Uwe Pfannenbecker

A proposed eye irritation testing strategy to reduce and replace in vivo studies using Bottom–Up and Top–Down approaches

In spite of over 20 years of effort, no single in vitro assay has been developed and validated as a full regulatory replacement for the Draize Eye Irritation test. However, companies have been using in vitro methods to screen new formulations and in some cases as their primary assessment of eye irritation potential for many years. The present report shows the outcome of an Expert Meeting convened by the European Centre for the Validation of Alternative Methods in February 2005 to identify test strategies for eye irritation. In this workshop test developers/users were requested to nominate methods to be considered as a basis for the identification of such testing strategies. Assays were evaluated and categorized based on their proposed applicability domains (e.g., categories of irritation severity, modes of action, chemical class, physicochemical compatibility). The analyses were based on the data developed from current practice and published studies, the ability to predict depth of injury (within the applicable range of severity), modes of action that could be addressed and compatibility with different physiochemical forms. The difficulty in predicting the middle category of irritancy (e.g. R36, GHS Categories 2A and 2B) was recognized. The testing scheme proposes using a Bottom-Up (begin with using test methods that can accurately identify non-irritants) or Top-Down (begin with using test methods that can accurately identify severe irritants) progression of in vitro tests (based on expected irritancy). Irrespective of the starting point, the approach would identify non-irritants and severe irritants, leaving all others to the (mild/moderate) irritant GHS 2/R36 categories.

A summary report of the COLIPA international validation study on alternatives to the draize rabbit eye irritation test.

The principal goal of this study was to determine whether the results from a set of selected currently available alternative methods as used by cosmetics companies are valid for predicting the eye irritation potential of cosmetics formulations and ingredients and, as a consequence, could be valid replacements for the Draize eye irritation test. For the first time in a validation study, prediction models (PMs) that convert the in vitro data from an assay to a prediction of eye irritation were developed for each alternative method before the study began. The PM is an unequivocal description of the relationship between the in vitro and the in vivo data and allows an objective assessment of the reliability and relevance of the alternative methods. In this study, 10 alternative methods were evaluated using 55 test substances selected as representative of substances commonly used in the cosmetics industry (23 ingredients and 32 formulations). Twenty of the single ingredients were common to the European Commission/British Home Office (EC/HO) eye irritation validation study (Balls et al., 1995b). The test substances were coded and supplied to the participating laboratories. The results were collected centrally and analysed independently, using statistical methods that had been agreed before the testing phase began. Each alternative method was then evaluated for reliability and relevance in assessing eye irritation potential. Using the criteria of both reliability and relevance as defined in the study, the preliminary results indicate that none of the alternative methods evaluated could be confirmed as a valid replacement for the Draize eye irritation test across the full irritation scale. However, three alternative methods-the fluorescein leakage test, the red blood cell assay (classification model) and the tissue equivalent assay-each satisfied one criterion of reliability or relevance. Further investigation of the decoded data from this study to explore more fully the relationship between the in vitro data and the in vivo data is recommended. Such a review may allow the development of new prediction models to be tested in a subsequent validation study.

Cosmetics Europe multi-laboratory pre-validation of the EpiOcular™ reconstituted human tissue test method for the prediction of eye irritation.

Cosmetics Europe, The Personal Care Association (known as Colipa before 2012), conducted a program of technology transfer and within/between laboratory reproducibility of MatTek Corporations EpiOcular™ Eye Irritation Test (EIT) as one of the two human reconstructed tissue test methods. This EIT EpiOcular™ used a single exposure period for each chemical and a prediction model based on a cut-off in relative survival [ ≤60%=irritant (I) (GHS categories 2 and 1); >60%=no classification (NC)]. Test substance single exposure time was 30 min with a 2-h post-exposure incubation for liquids and 90 min with an 18-h post-exposure incubation for solids. Tissue viability was determined by tetrazolium dye (MTT) reduction. Combinations of 20 coded chemicals were tested in 7 laboratories. Standardized laboratory documentation was used by all laboratories. Twenty liquids (11 NC/9 I) plus 5 solids (3 NC/2 I) were selected so that both exposure regimens could be assessed. Concurrent positive (methyl acetate) and negative (water) controls were tested in each trial. In all, 298 independent trials were performed and demonstrated 99.7% agreement in prediction (NC/I) across the laboratories. Coefficients of variation for the% survival for tissues from each treatment group across laboratories were generally low. This protocol has entered in 2010 the experimental phase of a formal ECVAM validation program.

