Total Saponins of Panax Notoginseng Leaves Modulate the "Microglial-NLRP3/Caspase-1" Axis associated with Gut Microbial/SCFAs Alterations: Correlative Insights into Cognitive Improvement in Senescence

The "Microglial-NLRP3/Caspase-1" axis-driven neuroinflammation contributes to senescence-related cognitive dysfunction, while the gut microbiota and its metabolites offer therapeutic potential. This study explored whether total saponins of Panax notoginseng leaves (TSPNL) are associated with alleviation senescence-related cognitive dysfunction in association with modulation of the "Microglial-NLRP3/Caspase-1" axis and gut microbiota-derived metabolites. A senescent rat model was induced by D-galactose. Rats received TSPNL for six weeks concurrently. Morris water maze and open-field tests were used to observe learning and cognitive functions. HE and Nissl staining observed pathological changes in the hippocampus. Western blot and qPCR detected the protein and mRNA relative expression of NLRP3, ASC, Caspase-1 and IL-1β in the hippocampal tissue of rats. ELISA measured inflammatory factors in hippocampus and serum. 16S rRNA gene high-throughput sequencing detected changes in gut microbiota. GC-MS measured levels of SCFAs. The NLRP3 inhibitor group was established to further verify the role of this pathway in microglial cells. Compared with the Mod group, the TSPNL_H group showed significant improvement in learning and cognitive functions, with a marked reduction in hippocampal histopathological damage. The protein and mRNA relative expression of NLRP3, Caspase-1, and IL-1β in the hippocampus were markedly reduced. IL-1β in both hippocampal tissue and serum was markedly decreased, while IL-10 was significantly increased. In cell experiments, TSPNL and the NLRP3 inhibitor were associated with reduced expression of inflammatory factors such as IL-1β, IL-6 and IL-18, and downregulated mRNA levels of NLRP3, Caspase-1 and ASC; Iba1 protein expression did not show statistically significant changes between groups. Gut-differentiated bacterial s_Neglectibacter timonensis was notably enriched in the TSPNL_H group, and propionic acid was significantly elevated. Additionally, propionic acid showed a negative correlation with the "Microglial-NLRP3/Caspase-1" axis, a negative correlation with IL-1β, and a positive correlation with IL-10. TSPNL is associated with alterations in the intestinal bacterial metabolite propionic acid and may contribute to the inhibition of the "Microglia-NLRP3/Caspase-1" axis, potentially reducing the release of inflammatory factors, alleviating neuroinflammation, and improving cognitive dysfunction associated with senescence.