Novel non-labile covalent binding of sulfamethoxazole reactive metabolites to cultured human lymphoid cells

Drug hapten-specific T-cell activation: Current status and unanswered questions

Drug haptens are formed from the irreversible, covalent binding of drugs to nucleophilic moieties on proteins, which can warrant adverse reactions in the body including severe delayed-type, T-cell mediated, drug hypersensitivity reactions (DHRs). While three main pathways exist for the activation of T-cells in DHRs, namely the hapten model, the pharmacological interaction model and the altered peptide repertoire model, the exact antigenic determinants responsible have not yet been defined. In recent years, progress has been made using advanced mass spectrometry-based proteomic methods to identify protein carriers and characterise the structure of drug-haptenated proteins. Since genome-wide association studies discovered a link between human leukocyte antigens (HLA) and an individual's susceptibility to DHRs, much effort has been made to define the drug-associated HLA ligands driving T-cell activation, including the elution of natural HLA peptides from HLA molecules and the generation of HLA-binding peptides. In this review, we discuss our current methodology used to design and synthesise drug-modified HLA ligands to investigate their immunogenicity using T-cell models, and thus their implication in drug hypersensitivity.

Sulfonamide derivatives as Mycobacterium tuberculosis inhibitors: in silico approach

Both DHPS (dihydropteroate synthase) and DHFR (dihydrofolate reductase) play important physiological roles in the survivability of Mycobacterium tuberculosis (MTB). Sulfonamides are the potent drugs to monitor growth and proliferation of MTBs by inhibiting the activity of DHPS and DHFR which could explain the mechanism of action of these molecules. In this work, 102 heterocyclic sulfonamides (HSF) have been screened by discovery studio molecular docking programme to search the best suitable molecule for the treatment of MTBs. Lipinski's rule of five protocols is followed to screen drug likeness of these molecules and ADMET (absorption, distribution, metabolism, excretion and toxicity) filtration has been used to value their toxicity. Only fourteen molecules are found to obey the Lipinski's rule and able to cross the ADMET filter. A small difference between HOMO and LUMO energy signifies the electronic excitation energy which is essential to calculate molecular reactivity and stability of the best docked compound and easy activation of drug in the protein environment. Both 4-amino-N-(6-hydroxypyridin-2-yl)benzenesulfonamide (M1) and 4-amino-N-(9H-carbazol-2-yl)benzenesulfonamide (M2) show the best theoretical efficiency with DHPS and DHFR, respectively. These compounds are also found to bind to the adenine-thymine region of tuberculosis DNA.

Structural characterization of new Schiff bases of sulfamethoxazole and sulfathiazole, their antibacterial activity and docking computation with DHPS protein structure

New Schiff bases (1, 2) of substituted salicylaldehydes and sulfamethoxazole (SMX)/sulfathiazole (STZ) are synthesized and characterized by elemental analysis and spectroscopic data. Single crystal X-ray structure of one of the compounds (E)-4-((3,5-dichloro-2-hydroxybenzylidene)amino)-N-(5-methylisoxazol-3-yl)benzenesulfonamide (1c) has been determined. Antimicrobial activities of the Schiff bases and parent sulfonamides (SMX, STZ) have been examined against several Gram-positive and Gram-negative bacteria and sulfonamide resistant pathogens; the lowest MIC is observed for (E)-4-((3,5-dichloro-2-hydroxybenzylidene)amino)-N-(thiazol-2-yl)benzene sulfonamide (2c) (8.0 μg mL(-1)) and (E)-4-((3,5-dichloro-2-hydroxybenzylidene)amino)-N-(5-methylisoxazol-3-yl)benzene sulfonamide (1c) (16.0 μg mL(-1)) against sulfonamide resistant pathogens. DFT optimized structures of the Schiff bases have been used to carry out molecular docking studies with DHPS (dihydropteroate synthase) protein structure (downloaded from Protein Data Bank) using Discovery Studio 3.5 to find the most preferred binding mode of the ligand inside the protein cavity. The theoretical data have been well correlated with the experimental results. Cell viability assay and ADMET studies predict that 1c and 2c have good drug like characters.

