Alterations in cerebrospinal fluid apolipoprotein E and amyloid beta-protein after traumatic brain injury

Higher cerebrospinal fluid tau is associated with history of traumatic brain injury and reduced processing speed in Vietnam-era veterans: A Department of Defense Alzheimer's Disease Neuroimaging Initiative (DOD-ADNI) study

INTRODUCTION

 Our goal was to determine whether cognitive and cerebrospinal fluid (CSF) markers of tau and amyloid beta 1-42 (Aβ42) differ between Vietnam-era veterans with and without history of traumatic brain injury (TBI) and whether TBI moderates the association between CSF markers and neurocognitive functioning.

METHODS

 A total of 102 male participants (52 TBI, 50 military controls [MCs]; mean age = 68) were included. Levels of CSF Aβ42, tau phosphorylated at the threonine 181 position (p-tau), and total tau (t-tau) were quantified. Group differences in CSF markers and cognition as well as the moderating effect of TBI on CSF and cognition associations were explored.

RESULTS

 Relative to MCs, the TBI group showed significantly higher p-tau (P = .01) and t-tau (P = .02), but no differences in amyloid (P = .09). TBI history moderated the association between CSF tau and performance on a measure of processing speed (t-tau: P  = .04; p-tau: P  = .02).

DISCUSSION

 Tau accumulation may represent a mechanism of dementia risk in older veterans with remote TBI.

Expression and secretion of apoE isoforms in astrocytes and microglia during inflammation

Neuroinflammation is a common feature in neurodegenerative diseases, modulated by the Alzheimer's disease risk factor, apolipoprotein E (APOE). In the brain, apoE protein is synthesized by astrocytes and microglia. We examined primary cultures of astrocytes and microglia from human APOE (E2, E3, and E4) targeted-replacement mice. Astrocytes secreted two species of apoE, whereas cellular apoE consisted of only one. Both forms of secreted astrocytic apoE were bound during glycoprotein isolation, and enzymatic removal of glycans produced a convergence of the two forms of apoE to a single form; thus, the two species of astrocyte-secreted apoE are differentially glycosylated. Microglia released only a single species of apoE, while cellular apoE consisted of two forms; the secreted apoE and one of the two forms of cellular apoE were glycosylated. We treated the primary glia with either endogenous (TNFα) or exogenous (LPS) pro-inflammatory stimuli. While LPS had no effect on astrocytic apoE, APOE2, and APOE3 microglia increased release of apoE; APOE4 microglia showed no effect. APOE4 microglia showed higher baseline secretion of TNFα compared to APOE2 and APOE3 microglia. TNFα treatment reduced the secretion and cellular expression of apoE only in APOE4 astrocytes. The patterns of apoE species produced by astrocytes and microglia were not affected by inflammation. No changes in APOE mRNA were observed in astrocytes after both treatments. Together, our data demonstrate that astrocytes and microglia differentially express and secrete glycosylated forms of apoE and that APOE4 astrocytes and microglia are deficient in immunomodulation compared to APOE2 and APOE3.

The Bidirectional Relationship Between Sleep and Inflammation Links Traumatic Brain Injury and Alzheimer's Disease

Traumatic brain injury (TBI) and Alzheimer's disease (AD) are diseases during which the fine-tuned autoregulation of the brain is lost. Despite the stark contrast in their causal mechanisms, both TBI and AD are conditions which elicit a neuroinflammatory response that is coupled with physical, cognitive, and affective symptoms. One commonly reported symptom in both TBI and AD patients is disturbed sleep. Sleep is regulated by circadian and homeostatic processes such that pathological inflammation may disrupt the chemical signaling required to maintain a healthy sleep profile. In this way, immune system activation can influence sleep physiology. Conversely, sleep disturbances can exacerbate symptoms or increase the risk of inflammatory/neurodegenerative diseases. Both TBI and AD are worsened by a chronic pro-inflammatory microenvironment which exacerbates symptoms and worsens clinical outcome. Herein, a positive feedback loop of chronic inflammation and sleep disturbances is initiated. In this review, the bidirectional relationship between sleep disturbances and inflammation is discussed, where chronic inflammation associated with TBI and AD can lead to sleep disturbances and exacerbated neuropathology. The role of microglia and cytokines in sleep disturbances associated with these diseases is highlighted. The proposed sleep and inflammation-mediated link between TBI and AD presents an opportunity for a multifaceted approach to clinical intervention.

Cerebrospinal fluid tau fragment correlates with tau PET: a candidate biomarker for tangle pathology

To date, there is no validated fluid biomarker for tau pathology in Alzheimer's disease, with contradictory results from studies evaluating the correlation between phosphorylated tau in CSF with tau PET imaging. Tau protein is subjected to proteolytic processing into fragments before being secreted to the CSF. A recent study suggested that tau cleavage after amino acid 368 by asparagine endopeptidase (AEP) is upregulated in Alzheimer's disease. We used immunoprecipitation followed by mass spectrometric analyses to evaluate the presence of tau368 species in CSF. A novel Simoa® assay for quantification of tau368 in CSF was developed, while total tau (t-tau) was measured by ELISA and the presence of tau368 in tangles was evaluated using immunohistochemistry. The diagnostic utility of tau368 was first evaluated in a pilot study (Alzheimer's disease = 20, control = 20), then in a second cohort where the IWG-2 biomarker criteria were applied (Alzheimer's disease = 37, control = 45), and finally in a third cohort where the correlation with 18F-GTP1 tau PET was evaluated (Alzheimer's disease = 38, control = 11). The tau368/t-tau ratio was significantly decreased in Alzheimer's disease (P < 0.001) in all cohorts. Immunohistochemical staining demonstrated that tau fragments ending at 368 are present in tangles. There was a strong negative correlation between the CSF tau368/t-tau ratio and 18F-GTP1 retention. Our data suggest that tau368 is a tangle-enriched fragment and that the CSF ratio tau368/t-tau reflects tangle pathology. This novel tau biomarker could be used to improve diagnosis of Alzheimer's disease and to facilitate the development of drug candidates targeting tau pathology. Furthermore, future longitudinal studies will increase our understanding of tau pathophysiology in Alzheimer's disease and other tauopathies.

