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

Possible Role of Cellular Polyamine Metabolism in Neuronal Apoptosis

Recent studies have shown that cellular levels of polyamines (PAs) are significantly altered in neurodegenerative diseases. Evidence from in vivo animal and in vitro cell experiments suggests that the cellular levels of various PAs may play important roles in the central nervous system through the regulation of oxidative stress, mitochondrial metabolism, cellular immunity, and ion channel functions. Dysfunction of PA metabolism related enzymes also contributes to neuronal injury and cognitive impairment in many neurodegenerative diseases. Therefore, in the current work, evidence was collected to determine the possible associations between cellular levels of PAs, and related enzymes and the development of several neurodegenerative diseases, which could provide a new idea for the treatment of neurodegenerative diseases in the future.

Comparative in-silico analysis of microbial dysbiosis discern potential metabolic link in neurodegenerative diseases

A healthy gut flora contains a diverse and stable commensal group of microorganisms, whereas, in disease conditions, there is a shift toward pathogenic microbes, termed microbial dysbiosis. Many studies associate microbial dysbiosis with neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Multiple sclerosis (MS), and Amyotrophic lateral sclerosis (ALS). Although, an overall comparative analysis of microbes and their metabolic involvement in these diseases is still lacking. In this study, we have performed a comparative analysis of microbial composition changes occurring in these four diseases. Our research showed a high resemblance of microbial dysbiosis signatures between AD, PD, and MS. However, ALS appeared dissimilar. The most common population of microbes to show an increase belonged to the phyla, Bacteroidetes, Actinobacteria, Proteobacteria, and Firmicutes. Although, Bacteroidetes and Firmicutes were the only phyla that showed a decrease in their population. The functional analysis of these dysbiotic microbes showed several potential metabolic links which can be involved in the altered microbiome-gut-brain axis in neurodegenerative diseases. For instance, the microbes with elevated populations lack pathways for synthesizing SCFA acetate and butyrate. Also, these microbes have a high capacity for producing L-glutamate, an excitatory neurotransmitter and precursor of GABA. Contrastingly, Tryptophan and histamine have a lower representation in the annotated genome of elevated microbes. Finally, the neuroprotective compound spermidine was less represented in elevated microbes' genomes. Our study provides a comprehensive catalog of potential dysbiotic microbes and their metabolic involvement in neurodegenerative disorders, including AD, PD, MS, and ALS.

Differential regulation of degradation and immune pathways underlies adaptation of the ectosymbiotic nematode Laxus oneistus to oxic-anoxic interfaces

Eukaryotes may experience oxygen deprivation under both physiological and pathological conditions. Because oxygen shortage leads to a reduction in cellular energy production, all eukaryotes studied so far conserve energy by suppressing their metabolism. However, the molecular physiology of animals that naturally and repeatedly experience anoxia is underexplored. One such animal is the marine nematode Laxus oneistus. It thrives, invariably coated by its sulfur-oxidizing symbiont Candidatus Thiosymbion oneisti, in anoxic sulfidic or hypoxic sand. Here, transcriptomics and proteomics showed that, whether in anoxia or not, L. oneistus mostly expressed genes involved in ubiquitination, energy generation, oxidative stress response, immune response, development, and translation. Importantly, ubiquitination genes were also highly expressed when the nematode was subjected to anoxic sulfidic conditions, together with genes involved in autophagy, detoxification and ribosome biogenesis. We hypothesize that these degradation pathways were induced to recycle damaged cellular components (mitochondria) and misfolded proteins into nutrients. Remarkably, when L. oneistus was subjected to anoxic sulfidic conditions, lectin and mucin genes were also upregulated, potentially to promote the attachment of its thiotrophic symbiont. Furthermore, the nematode appeared to survive oxygen deprivation by using an alternative electron carrier (rhodoquinone) and acceptor (fumarate), to rewire the electron transfer chain. On the other hand, under hypoxia, genes involved in costly processes (e.g., amino acid biosynthesis, development, feeding, mating) were upregulated, together with the worm's Toll-like innate immunity pathway and several immune effectors (e.g., bactericidal/permeability-increasing proteins, fungicides). In conclusion, we hypothesize that, in anoxic sulfidic sand, L. oneistus upregulates degradation processes, rewires the oxidative phosphorylation and reinforces its coat of bacterial sulfur-oxidizers. In upper sand layers, instead, it appears to produce broad-range antimicrobials and to exploit oxygen for biosynthesis and development.

Alzheimer's disease as a chronic maladaptive polyamine stress response

Polyamines are nitrogen-rich polycationic ubiquitous bioactive molecules with diverse evolutionary-conserved functions. Their activity interferes with numerous genes' expression resulting in cell proliferation and signaling modulation. The intracellular levels of polyamines are precisely controlled by an evolutionary-conserved machinery. Their transient synthesis is induced by heat stress, radiation, and other traumatic stimuli in a process termed the polyamine stress response (PSR). Notably, polyamine levels decline gradually with age; and external supplementation improves lifespan in model organisms. This corresponds to cytoprotective and reactive oxygen species scavenging properties of polyamines. Paradoxically, age-associated neurodegenerative disorders are characterized by upsurge in polyamines levels, indicating polyamine pleiotropic, adaptive, and pathogenic roles. Specifically, arginase overactivation and arginine brain deprivation have been shown to play an important role in Alzheimer's disease (AD) pathogenesis. Here, we assert that a universal short-term PSR associated with acute stimuli is beneficial for survival. However, it becomes detrimental and maladaptive following chronic noxious stimuli, especially in an aging organism. Furthermore, we regard cellular senescence as an adaptive response to stress and suggest that PSR plays a central role in age-related neurodegenerative diseases' pathogenesis. Our perspective on AD proposes an inclusive reassessment of the causal relationships between the classical hallmarks and clinical manifestation. Consequently, we offer a novel treatment strategy predicated upon this view and suggest fine-tuning of arginase activity with natural inhibitors to preclude or halt the development of AD-related dementia.

