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

Improvement of Triglyceride-Glucose Index Following Bariatric Surgery: a Systematic Review and Meta-analysis

BACKGROUND

Bariatric surgery is an effective intervention for the management of severe obesity and its associated comorbidities, including metabolic abnormalities. This meta-analysis aimed to evaluate the impact of bariatric surgery on the triglyceride-glucose (TyG) index, a novel marker of insulin resistance and metabolic syndrome.

METHODS

A systematic search was conducted in Embase, PubMed, Web of Science, and Scopus. The meta-analysis was performed using Comprehensive Meta-Analysis (CMA) V4 software. The overall effect size was determined by a random-effects meta-analysis and the leave-one-out approach.

RESULTS

A total of 9 trials including 1620 individuals confirmed a significant reduction in TyG following bariatric surgery (weighted mean difference (WMD) - 0.770, 95% CI - 1.006, - 0.534, p < 0.001). In a sub-analysis according to the type of bariatric surgery there was a significant reduction in TyG index for Roux-en-Y gastric bypass (WMD - 0.775, 95% CI - 1.000, - 0.550, p < 0.001), and sleeve gastrectomy (WMD - 0.920, 95% CI - 1.368, - 0.473, p < 0.001). In a sub-analysis according to the follow-up duration there was similarly a significant reduction in TyG index for both < 12 months (WMD - 1.645, 95% CI - 2.123, - 1.167, p < 0.001), and ≥ 12 months follow-up (WMD - 0.954, 95% CI - 1.606, - 0.303, p < 0.001).

CONCLUSION

The results of this meta-analysis demonstrated a significant reduction in the TyG index following bariatric surgery, indicating improved insulin sensitivity and metabolic health. These findings highlight the potential of bariatric surgery as a valuable therapeutic option for individuals with obesity and its metabolic consequences.

The role of weight control in the management of type 2 diabetes mellitus: Bariatric surgery

Diabetes mellitus is one of the major epidemics in the United States. It is heavily associated with obesity and multiple metabolic derangements that lead to long term morbidity, mortality as well as financial burden. Although medical therapy has been the mainstay in the management of diabetes mellitus, there remains a large portion of this patient population which struggles to obtain adequate glycemic control and long-term weight control with medical management alone. Bariatric surgery is a powerful tool in combating diabetes mellitus and affects glucose homeostasis through a variety of pathways. While it does provide a durable pathway for weight loss, improvement in glucose homeostasis is not only affected by the weight loss seen after bariatric surgery. Changes in gut hormone secretion, insulin regulation, and gut microbial composition also affect how these operations improve glucose homeostasis. Through improvement in the management of diabetes mellitus, comorbidities including cardiovascular disease, in turn demonstrate improvement. In this article, we will discuss the role of bariatric (metabolic) surgery as it relates to long term weight loss and the impact that weight loss has on improvement in diabetes mellitus.

Effects of bariatric surgery and dietary intervention on insulin resistance and appetite hormones over a 3 year period

To examine an impact of three types of bariatric surgery compared with dietary intervention (DIET), on concurrent changes in Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) and appetite hormones over 3 years. Fifty-five adults were studied during phase of weight loss (0-12 months) and during weight stability (12-36 months) post intervention. Measurements of HOMA-IR, fasting and postprandial PYY and GLP1, adiponectin, CRP, RBP4, FGF21 hormones and dual-Xray absorptiometry were performed throughout the study. All surgical groups achieved significant reductions in HOMA-IR with greatest difference between Roux-en-Y gastric bypass and DIET (- 3.7; 95% CI - 5.4, - 2.1; p = 0.001) at 12-36 months. Initial (0-12 months) HOMA-IR values were no different to DIET after adjustment for the lost weight. During 12-36 months, after controlling for treatment procedure and weight, for every twofold increase in postprandial PYY and adiponectin, HOMA-IR decreased by 0.91 (95% CI - 1.71, - 0.11; p = 0.030) and by 0.59 (95% CI - 1.10, - 0.10; p = 0.023) respectively. Initial, non-sustained changes in RBP4 and FGF21 were not associated with HOMA-IR values. While initial rapid weight loss reduces insulin resistance, the enhanced secretions of PYY and adiponectin may contribute to weight-independent improvements in HOMA-IR during weight stability.Clinical trial registration: Australian New Zealand Clinical Trials Registry (ANZCTR): ACTRN12613000188730.

