The influence of nutrients, biliary-pancreatic secretions, and systemic trophic hormones on intestinal adaptation in a Roux-en-Y bypass model

The effect of bariatric surgery on the expression of gastrointestinal taste receptors: A systematic review

Gastrointestinal nutrient sensing via taste receptors may contribute to weight loss, metabolic improvements, and a reduced preference for sweet and fatty foods following bariatric surgery. This review aimed to investigate the effect of bariatric surgery on the expression of oral and post-oral gastrointestinal taste receptors and associations between taste receptor alterations and clinical outcomes of bariatric surgery. A systematic review was conducted to capture data from both human and animal studies on changes in the expression of taste receptors in oral or post-oral gastrointestinal tissue following any type of bariatric surgery. Databases searched included Medline, Embase, Emcare, APA PsychInfo, Cochrane Library, and CINAHL. Two human and 21 animal studies were included. Bariatric surgery alters the quantity of many sweet, umami, and fatty acid taste receptors in the gastrointestinal tract. Changes to the expression of sweet and amino acid receptors occur most often in intestinal segments surgically repositioned more proximally, such as the alimentary limb after gastric bypass. Conversely, changes to fatty acid receptors were observed more frequently in the colon than in the small intestine. Significant heterogeneity in the methodology of included studies limited conclusions regarding the direction of change in taste receptor expression induced by bariatric surgeries. Few studies have investigated associations between taste receptor expression and clinical outcomes of bariatric surgery. As such, future studies should look to investigate the relationship between bariatric surgery-induced changes to gut taste receptor expression and function and the impact of surgery on taste preferences, food palatability, and eating behaviour.Registration code in PROSPERO: CRD42022313992.

Physical properties of food or bile redirection do not contribute to the intestinal adaptations after Roux-en-Y Gastric Bypass in rats

Objective

Metabolic and morphological adaptations of the intestine have been suggested to play a role in the various therapeutic benefits of Roux-en-Y Gastric Bypass (RYGB) surgery. However, the precise underlying mechanisms remain unclear. In this study, the effects of physical properties of ingested food and redirection of biliopancreatic secretions on intestinal remodeling were investigated in RYGB operated rats.

Methods

RYGB employing two different Roux Limb (RL) lengths was performed on high fat diet induced obese rats. Post-operatively, rats were fed either Solid or isocaloric Liquid diets. Metabolic and morphological remodeling of intestine was compared across both diet forms (Solid and Liquid diets) and surgical models (Short RL and Long RL).

Results

RYGB surgery in rats induced weight loss and improved glucose tolerance which was independent of physical properties of ingested food and biliopancreatic secretions. Intestinal glucose utilization after RYGB was not determined by either food form or biliopancreatic secretions. The GLUT-1 expression in RL was not influenced by physical properties of food. Furthermore, both physical properties of food and biliopancreatic secretions showed no effects on intestinal morphological adaptations after RYGB.

Conclusion

Results of this study demonstrate that physical properties of food and bile redirection are not major determinants of intestinal remodeling after RYGB in rats.

Effect of duodenal-jejunal bypass on diabetes in the early postoperative period

Metabolic surgery is an effective treatment for patients with type 2 diabetes mellitus (T2DM). The aim of this study was to investigate the effect of duodenal-jejunal bypass (DJB) in a rat model of T2DM during the early postoperative period. A rat model of non-obese T2DM was allocated to two groups: a sham group and a DJB group. On postoperative day 1 (1POD), oral glucose tolerance testing (OGTT) was performed and the changes of glucose transporter expressions in the small intestine was evaluated. [18F]-fluorodeoxyglucose ([18]-FDG) uptake was measured in sham- and DJB-operated rats using positron emission tomography-computed tomography (PET-CT). DJB improved the glucose tolerance of the rats on 1POD. The expression of sodium-glucose cotransporter 1 (SGLT1) and glucose transporter 1 (GLUT1) was high, and that of GLUT2 was low in the alimentary limb (AL) of rats in the DJB group. PET-CT showed that [18F]-FDG uptake was high in the proximal jejunum of DJB-operated rats. These results may show that DJB improve glucose tolerance in very early postoperative period as the result of glucose accumulation in the AL because of changes in glucose transporter expression.

Regulation of body weight: Lessons learned from bariatric surgery

BACKGROUND

Bariatric or weight loss surgery is currently the most effective treatment for obesity and metabolic disease. Unlike dieting and pharmacology, its beneficial effects are sustained over decades in most patients, and mortality is among the lowest for major surgery. Because there are not nearly enough surgeons to implement bariatric surgery on a global scale, intensive research efforts have begun to identify its mechanisms of action on a molecular level in order to replace surgery with targeted behavioral or pharmacological treatments. To date, however, there is no consensus as to the critical mechanisms involved.

SCOPE OF REVIEW

The purpose of this non-systematic review is to evaluate the existing evidence for specific molecular and inter-organ signaling pathways that play major roles in bariatric surgery-induced weight loss and metabolic benefits, with a focus on Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG), in both humans and rodents.

MAJOR CONCLUSIONS

Gut-brain communication and its brain targets of food intake control and energy balance regulation are complex and redundant. Although the relatively young science of bariatric surgery has generated a number of hypotheses, no clear and unique mechanism has yet emerged. It seems increasingly likely that the broad physiological and behavioral effects produced by bariatric surgery do not involve a single mechanism, but rather multiple signaling pathways. Besides a need to improve and better validate surgeries in animals, advanced techniques, including inducible, tissue-specific knockout models, and the use of humanized physiological traits will be necessary. State-of-the-art genetically-guided neural identification techniques should be used to more selectively manipulate function-specific pathways.

Measures of glucose homeostasis during and after duodenal exclusion using a duodenal-jejunal bypass liner in a normoglycemic, nonobese canine model

BACKGROUND

Discovering the role duodenal exclusion plays in weight loss and resolution of type 2 diabetes (T2D) may help refine the surgical and nonsurgical treatment of obesity and T2D.

OBJECTIVES

To assess changes in glucose homeostasis due to duodenal exclusion using a duodenal-jejunal bypass liner (DJBL) in a nonobese canine model.

SETTING

Academic laboratory setting.

METHODS

An intravenous glucose tolerance test (IVGTT), and a mixed-meal tolerance test (MMTT) at baseline, 1, and 6 weeks post DJBL implantation (I1 and I6, respectively), and 1 and 6 weeks post DJBL removal (R1 and R6, respectively) were done in canines (n = 7) fed a normal chow diet.

RESULTS

Placement of the DJBL induced weight loss that was maintained until 4 weeks post removal (R4), despite normal food intake. Total bile acids (TBA) and glucagon-like peptide-1 (GLP-1) during the MMTT were significantly increased at I1 and were associated with increased lactate and free fatty acids. Hypoglycemia counter-regulation was blunted during the IVGTT at I1 and I6, returning to baseline at R1. While there were no changes to insulin sensitivity during the experiment, glucose tolerance was significantly increased following the removal of the DJBL at R1.

CONCLUSION

These data show that in a normoglycemic, nonobese canine model, duodenal exclusion induces energy intake-independent weight loss and negative metabolic effects that are reversed following re-exposure of the small intestine to nutrients.

