TNFalpha promoter region gene polymorphisms in carbamazepine-hypersensitive patients

Adverse drug reactions and pharmacogenomics: recent advances

The concept of pharmacogenomics, the study of how variation in the human genome affects response to drugs, attracts attention from clinicians and the pharmaceutical industry alike. The aim is to distinguish, using appropriate genetic tests, individuals who may be harmed by certain drugs from those who may benefit from them. Adverse drug reactions cause significant morbidity and mortality and incur a large cost to healthcare systems. Pharmacogenomics may help in the prediction and prevention of adverse reactions to drugs. While some recent studies (e.g., abacavir hypersensitivity) have shown strong associations with single genetic factors, whether these represent the exceptions rather than the rule is unclear. Further studies on adverse drug reaction pharmacogenetics are needed – these should be adequately powered and utilize the most appropriate study design that allows for an evaluation of both genetic and environmental factors. For pharmacogenetic testing to become acceptable in clinical practice, it is important that such studies are also able to provide evidence of clinical validity and clinical utility.

SNP genotyping: technologies and biomedical applications

Single nucleotide polymorphisms (SNPs) are the most frequently occurring genetic variation in the human genome, with the total number of SNPs reported in public SNP databases currently exceeding 9 million. SNPs are important markers in many studies that link sequence variations to phenotypic changes; such studies are expected to advance the understanding of human physiology and elucidate the molecular bases of diseases. For this reason, over the past several years a great deal of effort has been devoted to developing accurate, rapid, and cost-effective technologies for SNP analysis, yielding a large number of distinct approaches. This article presents a review of SNP genotyping techniques and examines their principles of genotype determination in terms of allele differentiation strategies and detection methods. Further, several current biomedical applications of SNP genotyping are discussed.

Human leukocyte antigens and drug hypersensitivity

PURPOSE OF REVIEW

The present article reviews the recent literature on the identification of human leukocyte antigen (HLA) alleles as major susceptible genes for drug hypersensitivity and discusses the clinical implications.

RECENT FINDINGS

Several recent studies have reported strong genetic associations between HLA alleles and susceptibility to drug hypersensitivity. The genetic associations can be drug specific, such as HLA-B*1502 being associated with carbamazepine-induced Stevens-Johnson syndrome and toxic epidermal necrolysis (SJS/TEN), HLA-B*5701 with abacavir hypersensitivity and HLA-B*5801 with allopurinol-induced severe cutaneous adverse reactions. A genetic association can also be phenotype-specific, as B*1502 is associated solely with carbamazepine-SJS/TEN, and not with either maculopapular eruption or hypersensitivity syndrome. Furthermore, a genetic association can also be ethnicity specific; carbamazepine-SJS/TEN associated with B*1502 is seen in south-east Asians but not in whites, which may be explained by the different allele frequencies.

SUMMARY

The strong genetic association suggests a direct involvement of HLA in the pathogenesis of drug hypersensitivity when the HLA molecule presents an antigenic drug for T cell activation. The high sensitivity/specificity of some markers provides a plausible basis for developing tests to identify individuals at risk for drug hypersensitivity. Application of HLA-B*1502 genotyping as a screening tool before prescribing carbamazepine could be a valuable tool in preventing carbamazepine-induced SJS/TEN in south-east Asian countries.

Association of tumor necrosis factor-alpha -308G>A polymorphism with IgE-mediated allergy to betalactams in an Italian population

Tumor necrosis factor-alpha (TNF-alpha) is released from mast cells via an immunoglobulin E (IgE)-dependent mechanism. The variant G>A at -308 of TNFA is part of an extended haplotype HLA-A1-B8-DR3-DQ2 and influences the gene expression. We evaluated this variant in relation to IgE-mediated reactions to betalactams, in 427 subjects, including 167 cases and 260 age- and gender-paired controls. TNFA GG genotype was a significant independent predictor of the primary risk of betalactam allergy, concurrently with total IgE level, with an age- and sex-adjusted odds ratio estimated at 2.45 (95% confidence interval: 1.18-5.08, P=0.0163). Cases with -308AA genotype had a higher serum level of specific IgE than those with -308GA/GG genotype, with median levels (relative units) of 4.6 (inter-quartiles: 3.9-10.6) and 2.2 (1.4-4.3), respectively (P=0.0046). In conclusion, our results suggest an ambivalent influence of a genetic determinant of pro-inflammatory pathways on IgE-mediated hypersensitivity to betalactams.

