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

HIV-1 tat expression and sulphamethoxazole hydroxylamine mediated oxidative stress alter the disulfide proteome in Jurkat T cells

Background

Adverse drug reactions (ADRs) are a significant problem for HIV patients, with the risk of developing ADRs increasing as the infection progresses to AIDS. However, the pathophysiology underlying ADRs remains unknown. Sulphamethoxazole (SMX) via its active metabolite SMX-hydroxlyamine, when used prophylactically for pneumocystis pneumonia in HIV-positive individuals, is responsible for a high incidence of ADRs. We previously demonstrated that the HIV infection and, more specifically, that the HIV-1 Tat protein can exacerbate SMX-HA-mediated ADRs. In the current study, Jurkat T cell lines expressing Tat and its deletion mutants were used to determine the effect of Tat on the thiol proteome in the presence and absence of SMX-HA revealing drug-dependent changes in the disulfide proteome in HIV infected cells.

Protein lysates from HIV infected Jurkat T cells and Jurkat T cells stably transfected with HIV Tat and Tat deletion mutants were subjected to quantitative slot blot analysis, western blot analysis and redox 2 dimensional (2D) gel electrophoresis to analyze the effects of SMX-HA on the thiol proteome.

Results

Redox 2D gel electrophoresis demonstrated that untreated, Tat-expressing cells contain a number of proteins with oxidized thiols. The most prominent of these protein thiols was identified as peroxiredoxin. The untreated, Tat-expressing cell lines had lower levels of peroxiredoxin compared to the parental Jurkat E6.1 T cell line. Conversely, incubation with SMX-HA led to a 2- to 3-fold increase in thiol protein oxidation as well as a significant reduction in the level of peroxiredoxin in all the cell lines, particularly in the Tat-expressing cell lines.

Conclusion

SMX-HA is an oxidant capable of inducing the oxidation of reactive protein cysteine thiols, the majority of which formed intermolecular protein bonds. The HIV Tat-expressing cell lines showed greater levels of oxidative stress than the Jurkat E6.1 cell line when treated with SMX-HA. Therefore, the combination of HIV Tat and SMX-HA appears to alter the activity of cellular proteins required for redox homeostasis and thereby accentuate the cytopathic effects associated with HIV infection of T cells that sets the stage for the initiation of an ADR.

Electronic supplementary material

The online version of this article (10.1186/s12985-018-0991-x) contains supplementary material, which is available to authorized users.

A single-nucleotide polymorphism in the canine cytochrome b5 reductase (CYB5R3) gene is associated with sulfonamide hypersensitivity and is overrepresented in Doberman Pinschers

Canine sulfonamide hypersensitivity (HS) has been associated with a variant in the cytochrome b₅ reductase gene (CYB5R3 729A>G), which encodes a drug-detoxifying enzyme. Study objectives were to determine variant allele frequency in Doberman Pinschers (DOBE), a breed which may be predisposed to sulfonamide HS, and to characterize the effects of CYB5R3 729G on gene expression and function. CYB5R3 729A>G allele frequencies were compared between DOBE (n = 24) vs. non-Doberman (non-DOBE; n = 60) dogs. CYB5R3mRNA expression, protein expression, and reduction of sulfamethoxazole hydroxylamine were compared between banked canine liver samples of 729AA vs. GG genotype. The 729G allele was overrepresented in DOBE (1.00) vs. non-DOBE dogs (0.567, p < .0001). mRNA and protein expressions as well as cyt b₅ reductase activity were similar between livers of AA and GG genotype. All Doberman Pinschers in this study were homozygous for CYB5R3 729G, which could contribute to this breed's apparent predisposition to sulfonamide HS. However, CYB5R3 729G does not alter sulfamethoxazole detoxification capacity, so a direct role could not be demonstrated. It is possible that this marker is linked to another contributing variant.

Dapsone and Nitroso Dapsone Activation of Naı̈ve T-Cells from Healthy Donors

Dapsone (DDS) causes hypersensitivity reactions in 0.5-3.6% of patients. Although clinical diagnosis is indicative of a hypersensitivity reaction, studies have not been performed to define whether dapsone or a metabolite activates specific T-cells. Thus, the aims of this study were to explore the immunogenicity DDS and nitroso DDS (DDS-NO) using peripheral blood mononuclear cells from healthy donors and splenocytes from mice and generate human T-cell clones to characterize mechanisms of T-cell activation. DDS-NO was synthesized from DDS-hydroxylamine and shown to bind to the thiol group of glutathione and human and mouse albumin through sulfonamide and N-hydroxyl sulphonamide adducts. Naïve T-cell priming to DDS and DDS-NO was successful in three human donors. DDS-specific CD4+ T-cell clones were stimulated to proliferate in response to drug via a MHC class II restricted direct binding interaction. Cross reactivity with DDS-NO, DDS-analogues, and sulfonamides was not observed. DDS-NO clones were CD4+ and CD8+, MHC class II and I restricted, respectively, and activated via a pathway dependent on covalent binding and antigen processing. DDS and DDS-NO-specific clones secreted a mixture of Th1 and Th2 cytokines, but not granzyme-B. Splenocytes from mice immunized with DDS-NO were stimulated to proliferate in vitro with the nitroso metabolite, but not DDS. In contrast, immunization with DDS did not activate T-cells. These data show that DDS- and DDS-NO-specific T-cell responses are readily detectable.

