Changes in lipid metabolism in traumatized spinal cord

Carbonyl scavengers as pharmacotherapies in degenerative disease: Hydralazine repurposing and challenges in clinical translation

During cellular metabolism, spontaneous oxidative damage to unsaturated lipids generates many electrophilic carbonyl compounds that readily attack cell macromolecules, forming adducts that are potential drivers of tissue dysfunction. Since such damage is heightened in many degenerative conditions, researchers have assessed the efficacy of nucleophilic carbonyl-trapping drugs in animal models of such disorders, anticipating that they will protect tissues by intercepting toxic lipid-derived electrophiles (LDEs) within cells. This Commentary explores recent animal evidence for carbonyl scavenger efficacy in two disparate yet significant conditions known to involve LDE production, namely spinal cord injury (SCI) and alcoholic liver disease (ALD). Primary emphasis is placed on studies that utilised hydralazine, a clinically-approved "broad-spectrum" scavenger known to trap multiple LDEs. In addition to reviewing recent studies of hydralazine efficacy in animal SCI and ALD models, the Commentary reviews new insights concerning novel lifespan- and healthspan-extending properties of hydralazine obtained during studies in model invertebrate organisms, since the mechanisms involved seem of likely benefit during the treatment of degenerative disease. Finally, noting that human translation of the histoprotective properties of hydralazine have been limited, the final section of the Commentary will address two obstacles that hamper clinical translation of LDE-trapping therapies while also suggesting potential strategies for overcoming these problems.

Effects of Dietary Vitamin E Supplementation in Bladder Function and Spasticity during Spinal Cord Injury

Traumatic spinal cord injury (SCI) results in debilitating autonomic dysfunctions, paralysis and significant sensorimotor impairments. A key component of SCI is the generation of free radicals that contributes to the high levels of oxidative stress observed. This study investigates whether dietary supplementation with the antioxidant vitamin E (alpha-tocopherol) improves functional recovery after SCI. Female adult Sprague-Dawley rats were fed either with a normal diet or a dietary regiment supplemented with vitamin E (51 IU/g) for eight weeks. The rats were subsequently exposed either to a contusive SCI or sham operation, and evaluated using standard functional behavior analysis. We report that the rats that consumed the vitamin E-enriched diet showed an accelerated bladder recovery and significant improvements in locomotor function relative to controls, as determined by residual volumes and Basso, Beatie, and Bresnaham BBB scores, respectively. Interestingly, the prophylactic dietary intervention did not preserve neurons in the ventral horn of injured rats, but it significantly increased the numbers of oligodendrocytes. Vitamin E supplementation attenuated the depression of the H-reflex (a typical functional consequence of SCI) while increasing the levels of supraspinal serotonin immunoreactivity. Our findings support the potential complementary use of vitamin E to ameliorate sensory and autonomic dysfunctions associated with spinal cord injury, and identified promising new cellular and functional targets of its neuroprotective effects.

The effects of hyperbaric oxygen on macrophage polarization after rat spinal cord injury

The immunoreactive responses are a two-edged sword after spinal cord injury (SCI). Macrophages are the predominant inflammatory cells responsible for this response. However, the mechanism underlying the effects of HBOT on the immunomodulation following SCI is unclear now. The present study was performed to examine the effects of hyperbaric oxygen therapy (HBOT) on macrophage polarization after the rat compressive injury of the spinal cord. HBOT was associated with significant increases in IL-4 and IL-13 levels, and reductions in TNF-α and IFN-ɣ levels. This was associated simultaneously with the levels of alternatively activated macrophages (M2 phenotype: arginase-1- or CD206-positive), and decreased levels of classically activated macrophages (M1 phenotype: iNOS- or CD16/32-positive). These changes were associated with functional recovery in the HBOT-transplanted group, which correlated with preserved axons and increased myelin sparing. Our results suggested that HBOT after SCI modified the inflammatory environment by shifting the macrophage phenotype from M1 to M2, which may further promote the axonal extension and functional recovery.

Dietary omega-3 polyunsaturated fatty acids improve the neurolipidome and restore the DHA status while promoting functional recovery after experimental spinal cord injury

Omega-3 polyunsaturated fatty acids (ω-3 PUFAs) confer multiple health benefits and decrease the risk of neurological disorders. Studies are needed, however, to identify promising cellular targets and to assess their prophylactic value against neurodegeneration. The present study (1) examined the efficacy of a preventive diet enriched with ω-3 PUFAs to reduce dysfunction in a well-established spinal cord injury (SCI) animal model and (2) used a novel metabolomics data analysis to identify potential neurolipidomic targets. Rats were fed with either control chow or chow enriched with ω-3 PUFAs (750 mg/kg/day) for 8 weeks before being subjected to a sham or a contusion SCI operation. We report new evidence showing that rats subjected to SCI after being pre-treated with a diet enriched with ω-3 PUFAs exhibit significantly better functional outcomes. Pre-treated animals exhibited lower sensory deficits, autonomic bladder recovery, and early improvements in locomotion that persisted for at least 8 weeks after trauma. We found that SCI triggers a robust alteration in the cord PUFA neurolipidome, which was characterized by a marked docosahexaenoic acid (DHA) deficiency. This DHA deficiency was associated with dysfunction and corrected with the ω-3 PUFA-enriched diet. Multivariate data analyses revealed that the spinal cord of animals consuming the ω-3 PUFA-enriched diet had a fundamentally distinct neurolipidome, particularly increasing the levels of essential and long chain ω-3 fatty acids and lysolipids at the expense of ω-6 fatty acids and its metabolites. Altogether, dietary ω-3 PUFAs prophylaxis confers resiliency to SCI mediated, at least in part, by generating a neuroprotective and restorative neurolipidome.

The effects of medroxy progesterone acetate on the pro-inflammatory cytokines, TNF-alpha and IL-1beta in the early phase of the spinal cord injury

OBJECTIVES

Spinal cord injuries (SCIs) have high morbidity and mortality rates and currently the definitive treatment of complete SCIs are still not possible. We investigated the effects of the medroxy progesterone acetate on the pro-inflammatory cytokines, TNF-alpha and IL-1beta in the early phase of the SCI.

METHODS

Forty-eight Wistar albino male rats were divided equally into four groups each consisting of 12 rats. All animals underwent T10-T12 laminectomy. We administered placebo, and 8 mg/kg medroxy progesterone acetate (MPA) intra-peritoneally into control and progesterone group at 30 minutes after the clip-compression trauma in spinal cord. We performed only T10-T12 laminectomy and clip-compression trauma in laminectomy and trauma group, respectively. Half of the rats from each group were killed at 1 hour and the other half were killed at 6 hours after the trauma. Spinal cord segments were then removed and stored at -80 °C in phosphate buffer. TNF-alpha and IL-1beta levels were determined using ELISA kit.

RESULTS

We have found that there was an increase only in the TNF-alpha level at 6 hours after the trauma comparing to control group. MPA appeared to lower the TNF-alpha level significantly in the trauma group.

DISCUSSION

This experimentally proven anti-inflammatory effect of MPA via acting upon TNF-alpha may offer new therapeutic options in human subjects with SCIs.

