Polyamines can protect against ischemia-induced nerve cell death in gerbil forebrain

Ornithine decarboxylase activity in cerebral post-ischemic reperfusion damage: effect of methionine sulfoximine

Excessive activation of glutamate receptors via the N-methyl-D-aspartate (NMDA) subtype appears to play a role in the sequence of cellular events which lead to irreversible ischemic damage to neurons. Furthermore, NMDA receptor activation induces a stimulation of ornithine decarboxylase (ODC), the rate-limiting enzyme for polyamine (PA) biosynthesis. In order to better understand the role of PA we have measured ODC activity and the effect of methionine sulfoximine (MSO), a molecule able to stimulate ODC, on a model of transient cerebral ischemia. There was a significant increase in ODC activity in the rat cerebral cortex during post-ischemic reperfusion. The treatment with MSO induced a significant decrease in cerebral glutamine synthetase activity accompanied by a marked increase in ODC activity. In MSO-pretreated rats there was a significant decrease in the survival rate when compared to untreated ischemic rats.

Free radical-induced elevation of ornithine decarboxylase activity in developing rat brain slices

OBJECTIVE

In developing brain, we have previously shown both in vivo [L.D. Longo, S. Packianathan, J.A. McQueary, R.B. Stagg, C.V. Byus and C.D. Cain, Acute hypoxia increases ornithine decarboxylase activity and polyamine concentrations in fetal rat brain, Proc. Natl. Acad. Sci. USA, Vol. 90 (1993) 692-696] and in vitro [S. Packianathan, C.D. Cain, B.H. Liwnicz and L.D. Longo, Ornithine decarboxylase activity in vitro in response to acute hypoxia: a novel use of newborn rat brain slices, Brain Res., Vol. 688 (1995) 61-71] that acute hypoxia is associated with a significant increase in ornithine decarboxylase (ODC) activity and polyamine concentrations. We tested the hypothesis that oxygen free radicals induce an increase in ODC activity similar to that of hypoxia and that both this and the hypoxia-induced response are inhibited by free radical scavengers.

MATERIALS AND METHODS

Slices of cerebrum, 300-500 microm thick, were made from P3 newborn Sprague-Dawley rat pups and equilibrated for 1 h in artificial cerebrospinal fluid continuously bubbled with 95% O2/5% CO2. Free radical-induced ODC activity response was measured beginning after a 1-h recovery period. Experiments were performed on slices treated with 5 X 10(-7) M xanthine (X) + 10 mU/ml xanthine oxidase (XO), with or without the free radical scavengers superoxide dismutase (SOD; 100 U/ml), catalase (CAT; 700 U/ml) or glutathione peroxidase (GPX; 3 U/ml). We also quantified slice malonaldehyde concentrations in response to hypoxia (21% O2/5% CO2/74% N2).

RESULTS

Under control conditions, ODC activity was stable during the 2-h post-recovery period. In response to X/XO treatment, ODC activity increased 2.3-fold at 1.5 h post-recovery. In examining ODC activity as a function of xanthine dose, we noted that ODC activity increased in response to 2.5 X 10(-7) M xanthine; however, it decreased in response to 7.5 X 10(-7) M or higher concentrations. Free radical-induced ODC activity was significantly decreased by addition of the free radical scavengers, SOD, CAT or GPX. In addition, the hypoxic-induced increases in ODC activity and malonaldehyde concentration was also eliminated by the addition of SOD with CAT.

CONCLUSIONS

(1) Oxygen free radicals, particularly hydroxyl radical (OH.), appear to trigger an induction of ODC activity in newborn rat cerebrum slices. (2) Oxygen free radicals also appear to mediate the hypoxic-induced increase in ODC activity. (3) Any consequent increase in polyamine synthesis may have profound effects on neurogenesis and neurodifferentiation in the developing brain.

Postischemic, systemic administration of polyamine-modified superoxide dismutase reduces hippocampal CA1 neurodegeneration in rat global cerebral ischemia

Antioxidant enzymes such as superoxide dismutase (SOD) have shown neuroprotective effects in animal models of cerebral ischemia, but only at very high doses. Modifications to increase the plasma half-life or blood-brain barrier (BBB) permeability of SOD have resulted in limited neuroprotective effects. No one has demonstrated neuroprotection with postischemic administration. The specific aim of the present study was to administer systemically a polyamine-modified SOD, having increased BBB permeability and preserved enzymatic activity, following global cerebral ischemia in rats and analyze the effects on the selective vulnerability of CA1 hippocampal neurons. Following 12 min of four-vessel occlusion, global cerebral ischemia, male Wistar rats were dosed (i.v.) with either saline, native SOD (5000 U/kg), polyamine-modified SOD (5000 U/kg), or enzymatically inactive, polyamine-modified SOD (2.1 mg/kg) twice daily for 3 days. Neuroprotective effects on hippocampal CA1 neurons were assessed using standard histological methods. Saline-treated animals had very few remaining CA1 neurons (1.44 +/- 0.60 neurons/reticle; x +/- S.E.M.) compared to sham rats (58.57 +/- 0.69). Native (10.38 +/- 2.96) or inactive, polyamine-modified SOD (7.32 +/- 2.68) did not show significant neuroprotective effects. Polyamine-modified SOD, however, resulted in the survival of significantly more CA1 neurons (24.61 +/- 5.90; P < 0.01). Postischemic, systemic administration of polyamine-modified SOD, having increased BBB permeability and preserved enzymatic activity, significantly reduced hippocampal CA1 neuron loss following global cerebral ischemia. Similar modification of other antioxidant enzymes and neurotrophic factors with polyamines may provide a useful technique for the systemic delivery of therapeutic proteins across the BBB for the treatment of stroke and other neurodegenerative disorders.

