Effect of difluoromethylornithine treatment on regional ornithine decarboxylase activity and edema formation after experimental brain injury

Delayed administration of alpha-difluoromethylornithine prevents hippocampus-dependent cognitive impairment after single and combined injury in mice

Radiation exposure due to radiological terrorism and military circumstances are a continuing threat for the civilian population. In an uncontrolled radiation event, it is likely that there will be other types of injury involved, including trauma. While radiation combined injury is recognized as an area of great significance, overall there is a paucity of information regarding the mechanisms underlying the interactions between irradiation and other forms of injury, or what countermeasures might be effective in ameliorating such changes. The objective of this study was to determine if difluoromethylornithine (DFMO) could reduce the adverse effects of single or combined injury if administered beginning 24 h after exposure. Eight-week-old C57BL/J6 young-adult male mice received whole-body cesium-137 ((137)Cs) irradiation with 4 Gy. Immediately after irradiation, unilateral traumatic brain injury was induced using a controlled cortical impact system. Forty-four days postirradiation, animals were tested for hippocampus-dependent cognitive performance in the Morris water maze. After cognitive testing, animals were euthanized and their brains snap frozen for immunohistochemical assessment of neuroinflammation (activated microglia) and neurogenesis in the hippocampal dentate gyrus. Our data show that single and combined injuries induced variable degrees of hippocampus-dependent cognitive dysfunction, and when given 24 h post trauma, DFMO treatment ameliorated those effects. Cellular changes including neurogenesis and numbers of activated microglia were generally not associated with the cognitive changes. Further analyses also revealed that DFMO increased hippocampal protein levels of the antioxidants thioredoxin 1 and peroxiredoxin 3 compared to vehicle treated animals. While the mechanisms responsible for the improvement in cognition after DFMO treatment are not yet clear, these results constitute a basis for further development of DFMO as a countermeasure for ameliorating the of risks for cognitive dysfunction in individuals subjected to trauma and radiation combined injury.

The polyamine inhibitor alpha-difluoromethylornithine modulates hippocampus-dependent function after single and combined injuries

Exposure to uncontrolled irradiation in a radiologic terrorism scenario, a natural disaster or a nuclear battlefield, will likely be concomitantly superimposed on other types of injury, such as trauma. In the central nervous system, radiation combined injury (RCI) involving irradiation and traumatic brain injury may have a multifaceted character. This may entail cellular and molecular changes that are associated with cognitive performance, including changes in neurogenesis and the expression of the plasticity-related immediate early gene Arc. Because traumatic stimuli initiate a characteristic early increase in polyamine metabolism, we hypothesized that treatment with the polyamine inhibitor alpha-difluoromethylornithine (DFMO) would reduce the adverse effects of single or combined injury on hippocampus structure and function. Hippocampal dependent cognitive impairments were quantified with the Morris water maze and showed that DFMO effectively reversed cognitive impairments after all injuries, particularly traumatic brain injury. Similar results were seen with respect to the expression of Arc protein, but not neurogenesis. Given that polyamines have been found to modulate inflammatory responses in the brain we also assessed the numbers of total and newly born activated microglia, and found reduced numbers of newly born cells. While the mechanisms responsible for the improvement in cognition after DFMO treatment are not yet clear, the present study provides new and compelling data regarding the potential use of DFMO as a potential countermeasure against the adverse effects of single or combined injury.

