Cysteinyl leukotriene 2 receptor-mediated vascular permeability via transendothelial vesicle transport

Distribution of the cysteinyl leukotriene system components in the human, rat and mouse eye

The cysteinyl leukotrienes (CysLTs) have important functions in the regulation of inflammation and cellular stress. Blocking the CysLT receptors (CysLTRs) with specific antagonists is beneficial against progression of retinopathies (e.g. diabetic retinopathy, wet AMD). However, the exact cellular localization of the CysLTRs and their endogenous ligands in the eye have not been elucidated in detail yet. It is also not known whether the expression patterns differ between humans and animal models. Therefore, the present study aimed to describe and compare the distribution of two important enzymes in CysLT biosynthesis, 5-lipoxygenase (5-LOX) and 5-lipoxygenase-activating protein (FLAP), and of CysLTR1 and CysLTR2 in healthy human, rat and mouse eyes. Human donor eyes (n = 10) and eyes from adult Sprague Dawley rats (n = 5) and CD1 mice (n = 8) of both sexes were collected. The eyes were fixed in 4% paraformaldehyde and cross-sections were investigated by immunofluorescence with specific antibodies against 5-LOX, FLAP (human tissue only), CysLTR1 and CysLTR2. Flat-mounts of the human choroid were prepared and processed similarly. Expression patterns were assessed and semiquantitatively evaluated using a confocal fluorescence microscope (LSM710, Zeiss). We observed so far unreported expression sites for CysLT system components in various ocular tissues. Overall, we detected expression of 5-LOX, CysLTR1 and CysLTR2 in the human, rat and mouse cornea, conjunctiva, iris, lens, ciliary body, retina and choroid. Importantly, expression profiles of CysLTR1 and CysLTR2 were highly similar between human and rodent eyes. FLAP was expressed in all human ocular tissues except the lens. Largely weak immunoreactivity of FLAP and 5-LOX was observed in a few, yet unidentified, cells of diverse ocular tissues, indicating low levels of CysLT biosynthesis in healthy eyes. CysLTR1 was predominantly detected in ocular epithelial cells, supporting the involvement of CysLTR1 in stress and immune responses. CysLTR2 was predominantly expressed in neuronal structures, suggesting neuromodulatory roles of CysLTR2 in the eye and revealing disparate functions of CysLTRs in ocular tissues. Taken together, we provide a comprehensive protein expression atlas of CysLT system components in the human and rodent eye. While the current study is purely descriptive and therefore does not allow significant functional conclusions yet, it represents an important basis for future studies in diseased ocular tissues in which distribution patterns or expression levels of the CysLT system might be altered. Furthermore, this is the first comprehensive study to elucidate expression patterns of CysLT system components in human and animal models that will help to identify and understand functions of the system as well as mechanisms of action of potential CysLTR ligands in the eye.

Targeting Mammalian 5-Lipoxygenase by Dietary Phenolics as an Anti-Inflammatory Mechanism: A Systematic Review

5-Lipoxygenase (5-LOX) plays a key role in inflammation through the biosynthesis of leukotrienes and other lipid mediators. Current evidence suggests that dietary (poly)phenols exert a beneficial impact on human health through anti-inflammatory activities. Their mechanisms of action have mostly been associated with the modulation of pro-inflammatory cytokines (TNF-α, IL-1β), prostaglandins (PGE2), and the interaction with NF-κB and cyclooxygenase 2 (COX-2) pathways. Much less is known about the 5-lipoxygenase (5-LOX) pathway as a target of dietary (poly)phenols. This systematic review aimed to summarize how dietary (poly)phenols target the 5-LOX pathway in preclinical and human studies. The number of studies identified is low (5, 24, and 127 human, animal, and cellular studies, respectively) compared to the thousands of studies focusing on the COX-2 pathway. Some (poly)phenolics such as caffeic acid, hydroxytyrosol, resveratrol, curcumin, nordihydroguaiaretic acid (NDGA), and quercetin have been reported to reduce the formation of 5-LOX eicosanoids in vitro. However, the in vivo evidence is inconclusive because of the low number of studies and the difficulty of attributing effects to (poly)phenols. Therefore, increasing the number of studies targeting the 5-LOX pathway would largely expand our knowledge on the anti-inflammatory mechanisms of (poly)phenols.

Targeting Leukotrienes as a Therapeutic Strategy to Prevent Comorbidities Associated with Metabolic Stress

Leukotrienes (LTs) are potent lipid mediators that exert a variety of functions, ranging from maintaining the tone of the homeostatic immune response to exerting potent proinflammatory effects. Therefore, LTs are essential elements in the development and maintenance of different chronic diseases, such as asthma, arthritis, and atherosclerosis. Due to the pleiotropic effects of LTs in the pathogenesis of inflammatory diseases, studies are needed to discover potent and specific LT synthesis inhibitors and LT receptor antagonists. Even though most clinical trials using LT inhibitors or antagonists have failed due to low efficacy and/or toxicity, new drug development strategies are driving the discovery for LT inhibitors to prevent inflammatory diseases. A newly important detrimental role for LTs in comorbidities associated with metabolic stress has emerged in the last few years and managing LT production and/or actions could represent an exciting new strategy to prevent or treat inflammatory diseases associated with metabolic disorders. This review is intended to shed light on the synthesis and actions of leukotrienes, the most common drugs used in clinical trials, and discuss the therapeutic potential of preventing LT function in obesity, diabetes, and hyperlipidemia.