Polyamines prevent apoptotic cell death in cultured cerebellar granule neurons

Polyamines play critical roles during the development of brain neurons. In the present study we examined the effects of polyamines on neuronal apoptotic death. Rat cerebellar granule neurons were cultured in the presence of a depolarizing concentration of KCl (25 mM) in the medium. Apoptotic neuronal death was induced by changing the medium to that containing 5.6 mM KCl without serum. Spermine as well as spermidine and putrescine prevented cell death in a concentration-dependent manner with the order of potency being spermine > spermidine > putrescine. The effect of spermine was partially blocked by several NMDA-type glutamate receptor antagonists including (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801). MK-801-sensitive neuroprotection by spermine depended on cell density. Activation of CPP32 (caspase-3/Yama/apopain)-like proteolytic activity, a key mediator of apoptosis, precedes neuronal death, and polyamines prevented an increase in this activity. These results demonstrate that polyamines protect neurons from apoptotic cell death through both NMDA receptor-dependent and -independent mechanisms, acting upstream from the activation of CPP32-like protease(s).

Transgenic rats as models for studying the role of ornithine decarboxylase expression in permanent middle cerebral artery occlusion

BACKGROUND AND PURPOSE

Cerebral ischemia causes activation of ornithine decarboxylase (ODC) gene and subsequent accumulation of putrescine, which might either directly or indirectly affect the outcome of cerebral infarct. We developed a transgenic rat overexpressing human ODC, which was used to explore the effect of abnormally high putrescine concentration in the brain on the infarct volume after permanent middle cerebral artery (MCA) occlusion.

METHODS

The transgenic rats were produced by the pronuclear injection technique with the use of cloned human ODC gene. The right MCA was permanently occluded through craniotomy. ODC activity and polyamines were assayed in the infarcted and contralateral hemispheres. MRI was used to quantify T2 relaxation time, apparent diffusion constant (ADC), and infarct volume, which was also determined by 2,3,5-triphenyltetrazolium chloride.

RESULTS

Permanent MCA occlusion resulted in extensive activation of ODC, which was approximately sevenfold greater than in syngenic animals at 20 hours after occlusion. Consequently, putrescine increased from approximately 10 and 230 pmol/mg to 160 and 410 pmol/mg in the infarcted hemisphere of syngenic and transgenic animals, respectively, but all the other polyamines were unchanged. This high putrescine in the transgenic rats did not influence infarct size evolution, as determined by MRI, T2, ADC, or the infarct volume by 2,3,5-triphenyltetrazolium chloride at 48 hours.

CONCLUSIONS

Data from the ODC transgenic rat model show that the development of brain infarct after permanent MCA occlusion was not influenced by extensive levels of putrescine, indicating that this endogenous amine is not involved in maturation and spread of stroke lesion in vivo. Thus, it seems that ODC activation reflects an endogenous adaptation of neural cells to a noxious stimulus that does not directly influence lesion development.

Beneficial effects of S-adenosyl-L-methionine on blood-brain barrier breakdown and neuronal survival after transient cerebral ischemia in gerbils

We have studied the beneficial effects of S-adenosyl-L-methionine (SAM) tosylate on blood-brain barrier (BBB) breakdown and neuronal survival after transient cerebral ischemia in gerbils. BBB breakdown experiments were performed in pentobarbital anesthetized gerbils subjected to 10 min of bilateral carotid artery occlusion and 6 h of reperfusion. For BBB breakdown measurements, SAM (120 mg/kg, i.p.) was administered to gerbils just after occlusion and thereafter every hour up to 5 h. Fluorometric measurements quantified the blood-brain permeability tracer, Evans blue (EB). SAM treatment significantly reduced the BBB breakdown as indicated by reduced levels of EB fluorescence. Neuronal count experiments were conducted in gerbils subjected to transient ischemia and 7 days of reperfusion. For neuronal count experiments SAM (15-120 mg/kg) was administered at 6 and 12 h after reperfusion, and twice each day thereafter for 7 days. SAM dose dependently protected the hippocampal CA1 neurons assessed by histopathological methods. SAM has a beneficial effect on the outcome of ischemic injury by reducing the BBB breakdown and neuronal death.

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.

Spermine partially normalizes in vivo antioxidant defense potential in certain brain regions in transiently hypoperfused rat brain

Activities of the antioxidant enzymes such as superoxide dismutase (Cu,Zn-SOD), glutathione peroxidase (GSH-Px), glutathione reductase (GSSG-R) as well as the level of reduced glutathione and the concentration of thiobarbituric acid-reactive substance (TBARS) in brain regions in transiently hypoperfused rat brain with or without intravenous infusion of spermine were evaluated. Cerebral hypoperfusion was induced by temporary occlusion of common carotid arteries for 30 min and subsequently, by reperfusion for 60 min. Infusion of spermine reversed the decrease in SOD activity in the cerebral cortex, striatum, hippocampus, hypothalamus and midbrain, and amounted to 50.1 U, 61.5 U, 50.3 U, 30.0 U, 38.0 U, respectively, while GSH-Px restored to normal values only in the cerebral cortex and striatum and amounted to 100 U and 110 U, respectively. During hypoperfusion/reperfusion and after use of spermine no changes in GSSG-R were seen in the hypothalamus and midbrain. The activity of GSSG-R was in accordance with the control for the striatum and amounted to 39.0 IU after using spermine. GSH content returned to normal values in the striatum and midbrain after i.v. use of spermine and amounted to 210 and 240 nmol/g of wet tissue, respectively. In addition, the production of TBARS dropped markedly (P < 0.05) in the hippocampus and midbrain and amounted to 100 and 105 mumol/g of wet tissue, respectively. Partially beneficial effect of spermine could result from the inhibition of free radical generation and capability of chelate formation with iron ions.

