Chemical substances and contact allergy--244 substances ranked according to allergenic potency

Use of Lhasa Limited Products for the In Silico Prediction of Drug Toxicity

Lhasa Limited have had a role in the in silico prediction of drug and other chemical toxicity for over 30 years. This role has always been multifaceted, both as a provider of predictive software such as Derek Nexus, and as an honest broker for the sharing of proprietary chemical and toxicity data. A changing regulatory environment and the drive for the Replacement, Reduction and Refinement (the 3Rs) of animal testing have led both to increased acceptance of in silico predictions and a desire for the sharing of data to reduce duplicate testing. The combination of these factors has led to Lhasa Limited providing a suite of products and coordinating numerous data-sharing consortia that do indeed facilitate a significant reduction in the testing burden that companies would otherwise be laboring under. Many of these products and consortia can be organized into workflows for specific regulatory use cases, and it is these that will be used to frame the narrative in this chapter.

Allergenic components, biocides, and analysis techniques of some essential oils used in food products

Nowadays, almost 300 essential oils (EOs) are commonly traded in the world market, with a prediction to be worth over $14 billion in 2024. EOs are natural preservatives for food products in order to reduce the activity of pathogenic microorganisms, therefore their use as an antioxidant or a preservative in foods has been encouraged. They are not only considered as antimicrobial or flavoring agents, but are also incorporated into food packaging materials. There are several types of EOs which have been approved as food additives by the Food and Drug Administration. Hence, it is important to use safe EO products to minimize possible adverse effect risks such as nausea, vomiting, necrosis, nephropathy, mucous membrane, and skin irritation. This review article gives information about some EOs that are used in the food industries and the types of some allergenic compounds and biocides which could make the EOs hazardous or may cause allergenic reactions in the human body. Besides, some analysis techniques of possible allergenic compounds or biocides in EOs were introduced and supported with the most relevant studies. The overall conclusion from the study is that pregnant women, patients taking drugs (e.g., diabetics) or the having a history of allergy are the most prone to be affected from EO allergenic components. As regards to biocides, organochlorine and organophosphorus types of pesticides that are carried over from the plant may be found mostly in EOs. The most common allergic reaction is skin sensitization and irritation if the EO components are oxidized during storage or transportation. Moreover, drug interactions are one of the other possible adverse effect. Hence, determination of biocides and possible allergenic component concentrations is an essential factor when they are used as a preservative or flavoring agent. The most prominent analysis techniques are gas and liquid chromatography because most of the allergens and biocides are mainly composed of volatile components. PRACTICAL APPLICATION: Determining of the essential oil's content will be crucial if oils are used for food preservation or flavoring because they may have some hazardous effects, such as nausea, vomiting, necrosis and nephropathy. Therefore, after applying them to the food products, consumers (especially pregnant women) should be informed about their concentration levels and their possible adverse effects are taken into account when they are consumed over toxic limit. For this reason, we reviewed in our study that some allergenic components, biocides and toxic limits of EOs to be used in food products. In addition to this, recent analytical techniques have been explained and discussed which methods are suitable for analysis.

Therapeutic Potential of Citronella Essential Oil: A Review

Mosquito-borne diseases such as malaria, filariasis, chikunguniya, yellow fever, dengue and Japanese encephalitis are the major cause of remarkable morbidity and mortality in livestock and humans worldwide. Since ancient times, aromatic plants are used for their medicinal value. Essential oils derived from these plants may be used as effective alternatives/adjuvants in pharmaceuticals, biomedical, cosmetic, food, veterinary and agriculture applications. These oils have also gained popularity and interest for prevention and treatment of various disorders. However, several reports on adverse effects including skin eruption, contact artricaria or toxic encephalopathy in children are available for synthetic repellent in the literature. Thus, natural insect repellents like essential oils have been explored recently as an alternative. One such essential oil studied widely, is citronella oil, extracted mainly from Cymbopogon nardus. This essential oil has exhibited good efficacy against mosquitoes. It is a mixture of components including citronellal, citronellol, geraniol as major constituents contributing to various activities (antimicrobial, anthelmintic, antioxidant, anticonvulsant antitrypanosomal and wound healing), besides mosquito repellent action. Citronella essential oil is registered in US EPA (Environmental protection agency) as insect repellent due to its high efficacy, low toxicity and customer satisfaction. However, poor stability in the presence of air and high temperature limits its practical applications. Since specific knowledge on properties and chemical composition of oil is fundamental for its effective application, the present review compiles and discusses biological properties of citronella oil. It also sheds light on various formulations and applications of this essential oil.

Read-across can increase confidence in the Next Generation Risk Assessment for skin sensitisation: A case study with resorcinol

Historically skin sensitisation risk assessment for cosmetic ingredients was based on animal models, however regulatory demands have led to Next Generation Risk Assessment (NGRA), using data from New Approach Methodologies (NAM) and Defined Approaches (DA). This case study was meant to investigate if the use of resorcinol at 0.2% in a face cream was safe and a maximum use concentration could be defined. The NAM data and DA predictions could not provide sufficient confidence to determine a point of departure (POD). Therefore, the application of read-across was explored to increase the level of confidence. Analogue searches in various tools and databases using "mode of action" and "chemical structural features" retrieved 535 analogues. After refinement by excluding analogues without a defined structure, similar reactivity profile and skin sensitisation data, 39 analogues remained. A final selection was made based on three approaches: expert judgment, chemical similarity or Local Lymph Node Assay data (LLNA). All read-across approaches supported a moderate potency. A POD derived from the LLNA EC3 of 3.6% was determined leading to a favourable NGRA conclusion and a maximum use concentration of 0.36%. This was supported by a traditional risk assessment based on the available animal data for resorcinol.