Mapping lipid alterations in traumatically injured rat spinal cord by desorption electrospray ionization imaging mass spectrometry

Desorption electrospray ionization (DESI) mass spectrometry (MS) is used in an imaging mode to interrogate the lipid profiles of 15 μm thin tissue cross sections of injured rat spinal cord and normal healthy tissue. Increased relative intensities of fatty acids, diacylglycerols, and lysolipids (between +120% and +240%) as well as a small decrease in intensities of lipids (-30%) were visualized in the lesion epicenter and adjacent areas after spinal cord injury. This indicates the hydrolysis of lipids during the demyelination process due to activation of phospholipase A(2) enzyme. In addition, signals corresponding to oxidative degradation products, such as prostaglandin and hydroxyeicosatetraenoic acid, exhibited increased signal intensity by a factor of 2 in the negative ion mode in lesions relative to the normal healthy tissue. Analysis of malondialdehyde, a product of lipid peroxidation and marker of oxidative stress, was accomplished in the ambient environment using reactive DESI mass spectrometry imaging. This was achieved by electrospraying reagent solution containing dinitrophenylhydrazine as high-velocity charged droplets onto the tissue section. The hydrazine reacts selectively and rapidly with the carbonyl groups of malondialdehyde, and signal intensity of twice the intensity was detected in the lesions compared to healthy spinal cord. With a small amount of tissue sample, DESI-MS imaging provides information on the composition and distribution of specific compounds (limited by the occurrence of isomeric lipids with very similar fragmentation patterns) in lesions after spinal cord injury in comparison with normal healthy tissue allowing identification of the extent of the lesion and its repair.

Modulation of the secondary injury process after spinal cord injury in Bach1-deficient mice by heme oxygenase-1

OBJECT

Oxidative stress contributes to secondary injury after spinal cord injury (SCI). The expression of heme oxygenase-1 (HO-1), which protects cells from various insults including oxidative stress, is upregulated in injured spinal cords. Mice deficient in Bach1 (Bach1-/-), a transcriptional repressor of the HO-1 and beta-globin genes, express high levels of HO-1 mRNA and protein in various organs. The authors hypothesized that HO-1 modulates the secondary injury process after SCI in Bach1(-/-) mice.

METHODS

Male C57BL/6 (wild-type) and homozygous Bach1(-/-) C57BL/6 mice were subjected to moderate SCI, and differences in hindlimb motor function, and electrophysiological, molecular biological, and histopathological changes were assessed for 2 weeks.

RESULTS

Functional recovery was greater, and motor evoked potentials were significantly larger in Bach1(-/-) mice than in wild-type mice throughout the observation period. The expression of HO-1 mRNA in the spinal cord was significantly increased in both mice until 3 days after injury, and it was significantly higher in Bach1(-/-) mice than in wild-type mice at every assessment point. Histological examination using Luxol fast blue staining at 1 day after injury showed that the injured areas were smaller in Bach1(-/-) mice than in wild-type mice. The HO-1 immunoreactivity was not detected in uninjured spinal cord, but 3 days postinjury the number of HO-1-immunoreactive cells was obviously higher in the injured area in both mice, particularly in Bach1(-/-) mice. The HO-1 was primarily induced in microglia/macrophage in both mice.

CONCLUSIONS

These results suggest that HO-1 modulates the secondary injury process, and high HO-1 expression may preserve spinal cord function in the early stages after SCI in Bach1(-/-) mice. Treatment that induces HO-1 expression at these early stages may preserve the functional outcome after SCI.

Role of secretory phospholipase a(2) in CNS inflammation: implications in traumatic spinal cord injury

Secretory phospholipases A(2) (sPLA(2)s) are a subfamily of lipolytic enzymes which hydrolyze the acyl bond at the sn-2 position of glycerophospholipids to produce free fatty acids and lysophospholipids. These products are precursors of bioactive eicosanoids and platelet-activating factor (PAF). The hydrolysis of membrane phospholipids by PLA(2) is a rate-limiting step for generation of eicosanoids and PAF. To date, more than 10 isozymes of sPLA(2) have been found in the mammalian central nervous system (CNS). Under physiological conditions, sPLA(2)s are involved in diverse cellular responses, including host defense, phospholipid digestion and metabolism. However, under pathological situations, increased sPLA(2) activity and excessive production of free fatty acids and their metabolites may lead to inflammation, loss of membrane integrity, oxidative stress, and subsequent tissue injury. Emerging evidence suggests that sPLA(2) plays a role in the secondary injury process after traumatic or ischemic injuries in the brain and spinal cord. Importantly, sPLA(2) may act as a convergence molecule that mediates multiple key mechanisms involved in the secondary injury since it can be induced by multiple toxic factors such as inflammatory cytokines, free radicals, and excitatory amino acids, and its activation and metabolites can exacerbate the secondary injury. Blocking sPLA(2) action may represent a novel and efficient strategy to block multiple injury pathways associated with the CNS secondary injury. This review outlines the current knowledge of sPLA(2) in the CNS with emphasis placed on the possible roles of sPLA(2) in mediating CNS injuries, particularly the traumatic and ischemic injuries in the brain and spinal cord.

Does hypothermic treatment provide an advantage after spinal cord injury until surgery? An experimental study

We compared the effects of early and late stage hypothermia treatment after spinal cord injury. Five groups each consisting of seven rats were included in this study. In Group 1a (Clip applied-non-treatment group) and Group 1b (Clip applied-treated group) the spinal cords were harvested 1 h after the injury. In Group 2a (clip applied, non-treated group) and Group 2b (clip applied-treated group) the injured segments were harvested 24 h after injury. Group 3 was designed as the sham-operated group. The significantly lower levels of TBARS and GSH-Px in Group 2a, as compared with Group 1b suggests that the hypothermia was effective in the early stage of treatment (P < 0.05). In contrast, TBARS and GSH-Px levels were significantly increased at the 24 h timepoint following treatment (P < 0.05). Short-term systemic hypothermia reduces lipid peroxidation in the early stages after spinal cord injury. This beneficial effect disappears 24 h following systemic hypothermic treatment.

Neuroprotective effects of infliximab in experimental spinal cord injury

BACKGROUND

The aim of the study is to assess the effects of infliximab, a TNF-alpha receptor blocker, in a spinal cord clip compression injury model.

METHODS

Clip compression injury model was used for producing spinal cord injury on 32 adult, male Wistar rats (Gazi University Animal Research Laboratory, Ankara, Turkey). After exposing the vertebral column between T7 and T10, total laminectomy was performed with the assistance of a high-speed drill and a surgical microscope. The dura was left intact. Spinal cord injury was performed on all rats with application of a 70-g closing force aneurysm clip for 1 minute. The rats were randomly allocated into 4 groups. Control group received no further therapy, whereas the other 3 groups received methylprednisolone (30 mg/kg intraperitoneal), infliximab (5 mg/kg subcutaneous), and a mixture of these 2 agents. All rats were killed 72 hours later, and the level of lipid peroxides in traumatized spinal cord tissue were measured as thiobarbituric acid-reactive material and determined using the method of Mihara and Uchiyama (Determination of malonaldehyde precursor in tissue by thiobarbituric acid test. Anal Biochem 1978;86(1):271-8).

RESULTS

Treatment with infliximab and methylprednisolone decreased MDA levels in rats with spinal cord injury with a statistically significant difference. In addition, combined therapy achieved a more profound decrease in tissue MDA levels, which was also statistically significant.

CONCLUSIONS

Infliximab is found as effective as methylprednisolone on spinal cord clip compression injury. Moreover, the combination of these 2 agents demonstrated higher efficacy suggesting a synergistic effect between these 2 agents. However, further studies regarding functional and behavioral analyses as well as biochemical markers are required.

Potentialities and pitfalls accompanying chemico-pharmacological strategies against endogenous electrophiles and carbonyl stress

The use of powerful analytical technologies to detect endogenous carbonyls formed as byproducts of oxidative cell injury has revealed that these species contribute to many human diseases. As electrophiles, they are attacked by reactive centers in cell macromolecules to form adducts, the levels of which serve as useful biomarkers of oxidative cell injury. Because the pathobiological significance of such damage is often unclear, the possibility of using low molecular weight drugs as exploratory sacrificial nucleophiles to intercept reactive carbonyls within cells and tissues is appealing. This perspective highlights the potential benefits of using carbonyl scavengers to evaluate the significance of endogenous carbonyls in particular diseases but also canvasses a number of challenges confronting this therapeutic strategy. Chief among the latter is the task of confirming that carbonyl sequestration underlies any suppression of disease symptoms elicited by these multipotent reagents, an issue needing clarification if these compounds are to command consideration as drug interventions in humans. Other problems include adverse consequences of reactions between carbonyl scavengers and important endogenous carbonyls (e.g., neurotoxicity due to pyridoxal depletion), as well as the potential for drugs to form ternary complexes with carbonylated cell proteins, raising the prospect of immunotoxicological outcomes. Strategies for moving carbonyl sequestering reagents from the laboratory bench to a clinical testing environment are discussed within the context of the search for new treatments for spinal cord injury, one of the most debilitating medical conditions sustainable by humans. This condition seems an appropriate test case for assessing carbonyl sequestering drugs given growing evidence for noxious carbonyls in the wave of neuronal cell death that follows traumatic injury to the spinal cord.

