Selectively targeting prostanoid E (EP) receptor-mediated cell signalling pathways: Implications for lung health and disease

Airways Relaxant and Antiasthmatic Activity of Aconitum heterophyllum Wall ex Royle. Roots: A Mechanistic Insight

Aconitum heterophyllum Wall ex Royle. (Ranunculaceae) is a traditional medicinal herb that has shown extensive pharmacological potential to treat cough, diarrhea, and infectious diseases but no scientific evidence is available to validate its antiasthmatic potential. In this study, we have investigated the tracheal relaxation and antiasthmatic activity of the selected bioactive fraction of A. heterophyllum. Chemical profiling of the most effective fraction obtained via bioassay-guided fractionation was done using LC-MS (Liquid chromatography-mass spectrometry, a technique utilized in the identification, separation, and quantification of known and unknown compounds). Molecular docking analysis of characterized constituents was performed to recognize the binding receptors, followed by an evaluation of the tracheal relaxation ability of active fraction. An acute oral toxicity study of the most effective fraction was done using OECD guidelines 423. Further, the therapeutic efficacy of the fraction was validated in asthma using a guinea pig model of ovalbumin (OVA) induced allergic asthma. The bio-guided activity revealed that hydro-methanolic extract of A. heterophyllum roots (F-1) was the most active fraction. LC-MS analysis of F-1 showed the presence of six major bioactive compounds in F-1. Molecular docking studies revealed strong binding affinities of identified constituents with histaminic receptor (H1) and muscarinic receptor (M3). The ex vivo study demonstrated smooth muscle relaxant activity of F-1 via dysregulating diverse signal transduction pathways viz. histaminic and muscarinic receptors antagonism (non-competitive), stimulation of β2-adrenergic receptor pathway, and soluble guanylyl cyclase activation. The findings of acute oral toxicity studies revealed that F-1 had no toxicity up to the dose of 2000 mg/Kg. The anti-asthmatic therapeutic efficacy of F-1 was further confirmed by the amelioration of respiratory hyperresponsiveness in asthmatic guinea pigs. This is the first evidence-based study showing the antiasthmatic therapeutic potential of the traditionally used herb A. heterophyllum through, computational and animal studies.

Prostaglandin E2 in the Tumor Microenvironment, a Convoluted Affair Mediated by EP Receptors 2 and 4

The involvement of the prostaglandin E2 (PGE2) system in cancer progression has long been recognized. PGE2 functions as an autocrine and paracrine signaling molecule with pleiotropic effects in the human body. High levels of intratumoral PGE2 and overexpression of the key metabolic enzymes of PGE2 have been observed and suggested to contribute to tumor progression. This has been claimed for different types of solid tumors, including, but not limited to, lung, breast, and colon cancer. PGE2 has direct effects on tumor cells and angiogenesis that are known to promote tumor development. However, one of the main mechanisms behind PGE2 driving cancerogenesis is currently thought to be anchored in suppressed antitumor immunity, thus providing possible therapeutic targets to be used in cancer immunotherapies. EP2 and EP4, two receptors for PGE2, are emerging as being the most relevant for this purpose. This review aims to summarize the known roles of PGE2 in the immune system and its functions within the tumor microenvironment. SIGNIFICANCE STATEMENT: Prostaglandin E2 (PGE2) has long been known to be a signaling molecule in cancer. Its presence in tumors has been repeatedly associated with disease progression. Elucidation of its effects on immunological components of the tumor microenvironment has highlighted the potential of PGE2 receptor antagonists in cancer treatment, particularly in combination with immune checkpoint inhibitor therapeutics. Adjuvant treatment could increase the response rates and the efficacy of immune-based therapies.

Revisiting prostaglandin E2: A promising therapeutic target for osteoarthritis

Osteoarthritis (OA) is a complex disease characterized by cartilage degeneration and persistent pain. Prostaglandin E2 (PGE2) plays a significant role in OA inflammation and pain. Recent studies have revealed the significant role of PGE2-mediated skeletal interoception in the progression of OA, providing new insights into the pathogenesis and treatment of OA. This aspect also deserves special attention in this review. Additionally, PGE2 is directly involved in pathologic processes including aberrant subchondral bone remodeling, cartilage degeneration, and synovial inflammation. Therefore, celecoxib, a commonly used drug to alleviate inflammatory pain through inhibiting PGE2, serves not only as an analgesic for OA but also as a potential disease-modifying drug. This review provides a comprehensive overview of the discovery history, synthesis and release pathways, and common physiological roles of PGE2. We discuss the roles of PGE2 and celecoxib in OA and pain from skeletal interoception and multiple perspectives. The purpose of this review is to highlight PGE2-mediated skeletal interoception and refresh our understanding of celecoxib in the pathogenesis and treatment of OA.

