Secondary Injury Factors Research Articles

Pericyte-derived exosomal miR-210 improves mitochondrial function and inhibits lipid peroxidation in vascular endothelial cells after traumatic spinal cord injury by activating JAK1/STAT3 signaling pathway

BackgroundSpinal cord injury (SCI) remains a significant health concern, with limited available treatment options. This condition poses significant medical, economic, and social challenges. SCI is typically categorized into primary and secondary injuries. Inflammation, oxidative stress, scar formation, and the immune microenvironment impede axon regeneration and subsequent functional restoration. Numerous studies have shown that the destruction of the blood–brain barrier (BBB) and microvessels is a crucial factor in severe secondary injury. Additionally, reactive oxygen species (ROS)-induced lipid peroxidation significantly contributes to endothelial cell death. Pericytes are essential constituents of the BBB that share the basement membrane with endothelial cells and astrocytes. They play a significant role in the establishment and maintenance of BBB.ResultsImmunofluorescence staining at different time points revealed a consistent correlation between pericyte coverage and angiogenesis, suggesting that pericytes promote vascular repair via paracrine signaling. Pericytes undergo alterations in cellular morphology and the transcriptome when exposed to hypoxic conditions, potentially promoting angiogenesis. We simulated an early ischemia-hypoxic environment following SCI using glucose and oxygen deprivation and BBB models. Co-culturing pericytes with endothelial cells improved barrier function compared to the control group. However, this enhancement was reduced by the exosome inhibitor, GW4869. In vivo injection of exosomes improved BBB integrity and promoted motor function recovery in mice following SCI. Subsequently, we found that pericyte-derived exosomes exhibited significant miR-210-5p expression based on sequencing analysis. Therefore, we performed a series of gain- and loss-of-function experiments in vitro.ConclusionOur findings suggest that miR-210-5p regulates endothelial barrier function by inhibiting JAK1/STAT3 signaling. This process is achieved by regulating lipid peroxidation levels and improving mitochondrial function, suggesting a potential mechanism for restoration of the blood-spinal cord barrier (BSCB) after SCI.

Deferoxamine ameliorates neurological dysfunction by inhibiting ferroptosis and neuroinflammation after traumatic brain injury

Traumatic brain injury (TBI) is an important reason of neurological damage and has high morbidity and mortality rates. The secondary damage caused by TBI leads to a poor clinical prognosis. According to the literature, TBI leads to ferrous iron aggregation at the site of trauma and may be a key factor in secondary injury. Deferoxamine (DFO), which is an iron chelator, has been shown to inhibit neuron degeneration; however, the role of DFO in TBI is unclear. The purpose of this study was to explore whether DFO can ameliorate TBI by inhibiting ferroptosis and neuroinflammation. Here, our findings suggest that DFO can reduce the accumulation of iron, lipid peroxides, and reactive oxygen species (ROS) and modulate the expression of ferroptosis-related indicators. Moreover, DFO may reduce NLRP3 activation via the ROS/NF-κB pathway, modulate microglial polarization, reduce neutrophil and macrophage infiltration, and inhibit the release of inflammatory factors after TBI. Additionally, DFO may reduce the activation of neurotoxic responsive astrocytes. Finally, we demonstrated that DFO can protect motor memory function, reduce edema and improve peripheral blood perfusion at the site of trauma in mice with TBI, as shown by behavioral experiments such as the Morris water maze test, cortical blood perfusion assessment and animal MRI. In conclusion, DFO ameliorates TBI by reducing iron accumulation to alleviate ferroptosis and neuroinflammation, and these findings provide a new therapeutic perspective for TBI.

