Mechanisms underlying weight loss and metabolic improvements in rodent models of bariatric surgery

Vertical sleeve gastrectomy and semaglutide have distinct effects on skeletal health and heart function in obese male mice

Obesity is a global health challenge associated with significant metabolic and cardiovascular risks. Bariatric surgery and glucagon-like peptide-1 (GLP-1) receptor agonists (GLP-1RAs) are effective interventions for weight loss and metabolic improvement, yet their comparative effects on systemic metabolism-particularly energy metabolism, bone health, and heart function-remain unclear. In this study, obese male mice underwent vertical sleeve gastrectomy (VSG), 6 wk of GLP-1RA (semaglutide) treatment, or sham procedure with saline injection as controls. Dynamic changes in body weight, food intake, fat mass, lean mass, and bone mineral density were monitored. Energy metabolism was assessed using indirect calorimetry. Bone parameters and heart function were evaluated by microcomputed tomography or echocardiography, respectively. Compared with obese controls, VSG and semaglutide treatment comparably reduced body weight and improved glucose metabolism. However, VSG decreased energy expenditure, whereas both treatments similarly promoted lipid utilization. Semaglutide treatment increased ambulatory activity during nighttime. VSG led to significant bone loss, although 6 wk of semaglutide treatment had no significant effects on the skeleton. Cardiovascular outcomes also differed: VSG increased stroke volume without altering heart mass, whereas semaglutide reduced heart mass and transiently elevated heart rate. These findings underscore the importance of carefully weighing the benefits and potential risks of different weight loss treatments when addressing obesity and its systemic complications.NEW & NOTEWORTHY Comparative studies of surgical and pharmaceutical approaches to weight loss offer critical insights that can guide clinical decision-making for managing obesity. VSG and semaglutide exhibit comparable efficacy in promoting weight reduction and improving glucose metabolism. VSG reduces energy expenditure, whereas semaglutide increases animal activity during nighttime. VSG leads to significant bone loss, whereas semaglutide preserves bone mass independent of weight loss. VSG improves cardiac outcomes, whereas semaglutide transiently affects heart function.

Intestinal epithelial cell NCoR deficiency ameliorates obesity and metabolic syndrome

Nuclear receptor corepressor (NCoR1) interacts with various nuclear receptors and regulates the anabolism and catabolism of lipids. An imbalance in lipid/energy homeostasis is also an important factor in obesity and metabolic syndrome development. In this study, we found that the deletion of NCoR1 in intestinal epithelial cells (IECs) mainly activated the nuclear receptor PPARα and attenuated metabolic syndrome by stimulating thermogenesis. The increase in brown adipose tissue thermogenesis was mediated by gut-derived tricarboxylic acid cycle intermediate succinate, whose production was significantly enhanced by PPARα activation in the fed state. Additionally, NCoR1 deletion derepressed intestinal LXR, increased cholesterol excretion, and impaired duodenal lipid absorption by decreasing bile acid hydrophobicity, thereby reversing the possible negative effects of intestinal PPARα activation. Therefore, the simultaneous regulatory effect of intestinal NCoR1 on both lipid intake and energy expenditure strongly suggests that it is a promising target for developing metabolic syndrome treatment.

Inhibition of somatostatin enhances the long-term metabolic outcomes of sleeve gastrectomy in mice

OBJECTIVE

Bariatric surgery is an effective treatment to obesity, leading to weight loss and improvement in glycemia, that is characterized by hypersecretion of gastrointestinal hormones. However, weight regain and relapse of hyperglycemia are not uncommon. We set to identify mechanisms that can enhance gastrointestinal hormonal secretion following surgery to sustain weight loss.

METHODS

We investigated the effect of somatostatin (Sst) inhibition on the outcomes of bariatric surgery using a mouse model of sleeve gastrectomy (SG).

RESULTS

Sst knockout (sst-ko) mice fed with a calorie-rich diet gained weight normally and had a mild favorable metabolic phenotype compared to heterozygous sibling controls, including elevated plasma levels of GLP-1. Mathematical modeling of the feedback inhibition between Sst and GLP-1 showed that Sst exerts its maximal effect on GLP-1 under conditions of high hormonal stimulation, such as following SG. Obese sst-ko mice that underwent SG had higher levels of GLP-1 compared with heterozygous SG-operated controls. The SG-sst-ko mice regained less weight than controls and maintained lower glycemia months after surgery. Obese wild-type mice that underwent SG and were treated daily with a Sst receptor inhibitor for two months had higher GLP-1 levels, regained less weight, and improved metabolic profile compared to saline-treated SG-operated controls, and compared to inhibitor or saline-treated sham-operated obese mice.

CONCLUSIONS

Our results suggest that inhibition of Sst signaling enhances the long-term favorable metabolic outcomes of bariatric surgery.

Bariatric Surgery as Treatment Strategy of Obesity in Saudi People: Effects of Gut Microbiota

Obesity prevalence is rising globally, as are the number of chronic disorders connected with obesity, such as diabetes, non-alcoholic fatty liver disease, dyslipidemia, and hypertension. Bariatric surgery is also becoming more common, and it remains the most effective and long-term treatment for obesity. This study will assess the influence of Laparoscopic Sleeve Gastrectomy (LSG) on gut microbiota in people with obesity before and after surgery. The findings shed new light on the changes in gut microbiota in Saudi people with obesity following LSG. In conclusion, LSG may improve the metabolic profile, resulting in decreased fat mass and increased lean mass, as well as improving the microbial composition balance in the gastrointestinal tract, but this is still not equivalent to normal weight microbiology. A range of factors, including patient characteristics, geographic dispersion, type of operation, technique, and nutritional and caloric restriction, could explain differences in abundance between studies. This information could point to a novel and, most likely, tailored strategy in obesity therapy, which could eventually be incorporated into health evaluations and monitoring in preventive health care or clinical medicine.

Sleeve Gastrectomy Reduces Glycemia but Does Not Affect Cognitive Impairment in Lean 5xFAD Mice

Obesity and hyperglycemia are risk factors for cognitive decline and for the development of Alzheimer’s Disease (AD). Bariatric surgery is an effective treatment for obesity that was shown to improve cognitive decline in obese patients. Bariatric surgery was shown to exert weight loss independent effects on metabolic diseases such as type 2 diabetes. We tested whether sleeve gastrectomy (SG), a common bariatric surgery, can affect the cognitive impairment in lean, normoglycemic female 5xFAD mice, a genetic model for AD. 5xFAD mice and wild-type (WT) littermates underwent SG or sham surgery at the age of 5 months and were tested for metabolic, behavioral, and molecular phenotypes 90 days later. SG led to a reduction in blood glucose levels and total plasma cholesterol levels in 5xFAD mice without inducing weight loss. However, the surgery did not affect the outcomes of long-term spatial memory tests in these mice. Analysis of β-Amyloid plaques corroborated the behavioral studies in showing no effect of surgery on the molecular phenotype of 5xFAD mice. In conclusion, SG leads to an improved metabolic profile in lean female 5xFAD mice without inducing weight loss but does not affect the brain pathology or behavioral phenotype. Our results suggest that the positive effects of bariatric surgery on cognitive decline in obese patients are likely attributed to weight loss and improvement in obesity sequelae, and not to weight loss independent effects of surgery.

