DNA fragmentation in V79 cells irradiated with light ions as measured by pulsed-field gel electrophoresis. II. Simulation with a generalized broken stick model

Purpose: To characterize the differences among the experimental DNA fragmentation spectra induced in Chinese hamster V79 cells by (gamma)-rays, lowenergy protons and alpha-particles through the use of a phenomenological model. Materials and methods: A model of DNA fragmentation was developed as a generalization of the broken-stick model, in which the double-strand breaks induced by radiation were considered randomly placed, but in which the manifestly non-random fragmentation of the control sample was fully taken into account and considered as the initial fragment distribution. Further, an analytical method was introduced that allowed an evaluation of the deviation from randomness of the fragmentation induced by radiation. Results: The analysis of the experimental distribution of DNA fragments showed that there was a progressive departure from randomness in radiation-induced fragmentation going from (gamma)-rays to protons and then to alpha-particles. This deviation was characterized by an enhanced induction of fragments, and therefore by a larger correlation of double-strand breaks, in the experimental range of lower molecular weights. Conclusion: The analysis shows that low-energy light ions induce DNA fragmentation, at the loop level of the chromatin organization, that can be significantly nonrandom. The same analysis can readily be applied at different length scales, and thus it could offer a basis for the study of the link between DNA damage, correlated at various spatial scales and biological end-points.