Direct and metabolism-dependent toxicity of sulphasalazine and its principal metabolites towards human erythrocytes and leucocytes

Successful Treatment of Linear IgA Disease and Ulcerative Colitis With Sulfasalazine

Linear IgA disease (LAD) is an uncommon autoimmune blistering disease that has been associated with medications, malignancy, and other autoimmune diseases, such as ulcerative colitis (UC). In this case report, a patient with a history of UC developed characteristic LAD lesions. While dapsone is considered first-line therapy for LAD, the treatment team opted for an underutilized, plausibly less toxic, and more simplified treatment regimen with sulfasalazine, successfully utilizing the two distinct actions of sulfasalazine's components - sulfapyridine and 5-aminosalicylate (5-ASA) - to concurrently treat both the LAD and UC symptoms. The authors discuss the pathophysiology of LAD and UC and expound on the mechanistic theory of their association. Additionally, the pharmacodynamics of sulfasalazine and considerations of its side effect profile are examined.

Checkpoint inhibition reduces the threshold for drug-specific T-Cell priming and increases the incidence of sulfasalazine hypersensitivity

An emerging clinical issue associated with immune-oncology agents is the collateral effects on the tolerability of concomitant medications. One report of this phenomenon was the increased incidence of hypersensitivity reactions observed in patients receiving concurrent immune checkpoint inhibitors and sulfasalazine. Thus, the aim of this study was to characterize the T-cells involved in the pathogenesis of such reactions, and recapitulate the effects of inhibitory checkpoint blockade on de-novo priming responses to compounds within in-vitro platforms. A regulatory competent human dendritic cell/T-cell co-culture assay was used to model the effects of immune checkpoint inhibitors on de-novo nitroso sulfamethoxazole- and sulfapyridine (the sulfonamide component of sulfasalazine) hydroxylamine-specific priming responses. The role of T-cells in the pathogenesis of the observed reactions was explored in three patients through phenotypic characterization of sulfapyridine/sulfapyridine hydroxylamine-responsive T-cell clones, and assessment of cross-reactivity and pathways of T-cell activation. Augmentation of the frequency of responding drug-specific T-cells and intensity of the T-cell response was observed with PD-1/PD-L1 blockade. Monoclonal populations of sulfapyridine- and sulfapyridine hydroxylamine-responsive T-cells were isolated from all three patients. A core secretory effector molecule profile (IFN-γ, IL-13, granzyme B and perforin) was identified for sulfapyridine and sulfapyridine hydroxylamine responsive T-cell clones, which proceeded through Pi and hapten mechanisms, respectively. Data presented herein provides evidence that drug-responsive T-cells are effectors of hypersensitivity reactions observed in oncology patients administered immune checkpoint inhibitors and sulfasalazine. Perturbation of drug-specific T-cell priming is a plausible explanation for clinical observations of how an increased incidence of these adverse events is occurring.

Sulfasalazine-Induced Agranulocytosis Is Associated With the Human Leukocyte Antigen Locus

Agranulocytosis is a serious, although rare, adverse reaction to sulfasalazine, which is used to treat inflammatory joint and bowel disease. We performed a genome-wide association study comprising 9,380,034 polymorphisms and 180 HLA alleles in 36 cases of sulfasalazine-induced agranulocytosis and 5,170 population controls. Sulfasalazine-induced agranulocytosis was significantly associated with the HLA region on chromosome 6. The top hit (rs9266634) was located close to HLA-B, odds ratio (OR) 5.36 (95% confidence interval (CI) (2.97, 9.69) P = 2.55 × 10^-8 ). We HLA-sequenced a second cohort consisting of 40 cases and 142 treated controls, and confirmed significant associations with HLA-B*08:01, OR = 2.25 (95% CI (1.02, 4.97) P = 0.0439), in particular the HLA-B*08:01 haplotype HLA-DQB1*02:01-DRB1*03:01-B*08:01-C*07:01, OR = 3.79 (95% CI (1.63, 8.80) P = 0.0019), and with HLA-A*31:01, OR = 4.81 (95% CI (1.52, 15.26) P = 0.0077). The number needed to test for HLA-B*08:01 and HLA-A*31:01 to avoid one case was estimated to be 1,500. We suggest that intensified monitoring or alternative treatment should be considered for known carriers of HLA-B*08:01 or HLA-A*31:01.

Mechanism of action of 5-arninosalicylic acid

5-Aminosalicylic Acid (5-ASA) has been used for over 50 years in the treatment of inflammatory bowel disease in the pro-drug form sulphasalazine (SASP). SASP is also used to treat rheumatoid arthritis. However whether the therapeutic properties of SASP are due to the intact molecule, the 5-ASA or sulphapyridine components is unknown. Several mechanisms of action have been proposed for 5-ASA and SASP including interference in the metabolism of arachidonic acid to prostaglandins and leukotrienes, scavenging,of reactive oxygen species, effects on leucocyte function and production of cytokines. However, it is unlikely that the anti-inflammatory properties of SASP and 5-ASA are due to several different properties but more likely that a single property of 5-ASA explains the theraapeutic effects of 5-ASA and SASP. Reactive oxygen species (ROS) are involved in the metabolism of prostaglandins and leukotrienes and can act as second messengers, and so the scavenging of ROS may be the single mechanism of action of 5-ASA that gives rise to its antiinflammatory effects in both inflammatory bowel disease and rheumatoid arthritis.

