Entamoeba histolytica: virulence potential and sensitivity to metronidazole and emetine of four isolates possessing nonpathogenic zymodemes

Mechanisms of antiviral action and toxicities of ipecac alkaloids: Emetine and dehydroemetine exhibit anti-coronaviral activities at non-cardiotoxic concentrations

The emergence of highly infectious pathogens with their potential for triggering global pandemics necessitate the development of effective treatment strategies, including broad-spectrum antiviral therapies to safeguard human health. This study investigates the antiviral activity of emetine, dehydroemetine (DHE), and congeneric compounds against SARS-CoV-2 and HCoV-OC43, and evaluates their impact on the host cell. Concurrently, we assess the potential cardiotoxicity of these ipecac alkaloids. Significantly, our data reveal that emetine and the (-)-R,S isomer of 2,3-dehydroemetine (designated in this paper as DHE4) reduce viral growth at nanomolar concentrations (i.e., IC50 ∼ 50-100 nM), paralleling those required for inhibition of protein synthesis, while calcium channel blocking activity occurs at elevated concentrations (i.e., IC50 ∼ 40-60 µM). Our findings suggest that the antiviral mechanisms primarily involve disruption of host cell protein synthesis and is demonstrably stereoisomer specific. The prospect of a therapeutic window in which emetine or DHE4 inhibit viral propagation without cardiotoxicity renders these alkaloids viable candidates in strategies worthy of clinical investigation.

Creep in nitroimidazole inhibitory concentration among the Entamoeba histolytica isolates causing amoebic liver abscess and screening of andrographolide as a repurposing drug

Infections by Entamoeba histolytica (E. histolytica) lead to considerable morbidity and mortality worldwide and treatment is reliant on a single class of drugs, nitroimidazoles. Treatment failures and intermittent reports of relapse from different parts of world indicate towards development of clinical drug resistance. In the present study, susceptibility testing of clinical isolates of E. histolytica was carried against metronidazole and tinidazole. Additionally, anti-amoebic property of active compounds of Andrographis paniculata was also evaluated. Prevalence of metronidazole resistance gene (nim) in patients attending hospital was also done to get comprehensive insight of present situation of drug resistance in E. histolytica. Mean inhibitory concentration 50 (IC50) value of E. histolytica isolates against metronidazole and tinidazole was 20.01 and 16.1 µM respectively. Andrographolide showed minimum mean IC50 value (3.06 µM). Significant percentage inhibition of E. histolytica isolates by andrographolide was seen as compared to metronidazole (p = 0.0495). None of E. histolytica isolates showed presence of nim gene. However, in stool samples from hospital attending population, prevalence of nimE gene was found to be 76.6% (69/90) and 62.2% (56/90) in diarrheal and non-diarrheal samples respectively. Inhibitory concentration of commonly used nitroimidazoles against clinical isolates of E. histolytica are on rise. Percentage inhibition of E. histolytica isolates by andrographolide was significantly higher than control drug metronidazole.

Diversity and Plasticity of Virulent Characteristics of Entamoeba histolytica

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

Prevalence and impact of antimicrobial resistance in gastrointestinal infections: A review

Antimicrobial resistance has become a worldwide problem due to its excessive increase in recent years. The aim of the present review was to bring together data from different articles describing the levels of antimicrobial resistance in the most common gastrointestinal infections reported across the globe. The literature search was carried out in Google Scholar, Medline, Embase, and Pubmed, with the terms "antimicrobial resistance", "resistance in gastrointestinal disorders", and "resistance in amoebiasis", in Spanish and English. Mexican treatment guidelines and consensuses from 2017 to the present were utilized. Publications from the last ten years were chosen to describe the level of resistance. They had adequate sample sizes, the Material and Methods sections were precise, and they included multicenter studies, national and international consensuses, meta-analyses, systematic reviews, and extensive texts. The final number of articles was 51. The microorganisms that demonstrated the highest percentage of resistance were Helicobacter pylori (metronidazole 50%-80%, clarithromycin 20%-40%, and levofloxacin 30%-35%), Clostridioides difficile (clindamycin 8.3%-100%, cephalosporines 51%), Campylobacter jejuni and Campylobacter coli (fluoroquinolones 85%), Escherichia coli (ampicillin 76.5%), Entamoeba histolytica (metronidazole 50%), and bacterial peritonitis (third-generation cephalosporines 40%, methicillin 85%). Antimicrobial resistance is reaching elevated percentages, making it necessary to evaluate the situation of each patient, to successfully treat gastrointestinal infections.