Leukotrienes in Tumor-Associated Inflammation

Leukotrienes are biologically active eicosanoid lipid mediators that originate from oxidative metabolism of arachidonic acid. Biosynthesis of leukotrienes involves a set of soluble and membrane-bound enzymes that constitute a machinery complex primarily expressed by cells of myeloid origin. Leukotrienes and their synthetic enzymes are critical immune modulators for leukocyte migration. Increased concentrations of leukotrienes are implicated in a number of inflammatory disorders. More recent work indicates that leukotrienes may also interact with a variety of tissue cells, contributing to the low-grade inflammation of cardiovascular, neurodegenerative, and metabolic conditions, as well as that of cancer. Leukotriene signaling contributes to the active tumor microenvironment, promoting tumor growth and resistance to immunotherapy. This review summarizes recent insights into the intricate roles of leukotrienes in promoting tumor growth and metastasis through shaping the tumor microenvironment. The emerging possibilities for pharmacological targeting of leukotriene signaling in tumor metastasis are considered.

A Novel Strategy to Mitigate the Hyperinflammatory Response to COVID-19 by Targeting Leukotrienes

SARS-CoV-2 causing coronavirus disease 2019 (COVID-19) has wreaked havoc during the global pandemic of 2020 infecting millions and leaving over a half million dead. As a new virus, not previously in the human population, but with similarities to other coronaviruses causing severe acute respiratory distress syndrome (SARS/ARDS), and no known treatments, the race to re-purpose existing drugs and to enlist novel therapeutics is underway. In the half-year since the first cases, we have acquired substantial knowledge of this virus and the clinical course of COVID-19 progression. Results from early clinical trials have revealed two treatments (remdesivir, dexamethasone) that mitigate disease progression but clearly, there is much room for improvement. Initial case reports indicated many succumb to COVID-19 of hypoxic respiratory failure due to ARDS. However, ensuing studies revealed an atypical, immune cell-sequestered, vasculature-inflamed state leading to multiorgan thrombotic complications and end organ failure likely due to hyperinflammatory host responses. This Perspective focuses on a potential mechanism for a key COVID-19 disease progression turning point related to vascular and airway inflammation. The leukotriene lipid mediators have been overlooked with discussion centering on cytokine storms unleashing the deadly form of COVID-19. Leukotrienes possess some of the most potent known activities on immune cell trafficking and vascular leakage. We offer a simple treatment paradigm using two generic drugs targeting the hyperinflammatory response that characterizes the turning point from mild to severe/critical COVID-19 by targeting leukotriene biosynthesis with zileuton (Zyflo^® controlled release formulation) and antagonism of the cysteinyl leukotriene 1 receptor with montelukast (Singulair^®).

[Leukotriene D4 bronchial provocation test for detection of airway hyper-responsiveness in children]

OBJECTIVE

To explore the value of leukotriene D4 (LTD4) bronchial provocation test (BPT) in detection of airway hyper-responsiveness (AHR) in children.

METHODS

A total of 151 children aged 6 to 14 years, including 86 in remission of asthma and 65 with acute bronchitis, who were followed up in our respiratory clinic between November, 2017 and August, 2018. The children were randomly divided into LTD4 group (78 cases) and methacholine (MCH) group (73 cases). In LTD4 group, the 78 children underwent LTD4-BPT, including 46 with asthma and 32 children having re-examination for previous episodes of acute bronchitis; in MCH group, the 73 children underwent MCH-BPT, including 40 with asthma and 33 with acute bronchitis. MCH-BPT was also performed in the asthmatic children in the LTD4 group who had negative responses to LTD4 after an elution period. The major adverse reactions of the children to the two BPT were recorded. The diagnostic values of the two BPT were evaluated using receiver-operating characteristic (ROC) curve.

RESULTS

There was no significant difference in the results of basic lung function tests between LTD4 group and MCH group (P>0.05). The positive rate of BPT in asthmatic children in the LTD4 group was significantly lower than that in the MCH group (26.1% vs 72.5%; P < 0.05). The positive rate of BPT in children with previous acute bronchitis in the LTD4 group was lower than that in the MCH group (3.1% vs 15.2%). The positive rate of MCH-BPT in asthmatic children had negative BPT results in LTD4 group was 58.8%, and their asthma was mostly mild. The sensitivity was lower in LTD4 group than in MCH group (0.2609 vs 0.725), but the specificity was slightly higher in LTD4 group (0.9688 vs 0.8485).The area under ROC curvein LTD4 group was lower than that in MCH group (0.635 vs 0.787). In children with asthma in the LTD4 group, the main adverse reactions in BPT included cough (34.8%), shortness of breath (19.6%), chest tightness (15.2%), and wheezing (10.9%). The incidence of these adverse reactions was significantly lower in LTD4 group than in MCH group (P < 0.05). Serious adverse reactions occurred in neither of the two groups.

CONCLUSIONS

LTD4-BPT had high safety in clinical application of children and was similar to the specificity of MCH-BPT. However, it had low sensitivity, low diagnostic value, and limited application value in children's AHR detection.

