0416 Poor Sleep Quality Predicts Serum Markers of Neurodegeneration and Cognitive Deficits in Warriors with Mild Traumatic Brain Injury

Introduction

Increasing evidence links neurodegeneration to traumatic brain injury (TBI), and a separate body of literature links neurodegeneration to sleep dysfunction, implicating increased toxin production and decreased glymphatic clearance. Sleep disorders affect 50% of TBI patients, yet the sleep-neurodegeneration connection in these patients remains unexplored. We hypothesized that warfighters with TBI and sleep dysfunction would have increased neuronal injury, revealing potential mechanistic underpinnings for TBI outcomes. We measured plasma biomarkers, cognitive function and sleep surveys for correlation analysis.

Methods

In a retrospective cross-sectional study of warfighters (n=113 chronic mild TBI patients), the Pittsburgh sleep quality index (PSQI) was compared with amyloid β42 (Aβ42), neurofilament light (NFL), tau, and phospho-tau (threonine 181) isolated from plasma and exosomes. Executive function was tested with the categorical fluency test. Exosomes were precipitated from plasma. Proteins were measured with the Single Molecule Array (Quanterix). Linear models were adjusted for age, ApoE, and number of TBIs.

Results

Poor sleepers with TBI (PSQI>8) had elevated NFL compared to good sleepers in plasma (p=0.007) and exosomes (p=0.00017), and PSQI directly correlated with NFL (plasma: Beta=0.23, p=0.0079; exosomes: Beta=2.19, p=0.0013) stronger than any other marker of neurodegeneration. Poor sleepers also showed higher obstructive sleep apnea (OSA) risk compared to good sleepers by STOP-BANG scores (3.6, SD=1.6 vs 2.8, SD=1.74; p=0.0014) as well as decreased categorical fluency (20.7, SD=4.1) (18.3, SD=4.6, p=.0067). Plasma tau and Aβ42 also correlated with PSQI (Beta=0.64, p=0.028, and Beta=0.40, p=0.049 respectively).

Conclusion

This is the first reported data correlating markers of neuronal injury and cognitive deficits with sleep complaints and OSA risk in patients with TBI - possibly identifying treatable pathophysiological mediators of TBI neurodegeneration. Limitations include a small sample size, lack of objective sleep measures, and inability to establish directionality due to cross-sectional design. Prospective trials will be required to further explore our proposed hypothesis. If confirmed, these findings would call for targeting sleep disorders in the TBI population to mitigate risk of neurodegeneration.

Support

This work was supported by grant funding from: Department of Defense, Chronic Effects of Neurotrauma Consortium (CENC) Award W81XWH-13-2-0095 and Department of Veterans Affairs CENC Award I01 CX001135.

1118 Examining the Role of Serum and Exosomal Biomarkers in Symptoms of Fatigue and Daytime Sleepiness Following Traumatic Brain Injury

Introduction

Fatigue and daytime sleepiness are two of the most common chronic symptoms reported after traumatic brain injury (TBI). However, there is limited understanding of the pathophysiological mechanisms following TBI that result in these symptoms. Previous research has observed elevations in peripheral blood levels of proteins in TBI patients versus controls, including neurofilament light chain (NFL)—predominantly expressed in long myelinated subcortical axons—and glial fibrillary acidic protein (GFAP)—predominantly expressed in reactive astrocytes responding to central nervous system injuries. This study examines the relationship between serum and exosomal NFL and GFAP, and symptoms of fatigue and daytime sleepiness in TBI patients 1-year after injury.

Methods

Sixty-seven patients with TBIs ranging from mild to severe were included in this study. Blood samples were collected from all participants 1-year post TBI, with concentrations of GFAP and NFL measured in serum and exosomes using Single Molecule Array technology (Simoa), an ultrasensitive assay. Participants reported fatigue using the Fatigue Severity Scale (FSS), and daytime sleepiness using the Epworth Sleepiness Scale (ESS).

Results

A linear regression model of fatigue symptoms and exosomal NFL controlling for age revealed that fatigue was negatively associated with exosomal NFL concentrations (β = -.317, p = .041, ηp2 = -.343) and accounted for 20.2% of the change in NFL. Serum NFL concentrations were not associated with fatigue, nor were GFAP serum or exosomes. No significant associations were found between NFL, GFAP, and daytime sleepiness.

Conclusion

Our findings suggest that exosomal NFL may be related to mechanisms underlying TBI-related fatigue and the potential of NFL as a biomarker of fatigue. To our knowledge, this study is the first to examine the relationship between post-TBI NFL levels and fatigue symptoms. Further investigation into serum and exosome biomarkers of TBI-related fatigue and daytime sleepiness is warranted.

Support

National Institutes of Health and Center for Neuroscience and Regenerative Medicine