Furthermore, hydroxycarboxylic acid receptor 3 (HCAR3) and nicotinamide N-methyltransferase (NNMT) were recognized as potential drug targets for reverting IBD-related changes in mucosal levels of Trp, kynurenine (Kyn), nicotinamide adenine dinucleotide (NAD+), and related metabolites. Here, HCAR3 is linked to inflammatory bowel disease.