Free fatty acids and energy metabolites in ischemic cerebral cortex with noradrenaline depletion

The role of bioactive lipids in attenuating the neuroinflammatory cascade in traumatic brain injury

Traumatic brain injury (TBI) is a major cause of morbidity, mortality, and economic burden. Despite this, there are no proven medical therapies in the pharmacologic management of TBI. A better understanding of disease pathophysiology might lead to novel approaches. In one area of increasing interest, bioactive lipids known to attenuate inflammation might serve as an important biomarker and mediator of disease after TBI. In this review, we describe the pathophysiology of inflammation following TBI, the actions of endogenous bioactive lipids in attenuating neuroinflammation, and their possible therapeutic role in the management of TBI. In particular, specialized pro‐resolving lipid mediators (SPMs) of inflammation represent endogenous compounds that might serve as important biomarkers of disease and potential therapeutic targets. We aim to discuss the current literature from animal models of TBI and limited human experiences that suggest that bioactive lipids and SPMs are mechanistically important to TBI recovery, and by doing so, aim to highlight the need for further clinical and translational research. Early investigations of dietary and parenteral supplementation of pro‐resolving bioactive lipids have been promising. Given the high morbidity and mortality that occurs with TBI, novel approaches are needed.

Docosanoids and elovanoids from omega-3 fatty acids are pro-homeostatic modulators of inflammatory responses, cell damage and neuroprotection

The functional significance of the selective enrichment of the omega-3 essential fatty acid docosahexaenoic acid (DHA; 22C and 6 double bonds) in cellular membrane phospholipids of the nervous system is being clarified by defining its specific roles on membrane protein function and by the uncovering of the bioactive mediators, docosanoids and elovanoids (ELVs). Here, we describe the preferential uptake and DHA metabolism in photoreceptors and brain as well as the significance of the Adiponectin receptor 1 in DHA retention and photoreceptor cell (PRC) survival. We now know that this integral membrane protein is engaged in DHA retention as a necessary event for the function of PRCs and retinal pigment epithelial (RPE) cells. We present an overview of how a) NPD1 selectively mediates preconditioning rescue of RPE and PR cells; b) NPD1 restores aberrant neuronal networks in experimental epileptogenesis; c) the decreased ability to biosynthesize NPD1 in memory hippocampal areas of early stages of Alzheimer's disease takes place; d) NPD1 protection of dopaminergic circuits in an in vitro model using neurotoxins; and e) bioactivity elicited by DHA and NPD1 activate a neuroprotective gene-expression program that includes the expression of Bcl-2 family members affected by Aβ42, DHA, or NPD1. In addition, we highlight ELOVL4 (ELOngation of Very Long chain fatty acids-4), specifically the neurological and ophthalmological consequences of its mutations, and their role in providing precursors for the biosynthesis of ELVs. Then we outline evidence of ELVs ability to protect RPE cells, which sustain PRC integrity. In the last section, we present a summary of the protective bioactivity of docosanoids and ELVs in experimental ischemic stroke. The identification of early mechanisms of neural cell survival mediated by DHA-synthesized ELVs and docosanoids contributes to the understanding of cell function, pro-homeostatic cellular modulation, inflammatory responses, and innate immunity, opening avenues for prevention and therapeutic applications in neurotrauma, stroke and neurodegenerative diseases.

Palmitate Increases β-site AβPP-Cleavage Enzyme 1 Activity and Amyloid-β Genesis by Evoking Endoplasmic Reticulum Stress and Subsequent C/EBP Homologous Protein Activation

Epidemiological studies implicate diets rich in saturated free fatty acids (sFFA) as a potential risk factor for developing Alzheimer's disease (AD). In particular, high plasma levels of the sFFA palmitic acid (palmitate) were shown to inversely correlate with cognitive function. However, the cellular mechanisms by which sFFA may increase the risk for AD are not well known. Endoplasmic reticulum (ER) stress has emerged as one of the signaling pathways initiating and fostering the neurodegenerative changes in AD by increasing the aspartyl protease β-site AβPP cleaving enzyme 1 (BACE1) and amyloid-β (Aβ) genesis. In this study, we determined the extent to which palmitate increases BACE1 and Aβ levels in vitro and in vivo as well as the potential role of ER stress as cellular mechanism underlying palmitate effects. We demonstrate, in palmitate-treated SH-SY5Y neuroblastoma cells and in the hippocampi of palmitate-enriched diet-fed mice, that palmitate evokes the activation of the C/EBP Homologous Protein (CHOP), a transcription factor that is specifically responsive to ER stress. Induction of CHOP expression is associated with increased BACE1 mRNA, protein and activity levels, and subsequent enhanced amyloidogenic processing of amyloid-β protein precursor (AβPP) that culminates in a substantial increase in Aβ genesis. We further show that CHOP is an indispensable molecular mediator of palmitate-induced upregulation in BACE1 activity and Aβ genesis. Indeed, we show that Chop-/- mice and CHOP knocked-down SH-SY5Y neuroblastoma cells do not exhibit the same commensurate degree of palmitate-induced increase in BACE1 expression levels and Aβ genesis.