DEPENDENCE ON ANESTHESIOLOGY SUPPORT IN VICTIMS WITH COMBINED MINE-EXPLOSIVE THORACO-ABDOMINAL INJURIES AND PENETRATING HEAD INJURIES AT THE STAGE OF PREPARATION AND CONDUCTING OF AEROMEDICAL EVACUATION

Introduction. Explosive explosive injuries account for more than 50% of all injuries received in military battles, and the proportion of casualties among the civilian population is also increasing [1]. However, only limited research has been conducted on the pathophysiology of blast-induced brain injury, and the effect of changes in cerebral blood flow (CBF) or cerebral vascular reactivity on blast-induced brain injury has not been investigated [2]. Although secondary hypotension and hypoxemia are associated with increased mortality and morbidity after blunt head injury, the effect of secondary injury factors in blast injury is unknown [2]. TBI itself causes cerebral hypoperfusion, reduced oxygen delivery to the brain, excitotoxicity, and disruption of cerebral blood flow autoregulation, which explains the vulnerability of the affected brain to hypoxia and hypotension caused by blood loss [2,3].

Experimental study of new derivatives of 3-hydroxypyridine as pharmacological agents for the correction of ischemic brain injury after intracerebral hemorrhage

Introduction: Limiting the action of secondary injury factors can improve the prognosis in acute cerebral accidents. The aim of the investigation is to study the neuroprotective effects of 3-hydroxypyridine derivatives.
 Materials and methods: The study was performed in Wistar rats. An intracerebral hemorrhage (ICH) model was used. The animals were once administered intraperitoneally with the test drugs 1 hour before the surgery and on the 1st, 2nd and 3rd days. The registration of behaviors and condition of the animals on days 1, 3, 7 and 14 and the morphological examination of the brain were performed.
 Results and discussion: The use of the substances LKhT 4-97 and LKhT 11-02 in the treatment of experimental ICH had a positive effect on the survival rate of the animals and on the resolution rate of pathological signs (p<0.05). Clinical observations were confirmed by the results of analysis of the S100b brain damage marker and morphometry. The efficacy of LKhT 3-15 was largely comparable to that of the reference drug Mexidol. The efficacy of LKhT 01-09 was significantly inferior to that of the reference drug Mexidol. Differences in the neuroprotective effects of the studied substances are related to the metabolism of their various pharmacophores. A hypothetical mechanism for the induction of their neuroprotective effects has been proposed.
 Conclusion: Three of the four 3-hydroxypyridine derivatives under study have a neuroprotective effect, which is manifested in a more rapid resolution of pathological symptoms and less pronounced signs of neurodegeneration.

Predictive value of magnetic resonance spectroscopy combined with diffusion weighted imaging in patients with secondary brain insult after spontaneous intra-cerebral hemorrhage

To investigate the correlations between the changes of N-acetylaspartate/creatine (NAA/Cr) detected by magnetic resonance spectroscopy (MRS), and of the relative apparent diffusion coefficient (rADC) detected by diffusion weighted imaging (DWI) and the occurrence and outcome of secondary brain injury (SBI) in patients with spontaneous intra-cerebral hemorrhage (SICH). One hundred and eight SICH patients diagnosed by CT from January 2014 to December 2019 in the First People's Hospital of Huzhou were selected as the research objects. MRS and DWI examinations were performed on day 2 after admission. The body temperature, blood pressure, blood glucose, blood sodium, arterial oxygen partial pressure (PaO2) and other indexes were continuously monitored. The patients were divided into two groups: SBI group (46 cases) and control group (62 cases) according to whether there were secondary brain injury factors (SBIF). The differences in NAA/Cr and rADC of the edema area and Glasgow outcome score (GOS) after 6 months were compared between the two groups; multivariate Logistic regression analysis was used to analyze the risk factors of SBI. The NAA/Cr and rADC of perihematoma edema area and GOS after 6 months in SBI group were significantly lower than those in control group [NAA/Cr: 1.64±0.35 vs. 1.87±0.41, rADC: 2.57±0.39 vs. 2.75±0.45, GOS after 6 months (points): 3.47±0.59 vs. 3.76±0.65], with significant differences (all P < 0.05). Logistic regression analysis showed that NAA/Cr and rADC were the risk factors for the occurrence of SBI [odds ratio (OR) values were 0.172, 0.343, 95% confidence intervals (95%CI) were 0.048-0.609 and 0.118-0.996, respectively, both P < 0.05]. MRS combined with DWI has a certain value in predicting SBI after SICH. SBI can aggravate brain injury and affect the prognosis of patients. SBI should be actively prevented and intervention, carried out.

