Regional profile of polyamines in reversible cerebral ischemia of Mongolian gerbils

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.

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.

Effects of MDL 72527, a specific inhibitor of polyamine oxidase, on brain edema, ischemic injury volume, and tissue polyamine levels in rats after temporary middle cerebral artery occlusion

The possible effects of the polyamine interconversion pathway on tissue polyamine levels, brain edema formation, and ischemic injury volume were studied by using a selective irreversible inhibitor, MDL 72527, of the interconversion pathway enzyme, polyamine oxidase. In an intraluminal suture occlusion model of middle cerebral artery in spontaneously hypertensive rats, 100 mg/kg MDL 72527 changed the brain edema formation from 85.7 +/- 0.3 to 84.5 +/- 0.9% in cortex (p < 0.05) and from 79.9 +/- 1.7 to 78.4 +/- 2.0% in subcortex (difference not significant). Ischemic injury volume was reduced by 22% in the cortex (p < 0.05) and 17% in the subcortex (p < 0.05) after inhibition of polyamine oxidase by MDL 72527. There was an increase in tissue putrescine levels together with a decrease in spermine and spermidine levels at the ischemic site compared with the nonischemic site after ischemia-reperfusion injury. The increase in putrescine levels at the ischemic cortical and subcortical region was reduced by a mean of 45% with MDL 72527 treatment. These results suggest that the polyamine interconversion pathway has an important role in the postischemic increase in putrescine levels and that blocking of this pathway can be neuroprotective against neuronal cell damage after temporary focal cerebral ischemia.

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.

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.

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.

The in vitro action of polyamines on rat basilar and femoral artery contractile activity

This study was performed to assess the role of exogenously administered polyamines on rat basilar and femoral artery contractile activity in vitro. With the endothelium removed, rings of tissue were set up in organ chambers to measure isometric tension. The polyamines (0.1-3 mM), putrescine, spermidine, and spermine, were added to the tissue baths; after 30 min of incubation a cumulative concentration response curve (CRC) was obtained with either KCl or serotonin (5-HT). Additional CRCs were run with Ca(2+) in high K+ Krebs (60 mM). In both tissues, the CRCs to KCl were shifted to the right in a dose-dependent manner for spermidine and spermine (1 & 3 mM) but not putrescine. Spermine (3 mM) depressed the KCl maxima by 18.6% and 10.1% in the basilar and femoral artery respectively. For 5-HT CRCs, only spermine (3 mM) slightly inhibited the maximal response in both tissues. The most potent action of spermine was on inhibition of Ca(2+) responses in high K+ where the EC50S were shifted 3.5 and 10 fold over control values in the basilar and femoral respectively. We conclude spermidine and spermine, but not putrescine, attenuate vascular smooth muscle contractions on the basilar and femoral arteries in vitro. The exact nature of the inhibition remains to be fully explored, but blockade of calcium entry through voltage operated Ca channels may play a role. Thus, certain polyamines may affect cerebral perfusion by inhibition of vascular contractility.

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

This study examined the effect of difluoromethylornithine (DFMO) on regional activities of ornithine decarboxylase (ODC) and edema formation in bilateral cerebral cortex and hippocampus after a unilateral controlled cortical-impact (CCI) injury in rats. To measure the activity of ODC, the brains of injured and control rats were frozen in situ at 30 min, 3, 6, and 24 h after CCI brain injury of moderate severity. The specific gravity, an indicator of edema formation, was examined in decapitated animals at corresponding time points. Brain injury induced significant increases of ODC in the ipsilateral hippocampus, adjacent and injury-site cortices, and in the contralateral cortex and hippocampus at 3 and 6 h after injury. No significant edema formation was found in any brain region at 30 min after injury. A significant edema formation was first found only in the injury-site cortex at 3 h after injury. At 6 and 24 h after injury, significant edema was found in all regions ipsilateral to the injury-site. At 24 h after injury, significant but less severe edema was also found in the contralateral cortex and hippocampus. DFMO, an irreversible inhibitor of ODC, abolished the increase in ODC in all regions. It also attenuated edema formation in the adjacent cortex and in the contralateral cortex and hippocampus. These findings indicate that polyamines may play a role in posttraumatic brain edema formation, particularly in important brain regions remote from the injury-site.