The Obesogenic and Glycemic Effect of Bariatric Surgery in a Family with a Melanocortin 4 Receptor Loss-of-Function Mutation

We report the long-term response to bariatric surgery in a singular family of four adolescents with severe obesity (41–82 kg/m2), homozygous for the C271R loss-of-function mutation in the melanocortin 4 receptor (MC4R), and three adults heterozygous for the same mutation. All patients had similar sociodemographic backgrounds and were followed for an average of 7 years. Three of the four homozygous patients regained their full weight (42–77 kg/m2), while the fourth lost weight but remained obese with a body mass index of 60 kg/m2. Weight regain was associated with relapse of most comorbidities, yet hyperglycemia did not relapse or was delayed. A1c levels were reduced in homozygous and heterozygous patients. The long-term follow-up data on this very unique genetic setting show that weight loss and amelioration of obesity following bariatric surgery require active MC4R signaling, while the improvement in glycemia is in part independent of weight loss. The study validates animal models and demonstrates the importance of biological signaling in the regulation of weight, even after bariatric surgery.

Generation and characterization of a mouse model for one anastomosis gastric bypass surgery

One anastomosis gastric bypass (OAGB) surgery became a common bariatric procedure in recent years. In this surgery, the distal stomach, duodenum, and proximal jejunum are bypassed, leading to weight loss, improvement in metabolic parameters, and a change in hormonal secretion. We sought to generate and characterize a mouse model for OAGB. Mice fed for 26 wk on a high-fat diet were assigned to OAGB, sham surgery, or caloric restriction and were followed for 50 more days on a high-fat diet. Physiological and histological parameters of the mice were compared during and at the end of the experiment. OAGB-operated mice lost weight and displayed low levels of plasma lipids, high insulin sensitivity, and rapid glucose metabolism compared with sham-operated mice. OAGB-operated mice had higher energy expenditure, higher levels of glucagon-like peptide (GLP-1), and lower albumin than weight-matched calorie-restricted mice. There was no difference in the histology of the endocrine pancreas. The livers of OAGB mice had little hepatic steatosis yet presented with a large number of phagocytic cells. The OAGB mouse model recapitulates many of the phenotypes described in patients that underwent OAGB and enables molecular and physiological studies on the outcome of this surgery.NEW & NOTEWORTHY A mouse model for one anastomosis gastric bypass (OAGB) surgery displays similar outcomes to clinical reports and enables to study the weight loss-dependent and -independent effects of this bariatric surgery.

Internal senses of the vagus nerve

The vagus nerve is an indispensable body-brain connection that controls vital aspects of autonomic physiology like breathing, heart rate, blood pressure, and gut motility, reflexes like coughing and swallowing, and survival behaviors like feeding, drinking, and sickness responses. Classical physiological studies and recent molecular/genetic approaches have revealed a tremendous diversity of vagal sensory neuron types that innervate different internal organs, with many cell types remaining poorly understood. Here, we review the state of knowledge related to vagal sensory neurons that innervate the respiratory, cardiovascular, and digestive systems. We focus on cell types and their response properties, physiological/behavioral roles, engaged neural circuits and, when possible, sensory receptors. We are only beginning to understand the signal transduction mechanisms used by vagal sensory neurons and upstream sentinel cells, and future studies are needed to advance the field of interoception to the level of mechanistic understanding previously achieved for our external senses.

Hypoglycemia and Dysautonomia After Bariatric Surgery: a Systematic Review and Perspective

INTRODUCTION

With the increasing performance of bariatric surgery, rare complications are becoming prevalent. We review the diagnosis and treatment of dysautonomia after bariatric surgery and the limited treatment options available. We summarize the suggested mechanisms and explain why a complete understanding of the etiology has yet to be determined.

METHODS

In accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a systematic review was performed.

RESULTS

Of 448 studies identified in the literature search, 4 studies were reviewed, describing 87 patients diagnosed with dysautonomia. We present a patient who developed severe dysautonomia following conversion of sleeve gastrectomy to gastric bypass.

CONCLUSION

Treatment needs to focus on optimizing nutrition, avoiding hypoglycemia, and optimizing volume status.

Sleeve Gastrectomy Suppresses Hepatic Glucose Production and Increases Hepatic Insulin Clearance Independent of Weight Loss

Bariatric operations induce weight loss, which is associated with an improvement in hepatic steatosis and a reduction in hepatic glucose production. It is not clear whether these outcomes are entirely due to weight loss, or whether the new anatomy imposed by the surgery contributes to the improvement in the metabolic function of the liver. We performed vertical sleeve gastrectomy (VSG) on obese mice provided with a high-fat high-sucrose diet and compared them to diet and weight-matched sham-operated mice (WMS). At 40 days after surgery, VSG-operated mice displayed less hepatic steatosis compared with WMS. By measuring the fasting glucose and insulin levels in the blood vessels feeding and draining the liver, we showed directly that hepatic glucose production was suppressed after VSG. Insulin levels were elevated in the portal vein, and hepatic insulin clearance was elevated in VSG-operated mice. The hepatic expression of genes associated with insulin clearance was upregulated. We repeated the experiment in lean mice and observed that portal insulin and glucagon are elevated, but only insulin clearance is increased in VSG-operated mice. In conclusion, direct measurement of glucose and insulin in the blood entering and leaving the liver shows that VSG affects glucose and insulin metabolism through mechanisms independent of weight loss and diet.

Bile acids and metabolic surgery

The epidemic of obesity and its co-mortalities has reached an alarming level worldwide. Currently, metabolic surgeries, especially the Roux-en-Y gastric bypass and vertical sleeve gastrectomy, are the most effective and sustainable treatments for obesity, type 2 diabetes, non-alcoholic steatohepatitis, as well as other metabolic diseases. However, the invasive nature of the surgeries limits their broad applications to the general public. Therefore, developing alternative non-invasive approaches to mimic metabolic surgery is an important direction of the field. Recent studies have identified several potential metabolic surgery-induced downstream endocrine mediators, among which bile acids are key candidate signaling molecules. Bile acids are profoundly altered by metabolic surgery, which contributes to the metabolic effects of the surgery. In this review, we focus on the most recent studies on the roles of bile acids and bile acid receptors farnesoid X receptor and Takeda G protein-coupled receptor 5 in mediating the metabolic effects of metabolic surgery. We conclude that targeting bile acid pathways may be a promising pharmacological approach to mimic the beneficial effects of metabolic surgery.

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.

Biliopancreatic Limb Length of Small Intestinal Bypass in Non-obese Goto-Kakizaki (GK) Rats Correlates with Gastrointestinal Hormones, Adipokines, and Improvement in Type 2 Diabetes

BACKGROUND

The purpose of this study was to explore the effects on type 2 diabetes, gastrointestinal hormones, and adipokines after the small intestinal bypass of different biliopancreatic limb (BPL) lengths in non-obese type 2 diabetic rats.

METHOD

Small intestinal bypass with the BPL length at 10cm, 20cm, 30cm, and 40cm, respectively, and sham surgery were performed in non-obese GK rats. Fasting serum was collected at 2 days preoperatively and 1, 3, 6, and 9 weeks postoperatively. Body weight and fasting blood glucose (FBG) were measured during the experiment. Glycated hemoglobin (GHb), fasting insulin (FINS), C-peptide, ghrelin, leptin, adiponectin, and somatostatin were measured postoperatively.

RESULT

Rats with a bypassed length of 40cm died within 5-9 weeks. No statistically significant was observed in body weight between the sham group and the bypass groups at the 9th week postoperatively. FBG, GHb, FINS, C-peptide, and HOMA-IR in the bypass groups were lower than those in the sham group postoperatively and were negatively correlated with BPL length. Ghrelin and leptin declined compared with preoperative but were not associated with BPL length. Adiponectin of the bypass groups increased after operation and was positively correlated with BPL length. Somatostatin remained stable among groups during the experiment.