Blood biomarkers for assessment of mild traumatic brain injury and chronic traumatic encephalopathy

Mild traumatic brain injuries (mTBI) are prevalent and can result in significant debilitation. Current diagnostic methods have implicit limitations, with clinical assessment tools reliant on subjective self-reported symptoms or non-specific clinical observations, and commonly available imaging techniques lacking sufficient sensitivity to detect mTBI. A blood biomarker would provide a readily accessible detector of mTBI to meet the current measurement gap. Suitable options would provide objective and quantifiable information in diagnosing mTBI, in monitoring recovery, and in establishing a prognosis of resultant neurodegenerative disease, such as chronic traumatic encephalopathy (CTE). A biomarker would also assist in progressing research, providing suitable endpoints for testing therapeutic modalities and for further exploring mTBI pathophysiology. This review highlights the most promising blood-based protein candidates that are expressed in the central nervous system (CNS) and released into systemic circulation following mTBI. To date, neurofilament light (NF-L) may be the most suitable candidate for assessing neuronal damage, and glial fibrillary acidic protein (GFAP) for assessing astrocyte activation, although further work is required. Ultimately, the heterogeneity of cells in the brain and each marker's limitations may require a combination of biomarkers, and recent developments in microRNA (miRNA) markers of mTBI show promise and warrant further exploration.

Subchronic Pathobiological Response Following Chronic Repetitive Mild Traumatic Brain Injury in an Aged Preclinical Model of Amyloid Pathogenesis

Repetitive mild traumatic brain injury (r-mTBI) is a risk factor for Alzheimer disease (AD). The precise nature of how r-mTBI leads to, or precipitates, AD pathogenesis remains unclear. In this study, we explore subchronic effects of chronic r-mTBI (12-impacts) administered over 1-month in aged-PS1/APP mice and littermate controls. We investigate specific mechanisms that may elucidate the molecular link between AD and r-mTBI, focusing primarily on amyloid and tau pathology, amyloid processing, glial activation states, and associated clearance mechanisms. Herein, we demonstrate r-mTBI in aged PS1/APP mice does not augment, glial activation, amyloid burden, or tau pathology (with exception of pS202-positive Tau) 1 month after exposure to the last-injury. However, we observed a decrease in brain soluble Aβ42 levels without any appreciable change in peripheral soluble Aβ42 levels. This was accompanied by an increase in brain insoluble to soluble Aβ42 ratio in injured PS1/APP mice compared with sham injury. A parallel reduction in phagocytic receptor, triggering receptor expressed on myeloid cells 2, was also observed. This study demonstrates very subtle subchronic effects of r-mTBI on a preexisting amyloid pathology background, which may be on a continuum toward a slow and worsening neurodegenerative outcome compared with sham injury, and therefore, have many implications, especially in the elderly population exposed to TBI.

The Administration of the New Pyrimidine Derivative-4-{2-[2-(3,4-Dimethoxyphenyl)-Vinyl]-6-Ethyl-4-Oxo-5-Phenyl-4H-Pyrimidine-1-Il}Benzsulfamide Restores the Activity of Brain Cells in Experimental Chronic Traumatic Encephalopathy by Maintaining Mitochondrial Function

Background and objectives: To evaluate the effect of a new pyrimidine derivative on the change of mitochondrial function in experimental chronic traumatic encephalopathy. Materials and methods: The study was performed on male mice of the BALB/c line (acute toxicity was assessed) and male rats of the Wistar line, which were modeled chronic traumatic encephalopathy by the method of free fall of the load (weight 150 g from a 50 cm height). The injury to rats was reproduced once a day for 7 days. Further, cognitive functions, changes in sensorimotor deficiency, cerebral blood flow, neuron-specific enolase(NSE), S100β, glial fibrillary acidic protein (GFAP) (in blood serum) and β-amyloid, adenosine triphosphate (ATP) (in brain tissue supernatant) were evaluated. Mitochondrial respiration was also measured. Choline alfoscerate (100 mg/kg) was used as a reference drug. Results: The study found that the use of a new pyrimidine derivative contributed to the preservation of the mitochondrial respirometric function and cognitive functions in rats. In addition, against the administration of test-object marked increase in the concentration of ATP, the velocity of cerebral blood flow was 4.2 times (p < 0.05) and 35.6% (p < 0.05), respectively, as well as reduced concentration and GFAP, NSE, S100β, β-amyloid and sensorimotor deficit at 2.7 (p < 0.05) times; 2 times (p < 0.05); 2.4 times (p < 0.05); of 30.4% (p < 0.05 and 46.5% (p < 0.05), respectively. The LD₅₀ (per os) for the test-object was 4973.56 ± 573.72 mg/kg. Conclusion: Based on the obtained data, high therapeutic efficacy and low systemic toxicity of the application are assumed 4-{2-[2-(3,4-dimethoxyphenyl)-vinyl]-6-ethyl-4-oxo-5-phenyl-4H-pyrimidine-1-Il}benzsulfamide in chronic traumatic encephalopathy.

Apolipoprotein E in lipoprotein metabolism, health and cardiovascular disease

Apolipoprotein E (apoE), a 34 kDa circulating glycoprotein of 299 amino acids, predominantly synthesised in the liver, associates with triglyceride-rich lipoproteins to mediate the clearance of their remnants after enzymatic lipolysis in the circulation. Its synthesis in macrophages initiates the formation of high density-like lipoproteins to effect reverse cholesterol transport to the liver. In the nervous system apoE forms similar lipoproteins which perform the function of distributing lipids amongst cells. ApoE accounts for much of the variation in plasma lipoproteins by three common variants (isoforms) that influence low-density lipoprotein concentration and the risk of atherosclerosis. ApoE2 generally is most favourable and apoE4 least favourable for cardiovascular and neurological health. The apoE variants relate to different amino acids at positions 112 and 158: cysteine in both for apoE2, arginine at both sites for apoE4, and respectively cysteine and arginine for apoE3 that is viewed as the wild type. Paradoxically, under metabolic stress, homozygosity for apoE2 may result in dysbetalipoproteinaemia in adults owing to impaired binding of remnant lipoproteins to the LDL receptor and related proteins as well as heparan sulphate proteoglycans. This highly atherogenic condition is also seen with other mutations in apoE, but with autosomal dominant inheritance. Mutations in apoE may also cause lipoprotein glomerulopathy. In the central nervous system apoE binds amyloid β-protein and tau protein and fragments may incur cellular damage. ApoE4 is a strong risk factor for the development of Alzheimer's disease. ApoE has several other physiological effects that may influence health and disease, including supply of docosahexaenoic acid for the brain and modulating immune and inflammatory responses. Genotyping of apoE may have application in disorders of lipoprotein metabolism as well as glomerulopathy and may be relevant to personalised medicine in understanding cardiovascular risk, and the outcome of nutritional and therapeutic interventions. Quantitation of apoE will probably not be clinically useful. ApoE is also of interest as it may generate peptides with biological function and could be employed in nanoparticles that may allow crossing of the blood-brain barrier. Therapeutic options may emerge from these newer insights.

