Review Reports - Mucoactive Agents in Muco-Obstructive Lung Diseases: A Critical Reappraisal of Pharmacological Effects and Clinical Outcomes

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Overall impression

This manuscript addresses an important and clinically relevant topic, namely the role of mucolytic agents in muco-obstructive lung diseases. The integration of mechanistic considerations with clinical data is commendable, and the topic is timely given the ongoing interest in airway mucus biology and targeted therapies.

However, in its current form, the review does not fully achieve the level of critical reappraisal suggested by the title. While the manuscript provides a broad overview of pharmacological mechanisms and selected clinical evidence, the analytical depth remains limited, and the degree of conceptual novelty appears modest. Substantial revision would be required to strengthen the scientific rigor, critical interpretation, and translational clarity of the work.

2. Major points

Lack of a true 'critical reappraisal'

Although the manuscript is framed as a “reappraisal,” the current structure remains largely descriptive rather than critically analytical. The review summarizes established pharmacological mechanisms and selected clinical trial outcomes; however, it does not consistently interrogate the strength, limitations, or internal inconsistencies of the evidence base.

For example, when discussing NAC and erdosteine in COPD, the manuscript cites reductions in exacerbation rates but does not adequately address the heterogeneity of study populations, variability in dosing regimens (e.g., 600 mg vs. 1200 mg NAC), or differences between chronic bronchitis-predominant and emphysema-predominant phenotypes. Similarly, conflicting findings across trials are not sufficiently dissected. A critical reappraisal would require a more explicit evaluation of:

Study design quality (RCT vs. observational data),
Risk of bias,
Population selection criteria,
Duration of treatment,
and statistical robustness.

In its current form, the manuscript compiles evidence but does not systematically evaluate its reliability or comparative weight. A structured critical framework—potentially in the form of summary tables stratified by disease subtype, endpoint, and evidence level—would significantly enhance the manuscript’s analytical rigor.

Limited conceptual novelty and added value

The manuscript does not clearly define its added value relative to the substantial body of existing reviews and meta-analyses on mucolytics. Several high-quality reviews have already evaluated NAC, carbocisteine, and erdosteine in COPD, as well as dornase alfa in cystic fibrosis. Without a clearly articulated differentiating angle, the manuscript risks appearing as a consolidation of known information rather than a conceptual advancement.

To strengthen its originality, the authors could consider:

Proposing a unifying mechanistic model linking mucin cross-linking, extracellular DNA, oxidative stress, and inflammatory amplification.
Providing an updated synthesis of post-2020 clinical trials.
Stratifying therapeutic efficacy according to biomarkers or mucus composition.
Reframing mucolytics within the context of precision airway medicine.

At present, the review outlines mechanisms and outcomes but does not introduce a new interpretative lens or integrative framework. Clarifying this dimension would significantly enhance the manuscript’s scientific contribution.

Insufficient translational stratification

The manuscript acknowledges that therapeutic effects may vary across diseases but does not adequately operationalize this variability. Muco-obstructive lung diseases are biologically heterogeneous, and therapeutic response is likely influenced by mucus composition (e.g., mucin concentration vs. neutrophil extracellular trap burden), inflammatory phenotype, and infection status. For instance: In COPD, are mucolytics more effective in chronic bronchitis-dominant patients? Is high-dose NAC more beneficial in frequent exacerbators? Does carbocisteine exert differential effects depending on mucus glycosylation patterns? Outside cystic fibrosis, what is the evidence supporting dornase alfa in non-CF bronchiectasis?

These clinically relevant stratifications are either briefly mentioned or not fully developed. A more structured translational section—perhaps including a schematic decision algorithm—would enhance clinical applicability and distinguish this review from purely descriptive summaries.

Emerging strategies: conceptual but underdeveloped

The discussion of emerging strategies—such as targeting mucin–DNA interactions or improving inhalation delivery systems—is conceptually appealing. However, the section remains general and lacks depth in mechanistic or translational substantiation.

For example, are there specific agents currently in phase II or III trials targeting mucin polymerization? Are nanoparticle-based delivery systems being clinically evaluated? Is there preclinical evidence that selectively disrupting mucin–DNA cross-linking improves airway clearance beyond traditional thiol-based agents?

Without concrete examples, trial identifiers, or quantitative data, this section reads more as a forward-looking perspective than an evidence-grounded analysis. Expanding this section with specific pipeline candidates or mechanistic diagrams would greatly enhance its credibility and impact.