Inhibition of 15-hydroxyprostaglandin dehydrogenase protects neurons from ferroptosis in ischemic stroke

Ischemic stroke is an acute serious cerebrovascular disease with high mortality and disability. Ferroptosis is an important regulated cell death (RCD) in ischemic stroke. 15-Hydroxyprostaglandin dehydrogenase (15-PGDH), a degrading enzyme of prostaglandin E2 (PGE2), is shown to regulate RCD such as autophagy and apoptosis. The study aimed to determine whether 15-PGDH regulates ferroptosis and ischemic stroke, and further the exact mechanism. We demonstrated that overexpression of 15-PGDH in the brain tissues or primary cultured neurons significantly aggravated cerebral injury and neural ferroptosis in ischemic stroke. While inhibition of 15-PGDH significantly protected against cerebral injury and neural ferroptosis, which benefits arise from the activation of the PGE2/PGE2 receptor 4 (EP4) axis. While the impact of 15-PGDH was abolished with glutathione peroxidase 4 (GPX4) deficiency. Then, 15-PGDH inhibitor was found to promote the activation of cAMP-response element-binding protein (CREB) and nuclear factor kappa-B (NF-κB) via the PGE2/EP4 axis, subsequently transcriptionally upregulate the expression of GPX4. In summary, our study indicates that inhibition of 15-PGDH promotes the activation PGE2/EP4 axis, subsequently transcriptionally upregulates the expression of GPX4 via CREB and NF-κB, and then protects neurons from ferroptosis and alleviates the ischemic stroke. Therefore, 15-PGDH may be a potential therapeutic target for ischemic stroke.

Tylophora indica (Burm. f.) Merr alleviates tracheal smooth muscle hyperresponsiveness in ovalbumin-induced allergic-asthma model in guinea-pigs: Evidences from ex vivo, in silico and in vivo studies

BACKGROUND

Tylophora indica (Burm. f.) Merr is a climbing perennial plant reported in Indian traditional system of medicine for its use in allergy and asthma. However, only few scientific studies have been performed in the past to validate its antiasthmatic potential.

OBJECTIVES

The present study deals with investigation of airway smooth muscle relaxant and antiasthmatic potential of extract and subsequent fractions prepared from T. indica.

METHODS

The most active fraction of T. indica leaves selected through bio-guided activity was subjected to liquid chromatography-mass spectrometry (LC-MS) analysis for chemical profiling. The binding affinity of identified compounds in fraction towards M3 and H1 receptors was determined by molecular docking study. F-2 (chloroform fraction prepared from methanolic extract of T. indica leaves) was examined for its smooth muscle relaxant properties using isolated trachea of guinea-pig. Further, F-2 was evaluated through in vivo studies employing ovalbumin-induced asthma model in guinea-pigs.

RESULTS

F-2 was found most effective in bioassay-guided fractionation. Characterization by LC-MS analysis revealed presence of five major bioactive compounds in F-2 that showed good docking interactions with M3 and H1 receptors. The ex vivo study demonstrated that F-2 could significantly relax tracheal rings via targeting multiple signalling pathways videlicet, namely, noncompetitive antagonism of the histamine and muscarinic receptors, β2-adrenergic stimulation and activation of soluble guanylyl cyclase. In in vivo studies, F-2 ameliorated airway hyperresponsiveness and decreased broncho alveolar lavage fluid (BALF) levels of inflammatory cytokines and immunoglobulin E (IgE).

CONCLUSION

These results confirm the traditional use of T. indica as an antiasthmatic agent which are evidenced through ex vivo, in silico and in vivo studies.