Regional activity of ornithine decarboxylase and edema formation after traumatic brain injury

This study examined ornithine decarboxylase (ODC) activity and edema formation bilaterally in brain cortices and hippocampi after lateral controlled cortical-impact injury in rats. To measure the activity of ODC, the brains of injured and control rats were frozen in situ at 30 minutes and at 6, 24, and 72 hours after controlled cortical-impact injury of moderate severity. The specific gravity of these regions was examined in decapitated animals at corresponding time points as an indicator of edema formation. Thirty minutes after injury, ODC activity did not increase in the injury-site cortex and ipsilateral hippocampus. At 6 hours after injury, ODC activity had increased by nine times that of the control in the injury-site cortex, by five times in the adjacent cortex, and by five and one-half times in the ipsilateral hippocampus. Twenty-four hours after injury, ODC activity had increased by three times that of the control in the injury-site cortex and two times in the ipsilateral hippocampus. Seventy-two hours after injury, activity had returned to control levels. ODC activity increased significantly in the contralateral cortex and hippocampus only at 6 and 24 hours. The injury-site and adjacent cortices and the ipsilateral hippocampus showed significant edema at 6, 24, and 72 hours but not at 30 minutes after injury. These findings indicate that polyamine metabolism is significantly altered in traumatic brain injury. The temporal association between ODC activity and edema formation indicates that polyamines might be a contributing factor in edema formation after traumatic brain injury. The delayed induction of ODC after brain injury suggests a potential therapeutic window for future pharmacological intervention to decrease posttraumatic secondary cerebral injury.

Effect of hypoxia and reoxygenation on the activity of transglutaminase in brain of newborn piglets

The transglutaminase activity in five regions of the brain of newborn piglets was measured and the effects of hypoxia and posthypoxic period on this activity evaluated. Enzyme activity was measured in homogenates from cortex, hippocampus, striatum, thalamus and midbrain. The control activities were 7.2, 6.2, 6.0, 5.7 and 4.6 pmol/mg protein/min, respectively. The activities at the end of an 18 min period of hypoxia induced by an FiO2 of 9% were not significantly different from control activities. By 3 h after the hypoxic episode, however, the transglutaminase activities were significantly above control levels in all five regions of the brain. Measurements of the kinetic constants of tranglutaminase indicated that increases in enzyme activity were associated with an increase in Vmax with no significant change in the apparent affinity of the enzyme for the substrate, putrescine. The increased activity of transglutaminase during the posthypoxic period, with no changes immediately after hypoxia, suggest that the increases could be due to increased enzyme synthesis rather than activation of existing enzyme. The rise in transglutaminase activity subsequent to a hypoxic episode may contribute significantly to the long-term disturbances in cellular metabolism in the immature brain induced by hypoxic episodes.

Kainate-induced seizure activity stimulates the polyamine interconversion pathway in rat brain

Systemic injection of kainic acid in adult rat is accompanied by a large increase in the accumulation of acetylated derivatives of spermidine and spermine in the hippocampus and piriform cortex of animals pretreated with the polyamine oxidase inhibitor, MDL 72527. Furthermore, the activity of the enzyme spermine/spermidine acetyltransferase is increased at 8 and 16 h after kainate injection in piriform cortex and hippocampus. These results indicate that the polyamine interconversion pathway is rapidly activated in limbic areas following kainate-induced seizure activity, and suggest that this pathway might participate in the resulting neuronal damage.

Difluoromethylornithine decreases postischemic brain edema and blood-brain barrier breakdown

Brain polyamines have been associated with posttraumatic vasogenic edema and blood-brain barrier (BBB) breakdown seen in some models of brain injury. We hypothesized that the inhibition of the enzyme responsible for polyamine production with the decarboxylase difluoromethylornithine (DFMO) may decrease BBB breakdown after a focal brain ischemic stroke. Thirty-two cats underwent 8 hours of middle cerebral artery occlusion and one of four treatments: sham operation (Sham), ischemia (Isc), ischemia/DFMO (Isc/DF), and ischemia/DFMO/putrescine (Isc/DF/PU). The regional brain specific gravity and the volume of Evans blue (EB) extravasation were measured at the time of death. The groups were monitored for temperature, heart rate, blood pressure, and arterial blood gases, and the values did not differ outside normal physiological ranges. EB results were expressed as the percentage of the hemisphere stained and showed the following: Sham, 2.23%; Isc, 32.8%; Isc/DF, 5.6%; Isc/DF/PU, 36.3%. As a measure of BBB, ischemia increased EB staining; DFMO pretreatment decreased the amount of EB staining to control levels; and the polyamine putrescine abolished the protective effect of DFMO (all significant at P = 0.05). DFMO pretreatment also resulted in a significant (P = 0.05) return to control values for specific gravity in the EB-stained regions (1.0328) of ischemic animals. This effect was present primarily in the white matter. Treatment with DFMO, an ornithine decarboxylase inhibitor, significantly decreased postischemic BBB breakdown and vasogenic edema in this model.

