Therapeutic approaches for the prevention of secondary brain injury:

Systematic Review and Dosage Analysis: Hyperbaric Oxygen Therapy Efficacy in Mild Traumatic Brain Injury Persistent Postconcussion Syndrome

Background

Mild traumatic brain injury results in over 15% of patients progressing to Persistent Postconcussion Syndrome, a condition with significant consequences and limited treatment options. Hyperbaric oxygen therapy has been applied to Persistent Postconcussion Syndrome with conflicting results based on its historical understanding/definition as a disease-specific therapy. This is a systematic review of the evidence for hyperbaric oxygen therapy (HBOT) in Persistent Postconcussion Syndrome using a dose-analysis that is based on the scientific definition of hyperbaric oxygen therapy as a dual-component drug composed of increased barometric pressure and hyperoxia.

Methods

In this review, PubMed, CINAHL, and the Cochrane Systematic Review Database were searched from August 8–22, 2021 for all adult clinical studies published in English on hyperbaric oxygen therapy in mild traumatic brain injury Persistent Postconcussion Syndrome (symptoms present at least 3 months). Randomized trials and studies with symptomatic and/or cognitive outcomes were selected for final analysis. Randomized trials included those with no-treatment control groups or control groups defined by either the historical or scientific definition. Studies were analyzed according to the dose of oxygen and barometric pressure and classified as Levels 1–5 based on significant immediate post-treatment symptoms or cognitive outcomes compared to control groups. Levels of evidence classifications were made according to the Centre for Evidence-Based Medicine and a practice recommendation according to the American Society of Plastic Surgeons. Methodologic quality and bias were assessed according to the PEDro Scale.

Results

Eleven studies were included: six randomized trials, one case-controlled study, one case series, and three case reports. Whether analyzed by oxygen, pressure, or composite oxygen and pressure dose of hyperbaric therapy statistically significant symptomatic and cognitive improvements or cognitive improvements alone were achieved for patients treated with 40 HBOTS at 1.5 atmospheres absolute (ATA) (four randomized trials). Symptoms were also improved with 30 treatments at 1.3 ATA air (one study), positive and negative results were obtained at 1.2 ATA air (one positive and one negative study), and negative results in one study at 2.4 ATA oxygen. All studies involved <75 subjects/study. Minimal bias was present in four randomized trials and greater bias in 2.

Conclusion

In multiple randomized and randomized controlled studies HBOT at 1.5 ATA oxygen demonstrated statistically significant symptomatic and cognitive or cognitive improvements alone in patients with mild traumatic brain injury Persistent Postconcussion Syndrome. Positive and negative results occurred at lower and higher doses of oxygen and pressure. Increased pressure within a narrow range appears to be the more important effect than increased oxygen which is effective over a broad range. Improvements were greater when patients had comorbid Post Traumatic Stress Disorder. Despite small sample sizes, the 1.5 ATA HBOT studies meet the Centre for Evidence-Based Medicine Level 1 criteria and an American Society of Plastic Surgeons Class A Recommendation for HBOT treatment of mild traumatic brain injury persistent postconcussion syndrome.

Therapeutics targeting the inflammasome after central nervous system injury

Innate immunity is part of the early response of the body to deal with tissue damage and infections. Because of the early nature of the innate immune inflammatory response, this inflammatory reaction represents an attractive option as a therapeutic target. The inflammasome is a component of the innate immune response involved in the activation of caspase 1 and the processing of pro-interleukin 1β. In this article, we discuss the therapeutic potential of the inflammasome after central nervous system (CNS) injury and stroke, as well as the basic knowledge we have gained so far regarding inflammasome activation in the CNS. In addition, we discuss some of the therapies available or under investigation for the treatment of brain injury, spinal cord injury, and stroke.

G-CSF as an adjunctive therapy with umbilical cord blood cell transplantation for traumatic brain injury

Traumatic brain injury (TBI), a major contributor to deaths and permanent disability worldwide, has been recently described as a progressive cell death process rather than an acute event. TBI pathophysiology is complicated and can be distinguished by the initial primary injury and the subsequent secondary injury that ensues days after the trauma. Therapeutic opportunities for TBI remain very limited with patients subjected to surgery or rehabilitation therapy. The efficacy of stem cell-based interventions, as well as neuroprotective agents in other neurological disorders of which pathologies overlap with TBI, indicates their potential as alternative TBI treatments. Furthermore, their therapeutic limitations may be augmented when combination therapy is pursued instead of using a single agent. Indeed, we demonstrated remarkable combined efficacy of human umbilical cord blood (hUCB) cell therapy and granulocyte-colony-stimulating factor (G-CSF) treatment in TBI models, providing essential evidence for the translation of this approach to treat TBI. Further studies are warranted to determine the mechanisms underlying therapeutic benefits exerted by hUCB + G-CSF in order to enhance its safety and efficacy in the clinic.

