The Terminal Pathway of the Complement System Is Activated in Focal Penetrating But Not in Mild Diffuse Traumatic Brain Injury

Establishing a 3-Tesla Magnetic Resonance Imaging Method for Assessing Diffuse Axonal Brain Injury in Rats

Traumatic brain injury (TBI) significantly contributes to death and disability worldwide. However, treatment options remain limited. Here, we focus on a specific pathology of TBI, diffuse axonal brain injury (DABI), which describes the process of the tearing of nerve fibers in the brain after blunt injury. Most protocols to study DABI do not incorporate a specific model for that type of pathology, limiting their ability to identify mechanisms and comorbidities of DABI. In this study, we developed a magnetic resonance imaging (MRI) protocol for DABI in a rat model using a 3-T clinical scanner. We compared the neuroimaging outcomes with histologic and neurologic assessments. In a sample size of 10 rats in the sham group and 10 rats in the DABI group, we established neurological severity scores before the intervention and at 48 h following DABI induction. After the neurological evaluation after DABI, all rats underwent MRI scans and were subsequently euthanized for histological evaluation. As expected, the neurological assessment showed a high sensitivity for DABI lesions indicated using the β-APP marker. Surprisingly, however, we found that the MRI method had greater sensitivity in assessing DABI lesions compared to histological methods. Out of the five MRI parameters with pathological changes in the DABI model, we found significant changes compared to sham rats in three parameters, and, as shown using comparative tests with other models, MRI was the most sensitive parameter, being even more sensitive than histology. We anticipate that this DABI protocol will have a significant impact on future TBI and DABI studies, advancing research on treatments specifically targeted towards improving patient quality of life and long-term outcomes.

Extracellular vesicles in plasma and cerebrospinal fluid in patients with COVID-19 and neurological symptoms

INTRODUCTION

Increased levels of extracellular vesicles (EVs) are associated with haemostatic disturbances in various clinical settings. However, their role in COVID-19 patients is still not fully clear. In the present study we investigated EVs in plasma from patients with COVID-19 and neurological symptoms in relation to the activation of coagulation.

METHODS

Nineteen COVID-19 patients with neurological symptoms and twenty-three aged-matched healthy individuals were included. Global coagulation assays were performed and levels of EVs were determined by flow-cytometry in plasma and cerebrospinal fluid (CSF).

RESULTS

A procoagulant state characterized by significantly increased overall coagulation- (OCP) and overall haemostatic potential (OHP), diminished overall fibrinolytic potential (OFP) together with a denser fibrin structure was found in patients with COVID-19. Flow cytometry revealed elevated levels of plasma circulating EVs derived from neutrophils (MPO+) and platelets (CD61+), as well as EVs expressing phosphatidylserine (PS+) and complement component C5b-9 (TCC+) in patients with COVID-19 compared with controls. The concentrations of PS+, CD61+ and TCC+ EVs were positively correlated with OCP and OHP in COVID-19 patients. Moreover, we identified CD61+, MPO+ and endothelial cell-derived EVs, as well as EVs exposing PS and TCC in the CSF of patients suffering from neurological symptoms during COVID-19.

CONCLUSION

The unique finding in this study was the presence of EVs in the CSF of COVID-19 patients with neurologic manifestations as well as higher expression of complement protein on circulating plasma EVs. EVs may indicate blood-brain barrier damage during SARS-COV-2 infection.