Cosmetics Europe multi-laboratory pre-validation of the SkinEthic™ reconstituted human corneal epithelium test method for the prediction of eye irritation

Cosmetics Europe, The Personal Care Association, known as Colipa before 2012, conducted a program of technology transfer and assessment of Within/Between Laboratory (WLV/BLV) reproducibility of the SkinEthic™ Reconstituted Human Corneal Epithelium (HCE) as one of two human reconstructed tissue eye irritation test methods. The SkinEthic™ HCE test method involves two exposure time treatment procedures - one for short time exposure (10 min - SE) and the other for long time exposure (60 min - LE) of tissues to test substance. This paper describes pre-validation studies of the SkinEthic™ HCE test method (SE and LE protocols) as well as the Eye Peptide Reactivity Assay (EPRA). In the SE WLV study, 30 substances were evaluated. A consistent outcome with respect to viability measurement across all runs was observed with all substances showing an SD of less than 18%. In the LE WLV study, 44 out of 45 substances were consistently classified. These data demonstrated a high level of reproducibility within laboratory for both the SE and LE treatment procedures. For the LE BLV, 19 out of 20 substances were consistently classified between the three laboratories, again demonstrating a high level of reproducibility between laboratories. The results for EPRA WLV and BLV studies demonstrated that all substances analysed were categorised similarly and that the method is reproducible. The SkinEthic™ HCE test method entered into the experimental phase of a formal ECVAM validation program in 2010.

COLIPA validation project on in vitro eye irritation tests for cosmetic ingredients and finished products (phase I): the red blood cell test for the estimation of acute eye irritation potentials. Present status

The red blood cell test (RBC test) is part of the COLIPA Validation Project on Alternatives to Draize Eye Irritation. It shows good intra- and interlaboratory reproducibility (reliability) and represents one of the promising in vitro alternatives of this project with a good fit to prediction models (relevance) for the assessment of acute ocular irritancy caused by certain classes of chemicals (mainly surfactants) and formulations. Results obtained during the period of test development, prevalidation, and validation are summarized. The method is based on that of Pape et al. (1987), Pape and Hoppe (1990) and Lewis et al. (1993). The protocol has two endpoints: cellular lysis and changes in protein conformation which can be correlated with initial events in tissue injury inducing inflammatory responses as assessed by Draize eye irritation scoring. Both endpoints are detected by spectrophotometric changes in the haemoglobin absorption at 541nm. The protocol also includes a set of prediction models (PM). One PM is designed to predict three classes of irritancy (classification model) based on both endpoints and the three other PMs are designed to predict modified maximum average scores (MMAS) by algorithms based on data from cellular lysis only. These three PMs [with prediction intervals (PIs)] are: (i) for surfactant ingredients, (ii) for surfactant containing finished products, and (iii) for both groups together. The three PMs are based on a common algorithm derived from historic data. It is shown that PMs derived from historic data from several laboratories, by the same procedure, also produce a good fit with the presented data. Therefore, participating laboratories concluded that the protocol as used in this formal validation study can be considered to be validated for the estimation of acute eye irritation potential of surfactant-containing finished products.

