A homologue of the cysteine proteinase gene (ACP1 or Eh-CPp3) of pathogenic Entamoeba histolytica is present in non-pathogenic E. dispar strains

One of the three cysteine proteinase genes, ACP1 (or CP 3), has been reported to be missing in non-pathogenic strains of Entamoeba histolytica (or Entamoeba dispar as recently labeled). Unexpectedly, a gene fragment very similar in its sequence (95% homology) to ACP1 of pathogenic strains was obtained by use of the polymerase chain reaction from genomic DNA and cDNA of various cloned non-pathogenic strains as well as in 23 clinical isolates from asymptomatic carriers. The finding of the ACP1 homologue in non-pathogenic or E. dispar strains rules out the proposed use of its absence for diagnostic purposes.

Evidence for the existence of ganglioside molecules in the antigen of Entamoeba histolytica

Gangliosides were found to be present in Entamoeba histolytica. They were extracted from lyophilized trophozoites of the pathogenic strain HM-1:IMSS and purified by high performance thin-layer chromatography. Two resorcinol-positive bands, comigrating with GM2 and GD1a were demonstrated, revealing the existence of ganglioside molecules in Entamoeba histolytica. The GM2 content, determined as lipid-bound sialic acid, was 1.5 micrograms/10(8) amoebae, the content of the GD1a comigrating band was 0.32 microgram/10(8) amoebae. The identity of the GM2 comigrating band was confirmed by TLC immunostaining, using the monoclonal anti-GM2 antibody GMB28. Furthermore, six out of ten anti-amoeba positive sera selectively reacted with the GM2 comigrating band, as revealed by immunostaining on TLC plates. Absorption tests revealed that preincubation of anti-amoeba positive sera with standard GM2 was followed by a significant decrease in the reaction with amoeba trophozoites by indirect immunofluorescence. These results demonstrate that a GM2 comigrating component of Entamoeba histolytica may be one of the antigens responsible for the appearance of circulating antibodies in patients with amoebiasis.

Alteration of lipid profile in hyperlipidemic rabbits by allicin, an active constituent of garlic

BACKGROUND

The effect of garlic on the serum lipid profile has been the subject of controversy. This study was therefore designed to examine the effects of allicin, an active constituent of garlic, on the lipid profile in a rabbit model.

METHODS

Allicin was produced by reacting alliin, synthesized in our laboratory, with purified alliinase. Nineteen New Zealand White rabbits were fed a cholesterol-rich diet (0.25% cholesterol) for 18 weeks. Ten rabbits received freshly produced allicin (3 mg/kg orally) starting at 8 weeks, and nine received placebo. There was no significant difference between the lipid profiles of the two groups at baseline up to 8 weeks.

RESULTS

From day 28 of allicin supplementation a significant difference was found between the allicin and placebo groups in the graph regression lines describing the influence of allicin on serum cholesterol: Y = 41.39 + 8.69 multiplied by day (control) versus Y = -877.24 + 17.67 multiplied by day (allicin). The same trend was found for low-density lipoprotein concentrations: Y = 10.3 + 8.4 multiplied by (control) versus Y = -750.4 + 15.7 multiplied by day (allicin). The serum high-density lipoprotein levels also differed significantly between the groups: Y = 20.29 + 0.24 multiplied by day (control) versus Y = -109.9 + 1.65 multiplied by day (allicin).

CONCLUSIONS

Our results indicate that allicin has a beneficial effect on the serum lipid profile in hyperlipidemic rabbits, and should be further tested clinically.

Alliinase (alliin lyase) from garlic (Alliium sativum) is glycosylated at ASN146 and forms a complex with a garlic mannose-specific lectin

Alliinase (EC 4.4.1.4) catalyses the production of allicin (thio-2-propene-1-sulfinic acid S-allyl ester), a biologically active compound which is also responsible for the characteristic smell of garlic. It was demonstrated that alliinase which contains 5.5-6% of neutral sugars, gives clear PAS-staining, binds to Con A and can form a complex with garlic mannose-specific lectin (ASA). Evidence that the formation of such a complex is mediated by the interaction of the carbohydrate of the glycoprotein enzyme with the lectin was obtained from a radioligand assay which demonstrated the binding of alliinase to ASA and competitive inhibition of this binding by methyl alpha-D-mannoside. ASA I was shown as the lectin mainly present in the complex with alliinase. The results of this study also demonstrate that alliinase is glycosylated at Asn146 in the sequence Asn146-Met147-Thr148.