Polydatin prevents the induction of secondary brain injury after traumatic brain injury by protecting neuronal mitochondria.

Polydatin is thought to protect mitochondria in different cell types in various diseases. Mitochondrial dysfunction is a major contributing factor in secondary brain injury resulting from traumatic brain injury. To investigate the protective effect of polydatin after traumatic brain injury, a rat brain injury model of lateral fluid percussion was established to mimic traumatic brain injury insults. Rat models were intraperitoneally injected with polydatin (30 mg/kg) or the SIRT1 activator SRT1720 (20 mg/kg, as a positive control to polydatin). At 6 hours post-traumatic brain injury insults, western blot assay was used to detect the expression of SIRT1, endoplasmic reticulum stress related proteins and p38 phosphorylation in cerebral cortex on the injured side. Flow cytometry was used to analyze neuronal mitochondrial superoxide, mitochondrial membrane potential and mitochondrial permeability transition pore opened. Ultrastructural damage in neuronal mitochondria was measured by transmission electron microscopy. Our results showed that after treatment with polydatin, release of reactive oxygen species in neuronal mitochondria was markedly reduced; swelling of mitochondria was alleviated; mitochondrial membrane potential was maintained; mitochondrial permeability transition pore opened. Also endoplasmic reticulum stress related proteins were inhibited, including the activation of p-PERK, spliced XBP-1 and cleaved ATF6. SIRT1 expression and activity were increased; p38 phosphorylation and cleaved caspase-9/3 activation were inhibited. Neurological scores of treated rats were increased and the mortality was reduced compared with the rats only subjected to traumatic brain injury. These results indicated that polydatin protectrd rats from the consequences of traumatic brain injury and exerted a protective effect on neuronal mitochondria. The mechanisms may be linked to increased SIRT1 expression and activity, which inhibits the p38 phosphorylation-mediated mitochondrial apoptotic pathway. This study was approved by the Animal Care and Use Committee of the Southern Medical University, China (approval number: L2016113) on January 1, 2016.

Notch inhibitor can attenuate apparent diffusion coefficient and improve neurological function through downregulating NOX2-ROS in severe traumatic brain injury.

IntroductionSecondary brain injury is a major factor that affects the prognosis and outcome of traumatic brain injury (TBI) patients. Secondary brain edema is considered to be an initiating factor in secondary brain injury after TBI. A previous study has indicated that Notch signaling activation contributes to neuron death in mice affected by stroke; however, its role in neuronal oxidation stress for brain edema after TBI is not well established. Apparent diffusion coefficient (ADC) values can represent the brain edema after TBI.MethodsWe established a rat model of acute craniocerebral injury, using functional MRI to evaluate the ADC and cerebral blood flow values. The present study was designed to determine the effect of Notch inhibitor DAPT upon oxidation stress for brain edema after TBI. Rats were randomly distributed into five groups, control group, severe TBI group, severe TBI + vehicle group, severe TBI + DAPT group, and severe TBI + DPI group. All rats were sacrificed at 24 hours after TBI.ResultsOur data indicated that Notch signaling inhibitor DAPT significantly reduced the ADC values and improved the neurological function after TBI. In addition, DAPT decreased NOX2 levels and the ROS levels. Furthermore, DPI can decrease NOX2 levels and ROS levels.ConclusionThis study indicated that DAPT Notch signal inhibitors can inhibit NOX2-ROS generation, reduce the ADC values, relieve cerebral edema, and improve nerve function.

Current Opportunities for Clinical Monitoring of Axonal Pathology in Traumatic Brain Injury.

