Second-phase validation study of short time exposure test for assessment of eye irritation potency of chemicals

A Short Time Exposure (STE) test is a cytotoxicity test that uses SIRC cells (rabbit corneal cell line) to assess eye irritation potency following a 5-min chemical exposure. This second-phase validation study assessed the predictive capacity of the STE test using 40 coded test substances at three laboratories. A Validation Management Team (VMT) then evaluated the predictivity of the STE test for United Nation (UN) Globally Harmonized System (GHS) categories using 63 test substances including the results of the first-phase validation study.The STE test can assess not only the severe or corrosive ocular irritants (corresponding to the UN GHS Category 1) but also non-irritant (corresponding to UN GHS Non Category) from other toxicity classes, especially for limited types of test substances. The predictivity by STE test, however, was insufficient for identification of UN GHS categories (Category 1, Category 2, or Non Category).These results suggest that the STE test can be recommended as an initial step in a top-down approach to identification of severe irritants and test substances that require classification for eye irritation (UN GHS Category 1) as well as an initial step in a bottom-up approach to identification of test substances that do not require classification for eye irritation (UN GHS Non Category) from other toxicity classes, especially for limited types of test substances. On the other hand, the STE test is not considered adequate for the identification of mild or moderate irritants (i.e., UN GHS Categories 2A and 2B) and severe irritants (UN GHS Category 1).     

Distribution of eye irritation scores of industrial chemicals

Eye irritation results obtained in tests on agricultural and industrial chemicals (raw materials, intermediates, formulation components and sales products) were classified on the basis of an arbitrary breakdown of the scores (which ranged from 0 (no irritation) to a maximum of 110) into six categories. This showed that of the materials (about 600) tested over a 2-year period, 18-31% caused no irritation at all, 42-51% caused minimal irritation (scores of 0.1-10.9), 9-17% were classed as slightly irritant (11.0-25.9) and 8-12% as moderately irritant (26.0-55.9), while 2-6 and 1-5% came into the categories of strong and extreme irritants, respectively (with scores of 56.0-84.0 and 84.1-110). Testing of the last two groups involves the test animals in discomfort, but because of the seriousness of eye damage to man this cannot always be avoided.     

Eye irritation potential: usefulness of the HET-CAM under the Globally Harmonized System of classification and labeling of chemicals (GHS)

Extensive research has been conducted over the past decades to develop alternatives to the rabbit eye irritation test (Draize test) used in a regulatory context to assess eye irritation potentials. Although no single in vitro test has emerged as being completely acceptable for full replacement, various tests are considered to be suitable and are regularly used to assess certain aspects. Amongst these, the Hen's Egg Test Chorioallantoic Membrane (HET-CAM) has gained regulatory acceptance in various countries to classify severe eye irritants. In this retrospective study, historical eye irritation data (in vivo and in vitro) from 137 samples (approx. 75% non-irritants; 25% (severe) irritants) tested both in the HET-CAM and Draize eye test was compared with regard to the predicted eye irritation classes under the GHS and the traditional EU classification system (DSD).The overall concordance was in the range of 80-90%. A high specificity (96-98%, depending on the classification system and the chosen discrimination) but rather low sensitivity (48-65%) was observed. The study indicates that HET-CAM results are useful as part of weight-of-evidence assessments or in tiered approaches to assess eye irritation potentials rather than as stand-alone classification method.     

Prediction of ocular irritancy potential from dermal irritation test results

In a survey of the test files of Haskell Laboratory, it was found that of the materials that had been tested on rabbit skin for primary irritation or corrosivity, 60 were severe irritants or corrosive on the skin and had also been tested for ocular irritancy. Of these 60 materials only 39 were severe eye irritants, while 15 were mild irritants or non-irritants and the remainder were considered to be moderate irritants. Thus, to suggest that materials are eye irritants solely on the basis of their skin-irritation properties may be misleading, even when severe dermal irritants are considered.     

