Temporally resolved differential proteomic analysis of human ventricular CSF for monitoring traumatic brain injury biomarker candidates

Research progress in the application of proteomics technology in brain injury

The aim of this article is to review the application progress of proteomics technology in brain injury research in recent years, point out the current problems that need to be overcome, and explore the application prospects of proteomics analysis in brain injury. This study also aims to retrieve all literature on brain injury and proteomics and summarize it. Through searching and screening, the widespread application of proteomics technology in the treatment of traumatic brain injury (TBI) and the use of a large number of TBI biomarkers were discovered. The pathways mediated by some biomarkers and the physiological and pathological mechanisms of occurrence were elucidated. The current classification of brain injury is mainly based on subjective evaluation of clinical symptoms, combined with objective imaging. However, its practical value is often limited when applied to prognosis evaluation in brain injury. Proteomics technology can make up for this deficiency and provide a reference for the prevention and treatment of brain injury.

Time-Dependent Changes in the Biofluid Levels of Neural Injury Markers in Severe Traumatic Brain Injury Patients-Cerebrospinal Fluid and Cerebral Microdialysates: A Longitudinal Prospective Pilot Study

Monitoring protein biomarker levels in the cerebrospinal fluid (CSF) can help assess injury severity and outcome after traumatic brain injury (TBI). Determining injury-induced changes in the proteome of brain extracellular fluid (bECF) can more closely reflect changes in the brain parenchyma, but bECF is not routinely available. The aim of this pilot study was to compare time-dependent changes of S100 calcium-binding protein B (S100B), neuron-specific enolase (NSE), total Tau, and phosphorylated Tau (p-Tau) levels in matching CSF and bECF samples collected at 1, 3, and 5 days post-injury from severe TBI patients (n = 7; GCS 3-8) using microcapillary-based western analysis. We found that time-dependent changes in CSF and bECF levels were most pronounced for S100B and NSE, but there was substantial patient-to-patient variability. Importantly, the temporal pattern of biomarker changes in CSF and bECF samples showed similar trends. We also detected two different immunoreactive forms of S100B in both CSF and bECF samples, but the contribution of the different immunoreactive forms to total immunoreactivity varied from patient to patient and time point to time point. Our study is limited, but it illustrates the value of both quantitative and qualitative analysis of protein biomarkers and the importance of serial sampling for biofluid analysis after severe TBI.

The Cerebrospinal Fluid Proteomic Response to Traumatic and Nontraumatic Acute Brain Injury: A Prospective Study

BACKGROUND

Quantitative analysis of ventricular cerebrospinal fluid (vCSF) proteins following acute brain injury (ABI) may help identify pathophysiological pathways and potential biomarkers that can predict unfavorable outcome.

METHODS

In this prospective proteomic analysis study, consecutive patients with severe ABI expected to require intraventricular catheterization for intracranial pressure (ICP) monitoring for at least 5 days and patients without ABI admitted for elective clipping of an unruptured cerebral aneurysm were included. vCSF samples were collected within the first 24 h after ABI and ventriculostomy insertion and then every 24 h for 5 days. In patients without ABI, a single vCSF sample was collected at the time of elective clipping. Data-independent acquisition and sequential window acquisition of all theoretical spectra (SWATH) mass spectrometry were used to compare differences in protein expression in patients with ABI and patients without ABI and in patients with traumatic and nontraumatic ABI. Differences in protein expression according to different ICP values, intensive care unit outcome, subarachnoid hemorrhage (SAH) versus traumatic brain injury (TBI), and good versus poor 3-month functional status (assessed by using the Glasgow Outcome Scale) were also evaluated. vCSF proteins with significant differences between groups were compared by using linear models and selected for gene ontology analysis using R Language and the Panther database.

RESULTS

We included 50 patients with ABI (SAH n = 23, TBI n = 15, intracranial hemorrhage n = 6, ischemic stroke n = 3, others n = 3) and 12 patients without ABI. There were significant differences in the expression of 255 proteins between patients with and without ABI (p < 0.01). There were intraday and interday differences in expression of seven proteins related to increased inflammation, apoptosis, oxidative stress, and cellular response to hypoxia and injury. Among these, glial fibrillary acidic protein expression was higher in patients with ABI with severe intracranial hypertension (ICH) (ICP ≥ 30 mm Hg) or death compared to those without (log 2 fold change: + 2.4; p < 0.001), suggesting extensive primary astroglial injury or death. There were differences in the expression of 96 proteins between patients with traumatic and nontraumatic ABI (p < 0.05); intraday and interday differences were observed for six proteins related to structural damage, complement activation, and cholesterol metabolism. Thirty-nine vCSF proteins were associated with an increased risk of severe ICH (ICP ≥ 30 mm Hg) in patients with traumatic compared with nontraumatic ABI (p < 0.05). No significant differences were found in protein expression between patients with SAH versus TBI or between those with good versus poor 3-month Glasgow Outcome Scale score.

CONCLUSIONS

Dysregulated vCSF protein expression after ABI may be associated with an increased risk of severe ICH and death.

A nomogram based on serum cystatin C for predicting acute kidney injury in patients with traumatic brain injury

BACKGROUND

Acute kidney injury (AKI) is a common complication in traumatic brain injury (TBI) patients and is associated with unfavorable outcome of these patients. We designed this study to explore the value of serum cystatin C, an indicator of renal function, on predicting AKI after suffering TBI.

METHODS

Patients confirmed with TBI and hospitalized in the West China Hospital of Sichuan University between January 2015 and December 2019 were included. Patients were divided into two groups according to occurrence of AKI. Univariate and multivariate logistic regression analyses were sequentially utilized to find risk factors of AKI in included TBI patients. Nomogram composed of discovered risk factors for predicting AKI was constructed. Receiver operating characteristics (ROC) curves were drawn and area under the ROC curve (AUC) were calculated to evaluate the predictive value of cystatin C alone and the constructed nomogram.

RESULTS

Among 234 included TBI patients, 55 were divided into AKI group. AKI group had shorter length of stay (p < 0.001) and higher in-hospital mortality (p < 0.001). Multivariate logistic regression analysis showed absolute lymphocyte count (p = 0.034), serum creatinine (p < 0.001), serum cystatin C (p = 0.017) and transfusion of red blood cell (p = 0.005) were independently associated with development of AKI after TBI. While hypertonic saline use was not associated with the development of AKI (p = 0.067). The AUC of single cystatin C and predictive nomogram were 0.804 and 0.925, respectively.

CONCLUSION

Higher serum cystatin C is associated with development of AKI in TBI patients. Predictive nomogram incorporating cystatin C is beneficial for physicians to evaluate possibilities of AKI and consequently adjust treatment strategies to avoid occurrence of AKI.