CONCLUSION

Ghrelin and leptin of non-obese GK rats decreased postoperatively without a linear relationship with the BPL length, while adiponectin increased with positively correlation with the BPL length. In addition, somatostatin remained steady after small intestinal bypass. Further studies are expected to confirm the effect of the BPL length of small intestinal bypass on gastrointestinal hormones and adipokines.

Alterations of Serum Uric Acid Level and Gut Microbiota After Roux-en-Y Gastric Bypass and Sleeve Gastrectomy in a Hyperuricemic Rat Model

Background

The objective of this study was to observe alterations of serum uric acid (SUA) level and gut microbiota after Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) surgery in a hyperuricemic rat model.

Method

We performed Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) surgery in a hyperuricemic rat model. Serum uric acid (UA), xanthine oxidase (XO) activity, IL-6, TNF-α and lipopolysaccharide (LPS) level changes, and 16S rDNA of gut microbiota were analyzed.

Results

After the surgery, the RYGB and SG procedures significantly reduced body weight, serum UA, IL-6, TNF-α and LPS levels, and XO activity. In addition, the RYGB and SG procedures altered the diversity and taxonomic composition of the gut microbiota. Compared with Sham group, RYGB and SG procedures were enriched in the abundance of phylum Verrucomicrobia and species Akkermansia muciniphila, while the species Escherichia coli was reduced.

Discussion

We here concluded that bariatric surgery-induced weight loss and resolution of inflammatory remarkers as well as changes of gut microbiota may be responsible for the reduced XO activity and SUA level. To have a better understanding of the underlying mechanism of UA metabolism following bariatric surgery, further research is needed.

A surrogate of Roux-en-Y gastric bypass (the enterogastro anastomosis surgery) regulates multiple beta-cell pathways during resolution of diabetes in ob/ob mice

BACKGROUND

Bariatric surgery is an effective treatment for type 2 diabetes. Early post-surgical enhancement of insulin secretion is key for diabetes remission. The full complement of mechanisms responsible for improved pancreatic beta cell functionality after bariatric surgery is still unclear. Our aim was to identify pathways, evident in the islet transcriptome, that characterize the adaptive response to bariatric surgery independently of body weight changes.

METHODS

We performed entero-gastro-anastomosis (EGA) with pyloric ligature in leptin-deficient ob/ob mice as a surrogate of Roux-en-Y gastric bypass (RYGB) in humans. Multiple approaches such as determination of glucose tolerance, GLP-1 and insulin secretion, whole body insulin sensitivity, ex vivo glucose-stimulated insulin secretion (GSIS) and functional multicellular Ca2+-imaging, profiling of mRNA and of miRNA expression were utilized to identify significant biological processes involved in pancreatic islet recovery.

FINDINGS

EGA resolved diabetes, increased pancreatic insulin content and GSIS despite a persistent increase in fat mass, systemic and intra-islet inflammation, and lipotoxicity. Surgery differentially regulated 193 genes in the islet, most of which were involved in the regulation of glucose metabolism, insulin secretion, calcium signaling or beta cell viability, and these were normalized alongside changes in glucose metabolism, intracellular Ca2+ dynamics and the threshold for GSIS. Furthermore, 27 islet miRNAs were differentially regulated, four of them hubs in a miRNA-gene interaction network and four others part of a blood signature of diabetes resolution in ob/ob mice and in humans.

INTERPRETATION

Taken together, our data highlight novel miRNA-gene interactions in the pancreatic islet during the resolution of diabetes after bariatric surgery that form part of a blood signature of diabetes reversal.

FUNDING

European Union's Horizon 2020 research and innovation programme via the Innovative Medicines Initiative 2 Joint Undertaking (RHAPSODY), INSERM, Société Francophone du Diabète, Institut Benjamin Delessert, Wellcome Trust Investigator Award (212625/Z/18/Z), MRC Programme grants (MR/R022259/1, MR/J0003042/1, MR/L020149/1), Diabetes UK (BDA/11/0004210, BDA/15/0005275, BDA 16/0005485) project grants, National Science Foundation (310030-188447), Fondation de l'Avenir.

Leptin: Master Regulator of Biological Functions that Affects Breathing

Obesity is a global epidemic in developed countries accounting for many of the metabolic and cardiorespiratory morbidities that occur in adults. These morbidities include type 2 diabetes, sleep-disordered breathing (SDB), obstructive sleep apnea, chronic intermittent hypoxia, and hypertension. Leptin, produced by adipocytes, is a master regulator of metabolism and of many other biological functions including central and peripheral circuits that control breathing. By binding to receptors on cells and neurons in the brainstem, hypothalamus, and carotid body, leptin links energy and metabolism to breathing. In this comprehensive article, we review the central and peripheral locations of leptin's actions that affect cardiorespiratory responses during health and disease, with a particular focus on obesity, SDB, and its effects during early development. Obesity-induced hyperleptinemia is associated with centrally mediated hypoventilation with decrease CO₂ sensitivity. On the other hand, hyperleptinemia augments peripheral chemoreflexes to hypoxia and induces sympathoexcitation. Thus, "leptin resistance" in obesity is relative. We delineate the circuits responsible for these divergent effects, including signaling pathways. We review the unique effects of leptin during development on organogenesis, feeding behavior, and cardiorespiratory responses, and how undernutrition and overnutrition during critical periods of development can lead to cardiorespiratory comorbidities in adulthood. We conclude with suggestions for future directions to improve our understanding of leptin dysregulation and associated clinical diseases and possible therapeutic targets. Lastly, we briefly discuss the yin and the yang, specifically the contribution of relative adiponectin deficiency in adults with hyperleptinemia to the development of metabolic and cardiovascular disease. © 2020 American Physiological Society. Compr Physiol 10:1047-1083, 2020.

Sleeve gastrectomy enhances glucose utilization and remodels adipose tissue independent of weight loss

Sleeve gastrectomy (SG) induces weight loss-independent improvements in glucose homeostasis by unknown mechanisms. We sought to identify the metabolic adaptations responsible for these improvements. Nonobese C57BL/6J mice on standard chow underwent SG or sham surgery. Functional testing and indirect calorimetry were used to capture metabolic phenotypes. Tissue-specific glucose uptake was assessed by 18-fluorodeoxyglucose (18-FDG) PET/computed tomography, and RNA sequencing was used for gene-expression analysis. In this model, SG induced durable improvements in glucose tolerance in the absence of changes in weight, body composition, or food intake. Indirect calorimetry revealed that SG increased the average respiratory exchange ratio toward 1.0, indicating a weight-independent, systemic shift to carbohydrate utilization. Following SG, orally administered 18-FDG preferentially localized to white adipose depots, showing tissue-specific increases in glucose utilization induced by surgery. Transcriptional analysis with RNA sequencing demonstrated that increased glucose uptake in the visceral adipose tissue was associated with upregulation in transcriptional pathways involved in energy metabolism, adipocyte maturation, and adaptive and innate immune cell chemotaxis and differentiation. SG induces a rapid, weight loss-independent shift toward glucose utilization and transcriptional remodeling of metabolic and immune pathways in visceral adipose tissue. Continued study of this early post-SG physiology may lead to a better understanding of the anti-diabetic mechanisms of bariatric surgery.

Preferences for bariatric surgery: comparing surgeons and patients using a discrete choice experiment

BACKGROUND

Increased attention to shared decision-making is particularly important in bariatric surgery. It is unclear whether the large shift toward sleeve gastrectomy is evidence of good alignment between patient and surgeon preferences.

OBJECTIVE

To identify surgeon preferences for risks, benefits, and other attributes of treatment options available for bariatric surgery and to compare results with patient preferences.

