Ginkgolide B caused the activation of the Akt/eNOS pathway through the antioxidant effect of SOD1 in the diabetic aorta.

Ginkgo biloba extract (GBE) helps lower cardiovascular disease risk. Diabetes mellitus (DM)-induced endothelial dysfunction is a critical and initiating factor in the beginning of diabetic vascular complications. It was reported that GBE causes an endothelial-dependent relaxation. This study was designed to figure out the molecular basis on which GBE protects from endothelial dysfunction in diabetes because the underlying mechanisms are unclear. Studies were performed in a normal control group and streptozotocin/nicotinamide-induced DM group. In aortas, notably diabetic aortas, GBE, and ginkgolide B (GB), a constituent of GBE, produced a dose-dependent relaxation. The relaxation by GB was abolished by prior incubation with L-NNA (an endothelial nitric oxide synthase (NOS) inhibitor), LY294002 (a phosphoinositide 3-kinase (PI3K) inhibitor), and Akt inhibitor, confirming the essential role of PI3K/Akt/eNOS signaling pathway. We also demonstrated that GB induced the phosphorylation of Akt and eNOS in aortas. The superoxide dismutase1 (SOD1) expression level decreased in DM aortas, but GB stimulation increased SOD activity and SOD1 expression in DM aortas. Our novel findings suggest that in DM aortas, endothelial-dependent relaxation induced by GB was mediated by activation of SOD1, resulting in activation of the Akt/eNOS signaling pathway.

Endothelial dysfunction caused by circulating microparticles from diabetic mice is reduced by PD98059 through ERK and ICAM-1.

Endothelial dysfunction contributes to the development of diabetic complications and the production of circulating microparticles (MPs). Our previous study showed that diabetic mice-derived MPs (DM MPs) had increased levels of extracellular regulated protein kinase 1/2 (ERK1/2) and impaired endothelial-dependent relaxation in aortas when compared with control mice-derived MPs. This study was designed to investigate whether PD98059, an ERK1/2 inhibitor, affects the function of aortas and DM MPs. MPs were obtained from streptozotocin-induced DM, DM after PD98059 treatment, and ICR mice as control. The mice and MPs were then analyzed on the basis of their vascular function and enzyme expressions. Compared with the controls, platelet-derived MPs and ERK1/2 levels in the MPs were significantly elevated in the DM but showed little change in PD98059-treated DM. PD98059 mainly decreased ERK1/2 phosphorylation in the MPs. In the aortas of DM and DM MPs the endothelium-dependent vascular function was impaired, and there was a significantly greater improvement in the vascular function in the PD98059-treated DM aortas and the aortas treated with PD98059-treated DM MPs than in DM aortas and the aortas treated with DM MPs. Furthermore, DM MPs increased ERK1/2 and intracellular adhesion molecule-1 (ICAM-1) expressions in the aortas, but PD98059-treated DM MPs did not show these effects. For the first time, these results indicate that PD98059 treatment improves endothelial dysfunction in DM, and adhesion properties of DM MPs can be partly blocked by PD98059 via ERK and ICAM-1. These effects may explain some of the vascular complications in diabetes.

GLP-1 modulates insulin-induced relaxation response through ß-arrestin2 regulation in diabetic mice aortas.

AIMS: Diabetes impairs insulin-induced endothelium-dependent relaxation by reducing nitric oxide (NO) production. GLP-1, an incretin hormone, has been shown to prevent the development of endothelial dysfunction. In this study, we hypothesized that GLP-1 would improve the impaired insulin-induced relaxation response in diabetic mice. We also examined the underlying mechanisms. METHODS: Using aortic rings from ob/ob mice, an animal model of obesity and type 2 diabetes, and from lean mice, vascular relaxation responses and protein expressions were evaluated using insulin, GLP-1, and pathway-specific inhibitors to elucidate the mechanisms of response. In parallel experiments, ß-arrestin2 siRNA-transfected aortas were treated with GLP-1 to evaluate its effects on aortic response pathways. RESULTS: When compared to that of untreated ob/ob aortas, GLP-1 increased insulin-induced vasorelaxation and NO production. AMPK inhibition did not alter this vasorelaxation in both GLP-1-treated lean and ob/ob aortas, while Akt inhibition reduced vasorelaxation in both groups, and co-treatment with GLP-1 and insulin caused Akt/eNOS activation. Additionally, GLP-1 decreased GRK2 activity and enhanced ß-arrestin2 translocation from the cytosol to membrane in ob/ob aortas. ß-Arrestin2 siRNA decreased insulin-induced relaxation both in lean aortas and GLP-1-treated ob/ob aortas. CONCLUSIONS: We demonstrated that insulin-induced relaxation is dependent on ß-arrestin2 translocation and Akt activation via GLP-1-stimulated GRK2 inactivation in ob/ob aortas. We showed a novel cross-talk between GLP-1-responsive ß-arrestin2 and insulin signalling in diabetic aortas.

Glucagon-like peptide-1 increased the vascular relaxation response via AMPK/Akt signaling in diabetic mice aortas.

The incretin glucagon-like peptide-1 (GLP-1) elicits direct favorable effects on the cardiovascular system. This study aimed to evaluate the acute effects of GLP-1 on improving aortic endothelial dysfunction in diabetic mice. Additionally, we examined whether GLP-1 elucidated the underlying mechanisms. Using the diabetic mouse models induced by nicotinamide and streptozotocin, we investigated the functional changes in the aorta caused by GLP-1. Organ baths were performed for vascular reactivity in isolated aortic rings, and western blotting was used for protein analysis. The diabetic aortas showed enhanced GLP-1-induced relaxation response and nitric oxide (NO) production. However, the pretreatment of GLP-1 did not significantly change the endothelial-dependent relaxation response to acetylcholine and -independent relaxation response to sodium nitroprusside. On the other hand, the GLP-1-induced relaxation response and NO production were abolished by the endothelial NO synthase inhibitor, GLP-1 receptor antagonist, Akt inhibitor, and AMP-activated protein kinase (AMPK) inhibitor. Finally, in diabetic mice, considerable increases in phosphorylation of Akt and AMPK were found in aortas stimulated with GLP-1, both of which were decreased by pretreatment with the AMPK inhibitor. GLP-1 significantly enhanced endothelial-dependent relaxation in diabetic aortas. The effect may be mediated through activation of the AMPK/Akt pathway via a GLP-1 receptor-dependent mechanism.