Polyamines and Ca2+ mediate hyperosmolal opening of the blood-brain barrier: in vitro studies in isolated rat cerebral capillaries

Electroporation loading and flash photolysis to investigate intra- and intercellular Ca2+ signaling

Many cellular functions are driven by variations in the intracellular Ca(2+) concentration ([Ca(2+)]i), which may appear as a single-event transient [Ca(2+)]i elevation, repetitive [Ca(2+)]i increases known as Ca(2+) oscillations, or [Ca(2+)]i increases propagating in the cytoplasm as Ca(2+) waves. Additionally, [Ca(2+)]i changes can be communicated between cells as intercellular Ca(2+) waves (ICWs). ICWs are mediated by two possible mechanisms acting in parallel: one involving gap junctions that form channels directly linking the cytoplasm of adjacent cells and one involving a paracrine messenger, in most cases ATP, that is released into the extracellular space, leading to [Ca(2+)]i changes in neighboring cells. The intracellular messenger inositol 1,4,5-trisphosphate (IP3) that triggers Ca(2+) release from Ca(2+) stores is crucial in these two ICW propagation scenarios, and is also a potent trigger to initiate ICWs. Loading inactive, "caged" IP3 into cells followed by photolytic "uncaging" with UV light, thereby liberating IP3, is a well-established method to trigger [Ca(2+)]i changes in single cells that is also effective in initiating ICWs. We here describe a method to load cells with caged IP3 by local electroporation of monolayer cell cultures and to apply flash photolysis to increase intracellular IP3 and induce [Ca(2+)]i changes, or initiate ICWs. Moreover, the electroporation method allows loading of membrane-impermeable agents that interfere with IP3 and Ca(2+) signaling.

Endothelial calcium dynamics, connexin channels and blood-brain barrier function

Situated between the circulation and the brain, the blood-brain barrier (BBB) protects the brain from circulating toxins while securing a specialized environment for neuro-glial signaling. BBB capillary endothelial cells exhibit low transcytotic activity and a tight, junctional network that, aided by the cytoskeleton, restricts paracellular permeability. The latter is subject of extensive research as it relates to neuropathology, edema and inflammation. A key determinant in regulating paracellular permeability is the endothelial cytoplasmic Ca(2+) concentration ([Ca(2+)]i) that affects junctional and cytoskeletal proteins. Ca(2+) signals are not one-time events restricted to a single cell but often appear as oscillatory [Ca(2+)]i changes that may propagate between cells as intercellular Ca(2+) waves. The effect of Ca(2+) oscillations/waves on BBB function is largely unknown and we here review current evidence on how [Ca(2+)]i dynamics influence BBB permeability.

Effects of ethylenediamine in rodent models of seizure, motor coordination and anxiety

Ethylenediamine (EDA) activates GABA(A) receptors via both direct and indirect mechanisms. EDA has been shown to reduce seizures caused by systemic injection of proconvulsants in an animal model of generalized tonic-clonic seizures. However, there does not appear to have been any report on the effects of EDA in other seizure models. Hence, we used male Sprague-Dawley rats to test the effects of EDA on topically applied bicuculline (a model of simple partial seizures) and on maximal electroshock (MES, a model of generalized tonic-clonic seizures). We also examined the effects of EDA on motor coordination using a rotarod treadmill, and its potential anxiolytic properties using an elevated plus maze (EPM). EDA at concentrations of 50 μM and above reduced the frequency of epileptiform spikes on an electrocorticogram in a concentration-dependent manner. EDA at 100 and 1000 mg/kg i.p. increased the threshold for inducing limb extension on the MES. EDA did not affect the time spent by rats on the rotarod at 10 or 100mg/kg, but significantly reduced the time spent at doses of 1000 mg/kg. In the EPM, EDA at 10 or 100mg/kg significantly increased the frequency of entries and time spent in the open arms. We conclude that EDA has antiepileptic and anxiolytic activity at doses that do not affect motor coordination.

