GLP-1 action and glucose tolerance in subjects with remission of type 2 diabetes after gastric bypass surgery

Unimolecular Polypharmacy for Treatment of Diabetes and Obesity

Many complex diseases have historically proven to be defiant to the best mono-therapeutic approaches. Several examples of combination therapies have largely overcome such challenges, notably for the treatment of severe hypertension and tuberculosis. Obesity and its consequences, such as type 2 diabetes, have proven to be equally resistant to therapeutic approaches based on single medicines. Proper management of type 2 diabetes often requires adjunctive medications, and the recent registration of a few compound mixtures has set the precedent for combinatorial treatment of obesity. On the other hand, double or triple therapeutic combinations are more difficult to advance to regulatory approval than single molecules. More recently, several classes of novel unimolecular combination therapeutics have emerged with superior efficacy than currently prescribed options and pose the potential to reverse obesity and type 2 diabetes. Here, we summarize the discovery, pre-clinical validation, and first clinical test of such peptide hormone poly-agonist drug candidates.

A High-Throughput Automated Microfluidic Platform for Calcium Imaging of Taste Sensing

The human enteroendocrine L cell line NCI-H716, expressing taste receptors and taste signaling elements, constitutes a unique model for the studies of cellular responses to glucose, appetite regulation, gastrointestinal motility, and insulin secretion. Targeting these gut taste receptors may provide novel treatments for diabetes and obesity. However, NCI-H716 cells are cultured in suspension and tend to form multicellular aggregates, preventing high-throughput calcium imaging due to interferences caused by laborious immobilization and stimulus delivery procedures. Here, we have developed an automated microfluidic platform that is capable of trapping more than 500 single cells into microwells with a loading efficiency of 77% within two minutes, delivering multiple chemical stimuli and performing calcium imaging with enhanced spatial and temporal resolutions when compared to bath perfusion systems. Results revealed the presence of heterogeneity in cellular responses to the type, concentration, and order of applied sweet and bitter stimuli. Sucralose and denatonium benzoate elicited robust increases in the intracellular Ca(2+) concentration. However, glucose evoked a rapid elevation of intracellular Ca(2+) followed by reduced responses to subsequent glucose stimulation. Using Gymnema sylvestre as a blocking agent for the sweet taste receptor confirmed that different taste receptors were utilized for sweet and bitter tastes. This automated microfluidic platform is cost-effective, easy to fabricate and operate, and may be generally applicable for high-throughput and high-content single-cell analysis and drug screening.

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.

The incretin effect in healthy individuals and those with type 2 diabetes: physiology, pathophysiology, and response to therapeutic interventions

The incretin effect describes the phenomenon whereby oral glucose elicits higher insulin secretory responses than does intravenous glucose, despite inducing similar levels of glycaemia, in healthy individuals. This effect, which is uniformly defective in patients with type 2 diabetes, is mediated by the gut-derived incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). The importance of the incretin effect for the maintenance of glucose homoeostasis is clearly established, and incretin-based therapies are among the most promising new therapies for type 2 diabetes. However, despite the effectiveness of these therapies in many patients, the idea that they restore the incretin effect is a common misconception. In type 2 diabetes, the endocrine pancreas remains responsive to GLP-1 but is no longer responsive to GIP, which is the most likely reason for a reduced or absent incretin effect. Incretin-based drugs, including GLP-1 receptor agonists and dipeptidyl peptidase 4 (DPP-4) inhibitors, stimulate GLP-1 receptors and thus augment insulin secretion in response to both oral and intravenous glucose stimulation, thereby abolishing any potential difference in the responses to these stimuli. These drugs therefore do not restore the defective incretin effect in patients. By contrast, some bariatric surgical procedures enhance GLP-1 responses and also restore the incretin effect in obese individuals with type 2 diabetes. Thus, not all biological actions elicited by the stimulation of GLP-1 receptors lead to quantitative changes to the incretin effect.

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.

MANAGEMENT OF ENDOCRINE DISEASE: Metabolic effects of bariatric surgery

Obesity is associated with an increased risk of type 2 diabetes, hypertension, dyslipidemia, cardiovascular disease, osteoarthritis, numerous cancers and increased mortality. It is estimated that at least 2.8 million adults die each year due to obesity-related cardiovascular disease. Increasing in parallel with the global obesity problem is metabolic syndrome, which has also reached epidemic levels. Numerous studies have demonstrated that bariatric surgery is associated with significant and durable weight loss with associated improvement of obesity-related comorbidities. This review aims to summarize the effects of bariatric surgery on the components of metabolic syndrome (hyperglycemia, hyperlipidemia and hypertension), weight loss, perioperative morbidity and mortality, and the long-term impact on cardiovascular risk and mortality.

Weight Loss Decreases Excess Pancreatic Triacylglycerol Specifically in Type 2 Diabetes

OBJECTIVE

This study determined whether the decrease in pancreatic triacylglycerol during weight loss in type 2 diabetes mellitus (T2DM) is simply reflective of whole-body fat or specific to diabetes and associated with the simultaneous recovery of insulin secretory function.

RESEARCH DESIGN AND METHODS

Individuals listed for gastric bypass surgery who had T2DM or normal glucose tolerance (NGT) matched for age, weight, and sex were studied before and 8 weeks after surgery. Pancreas and liver triacylglycerol were quantified using in-phase, out-of-phase MRI. Also measured were the first-phase insulin response to a stepped intravenous glucose infusion, hepatic insulin sensitivity, and glycemic and incretin responses to a semisolid test meal.