Various pharmacogenetic aspects of antiepileptic drug therapy: a review

Pharmacogenetics concerns the influence of an individual's genetic background on the pharmacokinetics and pharmacodynamics of xenobiotics. Much of the pharmacogenetic data in the field of epilepsy deals with the pharmacokinetics of antiepileptic drugs (AEDs). In particular, two polymorphisms of cytochrome P450 2C9 are known to slow down the metabolism of phenytoin to a degree that increases the risk of the neurotoxic adverse effects of this drug among carriers of these polymorphisms. A significant number of patients with epilepsy do not respond to AEDs and such pharmacoresistance is a major, largely unsolved, problem that is likely to be multifactorial in nature. In this regard, genetic factors may influence transmembrane drug transporter proteins, thereby modifying the intracerebral penetration of AEDs. Monogenic idiopathic epilepsies are rare and frequently associated with ion channel mutations; however, to date, a consistent relationship between changes in channel properties and clinical phenotype has not been established nor has any association between genotype and response to specific treatment options. Polymorphisms of drug targets may represent another genetic facet in epilepsy: a recent study demonstrated for the first time a polymorphism of a drug target (the alpha-subunit of a voltage-gated sodium channel) associated in clinical practice with differing response to two classic AEDs. Adverse drug reactions and teratogenicity of AEDs remain a major concern. Whole-genome single nucleotide polymorphism profiling might in the future help to determine genetic predisposing factors for adverse drug reactions. Recently, in Han Chinese treated with carbamazepine and presenting with Stevens-Johnson syndrome, a strong association was found with HLA B*1502. If genetically targeted drug development becomes more affordable/cost efficient in the near future, the development of new drugs for relatively rare diseases could become economically viable for the pharmaceutical industry. The synergy of lower trial costs and efficacy-based prescribing may reduce the cost of medical treatment for a particular disease. This hypothetical advantage of the practical use of pharmacogenetics is, however, counterbalanced by several possible dangers, including illicit data mining and the development of a human 'genetic underclass' with the risk of exclusion from, for example employment or health insurance, because of an 'unfavourable' genetic profile.

Idiosyncratic adverse reactions to antiepileptic drugs

Idiosyncratic drug reactions may be defined as adverse effects that cannot be explained by the known mechanisms of action of the offending agent, do not occur at any dose in most patients, and develop mostly unpredictably in susceptible individuals only. These reactions are generally thought to account for up to 10% of all adverse drug reactions, but their frequency may be higher depending on the definition adopted. Idiosyncratic reactions are a major source of concern because they encompass most life-threatening effects of antiepileptic drugs (AEDs), as well as many other reactions requiring discontinuation of treatment. Based on the underlying mechanisms, idiosyncratic reactions can be differentiated into (1) immune-mediated hypersensitivity reactions, which may range from benign skin rashes to serious conditions such as drug-related rash with eosinophilia and systemic symptoms; (2) reactions involving unusual nonimmune-mediated individual susceptibility, often related to abnormal production or defective detoxification of reactive cytotoxic metabolites (as in valproate-induced liver toxicity); and (3) off-target pharmacology, whereby a drug interacts directly with a system other than that for which it is intended, an example being some types of AED-induced dyskinesias. Although no AED is free from the potential of inducing idiosyncratic reactions, the magnitude of risk and the most common manifestations vary from one drug to another, a consideration that impacts on treatment choices. Serious consequences of idiosyncratic reactions can be minimized by knowledge of risk factors, avoidance of specific AEDs in subpopulations at risk, cautious dose titration, and careful monitoring of clinical response.

Toxic epidermal necrolysis

Toxic epidermal necrolysis (TEN) is an unpredictable, life-threatening drug reaction associated with a 30% mortality. Massive keratinocyte apoptosis is the hallmark of TEN. Cytotoxic T lymphocytes appear to be the main effector cells and there is experimental evidence for involvement of both the Fas-Fas ligand and perforin/granzyme pathways. Optimal treatment for these patients remains to be clarified. Discontinuation of the offending drug and prompt referral to a burn unit are generally agreed upon steps. Beyond that, however, considerable controversy exists. Evidence both pro and con exists for the use of IVIG, systemic corticosteroid, and other measures. There is also evidence suggesting that combination therapies may be of value. All the clinical data, however, is anecdotal or based on observational or retrospective studies. Definitive answers are not yet available. Given the rarity of TEN and the large number of patients required for a study to be statistically meaningful, placebo controlled trials are logistically difficult to accomplish. The absence of an animal model further hampers research into this condition. This article reviews recent data concerning clinical presentation, pathogenesis and treatment of TEN.

LEARNING OBJECTIVES

At the conclusion of this learning activity, participants should have acquired a more comprehensive knowledge of our current understanding of the classification, clinical presentation, etiology, pathophysiology, prognosis, and treatment of TEN.

HLA-B locus in Caucasian patients with carbamazepine hypersensitivity

BACKGROUND

A strong pharmacogenetic association has been reported in Chinese patients between human leukocyte antigen (HLA)-B*1502 and carbamazepine (CBZ)-induced Stevens-Johnson syndrome (SJS).

METHODS

We have genotyped the HLA-B alleles in 56 Caucasian patients with varying severities of CBZ hypersensitivity and 43 controls on CBZ without adverse effects.

