absence of cooperative modulation and the prevalence of pyrophosphate-dependent (over ATP-dependent) enzymes. To determine the flux-control distribution of glycolysis and understand its underlying control mechanisms, a kinetic model of the pathway was constructed by using the software gepasi. The model was based on the kinetic parameters determined in the purified recombinant enzymes, and the enzyme activities, and steady-state fluxes and metabolite concentrations determined in amoebal trophozoites. The model predicted, with a high degree of accuracy, the flux and metabolite concentrations found in trophozoites, but only when the pyrophosphate concentration was held constant; at variable pyrophosphate, the model was not able to completely account for the ATP production/consumption balance, indicating the importance of the pyrophosphate homeostasis for amoebal glycolysis. Control analysis by the model revealed that hexokinase exerted the highest flux control (73%), as a result of its low cellular activity and strong AMP inhibition. 3-Phosphoglycerate mutase also exhibited significant flux control (65%) whereas the other pathway enzymes showed little or no control. The control of the ATP concentration was also mainly exerted by ATP consuming processes and 3-phosphoglycerate mutase and hexokinase (in the producing block). The model also indicated that, in order to diminish the amoebal glycolytic flux by 50%, it was required to decrease hexokinase or 3-phosphoglycerate mutase by 24% and 55%, respectively, or by 18% for both enzymes. By contrast, to attain the same reduction in flux by inhibiting the pyrophosphate-dependent enzymes pyrophosphate-phosphofructokinase and pyruvate phosphate dikinase, they should be decreased > 70%. On the basis of metabolic control analysis, steps whose inhibition would have stronger negative effects on the energy metabolism of this parasite were identified, thus becoming alternative targets for drug design.

Effects of antacid therapy in asymptomatic patients with presence of amoeba in stool report

Amoebic infection caused by the protozoan parasite Entamoeba histolytica is a prevalent infection in the developing countries. Milder form of this infection is associated with loose stool, flatulence and borborygmi, may or may not be associated with pain in abdomen and treated symptomatically by some physicians by antacid. To find out the effects of antacid (sorbacid) therapy in patients with amoeba in stools by examining the changes in the stool report, a study was conducted among 25 patients enrolled in the study with complaints of "gas" in the abdomen with stool reports positive for amoeba. Antacid (sorbacid) in a dose of one teaspoonful (5 ml) was given three times a day for 3 days and stool examination was repeated. The report showed a significant reduction in the amoeba and mucus in stool (p<0.05) and a trend towards reduction in the presence of occult blood. Other parameters in stool reports did not change. Moreover, all the patients gave the history of passing formed stools and no complaints of "gas" in abdomen thus providing the symptomatic benefit. Antacids may have some beneficial effects in amoebiasis. More studies are required to confirm the above finding and to find out the place of antacid as an adjuvant therapy along with the standard anti-amoebic drugs.

Effect of vitamin A and zinc supplementation on gastrointestinal parasitic infections among Mexican children

OBJECTIVE

Gastrointestinal parasites continue to be an important cause of morbidity and stunting among children in developing countries. We evaluated the effect of vitamin A and zinc supplementation on infections by Giardia lamblia, Ascaris lumbricoides, and Entamoeba histolytica.

METHODS

A randomized, double-blind, placebo-controlled trial was conducted among 707 children who were 6 to 15 months of age and from periurban areas of Mexico City, Mexico, between January 2000 and May 2002. Children, who were assigned to receive either vitamin A every 2 months, a daily zinc supplement, a combined vitamin A and zinc supplement, or a placebo, were followed for 1 year. The primary end points were the 12-month rates and durations of infection for the 3 parasites and rates of parasite-associated diarrheal disease as determined in stools collected once a month and after diarrheal episodes.

RESULTS

G. lamblia infections were reduced and A. lumbricoides infections increased among children in the combined vitamin A and zinc group or the zinc alone group, respectively. Durations of Giardia infections were reduced among children in all 3 treatment arms, whereas Ascaris infections were reduced in the vitamin A and zinc group. In contrast, E. histolytica infection durations were longer among zinc-supplemented children. Finally, E. histolytica- and A. lumbricoides-associated diarrheal episodes were reduced among children who received zinc alone or a combined vitamin A and zinc supplement, respectively.

