Temporal changes in bile acid levels and 12α-hydroxylation after Roux-en-Y gastric bypass surgery in type 2 diabetes

A small intestinal bile acid modulates the gut microbiome to improve host metabolic phenotypes following bariatric surgery

Bariatric surgical procedures such as sleeve gastrectomy (SG) provide effective type 2 diabetes (T2D) remission in human patients. Previous work demonstrated that gastrointestinal levels of the bacterial metabolite lithocholic acid (LCA) are decreased after SG in mice and humans. Here, we show that LCA worsens glucose tolerance and impairs whole-body metabolism. We also show that taurodeoxycholic acid (TDCA), which is the only bile acid whose concentration increases in the murine small intestine post-SG, suppresses the bacterial bile acid-inducible (bai) operon and production of LCA both in vitro and in vivo. Treatment of diet-induced obese mice with TDCA reduces LCA levels and leads to microbiome-dependent improvements in glucose handling. Moreover, TDCA abundance is decreased in small intestinal tissue from T2D patients. This work reveals that TDCA is an endogenous inhibitor of LCA production and suggests that TDCA may contribute to the glucoregulatory effects of bariatric surgery.

Research progress on the relationship between bile acid metabolism and type 2 diabetes mellitus

Bile acids, which are steroid molecules originating from cholesterol and synthesized in the liver, play a pivotal role in regulating glucose metabolism and maintaining energy balance. Upon release into the intestine alongside bile, they activate various nuclear and membrane receptors, influencing crucial processes. These bile acids have emerged as significant contributors to managing type 2 diabetes mellitus, a complex clinical syndrome primarily driven by insulin resistance. Bile acids substantially lower blood glucose levels through multiple pathways: BA-FXR-SHP, BA-FXR-FGFR15/19, BA-TGR5-GLP-1, and BA-TGR5-cAMP. They also impact blood glucose regulation by influencing intestinal flora, endoplasmic reticulum stress, and bitter taste receptors. Collectively, these regulatory mechanisms enhance insulin sensitivity, stimulate insulin secretion, and boost energy expenditure. This review aims to comprehensively explore the interplay between bile acid metabolism and T2DM, focusing on primary regulatory pathways. By examining the latest advancements in our understanding of these interactions, we aim to illuminate potential therapeutic strategies and identify areas for future research. Additionally, this review critically assesses current research limitations to contribute to the effective management of T2DM.

Mucosal and hormonal adaptations after Roux-en-Y gastric bypass

The aim of this study was to perform a comprehensive literature review regarding the relevant hormonal and histologic changes observed after Roux-en-Y gastric bypass (RYGB). We aimed to describe the relevant hormonal (glucagon-like peptides 1 and 2 [GLP-1 and GLP-2], peptide YY [PYY], oxyntomodulin [OXM], bile acids [BA], cholecystokinin [CCK], ghrelin, glucagon, gastric inhibitory polypeptide [GIP], and amylin) profiles, as well as the histologic (mucosal cellular) adaptations happening after patients undergo RYGB. Our review compiles the current evidence and furthers the understanding of the rationale behind the food intake regulatory adaptations occurring after RYGB surgery. We identify gaps in the literature where the potential for future investigations and therapeutics may lie. We performed a comprehensive database search without language restrictions looking for RYGB bariatric surgery outcomes in patients with pre- and postoperative blood work hormonal profiling and/or gut mucosal biopsies. We gathered the relevant study results and describe them in this review. Where human findings were lacking, we included animal model studies. The amalgamation of physiologic, metabolic, and cellular adaptations following RYGB is yet to be fully characterized. This constitutes a fundamental aspiration for enhancing and individualizing obesity therapy.

Gut microbiome and microbial metabolites in NAFLD and after bariatric surgery: Correlation and causality

Non-alcoholic fatty liver disease (NAFLD) is currently related to a heavy socioeconomic burden and increased incidence. Since obesity is the most prevalent risk factor for NAFLD, weight loss is an effective therapeutic solution. Bariatric surgery (BS), which can achieve long-term weight loss, improves the overall health of patients with NAFLD. The two most common surgeries are the Roux-en-Y gastric bypass and sleeve gastrectomy. The gut-liver axis is the complex network of cross-talking between the gut, its microbiome, and the liver. The gut microbiome, involved in the homeostasis of the gut-liver axis, is believed to play a significant role in the pathogenesis of NAFLD and the metabolic improvement after BS. Alterations in the gut microbiome in NAFLD have been confirmed compared to that in healthy individuals. The mechanisms linking the gut microbiome to NAFLD have been proposed, including increased intestinal permeability, higher energy intake, and other pathophysiological alterations. Interestingly, several correlation studies suggested that the gut microbial signatures after BS become more similar to those of lean, healthy controls than that of patients with NAFLD. The resolution of NAFLD after BS is related to changes in the gut microbiome and its metabolites. However, confirming a causal link remains challenging. This review summarizes characteristics of the gut microbiome in patients with NAFLD before and after BS and accumulates existing evidence about the underlying mechanisms of the gut microbiome.

Reversal of NAFLD After VSG Is Independent of Weight-Loss but RYGB Offers More Efficacy When Maintained on a High-Fat Diet

PURPOSE

Bariatric surgery is emerging as an effective treatment for obesity and the metabolic syndrome. Recently, we demonstrated that Roux-en-Y gastric bypass (RYGB), but not vertical sleeve gastrectomy (VSG), resulted in improvements to white adipose physiology and enhanced brown adipose functioning. Since beneficial alterations to liver health are also expected after bariatric surgery, comparing the post-operative effects of RYGB and VSG on liver physiology is essential to their application in the treatment of non-alcoholic fatty liver disease (NAFLD).

MATERIALS AND METHODS

The effects of RYGB and VSG on liver physiology were compared using diet induced mouse model of obesity. High-fat diet (HFD) was administered for 12 weeks after surgery and alterations to liver physiology were assessed.

RESULTS

Both RYGB and VSG showed decreased liver weight as well as reductions to hepatic cholesterol and triglyceride levels. There were demonstrable improvements to NAFLD activity score (NAS) and fibrosis stage scoring after both surgeries. In RYGB, these beneficial changes to liver function resulted from the downregulation of pro-fibrotic and upregulation anti-fibrotic genes, as well as increased fatty acid oxidation and bile acid flux. For VSG, though similar alterations were observed, they were less potent. However, VSG did significantly downregulate pro-fibrotic genes and showed increased glycogen content paralleled by decreased glycogenolysis which may have contributed to the resolution of NAFLD.

CONCLUSION

RYGB and VSG improve liver physiology and function, but RYGB is more efficacious. Resolutions of NAFLD in RYGB and VSG are achieved through different processes, independent of weight loss.

Duodenal mucosal resurfacing with a GLP-1 receptor agonist increases postprandial unconjugated bile acids in patients with insulin-dependent type 2 diabetes

Duodenal mucosal resurfacing (DMR) is a new endoscopic ablation technique aimed at improving glycemia and metabolic control in patients with type 2 diabetes mellitus (T2DM). DMR appears to improve insulin resistance, which is the root cause of T2DM, but its mechanism of action is largely unknown. Bile acids function as intestinal signaling molecules in glucose and energy metabolism via the activation of farnesoid X receptor and secondary signaling [e.g., via fibroblast growth factor 19 (FGF19)], and are linked to metabolic health. We investigated the effect of DMR and glucagon-like peptide-1 (GLP-1) on postprandial bile acid responses in 16 patients with insulin-dependent T2DM, using mixed meal tests performed at the baseline and 6 mo after the DMR procedure. The combination treatment allowed discontinuation of insulin treatment in 11/16 (69%) of patients while improving glycemic and metabolic health. We found increased postprandial unconjugated bile acid responses (all P < 0.05), an overall increased secondary bile acid response (P = 0.036) and a higher 12α-hydroxylated:non-12α-hydroxylated ratio (P < 0.001). Total bile acid concentrations were unaffected by the intervention. Postprandial FGF19 and 7-α-hydroxy-4-cholesten-3-one (C4) concentrations decreased postintervention (both P < 0.01). Our study demonstrates that DMR with GLP-1 modulates the postprandial bile acid response. The alterations in postprandial bile acid responses may be the result of changes in the microbiome, ileal bile acid uptake and improved insulin sensitivity. Controlled studies are needed to elucidate the mechanism linking the combination treatment to metabolic health and bile acids.NEW & NOTEWORTHY Glycemic and metabolic improvements are seen in patients with type 2 diabetes after replacing their insulin therapy with DMR and GLP-1. These changes are accompanied by changes in postprandial bile acid concentrations: increased unconjugated and secondary bile acids.

