Structural characterization and immunomodulatory activity of novel polysaccharides from Citrus aurantium Linn. variant amara Engl

Two polysaccharides CAVAP-I and CAVAP-II from Citrus aurantium L. var. amara Engl showed significant structural differences. Average molecular weights of CAVAP-I and CAVAP-II were 10.5 kDa and 4.5 kDa. Triple-helix conformation existed in CAVAP-II rather than CAVAP-I. Arabinose, mannose, glucose and galactose formed main components of CAVAP-I and CAVAP-II at different ratios. (1 → 3,6)-β-d-Gal and (1 → 5)-α-l-Ara composed the backbone of CAVAP-I and CAVAP-II. CAVAP-II displayed greater immune enhancement potential than CAVAP-I. CAVAP-II significantly promoted interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) production, and inducible nitric oxide synthase, IL-6, TNF-α and interleukin-1 beta mRNA expression by activating phosphorylated extracellular signal-regulated kinase, c-Jun N-terminal kinase, P38 and P65. These results indicated that structures were closely related to immunomodulatory activity of polysaccharides. CAVAP-II showed the greatest immunostimulation potential followed by CAVAP-I and CAVAPs by activating mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) pathways.