Mechanisms of drug-induced delayed-type hypersensitivity reactions in the skin

Why drug exposure is frequently associated with T-cell mediated cutaneous hypersensitivity reactions

Cutaneous hypersensitivity reactions represent the most common manifestation of drug allergy seen in the clinic, with 25% of all adverse drug reactions appearing in the skin. The severity of cutaneous eruptions can vastly differ depending on the cellular mechanisms involved from a minor, self-resolving maculopapular rash to major, life-threatening pathologies such as the T-cell mediated bullous eruptions, i.e., Stevens Johnson syndrome/toxic epidermal necrolysis. It remains a significant question as to why these reactions are so frequently associated with the skin and what factors polarise these reactions towards more serious disease states. The barrier function which the skin performs means it is constantly subject to a barrage of danger signals, creating an environment that favors elicitation. Therefore, a critical question is what drives the expansion of cutaneous lymphocyte antigen positive, skin homing, T-cell sub-populations in draining lymph nodes. One answer could be the heterologous immunity hypothesis whereby tissue resident memory T-cells that express T-cell receptors (TCRs) for pathogen derived antigens cross-react with drug antigen. A significant amount of research has been conducted on skin immunity in the context of contact allergy and the role of tissue specific antigen presenting cells in presenting drug antigen to T-cells, but it is unclear how this relates to epitopes derived from circulation. Studies have shown that the skin is a metabolically active organ, capable of generating reactive drug metabolites. However, we know that drug antigens are displayed systemically so what factors permit tolerance in one part of the body, but reactivity in the skin. Most adverse drug reactions are mild, and skin eruptions tend to be visible to the patient, whereas minor organ injury such as transient transaminase elevation is often not apparent. Systemic hypersensitivity reactions tend to have early cutaneous manifestations, the progression of which is halted by early diagnosis and treatment. It is apparent that the preference for cutaneous involvement of drug hypersensitivity reactions is multi-faceted, therefore this review aims to abridge the findings from literature on the current state of the field and provide insight into the cellular and metabolic mechanisms which may contribute to severe cutaneous adverse reactions.

Bilateral tonic seizures probably induced by eperisone hydrochloride: a case report

Eperisone hydrochloride is a central muscle relaxant used to treat osteoporosis. Seizures are rare side effects of eperisone hydrochloride and have been previously reported in the medical literature in overdose situations but not at regular doses. This case report describes a 42-year-old male painter who developed severe bilateral tonic seizures after the initiation of eperisone hydrochloride at regular doses for low back pain. Symptoms gradually eased in the days following the discontinuation of eperisone hydrochloride and antiepileptic treatment, with no recurrence. This rare adverse drug reaction warrants clinical awareness; however, the mechanisms underlying these adverse reactions remain to be clarified.

Nrf2 regulates the activation of THP-1 cells induced by chloral hydrate

Trichloroethylene (TCE) triggers a severe hypersensitivity syndrome in the occupational population dependent on dendritic cells (DCs). Chloral hydrate (CH), the major oxidative metabolite of TCE, has been proved to be the culprit causative substance of TCE-induced hypersensitivity by human patch tests. Because redox imbalance is essential for chemical sensitizers-induced maturation of DCs, we predicted that CH would activate DCs by the nuclear factor E2-related factor 2 (Nrf2)-mediated antioxidant response. This study selected THP-1 cells as the in vitro DC model, and we evaluated the cell activation markers, intracellular oxidative stress, and Nrf2 pathway related genes expression in response to CH in THP-1 cells. CH displayed significant stimulation of THP-1 cells activation, including CD54 and CD86 expression, IL-8 release, and cell migration, and damaged the redox balance by triggering ROS generation, GSH consumption, and antioxidase activities modulation. The levels of Nrf2 and its downstream genes (HO-1 and NQO1) in mRNA and protein expressions were upregulated by CH, and CH also promoted the nuclear translocation of Nrf2. Subsequently, we investigated the effects of antioxidant on Nrf2-mediated cell defense in CH treated cells. Pretreatment with curcumin dramatically reduced cell activation and oxidative stress triggered by CH in THP-1 cells. We also confirmed the specific role of Nrf2 in CH-induced cell activation using NRF2-knockout cells. Deficiency of Nrf2 inhibited cell activation and downregulated HO-1 and NQO1 expression in CH-challenged cells. These findings suggest that Nrf2-dependent redox homeostasis plays a pivotal role in CH-induced activation of THP-1 cells, thereby providing new knowledge of the allergen as well as the molecular mechanism involving in TCE-induce hypersensitivity syndrome.

Pharmacists' role in detection and evaluation of adverse drug reactions: Developing proactive systems for pharmacosurveillance

PURPOSE

To identify current challenges in detection of medication-related symptoms, and review technology-based opportunities to increase the patient-centeredness of postmarketing pharmacosurveillance to promote more accountable, safer, patient-friendly, and equitable medication prescribing.

SUMMARY

Pharmacists have an important role to play in detection and evaluation of adverse drug reactions (ADRs). The pharmacist's role in medication management should extend beyond simply dispensing drugs, and this article delineates the rationale and proactive approaches for pharmacist detection and assessment of ADRs. We describe a stepwise approach for assessment, best practices, and lessons learned from a pharmacist-led randomized trial, the CEDAR (Calling for Detection of Adverse Drug Reactions) project.