Diffuse traumatic brain injury and the sensory brain

In this review we discuss the consequences to the brain's cortex, specifically to the sensory cortex, of traumatic brain injury. The thesis underlying this approach is that long-term deficits in cognition seen after brain damage in humans are likely underpinned by an impaired cortical processing of the sensory information needed to drive cognition or to be used by cognitive processes to produce a response. We take it here that the impairment to sensory processing does not arise from damage to peripheral sensory systems, but from disordered brain processing of sensory input.

Transcranial low-level laser therapy improves neurological performance in traumatic brain injury in mice: effect of treatment repetition regimen

Low-level laser (light) therapy (LLLT) has been clinically applied around the world for a spectrum of disorders requiring healing, regeneration and prevention of tissue death. One area that is attracting growing interest in this scope is the use of transcranial LLLT to treat stroke and traumatic brain injury (TBI). We developed a mouse model of severe TBI induced by controlled cortical impact and explored the effect of different treatment schedules. Adult male BALB/c mice were divided into 3 broad groups (a) sham-TBI sham-treatment, (b) real-TBI sham-treatment, and (c) real-TBI active-treatment. Mice received active-treatment (transcranial LLLT by continuous wave 810 nm laser, 25 mW/cm², 18 J/cm², spot diameter 1 cm) while sham-treatment was immobilization only, delivered either as a single treatment at 4 hours post TBI, as 3 daily treatments commencing at 4 hours post TBI or as 14 daily treatments. Mice were sacrificed at 0, 4, 7, 14 and 28 days post-TBI for histology or histomorphometry, and injected with bromodeoxyuridine (BrdU) at days 21–27 to allow identification of proliferating cells. Mice with severe TBI treated with 1-laser Tx (and to a greater extent 3-laser Tx) had significant improvements in neurological severity score (NSS), and wire-grip and motion test (WGMT). However 14-laser Tx provided no benefit over TBI-sham control. Mice receiving 1- and 3-laser Tx had smaller lesion size at 28-days (although the size increased over 4 weeks in all TBI-groups) and less Fluoro-Jade staining for degenerating neurons (at 14 days) than in TBI control and 14-laser Tx groups. There were more BrdU-positive cells in the lesion in 1- and 3-laser groups suggesting LLLT may increase neurogenesis. Transcranial NIR laser may provide benefit in cases of acute TBI provided the optimum treatment regimen is employed.

Chronic traumatic brain injury in a dog

Chronic traumatic brain injury is rare in man and has not been previously documented in dogs. This report describes a 2-year-old female American Staffordshire bull terrier that was referred with forelimb and hindlimb ataxia, decreased vigilance and disorientation following repeated aggression and physical abuse by its owner. A diffuse cortical lesion was suspected. Cerebrospinal fluid analysis revealed neutrophilic pleocytosis and computed tomography showed marked widening of the cerebral sulci with mild bilateral ventriculomegaly. The dog was humanely destroyed in view of the poor prognosis. Necropsy examination revealed narrowing of the cerebral cortical gyri and consequent widening of the sulci without distortion or displacement of the neural parenchyma. These features were consistent with bilateral diffuse cortical atrophy. Microscopically, there were chronic subarachnoid haemorrhages and the cortical subpial layer displayed spongiosis, capillary hyperplasia, astrocytosis, microgliosis and frequent neuronal necrosis occurring in a characteristic laminar pattern. This histopathological pattern of damage was significantly different from that previously described in people suffering from repeated traumatic brain injuries over a long period of time.

Bilateral cortical atrophy after severe brain trauma and extradural homatoma

We report the case of a severe head injured 43-year old male patient with a large extradural hematoma, Glasgow Coma Scale 3 and dilated fixed pupils. Patient was promptly submitted to surgical evacuation of the lesion, but remained in persistent vegetative state in the post-operative time. Head computed tomography scans performed before surgery, and at early and late post-operative periods comparatively revealed extreme bilateral cortical atrophy. Late consequences of severe head trauma drastically affect the prognosis of patients, being its prevention, and neuroprotection against secondary injury still a therapeutical challenge for neurosurgeons.

