Minisatellite and Hprt mutations in V79 cells irradiated with helium ions and gamma rays

Abstract

Purpose : To evaluate and compare cytotoxic and mutational effects of graded doses of γ-rays and 4 He ++ ions at different LET values (nominally 80 and 123 keV/ μ m) in V79 cells. Materials and methods : 4 He ++ ion beams at 80 and 123 keV/ μ m were supplied by the 7 MV Van de Graaff CN accelerator of the INFN-LNL in the dose range 0.3-2.4 Gy at a dose rate of 1 Gy/min. Gamma-irradiation was performed by the 60 Co ' γbeam' of CNR-FRAE (at the INFN-LNL) in the dose range 0.5-6.0 Gy at a dose rate of 1 Gy/min. After irradiation, the cells were seeded to measure surviving fraction (SF) and mutant frequency (MF) at the Hprt locus on the basis of 6-thioguanine resistance. Alterations at minisatellite sequences (MS) of clones derived from irradiated and unirradiated cells were detected by Southern blot analysis using a multi-locus probe (DNA fingerprinting). Results : Survival data from 4 He ++ irradiation at two LET values (80 and 123 keV/ μ m) yielded similar results: α =(1.08 ±0.04)/Gy and (0.90 ±0.03)/Gy, respectively. The best fit for mutant induction at the Hprt locus after 80 keV/ μ m 4 He ++ was a linear function of the dose in the dose-interval 0-1.5 Gy: α =(47.77 ±16.01) ×10 -6 /Gy. The best fit for mutant induction after 123 keV/ μ m 4 He ++ in the dose-interval 0-1.2 Gy was a linear-quadratic function: α =(86.01 ±13.80) ×10 -6 /Gy; β =(42.87 ±11.03) ×10 -6 /Gy 2. For γ-irradiation, the best fit of Hprt mutation data gave: α =(4.14 ±2.67) ×10 -6 /Gy; β =(0.63 ±0.86) ×10 -6 /Gy 2. The best fitting of MS alteration data with linear-quadratic or linear relationships gave: for γ-rays, α =0.56 mutants/Gy and β =0.52 mutants/Gy 2 ; for 80 keV/ μ m 4 He ++, α =3.70 mutants/Gy and β =9.00 mutants/Gy 2 ; for 123 keV/ μ m 4 He ++, α =4.36 mutants/Gy. Conclusions : The results reported here confirmed the higher cytotoxic and mutagenic effects of helium ions in comparison with γ-irradiation and the ability of DNA fingerprint analysis to investigate DNA damage induced by different ionizing radiations. The results of the mutagenic effects measured by the two tests are in agreement.