Gut Microbiota Contribution to Weight-Independent Glycemic Improvements after Gastric Bypass Surgery.

Roux-en-Y gastric bypass surgery (RYGB) leads to improved glycemic control in individuals with severe obesity beyond the effects of weight loss alone. Here, We addressed the potential contribution of gut microbiota in mediating this favourable surgical outcome by using an established preclinical model of RYGB. 16S rRNA sequencing revealed that RYGB-treated Zucker fatty rats had altered fecal composition of various bacteria at the phylum and species levels, including lower fecal abundance of an unidentified Erysipelotrichaceae species, compared with both sham-operated (Sham) and body weight-matched to RYGB-treated (BWM) rats. Correlation analysis further revealed that fecal abundance of this unidentified Erysipelotrichaceae species linked with multiple indices of glycemic control uniquely in RYGB-treated rats. Sequence alignment of this Erysipelotrichaceae species identified Longibaculum muris to be the most closely related species, and its fecal abundance positively correlated with oral glucose intolerance in RYGB-treated rats. In fecal microbiota transplant experiments, the improved oral glucose tolerance of RYGB-treated compared with BWM rats could partially be transferred to recipient germfree mice, independently of body weight. Unexpectedly, providing L. muris as a supplement to RYGB recipient mice further improved oral glucose tolerance, while administering L. muris alone to chow-fed or Western style diet-challenged conventionally raised mice had minimal metabolic impact. Taken together, our findings provide evidence that the gut microbiota contributes to weight loss-independent improvements in glycemic control after RYGB and demonstrate how correlation of a specific gut microbiota species with a host metabolic trait does not imply causation. IMPORTANCE Metabolic surgery remains the most effective treatment modality for severe obesity and its comorbidities, including type 2 diabetes. Roux-en-Y gastric bypass (RYGB) is a commonly performed type of metabolic surgery that reconfigures gastrointestinal anatomy and profoundly remodels the gut microbiota. While it is clear that RYGB is superior to dieting when it comes to improving glycemic control, the extent to which the gut microbiota contributes to this effect remains untested. In the present study, we uniquely linked fecal Erysipelotrichaceae species, including Longibaculum muris, with indices of glycemic control after RYGB in genetically obese and glucose-intolerant rats. We further show that the weight loss-independent improvements in glycemic control in RYGB-treated rats can be transmitted via their gut microbiota to germfree mice. Our findings provide rare causal evidence that the gut microbiota contributes to the health benefits of metabolic surgery and have implications for the development of gut microbiota-based treatments for type 2 diabetes.

Gastric bypass surgery weight loss-independently induces gut Il-22 release in association with improved glycemic control in obese Zucker fatty rats.

Background: Roux-en-Y gastric bypass surgery (RYGB) improves glycemic control in individuals with severe obesity beyond the effects of weight loss alone. To identify potential underlying mechanisms, we asked how equivalent weight loss from RYGB and from chronic caloric restriction impact gut release of the metabolically beneficial cytokine interleukin-22 (Il-22). Methods: Obese male Zucker fatty rats were randomized into sham-operated (Sham), RYGB, and sham-operated, body weight-matched to RYGB (BWM) groups. Food intake and body weight were measured regularly for 4 weeks. An oral glucose tolerance test (OGTT) was performed on postoperative day 27. Portal vein plasma, systemic plasma, and whole-wall samples from throughout the gut were collected on postoperative day 28. Gut Il-22 mRNA expression was determined by real-time quantitative PCR. Plasma Il-22 levels were determined by enzyme-linked immunosorbant assay (ELISA). Results: RYGB and BWM rats had lower food intake and body weight as well as superior blood glucose clearing capability compared with Sham rats. RYGB rats also had superior blood glucose clearing capability compared with BWM rats despite having similar body weights and higher food intake. Il-22 mRNA expression was approximately 100-fold higher specifically in the upper jejunum in RYGB rats compared with Sham rats. Il-22 protein was only detectable in portal vein (34.1 ± 9.4 pg/mL) and systemic (46.9 ± 10.5 pg/mL) plasma in RYGB rats. Area under the curve of blood glucose during the OGTT, but not food intake or body weight, negatively correlated with portal vein and systemic plasma Il-22 levels in RYGB rats. Conclusions: These results suggest that induction of gut Il-22 release might partly account for the weight loss-independent improvements in glycemic control after RYGB, and further support the use of this cytokine for the treatment of metabolic disease.

Endothelial barrier dysfunction in systemic inflammation is mediated by soluble VE-cadherin interfering VE-PTP signaling.

Breakdown of endothelial barrier integrity determines organ dysfunction and outcome of patients with sepsis. Increased levels of soluble vascular endothelial (VE)-cadherin fragments (sVE-cadherin) have previously been linked with inflammation-induced loss of endothelial barrier function. We provide evidence for a causative role of sVE-cadherin to induce loss of endothelial barrier function. In patients with sepsis, sVE-cadherin levels were associated with organ dysfunction and the need for volume resuscitation. Similarly, LPS-induced systemic inflammation in rats with microvascular dysfunction was paralleled by augmented sVE-cadherin levels. Newly generated recombinant human sVE-cadherin (extracellular domains EC1-5) induced loss of endothelial barrier function in both human microvascular endothelial cells in vitro and in rat mesenteric microvessels in vivo and reduced microcirculatory flow. sVE-cadherinEC1-5 disturbed VE-cadherin-mediated adhesion and perturbed VE-protein tyrosine phosphatase (VE-PTP)/VE-cadherin interaction resulting in RhoGEF1-mediated RhoA activation. VE-PTP inhibitor AKB9778 and Rho-kinase inhibitor Y27632 blunted all sVE-cadherinEC1-5-induced effects, which uncovers a pathophysiological role of sVE-cadherin via dysbalanced VE-PTP/RhoA signaling.