Dietary Alpha-Ketoglutarate Partially Abolishes Adverse Changes in the Small Intestine after Gastric Bypass Surgery in a Rat Model

Alpha-ketoglutarate (AKG) is one of the key metabolites that play a crucial role in cellular energy metabolism. Bariatric surgery is a life-saving procedure, but it carries many gastrointestinal side effects. The present study investigated the beneficial effects of dietary AKG on the structure, integrity, and absorption surface of the small intestine after bariatric surgery. Male 7-week-old Sprague Dowley rats underwent gastric bypass surgery, after which they received AKG, 0.2 g/kg body weight/day, administered in drinking water for 6 weeks. Changes in small intestinal morphology, including histomorphometric parameters of enteric plexuses, immunolocalization of claudin 3, MarvelD3, occludin and zonula ocludens 1 in the intestinal mucosa, and selected hormones, were evaluated. Proliferation, mucosal and submucosal thickness, number of intestinal villi and Paneth cells, and depth of crypts were increased; however, crypt activity, the absorption surface, the expression of claudin 3, MarvelD3, occludin and zonula ocludens 1 in the intestinal epithelium were decreased after gastric bypass surgery. Alpha-ketoglutarate supplementation partially improved intestinal structural parameters and epithelial integrity in rats undergoing this surgical procedure. Dietary AKG can abolish adverse functional changes in the intestinal mucosa, enteric nervous system, hormonal response, and maintenance of the intestinal barrier that occurred after gastric bypass surgery.

Serum glucose excretion after Roux-en-Y gastric bypass: a potential target for diabetes treatment

OBJECTIVE

The mechanisms underlying type 2 diabetes resolution after Roux-en-Y gastric bypass (RYGB) are unclear. We suspected that glucose excretion may occur in the small bowel based on observations in humans. The aim of this study was to evaluate the mechanisms underlying serum glucose excretion in the small intestine and its contribution to glucose homeostasis after bariatric surgery.

DESIGN

2-Deoxy-2-[¹⁸F]-fluoro-D-glucose (FDG) was measured in RYGB-operated or sham-operated obese diabetic rats. Altered glucose metabolism was targeted and RNA sequencing was performed in areas of high or low FDG uptake in the ileum or common limb. Intestinal glucose metabolism and excretion were confirmed using ¹⁴C-glucose and FDG. Increased glucose metabolism was evaluated in IEC-18 cells and mouse intestinal organoids. Obese or ob/ob mice were treated with amphiregulin (AREG) to correlate intestinal glycolysis changes with changes in serum glucose homeostasis.

RESULTS

The AREG/EGFR/mTOR/AKT/GLUT1 signal transduction pathway was activated in areas of increased glycolysis and intestinal glucose excretion in RYGB-operated rats. Intraluminal GLUT1 inhibitor administration offset improved glucose homeostasis in RYGB-operated rats. AREG-induced signal transduction pathway was confirmed using IEC-18 cells and mouse organoids, resulting in a greater capacity for glucose uptake via GLUT1 overexpression and sequestration in apical and basolateral membranes. Systemic and local AREG administration increased GLUT1 expression and small intestinal membrane translocation and prevented hyperglycaemic exacerbation.

CONCLUSION

Bariatric surgery or AREG administration induces apical and basolateral membrane GLUT1 expression in the small intestinal enterocytes, resulting in increased serum glucose excretion in the gut lumen. Our findings suggest a novel, potentially targetable glucose homeostatic mechanism in the small intestine.

Progress in treatment of type 2 diabetes by bariatric surgery

The incidence of type 2 diabetes (T2D) is increasing at an alarming rate worldwide. Bariatric surgical procedures, such as the vertical sleeve gastrectomy and Roux-en-Y gastric bypass, are the most efficient approaches to obtain substantial and durable remission of T2D. The benefits of bariatric surgery are realized through the consequent increased satiety and alterations in gastrointestinal hormones, bile acids, and the intestinal microbiota. A comprehensive understanding of the mechanisms by which various bariatric surgical procedures exert their benefits on T2D could contribute to the design of better non-surgical treatments for T2D. In this review, we describe the classification and evolution of bariatric surgery and explore the multiple mechanisms underlying the effect of bariatric surgery on insulin resistance. Based upon our summarization of the current knowledge on the underlying mechanisms, we speculate that the gut might act as a new target for improving T2D. Our ultimate goal with this review is to provide a better understanding of T2D pathophysiology in order to support development of T2D treatments that are less invasive and more scalable.

Adaptations in gastrointestinal physiology after sleeve gastrectomy and Roux-en-Y gastric bypass

Linked to the growing obesity epidemic, demand for bariatric and metabolic surgery has increased, the most common procedures being sleeve gastrectomy and Roux-en-Y gastric bypass. Originally, bariatric procedures were described as purely restrictive, malabsorptive, or combined restrictive-malabsorptive procedures limiting food intake, nutrient absorption, or both. Nowadays, anatomical alterations are known to affect gastrointestinal physiology, which in turn affects the digestion and absorption of nutrients and drugs. Therefore, understanding gastrointestinal physiology is crucial to prevent postoperative nutritional deficiencies and to optimise postoperative drug therapy. Preclinical and clinical research indicates that sleeve gastrectomy accelerates liquid and solid gastric emptying and small intestinal transit, and increases bile acid serum levels, whereas its effects on gastrointestinal acidity, gastric and pancreatic secretions, surface area, and colonic transit remain largely unknown. Roux-en-Y gastric bypass diminishes gastric acid secretion, accelerates liquid gastric emptying, and increases bile acid serum levels, but its effects on intestinal pH, solid gastric emptying, intestinal transit time, gastric enzyme secretions, and surface area remain largely unknown. In this Review, we summarise current knowledge of the effects of these two procedures on gastrointestinal physiology and assess the knowledge gaps.

Alterations in Small Intestine and Liver Morphology, Immunolocalization of Leptin, Ghrelin and Nesfatin-1 as Well as Immunoexpression of Tight Junction Proteins in Intestinal Mucosa after Gastrectomy in Rat Model

The stomach is responsible for the processing of nutrients as well as for the secretion of various hormones which are involved in many activities throughout the gastrointestinal tract. Experimental adult male Wistar rats (n = 6) underwent a modified gastrectomy, while control rats (n = 6) were sham-operated. After six weeks, changes in small intestine (including histomorphometrical parameters of the enteric nervous plexuses) and liver morphology, immunolocalization of leptin, ghrelin and nesfatin-1 as well as proteins forming adherens and tight junctions (E-cadherin, zonula occludens-1, occludin, marvelD3) in intestinal mucosa were evaluated. A number of effects on small intestine morphology, enteric nervous system ganglia, hormones and proteins expression were found, showing intestinal enteroplasticity and neuroplasticity associated with changes in gastrointestinal tract condition. The functional changes in intestinal mucosa and the enteric nervous system could be responsible for the altered intestinal barrier and hormonal responses following gastrectomy. The results suggest that more complicated regulatory mechanisms than that of compensatory mucosal hypertrophy alone are involved.

Pharmacokinetics of oral levonorgestrel and ethinylestradiol in women after Roux-en-Y gastric bypass surgery

BACKGROUND

Most patients undergoing Roux-en-Y gastric bypass (RYGB) are women in reproductive age. It is not known if bariatric surgery affects the pharmacokinetics of oral contraceptives.

