tPA contributes to impaired NMDA cerebrovasodilation after traumatic brain injury through activation of JNK MAPK

Small molecule inhibitors of NLRP3 inflammasome and GSK-3β in the management of traumatic brain injury: A review

Traumatic brain injury (TBI) is a debilitating mental condition which causes physical disability and morbidity worldwide. TBI may damage the brain by direct injury that subsequently triggers a series of neuroinflammatory events. The activation of NLRP3 inflammasome and dysregulated host immune system has been documented in various neurological disorders such as TBI, ischemic stroke and multiple sclerosis. The activation of NLRP3 post-TBI increases the production of pro-inflammatory cytokines and caspase-1, which are major drivers of neuroinflammation and apoptosis. Similarly, GSK-3β regulates apoptosis through tyrosine kinase and canonical Wnt signalling pathways. Thus, therapeutic targeting of NLRP3 inflammasome and GSK-3β has emerged as promising strategies for regulating the post-TBI neuroinflammation and neurobehavioral disturbances. In this review, we discuss the identification & development of several structurally diverse and pharmacologically interesting small molecule inhibitors for targeting the NLRP3 inflammasome and GSK-3β in the management of TBI.

Role of statins in regulating molecular pathways following traumatic brain injury: A system pharmacology study

Traumatic brain injury (TBI) is a serious disorder with debilitating physical and psychological complications. Previous studies have indicated that genetic factors have a critical role in modulating the secondary phase of injury in TBI. Statins have interesting pleiotropic properties such as antiapoptotic, antioxidative, and anti-inflammatory effects, which make them a suitable class of drugs for repurposing in TBI. In this study, we aimed to explore how statins modulate proteins and pathways involved in TBI using system pharmacology. We first explored the target associations with statins in two databases to discover critical clustering groups, candidate hub and critical hub genes in the network of TBI, and the possible connections of statins with TBI-related genes. Our results showed 1763 genes associated with TBI. Subsequently, the analysis of centralities in the PPI network displayed 55 candidate hub genes and 15 hub genes. Besides, MCODE analysis based on threshold score:10 determined four modular clusters. Intersection analysis of genes related to TBI and statins demonstrated 204 shared proteins, which suggested that statins influence 31 candidate hub and 9 hub genes. Moreover, statins had the highest interaction with MCODE1. The biological processes of the 31 shared proteins are related to gene expression, inflammation, antioxidant activity, and cell proliferation. Biological enriched pathways showed Programmed Cell Death proteins, AGE-RAGE signaling pathway, C-type lectin receptor signalling pathway, and MAPK signaling pathway as top clusters. In conclusion, statins could target several critical post-TBI genes mainly involved in inflammation and apoptosis, supporting the previous research results as a potential therapeutic agent.

Early cerebrovascular and long-term neurological modifications ensue following juvenile mild traumatic brain injury in male mice

Clinical evidence suggests that a mild traumatic brain injury occurring at a juvenile age (jmTBI) may be sufficient to elicit pathophysiological modifications. However, clinical reports are not adequately integrated with experimental studies examining brain changes occurring post-jmTBI. We monitored the cerebrovascular modifications and assessed the long-term behavioral and electrographic changes resulting from experimental jmTBI. In vivo photoacoustic imaging demonstrated a decrease of cerebrovascular oxygen saturation levels in the impacted area hours post-jmTBI. Three days post-jmTBI oxygenation returned to pre-jmTBI levels, stabilizing at 7 and 30 days after the injury. At the functional level, cortical arterioles displayed no NMDA vasodilation response, while vasoconstriction induced by thromboxane receptor agonist was enhanced at 1 day post-jmTBI. Arterioles showed abnormal NMDA vasodilation at 3 days post-jmTBI, returning to normality at 7 days post injury. Histology showed changes in vessel diameters from 1 to 30 days post-jmTBI. Neurological evaluation indicated signs of anxiety-like behavior up to 30 days post-jmTBI. EEG recordings performed at the cortical site of impact 30 days post-jmTBI did not indicate seizures activity, although it revealed a reduction of gamma waves as compared to age matched sham. Histology showed decrease of neuronal filament staining. In conclusion, experimental jmTBI triggers an early cerebrovascular hypo‑oxygenation in vivo and faulty vascular reactivity. The exact topographical coherence and the direct casualty between early cerebrovascular changes and the observed long-term neurological modifications remain to be investigated. A potential translational value for cerebro-vascular oxygen monitoring in jmTBI is discussed.

