Synthetic studies on glycosphingolipids from Protostomia phyla: synthesis of amphoteric glycolipid analogues containing a phosphocholine residue from the earthworm Pheretima hilgendorfi

Two kinds of amphoteric glycosphingolipid analogues from the earthworm Pheretima hilgendorfi were synthesized as follows: The key reaction is a coupling of a phosphocholine group at the position C-6 of 1 and 6 which was attempted using 2-chloro-2-oxo-1,3,2-dioxaphospholane, followed by reaction of the resulting cyclic phosphate intermediate with anhydrous trimethylamine to give 2 and 7. Subsequent debenzylation afforded target compounds (3, 8). Their ability to inhibit the histamine release in vitro was examined.

Effect of Leishmania donovani lipophosphoglycan on ornithine decarboxylase activity in macrophages

Lipophosphoglycan (LPG), a major surface molecule from Leishmania donovani, stimulated ornithine decarboxylase (ODC) activity in macrophages in a dose- and time-dependent manner. LPG stimulated the rapid increase in ODC activity within 30 min after exposure, suggesting that the interaction of LPG with its receptor stimulated a specific signal transduction pathway. However, LPG-induced ODC activity was a transient event because 3 hr after exposure to LPG, no stimulation of ODC activity was detectable. ODC activity appeared to be coupled to the activation of protein kinase C (PKC) in macrophages, as activators of PKC caused a rapid increase in the ODC activity. Macrophages pretreated with LPG for 1 hr became unresponsive to subsequent stimulation by the PKC activators 1-oleoyl-2-acetyl-glycerol and the calcium ionophore A23187. In contrast, the ability of macrophages to express ODC activity in response to the cyclic AMP analogue dibutyryl cyclic AMP was not impaired by LPG.

Glycolipids support E-selectin-specific strong cell tethering under flow

This study provides functional evidence that glycosphingolipids constitute ligands for E-selectin but not P-selectin. Chinese hamster ovary (CHO) cells expressing E-selectin (CHO-E) or P-selectin (CHO-P) were perfused over alpha2,3-sialyl Lewis X (alpha2,3-sLe(x)) presented as the hexaosylceramide glycosphingolipid adsorbed in a monolayer containing phosphatidylcholine and cholesterol. CHO-E cells tethered extensively and formed slow, stable rolling interactions with alpha2,3-sLe(x) glycosphingolipid but not with the comparable alpha2,6-sLe(x) glycosphingolipid. Tethering/rolling varied with wall shear stress, selectin density, and ligand density. In contrast, alpha2,3-sLe(x) glycosphingolipid supported only limited, fast CHO-P cell rolling. As calculated from a stochastic model of cell rolling, the step size between successive bond releases from the alpha2,3-sLe(x) glycosphingolipid was smaller for CHO-E than CHO-P cells, whereas the opposite effect was observed for the waiting time between these events. Detachment assays revealed stronger adhesive interactions of CHO-E than CHO-P cells with alpha2,3-sLe(x) glycosphingolipid. These findings indicate that glycosphingolipids expressing an appropriate oligosaccharide mediate cell tethering/rolling via E-selectin but not P-selectin.

Inhibition of HIV-1-mediated syncytium formation and virus replication by the lipophosphoglycan from Leishmania donovani is due to an effect on early events in the virus life cycle

Previous findings have indicated that the major surface molecule of Leishmania, lipophosphoglycan (LPG), could abrogate HIV-1-induced syncytium formation and virus replication. In the present work, we were interested in characterizing this inhibitory process. Data from a new luciferase-based semiquantitative assay for syncytium formation, relying on the coincubation of a T-cell line containing an HIV-1 LTR-driven luciferase construct with a cell line chronically infected with HIV-1, confirmed that LPG was indeed a strong inhibitor of HIV-1-dependent syncytium formation and that this inhibition was dose-dependent. As determined by flow cytometric analyses, this inhibition was not apparently due to downregulation of CD4, CXCR4 or LFA-1, three distinct surface glycoproteins known to be important in HIV-1 mediated syncytium formation. Furthermore, LPG did not seem to affect signal transduction pathways in T cells as judged by measurement of HIV-1 LTR-driven reporter gene activity upon treatment with different stimuli. However, pretreatment of either of the cell lines used in the assay with LPG led to a significant decrease of virus-mediated syncytium formation, which was further accentuated when both cell lines were pretreated. LPG inhibition of HIV-1 replication was next assessed. When measuring either infection with luciferase-encoding recombinant HIV-1 particles or multinucleated giant cell formation following an acute virus infection, we again observed that LPG was efficient at blocking HIV-1 replication. Specific assays probing different steps of viral entry demonstrated that attachment was not hindered by LPG but that viral entry was modulated, suggesting that LPG targets a postbinding step. Hence, incorporation of LPG into a target cell membrane could influence its fluidity and diminish both the virus-cell and cell-to-cell fusion processes initiated by HIV-1.