Pharmacogenetics of idiosyncratic adverse drug reactions

Idiosyncratic adverse drug reactions are unpredictable and thought to have an underlying genetic etiology. With the completion of the human genome and HapMap projects, together with the rapid advances in genotyping technologies, we have unprecedented capabilities in identifying genetic predisposing factors for these relatively rare, but serious, reactions. The main roadblock to this is the lack of sufficient numbers of well-characterized samples from patients with such reactions. This is now beginning to be solved through the formation of international consortia, including developing novel ways of identifying and recruiting patients affected by these reactions, both prospectively and retrospectively. This has been led by the research on abacavir hypersensitivity - its association with HLA-B*5701 forms the gold standard of how we need to identify associations and implement them in clinical practice. Strong genetic predisposing factors have also been identified for hypersensitivity reactions such as are associated with carbamazepine, allopurinol, flucloxacillin, and statin-induced myopathy. However, for most other idiosyncratic adverse drug reactions, the genetic effect sizes have been low to moderate, although this may partly be due to the fact that only small numbers have been investigated and limited genotyping strategies have been utilized. It may also indicate that genetic predisposition will be dependent on multiple genes, with complex interactions with environmental factors. Irrespective of the strength of the genetic associations identified with individual idiosyncratic adverse drug reactions, it is important to undertake functional investigations to provide insights into the mechanism(s) of how the drug interacts with the gene variant to lead to a phenotype, which can take a multitude of clinical forms with variable severity. Such investigations will be essential in preventing the burden caused by idiosyncratic reactions, both in healthcare and in industry.

Glutathione-S-Transferase Pi Expression in Toxic Epidermal Necrolysis: A Marker of Putative Oxidative Stress in Keratinocytes

BACKGROUND

Toxic epidermal necrolysis (TEN) is a dramatic drug-induced emergency related to extensive destruction of the epidermis. There is evidence that its pathomechanism involves impaired detoxication of xenobiotics. Glutathione-S-transferase pi (GST-pi) is a phase II detoxifying enzyme involved in drug metabolization by human keratinocytes.

METHOD

Immunohistochemistry was performed in order to assess the expression of GST-pi in keratinocytes of TEN, other cutaneous adverse drug reactions and bullous pemphigoid.

RESULTS

GST-pi was disclosed in the involved epidermis of 16/16 TEN patients. It was present in the cytoplasm of suprabasal keratinocytes. GST-pi was also expressed in the clinically uninvolved skin in a majority (8/12) of TEN patients. By contrast, it was rarely and poorly expressed in the other tested dermatoses.

CONCLUSION

The pathomechanism of TEN is not related to an impaired quantitative expression of GST-pi. GST-pi expression is an early event in TEN. As oxidative stress is a major inducer of GST-pi, this mechanism might be involved in TEN. Its GST-pi expression mainly restricted to the suprabasal keratinocytes suggests that the pathomechanisms leading to keratinocyte death in TEN are distinct at different levels of the epidermis.

Increased adverse drug reactions to antimicrobials and anticonvulsants in patients with HIV infection

OBJECTIVE

To review the incidence, signs, symptoms, and mechanisms of adverse drug reactions (ADRs) to sulfonamides, anticonvulsants, and antimycobacterial medications among people with HIV.

DATA SOURCES

Searches of MEDLINE/PubMed (1980-November 2005) and National Library of Medicine Meeting Abstracts (1989-November 2005), as well as hand searches of journals and abstracts, were conducted to identify primary literature. Reference lists were reviewed to identify additional relevant reports.

STUDY SELECTION AND DATA EXTRACTION

Relevant articles and abstracts, particularly of in vitro experiments and clinical studies, were compiled and reviewed.

DATA SYNTHESIS

ADRs, especially in HIV-infected patients, are a cause for concern. Sulfonamides, anticonvulsants, and antimycobacterial drugs are commonly used to prevent and treat complications of HIV, including seizures and opportunistic infections. Patients with HIV have a much greater rate of ADRs to these drug classes, including severe and life-threatening hypersensitivity reactions. Several mechanisms of these ADRs have been postulated. Sulfamethoxazole and anticonvulsant hypersensitivity may involve the increased formation and decreased detoxification of reactive metabolites. The mechanisms for the marked increase in hypersensitivity ADRs to antimycobacterial drugs may be related to an altered immune profile in patients infected with both tuberculosis and HIV.

CONCLUSIONS

ADRs to antimicrobial and anticonvulsant therapy cause markedly increased morbidity and mortality in HIV-positive patients. Further research involving the interaction between HIV and the increased ADRs to these drugs is required.

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.

Genetic factors in the predisposition to drug-induced hypersensitivity reactions

Drug hypersensitivity reactions can occur with most drugs, although the frequency, severity, and clinical manifestations vary. Case reports have suggested that there may be familial clustering of drug hypersensitivity suggesting a genetic predisposition. As with most other forms of drug response, predisposition to drug hypersensitivity reactions is likely to be multifactorial and multigenic. Given the immune pathogenesis of these reactions, it is perhaps not surprising that the most significant genetic associations have been identified in the major histocompatibility complex for drugs such as abacavir, carbamazepine, and allopurinol. For abacavir, it has been suggested that preprescription genotyping for HLA-B*5701 in whites may reduce the incidence of hypersensitivity. It is likely that as our knowledge of variation in the human genome improves, coupled with improvements in technology, many more significant genetic predisposing factors for drug hypersensitivity are likely to be identified in the next decade. However, as we search for these genetic factors, it is important that we do not forget environmental predisposition, and to bear in mind that a genetic marker for drug hypersensitivity in one population may not necessarily be relevant for another population. Notwithstanding the advances in genetic technologies, the ultimate determinant of success in this area of research will be the identification and careful phenotyping of patients with drug hypersensitivity reactions. As we progress to whole genome scanning, in order to satisfy the requirements for adequate statistical power, the identification of large numbers of carefully phenotyped patients will be feasible only through international collaborations.

