Animal Models in Bariatric Surgery—A Review of the Surgical Techniques and Postsurgical Physiology

Bettie's travels: How pigs enable new connections between human health innovations and industrial agricultural pork production in Denmark

Drawing on ethnographic fieldwork, this paper unfolds the past and present uses of pigs that structured the emergence of a pig model of gut-hormone based appetite control, leading to the current scientific breakthrough in treatment of obesity. While the hyping of next generation medications for obesity and type 2 diabetes centers on the efficacy and profits attached to these drugs, I unfold how science embedded in this development had the in-vivo and in-vitro travels of Bettie-an obese Göttingen Minipig pig-at its heart. Tracing how she became embedded in a circuit of vitality connecting industrial agriculture and science on human health, I show how both are governed by a shared valuation of pigs' fat. Bettie's fat, however, was not to be eaten. Instead, Bettie was consumed in knowledge production. For pigs to enter this new trajectory, Bettie emerged as a promissory site for extraction of molecular information made possible by new visualization technologies and representational strategies that allowed for the coupling of human-pig physiology at the cellular level. While her travels were spurred by the hope of discovery of small molecules, Bettie allows us to grasp an important shift in science, as the insights derived from her work emphasized the importance of physiology and the environment for human obesity. In doing so, she served as a visceral model. On a larger scale, Bettie's entering science on human health reflects a recursive structure of knowledge in which the present problems with obesity and type 2 diabetes derive from the solutions to previous problems associated with alleviating hunger.

Leptin receptor deficiency impedes metabolic surgery related-weight loss through inhibition of energy expenditure in db/db mice

BACKGROUND

Roux-en-Y gastric bypass (RYGB) surgery is an effective metabolic surgery against diabetes and obesity. Clinical evidence indicates that patients with severe obesity have a poor curative effect in losing weight if they suffer from leptin or its receptor deficiency, but the underlying mechanism remains elusive. Here, we investigated the effect of leptin receptor deficiency on metabolic dysfunction in db/db mice treated by RYGB surgery.

METHODS

The db/db mice and their heterozygote control db/m mice were subjected to RYGB or sham surgery. Body weight, blood glucose, food intake and glucose tolerance were evaluated. Micro-PET/CT and histological analysis were performed to examine the glucose uptake of tissues and the fat changes in mice. The key factors in glucose and fatty acid metabolism were detected by western blot analysis.

RESULTS

Compared with the sham group, the db/db mice in the RYGB group showed more significant weight regain after surgical recovery and improvement in hyperinsulinemia and glucose tolerance. However, the total body fat and multiple organ lipid deposition of RYGB-treated db/db mice was increased. The underlying mechanism studies suggested that the activation of AMPK regulated GLUT4 to increase glucose uptake, but AMPK could not promote fatty acid oxidation through the JAK2/STAT3 pathway under leptin receptor deficiency in db/db mice.

CONCLUSION

We conclude that leptin receptor deficiency impedes the AMPK activation-mediated fat catabolism but does not affect AMPK-related glucose utilization after metabolic surgery in db/db mice. This result helps select surgical indications for patients with obesity and diabetes.

Efficacy of endoscopic gastrojejunal bypass in obese Yucatan pigs: a comparative animal study

BACKGROUND

Natural orifice transluminal endoscopy surgery (NOTES) gastrojejunal anastomosis (GJA) with duodenal exclusion (DE) could be used as a less invasive alternative to surgical gastric bypass. The aim of this study was to compare the efficacy and safety of both methods for bariatric purpose.

METHODS

This was a prospective, experimental and comparative study on 27 obese living pigs, comparing 4 groups: GJA alone (group 1, G1), GJA + DE (group 2, G2), surgical gastric bypass (group 3, G3), control group (group 4, G4). GJA was endoscopically performed, using NOTES technic and LAMS, while DE was performed surgically for limb length selection. Animals were followed for 3 months. Primary outcome included technical success and weight change, while secondary endpoints included the rate of perioperative mortality and morbidity, histological anastomosis analysis and biological analysis.

RESULTS

Technical success was 100% in each intervention group. No death related to endoscopic procedures occurred in the endoscopic groups, while early mortality (< 1 month) was 57,1% in the surgical group, all due to anastomotic dehiscence. At 3 months, compared to baseline, mean weight change was + 3,1% in G1 (p = 0,46); -14,9% in G2 (p = 0,17); +5,6% in G3 (p = 0,38) and + 25% in G4 (p = 0,029). Histopathological analysis of endoscopic GJA showed complete fusion of different layers without leak or abscess.

CONCLUSIONS

Endoscopic GJA with DE provides the efficacy of bypass on weight control in an animal model. Next steps consist of the development of devices to perform exclusively endoscopically limb length selection and DE.

