A Comparative Study of the Effect of Gastric Bypass, Sleeve Gastrectomy, and Duodenal-Jejunal Bypass on Type-2 Diabetes in non-Obese Rats

The Phantom Satiation Hypothesis of Bariatric Surgery

The excitation of vagal mechanoreceptors located in the stomach wall directly contributes to satiation. Thus, a loss of gastric innervation would normally be expected to result in abrogated satiation, hyperphagia, and unwanted weight gain. While Roux-en-Y-gastric bypass (RYGB) inevitably results in gastric denervation, paradoxically, bypassed subjects continue to experience satiation. Inspired by the literature in neurology on phantom limbs, I propose a new hypothesis in which damage to the stomach innervation during RYGB, including its vagal supply, leads to large-scale maladaptive changes in viscerosensory nerves and connected brain circuits. As a result, satiation may continue to arise, sometimes at exaggerated levels, even in subjects with a denervated or truncated stomach. The same maladaptive changes may also contribute to dysautonomia, unexplained pain, and new emotional responses to eating. I further revisit the metabolic benefits of bariatric surgery, with an emphasis on RYGB, in the light of this phantom satiation hypothesis.

Impact of Bariatric Surgery in Reducing Macrovascular Complications in Severely Obese T2DM Patients

BACKGROUND

Evidence from real-world studies have suggested a reduced rate of macrovascular complications following bariatric surgery. We undertook this meta-analysis to investigate the impact of bariatric surgery on macrovascular disease outcomes in severely obese type 2 diabetes mellitus (T2DM) patients.

METHODS

An extensive literature search was performed in PubMed from inception until March 2020. All cohort studies assessing the association between bariatric surgery and macrovascular complications in severely obese T2DM patients were included. Two independent reviewers screened the articles, extracted data, and assessed the quality using the Newcastle-Ottawa Scale. The primary outcome was to assess the impact of bariatric surgery and the risk of macrovascular complications. Statistical analysis was performed using Review Manager 5.3.

RESULTS

This meta-analysis comprised of five studies including 49,211 participants (75% female), of which 14,434 underwent bariatric surgery and 34,777 underwent usual care. Participants who underwent bariatric surgery had a significantly lower risk of macrovascular complications as compared to those with non-surgical interventions (RR: 0.50 [95% CI: 0.35-0.73], p = 0.0003). In the subgroup analysis, based on the geographical regions, studies conducted in the USA showed a higher reduction (RR: 0.41 [95% CI: 0.32-0.53], p < 0.00001) in macrovascular complications as compared to other parts of the world. The risk of all-cause mortality was also significantly lower in patients with bariatric surgery (RR 0.39 [95% CI: 0.30-0.50], p < 0.00001).

CONCLUSION

Bariatric surgery was associated with a 50% reduction in macrovascular complications along with 61% reduction in risk of all-cause mortality in morbidly obese T2DM patients.

Changes in Bile Acid Metabolism, Transport, and Signaling as Central Drivers for Metabolic Improvements After Bariatric Surgery

PURPOSE OF REVIEW

We review current evidence regarding changes in bile acid (BA) metabolism, transport, and signaling after bariatric surgery and how these might bolster fat mass loss and energy expenditure to promote improvements in type 2 diabetes (T2D) and nonalcoholic fatty liver disease (NAFLD).

RECENT FINDINGS

The two most common bariatric techniques, Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG), increase the size and alter the composition of the circulating BA pool that may then impact energy metabolism through altered activities of BA targets in the many tissues perfused by systemic blood. Recent reports in human patients indicate that gene expression of the major BA target, the farnesoid X receptor (FXR), is increased in the liver but decreased in the small intestine after RYGB. In contrast, intestinal expression of the transmembrane G protein-coupled BA receptor (TGR5) is upregulated after surgery. Despite these apparent conflicting changes in receptor transcription, changes in BAs after both RYGB and VSG are associated with elevated postprandial systemic levels of fibroblast growth factor 19 (from FXR activation) and glucagon-like peptide 1 (from TGR5 activation). These signaling activities are presumed to support fat mass loss and related metabolic benefits of bariatric surgery, and this supposition is in agreement with findings from rodent models of RYGB and VSG. However, inter-species differences in BA physiology limit direct translation and mechanistic understanding of how changes in individual BA species contribute to post-operative improvements of T2D and NAFLD in humans. Thus, details of all these changes and their influences on BAs' biological actions are still under scrutiny. Changes in BA physiology and receptor activities after RYGB and VSG likely support weight loss and promote sustained metabolic improvements.

Comparison of Diabetes Remission and Micronutrient Deficiency in a Mildly Obese Diabetic Rat Model Undergoing SADI-S Versus RYGB

BACKGROUND

Single-anastomosis duodeno-ileal bypass with sleeve gastrectomy (SADI-S) has launched a huge challenge to classic Roux-en-Y gastric bypass (RYGB). Our objective was to compare diabetes remission and micronutrient deficiency in a mildly obese diabetic rat model undergoing SADI-S versus RYGB.

