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

Effects of Clotrimazole on Experimental Spinal Cord Injury

BACKGROUND

We examined a possible neuroprotective effect of clotrimazole on spinal cord clip compression injury.

METHODS

Rivlin and Tator's acute extradural clip compression injury (CCI) model was used for producing SCI on 24 albino Wistar rats weighing 180-250 g. All rats were anesthetized with 30 mg/kg ketamine HCl intraperitoneally and were breathing spontaneously without tracheal intubation. Total laminectomy of T8-T12 was performed on all rats under operation microscope, and CCI was performed on all rats (expect those in group 1) with a 50-g closing force aneurysm clip for 1 min. Three hours later, all of the rats were killed with sodium pentobarbital. Spinal cords were excised for a length of 2 cm; 1 cm rostrally and caudally to the injury site and deep frozen at -76 degrees C for biochemical studies.

RESULTS

Treatment with clotrimazole decreased MDA levels in rats with SCI with a statistically significant difference.

CONCLUSIONS

To our knowledge, this the first study that shows the effects of clotrimazole on spinal cord clip compression injury. Clotrimazole was found to be effective on spinal cord clip compression injury, but further investigations are mandatory.

Thromboxane synthase and TP receptor mRNA in rat kidney and brain: effects of salt intake and ANG II

A TP receptor (TP-R) mimetic causes salt-sensitive hypertension and renal afferent arteriolar vasoconstriction. TP-Rs mediate effects of ANG II on renal vascular resistance and drinking. Therefore, we investigated the hypothesis that thromboxane A(2) synthase (TxA(2)-S) and/or TP-R expression is regulated by salt and/or ANG II. Rats (n = 6) received high-salt (HS) or low-salt (LS) diets. Additional HS-diet rats received ANG II while other HS- and LS-diet rats received the AT(1) receptor (AT(1)-R) antagonist losartan. Excretion of thromboxane B(2) by conscious rats was increased with the HS diet compared with the LS diet (126 +/- 10 vs. 48 +/- 5 pmol/24 h, respectively; P < 0.01). The mRNA abundance for TP-Rs (relative to beta-actin) in the kidney cortex was enhanced 30% by the HS diet (P < 0.001) and was reduced 50% by the addition of ANG II (P < 0.001). However, during losartan administration, the effects of salt were reversed; mRNA more than doubled during the LS diet (P < 0.001). Similarly, the mRNA abundance for TP-Rs in the brain stem was reduced by 50% with the addition of ANG II (P < 0.001) and during losartan administration was almost doubled by the LS diet (P < 0.001). The mRNA abundance for TxA(2)-S in the kidney cortex also was increased many times with the HS diet (P < 0.001). In contrast, the mRNA for TxA(2)-S in the brain was unaffected by salt. ANG II did not affect TxA(2)-S at either site. During losartan administration, TxA(2)-S increased modestly in the brain stem with the LS diet. mRNA abundance for TP-Rs in the kidney cortex and brain stem is suppressed by ANG II acting on AT(1)-Rs. In the absence of AT(1)-Rs, expression of TP-Rs at both sites is enhanced by LS intake. In contrast, ANG II does not affect the mRNA abundance for TxA(2)-S. Expression of TxA(2)-S is enhanced by HS intake in the kidney cortex but by LS intake in the brain stem only during losartan administration. Thus TP-Rs are strongly dependent on ANG II acting on AT(1)-Rs, whereas TxA(2)-S is regulated differentially in the kidney cortex and brain stem by salt intake.

An L-type calcium channel blocker, nimodipine influences trauma induced spinal cord conduction and axonal injury in the rat

The influence of the potent L-type Ca[2+] channel antagonist Nimodipine on spinal cord evoked potentials (SCEP) and axonal injury following trauma to the spinal cord was examined in a rat model. Spinal cord injury (SCI) was produced by an incision into the right dorsal horn of the T10-11 segments under urethane anaesthesia (1.5 g/kg, i.p.). SCEPs were recorded by epidural electrodes placed over the T9 (rostral) and T12 (caudal) segments after stimulation of the right tibial and sural nerves. SCI induced a pronounced decrease of the SCEP negative amplitude in the rostral (T9) recordings immediately after trauma. Axonal injury seen as degradation of myelin basic protein (MBP) immunostaining and myelin vesiculation at the ultrastructural level was most pronounced at 5 h. Continuous administration of Nimodipine (2 microg/kg/min, i.v.) from 30 min prior to injury until sacrifice markedly attenuated the changes in SCEP amplitude and latency. Axonal damage, loss of MBP, and myelin vesiculation were much less evident in the nimodipine treated traumatised rats. These observations suggest that Ca[2+] channels play an important role in the trauma induced alterations in SCEP and axonal injury, and indicate a therapeutic value of Ca[2+] blockers in SCI.