CONCLUSION

Health systems need to be redesigned to more fully utilize health information technologies and pharmacists in detecting and responding to ADRs.

Evaluation of Delayed-Type Hypersensitivity to Antineoplastic Drugs-An Overview

Nowadays, clinical practice encounters the problem of delayed-type hypersensitivity (DTH) induced by several drugs. Antineoplastic treatments are among the drugs which show an elevated proportion of DHT reactions, leading to the worsening of patients' quality of life. The range of symptoms in DHT reactions can vary from mild, such as self-limiting maculopapular eruptions, to severe, such as Stevens-Johnson Syndrome. The development of these reactions supposes a negative impact, not only by limiting patients' quality of life, but also leading to economic loss due to market withdrawal of the affected drugs and high hospitalization costs. However, despite this problem, there are no available standard in vitro or in vivo methods that allow for the evaluation of the sensitizing potential of drugs in the preclinical phase. Therefore, the aim of this review is to summarize the skin reactions caused by the different antineoplastic families, followed by a comprehensive evaluation of the in vitro and in vivo methods used to detect DTHs and that could be suitable to test antineoplastic hypersensitivity reactions.

Genomic Risk Factors Driving Immune-Mediated Delayed Drug Hypersensitivity Reactions

Adverse drug reactions (ADRs) remain associated with significant mortality. Delayed hypersensitivity reactions (DHRs) that occur greater than 6 h following drug administration are T-cell mediated with many severe DHRs now associated with human leukocyte antigen (HLA) risk alleles, opening pathways for clinical prediction and prevention. However, incomplete negative predictive value (NPV), low positive predictive value (PPV), and a large number needed to test (NNT) to prevent one case have practically prevented large-scale and cost-effective screening implementation. Additional factors outside of HLA contributing to risk of severe T-cell-mediated DHRs include variation in drug metabolism, T-cell receptor (TCR) specificity, and, most recently, HLA-presented immunopeptidome-processing efficiencies via endoplasmic reticulum aminopeptidase (ERAP). Active research continues toward identification of other highly polymorphic factors likely to impose risk. These include those previously associated with T-cell-mediated HLA-associated infectious or auto-immune disease such as Killer cell immunoglobulin-like receptors (KIR), epistatically linked with HLA class I to regulate NK- and T-cell-mediated cytotoxic degranulation, and co-inhibitory signaling pathways for which therapeutic blockade in cancer immunotherapy is now associated with an increased incidence of DHRs. As such, the field now recognizes that susceptibility is not simply a static product of genetics but that individuals may experience dynamic risk, skewed toward immune activation through therapeutic interventions and epigenetic modifications driven by ecological exposures. This review provides an updated overview of current and proposed genetic factors thought to predispose risk for severe T-cell-mediated DHRs.

Aspirin "Allergy"-Induced Thrombocytopenia: A Case Report

Aspirin is clinically widely used to inhibit platelet aggregation after coronary intervention. Herein we describe a case of aspirin-induced thrombocytopenia that may be related to allergy to aspirin. A 47-year-old man developed a delayed hypersensitivity reaction to aspirin, with pruritus, purpura and thrombocytopenia, increased peripheral blood eosinophils and enlarged inguinal lymph node. All the symptoms disappeared in 2 years after stopping aspirin. Aspirin-induced thrombocytopenia related to allergy is rarely reported. Aspirin hypersensitivity should be taken into consideration in case of unexplained thrombocytopenia in patients taking aspirin. Aspirin "allergy"-induced thrombocytopenia may involve both aspirin related IgG and IgE antibodies.

Drug-Induced Skin Adverse Reactions: The Role of Pharmacogenomics in Their Prevention

Adverse drug reactions (ADRs) affect many patients and remain a major public health problem, as they are a common cause of morbidity and mortality. It is estimated that ADRs are responsible for about 6% of hospital admissions and about 9% of hospitalization costs. Skin is the organ that is most frequently involved in ADRs. Drug-induced skin injuries vary from mild maculopapular eruptions (MPE) to severe cutaneous adverse reactions (SCARs) that are potentially life threatening. Genetic factors have been suggested to contribute to these SCARs, and most significant genetic associations have been identified in the major histocompatibility complex (MHC) genes. Common drugs associated with SCARs connected with strong genetic risk factors include antiepileptic drugs (AEDs), allopurinol, abacavir, nevirapine, sulfonamides, dapsone, non-steroidal anti-inflammatory drugs (NSAIDs), and analgesic drugs. However, genetic associations vary between different ethnic populations. Differences may in part be explained by the different prevalence of HLA (human leukocyte antigen) alleles among ethnic groups. In this review, we present and discuss the recent advances in genetic associations with ADRs in the skin. Many of these ADRs are now preventable with pharmacogenetic screening.