DFMO reduces cortical infarct volume after middle cerebral artery occlusion in the rat

Ornithine decarboxylase (ODC), a key enzyme in polyamine biosynthesis, is induced in ischemic tissue and may mediate vasogenic edema and delayed neuronal death. We determined the effects of alpha-difluoromethylornithine (DFMO), a specific inhibitor of ODC, on infarct size and ODC activity in a rat model of transient focal ischemia. DFMO blocked the ischemia-induced increase in ODC and significantly reduced infarct volumes by 57-45%, depending upon the treatment regimen. These studies suggest that polyamine metabolism plays a role in the development of cerebral infarction after focal ischemia and that DFMO may be useful in limiting injury after a stroke.

Transcriptional activation of ornithine decarboxylase in adult and neonatal hippocampal slices

Ornithine decarboxylase (ODC) is the rate-limiting enzyme in polyamine synthesis and is regulated by both transcription-dependent and transcription-independent mechanisms. We compared the effects of asparagine, an amino acid previously shown to increase ODC activity in adult hippocampal slices, on ODC mRNA and activity in adult and neonatal hippocampal slices. In addition, we evaluated the effects of asparagine on ODC activity following seizure activity elicited by systemic administration of kainic acid (KA) in both adult and neonatal rats. Asparagine produced an increase in ODC gene expression and activity in both adult and neonatal hippocampal slices. The increase in ODC activity elicited by asparagine in hippocampal slices was the same in control animals as in animals sacrificed 16 h after KA-induced seizure activity. The asparagine-elicited increase in ODC activity in neonatal and adult hippocampal slices was blocked by the RNA synthesis inhibitor, actinomycin D. Finally, polyamines produced an inhibition of ODC activity in neonatal hippocampal slices. The results indicate that the regulation of the expression and activity of ODC is similar in neonatal and adult hippocampus.

Alteration of the erythrocyte membrane via enzymatic degradation of ankyrin (band 2.1): subcellular surgery characterized by EPR spectroscopy

A fraction of band 3 protein, the major transmembrane protein of erythrocyte membranes, is held to the cytoskeletal protein spectrin via noncovalent interactions with the protein ankyrin (band 2.1). In this study, trypsin was used under defined conditions to selectively proteolyze ankyrin and thereby destroy the band 3-ankyrin linkage on the cytoplasmic side of erythrocyte ghost membranes. Electron paramagnetic resonance (EPR) spectroscopy, in conjunction with selective spin labeling methods, was used to monitor conformational changes occurring in cytoskeletal proteins or cell-surface carbohydrates as a result of this treatment. Treatment of RBC ghosts with TPCK-trypsin for 5 s at 0 degrees C caused an approx. 56% increase in the relevant EPR parameter of a maleimide spin label bound to spectrin (P < 0.004), indicative of increased segmental motion of the spin label and decreased protein-protein interactions. Analysis of the apparent rotational correlation time parameter tau of a spin label covalently and selectively bound to terminal sialic acid residues of glycophorin showed no significant effect from trypsin treatment. However, tau of spin label covalently and specifically bound to terminal galactose residues of cell-surface glycoconjugates of band 3 and other transmembrane glycoproteins significantly decreased with tryptic uncoupling of the ankyrin linkage (P < 0.005). These results suggest a marked conformational alteration in both cytoskeletal and transmembrane proteins as a result of uncoupling from ankyrin. Spermine (N,N'-bis(3-aminopropyl)tetramethylenediamine), a naturally occurring polyamine known to strengthen cytoskeletal protein-protein interactions (Wyse and Butterfield (1988) Biochim. Biophys. Acta 941, 141-149), was used to partially reverse the trypsin-induced cytoskeletal alterations. Addition of 2 mM spermine to ghosts previously treated with trypsin increased cytoskeletal protein-protein interactions as indicated by EPR (P < 0.002). SDS-PAGE was used to confirm the integrity of spectrin, band 3, and band 4.1 in all experiments. The results are discussed with reference to transmembrane signaling mechanisms and membrane-associated pathologies.

