title: Similar mutagenicity of photoactivated porphyrins and ultraviolet A radiation in mouse embryonic fibroblasts: involvement of oxidative DNA lesions in mutagenesis.
abstract: Ultraviolet A (UVA) radiation is implicated in the etiology of human skin cancer. However, the underlying mechanism of carcinogenicity for UVA is not fully delineated. A mutagenic role for UVA has been suggested, which involves activation of endogenous photosensitizers generating oxidative DNA damage. We investigated the mutagenicity of UVA alone and in combination with delta-aminolevulinic acid (delta-ALA), a precursor of the intracellular photosensitizers porphyrins, in transgenic Big Blue mouse embryonic fibroblasts. A significant generation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG), a typical promutagenic oxidative DNA lesion, was observed in cells treated with a combination of delta-ALA (1 mM) and UVA (0.06 J/cm(2)) as quantified by high-pressure liquid chromatography-tandem mass spectrometry (p < 0.001; relative to the control). The steady-state level of 8-oxo-dG, however, remained unchanged in cells irradiated with UVA or treated with delta-ALA alone. Other photolesions including cyclobutane pyrimidine dimers and pyrimidine (6-4) pyrimidone photoproducts were not detectable in cells treated with delta-ALA and/or irradiated with UVA as determined by terminal transferase-dependent polymerase chain reaction assay. Mutation analyses of the cII transgene in cells treated with a combination of delta-ALA and UVA showed an approximately 3-fold increase in mutant frequency relative to the control (p < 0.008), as well as a unique induced mutation spectrum as established by DNA sequence analysis (p < 0.005; 95% CI, 0.002-0.009). No mutagenic effects were observed in cells irradiated with UVA or treated with delta-ALA alone. The spectrum of mutations produced by delta-ALA plus UVA was characterized by a significantly increased frequency of G --> T transversions (p < 0.0003; relative to the control), which are the hallmark mutations induced by 8-oxo-dG. Notably, the 8-oxo-dG-mediated mutagenicity of UVA plus delta-ALA is similar to that established previously for UVA alone at a mutagenic dose of 18 J/cm(2). We conclude that, in the presence of exogenous photosensitizers, UVA at a nonmutagenic dose induces mutations through the same mechanism as does a mutagenic dose of UVA per se.
authors.affiliation: Division of Biology and Department of Medical Oncology, Beckman Research Institute of the City of Hope National Medical Center, 1450 East Duarte Road, Duarte, California 91010, USA. ania@coh.org
authors.forename: Ahmad
authors.initials: A
authors.lastname: Besaratinia
authors.forename: Steven E
authors.initials: SE
authors.lastname: Bates
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Synold
authors.forename: Gerd P
authors.initials: GP
authors.lastname: Pfeifer
mesh_terms: D000080242:8-Hydroxy-2'-Deoxyguanosine; D000622:Aminolevulinic Acid / Q000633:toxicity; D000818:Animals; D010582:Bacteriophage lambda / Q000235:genetics; D001483:Base Sequence; D002478:Cells, Cultured; D018736:DNA Adducts / Q000378:metabolism / Q000528:radiation effects; D004249:DNA Damage; D004252:DNA Mutational Analysis; D004260:DNA Repair; D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D004622:Embryo, Mammalian; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects*; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010084:Oxidation-Reduction; D010777:Photochemistry; D011166:Porphyrins / Q000378:metabolism* / Q000528:radiation effects*; D014157:Transcription Factors / Q000235:genetics; D014466:Ultraviolet Rays; D014764:Viral Proteins
chemical_list: D018736:DNA Adducts; D011166:Porphyrins; D014157:Transcription Factors; D014764:Viral Proteins; C039000:cII protein, bacteriophage lambda; D000622:Aminolevulinic Acid; D000080242:8-Hydroxy-2'-Deoxyguanosine; D003849:Deoxyguanosine