Exhaled breath condensate as a method of sampling airway nitric oxide and other markers of inflammation

Abstract

Most of the methods of investigating lung diseases have been invasive until the discovery that exhaled nitric oxide can be used as a surrogate marker of airway inflammation, particularly in asthma. Exhaled nitric oxide (NO) is now established as a marker of airway inflammation. It has been shown to correlate well with eosinophilic asthmatic airway inflammation, and to be able to predict decline in asthma control and airway function. Altered levels of NO are also associated with other inflammatory lung diseases. In addition, polymorphisms of the genes encoding the three nitric oxide synthases are associated with phenotypic differences associated with lung diseases. Exhaled NO is, however, non-specific. It is therefore of importance that collecting exhaled breath condensate (EBC) has emerged as a potential tool in the study of pulmonary diseases. The exhaled breath is collected in a cooling system which allows water vapour to condense. The EBC contains a number of mediators relating to the NO pathway, including nitrite as a metabolite of nitric oxide, nitrotyrosine, nitrosothiols plus small molecular mediators associated with oxidative stress, including hydrogen ions, and hydrogen peroxide. In addition, reports are emerging of the detection of larger molecules which not only include leukotrienes, prostaglandins, albumin and other proteins, such as cytokines, but also macromolecules, for example, DNA. EBC is becoming a technique which will allow repeated non-invasive sampling from the respiratory tract thus assisting pulmonary research and possibly the monitoring of lung diseases.