OBJECTIVES

The primary objective was to evaluate ethinylestradiol (EE) and levonorgestrel (LNG) absorption in women undergoing RYGB, compared with nonoperated controls matched by age and body mass index (BMI). A secondary objective was to assess whether the time since surgery and BMI in the postoperative period influenced the absorption parameters.

SETTING

University hospital, Brazil.

METHODS

This study was designed to compare the maximum plasma concentration (C_max), the time to the peak plasma level (T_max), the area under the curve (AUC_0-8 and AUC_0-∞) after a single dose of a combined oral contraceptive with 0.03 mg EE and 0.15 mg LNG among 20 women after RYGB and 20 controls. Blood samples were obtained for 8 hours.

RESULTS

The mean LNG AUC_0-8 and LNG AUC_0-∞ were higher in RYGB group (P = .048 and P = .004, respectively). We found a positive correlation for LNG AUC_0-8 (P = .045) and AUC_0-∞ (P = .004) and the time since surgery, and we found a negative correlation for LNG C_max (P = .018), AUC_0-8 (P = .003), and AUC_0-∞ (P = .001) and BMI.

CONCLUSION

No significant differences were found in oral EE pharmacokinetics. The operated group showed higher mean LNG AUC_0-8 and AUC_0-∞ but it was not considered clinically significant. The present study suggests that RYGB may not affect EE and LNG absorption.

Modifications of IGF2 and EGFR plasma protein concentrations in NAFLD patients after bariatric surgery

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is strictly associated with the epidemic of obesity and is becoming the most prevalent liver disease worldwide. In severe obesity, bariatric surgery (BS) is the most effective treatment not only for obesity but also for the associated metabolic co-morbidities, NAFLD, among others. To date, noninvasive diagnostic/prognostic methods cannot evaluate hepatic improvements following surgery.

OBJECTIVES

We aimed to measure plasma level of insulin-growth factor-2 protein (IGF2) and epithermal growth factor receptor (EGFR), and to assess their relationship with clinical and biochemical parameters during the 12 months follow-up.

METHODS

Demographic, clinical-biochemical data, and plasma IGF2 and EGFR were measured in 69 patients preoperatively (T0) and 6 and 12 months (T6M and T12M, respectively) after BS. Liver biopsy was performed at T0. Relationships between IGF2, EGFR, and several biochemical parameters were performed using Pearson or Spearman correlation analysis.

RESULTS

IGF2 plasma level increases during follow-up, passing from 2.5 (1.8-15.5) at baseline to 13.3 (8.6-19.1) at T12M, p < 0.001. Conversely, EGFR showed a not significant reduction. At T12M, the plasma level of both markers was comparable to those of lean subjects. The clinical-biochemical parameters (BMI, glycated hemoglobin, HOMA-IR) also return to the normal range at T12M. Correlation analysis demonstrated that IGF2 was significantly associated with total bilirubin, direct bilirubin, and albumin at T0 while with blood glucose, ALT, GGT, and AST/ALT ratio at T6M and T12M.

CONCLUSIONS

IGF2 plasma levels increase after bariatric surgery, and these changes are associated with the modification of hepatic biochemical parameters, even if other clinic or metabolic improvements cannot be excluded.

Intestinal plasticity in response to nutrition and gastrointestinal surgery

The plasticity of a material corresponds to its capacity to change its feature under the effect of an external action. Intestinal plasticity could be defined as the ability of the intestine to modify its size or thickness and intestinal cells to modulate their absorption and secretion functions in response to external or internal cues/signals. This review will focus on intestinal adaptation mechanisms in response to diet and nutritional status. These physiological mechanisms allow a fine and rapid adaptation of the gut to promote absorption of ingested food, but they can also lead to obesity in response to overnutrition. This plasticity could thus become a therapeutic target to treat not only undernutrition but also obesity. How the intestine adapts in response to 2 types of surgical remodeling of the digestive tract-extensive bowel resection leading to intestinal failure and surgical treatment of pathological obesity (ie, bariatric surgeries)-will also be reviewed.

Effect of different bariatric surgeries on dietary protein bioavailability in rats

Bariatric surgery may induce protein malabsorption, although data are scarce. This study aims at evaluating dietary protein bioavailability after different bariatric surgeries in rats. Diet-induced obese Wistar rats were operated for vertical sleeve gastrectomy (VSG) or Roux-en-Y gastric bypass (RYGB). The control group was composed of pair-fed, sham-operated rats (Sham). Two weeks after surgery, rats were fed a ¹⁵N protein meal. Protein bioavailability was assessed by determination of ¹⁵N recovery in the gastrointestinal tract and organs 6 h after the meal. Fractional protein synthesis rate (FSR) was assessed using a flooding dose of ¹³C valine. Weight loss was the highest in RYGB rats and the lowest in Sham rats. Surprisingly, RYGB (95.6 ± 0.7%) improved protein digestibility (P = 0.045) compared with Sham (93.5 ± 0.5%) and VSG (93.8 ± 0.6%). In contrast, ¹⁵N retained in the liver (P = 0.001) and plasma protein (P = 0.037) was lower than in Sham, with a similar trend in muscle (P = 0.052). FSR was little altered by bariatric surgery, except for a decrease in the kidney of RYGB (P = 0.02). The ¹⁵N distribution along the small intestinal tissue suggests that dietary nitrogen was considerably retained in the remodeled mucosa of RYGB compared with Sham. This study revealed that in contrast to VSG, RYGB slightly improved protein digestibility but altered peripheral protein bioavailability. This effect may be ascribed to a higher uptake of dietary amino acids by the remodeled intestine.NEW & NOTEWORTHY Using a sensitive ¹⁵N meal test, we found that gastric bypass slightly improved protein digestibility compared with sleeve gastrectomy or control but, in contrast, lowered protein retention in the liver and muscles. This paradox can be due to a higher uptake of dietary nitrogen by the intestinal mucosa that was hypertrophied. This study provides new insight on the digestive and metabolic fate of dietary protein in different models of bariatric surgery in rats.

The Impacts of Gastroileostomy Rat Model on Glucagon-like Peptide-1: a Promising Model to Control Type 2 Diabetes Mellitus

BACKGROUND

One of the new current treatment options for Diabetes Mellitus is about increasing glucagon-like peptide-1 (GLP-1) activity. GLP-1 with its incretin effect showed major role in glucose homeostasis. Gastroileostomy can increase GLP-1 secretion by rapid delivery of undigested food to the terminal ileum. We studied the early effects of a gastroileostomy on serum levels of GLP-1, glucose, and insulin in rats.

METHODS

Gastroileostomies with side-to-side anastomosis were performed on 15 male New Zealand rats. Blood samples were obtained before and 1 week after the gastroileostomy.

RESULTS

Our results showed that the rats lost a lot of weight from start (330 ± 15 g) to the end (240 ± 25 g) of the experiment (p = 0.048). The data analysis showed that the gastroileostomy surgery elevates the level of GLP-1in plasma significantly (89.1852 vs. 177.440 respectively; p < 0.001) and caused a significant decrease in plasma glucose as well (92.00 and 66.29 mg/dL respectively; p < 0.001). However, the insulin state elevated after the surgery significantly (8.03 vs. 9.89; p < 0.001).

