Yamamoto K, Kawanishi S
Department of Public Health, Faculty of Medicine, Kyoto University, Japan.
Chem Res Toxicol. 1992 May-Jun;5(3):440-6. doi: 10.1021/tx00027a019.
Phenylhydrazine cleaved isolated DNA in the presence of Cu(II), Mn(III), hemin, Fe(III)-EDTA, or peroxidase/H2O2, while phenelzine cleaved in the presence of Cu(II). DNA cleavage by phenylhydrazine in the presence of Mn(III), hemin, or Fe(III)-EDTA occurred without marked site specificity. Inhibitory effects of scavengers of hydroxyl free radical (.OH) on the DNA damage suggest the involvement of .OH. On the other hand, Cu(II)-mediated DNA cleavage by phenylhydrazine or phenelzine was inhibited by catalase and bathocuproine, a Cu(I)-specific chelator, but not by .OH scavengers. The predominant cleavage site was the thymine residue of 5'-GTC-3' sequence. Since the cleavage pattern was similar to that induced by Cu(I) plus H2O2 but not to that induced by Cu(II) plus H2O2, it is speculated that the copper-oxygen complex derived from the reaction of H2O2 with Cu(I) participates in DNA damage by phenylhydrazine or phenelzine in the presence of Cu(II). A comparison between scavenger effects on the DNA damage and those on radical production detected with ESR suggests that carbon-centered radicals (phenyl radical, 2-phenylethyl radical) do not play an important role in Cu(II)-, hemin-, or Fe(III)-EDTA-mediated DNA damage by phenylhydrazine or phenelzine of relatively low concentrations (less than 0.5 mM). However, during the oxidation of a high concentration (10 mM) of phenylhydrazine by ferricyanide, phenyl radical seemed to cause DNA damage, especially the breakage of the deoxyribose phosphate backbone. The possibility that active oxygen species (copper-oxygen complex, .OH) are more important in DNA damage induced by hydrazines in vivo than carbon-centered radicals is discussed.
苯肼在铜（II）、锰（III）、血红素、铁（III）-乙二胺四乙酸（EDTA）或过氧化物酶/H₂O₂存在的情况下能切割分离的DNA，而苯乙肼仅在铜（II）存在时能切割DNA。苯肼在锰（III）、血红素或铁（III）-EDTA存在时对DNA的切割没有明显的位点特异性。羟基自由基（·OH）清除剂对DNA损伤的抑制作用表明有·OH参与。另一方面，过氧化氢酶和铜（I）特异性螯合剂 bathocuproine 能抑制苯肼或苯乙肼由铜（II）介导的DNA切割，但·OH清除剂不能。主要的切割位点是5'-GTC-3'序列中的胸腺嘧啶残基。由于切割模式与铜（I）加H₂O₂诱导的相似，而与铜（II）加H₂O₂诱导的不同，推测H₂O₂与铜（I）反应产生的铜-氧复合物在铜（II）存在时参与了苯肼或苯乙肼对DNA的损伤。对清除剂对DNA损伤的影响与对用电子自旋共振（ESR）检测到的自由基产生的影响进行比较表明，在相对低浓度（小于0.5 mM）的苯肼或苯乙肼由铜（II）、血红素或铁（III）-EDTA介导的DNA损伤中，碳中心自由基（苯基自由基、2-苯乙基自由基）不起重要作用。然而，在铁氰化物氧化高浓度（10 mM）苯肼的过程中，苯基自由基似乎会导致DNA损伤，尤其是脱氧核糖磷酸主链的断裂。文中讨论了活性氧物种（铜-氧复合物、·OH）在体内肼诱导的DNA损伤中比碳中心自由基更重要的可能性。