SETTING

Online survey.

METHODS

A discrete choice experiment of weight loss procedures. Each procedure was described by the following set of attributes: (1) treatment method, (2) recovery and reversibility, (3) years treatment has been available, (4) expected weight loss, (5) effect on other medical conditions, (6) risk of complication, (7) side effects, (8) changes to diet, (9) out-of-pocket costs. Participants chose between surgical profiles by comparing attributes. A convenience sample of providers for the online survey was recruited via LISTSERVs of professional associations.

RESULTS

Respondents (n = 121) were most likely to select profiles of hypothetical procedures based on the resolution of existing medical conditions and higher expected weight loss. These results align with patient preferences. However, surgeons selected profiles based on lower risk of complications than did patients and surgeons were less sensitive to out-of-pocket costs than patients.

CONCLUSIONS

Results show strong alignment between the preferences of patients and the preferences of surgeons when they are asked to stand in the place of their patients. Some differences, especially those related to sensitivity to risk of complications and out-of-pocket costs indicate that shared decision-making would benefit from providers explaining their concerns about surgical risk and from appreciating the concern many patients have about financial costs.

Sleep Apnea, Obesity, and Disturbed Glucose Homeostasis: Epidemiologic Evidence, Biologic Insights, and Therapeutic Strategies

PURPOSE OF REVIEW

Obstructive sleep apnea (OSA), obesity, and disturbed glucose homeostasis are usually considered distinct clinical condition, although they are tightly related to each other. The aim of our manuscript is to provide an overview of the current evidence on OSA, obesity, and disturbed glucose homeostasis providing epidemiologic evidence, biological insights, and therapeutic strategies.

RECENT FINDINGS

The mechanisms hypothesized to be involved in this complex interplay are the following: (1) "direct weight-dependent" mechanisms, according to which fat excess compromises respiratory mechanics, and (2) "indirect weight-dependent" mechanisms such as hyperglycemia, insulin resistance and secondary hyperinsulinemia, leptin resistance and other hormonal dysregulations frequently found in subjects with obesity, type 2 diabetes, and/or sleep disorders. Moreover, the treatment of each of these clinical conditions, through weight loss induced by diet or bariatric surgery, the use of anti-obesity or antidiabetic drugs, and continuous positive airway pressure (CPAP), seems to positively influence the others. These recent data suggest not only that there are multiple connections among these diseases but also that treating one of them may result in an improvement of the others.

Multiorgan Systems Study Reveals Igfbp7 as a Suppressor of Gluconeogenesis after Gastric Bypass Surgery

Roux-en-Y gastric bypass (RYGB) surgery reduces weight in obese patients. A marked decrease in blood glucose levels occurs before weight loss; however, key molecules that improve the glycemic profile remain largely unknown. Using a murine RYGB surgery model, we performed multiorgan proteomics and bioinformatics to monitor the proteins and molecular pathways that change in this early glycemic response. Multiplexed proteomic kinetics data analysis revealed that the Roux limb, biliopancreatic limb, liver, and pancreas each exhibited unique temporal and molecular responses to the RYGB surgery. In addition, protein-protein network analysis indicated that the changes to the microbial environment in the intestine may play a crucial role in the beneficial effects of RYGB surgery. Furthermore, insulin-like growth factor binding protein 7 (Igfbp7) was identified as an early induced protein in the Roux limb. Known secretory properties of Igfbp7 prompted us to further investigate its role as a remote organ regulator of glucose metabolism. Igfbp7 overexpression decreased blood glucose levels in diet-induced obese mice and attenuated gluconeogenic gene expression in the liver. Secreted Igfbp7 appeared to mediate these beneficial effects. These results demonstrate that organs responded differentially to RYGB surgery and indicate that Igfbp7 may play an important role in improving blood glucose levels.

Bariatric Surgery in the Treatment of Type 2 Diabetes

PURPOSE OF REVIEW

We seek to characterize the impact of bariatric surgery on diabetes mellitus by recalling its history, examining the clinical data, exploring the putative mechanisms of action, and anticipating its future.

RECENT FINDINGS

Results of clinical trials reveal that bariatric surgery induces remission of diabetes in 33-90% of individuals at 1-year post-treatment versus 0-39% of medically managed. Remission rates decrease over time but remain higher in surgically treated individuals. Investigations have revealed numerous actions of surgery including effects on intestinal physiology, neuronal signaling, incretin hormone secretion, bile acid metabolism, and microbiome changes. Bariatric surgery improves control of diabetes through both weight-dependent and weight-independent actions. These various mechanisms help explain the difference between individuals treated surgically vs. medically. They also explain differing effects of various bariatric surgery procedure types. Understanding how surgery affects diabetes will help optimize utilization of the therapy for both disease prevention and treatment.

Metabolic Surgery: Weight Loss, Diabetes, and Beyond

The alarming rise in the worldwide prevalence of obesity is paralleled by an increasing burden of type 2 diabetes mellitus. Metabolic surgery is the most effective means of obtaining substantial and durable weight loss in individuals with obesity. Randomized trials have recently shown the superiority of surgery over medical treatment alone in achieving improved glycemic control, as well as a reduction in cardiovascular risk factors. The mechanisms seem to extend beyond the magnitude of weight loss alone and include improvements in incretin profiles, insulin secretion, and insulin sensitivity. Moreover, observational data suggest that the reduction in cardiovascular risk factors translates to better patient outcomes. This review describes commonly used metabolic surgical procedures and their current indications and summarizes the evidence related to weight loss and glycemic outcomes. It further examines their potential effects on cardiovascular outcomes and mortality and discusses future perspectives.

Reg3 Proteins as Gut Hormones?

C-type lectins of the Reg3 family belong to antimicrobial peptides (AMPs), which function as a barrier to protect body surfaces against microorganisms. Reg3 mainly expressed throughout the small intestine modulate host defense process via bactericidal activity. A wide range of studies indicate that Reg3 family plays an important role in the physical segregation of microbiota from host as well as the immune response induced by enteric pathogens. In this review, we review a growing literature on the potential metabolic functions of Reg3 proteins and their potential to act as important gut hormones.

Systemic bile acids induce insulin resistance in a TGR5-independent manner

Bile acids are involved in the emulsification and absorption of dietary fats, as well as acting as signaling molecules. Recently, bile acid signaling through farnesoid X receptor and G protein-coupled bile acid receptor (TGR5) has been reported to elicit changes in not only bile acid synthesis but also metabolic processes, including the alteration of gluconeogenic gene expression and energy expenditure. A role for bile acids in glucose metabolism is also supported by a correlation between changes in the metabolic state of patients (i.e., obesity or postbariatric surgery) and altered serum bile acid levels. However, despite evidence for a role for bile acids during metabolically challenging settings, the direct effect of elevated bile acids on insulin action in the absence of metabolic disease has yet to be investigated. The present study examines the impact of acutely elevated plasma bile acid levels on insulin sensitivity using hyperinsulinemic-euglycemic clamps. In wild-type mice, elevated bile acids impair hepatic insulin sensitivity by blunting the insulin suppression of hepatic glucose production. The impaired hepatic insulin sensitivity could not be attributed to TGR5 signaling, as TGR5 knockout mice exhibited a similar inhibition of insulin suppression of hepatic glucose production. Canonical insulin signaling pathways, such as hepatic PKB (or Akt) activation, were not perturbed in these animals. Interestingly, bile acid infusion directly into the portal vein did not result in an impairment in hepatic insulin sensitivity. Overall, the data indicate that acute increases in circulating bile acids in lean mice impair hepatic insulin sensitivity via an indirect mechanism.

