Polyphosphoinositides as a probable source of brain free fatty acids accumulated at the onset of ischemia

Brain vulnerability and viability after ischaemia

The susceptibility of the brain to ischaemic injury dramatically limits its viability following interruptions in blood flow. However, data from studies of dissociated cells, tissue specimens, isolated organs and whole bodies have brought into question the temporal limits within which the brain is capable of tolerating prolonged circulatory arrest. This Review assesses cell type-specific mechanisms of global cerebral ischaemia, and examines the circumstances in which the brain exhibits heightened resilience to injury. We suggest strategies for expanding such discoveries to fuel translational research into novel cytoprotective therapies, and describe emerging technologies and experimental concepts. By doing so, we propose a new multimodal framework to investigate brain resuscitation following extended periods of circulatory arrest.

Stop the rot. Enzyme inactivation at brain harvest prevents artifacts: A guide for preservation of the in vivo concentrations of brain constituents

Post-mortem metabolism is widely recognized to cause rapid and prolonged changes in the concentrations of multiple classes of compounds in brain, that is, they are labile. Post-mortem changes from levels in living brain include components of pathways of metabolism of glucose and energy compounds, amino acids, lipids, signaling molecules, neuropeptides, phosphoproteins, and proteins. Methods that stop enzyme activity at brain harvest were developed almost 50 years ago and have been extensively used in studies of brain functions and diseases. Unfortunately, these methods are not commonly used to harvest brain tissue for mass spectrometry-based metabolomic studies or for imaging mass spectrometry studies (IMS, also called mass spectrometry imaging, MSI, or matrix-assisted laser desorption/ionization-MSI, MALDI-MSI). Instead these studies commonly kill animals, decapitate, dissect out brain and regions of interest if needed, then 'snap' freeze the tissue to stop enzymatic activity after harvest, with post-mortem intervals typically ranging from ~0.5 to 3 min. To increase awareness of the importance of stopping metabolism at harvest and preventing the unnecessary complications of not doing so, this commentary provides examples of labile metabolites and the magnitudes of their post-mortem changes in concentrations during brain harvest. Brain harvest methods that stop metabolism at harvest eliminate post-mortem enzymatic activities and can improve characterization of normal and diseased brain. In addition, metabolomic studies would be improved by reporting absolute units of concentration along with normalized peak areas or fold changes. Then reported values can be evaluated and compared with the extensive neurochemical literature to help prevent reporting of artifactual data.

Distinguishing core from penumbra by lipid profiles using Mass Spectrometry Imaging in a transgenic mouse model of ischemic stroke

Detecting different lipid profiles in early infarct development may give an insight on the fate of compromised tissue. Here we used Mass Spectrometry Imaging to identify lipids at 4, 8 and 24 hours after ischemic stroke in mice, induced by transient middle cerebral artery occlusion (tMCAO). Combining linear transparency overlay, a clustering pipeline and spatial segmentation, we identified three regions: infarct core, penumbra (i.e. comprised tissue that is not yet converted to core), and surrounding healthy tissue. Phosphatidylinositol 4-phosphate (m/z = 965.5) became visible in the penumbra 24 hours after tMCAO. Infarct evolution was shown by 2D-renderings of multiple phosphatidylcholine (PC) and Lyso-PC isoforms. High-resolution Secondary Ion Mass Spectrometry, to evaluate sodium/potassium ratios, revealed a significant increase in sodium and a decrease in potassium species in the ischemic area (core and penumbra) compared to healthy tissue at 24 hours after tMCAO. In a transgenic mouse model with an enhanced susceptibility to ischemic stroke, we found a more pronounced discrimination in sodium/potassium ratios between penumbra and healthy regions. Insight in changes in lipid profiles in the first hours of stroke may guide the development of new prognostic biomarkers and novel therapeutic targets to minimize infarct progression.

[Phospholipids metabolism disorders in acute stroke]

The disturbances of cerebral circulation results in the violation of phospholipid metabolism. Activation of lipid peroxidation and protein kinase C and release of intracellular calcium leads to disruption of the homeostasis of phosphatidylcholine. The use of cytidine-5-diphosphocholine, which is used as an intermediate compound in the biosynthesis of phospholipids of the cell membrane, helps to stabilize cell membranes, and reduce the formation of free radicals.

Brain 2-Arachidonoylglycerol Levels Are Dramatically and Rapidly Increased Under Acute Ischemia-Injury Which Is Prevented by Microwave Irradiation

The involvement of brain 2-arachidonoylglycerol (2-AG) in a number of critical physiological and pathophysiological regulatory mechanisms highlights the importance for an accurate brain 2-AG determination. In the present study, we validated head-focused microwave irradiation (MW) as a method to prevent postmortem brain 2-AG alterations before analysis. We compared MW to freezing to prevent 2-AG induction and estimated exogenous and endogenous 2-AG stability upon exposure to MW. Using MW, we measured, for the first time, true 2-AG brain levels under basal conditions, 30 s after brain removal from the cranium, and upon exposure to 5 min of brain global ischemia. Our data indicate that brain 2-AG levels are instantaneously and dramatically increased approximately 60-fold upon brain removal from the cranium. With 5 min of brain global ischemia 2-AG levels are also, but less dramatically, increased 3.5-fold. Our data indicate that brain tissue fixation with MW is a required technique to measure both true basal 2-AG levels and 2-AG alterations under different experimental conditions including global ischemia, and 2-AG is stable upon exposure to MW.

Eicosanoid post-mortem induction in kidney tissue is prevented by microwave irradiation

Previously, we, and others, have demonstrated a rapid and significant post-mortem increase in brain prostanoid (PG) levels analyzed without microwave fixation, and this is not the result of PG trapping or destruction in microwave-irradiated brain tissue. In the present study, we demonstrate a dramatic increase in kidney eicosanoid levels when analyzed without microwave fixation which was mainly accounted for by the 142-, 81-, and 62-fold increase in medullary 6-ketoPGF1α, PGE2, and PGF2α, levels, respectively, while PGD2 and TXB2 levels were increased ~7-fold. Whole kidney and cortex PG were also significantly increased in non-microwaved tissue, but at lesser extent. Arachidonic acid and the lipoxygenase products hydroxyeicosatetraenoic acids (HETE) were also induced in whole kidney, cortex, and medulla 1.5- to 5.5-fold depending upon tissue and metabolite. Cyclooxygenase inhibition with indomethacin decreased PG mass in non-microwaved tissue to basal levels, however HETE and arachidonic acid were not decreased. These data demonstrate the critical importance of kidney tissue fixation to limiting artifacts during kidney eicosanoid analysis.

Differential modification of the phospholipid profile by transient ischemia in rat hippocampal CA1 and CA3 regions

The hippocampal CA1 region is most susceptible to cerebral ischemia in both rodents and humans, whereas CA3 is remarkably resistant. Here, we investigated the possible role of membrane lipids in differential susceptibility in these regions. Transient ischemia was induced in rats via bilateral occlusion of common carotid arteries and membrane lipids were analyzed by mass spectrometry. While lipid profile differences between the intact CA1 and CA3 were rather minor, ischemia caused significant pyramidal cell death with concomittant reduction of phosphatidylserine, phosphatidylinositol, phosphatidylethanolamine, plasmalogen and sphingomyelin only in CA1. The phospholipid loss was evenly distributed in most molecular species. Ischemia also significantly increased cell death mediator ceramides only in CA1. Our data suggests that differential susceptibility to ischemia between CA1 and CA3 is not linked to their unique phospholipid profile. Also, selective activation of phospholipase A2, which primarily releases polyunsaturated fatty acids, might not be characteristic to cell death in CA1.

