Limited recovery of β-cell function after gastric bypass despite clinical diabetes remission

Comparative impact of Roux-en-Y gastric bypass, sleeve gastrectomy or diet alone on beta-cell function in insulin-treated type 2 diabetes patients

Although bariatric surgery is an effective treatment for type 2 diabetes by inducing weight loss and augmenting gut hormone secretion, the immediate effect on beta-cell function itself remains to be elucidated in type 2 diabetes. Therefore, a prospective, randomized trial was performed in 30 patients with insulin-treated type 2 diabetes and a body mass index ≥ 35 kg/m2. Patients were randomly assigned (1:1:1) to Roux-en-Y gastric bypass (RYGB) or sleeve gastrectomy (SG) in combination with protein-sparing modified fast (PSMF), or to PSMF alone. Eu- and hyperglycemic clamps were performed before and 3 weeks after surgery and/or PSMF initiation. The primary outcome was the evolution of insulin sensitivity and beta-cell function after surgery, calculated using the composite measures of glucose disposal rate, insulin secretion rate, and disposition index (DI). Results revealed that markers of insulin sensitivity increased similarly in all arms (p = 0.43). A higher marker for maximal beta-cell function was observed when comparing SG to PSMF (p = 0.007). The DI showed a clear positive evolution after RYGB and SG, but not after PSMF alone. Altogether, these findings indicate that bariatric surgery results in an immediate beta-cell function recovery in insulin-treated type 2 diabetes.

The oral disposition index calculated from a meal tolerance test is a crucial indicator for evaluating differential normalization of postprandial glucose and triglyceride excursions in morbidly obese patients after laparoscopic sleeve gastrectomy

To determine the normalization of postprandial blood glucose (PG) and triglyceride (TG) excursions in 30 morbidly obese patients with or without diabetes mellitus (DM) 1-year after they underwent a laparoscopic sleeve gastrectomy (LSG) vs. their pre-surgery data, we administered the 75-g oral glucose tolerance test (OGTT) and a meal tolerance test (MTT) using a 75-g glucose-equivalent carbohydrate- and fat-containing meal. The results were as follows; (i) Postoperative body-weight reduction was associated with DM remission and reduced multiple cardiometabolic risks. (ii) OGTT data showing postprandial hyper-insulinemic hypoglycemia in many post-surgery patients were associated with overdiagnosis of improved glucose tolerance. However, postoperative MTT data without hypoglycemia showed no improvement in the glucose tolerance vs. pre-surgery data. (iii) The disposition index (DI) i.e., [Matsuda index] × (Glucose-induced insulin secretion) was progressively worsened from normal glucose tolerance to DM patients after LSG. These post-surgery DI values measured by the MTT were correlated with 2h-plasma glucose levels and were not normalized in DM patients. (iv) The baseline, 2h-TG, and an increase in 2h-TG values above baseline were correlated with the insulin resistance index, DI, or HbA1c; These TG values were normalized post-LSG. In conclusion, the glucose tolerance curve measured by the MTT was not normalized in T2DM patients, which was associated with impaired normalization of the DI values in those patients 1-year after the LSG. However, the baseline TG and a fat-induced 2h-TG values were normalized postoperatively. The MTT can be used to assess normalization in postprandial glucose and TG excursions after LSG.

Effects of Roux-en-Y Gastric Bypass and Sleeve Gastrectomy on β-Cell Function at 1 Year After Surgery: A Systematic Review

Bariatric surgery is a highly effective obesity treatment resulting in substantial weight loss and improved glucose metabolism. We hereby aimed to summarize available evidence of the effect of the 2 most common bariatric surgery procedures, Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG), on dynamic measures of β-cell function (BCF). A systematic search of the literature was conducted in 3 bibliographic databases for studies reporting effects of RYGB and/or SG on BCF assessed using dynamic metabolic perturbation (oral or intravenous bolus stimulation), performed before and 1 year (±3 months) after surgery. Twenty-seven unique studies (6 randomized controlled trials and 21 observational studies), involving a total of 1856 obese adults, were included for final analysis. Twenty-five and 9 studies report effects of RYGB and SG on BCF, respectively (7 studies compared the 2 procedures). Seven studies report results according to presurgical diabetes status. Owing to variable testing procedures and BCF indices reported, no meta-analysis was feasible, and data were summarized qualitatively. For both surgical procedures, most studies suggest an increase in BCF and disposition index, particularly when using oral stimulation, with a more pronounced increase in diabetic than nondiabetic individuals. Additionally, limited indications for greater effects after RYGB versus SG were found. The quality of the included studies was, in general, satisfactory. The considerable heterogeneity of test protocols and outcome measures underscore the need for a harmonization of BCF testing in future research.

Glucagon-like peptide-1 effect on β-cell function varies according to diabetes remission status after Roux-en-Y gastric bypass

AIMS

The contribution of endogenous glucagon-like peptide (GLP)-1 to β-cell function after Roux-en-Y gastric bypass surgery (RYGB) is well established in normoglycaemic individuals, but not in those with postoperative hyperglycaemia. We, therefore, studied the effect of GLP-1 on β-cell function in individuals with varying degrees of type 2 diabetes mellitus (T2D) control after RYGB.

MATERIALS AND METHODS

Glucose, insulin secretion rates, β-cell glucose sensitivity and glucagon were measured during an oral glucose tolerance test before (saline only) and at 3, 12 and 24 months after RYGB with and without infusion of the GLP-1 receptor blocker exendin9-39 (EX9). The cohort was retrospectively classified based on T2D remission (REM) status at the latest study time point: REM (n = 5), persistent T2D (n = 8), or impaired glucose tolerance (n = 16).

RESULTS

EX9 blunted the increase in β-cell glucose sensitivity at 3 months (-44.1%, p < .001) and 12 months (-43.3%, p < .001), but not at 24 months (-12.4%, p = .243). EX9 enhanced postprandial glucagon concentrations by 62.0% at 3 months (p = .008), 46.5% at 12 months (p = .055), and 30.4% at 24 months (p = .017). EX9 counterintuitively decreased glucose concentrations at 3 months in the entire cohort (p < .001) but had no effect on glycaemia at 12 and 24 months in persistent T2D and impaired glucose tolerance; it minimally worsened glycaemia in REM at 12 months.

CONCLUSIONS

GLP-1 blockade reversed the improvement in β-cell function observed after RYGB, but this effect varied temporally and by REM status. GLP-1 blockade transiently and minimally worsened glycaemia only in REM, and lowered postprandial glucose values at 3 months, regardless of REM status.

Loss of the Incretin Effect in Type 2 Diabetes: A Systematic Review and Meta-analysis

CONTEXT

Loss of the incretin effect (IE) in type 2 diabetes (T2D) contributes to hyperglycemia and the mechanisms underlying this impairment are unclear.

OBJECTIVE

To quantify the IE impairment in T2D and to investigate the factors associated with it using a meta-analytic approach.

METHODS

PubMed, Scopus, and Web-of-Science were searched. Studies measuring IE by the gold-standard protocol employing an oral glucose tolerance test (OGTT) and an intravenous glucose infusion at matched glucose levels were selected. We extracted IE, sex, age, body mass index (BMI), and hemoglobin A1c, fasting values, and area under curve (AUC) of glucose, insulin, C-peptide, glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide 1 (GLP-1). In subjects with T2D, we also recorded T2D duration, age at diagnosis, and the percentage of subjects taking antidiabetic medications.

RESULTS

The IE weighted mean difference between subjects with T2D and those with normal glucose tolerance (NGT) was -27.3% (CI -36.5% to -18.1%; P < .001; I2 = 86.6%) and was affected by age (P < .005). By meta-regression of combined NGT and T2D data, IE was inversely associated with glucose tolerance (lower IE in T2D), BMI, and fasting GIP (P < .05). By meta-regression of T2D studies only, IE was associated with the OGTT glucose dose (P < .0001). IE from insulin was larger than IE from C-peptide (weighted mean difference 11.2%, CI 9.2-13.2%; P < .0001; I2 = 28.1%); the IE difference was inversely associated with glucose tolerance and fasting glucose.

