SHORT-TERM EFFECTS OF OXIDIZED ASCORBIC-ACID ON BOVINE CORNEAL ENDOTHELIUM AND HUMAN PLACENTA

Studies on the toxic effects of dehydro-L-ascorbic acid (DHAA) have been extended to include evaluations over time periods up to 3 hr. and to test for specific effects on a membrane transport protein, a membrane-bound enzyme and a soluble intracellular enzyme. In studies on cultured corneal endothelial cells, DHAA concentrations of 1, 2, and 5 mM over 3 hr. had an inhibitory effect on subsequent uptake of DHAA present at a tracer level. Surviving fragments of human placenta and alkaline phosphatase activity of the placental brush-border membrane were susceptible to the effect of DHAA at a high concentration (10 mM). Because intracellular metabolism of DHAA was not affected, and an increase in membrane permeability was not detected, it is concluded that a specific membrane transport protein might be the site of DHAA-induced damage. These studies support the concept that the oxidized form of ascorbic acid (vitamin C) has potential toxic effects on biological systems and suggests that proteins that mediate transport and metabolism may be sites where DHAA causes damage.