Dietary fatty acid composition drives neuroinflammation and impaired behavior in obesity

Nutrient composition in obesogenic diets may influence the severity of disorders associated with obesity such as insulin-resistance and chronic inflammation. Here we hypothesized that obesogenic diets rich in fat and varying in fatty acid composition, particularly in omega 6 (ω6) to omega 3 (ω3) ratio, have various effects on energy metabolism, neuroinflammation and behavior. Mice were fed either a control diet or a high fat diet (HFD) containing either low (LO), medium (ME) or high (HI) ω6/ω3 ratio. Mice from the HFD-LO group consumed less calories and exhibited less body weight gain compared to other HFD groups. Both HFD-ME and HFD-HI impaired glucose metabolism while HFD-LO partly prevented insulin intolerance and was associated with normal leptin levels despite higher subcutaneous and perigonadal adiposity. Only HFD-HI increased anxiety and impaired spatial memory, together with increased inflammation in the hypothalamus and hippocampus. Our results show that impaired glucose metabolism and neuroinflammation are uncoupled, and support that diets with a high ω6/ω3 ratio are associated with neuroinflammation and the behavioral deterioration coupled with the consumption of diets rich in fat.

Enhancing Solubility and Bioefficacy of Stilbenes by Liposomal Encapsulation-The Case of Macasiamenene F

Stilbenes in food and medicinal plants have been described as potent antiphlogistic and antioxidant compounds, and therefore, they present an interesting potential for the development of dietary supplements. Among them, macasiamenene F (MF) has recently been shown to be an effective anti-inflammatory and cytoprotective agent that dampens peripheral and CNS inflammation in vitro. Nevertheless, this promising molecule, like other stilbenes and a large percentage of drugs under development, faces poor water solubility, which results in trickier in vivo administration and low bioavailability. With the aim of improving MF solubility and developing a form optimized for in vivo administration, eight types of conventional liposomal nanocarriers and one type of PEGylated liposomes were formulated and characterized. In order to select the appropriate form of MF encapsulation, the safety of MF liposomal formulations was evaluated on THP-1 and THP-1-XBlue-MD2-CD14 monocytes, BV-2 microglia, and primary cortical neurons in culture. Furthermore, the cellular uptake of liposomes and the effect of encapsulation on MF anti-inflammatory effectiveness were evaluated on THP-1-XBlue-MD2-CD14 monocytes and BV-2 microglia. MF (5 mol %) encapsulated in PEGylated liposomes with an average size of 160 nm and polydispersity index of 0.122 was stable, safe, and the most promising form of MF encapsulation keeping its cytoprotective and anti-inflammatory properties.

Unlocking Therapeutic Synergy: Tailoring Drugs for Comorbidities such as Depression and Diabetes through Identical Molecular Targets in Different Cell Types

Research in the field of pharmacology aims to generate new treatments for pathologies. Nowadays, there are an increased number of chronic disorders that severely and durably handicap many patients. Among the most widespread pathologies, obesity, which is often associated with diabetes, is constantly increasing in incidence, and in parallel, neurodegenerative and mood disorders are increasingly affecting many people. For years, these pathologies have been so frequently observed in the population in a concomitant way that they are considered as comorbidities. In fact, common mechanisms are certainly at work in the etiology of these pathologies. The main purpose of this review is to show the value of anticipating the effect of baseline treatment of a condition on its comorbidity in order to obtain concomitant positive actions. One of the implications would be that by understanding and targeting shared molecular mechanisms underlying these conditions, it may be possible to tailor drugs that address both simultaneously. To this end, we firstly remind readers of the close link existing between depression and diabetes and secondly address the potential benefit of the pleiotropic actions of two major active molecules used to treat central and peripheral disorders, first a serotonin reuptake inhibitor (Prozac ®) and then GLP-1R agonists. In the second part, by discussing the therapeutic potential of new experimental antidepressant molecules, we will support the concept that a better understanding of the intracellular signaling pathways targeted by pharmacological agents could lead to future synergistic treatments targeting solely positive effects for comorbidities.

The eukaryotic initiation factor 5A (eIF5A1), the molecule, mechanisms and recent insights into the pathophysiological roles

Since the demonstration of its involvement in cell proliferation, the eukaryotic initiation factor 5A (eIF5A) has been studied principally in relation to the development and progression of cancers in which the isoform A2 is mainly expressed. However, an increasing number of studies report that the isoform A1, which is ubiquitously expressed in normal cells, exhibits novel molecular features that reveal its new relationships between cellular functions and organ homeostasis. At a first glance, eIF5A can be regarded, among other things, as a factor implicated in the initiation of translation. Nevertheless, at least three specificities: (1) its extreme conservation between species, including plants, throughout evolution, (2) its very special and unique post-translational modification through the activating-hypusination process, and finally (3) its close relationship with the polyamine pathway, suggest that the role of eIF5A in living beings remains to be uncovered. In fact, and beyond its involvement in facilitating the translation of proteins containing polyproline residues, eIF5A is implicated in various physiological processes including ischemic tolerance, metabolic adaptation, aging, development, and immune cell differentiation. These newly discovered physiological properties open up huge opportunities in the clinic for pathologies such as, for example, the ones in which the oxygen supply is disrupted. In this latter case, organ transplantation, myocardial infarction or stroke are concerned, and the current literature defines eIF5A as a new drug target with a high level of potential benefit for patients with these diseases or injuries. Moreover, the recent use of genomic and transcriptomic association along with metadata studies also revealed the implication of eIF5A in genetic diseases. Thus, this review provides an overview of eIF5A from its molecular mechanism of action to its physiological roles and the clinical possibilities that have been recently reported in the literature.

Targeting oxidative stress, a crucial challenge in renal transplantation outcome

Disorders characterized by ischemia/reperfusion (I/R) are the most common causes of debilitating diseases and death in stroke, cardiovascular ischemia, acute kidney injury or organ transplantation. In the latter example the I/R step defines both the amplitude of the damages to the graft and the functional recovery outcome. During transplantation the kidney is subjected to blood flow arrest followed by a sudden increase in oxygen supply at the time of reperfusion. This essential clinical protocol causes massive oxidative stress which is at the basis of cell death and tissue damage. The involvement of both reactive oxygen species (ROS) and nitric oxides (NO) has been shown to be a major cause of these cellular damages. In fact, in non-physiological situations, these species escape endogenous antioxidant control and dangerously accumulate in cells. In recent years, the objective has been to find clinical and pharmacological treatments to reduce or prevent the appearance of oxidative stress in ischemic pathologies. This is very relevant because, due to the increasing success of organ transplantation, clinicians are required to use limit organs, the preservation of which against oxidative stress is crucial for a better outcome. This review highlights the key actors in oxidative stress which could represent new pharmacological targets.

