Gastric bypass increases energy expenditure in rats

Animal models of bariatric/metabolic surgery shed light on the mechanisms of weight control and glucose homeostasis: view from the chair

Bariatric/metabolic surgeries are remarkably effective in reducing weight over a sustained period of time, and they also have significant beneficial effects on glucose homeostasis. Interestingly, the metabolic benefits of these surgeries frequently occur before significant weight loss. Given these findings, it is perhaps not surprising that obesity researchers are asking, how does bariatric/metabolic surgery work? Establishing these mechanisms can offer new insights into the physiology of energy balance and the control of metabolism. In the second half of the 13(th) International Symposium of the Merck Frosst/CIHR Research Chair in Obesity, four papers that address the mechanisms of bariatric/metabolic surgery were presented. The papers that follow this viewpoint all make use of animal models to reveal the neurohumoral mechanisms underlying weight loss and improved glucose homeostasis after experimental bariatric surgery. The rodent models of the commonly used clinical procedures have shown that energy intake is increased, food reward is altered and that the proximal gut is important in the control of energy balance and glucose homeostasis. Taken together, these models shed light on the mechanisms of bariatric/metabolic surgery and offer new insights that, in the future, may lead to less invasive therapies.

The gut hormones in appetite regulation

Obesity has received much attention worldwide in association with an increased risk of cardiovascular diseases, diabetes, and cancer. At present, bariatric surgery is the only effective treatment for obesity in which long-term weight loss is achieved in patients. By contrast, pharmacological interventions for obesity are usually followed by weight regain. Although the exact mechanisms of long-term weight loss following bariatric surgery are yet to be fully elucidated, several gut hormones have been implicated. Gut hormones play a critical role in relaying signals of nutritional and energy status from the gut to the central nervous system, in order to regulate food intake. Cholecystokinin, peptide YY, pancreatic polypeptide, glucagon-like peptide-1, and oxyntomodulin act through distinct yet synergistic mechanisms to suppress appetite, whereas ghrelin stimulates food intake. Here, we discuss the role of gut hormones in the regulation of food intake and body weight.

Mechanisms responsible for excess weight loss after bariatric surgery

Obesity has increased alarmingly in the United States and is increasing in many countries of the world. Because obesity is an important risk factor for type 2 diabetes and other chronic diseases, it is important to develop approaches to counter the rapid increase in adiposity. One approach is bariatric surgery, the most successful clinical intervention known for treating obesity. Surgery can result in impressive weight loss and improvement of obesity-related comorbidities. Yet the mechanisms responsible for this remarkable effect of surgery remain controversial. It is now clear that caloric restriction, per se, does not explain all the reduction in stored fat mass after surgery. A number of gastrointestinal hormones, including glucagon-like peptide (GLP)-1, peptide YY, oxyntomodulin, GLP-2, glucose-dependent insulinotropic polypeptide, ghrelin, and others, can play roles in energy homeostasis and could be involved in bariatric-surgery-related weight loss and weight loss maintenance. Vagal innervation may play a role. In addition, there may be other yet-uncharacterized factors that could participate. This review discusses the possible roles of these hormonal mechanisms in various types of bariatric surgery to help elucidate some of the potential mechanisms at play in short-term and long-term post-bariatric surgery weight loss. Understanding such mechanisms could lead to new and efficacious means to control or even reduce the epidemic of obesity.

Metabolic surgery-principles and current concepts

INTRODUCTION

In the almost six decades of bariatric surgery, a variety of surgical approaches to treating morbid obesity have been developed.

HISTORY AND EVOLUTION

Rather than prior techniques being continually superseded by new ones, a broad choice of surgical solutions based on restrictive, malabsorptive, humoral effects, or combinations thereof, is now available. In fact, in recent years, the advent of surgically modifying human metabolism promises new approaches to ameliorate traditionally medically treated metabolic entities, i.e., diabetes, even in the non-obese. The understanding of the various metabolic effects have led to a paradigm shift from bariatric surgery as a solely weight-reducing procedure to metabolic surgery affecting whole body metabolism.

CONCLUSION

The bariatric surgeon now faces the challenge and opportunity of selecting the most suitable technique for each individual case. To assist in such decision-making, this review, Metabolic surgery-principles and current concepts, is presented, tracing the historical development; describing the various surgical techniques; elucidating the mechanisms by which glycemic control can be achieved that involve favorable changes in insulin secretion and insulin sensitivity, gut hormones, adipokines, energy expenditure, appetite, and preference for low glycemic index foods; as well as exploring the fascinating future potential of this new interdisciplinary field.

