Abstract
Cardiovascular disease is the primary cause of morbidity and mortality in patients with diabetes. Endothelial dysfunction is recognised to be a key early event in the atherogenic process that underpins vascular disease, and endothelial hyperglycaemic exposure or excursion could underpin this process. In addition, increased fructose consumption has been implicated in critical aspects of atherosclerosis. Although the adverse effects of high fructose consumption on hepatic metabolism have been extensively described, the direct effect of circulating fructose exposure on endothelial cell function is not fully understood. Furthermore, alteration of intracellular insulin signalling, described as vascular insulin resistance, could arise from the continuous hyperglycaemic exposure and consequent high insulin concentrations.In this study, the effect of chronic, acute and oscillating glucose exposure on a human-derived endothelial cell line, EA.Hy926, was examined. EA.hy926 cells were preconditioned with two distinctive pre-treatment glucose conditions during the cell growth phase: (“normal glucose”, NG; NGPC cells) or 25 mM glucose (“high glucose”, HG; HGPC cells). Both of these cell groups were exposed to three test carbohydrate concentrations (5.5, 12.5 and 25 mM) for 48 hours and the measurement of bioenergetics, cell function and key endothelial cell mediators compared for HGPC and NGPC cells.
Further complexity was incorporated into the model by partial substitution of glucose with fructose and by the inclusion of insulin. The impact of the various test conditions was measured in terms of bioenergetics, using a metabolic analyser, and cell function by measurement of key endothelial cell mediators (nitric oxide (NO), endothelin-1 and thrombolytic factors).
Chronic HG exposure modulated cell bioenergetics and decreased mitochondrial respiration, production of mediators of vessel tone (NO, endothelin-1) and fibrinolysis (tissue plasminogen activator, plasminogen activator inhibitor-1). These effects were not reversed after acute exposure to NG. Addition of fructose increased markers of metabolic activity, but reduced NO generation. The effect of insulin was complex, impacting both bioenergetics and NO generation and dependent upon the presence of fructose, as well as the glucose concentration of the medium.
In conclusion, this study showed that chronic glucose exposure induces long-lasting changes in bioenergetics, antioxidant defence and production of mediators of vascular tone and fibrinolysis in EA.hy926 cells. The results highlighted deleterious and long-lasting changes to endothelial cell function induced by chronic hyperglycaemia which could not be reversed in an improved glycaemic environment. Moreover, fructose introduces an additional adverse effect on cell function, which is further complicated by the presence of insulin. All taken together, this study reinforces the importance of the link between carbohydrate load, diabetes, endothelial function and cardiovascular disease.
| Date of Award | 29 Sep 2020 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Ian Megson (Supervisor) & Andrew Treweeke (Supervisor) |