Therapeutic Approaches for Chronic Obstructive Pulmonary Disease (COPD) Exacerbations

Chronic Obstructive Pulmonary Disease (COPD) is a progressive pulmonary disorder underpinned by poorly reversible airflow resulting from chronic bronchitis or emphysema. The prevalence and mortality of COPD continue to increase. Pharmacotherapy for patients with COPD has included antibiotics, bronchodilators, and anti-inflammatory corticosteroids (but with little success). Oral diseases have long been established as clinical risk factors for developing respiratory diseases. The establishment of a very similar microbiome in the mouth and the lung confirms the oral-lung connection. The aspiration of pathogenic microbes from the oral cavity has been implicated in several respiratory diseases, including pneumonia and chronic obstructive pulmonary disease (COPD). This review focuses on current and future pharmacotherapeutic approaches for COPD exacerbation including antimicrobials, mucoregulators, the use of bronchodilators and anti-inflammatory drugs, modifying epigenetic marks, and modulating dysbiosis of the microbiome.

Eicosanoid receptors as therapeutic targets for asthma

Eicosanoids comprise a group of oxidation products of arachidonic and 5,8,11,14,17-eicosapentaenoic acids formed by oxygenases and downstream enzymes. The two major pathways for eicosanoid formation are initiated by the actions of 5-lipoxygenase (5-LO), leading to leukotrienes (LTs) and 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE), and cyclooxygenase (COX), leading to prostaglandins (PGs) and thromboxane (TX). A third group (specialized pro-resolving mediators; SPMs), including lipoxin A4 (LXA4) and resolvins (Rvs), are formed by the combined actions of different oxygenases. The actions of the above eicosanoids are mediated by approximately 20 G protein-coupled receptors, resulting in a variety of both detrimental and beneficial effects on airway smooth muscle and inflammatory cells that are strongly implicated in asthma pathophysiology. Drugs targeting proinflammatory eicosanoid receptors, including CysLT1, the receptor for LTD4 (montelukast) and TP, the receptor for TXA2 (seratrodast) are currently in use, whereas antagonists of a number of other receptors, including DP2 (PGD2), BLT1 (LTB4), and OXE (5-oxo-ETE) are under investigation. Agonists targeting anti-inflammatory/pro-resolving eicosanoid receptors such as EP2/4 (PGE2), IP (PGI2), ALX/FPR2 (LXA4), and Chemerin1 (RvE1/2) are also being examined. This review summarizes the contributions of eicosanoid receptors to the pathophysiology of asthma and the potential therapeutic benefits of drugs that target these receptors. Because of the multifactorial nature of asthma and the diverse pathways affected by eicosanoid receptors, it will be important to identify subgroups of asthmatics that are likely to respond to any given therapy.

Pathophysiological regulation of lung function by the free fatty acid receptor FFA4

Increased prevalence of inflammatory airway diseases including asthma and chronic obstructive pulmonary disease (COPD) together with inadequate disease control by current frontline treatments means that there is a need to define therapeutic targets for these conditions. Here, we investigate a member of the G protein-coupled receptor family, FFA4, that responds to free circulating fatty acids including dietary omega-3 fatty acids found in fish oils. We show that FFA4, although usually associated with metabolic responses linked with food intake, is expressed in the lung where it is coupled to G_q/11 signaling. Activation of FFA4 by drug-like agonists produced relaxation of murine airway smooth muscle mediated at least in part by the release of the prostaglandin E₂ (PGE₂) that subsequently acts on EP₂ prostanoid receptors. In normal mice, activation of FFA4 resulted in a decrease in lung resistance. In acute and chronic ozone models of pollution-mediated inflammation and house dust mite and cigarette smoke-induced inflammatory disease, FFA4 agonists acted to reduce airway resistance, a response that was absent in mice lacking expression of FFA4. The expression profile of FFA4 in human lung was similar to that observed in mice, and the response to FFA4/FFA1 agonists similarly mediated human airway smooth muscle relaxation ex vivo. Our study provides evidence that pharmacological targeting of lung FFA4, and possibly combined activation of FFA4 and FFA1, has in vivo efficacy and might have therapeutic value in the treatment of bronchoconstriction associated with inflammatory airway diseases such as asthma and COPD.

