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

From 1985 to 2001 a group consisting of thirty experts including dermatologists from universities, representatives from the chemical industry and from regulatory authorities elaborated and consequently decided on the potency ranking of chemicals with contact allergenic properties. These chemicals were defined either as synthetic chemicals or as chemicals identified as ingredients in natural products. On 244 substances clinical and experimental data on humans and results of animal tests as documented in the scientific literature were carefully collected and evaluated. This careful evaluation and assessment of these chemicals clearly demonstrate that ranking of substances according to their allergenic potency is possible and justified. It was decided to rank the most potent contact allergens in Category A of substances having significant allergenic properties. Substances with a solid-based indication of a contact allergenic potential and substances with the capacity of cross-reactions were listed in Category B and substances with insignificant or questionable allergenic effects were listed in Category C. An assessment of these compiled data is published here. Three Appendices give a comprehensive overview of the 98 substances listed in Category A, the 77 substances listed in Category B and the 69 substances listed in Category C.

Dermal and inhalation acute toxic class methods: test procedures and biometric evaluations for the Globally Harmonized Classification System.

The acute toxic class (ATC) methods were developed for determining LD(50)/LC(50) estimates of chemical substances with significantly fewer animals than needed when applying conventional LD(50)/LC(50) tests. The ATC methods are sequential stepwise procedures with fixed starting doses/concentrations and a maximum of six animals used per dose/concentration. The numbers of dead/moribund animals determine whether further testing is necessary or whether the test is terminated. In recent years we have developed classification procedures for the oral, dermal and inhalation routes of administration by using biometric methods. The biometric approach assumes a probit model for the mortality probability of a single animal and assigns the chemical to that toxicity class for which the best concordance is achieved between the statistically expected and the observed numbers of dead/moribund animals at the various steps of the test procedure. In previous publications we have demonstrated the validity of the biometric ATC methods on the basis of data obtained for the oral ATC method in two-animal ring studies with 15 participants from six countries. Although the test procedures and biometric evaluations for the dermal and inhalation ATC methods have already been published, there was a need for an adaptation of the classification schemes to the starting doses/concentrations of the Globally Harmonized Classification System (GHS) recently adopted by the Organization for Economic Co-operation and Development (OECD). Here we present the biometric evaluation of the dermal and inhalation ATC methods for the starting doses/concentrations of the GHS and of some other international classification systems still in use. We have developed new test procedures and decision rules for the dermal and inhalation ATC methods, which require significantly fewer animals to provide predictions of toxicity classes, that are equally good or even better than those achieved by using the conventional LD(50)/LC(50) methods. In order to cope with rather narrow dose/concentration classes of the GHS we have, as in our previous publications, combined the outcome of all results that can be obtained during testing for the allocation to one of the defined toxicity classes of the GHS. Our results strongly recommend the deletion of the dermal LD(50) and the inhalation LC(50) test as regulatory tests and the adoption of the dermal and inhalation ATC methods as internationally accepted alternatives.

Development of a decision support system for the introduction of alternative methods into local irritancy/corrosivity testing strategies. Creation of fundamental rules for a decision support system.