Integrative Neuroinformatics for Precision Prognostication and Personalized Therapeutics in Moderate and Severe Traumatic Brain Injury

Despite changes in guideline-based management of moderate/severe traumatic brain injury (TBI) over the preceding decades, little impact on mortality and morbidity have been seen. This argues against the "one-treatment fits all" approach to such management strategies. With this, some preliminary advances in the area of personalized medicine in TBI care have displayed promising results. However, to continue transitioning toward individually-tailored care, we require integration of complex "-omics" data sets. The past few decades have seen dramatic increases in the volume of complex multi-modal data in moderate and severe TBI care. Such data includes serial high-fidelity multi-modal characterization of the cerebral physiome, serum/cerebrospinal fluid proteomics, admission genetic profiles, and serial advanced neuroimaging modalities. Integrating these complex and serially obtained data sets, with patient baseline demographics, treatment information and clinical outcomes over time, can be a daunting task for the treating clinician. Within this review, we highlight the current status of such multi-modal omics data sets in moderate/severe TBI, current limitations to the utilization of such data, and a potential path forward through employing integrative neuroinformatic approaches, which are applied in other neuropathologies. Such advances are positioned to facilitate the transition to precision prognostication and inform a top-down approach to the development of personalized therapeutics in moderate/severe TBI.

Fluid proteomics of CSF and serum reveal important neuroinflammatory proteins in blood-brain barrier disruption and outcome prediction following severe traumatic brain injury: a prospective, observational study

BACKGROUND

Severe traumatic brain injury (TBI) is associated with blood-brain barrier (BBB) disruption and a subsequent neuroinflammatory process. We aimed to perform a multiplex screening of brain enriched and inflammatory proteins in blood and cerebrospinal fluid (CSF) in order to study their role in BBB disruption, neuroinflammation and long-term functional outcome in TBI patients and healthy controls.

METHODS

We conducted a prospective, observational study on 90 severe TBI patients and 15 control subjects. Clinical outcome data, Glasgow Outcome Score, was collected after 6-12 months. We utilized a suspension bead antibody array analyzed on a FlexMap 3D Luminex platform to characterize 177 unique proteins in matched CSF and serum samples. In addition, we assessed BBB disruption using the CSF-serum albumin quotient (QA), and performed Apolipoprotein E-genotyping as the latter has been linked to BBB function in the absence of trauma. We employed pathway-, cluster-, and proportional odds regression analyses. Key findings were validated in blood samples from an independent TBI cohort.

RESULTS

TBI patients had an upregulation of structural CNS and neuroinflammatory pathways in both CSF and serum. In total, 114 proteins correlated with QA, among which the top-correlated proteins were complement proteins. A cluster analysis revealed protein levels to be strongly associated with BBB integrity, but not carriage of the Apolipoprotein E4-variant. Among cluster-derived proteins, innate immune pathways were upregulated. Forty unique proteins emanated as novel independent predictors of clinical outcome, that individually explained ~ 10% additional model variance. Among proteins significantly different between TBI patients with intact or disrupted BBB, complement C9 in CSF (p = 0.014, ΔR2 = 7.4%) and complement factor B in serum (p = 0.003, ΔR2 = 9.2%) were independent outcome predictors also following step-down modelling.

CONCLUSIONS

This represents the largest concomitant CSF and serum proteomic profiling study so far reported in TBI, providing substantial support to the notion that neuroinflammatory markers, including complement activation, predicts BBB disruption and long-term outcome. Individual proteins identified here could potentially serve to refine current biomarker modelling or represent novel treatment targets in severe TBI.

Serum cystatin C was a marker of poststroke fatigue in hypertensive intracerebral hemorrhage

INTRODUCTION

The relationship between poststroke fatigue (PSF) and serum Cystatin C (Cys-C) levels in hypertensive intracerebral hemorrhage (HICH) patients has not been determined. In this study, we investigated the association between serum Cys-C levels and PSF in HICH patients.

METHODS

A total of 125 patients with HICH were enrolled. Fatigue assessment was performed 6 months after HICH onset. The presence of PSF was defined as Fatigue Severity Scale (FSS) of 4 or more. Serum Cys-C levels were measured within 24 hr after admission. The correlation between FSS score and Cys-C level was analyzed by Spearman's correlation. Receiver operating characteristic (ROC) curves for PSF were calculated using Cys-C values.

RESULTS

Of enrolled 125 patients in the study, 36.0% who developed PSF were divided to the PSF group, which had higher Cys-C levels compared with the no-PSF group. There was significant positive correlation between FSS score and serum Cys-C level. Receiver operating characteristic curves for PSF revealed an area under the curve of 0.86 for Cys-C. High admission Cys-C (>0.75mg/L) yielded specificity of 93.7%, positive predictive value of 87.5%, and negative predictive value of 88.2%. In multivariate analysis, Cys-C increased by 1 mg/dl (0.1 mg/L), and the risk of PSF in patients increased by 2.55 times (odds ratio = 2.55, 95% CI: 1.65-3.95, p < .001).

CONCLUSIONS

High Cys-C levels have predictive value for PSF and can be used as one screening indicator for PSF occurrence.

Metabolomics in postmortem cerebrospinal fluid diagnostics: a state-of-the-art method to interpret central nervous system-related pathological processes

In the last few years, quantitative analysis of metabolites in body fluids using LC/MS has become an established method in laboratory medicine and toxicology. By preparing metabolite profiles in biological specimens, we are able to understand pathophysiological mechanisms at the biochemical and thus the functional level. An innovative investigative method, which has not yet been used widely in the forensic context, is to use the clinical application of metabolomics. In a metabolomic analysis of 41 samples of postmortem cerebrospinal fluid (CSF) samples divided into cohorts of four different causes of death, namely, cardiovascular fatalities, isoIated torso trauma, traumatic brain injury, and multi-organ failure, we were able to identify relevant differences in the metabolite profile between these individual groups. According to this preliminary assessment, we assume that information on biochemical processes is not gained by differences in the concentration of individual metabolites in CSF, but by a combination of differently distributed metabolites forming the perspective of a new generation of biomarkers for diagnosing (fatal) TBI and associated neuropathological changes in the CNS using CSF samples.

Blood-Related Toxicity after Traumatic Brain Injury: Potential Targets for Neuroprotection

Emergency visits, hospitalizations, and deaths due to traumatic brain injury (TBI) have increased significantly over the past few decades. While the primary early brain trauma is highly deleterious to the brain, the secondary injury post-TBI is postulated to significantly impact mortality. The presence of blood, particularly hemoglobin, and its breakdown products and key binding proteins and receptors modulating their clearance may contribute significantly to toxicity. Heme, hemin, and iron, for example, cause membrane lipid peroxidation, generate reactive oxygen species, and sensitize cells to noxious stimuli resulting in edema, cell death, and increased morbidity and mortality. A wide range of other mechanisms such as the immune system play pivotal roles in mediating secondary injury. Effective scavenging of all of these pro-oxidant and pro-inflammatory metabolites as well as controlling maladaptive immune responses is essential for limiting toxicity and secondary injury. Hemoglobin metabolism is mediated by key molecules such as haptoglobin, heme oxygenase, hemopexin, and ferritin. Genetic variability and dysfunction affecting these pathways (e.g., haptoglobin and heme oxygenase expression) have been implicated in the difference in susceptibility of individual patients to toxicity and may be target pathways for potential therapeutic interventions in TBI. Ongoing collaborative efforts are required to decipher the complexities of blood-related toxicity in TBI with an overarching goal of providing effective treatment options to all patients with TBI.

Post-mortem cerebrospinal fluid diagnostics: cytology and immunocytochemistry method suitable for routine use to interpret pathological processes in the central nervous system

Due to its protected anatomical location, cerebrospinal fluid (CSF) is a very stable fluid which undergoes comparatively little change in the early post-mortem phase. While many immunohistochemical markers already established for clinical diagnostic issues in tissue samples obtained by biopsy could meanwhile be translated also to post-mortem tissue, no systematic immunocytochemical investigations have generally been conducted on post-mortem body fluids and for CSF specifically, have not been established at all. CSF as the fluid directly surrounding the brain should also be examined to allow a more detailed characterization of processes in the central nervous system. Comparing traumatized tissue and CSF can complete forensic assessment and complement neuropathological evaluation.

