Alternative mechanisms for hydroperoxide-induced DNA single strand breakage

Area of Science:

• Cellular toxicology
• Molecular biology
• DNA damage mechanisms

Background:

• Hydroperoxides are reactive oxygen species implicated in cellular damage.
• Understanding the distinct mechanisms of organic vs. inorganic hydroperoxide-induced DNA damage is crucial.

Purpose of the Study:

• To investigate and compare the DNA-damaging effects of organic and inorganic hydroperoxides in human myeloid leukemia U937 cells.
• To elucidate the specific pathways involved in hydrogen peroxide (H2O2) and tert-butylhydroperoxide (tBu-OOH) induced DNA damage.

Main Methods:

• Treatment of U937 cells with H2O2 and tBu-OOH under various conditions (e.g., presence of iron chelators, antioxidants, glucose omission, catalase depletion, low temperature).
• Assessment of DNA single-strand breaks (SSBs) and DNA strand scission.
• Evaluation of the role of intracellular calcium concentration using ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA).
• Experiments on isolated nuclei and post-lysed DNA samples.

Main Results:

• Both H2O2 and tBu-OOH induced DNA single-strand breaks (SSBs) preventable by iron chelators and enhanced by catalase depletion.
• H2O2-induced SSBs were not affected by antioxidants or glucose omission, unlike tBu-OOH.
• H2O2, but not tBu-OOH, caused DNA strand scission in isolated nuclei and post-lysed DNA.
• Reduced intracellular calcium significantly decreased tBu-OOH DNA damage but only slightly affected H2O2-induced damage.

Conclusions:

• DNA damage by H2O2 is primarily mediated by hydroxyl radical formation.
• tBu-OOH-induced DNA single-strand breaks involve both H2O2 formation and a rise in cytosolic calcium ions.
• Organic and inorganic hydroperoxides exhibit distinct mechanisms of DNA damage in leukemia cells.