Apolipoprotein E4 impairs spontaneous blood brain barrier repair following traumatic brain injury

BACKGROUND

Traumatic Brain Injury (TBI) is a major cause of disability and mortality, to which there is currently no comprehensive treatment. Blood Brain Barrier (BBB) dysfunction is well documented in human TBI patients, yet the molecular mechanisms that underlie this neurovascular unit (NVU) pathology remains unclear. The apolipoprotein-E (apoE) protein has been implicated in controlling BBB integrity in an isoform dependent manner, via suppression of Cyclophilin A (CypA)-Matrix metallopeptidase-9 (MMP-9) signaling cascades, however the contribution of this pathway in TBI-induced BBB permeability is not fully investigated.

METHODS

We exposed C57Bl/6 mice to controlled cortical impact and assessed NVU and BBB permeability responses up to 21 days post-injury. We pharmacologically probed the role of the CypA-MMP-9 pathway in BBB permeability after TBI using Cyclosporin A (CsA, 20 mg/kg). Finally, as the apoE4 protein is known to be functionally deficient compared to the apoE3 protein, we used humanized APOE mice as a clinically relevant model to study the role of apoE on BBB injury and repair after TBI.

RESULTS

In C57Bl/6 mice there was an inverse relationship between soluble apoE and BBB permeability, such that damaged BBB stabilizes as apoE levels increase in the days following TBI. TBI mice displayed acute pericyte loss, increased MMP-9 production and activity, and reduced tight-junction expression. Treatment with the CypA antagonist CsA in C57Bl/6 mice attenuates MMP-9 responses and enhances BBB repair after injury, demonstrating that MMP-9 plays an important role in the timing of spontaneous BBB repair after TBI. We also show that apoe mRNA is present in both astrocytes and pericytes after TBI. We report that APOE3 and APOE4 mice have similar acute BBB responses to TBI, but APOE3 mice display faster spontaneous BBB repair than APOE4 mice. Isolated microvessel analysis reveals delayed pericyte repopulation, augmented and sustained MMP-9 expression at the NVU, and impaired stabilization of Zonula Occludens-1, Occludin and Claudin-5 expression at tight junctions in APOE4 mice after TBI compared to APOE3 mice.

CONCLUSIONS

These data confirm apoE as an important modulator of spontaneous BBB stabilization following TBI, and highlights the APOE4 allele as a risk factor for poor outcome after TBI.

Current and Emerging Technologies for Probing Molecular Signatures of Traumatic Brain Injury

Traumatic brain injury (TBI) is understood as an interplay between the initial injury, subsequent secondary injuries, and a complex host response all of which are highly heterogeneous. An understanding of the underlying biology suggests a number of windows where mechanistically inspired interventions could be targeted. Unfortunately, biologically plausible therapies have to-date failed to translate into clinical practice. While a number of stereotypical pathways are now understood to be involved, current clinical characterization is too crude for it to be possible to characterize the biological phenotype in a truly mechanistically meaningful way. In this review, we examine current and emerging technologies for fuller biochemical characterization by the simultaneous measurement of multiple, diverse biomarkers. We describe how clinically available techniques such as cerebral microdialysis can be leveraged to give mechanistic insights into TBI pathobiology and how multiplex proteomic and metabolomic techniques can give a more complete description of the underlying biology. We also describe spatially resolved label-free multiplex techniques capable of probing structural differences in chemical signatures. Finally, we touch on the bioinformatics challenges that result from the acquisition of such large amounts of chemical data in the search for a more mechanistically complete description of the TBI phenotype.

CSF β-amyloid as a putative biomarker of disease progression in multiple sclerosis

BACKGROUND

Neurodegeneration plays a major role in determining disability in multiple sclerosis (MS) patients. Hence, there is increasing need to identify reliable biomarkers, which could serve as prognostic measure of disease progression.

OBJECTIVES

To assess whether cerebrospinal fluid (CSF) tau and β-amyloid (Aβ) levels were altered in newly diagnosed MS patients and correlated with disability. Moreover, we investigated whether these CSF biomarkers associate with macroscopic brain tissue damage measures.

METHODS

CSF Aβ and tau levels were determined by enzyme-linked immunosorbent assay in CSF samples from 48 newly diagnosed MS patients, followed-up clinically for 3 years by recording their Expanded Disability Status Scale score at 6-month intervals, and 45 controls. All patients underwent magnetic resonance imaging at baseline and at the end of follow-up to quantify their lesion load (LL).

RESULTS

CSF Aβ levels were significantly reduced in patients compared to controls ( p < 0.001). Lower CSF Aβ levels at baseline were a disability predictor at 3-year follow-up ( p = 0.009). CSF tau levels correlated with T2- and T1-LL ( p < 0.001).

CONCLUSION

CSF Aβ reduction is a promising biomarker of neurodegeneration and may predict patients' clinical outcome. Therefore, CSF Aβ should be considered as a potential biomarker of prognostic value.

Traumatic brain injury as a risk factor for Alzheimer's disease: current knowledge and future directions

There is growing concern about the late effects of traumatic brain injury (TBI). This scoping review summarizes clinical research from the past 10 years that evaluates the relationship between TBI and Alzheimer's disease. This review identified five studies that found increased risk for dementia after TBI, two studies that found no increased risk and four studies that found a relationship only under certain conditions or in specified subsamples. Methodological differences across studies preclude direct comparison of results, and discrepant findings elucidate the complex course of post-TBI neurodegeneration. We discuss the factors that influence the strength and direction of the relationship between TBI and Alzheimer's disease, and the implications of this body of research for patient care and future research.

