title: Cytotoxicity of cigarette smoke condensate is not due to DNA double strand breaks: Comparative studies using radiosensitive mutant and wild-type CHO cells.
abstract: OBJECTIVE
  To determine whether cigarette smoke condensate (CSC) without metabolic activation induces direct DNA double strand breaks (DSB) in the G1 phase of various radiosensitive mutants of CHO cells and whether these breaks display collateral hypersensitivity to CSC with respect to cell killing.
  
  
  METHODS
  We treated the G1-phase cultures of wild-type and DNA repair deficient mutants of CHO cells with various concentrations of CSC and examined the cell survival by colony formation assay and the induction of DNA double strand breaks by constant field gel electrophoresis as well as the phophorylated histone H2-A variant X (gamma-H2AX) assay.
  
  
  RESULTS
  Gel analysis and gamma-H2AX focus assay showed significantly fewer, but still detectable levels of DSB per cell after CSC treatment compared to ionizing radiation (IR) exposures, even when equitoxic radiation exposures were delivered at a low dose rate over the same 8-hour exposure used for CSC treatments. None of the three non-homologous end joining (NHEJ) deficient mutants were remarkably hypersensitive to CSC compared to wild-type cells. In contrast, UV-1 cells that are hypersensitive to several base damage and cross-linking agents showed a higher sensitivity to CSC compared to the other CHO cell lines.
  
  
  CONCLUSIONS
  DNA DSB produced directly by CSC are not principally responsible for its cytotoxicity. Further, the present study does not rule out the possibility that some of these lesions may secondarily result in DSB, such as may occur during impeded DNA replication and whose repair may require systems other than NHEJ.
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, USA.
authors.forename: Takamitsu
authors.initials: T
authors.lastname: Kato
authors.forename: Hatsumi
authors.initials: H
authors.lastname: Nagasawa
authors.forename: Christy
authors.initials: C
authors.lastname: Warner
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Okayasu
authors.forename: Joel S
authors.initials: JS
authors.lastname: Bedford
mesh_terms: D000818:Animals; D016466:CHO Cells; D002470:Cell Survival / Q000187:drug effects* / Q000528:radiation effects; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA / Q000187:drug effects* / Q000502:physiology* / Q000528:radiation effects; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects* / Q000528:radiation effects; D004249:DNA Damage / Q000187:drug effects* / Q000502:physiology* / Q000528:radiation effects; D004305:Dose-Response Relationship, Drug; D011836:Radiation Tolerance / Q000187:drug effects / Q000502:physiology; D013638:Tars / Q000633:toxicity*; D014028:Tobacco Smoke Pollution
chemical_list: D013638:Tars; D014028:Tobacco Smoke Pollution; C024746:tobacco tar; D004247:DNA