A liquid chromatography/mass spectrometric method for simultaneous analysis of arachidonic acid and its endogenous eicosanoid metabolites prostaglandins, dihydroxyeicosatrienoic acids, hydroxyeicosatetraenoic acids, and epoxyeicosatrienoic acids in rat brain tissue

A sensitive, specific, and robust liquid chromatography/mass spectrometric (LC/MS) method was developed and validated that allows simultaneous analysis of arachidonic acid (AA) and its cyclooxygenase, cytochrome P450, and lipoxygenase pathway metabolites prostaglandins (PGs), dihydroxyeicosatrienoic acids (DiHETrEs), hydroxyeicosatetraenoic acids (HETEs) and epoxyeicosatrienoic acids (EETs), including PGF(2alpha), PGE(2), PGD(2), PGJ(2), 14,15-DiHETrE, 11,12-DiHETrE, 8,9-DiHETrE, 5,6-DiHETrE, 20-HETE, 15-HETE, 12-HETE, 9-HETE, 8-HETE, 5-HETE, 14,15-EET, 11,12-EET, 8,9-EET, and 5,6-EET in rat brain tissues. Deuterium labeled PGF(2alpha)-d(4), PGD(2)-d(4), 15(S)-HETE-d(8), 14,15-EET-d(8), 11,12-EET-d(8), 8,9-EET-d(8), and AA-d(8) were used as internal standards. Solid phase extraction was used for sample preparation. A gradient LC/MS method using a C18 column and electrospray ionization source under negative ion mode was optimized for the best sensitivity and separation within 35 min. The method validation, including LC/MS instrument qualification, specificity, calibration model, accuracy, precision (without brain matrix and with brain matrix), and extraction efficiency were performed. The linear ranges of the calibration curves were 2-1000 pg for PGs, DiHETrEs, HETEs, and EETs, 10-2400 pg for PGE(2) and PGD(2), and 20-2000 ng for AA, respectively.

Low-dose prostacyclin improves cortical perfusion following experimental brain injury in the rat

It was recently shown that prostacyclin at a low dose reduces cortical cell death following brain trauma in the rat. Conceivably, prostacyclin with its vasodilatory, anti-aggregatory, anti-adhesive and permeability-reducing properties improved a compromised perfusion caused by post-traumatic vasoconstriction, microthrombosis and increased microvascular permeability. The objective of the present study was therefore to investigate the hemodynamic effects of low-dose prostacyclin in the traumatized rat cortex. Following a fluid percussion brain injury or a sham procedure, animals were treated with a continuous intravenous infusion of prostacyclin of 1 or 2 ng x kg(-1) x min(-1), or vehicle. Blood flow ([(14)C]-iodoantipyrine), the permeability-surface area product (PS) for [(51)Cr]-EDTA, and brain water content were measured after 3 or 48 h of treatment. Blood flow values in the injured cortex were transiently reduced to 0.42 +/- 0.2 mL x min(-1) in the vehicle group 3 h following trauma from a corresponding value of about 1.6 mL x min(-1) in the sham group, with recovery of blood flow after 48 h. Prostacyclin treatment caused a dose-dependent increase in blood flow which reached statistical significance 48 h following trauma. Brain water content and PS increased in the injured cortex post trauma and the higher dose of prostacyclin increased these parameters further at 48 h compared to the vehicle group (p < 0.05). The latter effects of prostacyclin cannot be attributed to an increase in permeability, as prostacyclin did not influence PS or brain water content following sham trauma. In fact prostacyclin has been shown to have permeability-decreasing properties. We conclude that prostacyclin improves cortical perfusion following brain trauma. The simultaneous aggravation of brain edema can be explained by an increased surface area, perhaps in combination with increased capillary hydrostatic pressure.

Investigation of the effect of chlormethiazole on cerebral chemistry in neurosurgical patients: a combined study of microdialysis and a neuroprotective agent

AIMS

Promising pre-clinical results from laboratory studies of neuro-protective drugs for the treatment of patients with stroke and head injury have not been translated into benefit during clinical trials. The objective of the study was to assess the feasibility of administrating a potential neuro-protective drug (chlormethiazole) in conjunction with multimodality monitoring (including microdialysis) to patients with severe head injury in order to determine the effect of the agent on surrogate endpoints and penetration into the brain.

