Vincent Yip

HLA genotype and carbamazepine-induced cutaneous adverse drug reactions: a systematic review.

Carbamazepine (CBZ) therapy is associated with cutaneous adverse reactions in up to 10% of patients. Predisposition to these hypersensitivity reactions has been linked to the human leukocyte antigen (HLA) genotype. This systematic review determines the strength of these associations and accuracy of proposed genetic screening. We determined that carriage of HLA‐B*1502 in Asian patients was associated with a pooled odds ratio (OR) of 113.4 (95% confidence interval (CI) = 51.2–251.0, P < 1 × 10−5) for CBZ‐induced Stevens–Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). A total of 461 patients would need to be screened for HLA‐B*1502 to prevent one episode of SJS/TEN. HLA‐A*3101 is significantly associated with all phenotypes of CBZ hypersensitivity in multiple ethnicities with a pooled OR of 9.5 (95% CI = 6.4–13.9, P < 1 × 10−5). Between 47 and 67 patients would need to be tested for HLA‐A*3101 to prevent one episode of hypersensitivity. Our findings suggest that HLA testing before carbamazepine therapy would be effective at identifying individuals at risk of hypersensitivity and applicable to multiple populations providing hope for prevention in the future.

Genetics of Immune-Mediated Adverse Drug Reactions: a Comprehensive and Clinical Review

Adverse drug reactions (ADRs) are common and are a major problem in drug therapy. Patients experience unnecessary morbidity and mortality whilst many effective drugs are withdrawn because of ADRs in a minority of patients. Recent studies have demonstrated significant associations between human leukocyte antigens (HLA) and predisposition to ADRs such as drug-induced skin injury (DISI) and drug-induced liver injury (DILI). HLA-B*58:01 has been significantly associated with allopurinol-induced hypersensitivity. Associations between HLA and carbamazepine hypersensitivity reactions demonstrate both ethnicity and phenotype specificity; with HLA-B*15:02 associated with Stevens-Johnson syndrome and toxic epidermal necrolysis in South East Asian patients only whilst HLA-A*31:01 is associated with all phenotypes of hypersensitivity in multiple ethnicities. Studies of ximelagatran, an oral direct thrombin inhibitor withdrawn because of hepatotoxicity, found associations between HLA-DRB1*07:01 and HLA-DQA1*02:01 and ximelagatran DILI. Interestingly, HLA-B*57:01 is associated with both abacavir DISI and flucloxacillin DILI but the reasons for the different phenotype of ADR remains unknown. Pharmacogenetic screening for HLA-B*57:01 prior to abacavir therapy has significantly reduced the incidence of abacavir hypersensitivity syndrome in clinical practice. No other HLA associations have been translated into clinical practice because of multiple reasons including failure to replicate, inadequate sample sizes, and our lack of understanding of pathophysiology of ADRs. Here, we review genetic associations that have been reported with ADRs and discuss the challenges that scientists, clinicians, pharmaceutical industry and regulatory agencies face when attempting to translate these associations into clinically valid and cost-effective tests to reduce the burden of ADRs in future.

Cost‐effectiveness of screening for HLA‐A*31:01 prior to initiation of carbamazepine in epilepsy

Carbamazepine causes severe cutaneous adverse drug reactions that may be predicted by the presence of the HLA‐A*31:01 allele in northern European populations. There is uncertainty as to whether routine testing of patients with epilepsy is cost‐effective. We conducted an economic evaluation of HLA‐A*31:01 testing from the perspective of the National Health Service (NHS) in the United Kingdom.

Personalized medicine approaches in epilepsy

Epilepsy affects 50 million persons worldwide, a third of whom continue to experience debilitating seizures despite optimum anti‐epileptic drug (AED) treatment. Twelve‐month remission from seizures is less likely in female patients, individuals aged 11–36 years and those with neurological insults and shorter time between first seizure and starting treatment. It has been found that the presence of multiple seizures prior to diagnosis is a risk factor for pharmacoresistance and is correlated with epilepsy type as well as intrinsic severity. The key role of neuroinflammation in the pathophysiology of resistant epilepsy is becoming clear. Our work in this area suggests that high‐mobility group box 1 isoforms may be candidate biomarkers for treatment stratification and novel drug targets in epilepsy. Furthermore, transporter polymorphisms contributing to the intrinsic severity of epilepsy are providing robust neurobiological evidence on an emerging theory of drug resistance, which may also provide new insights into disease stratification. Some of the rare genetic epilepsies enable treatment stratification through testing for the causal mutation, for example SCN1A mutations in patients with Dravets syndrome. Up to 50% of patients develop adverse reactions to AEDs which in turn affects tolerability and compliance. Immune‐mediated hypersensitivity reactions to AED therapy, such as toxic epidermal necrolysis, are the most serious adverse reactions and have been associated with polymorphisms in the human leucocyte antigen (HLA) complex. Pharmacogenetic screening for HLA‐B*15:02 in Asian populations can prevent carbamazepine‐induced Stevens–Johnson syndrome. We have identified HLA‐A*31:01 as a potential risk marker for all phenotypes of carbamazepine‐induced hypersensitivity with applicability in European and other populations. In this review, we explore the currently available key stratification approaches to address the therapeutic challenges in epilepsy.