Release of IL-6 After Stroke Contributes to Impaired Cerebral Autoregulation and Hippocampal Neuronal Necrosis Through NMDA Receptor Activation and Upregulation of ET-1 and JNK

The sole FDA-approved drug treatment for ischemic stroke is tissue-type plasminogen activator (tPA). However, upregulation of JNK mitogen-activated protein kinase (MAPK) and endothelin 1 (ET-1) by tPA after stroke contributes to impaired cerebrovascular autoregulation. Wild-type (wt) tPA can bind to the lipoprotein-related receptor (LRP), which mediates vasodilation, or NMDA receptors (NMDA-Rs), exacerbating vasoconstriction. Elevations in IL-6, a marker of inflammation that accompanies stroke, are reported to be an adverse prognostic factor. We hypothesized that IL-6 released into CSF after stroke by wt-tPA through activation of NMDA-Rs and upregulation of ET-1 and JNK contribute to impairment of cerebrovascular autoregulation and increased histopathology. Results show that IL-6 was increased post stroke in pigs, which was increased further by wt-tPA. Co-administration of the IL-6 antagonist LMT-28 with wt-tPA prevented impairment of cerebrovascular autoregulation and necrosis of hippocampal cells. wt-tPA co-administered with the JNK inhibitor SP 600125 and the ET-1 antagonist BQ 123 blocked stroke-induced elevation of IL-6. Co-administration of LMT-28 with wt-tPA blocked the augmentation of JNK and ET-1 post stroke. In conclusion, IL-6 released after stroke, which is enhanced by wt-tPA through activation of NMDA-Rs and upregulation of ET-1 and JNK, impairs cerebrovascular autoregulation and increases histopathology. Strategies that promote fibrinolysis while limiting activation of NMDA-Rs and upregulation of IL-6 may improve the benefit/risk ratio compared to wt-tPA in treatment of stroke.

Release of IL-6 After Stroke Contributes to Impaired Cerebral Autoregulation and Hippocampal Neuronal Necrosis Through NMDA Receptor Activation and Upregulation of ET-1 and JNK

The sole FDA-approved drug treatment for ischemic stroke is tissue-type plasminogen activator (tPA). However, upregulation of JNK mitogen-activated protein kinase (MAPK) and endothelin 1 (ET-1) by tPA after stroke contributes to impaired cerebrovascular autoregulation. Wild-type (wt) tPA can bind to the lipoprotein-related receptor (LRP), which mediates vasodilation, or NMDA receptors (NMDA-Rs), exacerbating vasoconstriction. Elevations in IL-6, a marker of inflammation that accompanies stroke, are reported to be an adverse prognostic factor. We hypothesized that IL-6 released into CSF after stroke by wt-tPA through activation of NMDA-Rs and upregulation of ET-1 and JNK contribute to impairment of cerebrovascular autoregulation and increased histopathology. Results show that IL-6 was increased post stroke in pigs, which was increased further by wt-tPA. Co-administration of the IL-6 antagonist LMT-28 with wt-tPA prevented impairment of cerebrovascular autoregulation and necrosis of hippocampal cells. wt-tPA co-administered with the JNK inhibitor SP 600125 and the ET-1 antagonist BQ 123 blocked stroke-induced elevation of IL-6. Co-administration of LMT-28 with wt-tPA blocked the augmentation of JNK and ET-1 post stroke. In conclusion, IL-6 released after stroke, which is enhanced by wt-tPA through activation of NMDA-Rs and upregulation of ET-1 and JNK, impairs cerebrovascular autoregulation and increases histopathology. Strategies that promote fibrinolysis while limiting activation of NMDA-Rs and upregulation of IL-6 may improve the benefit/risk ratio compared to wt-tPA in treatment of stroke.

Mass Spectrometric Imaging of Ceramide Biomarkers Tracks Therapeutic Response in Traumatic Brain Injury

Traumatic brain injury (TBI) is a serious public health problem and the leading cause of death in children and young adults. It also contributes to a substantial number of cases of permanent disability. As lipids make up over 50% of the brain mass and play a key role in both membrane structure and cell signaling, their profile is of particular interest. In this study, we show that advanced mass spectrometry imaging (MSI) has sufficient technical accuracy and reproducibility to demonstrate the anatomical distribution of 50 μm diameter microdomains that show changes in brain ceramide levels in a rat model of controlled cortical impact (CCI) 3 days post injury with and without treatment. Adult male Sprague-Dawley rats received one strike and were euthanized 3 days post trauma. Brain MS images showed increase in ceramides in CCI animals compared to control as well as significant reduction in ceramides in CCI treated animals, demonstrating therapeutic effect of a peptide agonist. The data also suggests the presence of diffuse changes outside of the injured area. These results shed light on the extent of biochemical and structural changes in the brain after traumatic brain injury and could help to evaluate the efficacy of treatments.

tPA variant tPA-A296-299 Prevents impairment of cerebral autoregulation and necrosis of hippocampal neurons after stroke by inhibiting upregulation of ET-1

