Translational review: Neuroimmune mechanisms in cough and emerging therapeutic targets

Zhisou powder suppresses airway inflammation in LPS and CS-induced post-infectious cough model mice via TRPA1/TRPV1 channels

ETHNOPHARMACOLOGICAL RELEVANCE

Zhisou Powder (ZSP), a traditional Chinese medicine (TCM) prescription, has been widely used in the clinic for the treatment of post-infectious cough (PIC). However, the exact mechanism is not clear.

AIM OF THE STUDY

The aim of this study was to investigate the ameliorative effect of ZSP on PIC in mice. The possible mechanisms of action were screened based on network pharmacology, and the potential mechanisms were explored through molecular docking and in vivo experimental validation.

MATERIALS AND METHODS

Lipopolysaccharide (LPS) (80μg/50 μL) was used to induce PIC in mice, followed by daily exposure to cigarette smoke (CS) for 30 min for 30 d to establish PIC model. The effects of ZSP on PIC mice were observed by detecting the number of coughs and cough latency, peripheral blood and bronchoalveolar lavage fluid (BALF) inflammatory cell counts, enzyme-linked immunosorbent assay (ELISA), and histological analysis. The core targets and key pathways of ZSP on PIC were analyzed using network pharmacology, and TRPA1 and TRPV1 were validated using RT-qPCR and western blotting assays.

RESULTS

ZSP effectively reduced the number of coughs and prolonged the cough latency in PIC mice. Airway inflammation was alleviated by reducing the expression levels of the inflammatory mediators TNF-α and IL-1β. ZSP modulated the expression of Substance P, Calcitonin gene-related peptide (CGRP), and nerve growth factor (NGF) in BALF. Based on the results of network pharmacology, the mechanism of action of ZSP may exert anti-neurogenic airway-derived inflammation by regulating the expression of TRPA1 and TRPV1 through the natural active ingredients α-spinastero, shionone and didehydrotuberostemonine.

CONCLUSION

ZSP exerts anti-airway inflammatory effects through inhibition of TRPA1/TRPV1 channels regulating neuropeptides to alleviate cough hypersensitivity and has a favorable therapeutic effect on PIC model mice. It provides theoretical evidence for the clinical application of ZSP.

Evidence for vagal sensory neural involvement in influenza pathogenesis and disease

Influenza A virus (IAV) is a common respiratory pathogen and a global cause of significant and often severe morbidity. Although inflammatory immune responses to IAV infections are well described, little is known about how neuroimmune processes contribute to IAV pathogenesis. In the present study, we employed surgical, genetic, and pharmacological approaches to manipulate pulmonary vagal sensory neuron innervation and activity in the lungs to explore potential crosstalk between pulmonary sensory neurons and immune processes. Intranasal inoculation of mice with H1N1 strains of IAV resulted in stereotypical antiviral lung inflammation and tissue pathology, changes in breathing, loss of body weight and other clinical signs of severe IAV disease. Unilateral cervical vagotomy and genetic ablation of pulmonary vagal sensory neurons had a moderate effect on the pulmonary inflammation induced by IAV infection, but significantly worsened clinical disease presentation. Inhibition of pulmonary vagal sensory neuron activity via inhalation of the charged sodium channel blocker, QX-314, resulted in a moderate decrease in lung pathology, but again this was accompanied by a paradoxical worsening of clinical signs. Notably, vagal sensory ganglia neuroinflammation was induced by IAV infection and this was significantly potentiated by QX-314 administration. This vagal ganglia hyperinflammation was characterized by alterations in IAV-induced host defense gene expression, increased neuropeptide gene and protein expression, and an increase in the number of inflammatory cells present within the ganglia. These data suggest that pulmonary vagal sensory neurons play a role in the regulation of the inflammatory process during IAV infection and suggest that vagal neuroinflammation may be an important contributor to IAV pathogenesis and clinical presentation. Targeting these pathways could offer therapeutic opportunities to treat IAV-induced morbidity and mortality.

Xingbei antitussive granules ameliorate cough hypersensitivity in post-infectious cough guinea pigs by regulating tryptase/PAR2/TRPV1 pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Xingbei antitussive granules (XB) is a classic Chinese Medicine prescription for treating post-infectious cough(PIC), based on the Sanao Decoction from Formularies of the Bureau of People's Welfare Pharmacies in the Song Dynasty and Jiegeng decoction from Essentials of the Golden Chamber in the Han Dynasty. However, the therapeutic effects and pharmacological mechanisms are still ambiguous. In the present study, we endeavored to elucidate these underlying mechanisms.

AIMS OF THE STUDY

This study aimed to explore the potential impact and mechanism of XB on PIC, and provide a scientific basis for its clinical application.

MATERIALS AND METHODS

Cigarette smoking (CS) combined with lipopolysaccharide (LPS) nasal drops were administered to induce the PIC guinea pig with cough hypersensitivity status. Subsequently, the model guinea pigs were treated with XB and the cough frequency was observed by the capsaicin cough provocation test. The pathological changes of lung tissue were assessed by HE staining, and the levels of inflammatory mediators, mast cell degranulating substances, and neuropeptides were detected. The protein and mRNA expression of transient receptor potential vanilloid type 1(TRPV1), proteinase-activated receptor2(PAR2), and protein kinase C (PKC) were measured by Immunohistochemical staining, Western blot, and RT-qPCR. Changes in the abundance and composition of respiratory bacterial microbiota were determined by 16S rRNA sequencing.

RESULTS

After XB treatment, the model guinea pigs showed a dose-dependent decrease in cough frequency, along with a significant alleviation in inflammatory infiltration of lung tissue and a reduction in inflammatory mediators. In addition, XB high-dose treatment significantly decreased the levels of mast cell Tryptase as well as β-hexosaminidase (β-Hex) and downregulated the expression of TRPV1, PAR2, and p-PKC. Simultaneously, levels of neuropeptides like substance P (SP), calcitonin gene-related peptide (CGRP), neurokinin A (NKA), and nerve growth factor (NGF) were improved. Besides, XB also can modulate the structure of respiratory bacterial microbiota and restore homeostasis.