High-throughput mediation analysis of human proteome and metabolome identifies mediators of post-bariatric surgical diabetes control

To improve the power of mediation in high-throughput studies, here we introduce High-throughput mediation analysis (Hitman), which accounts for direction of mediation and applies empirical Bayesian linear modeling. We apply Hitman in a retrospective, exploratory analysis of the SLIMM-T2D clinical trial in which participants with type 2 diabetes were randomized to Roux-en-Y gastric bypass (RYGB) or nonsurgical diabetes/weight management, and fasting plasma proteome and metabolome were assayed up to 3 years. RYGB caused greater improvement in HbA1c, which was mediated by growth hormone receptor (GHR). GHR’s mediation is more significant than clinical mediators, including BMI. GHR decreases at 3 months postoperatively alongside increased insulin-like growth factor binding proteins IGFBP1/BP2; plasma GH increased at 1 year. Experimental validation indicates (1) hepatic GHR expression decreases in post-bariatric rats; (2) GHR knockdown in primary hepatocytes decreases gluconeogenic gene expression and glucose production. Thus, RYGB may induce resistance to diabetogenic effects of GH signaling.

Trial Registration: Clinicaltrials.gov NCT01073020.

Factors underlying the effects of gastric bypass surgery on glucose homeostasis are incompletely understood. Here the authors developed and applied high-throughput mediation analysis to identify proteome/metabolome mediators of improved glucose homeostasis after to gastric bypass surgery, and report that improved glycemia was mediated by the growth hormone receptor.

Characterization of one anastomosis gastric bypass and impact of biliary and common limbs on bile acid and postprandial glucose metabolism in a minipig model

The alimentary limb has been proposed to be a key driver of the weight-loss-independent metabolic improvements that occur upon bariatric surgery. However, the one anastomosis gastric bypass (OAGB) procedure, consisting of one long biliary limb and a short common limb, induces similar beneficial metabolic effects compared to Roux-en-Y Gastric Bypass (RYGB) in humans, despite the lack of an alimentary limb. The aim of this study was to assess the role of the length of biliary and common limbs in the weight loss and metabolic effects that occur upon OAGB. OAGB and sham surgery, with or without modifications of the length of either the biliary limb or the common limb, were performed in Gottingen minipigs. Weight loss, metabolic changes, and the effects on plasma and intestinal bile acids (BAs) were assessed 15 days after surgery. OAGB significantly decreased body weight, improved glucose homeostasis, increased postprandial GLP-1 and fasting plasma BAs, and qualitatively changed the intestinal BA species composition. Resection of the biliary limb prevented the body weight loss effects of OAGB and attenuated the postprandial GLP-1 increase. Improvements in glucose homeostasis along with changes in plasma and intestinal BAs occurred after OAGB regardless of the biliary limb length. Resection of only the common limb reproduced the glucose homeostasis effects and the changes in intestinal BAs. Our results suggest that the changes in glucose metabolism and BAs after OAGB are mainly mediated by the length of the common limb, whereas the length of the biliary limb contributes to body weight loss.NEW & NOTEWORTHY Common limb mediates postprandial glucose metabolism change after gastric bypass whereas biliary limb contributes to weight loss.

Adaptations in gastrointestinal physiology after sleeve gastrectomy and Roux-en-Y gastric bypass

Linked to the growing obesity epidemic, demand for bariatric and metabolic surgery has increased, the most common procedures being sleeve gastrectomy and Roux-en-Y gastric bypass. Originally, bariatric procedures were described as purely restrictive, malabsorptive, or combined restrictive-malabsorptive procedures limiting food intake, nutrient absorption, or both. Nowadays, anatomical alterations are known to affect gastrointestinal physiology, which in turn affects the digestion and absorption of nutrients and drugs. Therefore, understanding gastrointestinal physiology is crucial to prevent postoperative nutritional deficiencies and to optimise postoperative drug therapy. Preclinical and clinical research indicates that sleeve gastrectomy accelerates liquid and solid gastric emptying and small intestinal transit, and increases bile acid serum levels, whereas its effects on gastrointestinal acidity, gastric and pancreatic secretions, surface area, and colonic transit remain largely unknown. Roux-en-Y gastric bypass diminishes gastric acid secretion, accelerates liquid gastric emptying, and increases bile acid serum levels, but its effects on intestinal pH, solid gastric emptying, intestinal transit time, gastric enzyme secretions, and surface area remain largely unknown. In this Review, we summarise current knowledge of the effects of these two procedures on gastrointestinal physiology and assess the knowledge gaps.

Do Gut Hormones Contribute to Weight Loss and Glycaemic Outcomes after Bariatric Surgery?

Bariatric surgery is an effective intervention for management of obesity through treating dysregulated appetite and achieving long-term weight loss maintenance. Moreover, significant changes in glucose homeostasis are observed after bariatric surgery including, in some cases, type 2 diabetes remission from the early postoperative period and postprandial hypoglycaemia. Levels of a number of gut hormones are dramatically increased from the early period after Roux-en-Y gastric bypass and sleeve gastrectomy—the two most commonly performed bariatric procedures—and they have been suggested as important mediators of the observed changes in eating behaviour and glucose homeostasis postoperatively. In this review, we summarise the current evidence from human studies on the alterations of gut hormones after bariatric surgery and their impact on clinical outcomes postoperatively. Studies which assess the role of gut hormones after bariatric surgery on food intake, hunger, satiety and glucose homeostasis through octreotide use (a non-specific inhibitor of gut hormone secretion) as well as with exendin 9–39 (a specific glucagon-like peptide-1 receptor antagonist) are reviewed. The potential use of gut hormones as biomarkers of successful outcomes of bariatric surgery is also evaluated.

Metabolites and diabetes remission after weight loss

There is marked heterogeneity in the response to weight loss interventions with regards to weight loss amount and metabolic improvement. We sought to identify biomarkers predictive of type 2 diabetes remission and amount of weight loss in individuals with severe obesity enrolled in the Longitudinal Assessment of Bariatric Surgery (LABS) and the Look AHEAD (Action for Health in Diabetes) studies. Targeted mass spectrometry-based profiling of 135 metabolites was performed in pre-intervention blood samples using a nested design for diabetes remission over five years (n = 93 LABS, n = 80 Look AHEAD; n = 87 remitters), and for extremes of weight loss at five years (n = 151 LABS; n = 75 with high weight loss). Principal components analysis (PCA) was used for dimensionality reduction, with PCA-derived metabolite factors tested for association with both diabetes remission and weight loss. Metabolic markers were tested for incremental improvement to clinical models, including the DiaRem score. Two metabolite factors were associated with diabetes remission: one primarily composed of branched chain amino acids (BCAA) and tyrosine (odds ratio (95% confidence interval) [OR (95% CI)] = 1.4 [1.0–1.9], p = 0.045), and one with betaine and choline (OR [95% CI] = 0.7 [0.5–0.9], p = 0.02).These results were not significant after adjustment for multiple tests. Inclusion of these two factors in clinical models yielded modest improvements in model fit and performance: in a constructed clinical model, the C-statistic improved from 0.87 to 0.90 (p = 0.02), while the net reclassification index showed improvement in prediction compared to the DiaRem score (NRI = 0.26, p = 0.0013). No metabolite factors associated with weight loss at five years. Baseline levels of metabolites in the BCAA and trimethylamine-N-oxide (TMAO)-microbiome-related pathways are independently and incrementally associated with sustained diabetes remission after weight loss interventions in individuals with severe obesity. These metabolites could serve as clinically useful biomarkers to identify individuals who will benefit the most from weight loss interventions.

