Objective: Advanced glycation end products (AGEs) are involved in the pathogenesis of Alzheimer's disease (AD). Specific AGEs and related autoantibodies may be early AD markers. Apolipoprotein A1 (ApoA1) and its post-translational modifications (PTMs) are associated with neurodegeneration and thus selected to test the hypothesis. Methods: Serum samples from totally 64 AD or health control (HC) Taiwanese were analyzed. ApoA1 was isolated from the serum and examined through LC-MS/MS and PTM analyses. A specific AGE and its autoantibodies were determined using Western blotting or ELISA. Results: Nε-(Carboxyethyl)lysine (CEL) modification, a kind of AGEs, was identified on ApoA1 peptide 141-QKVEPLR-147 (ApoA1141–147) from AD serum. Total CEL adducts and autoantibodies against CEL on ApoA1141–147 were significantly increased in AD samples. The area under the receiver operating characteristic curve was 0.965 for anti-CEL-ApoA1141–147 IgM. Mini Mental State Examination scores of the AD patients were positively correlated with anti-CEL-ApoA1141–147 IgM, suggesting that the IgM level is high in early AD pathology and decreased with disease progression. Conclusion: CEL modification was increased on AD serum proteins including ApoA1, leading to an elevated anti-CEL IgM in early disease state. Both CEL and anti-CEL IgM may serve as AD biomarkers.
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