Exhaled nitric oxide and other major exhaled compounds for the diagnosis of metabolic diseases.

Background: Many metabolic diseases including obesity, cardiovascular disease and diabetes share common pathogenetic pathways, which may involve chronic oxidative stress and inflammation. There is increasing evidence that assessment of biomarkers on exhaled gases or exhaled breath condensate may serve as a non-invasive tool to detect abnormalities in metabolic diseases mirroring increased in oxidative stress, systemic inflammation and endothelial dysfunction. Methods: Among commonly used exhaled biomarkers, nitric oxide (NO) on exhaled air and some constituents of exhaled breath condensate in volatile or non-volatile form may represent suitable markers. Nasal, bronchial and alveolar NO could be analyzed separately, with implications in the assessment of systemic disease and endothelial dysfunction. Moreover, the profiles of several exhaled gases have a place in phenotyping diabetic patients and their risk of complications. Accordingly, metabolomics of the airway fluid using exhaled breath condensate has recently confirmed the value of this biological matrix for the evaluation of both volatile and non-volatile biomarkers. Conclusion: Normative studies for reference values are, however, lacking, and the influence of preanalytical variables on the methodology warrants further studies.