Polyamine metabolism in different pathological states of the brain

Biosynthesis of the polyamines spermidine and spermine and their precursor putrescine is controlled by the activity of the two key enzymes ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC). In the adult brain, polyamine synthesis is activated by a variety of physiological and pathological stimuli, resulting most prominently in an increase in ODC activity and putrescine levels. The sharp rise in putrescine levels observed following severe cellular stress is most probably the result of an increase in ODC activity and decrease in SAMDC activity or an activation of the interconversion of spermidine into putrescine via the enzymes spermidine N-acetyltransferase and polyamine oxidase. Spermidine and spermine levels are usually less affected by stress and are reduced in severely injured areas. Changes of polyamine synthesis and metabolism are most pronounced in those pathological conditions that induce cell injury, such as severe metabolic stress, exposure to neurotoxins or seizure. Putrescine levels correlate closely with the density of cell necrosis. Because of the close relationship between the extent of post-stress changes in polyamine metabolism and density of cellular injury, it has been suggested that polyamines play a role in the manifestation of structural defects. Four different mechanisms of polyamine-dependent cell injury are plausible: (1) an overactivation of calcium fluxes and neurotransmitter release in areas with an overshoot in putrescine formation; (2) disturbances of the calcium homeostasis resulting from an impairment of the calcium buffering capacity of mitochondria in regions in which spermine levels are reduced; (3) an overactivation of the NMDA receptor complex caused by a release of polyamines into the extracellular space during ischemia or after ischemia and prolonged recirculation in the tissue surrounding severely damaged areas; (4) an overproduction of hydrogen peroxide resulting from an activation of the interconversion of spermidine into putrescine via the enzymes spermidine N-acetyltransferase and polyamine oxidase. Insofar as a sharp activation of polyamine synthesis is a common response to a variety of physiological and pathological stimuli, studying stress-induced changes in polyamine synthesis and metabolism may help to elucidate the molecular mechanisms involved in the development of cell injury induced by severe stress.

Immunocytochemical study of an early microglial activation in ischemia

Transient arrest of the cerebral blood circulation results in neuronal cell death in selectively vulnerable regions of the rat brain. To elucidate further the involvement of glial cells in this pathology, we have studied the temporal and spatial distribution pattern of activated microglial cells in several regions of the ischemic rat brain. Transient global ischemia was produced in rats by 30 min of a four-vessel occlusion. Survival times were 1, 3, and 7 days after the ischemic injury. The microglial reaction was studied immunocytochemically using several monoclonal antibodies, e.g., against CR3 complement receptor and major histocompatibility complex (MHC) antigens. Two recently produced monoclonal antibodies against rat microglial cells, designated MUC 101 and 102, were also used to identify microglial cells. Following ischemia, the microglial reaction was correlated with the development of neuronal damage. The earliest presence of activated microglial cells was observed in the dorsolateral striatum, the CA1 area, and the dentate hilus of the dorsal hippocampus. However, the microglial reaction was not confined to areas showing selective neuronal damage, but also occurred in regions that are rather resistant to ischemia, such as the CA3 area. Particularly in the frontoparietal cortex, the appearance of MHC class II-positive microglial cells provided an early indication of the subsequent distribution pattern of neuronal damage. The microglial reaction would thus seem to be an early, sensitive, and reliable marker for the occurrence of neuronal damage in ischemia.

Changes in regional polyamine profiles in rat brains after transient cerebral ischemia (single versus repetitive ischemia): evidence for release of polyamines from injured neurons

Reversible cerebral ischemia (of 5 min, 15 min, or 3-times 5 min) was produced in 14 Mongolian gerbils by occluding both common carotid arteries. After 72 h of recirculation, brains were frozen and processed for measuring regional levels of the polyamines putrescine, spermidine and spermine using HPLC and fluorescent detector. Ischemia induced a marked increase in putrescine levels throughout the brain, most pronounced after 3-times 5 min ischemia (P less than or equal to 0.05 - P less than or equal to 0.001). Spermine levels were significantly reduced, in the hippocampal CA1-subfield after 5 min of ischemia and, in addition, in the striatum and thalamus after 3-times 5 min ischemia. It is suggested that polyamines are released from necrotic neurons and cleared into the blood. Spermine, released from neurons into the extracellular compartment, may bind to the N-methyl-D-aspartate (NMDA) receptor of cells located in close vicinity and may thus render neurons vulnerable to otherwise subtoxic levels of excitotoxins.

