Physicochemical Characterization of a Polysaccharide Fraction from Platycladus orientalis (L.) Franco and Its Macrophage Immunomodulatory and Anti-Hepatitis B Virus Activities

A polysaccharide fraction, here called POP1, was purified from the leaves of Platycladus orientalis (L.) Franco by water extraction and alcohol precipitation. Physicochemical characterization indicated that POP1 had a relative molecular weight of 8.10 × 10(3) Da and consisted of rhamnose (5.74%), arabinose (12.58%), mannose (10.97%), glucose (64.96%), and galactose (6.55%). The main linkage types of POP1 consisted of (1→5)-linked α-l-Ara, (1→3)-linked α-l-Man, (1→6)-linked β-l-Rha, (1→4)-linked α-d-Glc, (1→6)-linked α-d-Glc, (1→6)-linked β-d-Gal, (1→3,6)-linked β-d-Gal, and termination with α-l-Man and α-d-Glc residues based on periodate oxidation, Smith degradation, methylation, and NMR analysis. POP1 exhibited excellent immunostimulating activity by enhancing macrophage NO, TNF-α, IL-6, and IL-12 secretion and activating related mRNA expression. Besides, POP1 showed significant anti-HBV activity through inhibiting the expression of HBsAg (IC50 = 1.33 ± 0.12 mg/mL) and HBeAg (IC50 = 1.67 ± 0.13 mg/mL) and interfering with the HBV DNA replication (IC50 = 0.80 ± 0.03 mg/mL). The present study suggested that POP1 could be used as immunoregulatory agent in functional foods for the prevention of HBV infection.