Molecular pathways of Traditional Chinese medicine–derived compounds in cognitive decline and depressive disorders: Neuroinflammation, synaptic plasticity and stress axis regulation

Background: Central pathophysiological mechanisms underlying cognitive impairment and mood disorders are complex. Traditional Chinese Medicine (TCM)–derived bioactive compounds have significant research value in this field. Objective: This study aimed to synthesize current preclinical and emerging clinical evidence on the neuroprotective and psychotropic effects of key TCM constituents, with a particular focus on their roles in modulating neuroinflammatory signalling, synaptic plasticity, oxidative balance and stress-related neuroendocrine pathways. Methods: A narrative synthesis of experimental and early clinical studies was conducted, emphasizing mechanistic investigations in rodent models and exploratory human trials. Outcomes of interest included inflammatory cytokine expression, inflammasome activation, redox homeostasis, synaptic signalling pathways, neuroendocrine regulation, behavioural performance and translational pharmaceutical considerations. Results: Multiple TCM constituents attenuate microglial activation and inflammasome signalling, suppressing interleukin-1?, interleukin-6 and tumor necrosis factor-alpha through inhibition of nuclear factor ?B and NOD-like receptor pyrin domain-containing 3 pathways. These effects restore redox homeostasis, reduce synaptic loss and improve cognitive and behavioural outcomes in animal models. Concurrently, several compounds enhance synaptic resilience by upregulating brain-derived neurotrophic factor and tropomyosin receptor kinase B signalling, activating downstream mechanistic target of rapamycin complex 1 and cyclic adenosine monophosphate response element-binding protein pathways and preserving synaptic proteins. Key agents, including ginsenosides, baicalin and curcumin, have shown translational promise, with small human trials reporting improvements in depressive symptoms, cognitive function and biomarker profiles. Additionally, TCM compounds modulate HPA axis dynamics by attenuating stress-induced corticosterone elevation, restoring glucocorticoid receptor sensitivity and rebalancing monoaminergic and glutamatergic neurotransmission. However, pharmaceutical translation remains limited by challenges related to formulation, dosage standardization and poor oral bioavailability, particularly for flavonoids and saponins. Conclusion: TCM-derived compounds exert multifaceted neuroprotective and psychotropic effects, while successful clinical translation requires strengthened pharmaceutical characterization, standardized dosing strategies and advanced delivery systems such as nanoformulations, phytosomes and standardized granules to enhance bioavailability, reliability and regulatory acceptance.