G Protein-Coupled Receptors in Asthma Therapy: Pharmacology and Drug Action

Asthma is a heterogeneous inflammatory disease of the airways that is associated with airway hyperresponsiveness and airflow limitation. Although asthma was once simply categorized as atopic or nonatopic, emerging analyses over the last few decades have revealed a variety of asthma endotypes that are attributed to numerous pathophysiological mechanisms. The classification of asthma by endotype is primarily routed in different profiles of airway inflammation that contribute to bronchoconstriction. Many asthma therapeutics target G protein-coupled receptors (GPCRs), which either enhance bronchodilation or prevent bronchoconstriction. Short-acting and long-acting β 2-agonists are widely used bronchodilators that signal through the activation of the β 2-adrenergic receptor. Short-acting and long-acting antagonists of muscarinic acetylcholine receptors are used to reduce bronchoconstriction by blocking the action of acetylcholine. Leukotriene antagonists that block the signaling of cysteinyl leukotriene receptor 1 are used as an add-on therapy to reduce bronchoconstriction and inflammation induced by cysteinyl leukotrienes. A number of GPCR-targeting asthma drug candidates are also in different stages of development. Among them, antagonists of prostaglandin D2 receptor 2 have advanced into phase III clinical trials. Others, including antagonists of the adenosine A2B receptor and the histamine H4 receptor, are in early stages of clinical investigation. In the past decade, significant research advancements in pharmacology, cell biology, structural biology, and molecular physiology have greatly deepened our understanding of the therapeutic roles of GPCRs in asthma and drug action on these GPCRs. This review summarizes our current understanding of GPCR signaling and pharmacology in the context of asthma treatment. SIGNIFICANCE STATEMENT: Although current treatment methods for asthma are effective for a majority of asthma patients, there are still a large number of patients with poorly controlled asthma who may experience asthma exacerbations. This review summarizes current asthma treatment methods and our understanding of signaling and pharmacology of G protein-coupled receptors (GPCRs) in asthma therapy, and discusses controversies regarding the use of GPCR drugs and new opportunities in developing GPCR-targeting therapeutics for the treatment of asthma.

Modulation of neuroinflammation by cysteinyl leukotriene 1 and 2 receptors: implications for cerebral ischemia and neurodegenerative diseases

Neuroinflammation is a complex biological process and has been known to play an important role in age-related cerebrovascular and neurodegenerative disorders, such as cerebral ischemia, Alzheimer's disease, and Parkinson's disease. Cysteinyl leukotrienes (CysLTs) are potent inflammatory lipid mediators that exhibit actions mainly through activating type 1 and type 2 CysLT receptors (CysLT1 and CysLT2). Accumulating evidence shows that CysLT1 and CysLT2 are activated at different stages of pathological process in various cell types in the brain such as vascular endothelial cells, astrocytes, microglia, and neurons in response to insults. However, the precise roles and mechanisms of CysLT1 and CysLT2 in regulating the pathogenesis of cerebral ischemia, Alzheimer's disease, and Parkinson's disease are not fully understood. In this article, we focus on current advances that link activation of CysLT1 and CysLT2 to the pathological process during brain ischemia and neurodegeneration and discuss mechanisms by which CysLT1 and CysLT2 mediate inflammatory process and brain injury. Multitarget anti-inflammatory potentials of CysLT1 and CysLT2 antagonism for neuroinflammation and brain injury will also be reviewed.

Arachidonic Acid Metabolites in Cardiovascular and Metabolic Diseases

Lipid and immune pathways are crucial in the pathophysiology of metabolic and cardiovascular disease. Arachidonic acid (AA) and its derivatives link nutrient metabolism to immunity and inflammation, thus holding a key role in the emergence and progression of frequent diseases such as obesity, diabetes, non-alcoholic fatty liver disease, and cardiovascular disease. We herein present a synopsis of AA metabolism in human health, tissue homeostasis, and immunity, and explore the role of the AA metabolome in diverse pathophysiological conditions and diseases.

Leukotriene receptors as potential therapeutic targets

Leukotrienes, a class of arachidonic acid-derived bioactive molecules, are known as mediators of allergic and inflammatory reactions and considered to be important drug targets. Although an inhibitor of leukotriene biosynthesis and antagonists of the cysteinyl leukotriene receptor are clinically used for bronchial asthma and allergic rhinitis, these medications were developed before the molecular identification of leukotriene receptors. Numerous studies using cloned leukotriene receptors and genetically engineered mice have unveiled new pathophysiological roles for leukotrienes. This Review covers the recent findings on leukotriene receptors to revisit them as new drug targets.

Synopsis of arachidonic acid metabolism: A review

Arachidonic acid (AA), a 20 carbon chain polyunsaturated fatty acid with 4 double bonds, is an integral constituent of biological cell membrane, conferring it with fluidity and flexibility. The four double bonds of AA predispose it to oxygenation that leads to a plethora of metabolites of considerable importance for the proper function of the immune system, promotion of allergies and inflammation, resolving of inflammation, mood, and appetite. The present review presents an illustrated synopsis of AA metabolism, corroborating the instrumental importance of AA derivatives for health and well-being. It provides a comprehensive outline on AA metabolic pathways, enzymes and signaling cascades, in order to develop new perspectives in disease treatment and diagnosis.

Omega-3 and omega-6 polyunsaturated fatty acids: Dietary sources, metabolism, and significance - A review

Linoleic acid (LA) (n-6) and α-linolenic acid (ALA) (n-3) are essential fatty acids (EFAs) as they cannot be synthesized by humans or other higher animals. In the human body, these fatty acids (FAs) give rise to arachidonic acid (ARA, n-6), eicosapentaenoic acid (EPA, n-3), and docosahexaenoic acid (DHA, n-3) that play key roles in regulating body homeostasis. Locally acting bioactive signaling lipids called eicosanoids derived from these FAs also regulate diverse homeostatic processes. In general, ARA gives rise to pro-inflammatory eicosanoids whereas EPA and DHA give rise to anti-inflammatory eicosanoids. Thus, a proportionally higher consumption of n-3 PUFAs can protect us against inflammatory diseases, cancer, cardiovascular diseases, and other chronic diseases. The present review summarizes major sources, intake, and global consumption of n-3 and n-6 PUFAs. Their metabolism to biosynthesize long-chain PUFAs and eicosanoids and their roles in brain metabolism, cardiovascular disease, obesity, cancer, and bone health are also discussed.