Emetine Is Not Ipecac: Considerations for Its Use as Treatment for SARS-CoV2

Emetine is a potent antiviral that acts on many viruses in the low-nM range, with several studies in animals and humans demonstrating antiviral activity. Historically, emetine was used to treat patients with Spanish influenza, in the last stages of the pandemic in the early 1900s. Some of these patients were "black" with cyanosis. Emetine rapidly reversed the cyanosis and other symptoms of this disease in 12-24 h. However, emetine also has been shown to have anti-inflammatory properties and it appears it is these anti-inflammatory properties that were responsible for the effects seen in patients with Spanish influenza. Emetine, in the past, has also been used in 10s to 100s of millions of people at a dose of ~60 mg daily to treat amoebiasis. Based on viral inhibition data we can calculate a likely SARS-CoV2 antiviral dose of ~1/10th the amoebiasis dose, which should dramatically reduce the risk of any side effects. While there are no anti-inflammatory dose response data available, based on the potential mode of action, the anti-inflammatory actions may also occur at low doses. This paper also examines the toxicity of emetine seen in clinical practice and that seen in the laboratory, and discusses the methods of administration aimed at reducing side effects if higher doses were found to be necessary. While emetine is a "pure drug" as it is extracted from ipecac, some of the differences between emetine and ipecac are also discussed.

In Vitro Testing of Potential Entamoeba histolytica Pyruvate Phosphate Dikinase Inhibitors

Adverse effects and resistance to metronidazole have motivated the search for new antiamoebic agents against Entamoeba histolytica. Control of amoeba growth may be achieved by inhibiting the function of the glycolytic enzyme and pyruvate phosphate dikinase (PPDK). In this study, we screened 10 compounds using an in vitro PPDK enzyme assay. These compounds were selected from a virtual screening of compounds in the National Cancer Institute database. The antiamoebic activity of the selected compounds was also evaluated by determining minimal inhibitory concentrations (MICs) and IC₅₀ values using the nitro-blue tetrazolium reduction assay. Seven of the 10 compounds showed inhibitory activities against the adenosine triphosphate (ATP)/inorganic phosphate binding site of the ATP-grasp domain. Two compounds, NSC349156 (pancratistatin) and NSC228137 (7-ethoxy-4-[4-methylphenyl] sulfonyl-3-oxido-2, 1, 3-benzoxadiazol-3-ium), exhibited inhibitory effects on the growth of E. histolytica trophozoites with MIC values of 25 and 50 μM, and IC₅₀ values of 14 and 20.7 μM, respectively.

Host-Parasite interactions in Entamoeba histolytica and Entamoeba dispar: what have we learned from their genomes?

Invasive amoebiasis caused by Entamoeba histolytica is a major global health problem. Virulence is a rare outcome of infection, occurring in fewer than 1 in 10 infections. Not all strains of the parasite are equally virulent, and understanding the mechanisms and causes of virulence is an important goal of Entamoeba research. The sequencing of the genome of E. histolytica and the related avirulent species Entamoeba dispar has allowed whole-genome-scale analyses of genetic divergence and differential gene expression to be undertaken. These studies have helped elucidate mechanisms of virulence and identified genes differentially expressed in virulent and avirulent parasites. Here, we review the current status of the E. histolytica and E. dispar genomes and the findings of a number of genome-scale studies comparing parasites of different virulence.