Prostaglandin E2 receptors and their role in gastrointestinal motility - Potential therapeutic targets

Prostaglandin E2 (PGE2) is found throughout the gastrointestinal tract in a diverse variety of functions and roles. The recent discovery of four PGE2 receptor subtypes in intestinal muscle layers as well as in the enteric plexus has led to much interest in the study of their roles in gut motility. Gut dysmotility has been implicated in functional disease processes including irritable bowel syndrome (IBS) and slow transit constipation, and lubiprostone, a PGE2 derivative, has recently been licensed to treat both conditions. The diversity of actions of PGE2 in the intestinal tract is attributed to its differing effects on its downstream receptor types, as well as their varied distribution in the gut, in both health and disease. This review aims to identify the role and distribution of PGE2 receptors in the intestinal tract, and aims to elucidate their distinct role in gut motor function, with a specific focus on functional intestinal pathologies.

Effect of Prostanoids on Human Platelet Function: An Overview

Prostanoids are bioactive lipid mediators and take part in many physiological and pathophysiological processes in practically every organ, tissue and cell, including the vascular, renal, gastrointestinal and reproductive systems. In this review, we focus on their influence on platelets, which are key elements in thrombosis and hemostasis. The function of platelets is influenced by mediators in the blood and the vascular wall. Activated platelets aggregate and release bioactive substances, thereby activating further neighbored platelets, which finally can lead to the formation of thrombi. Prostanoids regulate the function of blood platelets by both activating or inhibiting and so are involved in hemostasis. Each prostanoid has a unique activity profile and, thus, a specific profile of action. This article reviews the effects of the following prostanoids: prostaglandin-D₂ (PGD₂), prostaglandin-E₁, -E₂ and E₃ (PGE₁, PGE₂, PGE₃), prostaglandin F_2α (PGF_2α), prostacyclin (PGI₂) and thromboxane-A₂ (TXA₂) on platelet activation and aggregation via their respective receptors.

International Union of Basic and Clinical Pharmacology. CIX. Differences and Similarities between Human and Rodent Prostaglandin E2 Receptors (EP1-4) and Prostacyclin Receptor (IP): Specific Roles in Pathophysiologic Conditions

Prostaglandins are derived from arachidonic acid metabolism through cyclooxygenase activities. Among prostaglandins (PGs), prostacyclin (PGI2) and PGE2 are strongly involved in the regulation of homeostasis and main physiologic functions. In addition, the synthesis of these two prostaglandins is significantly increased during inflammation. PGI2 and PGE2 exert their biologic actions by binding to their respective receptors, namely prostacyclin receptor (IP) and prostaglandin E2 receptor (EP) 1-4, which belong to the family of G-protein-coupled receptors. IP and EP1-4 receptors are widely distributed in the body and thus play various physiologic and pathophysiologic roles. In this review, we discuss the recent advances in studies using pharmacological approaches, genetically modified animals, and genome-wide association studies regarding the roles of IP and EP1-4 receptors in the immune, cardiovascular, nervous, gastrointestinal, respiratory, genitourinary, and musculoskeletal systems. In particular, we highlight similarities and differences between human and rodents in terms of the specific roles of IP and EP1-4 receptors and their downstream signaling pathways, functions, and activities for each biologic system. We also highlight the potential novel therapeutic benefit of targeting IP and EP1-4 receptors in several diseases based on the scientific advances, animal models, and human studies. SIGNIFICANCE STATEMENT: In this review, we present an update of the pathophysiologic role of the prostacyclin receptor, prostaglandin E2 receptor (EP) 1, EP2, EP3, and EP4 receptors when activated by the two main prostaglandins, namely prostacyclin and prostaglandin E2, produced during inflammatory conditions in human and rodents. In addition, this comparison of the published results in each tissue and/or pathology should facilitate the choice of the most appropriate model for the future studies.