RNA-seq analysis and compound screening highlight multiple signalling pathways regulating secondary cell death after acute CNS injury in vivo

Understanding the molecular mechanisms that regulate secondary cell death after acute central nervous system (CNS) injury is critical for the development of effective neuroprotective drugs. Previous research has shown that neurotoxic processes including excitotoxicity, oxidative stress and neuroinflammation can cause secondary cell death. Nevertheless, clinical trials targeting these processes have been largely unsuccessful, suggesting that the signalling pathways underlying secondary cell death remain incompletely understood. Due to their suitability for live imaging and their amenability to genetic and pharmacological manipulation, larval zebrafish provide an ideal platform for studying the regulation of secondary cell death in vivo Here, we use RNA-seq gene expression profiling and compound screening to identify signalling pathways that regulate secondary cell death after acute neural injury in larval zebrafish. RNA-seq analysis of genes upregulated in cephalic mpeg1⁺ macrophage-lineage cells isolated from mpeg1:GFP transgenic larvae after neural injury suggested an involvement of cytokine and polyamine signalling in secondary cell death. Furthermore, screening a library of FDA approved compounds indicated roles for GABA, serotonin and dopamine signalling. Overall, our results highlight multiple signalling pathways that regulate secondary cell death in vivo, and thus provide a starting point for the development of novel neuroprotective treatments for patients with CNS injury.This article has an associated First Person interview with the two first authors of the paper.

Multimodal Imaging of Amyloid Plaques: Fusion of the Single-Probe Mass Spectrometry Image and Fluorescence Microscopy Image

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases. The formation of amyloid plaques by aggregated amyloid beta (Aβ) peptides is a primary event in AD pathology. Understanding the metabolomic features and related pathways is critical for studying plaque-related pathological events (e.g., cell death and neuron dysfunction). Mass spectrometry imaging (MSI), due to its high sensitivity and ability to obtain the spatial distribution of metabolites, has been applied to AD studies. However, limited studies of metabolites in amyloid plaques have been performed due to the drawbacks of the commonly used techniques such as matrix-assisted laser desorption/ionization MSI. In the current study, we obtained high spatial resolution (∼17 μm) MS images of the AD mouse brain using the Single-probe, a microscale sampling and ionization device, coupled to a mass spectrometer under ambient conditions. The adjacent slices were used to obtain fluorescence microscopy images to locate amyloid plaques. The MS image and the fluorescence microscopy image were fused to spatially correlate histological protein hallmarks with metabolomic features. The fused images produced significantly improved spatial resolution (∼5 μm), allowing for the determination of fine structures in MS images and metabolomic biomarkers representing amyloid plaques.

The Biology of Glial Cells and Their Complex Roles in Alzheimer's Disease: New Opportunities in Therapy

Even though Alzheimer's disease (AD) is of significant interest to the scientific community, its pathogenesis is very complicated and not well-understood. A great deal of progress has been made in AD research recently and with the advent of these new insights more therapeutic benefits may be identified that could help patients around the world. Much of the research in AD thus far has been very neuron-oriented; however, recent studies suggest that glial cells, i.e., microglia, astrocytes, oligodendrocytes, and oligodendrocyte progenitor cells (NG2 glia), are linked to the pathogenesis of AD and may offer several potential therapeutic targets against AD. In addition to a number of other functions, glial cells are responsible for maintaining homeostasis (i.e., concentration of ions, neurotransmitters, etc.) within the central nervous system (CNS) and are crucial to the structural integrity of neurons. This review explores the: (i) role of glial cells in AD pathogenesis; (ii) complex functionalities of the components involved; and (iii) potential therapeutic targets that could eventually lead to a better quality of life for AD patients.

Effects of spermine and the passive avoidance learning (PAL) following cerebral ischemia in chicks: Association with neuroprotection of pyramidal cells

The aim of this study is to investigate the effects of spermine and the passive avoidance learning on hippocampus following transient cerebral ischemia in the chicks. The study is composed of the pure control (CG), sham (SG) and experimental groups (n=20). Experimental groups (ischemia group, IG and ischemia-spermine group, ISG) were exposed to ischemia for 20min whereas the SG was exposed to sham operation and CG group was not exposed to any operation. Passive avoidance learning (PAL) was applied to the half number of the subjects in each group. Both before and after 7days from the ischemia, operated animals were taken to PAL and then they were sacrificed. Total numbers of neurons in the hippocampus were stereologically estimated using Cresyl violet stained sections. We detected that number of neurons was increased following PAL and especially spermine treatment. According to our results, we suggested that spermine may reduce the deleterious effects of the ischemia by causing to increase in the neuronal number and so, it may be slightly supportive to the PAL.

Spermidine is protective against kidney ischemia and reperfusion injury through inhibiting DNA nitration and PARP1 activation

Kidney ischemia and reperfusion injury (IRI) is associated with a high mortality rate, which is attributed to tubular oxidative and nitrative stresses; however, an effective approach to limit IRI remains elusive. Spermidine, a naturally occurring polyamine, protects yeast cells against aging through the inhibition of oxidative stress and necrosis. In the present study, spermidine supplementation markedly attenuated histological damage and kidney dysfunction during IRI. In addition, exogenous spermidine potently inhibited poly(ADP-ribose) polymerase 1 (PARP1) activation and DNA nitrative/oxidative stress following IRI. Conversely, inhibition of ornithine decarboxylase (ODC) via siRNA transfection in vivo significantly enhanced DNA nitration, PARP1 activation, and functional damage during IRI. Finally, in ODC knockdown kidneys, PARP1 inhibition attenuated histological and functional damage induced by IRI, but not DNA nitrative stress. In conclusion, these data suggest that spermidine protects kidneys against IRI through blocking DNA nitration and PARP1 activation and this finding provides a novel target for prevention of acute kidney injury including IRI.

The role of glia in stress: polyamines and brain disorders

This review focuses on the roles of glia and polyamines (PAs) in brain function and dysfunction, highlighting how PAs are one of the principal differences between glia and neurons. The novel role of PAs, such as putrescine, spermidine, and spermine and their precursors and derivatives, is discussed. However, PAs have not yet been a focus of much glial research. They affect many neuronal and glial receptors, channels, and transporters. They are therefore key elements in the development of many diseases and syndromes, thus forming the rationale for PA-focused and glia-focused therapy for these conditions.

SP-8203 shows neuroprotective effects and improves cognitive impairment in ischemic brain injury through NMDA receptor

The extracts of earth worms, Eisenia andrei, have been used as a therapeutic agent for stroke in the traditional medicine. It is also reported that the protease fraction separated from the extracts has strong anti-thrombotic activity. Besides anti-thrombotic actions, we found that SP-8203, N-[3-(2,4-dioxo-1,4-dihydro-2H-quinazolin-3-yl)propyl]-N-{4-[3-(2,4-dioxo-1,4-dihydro-2H-quinazolin-3-yl)propylamino]butyl}acetamide, derived from the extracts of earth worms blocked N-methyl-(D)-aspartate (NMDA) receptor-mediated excitotoxicity in a competitive manner. The neuroprotective effects of SP-8203 were attributable to prevention of Ca(2+) influx through NMDA receptors. The systemic administration of SP-8203 markedly reduced neuronal death following middle cerebral artery occlusion in rats. SP-8203 significantly improved spatial learning and memory in the water maze test. These results provided strong pharmacological basis for its potential therapeutic roles in cerebral ischemia.