Development of an in vitro corrosion/irritation prediction assay using the EpiDerm skin model.

A validation of the in vitro skin corrosion method using the EpiDerm skin model was performed using 12 recommended chemicals. All chemicals were correctly classified by OECD test guideline 431. In order to predict corrosion and/or irritation potential, additional compound exposure times and IL-1alpha measurements were included in a tiered testing approach. Four exposure times were performed followed by MTT (viability) and IL-1alpha measurement. This allowed classification of corrosive chemicals (OECD guideline 431) and those likely to be severe irritants. If the chemical was found to be corrosive or a severe irritant, no further experimental work was performed, otherwise a second experiment was performed using three further exposure times (same endpoints). The second experiment provided information on whether the chemical was likely to be a moderate/mild irritant. If the chemical was negative following both experiments, it was predicted as non-corrosive/non-irritating. A total of 12 chemicals were tested in the irritation or combined assay (five non-irritants, seven irritants). Specificity (% non-irritants concurring with EU classification) was 60% (MTT) and 100% (MTT+IL-1alpha). Sensitivity (% irritants concurring with EU classification) was 86% (MTT) and 86% (MTT+IL-1alpha). Accuracy (% chemicals correctly identified) was 75% (MTT) and 92% (MTT+IL-1alpha).     

Studies on eye irritation caused by chemicals in rabbits--II. Structure-activity relationships and in vitro approach to primary eye irritation of salicylates in rabbits.

Structure-activity relationships and in vitro evaluation of eye irritation potential of salicylates in rabbits were studied. The primary eye irritation potential of ten salicylates was evaluated according to Draize method. The effects of chemicals on model protein and lipid were investigated in vitro. The effects of chemicals on the protein could be detected by the production of aggregates of human serum gamma-globulin (HSG) and a good correlation was obtained between the ability of salicylates to produce aggregation of HSG and the potential of corneal irritation. The effects on the lipid could be detected by the adhesion potential of chemicals on lipid membrane and a linear correlation was not obtained between the adhesionary effects of salicylates on lipid membrane and the potential eye irritation. The corneal irritation and protein aggregation potential of salicylates were correlated with the acid dissociation constant more closely than octanol/water partition coefficient. The destruction of alpha-helix of proteins in corneal surface by salicylates were observed from the nondestructive structural analysis of corneal surface by Fourier Transform (FT)-IR spectroscopy. These results suggest that eye irritation caused by salicylates are mainly the results of denaturation of proteins in ocular tissue and that the effects on protein depend on the dissociation potential of molecules.     

Ability of in vitro (corneal injury--eye organ--and chorioallantoic membrane) tests to represent histopathological features of acute eye inflammation

The spontaneous removal of substances from the eye in vivo and histopathological responses to mild or moderate irritants were examined to define the main features that may be reflected in a valid in vitro test for irritant potential. Solutions or fine particulate suspensions applied to the rabbit eye are quickly removed from the central corneal surface by the blink reflex, gravity and drainage. The histological changes in the first 24 hours of mild-to-moderate irritation show some thinning of, but no severe irreversible damage to, the corneal epithelium. Other changes are oedema, congestion, some leucocyte infiltration and variable degeneration and desquamation of the conjunctival epithelium. In vitro cell-culture cytotoxicity tests are a useful screen for direct cytotoxic damage to epithelial cells but there are anomalies between the results of such tests and in vivo eye responses. Test systems using inhibition of DNA synthesis in cultured fibroblasts and histamine release from mast cells have shown poor correlation between in vitro and in vivo test results. The in vitro corneal injury (eye organ) test of Burton et al. (Fd Cosmet. Toxicol. 1981, 19,471) predicts very effectively the activity of moderate-to-severe irritants, and that of mild irritants when the contact time is modified or fluorescein or histology are used. This method demonstrates the response of a specialized tissue of the eye and facilitates the examination of powders, acids and alkalies, for which cell systems are not suitable. So far the chorioallantoic membrane of the egg has not been found to predict for pure chemicals the activities demonstrated in in vivo or in vitro tests on the eye; the main change seen in the egg membrane is necrosis, with little evidence of inflammation.     

