Endothelin receptor antagonist preserves microvascular perfusion and reduces ischemic brain damage following permanent focal ischemia

Clinical Pharmacology of Clazosentan, a Selective Endothelin A Receptor Antagonist for the Prevention and Treatment of aSAH-Related Cerebral Vasospasm

Aneurysmal subarachnoid hemorrhage (aSAH) may lead to cerebral vasospasm and is associated with significant morbidity and mortality. It represents a major unmet medical need due to few treatment options with limited efficacy. The role of endothelin-1 (ET-1) and its receptor ET_A in the pathogenesis of aSAH-induced vasospasm suggests antagonism of this receptor as promising asset for pharmacological treatment. Clazosentan is a potent ET_A receptor antagonist for intravenous use currently under development for the prevention of aSAH-induced cerebral vasospasm. The pharmacokinetics of clazosentan are characterized by an intermediate clearance, a volume of distribution similar to that of the extracellular fluid volume, dose-proportional exposure, an elimination independent of drug-metabolizing enzymes, and a disposition mainly dependent on the hepatic uptake transporter organic anion transport polypeptide 1B1/1B3. In healthy subjects, clazosentan leads to an increase in ET-1 concentration and prevents the cardiac and renal effects mediated by infusion of ET-1. In patients, it significantly reduced the incidence of moderate or severe vasospasm as well as post-aSAH vasospasm-related morbidity and mortality. Clazosentan is well tolerated up to the expected therapeutic dose of 15 mg/h and, in aSAH patients, lung complications, hypotension, and anemia were adverse events more commonly reported following clazosentan than placebo. In summary, clazosentan has a pharmacokinetic, pharmacodynamic, and safety profile suitable to become a valuable asset in the armamentarium of therapeutic modalities to prevent aSAH-induced cerebral vasospasm.

Endothelin and diabetic complications: a brain-centric view

The global epidemic of diabetes is of significant concern. Diabetes associated vascular disease signifies the principal cause of morbidity and mortality in diabetic patients. It is also the most rapidly increasing risk factor for cognitive impairment, a silent disease that causes loss of creativity, productivity, and quality of life. Small vessel disease in the cerebral vasculature plays a major role in the pathogenesis of cognitive impairment in diabetes. Endothelin system, including endothelin-1 (ET-1) and the receptors (ET(A) and ET(B)), is a likely candidate that may be involved in many aspects of the diabetes cerebrovascular disease. In this review, we took a brain-centric approach and discussed the role of the ET system in cerebrovascular and cognitive dysfunction in diabetes.

Cerebral Perfusion and Cerebral Autoregulation after Cardiac Arrest

Out of hospital cardiac arrest is the leading cause of death in industrialized countries. Recovery of hemodynamics does not necessarily lead to recovery of cerebral perfusion. The neurological injury induced by a circulatory arrest mainly determines the prognosis of patients after cardiac arrest and rates of survival with a favourable neurological outcome are low. This review focuses on the temporal course of cerebral perfusion and changes in cerebral autoregulation after out of hospital cardiac arrest. In the early phase after cardiac arrest, patients have a low cerebral blood flow that gradually restores towards normal values during the first 72 hours after cardiac arrest. Whether modification of the cerebral blood flow after return of spontaneous circulation impacts patient outcome remains to be determined.

Early-stage minimally invasive procedures decrease perihematomal endothelin-1 levels and improve neurological functioning in a rabbit model of intracerebral hemorrhage

INTRODUCTION

To determine the effects of minimally invasive surgery (MIS) at various stages after intracerebral hemorrhage (ICH) on perihematomal endothelin (ET)-1 levels and neurological functioning.

METHODS

Sixty rabbits were randomly distributed into a model control group (MC group, 30 rabbits) or a MIS group (MI group, 30 rabbits). An ICH model was established in all animals. In the MI group, ICH was evacuated by MIS at 6, 12, 18, 24, and 48 hours (six rabbits at each time point) after the ICH was established. The animals in the MC group underwent the same procedures for ICH evacuation, but with a sham operation without hematoma aspiration. All the animals were sacrificed 7 days after the ICH was established. Neurological deficit scores were determined, and the perihematomal brain tissue was removed to determine the ET-1 levels, blood-brain barrier (BBB) permeability, and brain water content (BWC).

RESULTS

The neurological deficit scores, perihematomal ET-1 levels, BBB permeability, and BWC all decreased significantly in the MI group compared to the MC group. Performing the MIS for evacuating the ICH at 6 hours resulted in the most remarkable decreases in these indices, followed by a significant difference observed at 12 hours within the MI subgroups.

CONCLUSIONS

Performing MIS at 6-12 hours after ICH resulted in the most significant decreases in neurological deficit scores, ET-1 levels, BBB permeability, and brain edema. The optimal time window for performing MIS for ICH evacuation might be within 6-12 hours after hemorrhage.

Minimally modified LDL upregulates endothelin type A receptors in rat coronary arterial smooth muscle cells

Minimally modified low-density lipoprotein (mmLDL) is a risk factor for cardiovascular disease. The present study investigated the effects of mmLDL on the expression of endothelin type A (ET_A) receptors in coronary arteries. Rat coronary arteries were organ-cultured for 24 h. The contractile responses were recorded using a myographic system. ET_A receptor mRNA and protein expressions were determined using real-time PCR and western blotting, respectively. The results showed that organ-culturing in the presence of mmLDL enhanced the arterial contractility mediated by the ET_A receptor in a concentration-dependent and time-dependent manner. Culturing with mmLDL (10 μg/mL) for 24 h shifted the concentration-contractile curves toward the left significantly with increased E_max of 228% ± 20% from control of 100% ± 10% and significantly increased ET_A receptor mRNA and protein levels. Inhibition of the protein kinase C, extracellular signal-related kinases 1 and 2 (ERK1/2), or NF-κB activities significantly attenuated the effects of mmLDL. The c-Jun N-terminal kinase inhibitor or the p38 pathway inhibitor, however, had no such effects. The results indicate that mmLDL upregulates the ET_A receptors in rat coronary arterial smooth muscle cells mainly via activating protein kinase C, ERK1/2, and the downstream transcriptional factor, NF-κB.