CONCLUSIONS

We found that vitamin A and zinc supplementation was associated with distinct parasite-specific health outcomes. Vitamin A plus zinc reduces G. lamblia incidence, whereas zinc supplementation increases A. lumbricoides incidence but decreases E. histolytica-associated diarrhea.

Detection of excretory Entamoeba histolytica DNA in the urine, and detection of E. histolytica DNA and lectin antigen in the liver abscess pus for the diagnosis of amoebic liver abscess

BACKGROUND

Amoebic liver abscess (ALA) and pyogenic liver abscesses (PLA) appear identical by ultrasound and other imaging techniques. Collection of blood or liver abscess pus for diagnosis of liver abscesses is an invasive procedure, and the procedure requires technical expertise and disposable syringes. Collection of urine is a noninvasive procedure. Therefore, there has been much interest shown towards the use of urine as an alternative clinical specimen for the diagnosis of some parasitic infections. Here, we report for the first time the detection of E. histolytica DNA excreted in the urine for diagnosis of the cases of ALA.

RESULTS

E. histolytica DNA was detected in liver abscess pus specimen of 80.4% of ALA patients by a nested multiplex polymerase chain reaction (PCR) targeting 16S-like r RNA gene. The nested PCR detected E. histolytica DNA in all 37 (100%) liver abscess pus specimens collected prior to metronidazole treatment, but were detected in only 53 of 75 (70.6%) pus specimens collected after therapy with metronidazole. Similarly, the PCR detected E. histolytica DNA in 21 of 53 (39.6%) urine specimens of ALA patients. The test detected E. histolytica DNA in only 4 of 23 (17.4%) urine specimens collected prior to metronidazole treatment, but were detected in 17 of 30 (56.7%) urine specimens collected after treatment with metronidazole. The enzyme-linked immunosorbent assay (ELISA) for the detection of lectin E. histolytica antigen in the liver abscess pus showed a sensitivity of 50% and the indirect haemagglutination (IHA) test for detection of amoebic antibodies in the serum showed a sensitivity of 76.8% for the diagnosis of the ALA.

CONCLUSION

The present study for the first time shows that the kidney barrier in ALA patients is permeable to E. histolytica DNA molecule resulting in excretion of E. histolytica DNA in urine which can be detected by PCR. The study also shows that the PCR for detection of E. histolytica DNA in urine of patients with ALA can also be used as a prognostic marker to assess the course of the diseases following therapy by metronidazole. The detection of E. histolytica DNA in urine specimen of ALA patients provides a new approach for the diagnosis of ALA.

Amoebiasis cutis in HIV positive patient

Protozoan infections of the skin, particularly cutaneous amoebiasis, are rare in HIV-positive patients. We report a case of amoebiasis cutis in an HIV-positive truck driver with a history of frequent unprotected sexual exposures. He presented with multiple painful ulcers and sinuses with purulent discharge, necrotic slough and scarring in the perianal and gluteal region for the last 2 years. He was positive for HIV-1 and -2. Cutaneous biopsy revealed numerous Entamoeba histolytica in the trophozoite form, in addition to an inflammatory infiltrate and necrotic debris. He responded well to oral metronidazole and chloroquine. Amoebiasis cutis should be considered in the differential diagnosis of perianal ulcers, particularly in HIV-positive patients.

Amoebic hepatic abscesses in an HIV-positive patient

Herein we report the case of hepatic amoebic abscesses in an HIV-positive Italian seaman with a history of promiscuous heterosexual intercourse. In October 2004, the patient was hospitalized because of fever and recurring abdominal pain. Abdominal ultrasonography revealed six hepatic hypoechoid oval lesions with hyperechoid margins. Stool samples were negative for parasites and bacteria, and serology for Entamoeba histolytica was also negative. Therapy with meropenem plus levofloxacin was initiated. After a partial resolution of clinical symptoms and reduction of three hepatic lesions, the patient was again hospitalized in December 2004, because of recurring intense pain at the right hypochondrium and fever. At this time, one hepatic lesion at the sixth segment was enlarged, two lesions were unchanged, and the remaining three smaller abscesses were resolved. Serum antibodies for E. histolytica and amoebic antigens on the largest abscess drainage were positive; moreover, E. histolytica was also identified on drainage fluid with polymerase chain reaction (PCR). Therapy with metronidazole followed by paromomycin improved both symptoms and radiographic images. This case report suggests that in HIV-infected patients, invasive amoebiasis should be considered and atypical aspects, such as multiple hepatic lesions, delayed positivity of serology for E. histolytica, and possible bacterial superinfection should be evaluated.

