60 Years of the 3Rs symposium: Lessons learned and the road ahead.

When The Principles of Humane Experimental Technique was published in 1959, authors William Russell and Rex Burch had a modest goal: to make researchers think about what they were doing in the laboratory ­ and to do it more humanely. Sixty years later, their groundbreaking book was celebrated for inspiring a revolution in science and launching a new field: The 3Rs of alternatives to animal experimentation. On November 22, 2019, some pioneering and leading scientists and researchers in the field gathered at the Johns Hopkins Bloomberg School of Public Health in Bal­timore for the 60 Years of the 3Rs Symposium: Lessons Learned and the Road Ahead. The event was sponsored by the Johns Hopkins Center for Alternatives to Animal Testing (CAAT), the Foundation for Chemistry Research and Initiatives, the Alternative Research & Development Foundation (ARDF), the American Cleaning Institute (ACI), the International Fragrance Association (IFRA), the Institute for In Vitro Sciences (IIVS), John "Jack" R. Fowle III, and the Society of Toxicology (SoT). Fourteen pres­entations shared the history behind the groundbreaking publication, international efforts to achieve its aims, stumbling blocks to progress, as well as remarkable achievements. The day was a tribute to Russell and Burch, and a testament to what is possible when people from many walks of life ­ science, government, and industry ­ work toward a common goal.

William Russell and Rex Burch published their book The Principles of Humane Experimental Technique in 1959. The book encouraged researchers to replace animal experiments where it was possible, to refine experiments with animals in order to reduce their suffering, and to reduce the number of animals that had to be used for experiments to the minimum. Sixty years later, a group of pioneering and leading scientists and researchers in the field gathered to share how the publi­cation came about and how the vision inspired international collaborations and successes on many different levels including new laws. The paper includes an overview of important milestones in the history of alternatives to animal experimentation.

A European perspective on alternatives to animal testing for environmental hazard identification and risk assessment.

Tests with vertebrates are an integral part of environmental hazard identification and risk assessment of chemicals, plant protection products, pharmaceuticals, biocides, feed additives and effluents. These tests raise ethical and economic concerns and are considered as inappropriate for assessing all of the substances and effluents that require regulatory testing. Hence, there is a strong demand for replacement, reduction and refinement strategies and methods. However, until now alternative approaches have only rarely been used in regulatory settings. This review provides an overview on current regulations of chemicals and the requirements for animal tests in environmental hazard and risk assessment. It aims to highlight the potential areas for alternative approaches in environmental hazard identification and risk assessment. Perspectives and limitations of alternative approaches to animal tests using vertebrates in environmental toxicology, i.e. mainly fish and amphibians, are discussed. Free access to existing (proprietary) animal test data, availability of validated alternative methods and a practical implementation of conceptual approaches such as the Adverse Outcome Pathways and Integrated Testing Strategies were identified as major requirements towards the successful development and implementation of alternative approaches. Although this article focusses on European regulations, its considerations and conclusions are of global relevance.

In vitro tests to evaluate embryotoxicity and irritation of Chinese herbal medicine (Pentaherbs formulation) for atopic dermatitis.

ETHNOPHARMACOLOGICAL RELEVANCE: Atopic dermatitis (AD) is a common chronic inflammatory skin disorder and its prevalence is increasing in the last few decades. No treatment can cure the condition. Pregnancy often worsens the clinical manifestation. There are considerable interests in Chinese Herbal Medicine (CHM) as an alternative treatment for AD. A well tolerated CHM formula (Pentaherbs formulation, PHF) has been proven efficacious in improving life quality and reducing topical corticosteroid use in children with moderate-to-severe AD. However, safety data of PHF are not available. AIM OF THE STUDY: Our study aimed to evaluate the safety of PHF and its 5 individual herbal extracts, including embryotoxicity by Embryonic Stem Cell Test (EST) and irritation by Skin Irritation Test (SIT). MATERIALS AND METHODS: Quality of 5 herbal extracts of PHF was confirmed by chromatography. In EST, mouse embryonic stem cell line (D3) and mouse fibroblast cell line (3T3) were used to study potential embryotoxicity. Three endpoints were assessed by concentration-response curves after 10 days' culture: 50% inhibition of D3 differentiation into beating cardiomyocytes (ID50D3), 50% cytotoxic effects on D3 (IC50D3) and on fibroblasts (IC503T3). A biostatistically based prediction model (PM) was applied to predict the embryotoxic potentials of each CHM. In SIT, epidermis equivalent commercially available kits (EpiDerm™) were used, and concentration-viability curves were obtained by MTT assay to detect skin irritations of each CHM. RESULTS: Chemical authentication confirmed that 5 test herbal extracts contained their main active compounds. EST results indicated that the formula PHF and its individual CHMs were non-embryotoxic, except one CHM, Amur Corktree Bark (Huang Bai, Phellodendron chinense C.K.Schneid), was weakly embryotoxic. SIT results showed that cell viability was above 50% after treatment with different concentrations of all tested CHMs. CONCLUSIONS: Our in vitro tests provided preliminary evidence for safety of the formula PHF in embryonic stem cell test and skin irritation model, but PHF shall be cautiously used in pregnant women with AD. Further studies are needed to support its clinical application as an alternative treatment for AD, especially to the patients who plan for pregnancy or at lactation stages.