Inhibition of eIF5A hypusination pathway as a new pharmacological target for stroke therapy

In eukaryotes, the polyamine pathway generates spermidine that activates the hypusination of the translation factor eukaryotic initiation factor 5A (eIF5A). Hypusinated-eIF5A modulates translation, elongation, termination and mitochondrial function. Evidence in model organisms like drosophila suggests that targeting polyamines synthesis might be of interest against ischemia. However, the potential of targeting eIF5A hypusination in stroke, the major therapeutic challenge specific to ischemia, is currently unknown. Using in vitro models of ischemic-related stress, we documented that GC7, a specific inhibitor of a key enzyme in the eIF5A activation pathway, affords neuronal protection. We identified the preservation of mitochondrial function and thereby the prevention of toxic ROS generation as major processes of GC7 protection. To represent a thoughtful opportunity of clinical translation, we explored whether GC7 administration reduces the infarct volume and functional deficits in an in vivo transient focal cerebral ischemia (tFCI) model in mice. A single GC7 pre- or post-treatment significantly reduces the infarct volume post-stroke. Moreover, GC7-post-treatment significantly improves mouse performance in the rotarod and Morris water-maze, highlighting beneficial effects on motor and cognitive post-stroke deficits. Our results identify the targeting of the polyamine-eIF5A-hypusine axis as a new therapeutic opportunity and new paradigm of research in stroke and ischemic diseases.

Inhibition of eIF5A hypusination reprogrammes metabolism and glucose handling in mouse kidney

Inhibition of the eukaryotic initiation factor 5A activation by the spermidine analogue GC7 has been shown to protect proximal cells and whole kidneys against an acute episode of ischaemia. The highlighted mechanism involves a metabolic switch from oxidative phosphorylation toward glycolysis allowing cells to be transiently independent of oxygen supply. Here we show that GC7 decreases protein expression of the renal GLUT1 glucose transporter leading to a decrease in transcellular glucose flux. At the same time, GC7 modifies the native energy source of the proximal cells from glutamine toward glucose use. Thus, GC7 acutely and reversibly reprogrammes function and metabolism of kidney cells to make glucose its single substrate, and thus allowing cells to be oxygen independent through anaerobic glycolysis. The physiological consequences are an increase in the renal excretion of glucose and lactate reflecting a decrease in glucose reabsorption and an increased glycolysis. Such a reversible reprogramming of glucose handling and oxygen dependence of kidney cells by GC7 represents a pharmacological opportunity in ischaemic as well as hyperglycaemia-associated pathologies from renal origin.

Sortilin-derived peptides promote pancreatic beta-cell survival through CREB signaling pathway

Deterioration of insulin secretion and pancreatic beta-cell mass by inflammatory attacks is one of the main pathophysiological features of type 2 diabetes (T2D). Therefore, preserving beta-cell mass and stimulating insulin secretion only in response to glucose for avoiding the hypoglycemia risks, are the most state-of-the-art option for the treatment of T2D. In this study we tested two correlated hypothesis that 1/ the endogenous peptide released from sortilin, known as PE, that stimulates insulin secretion only in response to glucose, protects beta-cells against death induced by cytokines, and 2/ Spadin and Mini-Spadin, two synthetic peptides derived from PE, that mimic the effects of PE in insulin secretion, also provide beneficial effect on beta-cells survival. We show that PE and its derivatives by inducing a rise of intracellular calcium concentration by depolarizing the membrane protect beta-cells against death induced by Interleukin-1β. Using biochemical, confocal imaging and cell biology techniques, we reveal that the protective effects of PE and its derivatives rely on the activation of the CaM-Kinase pathway, and on the phosphorylation and activation of the transcription factor CREB. In addition, Mini-Spadin promotes beta-cell proliferation, suggesting its possible regenerative effect. This study highlights new possible roles of PE in pancreatic beta-cell survival and its derivatives as pharmacological tools against diabetes.

Therapeutic potential of prenylated stilbenoid macasiamenene F through its anti-inflammatory and cytoprotective effects on LPS-challenged monocytes and microglia

ETHNOPHARMACOLOGICAL RELEVANCE

Macaranga Thou. (Euphorbiaceae) is a large genus that comprises over 300 species distributed between Western Africa and the islands of the South Pacific. Plants of this genus have a long-standing history of use in traditional medicine for different purposes, including the treatment of inflammation. Fresh and dried leaves of certain Macaranga species (e.g. M. tanarius (L.) Müll.Arg.), have been used to treat cuts, bruises, boils, swellings, sores and covering of wounds in general. Several reports described Macaranga spp. being a rich source of polyphenols, such as prenylated stilbenoids and flavonoids, mostly responsible for its biological activity. Similarly, an abundant content of prenylated stilbenes was also described in M. siamensis S.J.Davies, species recently identified (2001) in Thailand. While the respective biological activity of the prenylated stilbenes from M. siamensis was poorly investigated to date, our recent study pointed out the interest as the natural source of several novel anti-inflammatory stilbenoids isolated from this species.

AIM OF THE STUDY

This work investigated the potential anti-inflammatory effects of the stilbenoid macasiamenene F (MF) isolated from M. siamensis S.J.Davies (Euphorbiaceae) on the lipopolysaccharide (LPS)-induced inflammation-like response of monocytes and microglia, major cells involved in the peripheral and central inflammatory response, respectively.

MATERIALS AND METHODS

LPS-induced stimulation of TLR4 signaling led to the activation of inflammatory pathways in in vitro models of THP-1 and THP-1-XBlue™-MD2-CD14 human monocytes, BV-2 mouse microglia, and an ex vivo model of brain-sorted mouse microglia. The ability of the stilbenoid MF to intervene in the IкB/NF-кB and MAPKs/AP-1 inflammatory cascade was investigated. The gene and protein expressions of the pro-inflammatory cytokines IL-1β and TNF-α were evaluated at the transcription and translation levels. The protective effect of MF against LPS-triggered microglial loss was assessed by cell counting and the LDH assay.

RESULTS

MF demonstrated beneficial effects, reducing both monocyte and microglial inflammation as assessed in vitro. It efficiently inhibited the degradation of IкBα, thereby reducing the NF-кB activity and TNF-α expression in human monocytes. Furthermore, the LPS-induced expression of IL-1β and TNF-α in microglia was dampened by pre-, co-, or post-treatment with MF. In addition to its anti-inflammatory effect, MF demonstrated a cytoprotective effect against the LPS-induced death of BV-2 microglia.

CONCLUSION

Our research into anti-inflammatory and protective effects of MF has shown that it is a promising candidate for further in vitro and in vivo investigations of MF interventions with respect to acute and chronic inflammation, including potentially beneficial effects on the inflammatory component of brain diseases such as stroke and Alzheimer's disease.

Dietary fat exacerbates postprandial hypothalamic inflammation involving glial fibrillary acidic protein-positive cells and microglia in male mice

In humans, obesity is associated with brain inflammation, glial reactivity, and immune cells infiltration. Studies in rodents have shown that glial reactivity occurs within 24 hr of high-fat diet (HFD) consumption, long before obesity development, and takes place mainly in the hypothalamus (HT), a crucial brain structure for controlling body weight. Here, we sought to characterize the postprandial HT inflammatory response to 1, 3, and 6 hr of exposure to either a standard diet (SD) or HFD. HFD exposure increased gene expression of astrocyte and microglial markers (glial fibrillary acidic protein [GFAP] and Iba1, respectively) compared to SD-treated mice and induced morphological modifications of microglial cells in HT. This remodeling was associated with higher expression of inflammatory genes and differential regulation of hypothalamic neuropeptides involved in energy balance regulation. DREADD and PLX5622 technologies, used to modulate GFAP-positive or microglial cells activity, respectively, showed that both glial cell types are involved in hypothalamic postprandial inflammation, with their own specific kinetics and reactiveness to ingested foods. Thus, recurrent exacerbated postprandial inflammation in the brain might promote obesity and needs to be characterized to address this worldwide crisis.