RESULTS

Weight loss after surgery was similar (NGT: 12.8 ± 0.8% and T2DM: 13.6 ± 0.7%) as was the change in fat mass (56.7 ± 3.3 to 45.4 ± 2.3 vs. 56.6 ± 2.4 to 43.0 ± 2.4 kg). Pancreatic triacylglycerol did not change in NGT (5.1 ± 0.2 to 5.5 ± 0.4%) but decreased in the group with T2DM (6.6 ± 0.5 to 5.4 ± 0.4%; P = 0.007). First-phase insulin response to a stepped intravenous glucose infusion did not change in NGT (0.24 [0.13-0.46] to 0.23 [0.19-0.37] nmol ⋅ min(-1) ⋅ m(-2)) but normalized in T2DM (0.08 [-0.01 to -0.10] to 0.22 [0.07-0.30]) nmol ⋅ min(-1) ⋅ m(-2) at week 8 (P = 0.005). No differential effect of incretin secretion was observed after gastric bypass, with more rapid glucose absorption bringing about equivalently enhanced glucagon-like peptide 1 secretion in the two groups.

CONCLUSIONS

The fall in intrapancreatic triacylglycerol in T2DM, which occurs during weight loss, is associated with the condition itself rather than decreased total body fat.

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.

Glucoregulatory Relevance of Small Intestinal Nutrient Sensing in Physiology, Bariatric Surgery, and Pharmacology

Emerging evidence suggests the gastrointestinal tract plays an important glucoregulatory role. In this perspective, we first review how the intestine senses ingested nutrients, initiating crucial negative feedback mechanisms through a gut-brain neuronal axis to regulate glycemia, mainly via reduction in hepatic glucose production. We then highlight how intestinal energy sensory mechanisms are responsible for the glucose-lowering effects of bariatric surgery, specifically duodenal-jejunal bypass, and the antidiabetic agents metformin and resveratrol. A better understanding of these pathways lays the groundwork for intestinally targeted drug therapy for the treatment of diabetes.

Effects of laparoscopic gastric plication (LGP) in patients with type 2 diabetes, one year follow-up

Background

Obesity is a major risk factor for the development of type 2 diabetes mellitus. Surgery is one of the most effective treatments for morbid obesity. In a prospective cohort study, we examined the effects of Laparoscopic Gastric Plication (LGP) as a new restrictive technique on remission of type 2 diabetes mellitus.

Methods

During six years of study from June 2007 through December 2013, 62 patients who underwent bariatric surgery were recruited for our study to determine the effects of weight loss. Sixty patients with diabetes mellitus type 2 were selected for a one year follow up period. The amount of weight loss, Fasting Blood Sugar (FBS), changes in the lipid profile, HbA1c and blood pressure were assessed during this period. The primary outcomes were safety and the percentage of patients experiencing diabetes remission.

Results

Sixty patients with the mean age of 39.7 ± 12.8 years, ranging from 18 to 62 years, were enrolled in the study for an average 12 months of follow up. The maximal weight loss of 57 kg was achieved at average after six months. FBS significantly decreased during this period, and after one year, remission of diabetes was achieved in 92 % of patients. In five patients, diabetes was controlled with decrease in taking oral medications.

Conclusions

Laparoscopic Gastric Plication (LGP) resulted in significant and sustained weight loss with minimal physiologic changes in gastrointestinal tract and ameliorated blood glucose control of type 2 diabetes in morbid obese patients.

Preoperative β-cell function in patients with type 2 diabetes is important for the outcome of Roux-en-Y gastric bypass surgery

The majority of the patients with type 2 diabetes (T2DM) show remission after Roux-en-Y gastric bypass (RYGB). This is the result of increased postoperative insulin sensitivity and β-cell secretion. The aim of the present study was to elucidate the importance of the preoperative β-cell function in T2DM for the chance of remission after RYGB. Fifteen patients with and 18 without T2DM had 25 g oral (OGTT) and intravenous (IVGTT) glucose tolerance tests performed at inclusion, after a diet-induced weight loss, and 4 and 18 months after RYGB. Postoperative first phase insulin secretion rate (ISR) during the IVGTT and β-cell glucose sensitivity during the OGTT increased in T2DM. Postoperative insulin sensitivity and the disposition index (DI) markedly increased in both groups. By stratifying the T2DM into two groups according to highest (T2DMhigh ) and lowest (T2DMlow ) baseline DI, a restoration of first phase ISR and β-cell glucose sensitivity were seen only in T2DMhigh . Remission of type 2 diabetes was 71 and 38% in T2DMhigh and T2DMlow , respectively. Postoperative postprandial GLP-1 concentrations increased markedly, but did not differ between the groups. Our findings emphasize the importance of the preoperative of β-cell function for remission of diabetes after RYGB.

The role of bile acids in reducing the metabolic complications of obesity after bariatric surgery: a systematic review

BACKGROUND

Bariatric surgery is currently the most efficacious treatment for obesity and its associated metabolic co-morbidities, such as diabetes. The metabolic improvements occur through both weight-dependent and weight-independent mechanisms. Bile acids (BAs) have emerged as key signalling molecules that have a central role in modulating many of the physiological effects seen after bariatric surgery. This systematic review assesses the evidence from both human and animal studies for the role of BAs in reducing the metabolic complications of obesity following bariatric surgery.

METHODS

We conducted a systematic search of Medline and Embase databases to identify all articles investigating the role of BAs in mediating the metabolic changes observed following bariatric surgery in both animal and human studies. Boolean logic was used with relevant search terms, including the following MeSH terms: 'bile acids and salts', 'bariatric surgery', 'metabolic surgery', 'gastrointestinal tract/surgery' and 'obesity/surgery'.

RESULTS

Following database searches (n=1197), inclusion from bibliography searches (n=2) and de-duplication (n=197), 1002 search results were returned. Of these, 132 articles were selected for full-text review, of which 38 articles were deemed relevant and included in the review. The findings support the effects of BAs on satiety, lipid and cholesterol metabolism, incretins and glucose homoeostasis, energy metabolism, gut microbiota and endoplasmic reticulum stress following bariatric surgery. Many of these metabolic effects are modulated through the BA receptors FXR and TGR5. We also explore a possible link between BAs and carcinogenesis following bariatric surgery.