DMSO-soluble cigarette smoke particles alter the expression of endothelin B receptor in rat coronary artery

In coronary artery diseases, cigarette smoking is a risk factor and the endothelin system plays a key role in the pathogenesis. This study was to examine if dimethylsulfoxide-soluble smoke particles (DSP) upregulate endothelin type-B (ETB) receptors in the coronary artery and investigate the mechanism. The isolated rat coronary arteries were organ-cultured for 24 h. The contractile response of the coronary artery was recorded by myograph. The mRNA and protein expression of the ETB receptors was studied using quantitative real-time PCR and immunohistochemistry. Results showed that the ETB receptor agonist, sarafotoxin 6c, induced a weak contraction in the fresh coronary artery. After culture, the contraction curve mediated by ETB receptor was shifted towards the left with an increased Emax of 152 ± 12%. DSP of 0.2 and 0.4 μl/ml shifted the concentration-contractile curves towards the left with further increased Emax of 270 ± 26 and 280 ± 29%, respectively. The culture increased ETB receptor mRNA and protein levels from fresh arteries, which was further enhanced by DSP. PD98059 (ERK1/2 inhibitor), wedelolactone (NF-κB inhibitor), actinomycin D or cycloheximide significantly inhibited the DSP-enhanced contraction and expression of mRNA and protein of the ETB receptor. However, SB203580 (p38 inhibitor) further increased DSP-enhanced contraction and protein expression of the ETB receptor. The results indicate that DSP upregulates ETB receptors in rat coronary artery via ERK1/2 and the NF-κB pathway.

Secondhand cigarette smoke exposure causes upregulation of cerebrovascular 5-HT(1) (B) receptors via the Raf/ERK/MAPK pathway in rats

AIM

Cigarette smoke exposure increases the risk of stroke. Upregulation of 5-hydroxytryptamine 1B (5-HT(1) (B) ) receptors is associated with the pathogenesis of cerebral ischaemia. This study examined the hypothesis that the expression of 5-HT(1) (B) receptors is altered in brain vessels after secondhand smoke (SHS) exposure.

METHODS

Rats were exposed to SHS in vivo for 200 min daily for 8 weeks. The contractile responses of isolated cerebral arteries were studies by a sensitive myograph. The mRNA and protein expression for 5-HT(1) (B) receptors were examined by real-time PCR, Western blot and immunofluorescence respectively. In addition, the phosphorylation of Raf/extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinases (MAPK) pathway was evaluated.

RESULTS

The results showed that SHS exposure shifted the 5-HT(1) (B) receptor-mediated concentration-contraction curve towards the left with a markedly increased maximal contraction. Furthermore, there were significant elevations in mRNA level and protein expression of 5-HT(1) (B) receptors in SHS-exposed rats. Immunostaining revealed that the 5-HT(1) (B) receptors were localized to the smooth muscle cells of cerebral arteries. SHS was also found to induce the phosphorylation of Raf-1 and ERK1/2 proteins. The administration of a Raf-1 inhibitor GW5074 attenuated the 5-HT(1) (B) receptor upregulation.

CONCLUSION

Secondhand smoke exposure upregulates cerebrovascular 5-HT(1) (B) receptors in rats. The receptor upregulation is associated with Raf/ERK/MAPK activation.

Neuroprotection afforded by antagonists of endothelin-1 receptors in experimental stroke

Endothelin-1 (ET-1) is involved on the development of cerebral edema in acute ischemic stroke. As edema is a therapeutic target in cerebral ischemia, our aim was to study the effect of antagonists for ET-1 receptors (Clazosentan® and BQ-788, specific antagonists for receptors A and B, respectively) on the development of edema, infarct volume and sensorial-motor deficits in rats subjected to ischemia by occlusion of the middle cerebral artery (MCAO). We used Wistar rats (280-320 g) submitted to ischemia by intraluminal transient (90 min) MCAO. After ischemia, rats were randomized into 4 groups (n = 6) treated with; 1) control group (saline), 2) Clazosentan® group (10 mg/kg iv), 3) BQ-788 group (3 mg/kg iv), and 4) combined treatment (Clazosentan® 10 mg/kg plus BQ-788 3 mg/kg iv). We observed that rats treated with Clazosentan® showed a reduction of edema, measured by MRI, at 72 h (hours) and at day 7 (both p < 0.0001), and a decrease in the serum levels of ET-1 at 72 h (p < 0.0001) and at day 7 (p = 0.009). The combined treatment also induced a reduction of edema at 24 h (p = 0.004), 72 h (p < 0.0001) and at day 7 (p < 0.0001), a reduction on infarct volume, measured by MRI, at 24 and 72 h, and at day 7 (all p < 0.01), and a better sensorimotor recovery at 24 and 72 h, and at day 7 (all p < 0.01). Moreover, Clazosentan® induced a decrease in AQP4 expression, while BQ-788 induced an increase in AQP9 expression. These results suggest that antagonists for ET-1 receptors may be a good therapeutic target for cerebral ischemia.

Kininogen deficiency protects from ischemic neurodegeneration in mice by reducing thrombosis, blood-brain barrier damage, and inflammation

Thrombosis and inflammation are hallmarks of ischemic stroke still unamenable to therapeutic interventions. High-molecular-weight kininogen (KNG) is a central constituent of the contact-kinin system which represents an interface between thrombotic and inflammatory circuits and is critically involved in stroke development. Kng(-/-) mice are protected from thrombosis after artificial vessel wall injury and lack the proinflammatory mediator bradykinin. We investigated the consequences of KNG deficiency in models of ischemic stroke. Kng(-/-) mice of either sex subjected to transient middle cerebral artery occlusion developed dramatically smaller brain infarctions and less severe neurologic deficits without an increase in infarct-associated hemorrhage. This protective effect was preserved at later stages of infarction as well as in elderly mice. Targeting KNG reduced thrombus formation in ischemic vessels and improved cerebral blood flow, and reconstitution of KNG-deficient mice with human KNG or bradykinin restored clot deposition and infarct susceptibility. Moreover, mice deficient in KNG showed less severe blood-brain barrier damage and edema formation, and the local inflammatory response was reduced compared with controls. Because KNG appears to be instrumental in pathologic thrombus formation and inflammation but dispensable for hemostasis, KNG inhibition may offer a selective and safe strategy for combating stroke and other thromboembolic diseases.

Cigarette smoke upregulates rat coronary artery endothelin receptors in vivo

BACKGROUND

Cigarette smoking is a strong cardiovascular risk factor and endothelin (ET) receptors are related to coronary artery diseases. The present study established an in vivo secondhand smoke (SHS) exposure model and investigated the hypothesis that cigarette smoke induces ET receptor upregulation in rat coronary arteries and its possible underlying mechanisms.