Bile acids and their receptors in metabolic disorders

Bile acids are a large family of atypical steroids which exert their functions by binding to a family of ubiquitous cell membrane and nuclear receptors. There are two main bile acid activated receptors, FXR and GPBAR1, that are exclusively activated by bile acids, while other receptors CAR, LXRs, PXR, RORγT, S1PR2and VDR are activated by bile acids in addition to other more selective endogenous ligands. In the intestine, activation of FXR and GPBAR1 promotes the release of FGF15/19 and GLP1 which integrate their signaling with direct effects exerted by theother receptors in target tissues. This network is tuned in a time ordered manner by circadian rhythm and is critical for the regulation of metabolic process including autophagy, fast-to-feed transition, lipid and glucose metabolism, energy balance and immune responses. In the last decade FXR ligands have entered clinical trials but development of systemic FXR agonists has been proven challenging because their side effects including increased levels of cholesterol and Low Density Lipoproteins cholesterol (LDL-c) and reduced High-Density Lipoprotein cholesterol (HDL-c). In addition, pruritus has emerged as a common, dose related, side effect of FXR ligands. Intestinal-restricted FXR and GPBAR1 agonists and dual FXR/GPBAR1 agonists have been developed. Here we review the last decade in bile acids physiology and pharmacology.

Changes in fasting bile acid profiles after Roux-en-Y gastric bypass and sleeve gastrectomy

BACKGROUND

Bile acid is an essential factor that plays a role in metabolic regulation, but how bile acid is regulated after Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) remains unclear. This meta-analysis aimed to investigate changes in the levels of fasting bile acids following RYGB and SG.

METHODS

A systematic literature search of the PubMed, EMBASE, Cochrane Library and Web of Science databases through July 2020 was performed in accordance with the Meta-analysis Of Observational Studies in Epidemiology (MOOSE) guidelines and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. The concentrations of bile acids were evaluated.

RESULTS

Thirteen studies with 289 patients were included. Our results showed that patients who underwent RYGB had increased levels of fasting total bile acids, primary bile acids, secondary bile acids, conjugated bile acids, and unconjugated bile acids, but no significant differences in all these bile acid levels were observed in patients who underwent SG. Furthermore, 12a-hydroxylated bile acid levels and the 12a-hydroxylated/non-12a-hydroxylated bile acid ratio also increased following RYGB.

CONCLUSION

In this study, we found that fasting bile acid levels, especially 12a-hydroxylated bile acids levels, were increased after RYGB. However, no differences in fasting bile acid levels were observed following SG.

Effects of Manipulating Circulating Bile Acid Concentrations on Postprandial GLP-1 Secretion and Glucose Metabolism After Roux-en-Y Gastric Bypass

BACKGROUND

Altered bile acid (BA) turnover has been suggested to be involved in the improved glucose regulation after Roux-en-Y gastric bypass (RYGB), possibly via stimulation of GLP-1 secretion. We investigated the role of exogenous as well as endogenous BAs for GLP-1 secretion after RYGB by administering chenodeoxycholic acid (CDCA) and the BA sequestrant colesevelam (COL) both in the presence and the absence of a meal stimulus.

METHODS

Two single-blinded randomized cross-over studies were performed. In study 1, eight RYGB operated participants ingested 200 ml water with 1) CDCA 1.25 g or 2) CDCA 1.25 g + colesevelam 3.75 g on separate days. In study 2, twelve RYGB participants ingested on separate days a mixed meal with addition of 1) CDCA 1.25 g, 2) COL 3.75 g or 3) COL 3.75 g × 2, or 4) no additions.

RESULTS

In study 1, oral intake of CDCA increased circulating BAs, GLP-1, C-peptide, glucagon, and neurotensin. Addition of colesevelam reduced all responses. In study 2, addition of CDCA enhanced meal-induced increases in plasma GLP-1, glucagon and FGF-19 and lowered plasma glucose and C-peptide concentrations, while adding colesevelam lowered circulating BAs but did not affect meal-induced changes in plasma glucose or measured gastrointestinal hormones.

CONCLUSION

In RYGB-operated persons, exogenous CDCA enhanced meal-stimulated GLP-1 and glucagon secretion but not insulin secretion, while the BA sequestrant colesevelam decreased CDCA-stimulated GLP-1 secretion but did not affect meal-stimulated GLP-1, C-peptide or glucagon secretion, or glucose tolerance. These findings suggest a limited role for endogenous bile acids in the acute regulation of postprandial gut hormone secretion or glucose metabolism after RYGB.

Bile acid, glucose, lipid profile, and liver enzyme changes in prediabetic patients 1 year after sleeve gastrectomy

Background

Few articles have studied individuals with prediabetes after sleeve gastrectomy. Bile acid and lipid levels remain inconsistent in postbariatric patients. The purpose of this study was to explore bile acid, glucose, lipid, and liver enzyme changes in patients with different diabetes statuses who underwent sleeve gastrectomy. The impact of bariatric surgery and its potential benefits for prediabetic patients was also discussed.

Methods

A total of 202 overweight and obese patients who underwent bariatric surgery in our hospital between January 2016 and October 2018 were retrospectively reviewed. Patients were divided into prediabetes (n = 32), nondiabetes (n = 144), and diabetes (n = 26) groups and analysed. Glucose and lipid data were collected from medical records at baseline and at each follow-up visit.

Result

Significant improvements in body weight, glucose and lipid levels, and liver enzymes (P ≤ 0.05) in prediabetic patients were found throughout the first year postoperatively. Improvement in glycaemic control was first seen one month postoperatively, followed by persistent improvement in the next 12 months. Total bile acid (TBA) decreased, which was associated with ALT improvement in prediabetic patients 1-year post-surgery. There were no significant differences in HbA1c, glucose, or triglycerides (TGs) between prediabetic and T2DM patients or between prediabetic and nondiabetic patients at 12 months post-surgery.

Conclusion

LSG is highly effective at interfering with glucose and lipid levels as well as total bile acid levels in prediabetic patients in the first year postoperatively. Thus, LSG is indeed an alternative for overweight and obese prediabetic patients.

Effects of laparoscopic sleeve gastrectomy on concentration and composition of bile acids in an Asian population with morbid obesity

Background:

Bile acids (BAs) are traditionally associated with lipid absorption and phase II detoxification by forming various BA conjugates. Recently, it has been discovered that BAs also regulate glucose metabolism, and the increase in BAs in patients following bariatric surgery may contribute to the post-surgery improvement in insulin resistance (IR). However, while Roux-en-Y gastric bypass can increase BA concentrations post-surgery, this may not be the case after laparoscopic sleeve gastrectomy (LSG). We hypothesized that the profiling of BAs that include the conjugated BA species could detect post-surgery BA changes after LSG. To test our hypothesis, we performed comprehensive profiling of BAs in Asian individuals with morbid obesity at baseline, and at 6 months following LSG.

Methods:

Fourteen subjects scheduled for LSG were recruited. Anthropometric measurements, oral glucose tolerance test, and biochemistry tests were performed at baseline and at 6 months after LSG. BAs were profiled using liquid chromatography–mass spectrometry.

Results:

At 6 months, subjects lost significant weight from 117.4±5.4 to 92.1±3.8 kg and demonstrated significant improvement in IR. HOMA-IR decreased from 6.2±0.7 to 2.0±0.2 and the Matsuda index increased from 1.9±0.3 to 3.3±0.3. We did not detect any significant post-operative change in the levels of total BAs (5237.1±1219.4 vs. 3631.7±457.9, p=0.181) or non-sulfated BAs after LSG. However, sulfated BA species increased significantly after LSG.

Conclusion:

Our study showed that the serum concentrations of sulfated BA species in morbidly obese Asian individuals increased significantly 6 months after LSG; the increase in sulfated BAs after LSG might contribute to the post-surgery improvement of metabolic health.

