An acidic polysaccharide (AGC3) isolated from North American ginseng (Panax quinquefolius) suspension culture as a potential immunomodulatory nutraceutical

Abstract

Polysaccharides isolated from Panax quinquefolius roots are widely used as nutraceuticals due to their immunomodulatory properties. Despite their popularity, several challenges exist in isolating ginseng root polysaccharides such as batch-to-batch structural inconsistencies and bacterial endotoxin contamination. A plant tissue culture-based platform offers a potential solution to isolate natural polysaccharide fractions with consistent chemical characteristics and reduced endotoxin content. In this study, an acidic polysaccharide fraction (AGC3) with immunomodulatory properties was isolated from Panax quinquefolius suspension cultures. The heterogeneous fraction (molecular weight: 4.81 and 32.14 kDa), purified by anion exchange chromatography, was predominantly composed of galactose (>60%) along with the presence of rhamnose, arabinose, glucose, glucuronic acid and galacturonic acid. The major glycosidic linkages were found to be t-Gal p (47.7%), 4-Gal p (15.6%), 2,4-Rha p (8.1%), 6-Gal p (8.1%) and 4-GalA p (6.8%). Structural analyses indicated the presence of a pectic rhamnogalacturonan I polysaccharide in AGC3. AGC3 significantly ( p < 0.05) stimulated RAW 264.7 murine macrophage cells and primary murine splenocytes by enhancing the production of several immunomodulatory mediators such as IL-6, TNF-α, GM-CSF and MCP-1 . The results also indicated the putative roles of NF-κB (p65/RelA) and MAPK (p38) signaling pathways in the immunostimulatory response. Additionally, AGC3 induced murine splenocyte proliferation, another major indicator of immunostimulation. Overall, AGC3 has the potential to be used as an immunostimulatory nutraceutical.

Panax quinquefolius (North American Ginseng) Polysaccharides as Immunomodulators: Current Research Status and Future Directions

“…Ghosh et al (2019) purified a neutral polysaccharide fraction AGC1 that was predominantly composed of arabinogalactan type II polysaccharides. The structural features of another acidic polysaccharide fraction (AGC3) from the NAG suspension culture was reported by Ghosh et al (2020) [37]. The linkage analysis indicated the presence of the RG-I type of pectic polysaccharides in AGC3.…”

“…Sequential anion-exchange and size-exclusion chromatography have been effectively used by several researchers to purify NAG polysaccharides [ 14 , 35 ]. Ideally, purified polysaccharides should be further eluted through an endotoxin removal resin (e.g., Pierce high capacity endotoxin removal resin) prior to the bioactivity screening [ 14 , 36 , 37 ]. Although this additional step may reduce the polysaccharide yield, it is vital to rule out potential false positives in immunomodulatory assays.…”

“…Apart from the monosaccharide composition, glycosidic linkages also reveal substantial information about the primary structure of polysaccharides. Samples are permethylated, hydrolyzed, reduced, acetylated, and the resulting partially methylated alditol acetates (PMAA) are analyzed by GC-MS for linkage analysis of polysaccharides [ 14 , 37 ]. However, the complete structure of polysaccharides including the sequence of constituent monosaccharides cannot be obtained by the above-mentioned methods.…”

“…All TLRs with the exception of TLR3 and TLR4 seem to be MyD88 dependent, and lead to the activation of NF-κB and MAPKs [ 72 ]. TLR4 has been indicated as one of the potential receptors for NAG polysaccharides, however, since NAG polysaccharides have been shown to activate the NF-κB, MAPK, and PI3K signal transduction pathways there are potentially other receptors involved [ 30 , 37 , 49 ].…”

“…An acidic polysaccharide containing RG-I pectin isolated from the NAG cell suspension culture has been shown to modulate the inflammatory response of RAW 264.7 cells increasing both the activation of NF-κB and p38 (MAPK) [ 37 ]. Though there are many different receptors which can lead to the activation of these two signaling pathways, pectins isolated from unripe papayas ( Carica papaya L; Un-1-WSF/Un-2-WSF), have been shown to induce an inflammatory response in THP-1 monocytes primarily through MyD88-dependent signaling [ 90 ].…”