Structural characterization and immunological function of a neutral polysaccharide from <i>Areca catechu</i> L. kernels

Areca nut kernels are the byproduct of areca nut processing. Some of the major bioactive components of the areca nut are polysaccharides. Polysaccharides are known to exert numerous biological activities. Thus, polysaccharides isolated from areca nut kernels may be clinically valuable. To determine the medicinal value of areca nut kernel polysaccharides (AKP), ultrasonic-assisted extraction, ethanol precipitation, and dialysis were used for separation and purification. SEM, XRD, FTIR, and NMR were used for structural characterization and RAW264.7 macrophages were used for in <italic>vitro</italic> immune activity assessment. The AKP were isolated was a neutral polysaccharide, and the molecular weight (M<italic>w</italic>) was 6.95 × 10⁵Da, primarily composed of mannose (58.7%) and galactose (33.6%); the main chain of AKP is →4)-<italic><italic>β</italic></italic>-D-Man<italic>p</italic>-(1→, and the branched chain was mainly of <italic><italic>α</italic></italic>-D-Gal<italic>p</italic>-(1→ attached to the O-6 position of →4,6)-<italic><italic>β</italic></italic>-D-Man<italic>p</italic>-(1→. Cell experiments show that AKP (20 μg/mL) exerts its immune function <italic>via</italic> the TLR4/NF-<italic>κ</italic>B signaling pathway regulation, decreasing TLR4, P65, I<italic>κ</italic>B-<italic>α</italic>, and MyD88, and reducing the release of TNF-<italic>α</italic>, NO, IL-6, and IL-1<italic>β</italic>. In addition, AKP immune activity might be ascribed to its high M<italic>w</italic> and rich monosaccharide composition. This study offers a solid scientific foundation for the development of AKP for wide clinical application.