The antioxidant vitamin E modulates amyloid β-peptide-induced creatine kinase activity inhibition and increased protein oxidation: Implications for the free radical hypothesis of Alzheimer's disease

Amyloid β-peptide (Aβ), the main constituent of senile plaques in Alzheimer's disease (AD) brain, is hypothesized to be a key factor in the neurodegeneration seen in AD. Recently it has been shown by us and others that the neurotoxicity of Aβ occurs in conjunction with free radical oxidative stress associated with the peptide. Aβ(1-40) and several other fragments of the Aβ sequence are associated with free radicals in solution that are detectable using electron paramagnetic resonance spectroscopy. These free radicals were shown to attack brain cell membranes, initiate lipid peroxidation, increase Ca²⁺ influx and damage membrane and cytosolic proteins. In AD brain obtained under rapid autopsy protocol, the activity of the oxidatively-sensitive enzyme creatine kinase was shown to be significantly reduced. We reasoned that Aβ-associated free radical-induced modification of creatine kinase activity and other markers of cellular damage might be modulated by free radical scavengers. Accordingly, this study demonstrates that vitamin E can modulate Aβ(25-35)induced oxidative damage to creatine kinase and cellular proteins in cultured embryonic hippocampal neurons. These results, consistent with the hypothesis of free radical- mediated Aβ toxicity in AD, are discussed with deference to potential free radical scavengers as therapeutic agents for slowing the progression of AD.