Mechanisms of leukotriene D4-induced constriction in human small bronchioles

Diclofenac and dexamethasone modulate the effect of cannabidiol on the rat colon motility ex vivo

Introduction

Due to the growing interest in the use of cannabinoids in supportive therapies, they are increasingly used together with anti-inflammatory drugs. Cannabinoids inhibit gastrointestinal motility, while steroidal and nonsteroidal anti-inflammatory drugs influence motility in other ways. The aim of the research was to study the interactions between cannabidiol (CBD) and these two classes of anti-inflammatory drugs in the context of gastrointestinal motility. Dexamethasone (DEX) was selected as a steroidal drug and diclofenac (DCF) as a nonsteroidal counterpart.

Material and Methods

The experiments were performed on isolated rat colon strips in isometric conditions. The contractile response to acetylcholine (ACh) (1 μM) was measured with no substance applied as a control value and was measured after application of CBD (80 μM), DEX (100 μM), DCF (100 μM), or a combination of these substances.

Results

Cannabidiol strongly inhibited intestinal motility mediated by ACh application, DCF inhibited it non-significantly, while DEX intensified it. When CBD was co-administered with DEX, the combination inhibited intestinal motility non-significantly relative to the ACh-only control. Co-administration of CBD with DCF inhibited motility more than when these substances were administered separately.

Conclusion

Inhibition of the intestinal response to ACh is likely due to the synergistic effect of CBD and endogenous cannabinoids. Dexamethasone lessened the inhibitory effect of CBD, likely because of diminished availability of the arachidonic acid necessary for endogenous cannabinoid synthesis. However, diclofenac may increase endogenous cannabinoid synthesis, because of the greater availability of arachidonic acid caused by DCF blocking the cyclooxygenation pathway.

Nutraceuticals and mitochondrial oxidative stress: bridging the gap in the management of bronchial asthma

Asthma is a chronic inflammatory disease primarily characterized by inflammation and reversible bronchoconstriction. It is currently one of the leading causes of morbidity and mortality in the world. Oxidative stress further complicates the pathology of the disease. The current treatment strategies for asthma mainly involve the use of anti-inflammatory agents and bronchodilators. However, long-term usage of such medications is associated with severe adverse effects and complications. Hence, there is an urgent need to develop newer, novel, and safe treatment modalities for the management of asthma. This has therefore prompted further investigations and detailed research to identify and develop novel therapeutic interventions from potent untapped resources. This review focuses on the significance of oxidative stressors that are primarily derived from both mitochondrial and non-mitochondrial sources in initiating the clinical features of asthma. The review also discusses the biological scavenging system of the body and factors that may lead to its malfunction which could result in altered states. Furthermore, the review provides a detailed insight into the therapeutic role of nutraceuticals as an effective strategy to attenuate the deleterious effects of oxidative stress and may be used in the mitigation of the cardinal features of bronchial asthma.

Cysteinyl Leukotriene Pathway and Cancer

Cancer remains a leading cause of death worldwide, despite many advances being made in recent decades. Changes in the tumor microenvironment, including dysregulated immunity, may contribute to carcinogenesis and cancer progression. The cysteinyl leukotriene (CysLT) pathway is involved in several signal pathways, having various functions in different tissues. We summarized major findings of studies about the roles of the CysLT pathway in cancer. Many in vitro studies suggested the roles of CysLTs in cell survival/proliferation via CysLT₁ receptor (CysLT₁R). CysLT₁R antagonism decreased cell vitality and induced cell death in several types of cancer cells, such as colorectal, urological, breast, lung and neurological malignancies. CysLTs were also associated with multidrug resistance of cancer, and CysLT₁R antagonism might reverse chemoresistance. Some animal studies demonstrated the beneficial effects of CysLT₁R antagonist in inhibiting tumorigenesis and progression of some cancer types, particularly colorectal cancer and lung cancer. The expression of CysLT₁R was shown in various cancer tissues, particularly colorectal cancer and urological malignancies, and higher expression was associated with a poorer prognosis. The chemo-preventive effects of CysLT₁R antagonists were demonstrated in two large retrospective cohort studies. In summary, the roles of the CysLT pathway in cancer have been delineated, whereas further studies are still warranted.

RhoA/Rho-kinases in asthma: from pathogenesis to therapeutic targets

Asthma is a chronic and heterogeneous disease characterised by airway inflammation and intermittent airway narrowing. The key obstacle in the prevention and treatment of asthma has been our incomplete understanding of its aetiology and biological mechanisms. The ras homolog family member A (RhoA) of the Rho family GTPases has been considered to be one of the most promising and novel therapeutic targets for asthma. It is well known that RhoA/Rho‐kinases play an important role in the pathophysiology of asthma, including airway smooth muscle contraction, airway hyper‐responsiveness, β‐adrenergic desensitisation and airway remodelling. However, recent advances have suggested novel roles for RhoA in regulating allergic airway inflammation. Specifically, RhoA has been shown to regulate allergic airway inflammation through controlling Th2 or Th17 cell differentiation and to regulate airway remodelling through regulating mesenchymal stem cell (MSC) differentiation. In this review, we evaluate the literature regarding the recent advances in the activation of RhoA/Rho‐kinase, cytokine and epigenetic regulation of RhoA/Rho‐kinase, and the role of RhoA/Rho‐kinase in regulating major features of asthma, such as airway hyper‐responsiveness, remodelling and inflammation. We also discuss the importance of the newly identified role of RhoA/Rho‐kinase signalling in MSC differentiation and bronchial epithelial barrier dysfunction. These findings indicate the functional significance of the RhoA/Rho‐kinase pathway in the pathophysiology of asthma and suggest that RhoA/Rho‐kinase signalling may be a promising therapeutic target for the treatment of asthma.

