title: Soluble interleukin 6 receptor: A novel marker of moderate to severe sleep-related breathing disorder.
abstract: BACKGROUND
  Given the previously described association between sleep-related breathing disorder (SRBD) and markers of inflammation, we assessed the relationship of SRBD with levels of both interleukin 6 (IL-6) and soluble IL-6 receptor (sIL-6R), a marker with more expansive physiologic effects than IL-6. The objectives were to explore the relationship between moderate to severe sleep apnea with IL-6 and sIL-6R levels and to examine morning and evening variability for each cytokine.
  
  
  METHODS
  A total of 385 adult participants (> or =18 years of age) in the Cleveland Family Study, Cleveland, Ohio, underwent sleep studies and determination of IL-6 and sIL-6R levels in samples obtained in the evening and morning of polysomnography. Moderate to severe SRBD was defined as a respiratory disturbance index greater than or equal to 30.
  
  
  RESULTS
  The subjects were aged 44.9 +/- 16.7 (mean +/- SD) years, 44% were male, and 48% were African American, with a body mass index (weight in kilograms divided by the height in meters squared) of 32.5 +/- 8.1 (mean +/- SD). Linear regression analysis showed that after adjustment for subject characteristics, waist circumference, and comorbidities, SRBD was not significantly associated with morning IL-6 levels. In contrast, linear regression analyses showed that, compared with the participants without SRBD, those with SRBD had significantly higher morning sIL-6R levels (mean +/- SD, 4.60 +/- 1.42 ng/mL [P = .001]), even after adjustment for subject characteristics, waist circumference, and comorbidities, which persisted after adjustment of evening sIL-6R levels.
  
  
  CONCLUSIONS
  Morning sIL-6R levels demonstrated stronger associations with moderate to severe SRBD than morning IL-6 levels. Associations with SRBD and morning sIL-6R levels persisted even after adjustment for waist circumference, cardiovascular disease, and evening sIL-6R levels, suggesting the potential utility of sIL-6R as a marker for measuring overnight SRBD stresses. Further investigation of this biomarker may provide insight into SRBD-related inflammation.
authors.affiliation: Department of Medicine, Case School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, USA. mehrar@ameritech.net
authors.forename: Reena
authors.initials: R
authors.lastname: Mehra
authors.forename: Amy
authors.initials: A
authors.lastname: Storfer-Isser
authors.forename: H Lester
authors.initials: HL
authors.lastname: Kirchner
authors.forename: Nathan
authors.initials: N
authors.lastname: Johnson
authors.forename: Nancy
authors.initials: N
authors.lastname: Jenny
authors.forename: Russell P
authors.initials: RP
authors.lastname: Tracy
authors.forename: Susan
authors.initials: S
authors.lastname: Redline
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D015992:Body Mass Index; D005260:Female; D006801:Humans; D015850:Interleukin-6 / Q000097:blood*; D016014:Linear Models; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D017286:Polysomnography; D019947:Receptors, Interleukin-6 / Q000097:blood*; D012720:Severity of Illness Index; D012891:Sleep Apnea Syndromes / Q000097:blood*; D013997:Time Factors; D049629:Waist-Hip Ratio
chemical_list: D015415:Biomarkers; D015850:Interleukin-6; D019947:Receptors, Interleukin-6