Entamoeba histolytica encephalitis diagnosed by PCR of cerebrospinal fluid

Extra-intestinal amebiasis is secondary to invasive intestinal infections and usually results in an amebic liver abscess. Other organs, including lungs, brain, skin, spleen and kidneys, may be involved. Diagnosis of the cerebral infection is of the utmost importance and is most often made by detection of the organism at the time of brain biopsy or at autopsy. We report the first case of Entamoeba histolytica encephalitis diagnosed by PCR of the cerebrospinal fluid. The patient was treated successfully with metronidazole. PCR is an increasingly useful tool for the diagnosis of central nervous system infection and can provide rapid diagnosis.

Multidrug resistance in amoebiasis patients

BACKGROUND & OBJECTIVES

Amoebiasis, caused by Entamoeba sp. a protozoan parasite, is a major public health problem in tropical and subtropical countries. The symptomatic patients are treated by specific chemotherapy. However, there are reports of treatment failure in some cases suggesting the possibility of drug resistance. The present study was therefore planned to assess the presence and expression of mRNA of multidrug resistance (MDR) gene in clinical isolates of Entamoeba histolytica and E. dispar.

METHODS

Forty five clinical isolates of Entamoeba sp. [E. histolytica (15) and E. dispar (30)] were maintained in polyxenic followed by monoxenic medium. DNA and total RNA were extracted from clinical isolates of Entamoeba sp. and from sensitive strain of E. histolytica (HM1: IMSS) and subjected to polymerase chain reaction (PCR) and multiplex reverse transcription (RT)-PCR techniques.

RESULTS

The 344 bp segment of E. histolytica DNA was seen by PCR using primers specific to EhPgp1 in all clinical isolates and sensitive strain of E. histolytica. Over expression of EhPgp1 was observed only in resistant mutant of E. histolytica; however, transcription of EhPgp1 was not seen in any clinical isolates and sensitive strain of E. histolytica.

INTERPRETATION & CONCLUSION

The findings of the present study indicate that, so far, drug resistance in clinical isolates of E. histolytica does not seem to be a major problem in this country. However, susceptibility of clinical isolates of E. histolytica against various antiamoebic drugs needs to be investigated for better management.

Drug resistance in amoebiasis

Amoebiasis caused by Entamoeba histolytica, is a major public health problem in developing countries. Morphologically similar E. dispar is non pathogenic. Because of the redefinition of E. histolytica and E. dispar, and the limited number of antiamoebic drugs available, a new approach to treat such individuals is necessary. The cost of treating asymptomatic individuals is highly exorbitant and not justifiable. The indiscriminate use of antiamoebic drugs can result in increased minimum inhibitory concentration (MIC) values against Entamoeba species, and treatment failure may emerge as an important public health problem. Development of new antiamoebic drugs is still in infancy and vaccine development appears to be distant dream. In future, the development of drug resistance may seriously affect the control of disease. This review discusses the factors involved in drug resistance mechanisms developed by the parasite.

The anti-amoebic activity of some medicinal plants used by AIDS patients in southern Thailand

The anti-amoebic activities of chloroform, methanol and water extracts from 12 Thai medicinal plants (39 extracts) commonly used by AIDS patients in southern Thailand were screened, at a concentration of 1,000 microg/ml, against Entamoeba histolytica strain HTH-56:MUTM and strain HM1:IMSS growing in vitro. The extracts were incubated with 2x10(5) E. histolytica trophozoites/ml of medium at 37 degrees C under anaerobic conditions for 24 h. The cultures were examined with an inverted microscope and scored (1-4) according to the appearance and numbers of the trophozoites. The extracts that caused inhibition were selected and retested using the same conditions but with concentrations that ranged from 31.25 to 1,000 microg/ml using E. histolytica strain HM1:IMSS, and the IC(50) values for each extract were calculated. The chloroform extracts from Alpinia galanga (IC(50) 55.2 microg/ml), Barleria lupulina (IC(50) 78.5 microg/ml), Boesenbergia pandurata (IC(50) 45.8 microg/ml), Piper betle (IC(50) 91.1 microg/ml) and Piper chaba (IC(50) 71.4 microg/ml) and the methanol extract from B. pandurata (IC(50) 57.6 microg/ml) were all classified as "active", i.e. with an IC(50) of less than 100 microg/ml, whereas those from Murraya paniculata (IC(50) 116.5 microg/ml) and Zingiber zerumbet (IC(50) 196.9 microg/ml) were classified as being "moderately active". The IC(50) of a standard drug, metronidazole, was 1.1 microg/ml.