METHODS

Multimodality monitoring including cerebral and peripheral microdialysis was applied to five head-injured patients on the neuro-intensive care unit. Chlormethiazole (0.8%) was administered as a rapid (10 ml min(-1)) intravenous loading infusion for 5 min followed by a slow (1 ml min(-1)) continuous infusion for 60 min. The following parameters were monitored: heart rate, mean arterial blood pressure, intracranial pressure, cerebral perfusion pressure, peripheral oxygen saturation, continuous arterial oxygen partial pressure, arterial carbon dioxide partial pressure, arterial pH, arterial temperature, cerebral tissue oxygen pressure, cerebral tissue carbon dioxide pressure, cerebral pH, cerebral temperature, electroencephalograph (EEG), bi-spectral index, plasma glucose, plasma chlormethiazole, and cerebral and peripheral microdialysis assay for chlormethiazole, glucose, lactate, pyruvate and amino acids.

RESULTS

Despite achieving adequate plasma concentrations, chlormethiazole was not detected in the peripheral or cerebral microdialysis samples. The drug was well tolerated and did not induce hypotension, hyperglycaemia or withdrawal seizures. The drug did not change the values of the physiological or chemical parameters including levels of GABA, lactate/pyruvate ratio and glutamate. The drug did, however, induce EEG changes, including burst suppression in two patients.

CONCLUSIONS

Chlormethiazole can be safely given to ventilated patients with severe head injury. There was no evidence of hypotension or withdrawal seizures. Combining a pilot clinical study of a neuro-protective agent with multimodality monitoring is feasible and, despite the lack of effect on physiological and chemical parameters in this study, may be a useful adjunct to the development of neuro-protective drugs in the future. Further investigation of the capability of microdialysis in this setting is required. By investigating the effect of a drug on surrogate end-points, it may be possible to identify promising agents from small pilot clinical studies before embarking on large phase III clinical trials.

Importance of posttraumatic hypothermia and hyperthermia on the inflammatory response after fluid percussion brain injury: biochemical and immunocytochemical studies

The purpose of this study was to investigate: 1) the temporal and regional profile of polymorphonuclear leukocyte (PMNL) infiltration after moderate traumatic brain injury using the parasagittal fluid percussion model and 2) the effects of posttraumatic hypothermia (30 degrees C) and hyperthermia (39 degrees C) on the acute and subacute inflammatory response. We hypothesized that posttraumatic hypothermia would reduce the degree of PMNL accumulation whereas hyperthermia would exacerbate this response to injury. In the first series of experiments we quantitated the temporal profile of altered myeloperoxidase activity under normothermic (37 degrees C) conditions (n = 20). The rats were allowed to survive for 3 hours, 24 hours, 3 days, or 7 days after trauma, and brains were dissected into cortical and subcortical regions ipsilateral and contralateral to injury. Additional animals were perfused and fixed for the immunocytochemical visualization of myeloperoxidase (n = 15). In the second series of experiments, rats (n = 25) were killed 3 hours or 3 days after the 3-hour monitoring period of normothermia (36.5 degrees C), hypothermia (30 degrees C), or hyperthermia (39 degrees C) (n = 4 to 5 per group), and myeloperoxidase activity was again quantitated. In normothermic rats, the enzymatic activity of myeloperoxidase was significantly increased (P < 0.05) at 3 hours within the anterior cortical segment (213.97 +/- 56.2 versus control 65.5 +/- 52.3 U/g of wet tissue; mean +/- SD) and posterior (injured) cortical and subcortical segments compared to sham-operated rats (305.76 +/- 27.8 and 258.67 +/- 101.4 U/g of wet tissue versus control 62.8 +/- 24.8 and 37.28 +/- 35.6 U/g of wet tissue; P < 0.0001, P < 0.05, respectively). At 24 hours and 7-days after trauma only the posterior cortical region (P < 0.005, P < 0.05, respectively) exhibited increased myeloperoxidase activity. However, 3 days after trauma, myeloperoxidase activity was also significantly increased within the anterior cortical segment (P < 0.05) and in posterior cortical and subcortical regions compared to sham-operated cortex (P < 0.0001, P < 0.05, respectively). Immunocytochemical analysis of myeloperoxidase reactivity at 3 hours, 24 hours, 3- and 7-days demonstrated large numbers of immunoreactive leukocytes within and associated with blood vessels, damaged tissues, and subarachnoid spaces. Posttraumatic hypothermia and hyperthermia had significant effects on myeloperoxidase activity at both 3 hours and 3 days after traumatic brain injury. Posttraumatic hypothermia reduced myeloperoxidase activity in the injured and noninjured cortical and subcortical segments compared to normothermic values (P < 0.05). In contrast, posttraumatic hyperthermia significantly elevated myeloperoxidase activity in the posterior cortical region compared to normothermic values at both 3 hours and 3 days (473.5 +/- 258.4 and 100.11 +/- 27.58 U/g of wet tissue, respectively, P < 0.05 versus controls). These results indicate that posttraumatic hypothermia decreases early and more prolonged myeloperoxidase activation whereas hyperthermia increases myeloperoxidase activity. Temperature-dependent alterations in PMNL accumulation appear to be a potential mechanism by which posttraumatic temperature manipulations may influence traumatic outcome.

