**9. Conclusions**

**Figure 14.** Evaluated clinical results: levels of LTB4

162 Biomarker - Indicator of Abnormal Physiological Process

EBC of COPD, asbestosis, and lung cancer patients.

of EBC for patients with lung cancer).

**8.5. Serotonin in EBC of SRA**

, 8-isoprostane, biomarkers of proteins and nucleic acids damage in

indicators of ongoing tissue necrosis processes is 8-isoprostane. The analysis of EBC showed that the levels of this biomarker are increased among COPD and asbestosis patients and even more among people suffering from lung cancer. Similar information is provided by the biomarkers of proteins damage (tyrosines) and nucleic acids damage (5-OHMeU, 8-OHG, and 8-OHdG). The levels of these molecules were elevated in EBC of patients with COPD and asbestosis and it can be said that the highest levels are specific for lung cancer (average concentration of tyrosines is approximately 75 pg/ml of EBC for healthy controls and 160 pg/ml

Based on the clinical experience, it is proved that SRA patients positively respond to SSRI (selective serotonin reuptake inhibitors) antidepressants therapy. SSRI antidepressants usually improve physical state of patients, which may seem as a quite logical coincidence. However, much more surprising is the fact that when SRA patients are prescribed SSRI antidepressants, their breath functions improve significantly. This phenomenon prompted to performed research aimed at the detection of serotonin in EBC of SRA. The obtained results were compared with serotonin levels in EBC of other asthma phenotypes and healthy control subjects. According to the results (**Figure 15**), it is obvious that the levels of serotonin in EBC of SRA are different as compared to other asthma phenotypes and healthy control subjects. However, Measurements of biomarkers in EBC offer a novel way of monitoring lung inflammation, damage by oxidation stress with an insight into the pathophysiology of different diseases. The described diagnostic method was based on the detection and quantification of biomarkers in a matrix specific for the respiratory tract—EBC. As the collection of EBC is completely noninvasive, the method offers a broad spectrum of application. The method is applicable to children as well as to senior people and it is appropriate also in case of longitudinal studies that are trying to precisely understand the processes occurring on the molecular level in the respiratory tract. The method can be easily repeated which proves its suitability for regular monitoring of the pharmacotherapy efficiency or the impact of various allergens. The results obtained from the EBC analysis represent reliable characterization of the exhaled biomarkers profile (LXs, cys-LTs, LTB<sup>4</sup> , 8-isoprostane, tyrosines, etc.), which is relevant for diagnostics, separation, and phenotyping of different respiratory diseases. Nevertheless, EBC analysis requires standardization and validation including sample collection and sample pre-analysis treatment (e.g., internal standardization, storing, pre-treatment method application, etc.).

**Author details**

**References**

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3 ESSENCE LINE, s.r.o., Prague 5, Czech Republic

2 Grammar School Nad Štolou 1, Prague 7, Czech Republic

4 National Institute of Mental Health, Klecany, Czech Republic

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Model clinical studies were carried out as a part of the work, which applied a methodology based on the molecular diagnostics of EBC. The method allowed an asthma phenotyping, which was founded on the fact that the concentration levels of cys-LTs and LXs are not only complementary but also intra-related by a dynamic equilibrium. This phenomenon, however, affords not only asthma phenotyping but also other diagnostics as, for example, monitoring of efficacy of the used pharmacotherapy. The analysis of EBC also showed that the detected biomarkers can be used for the differentiation of various pulmonary diseases (more specifically (apart from asthma) COPD, asbestosis, and lung cancer). Increased (or decreased) levels of some biomarkers are specific only for some diseases and thus these can be selectively differentiated as much as, for example, asthma from COPD.

Additionally, an experiment was conducted and focused on determining serotonin in EBC. The aim of this study was to assess the positive effects of the SSRI (selective serotonin re-uptake inhibitors) antidepressants on SRA. High levels of serotonin were detected in EBC of SRA patients, which was in contradiction to the initial assumption. Simultaneously, a hypothesis was formulated stating that SRA probably functions on different molecular principles. This could have probably been the reason for SRA inefficiency with the commonly used drugs.

For the future research, one can only recommend focusing on large longitudinal studies to ascertain whether sequential measurements in individual patients reflect asthma severity and the degree of a lung inflammation, and on studies engaged to the relationships between the concentrations of asthma biomarkers and its symptoms. In order to implement the EBC analysis to the clinical practice as well as reliably guiding the pharmacological treatment of asthma and the effect of drugs on asthma markers present in EBC, further controlled studies are required to be conducted. In particular, studies are recommended determining the expediency of the EBC analysis for predicting a treatment response, and assessing new therapies. Obviously, this outlines a great deal of work to be done. The fact that EBC analyses are currently used in various clinical trials and studies corroborates the above arguments. On the other hand, it is important to proclaim that the fact whether and when EBC analyses will become applicable to the clinical settings is still difficult to predict.