CONCLUSION

In this study, we showed the effectiveness of gastroileostomy treatment to decrease body weight and plasma glucose with increased GLP-1 in rats. This small rat model suggests the potential of this surgery to treat type 2 diabetes mellitus.

Combined loss of GLP-1R and Y2R does not alter progression of high-fat diet-induced obesity or response to RYGB surgery in mice

OBJECTIVE

Understanding the mechanisms underlying the remarkable beneficial effects of gastric bypass surgery is important for the development of non-surgical therapies or less invasive surgeries in the fight against obesity and metabolic disease. Although the intestinal L-cell hormones glucagon-like peptide-1 (GLP-1) and peptide tyrosine-tyrosine (PYY) have attracted the most attention, direct tests in humans and rodents with pharmacological blockade or genetic deletion of either the GLP1-receptor (GLP1R) or the Y2-receptor (Y2R) were unable to confirm their critical roles in the beneficial effects gastric bypass surgery on body weight and glucose homeostasis. However, new awareness of the power of combinatorial therapies in the treatment of metabolic disease would suggest that combined blockade of more than one signaling pathway may be necessary to reverse the beneficial effects of bariatric surgery.

METHODS

The metabolic effects of high-fat diet and the ability of Roux-en-Y gastric bypass surgery to lower food intake and body weight, as well as improve glucose handling, was tested in GLP1R and Y2R-double knockout (GLP1RKO/Y2RKO) and C57BL6J wildtype (WT) mice.

RESULTS

GLP1RKO/Y2RKO and WT mice responded similarly for up to 20 weeks on high-fat diet and 16 weeks after RYGB. There were no significant differences in loss of body and liver weight, fat mass, reduced food intake, relative increase in energy expenditure, improved fasting insulin, glucose tolerance, and insulin tolerance between WT and GLP1RKO/Y2RKO mice after RYGB.

CONCLUSIONS

Combined loss of GLP1R and Y2R-signaling was not able to negate or attenuate the beneficial effects of RYGB on body weight and glucose homeostasis in mice, suggesting that a larger number of signaling pathways is involved or that the critical pathway has not yet been identified.

Glucose Metabolism Parameters and Post-Prandial GLP-1 and GLP-2 Release Largely Vary in Several Distinct Situations: a Controlled Comparison Among Individuals with Crohn's Disease and Individuals with Obesity Before and After Bariatric Surgery

BACKGROUND

This study aims to compare the post-prandial curves of glucose, insulin, GLP-1, and GLP-2 among individuals with Crohn's disease (CD), obese individuals before and after bariatric surgery, and healthy controls.

METHODS

This an exploratory cross-sectional study that involved five groups of patients (two groups of individuals with CD-active and inactive), bariatric patients (pre- and post-surgery, who were their own controls), and a distinct separated control group of healthy volunteers. C-reactive protein (CRP) levels and the post-prandial curves of glucose, insulin, GLP-1, and GLP-2 curves were assessed and compared.

RESULTS

The pre-RYGB group presented significantly higher levels of CRP than the post-RYGB (p = 0.001) and the control group (p = 0.001). The inactive CD group presented a higher post-prandial GLP-1 area under the curve (AUC) than the pre-RYGB group (p = 0.009). The post-RYGB group presented significantly higher AUCs of GLP-2 than the pre-RYGB group (p < 0.0001), both inactive and active CD groups (p < 0.0001 in both situations), and the control group (p = 0.002). The pre-RYGB group presented a significantly higher AUC of glucose than the post-RYGB (p = 0.02) and both active and inactive CD groups (p = 0.019 and p = 0.046, respectively). The pre-RYGB group presented a significantly higher AUC of insulin than the control (p = 0.005) and both CD groups (p < 0.0001).

CONCLUSIONS

Obesity is associated with an inflammatory state comparable to the one observed in CD; inflammation may also be enrolled in the blockade of GLP-2. CD individuals present a more incretin-driven pattern of glucose metabolism, as a way to prevent hypoglycemia and compensate the carbohydrate malabsorption and GLP-2 blockade.

GLP-2 receptor signaling controls circulating bile acid levels but not glucose homeostasis in Gcgr-/- mice and is dispensable for the metabolic benefits ensuing after vertical sleeve gastrectomy

Objective

Therapeutic interventions that improve glucose homeostasis such as attenuation of glucagon receptor (Gcgr) signaling and bariatric surgery share common metabolic features conserved in mice and humans. These include increased circulating levels of bile acids (BA) and the proglucagon-derived peptides (PGDPs), GLP-1 and GLP-2. Whether BA acting through TGR5 (Gpbar1) increases PGDP levels in these scenarios has not been examined. Furthermore, although the importance of GLP-1 action has been interrogated in Gcgr^−/− mice and after bariatric surgery, whether GLP-2 contributes to the metabolic benefits of these interventions is not known.

Methods

To assess whether BA acting through Gpbar1 mediates improved glucose homeostasis in Gcgr^−/− mice we generated and characterized Gcgr^−/−:Gpbar1^−/− mice. The contribution of GLP-2 receptor (GLP-2R) signaling to intestinal and metabolic adaptation arising following loss of the Gcgr was studied in Gcgr^−/−:Glp2r^−/− mice. The role of the GLP-2R in the metabolic improvements evident after bariatric surgery was studied in high fat-fed Glp2r^−/− mice subjected to vertical sleeve gastrectomy (VSG).

Results

Circulating levels of BA were markedly elevated yet similar in Gcgr^−/−:Gpbar1^+/+ vs. Gcgr^−/−:Gpbar1^−/− mice. Loss of GLP-2R lowered levels of BA in Gcgr^−/− mice. Gcgr^−/−:Glp2r^−/− mice also exhibited shifts in the proportion of circulating BA species. Loss of Gpbar1 did not impact body weight, intestinal mass, or glucose homeostasis in Gcgr^−/− mice. In contrast, small bowel growth was attenuated in Gcgr^−/−:Glp2r^−/− mice. The improvement in glucose tolerance, elevated circulating levels of GLP-1, and glucose-stimulated insulin levels were not different in Gcgr^−/−:Glp2r^+/+ vs. Gcgr^−/−:Glp2r^−/− mice. Similarly, loss of the GLP-2R did not attenuate the extent of weight loss and improvement in glucose control after VSG.

Conclusions

These findings reveal that GLP-2R controls BA levels and relative proportions of BA species in Gcgr^−/− mice. Nevertheless, the GLP-2R is not essential for i) control of body weight or glucose homeostasis in Gcgr^−/− mice or ii) metabolic improvements arising after VSG in high fat-fed mice. Furthermore, despite elevations of circulating levels of BA, Gpbar1 does not mediate elevated levels of PGDPs or major metabolic phenotypes in Gcgr^−/− mice. Collectively these findings refine our understanding of the relationship between Gpbar1, elevated levels of BA, PGDPs, and the GLP-2R in amelioration of metabolic derangements arising following loss of Gcgr signaling or after vertical sleeve gastrectomy.

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GLP-2 receptor controls bile acid levels in Gcgr^−/− mice.

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Gpbar1 is not required for the metabolic benefits or elevated levels of PGDPs in Gcgr^−/− mice.

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GLP-2 regulates gut adaptation in Gcgr^−/− mice.

