Alternative Mechanisms for Hydroperoxide-Induced DNA Single Strand Breakage

Abstract

The results presented in this study point out the existence of similarities as well as differences in the DNA-damaging effects of organic vs. inorganic hydroper- oxides in human myeloid leukemia U937 cells. On the one hand, the formation of DNA single strand breaks (SSBs) induced by either hydrogen peroxide (H₂O₂) or tert-butylhydroperoxide (tBu-OOH) was prevented by iron chelators, was not affected by antioxidants or glucose omission before and during peroxide exposure and was enhanced by pRíor catalase depletion. Furthermore, H₂O₂- and tBu-OOH-induced DNA strand scission were also detected after treatment at 0°C. On the other hand, H₂O₂, but not tBu-OOH or cumene hydroperoxide (cum-OOH), produced DNA strand scission in isolated nuclei and post-lysed DNA samples. In addition, lowering the basal intracellular calcium concentration with ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) markedly reduced the DNA-damaging efficiency of tBu-OOH while promoting only a slight decline in the number of DNA SSBs induced by H₂O₂. Taken together, these results are consistent with the commonly held theory that DNA damage caused by H₂O₂ is mediated by the formation of hydroxyl radicals. tBu-OOH-induced DNA single strand breakage appears to involve both the formation of H₂O₂ and a rise in cytosolic calcium ions.

Key Words:

• Hydroperoxide
• DNA damage
• calcium ions