Author Response

Major points

Lack of a true 'critical reappraisal'

Study design quality (RCT vs. observational data),

Risk of bias,

Population selection criteria,

Duration of treatment,

and statistical robustness.

Limited conceptual novelty and added value

To strengthen its originality, the authors could consider:

Proposing a unifying mechanistic model linking mucin cross-linking, extracellular DNA, oxidative stress, and inflammatory amplification.

Providing an updated synthesis of post-2020 clinical trials.

Stratifying therapeutic efficacy according to biomarkers or mucus composition.

Reframing mucolytics within the context of precision airway medicine.

Insufficient translational stratification

With regard to the above comments, here are the following modifications introduced in the revised manuscript:

1) Abstract: we added a novel sentence in the Abstract clarifying our vision about the use of mucolytics: “A key interpretative message is that clinical benefit appears greatest when the dominant biophysical determinant of mucus pathology is specifically targeted, supporting a transition from broad disease-label prescribing to mechanism-informed, phenotype-aware mucolytic therapy.”

2) Introduction: we have better defined the pathobiology of the diseases considered stating that: “CF is an autosomal recessive disease caused by mutations in the CFTR gene, leading at the apical surface of airway epithelial cells to impaired ion and fluid homeostasis. This, in turn, leads to a marked reduction in mucociliary clearance, eventually promoting chronic infection and inflammation [31]. COPD is a heterogeneous condition tradition-ally linked to long-term exposure to toxic particles and gases, particularly tobacco smoke, leading to chronic airway inflammation, mucus hypersecretion, and impaired gas exchange [32]. More recently, acquired CFTR dysfunction has also been implicated in COPD pathogenesis More recently, an acquired CFTR dysfunction [33,34] has been claimed to have a role in COPD pathogenesis, especially in chronic bronchitis, that has in common with CF goblet cell metaplasia and mucin hypersecretion, mucus obstruc-tion of the small airways and chronic bacterial infection [35-37]. Components of tobacco smoke, including acrolein and cadmium, impair both the expression and function of the CFTR protein. This occurs through reduced mRNA and protein levels, accelerated endocytosis, and a lower probability of channel opening [38,39]. Specifically, acrolein – an aldehyde found in smoke – can directly modify CFTR’s amino acid residues [40]. Environmental factors like arsenic exposure also contribute to CFTR dysfunction and bronchitis symptoms [41]. Additionally, pollutants such as cigarette smoke and cadmium upregulate microRNAs like miR-101 [42], which suppress CFTR expression [43]. Proteases like neutrophil elastase, released during chronic bronchitis inflamma-tion, further degrade the CFTR protein while increasing ENaC (epithelial sodium channel) expression [44-46]. This synergy worsens airway surface liquid (ASL) dehydration. Since CF and COPD (particularly chronic bronchitis) share these pathological mechanisms, CFTR modulators – currently used for personalized CF treatment – are now being investigated as potential therapies for COPD [34].”

3) Introduction: we have proposed a unifying mechanistic model linking mucin cross-linking, extracellular DNA, oxidative stress, and inflammatory amplification.

4) Introduction: we have better defined the rational and the structure of our review: “In particular, we examine mucolytics according to four complementary axes: (i) their predominant biological target within the mucus compartment, including disulfide-rich mucin networks, extracellular DNA burden, mucin glycosylation, airway hydration, and mucociliary transport; (ii) the strength and limitations of the available clinical evidence, taking into account study design, treatment duration, endpoint selection, and population heterogeneity; (iii) disease- and phenotype-specific applicability; and (iv) the implications for precision airway medicine. Within this framework, the key issue is not whether mucolytics “work” in general, but rather in which biological and clinical context, at which dose, and for which outcome they are most likely to provide meaningful benefit”.

5) Methods: Literature Search & Selection Criteria: we have better defined the critical reappraisal by adding the following considerations: “For the purpose of critical reappraisal, the retrieved evidence was qualitatively appraised according to study design (randomized controlled trials, observational studies, post hoc analyses, and meta-analyses), sample size, treatment duration, end-point hierarchy (symptom relief and sputum properties versus exacerbations, lung function, and quality of life), and consistency across studies. Particular attention was paid to clinically relevant sources of heterogeneity, including dose, route of administration, background therapy, exacerbation history, chronic bronchitis predominance, infection status, and disease-specific mucus biology. Whenever possible, the interpretation of clinical outcomes was integrated with mechanistic considerations in order to identify settings in which a given mucolytic may be biologically plausible yet clinically diluted by unselected trial populations”.