CONCLUSIONS

Overall there is good evidence to support the role of BAs in the metabolic effects of bariatric surgery through the above mechanisms. BAs could serve as a novel therapeutic pharmacological target for the treatment of obesity and its associated co-morbidities.

Physiology of proglucagon peptides: role of glucagon and GLP-1 in health and disease

The preproglucagon gene (Gcg) is expressed by specific enteroendocrine cells (L-cells) of the intestinal mucosa, pancreatic islet α-cells, and a discrete set of neurons within the nucleus of the solitary tract. Gcg encodes multiple peptides including glucagon, glucagon-like peptide-1, glucagon-like peptide-2, oxyntomodulin, and glicentin. Of these, glucagon and GLP-1 have received the most attention because of important roles in glucose metabolism, involvement in diabetes and other disorders, and application to therapeutics. The generally accepted model is that GLP-1 improves glucose homeostasis indirectly via stimulation of nutrient-induced insulin release and by reducing glucagon secretion. Yet the body of literature surrounding GLP-1 physiology reveals an incompletely understood and complex system that includes peripheral and central GLP-1 actions to regulate energy and glucose homeostasis. On the other hand, glucagon is established principally as a counterregulatory hormone, increasing in response to physiological challenges that threaten adequate blood glucose levels and driving glucose production to restore euglycemia. However, there also exists a potential role for glucagon in regulating energy expenditure that has recently been suggested in pharmacological studies. It is also becoming apparent that there is cross-talk between the proglucagon derived-peptides, e.g., GLP-1 inhibits glucagon secretion, and some additive or synergistic pharmacological interaction between GLP-1 and glucagon, e.g., dual glucagon/GLP-1 agonists cause more weight loss than single agonists. In this review, we discuss the physiological functions of both glucagon and GLP-1 by comparing and contrasting how these peptides function, variably in concert and opposition, to regulate glucose and energy homeostasis.

What is the Mechanism Behind Weight Loss Maintenance with Gastric Bypass?

Obesity is an epidemic on the rise. With the failure of non-surgical strategies, bariatric surgery has emerged as the most effective therapeutic option for the treatment of severe obesity. Among various surgical options, Roux-en-Y gastric bypass (RYGB) results in sustained weight loss and profound metabolic improvements. The traditional view that gastric bypass and bariatric surgery in general works primarily through restriction/malabsorption of nutrients has become obsolete. It is now increasingly recognised that its mechanisms of action are primarily physiologic, not mechanic. In fact, clinical and translational studies over the last decade have shown that a number of gastrointestinal mechanisms, including changes in gut hormones, neural signalling, intestinal flora, bile acid and lipid metabolism can play a significant role in the effects of this procedure on energy homeostasis. The clinical efficacy and mechanisms of action of RYGB provide a compelling evidence for the role of the gastrointestinal tract in the regulation of appetite and satiety, body weight and glucose metabolism. This review discusses the physiologic changes that occur after RYGB and that contribute to its mechanisms of action.

Preoperative use of incretins is associated with increased diabetes remission after RYGB surgery among patients taking insulin: a retrospective cohort analysis

OBJECTIVE

The main goal of this study was to determine the effects of incretins on type 2 diabetes (T2D) remission after Roux-en-Y gastric bypass (RYGB) surgery for patients taking insulin.

BACKGROUND

Type 2 diabetes is a chronic disease with potentially debilitating consequences. RYGB surgery is one of the few interventions that can remit T2D. Preoperative use of insulin, however, predisposes to significantly lower T2D remission rates.

METHODS

A retrospective cohort of 690 T2D patients with at least 12 months follow-up and available electronic medical records was used to identify 37 T2D patients who were actively using a Glucagon-like peptide 1 (GLP-1) agonist in addition to another antidiabetic medication, during the preoperative period.

RESULTS

Here, we report that use of insulin, along with other antidiabetic medications, significantly diminished overall T2D remission rates 14 months after RYGB surgery (9%) compared with patients not taking insulin (56%). Addition of the GLP-1 agonist, however, increased significantly T2D early remission rates (22%), compared with patients not taking the GLP-1 agonist (4%). Moreover, the 6-year remission rates were also significantly higher for the former group of patients. The GLP-1 agonist did not improve the remission rates of diabetic patients not taking insulin as part of their pharmacotherapy.

CONCLUSIONS

Preoperative use of antidiabetic medication, coupled with an incretin agonist, could significantly improve the odds of T2D remission after RYGB surgery in patients also using insulin.

Immediate enhancement of first-phase insulin secretion and unchanged glucose effectiveness in patients with type 2 diabetes after Roux-en-Y gastric bypass

Roux-en-Y gastric bypass surgery (RYGB) in patients with type 2 diabetes often leads to early disease remission, and it is unknown to what extent this involves improved pancreatic β-cell function per se and/or enhanced insulin- and non-insulin-mediated glucose disposal (glucose effectiveness). We studied 30 obese patients, including 10 with type 2 diabetes, 8 with impaired glucose tolerance, and 12 with normal glucose tolerance before, 1 wk, and 3 mo after RYGB, using an intravenous glucose tolerance test (IVGTT) to estimate first-phase insulin response, insulin sensitivity (Si), and glucose effectiveness with Bergman's minimal model. In the fasting state, insulin sensitivity was estimated by HOMA-S and β-cell function by HOMA-β. Moreover, mixed-meal tests and oral GTTs were performed. In patients with type 2 diabetes, glucose levels normalized after RYGB, first-phase insulin secretion in response to iv glucose increased twofold, and HOMA-β already improved 1 wk postoperatively, with further enhancements at 3 mo. Insulin sensitivity increased in the liver (HOMA-S) at 1 wk and at 3 mo in peripheral tissues (Si), whereas glucose effectiveness did not improve significantly. During oral testing, GLP-1 responses and insulin secretion increased regardless of glucose tolerance. Therefore, in addition to increased insulin sensitivity and exaggerated postprandial GLP-1 levels, diabetes remission after RYGB involves early improvement of pancreatic β-cell function per se, reflected in enhanced first-phase insulin secretion to iv glucose and increased HOMA-β. A major role for improved glucose effectiveness after RYGB was not supported by this study.

