IRAG working group 5. Other assays. Interagency Regulatory Alternatives Group

The Performance of the Tissue Equivalent Assay using the Skin(2)(TM) ZK1200 Model in the COLIPA International Validation Study on Alternatives to the Draize Eye Irritation Test

The tissue equivalent assay (TEA) (Osborne et al., 1995) was used to evaluate 55 mixed ingredients and formulations in the COLIPA International Validation Study on Alternatives to the Draize Rabbit Eye Irritation Test (Brantom et al., 1997). The TEA can be used to test all types of materials since it uses a topical application approach and is not limited to only testing liquid or soluble materials. A prediction model (PM) for the test was developed using historical eye irritation data from a total of 132 materials on which in vivo and in vitro data were available. A regression model was derived from these data and used to relate the in vitro endpoint (t(50)) obtained in the study to a Draize MMAS (modified maximum average score). This provided a measure of the predicted in vivo eye irritation scores. In the current study, two separate laboratories used the same protocol to test the same set of coded materials and the results of both laboratories were compared to the initial PM. The TEA met the reliability criteria of the validation study in reproducing the predefined PM in both laboratories, and a good relationship between predicted and observed Draize MMAS values was obtained (r=0.906 and r=0.850). Good correlations were maintained when separate analyses were made of the formulations and ingredients included in the test set. Good relationships between the in vitro endpoint and individual Draize tissue scores (r>0.8) were also exhibited. Although insufficient data were available to make an assessment of interlaboratory variation, some difference in the reproducibility of the assay was noted between the two laboratories, particularly for the highly irritating materials. However, the consistency of data was encouraging and the discrepancies seen between the laboratories suggested a sensitivity of the model to subtle differences in application techniques, and in handling and timing. Taken together, these results indicate the utility of the TEA test for these types of substances and the need to more fully address the issue of interlaboratory reproducibility.

The neutral red release assay: a review

The neutral red release (NRR) assay is a cytotoxicity test that can be used to measure the immediate toxic effects of test substances on the cell membrane, resulting in the leaking of intracellular contents. The assay has already been used for several years to evaluate the cytotoxicities of various kinds of products, such as cosmetics, pharmaceuticals, industrial chemicals and household products. It has undergone in-house validation by many companies, and has been found to be particularly useful for identifying substances that are potentially capable of causing adverse reactions on coming into brief contact with the eye or the skin at relatively high concentrations, such as might occur in an adventitious splash into the eye or onto the skin, followed by a quick rinse. Because of the relatively long existence of the NRR assay, its practicality and its proven usefulness for particular purposes, ECVAM decided to review the status of the method, in order to decide whether prevalidation and formal validation studies on the test might be profitable. The review of the status of the test was carried out by performing a comprehensive review of the literature, and by conducting a survey involving companies and institutes with experience in using the test. Both the review and the survey revealed that the assay could provide extremely valuable information when it was used for particular purposes, such as for the evaluation and comparison of immediate toxic effects on the eye or the skin caused by certain products or chemicals such as surfactants. Most of those who responded in the survey favoured a prevalidation/validation study.