Simvastatin attenuates axonal injury after experimental traumatic brain injury and promotes neurite outgrowth of primary cortical neurons

Uncovering the protective potential of vanillic acid against traumatic brain injury-induced cognitive decline in male rats: Insights into underlying mechanisms

Traumatic brain injury (TBI) is a significant contributor to global mortality and disability, and there is still no specific drug available to treat cognitive deficits in survivors. Vanillic acid (VA), a bioactive phenolic compound, has shown protective effects in various models of neurodegeneration; however, its impact on TBI outcomes remains elusive. Therefore, this study aimed to elucidate the possible role of VA in ameliorating TBI-induced cognitive decline and to reveal the mechanisms involved. TBI was induced using the Marmarou impact acceleration model to deliver an impact force of 300 g, and treatment with VA (50 mg/kg; P.O.) was initiated 30 minutes post-TBI. The cognitive performance, hippocampal long-term potentiation (LTP), oxidative stress markers, neurological function, cerebral edema, and morphological changes were assessed at scheduled points in time. TBI resulted in cognitive decline in the passive avoidance task, impaired LTP in the perforant path-dentate gyrus (PP-DG) pathway, increased hippocampal oxidative stress, cerebral edema, neurological deficits, and neuronal loss in the rat hippocampus. In contrast, acute VA administration mitigated all the aforementioned TBI outcomes. The data suggest that reducing synaptic plasticity impairment, regulating oxidative and antioxidant defense, alleviating cerebral edema, and preventing neuronal loss by VA can be at least partially attributed to its protection against TBI-induced cognitive decline.

The protective effects of statins in traumatic brain injury

Traumatic brain injury (TBI), often referred to as the "silent epidemic", is the most common cause of mortality and morbidity worldwide among all trauma-related injuries. It is associated with considerable personal, medical, and economic consequences. Although remarkable advances in therapeutic approaches have been made, current treatments and clinical management for TBI recovery still remain to be improved. One of the factors that may contribute to this gap is that existing therapies target only a single event or pathology. However, brain injury after TBI involves various pathological mechanisms, including inflammation, oxidative stress, blood-brain barrier (BBB) disruption, ionic disturbance, excitotoxicity, mitochondrial dysfunction, neuronal necrosis, and apoptosis. Statins have several beneficial pleiotropic effects (anti-excitotoxicity, anti-inflammatory, anti-oxidant, anti-thrombotic, immunomodulatory activity, endothelial and vasoactive properties) in addition to promoting angiogenesis, neurogenesis, and synaptogenesis in TBI. Supposedly, using agents such as statins that target numerous and diverse pathological mechanisms, may be more effective than a single-target approach in TBI management. The current review was undertaken to investigate and summarize the protective mechanisms of statins against TBI. The limitations of conducted studies and directions for future research on this potential therapeutic application of statins are also discussed.

Possible mechanisms involved in the neuroprotective effects of chrysin against mild traumatic brain injury-induced spatial cognitive decline: An in vivo study in a rat model

Traumatic brain injury (TBI) is recognized as an important risk factor for cognitive deficits. The present study was designed to determine the potential neuroprotective effects of chrysin, a natural flavonoid compound, against TBI-induced spatial cognitive decline and the possible mechanisms involved. Oral administration of chrysin (25, 50, or 100 mg/kg/day) was initiated in rats immediately following the induction of the diffuse TBI model using the weight-dropping Marmarou model. Spatial cognitive ability, hippocampal synaptic plasticity, blood-brain barrier (BBB) permeability, brain water content, and histological changes were assessed at scheduled time points. The animals subjected to TBI exhibited spatial cognitive decline in the Morris water maze (MWM) test, which was accompanied by inhibition of hippocampal long-term potentiation (LTP) induction at the perforant path-dentate gyrus (PP-DG) synapses. Additionally, TBI caused BBB disruption, brain edema, and neuronal loss. Interestingly, treatment with chrysin (especially in the dose of 100 mg/kg) alleviated all the above-mentioned neuropathological changes related to TBI. The results provide evidence that chrysin improves TBI-induced spatial cognitive decline, which may be partly related to the amelioration of hippocampal synaptic dysfunction, alleviation of BBB disruption, reduction of brain edema, and prevention of neuronal loss.

HMG-CoA Reductase Inhibitors for Traumatic Brain Injury

Traumatic brain injuries (TBIs) are associated with high morbidity and mortality due to both the original insult as well as the destructive biological response that follows. Medical management aims to slow or even halt secondary neurological injury while simultaneously laying the groundwork for recovery. Statins are one class of medications that is showing increased promise in the management of TBI. Used extensively in cardiovascular disease, these drugs were originally developed as competitive inhibitors within the cholesterol production pipeline. They are now used in diverse disease states due to their pleiotropic effects on other biological processes such as inflammation and angiogenesis. Preclinical studies, retrospective reviews, and randomized clinical trials have shown a variety of benefits in the management of TBI, but to date, no large-scale randomized clinical trial has been performed. Despite this limitation, statins' early promise and well-tolerated side effect profile make them a promising new tool in the management of TBIs. More bench and clinical studies are needed to delineate proper treatment regimens as well as understand their true potential.