Effects of methylprednisolone and hyperbaric oxygen on oxidative status after experimental spinal cord injury: a comparative study in rats

The effects of hyperbaric oxygen (HBO) therapy or methylprednisolone on the oxidative status were evaluated in experimental spinal cord injury. Clip compression method was used to produce acute spinal cord injury rats. Hyperbaric oxygen was administered twice daily for a total of eight 90 min-sessions at 2.8 atmospheres. Methylprednisolone was first injected with a bolus of 30 mg/kg followed with an infusion rate of 5.4 mg/kg/h for 24 h. Five days after clip application animals were sacrificed and their traumatized spinal cord segment were excised. Tissue levels of thiobarbituric acid reactive substances (TBARS), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were evaluated to reflect oxidant/antioxidant status. Non-treated clip-operated animals reflected significantly higher SOD, GSH-Px and TBARS levels that were found to be significantly higher than the sham-operated. Methylprednisolone was not able to lower these levels. HBO administration diminished all measured parameters significantly; however, their levels appeared already to be high when compared with sham animals. According to these results obtained on the 5th day after induction, HBO, but not methylprednisolone, seems to procure prevention against oxidative spinal cord injury.

Effect of pinealectomy and melatonin replacement on morphological and biochemical recovery after traumatic brain injury

Numerous studies showed that melatonin, a free radical scavenger, is neuroprotective. In this study, we investigated the effect of pinealectomy and administration of exogenous melatonin on oxidative stress and morphological changes after experimental brain injury. The animals were divided into six groups, each having 12 rats. Group 1 underwent craniotomy alone. Group 2 underwent craniotomy followed by brain trauma and received no medication. Group 3 underwent craniotomy followed by brain trauma and received melatonin. Group 4 underwent pinealectomy and craniotomy alone. Group 5 underwent pinealectomy and craniotomy followed by brain injury and received no medication. Group 6 underwent pinealectomy and craniotomy followed by brain trauma and received melatonin. Melatonin (100 mg/kg) was given intraperitoneally immediately after trauma to the rats in Groups 3 and 6. Pinealectomy caused a significant increase in the malondialdehyde (MDA), nitric oxide (NO), glutathione (GSH), and xanthine oxidase (XO) levels, and a decrease in GSH levels as compared to the control group. Trauma to pinealectomized rats causes significantly higher oxidative stress. Exogeneous melatonin administration significantly reduced MDA, XO and NO levels, increased GSH levels, and attenuated tissue lesion area. These findings suggest that reduction in endogenous melatonin after pinealectomy makes the rats more vulnerable to trauma, and exogenous melatonin administration has an important neuroprotective effect.

Neuroprotection by resveratrol against traumatic brain injury in rats

Oxidative stress after traumatic brain injury may contribute to many of the pathophysiologic changes. Resveratrol, naturally present at high concentration in grape skin, seeds, and red wine, has significant antioxidant properties in a variety of in vitro and in vivo models. In this study, we investigate the effect of resveratrol on oxidative stress after traumatic brain injury in rat model.A total of 54 adult Wistar albino male rats weighing 250-300 g were used. The rats were allocated into three groups. The first group was control (sham-operated) group in which only a craniotomy was performed, the others were trauma and resveratrol groups. A 100 mg/kg single dose of resveratrol, freshly prepared by dissolving in 50% ethanol and diluted in physiological saline (2%), for resveratrol group, and 1 ml ethanol (2%) for trauma group, was administered intraperitoneally immediately after trauma. Weight-drop method was used for achieving head trauma. Then, all groups were separated into three subgroups for biochemical analysis, brain water content and histopathological assessment following trauma. Twenty-four hours after trauma brain water content and malondialdehyde (MDA), glutathione (GSH), nitric oxide (NO), xanthine oxidase (XO) levels of traumatic hemisphere were evaluated. Quantitative histopathological analysis was performed on 14th day postinjury. Trauma caused a significant increase in MDA, XO, NO levels and decrease in GSH level as compared to control group. Resveratrol administration significantly reduced MDA, XO and NO levels, increased GSH level, and also attenuated tissue lesion area. Our results indicate that treatment with resveratrol immediately after traumatic brain injury reduce oxidative stress and lesion volume. Future studies involving different doses and the dose-response relationship could promise better results.

Evaluation of the neuroprotective effects of citicoline after experimental spinal cord injury: improved behavioral and neuroanatomical recovery

Spinal cord injury (SCI) caused by trauma mainly occurs in two mechanisms as primary and secondary injury. Secondary injury following the primary impact includes various pathophysiological and biochemical events. Methylprednisolone is the only pharmacological agent having clinically proven beneficial effects on SCI. Citicoline has been shown to have clinical and experimental beneficial effects on brain ischemia. This study aims to investigate the neuroprotective effect of citicoline in an experimental SCI model in rats. Sixty adult Wistar albino rats were randomized into five groups. SCI was performed by the weight-drop model. Group 1 underwent laminectomy alone. The Group 2 underwent laminectomy followed by SCI and received no medication. Group3, Group 4 and Group 5 underwent laminectomy followed by SCI and received medication. Group 3 and Group 5 received citicoline and Group 4 and Group 5 received methylprednisolone. The rats were divided into two subgroups for biochemical analysis (sacrificed at 24 h after surgery) and neurobehavioral and histopathological evaluation (sacrificed at 6 weeks after surgery). Malondialdehyde levels, nitric oxide levels and trauma size ratios were lower and reduced glutathione levels were higher in Group 3, Group 4 and Group 5 as compared to Group 2. Posttraumatic neurological recovery after surgery was significantly better in Group 3, Group 4 and Group 5 compared to Group 2. In conclusion, this study demonstrates that citicoline is as effective as methylprednisolone. The efficacy of citicoline combined with methylprednisolone is not superior to either citicoline or methylprednisolone alone.

The antioxidant effect of beta-Glucan on oxidative stress status in experimental spinal cord injury in rats

This study was performed to investigate the antioxidant effect of beta-Glucan in experimental spinal cord injury (SCI). Injury was produced using weight-drop technique in rats. beta-Glucan was given by intraperitoneal injection following trauma. The rats were sacrificed at the sixth day of injury. Oxidative stress status was assessed by measuring the spinal cord tissue content of Malonyldialdehyde (MDA), Superoxide Dismutase (SOD) and Gluthatione Peroxidase (GSH-Px) activities. No effect of beta-Glucan on SOD and MDA activities was found but, GSH-Px levels were found to decrease to the baseline (preinjury) levels when it was compared to untreated group (U=0.000; p=0.002). According to our results, beta-Glucan works like a scavenger and has an antioxidant effect on lipid peroxidation in spinal cord injury.

Effect of indomethacin on motor activity and spinal cord free fatty acid content after experimental spinal cord injury in rabbits

STUDY DESIGN

Determination of functional and biochemical parameters as well as the effect of specific therapies on these parameters, in the experimental model of neurotrauma in rabbits.

OBJECTIVE

To assess the effect of indomethacin (0.1-3.0 mg/kg for 9 days), a potent inhibitor of endogenous prostaglandin synthesis, on the motor activity and on the spinal cord tissue concentration of free palmitic, stearic, oleic, arachidonic and docosahexaenoic acids in an experimental model of a spinal cord injury in rabbits.

