Individuals with insulin resistance and diabetes mellitus have increased cardiovascular morbidity and mortality, caused in part by vascular complications. Endothelial dysfunction has been implicated in the pathogenesis of vascular diabetic disease. This abnormal function of the vasculature precedes cardiovascular disease and is associated with impaired endothelium-dependent vasorelaxation. The main etiology of the increased mortality and morbidity of type 2 diabetic patients is atherosclerosis. Increased production of free radicals is associated with the pathophysiology of diabetes, resulting in oxidative damage to lipids and proteins. Reduction of oxidative stress in diabetic patients may delay the onset of atherogenesis and the appearance of micro- and macrovascular complications. Alpha-lipoic acid (LA) is a multifunctional antioxidant that has been shown to have beneficial effects on polyneuropathy and on markers of oxidative stress in various tissues. This study was conducted to investigate the effects of LA on endothelial function in diabetic and hyperlipidemic animal models. Carbohydrate and lipid metabolism, endothelial function, plasma malondialdehyde (MDA) and urinary 8-hydroxydeoxyguanosine (8-OHdG) were assessed in non-diabetic controls (Wistar rats), untreated diabetic Goto-Kakizaki (GK) rats and, atherogenic diet (AD)-fed GK rats (fed with atherogenic diet only, treated with alpha-lipoic acid and treated with vehicle, for 3 months). AD resulted in a 3-fold increase in both total and non-HDL serum cholesterol levels and in a 2-fold increase triglyceride levels while endothelial function was significantly reduce MDA and 8-OHdG levels were higher in the GK and GK hyperlipidemic groups and were completely reversed by the antioxidant. Hyperlipidemic GK diabetic rats showed significantly reduced endothelial function that was partially improved with LA. Furthermore, lipoic acid significantly reduced serum cholesterol levels, without lowering HDL cholesterol. Alpha-lipoic acid supplementation represents an achievable adjunct therapy to improve endothelial function and reduce oxidative stress, factors that are implicated in the pathogenesis of atherosclerosis in diabetes