The Effect of Inhibitory Signals on the Priming of Drug Hapten-Specific T Cells That Express Distinct Vβ Receptors

Drug hypersensitivity involves the activation of T cells in an HLA allele-restricted manner. Because the majority of individuals who carry HLA risk alleles do not develop hypersensitivity, other parameters must control development of the drug-specific T cell response. Thus, we have used a T cell-priming assay and nitroso sulfamethoxazole (SMX-NO) as a model Ag to investigate the activation of specific TCR Vβ subtypes, the impact of programmed death -1 (PD-1), CTL-associated protein 4 (CTLA4), and T cell Ig and mucin domain protein-3 (TIM-3) coinhibitory signaling on activation of naive and memory T cells, and the ability of regulatory T cells (Tregs) to prevent responses. An expansion of the TCR repertoire was observed for nine Vβ subtypes, whereas spectratyping revealed that SMX-NO-specific T cell responses are controlled by public TCRs present in all individuals alongside private TCR repertoires specific to each individual. We proceeded to evaluate the extent to which the activation of these TCR Vβ-restricted Ag-specific T cell responses is governed by regulatory signals. Blockade of PD-L1/CTLA4 signaling dampened activation of SMX-NO-specific naive and memory T cells, whereas blockade of TIM-3 produced no effect. Programmed death-1, CTLA4, and TIM-3 displayed discrete expression profiles during drug-induced T cell activation, and expression of each receptor was enhanced on dividing T cells. Because these receptors are also expressed on Tregs, Treg-mediated suppression of SMX-NO-induced T cell activation was investigated. Tregs significantly dampened the priming of T cells. In conclusion, our findings demonstrate that distinct TCR Vβ subtypes, dysregulation of coinhibitory signaling pathways, and dysfunctional Tregs may influence predisposition to hypersensitivity.

Immunogenicity of trimethoprim/sulfamethoxazole in a macaque model of HIV infection

BACKGROUND

Sulfonamide hypersensitivity has a high incidence in HIV infection and correlates with low CD4+ counts, but the mechanisms are not understood. The aims of this study were to determine whether trimethoprim/sulfamethoxazole (TMP/SMX) led to SMX adduct formation, immunogenicity, or signs of drug hypersensitivity in SIV-infected rhesus macaques, and whether differences in antioxidants, pro-inflammatory mediators, or SMX disposition were predictive of drug immunogenicity.

METHODS

Nine macaques chronically infected with SIVmac239 and 7 non-infected controls were studied. Baseline blood ascorbate, glutathione, IFN-γ, LPS, sCD14, and cytochrome b₅ reductase measurements were obtained, macaques were dosed with TMP/SMX (120mg/kg/day p.o. for 14days), and SMX metabolites, lymph node drug adducts, drug-responsive T cells, and anti-SMX antibodies were measured.

RESULTS

Four of 9 of SIV-positive (44%), and 3 of 7 SIV negative (43%) macaques had drug-responsive T cells or antibodies to SMX. Two macaques developed facial or truncal rash; these animals had the highest levels of lymph node drug adducts. Antioxidants, pro-inflammatory mediators, and SMX metabolites were not predictive of drug immunogenicity; however, the Mamu DRB1*0401/0406/0411 genotype was significantly over-represented in immune responders.

CONCLUSIONS

Unlike other animal models, macaques develop an immune response, and possible rash, in response to therapeutic dosages of TMP/SMX. Studying more animals with CD4+ counts <200cells/μl, along with moderately restricted ascorbate intake to match deficiencies seen in humans, may better model the risk of SMX hypersensitivity in HIV-infection. In addition, the role of Mamu-DRB1 genotype in modeling drug hypersensitivity in retroviral infection deserves further study.

Discovery of Orally Available Prodrugs of the Glutamate Carboxypeptidase II (GCPII) Inhibitor 2-Phosphonomethylpentanedioic Acid (2-PMPA)

2-Phosphonomethylpentanedioic acid (1, 2-PMPA) is a potent inhibitor of glutamate carboxypeptidase II which has demonstrated robust neuroprotective efficacy in many neurological disease models. However, 1 is highly polar containing a phosphonate and two carboxylates, severely limiting its oral bioavailability. We strategized to mask the polar groups via a prodrug approach, increasing the likelihood of passive oral absorption. Our initial strategy was to cover the phosphonate with hydrophobic moieties such as pivaloyloxymethyl (POM) and isopropyloxycarbonyloxymethyl (POC) while keeping the α- and γ-carboxylates unsubstituted. This attempt was unsuccessful due to the chemical instability of the bis-POC/POM derivatives. Addition of α,γ-diesters and α-monoesters enhanced chemical stability and provided excellent oral exposure in mice, but these mixed esters were too stable in vivo, resulting in minimal release of 1. By introducing POC groups on both the phosphonate and α-carboxylate, we synthesized Tris-POC-2-PMPA (21b), which afforded excellent release of 1 following oral administration in both mice and dog.

Selective CNS Uptake of the GCP-II Inhibitor 2-PMPA following Intranasal Administration