Tissue-type plasminogen activator (tPA) is neurotoxic and exacerbates uncoupling of cerebral blood flow (CBF) and metabolism after stroke, yet it remains the sole FDA-approved drug for treatment of ischemic stroke. Upregulation of c-Jun-terminal kinase (JNK) after stroke contributes to tPA-mediated impairment of autoregulation, but the role of endothelin-1 (ET-1) is unknown. Based on the Glasgow Coma Scale, impaired autoregulation is linked to adverse outcomes after TBI, but correlation with hippocampal histopathology after stroke has not been established. We propose that given after stroke, tPA activates N-Methyl-D-Aspartate receptors (NMDA-Rs) and upregulates ET-1 in a JNK dependent manner, imparing autoregulation and leading to histopathology. After stroke, CBF was reduced in the hippocampus and reduced further during hypotension, which did not occur in hypotensive sham pigs, indicating impairment of autoregulation. Autoregulation and necrosis of hippocampal CA1 and CA3 neurons were further impaired by tPA, but were preserved by the ET-1 antagonist BQ 123 and tPA-A,^296-299 a variant that is fibrinolytic but does not bind to NMDA-Rs. Expression of ET-1 was increased by stroke and potentiated by tPA but returned to sham levels by tPA-A^296-299 and the JNK antagonist SP600125. Results show that JNK releases ET-1 after stroke. Tissue-type plasminogen activator -A^296-299 prevents impairment of cerebral autoregulation and histopathology after stroke by inhibiting upregulation of ET-1.

K channel impairment determines sex and age differences in epinephrine-mediated outcomes after brain injury

Traumatic brain injury (TBI) is the leading cause of injury-related death in children, with boys and children under 4 years having particularly poor outcomes. Activation of ATP- and calcium-sensitive (K_ATP and K_Ca ) channels produces cerebrovasodilation and contributes to autoregulation, both of which are impaired after TBI, contributing to poor outcomes. Upregulation of the c-Jun-terminal kinase (JNK) isoform of mitogen-activated protein kinase produces K channel function impairment after CNS injury. Vasoactive agents can be used to normalize cerebral perfusion pressure. Epinephrine (EPI) prevents impairment of cerebral autoregulation and hippocampal neuronal cell necrosis after TBI in female and male newborn and female juvenile but not male juvenile pigs via differential modulation of JNK. The present study used anesthetized pigs equipped with a closed cranial window to address the hypothesis that differential K channel impairment contributes to age and sex differences in EPI-mediated outcomes after brain injury. Results show that pial artery dilation in response to the K_ATP and K_Ca channel agonists cromakalim and NS 1619 was impaired after TBI and that such impairment was prevented by EPI in female and male newborn and female juvenile but not male juvenile pigs. Using vasodilation as an index of function, these data indicate that EPI protects cerebral autoregulation and limits histopathology after TBI through protection of K channel function via blockade of JNK in an age- and sex-dependent manner. © 2017 Wiley Periodicals, Inc.

Vascular impairment as a pathological mechanism underlying long-lasting cognitive dysfunction after pediatric traumatic brain injury

Traumatic brain injury (TBI) is the leading cause of death and disability in children. Indeed, the acute mechanical injury often evolves to a chronic brain disorder with long-term cognitive, emotional and social dysfunction even in the case of mild TBI. Contrary to the commonly held idea that children show better recovery from injuries than adults, pediatric TBI patients actually have worse outcome than adults for the same injury severity. Acute trauma to the young brain likely interferes with the fine-tuned developmental processes and may give rise to long-lasting consequences on brain's function. This review will focus on cerebrovascular dysfunction as an important early event that may lead to long-term phenotypic changes in the brain after pediatric TBI. These, in turn may be associated with accelerated brain aging and cognitive dysfunction. Finally, since no effective treatments are currently available, understanding the unique pathophysiological mechanisms of pediatric TBI is crucial for the development of new therapeutic options.

Interactions between Sirt1 and MAPKs regulate astrocyte activation induced by brain injury in vitro and in vivo

Background

Astrocyte activation is a hallmark of traumatic brain injury resulting in neurological dysfunction or death for an overproduction of inflammatory cytokines and glial scar formation. Both the silent mating type information (Sirt1) expression and mitogen-activated protein kinase (MAPK) signal pathway activation represent a promising therapeutic target for several models of neurodegenerative diseases. We investigated the potential effects of Sirt1 upregulation and MAPK pathway pharmacological inhibition on astrocyte activation in vitro and in vivo. Moreover, we attempted to confirm the underlying interactions between Sirt1 and MAPK pathways in astrocyte activation after brain injury.

Methods

The present study employs an interleukin-1β (IL-1β) stimulated primary cortical astrocyte model in vitro and a nigrostriatal pathway injury model in vivo to mimic the astrocyte activation induced by traumatic brain injury. The activation of GFAP, Sirt1, and MAPK pathways were detected by Western blot; astrocyte morphological hypertrophy was assessed using immunofluorescence staining; in order to explore the neuroprotective effect of regulation Sirt1 expression and MAPK pathway activation, the motor and neurological function tests were assessed after injury.