RESULTS

None of our patients (including two with blistering skin rashes) were positive for the HLA-B*1502 allele. HLA-B*0702 allele may protect against severe CBZ hypersensitivity but warrants further study. Of secondary interest, the correlation between HLA-B*0801 and HLA-DR3, DQ2 and TNF -308 alleles (on the ancestral haplotype 8.1) is consistent with our previous findings.

CONCLUSION

HLA-B*1502 does not seem to be a marker for all forms of CBZ-induced hypersensitivity in a Caucasian population.

Genetic susceptibility to carbamazepine-induced cutaneous adverse drug reactions

The anticonvulsant carbamazepine (CBZ) frequently causes cutaneous adverse drug reactions (cADRs), including maculopapular eruption (MPE), hypersensitivity syndrome (HSS), Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). We reported that SJS/TEN caused by CBZ is strongly associated with the HLA-B*1502 gene in Han Chinese. Here, we extended our genetic study to different types of CBZ-cADRs (91 patients, including 60 patients with SJS/TEN, 13 patients with hypersensitivity syndrome and 18 with maculopapular exanthema versus 144 tolerant controls). We used MALDI-TOF mass spectrometry to screen the genetic association of 278 single nucleotide polymorphisms (SNPs), which cover the major histocompatibility complex (MHC) region, tumor necrosis factor-alpha, heat shock protein and CBZ-metabolic enzymes, including CYP3A4, 2B6, 2C8, 2C9, 1A2 and epoxide hydrolase 1. In addition, we genotyped 20 microsatellites in the MHC region and performed HLA-typing to construct the recombinant map. We narrowed the susceptibility locus for CBZ-SJS/TEN to within 86 kb flanking the HLA-B gene on the extended B*1502 haplotype, and confirmed the association of B*1502 with SJS/TEN [Pc=1.6x10, odds ratio (OR)=1357; 95% confidence interval (CI)=193.4-8838.3]. By contrast to CBZ-SJS/TEN, HLA-B*1502 association was not observed in the MPE or HSS groups: MPE was associated with SNPs in the HLA-E region and a nearby allele, HLA-A*3101 (Pc=2.2x10, OR=17.5; 95% CI=4.6-66.5), and HSS with SNPs in the motilin gene (Pc=0.0064, OR=7.11; 95% CI=3.1-16.5) located terminal to the MHC class II genes. No SNPs in genes involved in CBZ metabolism were associated with CBZ-induced cADRs. Our data suggest that HLA-B*1502 could contribute to the pathogenesis of CBZ-SJS/TEN, and that genetic susceptibility to CBZ-induced cADRs is phenotype-specific.

Genetic association studies in epilepsy pharmacogenomics: lessons learnt and potential applications

Although epilepsy is one of the most common neurological disorders and genetic factors are well known to play a role in response to antiepileptic drug (AED) treatment, the study of the pharmacogenetics of epilepsy has received relatively little attention and has not resulted in clinical applications to date. Our improved understanding of the pathogenesis of epilepsy and the mechanism of action of AEDs, together with recent advances in genetics and decreasing genotyping costs, have now paved the way for a more systematic application of pharmacogenetics in the field of epilepsy. It is hoped that the resulting knowledge will lead to a more rational treatment of epilepsy, development of more efficacious AEDs, and facilitation of clinical trials of new AEDs. However, there are formidable practical, methodological and theoretical hurdles to overcome before pharmacogenomic information will have any major utility in the clinical setting. Here, we discuss the evidence for a genetic contribution to AED response, review current knowledge in epilepsy pharmacogenetics and discuss potential future avenues with their implications, both for the clinical treatment of epilepsy and new AED development.

Serious carbamazepine-induced hypersensitivity reactions associated with the HSP70 gene cluster

OBJECTIVES

The use of carbamazepine (CBZ), the most commonly prescribed antiepileptic drug, is hampered by the occurrence of severe, potentially lethal hypersensitivity reactions. The pathogenesis of hypersensitivity is not yet known, but immune mechanisms are involved. Predisposition to CBZ hypersensitivity is likely to be genetically determined, and genes within the major histocompatibility complex (MHC) have been implicated. The heat shock protein (HSP70) gene cluster is located in the MHC class III region.

METHODS

Using a case-control study design, we compared 61 patients with CBZ hypersensitivity (22 with a severe reaction) to 44 patients on CBZ with no signs of hypersensitivity and 172 healthy controls. The genotyping strategy involved identification of common and rare single nucleotide polymorphisms (SNPs) within the HSP70 gene cluster by sequencing, estimation of linkage disequilibrium (LD) and haplotype structure, and thereafter, analysis of SNP/haplotype frequencies in the cases and controls. Population substructure was evaluated by genotyping of 34 microsatellites.

