Amyloid β-Cu2+ Complexes in both Monomeric and Fibrillar Forms Do Not Generate H2O2 Catalytically but Quench Hydroxyl Radicals
Amyloid β-Cu2+ Complexes in both Monomeric and Fibrillar Forms Do Not Generate H2O2 Catalytically but Quench Hydroxyl Radicals
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DOI：
10.1021/bi8011093
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发表时间：
2008-11-04
期刊：
影响因子：
2.9
通讯作者：
Viles, John H.
中科院分区：
文献类型：
--
作者：
Nadal, Rebecca C.;Rigby, Stephen E. J.;Viles, John H.
氧化应激在阿尔茨海默病(AD)中起着关键作用。此外，老年斑块中存在的异常高的Cu2+离子浓度引起了人们对斑块中发现的淀粉样β蛋白(Aβ)与氧化还原活性铜离子之间的关系的极大兴趣。已经有许多研究监测铜和抗坏血酸产生的活性氧物种(ROS)，表明Aβ作为产生过氧化氢的促氧化剂。然而，其他研究表明，Aβ是一种抗氧化剂，但到目前为止，大多数直接监测ROS的无细胞研究都没有支持这一假设。因此，我们选择在有氧条件下，在无细胞系统中，在Cu2+存在的情况下，在有/没有生物还原剂抗坏血酸的情况下，再次观察单体和纤维形式的Aβ产生ROS。我们使用了各种基于荧光和吸收的分析方法来监测ROS的产生以及Cu2+的还原。与以前的研究不同，我们在这里表明，Aβ不会产生比Cu2+和抗坏血酸对照组更多的ROS。抗坏血酸与Cu2+发生Fenton-Haber Weiss反应所产生的羟基自由基与Aβ发生快速反应，从而使潜在的有害自由基被猝灭。为了支持这一点，用H-1核磁共振检测了Aβ多肽的化学修饰，并在组氨酸和蛋氨酸残基上确定了该多肽中的特定氧化位点。我们的研究增加了修改的淀粉样级联假说的重要权重，在该假说中，散发性AD是Aβ上调的结果，作为对氧化应激的反应。然而，我们的结果并不排除Aβ以低聚形式聚集在神经细胞膜上具有氧化还原活性的铜从而引起脂质过氧化的可能性。
Oxidative stress plays a key role in Alzheimer's disease (AD). In addition, the abnormally high Cu2+ ion concentrations present in senile plaques has provoked a substantial interest in the relationship between the amyloid beta peptide (A beta) found within plaques and redox-active copper ions. There have been a number of studies monitoring reactive oxygen species (ROS) generation by copper and ascorbate that suggest that A beta acts as a prooxidant producing H2O2. However, others have indicated A beta acts as an antioxidant, but to date most cell-free studies directly monitoring ROS have not supported this hypothesis. We therefore chose to look again at ROS generation by both monomeric and fibrillar forms of A beta under aerobic conditions in the presence of Cu2+ with/without the biological reductant ascorbate in a cell-free system. We used a variety of fluorescence and absorption based assays to monitor the production of ROS, as well as Cu2+ reduction. In contrast to previous studies, we show here that A beta does not generate any more ROS than controls of Cu2+ and ascorbate. A beta does not silence the redox activity of Cu2+/+ via chelation, but rather hydroxyl radicals produced as a result of Fenton-Haber Weiss reactions of ascorbate and Cu2+ rapidly react with A beta; thus the potentially harmful radicals are quenched. In support of this, chemical modification of the A beta peptide was examined using H-1 NMR, and specific oxidation sites within the peptide were identified at the histidine and methionine residues. Our studies add significant weight to a modified amyloid cascade hypothesis in which sporadic AD is the result of A beta being upregulated as a response to oxidative stress. However, our results do not preclude the possibility that A beta in an oligomeric form may concentrate the redox-active copper at neuronal membranes and so cause lipid peroxidation.