Caracterização físico-química e atividade imunomoduladora de polissacarídeos de Lentinus strigosus (Schwein.) Fr., cultivado sob fermentação submersa

Abstract

In this study, polysaccharide fractions extracted from the mycelial biomass – obtained by submerged fermentation – from the Amazonian strain of edible mushroom Lentinus strigosus were studied. After extraction and purification, homogenous fractions (aqueous, LSW, and alkaline, LSK) were characterized regarding their structure, physicochemical and rheological properties, as well as immunomodulatory and adhesive effects on macrophages. Both polysaccharides were mostly composed of glucose, with trace amounts of galactose, mannose, arabinose, and xylose. Uronic acids were not detected. 1H, 13C and DEPT-135 nuclear magnetic resonance (NMR) analysis suggests the presence of →6)-β-D-Glcp-(1→, →4)-α-D-Glcp-(1→ and →6)-α-D-Galp-(1→ as major units in LSW, while LSK is mostly composed of β-D-Glcp-(1→, →3)-β-D-Glcp-(1→ and →3,6)-β-D-Glcp-(1→. Dynamic light scattering (DLS) showed an average diameter of 609.37 nm for particles present in the LSW fraction, and 301.17 nm for LSK, both with homogeneous size dispersion. Zeta potential of the two fractions was similar, around -6.58 mV for LSW and -5.47 mV for LSK, therefore with a density of superficial electric charges close to neutrality, but slightly negative. Rheological properties of polysaccharide solutions were estimated in terms of elastic storage modulus (G’), viscous loss modulus (G”), and complex viscosity (η*), suggesting a weak gel-like character for LSW and viscous-fluid for LSK, not exhibiting significant thermal hysteresis. Both fractions showed a strong immunomodulatory effect in murine macrophages, estimated through ELISA-mediated cytokine dosing. In RAW 264.7 cells, LSW stimulated the release of IL-6 and TNF-α, inhibiting the production of IL-10, while LSK did not show significant induction or inhibition of these cytokines. In J774.1 cells, both fractions showed similar activity, enhancing TNF-α production, inhibiting IL-10, and no influence on IL-6. Polystyrene microspheres coated with the polysaccharides were manipulated with optical tweezers (OT) to interact with live macrophages in culture. It was observed that samples had a characteristic time required for adhesion to cell surface much lower than control, around 13.38 s (LSW) and 13.94 s (LSK), suggesting they are rapidly recognized by macrophages. Considering the results, polysaccharides from L. strigosus have distinct properties when obtained via aqueous and alkaline extraction, showing in vitro immunostimulant activity, verified through a probable inflammatory response and rapid adhesion/recognition by macrophages. These results contribute to the knowledge about the potential of Amazonian L. strigosus as a producer of biomolecules with health benefits and nutraceutical or functional properties, with a focus on immune modulation. As future perspectives, further characterization of structure, activated immunological mechanisms, and screening of other biological activities of these polymers are highly recommended, as well as production optimization and upscaling.