Potential contribution of the gut microbiota to hypoglycemia after gastric bypass surgery

Obesity has become a global health problem. Lifestyle modification and medical treatment only appear to yield short-term weight loss. Roux-en-Y gastric bypass (RYGB) is the most popular bariatric procedure, and it sustains weight reduction and results in the remission of obesity-associated comorbidities for obese individuals. However, patients who undergo this surgery may develop hypoglycemia. To date, the diagnosis is challenging and the prevalence of post-RYGB hypoglycemia (PRH) is unclear. RYGB alters the anatomy of the upper gastrointestinal tract and has a combined effect of caloric intake restriction and nutrient malabsorption. Nevertheless, the physiologic changes after RYGB are complex. Although hyperinsulinemia, incretin effects, dysfunction of β-cells and α-cells, and some other factors have been widely investigated and are reported to be possible mediators of PRH, the pathogenesis is still not completely understood. In light of the important role of the gut microbiome in metabolism, we hypothesized that the gut microbiome might also be a critical link between RYGB and hypoglycemia. In this review, we mainly highlight the current possible factors predisposing individuals to PRH, particularly related to the gut microbiota, which may yield significant insights into the intestinal regulation of glucose metabolic homeostasis and provide novel clues to improve the treatment of type 2 diabetes mellitus.

Effect of bariatric surgery on circulating FGF-19: A systematic review and meta-analysis

Fibroblast growth factor-19 (FGF-19) is a gut hormone which interacts with metabolism and is depleted in obesity. There is some indication that the hormone undergoes a resurgence following bariatric surgery (BS), an effect which may contribute to the beneficial outcomes of such procedures. This systematic review and meta-analysis aims to synthesize the available literature on FGF-19 levels before and after BS. MEDLINE, Scopus and Web of Science databases were searched, and the effect of different surgical procedures and degrees of body mass index (BMI) reduction on FGF-19 levels was assessed by DerSimonian and Laird random-effects model in meta-analysis and dose-response analyses. This meta-analysis, which included 474 patients from 25 arms undergoing one of five BS procedures, revealed a significant increase in the levels of circulating FGF-19 following all-type BS. Vertical sleeve gastrectomy, duodenal-jejunal bypass liner and Roux-en-Y gastric bypass all significantly increased circulating FGF-19 levels from baseline. However, gastric banding failed to achieve the same, and in fact, biliopancreatic diversion was associated with decreased circulating FGF-19. Finally, an inverse association between FGF-19 and the degree of BMI-reduction post-operatively was noted. FGF-19 is increased by BS and may represent a pharmaceutical target in efforts to reproduce the beneficial effects of BS in a medical setting.

Surgery-Induced Weight Loss and Changes in Hormonally Active Fibroblast Growth Factors: a Systematic Review and Meta-Analysis

This systematic review and meta-analysis was performed to investigate the possible changes of FGF-19 and FGF-21 after bariatric surgery (BS). Electronic databases including PubMed and Scopus were systematically searched up to February 2020 to identify pertinent studies. A total of 25 different studies were included. The overall pooled analysis identified that BS caused a significant increase in FGF-19, but had no significant effect on FGF-21. For FGF-19, this finding was supported in the subgroup analyses. For FGF-21, Roux-en-Y gastric bypass (RYGB) surgery significantly increased FGF-21 levels, whereas, in studies with follow-up duration ≥ 1 year, FGF-21 levels decreased significantly. BS reduces circulating concentration of FGF-19, but might increase FGF-21 after RYGB or decrease FGF-21 after ≥ 1 year.

Targeting bile acid metabolism in obesity reduction: A systematic review and meta-analysis

A systematic review and meta-analysis was conducted of studies that address the association of bile acid (BA) with obesity and of studies on the effects of treatment in patients with obesity on BA metabolism, assessed from systemic BA, fibroblast growth factor 19 (FGF19), 7α-hydroxy-4-cholesten-3-one (C4) level, and faecal BA. We searched PubMed, Embase, and the Cochrane Library from inception to 1 August 2019 using the keywords obesity, obese, body mass index, and overweight with bile acid, FGF19, FXR, and TGR5. Two reviewers independently searched, selected, and assessed the quality of studies. Data were analysed using either fixed or random effect models with inverse variance weighting. Of 3771 articles, 33 papers were relevant for the association of BA with obesity of which 22 were included in the meta-analysis, and 50 papers were relevant for the effect of obesity interventions on BA of which 20 were included in the meta-analysis. Circulating fasting total BA was not associated with obesity. FGF19 was inversely and faecal BA excretion was positively associated with obesity. Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) modulated BA metabolism, ie, increased BA and FGF19. Our results indicate that BA metabolism is altered in obesity. Certain bariatric surgeries including RYGB and SG modulate BA, whether these underlie the beneficial effect of the treatment should be investigated.

Bilio-enteric flow and plasma concentrations of bile acids after gastric bypass and sleeve gastrectomy

BACKGROUND/OBJECTIVES

Bile acids in plasma are elevated after bariatric surgery and may contribute to metabolic improvements, but underlying changes in bile flow are poorly understood. We assessed bilio-enteric flow of bile and plasma bile concentrations in individuals with Roux-en-Y gastric bypass (RYGB) or sleeve gastrectomy (SG) surgery compared with matched non-surgical controls (CON).

SUBJECTS/METHODS

Fifteen RYGB, 10 SG and 15 CON underwent ⁹⁹Tc-mebrofenin cholescintigraphy combined with intake of a high-fat ¹¹¹In-DTPA-labelled meal and frequent blood sampling. A ⁷⁵Se-HCAT test was used to assess bile acid retention.

RESULTS

After RYGB, gallbladder filling was decreased (p = 0.045 versus CON), basal flow of bile into the small intestine increased (p = 0.005), bile acid retention augmented (p = 0.021) and basal bile acid plasma concentrations elevated (p = 0.009). During the meal, foods passed unimpeded through the gastric pouch resulting in almost instant postprandial mixing of bile and foods, but the postprandial rise in plasma bile acids was brief and associated with decreased overall release of fibroblast growth factor-19 (FGF-19) compared with CON (p = 0.033). After SG, bile flow and retention were largely unaltered (p > 0.05 versus CON), but gastric emptying was accelerated (p < 0.001) causing earlier mixture of bile and foods also in this group. Neither basal nor postprandial bile acid concentrations differed between SG and CON.

CONCLUSIONS

Bilio-enteric bile flow is markedly altered after RYGB resulting in changes in plasma concentrations of bile acids and FGF-19, whereas bile flow and plasma concentrations are largely unaltered after SG.

Effects of different metabolic states and surgical models on glucose metabolism and secretion of ileal L-cell peptides: results from the HIPER-1 study

AIM

To compare the impact of four surgical procedures (mini-gastric bypass, sleeve gastrectomy, ileal transposition and transit bipartition) vs medical management on gut peptide secretion, β-cell function and resolution of hyperglycaemia in people with type 2 diabetes.

RESEARCH DESIGN AND METHODS

A mixed-meal tolerance test was administered 6-24 months after each surgical procedure (mini-gastric bypass, sleeve gastrectomy, ileal transposition and transit bipartition; n=30 in each group) and the results were compared with those obtained in matched lean (n=30) and obese (n=30) people with type 2 diabetes undergoing medical management.

RESULTS

Participants in the mini-gastric bypass and ileal transposition groups had a greater increase in plasma glucose concentration after the mixed-meal tolerance test than those in the sleeve gastrectomy and transit bipartition groups. Participants in the mini-gastric bypass group exhibited the greatest increase in the incremental area under the curve of plasma glucose concentration above baseline (P<0.0001). Insulin sensitivity was similar across surgical groups, and statistically greater in participants in the surgical groups than in obese participants in the non-surgical group (P<0.0001). β-cell responsiveness to glucose was greater in participants in the sleeve gastrectomy and transit bipartition groups than in the mini-gastric bypass and ileal transposition groups (P<0.001) despite a smaller incremental increase above baseline in the area under the plasma glucagon-like peptide-1 concentration curve relative to ileal transposition. Postoperative β-cell function was the strongest predictor of hyperglycaemia resolution.

CONCLUSIONS

The present study showed that the level of β-cell function after bariatric surgery is the strongest predictor of hyperglycaemia resolution. The study also demonstrates a disconnect between postprandial GLP-1 levels and β-cell function among the studied surgical procedures.