Xenobiotica-metabolizing enzymes in the skin of rat, mouse, pig, guinea pig, man, and in human skin models

Studies on the metabolic fate of medical drugs, skin care products, cosmetics and other chemicals intentionally or accidently applied to the human skin have become increasingly important in order to ascertain pharmacological effectiveness and to avoid toxicities. The use of freshly excised human skin for experimental investigations meets with ethical and practical limitations. Hence information on xenobiotic-metabolizing enzymes (XME) in the experimental systems available for pertinent studies compared with native human skin has become crucial. This review collects available information of which—taken with great caution because of the still very limited data—the most salient points are: in the skin of all animal species and skin-derived in vitro systems considered in this review cytochrome P450 (CYP)-dependent monooxygenase activities (largely responsible for initiating xenobiotica metabolism in the organ which provides most of the xenobiotica metabolism of the mammalian organism, the liver) are very low to undetectable. Quite likely other oxidative enzymes [e.g. flavin monooxygenase, COX (cooxidation by prostaglandin synthase)] will turn out to be much more important for the oxidative xenobiotic metabolism in the skin. Moreover, conjugating enzyme activities such as glutathione transferases and glucuronosyltransferases are much higher than the oxidative CYP activities. Since these conjugating enzymes are predominantly detoxifying, the skin appears to be predominantly protected against CYP-generated reactive metabolites. The following recommendations for the use of experimental animal species or human skin in vitro models may tentatively be derived from the information available to date: for dermal absorption and for skin irritation esterase activity is of special importance which in pig skin, some human cell lines and reconstructed skin models appears reasonably close to native human skin. With respect to genotoxicity and sensitization reactive-metabolite-reducing XME in primary human keratinocytes and several reconstructed human skin models appear reasonably close to human skin. For a more detailed delineation and discussion of the severe limitations see the Conclusions section in the end of this review.

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

Background

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

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

Results

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

Conclusion

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

Electronic supplementary material

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

Immune responses induced by diclofenac or carbamazepine in an oral exposure model using TNP-Ficoll as reporter antigen

Immune-mediated drug hypersensitivity reactions (IDHR) may result from immuno-sensitization to a drug-induced neo-antigen. They rarely occur in patients and are usually not predicted preclinically using standard toxicity studies. To assess the potential of a drug to induce T-cell sensitization, trinitrophenyl (TNP)-Ficoll was used here as a bystander antigen in animal experiments. TNP-Ficoll will only elicit TNP-specific IgG antibodies in the presence of non-cognate T-cell help. Therefore, the presence of TNP-specific IgG antibodies after co-injection of drug and TNP-Ficoll was indicative of T-cell sensitization potential. This TNP-Ficoll-approach was used here to characterize T-cell help induced by oral exposure to diclofenac (DF) or carbamazepine (CMZ). DF or CMZ was administered orally to BALB/c mice and after 3 w, the mice were challenged in a hind paw with TNP-Ficoll and a dose of the drug that by itself does only elicit a sub-optimal popliteal lymph node assay (PLNA) response. T-cell-dependent responses were then evaluated in paw-draining popliteal lymph nodes (PLN). Also, shortly after oral exposure, mesenteric lymph nodes (MLN) were excised for evaluation of local responses. Both drugs were able to increase PLN cellularity and TNP-specific IgG₁ production after challenge. Both DF and CMZ stimulated CD4⁺and CD8⁺ T-cells and caused shifts of the subsets toward an effector phenotype. DF, but not CMZ, appeared to stimulate interferon (IFN)-γ production. Remarkably, depletion of CD8⁺, but not CD4⁺, T-cells reduced TNP-specific IgG₁ production, and was more pronounced in CMZ- than in DF-exposed animals. Local responses in the MLN caused by DF or CMZ also showed shifts of CD4⁺and CD8⁺-cells toward a memory phenotype. Together, the data indicate that oral exposure to CMZ and DF differentially induced neo-antigen-specific T-cell reactions in the PLNA.

Pharmacogenomics of off-target adverse drug reactions

Off-target adverse drug reactions (ADRs) are associated with significant morbidity and costs to the healthcare system, and their occurrence is not predictable based on the known pharmacological action of the drug's therapeutic effect. Off-target ADRs may or may not be associated with immunological memory, although they can manifest with a variety of shared clinical features, including maculopapular exanthema, severe cutaneous adverse reactions (SCARs), angioedema, pruritus and bronchospasm. Discovery of specific genes associated with a particular ADR phenotype is a foundational component of clinical translation into screening programmes for their prevention. In this review, genetic associations of off-target drug-induced ADRs that have a clinical phenotype suggestive of an immunologically mediated process and their mechanisms are highlighted. A significant proportion of these reactions lack immunological memory and current data are informative for these ADRs with regard to disease pathophysiology, therapeutic targets and biomarkers which may identify patients at greatest risk. Although many serious delayed immune-mediated (IM)-ADRs show strong human leukocyte antigen associations, only a small subset have successfully been implemented in screening programmes. More recently, other factors, such as drug metabolism, have been shown to contribute to the risk of the IM-ADR. In the future, pharmacogenomic targets and an understanding of how they interact with drugs to cause ADRs will be applied to drug design and preclinical testing, and this will allow selection of optimal therapy to improve patient safety.

