The performance of plasma amyloid beta measurements in identifying amyloid plaques in Alzheimer's disease: a literature review

The extracellular buildup of amyloid beta (A beta) plaques in the brain is a hallmark of Alzheimer's disease (AD). Detection of A beta pathology is essential for AD diagnosis and for identifying and recruiting research participants for clinical trials evaluating disease-modifying therapies. Currently, AD diagnoses are usually made by clinical assessments, although detection of AD pathology with positron emission tomography (PET) scans or cerebrospinal fluid (CSF) analysis can be used by specialty clinics. These measures of A beta aggregation, e.g. plaques, protofibrils, and oligomers, are medically invasive and often only available at specialized medical centers or not covered by medical insurance, and PET scans are costly. Therefore, a major goal in recent years has been to identify blood-based biomarkers that can accurately detect AD pathology with cost-effective, minimally invasive procedures. To assess the performance of plasma A beta assays in predicting amyloid burden in the central nervous system (CNS), this review compares twenty-one different manuscripts that used measurements of 42 and 40 amino acid-long A beta (A beta 42 and A beta 40) in plasma to predict CNS amyloid status. Methodologies that quantitate A beta 42 and 40 peptides in blood via immunoassay or immunoprecipitation-mass spectrometry (IP-MS) were considered, and their ability to distinguish participants with amyloidosis compared to amyloid PET and CSF A beta measures as reference standards was evaluated. Recent studies indicate that some IP-MS assays perform well in accurately and precisely measuring A beta and detecting brain amyloid aggregates.