Chronic cerebrovascular abnormalities in a mouse model of repetitive mild traumatic brain injury.

PRIMARY OBJECTIVE: To investigate the status of the cerebrovasculature following repetitive mild traumatic brain injury (r-mTBI). RESEARCH DESIGN: TBI is a risk factor for development of various neurodegenerative disorders. A common feature of neurodegenerative disease is cerebrovascular dysfunction which includes alterations in cerebral blood flow (CBF). TBI can result in transient reductions in CBF, with severe injuries often accompanied by varying degrees of vascular pathology post-mortem. However, at this stage, few studies have investigated the cerebrovasculature at chronic time points following repetitive mild brain trauma. METHODS AND PROCEDURES: r-mTBI was delivered to wild-type mice (12 months old) twice per week for 3 months and tested for spatial memory deficits (Barnes Maze task) at 1 and 6 months post-injury. At 7 months post-injury CBF was assessed via Laser Doppler Imaging and, following euthanasia, the brain was probed for markers of cerebrovascular dysfunction and inflammation. MAIN OUTCOMES AND RESULTS: Memory impairment was identified at 1 month post-injury and persisted as late as 6 months post-injury. Furthermore, significant immunopathological insult, reductions in global CBF and down-regulation of cerebrovascular-associated markers were observed. CONCLUSIONS: These results demonstrate impaired cognitive behaviour alongside chronic cerebrovascular dysfunction in a mouse model of repetitive mild brain trauma.

Plasma von Willebrand Factor Is Elevated Hyperacutely After Mild Traumatic Brain Injury.

Each year in the United States, ∼2.7 million persons seek medical attention for traumatic brain injury (TBI), of which ∼85% are characterized as being mild brain injuries. Many different cell types in the brain are affected in these heterogeneous injuries, including neurons, glia, and the brain vasculature. Efforts to identify biomarkers that reflect the injury of these different cell types have been a focus of ongoing investigation. We hypothesized that von Willebrand factor (vWF) is a sensitive biomarker for acute traumatic vascular injury and correlates with symptom severity post-TBI. To address this, blood was collected from professional boxing athletes (n = 17) before and within 30 min after competition. Plasma levels of vWF and neuron-specific enolase were measured using the Meso Scale Discovery, LLC. (MSD) electrochemiluminescence array-based multi-plex format (MSD, Gaithersburg, MD). Additional symptom and outcome data from boxers and patients, such as the Rivermead symptom scores (Rivermead Post Concussion Symptoms Questionnaire [RPQ-3]), were collected. We found that, subsequent to boxing bouts, there was a 1.8-fold increase in vWF levels within 30 min of injury (p < 0.0009). Moreover, fold-change in vWF correlates moderately (r = 0.51; p = 0.03) with the number of head blows. We also found a positive correlation (r = 0.69; p = 0.002) between fold-change in vWF and self-reported post-concussive symptoms, measured by the RPQ-3. The receiver operating curve analysis of vWF plasma levels and RPQ-3 scoring yielded a sensitivity of 94.12% and a specificity of 76.5% with an area under the curve of 83% for boxers after a fight compared to the pre-bout baseline. This study suggests that vWF is a potential blood biomarker measurable in the hyperacute period after blunt mild TBI. This biomarker may prove to be useful in diagnosing and monitoring traumatic vascular injury.

Neuroinflammatory Biomarkers for Traumatic Brain Injury Diagnosis and Prognosis: A TRACK-TBI Pilot Study.

