The effects of nasal histamine challenge on cough reflex in healthy volunteers

Changes of the airway reactivity in patients with rhinosinusitis

Rhinosinusitis is one of the most common conditions in primary and secondary care all over the world. Rhinosinusitis together with asthma and gastroesophageal reflux disease represent the most common causes of chronic cough. The relationship between rhinosinusitis and cough is still not completely understood, however, direct stimulation of nasal mucosa, upper airway cough syndrome, inflammation of the airways, and cough reflex sensitisation play the crucial role in the pathogenesis of chronic cough.

WAO-ARIA consensus on chronic cough - Part II: Phenotypes and mechanisms of abnormal cough presentation - Updates in COVID-19

BACKGROUND

Chronic cough can be triggered by respiratory and non-respiratory tract illnesses originating mainly from the upper and lower airways, and the GI tract (ie, reflux). Recent findings suggest it can also be a prominent feature in obstructive sleep apnea (OSA), laryngeal hyperresponsiveness, and COVID-19. The classification of chronic cough is constantly updated but lacks clear definition. Epidemiological data on the prevalence of chronic cough are informative but highly variable. The underlying mechanism of chronic cough is a neurogenic inflammation of the cough reflex which becomes hypersensitive, thus the term hypersensitive cough reflex (HCR). A current challenge is to decipher how various infectious and inflammatory airway diseases and esophageal reflux, among others, modulate HCR.

OBJECTIVES

The World Allergy Organization/Allergic Rhinitis and its Impact on Asthma (WAO/ARIA) Joint Committee on Chronic Cough reviewed the current literature on classification, epidemiology, presenting features, and mechanistic pathways of chronic cough in airway- and reflux-related cough phenotypes, OSA, and COVID-19. The interplay of cough reflex sensitivity with other pathogenic mechanisms inherent to airway and reflux-related inflammatory conditions was also analyzed.

OUTCOMES

Currently, it is difficult to clearly ascertain true prevalence rates in epidemiological studies of chronic cough phenotypes. This is likely due to lack of standardized objective measures needed for cough classification and frequent coexistence of multi-organ cough origins. Notwithstanding, we emphasize the important role of HCR as a mechanistic trigger in airway- and reflux-related cough phenotypes. Other concomitant mechanisms can also modulate HCR, including type2/Th1/Th2 inflammation, presence or absence of deep inspiration-bronchoprotective reflex (lower airways), tissue remodeling, and likely cough plasticity, among others.

Upper Airway Cough Syndrome in Pathogenesis of Chronic Cough

Cough is one of the most important defensive reflexes. However, extensive non- productive cough is a harmful mechanism leading to the damage of human airways. Cough is initiated by activation of vagal afferents in the airways. The site of their convergence is particularly the nucleus of the solitary tract (nTS). The second-order neurons terminate in the pons, medulla and spinal cord and there is also the cortical and subcortical control of coughing.Upper airway cough syndrome (UACS) - previously postnasal drip syndrome - is one of the most common causes of chronic cough together with asthma and gastroesophageal reflux. The main mechanisms leading to cough in patients with nasal and sinus diseases are postnasal drip, direct irritation of nasal mucosa, inflammation in the lower airways, upper airway inflammation and the cough reflex sensitization. The cough demonstrated by UACS patients is probably due to hypersensitivity of the upper airways sensory nerve or lower airways sensory nerve, or a combination of both. Further studies are needed to clarify this mechanism.

The Prospect for Potent Sodium Voltage-Gated Channel Blockers to Relieve an Excessive Cough

An excessive, irritable, productive or non-productive coughing associated with airway inflammation belongs to pathological cough. Increased activation of airway vagal nociceptors in pathological conditions results from dysregulation of the neural pathway that controls cough. A variety of mediators associated with airway inflammation overstimulate these vagal airway fibers including C-fibers leading to hypersensitivity and hyperreactivity. Because current antitussives have limited efficacy and unwanted side effects there is a continual demand for the development of a novel more effective antitussives for a new efficacious and safe cough treatment. Therefore, inhibiting the activity of these vagal C-fibers represents a rational approach to the development of effective antitussive drugs. This may be achieved by blocking inflammatory mediator receptors or by blocking the generator potential associated with the specific ion channels. Because voltage-gated sodium channels (NaVs) are absolutely required for action potentials initiation and conduction irrespective of the stimulus, NaVs become a promising neural target. There is evidence that NaV1.7, 1.8 and 1.9 subtypes are predominantly expressed in airway cough-triggering nerves. The advantage of blocking these NaVs is suppressing C-fiber irrespective to stimuli, but the disadvantage is that by suppressing the nerves is may also block beneficial sensations and neuronal reflex behavior. The concept is that new antitussive drugs would have the benefit of targeting peripheral airway nociceptors without inhibiting the protective cough reflex.

