DNA Strand Break and Rejoining in Cultured Human Fibroblasts Exposed to Fast Neutrons or Gamma Rays

Summary

The production and rejoining of DNA single-strand and double-strand breaks have been monitored in monolayer cultures of proliferating human skin fibroblasts by means of sensitive techniques.

Cells were irradiated with low doses of either ⁶⁰Co γ-rays or 14·6 MeV neutrons at 0°C (0–5 Gy for measurement of single-strand breaks by alkaline elution and 0–50 Gy for double-strand breaks measured by neutral elution). The yield of single-strand breaks induced by neutrons was 30 per cent of that produced by the same dose of γ-rays; whilst in the induction of double-strand breaks neutrons were 1·6 times as effective as γ-rays. Upon post-irradiation incubation of cells at 37°C, neutron-induced single-strand and double-strand breaks were rejoined with a similar time-course to γ-induced breaks. Rejoining followed biphasic kinetics; of the single-strand breaks, 50 per cent disappeared within 2 min after γ-rays and 6–10 min after neutrons. Fifty per cent of the double-strand breaks disappeared within 10 min, after γ-rays and neutrons. Cells derived from patients suffering from ataxia-telangiectasia showed the same capacity for repair of single- and double-strand breaks induced by 14·6 MeV neutrons, as cells established from normal donors.

The comparison of neutrons and γ-rays in the induction of DNA breaks did not explain the elevated r.b.e. on high LET radiation. However, a study of the variation in the spectrum of lesions induced by different radiation sources will probably contribute to the clarification of the relative importance of other radio products.

• DNA breakage
• fibroblasts
• neutrons
• gamma rays