Subacute Changes in Cleavage Processing of Amyloid Precursor Protein and Tau following Penetrating Traumatic Brain Injury

Traumatic brain injury (TBI) is an established risk factor for the development of Alzheimer's disease (AD). Here the effects of severe penetrating TBI on APP and tau cleavage processing were investigated in a rodent model of penetrating ballistic-like brain injury (PBBI). PBBI was induced by stereotactically inserting a perforated steel probe through the right frontal cortex of the anesthetized rat and rapidly inflating/deflating the probe's elastic tubing into an elliptical shaped balloon to 10% of total rat brain volume causing temporary cavitation injury. Separate animals underwent probe injury (PrI) alone without balloon inflation. Shams underwent craniectomy. Brain tissue was collected acutely (4h, 24h, 3d) and subacutely (7d) post-injury and analyzed by immunoblot for full length APP (APP-FL) and APP beta c-terminal fragments (βCTFs), full length tau (tau-FL) and tau truncation fragments and at 7d for cytotoxic Beta amyloid (Aβ) peptides Aβ40 and Aβ42 analysis. APP-FL was significantly decreased at 3d and 7d following PBBI whereas APP βCTFs were significantly elevated by 4h post-injury and remained elevated through 7d post-injury. Effects on βCTFs were mirrored with PrI, albeit to a lesser extent. Aβ40 and Aβ42 were significantly elevated at 7d following PBBI and PrI. Tau-FL decreased substantially 3d and 7d post-PBBI and PrI. Importantly, a 22 kDa tau fragment (tau22), similar to that found in AD, was significantly elevated by 4h and remained elevated through 7d post-injury. Thus both APP and tau cleavage was dramatically altered in the acute and subacute periods post-injury. As cleavage of these proteins has also been implicated in AD, TBI pathology shown here may set the stage for the later development of AD or other tauopathies.

The Effect of the APOE4 Gene on Accumulation of Aβ40 After Brain Injury Cannot Be Reversed by Increasing apoE4 Protein

The apolipoprotein E (apoE) protein is involved in clearance of β-amyloid (Aβ) from the brain; and the APOE4 gene is associated with Aβ plaque formation in humans following traumatic brain injury (TBI). Here, we examined the association between apoE and Aβ₄₀ after experimental TBI and the effects of APOE alleles on this relationship. We report a biphasic response of soluble apoE protein after TBI with an acute reduction at 1 day postinjury followed by an increase at 7 days postinjury. TBI-induced Aβ₄₀ levels decreased as soluble apoE levels increased. In APOE4 mice there was a diminished apoE response to TBI that corresponded to prolonged accumulation of TBI-induced Aβ₄₀ versus that in APOE3 mice. Amyloid precursor protein processing was similar in APOE3 and APOE4 mice suggesting that impaired clearance was responsible for the abnormal accumulation of Aβ₄₀ in the latter. Treatment of APOE4 mice with bexarotene for 7 days increased apoE4 protein levels but was not sufficient to reduce TBI-induced Aβ₄₀ Thus, rapid clearance of TBI-induced Aβ₄₀ occurs in mice but these pathways are impaired in APOE4 carriers. These data may help explain the deposition of Aβ in APOE4 carriers and the increased incidence of brain Aβ plaques following TBI.

CSF and plasma amyloid-β temporal profiles and relationships with neurological status and mortality after severe traumatic brain injury

The role of amyloid-β (Aβ) neuropathology and its significant changes in biofluids after traumatic brain injury (TBI) is still debated. We used ultrasensitive digital ELISA approach to assess amyloid-β_1-42 (Aβ42) concentrations and time-course in cerebrospinal fluid (CSF) and in plasma of patients with severe TBI and investigated their relationship to injury characteristics, neurological status and clinical outcome. We found decreased CSF Aβ42 levels in TBI patients acutely after injury with lower levels in patients who died 6 months post-injury than in survivors. Conversely, plasma Aβ42 levels were significantly increased in TBI with lower levels in patients who survived. A trend analysis showed that both CSF and plasma Aβ42 levels strongly correlated with mortality. A positive correlation between changes in CSF Aβ42 concentrations and neurological status as assessed by Glasgow Coma Scale (GCS) was identified. Our results suggest that determination of Aβ42 may be valuable to obtain prognostic information in patients with severe TBI as well as in monitoring the response of the brain to injury.

Increased CSF levels of phosphorylated neurofilament heavy protein following bout in amateur boxers

Introduction

Diagnosis of mild TBI is hampered by the lack of imaging or biochemical measurements for identifying or quantifying mild TBI in a clinical setting. We have previously shown increased biomarker levels of protein reflecting axonal (neurofilament light protein and tau) and glial (GFAP and S-100B) damage in cerebrospinal fluid (CSF) after a boxing bout. The aims of this study were to find other biomarkers of mild TBI, which may help clinicians diagnose and monitor mild TBI, and to calculate the role of APOE ε4 allele genotype which has been associated with poor outcome after TBI.

Materials and Methods

Thirty amateur boxers with a minimum of 45 bouts and 25 non-boxing matched controls were included in a prospective cohort study. CSF and blood were collected at one occasion between 1 and 6 days after a bout, and after a rest period for at least 14 days (follow up). The controls were tested once. CSF levels of neurofilament heavy (pNFH), amyloid precursor proteins (sAPPα and sAPPβ), ApoE and ApoA1 were analyzed. In blood, plasma levels of Aβ42 and ApoE genotype were analyzed.

Results

CSF levels of pNFH were significantly increased between 1 and 6 days after boxing as compared with controls (p<0.001). The concentrations decreased at follow up but were still significantly increased compared to controls (p = 0.018). CSF pNFH concentrations correlated with NFL (r =  0.57 after bout and 0.64 at follow up, p<0.001). No significant change was found in the other biomarkers, as compared to controls. Boxers carrying the APOE ε4 allele had similar biomarker concentrations as non-carriers.

Conclusions

Subconcussive repetitive trauma in amateur boxing causes a mild TBI that may be diagnosed by CSF analysis of pNFH, even without unconsciousness or concussion symptoms. Possession of the APOE ε4 allele was not found to influence biomarker levels after acute TBI.

