Didang decoction improves gut microbiota and cognitive function in TDACD rats: Combined proteomics and 16S rRNA sequencing.

Background: Type 2 diabetes mellitus (T2DM) significantly elevates the risk of cognitive impairment. Didang Decoction (DDD), a classical Traditional Chinese Medicine (TCM) formula, has shown promise in alleviating diabetic symptoms and improving cognitive performance. Although historical TCM records suggest neuroprotective properties, ​the mechanistic basis for DDD's therapeutic effects on T2DM-associated cognitive dysfunction (TDACD) remains unexplored.

Purpose: This work sought to clarify the chemical composition and mechanisms of action of DDD by pursuing three primary objectives: (1) identification of the major active constituents of DDD; (2) validating of the hypothesis that DDD ameliorates TDACD via regulation of the gut microbiota; and (3) investigating DDD's regulatory effects on hippocampal lipid metabolism and autophagy pathways.

Methods: Ultra-high performance liquid chromatography-Q exactive mass spectrometry (UHPLC-QE-MS/MS) was employed to analyze the chemical composition of DDD. Cognitive function was assessed through behavioral tests. Histopathological examinations and western blotting (WB) were conducted to assess the effects of DDD on the hippocampus of TDACD rats. 16S ribosomal RNA (16S rRNA) sequencing was conducted to characterize gut microbiota, composition, and proteomics was used to evaluate hippocampal proteins expression.

Results: The major bioactive components of DDD were identified, including dihydrotanshinone I, aloe-emodin, chrysophanol, calycosin, sakuranetin, gallic acid, kaempferol, and rhein, emodin, etc. DDD increased neuronal density and synaptic function in the hippocampus of TDACD rats, hereby improving working memory and long-term memory. DDD boosted the relative abundance of beneficial bacteria, including Roseburia, [Eubacterium] coprostanoligenes group, Christensenellaceae R-7 group, and Alistipes, which were diminished in the TDACD group. Proteomics analysis indicated that DDD enhanced hippocampal energy metabolism and reduced neuronal damage in TDACD rats via pathways related to cholesterol and fatty acid metabolism, as well as autophagy.

Conclusions: DDD demonstrates potential as an adjuvant therapeutic agent for TDACD, with dual benefits in ameliorating glucose metabolism and cognitive impairments. Mechanistically, the neuroprotective effects of DDD are attributed to the regulation of hippocampal lipid energy metabolism and autophagic homeostasis, as well as the enhancement of beneficial gut microbes.