Structure and hepatoprotective activity of autophagy-related Butyriboletus roseoflavus polysaccharide

Alcoholic liver disease (ALD) poses a growing therapeutic challenge due to the scarcity of effective pharmacotherapies. Here, BRP2, a novel polysaccharide from Butyriboletus roseoflavus, was isolated and structurally characterized, featuring a complex backbone comprising →6)-α-Galp-(1→, →2,6)-α-Galp-(1→, and →2,6)-β-Manp-(1 → 3)-β-Fucp-(1→. This unique polysaccharide significantly ameliorated hepatic steatosis and DNA damage in both acute and chronic ALD models. Mechanistically, BRP2 reshaped the gut microbiota by enriching Akkermansia and suppressing Desulfovibrio, leading to a marked reduction in the microbial metabolite trimethylamine N-oxide (TMAO). Reduced TMAO levels alleviated inhibition of AMPK phosphorylation and enhanced Sirt1 deacetylase activity, which subsequently suppressed mTORC1 signaling. This cascade potently activated hepatoprotective autophagy, as evidenced by decreased p62/SQSTM1 and increased LC3-II levels. Collectively, this study reveals a BRP2-driven, microbiota-TMAO-dependent pathway that alleviates ALD through the AMPK/Sirt1/mTORC1-mediated autophagy axis, offering new insights into polysaccharide-based interventions for liver diseases.