Structural characterization of a novel pectic polysaccharide from Abelmoschi Corolla and evaluation of its immunological activities.

Abelmoschi Corolla, a traditional Chinese herbal material, is known for its pharmacological properties, including diuretic effects, urinary tract-cleansing, heat and dampness elimination, anti-oedema, and detoxification. Polysaccharides and flavonoids are the primary bioactive constituents of Abelmoschi Corolla. Although the structure-function relationships of flavonoids are well understood, polysa1ccharides, particularly those with potential immunotherapeutic applications, remain comparatively understudied. In this study, we isolated and purified a novel pectin polysaccharide from Abelmoschi Corolla, designated AMFP-3a. The structural characteristics of AMFP-3a were analysed by HPSEC, HPLC, IR, GC-MS, and multidimensional NMR spectroscopy (1D/2D). The analytical results demonstrated that AMFP-3a is a homogeneous pectic polysaccharide with a relative molecular mass of 264.92 kDa. AMFP-3a is highly methoxylated, with a backbone structure comprising homogalacturonan (HG) domains with 1,4-α-D-GalpA linkages and rhamnogalacturonan-I (RG-I)-like domains connected by 1,3,4-α-D-GalpA residues. The branched side chains predominantly consist of 1,5-α-L-Araf, 1,3,5-α-L-Araf, and 1,3-α-L-Rhap residues, which are attached to the O-3 position of the 1,3,4-α-D-GalpA residues, forming a complex branching structure. Furthermore, AMFP-3a significantly enhanced the proliferation and phagocytic activity of RAW 264.7 cells, as well as cytokine secretion. It demonstrated potent immunomodulatory activity by activating the mitogen-activated protein kinase (MAPK)/nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signalling pathway. Collectively, these findings indicate the therapeutic potential of AMFP-3a as a candidate for the development of immune-modulating nutraceuticals.