Rees Martin D, Bottle Steven E, Fairfull-Smith Kathryn E, Malle Ernst, Whitelock John M, Davies Michael J
The Heart Research Institute, 114 Pyrmont Bridge Rd, Camperdown, Sydney, NSW 2050, Australia.
Biochem J. 2009 Jun 12;421(1):79-86. doi: 10.1042/BJ20090309.
Tissue damage resulting from the extracellular production of HOCl (hypochlorous acid) by the MPO (myeloperoxidase)-hydrogen peroxide-chloride system of activated phagocytes is implicated as a key event in the progression of a number of human inflammatory diseases. Consequently, there is considerable interest in the development of therapeutically useful MPO inhibitors. Nitroxides are well established antioxidant compounds of low toxicity that can attenuate oxidative damage in animal models of inflammatory disease. They are believed to exert protective effects principally by acting as superoxide dismutase mimetics or radical scavengers. However, we show here that nitroxides can also potently inhibit MPO-mediated HOCl production, with the nitroxide 4-aminoTEMPO inhibiting HOCl production by MPO and by neutrophils with IC50 values of approx. 1 and 6 microM respectively. Structure-activity relationships were determined for a range of aliphatic and aromatic nitroxides, and inhibition of oxidative damage to two biologically-important protein targets (albumin and perlecan) are demonstrated. Inhibition was shown to involve one-electron oxidation of the nitroxides by the compound I form of MPO and accumulation of compound II. Haem destruction was also observed with some nitroxides. Inhibition of neutrophil HOCl production by nitroxides was antagonized by neutrophil-derived superoxide, with this attributed to superoxide-mediated reduction of compound II. This effect was marginal with 4-aminoTEMPO, probably due to the efficient superoxide dismutase-mimetic activity of this nitroxide. Overall, these data indicate that nitroxides have considerable promise as therapeutic agents for the inhibition of MPO-mediated damage in inflammatory diseases.
活化吞噬细胞的髓过氧化物酶（MPO）-过氧化氢-氯化物系统在细胞外产生次氯酸（HOCl）所导致的组织损伤，被认为是多种人类炎症性疾病进展中的关键事件。因此，开发具有治疗作用的MPO抑制剂引起了人们的极大兴趣。氮氧化物是毒性低且已被充分证实的抗氧化化合物，可减轻炎症性疾病动物模型中的氧化损伤。人们认为它们主要通过充当超氧化物歧化酶模拟物或自由基清除剂来发挥保护作用。然而，我们在此表明，氮氧化物还能有效抑制MPO介导的HOCl生成，其中氮氧化物4-氨基TEMPO抑制MPO和中性粒细胞产生HOCl的IC50值分别约为1和6 microM。确定了一系列脂肪族和芳香族氮氧化物的构效关系，并证明了其对两个生物学上重要的蛋白质靶点（白蛋白和基底膜聚糖）的氧化损伤具有抑制作用。结果表明，抑制作用涉及MPO的化合物I形式使氮氧化物发生单电子氧化以及化合物II的积累。还观察到一些氮氧化物会导致血红素破坏。氮氧化物对中性粒细胞HOCl生成的抑制作用会被中性粒细胞衍生的超氧化物拮抗，这归因于超氧化物介导的化合物II的还原。对于4-氨基TEMPO，这种作用很微弱，可能是由于该氮氧化物具有高效的超氧化物歧化酶模拟活性。总体而言，这些数据表明，氮氧化物作为抑制炎症性疾病中MPO介导损伤的治疗药物具有很大的潜力。