Bridging the Gap Between Diabetes and Stroke in Search of High Clinical Relevance Therapeutic Targets

Diabetes affects more than 425 million people worldwide, a scale approaching pandemic proportion. Diabetes represents a major risk factor for stroke, and therefore is actively addressed for stroke prevention. However, how diabetes affects stroke severity has not yet been extensively considered, which is surprising given the evident but understudied common mechanistic features of both pathologies. The increase in number of diabetic people, incidence of stroke in the presence of this specific risk factor, and the exacerbation of ischemic brain damage in diabetic conditions (at least in animal models) warrants the need to integrate this comorbidity in preclinical studies of brain ischemia to develop novel therapeutic approaches. Therefore, a better understanding of the commonalties involved in the course of both diseases would offer the promise of discovering novel neuroprotective pathways that would be more appropriated to clinical scenarios. In this article, we will review the relevant mechanisms that have been identified as common traits of both pathologies and that could be, to our knowledge, potential targets in both pathologies.

Sortilin in Glucose Homeostasis: From Accessory Protein to Key Player?

The pharmacological properties and physiological roles of the type I receptor sortilin, also called neurotensin receptor-3, are various and complex. Sortilin is involved in important biological functions from neurotensin and pro-Nerve Growth Factor signaling in the central nervous system to regulation of glucose and lipid homeostasis in the periphery. The peripheral functions of sortilin being less extensively addressed, the focus of the current review is to discuss recent works describing sortilin-induced molecular mechanisms regulating blood glucose homeostasis and insulin signaling. Thus, an overview of several roles ascribed to sortilin in diabetes and other metabolic diseases are presented. Investigations on crucial cellular pathways involved in the protective effect of sortilin receptor on beta cells, including recent discoveries about regulation of cell fate, are also detailed. In addition, we provide a special focus on insulin secretion regulation involving complexes between sortilin and neurotensin receptors. The last section comments on the future research areas which should be developed to address the function of new effectors of the sortilin system in the endocrine apparatus.

Ionic Homeostasis Maintenance in ALS: Focus on New Therapeutic Targets

Amyotrophic lateral sclerosis (ALS) is one of the most threatening neurodegenerative disease since it causes muscular paralysis for the loss of Motor Neurons in the spinal cord, brainstem and motor cortex. Up until now, no effective pharmacological treatment is available. Two forms of ALS have been described so far: 90% of the cases presents the sporadic form (sALS) whereas the remaining 10% of the cases displays the familiar form (fALS). Approximately 20% of fALS is associated with inherited mutations in the Cu, Zn-superoxide dismutase 1 (SOD1) gene. In the last decade, ionic homeostasis dysregulation has been proposed as the main trigger of the pathological cascade that brings to motor-neurons loss. In the light of these premises, the present review will analyze the involvement in ALS pathophysiology of the most well studied metal ions, i.e., calcium, sodium, iron, copper and zinc, with particular focus to the role of ionic channels and transporters able to contribute in the regulation of ionic homeostasis, in order to propose new putative molecular targets for future therapeutic strategies to ameliorate the progression of this devastating neurodegenerative disease.

Tackling issues in the path toward clinical translation in brain conditioning: Potential offered by nutraceuticals

Brief periods of ischemia have been shown in many experimental setups to provide tolerance against ischemia in multiple organs including the brain, when administered before (preconditioning) or even after (postconditioning) the normally lethal ischemia. In addition to these so-called ischemic conditionings, many pharmacological and natural agents (e.g., chemicals and nutraceuticals) can also act as potent pre- and post-conditioners. Deriving from the original concept of ischemic preconditioning, these various conditioning paradigms may be promising as clinical-stage therapies for prevention of ischemic-related injury, especially stroke. As no proven experimentally identified strategy has translated into clinical success, the experimental induction of neuroprotection using these various conditioning paradigms has raised several questions, even before considering translation to clinical studies in humans. The first aim of the review is to consider key questions on preclinical studies of pre- or post-conditioning modalities including those induced by chemical or nutraceuticals. Second, we make the argument that several key issues can be addressed by a novel concept, nutraceutical preconditioning. Specifically, α-linolenic acid (alpha-linolenic acid [ALA] an omega-3 polyunsaturated fatty acid), contained in plant-derived edible products, is essential in the daily diet, and a body of work has identified ALA as a pre- and post-conditioner of the brain. Nutritional intervention and functional food development are an emerging direction for preventing stroke damage, offering the potential to improving clinical outcomes through activation of the endogenous protective mechanisms known collectively as conditioning.

Targeting eIF5A Hypusination Prevents Anoxic Cell Death through Mitochondrial Silencing and Improves Kidney Transplant Outcome

The eukaryotic initiation factor 5A (eIF5A), which is highly conserved throughout evolution, has the unique characteristic of post-translational activation through hypusination. This modification is catalyzed by two enzymatic steps involving deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH). Notably, eIF5A may be involved in regulating the lifespan of Drosophila during long-term hypoxia. Therefore, we investigated the possibility of a link between eIF5A hypusination and cellular resistance to hypoxia/anoxia. Pharmacologic targeting of DHPS by N1-guanyl-1,7-diaminoheptane (GC7) or RNA interference-mediated inhibition of DHPS or DOHH induced tolerance to anoxia in immortalized mouse renal proximal cells. Furthermore, GC7 treatment of cells reversibly induced a metabolic shift toward glycolysis as well as mitochondrial remodeling and led to downregulated expression and activity of respiratory chain complexes, features characteristic of mitochondrial silencing. GC7 treatment also attenuated anoxia-induced generation of reactive oxygen species in these cells and in normoxic conditions, decreased the mitochondrial oxygen consumption rate of cultured cells and mice. In rats, intraperitoneal injection of GC7 substantially reduced renal levels of hypusinated eIF5A and protected against ischemia-reperfusion-induced renal injury. Finally, in the preclinical pig kidney transplant model, intravenous injection of GC7 before kidney removal significantly improved graft function recovery and late graft function and reduced interstitial fibrosis after transplant. This unconventional signaling pathway offers an innovative therapeutic target for treating hypoxic-ischemic human diseases and organ transplantation.

Hypothalamic Inflammation and Energy Balance Disruptions: Spotlight on Chemokines

The hypothalamus is a key brain region in the regulation of energy balance as it controls food intake and both energy storage and expenditure through integration of humoral, neural, and nutrient-related signals and cues. Many years of research have focused on the regulation of energy balance by hypothalamic neurons, but the most recent findings suggest that neurons and glial cells, such as microglia and astrocytes, in the hypothalamus actually orchestrate together several metabolic functions. Because glial cells have been described as mediators of inflammatory processes in the brain, the existence of a causal link between hypothalamic inflammation and the deregulations of feeding behavior, leading to involuntary weight loss or obesity for example, has been suggested. Several inflammatory pathways that could impair the hypothalamic control of energy balance have been studied over the years such as, among others, toll-like receptors and canonical cytokines. Yet, less studied so far, chemokines also represent interesting candidates that could link the aforementioned pathways and the activity of hypothalamic neurons. Indeed, chemokines, in addition to their role in attracting immune cells to the inflamed site, have been suggested to be capable of neuromodulation. Thus, they could disrupt cellular activity together with synthesis and/or secretion of multiple neurotransmitters/mediators involved in the maintenance of energy balance. This review discusses the different inflammatory pathways that have been identified so far in the hypothalamus in the context of feeding behavior and body weight control impairments, with a particular focus on chemokines signaling that opens a new avenue in the understanding of the major role played by inflammation in obesity.