CONCLUSION

XB treatment alleviates cough hypersensitivity and inflammatory responses, inhibits the degranulation of mast cells, and ameliorates neurogenic inflammation in PIC guinea pigs whose mechanism may be associated with the inhibition of Tryptase/PAR2/PKC/TRPV1 and the recovery of respiratory bacterial microbiota.

Optimal compatibility proportional screening of Trichosanthis Pericarpium - Trichosanthis Radix and its anti - Inflammatory components effect on experimental zebrafish and coughing mice

ETHNOPHARMACOLOGICAL RELEVANCE

The herbal pair of Trichosanthis Pericarpium (TP) - Trichosanthis Radix (TR) can be seen in the famous formula "Beimu Gualou San". It is a commonly selected combination of medicinal herbs for the treatment of cough with lung heat. Both drugs are derived from Trichosanthes kirilowii Maxim, a medicinal plant known for its ability to clear heat, resolve phlegm, produce saliva, and alleviate dryness. However, the optimal combination ratio and active ingredients of TP-TR have yet to be determined.

AIM OF THE STUDY

This study aims to investigate the optimal combination ratio of TP-TR and its anti-inflammatory active ingredients in cough treatment.

MATERIALS AND METHODS

A zebrafish (Danio rerio) inflammatory injury model and response surface method were applied in the present study to determine the appropriate proportion of TP-TR. Chemical constituents in TP-TR were identified using HPLC-ELSD and UPLC-MS/MS methods. Subsequently, a cough mouse model was created using an ammonia solution to evaluate the effectiveness of the optimal TP-TR ratio. Network pharmacology and intestinal flora sequencing were used to validate the anti-inflammatory components of TP-TR.

RESULTS

The herbal pair of TP - TR at the ratio of 1:2 showed an optimal anti-inflammatory effect, with a composite inflammatory factor score of 119.645 in the zebrafish experiment. TP-TR combination facilitated the dissolution of glutamine, inosine, cytosine, isoquercetin, and other substances. In the animal model, the TP-TR (1:2) treatment significantly reduced the frequency of coughs and prolonged cough latency compared to the model group. Results of the network pharmacology indicated that inflammatory-related factors such as TLR4, STAT3, EGFR, and AKT1 played crucial roles in cough treatment with TP-TR, consistent with the validation experiment. The 16s rDNA sequencing results revealed a significant increase in the abundance of Clostridia_UCG-014, Lachnospiraceae, Christenella, Ruminococcus, and other species in the intestinal tract of mice after modelling. TP-TR (1:2) reduced the abundance of pro-inflammatory flora such as Clostridium_UCG-014 and Lachnospira, which were closely associated with L-lysine and trans-4-hydroxy-L-proline present in TP-TR according to correlation analysis.

CONCLUSION

TP-TR may promote the dissolution of glutamine, thymidine, inosine, cytosine, isoquercetin, and other components through their combination, thereby regulating the abundance of Clostridium_UCG-014 and Lachnospira and exerting an antitussive effect. This study, for the first time, showed that TP-TR at a 1:2 ratio exhibits superior anti-inflammatory effects. In addition to inflammatory mediators like EGFR, TLR4, AKT1, and STAT3, gut microbes could also serve as potential regulatory targets of TP-TR in the treatment of cough. 2'-Deoxyguanosine monohydrate, L-lysine, L-leucine, γ-aminobutyric acid, L-valine, L-tryptophan, L-proline, trans-4-hydroxy-L-proline, L-methionine, uridine, 2'-deoxyinosine, guanosine, cucurbitacin B and cucurbitacin D were identified as its anti-inflammatory active ingredients.

Evaluation and management of chronic cough in adults

Background: Chronic cough (CC), a cough that lasts > 8 weeks, has an overall prevalence of 5-11% in adults, peaking between 60 and 80 years of age. Of the 15% of patients who remain undiagnosed or refractory to treatment, two thirds are women. Objective: The objective was to present an updated evidence-based algorithmic approach for evaluating and managing CC, with emphasis on treatment modalities for refractory CC. Methods: A literature search was conducted of medical literature data bases for guidelines, position papers, systematic reviews, and clinical trials from January 2022 to June 2023, on the evaluation and management of CC. Results: The initial assessment should be limited to a detailed history, physical examination, chest radiograph, spirometry, exhaled nitric oxide, blood eosinophil count, and measurement of cough severity and quality of life by using validated instruments. The top diagnoses to consider are asthma, chronic obstructive pulmonary disease, nonasthmatic eosinophilic bronchitis, gastroesophageal reflux disease, and upper airway cough syndrome. Additional studies are only obtained when red flags are present or the patient fails to respond after avoidance of high-risk factors, e.g., smoking and angiotensin-converting enzyme inhibitors, and 4-6 weeks of empiric treatment for the most likely respiratory and gastrointestinal diseases. When diagnostic tests and/or specific directed treatments fail to control CC, low-dose morphine (preferred), gabapentin, pregabalin, and/or cough control therapy are recommended. Non-narcotic purinergic 2×3 (P2×3) receptor antagonists, gafapixant and campilixant, are currently being studied for CC. Conclusion: For the evaluation and management of patients with CC, clinicians should use an algorithmic approach and identify "red flags," reduce high-risk factors, and use empiric treatment for the five top diagnoses before extensive diagnostic testing. Current treatment for refractory cough is limited to symptomatic management.