Cough modulation by upper airway stimuli in cat - potential clinical application?

The modulation of mechanically induced tracheobronchial cough was tested by applying various stimuli and the elicitation of other airway protective behaviors in pentobarbital anesthetized cats. Capsaicin and histamine were injected in the nose, and mechanical nylon fiber and / or air puff stimulation was applied to the nose and nasopharynx. Reflex responses of cough, sneeze, aspiration reflex and expiration reflex were induced mechanically. Swallow was initiated by the injection of water into oropharynx. Subthreshold mechanical stimulation of nasopharyngeal and nasal mucosa, as well as water stimulation in the oropharynx and larynx, with no motor response, had no effect on rhythmic coughing. Cough responsiveness and excitability increased with capsaicin and air puff stimuli delivered to the nose. Vice versa, the number of cough responses was reduced and cough latency increased when aspiration reflexes (>1) occurred before the cough stimulus or within inter-cough intervals (passive E2 cough phase). The occurrence of swallows increased the cough latency as well. Cough inspiratory and / or expiratory motor drive was enhanced by the occurrence of expiration reflexes, swallows, and sneezes and also by aspiration reflex within the inspiratory phase of cough and by nasal air puff stimuli. Complex central interactions, ordering and sequencing of motor acts from the airways may result in the disruption of cough rhythmic sequence but also in the enhancement of cough. Our data confirm that number of peripheral stimuli and respiratory motor responses significantly alters cough performance. We propose developing and testing stimulation paradigms that modify coughing and could be employed in correcting of inappropriate or excessive coughing.

Mechanical Stimulation by Postnasal Drip Evokes Cough

Cough affects all individuals at different times, and its economic burden is substantial. Despite these widespread adverse effects, cough research relies on animal models, which hampers our understanding of the fundamental cause of cough. Postnasal drip is speculated to be one of the most frequent causes of chronic cough; however, this is a matter of debate. Here we show that mechanical stimuli by postnasal drip cause chronic cough. We distinguished human cough from sneezes and expiration reflexes by airflow patterns. Cough and sneeze exhibited one-peak and two-peak patterns, respectively, in expiratory airflow, which were also confirmed by animal models of cough and sneeze. Transgenic mice with ciliary dyskinesia coughed substantially and showed postnasal drip in the pharynx; furthermore, their cough was completely inhibited by nasal airway blockade of postnasal drip. We successfully reproduced cough observed in these mice by injecting artificial postnasal drip in wild-type mice. These results demonstrated that mechanical stimulation by postnasal drip evoked cough. The findings of our study can therefore be used to develop new antitussive drugs that prevent the root cause of cough.

Cough reflex sensitization from esophagus and nose

The diseases of the esophagus and nose are among the major factors contributing to chronic cough although their role in different patient populations is debated. Studies in animal models and in humans show that afferent C-fiber activators applied on esophageal or nasal mucosa do not initiate cough, but enhance cough induced by inhaled irritants. These results are consistent with the hypothesis that activation of esophageal and nasal C-fibers contribute to cough reflex hypersensitivity observed in chronic cough patients with gastroesophageal reflux disease (GERD) and chronic rhinitis, respectively. The afferent nerves mediating cough sensitization from the esophagus are probably the neural crest-derived vagal jugular C-fibers. In addition to their responsiveness to high concentration of acid typical for gastroesophageal reflux (pH < 5), esophageal C-fibers also express receptors for activation by weakly acidic reflux such as receptors highly sensitive to acid and receptors for bile acids. The nature of sensory pathways from the nose and their activators relevant for cough sensitization are less understood. Increased cough reflex sensitivity was also reported in many patients with GERD or rhinitis who do not complain of cough indicating that additional endogenous or exogenous factors may be required to develop chronic coughing in these diseases.