Central CCL2 signaling onto MCH neurons mediates metabolic and behavioral adaptation to inflammation

Sickness behavior defines the endocrine, autonomic, behavioral, and metabolic responses associated with infection. While inflammatory responses were suggested to be instrumental in the loss of appetite and body weight, the molecular underpinning remains unknown. Here, we show that systemic or central lipopolysaccharide (LPS) injection results in specific hypothalamic changes characterized by a precocious increase in the chemokine ligand 2 (CCL2) followed by an increase in pro-inflammatory cytokines and a decrease in the orexigenic neuropeptide melanin-concentrating hormone (MCH). We therefore hypothesized that CCL2 could be the central relay for the loss in body weight induced by the inflammatory signal LPS. We find that central delivery of CCL2 promotes neuroinflammation and the decrease in MCH and body weight. MCH neurons express CCL2 receptor and respond to CCL2 by decreasing both electrical activity and MCH release. Pharmacological or genetic inhibition of CCL2 signaling opposes the response to LPS at both molecular and physiologic levels. We conclude that CCL2 signaling onto MCH neurons represents a core mechanism that relays peripheral inflammation to sickness behavior.

Alpha-linolenic acid given as enteral or parenteral nutritional intervention against sensorimotor and cognitive deficits in a mouse model of ischemic stroke

Stroke is a leading cause of disability and death worldwide. Numerous therapeutics applied acutely after stroke have failed to improve long-term clinical outcomes. An emerging direction is nutritional intervention with omega-3 polyunsaturated fatty acids acting as disease-modifying factors and targeting post-stroke disabilities. Our previous studies demonstrated that the omega-3 precursor, alpha-linolenic acid (ALA) administrated by injections or dietary supplementation reduces stroke damage by direct neuroprotection, and triggering brain artery vasodilatation and neuroplasticity. Successful translation of putative therapies will depend on demonstration of robust efficacy on common deficits resulting from stroke like loss of motor control and memory/learning. This study evaluated the value of ALA as adjunctive therapy for stroke recovery by comparing whether oral or intravenous supplementation of ALA best support recovery from ischemia. Motor and cognitive deficits were assessed using rotarod, pole and Morris water maze tests. ALA supplementation in diet was better than intravenous treatment in improving motor coordination, but this improvement was not due to a neuroprotective effect since infarct size was not reduced. Both types of ALA supplementation improved spatial learning and memory after stroke. This cognitive improvement correlated with higher survival of hippocampal neurons. These results support clinical investigation establishing therapeutic plans using ALA supplementation.

The complex contribution of chemokines to neuroinflammation: switching from beneficial to detrimental effects

Inflammation is an innate mechanism that defends organisms against harmful stimuli. Inflammation leads to the production and secretion of proinflammatory mediators that activate and recruit immune cells to damaged tissues, including the brain, to resolve the cause of inflammation. In the central nervous system, inflammation is referred to as neuroinflammation, which occurs in various pathological conditions of the brain. The primary role of neuroinflammation is to protect the brain. However, prolonged and/or inappropriate inflammation can be harmful for the brain, from individual cells to the whole tissue. This review focuses on a particular type of inflammatory mediator, chemokines, and describes their complex effects both under physiological and pathophysiological conditions of the brain. The clinical relevance of the multiple characters of chemokines is highlighted with respect to acute and chronic inflammation of the brain, including their actions in stroke and Alzheimer's disease, respectively.

The nutraceutical potential of omega-3 alpha-linolenic acid in reducing the consequences of stroke

Stroke is a worldwide major cause of mortality and morbidity. Preclinical studies have identified over 1000 molecules with brain-protective properties. More than 200 clinical trials have evaluated neuroprotective candidates for ischemic stroke yet, to date almost all failed, leading to a re-analysis of treatment strategies against stroke. An emerging view is to seek combinatory therapy, or discovering molecules able to stimulate multiple protective and regenerative mechanisms. A pertinent experimental approach to identify such candidates is the study of brain preconditioning, which refers to how the brain protects itself against ischemia and others stress-inducing stimuli. The recent discovery that nutrients like alpha-linolenic acid (ALA is an essential omega-3 polyunsaturated fatty acid required as part of our daily diet), may be an efficient brain preconditionner against stroke fosters the novel concept of brain preconditioning by nutraceuticals. This review stresses the underestimated role of nutrition in preventing and combating stroke. Although there is a consensus that increased consumption of salt, fatty foods and alcoholic beverages may promote pathologies like hypertension, obesity and alcoholism - all of which are well known risk factors of stroke - few risk factors are attributed to a deficiency in an essential nutrient in the diet. The ALA deficiency observed in the Western modern diets may itself constitute a risk factor. This review outlines how ALA supplementation by modification of the daily diet prevented mortality and cerebral damage in a rodent model of ischemic stroke. It also describes the pleiotropic ability of ALA to trigger responses that are multicellular, mechanistically diverse, resulting in neuronal protection, stimulation of neuroplasticity, and brain artery vasodilation. Overall, this review proposes a promising therapeutic opportunity by integrating a nutritional-based approach focusing on enriching the daily diet in ALA to prevent the devastating damage caused by stroke.

Peroxisome proliferator-activated receptor gamma induces apoptosis and inhibits autophagy of human monocyte-derived macrophages via induction of cathepsin L: potential role in atherosclerosis

Macrophages play a pivotal role in the pathophysiology of atherosclerosis. These cells express cathepsin L (CatL), a cysteine protease that has been implicated in atherogenesis and the associated arterial remodeling. In addition, macrophages highly express peroxisome proliferator-activated receptor (PPAR) γ, a transcription factor that regulates numerous genes important for lipid and lipoprotein metabolism, for glucose homeostasis, and inflammation. Hence, PPARγ might affect macrophage function in the context of chronic inflammation such as atherogenesis. In the present study, we examined the effect of PPARγ activation on the expression of CatL in human monocyte-derived macrophages (HMDM). Activation of PPARγ by the specific agonist GW929 concentration-dependently increased the levels of CatL mRNA and protein in HMDM. By promoter analysis, we identified a functional PPAR response element-like sequence that positively regulates CatL expression. In addition, we found that PPARγ-induced CatL promotes the degradation of Bcl2 without affecting Bax protein levels. Consistently, degradation of Bcl2 could be prevented by a specific CatL inhibitor, confirming the causative role of CatL. PPARγ-induced CatL was found to decrease autophagy through reduction of beclin 1 and LC3 protein levels. The reduction of these proteins involved in autophagic cell death was antagonized either by the CatL inhibitor or by CatL knockdown. In conclusion, our data show that PPARγ can specifically induce CatL, a proatherogenic protease, in HMDM. In turn, CatL inhibits autophagy and induces apoptosis. Thus, the proatherogenic effect of CatL could be neutralized by apoptosis, a beneficial phenomenon, at least in the early stages of atherosclerosis.