Sphingosine-1-phosphate induces apoptosis of cultured hippocampal neurons that requires protein phosphatases and activator protein-1 complexes

In this study, we report that mobilization of internal Ca2+ by sphingosine-1-phosphate, a metabolite of ceramide, induces apoptosis in cultured hippocampal neurons. This sphingosine-1-phosphate-induced apoptosis is dependent upon the activation of protein phosphatases, possibly calcineurin and phosphatase 2A (or a related phosphatase). In addition, pretreatment of neurons with double-stranded oligonucleotides containing the metallothionein phorbol-12-myristate-13-acetate response element sequence as transcription factor decoys suppressed apoptosis. In contrast, double-stranded oligonucleotides containing either the c-jun or SV40 phorbol-12-myristate-13-acetate response element sequences were ineffective. Electrophoretic mobility shift assays and supershift assays revealed that c-Fos-containing activator protein- complexes preferentially bound the metallothionein phorbol-12-myristate-13-acetate response element sequence-containing oligonucleotides. Furthermore, antisense oligonucleotides to c-fos and c-jun were also protective. The apoptotic death of hippocampal neurons has been hypothesized to contribute to the cognitive impairments observed following insults to the brain. While increases in intracellular calcium are thought to be key mediators of neuronal apoptosis, the biochemical cascade(s) activated as a result of increased Ca2+ which mediates apoptosis of hippocampal neurons is (are) not well understood. The findings presented in this study suggest that mobilization of internal calcium via prolonged exposure of sphingosine-1-phosphate induces apoptosis of hippocampal neurons in culture. Sustained increases in intracellular calcium activate a phosphatase cascade that includes calcineurin and a phosphatase 2A-like phosphatase, and leads to the expression of genes containing metallothionein phorbol-12-myristate-13-acetate response element (TGAGTCA)-type enhancer sequences. The expression of genes containing TGAGTCA-type enhancer sequences appears to be essential for sphingosine-1-phosphate-induced apoptosis of hippocampal neurons.

Detection of ultra-early brain damage after acute subdural hematoma in the rat by magnetic resonance imaging

We measured serial changes in diffusion-weighted magnetic resonance imaging (DW) and in apparent diffusion coefficient (ADC) 1 to 3 hours after induction of acute subdural hematoma (ASDH) in rats, to assess the rate of development of cytotoxic edema and ischemic brain damage observed in this model. Cortical ADC values underneath the hematoma in ASDH rats (n = 12) were significantly lower than those in sham-operated rats (n = 5) at 1 hour. By 3 hours, the area of ADC abnormality had further increased. The lesion areas, as percentage of hemispheric areas on 1- and 3-hour ADC maps, correlated significantly with those on the histologic sections stained with hematoxylin and eosin. The results indicate that DWI with ADC mapping may provide a valuable diagnostic tool for monitoring of early pathologic changes following subdural hematoma in head-injured patients.

