title: Comparison of biomarkers of subclinical lung injury in obstructive sleep apnea.
abstract: BACKGROUND
  Obstructive sleep apnea (OSA) has both systemic and local effects partly through the increased oxidative stress caused by intermittent hypoxia and reoxygenation. However, lung-specific biomarkers in OSA have not been fully assessed in comparison with systemic biomarkers such as C-reactive protein (CRP), although results of a recent study having a small sample size indicated KL-6 as one candidate.
  
  
  METHODS
  Subjects of the present study were 197 patients suspected to have OSA. In addition to polysomnography, we also measured serum levels of KL-6, surfactant protein-D (SP-D) and CRP and pulmonary function. We examined the relationships of different biomarkers with OSA severity and pulmonary function.
  
  
  RESULTS
  The apnea/hypopnea index (AHI) was significantly positively correlated with serum KL-6 levels even after adjustment for body mass index (BMI) and smoking (p = 0.03), but not with SP-D and CRP. Also, a significant trend for an increase in serum KL-6 was noted in accordance with the severity of OSA even after adjustment for BMI and smoking (β coefficient = 0.18, p = 0.02). Additionally, elevated KL-6 levels were significantly associated with restrictive lung function disturbance and gas exchange derangement after adjustment for obesity and smoking, which contrasted with CRP whose elevations were significantly associated with worsened airflow limitation and increased lung volume.
  
  
  CONCLUSIONS
  Serum KL-6 levels may reflect the degree of subclinical lung injury associated with OSA independently of obesity or smoking, unlike CRP. We consider that KL-6 can be a potential candidate as a lung-specific biomarker of OSA and might provide complementary information on systemic biomarkers in assessing OSA.
authors.affiliation: Department of Respiratory Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Kensaku
authors.initials: K
authors.lastname: Aihara
authors.forename: Toru
authors.initials: T
authors.lastname: Oga
authors.forename: Yuka
authors.initials: Y
authors.lastname: Harada
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Chihara
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Handa
authors.forename: Kiminobu
authors.initials: K
authors.lastname: Tanizawa
authors.forename: Kizuku
authors.initials: K
authors.lastname: Watanabe
authors.forename: Tomomasa
authors.initials: T
authors.lastname: Tsuboi
authors.forename: Takefumi
authors.initials: T
authors.lastname: Hitomi
authors.forename: Michiaki
authors.initials: M
authors.lastname: Mishima
authors.forename: Kazuo
authors.initials: K
authors.lastname: Chin
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D001784:Blood Gas Analysis; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000209:etiology / Q000503:physiopathology*; D055370:Lung Injury / Q000209:etiology / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D018384:Oxidative Stress / Q000502:physiology*; D017286:Polysomnography; D012129:Respiratory Function Tests / Q000379:methods; D020181:Sleep Apnea, Obstructive / Q000097:blood / Q000150:complications / Q000503:physiopathology*
chemical_list: D015415:Biomarkers