RESULTS

Twenty-five SNPs were detected across the three HSP70 genes. Analyses revealed that alleles G, T and C at the SNPs HSPA1A +1911 C/G, HSPA1A +438 C/T and HSPA1L +2437 T/C, respectively, were associated with protection from serious hypersensitivity reactions to CBZ, with the associated alleles falling on a common haplotype. We were unable to detect the presence of population stratification in our patients and controls.

CONCLUSIONS

Our data show that HSP70 gene variants are associated with serious CBZ hypersensitivity reactions, but whether this is causal or reflects LD with another gene within the MHC requires further study.

Noncovalent interactions of drugs with immune receptors may mediate drug-induced hypersensitivity reactions

Drug-induced hypersensitivity reactions are instructive examples of immune reactions against low molecular weight compounds. Classically, such reactions have been explained by the hapten concept, according to which the small antigen covalently modifies an endogenous protein; recent studies show strong associations of several HLA molecules with hypersensitivity. In recent years, however, evidence has become stronger that not all drugs need to bind covalently to the major histocompatibility complex (MHC)-peptide complex in order to trigger an immune response. Rather, some drugs may bind reversibly to the MHC or possibly to the T-cell receptor (TCR), eliciting immune reactions akin to the pharmacological activation of other receptors. While the exact mechanism is still a matter of debate, noncovalent drug presentation clearly leads to the activation of drug-specific T cells. In some patients with hypersensitivity, such a response may occur within hours of even the first exposure to the drug. Thus, the reaction to the drug may not be the result of a classical, primary response but rather be mediated by existing, preactivated T cells that display cross-reactivity for the drug and have additional (peptide) specificity as well. In this way, certain drugs may circumvent the checkpoints for immune activation imposed by the classical antigen processing and presentation mechanisms, which may help to explain the idiosyncratic nature of many drug hypersensitivity reactions.

The potential of pharmacogenetics in the treatment of epilepsy

Pharmacogenetics studies how genetic variants influence individual drug responses. Although pharmacogenetics is currently the subject of intensive research in several disease domains, it remains relatively unexplored in the field of epilepsy. Drug treatment of epilepsy is characterized by unpredictability of efficacy, adverse drug reactions and optimal doses in individual patients. Moreover, a substantial fraction of patients develop drug refractory epilepsy despite optimal treatment. Insights in the pathogenesis of epilepsy and the mechanisms of action of antiepileptic drugs (AEDs) have improved our understanding of the genetic determinants of AED response. The first reports in epilepsy pharmacogenetics are becoming available, and large-scale pharmacogenetic studies are now possible thanks to recent advances in genetics and decreasing genotyping costs. It is hoped that ultimately, findings in epilepsy pharmacogenetics will lead to a more efficacious and less harmful treatment of epilepsy, development of more effective AEDs and facilitation of clinical trials of new AEDs. However, although pharmacogenetics will undoubtedly improve our insight into the mechanisms underlying response to AEDs and perhaps into the pathogenesis of drug refractory epilepsy, clinical application of any findings is expected to be a long process, and considerable practical and theoretical hurdles need to be overcome before pharmacogenetic information will prove of any major utility in the clinical setting. This review addresses current knowledge on genetic factors contributing to AED response and discusses the potential of epilepsy pharmacogenetics in the clinical treatment of epilepsy and new AED development.

Pharmacological interaction of drugs with immune receptors: the p-i concept

Drug-induced hypersensitivity reactions have been explained by the hapten concept, according to which a small chemical compound is too small to be recognized by the immune system. Only after covalently binding to an endogenous protein the immune system reacts to this so called hapten-carrier complex, as the larger molecule (protein) is modified, and thus immunogenic for B and T cells. Consequently, a B and T cell immune response might develop to the drug with very heterogeneous clinical manifestations. In recent years, however, evidence has become stronger that not all drugs need to bind covalently to the MHC-peptide complex in order to trigger an immune response. Rather, some drugs may bind directly and reversibly to immune receptors like the major histocompatibility complex (MHC) or the T cell receptor (TCR), thereby stimulating the cells similar to a pharmacological activation of other receptors. This concept has been termed pharmacological interaction with immune receptors the (p-i) concept. While the exact mechanism is still a matter of debate, non-covalent drug presentation clearly leads to the activation of drug-specific T cells as documented for various drugs (lidocaine, sulfamethoxazole (SMX), lamotrigine, carbamazepine, p-phenylendiamine, etc.). In some patients with drug hypersensitivity, such a response may occur within hours even upon the first exposure to the drug. Thus, the reaction to the drug may not be due to a classical, primary response, but rather be mediated by stimulating existing, pre-activated, peptide-specific T cells that are cross specific for the drug. In this way, certain drugs may circumvent the checkpoints for immune activation imposed by the classical antigen processing and presentation mechanisms, which may help to explain the peculiar nature of many drug hypersensitivity reactions.

