Ischaemic preconditioning of the endothelium and smooth muscle of cerebral arteries

Palmitoylethanolamide protects dentate gyrus granule cells via peroxisome proliferator-activated receptor-α

Endocannabinoids like 2-arachidonoylglycerol strongly modulate the complex machinery of secondary neuronal damage and are shown to improve neuronal survival after excitotoxic lesion. Palmitoylethanolamide (PEA), the naturally occurring fatty acid amide of ethanolamine and palmitic acid, is an endogenous lipid known to mimic several effects of endocannabinoids even without binding to cannabinoid receptors. Here we show that PEA (0.001-1 μM) and the synthetic peroxisome proliferator-activated receptor (PPAR)-alpha agonist 4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio acetic acid (Wy-14,643; 0.1-1 μM) reduced the number of microglial cells and protected dentate gyrus granule cells in excitotoxically lesioned organotypic hippocampal slice cultures (OHSCs). Treatment with the PPAR-alpha antagonist N-((2S)-2-(((1Z)-1-Methyl-3-oxo-3-(4-(trifluoromethyl)phenyl)prop-1-enyl)amino)-3-(4-(2-(5-methyl-2-phenyl-1,3-oxazol-4-yl)ethoxy)phenyl)propyl)propanamide (GW6471; 0.05-5 μM) blocked PEA-mediated neuroprotection and reduction of microglial cell numbers whereas the PPAR-gamma antagonist 2-chloro-5-nitro-N-phenyl-benzamide (GW9662; 0.01-1 μM) showed no effects. Immunocytochemistry and Western blot analyses revealed a strong PPAR-alpha immunoreaction in BV-2 microglial cells and in HT22 hippocampal cells. Intensity and location of PPAR-alpha immunoreaction remained constant during stimulation with PEA (0.01 μM; 1-36 h). In conclusion our data provide evidence that (1) PEA counteracted excitotoxically induced secondary neuronal damage of dentate gyrus granule cells, (2) PPAR-alpha but not PPAR-gamma is the endogenous binding site for PEA-mediated neuroprotection, and (3) PEA may activate PPAR-alpha in microglial cells and hippocampal neurons to exert its neuroprotective effects. In addition to classical endocannabinoids, PEA-mediated PPAR-alpha activation represents a possible target for therapeutic interventions to mitigate symptoms of secondary neuronal damage.

The neuroprotective effect of the antioxidant flavonoid derivate di-tert-butylhydroxyphenyl is parallel to the preventive effect on post-ischemic Kir2.x impairment but not to post-ischemic endothelial dysfunction

In the rat model of transient cerebral ischemia induced by intraluminal occlusion of the middle cerebral artery, we investigated the respective roles of ischemia and reperfusion in endothelium-dependent relaxation and smooth muscle relaxation related to the inward rectifier potassium current (Kir2.x), using the Halpern arteriography technique and/or patch-clamp technique. We first demonstrated that reperfusion is necessary to induce a significant impairment of smooth muscle Kir2.x, since ischemia alone has no effect on Kir2.x current density and function. In addition, we demonstrated that both ischemia and reperfusion are necessary for the occurrence of maximal post-ischemic endothelial dysfunction. The crucial role of reperfusion in post-ischemic vascular impairment prompted us to characterize the effect of a new antioxidant synthetic flavonoid derivate, 3'5'di- tert-butylhydroxyphenyl (dt-BC), on both neuronal and vascular injuries. Dt-BC (10 mg/kg) induced a neuroprotective effect as demonstrated by a significant decrease in infarct size, while there was no protective effect with the doses of 3 mg/kg and 30 mg/kg. Parallel to neuroprotection, dt-BC at a dose of 10 mg/kg, but not with doses of 3 mg/kg and 30 mg/kg, prevented post-ischemic impairment of smooth muscle Kir2.x current density and function, while dt-BC had no effect on the post-ischemic alteration of endothelial function whatever doses are used. These data demonstrate the potential of a new synthetic flavonoid derivate to induce neurovascular protection and support a possible relationship between vascular and neuronal protection via pharmacological modulation of oxidative stress.

Protection cellulaire par activation des récepteurs nucléaires PPAR

Apart from their effects on lipid and glucose metabolism, the nuclear receptors PPARs (peroxysome proliferator-activated receptors) could also be involved in cellular protection. Indeed, an increasing body of literature provides arguments in favour of a protective role of PPAR alpha (fenofibrate, gemfibrozil) and PPAR gamma (ciglitazone, pioglitazone, rosiglitazone, troglitazone) agonists, particularly in myocardial or cerebral ischaemia as well as in neurodegenerative diseases. Such cellular protection could be the result of the modulation, at a molecular level, of inflammation pathways, oxidative stress and apoptosis. If these experimental results are confirmed by appropriate clinical trials, pharmacological modulation of the nuclear receptor PPARs, as well as the development of highly selective and more effective PPAR agonists, could become an important challenge in the field of cellular protection.