Proceedings of the 2017 ASPEN Research Workshop-Gastric Bypass: Role of the Gut

The goal of the National Institutes of Health-funded American Society for Parenteral and Enteral Nutrition 2017 research workshop (RW) "Gastric Bypass: Role of the Gut" was to focus on the exciting research evaluating gut-derived signals in modulating outcomes after bariatric surgery. Although gastric bypass surgery has undoubted positive effects, the mechanistic basis of improved outcomes cannot be solely explained by caloric restriction. Emerging data suggest that bile acid metabolic pathways, luminal contents, energy balance, gut mucosal integrity, as well as the gut microbiota are significantly modulated after bariatric surgery and may be responsible for the variable outcomes, each of which was rigorously evaluated. The RW served as a timely and novel academic meeting that brought together clinicians and researchers across the scientific spectrum, fostering a unique venue for interdisciplinary collaboration among investigators. It promoted engaging discussion and evolution of new research hypotheses and ideas, driving the development of novel ameliorative, therapeutic, and nonsurgical interventions targeting obesity and its comorbidities. Importantly, a critical evaluation of the current knowledge regarding gut-modulated signaling after bariatric surgery, potential pitfalls, and lacunae were thoroughly addressed.

Differential effects of a 40-hour fast and bile acid supplementation on human GLP-1 and FGF19 responses

Bile acids, glucagon-like peptide-1 (GLP-1), and fibroblast growth factor 19 (FGF19) play an important role in postprandial metabolism. In this study, we investigated the postprandial bile acid response in plasma and its relation to insulin, GLP-1, and FGF19. First, we investigated the postprandial response to 40-h fast. Then we administered glycine-conjugated deoxycholic acid (gDCA) with the meal. We performed two separate observational randomized crossover studies on healthy, lean men. In experiment 1: we tested 4-h mixed meal after an overnight fast and a 40-h fast. In experiment 2, we tested a 4-h mixed meal test with and without gDCA supplementation. Both studies measured postprandial glucose, insulin, bile acids, GLP-1, and FGF19. In experiment 1, 40 h of fasting induced insulin resistance and increased postprandial GLP-1 and FGF19 concentrations. After an overnight fast, we observed strong correlations between postprandial insulin and gDCA levels at specific time points. In experiment 2, administration of gDCA increased GLP-1 levels and lowered late postprandial glucose without effect on FGF19. Energy expenditure was not affected by gDCA administration. Unexpectedly, 40 h of fasting increased both GLP-1 and FGF19, where the former appeared bile acid independent and the latter bile acid dependent. Second, a single dose of gDCA increased postprandial GLP-1. Therefore, our data add complexity to the physiological regulation of the enterokines GLP-1 and FGF19 by bile acids.

Acute Changes of Bile Acids and FGF19 After Sleeve Gastrectomy and Roux-en-Y Gastric Bypass

CONTEXT

Gastric bypass (GBP) and sleeve gastrectomy (SG) are both effective bariatric treatments that cause sustained weight loss as well as improvement of type 2 diabetes mellitus (T2DM). The underlying mechanisms are under investigation, including the contribution of alterations in bile acids (BAs) in achieving or maintaining the beneficial metabolic effects after bariatric surgery.

AIMS

The aim of this study is to investigate the acute and short-term effects of GBP and SG on BA compositions and fibroblast growth factor 19 (FGF19) in obese individuals with T2DM and to evaluate any correlations between changes in these measures with glucose metabolic improvements.

METHODS

The levels of both fasting and postprandial plasma BA compositions after oral glucose tolerance test (OGTT), fasting FGF19 and various metabolic indices were measured 1 day before and at 3 days and 3 months after GBP and SG in 19 obese patients (GBP = 8, SG = 11) with T2DM.

RESULTS

Body weight loss was observed after both GBP and SG 3 months post-operatively, with no significant difference between the two intervention groups (15.0 ± 3.1% vs. 13.9 ± 5.2%, P = 0.761). At 3 days post-operation, FGF19 levels increased significantly in both surgery groups (GBP, 118.3 ± 57.3 vs. 363.6 ± 131.0 pg mL^-1, post-operation P = 0.008; SG, 173.2 ± 127.8 vs. 422.0 ± 243.6 pg mL^-1, post-operation P = 0.001). Fasting and postprandial increases from pre-operative values in secondary (r = 0.57, P = 0.02; r = 0.58, P = 0.01), conjugated (r = 0.50, P = 0.01; r = 0.48, P = 0.04), glycine-conjugated (r = 0.52, P = 0.05; r = 0.46, P = 0.05) and secondary-conjugated (r = 0.53, P = 0.02; r = 0.60, P = 0.01) BAs correlated with decreases in the postprandial states of glucose (defined by area under the curve (AUC) over 120 min (AUC_0-120min)). Increases in postprandial primary-conjugated BAs were found to be associated with decreases in HOMA-IR (r = 0.45, P = 0.05). However, increases in fasting and postprandial taurine-conjugated BA correlated with decreases in both basal insulin secretion rate (r = 0.47, P = 0.04; r = 0.48, P = 0.04) and C-peptide level (r = 0.45, P = 0.05; r = 0.47, P = 0.04). After 3 months, fasting and postprandial increases in secondary (r = 0.51, P = 0.03; r = 0.48, P = 0.04), secondary-conjugated (r = 0.52, P = 0.02; r = 0.51, P = 0.03) and non-12α-OH (r = 0.51, P = 0.02; r = 0.58, P = 0.01) BAs were found to correlate with increases in Stumvoll Insulin Sensitivity Index. Increases in both fasting and postprandial 12α-OH BAs were correlated with the decreases in glucose AUC (r = 0.46, P = 0.05; r = 0.41, P = 0.04).

CONCLUSIONS

Both GBP and SG achieve increases in many BA species as early as 3 days post-operation, which are sustained at 3 months post-operation. Rises in secondary BA and conjugated forms are correlated with early improvements in glucose metabolism at 3 days post-operation. These along with 12α-OH BA correlated with improved glucose metabolism at 3 months post-operation, suggesting they may contribute to the observed T2DM remission after bariatric surgery.

Bile acid changes after metabolic surgery are linked to improvement in insulin sensitivity

Background

Metabolic surgery is associated with a prompt improvement in insulin resistance, although the mechanism of action remains unknown. The literature on bile acid changes after metabolic surgery is conflicting, and insulin sensitivity is generally assessed by indirect methods. The aim of this study was to investigate the relationship between improvement in insulin sensitivity and concentration of circulating bile acids after biliopancreatic diversion (BPD) and Roux‐en‐Y gastric bypass (RYGB).

Methods

This was a prospective observational study of nine patients who underwent BPD and six who had RYGB. Inclusion criteria for participation were a BMI in excess of 40 kg/m², no previous diagnosis of type 2 diabetes and willingness to participate. Exclusion criteria were major endocrine diseases, malignancies and liver cirrhosis. Follow‐up visits were carried out after a mean(s.d.) of 185·3(72·9) days. Fasting plasma bile acids were assessed by ultra‐high‐performance liquid chromatography coupled with a triple quadrupole mass spectrometer, and insulin sensitivity was measured by means of a hyperinsulinaemic–euglycaemic clamp.

Results

A significant increase in all bile acids, as well as an amelioration of insulin sensitivity, was observed after metabolic surgery. An increase in conjugated secondary bile acids was significantly associated with an increase in insulin sensitivity. Only the increase in glycodeoxycholic acid was significantly associated with an increase in insulin sensitivity in analysis of individual conjugated secondary bile acids.

Conclusion

Glycodeoxycholic acid might drive the improved insulin sensitivity after metabolic surgery.

Longitudinal changes of microbiome composition and microbial metabolomics after surgical weight loss in individuals with obesity

BACKGROUND

Some of the metabolic effects of bariatric surgery may be mediated by the gut microbiome.

OBJECTIVES

To study the effect of bariatric surgery on changes to gut microbiota composition and bacterial pathways, and their relation to metabolic parameters after bariatric surgery.

SETTINGS

University hospitals in the United States and Spain.

METHODS

Microbial diversity and composition by 16 S rRNA sequencing, putative bacterial pathways, and targeted circulating metabolites were studied in 26 individuals with severe obesity, with and without type 2 diabetes, before and at 3, 6, and 12 months after either gastric bypass or sleeve gastrectomy.

RESULTS

Bariatric surgery tended to increase alpha diversity, and significantly altered beta diversity, microbiota composition, and function up to 6 months after surgery, but these changes tend to regress to presurgery levels by 12 months. Twelve of 15 bacterial pathways enriched after surgery also regressed to presurgery levels at 12 months. Network analysis identified groups of bacteria significantly correlated with levels of circulating metabolites over time. There were no differences between study sites, surgery type, or diabetes status in terms of microbial diversity and composition at baseline and after surgery.