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Bile acid profiles are altered in Gcgr^−/− mice following loss of GLP-2R.

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GLP-2R is not required for improvements in glucose homeostasis or weight loss after VSG in mice.

Regulation of Energy Homeostasis After Gastric Bypass Surgery

The obesity epidemic continues to escalate each year in the United States more than anywhere else in the world. The existing pharmaceutical and other nonsurgical treatments for morbid obesity produce suboptimal physiologic outcomes compared with those of Roux-en-Y gastric bypass (RYGB) surgery. RYGB has been the gold standard of bariatric surgery because the beneficial long-term outcomes, which include sustainable weight loss and type 2 diabetes mellitus (T2DM) resolution, are far superior to those obtained with other bariatric surgeries. However, the current understanding of RYGB's mechanisms of actions remains limited and incomplete. There is an urgent need to understand these mechanisms as gaining this knowledge may lead to the development of innovative and less invasive procedures and/or medical devices, which can mirror the favorable outcomes of RYGB surgery. In this review, we highlight current observations of the metabolic and physiologic events following RYGB, with a particular focus on the role of the anatomical reconfiguration of the gastrointestinal tract after RYGB.

A gut-brain axis regulating glucose metabolism mediated by bile acids and competitive fibroblast growth factor actions at the hypothalamus

OBJECTIVE

Bile acids have been implicated as important regulators of glucose metabolism via activation of FXR and GPBAR1. We have previously shown that FGF19 can modulate glucose handling by suppressing the activity of hypothalamic AGRP/NPY neurons. As bile acids stimulate the release of FGF19/FGF15 into the circulation, we pursued the potential of bile acids to improve glucose tolerance via a gut-brain axis involving FXR and FGF15/FGF19 within enterocytes and FGF receptors on hypothalamic AGRP/NPY neurons.

METHODS

A 5-day gavage of taurocholic acid, mirroring our previous protocol of a 5-day FGF19 treatment, was performed. Oral glucose tolerance tests in mice with genetic manipulations of FGF signaling and melanocortin signaling were used to define a gut-brain axis responsive to bile acids.

RESULTS

The taurocholic acid gavage led to increased serum concentrations of taurocholic acid as well as increases of FGF15 mRNA in the ileum and improved oral glucose tolerance in obese (ob/ob) mice. In contrast, lithocholic acid, an FXR antagonist but a potent agonist for GPBAR1, did not improve glucose tolerance. The positive response to taurocholic acid is dependent upon an intact melanocortinergic system as obese MC4R-null mice or ob/ob mice without AGRP did not show improvements in glucose tolerance after taurocholate gavage. We also tested the FGF receptor isoform necessary for the bile acid response, using AGRP:Fgfr1-/- and AGRP:Fgfr2-/- mice. While the absence of FGFR1 in AGRP/NPY neurons did not alter glucose tolerance after taurocholate gavage, manipulations of Fgfr2 caused bidirectional changes depending upon the experimental model. We hypothesized the existence of an endogenous hypothalamic FGF, most likely FGF17, that acted as a chronic activator of AGRP/NPY neurons. We developed two short peptides based on FGF8 and FGF17 that should antagonize FGF17 action. Both of these peptides improved glucose homeostasis after a 4-day course of central and peripheral injections. Significantly, daily average blood glucose from continuous glucose monitoring was reduced in all tested animals but glucose concentrations remained in the euglycemia range.

CONCLUSIONS

We have defined a gut-brain axis that regulates glucose metabolism mediated by antagonistic fibroblast growth factors. From the intestine, bile acids stimulate FGF15 secretion, leading to activation of the FGF receptors in hypothalamic AGRP/NPY neurons. FGF receptor intracellular signaling subsequently silences AGRP/NPY neurons, leading to improvements of glucose tolerance that are likely mediated by the autonomic nervous system. Finally, short peptides that antagonize homodimeric FGF receptor signaling within the hypothalamus have beneficial effects on glucose homeostasis without inducing hypoglycemia. These peptides could provide a new mode of regulating glucose metabolism.

Luminal chemosensing in the gastroduodenal mucosa

PURPOSE OF REVIEW

We report recently published knowledge regarding gut chemosensory mechanisms focusing on nutrient-sensing G protein-coupled receptors (GPCRs) expressed on gut enteroendocrine cells (EECs), tuft cells, and in afferent nerves in the gastroduodenal mucosa and submucosa.

RECENT FINDINGS

Gene profiling of EECs and tuft cells have revealed expression of a variety of nutrient-sensing GPCRs. The density of EEC and tuft cells is altered by luminal environmental changes that may occur following bypass surgery or in the presence of mucosal inflammation. Some EECs and tuft cells are directly linked to sensory nerves in the subepithelial space. Vagal afferent neurons that innervate the intestinal villi express nutrient receptors, contributing to the regulation of duodenal anion secretion in response to luminal nutrients. Nutrients are also absorbed via specific epithelial transporters.

SUMMARY

Gastric and duodenal epithelial cells are continually exposed to submolar concentrations of nutrients that activate GPCRs expressed on EECs, tuft cells, and submucosal afferent nerves and are also absorbed through specific transporters, regulating epithelial cell proliferation, gastrointestinal physiological function, and metabolism. The chemical coding and distribution of EECs and tuft cells are keys to the development of GPCR-targeted therapies.

Roux-en-Y Gastric Bypass Surgery Suppresses Hepatic Gluconeogenesis and Increases Intestinal Gluconeogenesis in a T2DM Rat Model

BACKGROUND

Roux-en-Y gastric bypass (RYGB) is an effective surgical treatment for type 2 diabetes mellitus (T2DM). The present study aimed to investigate the effects of RYGB on glucose homeostasis, lipid metabolism, and intestinal morphological adaption, as well as hepatic and intestinal gluconeogenesis.

METHODS

Twenty adult male T2DM rats induced by high-fat diet and low dose of streptozotocin were randomly divided into sham and RYGB groups. The parameters of body weight, food intake, glucose tolerance, insulin sensitivity, and serum lipid profiles were assessed to evaluate metabolic changes. Intestinal sections were stained with hematoxylin and eosin (H&E) for light microscopy examination. The messenger RNA (mRNA) and protein expression levels of key regulatory enzymes of gluconeogenesis [phosphoenolpyruvate carboxykinase (PEPCK), glucose-6-phosphatase (G6Pase)] were determined through reverse-transcription PCR (RT-PCR) and Western blotting, respectively.

RESULTS

RYGB induced significant improvements in glucose tolerance and insulin sensitivity, along with weight loss and decreased food intake. RYGB also decreased serum triglyceride (TG) and free fatty acid (FFA) levels. The jejunum and ileum exhibited a marked increase in the length and number of intestinal villi after RYGB. The RYGB group exhibited downregulated mRNA and protein expression levels of PEPCK and G6Pase in the liver and upregulated expression of these enzymes in the jejunum and ileum tissues.

CONCLUSIONS

RYGB ameliorates glucose and lipid metabolism accompanied by weight loss and calorie restriction. The small intestine shows hyperplasia and hypertrophy after RYGB. Meanwhile, our study demonstrated that the reduced hepatic gluconeogenesis and increased intestinal gluconeogenesis may contribute to improved glucose homeostasis after RYGB.

