Tryptophan-kynurenine metabolism: A link between the gut microbiota dysbiosis and cognitive impairment

Cognitive impairment is a central feature of neuropsychiatric and neurodegenerative disorders, significantly diminishing patients' quality of life. Emerging evidence underscores the role of gut microbiota dysbiosis in the progression of cognitive decline. The gut microbiota influences brain function through various mechanisms, with the kynurenine pathway standing out as a key biochemical route linking peripheral metabolism to central nervous system function, thereby impacting cognitive performance. Dysregulation of the kynurenine pathway has been closely associated with neurotransmitter imbalances, exacerbated neuroinflammation, and metabolic dysfunction, all of which contribute to the onset and progression of cognitive impairment. Recent studies suggest that interventions targeting the gut microbiota, such as probiotics, antibiotics, and fecal microbiota transplantation, may improve cognitive function by modulating the kynurenine pathway. This review examines the complex relationship between gut microbiota, the kynurenine pathway, and cognition, highlighting the potential of targeting kynurenine pathway-related enzymes and microbiota modulation as therapeutic strategies. Despite promising findings, the precise mechanisms and therapeutic potential of these interventions remain under investigation, offering new avenues for the treatment of cognitive disorders.