Can mutations in ELA2, neutrophil elastase expression or differential cell toxicity explain sulphasalazine-induced agranulocytosis?

We screened for genetic differences in ELA2 in DNA from 36 patients who had suffered from sulphasalazine-induced agranulocytosis, and compared them with 72 patients treated with sulphasalazine without blood reactions. We also performed in vitro studies of the blood cell lines HL60 and U937 after sulphasalazine exposure with respect to cell survival index, neutrophil elastase protein expression and activity.None of the mutations in ELA2, which previously have been reported to be associated with SCN, was found in this material. Protein expression of human neutrophil elastase in lymphoma U937 cells was not affected by treatment with concentrations equivalent to therapeutic doses. Cell survival of lymphoma U937 and promyelocytic leukemia HL-60 cells was not affected in this concentration range, but exhibited a decreased proliferative capacity with higher sulphasalazine concentrations. Interestingly the promyelocytic cells were more sensitive to sulphasalazine than the lymphoma cell line.Neutrophil elastase expression and ELA2 mutations do, however, not seem to be involved in the etilogy of sulphasalazine-induced agranulocytosis. Why sulphasalazine is more toxic to promyelocytes than to lymphocytes remains to be explained.Sulphasalazine (SA) has anti-inflammatory, immunosuppressive and antibiotic actions, and is a component in the therapy of Crohn's disease, ulcerative colitis and rheumatoid arthritis. Bacterial enzymes in the colon split sulphasalazine into sulphapyridine and 5-aminosalicylic acid before it is absorbed. Sulphapyridine acts as a sulphonamide antibiotic, whereas 5-aminosalicylic acid is believed to be the anti-inflammatory metabolite. Common side/toxic effects are vomiting, skin rash and headache. The incidence of the hematological adverse effects associated with sulphasalazine is generally low, but the reactions can be severe and sometimes fatal. The risk of sulphasalazine-induced agranulocytosis, i.e. profoundly depressed circulating neutrophils is high