The role of gut adaptation in the potent effects of multiple bariatric surgeries on obesity and diabetes

Bariatric surgical procedures such as vertical sleeve gastrectomy (VSG) and Roux-en-Y gastric bypass (RYGB) are the most potent treatments available to produce sustained reductions in body weight and improvements in glucose regulation. While traditionally these effects are attributed to mechanical aspects of these procedures, such as restriction and malabsorption, a growing body of evidence from mouse models of these procedures points to physiological changes that mediate the potent effects of these surgeries. In particular, there are similar changes in gut hormone secretion, bile acid levels, and composition after both of these procedures. Moreover, loss of function of the nuclear bile acid receptor (FXR) greatly diminishes the effects of VSG. Both VSG and RYGB are linked to profound changes in the gut microbiome that also mediate at least some of these surgical effects. We hypothesize that surgical rearrangement of the gastrointestinal tract results in enteroplasticity caused by the high rate of nutrient presentation and altered pH in the small intestine that contribute to these physiological effects. Identifying the molecular underpinnings of these procedures provides new opportunities to understand the relationship of the gastrointestinal tract to obesity and diabetes as well as new therapeutic strategies to harness the effectiveness of surgery with less-invasive approaches.

Updates in weight loss surgery and gastrointestinal peptides

PURPOSE OF REVIEW

Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy are referred to as 'metabolic surgery' due to hormonal shifts with impacts on diabetes remission and weight loss. The purpose of this review is to summarize recent findings in mechanisms underlying beneficial effects of weight loss surgery.

RECENT FINDINGS

Importantly, gut hormone secretion is altered after RYGB and sleeve gastrectomy due to accelerated transit of nutrients to distal parts of the small intestine, leading to excessive release of L-cell peptide hormones [e.g. glucagon-like peptide-1 (GLP-1), peptide YY].Improved glucose metabolism after RYGB and sleeve gastrectomy involves several mechanisms: early increased hepatic insulin sensitivity, resulting from reduced liver fat content in response to the postoperative caloric restriction, improved beta-cell function mediated by exaggerated postprandial GLP-1 secretion; as demonstrated by relapse of impaired glucose tolerance in studies blocking the GLP-1 receptor by exendin 9-39, and later after major weight loss increased peripheral insulin sensitivity. Gut hormone secretion changes towards a more anorectic profile and is likely important for less caloric intake and weight loss.

SUMMARY

Changes in gut hormone secretion after RYGB and sleeve gastrectomy surgery induce the beneficial effects on weight and glycemic control through the influence on appetite regulation and insulin secretion.

GLP-1 plays a limited role in improved glycemia shortly after Roux-en-Y gastric bypass: a comparison with intensive lifestyle modification

Rapid glycemic improvements following Roux-en-Y gastric bypass (RYGB) are frequently attributed to the enhanced GLP-1 response, but causality remains unclear. To determine the role of GLP-1 in improved glucose tolerance after surgery, we compared glucose and hormonal responses to a liquid meal test in 20 obese participants with type 2 diabetes mellitus who underwent RYGB or nonsurgical intensive lifestyle modification (ILM) (n = 10 per group) before and after equivalent short-term weight reduction. The GLP-1 receptor antagonist exendin(9-39)-amide (Ex-9) was administered, in random order and in double-blinded fashion, with saline during two separate visits after equivalent weight loss. Despite the markedly exaggerated GLP-1 response after RYGB, changes in postprandial glucose and insulin responses did not significantly differ between groups, and glucagon secretion was paradoxically augmented after RYGB. Hepatic insulin sensitivity also increased significantly after RYGB. With Ex-9, glucose tolerance deteriorated similarly from the saline condition in both groups, but postprandial insulin release was markedly attenuated after RYGB compared with ILM. GLP-1 exerts important insulinotropic effects after RYGB and ILM, but the enhanced incretin response plays a limited role in improved glycemia shortly after surgery. Instead, enhanced hepatic metabolism, independent of GLP-1 receptor activation, may be more important for early postsurgical glycemic improvements.

Effect of bariatric surgery combined with medical therapy versus intensive medical therapy or calorie restriction and weight loss on glycemic control in Zucker diabetic fatty rats

Bariatric surgery rapidly improves Type 2 diabetes mellitus (T2DM). Our objective was to profile and compare the extent and duration of improved glycemic control following Roux-en-Y gastric (RYGB) bypass surgery and vertical sleeve gastrectomy (SG) and compare against calorie restriction/weight loss and medical combination therapy-based approaches using the Zucker diabetic fatty rat (ZDF) rodent model of advanced T2DM. Male ZDF rats underwent RYGB (n = 15) or SG surgery (n = 10) at 18 wk of age and received postsurgical insulin treatment, as required to maintain mid-light-phase glycemia within a predefined range (10-15 mmol/l). In parallel, other groups of animals underwent sham surgery with ad libitum feeding (n = 6), with body weight (n = 8), or glycemic matching (n = 8) to the RYGB group, using food restriction or a combination of insulin, metformin, and liraglutide, respectively. Both bariatric procedures decreased the daily insulin dose required to maintain mid-light-phase blood glucose levels below 15 mmol/l, compared with those required by body weight or glycemia-matched rats (P < 0.001). No difference was noted between RYGB and SG with regard to initial efficacy. SG was, however, associated with higher food intake, weight regain, and higher insulin requirements vs. RYGB at study end (P < 0.05). Severe hypoglycemia occurred in several rats after RYGB. RYGB and SG significantly improved glycemic control in a rodent model of advanced T2DM. While short-term outcomes are similar, long-term efficacy appears marginally better after RYGB, although this is tempered by the increased risk of hypoglycemia.