The Short Time Exposure (STE) test for predicting eye irritation potential: Intra-laboratory reproducibility and correspondence to globally harmonized system (GHS) and EU eye irritation classification for 109 chemicals

Short Time Exposure (STE) test is an easy in vitro eye irritation test that assesses cytotoxicity in SIRC cells (rabbit corneal cell line) following a 5 min dose treatment. To assess intra-laboratory reproducibility, medium control, three vehicles (saline, saline containing 5% (w/w) dimethyl sulfoxide, and mineral oil) and three standard chemicals (sodium lauryl sulfate, calcium thioglycolate, and Tween 80) were evaluated. Assessments were repeated 30 times for vehicles and 18 times for standard chemicals; resulting in almost the same cell viability and a low coefficient of variation value. In addition, the STE eye irritation rankings of three standard chemicals, as calculated on the cell viabilities in 5% and 0.05% solutions were in agreement in all tests. Based on these results, high intra-laboratory reproducibility was confirmed.In addition, the irritation category (irritant and non-irritant) was evaluated for 109 chemicals with STE test, globally harmonized system (GHS) classification, and European Union (EU) classification. The results of the evaluation found the STE classification to have an accuracy with GHS classification of 87% and with EU classification of 83%, which confirmed the excellent correspondence.The correspondence of STE rankings (1, 2, and 3) based on the prediction model by STE test with the eye irritation rankings by GHS (non-irritant, categories 2 and 1) and EU (non-irritant, R36, and R41) was 76% and 71%, respectively.Based on the above results, STE test was considered to be a promising alternative method for assessing eye irritation that has high intra-laboratory reproducibility as well as an excellent predictability of eye irritation.     

Reconstituted human corneal epithelium: a new alternative to the Draize eye test for the assessment of the eye irritation potential of chemicals and cosmetic products.

The aim of this study was to evaluate the interest of a new three-dimensional epithelial model cultivated from human corneal cells to replace animal testing in the assessment of eye tolerance. To this end, 65 formulated cosmetic products and 36 chemicals were tested by means of this in vitro model using a simplified toxicokinetic approach. The chemicals were selected from the ECETOC data bank and the EC/HO International validation study list. Very satisfactory results were obtained in terms of concordance with the Draize test data for the formulated cosmetic products. Moreover, the response of the corneal model appeared predictive of human ocular response clinically observed by ophthalmologists. The in vitro scores for the chemicals tested strongly correlated with their respective scores in vivo. For all the compounds tested, the response of the corneal model to irritants was similar regardless of their chemical structure, suggesting a good robustness of the prediction model proposed. We concluded that this new three-dimensional epithelial model, developed from human corneal cells, could be promising for the prediction of eye irritation induced by chemicals and complex formulated products, and that these two types of materials should be tested using a similar protocol. A simple shortening of the exposure period was required for the chemicals assumed to be more aggressively irritant to the epithelial tissues than the cosmetic formulae.     

A quantitative structure-activity relationship for the eye irritation potential of neutral organic chemicals

Quantitative structure-activity relationships (QSARs) have been derived relating eye irritation data of a set of neutral organic chemicals to log(octanol-water partition coefficient), the minor principal inertial axes (R_y and R_z) and dipole moment. Datasets were analysed using principal components analysis; plots of the first 2 principal components of the above parameters showed that the analysis was able to discriminate well between the irritant and non-irritant chemicals in the dataset. The derived QSAR could be useful for the prediction of the eye irritation potential of new or untested chemicals within this category.     