Glutamate carboxypeptidase II (GCP-II) is a brain metallopeptidase that hydrolyzes the abundant neuropeptide N-acetyl-aspartyl-glutamate (NAAG) to NAA and glutamate. Small molecule GCP-II inhibitors increase brain NAAG, which activates mGluR3, decreases glutamate, and provide therapeutic utility in a variety of preclinical models of neurodegenerative diseases wherein excess glutamate is presumed pathogenic. Unfortunately no GCP-II inhibitor has advanced clinically, largely due to their highly polar nature resulting in insufficient oral bioavailability and limited brain penetration. Herein we report a non-invasive route for delivery of GCP-II inhibitors to the brain via intranasal (i.n.) administration. Three structurally distinct classes of GCP-II inhibitors were evaluated including DCMC (urea-based), 2-MPPA (thiol-based) and 2-PMPA (phosphonate-based). While all showed some brain penetration following i.n. administration, 2-PMPA exhibited the highest levels and was chosen for further evaluation. Compared to intraperitoneal (i.p.) administration, equivalent doses of i.n. administered 2-PMPA resulted in similar plasma exposures (AUC_{0-t, i.n}./AUC_{0-t, i.p.} = 1.0) but dramatically enhanced brain exposures in the olfactory bulb (AUC_{0-t, i.n}./AUC_{0-t, i.p.} = 67), cortex (AUC_{0-t, i.n}./AUC_{0-t, i.p.} = 46) and cerebellum (AUC_{0-t, i.n}./AUC_{0-t, i.p.} = 6.3). Following i.n. administration, the brain tissue to plasma ratio based on AUC_0-t in the olfactory bulb, cortex, and cerebellum were 1.49, 0.71 and 0.10, respectively, compared to an i.p. brain tissue to plasma ratio of less than 0.02 in all areas. Furthermore, i.n. administration of 2-PMPA resulted in complete inhibition of brain GCP-II enzymatic activity ex-vivo confirming target engagement. Lastly, because the rodent nasal system is not similar to humans, we evaluated i.n. 2-PMPA also in a non-human primate. We report that i.n. 2-PMPA provides selective brain delivery with micromolar concentrations. These studies support intranasal delivery of 2-PMPA to deliver therapeutic concentrations in the brain and may facilitate its clinical development.

In vitro diagnosis of delayed-type drug hypersensitivity: mechanistic aspects and unmet needs

Several laboratories use the lymphocyte transformation test for the diagnosis of delayed-type drug hypersensitivity reactions. Recently, the availability of multiple readouts has improved our ability to diagnose reactions. It is important to note that most published studies characterizing the usefulness of diagnostic tests utilize blood samples from well-defined test and control patient groups. The purpose of this article is to briefly summarize the cellular and chemical basis of delayed-type drug hypersensitivity reactions and to review in vitro assays that are available for drug hypersensitivity diagnosis.

Characterization of Peroxidases Expressed in Human Antigen Presenting Cells and Analysis of the Covalent Binding of Nitroso Sulfamethoxazole to Myeloperoxidase

Drug hypersensitivity remains a major concern, as it causes high morbidity and mortality. Understanding the mechanistic basis of drug hypersensitivity is complicated by the multiple risk factors implicated. This study utilized sulfamethoxazole (SMX) as a model drug to (1) relate SMX metabolism in antigen presenting cells (APCs) to the activation of T-cells and (2) characterize covalent adducts of SMX and myeloperoxidase, which might represent antigenic determinants for T-cells. The SMX metabolite nitroso-SMX (SMX-NO) was found to bind irreversibly to APCs. Time- and concentration-dependent drug-protein adducts were also detected when APCs were cultured with SMX. Metabolic activation of SMX was significantly reduced by the oxygenase/peroxidase inhibitor methimazole. Similarly, SMX-NO-specific T-cells were activated by APCs pulsed with SMX, and the response was inhibited by pretreatment with methimazole or glutaraldehyde, which blocks antigen processing. Western blotting, real-time polymerase chain reaction (RT-PCR), and mass spectrometry analyses suggested the presence of low concentrations of myeloperoxidase in APCs. RT-PCR revealed mRNA expression for flavin-containing monooxygenases (FMO1-5), thyroid peroxidase, and lactoperoxidase, but the corresponding proteins were not detected. Mass spectrometric characterization of SMX-NO-modified myeloperoxidase revealed the formation of N-hydroxysulfinamide adducts on Cys309 and Cys398. These data show that SMX's metabolism in APCs generates antigenic determinants for T-cells. Peptides derived from SMX-NO-modified myeloperoxidase may represent one form of functional antigen.

Towards the development of mechanism-based biomarkers to diagnose drug hypersensitivity

T-cells are activated by different mechanisms in the presence of drugs, metabolites or haptens, and they release several molecules that can be used in the diagnosis of drug hypersensitivity.

Short- and long-term cure rates of short-duration trimethoprim-sulfamethoxazole treatment in female dogs with uncomplicated bacterial cystitis

Background

Long‐duration beta‐lactam antibiotics are used for empirical treatment in female dogs with uncomplicated bacterial cystitis. However, women with bacterial cystitis are treated with short‐duration potentiated sulfonamides because longer courses of beta‐lactams result in lower cure and higher recurrence rates.

Hypothesis/Objectives

Short‐duration potentiated sulfonamide treatment is more efficacious than long‐duration beta‐lactam treatment in achieving clinical and microbiological cures in female dogs with uncomplicated bacterial cystitis.

Animals

Thirty‐eight client‐owned female dogs.

Methods

Randomized, double‐blinded, placebo‐controlled clinical trial. Dogs were treated with TMP‐SMX (15 mg/kg PO q12h for 3 days followed by a placebo capsule PO q12h for 7 days; Group SDS; n = 20) or cephalexin (20 mg/kg PO q12h for 10 days; Group LDBL; n = 18). Dogs were monitored for clinical and microbiological cure during treatment and at short‐ and long‐term follow‐up.

Results

No statistically significant differences were found between treatment groups in clinical cure rates after 3 days of treatment (89% SDS, 94% LDBL; P = 1.00) and 4 days (85% SDS, 72% LDBL; P = .44) or >30 days (50% SDS, 65% LDBL; P = .50) after conclusion of treatment or in microbiological cure rates 4 days (59% SDS, 36% LDBL; P = .44) or >30 days (44% SDS, 20% LDBL; P = .40) after conclusion of treatment.

Conclusions and Clinical Importance

We did not identify a difference in cure rates between short‐duration sulfonamide and long‐duration beta‐lactam treatments in female dogs with uncomplicated cystitis. Long‐term cure rates in both treatment groups were low. In some female dogs, “uncomplicated” bacterial cystitis may be more complicated than previously recognized.