CONCLUSIONS

The association among changes in microbiome with decreased circulating biomarkers of inflammation, increased bile acids, and products of choline metabolism and other bacterial pathways suggest that the microbiome partially mediates improvement of metabolism during the first year after bariatric surgery.

Duodenal-jejunal lining increases postprandial unconjugated bile acid responses and disrupts the bile acid-FXR-FGF19 axis in humans

BACKGROUND AND AIMS

Placement of the duodenal-jejunal bypass liner (DJBL) leads to rapid weight loss and restoration of insulin sensitivity in a similar fashion to bariatric surgery. Increased systemic bile acid levels are candidate effectors for these effects through postprandial activation of their receptors TGR5 and FXR. We aimed to quantify postprandial bile acid, GLP-1 and FGF19 responses and assess their temporal relation to the weight loss and metabolic and hormonal changes seen after DJBL placement.

METHODS

We performed mixed meal testing in 17 obese patients with type 2 diabetes mellitus (DM2) directly before, one week after and 6 months after DJBL placement.

RESULTS

Both fasting and postprandial bile acid levels were unchanged at 1 week after implantation, and greatly increased 6 months after implantation. The increase consisted of unconjugated bile acid species. 3 hour-postprandial GLP-1 levels increased after 1 week and were sustained, whereas FGF19 levels and postprandial plasma courses were unaffected.

CONCLUSIONS

DJBL placement leads to profound increases in unconjugated bile acid levels after 6 months, similar to the effects of bariatric surgery. The temporal dissociation between the changes in bile acids, GLP-1 and FGF19 and other gut hormone responses warrant caution about the beneficial role of bile acids after DJBL placement. This observational uncontrolled study emphasizes the need for future controlled studies.

Food Intake and Eating Behavior After Bariatric Surgery

Obesity is an escalating global chronic disease. Bariatric surgery is a very efficacious treatment for obesity and its comorbidities. Alterations to gastrointestinal anatomy during bariatric surgery result in neurological and physiological changes affecting hypothalamic signaling, gut hormones, bile acids, and gut microbiota, which coalesce to exert a profound influence on eating behavior. A thorough understanding of the mechanisms underlying eating behavior is essential in the management of patients after bariatric surgery. Studies investigating candidate mechanisms have expanded dramatically in the last decade. Herein we review the proposed mechanisms governing changes in eating behavior, food intake, and body weight after bariatric surgery. Additive or synergistic effects of both conditioned and unconditioned factors likely account for the complete picture of changes in eating behavior. Considered application of strategies designed to support the underlying principles governing changes in eating behavior holds promise as a means of optimizing responses to surgery and long-term outcomes.

Fibroblast Growth Factor 15/19: From Basic Functions to Therapeutic Perspectives

Discovered 20 years ago, fibroblast growth factor (FGF)19, and its mouse ortholog FGF15, were the first members of a new subfamily of FGFs able to act as hormones. During fetal life, FGF15/19 is involved in organogenesis, affecting the development of the ear, eye, heart, and brain. At adulthood, FGF15/19 is mainly produced by the ileum, acting on the liver to repress hepatic bile acid synthesis and promote postprandial nutrient partitioning. In rodents, pharmacologic doses of FGF19 induce the same antiobesity and antidiabetic actions as FGF21, with these metabolic effects being partly mediated by the brain. However, activation of hepatocyte proliferation by FGF19 has long been a challenge to its therapeutic use. Recently, genetic reengineering of the molecule has resolved this issue. Despite a global overlap in expression pattern and function, murine FGF15 and human FGF19 exhibit several differences in terms of regulation, molecular structure, signaling, and biological properties. As most of the knowledge originates from the use of FGF19 in murine models, differences between mice and humans in the biology of FGF15/19 have to be considered for a successful translation from bench to bedside. This review summarizes the basic knowledge concerning FGF15/19 in mice and humans, with a special focus on regulation of production, morphogenic properties, hepatocyte growth, bile acid homeostasis, as well as actions on glucose, lipid, and energy homeostasis. Moreover, implications and therapeutic perspectives concerning FGF19 in human diseases (including obesity, type 2 diabetes, hepatic steatosis, biliary disorders, and cancer) are also discussed.

Targeting FXR and FGF19 to Treat Metabolic Diseases-Lessons Learned From Bariatric Surgery

Bariatric surgery procedures, such as Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG), are the most effective interventions available for sustained weight loss and improved glucose metabolism. Bariatric surgery alters the enterohepatic bile acid circulation, resulting in increased plasma bile levels as well as altered bile acid composition. While it remains unclear why both VSG and RYGB can alter bile acids, it is possible that these changes are important mediators of the effects of surgery. Moreover, a molecular target of bile acid synthesis, the bile acid-activated transcription factor FXR, is essential for the positive effects of VSG on weight loss and glycemic control. This Perspective examines the relationship and sequence of events between altered bile acid levels and composition, FXR signaling, and gut microbiota after bariatric surgery. We hypothesize that although bile acids and FXR signaling are potent mediators of metabolic function, unidentified downstream targets are the main mediators behind the benefits of weight-loss surgery. One of these targets, the gut-derived peptide FGF15/19, is a potential molecular and therapeutic marker to explain the positive metabolic effects of bariatric surgery. Focusing research efforts on identifying these complex molecular mechanisms will provide new opportunities for therapeutic strategies to treat obesity and metabolic dysfunction.

Complementary intestinal mucosa and microbiota responses to caloric restriction

The intestine is key for nutrient absorption and for interactions between the microbiota and its host. Therefore, the intestinal response to caloric restriction (CR) is thought to be more complex than that of any other organ. Submitting mice to 25% CR during 14 days induced a polarization of duodenum mucosa cell gene expression characterised by upregulation, and downregulation of the metabolic and immune/inflammatory pathways, respectively. The HNF, PPAR, STAT, and IRF families of transcription factors, particularly the Pparα and Isgf3 genes, were identified as potentially critical players in these processes. The impact of CR on metabolic genes in intestinal mucosa was mimicked by inhibition of the mTOR pathway. Furthermore, multiple duodenum and faecal metabolites were altered in CR mice. These changes were dependent on microbiota and their magnitude corresponded to microbial density. Further experiments using mice with depleted gut bacteria and CR-specific microbiota transfer showed that the gene expression polarization observed in the mucosa of CR mice is independent of the microbiota and its metabolites. The holistic interdisciplinary approach that we applied allowed us to characterize various regulatory aspects of the host and microbiota response to CR.

Increased Bile Acids and FGF19 After Sleeve Gastrectomy and Roux-en-Y Gastric Bypass Correlate with Improvement in Type 2 Diabetes in a Randomized Trial

BACKGROUND

Sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGB) are both effective bariatric procedures to treat type 2 diabetes (T2DM) and obesity. The contribution of changes in bile acids (BAs) and fibroblast growth factor19 (FGF19) to such metabolic improvements is unclear.

METHODS

We examined associations between changes in BAs, FGF19 (fasting and prandial), with changes in body weight, glycemia, and other metabolic variables in 61 obese patients with T2DM before and 1 year after randomization to SG or RYGB.

RESULTS

Weight loss and diabetes remission (defined by HbA1c < 39 mmol/mol [< 5.7%] in the absence of glucose-lowering therapy) after RYGB and SG was similar (mean weight loss - 29 vs - 31 kg, p = 0.50; diabetes remission proportion 37.5 vs 34%, p = 1.0). Greater increments in fasting and prandial levels of total, secondary, and unconjugated BAs were seen after RYGB than SG. Fasting and prandial increases in total (r = - 0.3, p = 0.01; r = - 0.2, p = 0.04), secondary (r = - 0.3, p = 0.01; r = - 0.4, p = 0.01) and unconjugated BA (r = - 0.3, p = 0.01; r = 0.4, p < 0.01) correlated with decreases in HbA1c, but not weight. Changes in 12α-OH/non 12α-OH were positively associated with prandial glucose increments (r = 0.2, p = 0.03), HbA1c (r = 0.3, p = 0.01), and negatively associated with changes in insulinogenc index (r = - 0.3, p = 0.01). Only changes in prandial FGF19 were negatively associated with HbA1c (r = - 0.4, p < 0.01) and visceral fat (r = - 0.3, p = 0.04).

