Abstract
In continuation of our research on the influence of selenium incorporation on the biosynthesis, structure, and immunomodulatory and antioxidant activities of polysaccharides of fungal origin, we have isolated from a post-culture medium of Lentinula edodes a selenium (Se)-containing exopolysaccharide fraction composed mainly of a highly branched 1-6-α-mannoprotein of molecular weight 4.5 × 106 Da, with 15% protein component. The structure of this fraction resembled mannoproteins isolated from yeast and other mushroom cultures, but it was characterized by a significantly higher molecular weight. X-ray absorption fine structure spectral analysis in the near edge region (XANES) suggested that selenium in the Se-exopolysaccharide structure was present mainly at the IV oxidation state. The simulation analysis in the EXAFS region suggested the presence of two oxygen atoms in the region surrounding the selenium. On the grounds of our previous studies, we hypothesized that selenium-enriched exopolysaccharides would possess higher biological activity than the non-Se-enriched reference fraction. To perform structure–activity studies, we conducted the same tests of biological activity as for previously obtained mycelial Se-polyglucans. The Se-enriched exopolysaccharide fraction significantly enhanced cell viability when incubated with normal (human umbilical vein endothelial cells (HUVEC)) cells (but this effect was absent for malignant human cervical HeLa cells) and this fraction also protected the cells from oxidative stress conditions. The results of tests on the proliferation of human peripheral blood mononuclear cells suggested a selective immunosuppressive activity, like previously tested Se-polyglucans isolated from L. edodes mycelium. The Se-exopolysaccharide fraction, in concentrations of 10–100 µg/mL, inhibited human T lymphocyte proliferation induced by mitogens, without significant effects on B lymphocytes. As with previously obtained Se-polyglucans, in the currently tested Se-polymannans, the selenium content increased the biological activity. However, the activity of selenium exopolysaccharides in all tests was significantly lower than that of previously tested mycelial isolates, most likely due to a different mode of selenium binding and its higher degree of oxidation.
Highlights
Mushroom-derived polysaccharides are compounds of various structure, variable functionality and diverse biological activity [1]
OKT3 stimulates T cells via CD3-mediated signaling [74]. We found that both exopolysaccharide samples, Le-P-Se and Le-P-0, in concentrations of 10 and 100 μg/mL, significantly inhibited proliferation of the T lymphocytes stimulated by OKT3, which suggests their potential effects on the T cell receptor (TCR)/CD3 pathway
We found that the Se-exopolysaccharide fraction secreted into the culture medium by
Summary
Mushroom-derived polysaccharides are compounds of various structure, variable functionality and diverse biological activity [1]. They are active as antioxidants and have antitumor, immunomodulating, antibacterial, antimicrobial, antiviral, anti-obesity, hypolipidemic, antidiabetic, and hepato-protective properties, among other activities [2,3,4,5,6]. A similar pharmacological effect of selenium and fungal polysaccharides, despite the difference in the mechanism, suggests the possibility of hyperadditive synergism (potentiation of action) of both components [12,13,14,15,16,17]. It has been hypothesized that the introduction of selenium to the polysaccharide structure would increase the immunomodulatory activity. The increased activity of polysaccharides resulting from selenium incorporation has been confirmed by studies conducted in many research laboratories, the mechanism of this action is still unclear [18]
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