Role of the Cysteinyl Leukotrienes in the Pathogenesis and Progression of Cardiovascular Diseases

Cysteinyl leukotrienes (CysLTs) are potent lipid inflammatory mediators synthesized from arachidonic acid, through the 5-lipoxygenase (5-LO) pathway. Owing to their properties, CysLTs play a crucial role in the pathogenesis of inflammation; therefore, CysLT modifiers as synthesis inhibitors or receptor antagonists, central in asthma management, may become a potential target for the treatment of other inflammatory diseases such as the cardiovascular disorders. 5-LO pathway activation and increased expression of its mediators and receptors are found in cardiovascular diseases. Moreover, the cardioprotective effects observed by using CysLT modifiers are promising and contribute to elucidate the link between CysLTs and cardiovascular disease. The aim of this review is to summarize the state of present research about the role of the CysLTs in the pathogenesis and progression of atherosclerosis and myocardial infarction.

IP3 receptor signaling and endothelial barrier function

The endothelium, a monolayer of endothelial cells lining vessel walls, maintains tissue-fluid homeostasis by restricting the passage of the plasma proteins and blood cells into the interstitium. The ion Ca²⁺, a ubiquitous secondary messenger, initiates signal transduction events in endothelial cells that is critical to control of vascular tone and endothelial permeability. The ion Ca²⁺ is stored inside the intracellular organelles and released into the cytosol in response to environmental cues. The inositol 1,4,5-trisphosphate (IP₃) messenger facilitates Ca²⁺ release through IP₃ receptors which are Ca²⁺-selective intracellular channels located within the membrane of the endoplasmic reticulum. Binding of IP₃ to the IP₃Rs initiates assembly of IP₃R clusters, a key event responsible for amplification of Ca²⁺ signals in endothelial cells. This review discusses emerging concepts related to architecture and dynamics of IP₃R clusters, and their specific role in propagation of Ca²⁺ signals in endothelial cells.

Thrombocytopathy leading to impaired in vivo haemostasis and thrombosis in platelet type von Willebrand disease

Platelet defects due to hyper-responsive GPIbα causing enhanced VWF interaction, counter-intuitively result in bleeding rather than thrombosis. The historical explanation of platelet/VWF clearance fails to explain mechanisms of impaired haemostasis particularly in light of reported poor platelet binding to fibrinogen. This study aimed to evaluate the defects of platelets with hyper-responsive GPIbα and their contribution to impaired in vivo thrombosis. Using the PT-VWD mouse model, platelets from the hTg^G233V were compared to control hTg^WT mice. Platelets' pro-coagulant capacity was evaluated using flowcytometry assessment of P-selectin and annexin V. Whole blood platelet aggregation in response to ADP, collagen and thrombin was tested. Clot kinetics using laser injury thrombosis model and the effect of GPIbα inhibition in vivo using 6B4; a monoclonal antibody, were evaluated. Thrombin-induced platelet P-selectin and PS exposure were significantly reduced in hTg^G233V compared to hTg^WT and not significantly different when compared to unstimulated platelets. The hTg^G233V platelets aggregated normally in response to collagen, and had a delayed response to ADP and thrombin, when compared to hTg^WT platelets. Laser injury showed significant impairment of in vivo thrombus formation in hTg^G233V compared to hTg^WT mice. There was a significant lag in in vitro clot formation in turbidity assay but no impairment in thrombin generation was observed using thromboelastography. The in vivo inhibition of GPIbα facilitated new - unstable - clot formation but did not improve the lag. We conclude platelets with hyper-responsive GPIbα have complex intrinsic defects beyond the previously described mechanisms. Abnormal signalling through GPIbα and potential therapy using inhibitors require further investigations.

Cytochrome P450 and Lipoxygenase Metabolites on Renal Function

Arachidonic acid metabolites have a myriad of biological actions including effects on the kidney to alter renal hemodynamics and tubular transport processes. Cyclooxygenase metabolites are products of an arachidonic acid enzymatic pathway that has been extensively studied in regards to renal function. Two lesser-known enzymatic pathways of arachidonic acid metabolism are the lipoxygenase (LO) and cytochrome P450 (CYP) pathways. The importance of LO and CYP metabolites to renal hemodynamics and tubular transport processes is now being recognized. LO and CYP metabolites have actions to alter renal blood flow and glomerular filtration rate. Proximal and distal tubular sodium transport and fluid and electrolyte homeostasis are also significantly influenced by renal CYP and LO levels. Metabolites of the LO and CYP pathways also have renal actions that influence renal inflammation, proliferation, and apoptotic processes at vascular and epithelial cells. These renal LO and CYP pathway actions occur through generation of specific metabolites and cell-signaling mechanisms. Even though the renal physiological importance and actions for LO and CYP metabolites are readily apparent, major gaps remain in our understanding of these lipid mediators to renal function. Future studies will be needed to fill these major gaps regarding LO and CYP metabolites on renal function.

Eicosanoid storm in infection and inflammation

Controlled immune responses to infection and injury involve complex molecular signalling networks with coordinated and often opposing actions. Eicosanoids and related bioactive lipid mediators derived from polyunsaturated fatty acids constitute a major bioactive lipid network that is among the most complex and challenging pathways to map in a physiological context. Eicosanoid signalling, similar to cytokine signalling and inflammasome formation, has primarily been viewed as a pro-inflammatory component of the innate immune response; however, recent advances in lipidomics have helped to elucidate unique eicosanoids and related docosanoids with anti-inflammatory and pro-resolution functions. This has advanced our overall understanding of the inflammatory response and its therapeutic implications. The induction of a pro-inflammatory and anti-inflammatory eicosanoid storm through the activation of inflammatory receptors by infectious agents is reviewed here.