CONCLUSIONS/INTERPRETATION

The association between increases in secondary, unconjugated BAs and improvements in HBA1c (but not weight) achieved after both RYGB and SG suggest manipulation of BA as a potential strategy for controlling T2DM through weight-independent means.

Intestinal and Gastric Origins for Diabetes Resolution After Bariatric Surgery

PURPOSE OF REVIEW

This paper will review the intestinal and gastric origins for diabetes resolution after bariatric surgery.

RECENT FINDINGS

In addition to the known metabolic effects of changes in the gut hormonal milieu, more recent studies investigating the role of the microbiome and bile acids and changes in nutrient sensing mechanisms have been shown to have glycemic effects in human and animal models. Independent of weight loss, there are multiple mechanisms that may lead to amelioration or resolution of diabetes following bariatric surgery. There is abundant evidence pointing to changes in gut hormones, bile acids, gut microbiome, and intestinal nutrient sensing; more research is needed to clearly delineate their role in regulating energy and glucose homeostasis after bariatric surgery.

Bile acid profiles within the enterohepatic circulation in a diabetic rat model after bariatric surgeries

Bile acids (BAs), which are synthesized in the liver and cycled in the enterohepatic circulation, have been recognized as signaling molecules by activating their receptors in the intestine and liver. Serum taurine-conjugated BAs have been shown to be elevated after bariatric surgeries although the postoperative BA profiles within the enterohepatic circulation have not been investigated. Clarification of these profiles could help explain the mechanisms by which bariatric surgery leads to BA profile alterations and subsequent metabolic effects. We performed duodenal-jejunal bypass (DJB), sleeve gastrectomy (SG), and sham procedures in an obese diabetic rat model induced by high-fat diet and streptozotocin. The weight loss and antidiabetic effects were evaluated postsurgery. BA profiles in the systemic serum and within the enterohepatic circulation were analyzed, together with the expression of related BA transporters and enzymes at week 12 after surgery. Compared with sham, SG induced sustained weight loss, and both DJB and SG significantly improved glucose tolerance and insulin sensitivity with enhanced glucagon-like peptide 1 secretion. Similar to changes in the serum, BAs, especially taurine-conjugated species, were also elevated in the enterohepatic circulation (bile and portal vein) after DJB and SG. In addition, the expression of key BA transporters and conjugational enzymes was elevated postoperatively, whereas the enzymes responsible for BA synthesis were decreased. In conclusion, DJB and SG elevated BA levels in the systemic serum and enterohepatic circulation, especially taurine-conjugated species, which likely indicates increased ileal reabsorption and hepatic conjugation rather than synthesis. NEW & NOTEWORTHY Bile acids (BAs) have been implicated as potential mediators of the weight-independent effects of bariatric surgery. For the first time, we discovered that duodenal-jejunal bypass and sleeve gastrectomy elevated BAs, particularly the taurine-conjugated species in the enterohepatic circulation, likely through the promotion of ileal reabsorption and hepatic conjugation rather than BA synthesis. These findings will improve our understanding of BA metabolism after bariatric surgery and their subsequent metabolic effects.

Early Effects of Sleeve Gastrectomy on Obesity-Related Cytokines and Bile Acid Metabolism in Morbidly Obese Japanese Patients

BACKGROUND

Laparoscopic sleeve gastrectomy (LSG) has wide-ranging positive effects on adipocytokine metabolism, bile acid profile, and chronic low-grade inflammation related to obesity. However, the early temporal changes in these markers following LSG have not been well investigated. This study aimed to evaluate the early effects of LSG on adipocytokines, bile acid profile, and inflammatory markers.

METHODS

This was a nonrandomized prospective study examining morbidly obese Japanese patients undergoing LSG. Serial measurements of leptin, adiponectin, bile acids, fibroblast growth factor (FGF)-19, and inflammatory markers were performed preoperatively and 1 and 6 months after LSG.

RESULTS

The study included ten patients (five females) with a mean age of 48.8 years and BMI 40.9 kg/m². At baseline, 90% of the patients had T2DM, 70% had dyslipidemia, and 90% had hypertension. Patients lost 5.1 kg/m² BMI at 1 month and 10.1 kg/m² BMI at 6 months. The leptin levels sharply decreased, and FGF-19 increased significantly as early as 1 month postoperatively. Adiponectin levels showed an increasing trend at 1 month and a significant increase at 6 months. A significant decrease in high-sensitivity CRP and plasminogen activator inhibitor-1 was observed at 6 months. No significant changes were observed in interleukin (IL)-6, IL-8, tumor necrosis factor-α, serum amyloid A protein, or monocyte chemotactic protein-1 throughout the study.

CONCLUSIONS

LSG improved the secretion of adipocytokines, increased FGF-19 secretion soon after surgery, and slowly ameliorated inflammation related to obesity through significant weight loss.

Surgery for Diabetes: Clinical and Mechanistic Aspects

According to the most recent publication by the Canadian Public Health Agency, obesity affects 25% of adults. In addition, there is a clear association between the recent rise in obesity and the increased prevalence of type 2 diabetes. Medical therapy for obesity has shown limited long-term effectiveness, and surgical treatment is now recognized by medical authorities as part of the armamentarium for the management of type 2 diabetes in severely obese patients. The current indications for obesity surgery and postoperative management are reviewed. The choice of surgery should balance expected benefits associated with weight loss (including remission rate of type 2 diabetes), side effects and the risks for early and long-term complications. Long-term outcomes of metabolic surgery for diabetes vary according to the type of surgery (ranging between 20% and 90% remission rates) and the underlying metabolic changes. Several controlled trials have been published in recent years confirming the superiority of metabolic surgery over medical treatment for the management of type 2 diabetes associated with severe obesity. Some of the known underlying mechanisms of action include a combination of caloric restriction, hormonal changes, decreased nutrient absorption and changes in bile acids, microbiota and incretins. Further research is needed to clarify the mechanistic changes associated with each surgical procedure and their respective long-term outcomes.

Gastric Bypass-Related Effects on Glucose Control, β Cell Function and Morphology in the Obese Zucker Rat

BACKGROUND

Roux-en-Y gastric bypass (RYGB) may improve beta cell function by mechanisms other than caloric restriction and body weight loss. We aimed to assess the impact of anatomical and hormonal alterations specific to RYGB on glucose homeostasis, β cell function and morphology.

METHODS

Male Zucker(fa/fa) rats underwent either RYGB (n = 11) or sham surgeries (n = 10). Five of the shams were then food restricted and body weight matched (BWM) to the RYGB rats. Six male Zucker(fa/+) rats underwent sham surgery and served as additional lean controls. Twenty-seven days after surgery, an oral glucose tolerance test (OGTT) was performed and plasma levels of glucose, insulin and glucagon-like peptide-1 (GLP-1) were measured. Immunohistological analysis of pancreatic islets was performed, and GLP-1 receptor and PDX-1 mRNA content were quantified.

RESULTS

Shams consumed more food and gained more weight compared to both RYGB and BWM (p < 0.001). Hyperglycaemia was evident in ad libitum-fed shams, whilst postprandial glucose levels were lower in RYGB compared to the BWM sham group (p < 0.05). During the OGTT, RYGB rats responded with >2.5-fold increase of GLP-1. Histology revealed signs of islet degeneration in ad libitum-fed shams, but not in RYGB and sham BWM controls (p < 0.001). GLP-1 receptor and PDX-1 mRNA content was similar between the RYGB and BWM shams but higher compared to ad libitum shams (p < 0.05).

CONCLUSIONS

Combined molecular, cellular and histological analyses of pancreatic function suggest that weight loss alone, and not the enhancement of GLP-1 responses, is predominant for the short-term β cell protective effects of RYGB.