CONCLUSION

The IE impairment in T2D vs NGT is consistent though considerably variable, age being a possible factor affecting the IE difference. Glucose tolerance, BMI, and fasting GIP are independently associated with IE; in subjects with T2D only, the OGTT dose is a significant covariate.

Effects of a 13-Week Personalized Lifestyle Intervention Based on the Diabetes Subtype for People with Newly Diagnosed Type 2 Diabetes

A type 2 diabetes mellitus (T2DM) subtyping method that determines the T2DM phenotype based on an extended oral glucose tolerance test is proposed. It assigns participants to one of seven subtypes according to their β-cell function and the presence of hepatic and/or muscle insulin resistance. The effectiveness of this subtyping approach and subsequent personalized lifestyle treatment in ameliorating T2DM was assessed in a primary care setting. Sixty participants, newly diagnosed with (pre)diabetes type 2 and not taking diabetes medication, completed the intervention. Retrospectively collected data of 60 people with T2DM from usual care were used as controls. Bodyweight (p < 0.01) and HbA1c (p < 0.01) were significantly reduced after 13 weeks in the intervention group, but not in the usual care group. The intervention group achieved 75.0% diabetes remission after 13 weeks (fasting glucose ≤ 6.9 mmol/L and HbA1c < 6.5% (48 mmol/mol)); for the usual care group, this was 22.0%. Lasting (two years) remission was especially achieved in subgroups with isolated hepatic insulin resistance. Our study shows that a personalized diagnosis and lifestyle intervention for T2DM in a primary care setting may be more effective in improving T2DM-related parameters than usual care, with long-term effects seen especially in subgroups with hepatic insulin resistance.

Role of the Gut in the Temporal Changes of β-Cell Function After Gastric Bypass in Individuals With and Without Diabetes Remission

OBJECTIVE

The role of the gut in diabetes remission after Roux-en-Y gastric bypass (RYGB) is incompletely understood. We assessed the temporal change in insulin secretory capacity after RYGB, using oral and intravenous (IV) glucose, in individuals with type 2 diabetes.

RESEARCH DESIGN AND METHODS

Longitudinal, prospective measures of β-cell function were assessed after oral glucose intake and graded glucose infusion in individuals with severe obesity and diabetes studied at 0, 3 (n = 29), 12 (n = 24), and 24 (n = 20) months after RYGB. Data were collected between 2015 and 2019 in an academic clinical research center.

RESULTS

The decreases in body weight, fat mass, waist circumference, and insulin resistance after surgery (all P < 0.001 at 12 and 24 months) did not differ according to diabetes remission status. In contrast, both the magnitude and temporal changes in β-cell glucose sensitivity after oral glucose intake differed by remission status (P = 0.04): greater (6.5-fold; P < 0.01) and sustained in those in full remission, moderate and not sustained past 12 months in those with partial remission (3.3-fold; P < 0.001), and minimal in those not experiencing remission (2.7-fold; P = not significant). The improvement in β-cell function after IV glucose administration was not apparent until 12 months, significant only in those in full remission, and only ∼33% of that observed after oral glucose intake. Preintervention β-cell function and its change after surgery predicted remission; weight loss and insulin sensitivity did not.

CONCLUSIONS

Our data show the time course of changes in β-cell function after RYGB. The improvement in β-cell function after RYGB, but not changes in weight loss or insulin sensitivity, drives diabetes remission.

Determinants of type 2 diabetes remission after bariatric surgery in obese Japanese patients: a retrospective cohort study

Objective

Bariatric surgery (BS) improves glycemic control in type 2 diabetes; however, some patients show insufficient improvement. Understanding the pathophysiology of type 2 diabetes in obese patients can facilitate appropriate treatment for type 2 diabetes after BS. The homeostatic model assessment (HOMA) 2 enables the calculation of the values from C-peptide data and evaluation of insulin users. We aimed to evaluate the pathophysiology of type 2 diabetes using pre- and postoperative parameters and HOMA2 in obese patients who underwent BS.

Methods

We retrospectively reviewed data from 45 obese patients with type 2 diabetes who underwent BS. They were followed-up for 12 months. The relationship between the HOMA2 score and complete remission (CR) of type 2 diabetes after BS was analyzed. Patients with and without CR were assigned to the CR and non-CR groups, respectively. Multiple regression analysis was used to identify factors associated with improvement in type 2 diabetes after BS.

Results

BS significantly improved body weight and glucose metabolism. The preoperative glycosylated hemoglobin A1c level and insulin secretion (HOMA2-%B) significantly differed between the CR and non-CR groups. Postoperative weight reduction and improved insulin sensitivity correlated significantly with CR; multiple regression showed that the preoperative HOMA 2-%B independently predicted CR of type 2 diabetes after BS.

Conclusion

Preoperative insulin secretion, improvement in insulin sensitivity, and weight reduction after BS are related to CR of type 2 diabetes after BS. The results better reveal the pathophysiology of and treatment for type 2 diabetes in obese patients who undergo BS.

Preintervention Clinical Determinants and Measured β-Cell Function As Predictors of Type 2 Diabetes Remission After Roux-en-Y Gastric Bypass Surgery

BACKGROUND

Bariatric surgery results in improved glycemic control in individuals with type 2 diabetes. Single and clusters of clinical determinants have been identified as presurgery predictors of postsurgery diabetes remission. Our goal was to assess whether the addition of measured preoperative β-cell function would improve established clinical models of prediction of diabetes remission.

RESEARCH DESIGN AND METHODS

Presurgery clinical characteristics, metabolic markers, and β-cell function after oral and intravenous (IV) glucose challenges were assessed in 73 individuals with severe obesity and type 2 diabetes and again 1 year after gastric bypass surgery. Single and multivariate analyses were conducted with preoperative variables to determine the best predictive models of remission.

RESULTS

Presurgery β-cell glucose sensitivity, a surrogate of β-cell function, was negatively correlated with known diabetes duration, HbA1c, insulin use, and the diabetes remission scores DiaRem and advanced (Ad)-DiaRem (all P < 0.001). Measured β-cell function after oral glucose was 1.6-fold greater than after the IV glucose challenge and more strongly correlated with preoperative clinical and metabolic characteristics. The addition of preoperative β-cell function to clinical models containing well-defined diabetes remission scores did not improve the model's ability to predict diabetes remission after Roux-en-Y gastric bypass.

CONCLUSIONS

The addition of measured β-cell function does not add predictive value to defined clinical models of diabetes remission 1 year after surgical weight loss.

Metabolic effects of duodenojejunal bypass surgery in a rat model of type 1 diabetes

BACKGROUND

Metabolic surgery has beneficial metabolic effects, including remission of type 2 diabetes. We hypothesized that duodenojejunal bypass (DJB) surgery can protect against development of type 1 diabetes (T1D) by enhancing regulation of cellular and molecular pathways that control glucose homeostasis.

METHODS

BBDP/Wor rats, which are prone to develop spontaneous autoimmune T1D, underwent loop DJB (n = 15) or sham (n = 15) surgery at a median age of 41 days, before development of diabetes. At T1D diagnosis, a subcutaneous insulin pellet was implanted, oral glucose tolerance test was performed 21 days later, and tissues were collected 25 days after onset of T1D. Pancreas and liver tissues were assessed by histology and RT-qPCR. Fecal microbiota composition was analyzed by 16S V4 sequencing.

RESULTS

Postoperatively, DJB rats weighed less than sham rats (287.8 vs 329.9 g, P = 0.04). In both groups, 14 of 15 rats developed T1D, at similar age of onset (87 days in DJB vs 81 days in sham, P = 0.17). There was no difference in oral glucose tolerance, fasting and stimulated plasma insulin and c-peptide levels, and immunohistochemical analysis of insulin-positive cells in the pancreas. DJB rats needed 1.3 ± 0.4 insulin implants vs 1.9 ± 0.5 in sham rats (P = 0.002). Fasting and glucose stimulated glucagon-like peptide 1 (GLP-1) secretion was elevated after DJB surgery. DJB rats had reduced markers of metabolic stress in liver. After DJB, the fecal microbiome changed significantly, including increases in Akkermansia and Ruminococcus, while the changes were minimal in sham rats.