Post-mortem in situ stability of serum markers of cerebral damage and acute phase response

The aim of the given study was to test the in situ stability of biochemical markers of cerebral damage and acute phase response in the early post-mortem interval to assess their usability for forensic pathology. A monocentric, prospective study investigated post-mortem femoral venous blood samples at four time points obtained within 48 h post-mortem starting at the death of 20 deceased, using commercial immunoassays for the ten parameters: S100 calcium-binding protein B (S100B), glial fibrillary acidic protein (GFAP), neuron-specific enolase (NSE), brain-derived neurotrophic factor (BDNF), interleukin-6 (IL-6), C-reactive protein (CRP), procalcitonin (PCT), ferritin, soluble tumor necrosis factor receptor type 1 (sTNFR1), and lactate dehydrogenase (LDH). Significant changes in serum levels were observed only later than 2 h after death for all markers. Inter-laboratory comparability was high, and intra-assay precision was sufficient for most markers. Most of the biomarker levels depended on the severity of hemolysis and lipemia but were robust against freeze-thaw cycles. Serum levels increased with longer post-mortem intervals for S100B, NSE, ferritin, sTNFR1, and LDH (for all p < 0.001) but decreased over this period for CRP (p = 0.089) and PCT (p < 0.001). Largely unchanged median values were found for GFAP (p = 0.139), BDNF (p = 0.106), and IL-6 (p = 0.094). Serum levels of CRP (p = 0.059) and LDH (p = 0.109) did not differ significantly between the final ante-mortem (resuscitation) and the first post-mortem sample (moment of death). Collecting the post-mortem blood sample as soon as possible will reduce the influence of post-mortem blood changes. Serum GFAP for detection of cerebral damage as well as serum IL-6 and CRP as proof of acute phase response seemed to be preferable due to their in situ stability in the first 2 days after death.

Measurement of Cerebral Biomarkers Proving Traumatic Brain Injuries in Post-Mortem Body Fluids

Until now, it is impossible to identify a fatal traumatic brain injury (TBI) before post-mortem radiological investigations or an autopsy take place. It would be preferable to have an additional diagnostic tool such as post-mortem biochemistry to get greater insight into the pathological pathways and survival times after sustaining TBI. Cerebrospinal fluid (CSF) and serum samples of 84 autopsy cases were collected from forensic autopsies with post-mortem intervals (PMI) of up to 148 h. The cases were categorized into a fatal TBI case group (n = 42) and non-TBI controls (n = 42). The values of glial fibrillary acidic protein (GFAP), brain-derived neurotrophic factor (BDNF), and neutrophil gelatinase-associated lipocalin (NGAL) were analyzed by means of quantitative chemiluminescent multiplex immunoassays. The main results indicate that the usage of liquid samples with good macroscopic quality is more relevant for meaningful biomarker analyses than the length of the PMI. All three proteins were shown to differentiate TBI fatalities from the controls in CSF. In serum, only GFAP could be shown to be able to identify TBI cases. This study is the first approach to measure the three proteins together in CSF and serum in autopsy cases. Determined threshold values may differentiate between fatal TBI and control cases. The presented results emphasize the possible use of post-mortem biochemistry as a supplemental tool in everyday forensic routine.

Proteomic differences between focal and diffuse traumatic brain injury in human brain tissue

The early molecular response to severe traumatic brain injury (TBI) was evaluated using biopsies of structurally normal-appearing cortex, obtained at location for intracranial pressure (ICP) monitoring, from 16 severe TBI patients. Mass spectrometry (MS; label free and stable isotope dimethyl labeling) quantitation proteomics showed a strikingly different molecular pattern in TBI in comparison to cortical biopsies from 11 idiopathic normal pressure hydrocephalus patients. Diffuse TBI showed increased expression of peptides related to neurodegeneration (Tau and Fascin, p < 0.05), reduced expression related to antioxidant defense (Glutathione S-transferase Mu 3, Peroxiredoxin-6, Thioredoxin-dependent peroxide reductase; p < 0.05) and increased expression of potential biomarkers (e.g. Neurogranin, Fatty acid-binding protein, heart p < 0.05) compared to focal TBI. Proteomics of human brain biopsies displayed considerable molecular heterogeneity among the different TBI subtypes with consequences for the pathophysiology and development of targeted treatments for TBI.

Post-mortem biochemistry of NSE and S100B: A supplemental tool for detecting a lethal traumatic brain injury?

PURPOSE

Traumatic brain injury (TBI) is a very common entity that leads to numerous fatalities all over the world. Therefore, forensic pathologists are in desperate need of supplemental methodological tools for the diagnosis of TBI in everyday practice besides the standard autopsy. The present study determined post-mortem neuron specific enolase (NSE) and S100 calcium-binding protein B (S100B) levels as biological markers of an underlying TBI in autopsy cases.

METHODS

Paired serum and CSF samples of 92 fatalities were collected throughout routine autopsies. Afterwards, the marker levels were assessed using commercially available immunoassays (ECLIA, Roche Diagnostics). For statistical analysis, we compared the TBI cases to three control groups (sudden natural death by acute myocardial infarction, traumatic death without impact on the head, cerebral hypoxia). Moreover, the TBI cases were subdivided according to their survival time of the trauma. Brain specimens have been collected and stained immunohistochemically against the aforementioned proteins to illustrate their typical cellular staining patterns with an underlying TBI compared to non-TBI fatalities.

PRINCIPAL RESULTS

CSF NSE and S100B levels were elevated after TBI compared to all control groups (p < 0.001). Although this finding can already be investigated among the TBI cases dying immediately subsequent to the trauma, the marker levels in CSF increase with longer survival times until a peak level within the first three days after trauma. There is a strong correlation between both marker levels in CSF (r = 0.67). The presence or absence of cerebral tissue contusion following the initial trauma does not seem to affect the CSF levels of both proteins (p > 0.05). Post-mortem serum levels of both proteins were not elevated in TBI cases compared to controls (p > 0.05). Former elaborated cut-off values in CSF were confirmed and were only exceeded when a TBI survival time of at least 30 min was reached.

MAJOR CONCLUSIONS

The present results report that post-mortem NSE and S100B CSF levels are significantly elevated subsequent to a fatal TBI.