Cross Hypersensitivity Syndrome between Phenytoin and Carbamazepine

OBJECTIVE

To evaluate the incidence of cross anticonvulsant hypersensitivity syndrome (AHS) between phenytoin (PHT) and carbamazepine (CBZ) in hospitalized patients.

METHOD

Retrospective chart review about the cross AHS was retrieved from pharmacy adverse drug reaction program from 1998 to 2002 in a 450-bed teaching hospital.

MAIN OUTCOME MEASURES

AHS was defined as the appearance of at least two symptoms with the first anticonvulsant drug (ACD). Cross AHS was considered if after withdrawal of a first ACD because of hypersensitivity symptoms, a new episode with similar or new symptoms appeared after exposure to a second ACD. The following symptoms were considered- rash, fever, hepatotoxicity, lymphadenopathies or hematological disturbances.

RESULTS

Cross AHS between PHT and CBZ was observed in nine cases (45). After the cross-reaction event, four of them were treated with valproic acid, two with vigabatrin, two with phenobarbital and one with no treatment without developing further AHS.

CONCLUSIONS

AHS is a severe complication of aromatic ACD that can compromise the future choice of therapy. Because of the high incidence of clinical cross-reaction between these two drugs, non-aromatic ACD alternatives, must be considered.

Methemoglobinemia induced by topical vaginal sulfanilamide cream in a patient with cervical cancer: a case report

BACKGROUND

Methemoglobinemia is a rare disorder most commonly associated with the ingestion or topical application of an offending exogenous agent. The clinical consequences of acute methemoglobinemia can be devastating and include lethargy, headache, and dyspnea and, as methemoglobin concentrations rise, respiratory depression, confusion, seizures, and even death.

CASE

Here we present a case of acute methemoglobinemia induced by exposure to topical vaginal sulfanilamide cream in a 36-year-old woman with a FIGO stage IIIB squamous cell cervical carcinoma.

CONCLUSION

Although methemoglobinemia associated with topical anesthetics has been well documented, to our knowledge this is the first reported case of methemoglobinemia induced by exposure to topical sulfanilamide cream. Although patients undergoing intracavitary radiation treatment for cervical cancer are at risk for cyanosis due to the development of deep vein thromboses and pulmonary embolism, methemoglobinemia should be suspected in the setting of acute cyanosis with a normal arterial oxygen pressure.

Novel Treatments for Drug-Induced Toxic Epidermal Necrolysis (Lyell’s Syndrome)

Drug-induced toxic epidermal necrolysis (TEN) is a life-threatening disease characterized by extensive destruction of the epidermis. It apparently results from the formation of specific toxic drug metabolites by the keratinocytes. The mortality rate which averages 25-30% is mainly due to secondary septicemia, and to ionic and metabolic disturbances following loss of epidermal integrity. Apoptosis is the likely mechanism leading to massive keratinocyte death in TEN. Dysregulations in the tumor necrosis factor-alpha (TNF-alpha) pathway, CD95 system (Fas ligand, CD95L; Fas receptor, CD95R) and calcium homeostasis in the epidermis are involved in this apoptotic process. An active role has also been ascribed to T lymphocytes, macrophages and factor XIIIa-positive dermal dendrocytes. Despite progress, treatment of TEN remains controversial. In the past, systemic glucocorticoids were used in order to target the inflammatory reaction in TEN. However, there was no evidence for improvement of the healing process, while corticosteroids worsened the prognosis by increasing the risk of septicemia. Only a few cases have been treated with other drugs including cyclophosphamide, pentoxyfilline, thalidomide, anti-TNF-alpha antibodies and cyclosporin A. In the recent past, some TEN patients were treated with intravenous human immunoglobulins (IVIG). The rationale for such a treatment was to block the CD95 system on keratinocytes. The early promising clinical results of IVIG treatment in TEN were subsequently challenged. This review compares the effectiveness and drawbacks of the major drugs presently used in TEN treatment. Some future prospects in TEN management are also discussed.

Dapsone-Induced Hypersensitivity Pneumonitis Mimicking Pneumocystis carinii Pneumonia in a Patient with AIDS

Interstitial pneumonitis, often related to infectious etiologies, occurs commonly in HIV-infected patients. However, hypersensitivity pneumonitis from noninfectious etiologies, including environmental stimuli or drug exposure, is an unusual etiology of interstitial pneumonitis in HIV-infected patients. We report a patient with AIDS who developed a dapsone-induced hypersensitivity pneumonitis mimicking Pneumocystis carinii (PCP) pneumonia. We believe drug-induced hypersensitivity pneumonitis should be considered in the differential diagnosis of interstitial pneumonia in HIV-infected patients in whom infectious etiologies have been ruled out.

Carbamazepine-provoked hepatotoxicity and possible aetiopathological role of glutathione in the events. Retrospective review of old data and call for new investigation

The antiepileptic drug (AED) carbamazepine is widely used in the treatment of different kinds of seizures as well as affective and behavioural disorders. This paper presents an epidemiological study of carbamazepine-induced hepatic injuries and death, and describes the possible mechanisms of its toxicity. A retrospective analysis of clinical data revealed that the likelihood of hepatic death was comparatively higher in children, particularly when they were receiving medication with multiple AEDs, whereas reversible hepatic injuries were more likely to be seen in elderly patients. As suggested in this paper, the development of carbamazepine hepatotoxicity is rare, and unpredictable with the present state of knowledge, but it is somehow related to disturbance of glutathione metabolism, although data in this regard are imperfect. There appear to be two types of carbamazepine-initiated idiosyncratic liver injury, hypersensitivity and toxin-induced. It is feasible that both are due to the accumulation of toxic metabolite(s), and arene oxides may probably be considered as damaging derivatives of carbamazepine metabolism. Despite the lack of clear-cut underlying clinical and experimental findings in those patients in whom an inherited weakness of drug eliminating capacity is present, those conditions that may deteriorate glutathione balance, may increase the possibility of the emergence of toxic events during carbamazepine therapy. Finally, some recommendations for carbamazepine therapy are presented.