The notification procedure of the European Union (EU) for new chemicals requires the application of protocols on physicochemical and toxicological tests for the evaluation of physicochemical properties and probable toxic effects of each notified substance. A computerised database was developed from data sets and toxicological test protocols relating to substance properties responsible for skin and eye irritation/corrosion. To develop specific structure-activity relationship (SAR) models and to find rules for a decision support system (DSS) to predict local irritation/corrosion, physical property data, chemical structure data and toxicological data for approximately 1300 chemicals, each having a purity of 95% or more, were evaluated. The evaluation demonstrated that the lipid solubility and aqueous solubility of a chemical are relevant to, or - in some cases - responsible for, the observed local effects of a substance on the skins and eyes of rabbits. The octanol/water partition coefficient and the measured value of the surface tension of a saturated aqueous solution of the substance give additional information that permits the definition of detailed SAR algorithms that use measured solubility values. Data on melting points and vapour pressure can be used to assess the intensity and duration of local contact with a chemical. Considerations relating to the reactivity of a pure chemical can be based on molecular weight and the nature of the heteroatoms present. With respect to local lesions produced following contact with the skin and eyes of rabbits, the data evaluation revealed that no general "local irritation/corrosion potential" of a chemical can be defined. A variety of mechanisms are responsible for the formation of local lesions on the skin or in the eyes: serious lesions are produced by mechanisms different from those that cause moderate irritation in these organs. In order to develop a DSS that uses the information extracted from the database, chemical main groups were categorised on the basis of their empirical formulae, and rules were defined of the type IF (physicochemical property) A, THEN not (toxic) effect B, based on correlations between specific local effects and measured physicochemical values. Other rules of the type IF substructure A, THEN effect B were developed based on correlations between specific local effects and the submitted structural formulae. Reactive chemical substructures relevant to the formation of local lesions and rules for the prediction of the absence of any skin irritation potential were identified. Proposals are made relating to the development of alternatives to eye irritation testing with rabbits.

Development of a decision support system for the introduction of alternative methods into local irritancy/corrosivity testing strategies. Development of a relational database.

For new chemical substances that are notified within the European Union, data sets have to be submitted to the National Competent Authorities. The data submitted have to demonstrate the physicochemical and toxic properties of the new chemical, such as solubility, partition coefficients and spectra, as well as acute toxic properties and the potential to cause local irritant or corrosive effects. In order to minimise testing for notification purposes (for example, animal testing), it is necessary to develop stepwise assessment procedures, including structure-activity considerations, alternative methods (for example, in vitro tests), and computerised structure-activity relationship (SAR) models. An electronic database was developed which contains physicochemical and toxicological data on approximately 1300 chemical substances. It is used for regulatory structure-property relationship (SPR) and SAR considerations, and for the development of rules for a decision support system (DSS) for the introduction of alternative methods into local irritancy/corrosivity testing strategies. The information stored in the database is derived from proprietary data, so it is not possible to publish the data directly. Therefore, the database is evaluated by regulators, and the information derived from the data is used for the development of scientific information about SARs. This information can be published, for example, by means of tables correlating measured physicochemical values and specific toxic effects caused by the measured chemical. This information is introduced to the public by means of a DSS that predicts local irritant/corrosive potential of a chemical by listing so called exception rules of the kind IF (physicochemical property) A THEN not (toxic) Effect B and so-called structural rules of the kind IF Substructure A THEN Effect B. These DSS rules "translate" proprietary data into scientific knowledge that can be published.

Local irritation/corrosion testing strategies: development of a decision support system for the introduction of alternative methods.

The notification procedure for new chemicals of the European Union (EU) requires protocols on physicochemical and toxicological tests for the evaluation of physicochemical properties and probable toxic effects of each notified substance. In order to reduce the amount of animal testing, alternative methods should be introduced into toxicity testing. Therefore, we have developed a rule-based decision support system (DSS) for the prediction of the local corrosive/irritant properties of new chemicals. To this end, data on more than 1000 substances were examined, which resulted in approximately 180 "exception-rules" of the kind IF (physicochemical property) A THEN not (toxic) Effect B. In addition, the structural formulae of the chemicals were analysed, which resulted in approximately 160 "structure-rules" of the kind IF Substructure A THEN Effect B. The DSS can predict (based on theoretical structure-activity relationships) whether a chemical produces: a) corrosive effects (i.e. no testing is necessary; b) might have corrosive effects (i.e. no animal testing, in vitro tests are suitable) ; and c) will produce no effects or only marginal effects (i.e. animal tests are necessary based on current EU legislation for hazard assessment purposes). In addition, the DSS provides reliable data for legal classification and labelling based on a specific result.

Acute Toxic Class Methods: Alternatives to LD/LC50 Tests.

