Interleukin-6 and its soluble receptor in serum and cerebrospinal fluid after cerebral trauma

Circulating soluble CD163 is associated with reduced Glasgow Coma Score and 1-year all-cause mortality in traumatized patients

Soluble CD163 (sCD163) is a biomarker of macrophage activation, not previously investigated in the circulation of traumatized patients. A biobank of 398 adult trauma patients was analyzed. Patients with an Injury Severity Score (ISS) >8 served as trauma patients (n = 195) and those with ISS ≤ 8 as trauma controls (n = 203). Serum samples obtained upon admission, 15h and 72h after were analyzed for sCD163 using an in-house ELISA. Multiple linear regression was used to analyze the association between admission levels of sCD163 with, 1: overall trauma severity (ISS), and 2: severity of injury to specified organs using Abbreviated Injury Score (AIS) and Glasgow Coma Scale (GCS). The association between the peak level of sCD163 with 1-year all-cause mortality was analyzed by logistic regression analysis. Median admission levels of sCD163 were higher in trauma patients than trauma controls [2.32 (IQR 1.73 to 2.86) vs. 1.92 (IQR 1.41 to 2.51) mg/L, p < 0.01]. Worsening GCS score was associated with a 10.3% (95% CI: 17.0 to 3.1, p < 0.01) increase in sCD163. Increasing Head-AIS score was associated with a 5.1% (95% CI: -0.5 to 11.0, p = 0.07) increase in sCD163. The remaining AIS scores and ISS were not consistently associated with sCD163 admission levels. Each mg/L increase in sCD163 peak level had an odds ratio 1.34 (95%CI: 0.98 to 1.83), p = 0.06) after adjustment for age, sex, and GCS. Circulating sCD163 is increased in traumatized patients and associated with worsening GCS. Our findings suggest an association between circulating sCD163 levels with 1-year all-cause mortality.

Acute IL-6 exposure triggers canonical IL6Ra signaling in hiPSC microglia, but not neural progenitor cells

BACKGROUND

Prenatal exposure to elevated interleukin (IL)-6 levels is associated with increased risk for psychiatric disorders with a putative neurodevelopmental origin, such as schizophrenia (SZ), autism spectrum condition (ASC) and bipolar disorder (BD). Although rodent models provide causal evidence for this association, we lack a detailed understanding of the cellular and molecular mechanisms in human model systems. To close this gap, we characterized the response of human induced pluripotent stem cell (hiPSC-)derived microglia-like cells (MGL) and neural progenitor cells (NPCs) to IL-6 in monoculture.

RESULTS

We observed that human forebrain NPCs did not respond to acute IL-6 exposure in monoculture at both protein and transcript levels due to the absence of IL6R expression and soluble (s)IL6Ra secretion. By contrast, acute IL-6 exposure resulted in STAT3 phosphorylation and increased IL6, JMJD3 and IL10 expression in MGL, confirming activation of canonical IL6Ra signaling. Bulk RNAseq identified 156 up-regulated genes (FDR < 0.05) in MGL following acute IL-6 exposure, including IRF8, REL, HSPA1A/B and OXTR, which significantly overlapped with an up-regulated gene set from human post-mortem brain tissue from individuals with schizophrenia. Acute IL-6 stimulation significantly increased MGL motility, consistent with gene ontology pathways highlighted from the RNAseq data and replicating rodent model indications that IRF8 regulates microglial motility. Finally, IL-6 induces MGLs to secrete CCL1, CXCL1, MIP-1α/β, IL-8, IL-13, IL-16, IL-18, MIF and Serpin-E1 after 3 h and 24 h.

CONCLUSION

Our data provide evidence for cell specific effects of acute IL-6 exposure in a human model system, ultimately suggesting that microglia-NPC co-culture models are required to study how IL-6 influences human cortical neural progenitor cell development in vitro.

Oxidative Stress in Traumatic Brain Injury

Traumatic Brain Injury (TBI) remains a major cause of disability worldwide. It involves a complex neurometabolic cascade, including oxidative stress. The products of this manuscript is examining the underlying pathophysiological mechanism, including reactive oxygen species (ROS) and reactive nitrogen species (RNS). This process in turn leads to secondary injury cascade, which includes lipid peroxidation products. These reactions ultimately play a key role in chronic inflammation and synaptic dysfunction in a synergistic fashion. Although there are no FDA approved antioxidant therapy for TBI, there is a number of antioxidant therapies that have been tested and include free radical scavengers, activators of antioxidant systems, inhibitors of free radical generating enzymes, and antioxidant enzymes. Antioxidant therapies have led to cognitive and functional recovery post TBI, and they offer a promising treatment option for patients recovering from TBI. Current major challenges in treatment of TBI symptoms include heterogenous nature of injury, as well as access to timely treatment post injury. The inherent benefits of antioxidant therapies include minimally reported side effects, and relative ease of use in the clinical setting. The current review also provides a highlight of the more studied anti-oxidant regimen with applicability for TBI treatment with potential use in the real clinical setting.

Synergistic effect of mild traumatic brain injury and alcohol aggravates neuroinflammation, amyloidogenesis, tau pathology, neurodegeneration, and blood-brain barrier alterations: Impact on psychological stress

After a mild traumatic brain injury (mTBI), victims often experience emotional/psychological stress such as heightened irritability, anxiety, apathy, and depression. Severe mental health complications are common in military populations following a combat-acquired TBI and intensified unhealthy alcohol use. The high prevalence of alcohol abuse among TBI victims underscores how alcohol abuse exacerbates emotional/psychological symptoms such as depression and anxiety. The experimental mTBI was induced in vivo by fluid percussion injury (15 psi) in mice and ethanol diet feeding continued for 28 days. We analyzed different biomarkers of the biochemical mechanisms and pathophysiology of neurological damage, and functional outcome of psychological stress by sucrose preference, and light-dark tests. We demonstrated that the synergistic effect of TBI and alcohol leads to psychological stress such as depression and anxiety. The studies showed that oxidative stress, amyloidogenesis, tau pathology, neuroinflammation, and neurodegeneration markers were elevated, and glial activation and blood-brain barrier (BBB) damage were exacerbated during the synergistic effect of TBI and alcohol. Further, we studied the biochemical mechanisms of psychological stress that showed the significant reduction of 5-HT1AR, neuropeptide-Y, and norepinephrine, and an increase in monoamine oxidase-a in the combined effect of TBI and alcohol. This work suggested that the combined TBI and alcohol-induced effect leads to depression and anxiety, via sequential biochemical changes that cause neuroinflammation, amyloidogenesis, tau pathology, neurodegeneration, and BBB alterations. This clinically relevant study will contribute to developing a comprehensive therapeutic approach for patients suffering from TBI and alcohol-mediated neurological damage and psychological stress.

Antimicrobial protein REG3A and signaling networks are predictive of stroke outcomes

Regenerating Family Member 3 Alpha (REG3A) is a multifunctional protein with antimicrobial activity, and primarily secreted by the intestine and pancreas. Studies have shown an increased expression of REG3A in systemic inflammatory responses to acute injury and infection, but studies investigating REG3A during the pathogenesis of ischemic stroke are limited. The aims of this study were to examine the associations between arterial expression of REG3A and other arterial inflammatory proteins implicated in stroke pathogenesis, as well as associations between REG3A and markers of poor outcome for ischemic stroke. The University of Kentucky Blood and Clot Thrombectomy Registry and Collaboration (BACTRAC) protocol (clinicaltrials.gov NCT03153683) utilizes thrombectomy to isolate intracranial arterial blood (i.e. distal to thrombus) and systemic arterial blood (i.e. carotid). Samples were analyzed by Olink Proteomics for N = 42 subjects. Statistical analyses of plasma proteins included 2-sample t-tests, spearman and biserial correlations, and robust regression models to elucidate network signaling and association to clinical outcomes. Results indicated that levels of systemic REG3A were positively correlated with inflammatory proteins interleukin IL6 (R = 0.344, p = 0.030) and IL17C (R = 0.468, p = 0.002). 2-sided t- tests examining differences of systemic REG3A within quartiles of NIHSS admission score depicted significant differences between quartiles. Those with NIHSS scores corresponding to moderate and moderate-severe neurofunctional deficits had significantly higher levels of systemic REG3A compared to those with NIHSS scores corresponding to mild and mild-moderate neurofunctional deficits (p = 0.016). STRING analyses of proteins in each robust regression model demonstrated substantial networking between REG3A and other systemic proteins highly relevant to ischemic stroke. The present study provides novel data on systemic REG3A in the context of ischemic stroke. These results demonstrate the influential role of REG3A regarding surrogate functional and radiographic outcomes of stroke severity. Additionally, they provide novel insight into the role of REG3A and related proteins during the complex neuroinflammatory process of ischemic stroke. These data provide a foundation for future studies to investigate REG3A and related networking proteins as potential biomarkers with prognostic potential, as well as potential therapeutic targets.