Anticonvulsant hypersensitivity syndrome in children: incidence, prevention and management

Anticonvulsant hypersensitivity syndrome (AHS) is a rare, but potentially fatal, adverse reaction that occurs in patients, including children, who are treated with anticonvulsants. During metabolism of the anticonvulsant, toxic arene-oxide compounds are produced. AHS is associated with both cutaneous and systemic symptoms and is associated with multiorgan involvement. Liver damage, in particular, seems to be associated with fatal outcomes. The pathophysiology of AHS is still uncertain but it may be linked to a genetically determined inability to detoxify reactive drug metabolites. The prompt recognition of the first clinical signs of AHS, and the rapid withdrawal of the anticonvulsant, often avoids the progression of symptoms. Pharmacological treatment is essentially based on systemic corticosteroids in association with enteral nutrition, intravenous fluid augmentation, pain relief and ocular care. Intravenous immunoglobulins may also have a possible therapeutic role in some cases. Diagnostic tests, such as patch tests or in vitro assays, for AHS could help to identify patients at risk of developing the syndrome and could represent a first step of primary prevention when applied to relatives of patients.

Blood parameters indicative of oxidative stress are associated with symptom expression in chronic fatigue syndrome

Full blood counts, ESR, CRP, haematinics and markers for oxidative stress were measured for 33 patients diagnosed with chronic fatigue syndrome (CFS) and 27 age and sex matched controls. All participants also completed symptom questionnaires. CFS patients had increases in malondialdehyde (P <0.006), methaemoglobin (P <0.02), mean erythrocyte volume (P <0.02) and 2,3-diphosphoglycerate (P <0.04) compared with controls. Multiple regression analysis found methaemoglobin to be the principal component that differentiated between CFS patients and control subjects. Methaemoglobin was found to be the major component associated with variation in symptom expression in CFS patients (R(2) = 0.99, P <0.00001), which included fatigue, musculoskeletal symptoms, pain and sleep disturbance. Variation in levels of malondialdehyde and 2,3-diphosphoglycerate were associated with variations in cognitive symptoms and sleep disturbance (R(2) = 0.99, P <0.00001). These data suggest that oxidative stress due to excess free radical formation is a contributor to the pathology of CFS and was associated with symptom presentation.

Polymorphisms of NAT2 in relation to sulphasalazine-induced agranulocytosis

Agranulocytosis is a rare, but serious adverse reaction to sulphasalazine. The polymorphic enzyme N-acetyltransferase 2 (NAT2) plays an important role in the metabolism of sulphasalazine. This study was conducted to analyse whether the risk of sulphasalazine-induced agranulocytosis is increased in slow acetylators. Patients were treated for inflammatory disease, mostly joint disease, with a mean dose of 2 g sulphasalazine daily. Thirty-nine patients reacted with agranulocytosis, while 75 patients had been treated for a minimum of 3 months without haematological side-effects. A population-based control panel of 448 individuals was used for comparison. All subjects were genotyped for NAT2 by polymerase chain reaction followed by restriction enzyme digestion. The six most common allelic variants were analysed: NAT2*4, NAT2*5A, NAT2*5B, NAT2*5C, NAT2*6 and NAT2*7. The proportion of slow acetylators was significantly higher in patients with sulphasalazine-induced agranulocytosis (69%) and population-based controls (64%) compared to patients who tolerated sulphasalazine (45%); odds ratio 2.71 [95% confidence interval (CI) 1.20; 6.15], P = 0.015, and odds ratio 2.17 (95% CI 1.32; 3.56), P = 0.002, respectively. Patients who developed agranulocytosis did not differ from population-based control subjects in the frequency of slow acetylators; odds ratio 1.25 (95% CI 0.62; 2.53), P = 0.535. The risk of agranulocytosis did not appear to be increased in slow acetylators, provided that the difference compared with sulphasalazine-treated control subjects was not due to a predominance of fast acetylators among patients with inflammatory joint disease. Instead, selection bias was suspected since more slow acetylators may have discontinued sulphasalazine therapy because of drug-intolerance.

Carbamazepine-induced hypersensitivity syndrome in a child with epilepsy

Carbamazepine is an effective anticonvulsant and is considered the drug of first choice for the treatment of partial and secondarily generalized seizures. Although carbamazepine is well tolerated, many side effects have been reported in the literature. The majority of these adverse effects are transient and do not lead to the discontinuation of the therapy. We present a case of a female child, aged 11 years and 6 months, who showed an anticonvulsant hypersensitivity syndrome induced by carbamazepine. This syndrome is a rare, potentially life-threatening adverse drug reaction. The patient developed a cutaneous nonpruritic rash, associated with high fever, diffuse lymphadenopathy, and arthralgias on the knees and the ankles with local signs of arthritis. Laboratory examination showed a lymphocytosis, mild thrombocytopenia, marked eosinophilia, and high transaminases. Corticosteroid therapy (betametasone 0,5 mg x 3 day) was started and carbamazepine was gradually withdrawn changing to valproic acid, with complete control of the seizures. The fever and the rash reduced gradually, beginning from the face and then disappearing completely after 10 days. Laboratory results showed a clear improvement: after 7 days the patient showed a complete normalization of the above parameters, except for transaminases. The complete normalization of these enzymes was observed after 2 weeks from the disappearance of the skin rash.