Assaying embryotoxicity in the test tube: current limitations of the embryonic stem cell test (EST) challenging its applicability domain.

Testing for embryotoxicity in vitro is an attractive alternative to animal experimentation. The embryonic stem cell test (EST) is such a method, and it has been formally validated by the European Centre for the Validation of Alternative Methods. A number of recent studies have underscored the potential of this method. However, the EST performed well below the 78% accuracy expected from the validation study using a new set of chemicals and pharmaceutical compounds, and also of toxicity criteria, tested to enlarge the database of the validated EST as part of the Work Package III of the ReProTect Project funded within the 6th Framework Programme of the European Union. To assess the performance and applicability domain of the EST we present a detailed review of the substances and their effects in the EST being nitrofen, ochratoxin A, D-penicillamine, methylazoxymethanol, lovastatin, papaverine, warfarin, ß-aminopropionitrile, dinoseb, furosemide, doxylamine, pravastatin, and metoclopramide. By delineation of the molecular mechanisms of the substances we identify six categories of reasons for misclassifications. Some of these limitations might also affect other in vitro methods assessing embryotoxicity. Substances that fall into these categories need to be included in future validation sets and in validation guidelines for embryotoxicity testing. Most importantly, we suggest conceivable improvements and additions to the EST which will resolve most of the limitations.

Pluripotent stem cell assays: Modalities and applications for predictive developmental toxicity.

This manuscript provides a review focused on embryonic stem cell-based models and their place within the landscape of alternative developmental toxicity assays. Against the background of the principles of developmental toxicology, the wide diversity of alternative methods using pluripotent stem cells developed in this area over the past half century is reviewed. In order to provide an overview of available models, a systematic scoping review was conducted following a published protocol with inclusion criteria, which were applied to select the assays. Critical aspects including biological domain, readout endpoint, availability of standardized protocols, chemical domain, reproducibility and predictive power of each assay are described in detail, in order to review the applicability and limitations of the platform in general and progress moving forward to implementation. The horizon of innovative routes of promoting regulatory implementation of alternative methods is scanned, and recommendations for further work are given.

A critical evaluation of the 2011 ECHA reports on compliance with the REACH and CLP regulations and on the use of alternatives to testing on animals for compliance with the REACH regulation.

On 30 June 2011, the European Chemicals Agency published two reports, one on the functioning of the REACH system, the other on the use of alternatives to animal testing in compliance with that system. The data presented are based on information gained during the first registration period under the REACH system, which included high production volume chemicals and substances of very high concern, which have the most extensive information requirements. A total of 25,460 registration dossiers were received, covering 3,400 existing, so-called 'phase-in', substances, and 900 new, so-called 'non-phase-in', substances. Data sharing and the joint submission of data are reported to have worked successfully. In the registration dossiers for these substances, results from new animal tests were included for less than 1% of all the endpoints; testing proposals (required for 'higher-tier' information requirements) were submitted for 711 in vivo tests involving vertebrate animals. The registrants mainly used old, existing experimental data, or options for the adaptation (waiving) of information requirements, before collecting new information. For predicting substance toxicity, 'read-across' was the second most-used approach, followed by 'weight-of-evidence'. In vitro toxicity tests played a minor role, and were only used when the respective test methods had gained the status of regulatory acceptance. All in all, a successful start to the REACH programme was reported, particularly since, in contrast to most predictions, it did not contribute to a significant increase in toxicity testing in animals.