Management of type 2 diabetes: new and future developments in treatment

The increasing prevalence, variable pathogenesis, progressive natural history, and complications of type 2 diabetes emphasise the urgent need for new treatment strategies. Longacting (eg, once weekly) agonists of the glucagon-like-peptide-1 receptor are advanced in development, and they improve prandial insulin secretion, reduce excess glucagon production, and promote satiety. Trials of inhibitors of dipeptidyl peptidase 4, which enhance the effect of endogenous incretin hormones, are also nearing completion. Novel approaches to glycaemic regulation include use of inhibitors of the sodium-glucose cotransporter 2, which increase renal glucose elimination, and inhibitors of 11β-hydroxysteroid dehydrogenase 1, which reduce the glucocorticoid effects in liver and fat. Insulin-releasing glucokinase activators and pancreatic-G-protein-coupled fatty-acid-receptor agonists, glucagon-receptor antagonists, and metabolic inhibitors of hepatic glucose output are being assessed. Early proof of principle has been shown for compounds that enhance and partly mimic insulin action and replicate some effects of bariatric surgery.

Gastric bypass reduces fat intake and preference

Roux-en-Y gastric bypass is the most effective therapy for morbid obesity. This study investigated how gastric bypass affects intake of and preference for high-fat food in an experimental (rat) study and within a trial setting (human). Proportion of dietary fat in gastric bypass patients was significantly lower 6 yr after surgery compared with patients after vertical-banded gastroplasty (P = 0.046). Gastric bypass reduced total fat and caloric intake (P < 0.001) and increased standard low-fat chow consumption compared with sham controls (P < 0.001) in rats. Compared with sham-operated rats, gastric bypass rats displayed much lower preferences for Intralipid concentrations > 0.5% in an ascending concentration series (0.005%, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 5%) of two-bottle preference tests (P = 0.005). This effect was demonstrated 10 and 200 days after surgery. However, there was no difference in appetitive or consummatory behavior in the brief access test between the two groups (P = 0.71) using similar Intralipid concentrations (0.005% through 5%). Levels of glucagon-like peptide-1 (GLP-1) were increased after gastric bypass as expected. An oral gavage of 1 ml corn oil after saccharin ingestion in gastric bypass rats induced a conditioned taste aversion. These findings suggest that changes in fat preference may contribute to long-term maintained weight loss after gastric bypass. Postingestive effects of high-fat nutrients resulting in conditioned taste aversion may partially explain this observation; the role of GLP-1 in mediating postprandial responses after gastric bypass requires further investigation.

Comparison of the effects of Roux-en-Y gastric bypass and ileal transposition surgeries on food intake, body weight, and circulating peptide YY concentrations in rats

BACKGROUND

Roux-en-Y gastric bypass (RYGB) surgery is one of the most effective treatments for obesity producing long-term weight loss. The anorexia and weight loss from RYGB could be due to gastric restriction, malabsorption, enhanced lower gut stimulation, increased energy expenditure, and/or other metabolic adaptations. In ileal transposition (IT) surgery, a segment of the ileum is transposed to the upper jejunum with no gastric restriction or malabsorption. Our objective is to compare the effects of RYGB and IT surgeries on food intake, body weight, and plasma concentrations of the anorexigenic lower gut hormone Peptide YY (PYY) in rats.

METHODS

Adult male Sprague-Dawley rats were subjected to either RYGB (n = 9), IT (n = 9) or sham surgeries (n = 16). A subset of sham animals were either pair-fed to RYGB (n = 9) or ad lib fed (n = 7) on a highly palatable mixed nutrient liquid food (Ensure). Food intake, body weight and plasma PYY concentrations were measured.

RESULTS

The data demonstrate that (1) RYGB produces a sustained reduction in food intake and weight gain, (2) the anorexic effects of IT are relatively transient lasting for 5 weeks, (3) the reduction in weight gain resulting from IT is similar to that of animals pair-fed to RYGB, and (4) RYGB and IT surgeries are associated with elevated postprandial plasma PYY concentrations.

CONCLUSIONS

We demonstrate in our rat models that RYGB surgery produces a greater reduction in food intake and weight gain than IT surgery, and that both surgeries are associated with enhanced plasma concentrations of Peptide YY.