SETTING

Faculty of Medicine, University of Rijeka, Croatia.

METHODS

The animals were randomly divided into nine experimental groups, four sham and/or vehicle-treated and five indomethacin-treated (including one sham-operated and four injured groups). Laminectomy was followed by contusion of the spinal cord, using a modification of the technique of Albin. Motor activity was controlled daily during the course of the next nine postoperation days and scored using Tarlov's system. Spinal cord samples from the impact injury site were taken and frozen in liquid nitrogen. Total lipids were isolated and purified by a modification of the method of Folch. Free fatty acids (FFAs) were separated from the total lipid extract by preparative thin-layer chromatography, converted to the corresponding methyl esters and identified using gas chromatography, using nonadecanoic acid as the internal standard.

RESULTS

The concentrations of all analysed free fatty acids were increased in the spinal cord after neurotrauma, in comparison to control tissues. Treatment of injured rabbits with indomethacin resulted in a significant decrease in spinal cord FFAs and exerted a positive effect on neurotrauma-induced motor impairment.

CONCLUSION

These results indicate a mechanism whereby indomethacin protects rabbits from the sequellae of neuronal damage caused by trauma, and suggests that it may be beneficial in the therapy of neurotrauma.

SPONSORSHIP

This work was supported by the Croatian Ministry of Science and Technology (project 062019).

Exacerbation of neuronal cell death by activation of group I metabotropic glutamate receptors: role of NMDA receptors and arachidonic acid release

Both ionotropic and metabotropic glutamate receptors have been implicated in the pathogenesis of neuronal injury. Activation of group I metabotropic glutamate receptors (mGluR) exacerbates neuronal cell death, whereas inhibition is neuroprotective. However, the mechanisms involved remain unknown. Activation of group I mGluR modulates multiple signal transduction pathways including stimulation of phosphoinositide hydrolysis, potentiation of NMDA receptor activity, and release of arachidonic acid. Here we demonstrate that whereas activation of group I mGluR by (S)-3,5-dihydroxyphenylglycine (DHPG) potentiates NMDA-induced currents and intracellular calcium increases in rat cortical neuronal cultures, partial effects of group I mGluR activation or inhibition on neuronal injury induced by oxygen-glucose deprivation remain despite NMDA receptor blockade. DHPG stimulation also increases basal arachidonic acid release from rat neuronal-glial cultures and potentiates injury-induced arachidonic acid release in these cultures. Thus, activation of group I mGluR may exacerbate neuronal injury through multiple mechanisms, which include positive modulation of NMDA receptors and enhanced release of arachidonic acid.

Prostaglandin release by spinal cord injury mediates production of hydroxyl radical, malondialdehyde and cell death: a site of the neuroprotective action of methylprednisolone

The present study explores in vivo whether and how prostaglandin F(2alpha) (PGF(2alpha)), a membrane phospholipid hydrolysis product, causes neuronal death. The concentration of PGF(2alpha) measured by microdialysis sampling increased threefold immediately following impact injury to the rat spinal cord. Administration of PGF(2alpha) into the cord through a dialysis fiber caused significant cell loss, increased extracellular levels of hydroxyl radicals and malondialdehyde - an end product of membrane lipid peroxidation - to 3.3 and 2.3 times basal levels, respectively. This suggests that PGF(2alpha)-induced cell death is partly due to hydroxyl radical-triggered peroxidation. Generating hydroxyl radical by administering Fenton's reagents into the cord through the fibers significantly increased malondialdehyde production - the first direct in vivo evidence that hydroxyl radical triggers membrane lipid peroxidation. Methylprednisolone significantly reduced the release of PGF(2alpha) upon spinal cord injury and blocked PGF(2alpha)-induced hydroxyl radical and malondialdehyde production, but did not significantly reduce Fenton's reagent-induced malondialdehyde production, despite the production of more malondialdehyde by PGF(2alpha). This suggests that methylprednisolone may not directly scavenge hydroxyl radical, and that its 'antioxidant' effect is a consequence of blocking the pathways for producing toxic PGF(2alpha) and for PGF(2alpha)-induced hydroxyl radical formation, thereby reducing membrane lipid peroxidation.

Oxidative stress following traumatic brain injury in rats: quantitation of biomarkers and detection of free radical intermediates

Oxidative stress may contribute to many pathophysiologic changes that occur after traumatic brain injury. In the current study, contemporary methods of detecting oxidative stress were used in a rodent model of traumatic brain injury. The level of the stable product derived from peroxidation of arachidonyl residues in phospholipids, 8-epi-prostaglandin F(2alpha), was increased at 6 and 24 h after traumatic brain injury. Furthermore, relative amounts of fluorescent end products of lipid peroxidation in brain extracts were increased at 6 and 24 h after trauma compared with sham-operated controls. The total antioxidant reserves of brain homogenates and water-soluble antioxidant reserves as well as tissue concentrations of ascorbate, GSH, and protein sulfhydryls were reduced after traumatic brain injury. A selective inhibitor of cyclooxygenase-2, SC 58125, prevented depletion of ascorbate and thiols, the two major water-soluble antioxidants in traumatized brain. Electron paramagnetic resonance (EPR) spectroscopy of rat cortex homogenates failed to detect any radical adducts with a spin trap, 5,5-dimethyl-1-pyrroline N:-oxide, but did detect ascorbate radical signals. The ascorbate radical EPR signals increased in brain homogenates derived from traumatized brain samples compared with sham-operated controls. These results along with detailed model experiments in vitro indicate that ascorbate is a major antioxidant in brain and that the EPR assay of ascorbate radicals may be used to monitor production of free radicals in brain tissue after traumatic brain injury.

Elevation of hydrogen peroxide after spinal cord injury detected by using the Fenton reaction

To reveal whether reactive oxygen species (ROS) play a role after spinal cord injury, we developed a unique method for assaying hydrogen peroxide (H2O2) and determined the time course of its concentration changes following impact injury to the rat spinal cord. Microdialysis was used to sample H2O2 in the extracellular space and the dialysates were collected into a vial containing salicylate and ferrous chloride (FeCl2). H2O2 collected in the vial was converted to hydroxyl radicals (*OH) by FeCl2 catalysis. 2,3- and 2,5-dihydroxybenzoic acid produced by reaction of *OH with salicylate in the collecting vial were measured by HPLC and calibrated to H2O2 concentrations. The postinjury levels of H2O2 were significantly increased (p = 0.02) for over 11 h. FeCl2 administered through the dialysis fiber catalyzes H2O2 conversion in the cord to *OH. This *OH does not reach the collecting vial due to its extremely short lifetime (nanoseconds). The reduced H2O2 levels in the vials validate the measurement of H2O2. The relatively long-lasting formation of H2O2 and superoxide reported herein and previously suggests that ROS may be important in secondary spinal cord damage and that removal of ROS may be a realistic treatment strategy for reducing injury caused by free radicals.

Somatosensory spinal cord evoked potentials in the evaluation of the effect of dexamethasone in experimental spinal cord injury

We studied the effects of high-dose dexamethasone on amplitude and latency values of spinal cord evoked potentials. Thirty-three rabbits were divided into three equal groups. The first group served as the control group, the others received high-dose (2.5 mg/kg) dexamenthasone, the second group 1 hour prior to and the third group immediately after the induction of a spinal cord trauma in segment T12. The spinal cord evoked potentials were recorded epidurally from T12 segment 5 min before and 5, 30, 60, 90, 120 and 150 min after trauma. Pretreatment with dexamethasone (group II) prevented the latency delay, and later treatment with dexemethasone (group III) prevented the latency delay partially. Our results suggest that when dexamethasone is given prophylactically it prevents latency alteration, while treatment with dexamethasone after lesioning prevents latency alteration partially. From our results we conclude that pretreatment with dexamethasone may involve different mechanisms than were activated in the posttreatment group.

