Mild traumatic brain injury (mTBI) disproportionately affects military service members and is very difficult to diagnose. To-date, there is currently no blood-based, diagnostic biomarker for mTBI cases with persistent post concussive symptoms. To examine the potential of neuronally-derived (NDE) and astrocytic-derived (ADE) exosome cargo proteins as biomarkers of chronic mTBI in younger adults, we examined plasma exosomes from a prospective longitudinal study of combat-related risk and resilience, marine resiliency study II (MRSII). After return from a combat-deployment participants were interviewed to assess TBI exposure while on deployment. Plasma exosomes from military service members with mTBI (mean age, 21.7 years, n = 19, avg. days since injury 151), and age-matched, controls (deployed service members who did not endorse a deployment-related TBI or a pre-deployment history of TBI; mean age, 21.95 years, n = 20) were precipitated and enriched against a neuronal adhesion protein, L1-CAM, and an astrocyte marker, glutamine aspartate transporter (GLAST) using magnetic beads to immunocapture the proteins and subsequently selected by fluorescent activated cell sorting (FACS). Extracted protein cargo from NDE and ADE preparations were quantified for protein levels implicated in TBI neuropathology by standard ELISAs and on the ultra-sensitive single molecule assay (Simoa) platform. Plasma NDE and ADE levels of Aβ42 were significantly higher while plasma NDE and ADE levels of the postsynaptic protein, neurogranin (NRGN) were significantly lower in participants endorsing mTBI exposure compared to controls with no TBI history. Plasma NDE and ADE levels of Aβ40, total tau, and neurofilament light (NFL), P-T181-tau, P-S396-tau were either undetectable or not significantly different between the two groups. In an effort to understand the pathogenetic potential of NDE and ADE cargo proteins, neuron-like cultures were treated with NDE and ADE preparations from TBI and non-TBI groups. Lastly, we determined that plasma NDE but not ADE cargo proteins from mTBI samples were found to be toxic to neuron-like recipient cells in vitro. These data support the presence of markers of neurodegeneration in NDEs of mTBI and suggest that these NDEs can be used as tools to identify pathogenic mechanisms of TBI.

INTRODUCTION: Alzheimers disease (AD) biomarkers of Amyloid(A), Tau(T), and Neurodegeneration(N) have been increasingly studied to fill the gap in our understanding of racial and ethnic differences. This study aimed to examine the relationship between plasma AT(N) biomarkers and (1) AT(N) neuroimaging biomarkers, (2) demographics, (3) medical comorbidities, and (4) cognitive diagnosis. METHODS: Data were analyzed from n = 764 non-Hispanic Black (NHB), n = 1230 Hispanic, and n = 1232 non-Hispanic White (NHW) participants. Plasma AT(N) biomarkers were derived using single molecule array (SIMOA) technology on an HD-X imager and included amyloid beta (Aβ)42/40, total tau, ptau181, and neurofilament light chain (NfL). Clinical reads of positron emission tomography (PET) amyloid and tau positivity were used to examine the link between AT(N) plasma and neuroimaging biomarkers. Generalized linear models were conducted to examine the relationship between plasma AT(N) biomarkers and select demographic, diagnostic, and medical comorbidities (hypertension, diabetes, dyslipidemia, chronic kidney disease). RESULTS: Differences in the AT(N) biomarkers were found across racial/ethnic groups. Plasma Aβ42/40 was found to be associated with PET amyloid positivity only among NHW participants, while plasma NfL was found to correlate with Meta-ROI among NHB and Hispanic participants. Ptau181 was associated with PET amyloid positivity among NHB and NHW participants and well as PET tau positivity among the latter group and Hispanic participants. Diabetes was related to increased plasma AT(N) biomarkers among NHB and Hispanic participants. CKD was associated with increased AT(N) biomarkers for all race/ethnic groups with the exception of Aβ42/40. While Aβ42/40, total tau, ptau181, and NfL were found to be related to a dementia diagnosis among NHW participants, only ptau181 and NfL were found to be related to this same diagnostic category among NHB and Hispanic participants. DISCUSSION: Our findings indicate differential relationships between comorbidities (demographic, medical, diagnostic) across NHB, Hispanic, and NHW participants. This work expands our knowledge regarding the associations of plasma biomarkers to AD pathology in diverse populations. HIGHLIGHTS: Differences in AT(N) plasma biomarkers were found in a diverse community cohort.While plasma Aβ42/40 was associated with PET amyloid positivity among non-Hispanic white participants, this did not apply to non-Hispanic Black or Hispanic participants.Medical comorbidity of diabetes and chronic kidney disease was related to increased plasma AT(N) biomarkers among the ethnically diverse segment of the cohort.Plasma AT(N) biomarkers were more so related to a diagnosis of dementia for non-Hispanic white as compared to Hispanic or non-Hispanic Black participants.Across racial/ethnic groups, the plasma biomarkers of neurodegeneration (NfL) and ptau181 were related to a diagnosis of dementia.

Background

The need for diagnostic biomarkers of cognitive decline is particularly important among aging adults with Down syndrome (DS). Growing empirical support has identified the utility of plasma derived biomarkers among neurotypical adults with mild cognitive impairment (MCI) and Alzheimer's disease (AD); however, the application of such biomarkers has been limited among the DS population.

Objective

This study aimed to investigate the cross-sectional diagnostic performance of plasma neurofilament light chain (Nf-L) and total-tau, individually and in combination among a cohort of DS adults.

Methods

Plasma samples were analyzed from n = 305 (n = 225 cognitively stable (CS); n = 44 MCI-DS; n = 36 DS-AD) participants enrolled in the Alzheimer's Biomarker Consortium -Down Syndrome.

Results

In distinguishing DS-AD participants from CS, Nf-L alone produced an AUC of 90%, total-tau alone reached 74%, and combined reached an AUC of 86%. When age and gender were included, AUC increased to 93%. Higher values of Nf-L, total-tau, and age were all shown to be associated with increased risk for DS-AD. When distinguishing MCI-DS participants from CS, Nf-L alone produced an AUC of 65%, while total-tau alone reached 56%. A combined model with Nf-L, total-tau, age, and gender produced an AUC of 87%. Both higher values in age and total-tau were found to increase risk for MCI-DS; Nf-L levels were not associated with increased risk for MCI-DS.

Conclusion

Advanced assay techniques make total-tau and particularly Nf-L useful biomarkers of both AD pathology and clinical status in DS and have the potential to serve as outcome measures in clinical trials for future disease-modifying drugs.