title: Clustered DNA damages induced in isolated DNA and in human cells by low doses of ionizing radiation.
abstract: Clustered DNA damages-two or more closely spaced damages (strand breaks, abasic sites, or oxidized bases) on opposing strands-are suspects as critical lesions producing lethal and mutagenic effects of ionizing radiation. However, as a result of the lack of methods for measuring damage clusters induced by ionizing radiation in genomic DNA, neither the frequencies of their production by physiological doses of radiation, nor their repairability, nor their biological effects are known. On the basis of methods that we developed for quantitating damages in large DNAs, we have devised and validated a way of measuring ionizing radiation-induced clustered lesions in genomic DNA, including DNA from human cells. DNA is treated with an endonuclease that induces a single-strand cleavage at an oxidized base or abasic site. If there are two closely spaced damages on opposing strands, such cleavage will reduce the size of the DNA on a nondenaturing gel. We show that ionizing radiation does induce clustered DNA damages containing abasic sites, oxidized purines, or oxidized pyrimidines. Further, the frequency of each of these cluster classes is comparable to that of frank double-strand breaks; among all complex damages induced by ionizing radiation, double-strand breaks are only about 20%, with other clustered damage constituting some 80%. We also show that even low doses (0.1-1 Gy) of high linear energy transfer ionizing radiation induce clustered damages in human cells.
authors.affiliation: Biology Department, Brookhaven National Laboratory, Upton, NY 11973-5000, USA. bms@bnl.gov
authors.forename: B M
authors.initials: BM
authors.lastname: Sutherland
authors.forename: P V
authors.initials: PV
authors.lastname: Bennett
authors.forename: O
authors.initials: O
authors.lastname: Sidorkina
authors.forename: J
authors.initials: J
authors.lastname: Laval
mesh_terms: D017123:Bacteriophage T7; D019757:Carbon-Oxygen Lyases; D002470:Cell Survival; D004247:DNA / Q000737:chemistry / Q000528:radiation effects*; D004249:DNA Damage / Q000235:genetics*; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D043382:DNA-Formamidopyrimidine Glycosylase; D043224:Deoxyribonuclease (Pyrimidine Dimer); D043223:Deoxyribonuclease IV (Phage T4-Induced); D004587:Electrophoresis, Agar Gel; D004706:Endodeoxyribonucleases; D029968:Escherichia coli Proteins; D005720:Gamma Rays; D006801:Humans; D009000:Monocytes / Q000528:radiation effects*; D009699:N-Glycosyl Hydrolases; D011743:Pyrimidines / Q000737:chemistry; D014965:X-Rays
chemical_list: D029968:Escherichia coli Proteins; D011743:Pyrimidines; D004247:DNA; D004706:Endodeoxyribonucleases; D043223:Deoxyribonuclease IV (Phage T4-Induced); D043224:Deoxyribonuclease (Pyrimidine Dimer); C106403:NTH protein, E coli; D009699:N-Glycosyl Hydrolases; D043382:DNA-Formamidopyrimidine Glycosylase; D019757:Carbon-Oxygen Lyases; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase