5-Hydroxyindole-3-acetic acid

5-hydroxy Indole-3-acetic acid (5-HIAA) is the primary metabolite of serotonin, metabolized by monoamine oxidase and aldehyde dehydrogenase in the liver. As the catabolic end product of the serotonin pathway, 5-HIAA is present in body fluids like cerebrospinal fluid (CSF), blood and urine. It can be used as an internal standard for the quantification of serotonin metabolism. 5-HIAA is a potent GPR35 receptor ligand, an inflammatory mediator for immune and non-immune cell populations. 5-HIAA is secreted by platelets and mast cells during inflammation and by binding to neutrophils has a chemoattractant role. 5-HIAA deficient mice show a loss of GPR35-mediated neutrophil recruitment to inflamed tissue. The chemoattractant GPR35-5-HIAA receptor-ligand system cooperates with other inflammation-induced factors in mediating neutrophil recruitment to sites of inflammation. 5-HIAA is excreted in urine and has been used as a biomarker for the detection of neuroendocrine tumors, Celiac disease and Whipple disease, where serotonin expression levels are increased. It also has been associated with metabolic syndrome and low-grade inflammation. 5-HIAA levels are low in CSF in patients with bipolar 1 disorder with childhood attention-deficit hyperactivity disorder (ADHD) or sepiapterin reductase deficiency. 5-HIAA has also been associated with autism, insomnia and chronic migraine and is used as a marker for alcohol abuse.