Increased expression of cysteinyl leukotriene receptor-1 in the brain mediates neuronal damage and astrogliosis after focal cerebral ischemia in rats

Blocking leukotriene synthesis attenuates the pathophysiology of traumatic brain injury and associated cognitive deficits

Neuroinflammation is a component of secondary injury following traumatic brain injury (TBI) that can persist beyond the acute phase. Leukotrienes are potent, pro-inflammatory lipid mediators generated from membrane phospholipids. In the absence of injury, leukotrienes are undetectable in the brain, but after trauma they are rapidly synthesized by a transcellular event involving infiltrating neutrophils and endogenous brain cells. Here, we investigate the efficacy of MK-886, an inhibitor of 5-lipoxygenase activating protein (FLAP), in blocking leukotriene synthesis, secondary brain damage, synaptic dysfunction, and cognitive impairments after TBI. Male Sprague Dawley rats (9-11weeks) received either MK-886 or vehicle after they were subjected to unilateral moderate fluid percussion injury (FPI) to assess the potential clinical use of FLAP inhibitors for TBI. MK-886 was also administered before FPI to determine the preventative potential of FLAP inhibitors. MK-886 given before or after injury significantly blocked the production of leukotrienes, measured by reverse-phase liquid chromatography coupled to tandem mass spectrometry (RP LC-MS/MS), and brain edema, measured by T2-weighted magnetic resonance imaging (MRI). MK-886 significantly attenuated blood-brain barrier disruption in the CA1 hippocampal region and deficits in long-term potentiation (LTP) at CA1 hippocampal synapses. The prevention of FPI-induced synaptic dysfunction by MK-886 was accompanied by fewer deficits in post-injury spatial learning and memory performance in the radial arm water maze (RAWM). These results indicate that leukotrienes contribute significantly to secondary brain injury and subsequent cognitive deficits. FLAP inhibitors represent a novel anti-inflammatory approach for treating human TBI that is feasible for both intervention and prevention of brain injury and neurologic deficits.

Cysteinyl leukotriene receptor 1 mediates LTD4-induced activation of mouse microglial cells in vitro

AIM

To investigate the roles of cysteinyl leukotriene receptors CysLT1R and CysLT2R in leukotriene D4 (LTD4)-induced activation of microglial cells in vitro.

METHODS

Mouse microglial cell line BV2 was transfected with pcDNA3.1(+)-hCysLT1R or pcDNA3.1(+)-hCysLT2R. The expression of relevant mRNAs and proteins in the cells was detected using RT-PCR and Western blotting, respectively. Phagocytosis was determined with flow cytometry analysis. The release of interleukin-1β (IL-1β) from the cells was measured using an ELISA assay.

RESULTS

The expression of CysLT1R or CysLT2R was considerably increased in the transfected BV2 cells, and the receptors were mainly distributed in the plasma membrane and cytosol. Treatment of the cells expressing CysLT1R or CysLT2R with CysLT receptor agonist LTD4 (0.1-100 nmol/L) concentration-dependently enhanced the phagocytosis, and increased mRNA expression and release of IL-1β. Moreover, the responses of hCysLT1R-BV2 cells to LTD4 were significantly larger than those of hCysLT2R-BV2 or WT-BV2 cells. Pretreatment of hCysLT1R-BV2 cells with the selective CysLT1R antagonist montelukast (1 μmol/L) significantly blocked LTD4-induced phagocytosis as well as the mRNA expression and release of IL-1β, whereas the selective CysLT2R antagonist HAMI 3379 (1 μmol/L) had no such effects.

CONCLUSION

CysLT1R mediates LTD4-induced activation of BV2 cells, suggesting that CysLT1R antagonists may exert anti-inflammatory activity in brain diseases.

The role of astrocytes in mediating exogenous cell-based restorative therapy for stroke

Astrocytes have not been a major therapeutic target for the treatment of stroke, with most research emphasis on the neuron. Given the essential role that astrocytes play in maintaining physiological function of the central nervous system and the very rapid and sensitive reaction astrocytes have in response to cerebral injury or ischemic insult, we propose to replace the neurocentric view for treatment with a more nuanced astrocytic centered approach. In addition, after decades of effort in attempting to develop neuroprotective therapies, which target reduction of the ischemic lesion, there are no effective clinical treatments for stroke, aside from thrombolysis with tissue plasminogen activator, which is used in a small minority of patients. A more promising therapeutic approach, which may affect nearly all stroke patients, may be in promoting endogenous restorative mechanisms, which enhance neurological recovery. A focus of efforts in stimulating recovery post stroke is the use of exogenously administered cells. The present review focuses on the role of the astrocyte in mediating the brain network, brain plasticity, and neurological recovery post stroke. As a model to describe the interaction of a restorative cell-based therapy with astrocytes, which drives recovery from stroke, we specifically highlight the subacute treatment of stroke with multipotent mesenchymal stromal cell therapy.

