Protective Effects Of Alpha-linolenic Acid On High Glucose-induced Damage On Endothelial Cells

BackgroundDiabetic vascular complications, such as atherosclerosis, thrombus-induced coronary artery disease,cerebral and peripheral vessel disease, are the main causes of the high mortality and mutilation in diabetic patients. Therefore, the American Heart Association(AHA) declared that"Diabetes is cardiovascular disease"in 1999. Endothelial cells are considered as candidates involved in the pathogenesis of diabetic vascular complications. Long-term hyperglycemia and hyperlipidemia are the main risk factors of endothelial dysfunction(ED), and ED is generally regarded as the central initiating factor and early phenomena, which acts as an important event in the process of diabetes-associated vascular complications. It is, therefore, thought that prevention of high glucose-induced endothelial dysfunction may have important implication for pharmacological attempts to prevent these complications.Alpha-linolenic acis(ALA), a kind of n-3 essential fatty acids presenting in vegetable oil, is a precursor for long-chain n-3 fatty acids eicosapentaenoic acid(EPA) and docosahecaenoic acid(DHA). While most studies have mainly focused on long-chain n-3 fatty acids in the past, the necessary of ALA in physiological functions, its effect on growth, the importance in disease development and maintaining health attract extensively attentions. And marine n-3 fatty acids are not as widely available as ALA because of the cost and supply constraints of seafood compared to plant sources. Therefore, the effect of ALA on coronary heart diseases(CHD) risk is of considerable public health importance, particularly for populations with low consumption or availability of fatty fish. In fact, there is growing evidence demonstrating a significant cardioprotective effect of ALA consumption, including anti-arrhythmic effect, anti-inflammatory responses, anti-atherosclerotic properties, beneficial effects on thrombosis,endothelial cell function and artery compliance. Additionally, several recent studies have demonstrated that ALA can abrogate chemically induced diabetes, improve insulin sensitivity in experimental animals. However, as far as we know, little evidence exists about the effect of ALA on damage in endothelial cells induced by high glucose condition. Another key question has not been definitively resolved is whether the cardioprotective effects of ALA are direct or, alternatively, mediated by EPA and/or DHA.AimTherefore, the aims of the present study were: (1) to determine whether diet rich in ALA may preserve artery function and attenuate endothelial dysfunction associated with diabetes; (2) to investigate the effect of ALA on high glucose-mediated inflammation and the underlying mechanisms; (3) to determine whether the protective effect of ALA on high glucose-induced endothelial dysfunction may be ascribed to its anti-apoptotic effect, and if so, to elucidate the signaling pathway involved.Results1. Diabetic animal model was successfully reproduced by using the high fatty diet plus low dose STZ intraperitoneal injection in rats.2. Treatment with ALA significantly preserved endothelium-dependent vasorelaxation of diabetic rats, decreased the levels of soluble cellular adhesion molecules(ICAM-1,P-selectin) and ET-1, and restored NO production in diabetic animals.3. We provided direct in vitro evidences that treatment with different concentrations of ALA induced different responses in endothelial cell growth and inflammation in high glucose condition: The lower, more physiological concentrations(10,50,100μmol/L) of ALA inhibited endothelial-neutrophil adhesion and improved the loss of endothelial cell viability induced by high glucose, attenuated the cytotoxicity; a higher concentration(200μmol/L) of ALA, which is beyond the physiological concentration, aggravated the damage on cultured HUVEC induced by high glucose.4. ALA with physiological concentration suppressed the high glucose-stimulated expression of CAMs(ICAM-1 and P-selectin) in cultured HUVEC, both on cell surface and on protein level, and this inhibition effect could be abolished by PI3K inhibitor LY294002.5. Low concentration ALA inhibited high glucose-induced apoptosis of cultured HUVEC, with subsequent increase in Akt and eNOS phosphorylation and NO production; while blocking the PI3K/Akt/eNOS pathway significantly abolished the anti-apoptotic effect of ALA.Conclusions1. These results demonstrate that diet rich in ALA has the potential to attenuate endothelial dysfunction and lower the risk of diabetes-associated vascular diseases.2. ALA with physiological concentration acts directly on cultured HUVEC to attenuate the high glucose-induced neutrophil–endhothelial cell adhesion and expression of adhesion molecules via a PI3k/Akt-dependent pathway, which might contribute to the anti-atherosclerotic effects of ALA.3. ALA exerts an anti-apoptotic effect by activating the PI3K/Akt/eNOS /NO pathway, which may play a critical role in its cardioprotective effects.