**5. Conclusions**

We have shown increased levels of amino acid and protein hydroperoxides measured in the serum of asthmatic patients, using a recently developed technically undemanding real-time CBA assay. Furthermore, estimated oxidative stress was related to BAL and blood inflammatory biomarkers, spirometry values, and CT airway geometry measures, but not asthma severity or histological indices of airway remodeling. More prospective and experimental studies are needed to verify the biological role of increased circulating oxidative stress in the clinical course of asthma and extrapulmonary complications.

**Supplementary Materials:** The following supporting information can be downloaded at https: //www.mdpi.com/article/10.3390/biomedicines10071499/s1. Table S1: Clinical characteristics of asthmatic patients divided into mild, moderate, and severe disease stages, including airway imaging and histo(cyto)logy.

**Author Contributions:** Conceptualization, S.B.-S. and K.W.; funding acquisition, S.B.-S.; patient recruitment, S.B.-S., M.C.-L. and K.W.; CBA assay, J.P., M.O., T.S. and K.W.; bronchoscopy, J.S.; lung CT, J.Z.; histopathological examination, K.O.; validation, S.B.-S., M.S., J.G.B. and B.J.; CBA assay parameters analysis, L.Z. and J.G.B.; statistical Analysis, L.Z.; writing—original draft preparation, S.B.-S., B.J., M.C.-L. and D.P.P.; writing—review, critical revision, and final approval, all authors. All authors have read and agreed to the published version of the manuscript.

**Funding:** This project was funded by the National Science Centre, Poland, based on decision No. DEC-2013/09/B/NZ5/00758 (to S.B.-S.).

**Institutional Review Board Statement:** The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of the Jagiellonian University approved the study (approval number: KBET/151/B/2013).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The data presented in this study are available upon request from the corresponding author. The data are not publicly available due to patients' origin.

**Conflicts of Interest:** The authors declare no conflict of interest.