Patient Preferences for Bariatric Surgery: Findings From a Survey Using Discrete Choice Experiment Methodology

Importance

Surgical options for weight loss vary considerably in risks and benefits, but the relative importance of procedure-associated characteristics in patient decision making is largely unknown.

Objective

To identify patient preferences for risks, benefits, and other attributes of treatment options available to individuals who are candidates for bariatric surgery.

Design, Setting, and Participants

This discrete choice experiment of weight loss procedures was performed as an internet-based survey administered to patients recruited from bariatric surgery information sessions in the State of Michigan. Each procedure was described by the following set of attributes: (1) treatment method, (2) recovery and reversibility, (3) time that treatment has been available, (4) expected weight loss, (5) effect on other medical conditions, (6) risk of complication, (7) adverse effects, (8) changes to diet, and (9) out-of-pocket costs. Participants chose between surgical profiles by comparing attributes. Survey data were collected from May 1, 2015, through January 30, 2016, and analyzed from February 1 to June 30, 2016.

Main Outcomes and Measures

Estimated relative value of risks and benefits for leading weight-loss surgical options and marginal willingness to pay for procedure attributes. A latent class analysis identified respondent subgroups.

Results

Among the 815 respondents (79.9% women; mean [SD] age, 44.5 [12.0] years), profiles of hypothetical procedures that included resolution of medical conditions (coefficient for full resolution, 0.229 [95% CI, 0.177 to 0.280; P < .001]; coefficient for no resolution, -0.207 [95% CI, -0.254 to -0.159; P < .001]), higher total weight loss (coefficient for each additional 20% loss, 0.185 [95% CI, 0.166 to 0.205; P < .001]), and lower out-of-pocket costs (coefficient for each additional $1000, -0.034 [95% CI, -0.042 to -0.025; P < .001]) were most likely to be selected. Younger respondents were more likely than older respondents to choose treatments with higher weight loss (coefficient for loss of 80% excess weight 0.543 [95% CI, 0.435-0.651] vs 0.397 [95% CI, 0.315-0.482]) and were more sensitive to out-of-pocket costs (coefficient for $100 out-of-pocket costs, 0.346 [95% CI, 0.221-0.470] vs 0.262 [95% CI, 0.174 to 0.350]; coefficient for $15 000 in out-of-pocket costs, -0.768 [95% CI, -0.938 to -0.598] vs -0.384 [95% CI, -0.500 to -0.268]). Marginal willingness to pay indicated respondents would pay $5470 for losing each additional 20% of excess body weight and $12 843 for resolution of existing medical conditions, the most desired procedure attributes. Latent class analysis identified the following 3 unobserved subgroups: cost-sensitive (most concerned with costs); benefit-focused (most concerned with excess weight loss and resolution of medical conditions); and procedure-focused (most concerned with how the treatment itself worked, including recovery and reversibility).

Conclusions and Relevance

Candidates for bariatric surgery identified costs, expected weight loss, and resolution of medical conditions as the most important characteristics of weight loss surgery decisions. Other information, such as risk of complications and adverse effects, were important to patients but less so.

Vertical sleeve gastrectomy improves ventilatory drive through a leptin-dependent mechanism

Obesity hypoventilation syndrome (OHS) is a serious disorder characterized by daytime hypercapnia, disordered breathing, and a reduction in chemosensitivity. Vertical sleeve gastrectomy (VSG), a bariatric surgical procedure resulting in weight loss and weight-independent improvements in glucose metabolism, has been observed to substantially improve sleep-disordered breathing. However, it is unclear if the ventilatory effects of VSG are secondary to weight loss or the marked change in metabolic physiology. Using preclinical mouse models, we found that VSG leads to an improvement in the hypercapnic ventilatory response (HCVR) and reductions in circulating leptin levels independent of reductions in body mass, fat mass, and caloric intake. In the absence of leptin, VSG continues to improve body mass, fat mass, and glucose tolerance in ob/ob mice but no longer affects HCVR. However, the HCVR of ob/ob mice can be returned to wild-type levels with leptin treatment. These data demonstrate that VSG improves chemosensitivity and ventilatory drive via a leptin-dependent mechanism. Clinically, these data downgrade the relative contribution of physical, mechanical load in the pathogenesis of OHS, and instead point to physiological components of obesity, including alterations in leptin signaling, as key drivers in OHS.

Targeting Bile Acid-Activated Receptors in Bariatric Surgery

Bariatric surgical procedures, including Roux-en-Y gastric bypass and vertical sleeve gastrectomy, are currently the most effective clinical approaches to achieve a significant and sustainable weight loss. Bariatric surgery also concomitantly improves type 2 diabetes and other metabolic diseases such as nonalcoholic steatohepatitis, cardiovascular diseases, and hyperlipidemia. However, despite the recent exciting progress in the understanding how bariatric surgery works, the underlying molecular mechanisms of bariatric surgery remain largely unknown. Interestingly, bile acids are emerging as potential signaling molecules to mediate the beneficial effects of bariatric surgery. In this review, we summarize the recent findings on bile acids and their activated receptors in mediating the beneficial metabolic effects of bariatric surgery. We also discuss the potential to target bile acid-activated receptors in order to treat obesity and other metabolic diseases.

Roux-en-Y gastric bypass surgery alters serum metabolites and fatty acids in patients with morbid obesity

AIM

Bariatric surgery induces significant weight loss, increases insulin sensitivity, and reduces mortality, but the underlying mechanisms are not clear. It was hypothesized that Roux-en-Y gastric bypass (RYGB) surgery improves metabolic profile along with weight loss. The objective of this pilot study was to evaluate changes in serum metabolites and fatty acids (FA) at 2 weeks and 6 months after RYGB.

MATERIALS AND METHODS

Serum samples were collected pre-surgery, at 2 weeks and 6 months post-surgery from 20 patients undergoing RYGB surgery. Serum non-esterified free FA (NEFA) were measured. Serum metabolites and FA were measured using nuclear magnetic resonance spectroscopy and improved direct fatty acid methyl ester synthesis and the gas chromatography/mass spectrometry method, respectively, in subjects who completed follow-up at 6 months (n = 8).

RESULTS

Mean (standard deviation) percent total weight loss was 6.70% (1.7) and 24.91% (6.63) at 2 weeks (n = 15) and 6 months (n = 8) post-surgery, respectively. NEFA were significantly reduced at 6 months post-surgery (P = 0.001, n = 8). Serum branched chain amino acids, 2-aminobutyrate, butyrate, 2-hydroxybutyrate, 3-hydroxybutyrate, acetone, 2-methylglutarate, and 2-oxoisocaproate were significantly reduced, while serum alanine, glycine, pyruvate, and taurine were significantly elevated at 6 months post-surgery compared with pre-surgery (n = 8, P < 0.05). Also, serum FA C10:0, C13:0, C14:0, C15:0, and C18:0 increased significantly (n = 8, P < 0.05) by 6 months post-surgery.

CONCLUSIONS

Changes in serum metabolites and FA at 6 months post-RYGB surgery in this pilot study with limited number of participants are suggestive of metabolic improvement; larger studies are warranted for confirmation.

Metabolic comparison of one-anastomosis gastric bypass, single-anastomosis duodenal-switch, Roux-en-Y gastric bypass, and vertical sleeve gastrectomy in rat

BACKGROUND

One-anastomosis gastric bypass (OAGB) and single-anastomosis duodenal switch (SADS) have become increasingly popular weight loss strategies. However, data directly comparing the effectiveness of these procedures with Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (SG) are limited.