Intrapulmonary IFN-γ instillation causes chronic lymphocytic inflammation in the spleen and lung through the CXCR3 pathway

Some patients with chronic refractory cough have high levels of pulmonary IFN-γ and IFN-γ-producing T lymphocytes. Pulmonary IFN-γ administration causes acute airway lymphocytic inflammation and cough hypersensitivity by increasing the number of pulmonary IFN-γ-producing T lymphocytes, but these lymphocytes may be recruited from other organs. Intraperitoneal IFN-γ injection can increase the spleen weight of mice. It remains elusive whether pulmonary IFN-γ can induce chronic airway lymphocytic inflammation and cough hypersensitivity by stimulating the proliferation of IFN-γ -producing T lymphocytes in the spleen. Here, we found that pulmonary IFN-γ administration induced chronic airway inflammation and chronic cough hypersensitivity with an increased number of IFN-γ-producing T lymphocytes in the spleen, blood and lung. Pulmonary IFN-γ administration also increased 1) the proliferation of spleen lymphocytes in vivo and 2) the IP-10 level and CXCR3+ T lymphocyte numbers in the spleen and lung of mice. IP-10 could promote the proliferation of spleen lymphocytes in vitro but not blood lymphocytes or lung-resident lymphocytes. AMG487, a potent inhibitor of binding between IP-10 and CXCR3, could block pulmonary IFN-γ instillation-induced chronic airway lymphocytic inflammation and the proliferation of IFN-γ-producing T lymphocytes in mouse spleens. In conclusion, intrapulmonary IFN-γ instillation may induce the proliferation of splenic IFN-γ-producing T lymphocytes through IP-10 and the CXCR3 pathway. The IFN-γ-producing T lymphocytes in blood, partly released from the mouse spleen, may be partly attracted to the lung by pulmonary IP-10 through the CXCR3 pathway. IFN-γ-producing T lymphocytes and IFN-γ in the lung may cause chronic airway lymphocytic inflammation and chronic cough hypersensitivity.

Population pharmacokinetic analysis of the P2X3-receptor antagonist gefapixant

Gefapixant, a P2X3-receptor antagonist, demonstrated objective and subjective efficacy in individuals with refractory or unexplained chronic cough. We report a population pharmacokinetic (PopPK) analysis that characterizes gefapixant pharmacokinetics (PKs), quantifies between- and within-participant variability, and evaluates the impact of intrinsic and extrinsic factors on gefapixant exposure. The PopPK model was initially developed using PK data from six phase I studies. Stepwise covariate method was utilized to identify covariates impacting PK parameters; the model was re-estimated and covariate effects were re-assessed after integrating PK data from three phase II and III studies. Simulations were conducted to evaluate the magnitude of covariate effects on gefapixant exposure. Of 1677 participants included in this data set, 1618 had evaluable PK records. Age, body weight, and sex had statistically significant, but not clinically relevant, effects on exposure. Degree of renal impairment (RI) had statistically significant and clinically relevant effects on exposure; exposure was 17% to 89% higher in those with versus without RI. Simulation results indicated that gefapixant 45 mg administered once daily to patients with severe RI has similar exposure to gefapixant 45 mg administered twice daily to patients with normal renal function. There were no significant effects of proton pump inhibitors or food. Of evaluated intrinsic and extrinsic factors, only RI had a clinically relevant effect on gefapixant exposure. Patients with mild or moderate RI do not require dosage adjustments; however, for patients with severe RI who are not on dialysis, gefapixant 45 mg once daily is recommended.

Effects of Shiwei Longdanhua formula on LPS induced airway mucus hypersecretion, cough hypersensitivity, oxidative stress and pulmonary inflammation

Shiwei Longdanhua Granule (SWLDH) is a classic Tibetan medicine (TM) ranking in the top 20 Chinese patent medicines in prescription rate to treat respiratory diseases like pneumonia, acute and chronic tracheobronchitis, acute exacerbation of COPD and bronchial asthma in solution of inflammation, cough and phlegm obstruction in clinical practice. However, its systematic pharmacological mechanisms have not been elucidated yet. Here, we studied the therapeutic efficacy of SWLDH in treatment of acute respiratory diseases in BALB/c mice by comprehensive analysis of airway inflammation, oxidative stress, mucus hypersecretion, cough hypersensitivities and indicators associated with the development of chronic diseases. Our results show that SWLDH might exhibit its inhibitory effects on pulmonary inflammation by interference with arachidonic acid (AA) metabolism pathways. Oxidative stress that highly related to the degree of tissue injury could be alleviated by enhancing the reductive activities of glutathione redox system, thioredoxin system and the catalytic activities of catalase and superoxide dismutase (SOD) after SWLDH treatment. In addition, SWLDH could significantly abrogate the mucus hypersecretion induced bronchiole obstruction by inactivate the globlet cells and decrease the secretion of gel-forming mucins (MUC5AC and MUC5B) under pathological condition, demonstrating its mucoactive potency. SWLDH also showed reversed effects on the release of neuropeptides that are responsible for airway sensory hypersensitivity. Simultaneously observed inhibition of calcium influx, reduction in in vivo biosynthesis of acetylcholine and the recovery of the content of cyclic adenosine monophosphate (cAMP) might collaboratively contribute to cause airway smooth muscle cells (ASMCs) relexation. These findings indicated that SWLDH might exhibited antitussive potency via suppression of the urge to cough and ASMCs contraction. Moreover, SWLDH might affect airway remodeling. We found SWLDH could retard the elevation of TGF-β1 and α-SMA, which are important indicators for hyperplasia and contraction during the progression of the chronic airway inflammatory diseases like COPD and asthma.

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.

Trajectories of cough without a cold in early childhood and associations with atopic diseases

BACKGROUND

Although children can frequently experience a cough that affects their quality of life, few epidemiological studies have explored cough without a cold during childhood.

