Polyamines stimulate mitochondrial calcium transport in rat brain

Mechanisms of dual modulatory effects of spermine on the mitochondrial calcium uniporter complex

The mitochondrial Ca 2 + uniporter mediates the crucial cellular process of mitochondrial Ca 2 + uptake, which regulates cell bioenergetics, intracellular Ca 2 + signaling, and cell death initiation. The uniporter contains the pore-forming MCU subunit, an EMRE protein that binds to MCU, and the regulatory MICU1 subunit, which can dimerize with MICU1 or MICU2 and under resting cellular [Ca 2 + ] occludes the MCU pore. It has been known for decades that spermine, which is ubiquitously present in animal cells, can enhance mitochondrial Ca 2 + uptake, but the underlying mechanisms remain unclear. Here, we show that spermine exerts dual modulatory effects on the uniporter. In physiological concentrations of spermine, it enhances uniporter activity by breaking the physical interactions between MCU and the MICU1-containing dimers to allow the uniporter to constitutively take up Ca 2 + even in low [Ca 2 + ] conditions. This potentiation effect does not require MICU2 or the EF-hand motifs in MICU1. When [spermine] rises to millimolar levels, it inhibits the uniporter by targeting the pore region in a MICU-independent manner. The MICU1-dependent spermine potentiation mechanism proposed here, along with our previous finding that cardiac mitochondria have very low MICU1, can explain the puzzling observation in the literature that mitochondria in the heart show no response to spermine.

Development of a Redox-Sensitive Spermine Prodrug for the Potential Treatment of Snyder Robinson Syndrome

Snyder Robinson Syndrome (SRS) is a rare disease associated with a defective spermine synthase gene and low intracellular spermine levels. In this study, a spermine replacement therapy was developed using a spermine prodrug that enters cells via the polyamine transport system. The prodrug was comprised of three components: a redox-sensitive quinone "trigger", a "trimethyl lock (TML)" aryl "release mechanism", and spermine. The presence of spermine in the design facilitated uptake by the polyamine transport system. The quinone-TML motifs provided a redox-sensitive agent, which upon intracellular reduction generated a hydroquinone, which underwent intramolecular cyclization to release free spermine and a lactone byproduct. Rewardingly, most SRS fibroblasts treated with the prodrug revealed a significant increase in intracellular spermine. Administering the spermine prodrug through feeding in a Drosophila model of SRS showed significant beneficial effects. In summary, a spermine prodrug is developed and provides a lead compound for future spermine replacement therapy experiments.

Spermidine protects from age-related synaptic alterations at hippocampal mossy fiber-CA3 synapses

Aging is associated with functional alterations of synapses thought to contribute to age-dependent memory impairment (AMI). While therapeutic avenues to protect from AMI are largely elusive, supplementation of spermidine, a polyamine normally declining with age, has been shown to restore defective proteostasis and to protect from AMI in Drosophila. Here we demonstrate that dietary spermidine protects from age-related synaptic alterations at hippocampal mossy fiber (MF)-CA3 synapses and prevents the aging-induced loss of neuronal mitochondria. Dietary spermidine rescued age-dependent decreases in synaptic vesicle density and largely restored defective presynaptic MF-CA3 long-term potentiation (LTP) at MF-CA3 synapses (MF-CA3) in aged animals. In contrast, spermidine failed to protect CA3-CA1 hippocampal synapses characterized by postsynaptic LTP from age-related changes in function and morphology. Our data demonstrate that dietary spermidine attenuates age-associated deterioration of MF-CA3 synaptic transmission and plasticity. These findings provide a physiological and molecular basis for the future therapeutic usage of spermidine.

Developmental upregulation of presynaptic NCKX underlies the decrease of mitochondria-dependent posttetanic potentiation at the rat calyx of Held synapse

The sensitivity of posttetanic potentiation (PTP) to high-frequency stimulation (HFS) steeply decays during the first 2 postnatal weeks. We investigated the underlying mechanisms for the developmental change of PTP induced by HFS (100 Hz, 2 s) at postnatal days 4-6 and 9-11 at the rat calyx of Held synapse. Low-concentration tetraphenylphosphonium (2 μM), an inhibitor of mitochondrial Na(+)/Ca(2+) exchanger, suppressed the amount of posttetanic residual Ca(2+) and PTP to a larger extent at the immature calyx synapse, indicating a developmental reduction of mitochondrial contribution to PTP. The higher amount of mitochondrial Ca(2+) uptake during HFS and consequent posttetanic residual Ca(2+) at the immature calyx of Held was associated with higher peak of HFS-induced Ca(2+) transients, most likely because the mitochondrial Ca(2+) uptake during HFS was supralinearly dependent on the presynaptic resting Ca(2+) level. Probing into the contribution of Na(+)/Ca(2+) exchangers to Ca(2+) clearance, we found a specific upregulation of the K(+)-dependent Na(+)/Ca(2+) exchanger (NCKX) activity in the mature calyx of Held. We conclude that the upregulation of NCKX limits the Ca(2+) buildup and inhibits mitochondrial Ca(2+) uptake during HFS, which in turn results in the reduction of posttetanic residual Ca(2+) and PTP at the mature calyx of Held synapse.