The Acute Toxic Class (ATC) Methods for the oral, dermal and inhalation routes were developed as alternatives to the respective LD/LC50 Tests. The ATC Methods use at least 40% (and up to 90%) fewer animals and their reliability with respect to classification probabilities into one of several toxicity classes is in the same order of magnitude or even better in comparison to the LD/LC50 Tests. The ATC Methods are stepwise procedures with the use of three fixed starting doses/concentrations, three animals per step and a maximum of 6 animals per dose/concentration. The outcome (numbers of dead or moribund animals) will determine if further testing is necessary or if the test is terminated. Like the previous tests the biometric basis of the ATC Methods is the Probit model. The oral ATC Method is already an official Test Guideline of the OECD and the EU and it is widely used for the notification of new chemicals in the EU. This oral ATC Method was validated by two animal ring studies together with biometric evaluations. With respect to classification probabilities and expected animal numbers the agreement between animal data and biometric evaluations was very good. Therefore for the dermal and inhalation routes of administration the ATC Methods were entirely developed on a biometric basis. These two methods have still to be adopted by OECD. However, in view of the recently agreed Global Harmonisation System (GHS) of classification for acute toxicity all three ATC Methods have to be revised in order to include these new classification systems.

The dermal acute toxic class method: test procedures and biometric evaluations.

A dermal acute toxic class (ATC) method is presented with the use of significantly fewer animals in comparison with the classical dermal 50% lethal dose (LD50) test. The principle of the dermal ATC method is based on the oral and the inhalation ATC method. The method was developed for three fixed starting doses. Depending on the dermal LD50, the slope, the classification system and the starting dose on average 40 to 90% fewer animals will be used in comparison to at least 30 animals with the dermal LD50 test. The method was biometrically evaluated by using the Probit model for dose-response relationships. At present, there are eight different international classification systems based on dermal LD50 values. The test procedures and the calculations of the classification probabilities demonstrate that the dermal ATC method is a reliable alternative to the dermal LD50 test with the use of significantly fewer animals. Classification probabilities are presented for all classification systems currently in use, and expected numbers of experimental and of moribund/dead animals are demonstrated for the system of chemicals in the European Union for all three starting doses. The conclusion is justified that, similarly to the inhalation ATC method, there is no need to validate the dermal ATC method with the use of experimental animals.

Evaluation of eye irritation potential: statistical analysis and tier testing strategies.

Eye irritation testing, specifically the Draize test, has been the centre of controversy for many reasons. Several alternatives, based on the principles of reduction, refinement and replacement, have been proposed and are being used by the industry and government authorities. However, no universally applicable, validated non-animal alternative(s) is currently available. This report presents a statistical analysis and two testing approaches: the partial least squares multivariate statistical analysis of de Silva and colleagues from France, the tier-testing approach for regulatory purposes described by Gerner and colleagues from Germany, and the three-step tier-testing approach of the US Interagency Regulatory Alternatives Group described by Gupta and Hill. These approaches were presented as three separate papers at the November 1993 Interagency Regulatory Alternatives Group (IRAG) Workshop on Eye Irritation Testing; they have been summarized and combined into the following three-part report. The first part (de Silva et al.) presents statistical techniques for establishing test batteries of in vitro alternatives to the eye irritation test. The second (Gerner et al.) and third (Gupta and Hill) parts are similar in that they stage assessment of information by using a combination of screening information and animal testing to effect reductions in animal use and distress.

The inhalation acute toxic class method: test procedures and biometric evaluations.

A method of inhalation acute toxic (ATC) classification is presented with the use of significantly fewer animals in comparison with the classical LC50 test. The principle of the inhalation ATC method is based on the oral ATC method, which has been adopted in 1996 as an official test guideline of the OECD and the European Union. The inhalation ATC method, like the oral ATC method, is a stepwise procedure; three animals of each sex are used simultaneously for each tested concentration, and not, as in the oral ATC method, three animals of each sex separately for each dose. The method was developed for three starting concentrations and two reference systems (based on ppm and mg/l). Depending on the LC50, slope, classification system and starting concentration, on average 50 to 80% fewer animals will be used in comparison to at least 30 animals with the classical LC50 test. The method was biometrically evaluated with the use of the probit model for dose-response relationships. At present, there are 12 different international classification systems based on LC50 values: 6 systems referring to mg/litre and 6 systems based on ppm values, and exposure time varying from 1 to 4 h. The test procedures and the calculations of the classification probabilities demonstrate that the inhalation ATC method is a reliable alternative to the classical LC50 test with the use of significantly fewer animals. Classification probabilities are presented for all classification systems currently in use, and expected numbers of experimental and of moribund/dead animals are demonstrated for one system of each reference system and for all three starting concentrations. The conclusion is justified that there is no need to validate the inhalation ATC method with the use of experimental animals.