Traumatic brain injury (TBI) is a multidimensional and highly complex disease commonly resulting in widespread injury to axons, due to rapid inertial acceleration/deceleration forces transmitted to the brain during impact. Axonal injury leads to brain network dysfunction, significantly contributing to cognitive and functional impairments frequently observed in TBI survivors. Diffuse axonal injury (DAI) is a clinical entity suggested by impaired level of consciousness and coma on clinical examination and characterized by widespread injury to the hemispheric white matter tracts, the corpus callosum and the brain stem. The clinical course of DAI is commonly unpredictable and it remains a challenging entity with limited therapeutic options, to date. Although axonal integrity may be disrupted at impact, the majority of axonal pathology evolves over time, resulting from delayed activation of complex intracellular biochemical cascades. Activation of these secondary biochemical pathways may lead to axonal transection, named secondary axotomy, and be responsible for the clinical decline of DAI patients. Advances in the neurocritical care of TBI patients have been achieved by refinements in multimodality monitoring for prevention and early detection of secondary injury factors, which can be applied also to DAI. There is an emerging role for biomarkers in blood, cerebrospinal fluid, and interstitial fluid using microdialysis in the evaluation of axonal injury in TBI. These biomarker studies have assessed various axonal and neuroglial markers as well as inflammatory mediators, such as cytokines and chemokines. Moreover, modern neuroimaging can detect subtle or overt DAI/white matter changes in diffuse TBI patients across all injury severities using magnetic resonance spectroscopy, diffusion tensor imaging, and positron emission tomography. Importantly, serial neuroimaging studies provide evidence for evolving axonal injury. Since axonal injury may be a key risk factor for neurodegeneration and dementias at long-term following TBI, the secondary injury processes may require prolonged monitoring. The aim of the present review is to summarize the clinical short- and long-term monitoring possibilities of axonal injury in TBI. Increased knowledge of the underlying pathophysiology achieved by advanced clinical monitoring raises hope for the development of novel treatment strategies for axonal injury in TBI.

Targeting Enolase in Reducing Secondary Damage in Acute Spinal Cord Injury in Rats.

Spinal cord injury (SCI) is a complex debilitating condition leading to permanent life-long neurological deficits. The complexity of SCI suggests that a concerted multi-targeted therapeutic approach is warranted to optimally improve function. Damage to spinal cord is complicated by an increased detrimental response from secondary injury factors mediated by activated glial cells and infiltrating macrophages. While elevation of enolase especially neuron specific enolase (NSE) in glial and neuronal cells is believed to trigger inflammatory cascades in acute SCI, alteration of NSE and its subsequent effects in acute SCI remains unknown. This study measured NSE expression levels and key inflammatory mediators after acute SCI and investigated the role of ENOblock, a novel small molecule inhibitor of enolase, in a male Sprague-Dawley (SD) rat SCI model. Serum NSE levels as well as cytokines/chemokines and metabolic factors were evaluated in injured animals following treatment with vehicle alone or ENOblock using Discovery assay. Spinal cord samples were also analyzed for NSE and MMPs 2 and 9 as well as glial markers by Western blotting. The results indicated a significant decrease in serum inflammatory cytokines/chemokines and NSE, alterations of metabolic factors and expression of MMPs in spinal cord tissues after treatment with ENOblock (100µg/kg, twice). These results support the hypothesis that activation of glial cells and inflammation status can be modulated by regulation of NSE expression and activity. Analysis of SCI tissue samples by immunohistochemistry confirmed that ENOblock decreased gliosis which may have occurred through reduction of elevated NSE in rats. Overall, elevation of NSE is deleterious as it promotes extracellular degradation and production of inflammatory cytokines/chemokines and metabolic factors which activates glia and damages neurons. Thus, reduction of NSE by ENOblock may have potential therapeutic implications in acute SCI.