Role of peripheral polyamines in the development of inflammatory pain

Polyamines (putrescine, spermidine and spermine) are aliphatic amines that are produced by the action of ornithine decarboxylase (ODC) in a rate-limiting and protein kinase C (PKC)-regulated step. Because high levels of polyamines are found in the synovial fluid of arthritic patients, the aim of the present study was to identify the role of peripherally produced polyamines in a model of inflammatory pain induced by adjuvant. The subcutaneous injection of Complete Freund's adjuvant (CFA, 50 μL/paw) caused the development of mechanical allodynia and edema. Moreover, it increased ODC expression and activity and PKC activation. Administration of the selective ODC inhibitor DFMO (10 μmol/paw) attenuated the development of allodynia and edema and decreased ODC activity in both control and CFA-treated animals. Furthermore, administration of the PKC inhibitor GF109203X (1 nmol/paw) reduced allodynia and ODC activity in animals injected with CFA. A subcutaneous injection of putrescine (10 μmol/paw), spermidine (3-10 μmol/paw) or spermine (0.3-3 μmol/paw) into the rat paw also caused mechanical allodynia and edema. The present results suggest that endogenously synthesized polyamines are involved in the development of nociception and edema caused by an adjuvant. Moreover, polyamine production in inflammatory sites seems to be related to an increase in ODC activity stimulated by PKC activation. Thus, controlling polyamine synthesis and action could be a method of controlling inflammatory pain.

Polyamine catabolism is enhanced after traumatic brain injury

Polyamines spermine and spermidine are highly regulated, ubiquitous aliphatic cations that maintain DNA structure and function as immunomodulators and as antioxidants. Polyamine homeostasis is disrupted after brain injuries, with concomitant generation of toxic metabolites that may contribute to secondary injuries. To test the hypothesis of increased brain polyamine catabolism after traumatic brain injury (TBI), we determined changes in catabolic enzymes and polyamine levels in the rat brain after lateral controlled cortical impact TBI. Spermine oxidase (SMO) catalyzes the degradation of spermine to spermidine, generating H2O2 and aminoaldehydes. Spermidine/spermine-N(1)-acetyltransferase (SSAT) catalyzes acetylation of these polyamines, and both are further oxidized in a reaction that generates putrescine, H2O2, and aminoaldehydes. In a rat cortical impact model of TBI, SSAT mRNA increased subacutely (6-24 h) after TBI in ipsilateral cortex and hippocampus. SMO mRNA levels were elevated late, from 3 to 7 days post-injury. Polyamine catabolism increased as well. Spermine levels were normal at 6 h and decreased slightly at 24 h, but were normal again by 72 h post-injury. Spermidine levels also decreased slightly (6-24 h), then increased by approximately 50% at 72 h post-injury. By contrast, normally low putrescine levels increased up to sixfold (6-72 h) after TBI. Moreover, N-acetylspermidine (but not N-acetylspermine) was detectable (24-72 h) near the site of injury, consistent with increased SSAT activity. None of these changes were seen in the contralateral hemisphere. Immunohistochemical confirmation indicated that SSAT and SMO were expressed throughout the brain. SSAT-immunoreactivity (SSAT-ir) increased in both neuronal and nonneuronal (likely glial) populations ipsilateral to injury. Interestingly, bilateral increases in cortical SSAT-ir neurons occurred at 72 h post-injury, whereas hippocampal changes occurred only ipsilaterally. Prolonged increases in brain polyamine catabolism are the likely cause of loss of homeostasis in this pathway. The potential for simple therapeutic interventions (e.g., polyamine supplementation or inhibition of polyamine oxidation) is an exciting implication of these studies.

Effect of difluoromethylornithine on reperfusion injury after temporary middle cerebral artery occlusion

Polyamines have been shown to play an important role in the disturbance of the blood-brain barrier (BBB) in a number of pathological states including ischemia. BBB disturbances may be almost completely prevented by treating animals with the ornithine decarboxylase (ODC) inhibitor, alpha-difluoromethylornithine (DFMO). DFMO has been also shown to prevent N-Methyl-D-aspartate (NMDA) toxicity in tissue cultures. It has been suggested that the pathological disturbances in polyamine metabolism observed following cerebral ischemia, particularly the post-ischemic increase in putrescine, may contribute to the ischemic injury that is most evident in the CA1 subfield of the hippocampus. In this study, effects of DFMO in cerebral ischemia and reperfusion were examined. The results showed that inhibition of the polyamine system by DFMO decreased ischemic injury volume and brain tissue water content in a dose-dependent manner, without change in vital signs, including systemic arterial blood pressure, arterial partial oxygen pressure, regional cerebral blood flow and body temperature.

