Structural characterization and immunomodulatory activity analysis of a novel pectic polysaccharide extracted from Tetrastigma hemsleyanum Diels et Gilg and its hydrolysis products.

Tetrastigma hemsleyanum Diels et Gilg (T. hemsleyanum) is a rare traditional Chinese medicine with high medicinal value and T. hemsleyanum polysaccharides (THPs) have attracted increasing attention in recent years. However, detailed structural and functional insights into THPs remain limited. Here, a novel pectic polysaccharide (STHP4) with an average molecular weight (Mw) of 119 kDa was extracted and purified from the aboveground part of T. hemsleyanum. Structurally, STHP4 was mainly composed of galacturonic acid, glucuronic acid, and galactose, with minor glucose, rhamnose, arabinose, and mannose, and its primary backbone was 1,4-GalA. Pectinase treatment of STHP4 yields two distinct fractions: STHP4-1 and STHP4-2. STHP4-1 shared the same types of monosaccharides with STHP4, except for the absence of glucose, but had a broad Mw distribution (9.9 to 251 kDa). Another product, STHP4-2, a mixture of oligosaccharides and free monosaccharides, has a Mw of 1.387 kDa. Their structures were further elucidated via methylation analysis and NMR spectra. Furthermore, STHP4-1 exhibited superior immune regulatory effects on macrophages, including increased nitric oxide release and elevated interleukin-6, interleukin-1β, and tumor necrosis factor α expression. These findings suggest that STHP4-1 might be the core active domain of STHP4, and both STHP4 and STHP4-1 are potential immune enhancers.