Results

GFAP level and morphological hypertrophy of astrocytes are elevated after injury in vitro or in vivo. Furthermore, the expressions of phosphorylated extracellular regulated protein kinases (p-ERK), phosphorylated c-Jun N-terminal kinase (p-JNK), and phosphorylated p38 activation (p-p38) are upregulated, but the Sirt1 expression is downregulated. Overexpression of Sirt1 significantly increases the p-ERK expression and reduces the p-JNK and p-p38 expressions. Inhibition of ERK, JNK, or p38 activation respectively with their inhibitors significantly elevated the Sirt1 expression and attenuated the astrocyte activation. Both the overproduction of Sirt1 and inhibition of ERK, JNK, or p38 activation can alleviate the astrocyte activation, thereby improving the neurobehavioral function according to the modified neurological severity scores (mNSS) and balance latency test.

Conclusions

Thus, Sirt1 plays a protective role against astrocyte activation, which may be associated with the regulation of the MAPK pathway activation induced by brain injury in vitro and in vivo.

tPA Modulation of the Blood-Brain Barrier: A Unifying Explanation for the Pleiotropic Effects of tPA in the CNS

The plasminogen activation (PA) system is best known for its role in fibrinolysis. However, it has also been shown to regulate many nonfibrinolytic functions in the central nervous system (CNS). In particular, tissue-type plasminogen activator (tPA) is reported to have pleiotropic activities in the CNS, regulating events such as neuronal plasticity, excitotoxicity, and cerebrovascular barrier integrity, whereas urokinase-type plasminogen activator is mainly associated with tissue remodeling and cell migration. It has been suggested that the role tPA plays in controlling barrier integrity may provide a unifying mechanism for the reported diverse, and often opposing, functions ascribed to tPA in the CNS. Here we will review the possibility that the pleiotropic effects reported for tPA in physiologic and pathologic processes in the CNS may be a consequence of its role in the neurovascular unit in regulation of cerebrovascular responses and subsequently parenchymal homeostasis. We propose that this might offer an explanation for the ongoing debate regarding the neurotoxic versus neuroprotective roles of tPA.

Sex and Age Differences in Epinephrine Mechanisms and Outcomes after Brain Injury

Traumatic brain injury (TBI) is the leading cause of injury-related death in children, with boys and children <4 years of age having particularly poor outcomes. Cerebral autoregulation is often impaired after TBI, contributing to poor outcome. Cerebral perfusion pressure can be normalized by use of vasoactive agents. The c-Jun-terminal kinase (JNK) isoform of mitogen activated protein kinase (MAPK) produces hemodynamic impairment after TBI, but less is known about its role in histopathology. We investigated whether epinephrine (EPI), age, and sex dependently protected cerebral autoregulation and limited histopathology after TBI, and sought to determine the role of JNK in that outcome. Lateral fluid percussion injury (FPI) was produced in anesthetized pigs. Pial artery reactivity was measured via a closed cranial window. Phosphorylated JNK MAPK was quantified by enzyme-linked immunosorbent assay (ELISA). Results show that EPI preserves autoregulation, prevents histopathology, and blocks phosphorylated JNK upregulation in newborn males and females and juvenile females but not juvenile males after TBI. These data indicate that EPI preserves cerebral autoregulation and limits histopathology after TBI through blockade of JNK in an age- and sex-dependent manner.

Tissue-Type Plasminogen Activator-A296-299 Prevents Impairment of Cerebral Autoregulation After Stroke Through Lipoprotein-Related Receptor-Dependent Increase in cAMP and p38

BACKGROUND AND PURPOSE

The sole Food and Drug Administration-approved treatment for stroke is tissue-type plasminogen activator (tPA), but its brief therapeutic window and complications of treatment constrain its use. One limitation may be its potential to exacerbate impairment of cerebral autoregulation after stroke. Vasodilation is maintained by elevations in cAMP. However, cAMP levels fall after stroke because of overactivation of N-methyl-d-aspartate receptors by toxic levels of glutamate, an effect that is exacerbated by tPA. Binding of wild-type (wt) tPA to the low-density lipoprotein-related receptor (LRP) mediates dilation. We propose that binding of wt-tPA to N-methyl-d-aspartate receptor reduces cAMP and impairs vasodilation. We hypothesize that tPA-A(296-299), a variant that is fibrinolytic but cannot bind to N-methyl-d-aspartate receptor, preferentially binds to LRP and increases cAMP and p38, limiting autoregulation impairment after stroke.

METHODS

Stroke was induced by photothrombosis in pigs equipped with a closed cranial window, cerebral blood flow determined by microspheres, and cerebrospinal fluid cAMP and p38 determined by ELISA.

RESULTS

Stroke decreased cerebral blood flow. Cerebral blood flow was reduced further during hypotension, indicating impairment of autoregulation. Autoregulation was further impaired by wt-tPA, which was prevented by MK801 and tPA-A(296-299). Protection by tPA-A(296-299) was blocked by anti-LRP Ab, the LRP antagonist receptor-associated protein, and the p38 inhibitor SB 203580, but not by control IgG. Stroke reduced cerebrospinal fluid cAMP, which was reduced further by wt-tPA, but augmented by tPA-A(296-299). Cerebrospinal fluid p38 was unchanged by wt-tPA, increased by tPA-A(296-299), and decreased by anti-LRP Ab and receptor-associated protein.