Bovine trichomoniasis as a model for development of vaccines against sexually-transmitted disease

PROBLEM

Human sexually transmitted diseases (STDs) are widespread but effective vaccines are rare. Experimental and commercially available vaccines for bovine trichomoniasis have been well studied. Principles for immune protection of the female genital tract derived from studies of bovine trichomoniasis may be generally applicable to human trichomoniasis and other STDs.

METHOD OF STUDY

A bovine model of trichomoniasis has been developed for study of mechanisms of immunoprophylaxis.

RESULTS

Both systemic and local immunization with an immunoaffinity purified antigen cleared the genital tract of trichomonads significantly earlier than non-immunized controls. Predominantly IgA responses or predominantly IgG responses in uterine and vaginal secretions were essentially equally protective. Uterine and vaginal IgA responses could be induced by systemic priming and local boosting via either the vaginal or nasal mucosa. In either case, lymphoid aggregates were formed in the uterine and vaginal mucosa which were not present in the genital mucosa of naïve animals.

CONCLUSIONS

Systemic immunization or systemic priming with local boosting protects against bovine trichomoniasis via IgG or IgA antibodies (respectively) to a major surface antigen of trichomonads. Immunization of the genital mucosa results in formation of inductive sites for a local IgA response.

Anti-metastatic effect of the sialyl Lewis-X analog GSC-150 on the human colon carcinoma derived cell line KM12-HX in the mouse

We investigated the inhibitory effect of the sialyl Lewis-X (sLeX) analog, GSC-150, on hepatic metastasis of the human colon carcinoma derived cell line, KM12-HX, which highly expresses sLeX antigen on the cell surface. The number of cancer nodules found in BALB/c nude mouse liver 6 weeks after intrasplenic injection of KM12-HX cells was significantly reduced by co-administration of GSC-150. The amount of [3H]thymidine-labeled KM12-HX cells distributed in liver was also significantly reduced by GSC-150 co-administration in lipopolysaccharide (LPS)-treated mice at 48 h after administration of the tumor cells, while GSC-150 did not reduce the amount of HX cells distributed at 30 min. Considering our previous report that the initial phase of the distribution of KM12-HX cells in liver is governed by their being trapped in the hepatic microvessels because of their large size (Mizuno et al., J. Hepatol., 28, 865-877, 1998), these results suggest that GSC-150 does not inhibit this first-pass trapping by microvessels, but inhibits the subsequent process which is more directly related to final metastasis. GSC-150 inhibited the adhesion of KM12-HX cells to tumor necrosis factor-alpha (TNF-alpha)-activated human umbilical vein endothelial cells (HUVECs). These findings imply that the anti-metastatic effect of GSC-150 in vivo could be explained by its inhibition of cell-cell interactions between cancer and host cells.

Impairment of Leishmania mexicana phagocytosis in peritoneal macrophages induced by Amaranthus leucocarpus lectin

The lectin from Amaranthus leucocarpus (ALL) is specific for N-acetyl-D-galactosamine and inhibits phagocytosis of Leishmania mexicana promastigotes in Balb/c mice peritoneal macrophages by 38%. The lipophosphoglycan (LPG) purified from L. mexicana inhibits penetration of promastigotes into peritoneal macrophages by 31%; interestingly, treatment of macrophages with both, ALL and LPG, inhibits phagocytosis of promastigotes by 72%, confirming that ALL induces modification of the macrophage's phagocytic activity by a different route than mannose or C3b receptors. The Inhibitory effect of ALL was time-dependent. N-acetyl-D-galactosamine (GalNAc) or O-glycosidically linked glycoproteins modified macrophage phagocytosis of Leishmania. These results suggest that macrophage membrane glycoproteins, possessing constitutive GalNAc, can influence the signaling pathways used by this intracellular parasite to infect.

Purification and structure of neurostatin, an inhibitor of astrocyte division of mammalian brain

Neurostatin was originally described as an inhibitor of astroblast and astrocytoma division present in rat brain extracts and immunologically related to the sugar moiety of epidermal growth factor receptor and to blood group antigens. It was purified recently from mammalian brain extracts and characterized as a glycosphingolipid, but its precise structure remained unknown. Neurostatin has now been purified to apparent homogeneity from ganglioside extracts of rat, bovine, and porcine brain. It is cytostatic for astroblasts, C6 glioma cells, and various human astrocytomas grades III and IV, with IC(50) values ranging from 250 to 450 nM, but does not affect the division of primary or transformed fibroblasts up to concentrations >4 microM. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry of purified pig neurostatin showed a molecular ion of 1, 905 Da and ions of 1,863 and 1,934 Da, compatible with a disialoganglioside. Mono- and bidimensional NMR spectra, together with biochemical studies, suggest that neurostatin may be the 9-O-monoacetyl ester of GD1b.

