Cytotoxicity of sulfonamide reactive metabolites: apoptosis and selective toxicity of CD8(+) cells by the hydroxylamine of sulfamethoxazole

Treatment with sulfonamide antibiotics in HIV-infected patients is associat ed with a high incidence (> 40%) of adverse drug events, including severe h ypersensitivity reactions. Sulfonamide reactive metabolites have been impli cated in the pathogenesis of these adverse reactions, Sulfamethoxazole hydr oxylamine (SMX-HA) induces lymphocyte toxicity and suppression of prolifera tion in vitro; the mechanism(s) of these immunomodulatory effects remain un known, We investigated the cytotoxicity of SMX-HA via apoptosis on human pe ripheral blood mononuclear cells and purified cell subpopulations in vitro. CD19(+), CD4(+), and CD8(+) cells were isolated from human peripheral bloo d by positive selection of cell surface molecules by magnetic bead separati on. SMX-HA induced significant CD8(+) cell death (67 +/- 7%) at 100 mu M SM X-HA, with only minimal CD4(+) cell death (8 +/- 4%). No significant subpop ulation toxicity was shown when incubated with parent drug (SMX). Flow cyto metry measuring phosphatidylserine externalization 24 h after treatment wit h 100 mu M and 400 mu M SMX-HA revealed 14.1 +/- 0.7% and 25.6 +/- 4.2% ann exin-positive cells, respectively, compared to 3.7 +/- 1.2% in control PBMC s treated with 400 mu M SMX. Internucleosomal DNA fragmentation was observe d in quiescent and stimulated PBMCs 48 h after incubation with SMX-HA. Our data show that CD8(+) cells are highly susceptible to the toxic effects of SMX-HA through enhanced cell death by apoptosis.-Hess, D. A., Sisson, M. E. , Suria, H., Wijsman, J., Puvanesasingham, R., Madrenas, J., Rieder, M. J. Cytotoxicity of sulfonamide reactive metabolites: apoptosis and selective t oxicity of CD8(+) cells by the hydroxylamine of sulfamethoxazole.