Evaluation of cytokines and structural proteins to analyze the pathology of febrile central nervous system disease

This study was designed to examine the pathophysiological differences in interleukin (IL) and structural protein levels between central nervous system (CNS) disorders associated with heat stroke and CNS stimulants. We measured the concentrations of IL-6, IL-8, neuron-specific enolase (NSE), and myelin basic protein (MBP) in blood and cerebrospinal fluid (CSF) from 87 autopsy cases. In addition, to examine changes in each marker, we cultured nerve cells at 40 °C as a heat stroke model and administered 4-aminopyridine and ephedrine in cultured cells as a CNS stimulant model. IL-6 levels in blood and CSF were significantly higher in the stimulant compared with the heat stroke group. IL-8 levels in blood and CSF were relatively high in the stimulant, heat stroke, and psychotropic addiction groups. NSE levels in blood were high in the stimulant and heat stroke groups, while those in CSF were significantly higher in the heat stroke group. MBP levels in blood were markedly higher in the stimulant and heat stroke groups, but no differences were seen in CSF. Compared with the CNS stimulant model, the heat stroke model with cultured human nerve cells showed high values for each marker. The results of the autopsy and laboratory tests in the present cases and those of cultured cell experiments indicated that CNS disorders caused by CNS stimulants such as amphetamines led to changes in IL-6 as an immune response, which suggests that IL-8 may help protect nerve cells in cases involving heat stroke and stimulants.

Effects of leptin, ghrelin and neuropeptide y on spike-wave discharge activity and certain biochemical parameters in WAG/Rij rats with genetic absence epilepsy

This study aimed to evaluate the effects of leptin, ghrelin and neuropeptide-Y on the development of nonconvulsive seizure activity and their role on combating oxidative stress and cytokines produced by the systemic immune response in the WAG/Rij rat model for genetic absence epilepsy. Current study showed that all three peptides aggravated spike wave discharges activity and affected the oxidative stress in WAG/Rij rats without any significant changes in the levels of IL-1β, IL-6 and TNF-α except leptin that only induced an increment in the concentration of IL-1β. Our results support the modulatory role of these endogenous peptides on absence epilepsy.

Survival-time dependent increase in neuronal IL-6 and astroglial GFAP expression in fatally injured human brain tissue

Knowledge on trauma survival time prior to death following a lethal traumatic brain injury (TBI) may be essential for legal purposes. Immunohistochemistry studies might allow to narrow down this survival interval. The biomarkers interleukin-6 (IL-6) and glial fibrillary acidic protein (GFAP) are well known in the clinical setting for their usability in TBI prediction. Here, both proteins were chosen in forensics to determine whether neuronal or glial expression in various brain regions may be associated with the cause of death and the survival time prior to death following TBI. IL-6 positive neurons, glial cells and GFAP positive astrocytes all concordantly increase with longer trauma survival time, with statistically significant changes being evident from three days post-TBI (p < 0.05) in the pericontusional zone, irrespective of its definite cortical localization. IL-6 staining in neurons increases significantly in the cerebellum after trauma, whereas increasing GFAP positivity is also detected in the cortex contralateral to the focal lesion. These systematic chronological changes in biomarkers of pericontusional neurons and glial cells allow for an estimation of trauma survival time. Higher numbers of IL-6 and GFAP-stained cells above threshold values in the pericontusional zone substantiate the existence of fatal traumatic changes in the brain with reasonable certainty.

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.

Angiotensin II Causes Neuronal Damage in Stretch-Injured Neurons: Protective Effects of Losartan, an Angiotensin T1 Receptor Blocker

Angiotensin II (Ang II) is a mediator of oxidative stress via activation/induction of reactive oxygen and nitrogen species-generating enzymes, NADPH oxidase (NOX) and inducible nitric oxide synthase (iNOS). We investigated the hypothesis that overproduction of Ang II during traumatic brain injury (TBI) induces the activation of the oxidative stress, which triggers neuroinflammation and cell apoptosis in a cell culture model of neuronal stretch injury. We first established that stretch injury causes a rapid increase in the level of Ang II, which causes the release of pro-inflammatory cytokines, IL-1β and TNF-α, via the induction of oxidative stress. Since angiotensin-converting enzyme (ACE) mediates the production of Ang II via the conversion of Ang I into Ang II, we analyzed the expression of ACE by western blotting. Further, we analyzed caspase-3-mediated apoptosis by TUNEL staining and annexin V western blotting. Angiotensin type I (AT₁) receptor antagonist losartan attenuated Ang II-induced oxidative stress and associated neuroinflammation and cell death in cultured neurons. Remarkably, we noticed that the expression of Ang II type 1 receptor (AngT₁R) upregulated in neuronal stretch injury; losartan mitigates this upregulation. Findings from this study significantly extend our understanding of the pathophysiology of TBI and may have significant implications for developing therapeutic strategies for TBI-associated brain dysfunctions.

Transforming growth factor-beta 1 signaling regulates neuroinflammation and apoptosis in mild traumatic brain injury

Mild traumatic brain injury (mTBI) is a low-level injury, which often remains undiagnosed, and in most cases it leads to death and disability as it advances as secondary injury. Therefore, it is important to study the underlying signaling mechanisms of mTBI-associated neurological ailments. While transforming growth factor-beta1 (TGF-β1) has a significant role in inflammation and apoptosis in myriads of other pathophysiological conditions, the precise function of increased TGF-β1 after mTBI is unknown. In this study, our objective is to study the physiological relevance and associated mechanisms of TGF-β1-mediated inflammation and apoptosis in mTBI. Using an in vitro stretch-injury model in rat neuronal cultures and the in vivo fluid percussion injury (FPI) model in rats, we explored the significance of TGF-β1 activation in mTBI. Our study demonstrated that the activation of TGF-β1 in mTBI correlated with the induction of free radical generating enzyme NADPH oxidase 1 (NOX1). Further, using TGF-β type I receptor (TGF-βRI) inhibitor SB431542 and transfection of TGF-β1 siRNA and TGF-β antagonist Smad7, we established the neuroinflammatory and apoptotic role of TGF-β1 in mTBI. Inhibition of TGF-βRI or TGF-β1 diminished TGF-β1-induced inflammation and apoptosis. Further, the enhanced TGF-β1 activation increased the phosphorylation of R-Smads including Smad2 and Smad3 proteins. By immunofluorescence, western blotting, ELISA and TUNEL experiments, we demonstrated the up-regulation of pro-inflammatory cytokines IL-1β and TNF-α and apoptotic cell death in neurons. In conclusion, this study could establish the significance of TGF-β1 in transforming the pathophysiology of mTBI into secondary injury.

Cerebrospinal Fluid and Microdialysis Cytokines in Severe Traumatic Brain Injury: A Scoping Systematic Review

Objective

To perform two scoping systematic reviews of the literature on cytokine measurement in: 1. cerebral microdialysis (CMD) and 2. cerebrospinal fluid (CSF) in severe traumatic brain injury (TBI) patients.

Methods

Two separate systematic reviews were conducted: one for CMD cytokines and the second for CSF cytokines. Both were conducted in severe TBI (sTBI) patients only.

Data sources

Articles from MEDLINE, BIOSIS, EMBASE, Global Health, Scopus, Cochrane Library (inception to October 2016), reference lists of relevant articles, and gray literature were searched.

Study selection

Two reviewers independently identified all manuscripts utilizing predefined inclusion/exclusion criteria. A two-tier filter of references was conducted.

Data extraction

Patient demographic and study data were extracted to tables.

Results

There were 19 studies identified describing the analysis of cytokines via CMD in 267 sTBI patients. Similarly, there were 32 studies identified describing the analysis of CSF cytokines in 1,363 sTBI patients. The two systematic reviews demonstrated: 1. limited literature available on CMD cytokine measurement in sTBI, with some preliminary data supporting feasibility of measurement and associations between cytokines and patient outcome. 2. Various CSF measured cytokines may be associated with patient outcome at 6–12 months, including interleukin (IL)-1b, IL-1ra, IL-6, IL-8, IL-10, and tumor necrosis factor 3. There is little to no literature in support of an association between CSF cytokines and neurophysiologic or tissue outcomes.

Conclusion

The evaluation of CMD and CSF cytokines is an emerging area of the literature in sTBI. Further, large prospective multicenter studies on cytokines in CMD and CSF need to be conducted.

