Iannone A, Hu H P, Tomasi A, Vannini V, Swartz H M
University of Illinois College of Medicine, Urbana.
Biochim Biophys Acta. 1989 Apr 25;991(1):90-6. doi: 10.1016/0304-4165(89)90033-0.
The optimum use of nitroxides in viable biological systems, including live animals, requires knowledge of the metabolism of nitroxides by major organ systems, especially the liver. We report here details of the metabolism of several prototypic aqueous soluble nitroxides in suspensions of freshly isolated hepatocytes. The general patterns of metabolism were similar to those observed in other types of cells (previous studies have been done principally in cells from tissue culture, such as CHO cells) including the primary initial reaction being reduction to the hydroxylamine, an increased rate of metabolism of some nitroxides in hypoxic cells, faster rates of reduction of nitroxides on six-membered piperidine rings compared to five-membered pyrrolidine rings, and most metabolism being intracellular. Metabolism in hepatocytes differed from other cell lines in having (1) significant reduction in the extracellular medium due to ascorbate that was released from damaged hepatocytes; (2) decreased rates of metabolism in freeze-thawed cells due to damage to subcellular organelles. These results provide much of the data needed to understand the role of the liver in the metabolism of nitroxides by intact animals and explain some previously puzzling results which indicated an apparent unusually high rate of metabolism of a charged nitroxide (Cat1) by hepatocytes. Our results also indicate that the use of freshly isolated cells or tissue homogenates may introduce experimental artifacts in the study of the metabolism of nitroxides.
在包括活体动物在内的可行生物系统中，一氧化氮自由基的最佳使用需要了解主要器官系统，尤其是肝脏对一氧化氮自由基的代谢情况。我们在此报告几种原型水溶性一氧化氮自由基在新鲜分离的肝细胞悬液中的代谢细节。代谢的一般模式与在其他类型细胞中观察到的模式相似（之前的研究主要在组织培养的细胞中进行，如CHO细胞），包括最初的主要反应是还原为羟胺，一些一氧化氮自由基在缺氧细胞中的代谢速率增加，与五元吡咯烷环相比，六元哌啶环上的一氧化氮自由基还原速率更快，并且大多数代谢发生在细胞内。肝细胞中的代谢与其他细胞系不同之处在于：（1）由于受损肝细胞释放的抗坏血酸，细胞外培养基中有显著的还原作用；（2）冻融细胞中由于亚细胞器受损，代谢速率降低。这些结果提供了许多理解肝脏在完整动物体内一氧化氮自由基代谢中作用所需的数据，并解释了一些先前令人困惑的结果，这些结果表明肝细胞对带电荷的一氧化氮自由基（Cat1）的代谢速率明显异常高。我们的结果还表明，在一氧化氮自由基代谢研究中使用新鲜分离的细胞或组织匀浆可能会引入实验假象。
