The toxicity of hydrogen sulfide(H2S) has been known for a long time, as it is prevalent in the atmosphere. However accumulative data suggest that H2 S is also endogenously produced in mammals, including man, and is the third important gas signaling molecule, besides nitric oxide and carbon monoxide. H2 S can be produced via non enzymatic pathways, but is mainly synthesizedfrom L-cysteine by the enzymes cystathionine-γ-lyase, cystathionine-β-synthetase, cysteine amino transferase and 3-mercaptopyruvate sulfurtransferase(3MTS). The formation of H2 S from D-cysteine via the enzyme D-amino acid oxidase and 3MTS has also been described. Endogenous H2 S not only participates in the regulation of physiological functions of the respiratory system, but also seems to contribute to the pathophysiology of airway diseases such as chronic obstructive pulmonary disease, asthma and pulmonary fibrosis, as well as in inflammation, suggesting its possible use as a biomarker for these diseases. This review summarizes the different implications of hydrogen sulfide in the physiology of airways and the pathophysiology of airway diseases.
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