Breath exosomes: Proteomics and functional enrichment analysis in the development of methodology for future diagnostic devices.

Exosomes are a type of extracellular vesicle that carry cargo, including proteins and nucleic acids, that reports on the conditions of their cell of origin. Exosomes can be isolated from a range of biological fluids, including blood and urine, and their use in clinical diagnostic applications has been extensively researched. Breath is an excellent source of biomarkers. Exosomes collected from exhaled breath concentrate offer untapped potential in the field. For example, exosomes secreted from the cells of the lung carry biomarkers of lung health and so report selectively on lung health. However, whilst several publications report the presence of breath exosomes, and some discuss potential applications, there is no published work on developing standardized procedures for isolating high purity exosomes for biomarker identification, nor have breath exosomes been extensively characterized. Studying exosomes can potentially increase the specificity of diagnosis with an ultimate goal to translate early diagnosis into early treatment.

In this study we report results of optimized methodology for isolation of exosomes from human breath and undertaken phenotyping of breath exosomes by comparing them to cell-derived exosomes. Determining the benchmark proteome of breath exosomes became the major achievement of this study. The proteome profile of breath-derived exosomes was identified for the first time from exosomes obtained from the breath of 55 healthy volunteers indicating that the protein cargo of cell- and breath-derived exosomes are somewhat similar. The results of this study suggest that the exosomal breath proteome may be used in future studies identifying new biomarkers of lung dysfunction, including lung cancer. The possibility of identifying putative lung cancer biomarkers was shown using exosomes isolated from the lung cancer cell model (A549), from which four candidates were selected and examined. Promising results from time-resolved studies concluded that a FRET-based assay can be considered as a new way to prove the presence of exosomes and with an ability to differentiate between cancer and normal cells. We foresee the use of exosomes in non-invasive breath-based clinical applications for medical diagnostics for lung cancer as an important future application.