Increased plasma Glucagon Like Peptide-1 improves endothelial dysfunction immediately after Roux-en-Y gastric bypass prior to body weight loss inhibiting the c-Jun N-terminal Protein Kinase Signaling

Abstract

Purpose: Roux-en-Y Gastric Bypass (RYGB) reduces weight and cardiovascular risk in obese patients. The mechanism of RYGB cardiovascular protection (CV) seems to be partly weight-independent, but still unclear. Glucagon Like Peptide 1 (GLP-1) exerts endothelial protective actions, through endothelial-NO-Synthase (eNOS) activation. Thus, we investigated the role of GLP-1 in obesity-induced endothelial dysfunction in rats after RYBG, prior to significant weight loss. Methods: After 7 weeks of high fat-high-cholesterol diet, obese Wistar male rats underwent RYGB and were compared to sham-operated rats fed Ad Lib (AL) or body weight-matched (BWM) to rats receiving RYGB. Thoracic aortic rings were suspended for isometric tension recording; cumulative relaxation responses were performed to peptide GLP-1 (7–36) amide (10-12-10-6mol/L) after submaximal contraction with norepinephrine (10-6mol/L) and repeated after preincubation with GLP-1 receptor antagonist exendin (9-39) (10-7 mol/L) and eNOS-inhibitor (L-NAME, 10-4mol/L). Western blotting of aortic lysates using GLP-1 receptor (GLP-1r), eNOS, Protein Kinase A (PKA) and c-Jun N-terminal Protein Kinase (JNK) antibodies was performed to address the role of GLP-1 signaling in endothelial function. GLP-1 and bile acids plasma fasting levels were measured. Results: 8 days post-surgery body weight difference among the 3 groups was not yet significant. GLP-1-induced vasorelaxation was impaired in sham AL and BWM compared with RYGB rats (max relaxations: 17±3.1% and 15±2.8 vs 36±4.8, respectively, n=6-8, p<0.05). Exendin (9-36) and L-NAME inhibited GLP-1-induced vasodilation, suggesting GLP-1 receptor and eNOS activation. Interestingly, GLP-1r protein expression was decreased in aortic lysates from sham AL and BWM compared to RYGB (respectively 0.44±0.1; 0.49±0.1 vs 0.86±0.2 relative units, p<0.05) while eNOS expression was reduced (sham AL 0.45±0.1and BWM 0.34±0.1 vs RYGB 0.74±0.1). Moreover, PKA which is downstream of GLP-1r activation and inhibits JNK signaling, was upregulated in RYGB compared to the AL and BWM sham rats. Accordingly, JNK phosphorylation was blunted only in the aortae of RYGB rats. Plasma fasting levels of GLP-1 were higher after RYGB compared to sham AL and BWM (AL 0.8±0.1; BWM 2.0±0.9; RYGB 10±2.8 pg/ml, p<0.05). Furthermore, plasma bile acids, which stimulate GLP-1 secretion from L cells in the lower intestine, were also increased in RYGB compared to both sham AL and BWM. Conclusions: Our study suggests that GLP-1 may be a crucial mediator of the endothelial function improvement observed immediately after RYGB, in addition to weight loss.