6) For each compound discussed a critical appraisal and translational positioning has been introduced as it follows:

3.4 Critical appraisal and translational positioning for NAC: “The clinical signal for NAC in COPD should be interpreted with caution because the label “COPD” encompasses biologically heterogeneous mucus phenotypes. Ap-parent benefits on exacerbation reduction are more coherent in studies using higher doses and longer treatment duration, but are likely diluted by variability in chronic bronchitis burden, baseline exacerbation risk, inhaled background therapy, and end-point definition. Moreover, not all studies have enrolled populations enriched for productive cough or chronic mucus hypersecretion, which may partly explain the inconsistent magnitude of benefit across trials. Therefore, NAC should not be viewed as a uniformly effective therapy across the entire COPD spectrum, but rather as a candidate adjunctive treatment in selected chronic bronchitic or frequent-exacerbator phenotypes, in whom mucus hyperconcentration and oxidative stress are more likely to coexist. This interpretation also helps explain why mechanistic plausibility has often exceeded the strength of the clinical effect observed in unselected populations.

4.4 Critical appraisal and translational positioning for erdosteine: “Compared with several other oral mucolytics, erdosteine is supported by relatively consistent clinical data in COPD, yet the strength of the signal remains end-point-dependent. The reduction in total and mild exacerbations appears more convincing than any effect on moderate-to-severe exacerbations, broad lung function improvement, or universally reproducible quality-of-life gains. This suggests a clinically relevant but circumscribed role, possibly in patients with recurrent mucus-rich exacerbations rather than across the full COPD spectrum. In addition, because erdosteine is a prodrug requiring hepatic metabolic activation, interindividual variability in pharmacokinetic processing may contribute to differential response. Taken together, the available evidence supports erdosteine as a plausible adjunctive option in selected patients, but does not justify an undifferentiated indication across all COPD phenotypes.

5.4 Critical appraisal and translational positioning for carbocisteine: “Carbocisteine illustrates well the gap between mechanistic plausibility and clinical operationalization. Its proposed effects on mucin glycosylation, chloride transport, and ciliary function are biologically attractive, but their translation into consistently measurable clinical benefit remains supported by a relatively limited and heterogeneous evidence base. The available studies suggest that benefit is more likely to emerge with prolonged administration, which raises the possibility that carbocisteine acts less as an acute mucus “breaker” and more as a long-term muco-regulatory therapy. This temporal profile, together with its mechanistic features, supports the hypothesis that carbocisteine may be better suited to chronic bronchitic phenotypes characterized by persistent sputum production and altered mucus composition than to emphysema-predominant disease. However, the lack of routine biomarkers of mucin glycosylation or mucus subtype remains a major obstacle to a more precise clinical positioning.”

6.4 Critical appraisal and translational positioning for Bromexine: “Bromhexine is supported by a relatively modest and historically dated evidence base, with many studies relying on mixed respiratory populations, short-term outcomes, and symptom-oriented endpoints rather than contemporary exacerbation or quality-of-life measures. Its clinical effects appear more consistent on sputum properties and ease of expectoration than on robust functional or long-term outcomes. Accordingly, bromhexine may retain a limited but plausible role as a secretion-mobilizing adjunct in chronic bronchitic states or selected exacerbations with retained sputum, whereas its positioning as a broadly effective mucolytic across muco-obstructive diseases is not supported by strong modern evidence”.

7.4 Critical appraisal and translational positioning for Ambroxol: “Ambroxol occupies an intermediate position between classical mucolytics and broader mucoactive agents because its pharmacological profile includes secretolytic, surfactant-stimulating, antioxidant, and anti-inflammatory properties. However, the clinical evidence remains heterogeneous, with some signals of benefit in symptom control, sputum clearance, and selected COPD subgroups, but limited consistency for major long-term outcomes across unselected populations. This suggests that ambroxol may be more relevant in mucus-rich phenotypes with impaired expectoration than as a universally effective therapy, although its broader biological actions justify further evaluation in stratified clinical settings”.

8.4 Critical appraisal and translational positioning for Dornase alfa: “Dornase alfa provides the clearest proof that mucolytic efficacy is maximized when the dominant rheological determinant of mucus is correctly targeted. In cystic fibrosis, where extracellular DNA substantially contributes to secretion tenacity and impaired clearance, recombinant DNase has demonstrated robust and reproducible benefits on lung function and exacerbation-related outcomes. By contrast, the lack of benefit—and potential harm—in non-CF bronchiectasis argues strongly against indiscriminate extrapolation across muco-obstructive diseases [30]. This divergence is biologically informative rather than disappointing: it indicates that mucus burden alone is not sufficient to predict response, and that extracellular DNA must represent a major functional component of mucus pathology for dornase alfa to be beneficial. In this sense, dornase alfa in cystic fibrosis can be viewed as the current benchmark of successful target-matched mucolytic therapy within precision airway medicine”.

