Haptenation of sulfonamide reactive metabolites to cellular proteins

Adverse drug reactions are a major problem complicating medical therapy. The pathogenesis of many severe adverse drug reactions, notably hypersensitivity reactions, is poorly understood. The sulfonamides are associated with severe hypersensitivity reactions. The initial pathogenesis seems to be caused by bioactivation of the parent drug to a reactive intermediate and subsequent propagation by the immune system. The determinants of the immune response are not known. We explored the formation of sulfonamide haptens in Molt-3 and HEPA 1C1C7 cells after incubation with sulfamethoxazole (SMX), the hydroxylamine of sulfamethoxazole (SMX-HA), or the nitroso of sulfamethoxazole (SMX-NO). Haptenation was demonstrated with SMX-HA and SMX-NO but not SMX; this occurred at concentrations below that associated with toxicity (significant haptenation was seen at 25 to 50 microM). Thus, haptenation occurred presumably onto viable cells. Haptenation occurred rapidly; haptenation of cell surface proteins was demonstrated within 5 min. This did not occur indiscriminately; confocal microscopy demonstrated haptenation onto specific sites on the cell membrane. We found that haptenation was significantly inhibited by thiols and other antioxidants (p < 0.05). Sulfonamide-specific haptens were rapidly internalized by what seemed to be a caveolae-dependent process. It seems that sulfonamide reactive metabolites haptenated specific cell surface proteins that are rapidly internalized. Understanding the specific protein target(s) for haptenation and how these haptens are processed will be important in understanding the immune mediation of sulfonamide hypersensitivity adverse drug reactions.