Abstract: Purpose: The effect of natto on the behavioral ability and nutrient metabolism of aging mice was investigated from the perspectives of the liver, muscle and intestine. Methods: A mouse model of subacute aging was established by intraperitoneal injection of 500 mg/kg of D-galactose, and the mice were fed a diet supplemented with natto (2.5% m/m) for 10 weeks. Behavioral assays were performed, liver function was evaluated by serum biochemical analysis, histopathological analysis and immunohistochemistry, and real-time quantitative polymerase chain reaction was used to detect the expression of genes involved in signaling pathways. The intestinal flora diversity and intestinal metabolome were analyzed. Results: Natto significantly inhibited body mass loss, behavioral and memory impairment and organ tissue damage in aging mice, and significantly improved oxidative stress levels in the liver, kidney and skeletal muscle. Natto also significantly suppressed the abnormal elevation of the protein and gene expression of phosphatidylinositol 3-kinase (PI3K) and serine/threonine kinase 1 (Akt1) in the liver of aging mice. Meanwhile, natto changed the intestinal flora composition of aging mice mainly by increasing the relative abundance of Akkermansia, Bacteroides, Sutterella and Enterococcus, and decreasing the relative abundance of Streptococcus, Desulfovibrio and Roseburia, and it improved intestinal function by enriching the gene expression of carbohydrate metabolism, amino acid metabolism, cofactor and vitamin metabolism. Furthermore, non-targeted metabolomics analysis showed that ATP-binding cassette transporter and tryptophan metabolism were the major regulatory pathways for natto to alleviate the symptoms in aging mice. 5-Hydroxyindoleacetic acid and xanthurenic acid as well as the legume-specific flavonoid metabolites daidzein and glycitein, which were significantly enriched in the natto treatment group, were positively correlated with body mass and liver superoxide dismutase (SOD) activity, and negatively correlated with behavioral indexes, uric acid and liver malondialdehyde (MDA) levels. Conclusion: Natto alleviates age-related liver and intestinal damage by inhibiting the liver PI3K/Akt signaling pathway, increasing the intestinal abundance of Akkermansia, Sutterella and Enterococcus, decreasing the abundance of Streptococcus and Desulfovibrio, elevating tryptophan and flavonoid metabolite levels, and enhancing nutrient absorption and energy metabolism. These findings provide a theoretical basis for the research and development of natto products suitable for the elderly.

Key words: natto; aging; liver; intestinal flora; phosphatidylinositol 3-kinase/serine/threonine kinase signaling pathway; non-targeted metabolomics