7) To better address the topic of “translational stratification” in the revised manuscript we have introduced this novel section 9. Translational stratification: from pharmacological classes to mucus-informed use: “A major reason for the inconsistent clinical performance of mucolytics is the mismatch between drug mechanism and mucus composition. Disease labels such as COPD, bronchiectasis, or cystic fibrosis do not adequately capture the biological heterogeneity of airway secretions, which may differ in mucin concentration, disulfide cross-linking, extracellular DNA burden, infection status, hydration, and mucociliary transport. As a result, the same agent may perform differently across apparently similar clinical populations. Thiol-based agents such as NAC and erdosteine are most plausibly effective when mucus hyperviscosity is driven by mucin cross-linking and oxidative stress, as may occur in chronic bronchitis-predominant COPD or in frequent mucus-rich exacerbators. Carbocisteine may be better viewed as a long-term muco-regulatory therapy, potentially more suitable for patients with chronic productive cough, altered mucus composition, and impaired ciliary function than for emphysema-predominant disease. Bromhexine and ambroxol are more plausibly positioned in phenotypes characterized by impaired mucus transport and difficult expectoration, where secretion mobilization and improved mucociliary clearance may be more relevant than direct targeting of mucin cross-linking or extracellular DNA. Between the two, ambroxol may have broader translational appeal because, beyond secretolysis, it also shows surfactant-stimulating, antioxidant, and anti-inflammatory properties, whereas bromhexine seems to retain a narrower adjunctive role as a secretion-mobilizing agent. By contrast, dornase alfa remains the clearest example of target-matched mucolytic therapy: it is highly effective in cystic fibrosis, where extracellular DNA is a major determinant of mucus tenacity, but not in non-CF bronchiectasis, where mucus composition and airway pathobiology are different. This divergence highlights a key principle: mucus burden alone does not predict response; efficacy is greatest when the dominant biophysical determinant of secretion pathology is specifically targeted. Overall, these considerations support a shift from broad disease-label prescribing to mechanism-informed pre-scribing. Future mucolytic strategies should identify responsive subgroups according to mucus composition, inflammatory and infectious context, mucociliary dysfunction, and exacerbation profile, in line with the broader paradigm of precision airway medicine”.

8) These clinically relevant stratifications are either briefly mentioned or not fully developed. A more structured translational section—perhaps including a schematic decision algorithm—would enhance clinical applicability and distinguish this review from purely descriptive summaries.

This aspect has not been deepened in the revised manuscript; indeed, we believe it goes well beyond the scope of this review which was originally thought not to be excessively clinically oriented.

9) Emerging strategies: conceptual but underdeveloped. The discussion of emerging strategies—such as targeting mucin–DNA interactions or improving inhalation delivery systems—is conceptually appealing. However, the section remains general and lacks depth in mechanistic or translational substantiation.

9a) In the revised manuscript we have enlarged section: “10. Challenges and innovations in mucolytic therapy” by adding the following sentences: “One of the main challenges in mucolytic therapy is that clinical development has historically relied on broad diagnostic labels rather than on biologically informed patient selection. This has likely diluted treatment effects in trials that enrolled patients with markedly different mucus properties under the same disease umbrella. Future innovation should therefore not only aim at developing more potent or better-delivered compounds, but also at identifying the patients most likely to benefit from each mechanism of action. In this respect, biomarkers reflecting mucus concentration, extracellular DNA burden, mucin subtype distribution, airway infection, and inflammatory phenotype may become essential tools for both clinical trials and routine implementation”. Moreover, we added the following sentences (lines 1191-1193: “Overall, these developments indicate that future progress in mucolytic therapy will depend not only on more effective compounds and delivery systems, but also on biologically informed patient selection and stratified trial design”:

For example, are there specific agents currently in phase II or III trials targeting mucin polymerization?

9b) To answer this comment, in the revised manuscript we have included the following sentences: “To the best of our knowledge, there are no specific, newly approved drugs exclusively targeting mucin polymerization that are in Phase III trials for COPD. Despite this, a number of agents targeting mucus viscosity via the disruption of disulfide bonds are under investigation for COPD management”.