Peptide-Tethered Hydrogel Scaffold Promotes Recovery from Spinal Cord Transection via Synergism with Mesenchymal Stem Cells.

Spinal cord injury (SCI) is one of the most devastating injuries. Treatment strategies for SCI are required to overcome comprehensive issues. Implantation of biomaterial scaffolds and stem cells has been demonstrated to be a promising strategy. However, a comprehensive recovery effect is difficult to achieve. In the comprehensive treatment process, the specific roles of the implanted scaffolds and of stem cells in combined strategy are usually neglected. In this study, a peptide-modified scaffold is developed based on hyaluronic acid and an adhesive peptide PPFLMLLKGSTR. Synchrotron radiation micro computed tomography measurement provides insights to the three-dimensional inner topographical property and perspective porous structure of the scaffold. The modified scaffold significantly improves cellular survival and adhesive growth of mesenchymal stem cells during 3D culture in vitro. After implantation in transected spinal cord, the modified scaffold and mesenchymal stems are found to function in synergy to restore injured spinal cord tissue, with respective strengths. Hindlimb motor function scores exhibit the most significant impact of the composite implant at 2 weeks post injury, which is the time secondary injury factors begin to take hold. Investigation on the secondary injury factors including inflammatory response and astrocyte overactivity at 10 days post injury reveals the possible underlying reason. Implants of the scaffold, cells, and especially the combination of both elicit inhibitory effects on these adverse factors. The study develops a promising implant for spinal cord tissue engineering and reveals the roles of the scaffold and stem cells. More importantly, the results provide the first understanding of the bioactive peptide PPFLMLLKGSTR concerning its functions on mesenchymal stem cells and spinal cord tissue restoration.

Neuroprotective role of hydralazine in rat spinal cord injury‐attenuation of acrolein‐mediated damage

Acrolein, an α,β-unsaturated aldehyde and a reactive product of lipid peroxidation, has been suggested as a key factor in neural post-traumatic secondary injury in spinal cord injury (SCI), mainly based on in vitro and ex vivo evidence. Here, we demonstrate an increase of acrolein up to 300%; the elevation lasted at least 2 weeks in a rat SCI model. More importantly, hydralazine, a known acrolein scavenger can provide neuroprotection when applied systemically. Besides effectively reducing acrolein, hydralazine treatment also resulted in significant amelioration of tissue damage, motor deficits, and neuropathic pain. This effect was further supported by demonstrating the ability of hydralazine to reach spinal cord tissue at a therapeutic level following intraperitoneal application. This suggests that hydralazine is an effective neuroprotective agent not only in vitro, but in a live animal model of SCI as well. Finally, the role of acrolein in SCI was further validated by the fact that acrolein injection into the spinal cord caused significant SCI-like tissue damage and motor deficits. Taken together, available evidence strongly suggests a critical causal role of acrolein in the pathogenesis of spinal cord trauma. Since acrolein has been linked to a variety of illness and conditions, we believe that acrolein-scavenging measures have the potential to be expanded significantly ensuring a broad impact on human health.

Expression of C/EBP homology protein in patients with severe traumatic brain injury