Polyamine metabolism in transient focal ischemia of rat brain

Polyamine metabolism was studied in rat brains subjected to 30 min transient cerebral ischemia by measuring the activity of the key enzyme ornithine decarboxylase (ODC) and levels of the polyamines putrescine, spermidine and spermine. A transient increase in ODC activity was apparent after 4 h of recirculation in the ipsilateral cortex and striatum (P less than 0.05). Putrescine levels were significantly increased in the ipsilateral striatum after 4 h of recirculation, and after 24 h of recirculation in both the ipsilateral cortex and striatum. During ischemia spermidine levels were significantly reduced in the ipsilateral hemisphere and spermine levels in the ipsilateral cortex. It is suggested that during ischemia polyamines are released from neurons into the extracellular compartment and cleared into the blood.

Complex interactions between polyamines and calpain-mediated proteolysis in rat brain

Polyamine synthesis is induced by various extracellular signals, and it is widely held that this biochemical response participates in cell growth and differentiation. Certain of the triggers for synthesis in brain tissues also increase the breakdown of high-molecular-weight structural proteins, apparently by activating calcium-dependent proteases (calpains). The present experiments tested the possibility that calpain activity is modulated by polyamines. Spermine, spermidine, and putrescine all increased calcium-dependent proteolysis of [14C]casein by soluble fractions of rat brain. The order of potency was spermine greater than spermidine greater than putrescine, with apparent affinities of 30, 300, and 6,000 microM, respectively. Each of the three polyamines at physiological concentrations also potentiated the calcium-dependent breakdown of two endogenous high-molecular-weight structural proteins known to be substrates of calpain, in both supernatant and membrane fractions. The thiol protease inhibitor leupeptin, a known calpain inhibitor, also inhibited calcium-dependent proteolysis in the presence and absence of polyamines. The polyamines did not increase the activity of purified calpain I or calpain II determined with either [14C]casein or purified spectrin as the substrate, nor did they interfere with the inhibitory effects of calpastatin, an endogenous inhibitor of calpain. However, polyamines potentiated the stimulation of endogenous but not purified calpain activity produced by an endogenous calpain activator. These results suggest a role for polyamines in protein degradation as well as protein synthesis.

Changes in polyamine levels in rat brain after systemic kainic acid administration: relationship to convulsant activity and brain damage

We have examined the effects of systemic kainic acid (KA) administration (9 mg/kg, i.p.) on rat behavior, brain damage, and polyamine levels and the action of the specific ornithine decarboxylase inhibitor alpha-difluoromethylornithine (DFMO) on these effects. KA elicited convulsant activity in 63% of the animals. In the acute convulsant phase (1-3 h after KA), a rapid decline (-39% at 3 h) of spermidine content in frontal cortex was found. After the acute convulsant phase, levels of hippocampal spermidine and spermine were reduced (-70 and -66%, respectively, at 8 h). A dramatic increase of putrescine content (68.1, 1,382, and 336% at 8 h, 24 h, and 9 days, respectively, after KA) was found, associated with histological signs of cortical brain damage (ischemia and necrosis). There was a close relationship between the concentration of putrescine and signs of delayed toxicity (body weight losses) 24 h and 9 days after KA. DFMO partially antagonized the convulsant activity and reduced the increased putrescine levels to approximately 50% of values in KA-treated animals at 24 h but did not change the pattern of histological damage. The role of polyamines in the early and late phases of KA-induced neurotoxicity is discussed.