The time course of malondialdehyde production following impact injury to rat spinal cord as measured by microdialysis and high pressure liquid chromatography

This paper reports a highly sensitive, specific, and reproducible method for the analysis of malondialdehyde (MDA) from microdialysates. The microdialysates were reacted with 2-thiobarbituric acid, and the TBA adducts were separated by HPLC and detected using a fluorescence detector. Butylated hydroxytoluene was used as an antioxidant to minimize formation of artifacts. The time course of MDA production following impact injury to the rat spinal cord was obtained using this improved method. MDA concentrations in the extracellular space gradually increased from a basal level of 20 +/- 3.6 nM to 44 +/- 18.1 nM during the first 2 hr, reached a maximum of 95 +/- 19.8 nM at 5 hr, and then decreased to 36 +/- 9.5 nM at 9 hr. The findings support the hypothesis that spinal cord injury leads to increased membrane lipid peroxidation.

Effects of alpha-phenyl-N-tert-butyl nitrone (PBN) on compression injury of rat spinal cord

alpha-Phenyl-N-tert-butyl Nitrone (PBN) is a free radical scavenger which recently has proved to be neuroprotective in experimental studies on focal cerebral ischemia and infarction. We therefore studied the effect of this drug in a model of moderate compression injury to rat spinal cord at the midthoracic level. The compound was given intraperitoneally 0.5 h before (100 mg/kg b.w) and at 1.5 h (50 mg/kg b.w) and 3.5 h (50 mg/kg b.w) after compression. Treated animals and controls (vehicle alone) were allowed to survive for 1 or 9 days following trauma. The functional outcome was tested by the inclined plane method and the motor performance score. By using MAP2 immunostaining the number of nerve cell bodies in the ventral horn and the ratio of MAP2 immunostained area to area of whole section of the cord were assessed to detect loss of neurons and loss of dendrites in the compressed segment. beta APP and PGP9.5 immunostaining was used to demonstrate axonal lesions. Treated and control rats showed at day 1 when tested with the inclined plane method a marked reduction of the capacity angle. This abnormality recovered gradually over the following days and was normalized at day 9. The motor performance score showed a marked reduction at day 1 which almost normalized at day 9. There was no difference regarding the functional outcome between rats given PBN and controls in none one of these functional tests. The spinal cord of normal rats presented immunoreactivity to MAP2 in nerve cell bodies and dendrites but not in axons and other structures. Following compression there was at day 1 and 9 a marked loss of MAP2 immunoreactivity in dendrites and nerve cell bodies. We could not detect any difference between the PBN and the control rats regarding the degree of cell loss or degree of reduction of dendrite staining. No difference between the two groups was seen with the axonal immunostainings (beta APP and PGP9.5). In conclusion, our study did not reveal any neuroprotective effect of PBN on the functional outcome and morphology (immunostaining to MAP2, beta APP and PGP9.5) in this model of moderate compression trauma to rat spinal cord.

Oxidative stress following traumatic brain injury in rats

BACKGROUND

Free radicals may be involved in the pathophysiology of traumatic brain injury (TBI) through oxidative damage of neurovascular structures. Endogenous antioxidants, such as ascorbate and alpha-tocopherol, may play a critical role in combating these oxidative reactions and their oxidized products can serve as an important index of oxidative stress.

METHODS

We used electron spin resonance (ESR) spectroscopy and in vivo spin trapping (reaction of an organic compound with free radical species) to detect the possible generation of free radicals after TBI. Injury was inflicted by a weight drop technique over the head (5.7 kg-cm). Rats were intravenously infused with either 1 mL, 0.1 M of the spin trap, alpha-phenyl-N-tert-butyl nitrone (PBN), or an equivalent volume of saline immediately before TBI or sham-injury. Animals were divided into four groups: (1) Group I: PBN-infused sham-injured, (2) Group II: PBN-infused injured, (3) Group III: saline-infused sham-injured, and (4) Group IV: saline-infused injured. Additional groups of saline-infused uninjured, saline-infused, and PBN-infused injured animals were used for histopathology. Sixty minutes after TBI or sham-injury, rats were again anesthetized and decapitated. The brains were removed within 1 minute, homogenized, and extracted for lipids. The extracts were analyzed by ESR spectroscopy. Brain ascorbic acid (AA) concentration was determined spectrophotometrically, using the ascorbate oxidase assay.

RESULTS

No PBN spin adduct signals (indicating trapped free radical species) were visible 60 minutes after TBI. All groups of rats showed an ascorbyl free radical signal. The ascorbyl signal intensity (AI) was, however, significantly higher in the injured rats, while the brain (AA) was significantly reduced. In addition, the ratio of AI/AA, which eliminates the effect of variable ascorbate concentrations in the brain, was also significantly higher in the injured animals.

CONCLUSIONS

We conclude that 60 minutes following TBI there was a significantly increased level of oxidative stress in the brain. This may reflect formation of free radical species with subsequent interaction with ascorbate (antioxidant) during the 60 minute period. The lack of PBN spin adduct signals 1 hour after TBI may indicate that free radical generation is time dependent and might be detectable earlier or later than the 60 minute period.

Redox changes in perfusates following intracerebral penetration of microdialysis probes

Microdialysis probe insertion into rat cerebral cortex significantly affects the levels of redox-active substances in brain extracellular fluid. Ascorbic acid levels are high immediately after probe insertion, decline rapidly, and then rise as the rat recovers from anesthesia 5-8 hours after surgery. Uric acid is at a low level for 5 hours and then rapidly increases in parallel with ascorbic acid. High ascorbic acid levels immediately after probe insertion are likely due to a shift from intracellular to extracellular fluids, whereas the delayed increase in uric acid may be due to increased enzymatic formation. After removal from the brain, hydrogen peroxide (H2O2) in microdialysis samples produces catalase-sensitive oxidative chemiluminescence. Microdialysis samples also produce high level catalase-resistant chemiluminescence associated with ascorbic acid levels after penetration injury. Although ascorbic acid is likely an antioxidant at concentrations estimated to be in brain extracellular fluid, it may have prooxidant effects when complexed with transition metals released into the neuronal microenvironment during traumatic brain injury.

Separation of neutral lipids by high-performance liquid chromatography: quantification by ultraviolet, light scattering and fluorescence detection

The recent increased use of cell cultures to model physiological events, in particular signal transduction and traumatic injury, has produced a need for a quantitative, high-performance liquid chromatographic separation of neutral lipid classes with a high degree of resolution and reproducibility. We report an isocratic separation using a Phenomenex Selectosil silica column (5 microns). Two solvents were used, 1.2% 2-propanol in n-hexane containing 0.1% acetic acid (90%) and n-hexane (10%) at a flow-rate of 0.6 ml/min. Column temperature was maintained at 55 degrees C and this temperature was critical for baseline resolution of 1,3-diacylglycerol and cholesterol. The use of 10% n-hexane permitted the resolution of low polarity compounds such as butylated hydroxytoluene, triacylglycerols and cholesteryl esters. All of the detectors used produced standard curves with linearity over a wide concentration range.

Role of N-methyl-D-aspartate receptor in acute spinal cord injury

To clarify the role of N-methyl-D-aspartate (NMDA) receptors in acute spinal cord injury, changes in the intraspinal microcirculation after acute spinal cord injury in rabbits were examined. Systemic administration of MK-801, an NMDA receptor antagonist, at a dose of 5 mg/kg, significantly improved motor recovery after injury and significantly reduced edema formation at the injured site without altering spinal cord blood flow or vascular permeability at the injured site. These findings indicate that excitatory amino acids contribute to secondary spinal cord damage, especially edema formation, mediated by NMDA receptors in the early stage after injury.