Objective To investigate the expression of C/EBP homology protein (CHOP) in peripheral brain tissue of patients with severe traumatic brain injury (TBI) and its correlation with the injury severity.Methods The study included peripheral brain tissues of 41 TBI patients (TBI group).Another 16 autopsy specimens succumbed to other diseases (except for TBI or other central nervous system diseases) were selected as controls.The control group and TBI group were subdivided into immaturity group (≤18 years),adult group (18-59 years) and elderly group (＞59 years).According to Glasgow Coma Scale (GCS) on admission,TBI group was classified as severe TBI group (GCS of 6-8) and particularly-severe TBI group (GCS of 3-5).CHOP expression in peripheral tissues after TBI was compared in between different age,gender and GCS.Nerve cell apoptosis was detected by TUNEL technique and correlation between CHOP level and apoptotic number was analyzed.Results There were no age and gender differences regarding CHOP expression in control group (P ＜ 0.05).Compared with control group,expression of CHOP presented notable up-regulation in TBI group (P ＜ 0.05).Expression of CHOP presented no gender difference in TBI group (P ＞ 0.05),but its expression was lower in the aged than in adult or immaturity (P ＜ 0.05) as well as notably higher in particularly-severe TBI group than in severe TBI group (P ＜ 0.05).Nerve cell apoptosis in TBI group was far greater in number than that in control group (P ＜0.05).A positive correlation was observed between CHOP level and apoptotic index (r =0.72,P ＜ 0.05).Conclusion Expression level of CHOP after TBI is closely related to the injury severity and nerve cell apoptosis,but the apoptosis pathway induced by CHOP may not be a major factor in secondary brain injury after TBI in the aged patients. Key words: Brain injuries; Apoptosis; C/EBP homology protein

The role of substance p in ischaemic brain injury.

Stroke is a leading cause of death, disability and dementia worldwide. Despite extensive pre-clinical investigation, few therapeutic treatment options are available to patients, meaning that death, severe disability and the requirement for long-term rehabilitation are common outcomes. Cell loss and tissue injury following stroke occurs through a number of diverse secondary injury pathways, whose delayed nature provides an opportunity for pharmacological intervention. Amongst these secondary injury factors, increased blood-brain barrier permeability and cerebral oedema are well-documented complications of cerebral ischaemia, whose severity has been shown to be associated with final outcome. Whilst the mechanisms of increased blood-brain barrier permeability and cerebral oedema are largely unknown, recent evidence suggests that the neuropeptide substance P (SP) plays a central role. The aim of this review is to examine the role of SP in ischaemic stroke and report on the potential utility of NK1 tachykinin receptor antagonists as therapeutic agents.

Substance P Antagonists as a Therapeutic Approach to Improving Outcome Following Traumatic Brain Injury

Although a number of secondary injury factors are known to contribute to the development of morphological injury and functional deficits following traumatic brain injury, accumulating evidence has suggested that neuropeptides, and in particular substance P, may play a critical role. Substance P is released early following acute injury to the CNS as part of a neurogenic inflammatory response. In so doing, it facilitates an increase in the permeability of the blood-brain barrier and the development of vasogenic edema. At the cellular level, substance P has been shown to directly result in neuronal cell death; functionally, substance P has been implicated in learning and memory, mood and anxiety, stress mechanisms, emotion-processing, migraine, emesis, pain, and seizures, all of which may be adversely affected after brain injury. Inhibition of post-traumatic substance P activity, either by preventing release or by antagonism of the neurokinin-1 receptor, has consistently resulted in a profound decrease in development of edema and marked improvements in functional outcome. This review summarizes the current evidence supporting a role for substance P in acute brain injury.

Association Between Alcohol and Mortality in Patients With Severe Traumatic Head Injury—Invited Critique

Invited comments upon: Arch Surg. 2006;141(12):1185-1191. This is a well-designed, retrospective study using a large Canadian trauma system database. Tien et al examine the hypothesis that admission blood alcohol concentration is associated with in-hospital death in patients with severe brain injury from blunt head trauma. There is a long-held myth that intoxicated trauma victims are more relaxed and, therefore, fare better than nonintoxicated patients. In the interest of public health, this is a myth to be discredited. However, this study did find that the cohort of patients with severe TBI and a low BAC had a higher survival rate than those with no BAC. This finding should stimulate clinical research to better understand the potential neuroprotective effects of a low BAC, but it should clearly not be a call for trauma patients with severe TBI to premedicate with alcohol. Rather, the emphasis more appropriately should be placed on the fact that 30% to 50% of all hospitalized trauma patients are intoxicated at the time of injury. Conversely, a high BAC was associated with higher mortality. This suggests a detrimental effect of a high BAC on homeostasis (eg, hypotension), and we know that hypotension is a critical, negative factor in secondary brain injury. This finding should also stimulate clinical research to better understand and counter these negative physiologic changes. It also speaks to the trauma prevention dictum that decries drinking and driving. This study should be further impetus for clinical research that will better define the dose-related effect, positive or negative, of alcohol on the physiologic status and outcome in patients with severe TBI. Perhaps this research can help answer the question as to whether there is a therapeutic role for alcohol in our management of the patient with severe TBI after adequate resuscitation.