The effect of leptin, ghrelin, and neuropeptide-Y on serum Tnf-Α, Il-1β, Il-6, Fgf-2, galanin levels and oxidative stress in an experimental generalized convulsive seizure model

The objective of this study is to examine the effects of the endogenous ligands leptin, ghrelin, and neuropeptide Y (NPY) on seizure generation, the oxidant/antioxidant balance, and cytokine levels, which are a result of immune response in a convulsive seizure model. With this goal, Wistar rats were divided into 5 groups-Group 1: Saline, Group 2: Saline+PTZ (65mg/kg), Group 3: leptin (4mg/kg)+PTZ, Group 4: ghrelin (80μg/kg)+PTZ, and Group 5: NPY (60μg/kg)+PTZ. All injections were delivered intraperitoneally, and simultaneous electroencephalography (EEG) records were obtained. Seizure activity was scored by observing seizure behavior, and the onset time, latency, and seizure duration were determined according to the EEG records. At the end of the experiments, blood samples were obtained in all groups to assess the serum TNF-α, IL-1β, IL-6, FGF-2, galanin, nitric oxide (NOֹ), malondialdehyde (MDA), and glutathione (GSH) levels. The electrophysiological and biochemical findings (p<0.05) of this study show that all three peptides have anticonvulsant effects in the pentylenetetrazol (PTZ)-induced generalized tonic-clonic convulsive seizure model. The reduction of the levels of the pro-inflammatory cytokines TNF-α, IL-1β, and IL-6 caused by leptin, ghrelin, and NPY shows that these peptides may have anti-inflammatory effects in epileptic seizures. Also, leptin significantly increases the serum levels of the endogenous anticonvulsive agent galanin. The fact that each one of these endogenous peptides reduces the levels of MDA and increases the serum levels of GSH leads to the belief that they may have protective effects against oxidative damage that is thought to play a role in the pathogenesis of epilepsy. Our study contributes to the clarification of the role of these peptides in the brain in seizure-induced oxidative stress and immune system physiology and also presents new approaches to the etiology and treatment of tendency to epileptic seizures.

High Ca2+ Influx During Traumatic Brain Injury Leads to Caspase-1-Dependent Neuroinflammation and Cell Death

We investigated the hypothesis that high Ca²⁺ influx during traumatic brain injury induces the activation of the caspase-1 enzyme, which triggers neuroinflammation and cell apoptosis in a cell culture model of neuronal stretch injury and an in vivo model of fluid percussion injury (FPI). We first established that stretch injury causes a rapid increase in the intracellular Ca²⁺ level, which activates interleukin-converting enzyme caspase-1. The increase in the intracellular Ca²⁺ level and subsequent caspase-1 activation culminates into neuroinflammation via the maturation of IL-1β. Further, we analyzed caspase-1-mediated apoptosis by TUNEL staining and PARP western blotting. The voltage-gated sodium channel blocker, tetrodotoxin, mitigated the stretch injury-induced neuroinflammation and subsequent apoptosis by blocking Ca²⁺ influx during the injury. The effect of tetrodotoxin was similar to the caspase-1 inhibitor, zYVAD-fmk, in neuronal culture. To validate the in vitro results, we demonstrated an increase in caspase-1 activity, neuroinflammation and neurodegeneration in fluid percussion-injured animals. Our data suggest that neuronal injury/traumatic brain injury (TBI) can induce a high influx of Ca²⁺ to the cells that cause neuroinflammation and cell death by activating caspase-1, IL-1β, and intrinsic apoptotic pathways. We conclude that excess IL-1β production and cell death may contribute to neuronal dysfunction and cognitive impairment associated with TBI.

Anti-IL-6 neutralizing antibody modulates blood-brain barrier function in the ovine fetus

Impaired blood-brain barrier function represents an important component of hypoxic-ischemic brain injury in the perinatal period. Proinflammatory cytokines could contribute to ischemia-related blood-brain barrier dysfunction. IL-6 increases vascular endothelial cell monolayer permeability in vitro. However, contributions of IL-6 to blood-brain barrier abnormalities have not been examined in the immature brain in vivo. We generated pharmacologic quantities of ovine-specific neutralizing anti-IL-6 mAbs and systemically infused mAbs into fetal sheep at 126 days of gestation after exposure to brain ischemia. Anti-IL-6 mAbs were measured by ELISA in fetal plasma, cerebral cortex, and cerebrospinal fluid, blood-brain barrier permeability was quantified using the blood-to-brain transfer constant in brain regions, and IL-6, tight junction proteins, and plasmalemma vesicle protein (PLVAP) were detected by Western immunoblot. Anti-IL-6 mAb infusions resulted in increases in mAb (P < 0.05) in plasma, brain parenchyma, and cerebrospinal fluid and decreases in brain IL-6 protein. Twenty-four hours after ischemia, anti-IL-6 mAb infusions attenuated ischemia-related increases in blood-brain barrier permeability and modulated tight junction and PLVAP protein expression in fetal brain. We conclude that inhibiting the effects of IL-6 protein with systemic infusions of neutralizing antibodies attenuates ischemia-related increases in blood-brain barrier permeability by inhibiting IL-6 and modulates tight junction proteins after ischemia.

Temporal profile of cerebrospinal fluid, plasma, and brain interleukin-6 after normothermic fluid-percussion brain injury: effect of secondary hypoxia

Interleukin-6 (IL-6) is a proinflammatory cytokine that may play multiple roles in the pathogenesis of traumatic brain injury (TBI). The present study determined time-dependent changes in IL-6 concentrations in vulnerable brain regions, cerebrospinal fluid (CSF) samples, and plasma after normothermic TBI. Because secondary insults are common in head injured patients, we also assessed the consequences of a post-traumatic secondary hypoxic insult on this pleiotropic cytokine. Male Sprague-Dawley rats were intubated, anesthetized, and underwent a moderate parasagittal fluid-percussion brain injury (1.8-2.1 atm, 37°C) followed by either 30 minutes of normoxic or hypoxic (pO₂ = 30-40 mmHg) gas levels. Rats were sacrificed 3, 6, or 24 hours after TBI or shamoperated procedures. Brain samples, including the ipsilateral cerebral cortex and hippocampus were dissected and analyzed. Plasma and CSF samples were collected at similar times and stored at -80°C until analysis. IL-6 levels were significantly increased ( p < 0.05) at 3, 6, and 24 hours in the cerebral cortex and at 6 hours in the hippocampus after TBI. IL-6 levels in the TBI normoxic group for both structures returned to control levels by 24 hours. Plasma levels of IL-6 were elevated at all time points, while CSF levels were high at 3 and 6 hours, but normalized by 24 hours. Post-traumatic hypoxia led to significantly elevated ( p < 0.05) IL-6 protein levels in the cerebral cortex at 24 hours compared to sham-operated controls. These findings demonstrate that moderate TBI leads to an early increase in IL-6 brain, plasma, and CSF protein levels. Secondary post-traumatic hypoxia, a common secondary injury mechanism, led to prolonged elevations in plasma IL-6 levels that may participate in the pathophysiology of this complicated TBI model.

Interactions of oxidative stress and neurovascular inflammation in the pathogenesis of traumatic brain injury

Traumatic brain injury (TBI) is a major cause of death in the young age group and leads to persisting neurological impairment in many of its victims. It may result in permanent functional deficits because of both primary and secondary damages. This review addresses the role of oxidative stress in TBI-mediated secondary damages by affecting the function of the vascular unit, changes in blood-brain barrier (BBB) permeability, posttraumatic edema formation, and modulation of various pathophysiological factors such as inflammatory factors and enzymes associated with trauma. Oxidative stress plays a major role in many pathophysiologic changes that occur after TBI. In fact, oxidative stress occurs when there is an impairment or inability to balance antioxidant production with reactive oxygen species (ROS) and reactive nitrogen species (RNS) levels. ROS directly downregulate proteins of tight junctions and indirectly activate matrix metalloproteinases (MMPs) that contribute to open the BBB. Loosening of the vasculature and perivascular unit by oxidative stress-induced activation of MMPs and fluid channel aquaporins promotes vascular or cellular fluid edema, enhances leakiness of the BBB, and leads to progression of neuroinflammation. Likewise, oxidative stress activates directly the inflammatory cytokines and growth factors such as IL-1β, tumor necrosis factor-α (TNF-α), and transforming growth factor-beta (TGF-β) or indirectly by activating MMPs. In another pathway, oxidative stress-induced degradation of endothelial vascular endothelial growth factor receptor-2 (VEGFR-2) by MMPs leads to a subsequent elevation of cellular/serum VEGF level. The decrease in VEGFR-2 with a subsequent increase in VEGF-A level leads to apoptosis and neuroinflammation via the activation of caspase-1/3 and IL-1β release.

Transcriptome analysis of HIV-infected peripheral blood monocytes: gene transcripts and networks associated with neurocognitive functioning

Immunologic dysfunction, mediated via monocyte activity, has been implicated in the development of HIV-associated neurocognitive disorder (HAND). We hypothesized that transcriptome changes in peripheral blood monocytes relate to neurocognitive functioning in HIV+ individuals, and that such alterations could be useful as biomarkers of worsening HAND.