The crystal structure of sulfamethoxazole, interaction with DNA, DFT calculation, and molecular docking studies

Sulfamethoxazole (SMX) [4-amino-N-(5-methyl-1,2-oxazol-3-yl)benzenesulfonamide] is structurally established by single crystal X-ray diffraction measurement. The crystal packing shows H-bonded 2D polymer through N(7)-H(7A)-O(2), N(7)-H(7B)-O(3), N(1)-H(1)-N(2), C(5)-H(5)-O(3)-S(1) and N(7)-(H7A)-O(2)-S(1). Density Functional Theory (DFT) and Time Dependent-DFT (TD-DFT) computations of optimized structure of SMX determine the electronic structure and has explained the electronic spectral transitions. The interaction of SMX with CT-DNA has been studied by absorption spectroscopy and the binding constant (Kb) is 4.37×10(4)M(-1). The in silico test of SMX with DHPS from Escherichia coli and Streptococcus pneumoniae helps to understand drug metabolism and accounts the drug-molecule interactions. The molecular docking of SMX-DNA also helps to predict the interaction feature.

Integrated biomarker responses in zebrafish exposed to sulfonamides

Dispersed pharmaceuticals such as sulfonamides pose a threat to aquatic ecosystems. We evaluated potential biomarkers of sulfonamide exposure using an extended zebrafish (Danio rerio) toxicity test. The tested sulfonamides induced obvious effects on spontaneous swimming activity and heartbeat rate in zebrafish. Glutathione S-transferase (GST) and malondialdehyde (MDA) were examined to reflect the biomarker response of zebrafish exposed to three sulfonamides (sulfamethoxazole, sulfadiazine (SDZ) and sulfadimidine). Both GST and MDA showed time-dependent responses to sulfonamide exposure. GST activity was significantly increased after exposure to sulfonamides for 3 days, while MDA concentration reached a maximum during the first day and then declined. These results suggest that MDA may be a more sensitive biomarker of sulfonamide toxicity than GST. These investigations demonstrated that SDZ was a typical inducer of metabolic enzymes, suggesting that it poses a potential ecotoxicological risk to aquatic ecosystems.

Idiosyncratic adverse drug reactions: current concepts

Idiosyncratic drug reactions are a significant cause of morbidity and mortality for patients; they also markedly increase the uncertainty of drug development. The major targets are skin, liver, and bone marrow. Clinical characteristics suggest that IDRs are immune mediated, and there is substantive evidence that most, but not all, IDRs are caused by chemically reactive species. However, rigorous mechanistic studies are very difficult to perform, especially in the absence of valid animal models. Models to explain how drugs or reactive metabolites interact with the MHC/T-cell receptor complex include the hapten and P-I models, and most recently it was found that abacavir can interact reversibly with MHC to alter the endogenous peptides that are presented to T cells. The discovery of HLA molecules as important risk factors for some IDRs has also significantly contributed to our understanding of these adverse reactions, but it is not yet clear what fraction of IDRs have a strong HLA dependence. In addition, with the exception of abacavir, most patients who have the HLA that confers a higher IDR risk with a specific drug will not have an IDR when treated with that drug. Interindividual differences in T-cell receptors and other factors also presumably play a role in determining which patients will have an IDR. The immune response represents a delicate balance, and immune tolerance may be the dominant response to a drug that can cause IDRs.

Enhanced antigenicity leads to altered immunogenicity in sulfamethoxazole-hypersensitive patients with cystic fibrosis

BACKGROUND

Exposure of patients with cystic fibrosis to sulfonamides is associated with a high incidence of hypersensitivity reactions.