Traumatic Cerebral Vascular Injury: The Effects of Concussive Brain Injury on the Cerebral Vasculature

In terms of human suffering, medical expenses, and lost productivity, head injury is one of the major health care problems in the United States, and inadequate cerebral blood flow is an important contributor to mortality and morbidity after traumatic brain injury. Despite the importance of cerebral vascular dysfunction in the pathophysiology of traumatic brain injury, the effects of trauma on the cerebral circulation have been less well studied than the effects of trauma on the brain. Recent research has led to a better understanding of the physiologic, cellular, and molecular components and causes of traumatic cerebral vascular injury. A more thorough understanding of the direct and indirect effects of trauma on the cerebral vasculature will lead to improvements in current treatments of brain trauma as well as to the development of novel and, hopefully, more effective therapeutic strategies.

Effects of delayed administration of (-)-epigallocatechin gallate, a green tea polyphenol on the changes in polyamine levels and neuronal damage after transient forebrain ischemia in gerbils

(-)-Epigallocatechin gallate has a potent antioxidant property and can reduce free radical-induced lipid peroxidation as a green tea polyphenol. In previous study, systemic administration of (-)-epigallocatechin gallate immediately after ischemia has been shown to inhibit the hippocampal neuronal damage in the gerbil model of global ischemia. Polyamines are thought to be important in the generation of brain edema and neuronal cell damage associated with various types of excitatory neurotoxicity. We examined the effects of delayed administration of (-)-epigallocatechin gallate on the changes in polyamine levels and neuronal damage after transient global ischemia in gerbils. To produce transient global ischemia, both common carotid arteries were occluded for 3 min with micro-clips. The gerbils were treated with (-)-epigallocatechin gallate (50 mg/kg, i.p.) at 1 or 3 h after ischemia. The polyamines; putrescine, spermidine, and spermine levels were examined using high performance liquid chromatography in the cerebral cortex and hippocampus 24 h after ischemia. Putrescine levels in the cerebral cortex and hippocampus were increased significantly after ischemia and the delayed administrations of (-)-epigallocatechin gallate (1 or 3 h after ischemia) attenuated the increases. Only minor changes were noted in the spermidine and spermine levels after ischemia. In histology, neuronal injuries in the hippocampal CA1 regions were evaluated quantitatively 5 days after ischemia. (-)-Epigallocatechin gallate administered 1 h or 3 after ischemia significantly reduced hippocampal neuronal damage. The present results show that the delayed administrations of (-)-epigallocatechin gallate inhibit the transient global ischemia-induced increase of putrescine levels in the cerebral cortex and hippocampus. (-)-Epigallocatechin gallate is neuroprotective against neuronal damage even when administered up to 3 h after global ischemia. These findings suggest that (-)-epigallocatechin gallate may be promising in the acute treatment of stroke.

Polyamines and central nervous system injury: spermine and spermidine decrease following transient focal cerebral ischemia in spontaneously hypertensive rats

Polyamines (putrescine, spermidine and spermine) are ubiquitous cellular components, but their specific role in central nervous system (CNS) injury has yet to be characterized. CNS injury results in increased activities of ornithine decarboxylase and spermidine/spermine-N(1)-acetyltransferase, and accumulation of putrescine. The present study determined the polyamine profile in three models of CNS injury, in two different species (gerbil and rat) and two strains of rats (Sprague-Dawley and spontaneously hypertensive): (1) transient focal cerebral ischemia in spontaneously hypertensive rats (SHR); (2) traumatic brain injury in Sprague-Dawley rats; and (3) transient forebrain ischemia in gerbils. While there was a significant increase in putrescine in all three models, spermine and spermidine levels were unaltered in forebrain ischemia and traumatic brain injury. However, transient focal cerebral ischemia shows depletion of spermine and spermidine levels in injured hemisphere compared to contralateral region. Exogenous spermine significantly restored the spermine as well as spermidine levels in the ipsilateral hemisphere after transient focal cerebral ischemia, but did not alter putrescine levels or the ratio of spermidine to spermine. The loss of spermine in particular, may have several consequences that contribute to ischemic injury, including destabilization of chromatin, decreased mitochondrial Ca(2+) buffering capacity, and increased susceptibility to oxidative stress. Based on our and other studies, we propose a tentative antioxidant mechanism of spermine neuroprotection.