Effect of synthetic sialyl 2-->1 sphingosine and other glycosylsphingosines on the structure and function of the "glycosphingolipid signaling domain (GSD)" in mouse melanoma B16 cells

Mouse melanoma B16 cells are characterized by a high concentration of GM3 ganglioside, which has been identified as a melanoma-associated antigen and is present as a clustered microdomain organized with major signal transducers, c-Src, small G-protein (Rho A), and focal adhesion kinase (FAK), to form a "glycosphingolipid signaling domain" or "glycosignaling domain" (GSD) separable from cholesterol- and caveolin-enriched microdomain, "caveolae." Cholesterol-binding reagents, filipin and nystatin, disrupt the structure and function of caveolae, but have no effect on GSD function [Iwabuchi, K., et al. (1998) J. Biol. Chem. 273, 33766-33773]. In this study, we searched for compounds which disrupt the structure and function of GSD in B16 cells. Such compounds should have structural features analogous to those of GM3, destroy or reduce clustering of GM3 in GSD, and inhibit GM3-dependent adhesion and signaling. The simplest compound so far found with these properties is sialyl alpha2-->1 sphingosine (Sph). We describe the synthesis of this compound and its analogues, and their effects on GM3 expression pattern and GSD function, in comparison with effects of lyso-GM3 and other lyso compounds, in B16 cells. Incubation of B16 cells with 0.5-10 microM sialyl alpha2-->1 Sph or 1-5 microM lyso-GM3 reduced GM3 clustering and GM3-dependent adhesion, and inhibited adhesion-dependent cellular FAK activity. The c-Src activation response of GSD isolated from B16 cells was inhibited strongly by sialyl alpha2-->1 Sph. Substitution of the Sph amino group with a chloroacetyl or N,N-dimethyl group strongly reduced the inhibitory effect of sialyl alpha2-->1 Sph on GM3-dependent adhesion, FAK, and c-Src response. Other lyso compounds such as lyso-phosphatidylcholine, galactosyl-Sph (psychosine), and lactosyl-Sph at 0.5-10 microM did not show the same effect as sialyl alpha2-->1 Sph. Thus, adhesion coupled with signal transduction, initiated by clusters of GM3 in GSD, is blocked by sialyl alpha2-->1 Sph or lyso-GM3. Analogues with N-substitution of Sph in sialyl alpha2-->1 Sph, other lyso-phospholipids, and galactosyl- or lactosyl-Sph did not block such adhesion, coupled with activation of c-Src and FAK.

Inhibition of interferon-gamma signaling by Leishmania donovani

Leishmania infection causes marked down-regulation of interferon (IFN)-gamma-induced gene activity in macrophages, but the mechanism of the blockade has not been fully defined. The IFN-gamma signal transduction pathway was analyzed in Leishmania donovani-infected phorbol-differentiated U937 human promonocytic cells. IFN-gamma stimulation induced marked phosphorylation of its own receptor (IFN-gammaR)-alpha chain. Phosphorylation of the receptor subunit was significantly inhibited after 24 h of infection with the parasite, apparently because of decreased amounts of the receptor subunit. Formation of the IFN-gammaR complex, as assessed by tyrosine phosphorylation and association of Jak2, was strongly inhibited in cells infected for 24 h. Inhibition of the IFN-gammaR complex formation correlated with inhibition of STAT1alpha binding to the IFN-gamma response region. Pretreatment with purified parasite lipophosphoglycan before IFN-gamma stimulation had no effect on tyrosine phosphorylation. Thus, inhibition of tyrosine phosphorylation of the IFN-gammaR-alpha chain and subsequent signal transduction are most likely due to the decreased amount of IFN-gammaR-alpha protein after infection.

