Kenneth A. Livingston

Introduction: Disease-modifying interventions for Alzheimer Disease (AD) are suspected to be most efficacious in the earliest and asymptomatic, or preclinical, phase of the disease.¹ To date, methods for reliably detecting pathologic changes of AD – mainly β-amyloid deposition in the brain – are invasive and expensive, requiring measurement of β-amyloid in cerebrospinal fluid or positron-emission-tomography imaging.² Developing a cost-effective, blood-based method for detecting biomarkers associated with preclinical AD is desirable. Here, plasma extracellular vesicles (EVs) of neuronal origin are presented as candidates for a sensitive and effective method to detect preclinical AD.  Methods: Isolating EVs of neuronal origin. Neural cell adhesion molecules (LCAM1) were detected via immunoprecipitation following a high-throughput particle precipitation (Exoquick).⁴ Further support was offered via Imuno-electron microscopy which used biotinylated antibodies to detect LCAM1+ EVs in peripheral blood. Transgenic mice expressing green fluorescent protein on nestin, a protein specific for the nervous system (CNS), and western blot analysis revealed a higher concentration of markers specific for the CNS.⁴  Results: L1CAM+ EVs from peripheral blood contain sufficient levels of brain-derived proteins, such as p-T181-tau, brain-derived neurotrophic factor (BDNP), and pro-BDNF to serve as potential biomarkers of pre-clinical AD. First, immunoprecipitation showed a 2.35-fold difference (p<0.0001) for neuronal enolase in L1CAM+ EVs compared to CD81+ EVs. Second, L1CAM+ EVs contained significantly higher levels of p-T181-tau, BDNF, and pro-BDNF relative to serum or plasma alone.⁴ Third, detection levels (~450pg/ml) for p-T181-tau in L1CAM+ EVs were significantly higher compared to previous studies which used exosomal protein levels of p-T181-tau (85.7±3.75 pg/ml) to successfully detect preclinical AD (10 years prior to clinical diagnosis).^4,5 Together, these findings support L1CAM+ EV’s use as precise biomarkers which reflect metabolic processes occurring in the brain. Conclusion: Isolating EVs of neuronal origin allows for unique insight regarding the pathophysiological processes of the brain. As blood-based biomarkers, EVs of neuronal origin offer an inexpensive and non-invasive method for screening patients. They offer increased sensitivity and lower detection threshold (due to the higher concentration of proteins in L1CAM+ EVs) for biomarkers related to AD.⁴ Due to their abundance of mechanism-specific molecules, EVs of neural origin may even serve as biomarkers for therapeutic response to intervention.

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