title: Habitual physical activity is associated with circulating irisin in healthy controls but not in subjects with diabetes mellitus type 2.
abstract: BACKGROUND
  Irisin, a novel myokine, has been shown to increase following vigorous exercise, with studies suggesting that it mediates some of the beneficial effects of exercise. Irisin might play a role in 'browning' of white adipocytes, thus increasing energy expenditure. The role of irisin in exercise and energy expenditure in subjects with diabetes mellitus type 2 (DMT2) remains largely unknown. We aimed to investigate the association between circulating irisin and habitual physical activity in subjects with and without DMT2.
  
  
  METHODS
  In this cross-sectional study, 164 Saudi adults: 81 non-DMT2 controls [age: (mean ± SD) 51.6 ± 10.9; BMI: 29.6 ± 4.3 kg/m(2) ] and 83 DMT2 subjects [age: 54.3 ± 10.3 year; BMI: 29.4 ± 4.7 kg/m(2) ] were studied. Anthropometric and fasting serum biochemical data were collected. Circulating irisin was measured using an enzyme-linked immunosorbent assay (ELISA). Frequency intensity time (FIT) index was used to assess the level of habitual physical activity.
  
  
  RESULTS
  We observed significantly higher levels of irisin in DMT2 subjects than in controls (P < 0.001). FIT index was positively associated (r = 0.20, P = 0.03) with circulating irisin in controls only. Additionally, irisin levels were significantly higher in tertile 3 (0.75 ± 0.07 μg/mL) than tertile 1 (0.49 ± 0.06 μg/mL) of the FIT index in healthy controls, whilst no such relation with physical activity was observed in DMT2 subjects.
  
  
  CONCLUSIONS
  This cross-sectional study has shown a weak association of irisin with physical activity levels in healthy controls but not in DMT2 subjects, suggesting the possibility of discordant regulation in the condition of DMT2.
authors.affiliation: Biomarkers Research Program, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia.|Prince Mutaib Chair for Biomarkers of Osteoporosis, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia.
authors.forename: Nasser M
authors.initials: NM
authors.lastname: Al-Daghri
authors.affiliation: Biomarkers Research Program, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia.|Prince Mutaib Chair for Biomarkers of Osteoporosis, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia.
authors.forename: Majed S
authors.initials: MS
authors.lastname: Alokail
authors.affiliation: Biomarkers Research Program, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia.
authors.forename: Shakilur
authors.initials: S
authors.lastname: Rahman
authors.affiliation: Biomarkers Research Program, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia.
authors.forename: Osama E
authors.initials: OE
authors.lastname: Amer
authors.affiliation: Biomarkers Research Program, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia.|Prince Mutaib Chair for Biomarkers of Osteoporosis, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia.
authors.forename: Omar S
authors.initials: OS
authors.lastname: Al-Attas
authors.affiliation: Prince Mutaib Chair for Biomarkers of Osteoporosis, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia.|Department of Food Science and Nutrition, College of Food Science and Agriculture, King Saud University, Riyadh, Saudi Arabia.
authors.forename: Hanan
authors.initials: H
authors.lastname: Alfawaz
authors.affiliation: Division of Translational and Systems Medicine, Warwick Medical School, University of Warwick, Coventry, UK.
authors.forename: Gyanendra
authors.initials: G
authors.lastname: Tripathi
authors.affiliation: Biomarkers Research Program, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia.
authors.forename: Shaun
authors.initials: S
authors.lastname: Sabico
authors.affiliation: First Department of Pediatrics, Athens University Medical School, Athens, Greece.
authors.forename: George P
authors.initials: GP
authors.lastname: Chrousos
authors.affiliation: Division of Translational and Systems Medicine, Warwick Medical School, University of Warwick, Coventry, UK.
authors.forename: Philip G
authors.initials: PG
authors.lastname: McTernan
authors.affiliation: Division of Translational and Systems Medicine, Warwick Medical School, University of Warwick, Coventry, UK.
authors.forename: Milan K
authors.initials: MK
authors.lastname: Piya
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D003924:Diabetes Mellitus, Type 2 / Q000097:blood*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005353:Fibronectins / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity; D012529:Saudi Arabia
chemical_list: C577593:FNDC5 protein, human; D005353:Fibronectins
keywords: Diabetes; frequency intensity time index; irisin; physical activity