A gut feeling to cure diabetes: potential mechanisms of diabetes remission after bariatric surgery

A cure for type 2 diabetes was once a mere dream but has now become a tangible and achievable goal with the unforeseen success of bariatric surgery in the treatment of both obesity and type 2 diabetes. Popular bariatric procedures such as Roux-en-Y gastric bypass and sleeve gastrectomy exhibit high rates of diabetes remission or marked improvement in glycemic control. However, the mechanism of diabetes remission following these procedures is still elusive and appears to be very complex and encompasses multiple anatomical and physiological changes. In this article, calorie restriction, improved β-cell function, improved insulin sensitivity, and alterations in gut physiology, bile acid metabolism, and gut microbiota are reviewed as potential mechanisms of diabetes remission after Roux-en-Y gastric bypass and sleeve gastrectomy.

Attenuated improvements in adiponectin and fat loss characterize type 2 diabetes non-remission status after bariatric surgery

AIM

To identify the metabolic determinants of type 2 diabetes non-remission status after bariatric surgery at 12 and 24 months.

METHODS

A total of 40 adults [mean ± sd body mass index 36 ± 3 kg/m(2) , age 48 ± 9 years, glycated haemoglobin (HbA1c) 9.7 ± 2%) undergoing bariatric surgery [Roux-en-Y gastric bypass (RYGB) or sleeve gastrectomy (SG)] were enrolled in the present study, the Surgical Treatment and Medication Potentially Eradicate Diabetes Efficiently (STAMPEDE) trial. Type 2 diabetes remission was defined as HbA1c <6.5% and fasting glucose <126 mg/dl (i.e. <7 mmol/l) without antidiabetic medication. Indices of insulin secretion and sensitivity were calculated from plasma glucose, insulin and C-peptide values during a 120-min mixed-meal tolerance test. Body fat, incretins (glucagon-like polypeptide-1, gastric inhibitory peptide, ghrelin) and adipokines [adiponectin, leptin, tumour necrosis factor-α, high-sensitivity C-reactive protein (hs-CRP)] were also assessed.

RESULTS

At 24 months, 37 patients had available follow-up data (RYGB, n = 18; SG, n = 19). Bariatric surgery induced type 2 diabetes remission rates of 40 and 27% at 12 and 24 months, respectively. Total fat/abdominal fat loss, insulin secretion, insulin sensitivity and β-cell function (C-peptide0-120 /glucose0-120 × Matsuda index) improved more in those with remission at 12 and 24 months than in those without remission. Incretin levels were unrelated to type 2 diabetes remission, but, compared with those without remission, hs-CRP decreased and adiponectin increased more in those with remission. Only baseline adiponectin level predicted lower HbA1c levels at 12 and 24 months, and elevated adiponectin correlated with enhanced β-cell function, lower triglyceride levels and fat loss.

CONCLUSIONS

Smaller rises in adiponectin level, a mediator of insulin action and adipose mass, characterize type 2 diabetes non-remission up to 2 years after bariatric surgery. Adjunctive strategies promoting greater fat loss and/or raising adiponectin may be key to achieving higher type 2 diabetes remission rates after bariatric surgery.

Specificity and sensitivity of commercially available assays for glucagon-like peptide-1 (GLP-1): implications for GLP-1 measurements in clinical studies

AIMS

To evaluate the performances of commercially available glucagon-like peptide-1 (GLP-1) assays and the implications for clinical studies.

METHODS

Known concentrations (5-300 pmol/l) of synthetic GLP-1 isoforms (GLP-1 1-36NH2, 7-36NH2, 9-36NH2, 1-37, 7-37 and 9-37) were added to the matrix (assay buffer) supplied with 10 different kits and to human plasma, and recoveries were determined. Assays yielding meaningful results were analysed for precision and sensitivity by repeated analysis and ability to discriminate low concentrations. Endogenous GLP-1 levels in clinical samples were assessed using three commercial kits.

RESULTS

The USCN LIFE assay detected none of the GLP-1 isoforms. The active GLP-1 enzyme-linked immunosorbent assays (ELISAs) from Millipore and DRG appeared identical and were specific for intact GLP-1 in buffer and plasma. The Meso Scale Discovery (MSD) total GLP-1 kit detected all six GLP-1 isoforms, although recovery of non-active forms was incomplete, especially in plasma. Millipore total GLP-1 ELISA kit detected all isoforms in buffer, but mainly amidated forms in plasma. The Alpco, Phoenix and Bio-Rad kits detected only amidated GLP-1, but the Alpco kit had a limited measurement range (30 pmol/l), the Phoenix kit had incomplete recovery in plasma and the Bio-Rad kit was insensitive (detection limit in plasma 40 pmol/l). The pattern of postprandial GLP-1 responses in clinical samples was similar between the kits tested, but the absolute concentrations measured varied.

CONCLUSIONS

The specificity and sensitivity of commercially available kits for the analysis of GLP-1 levels vary considerably. This should be taken into account when selecting which assay to use and when comparing data from different studies.