Peroxisome proliferator-activated receptor-alpha activation as a mechanism of preventive neuroprotection induced by chronic fenofibrate treatment

The treatment of ischemic strokes is limited to the prevention of cerebrovascular risk factors and to the modulation of the coagulation cascade during the acute phase. A new therapeutic strategy could be to preventively protect the brain against noxious biological reactions induced by cerebral ischemia such as oxidative stress and inflammation to minimize their neurological consequences. Here, we show that a peroxisome proliferator-activated receptor (PPAR-alpha) activator, fenofibrate, protects against cerebral injury by anti-oxidant and anti-inflammatory mechanisms. A 14 d preventive treatment with fenofibrate reduces susceptibility to stroke in apolipoprotein E-deficient mice as well as decreases cerebral infarct volume in C57BL/6 wild-type mice. The neuroprotective effect of fenofibrate is completely absent in PPAR-alpha-deficient mice, suggesting that PPAR-alpha activation is involved as a mechanism of the protection against cerebral injury. Furthermore, this neuroprotective effect appears independently of any improvement in plasma lipids or glycemia and is associated with (1) an improvement in middle cerebral artery sensitivity to endothelium-dependent relaxation unrelated to an increase in nitric oxide synthase (NOS) type III expression, (2) a decrease in cerebral oxidative stress depending on the increase in numerous antioxidant enzyme activities, and (3) the prevention of ischemia-induced expression of vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 in cerebral vessels without any change in NOS II expression. These data demonstrate that PPAR-alpha could be a new pharmacological target to preventively reduce the deleterious neurological consequences of stroke in mice and suggest that PPAR-alpha activators could preventively decrease the severity of stroke in humans.

Statins and stroke

An important issue for stroke prevention is the identification and treatment of risk factors such as hypercholesterolaemia. The 4 reasons to test if the statins have a role in stroke prevention are: (i) a statistical link between elevated low density lipoprotein-cholesterol or decreased high density lipoprotein-cholesterol and ischaemic stroke; (ii) a reduction in vascular risk with statins in randomised trials in patients with coronary heart disease; (iii) evidence of a decreased plaque progression under statins; and (iv) pooled analyses of primary and secondary prevention trials showing that reduction of total serum cholesterol reduces the incidence of stroke, especially with the highest rate of cholesterol reduction, and in patients with the highest risk of stroke (i.e. with statins in secondary prevention trials). The question of whether statins also have a neuroprotective effect in humans and reduce the risk of post-stroke dementia remains unsettled.

[Antilipemics: from prevention to protection]

Statins and fibrates have been demonstrated to prevent both cardiovascular events and stroke. While this preventive effect was initially thought to be related to their lipid-lowering effects, in particular hypocholesterolaemic effect, analysis of primary and secondary prevention trials suggest that these preventive effects could be partly independent of their effects on lipid disorders. The pleiotropic effects, such as vascular, anti-inflammatory or anti-oxidants effects, were described for both the statins and fibrates. In addition to the preventive effects, these pleiotropic effects could partially explain the decrease in myocardial or cerebral ischemia consequences in experimental models. These cellular protective effects may have a therapeutic interest to decrease severity of stroke or coronary acute syndrome. They could also explain the drugs' lipid-lowering preventive effects independent of the treatment of lipid disorders. Beyond vascular pathologies, the pleiotropic effects of lipid-lowering drugs could explain their potentially beneficial effect in different diseases, such as dementia or cancer.

Hypolipemic agents for stroke prevention

An important issue for stroke prevention is identification and treatment of risk factors such as hypercholesterolemia. The four reasons to test hypolipidemic agents in stroke prevention are: (i) a statistical link between elevated low-density lipoprotein cholesterol (LDL-c) or decreased high-density lipoprotein cholesterol (HDL-c) and ischemic stroke; (ii) a reduction in vascular risk in randomized trials in patients with coronary heart disease; (iii) evidence of a decreased plaque progression under statins, (iv) pooled analyses of primary and secondary prevention trials showing that reduction of total serum cholesterol reduces the incidence of stroke, especially with the highest rate of cholesterol reduction, and in patients with the highest risk of stroke (i.e., with statins in secondary prevention trials), and (v) prophylactic neuroprotection induced by hypolipidemic agents in animal models of cerebral ischemia. Data provided by trials conducted in subjects with coronary heart disease and in asymptomatic individuals should now be confirmed in stroke patient.

Temporal profile of enhanced vulnerability of the postthrombotic brain to secondary embolic events

BACKGROUND AND PURPOSE

Patients with vascular or cardiac disease may experience recurrent thrombosis and embolization to the cerebral vasculature. Transient distal platelet accumulation after common carotid artery thrombosis (CCAT) leads to hemodynamic, metabolic, and molecular events that may influence the response of the postthromboembolic brain to secondary emboli. We investigated the effect of repeated embolic episodes on histopathological outcome at various time intervals using a clinically relevant model of embolic stroke.

METHODS

Six groups of rats underwent either photochemically induced CCAT followed by sham surgery or 2 episodes of CCAT separated by 10 minutes or 1, 3, 5, or 7 days. Outcome measures included routine histopathological analysis and determination of the number of infarct loci and their total volume.

RESULTS

Rats that underwent a second CCAT at 1, 3, or 5 days after the first insult had 20 to 30 times larger infarct volumes than rats in the single-CCAT group (P<0.05). In addition, rats in the 10-minute and 1-, 3-, and 5-day groups had 2 to 3 times as many infarcts as those in the single-CCAT group (P<0.05). Infarcts produced by double insults commonly extended through the neuraxis and were necrotic, edematous, and sometimes hemorrhagic.

CONCLUSIONS

A prior thromboembolic event puts the brain at risk for severe infarction after a second embolic event. These findings cannot be explained solely by a greater number of infarcts. Elucidating pathomechanisms responsible for the vulnerability of the postthromboembolic brain may provide targets for new treatment strategies to prevent the severe consequences of embolic stroke.