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.

Canonical Transient Potential Receptor-3 Channels in Normal and Diseased Airway Smooth Muscle Cells

All seven canonical transient potential receptor (TRPC1-7) channel members are expressed in mammalian airway smooth muscle cells (ASMCs). Among this family, TRPC3 channel plays an important role in the control of the resting [Ca²⁺]_i and agonist-induced increase in [Ca²⁺]_i. This channel is significantly upregulated in molecular expression and functional activity in airway diseases. The upregulated channel significantly augments the resting [Ca²⁺]_i and agonist-induced increase in [Ca²⁺]_i, thereby exerting a direct and essential effect in airway hyperresponsiveness. The increased TRPC3 channel-mediated Ca²⁺ signaling also results in the transcription factor nuclear factor-κB (NF-κB) activation via protein kinase C-α (PKCα)-dependent inhibitor of NFκB-α (IκBα) and calcineurin-dependent IκBβ signaling pathways, which upregulates cyclin-D1 expression and causes cell proliferation, leading to airway remodeling. TRPC3 channel may further interact with intracellular release Ca²⁺ channels, Orai channels and Ca²⁺-sensing stromal interaction molecules, mediating important cellular responses in ASMCs and the development of airway diseases.

Reduction of Asthmatic Parameters by Sea Hare Hydrolysates in a Mouse Model of Allergic Asthma

Sea hare has a variety of biological activities. However, little is known regarding the anti-asthmatic effects of sea hare. This study was performed to identify the effect of sea hare hydrolysates (SHH) on an ovalbumin (OVA)-induced allergic asthma model. The experimental asthma model was sensitized and challenged with OVA. We found that a high-dose of SHH (HSHH) significantly inhibited OVA-induced airway inflammation and mucus production around the airway in lung sections, while low- and medium-dose SHH showed an insignificant effect. In addition, HSHH highly reduced OVA-induced production of interleukin-4, -5, -13, leukotriene D4, E4, and histamine in bronchoalveolar lavage fluid. HSHH decreased the histamine-induced increase in the intracellular Ca²⁺ level and contractions in asthmatic smooth muscle cells. Furthermore, HSHH did not affect the weights of the spleen nor thymus, whereas dexamethasone (DEX), a steroidal anti-inflammatory drug, reduced them. Taken together, these results showed that HSHH reduced asthmatic parameters in a mouse model of allergic asthma, and suggest that SHH could be used as a potential therapeutic agent for asthma.

Emerging airway smooth muscle targets to treat asthma

Asthma is characterized in part by variable airflow obstruction and non-specific hyperresponsiveness to a variety of bronchoconstrictors, both of which are mediated by the airway smooth muscle (ASM). The ASM is also involved in the airway inflammation and airway wall remodeling observed in asthma. For all these reasons, the ASM provides an important target for the treatment of asthma. Several classes of drugs were developed decades ago which targeted the ASM - including β-agonists, anti-cholinergics, anti-histamines and anti-leukotrienes - but no substantially new class of drug has appeared recently. In this review, we summarize the on-going work of several laboratories aimed at producing novel targets and/or tools for the treatment of asthma. These range from receptors and ion channels on the ASM plasmalemma, to intracellular effectors (particularly those related to cyclic nucleotide signaling, calcium-homeostasis and phosphorylation cascades), to anti-IgE therapy and outright destruction of the ASM itself.

The CatSper channel: a polymodal chemosensor in human sperm

The sperm-specific CatSper channel controls the intracellular Ca(2+) concentration ([Ca(2+)](i)) and, thereby, the swimming behaviour of sperm. In humans, CatSper is directly activated by progesterone and prostaglandins-female factors that stimulate Ca(2+) influx. Other factors including neurotransmitters, chemokines, and odorants also affect sperm function by changing [Ca(2+)](i). Several ligands, notably odorants, have been proposed to control Ca(2+) entry and motility via G protein-coupled receptors (GPCRs) and cAMP-signalling pathways. Here, we show that odorants directly activate CatSper without involving GPCRs and cAMP. Moreover, membrane-permeable analogues of cyclic nucleotides that have been frequently used to study cAMP-mediated Ca(2+) signalling also activate CatSper directly via an extracellular site. Thus, CatSper or associated protein(s) harbour promiscuous binding sites that can host various ligands. These results contest current concepts of Ca(2+) signalling by GPCR and cAMP in mammalian sperm: ligands thought to activate metabotropic pathways, in fact, act via a common ionotropic mechanism. We propose that the CatSper channel complex serves as a polymodal sensor for multiple chemical cues that assist sperm during their voyage across the female genital tract.

Molecular expression and functional role of canonical transient receptor potential channels in airway smooth muscle cells

Multiple canonical or classic transient receptor potential (TRPC) molecules are expressed in animal and human airway smooth muscle cells (SMCs). TRPC3, but not TRPC1, is a major molecular component of native non-selective cation channels (NSCCs) to contribute to the resting [Ca(2+)](i) and muscarinic increase in [Ca(2+)](i) in freshly isolated airway SMCs. TRPC3-encoded NSCCs are significantly increased in expression and activity in airway SMCs from ovalbumin-sensitized/challenged "asthmatic" mice, whereas TRPC1-encoded channel activity, but not its expression, is largely augmented. The upregulated TRPC3- and TRPC1-encoded NSCC activity both mediate "asthmatic" membrane depolarization in airway SMCs. Supportively, tumor necrosis factor-α (TNFα), an important asthma mediator, increases TRPC3 expression, and TRPC3 gene silencing inhibits TNFα-mediated augmentation of acetylcholine-evoked increase in [Ca(2+)](i) in passaged airway SMCs. In contrast, TRPC6 gene silencing has no effect on 1-oleoyl-2-acetyl-sn-glycerol (OAG)-evoked increase in [Ca(2+)](i) in primary isolated cells. These findings provide compelling information indicating that TRPC3-encoded NSCCs are important for physiological and pathological cellular responses in airway SMCs. However, continual studies are necessary to further determine whether, which, and how TRPC-encoded channels are involved in cellular responses in normal and diseased (e.g., asthmatic) airway SMCs.