Animal models of neurological disease

The use of animal models to study human pathology has proved valuable in a number of fields. Animal models of neurological disease have successfully and accurately recreated many aspects of human illness allowing for in-depth study ofneuropathophysiology. These models have been the source of a plethora of information, such as the importance of certain molecular mechanisms and genetic contributions in neurological disease. Additionally, animal models have been utilized in the discovery and testing of possible therapeutic treatments. Although most neurological diseases are still not yet completely understood and reliable treatment is lacking, animal models provide a major step in the right direction.

Formation of eicosanoids, E2/D2 isoprostanes, and docosanoids following decapitation-induced ischemia, measured in high-energy-microwaved rat brain

Inflammatory lipid mediators derived from arachidonic acid (AA) and docosahexaenoic acid (DHA) modify the pathophysiology of brain ischemia. The goal of this work was to investigate the formation of eicosanoids and docosanoids generated from AA and DHA, respectively, during no-flow cerebral ischemia. Rats were subjected to head-focused microwave irradiation 5 min following decapitation (complete ischemia) or prior to decapitation (controls). Brain lipids were extracted and analyzed by reverse-phase liquid chromatography-tandem mass spectrometry. After complete ischemia, brain AA, DHA, and docosapentaenoic acid concentrations increased 18-, 5- and 4-fold compared with controls, respectively. Prostaglandin E(2) (PGE(2)) and PGD(2) could not be detected in control microwaved rat brain, suggesting little endogenous PGE(2)/D(2) production in the brain in the absence of experimental manipulation. Concentrations of thromboxane B(2), E(2)/D(2)-isoprostanes, 5-hydroxyeicosatetraenoic acid (5-HETE), 5-oxo-eicosatetraenoic acid, and 12-HETE were significantly elevated in ischemic brains. In addition, DHA products such as mono-, di- and trihydroxy-DHA were detected in control and ischemic brains. Monohydroxy-DHA, identified as 17-hydroxy-DHA and thought to be the immediate precursor of neuroprotectin D(1), was 6.5-fold higher in ischemic than in control brain. The present study demonstrated increased formation of eicosanoids, E(2)/D(2)-IsoPs, and docosanoids following cerebral ischemia. A balance of these lipid mediators may mediate immediate events of ischemic injury and recovery.

Brain prostaglandin formation is increased by alpha-synuclein gene-ablation during global ischemia

We have previously demonstrated that alpha-synuclein (Snca) gene ablation reduces brain arachidonic acid (20:4n-6) turnover rate in phospholipids through modulation of endoplasmic reticulum-localized acyl-CoA synthetase activity. Although 20:4n-6 is a precursor for prostaglandin (PG), Snca effect on PG levels is unknown. In the present study, we examined the effect of Snca ablation on brain PG level at basal conditions and following 30s of global ischemia. Brain PG were extracted with methanol, purified on C(18) cartridges, and analyzed by LC-MS/MS. We demonstrate, for the first time, that Snca gene ablation did not affect brain PG mass under normal physiological conditions. However, total PG mass and masses of individual PG were elevated approximately 2-fold upon global ischemia in the absence of Snca. These data are consistent with our previously observed reduction in 20:4n-6 recycling through endoplasmic reticulum-localized acyl-CoA synthetase in the absence of Snca, which may result in the increased 20:4n-6 availability for PG production in the absence of Snca during global ischemia and suggest a role for Snca in brain inflammatory response.

Lanthanum suppresses arachidonic acid-induced cell death and mitochondrial depolarization in PC12 cells

Within the framework of studying the mechanisms of acute toxicity of arachidonic acid and the role of ambient cations, we have investigated the effects of extracellular La(3+) on arachidonic acid-induced death (lactate dehydrogenase release) and mitochondrial depolarization (rhodamine 123 fluorescence) in PC12 cells. Micromolar La(3+) profoundly suppressed arachidonic acid toxicity and this effect was dependent on the presence of other cations. Whereas in the cation-free solution 10-20 microM La(3+) protected most cells from death caused by a 2 hour-long exposure to 20 microM arachidonic acid, the cytoprotective effect of 100 microM La(3+) was reduced to approximately 70% in the presence of a normal complement of monovalent cations and was hardly detectable with 5 mM Ca(2+) in the bath. Increasing the concentration of arachidonic acid could defeat La(3+) cytoprotection. In fluorescence experiments, arachidonic acid caused a decrease in the mitochondrial membrane potential, with the rate and extent of depolarization increasing with an increase in the concentration of arachidonic acid. La(3+) countered the depolarizing effect of arachidonic acid in a manner consistent with a decrease in the effective arachidonic acid concentration. The results suggest that extracellular cations modulate cellular effects of arachidonic acid by reducing its ability to pass through the plasma membrane, possibly by binding the fatty acid. The similarities of the La(3+) effects on arachidonic acid-induced cell death and arachidonic acid-induced mitochondrial depolarization strongly support the causal relations between the two events and suggest that mitochondria are the primary target of arachidonic acid at the cellular level.

Phospholipase A2, reactive oxygen species, and lipid peroxidation in cerebral ischemia

Ischemic stroke is caused by obstruction of blood flow to the brain, resulting in energy failure that initiates a complex series of metabolic events, ultimately causing neuronal death. One such critical metabolic event is the activation of phospholipase A2 (PLA2), resulting in hydrolysis of membrane phospholipids and release of free fatty acids including arachidonic acid, a metabolic precursor for important cell-signaling eicosanoids. PLA2 enzymes have been classified as calcium-dependent cytosolic (cPLA2) and secretory (sPLA2) and calcium-independent (iPLA2) forms. Cardiolipin hydrolysis by mitochondrial sPLA2 disrupts the mitochondrial respiratory chain and increases production of reactive oxygen species (ROS). Oxidative metabolism of arachidonic acid also generates ROS. These two processes contribute to formation of lipid peroxides, which degrade to reactive aldehyde products (malondialdehyde, 4-hydroxynonenal, and acrolein) that covalently bind to proteins/nucleic acids, altering their function and causing cellular damage. Activation of PLA2 in cerebral ischemia has been shown while other studies have separately demonstrated increased lipid peroxidation. To the best of our knowledge no study has directly shown the role of PLA2 in lipid peroxidation in cerebral ischemia. To date, there are very limited data on PLA2 protein by Western blotting after cerebral ischemia, though some immunohistochemical studies (for cPLA2 and sPLA2) have been reported. Dissecting the contribution of PLA2 to lipid peroxidation in cerebral ischemia is challenging due to multiple forms of PLA2, cardiolipin hydrolysis, diverse sources of ROS arising from arachidonic acid metabolism, catecholamine autoxidation, xanthine oxidase activity, mitochondrial dysfunction, activated neutrophils coupled with NADPH oxidase activity, and lack of specific inhibitors. Although increased activity and expression of various PLA2 isoforms have been demonstrated in stroke, more studies are needed to clarify the cellular origin and localization of these isoforms in the brain, their responses in cerebral ischemic injury, and their role in oxidative stress.

