The ability to repair 'mis-instructive', O6-methylguanine, and 'non-instructive', AP sites, DNA lesions in Fischer 344 rat livers at various ages was determined. Different behaviours were observed. While the AP-endodesoxyribonuclease enzymes displayed a high constant level throughout the animals' lifetime, the O6-methylguanine-DNA methyltransferase activity presented a stepwise modulation (DNA normalization of results): the O6-MT activity significantly increased within the first month of animal life and enhanced again after 6 months reaching a maximum plateau in the 12-18-month-old animals. Thereafter a net significant decrease of O6-MT enzyme was detected in the 24-month-old group. While the repair of the widely formed AP sites appeared uniformly efficient like 'house keeping' functions, the removal of the rare precancerous O6-methylguanine is age-dependent indicating a decreased protection of the youngest and oldest animals against this 'mis-instructive' damage. However, any extrapolation of the age-associated cancer risk needs further assessment. © 1992.
Pardini, C., Mariani, L., Voliani, M., Rainaldi, G., & Citti, L. (1992). The ability of liver extracts from different-aged rats to repair “mis-instructive” and “non-instructive” lesions of DNA. Mutation Research DNAging, 275(1), 1–6. https://doi.org/10.1016/0921-8734(92)90002-7