Molecular psychiatryOct 30, 2026

How Gut-Brain Tryptophan Processing Relates to Different Forms of Depression and Treatment Options

Gut-Brain Axis Weekly Brief ↗PubMed ↗DOI ↗OA ↗

Updated Nov 2, 2026

Abstract

Dysregulated tryptophan metabolism may play a pivotal role in the biological heterogeneity of depression.

Depression is characterized by substantial variability in symptoms and treatment responses.
The interaction between tryptophan metabolism and gut microbiota is linked to depression's pathophysiology.
Three key tryptophan metabolic pathways—kynurenine, serotonin, and microbial indole pathways—affect neuroimmune signaling and neurotransmitter function.
Distinct microbiota-dependent tryptophan metabolism profiles are observed across different depressive phenotypes.
Emerging therapeutic strategies targeting microbiota-related tryptophan metabolism include various pharmacological and nutritional interventions.
Future research should utilize advanced methods to clarify the relationship between microbiota-associated tryptophan metabolism and depression.

Simplified

Depression is a highly heterogeneous psychiatric disorder, characterized by substantial variability in clinical manifestations, treatment responses, and disease progression, thereby posing significant challenges to precision diagnosis and therapeutic intervention. Accumulating evidence indicates that dysregulated tryptophan metabolism, mediated through dynamic crosstalk with the gut microbiota and the gut-brain axis (GBA), plays a pivotal role in both the pathophysiology and biological heterogeneity of depression. In this review, we delineate the contributions of the three principal tryptophan metabolic pathways-the kynurenine, serotonin, and microbial indole pathways-in modulating neuroimmune signaling, neurotransmitter function, and gut-brain communication. Moreover, we synthesize current evidence demonstrating that microbiota-dependent tryptophan metabolism exhibits distinct profiles across clinical, demographic, immunometabolic, trauma-related, and genetically defined depressive phenotypes, thereby establishing its role as a unifying biological framework underlying depressive heterogeneity. We further provide a critical appraisal of emerging therapeutic strategies targeting microbiota-associated tryptophan metabolism, including pharmacological, nutritional, microbial, and traditional Chinese medicine-based interventions. Future investigations should integrate multi-omics approaches, longitudinal study designs, and mechanistic validation with artificial intelligence to elucidate causal relationships between microbiota-associated tryptophan metabolism and depressive heterogeneity, ultimately facilitating biomarker discovery and the development of precision therapeutics.

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How Gut-Brain Tryptophan Processing Relates to Different Forms of Depression and Treatment Options

Abstract

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