Chronic administration of ethyl docosahexaenoate decreases mortality and cerebral edema in ischemic gerbils

Dietary docosahexaenoic acid (DHA) intake can decrease the level of membrane arachidonic acid (AA), which is liberated during cerebral ischemia and implicated in the pathogenesis of brain damage. Therefore, in the present study, we investigated the effects of chronic ethyl docosahexaenoate (E-DHA) administration on mortality and cerebral edema induced by transient forebrain ischemia in gerbils. Male Mongolian gerbils were orally pretreated with either E-DHA (100, 150 mg/kg) or vehicle, once a day, for 4 weeks and were subjected to transient forebrain ischemia by bilateral common carotid occlusion for 30 min. The content of brain lipid AA at the termination of treatment, the survival ratio, change of regional cerebral blood flow (rCBF), brain free AA level, thromboxane B(2) (TXB(2)) production and cerebral edema formation following ischemia and reperfusion were evaluated. E-DHA (150 mg/kg) pretreatment significantly increased survival ratio, prevented post-ischemic hypoperfusion and attenuated cerebral edema after reperfusion compared with vehicle, which was well associated with the reduced levels of AA and TXB(2) in the E-DHA treated brain. These data suggest that the effects of E-DHA pretreatment on ischemic mortality and cerebral edema could be due to reduction of free AA liberation and accumulation, and its metabolite synthesis after ischemia and reperfusion by decreasing the content of membrane AA.

A potentially critical role of phospholipases in central nervous system ischemic, traumatic, and neurodegenerative disorders

Phospholipases are a diverse group of enzymes whose activation may be responsible for the development of injury following insult to the brain. Amongst the numerous isoforms of phospholipase proteins expressed in mammals are 19 different phospholipase A2's (PLA2s), classified functionally as either secretory, calcium dependent, or calcium independent, 11 isozymes belonging to three structural groups of PLC, and 3 PLD gene products. Many of these phospholipases have been identified in selected brain regions. Under normal conditions, these enzymes regulate the turnover of free fatty acids (FFAs) in membrane phospholipids affecting membrane stability, fluidity, and transport processes. The measurement of free fatty acids thus provides a convenient method to follow phospholipase activity and their regulation. Phospholipase activity is also responsible for the generation of an extensive list of intracellular messengers including arachidonic acid metabolites. Phospholipases are regulated by many factors including selective phosphorylation, intracellular calcium and pH. However, under abnormal conditions, excessive phospholipase activation, along with a decreased ability to resynthesize membrane phospholipids, can lead to the generation of free radicals, excitotoxicity, mitochondrial dysfunction, and apoptosis/necrosis. This review evaluates the critical contribution of the various phospholipases to brain injury following ischemia and trauma and in neurodegenerative diseases.

Measurement of free fatty acids in cerebrospinal fluid from patients with hemorrhagic and ischemic stroke

Free fatty acid (FFA) concentrations in cerebrospinal fluid (CSF) from patients with ischemic and hemorrhagic stroke (n=25) and in contemporary controls (n=73) were examined using HPLC. Concentrations of CSF FFAs from ischemic and hemorrhagic stroke patients obtained within 48 h of the insult were significantly greater than in control patients. Higher concentrations of polyunsaturated fatty acids (PUFAs) in CSF obtained within 48 h of insult were associated with significantly lower (P<0.05) admission Glasgow Coma Scale scores and worse outcome at the time of hospital discharge, using the Glasgow Outcome Scale (P<0.01).

Animal models of focal and global cerebral ischemia

The use of appropriate animal models is essential to predict the value and effect of therapeutic approaches in human subjects. Focal (stroke) and global (cardiac arrest) cerebral ischemia represents diseases that are common in the human population. Stroke and cardiac arrest, which are major causes of death and disability, affect millions of individuals around the world and are responsible for the leading health care costs of all diseases. Understanding the mechanisms of injury and neuroprotection in these diseases is critical if we are ever to learn new target sites to treat ischemia. There are many animal models available to investigate injury mechanisms and neuroprotective strategies. This review summarizes many (but not all) small and large animal models of focal and global cerebral ischemia and discusses their advantages and disadvantages.

N-Acylphosphatidylethanolamine accumulation in potato cells upon energy shortage caused by anoxia or respiratory inhibitors

A minor phospholipid was isolated from potato (Solanum tuberosum L. cv Bintje) cells, chromatographically purified, and identified by electrospray ionization mass spectrometry as N-acylphosphatidylethanolamine (NAPE). The NAPE level was low in unstressed cells (13 +/- 4 nmol g fresh weight(-1)). According to acyl chain length, only 16/18/18 species (group II) and 18/18/18 species (group III) were present. NAPE increased up to 13-fold in anoxia-stressed cells, but only when free fatty acids (FFAs) started being released, after about 10 h of treatment. The level of groups II and III was increased by unspecific N-acylation of phosphatidylethanolamine, and new 16/16/18 species (group I) appeared via N-palmitoylation. NAPE also accumulated in aerated cells treated with NaN(3) plus salicylhydroxamate. N-acyl patterns of NAPE were dominated by 18:1, 18:2, and 16:0, but never reflected the FFA composition. Moreover, they did not change greatly after the treatments, in contrast with O-acyl patterns. Anoxia-induced NAPE accumulation is rooted in the metabolic homeostasis failure due to energy deprivation, but not in the absence of O(2), and is part of an oncotic death process. The acyl composition of basal and stress-induced NAPE suggests the existence of spatially distinct FFA and phosphatidylethanolamine pools. It reflects the specificity of NAPE synthase, the acyl composition, localization and availability of substrates, which are intrinsic cell properties, but has no predictive value as to the type of stress imposed. Whether NAPE has a physiological role depends on the cell being still alive and its compartmentation maintained during the stress period.

Rewarming eliminates the protective effect of cooling against delayed neuronal death

Mild intra-ischemic hypothermia provides neuroprotection against delayed neuronal death in the hippocampal CA1. It has recently been reported that reduction in the metabolic rate of arachidonic acid (AA) liberated during ischemia might contribute to this neuroprotection. To examine whether rewarming during the early period of recirculation accelerates AA consumption and eliminates the neuroprotection, we measured the levels of AA in the hippocampus after various recirculation times under normothermia and hypothermia with or without rewarming. The tendency for AA to disappear was significantly different between each pair of groups. Histological examination 7 days after ischemia revealed no protection in the rewarmed group. These results suggest that neuronal injury during rewarming after hypothermia may be attributed to the rate of AA metabolism.

Regional distribution of ethanolamine plasmalogen in the hippocampal CA1 and CA3 regions and cerebral cortex of the gerbil

Although ethanolamine plasmalogens (EtnPm) are the predominant phospholipids in neural tissue, their physiological role has not been clarified. The biophysical conformation of EtnPm in the proteoliposome enhances the activity of the sodium-calcium exchanger, which has been proposed to induce intracellular calcium ion accumulation during ischemia and early reperfusion. The levels of EtnPm in the areas of the gerbil brain selectively vulnerable to ischemia, namely the hippocampal CA1 and CA3 regions and the cerebral cortex, were measured by high-performance thin-layer chromatography and gas-liquid chromatography. The concentration of EtnPm in the CA1 region, which is the most vulnerable to ischemic and anoxic stress, was 2.6- and 2.7-fold higher than that in the CA3 region and cerebral cortex, respectively. The significantly higher concentration of EtnPm in the hippocampal CA1 region may enhance sodium-calcium exchanger activity and play an important role in the vulnerability of this region to ischemia.

