Britigan B E, Edeker B L
Research Service, Veterans Administration Medical Center, Iowa City, Iowa.
J Clin Invest. 1991 Oct;88(4):1092-102. doi: 10.1172/JCI115408.
In vivo most extracellular iron is bound to transferrin or lactoferrin in such a way as to be unable to catalyze the formation of hydroxyl radical from superoxide (.O2-) and hydrogen peroxide (H2O2). At sites of Pseudomonas aeruginosa infection bacterial and neutrophil products could possibly modify transferrin and/or lactoferrin forming catalytic iron complexes. To examine this possibility, diferrictransferrin and diferriclactoferrin which had been incubated with pseudomonas elastase, pseudomonas alkaline protease, human neutrophil elastase, trypsin, or the myeloperoxidase product HOCl were added to a hypoxanthine/xanthine oxidase .O2-/H2O2 generating system. Hydroxyl radical formation was only detected with pseudomonas elastase treated diferrictransferrin and, to a much lesser extent, diferriclactoferrin. This effect was enhanced by the combination of pseudomonas elastase with other proteases, most prominently neutrophil elastase. Addition of pseudomonas elastase-treated diferrictransferrin to stimulated neutrophils also resulted in hydroxyl radical generation. Incubation of pseudomonas elastase with transferrin which had been selectively iron loaded at either the NH2- or COOH-terminal binding site yielded iron chelates with similar efficacy for hydroxyl radical catalysis. Pseudomonas elastase and HOCl treatment also decreased the ability of apotransferrin to inhibit hydroxyl radical formation by a Fe-NTA supplemented hypoxanthine/xanthine oxidase system. However, apotransferrin could be protected from the effects of HOCl if bicarbonate anion was present during the incubation. Apolactoferrin inhibition of hydroxyl radical generation was unaffected by any of the four proteases or HOCl. Alteration of transferrin by enzymes and oxidants present at sites of pseudomonas and other bacterial infections may increase the potential for local hydroxyl radical generation thereby contributing to tissue injury.
在体内，大多数细胞外铁以与转铁蛋白或乳铁蛋白结合的形式存在，因而无法催化超氧化物（·O₂⁻）和过氧化氢（H₂O₂）形成羟基自由基。在铜绿假单胞菌感染部位，细菌和中性粒细胞产物可能会修饰转铁蛋白和/或乳铁蛋白，形成具有催化活性的铁复合物。为了验证这种可能性，将与铜绿假单胞菌弹性蛋白酶、铜绿假单胞菌碱性蛋白酶、人中性粒细胞弹性蛋白酶、胰蛋白酶或髓过氧化物酶产物次氯酸（HOCl）孵育过的双铁转铁蛋白和双铁乳铁蛋白添加到次黄嘌呤/黄嘌呤氧化酶·O₂⁻/H₂O₂生成系统中。仅在经铜绿假单胞菌弹性蛋白酶处理的双铁转铁蛋白中检测到羟基自由基的形成，而经该酶处理的双铁乳铁蛋白中检测到的羟基自由基形成量则少得多。铜绿假单胞菌弹性蛋白酶与其他蛋白酶（最显著的是中性粒细胞弹性蛋白酶）联合使用可增强这种效应。将经铜绿假单胞菌弹性蛋白酶处理的双铁转铁蛋白添加到受刺激的中性粒细胞中也会导致羟基自由基的产生。将铜绿假单胞菌弹性蛋白酶与在NH₂-或COOH-末端结合位点选择性负载铁的转铁蛋白孵育，产生的铁螯合物对羟基自由基催化具有相似的效力。铜绿假单胞菌弹性蛋白酶和HOCl处理还降低了脱铁转铁蛋白对由补充了Fe-NTA的次黄嘌呤/黄嘌呤氧化酶系统形成羟基自由基的抑制能力。然而，如果在孵育过程中存在碳酸氢根阴离子，则脱铁转铁蛋白可免受HOCl的影响。四种蛋白酶或HOCl中的任何一种都不会影响脱铁乳铁蛋白对羟基自由基生成的抑制作用。铜绿假单胞菌和其他细菌感染部位存在的酶和氧化剂对转铁蛋白的改变可能会增加局部产生羟基自由基的可能性，从而导致组织损伤。
