Kynurenine emerges from the shadows - Current knowledge on its fate and function

Area of Science:

• Biochemistry
• Immunology
• Metabolomics

Background:

• Kynurenine (KYN) is a primary tryptophan metabolite influencing physiological and pathological processes.
• While KYN's role in the central nervous system is studied, its peripheral functions remain largely unexplored.
• KYN acts as a ligand for the aryl hydrocarbon receptor (AhR), impacting inflammation and carcinogenesis.

Purpose of the Study:

• To review the current understanding of kynurenine's exogenous sources, metabolic fate, and functions.
• To highlight KYN's significance in peripheral physiological and pathological conditions.
• To emphasize the potential of targeting KYN synthesis for novel immunotherapies.

Main Methods:

• Literature review of existing studies on kynurenine metabolism and function.
• Analysis of the role of kynurenine in inflammation and cancer.
• Exploration of kynurenine's interaction with the aryl hydrocarbon receptor (AhR).

Main Results:

• Kynurenine (KYN) is produced by tryptophan 2,3-dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO), with increased IDO activity during inflammation and tumorigenesis.
• KYN and its metabolites are ligands for the aryl hydrocarbon receptor (AhR), implicated in various diseases.
• KYN suppresses immune responses and promotes carcinogenesis and tumor metastasis.
• Reducing KYN synthesis via TDO/IDO inhibition or genetic methods may enhance immunotherapy efficacy.
• However, reducing tryptophan catabolism to KYN does not always lower circulating KYN levels.

Conclusions:

• Kynurenine (KYN) is a critical mediator in peripheral inflammatory and carcinogenic processes.
• Targeting KYN synthesis pathways presents a promising strategy for cancer immunotherapy.
• Further research is needed to fully elucidate KYN's complex roles and optimize therapeutic interventions.