Progesterone attenuates neurological deficits and exerts a protective effect on damaged axons via the PI3K/AKT/mTOR-dependent pathway in a mouse model of intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating event with high disability and fatality rates. However, there is a lack of effective treatments for this condition. We aimed to investigate the neuroprotective and axonal regenerative effects of progesterone after ICH. For this purpose, an ICH model was established in adult mice by injecting type VII collagenase into the striatum; the mice were then treated with progesterone (8 mg/kg). Hematoma absorption, neurological scores, and brain water content were evaluated on days one, three, and seven after the ICH. The effect of progesterone on inflammation and axonal regeneration was examined on day three after the ICH using western blotting, immunohistochemistry, immunofluorescence, as well as hematoxylin-eosin, Nissl, and Luxol fast blue staining. In addition, we combined progesterone with the phosphoinositide 3-kinase/serine/threonine-specific protein kinase (PI3K/AKT) inhibitor, LY294002, to explore its potential neuroprotective mechanisms. Administration of progesterone attenuated the neurological deficits and expression of inflammatory cytokines and promoted axonal regeneration after ICH, this effect was blocked by LY294002. Collectively, these results suggest that progesterone could reduce axonal damage and produced partial neuroprotective effects after ICH through the PI3K/AKT/mTOR pathway, providing a new therapeutic target and basis for the treatment of ICH.

Mammalian target of rapamycin (mTOR) signaling pathway and traumatic brain injury: A novel insight into targeted therapy

Traumatic brain injury (TBI) is one of the most concerning health issues in which the normal brain function may be disrupted as a result of a blow, bump, or jolt to the head. Loss of consciousness, amnesia, focal neurological defects, alteration in mental state, and destructive diseases of the nervous system such as cognitive impairment, Parkinson's, and Alzheimer's disease. Parkinson's disease is a chronic progressive neurodegenerative disorder, characterized by the early loss of striatal dopaminergic neurons. TBI is a major risk factor for Parkinson's disease. Existing therapeutic approaches have not been often effective, indicating the necessity of discovering more efficient therapeutic targets. The mammalian target of rapamycin (mTOR) signaling pathway responds to different environmental cues to modulate a large number of cellular processes such as cell proliferation, survival, protein synthesis, autophagy, and cell metabolism. Moreover, mTOR has been reported to affect the regeneration of the injured nerves throughout the central nervous system (CNS). In this context, recent evaluations have revealed that mTOR inhibitors could be potential targets to defeat a group of neurological disorders, and thus, a number of clinical trials are investigating their efficacy in treating dementia, autism, epilepsy, stroke, and brain injury, as irritating neurological defects. The current review describes the interplay between mTOR signaling and major CNS-related disorders (esp. neurodegenerative diseases), as well as the mTOR signaling-TBI relationship. It also aims to discuss the promising therapeutic capacities of mTOR inhibitors during the TBI.

Vascular Dysfunction after Modeled Traumatic Brain Injury Is Preserved with Administration of Umbilical Cord Derived Mesenchymal Stromal Cells and Is Associated with Modulation of the Angiogenic Response

Vascular dysfunction arising from blood-brain barrier (BBB) breakdown after traumatic brain injury (TBI) can adversely affect neuronal health and behavioral outcome. Pericytes and endothelial cells of the neurovascular unit (NVU) function collectively to maintain strict regulation of the BBB through tight junctions. Secondary injury mechanisms, such as pro-angiogenic signals that contribute to pericyte loss, can prolong and exacerbate primary vascular injury. Human umbilical cord perivascular cells (HUCPVCs) are a source of mesenchymal stromal cells (MSCs) that have been shown to reduce vascular dysfunction after neurotrauma. We hypothesized that the perivascular properties of HUCPVCs can reduce vascular dysfunction after modeled TBI by preserving the pericyte-endothelial interactions. Rats were subjected to a moderate fluid percussion injury (FPI) and intravenously infused with 1,500,000 HUCPVCs post-injury. At acute time points (24 h and 48 h) quantitative polymerase chain reaction (qPCR) analysis demonstrated that the gene expression of angiopoietin-2 was increased with FPI and reduced with HUCPVCs. Immunofluorescent assessment of RECA-1 (endothelial cells) and platelet-derived growth factor receptors (PDGFR-β) (pericytes) revealed that capillary and pericyte densities as well as the co-localization of the two cells were decreased with FPI and preserved with HUCPVC administration. These acute HUCPVC-mediated protective effects were associated with less permeability to Evan's blue dye and increased expression of the tight junction occludin, suggesting less vascular leakage. Further, at 4 weeks post-injury, HUCPVC administration was associated with reduced anxiety and decreased β-amyloid precursor protein (β-APP) accumulation. In summary, HUCPVCs promoted pericyte-endothelial barrier function that was associated with improved long-term outcome.

