Inhibition of choriogonadotropin-activated steroidogenesis in cultured Leydig tumor cells by the Rp diastereoisomer of adenosine 3',5'-cyclic phosphorothioate

The diastereoisomers of adenosine 3',5'-cyclic phosphorothioate, (Sp)-cAMPS and (Rp)-cAMPS, have been previously shown to act as agonists and antagonists, respectively, in the activation of several mammalian cAMP-dependent protein kinases. In an effort to characterize further the involvement of cAMP in the activation of Leydig cell steroidogenesis by lutropin/choriogonadotropin (LH/CG), we examined the effects of these cyclic nucleotide analogues on a clonal strain of cultured murine Leydig tumor cells (designated MA-10). Our results show that (i) (Sp)-cAMPS activates and (Rp)-cAMPS inhibits the isolated cAMP-dependent protein kinase of the MA-10 cells; (ii) both analogues inhibit the isolated cAMP phosphodiesterase(s); (iii) (Sp)-cAMPS activates steroid biosynthesis in intact cells, but (Rp)-cAMPS does not; and (iv) (Rp)-cAMPS is a competitive inhibitor of the activation of steroidogenesis by (Sp)-cAMPS, 8-bromo-cAMP, human CG, cholera toxin, and forskolin. However, (Rp)-cAMPS is a more effective inhibitor when steroidogenesis is activated by (Sp)-cAMPS or 8-bromo-cAMP than when it is activated by human CG, cholera toxin, or forskolin. This difference appears to be related to the combined effects of (Rp)-cAMPS on the cAMP-dependent protein kinases and cAMP phosphodiesterase(s). We conclude that cAMP is a quantitatively important mediator of the activation of steroidogenesis by LH/CG even at low concentrations of hormone where an increase in steroid biosynthesis cannot be easily correlated with increased cAMP accumulation. Thus, our data indicate that if other second messengers are involved in the activation of steroidogenesis by LH/CG, they must do so by acting together with, rather than independently of, cAMP.

Specific inhibition of Trypanosoma cruzi neuraminidase by the human plasma glycoprotein "cruzin"

Plasma of normal human individuals was shown to contain an inhibitor of Trypanosoma cruzi neuraminidase (NAase; acylneuraminyl hydrolase, sialidase, EC 3.2.1.18). The inhibitor has been purified to homogeneity by PEG precipitation, CM Affi-Gel Blue Sepharose chromatography, and gel filtration. The purified preparation inhibits T. cruzi NAase at a concentration as low as 10(-9) M and has no effect at concentrations at least 100 times higher on any of the other NAases tested, including those from influenza virus, the closely related trypanosome Trypanosoma rangeli, and mammalian NAases. The inhibitor is unique in that it prevents T. cruzi desialylation of intact mammalian cells but does not prevent desialylation of soluble glycoconjugates. In addition, the isolated material is effective in inhibiting the T. cruzi NAase whether the enzyme is on the parasite outer membrane or in solution. Molecular characterization indicates that the inhibitor is a glycoprotein with a Mr of 246,000 +/- 20,000 composed of subunits of Mr 28,000 +/- 2000. Its plasma concentration is at least 60 micrograms/ml. The mechanism of action has not been fully elucidated, but it appears to be noncompetitive. Attempts to match the isolated NAase inhibitor with known plasma glycoproteins have not been successful. In view of this and of the specificity of the inhibitor for T. cruzi, we have named the inhibitor "cruzin." This finding suggests a different approach in investigating the role that NAase plays in host-parasite interaction.