HAMI 3379, a CysLT2 receptor antagonist, attenuates ischemia-like neuronal injury by inhibiting microglial activation

The cysteinyl leukotrienes (CysLTs) are inflammatory mediators closely associated with neuronal injury after brain ischemia through the activation of their receptors, CysLT1R and CysLT2R. Here we investigated the involvement of both receptors in oxygen-glucose deprivation/recovery (OGD/R)-induced ischemic neuronal injury and the effect of the novel CysLT2R antagonist HAMI 3379 [3-({[(1S,3S)-3- carboxycyclohexyl]amino}carbonyl)-4-(3-{4-[4-(cyclo-hexyloxy)butoxy]phenyl}propoxy)benzoic acid] in comparison with the CysLT1R antagonist montelukast. In primary neurons, neither the nonselective agonist leukotriene D4 (LTD4) nor the CysLT2R agonist N-methyl-leukotriene C4 (NMLTC4) induced neuronal injury, and HAMI 3379 did not affect OGD/R-induced neuronal injury. However, in addition to OGD/R, LTD4 and NMLTC4 induced cell injury and neuronal loss in mixed cultures of cortical cells, and neuronal loss and necrosis in neuron-microglial cocultures. Moreover, they induced phagocytosis and cytokine release (interleukin-1β and tumor necrosis factor-α) from primary microglia, and conditioned medium from the treated microglia induced neuronal necrosis. HAMI 3379 inhibited all of these responses, and its effects were the same as those of CysLT2R interference by CysLT2R short hairpin RNA, indicating CysLT2R dependence. In comparison, montelukast moderately inhibited OGD/R-induced primary neuronal injury and most OGD/R- and LTD4-induced (but not NMLTC4-induced) responses in mixed cultures, cocultures, and microglia. The effects of montelukast were both dependent and independent of CysLT1Rs because interference by CysLT1R small interfering RNA had limited effects on neuronal injury in neuron-microglial cocultures and on cytokine release from microglia. Our findings indicated that HAMI 3379 effectively blocked CysLT2R-mediated microglial activation, thereby indirectly attenuating ischemic neuronal injury. Therefore, CysLT2R antagonists may represent a new type of therapeutic agent in the treatment of ischemic stroke.

Montelukast potentiates the protective effect of rofecoxib against kainic acid-induced cognitive dysfunction in rats

There is an evolving consensus that mild cognitive impairment (MCI) serves as a prodrome to Alzheimer's disease. Antioxidants and COX-2 (cyclo-oxygenase-2) inhibitors have also been reported to have beneficial effects against conditions of memory impairment. Newer drugs like cysteinyl leukotriene inhibitors have shown neuroprotective effect in animal models of ischemia. Thus, the present study purports to explore the potential role of montelukast (a cysteinyl leukotriene inhibitor) in concert with rofecoxib (COX-2 inhibitor) and caffeic acid (a 5-LOX inhibitor and potent antioxidant) against kainic acid induced cognitive dysfunction in rats. In the experimental protocol, kainic acid (0.4 μg/2 μl) in artificial cerebrospinal fluid (ACSF) was given intrahippocampally (CA3 region) to induce a condition similar to MCI. Memory performance was measured on days 10-14 and the locomotor activity was measured on days 1, 7 and 14. For estimation of biochemical, mitochondrial and histopathological parameters, animals were sacrificed on day 14, stored at -80 °C and the estimation was done on the 15th day. The treatment groups consisting of montelukast (0.5 and 1 mg/kg), rofecoxib (5 and 10 mg/kg) and caffeic acid (5 and 10 mg/kg) showed significant improvement in memory performance, oxidative stress parameters and mitochondrial function as compared to that of control (kainic acid treated), however, combination of montelukast with rofecoxib showed significant improvement in their protective effect. Thus the present study emphasizes the positive modulation of cysteinyl leukotriene receptor inhibition on COX (cyclooxygenase) and LOX (lipoxygenase) pathways in the control of the neuroinflammation in kainic acid induced cognitive dysfunction in rats.

Nuclear translocation of cysteinyl leukotriene receptor 1 is involved in oxygen-glucose deprivation-induced damage to endothelial cells

AIM

Cysteinyl leukotriene receptor 1 (CysLT(1) receptor) is located in epithelial cells, and translocates from the plasma membrane to the nucleus in a ligand-dependent manner. Here, we investigated whether CysLT(1) receptors translocated to the nucleus in endothelial cells after ischemic insult in vitro and whether it was involved in ischemic injury to endothelial cells.

METHODS

EA.hy926 cell line, derived from human umbilical vein endothelial cells, was subjected to oxygen-glucose deprivation (OGD). The expression and distribution of CysLT(1) receptors were detected by immunofluorescent staining, immunogold labeling and immunoblotting analyses. Cell viability was evaluated using MTT reduction assay. Necrosis and apoptosis were determined by double fluorescent staining with propidium iodide and Hoechst 33342.

RESULTS

CysLT(1) receptors were primarily distributed in the cytoplasm and nucleus in EA.hy926 cells, and few was found in the cell membrane. OGD induced the translocation of CysLT(1) receptors from the cytoplasm to the nucleus in a time-depen dent manner, with a peak reached at 6 h. OGD-induced nuclear translocation of CysLT(1) receptors was inhibited by pretreatment with the CysLT(1) receptor antagonist pranlukast (10 μmol/L), or by preincubation with NLS-pep, a peptide corresponding to the nuclear localization sequence of CysLT(1) receptor (10 μg/mL). However, zileuton, an inhibitor of 5-lipoxygenase that was a key enzyme in cysteinyl leukotriene generation, did not inhibit the nuclear translocation of CysLT(1) receptors. Moreover, preincubation with NLS-pep (0.4 μg/mL) significantly ameliorated OGD-induced cell viability reduction and necrosis.

CONCLUSION

CysLT(1) receptors in endothelial cells translocate to the nucleus in a ligand-independent manner after ischemic insult in vitro, and it is involved in the ischemic injury.

Disruption of the alox5ap gene ameliorates focal ischemic stroke: possible consequence of impaired leukotriene biosynthesis

Background

Leukotrienes are potent inflammatory mediators, which in a number of studies have been found to be associated with ischemic stroke pathology: gene variants affecting leukotriene synthesis, including the FLAP (ALOX5AP) gene, have in human studies shown correlation to stroke incidence, and animal studies have demonstrated protective properties of various leukotriene-disrupting drugs. However, no study has hitherto described a significant effect of a genetic manipulation of the leukotriene system on ischemic stroke. Therefore, we decided to compare the damage from focal cerebral ischemia between wild type and FLAP knockout mice. Damage was evaluated by infarct staining and a functional test after middle cerebral artery occlusion in 20 wild type and 20 knockout male mice.