Potential Hormone Mechanisms of Bariatric Surgery

PURPOSE OF REVIEW

In recent years, the role of the gastrointestinal (GI) tract in energy homeostasis through modulation of the digestion and absorption of carbohydrates and the production of incretin hormones is well recognized.

RECENT FINDINGS

Bariatric surgery for obesity has been a very effective method in substantially improving weight, and numerous studies have focused on intestinal adaptation after bariatric procedures. A number of structural and functional changes in the GI tract have been reported postsurgery, which could be responsible for the altered hormonal responses. Furthermore, the change in food absorption rate and the intestinal regions exposed to carbohydrates may affect blood glucose response. This review hopes to give new insights into the direct role of gut hormones, by summarising the metabolic effects of bariatric surgery.

Intestinal adaptations following bariatric surgery: towards the identification of new pharmacological targets for obesity-related metabolic diseases

Although the gastrointestinal tract is the primary target of bariatric surgery, its contributions to the metabolic changes observed after surgery are still underestimated. Changes in the number of incretin-producing cells could result in the modified hormonal response seen after surgery. Additionally, the rate of absorption and consumption of glucose could contribute to the ameliorated glycaemia. Moreover, decreased intestinal permeability could prevent endotoxemia. Recently, numerous studies have focused on intestinal adaptation following bariatric surgeries. These studies bring new insight into the different roles the GI tract plays in the metabolic outcomes of bariatric surgery and open new avenues for therapeutic treatments.

Timeline of Intestinal Adaptation After Malabsortive Surgery: Effect of Luminal Nutrients, Biliopancreatic Secretion, and Glutamine Supplementation

BACKGROUND

The aim of this study was to study the process of intestinal adaptation in the three limbs of the small intestine after malabsorptive bariatric surgery: the biliopancreatic limb, the alimentary limb, and the common channel. These limbs are exposed to different stimuli, namely, gastrointestinal transit and nutrients in the alimentary limb, biliopancreatic secretions in the biliopancreatic limb, and a mix of both in the common channel. We also wished to investigate the effect of glutamine supplementation on the adaptation process.

METHODS

Three types of surgery were performed using a porcine model: biliopancreatic bypass (BPBP), massive (75%) short bowel resection as the positive control, and a sham operation (transection) as the negative control. We measured the height and width of intestinal villi, histidine decarboxylase (HDC) activity, and amount of HDC messenger RNA (mRNA) (standard diet or a diet supplemented with glutamine).

RESULTS

An increase in HDC activity and mRNA expression was observed in the BPBP group. This increase coincided with an increase in the height and width of the intestinal villi. The increase in villus height was observed immediately after surgery and peaked at 2 weeks. Levels remained higher than those observed in sham-operated pigs for a further 4 weeks.

CONCLUSIONS

The intestinal adaptation process in animals that underwent BPBP was less intense than in those that underwent massive short bowel resection and more intense than in those that underwent transection only. Supplementation with glutamine did not improve any of the parameters studied, although it did appear to accelerate the adaptive process.

Intestinal Adaptations after Bariatric Surgery: Consequences on Glucose Homeostasis

The gastrointestinal (GI) tract can play a direct role in glucose homeostasis by modulating the digestion and absorption of carbohydrates and by producing the incretin hormones. In recent years, numerous studies have focused on intestinal adaptation following bariatric surgeries. Changes in the number of incretin (glucagon-like peptide 1 and glucose-dependent insulinotropic polypeptide) producing cells have been reported, which could result in the modified hormonal response seen after surgery. In addition, the rate of absorption and the intestinal regions exposed to sugars may affect the time course of appearance of glucose in the blood. This review gives new insights into the direct role of the GI tract in the metabolic outcomes of bariatric surgery, in the context of glucose homeostasis.

GLP-2: A POORLY UNDERSTOOD MEDIATOR ENROLLED IN VARIOUS BARIATRIC/METABOLIC SURGERY-RELATED PATHOPHYSIOLOGIC MECHANISMS

Introduction:

Glucagon-like peptide-2 (GLP-2) is a gastrointestinal hormone whose effects are predominantly trophic on the intestinal mucosa.

Aim:

Critically evaluate the current literature on the influence of bariatric/metabolic surgery on the levels of GLP-2 and its potential clinical implications.

Method

s: Narrative review through online research on the databases Medline and Lilacs. There were six prospective human studies, two cross-sectional human studies, and three experimental animal studies selected.

Results:

There is evidence demonstrating significant increase in the levels of GLP-2 following gastric bypass, Scopinaro operation, and sleeve gastrectomy. There are no differences between gastric bypass and sleeve gastrectomy in regards to the increase in the GLP-2 levels. There is no correlation between the postoperative levels of GLP-2 and the occurrence of adequate or insufficient postoperative weight loss.

Conclusion:

GLP-2 plays significant roles on the regulation of nutrient absorption, permeability of gut mucosa, control of bone resorption, and regulation of satiety. The overall impact of these effects potentially exerts a significant adaptive or compensatory effect within the context of varied bariatric surgical techniques.

The role of nutrient sensing in the metabolic changes after gastric bypass surgery

Taste receptors coupled to the gustatory G-protein, gustducin, on enteroendocrine cells sense nutrients to regulate gut hormone release. During Roux-en-Y gastric bypass (RYGB) surgery, the altered nutrient flow to more distal regions can affect gustducin-mediated gut hormone release and hence energy and glucose homeostasis. We studied the role of gustducin-mediated signaling in the metabolic improvements and intestinal adaptations along the gut after RYGB surgery in wild-type (WT) and α-gustducin^-/- (α-gust^-/-) mice. RYGB surgery decreased body weight in WT and α-gust^-/- mice, whereas food intake was only decreased in WT mice. Pair-feeding to the RYGB group improved glucose homeostasis to a similar extent in WT mice. GLP1 levels were increased in both genotypes, PYY levels in α-gust^-/- mice and octanoyl ghrelin levels were not affected after RYGB surgery. In WT mice, nutrients act via α-gustducin to increase L-cell differentiation (foregut) and L-cell number (foregut and hindgut) in a region-dependent manner. In α-gust^-/- mice, the effect on gut hormone levels is probably tuned via increased peptide sensor and glucose transporter expression in the Roux limb and increased caecal butyrate and propionate levels in the hindgut that activate free fatty acid receptors. Finally, signaling via α-gustducin plays a role in the increased ion transport of the foregut but not in the improvement in colonic barrier function. In conclusion, RYGB surgery decreased body weight in both WT and α-gust^-/- mice. Elevated plasma GLP1 and PYY levels might mediate this effect, although α-gustducin differentially affects several regulatory systems in the foregut and hindgut, tuning gut hormone release.

CORRELATION BETWEEN PRE AND POSTOPERATIVE LEVELS OF GLP-1/GLP-2 AND WEIGHT LOSS AFTER ROUX-EN-Y GASTRIC BYPASS: A PROSPECTIVE STUDY

Background:

The role of gut hormones in glucose homeostasis and weight loss achievement and maintenance after bariatric surgery appears to be a key point in the understanding of the beneficial effects observed following these procedures.

Aim:

To determine whether there is a correlation between the pre and postoperative levels of both GLP-1 and GLP-2 and the excess weight loss after Roux-en-Y gastric bypass (RYGB).