Interleukin-1 Receptor Antagonist as Therapy for Traumatic Brain Injury

Traumatic brain injury is a common type of acquired brain injury of varying severity carrying potentially deleterious consequences for the afflicted individuals, families, and society. Following the initial, traumatically induced insult, cellular injury processes ensue. These are believed to be amenable to treatment. Among such injuries, neuroinflammation has gained interest and has become a specific focus for both experimental and clinical researchers. Neuroinflammation is elicited almost immediately following trauma, and extend for a long time, possibly for years, after the primary injury. In the acute phase, the inflammatory response is characterized by innate mechanisms such as the activation of microglia which among else mediates cytokine production. Among the earliest cytokines to emerge are the interleukin- (IL-) 1 family members, comprising, for example, the agonist IL-1β and its competitive antagonist, IL-1 receptor antagonist (IL-1ra). Because of its early emergence following trauma and its increased concentrations also after human TBI, IL-1 has been hypothesized to be a tractable treatment target following TBI. Ample experimental data supports this, and demonstrates restored neurological behavior, diminished lesion zones, and an attenuated inflammatory response following IL-1 modulation either through IL-1 knock-out experiments, IL-1β inhibition, or IL-1ra treatment. Of these, IL-1ra treatment is likely the most physiological. In addition, recombinant human IL-1ra (anakinra) is already approved for utilization across a few rheumatologic disorders. As of today, one randomized clinical controlled trial has utilized IL-1ra inhibition as an intervention and demonstrated its safety. Further clinical trials powered for patient outcome are needed in order to demonstrate efficacy. In this review, we summarize IL-1 biology in relation to acute neuroinflammatory processes following TBI with a particular focus on current evidence for IL-1ra treatment both in the experimental and clinical context.

Complement in the Development of Post-Traumatic Epilepsy: Prospects for Drug Repurposing

Targeting neuroinflammation is a novel frontier in the prevention and treatment of epilepsy. A substantial body of evidence supports a key role for neuroinflammation in epileptogenesis, the pathological process that leads to the development and progression of spontaneous recurrent epileptic seizures. It is also well recognized that traumatic brain injury (TBI) induces a vigorous neuroinflammatory response and that a significant proportion of patients with TBI suffer from debilitating post-traumatic epilepsy. The complement system is a potent effector of innate immunity and a significant contributor to secondary tissue damage and to epileptogenesis following central nervous system injury. Several therapeutic agents targeting the complement system are already on the market to treat other central nervous system disorders or are well advanced in their development. The purpose of this review is to summarize findings on complement activation in experimental TBI and epilepsy models, highlighting the potential of drug repurposing in the development of therapeutics to ameliorate post-traumatic epileptogenesis.

A Systematic Review of Closed Head Injury Models of Mild Traumatic Brain Injury in Mice and Rats

Mild TBI (mTBI) is a significant health concern. Animal models of mTBI are essential for understanding mechanisms, and pathological outcomes, as well as to test therapeutic interventions. A variety of closed head models of mTBI that incorporate different aspects (i.e., biomechanics) of the mTBI have been reported. The aim of the current review was to compile a comprehensive list of the closed head mTBI rodent models, along with the common data elements, and outcomes, with the goal to summarize the current state of the field. Publications were identified from a search of PubMed and Web of Science and screened for eligibility following PRISMA guidelines. Articles were included that were closed head injuries in which the authors classified the injury as mild in rats or mice. Injury model and animal-specific common data elements, as well as behavioral and histological outcomes, were collected and compiled from a total of 402 articles. Our results outline the wide variety of methods used to model mTBI. We also discovered that female rodents and both young and aged animals are under-represented in experimental mTBI studies. Our findings will aid in providing context comparing the injury models and provide a starting point for the selection of the most appropriate model of mTBI to address a specific hypothesis. We believe this review will be a useful starting place for determining what has been done and what knowledge is missing in the field to reduce the burden of mTBI.

Activation of mGluR1 Mediates C1q-Dependent Microglial Phagocytosis of Glutamatergic Synapses in Alzheimer's Rodent Models

Microglia and complements appear to be involved in the synaptic and cognitive deficits in Alzheimer's disease (AD), though the mechanisms remain elusive. In this study, utilizing two types of rodent model of AD, we reported increased complement C1q-mediated microglial phagocytosis of hippocampal glutamatergic synapses, which led to synaptic and cognitive deficits. We also found increased activity of the metabotropic glutamate receptor 1 (mGluR1) in hippocampal CA1 in the modeled rodents. Artificial activation of mGluR1 signaling promoted dephosphorylation of fragile X mental retardation protein (FMRP) and facilitated the local translation machinery of synaptic C1q mRNA, thus mimicking the C1q-mediated microglial phagocytosis of hippocampal glutamatergic synapses and synaptic and cognitive deficiency in the modeled rodents. However, suppression of mGluR1 signaling inhibited the dephosphorylation of FMRP and repressed the local translation of synaptic C1q mRNA, which consequently alleviated microglial phagocytosis of synapses and restored the synaptic and cognitive function in the rodent models. These findings illustrate a novel molecular mechanism underlying C1q-mediated microglial phagocytosis of hippocampal glutamatergic synapses in AD.

