Glucagon-like peptide-1 protects against cardiac microvascular endothelial cells injured by high glucose

Sitagliptin, a dipeptidyl peptidase-4 inhibitor, attenuates apoptosis of vascular smooth muscle cells and reduces atherosclerosis in diabetic apolipoprotein E-deficient mice

Sitagliptin, a dipeptidyl peptidase-4(DPP-4) Inhibitor, has been found to have an anti-atherosclerotic effect. Since apoptosis of vascular smooth muscle cells (VSMCs) contributes to the occurrence of diabetic atherosclerosis. This study aimed to examine whether sitagliptin suppresses the atherosclerosis progression to hyperglycemia in a low-dose streptozotocin (STZ)-induced diabetic mouse model, and then investigated the effect of sitagliptin on VSMCs apoptosis and its underlying mechanism. In vivo studies, eight-week-old low-dose STZ-induced diabetic apolipoprotein E (apoE)-deficient (apoE-/-) mice fed a high-fat diet were administered a DPP-4 inhibitor, sitagliptin, 200 mg/kg/day, or Lantus insulin by daily subcutaneous injection of 1 unit/mouse over a period of 12 weeks. Aortic atherosclerosis and apoptosis in the plaque were determined using dUTP-biotin nick end labeling (TUNEL) staining and immunohistochemistry. In vitro studies utilized the VSMCs for determination of glucagon-like peptide 1 receptor (GLP-1R) and DPP-4 expression and flow cytometry and Western blotting were used to determine apoptosis and protein expression, respectively. Sitagliptin significantly reduced atherosclerotic lesion area (7.00 ± 0.13 vs. 12.80 ± 2.7%, p = 0.003) and suppressed vascular smooth muscle cell apoptosis (2.30 ± 1.34 vs. 4.8 ± 1.93%, p = 0.003) compared with vehicle treatment. In addition, sitagliptin significantly increased the expression of β-catenin in the aortic tissue(0.56 ± 0.13 vs.0.17 ± 0.02, p = 0.008)compared with vehicle treatment. In cultured mouse VSMCs, sitagliptin enhanced GLP-1 activity significantly retarded oxidative stress (H₂O₂)-induced apoptosis compared with GLP-1 or sitagliptin alone. Sitagliptin increased GLP-1-induced cytosolic levels of β-catenin compared with GLP-1 alone, resulted in increasing the expression of survivin, and suppressed proinflammatory cytokines, i.e., interleukin-6(IL-6) and tumor necrosis factor-alpha(TNF-α), production in response to H₂O₂. In conclusion, these results indicated that the anti-atherosclerotic effect of sitagliptin is mediated, at least in part, by its inhibition of VSMCs apoptosis.

Difference in protective effects of GIP and GLP-1 on endothelial cells according to cyclic adenosine monophosphate response

Receptors for glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) are present in vascular endothelial cells. Previous studies investigating euglycemic status have demonstrated that GIP is directly involved in the physiology of blood vessels by controlling the blood flow rate of portal veins and that GLP-1 has a protective effect on blood vessels by acting on endothelial cells. However, to the best of our knowledge, the effects of GIP and GLP-1 on endothelial cells in patients with hyperglycemia remain unknown. Therefore, the present study investigated whether the effect of the incretin hormones GLP-1 and GIP differed with regards to the reversal of endothelial cell dysfunction caused by hyperglycemia. The production of nitric oxide (NO) was measured using the Griess reagent system kit and the expression of cyclic adenosine monophosphate (cAMP) in the cell was measured at a wavelength of 405 nm with the ELISA reader using the cyclic AMP EIA kit. Exposure of human umbilical vein endothelial cells (HUVEC) to a high glucose concentration decreased NO and endothelial nitric oxide synthase (eNOS) levels but increased inducible NOS (iNOS) levels. However, when HUVECs were pretreated with GLP-1, a reduction of iNOS expression was observed and the expression of eNOS and NO were increased, as opposed to pretreatment with GIP. The results differed according to the response of cAMP, the second messenger of incretin hormones: The GIP pretreatment group did not exhibit an increase in cAMP levels while the GLP-1 pretreatment group did. The results of the present study provide evidence that GLP-1, but not GIP, has a protective effect on endothelial function associated with cardiovascular disease, as it is associated with increased eNOS expression and the levels of NO. This effect may be due to an increase in the cAMP concentration during hyperglycemic events.