Skin Exposure Contributes to Chemical-Induced Asthma: What is the Evidence? A Systematic Review of Animal Models

It is generally assumed that allergic asthma originates primarily through sensitization via the respiratory mucosa, but emerging clinical observations and experimental studies indicate that skin exposure to low molecular weight (LMW) agents, i.e. “chemicals,” may lead to systemic sensitization and subsequently develop asthma when the chemical is inhaled. This review aims to evaluate the accumulating experimental evidence that adverse respiratory responses can be elicited upon inhalation of an LMW chemical sensitizer after previous sensitization by dermal exposure. We systematically searched the PubMed and Embase databases up to April 15, 2017, and conducted forward and backward reference tracking. Animal studies involving both skin and airway exposure to LMW agents were included. We extracted 6 indicators of “selective airway hyper-responsiveness” (SAHR)—i.e. respiratory responses that only occurred in previously sensitized animals—and synthesized the evidence level for each indicator into strong, moderate or limited strength. The summarized evidence weight for each chemical agent was graded into high, middle, low or “not possible to assess.” We identified 144 relevant animal studies. These studies involved 29 LMW agents, with 107 (74%) studies investigating the occurrence of SAHR. Indicators of SAHR included physiological, cytological/histological and immunological responses in bronchoalveolar lavage, lung tissue and airway-draining lymph nodes. Evidence for skin exposure-induced SAHR was present for 22 agents; for 7 agents the evidence for SAHR was inconclusive, but could not be excluded. The ability of a chemical to cause sensitization via skin exposure should be regarded as constituting a risk of adverse respiratory reactions.

Environmentally benign non-wettable textile treatments: A review of recent state-of-the-art

Among superhydrophobic materials, non-wettable textiles are probably the ones that come in contact or interact with the human body most frequently. Hence, textile treatments for water or oil repellency should be non-toxic, biocompatible, and comply with stringent health standards. Moreover, considering the volume of the worldwide textile industry, these treatments should be scalable, sustainable, and eco-friendly. Due to this awareness, more and more non-wettable textile treatments with eco-friendly processes and green or non-toxic chemicals are being adopted and reported. Although fluorinated alkylsilanes or fluorinated polymers with C8 chemistry (with ≥ 8 fluorinated carbon atoms) are the best performing materials to render textiles water or oil repellent, they pose substantial health and environmental problems and are being banned. For this reason, water/solvent-borne, C8-free vehicles for non-wettable treatment formulations are probably the only ones that can have commercialization prospects. Hence, researchers have come up with a variety of new, non-toxic, green formulations and materials to render fabrics liquid repellent that constitute the focus of this review paper. As such, this review article discusses and summarizes recent developments and techniques on various sustainable superhydrophobic treatments for textiles, with comparable performance and durability to formulations based on fluorinated C8 compounds. The current state-of-the-art technologies, potential commercialization prospects, and relevant limitations are discussed and summarized with examples. The review also attempts to indicate promising future strategies and new materials that can transform the process for non-wettable textiles into an all-sustainable technology.

Evaluation and improvement of QSAR predictions of skin sensitization for pesticides

In vivo skin sensitization assays have to be provided by applicants to the competent authorities in the European Union for the approval of active substances (AS) in pesticides. This study aimed to test the practicability of in silico predictions for AS by freely available (Q)SAR tools to evaluate their use as a time- and cost-effective alternative to animal testing in the context of the 3R concept. Predictions of skin sensitization for 48 selected sensitizing and non-sensitizing AS by the software programs CAESAR, Toxtree, OECD (Q)SAR Toolbox, CASE Ultra, Leadscope and SciQSAR were collected and compared. Different data evaluation methodologies (score definition, mean, weighted mean, threshold score definition) were applied to optimize the predictions. The calculation methods were internally cross-validated and further validated with an additional validation set of 80 AS. Although the presented calculation methodologies are not suitable as a stand-alone method, this study has shown weaknesses and strengths of some prominent (Q)SAR programs and diverse combinatorial options in the prediction of skin sensitization by pesticidal AS. The present study will help to foster discussions on in silico alternatives to animal testing in the pesticide area.

Biological Activities and Safety of Citrus spp. Essential Oils

Citrus fruits have been a commercially important crop for thousands of years. In addition, Citrus essential oils are valuable in the perfume, food, and beverage industries, and have also enjoyed use as aromatherapy and medicinal agents. This review summarizes the important biological activities and safety considerations of the essential oils of sweet orange (Citrus sinensis), bitter orange (Citrus aurantium), neroli (Citrus aurantium), orange petitgrain (Citrus aurantium), mandarin (Citrus reticulata), lemon (Citrus limon), lime (Citrus aurantifolia), grapefruit (Citrus × paradisi), bergamot (Citrus bergamia), Yuzu (Citrus junos), and kumquat (Citrus japonica).