HAMI 3379, a CysLT2R antagonist, dose- and time-dependently attenuates brain injury and inhibits microglial inflammation after focal cerebral ischemia in rats

Cysteinyl leukotrienes (CysLTs) induce inflammatory responses by activating their receptors, CysLT1R and CysLT2R. We have reported that CysLT2R is involved in neuronal injury, astrocytosis, and microgliosis, and that intracerebroventricular (i.c.v.) injection of the selective CysLT2R antagonist HAMI 3379 protects against acute brain injury after focal cerebral ischemia in rats. In the present study, we clarified features of the protective effect of intraperitoneally-injected HAMI 3379 in rats. We found that HAMI 3379 attenuated the acute brain injury 24 h after middle cerebral artery occlusion (MCAO) with effective doses of 0.1-0.4 mg/kg and a therapeutic window of ∼1h. It attenuated the neurological deficits, and reduced infarct volume, brain edema, and neuronal loss and degeneration 24 and 72h after MCAO. RNA interference with i.c.v. injection of CysLT2R short hairpin RNA (shRNA) attenuated the acute injury as well. Also, HAMI 3379 inhibited release of the cytokines IL-1β, interferon-γ (IFN-γ), and tumor necrosis factor-α (TNF-α) into the serum and cerebrospinal fluid 24h after MCAO. Moreover, HAMI 3379 ameliorated the microglial activation and neutrophil accumulation in the ischemic regions, but did not affect astrocyte proliferation 72h after MCAO. In comparison, the CysLT1R antagonist pranlukast did not affect microglial activation and IFN-γ release, but inhibited astrocyte proliferation and reduced serum IL-4. Thus, we conclude that HAMI 3379 has a protective effect on acute and subacute ischemic brain injury, and attenuates microglia-related inflammation. CysLT2R antagonist(s) alone or in combination with CysLT1R antagonists may be a novel class of therapeutic agents in the treatment of ischemic stroke.

Multiple-site activation of the cysteinyl leukotriene receptor 2 is required for exacerbation of ischemia/reperfusion injury

OBJECTIVE

Transgenic overexpression of the human cysteinyl leukotriene receptor 2 (CysLT2R) in murine endothelium exacerbates vascular permeability and ischemia/reperfusion injury. Here, we explore the underlying mechanisms of CysLT2R activation-mediated inflammation and delineate the relative contributions of endogenous murine CysLT2R and the transgene-derived receptor.

APPROACH AND RESULTS

We created a novel mouse with only endothelial-expressed CysLT2R (endothelium-targeted overexpression mice [EC]/CysLT2R-knockout mice [KO]) by crossing EC with KO to dissect the role of endothelial CysLT2R in tissue injury. Surprisingly, we discovered that damage in EC/KO mice was not elevated (24% versus 47% EC) after ischemia/reperfusion. We examined vascular permeability and leukocyte recruitment/rolling responses in the cremaster vasculature after cysteinyl leukotriene (cysLT) stimulation. Mice possessing transgenic endothelial CysLT2R overexpression, whether EC or EC/KO, when stimulated with cysLTs, exhibited vascular hyperpermeability, declining leukocyte flux, and a transient increase in slow-rolling leukocyte fraction. Mice lacking endogenous CysLT2R (both KO [20 ± 3 cells/min] EC/KO [24 ± 3]) showed lower-rolling leukocyte flux versus wild-type (38 ± 6) and EC (35 ± 6) mice under unstimulated conditions. EC/KO mice differed from EC counterparts in that vascular hyperpermeability was not present in the absence of exogenous cysLTs.

CONCLUSIONS

These results indicate that endothelial and nonendothelial CysLT2R niches have separate roles in mediating inflammatory responses. Endothelial receptor activation results in increased vascular permeability and leukocyte slow-rolling, facilitating leukocyte transmigration. Nonendothelial receptors, likely located on resident/circulating leukocytes, facilitate endothelial receptor activation and leukocyte transit. Activation of both receptor populations is required for injury exacerbation.

Cysteinyl leukotrienes regulate endothelial cell inflammatory and proliferative signals through CysLT₂ and CysLT₁ receptors

Cysteinyl leukotrienes (cys-LTs), LTC₄, LTD₄, LTE₄ are potent inflammatory lipid mediators that act through two distinct G-protein-coupled receptors, CysLT₁R and CysLT₂R. Although cys-LTs are shown to induce vascular leakage and atherosclerosis, the molecular mechanism by which cys-LTs modulate endothelial function is not known. Here, we show that cys-LTs (LTC₄ and LTD₄) induce robust calcium influx in human umbilical vein endothelial cells (HUVECs) through CysLT₂R, but not CysLT₁R. Further, cys-LT treatment induced endothelial cell (EC) contraction leading to monolayer disruption via CysLT₂R/Rho kinase dependent pathway. Furthermore, stimulation with cys-LTs potentiated TNFα-induced VCAM-1 expression and leukocyte recruitment to ECs through CysLT₂R. In contrast, we found that both LTC₄ and LTD₄ stimulated EC proliferation through CysLT₁R. Taken together, these results suggest that cys-LTs induce endothelial inflammation and proliferation via CysLT₂R/Rho kinase and CysLT₁R/Erk dependent pathways, respectively, which play critical role in the etiology of cardiovascular diseases such as atherosclerosis and myocardial infarction.