OBJECTIVES

To examine the metabolic outcomes of OAGB, SADS, RYGB, and SG in a controlled rodent model.

SETTING

Academic research laboratory, United States.

METHODS

Surgeries were performed in diet-induced obese Long-Evans rats, and metabolic outcomes were monitored before and for 15 weeks after surgery.

RESULTS

All bariatric procedures induced weight loss compared with sham that lasted throughout the course of the study. The highest percent fat loss occurred after OAGB and RYGB. All bariatric procedures had improved glucose dynamics associated with an increase in insulin (notably OAGB and SADS) and/or glucagon-like protein-1 secretion. Circulating cholesterol was reduced in OAGB, SG, and RYGB. OAGB and SG additionally decreased circulating triglycerides. Liver triglycerides were most profoundly reduced after OAGB and RYGB. Circulating iron levels were decreased in all surgical groups, associated with a decreased hematocrit value and increased reticulocyte count. The fecal microbiome communities of OAGB, SADS, and RYGB were significantly altered; however, SG exhibited no change in microbiome diversity or composition.

CONCLUSIONS

These data support the use of the rat for modeling bariatric surgical procedures and highlight the ability of the OAGB to meet or exceed the metabolic improvements of RYGB. These data point to the likelihood that each surgery accomplishes metabolic improvements through both overlapping and distinct mechanisms and warrants further research.

The Bidirectional Relationship Between Obstructive Sleep Apnea and Metabolic Disease

Obstructive sleep apnea (OSA) is a common sleep disorder, effecting 17% of the total population and 40-70% of the obese population (1, 2). Multiple studies have identified OSA as a critical risk factor for the development of obesity, diabetes, and cardiovascular diseases (3-5). Moreover, emerging evidence indicates that metabolic disorders can exacerbate OSA, creating a bidirectional relationship between OSA and metabolic physiology. In this review, we explore the relationship between glycemic control, insulin, and leptin as both contributing factors and products of OSA. We conclude that while insulin and leptin action may contribute to the development of OSA, further research is required to determine the mechanistic actions and relative contributions independent of body weight. In addition to increasing our understanding of the etiology, further research into the physiological mechanisms underlying OSA can lead to the development of improved treatment options for individuals with OSA.

Refinement of Perioperative Feeding in a Mouse Model of Vertical Sleeve Gastrectomy

Provision of liquid enteral nutrition (LEN) during the perioperative period is standard practice for rodents undergoing bariatric surgery, yet these diets are associated with several challenges, including coagulation of the liquid diet within the delivery system and decreased postoperative consumption. We investigated the use of a commercially available high-calorie dietary gel supplement (DG) as an alternative food source for mice during the perioperative period. C57BL/6J male mice were fed high-fat diet for 8 to 10 wk prior to surgery. The study groups were: vertical sleeve gastrectomy (VSG) +DG, VSG+LEN, sham surgery+DG, and sham+LEN. Food and water intakes, body weight, and body fat composition was monitored throughout the study. Mice that received DG lost significantly more weight preoperatively than those fed LEN. However, during the postoperative period, body weight, body fat composition, and water and caloric intake were similar among all experimental diet groups. Three mice in the VSG+LEN group were euthanized due to clinical illness during the course of the study. In summary, feeding a high-calorie DG to mice undergoing VSG surgery is a viable alternative to LEN, given that DG does not significantly affect the surgical model of weight loss or result in adverse clinical outcomes. We recommend additional metabolic characterization of DG supplementation to ensure that this novel diet does not confound specific research goals in the murine VSG model.

Vertical sleeve gastrectomy corrects metabolic perturbations in a low-exercise capacity rat model

OBJECTIVE

Bariatric surgery is currently our most effective strategy at weight loss, yet the mechanisms for its success remain unknown. Low exercise capacity, in humans and rodents, predicts poor metabolic outcome. The objective of this manuscript was to determine if bariatric surgery could restore metabolic perturbations in rats with low intrinsic exercise capacity.

METHODS

We performed vertical sleeve gastrectomy (VSG) or sham surgery in high fat-fed rats selectively bred for low running capacity.

RESULTS

We found that VSG reduced body mass through a reduction in fat mass, caused early reductions in food intake, and shifted macronutrient preference away from fat and toward carbohydrates. VSG had no impact on basal glucose but did improve the return to baseline after an oral glucose load. As has been shown previously, VSG increased postprandial insulin, GLP-1, and bile acids. There was no significant impact of VSG on plasma triglycerides, hepatic triglycerides, or cholesterol. Interestingly, the brown adipose tissue to white adipose tissue ratio tended to be greater in VSG compared to sham surgery animals. While VSG positively impacted several aspects of metabolism, it did not enhance maximal oxygen capacity and seemed to lower metabolic efficiency as indicated by lower resting oxygen consumption and fat and carbohydrate oxidation.

CONCLUSION

VSG can improve the metabolic status of animals with a low exercise capacity independently of exercise capacity.

Gastric mucosal devitalization reduces adiposity and improves lipid and glucose metabolism in obese rats

BACKGROUND AND AIMS

The gastric mucosa is an endocrine organ that regulates satiation pathways by expression of orexigenic and anorexigenic hormones. Vertical sleeve gastrectomy (VSG) excludes gastric mucosa and reduces gastric volume. Our study aimed to investigate the independent effects of altering gastric mucosa on obesity and its related comorbidities.

METHODS

Gastric mucosa devitalization (GMD) of 70% of the stomach was achieved by argon plasma coagulation in a high-fat diet rat model and was compared with VSG and sham surgery. In an 8-week follow-up study, we quantified body weight, visceral adiposity, insulin resistance index, cholesterol profiles, and free fatty acid profiles by enzyme-linked immunosorbent assay (ELISA). Following a 2-hour oral glucose tolerance test, the kinetics of ghrelin, glucagon-like peptide-1, peptide YY, and serum and liver bile acid levels were measured. Liver lipid content was quantified by ELISA.

RESULTS

GMD resulted in significant reductions in body weight, visceral and subcutaneous adipose tissue, and hepatic steatosis as well as an improvement in lipid metabolism. GMD resulted in significant reductions in food intake and intestinal malabsorption of free fatty acids, both contributing to improved body composition and metabolic profile. Mechanistically, GMD resulted in a significant reduction in serum palmitate levels as well as an increase in serum and liver bile acid levels, known to alter glucose and lipid metabolism. Similar changes were noted when VSG rats were compared with sham surgery rats.

CONCLUSIONS

Devitalization of gastric mucosa, independent of altering gastric volume, was able to reduce obesity-related comorbidities. The gastric mucosa may be a potential target for treating obesity and its associated comorbidities.

[Quality indicators for metabolic and bariatric surgery in Germany : Evidence-based development of an indicator panel for the quality of results, indications and structure]

An expert committee was appointed by the German Society for General and Visceral Surgery to develop a panel of appropriate quality indicators to collate the quality of results, indications and structure in metabolic and bariatric surgery. This entailed assimilating the available evidence (systematic literature search), results from the national registry of the society (StuDoQ|MBE) and specific socioeconomic aspects (e. g. severely limited access to metabolic and bariatric surgery in Germany). These quality parameters were to be incorporated into the national guidelines and the rules of procedure for certification in the future. The committee concluded that mortality, MTL30 and severe complications needing intervention (Clavien-Dindo ≥ 3b) are suitable indicators to measure surgical outcome quality due to their relevance, scientific soundness and practicability. As a systematic follow-up is mandatory after bariatric surgery, a minimum follow-up quota is now required using reported quality of life data as an indicator of process quality. As intestinal bypass procedures have been shown to be superior in the treatment of type 2 diabetes, these procedures should be offered to eligible patients and also be performed. The proposed threshold values based on the results of the available literature and StuDoQ registry are to be considered as preliminary and need to be validated and adjusted if necessary in the future. The StuDoQ|MBE is considered a valuable tool to gather this information and also represents the appropriate infrastructure for the collation of relevant risk adjustors.

