Lethal effect of neutral mannan fraction of bakers' yeast in mice

Characterization and toxicity of a phosphate-binding exobiopolymer produced by Acinetobacter haemolyticus MG606

A novel, phosphate-binding exobiopolymer (EBP) produced by Acinetobacter haemolyticus MG606 was characterized and its biocompatibility evaluated in RAW 264.7 cells and in mice. EBP was identified as a 50 kDa heteropolysaccharide composed of pentose and hexose sugars. EBP exhibited cytotoxicity, stimulation of free radical production and loss of mitochondrial and lysosomal integrity in RAW 264.7 cells at 500 μg/mL concentration while lower concentrations exhibited no significant (p > 0.05) effect on these parameters. EBP exhibited dose-dependent mortality, body weight reduction, hypothermia and clinical signs of toxicity in mice following intraperitoneal administration. The LD₅₀ of EBP was determined to be 92.31 mg/kg. Overall, the results of our study suggest that composition of EBP produced by A. haemolyticus MG606 is distinct from EBP produced by other Acinetobacter spp. The high biocompatibility supports application of EBP as a safe biosorbent for phosphate remediation.

Inhibition of DC-SIGN-mediated HIV infection by a linear trimannoside mimic in a tetravalent presentation

HIV infection is pandemic in humans and is responsible for millions of deaths every year. The discovery of new cellular targets that can be used to prevent the infection process represents a new opportunity for developing more effective antiviral drugs. In this context, dendritic cell-specific ICAM-3 grabbing non-integrin (DC-SIGN), a lectin expressed at the surface of immature dendritic cells and involved in the initial stages of HIV infection, is a promising therapeutic target. Herein we show the ability of a new tetravalent dendron containing four copies of a linear trimannoside mimic to inhibit the trans HIV infection process of CD4+ T lymphocytes at low micromolar range. This compound presents a high solubility in physiological media, a neglectable cytotoxicity, and a long-lasting effect and is based on carbohydrate-mimic units. Notably, the HIV antiviral activity is independent of viral tropism (X4 or R5). The formulation of this compound as a gel could allow its use as topical microbicide.

Candida albicans derived fungal PAMPS, CAWS, water soluble mannoprotein-beta-glucan complex shows similar immunotoxicological activity with bacterial endotoxin from Escherichia coli O9

Candida albicans water soluble fraction (CAWS), water soluble fraction of Candida albicans mainly composed of mannoprotein-beta-glucan complex, has various biological effects, such as anaphylactoid shock and coronary arteritis. These toxicological effects fit CAWS as one of PAMPs, pathogen-associated molecular patterns. Acute anaphylactoid reaction is known to be induced by lipopolysaccharide from Escherichia coli O9 (O9 LPS), which possesses the mannose homopolysaccharide as the O-antigen region. In the present study, we compared immunotoxicological and immunochemical similarity between CAWS and O9 LPS. CAWS strongly reacted with Candida serum factors, and the reactivity was found to be partially competed with O9 LPS. CAWS induced lethal toxicity was inhibited by pretreatment of mice with i.v. injection of CAWS. The lethality was found to be inhibited by i.v. injection of O9 LPS. Vice versa, O9 LPS induced acute lethal toxicity was also inhibited by pretreatment of mice with CAWS. These results suggested that CAWS, fungal PAMPs, and O9 LPS from Gram-negative bacteria share, at least in part, immunochemical and immunotoxicological activities.

Saccharomyces cerevisiae- and Candida albicans-derived mannan induced production of tumor necrosis factor alpha by human monocytes in a CD14- and Toll-like receptor 4-dependent manner

The cytokine-inducing activities of fungal polysaccharides were examined in human monocytes in culture, with special reference to CD14 and Toll-like receptors (TLRs). Tumor necrosis factor alpha (TNF-alpha) production by monocytes was markedly induced in a dose-dependent manner upon stimulation with cell walls from Candida albicans and mannan from Saccharomyces cerevisiae and C. albicans, although relatively high concentrations (10 to 100 microg/ml) of stimulants were required for activation as compared with the reference lipopolysaccharide (LPS) (1 to 10 ng/ml). The yeast form C. albicans and its mannan and cell wall fractions exhibited higher TNF-alpha production than respective preparations from the hyphal form. Only slight TNF-alpha production was induced by the S. cerevisiae glucan. The TNF-alpha production triggered by reference LPS and purified fungal mannans required the presence of LPS-binding protein (LBP), and these responses were inhibited by anti-CD14 and anti-TLR4 antibodies, but not by anti-TLR2 antibody. In contrast to the activity of LPS, the activity of purified S. cerevisiae mannan was not inhibited by polymyxin B. These findings suggested that the mannan-LBP complex is recognized by CD14 on monocytes and that signaling through TLR4 leads to the production of proinflammatory cytokines in a manner similar to that induced by LPS.

Liposome oligomannose-coated with neoglycolipid, a new candidate for a safe adjuvant for induction of CD8+ cytotoxic T lymphocytes

The cytotoxic T lymphocyte (CTL) response has recently been shown to play a role in protection against human immunodeficiency virus (HIV) and it is therefore thought that a vaccine against HIV must be able to elicit a CTL response. The development of a safe, effective adjuvant is very important because alum, the only adjuvant available for use in humans at present, can barely induce a response of this type. We demonstrate here that liposomes that contain an immunodominant peptide (15 amino acids) of the envelope glycoprotein gp120 of HIV-1 and that are coated with mannopentaose-dipalmitoylphosphatidylethanolamine conjugate induce a major histocompatibility complex class I-restricted CD8+ CTL response in mice with a single subcutaneous immunization, whereas non-coated liposomes do not. Since no damage to the skin at the injection site was caused by the liposomes, and since the oligomannose-coated liposomes consist of innocuous materials ubiquitously distributed throughout the human body, they may be highly suitable for use as a safe adjuvant in vaccines inducing a CTL response against HIV.