Protein biomarkers for in vitro testing of embryotoxicity.

There are new challenges for hazard and risk assessment in the chemical industry with regard to REACH legislation in Europe and related activities in the U.S. and Japan, which require the development of novel in vitro models for the molecular characterization of drug- or chemical-related effects replacing conventional animal testing. In the frame of a European FP6 project on reproductive toxicology ( www.reprotect.eu ), we prepared protein samples from mouse embryonic stem cells differentiated into contracting cardiomyocytes according to the validated embryonic stem cell test (EST) protocol, which had been exposed to toxic substances selected by an expert committee from different in vivo categories of embryotoxicity. Lysates were used to carry out the following investigations: (i) identify optimal dose range conditions in the EST that are suitable for (ii) performing a differential quantitative proteomic study of underlying molecular pathways, (iii) define classes of substances with similar proteomic response patterns, (iv) relate these classes to the traditional in vivo categories of embryotoxicity with (v) the final goal to identify novel surrogate protein biomarker candidates for embryo toxicity. We found two distinct classes of toxic substances (Dinoseb, Ochratoxin-A, and Nitrofen vs ß-aminoproprionitril, Metoclopramide, Doxylamine succinate, and d-penicillamine) with clear pathway-related differences in their proteomic patterns. Most notably, different responses to cluster 1 and cluster 2 substances were observed for Heat shock protein ß-1, Ras-GTPase-activating protein SH3-domain binding protein, Ran binding protein 5, and Calreticulin, Dihydropyrimidinase-like 2 (Ulip2 protein). On the other hand, Heat shock protein 8 and Fscn1 protein were down-regulated by all compounds from both clusters.

A 1-year toxicity study in dogs is no longer a scientifically justifiable core data requirement for the safety assessment of pesticides.

A review of publications on pesticides assessing the need for 1-year toxicity studies in dogs was performed. Four key peer-reviewed papers with different approaches investigated the value of a 1-year dog study in addition to a 3-month study. Despite different databases and approaches, each concluded with the recommendation to limit the testing of pesticides in dogs to a duration of 3 months. The combined weight of evidence presented in this review reinforces these independent conclusions. Therefore, the routine inclusion of a 1-year dog study as a mandated regulatory requirement for the safety assessment of pesticides is no longer justifiable and a globally harmonized approach should be taken to match the latest legislation of the European Union and the US EPA.

The way forward in reproductive/developmental toxicity testing.

The use of experimental animals in reproductive toxicity testing is critically reviewed on the occasion of the 50th anniversary of the publication of the Three Rs concept by Russell and Burch, since there is major concern that reproductive toxicity testing will significantly increase due to the requirements of the EU Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) system. A comparison of the test guidelines for drugs, agrochemicals and industrial chemicals shows that, for historical reasons, significantly different testing strategies are applied. The current status of development and validation of in vitro tests in reproductive toxicology is also critically evaluated. The mouse embryonic stem cell test (mEST) is the most advanced and promising of the in vitro tests. Although it has not yet been accepted for regulatory purposes, its use in preclinical drug development is well established. Moreover, promising molecular endpoints have been established in the mEST, including proteomic and toxicogenomic endpoints. Preliminary results have been obtained with a human EST (hEST). In addition, an overview is given on new in vitro reproductive toxicity tests that are currently being developed in the EU FP6 project, ReProTect, since the ReProTect test battery, which covers the essential steps of female and male fertility, implantation and embryotoxicity, holds promise for use as a screening assay for reproductive toxicity testing according to the EU REACH legislation. However, since validated in vitro methods will not be available in the short term, opportunities for the refinement of the standard in vivo tests are discussed, in order to reduce the numbers of animal used in reproductive toxicity testing. Finally, recommendations for toxicity testing in the 21st century call for the harmonisation of test methods across all areas of regulatory testing as a first step. Since the REACH system testing framework for industrial chemicals is driven by the reproductive safety testing requirements of agrochemicals, a shift is proposed to exposure-driven testing of industrial chemicals. In particular, the implementation of a new 'extended one-generation reproductive toxicity study' (EOGRTS), which includes triggers for additional testing for fertility, developmental neurotoxicity and immunotoxicity, would significantly reduce test animal numbers. It is concluded that in vitro methods hold great promise for reproductive toxicity testing in the 21st century, e.g. the ReProTect in vitro battery and the embryonic stem cell (ESC) technology focusing on molecular endpoints in both the mEST and the hEST.