Extracellular signal-related kinase (ERK) and p38 mitogen-activated protein (MAP) kinases differentially regulate the lipopolysaccharide-mediated induction of inducible nitric oxide synthase and IL-12 in macrophages: Leishmania phosphoglycans subvert macrophage IL-12 production by targeting ERK MAP kinase

Macrophage activation by cytokines or microbial products such as LPS results in the induction and release of several key immune effector molecules including NO and IL-12. These have been shown to play crucial roles in the development of immunity to intracellular pathogens such as Leishmania. The molecular mechanisms underlying the induction of these effector molecules are not fully understood. We now show that the extracellular signal-related kinase (ERK) and p38 mitogen-activated protein (MAP) kinases play differential roles in the regulation of LPS-stimulated inducible NO synthase and IL-12 gene expression. In macrophages, LPS stimulates the simultaneous activation of all three classes of MAP kinases, ERK, c-jun N-terminal kinase, and p38, albeit with differential activation kinetics. However, studies using inhibitors selective for ERK (PD98059) and p38 (SB203580) show that while p38 plays an essential role in the induction of inducible NO synthase, ERK MAP kinases play only a minor role in promoting NO generation. In contrast, while p38 promotes induction of IL-12 (p40) mRNA, ERK activation suppresses LPS-mediated IL-12 transcription. The biological relevance of these regulatory signals is demonstrated by our finding that Leishmania lipophosphoglycans, which promote parasite survival, act by stimulating ERK MAP kinase to inhibit macrophage IL-12 production. Thus, as ERK and p38 MAP kinases differentially regulate the induction of the macrophage effector molecules, inducible NO synthase and IL-12, these kinases are potential targets not only for the development of novel strategies to combat intracellular pathogens but also for therapeutic immunomodulation.

Adversarial relationship between the leishmania lipophosphoglycan and protein kinase C of host macrophages

The dominant glycoconjugate on the cell surface of all Leishmania promastigotes is an unusual glycoconjugate named lipophosphoglycan (LPG). Its relative abundance, unique structure, and cellular location have implicated LPG as an essential virulence determinant. One feature of LPG resides in its strong inhibitory effect on the activity of protein kinase C (PKC) of host macrophages. This article summarizes the evidence that LPG is inhibitory toward PKC activation in macrophages and discusses the implication of such inhibition on intramacrophage survival of the parasite.

Role of Leishmania donovani and its lipophosphoglycan in CD4+ T-cell activation-induced human immunodeficiency virus replication

Chronic immune activation by coinfecting pathogens has been suggested as a cofactor in human immunodeficiency virus (HIV) disease progression, particularly in the setting of developing countries. Here, we used in vivo-infected mononuclear cells to examine the role of the protozoan parasite Leishmania donovani and its major membrane constituent, lipophosphoglycan (LPG), in mediating CD4+ T-lymphocyte activation-induced HIV replication and CD4+ T-cell death. We found that Leishmania antigens upregulated HIV replication in CD8-depleted peripheral blood mononuclear cells from asymptomatic HIV-infected donors compared to unstimulated cells. L. donovani-induced viral replication was associated with cellular proliferation, increased expression of the cellular immune activation markers CD25 and HLA-DR within the CD4+ subpopulation, and enhanced secretion of tumor necrosis factor alpha (TNF-alpha), interleukin 2 (IL-2), and IL-6. LPG induced TNF-alpha secretion in the absence of increased expression of cellular activation markers. Moreover, in a few cases we observed that L. donovani induced HIV replication without significant cellular activation but with cytokine secretion. The rate of apoptosis was accelerated in these latently infected CD4+ T cells primed with Leishmania antigens compared to controls, and TNF-alpha production appeared to be the central event necessary for this effect. Furthermore, we demonstrate that thalidomide inhibited Leishmania-induced virus replication coupled with abrogated Leishmania-induced TNF-alpha secretion but not IL-2 or IL-6 production. Furthermore, thalidomide did not affect Leishmania-induced apoptosis. The results suggest that Leishmania and its product, LPG, up-regulate HIV replication in latently infected cells through distinct antigen-specific and non-antigen-specific cellular immune activation mechanisms and that TNF-alpha secretion is pivotal in this process. The immunomodulatory role of thalidomide raises interest as a potential adjuvant to reduce HIV disease progression in Leishmania-HIV coinfected individuals.

Sialic acid-containing components of lipoproteins influence lipoprotein-proteoglycan interactions