Inflammatory-induced hibernation in the fetus: priming of fetal sheep metabolism correlates with developmental brain injury

Prenatal inflammation is considered an important factor contributing to preterm birth and neonatal mortality and morbidity. The impact of prenatal inflammation on fetal bioenergetic status and the correlation of specific metabolites to inflammatory-induced developmental brain injury are unknown. We used a global metabolomics approach to examine plasma metabolites differentially regulated by intrauterine inflammation. Preterm-equivalent sheep fetuses were randomized to i.v. bolus infusion of either saline-vehicle or LPS. Blood samples were collected at baseline 2 h, 6 h and daily up to 10 days for metabolite quantification. Animals were killed at 10 days after LPS injection, and brain injury was assessed by histopathology. We detected both acute and delayed effects of LPS on fetal metabolism, with a long-term down-regulation of fetal energy metabolism. Within the first 3 days after LPS, 121 metabolites were up-regulated or down-regulated. A transient phase (4–6 days), in which metabolite levels recovered to baseline, was followed by a second phase marked by an opposing down-regulation of energy metabolites, increased pO₂ and increased markers of inflammation and ADMA. The characteristics of the metabolite response to LPS in these two phases, defined as 2 h to 2 days and at 6–9 days, respectively, were strongly correlated with white and grey matter volumes at 10 days recovery. Based on these results we propose a novel concept of inflammatory-induced hibernation of the fetus. Inflammatory priming of fetal metabolism correlated with measures of brain injury, suggesting potential for future biomarker research and the identification of therapeutic targets.

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.

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.

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.

Effects of polyamines on mitochondrial Ca2+ transport

Mammalian mitochondria are able to enhance Ca(2+) accumulation in the presence of polyamines by activating the saturable systems of Ca(2+) inward transport and buffering extramitochondrial Ca(2+) concentrations to levels similar to those in the cytosol of resting cells. This effect renders them responsive to regulate free Ca(2+) concentrations in the physioloical range. The mechanism involved is due to a rise in the affinity of the Ca(2+) transport system, induced by polyamines, most probably exhibiting allosteric behaviour. The regulatory site of this mechanism is the so-called S(1) binding site of polyamines, which operates in physiological conditions and is located in the energy well between the two peaks present in the energy profile of mitochondrial spermine transport. Spermine is bidirectionally transported across teh inner membrane by cycling, in which influx and efflux are driven by electrical and pH gradients, respectively. Most probably, polyamine affects the Ca(2+) transport system when it acts from the outside-that is, in the direction of its uniporter channel, in order to reach the S(1) site. Important physiological functions are related to activation of Ca(2+) transport systems by polyamines and their interactions with the S(1) site. These functions include a rise in the metabolic rate for energy supply and modulation of mitochondrial permeability transition induction, with consequent effects on the triggering of the apoptotic pathway.

Ca(2+) efflux in mitochondria from the yeast Endomyces magnusii

Calcium release pathways in Ca(2+)-preloaded mitochondria from the yeast Endomyces magnusii were studied. In the presence of phosphate as a permeant anion, Ca(2+) was released from respiring mitochondria only after massive cation loading at the onset of anaerobiosis. Ca(2+) release was not affected by cyclosporin A, an inhibitor of the mitochondrial permeability transition. Aeration of the mitochondrial suspension inhibited the efflux of Ca(2+) and induced its re-uptake. With acetate as the permeant anion, a spontaneous net Ca(2+) efflux set in after uptake of approximately 150 nmol of Ca(2+)/mg of protein. The rate of this efflux was proportional to the Ca(2+) load and insensitive to aeration, protonophorous uncouplers, and Na(+) ions. Ca(2+) efflux was inhibited by La(3+), Mn(2+), Mg(2+), tetraphenylphosphonium, inorganic phosphate, and nigericin and stimulated by hypotonicity, spermine, and valinomycin in the presence of 4 mm KCl. Atractyloside and t-butyl hydroperoxide were without effect. Ca(2+) efflux was associated with contraction, but not with mitochondrial swelling. We conclude that the permeability transition pore is not involved in Ca(2+) efflux in preloaded E. magnusii mitochondria. The efflux occurs via an Na(+)-independent pathway, in many ways similar to the one in mammalian mitochondria.

Effects of dietary 1,4-diaminobutane (putrescine) on eggshell quality and laying performance of hens laying thin-shelled eggs

Experiments were conducted to evaluate the potential for dietary 1,4-diaminobutane (putrescine) to influence eggshell quality and overall laying performance in hens. Forty-eight, 60-wk-old White Leghorn hens laying thin-shelled eggs were fed a corn and soybean meal-based diet supplemented with 0.00 (control), 0.05, 0.10, or 0.15% putrescine for 4 wk. Twelve hens that laid thick-shelled eggs were also fed the control diet. The feeding of supplemental putrescine decreased feed consumption; however, egg weight decreased only at higher levels of supplementation. Increasing dietary levels of putrescine responded quadratically in eggshell deformation, eggshell weight, and eggshell weight as a percentage of egg weight (P < 0.05). There were no significant differences in shell deformation, shell thickness, or shell weight when comparing hens laying thick-shelled eggs and those laying thin-shelled eggs that were fed 0.05% supplemental putrescine. Calcium intake, calcium retention, and calcium balance decreased linearly (P < 0.05) with increasing levels of dietary putrescine. Pancreatic putrescine concentrations were significantly higher (P < 0.05) in hens laying thick-shelled eggs compared with hens laying thin-shelled eggs. It appeared that pancreatic cells synthesized more polyamines in hens laying thick-shelled eggs. This increase in polyamines might have caused improved eggshell quality by increasing calcium transport. It was concluded that 0.05% supplemental putrescine improved eggshell quality; however, higher levels proved to be toxic.