Eight International London Cough Symposium 2014: Cough hypersensitivity syndrome as the basis for chronic cough

At the Eighth International London Cough Conference held in London in July 2014, the focus was on the relatively novel concept of cough hypersensitivity syndrome (CHS) as forming the basis of chronic cough. This concept has been formulated following understanding of the neuronal pathways for cough and a realisation that not all chronic cough is usually associated with a cause. The CHS is defined by troublesome coughing triggered by low level of thermal, mechanical or chemical exposure. It also encompasses other symptoms or sensations such as laryngeal hypersensitivity, nasal hypersensitivity and possibly also symptoms related to gastrooesopahgeal reflux. The pathophysiologic basis of the CHS is now being increasingly linked to an enhancement of the afferent pathways of the cough reflex both at the peripheral and central levels. Mechanisms involved include the interactions of inflammatory mechanisms with cough sensors in the upper airways and with neuronal pathways of cough, associated with a central component. Tools for assessing CHS in the clinic need to be developed. New drugs may be developed to control CHS. A roadmap is suggested from the inception of the CHS concept towards the development of newer antitussives at the Symposium.

The effect of selective antagonist of H4 receptor JNJ7777120 on nasal symptoms, cough, airway reactivity and inflammation in guinea pigs

The efficacy of H4R antagonist JNJ7777120 on nasal symptoms, cough, airway resistance (Raw), inflammatory cell count in bronchoalveolar lavage (BAL) and blood in ovalbumin (OVA) induced allergic rhinitis (AR) was studied in guinea pigs. Animals (n=8) were sensitized by i.p. OVA and were repeatedly challenged with nasal OVA to induce rhinitis, seven animals were not sensitized. Animals were pre-treated with JNJ7777120 2.5 and 5mg/kg i.p. 30 min prior OVA. Cough was induced by inhalation of citric acid, Raw was measured in vivo by Pennock's method as baseline, during AR and after JNJ7777120 treatment. Leucocyte count in BAL and blood was analyzed. JNJ7777120 (5mg/kg) significantly suppressed nasal symptoms and the number of coughs. This compound significantly inhibited airway reactivity to histamine, but not methacholine. Pre-treatment with JNJ7777120 5mg/kg did not influence significantly the leucocyte count in BAL and blood except for a significant decrease in monocyte count in blood compared to the control group (p<0.05). We conclude that the antitussive action of JNJ7777120 is peripheral. The primary effect of the compound is anti-inflammatory, and the suppression of cough is a consequence of reduced airway inflammation.

Advances in upper airway cough syndrome

Upper airway cough syndrome (UACS), previously referred to as postnasal drip syndrome, is one of the most common causes of chronic cough. However, the pathogenesis of UACS/postnasal drip syndrome remains unclear, and physicians in countries throughout the world have different definitions and ways of treating this disease. The various proposed pathogeneses of UACS include the early postnasal drip theory, subsequent chronic airway inflammation theory, and a recent sensory neural hypersensitivity theory. Additionally, some researchers suggest that UACS is a clinical phenotype of cough hypersensitivity syndrome. While the general principles involved in treating UACS are similar throughout the world, the specific details of treatment differ. This review summarizes the various definitions, pathogenic mechanisms, treatments, and other aspects of UACS, to aid clinicians in expanding their knowledge of how to diagnose and treat this syndrome.

Azelastine and budesonide (nasal sprays): Effect of combination therapy monitored by acoustic rhinometry and clinical symptom score in the treatment of allergic rhinitis