Acute inhalation toxicity testing: considerations of technical and regulatory aspects.

The EU regulatory statute for the acute hazard identification of chemicals requires selection of the two most appropriate routes of administration. Testing employing the oral route is mandatory, whereas selection of the dermal or inhalation route requires expert judgement, i.e. considerations of structural alerts with regard to the inherent acute inhalation toxicity as well as the likelihood of dermal and inhalation exposure, respectively. Currently, testing of chemicals requires acute inhalation exposure of 4-h and 1-h durations according the EU classification and labelling and UN Transport Guidelines, respectively. The analysis made revealed that 1-h exposures appear to add little knowledge in addition to existing 4-h LC50 values and a default value of 4 should be used for conversion of 4-h to 1-h LC50 values, independently of the physical state of the chemical. Therefore, also the unit of concentration of exposure atmospheres should be independent of nominal features of the test substance. Hence, the preferred dose metric is mass (mg/liter air) rather than volume (ppm). Taking into account the overall variability of acute toxicity data the recommendations given are classification into the following groups of 4-h LC50 values: < or = 0.05, > 0.05-0.2, > 0.2-1, > 1-5 and > 5.0 mg/l. No distinction should be made concerning vapours and aerosols with regard to units and conversion factors from 4-h to 1-h LC50 values and the default factor of 4 appears to be most suitable. Further differentiation of classification is not indicated due to technical variability of acute inhalation testing and resolution of the acute bioassay.

Testing for skin sensitization according to the notification procedure for new chemicals: the Magnusson and Kligman test.

The notification procedure for new chemicals in the European Union (called the Chemicals Act in Germany) requires a skin sensitization test when the amount of a new chemical produced exceeds 100 kg/year. The preferred test is that of Magnusson and Kligman; more than 90% of the tests submitted are performed with it. Though the Magnusson and Kligman test is described in the literature, and in the test guidelines of the European Union and of the OECD, discrepancies do occur in the performance of the test between test laboratories. In this paper, recommendations are given for standardized performance of the Magnusson and Kligman test.

The international validation study of the acute toxic class method (oral).

An alternative to the oral LD50 test, the acute toxic class (ATC) method (oral), was validated with 20 substances in an international collaborative study with nine laboratories in five countries. The ATC method is a stepwise procedure with the use of three animals per step. It has been designed with three fixed doses (25, 200 and 2000 mg/kg). In general, this testing is sufficient for allocation to the toxicity classes of the majority of the international classification systems currently in use. The selection of testing at additional fixed doses (5, 50 and 500 mg/kg) may be considered if further refinement is necessary or for specific allocation to those international classification systems with a cut-off value of 5 mg/kg. On average, two to four steps are necessary to complete a test. With the ATC method substances can be ranked in a similar or even better manner than with an LD50 test but it uses up to 90% fewer animals, the average being 70% fewer. This also results in substantially fewer moribund/dead animals. The ATC method is based on biometric evaluations that, together with the experimental results, demonstrate that this method is a sensitive and reliable alternative to the LD50 test.

The biometric evaluation of the acute-toxic-class method (oral).

The acute toxic class method (ATC method) is an alternative to the LD50 test, with the use of substantially fewer animals needed for the classification of substances. Like the classical LD50 test the biometry of the ATC method is based on the probit model. The biometric calculations of the ATC method were carried out not only for the classification categories of the European Union but also for the classification criteria of various countries and organizations, currently in use. It is demonstrated that in comparison with the LD50 test in general the same classification is obtained with the ATC method and with the use of substantially fewer animals. Substances with high slopes are likely to be allocated to the predicted toxicity class in comparison with substances having low slopes, with both the ATC method and the LD50 test. Substances are more likely to be allocated into a lower toxicity class with the LD50 test than with the ATC method.

