Two novel antioxidants, U74006F and U78517F, inhibit oxidant-stimulated calcium influx

Incubation of UC11MG human astrocytoma cells with 250 microM hydrogen peroxide (H2O2) plus 50 microM ferrous ammonium sulfate resulted in two temporally distinct increases in intracellular calcium. The first peak, which occurred within 1 min, was due to release from intracellular stores, whereas the second increase was the result of influx of extracellular calcium. Both U74006F and U78517F, two novel antioxidants, specifically inhibited the second, but not the first peak of calcium. The calcium increase was inhibited 70-80% with incubation with either 0.1 microM U78517F or 10 microM U74006F. Treatment with the drugs also protected against oxidant-induced loss in cell viability. In experiments using the membrane potential dye DiBAC4(3), hydrogen peroxide treatment of cells resulted in membrane depolarization. However, at concentrations up to 100 microM, neither of the drugs had any effect on the H2O2-induced depolarization. The drugs also did not affect membrane depolarization resulting from treatment with tetrapropyl ammonium bromide, a potassium channel blocker. These results indicate that U74006F and U78517F act to inhibit injury-induced calcium fluxes, which may contribute to their in vivo efficacy.