Cellular disposition of sulphamethoxazole and its metabolites: implications for hypersensitivity

1. Bioactivation of sulphamethoxazole (SMX) to chemically-reactive metabolites and subsequent protein conjugation is thought to be involved in SMX hypersensitivity. We have therefore examined the cellular metabolism, disposition and conjugation of SMX and its metabolites in vitro. 2. Flow cytometry revealed binding of N-hydroxy (SMX-NHOH) and nitroso (SMX-NO) metabolites of SMX, but not of SMX itself, to the surface of viable white blood cells. Cellular haptenation by SMX-NO was reduced by exogenous glutathione (GSH). 3. SMX-NHOH and SMX-NO were rapidly reduced back to the parent compound by cysteine (CYS), GSH, human peripheral blood cells and plasma, suggesting that this is an important and ubiquitous bioinactivation mechanism. 4. Fluorescence HPLC showed that SMX-NHOH and SMX-NO depleted CYS and GSH in buffer, and to a lesser extent, in cells and plasma. 5. Neutrophil apoptosis and inhibition of neutrophil function were induced at lower concentrations of SMX-NHOH and SMX-NO than those inducing loss of membrane viability, with SMX having no effect. Lymphocytes were significantly (P<0.05) more sensitive to the direct cytotoxic effects of SMX-NO than neutrophils. 6. Partitioning of SMX-NHOH into red blood cells was significantly (P<0.05) lower than with the hydroxylamine of dapsone. 7. Our results suggest that the balance between oxidation of SMX to its toxic metabolites and their reduction is an important protective cellular mechanism. If an imbalance exists, haptenation of the toxic metabolites to bodily proteins including the surface of viable cells can occur, and may result in drug hypersensitivity.

Mechanisms of idiosyncratic hypersensitivity reactions to antiepileptic drugs

Hypersensitivity reactions to the aromatic antiepileptic drugs (AEDs) phenytoin (PHT) and carbamazepine (CBZ) appear to have an immune etiology. Current models of drug hypersensitivity center around the concept of drug bioactivation to reactive metabolites that irreversibly modify cellular proteins. These modified proteins are believed to initiate (or serve as targets of) an autoimmune-like attack on specific drug-modified proteins in target organs (e.g., liver, skin) of susceptible individuals. Consistent with this model, antibodies to drug-modified and native proteins have been identified in the sera of patients experiencing several drug hypersensitivity reactions. New models must incorporate an understanding of the mechanisms by which drug-modified proteins are processed and presented to the immune system in the appropriate context to culminate in the clinical manifestations of "hypersensitivity." Idiosyncratic toxicities associated with new AEDs, such as lamotrigine and felbamate, appear mechanistically distinct from PHT and CBZ hypersensitivity but may involve similar processes: bioactivation, detoxification, covalent adduct formation, processing and presentation of antigen to the immune system, and consequent formation of antibody and T-cell immune effectors. The goal of research is to develop a "susceptibility profile" for identifying individuals at risk for these forms of drug toxicity.

Bioactivation of benzocaine to a methaemoglobin-forming metabolite by rat and human microsomes in vitro

Benzocaine-mediated methaemoglobin-generation was compared with that of dapsone in vitro. Direct incubation of benzocaine with washed human erythrocytes alone at up to 15 mM did not result in significant methaemoglobin formation (0.4 ± 0.1%). With rat microsomes, dapsone-dependent methaemoglobin formation was almost two-fold that of benzocaine at 30 min (56.5 ± 0.7% vs 31.6 ± 2.4% P < 0.005)). Benzocaine-mediated methaemoglobin formation was significantly reduced in the presence of DDC (diethyldithiocarbamate) at the 10 (P < 0.005) and 20 (P < 0.025) min time points. At 30 min, cimetidine reduced benzocaine-mediated methaemoglobin from 34.4 ± 8.7% to less than 3% (P < 0.005). The methaemoglobin forming capacity of dapsone was significantly inhibited at all three time points by both DDC (P < 0.005) and cimetidine (P < 0.005). Incubation of benzocaine with microsomes from five human livers showed that each liver produced methaemoglobin-forming metabolites. No inhibitory effect was seen with DDC, although cimetidine caused a significant reduction (32.8 ± 12.4% overall) in benzocaine-mediated methaemoglobin formation in the four livers tested.

Allergy to carbamazepine: parallel in vivo and in vitro detection

PURPOSE

Five to 20% of patients discontinue antiepileptic drug (AED) therapy because of adverse reactions. Careful reintroduction, however, may be considered if true drug allergy can be ruled out. Definitive assessment of such immunologically mediated reactions requires demonstration of either specific antibodies or sensitized lymphocytes.

METHODS

We investigated whether skin patch tests (PTs) and in vitro lymphocyte proliferation assays (LPAs) were suitable for detection of allergy to carbamazepine (CBZ) and the possibly cross-reactive oxcarbazepine (OCBZ). Data of 65 patients displaying a wide range of possibly allergic side effects to CBZ were available for analysis. Data of CBZ users without any side effects and healthy volunteers served as controls. Both PTs and LPAs were done with CBZ, OCBZ and three metabolites [CBZ-10,11-epoxide (CBZ-E), 10-monohydroxy-CBZ (MHD), and 10,11-dihydroxy-CBZ (DIOL)].