10) Are nanoparticle-based delivery systems being clinically evaluated?

To answer this comment, in the revised manuscript we have included the following sentences: Regardless of the drugs to be used, an emerging strategy to improve drug delivery to pulmonary diseases such as COPD is represented by the Nanoparticle (NP) tech-nology. NP use, despite being mainly in the preclinical research phases, holds great promise to improve the efficiency of drug delivery and minimize side effects. Particu-larly attractive are inhaled delivery strategies due to the extensive surface area of the lungs (approximately 140 m2 at the alveolar level [223] that ensures direct access to the sites of mucus production. Unfortunately, airway mucus constitutes a highly efficient barrier that critically limits the effectiveness of NP-based pulmonary drug delivery. As a visco-elastic hydrogel composed primarily of mucin glycoproteins, it is designed to trap and eliminate inhaled pathogens and particulates through a combination of steric obstruction and adhesive interactions. In line with its physiological role across muco-sal tissues, mucus in the respiratory tract can both physically hinder nanoparticle dif-fusion—particularly for particles approaching or exceeding the mesh pore size—and chemically bind them via hydrophobic and electrostatic interactions, depending on their surface properties. Consequently, these barrier functions significantly reduce nanoparticle mobility, promote rapid mucociliary clearance, and ultimately limit local bioavailability and therapeutic efficacy in the lungs [224]. Thus, particularly attractive are approaches considering NPs equipped with mucus penetrating moieties able to de-liver drugs also in the inner part of the mucus layer. Moreover, NPs within the na-nometer range, have deep lung penetration capacity thus enhancing drug absorption, bioavailability, solubility and diffusion kinetics [225]. Future clinical trials are needed to confirm the potential of NP in the clinic.”

11) Is there preclinical evidence that selectively disrupting mucin–DNA cross-linking improves airway clearance beyond traditional thiol-based agents?

We thank the reviewer for this important and insightful question. At present, there are no clinically approved agents that selectively disrupt mucin–DNA cross-linking. However, enzymatic degradation of DNA by dornase alfa has been consistently shown to improve mucus transportability and airway clearance more effectively than non-specific thiol-based mucolytics, when DNA burden is high. This differential efficacy provides a proof-of-concept that selective targeting of a dominant biophysical determinant of mucus pathology yields superior functional outcomes compared with broad mucolysis. We have clarified this point in the manuscript by explicitly reframing dornase alfa as the benchmark example of successful target-matched mucolytic therapy, while noting that emerging approaches aimed at mucin–DNA interactions remain at the preclinical stage. The revised text has been added to the section “Challenges and innovations in mucolytic therapy”.

12) Without concrete examples, trial identifiers, or quantitative data, this section reads more as a forward-looking perspective than an evidence-grounded analysis. Expanding this section with specific pipeline candidates or mechanistic diagrams would greatly enhance its credibility and impact.

In the revised manuscript we have added the novel section “11. Conclusion” to better clarify the future perspective in the field: “The main lesson emerging from the available literature is not that mucolytics are broadly ineffective, but that their efficacy is highly context-dependent and often obscured by biologically unselected trial populations. The clinical performance of these agents varies according to mucus composition, inflammatory and infectious context, disease phenotype, dose, and treatment duration. In this perspective, dornase alfa in cystic fibrosis represents the strongest example of successful target-matched mucolytic therapy, whereas NAC, erdosteine, and carbocisteine appear more promising when interpreted as phenotype-dependent rather than universally active treatments. The field should therefore move from disease-label prescribing to mechanism-informed prescribing, in which mucus biology helps guide drug selection. Such a shift would not only improve the translational relevance of future trials, but also provide a clearer conceptual framework for integrating mucolytics into precision airway medicine”.

Reviewer 2 Report

Comments and Suggestions for Authors

Recommendation: Minor Revision

In their manuscript entitled “Mucolytics in muco‑obstructive lung diseases: a reappraisal of pharmacological effects and clinical outcome”, Domenico Larobina et al. aim to critically reassess the pharmacological mechanisms and clinical outcomes of the main mucolytic agents used in muco‑obstructive lung diseases.