Natural antibodies to dietary proteins: the existence of natural antibodies to alliinase (Alliin lyase) and mannose-specific lectin from garlic (Allium sativum) in human serum

It is known that human serum contains natural antibodies to self and non-self proteins. We wished to determine whether normal human serum contains antibodies to dietary proteins that were never injected. We found that human serum contains antibodies to the two major proteins from cloves of garlic (Allium sativum) which is used as a flavorigard dietary food additive. The antibodies found were directed against alliinase and mannose-specific Allium sativum agglutinin (ASA). The antibodies were purified by affinity chromatography on their corresponding antigens. The purified immunoglobulins were mainly of the IgG and IgM classes and could be divided into two categories--specific and crossreactive. The anti-alliinase antibodies were highly specific, while anti-ASA antibodies were polyreactive. Some of the possible reasons for this difference in specificity are suggested.

Molecular cloning of a 30-kilodalton lysine-rich surface antigen from a nonpathogenic Entamoeba histolytica strain and its expression in a pathogenic strain

A monoclonal antibody (MAb), 318-28, that specifically reacts with a 30-kDa antigen present on membrane surfaces of all nonpathogenic (NP) Entamoeba histolytica strains tested and which did not react with pathogenic (P) strains was used for the isolation of the cDNA coding for this antigen from an expression library of an NP E. histolytica strain. The deduced amino acid composition was rich in lysine residues (14.5%), with some sequence similarity to a polyadenylate-binding protein. Southern and Northern (RNA) blot analyses, as well as amplifications of DNA segments by PCR, indicate that a very similar gene (identity of 96.5%) exists in P strains of E. histolytica. Unexpectedly, the NP-specific antigen was also identified by MAb 318-28 on the surfaces of a cloned, xenically cultivated and well-characterized P strain (BNI:0591) that was recently isolated from a human liver abscess. Binding of the MAb, both to the cell surfaces and to Western blots (immunoblots), was abolished, however, upon axenization of the BNI:0591 cultures. Oligonucleotide primers, designed to anneal only to specific DNA sequences of the NP 30-kDa protein gene copy, amplified a DNA segment from P strain BNI:0591 which was identical in sequence to that of the NP 30-kDa protein gene. Our findings indicate that a P strain of E. histolytica can possess and express, under certain growth conditions, an antigen that is usually detected only in NP strains.

Characterization of two distinct gene transcripts for ribosomal protein L21 from pathogenic and nonpathogenic strains of Entamoeba histolytica

A second gene (rp-L21) copy, clone g34, coding for ribosomal (r-) protein L21, was isolated from the pathogenic (P) strain HM-1:IMSS cl6 of the intestinal parasite Entamoeba histolytica (Eh). The gene was compared to the previously isolated copy, gLE3 [Petter et al., Mol. Biochem. Parasitol. 56 (1992) 329-334], with respect to its primary structure, mRNA levels and binding to the r-complex during translation. Unlike the gLE3 gene copy [Petter et al., Mol. Biochem. Parasitol. 56 (1992) 329-334], g34 was found not to be physically connected to an actin gene copy. Homologous copies of the two rp-L21 genes were also characterized from the nonpathogenic (NP) strain SAW1734R clAR, as well as from its P derivative. Sequence comparison of the coding regions of the two rp-L21 revealed almost full identity. Significant differences were found, however, within their 3' and 5' flanking regions. Using the 3' rapid amplification of cDNA ends (3' RACE) method [Frohman et al., Proc. Natl. Acad. Sci. USA 85 (1988) 8998-9002], as well as Northern and slot blot hybridizations, it was demonstrated that both rp-L21 mRNAs are found in similar amounts. However, as was shown by differential hybridization, the relative binding of each transcript to the r-complex varied somewhat between P and NP strains. This finding suggests that the control of expression of rp-L21 in Eh may involve regulation at the post-transcriptional level.

Alliin lyase (Alliinase) from garlic (Allium sativum). Biochemical characterization and cDNA cloning