Results

Mortality-adjusted median infarct size was 18.4 (3.2-76.7) mm³ in the knockout group, compared to 72.0 (16.7-174.0) mm³ in the wild type group (p < 0.0005). There was also a tendency of improved functional score in the knockout group (p = 0.068). Analysis of bone marrow cells confirmed that knockout animals had lost their ability to form leukotrienes.

Conclusions

Since the local inflammatory reaction after ischemic stroke is known to contribute to the brain tissue damage, the group difference seen in the current study could be a consequence of a milder inflammatory reaction in the knockout group. Our results add evidence to the notion that leukotrienes are important in ischemic stroke, and that blocked leukotriene production ameliorates cerebral damage.

Aggravated inflammation and increased expression of cysteinyl leukotriene receptors in the brain after focal cerebral ischemia in AQP4-deficient mice

OBJECTIVE

Aquaporin-4 (AQP4), the main water channel protein in the brain, plays a critical role in water homeostasis and brain edema. Here, we investigated its role in the inflammatory responses after focal cerebral ischemia.

METHODS

In AQP4-knockout (KO) and wild-type mice, focal cerebral ischemia was induced by 30 min of middle cerebral arterial occlusion (MCAO). Ischemic neuronal injury and cellular inflammatory responses, as well as the expression and localization of cysteinyl leukotriene CysLT(2) and CysLT(1) receptors, were determined at 24 and 72 h after MCAO.

RESULTS

AQP4-KO mice showed more neuronal loss, more severe microglial activation and neutrophil infiltration, but less astrocyte proliferation in the brain after MCAO than wild-type mice. In addition, the protein levels of both CysLT(1) and CysLT(2) receptors were up-regulated in the ischemic brain, and the up-regulation was more pronounced in AQP4-KO mice. The CysLT(1) and CysLT(2) receptors were primarily localized in neurons, microglia and neutrophils; those localized in microglia and neutrophils were enhanced in AQP4-KO mice.

CONCLUSION

AQP4 may play an inhibitory role in postischemic inflammation.

Intracerebroventricular injection of HAMI 3379, a selective cysteinyl leukotriene receptor 2 antagonist, protects against acute brain injury after focal cerebral ischemia in rats

Cysteinyl leukotrienes (CysLTs) induce inflammatory responses by activating their receptors, CysLT(1)R and CysLT(2)R. We recently reported that CysLT(2)R is involved in neuronal injury, astrocytosis and microgliosis after focal cerebral ischemia in rats. Here, we determined whether HAMI 3379, a selective CysLT(2)R antagonist, protects against acute brain injury after focal cerebral ischemia in rats. We induced transient focal cerebral ischemia by 30 min of middle cerebral artery occlusion (MCAO), followed by 24h of reperfusion. HAMI 3379 (1, 10 or 100 ng) was injected intracerebroventricularly (i.c.v.) 30 min before MCAO, and the CysLT(1)R antagonist pranlukast (0.1mg/kg, i.p.) was used as a positive control. HAMI 3379 at 10 and 100 ng (but not at 1 ng) attenuated the neurological deficits, and reduced infarct volume, brain edema, IgG exudation, neuronal degeneration and neuronal loss. This protective effect was similar to that of pranlukast. Thus, HAMI 3339 at 10-100 ng i.c.v. is neuroprotective against acute brain injury after focal cerebral ischemia in rats. These findings suggest therapeutic potential for CysLT(2)R antagonists in the treatment of ischemic stroke.

Transforming growth factor β1-induced astrocyte migration is mediated in part by activating 5-lipoxygenase and cysteinyl leukotriene receptor 1

BACKGROUND

Transforming growth factor-β 1 (TGF-β 1) is an important regulator of cell migration and plays a role in the scarring response in injured brain. It is also reported that 5-lipoxygenase (5-LOX) and its products, cysteinyl leukotrienes (CysLTs, namely LTC₄, LTD₄ and LTE₄), as well as cysteinyl leukotriene receptor 1 (CysLT₁R) are closely associated with astrocyte proliferation and glial scar formation after brain injury. However, how these molecules act on astrocyte migration, an initial step of the scarring response, is unknown. To clarify this, we determined the roles of 5-LOX and CysLT₁R in TGF-β 1-induced astrocyte migration.

METHODS

In primary cultures of rat astrocytes, the effects of TGF-β 1 and CysLT receptor agonists on migration and proliferation were assayed, and the expression of 5-LOX, CysLT receptors and TGF-β1 was detected. 5-LOX activation was analyzed by measuring its products (CysLTs) and applying its inhibitor. The role of CysLT₁R was investigated by applying CysLT receptor antagonists and CysLT₁R knockdown by small interfering RNA (siRNA). TGF-β 1 release was assayed as well.

RESULTS

TGF-β 1-induced astrocyte migration was potentiated by LTD₄, but attenuated by the 5-LOX inhibitor zileuton and the CysLT₁R antagonist montelukast. The non-selective agonist LTD₄ at 0.1 to 10 nM also induced a mild migration; however, the selective agonist N-methyl-LTC₄ and the selective antagonist Bay cysLT2 for CysLT₂R had no effects. Moreover, CysLT₁R siRNA inhibited TGF-β 1- and LTD₄-induced astrocyte migration by down-regulating the expression of this receptor. However, TGF-β 1 and LTD4 at various concentrations did not affect astrocyte proliferation 24 h after exposure. On the other hand, TGF-β 1 increased 5-LOX expression and the production of CysLTs, and up-regulated CysLT1R (not CysLT₂R), while LTD4 and N-methyl-LTC4 did not affect TGF-β 1 expression and release.