[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.

Arachidonic acid binds 14-3-3zeta, releases 14-3-3zeta from phosphorylated BAD and induces aggregation of 14-3-3zeta

Polyunsaturated fatty acids, like arachidonic acid, can bind proteins and affect their function. The 14-3-3 proteins bind phosphorylated sites on a diverse array of client proteins and, in this way, are involved in many intracellular signaling pathways. In this study, we used a novel approach to discover that 14-3-3zeta is able to directly bind arachidonic acid. Furthermore, arachidonic acid, at physiological concentrations, reduced the binding of 14-3-3zeta to phosphorylated BAD, an interaction that is important in regulating apoptosis. In addition, high concentrations of arachidonic acid caused the polymerization of 14-3-3zeta, an event observed in neurodegenerative disorders. Taken together, these results indicate that arachidonic acid directly interacts with 14-3-3zeta and that this interaction may be important in both normal and pathological cellular events. If so, then factors that mediate the release, metabolism and reacylation of arachidonic acid into membranes represent key points of regulation.

Neuroprotectin D1 (NPD1): a DHA-derived mediator that protects brain and retina against cell injury-induced oxidative stress

The biosynthesis of oxygenated arachidonic acid messengers triggered by cerebral ischemia-reperfusion is preceded by an early and rapid phospholipase A2 activation reflected in free arachidonic and docosahexaenoic acid (DHA) accumulation. These fatty acids are released from membrane phospholipids. Both fatty acids are derived from dietary essential fatty acids; however, only DHA, the omega-3 polyunsaturated fatty acyl chain, is concentrated in phospholipids of various cells of brain and retina. Synaptic membranes and photoreceptors share the highest content of DHA of all cell membranes. DHA is involved in memory formation, excitable membrane function, photoreceptor cell biogenesis and function, and neuronal signaling, and has been implicated in neuroprotection. In addition, this fatty acid is required for retinal pigment epithelium cell (RPE) functional integrity. Here we provide an overview of the recent elucidation of a specific mediator generated from DHA that contributes at least in part to its biological significance. In oxidative stress-challenged human RPE cells and rat brain undergoing ischemia-reperfusion, 10,17S-docosatriene (neuroprotectin D1, NPD1) synthesis evolves. In addition, calcium ionophore A23187, IL-1beta, or the supply of DHA enhances NPD1 synthesis. A time-dependent release of endogenous free DHA followed by NPD1 formation occurs, suggesting that a phospholipase A2 releases the mediator's precursor. When NPD1 is infused during ischemia-reperfusion or added to RPE cells during oxidative stress, apoptotic DNA damage is down-regulated. NPD1 also up-regulates the anti-apoptotic Bcl-2 proteins Bcl-2 and BclxL and decreases pro-apoptotic Bax and Bad expression. Moreover, NPD1 inhibits oxidative stress-induced caspase-3 activation. NPD1 also inhibits IL-1beta-stimulated expression of COX-2. Overall, NPD1 protects cells from oxidative stress-induced apoptosis. Because photoreceptors are progressively impaired after RPE cell damage in retinal degenerative diseases, understanding of how these signals contribute to retinal cell survival may lead to the development of new therapeutic strategies. Moreover, NPD1 bioactivity demonstrates that DHA is not only a target of lipid peroxidation, but rather is the precursor to a neuroprotective signaling response to ischemia-reperfusion, thus opening newer avenues of therapeutic exploration in stroke, neurotrauma, spinal cord injury, and neurodegenerative diseases, such as Alzheimer disease, aiming to up-regulate this novel cell-survival signaling.

