Production of low-molecular weight soluble yeast ß-glucan by an acid degradation method.

ß-glucan is widely distributed in nature as water soluble and insoluble forms. Both forms of ß-glucan are utilized in several fields, especially for functional foods. Yeast ß-glucan is a medically important insoluble particle. Solubilization of yeast ß-glucan may be valuable for improving functional foods and in medicinal industries. In the present study, we applied an acid degradation method to solubilize yeast ß-glucan and found that ß-glucan was effectively solubilized to low-molecular weight ß-glucans by 45% sulfuric acid treatment at 20°C. The acid-degraded soluble yeast ß-glucan (ad-sBBG) was further fractionated into a higher-molecular weight fraction (ad-sBBG-high) and a lower-molecular weight fraction (ad-sBBG-low). Since ad-sBBG-high contained mannan, while ad-sBBG-low contained it only scarcely, it was possible to prepare low-molecular weight soluble ß-glucan with higher purity. In addition, ad-sBBG-low bound to dectin-1, which is an innate immunity receptor of ß-glucan, and showed antagonistic activity against reactive oxygen production and cytokine synthesis by macrophages. Thus, this acid degradation method is an important procedure for generating immune-modulating, low-molecular weight, soluble yeast ß-glucan.

Modulation of an innate immune response by soluble yeast ß-glucan prepared by a heat degradation method.

ß-glucan is widely distributed in nature as water soluble and insoluble forms. Both forms of ß-glucan are applied in several fields, especially for functional foods. Yeast ß-glucan is a medically important insoluble particle. Solubilization of yeast ß-glucan may be a valuable approach to increase functional foods and medicinal fields. We have applied a heat degradation method to solubilize yeast ß-glucan and found that it was effectively solubilized by treatment with an aqueous suspension at 135°C for several hours. The solubilized yeast ß-glucan (hd-sBBG) exhibited antagonistic activity to the reactive oxygen production of macrophages and to the cytokine synthesis of macrophages. hd-sBBG strongly reacted with the anti-ß-glucan antibody in human sera and with dectin-1, the innate immune receptor of ß-glucan. From these findings, the heat degradation method is an important procedure for making immune modulating soluble yeast ß-glucan.

Protective effects of oral administration of yeast thioredoxin against gastric mucosal injury.

Thioredoxin (TRX) is a redox regulating protein which has protective effects against oxidative stress-induced damage to cells and tissues. In this study, we investigated the effects of orally administered TRX derived from edible yeast, Saccharomyces cerevisiae, on gastric mucosa. First, we examined the digestibility of orally administered yeast TRX in mice, and detected yeast TRX in the stomach for 4 h after administration. Next, we investigated the mitigation of gastric mucosal injury after the oral administration of yeast TRX in water-immersion restraint stress and HCl/ethanol-induced gastric ulcer models. Furthermore, we conducted DNA microarray analysis, using the HCl/ethanol-induced model, which revealed that several groups of genes related to tissue repair were upregulated in ulcer regions in the stomachs of rats administered with yeast TRX. These results demonstrated the viability of the use of oral administrations of yeast TRX to protect the gastric mucosa.

Isolation of diploid baker's yeast capable of strongly activating immune cells and analyses of the cell wall structure.

Diploid baker's yeast capable of strongly activating a mouse macrophage was constructed based on haploid mutant AQ-37 obtained previously. The obtained strain BQ-55 activated also human immune cells. To clarify a factor for the activation, the cell wall structure, especially the ß-glucan structure, was analyzed, suggesting that the length of branching, ß-1,6-glucan, may be one of the factors.

Isolation and characterization of baker's yeast capable of strongly activating a macrophage.

A physiological function of the ß-glucans which constitute the cell wall of Saccharomyces cerevisiae is to activate immune cells. Here, we focused on the immunostimulation ability of S. cerevisiae itself to give this ability to fermented foods including yeast. Previously, we found that in S. cerevisiae the deletion of MCD4 gene causes exposure of ß-glucans on the cell surface and that the mcd4 deletion mutant strongly enhances immunity in vitro and in vivo. However, this is not a practical strain but a genetically modified strain with an antibiotic resistance gene, and growth was very slow. The aim of this study was to acquire a practical strain capable of strongly activating a macrophage. The parental strain y-21 was mutated with ethyl methanesulfonate, and the resulting strain was screened. Two mutants (AP-57 and AQ-37) were obtained. AQ-37 had the same fermentation capacity as y-21. In addition, a mutation point of AQ-37 was identified, suggesting that the mutation of NDD1 gene affects the cell wall structure and confers a high ability for macrophage stimulation. The obtained yeast may activate immune cells in materials to which the yeast is added.

Yeast thioredoxin-enriched extracts for mitigating the allergenicity of foods.

Thioredoxin (TRX) catalyzes the reduction of disulfide bonds in proteins via the NADPH-dependent thioredoxin reductase system. Reducing the disulfide bonds of allergenic proteins in food by TRX lowers the allergenicity. We established in this study a method to prepare TRX-enriched extracts from the edible yeast, Saccharomyces cerevisiae, on a large and practical scale, with the objective of developing TRX-containing functional foods to mitigate food allergy. Treating with the yeast TRX-enriched extracts together with NADPH and yeast thioredoxin reductase enhanced the pepsin cleavage of ß-lactoglobulin and ovomucoid (OM). We also examined whether yeast TRX can mitigate the allergenicity of OM by conducting immediate allergy tests on guinea pigs. The treatment with TRX reduced the anaphylactic symptoms induced by OM in these tests. These results indicate that yeast TRX was beneficial against food allergy, raising the possibility that yeast TRX-enriched extracts can be applied to food materials for mitigating food allergy.

Electron-microscopic imaging of single-walled carbon nanotubes grown on silicon and silicon oxide substrates.

Direct imaging of single-walled carbon nanotubes (SWNTs) suspended on pillar-patterned Si or SiO2 substrates is investigated using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The suspended nanotubes are successfully observed by direct TEM imaging and it is seen that they have either individual or bundles of SWNTs. Low energy (< or =2 keV) SEM produces high contrast images of suspended SWNTs. On the contrary, when SWNTs contact a SiO2 substrate, they are imaged using electron-beam induced current. The image brightness depends on the length of SWNTs.