CONCLUSIONS

TGF-β 1-induced astrocyte migration is, at least in part, mediated by enhanced endogenous CysLTs through activating CysLT₁R. These findings indicate that the interaction between the cytokine TGF-β 1 and the pro-inflammatory mediators CysLTs in the regulation of astrocyte function is relevant to glial scar formation.

Cysteinyl leukotriene receptor antagonism alleviates renal injury induced by ischemia-reperfusion in rats

BACKGROUND

Renal inflammation has an important role in the development of ischemia-reperfusion injury of the kidney. Cysteinyl leukotrienes have been implicated in many inflammatory conditions. The aim of this study was to investigate the ability of the cysteinyl leukotriene receptor blocker, zafirlukast, to alleviate renal dysfunction and injury in a rat model of renal ischemia-reperfusion injury.

METHODS

We induced renal ischemia for 45 min, followed by 24 h reperfusion. We gave zafirlukast at a dose of 20 mg/kg/d for 3 d before ischemia-reperfusion. At the end of the reperfusion (24 h), we collected blood samples to measure blood urea nitrogen, creatinine, tumor necrosis factor-α, intercellular adhesion molecule-1, and nitrite/nitrate. We took kidney samples for histological and immunohistochemical assessment, and to measure malondialdehyde, glutathione content, and myeloperoxidase activity.

RESULTS

Induction of renal ischemia-reperfusion resulted into renal dysfunction, as indicated by elevated levels of blood urea nitrogen and serum creatinine, serum nitrite and nitrate, serum tumor necrosis factor-α, and intercellular adhesion molecule-1. An oxidative stress marker, renal malondialdehyde concentration, was increased, whereas renal reduced glutathione content was decreased. Myeloperoxidase activity, suggestive of neutrophil infiltration, was elevated in renal tissues. Histological changes confirmed these biochemical changes, as did P-selectin overexpression in renal tissues subjected to ischemia-reperfusion. Administration of zafirlukast before ischemia-reperfusion improved renal functions and reduced serum levels of nitrite and nitrate, tumor necrosis factor-α, and intercellular adhesion molecule-1, renal concentration of myeloperoxidase activity, and malondialdehyde concentration, whereas increased renal reduced glutathione concentration. Moreover, zafirlukast reduced histopathological features of tubular injury and P-selectin overexpression in both cortex and medulla.

CONCLUSIONS

These results demonstrate that zafirlukast significantly reduces the severity of ischemic acute renal failure, probably via anti-inflammatory action, reduction of neutrophil infiltration into renal tissues, and oxidative stress subsequent to an attenuation of P-selectin expression.

The new P2Y-like receptor G protein-coupled receptor 17 mediates acute neuronal injury and late microgliosis after focal cerebral ischemia in rats

G protein-coupled receptor 17 (GPR17), the new P2Y-like receptor, is phylogenetically related to the P2Y and cysteinyl leukotriene receptors, and responds to both uracil nucleotides and cysteinyl leukotrienes. GPR17 has been proposed to be a damage sensor in ischemic stroke; however, its role in brain inflammation needs further detailed investigation. Here, we extended previous studies on the spatiotemporal profiles of GPR17 expression and localization, and their implications for brain injury after focal cerebral ischemia. We found that in the ischemic core, GPR17 mRNA and protein levels were upregulated at both 12-24 h and 7-14 days, but in the boundary zone the levels increased 7-14 days after reperfusion. The spatiotemporal pattern of GPR17 expression well matched the acute and late (subacute/chronic) responses in the ischemic brain. According to previous findings, in the acute phase, after ischemia (24 h), upregulated GPR17 was localized in injured neurons in the ischemic core and in a few microglia in the ischemic core and boundary zone. In the late phase (14 days), it was localized in microglia, especially in activated (ED1-positive) microglia in the ischemic core, but weakly in most microglia in the boundary zone. No GPR17 was detectable in astrocytes. GPR17 knockdown by a small interfering RNA attenuated the neurological dysfunction, infarction, and neuron loss at 24 h, and brain atrophy, neuron loss, and microglial activation at 14 days after reperfusion. Thus, GPR17 might mediate acute neuronal injury and late microgliosis after focal cerebral ischemia.

International Union of Basic and Clinical Pharmacology. LXXXIV: leukotriene receptor nomenclature, distribution, and pathophysiological functions

The seven-transmembrane G protein-coupled receptors activated by leukotrienes are divided into two subclasses based on their ligand specificity for either leukotriene B(4) or the cysteinyl leukotrienes (LTC(4), LTD(4), and LTE(4)). These receptors have been designated BLT and CysLT receptors, respectively, and a subdivision into BLT(1) and BLT(2) receptors and CysLT(1) and CysLT(2) receptors has been established. However, recent findings have also indicated the existence of putative additional leukotriene receptor subtypes. Furthermore, other ligands interact with the leukotriene receptors. Finally, leukotrienes may also activate other receptor classes, such as purinergic receptors. The aim of this review is to provide an update on the pharmacology, expression patterns, and pathophysiological roles of the leukotriene receptors as well as the therapeutic developments in this area of research.

