Increased Levels of Protein-methionine Sulfoxide in Plasma Correlate with a Shift from a Mild Cognitive Impairment to an Alzheimer's Disease Stage.

: Objective: Sporadic Alzheimer's disease (AD) is an oxidative, stress-dependent neurodegenerative disease. We investigated whether the levels of protein-methionine sulfoxide (MetO) in plasma could be a possible marker for AD in individuals with mild cognitive impariment (MCI). Design: We evaluated blood samples from patients with AD or MCI, as well as from normal controls, testing their MetO levels and superoxide dismutase (SOD) specific activity. Results: An increase of MetO levels of a particular protein of human plasma and a decrease of SOD activity were observed only in AD plasma. Conclusion: Monitoring the patterns of these plasma markers in patients with MCI could provide a warning sign for disease progression into AD.