Amyloid-β Peptides and Tau Protein as Biomarkers in Cerebrospinal and Interstitial Fluid Following Traumatic Brain Injury: A Review of Experimental and Clinical Studies

Traumatic brain injury (TBI) survivors frequently suffer from life-long deficits in cognitive functions and a reduced quality of life. Axonal injury, observed in many severe TBI patients, results in accumulation of amyloid precursor protein (APP). Post-injury enzymatic cleavage of APP can generate amyloid-β (Aβ) peptides, a hallmark finding in Alzheimer’s disease (AD). At autopsy, brains of AD and a subset of TBI victims display some similarities including accumulation of Aβ peptides and neurofibrillary tangles of hyperphosphorylated tau proteins. Most epidemiological evidence suggests a link between TBI and AD, implying that TBI has neurodegenerative sequelae. Aβ peptides and tau may be used as biomarkers in interstitial fluid (ISF) using cerebral microdialysis and/or cerebrospinal fluid (CSF) following clinical TBI. In the present review, the available clinical and experimental literature on Aβ peptides and tau as potential biomarkers following TBI is comprehensively analyzed. Elevated CSF and ISF tau protein levels have been observed following severe TBI and suggested to correlate with clinical outcome. Although Aβ peptides are produced by normal neuronal metabolism, high levels of long and/or fibrillary Aβ peptides may be neurotoxic. Increased CSF and/or ISF Aβ levels post-injury may be related to neuronal activity and/or the presence of axonal injury. The heterogeneity of animal models, clinical cohorts, analytical techniques, and the complexity of TBI in the available studies make the clinical value of tau and Aβ as biomarkers uncertain at present. Additionally, the link between early post-injury changes in tau and Aβ peptides and the future risk of developing AD remains unclear. Future studies using methods such as rapid biomarker sampling combined with enhanced analytical techniques and/or novel pharmacological tools could provide additional information on the importance of Aβ peptides and tau protein in both the acute pathophysiology and long-term consequences of TBI.

Olympic boxing is associated with elevated levels of the neuronal protein tau in plasma

OBJECTIVES

The aim of this study was to investigate if olympic (amateur) boxing is associated with elevation of brain injury biomarkers in peripheral blood compared to controls.

MATERIALS AND METHODS

Thirty olympic boxers competing in at least 47 bouts were compared to 25 controls. Blood was collected from the controls at one occasion and from the boxers within 1-6 days after a bout and after a rest period of at least 14 days. Tau concentration in plasma was determined using a novel single molecule ELISA assay and S-100B, glial fibrillary acidic protein, brain-derived neurotrophic factor and amyloid β 1-42 were determined using standard immunoassays.

RESULTS

None of the boxers had been knocked-out during the bout. Plasma-tau was significantly increased in the boxers after a bout compared to controls (mean ± SD, 2.46 ± 5.10 vs. 0.79 ± 0.961 ng L(-1), p = 0.038). The other brain injury markers did not differ between the groups. Plasma-tau decreased significantly in the boxers after a resting period compared to after a bout (p = 0.030).

CONCLUSIONS

Olympic boxing is associated with elevation of tau in plasma. The repetitive minimal head injury in boxing may lead to axonal injuries that can be diagnosed with a blood test.

Peptidergic drugs for the treatment of traumatic brain injury

Traumatic brain injury (TBI) is a devastating medical condition that has an enormous socioeconomic impact because it affects more than 10 million people annually worldwide and is associated with high rates of hospitalization, mortality and disability. Although TBI survival has improved continuously for decades, particularly in developing countries, implementation of an effective drug therapy for TBI represents an unmet clinical need. All confirmatory trials conducted to date with drugs targeting a single TBI pathological pathway failed to show clinical efficacy, probably because TBI pathophysiology involves multiple cellular and molecular mechanisms of secondary brain damage. According to current scientific evidence of the participation of peptide-mediated mechanisms in the processes of brain injury and repair after TBI, peptidergic drugs represent a multimodal therapy alternative to improve acute outcome and long-term recovery in TBI patients. Preliminary randomized-controlled clinical trials and open-label studies conducted to date with the peptidergic drug Cerebrolysin® (Ever Neuro Pharma GmbH, Unterach, Austria) and with the endogenous neuropeptides progesterone and erythropoietin, showed positive clinical results. Cerebrolysin-treated patients had a faster clinical recovery, a shorter hospitalization time and a better long-term outcome. Treatment with progesterone showed advantages over placebo regarding TBI mortality and clinical outcome, whereas erythropoietin only reduced mortality. Further validation of these promising findings in confirmatory randomized-controlled clinical trials is warranted. This article reviews the scientific basis and clinical evidence on the development of multimodal peptidergic drugs as a therapeutic option for the effective treatment of TBI patients.

Clinical Relevance of Biomarkers for Traumatic Brain Injury

Approximately 1.4 million people in the United States sustain a traumatic brain injury (TBI) each year, resulting in more than 235 000 hospitalizations and 50 000 deaths. An estimated 5.3 million Americans have current long-term disabilities as a result of TBI, which results in an estimated $60 billion in healthcare expenditures. Mild TBI (mTBI), which accounts for 80% to 90% of all cases, is the most prevalent form of brain injury in athletes. Many of these traumas still remain undetected, as they are difficult to diagnose. New biomarkers of TBI may allow more rapid diagnosis of TBI, improving early identification and treatment, and could help to predict clinical outcome. The field of TBI biomarkers is rapidly evolving. This chapter will discuss some of the most clinically relevant biomarkers for TBI that have been recently studied in human subjects.

CSF-biomarkers in Olympic boxing: diagnosis and effects of repetitive head trauma

Background

Sports-related head trauma is common but still there is no established laboratory test used in the diagnostics of minimal or mild traumatic brain injuries. Further the effects of recurrent head trauma on brain injury markers are unknown. The purpose of this study was to investigate the relationship between Olympic (amateur) boxing and cerebrospinal fluid (CSF) brain injury biomarkers.

Methods

The study was designed as a prospective cohort study. Thirty Olympic boxers with a minimum of 45 bouts and 25 non-boxing matched controls were included in the study. CSF samples were collected by lumbar puncture 1–6 days after a bout and after a rest period for at least 14 days. The controls were tested once. Biomarkers for acute and chronic brain injury were analysed.