Statins' Effect on Cognitive Outcome After Traumatic Brain Injury: A Systematic Review

Traumatic brain injury (TBI), also known as the "Silent Epidemic," is a growing devastating global health problem estimated to affect millions of individuals yearly worldwide with little public recognition, leading to many individuals living with a TBI-related disability. TBI has been associated with up to five times increase in the risk of dementia among multiple neurologic complications compared with the general population. Several therapies, including statins, have been tried and showed promising benefits for TBI patients. In this systematic review, we evaluated the recent literature that tested the role of statins on neurological and cognitive outcomes such as Alzheimer's Disease and non-Alzheimer's dementia in survivors of TBI with various severities. We conducted a systematic search on PubMed, PubMed Central, MEDLINE, and Google Scholar. MeSH terms and keywords were used to search for full-text randomized clinical trials (RCTs), cross-sectional, case-control, cohort studies, systematic reviews, and animal studies published in English. Inclusion and exclusion criteria were applied, and the articles were subjected to quality appraisal by two reviewers. Our data search retrieved 4948 nonduplicate records. A total of 18 studies were included - nine human studies, and nine animal laboratory trials - after meeting inclusion, eligibility, and quality assessment criteria. Simvastatin was the most tested statin, and the oral route of administration was the most used. Eight human studies showed a significant neuroprotective effect and improvement in the cognitive outcomes, including dementia. Four randomized clinical trials with 296 patients showed that statins play a neuroprotective role and improve cognitive outcomes through different mechanisms, especially their anti-inflammatory effect; they were shown to lower tumor necrosis factor (TNF)-α and C-reactive protein (CRP) levels. Also, they decreased axonal injury and cortical thickness changes. In addition, four cohort studies compared a total of 867.953 patients. One study showed a decrease in mortality in statin-treated patients (p=0.05). Another study showed a reduction in the incidence of Alzheimer's disease and related dementias (RR, 0.77; 95% CI, 0.73-0.81), while one study showed a decreased risk of dementia after concussions by 6.13% (p=0.001). On the other hand, one cohort study showed no significant difference with the use of statins. In eight animal trials, statins showed a significant neuroprotective effect, improved cognitive outcomes, and neurological functions. Different molecular and cellular mechanisms were suggested, including anti-inflammatory effects, promoting angiogenesis, neurogenesis, increasing cerebral blood flow, neurite outgrowth, promoting the proliferation and differentiation of neural stem cells, and reducing axonal injury. On the contrary, one study showed no benefit and actual adverse effect on the cognitive outcome. Most of the studies showed promising neuroprotective effects of statins in TBI patients. Cognitive outcomes, especially dementia, were improved. However, the optimal therapeutic protocol is still unknown. Thus, statins are candidates for more advanced studies to test their efficacy in preventing cognitive decline in patients with TBI.

FPS-ZM1 Alleviates Neuroinflammation in Focal Cerebral Ischemia Rats via Blocking Ligand/RAGE/DIAPH1 Pathway

Receptor for advanced glycation end products (RAGEs), a multiligand receptor belonging to the cell-surface immunoglobulin superfamily, has been reported to play a crucial role in neuroinflammation and neurodegenerative diseases. Here, we tested our hypothesis that the RAGE-specific antagonist FPS-ZM1 is neuroprotective against ischemic brain injury. Distal middle cerebral artery occlusion (MCAO) or sham operation was performed on anesthetized Sprague-Dawley male rats (n = 60), which were then treated with FPS-ZM1 or vehicle (four groups in total = Vehicle + MCAO, FPS-ZM1 + MCAO, Vehicle + sham, and FPS-ZM1 + sham). After 1 week, neurological function was evaluated, and then, brain tissues were collected for 2,3,5-triphenyltetrazolium chloride staining, Nissl staining, TUNEL staining, Western blotting, and immunohistochemical analyses. FPS-ZM1 treatment after MCAO markedly attenuated neurological deficits and reduced the infarct area. More interestingly, FPS-ZM1 inhibited ischemia-induced astrocytic activation and microgliosis and decreased the elevated levels of proinflammatory cytokines. Furthermore, FPS-ZM1 blocked the increase in the level of RAGE and, notably, of DIAPH1, the key cytoplasmic hub for RAGE-ligand-mediated activation of cellular signaling. Accordingly, FPS-ZM1 also reversed the MCAO-induced increase in phosphorylation of NF-κB targets that are potentially downstream from RAGE/DIAPH1. Our findings reveal that FPS-ZM1 treatment reduces neuroinflammation in rats with focal cerebral ischemia and further suggest that the ligand/RAGE/DIAPH1 pathway contributes to this FPS-ZM1-mediated alleviation of neuroinflammation.

Wnt Pathway: An Emerging Player in Vascular and Traumatic Mediated Brain Injuries

The Wnt pathway, which comprises the canonical and non-canonical pathways, is an evolutionarily conserved mechanism that regulates crucial biological aspects throughout the development and adulthood. Emergence and patterning of the nervous and vascular systems are intimately coordinated, a process in which Wnt pathway plays particularly important roles. In the brain, Wnt ligands activate a cell-specific surface receptor complex to induce intracellular signaling cascades regulating neurogenesis, synaptogenesis, neuronal plasticity, synaptic plasticity, angiogenesis, vascular stabilization, and inflammation. The Wnt pathway is tightly regulated in the adult brain to maintain neurovascular functions. Historically, research in neuroscience has emphasized essentially on investigating the pathway in neurodegenerative disorders. Nonetheless, emerging findings have demonstrated that the pathway is deregulated in vascular- and traumatic-mediated brain injuries. These findings are suggesting that the pathway constitutes a promising target for the development of novel therapeutic protective and restorative interventions. Yet, targeting a complex multifunctional signal transduction pathway remains a major challenge. The review aims to summarize the current knowledge regarding the implication of Wnt pathway in the pathobiology of ischemic and hemorrhagic stroke, as well as traumatic brain injury (TBI). Furthermore, the review will present the strategies used so far to manipulate the pathway for therapeutic purposes as to highlight potential future directions.