Sialic acid is a negatively charged sugar associated with the protein and lipid portions of lipoproteins. Sialic acid has been hypothesised to play an anti-atherogenic role in lipoprotein metabolism through the electrostatic inhibition of lipoprotein interactions with chondroitin-6-sulphate-rich arterial proteoglycans (APG). We conducted a series of studies using native and modified lipoproteins (VLDL1 Sf 60-400, VLDL2 Sf 20-60, IDL1 Sf 16-20, IDL2 Sf 12-16, LDL(A) Sf 8-12, and LDL(B) Sf0-8) that vary in their sialic acid content to examine the relationship between lipoprotein sialic acid content and its interaction with APG. Lipoprotein sialic acid was greatest in VLDL1 and decreased progressively with particle density until the IDL2 fraction (VLDL1 > VLDL2 > IDL1 > IDL2 = LDL(A) = LDL(B)). The pattern of reactivity of each fraction with APG was different from the pattern observed for lipoprotein sialic acid content (IDL2 > LDL(A) > LDL(B) > IDL1 > VLDL2 > VLDL1). Levels of sialic acid were lower in subjects with CHD as compared to control subjects but the presence of CHD had no effect on lipoprotein-APG complex formation when sex and plasma triglyceride levels were taken into account. There was also no significant relationship between the lipoprotein sialic acid content and the reactivity with APG within each lipoprotein fraction. Treatment of hypertriglyceridaemic subjects with ciprofibrate decreased lipoprotein-APG complex formation in all lipoprotein fractions. This was associated with a decrease in the total sialic acid content of apo B100-containing lipoproteins suggesting that the total sialic acid content of apo B100-containing lipoproteins has no influence on lipoprotein-APG complex formation. We next conducted in vitro experiments to manipulate LDL sialic acid content. Enzymatic removal of sialic acid from LDL with neuraminidase resulted in an increase in LDL-APG complex formation. This was accompanied by an increase in the exposure of free amino groups on LDL possibly due to disruption of interactions between free amino groups and sialic acid-containing components on LDL. Increasing LDL sialic acid content through incubation with ganglioside resulted in a decrease in lipoprotein-APG complex formation without any changes in the exposure of free amino groups on LDL. We conclude that total sialic acid content of lipoproteins is not a major determinant of their binding to APG. However, specific sialic acid-containing components on lipoproteins can affect their interaction with APG.

Adhesion of Tritrichomonas foetus to bovine vaginal epithelial cells

An in vitro culture system of bovine vaginal epithelial cells (BVECs) was developed to study the cytopathogenic effects of Tritrichomonas foetus and the role of lipophosphoglycan (LPG)-like cell surface glycoconjugates in adhesion of parasites to host cells. Exposure of BVEC monolayers to T. foetus resulted in extensive damage of monolayers. Host cell disruption was measured quantitatively by a trypan blue exclusion assay and by release of (3)H from [(3)H]thymidine-labeled host cells. Results indicated contact-dependent cytotoxicity of host cells by T. foetus. The cytopathogenic effect was a function of T. foetus density. Metronidazole- or periodate-treated T. foetus showed no damage to BVEC monolayers. A related human trichomonad, Trichomonas vaginalis, showed no cytotoxic effects, indicating species-specific host-parasite interactions. A direct binding assay was developed and used to investigate the role of a major cell surface LPG-like molecule in host-parasite adhesion. The results of competition experiments showed that the binding to BVECs was displaceable, was saturable, and yielded a typical binding curve, suggesting that specific receptor-ligand interactions mediate the attachment of T. foetus to BVECs. Progesterone-treated BVECs showed enhanced parasite binding. T. foetus LPG inhibited the binding of T. foetus to BVECs; the LPG from T. vaginalis and a variety of other glycoconjugates did not. These data imply specificity of LPG on host-parasite adhesion. Periodate-treated parasites showed no adherence to host cells, indicating the involvement of carbohydrate containing molecules in the adhesion process.

Tenascin-C inhibits beta1 integrin-dependent cell adhesion and neurite outgrowth on fibronectin by a disialoganglioside-mediated signaling mechanism

We have previously shown that the extracellular matrix molecule tenascin-C inhibits fibronectin-mediated cell adhesion and neurite outgrowth by an interaction with a cellular RGD-independent receptor which interferes with the adhesion and neurite outgrowth promoting activities of the fibronectin receptor(s). Here we demonstrate that the inhibitory effect of tenascin-C on beta1integrin-dependent cell adhesion and neurite outgrowth is mediated by the interaction of the protein with membrane-associated disialogangliosides, which interferes with protein kinase C-related signaling pathways. First, in substratum mixtures with fibronectin, an RGD sequence-containing fragment of the molecule or synthetic peptide, tenascin-C inhibited cell adhesion and spreading by a disialoganglioside-dependent, sialidase-sensitive mechanism leading to an inhibition of protein kinase C. Second, the interaction of intact or trypsinized, i.e., cell surface glycoprotein-free, cells with immobilized tenascin-C was strongly inhibited by gangliosides or antibodies to gangliosides and tenascin-C. Third, preincubation of immobilized tenascin-C with soluble disialogangliosides resulted in a delayed cell detachment as a function of time. Similar to tenascin-C, immobilized antibody to GD2 (3F8) or sphingosine, a protein kinase C inhibitor, strongly inhibited RGD-dependent cell spreading. Finally, the degree of tenascin-C-induced inhibition of cell adhesion was proportional to the degree of disialoganglioside levels of expression by different cells suggesting the relevance of such mechanism in modulating integrin-mediated cell-matrix interactions during pattern formation or tumor progression.

