Structural and immunomodulatory properties of bioactive polysaccharide from solid-state fermented brown rice with Antrodia cinnamomea mycelia

Natural polysaccharides derived from edible fungi efficiently modulate the immune system typically without adverse effects. In this work, a strain isolated from wild fruiting bodies of Antrodia cinnamomea (AC), identified via 18S ribosomal RNA gene sequencing, was used in solid-state fermentation of brown rice at 27°C for 3, 6, and 10 months to develop polysaccharide. Bioactive polysaccharide was isolated by ultrasonic-assisted enzymatic extraction and gel permeation chromatography prior to structural analysis and immunomodulatory studies in rat peripheral blood mononuclear cells (PBMCs) and RAW 264.7 mouse macrophages. AC polysaccharide fraction I (ACP-I) increased by 20.8-fold (47.08 µg/mL) at 6 months of fermentation. Unlike typical fungal heteroglucans, ACP-I was identified as a unique heterogalactan (29.2 kDa), predominantly featuring terminal fucose residues. The immunomodulatory studies in lipopolysaccharide-stimulated macrophages demonstrated that ACP-I sup-pressed nitric oxide (NO) production through downregulating inducible NO synthase level and nuclear factor kappa B activation, which consequently suppressed pro-inflammatory cytokine expression, including interleukin 8, interferon beta-1, and CC chemokine RANTES, without affecting macrophage inflammatory protein-2 levels. Additionally, ACP-I promoted a 2.2-fold increase in PBMC proliferation, compared to concanavalin A, indicating dual immunomodulatory activity, which highlighted its potential as a nutraceutical and functional food ingredient for food and pharmaceutical applications.