Changes in Bile Acid Profile After Laparoscopic Sleeve Gastrectomy are Associated with Improvements in Metabolic Profile and Fatty Liver Disease. Obes Surg. 2016;26:1195-1202. [PMID: 26337697 DOI: 10.1007/s11695-015-1878-1]

Increased glycine-amidated hyocholic acid correlates to improved early weight loss after sleeve gastrectomy

BACKGROUND

Bile acids (BAs) are post-prandial hormones that play an important role in glucose and lipid homeostasis as well as energy expenditure. Total and glycine-amidated BAs increase after sleeve gastrectomy (SG) and correlate to improved metabolic disease. No specific bile acid subtype has been shown conclusively to mediate the weight loss effect. Therefore, the objective of this study was to prospectively evaluate the comprehensive changes in meal-stimulated BAs after SG and determine if a specific change in the BA profile correlates to the early weight loss response.

METHODS

Patients were prospectively enrolled at the University of Nebraska Medical Center who were undergoing a SG for treatment of morbid obesity. Primary and secondary plasma bile acids and their amidated (glycine, G-, or taurine, T-) subtypes were measured at fasting, 30 and 60 min after a liquid meal performed pre-op, and at 6 and 12 weeks post-op. Area under the curve (AUC) was calculated for the hour meal test for each bile acid subtype. BAs that were significantly increased post-op were correlated to body mass index (BMI) loss.

RESULTS

Total BA AUC was significantly increased at 6 (p < 0.01) and 12 weeks post-op (p < 0.01) compared to pre-operative values. The increase in total BA AUC was due to a statistically significant increase in G-BAs. Nine different BA AUC subtypes were significantly increased at both 6 and 12 weeks post-op. Increased total and G-chenodeoxycholic acid AUC was significantly correlated to the 6 week BMI loss (p = 0.03). Increased G-hyocholic acid was significantly correlated to increased weight loss at both 6 (p = 0.05) and 12 weeks (p = 0.006).

CONCLUSIONS

SG induced an early and persistent post-prandial surge in multiple bile acid subtypes. Increased G-hyocholic consistently correlated with greater early BMI loss. This study provides evidence for a role of BAs in the surgical weight loss response after SG.

Bile acids and bariatric surgery

Bariatric surgery, specifically Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG), are the most effective and durable treatments for morbid obesity and potentially a viable treatment for type 2 diabetes (T2D). The resolution rate of T2D following these procedures is between 40 and 80% and far surpasses that achieved by medical management alone. The molecular basis for this improvement is not entirely understood, but has been attributed in part to the altered enterohepatic circulation of bile acids. In this review we highlight how bile acids potentially contribute to improved lipid and glucose homeostasis, insulin sensitivity and energy expenditure after these procedures. The impact of altered bile acid levels in enterohepatic circulation is also associated with changes in gut microflora, which may further contribute to some of these beneficial effects. We highlight the beneficial effects of experimental surgical procedures in rodents that alter bile secretory flow without gastric restriction or altering nutrient flow. This information suggests a role for bile acids beyond dietary fat emulsification in altering whole body glucose and lipid metabolism strongly, and also suggests emerging roles for the activation of the bile acid receptors farnesoid x receptor (FXR) and G-protein coupled bile acid receptor (TGR5) in these improvements. The limitations of rodent studies and the current state of our understanding is reviewed and the potential effects of bile acids mediating the short- and long-term metabolic improvements after bariatric surgery is critically examined.

Increased Secondary/Primary Bile Acid Ratio in Chronic Heart Failure

OBJECTIVE

Bile acids (BAs) are now recognized as signaling molecules and emerging evidence suggests that BAs affect cardiovascular function. The gut microbiota has recently been linked to the severity of heart failure (HF), and microbial metabolism has a major impact on BA homeostasis. We aimed to investigate the pattern of BAs, and particularly microbiota-transformed (secondary) BAs, in patients with chronic HF.

METHODS AND RESULTS

This was a prospective, observational, single-center study including 142 patients with chronic HF and 20 age- and sex-matched healthy control subjects. We measured plasma levels of primary, secondary, and total BAs, and explored their associations with clinical characteristics and survival. Plasma levels of primary BAs were lower (P < .01) and the ratios of secondary to primary BAs higher (P < .001) in patients with HF compared with control subjects. Approximately 40% of patients in the upper tertile of the ratio of secondary to primary BAs died during 5.6 years of follow-up (unadjusted Cox regression: hazard ratio 1.93, 95% confidence interval 1.01-3.68, compared with the lower tertiles). However, this association was attenuated and no longer significant in multivariate analyses.