METHODOLOGY/PRINCIPAL FINDINGS

Rats were exposed to SHS for 200 min daily for 8 weeks. The coronary arteries were isolated and examined. The vasoconstriction was studied by a sensitive myograph. The expression of mRNA and protein for receptors was examined by real-time PCR, Western blot and immunofluorescence. Compared to fresh air exposure, SHS increased contractile responses mediated by endothelin type A (ET(A)) and type B (ET(B)) receptors in coronary arteries. In parallel, the expression of mRNA and protein for ET(A) and ET(B) receptors of smoke exposed rats were higher than that of animals exposed to fresh air, suggesting that SHS upregulates ET(A) and ET(B) receptors in coronary arteries in vivo. Immunofluorescence staining showed that the enhanced receptor expression was localized to the smooth muscle cells of coronary arteries. The protein levels of phosphorylated (p)-Raf-1 and p-ERK1/2 in smoke exposed rats were significantly higher than in control rats, demonstrating that SHS induces the activation of the Raf/ERK/MAPK pathway. Treatment with Raf-1 inhibitor GW5074 suppressed SHS-induced enhanced contraction mediated by ET(A) receptors, and inhibited the elevated mRNA and protein levels of ET(A) and ET(B) receptors caused by SHS. The results of correlation and regression analysis showed that phosphorylation of Raf and ERK1/2 were independent determinants to affect protein expression of ET(B) and ET(A) receptors.

CONCLUSIONS/SIGNIFICANCE

Cigarette smoke upregulates ET(B) and ET(A) receptors in rat coronary artery, which is associated with the activation of the Raf/ERK/MAPK pathway.

Brain endothelial barrier passage by monocytes is controlled by the endothelin system

Homeostasis of the brain is dependent on the blood-brain barrier (BBB). This barrier tightly regulates the exchange of essential nutrients and limits the free flow of immune cells into the CNS. Perturbations of BBB function and the loss of its immune quiescence are hallmarks of a variety of brain diseases, including multiple sclerosis (MS), vascular dementia, and stroke. In particular, diapedesis of monocytes and subsequent trafficking of monocyte-derived macrophages into the brain are key mediators of demyelination and axonal damage in MS. Endothelin-1 (ET-1) is considered as a potent pro-inflammatory peptide and has been implicated in the development of cardiovascular diseases. Here, we studied the role of different components of the endothelin system, i.e., ET-1, its type B receptor (ET(B)) and endothelin-converting enzyme-1 (ECE-1) in monocyte diapedesis of a human brain endothelial cell barrier. Our pharmacological inhibitory and specific gene knockdown studies point to a regulatory function of these proteins in transendothelial passage of monocytes. Results from this study suggest that the endothelin system is a putative target within the brain for anti-inflammatory treatment in neurological diseases.

Vascular plasticity in cerebrovascular disorders

Cerebral ischemia remains a major cause of morbidity and mortality with little advancement in subacute treatment options. This review aims to cover and discuss novel insight obtained during the last decade into plastic changes in the vasoconstrictor receptor profiles of cerebral arteries and microvessels that takes place after different types of stroke. Receptors like the endothelin type B, angiotensin type 1, and 5-hydroxytryptamine type 1B/1D receptors are upregulated in the smooth muscle layer of cerebral arteries after different types of ischemic stroke as well as after subarachnoid hemorrhage, yielding rather dramatic changes in the contractility of the vessels. Some of the signal transduction processes mediating this receptor upregulation have been elucidated. In particular the extracellular regulated kinase 1/2 pathway, which is activated early in the process, has proven to be a promising therapeutic target for prevention of vasoconstrictor receptor upregulation after stroke. Together, those findings provide new perspectives on the pathophysiology of ischemic stroke and point toward a novel way of reducing vasoconstriction, neuronal cell death, and thus neurologic deficits after stroke.

Endothelin-1-mediated cerebrovascular remodeling is not associated with increased ischemic brain injury in diabetes

Diabetes increases the risk of as well as poor outcome after stroke. Matrix metalloprotease (MMP) activation disrupts blood-brain barrier integrity after cerebral ischemia. We have previously shown that type 2 diabetes promotes remodeling of middle cerebral arteries (MCA) characterized by increased media/lumen (M/L) ratio and MMP activity in an endothelin (ET)-1-dependent manner in the Goto-Kakizaki (GK) rat model. In the present study, we examined the effects of ET-1-mediated vascular remodeling on neurovascular damage following cerebral ischemic injury in GK rats 5 and 12 weeks after the onset of diabetes. The MCA structure, cerebral perfusion as well as infarct size, and hemorrhage were measured in control and diabetic rats subjected to transient MCA occlusion. M/L ratio was increased after 12 but not 5 weeks of diabetes. The baseline cerebral perfusion was lower and the infarct volume smaller in diabetic rats in both age groups. The incidence of hemorrhagic transformation was higher after 5 weeks of diabetes as compared to that after 12 weeks or in the control groups. These findings provide evidence that ET-1-mediated cerebrovascular remodeling does not worsen the neurovascular damage of ischemic brain injury in diabetes. It is possible that this early remodeling response is compensatory in nature to regulate vascular tone and integrity, especially when ischemia is layered on diabetic vascular disease.

Vascular Protection Following Cerebral Ischemia and Reperfusion

Despite considerable research that has contributed to a better understanding of the pathophysiology of stroke, translation of this knowledge into effective therapies has largely failed. The only effective treatment for ischemic stroke is rapid recanalization of an occluded vessel by dissolving the clot with tissue plasminogen activator (tPA). However, stroke adversely affects vascular function as well that can cause secondary brain injury and limit treatment that depends on a patent vasculature. In middle cerebral arteries (MCA), ischemia/reperfusion (I/R) cause loss of myogenic tone, vascular paralysis, and endothelial dysfunction that can lead to loss of autoregulation. In contrast, brain parenchymal arterioles retain considerable tone during I/R that likely contributes to expansion of the infarct into the penumbra. Microvascular dysregulation also occurs during ischemic stroke that causes edema and hemorrhage, exacerbating the primary insult. Ischemic injury of vasculature is progressive with longer duration of I/R. Early postischemic reperfusion has beneficial effects on stroke outcome but can impair vascular function and exacerbate ischemic injury after longer durations of I/R. This review focuses on current knowledge on the effects of I/R on the structure and function of different vascular segments in the brain and highlight some of the more promising targets for vascular protection.

