Nackerdien Z, Kasprzak K S, Rao G, Halliwell B, Dizdaroglu M
Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899.
Cancer Res. 1991 Nov 1;51(21):5837-42.
Nickel compounds are known to be carcinogenic to humans and animals. Cobalt compounds produce tumors in animals and are probably carcinogenic to humans. The mechanisms of the carcinogenicity of these metal compounds, however, have remained elusive. In the present work, we have investigated the ability of Ni(II) and Co(II) ions in the presence of H2O2 to cause chemical changes in DNA bases in chromatin extracted from cultured cells of human origin. Eleven modified DNA bases in chromatin were identified and quantitated by the use of gas chromatography-mass spectrometry. 2-Hydroxyadenine (isoguanine), which has not previously been shown to occur DNA or chromatin, was also identified. Products identified were typical hydroxyl radical-induced products of DNA bases, suggesting that the hydroxyl radical was involved in their formation. This idea was supported by partial inhibition of product formation by typical scavengers of hydroxyl radical. Partial inhibition of product formation indicated a possible "site-specific" formation of hydroxyl radical by unchelated Ni(II) and Co(II) ions bound to chromatin. Although treatment of chromatin for 1 h with Co(II)/H2O2 caused formation of significant amounts of products, treatment with Ni(II)/H2O2 required incubation times of more than 5 h and an increase in Ni(II) concentration before increases in product amounts above background levels became detectable. In both cases, ascorbic acid did not increase product yields. Glutathione at a physiologically relevant concentration had little overall effect on DNA base modification. Superoxide dismutase increased the yields of most products. Chelation of Ni(II) and Co(II) ions with EDTA almost completely inhibited product formation. Ni(II) in the presence of H2O2 produced greater base damage to the DNA in chromatin than to isolated DNA, unlike other metal ions tested. DNA damage in chromatin caused by Ni(II) and Co(II) ions in the presence of H2O2 may contribute to the established genotoxicity and carcinogenicity of these metal ions.
已知镍化合物对人类和动物具有致癌性。钴化合物可在动物体内产生肿瘤，对人类可能也具有致癌性。然而，这些金属化合物致癌性的机制仍不清楚。在本研究中，我们研究了在过氧化氢存在下，镍（II）和钴（II）离子对从人源培养细胞中提取的染色质中DNA碱基造成化学变化的能力。通过气相色谱 - 质谱法鉴定并定量了染色质中的11种修饰DNA碱基。还鉴定出了2 - 羟基腺嘌呤（异鸟嘌呤），此前它未在DNA或染色质中被发现过。鉴定出的产物是典型的DNA碱基羟基自由基诱导产物，这表明羟基自由基参与了它们的形成。典型的羟基自由基清除剂对产物形成的部分抑制支持了这一观点。产物形成的部分抑制表明与染色质结合的未螯合镍（II）和钴（II）离子可能会“位点特异性”地形成羟基自由基。虽然用钴（II）/过氧化氢处理染色质1小时会导致大量产物形成，但用镍（II）/过氧化氢处理则需要超过5小时的孵育时间，并且在镍（II）浓度增加后，产物量才会在背景水平之上开始增加并被检测到。在这两种情况下，抗坏血酸都不会增加产物产量。生理相关浓度的谷胱甘肽对DNA碱基修饰总体影响很小。超氧化物歧化酶增加了大多数产物的产量。用乙二胺四乙酸螯合镍（II）和钴（II）离子几乎完全抑制了产物形成。与其他测试的金属离子不同，在过氧化氢存在下，镍（II）对染色质中的DNA造成的碱基损伤比对分离的DNA造成的损伤更大。在过氧化氢存在下，镍（II）和钴（II）离子对染色质造成的DNA损伤可能导致了这些金属离子已确定的遗传毒性和致癌性。