Lethal forebrain ischemia stimulates sphingomyelin hydrolysis and ceramide generation in the gerbil hippocampus

Ceramide, a hydrolyzed product of sphingomyelin, is reported to play an important role in apoptosis. In this study, we measured the sphingomyelin and ceramide levels in the hippocampus of the gerbil after transient forebrain ischemia for 5 min (lethal) or 2 min (sublethal). The aim was to examine alterations in the sphingomyelin cycle during delayed neuronal death, which we considered could be due to apoptosis. Sphingolipids were separated on high-performance thin-layer chromatography plates and analyzed by gas-liquid chromatography. At 30 min and 24 h after lethal ischemia, sphingomyelin levels were decreased and ceramide levels were increased compared with control levels. No significant changes were observed after sublethal ischemia. These results suggest that the sphingomyelin cycle may have a role in neuronal death.

Deacylation and reacylation of neural membrane glycerophospholipids

The deacylation-reacylation cycle is an important mechanism responsible for the introduction of polyunsaturated fatty acids into neural membrane glycerophospholipids. It involves four enzymes, namely acyl-CoA synthetase, acyl-CoA hydrolase, acyl-CoA: lysophospholipid acyltransferase, and phospholipase A2. All of these enzymes have been purified and characterized from brain tissue. Under normal conditions, the stimulation of neural membrane receptors by neurotransmitters and growth factors results in the release of arachidonic acid from neural membrane glycerophospholipids. The released arachidonic acid acts as a second messenger itself. It can be further metabolized to eicosanoids, a group of second messengers involved in a variety of neurochemical functions. A lysophospholipid, the second product of reactions catalyzed by phospholipase A2, is rapidly acylated with acyl-CoA, resulting in the maintenance of the normal and essential neural membrane glycerophospholipid composition. However, under pathological situations (ischemia), the overstimulation of phospholipase A2 results in a rapid generation and accumulation of free fatty acids including arachidonic acid, eicosanoids, and lipid peroxides. This results in neural inflammation, oxidative stress, and neurodegeneration. In neural membranes, the deacylation-reacylation cycle maintains a balance between free and esterified fatty acids, resulting in low levels of arachidonic acid and lysophospholipids. This is necessary for not only normal membrane integrity and function, but also for the optimal activity of the membrane-bound enzymes, receptors, and ion channels involved in normal signal-transduction processes.

Free radicals are involved in the damage to protein synthesis after anoxia/aglycemia and NMDA exposure

Neuronal protein synthesis is inhibited in CA1 pyramidal neurons for many hours after ischemia, hypoxia or hypoglycemia. This inhibition precedes cell death, is a hallmark characteristic of necrotic damage and may play a key role in the death of vulnerable neurons after these insults. The sequence of events leading to this inhibition remains to be fully elucidated. The protein synthesis failure after 7.5 min anoxia/aglycemia in the rat hippocampal slice can be prevented by blocking N-methyl-D-aspartate receptors in a reduced calcium environment during the insult. In this study, we demonstrate that N-methyl-D-aspartate exposure directly causes a dose-dependent, receptor-mediated and prolonged protein synthesis inhibition in CA1 pyramidal neurons. The free radical scavenger Vitamin E significantly attenuates this damage due to low concentrations of N-methyl-D-aspartate (10 microM). Free radical generation by xanthine/xanthine oxidase (XOD) can directly damage protein synthesis in neurons of the slice. Vitamin E, ascorbic acid and N-acetylcysteine can each prevent the damage due to anoxia/aglycemia and to higher concentrations of N-methyl-D-aspartate (50 microM), provided calcium levels are reduced concomitantly. These findings indicate that both free radicals and calcium play a role in the sequence of events leading to protein synthesis failure after energetic stress like anoxia/aglycemia. They further suggest that the mechanism by which N-methyl-D-aspartate receptor activation damages protein synthesis involves free radical generation.

Arachidonic acid and leukotriene C4: role in transient cerebral ischemia of gerbils

Accumulation of arachidonic acid (AA) is greatest in brain regions most sensitive to transient ischemia. Free AA released after ischemia is either: 1) reincorporated into the membrane phospholipids, or 2) oxidized during reperfusion by lipoxygenases and cyclooxygenases, producing leukotrienes (LT), prostaglandins, thromboxanes and oxygen radicals. AA, its metabolite LTC4 and lipid peroxides (generated during AA metabolism) have been implicated in the blood-brain barrier (BBB) dysfunction, edema and neuronal death after ischemia/reperfusion. This report describes the time course of AA release, LTC4 accumulation and association with the physiological outcome during transient cerebral ischemia of gerbils. Significant amount of AA was detected immediately after 10 min ischemia (0 min reperfusion) which returned to sham levels within 30 min reperfusion. A later release of AA occurred after 1 d. LTC4 levels were elevated at 0-6 h and 1 d after ischemia. Increased lipid peroxidation due to AA metabolism was observed between 2-6 h. BBB dysfunction occurred at 6 h. Significant edema developed at 1 and 2 d after ischemia and reached maximum at 3 d. Ischemia resulted in approximately 80% neuronal death in the CA1 hippocampal region. Pretreatment with a 5-lipoxygenase inhibitor, AA861 resulted in significant attenuation of LTC4 levels (Baskaya et al. 1996. J. Neurosurg. 85: 112-116) and CA1 neuronal death. Accumulation of AA and LTC4, together with highly reactive oxygen radicals and lipid peroxides, may alter membrane permeability, resulting in BBB dysfunction, edema and ultimately to neuronal death.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

Lactate and free fatty acids after subarachnoid hemorrhage

The hypothesis that lactate and free fatty acids (FFA) are elevated in the first minutes after subarachnoid hemorrhage (SAH) is tested. Adult rats were subjected to an endovascular SAH through the right internal carotid artery while under anesthesia. The brains were frozen in-situ at 15, 30, 60 min, and 24 h post-hemorrhage. Regional measures of tissue lactic acid and FFA were made in the hippocampi, ipsilateral cortex, contralateral cortex, and cerebellum. Lactic acid levels were significantly elevated from sham animals in each region within the first hour (p<0.0001 cerebellum, right, and contralateral cortex, p<0.01 hippocampus), but did not change significantly over the first hour. At 24 h post-hemorrhage, there was no significant difference in the lactic acid levels from controls. Similarly, total FFA were significantly higher in each region as compared to sham operated controls within the first hour (p<0.001 cerebellum, p<0.05 hippocampus, p<0.05 contralateral cortex, p<0.0001 ipsilateral cortex). By 24 h, there was no significant difference in FFA levels from shams. The data indicate that aerobic metabolism fails and cellular damage with degradation of cell membranes occurs in the first minutes after SAH, and lasts for at least 1 h. However, this process is stabilized within 24 h in our model. Although the largest effect was seen in the ipsilateral cortex, all areas of the brain were effected.