Traumatic brain injury: developmental differences in glutamate receptor response and the impact on treatment

Perinatal brain injury following trauma, hypoxia, and/or ischemia represents a substantial cause of pediatric disabilities including mental retardation. Such injuries lead to neuronal cell death through either necrosis or apoptosis. Numerous in vivo and in vitro studies implicate ionotropic (iGluRs) and metabotropic (mGluRs) glutamate receptors in the modulation of such cell death. Expression of glutamate receptors changes as a function of developmental age, with substantial implications for understanding mechanisms of post-injury cell death and its potential treatment. Recent findings suggest that the developing brain is more susceptible to apoptosis after injury and that such caspase mediated cell death may be exacerbated by treatment with N-methyl-D-aspartate receptor antagonists. Moreover, group I metabotropic glutamate receptors appear to have opposite effects on necrotic and apoptotic cell death. Understanding the relative roles of glutamate receptors in post-traumatic or post-ischemic cell death as a function of developmental age may lead to novel targeted approaches to the treatment of pediatric brain injury.

Polyamine metabolism and glutamate receptor agonists-mediated excitotoxicity in the rat brain

Putrescine (PUT) increases have been seen in a range of models of neuropathological disturbances. The present study was designed to compare the ability of various types of glutamate receptor agonist to promote excitotoxic brain damage and to examine whether a PUT increase is a general marker of excitotoxic brain damage. To that end, we evaluated features of brain damage associated with the excitotoxicity induced by both ionotropic glutamate receptor (iGluR) and metabotropic glutamate receptor (mGluR) agonists in the conscious rat and the changes produced in the regulation of polyamine metabolism. Intracerebroventricular infusion of N-methyl-D-aspartate (NMDA; 80 nmol), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA; 15 nmol), kainic acid (KA; 2.3 nmol), (R,S)-3,5-dihydroxyphenylglycine (3,5-DHPG; 1.5 micromol), and (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD; 2 micromol) produced similar seizure incidences (76-84%) in the rat. The convulsant episodes appeared sooner after iGluR (13-22 min) than after mGluR agonists (50-179 min). Histological analysis of the hippocampus 24 hr after seizures indicated several degrees of excitotoxic injury after equiconvulsive doses of the iGluR and mGluR agonists assayed. The agonists can be placed in the following order, according to the degree of damage they produce: AMPA > 3,5-DHPG approximately KA > NMDA > 1S,3R-ACPD. In the frontal cortex, moderate to low levels of damage were observed after all GluR agonists. Both iGluR- and mGluR-induced seizures produced an overshoot in the hippocampal and cortical PUT concentration, whereas spermidine and spermine levels were similar to control. Moreover, a concurrence of increased PUT levels and brain damage was observed, indicating that PUT is a general marker of excitotoxic brain damage.