METHODS

mRNA was isolated from the monocytes of 86 HIV+ adults and analyzed with the Illumina HT-12 v4 Expression BeadChip. Neurocognitive functioning, HAND diagnosis, and other clinical and virologic variables were determined. Data were analyzed using standard expression analysis and weighted gene co-expression network analysis (WGCNA).

RESULTS

Neurocognitive functioning was correlated with multiple gene transcripts in the standard expression analysis. WGCNA identified two nominally significant co-expression modules associated with neurocognitive functioning, which were enriched with genes involved in mitotic processes and translational elongation.

CONCLUSIONS

Multiple modified gene transcripts involved in inflammation, cytoprotection, and neurodegeneration were correlated with neurocognitive functioning. The associations were not strong enough to justify their use as biomarkers of HAND; however, the associations of two co-expression modules with neurocognitive functioning warrant further exploration.

Guilty molecules, guilty minds? The conflicting roles of the innate immune response to traumatic brain injury

Traumatic brain injury (TBI) is a complex disease in the most complex organ of the body, whose victims endure lifelong debilitating physical, emotional, and psychosocial consequences. Despite advances in clinical care, there is no effective neuroprotective therapy for TBI, with almost every compound showing promise experimentally having disappointing results in the clinic. The complex and highly interrelated innate immune responses govern both the beneficial and deleterious molecular consequences of TBI and are present as an attractive therapeutic target. This paper discusses the positive, negative, and often conflicting roles of the innate immune response to TBI in both an experimental and clinical settings and highlights recent advances in the search for therapeutic candidates for the treatment of TBI.

The role of estrogen and progesterone, administered alone and in combination, in modulating cytokine concentration following traumatic brain injury

Cytokines play an important role in the pathophysiology of traumatic brain injury (TBI). This study was designed to determine the effects of administering progesterone (P) and estrogen (E), alone and in combination, on brain water content, blood-brain barrier (BBB) disturbance, and brain level of cytokines following diffuse TBI. Ovariectomized rats were divided into 9 groups, treated with vehicle, E1, E2, P1, P2, E1+P1, E1+P2, E2+P1, and E2+P2. Levels of BBB disruption (5 h), cytokines, and water content (24 h) were evaluated after TBI induced by the Marmarou method. Physiological (E1 and P1) and pharmacological (E2 and P2) doses of estrogen and progesterone were administered 30 min after TBI. Water content in the E1+P2-treated group was higher than in the E1-treated group. The inhibitory effect of E2 on water content was reduced by adding progesterone. The inhibitory effect of E1 and E2 on Evans blue content was reduced by treatment with E1+P1 and E2+P2, respectively. The brain level of IL-1β was reduced in E1 and E2, after TBI. In the E2+P2-treated group, this level was higher than in the E2-treated group. The brain level of TGF-β was also elevated by the administration of progesterone and estrogen alone, and reduced when the hormones were administered in combination. In conclusion, a combined administration of progesterone and estrogen inhibited the decreasing effects of administration of progesterone and estrogen alone on water content and BBB disruption that mediated to change the proinflammatory cytokines.

Post-traumatic hypoxia exacerbates neurological deficit, neuroinflammation and cerebral metabolism in rats with diffuse traumatic brain injury

Background

The combination of diffuse brain injury with a hypoxic insult is associated with poor outcomes in patients with traumatic brain injury. In this study, we investigated the impact of post-traumatic hypoxia in amplifying secondary brain damage using a rat model of diffuse traumatic axonal injury (TAI). Rats were examined for behavioral and sensorimotor deficits, increased brain production of inflammatory cytokines, formation of cerebral edema, changes in brain metabolism and enlargement of the lateral ventricles.

Methods

Adult male Sprague-Dawley rats were subjected to diffuse TAI using the Marmarou impact-acceleration model. Subsequently, rats underwent a 30-minute period of hypoxic (12% O₂/88% N₂) or normoxic (22% O₂/78% N₂) ventilation. Hypoxia-only and sham surgery groups (without TAI) received 30 minutes of hypoxic or normoxic ventilation, respectively. The parameters examined included: 1) behavioural and sensorimotor deficit using the Rotarod, beam walk and adhesive tape removal tests, and voluntary open field exploration behavior; 2) formation of cerebral edema by the wet-dry tissue weight ratio method; 3) enlargement of the lateral ventricles; 4) production of inflammatory cytokines; and 5) real-time brain metabolite changes as assessed by microdialysis technique.

Results

TAI rats showed significant deficits in sensorimotor function, and developed substantial edema and ventricular enlargement when compared to shams. The additional hypoxic insult significantly exacerbated behavioural deficits and the cortical production of the pro-inflammatory cytokines IL-6, IL-1β and TNF but did not further enhance edema. TAI and particularly TAI+Hx rats experienced a substantial metabolic depression with respect to glucose, lactate, and glutamate levels.

Conclusion

Altogether, aggravated behavioural deficits observed in rats with diffuse TAI combined with hypoxia may be induced by enhanced neuroinflammation, and a prolonged period of metabolic dysfunction.

Peripheral immune cells in the pathology of traumatic brain injury?

PURPOSE OF REVIEW

This review will consider the reasons why the inhibition of leucocyte recruitment after traumatic brain injury has not been demonstrated but should remain an area of active interest.

RECENT FINDINGS

Focal lesions to the brain display a characteristic inflammatory response with infiltration of peripheral immune cells after injury. These cells are believed to be important because they contain and release a multitude of inflammatory mediators associated with increased tissue injury. Furthermore a large body of evidence from ischaemic injuries suggests that inhibition of leucocyte recruitment can reduce injury and improve outcome. However, therapeutic efficacy has not been demonstrated in clinical trials and for traumatic injuries the results are less convincing.

SUMMARY

A greater appreciation of the timing of assessment, leucocyte subsets and the extended inflammatory response will be discussed.

Lack of correlation among intracerebral cytokines, intracranial pressure, and brain tissue oxygenation in patients with traumatic brain injury and diffuse lesions

OBJECTIVES

To determine the evolution of cytokine patterns using microdialysis in patients with traumatic brain injury with diffuse lesions and to study the relationship between cytokines and intracranial pressure, brain tissue oxygenation and lesion type on the computed cranial tomography scan (patients with and without brain swelling).

DESIGN

Prospective and observational study.

SETTING

Third-level university hospital.

PATIENTS

Patients between 15 and 65 yrs with severe traumatic brain injury and a diffuse lesion requiring intracranial pressure and brain tissue oxygenation monitoring were eligible.

INTERVENTIONS

Microdialysis catheters with a high-cutoff membrane of 100 kDa were inserted.

RESULTS

Sixteen patients were included in the analysis. There was a substantial interindividual variability between cytokine values. The highest concentrations for the interleukin-1β, interleukin-6, and interleukin-8 were measured during the first 24 hrs followed by a gradual decline. The average concentration for interleukin-10 did not vary over time. This pattern is the most frequent in patients with traumatic brain injury with diffuse lesions. The intracranial pressure-cytokines correlation coefficients for the 16 patients varied substantially: interleukin-1β-intracranial pressure (-0.76 to 0.63); interleukin-6-intracranial pressure (-0.83 to 0.78); interleukin-8-intracranial pressure (-0.86 to 0.84); and interleukin-10-intracranial pressure (-0.36 to 0.65). The brain tissue oxygenation-cytokine correlation coefficients, like with intracranial pressure, also varied between patients: interleukin-1β-brain tissue oxygenation (-0.49 to 0.68), interleukin-6-brain tissue oxygenation (-0.99 to 0.84); interleukin-8-brain tissue oxygenation (-0.65 to 0.74); and interleukin-10-brain tissue oxygenation (-0.34 to 0.52). Similarly, we found no difference in the cytokine values inpatient microdialysis with and without swelling in the computed tomographic scan.

CONCLUSIONS

No clear relationship was found between the temporal pattern of cytokines and the behavior of the intracranial pressure, brain tissue oxygenation, and the presence or absence of swelling in the computed tomography scan. This study demonstrates the feasibility of microdialysis in recovering cytokines for a prolonged time, although there may be some nonresolved methodologic problems with this technique when we try to study the inflammation during traumatic brain injury that could affect the results and make interpretation of microdialysis data prone to difficulties.

Local renal complement C3 induction by donor brain death is associated with reduced renal allograft function after transplantation

BACKGROUND

Kidneys derived from brain-dead donors have inferior outcomes after transplantation compared to kidneys from living donors. Strikingly, early and profound serum levels of IL-6 in brain-dead donors are observed. IL-6 is the main regulator of the acute phase response (APR). The aim of this translational study was to investigate the expression of renal acute phase proteins (APPs) following brain death (BD) and to assess the association with renal allograft outcome after transplantation.