METHODS

Thirty adult male mildly obese diabetic rats were randomly assigned to sham (S), SADI-S, and RYGB groups. Body weight, food intake, fasting plasma glucose (FPG), oral glucose tolerance test (OGTT), plasma insulin, GLP-1, and ghrelin levels were measured at indicated time points. Meanwhile, insulin sensitivity and pancreatic β cell function were assessed during OGTT. Finally, plasma micronutrient evaluation and islet β cell mass analysis were performed after all animals were sacrificed.

RESULTS

As compared to sham, the SADI-S and RYGB groups achieved almost equivalent efficacy in caloric restriction and FPG control without excessive weight loss. During OGTT, the SADI-S and RYGB groups also provided comparable effects on glycemic excursion, insulin sensitivity, and β cell function; however, only rats in the RYGB group showed significant changes in gut hormones, whereas the three groups were found to exhibit no significant difference in β cell mass. In addition, only vitamin E in the RYGB group was deficient as compared with the SADI-S and S groups.

CONCLUSION

In mildly obese diabetic rat, SADI-S and RYGB procedures have comparable efficacy in diabetes remission and risk of micronutrient deficiency. These data show that each of the surgery accomplishes diabetes improvements through both overlapping and distinct mechanisms requiring further investigation.

Duodenal-Jejunal Bypass Surgery Reverses Diabetic Phenotype and Reduces Obesity in db/db Mice

Type 2 diabetes mellitus (T2DM), a complex metabolic disorder typically accompanying weight gain, is associated with progressive β-cell failure and insulin resistance. Bariatric surgery ameliorates glucose tolerance and provides a near-perfect treatment. Duodenal-jejunal bypass (DJB) is an experimental procedure and has been studied in several rat models, but its influence in db/db mice, a transgenic model of T2DM, remains unclear. To investigate the effectiveness of DJB in db/db mice, we performed the surgery and evaluated metabolism improvement. Results showed that mice in DJB group weighed remarkably less than sham group two weeks after surgery. Compared to the preoperative level, postoperative fasting blood glucose (FBG) was dramatically reduced. Statistical analysis revealed that changes in body weight and FBG were significantly correlated. Besides, DJB surgery altered plasma insulin level with approximate 40% reduction. Thus, for the first time we proved that DJB can achieve rapid therapeutic effect in transgenic db/db mice with severe T2DM as well as obesity. In addition, decreased insulin level reflected better insulin sensitivity induced by DJB. In conclusion, our study demonstrates that DJB surgery may be a potentially effective way to treat obesity-associated T2DM.

Alterations of Gut Microbiota After Roux-en-Y Gastric Bypass and Sleeve Gastrectomy in Sprague-Dawley Rats

BACKGROUND

The objective of the study was to compare gut microbiota post Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG).

METHODS

Sprague-Dawley rats were randomized to RYGB, SG, or sham surgery. Body weight was measured. Fecal samples were collected before and 1, 3, 6, and 9 weeks postoperatively. Fecal microbiota was profiled by 16S ribosomal DNA gene sequencing and analyzed using Quantitative Insights into Microbial Ecology (QIIME) to determine the α and β diversities of gut microbiota.

RESULTS

The body weight of the RYGB and SG group was significantly lower than that of the sham group. Unweighted UniFrac-based principal coordinate analysis of 5,323,091 sequences from 85 fecal samples from 17 rats revealed a distinct cluster of gut microbiota post RYGB from SG and sham surgery. The percentage of Proteobacteria in the SG and sham group remained markedly lower than that of the RYGB group from 3 weeks postoperatively, while the proportion of Gammaproteobacteria in the RYGB group was significantly higher than that of the SG group and the sham group from 3 weeks postoperatively. Furthermore, the RYGB group was postoperatively enriched for Gammaproteobacteria and Bacteroidaceae, whereas the SG group was postoperatively enriched for Desulfovibrionaceae and Cyanobacteria. Compared to the pre-operative parameters, the RYGB group had a persistent increase in the relative abundance of Gammaproteobacteria and a decrease in the Shannon index, while the SG group only transiently exhibited these changes within the first week after surgery. The relative abundance of Gammaproteobacteria was negatively correlated, whereas the Shannon index was positively correlated with weight after surgery.

CONCLUSIONS

RYGB, but not SG, alters the gut microbiota of Sprague-Dawley rats. RYGB also reduces the diversity of gut microbiota. Furthermore, the abundance of Gammaproteobacteria negatively correlates with postoperative body weight and may be one of the potential contributors to stable weight loss after bariatric surgery.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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