Cerebral polyamine metabolism in reversible hypoglycemia of rat: relationship to energy metabolites and calcium

Thirty minutes of insulin-induced reversible hypoglycemic coma (defined in terms of cessation of EEG activity) was produced in anesthetized rats. At the end of the hypoglycemic coma or after recovery for 3, 24, or 72 h induced by glucose infusion, the animals were reanesthetized and their brains frozen in situ. Two control groups were used: untreated controls without prior manipulations, and insulin controls, which received injections of insulin followed by glucose infusion to maintain blood glucose within the physiological range. The brains of these latter animals were frozen 3, 24, or 72 h after glucose infusion. Tissue samples from the cortex, striatum, hippocampus, and thalamus were taken to measure ornithine decarboxylase (ODC) activity, and putrescine and spermidine levels, as well as phosphocreatine (PCr), ATP, glucose, and lactate content. In addition, 20-microns thick coronal sections taken from the striatum and dorsal hippocampus were used for histological evaluation of cell damage and also stained for calcium. Insulin in the absence of hypoglycemia produced a significant increase in ODC activity and putrescine level but had no effect on the profiles of energy metabolites or spermidine. During hypoglycemic coma, brain PCr, ATP, glucose, and lactate levels were sharply reduced, as expected. Energy metabolites normalized after 3 h of recovery. In the striatum, significant secondary decreases in PCr and ATP contents and rises in glucose and lactate levels were observed after 24 h of recovery. ODC activity, and putrescine and spermidine levels were unchanged during hypoglycemic coma. After 3 h of recovery, ODC activity increased markedly throughout the brain, except in the striatum. After 24 h of recovery, ODC activity decreased and approached control values 2 days later. Putrescine levels increased significantly throughout the brain after reversible hypoglycemic coma, the highest values observed after 24 h of recovery (p less than or equal to 0.001, compared with controls). After 72 h of recovery, putrescine levels decreased, but still significantly exceeded control values. Reversible hypoglycemic coma did not produce significant changes in regional spermidine levels except in the striatum, where an approximately 30% increase was observed after 3 and 72 h of recovery (p less than or equal to 0.01 and p less than or equal to 0.05, respectively). Twenty-four hours after hypoglycemic coma, intense calcium staining was apparent in layer III of the cerebral cortex, the lateral striatum, and the crest of the dentate gyrus. After 72 h of recovery, the intense calcium staining included also cortical layer II, the septal nuclei, the subiculum, and the hippocampal CA1-subfield.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of N-methyl-D-aspartate and kainate lesions of the rat striatum on striatal ornithine decarboxylase activity and polyamine levels

The intrastriatal injection of N-methyl-D-aspartate (NMDA) (250 nmol) produced a delayed and marked increase in striatal ornithine decarboxylase (ODC) activity and putrescine levels which peaked 6-15 h following the injection of NMDA. Striatal ODC activity subsequently returned to normal values while putrescine levels remained significantly elevated for up to 4 days following the lesion. NMDA produced an early and progressive decline in striatal spermine and spermidine levels, preceding the increase in ODC activity, with a maximum effect 2 h following injection. Spermidine levels returned to normal 6 h post-NMDA infusion, and subsequently increased to above normal levels 36 h and 4 days after the infusion of NMDA. This late increase in striatal spermidine levels paralleled an increase in the binding of the glial cell/macrophage marker [3H]PK 11195. Spermine levels tended to return to normal values 6 h after the injection of NMDA but may be further depressed at later intervals (15 h to 4 days). The intrastriatal injection of saline also resulted in a delayed increase in striatal ODC activity and putrescine levels, but these changes were minor compared to those produced by NMDA. Intrastriatal saline injection provoked no consistent change in striatal spermine or spermidine levels. The changes in polyamine metabolism produced by the intrastriatal injection of kainic acid (4 nmol) were only analysed at 6 and 15 h following injection but were qualitatively similar to those produced by NMDA although perhaps following a slightly more delayed time-course.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential response of rat brain polyamines to convulsant agents

The polyamines putrescine (PUT), spermidine (SD) and spermine (SM) have been studied in rat brain after treatment with several convulsant agents. Kainic acid (10 mg/kg), picrotoxinin (1.5 mg/kg), pentylenetetrazol (60 mg/kg) and lindane (gamma-hexachlorocyclohexane) (60 mg/kg) were given to male Wistar rats. Twenty-four hours later, the animals were sacrificed and their brains removed. Cortical polyamines were analyzed by HPLC with fluorimetric detection of their respective dansyl derivatives, using 1,6-diaminohexane as internal standard for the measurements. Polyamine levels are not affected by short periods of time (30 min) of brain exposure to room temperature before freezing the samples, as compared to a quick procedure (less than 40 s from animal death). Kainic acid induced a 14-fold increase of cortical PUT with respect to control values, leaving unchanged the other polyamines. Lindane also increased cortical PUT (4-fold) without affecting SM or SD. Neither picrotoxinin, nor pentylenetetrazol groups were different from controls for any of the polyamines assayed. The results are discussed in relation to the possible mechanism of action of these convulsant agents and the role of the polyamines in cell injury.

