A Rodent Model of Adjustable Gastric Band Surgery—Implications for the Understanding of Underlying Mechanisms

The Effect of Bariatric Surgery upon Diabetes Mellitus: A Proof of Concept by Using the Case of the Mid-Term Effect of Lap Adjustable Gastric Banding (LAGB) on Patients with Diabetes

Obesity is a worldwide epidemic, with numbers on the rise in the world. Obesity is strongly correlated with increased morbidity and mortality. One of the major factors affecting this increase is comorbid diseases such as diabetes mellitus (DM), which is strongly associated with and dependent on the degree of obesity. Thus, it is not surprising that when efficient surgical treatments were found to battle obesity, researchers soon found them to be relevant and effective for battling DM as well. Laparoscopic Adjustable Gastric Banding (LAGB) is a common surgical treatment for morbid obesity. LAGB has the potential to improve control of the comorbidities of morbid obesity, primarily diabetes mellitus (DM). Our hypothesis was that patients treated with LAGB would have a long-term improvement in the control of DM and that due to its unique mechanism of action, this can lend us a better understanding of how to battle diabetes in an efficient and effective way. This was a cohort study based on patients who underwent LAGB surgery in our institution 4 to 7 years previously and had DM type 2 at the time of surgery. Data were collected from patient’s charts and a telephone interview-based questionnaire including demographics, health status, and quality-of-life assessment (Bariatric Analysis and Reporting Outcome System [BAROS]). Seventy patients participated in the current study. The average follow-up time was 5.1 ± 0.9 years post-surgery. The average weight prior to surgery was 122.0 ± 20.2 kg, and on the day of the interview it was 87.0 ± 17.6 kg (p < 0.001). The average body mass index before surgery was 43.8 ± 5.1, and on the day of the interview it was 31.2 ± 4.8 (p < 0.001). On the day of the interview, 47.1% of the participants were cured of DM (not receiving treatment, whether dietary or pharmacologic). The sum of ranks for diabetes was lower after the surgery (p < 0.001), as was HTN and its treatment (p < 0.001). We have shown in this study that LAGB is an effective treatment for morbid obesity, as well as two comorbidities that come with it—DM type 2 and Hypertension (HTN)—in a longer period than previously shown, and with a unique look at the underlying mechanism of action of this procedure. There is a need for further studies to consolidate our findings and characterize which patients are more prone to enjoy these remarkable surgical benefits.

Visceral Obesity, Metabolic Syndrome, and Esophageal Adenocarcinoma

Esophageal adenocarcinoma (EAC) represents an exemplar of obesity-associated carcinogenesis, with a progressive increase in EAC risk with increased body mass index. In this context, there is increased focus on visceral adipose tissue and associated metabolic dysfunction, including hypertension, diabetes mellitus and hyperlipidemia, or combinations of these in the metabolic syndrome. Visceral obesity (VO) may promote EAC via both directly impacting on gastro-esophageal reflux disease and Barrett's esophagus, as well as via reflux-independent effects, involving adipokines, growth factors, insulin resistance, and the microbiome. In this review these pathways are explored, including the impact of VO on the tumor microenvironment, and on cancer outcomes. The current evidence-based literature regarding the role of dietary, lifestyle, pharmacologic and surgical interventions to modulate the risk of EAC is explored.

Upper Gastrointestinal Function in Morbidly Obese Adolescents Before and 6 Months After Gastric Banding

BACKGROUND

The effects of laparoscopic adjustable gastric band (LAGB) placement on upper gastrointestinal tract function in obese adolescents are unknown. Therefore, our aim was to determine the short-term effects of LAGB on esophageal motility, gastroesophageal reflux, gastric emptying, appetite-regulatory hormones, and perceptions of post-prandial hunger and fullness.

METHODS

This study was part of a prospective cohort study (March 2009-December 2015) in one tertiary referral hospital. The study included obese adolescents (14-18 years) with a body mass index (BMI) > 40 (or ≥ 35 with comorbidities). Gastric emptying was assessed by ¹³C-octanoic acid breath test, pharyngeal, and esophageal motor function by high-resolution manometry with impedance (HRIM), and appetite and other perceptions using 100-mm visual analogue scales. Dysphagia symptoms were scored using a Dakkak questionnaire. Data were compared pre- and post-LAGB placement and at a 6-month follow-up.

RESULTS

Based upon analysis of 15 adolescents, at the 6-month follow-up, LAGB placement: (i) led to a significant reduction in weight and BMI; (ii) increased fullness and decreased hunger post-meal; (iii) increased symptoms of dysphagia after solid food; and, despite these effects, (iv) caused little or no changes to appetite hormones, while (v) effects on gastric emptying, esophageal motility, esophageal bolus transport, and esophageal emptying were not significant.

