Hericium erinaceus polysaccharides ameliorate nonalcoholic fatty liver disease via gut microbiota and tryptophan metabolism regulation in an aged laying hen model

Polysaccharides extracted from Hericium erinaceus (HEP) exhibit hepatoprotective activity in the alleviation of non-alcoholic fatty liver disease (NAFLD); however, the mechanisms underlying whether and how HEP regulation of the gut microbiota to alleviate liver-associated metabolic disorders are not well understood. This study used an aged laying hen model to explore the mechanisms through which HEP alleviates NAFLD, with a focus on regulatory function of HEP in the gut microbiome. The results showed that HEP ameliorated hepatic damage and metabolic disorders by improving intestinal barrier function and shaping the gut microbiota and tryptophan metabolic profiles. HEP increased the abundance of Lactobacillus and certain tryptophan metabolites, including indole-3-carboxylic acid, kynurenic acid, and tryptamine in the cecum. These metabolites upregulated the expression of ZO-1 and Occludin by activating the AhR and restoring the intestinal barrier integrity. The increased intestinal barrier functions decreased LPS transferring from the intestine to the liver, inhibited hepatic LPS/TLR4/MyD88/NF-κB pathway activation, and reduced hepatic inflammatory response and apoptosis. Fecal microbiota transplantation experiments further confirmed that the hepatoprotective effect is likely mediated by HEP-altered gut microbiota and their metabolites. Overall, dietary HEP could ameliorate the hepatic damage and metabolic disorders of NAFLD through regulating the "gut-liver" axis.