Results

NFL (mean ± SD, 532±553 vs 135±51 ng/L p = 0.001), GFAP (496±238 vs 247±147 ng/L p<0.001), T-tau (58±26 vs 49±21 ng/L p<0.025) and S-100B (0.76±0.29 vs 0.60±0.23 ng/L p = 0.03) concentrations were significantly increased after boxing compared to controls. NFL (402±434 ng/L p = 0.004) and GFAP (369±113 ng/L p = 0.001) concentrations remained elevated after the rest period.

Conclusion

Increased CSF levels of T-tau, NFL, GFAP, and S-100B in >80% of the boxers demonstrate that both the acute and the cumulative effect of head trauma in Olympic boxing may induce CSF biomarker changes that suggest minor central nervous injuries. The lack of normalization of NFL and GFAP after the rest period in a subgroup of boxers may indicate ongoing degeneration. The recurrent head trauma in boxing may be associated with increased risk of chronic traumatic brain injury.

Characterisation of the effect of knockout of the amyloid precursor protein on outcome following mild traumatic brain injury

The amyloid precursor protein (APP) increases following traumatic brain injury (TBI), although the functional significance of this remains unclear largely because the functions of the subsequent APP metabolites are so different: Aβ is neurotoxic whilst sAPPα is neuroprotective. To investigate this further, APP wildtype and knockout mice were subjected to mild diffuse TBI and their outcomes compared. APP knockout mice displayed significantly worse cognitive and motor deficits, as demonstrated by the Barnes Maze and rotarod respectively, than APP wildtype mice. This was associated with a significant increase in hippocampal and cortical cell loss, as well as axonal injury, in APP knockout mice and an impaired neuroreparative response as indicated by diminished GAP-43 immunoreactivity when compared to APP wildtype mice. This study is the first to demonstrate that endogenous APP is beneficial following mild TBI, suggesting that the upregulation of APP observed following injury is an acute protective response.

Tau elevations in the brain extracellular space correlate with reduced amyloid-β levels and predict adverse clinical outcomes after severe traumatic brain injury

Axonal injury is believed to be a major determinant of adverse outcomes following traumatic brain injury. However, it has been difficult to assess acutely the severity of axonal injury in human traumatic brain injury patients. We hypothesized that microdialysis-based measurements of the brain extracellular fluid levels of tau and neurofilament light chain, two low molecular weight axonal proteins, could be helpful in this regard. To test this hypothesis, 100 kDa cut-off microdialysis catheters were placed in 16 patients with severe traumatic brain injury at two neurological/neurosurgical intensive care units. Tau levels in the microdialysis samples were highest early and fell over time in all patients. Initial tau levels were >3-fold higher in patients with microdialysis catheters placed in pericontusional regions than in patients in whom catheters were placed in normal-appearing right frontal lobe tissue (P = 0.005). Tau levels and neurofilament light-chain levels were positively correlated (r = 0.6, P = 0.013). Neurofilament light-chain levels were also higher in patients with pericontusional catheters (P = 0.04). Interestingly, initial tau levels were inversely correlated with initial amyloid-β levels measured in the same samples (r = -0.87, P = 0.000023). This could be due to reduced synaptic activity in areas with substantial axonal injury, as amyloid-β release is closely coupled with synaptic activity. Importantly, high initial tau levels correlated with worse clinical outcomes, as assessed using the Glasgow Outcome Scale 6 months after injury (r = -0.6, P = 0.018). Taken together, our data add support for the hypothesis that axonal injury may be related to long-term impairments following traumatic brain injury. Microdialysis-based measurement of tau levels in the brain extracellular space may be a useful way to assess the severity of axonal injury acutely in the intensive care unit. Further studies with larger numbers of patients will be required to assess the reproducibility of these findings and to determine whether this approach provides added value when combined with clinical and radiological information.

The association between apolipoprotein E and traumatic brain injury severity and functional outcome in a rehabilitation sample

Traumatic brain injury (TBI) can result in significant disability, but outcome is variable. The impact of known predictors accounts for a limited proportion of the variance in outcomes. Apolipoprotein E (ApoE) genotype has been investigated as an additional source of variability in injury severity and outcome, with mixed findings reflecting variable methodology and generally limited sample sizes. This study aimed to examine whether possession of the ApoE ɛ4 allele was associated with greater acute injury severity and poorer long-term outcome in patients referred for rehabilitation following TBI. ApoE genotype was determined for 648 patients with TBI, who were prospectively followed up a mean of 1.9 years post-injury. Hypotheses that ɛ4 carriers would have lower Glasgow Coma Scale (GCS) scores and longer post-traumatic amnesia (PTA) duration were not supported. Prediction of worse Glasgow Outcome Scale-Extended (GOSE) scores for ɛ4 carriers was supported with greater susceptibility seen in females. These results indicate the ApoE ɛ4 allele may be associated with poorer long-term outcome, but not acute injury severity. Possible mechanisms include differential effects of the ɛ4 allele on inflammatory and cellular repair processes, and/or amyloid deposition.

Traumatic brain injury and amyloid-β pathology: a link to Alzheimer's disease?

Traumatic brain injury (TBI) has devastating acute effects and in many cases seems to initiate long-term neurodegeneration. Indeed, an epidemiological association between TBI and the development of Alzheimer's disease (AD) later in life has been demonstrated, and it has been shown that amyloid-β (Aβ) plaques — one of the hallmarks of AD — may be found in patients within hours following TBI. Here, we explore the mechanistic underpinnings of the link between TBI and AD, focusing on the hypothesis that rapid Aβ plaque formation may result from the accumulation of amyloid precursor protein in damaged axons and a disturbed balance between Aβ genesis and catabolism following TBI.

Apolipoprotein E and central nervous system disorders: reviews of clinical findings

Dementia is a major health problem in developed countries with over 25 million people affected worldwide and probably over 75 million people at risk during the next 20 years. Alzheimer's disease (AD) is the most frequent cause of dementia (50-70%), followed by vascular dementia (30-40%), and mixed dementia (15-20%). AD pathogenesis is still to be elucidated but it is believed to be the complex interaction between genetic and environmental factors in later life. Three causative genes for familial AD have been identified: amyloid precursor protein, presenilin-1, and presenilin-2. There are 150 genes involved with increased neuronal vulnerability to premature death in the AD brain. Among these susceptibility genes, the apolipoprotein E (ApoE) gene is the most prevalent as a risk for AD pathogenic process in which complex interactions between genetic and environmental factors are involved, leading to a cascade of pathogenic events converging in final pathways to premature neuronal death. Some of these mechanisms are common to several neurodegenerative disorders that differ depending upon the genes affected and the involvement of environmental conditions. ApoE is a key lipoprotein in lipid and cholesterol metabolism and it is also the major risk gene for AD and many other central nervous system disorders. The pathogenic role of ApoE-4 is still to be clarified; however, diverse evidence suggests that ApoE may play pleiotropic functions in dementia and central nervous system disorders.