Methylmercury-induced IL-6 release requires phospholipase C activities

Methylmercury (MeHg) is a neurotoxin capable of causing severe damage to the CNS, especially in the developing fetus. Glia in the CNS release a number of cytokines that are important for proper CNS development and function. We reported earlier that MeHg could induce interleukin-6 (IL-6) release in primary mouse glia. This finding is significant considering previous reports indicating that sustained IL-6 exposure could be detrimental to cerebellar granule neurons, one of the major cellular targets of MeHg cytotoxicity. By using pharmacological antagonists against phophatidycholine- and phosphoinositol-specific phospholipase C, the current study indicated that phospholipase C activity was necessary for MeHg-induced IL-6 release. Results from pharmacological antagonists further suggested that the calcium signaling initiated by phospholipase C appeared essential for this event. In contrast, protein kinase C activity did not appear to be important. Even though mitogen-activated protein kinases were important for IL-6 release in some experimental systems, these enzymes did not appear to be required for MeHg-induced IL-6 release in glia. Based on these data and those reported by us and others, there is a possibility that MeHg-induced phospholipase C activation initiates a calcium signaling that causes phospholipase A(2) activation. This, in turn, leads to arachidonic acid and lysophosphatidyl choline generation, both of which are potent inducers for IL-6 release.

Lipoxygenase and cyclooxygenase inhibitors reveal a complementary role of arachidonic acid derivatives in pregnant human myometrium

OBJECTIVE

The aim of this study was to assess the involvement of lipoxygenase (LOX) metabolic pathways in uterine tissues from pregnant women as well as the combined inhibition of LOX and cyclooxygenase (COX) on contractile activity.

STUDY DESIGN

Uterine biopsies were performed from consenting women undergoing elective caesarean sections at term (n = 24). Western blot analysis and isometric tension measurements were performed in vitro on fresh human myometrial strips. Concentration-response curves to arachidonic acid (AA) 861 and baicalein (5- and 12-LOX inhibitors, respectively) were performed. The combined effects of baicalein and indomethacin were also assessed. Contractile activities were quantified by calculating both amplitude and the area under the curve over 20 minute periods.

RESULTS

5- and 12-LOX were present in all tested tissues. Addition of AA861 or baicalein resulted in tocolytic effects (P < .05). Finally, the combined inhibition of both COX and 12-LOX pathways resulted in additive tocolytic effects.

CONCLUSION

5- and 12-LOX pathways modulate human myometrium contractility.

Functional role of canonical transient receptor potential 1 and canonical transient receptor potential 3 in normal and asthmatic airway smooth muscle cells

Canonical transient receptor potential (TRPC)-encoded nonselective cation channels (NSCCs) are crucial for many cellular responses in a variety of cells; however, their molecular expression and functional roles in airway smooth muscle cells (ASMCs) remain obscure. The objective of this study was to determine whether TRPC1 and TRPC3 molecules could be important molecular constituents of native NSCCs controlling the resting membrane potential (Vm) and [Ca(2+)](i) in freshly isolated normal and ovalbumin (OVA)-sensitized/-challenged mouse ASMCs. Western blotting, RT-PCR, single-channel recording, whole-cell current-clamp recording, and a fluorescence imaging system were used to determine TRPC expression, NSCC activity, resting Vm, and resting [Ca(2+)](i). Specific individual TRPC antibodies and siRNAs were applied to test their functional roles. TRPC1 and TRPC3 proteins and mRNAs were expressed in freshly isolated ASM tissues. TRPC3 antibodies blocked the activity of NSCCs and hyperpolarized the resting Vm in ASMCs, whereas TRPC1 antibodies had no effect. TRPC3, but not TRPC1 gene silencing, largely diminished NSCC activity, hyperpolarized the resting Vm, lowered the resting [Ca(2+)](i), and inhibited methacholine-induced increase in [Ca(2+)](i). In OVA-sensitized/-challenged ASMCs, NSCC activity was greatly augmented, resting Vm was depolarized, and TRPC3 protein expression was increased. TRPC1 and TRPC3 antibodies blocked the increased activity of NSCCs and membrane depolarization in OVA-sensitized/-challenged cells. TRPC3 is an important molecular component of native NSCCs contributing to the resting Vm and [Ca(2+)](i) in normal ASMCs, as well as membrane depolarization and hyperresponsiveness in OVA-sensitized/-challenged cells, whereas TRPC1-encoded NSCCs are only activated in OVA-sensitized/-challenged airway myocytes.

Role of Ca2+ mobilization and Ca2+ sensitization in 8-iso-PGF 2 alpha-induced contraction in airway smooth muscle

BACKGROUND

Isoprostanes are prostaglandin (PG)-like compounds synthesized by oxidative stress, not by cyclooxygenase, and increase in bronchoalveolar lavage fluid of patients with asthma. The airway inflammation implicated in this disease may be amplified by oxidants. Although isoprostanes are useful biomarkers for oxidative stress, the action of these agents on airways has not been fully elucidated.

OBJECTIVE

This study was designed to determine the intracellular mechanisms underlying the effects of oxidative stress on airway smooth muscle, focused on Ca(2+) signalling pathways involved in the effect of 8-iso-PGF(2 alpha).

METHODS

Using simultaneous recording of isometric tension and F(340)/F(380) (an indicator of intracellular concentrations of Ca(2+), [Ca(2+)]i, we examined the correlation between tension and [Ca(2+)]i in response to 8-iso-PGF(2 alpha) in the fura-2 loaded tracheal smooth muscle.

