SULFUR-DIOXIDE - A POTENT GLUTATHIONE DEPLETING AGENT

Sulphur dioxide (SO2) is an air pollutant implicated in the initiation of asthmatic symptoms. Glutathione (GSH) has been proposed to play a role in detoxification of SO2 through the sulfitolysis of glutathione disulphide (GSSG) to S-sulpoglutathione (GSSO(3)(-)). Rats were expose d to concentrations of SO2 between 5 and 100 ppm for 5 hr a day betwee n 7 and 28 days. Lung injury as assessed by bronchoalveolar lavage and tissue GSH status were evaluated. SO2 5 ppm failed to elicit any lung injury or inflammatory response but did deplete GSH pools in lung, li ver, heart and kidney. Activities of gamma-glutamylcysteine synthetase (GCS), glutathione peroxidase (GPx), glutathione S-transferase (GST) and glutathione reductase (GRed) in lung were lowered relative to thos e in control animals. In liver, GRed activity was decreased. SO2 50 pp m exposure also failed to elicit injury or inflammation but did lower inflammatory cell numbers in the circulation. Rats exposed to 50 ppm S O2 maintained tissue GSH status, but activities of GCS, GPx, GRed and gamma-glutamyltranspeptidase in lung and hepatic GRed and GPx were sig nificantly lower than in control rats. Unaltered GST activity in lung and liver was suggestive of an impairment of the sulfitolysis reaction in these animals, perhaps through lower substrate flux through the GP x reaction, as GSSO(3)- is a known inhibitor of GST in the rat. Rats e xposed to 100 ppm SO2 exhibited evidence of inflammation (120-fold inc rease in neutrophil numbers recovered in lavage fluid) and like the 5 ppm exposed rats had lower tissue GSH concentrations and GSH-related e nzyme activities in lung. We conclude that sulfitolysis of GSSG does o ccur in vivo during SO2 exposure and that SO2, even in the absence of pulmonary injury, is a potent glutathione depleting agent.