Oral exposure to immunostimulating drugs results in early changes in innate immune parameters in the spleen

The development of immune-dependent drug hypersensitivity reactions (IDHR) is likely to involve activation of the innate immune system to stimulate neo-antigen specific T-cells. Previously it has been shown that, upon oral exposure to several drugs with immune-adjuvant capacity, mice developed T-cell-dependent responses to TNP-OVA. These results were indicative of the adjuvant potential of these drugs. The present study set out to evaluate the nature of this adjuvant potential by focusing on early immune changes in the spleen, by testing several drugs in the same experimental model. Mice were exposed to one or multiple oral doses of previously-tested drugs: the non-steroidal-anti-inflammatory drug (NSAID) diclofenac (DF), the analgesic acetaminophen (APAP), the anti-epileptic drug carbamazepine (CMZ) or the antibiotic ofloxacin (OFLX). Within 24 h after the final dosing, early innate and also adaptive immune parameters in the spleen were examined. In addition, liver tissue was also evaluated for damage. Exposure to APAP resulted in severe liver damage, increased levels of serum alanine aminotransferase (ALT) and local MIP-2 expression. DF exposure did not cause visible liver damage, but did increase liver weight. DF also elicited clear effects on splenic innate and adaptive immune cells, i.e. increased levels of NK cells and memory T-cells. Furthermore, an increase in plasma MIP-2 levels combined with an influx of neutrophils into the spleen was observed. OFLX and CMZ exposure resulted in increased liver weights, MIP-2 expression and up-regulation of co-stimulatory molecules on antigen-presenting cells (APC). The data suggested that multiple immune parameters were altered upon exposure to drugs known to elicit immunosensitization and that broad evaluation of immune changes in straightforward short-term animal models is needed to determine whether a drug may harbor the hazard to induce IDHR. The oral exposure approach as used here may be applied in the future as an immunotoxicological research tool in this type of evaluation.

Allopurinol induces innate immune responses through mitogen-activated protein kinase signaling pathways in HL-60 cells

Allopurinol, an inhibitor of xanthine oxidase, is a frequent cause of severe cutaneous adverse reactions (SCARs) in humans, including drug rash with eosinophilia and systemic symptoms, Stevens-Johnson syndrome and toxic epidermal necrolysis. Although SCARs have been suspected to be immune-mediated, the mechanisms of allopurinol-induced SCARs remain unclear. In this study, we examined whether allopurinol has the ability to induce innate immune responses in vitro using human dendritic cell (DC)-like cell lines, including HL-60, THP-1 and K562, and a human keratinocyte cell line, HaCaT. In this study, we demonstrate that treatment of HL-60 cells with allopurinol significantly increased the mRNA expression levels of interleukin-8, monocyte chemotactic protein-1 and tumor necrosis factor α in a time- and concentration-dependent manner. Furthermore, allopurinol induced the phosphorylation of mitogen-activated protein kinases (MAPK), such as c-Jun N-terminal kinase and extracellular signal-regulated kinase, which regulate cytokine production in DC. In addition, allopurinol-induced increases in cytokine expression were inhibited by co-treatment with the MAPK inhibitors. Collectively, these results suggest that allopurinol has the ability to induce innate immune responses in a DC-like cell line through activation of the MAPK signaling pathways. These results indicate that innate immune responses induced by allopurinol might be involved in the development of allopurinol-induced SCARs. Copyright © 2015 John Wiley & Sons, Ltd.

Skin response to a carcinogen involves the xenobiotic receptor pregnane X receptor

Skin is in daily contact with potentially harmful molecules from the environment such as cigarette smoke, automobile emissions, industrial soot and groundwater. Pregnane X receptor (PXR) is a transcription factor expressed in liver and intestine that is activated by xenobiotic chemicals including drugs and environmental pollutants. Topical application of the tumor initiator 7,12-dimethylbenz(a)anthracene (DMBA) enhances Pxr, Cyp1a1, Cyp1b1 and Cyp3a11, but not Ahr expression in the skin. Surprisingly, DMBA-induced Pxr upregulation is largely impaired in Langerin(+) cell-depleted skin, suggesting that DMBA mainly triggers Pxr in Langerin(+) cells. Furthermore, PXR deficiency protects from DNA damage in epidermal cells but to a lesser extent than aryl hydrocarbon receptor (AHR) deficiency. Interestingly, skin exposure to low doses of DMBA induces migration of PXR-deficient but not of wild-type and AHR-deficient Langerhans cells (LCs). PXR-humanized mice show a marked increase in DNA damage to epidermal cells after topical application of DMBA, demonstrating relevance of these findings in human tissue. This is the first report suggesting that carcinogens might trigger PXR in epidermal cells, particularly in LCs, thus leading to DNA damage. Further studies are required to better delineate the role of PXR in cutaneous carcinogenesis.

Xenobiotic-metabolizing enzymes in the skin of rat, mouse, pig, guinea pig, man, and in human skin models

The exposure of the skin to medical drugs, skin care products, cosmetics, and other chemicals renders information on xenobiotic-metabolizing enzymes (XME) in the skin highly interesting. Since the use of freshly excised human skin for experimental investigations meets with ethical and practical limitations, information on XME in models comes in the focus including non-human mammalian species and in vitro skin models. This review attempts to summarize the information available in the open scientific literature on XME in the skin of human, rat, mouse, guinea pig, and pig as well as human primary skin cells, human cell lines, and reconstructed human skin models. The most salient outcome is that much more research on cutaneous XME is needed for solid metabolism-dependent efficacy and safety predictions, and the cutaneous metabolism comparisons have to be viewed with caution. Keeping this fully in mind at least with respect to some cutaneous XME, some models may tentatively be considered to approximate reasonable closeness to human skin. For dermal absorption and for skin irritation among many contributing XME, esterase activity is of special importance, which in pig skin, some human cell lines, and reconstructed skin models appears reasonably close to human skin. With respect to genotoxicity and sensitization, activating XME are not yet judgeable, but reactive metabolite-reducing XME in primary human keratinocytes and several reconstructed human skin models appear reasonably close to human skin. For a more detailed delineation and discussion of the severe limitations see the “Overview and Conclusions” section in the end of this review.