Hepatotoxicity of antibiotics: a review and update for the clinician

Collectively, the various classes of antibiotics are a leading cause of drug-induced liver injury (DILI). However, acute antibiotic-associated DILI can be difficult to diagnose, as the course of therapy is usually brief, and other confounding factors are often present. In addition to the broad clinicopathologic spectrum of hepatotoxicity associated with the antimicrobials, the underlying infectious disease being treated may itself be associated with hepatic dysfunction and jaundice. This review provides summarized information on several classes of antimicrobial agents, highlighting new agents causing DILI and updating information on older agents.

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.

Safety and efficacy of co-trimoxazole for treatment and prevention of Plasmodium falciparum malaria: a systematic review

INTRODUCTION

Cotrimoxazole (CTX) has been used for half a century. It is inexpensive hence the reason for its almost universal availability and wide clinical spectrum of use. In the last decade, CTX was used for prophylaxis of opportunistic infections in HIV infected people. It also had an impact on the malaria risk in this specific group.

OBJECTIVE

We performed a systematic review to explore the efficacy and safety of CTX used for P.falciparum malaria treatment and prophylaxis.

RESULT

CTX is safe and efficacious against malaria. Up to 75% of the safety concerns relate to skin reactions and this increases in HIV/AIDs patients. In different study areas, in HIV negative individuals, CTX used as malaria treatment cleared 56%-97% of the malaria infections, reduced fever and improved anaemia. CTX prophylaxis reduces the incidence of clinical malaria in HIV-1 infected individuals from 46%-97%. In HIV negative non pregnant participants, CTX prophylaxis had 39.5%-99.5% protective efficacy against clinical malaria. The lowest figures were observed in zones of high sulfadoxine-pyrimethamine resistance. There were no data reported on CTX prophylaxis in HIV negative pregnant women.

CONCLUSION

CTX is safe and still efficacious for the treatment of P.falciparum malaria in non-pregnant adults and children irrespective of HIV status and antifolate resistance profiles. There is need to explore its effect in pregnant women, irrespective of HIV status. CTX prophylaxis in HIV infected individuals protects against malaria and CTX may have a role for malaria prophylaxis in specific HIV negative target groups.

Evaluation of polymorphisms in the sulfonamide detoxification genes NAT2, CYB5A, and CYB5R3 in patients with sulfonamide hypersensitivity

OBJECTIVE

To determine whether polymorphisms in the sulfonamide detoxification genes, CYB5A (encoding cytochrome b(5)), CYB5R3 (encoding cytochrome b(5) reductase), or NAT2 (encoding N-acetyltransferase 2) were over-represented in patients with delayed sulfonamide drug hypersensitivity, compared with control patients who tolerated a therapeutic course of trimethoprim-sulfamethoxazole without adverse event.

METHODS

DNA from 99 nonimmunocompromised patients with sulfonamide hypersensitivity who were identified from the Personalized Medicine Research Project at the Marshfield Clinic, and from 99 age-matched, race-matched, and sex-matched drug-tolerant controls, were genotyped for four CYB5A and five CYB5R3 polymorphisms, and for all coding NAT2 SNPs.

RESULTS

CYB5A and CYB5R3 SNPs were found at low allele frequencies (<3-4%), which did not differ between hypersensitive and tolerant patients. NAT2 allele and haplotype frequencies, as well as inferred NAT2 phenotypes, also did not differ between groups (60 vs. 59% slow acetylators). Finally, no difference in NAT2 status was found in a subset of patients with more severe hypersensitivity signs (drug reaction with eosinophilia and systemic symptoms) compared with tolerant patients.

CONCLUSION

We found no evidence of a substantial involvement of these nine CYB5A or CYB5R3 polymorphisms in sulfonamide hypersensitivity risk, although minor effects cannot be completely ruled out. Despite careful medical record review and full resequencing of the NAT2 coding region, we found no association of NAT2 coding alleles with sulfonamide hypersensitivity (predominantly cutaneous eruptions) in this adult Caucasian population.

Evaluation of polymorphisms in the sulfonamide detoxification genes CYB5A and CYB5R3 in dogs with sulfonamide hypersensitivity

BACKGROUND

Delayed hypersensitivity (HS) reactions to potentiated sulfonamide antimicrobials occur in both dogs and humans, and involve an intermediate hydroxylamine metabolite that is detoxified by cytochrome b(5) and NADH cytochrome b(5) reductase.

HYPOTHESIS/OBJECTIVES

We hypothesized that polymorphisms in the genes (CYB5A and CYB5R3) encoding these 2 enzymes would be associated with risk of sulfonamide HS in dogs.

ANIMALS

A total of 18 dogs with delayed HS to potentiated sulfonamide antimicrobials and 16 dogs that tolerated (TOL) a therapeutic course of these drugs without adverse effect.

METHODS

CYB5A and CYB5R3 were sequenced from canine liver, and the promoter, exons, and 3' untranslated regions of both genes were resequenced from genomic DNA obtained from all dogs.

RESULTS

Multiple polymorphisms were found in both genes. When controlled for multiple comparisons, the 729GG variant in CYB5R3 was significantly overrepresented in dogs with sulfonamide HS (78% of dogs), compared to TOL dogs (31%; P = .003).

CONCLUSIONS AND CLINICAL IMPORTANCE

The CYB5R3 729GG variant may contribute to the risk of sulfonamide HS in dogs. Functional characterization of this polymorphism, as well as genotyping in a larger number of HS and TOL dogs, is warranted.