CONCLUSIONS

tPA-A(296-299) prevents impairment of cerebral autoregulation after stroke through an LRP-dependent increase in cAMP and p38.

Combination Therapies for Traumatic Brain Injury: Retrospective Considerations

Patients enrolled in clinical trials for traumatic brain injury (TBI) may present with heterogeneous features over a range of injury severity, such as diffuse axonal injury, ischemia, edema, hemorrhage, oxidative damage, mitochondrial and metabolic dysfunction, excitotoxicity, inflammation, and other pathophysiological processes. To determine whether combination therapies might be more effective than monotherapy at attenuating moderate TBI or promoting recovery, the National Institutes of Health funded six preclinical studies in adult and immature male rats to evaluate promising acute treatments alone and in combination. Each of the studies had a solid rationale for its approach based on previous research, but only one reported significant improvements in long-term outcomes across a battery of behavioral tests. Four studies had equivocal results because of a lack of sensitivity of the outcome assessments. One study demonstrated worse results with the combination in comparison with monotherapies. While specific research findings are reported elsewhere, this article provides an overview of the study designs, insights, and recommendations for future research aimed at therapy development for TBI.

Subconjunctival injection of XG-102, a JNK inhibitor peptide, in patients with intraocular inflammation: a safety and tolerability study

PURPOSE

We aimed to investigate the safety, tolerability, and systemic diffusion of a single escalating dose of XG-102 (a 31-D-amino-acid peptide inhibiting JNK pathway activation), administered subconjunctivally in the treatment of post-surgery or post-trauma intraocular inflammation.

METHODS

This is a dose-escalating, tolerance Phase Ib study. Twenty patients with post-surgery or post-traumatic intraocular inflammation were assigned to 1 of the 4 dose escalating (45, 90, 450, or 900 μg XG-102) groups of 5 patients each. Patients were evaluated at 24, 48 h, 8, and 28 days following the administration of XG-102, including laboratory tests, standard eye examinations, vital signs, and occurrence of adverse events. A single plasma quantification of XG-102 was performed 30 min after administration, according to previous pharmacokinetics studies performed on volunteers.

RESULTS

A total of 17 non-serious adverse events, considered unrelated to the study treatment, were reported for 10 patients. The adverse event incidence was not related to the drug dose. All patients experienced a decrease in intraocular inflammation as of 24 h post-administration and this decrease was sustained up to 28 days thereafter. No patient required local injection or systemic administration of corticoids following the administration of XG-102. XG-102 was undetectable in the first 3 dose groups. In the fourth-dose group (900 μg) the XG-102 plasma levels were above the limit of detection for 3 patients and above the limit of quantification for 1 patient.

CONCLUSIONS

In this first clinical trial using XG-102, administered as a single subconjunctival injection as adjunct therapy, in patients with recent post-surgery or post-trauma intraocular inflammation is safe and well tolerated. Further studies are required to evaluate its efficacy.

Subacute intranasal administration of tissue plasminogen activator promotes neuroplasticity and improves functional recovery following traumatic brain injury in rats

Traumatic brain injury (TBI) is a major cause of death and long-term disability worldwide. To date, there are no effective pharmacological treatments for TBI. Recombinant human tissue plasminogen activator (tPA) is the effective drug for the treatment of acute ischemic stroke. In addition to its thrombolytic effect, tPA is also involved in neuroplasticity in the central nervous system. However, tPA has potential adverse side effects when administered intravenously including brain edema and hemorrhage. Here we report that tPA, administered by intranasal delivery during the subacute phase after TBI, provides therapeutic benefit. Animals with TBI were treated intranasally with saline or tPA initiated 7 days after TBI. Compared with saline treatment, subacute intranasal tPA treatment significantly 1) improved cognitive (Morris water maze test) and sensorimotor (footfault and modified neurological severity score) functional recovery in rats after TBI, 2) reduced the cortical stimulation threshold evoking ipsilateral forelimb movement, 3) enhanced neurogenesis in the dentate gyrus and axonal sprouting of the corticospinal tract originating from the contralesional cortex into the denervated side of the cervical gray matter, and 4) increased the level of mature brain-derived neurotrophic factor. Our data suggest that subacute intranasal tPA treatment improves functional recovery and promotes brain neurogenesis and spinal cord axonal sprouting after TBI, which may be mediated, at least in part, by tPA/plasmin-dependent maturation of brain-derived neurotrophic factor.

Plasmin-dependent modulation of the blood-brain barrier: a major consideration during tPA-induced thrombolysis?

Plasmin, the principal downstream product of tissue-type plasminogen activator (tPA), is known for its potent fibrin-degrading capacity but is also recognized for many non-fibrinolytic activities. Curiously, plasmin has not been conclusively linked to blood-brain barrier (BBB) disruption during recombinant tPA (rtPA)-induced thrombolysis in ischemic stroke. This is surprising given the substantial involvement of tPA in the modulation of BBB permeability and the co-existence of tPA and plasminogen in both blood and brain throughout the ischemic event. Here, we review the work that argues a role for plasmin together with endogenous tPA or rtPA in BBB alteration, presenting the overall controversy around the topic yet creating a rational case for an involvement of plasmin in this process.

