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ERJ Open Res
ERJ Open Res
ERJOR
erjor
ERJ Open Research
2312-0541
European Respiratory Society

10.1183/23120541.00296-2024
00296-2024
Version of Record
Research Letters
2
14
Revealing the gap: fractional exhaled nitric oxide and clinical responsiveness to biological therapy in severe asthma – a retrospective study
FENO variations in severe asthma
Maniscalco Mauro 12
https://orcid.org/0000-0002-5888-8781
Candia Claudio 2
https://orcid.org/0000-0003-2298-1623
Visca Dina 3
D'Amato Maria 2
Calabrese Cecilia 4
Ambrosino Pasquale 5
Molino Antonio 2
Fuschillo Salvatore 1
1 Istituti Clinici Scientifici Maugeri IRCCS, Pulmonary Rehabilitation Unit of Telese Terme, Telese Terme, Italy
2 Department of Clinical Medicine and Surgery, University of Naples “Federico II”, Naples, Italy
3 Istituti Clinici Scientifici Maugeri IRCCS, Pulmonary Rehabilitation Unit of Tradate Institute, Telese Terme, Italy
4 University of Campania “Luigi Vanvitelli”, Naples, Italy
5 Istituti Clinici Scientifici Maugeri IRCCS, Directorate of Telese Terme Institute, Telese Terme, Italy
Mauro Maniscalco (mauro.maniscalco@icsmaugeri.it)
9 2024
23 9 2024
10 5 00296-202427 2 2024
24 4 2024
Copyright ©The authors 2024
2024
https://creativecommons.org/licenses/by-nc/4.0/ This version is distributed under the terms of the Creative Commons Attribution Non-Commercial Licence 4.0. For commercial reproduction rights and permissions contact permissions@ersnet.org
Extract

Patients with severe asthma often require treatment with a biological drug directed at pivotal immune regulators, including interleukin (IL)-4, IL-5, IL-13, immunoglobulin E (IgE) and, more recently, thymic stromal lymphopoietin [1]. In this regard, biomarkers of type 2-high inflammation, such as exhaled nitric oxide fraction (FENO), have been progressively and successfully utilised for the endotyping of severe asthma patients [2] in order to improve their therapeutical management. However, there has been relatively little focus on monitoring the dynamics of these biomarkers after treatment initiation and on understanding the correlation between drug-induced changes and the observed clinical response [3].

Shareable abstract

A proportion of patients with severe asthma treated with biological drugs undergoes a significant decline in FENO. However, variations in FENO are largely independent of the clinical efficacy of the biological drug therapy. https://bit.ly/3xWszYJ

Ministero della Salute http://dx.doi.org/10.13039/501100003196
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pmc To the Editor:

Patients with severe asthma often require treatment with a biological drug directed at pivotal immune regulators, including interleukin (IL)-4, IL-5, IL-13, immunoglobulin E (IgE) and, more recently, thymic stromal lymphopoietin [1]. In this regard, biomarkers of type 2-high inflammation, such as exhaled nitric oxide fraction (FENO), have been progressively and successfully utilised for the endotyping of severe asthma patients [2] in order to improve their therapeutical management. However, there has been relatively little focus on monitoring the dynamics of these biomarkers after treatment initiation and on understanding the correlation between drug-induced changes and the observed clinical response [3]. In the current retrospective study, we evaluated a cohort of patients with severe asthma undergoing treatment with different biologics and investigated the association between the documented clinical response and changes in FENO levels after 6 months of therapy.

Patients diagnosed with severe asthma were evaluated for inclusion. The inclusion criteria comprised: age ≥18 years, clinical diagnosis of severe asthma [4], satisfactory spirometry and FENO results at baseline and at follow-up, treatment with any biological drug for severe asthma. Exclusions were applied to patients with contraindications to biological drug therapy, those unable to perform acceptable and repeatable spirometry tests, those lost to follow-up, those with significant missing data in their records, and current or former smokers (defined as abstinent from smoking for ≥6 months) with a smoking history ≥10 pack-years.

