DNA repair systems in early and persistent hepatocyte nodules in the rat.

The repair of three DNA lesions, namely O6-methylguanine, 7-methylguanine, and 3-methyladenine, was investigated within early and persistent hepatocyte nodules generated in Fischer 344 rats by a modified Solt-Farber procedure (diethylnitrosamine initiation followed by a 2-acetylaminofluorene/CCl4 cycle). The O6-methylguanine-DNA methyltransferase concentration within both hepatocyte nodule types was always higher than that found in age-matched controls (normal, initiated-only and promoted-only livers). As far as 3-methyladenine and 7-methylguanine-DNA glycosylases are concerned, the early hepatocyte nodules showed far higher activities for both enzymes than were found in the controls, whereas in the persistent ones they underwent a significant decrease. In conclusion hepatocyte nodules are endowed with a high DNA repair activity, which is partly adaptive, partly constitutive; along with others, such a defence mechanism could allow transformed cells to resist many cytotoxic drugs.