Heterogeneous distribution of neuraminidase activity in strains and clones of Trypanosoma cruzi and its possible association with parasite myotropism

Various strains, stocks, and clones of Trypanosoma cruzi were analyzed for neuraminidase (NA) activity using fetuin and human erythrocytes as substrate. In all cases the activity was found to be developmentally regulated. Zymodeme type I strains, which are histotropic for skeletal muscle, had greater NA activity than zymodeme type II strains which are histotropic for either macrophages or cardiac muscle cells. Heterogeneity of NA expression within strains is suggested by the finding that one Silvio X10 clone had greater NA activity than another clone of the same stock. The differences observed were more pronounced when human erythrocytes and not fetuin were used as substrate. Trypomastigotes of the high producing strains reared in bovine artery smooth muscle cells had enhanced expression compared to trypomastigotes reared in 3T3 or human fibroblast cells. The first harvest of trypomastigotes from cell cultures had greater NA activity than trypomastigotes harvested on subsequent days.

Lectin activation in Giardia lamblia by host protease: a novel host-parasite interaction

A lectin in Giardia lamblia was activated by secretions from the human duodenum, the environment where the parasite lives. Incubation of the secretions with trypsin inhibitors prevented the appearance of lectin activity, implicating proteases as the activating agent. Accordingly, lectin activation was also produced by crystalline trypsin and Pronase; other proteases tested were ineffective. When activated, the lectin agglutinated intestinal cells to which the parasite adheres in vivo. The lectin was most specific to mannose-6-phosphate and apparently was bound to the plasma membrane. Activation of a parasite lectin by a host protease represents a novel mechanism of host-parasite interaction and may contribute to the affinity of Giardia lamblia to the infection site.

Cell surface carbohydrate of Leishmania mexicana amazonensis: differences between infective and non-infective forms

The cell surface carbohydrates of Leishmania mexicana amazonensis (amastigotes and promastigotes, both infective and non-infective forms) were comparatively analyzed by agglutination assay employing 28 highly purified lectins, and by binding assay using 125I-labeled lectins. Among the D-GalNAc binding lectins, Bandeiraea simplicifolia-I, Dolichos biflorus, Phaseolus vulgaris and Glycine max were highly specific for the amastigotes, while that from Maclura aurantiaca selectively agglutinated promastigotes. The lectins from Wistaria floribunda, Phaseolus lunatus (D-GalNAc), Arachis hypogaea (D-Gal) and Triticum vulgaris (D-GlcNAc) were selective for the infective forms (both amastigotes and promastigotes), not reacting with the non-infective ones. Conversely, no parasite agglutination occurred with the L-fucose binding lectins Lotus tetragonolobus and Ulex europaeus-I. Binding studies with 125I-labeled lectins from Wistaria floribunda, Triticum vulgaris and Arachis hypogaea were performed to find whether unagglutinated non-infective promastigotes might have receptors for these lectins, in which case absence of agglutination could be due to a peculiar arrangement of the receptors. These assays essentially confirmed the selectivity, demonstrated in the agglutination assays of these lectins for the infective promastigotes.

Killing of Giardia lamblia by human milk lipases: an effect mediated by lipolysis of milk lipids

Killing of Giardia lamblia by fresh human milk requires the presence of bile salt, a known activator of bile salt-stimulated lipase, the major lipase in human milk. Purified enzyme did not kill the parasite even in the presence of activator unless milk lipids were also present in the reaction mixture. Free fatty acids had a marked giardiacidal effect, a phenomenon supporting the view that fatty acids, released during hydrolysis of milk triglycerides, are responsible for the killing of G. lamblia by human milk. Bile salt-independent lipolysis took place in milk during storage at 4 C. This lipolysis correlated strongly with activity of lipoprotein lipase, also present in human milk. During such storage, raw human as well as bovine milk developed giardiacidal activity that could be prevented by inactivation or inhibition of the milk lipases by pasteurization or addition of eserine to the milk, respectively, before storage.