CONCLUSION

DJB does not protect against autoimmune T1D in BBDP/Wor rats, but reduces the need for exogenous insulin and facilitates other metabolic benefits including weight loss, increased GLP-1 secretion, reduced hepatic stress, and altered gut microbiome.

Metabolomic profiling identifies complex lipid species and amino acid analogues associated with response to weight loss interventions

Obesity is an epidemic internationally. While weight loss interventions are efficacious, they are compounded by heterogeneity with regards to clinically relevant metabolic responses. Thus, we sought to identify metabolic biomarkers that are associated with beneficial metabolic changes to weight loss and which distinguish individuals with obesity who would most benefit from a given type of intervention. Liquid chromatography mass spectrometry-based profiling was used to measure 765 metabolites in baseline plasma from three different weight loss studies: WLM (behavioral intervention, N = 443), STRRIDE-PD (exercise intervention, N = 163), and CBD (surgical cohort, N = 125). The primary outcome was percent change in insulin resistance (as measured by the Homeostatic Model Assessment of Insulin Resistance [%ΔHOMA-IR]) over the intervention. Overall, 92 individual metabolites were associated with %ΔHOMA-IR after adjustment for multiple comparisons. Concordantly, the most significant metabolites were triacylglycerols (TAGs; p = 2.3e-5) and diacylglycerols (DAGs; p = 1.6e-4), with higher baseline TAG and DAG levels associated with a greater improvement in insulin resistance with weight loss. In tests of heterogeneity, 50 metabolites changed differently between weight loss interventions; we found amino acids, peptides, and their analogues to be most significant (4.7e-3) in this category. Our results highlight novel metabolic pathways associated with heterogeneity in response to weight loss interventions, and related biomarkers which could be used in future studies of personalized approaches to weight loss interventions.

Glucose Homeostasis, Fetal Growth and Gestational Diabetes Mellitus in Pregnancy after Bariatric Surgery: A Scoping Review

Background: Pregnancies in women with a history of bariatric surgery are becoming increasingly prevalent. Surgically induced metabolic changes benefit mother and child, but can also lead to some adverse pregnancy outcomes. Knowledge about glucose homeostasis in these pregnancies could elucidate some of the mechanisms behind these outcomes. This review focusses on glucose homeostasis and birth weight. Methods: We considered papers dealing with glucose homeostasis, gestational diabetes mellitus (GDM) and/or small-for-gestational age infants (SGA) in pregnancies with a history of sleeve gastrectomy (SG) or Roux-en-y gastric bypass (RYGB). Results: Since an OGTT is unreliable to diagnose GDM in a pregnancy after bariatric surgery, the true incidence of GDM is unknown. Alternative screening strategies are needed. Furthermore, these pregnancies are marked by frequent hypoglycemic events as well as wide and rapid glycemic excursions, an issue that is very likely underreported. There is a lack of uniformity in reporting key outcomes and a large variation in study design and control population. Conclusion: Alteration of glucose homeostasis in a pregnancy after bariatric surgery should be further studied using unequivocal definition of key concepts. Glycemic control may prove to be a modifiable risk factor for adverse pregnancy outcomes such as the delivery of an SGA baby.

Effect of Laparoscopic Sleeve Gastrectomy on Static and Dynamic Measures of Glucose Homeostasis and Incretin Hormone Response 4-Years Post-Operatively

INTRODUCTION

There is limited literature available on the long-term effect of bariatric surgery especially laparoscopic sleeve gastrectomy (LSG) on the incretin hormone response.

AIM

Our primary aim was to investigate changes in glucose metabolism and incretin hormone responses in participants with impaired glucose regulation approximately 4 years after LSG. The secondary aim was to examine the long-term incretin hormone changes of biliopancreatic diversion (BPD).

METHOD

A non-randomised prospective study comprising of 10 participants undergoing LSG and 6 participants undergoing BPD. Serial measurements of glucose, insulin, C-peptide, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) were performed during an oral glucose tolerance test pre-operatively and 1 month, 6 months and at approximately 4-7 years post-operatively. Area under the curve (AUC) was examined at 60 and 120 min.

RESULTS

In the LSG group, a significant reduction in 2-h plasma glucose (2 h PG), HbA1c and HOMA-IR was observed at 4 years. Compared with pre-operative levels, significant increases in post-glucose GLP-1 secretion were observed at 1 and 6 months, but not maintained at 4 years. A linear increase was seen in post-glucose GIP response at 1 month and 6 months and 4 years. Within the BPD group, a reduction in HbA1c along with an increase GLP-1 response was observed at 7 years.

CONCLUSION

An increase in GLP-1 response was not preserved at 4 years, but a significant increase in GIP response was observed along with improved glycaemic control following LSG.

Anthropometrics by Three-Dimensional Photonic Scanner in Patients with Obesity Before and After Bariatric Surgery

BACKGROUND

We studied body composition by three-dimensional photonic scanning (3DPS) and metabolic biomarkers in a large ethnically diverse cohort of individuals with severe obesity before and after weight loss by Roux-en-Y gastric bypass (RYGB) or adjustable gastric banding (AGB) surgery.

MATERIALS AND METHODS

Male and female participants (n = 95) underwent 3DPS testing in the weeks preceding bariatric surgery (baseline), and 1 year after either RYGB (n = 34) or AGB (n = 9).

RESULTS

Principal component analysis showed that A1C and HDL cholesterol clustered with waist-to-hip ratio (WHR). Both RYGB and AGB surgeries led to similar improvements in A1C and lipids after 1 year. RYGB led to greater decreases in body weight, and in most anthropometric measures, compared with AGB at 1 year. However, after accounting for weight loss differences, RYGB and AGB groups did not differ in regional decreases in circumferences or volumes; the exception was a greater reduction in lean mass in RYGB compared with AGB.

CONCLUSION

Distribution of weight loss, assessed by 3DPS, did not differ between RYGB and AGB, but surgery type predicted change in lean mass at 1 year.

Sera of Obese Type 2 Diabetic Patients Undergoing Metabolic Surgery Instead of Conventional Treatment Exert Beneficial Effects on Beta Cell Survival and Function: Results of a Randomized Clinical Study

BACKGROUND

Pancreatic beta cells are highly sensitive to oxidative and endoplasmic reticulum (ER) stress, commonly occurring in type 2 diabetes (T2D) and obesity.

OBJECTIVE

We aimed at investigating cellular responses of human beta cells exposed to sera from obese T2D patients treated differently, namely by conventional therapy or laparoscopic sleeve gastrectomy (LSG).

METHODS

Serum samples from obese T2D men randomized to conventional treatment or LSG were taken at baseline and 6 months later. After exposing 1.1B4 cells to study patients' sera, the following were assessed: cellular viability and proliferation (by MTT and xCELLigence assays), reactive oxygen species (ROS) production (with DCFH-DA), and expression of ER stress markers, oxidative- or autophagy-related proteins and insulin (by real-time PCR and Western blot).

RESULTS

At 6-month follow-up, patients undergoing LSG achieved an adequate glycemic control, whereas conventionally treated patients did not. As compared to 1.1B4 cells incubated with baseline sera (control), cells exposed to sera from LSG-treated participants exhibited (i) increased viability and proliferation (p < 0.05); (ii) diminished levels of ROS and p53 (p < 0.05); (iii) enhanced protein expression of autophagy-related SIRT1 and p62/SQSTM1 (p < 0.05); (iv) significantly decreased transcript levels of ER stress markers (p < 0.05); and (v) augmented insulin expression (p < 0.05). Conversely, the 6-month conventional therapy appeared not to impact on circulating redox status. Moreover, 1.1B4 cells exposed to sera from conventionally treated patients experienced mild ER stress.