Genetic and epigenetic influences on expression of spermine synthase and spermine oxidase in suicide completers

Alterations in the levels of spermine synthase (SMS) and spermine oxidase (SMOX), two enzymes involved in polyamine metabolism, have previously been observed in brains of suicide completers. To characterize the roles played by genetic and epigenetic factors in determining expression levels of these genes, as well as to identify potential mechanisms by which to explain our findings in suicide completers, we (1) assessed the role of promoter polymorphisms in determining expression in the brain and in vitro, and (2) examined CpG methylation and levels of methylated histone H3 lysine-27 in the promoter regions of these genes in the prefrontal cortex of suicide completers and healthy controls. We identified several promoter haplotypes in SMS and SMOX, but found no consistent effects of haplotype on expression levels in either the brain or in reporter gene assays performed in three different cell lines. We also found no overall effects of epigenetic factors in determining expression, with the exception of a relationship between CpG methylation at one site in the promoter of SMOX and its expression in Brodmann area 8/9. In conclusion, the genetic and epigenetic factors examined in this study show little influence on the expression levels of SMS and SMOX, and do not appear to be responsible for the dysregulated expression of these genes in suicide completers.

Complex rectification of Müller cell Kir currents

Although Kir4.1 channels are the major inwardly rectifying channels in glial cells and are widely accepted to support K+- and glutamate-uptake in the nervous system, the properties of Kir4.1 channels during vital changes of K+ and polyamines remain poorly understood. Therefore, the present study examined the voltage-dependence of K+ conductance with varying physiological and pathophysiological external [K+] and intrapipette spermine ([SP]) concentrations in Müller glial cells and in tsA201 cells expressing recombinant Kir4.1 channels. Two different types of [SP] block were characterized: "fast" and "slow." Fast block was steeply voltage-dependent, with only a low sensitivity to spermine and strong dependence on extracellular potassium concentration, [K+]o. Slow block had a strong voltage sensitivity that begins closer to resting membrane potential and was essentially [K+]o-independent, but with a higher spermine- and [K+]i-sensitivity. Using a modified Woodhull model and fitting i/V curves from whole cell recordings, we have calculated free [SP](in) in Müller glial cells as 0.81 +/- 0.24 mM. This is much higher than has been estimated previously in neurons. Biphasic block properties underlie a significantly varying extent of rectification with [K+] and [SP]. While confirming similar properties of glial Kir and recombinant Kir4.1, the results also suggest mechanisms underlying K+ buffering in glial cells: When [K+]o is rapidly increased, as would occur during neuronal excitation, "fast block" would be relieved, promoting potassium influx to glial cells. Increase in [K+]in would then lead to relief of "slow block," further promoting K+-influx.

Structural and functional recovery elicited by combined putrescine and aminoguanidine treatment after aspirative lesion of the fimbria-fornix and overlying cortex in the adult rat

Damage to the adult CNS often causes permanent deficits. Based on a lesion model of septohippocampal pathway aspiration in the rat, we attempted to promote neuronal cell survival and post-traumatic recovery by using a pharmacological treatment combining aminoguanidine and putrescine (AGP). The functional recovery was followed over 15 weeks before morphological analysis. AGP treatment produced a persistent attenuation (approximately 50%) of the lesion-induced hyperactivity, a reduction (approximately 60%) in the sensorimotor impairments and an improved performance in the water-maze task which did not, however, rely upon improved memory capabilities. AGP weakened the lesion-induced decrease in ChAT-positive neurons in the medial septum and the extent of thalamic retrograde necrosis (by approximately 30% in each case) and resulted in a partial cholinergic reinnervation of the dentate gyrus. These promising results support the idea that coadministration of putrescine and aminoguanidine might become a potent way to foster structural and functional recovery (or compensation) in the adult mammalian CNS after injury.

Polyamine and aminoguanidine treatments to promote structural and functional recovery in the adult mammalian brain after injury: a brief literature review and preliminary data about their combined administration

The regeneration potential of the adult mammalian central nervous system (CNS) is very modest, due to, among other factors, the presence of either a glial scar, or myelin-associated regeneration inhibitors such as Nogo-A, MAG and OMgp, which all interact with the same receptor (NgR). After a brief review of the key proteins (Rho and PKC) implicated in NgR-mediated signalling cascades, we will tackle the implications of cAMP and Arginase I in overcoming myelin growth-inhibitory influence, and then will focus on the effects of polyamines and aminoguanidine to propose (and to briefly support this proposal by our own preliminary data) that their association might be a potent way to enable functionally-relevant regeneration in the adult mammalian CNS.

Altered subcellular localization of ornithine decarboxylase in Alzheimer's disease brain

The amyloid precursor protein can through ligand-mimicking induce expression of ornithine decarboxylase (ODC), the initial and rate-limiting enzyme in polyamine biosynthesis. We report here the regional distribution and cellular localization of ODC immunoreactivity in Alzheimer's disease (AD) brains. In frontal cortex and hippocampus of control cases, the most pronounced ODC immunoreactivity was found in the nucleus. In possible and definite AD the immunoreactivity had shifted to the cytoplasm. In cerebellum of control cases, ODC staining was found in a small portion of Purkinje cells, mostly in the nucleus. In AD, both possible and definite, the number of stained Purkinje cells increased significantly and immunoreactivity was shifted to the cytoplasm, even though it was still prominent in the nucleus. In conclusion, our study reveals an early shift of the ODC immunoreactivity in AD from the nuclear compartment towards the cytoplasm.

Gene profiling the response to kainic acid induced seizures

Kainic acid activates non-N-methyl-d-aspartate (NMDA) glutamate receptors where it increases synaptic activity resulting in seizures, neurodegeneration, and remodeling. We performed microarray analysis on rat hippocampal tissue following kainic acid treatment in order to study the signaling mechanisms underlying these diverse processes in an attempt to increase our current understanding of mechanisms contributing to such fundamental processes as neuronal protection and neuronal plasticity. The kainic acid-treated rats used in our array experiments demonstrated severe seizure behavior that was also accompanied by neuronal degeneration which is suggested by fluoro-jade B staining and anti-caspase-3 immunohistochemistry. The gene profile revealed 36 novel kainic acid regulated genes along with additional genes previously reported. The functional roles of these novel genes are discussed. These genes mainly have roles in transcription and to a lesser extent have roles in cell death, extracellular matrix remodeling, cell cycle progression, neuroprotection, angiogenesis, and synaptic signaling. Gene regulation was confirmed via quantitative real time polymerase chain reaction and in situ hybridization.