Acute phase response after fatal traumatic brain injury

An inflammatory response occurring after fatal traumatic brain injury (TBI) initiates time-dependent cascades of acute phase response. This may offer the potential to monitor postmortem biomarker levels of several pro-inflammatory cytokines to gain information about the cause of death and the trauma survival time. Cerebrospinal fluid (CSF) and serum samples were collected from forensic autopsies of 95 adult cadavers after postmortem intervals up to 6 days. The cases were divided according to their cause of death into fatal TBI (n = 46) with different survival times and age- and gender-matching non-TBI fatalities as controls (n = 49). Quantitative marker levels of interleukin-6 (IL-6), ferritin, soluble tumor necrosis factor receptor type 1, C-reactive protein, and lactate dehydrogenase were analyzed using immunoassays. Standardized statistical tests were performed to differentiate causes of death and survival time of TBI cases. The CSF IL-6, ferritin, and LDH levels after TBI were significantly higher than those in the controls (p < 0.001). Only serum IL-6 values showed comparable differences (p < 0.05). Both CSF and serum ferritin levels were discriminative between early and delayed death after TBI (p < 0.05). There were partly distinctive correlations between marker levels in both fluids with rising values after longer survival. There were up to moderate correlation between the marker levels and the postmortem interval due to postmortem hemolysis. However, neither CSF nor serum level ranges were affected by the age or gender of the subjects. This study is the first to measure all five proteins systematically in postmortem trauma cases. Ferritin and IL-6 proved themselves to be interesting postmortem biomarkers to provide specific information on the injury pattern and the survival time of traumatic fatalities. Such forensic investigations could serve as inexpensive and fast laboratory tests.

Quantitative Proteomic Study Reveals Up-Regulation of cAMP Signaling Pathway-Related Proteins in Mild Traumatic Brain Injury

Traumatic brain injury (TBI), as a neurological injury, becomes a leading cause of disability and mortality due to lacking effective therapy. About 75% of TBI is mild traumatic brain injury (mTBI). However, the complex molecular mechanisms underlying mTBI pathophysiology remains to be elucidated. In this study, iTRAQ-based quantitative proteomic approach was employed to measure temporal-global proteome changes of rat brain tissues from different time points (1 day, 7 day and 6 months) post single mTBI (smTBI) and repetitive mTBI (rmTBI). A total of 5169 proteins were identified, of which, 237 proteins were significantly changed between control rats and mTBI model rats. Fuzzy c-means (FCM) clustering analysis classified these 237 proteins into six clusters according to their temporal pattern of protein abundance. Functional bioinformatics analysis and protein-protein interaction (PPI) network mapping of these FCM clusters showed that phosphodiesterase 10A (Pde10a) and guanine nucleotide-binding protein G (olf) subunit alpha (Gnal) were the node proteins in the cAMP signaling pathway. Other biological processes, such as cell adhesion, autophagy, myelination, microtubule depolymerization and brain development, were also over-represented in FCM clusters. Further Western Blot experiments confirmed that Pde10a and Gnal were acutely up-regulated in severity-dependent manner by mTBI, but these two proteins could not be down-regulated to basal level at the time point of 6 months post repetitive mTBI. Our study demonstrated that different severity of mTBI cause significant temporal profiling change at the proteomic level and pointed out the cAMP signaling pathway-related proteins, Pde10a and Gnal, may play important roles in the pathogenesis and recovery of mTBI.

New astroglial injury-defined biomarkers for neurotrauma assessment

Traumatic brain injury (TBI) is an expanding public health epidemic with pathophysiology that is difficult to diagnose and thus treat. TBI biomarkers should assess patients across severities and reveal pathophysiology, but currently, their kinetics and specificity are unclear. No single ideal TBI biomarker exists. We identified new candidates from a TBI CSF proteome by selecting trauma-released, astrocyte-enriched proteins including aldolase C (ALDOC), its 38kD breakdown product (BDP), brain lipid binding protein (BLBP), astrocytic phosphoprotein (PEA15), glutamine synthetase (GS) and new 18-25kD-GFAP-BDPs. Their levels increased over four orders of magnitude in severe TBI CSF. First post-injury week, ALDOC levels were markedly high and stable. Short-lived BLBP and PEA15 related to injury progression. ALDOC, BLBP and PEA15 appeared hyper-acutely and were similarly robust in severe and mild TBI blood; 25kD-GFAP-BDP appeared overnight after TBI and was rarely present after mild TBI. Using a human culture trauma model, we investigated biomarker kinetics. Wounded (mechanoporated) astrocytes released ALDOC, BLBP and PEA15 acutely. Delayed cell death corresponded with GFAP release and proteolysis into small GFAP-BDPs. Associating biomarkers with cellular injury stages produced astroglial injury-defined (AID) biomarkers that facilitate TBI assessment, as neurological deficits are rooted not only in death of CNS cells, but also in their functional compromise.

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.

Association between apoptotic neural tissue and cell proliferation in the adult teleost brain

Injury to neuronal tissues in the central nervous system (CNS) of mammals results in neural degeneration and sometime leads to loss of function, whereas fish retain a remarkable potential for neuro-regeneration throughout life. Thus, understanding the mechanism of neuro-regeneration in fish CNS would be useful to improve the poor neuro-regenerative capability in mammals. In the present study, we characterized a neuro-regenerative process in the brain of a cichlid, tilapia, Oreochromis niloticus. Morphological observations showed that the damaged brain region (habenula) successfully regrew and reinnervated axonal projections by 60 days post-damage. A fluorescent carbocyanine tracer, DiI tracing revealed a recovery of the major neuronal projection from the regenerated habenula to the interpenduncular nucleus by 60 days post-damage. TUNEL assay showed a significant increase of apoptotic cells (~234%, P<0.01) at one day post-damage, while the number of bromodeoxyuridine (BrdU)-positive proliferative cells were significantly increased (~92%, P<0.05) at 7 days post-damage compared with sham-control fish. To demonstrate a potential role of apoptotic activity in the neuro-regeneration, effects of degenerative neural tissue on cell proliferation were examined in vivo. Implantation of detached neural but not non-neural tissues into the cranial cavity significantly (P<0.01) increased the number of BrdU-positive cells nearby the implantation regions at 3 days after the implantation. Furthermore, local injection of the protein extract and cerebrospinal fluid collected from injured fish brain significantly induced cell proliferation in the brain. These results suggest that factor(s) derived from apoptotic neural cells may play a critical role in the neuro-regeneration in teleost brain.

Current status of fluid biomarkers in mild traumatic brain injury

Mild traumatic brain injury (mTBI) affects millions of people annually and is difficult to diagnose. Mild injury is insensitive to conventional imaging techniques and diagnoses are often made using subjective criteria such as self-reported symptoms. Many people who sustain a mTBI develop persistent post-concussive symptoms. Athletes and military personnel are at great risk for repeat injury which can result in second impact syndrome or chronic traumatic encephalopathy. An objective and quantifiable measure, such as a serum biomarker, is needed to aid in mTBI diagnosis, prognosis, return to play/duty assessments, and would further elucidate mTBI pathophysiology. The majority of TBI biomarker research focuses on severe TBI with few studies specific to mild injury. Most studies use a hypothesis-driven approach, screening biofluids for markers known to be associated with TBI pathophysiology. This approach has yielded limited success in identifying markers that can be used clinically, additional candidate biomarkers are needed. Innovative and unbiased methods such as proteomics, microRNA arrays, urinary screens, autoantibody identification and phage display would complement more traditional approaches to aid in the discovery of novel mTBI biomarkers.

