Higher sensitivity for the detection of chemically-induced DNA damage: role of DNA unfolding in determining alkaline elution rate

: CHO-K1 cells exposed to log-spaced concentrations of methyl methanesulfonate (MMS) and liver cells from rats treated with log-spaced single i.p. doses of N-nitrosodimethylamine (DMN) were examined for changes in the rate of DNA alkaline elution induced by incubation in high ionic strength non-denaturing (pH 10) lysing solution. While the elution rate of DNA from control cells was marginally modified, that of treated cells increased proportionally to the length (from 0.5 to 48 h) of incubation, without any significant reduction of DNA average mol. wt. These experiments were suggested and then explained by a recently described physico-chemical model which has shown that the changes in DNA elution profiles are strongly determined also by related changes in DNA chain flexibility and packing. These chemical-induced changes in DNA superpacking and the subsequent differential kinetics of DNA unfolding in the lysing solution are compatible with previous results by independent physical methods. This allows significantly higher sensitivity in the detection of chemically-induced DNA damage, now possible even for a quite low chemical concentration. At the same time, it may be inferred that any material capable of altering DNA superpacking--by damaging either DNA itself or any other chromosomal constituents, such as protein--may well give rise to an increased elution of DNA from the filter.