Dietary supplementation of alpha-linolenic acid in an enriched rapeseed oil diet protects from stroke

Populations of Western countries are severely deficient in omega-3 intake, both in the form of alpha-linolenic acid (ALA) and the Long Chain derivatives (LC-n-3), Eicosa-Pentaenoic-Acid and Docosa-Hexaenoic-Acid. Omega-3 insufficiency is a risk factor for cardiovascular and cerebral diseases such as coronary heart disease and stroke. Stroke is a major cause of mortality and morbidity, and induces a significant socioeconomic cost and a marked increase in patient/family burden. To date, preventive treatments and neuroprotective drugs identified in preclinical studies failed in clinical trials, in part because of an inability to tolerate drugs at neuroprotective concentrations. Therefore testing alternative protective strategies, such as functional foods/nutraceuticals, are of considerable interest. We have previously demonstrated that a single injection of ALA reduced ischemic damage by limiting glutamate-mediated neuronal death, whereas repeated injections displayed additive protective benefits as a result of increased neurogenesis, synaptogenesis and neurotrophin expression. Because intravenous injections are not a suitable long-term strategy in humans, the present study investigated the effect of ALA supplementation by an experimental diet containing rapeseed oil (RSO, a rich source of ALA) as the only source of lipids for stroke prevention. We tested several experimental diets which included 5, 10, and 20% RSO-enriched diet and feeding paradigms (fresh diet was provided once or twice a week for 4 or 6 weeks). Our results showed that ALA supplemented diets are more sensitive to lipid peroxidation than a regular chow diet. Because the diet affected feeding behavior and animal growth, we defined concrete guidelines to investigate the effect of omega-3 supplementation on neuropathology. Among the different sets of experiments, animals fed with 10% and 20% RSO-enriched diet displayed a reduced mortality rate, infarct size and increased probability of spontaneous reperfusion in the post-ischemic period. In addition, a drastic reduction of lipid peroxidation levels was observed in the ischemic brain of RSO-fed animals. Overall, our findings provide new insights into the potential of employing rapeseed oil as a functional food/nutraceutical aiding in stroke prevention and protection.

Subchronic alpha-linolenic acid treatment enhances brain plasticity and exerts an antidepressant effect: a versatile potential therapy for stroke

Omega-3 polyunsaturated fatty acids are known to have therapeutic potential in several neurological and psychiatric disorders. However, the molecular mechanisms of action underlying these effects are not well elucidated. We previously showed that alpha-linolenic acid (ALA) reduced ischemic brain damage after a single treatment. To follow-up this finding, we investigated whether subchronic ALA treatment promoted neuronal plasticity. Three sequential injections with a neuroprotective dose of ALA increased neurogenesis and expression of key proteins involved in synaptic functions, namely, synaptophysin-1, VAMP-2, and SNAP-25, as well as proteins supporting glutamatergic neurotransmission, namely, V-GLUT1 and V-GLUT2. These effects were correlated with an increase in brain-derived neurotrophic factor (BDNF) protein levels, both in vitro using neural stem cells and hippocampal cultures and in vivo, after subchronic ALA treatment. Given that BDNF has antidepressant activity, this led us to test whether subchronic ALA treatment could produce antidepressant-like behavior. ALA-treated mice had significantly reduced measures of depressive-like behavior compared with vehicle-treated animals, suggesting another aspect of ALA treatment that could stimulate functional stroke recovery by potentially combining acute neuroprotection with long-term repair/compensatory plasticity. Indeed, three sequential injections of ALA enhanced protection, either as a pretreatment, wherein it reduced post-ischemic infarct volume 24 h after a 1-hour occlusion of the middle cerebral artery or as post-treatment therapy, wherein it augmented animal survival rates by threefold 10 days after ischemia.

Distribution of sphingosine kinase activity and mRNA in rodent brain

Sphingosine-1-phosphate (S1P) is a lipid mediator that exerts multiple cellular functions through activation of a subfamily of G-protein-coupled receptors. Although there is evidence that S1P plays a role in the developing and adult CNS, little is known about the ability of brain parenchyma to synthesize this lipid. We have therefore analyzed the brain distribution of the enzymatic activity of the S1P synthesizing enzyme, sphingosine kinase (SPHK) [EC:2.7.1.91], as well as mRNA distribution for one of the two isoforms of this enzyme, sphingosine kinase 2. SPHK activity, measured by the conversion of [(3)H]sphingosine to [(3)H]S1P, is highest in cerebellum, followed by cortex and brainstem. Lowest activities were found in striatum and hippocampus. Sensitivity to 0.1% Triton-X suggests that this activity is accounted for by SPHK2. RT-PCR and in situ hybridization studies show that mRNA for this isoform has a distribution similar to that of SPHK activity. In vivo and in vitro ischemia increase SPHK activity and SPHK2 mRNA levels. These results indicate that SPHK2 is the predominant S1P-synthesizing isoform in normal brain parenchyma. Its heterogeneous distribution, in particular laminar distribution in cortex, suggests a neuronal localization and a possible role in cortical and cerebellar functions, in normal as well as ischemic brain.

A tarantula peptide against pain via ASIC1a channels and opioid mechanisms

Psalmotoxin 1, a peptide extracted from the South American tarantula Psalmopoeus cambridgei, has very potent analgesic properties against thermal, mechanical, chemical, inflammatory and neuropathic pain in rodents. It exerts its action by blocking acid-sensing ion channel 1a, and this blockade results in an activation of the endogenous enkephalin pathway. The analgesic properties of the peptide are suppressed by antagonists of the mu and delta-opioid receptors and are lost in Penk1-/- mice.

Polyunsaturated fatty acids are cerebral vasodilators via the TREK-1 potassium channel

Vessel occlusion is the most frequent cause for impairment of local blood flow within the brain resulting in neuronal damage and is a leading cause of disability and death worldwide. Polyunsaturated fatty acids and especially alpha-linolenic acid improve brain resistance against cerebral ischemia. The purpose of the present study was to evaluate the effects of polyunsaturated fatty acids and particularly alpha-linolenic acid on the cerebral blood flow and on the tone of vessels that regulate brain perfusion. alpha-Linolenic acid injections increased cerebral blood flow and induced vasodilation of the basilar artery but not of the carotid artery. The saturated fatty acid palmitic acid did not produce vasodilation. This suggested that the target of the polyunsaturated fatty acids effect was the TREK-1 potassium channel. We demonstrate the presence of this channel in basilar but not in carotid arteries. We show that vasodilations induced by the polyunsaturated fatty acid in the basilar artery as well as the laser-Doppler flow increase are abolished in TREK-1(-/-) mice. Altogether these data indicate that TREK-1 activation elicits a robust dilation that probably accounts for the increase of cerebral blood flow induced by polyunsaturated fatty acids such as alpha-linolenic acid or docosahexanoic acid. They suggest that the selective expression and activation of TREK-1 in brain collaterals could play a significant role in the protective mechanisms of polyunsaturated fatty acids against stroke by providing residual circulation during ischemia.

