ABSTRACT
It has been established that irradiation with higher linear energy transfer (LET) increases lethality and mutagenicity more than that with lower LET. However, the characteristics specific to carbon ion beam have not yet been elucidated. Yeast cells were irradiated with carbon ions with an LET of 13 or 50keV/µm, and cell survival and mutation frequency were analyzed. The results, combined with our previous findings for ions with an LET of 107keV/µm, demonstrated that, in conjunction with an increase in LET, cell survival decreased, while mutation frequency increased. This indicates that a carbon ion beam with a higher LET is more mutagenic than one with a lower LET.
Subject(s)
Heavy Ion Radiotherapy , Linear Energy Transfer , Mutagenesis/radiation effects , Mutation Rate , Saccharomyces cerevisiae/radiation effects , Carbon , Cell Survival/radiation effects , Dose-Response Relationship, Radiation , Heavy IonsABSTRACT
Clustered DNA damages are induced by ionizing radiation, particularly of high linear energy transfer (LET). Compared to isolated DNA damage sites, their biological effects can be more severe. We investigated a clustered DNA damage induced by high LET radiation (C 290 MeV u(-1) and Fe 500 MeV u(-1)) in pBR322 plasmid DNA. The plasmid is dissolved in pure water or in aqueous solution of one of the three scavengers (coumarin-3-carboxylic acid, dimethylsulfoxide, and glycylglycine). The yield of double strand breaks (DSB) induced in the DNA plasmid-scavenger system by heavy ion radiation was found to decrease with increasing scavenging capacity due to reaction with hydroxyl radical, linearly with high correlation coefficients. The yield of non-DSB clusters was found to occur twice as much as the DSB. Their decrease with increasing scavenging capacity had lower linear correlation coefficients. This indicates that the yield of non-DSB clusters depends on more factors, which are likely connected to the chemical properties of individual scavengers.
Subject(s)
DNA Breaks, Double-Stranded/drug effects , DNA Breaks, Double-Stranded/radiation effects , DNA Breaks, Single-Stranded/drug effects , DNA Breaks, Single-Stranded/radiation effects , Free Radical Scavengers/pharmacology , Intracellular Space/metabolism , Dose-Response Relationship, Radiation , Heavy Ions/adverse effects , Intracellular Space/drug effects , Intracellular Space/radiation effects , Plasmids/geneticsABSTRACT
The biological dosemeter that measures biological responses to ionising radiation is useful for radiation protection. This paper presents the development and characterisation of a gamma ray irradiation dosimetry system based on real-time PCR (polymerase chain reaction) methodology. Real-time PCR is used to amplify and simultaneously quantify a targeted DNA molecule. If there are no limitations due to limiting substrates or reagents, at each extension step, the amount of DNA target is doubled, leading to exponential (geometric) amplification of the specific DNA fragment. The essential point of this assay is that DNA lesions caused by ionising radiation block DNA synthesis by DNA polymerase, resulting in a decrease in the amplification of a damaged DNA template compared with that of non-damaged DNA templates.
Subject(s)
DNA Damage/radiation effects , DNA/radiation effects , Gamma Rays/adverse effects , Radiation Monitoring , Cobalt Radioisotopes , DNA-Directed DNA Polymerase/metabolism , Humans , Polymerase Chain ReactionABSTRACT
To investigate the nature of mutations induced by accelerated ions in eukaryotic cells, the effects of carbon-ion irradiation were compared with those of gamma-ray irradiation in the budding yeast Saccharomyces cerevisiae. The mutational effect and specificity of carbon-ion beams were studied in the URA3 gene of the yeast. Our experiments showed that the carbon ions generated more than 10 times the number of mutations induced by gamma-rays, and that the types of base changes induced by carbon ions include transversions (68.7%), transitions (13.7%) and deletions/insertions (17.6%). The transversions were mainly G:C-->T:A, and all the transitions were G:C-->A:T. In comparison with the surrounding sequence context of mutational base sites, the C residues in the 5'-AC(A/T)-3' sequence were found to be easily changed. Large deletions and duplications were not observed, whereas ion-induced mutations in Arabidopsis thaliana were mainly short deletions and rearrangements. The remarkable feature of yeast mutations induced by carbon ions was that the mutation sites were localized near the linker regions of nucleosomes, whereas mutations induced by gamma-ray irradiation were located uniformly throughout the gene.