Pathogenicity of Entamoeba dispar under xenic and monoxenic cultivation compared to a virulent E. histolytica

Two xenic isolates and cloned cultures of Entamoeba dispar were submitted to monoxenization using Crithidia fasciculata as the associated organism. Growth in monoxenic cultivation and ability of xenic and monoxenic trophozoites to destroy VERO cells and produce lesions in hamster livers were compared to those of a virulent E. histolytica. Parental and cloned E. dispar under monoxenic cultivation showed a remarkable lower growth than the monoxenic E. histolytica and were avirulent in both in vivo and in vitro tests. When xenically cultured, trophozoites of E. dispar showed a moderate lytic activity against VERO cells (1.5 to 41.8% of destruction) but caused severe hepatic lesions in hamsters as those caused by the virulent E. histolytica (29 to 100% in prevalence and 0.86 to 4.00 in lesion degree). Although E. dispar has not been associated with invasive disease in men, the ability of xenic trophozoites to produce prominent tissue damage in experimental conditions has indicated that some strains have a considerable pathogenic potential when in presence of bacteria.

Comparative proteomic analysis of two Entamoeba histolytica strains with different virulence phenotypes identifies peroxiredoxin as an important component of amoebic virulence

Entamoeba histolytica is a protozoan intestinal parasite that causes amoebic colitis and amoebic liver abscess. To identify virulence factors of E. histolytica, we first defined the phenotypes of two E. histolytica strains, HM-1:IMSS, the prototype virulent strain, and E. histolytica Rahman, a strain that was reportedly less virulent than HM-1:IMSS. We found that compared with HM-1:IMSS, Rahman has a defect in erythrophagocytosis and the ability to cause amoebic colitis in human colonic xenografts. We used differential in-gel 2D electrophoresis to compare the proteome of Rahman and HM-1:IMSS, and identified six proteins that were differentially expressed above a fivefold level between the two organisms. These included two proteins with antioxidative properties (peroxiredoxin and superoxide dismutase), and three proteins of unknown function, grainin 1, grainin 2 and a protein containing a LIM-domain. Overexpression of peroxiredoxin in Rahman rendered the transgenic trophozoites more resistant to killing by H2O2 in vitro, and infection with Rahman trophozoites expressing higher levels of peroxiredoxin was associated with higher levels of intestinal inflammation in human colonic xenografts, and more severe disease based on histology. In contrast, higher levels of grainin appear to be associated with a reduced virulence phenotype, and E. histolytica HM-1:IMSS trophozoites infecting human intestinal xenografts show marked decreases in grainin expression. Our data indicate that there are definable molecular differences between Rahman and HM-1:IMSS that may explain the phenotypic differences, and identify peroxiredoxin as an important component of virulence in amoebic colitis.

In vitro activity of antiamoebic drugs against clinical isolates of Entamoeba histolytica and Entamoeba dispar

Background

Amoebiasis is a major public health problem in tropical and subtropical countries. Although a number of antiamoebic agents are used for its treatment, yet the susceptibility data on clinical isolates of Entamoeba histolytica and Entamoeba dispar are not available. Therefore, the present study was aimed to assess the in vitro susceptibility of clinical isolates of E. histolytica and E. dispar to metronidazole, chloroquine, emetine and tinidazole.

Methods

A total of 45 clinical isolates (15 E. histolytica and 30 E. dispar) were maintained in polyxenic cultures followed by monoxenic cultures. In vitro drug sensitivity (IC₅₀) of clinical isolates and standard reference strain of E. histolytica (HM1: IMSS) was assessed by nitro blue tetrazolium (NBT) reduction assay after exposure to various concentrations of each drug.

Results

The results showed that all clinical isolates had a higher IC₅₀ compared to reference strain to all the four drugs. E. histolytica isolates appeared to be more susceptible [IC₅₀ (μm) 13.2,26.3,31.2 and 12.4] compared to E. dispar isolates [IC₅₀(μm) 15.6,28.9,32.8 and 13.2] and the reference strain of E. histolytica [IC₅₀ (μm) 9.5, 15.5, 29.9 and 10.2] to the metronidazole, chloroquine, emetine and tinidazole respectively.