A national validation study of the acute-toxic-class method--an alternative to the LD50 test.

In a national collaborative study an alternative to the classical LD50 test--the acute-toxic-class method--was validated. With this testing procedure mortality ranges are determined between defined dose levels that are used for classification and labelling in the European Community. The results were compared with LD50 data obtained from the literature which were categorized according to the defined dose levels. The results of this collaborative study have shown that the acute-toxic-class method allows allocation to the toxicity classes of very toxic, toxic, harmful and unclassified in the same manner as on the basis of the classical LD50 tests. The acute-toxic-class method uses fewer animals and subjects fewer animals to pain and distress than the LD50 test and yields the same information on toxic signs in the treated animals. Identical classifications were obtained by the six participating laboratories in 86% of the tests. This demonstrates that the acute-toxic-class method results in excellent reproducibility in comparison to the classical LD50 test and that this new method is a reliable alternative to the LD50 test.

A differentiated approach to testing skin sensitization. Proposal for a new test guideline skin sensitization.

The present EEC and OECD Guidelines for testing skin sensitization have been reviewed in light of scientific evidence demonstrating that those methods which use Freund's Complete Adjuvant (FCA) are likely to be more accurate in predicting a probable skin-sensitizing effect of a new substance in humans than those methods not employing Freund's Complete Adjuvant. In this new test guideline, therefore, the primary testing of a substance should be carried out using one of the recommended Adjuvant methods. In special cases a non-adjuvant method may be performed in addition. Not all of the seven methods in the EEC Guideline or eight methods in the OECD Guideline have been included, but in a proposal for an updated test protocol two Adjuvant tests (Maximization test by Magnusson and Kligman and Optimization test by Maurer), and two non-Adjuvant tests (Open Epicutaneous test by Klecak and Buehler test) are suggested. The criteria for selecting these methods are based on the fact that they are well validated and widely used on a broad basis by the scientific community. Furthermore, it is considered appropriate to permit the use of a lower number of animals than presently recommended for the testing of skin sensitization. This is also in agreement with aspects of animal welfare.

Benzo(a)pyrene metabolism in hepatic microsomes from female DA rats with a genetic sparteine oxidation deficiency.

The impact of the genetic hydroxylation deficiency described for several drugs such as sparteine, debrisoquine, and phenformin, has been studied with respect to benzo(a)pyrene (BP) metabolite formation. 14C-BP (80 microM) was incubated with liver microsomes from female DA rats deficient in sparteine oxidation; microsomes from female Sprague-Dawley rats served as controls. BP metabolites were separated by high pressure liquid chromatography (HPLC). No significant differences were detected in the overall formation rate of 9,10-,4,5-, and 7,8-dihydrodiol-BP, of 4 quinones, or of 9-OH- and 3-OH-BP. Thus, the study suggested no association between genetic hydroxylation polymorphism (debrisoquine/sparteine type) and the formation of at least 6 BP metabolites.

Studies on the mechanism of stimulation of microsomal H2O2 formation and benzo(a)pyrene hydroxylation by substrates and flavone.

The addition of activators like flavone and hexobarbital to hepatic microsomes markedly stimulates H2O2 formation. The similar increase observed with flavone of microsomal hydroxylation of benzo(a)pyrene and its inhibition by catalase and methanol suggests but does not prove a necessary interaction of microsomal H2O2 production with benzo(a)pyrene hydroxylation. Hexobarbital and flavone-stimulated H2O2 formation is optimal at a stoichiometric relationship of these activators and NADPH. This implies either their direct participation as electron donors or their indirect involvement in electron transport by facilitation of stoichiometric substrate cytochrome P-450/NADPH flavoprotein interactions. Steady state kinetics data are consistent with a scheme in which the formation in microsomes of a complex of 1 mole of NADPH with NADPH-cytochrome P-450 reductase and 1 mole hexobarbital with cytochrome P-450 regulates H2O2 formation.