After the protocol approval by the Institutional Review Board Campania 2 (number AOC-0010488-2024), we screened patients for inclusion and collected relevant demographical and clinical data from our records, as well as blood eosinophil count (BEC), FENO, lung function parameters and patient-reported outcomes (Asthma Control Test (ACT) and Asthma Control Questionnaire (ACQ)5). FENO had been assessed with an electrochemical device (Vivatmo Pro; Bosch, Germany) following the latest available recommendations [5, 6], while lung function parameters had been measured with an automated equipment (Vmax Encore; Vyasis Healthcare, Italy), in line with the most recent guidelines [5, 7]. The study procedures were performed both at baseline, before starting the biological drug treatment and after 6 months of therapy. Following the 2022 consensus paper on minimal clinically important differences for asthma endpoints [8], a FENO reduction of ≥20% was considered as clinically significant. Statistical analysis was performed with the SPSS package version 29.0 (IBM, USA).

Of 192 asthmatic patients in total from our database, 97 were eligible and were included in the final analysis. The included subjects had a median annual exacerbation rate of 2.0 (interquartile range (IQR) 1.0–3.0) and mostly presented with an eosinophilic phenotype, demonstrated by a median BEC of 449.5 cells per mm3 (IQR 305.2–663.8 cells per mm3). 27 (27.8%) patients reported a smoking history, with a mean±sd exposure score of 5.0±1.2 pack-years. Collectively, FENO was elevated at baseline (median 31.0 ppb, IQR 23.0–60.0 ppb). No patient was taking oral steroids (OCS) at enrolment and asthma control was poor (median ACT score 16.5 (IQR 11.0–20.0) and ACQ5 of 4.0 (IQR 3.1–4.3)). In order to assess the presence of selection bias, we compared the included subjects to those excluded, and observed no statistically significant difference in demographics, asthma control or lung function (data not shown).

Based on a FENO reduction of ≥20%, we then identified 50 FENO decliners and 47 nondecliners. The main results are summarised in table 1. At baseline, a significant difference was found in the values of FENO, which were, of course, higher among decliners compared to nondecliners (34.5 ppb, (IQR 27.8–69.5 ppb) versus 25.0 ppb (IQR 18.0–46.0 ppb), p=0.004). Conversely, decliners had lower baseline ACQ5 scores (p=0.005). After treatment, variations (Δ) of comparable magnitudes were observed in the two groups for all the main outcomes (always nonsignificant). The only exception that met statistical significance was forced vital capacity (FVC), both expressed as absolute values (median ΔFVC 0.06 L (IQR −0.11–0.24 L) among nondecliners versus 0.20 L (IQR 0.07–0.44 L) among decliners, p=0.017) and as percentage of the predicted value (median ΔFVC 2.0% (IQR −3.0–6.0%) predicted among nondecliners versus 5.0% (1.0–14.0%) predicted among decliners, p=0.008). Among FENO decliners, ΔFENO was associated by linear correlations both with baseline ACT (r= −0.346, p=0.019) and baseline ACQ5 (r=0.530, p=0.005), as well as with baseline FENO values (r= −0.921, p<0.001); such data were further confirmed by using Spearman's nonparametric coefficients. After adjusting for age, sex, smoking history and presence of nasal polyps, ACQ5 was found to be the most important predictor of ΔFENO (r2=0.407, β=0.679; p=0.004), with higher baseline values predicting lower decreases in FENO.

TABLE 1 Major clinical and functional parameters at baseline and after 6 months of therapy with biologic drugs in patients with severe asthma stratified and compared by exhaled nitric oxide (FENO) response

