Regulation of apoptosis by vitamin C. Specific protection of the apoptotic machinery against exposure to chlorinated oxidants.
We have investigated the ability of intracellular vitamin C to protect human umbilical vein endothelial cells from exposure to hypochlorous acid (HOCl) and a range of derived chloramines. Ascorbate provided minimal protection against the cytotoxicity induced by these oxidants, as measured by propidium iodide uptake. In contrast, there was a marked effect on apoptosis, monitored by caspase-3 activation and phosphatidylserine exposure. Extended incubation of the cells with glycine chloramine or histamine chloramine completely blocked apoptosis initiated in the cells by serum withdrawal. This effect was significantly abrogated by ascorbate. Inhibition of apoptosis required the oxidant to be present for an extended period after serum withdrawal and occurred prior to caspase-3 activation. General protection of thiols by ascorbate was not responsible for the protection of apoptosis, because intracellular oxidation by HOCl or chloramines was not prevented in supplemented cells. The results suggest a new role for vitamin C in the regulation of apoptosis. We propose that, by protection of an oxidant-sensitive step in the initiation phase, ascorbate allows apoptosis to proceed in endothelial cells under sustained oxidative stress.
Vissers
M C
MC
Pathology Department, Free Radical Research Group, Christchurch School of Medicine and Health Sciences, P. O. Box 4345, Christchurch 8001, New Zealand. margret.vissers@chmeds.ac.nz
Lee
W G
WG
Hampton
M B
MB
D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis; D001205:Ascorbic Acid / Q000378:metabolism* / Q000494:pharmacology; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival; D002478:Cells, Cultured; D002713:Chlorine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D006997:Hypochlorous Acid / Q000494:pharmacology / Q000633:toxicity; D008954:Models, Biological; D009336:Necrosis; D016877:Oxidants / Q000494:pharmacology; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism; D013997:Time Factors; D014471:Umbilical Veins / Q000166:cytology
D000975:Antioxidants; D016877:Oxidants; D002713:Chlorine; D006997:Hypochlorous Acid; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D001205:Ascorbic Acid; D010100:Oxygen