CONCLUSION

In adolescents, LAGB improved BMI and altered the sensitivity to nutrients without significant effects on upper gastrointestinal tract physiology at the 6-month follow-up.

Meal patterns after bariatric surgery in mice and rats

With behavioral and pharmacological interventions continuously failing to tackle the obesity epidemic, bariatric surgery has been hailed as the most effective treatment strategy. Current literature suggests that bariatric surgery successfully decreases body weight and excess fat mass through targeting both variables of the energy homeostasis - energy intake and energy expenditure. Here we review current knowledge on changes in caloric consumption, an important arm in the energy balance equation, in rodent models of bariatric surgery. In particular, circadian feeding dynamics, post-surgical caloric intake at both "rapid weight loss" phase and "weight maintenance" phase, as well as meal pattern analysis will be the subject of this review. Considering that different types of bariatric surgery may trigger differential energy intake dynamics resulting in variable weight loss outcomes, the effects of most popular surgeries - vertical sleeve gastrectomy (VSG), Roux-en-Y gastric bypass (RYGB), and gastric banding (GB) - are elaborated. Potential candidate mechanisms underlying alterations in food intake and meal patterns following different bariatric procedures are briefly discussed at the end.

Serum Leptin, Obestatin, and Ghrelin Levels and Gastric Emptying Rates of Liquid and Solid Meals in Non-obese Rats with Roux-en-Y Bypass Surgery or Prosthesis Placement: Implications for the Role of Vagal Afferents

BACKGROUND

The present study aimed to investigate the effects of Roux-en-Y gastric bypass (RYGB) and prosthesis placement on gastric emptying rate in conjunction with serum ghrelin-obestatin-leptin responses in non-obese rats with intact or denervated afferent innervation.

METHODS

Under anesthesia, male Sprague-Dawley rats underwent either sham operation, RYGB, prosthesis, and/or Gregory cannula placement. Three weeks later, liquid or solid gastric emptying tests were performed and serum ghrelin, leptin and obestatin levels were measured.

RESULTS

Both prosthesis placement and RYGB surgery delayed non-nutrient liquid emptying; while solid nutrient emptying was delayed only by RYGB. Nutrient-dependent (acid, hyperosmolal and peptone) delay in liquid emptying was abolished in rats with prosthesis. By vagal afferent denervation, delayed liquid emptying was abolished, while solid emptying was further delayed in rats with prosthesis. Ghrelin and obestatin levels were depressed in prosthesis-placed rats, but RYGB surgery had no impact on both levels. Leptin level was elevated in solid-food-given rats with prosthesis, but not changed in RYGB group, while it was reduced following liquid meal. All the changes observed in ghrelin, obestatin, or leptin levels in response to meal ingestion were reversed with vagal afferent denervation.

CONCLUSIONS

Both RYGB and prosthesis placement had delaying effects on gastric emptying rate of non-obese rats. Our results indicate that the short-term changes in gastric motility and hormone responses induced by volume reduction are reversed by afferent denervation, suggesting that sparing the vagal innervation could be essential for reaching optimum motility and hormone changes expected after bariatric surgery.

Improving efficacy of the adjustable gastric band: studies of the use of adjuvant approaches in a rodent model

BACKGROUND

The laparoscopic adjustable gastric band (AGB) has been effective in reducing excess weight by approximately 50% for at least 16 years. However, as with all weight loss approaches, reduction in weight resulting from bariatric surgery is associated with a compensatory reduction in energy expenditure, which may confound and limit weight loss. Adjuvant therapies that reduce food intake and increase energy expenditure may be used to improve weight loss outcomes by ameliorating, or even reversing, this reduction in energy expenditure.

METHODS

Rats were either fitted with an AGB or were sham operated and received one of 2 adjunctive pharmacologic treatments, (1) thyroxine or (2) bupropion/naltrexone (Contrave), at a range of doses and matched with vehicle controls (n = 6-8/group) over a 4-week period of combined treatments. Metabolic parameters including food intake, weight, fat mass, and energy expenditure in brown adipose tissue (BAT), whole body calorimetry, and physical activity were assessed.

RESULTS

Inflation of the AGB caused a reduction in weight gain that was further enhanced by cotreatment with either thyroxine or Contrave (P<.05). Thyroxine completely ameliorated the reduction in AGB-induced BAT thermogenesis and significantly improved weight loss, particularly in fat mass. Contrave also augmented the loss of weight and fat mass associated with the AGB and increased BAT thermogenesis in banded rats even at doses below that required to change food intake.

