Christiane Albert-Weissenberger

Experimental traumatic brain injury

Traumatic brain injury, a leading cause of death and disability, is a result of an outside force causing mechanical disruption of brain tissue and delayed pathogenic events which collectively exacerbate the injury. These pathogenic injury processes are poorly understood and accordingly no effective neuroprotective treatment is available so far. Experimental models are essential for further clarification of the highly complex pathology of traumatic brain injury towards the development of novel treatments. Among the rodent models of traumatic brain injury the most commonly used are the weight-drop, the fluid percussion, and the cortical contusion injury models. As the entire spectrum of events that might occur in traumatic brain injury cannot be covered by one single rodent model, the design and choice of a specific model represents a major challenge for neuroscientists. This review summarizes and evaluates the strengths and weaknesses of the currently available rodent models for traumatic brain injury.

C1-Inhibitor Protects From Brain Ischemia-Reperfusion Injury by Combined Antiinflammatory and Antithrombotic Mechanisms

Background and Purpose— Inflammation and thrombosis are pathophysiological hallmarks of ischemic stroke still unamenable to therapeutic interventions. The contact-kinin system represents an interface between inflammatory and thrombotic circuits and is involved in stroke development. C1-inhibitor counteracts activation of the contact-kinin system at multiple levels. We investigated the therapeutic potential of C1-inhibitor in models of ischemic stroke. Methods— Male and female C57Bl/6 mice and rats of different ages were subjected to middle cerebral artery occlusion and treated with C1-inhibitor after 1 hour or 6 hours. Infarct volumes and functional outcomes were assessed between day 1 and day 7, and findings were validated by magnetic resonance imaging. Blood–brain barrier damage, thrombus formation, and the local inflammatory response were determined poststroke. Results— Treatment with 15.0 U C1-inhibitor, but not 7.5 U, 1 hour after stroke reduced infarct volumes by ≈60% and improved clinical scores in mice of either sex on day 1. This protective effect was preserved at later stages of infarction as well as in elderly mice and in another species, ie, rats. Delayed C1-inhibitor treatment still improved clinical outcome. Blood–brain barrier damage, edema formation, and inflammation were significantly lower compared with controls. Moreover, C1-inhibitor showed strong antithrombotic effects. Conclusions— C1-inhibitor is a multifaceted antiinflammatory and antithrombotic compound that protects from ischemic neurodegeneration in clinically meaningful settings.

Blocking of bradykinin receptor B1 protects from focal closed head injury in mice by reducing axonal damage and astroglia activation

The two bradykinin receptors B1R and B2R are central components of the kallikrein–kinin system with different expression kinetics and binding characteristics. Activation of these receptors by kinins triggers inflammatory responses in the target organ and in most situations enhances tissue damage. We could recently show that blocking of B1R, but not B2R, protects from cortical cryolesion by reducing inflammation and edema formation. In the present study, we investigated the role of B1R and B2R in a closed head model of focal traumatic brain injury (TBI; weight drop). Increased expression of B1R in the injured hemispheres of wild-type mice was restricted to the later stages after brain trauma, i.e. day 7 (P<0.05), whereas no significant induction could be observed for the B2R (P>0.05). Mice lacking the B1R, but not the B2R, showed less functional deficits on day 3 (P<0.001) and day 7 (P<0.001) compared with controls. Pharmacological blocking of B1R in wild-type mice had similar effects. Reduced axonal injury and astroglia activation could be identified as underlying mechanisms, while inhibition of B1R had only little influence on the local inflammatory response in this model. Inhibition of B1R may become a novel strategy to counteract trauma-induced neurodegeneration.

Combined [ 18 F]DPA-714 micro-positron emission tomography and autoradiography imaging of microglia activation after closed head injury in mice