OBJECTIVE

To compare mechanisms of antigen presentation and characterize the phenotype and function of T cells from sulfamethoxazole-hypersensitive patients with and without cystic fibrosis.

METHODS

T cells were cloned from 6 patients and characterized in terms of phenotype and function. Antigen specificity and mechanisms of antigen presentation to specific clones were then explored. Antigen-presenting cell metabolism of sulfamethoxazole was quantified by ELISA. The involvement of metabolism in antigen presentation was evaluated by using enzyme inhibitors.

RESULTS

Enzyme inhibitable sulfamethoxazole-derived protein adducts were detected in antigen-presenting cells from patients with and without cystic fibrosis. A significantly higher quantity of adducts were detected with cells from patients with cystic fibrosis. Over 500 CD4(+) or CD8(+) T-cell clones were generated and shown to proliferate and kill target cells. Three patterns of MHC-restricted reactivity (sulfamethoxazole-responsive, sulfamethoxazole metabolite-responsive, and cross-reactive) were observed with clones from patients without cystic fibrosis. From patients with cystic fibrosis, sulfamethoxazole metabolite-responsive and cross-reactive, but not sulfamethoxazole-responsive, clones were observed. The response of the cross-reactive clones to sulfamethoxazole was dependent on adduct formation and was blocked by glutathione and enzyme inhibitors. Antigen-stimulated clones from patients with cystic fibrosis secreted higher levels of IFN-γ, IL-6, and IL-10, but lower levels of IL-17.

CONCLUSION

Sulfamethoxazole metabolism and protein adduct formation is critical for the stimulation of T cells from patients with cystic fibrosis. T cells from patients with cystic fibrosis secrete high levels of IFN-γ, IL-6, and IL-10.

Stimulation of human T cells with sulfonamides and sulfonamide metabolites

BACKGROUND

Exposure to sulfonamides is associated with a high incidence of hypersensitivity reactions. Antigen-specific T cells are involved in the pathogenesis; however, the nature of the antigen interacting with specific T-cell receptors is not fully defined.

OBJECTIVE

We sought to explore the frequency of sulfamethoxazole (SMX)- and SMX metabolite-specific T cells in hypersensitive patients, delineate the specificity of clones, define mechanisms of presentation, and explore additional reactivity with structurally related sulfonamide metabolites.

METHODS

SMX- and SMX metabolite-specific T-cell clones were generated from 3 patients. Antigen specificity, mechanisms of antigen presentation, and cross-reactivity of specific clones were then explored. Low-lying energy conformations of drugs (metabolites) were modeled, and the energies available for protein binding was estimated.

RESULTS

Lymphocytes proliferated with parent drugs (SMX, sulfadiazine, and sulfapyridine) and both hydroxylamine and nitroso metabolites. Three patterns of drug (metabolite) stimulation were seen: 44% were SMX metabolite specific, 43% were stimulated with SMX metabolites and SMX, and 14% were stimulated with SMX alone. Most metabolite-responsive T cells were stimulated with nitroso SMX-modified protein through a hapten mechanism involving processing. In contrast to SMX-responsive clones, which were highly specific, greater than 50% of nitroso SMX-specific clones were stimulated with nitroso metabolites of sulfapyridine and sulfadiazine but not nitrosobenzene. Pharmacophore modeling showed that the summation of available binding energies for protein interactions and the preferred spatial arrangement of atoms in each molecule determine a drug's potential to stimulate specific T cells.

CONCLUSIONS

Nitroso sulfonamide metabolites form potent antigenic determinants for T cells from hypersensitive patients. T-cell responses against drugs (metabolites) bound directly to MHC or MHC/peptide complexes can occur through cross-reactivity with the haptenic immunogen.