Linking traumatic brain injury to chronic traumatic encephalopathy: identification of potential mechanisms leading to neurofibrillary tangle development

Significant attention has recently been drawn to the potential link between head trauma and the development of neurodegenerative disease, namely chronic traumatic encephalopathy (CTE). The acute neurotrauma associated with sports-related concussions in athletes and blast-induced traumatic brain injury in soldiers elevates the risk for future development of chronic neurodegenerative diseases such as CTE. CTE is a progressive disease distinguished by characteristic tau neurofibrillary tangles (NFTs) and, occasionally, transactive response DNA binding protein 43 (TDP43) oligomers, both of which have a predilection for perivascular and subcortical areas near reactive astrocytes and microglia. The disease is currently only diagnosed postmortem by neuropathological identification of NFTs. A recent workshop sponsored by National Institute of Neurological Disorders and Stroke emphasized the need for premortem diagnosis, to better understand disease pathophysiology and to develop targeted treatments. In order to accomplish this objective, it is necessary to discover the mechanistic link between acute neurotrauma and the development of chronic neurodegenerative and neuropsychiatric disorders such as CTE. In this review, we briefly summarize what is currently known about CTE development and pathophysiology, and subsequently discuss injury-induced pathways that warrant further investigation. Understanding the mechanistic link between acute brain injury and chronic neurodegeneration will facilitate the development of appropriate diagnostic and therapeutic options for CTE and other related disorders.

RBC-coupled tPA Prevents Whereas tPA Aggravates JNK MAPK-Mediated Impairment of ATP- and Ca-Sensitive K Channel-Mediated Cerebrovasodilation After Cerebral Photothrombosis

The sole Food and Drug Administration-approved treatment for acute stroke is tissue-type plasminogen activator (tPA), but tPA aggravates impairment of cerebrovasodilation during hypotension in a newborn pig photothrombotic model of stroke. Coupling to carrier red blood cells (RBC) enhances thrombolytic effects of tPA, while reducing its side effects. ATP- and Ca-sensitive K channels (Katp and Kca) are important regulators of cerebrovascular tone and mediate cerebrovasodilation during hypotension. Mitogen-activated protein kinase, a family of at least three kinases, ERK, p38, and c-Jun-N-terminal kinase (JNK), is upregulated after photothrombosis. This study examined the effect of photothrombosis on Katp- and Kca-induced cerebrovasodilation and the roles of tPA and JNK during/after injury. Photothrombosis blunted vasodilation induced by the Katp agonists cromakalim, calcitonin gene-related peptide, and the Kca agonist NS 1619, which was aggravated by injection of tPA. In contrast, both pre- or post-injury thrombosis injection of RBC-tPA and JNK antagonist SP 600125 prevented impairment of Katp- and Kca-induced vasodilation. Therefore, JNK activation in thrombosis impairs K channel-mediated cerebrovasodilation. Standard thrombolytic therapy of central nervous system ischemic disorders using free tPA poses the danger of further dysregulation of cerebrohemodynamics by impairing cation-mediated control of cerebrovascular tone, whereas RBC-coupled tPA both restores reperfusion and normalizes cerebral hemodynamics.

XG-102 administered to healthy male volunteers as a single intravenous infusion: a randomized, double-blind, placebo-controlled, dose-escalating study

The aim of the study is to evaluate the safety, tolerability and pharmacokinetics (PK) of the JNK inhibitor XG-102 in a randomized, double blind, placebo controlled, sequential ascending dose parallel group Phase 1 Study. Three groups of male subjects received as randomly assigned ascending single XG-102 doses (10, 40, and 80 μg/kg; 6 subjects per dose) or placebo (2 subjects per dose) as an intravenous (IV) infusion over 60 min. Safety and tolerability were assessed by physical examination, vital signs, electrocardiography, eye examination, clinical laboratory tests and adverse events (AEs). PK was analyzed using noncompartmental methods. All reported AEs were mild to moderate and neither their number nor their distribution by System Organ Class suggest a dose relationship. Only headache and fatigue were considered probably or possibly study drug related. Headache frequency was similar for active and placebo, consequently this was not considered to be drug related but probably to study conditions. The other examinations did not show clinically relevant deviations or trends suggesting a XG-102 relationship. Geometric mean half-life was similar among doses, ranging from 0.36 to 0.65 h. Geometric mean XG-102 AUC_0–last increased more than linearly with dose, 90% confidence intervals (CIs) did not overlap for the two highest doses. Geometric mean dose normalized C_max values suggest a more than linear increase with dose but 90% CIs overlap. It may be concluded that XG-102 single IV doses of 10–80 μg/kg administered over 1 h to healthy male subjects were safe and well tolerated.

tPA-S(481)A prevents impairment of cerebrovascular autoregulation by endogenous tPA after traumatic brain injury by upregulating p38 MAPK and inhibiting ET-1