Effect of lacto-N-neotetraose, asialoganglioside-GM1 and neuraminidase on adherence of otitis media-associated serotypes of Streptococcus pneumoniae to chinchilla tracheal epithelium

The adherence of Streptococcus pneumoniae (Spn) otitis media-associated serotypes 3, 6A and 14 to ciliated chinchilla respiratory epithelium was investigated using a whole organ perfusion technique. We demonstrated that Spn adhere to chinchilla tracheal epithelium within 30 min and exhibit saturation kinetics indicating that the effect being observed is receptor mediated. Inhibition of adherence was achieved by prior incubation of Spn with lacto-N-neotetraose (LNnT) or asialoIganglioside GM1 (aGM1), recognized by glycoconjugate analogs of known Spn receptors. NeurIaminidase treatment of the tracheae increased Spn adherence in vitro and reversed the inhibition effect of LNnT suggesting that neuraminidase treatment resulted in an increase in the number of available receptors for Spn. The chinchilla trachea organ perfusion culture system used in this study imitates eustachian tube conditions more closely than isolated cell culture systems and is a useful model for investigating the role of Spn adherence in vitro in the pathogenesis of OM.

Accelerated transport and maturation of lysosomal alpha-galactosidase A in Fabry lymphoblasts by an enzyme inhibitor

Fabry disease is a disorder of glycosphingolipid metabolism caused by deficiency of lysosomal alpha-galactosidase A (alpha-Gal A), resulting in renal failure along with premature myocardial infarction and strokes. No effective treatment of this disorder is available at present. Studies of residual activities of mutant enzymes in many Fabry patients showed that some of them had kinetic properties similar to those for normal alpha-Gal A, but were significantly less stable, especially in conditions of neutral pH (refs. 3-5). The biosynthetic processing was delayed in cultured fibroblasts of a Fabry patient, and the mutant protein formed an aggregate in endoplasmic reticulum, indicating that the enzyme deficiency in some mutants was mainly caused by abortive exit from the endoplasmic reticulum, leading to excessive degradation of the enzyme. We report here that 1-deoxy-galactonojirimycin (DGJ), a potent competitive inhibitor of alpha-Gal A, effectively enhanced alpha-Gal A activity in Fabry lymphoblasts, when administrated at concentrations lower than that usually required for intracellular inhibition of the enzyme. DGJ seemed to accelerate transport and maturation of the mutant enzyme. Oral administration of DGJ to transgenic mice overexpressing a mutant alpha-Gal A substantially elevated the enzyme activity in some organs. We propose a new molecular therapeutic strategy for genetic metabolic diseases of administering competitive inhibitors as 'chemical chaperons' at sub-inhibitory intracellular concentrations.

Fusion of Sendai virus and individual host cells and inhibition of fusion by lipophosphoglycan measured with image correlation spectroscopy

Fusion between Sendai virus (SV) and individual host cells was investigated with confocal laser scanning microscopy (CLSM) and image correlation spectroscopy (ICS). SV was labeled with the fluorescent probe 7-octadecylamino-4-nitrobenz-2-oxa-1,3-diazole (NBD-NH-C18) and was allowed to bind to host cells (HEp-2, BALB-3T3) at 4 degrees C. The effect of lipophosphoglycan (LPG), isolated from Leishmania donovani, on virus fusion was investigated by incorporation of LPG (0, 5, 10 or 20 microM) into the host cell membrane (HEp-2) before addition of SV. LPG did not affect the number of SV bound per cell. After incubation at 37 degrees C for 15 min without LPG, CLSM revealed a redistribution of NBD-NH-C18 from the SV envelope to the host cell membrane and an increase in average fluorescence intensity, indicating dequenching. ICS analysis of images obtained after incubation at 37 degrees C showed an increased mean cluster density to 260% of the value at 4 degrees C, reflecting the disappearance of labeled SV from the cell surface and diffusion of NBD-NH-C18 into the host cell membrane. Preincubation of the cells with LPG inhibited the temperature-induced redistribution and dequenching of NBD-NH-C18 in a concentration-dependent manner, with a total inhibition of fusion at 20 microM LPG. Together, the results demonstrate that CLSM combined with ICS is a powerful tool for studies of fusion of enveloped viruses with individual host cells and that LPG inhibits the fusion process at or before the hemifusion (lipid mixing) stage of SV interaction with cells.

