title: Hydrogen peroxide lethality is associated with a decreased ability to maintain positive DNA supercoiling.
abstract: Hydrogen peroxide is more toxic to mammalian cells at 37 degrees C than 0 degree C at all concentrations studied. Histone-free nuclei (nucleoids) extracted from treated cells have a reduced ability to maintain positive DNA supercoiling, with the maximum effect at the higher temperature. Prior exposure of cells to sodium ascorbate at 0 degree C increased both toxicity and the inhibition of nuclear supercoil rewinding. After exposure at 0 degrees C, normal levels of supercoiling returned with both a fast and a slow component, kinetics characteristic of DNA single-strand break repair; the fast component was eliminated when cells were exposed at 37 degrees C due to in situ rejoining. At least a portion of the lethal lesions induced by hydrogen peroxide are DNA double-strand breaks (dsb) because the dsb repair-deficient mutant, xrs-5, is approximately two to three times more sensitive than wild-type cells over the initial portion of the survival curve. However, the increased toxicity found after exposure at 37 degrees C is observed equally in both cell lines, indicating that temperature-dependent cell killing is not directly linked to DNA dsb. It is suggested that cell killing at 37 degrees C is mediated through two linked processes. First, hydrogen peroxide may disrupt cation-stabilized nuclear supercoiling by direct ion oxidation. Second, as a part of the oxidation process, hydrogen peroxide will produce potentially cytotoxic free radicals close to the DNA-linked metal site, limited in extent only by the presence of chemicals capable of reducing metal ions prior to reoxidation.
authors.affiliation: Loyola-Hines Department of Radiotherapy, Illinois 60141.
authors.forename: A T
authors.initials: AT
authors.lastname: Vaughan
authors.forename: D J
authors.initials: DJ
authors.lastname: Gordon
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology; D016466:CHO Cells; D016923:Cell Death; D002460:Cell Line; D006224:Cricetinae; D004260:DNA Repair; D004278:DNA, Superhelical / Q000187:drug effects*; D006861:Hydrogen Peroxide / Q000633:toxicity*; D007700:Kinetics; D013696:Temperature
chemical_list: D004278:DNA, Superhelical; D006861:Hydrogen Peroxide; D001205:Ascorbic Acid