Department of Neurology, University Hospital Zurich Zurich, Switzerland.
Division of Psychiatry Research, University of Zurich Schlieren, Switzerland.
Front Aging Neurosci. 2014 Sep 8;6:237. doi: 10.3389/fnagi.2014.00237. eCollection 2014.
Hyperhomocysteinemia is a risk factor for Alzheimer's disease (AD). Both homocysteine (Hcy) and amyloid β (Aβ), which accumulates in the brain of AD patients, bind copper. Aim of this study was to test the hypothesis that the association of Hcy and AD results from a molecular interaction between Hcy and Aβ that is mediated by copper. We established a microtiter plate format thioflavin T aggregation assay to monitor Aβ42 fibrillization. Copper (5 μM) completely prevented Aβ42 (5 μM) fibrillization. Homocysteine in the absence of copper did not impact Aβ42 fibrillization, but physiological concentrations of Hcy (10-100 μM) attenuated the inhibitory effect of copper on Aβ42 fibril formation. These results were qualitatively confirmed by electron microscopy, which did not reveal morphological differences. To compare the toxicity of fibrillar and non-fibrillar Aβ42 exposed to copper or Hcy, rat primary cortical neurons were treated in vitro with 5 μM Aβ42 for 72 h. After incubation with 5 μM Aβ42 that had been aggregating in the absence of Hcy or copper, cell viability was reduced to 40%. Incubation with 5 μM Aβ42, in which fibril formation had been prevented or reverted by the addition of 5 μM copper, resulted in cell viability of approximately 25%. Accordingly, viability was reduced to 25% after incubation with 5 μM monomeric, i.e., non-fibrillized, Aβ42. The addition of Hcy plus copper to 5 μM Aβ42 yielded 50% viability. In conclusion, copper prevents and reverts Aβ fibril formation leading rather to formation of lower order oligomers or amorphous aggregates, and Hcy reduces these effects. Such mechanisms may explain the association of hyperhomocysteinemia and AD, leading to novel therapeutic strategies in the prevention and treatment of this disease.
高同型半胱氨酸血症是阿尔茨海默病（AD）的一个风险因素。同型半胱氨酸（Hcy）和淀粉样β（Aβ）都在 AD 患者的大脑中积累，它们都与铜结合。本研究的目的是检验以下假设：Hcy 与 AD 的关联是由于 Hcy 与 Aβ 之间的分子相互作用所致，而这种相互作用是由铜介导的。我们建立了一种微量板格式的硫黄素 T 聚集测定法来监测 Aβ42 的纤维化。铜（5 μM）完全阻止了 Aβ42（5 μM）的纤维化。在没有铜的情况下，同型半胱氨酸不会影响 Aβ42 的纤维化，但生理浓度的 Hcy（10-100 μM）减弱了铜对 Aβ42 纤维形成的抑制作用。这些结果通过电子显微镜得到了定性确认，电子显微镜没有显示出形态上的差异。为了比较暴露于铜或 Hcy 的纤维状和非纤维状 Aβ42 的毒性，将原代大鼠皮质神经元在体外用 5 μM Aβ42 处理 72 小时。在用没有 Hcy 或铜的情况下聚集的 5 μM Aβ42 孵育后，细胞活力降低至 40%。在用 5 μM Aβ42 孵育后，用 5 μM 铜阻止或逆转纤维形成，细胞活力约为 25%。因此，在用 5 μM 单体，即非纤维化的 Aβ42 孵育后，活力降低至 25%。向 5 μM Aβ42 中加入 Hcy 和铜可产生 50%的活力。总之，铜可阻止和逆转 Aβ 纤维形成，导致形成较低阶寡聚物或无定形聚集体，而 Hcy 则降低了这些效果。这些机制可能解释了高同型半胱氨酸血症与 AD 的关联，为该疾病的预防和治疗提供了新的治疗策略。
