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

Neural Mechanisms Underlying the Coughing Reflex

Breathing is an intrinsic natural behavior and physiological process that maintains life. The rhythmic exchange of gases regulates the delicate balance of chemical constituents within an organism throughout its lifespan. However, chronic airway diseases, including asthma and chronic obstructive pulmonary disease, affect millions of people worldwide. Pathological airway conditions can disrupt respiration, causing asphyxia, cardiac arrest, and potential death. The innervation of the respiratory tract and the action of the immune system confer robust airway surveillance and protection against environmental irritants and pathogens. However, aberrant activation of the immune system or sensitization of the nervous system can contribute to the development of autoimmune airway disorders. Transient receptor potential ion channels and voltage-gated Na+ channels play critical roles in sensing noxious stimuli within the respiratory tract and interacting with the immune system to generate neurogenic inflammation and airway hypersensitivity. Although recent studies have revealed the involvement of nociceptor neurons in airway diseases, the further neural circuitry underlying airway protection remains elusive. Unraveling the mechanism underpinning neural circuit regulation in the airway may provide precise therapeutic strategies and valuable insights into the management of airway diseases.

Potential applications of P2X3 receptor antagonists in the treatment of refractory cough

Refractory chronic cough is defined as a clinical condition in which the cause of the cough remains unclear after comprehensive examination and treatment, or the cause is clear but symptomatic treatment is ineffective. Patients with refractory chronic cough experience a variety of physiological and psychological issues that significantly lower their quality of life and place a significant socio-economic burden on society. As a result, research both domestically and internationally has turned heavily toward these patients. Recently, several studies have identified P2X3 receptor antagonists for the treatment of refractory chronic cough, and this paper reviews the background, mechanism of action, evidence-based proof and application prospects of this class of drugs. KEY MESSAGE: There were plenty of studies about P2X3 receptor antagonists in the past, and in recent years this series of drugs are effective in refractory chronic cough. Although review articles summarizing have been published previously, most have focused on their chemical properties rather than their clinical aspects, with some omitting drugs that have been in clinical studies for nearly two years such as Eliapixant and Sivopixant. Focusing on four P2X3 receptor antagonists with proven efficacy in clinical studies, we analyzed the characteristics and disadvantages of each drug by comparing their clinical results of them and theoretically explained the common side effects of these drugs, as well as their potential for treating refractory chronic cough. This article can be used as a reference for the follow-up studies of P2X3 receptor antagonists in chronic cough. Additionally, it also has implications for the clinical focus of the drug and the approaches to relieve some side effects.

Effects of TRPV4 channel blocker on airway inflammation and airway defense reflexes in experimentally induced model of allergic asthma

The transient receptor potential (TRP) channels regulate physiological and pathological processes. Changes in their activity and sensitivity may be involved in the pathophysiology of asthma. The present study investigates the effect of an inhaled TRPV4 channel blocker HC-067047 in an experimental guinea pig model of ovalbumin-induced allergic asthma. We monitored the effect of 50 nM, 100 nM, and 150 nM HC-067047 concentrations on airway defense reflexes in vivo and tracheal smooth muscle contractility in vitro. The anti-inflammatory action of HC-067047 was investigated by analysis of chronic inflammation markers from lung homogenates. The results suggest that HC-067047 can suppress airway defense reflexes in vivo and acetylcholine-induced contractility in vitro. Immunological analysis revealed that TRPV4 channel blockade leads to a decrease in the levels of inflammatory cytokines. An effect on airway defence reflexes and airway inflammation was observed using tested concentrations (50 mM, 100 mM, 150 mM) of HC-067047. The effects of HC-067047 on both airway defense reflexes and inflammation underline the role of TRPV4 channels in asthma and uncover therapeutic targets for developing innovative drugs in asthma therapy.

Chronic Cough-Related Differences in Brain Morphometry in Adults: A Population-Based Study

BACKGROUND

Individuals with cough hypersensitivity have increased central neural responses to tussive stimuli, which may result in maladaptive morphometric changes in the central cough processing systems.

RESEARCH QUESTION

Are the volumes of the brain regions implicated in cough hypersensitivity different in adults with chronic cough compared with adults without chronic cough?

STUDY DESIGN AND METHODS

Between 2009 and 2014, participants in the Rotterdam Study, a population-based cohort, underwent brain MRI and were interviewed for chronic cough, which was defined as daily coughing for at least 3 months. Regional brain volumes were quantified with the use of parcellation software. Based on literature review, we identified and studied seven brain regions that previously had been associated with altered functional brain activity in chronic cough. The relationship between chronic cough and regional brain volumes was investigated with the use of multivariable regression models.

RESULTS

Chronic cough was prevalent in 9.6% (No. = 349) of the 3,620 study participants (mean age, 68.5 ± 9.0 years; 54.6% women). Participants with chronic cough had significantly smaller anterior cingulate cortex volume than participants without chronic cough (mean difference, -126.16 mm³; 95% CI, -245.67 to -6.66; P = .039). Except for anterior cingulate cortex, there were no significant difference in the volume of other brain regions based on chronic cough status. The volume difference in the anterior cingulate cortex was more pronounced in the left hemisphere (mean difference, -88.11 mm³; 95% CI, -165.16 to -11.06; P = .025) and in men (mean difference, -242.58 mm³; 95% CI, -428.60 to -56.55; P = .011).

INTERPRETATION

Individuals with chronic cough have a smaller volume of the anterior cingulate cortex, which is a brain region involved in cough suppression.

CLINICAL TRIAL REGISTRATION

The Netherlands National Trial Registry (NTR; www.trialregister.nl) and the World Health Organization's International Clinical Trials Registry Platform (ICTRP; www.who.int/ictrp/network/primary/en/) under the joint catalogue number NTR6831.