Novel docosanoids inhibit brain ischemia-reperfusion-mediated leukocyte infiltration and pro-inflammatory gene expression

Ischemic stroke triggers lipid peroxidation and neuronal injury. Docosahexaenoic acid released from membrane phospholipids during brain ischemia is a major source of lipid peroxides. Leukocyte infiltration and pro-inflammatory gene expression also contribute to stroke damage. In this study using lipidomic analysis, we have identified stereospecific messengers from docosahexaenoate-oxygenation pathways in a mouse stroke model. Aspirin, widely used to prevent cerebrovascular disease, activates an additional pathway, which includes the 17R-resolvins. The newly discovered brain messenger 10,17S-docosatriene potently inhibited leukocyte infiltration, NFkappaB, and cyclooxygenase-2 induction in experimental stroke and elicited neuroprotection. In addition, in neural cells in culture, this lipid messenger also inhibited both interleukin 1-beta-induced NFkappaB activation and cyclooxygenase-2 expression. Thus, the specific novel bioactive docosanoids generated in vivo counteract leukocyte-mediated injury as well as pro-inflammatory gene induction. These results challenge the view that docosahexaenoate only participates in brain damage and demonstrate that this fatty acid is also the endogenous precursor to a neuroprotective signaling response to ischemia-reperfusion.

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.

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.

Controle do fornecimento e da utilização de substratos energéticos no encéfalo

Correspondendo a apenas 2% do peso corpóreo, o cérebro apresenta taxa metabólica superior à maioria dos demais órgãos e sistemas. A maior parte do consumo energético encefálico ocorre no transporte iônico para manutenção do potencial de membrana celular. Praticamente desprovido de estoques, os substratos energéticos para o encéfalo são fornecidos necessariamente pela circulação sanguínea.O suprimento desses substratos sofre também a ação seletiva da barreira hemato-encefálica (BHE). O principal substrato, que é a glicose, tem uma demanda de 150 g/dia (0,7 mM/g/min). A metabolização intracelular parece ser controlada pela fosfofrutoquinase. A manose e os produtos intermediários do metabolismo (frutose 1,6 bifosfato, piruvato, lactato e acetato) podem substituir, em parte, a glicose, quando os níveis sangüíneos desta encontram-se elevados. Quando oxidado, o lactato chega a responder por 21% do consumo cerebral de Ov Em situações de isquemia e inflamação infecciosa, o tecido cerebral passa de consumidor a produtor de lactato. Os corpos cetônicos também podem reduzir as necessidades cerebrais de glicose desde que oferecidos em quantidades suficientes ao encéfalo. Entretanto, devem ser considerados como um substrato complementar e nunca alternativo da glicose, pois comprometem a produção cerebral de succinil CoA e GTP. Quanto aos demais substratos, embora apresentem condições metabólicas, não existem demonstrações consistentes de que o cérebro produza energia a partir dos ácidos graxos sistêmicos, mesmo em situações de hipoglicemia. De maneira análoga, etanol e glicerol são considerados apenas a nível de experimentação. A utilização dos aminoácidos é dependente da sua captação, limitada tanto pela baixa concentração sangüínea, como pela seletividade da BHE. A maior captação ocorre para os de cadeia ramificada e destes, a valina. A menor captação é a de aminoácidos sintetizados no cérebro (aspartato,gluconato e alanina). Todos podem ser oxidados a CO, e H(2)0. Entretanto, mesmo com o consumo de glicose reduzido a 50%, a contribuição energética dos aminoácidos não ultrapassa 10%. Para manter o suprimento adequado de glicose e oxigênio, o fluxo sangüíneo cerebral é da ordem de 800 ml/min (15% do débito cardíaco). O consumo de O, pelo cérebro é equivalente a 20% do total consumido pelo corpo. Esses mecanismos, descritos como controladores da utilização de substratos energéticos pelo cérebro, sofrem a influência da idade apenas no período perinatal, com a oxidação do lactato na fase pré-latente e dos corpos cetônicos, no início da amamentação.

Synaptosomal glutamate uptake in a model of experimental cerebral ischemia

In the present investigation we studied the synaptosomal uptake of glutamate in brain omogenate of Mongolian gerbils submitted to bilateral common carotid occlusion, with and without subsequent return of blood flow. The results show that glutamate uptake after ischemia is reduced by about 35%. The damage appears to be persistent, since return of blood flow restores uptake only slightly. The membrane alterations occurring in ischemia could explain the persistence of glutamate transporter impairment. Besides the blockade of NMDA receptors, the stimulation and/or the protection of the uptake systems for glutamate could be of help in preventing neuronal ischemic damage.

