title: Photomicronucleus assay of phototoxic and pseudophotoclastogenic chemicals in human keratinocyte NCTC2544 cells.
abstract: Photochemical genotoxicity was evaluated in human keratinocyte NCTC2544 cells. The cells were pre-treated with photogenotoxic or pseudophotoclastogenic chemicals and irradiated with a solar-simulator for 50min at a total UV dose of 5J/cm(2) or placed in the dark for the same period. After washing, the cells were cultured for 1.5-2 cell cycles with fresh culture medium. At the end of culturing, slide specimens were prepared and examined for micronucleus formation. 8-Methoxypsoralen, a photogenotoxic chemical, strongly induced micronucleated cells with UV irradiation but not under non-irradiation conditions. Therefore, NCTC2544 cells were subjected to further investigation to evaluate the possible photogenotoxicity of other chemicals. 6-Methylcoumarin, 3,3',4',5-tetrachlorosalicylanilide and protoporphyrin IX disodium salt, which are all known phototoxic substances, induced micronucleated cells with irradiation but not in the non-irradiation state. These phototoxic substances were confirmed to be photogenotoxic. Tetrabenzoporphine and 5-aminolevulinic acid, which are used for photodynamic therapy, showed phototoxicity. However, these chemicals did not induce micronucleated cells in the irradiated or non-irradiated state, suggesting a lack of photogenotoxicity. Among 3 pseudophotoclastogenic chemicals having no light absorbance at 290-700nm, neither cycloheximide nor disulfoton induced micronucleated cells with or without irradiation; zinc oxide induced micronucleated cells with irradiation and, to a lesser extent, without irradiation. Based on the results of the photogenotoxicity assays of these 9 chemicals, NCTC2544 cells are considered to be a suitable test system to evaluate the photogenotoxic potential of chemicals.
authors.affiliation: Takeda Pharmaceutical Company Limited, Jusohonmachi 2-chome, Yodogawa-ku, Osaka, Japan. Horinouchi_Mayumi@takeda.co.jp
authors.forename: Mayumi
authors.initials: M
authors.lastname: Horinouchi
authors.forename: Sakae
authors.initials: S
authors.lastname: Arimoto-Kobayashi
mesh_terms: D002460:Cell Line; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D015603:Keratinocytes / Q000187:drug effects* / Q000528:radiation effects*; D008730:Methoxsalen / Q000633:toxicity; D015162:Micronucleus Tests / Q000379:methods*; D010778:Photochemotherapy / Q000009:adverse effects; D011524:Protoporphyrins / Q000633:toxicity; D012458:Salicylanilides / Q000633:toxicity; D014466:Ultraviolet Rays / Q000009:adverse effects*
chemical_list: D011524:Protoporphyrins; D012458:Salicylanilides; C028025:protoporphyrin IX; C003390:3,3',4',5-tetrachlorosalicylanilide; D008730:Methoxsalen