GLP-1 and glucose tolerance after sleeve gastrectomy in morbidly obese subjects with type 2 diabetes

Although GLP-1 has been suggested as a major factor for the marked improvement of glucose tolerance commonly seen after sleeve gastrectomy (SG), several observations challenge this hypothesis. To better understand the role of GLP-1 in the remission of type 2 diabetes mellitus (T2DM) long term after SG in humans, we conducted two separate cross-sectional studies: 1) the GLP-1 response to a standardized mixed liquid meal (SMLM) was compared in subjects with T2DM antedating SG but with different long-term (>2 years) T2DM outcomes (remission, relapse, or lack of remission) (study 1) and 2) the effect of GLP-1 receptor blockade with exendin (9-39) on glucose tolerance was examined in subjects with T2DM antedating surgery, who had undergone SG and presented with long-term T2DM remission (study 2). In study 1, we observed a comparable GLP-1 response to the SMLM regardless of the post-SG outcome of T2DM. In study 2, the blockade of GLP-1 action resulted in impaired insulin secretion but limited deterioration of glucose tolerance. Thus, our data suggest the enhanced GLP-1 secretion observed long term after SG is neither sufficient nor critical to maintain normal glucose tolerance in subjects with T2DM antedating the surgery.

Effects of glucagon like peptide-1 to mediate glycemic effects of weight loss surgery

To date, weight loss surgeries are the most effective treatment for obesity and glycemic control in patients with type 2 diabetes. Roux-en-Y gastric bypass surgery (RYGB) and sleeve gastrectomy (SG), two widely used bariatric procedures for the treatment of obesity, induce diabetes remission independent of weight loss while glucose improvement after adjustable gastric banding (AGB) is proportional to the amount of weight loss. The immediate, weight-loss independent glycemic effect of gastric bypass has been attributed to postprandial hyperinsulinemia and an enhanced incretin effect. The rapid passage of nutrients into the intestine likely accounts for significantly enhanced glucagon like-peptide 1 (GLP-1) secretion, and postprandial hyperinsulinemia after GB is typically attributed to the combined effects of elevated glucose and GLP-1. For this review we focus on the beneficial effects of the three most commonly performed bariatric procedures, RYGB, SG, and AGB, on glucose metabolism and diabetes remission. Central to this discussion will be the extent to which the effects of surgery are mediated by GLP-1. Better understanding of these mechanisms could provide insight to development of novel therapeutic strategies for treatment of diabetes as well as refinement of surgical techniques.

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

The mechanisms responsible for the remarkable remission of type 2 diabetes after Roux-en-Y gastric bypass (RYGBP) are still puzzling. To elucidate the role of the gut, we compared β-cell function assessed during an oral glucose tolerance test (OGTT) and an isoglycemic intravenous glucose clamp (iso-IVGC) in: 1) 16 severely obese patients with type 2 diabetes, up to 3 years post-RYGBP; 2) 11 severely obese normal glucose-tolerant control subjects; and 3) 7 lean control subjects. Diabetes remission was observed after RYGBP. β-Cell function during the OGTT, significantly blunted prior to RYGBP, normalized to levels of both control groups after RYGBP. In contrast, during the iso-IVGC, β-cell function improved minimally and remained significantly impaired compared with lean control subjects up to 3 years post-RYGBP. Presurgery, β-cell function, weight loss, and glucagon-like peptide 1 response were all predictors of postsurgery β-cell function, although weight loss appeared to be the strongest predictor. These data show that β-cell dysfunction persists after RYGBP, even in patients in clinical diabetes remission. This impairment can be rescued by oral glucose stimulation, suggesting that RYGBP leads to an important gastrointestinal effect, critical for improved β-cell function after surgery.

Duodenal-jejunal bypass and jejunectomy improve insulin sensitivity in Goto-Kakizaki diabetic rats without changes in incretins or insulin secretion

Gastric bypass surgery can dramatically improve type 2 diabetes. It has been hypothesized that by excluding duodenum and jejunum from nutrient transit, this procedure may reduce putative signals from the proximal intestine that negatively influence insulin sensitivity (SI). To test this hypothesis, resection or bypass of different intestinal segments were performed in diabetic Goto-Kakizaki and Wistar rats. Rats were randomly assigned to five groups: duodenal-jejunal bypass (DJB), jejunal resection (jejunectomy), ileal resection (ileectomy), pair-fed sham-operated, and nonoperated controls. Oral glucose tolerance test was performed within 2 weeks after surgery. Baseline and poststimulation levels of glucose, insulin, glucagon-like peptide 1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP) were measured. Minimal model analysis was used to assess SI. SI improved after DJB (SI = 1.14 ± 0.32 × 10(-4) min(-1) ⋅ pM(-1)) and jejunectomy (SI = 0.80 ± 0.14 × 10(-4) min(-1) ⋅ pM(-1)), but not after ileectomy or sham operation/pair feeding in diabetic rats. Both DJB and jejunal resection normalized SI in diabetic rats as shown by SI levels equivalent to those of Wistar rats (SI = 1.01 ± 0.06 × 10(-4) min(-1) ⋅ pM(-1); P = NS). Glucose effectiveness did not change after operations in any group. While ileectomy increased plasma GIP levels, no changes in GIP or GLP-1 were observed after DJB and jejunectomy. These findings support the hypothesis that anatomic alterations of the proximal small bowel may reduce factors associated with negative influence on SI, therefore contributing to the control of diabetes after gastric bypass surgery.

Effects on GLP-1, PYY, and leptin by direct stimulation of terminal ileum and cecum in humans: implications for ileal transposition

BACKGROUND

We do not have a unified, scientifically tested theory of causation for obesity and its co-morbidities, nor do we have explanations for the mechanics of the metabolic/bariatric surgery procedures. Integral to proffered hypotheses are the actions of the hormones glucagon-like peptide-1 (GLP-1), peptide YY (PYY), and leptin. The objective of this study was to obtain blood levels of GLP-1, PYY, and leptin after stimulation of the terminal ileum and cecum by a static infusion of a food hydrolysate in morbidly obese patients undergoing a duodenal switch procedure.

SETTING

University Hospital.

METHODS

Plasma levels of GLP-1, PYY, and leptin were obtained at 0, 30, 60, 90, and 120 minutes after instillation of 240 mL of a food hydrolysate into the ileum or cecum.