"Danger" conditions increase sulfamethoxazole-protein adduct formation in human antigen-presenting cells

Antigen-presenting cells (APC) are thought to play an important role in the pathogenesis of drug-induced immune reactions. Various pathological factors can activate APC and therefore influence the immune equilibrium. It is interesting that several diseases have been associated with an increased rate of drug allergy. The aim of this project was to evaluate the impact of such "danger signals" on sulfamethoxazole (SMX) metabolism in human APC (peripheral blood mononuclear cells, Epstein-Barr virus-modified B lymphocytes, monocyte-derived dendritic cells, and two cell lines). APC were incubated with SMX (100 microM-2 mM; 5 min-24 h), in the presence of pathological factors: bacterial endotoxins (lipopolysaccharide and staphylococcal enterotoxin B), flu viral proteins, cytokines [interleukin (IL)-1beta, IL-6, IL-10; tumor necrosis factor-alpha; interferon-gamma; and transforming growth factor-beta], inflammatory molecules (prostaglandin E2, human serum complement, and activated protein C), oxidants (buthionine sulfoximine and H(2)O(2)), and hyperthermia (37.5-39.5 degrees C). Adduct formation was evaluated by enzyme-linked immunosorbent assay and confocal microscopy. SMX-protein adduct formation was time- and concentration-dependent for each cell type tested, in both physiological and danger conditions. A danger environment significantly increased the formation of SMX-protein adducts and significantly shortened the delay for their detection. An additive effect was observed with a combination of danger signals. Dimedone (chemical selectively binding cysteine sulfenic acid) and antioxidants decreased both baseline and danger-enhanced SMX-adduct formation. Various enzyme inhibitors were associated with a significant decrease in SMX-adduct levels, with a pattern varying depending on the cell type and the culture conditions. These results illustrate that danger signals enhance the formation of intracellular SMX-protein adducts in human APC. These findings might be relevant to the increased frequency of drug allergy in certain disease states.

Multiple adduction reactions of nitroso sulfamethoxazole with cysteinyl residues of peptides and proteins: implications for hapten formation

Sulfamethoxazole (SMX) induces immunoallergic reactions that are thought to be a result of intracellular protein haptenation by its nitroso metabolite (SMX-NO mass, 267 amu). SMX-NO reacts with protein thiols in vitro, but the conjugates have not been defined chemically. The reactions of SMX-NO with glutathione (GSH), a synthetic peptide (DS3), and two model proteins, human GSH S-transferase pi (GSTP) and serum albumin (HSA), were investigated by mass spectrometry. SMX-NO formed a semimercaptal (N-hydroxysulfenamide) conjugate with GSH that rearranged rapidly (1-5 min) to a sulfinamide. Reaction of SMX-NO with DS3 also yielded a sulfinamide adduct (mass increment, 267 amu) on the cysteine residue. GSTP was exclusively modified at the reactive Cys47 by SMX-NO and exhibited mass increments of 267, 283, and 299 amu, indicative of sulfinamide, N-hydroxysulfinamide, and N-hydroxysulfonamide adducts, respectively. HSA was modified at Cys34, forming only the N-hydroxysulfinamide adduct. HSA modification by SMX-NO under these conditions was confirmed with ELISA and immunoblotting with an antisulfonamide antibody. It is proposed that cysteine-linked N-hydroxysulfinamide and N-hydroxysulfonamide adducts of SMX are formed via the reaction of SMX-NO with cysteinyl sulfoxy acids. Evidence for a multistep assembly of model sulfonamide epitopes on GSH and polypeptides via hydrolyzable intermediates is also presented. In summary, novel, complex, and metastable haptenic structures have been identified on proteins exposed in vitro to the nitroso metabolite of SMX.