Cytokine and chemokine responses in patients co-infected with Entamoeba histolytica/dispar, Necator americanus and Mansonella perstans and changes after anti-parasite treatment

This study examined the impact of concurrent parasite infections (amoebiasis, filariasis, necatoriasis) and the effect of anti-parasite treatment on cytokine and chemokine responses in singly and poly-parasitized patients. Cellular reactivity and parasite-specific Th1- and Th2-type cytokine and chemokine profiles were investigated before and six weeks after treatment. In those patients infected with three parasite species, cellular secretion of interleukin 5 (IL-5) and IL-12p40 by PBMC was strongly diminished (p<0.005) but IL-10 was elevated in parasite-infected patients (p<0.0001) in response to protozoa- and helminth-specific as well as bacteria-specific antigens. Macrophage inflammatory chemokines (MIP-1alpha/CCL3 and MIP-1beta/CCL4), macrophage-derived chemokine (MDC/CCL22) and neutrophil activating chemokine (IL-8/CXCL8) were produced by PBMC in similar amounts in endemic controls and singly and poly-parasitized patients, but thymus and activation-regulated chemokine (TARC/CCL17) was produced the highest by PBMC from patients with triple parasite infections (p<0.0001). Following anti-parasite therapy, secretion of IL-12p40 and IL-5 augmented significantly in treated patients while IL-10, MDC, MIP-1alpha, TARC and IL-8 substantially diminished (all p<10(-5)) when their PBMC were activated with parasite- and bacteria-specific antigens. In summary, PBMC from poly-parasitized patients responded to protozoa- and helminth-specific antigens with a compromised IL-5 and IL-12p40 but high IL-10 and a substantial chemokine release. Chemokines may attract and activate effector cells in peri-parasitic tissues to limit parasite proliferation and dissemination, while depressed IL-5 and IL-12p40 but prominent IL-10 may prevent eosinophil and cytotoxic cell-mediated inflammatory processes and pathogenesis to the host. The changes in this profile following anti-parasite therapy disclosed the dynamics of an immune adaptation associated with parasite accumulation and also with clearance of parasite infections.

[Amoebic infections of the lung and pleura]

INTRODUCTION

Pleuropulmonary involvement is the second most common extra-intestinal manifestation of entamoeba histolytica infection after liver abscess.

CASE REPORT

We report 2 cases of pleuropulmonary disease occurring in two men aged 32 and 48 years following an episode of dysentery. Purulent pleural infection was noted in one case. In the other both lung and liver abscesses occurred.

CONCLUSION

The diagnosis was confirmed by strongly positive serology in both cases. Treatment with metronidazole (1.5 g per day) for 15 days combined with pleural drainage led to a satisfactory outcome in both cases.

Amoebic renal cyst: a case report

Entamoeba histolytica can infect any organ of the body, but only one case of renal involvement has been reported till now in the literature. We report a rare case of amoebic renal cyst in a 78-year showing favorable outcome with metronidazole treatment and therapeutic drainage.

Amebae and ciliated protozoa as causal agents of waterborne zoonotic disease

The roles free-living amebae and the parasitic protozoa Entamoeba histolytica and Balantidium coli play as agents of waterborne zoonotic diseases are examined. The free-living soil and water amebae Naegleria fowleri, Acanthamoeba spp., and Balamuthia mandrillaris are recognized etiologic agents of mostly fatal amebic encephalitides in humans and other animals, with immunocompromised and immunocompetent hosts among the victims. Acanthamoeba spp. are also agents of amebic keratitis. Infection is through the respiratory tract, breaks in the skin, or by uptake of water into the nostrils, with spread to the central nervous system. E. histolytica and B. coli are parasitic protozoa that cause amebic dysentery and balantidiasis, respectively. Both intestinal infections are spread via a fecal-oral route, with cysts as the infective stage. Although the amebic encephalitides can be acquired by contact with water, they are not, strictly speaking, waterborne diseases and are not transmitted to humans from animals. Non-human primates and swine are reservoirs for E. histolytica and B. coli, and the diseases they cause are acquired from cysts, usually in sewage-contaminated water. Amebic dysentery and balantidiasis are examples of zoonotic waterborne infections, though human-to-human transmission can occur. The epidemiology of the diseases is examined, as are diagnostic procedures, anti-microbial interventions, and the influence of globalization, climate change, and technological advances on their spread.

