Prostaglandin E2 mediates cough via the EP3 receptor: implications for future disease therapy

The role of neutrophils in chronic cough

Chronic cough is a common disorder lasting more than 8 weeks and affecting all age groups. The evidence supporting the role of neutrophils in chronic cough pathology is based on many patients with chronic cough developing airway neutrophilia. How neutrophils influence the development of chronic cough is unknown. However, they are likely involved in multiple aspects of cough etiology, including promoting airway inflammation, airway remodeling, hyper-responsiveness, local neurogenic inflammation, and other possible mechanisms. Neutrophilic airway inflammation is also associated with refractory cough, poor control of underlying diseases (e.g., asthma), and insensitivity to cough suppressant therapy. The potential for targeting neutrophils in chronic cough needs exploration, including developing new drugs targeting one or more neutrophil-mediated pathways or altering the neutrophil phenotype to alleviate chronic cough. How the airway microbiome differs, plays a role, and interacts with neutrophils in different cough etiologies is poorly understood. Future studies should focus on understanding the relationship between the airway microbiome and neutrophils.

Renal vein thrombosis in a patient secondary to high-grade rhabdoid renal cell carcinoma: a case report and review of literature

Introduction

Renal cell carcinoma, a common kidney tumour which is often incidentally discovered on imaging, can manifest with atypical symptoms. Renal cell carcinoma with rhabdoid features is a rare occurrence and even rarer in case of adults. Renal cell carcinoma has the tendency to form thrombus that can migrate to renal vein, inferior vena cava and even right atrium.

Case presentation

The authors report a case of an 81-year-old male with rhabdoid renal cell carcinoma presenting with persistent cough for 6-7 months. with tumour thrombus extending into the renal vein and hepatic inferior vena cava. The patient was found feeble for the surgery and hence was treated on anticancer drugs pembrolizumab and axitinib.

Conclusion

Renal cell carcinoma has the tendency to form tumour thrombus in renal vein and inferior vena cava. Prognosis without surgical intervention in these conditions is very poor.

Mast Cells in Aspirin-Exacerbated Respiratory Disease

PURPOSE OF REVIEW

Aspirin-exacerbated respiratory disease (AERD) is a syndrome of high type 2 inflammation and is known to critically involve mast cell activation. The mast cell is an important cell in the baseline inflammatory processes in the upper and lower airway by maintaining and amplifying type 2 inflammation. But it also is prominent in the hypersensitivity reaction to COX-1 inhibition which defines this condition.

RECENT FINDINGS

Recent work highlights the mast cell as a focal point in AERD pathogenesis. Using AERD as a specific model of both high type 2 asthma and chronic sinusitis, the role of mast cell activity can be better understood in other aspects of airway inflammation. Further dissecting out the mechanism of COX-1-mediated mast cell activation in AERD will be an important next phase in our understanding of NSAID-induced hypersensitivity as well as AERD pathophysiology.

Research Progress on TRPA1 in Diseases

For a long time, the physiological activity of TRP ion channels and the response to various stimuli have been the focus of attention, and the physiological functions mediated by ion channels have subtle links with the occurrence of various diseases. Our group has been engaged in the study of ion channels. In recent years, the report rate of TRPA1, the only member of the TRPA subfamily in the newly described TRP channel, has been very high. TRPA1 channels are not only abundantly expressed in peptidergic nociceptors but are also found in many nonneuronal cell types and tissues, and through the regulation of Ca2+ influx, various neuropeptides and signaling pathways are involved in the regulation of nerves, respiration, circulation, and various diseases and inflammation throughout the body. In this review, we mainly summarize the effects of TRPA1 on various systems in the body, which not only allows us to have a more systematic and comprehensive understanding of TRPA1 but also facilitates more in-depth research on it in the future.

Prorelaxant E-type Prostanoid Receptors Functionally Partition to Different Procontractile Receptors in Airway Smooth Muscle

Prostaglandin E2 imparts diverse physiological effects on multiple airway cells through its actions on four distinct E-type prostanoid (EP) receptor subtypes (EP1-EP4). Gs-coupled EP2 and EP4 receptors are expressed on airway smooth muscle (ASM), yet their capacity to regulate the ASM contractile state remains subject to debate. We used EP2 and EP4 subtype-specific agonists (ONO-259 and ONO-329, respectively) in cell- and tissue-based models of human ASM contraction-magnetic twisting cytometry (MTC), and precision-cut lung slices (PCLSs), respectively-to study the EP2 and EP4 regulation of ASM contraction and signaling under conditions of histamine or methacholine (MCh) stimulation. ONO-329 was superior (<0.05) to ONO-259 in relaxing MCh-contracted PCLSs (log half maximal effective concentration [logEC50]: 4.9 × 10-7 vs. 2.2 × 10-6; maximal bronchodilation ± SE, 35 ± 2% vs. 15 ± 2%). However, ONO-259 and ONO-329 were similarly efficacious in relaxing histamine-contracted PCLSs. Similar differential effects were observed in MTC studies. Signaling analyses revealed only modest differences in ONO-329- and ONO-259-induced phosphorylation of the protein kinase A substrates VASP and HSP20, with concomitant stimulation with MCh or histamine. Conversely, ONO-259 failed to inhibit MCh-induced phosphorylation of the regulatory myosin light chain (pMLC20) and the F-actin/G-actin ratio (F/G-actin ratio) while effectively inhibiting their induction by histamine. ONO-329 was effective in reversing induced pMLC20 and the F/G-actin ratio with both MCh and histamine. Thus, the contractile-agonist-dependent differential effects are not explained by changes in the global levels of phosphorylated protein kinase A substrates but are reflected in the regulation of pMLC20 (cross-bridge cycling) and F/G-actin ratio (actin cytoskeleton integrity, force transmission), implicating a role for compartmentalized signaling involving muscarinic, histamine, and EP receptor subtypes.

Association of lower plasma citric acid with prolonged cough: the Nagahama study

Little is known about the association of prolonged cough, a common and troublesome symptom, with metabolic pathways. We aimed to clarify this association using data from the Nagahama cohort, a prospective study of participants from the general population. Self-report questionnaires on prolonged cough were collected at baseline and 5-year follow-up assessments. Blood tests at follow-up were used for gas chromatography-mass spectrometry-based metabolomics. The association between metabolites and prolonged cough was examined using the partial least squares discriminant analysis and multiple regression analysis. Among the 7432 participants, 632 had newly developed prolonged cough at follow-up, which was defined as "new-onset prolonged cough". Low plasma citric acid was significantly associated with new-onset prolonged cough, even after the adjustment of confounding factors including the presence of asthma, upper airway cough syndrome (UACS), and gastroesophageal reflux disease (GERD). A similar association was observed for isocitric acid, 3-hydroxybutyric acid, and 3-hydroxyisobutyric acid. The analysis of these four metabolites revealed that citric acid had the strongest association with new-onset prolonged cough. This significant association remained even when the analysis was confined to participants with UACS or GERD at baseline or follow-up, and these associations were also observed in participants (n = 976) who had prolonged cough at follow-up regardless of baseline status. In conclusion, low blood citric acid may be associated with prolonged cough.