The Endoplasmic Reticulum in Xenobiotic Toxicity

The endoplasmic reticulum (ER) is involved in an array of cellular functions that play important roles in xenobiotic toxicity. The ER contains the majority of cytochrome P450 enzymes involved in xenobiotic metabolism, as well as a number of conjugating enzymes. In addition to its role in drug bioactivation and detoxification, the ER can be a target for damage by reactive intermediates leading to cell death or immune-mediated toxicity. The ER contains a set of luminal proteins referred to as ER stress proteins (including GRP78, GRP94, protein disulfide isomerase, and calreticulin). These proteins help regulate protein processing and folding of membrane and secretory proteins in the ER, calcium homeostasis, and ER-associated apoptotic pathways. They are induced in response to ER stress. This review discusses the importance of the ER in molecular events leading to cell death following xenobiotic exposure. Data showing that the ER is important in both renal and hepatic toxicity will be discussed.

Antibiotic use and risk of non-Hodgkin's lymphoma: a population-based case-control study

Antibiotic use in 759 non-Hodgkin's lymphoma (NHL) patients and 589 controls was compared. Neither total antibiotic use (odds ratio=0.7, 95% confidence interval=0.5-1.2), nor antibiotic use by site, was associated with total NHL, or NHL subtypes. There were no trends with frequency or age at first use (P trend=0.23 and 0.26, respectively).

Anti-myeloperoxidase and anti-cathepsin G antibodies in sulphonamide hypersensitivity

BACKGROUND

Anti-neutrophil cytoplasmic antibodies (ANCA) are associated with vasculitis in humans. Sulphonamide antimicrobials cause drug hypersensitivity (HS) reactions with some clinical signs that are suggestive of vasculitis.

OBJECTIVE

The purpose of this study was to determine whether sulphonamide HS is associated with anti-neutrophil antibodies, using the dog as a spontaneous clinical model.

METHODS

Thirty-four sulphonamide-HS dogs, 11 sulphonamide-'tolerant' dogs, and nine healthy sulphonamide-naïve dogs were evaluated for anti-neutrophil antibodies using a commercial ELISA against human myeloperoxidase (MPO), a commercial human ANCA Western blot protocol, and immunoblotting against whole canine neutrophils.

RESULTS

Using ELISA, anti-MPO antibodies were found with an apparent higher frequency in HS dogs (50%), compared with 'tolerant' dogs (18%), which also showed significantly lower absorbances. Among HS dogs, anti-MPO antibodies were significantly more common, with significantly higher absorbances, in dogs that did not survive the HS reaction (78%) compared with survivors (35%). Using immunoblotting, ANCA were detected with similar overall frequencies in HS and 'tolerant' dogs. However, one protein targeted by several HS dogs, but no 'tolerant' dogs, was identified as cathepsin G.

CONCLUSION

These data indicate that anti-MPO antibodies and anti-cathepsin G antibodies are associated with sulphonamide HS. Anti-MPO antibodies have been shown to be pathogenic both in vitro and in vivo, leading to vasculitis lesions and vasculitis-like syndromes. The present study therefore suggests that vasculitis might be one mechanism of tissue damage in this sulphonamide HS. Furthermore, the evaluation of ANCA, and its relationship to disease severity and clinical outcome, should be considered in human patients with sulphonamide drug HS.

Sulfamethoxazole and its metabolite nitroso sulfamethoxazole stimulate dendritic cell costimulatory signaling

Different signals in addition to the antigenic signal are required to initiate an immunological reaction. In the context of sulfamethoxazole allergy, the Ag is thought to be derived from its toxic nitroso metabolite, but little is known about the costimulatory signals, including those associated with dendritic cell maturation. In this study, we demonstrate increased CD40 expression, but not CD80, CD83, or CD86, with dendritic cell surfaces exposed to sulfamethoxazole (250-500 microM) and the protein-reactive metabolite nitroso sulfamethoxazole (1-10 microM). Increased CD40 expression was not associated with apoptosis or necrosis, or glutathione depletion. Covalently modified intracellular proteins were detected when sulfamethoxazole was incubated with dendritic cells. Importantly, the enzyme inhibitor 1-aminobenzotriazole prevented the increase in CD40 expression with sulfamethoxazole, but not with nitroso sulfamethoxazole or LPS. The enzymes CYP2C9, CYP2C8, and myeloperoxidase catalyzed the conversion of sulfamethoxazole to sulfamethoxazole hydroxylamine. Myeloperoxidase was expressed at high levels in dendritic cells. Nitroso sulfamethoxazole immunogenicity was inhibited in mice with a blocking anti-CD40L Ab. In addition, when a primary nitroso sulfamethoxazole-specific T cell response using drug-naive human cells was generated, the magnitude of the response was enhanced when cultures were exposed to a stimulatory anti-CD40 Ab. Finally, increased CD40 expression was 5-fold higher on nitroso sulfamethoxazole-treated dendritic cells from an HIV-positive allergic patient compared with volunteers. These data provide evidence of a link between localized metabolism, dendritic cell activation, and drug immunogenicity.