Inhibition of the early phase of free fatty acid liberation during cerebral ischemia by excitatory amino acid antagonist administered by microdialysis

In order to determine the role of excitatory amino acids (EAAs) in free fatty acid (FFA) liberation during cerebral ischemia, we examined the effect of in situ administration of kynurenic acid, a broad-spectrum antagonist of EAA receptors, by microdialysis on the increase in FFA levels during ischemia in the rat hippocampus. A transient rapid increase in FFA levels, superimposed on a continued slow increase, was observed beginning at 1-2 min after ischemia induction. The early rapid increase in FFAs was profoundly inhibited by kynurenic acid, suggesting that EAAs are critically involved in the early phase of FFA liberation. Development of massive ionic shifts during cerebral ischemia can be delayed for several minutes by kynurenic acid administered by the same procedure, suggesting a vital role for EAAs in the early appearance of anoxic depolarization. The observed inhibition of early FFA liberation may thus be attributable to the delay in development of massive ionic shifts and resultant neurotransmitter release which may activate phospholipase A2 and C.

Ischemic brain damage: focus on lipids and lipid mediators

The last two decades of research have produced detailed information not only on how ischemia causes degradation of phospholipids and accumulation of potentially cytotoxic breakdown products of such lipids, but also on reactions elicited by the subsequent conversion of these products into a series of lipids, mediating an array of cellular and intercellular reactions. It now seems clear that PAF, as well as several of the cyclooxygenase and lipoxygenase products of arachidonic acid, can induce changes, particularly in the microvasculature, which jeopardize cell survival in reperfused tissue. It is equally clear that, at least following long periods of ischemia, free radicals generated in reactions that are interacting with those producing eicosanoids and PAF play a similar role. A somewhat more speculative mechanism links sustained activation and membrane translocation of PKC to delayed neuronal death following transient ischemia. All of these interactions underscore the importance of lipolytic events for cell damage in ischemia and other conditions with a compromised cellular energy metabolism.

Pharmacological manipulations of anoxia-induced free fatty acid accumulation in the mouse brain

The accumulation of free fatty acid (FFA) in the brain occurs within minutes of anoxia, induced by exposing mice to a 100% N2 atmosphere. The rate of FFA release is high within the first minute and continues to increase moderately hereafter. FFA is apparently accumulated at the highest concentration in the cerebral hemispheres. The release of FFA can be inhibited partly by CNS depressants like N6-cyclopentyladenosine, pentobarbital, ethanol, or 4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridin-3(2H)-one (THIP). Antiadrenergic compounds such as reserpine, clondine, or prazosine were also found to be active. The N2 anoxia was initially and temporarily associated with motor excitation termed fight and flight reaction. This behavior could be reduced by administration of N6-cyclopentyl-adenosine, pentobarbital, ethanol, reserpine, and prazosine, but not by THIP or clonidine. The glutamate antagonist MK-801 inhibited the fight and flight reaction, but did not affect the FFA accumulation. The data are consistent with the view that brain anoxia initially increases FFA by receptor-mediated polyphosphoinositide breakdown and that the alpha-1 adrenergic receptor is one of the receptors involved. The data also indicate that the fight and flight reaction is dissociated from the events that lead to FFA release, and may involve the stimulation of glutaminergic NMDA receptors.

Rodent models of cerebral ischemia

The use of physiologically regulated, reproducible animal models is crucial to the study of ischemic brain injury--both the mechanisms governing its occurrence and potential therapeutic strategies. Several laboratory rodent species (notably rats and gerbils), which are readily available at relatively low cost, are highly suitable for the investigation of cerebral ischemia and have been widely employed for this purpose. We critically examine and summarize several rodent models of transient global ischemia, resulting in selective neuronal injury within vulnerable brain regions, and focal ischemia, typically giving rise to localized brain infarction. We explore the utility of individual models and emphasize the necessity for meticulous experimental control of those variables that modulate the severity of ischemic brain injury.

Ischemic modification of cerebrocortical membranes: 5-hydroxytryptamine receptors, fluidity, and inducible in vitro lipid peroxidation

The effect of ischemia on the properties of 5-hydroxytryptamine1A + B (5-HT1A+B) and 5-hydroxytryptamine1B (5-HT1B) binding sites, physical-state "fluidity" of the membrane, and its susceptibility to peroxidation in vitro was investigated in the cerebral cortex of gerbils. Ischemia was induced by bilateral carotid artery occlusion for 15 min alone or with release for 1 h. Ischemia both with and without reflow decreased the number of 5-HT1A + B and 5-HT1B binding sites, whereas ischemia and reflow altered the affinity for 5-HT1B binding sites. Resistance to the temperature-dependent increase in "fluidity" of the membrane was detected (by fluorescence anisotropy using 1,6-diphenyl-1,3,5-hexatriene as a probe) after ischemia and reflow but not in ischemia alone. Susceptibility of the membranes to Fe2+- and ascorbic acid-stimulated lipid peroxidation in vitro was decreased following ischemia and recirculation only. These findings strongly suggest that the composition and the function of the membrane are markedly disturbed during recirculation after ischemia.

