A flaxseed heteropolysaccharide stimulates immune responses and inhibits hepatitis B virus

A novel heteropolysaccharide defined as FP-1 was enriched from flaxseed hull through hot water extraction (boiling water, 2 h, twice) followed by ion-exchange and size exclusion chromatography. FP-1 is a highly purified heteropolysaccharide with an average molecular weight of 2626 kDa. Its monosaccharide composition includes xylose (35.2%), rhamnose (23.8%), galactose (23.4%), arabinose (10.6%), fucose (4.0%), glucose (2.7%) and mannose (0.3%). Main linkage type of FP-1 backbone includes →2)-α-L-Rhap-(1→, →4)-α-D-GalpA-(1→, →4)-β-D-Xylp-(1→, →3,5)-α-L-Araf-(1→, and →2)-α-D-Xylp-(1→. FP-1 has a triple-helix conformation, indicating its potential bioactivity. FP-1 could stimulate immune responses through inducing mRNA expression of tumor necrosis factor α (TNF-α), nitric oxide (NO), and interleukin (IL-6 and IL-12) in murine macrophages. FP-1 also inhibits hepatitis B virus (HBV) through inhibition of surface antigen (HBsAg) and envelope antigen (HBeAg) expression and interfering with HBV DNA replication. These findings suggest that FP-1 could be potentially developed as functional food ingredient, immune stimulant and vaccine adjuvant.