Selective vulnerability in the gerbil hippocampus: morphological changes after 5-min ischemia and long survival times

The morphology of the hippocampus of Mongolian gerbils was investigated by light and electron microscopy after 5-min forebrain ischemia and survival times of up to 10 months. After 3 weeks recirculation only 5.8% of pyramidal neurons of the CA1 (cornu ammonis 1) sector had survived but the thickness of the inner and outer hippocampal layers did not change. After recirculation times of 6 and 10 months the number of surviving neurons declined no further but all layers of the CA1 subfield shrank markedly. Ultrastructurally, many but not all surviving CA1 neurons were altered. After 3 weeks both "dark" and "pale" type neurons were present, while after 6 and 10 months only the "pale" type of injury persisted. Axonal enlargements and myelin breakdown were observed at all survival times up to 10 months of recirculation. The astrocytes of CA1 sector contained numerous glial fibrils which were most pronounced after the longer recirculation times. The stratum radiatum presented intact presynaptic terminals densely packed with an abundance of clear vesicles even after survival of 10 months. Initially, morphologically damaged postsynaptic structures were still attached to these terminals but they disappeared after longer recirculation times. However, even after 10 months some intact synapses were observed involving dendrites which probably originated from surviving CA1 neurons. In CA3 sector and dentate gyrus no ultrastructural changes occurred at any survival time.(ABSTRACT TRUNCATED AT 250 WORDS)

Ornithine decarboxylase activity and putrescine levels in reversible cerebral ischemia of Mongolian gerbils: effect of barbiturate

Reversible cerebral ischemia was produced in anesthetized Mongolian gerbils by occluding both common carotid arteries. After 5 min of ischemia, brains were recirculated for 8 or 24 h. Treated animals received a single intraperitoneal injection of pentobarbital (50 mg/kg) immediately after the aneurysm clips were removed. At the end of the experiments, animals were reanesthetized and their brains frozen in situ. Tissue samples were taken from the cerebral cortex, lateral striatum, CA1 subfield of the hippocampus, thalamus, and cerebellum for measuring ornithine decarboxylase (ODC) activity and putrescine levels. In addition, 20-microns-thick coronal tissue sections were taken from the level of the striatum and stained with hematoxylin/eosin for evaluating the extent of ischemic neuronal necrosis in the lateral striatum. In control animals ODC activity and putrescine levels amounted, respectively, to 0.32 +/- 0.03 nmol/g/h and 10.2 +/- 0.5 nmol/g in the cerebral cortex; 0.34 +/- 0.02 nmol/g/h and 12.8 +/- 0.5 nmol/g in the lateral striatum; 0.58 +/- 0.05 nmol/g/h and 10.5 +/- 0.7 nmol/g in the hippocampal CA1 subfield; 0.35 +/- 0.01 nmol/g/h and 9.8 +/- 0.4 nmol/g in the thalamus; and 0.25 +/- 0.01 nmol/g/h and 8.3 +/- 0.6 nmol/g in the cerebellum. After 5 min cerebral ischemia and 8 h recirculation, a significant 7- to 16-fold increase in ODC activity was observed in all forebrain structures studied. Following 24 h recirculation, ODC activity normalized in the cortex, striatum, and thalamus but was still significantly above control values in the hippocampal CA1 subfield.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of barbiturate treatment on post-ischemic protein biosynthesis in gerbil brain

The effect of barbiturate treatment on post-ischemic cerebral protein biosynthesis was studied in gerbils subjected to 5 min transient occlusion of carotid arteries followed by 2 h or 48 h recirculation. Ischemia induced a remarkable decline of amino acid incorporation into brain proteins in most forebrain structures. The initial inhibition recovered to near normal after 2 days recirculation in all regions except the vulnerable CA1 sector. Barbiturate treatment, which previously has been shown to prevent delayed neuronal death in CA1 sector, did not ameliorate the initial inhibition of protein synthesis but it significantly improved subsequent recovery, especially in the vulnerable CA1 sector of hippocampus. These observations indicate that delayed neuronal death in CA1 sector of hippocampus results from selective failure of post-ischemic recovery and not from selective ischemic injury of the protein synthesizing machinery. This explains that delayed neuronal death can be prevented by therapeutic interventions which are initiated during the post-ischemic recirculation phase.