Description and characterization of a surface lectin from Giardia lamblia

The mechanisms by which the human enteric pathogen Giardia lamblia colonizes the proximal small intestine are poorly understood. Although the parasite possesses an attachment organelle on its ventral surface, the "sucking" disk, we considered that like many bacteria and some protozoa, G. lamblia might also have a surface membrane-associated modality for adherence to its host. Using an erythrocyte mixed-agglutination model, we demonstrated a parasite surface lectin with specificities for D-glucosyl and D-mannosyl residues. This lectin is soluble in Triton X-100, is calcium dependent, and is maximally active at pH 5.5 to 6.0. Partial purification was achieved by serial extraction of parasites in Triton X-100 followed by Sephadex G-150 affinity chromatography. The lectin could not be surface radiolabeled with 125I-Bolton-Hunter reagent, but radiolabeling of the hapten eluate from an affinity column produced four bands of 57,000 to 78,000 Mr on sodium dodecyl sulfate-polyacrylamide gels under reducing conditions. The biological function of this lectin is unknown. The presence of mannosyl residues on the luminal surface of human small intestinal epithelial cells suggests that there are receptors for Giardia lectin at the site of colonization.

A neuraminidase from Trypanosoma cruzi removes sialic acid from the surface of mammalian myocardial and endothelial cells

Trypanosoma cruzi causes Chagasic heart disease, a major public health problem in Latin America. The mechanism of interaction of this protozooan parasite with host cells is poorly understood. We recently found that the infective trypomastigote form a T. cruzi exhibits neuraminidase activity and can desialylate mammalian erythrocytes. However, it is not known if T. cruzi can also modify the surfaces of cardiovascular cells that are directly involved in the most important clinical manifestations of this disease. Accordingly, this study determined whether T. cruzi can remove sialic acid from cultured rat myocardial or human vascular endothelial cells. Sialic acid was labeled metabolically with the precursor 3H-N-acetyl-D-mannosamine. Soluble neuraminidase, isolated from intact T. cruzi trypomastigotes, caused significant release of labeled material from myocardial cells (e.g., 2,174 +/- 27 dpm/h vs. spontaneous release of 306 +/- 30 dpm/h, n = 4, P less than 0.001). Chromatographic analysis showed that the bulk of the radioactivity released by T. cruzi neuraminidase was sialic acid. Intact T. cruzi trypomastigotes also released sialic acid from metabolically labeled myocardial cells in a concentration-dependent manner. In contrast, a noninfective form of T. cruzi, the amastigote, did not desialylate these cells. Galactose oxidase labeling demonstrated newly desialylated glycoproteins on the surface of myocardial cells treated with T. cruzi neuraminidase. Desialylation of myocardial cells was confirmed histochemically by the appearance of binding sites for peanut agglutinin, a lectin that binds to complex oligosaccharide moieties after removal of the terminal sialyl residue. T. cruzi neuraminidase also removed sialic acid from adult human saphenous vein endothelial cells, as determined by both histochemical and metabolic labeling studies. Thus, infective forms of T. cruzi can chemically modify the surfaces of myocardial and vascular endothelial cells by desialylation. This alteration may play a role in the initial interaction of this parasite with these important target cells of the host cardiovascular system.

Identification of chitin as a structural component of Giardia cysts

The intestinal parasite Giardia lamblia is a significant cause of diarrheal disease, which is perpetuated by the infective cyst form of the parasite. Although a rational approach to the control of giardiasis would be to inhibit cyst formation, nothing is known of the chemical composition of the cyst wall or of its biosynthesis. In these studies, we have shown that chitin is a major structural component of G. lamblia and G. muris cyst walls. This conclusion is based on the finding that chitinase specifically destroys the cyst wall, as revealed by electron microscopy. The presence of chitin was also shown directly by lectin binding studies. Of 12 lectins with diverse carbohydrate recognition specificity, only the N-acetylglucosamine-specific lectins wheat germ agglutinin, succinylated wheat germ agglutinin, and tomato lectin bound to cyst walls, as shown by fluorescence microscopy and cytochemistry. Wheat germ agglutinin binding was completely abolished by treatment of the cysts with purified chitinase. This effect was specific since it could be prevented by incubating the enzyme with chitin before treatment of the cysts. Treatment of cysts with N-acetyl-beta-glucosaminidase partially inhibited wheat germ agglutinin binding, whereas other glycosidases and proteases had no effect. These findings indicate that chitin is a major structural component of Giardia cyst walls and raise the possibility that inhibitors of chitin synthesis may be of use in preventing encystation and thus controlling spread of the disease.