Derangements of post-ischemic cerebral blood flow by protein kinase C delta

Cerebral ischemia causes blood flow derangements characterized by hyperemia (increased cerebral blood flow, CBF) and subsequent hypoperfusion (decreased CBF). We previously demonstrated that protein kinase C delta (δPKC) plays an important role in hippocampal neuronal death after ischemia. However, whether part of this protection is due to the role of δPKC on CBF following cerebral ischemia remains poorly understood. We hypothesized that δPKC exacerbates hyperemia and subsequent hypoperfusion resulting in CBF derangements following ischemia. Sprague-Dawley (SD) rats pretreated with a δPKC specific inhibitor (δV1-1, 0.5 mg/kg) exhibited attenuation of hyperemia and latent hypoperfusion characterized by vasoconstriction followed by vasodilation of microvessels after 2-vessel occlusion plus hypotension measured by 2-photon microscopy. In an asphyxial cardiac arrest model (ACA), SD rats treated with δV1-1 (pre- and post-ischemia) exhibited improved perfusion after 24 h and less hippocampal CA1 neuronal death 7 days after ACA. These results suggest possible therapeutic potential of δPKC in modulating CBF and neuronal damage after cerebral ischemia.

Endothelial endothelin-1 over-expression using receptor tyrosine kinase tie-1 promoter leads to more severe vascular permeability and blood brain barrier breakdown after transient middle cerebral artery occlusion

Endothelin-1 (ET-1) is up-regulated in the endothelial cells and astrocytes under ischemia. Transgenic mice with astrocytic ET-1 over-expression (GET-1) showed more severe neurological deficit and larger infarct after transient middle cerebral artery occlusion (MCAO). Here, the significance of endothelial ET-1 in ischemic brain injury was investigated using transgenic mice with the endothelial ET-1 over-expression (TET-1). Increased ET-1 level was observed in the TET-1 brain infarct core after transient MCAO. ET(A) receptor expression was induced in the penumbra and ET(A) antagonist (A-147627) partially normalized the infarct volume and neurological deficit. In the infarct core of TET-1 brain, superoxide, nitrotyrosine, and gp91(phox) levels were increased. TET-1 brain displayed increased matrix metalloproteinase-2 expression, water content, immunoglobulin leakage and decreased occludin level in the ipsilateral hemisphere indicative of BBB breakdown and hemispheric edema. Interestingly, AQP-4 expression was increased in the penumbra of TET-1 brain following transient MCAO leading to the water accumulation. Taken together, endothelial ET-1 over-expression and ETA receptor activation contributes to the increased oxidative stress, water accumulation and BBB breakdown after transient MCAO leading to more severe neurological deficit and increased infarct.

Clazosentan: a review of subarachnoid hemorrhage data

Clazosentan (Ro 61–1790, VML-588 or AXV-034) is a synthetic endothelin (ET)-receptor antagonist that was derived from one of the first nonselective synthetic ET-receptor antagonists, bosentan. The structural modifications were designed to increase selectivity for the ETA receptor and optimize aqueous solubility, both of which were fulfilled. Selectivity is approximately 1000-fold greater for the ETA receptor with a pA2 in the nanomolar range. The half-life in humans is less than 2 h and the main side effects are headache, nausea and vomiting in clinically important doses, although they are not reported to be a problem in target disease populations. Clazosentan reverses established vasospasm in dogs with subarachnoid hemorrhage (SAH) and in preliminary studies in humans. It also prevents vasospasm in the double hemorrhage model of vasospasm in dogs and significantly decreases angiographic vasospasm after aneurysmal SAH in humans. The doses required are in the range of 5 to 15 mg/h in humans and correspond to effective doses in animal studies. These doses are also associated with relevant plasma and cerebrospinal fluid concentrations of the drug. A dose-finding study of clazosentan for prevention of vasospasm after SAH in humans showed a significant dose-dependent decrease in vasospasm and was favorable enough to lead to a Phase III trial.

Protective effect of estrogen in endothelin-induced middle cerebral artery occlusion in female rats

Estrogen is a powerful endogenous and exogenous neuroprotective agent in animal models of brain injury, including focal cerebral ischemia. Although this protection has been demonstrated in several different treatment and injury paradigms, it has not been demonstrated in focal cerebral ischemia induced by intraparenchymal endothelin-1 injection, a model with many advantages over other models of experimental focal ischemia. Reproductively mature female Sprague-Dawley rats were ovariectomized and divided into placebo and estradiol-treated groups. Two weeks later, halothane-anesthetized rats underwent middle cerebral artery (MCA) occlusion by interparenchymal stereotactic injection of the potent vasoconstrictor endothelin 1 (180pmoles/2microl) near the middle cerebral artery. Laser-Doppler flowmetry (LDF) revealed similar reductions in cerebral blood flow in both groups. Animals were behaviorally evaluated before, and 2 days after, stroke induction, and infarct size was evaluated. In agreement with other models, estrogen treatment significantly reduced infarct size evaluated by both TTC and Fluoro-Jade staining and behavioral deficits associated with stroke. Stroke size was significantly correlated with LDF in both groups, suggesting that cranial perfusion measures can enhance success in this model.

Cooperative effect of angiotensin AT1 and endothelin ETA receptor antagonism limits the brain damage after ischemic stroke in rat

Cerebral ischemia results in enhanced expression of smooth muscle cell endothelin and angiotensin receptors in cerebral arteries. We hypothesise that this phenomenon may be detrimental and that acute treatment with a combined non-hypotensive dose of the angiotensin AT(1) receptor inhibitor candesartan and the endothelin ET(A) receptor antagonist ZD1611 reduces the infarct in experimental ischemic stroke. Transient middle cerebral artery occlusion was induced in male Wistar rats by the intraluminal filament technique for 2 h followed by recirculation. The animals received systemic candesartan (0.05 mg/kg/day), ZD1611 (0.15 mg/kg/day), both combined or vehicle with start immediately after the occlusion. After 48 h the rats were sacrificed, the brains sliced and stained with 1% 2, 3, 5-triphenyltetrazolium chloride (TTC) and the volume of ischemic damage determined. The middle cerebral arteries were harvested for immunocytochemical studies of angiotensin AT(1) and endothelin ET(A) receptor expression. Candesartan or ZD1611 did alone not significantly decrease the brain damage or improve neurological scores as compared to vehicle controls. The combined inhibition of angiotensin AT(1) and endothelin ET(A) receptors however decreased the brain damage and improved the neurological scores (both P<0.05). The treatment did not change resting mean arterial blood pressure. In addition, there was an upregulation of angiotensin AT(1) receptors in the ischemic middle cerebral artery smooth muscle cells, which was normalised by the combined treatment. In conclusion, the present study shows that combined inhibition of angiotensin AT(1) and endothelin ET(A) receptors reduces the brain damage and improves the neurological outcome after ischemic stroke in rat.