CONCLUSION

Adjuvant therapies can improve the efficacy of the AGB, at least in part by negating the compensatory reduction in energy expenditure, but also via a combined effect on food intake.

Neuroendocrine adaptations to bariatric surgery

The global epidemic of obesity and its related disease in combination with robust physiological defence of intentional weight loss generates a pressing need for effective weight loss therapies. Bariatric surgery, which works very effectively at delivering substantial sustained weight loss, has been an enigma with respect to mechanism of action. Naive concepts of restriction and malabsorption do not explain the efficacy of the most commonly used bariatric procedures. This century has seen increased interest in unravelling the mystery of the mechanisms underlying surgery associated weight loss with a focus on integrative gastrointestinal (GI) physiology, gut-brain signalling, and beyond weight loss effects on metabolism. GI interventions, some very minor, can alter GI wall stretch and pressure receptors; a range of GI hormones affecting hunger and satiety; bile acid metabolism and signalling; the characteristics of GI microbiome; portal vein nutrient sensing; and circulating concentrations of amino acids. Understanding the mechanisms involved should present targets for less invasive effective therapies.

Obesity and increased risk of esophageal adenocarcinoma

There has been a substantial increase in the incidence of esophageal adenocarcinoma over the past 40 years. Meta-analyses of large prospective cohorts and population-based case-control studies demonstrate consistent associations between obesity and the development of adenocarcinoma of the esophagus and esophago-gastric junction, with an approximate doubling of risk of esophageal adenocarcinoma among patients who are obese, and an almost five-fold increased risk among those with BMI >40 kg/m². The pathologic precursor, specialized intestinal metaplasia in Barrett's esophagus, is also associated with increased adiposity. Epidemiologic evidence suggests that this cancer risk is not solely due to increased gastro-esophageal reflux, and that adipose tissue itself, in particular visceral adipose, may fuel carcinogenesis through the production of adipokines, cytokines, growth factors, and increased inflammation. The robust epidemiologic evidence linking obesity with esophageal adenocarcinoma makes it an exemplar model for investigating the molecular mechanisms underpinning obesity-associated malignant progression, which are discussed in this review.

Pre-operative weight loss does not predict weight loss following laparoscopic adjustable gastric banding

BACKGROUND

This study aimed to test the hypothesis that the amount of weight lost on a mandatory 2-week pre-operative very-low-calorie diet (VLCD) would predict the longer-term outcomes of laparoscopic adjustable gastric banding (LAGB).

METHODS

All patients treated with a primary LAGB from 21 October 2008 until 30 June 2010, who were prescribed a 2-week pre-operative VLCD, have been included in the study. Patient age, weight, BMI and excess weight (defined as weight above a BMI of 25) were extracted on the day of first visit, day of surgery and at the post-operative visits at 3, 12 and 24 months. From these data, percent excess weight loss (EWL) was calculated and compared at all time points.

RESULTS

The weight loss achieved on a mandatory 2-week pre-operative diet did not predict weight outcomes at 2 years (r = -0.008; p = 0.931). Using multivariate analysis, the best predictor of 24-month percent EWL was percent EWL at 3 months post operation (sr(2) = 0.34; p = 0.003).

CONCLUSIONS

Results from a pre-operative diet should not be used to predict the ultimate outcome of bariatric surgery. The weight loss at 3 months following LAGB was a strong predictor of longer-term outcomes. There may be potential for improving longer-term results with LAGB by better supporting patients who are not achieving good weight loss at this early time point.

GLP-1R agonism enhances adjustable gastric banding in diet-induced obese rats

Bariatric procedures vary in efficacy, but overall are more effective than behavioral and pharmaceutical treatment. Roux-en-Y gastric bypass causes increased secretion of glucagon-like peptide 1 (GLP-1) and reduces body weight (BW) more than adjustable gastric banding (AGB), which does not trigger increased GLP-1 secretion. Since GLP-1-based drugs consistently reduce BW, we hypothesized that GLP-1 receptor (GLP-1R) agonists would augment the effects of AGB. Male Long-Evans rats with diet-induced obesity received AGB implantation or sham surgery. GLP-1R agonism, cannabinoid receptor-1 (CB1-R) antagonism, or vehicle was combined with inflation to evaluate interaction between AGB and pharmacological treatments. GLP1-R agonism reduced BW in both sham and AGB rats (left uninflated) compared with vehicle-treated animals. Subsequent band inflation was ineffective in vehicle-treated rats but enhanced weight loss stimulated by GLP1-R agonism. In contrast, there was no additional BW loss when CB1-R antagonism was given with AGB. We found band inflation to trigger neural activation in areas of the nucleus of the solitary tract known to be targeted by GLP-1R agonism, offering a potential mechanism for the interaction. These data show that GLP-1R agonism, but not CB1-R antagonism, improves weight loss achieved by AGB and suggest an opportunity to optimize bariatric surgery with adjunctive pharmacotherapy.