Arginine and ornithine decarboxylation in rodent brain: coincidental changes during development and after ischemia

Agmatine, product of arginine decarboxylation, is known to occur mainly in bacteria and plants where it serves as a precursor for the synthesis of polyamines. Recently however, agmatine and arginine decarboxylation were detected in mammalian brain. Here we examined changes in rodent brain arginine decarboxylation during cerebellum development and after global forebrain ischemia and compared them to changes in ornithine decarboxylase, the enzyme catalyzing the first limiting step in polyamine synthesis. The findings suggest that (1) arginine decarboxylation is transiently increased during development and after ischemia in parallel to ornithine decarboxylase activity. (2) Arginine decarboxylation reaction is catalyzed by ornithine decarboxylase. (3) Decarboxylation of both ornithine and arginine becomes more pronounced in membrane fractions, rather than in the cytosol, during brain maturation. (4) During development, ornithine decarboxylase activity is reduced in the cytosol, but increased in the membrane fractions.

Spermidine/spermine N1-acetyltransferase mRNA levels show marked and region-specific changes in the early phase after transient forebrain ischemia

Considerable evidence points to an involvement of natural polyamines (putrescine, spermidine and spermine) in trophic regulation of brain tissue. Spermidine/spermine N1-acetyltransferase is the key enzyme in the interconversion pathway which leads to the formation of spermidine and putrescine from spermine and spermidine, respectively. In the present paper we have studied using in situ hybridization histochemistry the levels of spermidine/spermine N1-acetyltransferase mRNA in the rat central nervous system after transient forebrain ischemia. In the first hours after the insult, a modest increase in spermidine/spermine N1-acetyltransferase mRNA levels was observed in ependymal cells and other non-neuronal cells of all telencephalic and diencephalic regions. In addition, major increases in spermidine/spermine N1-acetyltransferase mRNA levels were observed in regions selectively vulnerable to the ischemic insult, such as striatum, hippocampus and cerebral cortex, during the first day post-reperfusion. The time course and extent of labelling increase were subregion- and cell-specific. At the cellular level, the labelling appeared markedly increased in neurons (8-10 fold in ventromedial striatum and CA1 region) and, to a lesser extent, in non-neuronal cells. The increase in SSAT mRNA levels was not directly related to cell degeneration, as it was detected in both some vulnerable and some resistant cell populations. However, the peak increase of SSAT labelling was precocious in resistant neurons (such as those of ventromedial striatum and dentate gyrus granular layer) and delayed or very limited in vulnerable neurons (such as those of CA1 pyramidal layer and dorsolateral striatum). The increase in spermidine/spermine N1-acetyltransferase may contribute to the increase in putrescine and decrease in spermidine levels observed after ischemia and gives further support to the notion that polyamine metabolism in the early phase after lesion is oriented towards putrescine production. This phenomenon could be relevant in determining the prevalence of neurotrophic vs. neurotoxic effects of polyamines.

Polyamines induce blood-brain barrier disruption and edema formation in the rat

Polyamines (PA) are derived from ornithine by the enzyme ornithine decarboxylase (ODC), which is activated very rapidly as acute and delayed responses to brain ischemia and trauma. Polyamines play a role in the disruption of the blood-brain barrier (BBB) in different pathological states. This study examined the effect of exogenous polyamines, administered intracerebrally (i.c.v.) or intracarotidly on BBB function. Putrescine, spermidine and spermine, given individually, were found to disrupt BBB integrity within 15 min of i.c.v. administration (p = 0.03; p = 0.0013; p = 0.042 vs saline treated rats, respectively). The effect was still evident after 1 h; however, since the saline treated rats also showed increased permeability of Evans blue at this time, there was no statistical difference between polyamines or saline treated rats 1 h post injection. When injected into the carotid artery, rapid increase in BBB permeability was found 1 min after putrescine and spermidine (p < 0.01 vs saline), with a slight decline at 15 min. A slower effect was noticed after spermine administration which reached significance only at 15 min. These results suggest a role for PA as mediators of vasogenic edema formation in the brain soon after brain injuries which induce increased production of these compounds.

Agmatine treatment is neuroprotective in rodent brain injury models

Agmatine is a naturally occurring guanidino compound, found in bacteria and plants, with several proposed nervous system-related functions suggestive of beneficial effects in central nervous system injury. Here evidence is presented that agmatine can exert potent neuroprotection in both in vitro and in vivo rodent models of neurotoxic and ischemic brain injuries. The cumulative evidence lead us to suggest that agmatine, a relatively nontoxic compound, be tried for potential therapeutic use after neurotrauma and in neurodegenerative disorders.