Traumatic brain injury (TBI) is associated with loss of cerebrovascular autoregulation, which leads to cerebral hypoperfusion. Mitogen activated protein kinase (MAPK) isoforms ERK, p38, and JNK and endothelin-1 (ET-1) are mediators of impaired cerebral hemodynamics after TBI. Excessive tissue plasminogen activator (tPA) released after TBI may cause loss of cerebrovascular autoregulation either by over-activating N-methyl-D-aspartate receptors (NMDA-Rs) or by predisposing to intracranial hemorrhage. Our recent work shows that a catalytically inactive tPA variant (tPA-S(481)A) that competes with endogenous wild type (wt) tPA for binding to NMDA-R through its receptor docking site but that cannot activate it, prevents activation of ERK by wt tPA and impairment of autoregulation when administered 30 min after fluid percussion injury (FPI). We investigated the ability of variants that lack proteolytic activity but bind/block activation of NMDA-Rs by wt tPA (tPA-S(481)A), do not bind/block activation of NMDA-Rs but are proteolytic (tPA-A(296-299)), or neither bind/block NMDA-Rs nor are proteolytic (tPA-A(296-299)S(481)A) to prevent impairment of autoregulation after TBI and the role of MAPK and ET-1 in such effects. Results show that tPA-S(481)A given 3 h post-TBI, but not tPA-A(296-299) or tPA-A(296-299)S(481)A prevents impaired autoregulation by upregulating p38 and inhibiting ET-1, suggesting that tPA-S(481)A has a realistic therapeutic window and focuses intervention on NMDA-Rs to improve outcome.

The tissue-type plasminogen activator-plasminogen activator inhibitor 1 complex promotes neurovascular injury in brain trauma: evidence from mice and humans

The neurovascular unit provides a dynamic interface between the circulation and central nervous system. Disruption of neurovascular integrity occurs in numerous brain pathologies including neurotrauma and ischaemic stroke. Tissue plasminogen activator is a serine protease that converts plasminogen to plasmin, a protease that dissolves blood clots. Besides its role in fibrinolysis, tissue plasminogen activator is abundantly expressed in the brain where it mediates extracellular proteolysis. However, proteolytically active tissue plasminogen activator also promotes neurovascular disruption after ischaemic stroke; the molecular mechanisms of this process are still unclear. Tissue plasminogen activator is naturally inhibited by serine protease inhibitors (serpins): plasminogen activator inhibitor-1, neuroserpin or protease nexin-1 that results in the formation of serpin:protease complexes. Proteases and serpin:protease complexes are cleared through high-affinity binding to low-density lipoprotein receptors, but their binding to these receptors can also transmit extracellular signals across the plasma membrane. The matrix metalloproteinases are the second major proteolytic system in the mammalian brain, and like tissue plasminogen activators are pivotal to neurological function but can also degrade structures of the neurovascular unit after injury. Herein, we show that tissue plasminogen activator potentiates neurovascular damage in a dose-dependent manner in a mouse model of neurotrauma. Surprisingly, inhibition of activity following administration of plasminogen activator inhibitor-1 significantly increased cerebrovascular permeability. This led to our finding that formation of complexes between tissue plasminogen activator and plasminogen activator inhibitor-1 in the brain parenchyma facilitates post-traumatic cerebrovascular damage. We demonstrate that following trauma, the complex binds to low-density lipoprotein receptors, triggering the induction of matrix metalloproteinase-3. Accordingly, pharmacological inhibition of matrix metalloproteinase-3 attenuates neurovascular permeability and improves neurological function in injured mice. Our results are clinically relevant, because concentrations of tissue plasminogen activator: plasminogen activator inhibitor-1 complex and matrix metalloproteinase-3 are significantly elevated in cerebrospinal fluid of trauma patients and correlate with neurological outcome. In a separate study, we found that matrix metalloproteinase-3 and albumin, a marker of cerebrovascular damage, were significantly increased in brain tissue of patients with neurotrauma. Perturbation of neurovascular homeostasis causing oedema, inflammation and cell death is an important cause of acute and long-term neurological dysfunction after trauma. A role for the tissue plasminogen activator-matrix metalloproteinase axis in promoting neurovascular disruption after neurotrauma has not been described thus far. Targeting tissue plasminogen activator: plasminogen activator inhibitor-1 complex signalling or downstream matrix metalloproteinase-3 induction may provide viable therapeutic strategies to reduce cerebrovascular permeability after neurotrauma.

