Exendin‐4, a Glucagon‐like Peptide 1 (GLP‐1) Agonist, Attenuates Vascular Dysfunction in Type 2 Diabetes (T2DM) via Anti‐Inflammatory and Antioxidant Effects.

Cardiovascular diseases comprise the leading cause of morbidity and mortality amongst diabetic patients. While currently utilized anti‐hyperglycemic drugs effectively control blood glucose levels, they do not halt the development of cardiovascular complications. An important element in the pathogenesis of T2DM is an antecedent increase in serum levels of free fatty acids (FFAs) prior to the development of a hyperglycemic state. Our preliminary data has demonstrated that the FFA palmitate directly causes vascular dysfunction. Rat aortic rings were maintained in organ culture and treated with palmitate for 18 hours, followed by functional vascular studies using wire myograph. Relaxation and contraction were measured by concentration‐dependent response to acetylcholine (Ach) and phenylephrine (PE), respectively. Aortas incubated with palmitate displayed significant impairment of endothelium‐dependent relaxation (22% reduction vs. control, p<0.05, n=4) and greater contraction with PE (11 ±0.8 mN vs. 6.5 mN, p<0.001, n=4). Interestingly, we found that palmitate markedly upregulates the glucagon‐like peptide 1 (GLP‐1) receptor in endothelium (1.3 fold increase, p<0.05, n=4) as well as intact blood vessels (1.5 fold increase, p<0.05, n=4). GLP‐1 agonists are an emerging class of anti‐hyperglycemic drugs that confer a vasculo‐protective effect. However, the mechanisms by which GLP‐1 agonists protect the vasculature are not well understood. We hypothesize that GLP‐1 agonists attenuate vascular dysfunction in diabetic conditions through anti‐inflammatory and antioxidant effects. Using RT‐PCR, we found that 24 hours of stimulation with 0.1mM palmitate robustly upregulated gene expression of the CCL2 inflammatory marker in human umbilical vein endothelial cells (HUVEC). Further confirmation of inflammatory status was determined by NFKB protein expression. Incubation with palmitate significantly increased NFKB expression in intact rat aortas (3.1 fold increase vs. control, p<0.001, n=4), which was markedly mitigated by treatment with the GLP‐1 agonist exendin‐4 (EX‐4) (p<0.05, n=4). Palmitate also increased NFKB expression in HUVEC cultures (2.4 fold increase vs. control, p<0.05, n=3), and this effect was blunted in the presence of EX‐4 (p<0.05, n=4). This data demonstrates the anti‐inflammatory efficacy of EX‐4 under experimental diabetic conditions. Furthermore, we utilized sixteen‐week old male Goto‐Kakizaki (GK) rats as a non‐obese model of T2DM due to the similarity of their vascular complications with those of humans. Age‐matched male Wistar rats served as a control. Wire myograph studies were performed using aortas from GK rats incubated with and without 10nM of EX‐4. Aortas from GK rats exhibited a marked increase in PE‐induced contraction compared to the control group, which was reversed by EX‐4 treatment. Moreover, using dihydroethidium (DHE) staining, we found that the increased ROS levels in GK aortas (2.4 fold increase vs. control group, p<0.05) were robustly reduced with EX‐4 treatment (65% reduction, p<0.001, n=3). These results demonstrate that EX‐4 ameliorated inflammation and oxidative stress in diabetic vasculature. GLP‐1 agonists have anti‐inflammatory and antioxidant properties, and thus hold promise in reducing the incidence of the cardiovascular complications of diabetes, which are prominent causes of morbidity and mortality in the diabetic population. Support or Funding Information NIH 1Exendin‐4 decreases overproduction of reactive oxygen species in aortas from type 2 diabetic rats.