Collagen peptides from Skipjack tuna (Katsuwonus pelamis) bones: Composition, characterization, and mechanism of high-fat diet-induced NAFLD amelioration.

This study aimed to analyze the amino acid composition and characterize the sequences of collagen peptides from Skipjack tuna bones (TBCPs) by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and further investigate the function and mechanism of action of TBCPs in nonalcoholic fatty liver disease (NAFLD). The results showed that TBCPs contain 16 types of amino acids, among which glycine is the most abundant, and hydrophobic amino acids account for 40.75 %. Moreover, a total of twenty-eight active peptide sequences with an ALC ≥ 95 % were identified from TBCPs. In vivo test results revealed that TBCPs can reverse weight gain, liver lobular injury, hepatic cord disorders, and increased inflammatory cell levels in mice with high-fat diet (HFD)-induced NAFLD. Moreover, TBCPs contributed to reducing the number and size of lipid droplets and vacuoles in liver slices and decreased the degree of lipid degeneration. The mechanistic studies indicated that TBCPs can promote AMPK phosphorylation, reduce sterol synthesis, and decrease SREBP-1c synthesis, thereby reducing fat synthesis and decreasing the levels of TG, TC, AST, and ALT. Additionally, TBCPs can promote lipid β-oxidation by increasing PPAR-α and CPT-1 levels. Moreover, TBCPs can increase antioxidant levels to counteract oxidative stress by activating the Nrf2 pathway to increase the protein expression of HO-1 and NQO1; increase the activity of SOD, GSH-Px, and CAT; and reduce the MDA content. Moreover, TBCPs can alleviate the inflammatory response by reducing the expression levels of TLR4, MyD88, TNF-α, and IL-6. Therefore, TBCPs may be considered a beneficial dietary supplement for maintaining liver health.