Medusa's Head: The Complement System in Traumatic Brain and Spinal Cord Injury

Traumatic brain injury (TBI) and spinal cord injury (SCI) are critical medical conditions and a public health problem for which limited therapeutic options are available. The complement cascade is activated after TBI and SCI, and the resulting effects have been investigated in gene-knockout and pharmacological models. Multiple experimental studies support a net detrimental role of C3 and C5 activation in the early stages of TBI and SCI. Less firm experimental evidence suggests that, downstream of C3/C5, effector mechanisms, including the generation of membrane-activated complex and direct damage to membranes and neutrophils infiltration, may bring about the direct damage of central nervous system tissue and enhancement of neuroinflammation. The role of upstream classical, alternative, or extrinsic complement activation cascades remains unclear. Although several issues remain to be investigated, current evidence supports the investigation of a number of complement-targeting agents targeting C3 or C5, such as eculizumab, for repurposing in TBI and SCI treatment.

Neuroproteomics and Systems Biology Approach to Identify Temporal Biomarker Changes Post Experimental Traumatic Brain Injury in Rats

Traumatic brain injury (TBI) represents a critical health problem of which diagnosis, management, and treatment remain challenging. TBI is a contributing factor in approximately one-third of all injury-related deaths in the United States. The Centers for Disease Control and Prevention estimate that 1.7 million people suffer a TBI in the United States annually. Efforts continue to focus on elucidating the complex molecular mechanisms underlying TBI pathophysiology and defining sensitive and specific biomarkers that can aid in improving patient management and care. Recently, the area of neuroproteomics–systems biology is proving to be a prominent tool in biomarker discovery for central nervous system injury and other neurological diseases. In this work, we employed the controlled cortical impact (CCI) model of experimental TBI in rat model to assess the temporal–global proteome changes after acute (1 day) and for the first time, subacute (7 days), post-injury time frame using the established cation–anion exchange chromatography-1D SDS gel electrophoresis LC–MS/MS platform for protein separation combined with discrete systems biology analyses to identify temporal biomarker changes related to this rat TBI model. Rather than focusing on any one individual molecular entity, we used in silico systems biology approach to understand the global dynamics that govern proteins that are differentially altered post-injury. In addition, gene ontology analysis of the proteomic data was conducted in order to categorize the proteins by molecular function, biological process, and cellular localization. Results show alterations in several proteins related to inflammatory responses and oxidative stress in both acute (1 day) and subacute (7 days) periods post-TBI. Moreover, results suggest a differential upregulation of neuroprotective proteins at 7 days post-CCI involved in cellular functions such as neurite growth, regeneration, and axonal guidance. Our study is among the first to assess temporal neuroproteome changes in the CCI model. Data presented here unveil potential neural biomarkers and therapeutic targets that could be used for diagnosis, for treatment and, most importantly, for temporal prognostic assessment following brain injury. Of interest, this work relies on in silico bioinformatics approach to draw its conclusion; further work is conducted for functional studies to validate and confirm the omics data obtained.

Protein profiling in serum after traumatic brain injury in rats reveals potential injury markers

INTRODUCTION

The serum proteome following traumatic brain injury (TBI) could provide information for outcome prediction and injury monitoring. The aim with this affinity proteomic study was to identify serum proteins over time and between normoxic and hypoxic conditions in focal TBI.