Traumatically injured astrocytes release a proteomic signature modulated by STAT3-dependent cell survival

Molecular markers associated with CNS injury are of diagnostic interest. Mechanical trauma generates cellular deformation associated with membrane permeability with unknown molecular consequences. We used an in vitro model of stretch-injury and proteomic analyses to determine protein changes in murine astrocytes and their surrounding fluids. Abrupt pressure-pulse stretching resulted in the rapid release of 59 astrocytic proteins with profiles reflecting cell injury and cell death, i.e., mechanoporation and cell lysis. This acute trauma-release proteome was overrepresented with metabolic proteins compared with the uninjured cellular proteome, bearing relevance for post-traumatic metabolic depression. Astrocyte-specific deletion of signal transducer and activator of transcription 3 (STAT3-CKO) resulted in reduced stretch-injury tolerance, elevated necrosis and increased protein release. Consistent with more lysed cells, more protein complexes, nuclear and transport proteins were released from STAT3-CKO versus nontransgenic astrocytes. STAT3-CKO astrocytes had reduced basal expression of GFAP, lactate dehydrogenase B (LDHB), aldolase C (ALDOC), and astrocytic phosphoprotein 15 (PEA15), and elevated levels of tropomyosin (TPM4) and α actinin 4 (ACTN4). Stretching caused STAT3-dependent cellular depletion of PEA15 and GFAP, and its filament disassembly in subpopulations of injured astrocytes. PEA15 and ALDOC signals were low in injured astrocytes acutely after mouse spinal cord crush injury and were robustly expressed in reactive astrocytes 1 day postinjury. In contrast, α crystallin (CRYAB) was present in acutely injured astrocytes, and absent from uninjured and reactive astrocytes, demonstrating novel marker differences among postinjury astrocytes. These findings reveal a proteomic signature of traumatically-injured astrocytes reflecting STAT3-dependent cellular survival with potential diagnostic value.

Quantitative proteomics analysis to identify diffuse axonal injury biomarkers in rats using iTRAQ coupled LC-MS/MS

Diffuse axonal injury (DAI) is fairly common during a traumatic brain injury (TBI) and is associated with high mortality. Making an early diagnosis, appropriate therapeutic decisions, and an accurate prognostic evaluation of patients with DAI still pose difficulties for clinicians. The detailed mechanisms of axonal injury after head trauma have yet to be clearly defined and no reliable biomarkers are available for early DAI diagnosis. Therefore, this study employed an established DAI animal model in conjunction with an isobaric tag for relative and absolute quantification (iTRAQ)-based protein identification/quantification approach. Alterations in rat cerebral protein expression were quantified using iTRAQ coupled LC-MS/MS, with differentially expressed proteins between the control groups, sham and sham-injured, and the injury groups, animals that died immediately post-injury and those sacrificed at 1h, 6h, 1d, 3d and 7d post-injury, identified. A total of 1858 proteins were identified and quantified and comparative analysis identified ten candidate proteins that warranted further examination. Of the ten candidate DAI biomarkers, four proteins, citrate synthase (CS), synaptosomal-associated protein 25 (Snap25), microtubule-associated protein 1B (MAP1B) and Rho-associated protein kinase 2 (Rock2), were validated by subsequent Western blot and immunohistochemistry analyses. Our studies not only identified several novel biomarkers that may provide insight into the pathophysiological mechanisms of DAI, but also demonstrated the feasibility of iTRAQ-based quantitative proteomic analysis in cerebral tissue research.

Bench-to-Bedside and Bedside Back to the Bench; Seeking a Better Understanding of the Acute Pathophysiological Process in Severe Traumatic Brain Injury

Despite substantial investments, traumatic brain injury (TBI) remains one of the major disorders that lack specific pharmacotherapy. To a substantial degree, this situation is due to lack of understanding of the pathophysiological process of the disease. Experimental TBI research offers controlled, rapid, and cost-effective means to identify the pathophysiology but translating experimental findings into clinical practice can be further improved by using the same or similar outcome measures and clinically relevant time points. The pathophysiology during the acute phase of severe TBI is especially poorly understood. In this Mini review, I discuss some of the incongruences between current clinical practices and needs versus information provided by experimental TBI research as well as the benefits of designing animal experiments with translation into clinical practice in mind.

Addressing the needs of traumatic brain injury with clinical proteomics

Background

Neurotrauma or injuries to the central nervous system (CNS) are a serious public health problem worldwide. Approximately 75% of all traumatic brain injuries (TBIs) are concussions or other mild TBI (mTBI) forms. Evaluation of concussion injury today is limited to an assessment of behavioral symptoms, often with delay and subject to motivation. Hence, there is an urgent need for an accurate chemical measure in biofluids to serve as a diagnostic tool for invisible brain wounds, to monitor severe patient trajectories, and to predict survival chances. Although a number of neurotrauma marker candidates have been reported, the broad spectrum of TBI limits the significance of small cohort studies. Specificity and sensitivity issues compound the development of a conclusive diagnostic assay, especially for concussion patients. Thus, the neurotrauma field currently has no diagnostic biofluid test in clinical use.

Content

We discuss the challenges of discovering new and validating identified neurotrauma marker candidates using proteomics-based strategies, including targeting, selection strategies and the application of mass spectrometry (MS) technologies and their potential impact to the neurotrauma field.

Summary

Many studies use TBI marker candidates based on literature reports, yet progress in genomics and proteomics have started to provide neurotrauma protein profiles. Choosing meaningful marker candidates from such ‘long lists’ is still pending, as only few can be taken through the process of preclinical verification and large scale translational validation. Quantitative mass spectrometry targeting specific molecules rather than random sampling of the whole proteome, e.g., multiple reaction monitoring (MRM), offers an efficient and effective means to multiplex the measurement of several candidates in patient samples, thereby omitting the need for antibodies prior to clinical assay design. Sample preparation challenges specific to TBI are addressed. A tailored selection strategy combined with a multiplex screening approach is helping to arrive at diagnostically suitable candidates for clinical assay development. A surrogate marker test will be instrumental for critical decisions of TBI patient care and protection of concussion victims from repeated exposures that could result in lasting neurological deficits.

S100B and NSE as useful postmortem biochemical markers of traumatic brain injury in autopsy cases

Postmortem analysis of relevant biomarkers might aid in characterizing causes of death and survival times in legal medicine. However, there are still no sufficiently established results of practical postmortem biochemical investigations in cases of traumatic brain injury (TBI). The two biomarkers--S100 protein subunit B (S100B) and neuronal specific enolase (NSE)--could be of special interest. Therefore, the aim of the present study was to investigate changes in their postmortem levels for further determination of brain damage in TBI. In 17 cases of TBI (average age, 58 years) and in 23 controls with different causes of death (average age, 59 years), serum and cerebrospinal fluid (CSF) samples were analyzed with a chemiluminescence immunoassay for marker expression. An increase in serum S100B, as well as a subsequent decrease after survival times>4 days, were detected in TBI cases (p<0.01). CSF NSE values >6,000 ng/mL and CSF S100B levels >10,000 ng/mL seem to indicate a TBI survival time of at least 15 min (p<0.01). It is of particular interest that CSF S100B levels (p<0.01) and serum S100B levels (p<0.05) as well as CSF NSE values (p<0.01) were significantly higher in TBI cases in comparison to the controls, especially when compared with fatal non-head injuries. In conclusion, the present findings emphasize that S100B and NSE are useful markers in postmortem biochemistry in cases of suspected TBI. Further, S100B may be helpful to estimate the survival time of fatal injuries in legal medicine.

