Effect and Mechanism of Apple Polyphenols in Regulating Intestinal Flora and Inhibiting the TLR4/NF-κB/TGF-β Signaling Pathway to Alleviate Alcoholic Liver Fibrosis

Apple polyphenols (APs) have gained attention for their various bioactivities, while no studies on anti-liver fibrosis activity are reported. This study evaluated the protective effect of APs on liver fibrosis using LPS-treated activated HSC-T6 cells and alcohol-treated liver fibrosis (ALF) mice. The results indicated that APs inhibited HSC-T6 cells activation in vitro and reduced the level of serum hyaluronic acid (HA) (p < 0.05), decreased fibrogenesis marker expression (p < 0.05), thereby alleviating ALF. In addition, APs (800 mg/kg b.w.) decreased the Firmicutes/Bacteroidetes ratio (p < 0.05) in ALF mice, inhibited LPS accumulation in the liver tissue and serum (p < 0.05), and significantly inhibited the TLR4/NF-κB/TGF-β signaling in mice liver. In conclusion, APs markedly ameliorated ALF, possibly by improving gut microbiota homeostasis, decreasing the translocation of bacterial endotoxins to the blood, and suppressing the TLR4/NF-κB/TGF-β signaling pathway, indicating its potential as lead compounds for functional foods and/or drugs against ALF.