Offer Tal, Samuni Amram
Department of Molecular Biology, Faculty of Medicine, The Hebrew University, Jerusalem, Israel.
Free Radic Biol Med. 2002 May 1;32(9):872-81. doi: 10.1016/s0891-5849(02)00750-5.
Nitroxides are cell-permeable stable radicals that protect biomolecules from oxidative damage in several ways. The mechanisms of protection studied to date include removal of superoxide radicals as SOD-mimics, oxidation of transition metal ions to preempt the Fenton reaction, and scavenging carbon-centered radicals. However, there is no agreement regarding the reaction of piperidine nitroxides with peroxyl radicals. The question of whether they can protect by scavenging peroxyl radicals is important because these radicals are formed in the presence of oxygen abundant in biological tissues. To further our understanding of the antioxidative behavior of piperidine nitroxides, we studied their effect on biochemical systems exposed to the water soluble radical initiator 2,2'-azobis (2-amidinopropane) hydrochloride (AAPH). AAPH thermally decomposes to yield tert-amidinopropane radicals (t-AP()) that readily react with oxygen to form peroxyl radicals (t-APOO()). It has recently been reported that piperidine nitroxides protect plasmid DNA from t-AP() though not from t-APOO(). The present study was directed at the question of whether these nitroxides can protect biological systems from damage inflicted by peroxyl radicals. The reaction of nitroxides with AAPH-derived radicals was followed by cyclic voltammetry and electron paramagnetic resonance spectroscopy, whereas the accumulation of peroxide was iodometrically assayed. Assaying DNA damage in vitro, we demonstrate that piperidine nitroxides protect from both t-AP() and t-APOO(). Similarly, nitroxides inhibit AAPH-induced enzyme inactivation. The results indicate that piperidine nitroxides protect the target molecule by reacting with and detoxifying peroxyl radicals.
氮氧化物是可透过细胞的稳定自由基，可通过多种方式保护生物分子免受氧化损伤。迄今为止所研究的保护机制包括作为超氧化物歧化酶（SOD）模拟物清除超氧自由基、氧化过渡金属离子以防止芬顿反应以及清除碳中心自由基。然而，关于哌啶氮氧化物与过氧自由基的反应尚无定论。它们是否能通过清除过氧自由基来提供保护这一问题很重要，因为这些自由基是在生物组织中富含氧气的情况下形成的。为了进一步了解哌啶氮氧化物的抗氧化行为，我们研究了它们对暴露于水溶性自由基引发剂2,2'-偶氮双（2-脒基丙烷）盐酸盐（AAPH）的生化系统的影响。AAPH热分解产生叔脒基丙烷自由基（t-AP()），其很容易与氧气反应形成过氧自由基（t-APOO()）。最近有报道称，哌啶氮氧化物可保护质粒DNA免受t-AP()的损伤，但不能免受t-APOO()的损伤。本研究针对这些氮氧化物是否能保护生物系统免受过氧自由基造成的损伤这一问题展开。通过循环伏安法和电子顺磁共振光谱跟踪氮氧化物与AAPH衍生自由基的反应，而过氧化物的积累则通过碘量法测定。在体外测定DNA损伤时，我们证明哌啶氮氧化物既能保护免受t-AP()的损伤，也能保护免受t-APOO()的损伤。同样，氮氧化物可抑制AAPH诱导的酶失活。结果表明，哌啶氮氧化物通过与过氧自由基反应并使其解毒来保护目标分子。