The aim of this study was to objectively evaluate the effects of intranasal therapy with azelastine (AZE), budesonide (BUD), and combined AZE plus BUD (AZE/BUD) using a nasal provocation test (NPT) and acoustic rhinometry in patients with allergic rhinitis. A randomized, single-blind, crossover study with three treatment sequences was used. Thirty patients with persistent AR received the three treatments using a nasal spray twice daily for 30 days and were evaluated by an NPT with histamine before and after each period of treatment. The treatment comparison, assessed by the nasal responsiveness to histamine, was monitored based on subjective (symptom score) and objective parameters (acoustic rhinometry). The minimal cross-area 2 (MCA2) was measured by acoustic rhinometry at 1, 4, 8, and 12 minutes after NPT for each histamine concentration administered (0.5, 1, 2, 4, and 6 mg/mL) up to at least a 20% reduction in the MCA2 from baseline (NPT₂₀). The subjects were scored regarding nasal response encompassing histamine dose and time after histamine administration that caused nasal obstruction (NPT₂₀ score) to assess the treatments' effects. Combination therapy produced a significant increase in baseline MCA2, viz., the improvement of nasal patency (p = 0.005). The symptoms score was significantly decreased after treatment with AZE (p = 0.03), BUD (p < 0.0001), and AZE/BUD (p < 0.0001), compared with pretreatment. The NPT₂₀ score was significantly higher (p = 0.0009) after AZE/BUD, compared with AZE and BUD on their own. Thus, AZE therapy combined with BUD might provide more therapeutic benefits than the isolated drugs for improving nasal patency.

Chronic cough in subjects with upper airway diseases - analysis of mechanisms and clinical applications

Cough is the commonest respiratory symptom leading to a medical consultation. Although acute cough which is usually associated with respiratory viral infection is not a problem to manage, chronic cough is frequently a diagnostic and therapeutic challenge as it does not respond to usual treatments. Specific group of chronic coughers are considered to have upper airway diseases, lately categorized as having upper airway cough syndrome. There is an increasing pool of evidence that upper airway diseases have significant involvements in the regulation of cough reflex, indicating that they must be taken into considerations as major triggers of coughing in the patients. Here we summarize current literature and experiences on the pathogenesis of upper airway cough syndrome, and discuss further clinical applications.

Modulation of cough response by sensory inputs from the nose - role of trigeminal TRPA1 versus TRPM8 channels

Background

Cough, the most important airways defensive mechanism is modulated by many afferent inputs either from respiratory tussigenic areas, but also by afferent drive from other organs. In animal models, modulation of cough by nasal afferent inputs can either facilitate or inhibit the cough response, depending on the type of trigeminal afferents stimulated.

Methods

In this study we addressed the question of possible bidirectional modulation of cough response in human healthy volunteers by nasal challenges with TRPA1 and TRPM8 agonists respectively. After nasal challenges with isocyanate (AITC), cinnamaldehyde, (−) menthol and (+) menthol (all 10^-3 M) nasal symptom score, cough threshold (C2), urge to cough (Cu) and cumulative cough response were measured).

Results

Nasal challenges with TRPA1 relevant agonists induced considerable nasal symptoms, significantly enhanced urge to cough (p<0.05) but no statistically significant modulation of the C2 and cumulative cough response. In contrast, both TRPM8 agonists administered to the nose significantly modulated all parameters including C2 (p<0.05), Cu (p<0.01) and cumulative cough response (p <0.01) documenting strong anti irritating potential of menthol isomers.

Conclusions

In addition to trigeminal afferents expressing TRP channels, olfactory nerve endings, trigemino – olfactoric relationships, the smell perception process and other supramedullar influences should be considered as potential modulators of the cough response in humans.

Relationship between rhinitis and nocturnal cough in school children

BACKGROUND

There is a complex relationship between rhinitis, asthma, and nocturnal cough.

METHODS

To evaluate whether rhinitis is an important risk factor for nocturnal cough and whether this effect is independent of asthma, we analyzed data collected using the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire in a population-based nationwide survey. A child who had experienced a dry cough at night in the past 12 months in the absence of a cold was defined as having nocturnal cough.

RESULTS

After excluding 11,475 records with incomplete data, data from 136,506 children were analyzed. Nocturnal cough was significantly more prevalent in children with current rhinitis compared with children without rhinitis. The association between rhinitis and nocturnal cough was significant in children who had current asthma (adjusted OR [95% CI]: 2.26 [2.00-2.56] in children aged 6-7 yr, 1.90 [1.58-2.30] in those aged 13-14 yr, and 1.86 [1.60-2.19] in those aged 16-17 yr), and this association was even higher among children who had no asthma (adjusted OR [95% CI]: 3.65 [3.36-3.97] in children aged 6-7 yr, 3.05 [2.79-3.32] in those aged 13-14 yr, and 2.69 [2.51-2.88] in those aged 16-17 yr).