An evaluation of selected (Q)SARs/expert systems for predicting skin sensitisation potential

Predictive testing to characterise substances for their skin sensitisation potential has historically been based on animal models such as the Local Lymph Node Assay (LLNA) and the Guinea Pig Maximisation Test (GPMT). In recent years, EU regulations, have provided a strong incentive to develop non-animal alternatives, such as expert systems software. Here we selected three different types of expert systems: VEGA (statistical), Derek Nexus (knowledge-based) and TIMES-SS (hybrid), and evaluated their performance using two large sets of animal data: one set of 1249 substances from eChemportal and a second set of 515 substances from NICEATM. A model was considered successful at predicting skin sensitisation potential if it had at least the same balanced accuracy as the LLNA and the GPMT had in predicting the other outcomes, which ranged from 79% to 86%. We found that the highest balanced accuracy of any of the expert systems evaluated was 65% when making global predictions. For substances within the domain of TIMES-SS, however, balanced accuracies for the two datasets were found to be 79% and 82%. In those cases where a chemical was within the TIMES-SS domain, the TIMES-SS skin sensitisation hazard prediction had the same confidence as the result from LLNA or GPMT.

Skin Sensitization: Modeling Based on Skin Metabolism Simulation and Formation of Protein Conjugates

A quantitative structure-activity relationship (QSAR) system for estimating skin sensitization potency has been developed that incorporates skin metabolism and considers the potential of parent chemicals and/or their activated metabolites to react with skin proteins. A training set of diverse chemicals was compiled and their skin sensitization potency assigned to one of three classes. These three classes were, significant, weak, or nonsensitizing. Because skin sensitization potential depends upon the ability of chemicals to react with skin proteins either directly or after appropriate metabolism, a metabolic simulator was constructed to mimic the enzyme activation of chemicals in the skin. This simulator contains 203 hierarchically ordered spontaneous and enzyme controlled reactions. Phase I and phase II metabolism were simulated by using 102 and 9 principal transformations, respectively. The covalent interactions of chemicals and their metabolites with skin proteins were described by 83 reactions that fall within 39 alerting groups. The SAR/QSAR system developed was able to correctly classify about 80% of the chemicals with significant sensitizing effect and 72% of nonsensitizing chemicals. For some alerting groups, three-dimensional (3D)-QSARs were developed to describe the multiplicity of physicochemical, steric, and electronic parameters. These 3D-QSARs, so-called pattern recognition-type models, were applied each time a latent alerting group was identified in a parent chemical or its generated metabolite(s). The concept of the mutual influence amongst atoms in a molecule was used to define the structural domain of the skin sensitization model. The utility of the structural model domain and the predictability of the model were evaluated using sensitization potency data for 96 chemicals not used in the model building. The TIssue MEtabolism Simulator (TIMES) software was used to integrate a skin metabolism simulator and 3D-QSARs to evaluate the reactivity of chemicals thus predicting their likely skin sensitization potency.

Integrated Computational Solution for Predicting Skin Sensitization Potential of Molecules

Introduction

Skin sensitization forms a major toxicological endpoint for dermatology and cosmetic products. Recent ban on animal testing for cosmetics demands for alternative methods. We developed an integrated computational solution (SkinSense) that offers a robust solution and addresses the limitations of existing computational tools i.e. high false positive rate and/or limited coverage.

Results

The key components of our solution include: QSAR models selected from a combinatorial set, similarity information and literature-derived sub-structure patterns of known skin protein reactive groups. Its prediction performance on a challenge set of molecules showed accuracy = 75.32%, CCR = 74.36%, sensitivity = 70.00% and specificity = 78.72%, which is better than several existing tools including VEGA (accuracy = 45.00% and CCR = 54.17% with ‘High’ reliability scoring), DEREK (accuracy = 72.73% and CCR = 71.44%) and TOPKAT (accuracy = 60.00% and CCR = 61.67%). Although, TIMES-SS showed higher predictive power (accuracy = 90.00% and CCR = 92.86%), the coverage was very low (only 10 out of 77 molecules were predicted reliably).

Conclusions

Owing to improved prediction performance and coverage, our solution can serve as a useful expert system towards Integrated Approaches to Testing and Assessment for skin sensitization. It would be invaluable to cosmetic/ dermatology industry for pre-screening their molecules, and reducing time, cost and animal testing.

Low Young's modulus Ti-based porous bulk glassy alloy without cytotoxic elements

A new a biocompatible Ti42Zr40Ta3Si15 (atomic %) porous bulk glassy alloy was produced by combination of rapid solidification and powder metallurgy techniques. Amorphous alloy ribbons were fabricated by melt spinning, i.e. extremely fast quenching the molten alloy with 10(6)K/s from T=1973K down to room temperature. The ribbons were then cryo-milled at liquid nitrogen temperature in order to produce powder, which was subsequently hot pressed. The resulting thick pellets have a porosity of about 14vol%, a high compression strength of 337MPa and a Young's modulus of about E=52GPa, values very close to those characteristic of cortical bone. Moreover, the morphology of the samples is very similar to that of cortical bone. The biocompatibility, which is due to the absence of any toxic element in the chemical composition, together with the suitable mechanical behavior, make these samples promising for orthopedic and dentistry applications.