BackgroundTraumatic brain injury (TBI) is a major cause of death and disability. Neuroinflammation contributes to acute damage after TBI and modulates long-term evolution of degenerative and regenerative responses to injury. The aim of the present study was to evaluate the relationship of microglia activation to trauma severity, brain energy metabolism, and cellular reactions to injury in a mouse closed head injury model using combined in vivo PET imaging, ex vivo autoradiography, and immunohistochemistry.MethodsA weight-drop closed head injury model was used to produce a mixed diffuse and focal TBI or a purely diffuse mild TBI (mTBI) in C57BL6 mice. Lesion severity was determined by evaluating histological damage and functional outcome using a standardized neuroscore (NSS), gliosis, and axonal injury by immunohistochemistry. Repeated intra-individual in vivo μPET imaging with the specific 18-kDa translocator protein (TSPO) radioligand [18F]DPA-714 was performed on day 1, 7, and 16 and [18F]FDG-μPET imaging for energy metabolism on days 2–5 after trauma using freshly synthesized radiotracers. Immediately after [18F]DPA-714-μPET imaging on days 7 and 16, cellular identity of the [18F]DPA-714 uptake was confirmed by exposing freshly cut cryosections to film autoradiography and successive immunostaining with antibodies against the microglia/macrophage marker IBA-1.ResultsFunctional outcome correlated with focal brain lesions, gliosis, and axonal injury. [18F]DPA-714-μPET showed increased radiotracer uptake in focal brain lesions on days 7 and 16 after TBI and correlated with reduced cerebral [18F]FDG uptake on days 2–5, with functional outcome and number of IBA-1 positive cells on day 7. In autoradiography, [18F]DPA-714 uptake co-localized with areas of IBA1-positive staining and correlated strongly with both NSS and the number of IBA1-positive cells, gliosis, and axonal injury. After mTBI, numbers of IBA-1 positive cells with microglial morphology increased in both brain hemispheres; however, uptake of [18F]DPA-714 was not increased in autoradiography or in μPET imaging.Conclusions[18F]DPA-714 uptake in μPET/autoradiography correlates with trauma severity, brain metabolic deficits, and microglia activation after closed head TBI.

Role of the kallikrein–kinin system in traumatic brain injury

Traumatic brain injury (TBI) is a major cause of mortality and morbidity worldwide. Despite improvements in acute intensive care, there are currently no specific therapies to ameliorate the effects of TBI. Successful therapeutic strategies for TBI should target multiple pathophysiologic mechanisms that occur at different stages of brain injury. The kallikrein–kinin system is a promising therapeutic target for TBI as it mediates key pathologic events of traumatic brain damage, such as edema formation, inflammation, and thrombosis. Selective and specific kinin receptor antagonists and inhibitors of plasma kallikrein and coagulation factor XII have been developed, and have already shown therapeutic efficacy in animal models of stroke and TBI. However, conflicting preclinical evaluation, as well as limited and inconclusive data from clinical trials in TBI, suggests that caution should be taken before transferring observations made in animals to humans. This review summarizes current evidence on the pathologic significance of the kallikrein–kinin system during TBI in animal models and, where available, the experimental findings are compared with human data.

C1-Inhibitor protects from focal brain trauma in a cortical cryolesion mice model by reducing thrombo-inflammation

Traumatic brain injury (TBI) induces a strong inflammatory response which includes blood-brain barrier damage, edema formation and infiltration of different immune cell subsets. More recently, microvascular thrombosis has been identified as another pathophysiological feature of TBI. The contact-kinin system represents an interface between inflammatory and thrombotic circuits and is activated in different neurological diseases. C1-Inhibitor counteracts activation of the contact-kinin system at multiple levels. We investigated the therapeutic potential of C1-Inhibitor in a model of TBI. Male and female C57BL/6 mice were subjected to cortical cryolesion and treated with C1-Inhibitor after 1 h. Lesion volumes were assessed between day 1 and day 5 and blood-brain barrier damage, thrombus formation as well as the local inflammatory response were determined post TBI. Treatment of male mice with 15.0 IU C1-Inhibitor, but not 7.5 IU, 1 h after cryolesion reduced lesion volumes by ~75% on day 1. This protective effect was preserved in female mice and at later stages of trauma. Mechanistically, C1-Inhibitor stabilized the blood-brain barrier and decreased the invasion of immune cells into the brain parenchyma. Moreover, C1-Inhibitor had strong antithrombotic effects. C1-Inhibitor represents a multifaceted anti-inflammatory and antithrombotic compound that prevents traumatic neurodegeneration in clinically meaningful settings.

Alleviation of secondary brain injury, posttraumatic inflammation, and brain edema formation by inhibition of factor XIIa

