p-Synephrine, synergistically with Gastrodin, alleviates reserpine-induced depressive pathologies by binding to MT₁...

p-Synephrine (p-Syn), a natural alkaloid isolated from Citrus aurantium L., promotes fat oxidation and is therefore widely used as a weight loss dietary supplement. It was recently reported to exert a potent antidepressant effect. However, its molecular targets remain undefined. Gastrodin (Gas), extracted from Gastrodia elata Blume, exerts antidepressant effects by targeting Melatonin Receptor 1A (MT₁).

This study aimed to evaluate whether MT₁ is a target of p-Syn, and to verify the antidepressant effects of p-Syn and Gas.

Network pharmacology was applied to predict potential targets and associated signaling pathways for p-Syn and Gas. Molecular Docking simulations were employed to predict the possible binding sites of MT₁ with p-Syn. Solvent-induced Protein Precipitation (SIP) and Fluorescence Correlation Spectroscopy (FCS) were employed to validate p-Syn's binding affinity with MT_1. Cellular Thermal Shift Assay (CETSA) was used to confirm the predicted key binding sites in exogenously overexpressed site-mutated MT_1. of Extracellular regulated protein kinases (ERK) and cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB) downstream of MT_1, following treatment with p-Syn or Gas, or the synergistic use of both, was investigated by Western blotting.

Using a network pharmacology approach and in vitro assays, we found that both p-Syn and Gas bind to MT1, activate the ERK/CREB signaling pathway, and up-regulate BDNF. In vivo assays showed that p-Syn alleviated Reserpine (Res)-induced depression-like symptoms in AB zebrafish larvae and C57 mice. Furthermore, p-Syn and Gas showed a remarkable synergistic effect.

This study identifies a novel target for p-Syn and provides new insights into the antidepressant mechanisms of p-Syn and Gas that may contribute to the clinical application of these compounds in the development of new drugs for the treatment of depression.