Use of HPLC/UPLC-spectrophotometry for detection of formazan in in vitro Reconstructed human Tissue (RhT)-based test methods employing the MTT-reduction assay to expand their applicability to strongly coloured test chemicals

A number of in vitro test methods using Reconstructed human Tissues (RhT) are regulatory accepted for evaluation of skin corrosion/irritation. In such methods, test chemical corrosion/irritation potential is determined by measuring tissue viability using the photometric MTT-reduction assay. A known limitation of this assay is possible interference of strongly coloured test chemicals with measurement of formazan by absorbance (OD). To address this, Cosmetics Europe evaluated use of HPLC/UPLC-spectrophotometry as an alternative formazan measurement system. Using the approach recommended by the FDA guidance for validation of bio-analytical methods, three independent laboratories established and qualified their HPLC/UPLC-spectrophotometry systems to reproducibly measure formazan from tissue extracts. Up to 26 chemicals were then tested in RhT test systems for eye/skin irritation and skin corrosion. Results support that: (1) HPLC/UPLC-spectrophotometry formazan measurement is highly reproducible; (2) formazan measurement by HPLC/UPLC-spectrophotometry and OD gave almost identical tissue viabilities for test chemicals not exhibiting colour interference nor direct MTT reduction; (3) independent of the test system used, HPLC/UPLC-spectrophotometry can measure formazan for strongly coloured test chemicals when this is not possible by absorbance only. It is therefore recommended that HPLC/UPLC-spectrophotometry to measure formazan be included in the procedures of in vitro RhT-based test methods, irrespective of the test system used and the toxicity endpoint evaluated to extend the applicability of these test methods to strongly coloured chemicals.

Performance of the Pollen Tube Growth Test in the COLIPA Validation Study on Alternatives to the Rabbit Eye Irritation Test.

In the present paper, we describe and analyse the performance and the results of the pollen tube growth (PTG) test applied to the COLIPA international validation study of in vitro alternatives to the Draize eye irritation test. The PTG test, based on photometric quantification of in vitro pollen tube mass production, was used by three independent laboratories to estimate the acute eye irritation potentials of 23 ingredients and 32 cosmetic formulations. Basing on historical Draize test data and on IC(50) values of previously tested cosmetic formulations, a mathematical formula was generated to predict rabbit eye irritation potentials from PTG test results. Statistical evaluation of the calculated modified maximal average scores (MMAS) revealed a high prediction capability of the PTG test in regard to the finished formulations but a relatively low one for alcohols, higher concentrated cationic surfactants, and acidic and alkaline materials. Furthermore, our results indicated that the PTG test was able to produce precise IC(50) values without any limitations from all of the 55 test substances with good intra- and interlaboratory reproducibility. From these findings we suggest that the PTG test is not a validated test at present but is considered to be a potent candidate for further validation processes. For this purpose an additional prediction model for ingredient classes as mentioned above must be generated.

Assessment of cosmetic ingredients in the in vitro reconstructed human epidermis test method EpiSkin™ using HPLC/UPLC-spectrophotometry in the MTT-reduction assay.

Cosmetics Europe recently established HPLC/UPLC-spectrophotometry as a suitable alternative endpoint detection system for measurement of formazan in the MTT-reduction assay of reconstructed human tissue test methods irrespective of the test system involved. This addressed a known limitation for such test methods that use optical density for measurement of formazan and may be incompatible for evaluation of strong MTT reducer and/or coloured chemicals. To build on the original project, Cosmetics Europe has undertaken a second study that focuses on evaluation of chemicals with functionalities relevant to cosmetic products. Such chemicals were primarily identified from the Scientific Committee on Consumer Safety (SCCS) 2010 memorandum (addendum) on the in vitro test EpiSkin™ for skin irritation testing. Fifty test items were evaluated in which both standard photometry and HPLC/UPLC-spectrophotometry were used for endpoint detection. The results obtained in this study: 1) provide further support for Within Laboratory Reproducibility of HPLC-UPLC-spectrophotometry for measurement of formazan; 2) demonstrate, through use a case study with Basazol C Blue pr. 8056, that HPLC/UPLC-spectrophotometry enables determination of an in vitro classification even when this is not possible using standard photometry and 3) addresses the question raised by SCCS in their 2010 memorandum (addendum) to consider an endpoint detection system not involving optical density quantification in in vitro reconstructed human epidermis skin irritation test methods.