Conclusions

The results indicate that till date, Entamoeba isolates in India do not seem to be resistant to the commonly used antiamoebic drugs.

A virulence attenuated amoebapore-less mutant of Entamoeba histolytica and its interaction with host cells

Entamoeba histolytica, the protozoan parasite which causes amoebiasis, is an exclusively human pathogen so developing a vaccine could effectively impact the spread of the disease. Recently we developed a genetically modified avirulent strain, termed G3, from the virulent E. histolytica strain HM-1:IMSS. The new strain lacks the important virulence factor, the amoebapore-A. The objective of our current study was to investigate the avirulence of the attenuated strain as well as to examine the antigenic and immunogenic responses of these trophozoites as potential candidates for a live vaccine. Functional assays were conducted to characterise the virulent behaviour of the G3 strain. This behaviour was compared to the virulent strain HM-1:IMSS and the non-virulent strain Rahman. Western blots were conducted to confirm the lack of amoebapore-A in the E. histolytica G3 strain and to demonstrate that it had no influence on the presence of other virulence factors. Results of these two sets of tests proved the G3 strain to be phenotypically similar to the avirulent Rahman strain while antigenically identical to the virulent HM-1:IMSS, apart from the lack of the amoebapore-A protein. Intraperitoneal immunisation of hamsters with G3 trophozoites compared to sham immunised hamsters resulted in IgG anti-HM-1:IMSS antibodies. The level of humoral response was variable and further testing has to take place before introducing this new strain as a vaccine.

Cellular location and function of the P-glycoproteins (EhPgps) in Entamoeba histolytica multidrug-resistant trophozoites

We have studied the cellular location and the efflux pump function of the Entamoeba histolytica P-glycoproteins (EhPgps) in drug-sensitive and -resistant trophozoites. Polyclonal antibodies against the EhPgp384 polypeptide (375-759 amino acids) revealed a 147-kDa protein by Western blot. The band intensity correlated with the emetine-resistance of the trophozoites. Through the confocal microscope, using the anti-EhPgp384 and fluorescein secondary antibodies, the EhPgps were found in a complex vesicular network, in the plasma membrane and outside of the cells. Transmission electron microscopy assays confirmed that drug-resistant trophozoites presented four to five times more EhPgps than sensitive cells. Fluorescence co-localization experiments using rhodamine-123 (R123) and the anti-EhPgp384 antibodies suggested the interaction between EhPgps and the drug. R123 efflux kinetics evidenced that the emetine-resistant trophozoites displayed a drug efflux kinetic four times higher than the drug-sensitive trophozoites, which was reduced by verapamil in both cases. EhPgps may participate in avoiding drug accumulation in the trophozoites by two putative mechanisms: (1) the direct extrusion of the drug from the plasma membrane, and (2) an indirect transport mechanism in which the drug is trapped by EhPgps and concentrated within vesicles that drive the drug to the plasma membrane.

Multidrug resistance in the protozoan parasite Entamoeba histolytica

In this review we discuss the mechanisms and molecules involved in the multidrug resistance (MDR) of the protozoan parasite Entamoeba histolytica. Drug resistant mutants exhibited the main characteristics presented by the MDR mammalian cells. They showed cross-resistance to several unrelated drugs that is reverted by calcium channel blockers. MDR phenotype in E. histolytica is regulated at a transcriptional level by the EhPgp1 gene, which is constitutively expressed and by the EhPgp5 gene, whose expression is induced in the presence of the drug. Transcription factors participate in the expression regulation of these genes. After over transcription, the EhPgp genes are amplified, cooperating to produce the MDR phenotype. Post-transcriptional mechanisms such as mRNA stability seem to be involved in this phenomenon. As for other mdr gene products, the EhPGP5 protein functions as a chloride current inductor or as a regulator of cellular regulatory volume decrease.