The development of in vitro culture methods to characterize primary T-cell responses to drugs

Adverse drug reactions represent a major stumbling block to drug development and those with an immune etiology are the most difficult to predict. We have developed an in vitro T-cell priming culture method using peripheral blood from healthy volunteers to assess the allergenic potential of drugs. The drug metabolite nitroso sulfamethoxazole (SMX-NO) was used as a model drug allergen to establish optimum assay conditions. Naive T cells were cocultured with monocyte-derived dendritic cells at a ratio of 25:1 in the presence of the drug for a period of 8 days, to expand the number of drug-responsive T cells. The T cells were then incubated with fresh dendritic cells, and drug and their antigen responsiveness analyzed using readouts for proliferation, cytokine secretion, and cell phenotype. All five volunteers showed dose-dependent proliferation as measured by 5-(and 6)-carboxyfluorescein diacetate succinimidyl ester content and by (3)H-thymidine uptake. CD4 T cells that had divided in the presence of SMX-NO had changed from a naive phenotype (CD45RA+) to a memory phenotype (CD45RO+). These memory T cells expressed the chemokine receptors CCR2, CCR4, and CXCR3 suggesting a mixture of T(H)1 and T(H)2 cells in the responding population, with a propensity for homing to the skin. Drug stimulation was also associated with the secretion of a mixture of T(H)1 cytokines (interferon γ) and T(H)2 cytokines (interleukin [IL]-5 and IL-13) as detected by ELISpot. We are currently developing this approach to investigate the allergenic potential of other drugs, including those where an association between specific human leucocyte antigen alleles and susceptibility to an immunological reaction has been established.

Evaluation of sulfonamide detoxification pathways in haematologic malignancy patients prior to intermittent trimethoprim-sulfamethoxazole prophylaxis

AIMS

Patients with haematologic malignancies have a reportedly high incidence of sulfamethoxazole (SMX) hypersensitivity. The objective of this study was to determine whether deficiencies in sulfonamide detoxification pathways, to include glutathione (GSH) and ascorbate (AA), and cytochrome b(5) (b5) and cytochrome b(5) reductase (b5R), were prevalent in these patients. A secondary pilot objective was to determine whether the incidence of drug hypersensitivity following intermittent trimethoprim-SMX (TMP-SMX) prophylaxis approached that reported for high dose daily regimens.

METHODS

Forty adult patients with haematologic malignancies (HM) and 35 healthy adults were studied; an additional 13 HM patients taking ascorbate supplements (HM-AA) were also evaluated. Twenty-two of 40 HM patients were prescribed and were compliant with TMP-SMX 960 mg three to four times weekly.

RESULTS

There were no significant differences between HM and healthy groups in plasma AA (median 37.2 µm vs. 33.9 µm) or red blood cell GSH (1.9 mmvs. 1.8 mm). However, plasma AA was correlated significantly with leucocyte b5/b5R reduction (r= 0.39, P= 0.002). Deficient b5/b5R activities were not found in HM patients. In fact, patients with chronic lymphocytic leukaemia or myeloma had significantly higher median activities (80.7 µmol mg(-1) min(-1)) than controls (18.9 µmol mg(-1) min(-1), P= 0.008). After 3-4 weeks of treatment, no patients developed SMX-specific T cells and only one patient developed rash.

CONCLUSIONS

Deficiencies of blood antioxidants and b5/b5R reduction were not found in this population with haematologic malignancies, and the development of skin rash and drug-specific T cells appeared to be uncommon with intermittent TMP-SMX prophylaxis.

Mass spectrometric characterization of circulating and functional antigens derived from piperacillin in patients with cystic fibrosis

A mechanistic understanding of the relationship between the chemistry of drug Ag formation and immune function is lacking. Thus, mass spectrometric methods were employed to detect and fully characterize circulating Ags derived from piperacillin in patients undergoing therapy and the nature of the drug-derived epitopes on protein that can function as an Ag to stimulate T cells. Albumin modification with piperacillin in vitro resulted in the formation of two distinct haptens, one formed directly from piperacillin and a second in which the dioxopiperazine ring had undergone hydrolysis. Modification was time and concentration dependent, with selective modification of Lys(541) observed at low concentrations, whereas at higher concentrations, up to 13 out of 59 lysine residues were modified, four of which (Lys(190), Lys(195), Lys(432), and Lys(541)) were detected in patients' plasma. Piperacillin-specific T lymphocyte responses (proliferation, cytokines, and granzyme B release) were detected ex vivo with cells from hypersensitive patients, and analysis of incubation medium showed that modification of the same lysine residues in albumin occurred in situ. The antigenicity of piperacillin-modified albumin was confirmed by stimulation of T cells with characterized synthetic conjugates. Analysis of minimally modified T cell-stimulatory albumin conjugates revealed peptide sequences incorporating Lys(190), Lys(432), and Lys(541) as principal functional epitopes for T cells. This study has characterized the multiple haptenic structures on albumin in patients and showed that they constitute functional antigenic determinants for T cells.

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.

Drug antigenicity, immunogenicity, and costimulatory signaling: evidence for formation of a functional antigen through immune cell metabolism

Recognition of drugs by immune cells is usually explained by the hapten model, which states that endogenous metabolites bind irreversibly to protein to stimulate immune cells. Synthetic metabolites interact directly with protein-generating antigenic determinants for T cells; however, experimental evidence relating intracellular metabolism in immune cells and the generation of physiologically relevant Ags to functional immune responses is lacking. The aim of this study was to develop an integrated approach using animal and human experimental systems to characterize sulfamethoxazole (SMX) metabolism-derived antigenic protein adduct formation in immune cells and define the relationship among adduct formation, cell death, costimulatory signaling, and stimulation of a T cell response. Formation of SMX-derived adducts in APCs was dose and time dependent, detectable at nontoxic concentrations, and dependent on drug-metabolizing enzyme activity. Adduct formation above a threshold induced necrotic cell death, dendritic cell costimulatory molecule expression, and cytokine secretion. APCs cultured with SMX for 16 h, the time needed for drug metabolism, stimulated T cells from sensitized mice and lymphocytes and T cell clones from allergic patients. Enzyme inhibition decreased SMX-derived protein adduct formation and the T cell response. Dendritic cells cultured with SMX and adoptively transferred to recipient mice initiated an immune response; however, T cells were stimulated with adducts derived from SMX metabolism in APCs, not the parent drug. This study shows that APCs metabolize SMX; subsequent protein binding generates a functional T cell Ag. Adduct formation above a threshold stimulates cell death, which provides a maturation signal for dendritic cells.