Severity of experimental brain injury on lactate and free fatty acid accumulation and Evans blue extravasation in the rat cortex and hippocampus

Lactate and free fatty acids (FFAs) were extracted from the cortices and hippocampi of rats subjected to sham operation, or mild (1.25 atm) or moderate (2.0 atm) fluid percussion (FP) injury, and their total tissue concentrations were measured. The elevation of lactate in the injured left cortex (IC) and ipsilateral hippocampus (IH) was significantly greater in the moderate-injury than in the mild-injury group at most test times between 5 min and 48 h after injury. Levels of total FFAs were elevated in the IC and IH to a greater extent and for a longer period after injury in the moderate-injury (up to 48 h) than in the mild-injury group (up to 20 min). In general, the extent and duration of the elevation of most of the individual FFAs (palmitic, stearic, oleic, and arachidonic acids) in the IC and IH were also greater in the moderate-injury group than in the mild-injury group. In the contralateral cortex (CC) and hippocampus (CH), the elevation of lactate and total FFAs (and individual stearic and arachidonic acids) were also greater in the moderate-injury group than in the low-injury group at 5 min after injury. The extravasation of Evans blue in the IC and IH from 3 to 6 h after injury was also the greatest in the moderate-injury group. The hippocampal CA3 neuronal cell loss, but not cortical lesion volume, also increased with the severity of injury. These findings suggest that certain neurochemical, physiological (blood-brain barrier permeability), and morphologic responses increase with the severity of FP brain injury, and such relationships are consistent with the increased behavioral deficits observed with the increase of severity of brain injury.

Activation of cPLA2, PKC, and ERKs in the rat cerebral cortex during ischemia/reperfusion

Release of the excitotoxic amino acid, glutamate, into the extracellular space during ischemia/reperfusion contributes to neuronal injury and death. To gain insights into the signal transduction pathways involved in glutamate release we examined the time course of changes in enzyme levels and activities of cPLA2, PKC and ERKs in the rat cerebral cortex after four vessel (4VO) ischemia followed by reperfusion. Measurement both by enzymatic assay and Western blot analysis showed significant increases in the activity and protein levels of cPLA2 during 10-20 min of ischemia. Activity remained elevated at 10 min and 20 min of reperfusion, whereas cPLA levels had returned to base line levels after 20 min of reperfusion. PKC activity increased significantly in the particulate, but not in the cytosolic, fractions both during ischemia and reperfusion. Increases in PKCgamma levels were recorded in the particulate fraction during ischemia and reperfusion, and in the cytosolic fraction during ischemia. Western blot analysis with a phosphospecific antibody for characterization of MAPK (ERKs) activation revealed significantly increased phosphorylation of ERK1 and ERK2 in the particulate fraction, of ERK2 in the cytosolic fraction, during ischemia and of both enzymes in the particulate and cytosolic fractions after 10 min of reperfusion. The relevance of the results to glutamate release is discussed.

Role of the ryanodine receptor in ischemic brain damage--localized reduction of ryanodine receptor binding during ischemia in hippocampus CA1

1. The ryanodine receptor has recently been shown to play a pivotal role in the regulation of intracellular Ca2+ concentration via Ca(2+)-induced Ca2+ release (CICR). Effects of ischemia on CICR in the brain tissue, however, remain largely unknown since only a few reports have been published on this subject. In this paper we report on work in this area by our group and review related progress in this field. 2. We examined alterations of ryanodine receptor binding and local cerebral blood flow (LCBF) at 15 min, 30 min, and 2 hr after occlusion of the right common carotid artery in the gerbil brain. A quantitative autoradiographic method permitted simultaneous measurement of these parameters in the same brain. The LCBF was significantly reduced in most of the cerebral regions on the occluded side during each time period of ischemia. In contrast, only in the hippocampus CA1 on the occluded side was a significant reduction in ryanodine binding found at 15 min, 30 min and 2 hr after the occlusion. 3. These findings suggest that suppression of ryanodine binding in the hippocampus CA1 may be attributable to a regionally specific perturbation of CICR and that this perturbation may be closely associated with the pathophysiological mechanism that leads to be selective ischemic vulnerability of this region. 4. Other recent studies have also reported an important role for ryanodine receptors in neuronal injury such as the delayed neuronal death in the hippocampus CA1. These data suggest that derangement of CICR is likely to be involved in acute neuronal necrosis as well as in delayed neuronal death in ischemia. 5. Further studies on clarifying the role of CICR in ischemic brain damage are needed in order to develop new therapeutic strategies for stroke patients.

Acute effects of acetyl-L-carnitine on sodium cyanide-induced behavioral and biochemical deficits

In the present study we investigated the effects of acute treatment with acetyl-L-carnitine (50 mg/kg, i.v. 90 min before the sodium cyanide injection) on a sodium cyanide-induced behavioral deficit in the Morris water escape task. In a first experiment the spatial discrimination performance of the rats was found to be dose-dependently impaired after an i.c.v. injection of sodium cyanide (2.5 and 5.0 microg). Acute treatment with acetyl-L-carnitine was found to increase the behavioral deficit after sodium cyanide. These findings were replicated in a second experiment. Based on these results it can be argued that an acute administration of acetyl-L-carnitine appears to potentiate a sodium cyanide-induced behavioral deficit. An additional in vitro experiment with rat brain synaptosomes showed clear effects of administered sodium cyanide on the energy-dependent incorporation of inositol into phosphoinositides and on the ATP concentration. In vitro acetyl-L-carnitine administration had no effect on the sodium cyanide-induced energy depletion. The negative behavioral findings are in contrast with our previously found protective effect of chronic treatment with acetyl-L-carnitine (via drinking water) on the sodium cyanide-induced behavioral deficit. Since chronic acetyl-L-carnitine treatment has no effect on the phosphoinositide metabolism it was suggested that acetyl-L-carnitine may act via the formation of an ATP-independent reservoir of activated acyl groups. Thus, fatty acids as acylated derivatives can be used for reacylation processes during an acute period of energy depletion. However, we have no clear explanation for the discrepancy in behavioral results between the chronic vs acute treatment of acetyl-L-carnitine at present. Further research is needed to characterize the mechanism of action of acetyl-L-carnitine in relation to sodium cyanide.

Involvement of reactive oxygen species in membrane phospholipid breakdown and energy perturbation after traumatic brain injury in the rat

Interstitial glycerol may be a useful marker for posttraumatic and postischemic membrane phospholipid (PL) breakdown. Degradation of membrane PLs is thought to be triggered by both calcium and reactive oxygen species (ROS)-mediated mechanisms and to be associated with disturbed energy metabolism. In this study, we investigated the temporal changes of interstitial glycerol, lactate, and glucose after traumatic brain injury in the rat and the effect of pretreatment with the free radical spin trap alpha-phenyl-N-tert-butyl nitrone (PBN; 30 mg/kg i.v.). Microdialysate was sampled continuously in 10-min fractions from 1 h before, until 2 h after a cortical contusion injury produced by the weight-drop technique. The maximal concentration of interstitial glycerol (a ninefold increase) was seen 10-30 min after trauma and subsided during the following 2 h, but remained above base line as compared to sham operated animals. Concomitantly, there was an increase in interstitial lactate (fivefold) and a fall in interstitial glucose, indicating a posttraumatic energy perturbation. PBN treatment significantly attenuated the interstitial accumulation of glycerol and lactate. The results support the concept that ROS are involved in posttraumatic membrane PL breakdown and that PBN improves mitochondrial function after CNS injury. Monitoring of interstitial glycerol with microdialysis may be a valuable tool for studies on membrane PL degradation and the efficacy of neuroprotective drugs in acute CNS injury.