Methods:

An exploratory prospective study which enrolled 11 individuals who underwent RYGB and were followed-up for 12 months. GLP-1 and GLP-2 after standard meal tolerance test (MTT) were determined before and after surgery and then correlated with the percentage of excess loss (%EWL).

Results:

GLP-2 AUC presented a significant postoperative increase (945.3±449.1 vs.1787.9±602.7; p=0.0037); GLP-1 AUC presented a non-significant trend towards increase after RYGB (709.6±320.4 vs. 1026.5±714.3; p=0.3808). Mean %EWL was 66.7±12.2%. There was not any significant correlation between both the pre and postoperative GLP-1 AUCs and GLP-2 AUCs and the %EWL achieved after one year.

Conclusion:

There was no significant correlation between the pre and postoperative levels of the areas under the GLP-1 and GLP-2 curves with the percentage of weight loss reached after one year.

The role of obestatin in roux-en-Y gastric bypass-induced remission of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a complex and multifactorial disease that is generally characterized by insulin resistance and loss of β-cell function that develops in adulthood. To date, more than 6% of the world's population is affected by T2DM. The main treatments of T2DM are dietary and lifestyle changes. However, only dependent on behaviour modification and oral hypoglycemics, many patients are unable to maintain glycemic control. Emerging evidence indicates that up to 80% of patients with T2DM undergoing Roux-en-Y gastric bypass (RYGB) experience complete remission of their T2DM and the majority of remissions occur almost immediately following the operation. Obestatin is a 23-amino-acid peptide, which is not only thought to suppress food intake and decrease gastric emptying but also found to exert survival effects in pancreatic β cells, increase glucose-stimulated insulin secretion, and reduce insulin resistance and inflammation. In addition, some researchers demonstrated that obestatin is a nutritional marker reflecting body adiposity and insulin resistance. Although results from previous studies were conflicting, the peripheral blood concentrations of obestatin were changed after RYGB. Therefore, regulation of obestatin level may be another mechanism for RYGB-induced remission of T2DM. In this article, we review briefly the effect of RYGB on T2DM in humans and offer an overview of the published data on the effects of RYGB on obestatin level in patients with T2DM. Furthermore, the possible roles of obestatin in the remission of T2DM following RYGB are also reviewed. Copyright © 2015 John Wiley & Sons, Ltd.

The Use of Rat and Mouse Models in Bariatric Surgery Experiments

Animal models have been proven to be a crucial tool for investigating the physiological mechanisms underlying bariatric surgery in general and individual techniques in particular. By using a translational approach, most of these studies have been performed in rodents and have helped to understand how bariatric surgery may or may not work. However, data from studies using animal models should always be critically evaluated for their transferability to the human physiology. It is, therefore, the aim of this review to summarize both advantages and limitations of data generated by animal based experiments designed to investigate and understand the physiological mechanisms at the root of bariatric surgery.

Intestinal SGLT1 in metabolic health and disease

The Na(+)-glucose cotransporter 1 (SGLT1/SLC5A1) is predominantly expressed in the small intestine. It transports glucose and galactose across the apical membrane in a process driven by a Na(+) gradient created by Na(+)-K(+)-ATPase. SGLT2 is the major form found in the kidney, and SGLT2-selective inhibitors are a new class of treatment for type 2 diabetes mellitus (T2DM). Recent data from patients treated with dual SGLT1/2 inhibitors or SGLT2-selective drugs such as canagliflozin (SGLT1 IC50 = 663 nM) warrant evaluation of SGLT1 inhibition for T2DM. SGLT1 activity is highly dynamic, with modulation by multiple mechanisms to ensure maximal uptake of carbohydrates (CHOs). Intestinal SGLT1 inhibition lowers and delays the glucose excursion following CHO ingestion and augments glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) secretion. The latter is likely due to increased glucose exposure of the colonic microbiota and formation of metabolites such as L cell secretagogues. GLP-1 and PYY secretion suppresses food intake, enhances the ileal brake, and has an incretin effect. An increase in colonic microbial production of propionate could contribute to intestinal gluconeogenesis and mediate positive metabolic effects. On the other hand, a threshold of SGLT1 inhibition that could lead to gastrointestinal intolerability is unclear. Altered Na(+) homeostasis and increased colonic CHO may result in diarrhea and adverse gastrointestinal effects. This review considers the potential mechanisms contributing to positive metabolic and negative intestinal effects. Compounds that inhibit SGLT1 must balance the modulation of these mechanisms to achieve therapeutic efficacy for metabolic diseases.

Is insulin-like growth factor 1 (IGF-1) system an attractive target inflammatory bowel diseases? Benefits and limitation of potential therapy

Inflammatory bowel diseases (IBD) are chronic gastrointestinal disorders with unknown etiology, whose incidence dramatically increased over the past 50 years. Currently available strategies for IBD treatment, such as biological therapies, corticosteroids, and immunosuppressive agents are effective, but their side effects and economic costs cannot be ignored. Better understanding of IBD etiology and new therapeutics are thus needed. The aim of this paper is to briefly discuss IGF-1 dependent functions, with particular focus on IGF-1 use in IBD therapy. Data collection was based on records found in medical literature. Data analysis included records published between 1984 and 2014. The IGF-1 system is involved in major physiological functions, such as cell proliferation and metabolism, and growth promotion. Most importantly IGF-1 has anti-inflammatory properties and its use in IBD treatment can be recommended. However, potential IGF-1 therapy has some limitations, which include aggravation of fibrosis in Crohn's patients and facilitated transformation to malignancy. Taken into consideration their possible side effects, IGF-1 analogs and recombinants are nonetheless a promising target for IBD therapy for a specific group of patients. Further studies, at the clinical level are thus recommended.

Sleeve Gastrectomy Does Not Cause Hypertrophy and Reprogramming of Intestinal Glucose Metabolism in Rats

BACKGROUND

Clinical studies have shown similar rapid improvements in body mass and glycemic control after Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG). Evidence suggests that adaptive intestinal tissue growth and reprogramming of intestinal glucose disposal play a key role in the beneficial effects on glucose homeostasis after RYGB, but it is not known whether such adaptive changes also occur after sleeve gastrectomy.

METHODS

High-fat diet-induced obese rats were subjected to either VSG or RYGB, and intestinal growth and functional adaptations were assessed by using morphometric, immunohistochemical, and immuno-blot techniques, 3 months after surgery or sham surgery.

RESULTS

The cross-sectional areas of the Roux and common limbs are significantly increased after RYGB compared with sham surgery (Roux limb: 17.1 ± 4.0 vs. 5.5 ± 0.1 mm(2); common limb: 11.7 ± 0.6 vs. 5.1 ± 0.5 mm(2); p < 0.01), but the cross-sectional area of the corresponding jejunum is not different from controls after VSG. Similarly, mucosal thickness and the number of GLP-1 cells are not increased after VSG. Protein expression of hexokinase II is increased fourfold (p < 0.01) in the Roux limb after RYGB, but not in the jejunum after VSG.

CONCLUSIONS

Adaptive hypertrophy and reprogramming of glucose metabolism in the small intestine are not necessary for VSG to improve body composition and glycemic control. The similar beneficial effects of VSG and RYGB on glucose homeostasis might be mediated by different mechanisms.