Overall Assessment

This review addresses a timely and clinically relevant topic. The manuscript cites 194 references spanning publications from 1953 to 2025; the average publication year is 2003 and the median is 2012, indicating that half of the cited literature has been published within the past fourteen years. Importantly, 52 references (26.8%) originate from 2021 to 2025, showing that the authors incorporate a substantial proportion of recent advances in mucus biology, mucolytic therapies, rheology, and cystic fibrosis research, while earlier foundational studies from the 1950s to the 1990s provide essential biochemical, biophysical, and clinical context. The manuscript is generally clear and well-structured, but several aspects could be improved. In particular, although the authors mention personalized mucolytic therapy, this concept could be more explicitly highlighted and developed. Several recent publications would also strengthen the review by providing updated clinical evidence, mechanistic insights, and emerging therapeutic perspectives. Given the strengths of the manuscript and the areas requiring improvement, a minor revision is recommended to address these points and the detailed comments provided.

Detailed Comments

Affiliations should be carefully checked for accuracy and consistency across all authors.
The appendix contains numerous parameters, calculations, and technical details that are either not used or only minimally used in the main text. Its usefulness should be reassessed, and relevant content could be integrated into the main narrative.
The manuscript includes two Figures and two Tables, which clarity, caption quality, and relevance should be verified.
Including additional illustrations could enhance readability by visually supporting sections of the text that currently appear dense and potentially overwhelming for the reader.
Figure 1 is overly simplistic and would benefit from further development.
Figure 2 should be reworked to ensure uniformity in the representation of chemical structures.
Tables should be completed with appropriate references to support the information presented.
Emerging therapeutic platforms (e.g., nanomedicine, biotech pipelines) could be mentioned as future directions in section 9.
Additional references could be added to provide stronger links between rheology, drug design, and therapeutic innovation, which are currently underrepresented.
Reference formatting requires revision to ensure uniformity and compliance with the journal’s style guidelines.

Suggested Additional References

Mall MA, Danahay H, Boucher RC. Emerging concepts and therapies for mucoobstructive lung disease. Ann Am Thorac Soc. 2018;15(Suppl 3):S216–S226. https://doi.org/10.1513/AnnalsATS.201806-368AW

D’Antonio S, Pennisi A, Cazzola M. Mucolytic therapy in COPD: patient usage and preferences in real‑world Italian settings. Int J Chron Obstruct Pulmon Dis. 2025;20:479–486. https://doi.org/10.2147/COPD.S504577

Poole P, Chong J, Fortescue R. Mucolytic agents versus placebo for chronic bronchitis or chronic obstructive pulmonary disease. Cochrane Database Syst Rev. 2019;5:CD001287. https://pubmed.ncbi.nlm.nih.gov/31107966/

Kokkinis S, et al. Plant‑based therapeutics for chronic obstructive pulmonary diseases: nanoformulation strategies to overcome delivery challenges. Food Biosci. 2024;58:103761. https://doi.org/10.1016/j.fbio.2024.103761

Liu Z, Che B, Zhang H, Deng L. Airway mucus rheology: physical insights for navigating through health to pathology and clinical applications. arXiv preprint. 2025. arXiv:2510.15562. https://arxiv.org/html/2510.15562v1

Practice Nurse. Using mucolytics in the management of COPD symptoms. Practice Nurse. 2025. https://practicenurse.co.uk/modules/copd/using-mucolytics-in-the-management-of-copd-symptoms

DelveInsight. Novel therapies for non‑cystic fibrosis bronchiectasis treatment. 2023. https://www.delveinsight.com/blog/non-cystic-fibrosis-bronchiectasis-treatment

Author Response

Please see attached file.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

A review of “Mucolytics in muco-obstructive lung diseases, a reappraisal of pharmacological effects and clinical outcome” paper by D. Larobina, G. Franzino, F. Tescione, M. Abrami, D. Tierno, A. Biasin, F. Tonon, A. De Nes, M. Maggisano, P. Confalonieri, A. Carbone, M. Confalonieri, G. Grassi, S. Di Gioia, M. Grassi and M. Conese

The main question of “Mucolytics in muco-obstructive lung diseases, a reappraisal of pharmacological effects and clinical outcome” paper by D. Larobina, G. Franzino, F. Tescione, M. Abrami, D. Tierno, A. Biasin, F. Tonon, A. De Nes, M. Maggisano, P. Confalonieri, A. Carbone, M. Confalonieri, G. Grassi, S. Di Gioia, M. Grassi and M. Conese was to describe effects of mucolytics in the treatment of COPD and CF.

This topic has been discussed in variety of publications previously, but recently novel data have been published on the structure and different types of the airway mucins in respiratory different pathologies. So, this topic is still actual.

The authors focused the attention on two respiratory diseases, COPD and cystic fibrosis as well as CFTR dysfunction has been claimed to have a role in COPD pathogenesis.