The role of antioxidants in models of inflammation: Emphasis on l-arginine and arachidonic acid metabolism

Inflammatory processes are made up of a multitude of complex cascades. Under physiological conditions these processes aid in tissue repair. However, under pathophysiological environments, such as wound healing and hypoxia-ischaemia (HI), inflammatory mediators become imbalanced, resulting in tissue destruction. This review addresses the changes in reactive oxygen species (ROS), L-arginine and arachidonic acid metabolism in wound healing and HI and subsequent treatments with promising anti-oxidants. Even though these models may appear divergent, anti-oxidant treatments are nevertheless still having favourable effects. On the basis of recent findings, it is apparent that protection with anti-oxidants is not solely attributed to scavenging of ROS. In addition, the actions of anti-oxidants must be considered in light of the inflammatory process being assessed. To this end, there does not appear to be any universally applicable single mechanism to explain the actions of anti-oxidants.

The neuroprotective effects of N1-dansyl-spermine in the gerbil model of cerebral ischaemia

The effects of N1-dansyl-spermine, a polyamine antagonist, and ifenprodil, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, were investigated in the gerbil model of global cerebral ischaemia. Transient forebrain ischaemia was induced by 5-min bilateral occlusion of the common carotid arteries. N1-dansyl-spermine (2, 5 and 10 mg/kg) and ifenprodil (30 mg/kg) were administered intraperitoneally 30 min after bilateral carotid artery occlusion. On histological examination, 4 days (96 h) after ischaemia, there was a significant decrease in neuronal density of the hippocampal CA1 subfield. This reduction in neuronal density was attenuated in those animals treated with the 5 or 10 mg/kg dose of N1-dansyl-spermine and those treated with 30 mg/kg ifenprodil. However, unlike ifenprodil, N1-dansyl-spermine failed to attenuate the ischaemia-induced increase in locomotor activity. This demonstrates that polyamines play a significant role in the neuronal damage produced after cerebral ischaemia, while casting doubt on the suggestion that increased locomotor activity correlates with CA1 pyramidal cell damage.

Neuroprotective effects of spermine following hypoxia‐ischemia‐induced brain damage: A mechanistic study

The polyamines (spermine, putrescine, and spermidine) can have neurotoxic or neuroprotective properties in models of neurodegeneration. However, assessment in a model of hypoxia-ischemia (HI) has not been defined. Furthermore, the putative mechanisms of neuroprotection have not been elucidated. Therefore, the present study examined the effects of the polyamines in a rat pup model of HI and determined effects on key enzymes involved in inflammation, namely, nitric oxide synthase (NOS) and arginase. In addition, effects on mitochondrial function were investigated. The polyamines or saline were administered i.p. at 10mg/kg/day for 6 days post-HI. Histological assessment 7 days post-HI revealed that only spermine significantly (P<0.01) reduced infarct size from 46.14 +/- 10.4 mm3 (HI + saline) to 4.9 +/- 2.7 mm3. NOS activity was significantly increased following spermine treatment in the left (ligated) hemisphere compared with nonintervention controls (P<0.01) and HI + saline (P<0.05). In contrast, spermine decreased arginase activity compared with HI + saline but was still significantly elevated in comparison to nonintervention controls (P<0.01). Assessment of mitochondrial function in the HI + saline group, revealed significant and extensive damage to complex-I (P<0.01) and IV (P<0.001) and loss of citrate synthase activity (P<0.05). No effect on complex II-III was observed. Spermine treatment significantly prevented all these effects. This study has therefore confirmed the neuroprotective effects of spermine in vivo. However, for the first time, we have shown that this effect may, in part, be due to increased NOS activity and preservation of mitochondrial function.

Overview of the brain polyamine-stress-response: regulation, development, and modulation by lithium and role in cell survival

An early transient increase in brain polyamine (PA) metabolism, termed the PA-stress-response (PSR), is a common reaction to stressful stimuli, including physical, emotional, and hormonal stressors, with a magnitude related to the stress intensity. In the extreme, traumatic injury can result in an incomplete PSR, with persistent accumulation of putrescine and eventual reduction in the concentrations of the higher polyamines (PAs), spermidine and spermine. Chronic intermittent application of stressors causes a recurrence of the brain PSR, but, in contrast, it leads to habituation of the response in the periphery (liver). Severe continuous stress, however, may lead to accumulation of brain PAs. Long-term inhibition of PA synthesis depletes brain PAs and can result in altered emotional reactivity to stressors. Furthermore, the brain PSR, in contrast to the periphery, can be blocked by a long-term, but not by short-term, treatment with lithium, the most efficacious treatment of manic-depressive illness. The brain PSR is developmentally regulated, and the switch to the mature pattern coincides with the cessation of the "stress hyporesponsive period" in the hypothalamic-pituitary-adrenocortical (HPA) system. In contrast to the brain and liver, the PSR in the adrenal and thymus is down-regulated by acute stressors. Transient up-regulation of the PSR, as in the brain and liver, is implicated in cell survival while its down-regulation is implicated in cell death. Taken together, the findings indicate that the PSR is a dynamic process that varies with the type, intensity, and duration of stressors, and implicate this response as an adaptive mechanism in the reaction to stressful events. Under persistent stressful conditions, however, the PSR may be maladaptive as may be reflected by PA accumulation. This raises the hypothesis that proper regulation of brain PSR may be critical for neuronal function and for an appropriate behavioral response to stressors.

Ornithine decarboxylase activity in in vivo and in vitro models of cerebral ischemia

Ornithine decarboxylase (ODC) is considered the rate-limiting enzyme in polyamine biosynthesis, and an increase in putrescine after central nervous system (CNS) injury appears to be involved in neuronal death. Cerebral ischemia and reperfusion trigger an active series of metabolic events, which eventually lead to neuronal death. In the present study, ODC activity was evaluated following transient focal cerebral ischemia and reperfusion in rat. The middle cerebral artery (MCA) was occluded for 2 h in male rats with an intraluminal suture technique. Animals were sacrificed between 3 and 48 h of reperfusion following MCA occlusion, and ODC activity was assayed in cortex and striatum. ODC activity was also estimated in an in vitro ischemia model using primary rat cortical neuron cultures, at 6-24 h reoxygenation following 1 h oxygen-glucose deprivation (OGD). In cortex, following ischemia, ODC activity was increased at 3 h (P < .05), reached peak levels by 6-9 h (P < .001) and returned to sham levels by 48 h reperfusion. In striatum the ODC activity followed a similar time course, but returned to basal levels by 24 h. This suggests that ODC activity is upregulated in rat CNS following transient focal ischemia and its time course of activation is region specific. In vitro, ODC activity showed a significant rise only at 24 h reoxygenation following ischemic insult. The release of lactate dehydrogenase (LDH), an indicator for cell damage, was also significantly elevated after OGD. 0.25 mM alpha-difluoromethylornithine (DFMO) inhibited ischemia-induced ODC activity, whereas a 10-mM dose of DFMO appears to provide some neuroprotection by suppressing both ODC activity and LDH release in neuronal cultures, suggesting the involvement of polyamines in the development of neuronal cell death.