Isolated duodenal exclusion increases energy expenditure and improves glucose homeostasis in diet-induced obese rats

Roux-en-Y gastric bypass (RYGB) in rodent models reduces food intake (FI), increases resting energy expenditure (EE), and improves glycemic control. We have shown that mimicking the duodenal component of RYGB by implantation of a 10-cm endoluminal sleeve device (ELS-10) induces weight loss and improves glycemic control in diet-induced obese (DIO) rats. We sought to determine the mechanisms and structural requirements of these effects. We examined the effects of ELS-10 devices implanted in male DIO rats on body weight, food intake (FI), meal patterns, total and resting EE, and multiple parameters of glucose homeostasis, comparing them with sham-operated (SO) rats and with SO rats weight matched to the ELS-10-treated group. To determine the extent of duodenal exclusion required to influence metabolic outcomes, we compared the effects of implanting 10-, 4-, or 1-cm ELS devices. ELS-10 rats exhibited 13% higher total and 9% higher resting EE than SO controls. ELS-10 rats also exhibited enhanced postprandial GLP-1 secretion and improved glucose tolerance and insulin sensitivity out of proportion to the effects of weight loss alone. Implantation of 4- or 1-cm ELS devices had no effect on EE and limited effects on glucose homeostasis. Complete duodenal exclusion with ELS-10 induces weight loss by decreasing FI and increasing EE and improves glycemic control through weight loss-independent mechanisms. Thus signals originating in the proximal small intestine appear to exert a direct influence on the physiological regulation of EE and glucose homeostasis. Their selective manipulation could provide effective new therapies for obesity and diabetes that mimic the benefits of RYGB.

Assessment of different bariatric surgeries in the treatment of obesity and insulin resistance in mice

OBJECTIVE

To assess the effects of different bariatric surgical procedures on the treatment of obesity and insulin resistance in high fat diet-induced obese (DIO) mice.

BACKGROUND

Bariatric surgery is currently considered the most effective treatment for morbid obesity and its comorbidities; however, a systematic study of their mechanisms is still lacking.

METHODS

We developed bariatric surgery models, including gastric banding, sleeve gastrectomy, Roux-en-Y gastric bypass (RYGB), modified RYGB (mRYGB) and biliopancreatic diversion (BPD), in DIO mice. Body weight, body fat and lean mass, liver steatosis, glucose tolerance and pancreatic beta cell function were examined.

RESULTS

All bariatric surgeries resulted in significant weight loss, reduced body fat and improved glucose tolerance in the short term (4 weeks), compared with mice with sham surgery. Of the bariatric surgery models, sleeve gastrectomy and mRYGB had higher success rates and lower mortalities and represent reliable restrictive and gastrointestinal (GI) bypass mouse bariatric surgery models, respectively. In the long term, the GI bypass procedure produced more profound weight loss, significant improvement of glucose tolerance and liver steatosis than the restrictive procedure. DIO mice had increased insulin promoter activity, suggesting overactivation of pancreatic beta cells, which was regulated by the mRYGB procedure. Compared with the restrictive procedure, the GI bypass procedure showed more severe symptoms of malnutrition following bariatric surgery.

DISCUSSIONS

Both restrictive and GI bypass procedures provide positive effects on weight loss, fat composition, liver steatosis and glucose tolerance; however, in the long term, the GI bypass shows better results than restrictive procedures.

Metabolic surgery: an evolution through bariatric animal models

Metabolic surgery was developed through the application and experience gained from bariatric or weight loss procedures. Much of our knowledge from the procedures comes from the study of animal models, where they have revealed anatomic feasibility, systemic physiological elements and cellular metabolic effects. The first generation of operation included the jejunoileal bypass and partial ileal bypass that led to the development of the current procedures including Roux-en-Y gastric bypass, biliopancreatic diversion, adjustable gastric banding and sleeve gastrectomy. These operations carry significant metabolic benefits and can reduce the risk of diabetes, heart disease and cancer. Further insights from these animal models can reveal genetic, molecular and systemic effects that can enhance and develop the next generation of metabolic operations.