Fisher G R, Gutierrez P L
Division of Developmental Therapeutics, University of Maryland Cancer Center, Baltimore 21201.
Free Radic Biol Med. 1991;11(6):597-607. doi: 10.1016/0891-5849(91)90141-o.
One-electron reduction of diaziquone (AZQ) by purified rat liver NADPH cytochrome c reductase was associated with formation of AZQ semiquinone, superoxide anions, hydrogen peroxide, and hydroxyl radicals as indicated by ESR spin-trapping studies. Reactive oxygen formation correlated with AZQ-dependent production of single and double PM2 plasmid DNA strand breaks mediated by this system as detected by gel electrophoresis. Direct two-electron reduction of AZQ by purified rat liver NAD(P)H (quinone acceptor) oxidoreductase (QAO) was also associated with formation of AZQ semiquinone, superoxide anions, hydrogen peroxide, and hydroxyl radicals as detected by ESR spin trapping. Furthermore, PM2 plasmid DNA strand breaks were detected in the presence of this system. Plasmid DNA strand breakage was inhibited by dicumarol (49 +/- 5%), catalase (57 +/- 2.3%), SOD (42.2 +/- 3.6%) and ethanol (41.1 +/- 3.9%) showing QAO and reactive oxygen formation was involved in the PM2 plasmid DNA strand breaks observed. These results show that both one- and two-electron enzymatic reduction of AZQ give rise to formation of reactive oxygen species and DNA strand breaks. Autoxidation of the AZQ semiquinone and hydroquinone in the presence of molecular oxygen appears to be responsible for these processes. QAO appears to be involved in the metabolic activation of AZQ to free radical species. The cellular levels and distribution of this enzyme may play an important role in the response of tumor and normal cells to this antitumor agent.
通过电子自旋共振（ESR）自旋捕获研究表明，纯化的大鼠肝脏NADPH细胞色素c还原酶对重氮醌（AZQ）的单电子还原与AZQ半醌、超氧阴离子、过氧化氢和羟基自由基的形成有关。活性氧的形成与该系统介导的AZQ依赖性单链和双链PM2质粒DNA链断裂的产生相关，这可通过凝胶电泳检测到。纯化的大鼠肝脏NAD(P)H（醌受体）氧化还原酶（QAO）对AZQ的直接双电子还原也与ESR自旋捕获检测到的AZQ半醌、超氧阴离子、过氧化氢和羟基自由基的形成有关。此外，在该系统存在的情况下检测到了PM2质粒DNA链断裂。双香豆素（49±5%）、过氧化氢酶（57±2.3%）、超氧化物歧化酶（SOD，42.2±3.6%）和乙醇（41.1±3.9%）可抑制质粒DNA链断裂，表明QAO和活性氧的形成与观察到的PM2质粒DNA链断裂有关。这些结果表明，AZQ的单电子和双电子酶促还原均会导致活性氧的形成和DNA链断裂。在分子氧存在下，AZQ半醌和对苯二酚的自动氧化似乎是这些过程的原因。QAO似乎参与了AZQ向自由基物种的代谢活化。这种酶的细胞水平和分布可能在肿瘤细胞和正常细胞对这种抗肿瘤药物的反应中起重要作用。
