Changes in GIP gene expression following bariatric surgery

Background: After bariatric surgery, there is a significant improvement in type 2 diabetes (T2D). T2D has been linked to incretins, including glucose-dependent insulinotropic polypeptide (GIP). Analysis of bariatric surgery patients may help to understand the link between GIP and T2D. Methods: Twenty-three morbidly obese patients underwent Roux-en-Y gastric bypass (RYGB) or gastric banding. Overall, there were 12 RYGB (5 T2D; 7 nondiabetic) patients and 11 gastric band (7 T2D; 4 nondiabetic) patients. Preoperative and postoperative blood samples were collected. Total RNA was extracted, cDNA synthesized, and real-time quantitative PCR were used to quantify gene expression. Student's t test was used for statistical analysis. Results: Postoperatively, T2D resolved or improved in 83.3 % (10/12) of the diabetic patients. Six (4 RYGB, 2 bands) patients discontinued hypoglycemic medications and four (3 RYGB, 1 band) patients discontinued the majority of their hypoglycemic agents. The remaining two diabetic patients (bands) showed no improvement. Postoperative GIP gene expression increased 4.36-fold (p = 0.02) in diabetic RYGB patients, whereas diabetic band patients increased 1.4-fold (p = 0.25). All diabetic patients with either resolution or improvement of T2D, had a 3.4-fold increase (p = 0.01) but nonresponders decreased 0.69-fold (p = 0.41). Nondiabetic RYGB patients increased 2.21-fold (p = 0.07) versus a 0.81-fold (p = 0.37) decrease of nondiabetic band patients. Conclusions: This is one of the initial studies that show a significant increase in GIP gene expression following a RYGB. This increase correlates with the clinical resolution of T2D. The anatomical changes after RYGB may account for these changes. Based on this data, GIP may be a key peptide in the "foregut hypothesis" for resolution of T2D.