The Impact of Interventional Weight Loss on Bone Marrow Adipose Tissue in People Living with Obesity and Its Connection to Bone Metabolism

This review focuses on providing physicians with insights into the complex relationship between bone marrow adipose tissue (BMAT) and bone health, in the context of weight loss through caloric restriction or metabolic and bariatric surgery (MBS), in people living with obesity (PwO). We summarize the complex relationship between BMAT and bone health, provide an overview of noninvasive imaging techniques to quantify human BMAT, and discuss clinical studies measuring BMAT in PwO before and after weight loss. The relationship between BMAT and bone is subject to variations based on factors such as age, sex, menopausal status, skeletal sites, nutritional status, and metabolic conditions. The Bone Marrow Adiposity Society (BMAS) recommends standardizing imaging protocols to increase comparability across studies and sites, they have identified both water-fat imaging (WFI) and spectroscopy (1H-MRS) as accepted standards for in vivo quantification of BMAT. Clinical studies measuring BMAT in PwO are limited and have shown contradictory results. However, BMAT tends to be higher in patients with the highest visceral adiposity, and inverse associations between BMAT and bone mineral density (BMD) have been consistently found in PwO. Furthermore, BMAT levels tend to decrease after caloric restriction-induced weight loss. Although weight loss was associated with overall fat loss, a reduction in BMAT did not always follow the changes in fat volume in other tissues. The effects of MBS on BMAT are not consistent among the studies, which is at least partly related to the differences in the study population, skeletal site, and duration of the follow-up. Overall, gastric bypass appears to decrease BMAT, particularly in patients with diabetes and postmenopausal women, whereas sleeve gastrectomy appears to increase BMAT. More research is necessary to evaluate changes in BMAT and its connection to bone metabolism, either in PwO or in cases of weight loss through caloric restriction or MBS, to better understand the role of BMAT in this context and determine the local or systemic factors involved.

Effects of bariatric surgery on drug pharmacokinetics-Preclinical studies

With the rising worldwide obesity rates, bariatric surgeries are increasing. Although the surgery offers an effective treatment option for weight loss, the procedure causes dramatic physiological and metabolic changes. Animal models in rodents provide a valuable tool for studying the systemic effects of the surgery. Since the surgery may significantly influence the pharmacokinetic properties of medications, animal studies should provide essential insight into mechanisms underlying changes in how the body handles the drug. This review summarizes research work in rodents regarding the impact of standard bariatric procedures on pharmacokinetics. A qualitative literature search was conducted via PubMed, the Cochrane Central Register of Controlled Trials (CENTRAL), and EMBASE. Studies that examined bariatric surgery's effects on drug pharmacokinetics in rodent models were included. Clinical studies and studies not involving drug interventions were excluded. A total of 15 studies were identified and assessed in this review. These studies demonstrate the possible impact of bariatric surgery on drug absorption, distribution, metabolism, excretion, and potential mechanisms. Pharmacokinetic changes exhibited in the limited pre-clinical studies highlight a need for further investigation to fully understand the impact and mechanism of bariatric surgery on drug responses.

Bariatric Surgery Associates with Nonalcoholic Steatohepatitis/Hepatocellular Carcinoma Amelioration via SPP1 Suppression

Nonalcoholic steatohepatitis (NASH) is one of the most common chronic liver diseases worldwide and no effective drugs or treatments have been approved for disease management. Recently, bariatric surgery (BS) is considered to be a novel disease-modifying therapy for NASH and liver metabolic diseases, according to clinical follow-up studies. Despite the revealment of physiopathological alterations, underlying mechanisms and key factors remain indeterminate. This study included multiple bulk RNA-sequencing datasets to investigate transcriptome variation in one-year follow-up BS and diet management (Diet) NASH patients' liver biopsies. Liver functions, fibrosis, and carcinogenesis were predicted in liver samples via hallmark-based function enrichment analysis. Key factors generated from multi-dataset comparison were further assessed with hepatocellular carcinoma (HCC) progression and prognosis. BS leads to active gene expression alterations in NASH liver in comparison to diet management (Diet). Both approaches reduce cell stress and immune response, whereas BS contributes to higher metabolic levels and lower apoptosis levels. The macrophage infiltration, adipose accumulation, and fibroblast activation were revealed to be lower in post-BS NASH livers, further demonstrating positive correlations mutually. Seven key genes (MNDA, ALOX5AP, PECAM1, SPP1, CD86, FGF21, CSTA) were screened out as potential macrophage-associated and carcinogenetic factors suppressed by BS. SPP1 was identified as a crucial factor participating in BS intervened NASH-HCC progression. This study determined that BS exerts potentially superior protective functions in NASH livers compared to diet management. SPP1 may serve as a novel factor to study the functionalities of BS on NASH patients.

