Key role of sulfonylurea receptor 1 in progressive secondary hemorrhage after brain contusion

Effects of early rolipram treatment on histopathological outcome after controlled cortical impact injury in mice

Traumatic brain injury (TBI) pathology includes contusions, cavitation, cell death, all of which can be exacerbated by inflammation. We hypothesized that an anti-inflammatory drug, rolipram, may reduce pathology after TBI, since in several CNS injury models rolipram reduces inflammation and improves cell survival and functional recovery. Adult male C57BL/6 mice received a craniotomy over the right parietotemporal cortex. Vertically directed controlled cortical impact (CCI) injury was delivered. Naïve controls were used for comparison. At 30 min post-surgery, animals were treated with vehicle or rolipram (1 mg/kg), and then once per day for 3 days. On day 3, the brains were systematically sectioned and stained to visualize the resulting pathology using hematoxylin and eosin (H&E) staining and NeuN immunocytochemistry. Total parietotemporal cortical contusion and cavity volume were significantly increased in rolipram-treated as compared to vehicle-treated CCI animals. Contusion areas at specific bregma levels indicated a significant effect of drug across bregma levels. Neuronal cell loss in the dentate hilus and area CA3 of the hippocampus were similar between vehicle and rolipram-treated animals. Although rolipram is well known to reduce pathology and inflammation in several other CNS injury models, the pathology resulting from CCI was worsened with rolipram at this particular dose and administration schedule. These studies suggest that consideration of the unique characteristics of TBI pathology is important in the extrapolation of promising therapeutic interventions from other CNS injury models.

Sulfonylurea receptor 1 in central nervous system injury: a focused review

The sulfonylurea receptor 1 (Sur1)-regulated NC(Ca-ATP) channel is a nonselective cation channel that is regulated by intracellular calcium and adenosine triphosphate. The channel is not constitutively expressed, but is transcriptionally upregulated de novo in all cells of the neurovascular unit, in many forms of central nervous system (CNS) injury, including cerebral ischemia, traumatic brain injury (TBI), spinal cord injury (SCI), and subarachnoid hemorrhage (SAH). The channel is linked to microvascular dysfunction that manifests as edema formation and delayed secondary hemorrhage. Also implicated in oncotic cell swelling and oncotic (necrotic) cell death, the channel is a major molecular mechanism of 'accidental necrotic cell death' in the CNS. In animal models of SCI, pharmacological inhibition of Sur1 by glibenclamide, as well as gene suppression of Abcc8, prevents delayed capillary fragmentation and tissue necrosis. In models of stroke and TBI, glibenclamide ameliorates edema, secondary hemorrhage, and tissue damage. In a model of SAH, glibenclamide attenuates the inflammatory response due to extravasated blood. Clinical trials of an intravenous formulation of glibenclamide in TBI and stroke underscore the importance of recent advances in understanding the role of the Sur1-regulated NC(Ca-ATP) channel in acute ischemic, traumatic, and inflammatory injury to the CNS.

Computational analysis reveals increased blood deposition following repeated mild traumatic brain injury

Mild traumatic brain injury (mTBI) has become an increasing public health concern as subsequent injuries can exacerbate existing neuropathology and result in neurological deficits. This study investigated the temporal development of cortical lesions using magnetic resonance imaging (MRI) to assess two mTBIs delivered to opposite cortical hemispheres. The controlled cortical impact model was used to produce an initial mTBI on the right cortex followed by a second injury induced on the left cortex at 3 (rmTBI 3d) or 7 (rmTBI 7d) days later. Histogram analysis was combined with a novel semi-automated computational approach to perform a voxel-wise examination of extravascular blood and edema volumes within the lesion. Examination of lesion volume 1d post last injury revealed increased tissue abnormalities within rmTBI 7d animals compared to other groups, particularly at the site of the second impact. Histogram analysis of lesion T2 values suggested increased edematous tissue within the rmTBI 3d group and elevated blood deposition in the rm TBI 7d animals. Further quantification of lesion composition for blood and edema containing voxels supported our histogram findings, with increased edema at the site of second impact in rmTBI 3d animals and elevated blood deposition in the rmTBI 7d group at the site of the first injury. Histological measurements revealed spatial overlap of regions containing blood deposition and microglial activation within the cortices of all animals. In conclusion, our findings suggest that there is a window of tissue vulnerability where a second distant mTBI, induced 7d after an initial injury, exacerbates tissue abnormalities consistent with hemorrhagic progression.

Transporters and channels in cytotoxic astrocyte swelling

Brain edema is a severe clinical complication in a number of pathologies and is a major cause of increased morbidity and death. The swelling of astrocytes caused by a disruption of water and ion homeostasis, is the primary event contributing to the cytotoxic form of brain edema. Astrocyte cytotoxic swelling ultimately leads to transcapillary fluxes of ions and water into the brain parenchyma. This review focuses on the implication of transporters and channels in cytotoxic astrocyte swelling in hyponatremia, ischemia, trauma and hepatic encephalopathy. Emphasis is put on some salient features of the astrocyte physiology, all related to cell swelling, i.e. predominance of aquaporins, control of K(+) homeostasis and ammonia accumulation during the brain ammonia-detoxifying process.

