Bioactive proteins and antioxidant peptides from Litsea cubeba fruit meal: Preparation, characterization and ameliorating function on high-fat diet-induced NAFLD through regulating lipid metabolism, oxidative stress and inflammatory response

Non-alcoholic fatty liver disease (NAFLD) plays an increasingly significant threat to human health. In this study, the processing by-products of Litsea cubeba fruit meal were defatted by ultrasound-assisted methods, then the acetone-precipitated protein of L. cubeba (LCP) was obtained and structural analysis was performed. LCP was hydrolyzed by a two-step sequential hydrolysis method using alcalase and papain. Subsequently, antioxidant peptide fraction (IV2) was isolated and identified from the resultant hydrolysate through membrane ultrafiltration, Sephadex G-15 chromatography, and liquid chromatograph mass spectrometer (LC-MS). Animal experimentation indicated the potential of IV2 to mitigate hepatic steatosis. Moreover, IV2 could effectively reduce oxidative stress-induced damage by modulating the Keap1-Nrf2 pathway to activate downstream heme oxygenase-1 (HO-1) and NAD(P) H quinone oxidoreductase 1 (NQO1). Integrating metabolomics and transcriptomics revealed enrichment in pathways associated with glycerolipid metabolism and fatty acid beta-oxidation, suggesting the principal mechanisms underlying IV2's ameliorative effects on NAFLD. Transcriptome sequencing identified 3092 up-regulated and 3010 down-regulated genes following IV2 treatment. Interaction analyses based on different lipid compositions (DELs) and differentially expressed genes (DEGs) indicated that IV2 primarily alleviated hepatic steatosis by modulating peroxisome proliferator-activated receptor alpha (PPAR-alpha) related pathways, thereby augmenting fatty acid beta-oxidation within liver cells. These results indicate that IV2 shows potential in improving high-fat diet (HFD)-induced NAFLD, with improved fatty acid beta-oxidation and reduced triglyceride biosynthesis emerging as underlying mechanisms.