Effects of EGb 761 on fatty acid reincorporation during reperfusion following ischemia in the brain of the awake gerbil

Transient cerebral ischemia (5 min) releases unesterified fatty acids from membrane phospholipids, increasing brain concentrations of fatty acids for up to 1 h following reperfusion. To understand the reported anti-ischemic effect of Ginkgo biloba extract (EGb 761), we monitored its effect on brain fatty acid reincorporation in a gerbil-stroke model. Both common carotid arteries in awake gerbils were occluded for 5 min, followed by 5 min of reperfusion. Animals were infused intravenously with labeled arachidonic (AA) or palmitic acid (Pam), and rates of incorporation of unlabeled fatty acid from the brian acyl-CoA pool were calculated by the model of Robinson et al. (1992), using quantitative autoradiography and biochemical analysis of brain acyl-CoA. Animals were treated for 14 d with 50 or 150 mg/kg/d EGb 761 or vehicle. Ischemia-reperfusion had no effect on the rate of unlabeled Pam incorporation into brain phospholipids from palmitoyl-CoA; this rate also was unaffected by EGb 761. In contrast, ischemia-reperfusion increased the rate of incorporation of unlabeled AA from brain arachidonoyl-CoA by a factor of 2.3-3.3 compared with the control rate; this factor was further augmented to 3.6-5.0 by pretreatment with EGb 761. There is selective reincorporation of AA compared with Pam into brain phospholipids following ischemia. EGb 761 further accelerates AA reincorporation, potentially reducing neurotoxic effects of prolonged exposure of brain to high concentrations of AA and its metabolites.

Mild hypothermia reduces the rate of metabolism of arachidonic acid following postischemic reperfusion

Free fatty acid (FFA) accumulation during cerebral ischemia has been described as an indicator of ischemic damage. Furthermore arachidonic acid (AA) metabolites, liberated from glycerophospholipids, have been confirmed to induce disturbances of membrane functions. Are there differences in AA levels in the hippocampus of normo- and hypothermic gerbils following ischemia-reperfusion? In an attempt to answer this question, we first studied the time course of changes in the amount of AA liberated from glycerophospholipids using gerbils subjected to 5 min of ischemia-reperfusion under normo- and mild hypothermia. FFAs (including AA) were separated from total lipids by Bond Elut (NH2) column chromatography and analyzed by gas-liquid chromatography. Mild intra-ischemic hypothermia (MIH) did not affect the ischemia-induced AA accumulation following of 5 min of forebrain ischemia. The accumulated AA amounts under MIH tend to decrease more slowly to baseline levels from 15 to 30 min of reperfusion than do the levels under normothermia. These results suggested that MIH reduced the rate of metabolism of AA after reperfusion and might suppress the generation of free radical, eicosanoids and other bioactive metabolites.

Regional membrane phospholipid alterations in Alzheimer's disease

Regional levels of membrane phospholipids [phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylcholine (PC)] were measured in the brain of Alzheimer's disease (AD) and control subjects. The levels of PE-derived and PI-derived total fatty acids were significantly decreased in the hippocampus of AD subjects. Here significant decreases were found in PE-derived stearic, oleic and arachidonic and docosahexaenoic acids, and in PI-derived oleic and arachidonic acids. In the inferior parietal lobule of AD subjects, significant decreases were found only in PE and those decreases were contributed by stearic, oleic and arachidonic acids. In the superior and middle temporal gyri and cerebellum of AD subjects, no significant decreases were found in PC-, PE- and PI-derived fatty acids. The decrease of PE and PI, which are rich in oxidizable arachidonic and docosahexaenoic acids, but not of PC, which contains lesser amounts of these fatty acids, suggests a role for oxidative stress in the increased degradation of brain phospholipids in AD.

Effect of hypoxia and dopamine on arachidonic acid metabolism in superior cervical ganglion

Superior cervical ganglion (SCG) may play a modulatory role on ventilatory control through its efferent sympathetic fibres, which innervate cells in the carotid bodies. In this study the in vivo effect of acute hypoxia versus normoxia on arachidonic acid (AA) metabolism was investigated in cat SCG. Using SCG homogenate AA was incorporated into glycerolipids of normoxic SCG in the following order: neutral glycerolipids > phosphatidylcholine (PtdCh) > phosphatidylinositol (PtdIns) > phosphatidylethanolamine (PtdE) > phosphatidylserine (PtdS) > and phosphatidic acid (PA). In vivo hypoxic treatment caused a significant decrease in incorporation of [1-14C]AA into PtdIns. Hypoxia had no significant effect on the level of AA radioactivity in diacylglycerol (DAG) as compared to control but significantly enhanced the level of arachidonoyl-CoA (AA-CoA) radioactivity. It was observed that dopamine (DA) one of the most important neurotransmitter in SCG decreases AA uptake into phospholipids of normoxic SCG. In normoxic SCG, DA significantly decreased, AA incorporation into PtdCh, PtdIns and DAG. Moreover, DA decreased the level of AA-CoA radioactivity. Hypoxia and dopamine has no effect on AA metabolism in medulla oblongata isolated from the same animals. These results indicate that arachidonic acid metabolism in SCG is sensitive to hypoxia and dopamine action. Moreover, these results indicate that hypoxia inhibits selectively AA incorporation on the level of acylCoA-lysophosphatidylinositol-acyltransferase.

Relation between free fatty acid and acyl-CoA concentrations in rat brain following decapitation

To ascertain effects of total ischemia on brain phospholipid metabolism, anesthetized rats were decapitated and unesterified fatty acids and long chain acyl-CoA concentrations were analyzed in brain after 3 or 15 min. Control brain was taken from rats that were microwaved. Fatty acids were quantitated by extraction, thin layer chromatography and gas chromatography. Long-chain acyl-CoAs were quantitated by solubilization, solid phase extraction with an oligonucleotide purification cartridge and HPLC. Unesterified fatty acid concentrations increased significantly after decapitation, most dramatically for arachidonic acid (76 fold at 15 min) followed by docosahexaenoic acid. Of the acyl-CoA molecular species only the concentration of arachidonoyl-CoA was increased at 3 min and 15 min after decapitation, by 3-4 fold compared with microwaved brain. The concentration of docosahexaenoyl-CoA fell whereas concentrations of the other acyl-CoAs were unchanged. The increase in arachidonoyl-CoA after decapitation indicates that reincorporation of arachidonic acid into membrane phospholipids is possible during ischemia, likely at the expense of docosahexaenoic acid.

