title: Somatization, but not depression, is characterized by disorders in the tryptophan catabolite (TRYCAT) pathway, indicating increased indoleamine 2,3-dioxygenase and lowered kynurenine aminotransferase activity.
abstract: BACKGROUND
  Reduced plasma tryptophan occurs in depression and somatization. Induction of indoleamine 2,3-dioxygenase (IDO) with consequent synthesis of tryptophan catabolites (TRYCATs) and lowered tryptophan are associated with the onset of depression in the puerperium and during interferon-alpha treatment. Depression is accompanied by lowered kynurenic acid, a neuroprotectant, or increased kynurenine, a neurotoxic TRYCAT.
  
  
  OBJECTIVE
  To examine plasma tryptophan; kynurenine; kynurenic acid; the kynurenine / tryptophan (KY/TRP) ratio, indicating IDO activity; and the kynurenine / kynurenic acid (KY/KA) ratio, indicating kynurenine aminotransferase (KAT) activity, in somatization; depression; somatization + depression; and controls. Illness severity is measured by the Somatic Symptom Index (SSI), the Screening for Somatoform Symptoms (SOMS), and the Beck Depression Inventory (BDI).
  
  
  RESULTS
  Tryptophan is significantly lower in patients than in controls and lower in somatization than in depression. KY/TRP is significantly increased in somatization. Kynurenic acid is significantly lower in patients than in controls, and lower in somatization than in depression. KY/KA is significantly higher in somatization and somatization + depression than in depression and controls. There are significant correlations between the severity of somatization, but not depression, and KY/TRP and KY/KA (positive) and tryptophan (negative). Kynurenine and kynurenic acid are significantly correlated in controls, somatization + depression, and depression, but not in somatization.
  
  
  CONCLUSIONS
  Somatization is characterized by increased IDO activity and disorders in KAT activity and an increased neurotoxic potential. The TRYCAT pathway may play a role in the pathophysiology of somatizing and "psychosomatic" symptoms through effects on pain, gut motility, the autonomic nervous system, peripheral NMDA receptors, etc. Even more, biological disorders, such as aberrations in the TRYCAT pathway, which are considered to be a hallmark for depression, are in fact attributable to somatization rather than to depression per se. Future research in depression on the TRYCAT pathway should always control for the possible effects of somatization.
authors.affiliation: Maes Clinics @ Tria, Bangkok, Thailand. dr.michaelmaes@hotmail.com
authors.forename: Michael
authors.initials: M
authors.lastname: Maes
authors.forename: Piotr
authors.initials: P
authors.lastname: Galecki
authors.forename: Robert
authors.initials: R
authors.lastname: Verkerk
authors.forename: Winfried
authors.initials: W
authors.lastname: Rief
mesh_terms: D000328:Adult; D000367:Age Factors; D000704:Analysis of Variance; D015415:Biomarkers; D003866:Depressive Disorder / Q000235:genetics*; D039721:Diagnostic and Statistical Manual of Mental Disorders; D005260:Female; D006801:Humans; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000235:genetics / Q000378:metabolism*; D007736:Kynurenic Acid / Q000378:metabolism; D008297:Male; D011569:Psychiatric Status Rating Scales; D012727:Sex Characteristics; D013001:Somatoform Disorders / Q000235:genetics*; D000637:Transaminases / Q000235:genetics / Q000378:metabolism*; D014364:Tryptophan / Q000235:genetics*
chemical_list: D015415:Biomarkers; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D014364:Tryptophan; D000637:Transaminases; C021481:kynurenine-oxoglutarate transaminase; D007736:Kynurenic Acid