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.

Delayed oligodendrocyte degeneration induced by brief exposure to hydrogen peroxide

An in vitro model system of cultured oligodendrocytes was used to determine the susceptibility of these cells to oxidative stress induced by 15 min exposure to millimolar concentrations of hydrogen peroxide (H2O2). Following the exposure, the cells were incubated in normal growth medium, and analyzed at different time points. Although no cell loss was observed during the exposure period, there was a progressive depletion of adherent cells during the postexposure period as seen from either the number of recoverable nuclei, or from total RNA content of the cultures. Both the rate and the extent of cell deletion was directly dependent on H2O2 concentration. Cell death was preceded by structural alterations in the nuclear envelope resulting in "fragile" nuclei which disintegrated during isolation. Northern blot analysis showed that the expression of myelin-specific genes was rapidly downregulated in H2O2-treated cells. On the other hand, the expression of antiapoptotic gene, bcl-2 featured massive but transient upregulation. Oligodendrocyte degeneration also featured genomic DNA degradation into high molecular weight fragments, which are likely to represent cleaved chromosomal loops. The results demonstrate vulnerability of oligodendrocytes to oxidative stress that induces rapid degeneration and ultimately leads to delayed cell death. This feature is highly relevant to oligodendrocyte damage and depletion following ischemic, traumatic, or inflammatory insults to the central nervous system (CNS).

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.

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.

Increased production of eicosanoids, TXA2, PGI2 and LTC4 in experimental spinal cord injuries

Arachidonate metabolites have many kinds of bioactivities. Thromboxane A2 (TXA2) stimulates platelet aggregation and vasoconstriction, whereas prostaglandin I2 (PGI2) antagonises its activities. Thromboxane B2 (TXB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) are determined in biological materials. Production of TXB2, 6-keto-PGF1 alpha and leukotriene C4 (LTC4), which have potent vascular permeability, was measured by radioimmunoassay in experimental spinal cord injured animals. TXB2 level in the rat spinal cord reached a peak concentration of 133.6 +/- 3.8 pmol/g cord, and 6-keto-PGF1 alpha increased to 26.2 +/- 11.7 pmol/g cord 5 minutes after the injury. There was good correlation between TXB2 production and vascular damage as monitored by fluorescein uptake. When OKY-046 ((E)-3-[4-(1-imidazolylmethyl) phenyl]-2-propenoic acid), which selectively inhibits TXA2 synthetase activity, was administered 10 minutes before injury, the increase in TXB2 production was inhibited by more than 80%, but the degree of vascular damage was reduced by only 40%. In the guinea pig spinal cord, LTC4 levels reached a peak concentration of 2.2 +/- 0.4 pmol/g cord 10 minutes after compression, while that of TXB2 reached 146.8 +/- 6.2 pmol/g cord. The increased production of TXB2 was correlated with the degree of compression injury while that of LTC4 production did not. These findings suggest that vasoactive eicosanoids, TXA2, PGI2 and LTC4, play important roles in secondary damage following spinal cord injury, although their roles may be different among species of animals.

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.

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.

Kininogen and kinin in experimental spinal cord injury

Activation of the kallikrein-kinin system has been implicated in the pathogenesis of vasogenic brain edema and posttraumatic vascular injury. We determined the levels of kininogen and kinin in an experimental spinal cord injury model in the rat. Kininogen content in traumatized cord segments increased in a time-dependent manner. Western blot analysis showed that the kininogen in traumatized cord comigrates with 68K low-molecular-weight kininogen or T-kininogen. Trypsin treatment of the kininogen in traumatized cord released both bradykinin and T-kinin, which were separated by HPLC and quantified with a kinin radioimmunoassay. Endogenous kinin levels in the frozen spinal cord also increased up to 40-fold 2 h after injury as compared with controls. The results demonstrate an increased accumulation of kininogen and its conversion to vasoactive kinins in experimental spinal cord injury.

