The message in the air: Hydrogen sulfide metabolism in chronic respiratory diseases

Abstract

Hydrogen sulfide (H2S) is an important gasotransmitter in the mammalian respiratory system. The enzymes that produce H2S – mainly cystathionine-β-synthase and cystathionine-γ-lyase – are expressed in pulmonary and airway tissues. Endogenous H2S participates in the regulation of the respiratory system's physiological functions and pathophysiological alterations, such as chronic obstructive pulmonary disease, asthma, pulmonary fibrosis and hypoxia-induced pulmonary hypertension, to name a few. The cellular targets of H2S in the respiratory system are diverse, including airway smooth muscle cells, epithelial cells, fibroblasts, and pulmonary artery smooth muscle cells. H2S also regulates respiratory functions such as airway constriction, pulmonary circulation, cell proliferation or apoptosis, fibrosis, oxidative stress, and neurogenic inflammation. Cross-talk between H2S and other gasotransmitters also affects the net outcome of lung function. The metabolism of H2S in the lungs and airway may serve as a biomarker for specific respiratory diseases. It is expected that strategies targeted at the metabolism and function of H2S will prove useful for the prevention and treatment of selective chronic respiratory diseases.