High expression of EphA2 led to secondary injury by destruction of BBB integrity though the ROCK pathway after diffuse axonal injury

Blood-brain barrier (BBB) disruption exacerbates diffuse axonal injury (DAI), but the underlying mechanisms are not fully understood. Inactivation or deletion of erythropoietin-producing hepatoma (EPH) receptor A2 (EphA2) attenuated BBB damage and promoted tight junction formation. In this study, we aimed to investigate the role of EphA2 in the protection of BBB integrity and the relevant mechanisms involved in a rat model of DAI. Blocking activation of the EphA receptor by EphA2-Fc ameliorated axonal injury, cell apoptosis, and glial activation, protected BBB integrity and increased expression of the tight junction-associated proteins ZO-1, claudin-5 and occludin-1. In vitro BBB models established by human brain microvascular endothelial cells (HBMECs) were subjected to oxygen deprivation (OGD). Treatment with EphrinA1, which activates EphA2, exacerbated the OGD-induced destruction of permeability and integrity of the BBB models by reducing the expression of tight junction-associated proteins. However, inhibition of Rho-associated coiled coil-containing protein kinases 1 and 2 (ROCK1 and 2) abrogated all of the effects of EphrinA1 on the BBB models in vitro. In conclusion, we provide evidence that EphA2 plays an important role in the destruction of BBB integrity by decreasing the expression of tight junction proteins through the ROCK pathway.

The holy grail of epilepsy prevention: Preclinical approaches to antiepileptogenic treatments

A variety of acute brain insults can induce epileptogenesis, a complex process that results in acquired epilepsy. Despite advances in understanding mechanisms of epileptogenesis, there is currently no approved treatment that prevents the development or progression of epilepsy in patients at risk. The current concept of epileptogenesis assumes a window of opportunity following acute brain insults that allows intervention with preventive treatment. Recent results suggest that injury-induced epileptogenesis can be a much more rapid process than previously thought, suggesting that the 'therapeutic window' may only be open for a brief period, as in stroke therapy. However, experimental data also suggest a second, possibly delayed process ("secondary epileptogenesis") that influences the progression and refractoriness of the epileptic state over time, allowing interfering with this process even after onset of epilepsy. In this review, both methodological issues in preclinical drug development and novel targets for antiepileptogenesis will be discussed. Several promising drugs that either prevent epilepsy (antiepileptogenesis) or slow epilepsy progression and alleviate cognitive or behavioral comorbidities of epilepsy (disease modification) have been described in recent years, using diverse animal models of acquired epilepsy. Promising agents include TrkB inhibitors, losartan, statins, isoflurane, anti-inflammatory and anti-oxidative drugs, the SV2A modulator levetiracetam, and epigenetic interventions. Research on translational target validity and on prognostic biomarkers that can be used to stratify patients (or experimental animals) at high risk of developing epilepsy will hopefully soon lead to proof-of-concept clinical trials with the most promising drugs, which will be essential to make prevention of epilepsy a reality. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'.

In search of antiepileptogenic treatments for post-traumatic epilepsy

Post-traumatic epilepsy (PTE) is diagnosed in 20% of individuals with acquired epilepsy, and can impact significantly the quality of life due to the seizures and other functional or cognitive and behavioral outcomes of the traumatic brain injury (TBI) and PTE. There is no available antiepileptogenic or disease modifying treatment for PTE. Animal models of TBI and PTE have been developed, offering useful insights on the value of inflammatory, neurodegenerative pathways, hemorrhages and iron accumulation, calcium channels and other target pathways that could be used for treatment development. Most of the existing preclinical studies test efficacy towards pathologies of functional recovery after TBI, while a few studies are emerging testing the effects towards induced or spontaneous seizures. Here we review the existing preclinical trials testing new candidate treatments for TBI sequelae and PTE, and discuss future directions for efforts aiming at developing antiepileptogenic and disease-modifying treatments.

Pre-Clinical Testing of Therapies for Traumatic Brain Injury

Despite the large number of promising neuroprotective agents identified in experimental traumatic brain injury (TBI) studies, none has yet shown meaningful improvements in long-term outcome in clinical trials. To develop recommendations and guidelines for pre-clinical testing of pharmacological or biological therapies for TBI, the Moody Project for Translational Traumatic Brain Injury Research hosted a symposium attended by investigators with extensive experience in pre-clinical TBI testing. The symposium participants discussed issues related to pre-clinical TBI testing including experimental models, therapy and outcome selection, study design, data analysis, and dissemination. Consensus recommendations included the creation of a manual of standard operating procedures with sufficiently detailed descriptions of modeling and outcome measurement procedures to permit replication. The importance of the selection of clinically relevant outcome variables, especially related to behavior testing, was noted. Considering the heterogeneous nature of human TBI, evidence of therapeutic efficacy in multiple, diverse (e.g., diffuse vs. focused) rodent models and a species with a gyrencephalic brain prior to clinical testing was encouraged. Basing drug doses, times, and routes of administration on pharmacokinetic and pharmacodynamic data in the test species was recommended. Symposium participants agreed that the publication of negative results would reduce costly and unnecessary duplication of unsuccessful experiments. Although some of the recommendations are more relevant to multi-center, multi-investigator collaborations, most are applicable to pre-clinical therapy testing in general. The goal of these consensus guidelines is to increase the likelihood that therapies that improve outcomes in pre-clinical studies will also improve outcomes in TBI patients.