OBJECTIVES

The objective of the study was to describe the latent class trajectories of cough from one to 10 years old and analyse their association with wheezing, atopy and allergic diseases.

METHODS

Questions about cough, wheeze and allergic diseases were asked at 1, 1.5, 2, 3, 4, 5, 6 and 10 years of age in the European prospective cohort of Protection against Allergy: STUdy in Rural Environment (PASTURE). Specific IgE assays were performed at 10 years of age. Questions regarding a cough without a cold were used to build a latent class model of cough over time.

RESULTS

Among the 961 children included in the study, apart from the never/infrequent trajectory (59.9%), eight trajectories of cough without a cold were identified: five grouped acute transient classes (24.1%), moderate transient (6.8%), late persistent (4.8%) and early persistent (4.4%). Compared with the never/infrequent trajectory, the other trajectories were significantly associated with wheezing, asthma and allergic rhinitis. For asthma, the strongest association was with the early persistent trajectory (OR_a  = 31.00 [14.03-68.51]), which was inversely associated with farm environment (OR_a  = 0.39 [0.19-0.77]) and had a high prevalence of cough triggers and unremitting wheeze. Late and early persistent trajectories were also associated with food allergy. Atopic sensitization was only associated with the late persistent trajectory.

CONCLUSION

Late and early persistent coughs without a cold are positively associated with atopic respiratory diseases and food allergy. Children having recurrent cough without a cold with night cough and triggers would benefit from an asthma and allergy assessment. Growing up on a farm is associated with reduced early persistent cough.

Cough hypersensitivity and chronic cough

Chronic cough is globally prevalent across all age groups. This disorder is challenging to treat because many pulmonary and extrapulmonary conditions can present with chronic cough, and cough can also be present without any identifiable underlying cause or be refractory to therapies that improve associated conditions. Most patients with chronic cough have cough hypersensitivity, which is characterized by increased neural responsivity to a range of stimuli that affect the airways and lungs, and other tissues innervated by common nerve supplies. Cough hypersensitivity presents as excessive coughing often in response to relatively innocuous stimuli, causing significant psychophysical morbidity and affecting patients' quality of life. Understanding of the mechanisms that contribute to cough hypersensitivity and excessive coughing in different patient populations and across the lifespan is advancing and has contributed to the development of new therapies for chronic cough in adults. Owing to differences in the pathology, the organs involved and individual patient factors, treatment of chronic cough is progressing towards a personalized approach, and, in the future, novel ways to endotype patients with cough may prove valuable in management.

Pathophysiology of Airway Afferent Nerves

Vagal afferent nerves provide an airway defense mechanism which is ensured by their activation. These nerves can be activated mechanically mainly through mechanosensitive Aβ fibers which are divided into slowly adapting (SARs) and rapidly adapting stretch receptors (RARs). Chemical activation is provided by an interaction of chemical substances with specific receptors. C-fibers are highly sensitive to a direct chemical stimulation accomplished by an activation of ligand-gated ion channels. According to the large influence and mechanisms of vagal afferent nerves, there is a probability that an inappropriate activity of these nerves can cause the symptoms of the respiratory diseases, e.g. cough, dyspnoea, or airway hyperreactivity. The aim of this review is to summarize the physiology of airway afferent nerves and point out the role of vagal sensory nerves dysfunction in the pathogenesis of some respiratory diseases. The understanding of its mechanism could lead to new therapeutic strategies in patients with airway-related pathology.

WAO-ARIA consensus on chronic cough - Part 1: Role of TRP channels in neurogenic inflammation of cough neuronal pathways

BACKGROUND

Cough features a complex peripheral and central neuronal network. The function of the chemosensitive and stretch (afferent) cough receptors is well described but partly understood. It is speculated that chronic cough reflects a neurogenic inflammation of the cough reflex, which becomes hypersensitive. This is mediated by neuromediators, cytokines, inflammatory cells, and a differential expression of neuronal (chemo/stretch) receptors, such as transient receptor potential (TRP) and purinergic P2X ion channels; yet the overall interaction of these mediators in neurogenic inflammation of cough pathways remains unclear.

OBJECTIVES

The World Allergy Organization/Allergic Rhinitis and its Impact on Asthma (WAO/ARIA) Joint Committee on Chronic Cough reviewed the current literature on neuroanatomy and pathophysiology of chronic cough. The role of TRP ion channels in pathogenic mechanisms of the hypersensitive cough reflex was also examined.

OUTCOMES

Chemoreceptors are better studied in cough neuronal pathways compared to stretch receptors, likely due to their anatomical overabundance in the respiratory tract, but also their distinctive functional properties. Central pathways are important in suppressive mechanisms and behavioral/affective aspects of chronic cough. Current evidence strongly suggests neurogenic inflammation induces a hypersensitive cough reflex marked by increased expression of neuromediators, mast cells, and eosinophils, among others. TRP ion channels, mainly TRP V1/A1, are important in the pathogenesis of chronic cough due to their role in mediating chemosensitivity to various endogenous and exogenous triggers, as well as a crosstalk between neurogenic and inflammatory pathways in cough-associated airways diseases.

Cough in Idiopathic Pulmonary Fibrosis

Chronic cough is experienced by most patients with idiopathic pulmonary fibrosis (IPF). It is often the first symptom and is associated with reduced quality of life, increased rates of depression and anxiety, more severe physiological impairment, and disease progression. Although not fully understood, recent gains in understanding the pathophysiology of chronic cough in IPF have been made. The pathophysiology is likely multifactorial and includes alterations in mucous production and clearance, architectural distortion, and increased cough reflex sensitivity, suggesting a role for targeted therapies and multidisciplinary treatment. Modifiable comorbidities can also induce cough in patients with IPF. There is a renewed emphasis on measuring cough in IPF, with clinical trials of novel and repurposed therapies for chronic cough emerging in this population. This review provides an update on the clinical characteristics, pathophysiology, and measurement of chronic cough in patients with IPF and summarizes recent developments in non-pharmacological and pharmacological therapies.

