Amino-truncated beta-amyloid42 peptides in cerebrospinal fluid and prediction of progression of mild cognitive impairment.

Background: Early identification of patients with mild cognitive impairment (MCI) progressing to Alzheimer disease (MCI-AD) by use of biomarkers in cerebrospinal fluid (CSF) is an essential step toward improving clinical diagnosis and drug development. We evaluated whether different beta-amyloid(42) (Abeta42) peptides can add further information to the combined use of tau and Abeta1-42 for predicting risk of progression of MCI to AD.

Methods: We used xMAP technology to simultaneously quantify different Abeta42 peptides modified at the amino terminus, tau, and phosphorylated tau (P-tau181P) in CSF. Abeta42 peptide concentrations were measured by use of immunoreactivity toward Abeta monoclonal antibodies [3D6 (Abeta42-3D6), WO2 (Abeta42-WO2), 6E10 (Abeta42-6E10), and 4G8 (Abeta42-4G8)]. The discriminant ability of the markers was evaluated by ROC curve analysis.

Results: The areas under the curves for the separation of MCI-AD from nonprogressing MCI (MCI-N) were significantly higher when we used Abeta42-3D6/Abeta42-WO2, Abeta42-3D6/Abeta42-6E10, or Abeta42-3D6/Abeta42-4G8 compared with Abeta42-3D6. In addition, differentiation of MCI-N from MCI-AD was improved by quantification of full-length Abeta1-42 (Abeta42-3D6) compared with Abeta42-WO2, Abeta42-6E10, or Abeta42-4G8. Several Abeta42 peptides truncated at the amino terminus (Abeta11-42 and Abeta8-42) were identified in CSF by surface-enhanced laser desorption/ionization time-of-flight technology.

Conclusion: The CSF markers tau, Abeta42 forms, and P-tau181P, when used as adjuncts to clinical diagnosis, have the potential to help identify AD pathology and could be a valuable asset for early AD diagnosis.