A role for bioactivation and covalent binding within epidermal keratinocytes in sulfonamide-induced cutaneous drug Reactions

Cutaneous reactions are the most common manifestation of delayed-type hyper sensitivity caused by sulfamethoxazole and dapsone. In light of the recogni zed metabolic and immunologic activity of the skin, we investigated the pot ential role of normal human epidermal keratinocytes in the development of t hese reactions. Adult and neonatal normal human epidermal keratinocytes met abolized sulfamethoxazole and dapsone to N-4-hydroxylamine and N-acetyl der ivatives in a time-dependent manner. The latter was catalyzed by N-acetyltr ansferase 1 alone as normal human epidermal keratinocytes did not express m RNA for N-acetyltransferase 2. Investigation of metabolism-dependent toxici ty of sulfamethoxazole and dapsone, and subsequent incubation of normal hum an epidermal keratinocytes with the respective hydroxylamine metabolites, d emonstrated that these cells were resistant to the cytotoxic effects of sul famethoxazole hydroxylamine but not dapsone hydroxylamine. With prior deple tion of glutathione, however, normal human epidermal keratinocytes became s usceptible to the toxicity of sulfamethoxazole hydroxylamine. Covalent addu ct formation by sulfamethoxazole hydroxylamine was detected in normal human epidermal keratinocytes, even in the absence of cell death, and was increa sed with glutathione depletion. Major protein targets of sulfamethoxazole h ydroxylamine were observed in the region of 160, 125, 95, and 57 kDa. Dapso ne hydroxylamine also caused covalent adduct formation in normal human epid ermal keratinocytes. Together, these observations provide a basis for our h ypothesis that normal human epidermal keratinocytes are involved in the ini tiation and propagation of a cutaneous hypersensitivity response to these d rugs.