Profiling the physiological and molecular response to sulfonamidic drug in Procambarus clarkii

Sulfamethoxazole (SMZ) is one of the most widely employed sulfonamides. Because of the widespread use of SMZ, a considerable amount is indeed expected to be introduced into the environment. The cytotoxicity of SMZ relies mainly on arylhydroxylamine metabolites (S-NOH) of SMZ and it is associated with the production of reactive oxygen species (ROS). There is limited information about the toxic potential of SMZ at the cellular and molecular levels, especially in aquatic and/or non-target organisms. In the present study, the red swamp crayfish (Procambarus clarkii), being tolerant to extreme environmental conditions and resistant to disease, was used as a model organism to profile the molecular and physiological response to SMZ. Haemolymphatic-immunological parameters such as glucose serum levels and total haemocyte counts were altered; moreover, a significant increase in Hsp70 plasma levels was detected for the first time. Variations at the transcriptional level of proinflammatory genes (cyclooxygenase-1, COX 1, and cyclooxygenase-2, COX 2), antioxidant enzymes (glutathione-S-transferase, GST and manganese superoxide dismutase MnSOD), stress response and Fenton reaction inhibitor genes (heat-shock protein 70 HSP70, metallothionein, MT and ferritin, FT) were evaluated, and alterations in the canonical gene expression patterns emerged. Considering these results, specific mechanisms involved in maintaining physiological homeostasis and adaptation in response to perturbations are suggested.

Exploratory toxicology as an integrated part of drug discovery. Part II: Screening strategies

In an effort to reduce toxicity-related attrition, different strategies have been implemented throughout the pharmaceutical industry. Previously (in Part I), we have outlined our 'integrated toxicology' strategy, which aims to provide timely go/no-go decisions (fail early) but also to show a direction to the drug discovery teams (showing what will not fail). In this review (Part II of the series) we describe our compound testing strategies with respect to cardiovascular safety, hepatotoxicity, genotoxicity, immunotoxicity and exploratory in vivo toxicity. We discuss the in vitro, ex vivo and in vivo assays and models we employ to assess safety risks and optimize compound series during the drug discovery process, including their predictivity and the decisions they generate.

T-cell receptor and carbamazepine-induced Stevens-Johnson syndrome and toxic epidermal necrolysis: understanding a hypersensitivity reaction

Ample evidence exists to support the view that drug hypersensitivity is mediated by adaptive immunity, which involves MHC-restricted drug presentation, activation and clonal expansion of T cells. The specific MHC molecules implicated in hypersensitivity have been identified; for example, HLA-B*5701 in abacavir-induced drug hypersensitivity and HLA-B*1502 in carbamazepine-induced Stevens-Johnson syndrome. However, little is known about the role of drug-specific T cells and their T-cell receptors (TCRs) in the pathogenesis of drug hypersensitivity. Using the combination of a strong HLA-B*1502 predisposition in carbamazepine-induced Stevens-Johnson syndrome and applying global analysis of the TCR repertoire, restricted and common TCR usage in the development of severe drug hypersensitivity have recently been documented. This article reviews recent advances in the understanding of the pathogenic role of drug-specific T cells and their TCRs in the development of drug hypersensitivity and provides an analysis of their potential clinical implications.

Getting under the skin of adverse drug reactions

Cutaneous drug reactions are among the most commonly reported adverse drug reactions. Drugs prescribed by orthopedic surgeons, such as antibiotics, opiates, and nonsteroidal anti-inflammatory drugs, are common offenders. Cutaneous drug reactions can range from those that are common, mild nuisances to those that are rare, severe, and life-threatening. Medications should be considered part of a differential diagnosis for any dermatologic condition. It is important to recognize the different clinical features and common drugs that are related to each type of reaction. This review characterizes the different forms of cutaneous drug reactions and the clinical features, proposed mechanisms, and drugs frequently associated with each.

Piperacillin/tazobactam induced thrombocytopaenia--a delayed response

A 48-year-old lady who presented with sepsis secondary to a pelvi-ureteric junction obstruction was treated with an extended course of piperacillin/tazobactam. Four days after completing the course she developed thrombocytopaenia. Intravenous immunoglobulin was required to bring her platelet count back to normal. In the absence of other causes the authors believe that a delayed reaction to piperacillin/tazobactam was the cause of her thrombocytopaenia.

ABCC2 Haplotype is Associated With Antituberculosis Drug-Induced Maculopapular Eruption

Genetic variants in ATP-binding cassette (ABC) transporter genes are associated with increased susceptibility to adverse drug reactions. We hypothesized that genetic variant ABC transporters (ABCB1 and ABCC2) may be candidate markers for predicting maculopapular eruption (MPE) induced by antituberculosis therapy. We compared the genotype distributions of single nucleotide polymorphisms and haplotypes in the ABCB1 and ABCC2 genes between 62 antituberculosis drug (ATD)-induced MPE cases and 159 ATD-tolerant controls using multivariate logistic regression analysis. There was no significant association between genetic polymorphisms in ABCB1 and ATD-induced MPE (P>0.05). Among seven selected SNPs of ABCC2, IVS3-49C>T in intron and I1324I were associated with ATD-induced MPE (P=0.029 and 0.036, respectively). In an analysis of the ABCC2 haplotypes (ht; -1549G>A_-24C>T_IVS3-49C>T_V417I), ht1[G-C-C-G] was significantly associated with ATD-induced MPE (P=0.032, OR=0.35, 95% CI: 0.16-0.95). No significant association between the other haplotypes and ATD-induced MPE was observed. An ABCC2 haplotype is associated with the presence of ATD-induced MPE in patients with tuberculosis and may be a genetic risk factor for the development of MPE induced by ATD.