Plasmalogens, phospholipases A2 and signal transduction

Several lines of evidence indicate that the breakdown of plasmalogens in neural membranes during neurodegenerative diseases is a receptor-mediated process catalyzed by a plasmalogen-selective phospholipase A2. This enzyme has recently been purified from bovine brain. It does not require Ca2+ and is localized in cytosol. It has a molecular mass of 39 kDa and is strongly inhibited by glycosaminoglycans, with the pattern of inhibition being heparan sulfate > hyaluronic acid > chondroitin sulfate > heparin. This plasmalogen-selective phospholipase A2 is also inhibited by gangliosides and sialoglycoproteins. Substrate specificity and the effects of metal ions, detergents and inhibitors suggest that this phospholipase A2 is different from the well-known 85 kDa Ca(2+)-dependent cytosolic phospholipase A2 that has recently been cloned and is not plasmalogen-selective. The plasmalogen-selective phospholipase A2 may be regulated by glycosaminoglycans and sialoglycoconjugates and may be involved in the regulation of K+ channels. This enzyme, which plays a major role in the release of fatty acids during ischemic injury and reperfusion, shows promise as a major target for drug therapy.

Lack of effect of postinjury treatment with methylprednisolone or tirilazad mesylate on the increase in eicosanoid levels in the acutely injured cat spinal cord

Methylprednisolone (MP) improves motor recovery in spinal cord-injured patients when administered in a 24 h intensive high dose regimen beginning within 8 h after spinal cord injury (SCI). The rationale for this regimen has been based upon the need for high doses (i.e., 30 mg/kg initial IV dose) to inhibit posttraumatic lipid peroxidation (LP) in the injured spinal segment. However, injury also triggers the immediate calcium-mediated activation of phospholipase A2 (PLA2), the release of arachidonic acid, and the enzymatic formation of potentially deleterious prostaglandins (PGE2 alpha, PGE2), thromboxane A2 (TXA2), and leukotrienes (LTs). Thus, in view of the glucocorticoid receptor-mediated inhibition of PLA2 that underlies much of MP's antiinflammatory actions, an additional neuroprotective mechanism may relate to an inhibition of eicosanoid formation. Using the cat spinal cord compression model (180g x 5 min at L3; Na pentobarbitol anesthesia), we examined whether 30 min postinjury dosing with MP (30 mg/kg IV) could attenuate spinal tissue eicosanoid levels measured by enzyme immunoassay at 1 h (Experiment 1). Pial blood flow was measured over the dorsal columns at the injury site using laser doppler flowmetry to monitor posttraumatic hyperperfusion as an index of the microvascular pathophysiology of acute SCI. In vehicle treated animals at 1 h postinjury, there was a significant increase in the tissue levels of PGF2 alpha (+290%), PGE2 (+260%), TXB2 (stable analog of TXA2, +126%), and LTB4 (+73%) in comparison to sham, uninjured animals. However, 6-keto-PGF1 alpha (stable analog of prostacyclin or PGI2) and LTC4 did not increase. Methylprednisolone did not reduce the increase in eicosanoid production. In the case of LTB4 and LTC4, MP actually increased the levels further. In addition, we examined the effects of a double dose MP regimen (30 mg/kg IV at 30 min plus 15 mg/kg IV at 2.5 h postinjury) on spinal cord eicosanoid levels at 4 h postinjury (Experiment 2). At 4 h postinjury, significant increases in PGF2 alpha, PGE2, TXB2, and 6-keto-PGF1 alpha were observed, and with the exception of PGE2, no MP attenuation of the increased eicosanoids was seen. These results fail to provide evidence that postinjury administration of high dose MP exerts a significant anti-PLA2 action. On the other hand, MP effectively inhibited secondary spinal cord pial hyperperfusion, which is believed to be largely mediated by free radical-lipid peroxidative mechanisms. Thus, it seems likely that the protective action of MP on the acute microvascular pathophysiology of SCI is mediated by its well-documented effects on posttraumatic LP.(ABSTRACT TRUNCATED AT 400 WORDS)

Lipid alterations following impact spinal cord injury in the rat

A computer-controlled impactor was used to produce a severe spinal cord injury in the rat thoracic spinal cord. Cords were rapidly frozen in situ at 5, 15, 30, and 60 min and 6, 12, and 24 h postinjury. Control cords were noninjured cords from animals having undergone a laminectomy and allowed to recover for 90 min postlaminectomy. The cords were assayed for alterations in lipid metabolism. Specifically, there were rapid increases in prostaglandin F2 alpha and thromboxane, with a peak increase in thromboxane levels at 30 min. Prostaglandin F2 alpha levels peaked at 15 min with levels remaining nearly constant for 12 h. There were no detectable changes in phospholipid levels, although diacylglycerol levels and free fatty acid levels were increased. Total free fatty acids were increased at 12 and 24 h postinjury by 2.3- and 3.2-fold over control levels, respectively. Arachidonic acid levels were not significantly elevated at early time points, however, these early time points correspond to elevated eicosanoid synthesis and this may account for the lack of early detectable increases in arachidonic acid. After 6 h postinjury, arachidonic acid levels were 20-fold greater than control levels and remained elevated at 24 h. There were minimal decreases in cholesterol and no decrease in either choline or ethanolamine plasmalogen levels. These results suggest a rapid turnover of arachidonic acid following spinal cord injury with a concomitant increase in vasoconstrictive eicosanoid synthesis. The lack of changes in major membrane constituents suggests the mechanisms may not involve general membrane degradation, but an over-stimulation of phospholipase A2-linked membrane receptors.

Traumatic optic neuropathy

Knowledge concerning the pathophysiologic mechanisms of traumatic optic neuropathy is limited. The optic nerve is a tract of the brain. Therefore, the cellular and biochemical pathophysiology of brain and spinal cord trauma and ischemia provide insight into mechanisms that may operate in traumatic optic neuropathy. The dosage of methylprednisolone (30 mg/kg/6 hours) which was successful in the National Acute Spinal Cord Injury Study 2 (NASCIS 2) evolved from the unique pharmacology of corticosteroids as antioxidants. The management of traumatic optic neuropathy rests on an accurate diagnosis which begins with a comprehensive clinical assessment and appropriate neuroimaging. The results of medical and surgical strategies for treating this injury have not been demonstrated to be better than those achieved without treatment. The spinal cord is a mixed grey and white matter tract of the brain in contrast to the optic nerve which is a pure white matter tract. The treatment success seen with methylprednisolone in the NASCIS 2 study may not generalize to the treatment of traumatic optic neuropathy. Conversely, if the treatment does generalize to the optic nerve, NASCIS 2 data suggests that treatment must be started within eight hours of injury, making traumatic optic neuropathy one of the true ophthalmic emergencies. Given the uncertainties in the treatment, ophthalmologists involved in the management of traumatic optic neuropathy are encouraged to participate in the collaborative study of traumatic optic neuropathy.

Excitotoxicity and neurological disorders: involvement of membrane phospholipids

Excitatory amino acids and their receptors play an important role in membrane phospholipid metabolism. Persistent stimulation of excitatory amino acid receptors by glutamate may be involved in neurodegenerative diseases and brain and spinal cord trauma. The molecular mechanism of neurodegeneration induced by excitatory amino acids is, however, not known. Excitotoxin-induced calcium entry causes the stimulation of phospholipases and lipases. These enzymes act on neural membrane phospholipids and their stimulation results in accumulation of free fatty acids, diacylglycerols, eicosanoids, and lipid peroxides in neurodegenerative diseases and brain and spinal cord trauma. Other enzymes, such as protein kinase C and calcium-dependent proteases, may also contribute to the neuronal injury. Excitotoxin-induced alterations in membrane phospholipid metabolism in neurodegenerative diseases and neural trauma can be studied in animal and cell culture models. These models can be used to study the molecular mechanisms of the neurodegenerative processes and to screen the efficacy of therapeutic drugs.