Collaboration between ZEBET, FRAME, and ECVAM: FRAME's contribution to establishing the Three Rs in Europe.

FRAME has more than any other institution contributed to the implementation of the Three Rs concept in Europe. The first step was achieved by establishing the European Research Group on Alternatives to Toxicity Testing (ERGATT), in which individual scientists in several European countries began to collaborate to promote the development and validation of in vitro toxicity tests in order to refine, reduce and replace the use of animals in toxicity testing. The first successful project was the start of the INVITOX in vitro toxicology database, which is today managed by ECVAM. Major milestones were the establishment in 1989 of ZEBET, the first national centre for alternatives, in Germany, and of ECVAM in 1991. In 1990, ERGATT and CAAT organised a workshop in Amden, Switzerland, at which European and US scientists developed the concept of experimental validation of toxicity tests, which today remains the basis for the independent, scientific validation process. ECVAM has applied this validation concept in all of its successful validation studies, which have provided in vitro toxicity tests that have been accepted for regulatory purposes by the EU Commission and by the OECD. By re-launching the ATLA journal in 1983, FRAME provided another powerful scientific tool for promoting the Three Rs in Europe and around the world. The close cooperation of scientists from FRAME, ZEBET and ECVAM has most effectively promoted and established the Three Rs as the basic scientific, ethical and legal concept for refining, reducing and replacing the use of experimental animals.

Evaluation of in vitro embryotoxicity tests for Chinese herbal medicines.

Chinese herbal medicines (CHMs) have been widely used during pregnancy, but feto-embryo safety tests are lacking. Here we evaluated in vitro embryotoxicity tests (IVTs) as alternative methods in assessing developmental toxicity of CHMs. Ten CHMs were selected and classified as strongly, weakly and non-embryotoxic. Three well validated IVTs and prediction models (PMs), including embryonic stem cell test (EST), micromass (MM) and whole embryo culture (WEC), were compared. All strongly embryotoxic CHMs were predicted by MM and WEC PM2. While all weakly embryotoxic CHMs were predicted by MM and WEC PM1. All non-embryotoxic CHMs were classified by EST, MM, but over-classified as weakly embryotoxic by WEC PM1. Overall predictivity, precision and accuracy of WEC determined by PM2 were better than EST and MM tests. Compared with validated chemicals, performance of IVTs for CHMs was comparable. So IVTs are adequate to identify and exclude embryotoxic potential of CHMs in this training set.

Assessment of early acute lung injury in rats exposed to aerosols of consumer products: attempt to disentangle the "Magic Nano" conundrum.

