Acidic polysaccharide from the edible insect Protaetia brevitarsis seulensis activates antiviral immunity to suppress norovirus infection

Edible insects are gaining attention as potential nutraceutical sources with immunomodulatory properties. This study reports purification and structural characterization of polysaccharides from Protaetia brevitarsis seulensis larvae (PBSL) with antiviral activity against murine norovirus. Four polysaccharide fractions purified from PBSL water extracts exhibited varying molecular weights (458.5–627.3 kDa) and monosaccharide compositions, including glucose (42.4–99.2 %), galactose (5.9–13.9 %), rhamnose (0.7–18.7 %), arabinose (3.8–5.4 %), and glucuronic acid (0–15.3 %). The immunomodulatory activity, assessed by interferon-β (IFN-β) production, positively correlated with higher galactose, mannose, rhamnose, and uronic acid contents. Among the fractions, PBS-P, eluted with 0.5 M NaCl, demonstrated superior in vitro antiviral activity with IFN-β production exceeding 8-fold compared to other fractions and 82-fold higher than PBSL water extract, confirming it as the main antiviral active component. Structural analysis revealed PBS-P backbone consisted of α-(1 → 4)-D-Glcp, α-(1 → 4,6)-D-Glcp, α-(1 → 4)-D-GlcpA, α-(1 → 3)-D-Galp and α-(1 → 4)-D-Manp residues, and branched chains of α-D-Glcp-(1→, and α-L-Arap-(1 → 2)-α-L-Rhap-(1 → residues. PBS-P suppressed norovirus replication by stimulating IFN-β, TNF-α, and activating NF-κB, STAT1/2, and TBK1-IRF3 pathways, and its oral administration reduced viral loads in infected mice intestines. This study provides the first report on the detailed structural feature of polysaccharide from an edible insect and its antiviral mechanism, highlighting its potential as a new antiviral agent. [Display omitted]