RESULTS

Positive PTs with CBZ were seen in 20% and with OCBZ in 14% of the patients. Positive LPA results with CBZ and OCBZ, respectively, were found in 40 and 19%. Both tests were positive in 14 and 7% of the patients. Cross-reactivity to OCBZ was seen in -40% of CBZ-reactive patients in both PTs and LPAs.

CONCLUSION

These data illustrate the additional value of LPAs in the detection of CBZ allergy while showing that a major part of side effects to CBZ and OCBZ is not immunologically mediated, according to PTs and LPAs.

Studies on the toxicity of analogues of dapsone in-vitro using rat, human and heterologously expressed metabolizing systems

Three metabolizing systems (rat, heterologously expressed CYP3A4 and human liver) were used to evaluate 12 analogues of dapsone (4,4'diaminodiphenylsulphone) in-vitro. Methaemoglobin formation in a two-compartment and cytotoxicity in a single-compartment model were studied using human erythrocytes and neutrophils, respectively, as target cells. In the two-compartment system using rat microsomes as a generating system and methaemoglobin as an endpoint, the least potent methaemoglobin formers tested were the 2-methyl-4-propylamino (AXDD14), 2-hydroxy-4-4'amino (ABDD5) derivatives and a sulphone/trimethoprim derivative (K-130). Dapsone itself, a 2-methoxy-4-ethylamino (W10) and a 2-hydroxyl-4-ethylamino compound (ABDD39) were the most toxic. In the single-compartment cytotoxicity test using rat microsomes, AXDD14 was again among the least toxic, as was a 2-methyl 4-cyclopentyl derivative (AXDD17) and surprisingly ABDD39. The most cytotoxic compounds again included dapsone itself as well as two 2-trifluoromethyl derivatives. The only significant methaemoglobin formation and cytotoxicity shown with the heterologously expressed human CYP 3A4 was with AXDD14, which was extensively activated. Interestingly, metabolism of dapsone was low using the expressed CYP 3A4. In the two-compartment system using human liver microsomes, AXDD14, K-130 and ABDD5 were oxidized to a significantly lesser extent compared with dapsone and these preliminary findings indicate that future development of these compounds may be worthwhile.

Exfoliative dermatitis due to immunologically confirmed carbamazepine hypersensitivity

A 6-year-old Caucasian girl experienced a generalized erythematous skin rash during carbamazepine therapy. Over the next four days the eruption worsened into erythroderma with fever and generalized lymphadenopathy. Routine laboratory studies revealed increased serum levels of liver enzymes and eosinophilia. Immunologic reactivity to the anticonvulsant carbamazepine and its analogs was investigated both in vivo and in vitro by patch tests and lymphocyte proliferation assays, respectively.

Evaluation of the generation of genotoxic and cytotoxic metabolites of benzo[a]pyrene, aflatoxin B1, naphthalene and tamoxifen using human liver microsomes and human lymphocytes

1. The ability of model stable epoxides and metabolites generated by human liver microsomes from benzo[a]pyrene, aflatoxin B1, naphthalene and tamoxifen to produce cytotoxicity and genotoxicity in human peripheral lymphocytes has been investigated. 2. The stable epoxides 1,1,1 trichloropropene-2,3-oxide (100 microM) and trans stilbene oxide (100 microM) as well as metabolites generated from aflatoxin B1 (30 microM) and naphthalene (100 microM) by an extracellular metabolising system were toxic to isolated resting mononuclear leucocytes (MNLs), whereas glycidol (100 microM), benzo[a]pyrene (100 microM) and tamoxifen (50 microM) were not. 3. The stable epoxides 1,1,1 trichloropropene-2,3-oxide (100 microM) and trans stilbene oxide (100 microM) but not glycidol (100 microM) were toxic to dividing lymphocytes only after a 72-h exposure. Tamoxifen (30 microM), aflatoxin B1 (30 microM) and their metabolites were also toxic to dividing lymphocytes. Benzo[a]pyrene (100 microM) and naphthalene (100 microM) were not toxic either in the absence or presence of the extracellular metabolising system. 4. Benzo[a]pyrene (100 microM) and aflatoxin B1 (30 microM) were directly genotoxic to lymphocytes, this genotoxicity was significantly enhanced by the presence of the extracellular metabolising system. This indicates that both intracellular and extracellular bioactivation of these two compounds can produce genotoxicity. In contrast, naphthalene and tamoxifen were non-genotoxic.

CD8+ dermal T cells from a sulphamethoxazole-induced bullous exanthem proliferate in response to drug-modified liver microsomes

There is evidence that T lymphocytes play a critical role in the pathogenesis of drug-induced bullous exanthems. Sulphonamides are known to be among the most frequent aetiological agents in these severe drug-induced cutaneous hypersensitivity reactions. Several studies indicate that cytochrome P450-dependent metabolites of sulphonamides act as the nominal allergens. A 70-year-old woman with a severe blistering exanthem caused by cotrimoxazole (sulphamethoxazole and trimethoprim) was studied. We employed an in vitro approach to determine whether cytochrome P450-dependent enzymes activated drug-specific T lymphocytes from this patient. Immunohistochemical analysis of involved skin revealed a majority of epidermal CD8+ T lymphocytes, whereas the dermal infiltrate was composed of both CD4+ and CD8+ T cells. Dermal T lymphocytes isolated from lesional skin proliferated in response to sulphamethoxazole, but not to trimethoprim, in the presence of autologous mononuclear cells used as antigen-presenting cells. The antigen-specific response of sulphamethoxazole-specific T cells was significantly augmented in the presence of murine liver microsomes with P450-dependent catalytic activities. Our observations suggest that some cutaneous hypersensitivity reactions to sulphamethoxazole are due to drug-specific T lymphocytes. Cytochrome P450-dependent enzymes may play a critical role in the formation of the nominal antigen, which is recognized by antigen-specific T cells.