Role of polyamine metabolism in kainic acid excitotoxicity in organotypic hippocampal slice cultures

Polyamines are ubiquitous cations that are essential for cell growth, regeneration and differentiation. Increases in polyamine metabolism have been implicated in several neuropathological conditions, including excitotoxicity. However, the precise role of polyamines in neuronal degeneration is still unclear. To investigate mechanisms by which polyamines could contribute to excitotoxic neuronal death, the present study examined the role of the polyamine interconversion pathway in kainic acid (KA) neurotoxicity using organotypic hippocampal slice cultures. Treatment of cultures with N1,N(2)-bis(2,3-butadienyl)-1,4-butanediamine (MDL 72527), an irreversible inhibitor of polyamine oxidase, resulted in a partial but significant neuronal protection, especially in CA1 region. In addition, this pre-treatment also attenuated KA-induced increase in levels of lipid peroxidation, cytosolic cytochrome C release and glial cell activation. Furthermore, pre-treatment with a combination of cyclosporin A (an inhibitor of the mitochondrial permeability transition pore) and MDL 72527 resulted in an additive and almost total neuronal protection against KA toxicity, while the combination of MDL 72527 and EUK-134 (a synthetic catalase/superoxide dismutase mimetic) did not provide additive protection. These data strongly suggest that the polyamine interconversion pathway partially contributes to KA-induced neurodegeneration via the production of reactive oxygen species.

Effects of dietary 1, 4-diaminobutane (putrescine) on eggshell quality and laying performance of older hens

We conducted an experiment to evaluate the potential for dietary 1,4-diaminobutane (putrescine) to promote eggshell quality and overall laying hen performance. A total of 128, 60-wk-old Barred Rock hens were fed a corn and soybean meal-based layer diet supplemented with 0.0 (control), 0.2, 0.4, and 0.6% free base 1,4-diaminobutane for 4 wk. The feeding of supplemental putrescine decreased feed consumption (P < or = 0.05) and egg mass (P < or = 0.05) and tended to decrease egg production (P < 0.08). Albumen quality was not significantly affected (P < 0.09) by the end of the experiment, as determined by Haugh units. Eggshell thickness was not significantly improved with lower levels of dietary putrescine (P < 0.08). Although dietary putrescine did not have any effect on the relative weights of duodenum, jejunum + ileum, or pancreas, there was a linear increase in putrescine concentrations in tissues (P < or = 0.05). Supplementation of dietary putrescine also resulted in increased putrescine and spermidine concentrations in egg (P < or = 0.05). Egg weight and eggshell deformation increased over time; however, eggshell weight, eggshell weight as percentage of egg weight, and eggshell thickness decreased (P < or = 0.05). It appeared that eggshell quality declined regardless of diet over the 4-wk experimental period. It was concluded that the lack of effect of dietary putrescine on egg parameters, with the exception of albumen quality and eggshell thickness, was due to putrescine toxicity. Hens transferred excess dietary putrescine and metabolites to eggs.

Spermidine: A predictor for neurological outcome and infarct size in focal cerebral ischemia?

BACKGROUND AND PURPOSE

Polyamines are mainly restricted to the intracellular space. During focal cerebral ischemia, polyamines are released from the intracellular compartment. Experimental studies have implicated a marked elevation in brain tissue and blood. The aim of our study was to investigate whether the elevation of polyamines in the blood of patients with focal cerebral ischemia correlates with the clinical outcome and the infarct volume.

METHODS

Polyamines were measured in 16 patients with focal cerebral ischemia and in 8 healthy control subjects. Blood samples for polyamine measurement were taken at admission and at fixed time points for the next 28 days. Polyamines were analyzed in red blood cells by a high-pressure liquid chromatography system. Clinical findings were recorded with the NIH Stroke Scale score. Volume of infarction was analyzed from cranial CT at admission and on days 4 to 6 after ischemia.

RESULTS

A significant increase of the spermidine level in the peripheral blood could be observed in all patients with focal cerebral ischemia as compared with control subjects (P:<0.01), starting with the admission. Spermidine values correlated positively with the clinical outcome at several time points in the first 48 hours (r=0.90 to 0.40; P:<0.01) and with the infarct volume in cranial CT on days 4 to 6 (r=0.91; P:<0.01).

CONCLUSIONS

As hypothesized from experimental data, polyamine levels in blood increase in patients after focal cerebral ischemia. The results indicate that the peripheral spermidine level is closely associated with the clinical outcome as well as with the infarction volume. Therefore, polyamines may be used as a novel predictor for the prognosis of patients with focal cerebral ischemia.

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.