Serum-Based Phospho-Neurofilament-Heavy Protein as Theranostic Biomarker in Three Models of Traumatic Brain Injury: An Operation Brain Trauma Therapy Study

Glial fibrillary acidic protein (GFAP) and ubiquitin C-terminal hydrolase (UCH-L1), markers of glial and neuronal cell body injury, respectively, have been previously selected by the Operation Brain Trauma Therapy (OBTT) pre-clinical therapy and biomarker screening consortium as drug development tools. However, traumatic axonal injury (TAI) also represents a major consequence and determinant of adverse outcomes after traumatic brain injury (TBI). Thus, biomarkers capable of assessing TAI are much needed. Neurofilaments (NFs) are found exclusively in axons. Here, we evaluated phospho-neurofilament-H (pNF-H) protein as a possible new TAI marker in serum and cerebrospinal fluid (CSF) across three rat TBI models in studies carried out by the OBTT consortium, namely, controlled cortical impact (CCI), parasagittal fluid percussion (FPI), and penetrating ballistics-like brain injury (PBBI). We indeed found that CSF and serum pNF-H levels are robustly elevated by 24 h post-injury in all three models. Further, in previous studies by OBTT, levetiracetam showed the most promising benefits, whereas nicotinamide showed limited benefit only at high dose (500 mg/kg). Thus, serum samples from the same repository collected by OBTT were evaluated. Treatment with 54 mg/kg intravenously of levetiracetam in the CCI model and 170 mg/kg in the PBBI model significantly attenuated pNF-H levels at 24 h post-injury as compared to respective vehicle groups. In contrast, nicotinamide (50 or 500 mg/kg) showed no reduction of pNF-H levels in CCI or PBBI models. Our current study suggests that pNF-H is a useful theranostic blood-based biomarker for TAI across different rodent TBI models. In addition, our data support levetiracetam as the most promising TBI drug candidate screened by OBTT to date.

Statins impact primary embryonic mouse neural stem cell survival, cell death, and fate through distinct mechanisms

Statins inhibit HMG-CoA reductase, the rate-limiting enzyme in the cholesterol biosynthesis pathway (CBP), and are used for the prevention of cardiovascular disease. The anti-inflammatory effects of statins may also provide therapeutic benefits and have led to their use in clinical trials for preeclampsia, a pregnancy-associated inflammatory condition, despite their current classification as category X (i.e. contraindicated during pregnancy). In the developing neocortex, products of the CBP play essential roles in proliferation and differentiation of neural stem-progenitor cells (NSPCs). To understand how statins could impact the developing brain, we studied effects of pravastatin and simvastatin on primary embryonic NSPC survival, proliferation, global transcription, and cell fate in vitro. We found that statins dose dependently decrease NSPC expansion by promoting cell death and autophagy of NSPCs progressing through the G1 phase of the cell cycle. Genome-wide transcriptome analysis demonstrates an increase in expression of CBP genes following pravastatin treatment, through activation of the SREBP2 transcription factor. Co-treatment with farnesyl pyrophosphate (FPP), a CBP metabolite downstream of HMG-CoA reductase, reduces SREBP2 activation and pravastatin-induced PARP cleavage. Finally, pravastatin and simvastatin differentially alter NSPC cell fate and mRNA expression during differentiation, through a non-CBP dependent pathway.

MicroRNA let-7c-5p improves neurological outcomes in a murine model of traumatic brain injury by suppressing neuroinflammation and regulating microglial activation

MicroRNAs (miRNAs) are a class of non-coding small RNAs that regulate the expression of target genes. They derive from pre-miRNAs that are enzymatically processed by dicer to ∼22 nucleotide mature miRNAs. Members of the pre-miRNA lethal-7 (let-7) are known to regulate cell proliferation and apoptosis. Here, we showed that the level of let-7c-5p, a key member of the let-7 family, was rapidly reduced in the traumatically injured foci in brains of adult C57BL/6J mice and gradually recovered to the pre-injury level 14 days after traumatic brain injury (TBI) induction. This finding led us to test whether upregulating let-7c-5p in murine cerebral tissue by intracerebroventricular injection (ICV) of let-7c-5p mimic could improve the outcomes of mice subjected to controlled cortical impact (CCI). We found that let-7c-5p overexpression attenuated TBI-induced neurological dysfunction and brain edema. The improvements were attributed to let-7c-5p-mediated inhibiting neuroinflammation and attenuation of microglia/macrophage activation, both inhibiting M1 polarization and enhancing M2 polarization. In vitro experiments, we observed that let-7c-5p was decreased in primary microglia activated by LPS treatment or oxygen/glucose deprivation (OGD). Transfection of let-7c-5p mimic suppressed the release of inflammatory mediators in cultured activated primary microglia. In addition, the expressions of caspase-3, a let-7c-5p putative target gene, and the PKC-δ which mediates effect of caspase-3 were inhibited by let-7c-5p in a murine model of TBI. Taken together, these results define the biological activities of cerebral let-7c-5p and delineate its therapeutic potential for improving the neurological outcome of TBI.

Statin discontinuation and mortality in an older adult population with traumatic brain injury: A four-year, multi-centre, observational cohort study

INTRODUCTION

Statin discontinuation has been investigated in a wide range of diseases and injuries, but there is a paucity of data in the older adult population with traumatic brain injury (TBI). The purpose of this study was to re-examine the extent to which early discontinuation of pre-injury statin (PIS) therapy increases the risk of poor patient outcomes in older adult patients suffering a TBI.