Independent evaluation of the effects of glibenclamide on reducing progressive hemorrhagic necrosis after cervical spinal cord injury

These experiments were completed as part of an NIH-NINDS contract entitled "Facilities of Research Excellence - Spinal Cord Injury (FORE-SCI) - Replication". Our goal was to replicate pre-clinical data from Simard et al. (2007) showing that glibenclamide, an FDA approved anti-diabetic drug that targets sulfonylurea receptor 1 (SUR1)-regulated Ca(2+) activated, [ATP](i)-sensitive nonspecific cation channels, attenuates secondary intraspinal hemorrhage and secondary neurodegeneration caused by hemicontusion injury in rat cervical spinal cord. In an initial replication attempt, the Infinite Horizons impactor was used to deliver a standard unilateral contusion injury near the spinal cord midline. Glibenclamide was administered continuously via osmotic pump beginning immediately post-SCI. The ability of glibenclamide to limit intraspinal hemorrhage was analyzed at 6, 12 and 24 h post-injury using a colorimetric assay. Acute recovery (24 h) of forelimb function was also assessed. Analysis of data from these initial studies revealed no difference between glibenclamide and vehicle-treated SCI rats. Later, it was determined that differences in primary trauma affect the efficacy of glibenclamide. Indeed, the magnitude and distribution of primary intraspinal hemorrhage was greater when the impact was directed to the dorsomedial region of the cervical hemicord (as in our initial replication experiment), as compared to the dorsolateral spinal cord (as in the Simard et al. experiment). In three subsequent experiments, injury was directed to the dorsolateral spinal cord. In each case, glibenclamide reduced post-traumatic hemorrhage 24-48 h post-injury. In the third experiment, we also assessed function and found that acute reduction of hemorrhage led to improved functional recovery. Thus, independent replication of the Simard et al. data was achieved. These data illustrate that the injury model and type of trauma can determine the efficacy of pre-clinical pharmacological treatments after SCI.

On potential interactions between non-selective cation channel TRPM4 and sulfonylurea receptor SUR1

The sulfonylurea receptor SUR1 associates with Kir6.2 or Kir6.1 to form K(ATP) channels, which link metabolism to excitability in multiple cell types. The strong physical coupling of SUR1 with Kir6 subunits appears exclusive, but recent studies argue that SUR1 also modulates TRPM4, a member of the transient receptor potential family of non-selective cation channels. It has been reported that, following stroke, brain, or spinal cord injury, SUR1 is increased in neurovascular cells at the site of injury. This is accompanied by up-regulation of a non-selective cation conductance with TRPM4-like properties and apparently sensitive to sulfonylureas, leading to the postulation that post-traumatic non-selective cation currents are determined by TRPM4/SUR1 channels. To investigate the mechanistic hypothesis for the coupling between TRPM4 and SUR1, we performed electrophysiological and FRET studies in COSm6 cells expressing TRPM4 channels with or without SUR1. TRPM4-mediated currents were Ca(2+)-activated, voltage-dependent, underwent desensitization, and were inhibited by ATP but were insensitive to glibenclamide and tolbutamide. These properties were not affected by cotransfection with SUR1. When the same SUR1 was cotransfected with Kir6.2, functional K(ATP) channels were formed. In cells cotransfected with Kir6.2, SUR1, and TRPM4, we measured K(ATP)-mediated K(+) currents and Ca(2+)-activated, sulfonylurea-insensitive Na(+) currents in the same patch, further showing that SUR1 controls K(ATP) channel activity but not TRPM4 channels. FRET signal between fluorophore-tagged TRPM4 subunits was similar to that between Kir6.2 and SUR1, whereas there was no detectable FRET efficiency between TRPM4 and SUR1. Our data suggest that functional or structural association of TRPM4 and SUR1 is unlikely.

Comparative effects of glibenclamide and riluzole in a rat model of severe cervical spinal cord injury

Both glibenclamide and riluzole reduce necrosis and improve outcome in rat models of spinal cord injury (SCI). In SCI, gene suppression experiments show that newly upregulated sulfonylurea receptor 1 (Sur1)-regulated NC(Ca-ATP) channels in microvascular endothelial cells are responsible for "persistent sodium currents" that cause capillary fragmentation and "progressive hemorrhagic necrosis". Glibenclamide is a potent blocker of Sur1-regulated NC(Ca-ATP) channels (IC(50), 6-48 nM). Riluzole is a pleotropic drug that blocks "persistent sodium currents" in neurons, but in SCI, its molecular mechanism of action is uncertain. We hypothesized that riluzole might block the putative pore-forming subunits of Sur1-regulated NC(Ca-ATP) channels, Trpm4. In patch clamp experiments, riluzole blocked Sur1-regulated NC(Ca-ATP) channels in endothelial cells and heterologously expressed Trpm4 (IC(50), 31 μM). Using a rat model of cervical SCI associated with high mortality, we compared the effects of glibenclamide and riluzole administered beginning at 3h and continuing for 7 days after impact. During the acute phase, both drugs reduced capillary fragmentation and progressive hemorrhagic necrosis, and both prevented death. At 6 weeks, modified (unilateral) Basso, Beattie, Bresnahan locomotor scores were similar, but measures of complex function (grip strength, rearing, accelerating rotarod) and tissue sparing were significantly better with glibenclamide than with riluzole. We conclude that both drugs act similarly, glibenclamide on the regulatory subunit, and riluzole on the putative pore-forming subunit of the Sur1-regulated NC(Ca-ATP) channel. Differences in specificity, dose-limiting potency, or in spectrum of action may account for the apparent superiority of glibenclamide over riluzole in this model of severe SCI.