Infectious and Inflammatory Pathways to Cough

Coughing is a dynamic physiological process resulting from input of vagal sensory neurons innervating the airways and perceived airway irritation. Although cough serves to protect and clear the airways, it can also be exploited by respiratory pathogens to facilitate disease transmission. Microbial components or infection-induced inflammatory mediators can directly interact with sensory nerve receptors to induce a cough response. Analysis of cough-generated aerosols and transmission studies have further demonstrated how infectious disease is spread through coughing. This review summarizes the neurophysiology of cough, cough induction by respiratory pathogens and inflammation, and cough-mediated disease transmission.

Mini-review: Hypertussivity and allotussivity in chronic cough endotypes

In recent years our understanding of the neurophysiological basis of cough has increased substantially. In conjunction, concepts around the drivers of chronic coughing in patients have also significantly evolved. Increasingly it is recognised that dysregulation of the neuronal pathways mediating cough play an important role in certain phenotypes of chronic cough and therefore pathological processes affecting the nervous system are likely to represent key endotypes in patients. Taking inspiration from the study of neuropathic pain, the term hypertussia has been employed to describe the phenomenon of abnormal excessive coughing in response to airway irritation and allotussia to describe coughing in response to stimuli not normally provoking cough. This review aims to summarise current clinical evidence supporting a role for the hyperexcitability of neuronal pathways contributing to chronic coughing and suggest how these might align with the clinical features observed in patients.

The role of PGE2 and EP receptors on lung's immune and structural cells; possibilities for future asthma therapy

Asthma is the most common airway chronic disease with treatments aimed mainly to control the symptoms. Adrenergic receptor agonists, corticosteroids and anti-leukotrienes have been used for decades, and the development of more targeted asthma treatments, known as biological therapies, were only recently established. However, due to the complexity of asthma and the limited efficacy as well as the side effects of available treatments, there is an urgent need for a new generation of asthma therapies. The anti-inflammatory and bronchodilatory effects of prostaglandin E2 in asthma are promising, yet complicated by undesirable side effects, such as cough and airway irritation. In this review, we summarize the most important literature on the role of all four E prostanoid (EP) receptors on the lung's immune and structural cells to further dissect the relevance of EP2/EP4 receptors as potential targets for future asthma therapy.

Neurokinin 1 and 2 Receptors Are Involved in PEG2- and Citric Acid-Induced Cough and Ventilatory Responses

Exposure to aerosolized citric acid (CA, 150mM) and prostaglandin E₂ (PGE₂, 0.43mM) for 10min in guinea pigs reportedly produces the distinct cough patterns (Type I vs. II) and ventilatory responses (long-lasting hyperventilation vs. brief tachypnea) even though triggering the same cough numbers. Type I and II coughs are primarily mediated by activation of TRPV1 and EP3 receptors (a PGE₂ receptor) of vagal C-fibers respectively. Substance P (SP) and neurokinin A (NKA) released by vagal pulmonary sensory fibers peripherally are capable of affecting CA-induced cough and ventilation via preferentially activating neurokinin 1 and 2 receptors (NK₁R and NK₂R) respectively. This study aimed to define the impacts of CA- and PGE₂-exposure on pulmonary SP and NKA levels and the roles of NK₁R and NK₂R in modulating CA- and PGE₂-evoked cough and ventilatory responses. In unanesthetized guinea pigs, we determined: 1) pulmonary SP and NKA contents induced by the CA- or PGE₂-exposure; 2) effects of CP-99994 and SR-48968 (a NK₁R and a NK₂R antagonist respectively) given by intraperitoneal injection (IP) or aerosol inhalation (IH) on the CA- and PGE₂-evoked cough and ventilatory responses; and 3) immunocytochemical expressions of NK₁R/NK₂R in vagal C-neurons labeled by TRPV1 or EP3 receptors. We found that CA- and PGE₂-exposure evoked Type I and II cough respectively associated with different degrees of increases in pulmonary SP and NKA. Applications of CP-99994 and SR-48968 via IP and IH efficiently suppressed the cough responses to CA with less impact on the cough response to PGE₂. These antagonists inhibited or blocked the ventilatory response to CA and caused hypoventilation in response to PGE₂. Moreover, NK₁R and NK₂R were always co-expressed in vagal C-neurons labeled by TRPV1 or EP3 receptors. These results suggest that SP and NKA endogenously released by CA- and PGE₂-exposure play important roles in generating the cough and ventilatory responses to CA and PGE₂, at least in part, via activation of NK₁R and NK₂R expressed in vagal C-neurons (pulmonary C-neurons).

The Mechanism of Pertussis Cough Revealed by the Mouse-Coughing Model

Pertussis, also known as whooping cough, is a contagious respiratory disease caused by the Gram-negative bacterium Bordetella pertussis. This disease is characterized by severe and uncontrollable coughing, which imposes a significant burden on patients. However, its etiological agent and the mechanism are totally unknown because of a lack of versatile animal models that reproduce the cough. Here, we present a mouse model that reproduces coughing after intranasal inoculation with the bacterium or its components and demonstrate that lipooligosaccharide (LOS), pertussis toxin (PTx), and Vag8 of the bacterium cooperatively function to cause coughing. Bradykinin induced by LOS sensitized a transient receptor potential ion channel, TRPV1, which acts as a sensor to evoke the cough reflex. Vag8 further increased bradykinin levels by inhibiting the C1 esterase inhibitor, the major downregulator of the contact system, which generates bradykinin. PTx inhibits intrinsic negative regulation systems for TRPV1 through the inactivation of G_i GTPases. Our findings provide a basis to answer long-standing questions on the pathophysiology of pertussis cough.

Prostaglandin E2 sensitizes the cough reflex centrally via EP3 receptor-dependent activation of NaV 1.8 channels

Background

Cough hypersensitivity is a major characteristic feature associated with several types of cough, including chronic cough, but its underlying mechanisms remain to be fully understood. Inflammatory mediators, such as prostaglandin E₂ (PGE₂), have been implicated in both peripheral induction and sensitization of the cough reflex. In this study, using a conscious guinea pig model of cough, we investigated whether PGE₂ can sensitize the cough reflex via central actions and, if so, via which mechanisms.

Methods

All drugs were administered by intracerebroventricular (i.c.v.) route and whole-body plethysmograph set-up was used for both induction, using aerosolized citric acid (0.2 M), and recording of cough. Immunohistochemistry was performed to confirm the expression of NaV 1.8 channels in the nucleus tractus solitarius (nTS).