Drug susceptibility testing of anaerobic protozoa

A simple technique for routine, reproducible global surveillance of the drug susceptibility status of the anaerobic protozoa Trichomonas, Entamoeba, and Giardia is described. Data collected using this technique can be readily compared among different laboratories and with previously reported data. The technique employs a commercially available sachet and bag system to generate a low-oxygen environment and log(2) drug dilutions in microtiter plates, which can be monitored without aerobic exposure, to assay drug-resistant laboratory lines and clinically resistant isolates. MICs (after 2 days) of 3.2 and 25 microM indicated metronidazole-sensitive and highly clinically resistant isolates of T. vaginalis in anaerobic assays, respectively. The aerobic MICs were 25 and >200 microM. MICs (1 day) of 12.5 to 25 microM were found for axenic lines of E. histolytica, and MICs for G. duodenalis (3 days) ranged from 6.3 microM for metronidazole-sensitive isolates to 50 microM for laboratory metronidazole-resistant lines. This technique should encourage more extensive monitoring of drug resistance in these organisms.

Embryolethality induced by metronidazole (MTZ) in Rattus norvegicus

Parasitic illnesses is increasing all over the world, especially in developing countries, and metronidazole (MTZ) is the therapeutic agent usually administered to children as well as adults at the reproductive age. In this work, we propose an evaluation of MTZ in order to analyze the potential reproductive damage in females by using Rattus norvegicus (Sprague-Dawley) as an animal model. Adult female rats were mated after MTZ treatments, and they were sacrificed at 21 days of gestation. Different types of damage were evaluated by using mortality, phenotypic abnormalities and reproductive capacity as parameters, and were studied and scored in 70 adult specimens (450 g/bw). They were divided into five groups: a) untreated females as a control group; females treated with b) DMSO as a solvent control group or c) 500 mg/kg/bw of MTZ per day for 7 days as therapeutic dose (TD); d) a half therapeutic dose (HD); and e) a double therapeutic dose (DD). Pre-implantation death in MTZ-treated groups was not significantly different from controls. However, drug treatments significantly increased the frequency of post-implantation deaths and the dominant lethals were ranged between 12.0 % and 17.8 %.

Antisense inhibition of expression of the light subunit (35 kDa) of the Gal/GalNac lectin complex inhibits Entamoeba histolytica virulence

One of the under-represented genes identified by cDNA representational difference analysis (RDA) between avirulent Entamoeba histolytica strain Rahman and virulent strain HM-1:IMSS was the amoebic light (35 kDa) subunit of the Gal/GalNac lectin complex. This lectin complex, which mediates the adhesion of the parasite to the target cell, also contains a heavy (170 kDa) subunit, which has the carbohydrate-binding domain. Stable transfectants of the virulent strain in which the expression of the 35 kDa subunit was inhibited by antisense RNA were not significantly affected in their adhesion activity to mammalian or bacterial cells but were strongly inhibited in their cytopathic activity, cytotoxic activity and in their ability to induce the formation of liver lesions in hamsters. These findings suggest that the 35 kDa subunit may have a specific function in the pathogenic pathway and provides a new insight into the role of this component of the Gal/GalNac lectin complex in amoebic virulence.

Physiology and molecular genetics of multidrug resistance in Entamoeba histolytica

Entamoeba histolytica presents the evolutionarily conserved multidrug-resistance (MDR) phenotype, discovered in mammalian cells. MDR cells overexpress the membrane P-glycoprotein, which excludes unrelated drugs from the cytoplasm. E. histolytica mutants exhibit cross-resistance to unrelated drugs, which are pumped out from the cytoplasm. In drug-resistant trophozoites, the constitutively expressed EhPg1 gene appears to be up-regulated by a C/EBP-like factor and a multiprotein complex that were not found in drug-sensitive trophozoites. The drug-induced EhPgp5 gene, on the other hand, appears to be up-regulated by AP-1 and HOX factors. Here we review the main physiological and molecular facts of the MDR phenotype in E. histolytica. Copyright 1999 Harcourt Publishers Ltd.

