title: Improved pancreatic beta-cell function in type 2 diabetic patients after lifestyle-induced weight loss is related to glucose-dependent insulinotropic polypeptide.
abstract: OBJECTIVE
  Restoration of insulin secretion is critical for the treatment of type 2 diabetes. Exercise and diet can alter glucose-induced insulin responses, but whether this is due to changes in beta-cell function per se is not clear. The mechanisms by which lifestyle intervention may modify insulin secretion in type 2 diabetes have also not been examined but may involve the incretin axis.
  
  
  METHODS
  Twenty-nine older, obese (aged 65 +/- 1 years; BMI 33.6 +/- 1.0 kg/m(2)) subjects, including individuals with newly diagnosed type 2 diabetes (obese-type 2 diabetic) and individuals with normal glucose tolerance (obese-NGT), underwent 3 months of nutritional counseling and exercise training. beta-Cell function (oral glucose-induced insulin secretion corrected for insulin resistance assessed by hyperinsulinemic-euglycemic clamps) and the role of glucose-dependent insulinotropic polypeptide (GIP) were examined.
  
  
  RESULTS
  After exercise and diet-induced weight loss (-5.0 +/- 0.7 kg), oral glucose-induced insulin secretion was increased in the obese-type 2 diabetic group and decreased in the obese-NGT group (both P < 0.05). When corrected for alterations in insulin resistance, the change in insulin secretion remained significant only in the obese-type 2 diabetic group (1.23 +/- 0.26 vs. 2.04 +/- 0.46 arbitrary units; P < 0.01). Changes in insulin secretion were directly related to the GIP responses to oral glucose (r = 0.64, P = 0.005), which were augmented in the obese-type 2 diabetic group and only moderately suppressed in the obese-NGT group.
  
  
  CONCLUSIONS
  After lifestyle-induced weight loss, improvements in oral glucose-induced insulin secretion in older, obese, nondiabetic subjects seem to be largely dependent on improved insulin sensitivity. However, in older obese diabetic patients, improved insulin secretion is a consequence of elevated beta-cell function. We demonstrate for the first time that changes in insulin secretion after lifestyle intervention may be mediated via alterations in GIP secretion from intestinal K-cells.
authors.affiliation: Department of Pathobiology, Cleveland Clinic, Cleveland, Ohio, USA. kirwanj@ccf.org
authors.forename: Thomas P J
authors.initials: TP
authors.lastname: Solomon
authors.forename: Jacob M
authors.initials: JM
authors.lastname: Haus
authors.forename: Karen R
authors.initials: KR
authors.lastname: Kelly
authors.forename: Michael
authors.initials: M
authors.lastname: Rocco
authors.forename: Sangeeta R
authors.initials: SR
authors.lastname: Kashyap
authors.forename: John P
authors.initials: JP
authors.lastname: Kirwan
mesh_terms: D000368:Aged; D001786:Blood Glucose / Q000378:metabolism; D003924:Diabetes Mellitus, Type 2 / Q000178:diet therapy / Q000378:metabolism / Q000503:physiopathology; D004038:Diet, Reducing; D015444:Exercise / Q000502:physiology; D005260:Female; D005749:Gastric Inhibitory Polypeptide / Q000502:physiology*; D015309:Glucose Clamp Technique; D006801:Humans; D006946:Hyperinsulinism / Q000503:physiopathology; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance / Q000502:physiology; D050417:Insulin-Secreting Cells / Q000502:physiology*; D008019:Life Style; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000178:diet therapy / Q000378:metabolism / Q000503:physiopathology; D010809:Physical Fitness / Q000502:physiology; D015431:Weight Loss / Q000502:physiology*
chemical_list: D001786:Blood Glucose; D007328:Insulin; D005749:Gastric Inhibitory Polypeptide