title: Pro-inflammatory cytokines and leukocyte oxidative burst in chronic kidney disease: culprits or innocent bystanders?
abstract: BACKGROUND
  Pro-inflammatory cytokines are elevated in chronic kidney disease (CKD), a condition characterized by microinflammation with oxidative stress as key feature. However, their role in the inflammatory response at uraemic concentrations has not yet been defined. In this study, the contribution of cytokines on induction of leukocyte oxidative stress was investigated.
  
  
  METHODS
  Whole blood from healthy donors was incubated with 20-1400 pg/mL TNFα, 5-102.8 pg/mL IL-6, 20-400 pg/mL IL-1β and 75-1200 pg/mL IL-18 separately or in combination. Oxidative burst was measured, at baseline and after stimulation with fMLP (Phagoburst™). The effect of the TNFα blocker, adalimumab (Ada), was evaluated on TNFα-induced ROS production. Finally, the association between TNFα and the composite end point all-cause mortality or first cardiovascular event was analysed in a CKD population stage 4-5 (n = 121).
  
  
  RESULTS
  While interleukin (IL)-6, IL-1β and IL-18 alone induced no ROS activation of normal leukocytes, irrespective of concentrations, TNFα induced ROS activation at baseline (P < 0.01) and after fMLP stimulation (P < 0.05), but only at uraemic concentrations in the high range (400 and 1400 pg/mL). A similar pattern was observed with all cytokines in combination, but already at intermediate uraemic concentrations (all P < 0.05, except for monocytes after fMLP stimulation: n.s.), suggesting synergism between cytokines. ROS production induced by TNFα (400 pg/mL) and the cytokine combination was blocked with Ada. Uraemia-related oxidative stress in leukocytes of haemodialysis patients was however not blocked by Ada. In patients, TNFα was not associated to adverse events (HR: 1.52, 95% CI 0.81-2.85, P = 0.13).
  
  
  CONCLUSIONS
  Among several pro-inflammatory cytokines, TNFα alone was pro-oxidative but only at high-range uraemic concentrations. Adding a TNFα blocker, Ada, blocked this ROS production, but not the oxidative stress in blood samples from haemodialysis patients, suggesting that other uraemic toxins than TNFα are more crucial in this process. However, the lack of association between TNFα and mortality suggests that the role of TNFα-linked oxidative stress is limited.
authors.affiliation: Renal Division, Department of Internal Medicine, Ghent University Hospital, Ghent, Belgium.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Neirynck
authors.affiliation: Renal Division, Department of Internal Medicine, Ghent University Hospital, Ghent, Belgium.
authors.forename: Griet
authors.initials: G
authors.lastname: Glorieux
authors.affiliation: Renal Division, Department of Internal Medicine, Ghent University Hospital, Ghent, Belgium.
authors.forename: Eva
authors.initials: E
authors.lastname: Schepers
authors.affiliation: Renal Division, Department of Internal Medicine, Ghent University Hospital, Ghent, Belgium.
authors.forename: Annemieke
authors.initials: A
authors.lastname: Dhondt
authors.affiliation: Renal Division, Department of Internal Medicine, Ghent University Hospital, Ghent, Belgium.
authors.forename: Francis
authors.initials: F
authors.lastname: Verbeke
authors.affiliation: Renal Division, Department of Internal Medicine, Ghent University Hospital, Ghent, Belgium.
authors.forename: Raymond
authors.initials: R
authors.lastname: Vanholder
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016207:Cytokines / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007249:Inflammation / Q000276:immunology* / Q000473:pathology; D007962:Leukocytes / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects*; D051436:Renal Insufficiency, Chronic / Q000188:drug therapy / Q000276:immunology / Q000473:pathology*; D016897:Respiratory Burst / Q000187:drug effects*
chemical_list: D016207:Cytokines
keywords: CKD; haemodialysis; mortality; oxidative stress; tumour necrosis factor alpha