RESULTS

Augmented tension and F(340)/F(380) by 8-iso-PGF(2 alpha) were attenuated by ICI-192605, an antagonist of thromboxane A(2) receptors (TP receptors). Moreover, D609, an antagonist of phosphatidylcholine-specific phospholipase C, markedly reduced both the tension and F(340)/F(380) induced by 8-iso-PGF(2 alpha), whereas U73122, an antagonist of phosphatidylinositol-specific phospholipase C, modestly inhibited them by 8-iso-PGF(2 alpha). SKF96365, a non-selective antagonist of Ca(2+) channels, markedly reduced both tension and F(340)/F(380) by 8-iso-PGF(2 alpha). However, diltiazem and verapamil, voltage-dependent Ca(2+) channel inhibitors, modestly attenuated tension although their reduction of F(340)/F(380) was not different from that by SKF96365. Y-27632, an inhibitor of Rho-kinase, significantly attenuated contraction induced by 8-iso-PGF(2 alpha) without reducing F(340)/F(380), whereas GF109203X and Go6983, protein kinase C inhibitors, did not markedly antagonize them although reducing F(340)/F(380) with a potency similar to Y-27632.

CONCLUSION

8-iso-PGF(2 alpha) causes airway smooth muscle contraction via activation of TP receptors. Ca(2+) mobilization by SKF96365- and D609-sensitive Ca(2+) influx and Ca(2+) sensitization by Rho-kinase contribute to the intracellular mechanisms underlying the action of 8-iso-PGF(2 alpha). Rho-kinase may be a therapeutic target for the physiologic abnormalities induced by oxidative stress in airways.

The suppressive effects of YM-58483/BTP-2, a store-operated Ca2+ entry blocker, on inflammatory mediator release in vitro and airway responses in vivo

YM-58483/BTP-2, 4-methyl-4'-[3,5-bis(trifluoromethyl)-1H-pyrazol-1-yl]-1,2,3-thiadiazole-5-carboxanilide, blocks the store-operated Ca2+ entry (SOCE) that mediates the activation of non-excitable cells. This study investigated the pharmacological profile and therapeutic potential of YM-58483 as anti-asthma drug. YM-58483 inhibited DNP antigen-induced histamine release from and leukotrienes (LTs) production in IgE-primed RBL-2H3 cells, a rat basophilic leukemia cell line, with IC50 values of 460 and 310 nM, respectively. Prednisolone did not inhibit either of these responses. YM-58483 also inhibited phytohemagglutinin-P (PHA)-stimulated IL-5 and IL-13 production in human peripheral blood cells with IC50 values of 125 and 148 nM, respectively, which is approximately 5 times less potent than prednisolone. YM-58483 (30 mg/kg, p.o.) significantly suppressed ovalbumin (OVA)-induced bronchoconstriction in OVA-sensitized guinea pigs, whereas prednisolone did not. YM-58483 (3-30 mg/kg, p.o.) and prednisolone (100mg/kg, p.o.) both significantly and completely suppressed airway hyperresponsiveness (AHR) caused by OVA exposure. Since YM-58483 inhibits two major characteristic symptoms of bronchial asthma, namely bronchoconstriction and AHR via the suppression of inflammatory mediator and cytokine production, SOCE inhibition is a potential approach for treatment.

Montelukast inhibits inflammatory responses in small airways of the Guinea-pig

Increased resistance in the small airways is a major contributor of airway obstruction in asthma. The role of leukotrienes (LT) in determining inflammation and obstruction of small size bronchi is not completely understood. Here, we have examined the effect of the cysteinyl-leukotriene (CysLT 1) receptor antagonist, montelukast, against the bronchoconstriction and inflammatory responses induced by exogenous leukotriene and by allergen challenge in small size (<or=1mm) Guinea-pig bronchi. Montelukast potently (pA(2) 8.3) inhibited the contraction induced by LTD4 in small bronchi taken from naïve Guinea-pigs. Furthermore, montelukast reduced the contraction produced by in vitro ovalbumin (OVA) challenge in small size bronchi from sensitized Guinea-pigs. Montelukast (10 microg kg(-1)) also blocked plasma protein extravasation and accumulation of inflammatory cells (eosinophils) induced by OVA challenge in small intra-parenchymal bronchi of OVA sensitized animals. These findings provide additional evidence that CysLT 1 receptor antagonism reduces allergic reactions that cause contractile and inflammatory responses in Guinea-pig small airways during OVA challenge. If the anti-bronchospastic and anti-inflammatory actions of the CysLT 1 receptor antagonists observed in the small airways of Guinea-pigs occur also in man these effects may contribute to the beneficial effects of montelukast in asthmatic patients.

Discovery of a potent and long-acting bronchorelaxing capsazepinoid, RESPIR 4-95

BACKGROUND

Current drugs including beta-agonists have limited smooth muscle relaxant effects on human small airways. Yet this is a major site of obstruction in asthma and chronic obstructive pulmonary disease (COPD).

OBJECTIVE

This study explores human small airway relaxant effects of RESPIR 4-95, a novel chemical analogue (capsazepinoid) to capsazepine. Capsazepine was recently shown to relax small airways in a way which was independent of its TRPV1 antagonism and independent of current bronchodilator drug mechanisms.

METHOD

In vitro preparations of human small airways, 0.5-1.5mm in diameter and responding with reproducible contractions to leukotriene D4 (LTD4) for 12h, were used.

