Metrologically Traceable Quantification of 3 Apolipoprotein E Isoforms in Cerebrospinal Fluid

Area of Science:

• Biochemistry
• Neuroscience
• Analytical Chemistry

Background:

• Apolipoprotein E (apoE) genotype is linked to Alzheimer disease risk.
• Previous studies show conflicting results on apoE isoform concentrations in cerebrospinal fluid (CSF) in dementia.
• Standardized assays are needed to improve research reliability and generalizability.

Purpose of the Study:

• To develop, validate, and standardize a novel LC-MS/MS assay for measuring apoE isoforms in human CSF.
• To ensure metrological traceability of apoE measurements using characterized recombinant standards and matrix-matched calibrators.

Main Methods:

• Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was employed for apoE isoform measurement.
• Purified recombinant apoE standards (E2, E3, E4) were used for calibration.
• A matrix-matched calibration material was developed for SI-traceable measurements.

Main Results:

• The developed assay demonstrated high precision (≤11% CV) and accuracy for apoE isoforms in human CSF.
• No association was found between total apoE concentration and APOE ε4 allele count in 322 participants.
• Significant differences in isoform concentrations were observed in heterozygotes (E4 > E3 > E2) and associated with cognitive/motor symptoms.

Conclusions:

• A precise and accurate LC-MS/MS method for simultaneous apoE isoform measurement in CSF was established.
• A traceable matrix-matched calibrator was developed and is available to enhance interlaboratory agreement.