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 associated with a high incidence (> 40%) of adverse drug events, including severe hypersensitivity reactions. Sulfonamide reactive metabolites have been implicated in the pathogenesis of these adverse reactions, Sulfamethoxazole hydroxylamine (SMX-HA) induces lymphocyte toxicity and suppression of proliferation in vitro; the mechanism(s) of these immunomodulatory effects remain unknown, We investigated the cytotoxicity of SMX-HA via apoptosis on human peripheral blood mononuclear cells and purified cell subpopulations in vitro. CD19(+), CD4(+), and CD8(+) cells were isolated from human peripheral blood by positive selection of cell surface molecules by magnetic bead separation. SMX-HA induced significant CD8(+) cell death (67 +/- 7%) at 100 mu M SMX-HA, with only minimal CD4(+) cell death (8 +/- 4%). No significant subpopulation toxicity was shown when incubated with parent drug (SMX). Flow cytometry measuring phosphatidylserine externalization 24 h after treatment with 100 mu M and 400 mu M SMX-HA revealed 14.1 +/- 0.7% and 25.6 +/- 4.2% annexin-positive cells, respectively, compared to 3.7 +/- 1.2% in control PBMCs treated with 400 mu M SMX. Internucleosomal DNA fragmentation was observed 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 toxicity of CD8(+) cells by the hydroxylamine of sulfamethoxazole.