The HLA-A*31:01 allele: influence on carbamazepine treatment

Carbamazepine (CBZ) is an effective anticonvulsant that can sometimes cause hypersensitivity reactions that vary in frequency and severity. Strong associations have been reported between specific human leukocyte antigen (HLA) alleles and susceptibility to CBZ hypersensitivity reactions. Screening for HLA-B*15:02 is mandated in patients from South East Asia because of a strong association with Stevens–Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). HLA-A*31:01 predisposes to multiple phenotypes of CBZ hypersensitivity including maculopapular exanthema, hypersensitivity syndrome, and SJS/TEN in a range of populations including Europeans, Japanese, South Koreans and Han Chinese, although the effect size varies between the different phenotypes and populations. Between 47 Caucasians and 67 Japanese patients would need to be tested for HLA-A*31:01 in order to avoid a single case of CBZ hypersensitivity. A cost-effectiveness study has demonstrated that HLA-A*31:01 screening would be cost-effective. Patient preference assessment has also revealed that patients prefer pharmacogenetic screening and prescription of alternative anticonvulsants compared to current standard of practice without pharmacogenetic testing. For patients who test positive for HLA-A*31:01, alternative treatments are available. When alternatives have failed or are unavailable, HLA-A*31:01 testing can alert clinicians to 1) patients who are at increased risk of CBZ hypersensitivity who can then be targeted for more intensive monitoring and 2) increase diagnostic certainty in cases where hypersensitivity has already occurred, so patients can be advised to avoid structurally related drugs in the future. On the basis of the current evidence, we would favor screening all patients for HLA-A*31:01 and HLA-B*15:02 prior to starting CBZ therapy.

Mass Spectrometric Characterization of Circulating Covalent Protein Adducts Derived from Epoxide Metabolites of Carbamazepine in Patients

Carbamazepine (CBZ) is an effective antiepileptic drug that has been associated with hypersensitivity reactions. The pathogenesis of those reactions is incompletely understood but is postulated to involve a complex interplay between the drugs metabolism, genetic variation in human leukocyte antigens, and adverse activation of the immune system. Multiple T-cell activation mechanisms have been hypothesized including activation by drug-peptide conjugates derived from proteins haptenated by reactive metabolites. However, definitive evidence of the drug-protein adducts in patients has been lacking. In this study, mass spectrometry was used to characterize protein modifications by microsomally-generated metabolites of CBZ and in patients taking CBZ therapy. CBZ 10,11-epoxide (CBZE), a major electrophilic plasma metabolite of CBZ, formed adducts with glutathione-S-transferase pi (GSTP; Cys47) and human serum albumin (HSA; His146 and His338, but not Cys34) in vitro via notably divergent side-chain selectivity. Both proteins were adducted at the same residues by undefined monoxygenated metabolites ([O]CBZ) when they were incubated with human liver microsomes, NADPH and CBZ. There was also evidence for formation of a CBZ adduct at His146 and His338 of HSA derived via dehydration from an intermediate arene oxide adduct. Glutathione trapping of reactive metabolites confirmed microsomal production of CBZE and indicated simultaneous production of arene oxides. In 15 patients prescribed CBZ therapy, [O]CBZ-modified HSA (His146) was detected in all subjects. The relative amount of adduct was moderately positively correlated with plasma concentrations of CBZ (r2 = 0.44, p = 0.002) and CBZE (r2 = 0.35, p = 0.006). Our results have provided the first chemical evidence for microsomal production of [O]CBZ species that are able to escape the microsomal domain to react covalently with soluble proteins. This study has also demonstrated the presence of circulating [O]CBZ-modified HSA in patients without hypersensitivity reactions who were receiving standard CBZ therapy. The implications of those circulating adducts for susceptibility to CBZ hypersensitivity merit further immunological investigation in hypersensitive patients.

Covalent adduction of carbamazepine 10, 11-epoxide with human serum albumin and glutathione S-transferase pi: implications for carbamazepine hypersensitivity