EndothelinA receptor antagonist BSF-208075 causes immune modulation and neuroprotection after stroke in gerbils

Leukocytes contribute to the ischemia-reperfusion injury. Recent studies suggested endothelins could be important mediators for leukocyte activation in stroke. We tested if the endothelinA receptor antagonist BSF-208075 (ambrisentan) could reduce an ischemic lesion by modulation of leukocyte-endothelium interactions. Twenty-four gerbils underwent either a sham operation (n=6) or 15 min of bilateral carotid artery occlusion resulting in global cerebral ischemia. Ischemic animals received normal saline (n=6), 5 mg/kg BSF-208075 (n=6) or 30 mg/kg (n=6) administered intravenously at 10 min of reperfusion. Leukocytes rolling or adhering to endothelium were counted by intravital microscopy in parietal subsurface venules through a closed cranial window. BSF-208075 dose-dependently reduced postischemic leukocytes rolling (7.3+/-2.3 vs. 3.3+/-1.4 vs. 0.7+/-0.7 [n/100 microm/min]; p<0.05) and adhering (5.3+/-1.4 vs. 2.7+/-1.6 vs. 1.3+/-0.5 [n/100 microm/min]; p<0.05). Cerebral blood flow was not significantly changed by BSF-208075. Cortical neurons [n/mm2] in an area corresponding to the in vivo microscopy were dose-dependently preserved 7 days after ischemia (2456+/-687 vs. 3254+/-245 vs. 3780+/-168; p<0.05).

CONCLUSION

Endothelins mediate leukocyte activation in ischemic stroke. The endothelinA receptor antagonist BSF-208075 administered during reperfusion reduces the postischemic leukocyte activation and causes neuroprotection.

Inflammatory cell infiltration after endothelin-1-induced cerebral ischemia: histochemical and myeloperoxidase correlation with temporal changes in brain injury

Accumulation of neutrophils in brain after transient focal stroke remains controversial with some studies showing neutrophils to be deleterious, whereas others suggest neutrophils do not contribute to ischemic injury. Myeloperoxidase (MPO) has been used extensively as a marker for quantifying neutrophil accumulation, but is an indirect method and does not detect neutrophils alone. To elucidate the interaction of macrophages in the neutrophil inflammatory response, we conducted double-label immunofluorescence in brain sections at 0, 1, 2, 3, 7, and 15 days after ischemia. Each of these results was obtained from the same animal to determine correlations between neutrophil infiltration and ischemic damage. It was found that MPO activity increased up to 3 days after cerebral ischemia. Dual-staining revealed that macrophages engulf neutrophils in the brain and that this engulfment of neutrophils increased with time, with 50% of neutrophils in the brain engulfed at 3 days and approximately 85% at 15 days (N=5, P<0.05). Interestingly, at 7 days the amount of dual-staining was decreased to 20% (N=5, P<0.05). Neutrophil infiltration was positively correlated with ischemic damage in both the cortex and striatum (r(2)=0.86 and 0.80, respectively, P<0.01). The results of this study indicate that the MPO from neutrophils phagocytized by macrophages may continue to contribute to the overall MPO activity, and that previous assessments that have utilized this marker to measure neutrophil accumulation may have mis-calculated the number of neutrophils within the ischemic territory and hence their contribution to the evolution of the infarct at later time points. Thus any biphasic infiltration of neutrophils may have been masked by the accumulation of macrophages.

MEK1/2 inhibition attenuates vascular ETA and ETB receptor alterations after cerebral ischaemia

Cerebral ischaemia is associated with elevated levels of endothelin B (ETB) receptors in the ipsilateral middle cerebral artery (MCA). This up-regulation of ET receptors occurs via de novo transcription involving mitogen-activated protein kinases (MAPK). The aim of this study was to examine the effect of inhibition of the MAP kinase/ERK kinase (MEK)1/2 on ET receptor alteration, brain damage, and neurology in experimental cerebral ischaemia. Transient middle cerebral artery occlusion (MCAO) was induced in male Wistar rats by the intraluminal filament technique. The animals received 100 mg/kg intraperitoneally of the MEK1/2 inhibitor U0126 or vehicle in conjunction with the occlusion. After 24 h, the rats were decapitated and the brains removed. The middle cerebral arteries were dissected out and examined with myographs or immunohistochemistry. The ischaemic areas of the brains were compared. After the MCAO, the contractile responses of the ETA and ETB receptors were augmented in the ipsilateral MCA. U0126 decreased this alteration in ET receptor response. Furthermore, treatment with U0126 significantly decreased the brain damage and improved neurological scores. Immunohistochemistry showed that there were lower protein levels of phosphorylated extracellular signal-regulated kinases (ERK)1/2 and phosphorylated transcription factor Elk-1 in the U0126-treated rats compared to control. The results show that treatment with the MEK1/2 inhibitor U0126 in ischaemic stroke decreases brain damage, neurological symptoms, and ET receptor alteration. The vascular effects of U0126 provide new perspective on possible mechanisms of actions of MAPK inhibition in cerebral ischaemia.

Endothelin-a receptor blockade improves renal microvascular architecture and function in experimental hypercholesterolemia

Hypercholesterolemia (HC) may trigger early renal injury, partly by impairing the function or the structure of renal microvessels (MV). The endothelin (ET) system is upregulated in HC and can have an impact on the renal microcirculation by regulating MV tone, growth factors, and remodeling. It was hypothesized that ET-A blockade would protect the HC kidney by improving the function and attenuating the damage of intrarenal MV. Single-kidney function and hemodynamic responses to endothelium-dependent challenge were assessed in pigs after 12 wk of experimental HC, HC and chronic supplementation with the ET receptor A blocker ABT-627 (HC+ET-A, 0.75 mg/kg per d), and normal controls. Renal MV architecture then was studied ex vivo using three-dimensional microcomputed tomography imaging, and growth factors and remodeling pathways were explored in renal tissue. The HC kidney showed increased MV density compared with normal (77.68 +/- 5.1 versus 62.9 +/- 4.8 vessels/cm(2); P = 0.04) but blunted endothelial function. Chronic ET-A blockade in HC upregulated renal vascular growth factors, further increased renal MV density (139.9 +/- 8.4 vessels/cm(2); P = 0.001 versus normal and HC), and decreased renal tissue and MV remodeling. Furthermore, ET-A blockade in HC decreased MV tortuosity and improved MV endothelial function, suggesting accelerated stabilization and maturation of neo-vessels. Modulation of renal MV architecture and function in HC is mediated partly by the endogenous ET system. Notably, ET-A blockade enhanced the proliferation and facilitated the maturation of renal MV in the HC kidney and improved renal MV remodeling and function. This study suggests novel renoprotective effects of ET-A blockers and supports further exploration of strategies that target the ET pathway in HC and atherosclerosis.