The relationship between systemic inflammation and secondary injury in traumatic brain injury (TBI) is complex. We investigated associations between inflammatory markers and clinical confirmation of TBI diagnosis and prognosis. The prospective TRACK-TBI Pilot (Transforming Research and Clinical Knowledge in Traumatic Brain Injury Pilot) study enrolled TBI patients triaged to head computed tomography (CT) and received blood draw within 24 h of injury. Healthy controls (HCs) and orthopedic controls (OCs) were included. Thirty-one inflammatory markers were analyzed from plasma. Area under the receiver operating characteristic curve (AUC) was used to evaluate discriminatory ability. AUC >0.7 was considered acceptable. Criteria included: TBI diagnosis (vs. OC/HC); moderate/severe vs. mild TBI (Glasgow Coma Scale; GCS); radiographic TBI (CT positive vs. CT negative); 3- and 6-month Glasgow Outcome Scale-Extended (GOSE) dichotomized to death/greater relative disability versus less relative disability (GOSE 1-4/5-8); and incomplete versus full recovery (GOSE <8/ = 8). One-hundred sixty TBI subjects, 28 OCs, and 18 HCs were included. Markers discriminating TBI/OC: HMGB-1 (AUC = 0.835), IL-1b (0.795), IL-16 (0.784), IL-7 (0.742), and TARC (0.731). Markers discriminating GCS 3-12/13-15: IL-6 (AUC = 0.747), CRP (0.726), IL-15 (0.720), and SAA (0.716). Markers discriminating CT positive/CT negative: SAA (AUC = 0.767), IL-6 (0.757), CRP (0.733), and IL-15 (0.724). At 3 months, IL-15 (AUC = 0.738) and IL-2 (0.705) discriminated GOSE 5-8/1-4. At 6 months, IL-15 discriminated GOSE 1-4/5-8 (AUC = 0.704) and GOSE <8/ = 8 (0.711); SAA discriminated GOSE 1-4/5-8 (0.704). We identified a profile of acute circulating inflammatory proteins with potential relevance for TBI diagnosis, severity differentiation, and prognosis. IL-15 and serum amyloid A are priority markers with acceptable discrimination across multiple diagnostic and outcome categories. Validation in larger prospective cohorts is needed. ClinicalTrials.gov Registration: NCT01565551.

Cerebrovascular Reactivity Measures Are Associated With Post-traumatic Headache Severity in Chronic TBI; A Retrospective Analysis.

OBJECTIVE: To characterize the relationship between persistent post-traumatic headache (pPTH) and traumatic cerebrovascular injury (TCVI) in chronic traumatic brain injury (TBI). Cerebrovascular reactivity (CVR), a measure of the cerebral microvasculature and endothelial cell function, is altered both in individuals with chronic TBI and migraine headache disorder (Amyot et al., 2017; Lee et al., 2019b). The pathophysiologies of pPTH and migraine are believed to be associated with chronic microvascular dysfunction. We therefore hypothesize that TCVI may contribute to the underlying migraine-like mechanism(s) of pPTH. MATERIALS AND METHODS: 22 moderate/severe TBI participants in the chronic stage (>6 months) underwent anatomic and functional magnetic resonance imaging (fMRI) scanning with hypercapnia gas challenge to measure CVR as well as the change in CVR (ΔCVR) after single-dose treatment of a specific phosphodiesterase-5 (PDE-5) inhibitor, sildenafil, which potentiates vasodilation in response to hypercapnia in impaired endothelium, as part of a Phase2a RCT of sildenafil in chronic TBI (NCT01762475). CVR and ΔCVR measures of each participant were compared with the individual's pPTH severity measured by the headache impact test-6 (HIT-6) survey. RESULTS: There was a moderate correlation between HIT-6 and both CVR and ΔCVR scores [Spearman's correlation = -0.50 (p = 0.018) and = 0.46 (p = 0.03), respectively], indicating that a higher headache burden is associated with decreased endothelial function in our chronic TBI population. CONCLUSION: There is a correlation between PTH and CVR in chronic moderate-severe TBI. This relationship suggests that chronic TCVI may underlie the pathobiology of pPTH. Further, our results suggest that novel treatment strategies that target endothelial function and vascular health may be beneficial in refractory pPTH.

Imaging biomarkers of vascular and axonal injury are spatially distinct in chronic traumatic brain injury.

Traumatic Brain Injury (TBI) is associated with both diffuse axonal injury (DAI) and diffuse vascular injury (DVI), which result from inertial shearing forces. These terms are often used interchangeably, but the spatial relationships between DAI and DVI have not been carefully studied. Multimodal magnetic resonance imaging (MRI) can help distinguish these injury mechanisms: diffusion tensor imaging (DTI) provides information about axonal integrity, while arterial spin labeling (ASL) can be used to measure cerebral blood flow (CBF), and the reactivity of the Blood Oxygen Level Dependent (BOLD) signal to a hypercapnia challenge reflects cerebrovascular reactivity (CVR). Subjects with chronic TBI (n = 27) and healthy controls (n = 14) were studied with multimodal MRI. Mean values of mean diffusivity (MD), fractional anisotropy (FA), CBF, and CVR were extracted for pre-determined regions of interest (ROIs). Normalized z-score maps were generated from the pool of healthy controls. Abnormal ROIs in one modality were not predictive of abnormalities in another. Approximately 9-10% of abnormal voxels for CVR and CBF also showed an abnormal voxel value for MD, while only 1% of abnormal CVR and CBF voxels show a concomitant abnormal FA value. These data indicate that DAI and DVI represent two distinct TBI endophenotypes that are spatially independent.

