The Impact Of Glucagon-like Peptide1on High Glucose Induced Vascular Endothelial Dysfunction And Its Potential Mechanism

AIMDiabetic atherosclerosis, a very common complication of diabetes mellitus, is regarded as a coronary heart disease risk equivalents in clinic due to its high morbidity and mortality. The vascular endothelial dysfunction, which plays a key role in the initial phase of diabetic atherosclerosis, is a result from the inbalance between vasoactive substances, such as endothelin-1(ET-1) and nitric oxide synthase (NOS). The inappropriate release of vasoactive sunstances induces injury of endothelial, stimulates pro-inflammation factors like interleukin, and finally results in inflammation and atherogenesis. Thus, treatments that regulate vasoactive sunstances may prevent the occurrence of atherosclerosis. Recent studies showed that glucagon-like peptide1(GLP-1) may prevent atherosclerosis. However, its underlying mechanism remains unclear, and the study that helps to elucidate the relationship between GLP-1agonists and endothelial dysfunction is urgently needed. Thus, in this study, we aimed to find out the function of GLP-1on vasoactive substances using liraglutide, a GLP-1receptor agonist; check the effect of liraglutide on expression of ET-1, endothelial nitric oxide synthase (eNOS) and induced nitric oxide synthase (iNOS) in human umbilical vein endothelial cells (HUVECs); discuss its impact on endothelial dysfunction and atherosclerosis; and tried to demonstrate underlying potential mechanism in this process.MethodsHUVECs were cultured in both high glucose (25mmol/L) and low glucose (7mmol/L) medium and treated with different concentrations of liraglutide (10-1000ng/mL) for6-24h. Real-time quantitive PCR and western blotting were used for measuring mRNA and protein expression like ET-1, eNOS, iNOS, nuclear factor-kappa B (NF-κB p65) and inhibitor of kappa B alpha (IκBα). Immunofluorescence was used to detect NF-κB p65nuclear translocation. Further treating HUVECs with phorbol12-myristate13-acetate (PMA) and tumor necrosis factor alpha (TNF-α), after incubation with liraglutide (1000ng/mL) was to detect the role of NF-κB p65in this process. Moreover, checking protein expression of interleukin-6(IL-6) was to confirm the function of liraglutide on inflammation and atherosclerosis. Finally, we draw figure illustrating this signaling pathway.ResultsHigh glucose increased expression of ET-1, iNOS and NF-κB p65, decreased expression of eNOS, both at mRNA and protein levels.100-1000ng/mL of liraglutide significantly inhibited ET-1, iNOS, phosphate NF-κB p65, phosphate IκBα and IL-6expressions, while that increased eNOS and GLP-1R expression, both on transcriptional and translational levels. The NF-κB p65translocation was also observed, consistent with data from western blotting. These cytokines almost rebounded to the level before liraglutide treatment while cells were incubated with PMA and TNF-a.ConclusionGLP-1agonist liraglutide upregulates eNOS and downregulates ET-1and iNOS expression, both at mRNA and protein levels, through inhibiting NF-κB p65activation, and represses protein expression of IL-6, in the high glucose medium cultured HUVECs. Our results indicate a potential role of GLP-1that may improve endothelial dysfunction and subsequent diabetic atherogenesis.