Results

We show that both PGE₂ and the non-selective EP1/EP3 agonist, sulprostone, dose-dependently enhanced the citric acid-induced cough (P ≤ 0.001, P ≤ 0.01, respectively). Pretreatment with the EP1 antagonist, ONO-8130, did not affect the sulprostone-induced cough sensitization, whilst the EP3 antagonist, L-798,106, dose-dependently inhibited this effect (P ≤ 0.05). Furthermore, treatment with either the EP2 agonist, butaprost or the EP4 agonist, L-902,688, had no effect on cough sensitization. Additionally, pretreatment with either the TRPV1 antagonist, JNJ-17203212 or the TRPA1 antagonist, HC-030031, alone or in combination, nor with the NaV 1.1, 1.2, 1.3, 1.4, 1.6 and 1.7 channel blocker, tetrodotoxin, had any effect on the cough. In contrast, pretreatment with the NaV 1.8 antagonist, A-803467, dose-dependently inhibited this effect (P ≤ 0.05). Furthermore, NaV 1.8 channels were shown to be expressed in the nTS.

Conclusion

Collectively, our findings show that PGE₂ sensitizes the cough reflex centrally via EP3 receptor-dependent activation of NaV 1.8 but independently of TRPV1,TRPA1 and TTX-sensitive sodium channel activation. These results indicate that PGE₂ plays an important role in central sensitization of the cough reflex and suggest that central EP3 receptors and/or NaVv 1.8 channels may represent novel antitussive molecular targets.

Graphical Abstract

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.

Myeloid-Derived Suppressor Cells Dampen Airway Inflammation Through Prostaglandin E2 Receptor 4

Emerging evidence suggests a mechanistic role for myeloid-derived suppressor cells (MDSCs) in lung diseases like asthma. Previously, we showed that adoptive transfer of MDSCs dampens lung inflammation in murine models of asthma through cyclooxygenase-2 and arginase-1 pathways. Here, we further dissected this mechanism by studying the role and therapeutic relevance of the downstream mediator prostaglandin E2 receptor 4 (EP4) in a murine model of asthma. We adoptively transferred MDSCs generated using an EP4 agonist in a murine model of asthma and studied the consequences on airway inflammation. Furthermore, pegylated human arginase-1 was used to model MDSC effector activities. We demonstrate that the selective EP4 agonist L-902,688 increased the number and suppressive activity of MDSCs through arginase-1 and nitric oxide synthase-2. These results showed that adoptive transfer of EP4-primed MDSCs, EP4 agonism alone or arginase-1 administration ameliorated lung inflammatory responses and histopathological changes in asthmatic mice. Collectively, our results provide evidence that MDSCs dampen airway inflammation in murine asthma through a mechanism involving EP4.

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.

Can GPCRs Be Targeted to Control Inflammation in Asthma?

Historically, the drugs used to manage obstructive lung diseases (OLDs), asthma, and chronic obstructive pulmonary disease (COPD) either (1) directly regulate airway contraction by blocking or relaxing airway smooth muscle (ASM) contraction or (2) indirectly regulate ASM contraction by inhibiting the principal cause of ASM contraction/bronchoconstriction and airway inflammation. To date, these tasks have been respectively assigned to two diverse drug types: agonists/antagonists of G protein-coupled receptors (GPCRs) and inhaled or systemic steroids. These two types of drugs "stay in their lane" with respect to their actions and consequently require the addition of the other drug to effectively manage both inflammation and bronchoconstriction in OLDs. Indeed, it has been speculated that safety issues historically associated with beta-agonist use (beta-agonists activate the beta-2-adrenoceptor (β₂AR) on airway smooth muscle (ASM) to provide bronchoprotection/bronchorelaxation) are a function of pro-inflammatory actions of β₂AR agonism. Recently, however, previously unappreciated roles of various GPCRs on ASM contractility and on airway inflammation have been elucidated, raising the possibility that novel GPCR ligands targeting these GPCRs can be developed as anti-inflammatory therapeutics. Moreover, we now know that many GPCRs can be "tuned" and not just turned "off" or "on" to specifically activate the beneficial therapeutic signaling a receptor can transduce while avoiding detrimental signaling. Thus, the fledging field of biased agonism pharmacology has the potential to turn the β₂AR into an anti-inflammatory facilitator in asthma, possibly reducing or eliminating the need for steroids.

Characterisation of cough evoked by inhaled treprostinil and treprostinil palmitil

Cough is induced by inhaled prostacyclin analogues including treprostinil (TRE), and, at higher doses, treprostinil palmitil (TP), a prodrug of TRE. In this report, we have investigated mechanisms involved in TRE- and TP-induced cough, using a dry powder formulation of TP (TPIP) to supplement previous data obtained with an aqueous suspension formulation of TP (TPIS).

Experiments in guinea pigs and rats investigated the prostanoid receptor subtype producing cough and whether it involved activation of sensory nerves in the airways and vasculature. Experiments involved treatment with prostanoid, tachykinin and bradykinin receptor antagonists, a cyclooxygenase inhibitor and TRE administration to the isolated larynx or intravenously.

In guinea pigs, cough with inhaled TRE (1.23 µg·kg⁻¹) was not observed with an equivalent dose of TPIP and required higher inhaled doses (12.8 and 35.8 µg·kg⁻¹) to induce cough. TRE cough was blocked with IP and tachykinin NK₁ receptor antagonists but not with EP₁, EP₂, EP₃, DP₁ or bradykinin B₂ antagonists or a cyclooxygenase inhibitor. TRE administered to the isolated larynx or intravenously in rats produced no apnoea or swallowing, whereas citric acid, capsaicin and hypertonic saline had significant effects.

The mechanisms inducing cough with inhaled TRE likely involves the activation of prostanoid IP receptors on jugular C-fibres in the tracheobronchial airways. Cough induced by inhaled dry powder and nebulised formulations of TP occurs at higher inhaled doses than TRE, presumably due to the slow, sustained release of TRE from the prodrug resulting in lower concentrations of TRE at the airway sensory nerves.

Cough induced by inhaled treprostinil and treprostinil palmitil involves the activation of prostacyclin (IP) receptors located on airway tachykinin nerveshttps://bit.ly/37sXz1I

Cross-effect of TRPV1 and EP3 receptor on coughs and bronchopulmonary C-neural activities

