8-Oxodeoxyguanosine Formation in the DNA of Cultured Cells After Exposure to H2O2 Alone or with UVB or UVA Irradiation

Abstract— The purpose of the study was to determine if aluminum phthalocyanine tetrasulfonate (A1PcS₄) photodynamic therapy (PDT) induced the formation of micronuclei in vitro and whether micronuclei formation was dependent on fiuence or cell type. NIH-3T3 and EMT-6 monolayer cultures were incubated in AlPcS₄ (0 or 1 μg/mL) for 24 h, received 0.0, 0.5,1.0 or 1.5 J/cm ² of 675 nm light, then reincubated and harvested at either 24, 48 or 72 h. The micronucleus frequency was determined in binucleated cells using the cytochalasin-block method. Cytotoxicity was assessed by using the 3(4,5-dimenthylthiazoyl-2-yl)2,5(diphenyl-tetrazolium bromide) (MTT) method. The effect of treatment on cell cycle progression was determined by calculating a proliferative index.
Aluminum phthalocyanine tetrasulfonate PDT induced a fluence-dependent increase in the frequency of micro-nuclei in NIH-3T3 and EMT-6 cells. The maximal effect of PDT was obtained in both cell lines 24 h after treatment. NIH-3T3 and EMT-6 cells exposed to a low fiuence of 0.5 J/cm² had a significantly lower number of micro-nuclei per cell 48 h following PDT treatment compared to the number of micronuclei per cell observed 24 h following treatment; however, when cells were exposed to a fluence (1.0 or 1.5 J/cm²) the number of micronuclei per cell did not diminish until 72 h after PDT treatment. The results obtained from the micronucleus assay paralleled those results obtained from the MTT assay.