Effect of mild hypothermia on ischemia-induced release of neurotransmitters and free fatty acids in rat brain

We have demonstrated previously that mild intraischemic hypothermia confers a marked protective effect on the final histopathological outcome. The present study was carried out to evaluate whether this protective effect involves changes in the degree of local cerebral blood flow reductions, tissue accumulation of free fatty acids, or alterations in the extracellular release of glutamate and dopamine. Rats whose intraischemic brain temperature was maintained at 36 degrees C, 33 degrees C, or 30 degrees C were subjected to 20 minutes of ischemia by four-vessel occlusion combined with systemic hypotension. Levels of local cerebral blood flow, as measured autoradiographically, were reduced uniformly in all experimental animals at the end of ischemia by gas chromatography after tissue extraction and separation by thin layer chromatography. A massive ischemia-induced accumulation of individual free fatty acids was observed in animal groups whose intraischemic brain temperature was maintained at either 36 degrees C or 30 degrees C. Extracellular neurotransmitter levels were measured by microdialysis; the perfusate was collected before, during, and after ischemia. In rats whose intraischemic brain temperature was maintained at 36 degrees C, dopamine and glutamate increased significantly during ischemia and the early period of recirculation (by 500-fold and sevenfold, respectively). In animals whose brain temperature was maintained at 33 degrees C and 30 degrees C, the release of glutamate was completely inhibited, and the release of dopamine was significantly attenuated (by 60%). These results suggest that mild intraischemic hypothermia does not affect the ischemia-induced local cerebral blood flow reduction or free fatty acid accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipid hydroperoxides inhibit reacylation of phospholipids in neuronal membranes

The unsaturated fatty acids that rapidly accumulate during ischemia are thought to participate in inducing irreversible brain injury, especially because they are highly susceptible to peroxidation when the tissue is reoxygenated. Our hypothesis was that peroxidation products of unsaturated fatty acids interfere with the reacylation of synaptic phospholipids, a process essential to membrane repair. To test this hypothesis, we have examined the effect of fatty acid hydroperoxides on incorporation of [1-14C]arachidonic acid into synaptosomal phospholipids. Rat forebrain synaptosomes were incubated with arachidonic or linoleic acid hydroperoxides and [14C]arachidonate, and then lipids were extracted and separated by TLC. Both hydroperoxides inhibited [14C]arachidonate incorporation into phospholipids in a concentration-dependent manner, with 50% inhibition occurring at less than 25 microM hydroperoxide, in both the absence and presence of exogenous lysophospholipids. The inhibition was of the non-competitive type. It is concluded that (a) low levels of fatty acid hydroperoxides inhibit the reacylation of synaptosomal phospholipids, and (b) this inhibition may constitute an important mechanism whereby peroxidative processes contribute to irreversible brain damage.

Free fatty acids, lipid peroxidation, and lysosomal enzymes in experimental focal cerebral ischemia in primates: loss of lysosomal latency by lipid peroxidation

Experimental focal cerebral ischemia was produced in monkeys (Macaca radiata) by occlusion of the right middle cerebral artery (MCA). The release of the lysosomal glycosidases, beta-D-hexosaminidase, alpha-L-fucosidase and alpha-D-mannosidase into the soluble fraction in the right basal ganglia of the experimental animals was measured at different periods from 30 min to 12 hr after occlusion and compared with the corresponding sham operated control animals. There was a significant increase in the released lysosomal enzymes in the MCA occluded animals at all periods and particularly at 4 hr after occlusion. The CSF from the experimental animals also showed elevated levels of hexosaminidase and fucosidase. The free fatty acids (FFA) measured in the basal ganglia at 30 min and 2 hr after occlusion showed a 100 fold increase in the experimental animals. The predominant fatty acid released was linoleic acid (18:2) followed by arachidonic acid (20:4). Lipid peroxidation in the basal ganglia measured by the thiobarbituric acid (TBA) reaction in the presence or absence of ascorbic acid also showed a significant increase in the experimental animals at all periods with a maximum at 30 min to 2 hr after occlusion. In order to assess whether lipid peroxidation causes damage to the lysosomes and release of the enzymes, a lysosome enriched P2 fraction from the normal monkey basal ganglia was prepared and the effect of peroxidation studied. Maximum peroxidation in the P2 fraction was observed in the presence of arachidonic acid, ascorbic acid and Fe2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of hypoxia and recovery on brain eicosanoids and carbohydrate metabolites in rat brain cortex

