Uptake, recycling, and antioxidant actions of alpha-lipoic acid in endothelial cells.
Alpha-lipoic acid, which becomes a powerful antioxidant in its reduced form, has been suggested as a dietary supplement to treat diseases associated with excessive oxidant stress. Because the vascular endothelium is dysfunctional in many of these conditions, we studied the uptake, reduction, and antioxidant effects of alpha-lipoic acid in cultured human endothelial cells (EA.hy926). Using a new assay for dihydrolipoic acid, we found that EA.hy926 cells rapidly take up and reduce alpha-lipoic acid to dihydrolipoic acid, most of which is released into the incubation medium. Nonetheless, the cells maintain dihydrolipoic acid following overnight culture, probably by recycling it from alpha-lipoic acid. Acute reduction of alpha-lipoic acid activates the pentose phosphate cycle and consumes nicotinamide adenine dinucleotide phosphate (NADPH). Lysates of EA.hy926 cells reduce alpha-lipoic acid using both NADPH and nicotinamide adenine dinucleotide (NADH) as electron donors, although NADPH-dependent reduction is about twice that due to NADH. NADPH-dependent alpha-lipoic acid reduction is mostly due to thioredoxin reductase. Pre-incubation of cells with alpha-lipoic acid increases their capacity to reduce extracellular ferricyanide, to recycle intracellular dehydroascorbic acid to ascorbate, to decrease reactive oxygen species generated by redox cycling of menadione, and to generate nitric oxide. These results show that alpha-lipoic acid enhances both the antioxidant defenses and the function of endothelial cells.
Jones
Wright
W
Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232-6303, USA.
Li
Xia
X
Qu
Zhi-chao
ZC
Perriott
Laureta
L
Whitesell
Richard R
RR
May
James M
JM
D000975:Antioxidants / Q000378:metabolism* / Q000494:pharmacology*; D001205:Ascorbic Acid / Q000378:metabolism; D003683:Dehydroascorbic Acid / Q000378:metabolism; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000378:metabolism; D005292:Ferricyanides / Q000378:metabolism; D005452:Fluoresceins / Q000737:chemistry / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III; D010084:Oxidation-Reduction; D017382:Reactive Oxygen Species / Q000378:metabolism; D008063:Thioctic Acid / Q000378:metabolism* / Q000494:pharmacology*; D014471:Umbilical Veins
D000975:Antioxidants; D005292:Ferricyanides; D005452:Fluoresceins; D017382:Reactive Oxygen Species; C110423:dihydrofluorescein; D009243:NAD; C007931:hexacyanoferrate III; D009569:Nitric Oxide; D009249:NADP; D008063:Thioctic Acid; C496314:NOS3 protein, human; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; D005978:Glutathione; D005947:Glucose; D001205:Ascorbic Acid; D003683:Dehydroascorbic Acid