Modelling of Radiation Damage by¹²⁵I on a Nucleosome

Abstract

Studies of early physical interactions of ionizing radiation in biological medium have evolved from water cylinders or spheres to structured volumes representing nucleosomal DNA, based on spatial co-ordinates for each individual atom. Regarding the physico-chemical and chemical stages, the models of DNA have evolved from inactive geometrical objects to active participation of DNA in the reactions with the radical species. In this paper data are presented on the modelling of the interaction of low energy electrons with nucleosomal DNA. The nucleosome core unit has been modelled as a 146-bp helical DNA, containing > 9000 atoms, wound around the core unit. The yields of strand breaks for low energy electrons has been obtained by placing the nucleosome target in a liquid water environment and introducing a number of assumptions for the induction of strand breaks. The calculated results for the induction of ssb and dsb by 125I decays agree with experimental data, confirming the plausibility of this nucleosome model as well as the characterization of the interaction of ionizing radiation in terms of the energy deposition and the assumptions made for the strand breaks.

Monte Carlo simulation of DNA strand-break induction in supercoiled plasmid pBR322 DNA from indirect effects

“…Unexpectedly, this distance of 10 bp is exactly the value which has been frequently used for calculation (e.g. [7,42]). This value was also supported by ESR measurement [43], disintegration of 32 P atoms incorporated in λ phage DNA [44].…”

“…[5][6][7]). We have studied the history of the Monte Carlo methods and applied them to a simpler system, an aqueous plasmid DNA solution.…”

Can Monte Carlo track structure codes reveal reaction mechanism in DNA damage and improve radiation therapy?

“…Such a threshold energy deposition has been obtained from simulations of a very precise experimental data (Charlton and Humm, 1988;Nikjoo et al, 1996). Another method of converting energy deposition to strand breakage considers a physical event such as ionization (Terrissol, 1994). Our data base of frequencies of strand breakage by type and complexity are given for electrons, soft X-rays and ions (Nikjoo et al, , 2002.…”

Quantitative modelling of DNA damage using Monte Carlo track structure method

“…This has come about through the availability of computer codes describing molecular interactions [1,2] along the tracks of ionising particles, availability of fast computers and models of DNA in simple and more sophisticated forms [3][4][5]. These descriptions have progressed from considerations of direct effects of radiation alone [6,7] to include the contributions of radical species (indirect effect) [3,8,9] in the environment of the cell nucleus, causing DNA damage in the form of single-strand breaks (ssb), double-strand breaks (dsb), base damage and complex combinations within the cluster of damage.…”