The effects of hypoxia (respiration of 5% O2 for 30 min) and recovery (respiration of air up to 30 min) on brain levels of carbohydrate metabolites, of free arachidonate (FAA) and of several eicosanoids (E) were studied in the rat. Animals were sacrificed before or after 30 min of hypoxia, and during recovery, by microwave radiation (MW). At the end of the hypoxic period, arterial pO2 was reduced to 28 mm Hg and glycemia was elevated. Brain lactate and glucose levels were also elevated, whereas glycogen was unchanged. Levels of free FAA and of E were practically unchanged. During recovery, arterial pO2 values were raised above prehypoxic levels at 5 min and returned to normal within 30 min. The elevated serum glucose declined at 5 min and values returned to normal at 30. Brain glucose was still elevated at 5 min and returned to normal, together with lactate, at 30 min. Brain FAA did not change during recovery, but levels of prostaglandin F2 alpha (PGF2 alpha), prostaglandin E2 (PGF2) and thromboxane B2 (TxB2) were raised, at 5 min, and those of 6-keto-PGF1 alpha were reduced with respect to pre-hypoxia. At the end of recovery, all E were lower than during hypoxia. The results indicate that changes of brain E occur only during recovery from hypoxia. At 5 min of recovery, at high arterial pO2 values, concentrations of all E were elevated, with the exception of 6-keto-PGF1 alpha which was reduced. At 30 min a marked reduction of E levels was observed, possibly resulting from increased clearance following elevation of cerebral blood flow.

Cerebral phosphoinositide, triacylglycerol and energy metabolism during sustained seizures induced by bicuculline

In ventilated rats, levels of phosphatidylinositol (PI), phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol 4,5-bisphosphate (PIP2), diacylglycerol (DAG), triacylglycerol (TAG), free fatty acids (FFA) and phosphatidic acid, as well as their fatty acid contents, were measured in forebrain tissue after 1, 20 and 60 min of seizures induced by bicuculline. Cerebral energy state was also measured. PI decreased progressively throughout 60 min of seizures, whereas the levels of PIP and PIP2 did not change. DAG increased modestly and persistently. FFA increased markedly during the early seizure period, but decreased later. Following an initial drop, TAG rose above control. Phosphatidic acid did not change. The levels of ATP and energy charge potential decreased slightly and lactate accumulated. Stearic acid (18:0) and arachidonic acid (20:4) primarily accounted for the changes in the levels of the lipids. At the onset of seizures, the decrease of 18.0 and 20:4 in PI occurred in parallel with an enrichment of these fatty acids in FFA and DAG. Despite the fact that the losses of 18:0 and 20:4 from PI were quantitatively similar to each other at all times examined, the increase in free 18:0 was much larger than the increase in free 20:4 at 20 min of seizures. Concurrently there was a rise of 20:4 in TAG. As the FFA levels declined thereafter, 20:4 and docosahexaenoate (22:6) in TAG continued to increase. The results are consistent with the view that seizure activity stimulates the hydrolytic breakdown of brain phosphoinositides--the pathway catalyzed by phosphodiesterase of the phospholipase C type followed by lipases, and probably the pathway catabolized by phospholipases A as well. Preferential incorporation of polyunsaturated fatty acids into TAG-acyl residues may represent a mechanism to reduce the level of their free forms when the latter are produced in large amounts.

