Li Y, Trush M A
Department of Environmental Health Sciences, School of Hygiene and Public Health, Johns Hopkins University, Baltimore, MD 21205.
Carcinogenesis. 1993 Jul;14(7):1303-11. doi: 10.1093/carcin/14.7.1303.
The myelotoxicity, including leukemia, associated with benzene exposure has been attributed to the further activation of benzene-derived metabolites. In a previous study, we observed that (Cu(II) strongly mediates the oxidation of hydroquinone (HQ) producing benzoquinone (BQ) and H2O2 through Cu(II)/Cu(I) redox mechanism. Since copper exists in the nucleus and is closely associated with chromosomes and DNA, in this study we investigated whether this chemical--metal redox system induces strand breaks in phi X-174 RFI plasmid DNA. In the presence of micromolar concentrations of Cu(II) and HQ, both single and double strand breaks were induced, whereas HQ, Cu(II), H2O2 or BQ alone at the employed concentrations elicited no significant damage to DNA. The HQ/Cu(II) system was at least twice as efficient as a H2O2/Cu(II) system at inducing DNA strand breaks. Of Cu(II), Fe(III), Mn(II), Cd(II) and Zn(II), only HQ/Cu(II) induced extensive DNA strand breaks. Among HQ, 1,2,4-benzenetriol (BT), catechol and phenol, HQ/Cu(II) and BT/Cu(II) were the two most efficient DNA cleaving systems. The presence of bathocuproinedisulfonic acid (BCS) or catalase prevented the HQ/Cu(II)-induced DNA strand breaks. In addition, the HQ/Cu(II)-induced DNA strand breaks could be completely blocked by reduced glutathione and dithiothreitol, but not by L-cysteine. The interaction of L-cysteine with copper in the absence of HQ induced significant DNA strand breaks with the same pattern of DNA strand breaks as that of HQ/Cu(II) plus L-cysteine. In contrast to the HQ/Cu(II) system, a HQ/myeloperoxidase (MPO)/H2O2 system did not induce any DNA strand breaks, and furthermore, the presence of MPO inhibited the HQ/Cu(II)-induced DNA strand breaks. When DNA pretreated with Cu(II) was exposed to HQ, DNA strand breaks were formed that could be prevented by BCS or catalase, indicating that DNA-bound copper can undergo redox cycling in the presence of HQ, generating H2O2. Similar to the H2O2/Cu(II) system, the HQ/Cu(II)-induced DNA strand breaks could not be efficiently inhibited by hydroxyl radical scavengers but could be protected by singlet oxygen scavengers, indicating that the localized generation of singlet oxygen or a singlet oxygen-like entity, possibly a copper-peroxide complex, rather than free hydroxyl radical probably plays a role in the HQ/Cu(II)-induced DNA strand breaks. The above results suggest that macromolecule-associated copper and reactive oxygen generation may be important factors in the mechanism of HQ-induced DNA damage in target cells.
与苯接触相关的骨髓毒性，包括白血病，被认为是苯衍生代谢物进一步激活所致。在之前的一项研究中，我们观察到铜（II）通过铜（II）/铜（I）氧化还原机制强烈介导对苯二酚（HQ）的氧化，生成苯醌（BQ）和过氧化氢（H2O2）。由于铜存在于细胞核中并与染色体和DNA紧密相关，在本研究中我们调查了这种化学 - 金属氧化还原系统是否会诱导φX - 174 RFI质粒DNA发生链断裂。在存在微摩尔浓度的铜（II）和HQ的情况下，单链和双链断裂均被诱导，而在所使用浓度下单独的HQ、铜（II）、H2O2或BQ对DNA没有造成显著损伤。HQ/铜（II）系统在诱导DNA链断裂方面的效率至少是H2O2/铜（II）系统的两倍。在铜（II）、铁（III）、锰（II）、镉（II）和锌（II）中，只有HQ/铜（II）诱导了广泛的DNA链断裂。在HQ、1,2,4 - 苯三酚（BT）、邻苯二酚和苯酚中，HQ/铜（II）和BT/铜（II）是两种最有效的DNA切割系统。 bathocuproinedisulfonic acid（BCS）或过氧化氢酶的存在可防止HQ/铜（II）诱导的DNA链断裂。此外，HQ/铜（II）诱导的DNA链断裂可被还原型谷胱甘肽和二硫苏糖醇完全阻断，但不能被L - 半胱氨酸阻断。在没有HQ的情况下，L - 半胱氨酸与铜的相互作用诱导了显著的DNA链断裂，其DNA链断裂模式与HQ/铜（II）加L - 半胱氨酸的情况相同。与HQ/铜（II）系统相反，HQ/髓过氧化物酶（MPO）/H2O2系统未诱导任何DNA链断裂，此外，MPO的存在抑制了HQ/铜（II）诱导的DNA链断裂。当用铜（II）预处理的DNA暴露于HQ时，形成了可被BCS或过氧化氢酶阻止的DNA链断裂，这表明结合在DNA上的铜在HQ存在下可进行氧化还原循环，生成H2O2。与H2O2/铜（II）系统类似，HQ/铜（II）诱导的DNA链断裂不能被羟基自由基清除剂有效抑制，但可被单线态氧清除剂保护，这表明单线态氧或类似单线态氧的实体（可能是铜过氧化物复合物）的局部生成，而非游离羟基自由基，可能在HQ/铜（II）诱导的DNA链断裂中起作用。上述结果表明，与大分子相关的铜和活性氧的产生可能是目标细胞中HQ诱导DNA损伤机制的重要因素。