Modulation of Vagal Sensory Neurons via High Mobility Group Box-1 and Receptor for Advanced Glycation End Products: Implications for Respiratory Viral Infections

Vagal sensory neurons contribute to the symptoms and pathogenesis of inflammatory pulmonary diseases through processes that involve changes to their morphological and functional characteristics. The alarmin high mobility group box-1 (HMGB1) is an early mediator of pulmonary inflammation and can have actions on neurons in a range of inflammatory settings. We hypothesized that HMGB1 can regulate the growth and function of vagal sensory neurons and we set out to investigate this and the mechanisms involved. Culturing primary vagal sensory neurons from wildtype mice in the presence of HMGB1 significantly increased neurite outgrowth, while acute application of HMGB1 to isolated neurons under patch clamp electrophysiological investigation produced inward currents and enhanced action potential firing. Transcriptional analyses revealed the expression of the cognate HMGB1 receptors, Receptor for Advanced Glycation End products (RAGE) and Toll-like Receptor 4 (TLR4), in subsets of vagal sensory neurons. HMGB1-evoked growth and electrophysiological responses were significantly reduced in primary vagal sensory neurons harvested from RAGE deficient mice and completely absent in neurons from RAGE/TLR4 double deficient mice. Immunohistochemical analysis of vagal sensory neurons collected from mice after intranasal infection with murine pneumovirus or influenza A virus (IAV), or after intratracheal administration with the viral mimetic PolyI:C, revealed a significant increase in nuclear-to-cytoplasm translocation of HMGB1 compared to mock-inoculated mice. Neurons cultured from virus infected wildtype mice displayed a significant increase in neurite outgrowth, which was not observed for neurons from virus infected RAGE or RAGE/TLR4 deficient mice. These data suggest that HMGB1 can enhance vagal sensory neuron growth and excitability, acting primarily via sensory neuron RAGE. Activation of the HMGB1-RAGE axis in vagal sensory neurons could be an important mechanism leading to vagal hyperinnervation and hypersensitivity in chronic pulmonary disease.

Airway Sensory Nerve Plasticity in Asthma and Chronic Cough

Airway sensory nerves detect a wide variety of chemical and mechanical stimuli, and relay signals to circuits within the brainstem that regulate breathing, cough, and bronchoconstriction. Recent advances in histological methods, single cell PCR analysis and transgenic mouse models have illuminated a remarkable degree of sensory nerve heterogeneity and have enabled an unprecedented ability to test the functional role of specific neuronal populations in healthy and diseased lungs. This review focuses on how neuronal plasticity contributes to development of two of the most common airway diseases, asthma and chronic cough, and discusses the therapeutic implications of emerging treatments that target airway sensory nerves.

The impact of influenza pulmonary infection and inflammation on vagal bronchopulmonary sensory neurons

Influenza A virus (IAV) is rapidly detected in the airways by the immune system, with resident parenchymal cells and leukocytes orchestrating viral sensing and the induction of antiviral inflammatory responses. The airways are innervated by heterogeneous populations of vagal sensory neurons which also play an important role in pulmonary defense. How these neurons respond to IAV respiratory infection remains unclear. Here, we use a murine model to provide the first evidence that vagal sensory neurons undergo significant transcriptional changes following a respiratory IAV infection. RNA sequencing on vagal sensory ganglia showed that IAV infection induced the expression of many genes associated with an antiviral and pro-inflammatory response and this was accompanied by a significant increase in inflammatory cell recruitment into the vagal ganglia. Assessment of gene expression in single-vagal sensory neurons confirmed that IAV infection induced a neuronal inflammatory phenotype, which was most prominent in bronchopulmonary neurons, and also evident in some neurons innervating other organs. The altered transcriptome could be mimicked by intranasal treatment with cytokines and the lung homogenates of infected mice, in the absence of infectious virus. These data argue that IAV pulmonary infection and subsequent inflammation induces vagal sensory ganglia neuroinflammation and this may have important implications for IAV-induced morbidity.

Effects of respiratory muscle training on cough function in neurological disorders: A systematic review with meta-analysis

BACKGROUND

Patients with neurological disorders can present the weakness of respiratory muscle and impaired cough function. Previous studies have shown that respiratory muscle strength training (RMT) is an effective method of improving the strength of respiratory muscle. The effects of RMT on cough function remain controversial.

OBJECTIVE

We aimed to analyze randomized controlled trials (RCTs) that investigated the effects of RMT on cough function of patients with neurological disorders.

METHODS

Pubmed, Medline, Embase, and the Cochrane Library were searched electronically for RCTs. Two reviewers independently performed data extraction and quality assessment. Data were analyzed by using RevMan 5.3 software of The Cochrane Collaboration.

RESULTS

Five studies with 185 participants were included. The mean PEDro score was 6.2 (range 5 to 7), showing moderate methodological quality. Random-effects meta-analyses showed that respiratory muscle training improved peak expiratory cough flow of voluntary cough by 2.16 (95% CI 1.16 to 3.17) and involuntary cough by 2.84 (95% CI 1.29 to 4.39), with statistical significance (P < 0.0001, P = 0.0003). The experimental group had an improvement of 0.19 cmH2O (95% CI -0.12 to 0.5) on the maximal inspiratory pressure, 0.09 cmH2O (95% CI -0.23 to 0.42) on the maximal expiratory pressure, but with no statistical significance (P = 0.23, P = 0.58) between groups.

CONCLUSION

Respiratory muscle training was considered as an effective method for improving cough function. However, this review was insufficient to conclude whether respiratory muscle training was effective in improving inspiratory and expiratory muscle strength, this was opposite with previous meta-analysis. These effects might due to the small samples and different diseases.