CONCLUSION

Circulating factors in patients with improved diabetes after metabolic surgery exerted favorable effects on beta cell function and survival.

The Effects of Bariatric Surgery on Islet Function, Insulin Secretion, and Glucose Control

Although bariatric surgery was developed primarily to treat morbid obesity, evidence from the earliest clinical observations to the most recent clinical trials consistently demonstrates that these procedures have substantial effects on glucose metabolism. A large base of research indicates that bariatric surgeries such as Roux-en-Y gastric bypass (RYGB), vertical sleeve gastrectomy (VSG), and biliopancreatic diversion (BPD) improve diabetes in most patients, with effects frequently evident prior to substantial weight reduction. There is now unequivocal evidence from randomized controlled trials that the efficacy of surgery is superior to intensive life-style/medical management. Despite advances in the clinical understanding and application of bariatric surgery, there remains only limited knowledge of the mechanisms by which these procedures confer such large changes to metabolic physiology. The improvement of insulin sensitivity that occurs with weight loss (e.g., the result of diet, illness, physical training) also accompanies bariatric surgery. However, there is evidence to support specific effects of surgery on insulin clearance, hepatic glucose production, and islet function. Understanding the mechanisms by which surgery affects these parameters of glucose regulation has the potential to identify new targets for therapeutic discovery. Studies to distinguish among bariatric surgeries on key parameters of glucose metabolism are limited but would be of considerable value to assist clinicians in selecting specific procedures and investigators in delineating the resulting physiology. This review is based on literature related to factors governing glucose metabolism and insulin secretion after the commonly used RYGB and VSG, and the less frequently used BPD and adjustable gastric banding.

Insulin Clearance After Oral and Intravenous Glucose Following Gastric Bypass and Gastric Banding Weight Loss

OBJECTIVE

Hepatic insulin clearance is a significant regulator of glucose homestasis. We hypothesized that the improvement in insulin clearance rates (ICRs) under fasting conditions and in response to oral and intravenous (IV) glucose would improve similarly after Roux-en-Y gastric bypass (RYGB) and adjustable gastric banding (AGB) as a function of weight loss; the difference in ICR after oral and IV glucose stimulation will be enhanced after RYGB compared with AGB, an effect mediated by glucagon-like peptide 1 (GLP-1).

RESEARCH DESIGN AND METHODS

In study 1, the ICR was calculated under fasting condition (F-ICR), after oral glucose (O-ICR), and after an isoglycemic IV glucose clamp (IV-ICR) in individuals from an established cohort with type 2 diabetes mellitus (T2DM) before, after 10% matched weight loss, and 1 year after either RYGB (n = 22) or AGB (n = 12). In study 2, O-ICR was studied in a separate cohort of individuals with T2DM (n = 22), before and 3 months after RYGB, with and without exendin(9-39) infusion.

RESULTS

In study 1, age, BMI, T2DM duration and control, and ICR did not differ between RYGB and AGB preintervention. Weight loss at 1 year was two times greater after RYGB than after AGB (31.6 ± 5.9% vs. 16.6 ± 9.8%; P < 0.05). RYGB and AGB both significantly increased F-ICR, O-ICR, and IV-ICR at 1 year. ICR was inversely associated with insulinemia. The difference between IV-ICR and O-ICR was significantly greater after RYGB versus AGB. GLP-1 antagonism with exendin(9-39) led to an increase in O-ICR in subjects post-RYGB.

CONCLUSIONS

Weight loss increased ICR, an effect more pronounced after RYGB compared with AGB. Our data support a potential role for endogenous GLP-1 in the control of postprandial ICR after RYGB.

Comparison of Diabetes Remission and Micronutrient Deficiency in a Mildly Obese Diabetic Rat Model Undergoing SADI-S Versus RYGB

BACKGROUND

Single-anastomosis duodeno-ileal bypass with sleeve gastrectomy (SADI-S) has launched a huge challenge to classic Roux-en-Y gastric bypass (RYGB). Our objective was to compare diabetes remission and micronutrient deficiency in a mildly obese diabetic rat model undergoing SADI-S versus RYGB.

METHODS

Thirty adult male mildly obese diabetic rats were randomly assigned to sham (S), SADI-S, and RYGB groups. Body weight, food intake, fasting plasma glucose (FPG), oral glucose tolerance test (OGTT), plasma insulin, GLP-1, and ghrelin levels were measured at indicated time points. Meanwhile, insulin sensitivity and pancreatic β cell function were assessed during OGTT. Finally, plasma micronutrient evaluation and islet β cell mass analysis were performed after all animals were sacrificed.

RESULTS

As compared to sham, the SADI-S and RYGB groups achieved almost equivalent efficacy in caloric restriction and FPG control without excessive weight loss. During OGTT, the SADI-S and RYGB groups also provided comparable effects on glycemic excursion, insulin sensitivity, and β cell function; however, only rats in the RYGB group showed significant changes in gut hormones, whereas the three groups were found to exhibit no significant difference in β cell mass. In addition, only vitamin E in the RYGB group was deficient as compared with the SADI-S and S groups.

CONCLUSION

In mildly obese diabetic rat, SADI-S and RYGB procedures have comparable efficacy in diabetes remission and risk of micronutrient deficiency. These data show that each of the surgery accomplishes diabetes improvements through both overlapping and distinct mechanisms requiring further investigation.

Mechanisms Underlying Type 2 Diabetes Remission After Metabolic Surgery

Type 2 diabetes prevalence is increasing dramatically worldwide. Metabolic surgery is the most effective treatment for selected patients with diabetes and/or obesity. When compared to intensive medical therapy and lifestyle intervention, metabolic surgery has shown superiority in achieving glycemic improvement, reducing number of medications and cardiovascular risk factors, which translates in long-term benefits on cardiovascular morbidity and mortality. The mechanisms underlying diabetes improvement after metabolic surgery have not yet been clearly understood but englobe a complex interaction among improvements in beta cell function and insulin secretion, insulin sensitivity, intestinal gluconeogenesis, changes in glucose utilization, and absorption by the gut and changes in the secretory pattern and morphology of adipose tissue. These are achieved through different mediators which include an enhancement in gut hormones release, especially, glucagon-like peptide 1, changes in bile acids circulation, gut microbiome, and glucose transporters expression. Therefore, this review aims to provide a comprehensive appraisal of what is known so far to better understand the mechanisms through which metabolic surgery improves glycemic control facilitating future research in the field.

Weight-Independent Mechanisms of Glucose Control After Roux-en-Y Gastric Bypass

Roux-en-Y gastric bypass results in large and sustained weight loss and resolution of type 2 diabetes in 60% of cases at 1-2 years. In addition to calorie restriction and weight loss, various gastro-intestinal mediated mechanisms, independent of weight loss, also contribute to glucose control. The anatomical re-arrangement of the small intestine after gastric bypass results in accelerated nutrient transit, enhances the release of post-prandial gut hormones incretins and of insulin, alters the metabolism and the entero-hepatic cycle of bile acids, modifies intestinal glucose uptake and metabolism, and alters the composition and function of the microbiome. The amelioration of beta cell function after gastric bypass in individuals with type 2 diabetes requires enteric stimulation. However, beta cell function in response to intravenous glucose stimulus remains severely impaired, even in individuals in full clinical diabetes remission. The permanent impairment of the beta cell may explain diabetes relapse years after surgery.

Altered glucose metabolism after bariatric surgery: What's GLP-1 got to do with it?