MATERIAL AND METHODS

Sprague Dawley rats (n=73) received a 3mm deep controlled cortical impact ("severe injury"). Following injury, the rats inhaled either a normoxic (22% O₂) or hypoxic (11% O₂) air mixture for 30min before resuscitation. The rats were sacrificed at day 1, 3, 7, 14 and 28 after trauma. A total of 204 antibodies targeting 143 unique proteins of interest in TBI research, were selected. The sample proteome was analyzed in a suspension bead array set-up. Comparative statistics and factor analysis were used to detect differences as well as variance in the data.

RESULTS

We found that complement factor 9 (C9), complement factor B (CFB) and aldolase c (ALDOC) were detected at higher levels the first days after trauma. In contrast, hypoxia inducing factor (HIF)1α, amyloid precursor protein (APP) and WBSCR17 increased over the subsequent weeks. S100A9 levels were higher in hypoxic-compared to normoxic rats, together with a majority of the analyzed proteins, albeit few reached statistical significance. The principal component analysis revealed a variance in the data, highlighting clusters of proteins.

CONCLUSIONS

Protein profiling of serum following TBI using an antibody based microarray revealed temporal changes of several proteins over an extended period of up to four weeks. Further studies are warranted to confirm our findings.

An anticomplement agent that homes to the damaged brain and promotes recovery after traumatic brain injury in mice

Activation of complement is a key determinant of neuropathology and disability after traumatic brain injury (TBI), and inhibition is neuroprotective. However, systemic complement is essential to fight infections, a critical complication of TBI. We describe a targeted complement inhibitor, comprising complement receptor of the Ig superfamily (CRIg) fused with complement regulator CD59a, designed to inhibit membrane attack complex (MAC) assembly at sites of C3b/iC3b deposition. CRIg and CD59a were linked via the IgG2a hinge, yielding CD59-2a-CRIg dimer with increased iC3b/C3b binding avidity and MAC inhibitory activity. CD59-2a-CRIg inhibited MAC formation and prevented complement-mediated lysis in vitro. CD59-2a-CRIg dimer bound C3b-coated surfaces with submicromolar affinity (KD). In experimental TBI, CD59-2a-CRIg administered posttrauma homed to sites of injury and significantly reduced MAC deposition, microglial accumulation, mitochondrial stress, and axonal damage and enhanced neurologic recovery compared with placebo controls. CD59-2a-CRIg inhibited MAC-induced inflammasome activation and IL-1β production in microglia. Given the important anti-infection roles of complement opsonization, site-targeted inhibition of MAC should be considered to promote recovery postneurotrauma.

Inhibition of the membrane attack complex of the complement system reduces secondary neuroaxonal loss and promotes neurologic recovery after traumatic brain injury in mice

Traumatic brain injury (TBI) is the leading cause of disability and death in young adults. The secondary neuroinflammation and neuronal damage that follows the primary mechanical injury is an important cause of disability in affected people. The membrane attack complex (MAC) of the complement system is detected in the traumatized brain early after TBI; however, its role in the pathology and neurologic outcome of TBI has not yet been investigated. We generated a C6 antisense oligonucleotide that blocks MAC formation by inhibiting C6, and we compared its therapeutic effect to that of Ornithodoros moubata complement inhibitor (OmCI), a known inhibitor of C5 activation that blocks generation of the anaphylatoxin C5a and C5b, an essential component of MAC. Severe closed head injury in mice induced abundant MAC deposition in the brain. Treatment with C6 antisense reduced C6 synthesis (85%) and serum levels (90%), and inhibited MAC deposition in the injured brain (91-96%). Treatment also reduced accumulation of microglia/macrophages (50-88%), neuronal apoptosis, axonal loss and weight loss (54-93%), and enhanced neurologic performance (84-92%) compared with placebo-treated controls after injury. These data provide the first evidence, to our knowledge, that inhibition of MAC formation in otherwise complement-sufficient animals reduces neuropathology and promotes neurologic recovery after TBI. Given the importance of maintaining a functional complement opsonization system to fight infections, a critical complication in TBI patients, inhibition of the MAC should be considered to reduce posttraumatic neurologic damage. This work identifies a novel therapeutic target for TBI and will guide the development of new therapy for patients.