Abstract Background Carbamazepine (CBZ) is an effective antiepileptic drug. However, it can cause cutaneous adverse reactions in up to 10% of patients. These reactions include life-threatening conditions such as Stevens-Johnson syndrome and toxic epidermal necrolysis. It has been hypothesised that CBZ is metabolised to reactive metabolites that form haptens with cellular proteins, which are then presented by specific HLA alleles, HLA-B*1502 and HLA-A*3101, activating the immune system and triggering hypersensitivity in susceptible individuals. CBZ 10, 11-epoxide (CBZ-E) is a major circulating metabolite of CBZ and retains therapeutic activity. It is also sufficiently electrophilic to react with glutathione and proteins in vitro. However, the structures of the protein adducts were unknown. Our aim was to determine the structure of these CBZ-E protein adducts using high sensitivity proteomics tools. Methods Initially, synthetic CBZ-E was incubated with human glutathione S-transferase pi (hGSTP) or human serum albumin (HSA). Both proteins form adducts with various reactive chemicals. Subsequently, to determine whether metabolically generated CBZ-E could also form protein adducts, CBZ was incubated with human supersomes (CYP3A4, CYP2E1, CYP2B6) and hGSTP. Tryptic peptide analysis by advanced liquid chromatography-tandem mass spectrometry was used to characterise CBZ-E adduct formation. Findings An adduct was identified at cys-47 of hGSTP, and adducts were identified at his146 and his338 of HSA after incubation with CBZ-E. After incubation of CBZ with human supersomes and hGSTP the dihydrohydroxy thioether adduct at cys47 of hGSTP was again identified, indicating that metabolic activation of CBZ to CBZ-E in vivo might also yield stable protein adducts. Interpretation We have shown for the first time, to our knowledge, that CBZ-E, an abundant CBZ metabolite in man, can form covalent adducts with hGSTP and HSA in vitro. These adducts and similar adducts of other proteins could be responsible for triggering hypersensitivity reactions. Further work will focus on confirming the presence of HSA-CBZ-E adducts in patients and determining the immunogenicity of these adducts in vitro. Funding UK Medical Research Council, ICON, GlaxoSmithKline, AstraZeneca, the Medical Evaluation Unit.

Chapter 20 – Adverse Drug Reactions

Adverse drug reactions (ADRs) are a major problem in clinical practice and drug development. Estimates suggest that they represent 6.5–6.7% of acute hospital admissions. ADRs represent the most common reason for drug withdrawal and the failure of new drugs to reach the market. They are commonly classified as type A (augmented) or type B (bizarre). Type A ADRs are predictable from the known pharmacology of the drug, and research has focused on genetic variation in drug metabolism pathways, such as cytochrome P450 enzymes, to explain the variation in ADR susceptibility. Success with this approach has been highlighted by the tailoring of azathioprine dosages according to thiopurine S-methyltransferase status. Type B ADRs are not predictable from the known pharmacology of the drug and include hypersensitivity reactions to antiepileptics and statin-induced myopathy. Several strong human leukocyte antigen (HLA) associations have been reported for type B ADRs, and testing for human leukocyte antigen B*57:01 is now routine prior to abacavir therapy. This chapter reviews the reported genetic associations with ADRs and explains their significance in clinical practice and the barriers to their clinical implementation.

Assessment of gene expression profiles of peripheral blood mononuclear cells from patients with a history of carbamazepine hypersensitivity

Abstract Background Carbamazepine (CBZ) therapy is associated with hypersensitivity reactions, which can be multisystemic and sometimes fatal. The pathogenesis of these reactions is incompletely understood but heterologous immunity generated to viral antigens has been proposed as a potential mechanism. Our aim was to investigate changes in gene expression profiles of peripheral blood mononuclear cells (PBMCs) from patients with CBZ hypersensitivity to characterise the pathways involved in immune activation. Methods PBMCs were isolated from five individuals with a history of hypersensitivity to CBZ. The PBMCs were incubated for 24 h with CBZ, carbamazepine 10,11-epoxide (CBZE), cell culture medium, or tetanus toxoid. Expression profiles for mRNA and microRNA were generated with microarrays (Affymetrix, Santa Clara, CA, USA). Differential gene expression was undertaken by limma analysis in the R statistical software. Ingenuity pathway analysis (IPA) was used to define the molecular mechanisms in development of CBZ hypersensitivity. Findings Incubation of PBMCs with CBZ, CBZE, and tetanus toxoid led to significant differential expression (log 2 -fold change >1 or COX8A, IFI35, IFIT3, PARP9, PARP12, PTGES, RSAD2, USP18, USP41, miR433, miR455, miR3194, miR4723 , and miR345 . These genes were highly interconnected in functional networks and defined five top functional categories—namely, viral infection, psoriasis, inflammation of body region or organ, and antiviral response. Interpretation Incubation of PBMCs from CBZ hypersensitive individuals with CBZ or CBZE led to treatment-specific changes in gene expression associated with activation of antiviral and inflammatory pathways. These CBZ-specific and CBZE-specific mRNA and microRNA changes could potentially act as novel diagnostic biomarkers and treatment targets for CBZ hypersensitivity reactions, but further validation and confirmation of specificity in larger numbers of patients are needed. Funding VY was supported by the North West England Medical Research Council Fellowship Scheme (clinical pharmacology and therapeutics), which is funded by the Medical Research Council (grant number G1000417/94909), ICON, GlaxoSmithKline, AstraZeneca, and the Medical Evaluation Unit.

Response to “HLA Allelic Variants and Carbamazepine‐Induced Hypersensitivity”

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