Mutation, DNA strand cleavage and nitric oxide formation caused by N-nitrosoproline with sunlight: a possible mechanism of UVA carcinogenicity.
N-Nitrosoproline (NPRO) is endogenously formed from proline and nitrite. NPRO has been reported to be nonmutagenic and noncarcinogenic. In this study, we have detected the direct mutagenicity of NPRO plus natural sunlight towards Salmonella typhimurium. Furthermore, formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a mutagenic lesion, was observed in calf thymus DNA treated with NPRO plus simulated sunlight. The treatment with NPRO and sunlight induced single strand breaks in the superhelical replicative form of phage M13mp2 DNA. Single-strand DNA breaks also occurred in the human fibroblast cells on treatment with NPRO plus UVA, as detected by the comet assay. An analysis using scavengers suggested that both reactive oxygen species and NO radical mediate the strand breaks. The formation of nitric oxide was observed in NPRO solution irradiated with UVA. We analyzed the photodynamic spectrum of mutation induction and DNA breakage using monochromatic radiation at a series of wavelengths between 300 and 400 nm. Both mutation frequencies and DNA breakage were highest at the absorption maximum of NPRO, 340 nm. The co-mutagenic and co-toxic actions of NPRO and sunlight merit attention as possible mechanisms increasing the carcinogenic risk from UVA irradiation.
Arimoto-Kobayashi
Sakae
S
Faculty of Pharmaceutical Sciences, Okayama University, Tsushima, Okayama 700-8530, Japan. arimoto@cc.okayama-u.ac.jp
Ando
Yoshiko
Y
Horai
Yumi
Y
Okamoto
Keinosuke
K
Hayatsu
Hikoya
H
Lowe
Jillian E
JE
Green
Michael H L
MH
D000818:Animals; D001435:Bacteriophages / Q000235:genetics; D015197:Carcinogenicity Tests; D002417:Cattle; D004247:DNA / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D004249:DNA Damage; D004279:DNA, Viral / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D009152:Mutagenicity Tests; D009569:Nitric Oxide / Q000378:metabolism*; D009602:Nitrosamines / Q000633:toxicity*; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000235:genetics / Q000528:radiation effects; D013472:Sunlight / Q000009:adverse effects; D014466:Ultraviolet Rays / Q000009:adverse effects*
D004279:DNA, Viral; D009602:Nitrosamines; D009569:Nitric Oxide; D004247:DNA; C427203:calf thymus DNA; C010259:nitrosoproline