METHODS

BD was induced in rats by inflating a subdurally placed balloon catheter. Kidney biopsies were obtained from human living and brain-dead donors at donation, after cold preservation and reperfusion. In vitro, renal proximal tubular epithelial cells (HK-2 cells) were stimulated with IL-6.

RESULTS

Both in human and rat brain-dead donors, C3 and FBG expression was enhanced at donation compared to living donors and sham-operated animals. In human donors, no additional expression was found after cold ischaemia or reperfusion. C3 expression after reperfusion was independently associated with decreased short-term function after transplantation in grafts from brain-dead donors. In cultured HK-2 cells, C3 production was induced in the presence of IL-6.

CONCLUSIONS

In conclusion, BD induces renal C3 and FBG expression. Moreover, C3 expression is associated with a worse allograft function early after transplantation. Therefore, targeting renal APPs in brain-dead donors, especially complement C3, may improve transplant outcome.

Serum IL-6: a candidate biomarker for intracranial pressure elevation following isolated traumatic brain injury

Background

Increased intracranial pressure (ICP) is a serious, life-threatening, secondary event following traumatic brain injury (TBI). In many cases, ICP rises in a delayed fashion, reaching a maximal level 48-96 hours after the initial insult. While pressure catheters can be implanted to monitor ICP, there is no clinically proven method for determining a patient's risk for developing this pathology.

Methods

In the present study, we employed antibody array and Luminex-based screening methods to interrogate the levels of inflammatory cytokines in the serum of healthy volunteers and in severe TBI patients (GCS≤8) with or without incidence of elevated intracranial pressure (ICP). De-identified samples and ELISAs were used to confirm the sensitivity and specificity of IL-6 as a prognostic marker of elevated ICP in both isolated TBI patients, and polytrauma patients with TBI.

Results

Consistent with previous reports, we observed sustained increases in IL-6 levels in TBI patients irrespective of their ICP status. However, the group of patients who subsequently experienced ICP ≥ 25 mm Hg had significantly higher IL-6 levels within the first 17 hours of injury as compared to the patients whose ICP remained ≤20 mm Hg. When blinded samples (n = 22) were assessed, a serum IL-6 cut-off of <5 pg/ml correctly identified 100% of all the healthy volunteers, a cut-off of >128 pg/ml correctly identified 85% of isolated TBI patients who subsequently developed elevated ICP, and values between these cut-off values correctly identified 75% of all patients whose ICP remained ≤20 mm Hg throughout the study period. In contrast, the marker had no prognostic value in predicting elevated ICP in polytrauma patients with TBI. When the levels of serum IL-6 were assessed in patients with orthopedic injury (n = 7) in the absence of TBI, a significant increase was found in these patients compared to healthy volunteers, albeit lower than that observed in TBI patients.

Conclusions

Our results suggest that serum IL-6 can be used for the differential diagnosis of elevated ICP in isolated TBI.

The genomic profile of the cerebral cortex after closed head injury in mice: effects of minocycline

Microarray analysis was used to delineate gene expression patterns and profile changes following traumatic brain injury (TBI) in mice. A parallel microarray analysis was carried out in mice with TBI that were subsequently treated with minocycline, a drug proposed as a neuroprotectant in other neurological disorders. The aim of this comparison was to identify pathways that may be involved in secondary injury processes following TBI and potential specific pathways that could be targeted with second generation therapeutics for the treatment of neurotrauma patients. Gene expression profiles were measured with the compugen long oligo chip and real-time PCR was used to validate microarray findings. A pilot study of effect of minocycline on gene expression following TBI was also carried out. Gene ontology comparison analysis of sham TBI and minocycline treated brains revealed biological pathways with more genes differentially expressed than predicted by chance. Among 495 gene ontology categories, the significantly different gene ontology groups included chemokines, genes involved in cell surface receptor-linked signal transduction and pro-inflammatory cytokines. Expression levels of some key genes were validated by real-time quantitative PCR. This study confirms that multiple regulatory pathways are affected following brain injury and demonstrates for the first time that specific genes and molecular networks are affected by minocycline following brain injury.

Post-injury baicalein improves histological and functional outcomes and reduces inflammatory cytokines after experimental traumatic brain injury

BACKGROUND AND PURPOSE

Traumatic brain injury (TBI) triggers a complex series of inflammatory responses that contribute to secondary tissue damage. The aim of this study was to investigate the effect of baicalein, a flavonoid possessing potent anti-inflammatory properties, on functional and histological outcomes and inflammatory cytokine expression, following TBI in rats.

EXPERIMENTAL APPROACH

Rats subjected to controlled cortical impact injury were injected with baicalein (30 mg kg(-1)) or vehicle immediately after injury or daily for 4 days. Neurological status was evaluated using the rotarod, adhesive removal, modified neurological severity scores and beam walk tests. Contusion volume and neuronal degeneration were measured using cresyl violet and FluoroJade B (FJB) histochemistry. Levels of tumour necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta) and interleukin-6 (IL-6) mRNA and protein were assessed by real-time quantitative reverse transcriptase-PCR, enzyme-linked immunosorbent assay and immunohistochemistry.

KEY RESULTS

Single-dose and multiple-dose treatment with baicalein significantly improved functional recovery and reduced contusion volumes up to day 28 post-injury, although multiple-dose baicalein was the more effective treatment. Single-dose baicalein also significantly reduced the number of degenerating neurons (31%) on post-injury day 1 as indicated by FJB staining. These changes were associated with significantly decreased levels, at the contusion site, of TNF-alpha, IL-1 beta and IL-6 mRNA at 6 h, and cytokine protein on day 1 post-injury.

CONCLUSIONS AND IMPLICATIONS

Post-injury treatment with baicalein improved functional and histological outcomes and reduced induction of proinflammatory cytokines in rat TBI. The neuroprotective effect of baicalein may be related to a decreased inflammatory response following the injury.

Early versus late onset of multiple organ failure is associated with differing patterns of plasma cytokine biomarker expression and outcome after severe trauma

Although multiple organ failure (MOF) remains the leading cause of death after trauma, the pathogenic cellular and molecular mechanisms underlying MOF are poorly understood. In addition to proinflammatory and anti-inflammatory mediator cascades, the temporal onset of MOF has generated recent interest because the organ systems involved into MOF seem to deteriorate in a time-dependent fashion after trauma. We therefore investigated the temporal course of MOF in traumatized human patients and evaluated and compared the distribution patterns of cytokine expression, including interleukin (IL) 6, IL-8, IL-10, and the soluble tumor necrosis factor-[alpha] receptors sTNF-R p55 and sTNF-R p75 in early-onset versus late-onset MOF. In addition, we analyzed the predictive value of cytokine biomarkers of MOF and lethal outcome. In a prospective observational cohort study conducted at three trauma centers, all patients (n = 352) admitted to two level 1 trauma centers in Germany were enrolled in the study based on the following inclusion criteria: severe traumatic brain injury (TBI) with a Glasgow Coma Scale (GCS) score of 8 or lower and/or distinct changes in cranial computed tomography and/or multiple injuries (MT) to the body (at least two regions had Abbreviated Injury Scale score of 3 or higher). The incidence of MOF was evaluated using the modified Goris-MOF score. The temporal onset of MOF was divided into early-onset MOF (EMOF, developing on days 0-3), late-onset MOF (LMOF, developing on days 4-10), combined early-onset and late-onset MOF (CMOF), and patients never showing signs of MOF during the observation period. In addition, the levels of the serum cytokine markers IL-6, IL-8, IL-10, sTNF-R p55, and sTNF-R p75 were analyzed at specific posttraumatic time points using established enzyme-linked immunosorbent assay techniques. A total of 352 patients (274 men and 78 women; TBI, 101; TBI + MT, 125; MT, 126) were enrolled into the study. Patients assigned to the EMOF group showed specific disruption of pulmonary and cardiocirculatory function, whereas LMOF was significantly associated with hepatic failure. The patients without signs of MOF and the EMOF patients had the same risk of lethal outcome (8.2% vs. 7.5%); LMOF and CMOF were found to be associated with a 3- to 4-fold increase in mortality (38.5% vs. 30.6%, respectively). Analysis of cytokine serum biomarkers revealed that patients with LMOF showed a biphasic elevation of IL-6 and significantly higher sTNF-R concentrations than did all other subgroups (P < 0.001). In addition, the initial values (days 0-1) of sTNF-R p55 and sTNF-R p75 expression levels had a good predictive capacity for the development of LMOF (p55, 0.75; p75, 0.72); values greater than 0.65 were accepted to have a predictive capacity. These results demonstrate that mortality differs significantly between the development of EMOF and LMOF after traumatic injury. Our results also suggest that serum cytokine measurements may be important early biochemical markers for predicting the development of delayed MOF.

