Advanced glycation end product-induced activation of NF-κB is suppressed by α-lipoic acid in cultured endothelial cells

Depletion of cellular antioxidant defense mechanisms and the generation of oxygen free radicals by advanced glycation end products (AGEs) have been proposed to play a major role in the pathogenesis of diabetic vascular complications. Here we demonstrate that incubation of cultured bovine aortic endothelial cells (BAECs) with AGE albumin (500 nmol/l) resulted in the impairment of reduced glutathione (GSH) and ascorbic acid levels. As a consequence, increased cellular oxidative stress led to the activation of the transcription factor NF-κB and thus promoted the upregulation of various NF- κB-controlled genes, including endothelial tissue factor. Supplementation of the cellular antioxidative defense with the natural occurring antioxidant α- lipoic acid before AGE albumin induction completely prevented the AGE albumin-dependent depletion of reduced glutathione and ascorbic acid. Electrophoretic mobility shift assays (EMSAs) revealed that AGE albumin- mediated NF-κB activation was also reduced in a time- and dose-dependent manner as long as α-lipoic acid was added at least 30 min before AGE albumin stimulation. Inhibition was not due to physical interactions with protein DNA binding, since α-lipoic acid, directly included into the binding reaction, did not prevent binding activity of recombinant NF-κB. Western blots further demonstrated that α-lipoic acid inhibited the release and translocation of NF-κB from the cytoplasm into the nucleus. As a consequence, α-lipoic acid reduced AGE albumin-induced NF-κB mediated transcription and expression of endothelial genes relevant in diabetes, such as tissue factor and endothelin- 1. Thus, supplementation of cellular antioxidative defense mechanisms by extracellularly administered α-lipoic acid reduces AGE albumin-induced endothelial dysfunction in vitro.