title: Factors influencing heterogeneity of radiation-induced DNA-damage measured by the alkaline comet assay.
abstract: BACKGROUND
  To investigate whether different conditions of DNA structure and radiation treatment could modify heterogeneity of response. Additionally to study variance as a potential parameter of heterogeneity for radiosensitivity testing.
  
  
  METHODS
  Two-hundred leukocytes per sample of healthy donors were split into four groups. I: Intact chromatin structure; II: Nucleoids of histone-depleted DNA; III: Nucleoids of histone-depleted DNA with 90 mM DMSO as antioxidant. Response to single (I-III) and twice (IV) irradiation with 4 Gy and repair kinetics were evaluated using %Tail-DNA. Heterogeneity of DNA damage was determined by calculation of variance of DNA-damage (V) and mean variance (Mvar), mutual comparisons were done by one-way analysis of variance (ANOVA).
  
  
  RESULTS
  Heterogeneity of initial DNA-damage (I, 0 min repair) increased without histones (II). Absence of histones was balanced by addition of antioxidants (III). Repair reduced heterogeneity of all samples (with and without irradiation). However double irradiation plus repair led to a higher level of heterogeneity distinguishable from single irradiation and repair in intact cells. Increase of mean DNA damage was associated with a similarly elevated variance of DNA damage (r = +0.88).
  
  
  CONCLUSIONS
  Heterogeneity of DNA-damage can be modified by histone level, antioxidant concentration, repair and radiation dose and was positively correlated with DNA damage. Experimental conditions might be optimized by reducing scatter of comet assay data by repair and antioxidants, potentially allowing better discrimination of small differences. Amount of heterogeneity measured by variance might be an additional useful parameter to characterize radiosensitivity.
authors.affiliation: Department of General Psychiatry I, PZN-Wiesloch, Teaching Hospital of Ruprecht-Karls-University Heidelberg, Heidelberger Str. 1a, Wiesloch 69168, Germany.
authors.forename: Clemens
authors.initials: C
authors.lastname: Seidel
authors.forename: Christine
authors.initials: C
authors.lastname: Lautenschläger
authors.forename: Jürgen
authors.initials: J
authors.lastname: Dunst
authors.forename: Arndt-Christian
authors.initials: AC
authors.lastname: Müller
mesh_terms: D000975:Antioxidants / Q000494:pharmacology*; D002470:Cell Survival / Q000528:radiation effects; D020552:Comet Assay; D004247:DNA / Q000528:radiation effects*; D004249:DNA Damage / Q000528:radiation effects*; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D006657:Histones / Q000528:radiation effects*; D006801:Humans; D007962:Leukocytes / Q000528:radiation effects; D011836:Radiation Tolerance / Q000528:radiation effects*
chemical_list: D000975:Antioxidants; D006657:Histones; D004247:DNA