The manuscript included a review of clinical and experimental studies on a role of several mucoactive agents, N-acetylcysteine, carbocysteine, erdosteine, bromhexine, and ambroxol, in patients COPD or bronchiectasis including CF.

My comments:
1. The “mycolytics” term is relevant to agents that can cleave mucus. This is a distinct group of pharmacological agents that does not include bromhexine and ambroxol. The latter agents should be referred as expectorants and mucoregulators (see Rogers DF. Mucoactive agents for airway mucus hypersecretory diseases. Respir Care. 2007 Sep;52(9):1176-93; discussion 1193-7.).
2. The reference 31 does not correspond to the content (lines 240-243). The authors wrote about tobacco smoke components that can decrease expression and function of the CFTR protein by decreasing CFTR mRNA and protein levels, etc., while the reference 31 is exclusively about antioxidant properties of N-acetylcysteine. The correct reference is needed. Moreover, the issue should be discovered more in detail because this can explain the choice of the respiratory diseases included in this review.
3. Consider the article Mucus Hypersecretion in Chronic Obstructive Pulmonary Disease and Its Treatment by Shah BK, Singh B, Wang Y, Xie S, Wang C., Mediators Inflamm. 2023 Jul 6;2023:8840594. doi: 10.1155/2023/8840594.
4. The authors aimed this review at the analysis of effects of mucolytics in the treatment of patients with COPD and CF. However, many studies mentioned in the manuscript included patients with non-CF bronchiectasis or with both CF and non-CF bronchiectasis. This does not correspond to the aim of this review. Moreover, the role of erdosteine in the treatment of CF and/or bronchiectasis was not described.
5. The conclusion does not correspond to the aim and the content of the manuscript.
The manuscript needs a major revision.

Author Response

This topic has been discussed in variety of publications previously, but recently novel data have been published on the structure and different types of the airway mucins in respiratory different pathologies. So, this topic is still actual.

The authors focused the attention on two respiratory diseases, COPD and cystic fibrosis as well as CFTR dysfunction has been claimed to have a role in COPD pathogenesis.

The manuscript included a review of clinical and experimental studies on a role of several mucoactive agents, N-acetylcysteine, carbocysteine, erdosteine, bromhexine, and ambroxol, in patients COPD or bronchiectasis including CF.

My comments:

The “mycolytics” term is relevant to agents that can cleave mucus. This is a distinct group of pharmacological agents that does not include bromhexine and ambroxol. The latter agents should be referred as expectorants and mucoregulators (see Rogers DF. Mucoactive agents for airway mucus hypersecretory diseases. Respir Care. 2007 Sep;52(9):1176-93; discussion 1193-7.).

We thank the Reviewer for this important and appropriate terminological clarification, and we fully agree with the distinction highlighted. In the revised manuscript, we have systematically implemented the Reviewer’s suggestion by adopting “mucoactive agents” as the overarching category describing drugs that facilitate airway mucus clearance through heterogeneous mechanisms. In contrast, the term “mucolytics” is now reserved specifically for agents that directly cleave or depolymerize mucus components (e.g., disulfide-rich mucins or extracellular DNA), in line with established pharmacological classifications.

Accordingly, we have:

Revised the title of the manuscript to refer to mucoactive agents rather than mucolytics, thereby ensuring conceptual accuracy from the outset.
Clarified definitions in the Introduction, explicitly distinguishing:
true mucolytics (e.g., thiol-based agents, dornase alfa), which directly modify mucus structure through chemical or enzymatic cleavage, from
non-cleaving mucoactive agents, which act primarily as expectorants or mucoregulators by enhancing secretion, surfactant production, or mucociliary transport.
Repositioned bromhexine and ambroxol consistently throughout the manuscript as mucoactive agents with expectorant and mucoregulatory properties, rather than as mucolytics in the strict sense. This distinction is now explicitly stated at the beginning of their respective sections, in full agreement with the classification proposed by Rogers and others.
Preserved the use of the term “mucolytic” only where mechanistically appropriate, including thiol-based compounds and enzymatic agents targeting mucus polymers or extracellular DNA.

These changes improve terminological precision without altering the scientific scope of the review and, we believe, strengthen the conceptual framework by aligning pharmacological classifications with the mechanistic heterogeneity of airway secretion clearance.

We are grateful to the Reviewer for prompting this refinement, which has substantially improved the clarity and rigor of the manuscript.