Prostaglandin E₂ (PGE₂)-induced coughs in vivo and vagal nerve depolarization in vitro are inhibited by systemic and local administration of prostaglandin EP3 receptor (L-798106) and TRPV1 antagonists (JNJ 17203212). These results indicate a modulating effect of TRPV1 on the EP3 receptor-mediated cough responses to PGE₂ likely through the vagal sensory nerve. This study aimed to determine whether 1) inhalation of aerosolized JNJ 17203212 and L-798106 affected cough responses to citric acid (CA, mainly stimulating TRPV1) and PGE₂; 2) TRPV1 and EP3 receptor morphologically are co-expressed and electrophysiologically functioned in the individual of vagal pulmonary C-neurons (cell bodies of bronchopulmonary C-fibers in the nodose/jugular ganglia); and 3) there was a cross-effect of TRPV1 and EP3 receptor on these neural excitations. To this end, aerosolized CA or PGE₂ was inhaled by unanesthetized guinea pigs pretreated without or with each antagonist given in aerosol form. Immunofluorescence was applied to identify the co-expression of TRPV1 and EP3 receptor in vagal pulmonary C-neurons (retrogradely traced by DiI). Whole-cell voltage patch clamp approach was used to detect capsaicin (CAP)- and PGE₂-induced currents in individual vagal pulmonary C-neurons and determine the effects of the TRPV1 and EP3 receptor antagonists on the evoked currents. We found that PGE₂-induced cough was attenuated by JNJ 17203212 or L-798106 and CA-evoked cough greatly suppressed only by JNJ 17203212. Approximately 1/4 of vagal pulmonary C-neurons co-expressed EP3 with a cell size < 20 μm. Both CAP- and PGE₂-induced currents could be recorded in the individuals of some vagal pulmonary C-neurons. The former was largely inhibited only by JNJ 17203212, while the latter was suppressed by JNJ 17203212 or L-798106. The similarity of the cross-effect of both antagonists on cough and vagal pulmonary C-neural activity suggests that a subgroup of vagal pulmonary C-neurons co-expressing TRPV1 and EP3 receptor is, at least in part, responsible for the cough response to PGE₂.

Prostanoid receptor subtypes involved in treprostinil-mediated vasodilation of rat pulmonary arteries and in treprostinil-mediated inhibition of collagen gene expression of human lung fibroblasts

Treprostinil (TRE) is a potent pulmonary vasodilator with effects on other pathological aspects of pulmonary arterial hypertension. In this study, the prostanoid receptors involved in TRE-induced relaxation of isolated rat pulmonary arteries and TRE-induced inhibition of increased gene expression in collagen synthesis and contractility of human lung fibroblasts were determined. TRE (0.01-100 μM) relaxed prostaglandin F2α-precontracted rat pulmonary arteries which was attenuated by denudation of the vascular endothelium. TRE-induced relaxation was predominantly blocked by the IP receptor antagonist RO3244194 (1 μM), with slightly greater inhibition in endothelium-denuded tissue. At higher TRE concentrations (> 1 μM), the DP1 receptor antagonist BW A868C (1 μM) also inhibited relaxation reaching significance above 10 μM. In contrast, the EP3 receptor antagonist L798106 (1 μM) accentuated TRE-induced relaxation of pulmonary arteries with intact endothelium. In human lung fibroblasts, the EP2 receptor antagonist PF-04418948 (1 μM) blocked transforming growth factor β1 (TGF-β1)-increased expression of collagen synthesis (COL1A1 and COL1A2) and fibroblast contractility (ACTG2) genes in presence of TRE (0.1 μM). In conclusion, the IP receptor located on rat pulmonary vascular smooth muscle and endothelium is the primary receptor mediating vasorelaxation, while the DP1 receptor present on the rat endothelium is involved only at higher TRE concentrations. In human lung fibroblasts, the EP2 receptor is the dominant receptor subtype involved in suppression of increased collagen synthesis and fibroblast contractility gene expression induced by TGF-β1 in the presence of TRE.

Could Arachidonic Acid-Derived Pro-Resolving Mediators Be a New Therapeutic Strategy for Asthma Therapy?

Asthma represents one of the leading chronic diseases worldwide and causes a high global burden of death and disability. In asthmatic patients, the exacerbation and chronification of the inflammatory response are often related to a failure in the resolution phase of inflammation. We reviewed the role of the main arachidonic acid (AA) specialized pro-resolving mediators (SPMs) in the resolution of chronic lung inflammation of asthmatics. AA is metabolized by two classes of enzymes, cyclooxygenases (COX), which produce prostaglandins (PGs) and thromboxanes, and lypoxygenases (LOX), which form leukotrienes and lipoxins (LXs). In asthma, two primary pro-resolving derived mediators from COXs are PGE₂ and the cyclopentenone prostaglandin15-Deoxy-Delta-12,14-PGJ₂ (15d-PGJ₂) while from LOXs are the LXA₄ and LXB₄. In different models of asthma, PGE₂, 15d-PGJ₂, and LXs reduced lung inflammation and remodeling. Furthermore, these SPMs inhibited chemotaxis and function of several inflammatory cells involved in asthma pathogenesis, such as eosinophils, and presented an antiremodeling effect in airway epithelial, smooth muscle cells and fibroblasts in vitro. In addition, PGE₂, 15d-PGJ₂, and LXs are all able to induce macrophage reprogramming to an alternative M2 pro-resolving phenotype in vitro and in vivo. Although PGE₂ and LXA₄ showed some beneficial effects in asthmatic patients, there are limitations to their clinical use, since PGE₂ caused side effects, while LXA₄ presented low stability. Therefore, despite the strong evidence that these AA-derived SPMs induce resolution of both inflammatory response and tissue remodeling in asthma, safer and more stable analogs must be developed for further clinical investigation of their application in asthma treatment.

Prostanoid Receptors of the EP4-Subtype Mediate Gene Expression Changes in Human Airway Epithelial Cells with Potential Anti-Inflammatory Activity

There is a clear, unmet clinical need to identify new drugs to treat individuals with asthma, chronic obstructive pulmonary disease (COPD), and idiopathic pulmonary fibrosis (IPF) in whom current medications are either inactive or suboptimal. In preclinical models, EP₄-receptor agonists display efficacy, but their mechanism of action is unclear. In this study, using human bronchial epithelial cells as a therapeutically relevant drug target, we hypothesized that changes in gene expression may play an important role. Several prostanoid receptor mRNAs were detected in BEAS-2B cells, human primary bronchial epithelial cells (HBECs) grown in submersion culture and HBECs grown at an air-liquid interface with PTGER4 predominating. By using the activation of a cAMP response element reporter in BEAS-2B cells as a surrogate of gene expression, Schild analysis determined that PTGER4 mRNAs encoded functional EP₄-receptors. Moreover, inhibitors of phosphodiesterase 4 (roflumilast N-oxide [RNO]) and cAMP-dependent protein kinase augmented and attenuated, respectively, reporter activation induced by 2-[3-[(1R,2S,3R)-3-hydroxy-2-[(E,3S)-3-hydroxy-5-[2-(methoxymethyl)phenyl]pent-1-enyl]-5-oxo-cyclopentyl]sulphanylpropylsulphanyl] acetic acid (ONO-AE1-329), a selective EP₄-receptor agonist. ONO-AE1-329 also enhanced dexamethasone-induced activation of a glucocorticoid response element reporter in BEAS-2B cells, which was similarly potentiated by RNO. In each airway epithelial cell variant, numerous genes that may impart therapeutic benefit in asthma, COPD, and/or IPF were differentially expressed by ONO-AE1-329, and those changes were often augmented by RNO and/or dexamethasone. We submit that an EP₄-receptor agonist, either alone or as a combination therapy, may be beneficial in individuals with chronic lung diseases in whom current treatment options are inadequate. SIGNIFICANCE STATEMENT: Using human bronchial epithelial cells as a therapeutically relevant drug target, we report that EP₄-receptor activation promoted gene expression changes that could provide therapeutic benefit in individuals with asthma, COPD, and IPF in whom current treatment options are ineffective or suboptimal.