Immunological principles of T-cell-mediated adverse drug reactions in skin

Drug hypersensitivity reactions in skin are an immune-mediated phenomenon associated with significant patient mortality and morbidity. Antigen-specific T cells, which have been isolated from the peripheral circulation and target organs of hypersensitive patients, are thought to propagate and regulate the development of clinical symptoms. The investigation of clinical cases with respect to the basic cellular and chemical mechanisms that underpin drug hypersensitivity has resulted in: i) the need to redress some aspects of present immunological dogma; and ii) additional fundamental immunological questions. Thus, the aim of this review article is to summarise present opinion on how and why drugs initiate a pathogenic T-cell response in a small section of the population and subsequently reflect on gaps in basic immunology and where future research might lead.

Evaluation of polyamidoamine (PAMAM) dendrimers as drug carriers of anti-bacterial drugs using sulfamethoxazole (SMZ) as a model drug

Sulfamethoxazole (SMZ), a sulfonamide with well-known anti-bacterial properties, is not freely soluble in water and causes problems in its clinical applications. In the present study we investigated the potential of ethylenediamine (EDA) core polyamidoamine (PAMAM) dendrimers as drug carriers of SMZ by aqueous solubility, in vitro release as well as anti-bacterial activity studies. Results showed that the aqueous solubility of SMZ was approximately proportional to dendrimer concentration (a 40-fold increase in solubility in 10mg/ml G3 PAMAM dendrimer solutions compared with that in double-distilled water at 37 degrees C). The in vitro release of SMZ in the presence of PAMAM dendrimers was significantly slower compared to pure SMZ dissolved in ethanol. Microbiology studies showed that PAMAM dendrimers could increase the anti-bacterial activity of SMZ (a 4- or 8-fold increase in the anti-bacterial activity of SMZ in dendrimer solution compared to pure SMZ dissolved in dimethylsulfoxide (DMSO) or 0.01 M NaOH solution). The in vitro release behavior and anti-bacterial activity studies indicated that PAMAM dendrimers might be considered as potential drug carriers of sulfonamides with a sustained release behavior under suitable conditions.

Roles of endogenous ascorbate and glutathione in the cellular reduction and cytotoxicity of sulfamethoxazole-nitroso

Sulfamethoxazole (SMX) is an effective drug for the management of opportunistic infections, but its use is limited by hypersensitivity reactions, particularly in HIV-infected patients. The oxidative metabolite SMX-nitroso (SMX-NO), is thought to be a proximate mediator of SMX hypersensitivity, and can be reduced in vitro by ascorbate or glutathione. Leukocytes from patients with SMX hypersensitivity show enhanced cytotoxicity from SMX metabolites in vitro; this finding has been attributed to a possible "detoxification defect" in some individuals. The purpose of this study was to determine whether variability in endogenous ascorbate or glutathione could be associated with individual differences in SMX-NO cytotoxicity. Thirty HIV-positive patients and 23 healthy control subjects were studied. Both antioxidants were significantly correlated with the reduction of SMX-NO to its hydroxylamine, SMX-HA, by mononuclear leukocytes, and both were linearly depleted during reduction. Controlled ascorbate supplementation in three healthy subjects increased leukocyte ascorbate with no change in glutathione, and significantly enhanced SMX-NO reduction. Ascorbate supplementation also decreased SMX-NO cytotoxicity compared to pre-supplementation values. Rapid reduction of SMX-NO to SMX-HA was associated with enhanced direct cytotoxicity from SMX-NO. When forward oxidation of SMX-HA back to SMX-NO was driven by the superoxide dismutase mimetic, Tempol, SMX-NO cytotoxicity was increased, without enhancement of adduct formation. This suggests that SMX-NO cytotoxicity may be mediated, at least in part, by redox cycling between SMX-HA and SMX-NO. Overall, these data indicate that endogenous ascorbate and glutathione are important for the intracellular reduction of SMX-NO, a proposed mediator of SMX hypersensitivity, and that redox cycling of SMX-HA to SMX-NO may contribute to the cytotoxicity of these metabolites in vitro.