[A Dutchman from Mali with a perianal ulcer caused by cutaneous amoebiasis]

A 66-year-old Dutchman, living in Mali, presented with an extensive progressive perianal ulcer despite local and antibiotic treatment. Microscopic examination of the stool revealed Entamoeba histolytica/dispar cysts and phagocytosing trophozoites were seen in fresh scrapings of the ulcer, a diagnostic feature of infection with E. histolytica. The diagnosis was cutaneous amoebiasis and the patient was effectively treated with metronidazole and local debridements. Primary cutaneous amoebiasis is a rare disease. Diagnosis and treatment are relatively simple but lack of familiarity with the disease may lead to misdiagnosis or diagnosis at a late stage ofthe infection.

Diabetes and Amoebiasis: a high risk encounter

Amoebiasis is the second most common parasitic disease worldwIde. It occurs mainly in developing countries. A high percentage of people in countries where it is endemic are asymptomatic carriers. It results in severe disease that can be fatal in rare cases. Diabetics are at increased risk of exposure as travel to countries where it is endemic becomes more frequent, as indicated by the present case. This patient suffered from amoebiasis that produced an amoeboma which is most rare in cases of colonic amoebiasis. The clinical picture was that of an occluding gut tumor, but it was treated only with drugs. Retrospective studies show that diabetics are at increased risk of suffering severe complications after amoebic infection. The frequency and severity of this diabetes-amoeba association requires patients to take prophylactic measures, especially when travelling in developing countries.

Entamoeba histolytica: an update

PURPOSE OF REVIEW

Over the past decade, since it was formally recognized that Entamoeba histolytica and Entamoeba dispar were two distinct species, studies in this field have made dramatic in-roads into the understanding of E. histolytica and the pathogenesis of invasive amoebiasis. Over the same period it has also become clear that the true incidence of E. histolytica infection, particularly in vulnerable populations such as low socioeconomic children, is exceedingly high. Understanding the epidemiology, pathophysiology, and the molecular and genetic biology of the organism will not only lead to improved diagnostic and treatment options but, ultimately, to the development of a safe and efficacious vaccine.

RECENT FINDINGS

The recent advances in the genetic and molecular sciences have increased our understanding of the mechanisms that make E. histolytica unique among enteric protozoa in causing invasive disease. In addition, host factors, which predispose individuals or populations to infection or disease, are beginning to be elucidated. New diagnostic tools specific to E. histolytica are being exploited by clinicians and researchers to identify and treat patients as well as to add to the knowledge of the epidemiology and natural history of this infection. The ultimate goal - eradication of disease - is theoretically feasible since humans and primates are the only reservoirs of E. histolytica. Many talented and dedicated individuals are pursuing the development of an effective and safe amoebiasis vaccine.

SUMMARY

E. histolytica remains an important pathogen in many populations of the world and although there has been substantial progress into understanding the disease major challenges still exist.

Effects of Bisphosphonates on the Growth of Entamoeba histolytica and Plasmodium Species in Vitro and in Vivo