Bariatric surgery is an effective treatment for obesity. The two widely performed weight-loss procedures, Roux-en-Y gastric bypass (GB) and sleeve gastrectomy (SG), alter postprandial glucose pattern and enhance gut hormone secretion immediately after surgery before significant weight loss. This weight-loss independent glycemic effects of GB has been attributed to an accelerated nutrient transit from stomach pouch to the gut and enhanced secretion of insulinotropic gut factors; in particular, glucagon-like peptide-1 (GLP-1). Meal-induced GLP-1 secretion is as much as tenfold higher in patients after GB compared to non-surgical individuals and inhibition of GLP-1 action during meals reduces postprandial hyperinsulinemia after GB two to three times more than that in persons without surgery. Moreover, in a subgroup of patients with the late complication of postprandial hyperinsulinemic hypoglycemia after GB, GLP1R blockade reverses hypoglycemia by reducing meal stimulated insulin secretion. The role of enteroinsular axis activity after SG, an increasingly popular alternative to GB, is less understood but, similar to GB, SG accelerates nutrient delivery to the intestine, improves glucose tolerance, and increases postprandial GLP-1 secretion. This review will focus on the current evidence for and against the role of GLP-1 on glycemic effects of GB and will also highlight differences between GB and SG.

Prospective evaluation of insulin and incretin dynamics in obese adults with and without diabetes for 2 years after Roux-en-Y gastric bypass

AIMS/HYPOTHESIS

In this prospective case-control study we tested the hypothesis that, while long-term improvements in insulin sensitivity (S_I) accompanying weight loss after Roux-en-Y gastric bypass (RYGB) would be similar in obese individuals with and without type 2 diabetes mellitus, stimulated-islet-cell insulin responses would differ, increasing (recovering) in those with diabetes but decreasing in those without. We investigated whether these changes would occur in conjunction with favourable alterations in meal-related gut hormone secretion and insulin processing.

METHODS

Forty participants with type 2 diabetes and 22 participants without diabetes from the Longitudinal Assessment of Bariatric Surgery (LABS-2) study were enrolled in a separate, longitudinal cohort (LABS-3 Diabetes) to examine the mechanisms of postsurgical diabetes improvement. Study procedures included measures of S_I, islet secretory response and gastrointestinal hormone secretion after both intravenous glucose (frequently-sampled IVGTT [FSIVGTT]) and a mixed meal (MM) prior to and up to 24 months after RYGB.

RESULTS

Postoperatively, weight loss and S_I-_FSIVGTT improvement was similar in both groups, whereas the acute insulin response to glucose (AIRglu) decreased in the non-diabetic participants and increased in the participants with type 2 diabetes. The resulting disposition indices (DI_FSIVGTT) increased by three- to ninefold in both groups. In contrast, during the MM, total insulin responsiveness did not significantly change in either group despite durable increases of up to eightfold in postprandial glucagon-like peptide 1 levels, and S_I-MM and DI_MM increased only in the diabetes group. Peak postprandial glucagon levels increased in both groups.

CONCLUSIONS/INTERPRETATION

For up to 2 years following RYGB, obese participants without diabetes showed improvements in DI that approach population norms. Those with type 2 diabetes recovered islet-cell insulin secretion response yet continued to manifest abnormal insulin processing, with DI values that remained well below population norms. These data suggest that, rather than waiting for lifestyle or medical failure, RYGB is ideally considered before, or as soon as possible after, onset of type 2 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00433810.

Beta-cell sensitivity to glucose is impaired after gastric bypass surgery

AIMS

Patients who have undergone Roux-en-Y gastric bypass surgery (GB) have exaggerated postprandial insulin secretion, which has been attributed to increased meal glucose appearance and enhanced incretin effect. Here, we sought to determine β-cell glucose sensitivity in the absence of meal stimulation and insulinotropic gut factors.

MATERIALS AND METHODS

A total of 12 non-diabetic subjects with prior GB, and 7 matched non-surgical control subjects with normal glucose tolerance were studied. Blood glucose and insulin secretion rates were measured during a graded glucose infusion at increasing and then decreasing rates. Insulin sensitivity (S_I ) and glucose effectiveness (S_G ) were determined by the minimal model.

RESULTS

GB subjects had S_I comparable to that of control subjects. GB subjects had relative hyperglycaemia during the highest dose of glucose infusion associated with significantly reduced β-cell glucose sensitivity throughout both step-up (GB: 34 ± 6, CN: 82 ± 9 pmol min^-1 mM^-1 L, P < .0001) and step-down (GB: 31 ± 6, CN: 74 ± 9 pmol min^-1 mM^-1 L, P < .0001) phases of the glucose infusion. GB subjects also had reduced S_G (GB: 0.04 ± 0.00, CN: 0.07 ± 0.01 min^-1 , P = .004).

CONCLUSION

In the absence of enteric stimuli, β-cell sensitivity to changes in glycaemia is blunted among individuals with GB, indicating a significant shift in a fundamental property of β-cell function several years after surgery.

From Diabetes Care to Diabetes Cure-The Integration of Systems Biology, eHealth, and Behavioral Change

From a biological view, most of the processes involved in insulin resistance, which drives the pathobiology of type 2 diabetes, are reversible. This theoretically makes the disease reversible and curable by changing dietary habits and physical activity, particularly when adopted early in the disease process. Yet, this is not fully implemented and exploited in health care due to numerous obstacles. This article reviews the state of the art in all areas involved in a diabetes cure-focused therapy and discusses the scientific and technological advancements that need to be integrated into a systems approach sustainable lifestyle-based healthcare system and economy. The implementation of lifestyle as cure necessitates personalized and sustained lifestyle adaptations, which can only be established by a systems approach, including all relevant aspects (personalized diagnosis and diet, physical activity and stress management, self-empowerment, motivation, participation and health literacy, all facilitated by blended care and ehealth). Introduction of such a systems approach in type 2 diabetes therapy not only requires a concerted action of many stakeholders but also a change in healthcare economy, with new winners and losers. A "call for action" is put forward to actually initiate this transition. The solution provided for type 2 diabetes is translatable to other lifestyle-related disorders.

Mid-Term Remission of Type 2 Diabetes Mellitus After Laparoscopic Roux En-Y Gastric Bypass

BACKGROUND

Laparoscopic Roux en-Y gastric bypass (LRYGB) is an established therapeutic modality for type 2 diabetes mellitus (T2DM). However, there is paucity of data on the outcomes of LRYGB on T2DM beyond 2 years. This study aimed to examine the medium-term effects of LRYGB on T2DM and determine the predictors of T2DM resolution.

METHODS

Prospective data were collected for all consecutive LRYGB performed from September 2009 to November 2010. The American Diabetes Association guidelines were used to define complete (CR) or partial (PR) remission of diabetes. Diabetes status was considered improved when there was >50 % reduction in the dose of medications or when glycaemic control was achieved after stopping insulin. The effects of baseline characteristics, diabetes data and weight loss data at 4 years on T2DM remission were studied.

RESULTS

Forty-six patients with T2DM underwent LRYGB with mean ± SD age and body mass index (BMI) of 48.6 ± 9.6 years and 50.4 ± 6.5 kg/m², respectively. Median (IQR, interquartile range) duration of T2DM preoperatively was 60 (36-126) months. Median (IQR) follow-up was 52 (50-57) months. T2DM remission was achieved in 64 % of patients (44 % CR, 20 % PR), and a further 28 % of patients had improvement in their diabetes status. Multivariate analyses demonstrated significant excess weight loss (EWL) [P = 0.008] and lower BMI [P = 0.04] at 4 years to be the only independent predictors of T2DM medium-term outcomes.

CONCLUSION

The medium-term effects of LRYGB on T2DM remission/improvement were maintained in 92 % of patients. EWL and lower BMI at 4 years were independent predictors of T2DM remission.