Clobazam, oxcarbazepine, tiagabine, topiramate, and other new antiepileptic drugs

Clinical investigators recently have studied at least 21 new antiepileptic drugs (AEDs) in people with epilepsy. This review briefly examines 15 of these new AEDs: clobazam (CLB), dezinamide, flunarizine (FNR), loreclezole, milacemide (MLM), MK-801, nafimidone, ORG-6370, oxcarbazepine (OCBZ), progabide (PGB), ralitoline, stiripentol, tiagabine (TGB), topiramate (TPM), and zonisamide (ZNS). CLB, PGB, and TGB represent agents that act on the GABA system, and MLM acts on the glycine system. MK-801 and ZNS (in part) are excitatory amino acid antagonists, and FNR is a calcium-channel antagonist. OCBZ is a keto analogue of carbamazepine, which is not metabolized to the epoxide and may have fewer side effects. The remaining agents are novel compounds with a variety of suspected mechanisms. TPM appears especially effective for intractable partial seizures but has a high incidence of cognitive side effects. None of these new AEDs is useful for all patients with inadequate seizure control or ongoing toxicity. The role of each will require further clinical study and experience.

Reduction of dapsone hydroxylamine to dapsone during methaemoglobin formation in human erythrocytes in vitro. III: Effect of diabetes

The fate of dapsone hydroxylamine has been investigated in diabetic and normal human erythrocytes. In erythrocytes from four type 1 (insulin dependent) diabetic subjects, there was a significant decrease in dapsone hydroxylamine-mediated methaemoglobin formation compared with cells drawn from normal individuals (P < 0.01). However, the ability of the diabetic cells to detoxify the hydroxylamine to dapsone was not correspondingly reduced and was not different to normal cells. The initial rate of the accelerating effect of diethyl dithiocarbamate (DDC) on hydroxylamine-mediated methaemoglobin and dapsone formation was significantly reduced in diabetic compared with normal cells. There was no significant difference in hydroxylamine-dependent methaemoglobin formation between diabetic erythrocytes pretreated with either statil or sorbinil and untreated diabetic cells. Dapsone recovery in diabetic erythrocytes incubated with statil was not significantly different from statil-free incubations. However, in the presence of sorbinil, there was a marked reduction in dapsone formation at all four time points, (P < 0.001 at 15 min). Mean measured levels of glutathione did not differ significantly between the normal (380 +/- 30.9 mg/L; N = 8) and diabetic (349 +/- 58.7 mg/L; N = 8) volunteers. In summary, although diabetic erythrocytes were less sensitive to the effect of dapsone hydroxylamine-mediated methaemoglobin formation in comparison with normal cells, glutathione-dependent hydroxylamine reduction to dapsone was unaffected.

Salicylates for ulcerative colitis--their mode of action

Delivery of 5-aminosalicylic acid to the colon by sulphasalazine, other azo-bonded compounds and controlled-release preparations is introduced in the context of metabolism by epithelial cells and therapeutic efficacy in ulcerative colitis. Potential modes of action are then reviewed, including actions on luminal bacteria, epithelial cell surface receptors, cellular events (such as nitric oxide release or butyrate oxidation), electrolyte transport and epithelial permeability. Evidence for an influence of salicylates on circulating and lamina propria inflammatory cells is presented, as well as actions on adhesion molecules, chemotactic peptides and inflammatory mediators, such as eicosanoids, platelet-activating factor, cytokines or reactive oxygen metabolites. The precise mechanism will remain uncertain as long as the aetiology of ulcerative colitis is unknown, but a pluripotential mode of action of salicylates is an advantage when influencing the network of events that constitute chronic inflammation.

The role of active metabolites in drug toxicity

Adverse drug reactions can be caused by the parent drug or a metabolite of that drug. The metabolite may be stable or chemically reactive, the resultant toxicity being either a direct extension of the pharmacology of the drug, or unrelated to the known pharmacology of the drug and dependent on the chemical properties of the compound. Many different organ systems may be affected, and there are several mechanisms involved in determining organ-specific, and sometimes cell-selective, toxicity. An imbalance between bioactivation of a drug to a toxic metabolite and its detoxification is of prime importance in determining individual susceptibility. Such an imbalance may be genetically determined or acquired and, furthermore, may be systemic or tissue-specific. Prevention of metabolite-mediated toxicity is possible once the mechanism of toxicity has been elucidated.

An investigation into the formation of stable, protein-reactive and cytotoxic metabolites from tacrine in vitro. Studies with human and rat liver microsomes