Astrocytes: targets for neuroprotection in stroke

In the past two decades, over 1000 clinical trials have failed to demonstrate a benefit in treating stroke, with the exception of thrombolytics. Although many targets have been pursued, including antioxidants, calcium channel blockers, glutamate receptor blockers, and neurotrophic factors, often the focus has been on neuronal mechanisms of injury. Broader attention to loss and dysfunction of non-neuronal cell types is now required to increase the chance of success. Of the several glial cell types, this review will focus on astrocytes. Astrocytes are the most abundant cell type in the higher mammalian nervous system, and they play key roles in normal CNS physiology and in central nervous system injury and pathology. In the setting of ischemia astrocytes perform multiple functions, some beneficial and some potentially detrimental, making them excellent candidates as therapeutic targets to improve outcome following stroke and in other central nervous system injuries. The older neurocentric view of the central nervous system has changed radically with the growing understanding of the many essential functions of astrocytes. These include K+ buffering, glutamate clearance, brain antioxidant defense, close metabolic coupling with neurons, and modulation of neuronal excitability. In this review, we will focus on those functions of astrocytes that can both protect and endanger neurons, and discuss how manipulating these functions provides a novel and important strategy to enhance neuronal survival and improve outcome following cerebral ischemia.

Montelukast, a cysteinyl leukotriene receptor-1 antagonist, attenuates chronic brain injury after focal cerebral ischaemia in mice and rats

OBJECTIVES

Previously we demonstrated the neuroprotective effect of montelukast, a cysteinyl leukotriene receptor-1 (CysLT(1) ) antagonist, on acute brain injury after focal cerebral ischaemia in mice. In this study, we have determined its effect on chronic brain injury after focal cerebral ischaemia in mice and rats.

METHODS

After transient focal cerebral ischaemia was induced by middle cerebral artery occlusion, montelukast was intraperitoneally injected in mice or orally administered to rats for five days. Behavioural dysfunction, brain infarct volume, brain atrophy and neuron loss were determined to evaluate brain lesions.

KEY FINDINGS

Montelukast (0.1 mg/kg) attenuated behavioural dysfunction, brain infarct volume, brain atrophy and neuron loss in mice, which was similar to pranlukast, another CysLT(1) receptor antagonist. Oral montelukast (0.5 mg/kg) was effective in rats and was more effective than edaravone, a free radical scavenger.

CONCLUSION

Montelukast protected mice and rats against chronic brain injury after focal cerebral ischaemia, supporting the therapeutic potential of CysLT(1) receptor antagonists.

CysLT2 receptor-mediated AQP4 up-regulation is involved in ischemic-like injury through activation of ERK and p38 MAPK in rat astrocytes

AIMS

We previously reported that cysteinyl leukotriene receptor 2 (CysLT(2)) mediates ischemic astrocyte injury, and leukotriene D(4)-activated CysLT(2) receptor up-regulates the water channel aquaporin 4 (AQP4). Here we investigated the mechanism underlying CysLT(2) receptor-mediated ischemic astrocyte injury induced by 4-h oxygen-glucose deprivation and 24-h recovery (OGD/R).

MAIN METHODS

Primary cultures of rat astrocytes were treated by OGD/R to construct the cell injury model. AQP4 expression was inhibited by small interfering RNA (siRNA). The expressions of AQP4 and CysLTs receptors, and the MAPK signaling pathway were determined.

KEY FINDINGS

OGD/R induced astrocyte injury, and increased expression of the CysLT(2) (but not CysLT(1)) receptor and AQP4. OGD/R-induced cell injury and AQP4 up-regulation were inhibited by a CysLT(2) receptor antagonist (Bay cysLT2) and a non-selective CysLT receptor antagonist (Bay u9773), but not by a CysLT(1) receptor antagonist (montelukast). Knockdown of AQP4 by siRNA attenuated OGD/R injury. Furthermore, OGD/R increased phosphorylation of ERK1/2 and p38, whose inhibitors relieved the cell injury and AQP4 up-regulation.

SIGNIFICANCE

The CysLT(2) receptor mediates AQP4 up-regulation in astrocytes, and up-regulated AQP4 leads to OGD/R-induced injury, which results from activation of the ERK1/2 and p38 MAPK pathways.

Pranlukast attenuates ischemia-like injury in endothelial cells via inhibiting reactive oxygen species production and nuclear factor-kappaB activation

The anti-inflammatory effects of pranlukast, an antagonist of cysteinyl leukotriene receptor 1, may be rendered not only by antileukotriene activity but also by other pharmacological activities. Previous studies indicate that pranlukast reduces ischemic tissue injury partially through decreasing vascular permeability, but its effect on ischemic injury in endothelial cells is not known. Thus, in this study, we investigated the effect of pranlukast on ischemia-like injury induced by oxygen-glucose deprivation (OGD) in EA.hy926 cells, a human endothelial cell line, and the possible mechanisms. We found that cell viability was reduced, lactate dehydrogenase release was increased 4-8 hours after OGD, and necrosis was induced 8 hours after OGD. Production of reactive oxygen species (ROS) increased by 211%, 176%, and 128%, respectively, 0.5, 1, and 2 hours after OGD. Nuclear factor-kappaB (NF-kappaB) was translocated to the nuclei 4-8 hours after OGD. Pranlukast ameliorated the reduced viability, the increased lactate dehydrogenase release, and necrosis after OGD. It also reduced ROS production and inhibited NF-kappaB nuclear translocation after OGD. The ROS scavenger, edaravone, inhibited OGD-induced nuclear translocation of NF-kappaB as well. Edaravone and pyrrolidine dithiocarbamate (a specific NF-kappaB inhibitor) protected endothelial cells from the OGD-induced injury. However, zileuton, a 5-lipoxygenase inhibitor, did not affect the cell injury, ROS production, and NF-kappaB nuclear translocation after OGD. The exogenous leukotriene D4 did not induce cell injury, ROS production, and NF-kappaB translocation. Thus, we conclude that pranlukast protects endothelial cells from ischemia-like injury via decreasing ROS production and inhibiting NF-kappaB activation, which is leukotriene independent.

