Successful prevalidation of the slug mucosal irritation test to assess the eye irritation potency of chemicals

A previous 'in house' validation study showed that the SMI assay can be used as an alternative to the in vivo Draize eye irritation test. The aim of this multi-centre study with four participating laboratories was to assess the transferability and inter-laboratory variability of the assay using 20 reference chemicals covering the whole irritancy range. The eye irritation potency of the chemicals was assessed by measuring the amount of mucus produced during a 60-min contact period with a 1% dilution, and a second 60-min treatment with a 3.5% dilution. After each contact period the protein release from the mucosal surface was measured. Linear discriminant equations were used to convert the results into the corresponding EU eye irritation categories (NI, R36 and R41). All the non-irritants were predicted correctly by the four laboratories resulting in a 100% specificity. For the R36 compounds a correct classification rate of 89% (VITO) and 100% (SPL, JNJ and UGent) was obtained. The R41 compounds were classified correctly in 78% of the cases for VITO, 89% for SPL and JNJ and 100% for UGent. We can conclude that the SMI assay is a relevant, easily transferable and reproducible alternative to predict the eye irritation potency of chemicals.

Refinement of the Slug Mucosal Irritation test as an alternative screening test for eye irritation

The objective of this study was to limit the test procedure time of the Slug Mucosal Irritation test to one day and to determine whether it is a relevant and reliable method to predict the eye irritation potential of chemicals. The irritation potential of several eye reference chemicals can be estimated by the amount of mucus produced when tested at a 1% concentration (60 min). Since some in vivo irritating chemicals did not influence this endpoint the effect of increasing concentrations on membrane damage was investigated. This study revealed that when tested at a 3.5% concentration (60 min) the underestimated chemicals induced an increased protein and/or enzyme release. A two-step classification prediction model was developed that classified the chemicals first by the amount of mucus produced (1%, 60 min). Chemicals that did not affect this endpoint were classified based on the membrane damage induced by a second treatment (3.5%, 60 min). The results were compared with the corresponding EU classification (NI, R36 and R41) and 71% of the chemicals were correctly classified with a specificity and sensitivity of 75% and 94%, respectively. Repeated testing of the chemicals revealed a good intra-laboratory reproducibility. The test seems to be a promising method for screening the eye irritating potential of chemicals.