The reference 31 does not correspond to the content (lines 240-243). The authors wrote about tobacco smoke components that can decrease expression and function of the CFTR protein by decreasing CFTR mRNA and protein levels, etc., while the reference 31 is exclusively about antioxidant properties of N-acetylcysteine. The correct reference is needed. Moreover, the issue should be discovered more in detail because this can explain the choice of the respiratory diseases included in this review.

The reference 31 has been corrected and we now provide a detailed explanation of the common pathogenetic steps between CF and COPD in the Introduction Section.

Consider the article Mucus Hypersecretion in Chronic Obstructive Pulmonary Disease and Its Treatment by Shah BK, Singh B, Wang Y, Xie S, Wang C., Mediators Inflamm. 2023 Jul 6;2023:8840594. doi: 10.1155/2023/8840594.

In the revised manuscript, the above reference has been introduced (new Ref. 9).

The authors aimed this review at the analysis of effects of mucolytics in the treatment of patients with COPD and CF. However, many studies mentioned in the manuscript included patients with non-CF bronchiectasis or with both CF and non-CF bronchiectasis. This does not correspond to the aim of this review. Moreover, the role of erdosteine in the treatment of CF and/or bronchiectasis was not described.

We have better defined the aim of this review by explicitly saying that the we analyze the effects of mucolytics in the treatment of the treatment of muco-obstructive lung diseases, namely COPD and CF, and bronchiectasis that can derive from CF and COPD but are also not associated with these conditions.

To the best of our knowledge, its specific, routine use in CF is not standard. Instead, erdosteine has been used in non-CF bronchiectasis and we report its efficacy in the relevant Section as detailed below:

“While erdosteine lacks extensive investigation within the context of CF [119], many standard treatments for bronchiectasis are generally adapted from the clinical evidence and experience established in CF care [30]. A short-term small (n=30) RCT in elderly patients with radiographic bronchiectasis and chronic hypersecretion found reduction in mucus density and purulence, significant improvement in the measured forced lung volumes and improved clinical outcomes (better cough and dyspnoea scores, 6 min walk test) on day 15 with erdosteine 225 mg BID [120]. To estimate a beneficial effect of erdosteine on bronchiectasis on the long term, an international multicentre, double-blind, placebo-RCT aimed to assess whether 12 months of erdosteine had an effect in children and adults with non-CF bronchiectasis, in particular on the rate of exacerbations [121]. However, results are still awaited. In conclusion, further high-level evidence of erdosteine efficacy in CF or bronchiectasis is warranted.”

The conclusion does not correspond to the aim and the content of the manuscript.

The revised manuscript has been substantially modified and expanded according to referee comments (see answers to referee 1 and 2). Particular focus was put on the concept of the “critical reappraisal”, translational stratification, and “Challenges and innovations in mucolytic therapy”. All this novel information has been harmonized in the novel section 11 Conclusion; thus, we believe that the conclusion now corresponds to the aim and content of the manuscript.

The manuscript needs a major revision.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

Thank you for submitting the revised version of your manuscript. The manuscript has improved in terms of clarity and organization compared to the previous version. However, several important concerns remain insufficiently addressed.

1. Lack of novelty and conceptual advance

While the manuscript provides a comprehensive overview of mucolytics, it still reads largely as a descriptive summary of existing literature. The revised version does not sufficiently establish a clear conceptual framework or highlight how this review advances beyond prior publications in this field. The authors are encouraged to explicitly define the unique perspective of this review and clarify what distinguishes it from existing reviews on mucolytics.

2. Limited critical analysis of clinical evidence

The section describing clinical outcomes has been reorganized, but it still lacks critical evaluation.Rather than listing study results, the authors should:

- critically compare conflicting findings

- discuss limitations of key studies

- provide interpretation of why outcomes differ across diseases or trials

Without this, the manuscript remains largely descriptive.

3. Mechanistic discussion remains superficial

Although additional explanations have been added, the discussion of pharmacological mechanisms is still relatively general. The authors should deepen this section by:

- linking mechanisms more explicitly to clinical outcomes

- addressing disease-specific differences

- highlighting unresolved mechanistic questions

4. Weak take-home message in Discussion/Conclusion

The Discussion and Conclusion sections have been slightly refined, but they still do not provide a strong or forward-looking message. The authors should:

- clearly summarize key insights

- propose future research directions

- discuss clinical implications more concretely

Overall impact

Despite improvements in readability, the manuscript still lacks the depth and critical insight expected for a high-impact review article.

Reviewer 3 Report

Comments and Suggestions for Authors

I thank the authors for the attention to my comments and the correction made.