title: Cysteine: a potential biomarker for obstructive sleep apnea.
abstract: OBJECTIVE
  Obstructive sleep apnea (OSA) is a risk factor for a number of cardiovascular conditions. Although homocysteine (Hcy) and cysteine (Cys) are regarded as cardiovascular risk factors, few studies have analyzed Hcy and Cys plasma concentrations in patients with OSA. The aim of this study was to evaluate the role of Hcy and Cys in OSA in comparison with subjects without OSA and to determine the possible influence of obesity on these variables.
  
  
  METHODS
  Patients who submitted to polysomnography studies were recruited to engage in an 8-h fasting period for blood sample withdrawal, physical examination, ECG, and echocardiogram. A subgroup of lean patients with OSA (BMI < 25 kg/m(2)) were analyzed to rule out the influence of obesity. Fifteen patients were randomly assigned to participate in a continuous positive airway pressure (CPAP) protocol to assess the influence of OSA treatment on the obtained measurements.
  
  
  RESULTS
  A total of 75 patients and 75 control subjects matched for age and sex were analyzed. The Cys plasma levels were higher in patients with OSA compared with control subjects (490.16 ± 67.00 μmol/L vs 439.81 ± 76.12 μmol/L, respectively, P < .01); however, the Hcy plasma levels did not differ between groups. Cys plasma levels were also higher in the OSA lean subgroup when compared with lean control subjects (484.21 ± 71.99 μmol/L vs 412.01 ± 70.73 μmol/L, respectively, P = .009). There was a significant decrease of Cys plasma levels after 6 months of CPAP effective therapy.
  
  
  CONCLUSIONS
  Cys is a potential biomarker of OSA in obese and nonobese patients and is reduced after effective OSA treatment.
authors.affiliation: Department of Psychobiology, Universidade Federal de São Paulo, Brazil. Electronic address: fatimacintra@interair.com.br.
authors.forename: Fatima
authors.initials: F
authors.lastname: Cintra
authors.affiliation: Department of Psychobiology, Universidade Federal de São Paulo, Brazil.
authors.forename: Sergio
authors.initials: S
authors.lastname: Tufik
authors.affiliation: Department of Psychobiology, Universidade Federal de São Paulo, Brazil; Department of Biosciences, Universidade Federal de São Paulo, Brazil.
authors.forename: Vânia
authors.initials: V
authors.lastname: D'Almeida
authors.affiliation: Department of Psychobiology, Universidade Federal de São Paulo, Brazil.
authors.forename: Bruno F A
authors.initials: BFA
authors.lastname: Calegare
authors.affiliation: Department of Medicine, Universidade Federal de São Paulo, Brazil.
authors.forename: Angelo
authors.initials: A
authors.lastname: de Paola
authors.affiliation: Department of Psychobiology, Universidade Federal de São Paulo, Brazil; Department of Medicine, Universidade Federal de São Paulo, Brazil.
authors.forename: Wercules
authors.initials: W
authors.lastname: Oliveira
authors.affiliation: Department of Medicine, Universidade Federal de São Paulo, Brazil.
authors.forename: Camila
authors.initials: C
authors.lastname: Rizzi
authors.affiliation: Department of Psychobiology, Universidade Federal de São Paulo, Brazil.
authors.forename: Suely
authors.initials: S
authors.lastname: Roizenblatt
authors.affiliation: Department of Psychobiology, Universidade Federal de São Paulo, Brazil.
authors.forename: Dalva
authors.initials: D
authors.lastname: Poyares
mesh_terms: D000704:Analysis of Variance; D015415:Biomarkers / Q000097:blood*; D016022:Case-Control Studies; D016009:Chi-Square Distribution; D045422:Continuous Positive Airway Pressure; D003545:Cysteine / Q000097:blood*; D004452:Echocardiography; D004562:Electrocardiography; D005260:Female; D006710:Homocysteine / Q000097:blood; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000097:blood; D017286:Polysomnography; D012307:Risk Factors; D020181:Sleep Apnea, Obstructive / Q000097:blood* / Q000628:therapy; D014815:Vitamins / Q000097:blood
chemical_list: D015415:Biomarkers; D014815:Vitamins; D006710:Homocysteine; D003545:Cysteine