Differential effects of traumatic brain injury on vesicular acetylcholine transporter and M2 muscarinic receptor mRNA and protein in rat

Experimental traumatic brain injury (TBI) produces cholinergic neurotransmission deficits that may contribute to chronic spatial memory deficits. Cholinergic neurotransmission deficits may result from presynaptic alterations in the storage and release of acetylcholine (ACh) or from changes in the receptors for ACh. The vesicular ACh transporter (VAChT) mediates accumulation of ACh into secretory vesicles, and the M2 muscarinic receptor subtype can modulate cholinergic neurotransmission via a presynaptic inhibitory feedback mechanism. We examined the effects of controlled cortical impact (CCI) injury on hippocampal VAChT and M2 muscarinic receptor subtype protein and medial septal mRNA levels at 4 weeks following injury. Rats were anesthetized and surgically prepared for CCI injury (4 m/sec, 2.5 to 2.9 mm in depth) and sham surgery. Animals were sacrificed, and coronal sections (35 microm thick) were cut through the dorsal hippocampus for VAChT and M2 immunohistochemistry. Semiquantitative measurements of VAChT and M2 protein in hippocampal homogenates from injured and sham rats were assessed with Western blot analysis. Changes in VAChT and M2 mRNA levels were evaluated by reverse transcriptase polymerase chain reaction (RT-PCR). At 4 weeks after injury, both immunohistochemical and Western blot methods demonstrated an increase in hippocampal VAChT protein. An increase in VAChT mRNA was also observed. Immunohistochemistry demonstrated a loss of M2; however, there was no significant change in M2 mRNA levels in comparison with sham controls. These changes may represent a compensatory response of cholinergic neurons to increase the efficiency of ACh neurotransmission chronically after TBI through differential transcriptional regulation.

Increased inspired oxygen concentration as a factor in improved brain tissue oxygenation and tissue lactate levels after severe human head injury

OBJECT

Early impairment of cerebral blood flow in patients with severe head injury correlates with poor brain tissue O2 delivery and may be an important cause of ischemic brain damage. The purpose of this study was to measure cerebral tissue PO2, lactate, and glucose in patients after severe head injury to determine the effect of increased tissue O2 achieved by increasing the fraction of inspired oxygen (FiO2).

METHODS

In addition to standard monitoring of intracranial pressure and cerebral perfusion pressure, the authors continuously measured brain tissue PO2, PCO2, pH, and temperature in 22 patients with severe head injury. Microdialysis was performed to analyze lactate and glucose levels. In one cohort of 12 patients, the PaO2 was increased to 441+/-88 mm Hg over a period of 6 hours by raising the FiO2 from 35+/-5% to 100% in two stages. The results were analyzed and compared with the findings in a control cohort of 12 patients who received standard respiratory therapy (mean PaO2 136.4+/-22.1 mm Hg). The mean brain PO2 levels increased in the O2-treated patients up to 359+/-39% of the baseline level during the 6-hour FiO2 enhancement period, whereas the mean dialysate lactate levels decreased by 40% (p < 0.05). During this O2 enhancement period, glucose levels in brain tissue demonstrated a heterogeneous course. None of the monitored parameters in the control cohort showed significant variations during the entire observation period.

CONCLUSIONS

Markedly elevated lactate levels in brain tissue are common after severe head injury. Increasing PaO2 to higher levels than necessary to saturate hemoglobin, as performed in the O2-treated cohort, appears to improve the O2 supply in brain tissue. During the early period after severe head injury, increased lactate levels in brain tissue were reduced by increasing FiO2. This may imply a shift to aerobic metabolism.

Calcium influx and activation of calpain I mediate acute reactive gliosis in injured spinal cord

Buffering extracellular pH at the site of a spinal cord crush-injury may stimulate axonal regeneration in rats (1; Guth et al., Exp. Neurol. 88: 44-55, 1985). We demonstrated in cultured astrocytes that acidic pH initiates a rapid increase in immunoreactivity for GFAP (GFAP-IR), a hallmark of reactive gliosis (2; Oh et al., Glia 13: 319-322, 1995). We extended these studies by investigating the effects of certain treatments on reactive gliosis developing in situ in a rat spinal cord injury model. A significant reactive gliosis was observed within 2 days of cord lesion in untreated crush or vehicle-treated, crush control animals as evidenced by increased GFAP-IR and hypertrophy of astrocytes. By contrast, infusion of Pipes buffer (pH 7.4) into the lesion site significantly reduced this increase. The increased GFAP-IR appeared to be linked to Ca2+ influx since infusion of a blocker of L-type calcium channels, nifedipine, reduced the ensuing reactive gliosis significantly. While Ca2+ modulates many signaling pathways within cells, its effect on reactive gliosis appeared to result from an activation of calpain I. Calpain inhibitor I, a selective inhibitor of mu-calpain, also significantly reduced reactive gliosis. However, calpain inhibitor II, a close structural analog which blocks m-calpain, had no salutary effect. We suggest, therefore, that the initial reactive gliosis seen in vivo may result from the activation of a neutral, Ca2+-dependent protease, calpain I, through calcium influx.