Role of spermine in amyloid beta-peptide-associated free radical-induced neurotoxicity

The polyamines, relatively low-molecular-weight aliphatic compounds, are the main inducers of eukaryotic cell growth and proliferation. Although polyamine requirements for cell growth are well defined, their role is still enigmatic. We have previously reported that amyloid beta-peptide (A beta), the main constituent of senile plaques in Alzheimer's disease (AD) brain, is toxic to neurons through a free radical-dependent oxidative stress mechanism and that A beta(1--42), the principal form of A beta in AD brain, causes an increase in polyamine metabolism manifested by up-regulated polyamine uptake and increased ornithine decarboxylase (ODC) activity. Both effects were prevented by the free radical scavenger vitamin E. Spermine has been reported to function directly as a free radical scavenger. In the current study, we aimed to address whether up-regulation of polyamine metabolism is a defense against, or a result of, A beta-induced oxidative stress by investigating the capability of spermine to quench A beta-associated free radicals in solution and to assert a protective function of spermine in neuronal culture against A beta. Pretreatment of cultured neurons with spermine prior to A beta exposure failed to prevent A beta-induced cell death. Indeed, A beta plus spermine added to cultured neurons was even more neurotoxic than either agent alone. Additionally, inhibition of the polyamine synthesis by difluoromethylornithine (DFMO) did not protect cells from A beta-induced free radical toxicity, and stimulation of the synthesis of putrescine and spermine by the aminopropyltransferase inhibitor S-adenosyl-1,8-diamino-thiooctane (AdoDATO), rather, further enhanced A beta-induced toxicity. Although spermine is capable of scavenging free radicals generated by A beta in solution as measured by electron paramagnetic resonance (EPR) spectroscopy, the up-regulated transport of exogenously added spermine together with A beta may lead to overaccumulation of a cellular spermine pool, with resulting enhanced neurotoxicity.

Melatonin attenuates the changes in polyamine levels induced by systemic kainate administration in rat brains

Systemically administered kainate has been demonstrated to induce neuronal damage and changes of the levels of biochemical substances related to neurotoxicity. Polyamines are thought to be important in the generation of edema and neuronal cell loss associated with various type of excitotoxicity. Melatonin exerts potent free radical scavenging, antioxidant, and neuroprotective properties. This study was designed to estimate the effect of exogenous melatonin administration on the changes of polyamine levels in rat brains after systemic administration of kainate. Kainate [10 mg/kg, intraperitoneally (i.p.)] was injected into the rats to produce excitotoxicity. Melatonin (15 mg/kg, i.p.) was administered 1 h before, immediately after, and 1 h after kainate treatment. We examined the polyamine [putrescine (PU), spermidine (SD) and spermine (SM)] levels in the cerebral cortex and hippocampus and neuronal density in the hippocampal CA1 and CA3 subsectors in brain sections. PU levels were increased 8 and 24 h after kainate treatment and the administration of melatonin attenuated these changes. Only minor changes were noted in the levels of the polyamine SD and SM after the kainate treatment. In histology, neuronal injuries in the hippocampal CA1 and CA3 subsectors were examined 3 days after kainate treatment and melatonin reduced the kainate-induced neuronal injuries. Our results show that melatonin inhibits the polyamine responses in the cerebral cortex and hippocampus following kainate-induced excitotoxicity and PU may be responsible for the protective effect of melatonin against kainate-induced excitotoxicity.

Spermine is neuroprotective against anoxia and N-methyl-D-aspartate in hippocampal slices

Polyamines were implicated as either neurotoxic or neuroprotective in several models of stroke. Spermine augments the excitotoxicity mediated by the N-methyl-D-aspartate (NMDA) receptor because this receptor is activated at micromolar spermine concentrations. However, at higher concentrations, spermine could be neuroprotective because it blocks the NMDA receptor and voltage-activated Ca(2+) channels. In this work, acute hippocampal slices were exposed to 1 mM spermine and either 10 min of anoxia or 0.5 mM NMDA. The percent recovery of population spikes was the measure of neuroprotection. One millimolar spermine was robustly neuroprotective; however, 0.1 mM spermine and 1 mM putrescine were not. The neuroprotective concentration of spermine was higher than the physiological concentration of free spermine. However, during an excitotoxic episode, extracellular Ca(2+) is decreased, enabling the inhibitory activity of lower spermine concentration. In addition, several noxious stimuli trigger the release of intracellular spermine and could raise local levels of spermine. Therefore, it is possible that spermine has a neuroprotective role in vivo.

