Hydrogen sulfide as a novel biomarker of asthma and chronic obstructive pulmonary disease

Hydrogen sulfide (H2S) has recently been recognised as the third important gas-signalling molecule, besides nitric oxide and carbon monoxide. H2S has been reported to be produced by many cell types in mammalian tissues and organs throughout the actions of H2S-generating enzymes or redox reactions between the oxidation of glucose and element of sulfur. Although the pathological role of H2S has not yet been fully elucidated, accumulative data suggest that H2S may have biphasic effects. Briefly, it mainly has anti-inflammatory and antioxidant roles, although it can also have pro-inflammatory effects under certain conditions where rapid release of H2S in tissues occur, such as sepsis. To date, there have been several clinical studies published on H2S in respiratory disorders, including asthma and chronic obstructive pulmonary disease (COPD). According to previous studies, H2S is detectable in serum, sputum, and exhaled breath, although a gold standard method for detection has not yet been established. In asthma and COPD, H2S levels in serum and sputum can vary depending on the underlying conditions such as an acute exacerbation. Furthermore, sputum H2S in particular correlates with sputum neutrophils and the degree of airflow limitation, indicating that H2S has potential as a novel promising biomarker for neutrophilic airway inflammation for predicting current control state as well as future risks of asthma. In the future, concurrent measures of H2S with conventional inflammatory biomarkers (fractional exhaled nitric oxide, eosinophils etc) may provide more useful information regarding the identification of inflammatory phenotypes of asthma and COPD for personalised treatment.