Sodium sulfite induces basophil degranulation through induction of oxidative stress
Authors: C.R. Collaco, D.J. Hochman, E.G. Brooks
Journal: Journal of Allergy and Clinical Immunology (2005)

RATIONALE: Sulfur dioxide has been shown to induce bronchoconstriction in asthmatics. It is a highly soluble gas with sulfite being one of the principal ions generated. Not much is known about the pathogenesis of sulfur dioxide mediated bronchoconstriction and the cells involved. We evaluated the effect of sulfite on basophil degranulation.METHODS: A rat basophil leukemia cell line (RBL-2H3) was exposed to varying concentrations of sodium sulfite to assess if it could induce direct degranulation of basophils. Granule release was assessed using the serotonin release and β-Hexosaminidase assays. Generation of reactive oxygen species post sulfite exposure was assessed by measuring fluorescence of 2′,7′-dichlorodihydrofluorescin diacetate.RESULTS: Direct exposure of RBL-2H3 cells to sodium sulfite induced degranulation. Maximum degranulation was observed at 2mM of sodium sulfite. Sulfite exposure also induced an increase in reactive oxygen species. This increase in ROS and basophil degranulation could be inhibited by pretreatment with the free radical scavenger tetramethylthiourea. Similar results were obtained using the NADPH oxidase inhibitor diphenyliodinium. In addition this process appears to be independent of extracellular calcium.CONCLUSIONS: Sodium sulfite the principal ion generated by sulfur dioxide in solution is capable of directly inducing the degranulation of RBL-2H3 cells. This exposure also induces the formation of reactive oxygen species. Both phenomena could be inhibited by treatment with antioxidants. Given the increased sensitivity of asthmatics to sulfur dioxide these data suggest that the direct effect of sulfite on basophils may be key to the pathogenesis of sulfur dioxide induced respiratory dysfunction. RATIONALE: Sulfur dioxide has been shown to induce bronchoconstriction in asthmatics. It is a highly soluble gas with sulfite being one of the principal ions generated. Not much is known about the pathogenesis of sulfur dioxide mediated bronchoconstriction and the cells involved. We evaluated the effect of sulfite on basophil degranulation. METHODS: A rat basophil leukemia cell line (RBL-2H3) was exposed to varying concentrations of sodium sulfite to assess if it could induce direct degranulation of basophils. Granule release was assessed using the serotonin release and β-Hexosaminidase assays. Generation of reactive oxygen species post sulfite exposure was assessed by measuring fluorescence of 2′,7′-dichlorodihydrofluorescin diacetate. RESULTS: Direct exposure of RBL-2H3 cells to sodium sulfite induced degranulation. Maximum degranulation was observed at 2mM of sodium sulfite. Sulfite exposure also induced an increase in reactive oxygen species. This increase in ROS and basophil degranulation could be inhibited by pretreatment with the free radical scavenger tetramethylthiourea. Similar results were obtained using the NADPH oxidase inhibitor diphenyliodinium. In addition this process appears to be independent of extracellular calcium. CONCLUSIONS: Sodium sulfite the principal ion generated by sulfur dioxide in solution is capable of directly inducing the degranulation of RBL-2H3 cells. This exposure also induces the formation of reactive oxygen species. Both phenomena could be inhibited by treatment with antioxidants. Given the increased sensitivity of asthmatics to sulfur dioxide these data suggest that the direct effect of sulfite on basophils may be key to the pathogenesis of sulfur dioxide induced respiratory dysfunction.