The garlic plant (Allium sativum) alliinase (EC 4.4.1.4), which catalyzes the synthesis of allicin, was purified to homogeneity from bulbs using various steps, including hydrophobic chromatography. Molecular and biochemical studies showed that the enzyme is a dimer of two subunits of MW 51.5 kDa each. Its Km using synthetic S-allylcysteine sulfoxide (+ isomer) as substrate was 1.1 mM, its pH optimum 6.5, and its isoelectric point 6.35. The enzyme is a glycoprotein containing 6% carbohydrate. N-terminal sequences of the intact polypeptide chain as well as of a number of peptides obtained after cyanogen bromide cleavage were obtained. Cloning of the cDNAs encoding alliinase was performed by a two-step strategy. In the first, a cDNA fragment (pAli-1-450 bp) was obtained by PCR using a mixed oligonucleotide primer synthesized according to a 6-amino acid segment near the N-terminal of the intact polypeptide. The second step involved screening of garlic lambda gt11 and lambda ZAPII cDNA libraries with pAli-1, which yielded two clones; one was nearly full length and the second was full length. These clones exhibited some degree of DNA sequence divergence, especially in their 3' noncoding regions, suggesting that they were encoded by separate genes. The nearly full length cDNA was fused in frame to a DNA encoding a signal peptide from alpha wheat gliadin, and expressed in Xenopus oocytes. This yielded a 50 kDa protein that interacted with the antibodies against natural bulb alliinase. Northern and Western blot analyses showed that the bulb alliinase was highly expressed in bulbs, whereas a lower expression level was found in leaves, and no expression was detected in roots. Strikingly, the roots exhibited an abundant alliinase activity, suggesting that this tissue expressed a distinct alliinase isozyme with very low homology to the bulb enzyme.

Electrophoretic karyotype and chromosome assignments for a pathogenic and a nonpathogenic strain of Entamoeba histolytica

The electrophoretic karyotypes of a pathogenic and a nonpathogenic strain of Entamoeba histolytica were determined by pulsed-field gel electrophoresis. A number of previously isolated genes were assigned to specific chromosomal bands. Significant differences between the chromosomal patterns of these strains as well as in the assignment of most genes were found.

Shigella flexneri transformants expressing type 1 (mannose-specific) fimbriae bind to, activate, and are killed by phagocytic cells

Shigella flexneri M90T (invasive) and BS176 (noninvasive) are typical nonfimbriated organisms that do not bind to or activate phagocytic cells. We demonstrate that S. flexneri M90Tp and BS176p, obtained by transformation of the strains named above with the cluster of genes encoding type 1 (mannose-specific) fimbriae of Escherichia coli, express the functional fimbriae, as shown by electron microscopy, by binding of antifimbria antibodies and by yeast cell aggregation. The transformants, but not the parental strains, bound to human granulocytes and mouse peritoneal macrophages. This binding was inhibited by methyl alpha-D-mannoside but not by methyl alpha-D-galactoside. The bound bacteria induced oxidative burst activation and degranulation of the granulocytes in vitro. With mouse peritoneal macrophages, the binding of the fimbriated bacteria induced degranulation in vitro. Injection of the bacteria into mouse peritoneum also induced degranulation of the macrophages in vivo; no such effect was observed with the nonfimbriated strains. The bound fimbriated transformants were effectively killed by the human granulocytes in vitro in the absence of opsonins or after opsonization with human anti-S. flexneri antiserum. The nonfimbriated strains were killed only after opsonization. These results provide further evidence for the role of type 1 fimbriae in lectin-mediated nonopsonic phagocytosis.

Interaction between trophozoites of Entamoeba histolytica and the human intestinal cell line HT-29 in the presence or absence of leukocytes

Studies on the interaction between trophozoites of Entamoeba histolytica of pathogenic or non-pathogenic origin and epithelial cells of the human intestine can contribute to the understanding of the pathogenesis of invasive amoebiasis. We have examined the interaction of virulent E. histolytica with the human colonic carcinoma cell line HT-29. Differentiated HT-29 cells are comparable to the mucosa cells to which E. histolytica attaches physiologically. Adherence between E. histolytica trophozoites and HT-29 cells was effectively inhibited by glycoconjugates containing galactose, indicating the importance of the 170-kDa lectin of E. histolytica in binding to intestinal cells. Adherence was not significantly inhibited by glycoconjugates containing N-acetyl-glucosamine, indicating that the 220-kDa lectin of E. histolytica is not involved in binding to HT-29 cells. The destruction of HT-29 cells by pathogenic E. histolytica was dependent on adherence. The destruction was enhanced when polymorphonuclear granulocytes were added to the E. histolytica trophozoites.

Effect of hamster liver passage on the isoenzyme patterns of Entamoeba histolytica

The effect of hamster liver passage on the isoenzyme patterns of isolates of Entamoeba histolytica was investigated. Three isolates, F, G and T were originally obtained from patients with acute amebic dysentery and another strain, C, was obtained from an asymptomatic carrier. All these strains were maintained for over two years in axenic culture. The isoenzyme pattern (zymodeme) of hexokinase (HK), phosphoglucomutase (PGM) and glucose phosphoisomerase (GPI) of these strains was found to belong to non-pathogenic group X, but the isoenzyme pattern of GPI resembled less pathogenic zymodeme XX and might be an intermediate type. Following inoculation of trophozoites into hamster livers and recovery after abscess formation, their isoenzyme pattern changed and revealed that they belonged to pathogenic type XIV. Liver passage caused an enhancement in amebic virulence as evidenced by their increased ability to destroy leukocytes. The results indicate that isoenzyme pattern is not a stable property of E. histolytica.