Pathophysiology of spinal cord trauma

This article reviews the pathophysiology of spinal cord injury. The focus is on the role of post-traumatic membrane lipid changes, including lipid hydrolysis with enzymatic lipid peroxidation (ie, eicosanoid production) and nonenzymatic, free radical-induced lipid peroxidation in the secondary autodestruction of injured spinal cord tissue. A speculative etiopathogenesis of secondary injury is presented in an attempt to explain the importance and order of the pathophysiologic events that result in tissue death and the apparent effectiveness of diverse pharmacologic agents in the treatment of experimental spinal cord injury.

Indomethacin, an inhibitor of prostaglandin synthesis attenuates alteration in spinal cord evoked potentials and edema formation after trauma to the spinal cord: an experimental study in the rat

The potential efficacy of indomethacin (a potent inhibitor of endogenous prostaglandin synthesis) on spinal cord-evoked potentials and edema formation occurring after a focal trauma to the spinal cord was examined in a rat model. The spinal cord evoked potentials were recorded in urethane-anesthetized male rats using monopolar electrodes placed epidurally over the T9 (rostral) and T12 (caudal) segments after stimulation of the ipsilateral right tibial and sural nerves. Reference electrodes were placed in the corresponding paravertebral muscles. The spinal cord evoked potential consisted of a small positive peak followed by a broad and high negative peak. Amplitudes and latencies of the maximal positive peak and the maximal negative peak were measured. The latencies and amplitudes 30 min before injury were used as references (100%). A complete loss was denoted as 0%. All the potentials were quite stable during 30 min of recording before injury. Infliction of trauma to the T10-T11 segments of the spinal cord with a sterile scalpel blade (about 5 mm longitudinal and 2 mm deep incision into the right dorsal horn extending to Rexed's laminae VII) in untreated animals resulted in an immediate depression of the rostral maximal negative peak amplitude (60-100%) which persisted during 5 h of recording. The latencies of the rostral as well as caudal maximal negative and positive peaks increased successively from 2 h post-trauma. In this group of animals, 5 h after injury the spinal cord water content in the traumatized segments was increased by more than 6% as compared with a group of uninjured animals. Pretreatment with indomethacin (10 mg/kg body weight i.p. 30 min before injury) markedly attenuated the immediate decrease in the maximal negative peak amplitude after injury, but did not influence the successive latency increase. However, the increase in the water content of the traumatized cord after 5 h was less pronounced compared with untreated injured rats. Our results show a beneficial effect of indomethacin on trauma-induced spinal cord evoked potential changes and edema formation. Prostaglandins may thus influence early bioelectrical changes occurring in traumatized spinal cord not reported earlier. The findings support the view that early recording of spinal cord evoked potential may be useful to predict the outcome in some forms of spinal cord injuries.

A model for compression trauma: pressure-induced injury in cell cultures

An increase in pressure up to 15 atm was used to condense the cellular membrane of cells in culture thereby eliciting a mechanical-like trauma. This trauma is similar to a compression-like spinal cord injury or brain injury. The cells used in this study were ROC-1 oligodendroglia, N1E-115 neuroblastoma, and human umbilical vein endothelial (HUVE) cells. Total fatty acid (FA) release and release of lactate dehydrogenase (LDH) into the extracellular medium were used as indices of cellular trauma. Pressure-induced FA release, dependent on pressure and pressure duration, occurred with all cell types. The level of pressure needed to cause the greatest increase in FA levels was 10 atm for ROC-1 cells (3 min duration), 15 atm for N1E-115 cells (3 min duration), and 15 atm for HUVE cells (10 min duration). With each cell type, the released FA were reacylated or metabolized between 10 and 30 min of recovery. Following a 12- to 24-h recovery period, N1E-115 and HUVE cells release more FA, indicating that the initial perturbation of the membrane was not fully reversible. LDH levels were significantly increased in both the N1E-115 and HUVE cultures following 24 h of recovery. This efflux of LDH indicates irreversible membrane damage, suggesting that the trauma may be irreversible at longer recovery times.

Early perifocal cell changes and edema in traumatic injury of the spinal cord are reduced by indomethacin, an inhibitor of prostaglandin synthesis. Experimental study in the rat

The possibility that prostaglandins participate in the formation of perifocal edema and cell changes following a localized trauma to the spinal cord was investigated in a rat model. A laminectomy was performed in urethane-anesthetized animals at the thoracic T10-11 segment. Using a scalpel blade a unilateral lesion, about 2 mm deep and 5 mm long was made 1 mm to the right of the midline. The deepest part of the injury occupied Rexed's lamina VII of the dorsal horn. Animals were pretreated with the prostaglandin synthesis inhibitor, indomethacin (10 mg/kg, i.p. 30 min prior to trauma). Five hours after the injury the water content was determined and cell changes in and around the primary lesion were examined by light and electron microscopy. Normal and injured rats without indomethacin pretreatment served as controls. Untreated injured rats showed a profound increase of water content in the traumatized T10-11, the rostral (T9) and caudal (T12) segments compared with normal rats. These segments also exhibited marked cell changes in ipsilateral and contralateral dorsal and ventral horns. The gray matter had a spongy appearance and some nerve cells were condensed and distorted. The white matter contained many distorted fibers. Immunostaining for myelin basic protein showed a marked reduction of reaction product in the injured animals compared with normal rats. Ultrastructurally widened extracellular spaces, cytoplasmic vacuolation, swollen and condensed neurons, swollen astrocytes and vesiculation of myelin were frequent findings. Pretreatment of rats with indomethacin significantly reduced the accumulation of water in the traumatized and in the rostral and caudal segments. The structural changes were less pronounced particularly in the cranial and caudal segments.(ABSTRACT TRUNCATED AT 250 WORDS)

Excitatory amino acid receptors, neural membrane phospholipid metabolism and neurological disorders

Excitatory amino acids and their receptors play an important role in membrane phospholipid metabolism. Persistent stimulation of excitatory amino acid receptors by glutamate may be involved in neurodegenerative diseases and brain and spinal cord trauma. The molecular mechanism of neurodegeneration induced by excitatory amino acids is, however, not known. Excitotoxin induced calcium entry causes the stimulation of phospholipases and lipases. These enzymes act on neural membrane phospholipids and their stimulation results in accumulation of free fatty acids, diacylglycerols, eicosanoids and lipid peroxides in neurodegenerative diseases and brain and spinal cord trauma. Other enzymes such as protein kinase C and calcium-dependent proteases may also contribute to the neuronal injury. Excitotoxin-induced alteration in membrane phospholipid metabolism in neurodegenerative diseases and neural trauma can be studied in animal and cell culture models. The models can be used to study the molecular mechanisms of the neurodegenerative processes and to screen the efficacy of therapeutic drugs for neurodegenerative disease and brain and spinal cord trauma.

Changes in lipid metabolites and enzymes in rat brain due to ischemia and recirculation

Thirty and 60-min ischemic insults resulted in an increase in free fatty acid and 1,2- diacylglycerol contents of rat forebrain. No significant changes were detected in phospholipids except phosphatidylinositol 4-monophosphate and phosphatidylinositol 4,5-bisphosphate during ischemic insult. Phosphatidylinositol 4-monohosphate and phosphatidylinositol 4,5-bisphosphate contents decreased during ischemia. Although the increase in free fatty acid contents continued, 1,2-diacylglycerol did not show further increase after 30-min ischemia. These results suggest that there may be another pathway for the accumulation of free fatty acids in addition to phospholipase C coupled to di- and monoacylglycerol lipase. Free fatty acid and 1,2-diacylglycerol contents increased transiently and thereafter decreased to control levels within 90 min after postischemic recirculation. The decrease in arachidonic acid content preceded those of other FFA. Phosphatidylinositol 4-monophosphate and phosphatidylinositol 4,5-bisphosphate contents gradually increased after the initiation of recirculation in ischemic brains. Lysophosphatidylcholine decreased gradually after temporary increase during 15 and 5-min recirculations in 30 and 60-min ischemic groups. Phospholipase A, phospholipase C, and di- and monoacylglycerol lipase activities did not show significant changes during entire course of recirculation. Total activities of lysophospholipase and acylation enzymes of lysophospholipid demonstrated 1.5-and 2.2-fold increase during 30-min recirculation.