Control of glial number: purification from mammalian brain extracts of an inhibitor of astrocyte division

Inhibitors of astrocyte cell division, immunologically related to the sugar moiety of epidermal growth factor receptor and to blood group antigens, have been purified from mammalian brain extracts. Mass spectra, high resolution proton magnetic resonance spectra, and chemical and enzymic analysis of the purified fraction indicated that the compounds isolated were glycosphingolipids, although signals compatible with the presence of aminoacid residues were also observed. Lectin binding indicated the presence of NAc-Neuraminic acid, NAc-glucosamine, fucose, galactose, and glucose. The inhibitor was cytostatic for astrocytes, C6 glioma cells, and endothelial cells, with approximate ID50 of 250 nM. Primary cultures of fibroblasts or 3T3 cells were not affected up to concentrations of 800 nM. Concentrations of the inhibitor of 800 nM or higher, caused non-specific cytotoxicity. The biological and immunological properties of this brain inhibitor were identical to those of the EGF receptor-related inhibitor previously described with the acronym ERI. Because of its source and cytostatic action, the glial inhibitor has been renamed neurostatin. Rabbit antibodies to neurostatin immunostained astrocytes and neurons, both in culture and in tissue sections.

The lipophosphoglycan of Leishmania donovani up-regulates HIV-1 transcription in T cells through the nuclear factor-kappaB elements

We have recently demonstrated that the parasite Leishmania donovani and its surface molecule, lipophosphoglycan (LPG), can activate HIV-1 replication in monocytoid cells. Our present interest was to determine whether LPG could also up-regulate HIV-1 transcription in T cells. Using a CD4-positive human lymphoid T cell line (1G5) containing a stably integrated HIV-1 long terminal repeat (LTR)-luciferase construct, we found that LPG is a potent inducer of HIV-1 LTR activity. Treatment of 1G5 cells with signaling antagonists revealed that protein tyrosine kinase- and protein kinase A-dependent pathways were actively participating in the LPG-induced enhancement of HIV-1 LTR-driven activity. Transfection of Jurkat E6.1 cells with plasmids containing wild-type and nuclear factor-kappaB (NF-kappaB)-mutated HIV-1 LTR-luciferase constructs has suggested a role for NF-kappaB binding sites in the LPG-mediated induction of HIV-1 LTR activity. An LPG-induced binding factor specific to the NF-kappaB consensus sequences could be observed using electrophoretic mobility shift assay. Finally, transfection experiments performed with a vector containing HIV-1 kappaB binding sites only showed similar LPG-mediated induction, which was abrogated by sodium salicylate, a known NF-kappaB inhibitor. We thus demonstrate that the LPG-mediated induction of HIV-1 LTR activity in T cells involves several second messengers culminating in activation of HIV-1 LTR-driven transcription via NF-kappaB-binding consensus sequences. In conclusion, these results reinforce the idea that L. donovani is a putative cofactor in HIV-1 pathogenesis.

A streptavidin-based neoglycoprotein carrying more than 140 GT1b oligosaccharides: quantitative estimation of the binding specificity of murine sialoadhesin expressed on CHO cells

We prepared a streptavidin-based neoglycoprotein which carries more than 140 GT1b oligosaccharides. GT1b oligosaccharides were covalently coupled to streptavidin by reductive amination, yielding a monomer form of streptavidin carrying 13 oligosaccharides. The monomer form of glycosylated streptavidin was polymerized with biotinylated-bovine serum albumin, which yielded a polymer carrying more than 140 oligosaccharides. Both the monomer and the polymer bound to Chinese hamster ovary cells expressing murine sialoadhesin. The relative binding potencies determined with the polymer, monomer, and free GT1b oligosaccharides were 3,500, 83, and 1, respectively, indicating that an increase in the number of oligosaccharide ligands is critical for high avidity. The high avidity of the polymer enabled us to develop a sensitive and quantitative binding assay, and the assay was applied to characterization of the binding specificity of sialoadhesin. The polymer binding was inhibited by various gangliosides, the order of the inhibitory potencies being GM3 (IC50 = 40 microM) > GD1a (100 microM) > sialylparagloboside (120 microM) > GT1b (310 microM) > GM2 (640 microM) > GM4 (2,100 microM) > GD1b>LacCer = GM1 = paragloboside (no inhibition). These results indicate that the binding specificity is comparable to that reported, i.e. the determinant structure is NeuAcalpha2-3Galbeta1-linked to either 3GalNAc, 3(4)GlcNAc, or 4Glc, and that the oligosaccharide structure on the polymer is properly presented to sialoadhesin on the cell surface. To determine the precise requirement of the NeuAc structure for binding, NeuAc of GM3 was converted into various derivatives, the inhibitory potencies of which were examined; i.e. GM3 containing NeuAc, IC50 = 40 microM; C7- or C8-aldehyde, 500 microM; C7- or C8-alcohol, 700 microM; C1-alcohol, 2,000 microM; C1-amide, 2,200 microM; and NeuGc,>3,000 microM. These results confirmed the requirement of the hydroxyl group at C9 and/or C8, the carboxyl group at C1, and the methyl group of the N-acetyl residue of NeuAc in a quantitative manner. Thus, this streptavidin-based neoglycoprotein is a useful multivalent glycoprobe, which exhibits high affinity and specificity to murine sialoadhesin on the cell surface.

