The Effects of Calorie Restriction and Bariatric Surgery on Circulating Proneurotensin Levels

Context: Proneurotensin (pNT) is associated with obesity and type 2 diabetes (T2D), but the effects of Roux-en-Y gastric bypass (RYGB) on postprandial pNT levels are not well studied. Objective: This work aimed to assess the effects of RYGB vs a very low-energy diet (VLED) on pNT levels in response to mixed-meal tests (MMTs), and long-term effects of RYGB on fasting pNT. Methods: Cohort 1: Nine normoglycemic (NG) and 10 T2D patients underwent MMT before and after VLED, immediately post RYGB and 6 weeks post RYGB. Cohort 2: Ten controls with normal weight and 10 patients with obesity and T2D, who underwent RYGB or vertical sleeve gastrectomy (VSG), underwent MMTs and glucose-dependent insulinotropic polypeptide (GIP) infusions pre surgery and 3 months post surgery. Glucagon-like peptide-1 (GLP-1) infusions were performed in normal-weight participants. Cohort 3: Fasting pNT was assessed pre RYGB (n = 161), 2 months post RYGB (n = 92), and 1year post RYGB (n = 118) in NG and T2D patients. pNT levels were measured using enzyme-linked immunosorbent assay. Results: Reduced fasting and postprandial pNT were evident after VLED and immediately following RYGB. Reintroduction of solid food post RYGB increased fasting and postprandial pNT. Prior to RYGB, all patients lacked a meal response in pNT, but this was evident post RYGB/VSG. GIP or GLP-1 infusion had no effect on pNT levels. Fasting pNTs were higher 1-year post RYGB regardless of glycemic status. Conclusion: RYGB causes a transient reduction in pNT as a consequence of caloric restriction. The RYGB/VSG-induced rise in postprandial pNT is independent of GIP and GLP-1, and higher fasting pNTs are maintained 1 year post surgically.