The leukotrienes: immune-modulating lipid mediators of disease

The leukotrienes are important lipid mediators with immune modulatory and proinflammatory properties. Classical bioactions of leukotrienes include chemotaxis, endothelial adherence, and activation of leukocytes, chemokine production, as well as contraction of smooth muscles in the microcirculation and respiratory tract. When formed in excess, these compounds play a pathogenic role in several acute and chronic inflammatory diseases, such as asthma, rheumatoid arthritis, and inflammatory bowel disease. An increasing number of diseases have been linked to inflammation implicating the leukotrienes as potential mediators. For example, recent investigations using genetic, morphological, and biochemical approaches have pointed to the involvement of leukotrienes in cardiovascular diseases including atherosclerosis, myocardial infarction, stroke, and abdominal aortic aneurysm. Moreover, new insights have changed our previous notion of leukotrienes as mediators of inflammatory reactions to molecules that can fine-tune the innate and adaptive immune response. Here, we review the most recent understanding of the leukotriene cascade with emphasis on recently identified roles in immune reactions and pathophysiology.

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.

Changes in the anti-inflammatory activity of soy isoflavonoid genistein versus genistein incorporated in two types of cyclodextrin derivatives

BACKGROUND

The isoflavonoid genistein represents the major active compound from soybean, the vegetal product from Glycine max (Fabaceae). The aim of this study is to prove that genistein was incorporated in two semisynthetic cyclodextrins, beta-cyclodextrin derivatives: hydroxypropyl-beta-cyclodextrin and randomly-methylated-beta-cyclodextrin as well as to compare the anti-inflammatory activity of genistein with that of genistein incorporated in these two types of semisynthetic cyclodextrins.

RESULTS

The animal studies were conducted on 8-week old C57BL/6 J female mice. Inflammation was induced in both ears of each mouse by topical application of 10 micrograms 12-O-tetradecanoylphorbol-3-acetate dissolved in 0.1 ml solvent (acetone : dimethylsulfoxide in a molar ratio 9:1). Thirty minutes later treatment was applied. The inflammatory reaction was correlated with increased values in ear thickness. Treatment with genistein and genistein incorporated in the two cyclodextrins led to decreased values for ear thickness. Better anti-inflammatory action was found for the complexes of genistein. Both haematoxylin-eosin analysis and CD45 marker expression are in agreement with these findings.

CONCLUSIONS

Results allow concluding that genistein is an active anti-inflammatory phytocompound and its complexation with hydrophilic beta-cyclodextrin derivatives leads to a stronger anti-inflammatory activity.

Role of reactive oxygen and nitrogen species in the vascular responses to inflammation

Inflammation is a complex and potentially life-threatening condition that involves the participation of a variety of chemical mediators, signaling pathways, and cell types. The microcirculation, which is critical for the initiation and perpetuation of an inflammatory response, exhibits several characteristic functional and structural changes in response to inflammation. These include vasomotor dysfunction (impaired vessel dilation and constriction), the adhesion and transendothelial migration of leukocytes, endothelial barrier dysfunction (increased vascular permeability), blood vessel proliferation (angiogenesis), and enhanced thrombus formation. These diverse responses of the microvasculature largely reflect the endothelial cell dysfunction that accompanies inflammation and the central role of these cells in modulating processes as varied as blood flow regulation, angiogenesis, and thrombogenesis. The importance of endothelial cells in inflammation-induced vascular dysfunction is also predicated on the ability of these cells to produce and respond to reactive oxygen and nitrogen species. Inflammation seems to upset the balance between nitric oxide and superoxide within (and surrounding) endothelial cells, which is necessary for normal vessel function. This review is focused on defining the molecular targets in the vessel wall that interact with reactive oxygen species and nitric oxide to produce the characteristic functional and structural changes that occur in response to inflammation. This analysis of the literature is consistent with the view that reactive oxygen and nitrogen species contribute significantly to the diverse vascular responses in inflammation and supports efforts that are directed at targeting these highly reactive species to maintain normal vascular health in pathological conditions that are associated with acute or chronic inflammation.

Co-regulation of transcellular and paracellular leak across microvascular endothelium by dynamin and Rac

Increased permeability of the microvascular endothelium to fluids and proteins is the hallmark of inflammatory conditions such as sepsis. Leakage can occur between (paracellular) or through (transcytosis) endothelial cells, yet little is known about whether these pathways are linked. Understanding the regulation of microvascular permeability is essential for the identification of novel therapies to combat inflammation. We investigated whether transcytosis and paracellular leakage are co-regulated. Using molecular and pharmacologic approaches, we inhibited transcytosis of albumin in primary human microvascular endothelium and measured paracellular permeability. Blockade of transcytosis induced a rapid increase in paracellular leakage that was not explained by decreases in caveolin-1 or increases in activity of nitric oxide synthase. The effect required caveolin-1 but was observed in cells depleted of clathrin, indicating that it was not due to the general inhibition of endocytosis. Inhibiting transcytosis by dynamin blockade increased paracellular leakage concomitantly with the loss of cortical actin from the plasma membrane and the displacement of active Rac from the plasmalemma. Importantly, inhibition of paracellular leakage by sphingosine-1-phosphate, which activates Rac and induces cortical actin, caused a significant increase in transcytosis of albumin in vitro and in an ex vivo whole-lung model. In addition, dominant-negative Rac significantly diminished albumin uptake by endothelia. Our findings indicate that transcytosis and paracellular permeability are co-regulated through a signaling pathway linking dynamin, Rac, and actin.