Magnesium sulfate treatment decreases caspase-3 activity after experimental spinal cord injury in rats

Background Apoptosis has increasingly been considered as an important factor in secondary injury after spinal cord injury (SCI). Manifestation of apoptotic cell death process involves activation of the caspase-3 apoptotic cascade. The aim of the study was to demonstrate the effect of magnesium sulfate on caspase-3 activity and to compare its effectiveness with methylprednisolone after acute SCI. Methods The rats were randomly and blindly allocated into 5 groups of 8 rats each. Spinal cord contusion injury was produced by the weight drop method. The control group consisted of noninjured rats. In the trauma group, no treatment was given, whereas 1 mL saline, 600 mg/kg magnesium sulfate, and 30 mg/kg methylprednisolone sodium succinate (MPSS) were administered in the vehicle and both treatment groups immediately after injury. Twenty-four hours after trauma, spinal cord samples were obtained, and tissue caspase-3 activity levels were examined. A 1-way analysis of variance and the post hoc test were used for statistical analysis. Results The results showed that caspase-3 activity increased to statistically significantly higher levels in spinal cord after contusion injury than in the control group. Caspase-3 enzyme activity levels were significantly reduced in animals treated either with magnesium sulfate or MPSS. Conclusions We have shown that magnesium sulfate decreases caspase-3 activity in rat spinal cord subjected to contusion injury. Magnesium sulfate may have potential therapeutic benefits by reducing apoptotic tissue damage after SCI.

The role of magnesium in traumatic brain injury.

In Japan, over 5,000 deaths per year are a result of traumatic brain injury (TBI) with most being due to motor vehicle accidents. Survivors of TBI number into the hundreds of thousands and are often left with debilitating neurological deficits. Recently it has been identified that much of the brain damage after TBI develops over time with the primary injury initiating a secondary injury cascade made up of deleterious pathophysiological and biochemical reactions. The delayed development of secondary injury creates an opportunity for therapeutic intervention and considerable effort is being directed toward identifying the secondary injury factors and developing interventions that may potentially prevent their actions. Several secondary injury factors have been identified including oxidative stress, changes in blood flow, neurotransmitters and ionic changes, oedema and energy failure. Of these, Mg(2+) decline has been identified as playing a crucial role in the secondary injury process, in part because of its central role in the regulation of a large number of other known injury factors. This brief review will summarize the experimental evidence supporting a critical role of Mg(2+) in the pathophysiology of TBI, and will examine the use of magnesium salts as a therapeutic intervention.

Early induction of secondary injury factors causing activation of calpain and mitochondria-mediated neuronal apoptosis following spinal cord injury in rats.