Androgens differentially potentiate mouse intestinal smooth muscle by nongenomic activation of polyamine synthesis and Rho kinase activation

We demonstrate that testosterone and its active metabolite 5alpha-dihydrotestosterone acutely (approximately 30 min) potentiate mouse ileal, but not duodenal, muscle activity. Androgens augment the amplitude of spontaneous peak-to-peak oscillations, alter the spontaneous activity frequency spectrum, and increase the amplitude of calcium-induced and carbachol-induced contractions. Concentration-dependence analyses revealed that maximal potentiation (449-910%) occurred at physiological concentrations of androgens (100 pM to 10 nM) with EC50 values in the picomolar range (8-20 pM). Western blot analyses using an antiandrogen receptor (anti-AR) antibody revealed the presence of two different AR proteins migrating at 87 and 110 kDa in ileal, but not duodenal, extracts. Androgen-induced potentiation was prevented by preincubation with AR antagonists flutamide or cyproterone acetate but was unaffected by pretreatment with cycloheximide plus actinomycin D, indicating that potentiation was mediated by ARs via a novel nongenomic mechanism. Androgen effects were mimicked by polyamines putrescine and spermine and were blocked by the ornithine decarboxylase and S-adenosyl-L-methionine decarboxylase inhibitors alpha-difluoromethylornithine and berenil, respectively. Accordingly, androgens increase alpha-difluoromethylornithine-sensitive ornithine-decarboxylase- mediated L-ornithine decarboxylation in ileal tissues within the same time course as isometric potentiation. Both putrescine and dihydrotestosterone induced Ca2+ sensitization of ionomycin-permeabilized ileal smooth muscle. Finally, inhibition of the Rho kinase (ROK) pathway with the specific inhibitor Y27632 completely prevented androgen-induced potentiation. In agreement, androgens elicited ROK-induced Ser19 phosphorylation of myosin light chain 2 in ileal muscle. These data indicate that androgens potentiate ileal contractile activity by an AR-dependent nongenomic mechanism involving intracellular polyamine signaling and Ca2+ sensitization via ROK activation.

Locoregional opening of the rodent blood-brain barrier for paclitaxel using Nd:YAG laser-induced thermo therapy: a new concept of adjuvant glioma therapy?

BACKGROUND AND OBJECTIVES

Nd:YAG laser-induced thermo therapy (LITT) of rat brains is associated with blood-brain barrier (BBB) permeability changes. We address the question of whether LITT-induced locoregional disruption of the BBB could possibly allow a locoregional passage of chemotherapeutic agents into brain tissue to treat malignant glioma.

STUDY DESIGN/MATERIALS AND METHODS

CD Fischer rats were subject to LITT of the left forebrain. Disruption of the BBB was analyzed using Evans blue and immunohistochemistry (IH). Animals were perfused with paclitaxel, and high-pressure liquid chromatography (HPLC) was employed to analyze the content of paclitaxel in brain and plasma samples.

RESULTS

LITT induces an opening of the BBB as demonstrated by locoregional extravasation of Evans blue, C3C, fibrinogen, and IgM. HPLC proved the passage of paclitaxel across the disrupted BBB.

CONCLUSIONS

LITT induces a locoregional passage of chemotherapeutic agents into the brain tissue. This is of potential interest for the treatment of brain tumors.

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

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

Effects of electromagnetic radiation of mobile phones on the central nervous system

With the increasing use of mobile communication, concerns have been expressed about the possible interactions of electromagnetic radiation with the human organism and, in particular, the brain. The effects on neuronal electrical activity, energy metabolism, genomic responses, neurotransmitter balance, blood-brain barrier permeability, cognitive function, sleep, and various brain diseases including brain tumors are reviewed. Most of the reported effects are small as long as the radiation intensity remains in the nonthermal range, and none of the research reviewed gives an indication of the mechanisms involved at this range. However, health risks may evolve from indirect consequences of mobile telephony, such as the sharply increased incidence rate of traffic accidents caused by telephony during driving, and possibly also by stress reactions which annoyed bystanders may experience when cellular phones are used in public places. These indirect health effects presumably outweigh the direct biological perturbations and should be investigated in more detail in the future.

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

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

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.