Drug metabolite-specific lymphocyte responses in sulfamethoxazole allergic patients with cystic fibrosis

Sulfamethoxazole (SMX) is an important antibiotic in the management of patients with cystic fibrosis, but allergic reactions may develop thus restricting therapy. The aim of this study was to utilize drug (metabolite) antigens to diagnose SMX-mediated allergic reactions in patients with cystic fibrosis. Lymphocytes from 2/12 allergic patients were stimulated to proliferate strongly with the SMX metabolite nitroso SMX (SMX-NO). In contrast, responses to SMX were weak. The introduction of an antigen-driven T-cell enrichment step prior to the analysis of proliferation increased the sensitivity of the assay. SMX-NO responses were detected with lymphocytes from all patients with cutaneous signs.

Knowledge and attitudes of American pharmacists concerning sulfonamide allergy cross-reactivity

OBJECTIVE

Pharmacists are commonly confronted with patients with a history of sulfonamide allergy. Basic immunologic and clinical data suggest a low likelihood of a patient with a history of sulfonamide hypersensitivity developing an allergic reaction to a non-antimicrobial sulfonamide drug. We conducted a survey to describe the knowledge and attitudes of licensed pharmacists concerning sulfonamide allergy cross-reactivity.

METHODS

A survey instrument was developed and sent to all licensed pharmacists in the state of Iowa. The survey recorded demographic information and included six patient scenarios designed to elicit responses concerning sulfonamide allergy cross-reactivity with a number of non-antimicrobial sulfonamides.

RESULTS

A total of 421 surveys were returned for a 39% response rate. There was a wide discrepancy in approaches to patients with a history of sulfonamide allergy prescribed a sulfonamide containing non-antibiotic. Differences depended on previous history of tolerating the medication in question, the degree of cautionary statements in product literature, and the familiarity the pharmacist had with the product.

CONCLUSION

Our survey suggests a significant diversity in knowledge and attitudes of pharmacists concerning cross-reactivity of sulfonamide antimicrobials and other drugs with a sulfonamide moiety. Depth of training in this area may be an associative factor.

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.

Combined ascorbate and glutathione deficiency leads to decreased cytochrome b5 expression and impaired reduction of sulfamethoxazole hydroxylamine

Sulfonamide antimicrobials such as sulfamethoxazole (SMX) have been associated with drug hypersensitivity reactions, particularly in patients with AIDS. A reactive oxidative metabolite, sulfamethoxazole-nitroso (SMX-NO), forms drug-tissue adducts that elicit a T-cell response. Antioxidants such as ascorbic acid (AA) and glutathione (GSH) reduce SMX-NO to the less reactive hydroxylamine metabolite (SMX-HA), which is further reduced to the non-immunogenic parent compound by cytochrome b (5) (b5) and its reductase (b5R). We hypothesized that deficiencies in AA and GSH would enhance drug-tissue adduct formation and immunogenicity toward SMX-NO and that these antioxidant deficiencies might also impair the activity of the b5/b5R pathway. We tested these hypotheses in guinea pigs fed either a normal or AA-restricted diet, followed by buthionine sulfoximine treatment (250 mg/kg SC daily, or vehicle); and SMX-NO (1 mg/kg IP 4 days per week, or vehicle), for 2 weeks. Guinea pigs did not show any biochemical or histopathologic evidence of SMX-NO-related toxicity. Combined AA and GSH deficiency in this model did not significantly increase tissue-drug adduct formation, or splenocyte proliferation in response to SMX-NO. However, combined antioxidant deficiency was associated with decreased mRNA and protein expression of cytochrome b (5), as well as significant decreases in SMX-HA reduction in SMX-NO-treated pigs. These results suggest that SMX-HA detoxification may be down-regulated in combined AA and GSH deficiency. This mechanism could contribute to the higher risk of SMX hypersensitivity in patients with AIDS with antioxidant depletion.

"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.

Drug-induced hypersensitivity syndrome: clinical and biologic disease patterns in 24 patients

Drug-induced hypersensitivity syndrome (DIHS), also called drug rash with eosinophilia and systemic symptoms (DRESS), is a severe reaction usually characterized by fever, rash, and multiorgan failure, occurring 1-8 weeks after drug introduction. It is an immune-mediated reaction involving macrophage and T-lymphocyte activation and cytokine release, although no consensus has been reached as to its etiology. The skin, hematopoietic system, and liver are frequently involved. DIHS can mimic severe sepsis, viral infection, adult-onset Still disease (AOSD), or lymphoproliferation.We describe 24 consecutive patients with DIHS who were hospitalized between September 2004 and March 2008. Criteria for inclusion in this observational study were suspected drug reaction, eosinophilia >or=500/microL and/or atypical lymphocytes, involvement of at least 2 organs (skin being 1 of them), with suggestive chronology and exclusion of other diagnoses. Our cohort of 12 women and 12 men had a median age of 49 years (range, 22-82 yr), and 11 had skin phototype V or VI. Patients with mild or no rash were immunocompromised (7/24)- defined as treatment with prednisone (>or=10 mg/d) and another immunosuppressant drug, or human immunodeficiency virus infection. All patients were febrile (>38 degrees C), 14 had localized or generalized edema, 7 had pharyngitis, 8 had lymphadenopathy, 22 had hepatitis, 4 had nephritis, 2 had noninfectious and nonlithiasic angiocholitis or cholecystitis. Ten patients were hypotensive, 5 of whom had associated laboratory signs and/or imaging findings suggestive of acute myocardial dysfunction. Half of the patients had hemogram abnormalities, including eosinophilia. Nine DIHS patients fulfilled the Fautrel criteria for AOSD diagnosis, including glycosylated ferritin <20% in 4/11, with or without laboratory characteristics of hemophagocytosis. Twenty DIHS episodes occurred during the less sunny months of October to March.We determined 25-hydroxyvitamin D3 (25[OH]D3) levels in 18 patients and found that 9 patients had vitamin D deficiency (<25 nmol/L or <10 microg/L) and 5 had vitamin D insufficiency (25-50 nmol/L). Moreover, 25(OH)D3 levels were inversely correlated with ferritin values. After culprit-drug withdrawal, outcomes were favorable for all patients, including those with cardiac abnormalities under slow tapering of glucocorticoids.We recommend looking for the frequent but underdiagnosed hypersensitivity myocarditis with noninvasive diagnostic tools, such as N-terminal probrain natriuretic peptide, and promptly withdrawing the culprit drug and starting glucocorticoids. Vitamin D deficiency might be a DIHS risk or severity factor, especially for patients with high skin phototype and during the winter. Because DIHS clinical and laboratory patterns share similarities with AOSD and hemophagocytosis, DIHS should be included in their differential diagnoses.