Protective effect of montelukast against quinolinic acid/malonic acid induced neurotoxicity: possible behavioral, biochemical, mitochondrial and tumor necrosis factor-α level alterations in rats

The present study has been designed to explore the protective effect of montelukast (leukotriene receptor antagonist) against intrastriatal quinolinic acid (QA; 300 nmol) and malonic acid (MA; 6 μmol) induced Huntington's like symptoms in rats. Quinolinic acid has been reported to induce excitotoxicity by stimulating the N-methyl-D-aspartate receptor, causing calcium overload which in turn leads to the neurodegeneration. On the other hand, MA, being a reversible inhibitor of mitochondrial enzyme complex-II, leads to energy crisis and free radical generation. Recent studies have reported the therapeutic potential of leukotriene receptor antagonists in different neurodegenerative disorders. However, their exact role is yet to be established. The present study accordingly, is an attempt to investigate the effect of montelukast against QA and MA induced behavioral, biochemical and molecular alterations in rat striatum. Oxidative stress, mitochondrial enzyme complex and tumor necrosis factor-alpha (TNF-α) were evaluated on day 21st and 14th post intrastriatal QA and MA treatment, respectively. Findings of the present study demonstrate significant alteration in the locomotor activity and motor coordination as well as oxidative burden (increased lipid peroxidation, nitrite concentration and decreased endogenous antioxidants), mitochondrial enzyme complex (I, II and IV) activities and TNF-α level, in both intrastriatal QA and MA treated animals. Further, montelukast (0.4, 0.8 mg/kg p.o.) treatment for 21 and 14 days respectively, attenuated the behavioral alterations, oxidative stress, mitochondrial dysfunction and TNF-α level in these models of Huntington's disease in a significant manner. In conclusion, the present study emphasizes the neuroprotective potential of montelukast in the therapeutic management of Huntington like symptoms.

Reports of suicidality in clinical trials of montelukast

BACKGROUND

In recent years, a number of drugs and drug classes have come under scrutiny by the US Food and Drug Administration regarding suicidality (including suicidal behavior and ideation).

OBJECTIVE

We sought to perform 2 reviews (requested by the US Food and Drug Administration) of the number of events possibly related to suicidality reported in Merck clinical trials of montelukast.

METHODS

Method 1 was a descriptive review of clinical adverse experiences (AEs) from 116 studies (double-blind and open-label, adult and pediatric, and single- and multiple-dose studies) completed as of March 2008. Summaries were constructed from investigator-reported AE terms possibly related to suicidality (completed suicide, suicide attempt, and suicidal ideation) or self-injurious behavior. Method 2 used a retrospective adjudication of investigator-reported AEs and other events listed in the study database described as possibly suicidality-related adverse events (PSRAEs) in a prespecified set of 41 double-blind, placebo-controlled trials completed as of April 2008.

RESULTS

No completed suicides were reported in any study. For the descriptive review, 20,131 adults and children received montelukast, 9,287 received placebo, and 8,346 received active control; AEs possibly related to suicidality were rare and were similar between the montelukast and placebo or active-control groups. For the adjudicated review across 22,433 patients, there were 730 adjudicated events. In 9,929 patients taking montelukast, 1 PSRAE was identified (classified as suicidal ideation); none were identified in 7,780 and 4,724 patients taking placebo and active control, respectively.

CONCLUSIONS

Assessed by using 2 complementary methods, there were no reports of completed suicide, and reports of PSRAEs were rare in patients receiving montelukast and similar to those seen in control subjects.

Analysis of behavior-related adverse experiences in clinical trials of montelukast

BACKGROUND

Frequencies of behavior-related adverse experiences (BRAEs) in controlled clinical studies of leukotriene modifier drugs have not been summarized.

OBJECTIVE

We sought to compare the frequency of BRAEs in patients receiving montelukast or placebo in a retrospective analysis of Merck clinical trial data.

METHODS

An adverse experience database was constructed to include all double-blind, placebo-controlled trials of montelukast meeting prespecified criteria. BRAEs (described using the Medical Dictionary for Regulatory Activities controlled vocabulary dictionary) were prespecified to include any term in the Psychiatric Disorders System Organ Class, selected terms related to general disorders, and terms related to akathisia. Frequencies of BRAEs (overall, leading to study discontinuation, and/or serious) were summarized. Analyses estimated the odds ratios (ORs) for montelukast versus placebo based on the frequency of patients with BRAEs in each study.

RESULTS

In total 35 adult and 11 pediatric placebo-controlled trials were included; 11,673 patients received montelukast, 8,827 received placebo, and 4,724 received active control. The frequency of patients with 1 or more BRAEs was 2.73% and 2.27% in the montelukast and placebo groups, respectively; the OR for montelukast versus placebo was 1.12 (95% CI, 0.93-1.36). The frequency of patients with a BRAE leading to study discontinuation was 0.07% and 0.11% in the montelukast and placebo groups, respectively (OR, 0.52; 95% CI, 0.17-1.51). The frequency of patients with a BRAE considered serious was 0.03% in both treatment groups.

CONCLUSION

Reports of BRAEs were infrequent in clinical trials of montelukast. Those leading to study discontinuation or considered serious were rare. Frequencies were similar regardless of treatment group.