Lectin intravital perfusion studies in tumor-bearing mice: micrometer-resolution, wide-area mapping of microvascular labeling, distinguishing efficiently and inefficiently perfused microregions in the tumor

Intravital lectin perfusion was combined with computer-guided scanning digital microscopy to map the perfused elements of the vasculature in tumor-bearing mice. High-precision composite images (spatial precision 1.3 micron and optical resolution 1.5 micron) were generated to permit exact positioning, reconstruction, analysis, and mapping of entire tumor cross-sections (c. 1 cm in diameter). Collation of these mosaics with nuclear magnetic resonance maps in the same tumor plane identified sites of rapid contrast medium uptake as tumor blood vessels. Digitized imaging after intravital double labeling allowed polychromatic visualization of two different types of mismatched staining. First, simultaneous application of two lectins, each bearing a different fluorochrome, revealed organ-specific differential processing in the microvascular wall. Second, sequential application of two boluses of one lectin, bearing different fluorochromes successively, distinguished between double-labeled microvessels, representing efficiently perfused vascular segments, and single-labeled microvessels, with inefficient or intermittent perfusion. Intravital lectin perfusion images of blood vessels in the vital functional state thus highlighted biologically significant differences in vessel function and served as high-resolution adjuncts to MR imaging.

Neurological effects of microwave exposure related to mobile communication

Due to the wide and growing use of mobile communication, there is increasing concern about the interactions of electromagnetic radiation with the human organism, and, in particular, with the brain. In the present report, experimental studies on putative electrophysiological, biochemical and morphological effects of continuous or pulsed microwave radiation are briefly reviewed. Such effects have been described in vitro and in vivo using animals and humans. Particularly, effects on neuronal electrical activity, cellular calcium homeostasis, energy metabolism, genomic responses, neurotransmitter balance and blood-brain barrier permeability have been reported. However, some results have either been disputed, since experimental replication led to contradictory findings, or been related to procedural side effects. Since neurological disturbances induced by mobile telephone devices would be of considerable interest for public health, the authors recognize that further experimental studies, involving strict positive and negative control conditions, will be required in the future. At the present state of knowledge there is no positive evidence that pulsed or continuous microwave exposure in the non-thermal range confers elevated risk to the health of the brain.

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

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

Blood-brain barrier permeability in rats is altered by exposure to magnetic fields associated with magnetic resonance imaging at 1.5 T

We have previously reported that exposure of rats to low-field (0.15 T) magnetic resonance imaging (MRI) increases blood-brain barrier (BBB) permeability. However, a number of investigators have failed to observe this effect when high-field MRI (1.5 T or higher) is used. Therefore, we investigated whether or not we would observe changes using our technique at these higher fields. Adult male Sprague-Dawley rats were anaesthetised and then exposed to a 22.5 min imaging or sham procedure. Immediately following exposure, rats were injected with 1 MBq of 153Gd-DTPA intracardially and then immediately re-exposed for an additional 22.5 min. The rats were killed 1h following the second MRI exposure, at which time the brain was resected and 3 ml of venous blood collected. The ratio of radioactivity per gram of brain to radioactivity per milliliter of blood, known as the brain-blood partition coefficient, was determined and used as a measure of BBB permeability. Groups of animals had different exposures. Group 1 (n = 9) was exposed to a clinically relevant MRI procedure. Group 2 (n = 20) was exposed to the same procedure except the rf specific absorption rate (SAR) was reduced to 25% and the animals were positioned 15 cm from imager centre to increase the time-varying magnetic field from 0.4 to 2.8 T/s. For the sham exposures (n = 21), the animals were placed in the imager with the static field ramped down to zero and exposed to a sound recording simulating a MRI examination.(ABSTRACT TRUNCATED AT 250 WORDS)

The blood-brain barrier in vitro: the second decade

Ever since the discovery of Paul Ehrlich (1885 Das Sauerstoff-bedürfnis des Organismus: Hirschwald, Berlin) about the restricted material exchange, existing between the blood and the brain, the ultimate goal of subsequent studies has been mainly directed towards the elucidation of relative importance of different cellular compartments in the peculiar penetration barrier consisting the structural basis of the blood-brain barrier (BBB). It is now generally agreed that, in most vertebrates, the endothelial cells of the central nervous system (CNS) are responsible for the unique penetration barrier, which restricts the free passage of nutrients, hormones, immunologically relevant molecules and drugs to the brain. After an era of studying with endogenous or exogenous tracers the unique permeability properties of cerebral endothelial cells in vivo, the next generation, i.e. the in vitro blood-brain barrier model system was introduced in 1973. Recent advances in our knowledge of the BBB have in part been made by studying the properties and function of cerebral endothelial cells (CEC) with this in vitro approach. This review summarizes the results obtained on isolated brain microvessels in the second decade of its advent.