Chronic effects of traumatic brain injury on hippocampal vesicular acetylcholine transporter and M2 muscarinic receptor protein in rats

Experimental traumatic brain injury (TBI) produces cholinergic neurotransmission deficits that may contribute to chronic spatial memory deficits. Cholinergic neurotransmission deficits may be due to presynaptic alterations in the storage and release of acetylcholine (ACh) or from changes in the receptors for ACh. The vesicular ACh transporter (VAChT) mediates accumulation of ACh into secretory vesicles, and M2 receptors can modulate cholinergic neurotransmission via a presynaptic inhibitory feedback mechanism. We examined the effects of controlled cortical impact (CCI) injury on hippocampal VAChT and M2 muscarinic subtype receptor protein levels at four time points: 1 day, 1 week, 2 weeks, and 4 weeks following injury. Rats were anesthetized and surgically prepared for controlled cortical impact injury (4 m/s, 2.5- to 2.9-mm depth) and sham surgery. Animals were sacrificed and coronal sections (35 micro(m) thick) were cut through the dorsal hippocampus for VAChT and M2 immunohistochemistry. Semiquantitative measurements of VAChT and M2 protein in hippocampal homogenates from injured and sham rats were assessed using Western blot analysis. Immunohistochemistry showed no obvious changes in VAChT and M2 immunoreactivity at 1 day and 1 week postinjury. At 2 and 4 weeks postinjury, an increase in hippocampal VAChT protein and a corresponding loss of hippocampal M2 protein was observed compared to sham controls. Consistent with these results, Western blot analyses at 4 weeks postinjury demonstrated a 40-50% increase in VAChT and a 25-30% decrease in M2. These changes may represent a compensatory response of cholinergic neurons to increase the efficiency of ACh neurotransmission chronically after TBI, by upregulating the storage capacity and subsequent release of ACh and downregulating presynaptic inhibitory receptors.

Neuroprotective effect of eliprodil: attenuation of a conditioned freezing deficit induced by traumatic injury of the right parietal cortex in the rat

We have previously demonstrated that a lateral fluid percussion-induced traumatic lesion of the right parietal cortex can lead to a deficit in a conditioned freezing response and that this deficit can be attenuated by both pre- and postlesion administration of the NMDA receptor antagonist dizocilpine. In the present study, we investigated the effects of eliprodil, a noncompetitive NMDA receptor antagonist acting at the polyamine modulatory site, which also acts as a Ca2+ channel blocker, on the trauma-induced conditioned freezing deficit. Eliprodil produced a 50% reduction in this deficit when administered as three 1 mg/kg injections i.v. at 15 min, 6 h, and 24 h following the lesion. Approximately the same degree of protection was afforded when 2 x 1.5 mg/kg were administered 6 and 24 h and equally at 12 and 24 h after surgery (56% and 59%, respectively). A single treatment (3 mg/kg) at 24 h was ineffective against the deficit. The protection afforded with treatment at 6 and 24 h after lesion was dose dependent, with a minimal active dose of 2 x 0.75 mg/kg. These data complement those previously published on the ability of eliprodil to reduce lesion volume following traumatic brain injury and show, in addition, that the neuroprotective effect has functional consequences.

pH dependency of mu-calpain and m-calpain activity assayed by casein zymography following traumatic brain injury in the rat

Studies employing casein zymographic assays analyzed the effects of varying pH (from pH 6.8 to pH 8.0) on changes in mu-calpain and m-calpain activity in naive, sham-injured and injured rat cortex 3 h following unilateral cortical impact injury. Mu-calpain activity following cortical impact injury was enhanced between pH values of 7.2 and 7.8, with pH 7.5 being optimal. m-Calpain activity was readily detected only between pH values of 7.2 and 7.4, with pH 7.3 producing the most prominent proteolytic activity. These observations suggest that strict control of pH is an important consideration in assessments of brain pH activation by casein zymography. Moreover, activation of different calpain isoforms, especially after traumatic brain injury, may be differentially influenced by smaller changes in physiological pH than previously recognized.

