Clara Hoi Ka Wu

Hydrogen sulphide (H₂S) is a recently discovered gasotransmitter. It is endogenously synthesized by cystathionine β synthetase, cystathionine γ lyase, cysteine aminotransferase, 3-mercaptopyruvate sulphurtransferase and cysteine lyase. Its metabolism leads to the production of sulphate (SO₄²⁻), methanthiol, dimethylsulphide and thiocynate. The gas interacts with ion channels, protein kinases and transcription factors. It is also involved in post-translational modification of proteins via S-sulphhydration. Although debate continues as to whether H₂S is pro- or anti-inflammatory, its anti-inflammatory properties seem to have beneficial effects in various lung diseases. Serum levels of H₂S differ between asthma, chronic obstructive pulmonary disease and pulmonary fibrosis, which makes it difficult for the gas to be used as a biomarker for lung diseases. Apart from exogenous sources of H₂S, targets to enhance or inhibit the gas can be found in its synthesis and metabolism pathway. H₂S-releasing non-steroidal anti-inflammatory drugs are currently being developed. Further research will aid to determine the precise role of H₂S in respiratory diseases.