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.

Modulation of TRPV-1 by prostaglandin-E2 and bradykinin changes cough sensitivity and autonomic regulation of cardiac rhythm in healthy subjects

A neurogenic pathway, involving airway TRPV-1, has been implicated in acute cardiovascular events occurring after peaks of air pollution. We tested whether inhaled prostaglandin-E₂ (PGE₂) and bradykinin (BK) regulate TRPV-1 activity in vivo by changing cough response to capsaicin (CPS) and affecting heart rate variability (HRV), while also taking into account the influence of TRPV-1 polymorphisms (SNPs). Moreover, we assessed the molecular mechanism of TRPV-1 modulation in vitro. Seventeen healthy volunteers inhaled 100 μg PGE₂, 200 μg BK or diluent in a randomized double-blind fashion. Subsequently, the response to CPS was assessed by cough challenge and the sympathetic activity by HRV, expressed by low (nLF) and high (nHF) normalized frequency components, as well as nLF/nHF ratio. Intracellular [Ca²⁺] was measured in HeLa cells, transfected with wild-type TRPV-1, pre-treated with increasing doses of PGE₂, BK or diesel exhaust particulate (DEP), after CPS stimulation. Six functional TRPV-1 SNPs were characterized in DNA from each subject. Inhalation of PGE₂ and BK was associated with significant increases in cough response induced by 30 μM of CPS (cough number after PGE₂ = 4.20 ± 0.42; p < 0.001, and after BK = 3.64 ± 0.37; p < 0.01), compared to diluent (2.77 ± 0.29) and in sympathetic activity (nLF/nHF ratio after PGE₂ = 6.1; p < 0.01, and after BK = 4.2; p < 0.05), compared to diluent (2.5–3.3). No influence of SNPs was observed on autonomic regulation and cough sensitivity. Unlike PGE₂ and BK, DEP directly activated TRPV-1. Inhalation of PGE₂ and BK sensitizes TRPV-1 and is associated with autonomic dysregulation of cardiac rhythm in healthy subjects.

Nonmetastatic renal cell carcinoma presenting with persistent cough: Case report with literature review

Renal cell carcinomas (RCC), constitute 80– 85% of primary renal neoplasms. The classic triad of RCC (flank pain, hematuria, and a palpable abdominal renal mass) occurs in approximately 9% of patients; it strongly suggests locally advanced disease. RCC may also be associated with a number of paraneoplastic syndromes. These are typically due to ectopic production of various hormones. We present a 69-year-old male patient previously healthy presented to the emergency department with recurrent persistent cough. A non-metastatic RCC was incidentally discovered. Eventually, he underwent left radical nephrectomy. One year has passed with no cough. This is a rare and unusual presentation of RCC that falls under the category of paraneoplastic syndrome with review of similar reported cases and summary of all paraneoplastic syndromes associated with RCC in literature.

Immune system in the pathogenesis of chronic cough

Chronic cough is a common symptom of various chronic diseases. However, the vast majority of individuals with conditions that are commonly associated with cough, such as asthma and GERD, do not have chronic cough. This implies that cough reflex sensitivities differ among individuals. It is known that in the pathogenesis of cough, the nervous system plays a vital role. Recently more information about the role of the immune system and its interaction with the nervous system in the pathogenesis of cough has appeared in the literature. The aim of this article is to review the most recent data about the role of the immune system in the pathogenesis of chronic cough.

IFN-γ Enhances the Cough Reflex Sensitivity via Calcium Influx in Vagal Sensory Neurons

RATIONALE

Cough hypersensitivity syndrome is often triggered by a viral infection. The viral infection might trigger cough hypersensitivity via increasing the release of IFN-γ from T lymphocytes in the lung.

OBJECTIVES

To investigate effects of IFN-γ on the vagal sensory neurons and the cough reflex.

METHODS

Effects of IFN-γ on the cough reflex were investigated in guinea pigs. Cellular immunofluorescence imaging, calcium imaging, and patch clamp techniques were used to study effects of IFN-γ in primary cultured rat vagal sensory neurons.

MEASUREMENTS AND MAIN RESULTS

Intratracheal instillation of IFN-γ enhanced the cough response to citric acid in vivo. IFN-γ significantly increased levels of phosphorylated signal transducer and activator of transcription-1 but not phosphorylated transient receptor potential vanilloid 1 in vitro. Not only did IFN-γ enhance the response of neurons to capsaicin and electric stimulation, but also it directly induced Ca²⁺ influx, membrane depolarization, and action potentials in neurons via the Janus kinase, protein kinase A, and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid pathways. However, IFN-γ did not elicit Ca²⁺ release from the endoplasmic reticulum via the phospholipase C pathway. Although IFN-γ-induced action potentials were suppressed by Ca²⁺ influx inhibitors, IFN-γ-induced Ca²⁺ influx was not altered by an inhibitor of rapid sodium channels.

CONCLUSIONS

The membrane potential in vagal sensory neurons may be depolarized by IFN-γ-induced Ca²⁺ influx. The depolarization of membrane potentials may enhance the cough reflex sensitivity and cause action potentials. IFN-γ may be a new target for treating cough hypersensitivity syndrome and postviral cough.

The Role of Airway Myofibroblasts in Asthma

Airway remodeling is a characteristic feature of asthma and is thought to play an important role in the pathogenesis of airway hyperresponsiveness. Myofibroblasts are key structural cells involved in injury and repair, and there is evidence that dysregulation of their normal function contributes to airway remodeling. Despite the importance of myofibroblasts, a lack of specific cellular markers and inconsistent nomenclature have limited recognition of their key role in airway remodeling. Myofibroblasts are increased several-fold in the airways in asthma, in proportion to the severity of the disease. Myofibroblasts are postulated to be derived from both tissue-resident and bone marrow-derived cells, depending on the stage of injury and the tissue. A small number of studies have demonstrated attenuation of myofibroblast numbers and also reversal of established myofibroblast populations in asthma and other inflammatory processes. In this article, we review what is currently known about the biology of myofibroblasts in the airways in asthma and identify potential targets to reduce or reverse the remodeling process. However, further translational research is required to better understand the mechanistic role of the myofibroblast in asthma.

Bradykinin sensitizes the cough reflex via a B2 receptor dependent activation of TRPV1 and TRPA1 channels through metabolites of cyclooxygenase and 12-lipoxygenase

Background

Inhaled bradykinin (BK) has been reported to both sensitize and induce cough but whether BK can centrally sensitize the cough reflex is not fully established. In this study, using a conscious guinea-pig model of cough, we investigated the role of BK in the central sensitization of the cough reflex and in airway obstruction.