Contribution of polyamine oxidase to brain injury after trauma

OBJECT

The possible role of the polyamine interconversion pathway on edema formation, traumatic injury volume, and tissue polyamine levels after traumatic brain injury (TBI) was studied using an inhibitor of the interconversion pathway enzyme, polyamine oxidase.

METHODS

Experimental TBI was induced in Sprague-Dawley rats by using a controlled cortical impact device at a velocity of 3 m/second, resulting in a 2-mm deformation. Immediately after TBI was induced, 100 mg/kg of N1,N4-bis(2,3-butadienyl)-1,4-butanediamine 2HCl (MDL 72527) or saline was injected intraperitoneally. Brain water content and tissue polyamine levels were measured at 24 hours after TBI. Traumatic injury volume was evaluated using 2% cresyl violet solution 7 days after TBI occurred. The MDL 72527 treatment significantly reduced brain edema (80.4+/-0.8% compared with 81.2+/-1.2%, p < 0.05) and injury volume (30.1+/-6.6 mm3 compared with 42.7+/-13.3 mm3, p < 0.05) compared with the saline treatment. The TBI caused a significant increase in tissue putrescine levels at the traumatized site (65.5+/-26.5 nmol/g [corrected] in the cortex and 70.9+/-22.4 nmol/g [corrected] in the hippocampus) compared with the nontraumatized site (7+/-2.4 nmol/g [corrected] in the cortex and 11.4+/-6.4 nmol/g [corrected] in the hippocampus). The increase in putrescine levels in both the traumatized and nontraumatized cortex and hippocampus was reduced by a mean of 60% with MDL 72527 treatment.

CONCLUSIONS

These results demonstrate, for the first time, that the polyamine interconversion pathway has an important role in the increase of putrescine levels after TBI and that the polyamine oxidase inhibitors, blockers of the interconversion pathway, can be neuroprotective against edema formation and necrotic cavitation after TBI.

Novel pharmacologic strategies in the treatment of experimental traumatic brain injury: 1998

The mechanisms underlying secondary or delayed cell death following traumatic brain injury are poorly understood. Recent evidence from experimental models suggests that widespread neuronal loss is progressive and continues in selectively vulnerable brain regions for months to years after the initial insult. The mechanisms underlying delayed cell death are believed to result, in part, from the release or activation of endogenous "autodestructive" pathways induced by the traumatic injury. The development of sophisticated neurochemical, histopathological and molecular techniques to study animal models of TBI have enabled researchers to begin to explore the cellular and genomic pathways that mediate cell damage and death. This new knowledge has stimulated the development of novel therapeutic agents designed to modify gene expression, synthesis, release, receptor or functional activity of these pathological factors with subsequent attenuation of cellular damage and improvement in behavioral function. This article represents a compendium of recent studies suggesting that modification of post-traumatic neurochemical and cellular events with targeted pharmacotherapy can promote functional recovery following traumatic injury to the central nervous system.

Brain lesions and delayed water maze learning deficits after intracerebroventricular spermine

The effects of spermine on the acquisition and retention of spatial learning in the Morris water maze were studied. Spermine 25 and 125 nmol i.c.v. did not alter the ability of rats to find a hidden platform in the water maze when administered before training over 5 days. However, the inhibitory effect of the benzodiazepine, diazepam (3 mg/kg i.p., 30 min prior to training), on path length to target was markedly potentiated by the higher dose of spermine, consistent with spermine acting as a functional antagonist at the NMDA receptor. This drug combination did not affect performance on visible platform trials. Administration of doses of 125 and 250 nmol (but not 62.5 nmol) of spermine i.c.v. in the week prior to training (daily for 5 days) dose-dependently inhibited subsequent learning of a platform position in the absence of drug. These higher doses of spermine produced neuronal loss and increased [3H]PK11195 binding indicating microglial activation predominantly in the hippocampus and to a lesser extent in the striatum, septum, thalamus and amygdala. Spermine 125 nmol i.c.v. (daily for 7 days) also abolished retention of a previously learned platform position when administered in an interval between training and retention testing. The inhibitory effects of spermine 125 nmol i.c.v. (daily for 7 days) on subsequent spatial learning were not antagonised by concomitant administration of 30 nmol dizocilpine. These results demonstrate that spermine produces a delayed neurotoxic effect in particular neuronal populations in the brain that selectively impair spatial learning and recall.

