Oxidative stress and neurodegeneration.

Oxidative stress is a well-studied early response in chronic neurodegenerative diseases, including Alzheimer's disease, where neuronal loss can exceed 90% in the vulnerable neuronal population. Oxidative stress affects all classes of macromolecules (sugar, lipids, proteins, and DNA), leading inevitably to neuronal dysfunction. We observed that Nepsilon-(carboxymethyl)lysine (CML), the predominant advanced glycation end product that accumulates in vivo, along with its glycation-specific precursor hexitol-lysine, are increased in neurons from cases of Alzheimer's disease, especially those containing intracellular neurofibrillary pathology. The increase in hexitol-lysine and CML can result from either lipid peroxidation or advanced glycation, whereas hexitol-lysine is solely a product of glycation, suggesting that two distinct oxidative processes act in concert in the neuropathology of the disease. Furthermore, using olfactory neurons as an experimental model, we observed an increase in glycation products in neurons derived from Alzheimer's disease patients. Our findings support the idea that aldehyde-mediated modifications, in concert with oxyradical-mediated modifications, are critical early pathogenic factors in Alzheimer's disease.