Fatty Acid Metabolic Remodeling During Type 2 Diabetes Remission After Bariatric Surgery

Hypertrophic remodeling of white adipose tissues is associated with overexposure of lean organs to circulating triglycerides (TGs) and nonesterified fatty acids (NEFAs), ultimately leading to insulin resistance. Bariatric surgery promotes type 2 diabetes (T2D) remission through a succession of weight loss-dependent and -independent mechanisms. However, the longitudinal contribution of adipocyte size reduction and fatty acid metabolic handling remain unknown. Here we show that severely obese participants with T2D display hypertriglyceridemia and excessive systemic lipolysis during intravenous lipid overload. Three days after biliopancreatic diversion with duodenal switch (DS), whole-body glycerol turnover was normalized and associated with lower HOMA-insulin resistance index. A mean excess weight loss of 84% was achieved 12 months after DS. The smaller subcutaneous adipocyte size predicted better glycemic control in T2D. TG disposal and acylcarnitine production during lipid overload, along with muscle insulin sensitivity, improved with weight loss. Nevertheless, systemic NEFA fluxes and NEFA spillover remained similar, suggesting that increased NEFA storage capacity per volume of adipose tissue exactly compensated for the decrease in fat mass during weight loss. In conclusion, T2D remission after DS is mainly associated with greater circulating TG disposal, lower systemic lipolysis, and better fatty acid handling by lean tissues.

Biliopancreatic diversion with duodenal switch leads to better postprandial glucose level and beta cell function than sleeve gastrectomy in individuals with type 2 diabetes very early after surgery

OBJECTIVE

The aim of this study was to compare the short-term effect of sleeve gastrectomy (SG) and biliopancreatic diversion with duodenal switch (DS) in order to determine if exclusion of the upper gastrointestinal tract confers greater metabolic improvement, independent of weight loss.

METHODS

Standard meals were administered before and on day 3 and 4 after SG to assess insulin sensitivity, β-cell function and gastrointestinal hormone responses in matched normoglycemic (NG) and type 2 diabetes (T2D) participants. A third group of matched T2D participants who underwent DS with the same meal test administered prior to and 3days after surgery was also recruited.

RESULTS

Despite significant metabolic improvement, T2D participants failed to fully normalize insulin resistance and β-cell dysfunction 3 and 4days after SG. Our results demonstrate the superiority of DS over SG in terms of short-term improvement in postprandial glucose excursion and β-cell function 3days after the surgery, with similar improvement in hepatic insulin sensitivity.

CONCLUSION

Our findings support the notion that caloric restriction represents an important mechanism to explain the very early anti-diabetic effects observed after bariatric surgery. However, exclusion of the upper gastrointestinal tract also provides further metabolic improvements, possibly mediated by gastrointestinal hormonal responses and altered postprandial glucose absorption.

The Role of PYY in Pancreatic Islet Physiology and Surgical Control of Diabetes

Bariatric surgery in obese individuals leads to rapid and lasting remission of type 2 diabetes (T2D). This phenomenon occurs independently of weight loss possibly via a combination of factors. The incretin hormone GLP-1 has so far been recognised as a critical factor. However, recent data have indicated that elevation in another gut hormone, peptide tyrosine tyrosine (PYY), may drive the beneficial effects of surgery. Here we discuss recent findings on PYY-mediated control of glucose homeostasis and its role in diabetes, in the context of what is known for GLP-1. Identification of factors that increase the expression of PYY following bariatric surgery and elucidation of its role in diabetes reversal may have clinical relevance as a nonsurgical therapy for T2D.

Targeting the gut to treat obesity and its metabolic comorbidities: focus on bariatric surgery - view from the chair

Over the past decade, bariatric surgery emerged as the most effective treatment modality for obesity and its complications, especially type 2 diabetes. Initially introduced on the basis of their capacity to restrict food intake and/or induce dietary fat malabsorption, the current bariatric surgery procedures result in many more physiological changes that may also partly explain their potent and sustained anti-obesity and anti-diabetic effects. In the session 2 of the 17th International Symposium of the Université Laval Research Chair in Obesity, outstanding speakers have provided insight into novel clinical and pathophysiological aspects in bariatric surgery. Dr Blandine Laferrère discussed the growing body of evidence implicating incretin hormones in the anti-diabetic effects of bariatric surgery and Dr Hans-Rudolf Berthoud explored emerging evidence suggesting that bariatric surgery may reset the defended body mass set point. As data are rapidly accruing about the beneficial effects of bariatric surgery, these procedures not only take a greater place in clinical practice, but they also offer outstanding occasions to peek into the intricate and complex links between diet and gastrointestinal track, and obesity and its complications.

Diabetes recurrence after metabolic surgeries correlates with re-impaired insulin sensitivity rather than beta-cell function

AIM

To investigate factors causing diabetes recurrence after sleeve gastrectomy (SG) and duodenal-jejunal bypass (DJB).

METHODS

SG and DJB were performed on rats with diabetes induced by high-fat diet (HFD) and streptozotocin (STZ). HFD was used to induce diabetes recurrence at 4 wk postoperatively. Body weight, oral glucose tolerance test, homeostatic model assessment of insulin resistance (HOMA-IR), insulin signaling [IR, insulin receptor substrate (IRS)1, IRS2, phosphatidylinositol 3-kinase and AKT in liver and skeletal muscle], oral glucose stimulated insulin secretion, beta-cell morphology (mass, apoptosis and insulin secretion), glucagon-like peptide (GLP)-1, PYY and ghrelin were compared among SG rats with common low-fat diet (SG-LFD), SG with HFD (SG-HFD), DJB rats with LFD (DJB-LFD), DJB with HFD (DJB-HFD) and sham-operation with LFD (Sham) at targeted postoperative times.

RESULTS

SG and DJB resulted in significant improvement in glucose tolerance, lower HOMA-IR, up-regulated hepatic and muscular insulin signaling, higher levels of oral glucose-stimulated insulin secretion, bigger beta-cell mass, higher immunofluorescence intensity of insulin, fewer transferase-mediated dUTP-biotin 3’ nick end-labeling (TUNEL)-positive beta cells and higher postprandial GLP-1 and PYY levels than in the Sham group. The improvement in glucose tolerance was reversed at 12 wk postoperatively. Compared with the SG-LFD and DJB-LFD groups, the SG-HFD and DJB-HFD groups showed higher HOMA-IR, down-regulated hepatic and muscular insulin signaling, and more TUNEL-positive beta cells. No significant difference was detected between HFD and LFD groups for body weight, glucose-stimulated insulin secretion, beta-cell mass, immunofluorescence intensity of insulin, and postprandial GLP-1 and PYY levels. Fasting serum ghrelin decreased in SG groups, and there was no difference between HFD-SG and LFD-SG groups.

CONCLUSION

HFD reverses the improvement in glucose homeostasis after SG and DJB. Diabetes recurrence may correlate with re-impaired insulin sensitivity, but not with alterations of beta-cell function and body weight.

Bariatric surgery and diabetic retinopathy: a systematic review and meta-analysis of controlled clinical studies

BACKGROUND

Uncontrolled studies have indicated appearance or progression of diabetic retinopathy in obese diabetic patients after bariatric surgery. The aim of this systematic review and meta-analysis was to compare the rate of appearance, as well as progression or regression of diabetic retinopathy in studies comparing medical and surgical treatment of obese type 2 diabetes.

METHODS AND FINDINGS

Intervention effect (new cases of retinopathy, and cases with any change of diabetic retinopathy score) was expressed as odds ratio (OR), with 95% confidence intervals (CIs); change of diabetic retinopathy score was expressed as standardized mean difference (SMD), with 95% CIs. Meta-analyses were performed by a random-effects model according to DerSimonian and Laird. Heterogeneity was assessed through Q and I2 statistics for each comparison, and potential sources of heterogeneity were discussed where appropriate. Appropriate methodology [preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement] was used. Seven studies were analyzed, and incident cases of retinopathy were fewer with bariatric surgery than with medical treatment; change of retinopathy score (three studies) was not different, while only two studies were available on numbers of patients showing progression or regression of retinopathy. Heterogeneity was not significant, and publication bias was not present.

CONCLUSIONS

Bariatric surgery seems to prevent new cases of diabetic retinopathy, but available studies are not sufficient to support progression or regression of retinopathy. Further studies are needed to draw firm conclusions on the effect of bariatric surgery on diabetic retinopathy.