Polyamines and cerebral ischemia

It has been well established that alterations in polyamine metabolism are associated with animal models of global ischemia. Recently, this has been extended to include models of focal ischemia and traumatic brain injury. There is much evidence to support the idea that polyamines may play a multifaceted detrimental role following ischemia reperfusion. Due to the deficit of knowledge about their physiology in the CNS, the link between ischemia-induced alterations in polyamine metabolism and neuronal injury remains to be substantiated. With the recent revelation that polyamines are major intracellular modulators of inward rectifier potassium channels and certain types of NMDA and AMPA receptors, the long wait for the physiologic relevance of these ubiquitous compounds may be in sight. Therefore, it is now conceivable that the alterations in polyamines could have major effects on ion homeostasis in the CNS, especially potassium, and thus account for the observed injury after cerebral ischemia.

Fluorometric assay of nitrite and nitrate in brain tissue after traumatic brain injury and cerebral ischemia

Nitric oxide synthase (NOS) is distributed within the brain, and nitric oxide (NO) is felt to be involved in the pathophysiology of deterioration after head injury and cerebral ischemia. This study determined the levels of the stable end products of NOS (NOx=nitrite+nitrate) after traumatic brain injury (TBI) and transient cerebral ischemia. A fluorometric assay using nitrate reductase and the NADPH regenerating system was used to quantitate NOx in ultrafiltered (10-kDa cutoff) cortical and hippocampal extracts after reduction of nitrate. In TBI rats, both the plasma and tissue showed a sharp increase in NOx levels 5 min after injury. Plasma NOx returned to control levels by 2 h after injury. Ipsilateral-cortex NOx levels returned to control levels approximately 6 h after injury and remained constant from 6-24 h. Contralateral-cortex returned near to control levels after 1 h. Hippocampus also followed a similar trend. In gerbils, there was a significant elevation in tissue NOx levels immediately after 10 min transient cerebral ischemia, which gradually returned to control levels over 24 h reperfusion. This striking burst of NO synthesis immediately after injury is clearly evident whether the injury is head trauma or ischemia, or whether the measurements were performed on tissue or plasma. It is unknown whether endothelial NOS, neuronal NOS, or both caused the elevation of the NO end products seen after the CNS insults.

Increased ornithine decarboxylase activity and protein level in the cortex following traumatic brain injury in rats

There is increasing evidence that the elevated levels of polyamines play an important role in the secondary injury following traumatic brain injury (TBI). Ornithine decarboxylase (ODC) is the rate-limiting enzyme of polyamine biosynthesis. Presently, we measured the ODC protein levels by Western blot analysis in the cerebral cortex of rats sacrificed at 2 h, 6 h, 24 h, 72 h and 168 h after controlled cortical impact injury. TBI resulted in a significant increase in ODC protein levels (2.5 to 5.5 fold, P<0.05) and enzyme activity (13 to 21 fold, p<0.01) between 2 and 6 h after the injury. ODC protein levels and enzyme activity returned to normal, control levels by 72 h after the injury. Increased ODC protein and enzyme activity could contribute to vasogenic edema and the pathogenesis of neuronal dysfunction after TBI by stimulating the formation of polyamines.