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.

Update on pharmacogenetics in epilepsy: a brief review

Recent developments in the pharmacogenetics of antiepileptic drugs provide new prospects for predicting the efficacy of treatment and potential side-effects. Epilepsy is a common, serious, and treatable neurological disorder, yet current treatment is limited by high rates of adverse drug reactions and lack of complete seizure control in a significant proportion of patients. The disorder is especially suitable for pharmacogenetic investigation because treatment response can be quantified and side-effects can be assessed with validated measures. Additionally, there is substantial knowledge of the pharmacodynamics and kinetics of antiepileptic drugs, and some candidate genes implicated in the disorder have been identified. However, recent studies of the association of particular genes and their genetic variants with seizure control and adverse drug reactions have not provided unifying conclusions. This article reviews the published work and summarises the state of research in this area. Future directions for research and the application of this technology to the clinical practice of individualising treatment for epilepsy are discussed.

Epidemiology of hypersensitivity drug reactions

PURPOSE OF REVIEW

Hypersensitivity drug reactions are but one of the many different types of adverse drug reactions. They may be potentially life-threatening, prolong hospitalization, affect drug prescribing patterns of physicians and result in socioeconomic costs. This review summarizes current knowledge on the incidence, prevalence, mortality and risk factors for these reactions in different populations.

RECENT FINDINGS

Hypersensitivity reactions represent about one third of all adverse drug reactions. Adverse drug reactions affect 10-20% of hospitalized patients and more than 7% of the general population. Severe reactions including anaphylaxis, drug hypersensitivity syndromes, Stevens Johnson syndrome and toxic epidermal necrolysis are also associated with significant morbidity and mortality. Although several risk factors have been identified, their clinical importance has not been fully understood. Future progress in immunogenetics and pharmacogenetics may help identify populations at risk for specific types of reactions.

SUMMARY

Well designed epidemiological studies on hypersensitivity drug reactions are lacking as most studies have been on adverse drug reactions. Such studies will be helpful in identifying patients at risk of developing such reactions, in particular severe reactions, and implementing early preventive measures.

Theragenomic knowledge management for individualised safety of drugs, chemicals, pollutants and dietary ingredients

Severe adverse drug reactions (ADRs) are a major problem in drug development and clinical practice and the most common cause of market withdrawals of drugs. Individualised drug safety aims at the prospective identification of single patients who carry genetic predispositions for the development of serious or fatal ADRs under drug treatment. For a comprehensive individualised drug safety evaluation a clearly structured organisation, linkage and representation of diverse and heterogeneous, yet related, knowledge is imperative. To efficiently support experts in this process a platform, coined OKAPI, was specified that combines multiple concepts in knowledge management to perform ontological knowledge acquisition, processing and integration. SafeBase (TheraSTrat) is an ontology driven implementation of the OKAPI specification and an innovative, user-friendly and interactive platform for storage, management and visualisation of knowledge across multiple scientific disciplines pertinent to current and future theragenomics-based drug discovery and development and to strategies of individualised drug safety.

HLA-B genotyping to detect carbamazepine-induced Stevens-Johnson syndrome: implications for personalizing medicine

Preventing severe adverse drug reactions by identifying people at risk with a simple genetic test is the goal of many pharmacogenomic studies. Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are related, life-threatening cutaneous adverse reactions, most often caused by medication. The overall incidence and the commonly offending drugs vary among different ethnic populations. Susceptibility to such idiosyncratic reactions is thought to be genetically determined and immune mediated. Finding a strong genetic association between a particular human leukocyte antigen (HLA)-B allele and the reaction to a specific drug provides evidence that the pathogenesis of the severe cutaneous adverse drug reactions involves major histocompatibility complex-restricted presentation of a drug or its metabolites for T-cell activation. In the case of carbamazepine-induced SJS/TEN, the tight association of the HLA-B*1502 allele (sensitivity 100%, specificity 97% and odds ratio 2504) provides a plausible basis for further development of such a test to identify individuals at risk of developing this life-threatening condition.

Carbamazepine-induced acute liver failure as part of the DRESS syndrome

Carbamazepine is a widely used drug. It is commonly associated with hepatic abnormalities, ranging from an asymptomatic rise in liver function tests to acute liver failure. The most severe reaction occurs as part of a generalised hypersensitivity reaction, also known as drug reaction, eosinophilia and systemic symptoms (DRESS). We describe a case of a young adult who presented with non-specific symptoms, which progressed to fulminant hepatic failure, displaying the hallmarks of DRESS. We highlight the need for awareness of such an association.

Cellular mechanisms of T cell mediated drug hypersensitivity

Noncovalent drug presentation leads to the activation of drug-specific T cells. In some patients with hypersensitivity, such a response occurs within hours even upon the first exposure to the drug. Thus, the reaction to the drug might not be due to a classical, primary response, but rather mediated by existing, preactivated T cells that are cross specific for the drug, and have an additional (peptide) specificity as well.