Transgenic animals as models in the study of the neurobiological role of polyamines

Natural polyamines, putrescine, spermidine and spermine, exhibit a number of neurophysiological and metabolic effects in brain preparations. In the in vitro studies, several specific sites of action have been identified such as ion channels, transmitter release and Ca2+ homeostasis. Polyamines have been linked to the development of neuronal degeneration caused by, for instance, epileptic seizures and stroke. The role of endogenous polyamines in the functioning brain is not clear, however. We review the work carried out using state-of-the-art transgenic animal models for polyamine research. A number of transgenic mouse lines carrying human ornithine decarboxylase, spermidine synthase and S-adenosylmethionine decarboxylase gene have been generated. Of these animals those with ornithine decarboxylase transgene show an extensive and constitutive expression of the enzyme in the brain with an exceedingly high putrescine concentration, a phenotype that is not encountered under physiological conditions. In this article we review the neurometabolic, behavioural and histological data that has been obtained from these transgenic mice.

Cerebral energy metabolism and immediate early gene induction following severe incomplete ischaemia in transgenic mice overexpressing the human ornithine decarboxylase gene: evidence that putrescine is not neurotoxic in vivo

Cerebral ischaemia causes activation of ornithine decarboxylase followed by accumulation of putrescine, and these biochemical phenomena have been thought to contribute to the development of neuronal damage. We have used a transgenic mouse line overexpressing the human ornithine decarboxylase gene in their neurons with constitutively high putrescine to study the possible role of putrescine in development of neuronal damage in forebrain ischaemia. An incomplete forebrain ischaemia model was developed in which common carotid arteries were bilaterally occluded and reduction of blood pressure caused by orthostatic reaction was used as a way of decreasing cerebral circulation. Cerebral high-energy metabolites, intracellular pH and lactate were monitored by means of 31P and 1H nuclear magnetic resonance spectroscopy respectively. Incomplete ischaemia for 15 min resulted in severe energy failure, as indicated by an increase in the inorganic phosphate/phosphocreatine ratio, intracellular acidification from a pH of approximately 7.1 to approximately 6.5 and an increase in lactate concentration from < 1 to approximately 10 mmol/kg in both syngenic and transgenic mice. Following deocclusion, recovery of energy metabolites intracellular pH and lactate were identical in both animal groups. Ornithine decarboxylase activity rose 9- and 3-fold in syngenic and transgenic mice respectively 6 h after ischaemia, which was approximately 50-fold greater than the basal level in syngenic mice. In situ hybridization experiments revealed induction of transcription factors c-Fos and zif-268 in the hippocampus, throughout the cerebral cortex and striatum 1-3 h after ischaemia. Messenger RNA of heat shock protein 70 was induced in dentate gyrus and CA3 and CA4 subfields of the hippocampus 1 h after ischaemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Urinary excretion of polyamines in the adult respiratory distress syndrome

Polyamines are low molecular weight polycations that are critically important in cellular proliferation and differentiation. To investigate their potential role in acute lung injury, the polyamines spermidine, spermine, and putrescine were measured in 24-h urine collections from intubated patients with ARDS (n = 12) or congestive heart failure with cardiogenic pulmonary edema (CHF, n = 10) and in normal subjects (n = 10). Mean concentrations of putrescine were similar between groups, but spermidine concentrations in patients with ARDS (52.7 +/- 19.7 nmol/mg creatinine) were significantly higher than in normal subjects (4.9 +/- 0.7 nmol/mg), p < .05. Mean concentrations of spermine in ARDS (270.6 +/- 78.1 nmol/mg) were higher than in CHF (1.0 +/- 0.5 nmol/mg), p < .05, and normal subjects (0.3 +/- 0.1 nmol/mg), p < .05. Concentrations of putrescine increased significantly during the first 7 days of ARDS (241.5 +/- 127.1% above baseline, n = 6), p < .05. Urinary polyamine excretion did not correlate with severity of gas exchange or death. These results are the first to suggest a potential role for polyamines in the pathophysiology of ARDS.

Increased immunostaining for L-ornithine decarboxylase occurs in neocortical neurons of Alzheimer's disease patients

We investigated the distribution of L-ornithine decarboxylase (ODC), an enzyme known to be involved in several developmental and restorative processes, in neocortical brain areas of Alzheimer's disease (AD) and normal patients by means of immunohistochemistry. While ODC immunoreactive material was only scarcely distributed in neocortical neurons of control brains, neocortical specimens from AD brains stood out by intense immunostaining for ODC. Dendrites and, to a lesser extent, axons of neurons from AD brains showed a strong immunoreaction to the enzyme, whereas neurons from non-affected brains displayed only a weak circumnuclear reaction pattern. Our results support the idea that neurorestorative processes take place in AD brains and that the ODC/polyamine system might be actively involved in this process.

Spermidine potentiates dizocilpine-induced impairment of learning performance by rats in a 14-unit T-maze

The NMDA receptor, a ligand-gated ion channel complex, has been reported to be involved in memory processes. Learning is impaired following administration of dizocilpine, a non-competitive antagonist of the NMDA receptor. Polyamines, such as spermine and spermidine, interact with the NMDA receptor to enhance binding of dizocilpine, which blocks the ion channel. The present study assessed action of polyamines as modulators of learning via NMDA receptor activation. Dizocilpine (0.05 mg/kg) was given i.p. before maze learning, at a dose that produced a slight, nonsignificant impairment of maze learning. Pretreatment with 80 mg/kg but not 15 or 40 mg/kg spermidine (i.p.) before dizocilpine impaired maze learning compared to saline controls. Administration of 80 mg/kg spermidine without dizocilpine did not impair maze learning. The results are consistent with the view that systemic injection of a polyamine can modulate learning processes involving the NMDA receptor.

