Decline of superoxide dismutase activity during antioxidant-induced apoptosis in HL-60 cells

Possible changes in Mn-containing superoxide dismutase (MnSOD) and Cu- and Zn-containing superoxide dismutase (CuZnSOD) activity during the apoptosis of human promyelocytic leukemia HL-60 cells, induced by three antioxidants, were investigated. Agarose gel electrophoresis of the DNA isolated from cells treated with sodium ascorbate, gallic acid or epigallocatechin gallate (EGCG) showed the internucleosomal DNA fragmentation, a biochemical hallmark of apoptosis. The optimum concentration for induction of DNA fragmentation was narrow and higher concentrations were rather inhibitory. Their effects were detected after 3 hours and reached a maximum level at 6 hours. Polyactylamide gel electrophoresis and activity staining demonstrated that both MnSOD and CuZnSOD activities were significantly reduced at cytotoxic concentrations of all these compounds. Incubation of an intracellular MnSOD-enriched fraction with apoptosis-inducing concentrations of sodium ascorbate, gallic acid or EGCG did not significantly reduce the MnSOD activity, suggesting that their actions might be cell-mediated. These data suggest the mitochondrial dysfunction at the early stages of apoptosis.