Edema development and ion changes in rat spinal cord after impact trauma: injury dose-response studies

Changes in the total tissue content of water, sodium, potassium, and magnesium were measured in spinal cord from pentobarbital-anesthetized rats subjected to impact trauma (T9) of varying severity (low, 25 g-cm; moderate, 50 g-cm; severe, 100 g-cm). Laminectomized animals served as controls. Spinal cord samples were taken from rats in the high injury group at 15 min, 60 min, 4 hr, 24 hr, 3 days, or 7 days posttrauma. Samples from the low and moderate injury groups were taken at 24 hr postinjury. In all groups, spinal cord tissue was rapidly removed (less than 30 sec), frozen in liquid N2, and dissected into the injured segment and adjacent two caudal and rostral segments. Severe injury caused significant increases in tissue water content; changes were present at 15 min, peaked at 24 hr, and continued at 3-7 days. Sodium levels were increased at 4 hr and remained elevated for up to 7 days. Potassium levels were decreased at 60 min, remained at low levels for up to 3 days, and partially recovered at 7 days. Tissue magnesium levels were significantly decreased only at 4 hr and 24 hr. Changes in water content and total sodium at 24 hr were not correlated with injury severity. Although potassium decreases did correlate with injury severity, alterations in magnesium levels had a much higher degree of correlation. Thus, reductions in magnesium content may contribute to the development of irreversible tissue damage. In contrast, edema formation after spinal cord trauma may be an epiphenomenon, since it was found to an equal degree in low, moderate, and severe injuries.

Changes in free fatty acids, phospholipids, and cholesterol following impact injury to the rat spinal cord

Free fatty acids (FFA), phospholipid, and cholesterol levels were measured in spinal cord samples from rats subjected to low (25 g-cm), moderate (50 g-cm), or severe (100 g-cm) impact trauma to the T10 spinal segment. All degrees of injury caused early (15 min) declines in total phospholipids after trauma; phospholipid levels remained significantly below controls in rats subjected to moderate and severe injuries for up to 3 days, whereas phospholipids had returned to baseline values by 4 hr in the low injury group. Rapid and persistent decreases in cholesterol levels were observed for all injury groups. Severe trauma was associated with biphasic increases in FFA levels: levels were elevated at 5 and 15 min post-trauma and had declined by 30 min; a second elevation was observed at 1 hr, progressively increasing to reach a maximum at 24 hr, before declining over the next 6 days. Low and moderate injuries caused similar early total FFA increases; later increases were significantly smaller than in the severely injured group. Among the free fatty acids, significant increases were observed in palmitate, stearate, oleate, linoleate, linolenate, arachidonate, and docosahexaenoate. These findings indicate that traumatic spinal cord injury results in early, transient, postinjury membrane phospholipid hydrolysis, the magnitude of which is relatively independent of the severity of injury. More delayed and sustained lipid hydrolysis also occurs after trauma, the magnitude of which is related to the severity of injury.

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 brain injury in the rat: effects on lipid metabolism, tissue magnesium, and water content

Tissue levels of free fatty acids (FFA), total phospholipid, cholesterol, thromboxane B2, water, Na+, K+, and Mg2+ were measured in rat brain after lateral fluid-percussion brain injury of moderate severity (2.0-2.2 atm). Brains of injured animals and sham-operated controls were frozen in situ with liquid N2 at 10 min, 4 h, and 24 h postinjury and removed. The left parietal cortex, which has been shown previously histologically to be the site of maximal injury, was dissected for analysis. Traumatic injury was associated with small increases in FFA levels at 10 min and 4 h and much larger increases at 24 h postinjury. Among the FFA, the largest increases were observed in stearate, arachidonate, and docosahexaenoate. Total phospholipid and cholesterol levels were decreased significantly at all experimental time points. Thromboxane levels were markedly elevated (30-fold) at 10 min posttrauma but substantially declined by 4 h and approached control values at 24 h. Total Mg2+ levels were significantly below control values at 4 h and 24 h posttrauma. No changes in water content were observed at any of these time points. Small decreases in tissue K+ occurred at 4 h; tissue Na+ levels were found to be slightly increased only at 24 h. These results are consistent with the hypothesis that changes in lipid metabolism and Mg2+ content of brain after injury may play a role in the pathophysiology of irreversible, posttraumatic tissue damage. In contrast, significant edema formation does not occur in this model and does not, therefore, appear to be a factor in the injury process.