STATEMENT OF SIGNIFICANCE

Ti-based alloys are nowadays the standard solution for biomedical implants. However, both the conventional crystalline and amorphous alloys have higher rigidity as the human bone, leading to the damage of the bone at the interface, and contains harmful elements like vanadium, aluminum, nickel or beryllium. The hierarchical porous structures based on glassy alloys with biocompatible elements is a much better alternative. This work presents for the first time the manufacturing of such porous bodies starting from Ti-based amorphous alloy ribbons, which contains only non-harmful elements. The morphology and the compressive mechanical properties of these new products are analyzed in regard with those characteristic to the cortical bone.

New Cu-Free Ti-Based Composites with Residual Amorphous Matrix

Titanium-based bulk metallic glasses (BMGs) are considered to have potential for biomedical applications because they combine favorable mechanical properties and good biocompatibility. Copper represents the most common alloying element, which provides high amorphization capacity, but reports emphasizing cytotoxic effects of this element have risen concerns about possible effects on human health. A new copper-free alloy with atomic composition Ti₄₂Zr₁₀Pd₁₄Ag₂₆Sn₈, in which Cu is completely replaced by Ag, was formulated based on Morinaga's d-electron alloy design theory. Following this theory, the actual amount of alloying elements, which defines the values of covalent bond strength Bo and d-orbital energy Md, situates the newly designed alloy inside the BMG domain. By mean of centrifugal casting, cylindrical rods with diameters between 2 and 5 mm were fabricated from this new alloy. Differential scanning calorimetry (DSC) and X-rays diffraction (XRD), as well as microstructural analyses using optical and scanning electron microscopy (OM/SEM) revealed an interesting structure characterized by liquid phase-separated formation of crystalline Ag, as well as metastable intermetallic phases embedded in residual amorphous phases.

Skin sensitization

Skin sensitization associated with allergic contact dermatitis is a common health problem and is an important consideration for toxicologists in safety assessment. Historically, in vivo predictive tests have been used with good success to identify substances that have the potential to induce skin sensitization, and these tests formed the basis of safety evaluation. These original tests are now being replaced gradually either by in vitro assays or by further refinements of in vivo methods such as the local lymph node assay. Human data have also been available to inform classification decisions for some substances and have been used by risk managers to introduce measures for exposure reduction. However, humans encounter hazards in the context of exposure rather than in the form of intrinsic hazards per se, and so in this article, we have examined critically the extent to which human data have been used to refine classification decisions and safety evaluations. We have also evaluated information on the burden of human allergic skin disease and used this to address the question of whether, and to what extent, the identification and evaluation of skin sensitization hazards has led to an improvement of public and/or occupational health.

Predicting chemically-induced skin reactions. Part I: QSAR models of skin sensitization and their application to identify potentially hazardous compounds

Repetitive exposure to a chemical agent can induce an immune reaction in inherently susceptible individuals that leads to skin sensitization. Although many chemicals have been reported as skin sensitizers, there have been very few rigorously validated QSAR models with defined applicability domains (AD) that were developed using a large group of chemically diverse compounds. In this study, we have aimed to compile, curate, and integrate the largest publicly available dataset related to chemically-induced skin sensitization, use this data to generate rigorously validated and QSAR models for skin sensitization, and employ these models as a virtual screening tool for identifying putative sensitizers among environmental chemicals. We followed best practices for model building and validation implemented with our predictive QSAR workflow using Random Forest modeling technique in combination with SiRMS and Dragon descriptors. The Correct Classification Rate (CCR) for QSAR models discriminating sensitizers from non-sensitizers was 71-88% when evaluated on several external validation sets, within a broad AD, with positive (for sensitizers) and negative (for non-sensitizers) predicted rates of 85% and 79% respectively. When compared to the skin sensitization module included in the OECD QSAR Toolbox as well as to the skin sensitization model in publicly available VEGA software, our models showed a significantly higher prediction accuracy for the same sets of external compounds as evaluated by Positive Predicted Rate, Negative Predicted Rate, and CCR. These models were applied to identify putative chemical hazards in the Scorecard database of possible skin or sense organ toxicants as primary candidates for experimental validation.

The Myeloid U937 Skin Sensitization Test (U-SENS) addresses the activation of dendritic cell event in the adverse outcome pathway for skin sensitization

The U-SENS™ assay, formerly known as MUSST (Myeloid U937 Skin Sensitization Test), is an in vitro method to assess skin sensitization. Dendritic cell activation following exposure to sensitizers was modelled in the U937 human myeloid cell line by measuring the induction of the expression of CD86 by flow cytometry. The predictive performance of U-SENS™ was assessed via a comprehensive comparison analysis with the available human and LLNA data of 175 substances. U-SENS™ showed 79% specificity, 90% sensitivity and 88% accuracy. A four laboratory ring study demonstrated the transferability, reliability and reproducibility of U-SENS™, with a reproducibility of 95% within laboratories and 79% between-laboratories, showing that the U-SENS™ assay is a promising tool in a skin sensitization risk assessment testing strategy.