Pharmacology and Therapeutics of Bronchodilators Revisited

Bronchodilators remain the cornerstone of the treatment of airway disorders such as asthma and chronic obstructive pulmonary disease (COPD). There is therefore considerable interest in understanding how to optimize the use of our existing classes of bronchodilator and in identifying novel classes of bronchodilator drugs. However, new classes of bronchodilator have proved challenging to develop because many of these have no better efficacy than existing classes of bronchodilator and often have unacceptable safety profiles. Recent research has shown that optimization of bronchodilation occurs when both arms of the autonomic nervous system are affected through antagonism of muscarinic receptors to reduce the influence of parasympathetic innervation of the lung and through stimulation of β ₂-adrenoceptors (β ₂-ARs) on airway smooth muscle with β ₂-AR-selective agonists to mimic the sympathetic influence on the lung. This is currently achieved by use of fixed-dose combinations of inhaled long-acting β ₂-adrenoceptor agonists (LABAs) and long-acting muscarinic acetylcholine receptor antagonists (LAMAs). Due to the distinct mechanisms of action of LAMAs and LABAs, the additive/synergistic effects of using these drug classes together has been extensively investigated. More recently, so-called "triple inhalers" containing fixed-dose combinations of both classes of bronchodilator (dual bronchodilation) and an inhaled corticosteroid in the same inhaler have been developed. Furthermore, a number of so-called "bifunctional drugs" having two different primary pharmacological actions in the same molecule are under development. This review discusses recent advancements in knowledge on bronchodilators and bifunctional drugs for the treatment of asthma and COPD. SIGNIFICANCE STATEMENT: Since our last review in 2012, there has been considerable research to identify novel classes of bronchodilator drugs, to further understand how to optimize the use of the existing classes of bronchodilator, and to better understand the role of bifunctional drugs in the treatment of asthma and chronic obstructive pulmonary disease.

Lippia alnifolia essential oil induces relaxation on Guinea-pig trachea by multiple pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Lippia alnifolia Mart. & Schauer, known as "alecrim-do-mato", "alecrim-de-vaqueiro" and "pedrécio", is used in folk medicine as antiseptic and to treat diseases that affect respiratory system, like bronchitis and asthma.

AIM OF THE STUDY

The aim of this work was to investigate the spasmolytic activity and relaxant mechanism of the Lippia alnifolia essential oil (EOLA) on isolated guinea-pig trachea and to correlate with its use in folk medicine.

MATERIALS AND METHODS

Leaves from L. alnifolia were collected in Pico das Almas, Chapada Diamantina, situated in the city of Rio de Contas, Bahia, Brazil. EOLA was extracted by hydrodistillation, analyzed by GC/FID and GC/MS and the volatile constituents were identified. Spasmolytic activity was assayed in isolated guinea-pig trachea pre-contracted with carbachol 1 μM or histamine 10 μM. Relaxant mechanism of EOLA was determined comparing concentration-response curves in the presence or absence of different blockers.

RESULTS

Chemical analysis revealed the presence of carvone (60 ± 0.8%) as major constituent. EOLA (1-243 μg/mL) relaxed isolated guinea-pig trachea pre-contracted with carbachol 1 μM [EC₅₀ = 53.36 (44.75-63.51) μg/mL] or histamine 10 μM [EC₅₀ = 5.42 (4.42-6.65) μg/mL]. The pre-incubation of 4-aminopyridine in histamine-induced contractions did not alter significantly the relaxant effect of EOLA. However, the presence of cesium chloride, glibenclamide, tetraethylammonium, propranolol, indomethacin, dexamethasone, hexamethonium, atropine, L-NAME, methylene blue or ODQ reduced EOLA relaxant effect. EOLA 18 μg/mL pre-incubation in calcium-free medium reduced histamine-evoked contractions, but did not alter histamine contractions in the presence of nifedipine.

CONCLUSIONS

Lippia alnifolia essential oil has spasmolytic activity on isolated guinea-pig trachea and its mechanism of action possibly involves the activation of multiple signal transduction pathways, which culminate in potassium channels activation and cytosolic calcium reduction.

The future of bronchodilation: looking for new classes of bronchodilators

Available bronchodilators can satisfy many of the needs of patients suffering from airway disorders, but they often do not relieve symptoms and their long-term use raises safety concerns. Therefore, there is interest in developing new classes that could help to overcome the limits that characterise the existing classes.At least nine potential new classes of bronchodilators have been identified: 1) selective phosphodiesterase inhibitors; 2) bitter-taste receptor agonists; 3) E-prostanoid receptor 4 agonists; 4) Rho kinase inhibitors; 5) calcilytics; 6) agonists of peroxisome proliferator-activated receptor-γ; 7) agonists of relaxin receptor 1; 8) soluble guanylyl cyclase activators; and 9) pepducins. They are under consideration, but they are mostly in a preclinical phase and, consequently, we still do not know which classes will actually be developed for clinical use and whether it will be proven that a possible clinical benefit outweighs the impact of any adverse effect.It is likely that if developed, these new classes may be a useful addition to, rather than a substitution of, the bronchodilator therapy currently used, in order to achieve further optimisation of bronchodilation.

