DNA Strand Breaks Induced by Low-energy Heavy Ions

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Abstract
The DNA unwinding method was used to estimate DNA breakage in Chinese hamster cells exposed to heavy ions with LET [linear energy transfer] in the range of 750-5000 keV/.mu.m. Comparison of the primary induced unwinding rate per dose unit for ions with various track diameters but similar LET showed a pronounced influence on the track diameter. Low-energy ions, producing thin tracks with diameters (penumbra) in the submicrometer region, were .apprx. 2 orders of magnitude less efficient than more energetic ions producing tracks with diameters of several micrometers and .apprx. 3 orders of magnitude less efficient than X-rays. For the thin tracks, clustering of breaks was indicated by comparison of the DNA unwinding rates in 2 different alkaline solutions. The unwinding rate apparently cannot be used as a good measurement for DNA breaks in this case. The residual unwinding remaining after 4 h of repair at 37.degree. C correlated well with the ability of the various ions to produce cell-killing.