Chemical and biochemical postlabeling methods for singling out specific oxidative DNA lesions

A survey of the main available chemical and biochemical postlabeling assays for measuring oxidative DNA damage is reported. Two main approaches, radio and fluorescent postlabeling, have been used in order to reach a high level of sensitivity of detection. This is required for the measurement of DNA damage within cells and tissues upon exposure to agents of oxidative stress. Most of the methods are based on liquid chromatographic separation of defined DNA modifications following either acidic hydrolysis or enzymic digestion of DNA. In a subsequent step, the isolated base or sugar damages are either radiolabeled or made fluorescent by chemical or enzymatic reactions. Emphasis is placed on the recently developed high performance liquid chromatographic ³²P-postlabeling assay, which allows the specific and sensitive measurement of various base damages including adenine N-1 oxide and 5-hydroxy-methyluracil at the level of one modification per 10⁷ normal bases in a sample size of 1 μg of DNA. Examples of application of radioactive postlabeling to the measurement of DNA base damage following exposure of human cells to oxidizing agents including hydrogen peroxide and UVA radiation are provided.