Decreased expression and increased oxidation of plasma haptoglobin in Alzheimer disease: Insights from redox proteomics

► Plasma haptoglobin is oxidized in mild cognitive impairment and Alzheimer disease. ► Oxidation of haptoglobin contributes to amyloid fibril formation. ► Extracellular chaperones are impaired in Alzheimer disease. ► Haptoglobin may be considered a putative marker of Alzheimer disease progression.