Ultrafiltered mulberry leaf glutelin mitigates non-alcoholic fatty liver disease through modulation of lipid metabolism, inflammation, and serum metabolomics

Non-alcoholic fatty liver disease (NAFLD) is a growing global health burden with limited therapeutic options. This study investigated the protective effects of mulberry leaf glutelin (UDG) on NAFLD using free fatty acid-induced HepG2 cells and a high-fat diet (HFD) mouse model. UDG inhibited pancreatic lipase and cholesterol esterase activities <i>in vitro</i>, promoted fecal lipid excretion, and reduced triglyceride and cholesterol accumulation in cells and liver tissue. <i>In vivo</i>, UDG administration significantly alleviated HFD-induced weight gain, dyslipidemia, hepatic steatosis, and liver injury (<i>p</i> < 0.05). Serum biochemical analyses showed improvements in ALT, AST, lipid profiles, and lipopolysaccharide levels, accompanied by decreased expression of inflammatory cytokines (IL-6, IL-1β, TNF-α) and suppression of the TLR4/MyD88/NF-κB signaling pathway. Furthermore, untargeted serum metabolomics revealed that UDG markedly regulated metabolic profiles, with enrichment in pathways related to bile acid metabolism, amino acid metabolism, and central carbon metabolism. Notably, metabolites such as cholic acid and chenodeoxycholic acid were negatively correlated with NAFLD indicators and restored by UDG intervention. These findings show that UDG exerts lipid-lowering, hepatoprotective, and anti-inflammatory effects against NAFLD, potentially through modulation of bile acid biosynthesis and serum metabolic pathways. This study highlights mulberry leaf glutelin as a promising plant protein source with functional food potential for NAFLD prevention and management.