Effects of fructose-1,6-bisphosphate on brain polyamine biosynthesis in a model of transient cerebral ischemia

We evaluated the effects on cerebral ischemia of a treatment with fructose-1,6-bisphosphate, a compound known to possess protective effects on acute ischemic injury in a variety of different tissues. We investigated the ability of the compound, administered either 15 minutes before or 15 minutes after the ischemic insult, in reducing the ischemia-induced changes in polyamine brain levels. The experiments were performed in adult, chloral hydrate-anesthetized Mongolian gerbils that underwent a 15 minutes ligation of the common carotid arteries followed by recirculation. Animals were sacrificed 1, 8 and 24 hours and immediately after the release of the occlusion. Polyamine brain levels were not modified during ischemia. Putrescine began to increase after eight hours from the release of the occlusion and we found it significantly increased after 24 hours in the hippocampus and striatum. We did not detect any significant changes in spermidine brain levels either during ischemia or during recirculation. Conversely, spermine appeared to decrease in the hippocampus while it did not show changes in striatum and medulla-pons. The activity of ornithine decarboxylase, a key enzyme in the biosynthesis of polyamines, resulted enhanced at the end of the ischemic period in all the brain regions tested and showed a peak at eight hours of recirculation in striatum and hippocampus whereas returned to control values in the medulla-pons. Fructose-1,6-bisphosphate significantly reduced the ischemia induced changes in polyamine brain content when administered before the ischemic insult while did not show protective properties when administered post-ischemically.

Ornithine decarboxylase activity in fetal and newborn rat brain: responses to hypoxic and carbon monoxide hypoxia

In response to acute maternal hypoxia, ornithine decarboxylase (ODC) activity increased significantly in fetal rat brain, peaking at 4 h. This was associated with increased ODC mRNA and elevated polyamine concentrations. To correlate this response with development, we measured ODC activity in the rat from gestational day E 17 to postnatal day P 10. We also examined to what extent hypoxia induces increased ODC activity in adult rat brains and whether the response to chronic hypoxia differed from that to acute hypoxia. To test the hypothesis that this increased activity is due to hypoxic hypoxia per se, we subjected pregnant dams to inspired carbon monoxide concentrations ranging from 150 to 1000 ppm and assayed ODC activity in the fetal brain 4 h later. In the fetus, ODC activity was elevated on E 17 in the cerebrum and cerebellum. It declined gradually to about one-tenth E 17 levels by E 21 and remained low thereafter except for a postnatal elevation in the cerebellum on P 3. In response to 10.5% O2, in the 3-day-old rat, ODC activity peaked between 2 and 3 h of hypoxia, increasing 3-fold in the hippocampus and 2-fold in cerebellum. Similar increases were seen in the hypoxic adult rat brain. In inspired oxygen dose-response studies, exposure of P 3 rat pups to 13.25% O2 for 2.5 h produced a 1.5-fold increase in ODC activity; 10.5% O2 produced a 2-3-fold increase while in response to 9% O2, ODC activity remained at baseline levels. With maternal CO-hypoxia, ODC activity increased in the fetal brain at 4 h, as seen with hypoxic-hypoxia. For example, in hippocampus, ODC activity doubled at 500 ppm and tripled at 600 ppm. We conclude: (1) apparently, the ability to respond thus is not lost as the animal ages and may represent an important cellular response to acute hypoxia; (2) the increase in hypoxic-induced ODC activity is relative to the already elevated activity seen from E 17 to E 20; a vast reserve for the induction of fetal ODC activity probably exists and may indicate the importance of this enzyme during this time frame for differentiation and growth promotion; and (3) the CO-hypoxia studies suggest that some aspects of the cellular responses to CO- and hypoxic-hypoxia are similar.

Endogenous ornithine in search for CNS functions and therapeutic applications

The vertebrate brain has the machinery to transport arginine and ornithine, and to form within nerve endings from these amino acids glutamate and GABA, the major excitatory and inhibitory neurotransmitters. Ornithine aminotransferase is a key enzyme of the Arg-->Orn-->Glu-->GABA pathway; the physiological significance of this pathway is still unclear. With 5-fluoromethylornithine, a selective inactivator of ornithine aminotransferase, a tool is in our hands that allows us to study biochemical and behavioral consequences of elevated tissue ornithine concentrations. Increase of the rate of hepatic urea formation, and of ornithine decarboxylation are the most important changes in vertebrates following inactivation of ornithine aminotransferase. Administration of 5-fluoromethylornithine prevented the accumulation of lethal concentrations of ammonia in brain, and ameliorated pathological consequences of thioacetamide intoxication. Inhibition of ornithine catabolism has, therefore, potentials in the therapy of those hyperammonemic states which are characterized by a conditional deficiency of ornithine. The enhancement of polyamine formation due to elevated ornithine concentrations may allow us to favorably affect tissue regeneration following injury.

