Covalent Binding of the Nitroso Metabolite of Sulfamethoxazole Is Important in Induction of Drug-Specific T-Cell Responses in Vivo

Abstract

Immune-mediated drug hypersensitivity reactions (IDHRs) represent a significant problem due to their unpredictable and severe nature, as well as the lack of understanding of the pathogenesis. Sulfamethoxazole (SMX), a widely used antibiotic, has been used as a model compound to investigate the underlying mechanism of IDHRs because it has been associated with a relatively high incidence of hypersensitivity. Previous studies by others showed that administration of 4-(nitroso)-N- (5-methyl-1,2-oxazol-3-yl)benzenesulfonamide (SMX-NO), the reactive metabolite of SMX, to rats resulted in the generation of SMX-specific antibodies and ex vivo splenocyte proliferative responses, as well as haptenation of skin keratinocytes, circulating peripheral blood mononuclear cells, and splenocytes. The objective of the present study was to further investigate SMX-NO-protein binding in relationship to its immunogenicity. In female DBA/1 mice treated with SMX-NO, varying degrees of SMX-NO-dependent T-cell responses and SMX-NO-protein adduct formation were observed in the spleen and in inguinal, brachial, and axillary lymph nodes. The data suggested a tissue-specific threshold of SMX-NO dosage that triggers the detection of adducts and immune response. Furthermore, serum albumin and immunoglobulin were identified as protein targets for SMX-NO modification. It seemed that these adducts were formed in the blood, circulated to lymphoid tissues, and initiated SMX-NO-dependent immune responses. Collectively, these data revealed a causal link between the deposition of SMX-NO-protein adducts in a lymphoid tissue and the induction of immune response in that tissue. Our findings also suggest that the immunogenicity of SMX-NO is determined by the immunogenic nature of the hapten, rather than special characteristics of the adducted protein.

Bioactivation of Trimethoprim to Protein-Reactive Metabolites in Human Liver Microsomes

“…Until now, the ADRs observed with TMP-SMX have been attributed solely to the SMX component (or its metabolites), but our results show that TMP undergoes metabolic activation and covalent binding at least as efficiently as SMX and several other hepatotoxic drugs (Cheng et al, 2008). Our findings support the hypothesis that TMP has the potential to contribute to IADR development in these patients exposed to TMP-SMX via the pathway of bioactivation followed by protein adduct formation.…”

Development and partial validation of a mouse model for predicting drug hypersensitivity reactions

“…For example, data exist which suggest that sulfamethoxazole (SMX) can induce T-cell-specific responses via both hapten and PI mechanisms (Cheng et al, 2008;Depta et al, 2004;Faulkner et al, 2012;Lavergne et al, 2009). There is also evidence that patient-specific risk factors play a role in contributing to the development of drug hypersensitivity reactions, such as genetic factors (e.g.…”

Development of a screening assay to evaluate the potential of drugs to cause immune-mediated hypersensitivity reactions

“…However, our previous study provides evidence to support that the abundance, rather than the particular characteristics of a protein determines whether it is targeted for RM modification. It is not the nature of the protein, but the reactivity of the RM that determines the immunogenicity of the RM-protein adducts (Cheng et al, 2008). Therefore, MSA used as a model protein in this assay should be sufficient to evaluate the immunogenicity of the RM.…”

“…The data suggest that all three strains of mice could be used in the assay. DBA/1 mice were selected for the majority of the experiments because they were previously shown to be a strain susceptible to SMX-NO-induced immune responses (Cheng et al, 2008).…”