Update on protein biomarkers in traumatic brain injury with emphasis on clinical use in adults and pediatrics

PURPOSE

This review summarizes protein biomarkers in mild and severe traumatic brain injury in adults and children and presents a strategy for conducting rationally designed clinical studies on biomarkers in head trauma.

METHODS

We performed an electronic search of the National Library of Medicine's MEDLINE and Biomedical Library of University of Pennsylvania database in March 2008 using a search heading of traumatic head injury and protein biomarkers. The search was focused especially on protein degradation products (spectrin breakdown product, c-tau, amyloid-beta(1-42)) in the last 10 years, but recent data on "classical" markers (S-100B, neuron-specific enolase, etc.) were also examined.

RESULTS

We identified 85 articles focusing on clinical use of biomarkers; 58 articles were prospective cohort studies with injury and/or outcome assessment.

CONCLUSIONS

We conclude that only S-100B in severe traumatic brain injury has consistently demonstrated the ability to predict injury and outcome in adults. The number of studies with protein degradation products is insufficient especially in the pediatric care. Cohort studies with well-defined end points and further neuroproteomic search for biomarkers in mild injury should be triggered. After critically reviewing the study designs, we found that large homogenous patient populations, consistent injury, and outcome measures prospectively determined cutoff values, and a combined use of different predictors should be considered in future studies.

Monitoring of brain interstitial total tau and beta amyloid proteins by microdialysis in patients with traumatic brain injury

OBJECT

Damage to axons contributes to postinjury disabilities and is commonly observed following traumatic brain injury (TBI). Traumatic brain injury is an important environmental risk factor for the development of Alzheimer disease (AD). In the present feasibility study, the aim was to use intracerebral microdialysis catheters with a high molecular cutoff membrane (100 kD) to harvest interstitial total tau (T-tau) and amyloid beta 1-42 (Abeta42) proteins, which are important biomarkers for axonal injury and for AD, following moderate-to-severe TBI.

METHODS

Eight patients (5 men and 3 women) were included in the study; 5 of the patients had a focal/mixed TBI and 3 had a diffuse axonal injury (DAI). Following the bedside analysis of the routinely measured energy metabolic markers (that is, glucose, lactate/pyruvate ratio, glycerol, and glutamate), the remaining dialysate was pooled and two 12-hour samples per day were used to analyze T-tau and Abeta42 by enzyme-linked immunosorbent assay from Day 1 up to 8 days postinjury.

RESULTS

The results show high levels of interstitial T-tau and Abeta42 postinjury. Patients with a predominantly focal lesion had higher interstitial T-tau levels than in the DAI group from Days 1 to 3 postinjury (p < 0.05). In contrast, patients with DAI had consistently higher Abeta42 levels when compared with patients with focal injury.

CONCLUSIONS

These results suggest that monitoring of interstitial T-tau and Abeta42 by using microdialysis may be an important tool when evaluating the presence and role of axonal injury following TBI.

Apolipoprotein E polymorphism and gender difference in outcome after severe traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is one of the most common causes of death and dismal outcome among children and young adults. The morbidity and mortality differ but more aggressive monitoring and more designated neuro intensive care units have improved the results. Studies have demonstrated a connection between apolipoprotein E (APOE) genotype and outcome after TBI, but few are prospective and none is from northern Europe. APOE has three alleles: epsilon2, epsilon3 and epsilon4.

METHODS

A total of 96 patients with Glasgow coma score (GCS) < or =8 were prospectively and consecutively included. APOE genotypes were all analyzed at the same laboratory from blood samples by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

All patients were assessed at 1 year with Glasgow outcome scale extended (GOSE), National Institute of Health Stroke Scale (NIHSS) and the Barthel daily living index. The genotype was available in all patients. Twenty-six patients expressed APOE epsilon4 while 70 patients did not. Outcome demonstrated that patients with APOE epsilon4 had worse outcome vs. those lacking this allele. When subdividing patients into gender, males with APOE epsilon4 did worse, a difference not detected among female patients.

CONCLUSIONS

APOE epsilon4 correlated to worse outcome in TBI patients. We also found that males with APOE epsilon4 had poor outcome while females did not. Thus, the results indicate that genetic polymorphism may influence outcome after TBI.

Cerebrospinal fluid markers before and after shunting in patients with secondary and idiopathic normal pressure hydrocephalus

Background

The aim of this study was to explore biochemical changes in the cerebrospinal fluid (CSF) induced by shunt surgery and the relationship between these changes and clinical improvement.

Methods

We measured clinical symptoms and analysed lumbar CSF for protein content, neurodegeneration and neurotransmission markers in patients with secondary (SNPH, n = 17) and idiopathic NPH (INPH, n = 18) before and 3 months after shunt surgery. Patients were divided into groups according to whether or not there was improvement in clinical symptoms after surgery.

Results

Preoperatively, the only pathological findings were elevated neurofilament protein (NFL), significantly more so in the SNPH patients than in the INPH patients, and elevated albumin content. Higher levels of NFL correlated with worse gait, balance, wakefulness and neuropsychological performance. Preoperatively, no differences were seen in any of the CSF biomarkers between patients that improved after surgery and those that did not improve. Postoperatively, a greater improvement in gait and balance performance correlated with a more pronounced reduction in NFL. Levels of albumin, albumin ratio, neuropeptide Y, vasoactive intestinal peptide and ganglioside GD3 increased significantly after shunting in both groups. In addition, Gamma amino butyric acid increased significantly in SNPH and tau in INPH.

Conclusion

We conclude that a number of biochemical changes occur after shunt surgery, but there are no marked differences between the SNPH and INPH patients. The results indicate that NFL may be a marker that can predict a surgically reversible state in NPH.

