title: Adipose tissue is influenced by hypoxia of obstructive sleep apnea syndrome independent of obesity.
abstract: OBJECTIVE
  Obstructive sleep apnea syndrome (OSAS) is associated with increased cardiovascular risk and diabetes independent of obesity. We investigated whether adipose tissue dysfunction is exacerbated due to increased tissue hypoxia.
  
  
  METHODS
  Adipose tissue (AT) oxygenation was measured with a Clarke-type electrode (pATO2) in 16 men with OSAS before and after 4 months of continuous positive airway pressure therapy (CPAP) and in BMI-matched controls. Oxygenation was simultaneously monitored in arterial blood by pulse oximetry (SaO2); mixed blood in AT microcirculation by reflectance spectroscopy (SATO2) along with blood flow. Markers of hypoxia, adipo- and angiogenesis, inflammation and fibrosis were analysed in AT and serum.
  
  
  RESULTS
  OSAS subjects were more insulin resistant. Despite lower arterial SaO2(95.4±1.3% vs. 97.1±1.6%, P=0.013) in subjects with OSAS, there was no difference in the oxygen content of AT microcirculation (61.6±18.4 vs. 72.2±7.0%, P=0.07) or pATO2(49.2±7.5 vs. 50.4±14.7mmHg, P=0.83) between groups. Resting AT blood flow was higher in OSAS compared to controls (108.5±22.7 vs. 78.9±24.9au, P<0.005) and strongly associated with inflammation markers IL-6 and MCP-1. AT of OSAS subjects showed increased inflammation (TNFA P=0.049) and fibrosis (COL3A1 P=0.02), a trend of higher HIF1A expression (P=0.06) and reduced adipogenesis (PPARG P=0.006). After CPAP, only expression of the lipid deposition marker LPL increased (30%, P=0.047).
  
  
  CONCLUSIONS
  Adipose tissue of awake OSAS subjects appears no more hypoxic than adipose tissue of BMI-matched controls despite daytime hypoxaemia. Increased adipose tissue blood flow may be explained by an increased inflammatory response. We observe features of adipose dysfunction in subjects with OSAS, which attribute to increased cardiometabolic risk associated with this condition.
authors.affiliation: Diabetes and Vascular Research Group, University of Exeter Medical School, Exeter, UK; NIHR Exeter Clinical Research Facility, University of Exeter Medical School, Exeter, UK.
authors.forename: C E
authors.initials: CE
authors.lastname: Thorn
authors.affiliation: Diabetes and Obesity Research Group, University of Exeter Medical School, Exeter, UK.
authors.forename: B
authors.initials: B
authors.lastname: Knight
authors.affiliation: Diabetes and Obesity Research Group, University of Exeter Medical School, Exeter, UK.
authors.forename: E
authors.initials: E
authors.lastname: Pastel
authors.affiliation: Diabetes and Obesity Research Group, University of Exeter Medical School, Exeter, UK.
authors.forename: L J
authors.initials: LJ
authors.lastname: McCulloch
authors.affiliation: Department of Respiratory Medicine, Royal Devon and Exeter NHS Foundation Trust, Exeter, UK.
authors.forename: B
authors.initials: B
authors.lastname: Patel
authors.affiliation: Diabetes and Vascular Research Group, University of Exeter Medical School, Exeter, UK; NIHR Exeter Clinical Research Facility, University of Exeter Medical School, Exeter, UK.
authors.forename: A C
authors.initials: AC
authors.lastname: Shore
authors.affiliation: Diabetes and Obesity Research Group, University of Exeter Medical School, Exeter, UK. Electronic address: K.Kos@exeter.ac.uk.
authors.forename: K
authors.initials: K
authors.lastname: Kos
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism / Q000503:physiopathology*; D000368:Aged; D016022:Case-Control Studies; D006801:Humans; D000860:Hypoxia / Q000378:metabolism / Q000503:physiopathology*; D007333:Insulin Resistance; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000378:metabolism / Q000503:physiopathology*; D010100:Oxygen / Q000032:analysis / Q000378:metabolism; D020181:Sleep Apnea, Obstructive / Q000378:metabolism / Q000503:physiopathology*
chemical_list: D010100:Oxygen
keywords: Adipose tissue; Hypoxia; Obesity; Obstructive sleep apnea syndrome