Subcellular localization and duration of mu-calpain and m-calpain activity after traumatic brain injury in the rat: a casein zymography study

Casein zymographic assays were performed to identify changes in mu-calpain and m-calpain activity in naive, sham-injured, and injured rat cortex at 15 minutes, 3 hours, 6 hours, and 24 hours after unilateral cortical impact brain injury. Cortical samples ipsilateral and contralateral to the site of injury were separated into cytosolic and total membrane fractions. Marked increases in mu-calpain activity in cytosolic fractions in the ipsilateral cortex occurred as early as 15 minutes, became maximal at 6 hours, and decreased at 24 hours to levels observed at 15 minutes after injury. A similar temporal profile of cytosolic mu-calpain activity in the contralateral cortex was observed, although the increases in the contralateral cortex were substantially lower than those in the ipsilateral cortex. Differences were also noted between cytosolic and total membrane fractions. The detection of a shift in mu-calpain activity to the total membrane fraction first occurred at 3 hours after traumatic brain injury and became maximal at 24 hours after traumatic brain injury. This shift in mu-calpain activity between the two fractions could be due to the redistribution of mu-calpain from the cytosol to the membrane. m-Calpain activity was detected only in cytosolic fractions. m-Calpain activity in cytosolic fractions did not differ significantly between ipsilateral and contralateral cortices, and increased in both cortices from 15 minutes to 6 hours after injury. Relative magnitudes of m-calpain versus mu-calpain activity in cytosolic fractions differed at different time points after injury. These studies suggest that traumatic brain injury can activate both calpain isoforms and that calpain activity is not restricted to sites of focal contusion and cell death at the site of impact injury but may represent a more global response to injury.

Immunohistochemical study of calpain-mediated breakdown products to alpha-spectrin following controlled cortical impact injury in the rat

This study examined the effect of unilateral controlled cortical impact on the appearance of calpain-mediated alpha-spectrin breakdown products (BDPs) in the rat cortex and hippocampus at various times following injury. Coronal sections were taken from animals at 15 min, 1 h, 3 h, 6 h, and 24 h after injury and immunolabeled with an antibody that recognizes calpain-mediated BDPs to alpha-spectrin (Roberts-Lewis et al., 1994). Sections from a separate group of rats were also taken at the same times and stained with hematoxylin and eosin. Analyses of early time points (15 min, 1 h, 3 h, and 6 h following injury) revealed alpha-spectrin BDPs in structurally intact neuronal soma and dendrites in cortex ipsilateral to site of injury that was not present in tissue from sham-injured control rats. By 24 h after injury labeling was not restricted to clearly defined neuronal structures in ipsilateral cortex, although there was an increased extent of diffuse labeling. BDPs to alpha-spectrin in axons were not detected until 24 h after injury, in contrast to the more rapid accumulation of BDPs observed in neuronal soma and dendrites. The presence of BDPs to alpha-spectrin in the cortex at the site of impact, and in the rostral and contralateral cortex, coincided with morphopathology detected by hematoxylin and eosin. alpha-Spectrin BDPs were also observed in the hippocampus ipsilateral to the injury in the absence of overt cell death. This investigation provides further evidence that calpain is activated after controlled cortical impact and could contribute to necrosis at the site of injury. The appearance of calpain-mediated BDPs at sites distal to the contusion site and in the hippocampus also suggests that calpain activation may precede and/or occur in the absence of extensive morphopathological changes.

Mechanisms of calpain proteolysis following traumatic brain injury: implications for pathology and therapy: implications for pathology and therapy: a review and update

Much recent research has focused on the pathological significance of calcium accumulation in the central nervous system (CNS) following cerebral ischemia, spinal cord injury (SCI), and traumatic brain injury (TBI). Disturbances in neuronal calcium homeostasis may result in the activation of several calcium-sensitive enzymes, including lipases, kinases, phosphatases, and proteases. One potential pathogenic event in a number of acute CNS insults, including TBI, is the activation of the calpains, calcium-activated intracellular proteases. This article reviews new evidence indicating that overactivation of calpains plays a major role in the neurodegenerative cascade following TBI in vivo. Further, this article presents an overview from in vivo and in vitro models of CNS injuries suggesting that administration of calpain inhibitors during the initial 24-h period following injury can attenuate injury-induced derangements of neuronal structure and function. Lastly, this review addresses the potential contribution of other proteases to neuronal damage following TBI.