Detection of repair of chemical-induced DNA damage in vivo by the nucleoid sedimentation assay.

The nucleoid sedimentation assay was used to study chemical-induced DNA repair in vivo. Nucleoid bodies were prepared from liver and lung of mice at various times after i.p. treatment with 1-methyl-1-nitrosourea or 4-nitroquinoline-1-oxide. Both carcinogens induced a dose-dependent loss in negative DNA supercoiling in liver and lung. The rate of DNA repair of 1-methyl-1-nitrosourea was similar in liver and lung whereas 4-nitroquinoline-1-oxide-induced DNA damage was repaired faster in lung than in liver. Results obtained by the nucleoid sedimentation technique corresponded to measurements of DNA repair by unscheduled DNA synthesis. The nucleoid sedimentation assay should be a useful tool to examine in vivo repair of chemical-induced DNA lesions in various tissues of laboratory animals.