Integration of proteomics, bioinformatics, and systems biology in traumatic brain injury biomarker discovery

Traumatic brain injury (TBI) is a major medical crisis without any FDA-approved pharmacological therapies that have been demonstrated to improve functional outcomes. It has been argued that discovery of disease-relevant biomarkers might help to guide successful clinical trials for TBI. Major advances in mass spectrometry (MS) have revolutionized the field of proteomic biomarker discovery and facilitated the identification of several candidate markers that are being further evaluated for their efficacy as TBI biomarkers. However, several hurdles have to be overcome even during the discovery phase which is only the first step in the long process of biomarker development. The high-throughput nature of MS-based proteomic experiments generates a massive amount of mass spectral data presenting great challenges in downstream interpretation. Currently, different bioinformatics platforms are available for functional analysis and data mining of MS-generated proteomic data. These tools provide a way to convert data sets to biologically interpretable results and functional outcomes. A strategy that has promise in advancing biomarker development involves the triad of proteomics, bioinformatics, and systems biology. In this review, a brief overview of how bioinformatics and systems biology tools analyze, transform, and interpret complex MS datasets into biologically relevant results is discussed. In addition, challenges and limitations of proteomics, bioinformatics, and systems biology in TBI biomarker discovery are presented. A brief survey of researches that utilized these three overlapping disciplines in TBI biomarker discovery is also presented. Finally, examples of TBI biomarkers and their applications are discussed.

Time-dependent changes of protein biomarker levels in the cerebrospinal fluid after blast traumatic brain injury

Time-dependent changes of protein biomarkers in the cerebrospinal fluid (CSF) can be used to identify the pathological processes in traumatic brain injury (TBI) as well as to follow the progression of the disease. We obtained CSF from a large animal model (swine) of blast-induced traumatic brain injury prior to and at 6, 24, 72 h, and 2 wk after a single exposure to blast overpressure, and determined changes in the CSF levels of neurofilament-heavy chain, neuron-specific enolase, brain-specific creatine kinase, glial fibrillary acidic protein, calcium-binding protein β (S100β), Claudin-5, vascular endothelial growth factor, and von Willebrand factor using reverse phase protein microarray. We detected biphasic temporal patterns in the CSF concentrations of all tested protein markers except S100β. The CSF levels of all markers were significantly increased 6 h after the injury compared to preinjury levels. Values were then decreased at 24 h, prior to a second increase in all markers but S100β at 72 h. At 2 wk postinjury, the CSF concentrations of all biomarkers were decreased once again; brain-specific creatine kinase, Claudin-5, von Willebrand factor, and S100β levels were no longer significantly higher than their preinjury values while neurofilament-heavy chain, neuron-specific enolase, vascular endothelial growth factor, and glial fibrillary acidic protein levels remained significantly elevated compared to baseline. Our findings implicate neuronal and glial cell damage, compromised vascular permeability, and inflammation in blast-induced traumatic brain injury, as well as demonstrate the value of determining the temporal pattern of biomarker changes that may be of diagnostic value.

Proteome analysis of human cerebrospinal fluid as a diagnostic biomarker in patients with meningioma

BACKGROUND

To identify meningioma-specific proteins, cerebrospinal fluid (CSF) from 4 patients with a meningioma and 4 patients with a non-brain tumorous lesion were analyzed.

MATERIAL/METHODS

Two-dimensional electrophoresis and electrospray quadrupole time-of-flight tandem mass spectrometry analyses revealed 10 unique spots, containing 11 independent proteins (spot #2 and #4 each contained 2 proteins and spot #3 was not identified) were evident in CSF associated with human meningioma: serum albumin precursor (3 different isoforms), Apolipoprotein E (Apo E), Apolipoprotein J precursor (Apo J), Transthyretin precursor (TTR), Prostaglandin D2 synthase 21 kDa (PTGDS), proapolipoprotein, Chain D hemoglobin Ypsilanti, alpha-1-antitrypsin (AAT), and beta-2-microglobulin precursor (β2M).

RESULTS

The contents of Apo E, Apo J and AAT were increased, while PTGDS, TTR and β2M were decreased.

CONCLUSIONS

The results observed by 2-dimensional electrophoresis were verified by Western blot analysis. The unique proteins may represent possible candidate biomarkers of meningioma.

High-capacity peptide-centric platform to decode the proteomic response to brain injury

Traumatic brain injury (TBI) is a progressive disease process underlain by dynamic and interactive biochemical mechanisms; thus, large-scale and unbiased assessments are needed to fully understand its highly complex pathobiology. Here, we report on a new high-capacity label-free proteomic platform to evaluate the post-TBI neuroproteome. Six orthogonal separation stages and data-independent MS were employed, affording reproducible quantitative assessment on 18 651 peptides across biological replicates. From these data 3587 peptides were statistically responsive to TBI of which 18% were post-translationally modified. Results revealed as many as 484 proteins in the post-TBI neuroproteome, which was fully nine times the number determined from our prior study of focal cortical injury. Yet, these data were generated using 25 times less brain tissue per animal relative to former methodology, permitting greater anatomical specificity and proper biological replication for increased statistical power. Exemplified by these data, we discuss benefits of peptide-centric differential analysis to more accurately infer novel biological findings testable in future hypothesis-driven research. The high-capacity label-free proteomic platform is designed for multi-factor studies aimed at expanding our knowledge on the molecular underpinnings of TBI and to develop better diagnostics and therapeutics.

Detection of structural and metabolic changes in traumatically injured hippocampus by quantitative differential proteomics

Traumatic brain injury (TBI) is a complex and common problem resulting in the loss of cognitive function. In order to build a comprehensive knowledge base of the proteins that underlie these cognitive deficits, we employed unbiased quantitative mass spectrometry, proteomics, and bioinformatics to identify and quantify dysregulated proteins in the CA3 subregion of the hippocampus in the fluid percussion model of TBI in rats. Using stable isotope 18O-water differential labeling and multidimensional tandem liquid chromatography (LC)-MS/MS with high stringency statistical analyses and filtering, we identified and quantified 1002 common proteins, with 124 increased and 76 decreased. The ingenuity pathway analysis (IPA) bioinformatics tool identified that TBI had profound effects on downregulating global energy metabolism, including glycolysis, the Krebs cycle, and oxidative phosphorylation, as well as cellular structure and function. Widespread upregulation of actin-related cytoskeletal dynamics was also found. IPA indicated a common integrative signaling node, calcineurin B1 (CANB1, CaNBα, or PPP3R1), which was downregulated by TBI. Western blotting confirmed that the calcineurin regulatory subunit, CANB1, and its catalytic binding partner PP2BA, were decreased without changes in other calcineurin subunits. CANB1 plays a critical role in downregulated networks of calcium signaling and homeostasis through calmodulin and calmodulin-dependent kinase II to highly interconnected structural networks dominated by tubulins. This large-scale knowledge base lays the foundation for the identification of novel therapeutic targets for cognitive rescue in TBI.