Neuraminidase activity in Trypanosoma rangeli

Supernatants of cultures and extracts of Trypanosoma rangeli readily release N-acetyl neuraminic acid from a variety of substrates. The activity in both supernatant and cell extract is precipitated between 30 and 50% ethanol, and between 40 and 70% ammonium sulfate. Fractionation of the culture supernatant by gel exclusion gives a single peak of neuraminidase activity of molecular weight 48 000. The culture supernatant releases sialic acid at different rates from the following substrates:fetuin, sialyllactose and orosomucoid but not from bovine submaxillary mucin and ovomucoid. The enzyme in the culture supernatant is also active against human erythrocytes of all ABO types. The enzyme showed an optimum pH of 5.0 for sialyllactose and erythrocyte substrates. Large amounts of the enzyme are preferentially secreted during growth in vitro.

Identification of glycoprotein storage diseases by lectins: a new diagnostic method

The specific diagnosis of glycoprotein storage diseases is made by demonstrating a deficiency in enzyme activity or an elevation of undegraded oligosaccharides in cells or body fluids. Prospective sampling and expensive specialized biochemistry, which is also time consuming, are required for such studies. We used lectin reagents on paraffin-embedded tissue sections to identify the specific sugars in undegraded stored substances. We studied 22 cases of glycoprotein storage diseases and differentiated histochemically between alpha- and beta-mannosidosis, fucosidosis, and sialisidosis. Cells affected with alpha-mannosidosis stained with Concanavalia ensiformis (Con A), Triticum vulgaris (WGA), and succinyl-WGA (S-WGA), while beta-mannosidosis cells did not stain with any of the lectins used. In fucosidosis the affected cells stained with Ulex europeus-I (UEA-I), while sialisidosis-affected cells stained with WGA, and in three cases with Arachis hypogea (PNA). This study indicates that lectin histochemistry provides a reliable specific diagnostic pattern for some glycoprotein storage diseases using a simple and inexpensive method.

Lectins discriminate between pathogenic and nonpathogenic South American trypanosomes

Cell surface carbohydrates of Trypanosoma cruzi, Trypanosoma rangeli, and Trypanosoma conorhini were analyzed by a micro-agglutination assay employing 27 highly purified lectins and by binding assays using various 125I-labeled lectins. The following seven lectins discriminated between the trypanosomes: 1) tomato lectin (an N-acetyl-D-glucosamine-binding protein), both in purified form and as crude tomato juice; 2) Bauhinea purpurea and Sophora japonica lectins (both N-acetyl-D-galactosamine-binding proteins), which selectively agglutinated T. cruzi; 3) Vicia villosa (an N-acetyl-D-galactosamine-binding protein) which was specific for T. rangeli; 4) peanut lectin (a D-galactose-binding protein) both in purified form and as crude saline extract; and 5) Ulex europaeus and Lotus tetragonolobus (both L-fucose-binding proteins) lectins which reacted only with T. conorhini. Binding studies with 125I-labeled lectins were performed to find whether unagglutinated cells of the three different species of trypanosomes might have receptors for these lectins, in which case absence of agglutination could be due to a peculiar arrangement of the receptors. These assays essentially confirmed the agglutination experiments.

Human amyloid P component: a circulating lectin that modulates immunological responses

Amyloid P component (AP/SAP), a glycoprotein, precipitated with purified snail galactans from Helix pomatia and Arianta arbustorum in a dose-dependent manner. Radiolabelled AP binds to human peripheral blood mononuclear cells (PBMC), erythrocytes, and cells derived from human non-T, non-B acute lymphocytic leukaemia. The AP cell binding is specific in that it is dose-dependent and can be blocked both by excess cold AP and by Helix pomatia galactan, although it cannot be blocked by an equal amount of the monosaccharide galactose. In vitro studies of human PBMC immune responses demonstrated that AP inhibits PBMC proliferation responses to mycobacterial purified protein derivative and to phytohaemagglutinin and the humoral, antibody response to pokeweed mitogen. The AP-induced suppression of non-specific antibody production by human PBMC was dependent on the time at which AP was added to the culture. AP was suppressive if added in the first 48 h of the 7-day culture, and the suppression could not be reversed by washing the cells after the exposure to AP. The mechanism of AP-induced immunosuppression is still unclear, but human SAP circulates as a pair of pentameric rings, having ten identical subunits that bind to galactose polymers, and our present data suggest that AP affects the immune response through its properties as a lectin.