Variable	FENO nondecliners	FENO decliners	Nondecliners versus decliners, p-value	
t 0	t 6	p-value	t 0	t 6	p-value	t 0	t 6	
Patients	47			50					
Demographics	
 Females	31 (66.0)			26 (52.0)			0.163		
 Age, years	55.1±14.2			55.9±11.5			0.769		
Clinical history	
 Smoking history	12 (25.5)			15 (30.0)			0.588		
 Exacerbations	2.0 (1.0–3.0)			2.0 (1.0–3.0)			0.634		
Markers of T2-high inflammation	
 Eosinophil count, cells per mm3	401.3 (300.0–630.8)	40.2 (0–118.6)	<0.001	477.0 (300.4–674.0)	57.4 (10.0–210.0)	<0.001	0.642	0.186	
 Eosinophil count, %	5.8 (3.7–8.9)	0.7 (0–1.4)	<0.001	5.6 (4.0–8.9)	0.8 (0–3.1)	<0.001	0.921	0.244	
 Δ Eosinophils, cells per mm3		−388.6 (−571.1– −243.4)			−329.0 (−565.7– −2.5)			0.221	
 FENO, ppb	25.0 (18.0–46.0)	24.0 (20.0–75.0)	0.045	34.5 (27.7–69.5)	22.0 (16.7–36.0)	<0.001	0.004	0.004	
 ΔFENO, ppb		2.0 (−4.0–14.0)			−14.0 (−30.5– −8.0)			<0.001	
 High FENO	23 (48.9)			41 (82.0)			<0.001		
Patient-reported outcomes	
 ACT score	16.4±5.5	21.9±3.8	<0.001	15.4±5.7	20.1±4.3	<0.001	0.389	0.035	
 ΔACT		5.4±4.4			4.7±5.1			0.494	
 ACQ5 score	4.3±0.5	2.9±0.7	<0.001	3.3±1.3	2.34±1.2	<0.001	0.005	0.198	
 ΔACQ5		−1.4±0.6			−1.0±1.2			0.372	
Lung function	
 FEV1, L	2.13±0.99	2.27±1.13	0.056	2.04±0.75	2.35±0.75	<0.001	0.633	0.662	
 ΔFEV1, L		0.14 (−0.06–0.35)			0.22 (0.12–0.51)			0.054	
 FEV1, % predicted	74.3±21.4	80.0±22.0	0.004	72.72±20.92	83.4±19.1	<0.001	0.715	0.423	
 ΔFEV1, % predicted		5.7±13.0			10.7±12.2			0.057	
 FVC, L	3.10±1.23	3.17±1.34	0.492	3.11±1.05	3.38±1.02	<0.001	0.972	0.398	
 ΔFVC, L		0.06 (−0.11–0.24)			0.20 (0.07–0.44)			0.017	
 FVC, % predicted	89.6±21.1	91.5±19.2	0.301	88.5±18.3	95.9±16.9	<0.001	0.794	0.232	
 ΔFVC, % predicted		2.0 (−3.0–6.0)			5.0 (1.0–14.0)			0.008	
 FEV1/FVC	66.2±12.0	69.0±11.7	0.030	66.1±12.1	69.3±12.4	0.006	0.945	0.881	
Use of biologic drugs	
 Benralizumab	19 (40.5)			21 (42.0)			0.961		
 Dupilumab	5 (10.6)			10 (20.0)			0.321		
 Mepolizumab	18 (38.3)			9 (18.0)			0.045		
 Omalizumab	5 (10.6)			10 (20.0)			0.321		
Comorbidities	
 CRSwNP	10 (21.3)			14 (28.0)			0.595		
 CRSsNP	6 (12.8)			9 (18.0)			0.666		
Data are presented as n, n (%), mean±sd or median (interquartile range), unless otherwise stated. Patients experiencing a decrease in FENO of ≥20% are classified as FENO decliners. t0: baseline; t6: 6-month follow-up; T2: type 2; Δ: change at 6-month follow-up; ACT: Asthma Control Test; ACQ: Asthma Control Questionnaire; FEV1: forced expiratory volume in 1 s; FVC: forced vital capacity; CRSwNP: chronic rhinosinusitis with nasal polyps; CRSsNP: chronic rhinosinusitis without nasal polyps. Bold indicates p<0.05.