Elevated seizure threshold and impaired spatial learning in transgenic mice with putrescine overproduction in the brain

We have studied the role of putrescine by using transgenic mouse lines overexpressing the human ornithine decarboxylase gene in most of their tissues. The aberrant expression of the transgene is most strikingly manifested in the brain, leading to an increase of up to 20-fold in putrescine content. We report that the transgenic mice with grossly elevated putrescine in all brain regions analysed (cortex, striatum, hippocampus and cerebellum) showed a significantly elevated seizure threshold to chemical and electrical stimuli, and impaired performance in spatial learning and memory tests. The view that putrescine may be primarily responsible for these changes was supported by the fact that the concentrations of the major neurotransmitter amino acids, glutamate and GABA in the brain, were not changed in the transgenic animals, and by the finding that a further increase in brain putrescine, achieved by inhibition of the catabolism of L-ornithine, appeared to provide additional protection against electroshock-induced seizures. These results suggest that the commonly observed increase in ornithine decarboxylase activity and the massive increase in brain putrescine in connection with neuron damage is a neuroprotective measure rather than a cause of the damage.

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.

Polyamines modulate the neurotoxic effects of NMDA in vivo

The ability of polyamines to alter NMDA-induced neurotoxicity in neonatal rats was examined to determine whether polyamines modulate NMDA receptor activity in vivo. Unilateral injections of NMDA and/or polyamines were made into the striatum of 7-day-old rats. After 5 days, the brains were removed and 20 microns thick coronal sections were cut and stained with Cresyl violet. A computer-based image analysis system was used to densitometrically measure the cross-sectional area of intact tissue in the control and injected hemispheres. Administration of NMDA (5-40 nmol) produced a dose-dependent tissue damage that ranged from 7 to 52% of the area of the uninjected hemisphere. The polyamine agonist spermine (10-500 nmol) dose-dependently exacerbated the toxicity of a 15 nmol dose of NMDA, increasing the size of the lesion by up to 50%. Administration of spermine alone produced dose-dependent tissue damage that ranged from 9 to 52%. The damage produced by both NMDA and spermine could be completely inhibited by co-administration of the NMDA antagonist MK-801. The polyamine inverse agonist 1,10-diaminodecane (DA-10, 50-400 nmol) inhibited the damage produced by NMDA in a dose-dependent manner, with a maximal inhibition of 50%. Administration of DA-10 alone produced limited damage at doses above 100 nmol. The weak partial agonist diethylenetriamine had no effect by itself or on NMDA-induced toxicity at the doses tested. These results indicate that polyamines can modulate the activity of NMDA receptors in vivo and suggest that polyamines or related compounds may have important therapeutic potential as neuroprotective agents.

Casein kinase II activity in the postischemic rat brain increases in brain regions resistant to ischemia and decreases in vulnerable areas

Casein kinase II (CKII) is a protein kinase acting in the intracellular cascade of reactions activated by growth factor receptors, and that has a profound influence on cell proliferation and survival. In this investigation, we studied the changes in the activity and levels of CKII in the rat brain exposed to 10, 15 and 20 min of transient forebrain ischemia followed by variable periods of reperfusion. The cytosolic CKII activity decreased during reperfusion by approximately 30 and approximately 50% in the selectively vulnerable areas, striatum and the CA1 region of the hippocampus, respectively. In the resistant CA3 region of hippocampus and neocortex, the activity increased by approximately 20 and approximately 60%, respectively. The postischemic changes in CKII activity were dependent on the duration of the ischemic insult. The levels of CKII did not change after ischemia, suggesting that the enzyme is modulated by covalent modification or is interacting with an endogenous inhibitor/activator. Treatment of the cytosolic fraction from cortex of rats exposed to ischemia and 1 h of reperfusion with agarose-bound phosphatase decreased the activity of CKII to control levels, suggesting that CKII activation after ischemia involves a phosphorylation of the enzyme. The correlation between postischemic CKII activity and neuronal survival implies that preservation or activation of CKII activity may be important for neuronal survival after cerebral ischemia.

Effects of polyamine synthesis blockade on neuronal loss and astroglial reaction after transient forebrain ischemia

Polyamines and ornithine decarboxylase, the polyamine biosynthetic enzyme, have been demonstrated to increase in the early phase of several types of brain lesion. However, their role in the pathogenesis of tissue damage is still debated. In the present paper the effects of treatments with alpha-difluoromethylornithine, a suicide inhibitor of ornithine decarboxylase, have been investigated in a model of transient forebrain ischemia. Three treatment schedules were used: alpha-difluoromethylornithine treatment was either started 3 hr before and repeated 1 hr after the insult, or started at the time of the insult and continued for 3 or 7 days after post-ischemic reperfusion. The rats were sacrificed 4 hr, 7 or 40 days after reperfusion, respectively. The acute experiment demonstrated that alpha-difluoromethylornithine can reduce the increase of glial fibrillary acid protein immunoreactivity, an early marker of astroglial reaction, in ischemic striatum. Subchronic and chronic alpha-difluoromethylornithine treatments induced a worsening of the morphological outcome of the ischemic lesion. In caudate-putamen a trend for an increase of the area of neuronal loss was present after both treatments. In the hippocampal formation, a significant increase in the severity of neuronal lesion was observed in the mildly lesioned CA3 field. In addition, other alterations of lesioned tissue were observed in alpha-difluoromethylornithine-treated animals, including increases of non-neuronal cells at 7 and especially 40 days post-lesion in striatum and CA3 hippocampal field. In conclusion, present data indicate that ornithine decarboxylase activation after ischemic lesion is a crucial factor for survival of mildly lesioned neurons and proper tissue reaction to the ischemic lesion. The experiment on acute alpha-difluoromethylornithine treatment suggests that these effects may be, at least in part, related to putrescine-induced activation of astroglial cells in the early post-lesion period.

