The therapeutic potential of diet on immune-related diseases: based on the regulation on tryptophan metabolism

Abstract

Tryptophan (TRP), as an essential amino acid, plays crucial roles in maintaining immune homeostasis due to its complex metabolism pathway, including the microbial metabolism, 5-hydroxytryptamine and kynurenine pathways (KP). Metabolites from these pathways can act antioxidant and endogenous ligand of aryl hydrocarbon receptor (including microbiota metabolites: indole, indole aldehyde, indole acetic acid, indole acrylic acid, indole lactate, indole pyruvate acid, indole propionic acid, skatole, tryptamine, and indoxyl sulfate; and KP metabolites: kynurenine, kynurenic acid, 3-hydroxyanthranilic acid, xanthurenic acid, and cinnabarinic acid) for regulating immune response. In immune-related diseases, the production of pro-inflammatory cytokine activates indoleamine-2,3-dioxygenase, a rate-limiting enzyme of KP, leading to abnormal TRP metabolism in vivo. Many recent studies found that TRP metabolism could be regulated by diet, and the diet regulation on TRP metabolism could therapy related diseases. Accordingly, this review provides a critical overview of the relationships among diet, TRP metabolism and immunity with the aim to seek a treatment opportunity for immune-related diseases.

Keywords:

• Aryl hydrocarbon receptor
• diet
• immune response
• oxidative stress
• tryptophan metabolism

Disclosure statement

The authors have no conflict of interest to declare.

Additional information

Funding

The authors declare no conflicts of interest. The authors are grateful for the financial support from the National Natural Science Foundation of China (No. 31201416) and Science and Technology Research Program of Guangdong Province (No. 2017A01010502) for the financial support.