Tulipalin A induced phytotoxicity

Tulipalin A induced phytotoxicity is a persistent allergic contact dermatitides documented in floral workers exposed to Alstroemeria and its cultivars.[1] The causative allergen is tulipalin A, a toxic glycoside named for the tulip bulbs from which it was first isolated.[2] The condition is characterized by fissured acropulpitis, often accompanied by hyperpigmentation, onychorrhexis, and paronychia. More of the volar surface may be affected in sensitized florists. Dermatitis and paronychia are extremely common conditions and diagnostic errors may occur. A thorough patient history, in conjunction with confirmatory patch testing with a bulb sliver and tuliposide A exposure, can prevent misdiagnosis. We report a case of Tulipalin A induced phytotoxicity misdiagnosed as an unresolved tinea manuum infection in a patient evaluated for occupational exposure.

Towards AOP application--implementation of an integrated approach to testing and assessment (IATA) into a pipeline tool for skin sensitization

Since the OECD published the Adverse Outcome Pathway (AOP) for skin sensitization, many efforts have focused on how to integrate and interpret nonstandard information generated for key events in a manner that can be practically useful for decision making. These types of frameworks are known as Integrated Approaches to Testing and Assessment (IATA). Here we have outlined an IATA for skin sensitization which focuses on existing information including non testing approaches such as QSAR and read-across. The IATA was implemented into a pipeline tool using OASIS technology to provide a means of systematically collating and compiling relevant information which could be used in an assessment of skin sensitization potential. A test set of 100 substances with available skin sensitization information was profiled using the pipeline IATA. In silico and in chemico profiling information alone was able to correctly predict skin sensitization potential, with a preliminary accuracy of 73.85%. Information from other relevant endpoints (e.g., Ames mutagenicity) was found to improve the accuracy (to 87.6%) when coupled with a reaction chemistry mechanistic understanding. This pipeline platform could be useful in the assessment of skin sensitization potential and marks a step change in how non testing approaches can be practically applied.

TIMES-SS--recent refinements resulting from an industrial skin sensitisation consortium

The TImes MEtabolism Simulator platform for predicting Skin Sensitisation (TIMES-SS) is a hybrid expert system, first developed at Bourgas University using funding and data from a consortium of industry and regulators. TIMES-SS encodes structure-toxicity and structure-skin metabolism relationships through a number of transformations, some of which are underpinned by mechanistic 3D QSARs. The model estimates semi-quantitative skin sensitisation potency classes and has been developed with the aim of minimising animal testing, and also to be scientifically valid in accordance with the OECD principles for (Q)SAR validation. In 2007 an external validation exercise was undertaken to fully address these principles. In 2010, a new industry consortium was established to coordinate research efforts in three specific areas: refinement of abiotic reactions in the skin (namely autoxidation) in the skin, refinement of the manner in which chemical reactivity was captured in terms of structure-toxicity rules (inclusion of alert reliability parameters) and defining the domain based on the underlying experimental data (study of discrepancies between local lymph node assay Local Lymph Node Assay (LLNA) and Guinea Pig Maximisation Test (GPMT)). The present paper summarises the progress of these activities and explains how the insights derived have been translated into refinements, resulting in increased confidence and transparency in the robustness of the TIMES-SS predictions.

Skin tumorigenic potential of benzanthrone: prevention by ascorbic acid

Benzanthrone (BA) exposed occupational workers have been found to exhibit toxicological manifestations in the skin, thus it is quite likely that long term exposure may lead to skin tumorigenicity. Thus, attempts were made to elucidate the tumor initiating and promoting potentials of pure (PBA) and commercial benzanthrone (CBA). Additionally, the preventive role of ascorbic acid (AsA) was also assessed. PBA showed tumor initiating activity while CBA demonstrated tumor initiating as well as promoting activities in two-stage mouse skin tumor protocol. Further, prior treatment of AsA to PBA and CBA followed by twice weekly application of 12-o-tetradecanoyl phorbal myristate acetate (TPA) resulted into delayed onset of tumor formation and similarly single application of 7,12-dimethylbenz [α] anthracene (DMBA) followed by twice weekly application of AsA and CBA showed an increase in the latency period. Thus, AsA showed a protective effect against CBA promoted skin tumor. Furthermore, the topical application of CBA significantly increased the levels of xenobiotic enzymes. The animals topically treated with AsA along with topical application of CBA, restored all the impairment observed in enzyme activities. Thus, this study suggested that AsA can be useful in preventing PBA and CBA induced skin tumorigenicity.

Simulation of chemical metabolism for fate and hazard assessment. V. Mammalian hazard assessment

Animals and humans are exposed to a wide array of xenobiotics and have developed complex enzymatic mechanisms to detoxify these chemicals. Detoxification pathways involve a number of biotransformations, such as oxidation, reduction, hydrolysis and conjugation reactions. The intermediate substances created during the detoxification process can be extremely toxic compared with the original toxins, hence metabolism should be accounted for when hazard effects of chemicals are assessed. Alternatively, metabolic transformations could detoxify chemicals that are toxic as parents. The aim of the present paper is to describe specificity of eukaryotic metabolism and its simulation and incorporation in models for predicting skin sensitization, mutagenicity, chromosomal aberration, micronuclei formation and estrogen receptor binding affinity implemented in the TIMES software platform. The current progress in model refinement, data used to parameterize models, logic of simulating metabolism, applicability domain and interpretation of predictions are discussed. Examples illustrating the model predictions are also provided.

