DNA repair capacity in the rat respiratory tract

A product of alkylating agents and DNA, O6-methylguanine, can mispair with thymine, resulting in initiation of a carcinogenic tissue response. O6-alkylguanine-DNA alkyltransferase (AGT) is an acceptor protein responsible for repairing O6-methylguanine. The purpose of our experiments was to characterize AGT activity in vitro in tissue and cell extracts of the respiratory tract, a target tissue for inhaled alkylating agents. Removal of [3H]Methyl from O6-methylguanine was measured by high-pressure liquid chromatography after incubation of tissue and cell extracts with the [3H]DNA. With the exception of tracheal and bronchial extracts, all tissues and cells analyzed contained AGT activity, which increased in proportion to the amount of protein added to reaction flasks. AGT activity in tracheal and bronchial extracts was only detected at the highest protein concentration used (1.5 mg protein/mL) and ranged from 10-15 fmole/mg protein. AGT activity in the respiratory tract was highest in the lung and a region of the nasal tissue (i.e., ethmoturbinates) and ranged from 45-75 fmole/mg protein. These data suggest that methylated DNA in specific regions of the rat respiratory tract should be readily repaired, albeit to different extents. (author)