RESULTS

RESPIR 4-95 reversibly prevented LTD4-induced contractions as well as relaxed the established tonic contraction by LTD4. RESPIR 4-95 exhibited marked improvements over the reference capsazepinoid, capsazepine, by being 10 times more potent, exhibiting twice as long duration of action after wash-out (9h), and inhibiting equally well LTD4-, histamine-, prostaglandin D2 (PGD2)-, and acetylcholine (ACh)-induced contractions. RESPIR 4-95 was distinguished from l-type calcium channel antagonist nifedipine by its greater efficacy and potency and by exhibiting increased relaxant effect by repeated exposures. Furthermore, RESPIR 4-95 was more efficacious and longer acting than the long-acting beta-agonist formoterol.

CONCLUSION

Efficacy, potency, duration of action, and inexhaustibility of its relaxation of human small airways make RESPIR 4-95 an interesting lead compound for further developments aiming at drug treatment of small airway obstruction in asthma and COPD. Further work is warranted to unveil the molecular biology behind its relaxant actions.

(±)3,4-Methylenedioxyamphetamine elicits action potential bursts in a central snail neuron

The effects of (+/-)3,4-methylenedioxyamphetamine (MDA) were studied in an identifiable RP4 neuron of the African snail, Achatina fulica Ferussac, using the two-electrode voltage-clamp method. The RP4 neuron generated spontaneous action potentials. Extracellular or intracellular application of MDA elicited action potential bursts of the central RP4 neuron. The action potential bursts elicited by MDA were not blocked when neurons were immersed in high-Mg2+ solution, Ca2+-free solution, nor after continuous perfusion with atropine, d-tubocurarine, propranolol, prazosin, haloperidol, sulpiride or methiothepin. Notably, the induction of action potential bursts was blocked by pretreatment with protein kinase C (PKC) inhibitors, chelerythrine and Ro 31-8220, but not by protein kinase A (PKA) inhibitors, KT-5720 and H89, nor by the phospholipase C (PLC) inhibitor, U73122. PKC activators, i.e., phorbol 12,13-dibutyrate (PDBu) and 1-oleoyl-2-acety-sn-glycerol (OAG; a membrane-permeant DAG analog), facilitate the induction of action potential bursts elicited by MDA. Voltage-clamp studies revealed that MDA decreased the delayed rectifying K+ current (I(KD)) of the RP4 neuron. Further, although Ro 31-8220 did not affect the I(KD), Ro 31-8220 decreased the inhibitory effect of MDA on the I(KD). These results suggest that the generation of action potential bursts elicited by MDA was not due to (1) the synaptic effects of neurotransmitters, (2) the cholinergic, adrenergic, dopaminergic or serotoninergic receptors of the excitable membrane. Instead, the MDA-elicited action potential bursts are closely related to PKC activity and the inhibitory effects on the I(KD).

Potential Protective Properties of a Stable, Slow-releasing Nitric Oxide Donor, GEA 3175, in the Lung

Nitric oxide (NO), is known to exert vasodilatory, bronchodilatory, and antiplatelet effects, and quantitative or functional NO deficiency has been implicated in various cardio-vascular and airway diseases. NO donors, which are drugs capable of releasing NO either spontaneously or tissue-dependently, represent a way of increasing NO. Here, we review our current understanding of the NO donor, GEA 3175, 1,2,3,4-oxatriazolium, 3-(3-chloro-2-methylphenyl)-5-[[(methylphenyl)sulphonyl]amino], hydroxide inner salt. GEA 3175 is a mesoionic 3-aryl substituted oxatriazole-5-imine derivative, which is a potent, stable, slow releasing NO donor with important actions in various organ systems. In isolated guinea pig trachea, rat bronchi and bovine and human small bronchioles, GEA 3175 induces potent, long-lasting relaxation. In vivo, in sensitized guinea pigs, GEA 3175 protects against antigen-induced bronchoconstriction. GEA 3175 also exerts potent vasodilatory properties. In isolated human pulmonary arteries, GEA 3175 induces relaxation which is long-lasting and more potent than in airways. In isolated systemic arteries, GEA 3175 is also a potent vasodilator. By intravenous infusion GEA 3175 reduces blood pressure similarly to nitroglycerin. Vascular and bronchiolar relaxations were shown to be mediated via NO dependent pathways. GEA 3175 is also a potent anti-inflammatory agent. Functions of polymorphnuclear cells (PMNs) such as leucotriene B(4) (LTB(4)) - synhesis, chemotaxis and superoxide (O(-) (2)) production are inhibited by GEA 3175. GEA3175 also inhibits upregulation of E-selectin in human umbilical vein endothelial cells (HUVECs) and hence adhesion of neutrophils. Another action of GEA 3175 on the endothelium is inhibition of prostacyclin release. Finally, GEA 3175 has been demonstrated to be an antiplatelet agent. Thrombin-induced platelet aggregation was inhibited by GEA 3175 in a cyclic GMP- and vasodilator-stimulated phosphoprotein (VASP)-phosphorylation-dependent manner. Thus, GEA 3175 has been demonstrated to exert bronchodilatory, pulmonary vasodilatory, antiplatelet as well as anti-inflammatory actions. Given these actions GEA 3175 may represent a potentially useful drug. The exact mechanism whereby GEA 3175 releases NO is, however, still unknown. In addition, most of the studies so far have been performed in isolated tissue preparations. Clearly, further in vivo studies involving animal models are required to clarify safety issues and whether GEA 3175 can be used in the treatment of pulmonary hypertension and/or airway diseases.

