Bile diversion to the distal small intestine has comparable metabolic benefits to bariatric surgery

The Gut Microbiota as a Therapeutic Target in IBD and Metabolic Disease: A Role for the Bile Acid Receptors FXR and TGR5

The gut microbiota plays a crucial role in regulating many physiological systems of the host, including the metabolic and immune system. Disturbances in microbiota composition are increasingly correlated with disease; however, the underlying mechanisms are not well understood. Recent evidence suggests that changes in microbiota composition directly affect the metabolism of bile salts. Next to their role in digestion of dietary fats, bile salts function as signaling molecules for bile salt receptors such as Farnesoid X receptor (FXR) and G protein-coupled bile acid receptor (TGR5). Complementary to their role in metabolism, FXR and TGR5 are shown to play a role in intestinal homeostasis and immune regulation. This review presents an overview of evidence showing that changes in bile salt pool and composition due to changes in gut microbial composition contribute to the pathogenesis of inflammatory bowel disease and metabolic disease, possibly through altered activation of TGR5 and FXR. We further discuss how dietary interventions, such as pro- and synbiotics, may be used to treat metabolic disease and inflammatory bowel disease (IBD) through normalization of bile acid dysregulation directly or indirectly through normalization of the intestinal microbiota.

Early Increases in Bile Acids Post Roux-en-Y Gastric Bypass Are Driven by Insulin-Sensitizing, Secondary Bile Acids

CONTEXT

Roux-en-Y gastric bypass (RYGB) is the most effective treatment for morbid obesity and resolution of diabetes. Over the last decade, it has become well accepted that this resolution of diabetes occurs before significant weight loss; however, the mechanisms behind this effect remain unknown and could represent novel therapeutic targets for obesity and diabetes. Bile acids have been identified as putative mediators of these weight loss-independent effects.

OBJECTIVE

To identify the longitudinal changes in bile acids after RYGB, which may provide mechanistic insight into the weight loss-independent effects of RYGB.

DESIGN

Observational study before/after intervention.

SETTING

Academic medical center.

PATIENTS/PARTICIPANTS

Samples were collected from morbidly obese patients (n = 21) before and after RYGB.

INTERVENTION

RYGB.

MAIN OUTCOME MEASURES

Seventeen individual bile acid species were measured preoperatively and at 1, 6, 12, and 24 months postoperatively. Anthropometric, hormonal, and hyperinsulinemic-euglycemic clamp data were also examined to identify physiological parameters associated with bile acid changes.

RESULTS

Fasting total plasma bile acids increased after RYGB; however, increases were bimodal and were observed only at 1 (P < .05) and 24 months (P < .01). One-month increases were secondary to surges in ursodeoxycholic acid and its glycine and taurine conjugates, bacterially derived bile acids with putative insulin-sensitizing effects. Increases at 24 months were due to gradual rises in primary unconjugated bile acids as well as deoxycholic acid and its glycine conjugate. Plasma bile acid changes were not significantly associated with any anthropometric or hormonal measures, although hepatic insulin sensitivity was significantly improved at 1 month.

CONCLUSIONS

Overall findings suggest that bacterially derived bile acids may mediate the early improvements at 1 month after RYGB. Future studies should examine the changes in specific bile acid chemical species after bariatric procedures and bile acid-specific signaling changes.