Altered acetylcholine, bradykinin and cutaneous pressure-induced vasodilation in mice lacking the TREK1 potassium channel: the endothelial link

The TWIK related K+ channel TREK1 is an important member of the class of two-pore-domain K+ channels. It is a background K+ channel and is regulated by hormones, neurotransmitters, intracellular pH and mechanical stretch. This work shows that TREK1 is present both in mesenteric resistance arteries and in skin microvessels. It is particularly well expressed in endothelial cells. Deletion of TREK1 in mice leads to an important alteration in vasodilation of mesenteric arteries induced by acetylcholine and bradykinin. Iontophoretic delivery of acetylcholine and bradykinin in the skin of TREK1+/+ and TREK1-/- mice also shows the important role of TREK1 in cutaneous endothelium-dependent vasodilation. The vasodilator response to local pressure application is also markedly decreased in TREK1-/- mice, mimicking the decreased response to pressure observed in diabetes. Deletion of TREK1 is associated with a marked alteration in the efficacy of the G-protein-coupled receptor-associated cascade producing NO that leads to major endothelial dysfunction.

Preconditioning and neurotrophins: a model for brain adaptation to seizures, ischemia and other stressful stimuli

The amino acid glutamate, the major excitatory neurotransmitter in the central nervous system, activates receptors coupled to calcium influx. Excessive activation of glutamate receptors in conditions such as severe epileptic seizures or stroke can kill neurons in a process called excitotoxicity. However, subtoxic levels of activation of the N-methyl-D-aspartate (NMDA) type of glutamate receptor elicit adaptive responses in neurons that enhance their ability to withstand more severe stress. A variety of stimuli induce adaptive responses to protect neurons. For example, sublethal ischemic episodes or a mild epileptic insult can protect neurons in a process referred to as tolerance. The molecular mechanisms that protect neurons by these different stressful stimuli are largely unknown but they share common features such as the transcription factor, nuclear factor kappa B (NF-kappaB), which is activated by ischemic and epileptic preconditioning as well as exposure to subtoxic NMDA concentrations. In this article, we describe stress-induced neuroprotective mechanisms highlighting the role of brain-derived neurotrophic factor (BDNF), a protein that plays a crucial role in neuronal survival and maintenance, neurogenesis and learning and memory.

Deletion of the background potassium channel TREK-1 results in a depression-resistant phenotype

Depression is a devastating illness with a lifetime prevalence of up to 20%. The neurotransmitter serotonin or 5-hydroxytryptamine (5-HT) is involved in the pathophysiology of depression and in the effects of antidepressant treatments. However, molecular alterations that underlie the pathology or treatment of depression are still poorly understood. The TREK-1 protein is a background K+ channel regulated by various neurotransmitters including 5-HT. In mice, the deletion of its gene (Kcnk2, also called TREK-1) led to animals with an increased efficacy of 5-HT neurotransmission and a resistance to depression in five different models and a substantially reduced elevation of corticosterone levels under stress. TREK-1-deficient (Kcnk2-/-) mice showed behavior similar to that of naive animals treated with classical antidepressants such as fluoxetine. Our results indicate that alterations in the functioning, regulation or both of the TREK-1 channel may alter mood, and that this particular K+ channel may be a potential target for new antidepressants.

TREK-1, a K+ channel involved in polymodal pain perception

The TREK-1 channel is a temperature-sensitive, osmosensitive and mechano-gated K+ channel with a regulation by Gs and Gq coupled receptors. This paper demonstrates that TREK-1 qualifies as one of the molecular sensors involved in pain perception. TREK-1 is highly expressed in small sensory neurons, is present in both peptidergic and nonpeptidergic neurons and is extensively colocalized with TRPV1, the capsaicin-activated nonselective ion channel. Mice with a disrupted TREK-1 gene are more sensitive to painful heat sensations near the threshold between anoxious warmth and painful heat. This phenotype is associated with the primary sensory neuron, as polymodal C-fibers were found to be more sensitive to heat in single fiber experiments. Knockout animals are more sensitive to low threshold mechanical stimuli and display an increased thermal and mechanical hyperalgesia in conditions of inflammation. They display a largely decreased pain response induced by osmotic changes particularly in prostaglandin E2-sensitized animals. TREK-1 appears as an important ion channel for polymodal pain perception and as an attractive target for the development of new analgesics.

Alpha-Linolenic acid and riluzole treatment confer cerebral protection and improve survival after focal brain ischemia

We investigated here the effects of alpha-linolenic acid and riluzole, both activators of the 2P-domain K+ channel family TREK/TRAAK, in a model of focal ischemia clinically relevant to stroke, not only assessing neuronal protection, but also long term survival. Moreover, all the drug treatments were initiated post-ischemia. Mice were subjected to transient middle cerebral artery occlusion (1 h) and reperfusion according to the intraluminal filament model. Drugs were injected into the jugular vein according to three protocols: (i) a single dose of 4 mg/kg riluzole or 500 nmol/kg alpha-linolenic acid at different reperfusion time; (ii) a three-day therapy (a single dose of 2 mg/kg riluzole and 250 nmol/kg alpha-linolenic acid given 1-2, 48 and 72 h after reperfusion); (iii) a three-week therapy (a single dose of 2 mg/kg riluzole and 250 nmol/kg alpha-linolenic acid given once a week during three weeks after reperfusion. A combined treatment with 2mg/kg riluzole+250 nmol/kg alpha-linolenic acid injected 2 h after reperfusion was also tested. A single dose of riluzole (4 mg/kg) or alpha-linolenic acid (500 nmol/kg) injected up to 3 h after reperfusion reduced drastically the stroke volume by 75% and 86%, respectively. Neurological deficits 24 h after ischemia were significantly improved by alpha-linolenic acid500 or riluzole4 with a neurological score of 1.8 as compared with 2.5 observed in vehicle-treated mice. Alpha-linolenic acid- and riluzole treatment were associated with a reduction in cytopathological features of cell injury, including DNA fragmentation and Bax expression in the cortex and the caudate putamen. With regard to the survival rate at 30 days, the best protections were obtained with the alpha-linolenic acid-injection in the three-week therapy as well as with a single dose of the combined treatment (2 mg/kg riluzole+250 nmol/kg alpha-linolenic acid). Palmitic acid, a saturated fatty acid that does not activate the 2P-domain K-channel TREK/TRAAK family, did not provide any neuroprotection. Taken together, these data suggest that the TREK/TRAAK K-channel family may be a promising target for neuroprotection, and that riluzole and alpha-linolenic acid could be of therapeutic value against focal ischemia/reperfusion injury to the brain.

La tolérance cérébrale : un choix prometteur vers de nouvelles thérapies contre les maladies neurologiques

Ischemia and seizures are common diseases that result in neuronal death. To-date, there are no available treatments to block or reverse neuronal death pathways in patients who suffer from these diseases. All drugs that have been shown to be neuroprotective in animal models have failed in human trials. Therefore, the potential of preventative strategies for therapy is increasingly explored. Experimental studies have demonstrated that a brief cerebral ischemic insult, that is not harmful by itself, results in a temporary protective adaptation in the brain against a subsequent ischemic episode that would otherwise be lethal. This process, termed ischemic preconditioning, has been confirmed in different models of cerebral ischemia. A similar phenomenon observed after a mild epileptic insult conferred a transitory tolerance to a subsequent epileptic episode. This process is termed epileptic tolerance. Other stresses, like hyperthermia or spreading depression, also enhanced brain resistance to detrimental effects of ischemic or epileptic injury. Recently, a cross tolerance between ischemia and epilepsy has been reported. Also, some retrospective studies in humans suggest that endogenous ischemic preconditioning exists in the brain. Altogether these insights of brain tolerance point to the future discovery of potentially useful targets for acute neuroprotection as well as preventive therapy.