A rapid and sensitive assay for neuraminidase using peanut lectin hemagglutination: application to Vibrio cholera and Trypanosoma cruzi

A neuraminidase assay based on peanut lectin agglutination is described. Human red blood cells are used both as substrate for the enzyme and as probe for the lectin. The validity of the method is ascertained by measuring the enzyme and lectin activities on erythrocytes whose outer membrane sialic acid was labeled with tritium after oxidation with sodium periodate followed by reduction with sodium borotritiide. The neuraminidases of Trypanosoma cruzi and Vibrio cholera are used as examples; in both cases, a linear relationship is observed between the degree of erythrocyte desialylation and the peanut hemagglutination titer. For the hemagglutination assay, lectin in homogeneous form as well as in crude peanut extracts may be used, and free sialic acid need not be separated from substrate-bound sialic acid. The hemagglutinating activity of peanut lectin is not affected by pre-treatment of the erythrocytes with various proteases. The method is particularly useful in the neuraminidase analysis of multiple samples, such as in gel filtration chromatography and for screening of hybridoma antibodies against neuraminidase.

The occurrence of N-acetyl- and N-glycoloylneuraminic acid in Trypanosoma cruzi

Different strain of Trypanosoma cruzi were analysed to have 65--105 micrograms of sialic acids per 10(10) cells. By thin-layer chromatography, and in part by gas liquid chromatography and gas-liquid chromatography-mass spectrometry, all strains were found to contain N-acetyl- and N-glycoloylneuraminic acid in various ratios. After incubation of the parasites with either [3H]acetate or N-acetyl-[3H]mannosamine, no radioactivity was found in the sialic acids, thus leading to the suggestion that the parasites are unable to synthesize sialic acids from their precursors.

A developmentally regulated neuraminidase activity in Trypanosoma cruzi

The human pathogen Trypanosoma cruzi (Y strain) contains a neuraminidase activity that varies widely in the different developmental stages of the parasite. The specific neuraminidase activity of infective trypomastigotes obtained from tissue culture and from the bloodstream of infected mice is 7 to 15 times higher than that of the acellular culture forms. Amastigotes were devoid of enzyme activity. The enzyme has a pH optimum of 6.0 to 6.5. Live trypanosomes released sialic acid from human erythrocytes and plasma glycoproteins. Several sialyl compounds were hydrolyzed by the parasite, but the best substrate was the protein orosomucoid. Erythrocytes from infected mice with T. cruzi parasitemia were agglutinated by peanut lectin and the hemagglutination titer was correlated with the degree of parasitemia.

Cell surface carbohydrates in Tritrichomonas foetus

The cell surface of Tritrichomonas foetus was characterized by using 18 highly purified lectins with specificities for N-acetyl glucosamine, N-acetyl galactosamine, galactose, mannose, and sialic acid. The specificity of the lectin-induced cell agglutination was verified by inhibition of the agglutination with the specific sugars. By using cytochemical techniques associated with electron microscopy, carbohydrates were detected on the cell surface of T. foetus. The following techniques were used: periodic acid--thiosemicarbazide--silver proteinate, concanavalin A--horseradish peroxidase, and ruthenium red. Anionic sites were detected on the cell surface of the protozoan at pH's 1.8 and 7.2 with the use of colloidal iron hydroxide and cationized ferritin particles, respectively. The binding of colloidal iron particles, as well as the agglutination induced by the lectin from Limulus polyphemus, indicated the presence of sialic acid on the cell surface of T. foetus.