Atrial natriuretic peptide enhances microvascular albumin permeability by the caveolae-mediated transcellular pathway

AIMS

Cardiac atrial natriuretic peptide (ANP) participates in the maintenance of arterial blood pressure and intravascular volume homeostasis. The hypovolaemic effects of ANP result from coordinated actions in the kidney and systemic microcirculation. Hence, ANP, via its guanylyl cyclase-A (GC-A) receptor and intracellular cyclic GMP as second messenger, stimulates endothelial albumin permeability. Ultimately, this leads to a shift of plasma fluid into interstitial pools. Here we studied the role of caveolae-mediated transendothelial albumin transport in the hyperpermeability effects of ANP.

METHODS AND RESULTS

Intravital microscopy studies of the mouse cremaster microcirculation showed that ANP stimulates the extravasation of fluorescent albumin from post-capillary venules and causes arteriolar vasodilatation. The hyperpermeability effect was prevented in mice with conditional, endothelial deletion of GC-A (EC GC-A KO) or with deleted caveolin-1 (cav-1), the caveolae scaffold protein. In contrast, the vasodilating effect was preserved. Concomitantly, the acute hypovolaemic action of ANP was abolished in EC GC-A KO and Cav-1(-/-) mice. In cultured microvascular rat fat pad and mouse lung endothelial cells, ANP stimulated uptake and transendothelial transport of fluorescent albumin without altering endothelial electrical resistance. The stimulatory effect on albumin uptake was prevented in GC-A- or cav-1-deficient pulmonary endothelia. Finally, preparation of caveolin-enriched lipid rafts from mouse lung and western blotting showed that GC-A and cGMP-dependent protein kinase I partly co-localize with Cav-1 in caveolae microdomains.

CONCLUSION

ANP enhances transendothelial caveolae-mediated albumin transport via its GC-A receptor. This ANP-mediated cross-talk between the heart and the microcirculation is critically involved in the regulation of intravascular volume.

Characterization of the cysteinyl leukotriene 2 receptor in novel expression sites of the gastrointestinal tract

Cysteinyl leukotrienes (cysLTs: LTC₄, LTD₄, and LTE₄) are pro-inflammatory lipid molecules synthesized from arachidonic acid. They exert their actions on at least two cysLT receptors (CysLT₁R and CysLT₂R). Endothelial expression and activation of these receptors is linked to vasoactive responses and to the promotion of vascular permeability. Here we track the expression pattern of CysLT₂R in a loss-of-function murine model (CysLT₂R-LacZ) to neurons of the myenteric and submucosal plexus in the small intestine, colonic myenteric plexus, dorsal root ganglia, and nodose ganglion. Cysteinyl leukotriene (LTC₄/D₄) stimulation of colonic submucosal venules elicited a greater permeability response in wild-type mice. In a dextran sulfate sodium-induced colon inflammation model, the disease activity index and colonic edema (measured by wet:dry weights and submucosal thickness) were significantly reduced in knockout (KO) mice compared to controls. Tumor necrosis factor-α levels in colon tissue were significantly lower in KO mice; however, myeloperoxidase activity was similar in both the KO and wild-type groups. Finally, patch-clamp recordings of basal neuronal activity of colonic-projecting nociceptive neurons from dorsal root ganglia (T9-13) revealed significantly higher excitability in KO neurons compared to wild type. These results suggest that a lack of neuronal expression of CysLT₂R in the murine colonic myenteric plexus attenuates colitis disease progression via a reduction in inflammation-associated tissue edema and increases neuronal sensitivity to nociceptive stimuli.

Differential signaling of cysteinyl leukotrienes and a novel cysteinyl leukotriene receptor 2 (CysLT₂) agonist, N-methyl-leukotriene C₄, in calcium reporter and β arrestin assays

The cysteinyl leukotrienes (cysLTs) LTC₄, LTD₄, and LTE₄ are lipid mediators with physiological and pathophysiological functions. They exert their effects through G protein-coupled receptors (GPCRs), most notably via CysLT₁ and CysLT₂ receptor. The roles of the CysLT₂ receptor are beginning to emerge. Both LTC₄ and LTD₄ are potent agonists for the CysLT₂ receptor; however, LTC₄ is rapidly converted to LTD₄, which is also the main endogenous ligand for the CysLT₁ receptor. A selective and potent agonist at the CysLT₂ receptor would facilitate studies to discern between receptor subtypes. We show here that N-methyl LTC₄ (NMLTC₄), a metabolically stable LTC₄ mimetic, is a potent and selective CysLT₂ receptor agonist. Two expression systems were used to evaluate the functional activity of NMLTC₄ at human and/or mouse CysLT₁ and CysLT₂ receptors. Through the aequorin cell-based assay for calcium-coupled GPCRs, NMLTC₄ was almost equipotent to LTC₄ at CysLT₂ receptors but was the least efficacious at CysLT₂ receptors. In a β-galactosidase-β-arrestin complementation assay, the human (h) CysLT₂ receptor can couple with β-arrestin-2, and NMLTC₄ is slightly more potent for eliciting β-arrestin-2 binding compared with cysLTs. Furthermore, LTE₄ is nearly inactive in this assay compared with its weak partial agonist activity in the aequorin system. In a vascular leakage assay, NMLTC₄ is potent and active in mice overexpressing hCysLT₂ receptor in endothelium, whereas the response is abrogated in CysLT₂ receptor knockout mice. Therefore, NMLTC₄ is a potent subtype selective agonist for the CysLT₂ receptor in vitro and in vivo, and it will be useful to elucidate its biological roles.