Hyperglycemia remission after Roux-en-Y gastric bypass: Implicated to altered monocyte inflammatory response in type 2 diabetes rats

Hyperglycemia remission by metabolic surgery is implicated in the resolution of low-grade inflammation in type 2 diabetes mellitus (T2DM). However, whether this beneficial effect of metabolic surgery is related to improving monocyte inflammatory response remains undefined. This investigation is addressed to evaluate this relationship. For this purpose, T2DM rats were subjected to Roux-en-Y gastric bypass (RYGB) and/or monocyte depletion or splenic sympathetic denervation. Fasting blood glucose (FBG), plasma tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) were measured, and monocyte inflammatory response was assessed in vitro. The data showed that RYGB significantly reduced lipopolysaccharide (LPS)-induced release of TNF-α and IL-1β from peripheral monocytes while alleviating hyperglycemia and reducing plasma TNF-α and IL-1β levels. Hyperglycemia resulting from monocyte depletion by injection of clodronate liposomes resolved one week earlier than vehicle control after RYGB. Splenic denervation abrogated the glucose-lowering effect and decreased LPS-stimulated TNF-α and IL-1β release from monocytes following RYGB. Overall, our results reveal that a marked reduction of monocyte inflammatory response after RYGB contributes to hyperglycemia remission in T2DM rats. The beneficial effect of RYGB is mediated through vagal-spleen axis anti-inflammatory activity.

Metabolomics in Bariatric and Metabolic Surgery Research and the Potential of Deep Learning in Bridging the Gap

During the past several years, there has been a shift in terminology from bariatric surgery alone to bariatric and metabolic surgery (BMS). More than a change in name, this signifies a paradigm shift that incorporates the metabolic effects of operations performed for weight loss and the amelioration of related medical problems. Metabolomics is a relatively novel concept in the field of bariatrics, with some consistent changes in metabolite concentrations before and after weight loss. However, the abundance of metabolites is not easy to handle. This is where artificial intelligence, and more specifically deep learning, would aid in revealing hidden relationships and would help the clinician in the decision-making process of patient selection in an individualized way.

A nonhuman primate model of vertical sleeve gastrectomy facilitates mechanistic and translational research in human obesity

The obesity epidemic significantly contributes to overall morbidity and mortality. Bariatric surgery is the gold standard treatment for obesity and metabolic dysfunction, yet the mechanisms by which it exerts metabolic benefit remain unclear. Here, we demonstrate a model of vertical sleeve gastrectomy (VSG) in nonhuman primates (NHP) that mimics the complexity and outcomes in humans. We also show that VSG confers weight loss and durable metabolic benefit, where equivalent caloric intake in shams resulted in significant weight gain following surgery. Furthermore, we show that VSG is associated with early, weight-independent increases in bile acids, short-chain fatty acids, and reduced visceral adipose tissue (VAT) inflammation with a polarization of VAT-resident immunocytes toward highly regulatory myeloid cells and Tregs. These data demonstrate that this strongly translational NHP model can be used to interrogate factors driving successful intervention to unravel the interplay between physiologic systems and improve therapies for obesity and metabolic syndrome.

The Role of Positron Emission Tomography in Bariatric Surgery Research: a Review

Bariatric surgery, initially understood as restricting or bypassing the amount of food that reaches the stomach to reduce food intake and/or increase malabsorption of food to promote weight loss, is now recognized to also affect incretin signaling in the gut and promote improvements in system-wide metabolism. Positron emission tomography (PET) is an imaging technique whereby patients are injected with picomolar concentrations of radioactive molecules, below the threshold of having physiological effects, to measure spatial distributions of blood flow, metabolism, receptor, and enzyme pharmacology. Recent advances in both whole-body PET imaging and radioligand development will allow for novel research that may help clarify the roles of peripheral and central receptor/enzyme systems in treating obesity with bariatric surgery.

Mining Gut Microbiota From Bariatric Surgery for MAFLD

The progression of metabolic dysfunction associated fatty liver disease (MAFLD) leads to steatohepatitis, liver fibrosis and hepatocellular carcinoma. Thus far, there have been no FDA-approved medications for MAFLD. Bariatric surgery (BS) has been found to improve insulin resistance, steatohepatitis and liver fibrosis but is not recommended for treating MAFLD due to its invasiveness. Recent studies suggest the improved glucose metabolism after BS is a result of, at least partly, alterations to the gut microbiota and its associated metabolites, including short chain fatty acids and bile acids. It makes sense the improved steatohepatitis and fibrosis after BS are also induced by the gut microbiota that involves in host metabolic modulation, for example, through altering bile acids composition. Given that the gut-liver axis is a path that may harbor unexplored mechanisms behind MAFLD, we review current literatures about disentangling the metabolic benefits of MAFLD after BS, with a focus on gut microbiota. Some useful research tools including the rodent BS model, the multiomics approach, and the human microbiota associated (HMA) mice are presented and discussed. We believe, by taking advantage of these modern translational tools, researchers will uncover microbiota related pathways to serve as potential therapeutic targets for treating MAFLD.

