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

Abstract

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-(+)-α-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 μmol/l–1 mmol/l) with/without different stimuli (high glucose, TNF-α, VEGF, wortmannin, LY-294002). Apoptosis, proliferation, cell cycle distribution, and protein expression were determined by DNA fragmentation assays, [3H]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-α: macEC, −75 ± 11%; micEC, −68 ± 13%) apoptosis. In HUVEC, inhibition of apoptosis by LA (500 μmol/l) was paralleled by reduction of NF-κB. LA's antiapoptotic activity was reduced by PI 3-kinase inhibitors (wortmannin, LY-294002), being in line with LA-induced Akt phosphorylation (Ser437, +159 ± 43%; Thr308, +98 ± 25%; P < 0.01). LA (500 μmol/l) inhibited ( P < 0.001) proliferation of macEC (−29 ± 3%) and micEC (−29 ± 3%) by arresting the cells at the G1/S transition due to an increased ratio of cyclin E/p27Kip (4.2-fold), upregulation of p21WAF-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.

α-Lipoic Acid Prevents Neointimal Hyperplasia Via Induction of p38 Mitogen-Activated Protein Kinase/Nur77-Mediated Apoptosis of Vascular Smooth Muscle Cells and Accelerates Postinjury Reendothelialization

“…This antiapoptot- ic action of ALA might be mediated through activation of AMP-activated protein kinase or acutely transforming retrovirus AKT8 in rodent T cell lymphoma (AKT), as suggested in previous studies. 24,27 Further studies are necessary to elucidate the molecular mechanism of antiapoptotic action of ALA in HAECs.…”

“…3,[7][8][9] Based on previous studies 24,27 showing protective effects of ALA on endothelial cells, we examined the effect of ALA on reendothelialization by immunohistochemical staining for CD31, an endothelial-specific marker, on the sections of arteries harvested at various points (3, 10, and 14 days after injury). ALA significantly increased CD31 reactivity on the luminal surface of arteries at 10 to 14 days after injury, whereas a CD31 signal was undetectable in injured arteries without ALA administration ( Figure 6A).…”

“…This antiapoptot- ic action of ALA might be mediated through activation of AMP-activated protein kinase or acutely transforming retrovirus AKT8 in rodent T cell lymphoma (AKT), as suggested in previous studies. 24,27 Further studies are necessary to elucidate the molecular mechanism of antiapoptotic action of ALA in HAECs.Recently, Nur77 family members have emerged as potentially important factors in the complex network of proteins that modulate endothelial cell activation and VSMC proliferation in atherosclerosis. 10,28 -30 Overexpression of TR3 in the arterial VSMCs and activation of Nur77 by 6-mercaptopurine protect against neointimal formation through inhibition of Figure 4.…”

Is α‐lipoic acid a scavenger of reactive oxygen species in vivo? Evidence for its initiation of stress signaling pathways that promote endogenous antioxidant capacity

“…LA induces Akt phosphorylation in human umbilical vascular endothelial cells (32) and the THP-1 human monocyte cell line (33). Using isolated rat hepatocytes, Diesel et al (34) also showed LA-induced PI3K activation, but suggested a mechanism different than as a thiol redox modulator.…”

Effect of -Lipoic Acid on Proteasomal Induction: Protection against Oxidative Damage in Human Skin Fibroblasts Cell Line NHDF

“…Although several studies shows the anti-proliferative capacity of LA on tumor cells [28] [29] [30], on the other hand, one recent study have reported the beneficial effect of LA promoting cell survival, angiogenesis and neuroregeneration after brain injury [31]. In our study, LA increased the number of cells after 8 days in culture suggesting the applicability of using LA in cell culture to quicken proliferation ( Figure 6).…”