Chemical sensitization and allergotoxicology

Chemical sensitization remains an important environmental and occupational health issue. A wide range of substances have been shown to possess the ability to induce skin sensitization or respiratory sensitization. As a consequence, there is a need to have appropriate methods to identify sensitizing agents. Although a considerable investment has been made in exploring opportunities to develop methods for hazard identification and characterization, there are, as yet, no validated nonanimal methods available. A state of the art of the different in vitro approaches to identify contact and respiratory capacity of chemicals is covered in this chapter.

NAT2, CYP2C9, CYP2C19, and CYP2E1 genetic polymorphisms in anti-TB drug-induced maculopapular eruption

PURPOSE

It has been suggested that drug-metabolizing enzymes might play important roles in the development of anti-tuberculosis drug (ATD)-induced maculopapular eruption (MPE), as in ATD-induced hepatitis. We investigated the associations between the genetic polymorphisms of drug-metabolizing enzymes and ATD-induced MPE.

METHODS

We enrolled 62 patients with ATD-induced MPE (mean age 47.2 ± 19.0, male 59.7%) and 159 patients without any adverse reactions to ATD (mean age 42.8 ± 17.6, male 65.4%), among patients with pulmonary tuberculosis (TB) and/or TB pleuritis and treated with first-line anti-TB medications, including isoniazid, rifampin, ethambutol, and pyrazinamide. We compared the genotype distributions of single nucleotide polymorphisms and haplotypes in four drug-metabolizing enzymes (N-acetyltransferase 2 (NAT2), cytochrome P450 (CYP) 2 C9, CYP2C19, and CYP2E1) among patients with ATD-induced MPE and patients tolerant to ATD using a multivariate logistic regression analysis. These analyses were made without identification of the responsible ATD.

RESULTS

-1565 C > T of CYP2C9 showed a significant association with ATD-induced MPE (P = 0.022, OR = 0.23, 95% CI 0.07-0.78), with a lower frequency of genotypes carrying minor alleles (CT or TT) in the case group than in the controls. Additionally, W212X of CYP2C19 was significantly associated with the risk of ATD-induced MPE (P = 0.042, OR = 0.27, 95% CI 0.09-0.82). In an analysis of the CYP2C19-CYP2C9 haplotypes (-1418 C > T_W212X_-1565 C > T_-1188 C > T), ht3[T-A-T-C] showed a significant association with the development of ATD-induced MPE (P = 0.012, OR = 0.13, 95% CI 0.03-0.57). No significant associations between the other genetic polymorphisms and ATD-induced MPE were observed.

CONCLUSIONS

CYP2C19 and CYP2C9 genetic polymorphisms are significantly associated with the risk of developing ATD-induced MPE, and the genetic variants in NAT2 and CYP2E1 are not closely related to the development of this adverse reaction.

The role of cytokines in the mechanism of adverse drug reactions

Cytokines are thought to play a role in acute and/or immune-mediated adverse drug reactions (ADRs) due to their ability to regulate the innate and adaptive immune systems. This role is highly complex owing to the pluripotent nature of cytokines, which enables the same cytokine to play multiple roles depending on target organ(s) involved. As a result, the discussion of cytokine involvement in ADRs is organized according to target organ(s); specifically, ADRs targeting skin and liver, as well as ADRs targeting multiple organs, such as drug-induced autoimmunity and infusion-related reactions. In addition to discussing the mechanism(s) by which cytokines contribute to the initiation, propagation, and resolution of ADRs, we also discuss the usefulness and limitations of current methodologies available to conduct such mechanistic studies. While animal models appear to hold the most promise for uncovering additional mechanisms, this field is plagued by a lack of good animal models and, as a result, the mechanism of cytokine involvement in ADRs is often studied using less informative in vitro studies. The recent formation of the Drug-Induced Liver Injury Network, whose goal is collect thousands of samples from drug-induced liver injury patients, has enormous potential to advance knowledge in this field, by enabling large-scale cytokine polymorphism studies. In conclusion, we discuss how further advances in this field could be of significant benefit to patients in terms of preventing, predicting, and treating ADRs.

Drug hypersensitivity reactions involving skin

Immune reactions to drugs can cause a variety of diseases involving the skin, liver, kidney, lungs, and other organs. Beside immediate, IgE-mediated reactions of varying degrees (urticaria to anaphylactic shock), many drug hypersensitivity reactions appear delayed, namely hours to days after starting drug treatment, showing a variety of clinical manifestations from solely skin involvement to fulminant systemic diseases which may be fatal. Immunohistochemical and functional studies of drug-specific T cells in patients with delayed reactions confirmed a predominant role for T cells in the onset and maintenance of immune-mediated delayed drug hypersensitivity reactions (type IV reactions). In these reactions, drug-specific CD4+ and CD8+ T cells are stimulated by drugs through their T cell receptors (TCR). Drugs can stimulate T cells in two ways: they can act as haptens and bind covalently to larger protein structures (hapten-carrier model), inducing a specific immune response. In addition, they may accidentally bind in a labile, noncovalent way to a particular TCR of the whole TCR repertoire and possibly also major histocompatibility complex (MHC)-molecules - similar to their pharmacologic action. This seems to be sufficient to reactivate certain, probably in vivo preactivated T cells, if an additional interaction of the drug-stimulated TCR with MHC molecules occurs. The mechanism was named pharmacological interaction of a drug with (immune) receptor and thus termed the p-i concept. This new concept may explain the frequent skin symptoms in drug hypersensitivity to oral or parenteral drugs. Furthermore, the various clinical manifestations of T cell-mediated drug hypersensitivity may be explained by distinct T cell functions leading to different clinical phenotypes. These data allowed a subclassification of the delayed hypersensitivity reactions (type IV) into T cell reactions which, by releasing certain cytokines and chemokines, preferentially activate and recruit monocytes (type IVa), eosinophils (type IVb), or neutrophils (type IVd).