To investigate a potential relationship between calpain and mitochondrial damage in spinal cord injury (SCI), a 40 gram-centimeter force (g-cm) injury was induced in rats by a weight-drop method and allowed to progress for 4 hr. One-centimeter segments of spinal cord tissue representing the adjacent rostral, lesion, and adjacent caudal areas were then removed for various analyses. Calcium green 2-AM staining of the lesion and penumbra sections showed an increase in intracellular free calcium (Ca(2+)) levels following injury, compared with corresponding tissue sections from sham-operated (control) animals. Western blot analysis showed increased calpain expression and activity in the lesion and penumbra segments following SCI. Double-immunofluorescent labeling indicated that increased calpain expression occurred in neurons in injured segments. Western blot analysis also showed an increased Bax:Bcl-2 ratio, indicating the induction of the mitochondria-mediated cell death pathway in the lesion and penumbra. The morphology of mitochondria was altered in lesion and penumbra following SCI: mostly hydropic change (swelling) in the lesion, with the penumbra shrunken or normal. At 4 hr after induction of injury, a substantial amount of cytochrome c had been released into the cytoplasm, suggesting a trigger for apoptosis through caspase 3 activation. Neuronal death after 4 hr of injury was detected by a combined TUNEL and double-immunofluoresence assay in the lesion and penumbra sections of injured cord, compared with sham controls. These results suggest that an early induction of secondary factors is involved in the pathogenesis of SCI. The increased Ca(2+) levels could activate calpain and mediate mitochondrial damage leading to neuronal death in lesion and penumbra following injury. Thus, secondary injury processes mediating cell death are induced as early as 4 hr after the injury, and calpain and caspase inhibitors may provide neuroprotection.

Harbingers of poor outcome the day after severe brain injury: hypothermia, hypoxia, and hypoperfusion.

Traumatic brain injury (TBI) can be compounded by physiologic derangements that produce secondary brain injury. The purpose of this study is to elucidate the frequency with which physiologic factors that are associated with secondary brain injury occur in patients with severe closed head injuries and to determine the impact of these factors on outcome. The records of 81 adult blunt trauma patients with Glasgow Coma Scale scores < or = 8 and transport times < 2 hours to a Level I trauma center were retrospectively reviewed searching for the following 11 secondary brain injury factors (SBIFs) in the first 24 hours postinjury: hypotension, hypoxia, hypercapnia, hypocapnia, hypothermia, hyperthermia, metabolic acidosis, seizures, coagulopathy, hyperglycemia, and intracranial hypertension. We recorded the worst SBIF during six time periods: hours 1, 2, 3, 4, 5 to 14, and 16 to 24. Occurrence of each SBIF was then correlated with outcome. Hypocapnia, hypotension, and acidosis occurred more frequently than other SBIFs (60-80%). Hypotension, hyperglycemia, and hypothermia were associated with increased mortality rate. Patients with episodes of hypocapnia, acidosis, and hypoxia had significantly longer intensive care unit length of stay (LOS). These three SBIFs and hyperglycemia related to longer hospital LOS as well. Hypotension and acidosis were associated with discharge to a rehabilitation facility rather than home. Finally, multivariate regression analysis revealed that hypotension, hypothermia, and Abbreviated Injury Scale score of the head were independently related to mortality, whereas other SBIFs, age, Injury Severity Score, and Glasgow Coma Scale score were not. Metabolic acidosis and hypoxia were related to longer intensive care unit and hospital LOS. Our early management of head-injured patients stresses avoidance and correction of SBIFs at all costs. Nonetheless, SBIFs occur frequently in the first 24 hours after traumatic brain injury. Six of the 11 factors studied are associated with significantly worse outcomes. Hypotension and hypothermia are independently related to mortality. Because these SBIFs are potentially preventable, protocols could be developed to decrease their frequency.

Neuroprotection and traumatic brain injury: the search continues.

During the last decade, experimental studies of traumatic brain injury (TBI) have provided important new insights into the pathophysiological mechanisms leading to posttraumatic tissue damage and associated neurological dysfunction. The concept of delayed or secondary tissue injury has strong experimental support and a cascade of secondary injury factors has been delineated. 1,2 These observations have led to the application of targeted pharmacotherapies, whose aim is to block specific pathobiological pathways. 2,3 Such research has been aided by the development of rodent models of head injury that simulate critical components of clinical neurotrauma, as well as by the development of novel neuroprotective agents. 3,4 These experimental studies have identified mechanisms of delayed tissue damage and have demonstrated the effectiveness of a number of pharmacological treatment strategies, 1-4 However, despite this enormous experimental promise, the clinical studies to date have been disappointing, 5,6 Here we explore the conceptual and methodological issues that have contributed to this discrepancy between preclinical and clinical studies.