[Perceptions of family doctors, pulmonologists and allergists on the approach to patients with chronic cough. Results of an anonymous survey]

OBJECTIVE

To understand the perception of family doctors, pulmonologists and allergists about the current approach to chronic cough and its impact on patients' quality of life.

MATERIAL AND METHODS

Cross-sectional and anonymous survey disseminated through the scientific societies SEAIC, SEMERGEN, semFYC, SEMG and SEPAR. The participants were 620 family doctors, 92 pulmonologists and 62 allergists. A descriptive analysis of the answers was conducted. Response percentages, medians and interquartile intervals were presented. The differences in the percentages between specialties were evaluated with the chi-square.

RESULTS

Only half of the respondents chose a duration greater than 8 weeks as a criterion for diagnosing chronic cough, and less than half considered refractory/unexplained chronic cough a disease in itself. Family doctors perceived that chronic cough had less impact on patients than did pulmonologists or allergists. After a diagnosis of refractory/unexplained chronic cough, all 3specialties considered the most common approach to be to initiate treatment and to do the follow-up of the patient themselves. Most stated that they had no protocols for managing chronic cough, and more than 90% considered these to be necessary.

CONCLUSIONS

The management of patients with chronic cough by family doctors, pulmonologists or allergists seems to be heterogeneous. There is a need for protocols that standardise diagnosis, referral and treatment criteria to optimise patients' management and reduce the impact of chronic cough.

An initial assessment of the involvement of transglutaminase2 in eosinophilic bronchitis using a disease model developed in C57BL/6 mice

The detailed pathogenesis of eosinophilic bronchitis (EB) remains unclear. Transglutaminase 2 (TG2) has been implicated in many respiratory diseases including asthma. Herein, we aim to assess preliminarily the relationship of TG2 with EB in the context of the development of an appropriate EB model through ovalbumin (OVA) sensitization and challenge in the C57BL/6 mouse strain. Our data lead us to propose a 50 μg dose of OVA challenge as appropriate to establish an EB model in C57BL/6 mice, whereas a challenge with a 400 μg dose of OVA significantly induced asthma. Compared to controls, TG2 is up-regulated in the airway epithelium of EB mice and EB patients. When TG2 activity was inhibited by cystamine treatment, there were no effects on airway responsiveness; in contrast, the lung pathology score and eosinophil counts in bronchoalveolar lavage fluid were significantly increased whereas the cough frequency was significantly decreased. The expression levels of interleukin (IL)-4, IL-13, IL-6, mast cell protease7 and the transient receptor potential (TRP) ankyrin 1 (TRPA1), TRP vanilloid 1 (TRPV1) were significantly decreased. These data open the possibility of an involvement of TG2 in mediating the increased cough frequency in EB through the regulation of TRPA1 and TRPV1 expression. The establishment of an EB model in C57BL/6 mice opens the way for a genetic investigation of the involvement of TG2 and other molecules in this disease using KO mice, which are often generated in the C57BL/6 genetic background.

The interrelatedness of chronic cough and chronic pain

Since chronic cough has common neurobiological mechanisms and pathophysiology with chronic pain, both clinical disorders might be interrelated. Hence, we examined the association between chronic cough and chronic pain in adult subjects in the Rotterdam Study, a large prospective population-based cohort study.Using a standardised questionnaire, chronic pain was defined as pain lasting up to 6 months and grouped into a frequency of weekly/monthly or daily pain. Chronic cough was described as daily coughing for at least 3 months duration. The longitudinal and cross-sectional associations were investigated bi-directionally.Of 7141 subjects in the study, 54% (n=3888) reported chronic pain at baseline. The co-prevalence of daily chronic pain and chronic cough was 4.4%. Chronic cough was more prevalent in subjects with daily and weekly/monthly chronic pain compared with those without chronic pain (13.8% and 10.3% versus 8.2%; p<0.001). After adjustment for potential confounders, prevalent chronic pain was significantly associated with incident chronic cough (OR 1.47, 95% CI 1.08-1.99). The association remained significant in subjects with daily chronic pain (OR 1.49, 95% CI 1.06-2.11) with a similar effect estimate, albeit non-significant in those with weekly/monthly chronic pain (OR 1.43, 95% CI 0.98-2.10). After adjustment for covariables, subjects with chronic cough had a significant risk of developing chronic pain (OR 1.63, 95% CI 1.02-2.62) compared with those without chronic cough.Chronic cough and chronic pain confer risk on each other among adult subjects, indicating that both conditions might share common risk factors and/or pathophysiologic mechanisms.

Global Physiology and Pathophysiology of Cough: Part 1: Cough Phenomenology - CHEST Guideline and Expert Panel Report

The purpose of this state-of-the-art review is to update the American College of Chest Physicians 2006 guideline on global physiology and pathophysiology of cough. A review of the literature was conducted using PubMed and MEDLINE databases from 1951 to 2019 and using prespecified search terms. We describe the basic phenomenology of cough patterns, behaviors, and morphological features. We update the understanding of mechanical and physiological characteristics of cough, adding a contemporary view of the types of cough and their associated behaviors and sensations. New information about acoustic characteristics is presented, and recent insights into cough triggers and the patient cough hypersensitivity phenotype are explored. Lastly, because the clinical assessment of patients largely focuses on the duration rather than morphological features of cough, we review the morphological features of cough that can be measured in the clinic. This is the first of a two-part update to the American College of Chest Physicians 2006 cough guideline; it provides a more global consideration of cough phenomenology, beyond simply the mechanical aspects of a cough. A greater understanding of the typical features of cough, and their variations, may allow a more informed interpretation of cough measurements and the clinical relevance for patients.