Differences in Alimentary Glucose Absorption and Intestinal Disposal of Blood Glucose After Roux-en-Y Gastric Bypass vs Sleeve Gastrectomy

BACKGROUND & AIMS

Bariatric procedures, such as Roux-en-Y gastric bypass (RYGB) or vertical sleeve gastrectomy (VSG), are the most effective approaches to resolve type 2 diabetes in obese individuals. Alimentary glucose absorption and intestinal disposal of blood glucose have not been directly compared between individuals or animals that underwent RYGB vs VSG. We evaluated in rats and humans how the gut epithelium adapts after surgery and the consequences on alimentary glucose absorption and intestinal disposal of blood glucose.

METHODS

Obese male rats underwent RYGB, VSG, or sham (control) operations. We collected intestine segments from all rats; we performed histologic analyses and measured levels of messenger RNAs encoding the sugar transporters SGLT1, GLUT1, GLUT2, GLUT3, GLUT4, and GLUT5. Glucose transport and consumption were assayed using ex vivo jejunal loops. Histologic analyses were also performed on Roux limb sections from patients who underwent RYGB 1-5 years after surgery. Roux limb glucose consumption was assayed after surgery by positron emission and computed tomography imaging.

RESULTS

In rats and humans that underwent RYGB, the Roux limb became hyperplasic, with an increased number of incretin-producing cells compared with the corresponding jejunal segment of controls. Furthermore, expression of sugar transporters and hypoxia-related genes increased and the nonintestinal glucose transporter GLUT1 appeared at the basolateral membrane of enterocytes. Ingested and circulating glucose was trapped within the intestinal epithelial cells of rats and humans that underwent RYGB. By contrast, there was no hyperplasia of the intestine after VSG, but the intestinal absorption of alimentary glucose was reduced and density of endocrine cells secreting glucagon-like peptide-1 increased.

CONCLUSIONS

The intestine adapts differently to RYGB vs VSG. RYGB increases intestinal glucose disposal and VSG delays glucose absorption; both contribute to observed improvements in glycemia.

Psychopharmacology and Bariatric Surgery

Currently, it has been demonstrated that psychotropic drugs, particularly antidepressants, are frequently prescribed for patients who seek bariatric surgery. Many bariatric surgery patients have a history of a mood disorder. Unlike medications for diabetes, hypertension or hyperlipidemia, which are generally reduced and at times discontinued, postsurgery antidepressants use is only slightly reduced. The Roux-en-Y procedure is most frequently associated with alteration in drug exposure. Medication disintegration, dissolution, absorption, metabolism and excretion have been found to be altered in postbariatric patients, although data are sparse at this time. This paper will review the current evidence regarding the effect of bariatric surgery on drug treatment including mechanism of interference as well as the extent of changes identified to date. Data will be presented as controlled trials followed by case series and reports.

Remodeling of the residual gastric mucosa after roux-en-y gastric bypass or vertical sleeve gastrectomy in diet-induced obese rats

Whereas the remodeling of intestinal mucosa after bariatric surgeries has been the matter of numerous studies to our knowledge, very few reported on the remodeling of the residual gastric mucosa. In this study, we analyzed remodeling of gastric mucosa after Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG) in rats. Diet-induced obese rats were subjected to RYGB, VSG or sham surgical procedures. All animals were assessed for food intake, body-weight, fasting blood, metabolites and hormones profiling, as well as insulin and glucose tolerance tests before and up to 5 weeks post-surgery. Remodeling of gastric tissues was analyzed by routine histology and immunohistochemistry studies, and qRT-PCR analyses of ghrelin and gastrin mRNA levels. In obese rats with impaired glucose tolerance, VSG and RYGB caused substantial weight loss and rats greatly improved their oral glucose tolerance. The remaining gastric mucosa after VSG and gastric pouch (GP) after RYGB revealed a hyperplasia of the mucous neck cells that displayed a strong immunoreactivity for parietal cell H⁺/K⁺-ATPase. Ghrelin mRNA levels were reduced by 2-fold in remaining fundic mucosa after VSG and 10-fold in GP after RYGB. In the antrum, gastrin mRNA levels were reduced after VSG in line with the reduced number of gastrin positive cells. This study reports novel and important observations dealing with the remaining gastric mucosa after RYGB and VSG. The data demonstrate, for the first time, a hyperplasia of the mucous neck cells, a transit cell population of the stomach bearing differentiating capacities into zymogenic and peptic cells.

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.

Ileal Interposition in Rats with Experimental Type 2 Like Diabetes Improves Glycemic Control Independently of Glucose Absorption

Bariatric operations in obese patients with type 2 diabetes often improve diabetes before weight loss is observed. In patients mainly Roux-en-Y-gastric bypass with partial stomach resection is performed. Duodenojejunal bypass (DJB) and ileal interposition (IIP) are employed in animal experiments. Due to increased glucose exposition of L-cells located in distal ileum, all bariatric surgery procedures lead to higher secretion of antidiabetic glucagon like peptide-1 (GLP-1) after glucose gavage. After DJB also downregulation of Na(+)-d-glucose cotransporter SGLT1 was observed. This suggested a direct contribution of decreased glucose absorption to the antidiabetic effect of bariatric surgery. To investigate whether glucose absorption is also decreased after IIP, we induced diabetes with decreased glucose tolerance and insulin sensitivity in male rats and investigated effects of IIP on diabetes and SGLT1. After IIP, we observed weight-independent improvement of glucose tolerance, increased insulin sensitivity, and increased plasma GLP-1 after glucose gavage. The interposed ileum was increased in diameter and showed increased length of villi, hyperplasia of the epithelial layer, and increased number of L-cells. The amount of SGLT1-mediated glucose uptake in interposed ileum was increased 2-fold reaching the same level as in jejunum. Thus, improvement of glycemic control by bariatric surgery does not require decreased glucose absorption.

Changes in intestinal permeability after Roux-en-Y gastric bypass

BACKGROUND

Roux-en-Y gastric bypass (RYGB) interferes considerably with the anatomy and physiology of the gastrointestinal tract. The study of intestinal permeability can provide important information regarding changes in the structure and function of the mucosal barrier after the procedure.

METHODS

The urinary excretion rates of lactulose and mannitol after oral intake of both substances were evaluated. We also evaluated the lactulose/mannitol excretion ratio. Tests were performed during the preoperative period (T0), at the first postoperative month (T1), and at the sixth postoperative month (T6).

RESULTS

The study included 16 morbidly obese patients. The excretion rate of mannitol was significantly lower at T1 compared with T0 and T6 (p = 0.003). There was no significant difference in the excretion rates of lactulose or in the lactulose/mannitol ratio during the three periods. Six patients (37.5%) exhibited a considerable increase in the excretion rate of lactulose at T6 (4-73 times higher than the preoperative value), accompanied by proportional variations in the lactulose/mannitol ratio.

CONCLUSIONS

The significant increase in mannitol excretion rate from T1 to T6 most likely reflects the occurrence of intestinal adaptation (mucosal hyperplasia), which would tend to minimize the malabsorption of macronutrients. A subgroup of patients who undergo RYGB exhibit pronounced increase in their intestinal permeability (assessed by the lactulose/mannitol ratio and the lactulose excretion rate) at T6.