Kynurenine is synthesized by the enzyme tryptophan dioxygenase, which is made primarily but not exclusively in the liver, and indoleamine 2,3-dioxygenase, which is made in many tissues in response to immune activation. Kynurenine and its further breakdown products carry out diverse biological functions, including dilating blood vessels during inflammation and regulating the immune response. Some cancers increase kynurenine production, which increases tumor growth.
Evidence suggests that increased kynurenine production may precipitate depressive symptoms associated with interferon treatment for hepatitis C. Cognitive deficits in schizophrenia are associated with imbalances in the enzymes that break down kynurenine. Kynurenine production is increased in Alzheimer's disease and cardiovascular disease where its metabolites are associated with cognitive deficits and depressive symptoms. Kynurenine is also associated with tics.
^ abOpitz CA, Litzenburger UM, Sahm F, Ott M, Tritschler I, Trump S, Schumacher T, Jestaedt L, Schrenk D, Weller M, Jugold M, Guillemin GJ, Miller CL, Lutz C, Radlwimmer B, Lehmann I, von Deimling A, Wick W, Platten M (2011). "An endogenous tumour-promoting ligand of the human aryl hydrocarbon receptor". Nature. 478 (7368): 197–203. Bibcode:2011Natur.478..197O. doi:10.1038/nature10491. PMID21976023.
^Guillemin GJ, Brew BJ, Noonan CE, Takikawa O, Cullen KM (2005). "Indoleamine 2,3 dioxygenase and quinolinic acid Immunoreactivity in Alzheimer's disease hippocampus". Neuropathology and Applied Neurobiology. 31 (4): 395–404. doi:10.1111/j.1365-2990.2005.00655.x. PMID16008823.
^Wirleitner B, Rudzite V, Neurauter G, Murr C, Kalnins U, Erglis A, Trusinskis K, Fuchs D (2003). "Immune activation and degradation of tryptophan in coronary heart disease". European Journal of Clinical Investigation. 33 (7): 550–4. doi:10.1046/j.1365-2362.2003.01186.x. PMID12814390.
^Swardfager W, Herrmann N, Dowlati Y, Oh PI, Kiss A, Walker SE, Lanctôt KL (2009). "Indoleamine 2,3-dioxygenase activation and depressive symptoms in patients with coronary artery disease". Psychoneuroendocrinology. 34 (10): 1560–6. doi:10.1016/j.psyneuen.2009.05.019. PMID19540675.
^ abHoekstra PJ, Anderson GM, Troost PW, Kallenberg CG, Minderaa RB (2007). "Plasma kynurenine and related measures in tic disorder patients". European Child & Adolescent Psychiatry. 16: 71–7. doi:10.1007/s00787-007-1009-1. PMID17665285.