METHODS

This was a retrospective observational cohort study of adult trauma patients with a blunt TBI across three trauma centres over four years. Patients were excluded because of no PIS use, age <55years, or a hospital length of stay (LOS) less than three days. Patients found to be intentionally discontinued from statin therapy within 48h of hospital admission for injury-related reasons were excluded. The primary and secondary outcomes were in-hospital mortality and a hospital LOS ≥1 week. Outcomes were analysed using logistic regression.

RESULTS

There were 266 patients in the continuation group, and 131 in the discontinuation group. The statin discontinuation group had a significantly higher proportion of patients with a moderate or severe head injury, intubation in emergency department (ED), and disposition to the intensive care unit or operating room. Overall, 23 (6%) patients died while in the hospital. After adjusting for ED Glasgow coma scale, the odds of dying in the hospital were not significantly larger for patients having been discontinued from PIS, compared to those who were continued (OR=1.75, 95%CI=0.71-4.31, p=0.22). Among patients who received an in-hospital statin, the median (interquartile range) time between hospital admission and first administration of statin medication did not differ between patients who died and those who survived (22.8h [10.96-28.91] vs. 22.9h [11.67-39.80], p=0.94). There were no significant differences between study groups in the proportion of patients with a hospital length of stay >1 week (continuation=29% vs. discontinuation=36%, p=0.19).

CONCLUSION

We did not observe a significantly increased odds of in-hospital mortality following PIS discontinuation, compared to PIS continuation, in an older adult population with TBI. It remains to be seen whether statin discontinuation is a proxy variable for injury severity, or whether it exerts deleterious effects after injury.

Diffusion-Derived Magnetic Resonance Imaging Measures of Longitudinal Microstructural Remodeling Induced by Marrow Stromal Cell Therapy after Traumatic Brain Injury

Using magnetic resonance imaging (MRI) and an animal model of traumatic brain injury (TBI), we investigated the capacity and sensitivity of diffusion-derived measures, fractional anisotropy (FA), and diffusion entropy, to longitudinally identify structural plasticity in the injured brain in response to the transplantation of human bone marrow stromal cells (hMSCs). Male Wistar rats (300-350g, n = 30) were subjected to controlled cortical impact TBI. At 6 h or 1 week post-injury, these rats were intravenously injected with 1 mL of saline (at 6 h or 1 week, n = 5/group) or with hMSCs in suspension (∼3 × 10⁶ hMSCs, at 6 h or 1 week, n = 10/group). In vivo MRI measurements and sensorimotor function estimates were performed on all animals pre-injury, 1 day post-injury, and weekly for 3 weeks post-injury. Bielschowsky's silver and Luxol fast blue staining were used to reveal the axon and myelin status, respectively, with and without cell treatment after TBI. Based on image data and histological observation, regions of interest encompassing the structural alterations were made and the values of FA and entropy were monitored in these specific brain regions. Our data demonstrate that administration of hMSCs after TBI leads to enhanced white matter reorganization particularly along the boundary of contusional lesion, which can be identified by both FA and entropy. Compared with the therapy performed at 1 week post-TBI, cell intervention executed at 6 h expedites the brain remodeling process and results in an earlier functional recovery. Although FA and entropy present a similar capacity to dynamically detect the microstructural changes in the tissue regions with predominant orientation of fiber tracts, entropy exhibits a sensitivity superior to that of FA, in probing the structural alterations in the tissue areas with complex fiber patterns.

Inhibition of Glycogen Synthase Kinase-3: An Emerging Target in the Treatment of Traumatic Brain Injury

Although traumatic brain injury (TBI) has been a major public health concern for decades, the pathophysiological mechanism of TBI is not clearly understood, and an effective medical treatment of TBI is not available at present. Of particular concern is sustained TBI, which has a strong tendency to take a deteriorating neurodegenerative course into chronic traumatic encephalopathy (CTE) and dementia, including Alzheimer's disease. Tauopathy and beta amyloid (Aβ) plaques are known to be the key pathological markers of TBI, which contribute to the progressive deterioration associated with TBI such as CTE and Alzheimer's disease. The multiple lines of evidence strongly suggest that the inhibition of glycogen synthase kinase-3 (GSK-3) is a potential target in the treatment of TBI. GSK-3 constitutively inhibits neuroprotective processes and promotes apoptosis. After TBI, GSK-3 is inhibited through the receptor tyrosine kinase (RTK) and canonical Wnt signaling pathways as an innate neuroprotective mechanism against TBI. GSK-3 inhibition via GSK-3 inhibitors and drugs activating RTK or Wnt signaling is likely to reinforce the innate neuroprotective mechanism. GSK-3 inhibition studies using rodent TBI models demonstrate that GSK-3 inhibition produces diverse neuroprotective actions such as reducing the size of the traumatic injury, tauopathy, Aβ accumulation, and neuronal death, by releasing and activating neuroprotective substrates from GSK-3 inhibition. These effects are correlated with reduced TBI-induced behavioral and cognitive symptoms. Here, we review studies on the therapeutic effects of GSK-3 inhibition in TBI rodent models, and critically discuss the issues that these studies address.

