title: The role of tryptophan degradation in the association between inflammatory markers and depressive symptoms in chronic dialysis patients.
abstract: BACKGROUND
  Among chronic dialysis patients, associations have been found between inflammatory markers and depressive symptoms. In this population, no studies have examined the mechanism linking the association between inflammatory markers and depressive symptoms. We examined whether the association between inflammatory markers and depressive symptoms is mediated by tryptophan (TRP) degradation along the kynurenine (KYN) pathway.
  
  
  METHODS
  The data are part of an observational, prospective cohort study in five urban dialysis centres in The Netherlands. Depressive symptoms were determined with the Beck Depression Inventory. Peripheral blood was collected before dialysis to measure inflammatory markers [high sensitivity C-reactive protein (HsCRP), interleukin (IL)-1β, IL-6, IL-10 and tumour necrosis factor-α (TNF-α)], TRP, KYN and 3-hydroxykynurenine. The KYN/TRP ratio was used as a measure of TRP degradation. The association between inflammatory markers and depressive symptoms was determined using linear regression analysis and adjusted for the KYN/TRP ratio.
  
  
  RESULTS
  In total, 490 chronic dialysis patients were included. HsCRP [ β = 3.8; confidence interval (CI): 1.0-6.6], IL-6 ( β = 9.1; CI: 4.0-14.1) and TNF-α ( β = 1.3; CI: 0.9-1.7) were associated with the KYN/TRP ratio. We found significant associations between HsCRP ( β = 0.8; CI: 0.3-1.3) and IL-6 ( β = 1.2; CI: 0.3-2.2) levels and depressive symptoms. However, this association was not attenuated after adjustment for the KYN/TRP ratio. Also, no significant associations were found between the KYN/TRP ratio and depressive symptoms.
  
  
  CONCLUSIONS
  The association between inflammatory markers and depressive symptoms in chronic dialysis patients was not mediated by TRP degradation along the KYN pathway.
authors.affiliation: Department of Nephrology, OLVG west, Amsterdam, The Netherlands.|Department of Psychiatry, OLVG west, Amsterdam, The Netherlands.
authors.forename: Gertrud L
authors.initials: GL
authors.lastname: Haverkamp
authors.affiliation: Department of Nephrology, OLVG west, Amsterdam, The Netherlands.|Department of Psychiatry, OLVG west, Amsterdam, The Netherlands.
authors.forename: Wim L
authors.initials: WL
authors.lastname: Loosman
authors.affiliation: Department of Nephrology, University Medical Centre Groningen, University of Groningen, Groningen, The Netherlands.
authors.forename: Casper F
authors.initials: CF
authors.lastname: Franssen
authors.affiliation: Department of Laboratory Medicine, University Medical Centre Groningen, University of Groningen, Groningen, The Netherlands.
authors.forename: Ido P
authors.initials: IP
authors.lastname: Kema
authors.affiliation: Department of Clinical Epidemiology, Leiden University Medical Centre, Leiden, The Netherlands.
authors.forename: Merel
authors.initials: M
authors.lastname: van Diepen
authors.affiliation: Department of Clinical Epidemiology, Leiden University Medical Centre, Leiden, The Netherlands.
authors.forename: Friedo W
authors.initials: FW
authors.lastname: Dekker
authors.affiliation: Department of Psychiatry, OLVG west, Amsterdam, The Netherlands.|Department of Psychiatry, VU Medical Centre, Amsterdam, The Netherlands.
authors.forename: Adriaan
authors.initials: A
authors.lastname: Honig
authors.affiliation: Department of Nephrology, OLVG west, Amsterdam, The Netherlands.
authors.forename: Carl E
authors.initials: CE
authors.lastname: Siegert
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood; D002097:C-Reactive Protein; D003863:Depression / Q000097:blood* / Q000175:diagnosis; D005260:Female; D005921:Glomerulonephritis / Q000097:blood / Q000175:diagnosis / Q000523:psychology*; D006801:Humans; D015994:Incidence; D016753:Interleukin-10 / Q000097:blood; D053583:Interleukin-1beta / Q000097:blood; D015850:Interleukin-6 / Q000097:blood; D007737:Kynurenine / Q000031:analogs & derivatives / Q000097:blood; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D006435:Renal Dialysis; D014364:Tryptophan / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000097:blood
chemical_list: D015415:Biomarkers; C508609:IL10 protein, human; C508585:IL1B protein, human; C508600:IL6 protein, human; D053583:Interleukin-1beta; D015850:Interleukin-6; C439524:TNF protein, human; D014409:Tumor Necrosis Factor-alpha; D016753:Interleukin-10; C005045:3-hydroxykynurenine; D007737:Kynurenine; D014364:Tryptophan; D002097:C-Reactive Protein
keywords: chronic dialysis patients; depressive symptoms; inflammatory markers; tryptophan degradation