Protective effect of the 5-lipoxygenase inhibitor AA-861 on cerebral edema after transient ischemia

This study examined the effect of AA-861, a specific 5-lipoxygenase inhibitor, on brain levels of leukotriene C4 (LTC4) and correlated any changes with changes in edema formation and cerebral blood flow (CBF) after transient ischemia in gerbils. Brain levels of LTC4 were observed to be increased at 1, 2, and 6 hours of reperfusion following 20 minutes of occlusion. At 2 hours of reperfusion, a pretreatment dose of 1000 mg/kg of AA-861 was required to inhibit more than 90% of the reperfusion-induced increases in brain LTC4. At this dose, inhibition of LTC4 production was observed at 2 and 6 hours of reperfusion. The specific gravity of both the cortex and subcortex was decreased at 6 hours of reperfusion after 20 minutes of occlusion. At 2 hours of reperfusion, no significant difference was observed in the specific gravity of the cortex and subcortex regions of gerbils pretreated with AA-861 or with vehicle, but at 6 hours of reperfusion significant positive differences were observed. Cerebral blood flow decreased to approximately 10% of preocclusion values during occlusion and returned to near-preocclusion values after 10 minutes of reperfusion. No significant differences were observed in regional CBF in the AA-861- and vehicle-pretreated gerbils during reperfusion. These findings indicate that LTC4 production after transient cerebral ischemia may be an important contributor to the development of cerebral edema and that CBF does not mediate the LTC4-involved development of edema.

Effects of glucose and oxygen deprivation on phosphoinositide hydrolysis in cerebral cortex slices from neonatal rats

The effects of glucose deprivation, hypoxia and glucose-free hypoxia conditions on phosphoinositide (PI) hydrolysis were studied in cortical slices from 8-day-old rats. Only glucose-free hypoxia induced a significant increase of inositol phosphate formation. The inositol phosphate formation induced by noradrenaline, carbachol and several excitatory amino acid receptor agonists, but not the Ca2+ ionophore A23187-induced stimulation, was blocked by glucose-free hypoxia and differentially reduced by glucose and oxygen deprivation depending on the neurotransmitter receptor agonist. The stimulatory effect of glucose-free hypoxia was not reduced by the muscarinic receptor antagonist atropine or by the inhibitors of the excitatory amino acid-stimulated PI hydrolysis DL-2-amino-3-phosphono-propionic acid and L-aspartate-beta-hydroxamate, and neither by the voltage-sensitive Na+ channel tetrodotoxin. The effect of glucose-free hypoxia was partially dependent on extracellular Ca2+ and it was blocked by verapamil and amiloride, but not by nifedipine, Co2+ and neomycin. These results suggest that Ca2+ influx through the Na(+)-Ca2+ exchanger underlies the PI hydrolysis stimulation induced by combined glucose and oxygen deprivation in neonatal cerebral cortical slices.

Alterations in brain protein kinase C after experimental brain injury

Regional activities and levels of protein kinase C were measured after lateral fluid percussion brain injury in rats. At 5 min and 20 min after injury, neither cofactor-dependent nor -independent PKC activities in the cytosol and membrane fractions changed in the injured and contralateral cortices or in the ipsilateral hippocampus. Western blot analysis revealed decreases in the levels of cytosolic PKC alpha and PKC beta in the injured cortex after brain injury. In the same site, a significant increase in the levels of membrane PKC alpha and PKC beta was observed after injury. Although the level of PKC alpha did not change and that of PKC beta decreased in the cytosol of the ipsilateral hippocampus, these levels did not increase in the membrane fraction after injury. The levels of PKC gamma were generally unchanged in the cytosol and the membrane, except for its decrease in the cytosol of the hippocampus. There were no changes in the levels of any PKC isoform in either the cytosol or the membrane of the contralateral cortex after injury. The present results suggest a translocation of PKC alpha and PKC beta from the cytosol to the membrane in the injured cortex after brain injury. The observation that such a translocation occurs only in the brain regions that undergo substantial neuronal loss suggests that membrane PKC may play a role in neuronal damage after brain injury.

Radioiodinated diacylglycerol analogue: a potential imaging agent for single-photon emission tomographic investigations of cerebral ischaemia

Phospholipid metabolism is closely related to membrane perturbation in cerebral ischaemia. We investigated in vivo topographical lipid metabolism using an iodine-123-labelled diacylglycerol analogue, (1-(15-(4-iodine-123-iodophenyl)-pentadecanoyl)-2-stearoyl-rac-gly cerol) (123I-labelled DAG), in a middle cerebral artery (MCA) occlusion model with the aim of positive imaging of ischaemic insult. Sprague-Dawley rats underwent coagulation of the MCA to induce permanent occlusion. MCA occlusion times prior to injection of 123I-labelled DAG ranged from 15 min to 14 days. Each rat was injected with 11-37 MBq of 123I-labelled DAG via a tail vein. After 30 min, in vivo autoradiographs were reconstructed. Scanning of the living rat brain in this MCA occlusion model was performed using a gamma camera with a pinhole collimator. Cerebral infarctions were recognized in the frontal cortex, the parietal cortex and the lateral portion of the caudate-putamen by 2,3,5-triphenyltetrazolium hydrochloride staining. In infarcted regions (region 1), 123I-labelled DAG incorporation showed a slight decrease up to 12 h; it then increased up to 6 days and decreased thereafter. In peri-infarcted regions (region 2), the incorporation showed almost no change up to 12 h, then increased up to 5-6 days and decreased thereafter. In other regions (region 3), the incorporation showed no change. Lipid analysis showed that 123I-labelled DAG was metabolized to 15-(4-iodine-123-iodophenyl)-pentadecanoic acid by DAG lipase and to 123I-labelled phosphatidylcholine. Scanning of the ischaemic region showed higher accumulation than on the non-lesioned side. We established a method to visualize ischaemic foci as positive images. The early changes in 123I-labelled DAG incorporation were closely related to DAG lipase, which degraded the accumulated intrinsic DAG, and increased 123I-labelled DAG incorporation in the chronic stage involves several aspects of neural destruction in the process of autolysis. It is concluded that the reported method could have a clinical future.

Brain accumulation of myo-inositol in the trisomy 16 mouse, an animal model of Down's syndrome

myo-Inositol and several other polyols were measured in the tissues of the trisomy 16 mouse (animal model of Down's Syndrome; human trisomy 21) and diploid controls. myo-Inositol was found to be selectively elevated in the brain of the trisomy 16 mouse. However, peripheral tissues showed no elevation. These results are consistent with the cerebrospinal fluid and plasma data reported previously on myo-inositol in Down's Syndrome subjects.

Activation of phosphatidylinositol bisphosphate signal transduction pathway after experimental brain injury: a lipid study

Regional levels of phosphatidylinositol 4,5-bisphosphate (PIP2), diacylglycerol (DG) and free fatty acids (FFA), involved in the signal transduction pathway of the excitatory neurotransmitter system, were measured after lateral fluid percussion (FP) brain injury in rats. At 5 min postinjury, tissue PIP2 concentrations were significantly reduced in the cortices and hippocampi of both ipsilateral and contralateral hemispheres. Only levels of stearic and arachidonic acids were substantially decreased in PIP2 in these regions of the brain. At the same time after injury, both DG and FFA were significantly increased in the cortices and hippocampi of both hemispheres. As was true for PIP2, only levels of stearic and arachidonic acids markedly changed in both DG and FFA in these regions of the brain. At 20 min postinjury, a significant decrease in PIP2 concentration and significant increases in levels of DG and FFA were observed only in the injured left cortex. In addition to the increases in stearic and arachidonic acids in FFA, increased amounts of palmitic and oleic acids were also found in the injured left cortex at 20 min after injury. These results suggest that the PIP2 signal transduction pathway is activated in the cortex and hippocampus at the onset of lateral FP brain injury and that the enhanced phospholipase C-catalyzed phosphodiestric breakdown of PIP2 is a major mechanism of liberation of FFA in these sites immediately after such injury.