Multi-laboratory validation of SkinEthic HCE test method for testing serious eye damage/eye irritation using liquid chemicals

A prospective multicentric study of the reconstructed human corneal epithelial tissue-based in vitro test method (SkinEthic™ HCE) was conducted to evaluate its usefulness to identify chemicals as either not classified for serious eye damage/eye irritation (No Cat.) or as classified (Cat. 1/Cat. 2) within UN GHS.The aim of this study was to demonstrate the transferability and reproducibility of the SkinEthic™ HCE EITL protocol for liquids and define its predictive capacity. Briefly, 60 chemicals were three times tested (double blinded) in 3 laboratories and 45 additional chemicals were tested three times in one laboratory. Good within laboratory reproducibility was achieved of at least 88.3% (53/60) and 92.4% (97/105) for the extended data set. Furthermore, the overall concordance between the laboratories was 93.3% (56/60). The accuracy of the SkinEthic™ HCE EITL for the extended dataset, based on bootstrap resampling, was 84.4% (95% CI: 81.9% to 87.6%) with a sensitivity of 99.0% (95% CI: 96.4% to 100%) and specificity of 68.5% (95% CI: 64.0% to 74.0%), thereby meeting all acceptance criteria for predictive capacity. This efficient transferable and reproducible assay is a promising tool to be integrated within a battery of assays to perform an eye irritation risk assessment.     

Extent of initial corneal injury as a basis for alternative eye irritation tests.

Based on studies that have characterized the extent of injury occurring with irritants of differing type and severity, we have proposed that extent of initial injury is the principal mechanism underlying ocular irritation. We report here our efforts to apply this hypothesis, as a mechanistic basis, to the development of an alternative eye irritation assay using an ex vivo rabbit corneal model. Rabbit eyes were obtained immediately after sacrifice or from an abattoir and 8.5-mm diameter corneal buttons were removed and cultured overnight at an air-liquid interface under serum-free conditions. Buttons were exposed to materials of differing type (surfactant, acid, base, alcohol and aldehyde) and irritancy (slight to severe) that had been previously characterized microscopically in the rabbit low-volume eye test. Exposure was accomplished by applying 1.5 microl of an irritant to a sterile, 3 mm diameter, filter paper disk and then placing the disk on the center of the corneal button for 10 s. After removal of the disk, buttons were washed and cultured for 3, 24 or 48 h. Buttons were then evaluated for extent of injury using a Live/Dead staining kit and fluorescent microscopy to measure cell size of live surface epithelial cells, area of epithelial denudation and depth of stromal injury. Ex vivo exposure to slight irritants generally reduced surface epithelial cell size (i.e. erosion) while exposure to mild irritants produced epithelial denudation with variable injury to the corneal stroma. Severe irritants generally produced extensive epithelial denudation and damaged the corneal stroma and endothelium. Overall, ex vivo extent of injury significantly correlated with in vivo extent of injury as measured in previous animal tests (r=0.81, P<0.001). These findings indicate that extent of corneal injury, as shown to be associated with ocular irritation occurring in vivo, can be applied to the development of a mechanistically-based alternative eye irritation model. We believe that this approach may ultimately lead to an alternative assay to replace the use of animals in ocular irritation testing.     

A new cell-based method for assessing the eye irritation potential of chemicals: an alternative to the Draize test

Using a human corneal cell line (HCE-T cells) and 2 evaluation criteria, we developed a new alternative method to assess the eye irritation potential of chemicals. We exposed HCE-T cells to different concentrations of 38 chemicals for 1h and measured relative cell viability (RCV) as an endpoint at each concentration. Using the RCV values, we calculated the RCV50. We also exposed HCE-T cells to 3 fixed concentrations of the 38 chemicals (5%, 0.5%, and 0.05%) for 1h and measured the RCV at each concentration. Using the RCV values at 5%, 0.5%, and 0.05%, we developed a new criterion for eye irritation potential (total eye irritation score, TEIS) and estimated the ocular irritancy. We then assessed the correlation of the results of RCV50 and TEIS with those of the Draize rabbit eye irritation. Both the RCV50 and TEIS results exhibited good positive correlations (sensitivity: 80.77%, specificity: 83.33%, and accuracy: 81.58% for TEIS; sensitivity: 73.08-76.92%, specificity: 75.00%, and accuracy: 73.68-76.32% for RCV50). We conclude that the new in vitro model using HCE-T cells is a good alternative evaluation model for the prediction of the eye irritation potential of chemicals.     