Tacrine (1,2,3,4-tetrahydro-9-aminoacridine hydrochloride; THA) is known to undergo extensive oxidative metabolism to a variety of mono- and dihydroxylated metabolites in animals and humans. The potential for tacrine to undergo metabolism to stable, protein-reactive and cytotoxic metabolites has been investigated in incubations with human and rat liver microsomes. Using lymphocytes as sensitive markers to quantify cytotoxicity, THA (50 microM) underwent NADPH-dependent bioactivation to a cytotoxic metabolite(s). NADPH-dependent cytotoxicity in the presence of rat and human microsomes was 9.8 +/- 3.1% (P < 0.05 cf. -NADPH control) and 6.2 +/- 2.0% (P < 0.05 cf. -NADPH control), respectively. Stable and protein-reactive metabolites were also formed in microsomes from both species. These accounted for 28.2 +/- 12.7% and 1.22 +/- 0.79% of incubated radioactivity in human microsomes and 6.4 +/- 2.2% and 0.4 +/- 0.1% of incubated radioactivity in rat microsomes. In microsomes pooled from six human livers the NADPH-dependent cytotoxicity was 9.4 +/- 1.1%. Formation of stable and protein-reactive metabolites accounted for 29.2 +/- 2.3% and 1.2 +/- 1.0% of incubated radioactivity. Reduced glutathione (500 microM) completely blocked NADPH-dependent cytotoxicity and inhibited protein-reactive metabolite formation by 60% (P < 0.05). Ascorbic acid (500 microM) inhibited the generation of cytotoxic and protein-reactive metabolites by 75% (P < 0.05) and 35% (P < 0.05), respectively. Cyclohexene oxide was without effect. Human serum albumin was found to protect the lymphocytes against toxicity. In microsomes prepared from the livers of four donors known to have been smokers there were no significant differences in the generation of metabolites from THA compared with microsomes prepared from livers of non-smokers. Enoxacin, a specific inhibitor of cytochrome P450 1A2 significantly inhibited all routes of THA metabolism. We have therefore demonstrated that THA may be oxidatively metabolized to stable, protein-reactive and cytotoxic metabolites in human and rat liver microsomes. A number of inhibitors may affect these process, whilst inhibition by enoxacin indicates a role for cytochrome P450 1A2 in THA metabolism.

Reduction of dapsone hydroxylamine to dapsone during methaemoglobin formation in human erythrocytes in vitro

The fate of the toxic metabolite of dapsone, dapsone hydroxylamine, has been studied in the human red cell. Twice-washed red cells were incubated at 37 degrees with dapsone hydroxylamine: at 3 and 5 min, 27.0 +/- 2.2 and 33.2 +/- 2.7% of the haemoglobin had been converted to methaemoglobin, leading to a maximum at 45 min (45 +/- 1.8%). HPLC analysis revealed that parent amine was produced from dapsone hydroxylamine during methaemoglobin formation in the red cells. At 3 min, conversion of dapsone hydroxylamine to dapsone reached 7.0 +/- 3.9% leading to a maximum at 30 min (18.1 +/- 3.7%). There was a linear relationship between hydroxylamine-dependent methaemoglobin formation and conversion of hydroxylamine to dapsone (r = 0.97). At 4 degrees, methaemoglobin and dapsone formation was greatly retarded, and did not exceed 10%. Co-incubation of diethyl dithiocarbamate (DDC) with dapsone hydroxylamine and red cells led to a marked increase in methaemoglobin formation (61.4 +/- 3.4%) compared with hydroxylamine and red cells alone (45.0 +/- 1.8%, P < 0.001) at 45 min, and conversion of dapsone hydroxylamine to dapsone was almost doubled at 45 min (35.7 +/- 5.3%) compared with hydroxylamine and red cells (18.1 +/- 2.5%). A linear relationship between methaemoglobin formation and dapsone formation (r = 0.96) was also shown to occur in the presence of DDC. Incubation of red cells with DDC and dapsone hydroxylamine caused a significantly greater reduction in glutathione levels (98.3 +/- 1.6%) compared with red cells and dapsone hydroxylamine alone (84.8 +/- 2.7%) at 5 min (P < 0.001), although there was no significant difference between the groups at 15 min (96.9 +/- 2.6 vs 98.1 +/- 2.2%). Intra-erythrocytic glutathione was then depleted by 75 +/- 3.4%, by pretreatment with diethyl maleate (6 mM), and these cells in the presence of the hydroxylamine showed a significant fall in both methaemoglobin generation (29.7 +/- 1.2 vs 35.0 +/- 1.7%) and parent amine formation (11.1 +/- 0.2 vs 16.5 +/- 1.1%) compared with untreated red cells at 45 min. It is possible that a cycle exists between hepatic oxidation of dapsone to its hydroxylamine and reduction to the amine within the red cell, which may lead to re-oxidation by hepatic cytochrome P450. This process may contribute to the persistence of the drug in vivo.

An investigation of the formation of cytotoxic, protein-reactive and stable metabolites from carbamazepine in vitro

The formation of chemically reactive metabolites from carbamazepine (CBZ) in the presence of mouse and human liver microsomes has been investigated using cytotoxicity and irreversible binding of radiolabelled compound as quantitative end-points. For comparison, the formation of the stable CBZ-10,11-epoxide (CBZ-10,11-E) has been measured. The formation of the cytotoxic, protein-reactive and stable metabolites of CBZ was increased by induction of the cytochrome P450 enzymes by phenobarbitone and reduced by co-incubation in vitro with ketoconazole (10-250 microM), suggesting that the formation of these metabolites is cytochrome P450 dependent. All human livers tested (N = 6) bioactivated CBZ to a protein-reactive metabolite, the mean covalent binding increasing from 0.08 +/- 0.01% (without NADPH) to 0.27 +/- 0.09% (with NADPH; P less than or equal to 0.05). The formation of the chemically reactive metabolites was reduced by a subphysiological concentration of reduced glutathione (GSH) (500 microM), while ascorbic acid (100 microM) had no effect. Neither compound affected the formation of CBZ-10,11-E. Microsomal epoxide hydrolase (mEH), but not cytosolic epoxide hydrolase, caused a concentration-dependent inhibition of cytotoxicity reaching a maximum of 60% at 100 U of mEH. Covalent binding was also reduced by 60% by 100 U mEH. The separated T- and B-lymphocytes showed no difference in sensitivity when incubated with CBZ and mouse microsomes. The study demonstrates that the balance between activation of CBZ by the cytochrome P450 enzymes to a chemically reactive arene oxide metabolite and its detoxification by mEH and GSH may contribute to individual susceptibility to CBZ idiosyncratic toxicity.