Transcriptional analysis of the EhPgp1 promoter of Entamoeba histolytica multidrug-resistant mutant

We present here the cloning and characterization of the EhPgp1 multidrug resistance gene promoter isolated from the Entamoeba histolytica drug-resistant mutant clone C2. The EhPgp1 promoter lacks the typical TATA box and the transcriptional initiation sequences described for other E. histolytica promoters. The major transcription initiation site of the EhPgp1 gene was located at the ATG start codon. The EhPgp1 core promoter located within the first 244 base pairs showed a higher chloramphenicol acetyltransferase expression in the transfected trophozoites of clone C2 than in those of the sensitive clone A. Gel shift assays revealed three specific DNA-protein complexes (Ia, IIa, and IIIc) using nuclear extracts from clone C2, whereas three main complexes (If, IIf, and IIg) were limited to clone A. Competition assays suggested the presence of C/EBP-like and OCT-like proteins in complexes Ia and IIa, respectively, probably involved in the expression of the EhPgp1 gene, whereas complex IIIc was competed by GATA-1, C/EBP, OCT, and HOX oligonucleotides. Thus, differential DNA-protein complexes may be formed by transcriptional factors involved in the regulation of the EhPgp1 gene expression.

Identification of significant variation in the composition of lipophosphoglycan-like molecules of E. histolytica and E. dispar

The lipophosphoglycan-like (LPG-like) molecules of E. histolytica virulent strains are clearly distinct from those of the avirulent E. histolytica and E. dispar strains. Abundant 'LPG' levels are apparently limited to virulent strains, while lipophosphopeptidoglycans ('LPPG's) are common to both virulent and avirulent strains of E. histolytica and E. dispar. It is therefore conceivable that 'LPPG' performs a function that is essential to survival within the host, while the 'LPG' performs a more specific function related to virulence.

Efficacy of a combined diloxanide furoate-metronidazole preparation in the treatment of amoebiasis and giardiasis

A combined formulation of diloxanide furoate and metronidazole was used to treat amoebiasis and giardiasis (cysts and vegetative forms) in 54 patients. Of these 34 patients had amoebiasis, 19 had giardiasis and one had mixed infection. Each patient took one tablet (containing 500 mg diloxanide furoate and 400 mg metronidazole), three times daily for 5 days, and the response to therapy was checked by clinical examination and by examination of fresh stools on days 3, 5 and 10. Abdominal pain was completely relieved in 91% and 84% of patients with amoebiasis and giardiasis, respectively, while parasitic clearance was 100% in both groups. Tolerance to the drug was adequate.

Susceptibility of an emetine-resistant mutant of Entamoeba histolytica to multiple drugs and to channel blockers

Previously a cloned emetine-resistant mutant of the protozoal parasite Entamoeba histolytica was shown to overexpress a gene for an ameba homolog of the mammalian P-glycoprotein, a plasma membrane pump that removes hydrophobic drugs from multidrug-resistant tumor cells. Three sets of experiments were performed to better characterize the multidrug-resistant phenotype of the emetine-resistant amebae. First, the emetine resistance of the mutant amebae was reversed by concentrations of calcium and sodium channel blockers effective in reversing drug resistance by multidrug-resistant tumor cells, but it was reversed only in the presence of very high concentrations of the tricyclic antidepressants. Second, the mutant amebae showed cross-resistance to antiamebic drugs used to treat luminal infection (iodoquinol and diloxanide) but were not cross-resistant to drugs used to treat invasive disease (chloroquine and metronidazole). Third, when amebae were loaded with radiolabeled emetine, the mutant parasites released the drug at approximately 1.6 times the rate of the wild-type organisms. We conclude that the emetine-resistant E. histolytica parasites have some but not all the features of the multidrug-resistant phenotype.

