Chaihu Shugan San exerts antidepressant effects by driving microglial M2 polarization via inhibition of the IL-1β/JNK signaling pathway.

ETHNOPHARMACOLOGICAL RELEVANCE: Chaihu Shugan San (CSS) is a classic traditional Chinese medicine formula originally recorded in Jingyue Quanshu, historically used for regulating Qi and relieving depression. Its composition, centered on Bupleuri Radix as the sovereign herb for soothing the liver, is combined with other herbs to regulate Qi, activate blood, and harmonize the middle energizer. Clinical evidence supports its efficacy in improving depressive mood and somatic symptoms, aligning with its traditional use, while modern studies suggest a multi-component, multi-target mechanism underlying its antidepressant effects.

AIM OF THE STUDY: This study sought to systematically elucidate the pharmacodynamic material basis of CSS responsible for its antidepressant effects, along with the related immunomodulatory mechanisms.

MATERIALS AND METHODS: The optimal active fraction of CSS was identified through a screening process utilizing a reserpine-induced zebrafish model of depression, with its chemical constituents characterized by UPLC-Q-TOF-MS/MS. The antidepressant efficacy of the identified optimal extract was further validated using a corticosterone-induced mouse model of depression. An integrated methodological approach, incorporating transcriptomics, network pharmacology, and molecular biology techniques, was employed to investigate the immunomodulatory mechanisms underlying the antidepressant effects of CSS. Spectrum-effect relationship analysis was conducted to identify key active components and elucidate their mechanisms of action.

RESULTS: The 95 % ethanol extract of CSS (CSS-95) demonstrated the most robust antidepressant activity, significantly enhancing behavioral parameters in depression models. It was observed to upregulate levels of 5-hydroxytryptamine (5-HT) and dopamine (DA), while downregulating corticosterone (CORT), adrenocorticotropic hormone (ACTH), and pro-inflammatory cytokines (TNF-α, IL-6, IL-1β, IL-18). Additionally, CSS-95 elevated anti-inflammatory cytokines (IL-10, TGF-β). Mechanistic investigations indicated that CSS-95 inhibited microglial M1 polarization by reducing the CD86, promoted M2 polarization by increasing the CD206, and suppressed the expression of key proteins in the IL-1β/JNK pathway, including IL-1β, MyD88, TRAF6, TAK1, MKK4, p-JNK, and c-Jun. Spectrum-effect correlation analysis, integrated with network pharmacology, identified 13 potential active components. Among these, seven monomers, such as albiflorin and liquiritin, were validated as effective in the zebrafish model, modulating the expression of genes associated with 5-HT, TNF-α, IL-6, and the IL-1β/JNK pathway. HPLC quantitative analysis confirmed the presence of albiflorin, liquiritin, chlorogenic acid, naringin, glycyrrhizic acid, and saikosaponin D as quality markers associated with the antidepressant effects.

CONCLUSION: CSS exhibits antidepressant effects through the synergistic actions of multiple components that inhibit the IL-1β/JNK signaling pathway, facilitate microglial polarization towards the M2 phenotype, and ultimately suppress neuroinflammation. These findings offer a scientific foundation for the clinical application and quality control of CSS.