Regulation of FFA by the acyltransferase pathway in focal cerebral ischemia-reperfusion

Cerebral insult is associated with a rapid increase in free fatty acids (FFA) and arachidonic acid release has been linked to the increase in eicosanoid biosynthesis. In transient focal cerebral ischemia induced by middle cerebral artery (MCA) occlusion, there is an inverse relationship between the increase in FFA and the decrease in ATP, both during the ischemia period and at later time periods after reperfusion. In this study, the focal cerebral ischemia model was used to examine incorporation of [14C]arachidonic acid into the glycerolipids in rat MCA cortex at different reperfusion times after a 60 min ischemia. The label was injected intracerebrally into left and right MCA cortex 1 hr prior to decapitation. Labeled arachidonic acid was incorporated into phosphatidylcholine, phosphatidylethanolamine and neutral glycerides. With increasing time (4-16 hr) after a 60 min ischemia, an inhibition of labeled arachidonate uptake could be found in the right ischemic MCA cortex, whereas the distribution of radioactivity among the major phospholipids was not altered. When compared to labeled PC, there was a 3-4 fold increase in incorporation of label into phosphatidic acid and triacylglycerols (TG) in the right MCA cortex, suggesting of an increase in de novo biosynthesis of TG. In an in vitro assay system, synaptosomal membranes isolated from MCA cortex 8 and 16 hr after a 60 min ischemia showed a significant decrease in arachidonoyl transfer to lysophospholipids, due mainly to a decrease in lysophospholipid:acylCoA acyltransferase activity. Assay of phospholipase A2 activity with both syaptosomes and cytosol, however, did not show differences between left and right MCA cortex or with time after reperfusion. These results suggest that besides ATP availability, the decrease in acyltransferase activity may also contribute to the increase in FFA in cerebral ischemia-reperfusion.

Mediators of injury in neurotrauma: intracellular signal transduction and gene expression

Membrane lipid-derived second messengers are generated by phospholipase A2 (PLA2) during synaptic activity. Overstimulation of this enzyme during neurotrauma results in the accumulation of bioactive metabolites such as arachidonic acid, oxygenated derivatives of arachidonic acid, and platelet-activating factor (PAF). Several of these bioactive lipids participate in cell damage, cell death, or repair-regenerative neural plasticity. Neurotransmitters may activate PLA2 directly when linked to receptors coupled to G proteins and/or indirectly as calcium influx or mobilization from intracellular stores is stimulated. The release of arachidonic acid and its subsequent metabolism to prostaglandins are early responses linked to neuronal signal transduction. Free arachidonic acid may interact with membrane proteins, i.e., receptors, ion channels, and enzymes, modifying their activity. It can also be acted upon by prostaglandin synthase isoenzymes (the constitutive prostaglandin synthase PGS-1 or the inducible PGS-2) and by lipoxygenases, with the resulting formation of different prostaglandins and leukotrienes. Glutamatergic synaptic activity and activation of postsynaptic NMDA receptors are examples of neuronal activity, linked to memory and learning processes, which activate PLA2 with the consequent release of arachidonic acid and platelet-activating factor (PAF), another lipid mediator. Both mediators may exert presynaptic and postsynaptic effects contributing to long-lasting changes in glutamate synaptic efficacy or long-term potentiation (LTP), PAF, a potential retrograde messenger in LTP, stimulates glutamate release. The PAF antagonist BN 52021 competes for receptors in presynaptic membranes and blocks this effect. PAF may also be involved in plasticity responses because PAF leads to the expression of early response genes and subsequent gene cascades. The PAF antagonist BN 50730, selective for PAF intracellular binding, blocks PAF-mediated induction of gene expression. A consequence of neural injury induced by ischemia, trauma, or seizures is an increased release of neurotransmitters, that in turn generates an overproduction of second messengers. Glutamate, a key player in excitotoxic neuronal damage, triggers increased permeation of calcium mediated by NMDA receptors and activation of PLA2 in postsynaptic neurons. NMDA receptor antagonists reduce the accumulation of free fatty acids and elicit neuroprotection in ischemic damage. Increased production of free arachidonic acid and PAF converges to exacerbate glutamate-mediated neurotransmission. These neurotoxic actions may be brought about by arachidonic acid-induced potentiation of NMDA receptor activity and decreased glutamate reuptake. On the other hand, PAF stimulates the further release of glutamate at presynaptic endings. The neuroprotective effects of the PAF antagonist BN 52021 in ischemia-reperfusion are due, at least in part, to an inhibition of presynaptic glutamate release. PAF also induces expression of the inducible prostaglandin synthase gene, and PAF antagonists selective for the intracellular sites inhibit this effect. The PAF antagonist also inhibits the enhanced abundance, due to vasogenic cerebral edema and ischemia-reperfusion damage, of inducible prostaglandin synthase mRNA in vivo. Therefore, PAF, an injury-generated mediator, may favor the formation of other cell injury and inflammation mediators by turning on the expression of the gene that encodes prostaglandin synthase.

Inositol trisphosphate, polyphosphoinositide turnover, and high-energy metabolites in focal cerebral ischemia and reperfusion

BACKGROUND AND PURPOSE

Although the signaling pathway involving polyphosphoinositide (poly-PI) hydrolysis and release of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] is an important mechanism for regulation of neuronal calcium homeostasis, the effect of cerebral ischemia-reperfusion on this calcium signaling pathway is not well understood. Because activity of this pathway is dependent on availability of ATP, this study is aimed at examining the poly-PI signaling pathway and high-energy metabolites in a rat stroke model.

METHODS

Focal cerebral ischemia in rats was induced by temporary occlusion of the right middle cerebral artery and both common carotid arteries. Levels of Ins(1,4,5)P3 were determined by use of the radioreceptor binding assay. Poly-PI turnover in rat cortex was assessed with an in vivo protocol involving intracerebral injection of [3H] inositol and systemic administration of lithium. High-energy metabolites (ATP, ADP, and AMP) were analyzed by high-performance liquid chromatography.

RESULTS

Ischemia induced an increase in poly-PI turnover in the right middle cerebral artery cortex, but reperfusion led to a decline in this signaling activity. However, Ins(1,4,5)P3 levels decreased during ischemia, and these levels were not restored if ischemic insults were longer than 30 minutes. ATP levels decreased to 26% of control during ischemia and recovered to 80% of control during the initial 4 hours of reperfusion; these changes were followed by a second phase of decline.

CONCLUSIONS

Results show an important relationship between ischemia-induced depletion of high-energy metabolites and poly-PI signaling activity. However, the uncoupling between Ins(1,4,5)P3 and ATP during reperfusion after severe ischemia suggests that metabolism of Ins(1,4,5)P3 is more stringently regulated than ATP.