Role of bioactivation in drug-induced hypersensitivity reactions

Drug-induced hypersensitivity reactions are a major problem in both clinical treatment and drug development. This review covers recent developments in our understanding of the pathogenic mechanisms involved, with special focus on the potential role of metabolism and bioactivation in generating a chemical signal for activation of the immune system. The possible role of haptenation and neoantigen formation is discussed, alongside recent findings that challenge this paradigm. Additionally, the essential role of costimulation is examined, as are the potential points whereby costimulation may be driven by reactive metabolites. The relevance of local generation of metabolites in determining the location and character of a reaction is also covered.

Medication use and risk of non-Hodgkin's lymphoma

Conflicting results from previous epidemiologic studies shed little light on whether medication use is associated with risk of non-Hodgkin's lymphoma (NHL). To investigate this question, the authors conducted a population-based case-control study in Denmark and Sweden from 1999 to 2002, including 3,055 incident NHL cases and 3,187 controls. Participants reported their past use of medications and history of particular medical conditions. Unconditional logistic regression was used to estimate multivariate odds ratios and 95% confidence intervals for the associations between medication use and risk of NHL; all statistical tests were two sided. Use of antibiotics more than 10 times during adulthood was positively associated with risk of NHL and most major NHL subtypes; when users were compared with nonusers, the odds ratio for NHL was 1.8 (95% confidence interval: 1.4, 2.3); p(trend) for total antibiotic use <0.001. In addition, high cumulative use of nonsteroidal anti-inflammatory drugs was marginally associated with elevated NHL risk. Other medications evaluated were not associated with risk of NHL or its most common subtypes. Findings suggest that inflammation, infections, susceptibility to infections, and/or use of antibiotics or nonsteroidal anti-inflammatory drugs to treat these conditions may increase the risk of NHL. However, most of the medications examined were not associated with NHL risk.

Drug bioactivation, covalent binding to target proteins and toxicity relevance

A number of therapeutic drugs with different structures and mechanisms of action have been reported to undergo metabolic activation by Phase I or Phase II drug-metabolizing enzymes. The bioactivation gives rise to reactive metabolites/intermediates, which readily confer covalent binding to various target proteins by nucleophilic substitution and/or Schiff's base mechanism. These drugs include analgesics (e.g., acetaminophen), antibacterial agents (e.g., sulfonamides and macrolide antibiotics), anticancer drugs (e.g., irinotecan), antiepileptic drugs (e.g., carbamazepine), anti-HIV agents (e.g., ritonavir), antipsychotics (e.g., clozapine), cardiovascular drugs (e.g., procainamide and hydralazine), immunosupressants (e.g., cyclosporine A), inhalational anesthetics (e.g., halothane), nonsteroidal anti-inflammatory drugs (NSAIDSs) (e.g., diclofenac), and steroids and their receptor modulators (e.g., estrogens and tamoxifen). Some herbal and dietary constituents are also bioactivated to reactive metabolites capable of binding covalently and inactivating cytochrome P450s (CYPs). A number of important target proteins of drugs have been identified by mass spectrometric techniques and proteomic approaches. The covalent binding and formation of drug-protein adducts are generally considered to be related to drug toxicity, and selective protein covalent binding by drug metabolites may lead to selective organ toxicity. However, the mechanisms involved in the protein adduct-induced toxicity are largely undefined, although it has been suggested that drug-protein adducts may cause toxicity either through impairing physiological functions of the modified proteins or through immune-mediated mechanisms. In addition, mechanism-based inhibition of CYPs may result in toxic drug-drug interactions. The clinical consequences of drug bioactivation and covalent binding to proteins are unpredictable, depending on many factors that are associated with the administered drugs and patients. Further studies using proteomic and genomic approaches with high throughput capacity are needed to identify the protein targets of reactive drug metabolites, and to elucidate the structure-activity relationships of drug's covalent binding to proteins and their clinical outcomes.

