Effect of sleeve gastrectomy and Roux-en-Y gastric bypass on gastrointestinal physiology

Bariatric Surgery Is Associated with Lower Concentrations of Fecal Secondary Bile Acids and Their Metabolizing Microbial Enzymes: A Pilot Study

INTRODUCTION

Excess body fat elevates colorectal cancer risk. While bariatric surgery (BRS) induces significant weight loss, its effects on the fecal stream and colon biology are poorly understood. Specifically, limited data exist on the impact of bariatric surgery (BRS) on fecal secondary bile acids (BA), including lithocholic acid (LCA), a putative promotor of colorectal carcinogenesis.

METHODS

This cross-sectional case-control study included 44 patients with obesity; 15 pre-BRS (controls) vs. 29 at a median of 24.1 months post-BRS. We examined the fecal concentrations of 11 BA by liquid chromatography and gene abundance of BA-metabolizing bacterial enzymes through fecal metagenomic sequencing. Differences were quantified using non-parametric tests for BA levels and linear discriminant analysis (LDA) effect size (LEfSe) for genes encoding BA-metabolizing enzymes.

RESULTS

Total fecal secondary BA concentrations trended towards lower levels post- vs. pre-BRS controls (p = 0.07). Individually, fecal LCA concentrations were significantly lower post- vs. pre-BRS (8477.0 vs. 11,914.0 uM/mg, p < 0.008). Consistent with this finding, fecal bacterial genes encoding BA-metabolizing enzymes, specifically 3-betahydroxycholanate-3-dehydrogenase (EC 1.1.1.391) and 3-alpha-hydroxycholanate dehydrogenase (EC 1.1.1.52), were also lower post- vs. pre-BRS controls (LDA of - 3.32 and - 2.64, respectively, adjusted p < 0.0001). Post-BRS fecal BA concentrations showed significant inverse correlations with weight loss, a healthy diet quality, and increased physical activity.

CONCLUSIONS

Concentrations of LCA, a secondary BA, and bacterial genes needed for BA metabolism are lower post-BRS. These changes can impact health and modulate the colorectal cancer cascade. Further research is warranted to examine how surgical alterations and the associated dietary changes impact bile acid metabolism.

Rerouting cardiovascular management following gastric bypass surgery: Dose optimization of carvedilol using population-based analysis

AIMS

A population-based pharmacokinetic (PK) modeling approach (PopPK) was used to investigate the impact of Roux-en-Y gastric bypass (RYGB) on the PK of (R)- and (S)-carvedilol. We aimed to optimize carvedilol dosing for these patients utilizing a pharmacokinetic/pharmacodynamic (PK/PD) link model.

METHODS

PopPK models were developed utilizing data from 52 subjects, including nonobese, obese, and post- RYGB patients who received rac- carvedilol orally. Covariate analysis included anthropometric and laboratory data, history of RYGB surgery, CYP2D6 and CYP3A4 in vivo activity, and relative intestinal abundance of major drug- metabolizing enzymes and transporters. A direct effect inhibitory Emax pharmacodynamic model was linked to the PK model of (S)- carvedilol to simulate the changes in exercise- induced heart rate.

RESULTS

A 2-compartmental model with linear elimination and parallel first-order absorptions best described (S)-carvedilol PK. RYGB led to a twofold reduction in relative oral bioavailability compared to nonoperated subjects, along with delayed absorption of both enantiomers. The intestinal ABCC2 mRNA expression increases the time to reach the maximum plasma concentration. The reduced exposure (AUC) of (S)-carvedilol post-RYGB corresponded to a 33% decrease in the predicted area under the effect curve (AUEC) for the 24-hour β-blocker response. Simulation results suggested that a 50-mg daily dose in post-RYGB patients achieved comparable AUC and AUEC to 25-mg dose in nonoperated subjects.

CONCLUSION

Integrated PK/PD modeling indicated that standard dosage regimens for nonoperated subjects do not provide equivalent β-blocking activity in RYGB patients. This study highlights the importance of personalized dosing strategies to attain desired therapeutic outcomes in this patient cohort.

Gut motility and hormone changes after bariatric procedures

PURPOSE OF REVIEW

Metabolic and bariatric surgery (MBS) and endoscopic bariatric therapies (EBT) are being increasingly utilized for the management of obesity. They work through multiple mechanisms, including restriction, malabsorption, and changes in the gastrointestinal hormonal and motility.

