An in vivo-in vitro alkaline DNA unwinding assay for hepatic DNA damage: comparison with the alkaline sucrose gradient centrifugation technique.

An in vivo-in vitro alkaline DNA unwinding assay for single-strand breaks and/or alkali-labile lesions in hepatic DNA is described. The assay involves isolation of hepatic nuclei from mice, alkaline denaturation and unwinding of hepatic DNA, separation of single- and double-stranded DNA by hydroxylapatite batch chromatography, and quantitation of DNA in chromatographic fractions by a fluorometric assay. The method allows for the sensitive detection of hepatic DNA damage following in vivo administration of xenobiotics. Using this procedure, DNA fragmentation was demonstrated in alkali after administration of as little as 0.5 mg/kg of N-nitrosodimethylamine (DMN) to male B6C3F1 mice. A comparison of this technique with a similar alkaline sucrose density gradient centrifugation assay demonstrated comparable limits of sensitivity for the two procedures.