Acute hypoxia increases ornithine decarboxylase activity and polyamine concentrations in fetal rat brain

The cellular responses to hypoxia are poorly understood. To test the hypothesis that ornithine decarboxylase (ODC; L-ornithine carboxy-lyase; EC 4.1.1.17) activity and polyamine concentrations change in response to acute hypoxia, we performed the following studies. Pregnant Sprague-Dawley rats inspired various O2 concentrations (9-21%) for various time periods (0.5-48 h) from days 15 to 21 of gestation. In fetal brains we measured the activity of ODC, ODC mRNA, and polyamines. In response to 4-h acute mild hypoxia, ODC activity in fetal rat brain (cerebrum, cerebellum, and hippocampus) increased to 330-450% from control values (P < 0.001), after which it declined to control levels in 6-8 h. The 4-h ODC response varied inversely with inspired O2 concentration and was not mimicked by beta 2 agonist or blocked by beta 2-antagonist administration. The ODC response was associated with an increase in fetal brain putrescine concentration to 190% above control at 4-6 h (P < 0.01) and an increase in the polyamines spermidine and spermine to about 115% above control at 6-8 h. We also observed that ODC mRNA increased significantly after 2-4 h of hypoxia. ODC activity and polyamine concentrations appear to be useful enzymatic markers for fetal brain hypoxia. The magnitude and time course of the acute hypoxic ODC increase were similar to responses to extracellular signals that result in differentiation or cell growth. Thus, the well-defined and regulated ODC activity response may represent a protective mechanism in brain to hypoxia.

The relevance of glial monoamine oxidase-B and polyamines to the action of selegiline in Parkinson's disease

Dopamine and 2-phenylethylamine levels in striatal tissue are known to be increased after administration of selegiline (L-deprenyl), but it is still difficult to explain why this treatment induces longevity or dopaminergic neuroprotection in Parkinson's disease. In the absence of significant polyamine or diamine oxidase activities in human brain, polyamines and histamine are detoxified by N-acetylation and methylation, respectively. Methylhistamine as well as N-acetylated polyamine derivatives are selective substrates for monoamine oxidase type B (MAO-B). Theoretically at least, MAO-B inhibition by selegiline could result in the increase in the levels of polyamines and their N-acetyl derivatives. This could have significance for the action of selegiline in Parkinson's disease, as overactive corticostriatal glutaminergic function has been implicated in the degeneration of nigrostriatal dopamine neurons, and polyamines are potent modulators of the excitotoxic NMDA (N-methyl-D-aspartate)-glutamate subtype receptor.

Polyamines in rat brain extracellular space after ischemia

This article reports measurements of extracellular polyamines in rat brain. Microdialysis probes were implanted in the striatum and microperfusion samples were collected before, during, and after transient (20 min) global ischemia. Polyamine levels in microperfusates were measured by reverse-phase high-performance liquid chromatography after precolumn derivatization. No significant changes in extracellular polyamines were detected for up to 3 h following ischemia. We conclude that extracellular levels of polyamines (1) are comparable to the low levels in other extracellular compartments, and (2) do not change during the initial period of reperfusion, the period most critical for neuron survival after ischemia.

Accumulation of exogenous polyamines in gerbil brain after ischemia

Regionally selective delayed neuronal degeneration is a characteristic sequel of cerebral ischemia. Recent evidence indicates that changes in brain polyamine metabolism may be critical for nerve cell survival after ischemia. Within hours after ischemia, intracellular putrescine levels are greatly increased and remain elevated for days, whereas only minor changes are noted in the levels of the polyamines spermine and spermidine. In contrast, the extracellular levels of all polyamines are low after ischemia. Injections of polyamines following ischemia, however, can protect neurons in the gerbil brain from delayed cell death, with spermine being the most potent of the polyamines. In the present study, therefore, we sought to determine if increased polyamine uptake occurs in the brain after ischemia. In the hippocampal slice preparation, temperature-dependent uptake was unique for spermine, but not for spermidine or putrescine. Uptake of [14C]spermine was transiently increased after ischemia, peaking at 150% of control by 12-13 h and subsiding by 24 h. Intravenous injections of [3H]spermidine resulted in a postischemic accumulation of this polyamine throughout the forebrain parenchyma. We conclude that: 1. Active cellular uptake of spermine is transiently increased early after ischemia; 2. A nonspecific accumulation of exogenous polyamines occurs early after ischemia probably owing to a compromised blood-brain barrier, and 3. The findings indicate that exogenous polyamines can exert their effect directly in the brain after ischemia.

Mechanisms of drug actions against neuronal damage caused by ischemia--an overview

1. Oxygen and energy deficits induces a cascade of pathological processes which lead to neuronal dysfunction and cell death. 2. The pathogenesis of ischemia-induced neuronal damage includes a disturbed calcium homeostasis, an excessive release of EAA and an enhanced formation of free oxygen radicals. 3. Calcium antagonists inhibit Ca2+ influx into the neuronal cell via VSCC. 4. Glutamate antagonists reduce intracellular Ca2+ concentration by inactivation of NMDA receptor-associated calcium channels (NMDA antagonists) or AMPA/quisqualate receptor-linked sodium channels (non-NMDA antagonists). 5. Furthermore, oxygen radical scavengers can avoid neuronal damage. 6. Agonists of the adenosinergic and serotonergic transmitter systems contribute to neuroprotection by hyperpolarization of the neuronal membrane due to an increase of K+ permeability.