SkinEthic HCE Time-to-Toxicity on solids: A test method for distinguishing chemicals inducing serious eye damage,eye irritation and not requiring classification and labelling

This study describes the development of a Time-to-Toxicity approach for solids (TTS) based on the SkinEthic™ HCE tissue construct, capable to distinguish chemicals that do not require classification for serious eye damage/eye irritation (No Cat.) from chemicals that require classification for eye irritation (Cat. 2), and serious eye damage (Cat. 1).Briefly, the time-to-toxicity of 69 solids was evaluated by exposing SkinEthic™ HCE tissue constructs to the test chemical for two different time periods (30-min, and 120-min). Based on the viability observed for the different exposure periods, a classification was assigned. The within laboratory reproducibility in terms of concordance in classifications (3 UN GHS categories), based on a set of 48 solids, was 93.7%. Furthermore, 73.6% Cat. 1 (N = 24), 55.6% Cat. 2 (N = 15) and 72.2% No Cat. (N = 30) were correctly identified with the SkinEthic™ HCE TTS test method. This study provides evidence that the SkinEthic™ HCE Time-to-Toxicity method (multiple exposure times) can distinguish Cat. 2 solids from Cat. 1 solids. This is an added value compared to the SkinEthic™ HCE EITS method (single exposure time) that can distinguish No Cat. chemicals from chemicals that do require classification and labelling for eye irritation/serious eye damage (Cat. 2/Cat. 1).     

Development of the SkinEthic HCE Time-to-Toxicity test method for identifying liquid chemicals not requiring classification and labelling and liquids inducing serious eye damage and eye irritation

This study describes the development of a Time-to-Toxicity approach for liquids (TTL) based on the SkinEthic™ HCE tissue construct, capable to distinguish chemicals that do not require classification for serious eye damage/eye irritation (No Cat.) from chemicals that require classification for eye irritation (Cat. 2), and serious eye damage (Cat. 1).Briefly, the Time-to-Toxicity of 56 liquids was evaluated by exposing SkinEthic™ HCE tissue constructs to the test chemical for three different time periods (5-min, 16-min, and 120-min). Based on the viability observed for the different exposure periods, a classification was assigned. The within laboratory reproducibility in terms of concordance in classifications (3 UN GHS categories), based on a set of 50 liquids, was 80.0%. Furthermore, 84.3% Cat. 1 (N = 17), 79.4% Cat. 2 (N = 21) and 72.2% No Cat. (N = 18) were correctly identified with the SkinEthic™ HCE TTL test method. This study provides evidence that the SkinEthic™ HCE Time-to-Toxicity method (multiple exposure times) is capable of distinguishing Cat. 2 liquids from Cat. 1 liquids. This is an advantage compared to the SkinEthic™ HCE EITL method (single exposure time) that can distinguish No Cat. chemicals from chemicals that do require classification and labelling for eye irritation/serious eye damage (Cat. 2/Cat. 1).     

Prediction models for eye irritation potential based on endpoints of the HETCAM and neutral red uptake tests

The aim of this study was to explore the possibility of distinguishing between eye irritants (I; EU risk phrases R36 and R41) and nonirritants (NI), by using in vitro endpoints of the hen's egg test on the chorioallantoic membrane (the HETCAM test) and the neutral red uptake (NRU) test. Prediction models were derived by applying binary logistic regression to the in vitro data for these endpoints, which were taken from the report of a German validation study on the use of the HETCAM and 3T3 NRU tests as alternatives to the Draize eye irritation test. Whereas the validation study led to the conclusion that the combined use of the two tests enables a satisfactory discrimination between severe (R41) and nonsevere (NI, R36) eye irritants, the results of the present study indicate that the two in vitro tests can also be used to discriminate between nonirritants (NI) and irritants (R36 and R41).     

