Effect of Organic Solvents and Biologically Relevant Ions on the Light-Induced DNA Cleavage by Pyrene and Its Amino and Hydroxy Derivatives

Polycyclic aromatic hydrocarbons (PAHs) are a class of carcinogenic compounds that are both naturally and artificially produced. Many PAHs are pro-carcinogens that require metabolic activation. Recently, it has been shown that PAH can induce DNA single strand cleavage and formation of PAH-DNA covalent adduct upon irradiation with UVA light. The light-induced DNA cleavage parallels phototoxicity in one instance. The DNA photocleavage efficiency depends on the structure of the PAHs. This article reports the effect of both organic solvents and the presence of biologically relevant ions, Na, Mg, Ca, K, Fe, Cu, Zn, Mn, and I, on the light-induced DNA cleavage by pyrene, 1hydroxypyrene and 1-aminopyrene. Since both 1-hydroxypyrene (0.6 μM) and 1aminopyrene (6 μM) dissolve well in the minimum organic solvents used (2% methanol, dimethylsulfoxide, and dimethylformamide), increasing the amount of the organic solvent resulted in the decrease of the amount of DNA single strand cleavage caused by the combination effect of 1-hydroxy or 1-aminopyrene and UVA light. The result with the less watersoluble pyrene shows that increase of the amount of the organic solvent can increase the amount of DNA single strand DNA photocleavage cause by the combination of pyrene and UVA light. Therefore, there are two effects by the organic solvents: (i) to dissolve PAH and (ii) to quench DNA photocleavage. The presence of Fe and Zn enhances, while the presence of Ca and Mn inhibits the DNA photocleavage caused by 1-aminopyrene and UVA light. Other metal ions have minimal effect. This means that the effect of ions on DNA Int. J. Mol. Sci. 2002, 3 938 photocleavage by PAHs is complex. The presence of KI enhances DNA photocleavage. This indicates that the triplet-excited state of 1-aminopyrene is involved in causing DNA cleavage.