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.

Polyamines in neurotrauma. Ubiquitous molecules in search of a function

In spite of their abundance, the function of PAs in the adult nervous system remains enigmatic. It is postulated that after trauma, the induction of polyamine metabolism (i.e. the polyamine response), which is inherently transient, is an integral part of a protective biochemical program that is essential for neuronal survival. Several functions ascribed to PAs may assume importance in cellular defense. Thus, regulation of the ionic environment, modulation of signal pathways, control of cellular Ca2+ homeostasis, inhibition of lipid peroxidation, and interaction with nucleic acids are all putative sites for PA action. During maturation, the CNS, unlike the peripheral nervous system, undergoes changes which result in the expression of an incomplete polyamine response after trauma. This may be due to an altered pattern of gene expression, and/or restrictive compartmentalization of the PAs and their metabolizing enzymes. Induction of this partial polyamine response after injury results in a sustained accumulation of putrescine, which by itself may be harmful, without the concomitant increase in spermidine and spermine. Administration of exogenous PAs after trauma exerts a neuroprotective effect. Exogenous PAs are postulated to gain access into cells via an induced uptake system after trauma, and function similarly to newly synthesized PAs. Besides the injured neurons themselves, tissues which are connected or associated with these neurons may be potential targets where PAs could act to stimulate neurotrophic factor production. Based on the neuroprotective effects of PAs in laboratory animals and on their proposed role in mechanisms of neuronal survival, the development of PA-based compounds as therapeutic neuroprotective agents should be pursued.

Differing effects of α-difluoromethylornithine and CGP 40116 on polyamine levels and infarct volume in a rat model of focal cerebral ischaemia

Focal cerebral ischaemia was induced in rats by occlusion of the left middle cerebral artery. Two days later, infarct volume was determined by magnetic resonance imaging and the concentrations of the polyamines putrescine (PU), spermine and spermidine by HPLC. In control (occluded) animals, PU levels were elevated in infarcted and non-infarcted areas of the left hemisphere. Treatment with the ornithine decarboxylase (ODC) inhibitor alpha-difluoromethylornithine, prevented the ischaemia-induced increase in tissue PU without affecting infarct volume. Conversely, administration of the N-methyl-D-aspartate (NMDA) receptor antagonist CGP 40116 decreased cortical infarction without changing the tissue content of PU. We conclude that there is no direct link between NMDA receptor activation and brain PU, or PU and post-ischaemic tissue damage, and that inhibitors of ODC are not cerebroprotective in this animal model of stroke.

Polyamines enhance recovery after sciatic nerve trauma in the rat

Spermine, a polyamine, is known to enhance motor functional recovery after a sciatic nerve lesion in the rat. The effect of spermine on the sensory axonal elongation after a sciatic crush was studied with the pinch-test from the sural nerve in the rat. The effect of spermidine, another polyamine, on the motor functional recovery after a trauma was studied by using the toe-spreading ability as an indicator of motor recovery after a sciatic crush in the rat. Spermine enhanced the rate of regeneration of the sensory axons by 16%. Spermidine enhanced the rate of the motor recovery by 30%. These results suggest that not only spermine but also spermidine enhance regeneration of peripheral somatic nerves.

Behavioral sequelae in young rats of acute intermittent antenatal hypoxia

Several studies have examined behavioral sequelae of acute or chronic pre- or postnatal hypoxia. However, few of these tested a large battery of behavioral functions, particularly those following relatively mild, intermittent hypoxia. Also, in few studies were the hypoxic pups cross-fostered or the experimenter blinded as to experimental group. In addition, in almost no studies were concomitant hypoxic-induced brain biochemicals measured. The present study tested the hypotheses that mild, intermittent antenatal hypoxia can lead to long-term alterations in neurobehavioral development, as well as neurochemical changes.

Ornithine decarboxylase in reversible cerebral ischemia: an immunohistochemical study

Anesthetized Mongolian gerbils were subjected to 5-min ischemia and 8 h of recirculation. Vibratom sections were taken for studying changes in ornithine decarboxylase (ODC) immunoreactivity using an antiserum to ODC, and tissue samples were taken for measuring ODC activity. After 5-min ischemia and 8-h recirculation ODC activity increased 11.5-, 5.9-, and 7.9-fold in the cerebral cortex, striatum and hippocampus, respectively (P less than or equal to 0.05 to 0.01). In the cortex, striatum and hippocampus of control animals immunoreactivity was low but clearly above the detection limit. The reaction was confined to neurons. After 5-min ischemia and 8-h recirculation a sharp increase in immunoreactivity was observed confined to neurons, indicating that the postischemic activation of polyamine metabolism is a neuronal response to ischemia. The immunoreactivity was markedly increased in the perinuclear cytoplasm and the dendrites. In the striatum the density of neurons exhibiting a sharp increase in immunoreactivity was more pronounced in the lateral than in the ventral part. In the hippocampus a strong reaction was present in all subfields but the CA1 subfield was particularly affected. The present study demonstrates for the first time that biosynthesis of a protein is markedly activated during the first 24 h of recirculation after 5-min cerebral ischemia of gerbils even in the vulnerable CA1 subfield, in which the overall protein synthesis is sharply reduced at the same time. Studying polyamine metabolism after ischemia may, thus, provide new information about the basic molecular mechanisms responsible for the altered gene expression after metabolic stress.