Glucose Metabolism After Gastric Banding and Gastric Bypass in Individuals With Type 2 Diabetes: Weight Loss Effect

OBJECTIVE

The superior effect of Roux-en-Y gastric bypass (RYGB) on glucose control compared with laparoscopic adjustable gastric banding (LAGB) is confounded by the greater weight loss after RYGB. We therefore examined the effect of these two surgeries on metabolic parameters matched on small and large amounts of weight loss.

RESEARCH DESIGN AND METHODS

Severely obese individuals with type 2 diabetes were tested for glucose metabolism, β-cell function, and insulin sensitivity after oral and intravenous glucose stimuli, before and 1 year after RYGB and LAGB, and at 10% and 20% weight loss after each surgery.

RESULTS

RYGB resulted in greater glucagon-like peptide 1 release and incretin effect, compared with LAGB, at any level of weight loss. RYGB decreased glucose levels (120 min and area under the curve for glucose) more than LAGB at 10% weight loss. However, the improvement in glucose metabolism, the rate of diabetes remission and use of diabetes medications, insulin sensitivity, and β-cell function were similar after the two types of surgery after 20% equivalent weight loss.

CONCLUSIONS

Although RYGB retained its unique effect on incretins, the superiority of the effect of RYGB over that of LAGB on glucose metabolism, which is apparent after 10% weight loss, was attenuated after larger weight loss.

Bariatric surgery and obesity: influence on the incretins

The gut hormone incretins have an important physiological role in meal-related insulin release and post-prandial glucose control. In addition to weight loss, the incretin hormones have a role in glucose control after bariatric surgery. The release of incretins, and specifically of glucagon-like peptide (GLP)-1, in response to the ingestion of nutrients, is greatly enhanced after gastric bypass (RYGBP). The rapid transit of food from the gastric pouch to the distal ileum is responsible for the greater GLP-1 release after RYGBP. The incretin effect on insulin secretion, or the greater insulin response to oral glucose compared to an isoglycemic intravenous glucose challenge, is severely impaired in patients with type 2 diabetes, but is recovered rapidly after RYGBP. The improvement in insulin secretion rate and β-cell sensitivity to oral glucose after RYGBP is mediated by endogenous GLP-1, and is abolished by exendin 9-39, a specific GLP-1 receptor antagonist. While calorie restriction and weight loss have major effects on the rapid and sustained improvement of fasted glucose metabolism, the enhanced incretin effect is a key player in post-prandial glucose control after RYGBP.

Bariatric surgery and type 2 diabetes: are there weight loss-independent therapeutic effects of upper gastrointestinal bypass?

Type 2 diabetes (T2D) is a major worldwide public health concern. Despite a large armamentarium of T2D medications, a large proportion of patients fail to achieve recommended treatment goals for glycemic control. Weight loss has profound beneficial effects on the metabolic abnormalities involved in the pathogenesis of T2D. Accordingly, bariatric surgery, which is the most effective available weight loss therapy, is also the most effective therapy for treating patients with T2D. Surgical procedures that bypass the upper gastrointestinal (UGI) tract are particularly effective in achieving partial and even complete remission of T2D, suggesting that UGI bypass has weight loss-independent effects on glycemic control. Although a number of hypotheses (e.g. a role for multiorgan insulin sensitivity, β-cell function, incretin response, the gut microbiome, bile acid metabolism, intestinal glucose metabolism and browning of adipose tissue) have been proposed to explain the potential unique effects of UGI tract bypass surgery, none has yet been adequately evaluated to determine therapeutic importance in patients with T2D. Here, we review the efficacy of UGI bypass surgery in treating T2D and the mechanisms that have been proposed to explain its potential weight loss-independent therapeutic effects.

An Untargeted Metabolomics Approach to Characterize Short-Term and Long-Term Metabolic Changes after Bariatric Surgery

Bariatric surgery is currently one of the most effective treatments for obesity and leads to significant weight reduction, improved cardiovascular risk factors and overall survival in treated patients. To date, most studies focused on short-term effects of bariatric surgery on the metabolic profile and found high variation in the individual responses to surgery. The aim of this study was to identify relevant metabolic changes not only shortly after bariatric surgery (Roux-en-Y gastric bypass) but also up to one year after the intervention by using untargeted metabolomics. 132 serum samples taken from 44 patients before surgery, after hospital discharge (1-3 weeks after surgery) and at a 1-year follow-up during a prospective study (NCT01271062) performed at two study centers (Austria and Switzerland). The samples included 24 patients with type 2 diabetes at baseline, thereof 9 with diabetes remission after one year. The samples were analyzed by using liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS, HILIC-QExactive). Raw data was processed with XCMS and drift-corrected through quantile regression based on quality controls. 177 relevant metabolic features were selected through Random Forests and univariate testing and 36 metabolites were identified. Identified metabolites included trimethylamine-N-oxide, alanine, phenylalanine and indoxyl-sulfate which are known markers for cardiovascular risk. In addition we found a significant decrease in alanine after one year in the group of patients with diabetes remission relative to non-remission. Our analysis highlights the importance of assessing multiple points in time in subjects undergoing bariatric surgery to enable the identification of biomarkers for treatment response, cardiovascular benefit and diabetes remission. Key-findings include different trend pattern over time for various metabolites and demonstrated that short term changes should not necessarily be used to identify important long term effects of bariatric surgery.

Metabolic responses to xenin-25 are altered in humans with Roux-en-Y gastric bypass surgery

Xenin-25 (Xen) is a neurotensin-related peptide secreted by a subset of enteroendocrine cells located in the proximal small intestine. Many effects of Xen are mediated by neurotensin receptor-1 on neurons. In healthy humans with normal glucose tolerance (NGT), Xen administration causes diarrhea and inhibits postprandial glucagon-like peptide-1 (GLP-1) release but not insulin secretion. This study determines (i) if Xen has similar effects in humans with Roux-en-Y gastric bypass (RYGB) and (ii) whether neural pathways potentially mediate effects of Xen on glucose homeostasis. Eight females with RYGB and no history of type 2 diabetes received infusions with 0, 4 or 12pmol Xen/kg/min with liquid meals on separate occasions. Plasma glucose and gastrointestinal hormone levels were measured and insulin secretion rates calculated. Pancreatic polypeptide and neuropeptide Y levels were surrogate markers for parasympathetic input to islets and sympathetic tone, respectively. Responses were compared to those in well-matched non-surgical participants with NGT from our earlier study. Xen similarly increased pancreatic polypeptide and neuropeptide Y responses in patients with and without RYGB. In contrast, the ability of Xen to inhibit GLP-1 release and cause diarrhea was severely blunted in patients with RYGB. With RYGB, Xen had no statistically significant effect on glucose, insulin secretory, GLP-1, glucose-dependent insulinotropic peptide, and glucagon responses. However, insulin and glucose-dependent insulinotropic peptide secretion preceded GLP-1 release suggesting circulating GLP-1 does not mediate exaggerated insulin release after RYGB. Thus, Xen has unmasked neural circuits to the distal gut that inhibit GLP-1 secretion, cause diarrhea, and are altered by RYGB.

Mechanisms of surgical control of type 2 diabetes: GLP-1 is the key factor-Maybe

Bariatric surgery is the most effective treatment for obesity and diabetes. The 2 most commonly performed weight-loss procedures, Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy, improve glycemic control in patients with type 2 diabetes independent of weight loss. One of the early hypotheses raised to explain the immediate antidiabetic effect of RYGB was that rapid delivery of nutrients from the stomach pouch into the distal small intestine enhances enteroinsular signaling to promote insulin signaling. Given the tenfold increase in postmeal glucagon-like peptide-1 (GLP-1) response compared to unchanged integrated levels of postprandial glucose-dependent insulinotropic peptide after RYGB, enhanced meal-induced insulin secretion after this procedure was thought to be the result of elevated glucose and GLP-1 levels. In this contribution to the larger point-counterpoint debate about the role of GLP-1 after bariatric surgery, most of the focus will be on RYGB.