Chronic cough in adults

Cough, a defense mechanism for clearing the airways of secretions, exudate, or foreign bodies, may become a troublesome symptom. Chronic cough, one of the most frequent symptoms requiring medical attention, is often not due to identifiable causes in adults. Chronic productive cough defines chronic bronchitis, and thus is present in 100% of these patients, and frequently in patients with bronchiectasis, cystic fibrosis, and chronic infectious respiratory diseases. However, chronic cough is most frequently dry. Thus, chronic cough in adults is a difficult syndrome requiring multidisciplinary approaches, particularly to diagnose and treat the most frequent identifiable causes, but also to decide which patients may benefit by treating the central cough hypersensitivity by neuromodulatory therapy and/or non-pharmacologic treatment (speech pathology therapy). Recent guidelines provide algorithms for diagnosis and assessment of cough severity; particularly chronic cough in adults. After excluding life-threatening diseases, chronic cough due to identifiable causes (triggers and/or diseases), particularly smoking and/or the most frequent diseases (asthma, chronic bronchitis, chronic obstructive pulmonary disease, eosinophilic bronchitis, and adverse reactions to drugs [angiotensin-converting enzyme inhibitors and sitagliptin]) should be treated by avoiding triggers and/or according to guidelines for each underlying disease. In patients with troublesome chronic cough due to unknown causes or persisting even after adequate avoidance of triggers, and/or treatment of the underlying disease(s), a symptomatic approach with neuromodulators and/or speech pathology therapy should be considered. Additional novel promising neuromodulatory agents in clinical development (e.g., P2X3 inhibitors) will hopefully become available in the near future.

Perspectives on neuroinflammation contributing to chronic cough

Chronic cough can be a troublesome clinical problem. Current thinking is that increased activity and/or enhanced sensitivity of the peripheral and central neural pathways mediates chronic cough via processes similar to those associated with the development of chronic pain. While inflammation is widely thought to be involved in the development of chronic cough, the true mechanisms causing altered neural activity and sensitisation remain largely unknown. In this back-to-basics perspective article we explore evidence that inflammation in chronic cough may, at least in part, involve neuroinflammation orchestrated by glial cells of the nervous system. We summarise the extensive evidence for the role of both peripheral and central glial cells in chronic pain, and hypothesise that the commonalities between pain and cough pathogenesis and clinical presentation warrant investigations into the neuroinflammatory mechanisms that contribute to chronic cough. We open the debate that glial cells may represent an underappreciated therapeutic target for controlling troublesome cough in disease.

A role for neurokinin 1 receptor expressing neurons in the paratrigeminal nucleus in bradykinin-evoked cough in guinea-pigs

KEY POINTS

Airway projecting sensory neurons arising from the jugular vagal ganglia terminate centrally in the brainstem paratrigeminal nucleus, synapsing upon neurons expressing the neurokinin 1 receptor. This study aimed to assess the involvement of paratrigeminal neurokinin 1 receptor neurons in the regulation of cough, breathing and airway defensive responses. Lesioning neurokinin 1 receptor expressing paratrigeminal neurons significantly reduced cough evoked by inhaled bradykinin but not inhaled ATP or tracheal mechanical stimulation. The reduction in bradykinin-evoked cough was not accompanied by changes in baseline or evoked respiratory variables (e.g. frequency, volume or timing), animal avoidance behaviours or the laryngeal apnoea reflex. These findings warrant further investigations into targeting the jugular ganglia and paratrigeminal nucleus as a therapy for treating cough in disease.

ABSTRACT

Jugular vagal ganglia sensory neurons innervate the large airways and are thought to mediate cough and associated perceptions of airway irritations to a range of chemical irritants. The central terminals of jugular sensory neurons lie within the brainstem paratrigeminal nucleus, where postsynaptic neurons can be differentiated based on the absence or presence of the neurokinin 1 (NK1) receptor. Therefore, in the present study, we set out to test the hypothesis that NK1 receptor expressing paratrigeminal neurons play a role in cough evoked by inhaled chemical irritants. To test this, we performed selective neurotoxin lesions of NK1 receptor expressing neurons in the paratrigeminal nucleus in guinea-pigs using substance P conjugated to saporin (SSP-SAP). Sham lesion control or SSP-SAP lesion guinea-pigs received nebulised challenges, with the pan-nociceptor stimulant bradykinin or the nodose ganglia specific stimulant adenosine 5'-triphosphate (ATP), in conscious whole-body plethysmography to study cough and associated behaviours. Laryngeal apnoea reflexes and cough evoked by mechanical stimulation of the trachea were additionally investigated in anaesthetised guinea-pigs. SSP-SAP significantly and selectively reduced the number of NK1 receptor expressing neurons in the paratrigeminal nucleus. This was associated with a significant reduction in bradykinin-evoked cough, but not ATP-evoked cough, mechanical cough or laryngeal apnoeic responses. These data provide further evidence for a role of jugular vagal pathways in cough, and additionally suggest an involvement of NK1 receptor expressing neurons in the paratrigeminal nucleus. Therefore, this neural pathway may provide novel therapeutic opportunities to treat conditions of chronic cough.

Identification of the Molecular Mechanisms of Peimine in the Treatment of Cough Using Computational Target Fishing

Peimine (also known as verticine) is the major bioactive and characterized compound of Fritillariae Thunbergii Bulbus, a traditional Chinese medicine that is most frequently used to relieve a cough. Nevertheless, its molecular targets and mechanisms of action for cough are still not clear. In the present study, potential targets of peimine for cough were identified using computational target fishing combined with manual database mining. In addition, protein-protein interaction (PPI), gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed using, GeneMANIA and Database for Annotation, Visualization and Integrated Discovery (DAVID) databases respectively. Finally, an interaction network of drug-targets-pathways was constructed using Cytoscape. The results identified 23 potential targets of peimine associated with cough, and suggested that MAPK1, AKT1 and PPKCB may be important targets of pemine for the treatment of cough. The functional annotations of protein targets were related to the regulation of immunological and neurological function through specific biological processes and related pathways. A visual representation of the multiple targets and pathways that form a network underlying the systematic actions of peimine was generated. In summary, peimine is predicted to exert its systemic pharmacological effects on cough by targeting a network composed of multiple proteins and pathways.