Effect of a new inhibitor of the synthesis of 20-HETE on cerebral ischemia reperfusion injury

BACKGROUND AND PURPOSE

Arachidonic acid that is released following cerebral ischemia can be metabolized to 20-hydroxyeicosatetraenoic acid (20-HETE). 20-HETE is a potent vasoconstrictor that may contribute to ischemic injury. This study examined the effects of blockading the synthesis of 20-HETE with TS-011 on infarct size after transient occlusion of the middle cerebral artery (MCAO) of rats and after thromboembolic stroke in monkeys.

METHODS

Rats were treated with TS-011 or vehicle at various times after MCAO. Infarct size was measured by 2,3,5-triphenyltetrazolium chloride (TTC) staining and plasma levels of 20-HETE were determined by liquid chromatography mass spectrometry (LC/MS). The effect of TS-011 on infarct size was also studied in monkeys after introduction of a clot into the internal carotid artery.

RESULTS

Plasma levels of 20-HETE increased after MCAO in rats. TS-011 (0.01 to 1.0 mg/kg per hour) reduced infarct volume by 40%. Chronic administration of TS-011 for 7 days reduced neurological deficits after MCAO in rats. TS-011 given in combination with tissue plasminogen activator also improved neurological outcome in the stroke model in monkeys.

CONCLUSIONS

These results suggest that blockade of the formation of 20-HETE with TS-011 may be useful for the treatment of ischemic stroke.

Sulfisoxazole, an endothelin receptor antagonist, protects retinal neurones from insults of ischemia/reperfusion or lipopolysaccharide

Endothelins exert pathological effects in the eye and much interest centres on their role in causing retinal neuronal death in ischemic diseases like glaucoma. In the present study the influence of the non-selective endothelin antagonist, sulfisoxazole on raised intraocular pressure-induced ischemia to the rat retina was investigated. Moreover, in vitro studies on primary rat retinal cultures were undertaken to see whether sulfisoxazole is able to blunt the toxic effect of lipopolysaccharide (LPS) to retinal neurones. In order to determine whether sulfisoxazole provides protection to the retina the a- and b-wave amplitudes of the electroretinogram (ERG), the localisation of retinal choline acetyltransferase (ChAT), nitric oxide synthase (nNOS) and Thy-1 and the retinal mRNA levels of Thy-1 and FGF-2 were deduced in retinas subjected to ischemia in the absence or presence of sulfisoxazole. The results showed that the ischemia-induced changes to the a- and b-wave amplitudes of the ERG and changes associated with the localisation of ChAT, nNOS and Thy-1 to be significantly blunted by sulfisoxazole. However, while the ischemia-induced changes to Thy-1 and FGF-2 mRNAs were reduced by sulfisoxazole, the reduction was non-significant. The in vitro studies provided support for the protective effect of sulfisoxazole. Here, it was clearly shown that sulfisoxazole attenuated the elevation of nitric oxide (deduced by measuring nitrite) and the reduction in numbers of GABA-containing neurones caused by LPS. The present study provides evidence for the first time that endothelin antagonist can protect the retina from ischemic-like insults as occurs in glaucoma.

Endothelin-1 overexpression leads to further water accumulation and brain edema after middle cerebral artery occlusion via aquaporin 4 expression in astrocytic end-feet

Stroke patients have increased levels of endothelin-1 (ET-1), a strong vasoconstrictor, in their plasma or cerebrospinal fluid. Previously, we showed high level of ET-1 mRNA expression in astrocytes after hypoxia/ischemia. It is unclear whether the contribution of ET-1 induction in astrocytes is protective or destructive in cerebral ischemia. Here, we generated a transgenic mouse model that overexpress ET-1 in astrocytes (GET-1) using the glial fibrillary acidic protein promoter to examine the role of astrocytic ET-1 in ischemic stroke by challenging these mice with transient middle cerebral artery occlusion (MCAO). Under normal condition, GET-1 mice showed no abnormality in brain morphology, cerebrovasculature, absolute cerebral blood flow, blood-brain barrier (BBB) integrity, and mean arterial blood pressure. Yet, GET-1 mice subjected to transient MCAO showed more severe neurologic deficits and increased infarct, which were partially normalized by administration of ABT-627 (ET(A) antagonist) 5 mins after MCAO. In addition, GET-1 brains exhibited more Evans blue extravasation and showed decreased endothelial occludin expression after MCAO, correlating with higher brain water content and increased cerebral edema. Aquaporin 4 expression was also more pronounced in astrocytic end-feet on blood vessels in GET-1 ipsilateral brains. Our current data suggest that astrocytic ET-1 has deleterious effects on water homeostasis, cerebral edema and BBB integrity, which contribute to more severe ischemic brain injury.

A selective endothelin ETA receptor antagonist, SB 234551, improves cerebral perfusion following permanent focal cerebral ischemia in rats

In recent experimental studies, a selective antagonist of endothelin ET(A) receptors, SB 234551, improved neurological and histological outcome in both head trauma and transient focal cerebral ischemia. The present study was conducted to ascertain the degree to which hemodynamic alterations are responsible for this therapeutic effect in a model of permanent middle cerebral artery occlusion (MCAo) in rats. Anesthetized Sprague-Dawley rats were subjected to permanent MCAo by insertion of an intraluminal nylon suture coated with poly-L-lysine. The agent (SB 234551, 30 microg/kg/min = 1.8 mg/kg/h) or vehicle (PBS; 0.6 ml/h) was administered by i.v. infusion beginning 15 min after onset of MCAo and lasting for 23.75 h. Autoradiographic measurement of local cerebral blood flow (lCBF) was performed at 24 h. Physiological data were similar among groups. SB 234551 augmented perfusion by 1.7- to 1.8-fold in both the ischemic hemisphere and in the contralateral (non-ischemic) hemisphere when compared to vehicle-treated ischemic animals. In the ischemic hemisphere, the brain regions significantly benefited were those lying outside the zone of most dense ischemia (i.e., paramedian cortex and thalamus), while in the non-ischemic hemisphere all regions measured showed significant lCBF augmentation. This study demonstrates that SB 234551 therapy results in significant improvement of local cerebral perfusion in the ischemic as well as in the non-ischemic hemispheres after permanent MCAo.

Treatments for stroke

Stroke is the third leading cause of death and the leading cause of disability in developed countries, yet remains a poorly treated condition. Treatments for stroke can be aimed at acutely improving blood flow or protecting brain tissue against ischaemia, enhancing stroke recovery or reducing the risk of stroke recurrence. This paper reviews each of these approaches, particularly focusing on mechanisms for which there are agents in clinical trials. There are a number of appealing neuroprotective agents in Phase II and III clinical trials. However, the majority of acute treatments are likely to suffer from a narrow therapeutic time window and hence limited patient access. Combinations of acute approaches are likely to offer the greatest benefit, but present challenges in development. Promotion of recovery following stroke offers enormous potential for successful therapeutic intervention. Excitingly, new developments in preclinical research have identified possible ways in which this may be achieved.