RESULTS

The mean±SD GLP-1 values by cecal stimulation for 0, 30, 60, 90, and 120 minutes were: 41.3±23.2; 39.6±21.8; 38.9±19.1; 47.4±22.3; 51.7±27.3 pM, and by ileal stimulation: 55.0±32.8; 83.4±16.1; 78.7±23.8; 84.7±23.5; 76.4±25.6. The mean±SD PYY values by cecal stimulation were: 62.1±24.8; 91.1±32.8; 102.1±39.6; 119.6±37.5; 130.3±36.7, and by ileal stimulation: 73.8±41.6; 138.1±17.7; 149.5±23.3; 165.7±24.3; 155.5±29.1. Percent change in PYY levels increased ~150%, GLP-1 increased ~50%, and leptin decreased ~20%.

CONCLUSION

Direct stimulation of the human terminal ileum and cecum by a food hydrolysate elicits significant plasma GLP-1 and PYY elevations and leptin decreases, peaking at 90-120 minutes. The ileal GLP-1 and PYY responses exceed those of the cecum, and the PYY effect is about 3-fold that of GLP-1. The results of this study question the satiety premise for ileal transposition.

Contribution of endogenous glucagon-like peptide 1 to glucose metabolism after Roux-en-Y gastric bypass

The contribution of elevated glucagon-like peptide 1 (GLP-1) to postprandial glucose metabolism after Roux-en-Y gastric bypass (RYGB) has been the subject of uncertainty. We used exendin-9,39, a competitive antagonist of GLP-1, to examine glucose metabolism, islet hormone secretion, and gastrointestinal transit in subjects after RYGB and in matched control subjects. Subjects were studied in the presence or absence of exendin-9,39 infused at 300 pmol/kg/min. Exendin-9,39 resulted in an increase in integrated postprandial glucose concentrations post-RYGB (3.6 ± 0.5 vs. 2.0 ± 0.4 mol/6 h, P = 0.001). Exendin-9,39 decreased insulin concentrations (12.3 ± 2.2 vs. 18.1 ± 3.1 nmol/6 h, P = 0.002) and the β-cell response to glucose (Total, 13 ± 1 vs. 11 ± 1 × 10(-9) min(-1), P = 0.01) but did not alter the disposition index (DI). In control subjects, exendin-9,39 also increased glucose (2.2 ± 0.4 vs. 1.7 ± 0.3 mol/6 h, P = 0.03) without accompanying changes in insulin concentrations, resulting in an impaired DI. Post-RYGB, acceleration of stomach emptying during the first 30 min by exendin-9,39 did not alter meal appearance, and similarly, suppression of glucose production and stimulation of glucose disappearance were unaltered in RYGB subjects. These data indicate that endogenous GLP-1 has effects on glucose metabolism and on gastrointestinal motility years after RYGB. However, it remains uncertain whether this explains all of the changes after RYGB.

The sum of many parts: potential mechanisms for improvement in glucose homeostasis after bariatric surgery

Bariatric surgery has emerged as the most durably effective treatment of type 2 diabetes (DM). However, the mechanisms governing improvement in glucose homeostasis have yet to be fully elucidated. In this review we discuss the various types of surgical interventions and the multitude of factors that potentially mediate the effects on glycemia, such as altered delivery of nutrients to the distal ileum, duodenal exclusion, gut hormone changes, bile acid reabsorption, and amino acid metabolism. Accumulating evidence that some of these changes seem to be independent of weight loss questions the rationale of using body mass index as the major indication for surgery in diabetic patients. Understanding the complex mechanisms and interactions underlying improved glycemic control could lead to novel therapeutic targets and would also allow for greater individualization of therapy and optimization of surgical outcomes.

Effects of Roux-en-Y gastric bypass on energy and glucose homeostasis are preserved in two mouse models of functional glucagon-like peptide-1 deficiency

Glucagon-like peptide-1 (GLP-1) secretion is greatly enhanced after Roux-en-Y gastric bypass (RYGB). While intact GLP-1exerts its metabolic effects via the classical GLP-1 receptor (GLP-1R), proteolytic processing of circulating GLP-1 yields metabolites such as GLP-1(9-36)amide/GLP-1(28-36)amide, that exert similar effects independent of the classical GLP-1R. We investigated the hypothesis that GLP-1, acting via these metabolites or through its known receptor, is required for the beneficial effects of RYGB using two models of functional GLP-1 deficiency - α-gustducin-deficient (α-Gust (-/-)) mice, which exhibit attenuated nutrient-stimulated GLP-1 secretion, and GLP-1R-deficient mice. We show that the effect of RYGB to enhance glucose-stimulated GLP-1 secretion was greatly attenuated in α-Gust (-/-) mice. In both genetic models, RYGB reduced body weight and improved glucose homeostasis to levels observed in lean control mice. Therefore, GLP-1, acting through its classical GLP-1R or its bioactive metabolites, does not seem to be involved in the effects of RYGB on body weight and glucose homeostasis.

Glucagon-like peptide-1: glucose homeostasis and beyond

Glucagon-like peptide-1 (GLP-1), an incretin hormone secreted primarily from the intestinal L-cells in response to meals, modulates nutrient homeostasis via actions exerted in multiple tissues and cell types. GLP-1 and its analogs, as well as compounds that inhibit endogenous GLP-1 breakdown, have become an effective therapeutic strategy for many subjects with type 2 diabetes. Here we review the discovery of GLP-1; its synthesis, secretion, and elimination from the circulation; and its multiple pancreatic and extrapancreatic effects. Finally, we review current options for GLP-1-based diabetes therapy, including GLP-1 receptor agonism and inhibition of GLP-1 breakdown, as well as the benefits and drawbacks of different modes of therapy and the potential for new therapeutic avenues.