BackgroundTraumatic brain injury (TBI) is a devastating neurological condition and a frequent cause of permanent disability. Posttraumatic inflammation and brain edema formation, two pathological key events contributing to secondary brain injury, are mediated by the contact-kinin system. Activation of this pathway in the plasma is triggered by activated factor XII. Hence, we set out to study in detail the influence of activated factor XII on the abovementioned pathophysiological features of TBI.MethodsUsing a cortical cryogenic lesion model in mice, we investigated the impact of genetic deficiency of factor XII and inhibition of activated factor XII with a single bolus injection of recombinant human albumin-fused Infestin-4 on the release of bradykinin, the brain lesion size, and contact-kinin system-dependent pathological events. We determined protein levels of bradykinin, intracellular adhesion molecule-1, CC-chemokine ligand 2, and interleukin-1β by enzyme-linked immunosorbent assays and mRNA levels of genes related to inflammation by quantitative real-time PCR. Brain lesion size was determined by tetrazolium chloride staining. Furthermore, protein levels of the tight junction protein occludin, integrity of the blood-brain barrier, and brain water content were assessed by Western blot analysis, extravasated Evans Blue dye, and the wet weight-dry weight method, respectively. Infiltration of neutrophils and microglia/activated macrophages into the injured brain lesions was quantified by immunohistological stainings.ResultsWe show that both genetic deficiency of factor XII and inhibition of activated factor XII in mice diminish brain injury-induced bradykinin release by the contact-kinin system and minimize brain lesion size, blood-brain barrier leakage, brain edema formation, and inflammation in our brain injury model.ConclusionsStimulation of bradykinin release by activated factor XII probably plays a prominent role in expanding secondary brain damage by promoting brain edema formation and inflammation. Pharmacological blocking of activated factor XII could be a useful therapeutic principle in the treatment of TBI-associated pathologic processes by alleviating posttraumatic inflammation and brain edema formation.

FTY720 does not protect from traumatic brain injury in mice despite reducing posttraumatic inflammation

Inflammation is a pathological hallmark of traumatic brain injury (TBI). Recent evidence suggests that immune cells such as lymphocytes are of particular relevance for lesion development after TBI. FTY720, a sphingosine-1-phosphate (S1P) receptor modulator, sequesters T lymphocytes in lymphoid organs and has been shown to improve outcome in a variety of neurological disease models. We investigated the mode of FTY720 action in models of TBI. Focal cortical cryolesion was induced in C57BL/6 mice treated with FTY720 (1mg/kg) or vehicle immediately before injury. Lesion size was assessed 24h later. Immune cells in the blood and brain were counted by flow cytometry and immunocytochemistry. The integrity of the blood-brain barrier was analyzed using Evans Blue dye. To validate the findings in a diffuse brain trauma model, FTY720-treated mice and controls were subjected to weight drop contusion injury and neurological deficits were assessed until day 7. As expected FTY720 significantly lowered the numbers of circulating lymphocytes and attenuated the invasion of immune cells into the damaged brain parenchyma. However, FTY720 was unable to improve lesion size or functional outcome in both trauma models at either stage, i.e. acute vs chronic. Accordingly, the extent of blood-brain barrier disruption and neuronal apoptosis was similar between FTY720-treated mice and controls. We conclude that pharmacological S1P receptor modulation is an unfavorable strategy to combat TBI. Moreover, our findings put into perspective the pathophysiological relevance of inflammatory cells in traumatic neurodegeneration.

Targeting coagulation factor XII as a novel therapeutic option in brain trauma

Traumatic brain injury is a major global public health problem for which specific therapeutic interventions are lacking. There is, therefore, a pressing need to identify innovative pathomechanism‐based effective therapies for this condition. Thrombus formation in the cerebral microcirculation has been proposed to contribute to secondary brain damage by causing pericontusional ischemia, but previous studies have failed to harness this finding for therapeutic use. The aim of this study was to obtain preclinical evidence supporting the hypothesis that targeting factor XII prevents thrombus formation and has a beneficial effect on outcome after traumatic brain injury.

The kallikrein-kinin system: a promising therapeutic target for traumatic brain injury.

Traumatic brain injury (TBI), which results from an outside force causing mechanical disruption of brain tissue, is potentially life-threatening and therefore a critical public health problem throughout the world. In the USA, approximately 1.7 million individuals per year sustain a TBI, and about 43% of patients hospitalized because of TBI develop long-term physical disability as well as psychological disorders, such as neurocognitive deficits, epilepsy, and depression (Roozenbeek et al., 2013). The primary brain damage that occurs due to the mechanical disruption of brain tissue is usually irreversible and therapeutically inaccessible. In the sequel, secondary injury processes, including blood-brain barrier disturbances, excitotoxicity with following generation of reactive oxygen species, and inflammation, contribute to the exacerbation of traumatic brain damage. One major predictor of outcome is the development of cerebral edema in the acute phase after brain injury. In addition to acute TBI, it has become evident over recent years that some TBI patients develop progressive brain atrophy and dementia, which is referred to as “chronic TBI”. It is speculated that in these “chronic TBI” conditions, neuroinflammation plays a decisive role. The treatment options for traumatic brain damage are limited and no specific drug therapy approved for TBI is available so far. Considering the highly relevant socio-economic burden of TBI, there is a pressing clinical demand for new therapeutic options. As the pathophysiology of TBI involves multiple mechanisms of secondary brain damage, successful therapeutic strategies must target its key pathological hallmarks. In this respect and according to current scientific evidence, drugs targeting the kallikrein-kinin system show promise in improving the outcome of TBI.