Spermine reduces infarction and neurological deficit following a rat model of middle cerebral artery occlusion: a magnetic resonance imaging study

The role of nitric oxide (NO) in post-ischemic cerebral infarction has been extensively examined, but few studies have investigated its role on the neurological deficit. In the present study, we investigated the effect of spermine on the temporal evolution of infarct volume, NO production and neurological deficit using magnetic resonance imaging in a model of permanent focal cerebral ischemia in rats. Spermine given at 10 mg/kg 2 h after ischemia reduced the infarct volume by 40% and abolished brain NO production and improved the neurological score 24 h, 48 h and 72 h after ischemia. Spermine also reduced the neurological deficit as evaluated by rotamex, grip strength and neurological severity score tests.

Circulating inhibitor of gonadotropin releasing hormone secretion by hypothalamic neurons in uremia

BACKGROUND

Previous studies have suggested a neuroendocrine defect underlying uremic hypogonadism, characterized by a reduced secretion of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH).

METHODS

We studied the GnRH-producing GT1-7 cell line and the LH-producing LbetaT-2 pituitary cell line under uremic conditions to investigate whether substances circulating in uremic plasma directly affect hypothalamic or pituitary hormone secretion. The cells were incubated with serum from 5/6-nephrectomized or sham-nephrectomized castrated rats, respectively. Furthermore, GT1 cells were incubated with delipidated sera, serum subfractions separated by molecular weight, or several peptide hormones. Cellular viability, apoptosis rate and extracellular hormone degradation were assessed separately. GnRH and LH were measured by RIA in supernatants and cell lysates. GnRH gene expression was assessed by Northern blot.

RESULTS

Uremic serum caused a reduction of extracellular GnRH concentration by 31%, whereas intracellular GnRH increased by 12%. This effect was independent of serum lipids and enzymatic GnRH degradation but was abolished by trypsin digestion. Cellular viability, apoptosis rates and GnRH gene expression did not differ between the two groups. The inhibitory activity was recovered from the high-molecular weight fraction, whereas the fraction <5 kD had stimulatory activity. In contrast, uremic serum did not affect LH secretion from LbetaT-2 cells, indicating that the hypoactivity of the hypothalamo-pituitary gonadotrope unit results from an inhibition at the hypothalamic rather than the pituitary level.

CONCLUSIONS

Our results suggest that uremic serum contains macromolecular and hydrophilic peptide(s) able to specifically suppress the neurosecretion of GnRH from GT1-7 cells.

Passage of spermidine across the blood-brain barrier in short recirculation periods following global cerebral ischemia: effects of mild hyperthermia

Transport of a polyamine (PA), spermidine (SPMD) into rat brain at various early postischemic periods was studied. Rats underwent 20 min of four-vessel occlusion (4VO) followed by 5, 10, 30 and 60 min of recirculation (RC) periods with natural brain temperature. 3H-aminoisobutyricacid (AIB) and 14C-SPMD were utilised to search dual functions of the blood-brain barrier (BBB); barrier and carrier functions, respectively. Unidirectional blood-to-brain transfer constant (Kin) was calculated for AIB and SPMD in four brain regions-parieto-temporal cortex, striatum, hippocampus and cerebellum. Kin for SPMD ranged between 1.2+/-0.3 x 10(3) ml g(-1) min(-1) (for striatum) and 2.2+/-0.4 x 10(3) ml g(-1) min(-1) (for cerebellum) in controls. Kin for AIB showed similar values. At 5 and 10 min RC periods, Kin for both substances increased in a non-specific manner in all brain regions studied. In the cortex, Kin for SPMD at 5 and 10 min RC periods were 3.2+/-0.4 x 10(3) and 2.9+/-0.3 x 10(3) ml g(-1) min(-1), respectively, and found to be maximum with respect to other brain regions studied. 30 and 60 min RC groups showed specific transport for SPMD, whilst there were no changes for Kin for AIB, in all brain regions studied. Hippocampus showed the maximum increase in Kin SPMD at 60 min RC (2.7+/-0.3 x 10(3) ml g(-1) min(-1)), corresponding to a percentage rise of 121%. Intraischemic mild brain hyperthermia (39 degrees C) gave rise to a striking increase in Kin at 60 min postischemia for both substances. These results suggest that there is a specific transport of SPMD into brain at 30 and 60 min RC periods following 20 min of forebrain ischemia. Moreover, dual functions of the BBB were perturbed with intracerebral mild hyperthermia during ischemia.

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.

Increase of the ornithine decarboxylase/polyamine system and transglutaminase upregulation in the spinal cord of aged rats

We have investigated changes in ornithine decarboxylase (ODC) activity and in polyamine levels in the central nervous system of aged rats. We measured a significant increase of ODC catalytic activity in the spinal cord from 30 month-old rats (+105%) as compared to 4 month-old rats. No changes were noticed in the cerebellum, cortex and hippocampus from the same animals. A related putrescine increase was measured in the spinal cord of 30 month-old rats (+168%), together with a smaller increase of spermidine (+33%). A parallel increase (+78%) of the Ca2+-dependent transglutaminase activity was detected in the spinal cord of 30 month-old rats, while no changes were apparent in the cortex and cerebellum. Our observations indicate a possible role of the ODC/polyamine system during the normal process of ageing in rats and point to the spinal cord as the most sensitive area for this kind of modification. A possible role of protein polyamination by transglutaminase is discussed.