Ion transport regulated by protease-activated receptor 2 in human airway Calu-3 epithelia

We examined the mechanisms underlying anion secretion mediated by protease-activated receptor 2 (PAR2) and its role in the regulation of ion transport, using polarized human airway Calu-3 cells. PAR2 stimulation by trypsin and a PAR2-activating peptide (PAR2AP), especially from the basolateral aspect, caused transient Cl(-) secretion due to cytosolic Ca(2+) mobilization. Antagonists of PI-PLC (U73122, ET-18-OCH(3)) and inositol 1,4,5-triphosphate (xestospongin C (Xest C)) were without effect on the PAR2AP-mediated Cl(-) secretion, whereas it was attenuated by D609 (a PC-PLC inhibitor) and phorbol 12-myristate 13 acetate (PMA, a PKC activator). Even 30 min after removal of PAR2AP after a 10-min-exposure, cells were still poorly responsive to PAR2 stimulation, but the reduced responsiveness was upregulated by a PKC inhibitor, GF109203X (GFX). Pretreatment with PAR2AP did not affect responses to anion secretagogues, such as isoproterenol, forskolin, thapsigargin, 1-ethyl-2-benzimdazolinone, and adenosine, but ATP-induced responses were significantly reduced. Nystatin permeabilization studies revealed that the presence of PAR2AP prevented ATP-induced increments in basolateral membrane K(+) conductance without affecting apical membrane Cl(-) conductance. ATP-elicited Ca(2+) mobilization, which was sensitive to D609 and PMA, was inhibited by the pretreatment with PAR2AP, and this inhibition was blunted by the presence of GFX. Collectively, stimulation of PAR2 generates a brief response of Cl(-) secretion through PC-PLC-mediated pathway, followed by not only auto-desensitization of PAR2 itself but also cross-desensitization of a PC-PLC-coupled purinoceptor. The two types of desensitization seem likely to have PKC-mediated downregulation of PC-PLC in common.

TRP channels in airway smooth muscle as therapeutic targets

Cation channels are of fundamental importance in regulating the function of airway smooth cells especially bronchoconstriction in response to spasmogens, and are therefore key players in the pathogenesis of asthma. To date, the identity of these cation channels remains a mystery. However, the recently emerged transient receptor potential (TRP) cation channel family has provided several promising channel candidates. The identification of the key TRP channels involved in regulating airway smooth muscle contractility, and therefore airway tone, could provide new and exciting prospects for the development of novel therapies for the treatment of airway diseases such as asthma.

Capsazepine, a vanilloid antagonist, abolishes tonic responses induced by 20-HETE on guinea pig airway smooth muscle

The aim of this study was to delineate the mode of action of 20-hydroxy-eicosatetraenoic acid (20-HETE) in airway smooth muscle (ASM) cells. ASM metabolizes arachidonic acid by various enzymatic pathways, including the cytochrome P-450 (CYP-450) omega-hydroxylase, which leads to the production of 20-HETE, a bronchoconstrictive eicosanoid. The present study demonstrated that 20-HETE induced concentration-dependent tonic responses in ASM, whereas transient responses were recorded in Ca2+-free solution, suggesting an intracellular Ca2+ release process. 20-HETE inotropic responses were abolished by 36 microM 2-aminoethoxydiphenyl borate or 1 microM thapsigargin but were insensitive to 10 microM ryanodine, indicating that inositol triphosphate receptors likely control the release of intracellular Ca2+. Sustained tension, which required Ca2+ entry, was partially blocked by 1 microM nifedipine (an L-type) and 100 microM Gd3+ (a nonselective cationic channel blocker). Moreover, in the absence of selective 20-HETE receptor antagonists, 20-HETE tonic responses were inhibited in a concentration-dependent manner (0.1-10 microM) by capsazepine, a well-characterized vanilloid receptor antagonist. Capsazepine was also observed to reverse cumulative responses to 20-HETE and capsaicin, a TRPV1 agonist. In addition, capsazepine pretreatment largely modified the sustained inotropic responses to 20-HETE, suggesting that 20-HETE cross-reacted with TRPV1 receptors with a low affinity (microM) or that its specific receptor was inhibited by the vanilloid antagonist. Data obtained using RHC-80267, ONO-RS-082, and eicosatetraynoic acid, respective inhibitors of diacylglycerol-lipase, phospholipase A2, and CYP-450 omega-hydroxylase, reveal that intracellular arachidonic acid production and its 20-HETE metabolite may be responsible for the activation of nonselective cationic channels and tonic responses.

5-Oxo-ETE regulates tone of guinea pig airway smooth muscle via activation of Ca2+pools and Rho-kinase pathway

5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is a proinflammatory mediator, but its effects on airway smooth muscle (ASM) have never been assessed. Tension measurements performed on guinea pig ASM showed that 5-oxo-ETE induced sustained concentration-dependent positive inotropic responses (EC50= 0.89 μM) of somewhat lower amplitude than those induced by carbamylcholine and the thromboxane A2(TXA2) agonist U-46619. Transient inotropic responses to 5-oxo-ETE were recorded in Ca2+-free medium, suggesting mobilization of intracellular Ca2+. Meanwhile, the sustained contraction, which required Ca2+entry, was partially blocked by 1 μM nifedipine (an L-type Ca2+channel blocker) but relatively insensitive to 100 μM Gd3+. The 5-oxo-ETE responses were also inhibited by indomethacin and SC-560 [a cyclooxygenase (COX-1) inhibitor] pretreatments but not by NS-398 (a selective COX-2 inhibitor). The contractile effects of 5-oxo-ETE on ASM were inhibited by the selective TXA2receptor (TP receptor) antagonist SQ-29548 (−75%) and by 2-(p-amylcinnamoyl) amino-4-chlorobenzoic acid pretreatment, a phospholipase A2inhibitor (−66%), suggesting that the major part of its effect is mediated by the release of TXA2. ASM responses to 5-oxo-ETE were also blocked by the Rho-kinase inhibitor Y-27632, which also partially inhibited the response to the TP receptor agonist U-46619, suggesting that the contractile response is due in part to Ca2+sensitization of ASM cell myofilaments.

