Pre-analytical characterization of CNS-derived extracellular vesicles from human saliva: effect of room temperature...

Blood-derived extracellular vesicles (EVs) from neurons and astrocytes carrying Alzheimer's disease (AD) biomarkers can predict progression from mild cognitive impairment (MCI) to AD; however, their potential in saliva remains largely unexplored. Saliva-derived extracellular vesicles (sEVs) represent a promising non-invasive biomarker source for AD and other age-related dementias (ADRD), but progress has been limited by a lack of standardized protocols for saliva collection, storage, and central nervous system (CNS)-derived EV isolation.

This study had two primary objectives: (1) to optimize enrichment of CNS cell-specific sEVs from the same individuals, and (2) to evaluate the impact of cellular origin and storage temperature (room temperature, 4°C, -20°C) on the stability and quantification of AD-related biomarkers and inflammatory cytokines. Saliva was collected via passive drool from participants in the Nathan Shock Healthy Aging Study (mean age 71.3 years; n = 15). EVs of neuronal, astrocytic, microglial, and oligodendrocyte origin were isolated using ExoQuick-TC precipitation followed by magnetic bead immunocapture. Executive function and attention were assessed using the NIH Toolbox Cognition Battery. Biomarkers were quantified using high-sensitivity immunoassays (MSD, SIMOA Qunaterix).

Astrocyte-derived EVs demonstrated significant enrichment of key AD biomarkers, including Aβ40, Aβ42, and total tau. Phosphorylated tau (p-tau217) was largely undetectable across all fractions. TDP-43 was most abundant in EV-depleted saliva, while inflammatory cytokines were broadly distributed across all fractions. Storage temperature did not consistently alter biomarker levels; however, -20°C storage yielded optimal biomarker quantification. Importantly, lower levels of inflammatory cytokines (IFN-γ, IL-10, and IL-6) in EV-depleted saliva were associated with better working memory performance.

This study provides proof-of-concept validation for the characterization and comparison of multiple CNS-derived salivary EV fractions within the same individuals. The findings support saliva as a feasible, non-invasive matrix for assessing neurodegenerative and neuroinflammatory biomarkers. Establishing a standardized methodology for salivary EV isolation and storage lays the groundwork for future longitudinal studies aimed at diagnosing and predicting AD progression using saliva-based biomarkers.