Ornithine decarboxylase knockdown exacerbates transient focal cerebral ischemia-induced neuronal damage in rat brain

Transient cerebral ischemia leads to increased expression of ornithine decarboxylase (ODC). Contradicting studies attributed neuroprotective and neurotoxic roles to ODC after ischemia. Using antisense oligonucleotides (ODNs), the current study evaluated the functional role of ODC in the process of neuronal damage after transient focal cerebral ischemia induced by middle cerebral artery occlusion (MCAO) in spontaneously hypertensive rats. Transient MCAO significantly increased the ODC immunoreactive protein levels and catalytic activity in the ipsilateral cortex, which were completely prevented by the infusion of antisense ODN specific for ODC. Transient MCAO in rats infused with ODC antisense ODN increased the infarct volume, motor deficits, and mortality compared with the sense or random ODN-infused controls. Results of the current study support a neuroprotective or recovery role, or both, for ODC after transient focal ischemia.

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

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

Accelerated functional recovery and neuroprotection by agmatine after spinal cord ischemia in rats

Treatment with agmatine, decarboxylated arginine, proved to be non-toxic and to exert neuroprotective effects in several models of neurotoxic and ischemic brain and spinal cord injuries. Here we sought to find out whether agmatine treatment would also prove beneficial in a rat spinal cord ischemia model (balloon occlusion of the abdominal aorta bellow the branching point of the left subclavian artery for 5 min). Agmatine was injected (100 mg/kg, i.p. ) 5 min after beginning of re-perfusion and again once daily for the next 3 post-operative days. Motor performance ('combined motor score') was recorded for up to 17 days post-operative and motoneuron cell counts (in representative spinal cord sections) performed on the 17th post-operative day. Agmatine treatment was found to accelerate recovery of motor deficits and to prevent the loss of motoneurons in the spinal cord after transient ischemia. Together, the present and previous findings demonstrate that agmatine is an efficacious neuroprotective agent and that this naturally occurring non-toxic compound should be tried for therapeutic use after neurotrauma and in neurodegenerative diseases.

Expression of ODC and its regulatory protein antizyme in the adult rat brain

Ornithine decarboxylase and its inhibitor protein, antizyme are key regulators of polyamine biosynthesis. We examined their expression in the adult rat brain using in situ hybridization and immunocytochemistry. Both genes were widely expressed and their expression patterns were mostly overlapping and relatively similar. The levels of antizyme mRNA were always higher than those of ornithine decarboxylase mRNA. The highest expression for both genes was detected in the cerebellar cortex, hippocampus, hypothalamic paraventricular and supraoptic nuclei, locus coeruleus, olfactory bulb, piriform cortex and pontine nuclei. Ornithine decarboxylase and antizyme mRNAs appeared to be localized in the nerve cells. ODC antibody displayed mainly cytoplasmic staining in all brain areas. Antizyme antibody staining was mainly cytoplasmic in the most brain areas, although predominantly nuclear staining was detected in some areas, most notably in the cerebellar cortex, anterior olfactory nucleus and frontal cortex. Our study is the first detailed and comparative analysis of ornithine decarboxylase and antizyme expression in the adult mammalian brain.

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

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

Exogenous spermine reduces ischemic damage in a model of focal cerebral ischemia in the rat

Alterations in polyamine metabolism during and after global or focal cerebral ischemia can produce a multiplicity of effects on brain such as modification in mitochondria calcium buffering capacity, exacerbating glutamate-mediated neurotoxicity, and impairment of the blood-brain barrier. In this study, the endogenous polyamine spermine was administered intravenously 30 min prior to temporary focal cerebral ischemia in rats induced by clipping of the left middle cerebral and bilateral common carotid arteries for 3 h. Three days after removal of the microclips, intracardiac perfusion with 2% 2,3,5-triphenyl tetrazolium chloride was performed. Coronal slices were cut, photographed, and examined for cortical infarct volume. Spermine reduced infarct volume in a dose-dependent fashion. This study demonstrates that the use of polyamines may be considered as a powerful tool in prevention of ischemic tissue damage following focal cerebral ischemia.

Overexpression of spermidine/spermine N-acetyltransferase in transgenic mice protects the animals from kainate-induced toxicity

We recently generated a transgenic mouse line with activated polyamine catabolism through overexpression of spermidine/spermine N1-acetyltransferase (SSAT). A detailed analysis of brain polyamine concentrations indicated that all brain regions of these animals showed distinct signs of activated polyamine catabolism, e.g. overaccumulation of putrescine (three- to 17-fold), appearance of N1-acetylspermidine and decreases in spermidine concentrations. In situ hybridization analyses revealed a marked overexpression of SSAT-specific mRNA all over the brain tissue of the transgenic animals. The transgenic animals appeared to tolerate subcutaneous injections of high-dose kainate substantially better as their overall mortality was less than 50% of that of their syngenic littermates. We used the expression of glial fibrillary acidic protein (GFAP) as a marker of brain injury in response to kainate. In situ hybridization analysis with GFAP oligonucleotide up to 7 days after the administration of sublethal kainate doses showed reduced GFAP expression in transgenic animals in comparison with their non-transgenic littermates. This difference was especially striking in the cerebral cortex of the transgenic mice where the exposure to kainate hardly induced GFAP expression. The treatment with kainate likewise resulted in loss of the hippocampal (CA3) neurons in non-transgenic but not transgenic animals. These results support our earlier findings indicating that elevated concentrations of brain putrescine, irrespective whether derived from an overexpression of ornithine decarboxylase, or as shown here, from an overexpression of SSAT, play in all likelihood a neuroprotective role in brain injury.

Casein kinase 2 as a potentially important enzyme in the nervous system

Protein kinase CK2 is a ubiquitous and pleiotropic seryl/threonyl protein kinase which is highly conserved in evolution indicating a vital cellular role for this kinase. The holoenzyme is generally composed of two catalytic (alpha and/or alpha') and two regulatory (beta) subunits, but the free alpha/alpha' subunits are catalytically active by themselves and can be present in cells under some circumstances. Special attention has been devoted to phosphorylation status and structure of these enzymic molecules, however, their regulation and roles remain intriguing. Until recently, CK2 was believed to represent a kinase especially required for cell cycle progression in non-neural cells. At present, with respect to recent findings, four essential features suggest potentially important roles for this enzyme in specific neural functions: (1) CK2 is much more abundant in brain than in any other tissue; (2) there appear to be a myriad of substrates for CK2 in both synaptic and nuclear compartments that have clear implications in development, neuritogenesis, synaptic transmission, synaptic plasticity, information storage and survival; (3) CK2 seems to be associated with mechanisms underlying long-term potentiation in hippocampus; and (4) neurotrophins stimulate activity of CK2 in hippocampus. In addition, some data are suggestive that CK2 might play a role in processes underlying progressive disorders due to Alzheimer's disease, ischemia, chronic alcohol exposure or immunodeficiency virus HIV. The present review focuses mainly on the latest data concerning the regulatory mechanisms and the possible neurophysiological functions of this enzyme.

