Increased 8‐Hydroxyguanine in DNA and Its Repair Activity in Hamster and Rat Lung after Intratracheal Instillation of Crocidolite Asbestos

Asbestos and man‐made‐mineral fibers are known to increase one type of oxidative DNA damage, 8‐hydroxyguanine (8‐OH‐Gua), in vitro. In this study, we analyzed the 8‐OH‐Gua level in DNA and its repair activity after a single intratracheal instillation of fibers (crocidolite or glass) or saline to Syrian hamsters or Wistar rats. The 8‐OH‐Gua level was measured with a high‐performance liquid chromatography‐electrochemical detector (HPLC‐ECD) system. The 8‐OH‐Gua repair enzyme activity was determined with an endonuclease nicking assay using a (32)P‐labeled or fluorescently labeled 22mer DNA that contains 8‐OH‐Gua at a specific position. A significant increase in the 8‐OH‐Gua level in the lung DNA was observed 1 day after the exposure to crocidolite, as compared to the saline control. The repair activity was increased significantly at 7 days. On the other hand, after exposure to glass fibers, little or no increase of these carcinogenicity indicators was detected. These assays of 8‐OH‐Gua and its repair activity in short‐term animal experiments will be useful for evaluating the carcinogenicity of fibers. This is the first report of the increase of 8‐OH‐Gua and its repair activity in the animal lung after the instillation of asbestos fibers.