Enhanced airway sensory nerve reactivity in non-eosinophilic asthma

Cough and cough hypersensitivity as treatable traits of asthma

Cough is a common and troublesome symptom in people with asthma and is often associated with poorer asthma control and exacerbations. Apart from asthma, other causes or comorbidities might underlie cough in asthma, such as rhinosinusitis and bronchiectasis. Eosinophilic inflammation and bronchoconstriction can lead to an acute episode of cough or worsen chronic cough. Cough hypersensitivity with laryngeal paraesthesia, allotussia, and hypertussia might underlie the cough of asthma through augmented sensory nerve excitability of upper-airway vagal sensory nerves. Cough associated with bronchoconstriction and type 2 inflammation should respond to inhaled corticosteroids and long-acting β-adrenoceptor agonist therapy. For cough hypersensitivity in adults, speech and language therapy and neuromodulators (eg, gabapentin) could be considered. In children, there is no consistent association of asthma with cough sensitivity or between cough and asthma severity. Further research is needed to realise the potential of cough as a measure of asthma control, to understand the mechanisms of cough in asthma, and to develop safe, effective treatments and a precision-medicine approach to the management of cough in asthma in children and adults.

Sputum inflammatory, neural, and remodelling mediators in eosinophilic and non-eosinophilic asthma

BACKGROUND

Neural and remodelling mechanisms may play a role in asthma, particularly non-eosinophilic asthma (NEA).

OBJECTIVE

To assess sputum mediators associated with neural, remodelling, and inflammatory mechanisms in eosinophilic asthma (EA), NEA, and non-asthmatics.

METHODS

111 participants with and 62 without asthma (14-21 years) underwent sputum induction, exhaled nitric oxide (FeNO), atopy, and spirometry tests. Twenty-four mediators were measured in sputum using ELISA or bead array. EA (n=52) and NEA (n=59) were defined using a sputum eosinophil cut-point of ≥2.5%.

RESULTS

Elevated levels of nociceptin (median: 39.1 vs 22.4 ng/mL, p=0.03), periostin (33.8 vs 9.4 ng/mL, p=0.01), and eosinophil cationic protein (ECP); (220.1 vs 83.7 ng/mL, p=0.03) were found in asthmatics compared with non-asthmatics. Nociceptin was elevated in EA (54.8 vs 22.4 ng/mL, p=0.02) compared with non-asthmatics. EA had higher levels of inflammatory (ECP: 495.5 vs 100.3 ng/mL, p≤0.01; interleukin-1β: 285.3 vs 209.3 pg/mL, p=0.03; histamine: 5805.0 vs 3172.5 pg/mL, p=<0.01) and remodelling (vascular endothelial growth factor A (VEGF-A); 3.3 vs 2.5 ng/mL, p=0.03; periostin: 47.7 vs 22.1 ng/mL, p=0.04) mediators than NEA. Whilst macrophages were associated with neural mediators e.g. neurokinin A (r=0.27, p=0.01) and nociceptin (r=0.30, p=0.02), granulocytes were associated with inflammatory/remodelling mediators; e.g. ECP and VEGF-A correlated with neutrophils (r=0.53 & r=0.33 respectively, p=<0.01) and eosinophils (r=0.53 & r=0.29 respectively, p≤0.01).

CONCLUSION

Elevated levels of nociceptin and inflammatory/remodelling markers were found in EA, but no evidence for neural and remodelling pathways was found in NEA. Neural and remodelling mechanisms appear to coexist with inflammation.

Heart rate variability as a marker of autonomic nervous system activity in young people with eosinophilic and non-eosinophilic asthma

OBJECTIVE

An imbalance in autonomic nervous system (ANS) activity may play a role in asthma, but it is unclear whether this is associated with specific pathophysiology. This study assessed ANS activity by measuring heart rate variability (HRV) in eosinophilic (EA) and non-eosinophilic asthma (NEA) and people without asthma.

METHODS

HRV, combined hypertonic saline challenge/sputum induction, exhaled nitric oxide (FeNO), skin prick tests to measure atopy, and spirometry tests were conducted in teenagers and young adults (14-21 years) with (n = 96) and without (n = 72) generally well-controlled asthma. HRV parameters associated with sympathetic and parasympathetic ANS branches were analyzed. EA and NEA were defined using a 2.5% sputum eosinophil cut-point. Airway hyperreactivity (AHR) was defined as ≥15% reduction in FEV₁ following saline challenge.

RESULTS

HRV parameters did not differ between asthmatics and non-asthmatics or EA and NEA. They were also not associated with markers of inflammation, lung function or atopy. However, increased absolute low frequency (LFµs²; representing increased sympathetic nervous system (SNS) activity) was found in asthmatics who used β-agonist medication compared to those who did not (median: 1611, IQR 892-3036 vs 754, 565-1592; p < 0.05) and increased normalized low frequency (LF nu) was found in those with AHR compared to without AHR (64, 48-71 vs 53, 43-66; p < 0.05).

CONCLUSION

ANS activity (as measured using HRV analysis) is not associated with pathophysiology or inflammatory phenotype in young asthmatics with generally well-controlled asthma. However, enhanced SNS activity can be detected in asthmatics with AHR or who use β-agonist medication.