Neurovascular and Cognitive failure in Alzheimer's Disease: Benefits of Cardiovascular Therapy

Alzheimer's disease (AD) is a multifactorial and multifaceted disease for which we currently have very little to offer since there is no curative therapy, with only limited disease-modifying drugs. Recent studies in AD mouse models that recapitulate the amyloid-β (Aβ) pathology converge to demonstrate that it is possible to salvage cerebrovascular function with a variety of drugs and, particularly, therapies used to treat cardiovascular diseases such as hypercholesterolemia and hypertension. These drugs can reestablish dilatory function mediated by various endothelial and smooth muscle ion channels as well as nitric oxide availability, benefits that result in normalized brain perfusion. These cerebrovascular benefits would favor brain perfusion, which may help maintain neuronal function and, possibly, delay cognitive failure. However, restoring cerebrovascular function in AD mouse models was not necessarily accompanied by rescue of cognitive deficits related to spatial learning and memory. The results with cardiovascular therapies rather suggest that drugs originally designed to treat cardiovascular diseases that concurrently restore cerebrovascular and cognitive function do so through their pleiotropic effects. Specifically, recent findings suggest that these drugs act directly on brain cells and neuronal pathways involved in memory formation, hence, working simultaneously albeit independently on neuronal and vascular targets. These findings may help select medications for patients with cardiovascular diseases at risk of developing AD with increasing age. Further, they may identify molecular targets for recovering memory pathways that bear potential for new therapeutic avenues.

Simvastatin Treatment in Traumatic Brain Injury: Operation Brain Trauma Therapy

Simvastatin, the fourth drug selected for testing by Operation Brain Trauma Therapy (OBTT), is a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor used clinically to reduce serum cholesterol. In addition, simvastatin has demonstrated potent antineuroinflammatory and brain edema reducing effects and has shown promise in promoting functional recovery in pre-clinical models of traumatic brain injury (TBI). The purpose of this study was to assess the potential neuroprotective effects of oral administration of simvastatin on neurobehavioral, biomarker, and histopathological outcome measures compared across three pre-clinical TBI animal models. Adult male Sprague-Dawley rats were exposed to either moderate fluid percussion injury (FPI), controlled cortical impact injury (CCI), or penetrating ballistic-like brain injury (PBBI). Simvastatin (1 or 5 mg/kg) was delivered via oral gavage at 3 h post-injury and continued once daily out to 14 days post-injury. Results indicated an intermediate beneficial effect of simvastatin on motor performance on the gridwalk (FPI), balance beam (CCI), and rotarod tasks (PBBI). No significant therapeutic benefit was detected, however, on cognitive outcome across the OBTT TBI models. In fact, Morris water maze (MWM) performance was actually worsened by treatment in the FPI model and scored full negative points for low dose in the MWM latency and swim distance to locate the hidden platform. A detrimental effect on cortical tissue loss was also seen in the FPI model, and there were no benefits on histology across the other models. Simvastatin also produced negative effects on circulating glial fibrillary acidic protein biomarker outcomes that were evident in the FPI and PBBI models. Overall, the current findings do not support the beneficial effects of simvastatin administration over 2 weeks post-TBI using the oral route of administration and, as such, it will not be further pursued by OBTT.

Novel High Content Screen Detects Compounds That Promote Neurite Regeneration from Cochlear Spiral Ganglion Neurons

The bipolar spiral ganglion neurons (SGN) carry sound information from cochlear hair cells to the brain. After noise, antibiotic or toxic insult to the cochlea, damage to SGN and/or hair cells causes hearing impairment. Damage ranges from fiber and synapse degeneration to dysfunction and loss of cells. New interventions to regenerate peripheral nerve fibers could help reestablish transfer of auditory information from surviving or regenerated hair cells or improve results from cochlear implants, but the biochemical mechanisms to target are largely unknown. Presently, no drugs exist that are FDA approved to stimulate the regeneration of SGN nerve fibers. We designed an original phenotypic assay to screen 440 compounds of the NIH Clinical Collection directly on dissociated mouse spiral ganglia. The assay detected one compound, cerivastatin, that increased the length of regenerating neurites. The effect, mimicked by other statins at different optimal concentrations, was blocked by geranylgeraniol. These results demonstrate the utility of screening small compound libraries on mixed cultures of dissociated primary ganglia. The success of this screen narrows down a moderately sized library to a single compound which can be elevated to in-depth in vivo studies, and highlights a potential new molecular pathway for targeting of hearing loss drugs.

Robust Neuritogenesis-Promoting Activity by Bis(heptyl)-Cognitin Through the Activation of alpha7-Nicotinic Acetylcholine Receptor/ERK Pathway

AIMS

Neurodegenerative disorders are caused by progressive neuronal loss in the brain, and hence, compounds that could promote neuritogenesis may have therapeutic values. In this study, the effects of bis(heptyl)-cognitin (B7C), a multifunctional dimer, on neurite outgrowth were investigated in both PC12 cells and primary cortical neurons.

METHODS

Immunocytochemical staining was used to evaluate the proneuritogenesis effects, and Western blot and short hairpin RNA assays were applied to explore the underlying mechanisms.