CONCLUSIONS

There was a close association between rhinitis and nocturnal cough in young children through adolescents, and this effect was independent of asthma. Upper airways should be examined in children with nocturnal cough.

Smooth emergence in men undergoing nasal surgery: the effect site concentration of remifentanil for preventing cough after sevoflurane-balanced anaesthesia

BACKGROUND

Suppression of cough during emergence after nasal surgery is practical to avoid bleeding from the surgical site. Previously recommended effect-site concentration of remifentanil for preventing cough during emergence is restricted to female patients undergoing thyroid surgery, so we evaluated effective effect-site concentration of remifentanil for preventing cough during emergence for men undergoing nasal surgery.

METHODS

Twenty-four American Society of Anesthesiologists (ASA) physical status I or II, between the ages of 18 and 60 years old, non-smoker male patients undergoing nasal surgery were enrolled in this study. The effective effect-site concentration for 50% of patients (EC(50) ) and and that for 95% of patients (EC(95) ) of remifentanil for preventing cough were determined by Dixon's up-and-down method and by isotonic regression method with a bootstrapping approach. Haemodynamic variables were compared in patients with cough and without cough during emergence.

RESULTS

The EC(50) of remifentanil for preventing cough during emergence by Dixon's method was 2.17 ng/ml [standard deviation (SD) 0.38]. The estimated EC(50) and EC(95) of remifentanil using isotonic regression model with a bootstrapping approach were 2.35 ng/ml [95% confidence interval (CI) 1.89-2.66] and 2.94 ng/ml (95% CI 2.83-2.97), respectively. Mean arterial pressure and heart rate were significantly higher in patients with cough during emergence. Three out of 13 patients that received more than 2.5 ng/ml of remifentanil experienced a brief episode of bradypnea.

CONCLUSIONS

The EC(95) of remifentanil for preventing cough in men after nasal surgery is 2.94 ng/ml. Remifentanil target-controlled infusion with established effect-site concentration could suppress cough in men during emergence from sevoflurane anaesthesia after nasal surgery, though reversible respiratory depression might arise at high effect-site concentration of remifentanil.

Workshop: tuning the 'cough center'

The Workshop considered the mechanisms whereby the 'cough center' could be tuned by various afferent inputs. There were particular presentations on the effects of inputs from the nose, mouth, respiratory tract and lungs, cerebral cortex, somatic tissues and the pharynx. From all these sites cough induced from the lungs could be increased or decreased in its strength or modified in its pattern. Thus 'tuning' of cough could be due to the interaction of afferent inputs, or to the sensitization or desensitization of brainstem neural pathways. The pattern of response depended on the 'type' of cough being studied and, in some instances, on the timing of the sensory input into the brainstem. Cough inputs could also affect various 'non-cough' motor outputs from the brain, although this was not the main theme of the Workshop. The main conclusion was that cough is not a stereotyped output from the medullary 'cough center', but that its pattern and strength depend on many afferent inputs acting on the 'cough center'.

Histamine in allergic rhinitis

Histamine plays a major role in allergic rhinitis. In susceptible individuals, allergen induces nasal mast cell degranulation and the release of histamine into the nasal mucosa. Histamine has been detected after controlled challenges with allergen and, when administered into the nasal cavity, elicits signs and symptoms similar to those elicited by allergen. All four histamine receptors have been demonstrated in the nasal mucosa. The role of the four histamine receptors in the pathophysiology of allergic rhinitis are discussed.

Mechanisms of the cough associated with rhinosinusitis

The diseases of the nose and paranasal sinuses (rhinosinusitis) often in combination with asthma and gastroesophageal reflux are common causes of chronic cough in patients with normal chest radiograph. The relationships between rhinosinusitis and cough are incompletely understood. We investigated modulation of the cough reflex by the inputs from the nose. We demonstrate that the cough reflex is sensitized by the intranasal administration of sensory nerve activators in animal models and in humans. Cough reflex is also sensitized in the guinea pig model of allergic nasal inflammation and in patients with allergic rhinitis. In patients with allergic rhinitis the cough sensitization is augmented during the allergen season. We conclude that the cough reflex can be sensitized from the nose. Our data indicate that this sensitization is mediated by nasal sensory nerves. We speculate that by inducing the cough reflex sensitization rhinosinusitis contributes to chronic cough. If combined with environmental or endogenous cough triggers, the cough reflex sensitization is predicted to cause excessive coughing. The potential endogenous cough triggers may be associated with rhinosinusitis (postnasal drip, aspiration of nasal secrets) or secondary to a coexistent disease such as asthma or gastroesophageal reflux.