Proteomic identification of biomarkers in the cerebrospinal fluid in a rat model of nigrostriatal dopaminergic degeneration

We have performed proteomic analysis in the cerebrospinal fluid in an animal model of Parkinson's disease induced by axotomy of the medial forebrain bundle. In this model, the degeneration of dopaminergic neurons was completed in 14 days, with a loss of about 50% dopaminergic neurons in the substantia nigra and a loss of more than 80% dopamine terminals in the striatum, with a similar diminution of dopamine levels in both structures. Proteins were separated by 2D electrophoresis and identified by matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF). We found significant increases of haptoglobin and transthyretin along with a decrease of Apo E concentrations in the cerebrospinal fluid of axotomized animals. Changes for haptoglobin and transthyretin were further confirmed in cerebrospinal fluid and plasma by Western blotting. These results suggest that monitoring plasma levels of these signals appears to be a promising biological marker of neuronal degeneration of the nigrostriatal dopaminergic system.

The association between APOE ε4, age and outcome after head injury: a prospective cohort study

Previous preliminary studies have suggested that possession of the APOE epsilon4 allele is associated with a poor outcome after head injury. This study was designed to confirm and extend those observations in a larger study with examination of additional variables. We prospectively identified admissions to a Neurosurgical Unit for head injury, collected demographic and clinical data, determined APOE genotypes and obtained follow-up information at 6 months. A total of 1094 subjects were enrolled (age range: 0-93 years, mean 37 years). Outcome was assessed using the Glasgow Outcome Scale. There was no overall association between APOE genotype and outcome, with 36% of APOE epsilon4 carriers having an unfavourable outcome compared with 33% of non-carriers of APOE epsilon4. However, there was evidence of an interaction between age and APOE genotype on outcome (P = 0.007) such that possession of APOE epsilon4 reduced the prospect of a favourable outcome in children and young adults. The influence of APOE genotype in younger patients after head injury can be expressed as, at age <15 years, carriage of APOE epsilon4 being equivalent to ageing by 25 years. This finding is consistent with experimental data suggesting that the effect of APOE genotype on outcome after head injury may be expressed through the processes of repair and recovery.

Quantification of apolipoprotein E receptors in human brain-derived cell lines by real-time polymerase chain reaction

Apolipoprotein (apo) E4 is a risk factor for Alzheimer's disease (AD) and other neurodegenerative diseases, compared to wild-type apoE3. The mechanism(s) is unknown. One possibility, demonstrated in peripheral tissue cell lines, is that apoE stimulates nitric oxide synthase (NOS) via a receptor-dependent signalling pathway and that apoE4 generates inappropriate amounts of nitric oxide (NO) compared to apoE3. Prior to biochemical investigations, we have quantified the expression of several candidate receptor genes, including low-density lipoprotein-receptor (LDL-r) family members and scavenger receptor class B, types I and II (SR-BI/II), as well as the three NOS isoenzymes and protein kinase B (Akt), in 38 human cell lines, of which 12 derive from brain. Expression of apoE receptor 2 (apoER2), a known signalling receptor in brain, was readily detected in SH-SY-5Y and CCF-STTG1 cells, common models of neurons and astrocytes, respectively, and was highest in H4 neuroglioma, NT-2 precursor cells and IMR-32 neuroblastoma cells. Transcripts of the other lipoprotein receptors were widely, but variably, distributed across the different cell types. Of particular note was the predominant expression of SR-BII over SR-BI in many of the brain-derived cells. As the C-terminus of SR-BII, like apoER2, contains potential SH3 signalling motifs, we suggest that in brain SR-BII functions as a signal transducer receptor.

Lateral fluid percussion brain injury: a 15-year review and evaluation

This article comprehensively reviews the lateral fluid percussion (LFP) model of traumatic brain injury (TBI) in small animal species with particular emphasis on its validity, clinical relevance and reliability. The LFP model, initially described in 1989, has become the most extensively utilized animal model of TBI (to date, 232 PubMed citations), producing both focal and diffuse (mixed) brain injury. Despite subtle variations in injury parameters between laboratories, universal findings are evident across studies, including histological, physiological, metabolic, and behavioral changes that serve to increase the reliability of the model. Moreover, demonstrable histological damage and severity-dependent behavioral deficits, which partially recover over time, validate LFP as a clinically-relevant model of human TBI. The LFP model, also has been used extensively to evaluate potential therapeutic interventions, including resuscitation, pharmacologic therapies, transplantation, and other neuroprotective and neuroregenerative strategies. Although a number of positive studies have identified promising therapies for moderate TBI, the predictive validity of the model may be compromised when findings are translated to severely injured patients. Recently, the clinical relevance of LFP has been enhanced by combining the injury with secondary insults, as well as broadening studies to incorporate issues of gender and age to better approximate the range of human TBI within study design. We conclude that the LFP brain injury model is an appropriate tool to study the cellular and mechanistic aspects of human TBI that cannot be addressed in the clinical setting, as well as for the development and characterization of novel therapeutic interventions. Continued translation of pre-clinical findings to human TBI will enhance the predictive validity of the LFP model, and allow novel neuroprotective and neuroregenerative treatment strategies developed in the laboratory to reach the appropriate TBI patients.

Common patterns of bcl-2 family gene expression in two traumatic brain injury models

Cell death/survival following traumatic brain injury (TBI) may be a result of alterations in the intracellular ratio of death and survival factors. Bcl-2 family genes mediate both cell survival and the initiation of cell death. Using lysate RNase protection assays, mRNA expression of the anti-cell death genes Bcl-2 and Bcl-xL, and the pro-cell death gene Bax, was evaluated following experimental brain injuries in adult male Sprague-Dawley rats. Both the lateral fluid-percussion (LFP) and the lateral controlled cortical impact (LCI) models of TBI showed similar patterns of gene expression. Anti-cell death bcl-2 and bcl-xL mRNAs were attenuated early and tended to remain depressed for at least 3 days after injury in the cortex and hippocampus ipsilateral to injury. Pro-cell death bax mRNA was elevated in these areas, usually following the decrease in anti-cell death genes. These common patterns of gene expression suggest an important role for Bcl-2 genes in cell death and survival in the injured brain. Understanding the regulation of these genes may facilitate the development of new therapeutic strategies for a condition that currently has no proven pharmacologic treatments.