title: Bariatric surgery in morbidly obese insulin resistant humans normalises insulin signalling but not insulin-stimulated glucose disposal.
abstract: OBJECTIVE
  Weight-loss after bariatric surgery improves insulin sensitivity, but the underlying molecular mechanism is not clear. To ascertain the effect of bariatric surgery on insulin signalling, we examined glucose disposal and Akt activation in morbidly obese volunteers before and after Roux-en-Y gastric bypass surgery (RYGB), and compared this to lean volunteers.
  
  
  METHODS
  The hyperinsulinaemic euglycaemic clamp, at five infusion rates, was used to determine glucose disposal rates (GDR) in eight morbidly obese (body mass index, BMI=47.3 ± 2.2 kg/m(2)) patients, before and after RYGB, and in eight lean volunteers (BMI=20.7 ± 0.7 kg/m2). Biopsies of brachioradialis muscle, taken at fasting and insulin concentrations that induced half-maximal (GDR50) and maximal (GDR100) GDR in each subject, were used to examine the phosphorylation of Akt-Thr308, Akt-473, and pras40, in vivo biomarkers for Akt activity.
  
  
  RESULTS
  Pre-operatively, insulin-stimulated GDR was lower in the obese compared to the lean individuals (P<0.001). Weight-loss of 29.9 ± 4 kg after surgery significantly improved GDR50 (P=0.004) but not GDR100 (P=0.3). These subjects still remained significantly more insulin resistant than the lean individuals (p<0.001). Weight loss increased insulin-stimulated skeletal muscle Akt-Thr308 and Akt-Ser473 phosphorylation, P=0.02 and P=0.03 respectively (MANCOVA), and Akt activity towards the substrate PRAS40 (P=0.003, MANCOVA), and in contrast to GDR, were fully normalised after the surgery (obese vs lean, P=0.6, P=0.35, P=0.46, respectively).
  
  
  CONCLUSIONS
  Our data show that although Akt activity substantially improved after surgery, it did not lead to a full restoration of insulin-stimulated glucose disposal. This suggests that a major defect downstream of, or parallel to, Akt signalling remains after significant weight-loss.
authors: School of Clinical Sciences, University of Bristol, Bristol, United Kingdom.
authors: Mimi Z
authors: MZ
authors: Chen
authors: School of Clinical Sciences, University of Bristol, Bristol, United Kingdom.
authors: Claire A
authors: CA
authors: Hudson
authors: School of Biochemistry, University of Bristol, Bristol, United Kingdom.
authors: Emma E
authors: EE
authors: Vincent
authors: Bristol Dermatology Centre, Bristol Royal Infirmary, Bristol, United Kingdom.
authors: David A R
authors: DA
authors: de Berker
authors: School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom.
authors: Margaret T
authors: MT
authors: May
authors: School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom.
authors: Ingeborg
authors: I
authors: Hers
authors: Institute of Molecular and Experimental Medicine, Cardiff University School of Medicine, Cardiff, United Kingdom.
authors: Colin M
authors: CM
authors: Dayan
authors: School of Clinical Sciences, University of Bristol, Bristol, United Kingdom.
authors: Robert C
authors: RC
authors: Andrews
authors: School of Biochemistry, University of Bristol, Bristol, United Kingdom.
authors: Jeremy M
authors: JM
authors: Tavaré
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000328:Adult; D050110:Bariatric Surgery; D005260:Female; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D007333:Insulin Resistance; D008297:Male; D008875:Middle Aged; D009767:Obesity, Morbid / Q000378:metabolism / Q000601:surgery*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction; D055815:Young Adult
chemical_list: C484523:AKT1S1 protein, human; D048868:Adaptor Proteins, Signal Transducing; D007328:Insulin; D051057:Proto-Oncogene Proteins c-akt; D005947:Glucose