LTD4 induces hyperresponsiveness to histamine in bovine airway smooth muscle: role of SR-ATPase Ca2+ pump and tyrosine kinase

Airway hyperresponsiveness is a key feature of asthma, but its mechanisms remain poorly understood. Leukotriene D(4) (LTD(4)) is one of the few molecules capable of producing airway hyperresponsiveness. In this study, LTD(4), but not leukotriene C(4) (LTC(4)), produced a leftward displacement of the concentration-response curve to histamine in bovine airway smooth muscle strips. Neither LTC(4) nor LTD(4) modified the concentration-response curve to carbachol. In simultaneous measurements of intracellular Ca(2+) ([Ca(2+)](i)) and contraction, histamine or carbachol produced a transient Ca(2+) peak followed by a plateau, along with a contraction. LTD(4) increased the histamine-induced transient Ca(2+) peak and contraction but did not modify responses to carbachol. Enhanced responses to histamine induced by LTD(4) were not modified by staurosporine or chelerythrine but were abolished by genistein. Western blot showed that carbachol, but not histamine, caused intense phosphorylation of extracellular signal-regulated kinase 1/2 and that LTD(4) significantly enhanced the phosphorylation induced by histamine, but not by carbachol. L-type Ca(2+) channel participation in the hyperresponsiveness to histamine was discarded because LTD(4) did not modify the [Ca(2+)](i) changes induced by KCl. In tracheal myocytes, LTD(4) enhanced the transient Ca(2+) peak induced by histamine (but not by carbachol) and the sarcoplasmic reticulum (SR) Ca(2+) refilling. Genistein abolished this last LTD(4) effect. Partial blockade of the SR-ATPase Ca(2+) pump with cyclopiazonic acid reduced the Ca(2+) transient peak induced by histamine but not by carbachol. These results suggested that LTD(4) induces hyperresponsiveness to histamine through activation of the tyrosine kinase pathway and an increasing SR-ATPase Ca(2+) pump activity. L-type Ca(2+) channels seemed not to be involved in this phenomenon.

Phospholipases C and A2 control lysosome-mediated IL-1 beta secretion: Implications for inflammatory processes

Blocking the activity of IL-1 beta has entered the clinical arena of treating autoimmune diseases. However, a successful outcome of this approach requires a clear definition of the mechanisms controlling IL-1 beta release. These are still unclear as IL-1 beta, lacking a secretory signal peptide, follows a nonclassical pathway of secretion. Here, we analyze the molecular mechanism(s) undergoing IL-1 beta processing and release in human monocytes and provide a unifying model for the regulated secretion of the cytokine. Our data show that in a first step, pro-caspase-1 and endotoxin-induced pro-IL-1 beta are targeted in part to specialized secretory lysosomes, where they colocalize with other lysosomal proteins. Externalization of mature IL-1 beta and caspase-1 together with lysosomal proteins is then facilitated by extracellular ATP. ATP triggers the efflux of K(+) from the cell, followed by Ca(2+) influx and activation of three phospholipases: phosphatidylcholine-specific phospholipase C and calcium-independent and -dependent phospholipase A(2). Whereas calcium-independent phospholipase A(2) is involved in processing, phosphatidylcholine-specific phospholipase C and calcium-dependent phospholipase A(2) are required for secretion. Dissection of the events that follow ATP triggering allowed to demonstrate that K(+) efflux is responsible for phosphatidylcholine-specific phospholipase C induction, which in turn allows the rise in intracellular free calcium concentration required for activation of phospholipase A(2). This activation is ultimately responsible for lysosome exocytosis and IL-1 beta secretion.

8-Bromo-cAMP decreases the Ca2+ sensitivity of airway smooth muscle contraction through a mechanism distinct from inhibition of Rho-kinase

To clarify whether cyclic AMP (cAMP)/cAMP-dependent protein kinase (PKA) activation and Rho-kinase inhibition share a common mechanism to decrease the Ca2+ sensitivity of airway smooth muscle contraction, we examined the effects of 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP), a stable cAMP analog, and (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexane carboxamide dihydrochloride, monohydrate (Y-27632), a Rho-kinase inhibitor, on carbachol (CCh)-, guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS)-, 4beta-phorbol 12,13-dibutyrate (PDBu)-, and leukotriene D4 (LTD4)-induced Ca2+ sensitization in alpha-toxin-permeabilized rabbit tracheal and human bronchial smooth muscle. In rabbit trachea, CCh-induced smooth muscle contraction was inhibited by 8-BrcAMP and Y-27632 to a similar extent. However, GTPgammaS-induced smooth muscle contraction was resistant to 8-BrcAMP. In the presence of a saturating concentration of Y-27632, PDBu-induced smooth muscle contraction was completely reversed by 8-BrcAMP. Conversely, PDBu-induced smooth muscle contraction was resistant to Y-27632. In the presence of a saturating concentration of 8-BrcAMP, GTPgammaS-induced Ca2+ sensitization was also reversed by Y-27632. The 8-BrcAMP had no effect on the ATP-triggered contraction of tracheal smooth muscle that had been treated with calyculin A in rigor solutions. The 8-BrcAMP and Y-27632 additively accelerated the relaxation rate of PDBu- and GTPgammaS-treated smooth muscle under myosin light chain kinase-inhibited conditions. In human bronchus, LTD4-induced smooth muscle contraction was inhibited by both 8-BrcAMP and Y-27632. We conclude that cAMP/PKA-induced Ca2+ desensitization contains at least two mechanisms: 1) inhibition of the muscarinic receptor signaling upstream from Rho activation and 2) cAMP/PKA's preferential reversal of PKC-mediated Ca2+ sensitization in airway smooth muscle.