Polyamine metabolism in reversible cerebral ischemia of Mongolian gerbils

Reversible cerebral ischemia was produced in Mongolian gerbils by occluding both common carotid arteries. Following 5 min of ischemia brains were recirculated for 8, 24, or 96 hr. At the end of the experiments tissue samples were taken from the cerebral cortex and CA1 subfield of the hippocampus for measuring putrescine content and ornithine decarboxylase (ODC) activity. In 5 of 10 animals subjected to 96 hr of recirculation pentobarbital (50 mg/kg) was injected during early recirculation, and the density of ischemic cell damage was determined in the CA1 subfield of the hippocampus in treated and untreated animals. Reversible cerebral ischemia induced a drastic increase in ODC activity after 8 hr of recirculation (about 14-fold in the cortex and 7-fold in the hippocampus), which was markedly reduced following 24 hr of recirculation. Putrescine, in contrast, was high following 8 hr of recirculation and increased even further from 8 to 24 hr of recirculation. Postischemic pentobarbital treatment of animals significantly reduced both the increase in putrescine and the density of ischemic cell damage in the hippocampus. The results are discussed in view of the known activities of putrescine.

Polyamine metabolism in reversible cerebral ischemia: effect of alpha-difluoromethylornithine

Severe forebrain ischemia was produced in rats by occluding both carotid and vertebral arteries. Following 30 min ischemia brains were recirculated for 8 or 24 h. Twelve animals subjected to 8 or 24 h recirculation (n = 6, each group) were given alpha-difluoromethylornithine (DFMO; injected intraperitoneally) immediately before recirculation. At the end of the experiments brains were frozen and samples were taken from the cerebellum, cortex, caudatoputamen and hippocampus. Samples from the left hemisphere were used for measuring ornithine decarboxylase (ODC) activity, and those from the right hemisphere for determining putrescine profiles. During recirculation ODC activity increased markedly in all brain structures, the most pronounced change being in the caudatoputamen after 8 h recirculation. Putrescine increased drastically after 8 h and even more after 24 h recirculation. DFMO-treatment significantly reduced ODC activity after 8 h recirculation and following 24 h recirculation. Putrescine, however, was significantly reduced following 24 h but not after 8 h recirculation. The discrepancy between reduction in ODC activity and putrescine levels in DFMO-treated animals was most prominent in the hippocampus after 8 h recirculation: here DFMO reduced ODC activity to control values without affecting putrescine levels. The results suggest that the observed overshoot in putrescine formation following ischemia is only partly caused by activation of ODC.

Relationship between putrescine content and density of ischemic cell damage in the brain of mongolian gerbils: effect of nimodipine and barbiturate

Twenty mongolian gerbils were anesthetized (1.5% halothane) and severe forebrain ischemia was produced in 15 animals by occluding both common carotid arteries. After 5 min ischemia brains were recirculated spontaneously. Immediately after ischemia nimodipine (1.5 mg/kg) or pentobarbital (50 mg/kg) was injected intraperitoneally into five animals. Four days later animals were reanesthetized (1.5% halothane); the brains were frozen with liquid nitrogen and cut in a cryostat. Ten-micrometer-thick coronal cryostat sections were stained with cresyl violet to assess the extent of ischemic cell damage in the lateral striatum, the CA1-layer of the hippocampus, and the thalamus. In addition, tissue samples (about 4 mg each) were taken from the lateral striatum, CA1 layer of the hippocampus and the thalamus. Putrescine levels were measured in these samples using reversed-phase high performance liquid chromatography and fluorescence detection. Reversible cerebral ischemia produced a significant increase in putrescine in the lateral striatum (from 11.15 +/- 0.79 to 44.83 +/- 11.76 nmol/g, P less than or equal to 0.05), the CA1 subfield of the hippocampus (from 11.27 +/- 0.64 to 41.80 +/- 3.62 nmol/g, P less than or equal to 0.05) and less so in the thalamus (from 11.28 +/- 0.70 to 16.50 +/- 1.71 nmol/g).(ABSTRACT TRUNCATED AT 250 WORDS)