Adverse hepatic drug reactions: inflammatory episodes as consequence and contributor

Susceptibility to drug toxicity is influenced by a variety of factors, both genetic and environmental. The focus of this article is the evidence addressing the hypothesis that inflammation is both a result of and a susceptibility factor for drug toxicity, with an emphasis on liver as a target organ. Results of studies suggesting a role for inflammatory mediators in the hepatotoxicity caused by acetaminophen or ethanol are discussed. For several drugs, the evidence from animal models that concurrent inflammation increases injury is presented. In addition, the occurrence of adverse drug reactions in people with preexisting inflammatory diseases is considered. The special case of idiosyncratic drug reactions is discussed and the potential raised for development of animal models for this type of drug toxicity. The conclusion is that inflammatory factors should be considered as determinants of sensitivity to adverse drug reactions.

Pharmacogenetics of antiretroviral therapy: genetic variation of response and toxicity

The application of a pharmacogenetic approach to antiretroviral drug therapy represents a significant challenge, as treatment involves multiple drugs and drug classes with the potential for significant variability in drug–host, as well as drug–drug, interactions. However, despite this inherent complexity, considerable gains have been made in understanding how genetic factors influence the efficacy and toxicity of HIV therapy. In this review the available evidence regarding genetic variation in drug disposition will be examined, including the potential for relatively polymorphic drug-metabolizing enzymes (e.g., cytochrome P450 isoforms) and drug transporters (e.g., P-glycoprotein) to influence the disposition of HIV protease inhibitor and non-nucleoside reverse transcriptase inhibitor drugs. In addition, the role of genetic variation in determining the immune response to drug-specific antigens will be considered as a potentially significant determinant of susceptibility to idiosyncratic drug reactions (e.g., major histocompatibility complex alleles associated with abacavir hypersensitivity). The current and potential clinical utility of pharmacogenetic testing in HIV management will also be emphasized.

Association of genetic variations in HLA-B region with hypersensitivity to abacavir in some, but not all, populations

Abacavir is an effective antiretroviral drug used to treat HIV-1 infection. Approximately 5% of patients treated with abacavir develop a hypersensitivity reaction that requires discontinuation of the drug. In an initial pharmacogenetic study conducted in a predominantly White male population, multiple markers in the human leukocyte antigen (HLA)-B chromosomal region were associated with hypersensitivity to abacavir. The HLA-B*5701 association has now been confirmed in White males in a subsequent, larger study (n=293, p=4.7 x 10(-18)) and is also observed in White females (n=56, p=6.8 x 10(-6)) and Hispanics (n=104, p=2.1 x 10(-4)). HLA-B*5701 was not associated with hypersensitivity in Blacks (n=78, p=0.27). HLA-B*5701 alone lacks sufficient predictive value to identify patients at risk for hypersensitivity to abacavir across diverse patient populations. Efforts are ongoing to identify markers with sufficient sensitivity and specificity to be clinically useful. Even after a marker set is identified, appropriate clinical identification and management of hypersensitivity to abacavir must remain the cornerstone of clinical practice.

Classification and epidemiology of hypersensitivity drug reactions

Nonimmune hypersensitivity reactions are unpredictable adverse drug reactions that are clinically similar to allergic reactions for which no drug-specific antibodies or T lymphocytes are identified. Few tools allow a definite diagnosis, and most of the available ones need to be validated. True epidemiologic data are limited, and most of the available information on the incidence, mortality, and socioeconomic impact should be discussed with caution.

Lipodystrophy in Patients with HIV-1 Infection: Effect of Stopping Protease Inhibitors on Tnf-α and Tnf-Receptor Levels, and on Metabolic Parameters

Objective

To evaluate the effects of stopping treatment with protease inhibitors (PIs) on tumour necrosis factor (TNF)-α and TNF-receptor levels, and on the metabolic and morphological abnormalities seen in patients with lipodystrophy.

Design

Longitudinal study.

Methods

Ten HIV-positive patients with lipodystrophy (LD) were studied whilst on PIs (LD1) and 3 months after stopping PIs (LD2) together with 10 HIV-positive subjects on PIs without LD (controls). TNF-α and TNF-receptor levels, insulin resistance parameters, lipid and hormonal profiles, body composition and fat distribution were measured in all subjects.

Results

TNF-α, TNF-receptor I (-RI) and TNF-RII levels were significantly lower in controls ( P=0.02) than in subjects with LD, and there was a significant decrease in TNF-RI and TNF-RII levels ( P=0.01 and 0.03, respectively) on stopping PIs. Insulin levels and the homeostasis model assessment for insulin resistance (HOMA-IR) index were significantly higher in LD1 subjects ( P=0.02) than in controls but did not alter when PIs were stopped. Bioelectrical impedance analysis showed a significant decrease on stopping PIs but CT scans showed no significant difference in fat distribution. Apart from high-density lipoprotein, there was no change in lipid parameters on stopping PIs. There was no difference in the level of testosterone, sex hormone binding globulin and cortisol between the three groups.

