Molecular evidence associating GLP-1 receptor agonists and brain-derived neurotrophic factors in neurodegenerative and psychiatric disorders: A systematic review

BACKGROUND: A converging mechanistic theme across mental disorders involves impaired neuroplasticity and reduced brain-derived neurotrophic factor (BDNF). Glucagon-like peptide-1 receptor agonists (GLP-1RAs), used for type 2 diabetes and obesity, have shown neuroprotective potential, but whether these effects are mediated by BDNF is unclear. OBJECTIVE: This systematic review synthesised molecular evidence linking GLP-1RA administration to BDNF changes and evaluated their contribution to illness progression in neurodegenerative and psychiatric disorders. METHODS: A systematic search of PubMed, Ovid and Google Scholar from inception to September 6, 2025, identified studies reporting BDNF-related outcomes following GLP-1RA treatment. Eligible studies included primary in vivo or in vitro research on GLP-1RAs in models of neurodegenerative or psychiatric disorders. Risk of bias was assessed using SYRCLE and QUIN tools. RESULTS: The initial search yielded 300 records, of which 18 met the inclusion criteria. Across these studies, GLP-1RAs consistently enhanced BDNF expression and signalling in models of diabetes, neurodegeneration and neurotoxicity, with diabetic models included for their relevance to GLP-1RA pharmacology and shared neuroinflammatory pathway. Reported increases in BDNF expression ranged from 76 % to 377 %, correlating with improved synaptic plasticity, cognition and neuronal survival. In vitro, GLP-1 and exendin-4 increased BDNF expression and axonal transport even under Aβ oligomer exposure. While most neuroprotection aligned with BDNF upregulation, some effects occurred independently through alternative pathways. CONCLUSION: GLP-1RAs upregulate BDNF in preclinical models, supporting its role as a key mediator of neuroprotection. Despite some BDNF-independent actions, the consistent restoration of neurotrophic support positions BDNF as a central pathway for disease modification.