Roux-en-Y gastric bypass alters intestinal glucose transport in the obese Zucker rat

INTRODUCTION

The gastrointestinal tract plays a major role in regulating glucose homeostasis and gut endocrine function. The current study examines the effects of Roux-en-Y gastric bypass (RYGB) on intestinal GLP-1, glucose transporter expression and function in the obese Zucker rat (ZR).

METHODS

Two groups of ZRs were studied: RYGB and sham surgery pair-fed (PF) fed rats. Body weight and food intake were measured daily. On post-operative day (POD) 21, an oral glucose test (OGT) was performed, basal and 30-minute plasma, portal venous glucose and glucagon-like peptide-1 (GLP-1) levels were measured. In separate ZRs, the biliopancreatic, Roux limb (Roux) and common channel (CC) intestinal segments were harvested on POD 21.

RESULTS

Body weight was decreased in the RYGB group. Basal and 30-minute OGT plasma and portal glucose levels were decreased after RYGB. Basal plasma GLP-1 levels were similar, while a 4.5-fold increase in GLP-1 level was observed in 30-minute after RYGB (vs. PF). The increase in basal and 30-minute portal venous GLP-1 levels after RYGB were accompanied by increased mRNA expressions of proglucagon and PC 1/3, GPR119 protein in the Roux and CC segments. mRNA and protein levels of FFAR2/3 were increased in Roux segment. RYGB decreased brush border glucose transport, transporter proteins (SGLT1 and GLUT2) and mRNA levels of Tas1R1/Tas1R3 and α-gustducin in the Roux and CC segments.

CONCLUSIONS

Reductions in intestinal glucose transport and enhanced post-prandial GLP-1 release were associated with increases in GRP119 and FFAR2/3 after RYGB in the ZR model. Post-RYGB reductions in the regulation of intestinal glucose transport and L cell receptors regulating GLP-1 secretion represent potential mechanisms for improved glycemic control.

The role of GLP-1 in postprandial glucose metabolism after bariatric surgery: a narrative review of human GLP-1 receptor antagonist studies

The Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) bariatric procedures lead to remission or improvement of type 2 diabetes. A weight loss-independent augmentation of postprandial insulin secretion contributes to the improvement in glycemic control after RYGB and is associated with a ∼10-fold increase in plasma concentrations of the incretin hormone glucagon-like peptide-1 (GLP-1). However, the physiologic importance of the markedly increased postprandial GLP-1 secretion after RYGB has been much debated. The effect of GLP-1 receptor blockade after RYGB has been investigated in 12 studies. The studies indicate a shift toward a more prominent role for GLP-1 in postprandial β-cell function after RYGB. The effect of GLP-1 receptor antagonism on glucose tolerance after RYGB is more complex and is associated with important methodological challenges. The postprandial GLP-1 response is less enhanced after SG compared with RYGB. However, the effect of GLP-1 receptor blockade after SG has been examined in 1 study only and needs further investigation.

Oral Processing, Satiation and Obesity: Overview and Hypotheses

Increasing the speed of eating or decreasing the amount of chewing of a test meal significantly decreases its satiation, increases concomitant caloric intake, and influences entero-endocrine secretion. Speed of eating is a strong risk factor for obesity and longitudinal studies suggest an etiological relationship. Individuals with obesity have an increase in bite size, less chewing per bite, decreased satiation, and greater food intake. Oral processing in terms of bite size and amount of chewing per gram of food is influenced by food texture and textural complexity. Soft foods increase bite size and decrease chewing per gram of food and meal duration compared to hard foods. An ultra-processed diet can lead to greater weight gain than a non-processed diet and a significant increase in eating rate. Many children with obesity are noted by their parents to have persistent hunger on a questionnaire and this is often extreme. Results of attempts to change eating behavior have been mixed in terms of producing long-term changes in eating behavior and body weight. It is hypothesized that there may be a unidirectional relationship between changes in oral processing, satiation and weight gain. However, the presence of persistent hunger can produce a vicious cycle that may exacerbate obesity and make treatment difficult. The increased energy density of foods as found particularly in ultra-processed foods also influences energy intake and obesity.

