Hydrogen Peroxide in Exhaled Breath Condensate as a Biomarker of Respiratory Inflammation

Hassan Bah^*
*Correspondence: Hassan Bah, Department of Experimental Immunology, University of Amsterdam, 1012 WX Amsterdam, Netherlands Antilles, Email:

Introduction

Respiratory inflammation is a hallmark of numerous chronic and acute pulmonary disorders, including asthma, Chronic Obstructive Pulmonary Disease (COPD) and interstitial lung diseases. Traditional methods for evaluating airway inflammation such as bronchoscopy, induced sputum analysis and tissue biopsy are effective but inherently invasive, often limiting their utility in routine clinical practice and in populations such as children or critically ill patients. Consequently, there is a growing demand for non-invasive, reproducible and biologically meaningful biomarkers capable of assessing pulmonary inflammation. Exhaled Breath Condensate (EBC), a biofluid obtained by cooling exhaled air, has emerged as a promising medium for such assessments. Among various biomarkers detectable in EBC, Hydrogen Peroxide (Hâ??Oâ??) has gained particular interest due to its direct association with oxidative stress and inflammatory processes in the airways. Hâ??Oâ?? is produced in the lungs by activated immune cells, such as neutrophils and macrophages, during respiratory oxidative bursts. Measuring its concentration in EBC offers a unique opportunity to monitor airway inflammation non-invasively and in real time. This paper aims to elucidate the role of hydrogen peroxide in exhaled breath condensate as a potential biomarker for respiratory inflammation, exploring its biological significance, clinical applicability and methodological considerations [1].

Description

Hydrogen peroxide plays a central role in host immune defense and inflammatory signaling within the respiratory tract. During episodes of pulmonary inflammation whether triggered by allergens, pathogens, pollutants, or underlying chronic disease activated leukocytes generate Reactive Oxygen Species (ROS) through enzymatic processes involving NADPH oxidase and myeloperoxidase systems. Among these ROS, hydrogen peroxide serves both as a mediator of cellular signaling and a marker of oxidative injury. Its presence in the airway surface liquid can be detected via collection of exhaled breath condensate, a method that involves the non-invasive condensation of humidified exhaled air using cooled surfaces. This technique captures aerosolized particles and volatile biomarkers from the lower respiratory tract, reflecting the biochemical milieu of the airway lining fluid [2].

Numerous studies have demonstrated that Hâ??Oâ?? levels in EBC are significantly elevated in individuals with respiratory conditions characterized by chronic or acute inflammation. In asthmatic patients, for example, elevated EBC hydrogen peroxide concentrations have been positively correlated with disease severity, airway hyperresponsiveness and exacerbation frequency. Similarly, in COPD, increased Hâ??Oâ?? in EBC reflects heightened neutrophilic inflammation and oxidative stress, both of which contribute to progressive airflow limitation and tissue remodeling. Interventional studies further support the utility of Hâ??Oâ?? as a dynamic biomarker; reductions in EBC hydrogen peroxide levels following treatment with inhaled corticosteroids, antioxidants, or anti-inflammatory agents suggest that it may serve as a responsive indicator of therapeutic efficacy [3].

Despite its promise, the clinical application of hydrogen peroxide in EBC faces several methodological and interpretative challenges. The lack of standardized protocols for EBC collection, storage and analysis contributes to inter-study variability and complicates the establishment of diagnostic thresholds. Techniques for quantifying Hâ??Oâ??, such as colorimetric assays using horseradish peroxidase and fluorometric detection, vary in sensitivity, specificity and susceptibility to contamination. Furthermore, Hâ??Oâ?? concentrations in EBC can be influenced by numerous extrinsic factors including ambient air pollution, recent dietary intake, smoking status and recent physical exertion. These confounding variables must be accounted for to ensure accurate and reproducible measurements. Current research efforts are focused on refining analytical methodologies, enhancing assay robustness and developing portable biosensors for point-of-care use [4].

Additionally, the interpretation of EBC hydrogen peroxide levels must be contextualized within a broader clinical and biological framework. It is increasingly recognized that respiratory diseases are phenotypically heterogeneous; thus, Hâ??Oâ?? may serve different diagnostic or prognostic roles across disease subtypes. For instance, in eosinophilic asthma, elevated Hâ??Oâ?? may reflect a distinct inflammatory endotype compared to neutrophilic asthma or non-inflammatory airflow limitation. Integration of Hâ??Oâ?? data with other biomarkers (e.g., nitric oxide, cytokines, lipid peroxidation products) and clinical parameters (spirometry, imaging, symptom scores) could enhance its diagnostic value and allow for a more nuanced understanding of disease activity [5].

Conclusion

Hydrogen peroxide in exhaled breath condensate represents a compelling and biologically relevant biomarker for assessing oxidative stress and inflammation in the respiratory tract. Its non-invasive nature, relative ease of collection and association with active disease processes position it as a valuable tool for both clinical monitoring and biomedical research. While current evidence supports its utility in conditions such as asthma and COPD, broader adoption in clinical settings will depend on the standardization of measurement techniques and further validation in diverse patient populations. Addressing the methodological variability and identifying normative reference ranges are essential steps toward its integration into routine diagnostics. Moreover, future investigations should aim to delineate the precise role of EBC hydrogen peroxide within the larger landscape of personalized and precision medicine in pulmonology. As technology evolves and our understanding deepens, Hâ??Oâ?? in EBC may emerge as a core component of non-invasive respiratory diagnostics, facilitating earlier detection, individualized treatment and improved disease management across the spectrum of airway inflammatory disorders.

Acknowledgement

None.

Conflict of Interest

None.

References

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