RESULTS

B7C (0.1-0.5 μM) induced robust neurite outgrowth in PC12 cells, as evidenced by the neurite-bearing morphology and upregulation of growth-associated protein-43 expression. In addition, B7C markedly promoted neurite outgrowth in primary cortical neurons as shown by the increase in the length of β-III-tubulin-positive neurites. Furthermore, B7C rapidly increased ERK phosphorylation. Specific inhibitors of alpha7-nicotinic acetylcholine receptor (α7-nAChR) and MEK, but not those of p38 or JNK, blocked the neurite outgrowth as well as ERK phosphorylation induced by B7C. Most importantly, genetic depletion of α7-nAChR significantly abolished B7C-induced neurite outgrowth in PC12 cells.

CONCLUSION

B7C promoted neurite outgrowth through the activation of α7-nAChR/ERK pathway, which offers novel insight into the potential application of B7C in the treatment of neurodegenerative disorders.

Simvastatin increases excitability in the hippocampus via a PI3 kinase-dependent mechanism

Simvastatin is an HMG-CoA reductase inhibitor commonly used in the clinic to treat hypercholesterolemia. In addition, simvastatin has been shown to cross the blood-brain barrier and pleiotropic effects of simvastatin have been reported including anti-inflammatory properties, enhancement of neurite outgrowth, and memory enhancement properties. However, little has been reported on the effects of simvastatin on basal synaptic transmission and neuronal excitability. Here we report that simvastatin increases the fEPSP, the N-methyl-D-aspartate (NMDA) receptor-mediated fEPSP using extracellular recordings in the dendritic region of the CA1 of hippocampal slices taken from 8-week-old C57Black6J mice. In addition, we found that simvastatin perfusion causes a change in the input/output curve and a decrease of the paired-pulse facilitation ratio, indicating respectively an increase of the neuronal excitability and neurotransmitter release. We have also observed that acute application of simvastatin increased the amplitude of the compound action potential in the CA1 region. Notably, using LY294002, we have demonstrated that this effect was PI3K dependent and was occluded if the animals had previously received a diet supplemented with simvastatin. We have finally shown that the simvastatin-mediated increase of the compound action potential amplitude was also present in hippocampal slices from aged mice.

Comparison of the effect of minocycline and simvastatin on functional recovery and gene expression in a rat traumatic brain injury model

The goal of this study was to compare the effects of minocycline and simvastatin on functional recovery and brain gene expression after a cortical contusion impact (CCI) injury. Dosage regimens were designed to provide serum concentrations in a rat model in the range obtained with clinically approved doses; minocycline 60 mg/kg q12h and simvastatin 10 mg/kg q12h for 72 h. Functional recovery was assessed using motor and spatial learning tasks and neuropathological measurements. Microarray-based transcriptional profiling was used to determine the effect on gene expression at 24 h, 72 h, and 7 days post-CCI. Gene Ontology analysis (GOA) was used to evaluate the effect on relevant biological pathways. Both minocycline and simvastatin improved fine motor function, but not gross motor or cognitive function. Minocycline modestly decreased lesion size with no effect of simvastatin. At 24 h post-CCI, GOA identified a significant effect of minocycline on chemotaxis, blood circulation, immune response, and cell to cell signaling pathways. Inflammatory pathways were affected by minocycline only at the 72 h time point. There was a minimal effect of simvastatin on gene expression 24 h after injury, with increasing effects at 72 h and 7 days. GOA identified a significant effect of simvastatin on inflammatory response at 72 h and 7 days. In conclusion, treatment with minocycline and simvastatin resulted in significant effects on gene expression in the brain reflecting adequate brain penetration without producing significant neurorestorative effects.

Bilateral substantia nigra and pyramidal tract changes following experimental intracerebral hemorrhage: an MR diffusion tensor imaging study

The amelioration of secondary neurological damage is among the most important therapeutic goals for patients with intracerebral hemorrhage (ICH). Secondary injury of the ipsilateral substantia nigra (SN) and pyramidal tract (PY) is common after cerebral stroke. Such injury has been characterized previously by anatomical or diffusion MRI, but not in a comprehensive manner, and the knowledge regarding the contralateral changes is relatively poor. This study examined longitudinally both contralateral and ipsilateral SN and PY changes following experimental ICH with diffusion tensor imaging (DTI) and histology. ICH was induced in 14 Sprague-Dawley rats by the infusion of collagenase into the right striatum. Four-shot, spin-echo, echo-planar DTI was performed at 7 T with a b value of 1000 s/mm(2) and 30 diffusion gradient directions at 3.5 h and days 1, 3, 7, 14, 42 and 120 after ICH. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (λ// ) and radial diffusivity (λ┴ ) were measured in SN and PY accordingly. Two to three rats were sacrificed at days 3, 7, 42 and 120 for histology. The contralateral SN showed an increase in λ// with perivascular enlargement during the first 3 days after ICH. The ipsilateral SN showed increases in FA, λ// , λ┴ and MD at day 1, dramatic decreases at day 3 with neuronal degeneration and neuropil vacuolation, and subsequent gradual normalization. The contralateral PY showed diffusivity decreases at day 1. The ipsilateral PY showed early decreases and then late increases in MD and λ┴, and continuously decreasing FA and λ// with progressive axonal loss and demyelination. In summary, DTI revealed early bilateral changes in SN and PY following ICH. The evolution of the ipsilateral parameters correlated with the histological findings. In the ipsilateral PY, λ// and λ┴ changes indicated evolving and complex pathological processes underlying the monotonic FA decrease. These results support the use of quantitative multiparametric DTI for the evaluation of SN and PY injuries in clinical and preclinical investigations of ICH.