Multiplex assessment of cytokine and chemokine levels in cerebrospinal fluid following severe pediatric traumatic brain injury: effects of moderate hypothermia

This study performed a comprehensive analysis of cerebrospinal fluid (CSF) cytokine levels after severe traumatic brain injury (TBI) in children using a multiplex bead array assay and to evaluate the effects of moderate hypothermia on cytokine levels. To this end, samples were collected during two prospective randomized controlled trials of therapeutic moderate hypothermia in pediatric TBI. Thirty-six children with severe TBI (Glasgow Coma Scale [GCS] score of <or=8) and 10 children with negative diagnostic lumbar punctures. All children with TBI had continuous monitoring of intracranial pressure and CSF drainage via an intraventricular catheter. Moderate hypothermia (32-33 degrees C) was maintained for 48 h in 17 patients, and they were slowly re-warmed at 48-72 h. A multiplex bead array assay was used to analyze serial CSF samples (<18 h, 24 +/- 6 h, 48 +/- 6 h, and 72 +/- 6 h) for 21 pro-and anti-inflammatory cytokines and chemokines. Interleukin (IL)-8 and transforming growth factor beta were measured by enzyme-linked immunosorbant assay (ELISA). There was a strong correlation (Spearman correlation coefficient = 0.92, p < 0.001) between multiplex assay and ELISA for IL-8. Pro-inflammatory IL-1beta, -6 and -12p70, anti-inflammatory IL-10 and chemokines IL-8 and MIP-1alpha were increased after TBI compared to controls, p < 0.05; however, there was no association between cytokines and age, gender, initial GCS, or outcome. Hypothermia did not attenuate the increases in CSF cytokine levels after TBI versus normothermia. This investigation confirmed that the multiplex bead array assay is a useful method to measure CSF cytokine levels. Severe TBI in infants and children induces increases in pro- and anti-inflammatory cytokines and chemokines. It is the first clinical report of increased levels of MIP-1alpha after TBI in any patient population and the most comprehensive assessment of cytokines after TBI to date. Moderate therapeutic hypothermia did not attenuate the increase in CSF cytokine levels in children after TBI.

High-sensitivity C-reactive protein levels in cerebrospinal fluid and serum in severe head injury: Relationship to tumor necrosis factor-α and interleukin-6

Recent studies have demonstrated the role of high-sensitivity C-reactive protein (hsCRP) in inflammatory diseases; however, it is unclear whether this molecule has a role after severe head injury (SHI). Our aim was to evaluate the levels of hsCRP in both cerebrospinal fluid (CSF) and serum from patients after SHI. The study focused on 11 patients with SHI, and evaluated CSF and serum levels of hsCRP, tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) in a 10-day period following the head trauma. The values were compared with those from nine control patients, who had normal pressure hydrocephalus. In the CSF and serum of the patients after SHI, HsCRP was found to be significantly higher, at all times, than in the controls; TNF-alpha and IL-6 levels were also higher in these patients. However, hsCRP levels did not correlate with either TNF-alpha or IL-6. TNF-alpha and IL-6 increased during the period immediately following the SHI, and intrathecal levels were always higher than those of the serum. This study demonstrates for the first time that hsCRP reaches high levels in both CSF and serum in patients with SHI, and it may therefore be used as an inflammatory index. This finding suggests a need for further studies in this area, which are larger in scope than the present study.

Modulation of immune response by head injury

Despite the fact that traumatic brain injury (TBI) is a silently growing epidemic, we are yet to understand its multifaceted pathogenesis, where various cellular pathways are initiated in response to both the primary mechanical insult and secondary physiologically mediated injury. Although the brain has traditionally been considered an immunologically privileged site, evidence to the contrary exists in studies of central nervous system (CNS) pathology, in particular TBI. Transmigration of leukocytes following blood brain barrier (BBB) disruption results in activation of resident cells of the CNS, such as microglia and astrocytes, to possess immunological function. Both infiltrating peripheral immune cells and activated resident cells subsequently engage in the intrathecal production of cytokines, important indicators of the presence of neuroinflammation. Cytokines can either promote this neurotoxicity, by encouraging excitotoxicity and propagating the inflammatory response, or attenuate the damage through neuroprotective and neurotrophic mechanisms, including the induction of cell growth factors. Certain cytokines perform both functions, for example, interleukin-6 (IL-6). This review article discusses the notion that the inflammatory response to TBI is no longer a peripherally mediated phenomenon, and that the CNS significantly influences the immunological sequence of events in the aftermath of injury.

[The relevance of the inflammatory response in the injured brain]

Research efforts in recent years have defined traumatic brain injury (TBI) as a predominantly immunological and inflammatory disorder. This perception is based on the fact that the overwhelming neuroinflammatory response in the injured brain contributes to the development of posttraumatic edema and to neuropathological sequelae which are, in large part, responsible for the adverse outcome. While the "key" mediators of neuroinflammation, such as the cytokine cascade and the complement system, have been clearly defined by studies in experimental TBI models, their exact pathways of interaction and pathophysiological implications remain to be further elucidated. This lack of knowledge is partially due to the concept of a "dual role" of the neuroinflammatory response after TBI. This notion implies that specific inflammatory molecules may mediate diverse functions depending on their local concentration and kinetics of expression in the injured brain. The inflammation-induced effects range from beneficial aspects of neuroprotection to detrimental neurotoxicity. The lack of success in pushing anti-inflammatory therapeutic concepts from"bench to bedside" for patients with severe TBI strengthens the further need for advances in basic research on the molecular aspects of the neuroinflammatory network in the injured brain. The present review summarizes the current knowledge from experimental studies in this field of research and discusses potential future targets of investigation.

Serum interleukin-6 soluble receptor in relation to interleukin-6 in stroke patients

Cerebral ischemia triggers interleukin-6 (IL-6) release into blood. IL-6 is a key mediator of acute phase reaction. Markers of acute phase reaction (C-reactive protein, fibrinogen, fever) have been linked to poor prognosis in stroke patients. Interleukin-6 soluble receptor (sIL-6R) can potentiate IL-6 pro-inflammatory activity. The aim of this study was to investigate the relationship between IL-6 and sIL-6R in stroke patients. Serum cytokine levels were measured in 18 stroke patients and 13 controls using the ELISA method. On the second day of stroke, IL-6 levels were significantly higher in stroke patients than in controls; sIL-6R levels did not differ significantly between groups. Three months after stroke, IL-6 levels did not differ significantly between groups; sIL-6R levels were significantly decreased in stroke patients when compared with that in controls and with levels in acute phase of stroke. Decreased sIL-6R early after stroke might reflect a regulatory mechanism attenuating inflammatory response.

Early expression and cellular localization of proinflammatory cytokines interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha in human traumatic spinal cord injury

STUDY DESIGN

Post-traumatic inflammatory response was studied in 11 human cases of acute spinal cord contusion injury.

OBJECTIVES

To examine the inflammatory cellular response and the immunocytochemical expression and localization of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha in human spinal cord after contusion injury.

SUMMARY OF BACKGROUND DATA

: The post-traumatic inflammatory response plays an important role in secondary injury mechanisms after spinal cord injury, and interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha are key inflammatory mediators.

METHODS

: The study group comprised 11 patients with spinal cord contusion injury and 2 normal individuals. Histologic and immunocytochemical assessments were undertaken to evaluate the inflammatory cellular response and the immunoexpression of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha in the injured human spinal cord. The cellular sources of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha were elucidated by immunofluorescence double-labeled confocal imaging.

RESULTS

: Increased immunoreactivity of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha was detected in neurons 0.5 hour after injury, and in neurons and microglia 5 hours after injury, but the expression of these proinflammatory cytokines was short-lived and declined sharply to baseline by 2 days after injury. In the inflammatory cellular response, as early as 0.5 hour after spinal cord injury, activated microglia were detected, and axonal swellings and axons were surrounded by microglial processes. Numerous neutrophils appeared in the injured cord 1 day after injury, and then their number declined dramatically, whereas macrophages progressively increased after day 1.

CONCLUSIONS

Endogenous cells (neurons and microglia) in the human spinal cord, not the blood-borne leukocytes, contribute to the early production of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha in the post-traumatic inflammatory response, and microglia are involved the early response to traumatic axonal injury.