Functional characterization of two isoforms of the P2Y-like receptor GPR17: [35S]GTPgammaS binding and electrophysiological studies in 1321N1 cells

The previously "orphan" G protein-coupled receptor GPR17 is structurally related to both P2Y nucleotide receptors and to receptors for cysteinyl leukotrienes. Genomic analysis revealed two putative open reading frames encoding for a "short" and a "long" receptor isoform of 339- and 367-amino acids, respectively, with the latter displaying a 28-amino acid longer NH(2) terminus. The short isoform has been recently "deorphanized," revealing dual responses to uracil nucleotides and cysteinyl leukotrienes. No information regarding the ligand specificity, tissue distribution, or pathophysiological roles of the long receptor isoform is available. In the present study, we cloned human long-GPR17, determined its tissue distribution, and characterized its pharmacological specificity in 1321N1 cells by [35S]GTPgammaS binding (which measures the ability of G protein-coupled receptor agonists to increase GTP binding to G proteins) and whole cell patch-clamp recording measuring receptor coupling to K+ channels. [35S]GTPgammaS binding in long-GPR17-expressing 1321N1 cells revealed concentration-dependent responses to uracil nucleotides (UDP-galactose = UDP > UDP-glucose) and cysteinyl leukotrienes (LTC4 > LTD4), which were counteracted by a purinergic (cangrelor) and a cysteinyl leukotriene antagonist (montelukast), respectively. The nonhydrolyzable ATP analog ATPgammaS also acted as an antagonist. GPR17 coupled to Gi and, to a lesser extent, Gq proteins. UDP-glucose and LTD(4) also induced increases in overall outward K+ currents, which were antagonized by the purinergic antagonists MRS2179 and cangrelor and by montelukast. We conclude that the previously uncharacterized long-GPR17 isoform is a functional receptor that is stimulated by both uracil nucleotides and cysteinyl leukotrienes. We also show that the signaling pathway of GPR17 involves the generation of outward K+ currents, an important protective mechanism that, in brain, is specifically aimed at reducing neuronal hyperexcitability and resultant neuronal injury.

Leukotriene D4 stimulates the migration but not proliferation of endothelial cells mediated by the cysteinyl leukotriene cyslt(1) receptor via the extracellular signal-regulated kinase pathway

The actions of cysteinyl leukotrienes (CysLTs) are mediated by activating CysLT receptors, CysLT(1), and CysLT(2). The CysLT(1) receptor mediates vascular responses to CysLTs; however, its effect on the proliferation and migration of endothelial cells is not clarified. To determine this effect, we observed proliferation and migration in EA.hy926 cells, a human endothelial cell line, and the involvement of activation of mitogen-activated protein kinases (MAPKs). We found that LTD(4) did not affect the proliferation, but significantly stimulated the migration of endothelial cells. LTD(4) also induced the phosphorylation of extracellular signal-regulated kinase (ERK) 1/2, but not those of p38 or JNK. The LTD(4)-induced migration and ERK1/2 phosphorylation were blocked by the CysLT(1)-receptor antagonist montelukast and the dual antagonist Bay u9773, but not by the CysLT(2)-receptor antagonist Bay cysLT2; the migration was also inhibited by the ERK1/2 inhibitor U0126. Our findings indicate that LTD(4) stimulates the CysLT(1) receptor-mediated migration of endothelial cells; this may be regulated by the ERK1/2 pathway.

Leukotriene signaling in atherosclerosis and ischemia

INTRODUCTION

The inflammatory process of atherosclerosis is associated with several pathophysiological reactions within the vascular wall. The arachidonic acid released by phospholipase A(2) serves as substrate for the production of a group of lipid mediators known as the leukotrienes, which induce pro-inflammatory signaling through activation of specific BLT and CysLT receptors.

DISCUSSION

Leukotriene signaling has been implicated in early lipid retention and foam cell accumulation, as well as in the development of intimal hyperplasia and advanced atherosclerotic lesions. Furthermore, the association of leukotrienes with degradation of extracellular matrix has suggested a role in atherosclerotic plaque rupture. Finally, studies of either myocardial or cerebral ischemia and reperfusion indicate that leukotriene signaling in addition may be involved in the development of ischemic injury.

CONCLUSION

Both leukotriene synthesis inhibitors and leukotriene receptor antagonists have been suggested to induce beneficial effects at different stages of the atherosclerosis process.

Leukotriene modifiers in the treatment of cardiovascular diseases

Cysteinyl-leukotrienes (Cys-LTs) and LTB4 are potent proinflammatory mediators derived from arachidonic acid through the 5-lipoxygenase (5-LO) pathway, which exerts important pharmacological effects through their interaction with specific receptors: Cys-LT receptors (CysLT1 and CysLT2) and LTB4 receptors (BLT1 and BLT2). Published evidence justifies a broader role for LT receptor antagonists (LTRAs), in particular, montelukast, in the treatment of bronchial asthma, allergic rhinitis, and recently, in cardiocerebrovascular disease. The actions of Cys-LTs on the cardiovascular (CV) system are well-documented and include a broad array of activities with promising therapeutic targets in animal models exploring the use of selective 5-LO (or 5-LO-activating protein) inhibitors or dual LO-cycloxygenase-blocking agents in experimentally induced acute myocardial infarction. The picture that emerges from studies with LTRAs is more controversial at the moment, and some findings suggest a role for Cys-LTs in the extension of ischemic damage and in cardiac dysfunction during reperfusion; others do not. The aim of this short review is to summarize the state of present research about LT modifier treatment in CV disease.

