R-(+)-alpha-lipoic acid inhibits endothelial cell apoptosis and proliferation: involvement of Akt and retinoblastoma protein/E2F-1.

R-(+)-alpha- lipoic acid inhibits endothelial cell apoptosis and proliferation: involvement of Akt and retinoblastoma protein/E2F-1. Am J Physiol Endocrinol Metab 293: E681-E689, 2007. First published June 12, 2007; doi:10.1152/ajpendo.00584.2006. - Lipoic acid was recently demonstrated to improve endothelial dysfunction or retinopathy not only in rats but also in diabetic patients. We tested the hypothesis that R-(+)-alpha- lipoic acid ( LA) directly affects human endothelial cell (EC) function ( e. g., apoptosis, proliferation, and protein expression), independent of the cells' vascular origin. Macrovascular EC (macEC), isolated from umbilical ( HUVEC) and adult saphenous veins and from aortae, as well as microvascular EC (micEC) from retinae, skin, and uterus, were exposed to LA (1 mu mol/ l-1 mmol/ l) with/without different stimuli ( high glucose, TNF-alpha, VEGF, wortmannin, LY-294002). Apoptosis, proliferation, cell cycle distribution, and protein expression were determined by DNA fragmentation assays, [H-3] thymidine incorporation, FACS, and Western blot analyses, respectively. In macro- and microvascular EC, LA ( 1 mmol/ l) reduced ( P < 0.05) basal ( macEC, -36 +/- 4%; micEC, -46 +/- 6%) and stimulus-induced (TNF-alpha: macEC, -75 +/- 11%; micEC, -68 +/- 13%) apoptosis. In HUVEC, inhibition of apoptosis by LA ( 500 mu mol/ l) was paralleled by reduction of NF- kappa B. LA's antiapoptotic activity was reduced by PI 3- kinase inhibitors ( wortmannin, LY-294002), being in line with LA-induced Akt phosphorylation ( Ser(437), +159 +/- 43%; Thr(308), + 98 +/- 25%; P < 0.01). LA ( 500 mu mol/l) inhibited ( P < 0.001) proliferation of macEC (-29 +/- 3%) and micEC (- 29 +/- 3%) by arresting the cells at the G(1)/S transition due to an increased ratio of cyclin E/p27(Kip) (4.2-fold), upregulation of p21(WAF- 1/Cip1) (+ 104 +/- 21%), and reduction of cyclin A (-32 +/- 11%), of hyperphosphorylated retinoblastoma protein ( macEC: - 51 +/- 7%; micEC: - 50 +/- 15%), and of E2F-1 ( macEC: - 48 +/- 3%; micEC: - 31 +/- 10%). LA's ability to inhibit apoptosis and proliferation of ECs could beneficially affect endothelial dysfunction, which precedes manifestation of late diabetic vascular complications.