In Germany in 2006 a series of rapidly developing and sometimes severe cases of pulmonary health impairment were observed after normal use of the "Magic Nano Glass & Ceramic" spray and "Magic Nano Bath" spray. In contrast, the previously marketed "Magic Nano" pump spray product (handheld trigger device without propellants) was unobtrusive. Analysis of particles discharged from these products did not reveal stable (solid) nano-sized particles. The precipitous increase of pulmonary health impairment in humans caused by "Magic Nano Sprays" triggered a comparative assessment of the acute inhalation toxicity of "Magic Nano Glass & Ceramic" spray, "Magic Nano Bath" spray, and "Magic Nano" pump spray in rats. The first two test specimens were examined as spray-can aerosols using an intermittent generation principle, whereas the undiluted liquid content of the pump spray was continuously aerosolized. Groups of Wistar rats were nose-only exposed for 4 h. However, due to mortality occurring already during exposure following exposure to Glass & Ceramic spray, the exposure duration was reduced to approximately 2 h in some groups. In addition to endpoints called for by contemporary testing guidelines, respiratory tract injury was also probed by respiratory function measurements during exposure supplemented by analyses in bronchoalveolar lavage (BAL) fluid on the first postexposure day, including lung histopathology in rats exposed to Glass & Ceramic spray. The Glass & Ceramic spray caused mortality at 2269 mg/m(3) and above, the pump spray was in the beginning lethal range at 81222 mg/m(3), while the bath spray was tolerated without mortality up to the maximum tested nominal concentrations of 28100 mg/m(3). The time-adjusted 4-h LC(50) of Glass & Ceramic spray was 5098 mg/m(3). The analysis of respiratory patterns revealed changes indicative of both upper and lower respiratory tract sensory irritation. In addition to clinical signs suggestive of marked lung irritation, especially in the rats exposed to the Glass & Ceramic spray, histopathology revealed lung inflammation, hemorrhages, edema, and focal septal thickening. Lung weights and BAL endpoints (lactate dehydrogenase [LDH], protein, gamma-glutamyltransaminase, and neutrophilic granulocytes) were markedly increased. In summary, this comparative study demonstrates that the conventional OECD 403 protocol is suitable to comparatively assess the potential and potency of these types of consumer products in their end-use configuration. Measurements in BAL were most suitable for the identification of acute lung injury. By contrast, lung function measurements during exposure did not demonstrate any conclusive association with lung injury. It does not appear that the particle size per se is a key determinant in the toxicity of "Magic Nano Glass & Ceramic" spray (approximately 100% mortality occurred at a MMAD of approximately 7 microm; GSD approximately 3). This might suggest that more volatile substances or substances contained in the test articles that co-evaporate with solvents or water may be causative for the findings observed. Hence, the findings of this study support the notion that the assessment of the acute inhalation toxicity of complex end-use products is methodologically challenging and cannot be readily anticipated based on compositional or physical (particle size) data. Accordingly, in the absence of predictive and validated in vitro assays, in vivo inhalation testing of potentially toxic commercialized spray products appears to be indispensable for consumer safety. In order to prevent indiscriminant testing of such products in bioassays, the development of standardized in vitro alternatives should be considered with high priority.

Successful validation of in vitro methods in toxicology by ZEBET, the National Centre for Alternatives in Germany at the BfR (Federal Institute for Risk Assessment).

A short description of the history of the 3Rs concept is given, which was developed as the scientific concept to refine, reduce and replace animal experiments by Russel and Burch more than 40 years ago. In addition, the legal framework in Europe for developing alternatives to animal experiments is given and the current status of in vitro systems in pharmacology and toxicology is described including an update on metabolising systems. The decrease in experimental animal numbers during the past decade in Europe is illustrated by the situation in Germany and the contribution of international harmonisation of test guidelines on reducing animal numbers in regulatory testing is described. A review of the development of the principles of experimental validation is given and the 3T3 NRU in vitro phototoxicity test is used as an example for a successful validation study, which led to the acceptance of the first in vitro toxicity test for regulatory purposes by the OECD. Finally, the currently accepted alternative methods for standardisation and safety testing of drugs, biologicals and medical devices are summarised.

The use of reconstructed human epidermis for skin absorption testing: Results of the validation study.

A formal validation study was performed, in order to investigate whether the commercially-available reconstructed human epidermis (RHE) models, EPISKIN, EpiDerm and SkinEthic, are suitable for in vitro skin absorption testing. The skin types currently recommended in the OECD Test Guideline 428, namely, ex vivo human epidermis and pig skin, were used as references. Based on the promising outcome of the prevalidation study, the panel of test substances was enlarged to nine substances, covering a wider spectrum of physicochemical properties. The substances were tested under both infinite-dose and finite-dose conditions, in ten laboratories, under strictly controlled conditions. The data were subjected to independent statistical analyses. Intra-laboratory and inter-laboratory variability contributed almost equally to the total variability, which was in the same range as that in preceding studies. In general, permeation of the RHE models exceeded that of human epidermis and pig skin (the SkinEthic RHE was found to be the most permeable), yet the ranking of substance permeation through the three tested RHE models and the pig skin reflected the permeation through human epidermis. In addition, both infinite-dose and finite-dose experiments are feasible with RHE models. The RHE models did not show the expected significantly better reproducibility, as compared to excised skin, despite a tendency toward lower variability of the data. Importantly, however, the permeation data showed a sufficient correlation between all the preparations examined. Thus, the RHE models, EPISKIN, EpiDerm and SkinEthic, are appropriate alternatives to human and pig skin, for the in vitro assessment of the permeation and penetration of substances when applied as aqueous solutions.