Mitochondria and neuronal survival

Mitochondria play a central role in the survival and death of neurons. The detailed bioenergetic mechanisms by which isolated mitochondria generate ATP, sequester Ca(2+), generate reactive oxygen species, and undergo Ca(2+)-dependent permeabilization of their inner membrane are currently being applied to the function of mitochondria in situ within neurons under physiological and pathophysiological conditions. Here we review the functional bioenergetics of isolated mitochondria, with emphasis on the chemiosmotic proton circuit and the application (and occasional misapplication) of these principles to intact neurons. Mitochondria play an integral role in both necrotic and apoptotic neuronal cell death, and the bioenergetic principles underlying current studies are reviewed.

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.

Extracellular calcium stimulates Na(+)-dependent putrescine uptake in B16 melanoma cells

The regulation of putrescine transport in difluoromethylornithine-treated B16 melanoma cells by extracellular Ca2+ has been investigated. It was found that physiological concentrations of Ca2+ were essential for optimum uptake of putrescine and spermidine, Mg2+, albeit at higher concentrations, also could potentiate polyamine transport. The maximum rate of putrescine uptake increased from 1698 +/- 67 pmol/min/min/mg DNA in the absence of Ca2+ to 3100 +/0 98 pmol/min/mg DNA in the presence of 0.5 mM Ca2+. There was no change in Km. While Ca2+ enhanced transport of both putrescine and spermidine it did not affect the uptake of deoxyglucose, thymidine or leucine. Putrescine did not alter Ca2+ fluxes suggesting that the two cations do not share a common transport system. The effects of Ca2+ on putrescine uptake appeared to be mediated extracellularly firstly because Ca2+ did not potentiate putrescine uptake in the presence of A23187 and secondly, because the effects of Ca2+ were completely inhibited by the lanthanide Tb3+, which binds to calcium-dependent proteins and does not readily cross biological membranes, Ca2+ did not affect putrescine transport in the absence of extracellular Na+. Moreover, the rate of putrescine uptake in the absence of Ca2+ was similar to that in the absence of extracellular Na+. The results from this study indicate that polyamine transport is stimulated by extracellular Ca2+ and suggest that Ca2+ is required for activity of the Na(+)-dependent transporter only. This transporter appears to possess a regulatory binding site for divalent cations.

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.

Brain polyamine levels are altered in Alzheimer's disease

Despite considerable evidence implicating polyamines in CNS function, little is known about the status of the polyamine system in normal or abnormal human brain. We measured the levels of the polyamines spermidine, spermine and their precursor putrescine, in cortical and subcortical areas of 12 patients with Alzheimer's disease (AD). As compared with the controls, mean levels of spermidine were markedly and significantly increased (70%) whereas putrescine levels were decreased (28%) in temporal cortex of the AD patients. No other statistically significant changes were observed with the exception of a mean 35% reduction in spermine concentration in occipital cortex. In view of the modulatory effects of polyamines on calcium flux and glutamate receptor function, our data suggest that abnormal polyamine system activity may be involved in the neurodegenerative processes occurring in brain of patients with AD.

Polyamines and their metabolizing enzymes in human frontal cortex and hippocampus: preliminary measurements in affective disorders

Affective disorders are associated with maladaptive response to stressful life events. Based on the observation that a transient increase in brain polyamine metabolism is a common response to stressful stimuli, our hypothesis is that a maladaptive polyamine stress response may be involved in the pathophysiology of affective disorders. Our current research efforts, therefore, concentrate on the characterization of this PA response, and on its pharmacological regulation. The present preliminary study is the first to measure the polyamines, putrescine, spermidine, and spermine, and their metabolizing enzymes, ornithine decarboxylase, S-adenosylmethionine decarboxylase, and spermidine/spermine N1 acetyltransferase, in brain autopsy samples from people who suffered from depressive disorders or schizophrenia, or from those who committed suicide. The data of affected individuals did not reveal significant differences when compared to those of suicide cases, or to those of people with no known neurologic or psychiatric abnormalities. The following regional differences were observed: spermidine concentrations and ornithine decarboxylase activity were higher, but S-adenosylmethionine decarboxylase activity was lower in the hippocampus as compared to the frontal cortex. Preliminary studies with rat brain indicate that an increase in polyamine metabolizing enzyme activities occurs within several hours after death and persists for at least 48 hours. These observations, in turn, indicate that earlier autopsies are crucial for detection of changes in polyamine metabolism. We conclude that further studies to test the polyamine hypothesis are warranted.