Leveraging the Gut to Treat Metabolic Disease

25 years ago, the future of treating obesity and diabetes focused on end organs known to be involved in energy balance and glucose regulation, including the brain, muscle, adipose tissue, and pancreas. Today, the most effective therapies are focused around the gut. This includes surgical options, such as vertical sleeve gastrectomy and Roux-en-Y gastric bypass, that can produce sustained weight loss and diabetes remission but also extends to pharmacological treatments that simulate or amplify various signals that come from the gut. The purpose of this Review is to discuss the wealth of approaches currently under development that seek to further leverage the gut as a source of novel therapeutic opportunities with the hope that we can achieve the effects of surgical interventions with less invasive and more scalable solutions.

The importance of the biliopancreatic limb length in gastric bypass: A systematic review

BACKGROUND

Bariatric surgery has proven to be the most durable treatment for obesity, and it also provides improvement of obesity's associated co-morbidities. Although several mechanisms for its metabolic effects have been studied, the implications of the surgically constructed anatomy on its functioning physiology have not been elucidated. This leaves some uncertainty regarding the recommended limb lengths in Roux-en-Y gastric bypass. The alimentary limb length and function has been studied extensively, but few have studied the influences of the biliopancreatic limb length.

OBJECTIVE

To present a systematic review of the literature comparing variations in length of BP limb and results in order to determine BP limb length influence.

SETTING

Academic Hospital, United States.

METHODS

We present a systematic review of all the articles comparing variations of the biliopancreatic limb length and their results.

RESULTS

Thirteen articles were identified and analyzed. Most of the articles are prospective studies. Weight loss was superior in longer limbs.

CONCLUSION

Based on our review of the subject, we can conclude that the release of enterohormones in response to a food load in the distal small bowel seems to play an important role in the remission of co-morbidities. Hence, the length of the biliopancreatic limb might affect this process.

A paradigm shift for the prevention and treatment of individual and global obesity

The prevalence of obesity and overweight has plateaued in developed countries, although at high levels, but in most parts of the world, it continues to increase. Current recommendations for preventing and treating obesity are based mainly on the notion that overeating results from hedonic eating as a result of unlimited access to palatable foods, particularly those high in sugar and fat, and that hedonic centers are able to "override" the body's homeostatic mechanisms. This article proposes that the homeostatic mechanisms affecting appetite and satiety are more important in chronic overeating, and that sufficient evidence exists for adopting a new paradigm for controlling individual and global obesity based on controlling energy homeostasis via the enteroendocrine and gut microbiota systems. Many obese children and adolescents have chronic hunger, supporting the notion that they have a homeostatic rather than hedonic abnormality. The effectiveness of weight loss drugs and bariatric surgery suggests that the brain centers controlling energy homeostasis are able to override centers controlling hedonic drives. Energy homeostasis can also be influenced by nutrition, in particular, by avoiding sweetened drinks and consuming whole grains, vegetables, fruits and other foods that are high in dietary fiber, and thereby influence appetite and satiety. New recommendations are outlined for preventing and treating individual and global obesity based on a paradigm that targets appetite and satiety.

Glucose kinetics: an update and novel insights into its regulation by glucagon and GLP-1

PURPOSE OF REVIEW

Glucagon and GLP-1 share the same origin (i.e., proglucagon); primarily GLP-1 is generated from intestinal L-cells and glucagon from pancreatic α-cell, but intestinal glucagon and pancreatic GLP-1 secretion is likely. Glucose kinetics are tightly regulated by pancreatic hormones insulin and glucagon, but other hormones, including glucagon-like peptide-1 (GLP-1), also play an important role. The purpose of this review is to describe the recent findings on the mechanisms by which these two hormones regulate glucose kinetics.

RECENT FINDINGS

Recent findings showed new important mechanisms of action of glucagon and GLP-1 in the regulation of glucose metabolism. Knock out of glucagon receptors protects against hyperglycemia without causing hypoglycemia. GLP-1 not only stimulates insulin secretion, but it has also an independent effect on the liver and inhibits glucose production. Moreover, when coinfused with glucagon, GLP-1 limits the hyperglycemic effects. Both hormones have also central effects on gastric emptying (delayed), intestinal motility (reduced), and satiety (increased).

