New roles of tryptophan byproducts and gut bacteria in metabolism and gut health

Around 5% of dietary tryptophan is metabolized by gut microbes.

• Tryptophan metabolism occurs locally in the gut primarily through host enzymes.
• Three significant metabolic pathways for tryptophan include indole, kynurenine, and related derivatives.
• Bacterial transformations of tryptophan to indole and its derivative indole-3 propionic acid are associated with human metabolic disease and gut permeability.
• Kynurenine is converted to kynurenic acid and xanthurenic acid by both host and bacterial enzymes.
• Increased mRNA expression for kynurenine pathway enzymes was observed in the colon of high-fat-fed mice, indicating potential disruption in metabolic disease.
• The interplay between host and microbiota may influence the production or regulation of kynurenine metabolites, affecting both host and microbiome health.

Simplified