Role of the PGE2 receptor subtypes EP1, EP2, and EP3 in repetitive traumatic brain injury

Aims

The goal was to explore the signaling pathways of PGE₂ to investigate therapeutic effects against secondary injuries following TBI.

Methods

Young (4.9 ± 1.0 months) and aged (20.4 ± 1.4 months) male wild type (WT) C57BL/6 and PGE₂ EP1, 2, and 3 receptor knockout mice were selected to either receive sham or repetitive concussive head injury. Immunohistochemistry protocols with Iba1 and GFAP were performed to evaluate microgliosis and astrogliosis in the hippocampus, two critical components of neuroinflammation. Passive avoidance test measured memory function associated with the hippocampus.

Results

No differences in hippocampal microgliosis were found when aged EP2^−/− and EP3^−/− mice were compared with aged WT mice. However, the aged EP1^−/− mice had 69.2 ± 7.5% less hippocampal microgliosis in the contralateral hemisphere compared with WT aged mice. Compared with aged EP2^−/− and EP3^−/−, EP1^−/− aged mice had 78.9 ± 5.1% and 74.7 ± 6.2% less hippocampal microgliosis in the contralateral hemisphere. Within the EP1^−/− mice, aged mice had 90.7 ± 2.7% and 81.1 ± 5.6% less hippocampal microgliosis compared with EP1^−/− young mice in the contralateral and ipsilateral hemispheres, respectively. No differences were noted in all groups for astrogliosis. There was a significant difference in latency time within EP1^−/−, EP2^−/−, and EP3^−/− on day 1 and day 2 in aged and young mice.

Conclusion

These findings demonstrate that the PGE₂ EP receptors may be potential therapeutic targets to treat repetitive concussions and other acute brain injuries.

Prostaglandin E2, but not cAMP nor β2-agonists, induce tristetraprolin (TTP) in human airway smooth muscle cells

Tristetraprolin (TTP) is an anti-inflammatory molecule known to post-transcriptionally regulate cytokine production and is, therefore, an attractive drug target for chronic respiratory diseases driven by inflammation, such as asthma and chronic obstructive pulmonary disease. Our recent in vitro studies in primary human airway smooth (ASM) cells have confirmed the essential anti-inflammatory role played by TTP as a critical partner in a cytokine regulatory network. However, several unanswered questions remain. While prior in vitro studies have suggested that TTP is regulated in a cAMP-mediated manner, raising the possibility that this may be one of the ways in which β₂-agonists achieve beneficial effects beyond bronchodilation, the impact of β₂-agonists on ASM cells is unknown. Furthermore, the effect of prostaglandin E₂ (PGE₂) on TTP expression in ASM cells has not been reported. We address this herein and reveal, for the first time, that TTP is not regulated by cAMP-activating agents nor following treatment with long-acting β₂-agonists. However, PGE₂ does induce TTP mRNA expression and protein upregulation in ASM cells. Although the underlying mechanism of action remains undefined, we can confirm that PGE₂-induced TTP upregulation is not mediated via cAMP, or EP₂/EP₄ receptor activation, and occurred in a manner independent of the p38 MAPK-mediated pathway. Taken together, these data confirm that β₂-agonists do not upregulate TTP in human ASM cells and indicate that another way in which PGE₂ may achieve beneficial effects in asthma and COPD may be via upregulation of the master controller of inflammation-TTP.