SUMMARY

The implications of these findings are very important for the management of type 2 diabetes given that GLP-1 receptor agonist are currently approved for the treatment of hyperglycemia and glucagon receptor antagonists and GLP-1/glucagon dual agonists are under development.

Enteroendocrine-derived glucagon-like peptide-2 controls intestinal amino acid transport

Objective

Glucagon-like peptide-2 (GLP-2) is co-secreted with GLP-1 from gut endocrine cells, and both peptides act as growth factors to expand the surface area of the mucosal epithelium. Notably, GLP-2 also enhances glucose and lipid transport in enterocytes; however, its actions on control of amino acid (AA) transport remain unclear. Here we examined the mechanisms linking gain and loss of GLP-2 receptor (GLP-2R) signaling to control of intestinal amino acid absorption in mice.

Methods

Absorption, transport, and clearance of essential AAs, specifically lysine, were measured in vivo by Liquid Chromatography triple quadrupole Mass Spectrometry (LC-MS/MS) and ex vivo with Ussing chambers using intestinal preparations from Glp2r^+/+ and Glp2r^−/− mice. Immunoblotting determined jejunal levels of protein components of signaling pathways (PI3K-AKT, and mTORC1-pS6-p4E-BP1) following administration of GLP-2, protein gavage, and rapamycin to fasted Glp2r^+/+ and Glp2r^−/− mice. Expression of AA transporters from full thickness jejunum and 4F2hc from brush border membrane vesicles (BBMVs) was measured by real-time PCR and immunoblotting, respectively.

Results

Acute administration of GLP-2 increased basal AA absorption in vivo and augmented basal lysine transport ex vivo. GLP-2-stimulated lysine transport was attenuated by co-incubation with wortmannin, rapamycin, or tetrodotoxin ex vivo. Phosphorylation of mTORC1 effector proteins S6 and 4E-BP1 was significantly increased in wild-type mice in response to GLP-2 alone, or when co-administered with protein gavage, and abolished following oral gavage of rapamycin. In contrast, activation of GLP-1R signaling did not enhance S6 phosphorylation. Disruption of GLP-2 action in Glp2r^−/− mice reduced lysine transport ex vivo and attenuated the phosphorylation of S6 and 4E-BP1 in response to oral protein. Moreover, the expression of cationic AA transporter slc7a9 in response to refeeding, and the abundance of 4F2hc in BBMVs following protein gavage, was significantly attenuated in Glp2r^−/− mice.

Conclusions

These findings reveal an important role for GLP-2R signaling in the physiological and pharmacological control of enteral amino acid sensing and assimilation, defining an enteroendocrine cell-enterocyte axis for optimal energy absorption.

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GLP-2 promotes intestinal amino acid absorption in vivo.

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Intestinal amino acid absorption is reduced in Glp2r^−/− mice.

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GLP-2 stimulates amino acid transport independently of blood flow.

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GLP-2, but not GLP-1, activates the mTORC1 signaling pathway.

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Amino acid transport by GLP-2 requires the enteric nervous system and mTORC1.

A resting-state fMRI study of obese females between pre- and postprandial states before and after bariatric surgery

Past studies utilizing resting-state functional MRI (rsfMRI), have shown that obese humans exhibit altered activity in brain areas related to reward compared to normal-weight controls. However, to what extent bariatric surgery-induced weight loss alters resting-state brain activity in obese humans is less well-studied. Thus, we measured the fractional amplitude of low-frequency fluctuations from eyes-closed, rsfMRI in obese females (n = 11, mean age = 42 years, mean BMI = 41 kg/m² ) in both a pre- and postprandial state at two time points: four weeks before, and four weeks after bariatric surgery. Several brain areas showed altered resting-state activity following bariatric surgery, including the putamen, insula, cingulate, thalamus and frontal regions. Activity augmented by surgery was also dependent on prandial state. For example, in the fasted state, activity in the middle frontal and pre- and postcentral gyri was found to be decreased after surgery. In the sated state, activity within the insula was increased before, but not after surgery. Collectively, our results suggest that resting-state neural functions are rapidly affected following bariatric surgery and the associated weight loss and change in diet.