Quantitative Measurement of Cerebrospinal Fluid Amyloid-ß Species by Mass Spectrometry.

ABSTRACT

BACKGROUND: High sensitivity liquid chromatography mass spectrometry (LC-MS/MS) was recently introduced to measure amyloid-ß (Aß) species, allowing for a simultaneous assay that is superior to ELISA, which requires more assay steps with multiple antibodies. OBJECTIVE: We validated the Aß1-38, Aß1-40, Aß1-42, and Aß1-43 assay by LC-MS/MS and compared it with ELISA using cerebrospinal fluid (CSF) samples to investigate its feasibility for clinical application. METHODS: CSF samples from 120 subjects [8 Alzheimer's disease (AD) with dementia (ADD), 2 mild cognitive dementia due to Alzheimer's disease (ADMCI), 14 cognitively unimpaired (CU), and 96 neurological disease subjects] were analyzed. Aß species were separated using the Shimadzu Nexera X2 system and quantitated using a Qtrap 5500 LC-MS/MS system. Aß1-40 and Aß1-42 levels were validated using ELISA. RESULTS: CSF levels in CU were 666±249 pmol/L in Aß1-38, 2199±725 pmol/L in Aß1-40, 153.7±79.7 pmol/L in Aß1-42, and 9.78±4.58 pmol/L in Aß1-43. The ratio of the amounts of Aß1-38, Aß1-40, Aß1-42, and Aß1-43 was approximately 68225161. Linear regression analyses showed correlations among the respective Aß species. Both Aß1-40 and Aß1-42 values were strongly correlated with ELISA measurements. No significant differences were observed in Aß1-38 or Aß1-40 levels between AD and CU. Aß1-42 and Aß1-43 levels were significantly lower, whereas the Aß1-38/1-42, Aß1-38/1-43, and Aß1-40/Aß1-43 ratios were significantly higher in AD than in CU. The basic assay profiles of the respective Aß species were adequate for clinical usage. CONCLUSION: A quantitative LC-MS/MS assay of CSF Aß species is as reliable as specific ELISA for clinical evaluation of CSF biomarkers for AD.