tPA-S481A prevents neurotoxicity of endogenous tPA in traumatic brain injury

Traumatic brain injury (TBI) is associated with loss of autoregulation due to impaired responsiveness to cerebrovascular dilator stimuli, which leads to cerebral hypoperfusion and neuronal impairment or death. Upregulation of tissue plasminogen activator (tPA) post-TBI exacerbates loss of cerebral autoregulation and NMDA-receptor-mediated impairment of cerebral hemodynamics, and enhances excitotoxic neuronal death. However, the relationship between NMDA-receptor activation, loss of autoregulation, and neurological dysfunction is unclear. Here, we evaluated the potential therapeutic efficacy of a catalytically inactive tPA variant, tPA S481A, that acts by competing with wild-type tPA for binding, cleavage, and activation of NMDA receptors. Lateral fluid percussion brain injury was produced in anesthetized piglets. Pial artery reactivity was measured via a closed cranial window, and cerebrospinal fluid (CSF) extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) was quantified by enzyme-linked immunosorbent assay (ELISA). tPA-S481A prevented impairment of cerebral autoregulation and reduced histopathologic changes after TBI by inhibiting upregulation of the ERK isoform of MAPK. Treatment with this tPA variant provides a novel approach for limiting neuronal toxicity caused by untoward NMDA-receptor activation mediated by increased tPA and glutamate following TBI.

Combination therapy with glucagon and a novel plasminogen activator inhibitor-1-derived peptide enhances protection against impaired cerebrovasodilation during hypotension after traumatic brain injury through inhibition of ERK and JNK MAPK

OBJECTIVE

Outcome of traumatic brain injury (TBI) is impaired by hypotension and glutamate, and TBI-associated release of endogenous tissue plasminogen activator (tPA) impairs cerebral autoregulation. Glucagon decreases central nervous system glutamate, lessens neuronal cell injury, and improves neurological score in mice after TBI. Glucagon partially protects against impaired cerebrovasodilation during hypotension after TBI in piglets by upregulating cAMP which decreases release of tPA. Pial artery dilation during hypotension is due to release of cAMP-dependent dilator prostaglandins (PG), such as PGE2 and PGI2. TBI impairs PGE2 and PGI2-mediated pial artery dilation, which contributes to disturbed cerebral autoregulation post-insult, by upregulating mitogen-activated protein kinase (MAPK). This study was designed to investigate relationships between tPA, prostaglandins, and MAPK as a mechanism to improve the efficacy of glucagon-mediated preservation of cerebrovasodilation during hypotension after TBI.

METHODS

Lateral fluid percussion brain injury (FPI) was induced in piglets equipped with a closed cranial window. ERK and JNK MAPK concentrations in cerebrospinal fluid were quantified by enzyme-linked immunosorbent assay.

RESULTS

Cerebrospinal fluid JNK MAPK was increased by FPI, but blunted by glucagon and the novel plasminogen activator inhibitor-1-derived peptide (PAI-1DP), Ac-RMAPEEIIMDRPFLYVVR-amide. FPI modestly increased, while glucagon and PAI-1DP decreased ERK MAPK. PGE2, PGI2, N-methyl-D-aspartate, and hypotension-induced pial artery dilation was blunted after FPI, partially protected by glucagon, and fully protected by glucagon+PAI-1DP, glucagon+JNK antagonist SP600125 or glucagon+ERK inhibitor U 0126.

DISCUSSION

Glucagon+PAI-1DP act in concert to protect against impairment of cerebrovasodilation during hypotension after TBI via inhibition of ERK and JNK MAPK.

Glucagon protects against impaired NMDA-mediated cerebrovasodilation and cerebral autoregulation during hypotension after brain injury by activating cAMP protein kinase A and inhibiting upregulation of tPA

Outcome of traumatic brain injury (TBI) is impaired by hyperglycemia, hypotension, and glutamate, and improved by insulin. Insulin reduces glutamate concentration, making it uncertain whether its beneficial effect accrues from euglycemia. Glucagon decreases CNS glutamate, lessens neuronal cell injury, and improves neurological scores in mice after TBI. In vitro, glucagon limits NMDA-mediated excitotoxicity by increasing cAMP and protein kinase A (PKA). NMDA receptor activation couples cerebral blood flow (CBF) to metabolism. Dilation induced by NMDA is impaired after fluid percussion brain injury (FPI) due to upregulation of endogenous tPA, which further disturbs cerebral autoregulation during hypotension after fluid percussion injury (FPI). We hypothesized that glucagon prevents impaired NMDA receptor-mediated dilation after FPI by upregulating cAMP, which decreases release of tPA. NMDA-induced pial artery dilation (PAD) was reversed to vasoconstriction after FPI. Glucagon 30 min before or 30 min after FPI blocked NMDA-mediated vasoconstriction and restored the response to vasodilation. PAD during hypotension was blunted after FPI, but protected by glucagon. Glucagon prevented FPI-induced reductions in CSF cAMP, yielding a net increase in cAMP, and blocked FPI-induced elevation of CSF tPA. Co-administration of the PKA antagonist Rp 8Br cAMPs prevented glucagon-mediated preservation of NMDA-mediated dilation after FPI. The pKA agonist Sp 8Br cAMPs prevented impairment of NMDA-induced dilation. These data indicate that glucagon protects against impaired cerebrovasodilation by upregulating cAMP, which decreases release of tPA, suggesting that it may provide neuroprotection when given after TBI, or prior to certain neurosurgical or cardiac interventions in which the incidence of perioperative ischemia is high.