Drug hypersensitivity reactions in skin: understanding mechanisms and the development of diagnostic and predictive tests

Cutaneous manifestations of drug hypersensitivity can be serious and potentially life threatening and may prevent effective drug therapy. T cells play an important role in the pathology of drug hypersensitivity reactions. Classical studies suggest that T-cell activation requires drug bioactivation, covalent binding to protein and antigen processing to stimulate an immune response. Recent studies have shown that drugs can also be presented to T cells in the absence of antigen processing and drug metabolism. In this article, sulfamethoxazole is used as a paradigm to describe the chemical mechanisms involved in the initiation and maintenance of an aberrant drug antigen specific T-cell response. Presentation of the same drug to different individuals can cause a variety of skin diseases. Such reactions have been classified according to the phenotype and functionality of the T-cell response. This review summarises the different forms of cutaneous hypersensitivity reactions and describes how T-cell clones generated from hypersensitive patients have been used to study the cellular mechanisms of anticonvulsant hypersensitivity. Potential uses of in vitro cell culture assays for patient diagnosis and drug evaluation are also discussed.

Characterization of sulfamethoxazole and sulfamethoxazole metabolite-specific T-cell responses in animals and humans

Sulfamethoxazole (SMX) is associated with hypersensitivity reactions. Identification of drug-specific lymphocytes from hypersensitive patients suggests involvement of the immune system. Lymphocytes from humans recognize SMX and nitroso-SMX (SMX-NO), whereas cells from sensitized rats recognize only SMX-NO. In this investigation, we study the nature of SMX-specific T cells in four species. Male rats, mice, and rabbits were immunized with SMX (50 mg kg-1) or SMX-NO (1 mg kg-1). Lymphocytes and/or splenocytes were isolated and incubated with SMX, SMX-hydroxylamine or SMX-NO and proliferation were measured. Lymphocytes were also isolated from SMX-hypersensitive patients (n = 3) and drug-specific proliferation was measured. In addition, rabbits were bled fortnightly for 4 months to determine whether SMX-NO-specific T cells cross-react with SMX. To confirm that SMX-NO responses were due to covalent binding and not cross-reactivity, cells were pulsed with SMX-NO and/or coincubated with glutathione. Splenocytes from mice, rats, and rabbits proliferated when stimulated with SMX-NO, but not SMX. A 2-h pulse with SMX-NO was sufficient for proliferation, whereas cells coincubated with SMX-NO and glutathione did not proliferate. Rabbit lymphocytes proliferated in the presence of SMX-NO and SMX-hydroxylamine, but not SMX. SMX-hydroxylamine was converted to SMX-NO in culture. The SMXNO-specific response of rabbit lymphocytes was maintained for at least 4 months and the cells did not cross-react with SMX. Human lymphocytes from hypersensitive patients proliferated in the presence of SMX and both metabolites. These results highlight important differences in T-cell recognition of drug (metabolite) antigens in animals that have been sensitized against a drug metabolite and patients with hypersensitivity to the drug.