Gastric Band Surgery Leads to Improved Insulin Secretion in Overweight People with Type 2 Diabetes

BACKGROUND

We aimed to determine the effects of laparoscopic adjustable gastric band (LAGB) on beta-cell function in overweight people with type 2 diabetes and to assess the relationship between baseline beta-cell function and glycemic outcomes.

METHODS

We studied 44 overweight but not obese people with type 2 diabetes who participated in a randomized trial whose primary outcome was the rate of diabetes remission after 2 years of multidisciplinary diabetes care (MDC group) or multidisciplinary care combined with LAGB. Dynamic beta-cell function was assessed by intravenous glucose challenge, and basal beta-cell function (HOMA-B) and insulin sensitivity (HOMA-S) were determined using the homeostatic model.

RESULTS

Twelve LAGB participants and two MDC participants were in diabetes remission at 2 years. HOMA-S and the C-peptide response to intravenous glucose increased significantly in LAGB but not in MDC participants. The insulin response to glucose did not change in LAGB participants, whereas their fasting C-peptide/insulin ratio increased. Baseline measures of beta-cell function correlated with diabetes remission but not with reduction in HbA1c following LAGB.

CONCLUSIONS

In overweight people with diabetes, LAGB improves endogenous beta-cell function after 2 years. Baseline beta-cell function correlated with diabetes remission, but not with HbA1c change following LAGB.

Mechanisms of Diabetes Improvement Following Bariatric/Metabolic Surgery

More than 20 years ago, Pories et al. published a seminal article, "Who Would Have Thought It? An Operation Proves to Be the Most Effective Therapy for Adult-Onset Diabetes Mellitus." This was based on their observation that bariatric surgery rapidly normalized blood glucose levels in obese people with type 2 diabetes mellitus (T2DM), and 10 years later, almost 90% remained diabetes free. Pories et al. suggested that caloric restriction played a key role and that the relative contributions of proximal intestinal nutrient exclusion, rapid distal gut nutrient delivery, and the role of gut hormones required further investigation. These findings of T2DM improvement/remission after bariatric surgery have been widely replicated, together with the observation that bariatric surgery prevents or delays incident T2DM. Over the ensuing two decades, important glucoregulatory roles of the gastrointestinal (GI) tract have been firmly established. However, the physiological and molecular mechanisms underlying the beneficial glycemic effects of bariatric surgery remain incompletely understood. In addition to the mechanisms proposed by Pories et al., changes in bile acid metabolism, GI tract nutrient sensing and glucose utilization, incretins, possible anti-incretin(s), and the intestinal microbiome are implicated. These changes, acting through peripheral and/or central pathways, lead to reduced hepatic glucose production, increased tissue glucose uptake, improved insulin sensitivity, and enhanced β-cell function. A constellation of factors, rather than a single overarching mechanism, likely mediate postoperative glycemic improvement, with the contributing factors varying according to the surgical procedure. Thus, different bariatric/metabolic procedures provide us with experimental tools to probe GI tract physiology. Embracing this approach through the application of detailed phenotyping, genomics, metabolomics, and gut microbiome studies will enhance our understanding of metabolic regulation and help identify novel therapeutic targets.

Effects of endogenous GLP-1 and GIP on glucose tolerance after Roux-en-Y gastric bypass surgery

Exaggerated secretion of glucagon-like peptide 1 (GLP-1) is important for postprandial glucose tolerance after Roux-en-Y gastric bypass (RYGB), whereas the role of glucose-dependent insulinotropic polypeptide (GIP) remains to be resolved. We aimed to explore the relative importance of endogenously secreted GLP-1 and GIP on glucose tolerance and β-cell function after RYGB. We used DPP-4 inhibition to enhance concentrations of intact GIP and GLP-1 and the GLP-1 receptor antagonist exendin-(9-39) (Ex-9) for specific blockage of GLP-1 actions. Twelve glucose-tolerant patients were studied after RYGB in a randomized, placebo-controlled, 4-day crossover study with standard mixed-meal tests and concurrent administration of placebo, oral sitagliptin, Ex-9 infusion, or combined Ex-9-sitagliptin. GLP-1 receptor antagonism increased glucose excursions, clearly attenuated β-cell function, and aggravated postprandial hyperglucagonemia compared with placebo, whereas sitagliptin had no effect despite two- to threefold increased concentrations of intact GLP-1 and GIP. Similarly, sitagliptin did not affect glucose tolerance or β-cell function during GLP-1R blockage. This study confirms the importance of GLP-1 for glucose tolerance after RYGB via increased insulin and attenuated glucagon secretion in the postprandial state, whereas amplification of the GIP signal (or other DPP-4-sensitive glucose-lowering mechanisms) did not appear to contribute to the improved glucose tolerance seen after RYGB.

Insulin Sensitivity and Secretion in Obese Type 2 Diabetic Women after Various Bariatric Operations

OBJECTIVE

To compare the effects of biliopancreatic diversion (BPD) and laparoscopic gastric banding (LAGB) on insulin sensitivity and secretion with the effects of laparoscopic gastric plication (P).

METHODS

A total of 52 obese women (age 30-66 years) suffering from type 2 diabetes mellitus (T2DM) were prospectively recruited into three study groups: 16 BPD; 16 LAGB, and 20 P. Euglycemic clamps and mixed meal tolerance tests were performed before, at 1 month and at 6 months after bariatric surgery. Beta cell function derived from the meal test parameters was evaluated using mathematical modeling.

RESULTS

Glucose disposal per kilogram of fat free mass (a marker of peripheral insulin sensitivity) increased significantly in all groups, especially after 1 month. Basal insulin secretion decreased significantly after all three types of operations, with the most marked decrease after BPD compared with P and LAGB. Total insulin secretion decreased significantly only following the BPD. Beta cell glucose sensitivity did not change significantly post-surgery in any of the study groups.

CONCLUSION

We documented similar improvement in insulin sensitivity in obese T2DM women after all three study operations during the 6-month postoperative follow-up. Notably, only BPD led to decreased demand on beta cells (decreased integrated insulin secretion), but without increasing the beta cell glucose sensitivity.

GLP-1: a mediator of the beneficial metabolic effects of bariatric surgery?

There has been increasing interest in the role that gut hormones may play in contributing to the physiological changes produced by certain bariatric procedures, such as Roux-en-Y gastric bypass and sleeve gastrectomy. Here, we review the evidence implicating one such gut hormone, glucagon-like peptide-1, as a mediator of the metabolic benefits of these two procedures.

Preserved Insulin Secretory Capacity and Weight Loss Are the Predominant Predictors of Glycemic Control in Patients With Type 2 Diabetes Randomized to Roux-en-Y Gastric Bypass

Improvement in type 2 diabetes after Roux-en-Y gastric bypass (RYGB) has been attributed partly to weight loss, but mechanisms beyond weight loss remain unclear. We performed an ancillary study to the Diabetes Surgery Study to assess changes in incretins, insulin sensitivity, and secretion 1 year after randomization to lifestyle modification and intensive medical management (LS/IMM) alone (n = 34) or in conjunction with RYGB (n = 34). The RYGB group lost more weight and had greater improvement in HbA1c. Fasting glucose was lower after RYGB than after LS/IMM, although the glucose area under the curve decreased comparably for both groups. Insulin sensitivity increased in both groups. Insulin secretion was unchanged after LS/IMM but decreased after RYGB, except for a rapid increase during the first 30 min after meal ingestion. Glucagon-like peptide 1 (GLP-1) was substantially increased after RYGB, while gastric inhibitory polypeptide and glucagon decreased. Lower HbA1c was most strongly correlated with the percentage of weight loss for both groups. At baseline, a greater C-peptide index and 90-min postprandial C-peptide level were predictive of lower HbA1c at 1 year after RYGB. β-Cell glucose sensitivity, which improved only after RYGB, and improved disposition index were associated with lower HbA1c in both groups, independent of weight loss. Weight loss and preserved β-cell function both predominantly determine the greatest glycemic benefit after RYGB.