Phospholipases in biology and medicine

Phospholipases, a group of enzymes that catalyze the hydrolysis of membrane phospholipids, are classified according to the bond cleaved in a phospholipid into PLA1 (EC 3.1.1.3), PLA2 (EC 3.1.1.4), PLB (EC 3.1.1.5), PLC (EC 3.1.4.3), and PLD (EC 3.1.4.4). This paper reviews source and structure of PLA2 and the involvement of PLA2 and PLC in several biological phenomena, such as, signal transduction, photoreception, biosynthesis of lung surfactant, sperm motility, and fertilization. New assays for PLA2 activity and concentration in biological fluids are discussed. Phospholipases are involved in many inflammatory reactions by making arachidonate available for eicosanoid biosynthesis. The determination of PLA2 activity and mass concentration in plasma is useful in the diagnosis and prognosis of pancreatitis and of septic shock. Naturally occurring phospholipase inhibitors, such as lipocortins act as second messengers in the anti-inflammatory response to steroids. Lipocortins may be valuable therapeutic agents, because they are more specific in their anti-inflammatory action than glucocorticoids; therefore, they are less likely to produce harmful side effects.

Effect of thyrotropin-releasing hormone on the time course of neurologic recovery after spinal cord injury in the rat

Spinal cord injuries in rats were experimentally produced by compressing the cord at the eleventh thoracic vertebral level for 60 minutes with stainless steel screws (2 mm in diameter and 2.8 mm in length). The main neurologic signs produced by cord compression were motor as well as sensory deficits and urinary incontinence. Rats with a neurologic score, based on both motor and sensory deficits, of 1 (complete paraplegia but responsive to tail pinching) 24 hours after injury were used to study the relative effect of subcutaneous treatment with TRH once or twice daily for 7 consecutive days on the time course of recovery after spinal cord injury and the dose-dependency of this effect. Once daily (5, 15, or 45 mg/kg/day) or twice daily (2.5, 7.5, or 22.5 mg/kg x 2/day) treatment with TRH starting 24 hours after injury improved the neurological signs and reduced the incidence of urinary incontinence, dose-dependently. The minimum effective doses for once and twice daily treatments were 45 mg/kg/day and 7.5 mg/kg x 2/day. These results indicate that the neurologic recovery-accelerating effect of TRH administered 24 hours after cord injury for 7 days is dose-dependent and that a twice daily dosage schedule tends to produce better improvement in the neurologic state than a once daily schedule dose.

Active oxygen in neuromuscular disorders

Although muscle and nerve are reasonably well protected against active oxygen and related free radicals, environmental or inherited malfunctions can overpower their defences. Active oxygen is involved in many neuropathies and myopathies. In every case the damage is caused by agents which exert effects disproportionately greater than the quantities encountered, through a variety of amplification mechanisms. We can categorize these amplification mechanisms as follows: (a) non-replacement of targets (e.g. loss of genetic information, ataxia telangectasia being an hereditary ataxia in which an oxygen mediated chromosomal instability is apparent), (b) non-removal of unwanted materials (e.g. lipofuscin accumulation in brain and heart), (c) redox cycling, usually involving catalysis by trace-metal ions (e.g. some forms of Parkinsonism), (d) non-redox catalysis (e.g. toxicity in cardiac muscle or brain due to vanadium or aluminium respectively), (e) modification of ion transport (e.g. calcium ionophore or acrylamide induce histopathological changes in muscle, similar in some respects to those seen in Duchenne muscular dystrophy), (f) compromised defences (e.g. muscle and nerve become particularly susceptible to free radical damage after loss of the protective actions of vitamin E), and (g) amplification by inflammatory and immune responses (e.g. multiple sclerosis, reperfusion injury to brain and heart, and traumatic injury to nervous tissue). Unfortunately, a variety of therapeutic agents which might be expected to protect against almost every conceivable form of oxygen mediated damage have proved clinically ineffective in most of these disorders. The reasons for this will be explored with an emphasis on common features, differences, mechanisms, and potential therapeutic approaches.

Effects of BW755C, a mixed cyclo-oxygenase-lipoxygenase inhibitor, following traumatic spinal cord injury in rats

BW755C is an inhibitor of both cyclo-oxygenase and lipoxygenase, which has been found to have protective effects after myocardial ischemia in dogs. Impact injury to the spinal cord is associated with tissue ischemia as well as with the accumulation of eicosanoids. In the present studies we evaluated the effects of BW755C after traumatic spinal cord injury in rats. Drug treatment reduced thromboxane B2 levels and improved neurological recovery as compared to treatment with equal-volume physiological saline. The findings suggest that this drug or related compounds may be useful for the treatment of clinical spinal cord injury.

Traumatic spinal cord injury in rats causes increases in tissue thromboxane but not peptidoleukotrienes

Spinal cord samples from rats subjected to three different levels of impact trauma (25, 50, 100 g-cm) were examined for immunoreactive thromboxane B2 and 6-sulfidopeptide-containing leukotrienes, using specific radioimmunoassays. Trauma resulted in pronounced increases in thromboxane levels as early as 5 min after injury, with maximum values at 1 hr. Although thromboxane values then slowly declined, they remained significantly above control values for up to 7 days. Significantly smaller thromboxane values were found in rats subjected to mild injury (25 g-cm) than in those that received more severe, irreversible impact injury (50 and 100 g-cm). No statistically significant changes were observed in leukotriene levels in any of the experimental groups. These findings are consistent with the hypothesis that cyclooxygenase products of arachidonic acid metabolism may contribute to secondary injury after spinal cord trauma and provides the rationale for the use of cyclooxygenase inhibitors in the treatment of such injury.

Effects of the 21-aminosteroid U74006F on posttraumatic spinal cord ischemia in cats

The ability of a single intravenous dose of the 21-aminosteroid U74006F to affect the development of posttraumatic spinal cord ischemia was examined in pentobarbital-anesthetized cats. After surgical preparation, each animal received a 300 gm-cm contusion injury to the exposed L-3 vertebral segment, followed by a single bolus injection of vehicle or U74006F (3 or 10 mg/kg) at 30 minutes postinjury. Spinal cord white matter blood flow (SCBF) was measured by hydrogen clearance in the dorsolateral funiculus in the center of the injured segment before and at various times up to 4 hours after injury. In vehicle-treated cats, there was a progressive decline in SCBF over the course of the experiment. By 4 hours postinjury, SCBF had decreased from a preinjury value of 15.9 +/- 2.4 ml/100 gm/min (mean +/- standard error of the mean) to 5.8 +/- 0.8 ml/100 gm/min, representing a decline of 63.5%. In contrast, the SCBF measured 4 hours postinjury in cats that were treated with a single 10-mg/kg dose of U74006F was 13.6 +/- 1.7 ml/100 gm/min (p less than 0.001 vs. vehicle). Animals that received a 3-mg/kg intravenous dose of U74006F displayed a drop in SCBF equal to that of vehicle-treated cats. However, when a 3-mg/kg dose of U74006F was given to four vehicle-treated cats at the end of the experiment, a partial reversal of ischemia was recorded. Blood flow increased within 30 minutes from a mean of 4.5 +/- 0.8 to 7.4 +/- 1.0 ml/100 gm/min or an increase of 64.4% (p less than 0.05). This rather surprising effect of U74006F in reversing posttraumatic ischemia once it has developed significantly is not shared by a 30-mg/kg intravenous dose of methylprednisolone sodium succinate (MP), although MP has previously been shown to attenuate the posttraumatic drop in SCBF when given before the SCBF drop occurs. The mechanism of action of U74006F in antagonizing posttraumatic ischemia development is believed to involve the ability of the compound to inhibit iron-dependent lipid peroxidation in central nervous system tissue.