Improved acylated ghrelin suppression at 2 years in obese patients with type 2 diabetes: effects of bariatric surgery vs standard medical therapy

OBJECTIVE

Roux-en-Y gastric bypass (RYGB) produces more durable glycemic control than sleeve gastrectomy (SG) or intensive medical therapy (IMT). However, the contribution of acylated ghrelin (AG), a gluco-regulatory/appetite hormone, to improve glucose metabolism and body composition in patients with type 2 diabetes (T2D) following RYGB is unknown.

DESIGN

STAMPEDE (Surgical Treatment and Medication Potentially Eradicate Diabetes Efficiently) was a prospective, randomized controlled trial.

SUBJECTS

Fifty-three (body mass index: 36±3 kg m(-2), age: 49±9 years) poorly controlled patients with T2D (HbA1c (glycated hemoglobin): 9.7±2%) were randomized to IMT, IMT+RYGB or IMT+SG and underwent a mixed-meal tolerance test at baseline, 12, and 24 months for evaluation of AG suppression (postprandial minus fasting) and beta-cell function (oral disposition index; glucose-stimulated insulin secretion × Matsuda index). Total/android body fat (dual-energy X-ray absorptiometry) was also assessed.

RESULTS

RYGB and SG reduced body fat comparably (15-23 kg) at 12 and 24 months, whereas IMT had no effect. Beta-cell function increased 5.8-fold in RYGB and was greater than IMT at 24 months (P<0.001). However, there was no difference in insulin secretion between SG vs IMT at 24 months (P=0.32). Fasting AG was reduced fourfold following SG (P<0.01) and did not change with RYGB or IMT at 24 months. AG suppression improved more following RYGB than SG or IMT at 24 months (P=0.01 vs SG, P=0.07 vs IMT). At 24 months, AG suppression was associated with increased postprandial glucagon-like peptide-1 (r=-0.32, P<0.02) and decreased android fat (r=0.38; P<0.006).

CONCLUSIONS

Enhanced AG suppression persists for up to 2 years after RYGB, and this effect is associated with decreased android obesity and improved insulin secretion. Together, these findings suggest that AG suppression is partly responsible for the improved glucose control after RYGB surgery.

Relevance of beta-cell function for improved glycemic control after gastric bypass surgery

BACKGROUND

Residual beta-cell function and gastrointestinal hormones have been suggested as relevant determinants of improved glycemic control ensuing Roux-en-Y gastric bypass (RYGB). The objective of this study was to compare the glycemic control up to 24 months after RYGB in C-peptide negative morbidly obese (MO) type 1 diabetes mellitus (T1 DM) women (n = 7) and C-peptide positive (>.6 ng/mL) MO women with type 2 diabetes mellitus (T2 DM, n = 7) on basal-bolus insulin therapy. The glucagon-like peptide 1 (GLP-1) and glucagon response to a mixed meal challenge were also compared between groups.

METHODS

Percent excess weight loss (%EWL), HbA1c, and daily insulin dose (DID) after RYGB were compared between groups. The GLP-1 and glucagon response (area under the curve 0-120 minutes) after a mixed meal at last follow-up visit were also compared.

RESULTS

At 24-months, marked %EWL was observed in women with T1 DM and women with T2 DM (mean±standard error, 82.6% ± 11.3% and 87.4% ± 30.5%, respectively; P = .722]. In women with T1 DM, HbA1c (4 months, P<.05) and DID improved transiently (P<.05, up to 8 months) but were comparable to baseline thereafter (HbA1c: baseline, 8.3 ± 1.2 and 24 months, 8.2 ± .9, P = 1.00; DID: baseline, .61 ± .17 and 24 months .62 ± .12 IU/kg/d, P = 1.00]. In contrast, in MO women with T2 DM, HbA1c decreased significantly throughout follow-up, with 2 patients presenting diabetes remission and all but one an HbA1c<7% at 24 months. The GLP-1 response was comparable between groups (P = .612), and was not accompanied by suppression of the glucagon response to meal intake.

CONCLUSIONS

In the absence of residual beta-cell, RYGB results in no significant benefit on glycemic control, despite a marked response of GLP-1 to meal intake.

Hormonal response to a mixed-meal challenge after reversal of gastric bypass for hypoglycemia

CONTEXT

Severe hypoglycemia is a rare and challenging complication of Roux-en-Y gastric bypass (RYGB), which is characterized by hypersecretion of insulin and incretin hormones in the postprandial state.

OBJECTIVE

The objective of the study was to determine the clinical and hormonal responses to a mixed-meal challenge after the reversal of RYGB in 2 patients with post-RYGB hypoglycemia. We hypothesized that the reversal of RYGB would lead to clinical improvement in hypoglycemia through the attenuation of incretin hormone secretion. DESIGN/SETTING/SUBJECTS/OUTCOME MEASURES: Two patients with post-RYGB hypoglycemia underwent a standardized meal tolerance test prior to and 8 and 18 months after RYGB reversal, respectively, with the measurement of glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), insulin, and glucose levels. Gastric bypass was reversed by reattaching the small gastric pouch to the bypassed distal stomach and resecting the Roux limb to restore the normal flow of food bolus.

RESULTS

Both subjects showed persistent evidence of hypoglycemia with marked hyperinsulinemia after the RYGB reversal. GLP-1 levels after the RYGB reversal decreased by 76% and 70%, respectively, from their prereversal levels and to the level of nonhypoglycemic post-RYGB controls. In contrast, GIP levels after the RYGB reversal increased by 3-10 times the level before the reversal and 8-26 times that of the nonhypoglycemic post-RYGB controls.

CONCLUSIONS

Reversal of RYGB did not alleviate hyperinsulinemic hypoglycemia upon a mixed-meal challenge in our patients, thus suggesting its limited clinical benefit as treatment of post-RYGB hypoglycemia. The marked increase in GIP levels and concurrent decrease in GLP-1 levels in our patients suggest a possible role of GIP in persistent hyperinsulinemic hypoglycemia after the reversal of RYGB.