Reaction mechanisms and evaluation of toxicity of the formation of nitric oxide from UVA-irradiated N-nitroso-compound

N-亚硝基脯氨酸(N-Nitrosoproline，NPRO)是由脯氨酸和亚硝酸盐内源形成的。据报道，NPRO是非诱变和非致癌的。我们发现NPRO加自然光对鼠伤寒沙门氏菌和M13mp2噬菌体具有直接致突变性。大多数诱导的序列变化是GC到TA和GC到CG的颠换。这表明鸟嘌呤残基的修饰是导致这些颠换的原因。研究了长波紫外线照射下NPRO溶液中一氧化氮(NO)的生成。我们分析了单色辐射在300-400 nm范围内突变和NO生成的光动力学光谱。突变频率和NO生成曲线与NPRO的吸收曲线一致。NPRO和UVA的共同诱变作用是增加UVA光辐射致癌风险的可能机制。烟草特有的亚硝胺4-(N-methylnitrosamino)-1-(3-pyridyl)-1-butanone(NNK)经历微粒体代谢，引起突变。我们在Ames细菌和M13mp2噬菌体中发现了NNK与UVA的直接作用致突变作用，在没有代谢激活的情况下。诱发突变以GC-CG、GC-TA和GC-AT为主。当NNK和UVA处理小牛胸腺DNA时，8oxodG/dG和O6meG/G的数量比未处理的对照组增加。在NNK和UVA处理后观察到DNA链断裂，并在氧和NO自由基清除剂存在的情况下被抑制。在经UVA照射的NNK液中也观察到了NO的生成。突变诱导图、8oxodG图和NO图与NNK的吸收曲线相吻合。我们的结论是，NNK可能作为光敏剂响应UVA，在DNA中形成8-oxodG和O6meG后产生NO和其他氧化和烷化中间产物，这可能导致突变和DNA链断裂。

N-Nitrosoproline (NPRO) is endogenously formed from proline and nitrite. NPRO had been reported to be nonmutagenic and noncarcinogenic. We discovered the direct mutagenicity of NPRO plus natural sunlight towards S.typhimurium and phage M13mp2. The majority of the induced sequence changes were GC to TA and GC to CG transversions. This suggested that modifications in guanine residues were responsible for these transversions. We explored the formation of nitric oxide (NO) in NPRO solution irradiated with UVA. We analyzed the photodynamic spectrum of mutation and NO formation using monochromatic radiation between 300 nm and 400 nm. The plots of mutation frequencies and NO formation were align with the absorption curve of NPRO. The co-mutagenic actions of NPRO and UVA merit attention as possible mechanisms increasing the carcinogenic risk from UVA irradiation.The tobacco-specific nitrosamine, 4-(N-methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) undergoes-microsomal metabolism, giving rise to mutation. We discovered the directly acting mutagenicity of NNK with UVA in Ames bacteria and phage Ml3mp2 in the absence of metabolic activation. The majority of induced mutation were comprised of GC to CG, GC to TA and GC to AT. When calf thymus DNA was treated with NNK and UVA, the amount of 8oxodG/dG and O6meG/G increased compared with the untreated control. DNA strand breaks were observed following NNK and UVA treatment, and were suppressed in the presence of scavengers for oxygen and NO radical. The formation of NO was also observed in NNK solutions irradiated with UVA. The plots of mutation induction, 8oxodG formation and NO formation were align with the absorption curve of NNK. We conclude that NNK may act as a photosensitizer in response to UVA to produce NO and other oxidative and alkylative intermediates following the formation of 8-oxodG and O6meG in DNA, which may lead to mutations and DNA strand breaks.