Exploring the clinical relevance of cough hypersensitivity syndrome

Introduction: Knowledge of the pathophysiology of cough has continued to advance over recent decades. Establishing anatomic-diagnostic protocols, based on the anatomy and distribution of vagus nerve pathways regulating the cough reflex, was the first breakthrough in modern clinical medicine for chronic cough. The unmet clinical need has prompted revised thinking regarding the pathophysiology of and the clinical approach to chronic cough.Areas covered: The paradigm of cough hypersensitivity syndrome (CHS) has been recently proposed, wherein aberrant neuro-pathophysiology is a common etiology. This review covers major findings on chronic cough and cough hypersensitivity, particularly focused on recently-published studies and explores the clinical relevance and applicability of CHS based on current knowledge and discuss knowledge gaps and future research directions.Expert opinion: This paradigm has provided new opportunities in managing chronic cough and evidence is accumulating to support the validity of CHS. It also warrants the re-appraisal of existing clinical evidence and investigation of how to refine our clinical strategy. While CHS highlights the importance of clinical thinking from the viewpoint of cough, the value of anatomic-diagnostic protocols should remain. Moreover, given the considerable heterogeneity in clinical presentation, cough-associated disease conditions, and treatment responses across different patients, precise molecular endotyping remains key to making further to advancing clinical practice .

Arnold Nerve Reflex: Vagal Hypersensitivity in Chronic Cough With Various Causes

BACKGROUND

A higher incidence of Arnold nerve reflex (ANR) has been observed in patients with chronic cough. However, the different ANR response in various causes of chronic cough remains unclear. Furthermore, it is unknown whether ANR will change after effective treatment.

METHODS

Patients with chronic cough were enrolled in the Guangzhou Institute of Respiratory Health. The causes of chronic cough were diagnosed via a validated management algorithm. Patients underwent an assessment of ANR response before and after 1 month of etiologic treatment.

RESULTS

A total of 127 patients with chronic cough and 55 healthy control subjects were enrolled. The positive response, defined as cough-only ANR or urge-to-cough (UTC), was present in 14.8% of patients with cough variant asthma (CVA), 11.1% of patients with upper airway cough syndrome, 15.4% of patients with gastroesophageal reflex related cough (GERC), 4.8% of patients with eosinophilic bronchitis, and 26.9% of patients with unexplained cough (UC). No ANR or UTC was found in the healthy control subjects. The incidence of the positive response was higher in subjects with CVA, GERC, and UC compared with healthy control subjects (all P < .05). No difference was observed among the different causes of chronic cough (all P > .05). After 1 month of treatment, 87.5% of patients identified with a positive response changed to a negative response. In a subgroup analysis, an increased cough sensitivity to capsaicin was found in the patients with a positive response compared with the patients with a negative response (P < .05).

CONCLUSIONS

A positive ANR appears to be a sign of vagal hypersensitivity and can be reversed after effective treatment of chronic cough. However, although various causes of chronic cough share a similar feature of an elevated ANR response in a minority of patients, there appears to be limited usefulness in assessing ANR because it does not appear to be a valid predictor of etiology of chronic cough or outcome of treatment.

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.

Bronchiectasis and cough: An old relationship in need of renewed attention

Bronchiectasis is an increasingly recognised respiratory condition with limited therapeutic options and a complex spectrum of clinical manifestations that invariably includes chronic cough. As the primary presentation of bronchiectasis in most cases, chronic cough and its mechanistic underpinnings are of central importance but remain poorly understood in this setting. Bronchiectasis is also increasingly identified as an underlying cause of chronic cough highlighting the interrelationship between the two conditions that share overlapping clinical features. Several therapeutic approaches have illustrated positive effects on bronchiectasis-associated cough, however, more focused treatment of heterogeneous cough subtypes may yield better outcomes for patients. A current challenge is the identification of bronchiectasis and cough endophenotypes that may allow improved patient stratification and more targeted therapeutic matching of the right treatment to the right patient. Here we discuss the complex disease phenotypes of bronchiectasis and their interrelationship with cough while considering current and emerging treatment options. We discuss some key cough promoters in bronchiectasis including infection, allergy and immune dysfunction.

Why chronic cough in children is different

Recently, there have been robust changes in our knowledge of the neurophysiology of cough and novel clinical etiologies. Specifically, cough hypersensitivity in adults and protracted bacterial bronchitis (PBB) in children have been increasingly investigated, and differences between chronic cough in children and adults have been widely reported. In young children, postinfectious cough, bronchiectasis, airway malacia, PBB, and asthma appear to be the main causes of cough; however, by adolescence, the causes of cough are more likely to become those common in adults, namely, gastroesophageal reflux, asthma, and upper airway syndrome. These differences are attributed to changes in various characteristics of the respiratory tract, immune system, and nervous system between children and adults. New knowledge about the neural aspects of cough has revealed a complex network of pathways that initiate cough. The effect of inflammation on cough neural processing occurs at multiple peripheral and central sites within the nervous system. Evidence exists that direct or indirect neuroimmune interaction induces a complex response, which can be altered by mediators released by the sensory or parasympathetic neurons and vice versa. During childhood, the respiratory tract and the nervous system undergo a series of anatomical and physiological maturation processes that produce the cough neural circuits. Alterations provoked by various pathological processes, noxious agents, infection, and inflammation during the developmental period can lead to persistent or irreversible modifications, which may explain why many adult patients, in addition to expressing high cough sensitivity, remain refractive to disease-specific therapies.