Use of an intragastric balloon for management of obesity in a dog

While various bariatric surgeries are commonplace in obesity medicine for humans, these techniques have not been commonly used in veterinary medicine. A technique used in humans consists in endoscopically placing an intragastric balloon. The intragastric balloon takes volume in the stomach causing a feeling of satiety and reducing food intake. A 57.6 kg, 9-year-old neutered female Labrador dog with chronic hypothyroidism was presented for overweight management. Combined levothyroxine treatment and dietary management with specific alimentation for obesity had failed to control overweight. An intragastric balloon was placed endoscopically in the stomach to allow the reduction of the gastric capacity and resulted in effective weight loss. The dog weight decreased to 40.9 kg at the time of intragastric balloon removal 198 days after placement. Further research including a larger sample size and long term follow-up is required to establish safety and effectiveness of this procedure.

Review: Impact of food, gut-brain signals and metabolic status on brain activity in the pig model: 10 years of nutrition research using in vivo brain imaging

The purpose of this review is to offer a panorama on 10 years of nutrition research using in vivo brain imaging in the pig model. First, we will review some work describing the brain responses to food signals, including basic tastants such as sweet and bitter at both oral and visceral levels, as well as conditioned preferred and aversive flavours. Second, we will have a look at the impact of weight gain and obesity on brain metabolism and functional responses, drawing the parallel with obese human patients. Third, we will evoke the concept of the developmental origins of health and diseases, and how the pig model can shed light on the importance of maternal nutrition during gestation and lactation for the development of the gut-brain axis and adaptation abilities of the progeny to nutritional environments. Finally, three examples of preventive or therapeutic strategies will be introduced: the use of sensory food ingredients or pre-, pro-, and postbiotics to improve metabolic and cognitive functions; the implementation of chronic vagus nerve stimulation to prevent weight gain and glucose metabolism alterations; and the development of bariatric surgery in the pig model for the understanding of its complex mechanisms at the gut-brain level. A critical conclusion will brush the limitations of neurocognitive studies in the pig model and put in perspective the rationale and ethical concerns underlying the use of pig experimentation in nutrition and neurosciences.

Modelos animais na síndrome metabólica

RESUMO O conhecimento sobre modelos animais para estudo metabólico representa a base da pesquisa nessa área. Este trabalho tem por objetivo revisar os principais modelos animais a serem utilizados no estudo da obesidade e da síndrome metabólica. Para isso, pesquisa no banco de dados Pubmed foi realizada usando as palavras-chave “animal models”, “obesity”, "metabolic syndrome”, e “bariatric surgery”. Várias espécies de animais podem ser usadas para o estudo de distúrbios metabólicos, no entanto, os roedores, tanto modelos monogênicos quanto modelos de obesidade induzida por dieta (DIO), são os animais mais utilizados nessa área. Animais monogênicos são a melhor escolha se apenas um aspecto estiver sendo avaliado. Animais DIO tendem a demonstrar melhor a interação entre doença, ambiente e gene. No entanto, eles ainda não são totalmente eficazes para a compreensão de todos os mecanismos dessa doença.

Greater curvature as a gastric pouch for sleeve gastrectomy: a novel bariatric procedure. Feasibility study in a canine model

BACKGROUND

Laparoscopic sleeve gastrectomy (LSG) has serious complications, such as leaks, reflux, stenosis, and kinks, which are also consequences of shortcomings in the LSG technique.

OBJECTIVES

We evaluated the feasibility and weight loss of a novel bariatric procedure, using the greater curvature as the gastric pouch for sleeve gastrectomy (SG) in dogs.

SETTING

Animal house in Faculty of Medicine, Cairo University.

METHODS

Five 20- to 25-kg stray mongrel male dogs were subjected to open SG using the greater curve as the gastric pouch (GCSG group). The weight was monitored at day of surgery and at postoperative weeks 2, 4, 6, and 8; weight progression was compared with a sham and a standard SG group. By the end of the follow-up period autopsy was done.

RESULTS

The mean operative time in GCSG group was 39.6 ± 3.97 minutes. At the end of the study, dogs in the sham group had gained 8% of their preoperative weight, while the GCSG and standard SG groups lost 24.7% and 25% of their preoperative weight, respectively. At autopsy, the gastric sleeve in the GCSG group showed excellent healing with no stenotic areas, kinks, or mucosal ulcerations.