Conclusion

Our results show that TNF-α activity in patients with LD is modulated by PIs. This was not accompanied by significant changes in body habitus or insulin resistance, although this may have been a consequence of the short follow-up in this study.

Characterization of drug-specific T cells in lamotrigine hypersensitivity

BACKGROUND

Lamotrigine is associated with hypersensitivity reactions, which are most commonly characterized by skin rash. An immune etiology has been postulated, though the nature of this is unclear.

OBJECTIVES

The aim of this study was to characterize the role of T cells in lamotrigine hypersensitivity.

METHODS

A lymphocyte transformation test was performed on 4 hypersensitive patients. Lymphocytes from 3 of 4 lamotrigine-hypersensitive patients proliferated when stimulated with lamotrigine. T-cell clones were generated from one patient to further characterize the nature of the T-cell involvement. Cells were characterized in terms of their phenotype, functionality, and mechanisms of antigen presentation and cytotoxicity.

RESULTS

Of the 44 drug-specific T-cell clones generated, most were CD4(+) with occasional CD8(+) cells. All clones expressed the alphabeta T-cell receptor; several Vbeta 5.1(+) or 9(+) T-cell clones were generated. All clones also expressed the skin-homing receptor cutaneous lymphocyte antigen. Lamotrigine-stimulated T cells were cytotoxic and secreted perforin, IFN-gamma, IL-5, and macrophage inflammatory protein 1alpha, macrophage inflammatory protein 1beta, RANTES, and I-309. Lamotrigine was present on HLA-DR and HLA-DQ by antigen-presenting cells in the absence of drug metabolism and processing. The T-cell receptor of certain clones could accommodate analogs of lamotrigine, but no cross-reactivity was seen with other anticonvulsants.

CONCLUSIONS

Our data provide evidence that T cells are involved in the pathogenesis of some lamotrigine-hypersensitivity reactions. The identification of drug-specific cells that express cutaneous lymphocyte antigen and type 1 cytokines after T-cell receptor activation is consistent with the clinical symptoms. Furthermore, identification of large numbers of Vbeta 5.1(+) T cells suggests that polymorphisms within T-cell receptor genes might act as determinants of susceptibility.

Hypersensitivity reactions to carbamazepine: characterization of the specificity, phenotype, and cytokine profile of drug-specific T cell clones

Administration of carbamazepine (CBZ) causes hypersensitivity reactions clinically characterized by skin involvement, eosinophilia, and systemic symptoms. These reactions have an immune etiology; however, the role of T cells is not well defined. The aim of this study was to characterize the specificity, phenotype, and cytokine profile of CBZ-specific T cells derived from hypersensitive individuals. Proliferation of blood lymphocytes was measured using the lymphocyte transformation test. CBZ-specific T cell clones were generated by serial dilution and characterized in terms of their cluster of differentiation and T cell receptor V beta phenotype. Proliferation, cytotoxicity, and cytokine secretion were measured by [(3)H]thymidine incorporation, (51)Cr release, and enzyme-linked immunosorbent assay, respectively. HLA blocking antibodies were used to study the involvement of antigen-presenting cells. The specificity of the drug T cell receptor interaction was studied using CBZ metabolites and other structurally related compounds. Lymphocytes from hypersensitive patients (stimulation index: 32.1 +/- 24.2 [10 microg ml(-1)]) but not control patients (stimulation index: 1.2 +/- 0.4 [10 microg ml(-1)]) proliferated upon stimulation with CBZ. Of 44 CBZ-specific T cell clones generated, 10 were selected for further analysis. All 10 clones were either CD4+ or CD4+/CD8+, expressed the alpha beta T cell receptor, secreted IFN-gamma, and were cytotoxic. T-cell recognition of CBZ was dependent on the presence of HLA class II (DR/DQ)-matched antigen-presenting cells. The T cell receptor of certain clones could accommodate some CBZ metabolites, but no cross-reactivity was seen with other anticonvulsants or structural analogs. These studies characterize drug-specific T cells in CBZ-hypersensitive patients that are phenotypically different from T cells involved in other serious cutaneous adverse drug reactions.

Immunopharmacology of hypersensitivity reactions to drugs

Drug hypersensitivity reactions are characterized by their unpredictability, lack of simple dose-dependency, host sensitivity, and potentially serious clinical outcome. They occur in a small proportion of patients, and usually the predisposing factors are unknown, although there is increasing evidence for genetic predisposition and disease being significant risk factors. The current understanding of the chemical basis of immune-mediated reactions is based on the hapten hypothesis, which requires drug bioactivation, covalent binding to proteins, followed by uptake, antigen processing, and a polyclonal immune response. The recently proposed "danger hypothesis" can be considered to be an essential addition to the hapten hypothesis. According to the danger hypothesis, the immune response to a drug-derived antigen requires the presence of co-stimulatory signals and cytokines, which propagate and determine the type of immune response. The "danger signal" might result from chemical, physical, or viral stress.

