Structural characterization and immunomodulatory activity of an acidic heteropolysaccharide isolated from the fermented burdock residue mediated by Rhizopus nigricans

An acidic heteropolysaccharide (RBAPS) with a relative molecular weight of 140.9 kDa was extracted from Rhizopus nigricans mediated burdock residue fermentation. Structural analysis indicated that RBAPS was mainly composed of Rha, Ara, Gal, GalA, GlcA, Glc and Xyl in a molar ratio of 14.5: 14.3: 30.1: 31.0: 5.5: 0.8: 3.8. The dominant backbone of RBAPS consisted of alpha-Rhap, alpha-GalAp, and alpha-Galp with the branched chains of beta-Galp and alpha-Araf. In macrophage RAW264.7 cells, RBAPS promoted proliferation, enhanced phagocytosis, hindered apoptosis, and promoted cytokines (NO, IL-6, TNF-alpha, and IL-1 beta) secretion. RBAPS also promoted M1 macrophage transformation and induced the secretion of NO and IL-6 in differentiated macrophages. The findings suggested that RBAPS has the potential immunomodulatory and anti-tumor effects, giving it application prospect in the health and pharmaceutical fields.

Automated summary

RBAPS, an acidic heteropolysaccharide extracted from Rhizopus nigricans mediated burdock residue fermentation, showed immunomodulatory and anti-tumor effects in vitro. RBAPS promoted cell proliferation and phagocytosis, inhibited cell apoptosis, and induced cytokine secretion in macrophages. It also promoted M1 macrophage transformation and induced the secretion of NO and IL-6.