Hemorrhagic progression of a contusion after traumatic brain injury: a review

The magnitude of damage to cerebral tissues following head trauma is determined by the primary injury, caused by the kinetic energy delivered at the time of impact, plus numerous secondary injury responses that almost inevitably worsen the primary injury. When head trauma results in a cerebral contusion, the hemorrhagic lesion often progresses during the first several hours after impact, either expanding or developing new, non-contiguous hemorrhagic lesions, a phenomenon termed hemorrhagic progression of a contusion (HPC). Because a hemorrhagic contusion marks tissues with essentially total unrecoverable loss of function, and because blood is one of the most toxic substances to which the brain can be exposed, HPC is one of the most severe types of secondary injury encountered following traumatic brain injury (TBI). Historically, HPC has been attributed to continued bleeding of microvessels fractured at the time of primary injury. This concept has given rise to the notion that continued bleeding might be due to overt or latent coagulopathy, prompting attempts to normalize coagulation with agents such as recombinant factor VIIa. Recently, a novel mechanism was postulated to account for HPC that involves delayed, progressive microvascular failure initiated by the impact. Here we review the topic of HPC, we examine data relevant to the concept of a coagulopathy, and we detail emerging data elucidating the mechanism of progressive microvascular failure that predisposes to HPC after head trauma.

Traumatic brain injury and resuscitation with blood products: what should we do?

The study by Dr Peiniger and colleagues in a recent issue of Critical Care indicates that transfusion strategies using an early and more balanced ratio between fresh frozen plasma and red blood cell transfusions provide a survival benefit in patients with acute traumatic coagulopathy requiring massive transfusion within the first 24 hours of hospitalization. However, this topic has never been explored in depth in patients with concomitant severe traumatic brain injury. While the study is retrospective and certainly not a substitute for a well-designed prospective trial, the authors nonetheless should be commended for addressing this issue with their current work. Currently, the optimum fluid resuscitation paradigm for patients with both severe traumatic brain injury and other injuries requiring significant volume resuscitation is not clear.

Glibenclamide reduces hippocampal injury and preserves rapid spatial learning in a model of traumatic brain injury

Cognitive disturbances after traumatic brain injury (TBI) are frequent, even when neuroimaging shows no overt hemorrhagic or other abnormality. Sulfonylurea receptor 1 (SUR1) plays a key role in various forms of CNS injury, but its role in hippocampal dysfunction after mild to moderate TBI is unknown. To assess the hypothesis that postinjury SUR1 upregulation in the hippocampus is associated with a later disturbance in learning, we studied a rat model of cortical impact TBI calibrated to avoid primary and secondary hemorrhage in the underlying hippocampus. The transcription factor, specificity protein 1, which regulates expression of SUR1 and caspase-3, was activated in the hippocampus 15 minutes after injury. Upregulation of SUR1 protein and of Abcc8 (which encodes SUR1) messenger RNA was evident by 6 hours. To assess the role of SUR1, injured rats were administered vehicle or a low dose of the specific sulfonylurea inhibitor glibenclamide for 1 week. At 2 weeks, the increase in activated caspase-3 in the hilus of glibenclamide-treated rats was half of that in vehicle-treated rats. Testing for rapid learning in a Morris water maze at 4 weeks showed significantly better performance in glibenclamide-treated rats; performance inversely correlated with Fluoro-Jade staining for degenerated neurons in the hilus. We conclude that glibenclamide may have long-term protective effects on the hippocampus after mild-to-moderate TBI.

Neuroprotection for traumatic brain injury: translational challenges and emerging therapeutic strategies

Traumatic brain injury (TBI) causes secondary biochemical changes that contribute to subsequent tissue damage and associated neuronal cell death. Neuroprotective treatments that limit secondary tissue loss and/or improve behavioral outcome have been well established in multiple animal models of TBI. However, translation of such neuroprotective strategies to human injury have been disappointing, with the failure of more than thirty controlled clinical trials. Both conceptual issues and methodological differences between preclinical and clinical injury have undoubtedly contributed to these translational difficulties. More recently, changes in experimental approach, as well as altered clinical trial methodologies, have raised cautious optimism regarding the outcomes of future clinical trials. Here we critically review developing experimental neuroprotective strategies that show promise, and we propose criteria for improving the probability of successful clinical translation.