Prior mechanical injury inhibits rise in intracellular Ca2+ concentration by oxygen-glucose deprivation in mouse hippocampal slices

Prior mechanical brain microinjury has been found to have a preventive effect on brain ischemia. To investigate the mechanism responsible for this, the effect of mechanical brain injury on changes in intracellular free Ca2+ concentration ([Ca2+]i) in response to ischemic insult was studied in mouse hippocampal slices. The mechanical injury was made by inserting a 25G hypodermic needle into the CA1 region of the hippocampus in mice anesthetized with pentobarbital. Sagittal slices of the hippocampus were prepared two hours, and 1, 3, 7, and 14 days after the brain injury. Changes in [Ca2+]i in the slices by oxygen-glucose deprivation were analyzed from fluorescence images, using fura-2. Increases in [Ca2+]i induced by oxygen-glucose deprivation were inhibited in the vicinity of the injury 1 and 3 days after injury. [Ca2+]i levels were lower in the posterior side from the injury than in the anterior side 1 and 3 days after injury. No significant regional differences in [Ca2+]i responses were found 2 h or 7 and 14 days after the injury. Membrane potential and membrane resistance of CA1 neurons in the vicinity of the injury measured 1 day after the injury were not significantly altered in comparison with non-injured slices. These results indicate that mechanical brain injury inhibits ischemic [Ca2+]i increase. This inhibition may be induced not only by damage of the presynaptic fibers projecting to the CA1 neurons but also by the other certain factor(s) that prevent [Ca2+]i increase, and it appears to be related to the protective effect of prior mechanical injury against ischemic neuronal damage.

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

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

Lithium exerts a time-dependent and tissue-selective attenuation of the dexamethasone-induced polyamine response in rat brain and liver

It has previously been shown that chronic, but not acute, lithium treatment indirectly prevents the dexamethasone-induced increase in brain polyamine-metabolizing enzymes. In the present study we determined the effects of lithium treatment on changes in cellular polyamines, 6 h after dexamethasone challenge (3 mg/kg intraperitoneally). The findings demonstrate that chronic lithium (daily intraperitoneal 2.5 mmol/kg injections for 2 weeks) treatment completely prevents the accumulation of putrescine, in parallel to its prevention of the dexamethasone-induced increase in ornithine decarboxylase activity. A partial attenuation of this polyamine response was also observed in the liver. Only minor and inconsistent changes were observed in the concentrations of the polyamines, spermidine and spermine. Acute lithium treatment (a single injection at times ranging from 1 to 24 h prior to dexamethasone challenge) did not attenuate the dexamethasone-induced increases in brain putrescine concentration nor in ornithine decarboxylase activity. It is suggested that prevention of the stress-induced polyamine response in the brain may be an important mechanism through which prophylactic lithium may exert its beneficial effect in manic-depressive illness.

Lipid peroxidation affects catalytic properties of rat liver mitochondrial monoamine oxidases and their sensitivity to proteolysis

1. Lipid peroxidation (LPO) in rat liver mitochondria decreased the activity of monoamine oxidase (MAO) with physiological substrates serotonin and 2-phenylethylamine (by 15-30%) and induced deamination of glucosamine, which was highly sensitive to selective MAO A inhibitor pirlindole. 2. The LPO-induced changes in catalytic properties of MAOs are accompanied by their increased susceptibility to trypsinolysis, however sensitivity to inhibition by imipramine, chlorpromazine and spermine are insignificantly changed. 3. It is suggested that these results reflect LPO-induced conformational changes of enzyme molecules in membrane rather than their membrane topography.

Yeast mitochondrial calcium uptake: regulation by polyamines and magnesium ions

Spermine, spermidine, and magnesium ions modulate the kinetic parameters of the Ca2+ transport system of Endomyces magnusii mitochondria. Mg2+ at concentrations up to 5 mM partially inhibits Ca2+ transport with a half-maximal inhibiting concentration of approximately 0.5 mM. In the presence of 2 mM MgCl2, the S0.5 value of the Ca2+ transport system increases from 220 to 490 microM, which indicates decreased affinity for the system. Spermine and spermidine exert an activating effect, having half-maximal concentrations of 12 and 50 microM, respectively. In the case of spermine, the S0.5 value falls to 50-65 microM, which implies an increase in the transport system affinity for Ca2+. Both Mg2+ and spermine cause a decrease of the Hill coefficient, giving evidence for a smaller degree of cooperativity. Spermine and spermidine enable yeast mitochondria to remove Ca2+ from the media completely. In contrast, Mg2+ lowers the mitochondrial buffer capacity. When both Mg2+ and spermine are present in the medium, their effects on the S0.5 value and the free extramitochondrial Ca2+ concentration are additive. The ability of spermine and Mg2+ to regulate yeast mitochondrial Ca2+ transport is discussed.

Role of polyamines in the regulation of proliferation and hormone production by insulin-secreting cells

This paper focuses on the mechanisms regulating proliferation and insulin production by normal and tumoral pancreatic beta-cells. In particular, the evidence for involvement of polyamines is reviewed. Pancreatic islet cells contain high levels of polyamines, and based on findings obtained using enzyme-directed inhibitors, it appears that putrescine and spermidine are necessary for proinsulin biosynthesis, whereas spermine may exert a stimulatory or permissive role in RNA transcription-stabilization and long-term insulin release. Islet polyamine content is not altered by short-term secretory stimulation, nor is the acute secretory response impeded by polyamine synthesis inhibitors, making it unlikely that these amines play any major role in short-term insulin release. Various mitogens increase islet polyamine contents and DNA synthesis, but increases in cytosolic polyamines do not seem to mediate their mitogenicity. Nuclear polyamine content is not altered by the inhibitors, suggesting that maintenance of polyamines within this organelle may be sufficient to sustain elevated DNA synthesis. In tumoral RINm5F cells, polyamine depletion results in decreased proliferation and increased cellular content of insulin and insulin secretory granules without affecting insulin mRNA levels or translation. Moreover, polyamine-depleted RINm5F cells display improved substrate metabolism and sensitivity of the stimulus-secretion coupling. Possible levels of polyamine interaction with Ca2+ metabolism are discussed.