CONCLUSION

Greater curvature SG is technically feasible in a canine model. Larger studies with longer follow-up period will be needed to assess weight progression and resolution of the metabolic co-morbidities.

Gastric mucosal devitalization is safe and effective in reducing body weight and visceral adiposity in a porcine model

BACKGROUND AND AIMS

The early improvement in metabolic profile after sleeve gastrectomy (SG) indicates that the significant benefits of metabolic surgery are gastric in origin. We have previously demonstrated that devitalization of the gastric mucosa (without a reduction in gastric volume) in metabolically disturbed obese rats results in an improvement of obesity and its associated comorbidities. The aims of this study were to assess the technical feasibility, efficacy, and safety of gastric mucosal devitalization (GMD) in a large animal (porcine) model.

METHODS

A 3-arm (GMD versus SG versus sham [SH]) prospective randomized controlled trial with an 8-week follow-up period was performed. The primary endpoint was relative weight loss. Secondary endpoints were absolute body weight, abdominal visceral adiposity, abdominal subcutaneous adiposity, organ lipid content, and serum ghrelin level.

RESULTS

GMD resulted in a significant relative weight loss of 36% over SH at 8 weeks (P < .05). There was no significant difference in relative weight loss between GMD and SG at 4 weeks; however, SG resulted in a 29% superior relative weight loss at 8 weeks (P < .05). With regard to visceral adiposity, there was a significant benefit of GMD over SH at 8 weeks. Despite differences in relative weight loss, there was no significant difference in visceral adiposity between SG and GMD at 8 weeks. Significant improvements in GMD over SH were noted with regard to skeletal and heart muscle lipid content. GMD pigs at 8 weeks demonstrated regeneration of the gastric mucosa without ulceration or significant scarring. Despite mucosal regeneration, the abundance of serum ghrelin was significantly lower in the GMD cohort compared with the SG and SH cohorts.

CONCLUSIONS

GMD was technically feasible and resulted in relative weight loss and an improvement in visceral adiposity. The benefits noted were out of proportion to what would be expected with weight loss alone.

Development of murine bariatric surgery models: lessons learned

Roux-en-Y gastric bypass (RYGB) improves comorbidities such as diabetes and hypertension and lowers the risk of obesity-related cancers. To better understand the physiologic and genetic influences of bariatric surgery, a reliable murine model is needed that can be extended to genetically engineered mice. Given the complexity of these procedures, few researchers have successfully implemented these techniques beyond larger rodent models. The purpose of our study was to develop a technically feasible and reproducible murine model for RYGB and sleeve gastrectomy (SG). Mice were converted to liquid diet perioperatively without fasting and housed in groups on raised wire platforms. SG involved significant reduction of stomach volume followed by multilayer repair of the gastrotomy. RYGB procedure consisted of side-to-side, functional end-to-side bowel anastomoses and exclusion of the stomach medial to the gastroesophageal junction. Sham surgeries consisted of enterotomies and gastrotomy followed by primary repair without resection or rerouting. Survival after incorporation of the aforementioned techniques was 100% in the SG group and 41% in the RYGB group at 1 mo after surgery. Only 26% of RYGB mortality was attributed to leak, obstruction, or stricture; the majority of postoperative mortality was due to stress, dumping, or malnutrition. Much of the survival challenge for this surgical model was related to perioperative husbandry, which is to be expected given their small stature and poor response to stress. Utilization of the perioperative and surgical techniques described will increase survival and feasibility of these technically challenging procedures, allowing for a better understanding of mechanisms to explain the beneficial effects of bariatric surgery.

A Large Animal Survival Model to Evaluate Bariatric Surgery Mechanisms

Background

The impact of Roux-en-Y gastric bypass (RYGB) on type 2 diabetes mellitus is thought to result from upper and/or lower gut hormone alterations. Evidence supporting these mechanisms is incomplete, in part because of limitations in relevant bariatric-surgery animal models, specifically the lack of naturally insulin-resistant large animals. With overfeeding, Ossabaw swine develop a robust metabolic syndrome, and may be suitable for studying post-surgical physiology. Whether bariatric surgery is feasible in these animals with acceptable survival is unknown.

Methods

Thirty-two Ossabaws were fed a high-fat, high-cholesterol diet to induce obesity and insulin resistance. These animals were assigned to RYGB (n = 8), RYGB with vagotomy (RYGB-V, n = 5), gastrojejunostomy (GJ, n = 10), GJ with duodenal exclusion (GJD, n = 7), or sham operation (n = 2) and were euthanized 60 days post-operatively. Post-operative changes in weight and food intake are reported.