Perspectives on Non-Animal Alternatives for Assessing Sensitization Potential in Allergic Contact Dermatitis

Skin sensitization remains a major environmental and occupational health hazard. Animal models have been used as the gold standard method of choice for estimating chemical sensitization potential. However, a growing international drive and consensus for minimizing animal usage have prompted the development of in vitro methods to assess chemical sensitivity. In this paper, we examine existing approaches including in silico models, cell and tissue based assays for distinguishing between sensitizers and irritants. The in silico approaches that have been discussed include Quantitative Structure Activity Relationships (QSAR) and QSAR based expert models that correlate chemical molecular structure with biological activity and mechanism based read-across models that incorporate compound electrophilicity. The cell and tissue based assays rely on an assortment of mono and co-culture cell systems in conjunction with 3D skin models. Given the complexity of allergen induced immune responses, and the limited ability of existing systems to capture the entire gamut of cellular and molecular events associated with these responses, we also introduce a microfabricated platform that can capture all the key steps involved in allergic contact sensitivity. Finally, we describe the development of an integrated testing strategy comprised of two or three tier systems for evaluating sensitization potential of chemicals.

Finding the Data to Develop and Evaluate (Q)SARs and Populate Categories for Toxicity Prediction

This chapter describes the sources of data for in silico modelling. It is assumed that the modeller will not normally have the facilities to experimentally determine toxicological data, thus they must rely on existing data. Data can be obtained from in-house sources (e.g. for industry) or from publicly available databases and the scientific literature. For the publicly available data, the sources of toxicologically information and the relevant advantages and disadvantages are defined. The sources include “well-established” datasets and the use of literature searching, through to the use of databases and more global (meta) data portals which call on a number of databases. To use the data collected efficiently, the modeller must define the required endpoint, allow the nature of the data to drive the modelling approach and control the quality of the data and implications for that on in silico models.

Potency values from the local lymph node assay: application to classification, labelling and risk assessment

Hundreds of chemicals are contact allergens but there remains a need to identify and characterise accurately skin sensitising hazards. The purpose of this review was fourfold. First, when using the local lymph node assay (LLNA), consider whether an exposure concentration (EC3 value) lower than 100% can be defined and used as a threshold criterion for classification and labelling. Second, is there any reason to revise the recommendation of a previous ECETOC Task Force regarding specific EC3 values used for sub-categorisation of substances based upon potency? Third, what recommendations can be made regarding classification and labelling of preparations under GHS? Finally, consider how to integrate LLNA data into risk assessment and provide a rationale for using concentration responses and corresponding no-effect concentrations. Although skin sensitising chemicals having high EC3 values may represent only relatively low risks to humans, it is not possible currently to define an EC3 value below 100% that would serve as an appropriate threshold for classification and labelling. The conclusion drawn from reviewing the use of distinct categories for characterising contact allergens was that the most appropriate, science-based classification of contact allergens according to potency is one in which four sub-categories are identified: 'extreme', 'strong', 'moderate' and 'weak'. Since draining lymph node cell proliferation is related causally and quantitatively to potency, LLNA EC3 values are recommended for determination of a no expected sensitisation induction level that represents the first step in quantitative risk assessment.

A proposal for guideline for prevention of allergic occupational asthma in conformity with the globally harmonized system of classification and labelling of chemicals (GHS)

The use of chemical products to enhance and improve life is a widespread worldwide practice. Alongside the benefits of these products, there is also the potential of chemicals for adverse effects to people or the environment. As a result, a number of countries or organizations have developed laws or regulations over the years that require information to be prepared and transmitted to those using chemicals, through labels or Safety Data Sheets (SDS). Their differences are significant enough to result in different labels or SDS for the same product in different countries. In July 2003, United Nations (UN) recommended the globally harmonized system of classification and labelling of chemicals (GHS). We, special committee of Japanese Society of Occupational and Environmental Allergy proposed a guideline for prevention of allergic occupational asthma and sensitizers (n=60) causing occupational asthma or contact dermatitis in conformity with respiratory and skin sensitization criteria of GHS. We should propose these 60 sensitizers to the chemical industry association and governments to control, regulate and label them in each country.

20 Years of standard patch testing in an eczema population with focus on patients with multiple contact allergies

Results of standard patch tests performed with the same methodology in one centre are rarely available over a large time span. This gives the unique opportunity to study not only prevalence but also persistency of contact allergy and characterize subpopulations. The objectives were to investigate sensitivity rates and persistencies of patch test results and characterize patients with multiple contact allergies. A 20-year retrospective database-based study of 14 998 patients patch tested with the European Standard Series was performed. 34.5% were sensitized, primarily women. Sensitivity to nickel was most frequent and least frequent to mercaptobenzothiazole, N-isopropyl-N-phenyl-p-phenylenediamine and benzocaine. Yearly proportion of negative, mono/double-allergic, and multiple-allergic cases remained stable. Persistency of positive reactions was high for para-phenylenediamine, Cl(Me)isothiazolinone, and primin and poor for paraben mix. 5.1% were multiple allergic, primarily women, and 90% got diagnosed by the first test. Frequency of multiple allergies increased with age. More multiple- than mono/double-allergic patients were tested multiple times. Persistency and sensitivity rates in a Danish eczema population are provided and are useful for decisions regarding the standard series. Patients with multiple contact allergies are typically elderly women who might have long-lasting and hard-to-treat eczema. Cumulative environmental exposure seems necessary to develop multiple allergies.

