Evaluation of Blood-Based Plasma Biomarkers as Potential Markers of Amyloid Burden in Preclinical Alzheimer’s Disease

Abstract

Background: Participant eligibility for the A4 Study was determined by amyloid PET imaging. Given the disadvantages of amyloid PET imaging in accessibility and cost, blood-based biomarkers may serve as a sufficient biomarker and more cost-effective screening tool for patient enrollment into preclinical AD trials. Objective: To determine if a blood-based screening test can adequately identify amyloid burden in participants screened into a preclinical AD trial. Methods: In this cross-sectional study, 224 participants from the A4 Study received an amyloid PET scan (18Florbetapir) within 90 days of blood sample collection. Blood samples from all study participants were processed within 2 h after phlebotomy. Plasma amyloid measures were quantified by Shimazdu and C2 N Diagnostics using mass spectrometry-based platforms. A corresponding subset of blood samples (n = 100) was processed within 24 h after phlebotomy and analyzed by C2 N. Results: Plasma Aβ 42/Aβ40 demonstrated the highest association for Aβ accumulation in the brain with an AUC 0.76 (95%CI = 0.69, 0.82) at C2 N and 0.80 (95%CI = 0.75, 0.86) at Shimadzu. Blood samples processed to plasma within 2 h after phlebotomy provided a better prediction of amyloid PET status than blood samples processed within 24 h (AUC 0.80 versus 0.64; p < 0.001). Age, sex, and APOE ɛ4 carrier status did not the diagnostic performance of plasma Aβ 42/Aβ 40 to predict amyloid PET positivity in A4 Study participants. Conclusion: Plasma Aβ 42/Aβ40 may serve as a potential biomarker for predicting elevated amyloid in the brain. Utilizing blood testing over PET imaging may improve screening efficiency into clinical trials.

Clinical utility of an antibody‐free LC‐MS method to detect brain amyloid deposition in cognitively unimpaired individuals from the screening visit of the A4 Study

“…The impact of pre-analytical variables on Aβ40 and Aβ42 levels has been investigated in other studies. Unlike Winston et al, 24 Verberk et al 21 observed that storage of blood samples up to 24 hours at 4 • C before centrifugation does not have an impact on Aβ levels. Further studies should address the potential causes of these observed variations and compare the sensitivity of different platforms, for example, platforms that include an immunocapture step versus platforms such as ABtest-MS that does not, to this pre-analytical variable.…”

“…Regarding this last point, a recent study has revealed large differences in the predictive value of plasma Aβ42/Aβ40 when two different plasma collection protocols were applied in A4 samples 24 . Although a direct comparison is not possible, because the same samples have not been analyzed, when plasma samples were processed within 24 hours from blood extraction, the C2N's IP‐LC‐MS/MS technology identified amyloid‐PET status with an AUC of 0.64, notably worse than the 0.78 reported by ABtest‐MS in the present study in plasma samples processed with the same protocol.…”

“…Although a direct comparison is not possible, because the same samples have not been analyzed, when plasma samples were processed within 24 hours from blood extraction, the C2N's IP‐LC‐MS/MS technology identified amyloid‐PET status with an AUC of 0.64, notably worse than the 0.78 reported by ABtest‐MS in the present study in plasma samples processed with the same protocol. On the other hand, in the study by Winston et al., 24 a dataset of 224 plasma samples was processed within 2 hours from blood extraction and analyzed by Shimadzu's and C2N's platforms. In this case, the AUCs for amyloid‐PET status were 0.80 and 0.76, respectively, which were comparable to the performance reported by ABtest‐MS in plasma samples processed within 24 hours.…”

Translating blood biomarkers into clinical practice for Alzheimer's disease: Challenges and perspectives

“…Notably, these algorithms need to be validated in independent cohorts. As seen in two recent studies, the performance of plasma Aβ42/40 ratio in identifying brain amyloid status was improved when combined in an algorithm with apoE proteotype and age in one study, 70 but was not improved in the other one 71 …”

The potential clinical value of plasma biomarkers in Alzheimer's disease

“…Furthermore, the Aβ42/Aβ40 ratio has been shown to have an inherently small dynamic range and hence low clinical robustness, 59 meaning that small technical differences when using the tests may result in patients being misclassified 59 . In addition, a 2023 publication found that including age, sex, and/or apolipoprotein E4 carrier status into a risk model did not improve the diagnostic performance compared to the plasma Aβ42/Aβ40 ratio alone, 60 a finding that should be considered when assessing the performance of tests that rely on the Aβ42/Aβ40 ratio in combination with age, sex, and/or apolipoprotein E4 carrier status.…”