Validation study of the Short Time Exposure (STE) test to assess the eye irritation potential of chemicals

Short Time Exposure (STE) test is a cytotoxicity test in SIRC cells (rabbit corneal cell line) that assesses eye irritation potential following a 5-min chemical exposure. This validation study assessed transferability, intra- and inter-laboratory reproducibility, and predictive capacity of STE test in five laboratories (supported by Japanese Society for Alternatives to Animal Experiments). Sodium lauryl sulfate, calcium thioglycolate, and Tween 80 were evaluated, in triplicate, using 5%, 0.5%, and 0.05% concentrations in physiological saline, to confirm transferability. Good transferability was noted when similar mean relative viabilities and rank classifications were obtained in all five laboratories and were comparable to data from test method developing laboratory. Good intra- and inter-laboratory reproducibility was obtained with four assay controls (three solvents and one positive control), and four assay controls and 25 chemicals, respectively. STE irritation category based on relative viability of a 5% solution of 25 blinded test chemicals showed good correlation with Globally Harmonized System (GHS) categories (NI; I: Cat. 1 and 2). The STE prediction model, using relative viability of the 5% and 0.05% solutions, provided an irritation rank (1, 2, or 3) that had a good correlation (above 80%), or predictive capacity, with GHS irritation ranks in all laboratories. Based on these findings, the STE test is a promising alternative eye irritation test that could be easily standardized.     

Prediction of eye irritation from organic chemicals using membrane-interaction QSAR analysis.

Eye irritation potency of a compound or mixture has traditionally been evaluated using the Draize rabbit-eye test (Draize et al., 1944). In order to aid predictions of eye irritation and to explore possible corresponding mechanisms of eye irritation, a methodology termed "membrane-interaction QSAR analysis" (MI-QSAR) has been developed (Kulkarni and Hopfinger 1999). A set of Draize eye-irritation data established by the European Center for Ecotoxicology and Toxicology of Chemicals (ECETOC) (Bagley et al., 1992) was used as a structurally diverse training set in an MI-QSAR analysis. Significant QSAR models were constructed based primarily upon aqueous solvation-free energy of the solute and the strength of solute binding to a model phospholipid (DMPC) monolayer. The results demonstrate that inclusion of parameters to model membrane interactions of potentially irritating chemicals provides significantly better predictions of eye irritation for structurally diverse compounds than does modeling based solely on physiochemical properties of chemicals. The specific MI-QSAR models reported here are, in fact, close to the upper limit in both significance and robustness that can be expected for the variability inherent to the eye-irritation scores of the ECETOC training set. The MI-QSAR models can be used with high reliability to classify compounds of low- and high-predicted eye irritation scores. Thus, the models offer the opportunity to reduce animal testing for compounds predicted to fall into these two extreme eye-irritation score sets. The MI-QSAR paradigm may also be applicable to other toxicological endpoints, such as skin irritation, where interactions with cellular membranes are likely.     

The chorioallantoic membrane test as a model to predict the potential human eye irritation induced by commonly used laboratory solvents.

The purpose of this study was to investigate the potential eye irritation of a range of solvents, extensively used in industry and laboratory and the capacity of the chorioallantoic membrane test to predict this eye irritation. The irritation has been evaluated by an in vitro method using the chorioallantoic membrane as an alternative to in vivo Draize rabbit test. All the solvents studied are potentially strongly irritants, even though diluted, except dimethyl sulfoxide which was moderately irritant at a concentration of 10% v/v. In some cases there is a correlation between the concentration of the solvent and the potential eye irritation induced. The method allows prediction of the potential eye irritation of the solvents studied.