Role of epidermal dendritic cells in drug-induced cutaneous adverse reactions

Drug-induced adverse reactions (ADR) include any undesirable pharmacological effect that occurs following drug administration at therapeutic doses. The appearance of ADR significantly limits the use of drugs in as much as their clinical symptoms may range from very mild discomfort such as cutaneous rash, up to very severe, or even fatal tissue necrolysis such as the Stevens Johnson syndrome.One of the most frequently involved organ during ADR is the skin. Drug-induced cutaneous reactions (CDR) incidence is variable but they may appear in 2-3% of ambulatory patients, and it may increase to 10-15% when patients are hospitalized, or even be as high as 60% when co morbidity includes the presence of virus, bacteria, or parasites.Due to the fact that skin is one of the organs most frequently involved in ADR, in this work we analyze and propose a mechanism by which epidermal dendritic cells operating as the sentinels of the skin neuro-immune-endocrine system may contribute to CDR via either immunogenic or tolerogenic immune responses towards drugs, whenever they are administered topic or systemically.

Skin diseases in intensive care medicine

Though most dermatoses are not life-threatening, skin diseases play an important role in intensive care medicine. Skin findings in intensive care patients may reflect the underlying disease or be complications of intensive medical care. Most important are drug reactions, infections, bacterial toxin reactions, erythroderma, ANCA-positive vasculitides (such as Wegener granulomatosis) and bleeding disorders.

Stevens-Johnson syndrome: pathogenesis, diagnosis, and management

Cutaneous drug reactions are the most common type of adverse drug reaction. These reactions, ranging from simple pruritic eruptions to potentially life-threatening events, are a significant cause of iatrogenic morbidity and mortality. Stevens-Johnson syndrome (SJS) is a serious and potentially life-threatening cutaneous drug reaction. Although progress has been made in the management of SJS through early detection, prompt hospitalization, and immediate cessation of offending agents, the prevalence of permanent disabilities associated with SJS remains unchanged. Nevertheless, despite being a problem that is global in scope, government and health care agencies worldwide have yet to find a consensus on either diagnostic criteria or therapy for this disorder. Here, we provide the internist and emergency room physician with a brief review the SJS literature and summarize the latest recommended interventions with the hope of improving early recognition of this disease and prevention of permanent sequelae and mortality that frequently complicate SJS.

Drug-metabolizing enzymes in the skin of man, rat, and pig

The mammalian skin has long been considered to be poor in drug metabolism. However, many reports clearly show that most drug metabolizing enzymes also occur in the mammalian skin albeit at relatively low specific activities. This review summarizes the current state of knowledge on drug metabolizing enzymes in the skin of human, rat, and pig, the latter, because it is often taken as a model for human skin on grounds of anatomical similarities. However only little is known about drug metabolizing enzymes in pig skin. Interestingly, some cytochromes P450 (CYP) have been observed in the rat skin which are not expressed in the rat liver, such as CYP 2B12 and CYP2D4. As far as investigated most drug metabolizing enzymes occur in the suprabasal (i.e. differentiating) layers of the epidermis, but the rat CYP1A1 rather in the basal layer and human UDP-glucuronosyltransferase rather in the stratum corneum. The pattern of drug metabolizing enzymes and their localization will impact not only the beneficial as well as detrimental properties of drugs for the skin but also dictate whether a drug reaches the blood flow unchanged or as activated or inactivated metabolite(s).

Delayed drug hypersensitivity reactions ? new concepts

Immune reactions to small molecular compounds such as drugs can cause a variety of diseases mainly involving skin, but also liver, kidney, lungs and other organs. In addition to the well-known immediate, IgE-mediated reactions to drugs, many drug-induced hypersensitivity reactions appear delayed. Recent data have shown that in these delayed reactions drug-specific CD4(+) and CD8(+) T cells recognize drugs through their T cell receptors (TCR) in an MHC-dependent way. Immunohistochemical and functional studies of drug-reactive T cells in patients with distinct forms of exanthems revealed that distinct T cell functions lead to different clinical phenotypes. Taken together, these data allow delayed hypersensitivity reactions (type IV) to be further subclassified into T cell reactions, which by releasing certain cytokines and chemokines preferentially activate and recruit monocytes (type IVa), eosinophils (type IVb), or neutrophils (type IVd). Moreover, cytotoxic functions by either CD4(+) or CD8(+) T cells (type IVc) seem to participate in all type IV reactions. Drugs are not only immunogenic because of their chemical reactivity, but also because they may bind in a labile way to available TCRs and possibly MHC-molecules. This seems to be sufficient to stimulate certain, probably preactivated T cells. The drug seems to bind first to the fitting TCR, which already exerts some activation. For full activation, an additional interaction of the TCR with the MHC molecules is needed. The drug binding to the receptor structures is reminiscent of a pharmacological interaction between a drug and its (immune) receptor and was thus termed the p-i concept. In some patients with drug hypersensitivity, such a response occurs within hours even upon the first exposure to the drug. The T cell reaction to the drug might thus not be due to a classical, primary response, but is due to peptide-specific T cells which happen to be stimulated by a drug. This new concept has major implications for understanding clinical and immunological features of drug hypersensitivity and a model to explain the frequent skin symptoms in drug hypersensitivity is proposed.