Bile acid signaling and bariatric surgery

The rapid worldwide rise in obesity rates over the past few decades imposes an urgent need to develop effective strategies for treating obesity and associated metabolic complications. Bariatric surgical procedures, such as Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG), currently provide the most effective treatment for obesity and type 2 diabetes (T2D), as well as for non-alcoholic steatohepatitis (NASH). However, the underlying mechanisms of the beneficial effects of bariatric surgery remain elusive. Recent studies have identified bile acids as potential signaling molecules involved in the beneficial effects of bariatric surgery. This review focuses on the most recent studies on the roles of bile acids and bile acid receptors Farnesoid X receptor (FXR) and G protein-coupled bile acid receptor 5 (TGR5) in bariatric surgery. We also discuss the possibility of modulating bile acid signaling as a pharmacological therapeutic approach to treating obesity and its associated metabolic complications.

Effect of bariatric surgery on adiposity and metabolic profiles: A prospective cohort study in Middle-Eastern patients

AIM

To investigate changes in adiposity and cardio-metabolic risk profile following Roux-en-Y gastric bypass in patients of Middle Eastern ethnicity with severe obesity.

METHODS

This prospective cohort study involved 92 patients who met the indications of bariatric surgery. Post-procedure markers of obesity and cardiometabolic profile were monitored regularly for a year.

RESULTS

Mean body mass index decreased by 29.5% from 41.9 to 29.5 kg/m2 between baseline and 12-mo follow-up, while mean fat mass decreased by 45.9% from 64.2 kg to 34.7 kg. An improvement was also observed in the gluco-metabolic profile with both fasting glucose and HbA1c substantially decreasing (P < 0.001).

CONCLUSION

The present study shows the short to medium term (1 year) health benefits of bariatric surgery for patients of Middle Eastern ethnicity.

Weight loss independent changes in adipose tissue macrophage and T cell populations after sleeve gastrectomy in mice

OBJECTIVE

In addition to adipocytes, adipose tissue contains large numbers of immune cells. A wide range of evidence links the activity of these cells to regulation of adipocyte and systemic metabolic function. Bariatric surgery improves several aspects of metabolic derangements and at least some of these effects occur in a weight-loss independent manner. We sought to investigate the impact of vertical sleeve gastrectomy (VSG) on adipose immune cell frequencies.

METHODS

We analyzed the frequencies of immune cells within distinct adipose tissue depots in obese mice that had VSG or sham surgery with a portion of the latter group pair-fed such that their body mass was matched to the VSG animals.

RESULTS

We demonstrate that VSG induced a shift in the epididymal adipose tissue leukocyte profile including increased frequencies of CD11c- macrophages, increased frequencies of T cells (CD4+, CD8+, and CD4-/CD8- T cells all increased), but a significantly decreased frequency of adipose tissue dendritic cells (ATDC) that, despite the continued high fat feeding of the VSG group, dropped below control diet levels.

CONCLUSIONS

These results indicate that VSG induces substantial changes in the immune populations residing in the adipose depots independent of weight loss.

Weight loss medications in Canada - a new frontier or a repeat of past mistakes?

Current methods for the treatment of excess weight can involve healthy behavior changes, pharmacotherapy, and surgical interventions. Many individuals are able to lose some degree of weight through behavioral changes; however, they are often unable to maintain their weight loss long-term. This is in part due to physiological processes that cannot be addressed through behavioral changes alone. Bariatric surgery, which is the most successful treatment for excess weight to date, does result in physiological changes that can help with weight loss and weight maintenance. However, many patients either do not qualify or elect to not have this procedure. Fortunately, research has recently identified changes in neurochemicals (i.e., orexigens and anorexigens) that occur during weight loss and contribute to weight regain. The neurochemicals and hormones may be able to be targeted by medications to achieve greater and more sustained weight loss. Two medications are approved in adjunction to lifestyle management for weight loss in Canada: orlistat and liraglutide. Both medications are able to target physiological processes to help patients lose weight and maintain a greater amount of weight loss than with just behavioral modifications alone. Two other weight management medications, which also target specific physiological processes to aid in weight loss and its maintenance, a bupropion/naltrexone combination and lorcaserin, are currently pending approval in Canada. Nonetheless, there remain significant barriers for health care professionals to prescribe medications for weight loss, such as a lack of training and knowledge in the area of obesity. Until this has been addressed, and we begin treating obesity as we do other diseases, we are unlikely to combat the increasing trend of obesity in Canada and worldwide.

Significant obesity-associated gene expression changes occur in the stomach but not intestines in obese mice

The gastrointestinal (GI) tract can have significant impact on the regulation of the whole‐body metabolism and may contribute to the development of obesity and diabetes. To systemically elucidate the role of the GI tract in obesity, we performed a transcriptomic analysis in different parts of the GI tract of two obese mouse models: ob/ob and high‐fat diet (HFD) fed mice. Compared to their lean controls, significant changes in the gene expression were observed in both obese mouse groups in the stomach (ob/ob: 959; HFD: 542). In addition, these changes were quantitatively much higher than in the intestine. Despite the difference in genetic background, the two mouse models shared 296 similar gene expression changes in the stomach. Among those genes, some had known associations to obesity, diabetes, and insulin resistance. In addition, the gene expression profiles strongly suggested an increased gastric acid secretion in both obese mouse models, probably through an activation of the gastrin pathway. In conclusion, our data reveal a previously unknown dominant connection between the stomach and obesity in murine models extensively used in research.

Pancreatic β-cell identity in diabetes

Recovery of functional β-cell mass continues to be an ongoing challenge in treating diabetes. Initial work studying β-cells suggested apoptotic β-cell death as a main contributor for the loss of β-cell mass in diabetes. Restoration of β-cells either by transplant or stimulating proliferation of remaining β-cells or precursors would then logically be a viable therapeutic option for diabetes. However, recent work has highlighted the inherent β-cell plasticity and the critical role of loss of β-cell identity in diabetes, and has suggested that β-cells fail to maintain a fully differentiated glucose-responsive and drug-responsive state, particularly in diabetic individuals with poorly controlled, long-lasting periods of hyperglycaemia. Understanding the underlying mechanisms of loss of β-cell identity and conversion in other cell types, as well as how to regain their mature differentiated functional state, is critical to develop novel therapeutic strategies to prevent or reverse these processes. In this review, we discuss the role of plasticity and loss of β-cell identity in diabetes, the current understanding of mechanisms involved in altering this mature functional β-cell state and potential progresses to identify novel therapeutic targets providing better opportunities for slowing or preventing diabetes progression.

Does bariatric surgery improve adipose tissue function?

Bariatric surgery is currently the most effective treatment for obesity. Not only do these types of surgeries produce significant weight loss but also they improve insulin sensitivity and whole body metabolic function. The aim of this review is to explore how altered physiology of adipose tissue may contribute to the potent metabolic effects of some of these procedures. This includes specific effects on various fat depots, the function of individual adipocytes and the interaction between adipose tissue and other key metabolic tissues. Besides a dramatic loss of fat mass, bariatric surgery shifts the distribution of fat from visceral to the subcutaneous compartment favoring metabolic improvement. The sensitivity towards lipolysis controlled by insulin and catecholamines is improved, adipokine secretion is altered and local adipose inflammation as well as systemic inflammatory markers decreases. Some of these changes have been shown to be weight loss independent, and novel hypothesis for these effects includes include changes in bile acid metabolism, gut microbiota and central regulation of metabolism. In conclusion bariatric surgery is capable of improving aspects of adipose tissue function and do so in some cases in ways that are not entirely explained by the potent effect of surgery. © 2016 World Obesity.

