DIFFERENTIAL-EFFECTS AND TRANSPORT KINETICS OF ASCORBATE DERIVATIVES IN LEUKEMIC-CELL LINES

In order to investigate the differential effects of ascorbate derivati ves on leukemic cell growth, we examined their stabilities and transme mbrane transport efficiencies. The growth of HL-60 and U937 cells was dose-dependently inhibited by ascorbic acid and sodium ascorbate, but not by dehydroascorbic acid and magnesium ascorbyl 2-phosphate up to 2 00 mu M. The growth-suppression by ascorbic acid was dependent on its redox state, showing a complete or partial reversion by ascorbate oxid ase or FeCl3 addition, respectively. Three different patterns of intra cellular ascorbic acid accumulation were observed by HPLC according to the species of ascorbate derivative applied for the incubation Compar ed with the reduced form of ascorbic acid, the oxidized forms (dehydro ascorbic acid, ascorbic acid plus ascorbate oxidase or FeCl3) were rap idly transported into cells and readily degraded, while magnesium asco rbyl 2-phosphate, a stable derivative of ascorbic acid, slowly elevate d the intracellular level of ascorbic acid, reaching a plateau at 24 h ours. We also measured the differential kinetics of ascorbic acid leve ls In culture supernatants following the addition of ascorbate derivat ives. Ascorbic acid at 40, 10 or 1 mu M was observed 3 hours following treatment with 100 mu M of ascorbic acid, ascorbic acid plus FeCl3 or magnesium ascorbyl 2-phosphate, respectively No ascorbic acid was fou nd in the culture supernatant treated with dehydroascorbic acid. This order of ascorbic acid concentrations in culture supernatant reflects their growth-inhibitory effects Thus the-growth inhibitory effect of a scorbic acid appears to be dependent on its concentration in culture m edium rather than its intracellular concentration. In conclusion, the results in this study indicate that the differential effects of ascorb ate derivatives appear to be due to the actual concentration differenc es of the reduced form of ascorbic acid in culture medium following th eir addition, which is determined by their stability and efficiency of cellular uptake.