Investigation of the immunogenicity of p-phenylenediamine and Bandrowski's base in the mouse

p-Phenylenediamine (PPD) exposure is associated with T-cell mediated contact dermatitis. T-cells from allergic patients proliferate following exposure to PPD and the oxido-conjugation product Bandrowski's base (BB). Both compounds are classified as sensitizers in the local lymph node assay; however, because of their instability the nature of the antigenic determinant remains ill-defined. The aim of this study was to explore the immunogenic potential of PPD and BB in mice. Spleen cell proliferation and cytokine secretion was measured ex vivo following antigen recall with soluble PPD or BB and either irradiated or glutaraldehyde fixed, antigen pulsed dendritic cells from syngeneic mice. Glutathione was added to certain incubations. LC-MS analysis and solvent extraction were used to monitor the fate of [(14)C]BB in culture and the extent of BB binding, respectively. Spleen cells from BB exposed, but not PPD- or vehicle-exposed, mice proliferated when stimulated with BB. Proliferating cells secreted high levels of IFN-gamma, GM-CSF and IL-2. Stimulation with PPD instigated low levels of proliferation. Irradiated, but not fixed, dendritic cells pulsed with BB stimulated proliferation signifying a classical hapten mechanism involving irreversible BB binding to protein and processing. BB bound preferentially to serum protein when incubated together with cells and serum. Degradation of BB in the presence of glutathione was associated with a stronger stimulation of specific T-cells at higher BB concentrations. These data demonstrate that BB is a potent immunogen in the mouse.

Activation of T-cells from allergic patients and volunteers by p-phenylenediamine and Bandrowski's base

Allergic contact dermatitis is commonly associated with exposure to p-phenylenediamine. The aim of this study was to determine whether p-phenylenediamine (PPD) and/or Bandrowski's base (BB) stimulate T cells from allergic patients and volunteers, and to explore the relationship between T-cell immunogenicity and allergy. Lymphocytes from allergic patients proliferated with PPD and BB (n=8). Lymphocytes from 14/16 non-allergic individuals also proliferated following stimulation, but only with BB; cord blood lymphocytes failed to respond (n=6). Glutathione, which prevented BB formation, but not binding of PPD to cells and serum, did not prevent p-phenylenediamine-specific stimulation of patient lymphocytes. T-cell clones generated from allergic patients were stimulated separately with PPD and BB, while clones from volunteers proliferated with BB alone. Patient and volunteer clones secreted IL-4, IL-5, IL-13, TNF-alpha, MIP-1alpha, MIP-1beta, and RANTES. These data show that activation of T lymphocytes from allergic individuals alone with PPD represents an important discrimination between allergic and non-allergic groups. BB-specific T cells are found in both allergic patients and volunteers, but not in cord blood. Their presence seems to reflect an acquired immune response, which is not translated into an allergic reaction.

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.

Sulfonamide allergy and cross-reactivity

Concerns about cross-allergenicity between sulfonamide antibiotics and nonantibiotic sulfonamide-containing drugs continue to complicate pharmacotherapy. Several elegant investigations have demonstrated unequivocal lack of interaction between the sulfonamide group and either cellular or humoral immunity. The immunologic determinant of type I immunologic responses to sulfonamide antibiotics is the N1 heterocyclic ring, and nonantibiotic sulfonamides lack this structural feature. Many non-type I hypersensitivity responses to sulfonamide antibiotics are attributable to reactive metabolites that cause either direct cytotoxicity or humoral or cellular responses. Metabolite formation is stereospecific to the N4 amino nitrogen of the sulfonamide antibiotics, a structure not found on any nonantibiotic sulfonamide drugs. Cellular immune responses to sulfonamide antibiotics are responsible for many non-immunoglobulin E-mediated dermatologic reactions; however, the stereospecificity of T-cell response renders cross-reactivity between sulfonamide antibiotics and nonantibiotics highly unlikely. Apparent cross-reactivity responses to sulfonamide-containing drugs likely represent multiple concurrent, rather than linked, drug hypersensitivities.

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.

Association of drug-serum protein adducts and anti-drug antibodies in dogs with sulphonamide hypersensitivity: A naturally occurring model of idiosyncratic drug toxicity

BACKGROUND

Sulphonamide antimicrobials, such as sulphamethoxazole (SMX), provide effective infection prophylaxis in immunocompromised patients, but can lead to drug hypersensitivity (HS) reactions. These reactions also occur in dogs, with a similar time course and clinical presentation as seen in humans.