TREK-1, a K+ channel involved in neuroprotection and general anesthesia

TREK-1 is a two-pore-domain background potassium channel expressed throughout the central nervous system. It is opened by polyunsaturated fatty acids and lysophospholipids. It is inhibited by neurotransmitters that produce an increase in intracellular cAMP and by those that activate the Gq protein pathway. TREK-1 is also activated by volatile anesthetics and has been suggested to be an important target in the action of these drugs. Using mice with a disrupted TREK-1 gene, we now show that TREK-1 has an important role in neuroprotection against epilepsy and brain and spinal chord ischemia. Trek1-/- mice display an increased sensitivity to ischemia and epilepsy. Neuroprotection by polyunsaturated fatty acids, which is impressive in Trek1+/+ mice, disappears in Trek1-/- mice indicating a central role of TREK-1 in this process. Trek1-/- mice are also resistant to anesthesia by volatile anesthetics. TREK-1 emerges as a potential innovative target for developing new therapeutic agents for neurology and anesthesiology.

Vascular sphingosine-1-phosphate S1P1 and S1P3 receptors

The sphingolipid sphingosine-1-phosphate (S1P) acts on five subtypes of G-protein- coupled receptors, termed S1P(1) (formerly endothelial differentiation gene-1 [Edg-1]), S1P(2) (Edg-5), S1P(3) (Edg-3), S1P(4) (Edg-6) and S1P(5) (Edg-8), and possibly several other "orphan" receptors, such as GPR3, GPR6 and GPR12. These receptors are coupled to different intracellular second messenger systems, including adenylate cyclase, phospholipase C, phosphatidylinositol 3-kinase/protein kinase Akt, mitogen-activated protein kinases, as well as Rho- and Ras-dependent pathways. Consistently with this receptor multiplicity and pleiotropic signaling mechanisms, S1P influences numerous cell functions. S1P(1)1, S1P(2) and S1P(3) receptors are the major S1P receptor subtypes in the cardiovascular system, where they mediate the effects of S1P released from platelets, and possibly other tissues (such as brain). Thus S1P(1) and S1P(3) receptors enhance endothelial and vascular smooth muscle cell proliferation and migration, playing a key role in developmental and pathological angiogenesis. In contrast, S1P(2) receptors inhibit migration of these cell types, probably because of their unique stimulatory effect on a GTPase-activating protein inhibiting the activity of Rac. S1P receptors can also cause relaxation and constriction of blood vessels. The former effect is mediated by pertussis toxin-sensitive receptors (possibly S1P(1)) located on the endothelium and stimulating phosphatidylinositol 3-kinase/Akt/endothelial nitric oxide synthase (eNOS). The vasoconstricting effect of S1P is likely to be mediated by S1P(2) and/or S1P(3) receptors, via Rho-Rho-kinase, and is more potent in coronary and cerebral blood vessels. Finally, S1P also protects endothelial cells from apoptosis through activation of phosphatidylinositol 3-kinase/Akt/eNOS via S1P(1) and S1P(3) receptors. The variety of these effects, taken together with the existence of multiple receptor subtypes, provides an abundance of therapeutic targets that currently still await the development of selective agents.

Linolenic acid prevents neuronal cell death and paraplegia after transient spinal cord ischemia in rats

PURPOSE

Spinal cord ischemia is a devastating complication of thoracic and thoracoabdominal aortic surgery. Recent studies have suggested a neuroprotective effect of polyunsaturated fatty acids against cerebral ischemia. We investigated the effect of linolenic acid (LIN) in a rat model of spinal cord ischemia.

METHODS

Rats were subjected to cross-clamping of the aortic arch and left subclavian artery for 14 minutes. Groups were as follows: sham operation (n = 15); ischemia (n = 15), receiving only vehicle; LIN A (n = 15), receiving LIN before clamping; and LIN B (n = 15), receiving LIN at onset of reperfusion. Neurologic status was assessed daily for 7 days. Spinal cords were harvested for histopathologic analysis, TUNEL staining, and immunohistochemistry for Bax, heat shock protein 70 (HSP70), and nuclear factor-kappaB.

RESULTS

Ischemic rats had severe and definitive paraplegia. LIN-treated rats had significantly better neurologic function. Histopathologic analysis disclosed severe neuronal necrosis in the lumbar gray matter of ischemic rats, whereas most of the LIN-treated rats sustained mild to moderate injury. LIN reduced the loss of motor neurons at 7 days (LIN A, 17 +/- 6, and LIN B, 15 +/- 7, versus ischemia, 6 +/- 2 per section; P <.05). LIN prevented apoptotic neuronal cell death, Bax immunoreactivity of the pro-apoptotic protein Bax, and the nuclear transcription factor NF-kappaB. Nuclear HSP70 immunoreactivity was noted exclusively in motor neurons from LIN-treated rats and not in motor neurons from ischemic rats.

CONCLUSION

These results suggest that LIN can induce protection against ischemia in the spinal cord, thereby preventing both necrosis and apoptosis of motor neurons.

A potent protective role of lysophospholipids against global cerebral ischemia and glutamate excitotoxicity in neuronal cultures

Lysophospholipids (LPLs) are important intermediates in the synthesis and degradation of membrane phospholipids. Here we show that certain LPLs, particularly lysophosphatidylcholine and lysophosphatidylinositol, prevent neuronal death both in an in vivo model of transient global ischemia and in an in vitro model of excitotoxicity using primary cultures of cerebellar granule cells exposed to high extracellular concentrations of glutamate (20-40 micromol/L). The intravenous injection of lysophosphatidylcholine or lysophosphatidylinositol at a concentration of 200 nmol/kg induced a survival of CA1 pyramidal neurons as high as approximately 95%, even when the treatment was started 30 minutes after 15-minute global ischemia. In contrast, lysophosphatidic acid induced no protection. This work also provides evidence that a pretreatment with lysophosphatidylcholine or lysophosphatidylinositol (200 nmol/kg) injected as long as 3 days before a severe 6-minute ischemia provided a potent tolerance against neurodegeneration. Neuroprotection was also observed in in vitro experiments with LPLs. Taken together, in vivo and in vitro data suggest a potential therapeutic use of LPLs as antiischemic compounds. The potential role of 2P-domain K+ channels as targets of LPLs in this potent neuroprotective effect is discussed.