Increases in brain polyamine concentrations in chemical kindling and single convulsion induced by pentylenetetrazol in rats

Concentrations of the polyamines, putrescine, spermidine and spermine were investigated in rat brains, in which chemical kindling or single convulsion had been induced by intraperitoneal injection of pentylenetetrazol (PTZ). A single injection of 60 mg/kg of PTZ produced tonic-clonic convulsion and increased the putrescine concentration 8 h after the injection. At lower doses of PTZ (10 and 30 mg/kg), neither marked behavioral seizure nor significant change in any polyamine concentration was observed. On the other hand, repeated injections of 30 mg/kg of PTZ eventually resulted in intense motor seizures (PTZ kindling) and increased the concentrations of all three polyamines. The most marked increase was detected in putrescine 1-48 h after the intense seizures. The increase in putrescine was clearly higher in PTZ kindling than in single convulsion. These results suggest that increases in polyamine concentrations are involved in neuronal excitability in the epileptic brain.

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.

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.

Dual effect of spermine on mitochondrial Ca2+ transport

1. A dual effect of the polyamine spermine on Ca2+ uptake by isolated rat liver, brain and heart mitochondria could be demonstrated by using a high-resolution system for studying mitochondrial Ca2+ transport. Depending on the experimental situation, spermine had an inhibiting or accelerating effects on mitochondrial Ca(2+)-uptake rate, but invariably increased the mitochondrial Ca2+ accumulation. 2. Both effects were concentration-dependent and clearly discernible on the basis of their different kinetic characteristics. For mitochondria from all three tissues the half-maximally effective concentration for inhibition of the initial rate of Ca2+ uptake was approx. 180 microM, whereas that for the subsequent stimulation of Ca2+ accumulation was approx. 50 microM. 3. Acceleration of the initial uptake rate could be seen when the mitochondria were preloaded with spermine during a 2 min preincubation period and thereafter incubated in a medium without spermine. 4. When such spermine-preloaded mitochondria were incubated in a spermine-containing medium, the increase in Ca(2+)-accumulation capacity was maintained in spite of an unchanged rate of Ca2+ uptake. 5. Mg2+ interacted with the effects of spermine in a differential manner, enhancing the initial inhibition of the rate of mitochondrial Ca2+ uptake and diminishing the subsequent stimulation of mitochondrial Ca2+ accumulation. 6. This dual effect of spermine on mitochondrial Ca2+ transport resolves the apparent paradox that a polycationic compound can act as a stimulator of Ca2+ uptake.

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.

The interaction of spermine with the ryanodine receptor from skeletal muscle

The effect of polyamines on ryanodine binding activity of junctional sarcoplasmic reticulum membranes is described. Spermine stimulated the binding of ryanodine to its receptor up to 5-fold, with half-maximal stimulation obtained with 3.5 mM. Spermidine and putrescine also stimulated ryanodine binding, but they were about 12-fold less potent. The degree of stimulation is dependent on the NaCl concentration present in the assay medium. Spermine has no effect on the Ca(2+)-dependency of ryanodine binding but it increases the ryanodine binding affinity (Kd) by about 5.6-fold. Both the rate of ryanodine association with, and dissociation from, its binding site were affected by spermine. Spermine also stimulates the photoaffinity labelling by 3-O-(4-benzoyl)benzoyl[alpha-32P]ATP ([alpha-32P]BzATP) of the ryanodine receptor, increasing the BzATP binding affinity. We suggest that the stimulatory effect of spermine on ryanodine binding is due to its specific interaction with the ryanodine receptor. This spermine interaction enabled us to develop a new, one-step, fast and with high yield method for the purification of ryanodine receptor (Shoshan-Barmatz, V. and Zarka, A. (1992) Biochem. J. 284, in press).

Polyamine metabolism in epileptic cortex

Polyamine (tissue) concentrations have been studied in hippocampus and temporal neocortex from patients with temporal lobe epilepsy. Depth electrode recordings demonstrated hippocampal origin of the seizures, the temporal neocortex being involved during the discharge propagation. Neuropathological examination of excised tissues showed glial proliferation or glioma in Ammon's horn (CA), whereas the temporal neocortex did not exhibit any histological abnormality. Polyamine (putrescine or PUT, spermidine or SPD, spermine or SPM) concentrations were determined on surgical samples from the hippocampus and various areas of temporal neocortex. Human post-mortem tissue from temporal lobe regions was used for controls. In post-mortem controls and temporal neocortex specimens from epileptic patients, polyamine levels were similar (in nmol/g wet weight: PUT = 40-100; SPD = 200-350; SPM = 100-200). In CA, polyamine levels exhibited striking changes: SPD content was significantly increased (350-700 nmol/g) while SPM was lowered (50-100). PUT was only increased in CA invaded by the tumoral process (100-180). Accordingly, a very high SPD/SPM molar ratio in the abnormal CA region was observed, indicating an acceleration of polyamine neosynthesis which is usually related to ornithine decarboxylase induction. Metabolic changes in polyamines appear to be selective of human epileptic hippocampus. A relationship between glial proliferation (gliosis or neoplasia), epileptic firing and polyamines is discussed.