Involvement of polyamines in apoptosis. Facts and controversies: effectors or protectors?

The natural polyamines (putrescine, spermidine and spermine) are ubiquitous low-molecular aliphatic amines that play multifunctional roles in cell growth and differentiation. Recently, evidence has merging that polyamines are actively involved in cell death. Changes in polyamine homeostasis have been reported during cell death of nerve cells, in programmed cell death of embryonic cells and in various in vitro models of apoptosis. Polyamines and many of their structural analogs exert cytotoxic effects in vitro as well in vivo. Furthermore, polyamine analogs and inhibitors of the polyamine anabolic/catabolic pathways modulate processes of cell death in a cell-type specific way. Much ambiguity exists in the working mechanisms by which polyamines mediate apoptosis since they have been shown to act as promoting, modulating or protective agents in apoptosis. Nevertheless, from the studies reviewed here it can be concluded that polyamines are critically involved in cellular survival which makes them suitable targets for therapeutic intervention that is specifically directed to cell death pathways.

Detailed genotyping demonstrates association between the slow acetylator genotype for N-acetyltransferase 2 (NAT2) and familial Parkinson's disease

In a preliminary report we demonstrated an association between the slow acetylator genotype of N-acetyltransferase 2 (NAT2) and familial cases of Parkinson's disease (FPD). Using a considerably more precise NAT2 typing method, which detects all mutant NAT2 alleles with a frequency of >1% in the white population, we have now retyped all the original patients and control subjects to investigate the reliability of our initial findings. The slow acetylator genotype remained considerably more common among FPD (73%) than normal control subjects (NPC, 43%) or the disease (Huntington's disease [HD]) control group (52%) with an odds ratio (OR) of 3.58 (95% confidence interval (CI): 1.96-6.56; p = 0.00003) for FPD versus NPC and an OR of 2.50 (95% CI: 1.37-4.56, p = 0.003) for FPD versus HD. Furthermore, the wild-type allele 4 conferred a protective effect with an OR of 0.39 (95% CI: 0.23-0.64; p = 0.0025) for FPD versus NPC and an OR of 0.50 (95% CI: 0.30-0.85, p = 0.01) for FPD versus HD. The results of this study support an association between the NAT2 slow acetylator genotype and FPD in our population.

Effects of spermidine treatment on neurobehavioral development in intrauterine growth retarded (IUGR) rats

It was previously shown that polyamine treatment could induce precocious development of several somatic and neurobehavioral functions in newborn rats. This study investigates the effects of daily injections of spermidine (SPMD) 50 microl/10 g s.c. on neurobehavioral development of newborn rats experiencing undernutrition. Neurobehavioral development was assessed by measurements of gripping and righting reflexes. SPMD treated intrauterine growth retarded (IUGR) rats reached righting reflex control values at 30 days postnatal (1.87 +/- 0.78 s vs 1.75 +/- 0.66 s). Beginning from 7 days postnatal, gripping reflex values of SPMD treated IUGR rats declined, reaching that of controls at 30 days postnatal (1.77 +/- 91 degrees vs 1.82 +/- 65 degrees). These results suggest the utility of exogenous SPMD in rats experiencing undernutrition, thus indicating a clinical relevance.

The Effect of Agmatine on Ischemic and Nonischemic Isolated Rat Heart

OBJECTIVE: the natural polyamines play a protective role during ischemic injury. We studied the effects of agmatine on ischemic and nonischemic isolated rat hearts. METHODS: Thirty-one rats were randomly assigned to one of four experimental groups. Sixteen rats were injected with saline (group 1, n = 9; group 3, n = 7), and 15 rats were injected with 100 mg/kg of agmatine (group 2, n = 8; group 4, n = 7). Injections were given twice: 24 hours and 1 hour before the experiment. Using the modified Langendorf model, rat hearts were perfused with Krebs-Henseleit solution for 105 minutes during phase 1 of the experiment (groups 1 and 2). During phase 2, hearts were exposed to 45 minutes of global ischemia (groups 3 and 4). RESULTS: During phase 1, no statistically significant differences were observed between the agmatine and the control groups. During phase 2, agmatine caused a significant increase in left ventricular pressure (P <.003). At the end of reperfusion, P(max) was 111% +/- 10% from the baseline levels versus only 82% +/- 5% in the control group. After 20 minutes of reperfusion, dP/dt (first-time derivative of the ventricular pressure) in the agmatine group reached full recovery of 106% +/- 12% versus only 64% +/- 14% in the saline group (P =.059). Agmatine also caused a significant increase in coronary flow rate (P <.004) throughout the reperfusion period. Quantitative immunohistochemical staining disclosed reduced cell damage in the agmatine-treated hearts (P <.02) versus the control group. CONCLUSION: Agmatine injection given before induced ischemia improves hemodynamic recovery by mechanisms that may be attributed to its vasodilatory properties.

Changes in ornithine decarboxylase activity and putrescine concentrations after spinal cord compression injury in the rat

Traumatic spinal cord injury results in direct physical damage to structures and the generation of local factors contributing to secondary pathogenesis. In the present study, we investigated changes in polyamine metabolism after spinal cord compression injury in the rat. This is a stress induced metabolic pathway, of which an activation may indicate both, secondary pathogenesis or induction of neuroprotective response. Ornithine decarboxylase (ODC) activity, the rate limiting step of polyamine synthesis, and levels of the diamine putrescine, the product of ornithine decarboxylase reaction, were analyzed in control (non-laminectomized) animals and at 2 and 4 h after laminectomy or compression injury at the L4 segmental level. ODC activity was significantly increased 4 h after laminectomy in L4 and in adjacent L3 and L5 segments and compression to L4 produced a further increase 4 h after injury as compared with the intact control group. Putrescine levels were likewise significantly elevated to the same extend in the laminectomized and injured cord as compared with the intact control group. These findings demonstrate increased ODC and putrescine levels in the laminectomized and traumatized spinal cord and suggest that laminectomy may be an important 'priming event' that contributes to secondary injury after spinal cord compression injury.