Clinical neuroproteomics and biomarkers: from basic research to clinical decision making

Clinical neuroproteomics aims to advance our understanding of disease and injury affecting the central and peripheral nervous systems through the study of protein expression and the discovery of protein biomarkers to facilitate diagnosis and treatment. The general premise of the biomarker field is that in vivo factors present in either tissue or circulating biofluids, reflect pathological changes, and can be identified and analyzed. This approach offers an opportunity to illuminate changes occurring at both the population and patient levels toward the realization of personalized medicine. This review is intended to provide research-driven clinicians with an overview of protein biomarkers of disease and injury for clinical use and to highlight methodology and potential pitfalls. We examine the neuroproteomic biomarker field and discuss the hallmarks and the challenges of clinically relevant biomarker discovery relating to central nervous system pathology. We discuss the issues in the maturation of potential biomarkers from discovery to Food and Drug Administration approval and review several platforms for protein biomarker discovery, including protein microarray and mass spectrometry-based proteomics. We describe the application of microfluidic technologies to the evolution of a robust clinical test. Finally, we highlight several biomarkers currently in use for cancer, ischemia, and injury in the central nervous system. Future efforts using these technologies will result in the maturation of existing and the identification of de novo biomarkers that could guide clinical decision making and advance diagnostic and therapeutic options for the treatment of neurological disease and injury.

Principal component analysis of the cytokine and chemokine response to human traumatic brain injury

There is a growing realisation that neuro-inflammation plays a fundamental role in the pathology of Traumatic Brain Injury (TBI). This has led to the search for biomarkers that reflect these underlying inflammatory processes using techniques such as cerebral microdialysis. The interpretation of such biomarker data has been limited by the statistical methods used. When analysing data of this sort the multiple putative interactions between mediators need to be considered as well as the timing of production and high degree of statistical co-variance in levels of these mediators. Here we present a cytokine and chemokine dataset from human brain following human traumatic brain injury and use principal component analysis and partial least squares discriminant analysis to demonstrate the pattern of production following TBI, distinct phases of the humoral inflammatory response and the differing patterns of response in brain and in peripheral blood. This technique has the added advantage of making no assumptions about the Relative Recovery (RR) of microdialysis derived parameters. Taken together these techniques can be used in complex microdialysis datasets to summarise the data succinctly and generate hypotheses for future study.

Proteomic analysis of cerebrospinal fluid in a fulminant case of multiple sclerosis

Multiple Sclerosis (MS) is a chronic disease, but in rare fulminant cases rapid progression may lead to death shortly after diagnosis. Currently there is no diagnostic test to predict disease course. The aim of this study was to identify potential biomarkers/proteins related to rapid progression. We present the case history of a 15-year-old male MS patient. Cerebrospinal fluid (CSF) was taken at diagnosis and at the time of rapid progression leading to the patient’s death. Using isobaric tag labeling and nanoflow liquid chromatography in conjunction with matrix assisted laser desorption/ionization time of flight tandem mass spectrometry we quantitatively analyzed the protein content of two CSF samples from the patient with fulminant MS as well as one relapsing-remitting (RR) MS patient and one control headache patient, whose CSF analysis was normal. Seventy-eight proteins were identified and seven proteins were found to be more abundant in both fulminant MS samples but not in the RR MS sample compared to the control. These proteins are involved in the immune response, blood coagulation, cell proliferation and cell adhesion. In conclusion, in this pilot study we were able to show differences in the CSF proteome of a rapidly progressing MS patient compared to a more typical clinical form of MS and a control subject.

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.

Multiplexed quantification of proteins adsorbed to surface-modified and non-modified microdialysis membranes

A simple and straightforward method for discovery and quantification of proteins adsorbed onto delicate and sensitive membrane surfaces is presented. The adsorbed proteins were enzymatically cleaved while still adsorbed onto the membranes using an on-surface enzymatic digestion (oSED). This was followed by isobaric tagging, nanoliquid chromatography, and tandem mass spectrometry. Protein adsorption on tri-block copolymer Poloxamer 407 surface-modified microdialysis (MD) membranes were compared with protein adsorption on unmodified MD membranes. Ventricular cerebrospinal fluid (vCSF) kept at 37 °C was used as sample matrix. In total, 19 proteins were quantified in two biological replicates. The surface-modified membranes adsorbed 33% less proteins than control membranes and the most abundant proteins were subunits of hemoglobin and clusterin. The adsorption of clusterin on the modified membranes was on average 36% compared to control membranes. The most common protein in vCSF, Albumin, was not identified adsorbed to the surface at all. It was also experimentally verified that oSED, in conjunction with tandem mass spectrometry can be used to quantify femtomole amounts of proteins adsorbed on limited and delicate surfaces, such as MD membranes. The method has great potential and can be used to study much more complex protein adsorption systems than previously reported.

Severe traumatic brain injury in children elevates glial fibrillary acidic protein in cerebrospinal fluid and serum

OBJECTIVES

1) To determine the levels of glial fibrillary acidic protein (GFAP) in both cerebrospinal fluid and serum; 2) to determine whether serum GFAP levels correlate with functional outcome; and 3) to determine whether therapeutic hypothermia, as compared with normothermia, alters serum GFAP levels in children with severe traumatic brain injury (TBI).

DESIGN

Laboratory-based analyses; postrandomized, controlled trial.

SETTING

Four Canadian pediatric intensive care units and a university-affiliated laboratory.

PATIENTS

Twenty-seven children, aged 2-17 yrs, with severe TBI (Glasgow Coma Scale score of ≤ 8).

INTERVENTIONS

Hypothermia therapy (32.5°C) for 24 hrs with cooling started within 8 hrs of injury and rewarming at a rate of 0.5°C every 2 hrs or normothermia (37.0°C).

MEASUREMENTS AND MAIN RESULTS

GFAP was measured in cerebrospinal fluid and serum, using enzyme-linked immunosorbent assay. Levels of GFAP were maximal on day 1 post-TBI, with cerebrospinal fluid GFAP (15.5 ± 6.1 ng/mL) 25-fold higher than serum GFAP (0.6 ± 0.2 ng/mL). Cerebrospinal fluid GFAP normalized by day 7, whereas serum GFAP decreased gradually to reach a steady state by day 10. Serum GFAP measured on day 1 correlated with Pediatric Cerebral Performance Category scores determined at 6 months post-TBI (ρ = 0.527; p = .008) but failed to correlate with the injury scoring on admission, physiologic variables, or indices of injury measured on computerized tomography imaging. The areas under the receiver operating characteristic curves for pediatric intensive care unit day 1 serum GFAP in determining good outcome were 0.80 (pediatric cerebral performance category, 1-2; normal-mild disability) and 0.91 (pediatric cerebral performance category, 1-3; normal-moderate disability). For a serum GFAP cutoff level of 0.6 ng/mL, sensitivity and specificity were 88% to 90% and 43% to 71%, respectively. Serum GFAP levels were similar among children randomized to either therapeutic hypothermia or normothermia.

CONCLUSIONS

GFAP was markedly elevated in cerebrospinal fluid and serum in children after severe TBI and serum GFAP measured on pediatric intensive care unit day 1 correlated with functional outcome at 6 months. Hypothermia therapy did not alter serum GFAP levels compared with normothermia after severe TBI in children. Serum GFAP concentration, together with other biomarkers, may have prognostic value after TBI in children.