The presence and severity of nonalcoholic steatohepatitis is associated with specific changes in circulating bile acids

The histologic spectrum of nonalcoholic fatty liver disease (NAFLD) includes fatty liver (NAFL) and steatohepatitis (NASH), which can progress to cirrhosis in up to 20% of NASH patients. Bile acids (BA) are linked to the pathogenesis and therapy of NASH. We (1) characterized the plasma BA profile in biopsy-proven NAFL and NASH and compared to controls and (2) related the plasma BA profile to liver histologic features, disease activity, and fibrosis. Liquid chromatography/mass spectrometry quantified BAs. Descriptive statistics, paired and multiple group comparisons, and regression analyses were performed. Of 86 patients (24 controls, 25 NAFL, and 37 NASH; mean age 51.8 years and body mass index 31.9 kg/m² ), 66% were women. Increased total primary BAs and decreased secondary BAs (both P < 0.05) characterized NASH. Total conjugated primary BAs were significantly higher in NASH versus NAFL (P = 0.047) and versus controls (P < 0.0001). NASH had higher conjugated to unconjugated chenodeoxycholate (P = 0.04), cholate (P = 0.0004), and total primary BAs (P < 0.0001). The total cholate to chenodeoxycholate ratio was significantly higher in NAFLD without (P = 0.005) and with (P = 0.02) diabetes. Increased key BAs were associated with higher grades of steatosis (taurocholate), lobular (glycocholate) and portal inflammation (taurolithocholate), and hepatocyte ballooning (taurocholate). Conjugated cholate and taurocholate directly and secondary to primary BA ratio inversely correlated to NAFLD activity score. A higher ratio of total secondary to primary BA decreased (odds ratio, 0.57; P = 0.004) and higher conjugated cholate increased the likelihood of significant fibrosis (F≥2) (P = 0.007). Conclusion: NAFLD is associated with significantly altered circulating BA composition, likely unaffected by type 2 diabetes, and correlated with histological features of NASH; these observations provide the foundation for future hypothesis-driven studies of specific effects of BAs on specific aspects of NASH. (Hepatology 2018;67:534-548).

Bile acids in glucose metabolism in health and disease

Bile acids (BAs) are cholesterol-derived metabolites that facilitate the intestinal absorption and transport of dietary lipids. Recently, BAs also emerged as pivotal signaling molecules controlling glucose, lipid, and energy metabolism by binding to the nuclear hormone farnesoid X receptor (FXR) and Takeda G protein receptor 5 (TGR5) in multiple organs, leading to regulation of intestinal incretin secretion, hepatic gluconeogenesis, glycogen synthesis, energy expenditure, inflammation, and gut microbiome configuration. Alterations in BA metabolism and signaling are associated with obesity and type 2 diabetes mellitus (T2DM), whereas treatment of T2DM patients with BA sequestrants, or bariatric surgery in morbidly obese patients, results in a significant improvement in glycemic response that is associated with changes in the BA profile and signaling. Herein, we review the roles of BAs in glucose metabolism in health and disease; highlight the limitations, unknowns, and challenges in understanding the impact of BAs on the glycemic response; and discuss how this knowledge may be harnessed to develop innovative therapeutic approaches for the treatment of hyperglycemia and diabetes.

TGR5 signalling promotes mitochondrial fission and beige remodelling of white adipose tissue

Remodelling of energy storing white fat into energy expending beige fat could be a promising strategy to reduce adiposity. Here, we show that the bile acid-responsive membrane receptor TGR5 mediates beiging of the subcutaneous white adipose tissue (scWAT) under multiple environmental cues including cold exposure and prolonged high-fat diet feeding. Moreover, administration of TGR5-selective bile acid mimetics to thermoneutral housed mice leads to the appearance of beige adipocyte markers and increases mitochondrial content in the scWAT of Tgr5^+/+ mice but not in their Tgr5^−/− littermates. This phenotype is recapitulated in vitro in differentiated adipocytes, in which TGR5 activation increases free fatty acid availability through lipolysis, hence fuelling β-oxidation and thermogenic activity. TGR5 signalling also induces mitochondrial fission through the ERK/DRP1 pathway, further improving mitochondrial respiration. Taken together, these data identify TGR5 as a druggable target to promote beiging with potential applications in the management of metabolic disorders.

White adipose tissue can undergo a process of beiging and acquire functional characteristics similar to brown adipose tissue, including the ability to dissipate energy via uncoupled respiration. Here, Velazquez-Villegas et al. show that activation of the bile acid membrane receptor, TGR5, leads to white adipocyte beiging by promoting mitochondrial fission.

The Role of GLP-1 in the Metabolic Success of Bariatric Surgery

Two of the most popular bariatric procedures, vertical sleeve gastrectomy (VSG) and Roux-en-Y gastric bypass (RYGB), are commonly considered metabolic surgeries because they are thought to affect metabolism in a weight loss-independent manner. In support of this classification, improvements in glucose homeostasis, insulin sensitivity, and even discontinuation of type 2 diabetes mellitus (T2DM) medication can occur before substantial postoperative weight loss. The mechanisms that underlie this effect are unknown. However, one of the common findings after VSG and RYGB in both animal models and humans is the sharp postprandial rise in several gut peptides, including the incretin and satiety peptide glucagonlike peptide-1 (GLP-1). The increase in endogenous GLP-1 signaling has been considered a primary pathway leading to postsurgical weight loss and improvements in glucose metabolism. However, the degree to which GLP-1 and other gut peptides are responsible for the metabolic successes after bariatric surgery is continually debated. In this review we discuss the mechanisms underlying the increase in GLP-1 and its potential role in the metabolic improvements after bariatric surgery, including remission of T2DM. Understanding the role of changes in gut peptides, or lack thereof, will be crucial in understanding the critical factors necessary for the metabolic success of bariatric surgery.

The role of bile acids in nonalcoholic fatty liver disease and nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease is growing in prevalence worldwide. It is marked by the presence of macrosteatosis on liver histology but is often clinically asymptomatic. However, it can progress into nonalcoholic steatohepatitis which is a more severe form of liver disease characterized by inflammation and fibrosis. Further progression leads to cirrhosis, which predisposes patients to hepatocellular carcinoma or liver failure. The mechanism by which simple steatosis progresses to steatohepatitis is not entirely clear. However, multiple pathways have been proposed. A common link amongst many of these pathways is disruption of the homeostasis of bile acids. Other than aiding in the absorption of lipids and lipid-soluble vitamins, bile acids act as ligands. For example, they bind to farnesoid X receptor, which is critically involved in many of the pathways responsible for maintaining bile acid, glucose, and lipid homeostasis. Alterations to these pathways can lead to dysregulation of energy balance and increased inflammation and fibrosis. Repeated insults over time may be the key to development of steatohepatitis. For this reason, current drug therapies target aspects of these pathways to try to reduce and halt inflammation and fibrosis. This review will focus on the role of bile acids in these various pathways and how changes in these pathways may result in steatohepatitis. While there is no approved pharmaceutical treatment for either hepatic steatosis or steatohepatitis, this review will also touch upon the multitude of potential therapies.

Bile Acid Control of Metabolism and Inflammation in Obesity, Type 2 Diabetes, Dyslipidemia, and Nonalcoholic Fatty Liver Disease

Bile acids are signaling molecules that coordinately regulate metabolism and inflammation via the nuclear farnesoid X receptor (FXR) and the Takeda G protein-coupled receptor 5 (TGR5). These receptors activate transcriptional networks and signaling cascades controlling the expression and activity of genes involved in bile acid, lipid and carbohydrate metabolism, energy expenditure, and inflammation by acting predominantly in enterohepatic tissues, but also in peripheral organs. In this review, we discuss the most recent findings on the inter-organ signaling and interplay with the gut microbiota of bile acids and their receptors in meta-inflammation, with a focus on their pathophysiologic roles in obesity, type 2 diabetes, dyslipidemia, and nonalcoholic steatohepatitis, and their potential therapeutic applications.

Diabetes after Bariatric Surgery

Bariatric surgery has now emerged as an effective means of glycemic control in individuals with diabetes and obesity. However, long-term data show recurrence of hyperglycemia years after the procedure. Although the exact prevalence of diabetes relapse is unknown because of attrition and limited data on long-term follow up after the surgery, a significant percentage of patients experience relapse of diabetes. The mechanism of diabetes relapse is not completely understood and is not always linked to weight regain. The clinical implications of hyperglycemia after bariatric surgery for patients and healthcare providers is reviewed.