Results

Survival to scheduled necropsy among surgical groups was 77%, living an average of 57 days post-operatively. Cardiac arrest under anesthesia occurred in 4 pigs. Greatest weight loss (18.0% ± 6%) and food intake decrease (57.0% ± 20%) occurred following RYGB while animals undergoing RYGB-V showed only 6.6% ± 3% weight loss despite 50.8% ± 25% food intake decrease. GJ (12.7% ± 4%) and GJD (1.2% ± 1%) pigs gained weight, but less than sham controls (13.4% ± 10%).

Conclusions

A survival model of metabolic surgical procedures is feasible, leads to significant weight loss, and provides the opportunity to evaluate new interventions and subtle variations in surgical technique (e.g. vagus nerve sparing) that may provide new mechanistic insights.

Cortical and trabecular deterioration in mouse models of Roux-en-Y gastric bypass

Roux-en-Y gastric bypass (RYGB) is a profoundly effective treatment for severe obesity, but results in significant bone loss in patients. Developing a murine model that recapitulates this skeletal phenotype will provide a robust tool with which to study the physiologic mechanisms of this bone loss. We studied adult male C57BL/6J mice who underwent either RYGB or sham operation. Twelve weeks after surgery, we characterized biochemical bone markers (parathyroid hormone, PTH; C-telopeptide, CTX; and type 1 procollagen, P1NP) and bone microarchitectural parameters as measured by microcomputed tomography. RYGB-treated mice had significant trabecular and cortical bone deficits compared with sham-operated controls. Although adjustment for final body weight eliminated observed cortical differences, the trabecular bone volume fraction remained significantly lower in RYGB mice even after weight adjustment. PTH levels were similar between groups, but RYGB mice had significantly higher indices of bone turnover than sham controls. These data demonstrate that murine models of RYGB recapitulate patterns of bone loss and turnover that have been observed in human clinical studies. Future studies that exploit this murine model will help delineate the alterations in bone metabolism and mechanisms of bone loss after RYGB.

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.

Bone metabolism after bariatric surgery

Bariatric surgery is a popular and effective treatment for severe obesity but may have negative effects on the skeleton. This review summarizes changes in bone density and bone metabolism from animal and clinical studies of bariatric surgery, with specific attention to Roux-en-Y gastric bypass (RYGB), adjustable gastric banding (AGB), and sleeve gastrectomy (SG). Skeletal imaging artifacts from obesity and weight loss are also considered. Despite challenges in bone density imaging, the preponderance of evidence suggests that bariatric surgery procedures have negative skeletal effects that persist beyond the first year of surgery, and that these effects vary by surgical type. The long-term clinical implications and current clinical recommendations are presented. Further study is required to determine mechanisms of bone loss after bariatric surgery. Although early studies focused on calcium/vitamin D metabolism and mechanical unloading of the skeleton, it seems likely that surgically induced changes in the hormonal and metabolic profile may be responsible for the skeletal phenotypes observed after bariatric surgery.

Sleeve gastrectomy and Roux-en-Y gastric bypass exhibit differential effects on food preferences, nutrient absorption and energy expenditure in obese rats

OBJECTIVE

All available treatments directed towards obesity and obesity-related complications are associated with suboptimal effectiveness/invasiveness ratios. Pharmacological, behavioral and lifestyle modification treatments are the least invasive, but also the least effective options, leading to modest weight loss that is difficult to maintain long-term. Gastrointestinal weight loss surgery (GIWLS) is the most effective, leading to >60-70% of excess body weight loss, but also the most invasive treatment available. Sleeve gastrectomy (SGx) and Roux-en-Y gastric bypass (RYGB) are the two most commonly performed GIWLS procedures. The fundamental anatomic difference between SGx and RYGB is that in the former procedure, only the anatomy of the stomach is altered, without surgical reconfiguration of the intestine. Therefore, comparing these two operations provides a unique opportunity to study the ways that different parts of the gastrointestinal (GI) tract contribute to the regulation of physiological processes, such as the regulation of body weight, food intake and metabolism.

DESIGN

To explore the physiologic mechanisms of the two procedures, we used rodent models of SGx and RYGB to study the effects of these procedures on body weight, food intake and metabolic function.

RESULTS

Both SGx and RYGB induced a significant weight loss that was sustained over the entire study period. SGx-induced weight loss was slightly lower compared with that observed after RYGB. SGx-induced weight loss primarily resulted from a substantial decrease in food intake and a small increase in locomotor activity. In contrast, rats that underwent RYGB exhibited a substantial increase in non-activity-related (resting) energy expenditure and a modest decrease in nutrient absorption. Additionally, while SGx-treated animals retained their preoperative food preferences, RYGB-treated rats experienced a significant alteration in their food preferences.