Methods

Drugs were administered, to guinea pigs, by the intracerebroventricular (i.c.v.) route. Aerosolized citric acid (0.2 M) was used to induce cough in a whole-body plethysmograph box, following i.c.v. infusion of drugs. An automated analyser recorded both cough and airway obstruction simultaneously.

Results

BK, administered by the i.c.v. route, dose-dependently enhanced the citric acid-induced cough and airway obstruction. This effect was inhibited following i.c.v. pretreatment with a B₂ receptor antagonist, TRPV1 and TRPA1 channels antagonists and cyclooxygenase (COX) and 12-lipoxygenase (12-LOX) inhibitors. Furthermore, co-administration of submaximal doses of the TRPV1 and TRPA1 antagonists or the COX and 12-LOX inhibitors resulted in a greater inhibition of both cough reflex and airway obstruction.

Conclusions

Our findings show that central BK administration sensitizes cough and enhances airway obstruction via a B₂ receptor/TRPV1 and/or TRPA1 channels which are coupled via metabolites of COX and/or 12-LOX enzymes. In addition, combined blockade of TRPV1 and TRPA1 or COX and 12-LOX resulted in a greater inhibitory effect of both cough and airway obstruction. These results indicate that central B₂ receptors, TRPV1/TRPA1 channels and COX/12-LOX enzymes may represent potential therapeutic targets for the treatment of cough hypersensitivity.

Graphical abstract

An advanced recording and analysis system for the differentiation of guinea pig cough responses to citric acid and prostaglandin E2 in real time

Cough number and/or sound have been used to assess cough sensitivity/intensity and to discriminate cough patterns in clinical settings. However, to date, only manual counting of cough number in an offline manner is applied in animal cough studies, which diminishes the efficiency of cough identification and hinders the diagnostic discrimination of cough patterns, especially in animals with pulmonary diseases. This study aims to validate a novel recording/analysis system by which cough numbers are automatically counted and cough patterns are comprehensively differentiated in real time. The experiment was carried out in conscious guinea pigs exposed to aerosolized citric acid (CA, 150 mM) and prostaglandin E2 (PGE2, 0.43 mM). Animal body posture (video), respiratory flow, and cough acoustics (audio) were simultaneously monitored and recorded. Cough number was counted automatically, and cough sound parameters including waveform, duration, power spectral density, spectrogram, and intensity, were analyzed in real time. Our results showed that CA- and PGE2-evoked coughs had the same cough numbers but completely different patterns [individual coughs vs. bout(s) of coughs]. Compared to CA-evoked coughs, PGE2-evoked coughs possess a longer latency, higher cough rate (coughs/min), shorter cough sound duration, lower cough sound intensity, and distinct cough waveforms and spectrograms. A few mucus- and wheeze-like coughs were noted in response to CA but not to PGE2. In conclusion, our recording/analysis system is capable of automatically counting the cough number and successfully differentiating the cough pattern by using valuable cough sound indexes in real time. Our system enhances the objectivity, accuracy, and efficiency of cough identification and count, improves the intensity evaluation, and offers ability for pattern discrimination compared to traditional types of cough identification. Importantly, this approach is beneficial for assessing the efficacy of putative antitussive drugs in animals without or with pulmonary diseases, particularly in cases without significant change in cough number.

Allergen challenge increases capsaicin-evoked cough responses in patients with allergic asthma

BACKGROUND

Cough is a common and troublesome symptom in asthmatic patients, but little is known about the neuronal pathways that trigger cough. The mechanisms by which airway inflammation, airway hyperresponsiveness, and variable airflow obstruction cause cough are unclear.

OBJECTIVE

We sought to investigate the effects of allergen exposure on cough reflex sensitivity.

METHODS

We performed a 9-visit, randomized, single-blind, placebo-controlled, 2-way crossover study comparing cough responses to inhaled capsaicin in patients with mild atopic asthma after allergen challenge compared with diluent control. Full-dose capsaicin challenge was performed at screening to determine the capsaicin dose inducing a half-maximal response, which was subsequently administered at 30 minutes and 24 hours after inhaled allergen/diluent challenge. Spontaneous coughing was measured for 24 hours after allergen/diluent. Methacholine challenge and sputum induction were performed before and after allergen/diluent challenge.

RESULTS

Twelve steroid-naive subjects completed the study (6 female subjects; mean age, 34.8 years). Allergen inhalation caused both an early (mean ± SD, 38.2% ± 13.0%) and late (mean ± SD, 23.7% ± 13.2%) decrease in FEV₁ and an increase in sputum eosinophil counts 24 hours later (after diluent: median, 1.9% [interquartile range, 0.8% to 5.8%]; after allergen: median, 14.9% [interquartile range, 8.9% to 37.3%]; P = .005). There was also an increase in capsaicin-evoked coughs after allergen exposure compared with diluent at both 30 minutes (geometric mean coughs, 21.9 [95% CI, 16.5-29.20] vs 12.1 [95% CI, 8.3-17.7]; P < .001) and 24 hours (geometric mean coughs, 16.1 [95% CI, 11.3-23.0] vs 9.8 [95% CI, 6.1-15.8]; P = .001). Allergen exposure was also associated with an increase in spontaneous coughs over 24 hours.

CONCLUSION

Allergen-induced bronchoconstriction and airway eosinophilia result in increased cough reflex sensitivity to capsaicin associated with an increase in 24-hour spontaneous coughing.

Cooperativity of E-prostanoid receptor subtypes in regulating signaling and growth inhibition in human airway smooth muscle

Prostaglandin E2 (PGE₂) is produced in the airway during allergic lung inflammation and both promotes and inhibits features of asthma pathology. These mixed effects relate to 4 E-prostanoid (EP) receptor subtypes (EP1, 2, 3 and 4) expressed at different levels on different resident and infiltrating airway cells. Although studies have asserted both EP2 and EP4 expression in human airway smooth muscle (HASM), a recent study asserted EP4 to be the functionally dominant EP subtype in HASM. Herein, we employ recently-developed subtype-selective ligands to investigate singular or combined EP2 and EP4 receptor activation in regulating HASM signaling and proliferation. The subtype specificity of ONO-AE1-259-01 (EP2 agonist) and ONO-AE1-329 (EP4 agonist) was first demonstrated in human embryonic kidney 293 cells stably expressing different EP receptor subtypes. EP receptor knockdown and subtype-selective antagonists demonstrated EP2 and EP4 receptor responsiveness in HASM cells to the specific ONO compounds, whereas PGE₂ appeared to preferentially signal via the EP4 receptor. Both singular EP2 and EP4 receptor agonists inhibited HASM proliferation, and combined EP2 and EP4 receptor agonism exhibited positive cooperativity in both chronic G_s-mediated signaling and inhibiting HASM proliferation. These findings suggest both EP2 and EP4 are functionally important in HASM, and their combined targeting optimally inhibits airway smooth muscle proliferation.-Michael, J. V. Gavrila, A., Nayak, A. P., Pera, T., Liberato, J. R., Polischak, S. R., Shah, S. D., Deshpande, D. A., Penn, R. B. Cooperativity of E-prostanoid receptor subtypes in regulating signaling and growth inhibition in human airway smooth muscle.