Mn2+ sequestration by mitochondria and inhibition of oxidative phosphorylation

Manganese is known to accumulate in mitochondria and in mitochondria-rich tissues in vivo. Although Ca2+ enhances mitochondrial Mn2+ uptake, ATP-bound Mn2+ is not sequestered by suspended rat brain mitochondria, and ATP binds Mn2+ even more tightly than it binds Mg2+. Physiological levels of the polyamine spermine enhanced 54 Mn2+ uptake at the low [Ca2+]s characteristic of unstimulated cells (approximately 100 nM). With succinate as substrate, Mn2+ inhibited oxygen consumption by suspensions of rat liver mitochondria after the addition of ADP but not after the addition of uncoupler. With glutamate/malate as substrate, Mn2+ inhibited ADP-stimulated respiration and also slightly inhibited uncoupler-stimulated respiration. State 4 (resting) respiration was unchanged in all cases, indicating that the inner membrane retained its impermeability to protons. These results suggest that Mn2+ was not oxidized and that it can interfere directly with oxidative phosphorylation, most likely by binding to the F1 ATPase. Mn2+ may also bind to the NADH dehydrogenase complex, but not strongly enough to affect electron transport in vivo. It is suggested that accumulation of manganese within the mitochondria of globus pallidus may help explain the distinctive pathology of manganism.

Ca2+/calmodulin regulation of putrescine uptake in cultured gastrointestinal epithelial cells

Regulation of putrescine uptake in a small intestinal crypt cell line, IEC-6 cells, was examined. Uptake of [14C]putrescine was measured throughout a normal growth curve and was found to be inversely related to growth. Kinetic analysis at low and high cell density revealed the inhibition of uptake in confluent cells was due to a five-fold reduction in Vmax of uptake, 199.5 vs. 43.1 pmol.10(5) cells-1.h-1, respectively. Three gastrointestinal hormones, gastrin, secretin, and cholecystokinin, produced partial inhibition of [14C]putrescine uptake. Conversely, treatment of quiescent cells with 5% fetal bovine serum to stimulate growth did not affect uptake. Influence of putrescine uptake on free ionized intracellular Ca2+ ([Ca2+]i) was measured by microspectrofluorometry using the Ca(2+)-sensitive fluoroprobe fura-2. Basal [Ca2+]i was calculated to be 112 nM and increased rapidly to 313 nM upon addition of 10 microM putrescine. Preventing the rise in [Ca2+]i using an intracellular Ca2+ buffer, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester, decreased [14C]putrescine uptake to 29.5 +/- 5.3% of control values. 45Ca2+ flux experiments and measurement of transport in 0 Ca2+ and 0.5 mM EDTA suggested an intracellular source of calcium was mobilized during putrescine uptake. Finally, use of the putative calmodulin antagonist N-(6-aminohexyl)-5-chloro-l-naphthalenesulfonamide caused a dose-dependent inhibition of [14C]putrescine uptake with 50% inhibitory concentration of approximately 7 microM. These data suggest that putrescine uptake in IEC-6 cells may be regulated by a Ca2+/calmodulin-dependent mechanism.

Nuclear magnetic resonance spectroscopy study on energy metabolism, intracellular pH, and free Mg2+ concentration in the brain of transgenic mice overexpressing human ornithine decarboxylase gene

We have generated a transgenic mouse line strikingly overexpressing the human ornithine decarboxylase (ODC) gene in their brain. Brain ODC activity was increased in the transgenic animals by a factor of 70 in comparison with their nontransgenic littermates. The content of brain putrescine, the product of ODC, was greater than 60 mumol/g of tissue in the transgenic mice, whereas in the normal animals it was below the level that could be detected by an HPLC method. The concentrations of the higher polyamines (spermidine and spermine) were not significantly different from control values. 31P nuclear magnetic resonance (31P NMR) spectroscopy analyses revealed a significantly reduced (40%) free Mg2+ concentration as calculated from the chemical shift differences of the nucleoside triphosphate alpha and beta peaks in the brains of the transgenic animals. The lower free Mg2+ concentration in the brains of ODC transgenic mice was not a consequence of altered intracellular pH or changes in cellular high-energy metabolites. 1H NMR showed no differences in brain choline/N-acetylaspartate and total creatine/N-acetylaspartate ratios between the two animal groups. These ODC transgenic animals may serve as models in vivo for studies on cerebral postischemic events and on epilepsy, as polyamines are supposed to be involved in these processes.