TIMES-SS—A promising tool for the assessment of skin sensitization hazard. A characterization with respect to the OECD validation principles for (Q)SARs and an external evaluation for predictivity

The TImes MEtabolism Simulator platform used for predicting Skin Sensitization (TIMES-SS) is a hybrid expert system that was developed at Bourgas University using funding and data from a Consortium comprising industry and regulators. The model was developed with the aim of minimizing animal testing and to be scientifically valid in accordance with the OECD principles for (Q)SAR validation. TIMES-SS encodes structure-toxicity and structure-skin metabolism relationships through a number of transformations, some of which are underpinned by mechanistic 3D QSARs. Here, we describe the extent to which the five OECD principles are met and in particular the results from an external evaluation exercise that was recently carried out. As part of this exercise, data were generated for 40 new chemicals in the murine local lymph node assay (LLNA) and then compared with predictions made by TIMES-SS. The results were promising with an overall good concordance (83%) between experimental and predicted values. Further evaluation of these results highlighted certain inconsistencies which were rationalized by a consideration of reaction chemistry principles for sensitization. Improvements for TIMES-SS were proposed where appropriate. TIMES-SS is a promising tool to aid in the evaluation of skin sensitization hazard under legislative programs such as REACH.

Time dependence in mixture toxicity with soft electrophiles: 1. Combined effects of selected SN2- and SNAr-reactive agents with a nonpolar narcotic

Frequently the toxicity of an organic chemical mixture is close to dose-additive, even when the agents are thought to induce toxicity at different molecular sites of action. These findings appear to conflict with the hypothesis that a strictly dose-additive combined effect will be observed for agents sharing a single molecular site of toxic action within the organism. In this study, several SN2-reactive (alpha-halogen) or S(N)Ar-reactive (halogenated dinitrobenzene) soft electrophiles were tested with a model nonpolar narcotic (NPN) to determine the toxicity of the combinations. A sham combination of the model NPN (3-methyl-2-butanone) was also tested as a positive control. The study design incorporated time-dependent toxicity (TDT) determinations at 15, 30, and 45 minutes using a Microtox (Vibrio fischeri) protocol that included testing seven duplicated concentrations for each single agent and mixture per combination. Additionally, in chemico reactivity was determined for each compound using thiol in glutathione as a model nucleophile. The model NPN alone lacked reactivity and TDT. The SN2-reactive agents individually showed varying levels of both reactivity and TDT alone, while the SNAr-reactive chemicals alone were reactive and had toxicity that was fully time-dependent between 15 and 45 minutes of exposure. Data analyses indicated that the sham combination was dose additive, as expected, whereas three of four SN2:NPN combinations showed effects close to that predicted for dose addition but with some differences. The fourth SN2:NPN combination, which included an alpha-halogen with full TDT, showed a less-than-dose-additive combined effect as did both of the SNAr:NPN pairings. By incorporating TDT values, shapes of the dose-response curves, chemical reactivity data with thiol, reactive mechanisms for the soft electrophiles, and quantitative structure activity relationship information on whether the toxicity of the individual soft electrophiles did or did not exceeded that predicted for baseline narcosis, the results suggested that the alpha-halogens elicited two toxic effects at the concentrations tested (reactivity and narcotizing effects), whereas toxicity induced by the halogenated dinitrobenzenes was essentially limited to reactive effects. Collectively, these results provide experimental evidence consistent with previous explanations as to why binary mixtures of industrial organic chemicals often show combined effects that are close to dose additive, even when the chemicals are thought to induce toxicity at different molecular sites of action.

Chemical mixture toxicity testing with Vibrio fischeri: combined effects of binary mixtures for ten soft electrophiles