Endothelin receptor expression in the normal and injured spinal cord: potential involvement in injury-induced ischemia and gliosis

The endothelins (ETs) are a family of peptides that exert their biological effects via two distinct receptors, the endothelin A receptor (ET(A)R) and the endothelin B receptor (ET(B)R). To more clearly define the potential actions of ETs following spinal cord injury, we used immunohistochemistry and confocal microscopy to examine the protein expression of ET(A)R and ET(B)R in the normal and injured rat spinal cord. In the normal spinal cord, ET(A)R immunoreactivity (IR) is expressed by vascular smooth muscle cells and a subpopulation of primary afferent nerve fibers. ET(B)R-IR is expressed primarily by radial glia, a small population of gray and white matter astrocytes, ependymal cells, vascular endothelial cells, and to a lesser extent in smooth muscle cells. Fourteen days following compression injury to the spinal cord, there was a significant upregulation in both the immunoexpression and number of astrocytes expressing the ET(B)R in both gray and white matter and a near disappearance of ET(B)R-IR in ependymal cells and ET(A)R-IR in primary afferent fibers. Conversely, the vascular expression of ET(A)R and ET(B)R did not appear to change. As spinal cord injury has been shown to induce an immediate increase in plasma ET levels and a sustained increase in tissue ET levels, ETs would be expected to induce an initial marked vasoconstriction via activation of vascular ET(A)R/ET(B)R and then days later a glial hypertrophy via activation of the ET(B)R expressed by astrocytes. Strategies aimed at blocking vascular ET(A)R/ET(B)R and astrocyte ET(B)Rs following spinal cord injury may reduce the resulting ischemia and astrogliosis and in doing so increase neuronal survival, regeneration, and function.

Impact of the endothelin-A receptor antagonist BQ 610 on microcirculation in global cerebral ischemia and reperfusion

The role of endogenous endothelin-1 in mediating microcirculatory disturbances after global cerebral ischemia was investigated in Mongolian gerbils. The pial microcirculation was studied by intravital fluorescent microscopy before, during, and up to 3 h after occlusion of both carotid arteries for 15 min. Pretreatment was achieved with the peptidergic selective endothelin-A (ET-A) receptor antagonist BQ 610. The neurological outcome was assessed daily for up to 4 days. The antagonist attenuated postischemic leukocyte-endothelium interactions in postcapillary venules, in particular the number of rolling leukocytes was found to be reduced (13.0+/-9.4 x 100 microm(-1) min(-1) in the control vs. 2.0+/-2.5 in the experimental group, P<0.05). The local microvascular perfusion, measured by the arterio-venous transit time, was improved during reperfusion by BQ 610 (1.3+/-0.5 s in the control vs. 0.7+/-0.2 s in the experimental group, P<0.05). The neurological deficit was significantly reduced in animals treated with the ET-A antagonist (P<0.05). The inhibition of the postischemic inflammatory reaction and the reversal of the delayed hypoperfusion may account for the improved neurological outcome. These observations suggest that application of endothelin-A antagonists may be a useful approach to interfere with derangements in cerebral ischemia/reperfusion.

Ischaemic penumbra: highlights

The ischaemic penumbra was described for the first time in the late 1970s as a ring of hypoperfused zone surrounding the region of complete infarction. The penumbral zone is a functionally silent tissue which is able to regain its function if promptly reperfused. This implies that the ischaemic penumbra is not a static but a "dynamic" and "time-dependent" concept. In this paper we describe the role of neuroimmaging tecniques such as single photon emission tomography (SPET), positron emission tomography (PET), and diffusion-weighted and perfusion-weighted magnetic resonance imaging (DWI and PWI) in the study of ischaemic penumbra. These functional imaging techniques have the advantage of giving "in vivo" quantitative estimate of cerebral blood flow (CBF) as well as information on how the ischaemic tissue metabolic changes develop. It follows that, as therapeutic options for treating acute stroke evolve, neuroimaging strategies are assuming an increasingly important role in the initial evaluation and management of the acute ischaemic patient. In this regard, a wide range of therapeutic approaches have been investigated for either ameliorating the perfusion, or interfering with the pathobiochemical cascade leading to ischaemic neuronal damage, or improving endogenous neuroprotection pathways. The "time windows" required for these treatments to be effective varies being rather short for reperfusion and longer for neuroprotection. Salvaging more penumbra would enhance recovery and thereby allow the most appropriate candidate for therapeutic trials to be selected.

Cortical expression of endothelin receptor subtypes A and B following middle cerebral artery occlusion in rats

This work aimed to define the spatial expression of endothelin A (ET(A)) and B (ET(B)) receptors in the cerebral cortex after permanent middle cerebral artery occlusion (MCAO) and to identify the phenotype of cells expressing ET(A) and ET(B) receptors. Cortical expression of ET(A) and ET(B) receptors was determined at the mRNA level by semi-quantitative reverse transcription-polymerase chain reaction and at the protein level by immunofluorescence staining, 12, 24 and 72 h after MCAO. Cells expressing endothelin receptors were phenotyped by double labelling with antibodies, anti-protein gene product (PGP9.5) and anti-ED1, towards neurons and activated microglia/macrophages, respectively. Both ET(A) and ET(B) receptor mRNA expressions increased significantly in the ipsilateral cortex in a time-dependent manner after MCAO. Robust expression of ET(A) receptors was noted in most neurons of the ischemic core and in several neurons in laminae 3 and 4 of the peri-infarct region 24 and 72 h after MCAO. ET(B) receptor immunoreactivity was observed in activated microglia/macrophages, beginning 24 h after MCAO. These results provide the first evidence that the action of endothelin during ischemia may be mediated by neuronal ET(A) receptors and activated microglia/macrophage ET(B) receptors. This differential localization of ET(A) and ET(B) receptors suggests that endothelin is involved in some complex neuron-glial interactions in addition to its vascular modulatory activity during ischemia.

Cerebral ischemia upregulates vascular endothelin ET(B) receptors in rat

BACKGROUND AND PURPOSE

Elevated levels of endothelin-1 (ET-1) have been reported in cerebral ischemia. A role for ET may prove more important if the vascular receptors were changed. We addressed whether there is any change in ET receptor expression in cerebral ischemia.