20-HETE inotropic effects involve the activation of a nonselective cationic current in airway smooth muscle

20-Hydroxyeicosatetraenoic acid (20-HETE) controls several mechanisms such as vasoactivity, mitogenicity, and ion transport in various tissues. Our goal was to quantify the effects of 20-HETE on the electrophysiological properties of airway smooth muscle (ASM). Isometric tension measurements, performed on guinea pig ASM, showed that 20-HETE induced a dose-dependent inotropic effect with an EC50 value of 1.5 microM. This inotropic response was insensitive to GF-109203X, a PKC inhibitor. The sustained contraction, requiring Ca2+ entry, was partially blocked by either 100 microM Gd3+ or 1 microM nifedipine, revealing the involvement of noncapacitative Ca2+ entry and L-type Ca2+ channels, respectively. Microelectrode measurements showed that 3 microM 20-HETE depolarized the membrane potential in guinea pig ASM by 13 +/- 2mV(n = 7), as did 30 microM 1-oleoyl-2-acetyl-sn-glycerol. Depolarizing effects were also observed in the absence of epithelium. Patch-clamp recordings demonstrated that 1 microM 20-HETE activated a nonselective cationic inward current that may be supported by the activation of transient receptor potential channels. The presence of canonical transient receptor potential mRNA was confirmed by RT-PCR in guinea pig ASM cells.

Effects of cysteinyl leukotrienes in small human bronchus and antagonist activity of montelukast and its metabolites

BACKGROUND

Evidence suggests that small airways contribute to clinically significant processes in asthma. Cysteinyl leukotrienes (CysLTs) are considered to be pivotal mediators in the pathogenesis of asthma. Montelukast (MK), a specific CysLT1 receptor antagonist, is metabolized in two main hydroxylated metabolites (termed M5 and M6, respectively).

OBJECTIVES

The aims of this study were to compare the responsiveness of small and large human bronchi to the three CysLTs, to evaluate the antagonist activity of MK, M5 and M6 in these preparations of human bronchi, and to characterize the CysLT receptors involved in the contractile response.

METHODS AND RESULTS

In isolated small bronchus (i.d. 0.5-2 mm), the potencies (-log molar EC50) of LTC4, LTD4 and LTE4 were 9.3 (n=11), 9.1 (n=30) and 8.4 (n=14), respectively. The three CysLTs were about 30-fold more potent in small bronchi than in larger bronchi (i.d. 4-6 mm). In small bronchi, MK significantly shifted to the right the CysLT concentration-effect curves with pA2 values against LTC4, LTD4 and LTE4 of 9.1 (n=3), 9.0 (n=11) and 8.7 (n=5), respectively. The antagonist potencies of M6 and M5 were similar to MK and fivefold lower, respectively. A similar activity of MK against the three CysLTs suggested that CysLT1 receptors are involved in the contraction of human bronchus. Analysis by RT-PCR also indicated that human bronchus mainly expressed CysLT1 receptors.

CONCLUSION

MK exerts a potent antagonist activity against the particularly potent constricting effects of CysLTs in isolated human small bronchi, which only expressed the CysLT1 receptor subtype. The metabolites of MK are also potent in vitro antagonists, but may not participate in the therapeutic activity of MK due to their low plasma concentrations in patients treated with the recommended dose of MK.

Transient receptor potential (TRP) channels as potential drug targets in respiratory disease

Calcium-permeable channels have traditionally been thought of as therapeutic targets in excitable cells. For instance, voltage-operated Ca2+ channels in neurones and smooth muscle cells for neurological and cardiovascular diseases although calcium-permeable channels are also functionally important in electrically non-excitable cells. In the lung, calcium channels play a pivotal role in the activation of all the cell types present, whether resident cells such as airway smooth muscle cells and macrophages or migratory cells such as neutrophils or lymphocytes.Previously, research in this area has been hindered by the lack of obvious molecular identity. More recently, the emergence of the transient receptor potential (TRP) cation family has yielded promising candidates which may underpin the different receptor-operated calcium influx pathways. The challenge now, is to ascribe function to the TRP channels expressed in each cell type as a first step in identifying which TRP channels may be potential drug targets for asthma and chronic obstructive pulmonary disease (COPD) (Fig. 1).

Regulation of capacitative and noncapacitative receptor-operated Ca2+ entry by rho-kinase in tracheal smooth muscle

To determine the mechanisms of Ca2+ mobilization induced by receptor agonists, we examined the role of Rho-kinase on the sarcoplasmic reticulum (SR) Ca2+ stores-dependent and -independent Ca2+ influx in guinea pig tracheal smooth muscle (TSM). Isometric tension and intracellular Ca2+ concentration ([Ca2+]i) were simultaneously measured using fura-2-loaded tissues. Depletion of the SR Ca2+ stores by thapsigargin caused an increase in [Ca2+]i and contraction, demonstrating capacitative Ca2+ entry (CCE). Because CCE was not inhibited by nifedipine, voltage-operated Ca2+ channels are not involved in CCE. Under the condition that CCE is fully activated, methacholine (MCh) and histamine caused further increases in [Ca2+]i and tension, demonstrating noncapacitative receptor-operated Ca2+ entry (non-CCE). The Ca2+ influx and contraction via non-CCE was inhibited by Y-27632, a Rho-kinase inhibitor, in a concentration-dependent fashion. In contrast, Y-27632 did not affect thapsigargin-induced CCE. Cytochalasin D, which disrupts actin cytoskeleton, inhibited contraction induced by CCE or MCh with no change in [Ca2+]i. Our results indicate that not only CCE but also non-CCE exist in TSM and that the latter is regulated by Rho-kinase, independent of actin cytoskeleton. In conclusion, Ca2+ influx regulated by the RhoA/Rho-kinase pathway may play a functional role in contraction by agonists.