Effects of anesthesia on polyamine metabolism and water content in the rat brain

Because variances have been noted in brain putrescine levels of anesthetized rats (control, SHAM-operated), we investigated the effects of several anesthetics on polyamine metabolism and water content in the adult rat brain. Short duration (5 min) anesthesia was studied in three groups: ketamine:xylazine [KX; 40 and 8 mg/kg, respectively, intraperitoneal injection (IP)], urethane (UR; 1.5 g/kg, IP), and isoflurane (IF, initially 3.5% in 100% O2, followed by a maintenance dose of 2.5% IF in 100% O2). Effects of IF at longer duration (30 min) were also studied because this paradigm is often used in our laboratory. Control rats received no anesthesia (NA). Following decapitation, tissue samples were obtained from 3 bilateral brain regions: parietal cortex, motor area (CPm); parietal cortex, somatosensory area (CPs); and the pyriform cortex (CPF). The polyamines, spermidine and spermine, and their precursor, putrescine, were quantified by HPLC-fluorometric detection and brain water content was determined by wet-to-dry weight measures. KX decreased putrescine (54%) and spermidine (20%) in the CPs, increased spermine (24%) in the CPF, and increased water content in all brain regions. UR decreased putrescine (51%) and slightly increased water content (0.7%) in the CPF. Short duration IF decreased putrescine and spermidine in all brain regions; decreased spermine in the CPm, and increased water content in the CPF (0.8%). In contrast, longer duration IF increased putrescine (181%) and spermidine (23%) in the CPm, with no change in water content. Anesthetics produce region-specific changes in putrescine, polyamines, and water content in the rat brain which could contribute to the experimental variability.

Regional brain polyamine levels in permanent focal cerebral ischemia

Transient global cerebral ischemia has been shown to induce marked changes in the polyamine pathway with a significant increase in putrescine, the product of the ornithine decarboxylase reaction. This study examined the relationship between tissue and extracellular polyamines and regional cerebral blood flow and brain edema. Six hours of focal ischemia in cats (n = 10) was produced by permanent middle cerebral artery occlusion. Extracellular polyamines were measured in extracellular fluid obtained by microdialysis. Regional cerebral blood flow using laser Doppler flowmetry and specific gravity, an indicator of brain edema, were measured in contralateral (non-ischemic), penumbra and densely ischemic brain regions. A significant increase in the tissue putrescine level was found in the penumbra but there was no difference in the putrescine levels between contralateral and densely ischemic regions. There was no significant change in the spermidine and spermine levels in the three regions. Extracellular levels of putrescine and spermidine were found to be significantly lower than the tissue levels and no change in polyamines was observed in any region. Significant edema formation was observed in densely ischemic and penumbra regions. This is the first demonstration that tissue putrescine is increased in the penumbra region, an area of incomplete ischemia that is developing brain edema.

Activation of ornithine decarboxylase and accumulation of putrescine after traumatic brain injury

Activation of ornithine decarboxylase (ODC), the initial enzyme in polyamine synthesis, and accumulation of putrescine are thought to mediate pathological processes in the ischemic and traumatized brain. Past studies have separately investigated either ODC or polyamines after head injury. The purpose of the present study was to quantify both ODC activity and polyamines in the rat parietal cortex before and after controlled cortical impact injury. Adult, male rats underwent a right craniectomy and were subjected to a 5 m/sec, 2-mm deformation impact injury. Rats were sacrificed 1, 4, 8, and 24 h postimpact and tissues from the injured (right) and contralateral (left) hemisphere were analyzed for ODC and polyamines. ODC activity was determined by measuring the decarboxylation of [14C]ornithine to putrescine. Putrescine, spermidine, and spermine were determined by high performance liquid chromatography. Cortical impact induced a 10- to 20-fold increase in ODC activity and a 4- to 5-fold increase in putrescine in the ipsilateral cortex. Spermidine and spermine did not significantly increase in the ipsilateral (right) cortex compared to controls (right cortex). In contrast, there was a slight increase in spermidine content in the contralateral (left) cortex after injury. The delayed increase in ODC activity and accumulation of putrescine may mediate pathophysiological changes observed after head injury.