OBJECTIVES

Drug-serum adducts and anti-drug antibodies have been identified in sulphonamide HS humans. The aim of this study was to determine whether similar markers were present in dogs with sulphonamide HS.

METHODS

Thirty-four privately owned sulphonamide HS dogs, 10 sulphonamide-'tolerant' dogs, 18 sulphonamide-naïve dogs, and four dogs experimentally dosed with SMX and the oxidative metabolite SMX-nitroso, were tested for drug-serum adducts by immunoblotting, and anti-drug antibodies by ELISA.

RESULTS

Sulphonamide-serum adducts were found in 10/20 HS dogs tested (50%), but in no tolerant dogs. Anti-sulphonamide IgG antibodies were detected in 17/34 HS dogs (50%), but in only one tolerant dog; antibody absorbance values were significantly higher in HS dogs. There was a significant association between the presence of sulphonamide-serum adducts and anti-sulphonamide antibodies (P = 0.009). Anti-drug antibodies were also found in dogs experimentally dosed with SMX-nitroso followed by SMX, but not in a dog dosed with drug vehicle, followed by SMX.

CONCLUSION

Similar humoral markers are present in dogs and humans with sulphonamide HS, supporting the use of dogs as a naturally occurring model for this syndrome in humans. These data suggest the potential use of drug-serum adducts and anti-drug antibodies as markers for sulphonamide HS. Preliminary data indicate that anti-sulphonamide antibodies may be triggered by the SMX-nitroso metabolite, not by the parent drug, in dogs.

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.

Drug-Specific T Cells in An HIV-Positive Patient with Nevirapine-Induced Hepatitis

Background

Nevirapine is associated with idiosyncratic reactions such as skin rash, hepatitis and hypersensitivity syndrome, which have the hallmarks of being immune mediated. However, there is little laboratory evidence to support an immune pathogenesis.

Methods

A HIV-positive individual who developed hepatitis within 6 weeks of starting nevirapine, in the absence of any cutaneous manifestations, is described. Other causes of hepatitis were excluded, and the patients liver function normalized on withdrawal of nevirapine. Lymphocytes from the patient, and six individuals with HIV who were on nevirapine without adverse effects, were exposed to nevirapine and its metabolites, and lymphocyte proliferation assessed by 3H-thymidine incorporation on day 5.

Results

The T cells taken from the nevirapine-hypersensitive patient proliferated in the presence of nevirapine with a stimulation index of greater than 2. There was no proliferation with nevirapine metabolites. T cells taken from HIV-positive control individuals showed no proliferation with either nevirapine or its metabolites.

Conclusion

The results from our patient suggest that T cells may be involved in the pathogenesis of nevirapine-induced hepatitis. Larger numbers of patients need to be studied to fully evaluate the role of T cells in nevirapine-induced hepatitis and nevirapine hypersensitivity syndrome.

Immune mechanisms in drug allergy

Clinicians had suspected for years that drug eruptions were probably mediated by immune mechanisms because their timing suggested sensitization and specific immunologic memory rather than direct toxicity. An immune response to medications was also demonstrated by positive skin tests and by several types of in vitro tests that evidenced immediate or delayed hypersensitivity. In the last decade several teams of researchers obtained in vitro drug-specific human T-cell clones, in a variety of clinical types of drug eruptions. These clones were produced from blood or skin mononuclear cells of patients with a history of drug reaction by stimulation in vitro with drug. They were either of CD4 or CD8 phenotypes. Drug specific clones were stimulated by the parent drug much more often than by reactive metabolites. That challenged the classical "hapten hypothesis" that the immune response was initiated by reactive metabolites combined to self proteins. The medication usually stimulated specific T-cells after non-covalent binding to major histocompatibility (MHC) molecules on antigen presenting cells. In toxic epidermal necrolysis, T-lymphocytes present at the site of lesions, exhibited a drug specific cytotoxicity against autologous target cells, or allogeneic cells that shared the same HLA than autologous cells. This MHC class I restriction and mediation of death by perforin/granzyme release, is the classical behavior of cytotoxic T lymphocytes, like those operating in the reject of a transplanted organ. MHC restriction could explain the key role of HLA genes as predisposing factors to severe drug reactions. A strong association between HLA and hypersensitivity to abacavir, SJS or TEN to carbamazepine or allopurinol has been recently demonstrated. Resemblance to graft rejection points to the possible therapeution value of immuno suppressive agents. Most drug eruptions appear to result from T-cell mediated delayed hypersensitivity. The secondary activation of different cascades of cytokines, may contribute to the heterogeneity of clinical presentations.

The role of metabolic activation in drug-induced hepatotoxicity

The importance of reactive metabolites in the pathogenesis of drug-induced toxicity has been a focus of research interest since pioneering investigations in the 1950s revealed the link between toxic metabolites and chemical carcinogenesis. There is now a great deal of evidence that shows that reactive metabolites are formed from drugs known to cause hepatotoxicity, but how these toxic species initiate and propagate tissue damage is still poorly understood. This review summarizes the evidence for reactive metabolite formation from hepatotoxic drugs, such as acetaminophen, tamoxifen, diclofenac, and troglitazone, and the current hypotheses of how this leads to liver injury. Several hepatic proteins can be modified by reactive metabolites, but this in general equates poorly with the extent of toxicity. Much more important may be the identification of the critical proteins modified by these toxic species and how this alters their function. It is also important to note that the toxicity of reactive metabolites may be mediated by noncovalent binding mechanisms, which may also have profound effects on normal liver physiology. Technological developments in the wake of the genomic revolution now provide unprecedented power to characterize and quantify covalent modification of individual target proteins and their functional consequences; such information should dramatically improve our understanding of drug-induced hepatotoxic reactions.