A model of interaction between Entamoeba histolytica and Shigella flexneri

The establishment of a relationship between Entamoeba histolytica and certain bacteria may contribute to the expression and/or enhancement of the pathogenicity of this parasite. Recent experiments have shown that bacteria expressing mannose-binding lectins on their surface could attach to mannose-containing molecules on the surface of amoebae. In this study, we established a model of interaction between. E. histolytica and Shigella flexneri. Using well-characterized mutants of S. flexneri, we studied the role of type I pili expression and the invasive phenotype of S. flexneri in the interaction between amoebae and the bacteria. Type I pili expression allowed attachment and subsequent internalization of S. flexneri by amoebae, these events were not observed in isogenic strains that did not express type I pili. Invasive as well as non-invasive variants of S. flexneri expressing type I pili were slowly digested by amoebae following internalization. Morphological studies showed that the specific features of the interaction depend on the dynamics of the distribution of mannose residues on the amoebic membrane during the interaction.

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.

Cloning and characterization of an unusual elongation factor-1 alpha cDNA from Entamoeba histolytica

The coding sequence deduced from two overlapping cDNA inserts obtained from a pathogenic strain of Entamoeba histolytica revealed a striking homology (greater than 85%) with elongation factor EF-1 alpha from Saccharomyces cerevisiae and Artemia salina. The deduced amino acid sequence predicted a size of 49 kDa, and antibodies raised against the S. cerevisiae EF-1 alpha cross-reacted with an amoebic protein of similar size (45-47 kDa). Sequence analysis of the cDNA revealed that the 5' untranslated region contained a stretch of 190 nucleotides which was perfectly complementary to a segment of the 3' terminal coding region situated 1015 bases downstream of the methionine initiation codon. Electron microscopy of self-renatured cDNA confirmed the potential of such molecules to form a stem-loop secondary structure. The presence of the complementary sequences was confirmed at the genomic level by sequence analysis of polymerase chain reaction-amplified segments which span both the 3' and 5' terminal complementary regions. Comparison of the deduced amino acid sequence of E. histolytica EF-1 alpha with Ef-Tu from Escherichia coli and EF-1 alpha from different sources, suggested that the major functional domains of the protein are located within the loop structure.

Autonomous replication sequences in an extrachromosomal element of a pathogenic Entamoeba histolytica

Entamoeba histolytica possesses a 24.5 kilobase plasmid-like molecule which encodes for the organism's ribosomal RNAs. Sequence analysis of this extrachromosomal element revealed the presence of AT rich sequences which show homology to the origin of replication of other lower eucaryotes. An 802 bp fragment containing these sequences was cloned into a yeast shuttle vector lacking the origin of replication and the construct tested for its ability to replicate autonomously in yeast. Mitotic stability tests as well as evidence for plasmid maintenance indicate that the transformed cells contained self-replicating episomes and not stably integrated molecules. The nucleotide sequence of this ARS-containing fragment is presented.

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.

Repetitive DNA elements characteristic of pathogenic Entamoeba histolytica strains can also be detected after polymerase chain reaction in a cloned nonpathogenic strain

Strains of Entamoeba histolytica which were isolated from symptomatic patients and which possess a characteristic pathogenic isoenzyme pattern (zymodeme) have extrachromosomal circular DNA molecules containing RNA genes and clusters of tandemly reiterated PvuI elements. The nucleotide sequence of comparable reiterated BamHI elements present in amebae with nonpathogenic zymodemes differs from that found in pathogenic ones. By using the polymerase chain reaction, it was demonstrated that the cloned, nonpathogenic E. histolytica strain SAW 1734R clAR also contains one or few of the tandemly repeated DNA PvuI elements characteristic of the pathogenic amebae. Sequences were detected by hybridization with the P-145 probe after in vitro amplification. Because of technical difficulties, it was impossible to resolve whether single copies of the nonpathogenic BamHI repetitive elements are present in pathogenic amebae. Our findings suggest that in the nonpathogenic amebae, the signal to start amplifying the PvuI-type elements may be induced during the process of elimination of bacterial associates from their growth environment.