Mechanistic perspectives on sulfonamide-induced cutaneous drug reactions

PURPOSE OF REVIEW

Idiosyncratic drug reactions continue to limit the therapeutic utility of sulfonamide drugs because of their associated morbidity and mortality. Cutaneous reactions are the predominant reasons for withdrawal of such drugs from use in patients. As a consequence of the recognized metabolic and immunologic capability of the skin, an understanding of the pathogenic role of this tissue in the development of sulfonamide-induced cutaneous drug reactions may provide insight into the mechanisms and risk factors for these and other adverse drug events.

RECENT FINDINGS

In the present review we discuss currently available mechanistic information, including issues related to drug bioactivation and adduct formation, immunoresponsiveness, and immune dysregulation, for the development of sulfonamide-induced (delayed-type) cutaneous drug reactions. The potential application of findings from several related areas of research are also discussed within the context of the pathogenesis of these cutaneous reactions.

SUMMARY

Despite progress, numerous unresolved issues support the testing of novel hypotheses, the search for additional risk factors, and the need for a global approach, including links between laboratory and clinical paradigms. These issues must be addressed if we are to gain an understanding of the mechanistic bases for these cutaneous drug reactions.

Association between presence of HLA-B*5701, HLA-DR7, and HLA-DQ3 and hypersensitivity to HIV-1 reverse-transcriptase inhibitor abacavir

BACKGROUND

The use of abacavir--a potent HIV-1 nucleoside-analogue reverse-transcriptase inhibitor--is complicated by a potentially life-threatening hypersensitivity syndrome in about 5% of cases. Genetic factors influencing the immune response to abacavir might confer susceptibility. We aimed to find associations between MHC alleles and abacavir hypersensitivity in HIV-1-positive individuals treated with abacavir.

METHODS

MHC region typing was done in the first 200 Western Australian HIV Cohort Study participants exposed to abacavir. Definite abacavir hypersensitivity was identified in 18 cases, and was excluded in 167 individuals with more than 6 weeks' exposure to the drug (abacavir tolerant). 15 individuals experienced some symptoms but did not meet criteria for abacavir hypersensitivity. p values were corrected for comparisons of multiple HLA alleles (p(c)) by multiplication of the raw p value by the estimated number of HLA alleles present within the loci examined.

FINDINGS

HLA-B*5701 was present in 14 (78%) of the 18 patients with abacavir hypersensitivity, and in four (2%) of the 167 abacavir tolerant patients (odds ratio 117 [95% CI 29-481], p(c)<0.0001), and the HLA-DR7 and HLA-DQ3 combination was found in 13 (72%) of hypersensitive and five (3%) of tolerant patients (73 [20-268], p(c)<0.0001 ). HLA-B*5701, HLA-DR7, and HLA-DQ3 were present in combination in 13 (72%) hypersensitive patients and none of the tolerant patients (822 [43-15 675], p(c)<0.0001). Other MHC markers also present on the 57.1 ancestral haplotype to which the three markers above belong confirmed the presence of haplotype-specific linkage disequilibrium, and mapped potential susceptibility loci to a region bounded by C4A6 and HLA-C. Within the entire abacavir-exposed cohort (n=200), presence of HLA-B*5701, HLA-DR7, and HLA-DQ3 had a positive predictive value for hypersensitivity of 100%, and a negative predictive value of 97%.

INTERPRETATION

Genetic susceptibility to abacavir hypersensitivity is carried on the 57.1 ancestral haplotype. In our population, withholding abacavir in those with HLA-B*5701, HLA-DR7, and HLA-DQ3 should reduce the prevalence of hypersensitivity from 9% to 2.5% without inappropriately denying abacavir to any patient.

Genetic susceptibility to adverse drug reactions

Adverse drug reactions (ADRs) are a major clinical problem. Genetic factors can determine individual susceptibility to both dose-dependent and dose-independent ADRs. Determinants of susceptibility include kinetic factors, such as gene polymorphisms in cytochrome P450 enzymes, and dynamic factors, such as polymorphisms in drug targets. The relative importance of these factors will depend on the nature of the ADR; however, it is likely that more than one gene will be involved in most instances. In the future, whole genome single nucleotide polymorphism (SNP) profiling might allow an unbiased method of determining genetic predisposing factors for ADRs, but might be limited by the lack of adequate numbers of patient samples. The overall clinical utility of genotyping in preventing ADRs needs to be proven by the use of prospective randomized controlled clinical trials.