Sleeve gastrectomy leads to weight loss in the Magel2 knockout mouse

BACKGROUND

Prader-Willi syndrome (PWS) is a genetic disorder characterized by hyperphagia, obesity, cardiopulmonary diseases, and increased mortality. Although successful weight loss improves health in PWS, few treatments cause sustained weight loss in obese patients let alone obese individuals with PWS.

OBJECTIVES

The present study uses the Magel2 knockout (KO) mouse, an animal model of PWS, to conduct a preclinical study on the efficacy of sleeve gastrectomy (SG) in PWS.

SETTING

Academic research laboratory, United States.

METHODS

We performed sham or SG surgeries in 24- to 28-week-old male Magel2 KO and wild-type littermate control mice (WT) who had been maintained on a high-fat diet for 10 weeks. We monitored weight, food intake, and fat and lean mass pre- and postoperatively. Fasting glucose, glucose tolerance, and counter-regulation were measured postoperatively.

RESULTS

Magel2 KO animals had similar recovery and mortality rates compared with WT. SG resulted in similar weight loss, specifically loss of fat but not lean mass, in both Magel2 KO and WT mice. SG also resulted in significantly lower fasting glucose levels and a reduction in fat intake in both Magel2 KO and WT mice. We also found that Magel2 KO mice failed to increase their food intake in response to the glucoprivic agent 2-deoxy-D-glucose, suggesting impaired glucose counter-regulation, but this occurred regardless of surgical status. All results were considered significant when P< .05.

CONCLUSION

We find in this mouse model of PWS, SG is a well-tolerated, effective strategy for weight and fat loss.

Influence of Roux-en-Y gastric bypass on plasma bile acid profiles: a comparative study between rats, pigs and humans

BACKGROUND

Roux-en-Y gastric bypass (RYGBP) is the most widely used bariatric surgery procedure, which induces profound metabolic and physiological effects, such as substantial improvements in obesity, type 2 diabetes and their comorbidities. Increasing evidence identifies bile acids (BAs) as signaling molecules that contribute to the metabolic improvement after RYGBP. However, how and to what extent BAs mediate the metabolic effects of RYGBP still remains unclear and requires mechanism of action studies using preclinical models. In this study, we compared plasma BA profiles before and after RYGBP in two animal models, rats and pigs, with humans to evaluate their translational potential.

METHODS

Plasma BAs were profiled in rats, pigs and humans by liquid chromatography coupled with tandem mass spectrometry before and after RYGBP.

RESULTS

RYGBP increased baseline plasma total BA concentrations in humans and in the two animal models to a similar extent (∼3-fold increase), despite differences in presurgery BA levels and profiles between the models. However, qualitatively, RYGBP differently affected individual plasma BA species, with similar increases in some free species (cholic acid (CA), chenodeoxycholic acid (CDCA) and deoxycholic acid (DCA)), different increases in glyco-conjugated species depending on the model and globally no increase in tauro-conjugated species whatever the model.

CONCLUSIONS

The tested animal models share similar quantitative RYGBP-induced increases in peripheral blood BAs as humans, which render them useful for mechanistic studies. However, they also present qualitative differences in BA profiles, which may result in different signaling responses. Such differences need to be taken into account when translating results to humans.

Jejunum-ileum circuit procedure improves glucose metabolism in diabetic rats independent of weight loss

OBJECTIVE

To introduce a lower-risk novel surgical procedure to achieve diabetes reversal along with associated hormonal changes.

METHODS

Diabetic rats were randomly assigned to jejunum-ileum circuit (JIC), sham-JIC, ileal interposition (IT), and sham-IT groups. The JIC group included two subgroups: short (JIC-S) and long (JIC-L), based on the length between anastomosis and Treitz ligament (LAT ). The body weight, food intake, blood glucose, glucose and insulin tolerance, and gut hormones were measured. The liver gene expression of glucose transporter 2 (GLUT2) and protein expression of glucose-6-phosphatase (G6P) and phosphoenolpyruvate carboxykinase (PKC) were also measured. Following a dye infusion, nutrient delivery was measured at termination day.

RESULTS

Compared to sham-JIC group, JIC-S group did not reduce body weight or food intake but significantly improved glucose tolerance and insulin resistance. With fast chyme transit, JIC-S not only promoted the secretion of insulin, glucagon-like peptide 1, and peptide YY and decreased leptin, but also upregulated hepatic GLUT2 and downregulated hepatic G6P and PKC. JIC-L group, however, failed to achieve remission of diabetes.

CONCLUSION

JIC-S relieves diabetes independent of weight loss, as it promotes the secretion of anti-diabetic hormones and inhibits hepatic glucose production. The prolonging of LAT , however, diminishes the hypoglycemic effect.

Striatal Dopamine Links Gastrointestinal Rerouting to Altered Sweet Appetite

Reductions in calorie intake contribute significantly to the positive outcome of bariatric surgeries. However, the physiological mechanisms linking the rerouting of the gastrointestinal tract to reductions in sugar cravings remain uncertain. We show that a duodenal-jejunal bypass (DJB) intervention inhibits maladaptive sweet appetite by acting on dopamine-responsive striatal circuitries. DJB disrupted the ability of recurrent sugar exposure to promote sweet appetite in sated animals, thereby revealing a link between recurrent duodenal sugar influx and maladaptive sweet intake. Unlike ingestion of a low-calorie sweetener, ingestion of sugar was associated with significant dopamine effluxes in the dorsal striatum, with glucose infusions into the duodenum inducing greater striatal dopamine release than equivalent jejunal infusions. Consistently, optogenetic activation of dopamine-excitable cells of the dorsal striatum was sufficient to restore maladaptive sweet appetite in sated DJB mice. Our findings point to a causal link between striatal dopamine signaling and the outcomes of bariatric interventions.

Metabolic effects of bariatric surgery in mouse models of circadian disruption

Background/Objectives

Mounting evidence supports a link between circadian disruption and metabolic disease. Humans with circadian disruption (e.g., night-shift workers) have an increased risk of obesity and cardiometabolic diseases compared to the non-disrupted population. However, it is unclear if the obesity and obesity-related disorders associated with circadian disruption respond to therapeutic treatments as well as individuals with other types of obesity.

Subjects/Methods

Here, we test the effectiveness of the commonly used bariatric surgical procedure, Vertical Sleeve Gastrectomy (VSG) in mouse models of genetic and environmental circadian disruption.

Results

VSG led to a reduction in body weight and fat mass in both Clock^Δ19 mutant and constant-light mouse models (P < .05), resulting in an overall metabolic improvement independent of circadian disruption. Interestingly, the decrease in body weight occurred without altering diurnal feeding or activity patterns (P > .05). Within circadian-disrupted models, VSG also led to improved glucose tolerance and lipid handling (P < .05).

Conclusions

Together these data demonstrate that VSG is an effective treatment for the obesity associated with circadian disruption, and that the potent effects of bariatric surgery are orthogonal to circadian biology. However, since the effects of bariatric surgery are independent of circadian disruption, VSG cannot be considered a cure for circadian disruption. These data have important implications for circadian-disrupted obese patients. Moreover, these results reveal new information about the metabolic pathways governing the effects of bariatric surgery as well as of circadian disruption.