Neuroproteomics: a biochemical means to discriminate the extent and modality of brain injury

Diagnosis and treatment of stroke and traumatic brain injury remain significant health care challenges to society. Patient care stands to benefit from an improved understanding of the interactive biochemistry underlying neurotrauma pathobiology. In this study, we assessed the power of neuroproteomics to contrast biochemical responses following ischemic and traumatic brain injuries in the rat. A middle cerebral artery occlusion (MCAO) model was employed in groups of 30-min and 2-h focal neocortical ischemia with reperfusion. Neuroproteomes were assessed via tandem cation-anion exchange chromatography-gel electrophoresis, followed by reversed-phase liquid chromatography-tandem mass spectrometry. MCAO results were compared with those from a previous study of focal contusional brain injury employing the same methodology to characterize homologous neocortical tissues at 2 days post-injury. The 30-min MCAO neuroproteome depicted abridged energy production involving pentose phosphate, modulated synaptic function and plasticity, and increased chaperone activity and cell survival factors. The 2-h MCAO data indicated near complete loss of ATP production, synaptic dysfunction with degraded cytoarchitecture, more conservative chaperone activity, and additional cell survival factors than those seen in the 30-min MCAO model. The TBI group exhibited disrupted metabolism, but with retained malate shuttle functionality. Synaptic dysfunction and cytoarchitectural degradation resembled the 2-h MCAO group; however, chaperone and cell survival factors were more depressed following TBI. These results underscore the utility of neuroproteomics for characterizing interactive biochemistry for profiling and contrasting the molecular aspects underlying the pathobiological differences between types of brain injuries.

Methodological aspects on microdialysis protein sampling and quantification in biological fluids: an in vitro study on human ventricular CSF

There is growing interest in sampling of protein biomarkers from the interstitial compartment of the brain and other organs using high molecular cutoff membrane microdialysis (MD) catheters. However, recent data suggest that protein sampling across such MD membranes is a highly complex process that needs to be further studied. Here, we report three major improvements for microdialysis sampling of proteins in complex biological matrixes. The improvements in this in vitro study using human ventricular cerebrospinal fluid as the sample matrix include increased fluid recovery control, decreased protein adsorption on the microdialysis membrane and materials, and novel quantitative mass spectrometry analysis. Dextrans in different concentrations and sizes were added to the perfusion fluid. It was found that dextrans with molecular mass 250 and 500 kDa provided a fluid recovery close to 100%. An improved fluid recovery precision could be obtained by self-assembly triblock polymer surface modification of the MD catheters. The modified catheters also delivered a significantly increased extraction efficiency for some of the investigated proteins. The final improvement was to analyze the dialysates with isobaric tagged (iTRAQ) proteomics, followed by tandem mass spectrometric analysis. By using this technique, 48 proteins could be quantified and analyzed with respect to their extraction efficiencies. The novel aspects of microdialysis protein sampling, detection, and quantification in biological fluids presented in this study should be considered as a first step toward better understanding and handling of the challenges associated with microdialysis sampling of proteins. The next step is to optimize the developed methodology in vivo.

Metabolic crisis after traumatic brain injury is associated with a novel microdialysis proteome

BACKGROUND

To examine if the metabolic distress after traumatic brain injury (TBI) is associated with a unique proteome.

METHODS

Patients with severe TBI prospectively underwent cerebral microdialysis for the initial 96 h after injury. Hourly sampling of metabolism was performed and patients were categorized as having normal or abnormal metabolism as evidenced by the lactate/pyruvate ratio (LPR) threshold of 40. The microdialysate was frozen for proteomic batch processing retrospectively. We employed two different routes of proteomic techniques utilizing mass spectrometry (MS) and categorized as diagnostic and biomarker identification approaches. The diagnostic approach was aimed at finding a signature of MS peaks which can differentiate these two groups. We did this by enriching for intact peptides followed by MALDI-MS analysis. For the biomarker identification approach, we applied classical bottom-up (trypsin digestion followed by LC-MS/MS) proteomic methodologies.

RESULTS

Five patients were studied, 3 of whom had abnormal metabolism and 2 who had normal metabolism. By comparison, the abnormal group had higher LPR (1609 +/- 3691 vs. 15.5 +/- 6.8, P < 0.001), higher glutamate (157 +/- 84 vs. 1.8 +/- 1.4 microM, P < 0.001), and lower glucose (0.27 +/- 0.35 vs. 1.8 +/- 1.1 mmol/l, P < 0.001). The abnormal group demonstrated 13 unique proteins as compared with the normal group in the microdialysate. These proteins consisted of cytoarchitectural proteins, as well as blood breakdown proteins, and a few mitochondrial proteins. A unique as yet to be characterized peptide was found at m/z (mass/charge) 4733.5, which may represent a novel biomarker of metabolic distress.

CONCLUSION

Metabolic distress after TBI is associated with a differential proteome that indicates cellular destruction during the acute phase of illness. This suggests that metabolic distress has immediate cellular consequences after TBI.

Confident assignment of intact mass tags to human salivary cystatins using top-down Fourier-transform ion cyclotron resonance mass spectrometry

A hybrid linear ion-trap Fourier-transform ion cyclotron resonance mass spectrometer was used for top-down characterization of the abundant human salivary cystatins, including S, S1, S2, SA, SN, C, and D, using collisionally activated dissociation (CAD) after chromatographic purification of the native, disulfide intact proteins. Post-translational modifications and protein sequence polymorphisms arising from single nucleotide polymorphisms (SNPs) were assigned from precursor and product ion masses at a tolerance of 10 ppm, allowing confident identification of individual intact mass tags. Cystatins S, S1, S2, SA, and SN were cleaved of a N-terminal 20 amino acid signal peptide and cystatin C a 26-residue peptide, to yield a generally conserved N-terminus. In contrast, cystatin D isoforms with 24 and 28 amino acid residue N-terminal truncations were found such that their N-termini were not conserved. Cystatin S1 was phosphorylated at Ser3, while S2 was phosphorylated at Ser1 and Ser3, in agreement with previous work. Both cystatin D isoforms carried the polymorphism C46R (SNP: rs1799841). The 14,328 Da isoform of cystatin SN previously assigned with polymorphism P31L due to a SNP (rs2070856) was found only in whole saliva. Parotid secretions contained no detectable cystatins while whole saliva largely mirrored the contents of submandibular/sublingual (SMSL) secretions. With fully characterized cystatin intact mass tags it will now be possible to examine the correlation between the abundance of these molecules and human health and disease.

Assessment of the partitioning capacity of high abundant proteins in human cerebrospinal fluid using affinity and immunoaffinity subtraction spin columns

The performance of three different affinity and immunoaffinity subtraction spin columns was investigated for the removal of the most abundant proteins in human cerebrospinal fluid (CSF). A pool of human CSF was processed with the spin columns and both the bound and flow through fractions were compared with each other and with intact CSF using 1D gel electrophoresis and nanoLC-MALDI-TOF/TOF-MS analysis. MASCOT MS/MS ionscores were compared before and after processing with the columns. The non-specific co-removal of proteins bound to the high abundant proteins, so called "sponge effect" was also examined for each spin column. The reproducibility of one of the spin columns, ProteomeLab IgY-12 proteome partitioning spin column, was further investigated by isobaric tags for relative and absolute quantification (iTRAQ) labeling and MS/MS analysis. Overall, 173 unique proteins were identified on a 95% MudPIT confidence scoring level. For all three spin columns, the number of proteins identified and their MASCOT scores were increased up to 10 times. The largest degree of non-specific protein removal was observed for a purely affinity based albumin removal column, where 28 other proteins also were present. The ProteomeLab IgY-12 proteome partitioning spin column showed very high reproducibility when combined with iTRAQ labeling and MS/MS analysis. The combined relative standard deviation (R.S.D.) for the high abundant protein removal, iTRAQ labeling and nanoLC-MALDI-TOF/TOF-MS analysis was less than 17.5%.