CONCLUSIONS

These results indicate a fundamental difference in the mechanisms of weight loss between SGx and RYGB, suggesting that the manipulation of different parts of the GI tract may lead to different physiologic effects. Understanding the differences in the physiologic mechanisms of action of these effective treatment options could help us develop less invasive new treatments against obesity and obesity-related complications.

Bariatric surgery and the central nervous system

Bariatric procedures are now known to have an effect on hunger as well as on metabolism. The role of central nervous pathways in causing these effects after bariatric surgery is now being elucidated. A brief overview of these pathways has been presented for the sake of bariatric surgeons. A PubMed search was made using various search phrases to retrieve all original articles concerning the effect of bariatric surgery on the neural pathways. The mechanisms regulating the food intake and energy expenditure can be broadly divided into homeostatic and hedonic systems. The effect of bariatric surgery on the homeostatic system in animal models is not clear. A decrease in preference for sweet taste and high calorie foods has been demonstrated in animal models. The effect of bariatric surgery on the hedonic system in humans has been consistent with decreased activation of the hedonic system being demonstrated by functional MRI and decreased preference for intake of high energy foods also being observed post-surgery. The effect of bariatric surgery on dopamine signaling, which is involved in the hedonic system, is however not clear. Functional MRI studies have also demonstrated increased activation of the hypothalamus after surgery. Various studies utilizing questionnaires have demonstrated increased satiety and decreased hunger after bariatric surgery.

Roux-en-Y gastric bypass operation in rats

Currently, the most effective therapy for the treatment of morbid obesity to induce significant and maintained body weight loss with a proven mortality benefit is bariatric surgery. Consequently, there has been a steady rise in the number of bariatric operations done worldwide in recent years with the Roux-en-Y gastric bypass (gastric bypass) being the most commonly performed operation. Against this background, it is important to understand the physiological mechanisms by which gastric bypass induces and maintains body weight loss. These mechanisms are yet not fully understood, but may include reduced hunger and increased satiation, increased energy expenditure, altered preference for food high in fat and sugar, altered salt and water handling of the kidney as well as alterations in gut microbiota. Such changes seen after gastric bypass may at least partly stem from how the surgery alters the hormonal milieu because gastric bypass increases the postprandial release of peptide-YY (PYY) and glucagon-like-peptide-1 (GLP-1), hormones that are released by the gut in the presence of nutrients and that reduce eating. During the last two decades numerous studies using rats have been carried out to further investigate physiological changes after gastric bypass. The gastric bypass rat model has proven to be a valuable experimental tool not least as it closely mimics the time profile and magnitude of human weight loss, but also allows researchers to control and manipulate critical anatomic and physiologic factors including the use of appropriate controls. Consequently, there is a wide array of rat gastric bypass models available in the literature reviewed elsewhere in more detail. The description of the exact surgical technique of these models varies widely and differs e.g. in terms of pouch size, limb lengths, and the preservation of the vagal nerve. If reported, mortality rates seem to range from 0 to 35%. Furthermore, surgery has been carried out almost 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 the comparison and identification of potential physiological mechanisms involved in gastric bypass. 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. This article therefore aims to summarize and discuss technical and experimental details of our previously validated and published gastric bypass rat model.

Sleeve gastrectomy induces weight loss in diet-induced obese rats even if high-fat feeding is continued

BACKGROUND

Sleeve gastrectomy (SG) has been used for the surgical treatment of morbid obesity as a first or definitive procedure with satisfactory results. The objective of this study in rats was to establish the effects of SG on weight loss depending on the post-surgical type of diet followed.

METHODS

Thirty male Wistar rats were fed ad libitum during 3 months on a high-fat diet (HFD) to induce obesity. After this first phase, rats were subdivided in three groups of ten rats each and underwent a sham intervention, an SG, or no surgery but were pair-fed to the amount of food eaten by the animals of the SG group. At this time point, half of the animals in each group continued to be fed on the HFD, while the other half was switched to a normal chow diet (ND). Thus, the following subgroups were established: sham-ND, sleeve-ND, pair-fed-ND as well as sham-HFD, sleeve-HFD, and pair-fed-HFD. Body weight and food intake were recorded daily for 4 weeks. The feed efficiency rate (FER) was determined from weekly weight gains and caloric consumption during this period.

RESULTS

Statistically significant (P < 0.05) differences in body weight were observed between the six experimental groups after 4 weeks of the interventions with rats in the sleeve-ND group experimenting the highest weight loss (-78.2 ± 10.3 g) and animals in the pair-fed-HFD group exhibiting the lowest weight reduction (-4.0 ± 0.1 g). Interestingly, the FER value of rats that underwent the SG and continued to be fed on a HFD was significantly (P < 0.05) lower than that of sham operated and pair-fed animals on the same diet.

