Rapid uptake of oxidized ascorbate induces loss of cellular glutathione and oxidative stress in liver slices.
The observation that ascorbate known to retain pro-oxidant properties induces cell death in a number of immortal cell lines, led us to examine its mechanism and whether it is involved in oxidative stress injury in such asocorbate-enriched tissue cells as hepatocytes. In rat liver homogenates, higher concentrations (1 and 3 mM) of ascorbate suppressed lipid peroxide productions but lower concentrations (0.1 and 0.3 mM) did not. In contrast to the homogenate, ascorbate increased lipid peroxide production in liver slices in a concentration dependant manner. Iso-ascorbate, the epimer of ascorbate did not cause an increase the oxidative stress in liver slices. This differential effect between homogenates and liver slices implies that cellular integrity is required for ascorbate to induce oxidative stress. Wortmannin, an inhibitor of the GLUT (glucose transporter) thought to transport dehydroascorbate into cells, inhibited [(14)C]-ascorbate uptake and suppressed oxidative stress in liver slices. Wortmannin suppressed that [(14)C]-ascorbate uptake by GLUT following oxidation to [(14)C]dehydroascorbate. Taken together, these observations support our hypothesis that ascorbate is oxidized to dehydroascorbate by molecular oxygen in solution (i.e., plasma and culture medium) which is then carried into hepatocytes (via a GLUT) where it is reduced back to ascorbate causing oxidative stress.
Song
Jing Hyang
JH
Department of Physiology, Queen's University Kingston, Ontario, Canada K7L 3N6.
Simons
Chantelle
C
Cao
Lily
L
Shin
Seon Ho
SH
Hong
Murray
M
Chung
Ill Min
IM
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism* / Q000494:pharmacology*; D001692:Biological Transport; D004492:Edetic Acid / Q000494:pharmacology; D005978:Glutathione / Q000378:metabolism*; D066298:In Vitro Techniques; D008099:Liver / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D010084:Oxidation-Reduction / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017392:Thiobarbituric Acid Reactive Substances / Q000378:metabolism; D013997:Time Factors; D000077191:Wortmannin
D000730:Androstadienes; D017392:Thiobarbituric Acid Reactive Substances; D004492:Edetic Acid; D005978:Glutathione; D001205:Ascorbic Acid; D000077191:Wortmannin