Leishmania lipophosphoglycan reduces monocyte transendothelial migration: modulation of cell adhesion molecules, intercellular junctional proteins, and chemoattractants

We previously identified the structural requirement for the inhibitory activity of Leishmania lipophosphoglycan (LPG) to block endothelial adhesion to monocytes. Here we showed that LPG reduces transendothelial migration of monocytes. LPG pretreatment of endothelial cells (2 microM, 1 h) reduced monocyte migration across endothelial cells activated by bacterial endotoxin (LPS) or IL-1beta (60 and 46%, respectively). A fragment of LPG (i.e., repeating phosphodisaccharide (consisting of galactosyl-mannose)) and LPG coincubated with LPG-neutralizing mAb lacks inhibitory activity on monocyte migration. Pretreatment of monocytes with LPG (2 microM, 1 h) also did not affect monocyte migration through control or LPS-activated endothelial cells. FACS analysis reveals that LPG treatment blocked the LPS-mediated expression of E-selectin, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 on endothelial cells and monocyte adhesion without altering the integrity of the endothelial monolayer. LPG (2 microM, 1 h) alone was capable of altering the expression and distribution of two junctional adhesion molecules, CD31 and vascular endothelium cadherin, as well as reversing the effects of LPS on these proteins. The induction of endothelial cells by LPS to transcribe and release monocyte chemoattractant protein-1 (MCP-1) was significantly reduced by LPG (40-65%). LPG treatment of nonactivated endothelial cells also suppressed by 55 to 75% the monocyte migration triggered by a MCP-1 chemoattractant gradient, and coincubation of LPG with neutralizing mAb abrogated the inhibitory activity. Together, these data point to a novel anti-inflammatory function of LPG in reducing monocyte migration across endothelial cells via a mechanism of inhibition of endothelial expression of cell adhesion molecules, modulation of intercellular junctional proteins, and synthesis of MCP-1.

Preparation of peptides which mimic glycosphingolipids by using phage peptide library and their modulation on beta-galactosidase activity

We describe the use of a phage-displayed random pentadecamer peptide library for searching glycosphingolipid mimicking peptides. Two phage clones (AD-1 and AD-2) were selected by biopanning using monoclonal antibody AD117m, directed to lactotetraosylceramide (Lc4Cer). The amino acid sequences of the selected clones showed high homology (VPPXFXXXY) in 9-mer. Three phage clones were selected by using monoclonal antibody H11, directed to neolactotetraosylceramide (nLc4Cer), the linkage isomer of Lc4Cer, and the displayed amino acid sequences were compared. One of these peptides showed the same amino acid sequence as that of AD-2 except for one amino acid substitution. Pentadecamer, 9-mer and point mutated 9-mer peptides were synthesized on the basis of the displayed amino acid sequences. Binding activity of the peptides to the monoclonal antibodies or Ricinus communis lectin showed that 9-mer peptides are enough to mimic the epitope carbohydrate structure. Furthermore, six of the synthesized peptides inhibited Jack bean beta-galactosidase activity towards nLc4Cer at a high concentration of the enzyme, whereas at lower enzyme concentrations some peptides showed potent activation of the enzyme activity. This is the first report of carbohydrate mimicking peptides which modulate glycosidase activity.

[Development of KRN7000, derived from agelasphin produced by Okinawan sponge]

New glycosphingolipids, named agelasphins, have been isolated as antitumoral compounds from an extract of a marine sponge, Agelas mauritianus. The absolute configurations of agelasphins were elucidated by the total synthesis. Various analogues of agelasphins were also synthesized and the relationship between their structures and biological activities was examined using an MLR assay. From the results, KRN7000, (2S,3S,4R)-1-O-(alpha-D- galactopyranosyl)-2-(N-hexacosanoylamino)-1,3,4-octadecanetriol , was selected as a candidate for clinical application. KRN7000 markedly stimulated lymphocytic proliferation in allogeneic MLR, and showed potent tumor growth inhibitory activities in B16-bearing mice and strongly inhibited tumor metastasis, suggesting that KRN7000 is a potent biological response modifier. These biological effects were exerted by the activation of dendritic cells by KRN7000.