The toxicity of 30 binary combinations of 10 soft electrophiles was examined in Microtox using dose-response curve (DRC) analysis. Chemicals from three groups of soft electrophiles-vinyl Michael acceptors (I--react with a thiol group), dicarbonyl reactive agents (II--react with a primary amine), and alpha-haloactivation compounds (III--react with a thiol group)--were selected for testing to evaluate the relationship between molecular site of chemical action and combined toxic effect. For each combination tested, each single agent was tested alone at six duplicated concentrations and three 1:1 mixtures of the agents were also tested, each at six duplicated concentrations. Exposure duration was 15 min for each single agent and mixture test. Sigmoid DRCs for each single chemical and mixture were constructed and the single chemical curves were used to develop a theoretical dose-addition DRC for the combination. Additivity quotient (AQ) values for slope and EC50 were calculated by dividing the actual mixture slope or EC50 for a given combination by the predicted slope or EC50, respectively, from the theoretical dose-addition DRC. Three criteria were selected for value in determining the combined effect obtained for each combination: (1) slope AQ 95% confidence interval (CI) overlap with 1.0 (1.0=dose addition), (2) EC50 AQ 95% CI overlap with 1.0, and (3) mean mixture data point 95% and 99% CI overlap with the theoretical dose-addition DRC. Each of three sham combinations showed combined effects consistent with dose addition for each criterion. Dose addition was expected for 15 nonsham combinations (nine within-group combinations and six group I:III combinations) and a nondose-additive effect was expected for 12 combinations (all I:II and II:III combinations). Actual combined effects obtained by incorporating all three criteria (noted above) showed only six instances of dose addition. Therefore, time-dependent toxicity (TDT) tests of each soft electrophile alone and for three nonpolar narcotic chemicals alone were conducted, using 15-, 30-, and 45-min exposure durations, to assess the time-dependent nature of the toxicity. Results of the TDT tests suggested that five had fully (or nearly fully) TDT (interpreted as an irreversible effect representing one molecular site of action), five of the soft electrophiles had partially TDT (i.e., representing two or more molecular sites of action for the agents, one irreversible and one reversible), and the three nonpolar narcotics had no TDT (i.e., a fully reversible toxic effect). With this TDT information, the combined effects for 25 of the 27 mixtures, although rather complex, could be explained. It is noteworthy that all combined effects obtained, whether concluded to be dose-additive or not, were close to dose-additive for hazard assessment purposes.

Late reactions to the patch-test preparations para-phenylenediamine and epoxy resin: a prospective multicentre investigation of the German Contact Dermatitis Research Group

BACKGROUND

Late patch-test reactions, developing at day (D) 7 or later have been described for several allergens. Late reactions may reflect patch-test sensitization. Para-phenylenediamine (PPD) and epoxy resins (ER) are potent allergens and therefore may potentially induce patch-test sensitization. Up to now, there has been no prospective study on the frequency of late reactions in routine patch testing with these allergens.

OBJECTIVES

To assess the frequency of late reactions to PPD and ER.

PATIENTS/METHODS

In 1748 patients PPD (PPD-base, 1% pet.) and ER [based on diglycidylether of bisphenol A (DGEBA, 1% pet.)], and in 812 patients, nickel sulphate (5% pet.) were removed from the test panel of the standard series and applied on the medial side of the upper arm. Patch-test occlusion time was 24 h in 588 (PPD and ER) and 241 patients (nickel sulphate), respectively, and 48 h in 1160 (PPD and ER) and 571 (nickel sulphate) patients, respectively. Patch tests were read on D1-3 and D2-3, respectively; additional late readings were performed on D7, D14 and D21 after patch-test application. Patients who were not able to return for all scheduled late readings were telephoned on D7, D14 or D21, and questioned about a reaction at the test sites. Patients were instructed to perform daily self-examination from D4 onwards and to return immediately to the clinic if a reaction at the upper arm became visible.

RESULTS

Data of 1428 patients (ER and PPD) and 638 patients (nickel) were evaluable. In 25 patients (1.8%), patch tests became positive not before D7, among them 21 reactions to PPD (1.5%) and four reactions to ER (0.3%). In five of seven patients, repeated patch tests with PPD disclosed patch-test sensitization as the cause of the late reaction. All late reactions, except for one, occurred in patients in whom patch tests were applied for 48 h. No late reactions were seen with nickel sulphate.

CONCLUSIONS

PPD (1% pet.) elicited late reactions in 1.5% of routine patch tests, the majority of them probably being caused by patch-test sensitization. Therefore, the German Contact Dermatitis Research Group decided to remove PPD 1% pet. from the German standard series and to take efforts to optimize the patch-test conditions of PPD. One way to optimize PPD testing could be to reduce the exposure of PPD 1% to 24 h. Alternatively the patch-test concentration of PPD might be reduced.

An European inter-laboratory validation of alternative endpoints of the murine local lymph node assay

The original local lymph node assay (LLNA) is based on the use of radioactive labelling to measure cell proliferation. Other endpoints for the assessment of proliferation are also authorized by the OECD Guideline 429 provided there is appropriate scientific support, including full citations and description of the methodology (OECD, 2002. OECD Guideline for the Testing of Chemicals; Skin Sensitization: Local Lymph Node Assay, Guideline 429. Paris, adopted 24th April 2002.). Here, we describe the outcome of the second round of an inter-laboratory validation of alternative endpoints in the LLNA conducted in nine laboratories in Europe. The validation study was managed and supervised by the Swiss Agency for Therapeutic Products (Swissmedic) in Bern. Ear-draining lymph node (LN) weight and cell counts were used to assess LN cell proliferation instead of [3H]TdR incorporation. In addition, the acute inflammatory skin reaction was measured by ear weight determination of circular biopsies of the ears to identify skin irritation properties of the test items. The statistical analysis was performed in the department of statistics at the university of Bern. Similar to the EC(3) values defined for the radioactive method, threshold values were calculated for the endpoints measured in this modification of the LLNA. It was concluded that all parameters measured have to be taken into consideration for the categorisation of compounds due to their sensitising potencies. Therefore, an assessment scheme has been developed which turned out to be of great importance to consistently assess sensitisation versus irritancy based on the data of the different parameters. In contrast to the radioactive method, irritants have been picked up by all the laboratories applying this assessment scheme.