Lessons learned from gastric bypass operations in rats

Numerous studies using gastric bypass rat models have been recently conducted to uncover underlying physiological mechanisms of Roux-en-Y gastric bypass. Reflecting on lessons learned from gastric bypass rat models may thus aid the development of gastric bypass models in mice and other species. This review aims to discuss technical and experimental details of published gastric bypass rat models to understand advantages and limitations of this experimental tool. The review is based on PubMed literature using the search terms 'animal model', 'rodent model', 'bariatric surgery', 'gastric bypass', and 'Roux-en-Y gastric bypass'. All studies published up until February 2011 were included. 32 studies describing 15 different rat gastric bypass models were included. Description of surgical technique differs in terms of pouch size, limb lengths, preservation of the vagal nerve, and mortality rate. Surgery was carried out exclusively in male rats of different strains and ages. Pre- and postoperative diets also varied significantly. Technical and experimental variations in published gastric bypass rat models complicate comparison and identification of potential physiological mechanisms involved in gastric bypass. In summary, there is no clear evidence that any of these models is superior, but there is an emerging need for standardization of the procedure to achieve consistent and comparable data.

Bariatric surgery: mechanisms, indications and outcomes

The rising problem of obesity is causing major health problems, reduced quality of life and reduced life expectancy. It now generates approximately 10% of all health costs. The progression of the problem indicates preventive measures have been unsuccessful so far. Only bariatric surgical treatments have been able to achieve substantial and durable weight loss. Gastric banding and gastric bypass are used in more than 90% of bariatric operations. The proportion of each varies from greater than 95% bands in Australia, about 50/50 in Europe and USA and nearly 100% bypass in South America. The availability of follow up is a prime determinant of choice. Understanding the mechanisms of effect for the bariatric procedures is central to optimizing their effect. The traditional narrow concepts of restrictive (blocking the transit of food) and malabsorptive (preventing the absorption of food) should be discarded and the importance of induction of satiety, change of taste, diversion of chyme, neural and hormonal mediation and the effects of aversion need to be included. The primary mechanism of effect for gastric banding is the generation of a background of satiety and early post-prandial satiation via specifically structured vagal afferents at the level of the band. At five years after banding or bypass, there is typically a loss of 30-35 kg representing 50-60% of excess weight. This weight loss has been shown to be associated with major improvement or complete resolution of multiple common and serious health problems plus improvement in quality of life and in survival. Level 1 evidence supports the use of the gastric band over optimal lifestyle therapy. Randomized controlled trials has shown gastric banding to achieve better weight loss, health and quality of life than optimal lifestyle therapies for adults above a BMI of 30 and adolescents above a BMI of 35. In adults with mild to severe obesity and type 2 diabetes gastric banding leads to remission in three out of four individuals. Perioperative risk is significant with gastric bypass and late revisional procedures can be required after both procedures. Gastric banding is indicated in any adult who has a BMI over 30, has problems with their obesity and has made substantial effort to reduce their weight by lifestyle methods. Gastric bypass or biliopancreatic diversion should be considered in those with BMI greater than 35 if banding is contraindicated or has been unsuccessful.

Vagal sparing surgical technique but not stoma size affects body weight loss in rodent model of gastric bypass

BACKGROUND

The aim of this study was to evaluate whether gastric bypass with or without vagal preservation resulted in a different outcome.

METHODS

Body weight, food intake and postprandial peptide YY (PYY) and glucagon-like peptide (GLP-1) levels were compared between gastric bypass (n = 55) and sham-operated rats (n = 27) in three groups. In group 1 (n = 17), the vagal nerve was not preserved, while in group 2 the vagal nerve was preserved during gastric bypass (n = 10). In group 3, gastric bypass rats (n = 28) were randomised for either one of the two techniques.

RESULTS

Rats in which the vagal nerve was preserved during gastric bypass showed a lower body weight (p < 0.001) and reduced food intake (p < 0.001) compared to rats in which the vagal nerve was not preserved during the gastric bypass operation. Levels of PYY and GLP-1 were significantly increased after gastric bypass compared to sham-operated controls (p < 0.05), but there was no difference between gastric bypass rats with and without vagal preservation. Differences in food intake and body weight were not related to the size of the gastro-jejunostomy in gastric bypass rats. There were no signs of malabsorption or inflammation after gastric bypass.

CONCLUSION

We propose that the vagal nerve should be preserved during the gastric bypass operation as this might play an important role for the mechanisms that induce weight loss and reduce food intake in rats. In contrast, the gastro-jejunal stoma size was found to be of minor relevance.