Acidic phospholipids, diacylglycerols, and free fatty acids in gerbil brain: a comparison of ischemic changes resulting from carotid ligation and decapitation

The levels of brain acidic phospholipids (poly-PI, PI, PA, and PS), DG, and FFA and their acyl group profiles were determined after induction of ischemia in gerbils by ligation of the common carotid arteries and decapitation. Ischemia induced by both procedures resulted in a significant decrease in poly-PI (20% for 1-min decapitation and 1-min ligation). Except for a 16% increase in PI in the 5-min decapitation group, no apparent change was found in other phospholipids after either ischemic condition. The level of DG was increased one- and three-fold after 1 and 5 min, respectively, of decapitative ischemic treatment. Ligation of the carotid arteries for 1 min resulted also in a one-fold increase in the DG level. The decapitative model resulted in a one- and five-fold increase in FFA level (with respect to 1 and 5 min, respectively), whereas ligation for 1 min resulted in an increase of 42% of the FFA. The acyl groups of poly-PI and PI in the control gerbil brain are enriched in 18:0 and 20:4, but those of DG, FFA, and PA have a higher proportion of 16:0 besides 18:0 and 20:4. However, a preferential increase in the proportion of 18:0 and 20:4 was shown for the DG and FFA in both types of ischemic treatments. It is concluded from the results that both models of ischemic treatment elicit a similar decrease in poly-PI and increase in DG, but differ in the amount of FFA release. The higher level of FFA release in the decapitative model suggests that other biochemical mechanisms may be activated to cause the additional release.

Cerebral phosphoinositide, triacylglycerol, and energy metabolism in reversible ischemia: origin and fate of free fatty acids

Levels of phosphatidylinositol 4,5-bisphosphate (PIP2), phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol (PI), phosphatidic acid, diacylglycerol (DAG), triacylglycerol (TAG), and free fatty acids (FFAs), as well as their fatty acid composition, were determined in rat forebrain during ischemia and postischemic recirculation. Cerebral energy state and electroencephalograms (EEGs) were also studied. Fifteen minutes of ischemia resulted in a decrease in PIP2 and PIP contents but not in PI content, concurrent with an enlargement of the FFA and DAG pools. The latter were enriched in stearate and arachidonate. Prolongation of ischemia did not produce further changes in content of any of the inositol phospholipids, but the increase in levels of FFAs and DAG continued. At the end of 45 min of ischemia, levels of both PIP2 and PIP decreased by 45-50%, and the total phosphoinositide content (PIP2 + PIP + PI) decreased by 21%, whereas levels of FFAs and DAG increased to 14- and 3.6-fold of control levels, respectively. During ischemia, the TAG-palmitate level decreased, but the TAG-arachidonate level increased; the tissue energy state deteriorated severely; and the EEG was suppressed. A 30-min recirculation period after 15 or 45 min of ischemia led to increases in PIP2, PIP, and total phosphoinositide contents, whereas levels of FFAs and DAG promptly decreased toward control values. The TAG-arachidonate level peaked and the TAG-palmitate level returned to a low control value during early recirculation. The ischemic changes in tissue lipids were completely reversed within 3 h of recirculation after both periods of ischemia. Adenylates were fully phosphorylated with as little as 30 min of reflow. The EEG activity partially recovered during reflow after 15 min of ischemia, whereas it remained depressed after prolonged ischemia. Thus, phosphodiesteric cleavage of PIP2 and PIP followed by deacylation of DAG is likely to contribute to the production of FFAs in early ischemia. Deacylation of undetermined lipids plays a role for the increment in levels of FFAs in the later period of ischemia. The rapid postischemic increase in levels of PIP2 and PIP indicates active synthesis not only from existing PI, but probably also by means of accumulated FFAs and DAG. These results indicate that the impaired resynthesis of inositol phospholipids cannot be a cause of the poor EEG activity after prolonged ischemia. Degradation and resynthesis of polyphosphoinositides and formation of TAG-arachidonate may be important for modulation of free arachidonic acid levels in the brain during temporary ischemia.

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

The quantitative relationship between phosphoinositides and free fatty acids (FFAs) in brain ischemia was studied by measuring contents of individual fatty acids in phosphatidylinositol 4,5-bisphosphate (PIP2), phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol (PI), phosphatidic acid (PA), diacylglycerol (DAG), and the FFA pool. Various periods of complete ischemia (1, 3, 10, and 30 min) were produced by decapitation. Ischemia of 1-3 min caused rapid decreases in PIP2 and PIP content together with preferential production of stearic and arachidonic acids in the DAG and FFA pools. The decrement in levels of these fatty acid residues in polyphosphoinositides was sufficient to account for their increment in levels in the enlarged DAG and FFA pools. After 10 min of ischemia, levels of PIP2, PIP, and DAG approached plateau values, but levels of all FFAs continued to increase. The increases in content of DAG and FFAs at later ischemic periods could not be accounted for by the decreases in content of PIP2 and PIP, PI and PA levels showed only transient and subtle changes. These results indicate that, at the onset of ischemia, phosphodiesteric cleavage of PIP2 and PIP and subsequent deacylation by lipases are primarily responsible for the preferential increase in levels of free stearic and arachidonic acids and that, later, hydrolysis of other phospholipids plays a major role in the continuous accumulation of FFAs.

