In addition, magnolol, a lignan found in Magnolia officinalis at a dose of 10 mg/kg, effectively increased the serum levels of tryptophan metabolites including kynurenic acid, 5-hydroxyindoleacetic acid, indole-3-acetic acid, indolelactic acid and indoxylsulfuric acid, which are endogenous AHR ligands to reduce pro-inflammatory cytokines (TNF-α, IL-6 and IL-1β) and attenuate dextran-induced colitis in rodents [75]. Here, TNF is linked to colitis.