CONCLUSION

The positive effects of SG on weight reduction are observed in obese rats submitted to the intervention and subsequently following an ND or even an HFD.

Probing the mechanisms of the metabolic effects of weight loss surgery in humans using a novel mouse model system

BACKGROUND

Gastrointestinal weight loss surgery, especially Roux-en-Y gastric bypass (RYGB), is the most effective treatment for severe obesity. RYGB is associated with a remarkable decrease in the rate of death from obesity-related complications, such as diabetes mellitus, coronary artery disease, and cancer. Dissecting the mechanisms of RYGB effects could augment our understanding about the pathogenesis of obesity and its complications.

OBJECTIVES AND METHODS

In this study, we describe in detail a mouse model of RYGB that closely reproduces the surgical steps of the human procedure.

RESULTS

We show that RYGB in mice has the same effects as in human patients, proving the high translational validity of this model system. We present an intraoperative video to facilitate the widespread use of this complex and difficult method.

CONCLUSIONS

The study of the mechanisms of RYGB using this model system can greatly facilitate our understanding about the effects of RYGB in human patients. The reverse engineering of the physiological mechanisms of RYGB could lead to discovery of new, effective, and less invasive treatments.

Challenges and pitfalls of experimental bariatric procedures in rats

INTRODUCTION

The impact of Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) on obesity and obesity-related diseases is unquestionable. Up to now, the technical descriptions of these techniques in animals/rats have not been very comprehensive.

METHODS

For SG and RYGB, operating time, learning curve, and intraoperative mortality in relation to weight of the rat and type of anesthesia were recorded. Furthermore, a review of the literature on experimental approaches towards SG and RYGB in rats was carried out, merging in a detailed technical description for both procedures.

RESULTS

The data presented here revealed that the mean operating time for SG (69.4 ± 22.2 min (SD)) was shorter than for RYGB (123.0 ± 20.7 min). There is a learning curve for both procedures, resulting in a reduced operating time of up to 60% in SG and 35% in RYGB (p < 0.05; t-test). However, with increased weight, operating time increases to about 80 min for SG and about 120 min for RYGB. Obese rats have an increased intraoperative mortality rate of up to 50%. After gaseous anesthesia the mortality can be even higher. The literature search revealed 40 papers dealing with SG and RYGB in rats. 18 articles (45%) contained neither photographs nor illustrations; 14 articles (35%) did not mention the applied type of anesthesia. The mortality rate was described in 15 papers (37.5%).

CONCLUSION

Experimental obesity surgery in rats is challenging. Because of the high mortality in obese rats operated under gaseous anesthesia, exercises to establish the techniques should be performed in small rats using intraperitoneal anesthesia.

Bariatric surgery reduces visceral adipose inflammation and improves endothelial function in type 2 diabetic mice

OBJECTIVE

Bariatric surgery is emerging as an effective method to alleviate a multitude of medical conditions associated with morbid obesity and type 2 diabetes. However, little is known about the effects and mechanisms of bariatric surgery on visceral fat inflammation and endothelial dysfunction in type 2 diabetes. We hypothesize that bariatric surgery ameliorates interferon-γ-mediated adipose tissue inflammation/oxidative stress and improves endothelial function in type 2 diabetic mice.

METHODS AND RESULTS

Control mice (m Lepr(db)) and diabetic mice (Lepr(db)) were treated with either sham surgery or improved gastric bypass surgery and then were evaluated at 5, 10, 20, and 30 days to assess postsurgical effects. Surgery reduced body weight, abdominal adiposity, blood glucose level, and food intake in Lepr(db). The surgery-induced decrease in visceral adiposity was accompanied by amelioration of T-lymphocytes and macrophage infiltration, as well as reduction in the expression of interferon-γ and other inflammatory cytokines in the mesenteric adipose tissue (MAT) of Lepr(db) mice. Furthermore, surgery improved endothelium-dependent, but not endothelium-independent, vasorelaxation in small mesenteric arteries (SMA) of Lepr(db) mice. The improvement in endothelial function was largely attenuated by nitric oxide synthase inhibitor (L-NAME) incubation. Interferon-γ treatment increased the mRNA expression of tumor necrosis factor-α in the MAT of control mice and incubation of SMA of control mice with tumor necrosis factor-α caused impairment of endothelial function. Superoxide production in MAT/SMA and nitrotyrosine protein level in SMA were elevated in diabetic mice. Surgery reduced MAT/SMA oxidative stress in Lepr(db) mice.

CONCLUSIONS

The amelioration of adipose tissue inflammation and the improvement of endothelial function may represent important mechanisms that result in cardiovascular benefits after bariatric surgery.