Polyunsaturated fatty acids induce ischemic and epileptic tolerance

The findings reported in this work show that pretreatment with polyunsaturated fatty acids, particularly linolenic acid, present in vegetable oils, can provide a potent tolerance against neurodegeneration in two models of neuronal death-generating treatments such as kainic acid injection and global ischemia. Rats were injected i.v. with 500 nmol/kg of linolenic acid as long as 3 days prior to 6 min global ischemia or received an injection of linolenic acid as long as 3 days prior to a dose of 7.5 mg/kg kainic acid. Neuronal degeneration, assessed by analysis of neuronal density on Cresyl Violet-stained hippocampal sections, was significantly reduced in linolenic acid-treated rats (94-85% of cell survival in the ischemic model and 99-79% of cell survival in the epileptic model in respective CA1 and CA3 subfields). The neuroprotection observed following the injection of linolenic acid 3 days prior to induction of a severe ischemic or epileptic challenge was associated with the induction of the neuroprotective HSP70 heat shock protein within the time window of protection. The injection of 500 nmol/kg of linolenic acid induced a maximal HSP70 expression of 387% at 72 h. In contrast, the overexpression of one well-known protein inducer of neuronal cell death, Bax, which is induced by both ischemic and kainic acid-induced epileptic insults, was prevented by linolenic acid in the 3-day window of protection. These results strengthen the idea of an interesting potential therapeutical value of polyunsaturated fatty acids in neuronal protection.

Activation of the nuclear factor-kappaB is a key event in brain tolerance

The transcription factor nuclear factor-kappaB (NFkappaB) is an ubiquitously expressed inducible regulator of a broad range of genes and plays a pivotal role in cell death and survival pathways. Three models of brain tolerance (ischemic, epileptic, and polyunsaturated fatty acid-induced preconditioning), known to confer resistance to neurons against ischemia or status epilepticus, were used to determine whether NFkappaB mediated the late preconditioning. A sublethal 3 min ischemia, a dose of 5 mg/kg kainic acid (KA5) or 500 nmol of linolenic acid (LIN500) led to a rapid increase of NFkappaB DNA-binding activity and nuclear translocation of p65 and p50 subunits of NFkappaB in neurons. Pretreatment with the NFkappaB inhibitor diethyldithiocarbamate or kappaB decoy DNA blocked the increased DNA-binding activity and the nuclear translocation of NFkappaB and abolished the neuroprotective effects of different delayed preconditionings against severe ischemia or epilepsy. The inhibition of NFkappaB observed in rats preconditioned with 3 min ischemia, KA5 or LIN500 treatments compared with ischemic or epileptic controls was correlated with the prevention of the inducible degradation of the inhibitory protein IkappaBalpha. Preconditioning probably inhibits the activation of NFkappaB by interfering with a pathway that leads to the direct transcriptional activation of IkappaBalpha by NFkappaB itself. The present work provides evidence that activation of NFkappaB is a crucial step in the signal transduction pathway that underlies the development of brain tolerance and may open new strategies in the prevention of cerebral diseases, such as ischemia or epilepsy.

K(ATP) channel openers, adenosine agonists and epileptic preconditioning are stress signals inducing hippocampal neuroprotection

Many models of induced ischemic and epileptic tolerance have now been described in the brain. Although detailed mechanisms underlying such protections still remain largely unknown, induction of heat shock proteins is amongst the endogenous responses believed to play an important role in cellular defense mechanisms. This study reveals that the development of epileptic tolerance also coincides with the induction of the 70,000 mol. wt heat shock protein expression within the time window of protection. Adenosine agonists or ATP-sensitive potassium channel openers have also been shown to exert strong neuroprotective effects when injected shortly prior to a severe ischemic or epileptic insult. The present work shows that adenosine receptor activation and ATP-sensitive potassium channel opening induce 70,000 mol. wt heat shock protein expression in the rat hippocampus and are able to mimic neuroprotection driven by preconditioning. R-phenylisopropyladenosine, a purine agonist, or (-)cromakalim, an ATP-sensitive potassium channel opener, was administered three days prior to a lethal ischemic or epileptic episode to mimic preconditioning. Neurodegeneration was assessed using Cresyl Violet staining and cellular DNA fragmentation visualized by the terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate-biotin nick end labeling method. 70, 000 mol. wt heat shock protein expression was analysed by western blotting and immunohistochemistry. The results show a long-lasting neuroprotection induced by activation of adenosine receptors or ATP-sensitive K(+) channels as early as three days prior to induction of a severe ischemic or epileptic challenge. This protective effect is associated with enhanced 70,000 mol. wt heat shock protein expression also occurring three days following administration of R-phenylisopropyladenosine or (-)cromakalim. These findings support the idea that preconditioning doses of R-phenylisopropyladenosine and (-)cromakalim act as mild cellular stresses inducing neuroprotection in a manner similar to a mild kainate treatment prior to a lethal ischemic or severe epileptic insult three days later. They also suggest that a delayed 70,000 mol. wt heat shock protein expression induced by excitatory neuronal stresses such as short ischemia, mild kainic acid treatment or activation of adenosine receptors and ATP-sensitive potassium channels is predictive of neuronal survival against a subsequent lethal injury.

ATP-sensitive potassium channels (K(ATP)) in retina: a key role for delayed ischemic tolerance

The objectives of the present study were to determine the localization of K(ATP) channels in normal retina and to evaluate their potential roles in ischemic preconditioning (IPC) in a rat model of ischemia induced by increased intraocular pressure (IOP). Brown Norway rats were subjected to sublethal 3-, lethal 20- and 40-min ischemia and the functional recovery was evaluated using electroretinography. The time interval between ischemic insults ranged from 1 to 72 h. The effects of K(ATP) channel blockade on IPC protection were studied by treatment with 0.01% glipizide. IPC was mimicked by injection of K(ATP) channel openers of 0.01% (-)cromakalim or 0.01% P1060 72 h before 20-min ischemia. Co-expression of K(ATP) channel subunits Kir6.2/SUR1 was observed in the retinal pigment epithelium, inner segments of photoreceptors, outer plexiform and ganglion cell layers and at the border of the inner nuclear layer. In contrast to a 20- or 40-min ischemia, a 3-min ischemia induced no alteration of the electroretinogram (ERG) and constituted the preconditioning stimulus. An ischemic challenge of 40 min in preconditioned rats induced impairment of retinal function. However, animals preconditioned 24, 48 and 72 h before 20-min ischemia had a significant improvement of the ERG. (-)Cromakalim and P1060 mimicked the effect of IPC. Glipizide significantly suppressed the protective effects of preconditioning. In conclusion, activation of K(ATP) channels plays an important role in the mechanism of preconditioning by enhancing the resistance of the retina against a severe ischemic insult.

Polyunsaturated fatty acids are potent neuroprotectors

Results reported in this work suggest a potential therapeutic value of polyunsaturated fatty acids for cerebral pathologies as previously proposed by others for cardiac diseases. We show that the polyunsaturated fatty acid linolenic acid prevents neuronal death in an animal model of transient global ischemia even when administered after the insult. Linolenic acid also protects animals treated with kainate against seizures and hippocampal lesions. The same effects have been observed in an in vitro model of seizure-like activity using glutamatergic neurons and they have been shown to be associated with blockade of glutamatergic transmission by low concentrations of distinct polyunsaturated fatty acids. Our data suggest that the opening of background K(+) channels, like TREK-1 and TRAAK, which are activated by arachidonic acid and other polyunsaturated fatty acids such as docosahexaenoic acid and linolenic acid, is a significant factor in this neuroprotective effect. These channels are abundant in the brain where they are located both pre- and post-synaptically, and are insensitive to saturated fatty acids, which offer no neuroprotection.