METHODS

The right middle cerebral artery (MCA) was occluded in male Wistar rats for 2 hours with the intraluminal filament method. The basilar artery and both MCAs were removed after 46 hours of recirculation. The contractile responses to ET-1, a combined ET(A) and ET(B) receptor agonist, and sarafotoxin 6c (S6c), a selective ET(B) receptor agonist, were examined in vitro, and ET receptor mRNA was quantified by real-time polymerase chain reaction.

RESULTS

S6c, which had no contractile effect per se on fresh or sham-operated rat cerebral arteries, induced a marked contraction in the occluded MCA (E(max) [maximum contraction, calculated as percentage of the contractile capacity of 63.5 mmol/L K+]=68+/-68%; P<0.0001), while there was no difference in the responses to ET-1 after cerebral ischemia. Real-time polymerase chain reaction revealed a significant upregulation of both the ET(A) and ET(B) receptors (both P<0.05) in the occluded MCA compared with the nonoccluded MCA from the same rats.

CONCLUSIONS

Focal cerebral ischemia in rat induces increased transcription of both ET(A) and ET(B) receptors, which results in the appearance of a contractile response to the ET(B) receptor agonist S6c. These results suggest a role for ET receptors in the pathogenesis of a vascular component after cerebral ischemia.

Endothelin B receptor deficiency augments neuronal damage upon exposure to hypoxia-ischemia in vivo

The role of functional endothelin-B (ETB)-receptors on neuronal survival upon hypoxia-ischemia (HI) has been investigated in 14-day-old ETB-receptor-deficient spotting lethal (sl/sl) and wildtype (+/+) rats. Carotid ligation followed by exposure to 8% oxygen for 2 h produced distinct cortical and hippocampal neuronal damage. Damage severity 24 h after HI was mild to intermediate in +/+ rats whereas large cortical infarcts and profound apoptosis of the hippocampus evolved in sl/sl rats. The number of apoptotic cells in the dentate 24 h after HI amounted to 30 +/- 7 cells/0.1 mm(2) in sl/sl compared to 9 +/- 3 cells/0.1 mm(2) in wildtype rats (mean +/- S.E.M., n=10-11, P=0.0093). In-vitro hypoxia (15 h) resulted in a comparable increase in cell death in primary pure neuronal hippocampal cultures from both groups (49.8 +/- 1.6% in sl/sl, 51.4 +/- 0.9% in +/+, mean +/- S.E.M., n=5, P=0.0560). To conclude, absence of functional ETB receptors is associated with an increased susceptibility to HI in-vivo, which is not intrinsic to neurons. Antagonism of ETB receptors seems not to be desirable in ischemic stroke.

Cerebral ischemia and trauma-different etiologies yet similar mechanisms: neuroprotective opportunities

Cerebral ischemia leads to brain damage caused by pathogenetic mechanisms that are also activated by neurotrauma. These mechanisms include among others excitotoxicity, over production of free radicals, inflammation and apoptosis. Furthermore, cerebral ischemia and trauma both trigger similar auto-protective mechanisms including the production of heat shock proteins, anti-inflammatory cytokines and endogenous antioxidants. Neuroprotective therapy aims at minimizing the activation of toxic pathways and at enhancing the activity of endogenous neuroprotective mechanisms. The similarities in the damage-producing and endogenous auto-protective mechanisms may imply that neuroprotective compounds found to be active against one of these conditions may indeed be also protective in the other. This review summarizes the pathogenetic events of ischemic and traumatic brain injury and reviews the neuroprotective strategies employed thus far in each of these conditions with a special emphasize on their clinical relevance and on future directions in the field of neuronal protection.

Pharmacological interventions for stroke: failures and future

Given the few options currently available for patients following ischaemic stroke, the recent disappointing failures of several large-scale Phase III clinical trials has made the search for novel therapeutic approaches even more critical. Experimental evidence has suggested that the majority of stroke patients have a slow evolution of brain injury which can occur over several hours. Progressive microcirculatory failure following the initial onset of ischaemia may contribute to the expansion of brain injury. Included among the pathophysiological changes that are speculated to occur as a secondary response to the initial ischaemia are free radical production, excitotoxicity (for example, glutamate) disruption of ionic homeostasis (for example, sodium and calcium influx), enzymatic changes, stimulation of the inflammatory process, endothelin release, activation of platelets and leukocytes, delayed coagulation and endothelial dysfunction. All of these pathophysiological reactions could contribute to an increase in local vascular resistance and therefore cause progressive hypoperfusion of the brain following the onset of stroke. The scope of this review will focus on recent clinical failures in addition to agents currently in clinical development, comparing vascular targets to the common neuroprotective strategies.

Endocannabinoids and neuroprotection

Traumatic brain injury (TBI) releases harmful mediators that lead to secondary damage. On the other hand, neuroprotective mediators are also released, and the balance between these classes of mediators determines the final outcome after injury. Recently, it was shown that the endogenous brain cannabinoids anandamide and 2-Arachidonoyl glycerol (2-AG) are also formed after TBI in rat and mouse respectively, and when administered after TBI, they reduce brain damage. In the case of 2-AG, better results are seen when it is administered together with related fatty acid glycerol esters. Significant reduction of brain edema, better clinical recovery, and reduced infarct volume and hippocampal cell death are noted. This new neuroprotective mechanism may involve inhibition of transmitter release and of inflammatory response. 2-AG is also a potent modulator of vascular tone, and counteracts the endothelin (ET-1)-induced vasoconstriction that aggravates brain damage; it may thus help to restore blood supply to the injured brain.

Endothelin-1 and monocyte chemoattractant protein-1 modulation in ischemia and human brain-derived endothelial cell cultures

Brain tissue damage due to ischemia/reperfusion has been shown to be caused, in part, by activated macrophages infiltrating into the post-ischemic brain. Using the Middle Cerebral Artery Occlusion (MCAO) mouse model, this study demonstrated that, in vivo, both endothelin-1 (Et-1), a potent vasoconstrictor, and the macrophage chemokine, monocyte chemoattractant factor-1 (MCP-1) are induced in ischemia. Further studies, using human brain-derived endothelial cells (CNS-EC), showed that in vitro, Et-1 can directly stimulate MCP-1 mRNA expression and MCP-1 protein; and this Et-1-induced MCP-1 production is mediated by the ET(A) receptor. Inflammatory cytokines, tumor necrosis factor alpha and interleukin-1beta, functioned additively and synergistically, respectively, with Et-1 to increase this MCP-1 production. Partial elucidation of the signal transduction pathways involved in Et-1-induced MCP-1 production demonstrated that protein kinase C-, but not cAMP-dependent pathways are involved. These data demonstrate that Et-1, functioning as an inflammatory peptide, increased levels of MCP-1, suggesting a mechanism for chemokine regulation during ischemia/reperfusion injury.