CONCLUSIONS

Levels of primary BAs were reduced and specific secondary BAs increased in patients with chronic HF. This pattern was associated with reduced overall survival in univariate analysis, but not in multivariate analyses. Future studies should assess the regulation and potential role of BA metabolism in HF.

Weight Loss Outcomes in Laparoscopic Vertical Sleeve Gastrectomy (LVSG) Versus Laparoscopic Roux-en-Y Gastric Bypass (LRYGB) Procedures: A Meta-Analysis and Systematic Review of Randomized Controlled Trials

PURPOSE

Laparoscopic Roux-en-Y gastric bypass (LRYGB) and laparoscopic vertical sleeve gastrectomy (LVSG) have been proposed as cost-effective strategies to manage morbid obesity. The aim of this meta-analysis was to compare the postoperative weight loss outcomes reported in randomized control trials (RCTs) for LVSG versus LRYGB procedures.

MATERIAL AND METHODS

RCTs comparing the weight loss outcomes following LVSG and LRYGB in adult population between January 2000 and November 2015 were selected from PubMed, Medline, Embase, Science Citation Index, Current Contents, and the Cochrane database. The review was prepared in accordance with Preferred Reporting of Systematic Reviews and Meta-Analyses (PRISMA).

RESULTS

Nine unique RCTs described over 10 publications involving a total of 865 patients (LVSG, n=437; LRYGB, n=428) were analyzed. Postoperative follow-up ranged from 3 months to 5 years. Twelve-month excess weight loss (EWL) for LVSG ranged from 69.7% to 83%, and for LRYGB, ranged from 60.5% to 86.4%. A number of studies reported slow weight gain between the second and third years of postoperative follow-up ranging from 1.4% to 4.2%EWL. This trend was seen to continue to 5 years postoperatively (8% to 10%EWL) for both procedures.

CONCLUSIONS

In conclusion, LRYGB and LVSG are comparable with regards to the weight loss outcomes in the short term, with LRYGB achieving slightly greater weight loss. Slow weight recidivism is observed after the first postoperative year following both procedures. Long-term reporting of outcomes obtained from well-designed studies using intention-to-treat analyses are identified as a major gap in the literature at present.

Bile acids at the cross-roads of gut microbiome-host cardiometabolic interactions

While basic and clinical research over the last several decades has recognized a number of modifiable risk factors associated with cardiometabolic disease progression, additional and alternative biological perspectives may offer novel targets for prevention and treatment of this disease set. There is mounting preclinical and emerging clinical evidence indicating that the mass of metabolically diverse microorganisms which inhabit the human gastrointestinal tract may be implicated in initiation and modulation of cardiovascular and metabolic disease outcomes. The following review will discuss this gut microbiome-host metabolism axis and address newly proposed bile-mediated signaling pathways through which dysregulation of this homeostatic axis may influence host cardiovascular risk. With a central focus on the major nuclear and membrane-bound bile acid receptor ligands, we aim to review the putative impact of microbial bile acid modification on several major phenotypes of metabolic syndrome, from obesity to heart failure. Finally, attempting to synthesize several separate but complementary hypotheses, we will review current directions in preclinical and clinical investigation in this evolving field.

Fibroblast growth factor 21 correlates with weight loss after vertical sleeve gastrectomy in adolescents

OBJECTIVE

Vertical sleeve gastrectomy (VSG) results in weight loss and increased bile acids (BA) and fibroblast growth factor 19 (FGF19) levels. FGF21 shares essential cofactors with FGF19, but its physiology early post-VSG has not been assessed.

METHODS

Ten adolescents (17.4 ± 0.5 years and BMI 51.5 ± 2.5 kg/m² ) were enrolled. Fasting and postmeal (100 mL Ensure™) samples (0-120 min) were collected (pre-VSG [V1], 1 [V2], and 3 months [V3] post-VSG) for analysis of BA, FGF19, and FGF21.

