Nicolas Blondeau

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.

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.

Mutually protective actions of kainic acid epileptic Preconditioning and sublethal global ischemia on hippocampal neuronal death: Involvement of adenosine A1 receptors and KATP channels

Preconditioning with sublethal ischemia attenuates the detrimental effects of subsequent prolonged ischemic insults. This research elucidates potential in vivo cross-tolerance between different neuronal death-generating treatments such as kainate administration, which induces seizures and global ischemia. This study also investigates the effects of a mild epileptic insult on neuronal death in rat hippocampus after a subsequent, lethal epileptic stress using kainic acid (KA) as a model of epilepsy. Three preconditioning groups were as follows: group 1 was injected with 5 mg/kg KA before a 6-minute global ischemia; group 2 received a 3-minute global ischemia before 7.5 mg/kg KA; and group 3 was injected with a 5-mg/kg dose of KA before a 7.5-mg/kg KA injection. The interval between treatments was 3 days. Neuronal degeneration, revealed by the silver impregnation method and analysis of cresyl violet staining, was markedly reduced in rats preconditioned with a sublethal ischemia or a 5-mg/kg KA treatment. Labeling with terminal deoxynucleotidyl transferase-mediated 2′-deoxyuridine 5′triphosphate-biotin nick-end labeling and DNA laddering confirmed the component of DNA fragmentation in the death of ischemic and epileptic neurons and its reduction in all preconditioned animals. The current study supports the existence of bidirectional cross-tolerance between KA excitotoxicity and global ischemia and suggests the involvement of adenosine A1 receptors and sulfonylurea- and ATP-sensitive K+ channels in this protective phenomenon.

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 α-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 α-linolenic acid on the cerebral blood flow and on the tone of vessels that regulate brain perfusion. α-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 α-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.

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.

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.

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.

Oxygen glucose deprivation-induced astrocyte dysfunction provokes neuronal death through oxidative stress

Understanding the role of astrocytes in stroke is assuming increasing prominence, not only as an important component on its own within the neurovascular unit, but also because astrocytes can influence neuronal outcome. Ischemia may induce astrogliosis and other phenotypic changes, but these remain poorly understood, in part due to limitations in reproducing these changes in vitro. Dibutyryl cyclic AMP-differentiated cultured astrocytes are more representative of the in vivo astroglial cell phenotype, and were much more susceptible than undifferentiated astrocytes to an ischemic-like stress, oxygen-glucose deprivation (OGD). OGD altered the expression/distribution and activity of glial glutamate transporters, impaired cellular glutamate uptake and decreased intracellular levels of glutathione preferentially in differentiated astrocytes. Resistance to OGD was conferred by inhibiting caspase-3 with DEVD-CHO and oxidative stress by the antioxidant N-acetylcysteine (NAC). The resistance of undifferentiated astrocytes to OGD may result from a transient but selective morphological transformation into Alzheimer type II astrocytes, an intermediary stage prior to transforming into reactive astrocytes. Co-culture of neurons with OGD-exposed astrocytes resulted in neurotoxicity, but at surprisingly lower levels with dying differentiated astrocytes. The antioxidant NAC or the 5-LOX inhibitor AA861 added upon co-culture delayed (day 1) but did not prevent neurotoxicity (day 3). Astrocytes undergoing apoptosis as a result of ischemia may represent a transient neuroprotective mechanism via ischemia-induced release of glutathione, but oxidative stress was responsible for neuronal demise when ischemia compromised astrocyte supportive functions.

Brain Adaptation to Stressful Stimuli: A New Perspective on Potential Therapeutic Approaches Based on BDNF and NMDA Receptors

A variety of sublethal or stressful stimuli induce a phenomenon in the brain known as tolerance, an adaptive response that protects the brain against the same stress, or against a different stress (cross-tolerance). Understanding the molecular mechanisms of brain preconditioning holds promise in developing innovative therapies to prevent and treat neurodegenerative disorders, particularly ischemic stroke. Many of the detailed steps involved in tolerance and cross-tolerance are unknown. It is also likely that different stressors differentially regulate sets of genes, transcription factors, and signal transduction pathways that depend upon the molecules that are released in response to the stressor, activation of particular receptors, and the surrounding milieu. The focus of this review is to highlight a few examples of stimuli that induce tolerance: 1) cortical spreading depression; 2) 3-nitropropionic acid; and 3) 2-deoxy-D-glucose. We will summarize by discussing one pathway where intracellular mediators may converge to upregulate intrinsic neuronal survival pathways to promote survival by resisting damage. This mechanism, activation of N-methyl-D-aspartate receptors and its integral relationship with brain-derived neurotrophic factor, may be a critical and general mechanism developed in brain to respond to stressful stimuli.

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.