Optimization of Se- and Zn-Enriched Mycelium of Lentinula edodes (Berk.) Pegler as a Dietary Supplement with Immunostimulatory Activity

Mycelial cultures of Lentinula edodes, an edible and medicinal mushroom, have been used in our previous research to obtain selenium-containing immunomodulatory preparations. Our current attempts to obtain a new preparation containing both selenium and zinc, two micronutrients necessary for the functioning of the immune system, extended our interest in the simultaneous accumulation of these elements by mycelia growing in media enriched with selenite and zinc(II) ions. Subsequently, we have studied the effects of new L. edodes mycelium water extracts with different concentrations of selenium and zinc on the activation of T cell fraction in human peripheral blood mononuclear cells (PBMCs). Flow cytometry analysis was used to measure the expression of activation markers on human CD4+ and CD8+ T cells stimulated by anti-CD3 and anti-CD3/CD28 antibodies (Abs). It was demonstrated that statistically significant changes were observed for PD-1 and CD25 antigens on CD8+ T cells. The selenium and zinc content in the examined preparations modified the immunomodulatory activity of mycelial polysaccharides; however, the mechanisms of action of various active ingredients in the mycelial extracts seem to be different.

Identification of the Primary Structure of Selenium-Containing Polysaccharides Selectively Inhibiting T-Cell Proliferation

We previously described the biosynthesis, isolation, and immunosuppressive activity of the selenium-containing polysaccharide fraction isolated from the mycelial culture of Lentinula edodes. Structural studies have shown that the fraction was a protein-containing mixture of high molar mass polysaccharides α- and β-glucans. However, which of the components of the complex fraction is responsible for the immunosuppressive activity non-typical for polysaccharides of fungal origin has not been explained. In the current study, we defined four-polysaccharide components of the Se-containing polysaccharide fraction determined their primary structure and examined the effect on T- and B-cell proliferation. The isolated Se-polysaccharides, α-1,4-glucan (M_w 2.25 × 10⁶ g/mol), unbranched β-1,6-d-glucan, unbranched β-1,3-d-glucan and β-1,3-branched β-1,6-d-glucan (M_w 1.10 × 10⁵ g/mol), are not typical as components of the cell wall of L. edodes. All are biologically active, but the inhibitory effect of the isolated polysaccharides on lymphocyte proliferation was weaker, though more selective than that of the crude fraction.

Biosynthesis of Se-methyl-seleno-l-cysteine in Basidiomycetes fungus Lentinula edodes (Berk.) Pegler

Background

The aim of the current study was to investigate whether the Basidiomycetes fungus Lentinula edodes can biosynthesize Se-methyl-seleno-l-cysteine, a seleno-amino acid with strong anticancer activity, and to optimize the culture conditions for its biosynthesis. We hypothesize that preparations obtained from Se-methyl-seleno-l-cysteine-enriched mycelia from this medicinal mushroom would possess stronger cancer-preventive properties than current preparations.

Results

By optimizing the concentration of selenium in the culture medium, we increased the mycelial concentration of Se-methyl-seleno-l-cysteine from essentially non-detectable levels to 120 µg/g dry weight. Significantly elevated levels of this amino acid also correlated with significant (twofold) inhibition of mycelial growth. Increases in the concentration of mycelial Se-methyl-seleno-l-cysteine appeared to be highly correlated with the enhanced biosynthesis of selenomethionine and total selenium content in mycelium.

Conclusions

We have demonstrated that in L. edodes, enhanced biosynthesis of this non-protein amino acid eliminates excess selenium.

Effect of selenium enrichment on antioxidant activities and chemical composition of Lentinula edodes (Berk.) Pegl. mycelial extracts

Preparations derived from Lentinula edodes (Berk.) Pegl. mycelium are worldwide used as dietary supplements containing compounds active as immune system enhancers, demonstrating chemopreventive and anticancer activity. L. edodes mycelium enriched with organic forms of selenium like selenized yeast possess putative, higher cancer preventive properties. The objective of this study was to test the effect of enrichment in selenium on antioxidant, reducing and free radical scavenging activity of water and alcohol extracts from mycelium of L. edodes (Berk.). To elucidate the cause of enhanced antioxidant activity of extracts, a preliminary selenium speciation by specific oxido-reduction reaction was performed. Se-enrichment enhanced antioxidant activity, reducing power and free radical scavenging effect of mycelial extracts by almost 100-400%. Increase of activity was particularly high for diluted extracts (concentrations 0.1-0.5 mg/ml). The chemical composition of extracts from both Se-enriched and non-enriched mycelium was compared by determination of polyphenols, proteins, carbohydrates and lipids. Results showed that Se-enrichment enhanced antioxidant activities of mycelial extracts, likely by high amounts of organic Se-compounds (-II oxidation state) and elemental red selenium, and by increased polyphenols content. Our results suggest that Se-enrichment is a good method for enhancement of important activities of human dietary supplements, including Shiitake preparations.

Relationship between selenium accumulation and mycelial cell composition in Lentinula edodes (Berk.) cultures

It was postulated that fractions enriched in selenium (Se) isolated from Lentinula edodes mycelium polysaccharide might possess higher biological activity than the non-enriched fractions currently used to treat cancer. In order to obtain Se-enriched mycelial preparations, L. edodes cultures were cultivated in media enriched with sodium selenite. In order to determine whether the concentration of Se in the culture medium affected the biosynthesis and composition of cell wall and cell membrane, concentrations of the exopolysaccharide (EPS), chitin, and sterol (ergosterol) were measured in harvested mycelia. In addition, the relationship between Se accumulation and content of polyphenols and vitamin D(2) in L. edodes mycelium was examined. The effects of Se levels on the mycelium cell composition were determined in culture media enriched with Se at concentrations ranging from 0 to 30 microg/ml. In each culture mycelial growth, total Se and Se distribution were determined between mycelial fractions of different polarity. The EPS, polyphenolics, and ergosterol content in harvested mycelia rose in proportion to Se concentration in the culture medium. The chitin content in mycelia increased with Se concentrations in the range 0-5 microg/ml, but at higher concentrations chitin levels decreased. Data showed that Se in culture medium exerted potent effects on the composition of the mushroom cell wall and semipermeable membrane, and on the content of polyphenolics that are involved in detoxification processes. Our findings indicate the optimal concentration of Se required in the culture medium for maximal yield of immunostimulatory-active selenated exopolysaccharides.