RESULTS

Post-VSG subjects lost weight (V2 11.8 ± 0.8 kg; V3 21.9 ± 1.7 kg). BA and FGF19 increased by V2, 143.6% at 30 min and 74.9% at 90 min post-meal, respectively. BA hydrophobicity index also improved by V3, 21.1% at 30 min post-meal. Interestingly, fasting and 120-min post-meal FGF21 levels at V2 were increased by 135.7% and 253.9%, respectively, but then returned to baseline at V3. BA levels correlated with FGF21 at V2 (P = 0.003, r = 0.89), and body weight lost post-VSG correlated with FGF21 levels (V2; P = 0.012, R = 0.82).

CONCLUSIONS

Expected changes were seen in BA and FGF19 biology after VSG in adolescents, but novel changes were seen in correlation between the early postsurgical increase in FGF21 and weight loss, suggesting that FGF21 may play a role in energy balance postoperatively, and further investigation is warranted.

Improved glucose metabolism following bariatric surgery is associated with increased circulating bile acid concentrations and remodeling of the gut microbiome

Clinical studies have indicated that circulating bile acid (BA) concentrations increase following bariatric surgery, especially following malabsorptive procedures such as Roux-en-Y gastric bypasses (RYGB). Moreover, total circulating BA concentrations in patients following RYGB are positively correlated with serum glucagon-like peptide-1 concentrations and inversely correlated with postprandial glucose concentrations. Overall, these data suggest that the increased circulating BA concentrations following bariatric surgery - independently of calorie restriction and body-weight loss - could contribute, at least in part, to improvements in insulin sensitivity, incretin hormone secretion, and postprandial glycemia, leading to the remission of type-2 diabetes (T2DM). In humans, the primary and secondary BA pool size is dependent on the rate of biosynthesis and the enterohepatic circulation of BAs, as well as on the gut microbiota, which play a crucial role in BA biotransformation. Moreover, BAs and gut microbiota are closely integrated and affect each other. Thus, the alterations in bile flow that result from anatomical changes caused by bariatric surgery and changes in gut microbiome may influence circulating BA concentrations and could subsequently contribute to T2DM remission following RYGB. Research data coming largely from animal and cell culture models suggest that BAs can contribute, via nuclear farnezoid X receptor (FXR) and membrane G-protein-receptor (TGR-5), to beneficial effects on glucose metabolism. It is therefore likely that FXR, TGR-5, and BAs play a similar role in glucose metabolism following bariatric surgery in humans. The objective of this review is to discuss in detail the results of published studies that show how bariatric surgery affects glucose metabolism and subsequently T2DM remission.

Obesity diabetes and the role of bile acids in metabolism

Bile acids have many activities over and above their primary function in aiding absorption of fat and fat soluble vitamins. Bile acids are synthesized from cholesterol, and thus are involved in cholesterol homeostasis. Bile acids stimulate glucagon-like peptide 1 (GLP1) production in the distal small bowel and colon, stimulating insulin secretion, and therefore, are involved in carbohydrate and fat metabolism. Bile acids through their insulin sensitising effect play a part in insulin resistance and type 2 diabetes. Bile acid metabolism is altered in obesity and diabetes. Both dietary restriction and weight loss due to bariatric surgery, alter the lipid carbohydrate and bile acid metabolism. Recent research suggests that the forkhead transcription factor FOXO is a central regulator of bile, lipid, and carbohydrate metabolism, but conflicting studies mean that our understanding of the complexity is not yet complete.

Recent advances in metabolic and bariatric surgery

Obesity and its associated medical conditions continue to increase and add significant burden to patients, as well as health-care systems, worldwide. Bariatric surgery is the most effective treatment for severe obesity and its comorbidities, and resolution of diabetes is weight loss-independent in the case of some operations. Although these weight-independent effects are frequently described clinically, the mechanisms behind them are not well understood and remain an intense area of focus in the growing field of metabolic and bariatric surgery. Perceptions of the mechanisms responsible for the beneficial metabolic effects of metabolic/bariatric operations have shifted from being mostly restrictive and malabsorption over the last 10 to 15 years to being more neuro-hormonal in origin. In this review, we describe recent basic and clinical findings of the major clinical procedures (adjustable gastric banding, vertical sleeve gastrectomy, Roux-en-Y gastric bypass, and biliopancreatic diversion) as well as other experimental procedures (ileal interposition and bile diversion) that recapitulate many of the metabolic effects of these complex operations in a simpler fashion. As the role of bile acids and the gut microbiome on metabolism is becoming increasingly well described, their potential roles in these improvements following metabolic surgery are becoming better appreciated. Bile acid and gut microbiome changes, in light of recent developments, are discussed in the context of these surgical procedures, as well as their implications for future study.