Activation of CysLT receptors induces astrocyte proliferation and death after oxygen-glucose deprivation

We recently found that 5-lipoxygenase (5-LOX) is activated to produce cysteinyl leukotrienes (CysLTs), and CysLTs may cause neuronal injury and astrocytosis through activation of CysLT(1) and CysLT(2) receptors in the brain after focal cerebral ischemia. However, the property of astrocyte responses to in vitro ischemic injury is not clear; whether 5-LOX, CysLTs, and their receptors are also involved in the responses of ischemic astrocytes remains unknown. In the present study, we performed oxygen-glucose deprivation (OGD) followed by recovery to induce ischemic-like injury in the cultured rat astrocytes. We found that 1-h OGD did not injure astrocytes (sub-lethal OGD) but induced astrocyte proliferation 48 and 72 h after recovery; whereas 4-h OGD moderately injured the cells (moderate OGD) and led to death 24-72 h after recovery. Inhibition of phospholipase A(2) and 5-LOX attenuated both the proliferation and death. Sub-lethal and moderate OGD enhanced the production of CysLTs that was inhibited by 5-LOX inhibitors. Sub-lethal OGD increased the expressions of CysLT(1) receptor mRNA and protein, while moderate OGD induced the expression of CysLT(2) receptor mRNA. Exogenously applied leukotriene D(4) (LTD(4)) induced astrocyte proliferation at 1-10 nM and astrocyte death at 100-1,000 nM. The CysLT(1) receptor antagonist montelukast attenuated astrocyte proliferation, the CysLT(2) receptor antagonist BAY cysLT2 reversed astrocyte death, and the dual CysLT receptor antagonist BAY u9773 exhibited both effects. In addition, LTD(4) (100 nM) increased the expression of CysLT(2) receptor mRNA. Thus, in vitro ischemia activates astrocyte 5-LOX to produce CysLTs, and CysLTs result in CysLT(1) receptor-mediated proliferation and CysLT(2) receptor-mediated death.

Cysteinyl leukotriene receptor 1 partially mediates brain cryoinjury in mice

AIM

To determine whether the cysteinyl leukotriene receptor 1 (CysLT1 receptor) modulates brain cryoinjury and whether the CysLT1 receptor antagonist pranlukast exerts a time-dependent protective effect on cryoinjury in mice.

METHODS

Brain cryoinjury was induced by applying a liquid nitrogen-cooled metal probe to the surface of the skull for 30 s. Brain lesion, neuron density, and endogenous IgG exudation were observed 24 h after cryoinjury. Transcription and the expression of the CysLT1 receptor were detected by RT-PCR and immunoblotting, and the localization of the receptor protein by double immunofluorescence.

RESULTS

The mRNA and protein expressions of the CysLT1 receptor were upregulated in the brain 6-24 h after cryoinjury, and the CysLT1 receptor protein was primarily localized in the neurons, not in the astrocytes or microglia. Pre-injury treatments with multi-doses and a single dose of pranlukast (0.1 mg/kg) attenuated cryoinjury; postinjury single dose (0.1 mg/kg) at 30 min (not 1 h) after cryoinjury was also effective.

CONCLUSION

The CysLT1 receptor modulates cryoinjury in mice at least partly, and postinjury treatment with its antagonist pranlukast exerts the protective effect with a therapeutic window of 30 min.

Spatio-temporal expression of cysteinyl leukotriene receptor-2 mRNA in rat brain after focal cerebral ischemia

Cysteinyl leukotrienes (CysLTs) induce inflammatory responses mediated by activating CysLT(1) and CysLT(2) receptors. We have recently reported that CysLT(1) receptor expression is increased in rat brain after focal cerebral ischemia and the increased expression is spatio-temporally related to acute neuronal injury and late astrocyte proliferation. Here we report spatio-temporal expression of CysLT(2) receptor mRNA in rat brain after focal cerebral ischemia induced by 30min of middle cerebral artery occlusion. We found that the neuron density was gradually decreased or disappeared in the ischemic core and boundary zone during 14 days after reperfusion, and the astrocyte population in the boundary zone was increased 3-14 days after reperfusion. In the ischemic core, the expression of CysLT(2) receptor mRNA was increased at 6, 12 and 24h and then recovered at 3, 7 and 14 days after reperfusion. In the boundary zone, the expression was significantly increased 3, 7 and 14 days after reperfusion. The results suggest that CysLT(2) receptor may be related to the acute neuronal injury and late astrocyte proliferation in the ischemic brain.

Leukotriene D4 induces brain edema and enhances CysLT2 receptor-mediated aquaporin 4 expression

Cysteinyl leukotrienes (including LTC(4), LTD(4), and LTE(4)), potent inflammatory mediators, can induce brain-blood barrier (BBB) disruption and brain edema. These reactions are mediated by their receptors, CysLT(1) and CysLT(2) receptors. On the other hand, aquaporin 4 (AQP4) primarily modulates brain water homeostasis and edema after various injuries. Here, we aimed to determine whether AQP4 is involved in LTD(4)-induced brain edema. LTD(4) (1ng in 0.5mul PBS) microinjection into the cortex increased endogenous IgG exudation (BBB disruption) and water content (brain edema), and enhanced AQP4 expression in mouse brain. The selective CysLT(1) receptor antagonist pranlukast inhibited the IgG exudation, but not the increased water content and AQP4 expression induced by LTD(4). In the cultured rat astrocytes, LTD(4) (10(-9)-10(-7)M, for 24h) similarly enhanced AQP4 expression. The enhanced AQP4 expression was inhibited by Bay u9773, a non-selective CysLT(1)/CysLT(2) receptor antagonist, but not by pranlukast. LTD(4) (10(-9)-10(-7)M) also induced the mRNA expression of CysLT(2) (not CysLT(1)) receptor in astrocytes. These results indicate that LTD(4) modulates brain edema; CysLT(1) receptor mediates vasogenic edema while CysLT(2) receptor may mediate cytotoxic edema via up-regulating AQP4 expression.