[52] Photodynarnic methods for oxy radical-induced DNA damage

Publisher Summary DNA damage in a cell associated with oxidative stress or exposure to ionizing radiation is in part induced by initial OH radical attack on DNA constituents. These reactions modify the chemical structure of DNA subunits, and they mark the onset of subsequent biochemical and biological effects observed in OH-generating systems. This chapter discusses the types of stable products that arise from the reactions of OH radicals with pyrimidine nucleosides of DNA and provides some insight into the rather complicated mechanism by which they are formed. Thymidine (dThd) and 2′-deoxycytidine (dCyd) are degraded into a mixture of products by photooxidation using 2-methyl-l,4-naphthoquinone (MQ) as a sensitizer and near-UV light (h > 320 nm). The same types of pyrimidine products are formed by this photochemical reaction as by OH radical-induced degradation in aqueous oxygenated solutions. However, the attack of OH radicals on nucleosides takes place at several sites on both the pyrimidine base (OH radical addition either at C-5 or C-6; H-abstraction from the C-5 methyl group of thymidine) and the deoxyribose moiety (H-abstraction from several sites), whereas in the photochemical reaction, the primary precursor of all products is generated specifically. Consequently, the product mixtures are cleaner and the products can be obtained in higher yields compared to using OH-generating systems. The chromatography techniques including high-performance liquid chromatography (HPLC) and thin layer chromatography (TLC) are presented in the chapter to provide analysis of these products.