Expression of cytokines and cytokine receptors in the rat brain after kainic acid-induced seizures

We have previously shown that IL-6 protein levels are increased in cerebrospinal fluid in humans after recent tonic-clonic seizures with unchanged levels of IL-1beta and TNFalpha. Here we studied the expression of cytokines IL-6, LIF, IL-1beta and TNFalpha and cytokine receptors IL-6R, LIFR and Gp130 in the rat brain after kainic acid-induced status epilepticus using Northern blot analysis and in situ hybridization histochemistry. After seizures, IL-6 mRNA was induced in the hippocampus, cortex, amygdala and meninges, and IL-6R was up-regulated in the hippocampus. LIF was up-regulated in the hippocampus, cortex and meninges after seizures, and LIFR mRNA was induced in the hippocampus and cortex. Gp130 was constitutively expressed in the brain. After seizures, Gp130 transcription was rapidly induced in the meninges. In thalamus, cortex, amygdala and hippocampus Gp130 mRNA was induced in a delayed fashion. IL-1beta transcription was induced in the temporal lobe cortex and thalamus, and TNFalpha in the hippocampus. In general, the cytokine and their receptor mRNA levels were low in intact rat brain, but were induced by seizures. Since IL-6 and LIF transcripts were induced in the meninges after seizures, the protein products of these transcripts may be more readily released in cerebrospinal fluid after seizures. In addition, the activity of IL-6 and LIF signaling pathways may be influenced by increased expression of their receptors after seizures.

Hypothalamic-pituitary-adrenal axis and interleukin-6 activity in children with head trauma and syndrome of inappropriate secretion of antidiuretic hormone

OBJECTIVE

Arginine vasopressin (AVP; anti-diuretic hormone) and corticotropin-releasing hormone are the two major secretagogues of hypophyseal adrenocorticotropin (ACTH). Interleukin-6 (IL-6) is a potent stimulator of the human hypothalamic-pituitary-adrenal axis (HPA) and a secretagogue of both parvocellular and magnocelullar AVP. We have previously suggested that IL-6-stimulated AVP secretion may be the origin of the syndrome of inappropriate antidiuretic hormone secretion (SIADH) in inflammatory conditions.

STUDY DESIGN

To further elucidate the relationship between IL-6 and SIADH as well as IL-6 and HPA axis activity, we studied eight previously healthy children (age 6.3 +/- 4.8 [mean +/- SD] years, weight 23.8 +/- 10.5 kg) who--after sustaining head trauma--presented SIADH during hospitalization (for 7.1 +/- 3.8 days) in the pediatric intensive care unit (P-ICU). Routine blood samples were taken twice daily at 08:00 and 20:00 hours. All children but one survived. Measurements included blood and urine osmolality (BlOsm and UrOsm, respectively), serum cortisol (F) and IL-6, plasma ACTH and AVP. Correlations were assessed with linear regression among the areas under the curve (AUC) of BlOsm, UrOsm, ACTH, F, IL-6 and AVP, separately for BlOsm values <280 mOsm (SIADH phase) and > or = 280 mOsm (non-SIADH phase).

RESULTS

During the SIADH phase AVP-AUC correlated positively with IL-6-AUC (r = +0.96, p<0.05), BlOsm-AUC correlated positively with AVP-AUC and F-AUC (r = +0.95 and +0.98, p<0.05, respectively) and F-AUC correlated positively with ACTH-AUC (r = +0.99, p<0.05). During the non-SIADH phase ACTH-AUC correlated positively with BlOsm-AUC (r = +0.96, p<0.05).

CONCLUSION

IL-6 secreted during an aseptic inflammatory state, such as sustaining head trauma with SIADH, is quantitatively correlated to AVP, indicating that this cytokine is directly and/or indirectly involved in the pathogenesis of SIADH.

Association between cerebrospinal fluid interleukin-6 concentrations and outcome after severe human traumatic brain injury

Acute inflammation plays a significant role in the pathophysiology of traumatic brain injury (TBI). However, the specific relationships between inflammatory mediators and patient outcome following TBI have not been fully established. In this study, we measured plasma and cerebrospinal fluid interleukin-1 (IL-1) and interleukin-6 (IL-6) concentrations in 36 patients, following severe TBI. Patients were monitored with continuous measurements of somatosensory-evoked potentials (SSEP) to derive an established surrogate outcome measurement, the 96-h evoked potential (SSEP96). Clinical outcomes were assessed at 3 months using the Glasgow Outcome Scale (GOS). Peak cerebrospinal fluid (CSF) IL-1 and IL-6 concentrations were significantly higher than those observed in the plasma [median 6.5 pg/mL (range 1.4-25.0) vs. 3.0 (0.8-7.6) for IL-1, and 650 (130-7,214) vs. 253 (52-1,506) for IL-6, p < 0.001 for both]. Peak CSF IL-6 levels correlated with SSEP96 (r = 0.42; p = 0.0133), and peak CSF IL-6 levels were higher with improved GOS (p = 0.024). Multiple regression analysis identified that age (p = 0.0072), pupillary abnormality (p = 0.021), the presence of mass lesion (p = 0.023), and peak CSF IL-6 concentrations (p = 0.026) were all statistically significant predictors of clinical outcome following TBI. These results suggest that peak CSF IL-6 concentrations correlate with improved outcome following TBI. This finding helps to characterize the inflammatory reaction associated with TBI and may help to develop improved treatment strategies for patients with TBI.

Prolonged intrathecal release of soluble Fas following severe traumatic brain injury in humans

The mechanisms underlying cell death following traumatic brain injury (TBI) are not fully understood. Apoptosis is believed to be one mechanism contributing to a marked and prolonged neuronal cell loss following TBI. Recent data suggest a role for Fas (APO-1, CD95), a type I transmembrane receptor glycoprotein of the nerve growth factor/tumor necrosis factor superfamily, and its ligand (Fas ligand, FasL) in apoptotic events in the central nervous system. A truncated form of the Fas receptor, soluble Fas (sFas) may indicate activation of the Fas/FasL system and act as a negative feedback mechanism, thereby inhibiting Fas mediated apoptosis. Soluble Fas was measured in cerebrospinal fluid (CSF) and serum of 10 patients with severe TBI (GCS< or =8) for up to 15 days post-trauma. No sFas was detected in CSF samples from patients without neurological pathologies. Conversely, after TBI 118 out of 120 CSF samples showed elevated sFas concentrations ranging from 56 to 4327 mU/ml. Paired serum samples showed above normal (8.5 U/ml) sFas concentrations in 5 of 10 patients. Serum levels of sFas were always higher than CSF levels. However, there was no correlation between concentrations measured in CSF and in serum (r(2)=0.078, p=0.02), suggesting that the concentrations in the two compartments are independently regulated. Also, no correlation was found between sFas in CSF and blood brain barrier (BBB) dysfunction as assessed by the albumin CSF/serum quotient (Q(A)), and concentrations of the cytotoxic cytokine tumor necrosis factor-alpha in CSF, respectively. Furthermore, there was no correlation with two markers of immune activation (soluble interleukin-2 receptor and neopterin) in CSF. Maximal CSF levels of sFas correlated significantly (r(2)=0.8191, p<0.001) with the early peaks of neuron-specific enolase in CSF (a marker for neuronal cell destruction), indicating that activation of the Fas mediated pathway of apoptosis may be in part the direct result of the initial trauma. However, the prolonged elevation of sFas in CSF may be caused by the ongoing inflammatory response to trauma and delayed apoptotic cell death.

Continuous interleukin-6 application in vivo via macroencapsulation of interleukin-6-expressing COS-7 cells induces massive gliosis

The inflammatory cytokine interleukin-6 (IL-6) was found in senile plaques of Alzheimer's patients and might be involved in the pathology of Parkinson's disease and multiple sclerosis. Interestingly, an astocytosis is also found in these neurodegenerative disorders. To evaluate the direct effects of IL-6 in vivo on glial cells, we created a new in vivo model. IL-6 and mock-transfected (control group) COS-7 cells were encapsulated in a poly-acryl-nitril membrane for implantation into the rat striatum. Afterward, the host immune reaction to the membrane without encapsulated cells and the biological action of IL-6-producing capsules was evaluated. Animals with an implanted membrane without cells showed a moderate astrocytosis 5 days after the operation. Furthermore, microglia and T-cells could be detected and after 30 days the astrocytosis decreased to a small layer around the membrane. In comparison to the control group, which received a sham operation, our results demonstrate that the response of glial cells is caused by the mechanical damage of the surgical procedure itself rather than due to the introduced membrane material. In contrast, we found a massive proliferation and activation of astrocytes and microglia after 10 days by IL-6-secreting capsules, indicating that IL-6 is involved in the induction of gliosis. Control animals that received encapsulated mock-transfected COS-7 cells showed only a weak response. These data point to an involvement of IL-6 in the proliferation and activation of glial cells as seen in neurodegenerative disorders.