Eicosanoid Control Over Antigen Presenting Cells in Asthma

Asthma is a common lung disease affecting 300 million people worldwide. Allergic asthma is recognized as a prototypical Th2 disorder, orchestrated by an aberrant adaptive CD4+ T helper (Th2/Th17) cell immune response against airborne allergens, that leads to eosinophilic inflammation, reversible bronchoconstriction, and mucus overproduction. Other forms of asthma are controlled by an eosinophil-rich innate ILC2 response driven by epithelial damage, whereas in some patients with more neutrophilia, the disease is driven by Th17 cells. Dendritic cells (DCs) and macrophages are crucial regulators of type 2 immunity in asthma. Numerous lipid mediators including the eicosanoids prostaglandins and leukotrienes influence key functions of these cells, leading to either pro- or anti-inflammatory effects on disease outcome. In this review, we will discuss how eicosanoids affect the functions of DCs and macrophages in the asthmatic lung and how this leads to aberrant T cell differentiation that causes disease.

Rabbit plasma metabolomic analysis of Nitroproston®: a multi target natural prostaglandin based-drug

INTRODUCTION

Nitroproston® is a novel multi-target drug bearing natural prostaglandin E₂ (PGE₂) and nitric oxide (NO)-donating fragments for treatment of inflammatory and obstructive diseases (i.e., asthma and obstructive bronchitis).

OBJECTIVES

To investigate the effects of Nitroproston® administration on plasma metabolomics in vivo.

METHODS

Experimental in vivo study randomly assigning the target drug (treatment group) or a saline solution without the drug (vehicle control group) to 12 rabbits (n = 6 in each group). Untargeted (5880 initial features; 1869 negative-4011 positive ion peaks; UPLC-IT-TOF/MS) and 84 targeted moieties (Nitroproston® related metabolites, prostaglandins, steroids, purines, pyrimidines and amino acids; HPLC-QQQ-MS/MS) were measured from plasma at 0, 2, 4, 6, 8, 12, 18, 24, 32 and 60 min after administration.

RESULTS

PGE₂, 13,14-dihydro-15-keto-PGE₂, PGB₂, 1,3-GDN and 15-keto-PGE₂ increased in the treatment group. Steroids (i.e., cortisone, progesterone), organic acids, 3-oxododecanoic acid, nicotinate D-ribonucleoside, thymidine, the amino acids serine and aspartate, and derivatives pyridinoline, aminoadipic acid and uric acid increased (p < 0.05 AUCROC curve > 0.75) after treatment. Purines (i.e., xanthine, guanine, guanosine), bile acids, acylcarnitines and the amino acids L-tryptophan and L-phenylalanine were decreased. Nitroproston® impacted steroidogenesis, purine metabolism and ammonia recycling pathways, among others.

CONCLUSION

Nitroproston®, a multi action novel drug based on natural prostaglandins, altered metabolites (i.e., guanine, adenine, cortisol, cortisone and aspartate) involved in purine metabolism, urea and ammonia biological cycles, steroidogenesis, among other pathways. Suggested mechanisms of action, metabolic pathway interconnections and useful information to further understand the metabolic effects of prostaglandin administration are presented.

Prostaglandins in asthma and allergic diseases

Prostaglandins are synthesized through the metabolism of arachidonic acid via the cyclooxygenase pathway. There are five primary prostaglandins, PGD₂, PGE₂, PGF₂, PGI₂, and thromboxane B₂, that all signal through distinct seven transmembrane, G-protein coupled receptors. The receptors through which the prostaglandins signal determines their immunologic or physiologic effects. For instance, the same prostaglandin may have opposing properties, dependent upon the signaling pathways activated. In this article, we will detail how inhibition of cyclooxygenase metabolism and regulation of prostaglandin signaling regulates allergic airway inflammation and asthma physiology. Possible prostaglandin therapeutic targets for allergic lung inflammation and asthma will also be reviewed, as informed by human studies, basic science, and animal models.

New targets for resolution of airway remodeling in obstructive lung diseases

Airway remodeling (AR) is a progressive pathological feature of the obstructive lung diseases, including asthma and chronic obstructive pulmonary disease (COPD). The pathology manifests itself in the form of significant, progressive, and (to date) seemingly irreversible changes to distinct respiratory structural compartments. Consequently, AR correlates with disease severity and the gradual decline in pulmonary function associated with asthma and COPD. Although current asthma/COPD drugs manage airway contraction and inflammation, none of these effectively prevent or reverse features of AR. In this review, we provide a brief overview of the features and putative mechanisms affecting AR. We further discuss recently proposed strategies with promise for deterring or treating AR.

Risks and Cough-Aggravating Factors in Prolonged Cough. Epidemiological Observations from the Nagahama Cohort Study

RATIONALE

Chronic cough hypersensitivity, a potentially important concept of chronic or prolonged cough, is featured by heightened cough response to low-intensity stimuli, which may be generated in the absence of airflow limitations or allergic conditions. However, there is little epidemiological evidence to support this.

OBJECTIVES

In this large-scale community survey, we aimed to determine risks and cough-aggravating factors of prolonged cough while focusing on serum IgE levels.

METHODS

Prevalence of prolonged cough, defined as cough lasting 3 weeks or longer, was determined in 9,804 residents from a baseline measurement of the Nagahama Cohort Study, conducted from 2008 to 2010. Risk assessment of prolonged cough was confined to subjects without asthma (n = 9,402). A follow-up measurement of the Nagahama Study was successively conducted from 2013 to 2015, recruiting the same residents living in Nagahama City, Japan (n = 8,292). Validation analysis was performed in the follow-up measurement.

RESULTS

In a baseline measurement, prolonged cough was reported by 9.5% of subjects without asthma and 32.3% of subjects with asthma. In subjects without asthma, various cough-aggravating factors were associated with prolonged cough. On the multivariate analysis, several cough-aggravating factors, including nighttime or early morning, weather, pollen season, and common cold, were associated with prolonged cough, independent of female sex, younger age, chronic obstructive pulmonary disease, postnasal drip, daytime sputum, and lower serum total IgE. Serum-specific IgE levels against Japanese cedar pollen were significantly higher in subjects who responded "yes" to "cough in the pollen season" than in those who did not respond, whereas, among subjects who responded "yes" to "cough in the pollen season," prolonged coughers showed lower serum IgE levels against Japanese cedar pollen than temporal coughers. Validation analysis in a follow-up measurement confirmed the associations between prolonged cough and cough-aggravating factors observed in the baseline measurement.

CONCLUSIONS

The presence of several cough-aggravating factors in the absence of severe allergic conditions may support the presence of cough hypersensitivity.

