A nonradioactive method for measuring DNA damage and its repair in nonproliferating tissues

The fluorometric assay of Kissane and Robins has been modified to monitor DNA in alkaline sucrose gradient fractions. Using this procedure the sedimentation analysis of DNA not only of liver, but also of brain, thymus, lung, pancreas, kidney, and skin was carried out. Like liver DNA, DNA released by the alkaline lysis of the above organs sedimented as heavy DNA (> 1 × 10⁹ daltons). A good correspondence was obtained for the sedimentation profiles of liver DNA whether DNA in the gradient fractions was determined by the fluorometric method or by measuring radioactivity.Using the fluorometric assay, the strand breaks not only of liver DNA but also of brain and kidney DNA have been demonstrated following the intravenous administration ofN-methylnitrosourea. Carcinogen-induced DNA damage and repair (as measured by sedimentation of DNA in alkaline sucrose gradients) in any organ including human biopsy specimens are potentially measurable by this procedure.