Huanglian Wendan ameliorates depression via gut-brain axis-related PPAR-α/allo pathways

Huanglian Wendan decoction (HLWD) is traditionally used to treat a syndrome characterized by symptoms such as insomnia, irritability, and digestive disturbances. Its historical application in addressing phlegm-heat-induced mental and emotional disorders offers both a cultural and clinical basis for investigating its potential mechanisms in alleviating depressive symptoms via gut-brain axis.

To explore the potential therapeutic mechanisms of HLWD in improving depression.

Behavioral outcomes were assessed using the SPT, TST, OFT, and SIT. Neurogenesis was evaluated by measuring dendritic length and neuronal intersections. Allopregnanolone levels were measured using ELISA. Inflammatory signaling pathways (TLR4, MyD88, NF-κB) and cytokines (IL-1β, TNF-α, IL-10, IL-4) in the hippocampus were analyzed via WB. The integrity of the intestinal barrier was further validated through immunofluorescence and histological examination. Finally, GW6471 was employed to investigate whether PPAR-α mediates the effects of HLWD.

The UPLC analysis identified 42 constituents, primarily comprising flavonoids, alkaloids, and coumarins. Behavioral assays demonstrated that HLWD effectively ameliorated depressive-like behaviors in mice. Mechanistically, HLWD elevated the levels of DCX-positive neurogenesis markers, inhibited microglial activation, protected the intestinal mucosal barrier, and reduced inflammatory responses in both the colon and hippocampus. The RNA-seq results indicated an enrichment of the PPAR signaling pathway in colon. Consistent with this finding, HLWD significantly upregulated both the protein and mRNA levels of PPAR-α in the colon. Meanwhile, it increased the concentration of allopregnanolone in hippocampal via peripheral circulation. Notably, the administration of the PPAR-α antagonist GW6471 reversed these neuroprotective effects and the associated protein changes, thereby underscoring the critical role of PPAR-α in the therapeutic mechanism of HLWD.

HLWD can elevate the levels of PPAR-α and allopregnanolone in the colon, subsequently influencing the levels of allopregnanolone in the hippocampus via peripheral circulation. This process may enhance neurological function and alleviate depressive symptoms.