Regulation of cytosolic free calcium concentration by intrasynaptic mitochondria

By the use of digitonin permeabilized presynaptic nerve terminals (synaptosomes), we have found that intrasynaptic mitochondria, when studied "in situ," i.e., surrounded by their cytosolic environment, are able to buffer calcium in a range of calcium concentrations close to those usually present in the cytosol of resting synaptosomes. Adenine nucleotides and polyamines, which are usually lost during isolation of mitochondria, greatly improve the calcium-sequestering activity of mitochondria in permeabilized synaptosomes. The hypothesis that the mitochondria contributes to calcium homeostasis at low resting cytosolic free calcium concentration ([Ca2+]i) in synaptosomes has been tested; it has been found that in fact this is the case. Intrasynaptic mitochondria actively accumulates calcium at [Ca2+]i around 10(-7) M, and this activity is necessary for the regulation of [Ca2+]i. When compared with other membrane-limited calcium pools, it was found that depending on external concentration the calcium pool mobilized from mitochondria is similar or even greater than the IP3- or caffeine-sensitive calcium pools. In summary, the results presented argue in favor of a more prominent role of mitochondria in regulating [Ca2+]i in presynaptic nerve terminals, a role that should be reconsidered for other cellular types in light of the present evidence.

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

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

Polyamine metabolism in transient focal ischemia of rat brain

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

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

We have previously demonstrated that administration of the polyamines putrescine, spermidine, or spermine can prevent neuronal degeneration in rats during naturally occurring cell death or after injurious treatments such as nerve injury or monosodium glutamate neurotoxicity. The present study demonstrates that also in adult gerbils polyamine treatment can protect forebrain neurons from degeneration after ischemia. Neurons in the hippocampus and striatum were rescued from delayed cell death after brief (5 min) global ischemia in gerbils which were treated with daily injections (10 mg/kg) of polyamines. The evidence accrued, so far, indicates that systemic polyamines can protect a wide variety of central and peripheral neurons from natural or induced degeneration.

The polyamine spermine affects omega-conotoxin binding and function at N-type voltage-sensitive calcium channels

1. The effects of the polyamines, spermine and spermidine on neuronal N-type voltage-sensitive calcium channels were investigated using the binding and function of the ligand omega-conotoxin GVIA (omega-CT). 2. Spermine and spermidine enhanced (EC50 approximately 0.16 and 0.45 microM) and, at higher concentrations, inhibited (IC50 of 9 and 240 microM) the binding of [125I]omega-CT to rat hippocampal synaptosomes. 3. Spermine and, less potently, spermidine inhibited the neurotransmitter-mediated, omega-CT-sensitive, electrical-field-stimulated contractile responses of the rat vas deferens. 4. The polyamines also inhibited the phenylephrine-evoked contractile responses of the vas deferens with the same rank order, consistent with a postsynaptic mechanism of inhibition. 5. However, pre-exposure to spermine prevented the irreversible inhibition of vas deferens twitch responses by omega-CT (previously found to be presynaptic). The prevention of inhibition by omega-CT demonstrates that the neuronal binding of spermine and omega-CT is mutually exclusive. Thus spermine (and presumably spermidine at higher concentrations) appears to modulate the actions of omega-CT at N-type voltage-sensitive calcium channels.

Regional differences in the activation of synaptosomal mitochondrial Ca2+ uptake by spermine in rat brain

Several properties of Ca2+ uptake by isolated synaptosomal mitochondria were characterized by using a repetitive Ca2+ loading technique. Synaptosomal mitochondria maintained extramitochondrial Ca2+ concentration at submicromolar levels when challenged with successive additions of small amounts of Ca2+. Ca2+ uptake under these conditions was markedly stimulated by the presence of spermine, a polyamine found in high concentrations in brain. Moreover, mitochondria isolated from telencephalic areas of rat brain were activated to a greater extent by spermine than were mitochondria from non-telencephalic brain regions. The present results support the idea that brain mitochondria could play a significant role in limiting the intraneuronal rise in Ca2+ that follows stimulation or injury. In addition, telencephalic mitochondria exhibit more flexibility in the regulation of Ca2+ uptake than do mitochondria from phylogenetically older non-telencephalic brain regions and this could be related to differences in Ca2+ influx mechanisms in these brain regions.

Regulation of Ca2+ transport in brain mitochondria. I. The mechanism of spermine enhancement of Ca2+ uptake and retention

Spermine enhances electrogenic Ca2+ uptake and inhibits Na(+)-independent Ca2+ efflux in rat brain mitochondria. As a result, Ca2+ retention by brain mitochondria increases greatly and the external free Ca2+ level at steady-state can be lowered to physiologically relevant concentrations. The stimulation of Ca2+ uptake by spermine is more pronounced at low concentrations of Ca2+, effectively lowering the apparent Km for Ca2+ uptake from 3 microM to 1.5 microM. However, the apparent Vmax is also increased. At low Ca2+ concentrations, Ca2+ uptake is diffusion-limited. Spermine strongly inhibits Ca2+ binding to anionic phospholipids and it is suggested that this increases the rate of surface diffusion which reduces the apparent Km for uptake. The same effect could inhibit the Na(+)-independent efflux if the rate of efflux is limited by Ca2+ dissociation from the efflux carrier. In brain mitochondria (but not in liver) the spermine effect depends on the presence of ADP. In a medium that contains physiological concentrations of Pi, Mg+, K+, ADP and spermine, brain mitochondria sequester Ca2+ down to 0.1 microM and below, depending on the matrix Ca2+ load. Moreover, brain mitochondria under the same conditions buffer the external medium at 0.4 microM, a concentration at which the set point becomes independent of the matrix Ca2+ content. Thus, mitochondria appear to be capable of modulating calcium oscillations in brain cells.