Measurement of brain-derived Tau in plasma using a novel luminescence immunoassay

Early detection of Alzheimer’s disease (AD) risk requires sensitive and specific biomarkers that can be reliably measured in blood. In this study, Roboscreen GmbH evaluated a novel Luminescence Immunoassay (LUM) for the quantification of brain-derived tau (BD-Tau) in EDTA plasma or serum. The assay incorporates an upstream enrichment step, termed Neuro-Immunoprecipitation (Neuro-IP), which employs a monoclonal antibody specific for BD-Tau.

Image Credit: Andrii Vodolazhskyi/Shutterstock.com

Methods

A total of 41 commercially available leftover EDTA plasma samples obtained from an Alzheimer’s disease risk screening procedure were analyzed using the Neuro-IP procedure followed by the BD-Tau LUM assay. Sixteen samples were derived from subjects without clinical signs of dementia and were considered controls, while 25 samples were classified as Alzheimer’s disease subjects.

For each sample, 200 µL of EDTA plasma was processed using the Neuro-Immunoprecipitation (Neuro-IP) Kit to reduce matrix effects and enrich brain-derived tau (BD-Tau). Multiple studies have demonstrated that immunoprecipitation significantly improves the diagnostic accuracy of blood-based Aβ and tau measurements compared to direct assay formats.

The Neuro-IP step uses pre-coated magnetic beads coupled with the highly specific monoclonal antibody 2B8, which binds to amino acids 121–128 of the human brain-derived tau molecule (BD-Tau, 2N4R).

Following immunoprecipitation, the eluates were analyzed using the BD-Tau Luminescence Immunoassay. Monoclonal antibodies specific for human tau (amino acids 155–181) are immobilized on the microtiter plate and capture tau molecules from eluates, standards, and controls. Detection is achieved using an enzyme-conjugated 2B8 antibody, enabling chemiluminescent readout for BD-Tau quantification.

Results

All samples were successfully measured, and BD-Tau concentrations were quantified. Figure 1 shows box plots illustrating differences between the control and AD groups. A statistically significant difference was observed between the two groups (Student’s t-test, p < 0.001), with higher plasma BD-Tau concentrations in the AD group compared to controls (mean and SD for control group: 16.9 ± 6.7 pg/mL vs. median concentration for AD group: 30.4 ± 10.8 pg/mL).

Figure 1. Box-plot analysis of BD-Tau concentrations measured in 200 µL EDTA plasma after Neuro-IP enrichment (IP eluate) using the human BD-Tau Luminescence ELISA. Group 0 = control; Group 1 = AD subjects. Image Credit: Roboscreen GmbH

Receiver operating characteristic (ROC) curve analysis yielded an area under the curve (AUC) of up to 0.906 for BD-Tau in discriminating AD subjects from controls, with a sensitivity of 73 % and a specificity exceeding 93 %. These results are consistent with previously published data obtained using alternative methodologies (Gonzalez-Ortiz et al., 2023).

Figure 2. ROC analysis for plasma BD-Tau in AD subjects (n = 25) and controls (n = 16), measured using the BD-Tau LUM following Neuro-IP enrichment. AUC = 0.905 (p < 0.001). Image Credit: Roboscreen GmbH

Conclusion

Measurement of BD-Tau is readily achievable in routine plasma samples using a standard luminescence microplate immunoassay following Neuro-IP enrichment. This assay combination is broadly accessible to laboratories, as it requires only standard laboratory equipment.

The immunoprecipitation step effectively minimizes matrix effects and enables reliable detection of BD-Tau in the pg/mL concentration range. Importantly, this enrichment procedure can be performed upstream of virtually any immunoassay platform.

Clear discrimination between control samples and clinically classified Alzheimer’s disease samples was achieved, confirming previous findings and supporting the validity of BD-Tau as a minimally invasive blood-based research biomarker. The BD-Tau LUM assay combined with Neuro-IP provides complementary information to existing plasma tau biomarkers and may enhance interpretation of patient status in the context of Alzheimer’s disease risk assessment and participant stratification.

References and Further Reading

1. Jack, C.R., et al. (2024). Revised criteria for the diagnosis and staging of Alzheimer’s disease. Nature Medicine. DOI: 10.1038/s41591-024-02988-7. https://www.nature.com/articles/s41591-024-02988-7.
2. Zeng, X., et al. (2024). Alzheimer blood biomarkers: practical guidelines for study design, sample collection, processing, biobanking, measurement and result reporting. Molecular neurodegeneration, 19(1). DOI: 10.1186/s13024-024-00711-1. https://link.springer.com/article/10.1186/s13024-024-00711-1.
3. Gonzalez-Ortiz, F., et al. (2022). Brain-derived tau: a novel blood-based biomarker for Alzheimer’s disease-type neurodegeneration. Brain, 146(3). DOI: 10.1093/brain/awac407. https://academic.oup.com/brain/article/146/3/1152/6960988.
4. Gonzalez-Ortiz, F., et al. (2024). Plasma brain-derived tau is an amyloid-associated neurodegeneration biomarker in Alzheimer’s disease. Nature communications, 15(1). DOI: 10.1038/s41467-024-47286-5. https://www.nature.com/articles/s41467-024-47286-5.

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