Lectins of distinct specificity in Rhodnius prolixus interact selectively with Trypanosoma cruzi

Lectins of different activities were found in the crop, midgut, and hemolymph of the insect Rhodnius prolixus. These were not specific for N-acetyl-D-mannosamine, alpha-N-acetyl-D-galactosamine, and alpha- and beta-galactose, respectively. Lectin receptors were detectable in epimastigote but not in trypomastigote forms of Trypanosoma cruzi, a protozoan parasite of the insect and of humans.

Lectin receptors as markers for Trypanosoma cruzi. Developmental stages and a study of the interaction of wheat germ agglutinin with sialic acid residues on epimastigote cells

Trypanosoma cruzi at various stages of maturation and differentiation have been isolated by conventional cellular fractionation procedures and characterized by cell surface markers using 30 highly purified lectins encompassing all known sugar specificities. Cell surface carbohydrates of the various T. cruzi stages were analyzed by agglutination and lectin-binding assays. Specific receptors for wheat germ agglutinin (WGA), Helix pomatia, Sophora japonica, and Bandeiraea simplicifolia lectin II were found only in culture epimastigotes, whereas peanut agglutinin (PNA) sites were present exclusively in amastigotes, those for Phaseolus vulgaris in bloodstream trypomastigotes and amastigotes, and for Wistaria floribunda hemagglutinin predominantly in culture forms of T. cruzi. The N-acetylgalactosamine (DGalNAc)-binding lectin from Bauhinia purpurea agglutinated and inhibited the movement of epimastigotes and bloodstream trypomastigotes, but it only inhibited--without agglutinating--culture trypomastigotes. Because both the agglutination and inhibition of movement were reversed by specific sugar haptens, Bauhinia purpurea sites were present in all the flagellated parasites. On the other hand, PNA sites were detectable on epimastigotes after the cells were treated with sialidase, whereas, at the same time, WGA receptors were completely removed and those for the other sialic acid-binding proteins, Aaptos papillata lectin II and Limulus polyphemus, were partially eliminated; moreover, the activity of Wistaria floribunda hemagglutinin, a DGalNAc-binding lectin, increased 4,000 times. Trypsinization and lyzozyme treatment of epimastigote cells did not significantly affect lectin agglutination or lectin binding. WGA reacted solely with sialic acid residues on epimastigote cell surface with an apparent association constant of 2 x 10(6) M-1, each epimastigote having an estimated average of 3 x 10(6) WGA sites, as determined by binding experiments and a minimum of 7.7 x 10(6) sialic acid residues, as calculated by colorimetric method after sialidase digestion. Evidences are presented that the sialyl residues are rapidly regenerated (in approximately 4 h) and that they, at least for the most part, are not adsorbed from the culture medium. The receptor for the D-mannose-binding lectins (concanavalin A [Con A] and Lens culinaris) must either be on the same carbohydrate moiety having the WGA site, or, if in a distinct molecule, both carrier molecules of Con A and WGA sites must be located close to each other in the plasma membrane of the parasite.

A versatile immunoadsorbent capable of binding lectins of various specificities and its use for the separation of cell populations

A procedure for cell fractionation using lectin-affinity chromatography is described. It consists of a single affinity adsorbent, hog gastric mucin blood group A+H substance covalently coupled to Sephadex or Sepharose, to which lectins of various specificities can bind. The complex formed, lectin in equilibrium hog A+H substance-Sephadex, then serves as an affinity probe for isolating and fractionating cells. The lectins from Ulex europaeus, Lotus tetragonolobus, Helix pomatia, Dolichos biflorus, and Phaseolus lunatus were used with the same blood group substance as adsorbent. The affinity columns retained erythrocytes with blood group specificity for the adsorbed lectin and thus fractionate cells in mixtures. Cells as well as lectins are eluted by specific sugar inhibitors. Mixtures of two kinds of cells can be separated when the proportion of the adsorbed cells is not too low.