Identification of cornifelin and early growth response-1 gene as novel biomarkers for in vitro eye irritation using a 3D reconstructed human cornea model MCTT HCE™.

Evaluation of the eye irritation is essential in the development of new cosmetic products. Draize rabbit eye irritation test has been widely used in which chemicals are directly applied to rabbit eye, and the symptoms and signs of eyes are scored. However, due to the invasive procedure, it causes substantial pain and discomfort to animals. Recently, we reported in vitro eye irritation test method using a 3D human corneal epithelial model (MCTT HCE™) which is reconstructed from remaining human tissues after a corneal transplantation. This model exhibited an excellent predictive capacity for 25 reference chemicals (sensitivity 100%, specificity 77% and accuracy 88% vs. GHS). To improve the test performance, we explored new biomarkers for the eye irritation through transcriptomic approach. Three surfactants were selected as model eye irritants that include sodium lauryl sulfate, benzalkonium chloride and triton X-100. After test chemicals were treated, we investigated differentially expressed genes through a whole-gene microarray (Affymetrix GeneChip(®) Human Gene 2.0 ST Array, 48,000 probes). As a result, we identified that mRNAs of cornifelin (CNFN), a constituent of the insoluble cornified cell envelope of stratified squamous epithelia, and early growth response-1 (EGR1), a nuclear transcriptional regulator, were significantly up-regulated by all three irritants. Up-regulation of CNFN and EGR1 was further confirmed by Q-RT-PCR, and immunohistochemistry revealed increased level of CNFN in irritant-treated tissues, supporting the relevance of CNFN and EGR1 as new biomarkers for eye irritation.

Me-too validation study for in vitro eye irritation test with 3D-reconstructed human cornea epithelium, MCTT HCETM.

The need for in vitro eye irritation test replacing in vivo is steadily increasing. The MCTT HCE™ eye irritation test (EIT) using 3D reconstructed human cornea-like epithelium, was developed to identify ocular irritants from non-irritants those that are not requiring classification and labelling for eye irritation. Here, we report the results of me-too validation study, which was conducted to evaluate the reliability and relevance of the MCTT HCETM EIT, according to performance standards (PS) of OECD TG 492. The optimal cutoff to determine irritation in the prediction model was preliminarily established at 45% with the receiver operation characteristics (ROC) curve for 141 reference substances. To demonstrate the reproducibility of within- and between-laboratory (WLR and BLR), a set of 30 PS reference chemicals were tested in three laboratories three times. The WLR and BLR concordance with the binary decision of whether non-irritant or irritant was estimated to be 90-100% and 90%, respectively, and both met the PS requirements. The predictive capacity of the respective laboratories for the 30 reference chemicals were evaluated based on three different estimation methods, and the results were comparable, with sensitivity ranging from 89.6 to 93.3%, the specificity ranging from 62.2 to 66.7%, and the accuracy ranging from 75.9 to 80.0%. Additional test with the new set of 30 PS substances in the revised OECD GD 216 yielded a performance of sensitivity ranging from 92.6-93.3%, the specificity 62.2-66.7% and the accuracy 77.4-80.0%. 95.0% sensitivity, 67.2% specificity, and 83.0% accuracy were obtained for 141 reference substances in total. Furthermore, separate cutoffs for liquids and solids, 35% and 60%, respectively, produced better predictivity, which was established as a final prediction model. Collectively, our study demonstrated that MCTT HCETM EIT meets the reproducibility and predictivity criteria stated in OECD TG 492 PS.

Nervonoylceramide (C24:1Cer), a lipid biomarker for ocular irritants released from the 3D reconstructed human cornea-like epithelium, MCTT HCE™.

Due to invasive and painful procedures during in vivo rabbit eye irritation test, in vitro alternative methods have been widely investigated. Recently, 3D reconstructed human cornea-like epitheliums (RhCEs) garner a huge attention. RhCEs employ the tissue viability as a primary endpoint to determine ocular irritancy but additional biomarkers may improve its predictive capacity. Here, we explored lipid biomarkers for ocular irritants in MCTT HCE™ RhCE model. Three irritants; sodium lauryl sulfate, benzalkonium chloride and triton X-100 were selected to represent anionic, cationic and non-ionic detergent respectively. After treating MCTT HCE™ with irritants, the alteration of lipids in the treated tissues was examined with Nile Red staining, which revealed the depletion of corneal lipids. We further quantitated the release of ceramides and free fatty acids, major lipid components of cornea, into the medium during the post-treatment incubation, employing a sensitive UPLC-MS/MS method. Among 44 lipid species, nervonoylceramide (C24:1Cer) was found to be released commonly by all three irritants in a concentration-dependent manner. Tests with 10 additional reference substances further supported that C24:1Cer release was significantly correlated with viability. Examination of the genes involved in the biosynthetic pathway for C24:1Cer revealed that stearoylCoA desaturase (SCD) and elongase1 (ELOVL1) were upregulated, suggesting that lipids and related genes may be employed as biomarkers for ocular irritants.