The effects of a series of 102 bisphosphonates on the inhibition of growth of Entamoeba histolytica and Plasmodium falciparum in vitro have been determined, and selected compounds were further investigated for their in vivo activity. Forty-seven compounds tested were active (IC(50) < 200 microM) versus E. histolytica growth in vitro. The most active compounds (IC(50) approximately 4-9 microM) were nitrogen-containing bisphosphonates with relatively large aromatic side chains. Simple n-alkyl-1-hydroxy-1,1-bisphosphonates, known inhibitors of the enzyme farnesylpyrophosphate (FPP) synthase, were also active, with optimal activity being found with C9-C10 side chains. However, numerous other nitrogen-containing bisphosphonates known to be potent FPP synthase inhibitors, such as risedronate or pamidronate, had little or no activity. Several pyridine-derived bisphosphonates were quite active (IC(50) approximately 10-20 microM), and this activity was shown to correlate with the basicity of the aromatic group, with activity decreasing with increasing pK(a) values. The activities of all compounds were tested versus a human nasopharyngeal carcinoma (KB) cell line to enable an estimate of the therapeutic index (TI). Five bisphosphonates were selected and then screened for their ability to delay the development of amebic liver abscess formation in an E. histolytica infected hamster model. Two compounds were found to decrease liver abscess formation at 10 mg/kg ip with little or no effect on normal liver mass. With P. falciparum, 35 compounds had IC(50) values <200 microM in an in vitro assay. The most active compounds were also simple n-alkyl-1-hydroxy-1,1-bisphosphonates, having IC(50) values around 1 microM. Five compounds were again selected for in vivo investigation in a Plasmodium berghei ANKA BALB/c mouse suppressive test. The most active compound, a C9 n-alkyl side chain containing bisphosphonate, caused an 80% reduction in parasitemia with no overt toxicity. Taken together, these results show that bisphosphonates appear to be useful lead compounds for the development of novel antiamebic and antimalarial drugs.

Antiprotozoal activity of the constituents of Teloxys graveolens

Antiprotozoal activity-guided fractionation of a methanol extract of the aerial parts of Teloxys graveolens led to the isolation of one coumarinic acid derivative, melilotoside, and five flavonoids, pinocembrine, pinostrobin, chrysin, narcissin and rutin. Among them, melilotoside exhibited the most potent activity toward Entamoeba histolytica and Giardia lamblia (IC(50) 12.5 and 16.8 micro g/mL, respectively). Narcissin showed selectivity against E. histolytlica (IC(50) 17.2 micro g/mL). The results support data for the traditional use of T. graveolens in some gastrointestinal diseases.

[The phagocytic activity of blood platelets in different parasitic diseases]

Blood platelets take part in immune reactions of the organism, especially in anti-parasitic immunity. We conducted the phagocytic activity of blood platelets. This experiments were done on 40 patients infected with Giardia intestinalis (26), Ascaris lumbricoides (8), Entamoeba histolytica/Entamoeba dispar (6). Blood for analysis was collected thrice, before treatment (P1), after two weeks (P2), and after two months treatment with anti-parasitic drugs (P3). Control group consisted of 32 healthy people. The evaluation of platelet phagocytic activity revealed that the mean percentage of phagocytizing platelets in patients was 2.87 (P1), 2.94 (P2), 2.86 (P3), being significantly lower in controls (mean 2.15), the difference was statistically significant (p < 0.05). No statistically significant difference was found in the mean phagocytic index between patients (P1, P2, P3) and controls. Our general conclusion is--parasites are able to stimulate phagocytic activity of blood platelets.

Amebiasis in the newborn

Infestation with Entamoeba histolytica is especially common in areas with low socioeconomic status. Extra intestinal invasive involvement is more frequent in young children with significant mortality. This disease is rarely reported in the newborns. This 19-day-old newborn who was infected with orally given surgar solution is presented. He was successfully treated with omidazole.

[Vulvar amebiasis. Report of a case and review of the literature]

Genital amebiasis by Entamoeba histolytica is rare, even in Mexico where the disease is endemic. We report a case of genital amebiasis in a female patient with a recto-perineal fistula and two-week history of a profuse vaginal discharge, a painful and friable vulvar ulcer and induration in gluteal and inner side of thighs. The PAP smear and the biopsy showed trophozoites, no malignant cells were observed. The findings were compatible with genital amebiasis. The serology test for E. histolytica was positive (> 1: 512). The patient was treated with metronidazol 750 mg tid for 3 weeks. Complete resolution was achieved. The long term fistula, the low socioeconomic status, the poor hygiene and diabetes mellitus of a recent onset were probably the risk factors associated to this infection. We reviewed the literature.

Nitric oxide inhibits cysteine proteinases and alcohol dehydrogenase 2 of Entamoeba histolytica

Nitric oxide is involved in the neutrophil and macrophage killing of the protozoan parasite Entamoeba histolytica. In the present study, we found that cysteine proteinases, significant contributors to amebic virulence and alcohol dehydrogenase 2, an enzyme absolutely required for the survival of the parasite, are both significantly inhibited by S-nitroso-glutathione, a physiological nitric oxide donor, within the concentration range 0.5-2.0 m M.