The duality of the inflammatory response to traumatic brain injury

One and a half to two million people sustain a traumatic brain injury (TBI) in the US each year, of which approx 70,000-90,000 will suffer from long-term disability with dramatic impacts on their own and their families' lives and enormous socio-economic costs. Brain damage following traumatic injury is a result of direct (immediate mechanical disruption of brain tissue, or primary injury) and indirect (secondary or delayed) mechanisms. These secondary mechanisms involve the initiation of an acute inflammatory response, including breakdown of the blood-brain barrier (BBB), edema formation and swelling, infiltration of peripheral blood cells and activation of resident immunocompetent cells, as well as the intrathecal release of numerous immune mediators such as interleukins and chemotactic factors. An overview over the inflammatory response to trauma as observed in clinical and in experimental TBI is presented in this review. The possibly harmful/beneficial sequelae of post-traumatic inflammation in the central nervous system (CNS) are discussed using three model mediators of inflammation in the brain, tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and transforming growth factor-beta (TGF-beta). While the former two may act as important mediators for the initiation and the support of post-traumatic inflammation, thus causing additional cell death and neurologic dysfunction, they may also pave the way for reparative processes. TGF-beta, on the other hand, is a potent anti-inflammatory agent, which may also have some deleterious long-term effects in the injured brain. The implications of this duality of the post-traumatic inflammatory response for the treatment of brain-injured patients using anti-inflammatory strategies are discussed.

Early cellular brain damage and systemic inflammatory response after cardiopulmonary resuscitation or isolated severe head trauma: a comparative pilot study on common pathomechanisms

Severe neurological deficits are common characteristics of patients surviving cardiopulmonary resuscitation (CPR) or isolated severe head trauma (SHT). For comparative evaluation of underlying pathomechanisms, 22 patients with out-of-hospital cardiac arrest and successful CPR as well as 10 patients with SHT were included in our prospective study. Circulating S-100B was determined as an indicator of cellular brain damage. Interleukin-8 (IL-8), soluble E-selectin (sE-selectin) and polymorphonuclear (PMN-) elastase were measured as markers of systemic inflammation following whole body ischaemia and reperfusion injury. Venous blood samples were drawn on scene (median time 11.0 min after starting basic life support) and in the intensive care unit (median time 12.5 h thereafter) in CPR patients and at admission to hospital (median time 43.8 min after trauma) and approx. 12 h later in SHT patients. Biochemical parameters in these samples were compared with specimens taken from 20 healthy volunteers. Initial median S-100B levels of the CPR and SHT patients were both significantly increased compared with the controls. Twelve hours later, significant falls in S-100B revealed no differences between the two patient groups, but did not reach control values. Median IL-8 and sE-selectin levels entry to the study were elevated in both patient groups compared with controls and showed further rises within the following 12 h. Finally, increased initial median levels of PMN-elastase revealed significant differences between the patient groups and between patients and controls. Twelve hours later, median PMN-elastase values were equally elevated in the CPR and SHT subjects. Our preliminary data suggest similar pathomechanisms occurring after both CPR and SHT. Both clinical entities seem to be associated with early transient cellular brain damage as shown by prolonged rapidly increasing and subsequent fall in S-100B serum levels. In contrast, the prolonged elevation of circulating IL-8, sE-selectin and PMN-elastase may indicate a very similar systemic inflammatory response by endothelial cells and neutrophils initiated by ischaemia and reperfusion injury in both conditions. Further studies should be carried out to determine the cause and the prognostic value of these biochemical parameters in relation to long-term neurological outcome.

The soluble interleukin 6 receptor: mechanisms of production and implications in disease

Interleukin 6 (IL-6) performs a prominent role during disease and has been described as both a pro- and anti-inflammatory cytokine. A key feature in the regulation of IL-6 responses has been the identification of a soluble interleukin 6 receptor (sIL-6R), which forms a ligand-receptor complex with IL-6 that is capable of stimulating a variety of cellular responses including proliferation, differentiation and activation of inflammatory processes. Elevated sIL-6R levels have been documented in numerous clinical conditions indicating that its production is coordinated as part of a disease response. Thus, sIL-6R has the potential to regulate both local and systemic IL-6-mediated events. This review will outline the central role of sIL-6R in the coordination of IL-6 responses. Details relating to the mechanisms of sIL-6R production will be provided, while the potential significance of sIL-6R during the development of clinical conditions will be emphasized. We want to convey, therefore, that when thinking about the inflammatory capability of IL-6, it is essential to consider not only the action of IL-6 itself, but also the effect sIL-6R may have on cellular processes.

Interleukin (IL)-10 inhibits IL-6 production in microglia by preventing activation of NF-kappaB

The purpose of this study was to determine if interleukin (IL)-10 inhibits lipopolysaccharide (LPS)-induced IL-6 production in microglia by inhibiting activation of nuclear factor-kappaB (NF-kappaB). N13 microglia (a murine microglial cell line) and primary microglia from neonatal mice were cultured in the presence or absence of LPS and increasing amounts of murine IL-10 for 24 h. As predicted, LPS treatment increased supernatant IL-6 concentration in both N13 and primary microglia cultures. Pretreatment with IL-10, however, decreased LPS-induced IL-6 secretion in a dose-dependent manner in both culture systems. Likewise, ribonuclease protection assays showed that LPS increased steady-state IL-6 mRNA levels, but that pretreatment with IL-10 blocked the LPS-induced increase in IL-6 mRNA. Because NF-kappaB is the predominant transcription factor responsible for IL-6 transcription in response to inflammatory stimuli, it was hypothesized that IL-10 inhibited IL-6 production by preventing nuclear translocation of NF-kappaB. Consistent with this idea, LPS increased nuclear translocation of NF-kappaB as assessed by gel mobility shift assay. Supershift assays and immunocytochemical staining showed that both the p50 and p65 subunits of NF-kappaB translocated from the cytoplasm to the nucleus upon LPS stimulation. Pretreatment with IL-10, however, inhibited LPS-induced activation of NF-kappaB. Furthermore, inhibition of NF-kappaB activity with tosyl-Phe-chloromethlyketone (a serine protease inhibitor that prevents degradation of the NF-kappaB-IkappaB complex), completely blocked LPS-induced IL-6 production. These data suggest that IL-10 inhibited IL-6 production in microglia by decreasing the activity of NF-kappaB and, therefore, extend what little is known of the intricate relationship between anti-inflammatory and inflammatory cytokines in the central nervous system.

Experimental closed head injury: analysis of neurological outcome, blood-brain barrier dysfunction, intracranial neutrophil infiltration, and neuronal cell death in mice deficient in genes for pro-inflammatory cytokines

Cytokines are important mediators of intracranial inflammation following traumatic brain injury (TBI). In the present study, the neurological impairment and mortality, blood-brain barrier (BBB) function, intracranial polymorphonuclear leukocyte (PMN) accumulation, and posttraumatic neuronal cell death were monitored in mice lacking the genes for tumor necrosis factor (TNF)/lymphotoxin-alpha (LT-alpha) (TNF/LT-alpha-/-) and interleukin-6 (IL-6) and in wild-type (WT) littermates subjected to experimental closed head injury (total n = 107). The posttraumatic mortality was significantly increased in TNF/LT-alpha-/- mice (40%; P < 0.02) compared with WT animals (10%). The IL-6-/- mice also showed a higher mortality (17%) than their WT littermates (5.6%), but the difference was not statistically significant (P > 0.05). The neurological severity score was similar among all groups from 1 to 72 hours after trauma, whereas at 7 days, the TNF/LT-alpha-/- mice showed a tendency toward better neurological recovery than their WT littermates. Interestingly, neither the degree of BBB dysfunction nor the number of infiltrating PMNs in the injured hemisphere was different between WT and cytokine-deficient mice. Furthermore, the analysis of brain sections by in situ DNA nick end labeling (TUNEL histochemistry) at 24 hours and 7 days after head injury revealed a similar extent of posttraumatic intracranial cell death in all animals. These results show that the pathophysiological sequelae of TBI are not significantly altered in mice lacking the genes for the proinflammatory cytokines TNF, LT-alpha, and IL-6. Nevertheless, the increased posttraumatic mortality in TNF/LT-alpha-deficient mice suggests a protective effect of these cytokines by mechanisms that have not been elucidated yet.

Interleukin-6 expression and regulation in astrocytes

The physiological function of interleukin-6 (IL-6) within the central nervous system (CNS) is complex; IL-6 exerts neurotrophic and neuroprotective effects, and yet can also function as a mediator of inflammation, demyelination, and astrogliosis, depending on the cellular context. In the normal brain, IL-6 levels remain low. However, elevated expression occurs in injury, infection, stroke, and inflammation. Given the diverse biological functions of IL-6 and its expression in numerous CNS conditions, it is critical to understand its regulation in the brain in order to control its expression and ultimately its effects. Accumulating data demonstrate that the predominant CNS source of IL-6 is the activated astrocyte. Furthermore, a wide range of factors have been demonstrated to be involved in IL-6 regulation by astrocytes. In this review, we summarize information concerning IL-6 regulation in astrocytes, focusing on the role of proinflammatory factors, neurotransmitters, and second messengers.