Adherence of pathogenic and non-pathogenicEntamoeba histolytica strains to neutrophils

The adherence of polymorphonuclear leukocytes (PMNs) to eight pathogenic and nine nonpathogenic strains of Entamoeba histolytica was examined. No difference between pathogenic and nonpathogenic strains was found. The addition of different carbohydrates confirmed the importance of the 170-kDa lectin of E. histolytica in binding to PMNs, corroborated by the finding that treatment of PMNs with galactosidase inhibited adherence. Inhibition of the microfilament system of E. histolytica using cytochalasin B resulted in a loss of adherence to PMNs. Inhibition of the microtubule system using nocodazole did not affect adherence. Preincubation of the trophozoites with serum resulted in enhanced adherence, but the serum factor responsible for this effect could not be identified. Fibronectin, vitronectin, integrins (CD11/CD18 molecules), complement, and mannose-binding protein did not seem to mediate adherence between E. histolytica and PMNs. In summary, these results indicate that defective adherence mechanisms are not a common feature of nonpathogenic E. histolytica strains.

Characterization of 20 Entamoeba histolytica strains isolated from patients with HIV infection

Twenty Entamoeba histolytica strains from patients with HIV-1 infection were isolated and compared with E. histolytica strains from patients without HIV infection. The isoenzyme pattern of the hexokinase as well as the hybridization with known DNA-probes were used as markers for pathogenicity. According to these markers, all 20 strains could be regarded as being nonpathogenic. Direct measurements of the virulence were carried out: destruction of monolayer tissue culture cells, capacity of phagocytosis and the ability to induce liver abscesses in the hamster. The virulence of strains from HIV patients was comparable to that of E. histolytica strains which had been isolated from HIV-negative asymptomatic carriers. In agreement with this, none of the HIV-positive patients showed symptoms of an invasive amebiasis. By PRC, no HIV-1 proviral DNA could be evidenced in the E. histolytica strains which had been isolated from HIV patients.

Antigens in electron-dense granules from Entamoeba histolytica as possible markers for pathogenicity

In vitro interaction of Entamoeba histolytica with collagen induces intracellular formation and release of electron-dense granules (EDG) and stimulation of collagenolytic activity. Purified EDG contain 1.66 U of collagenase per mg of protein. Thus, EDG may participate in tissue destruction during invasive amebiasis. Monoclonal antibodies (MAbs) L1.1 and L7.1 reacted specifically with EDG in enzyme-linked immunosorbent assay (ELISA) and immunofluorescence and immunoelectron microscopy. MAb L7.1 immunoprecipitated three polypeptides with molecular weights of 95,000, 68,000, and 28,000 from lysates of biosynthetically labeled E. histolytica. Both MAbs recognized the pathogenic E. histolytica axenic strains HM1:IMSS, HM38:IMSS, and HK-9 but failed to react in ELISA with Entamoeba moshkovskii, Entamoeba invadens, and E. histolytica-like Laredo. In addition, MAb L7.1 reacted with one E. histolytica isolate from a symptomatic patient but did not react with four of five isolates from asymptomatic patients. EDG antigens were detected by a MAb L7.1-based ELISA in E. histolytica-containing fecal samples from symptomatic, but not asymptomatic, individuals. These results suggest that the EDG antigen detected with MAb L7.1 may be differentially expressed in pathogenic and nonpathogenic E. histolytica.

