Diagnosing Alzheimer’s Disease from Circulating Blood Leukocytes Using a Fluorescent Amyloid Probe

Article type: Research Article

Authors: Black, Stefanie A.G.^{a; k} | Stepanchuk, Anastasiia A.^a | Templeton, George W.^k | Hernandez, Yda^f | Ota, Tomoko^a | Roychoudhury, Shyamosree^a | Smith, Eric E.^a | Barber, Philip A.^{a; b; d} | Ismail, Zahinoor^{a; c; d; e} | Fischer, Karyn^a | Zwiers, Angela^a | Poulin, Marc J.^{a; e; f} | Blennow, Kaj^{g; h} | Zetterberg, Henrik^{g; h; i; j} | Stys, Peter K.^a | Tsutsui, Shigeki^{a; k; *}

Affiliations: [a] Hotchkiss Brain Institute, Department of Clinical Neurosciences, Cumming School of Medicine, University of Calgary, Calgary AB, Canada | [b] Calgary Stroke Program, Seaman Family MR Center, Departments of Clinical Neurosciences and Radiology, Foothills Medical Centre, Calgary AB, Canada | [c] Department of Psychiatry, and the Mathison Centre for Mental Health Research & Education, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada | [d] Department of Community Health Sciences, University of Calgary, Calgary AB, Canada | [e] O’Brien Institute of Public Health, University of Calgary, Calgary AB, Canada | [f] Department of Physiology and Pharmacology, Libin Cardiovascular Institute of Alberta, Faculty of Kinesiology, University of Calgary, Calgary AB, Canada | [g] Clinical Neurochemistry Laboratory, Sahlgrenska University Hospital, Gothenburg, Sweden | [h] Department of Psychiatry and Neurochemistry, Institute of Neuroscience and Physiology, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden | [i] Department of Neurodegenerative Disease, University College London Queen Square Institute of Neurology, London, UK | [j] UK Dementia Research Institute, University College London, London, UK | [k] Amira Medical Technologies Inc., Calgary, AB, Canada

Correspondence: [*] Correspondence to: Shigeki Tsutsui, DVM, PhD, Hotchkiss Brain Institute, Department of Clinical Neurosciences, Cumming School of Medicine, University of Calgary, 3330 Hospital Drive, NW, Calgary, AB T2N 4N1, Canada. Tel.: 403 220 8462; E-mail: stsutsui@ucalgary.ca.

Abstract: Background:Toxic amyloid-β (Aβ) peptides aggregate into higher molecular weight assemblies and accumulate not only in the extracellular space, but also in the walls of blood vessels in the brain, increasing their permeability, and promoting immune cell migration and activation. Given the prominent role of the immune system, phagocytic blood cells may contact pathological brain materials. Objective:To develop a novel method for early Alzheimer’s disease (AD) detection, we used blood leukocytes, that could act as “sentinels” after trafficking through the brain microvasculature, to detect pathological amyloid by labelling with a conformationally-sensitive fluorescent amyloid probe and imaging with confocal spectral microscopy. Methods:Formalin-fixed peripheral blood mononuclear cells (PBMCs) from cognitively healthy control (HC) subjects, mild cognitive impairment (MCI) and AD patients were stained with the fluorescent amyloid probe K114, and imaged. Results were validated against cerebrospinal fluid (CSF) biomarkers and clinical diagnosis. Results:K114-labeled leukocytes exhibited distinctive fluorescent spectral signatures in MCI/AD subjects. Comparing subjects with single CSF biomarker-positive AD/MCI to negative controls, our technique yielded modest AUCs, which improved to the 0.90 range when only MCI subjects were included in order to measure performance in an early disease state. Combining CSF Aβ42 and t-Tau metrics further improved the AUC to 0.93. Conclusion:Our method holds promise for sensitive detection of AD-related protein misfolding in circulating leukocytes, particularly in the early stages of disease.

Keywords: Aβ₄₂, Alzheimer’s disease, cerebrospinal fluid, conformationally-sensitive amyloid probes, p-Tau, peripheral blood mononuclear cells, spectral confocal microscopy, t-Tau

DOI: 10.3233/JAD-215402

Journal: Journal of Alzheimer's Disease, vol. 85, no. 4, pp. 1721-1734, 2022