Lithocarpus polystachyus Rehd. leaves aqueous extract inhibits learning and memory impairment in Alzheimer's disease rats: Involvement of the SIRT6/NLRP3 signaling pathway.

Alzheimer's disease (AD) is a chronic and progressive neurodegenerative condition that is influenced by multiple factors along with neuroinflammation and oxidative stress. Our previous study proved that Lithocarpus polystachyus Rehd. aqueous extract (sweet tea aqueous extract, STAE) effectively inhibits hydrogen peroxide-induced neuronal cell injury. However, it is not clear whether STAE can protect against AD, and its underlying mechanisms are still uncertain. Therefore, the present study was designed to evaluate the possible behavioral and neurochemical effects of STAE on Aβ (25-35)-induced AD rats administered STAE (20, 40, 80 mg/mL) for 14 days. We showed that STAE administration significantly and dose-dependently ameliorated the cognitive deficits in the AD rat models, assessed in the Morris water maze (MWM) test, Y-maze test, and novel object recognition (NOR) test. The results of hematoxylin and eosin (H&E) staining and Nissl staining showed that after treatment with STAE, the pathological damage to the hippocampal CA1, CA3, and dentate gyrus (DG) neurons of rats was significantly improved. Furthermore, STAE dose-dependently inhibited microglia and astrocyte activation in the hippocampus of rats accompanied by increased protein expression of silent mating-type information regulation 2 homolog 6 (SIRT6) and decreased protein expression of nod-like receptor thermal protein domain-associated protein 3 (NLRP3) and its downstream pyroptosis-related genes after following Aβ (25-35). In summary, our findings indicate that STAE effectively inhibits Aβ (25-35)-induced learning and memory impairment in rats, and the mechanism is, at least partially, related to the regulation of SIRT6/NLRP3 signaling pathway.