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.

Capillary NMDA receptors regulate blood-brain barrier function and breakdown

Polyamines and their regulatory synthetic enzyme ornithine decarboxylase (ODC) have been implicated in blood-brain barrier (BBB) breakdown following cryogenic injury. ODC activation and BBB breakdown are prevented by MK-801, indicating involvement of NMDA receptors. Studies in isolated rat cerebral capillaries supports the presence of NMDA receptors linked to ODC. NMDA (1-50 microM) stimulated capillary uptake of horseradish peroxidase, 2-deoxy-[14C]glucose, and 45 Ca in a receptor-, concentration-, polyamine- and Ca(2+)-dependent manner. We suggest that NMDA receptors may couple capillary transport of nutrients to glutamate-mediated neuronal excitation, and when overestimated disrupt normal BBB function.

Polyamines enhance recovery after sciatic nerve trauma in the rat

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

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

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

Mechanisms of blood-brain barrier breakdown

The functional status of the blood-brain barrier (BBB) must be taken into account when designing and interpreting brain imaging techniques. The integrity of the BBB is affected in many diseases of the brain, with the potential involvement of a number of different but poorly understood cellular mechanisms. Factors known to disrupt the BBB experimentally include arachidonic acid and the eicosanoids, bradykinin, histamine and free radicals. These active compounds, released in pathological tissue, may alter cytosolic calcium levels and induce second messenger systems leading to an alteration in BBB permeability. Extravasation of plasma proteins may occur via disrupted tight junctions, stimulation of fluid-phase vesicular transport or the formation of transcellular pores or channels.

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

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

Polyamine accumulation and vasogenic oedema in the genesis of late delayed radiation injury of the central nervous system (CNS)

Polyamine (PA) accumulation has been associated with blood-brain barrier (BBB) disruption and vasogenic oedema after cold injury. PAs and water content were measured in a rat spinal cord model of late-delayed radiation injury and were found to be elevated at paralysis. The elevated PA levels could be significantly reduced by treatment with difluoromethylornithine (DFMO). In unirradiated rats DFMO reduced putrescine to undetectable levels after 10-12 weeks. These data suggest that blockade of PA synthesis may be useful in treating the vasogenic oedema of radiation injury and may improve CNS radiation tolerance.

Polyamines mediate the reversible opening of the blood-brain barrier by the intracarotid infusion of hyperosmolal mannitol

The blood-brain barrier (BBB) can be opened transiently by infusing a hyperosmolal solution of a non-electrolyte into the internal carotid artery. We investigated the hypothesis that capillary polyamines and their rate-regulating synthetic enzyme, ornithine decarboxylase (ODC), may be involved in mediating BBB breakdown in this model, as they are in BBB breakdown by focal cold injury. The intracarotid infusion of 1.6 M mannitol induced a prompt (less than 2 min) increase in ODC activity and the levels of polyamines in the ipsilateral hemisphere. Isolated cerebral capillary preparations and neural elements showed similar increases in ODC activity. The rank order of increase at 2 min, ODC (170%) greater than putrescine (90%) greater than spermidine (15%) greater than spermine (7%), was consistent with an activation of the ODC-regulated pathway of polyamine synthesis. The specific ODC inhibitor alpha-difluoromethylornithine (DFMO) blocked the 1.6 M mannitol-induced increase in ODC activity and the accumulation of polyamines, and concurrently prevented BBB breakdown, monitored by transport of intravenously administered Evans blue and alpha-[3H]aminoisobutyrate into cerebral tissue. Exogenous putrescine, the product of ODC activity, replenished brain polyamines and negated DFMO protection allowing BBB breakdown by 1.6 M mannitol. These experiments support the hypothesis that BBB breakdown induced by the intracarotid infusion of hyperosmolal mannitol is mediated by rapid, ODC-regulated synthesis of microvascular polyamines. In addition, increases in ODC-controlled polyamine synthesis in nerve cells may play a significant role in the pathophysiology of the reversible neuronal dysfunction, e.g. diazepam-sensitive seizure-like activity, enhanced glucose utilization, evoked by the intracarotid infusion of hyperosmolal mannitol.