In our study of severe asthma patients, we have demonstrated that variations in FENO following biological therapy are mostly independent from clinical outcomes and the specific drug utilised. No difference was observed between FENO decliners and nondecliners in terms of age, sex, annual exacerbation rate, smoking history, lung function, blood eosinophil count and ACT score at baseline, and no significant difference was found at follow-up in lung function and asthma control. However, we observed a striking difference between the two groups in FENO at baseline, which were, of course, higher among decliners, thus suggesting a higher degree of bronchial inflammation among such patients; we also observed a strong relationship between baseline FENO and the magnitude of ΔFENO, as the higher the inflammation at baseline, the wider the change. While FENO changes do not mean clinical improvement per se, it is interesting to notice that FENO decliners presented with a numerically higher forced expiratory volume in 1 s (FEV1) improvement (220 versus 140 mL) and a significantly higher FVC improvement (200 versus 70 mL), which suggests a more effective improvement of lung function in those patients with a more marked reduction of bronchial inflammation.

Our results are partially in line with those reported by Menigoz et al. [9] in a retrospective real-world study investigating the efficacy of anti-IL-5/anti-IL-5 receptor (IL-5R) treatment in patients with severe eosinophilic asthma. FENO changes were not associated with therapeutic response, as measured by ACT and FEV1. Another real-life study on 99 patients treated with mepolizumab concluded that baseline FENO was not different in patients defined as clinical “non-responders”, “responders” or “super-responders” [10].

Finally, in the present study we report that a 6-month course of biologic treatment with anti-IgE, anti-IL-5/IL-5R or anti-IL-4/IL-13 caused a significant decrease in FENO in a variable number of patients with uncontrolled severe eosinophilic asthma as compared to baseline, regardless of the type of biologic considered. This observation is in line with previous studies on the effects of biologics on FENO [11, 12], although other studies failed to show significant variations of FENO during omalizumab treatment [13]. Interestingly enough, we observed a lack of concordance between the trajectories of FENO decline and changes in BEC, which tended towards reduction in both groups, thus suggesting either that different inflammatory pathways or treatment dynamics might be involved.

In our study, the stronger predictor of FENO decline was the baseline ACQ5 score, with higher values being associated with smaller changes in FENO, thus suggesting a lower reduction of bronchial inflammation among more severe patients after treatment with biologics.

To date, researchers and clinicians have focused mainly on the role of biomarkers in predicting the response to biological treatment. However, much less attention has been paid to the dynamics of biomarkers during biologic treatment and to the relationship with the clinical response induced by such treatment. This is a novel finding presented by our study.

However, some important limitations should be addressed, such as: the study's retrospective design; the presence of unbalanced subgroups; a median exacerbation rate of 2.0 (IQR 1.0–3.0), which is slightly less than in most trials involving severe asthma patients; and an overall baseline population that did not use OCS on a regular basis. Finally, we could not infer any effect on acute exacerbations because although no exacerbation was reported during the study, exacerbation rates can only be calculated after a whole year of observation.

Despite such limitations, however, we can assert that biologic drugs effectively improve lung function and quality of life even when they do not directly affect FENO. Prospective trials are therefore necessary in order to identify biomarkers that accurately predict therapeutic response and early markers of response to biotherapy (monitoring biomarkers).

Provenance: Submitted article, peer reviewed.

Ethics statement: The Institutional Review Board Campania 2 reviewed and approved the protocol (number AOC-0010488-2024). We made efforts to contact all the individuals involved, with the aim of obtaining written informed consent from each participant.

Author contributions: M. Maniscalco and C. Candia conceived and designed the study. C. Candia and P. Ambrosino performed statistical analysis, interpreted results and drafted the first version of the manuscript. S. Fuschillo, C. Candia and C. Calabrese collected clinical data. S. Fuschillo, D. Visca, M. D'Amato, C. Calabrese and A. Molino drafted the manuscript and made critical revisions. S. Fuschillo and P. Ambrosino interpreted results and revised the manuscript into its final form. S. Fuschillo made critical revisions and supervised the project. All Authors read and approved the final version of the manuscript.

Conflict of interest: No competing financial interests exist.

Support statement: This research was partially supported by the Ricerca Corrente funding scheme of the Italian Ministry of Health. Funding information for this article has been deposited with the Crossref Funder Registry.
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