The ECVAM international validation study on in vitro tests for acute skin irritation: report on the validity of the EPISKIN and EpiDerm assays and on the Skin Integrity Function Test.

ECVAM sponsored a formal validation study on three in vitro tests for skin irritation, of which two employ reconstituted human epidermis models (EPISKIN, EpiDerm), and one, the skin integrity function test (SIFT), employs ex vivo mouse skin. The goal of the study was to assess whether the in vitro tests would correctly predict in vivo classifications according to the EU classification scheme, "R38" and "no label" (i.e. non-irritant). 58 chemicals (25 irritants and 33 non-irritants) were tested, having been selected to give broad coverage of physico-chemical properties, and an adequate distribution of irritancy scores derived from in vivo rabbit skin irritation tests. In Phase 1, 20 of these chemicals (9 irritants and 11 non-irritants) were tested with coded identities by a single lead laboratory for each of the methods, to confirm the suitability of the protocol improvements introduced after a prevalidation phase. When cell viability (evaluated by the MTT reduction test) was used as the endpoint, the predictive ability of both EpiDerm and EPISKIN was considered sufficient to justify their progression to Phase 2, while the predictive ability of the SIFT was judged to be inadequate. Since both the reconstituted skin models provided false predictions around the in vivo classification border (a rabbit Draize test score of 2), the release of a cytokine, interleukin-1alpha (IL-1alpha), was also determined. In Phase 2, each human skin model was tested in three laboratories, with 58 chemicals. The main endpoint measured for both EpiDerm and EPISKIN was cell viability. In samples from chemicals which gave MTT assay results above the threshold of 50% viability, IL-1alpha release was also measured, to determine whether the additional endpoint would improve the predictive ability of the tests. For EPISKIN, the sensitivity was 75% and the specificity was 81% (MTT assay only); with the combination of the MTT and IL-1alpha assays, the sensitivity increased to 91%, with a specificity of 79%. For EpiDerm, the sensitivity was 57% and the specificity was 85% (MTT assay only), while the predictive capacity of EpiDerm was not improved by the measurement of IL-1alpha release. Following independent peer review, in April 2007 the ECVAM Scientific Advisory Committee endorsed the scientific validity of the EPISKIN test as a replacement for the rabbit skin irritation method, and of the EpiDerm method for identifying skin irritants as part of a tiered testing strategy. This new alternative approach will probably be the first use of in vitro toxicity testing to replace the Draize rabbit skin irritation test in Europe and internationally, since, in the very near future, new EU and OECD Test Guidelines will be proposed for regulatory acceptance.

Use of murine embryonic stem cells in embryotoxicity assays: the embryonic stem cell test.

The embryonic stem cell test (EST) takes advantage of the potential of murine embryonic stem (ES) cells to differentiate in culture to test embryotoxicity in vitro. The EST represents a scientifically validated in vitro system for the classification of compounds according to their teratogenic potential based on the morphological analysis of beating cardiomyocytes in embryoid body outgrowths compared to cytotoxic effects on murine ES cells and differentiated 3T3 fibroblasts. Through a number of prevalidation and validation studies, the EST has been demonstrated to be a reliable alternative method for embryotoxicity testing based on the most important mechanisms in embryotoxicity-cytotoxicity and differentiation--as well as on differences in sensitivity between differentiated and embryonic tissues. Improvements of the EST protocol using flow cytometry analysis showed that differential expression of sarcomeric myosin heavy chain and alpha-actinin proteins quantified under the influence of a test compound is a useful marker for detecting potential teratogenicity. The in vitro embryotoxicity test described in this chapter is rapid, simple, and sensitive and can be usefully employed as a component of the risk/hazard assessment process.

Assessment of the human epidermis model SkinEthic RHE for in vitro skin corrosion testing of chemicals according to new OECD TG 431.

