Potassium 1H-indol-3-yl sulfate (Potassium 3-indoxyl sulfate) is an agonist for the human Aryl Hydrocarbon Receptor (AhR). The Aryl Hydrocarbon Receptor (AhR) has recently emerged as a pathophysiological regulator of immune-inflammatory conditions and potassium 1H-indol-3-yl sulfate has been shown to be a ligand for AhR. Potassium 1H-indol-3-yl sulfate is also a metabolite of tryptophan derived from dietary protein. Tryptophan is metabolized by intestinal bacteria into indole, which is absorbed into the blood and then further metabolized to indoxyl sulfate in the liver, which is normally excreted in urine. In chronic kidney disease patients where renal function is compromised, potassium 1H-indol-3-yl sulfate can accumulate in serum as a uremic toxin, inducing oxidative stress and accelerating progression of the disease. Potassium 1H-indol-3-yl sulfate at 250 μM can induce the activation of NF-Κb, promoting the expression of both TGF-β1 and Smad3 expression in proximal tubular cells of rats, which is associated with profibrotic activity.