Pathogenic and nonpathogenic strains of Entamoeba histolytica can be differentiated by monoclonal antibodies to the galactose-specific adherence lectin

Entamoeba histolytica infection results in either asymptomatic colonization or invasive colitis and liver abscess. E. histolytica isolates from patients with invasive disease have characteristic isoenzyme profiles (pathogenic zymodemes), suggesting a role for parasite factors in determining the severity of infection. A galactose-specific cell surface lectin from a pathogenic zymodeme was shown to mediate in vitro adherence to human colonic mucins and contact-dependent killing of target cells. Six nonoverlapping antigenic determinants were identified on the 170-kilodalton heavy subunit of the pathogenic lectin. Anti-lectin monoclonal antibodies (MAb) directed against epitopes 1 and 2 enhanced adherence whereas MAb to epitopes 3 through 6 either inhibited or had no effect on adherence. We tested 50 pathogenic and nonpathogenic strains for reactivity to these anti-lectin MAb by radioimmunoassay. MAb to epitopes 1 through 6 reacted in the radioimmunoassay with all 16 pathogenic zymodeme strains tested. In contrast, only MAb to epitopes 1 and 2 bound to the lectin from nonpathogenic strains. Western immunoblots with anti-lectin antibodies showed that the 170-kilodalton heavy subunit was present in the nonpathogenic amebae. Adherence of the nonpathogenic SAW 760 strain to human erythrocytes was enhanced by MAb to epitope 1 and blocked by galactose, confirming the presence of a functionally active lectin. A lectin radioimmunoassay based on MAb to epitopes 1 and 3 proved to be a simple and rapid method to distinguish pathogenic from nonpathogenic amebae in culture. Further exploration of the functional consequences of the antigenic differences demonstrated for the lectin may lead to a better understanding of its role in pathogenesis.

Specific labeling of cysteine proteinases in pathogenic and nonpathogenic Entamoeba histolytica

Growth of Entamoeba histolytica trophozoites was inhibited by 50% at low concentrations (2.0 micrograms/ml) of the diazopeptidyl inhibitor benzyloxycarbonyl-leucyl-L-tyrosyldiazomethane (Z-L-Leu-L-Tyr-CHN2). Iodination of the tyrosine residue lowered the growth inhibitory efficacy of the diazopeptidyl inhibitor (50% inhibition, approximately 10 micrograms/ml). However, even at this concentration, practically all of the cysteine proteinase activity of the cells was irreversibly inactivated as shown by fluorescence microscopy with the dipeptide substrate L-Arg-L-Arg-4-methoxy-beta-napthylamide or colorimetrically with azocasein as the substrate. Growth of trophozoites of E. histolytica from various strains, including both pathogenic and nonpathogenic zymodemes, was similarly inhibited. The concentration of inhibitor required to inactivate the proteinase activity of nonpathogenic cells was lower. Lysates from trophozoites grown in the presence of sublethal concentrations of 125I-labeled protease inhibitor (10 micrograms/ml) showed as many as eight radioactive bands by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (molecular sizes, 73, 68, 56, 40, 39, 35, 29, and 27 kilodaltons). Two of these bands (molecular sizes, 29 and 27 kilodaltons) could be seen in gels of the cytoplasmic fraction, whereas the high-molecular-size bands were mostly associated with the membrane fraction. The radioactive bands in pathogenic and nonpathogenic strains were very similar with only minor differences. The results obtained show that E. histolytica cells, irrespective of their pathogenicity, possess a number of cysteine proteinases of similar molecular sizes which are vital for cell growth.

Identification of protein kinase C and its potential substrate in Entamoeba histolytica

1. Protein kinase C (PKC) activity has been identified in various strains of the human parasite, Entamoeba histolytica. 2. An amoebic protein of mol. wt 78,000 was recognized by polyclonal antibodies raised against the 82,000 mol. wt rat brain protein kinase C. 3. A partially purified PKC preparation from E. histolytica phosphorylated histone I in the presence of calcium, phospholipids and diacylglycerol, and specifically bound tritiated phorbol ester at an apparent KD of 9 nM. 4. A relocalization of the amoebic PKC activity from the cytosol to the membrane fraction was observed when trophozoites were actively phagocytising bacteria. Under these conditions, a labelled phosphoprotein of mol. wt 68,000 was identified. 5. Similar to what was found during macrophage activation, a myristoylated mol. wt 68,000 protein was detected in amoebae grown in the absence of bacteria, but not in amoebae which were active in phagocytosis.