Based on two successfully completed ECVAM validation studies for in vitro skin corrosion testing of chemicals, the National Co-ordinators of OECD Test Guideline Programme endorsed in 2002 two new test guidelines: TG 430 'Transcutaneous Electrical Resistance assay' and TG 431 'Human Skin Model Test'. To allow all suitable in vitro human reconstructed (dermal or epidermal) models to be used for skin corrosion testing, the OECD TG 431 defines general and functional conditions that the model must meet before it will be routinely used for skin corrosion testing. In addition, the guideline requires correct prediction of 12 reference chemicals and assessment of intra- and inter-laboratory variability. To show that the OECD TG 431 concept works, in 2003 ZEBET tested several chemicals from the ECVAM validation trials on the SkinEthic reconstituted human epidermal (RHE) model. Based on knowledge that reconstructed human skin models perform similarly in toxicological studies, it was decided to adopt the validated EpiDerm skin corrosion test protocol and prediction model to the SkinEthic model. After minor technical changes, classifications were obtained in concordance with those reported for the validated human skin models EPISKIN and EpiDerm. To allow adequate determination of inter-laboratory reproducibility, a blind trial was conducted in three laboratories -- ZEBET (D), Safepharm (UK) and BASF (D), in which the 12 endorsed reference chemicals were tested. Results obtained with the SkinEthic epidermal model were reproducible, both within and between laboratories, and over time. Concordance between the in vitro predictions of skin corrosivity potential obtained with the SkinEthic model and the predictions obtained with the accepted tests of OECD TG 430 and TG 431 was very good. The new test was able to distinguish between corrosive and non-corrosive reference chemicals with an accuracy of 93%.

Assessment of the skin irritation potential of chemicals by using the SkinEthic reconstructed human epidermal model and the common skin irritation protocol evaluated in the ECVAM skin irritation validation study.

Currently, two reconstructed human skin models, EpiDerm and EPISKIN are being evaluated in an ECVAM skin irritation validation study. A common skin irritation protocol has been developed, differing only in minor technical details for the two models. A small-scale study, applying this common skin irritation protocol to the SkinEthic reconstructed human epidermis (RHE), was performed at ZEBET at the BfR, Berlin, Germany, to consider whether this protocol could be successfully transferred to another epidermal model. Twenty substances from Phase III of the ECVAM prevalidation study on skin irritation were tested with the SkinEthic RHE. After minor, model-specific adaptations for the SkinEthic RHE, almost identical results to those obtained with the EpiDerm and EPISKIN models were achieved. The overall accuracy of the method was more than 80%, indicating a reliable prediction of the skin irritation potential of the tested chemicals when compared to in vivo rabbit data. As a next step, inter laboratory reproducibility was assessed in a study conducted between ZEBET and the Department of Experimental Toxicology, Schering AG, Berlin, Germany. Six coded substances were tested in both laboratories, with three different batches of the SkinEthic model. The assay results showed good reproducibility and correct predictions of the skin irritation potential for all six test chemicals. The results obtained with the SkinEthic RHE and the common protocol were reproducible in both phases, and the overall outcome is very similar to that of earlier studies with the EPISKIN and EpiDerm models. Therefore, the SkinEthic skin irritation assay test protocol can now be evaluated in a formal "catch-up" validation study.

Reconstructed human epidermis for skin absorption testing: results of the German prevalidation study.

Exposure to chemicals absorbed by the skin can threaten human health. In order to standardise the predictive testing of percutaneous absorption for regulatory purposes, the OECD adopted guideline 428, which describes methods for assessing absorption by using human and animal skin. In this study, a protocol based on the OECD principles was developed and prevalidated by using reconstructed human epidermis (RHE). The permeation of the OECD standard compounds, caffeine and testosterone, through commercially available RHE models was compared to that of human epidermis and animal skin. In comparison to human epidermis, the permeation of the chemicals was overestimated when using RHE. The following ranking of the permeation coefficients for testosterone was obtained: SkinEthic > EpiDerm, EPISKIN > human epidermis, bovine udder skin, pig skin. The ranking for caffeine was: SkinEthic, EPISKIN > bovine udder skin, EpiDerm, pig skin, human epidermis. The inter-laboratory and intra-laboratory reproducibility was good. Long and variable lag times, which are a matter of concern when using human and pig skin, did not occur with RHE. Due to the successful transfer of the protocol, it is now in the validation process.