Exhaled breath condensate: lessons learned from veterinary medicine

Abstract

Exhaled breath condensate (EBC) describes any sample collected by cooling exhaled breath. Because the method of condensate collection is simple, non-invasive, repeatable and does not necessarily require patient cooperation, EBC is not only an interesting, but also challenging, biological sample. Despite a period of EBC research lasting for more than 15 years, there are still many open questions with respect to EBC collection and analysis, and many biomarkers are still awaiting careful validation. In veterinary research, EBC collection has been described in conscious animals including calves, pigs, horses, cats and dogs. Numerous studies performed in these domestic animals not only contributed substantially to the current knowledge about the potentials of EBC-based diagnoses but also demonstrated pitfalls in EBC collection, analysis and interpretation. This review summarizes information about the collection of EBC and the interpretation of EBC results, particularly with respect to proteins, leukotrienes, hydrogen peroxide, urea, ammonia and pH. Published data emphasize the need to standardize approaches to produce reproducible EBC data. Quantifying the concentration of the EBC component of interest exhaled in a defined volume of exhaled breath (instead of comparing concentrations of this component analysed in liquid EBC) is an important step of standardization that might help to overcome methodological limitations deriving from the EBC collection process. Although information is based on domestic animal studies, it contributes to the general understanding in EBC research-independent of any particular mammalian species-and opens new perspectives for further studies.

Isoprostanes-Biomarkers of Lipid Peroxidation: Their Utility in Evaluating Oxidative Stress and Analysis

“…Samples of EBC should be divided into parts and stored separately. At present, very little is known about the reproducibility and stability of biomarkers during long term storage [81]. However, it is well known that multiple frosting-defrosting cycles could destroy some biomarkers like prostaglandins [52].…”

Analytical methodologies for broad metabolite coverage of exhaled breath condensate

“…In the non-volatile EBC fraction, hundreds of individual compounds, both very polar (HILIC) and less polar and non-polar (RP) could be detected. In previous studies, the non-volatile compounds content of human [19, 45–48] and animals [39, 49] EBC was characterized. The identified compounds (Tables S3–S6 in Supplemental Materials) group according to the chromatography mode utilized.…”

Exhaled breath condensate hydrogen peroxide, pH and leukotriene B4 are associated with lower airway inflammation and airway cytology in the horse

“…All EBC samples were frozen during collection and stored at −80°C until analysis. Samples were batched based on previously described stability periods for each biomarker . Relative humidity (RH), ambient temperature (T a ), time of collection and respiratory rate (RR) during collection were recorded for all samples.…”

“…The analysis of biomarkers in exhaled breath condensate (EBC) is a commonly used noninvasive method for direct pulmonary assessment in human medical research . Constituents of EBC are likely to be present in concentrations that reflect those within the pulmonary epithelial lining fluid . However, biomarker concentrations may be influenced by methodological, physiological and environmental factors .…”