Impairment of cerebrovascular reactivity in response to hypercapnic challenge in a mouse model of repetitive mild traumatic brain injury.

Incidences of repetitive mild TBI (r-mTBI), like those sustained by contact sports athletes and military personnel, are thought to be a risk factor for development of neurodegenerative disorders. Those suffering from chronic TBI-related illness demonstrate deficits in cerebrovascular reactivity (CVR), the ability of the cerebral vasculature to respond to a vasoactive stimulus. CVR is thus an important measure of traumatic cerebral vascular injury (TCVI), and a possible in vivo endophenotype of TBI-related neuropathogenesis. We combined laser speckle imaging of CVR in response to hypercapnic challenge with neurobehavioral assessment of learning and memory, to investigate if decreased cerebrovascular responsiveness underlies impaired cognitive function in our mouse model of chronic r-mTBI. We demonstrate a profile of blunted hypercapnia-evoked CVR in the cortices of r-mTBI mice like that of human TBI, alongside sustained memory and learning impairment, without biochemical or immunohistopathological signs of cerebral vessel laminar or endothelium constituent loss. Transient decreased expression of alpha smooth muscle actin and platelet-derived growth factor receptor ß, indicative of TCVI, is obvious only at the time of the most pronounced CVR deficit. These findings implicate CVR as a valid preclinical measure of TCVI, perhaps useful for developing therapies targeting TCVI after recurrent mild head trauma.

Arterial Spin Labeling Reveals Elevated Cerebral Blood Flow with Distinct Clusters of Hypo- and Hyperperfusion after Traumatic Brain Injury.

Imaging detection of brain perfusion alterations after traumatic brain injury (TBI) may provide prognostic insights. In this study, we used arterial spin labeling (ASL) to quantify cross-sectional and longitudinal changes in cerebral blood flow (CBF) after TBI and correlated changes with clinical outcome. We analyzed magnetic resonance imaging scans from adult participants with TBI requiring hospitalization in the acute (2 weeks post-injury, n = 33) and chronic (6 months post-injury, n = 16) phases, with 13 participants scanned longitudinally at both time points. We also analyzed 18 age- and sex-matched healthy controls. Whole-brain CBF maps were derived using a three-dimensional pseudo-continuous arterial spin label technique. Mean CBF across tissue-based regions (whole brain, gray matter, and white matter) was compared cross-sectionally and longitudinally. In addition, individual-level clusters of abnormal perfusion were identified using voxel-based z-score analysis of relative CBF maps, and number and volume of abnormally hypo- and hyperperfused clusters were assessed cross-sectionally and longitudinally. Finally, all CBF measures were correlated with clinical outcome measures. Mean global and gray matter CBF were significantly elevated in acute and chronic TBI participants compared to controls. Participants with better outcome at 6 months post-injury tended to have higher CBF in the acute phase compared to those with poorer outcome. Acute TBI participants had a significantly greater volume of hypo- and hyperperfused brain tissue compared to controls, with these regions partially normalizing by the chronic phase. Our findings demonstrate global elevation of CBF with focal hypo- and hyperperfusion in the early post-injury period and suggest a reparative role for acute elevation in CBF post-TBI.

Apolipoprotein E isoforms differentially regulate matrix metallopeptidase 9 function in Alzheimer's disease.

Apolipoprotein E (APOE) has been shown to influence amyloid-ß (Aß) clearance from the brain in an isoform-specific manner. Our prior work showed that Aß transit across the blood-brain-barrier was reduced by apoE4, compared to other apoE isoforms, due to elevated lipoprotein receptor shedding in brain endothelia. Recently, we demonstrated that matrix metallopeptidase 9 (MMP-9) induces lipoprotein receptor proteolysis in an apoE isoform-dependent manner, which impacts Aß elimination from the brain. The current studies interrogated the relationship between apoE and MMP-9 and found that apoE impacted proMMP-9 cellular secretion from brain endothelia (apoE2 < apoE3 = apoE4). In a cell-free assay, apoE dose-dependently reduced MMP-9 activity, with apoE4 showing a significantly weaker ability to inhibit MMP-9 function than apoE2 or apoE3. Finally, we observed elevated MMP-9 expression and activity in the cerebrovasculature of both human and animal AD brain specimens with an APOE4 genotype. Collectively, these findings suggest a role for apoE in regulating MMP-9 disposition and may describe the effect of apoE4 on Aß pathology in the AD brain.