Arachidonic acid metabolism regulates Escherichia coli penetration of the blood-brain barrier

Escherichia coli K1 meningitis occurs following penetration of the blood-brain barrier, but the underlying mechanisms involved in E. coli penetration of the blood-brain barrier remain incompletely understood. We have previously shown that host cytosolic phospholipase A(2)α (cPLA(2)α) contributes to E. coli invasion of human brain microvascular endothelial cells (HBMEC), which constitute the blood-brain barrier, but the underlying mechanisms remain unclear. cPLA(2)α selectively liberates arachidonic acid from membrane phospholipids. Here, we provide the first direct evidence that host 5-lipoxygenase and lipoxygenase products of arachidonic acid, cysteinyl leukotrienes (LTs), contribute to E. coli K1 invasion of HBMEC and penetration into the brain, and their contributions involve protein kinase C alpha (PKCα). These findings demonstrate that arachidonic acid metabolism regulates E. coli penetration of the blood-brain barrier, and studies are needed to further elucidate the mechanisms involved with metabolic products of arachidonic acid for their contribution to E. coli invasion of the blood-brain barrier.

Pharmacological characterization of the first potent and selective antagonist at the cysteinyl leukotriene 2 (CysLT(2)) receptor

BACKGROUND AND PURPOSE

Cysteinyl leukotrienes (CysLTs) have been implicated in the pathophysiology of inflammatory and cardiovascular disorders. Their actions are mediated by CysLT(1) and CysLT(2) receptors. Here we report the discovery of 3-({[(1S,3S)-3-carboxycyclohexyl]amino}carbonyl)-4-(3-{4-[4-(cyclo-hexyloxy)butoxy]phenyl}propoxy) benzoic acid (HAMI3379), the first potent and selective CysLT(2) receptor antagonist.

EXPERIMENTAL APPROACH

Pharmacological characterization of HAMI3379 was performed using stably transfected CysLT(1) and CysLT(2) receptor cell lines, and isolated, Langendorff-perfused, guinea pig hearts.

KEY RESULTS

In a CysLT(2) receptor reporter cell line, HAMI3379 antagonized leukotriene D(4)- (LTD(4)-) and leukotriene C(4)- (LTC(4)-) induced intracellular calcium mobilization with IC(50) values of 3.8 nM and 4.4 nM respectively. In contrast, HAMI3379 exhibited very low potency on a recombinant CysLT(1) receptor cell line (IC(50) > 10 000 nM). In addition, HAMI3379 did not exhibit any agonistic activity on both CysLT receptor cell lines. In binding studies using membranes from the CysLT(2) and CysLT(1) receptor cell lines, HAMI3379 inhibited [(3)H]-LTD(4) binding with IC(50) values of 38 nM and >10 000 nM respectively. In isolated Langendorff-perfused guinea pig hearts HAMI3379 concentration-dependently inhibited and reversed the LTC(4)-induced perfusion pressure increase and contractility decrease. The selective CysLT(1) receptor antagonist zafirlukast was found to be inactive in this experimental setting.

CONCLUSIONS AND IMPLICATIONS

HAMI3379 was identified as a potent and selective CysLT(2) receptor antagonist, which was devoid of CysLT receptor agonism. Using this compound, we showed that the cardiac effects of CysLTs are predominantly mediated by the CysLT(2) receptor.

Pathogenic importance of cysteinyl leukotrienes in development of gastric lesions induced by ischemia/reperfusion in mice

We examined the role of cysteinyl leukotrienes (CysLTs) in the gastric ulcerogenic response to ischemia/reperfusion (I/R) in mice. Experiments were performed in male C57BL/6J mice after 18-h fasting. Under urethane anesthesia, the celiac artery was clamped for 30 min, and then reperfusion was achieved by removing the clamp. The stomach was examined for lesions 60 min thereafter. The severity of I/R-induced gastric damage was reduced by prior administration of pranlukast [CysLT receptor type 1 (CysLT(1)R) antagonist] as well as 1-[[5'-(3''-methoxy-4''-ethoxycarbonyl-oxyphenyl)-2',4'-pentadienoyl]aminoethyl]-4-diphenylmethoxypiperidine [TMK688; 5-lipoxygenase (5-LOX) inhibitor]. On the contrary, these lesions were markedly worsened by pretreatment with indomethacin, and this response was abrogated by the coadministration of TMK688 or pranlukast. The gene expression of CysLT(1)R but not 5-LOX was up-regulated in the stomach after I/R, but both expressions were increased under I/R in the presence of indomethacin. I/R slightly increased the mucosal CysLT content of the stomach, yet this increase was markedly enhanced when the animals were pretreated with indomethacin. The increased CysLT biosynthetic response to indomethacin during I/R was attenuated by TMK688. Indomethacin alone caused a slight increase of CysLT(1)R expression and markedly up-regulated 5-LOX expression in the stomach. We concluded that I/R up-regulated the expression of CysLT(1)R in the stomach; CysLTs play a role in the pathogenesis of I/R-induced gastric damage through the activation of CysLT(1)R; and the aggravation by indomethacin of these lesions may be brought about by the increase of CysLT production and the up-regulation of 5-LOX expression, in addition to the decreased prostaglandin production.

Opening the flood-gates: how neutrophil-endothelial interactions regulate permeability

Many diseases have an inflammatory component, where neutrophil interactions with the vascular endothelium lead to barrier dysfunction and increased permeability. Neutrophils increase permeability through secreted products such as the chemokines CXCL1, 2, 3, and 8, through adhesion-dependent processes involving beta(2) integrins interacting with endothelial ICAM-1, and through combinations where beta(2) integrin engagement leads to degranulation and secretion of heparin-binding protein. Some neutrophil products, such as arachidonic acid or the leukotriene LTA4, are further processed by endothelial enzymes via transcellular metabolism before the resulting products thromboxane A2 or LTC4 can activate their cognate receptors. Neutrophils also generate reactive oxygen species that induce vascular leakage. This review focuses on the mechanisms of neutrophil-mediated leakage.