Mononucleotide metabolism in the rat brain after transient ischemia

Nucleotide metabolism was studied in rats during and following the induction of 10 min of forebrain ischemia (four-vessel occlusion model). Purine and pyrimidine nucleotides, nucleotides, and bases in forebrain extracts were quantitated by HPLC with an ultraviolet detector. Ischemia resulted in a severe reduction in the concentration of nucleoside triphosphates (ATP, GTP, UTP, and CTP) and an increase in the concentration of AMP, IMP, adenosine, inosine, hypoxanthine, and guanosine. During the recovery period, both the phosphocreatine level and adenylate energy charge were rapidly and completely restored to the normal range. ATP was only 78% of the control value at 180 min after ischemic reperfusion. Levels of nucleosides and bases were elevated during ischemia but decreased to values close to those of control animals following recirculation. Both the decrease in the adenine nucleotide pool and the incomplete ATP recovery were caused by insufficient reutilization of hypoxanthine via the purine salvage system. The content of cyclic AMP, which transiently accumulated during the early recirculation period, returned to the control level, paralleling the decrease of adenosine concentration, which suggested that adenylate cyclase activity during reperfusion is modulated by adenosine A2 receptors. The recovery of CTP was slow but greater than that of ATP, GTP, and UTP. The GTP/GDP ratio was higher than that of the control animals following recirculation.

Cerebral norepinephrine depletion enhances recovery after brain ischemia

Monoamine neurotransmitters, especially norepinephrine (NE), may have an important role in the pathophysiological aspects of postischemic cerebral dysfunction. In previous studies of post-decapitation-induced ischemia, we found that NE depletion caused a delay in glycogen breakdown but did not influence any of the other known biochemical abnormalities that accompany brain ischemia. In this study, we have turned to a model of transient incomplete and diffuse forebrain ischemia in the rat to examine the effects of cerebral NE depletion on the recovery after brain ischemia of levels of high-energy phosphate compounds, products of intermediary oxidative metabolism, and free fatty acids. We found that a unilateral lesion of the locus ceruleus and the resultant depletion of NE in the ipsilateral cerebral cortex had no effect on sham-operated controls nor on rats subjected to ischemia alone. However, in rats subjected to ischemia followed by 15 minutes of recirculation, the NE-depleted cerebral cortex had significantly higher phosphocreatine and adenosine triphosphate levels and energy charge, and lower adenosine monophosphate and docosahexaenoic acid concentrations. With longer periods of recirculation, these side-to-side differences were not apparent. These results suggest that activity of the central NE systems during transient brain ischemia has deleterious effects on the biochemical recovery of the cerebral cortex from severe ischemic insults.

Postischemic cerebral lipid peroxidation in vitro: modification by dietary vitamin E

Using an in vitro system, we studied the effect of postischemic reoxygenation on cerebral lipid peroxidation in relation to the dietary intake of vitamin E (VE) in rats. Homogenates prepared from VE-deficient, -normal, and -supplemented brains, which were previously rendered ischemic for 30 min by decapitation, were incubated under air or nitrogen gas for 60 min. The extent of peroxidation in brain tissue was estimated by a thiobarbituric acid (TBA) test and by diene conjugation in total lipid extracts. The brain levels of alpha-tocopherol and of total and free fatty acids (FAs) were also determined. Aerobic incubation increased TBA reactants in all dietary groups; the effect was largest in the VE-deficient group, intermediate in the VE-normal group, and smallest in the VE-supplemented group. In contrast, nitrogen incubation did not alter the basal levels of TBA reactants except for a small rise associated with VE deficiency. Conjugated dienes changed in parallel with TBA reactants. alpha-Tocopherol decreased after aerobic incubation and also, to a lesser degree, after nitrogen incubation in each dietary group. Only in the reoxygenated samples of the VE-deficient group was there a significant fall in total polyunsaturated FAs. The levels of free FAs continuously increased throughout ischemia and subsequent incubation. However, the level of free polyunsaturated FAs was similar after aerobic and nitrogen incubation in each dietary group, and was not affected by VE. Thus, cerebral reoxygenation after ischemia propagates peroxidative reactions within esterified polyunsaturated FAs. The modification by VE of reoxygenation-induced lipid peroxidation suggests free radical mediation.