Histamine reverses IL-5-afforded human eosinophil survival by inducing apoptosis: pharmacological evidence for a novel mechanism of action of histamine

Eosinophils are essential inflammatory cells in the pathogenesis of asthma and atopic conditions. Histamine, released from mast cells and basophils in response to allergen exposure, is a critical mediator in the allergic response. Histamine exerts its effects via four unequivocally characterized histamine receptors, H(1-4). Several functions of eosinophils have previously been shown to be stimulated by histamine. However, its effects on eosinophil apoptosis are unknown. The aim of the present study was to resolve the effects of histamine on constitutive apoptosis of human eosinophils and on the survival-enhancing action of interleukin (IL)-5. Additional experiments were conducted to elucidate the histamine receptor(s) involved in any response seen and the associated signal transduction cascade. Human isolated peripheral blood eosinophils were cultured in the absence or presence of histamine, IL-5 and receptor antagonists/agonists or mediator inhibitors/analogues. Apoptosis was assessed by measuring the relative DNA content of propidium iodide (PI)-stained cells and the effects were confirmed by morphological analysis with bright field microscopy. Caspase activities were assessed by using commercial Caspase-Glo 3/7, 8 and 9 luminescence assays. Histamine (10-100 microM) partially reversed IL-5-induced human eosinophil survival by enhancing apoptosis as assessed by measuring the relative DNA content of PI-stained cells. This effect was not mediated through any of the known histamine receptors or through non-specific activation of 5-hydroxytryptamine receptors or alpha-adrenoceptors. Moreover, the reversal of IL-5-inhibited eosinophil apoptosis by histamine seemed not to utilize the conventional intracellular second-messenger pathways including cyclic AMP, protein kinase A or phospholipase C. Inhibition of caspase 6 and caspases 1, 10 or 12 reversed the effects of histamine but also inhibited apoptosis in general. In conclusion, the data presented herein indicate that histamine induces human eosinophil apoptosis in the presence of a survival-prolonging cytokine by a mechanism that does not apparently involve the activation of any of the currently known histamine receptor subtypes. The possibility exists that another, as yet unidentified, histamine receptor may exist in human eosinophils that regulates survival, although the participation of histamine receptor-independent mechanisms cannot be excluded.

Involvement of ionotropic purinergic receptors in the histamine-induced enhancement of the cough reflex sensitivity in guinea pigs

We examined the effect of inhaled histamine on citric acid-induced coughs and clarified the role of ionotropic purinergic receptors in the resulting changes. Although the inhalation of 0.1 M citric acid by itself produced only a few coughs in guinea pigs, exposure to histamine, at concentrations of 0.3 to 1 mM, for 2 min concentration dependently increased the number of citric acid-induced coughs. This histamine-induced increase in the number of citric acid-induced coughs was dose dependently and significantly reduced when animals were pretreated with fexofenadine, a histamine H1 receptor antagonist. The histamine-induced increase in the number of citric acid-induced coughs was completely reduced when animals were co-pretreated with 2',3'-O-(2,4,6-trinitrophenyl) adenosine 5-triphosphate (TNP-ATP, 50 microM), a P2X receptor antagonist, and reactive blue 2, a P2Y receptor antagonist, for 2 min. Furthermore, the ATP-induced increase in the number of citric acid-induced coughs was dose dependently and significantly decreased when animals were pretreated with fexofenadine, at doses of 0.3, 1 and 3 mg/kg, p.o. These results suggest that histamine enhances the excitability of rapidly adapting receptors to tussive stimuli via modulation of ATP release in the airways. Furthermore, ATP might act not only on P2X receptors to directly activate rapidly adapting receptors, but also on P2Y receptors to increase histamine release, indirectly increasing the cough reflex sensitivity.