Airway Defense Control Mediated via Voltage-Gated Sodium Channels

The Changes in Expression of NaV1.7 and NaV1.8 and the Effects of the Inhalation of Their Blockers in Healthy and Ovalbumin-Sensitized Guinea Pig Airways

Background: The presented study evaluated the suppositional changes in the airway expression of Nav1.8 and Nav1.7 and their role in the airway defense mechanisms in healthy animals and in an experimental asthma model. Methods: The effects of the blockers inhalation on the reactivity of guinea pig airways, number of citric-acid-induced coughs and ciliary beating frequency (CBF) were tested in vivo. Chronic inflammation simulating asthma was induced by repetitive exposure to ovalbumin. The expression of Nav1.7 and Nav1.8 was examined by ELISA. Results: The Nav 1.8 blocker showed complex antitussive and bronchodilatory effects and significantly regulated the CBF in healthy and sensitized animals. The Nav1.7 blockers significantly inhibited coughing and participated in CBF control in the ovalbumin-sensitized animals. The increased expression of the respective ion channels in the sensitized animals corresponded to changes in CBF regulation. The therapeutic potency of the Nav1.8 blocker was evidenced in combinations with classic bronchodilators. Conclusion: The allergic-inflammation-upregulated expression of Nav1.7 and Nav1.8 and corresponding effects of blocker inhalation on airway defense mechanisms, along with the Nav1.8 blocker’s compatibility with classic antiasthmatic drugs, bring novel possibilities for the treatment of various respiratory diseases. However, the influence of the Nav1.8 blocker on CBF requires further investigation.

Ciliary beat frequency in children with adenoid hypertrophy

BACKGROUND

Children with adenoid hypertrophy (AH) have impaired respiratory system defense mechanisms, such as mucociliary clearance. We hypothesized that AH negatively affects one of the most important aspects of mucociliary clearance-ciliary beat frequency (CBF) and that adenoidectomy could potentially restore this essential defence mechanism of the airways. This study evaluated the influence of AH and endoscopic adenoidectomy on the CBF of the nasal respiratory epithelium in children.

METHODS

This prospective study included 64 children with confirmed AH aged 3 to 18 years and 43 age- and sex-matched healthy controls. Nasal CBF was analyzed using a digital high-speed video microscope and the software application Ciliary Analysis (NI LabVIEW). The preoperative adenoid size was assessed according to Cassano. Clinical symptoms of chronic rhinosinusitis were evaluated using the SNOT-20 questionnaire.

RESULTS

Children with AH had a median CBF of 5.35 ± 1.06 Hz. Six months after surgery, the median CBF was significantly higher (6.48 ± 0.88 Hz; P < .001) and reached the values of healthy children (6.37 ± 0.71 Hz; P = .512). The size of the adenoid tissue did not correlate with the CBF. No influence of age or gender on the CBF was found. After adenoidectomy, a significant reduction of the mean total SNOT-20 score was recorded (P < .01).

CONCLUSION

Children with clinically symptomatic AH have impaired mucociliary clearance due to decreased nasal CBF. Removal of hypertrophic adenoid tissue normalizes the CBF and reduces the presence of clinical symptoms of rhinosinusitis.

Activation of TRPA1 by volatile organic chemicals leading to sensory irritation

Many volatile organic chemicals (VOCs) have not been tested for sensory pulmonary irritation. Development of in vitro non-animal sensory irritation assay suitable for a large number of chemicals is needed to replace the mouse assay. An adverse outcome pathway (AOP) is designed to provide a clear description of the biochemical and cellular processes leading to toxicological effects or an adverse outcome. The AOP for chemical sensory pulmonary irritation was developed according to the Organization for Economic Co-operation and Development guidance including the Bradford Hill criteria for a weight of evidence to determine the confidence of the AOP. The proposed AOP is based on an in-depth review of the relevant scientific literature to identify the initial molecular event for respiratory irritation. The activation of TRPA1 receptor (transient receptor potential cation channel, subfamily A, member 1) is the molecular initial event (MIE) leading to sensory irritation. A direct measure of TRPA1 activation in vitro should identify chemical sensory irritants and provide an estimate of potency. Fibroblasts expressing TRPA1 are used to determine TRPA1 activation and irritant potency. We report a linear relationship between the in vivo RD₅₀ and the in vitro pEC₅₀ values (R=0.81) to support this hypothesis. We propose that this in vitro assay after additional analysis and validation could serve as a suitable candidate to replace the mouse sensory irritation assay.

Antitussive therapy: A role for levodropropizine

Cough is a protective reflex that serves to clear the airways of excessive secretions and foreign matter and which sometimes becomes excessive, and troublesome to patients. Cough is one of the most common reasons why individuals seek medical attention. A range of drugs have been developed in the past with antitussive activity and different mechanisms of action, but there are still very few safe and effective treatments available. The poor tolerability of most available antitussives is closely related to their action on the central nervous system (CNS). An international group of experts specialized in cough met to discuss the need to identify an effective antitussive treatment with a good tolerability profile. The aim of this expert review is to increase the knowledge about the cough mechanism and the activity of levodropropizine, a peripherally acting antitussive drug.

Acid-Sensing Ion Channel 1a Contributes to Airway Hyperreactivity in Mice

Neurons innervating the airways contribute to airway hyperreactivity (AHR), a hallmark feature of asthma. Several observations suggested that acid-sensing ion channels (ASICs), neuronal cation channels activated by protons, might contribute to AHR. For example, ASICs are found in vagal sensory neurons that innervate airways, and asthmatic airways can become acidic. Moreover, airway acidification activates ASIC currents and depolarizes neurons innervating airways. We found ASIC1a protein in vagal ganglia neurons, but not airway epithelium or smooth muscle. We induced AHR by sensitizing mice to ovalbumin and found that ASIC1a^-/- mice failed to exhibit AHR despite a robust inflammatory response. Loss of ASIC1a also decreased bronchoalveolar lavage fluid levels of substance P, a sensory neuropeptide secreted from vagal sensory neurons that contributes to AHR. These findings suggest that ASIC1a is an important mediator of AHR and raise the possibility that inhibiting ASIC channels might be beneficial in asthma.