The cellular localization of the L-ornithine decarboxylase/polyamine system in normal and diseased central nervous systems

Natural polyamines, spermidine and spermine, and their precursor putrescine, are of considerable importance for the developing and mature nervous system. They exhibit a number of neurophysiological and metabolic effects in the nervous system, including control of nucleic acid and protein synthesis, modulation of ionic channels and calcium-dependent transmitter release. The polyamine system is also known to be involved in various brain pathologic events (seizures, stroke, Alzheimer's disease and others). While cerebral polyamine concentrations and the activities of polyamine-metabolizing enzymes have been studied in great detail, much less is known about the cells that are responsible for cerebral polyamine synthesis and interconversion. With the present review the attempt is made to show how exact knowledge about the regional distribution and cellular localization of polyamines and the polyamine-synthesizing enzymatic machinery (and especially of L-ornithine decarboxylase) may help to better understand the functional interplay between polyamines and other endogenous agents (transmitters, receptors, growth factors neuroactive drugs etc.). Polyamines have been localized both in neurones and glial cells. However, the main cellular locus of the ODC is the neuron--both in the immature and adult central nervous system. Each period of normal brain development and ageing seems to have its own, characteristic temporo-spatial pattern of neuronal ODC expression. During strong functional activation (kindling, epileptic seizures, neural transplantation) astrocytes and other non-neuronal cells do also express ODC and other polyamine-metabolizing enzymes. Astroglial expression of ODC is accompanied by an increase in glial fibrillary acidic protein in these cells. This shift in the cellular mechanisms of polyamine metabolism is currently far from being understood. In human brain diseases (Alzheimer's disease, schizophrenia) certain neurones show an increased expression of ODC, the first and rate-limiting enzyme of polyamine metabolism. Since polyamines are structurally related to psychoactive drugs (neuroleptics, antidepressants) the polyamine system might be of importance as a putative target for drug intervention in psychiatry.

Phencyclidine-like discriminative stimulus effects of polyamine modulators of N-methyl-D-aspartate receptor activity in rats

Excessive N-methyl-D-aspartate (NMDA) receptor activation has been implicated in many acute and chronic neuropathologies. NMDA antagonists might prove to be useful treatments, unfortunately, some can produce phencyclidine (PCP)-like side effects. The polyamine-site modulators, spermine (SPM) and spermidine (SPD), produce dose related biphasic modulation of NMDA channel currents while another polyamine, arcaine (ARC), produces only negative modulatory effects. The PCP-like effects of these compounds were tested in rats trained to discriminate PCP from saline in a standard two-lever drug discrimination paradigm under a fixed ratio schedule of food reinforcement. SPM, SPD and ARC occasioned little, if any, responding on the PCP-associated lever, even at response rate suppressing doses. The results provide further evidence that differences exist between the discriminative stimulus effects produced by drugs active at different sites on the NMDA receptor and suggest that the polyamine modulatory site should be a good target for development of NMDA antagonist medications with a reduced propensity for PCP-like acute behavioral effects.

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.

Neuroprotective role of ornithine decarboxylase activation in transient focal cerebral ischaemia: a study using ornithine decarboxylase-overexpressing transgenic rats

Nuclear magnetic resonance imaging (MRI) was used to study dynamics of maturation and the size of ischaemic stroke lesions in rats with greatly increased activity of ornithine decarboxylase (ODC). Syngenic rats, either with or without chronic pre-ischaemic treatment with an ODC inhibitor, alpha-difluoromethylornithine (DFMO), as well as ODC-overexpressing transgenic rats were subjected either to transient middle cerebral artery (MCA) occlusion or permanent occlusion of the cortical branch of MCA. The two models were chosen to assess the role of ODC activity in damage caused by ischaemia and reperfusion, respectively. Diffusion of water was quantified by means of the trace of the diffusion tensor (D(av) = 1/3 Trace D) to assess the extent of energy failure and cytotoxic oedema, whereas the spin-spin relaxation time (T2) was used as a quantitative indicator of irreversible damage by MRI. Exposure to transient MCA occlusion resulted in significantly smaller stroke lesions in the ODC-overexpressing transgenic (246+/-14 mm3) than in syngenic (320+/-9 mm3) or DFMO-treated (442+/-63 mm3) rats as determined 48 h after the occlusion. The differences in sizes were due to smaller lesions in the cortical tissue (transgenic vs. syngenic) or both in cortical and striatal regions (transgenic vs. DFMO-treated animals). The degree of irreversible oedema was greater in DFMO-treated rats than in syngenic or transgenic animals indicating accelerated development of a permanent damage in the absence of ODC induction. Cortical infarct following permanent MCA occlusion developed faster in the DFMO-treated than in syngenic or transgenic rats as the lesion sizes at 10 h were 26.2+/-4.3 mm3, 14.2+/-2.3 mm3 and 12.3+/-1.9 mm3, respectively. However, the stroke volumes by 48 h were not statistically different in the three animal groups. The present data demonstrate that ODC activation is an endogenous neuroprotective measure in transient cerebral ischaemia.

Induction of ornithine decarboxylase mRNA in transient focal cerebral ischemia in the rat

We used in situ hybridization to localize the long-term changes in ornithine decarboxylase (ODC) expression after a 90 min occlusion of the middle cerebral artery (MCAO) in the rat. The ODC mRNA was induced in the ipsilateral dentate gyrus (DG) and throughout the ischemic cortex at 12 h and still at 3 days after reperfusion. The induction was blocked by an N-methyl-D-aspartate (NMDA) receptor antagonist suggesting that ODC induction is NMDA receptor-mediated. The long-lasting up-regulation detected in regions where no cellular damage usually occurs, favors the hypothesis that ODC expression does not contribute to neuronal death after stroke.

Excess putrescine accumulation inhibits the formation of modified eukaryotic initiation factor 5A (eIF-5A) and induces apoptosis

DH23A cells, an alpha-difluoromethylornithine-resistant variant of the parental hepatoma tissue culture cells, express high levels of stable ornithine decarboxylase. Aberrantly high expression of ornithine decarboxylase results in a large accumulation of endogenous putrescine and increased apoptosis in DH23A cells when alpha-difluoromethylornithine is removed from the culture. Treatment of DH23A cells with exogenous putrescine in the presence of alpha-difluoromethylornithine mimics the effect of drug removal, suggesting that putrescine is a causative agent or trigger of apoptosis. Accumulation of excess intracellular putrescine inhibits the formation of hypusine in vivo, a reaction that proceeds by the transfer of the butylamine moiety of spermidine to a lysine residue in eukaryotic initiation factor 5A (eIF-5A). Treatment of DH23A cells with diaminoheptane, a competitive inhibitor of the post-translational modification of eIF-5A, causes both the suppression of eIF-5A modification in vivo and induction of apoptosis. These data support the hypothesis that rapid degradation of ornithine decarboxylase is a protective mechanism to avoid cell toxicity from putrescine accumulation. Further, these data suggest that suppression of modified eIF-5A formation is one mechanism by which cells may be induced to undergo apoptosis.