Hepatoprotective Potential of Walnut Oil Unsaponifiable Matter on Aging-Induced Liver Injury via Gut Microbiota-Liver Axis

Aging is characterized by the gradual deterioration of physiological functions. This research aimed to explore the protective effects of unsaponifiable matter (USM), a natural component found in walnut oil, against D-galactose (D-gal)-induced liver injury in aging mice. Male C57BL/6 mice received subcutaneous D-gal injections alongside oral USM (400 mg/kg) administration for 8 weeks. Systemic evaluations were subsequently conducted using biochemical assays, hepatic transcriptomics, and 16S rRNA sequencing. The results demonstrated that USM administration alleviated hepatic tissue damage, enhanced antioxidant activity, reduced pro-inflammatory cytokines, and improved serum lipid profiles. Transcriptomic analysis revealed that USM upregulated hepatic energy and lipid metabolism pathways while suppressing inflammatory cascades. Furthermore, USM restored intestinal barrier integrity by upregulating tight junction proteins and rebalanced the gut microbiota, enriching beneficial taxa (e.g., Akkermansia, Lactobacillaceae) while reducing the relative abundance of Firmicutes and Proteobacteria. In conclusion, this study elucidates that USM mitigates aging-associated liver injury by modulating microbial homeostasis and ameliorating intestinal barrier function via the gut-liver axis.