Oligomannose-coated liposomes as an adjuvant for the induction of cell-mediated immunity

The effect of the coating of ovalbumin-reconstituted liposomes with various oligosaccharides on their immunogenicity was investigated in mice. The coating of liposomes with oligomannose or yeast mannan drastically enhanced their ability to induce an ovalbumin-specific delayed-type footpad swelling response with a peak at 24 to 48 h post-challenge. Among various oligosaccharides tested, only those with mannose residue at the nonreducing termini manifested the activity when applied to liposomes. Since such oligosaccharides are ubiquitously found in the body, these results suggested the usefulness of oligomannose-coated liposomes as a safe adjuvant for the induction of cell-mediated immunity.

Induction of platelet-activating factor in mice by intravenous administration of a neutral fraction of bakers' yeast mannan

A neutral subfraction of mannan of bakers' yeast (WNM) was found to show a lethal effect in mice when administered intravenously. Symptoms caused by intravenous (i.v.) administration of WNM resembled those resulting from the administration of platelet-activating factor (PAF). CV-3988 and ONO-6240, selective PAF antagonists, prevented hypotension and death caused by the administration of WNM or PAF. A beta-adrenoceptor agonist was shown to prevent death caused by WNM, whereas propranolol increased the lethal activity of WNM. Intravenous administration of WNM into mice produced PAF in gall bladder fluid which was determined by platelet aggregation assay. The findings indicate that WNM is able to induce PAF in mice and that the resultant PAF may participate in the WNM-induced lethal activity observed in mice.

Candida cell wall mannan: a polysaccharide with diverse immunologic properties

It is clear that mannan has the potential to influence multiple biologic functions in vivo and in vitro, including both mannan-specific and mannan-nonspecific activities. Based on in vitro studies, various mechanisms have been proposed for the regulatory activities observed, ranging from interference with normal PMNL and monocyte function to the induction of T suppressor cells. It may well be, in fact, that different mechanisms function at different levels depending upon the specific phenomenon being influenced. Approaches to determining the mechanisms involved in these regulatory phenomena, however, have been complicated by the fact that many studies were performed with mannan extracted in the laboratory by traditional methods and used as such without further purification. Most laboratory-acquired mannans appear to be heterogeneous mixtures containing polymers of differing size and charge. When such mixtures have been separated on the basis of size or charge, it has been shown that biologic function can be correlated with individual fractions, and that a single bulk preparation of mannan can contain components with opposing biologic activities. Resolution of the specific mechanisms involved in the regulatory phenomena described, therefore, will not be complete until homogeneous preparations of mannan are employed to investigate the mechanisms.

Protective effect of acidic mannan fraction of bakers' yeast on experimental candidiasis in mice

An acidic fraction of bakers' yeast mannan, WAM025, showed a significant protective effect against Candida albicans infection in mice, but a neutral fraction of the same bakers' yeast mannan, WNM, did not exhibit this effect. Moreover, pretreatment with WAM025 resulted in a marked reduction of proliferation of C. albicans cells in the organs of the infected mice. We investigated the stimulative effect of these mannan fractions on the function of mouse peritoneal phagocytes, and found that mice administered WAM025 showed a greater increase in the number of peritoneal exudate cells, macrophages and polymorphonuclear leucocytes (PMN), than the mice treated with WNM, especially in the proportion of PMN. Peritoneal phagocytes, PMN and macrophages obtained from WAM025-treated mice showed marked candidacidal activity. Of the phagocytes, PMN were responsible for the larger part of the candidacidal activity. The myeloperoxidase activities of PMN and macrophages in WAM025-treated PEC were greater than in untreated macrophages. The myeloperoxidase activity of WAM025-treated PMN was significantly greater than that of WAM025-treated macrophages. This activity paralleled the active oxygen-releasing activity of the phagocytes. On the other hand, the phagocytic activity of phagocytes from mice administered WNM or WAM025 for C. albicans cells was identical to that of untreated phagocytes. WAM025 seems to cause enhance elimination of the pathogen from mice, by increasing the number and candidacidal activity of phagocytic cells.

Immunochemical study on the mannans of Candida albicans NIH A-207, NIH B-792, and J-1012 strains prepared by fractional precipitation with cetyltrimethylammonium bromide

The mannans of Candida albicans NIH A-207 (A strain, serotype A), C. albicans NIH B-792 (B strain, serotype B), and C. albicans J-1012 (J strain, serotype C) prepared by fractional precipitation with cetyltrimethylammonium bromide (Cetavlon) were investigated for their immunochemical properties. Upon treatment with 10 mM HCl at 100 degrees C for 60 min, the mannans of A and B strains each released a mixture of manno-oligosaccharides ranging from hexaose to mannose together with (for each one) an acid-modified mannan, while J-strain mannan released lower oligosaccharides, tetraose to mannose. The acid-modified mannan of B strain did not show antibody-precipitating activity against homologous antiserum, whereas acid-modified A- and J-strain mannans retained most of this activity. The acid-released oligosaccharides were assumed to consist of beta-1,2-linked D-mannopyranosyl residues from the results of specific rotation and proton magnetic resonance studies.