Astragalus polysaccharide protects human cardiac microvascular endothelial cells from hypoxia/reoxygenation injury: The role of PI3K/AKT, Bax/Bcl-2 and caspase-3

In the present study, the mechanisms associated with the Astragalus polysaccharide (APS)-mediated protection of human cardiac microvascular endothelial cells (HCMEC) against hypoxia/reoxygenation (HR) injury were investigated. Pretreatment of HCMECs with APS at various concentrations was performed prior to Na2S2O4-induced HR injury. Subsequently, cell viability and apoptosis were measured by MTT and Hoechst assays, respectively. The viability of HCMECs was reduced by Na2S2O4 and apoptosis was enhanced; however, cell viability was observed to be increased by APS via inhibition of apoptosis. Additionally, intracellular reactive oxygen species (ROS), Ca2+, nitric oxide (NO), malondialdehyde (MDA), superoxide dismutase (SOD), phosphatidylinositol 3-kinase (PI3K)-protein kinase B (AKT), B‑cell lymphoma‑2 (Bcl‑2), Bcl‑2 associated X protein (Bax) and caspase‑3 were measured using detection kits or western blot analysis. In HCMECs with HR injury, the levels of ROS and Ca2+, MDA and Bax expression levels, and the activity of caspase‑3 were elevated. By contrast, the level of NO, the protein expression levels of SOD, Bcl‑2 and PI3K, and the phosphorylation of AKT were decreased. However, compared with the HR group, the effects of HR injury were significantly reduced by APS, with APS providing a protective effect on HCMECs, particularly at higher doses. The current study concluded that APS protects HCMECs from Na2S2O4‑induced HR injury by reducing the levels of ROS, Ca2+, MDA and Bax, inhibiting the activity of caspase‑3, and enhancing the levels of NO, SOD, Bcl‑2, PI3K and phosphorylated AKT. These results may provide an insight into the clinical application of APS and novel therapeutic strategies for HR injury.

Protective Role of Glucagon-Like Peptide-1 Against High-Glucose-Induced Endothelial Oxidative Damage

To investigate the protective effect of glucagon-like peptide-1 (GLP-1) against cell damage induced by high glucose.Human umbilical vein endothelial cells (HUVECs) were divided into control group (5.5 mmol/L) and high glucose groups (19, 33, or 47 mmol/L), which were cultured with different concentrations of glucose for 48 hours, respectively. Cell viability was measured with MTT assay. Levels of intracellular reactive oxygen species (ROS) were monitored by flow cytometry and apoptotic cell death was measured by staining with Annexin V-FITC and propidium iodide. Cultured cells were detected with intercellular adhesion molecule 1 (ICAM-1), VCAM-1, and JNK on protein.Compared with the control group, cell viability was decreased by 20% and 37%, respectively, when cultured under 33 and 47 mM, while increased in different GLP-1-treated groups (0.01 L, 0.1, 1, and 10 nmol/L). The GLP-1 treatment significantly reduced the ROS level of high glucose treatment group but not impact on the control group. Meanwhile, the level of apoptosis was elevated in the high glucose treatment group. Early apoptosis was significantly reversed in the GLP-1-treated group (0.1, 1, and 10 nmol/L). Late apoptosis was uniquely decreased in the GLP-1 concentrations of 10 nmol/L. Furthermore, GLP-1 could also reduce the protein levels of ICAM-1, VCAM-1, and phospho JNK in the endothelial cells with high glucose treatment.GLP-1 could inhibit cell apoptosis and reduce ROS generation and JNK-Bax signaling pathway activation, which were induced by high glucose treatment.