Persistent cough as a paraneoplastic presenting symptom in six patients with renal cell carcinoma

Objective

With today's modern imaging modalities, patients diagnosed with renal cell carcinoma (RCC) rarely present symptomatically. In some cases, however, they can develop paraneoplastic syndromes with associated symptoms. To date, only three cases of RCC presenting with chronic dry cough have been reported. We describe six patients who presented with cough that improved following radical nephrectomy.

Methods

A retrospective review of patients undergoing partial or radical nephrectomy for renal masses between January 2015 and March 2016 was performed, and patients presenting with a cough were examined.

Results

Six patients presented with chronic cough and were discovered to have a large renal mass. Postoperative spontaneous resolution of cough was noted in all but one patient, in whom coughing was reduced and limited to the mornings. Cough duration ranged from 3 months to just over a year. All patients were treated with radical nephrectomy, which was cytoreductive in four patients. Average tumor size was 10.9 cm (SD = 2.2 cm). Five of the tumors had clear cell pathology, and every tumor was Fuhrman grade IV, unifocal, and demonstrated necrosis. Sarcomatoid features were reported in four of the tumors.

Conclusion

Our study presents the largest series of patients with RCC who presented with a chronic cough that was significantly improved following radical nephrectomy. We believe the cause of cough is multifactorial and further investigation is needed to clearly elucidate the etiology.

Cough and airway disease: The role of ion channels

Cough is the most common reason for patients to visit a primary care physician, yet it remains an unmet medical need. It can be idiopathic in nature but can also be a troublesome symptom across chronic lung diseases such as asthma, COPD and idiopathic pulmonary fibrosis (IPF). Chronic cough affects up to 12% of the population and yet there are no safe and effective therapies. The cough reflex is regulated by vagal, sensory afferent nerves which innervate the airway. The Transient Receptor Potential (TRP) family of ion channels are expressed on sensory nerve terminals, and when activated can evoke cough. This review focuses on the role of 4 TRP channels; TRP Vannilloid 1 (TRPV1), TRP Ankyrin 1 (TRPA1), TRP Vannilloid 4 (TRPV4) and TRP Melastatin 8 (TRPM8) and the purinergic P2X3 receptor and their possible role in chronic cough. We conclude that these ion channels, given their expression profile and their role in the activation of sensory afferents and the cough reflex, may represent excellent therapeutic targets for the treatment of respiratory symptoms in chronic lung disease.

Activating prostaglandin E2 receptor subtype EP4 increases secreted mucin from airway goblet cells

Prostaglandin E2 (PGE2) is a ligand of the E-type prostanoid receptors, EP1-4. PGE2 secretion is increased in the airways of patients with asthma by secretory phospholipases A₂, which also increases MUC5AC mucin in goblet cells. We hypothesized that PGE2 would also increase MUC5AC mRNA and secreted protein through specific EP receptor activation. We sought to assess the effect of specific EP receptor activation on MUC5AC secretion from ciliated-enriched cells or goblet-enriched cells induced by IL-13. We develop an enriched goblet cell epithelium by growing normal human bronchial epithelial cells at air liquid interface for 14 days in the presence of IL-13. We examined exposure to 4 specific EP receptor agonists at 24 h and 14 days in cells grown with or without IL-13 exposure, and measured MUC5AC mRNA and secreted protein, as well as airway culture morphology, and EP receptor expression. In ciliated-enriched cells grown in the absence of IL-13, the EP4 receptor agonist modestly increased both MUC5AC mRNA and secretion (p < 0.001, 241% increase of transcripts and p < 0.01, 86% increase of secreted protein) but did not visibly change cell morphology. In goblet-enriched cells grown in the presence of IL-13, the EP4 receptor agonist greatly increased both MUC5AC mRNA and protein (p < 0.001, 315% increase of transcripts and 92% increase of secreted protein). Specific activation of the other EP receptor had no effect on secreted mucin. EP4 receptor mRNA and protein were significantly increased in goblet-enriched cells, while the other receptor mRNA were decreased. We conclude that PGE2 stimulates airway mucin production predominantly by EP4 receptor activation in association with increased EP4 receptor expression. This may contribute to mucus hypersecretion as seen in severe asthma.

Role of prostaglandin E2 in bronchoconstriction-triggered cough response in guinea pigs

A feature of cough variant asthma is a heightened cough response to bronchoconstriction. The mediators of this response are unknown. This study was designed to elucidate the role of lipid mediators in bronchoconstriction-triggered cough response in an experimental animal model. We examined the influence of bronchoconstriction on cell components and mediators including prostaglandin E₂ (PGE₂) in bronchoalveolar lavage fluid (BALF). We studied the cough response to bronchoconstriction (CRB) by measuring the correlation between the increase in enhanced pause (Penh), an index of bronchoconstriction, and cough counts induced by methacholine (Mch) inhalation in conscious guinea pigs. We then examined the effects of intraperitoneal pretreatment with 16, 16-dimethyl-prostaglandin E₂ (dm-PGE₂) on CRB and cough counts. The total number of cells and cell components in the BALF were not influenced by bronchoconstriction. While levels of PGE₂, prostaglandin I₂, and cysteinyl leukotrienes were significantly increased, levels of prostaglandin D₂, thromboxane B₂, and substance P in the BALF were not. Dm-PGE₂ significantly decreased the Mch-induced increase in Penh. Following bronchoconstriction by additional Mch inhalation, dm-PGE₂ produced an increase in CRB and cough counts in a dose-dependent manner. Additionally, the heightened CRB following dm-PGE₂ treatment was suppressed by pretreatment with PGE₂ receptor (E-prostanoid EP) -1 and EP-3 antagonists in a dose-dependent manner, but not by EP-2 and EP-4 antagonists. The EP-1 antagonist also decreased cough counts. These results suggest that PGE₂ acts as an exacerbating factor for bronchoconstriction-triggered cough. EP1 and EP3 may provide new therapeutic targets for cough variant asthma.

Drugs Affecting TRP Channels

Chronic obstructive pulmonary disease (COPD) and asthma are both common respiratory diseases that are associated with airflow reduction/obstruction and pulmonary inflammation. Whilst drug therapies offer adequate symptom control for many mild to moderate asthmatic patients, severe asthmatics and COPD patients symptoms are often not controlled, and in these cases, irreversible structural damage occurs with disease progression over time. Transient receptor potential (TRP) channels, in particular TRPV1, TRPA1, TRPV4 and TRPM8, have been implicated with roles in the regulation of inflammation and autonomic nervous control of the lungs. Evidence suggests that inflammation elevates levels of activators and sensitisers of TRP channels and additionally that TRP channel expression may be increased, resulting in excessive channel activation. The enhanced activity of these channels is thought to then play a key role in the propagation and maintenance of the inflammatory disease state and neuronal symptoms such as bronchoconstriction and cough. For TRPM8 the evidence is less clear, but as with TRPV1, TRPA1 and TRPV4, antagonists are being developed by multiple companies for indications including asthma and COPD, which will help in elucidating their role in respiratory disease.