RECENT FINDINGS

Roux-en-Y gastric bypass (RYGB) and laparoscopic sleeve gastrectomy (LSG) cause decrease in leptin, increase in GLP-1 and PYY, and variable changes in ghrelin (generally thought to decrease). RYGB and LSG lead to rapid gastric emptying, increase in small bowel motility, and possible decrease in colonic motility. Endoscopic sleeve gastroplasty (ESG) causes decrease in leptin and increase in GLP-1, ghrelin, and PYY; and delayed gastric motility.

SUMMARY

Understanding mechanisms of action for MBS and EBT is critical for optimal care of patients and will help in further refinement of these interventions.

The Complexity of Bariatric Patient's Pharmacotherapy: Sildenafil Biopharmaceutics and Pharmacokinetics before vs. after Gastric Sleeve/Bypass

Postbariatric altered gastrointestinal (GI) anatomy/physiology may significantly harm oral drug absorption and overall bioavailability. In this work, sildenafil, the first phosphodiesterase-5 (PDE5) inhibitor, was investigated for impaired postbariatric solubility/dissolution and absorption; this research question is of particular relevance since erectile dysfunction (ED) is associated with higher body mass index (BMI). Sildenafil solubility was determined both in vitro and ex vivo, using pre- vs. postsurgery gastric contents aspirated from patients. Dissolution tests were done in conditions mimicking the stomach before surgery, after sleeve gastrectomy (post-SG, pH 5), and after one anastomosis gastric bypass (post-OAGB, pH 7). Finally, these data were included in physiologically based pharmacokinetic (PBPK) modelling (GastroPlus®) to simulate sildenafil PK before vs. after surgery. pH-dependent solubility was demonstrated with low solubility (0.3 mg/mL) at pH 7 vs. high solubility at pH 1-5, which was also confirmed ex vivo with much lower solubility values in postbariatric gastric samples. Hampered dissolution of all sildenafil doses was obtained under post-OAGB conditions compared with complete (100%) dissolution under both presurgery and post-SG conditions. PBPK simulations revealed delayed sildenafil absorption in postbariatric patients (increased tmax) and reduced Cmax, especially in post-OAGB patients, relative to a presurgery state. Hence, the effect of bariatric surgery on sildenafil PK is unpredictable and may depend on the specific bariatric procedure. This mechanistically based analysis suggests a potentially undesirable delayed onset of action of sildenafil following gastric bypass surgery.

Bariatric surgery alters mitochondrial function in gut mucosa

BACKGROUND

The obesity pandemic has worsened global disease burden, including type 2 diabetes, cardiovascular disease, and cancer. Metabolic/bariatric surgery (MBS) is the most effective and durable obesity treatment, but the mechanisms underlying its long-term weight loss efficacy remain unclear. MBS drives substrate oxidation that has been linked to improvements in metabolic function and improved glycemic control that are potentially mediated by mitochondria-a primary site of energy production. As such, augmentation of intestinal mitochondrial function may drive processes underlying the systemic metabolic benefits of MBS. Herein, we applied a highly sensitive technique to evaluate intestinal mitochondrial function ex vivo in a mouse model of MBS.

METHODS

Mice were randomized to surgery, sham, or non-operative control. A simplified model of MBS, ileal interposition, was performed by interposition of a 2-cm segment of terminal ileum into the proximal bowel 5 mm from the ligament of Treitz. After a four-week recovery period, intestinal mucosa of duodenum, jejunum, ileum, and interposed ileum were assayed for determination of mitochondrial respiratory function. Citrate synthase activity was measured as a marker of mitochondrial content.

RESULTS

Ileal interposition was well tolerated and associated with modest body weight loss and transient hypophagia relative to controls. Mitochondrial capacity declined in the native duodenum and jejunum of animals following ileal interposition relative to controls, although respiration remained unchanged in these segments. Similarly, ileal interposition lowered citrate synthase activity in the duodenum and jejunum following relative to controls but ileal function remained constant across all groups.

CONCLUSION

Ileal interposition decreases mitochondrial volume in the proximal intestinal mucosa of mice. This change in concentration with preserved respiration suggests a global mucosal response to segment specific nutrition signals in the distal bowel. Future studies are required to understand the causes underlying these mitochondrial changes.