EP2 and EP4 receptor antagonists: Impact on cytokine production and β2 -adrenergic receptor desensitization in human airway smooth muscle

Prostaglandin E₂ (PGE₂ ) is a key prostanoid known to have both proinflammatory and anti-inflammatory impact in the context of chronic respiratory diseases. We hypothesize that these opposing effects may be the result of different prostanoid E (EP) receptor-mediated signaling pathways. In this study, we focus on two of the four EP receptors, EP₂ and EP₄ , as they are known to induce cyclic adenosine monophosphate (cAMP)-dependent signaling pathways. Using primary human airway smooth muscle (ASM) cells, we first focussed on the PGE₂ -induced production of two cAMP-dependent proinflammatory mediators: interleukin 6 (IL-6) and cyclo-oxygenase 2 production. We show that PGE₂ -induced IL-6 protein secretion occurs via an EP₂ -mediated pathway, in a manner independent of receptor-mediated effects on messenger RNA (mRNA) expression and temporal activation kinetics of the transcription factor cAMP response element binding. Moreover, stimulation of ASM with PGE₂ did not establish a positive, receptor-mediated, feedback loop, as mRNA expression for EP₂ and EP₄ receptors were not upregulated and receptor antagonists were without effect. Our studies revealed that the EP₂ , but not the EP₄ , receptor is responsible for β₂ -adrenergic desensitization induced by PGE₂ . We demonstrate that PGE₂ -induced heterologous receptor desensitization responsible for tachyphylaxis to short- (salbutamol) or long- (formoterol) β₂ -agonists (measured by cAMP release) can be reversed by the EP₂ receptor antagonist PF-04418948. Importantly, this study highlights that inhibiting the EP₂ receptor restores β₂ -adrenergic receptor function in vitro and offers an attractive novel therapeutic target for treating infectious exacerbations in people suffering from chronic respiratory diseases in the future.

Altered lung biology of healthy never smokers following acute inhalation of E-cigarettes

Background

Little is known about health risks associated with electronic cigarette (EC) use although EC are rising in popularity and have been advocated as a means to quit smoking cigarettes.

Methods

Ten never-smokers, without exposure history to tobacco products or EC, were assessed at baseline with questionnaire, chest X-ray, lung function, plasma levels of endothelial microparticles (EMP), and bronchoscopy to obtain small airway epithelium (SAE) and alveolar macrophages (AM). One week later, subjects inhaled 10 puffs of “Blu” brand EC, waited 30 min, then another 10 puff; n = 7 were randomized to EC with nicotine and n = 3 to EC without nicotine to assess biological responses in healthy, naive individuals.

Results

Two hr. post-EC exposure, subjects were again assessed as at baseline. No significant changes in clinical parameters were observed. Biological changes were observed compared to baseline, including altered transcriptomes of SAE and AM for all subjects and elevated plasma EMP levels following inhalation of EC with nicotine.

Conclusions

This study provides in vivo human data demonstrating that acute inhalation of EC aerosols dysregulates normal human lung homeostasis in a limited cohort of healthy naïve individuals. These observations have implications to new EC users, nonsmokers exposed to secondhand EC aerosols and cigarette smokers using EC to quit smoking.

Trial registration

ClinicalTrials.gov NCT01776398 (registered 10/12/12), NCT02188511 (registered 7/2/14).

Electronic supplementary material

The online version of this article (10.1186/s12931-018-0778-z) contains supplementary material, which is available to authorized users.

EP4 Agonist L-902,688 Suppresses EndMT and Attenuates Right Ventricular Cardiac Fibrosis in Experimental Pulmonary Arterial Hypertension

Right ventricular (RV) hypertrophy is characterized by cardiac fibrosis due to endothelial–mesenchymal transition (EndMT) and increased collagen production in pulmonary arterial hypertension (PAH) patients, but the mechanisms for restoring RV function are unclear. Prostanoid agonists are effective vasodilators for PAH treatment that bind selective prostanoid receptors to modulate vascular dilation. The importance of prostanoid signaling in the RV is not clear. We investigated the effects of the EP4-specific agonist L-902,688 on cardiac fibrosis and TGF-β-induced EndMT. EP4-specific agonist treatment reduced right ventricle fibrosis in the monocrotaline (MCT)-induced PAH rat model. L-902,688 (1 µM) attenuated TGF-β-induced Twist and α-smooth muscle actin (α-SMA) expression, but these effects were reversed by AH23848 (an EP4 antagonist), highlighting the crucial role of EP4 in suppressing TGF-β-induced EndMT. These data indicate that the selective EP4 agonist L-902,688 attenuates RV fibrosis and suggest a potential approach to reducing RV fibrosis in patients with PAH.