Detection of Haptenated Proteins in Organotypic Human Skin Explant Cultures Exposed to Dapsone

Bioactivation of parent drug to reactive metabolite(s) followed by protein haptenation has been suggested to be a critical step in the elicitation of cutaneous drug reactions. Although liver is believed to be the primary organ of drug bioactivation quantitatively, other organs including skin may also metabolize drugs. Cultured human epidermal keratinocytes and dermal fibroblasts have been shown to be capable of bioactivating sulfonamides and sulfones, giving rise to haptenated proteins. It is, however, unclear whether metabolic events in these isolated cells reflect bioactivation in vivo. Hence, split-thickness human skin explants were exposed to dapsone (DDS) or its arylhydroxylamine metabolite (dapsone hydroxylamine, D-NOH) and probed for protein haptenation. DDS and D-NOH were applied either epicutaneously or mixed in the medium (to mimic its entry into skin from the systemic circulation). DDS-protein adducts were readily detected in skin explants exposed to either DDS or D-NOH. Adducts were detected mainly in the upper epidermal region in response to epicutaneous application, whereas adducts were formed all over the explants when DDS/D-NOH were mixed in the culture medium. In addition, adducts were visible in HLA-DR+ cells, indicating their presence in the dendritic cell population in the skin. Our results demonstrate the ability of intact human skin to bioactivate DDS leading to protein haptenation.

Sulfonamide allergy and cross-reactivity

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

Formation and Uptake of Arylhydroxylamine-Haptenated Proteins in Human Dendritic Cells

Bioactivation of sulfonamides and the subsequent formation of haptenated proteins is believed to be a critical step in the development of hypersensitivity reactions to these drugs. Numerous lines of evidence suggest that the presence of such adducts in dendritic cells (DCs) migrating to draining lymph nodes is essential for the development of cutaneous reactions to xenobiotics. Our objective was to determine the ability of human DCs to form drug-protein covalent adducts when exposed to sulfamethoxazole (SMX), dapsone (DDS), or their arylhydroxylamine metabolites [sulfamethoxazole hydroxylamine (S-NOH) and dapsone hydroxylamine (D-NOH)] and to take up preformed adduct. Naive and immature CD34+ KG-1 cells were incubated with SMX, DDS, or metabolites. Formation of haptenated proteins was probed using confocal microscopy and ELISA. Cells were also incubated with preformed adduct (drug-bovine serum albumin conjugate), and uptake was determined using confocal microscopy. Both naive and immature KG-1 cells were able to bioactivate DDS, forming drug-protein adducts, whereas cells showed very little protein haptenation when exposed to SMX. Exposure to S-NOH or D-NOH resulted in protein haptenation in both cell types. Both immature and naive KG-1 cells were able to take up preformed haptenated proteins. Thus, DCs may acquire haptenated proteins associated with drugs via intracellular bioactivation, uptake of reactive metabolites, or uptake of adduct formed and released by adjacent cells (e.g., keratinocytes).

Enzyme-mediated protein haptenation of dapsone and sulfamethoxazole in human keratinocytes: II. Expression and role of flavin-containing monooxygenases and peroxidases

Arylamine compounds, such as sulfamethoxazole (SMX) and dapsone (DDS), are metabolized in epidermal keratinocytes to arylhydroxylamine metabolites that auto-oxidize to arylnitroso derivatives, which in turn bind to cellular proteins and can act as antigens/immunogens. Previous studies have demonstrated that neither cytochromes P450 nor cyclooxygenases mediate this bioactivation in normal human epidermal keratinocytes (NHEKs). In this investigation, we demonstrated that methimazole (MMZ), a prototypical substrate of the flavin-containing monooxygenases (FMOs), attenuated the protein haptenation observed in NHEKs exposed to SMX or DDS. In addition, recombinant FMO1 and FMO3 were able to bioactivate both SMX and DDS, resulting in covalent adduct formation. Western blot analysis confirmed the presence of FMO3 in NHEKs, whereas FMO1 was not detectable. In addition to MMZ, 4-aminobenzoic acid hydrazide (ABH) also attenuated SMX- and DDS-dependent protein haptenation in NHEKs. ABH did not alter the bioactivation of these drugs by recombinant FMO3, suggesting its inhibitory effect in NHEKs was due to its known ability to inhibit peroxidases. Studies confirmed the presence of peroxidase activity in NHEKs; however, immunoblot analysis and reverse transcription-polymerase chain reaction indicated that myeloperoxidase, lactoperoxidase, and thyroid peroxidase were absent. Thus, our results suggest an important role for FMO3 and yet-to-be identified peroxidases in the bioactivation of sulfonamides in NHEKs.