Name: eye irritation test (eit) for hazard identification of eye irritating chemicals using reconstructed human cornea-like epithelial (rhce) tissue model
Uploaded: 2015-08-23T14:00:00.000+00:00
Duration: 10 min 13 s
Description: Watch this Scientific Journal Video about Eye Irritation Test EIT for Hazard Identification of Eye Irritating Chemicals using Reconstructed Human Cornea-like Epithelial RhCE Tissue Model at JoVE.com

The authors would like to thank Dr. John Harbell for his scientific support and time dedicated to the EIT project. The authors also would like to thank Beiersdorf AG (Germany), IIVS (USA), Mary Kay Inc. (USA), Avon Products Inc. (USA), Procter &#38; Gamble/Cosmital (Switzerland), Laboratoire Pierre Fabre (France), Harlan Laboratories (United Kingdom), and LVMH Parfume (France) for participation in Multi-center International Pre-Validation and Validation Studies of the Eye Irritation Test15.

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	<li>National Toxicology Program (NTP) Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM). <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Request+for+Ocular+Irritancy+Test+Data+From+Human,+Rabbit,+and+In+Vitro+Studies+Using+Standardized+Testing+Methods.">Request for Ocular Irritancy Test Data From Human, Rabbit, and In Vitro Studies Using Standardized Testing Methods.</a> Federal Register. 72 (109), 31582-31583 (2007).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+(EC)+No+1907/2006+of+the+European+Parliament+and+of+the+Council+of+18+December+2006+concerning+the+Registration,+Evaluation,+Authorisation+and+Restriction+of+Chemicals+(REACH),+establishing+a+European+Chemicals+Agency,+amending+Directive+1999/45/EC+and+repealing+Council+Regulation+(EEC)+No+793/93+and+Commission+Regulation+(EC)+No+1488/94+as+well+as+Council+Directive+76/769/EEC+and+Commission+Directives+91/155/EEC,+93/67/EEC,+93/105/EC+and+2000/21/EC.">Regulation (EC) No 1907/2006 of the European Parliament and of the Council of 18 December 2006 concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), establishing a European Chemicals Agency, amending Directive 1999/45/EC and repealing Council Regulation (EEC) No 793/93 and Commission Regulation (EC) No 1488/94 as well as Council Directive 76/769/EEC and Commission Directives 91/155/EEC, 93/67/EEC, 93/105/EC and 2000/21/EC.</a> OJ. L396 (49), 1-849 (2006).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Globally Harmonized System of Classification and Labelling of Chemicals (GHS). , (2013).</li><li>Draize, J. H., Woodard, G., Calvery, H. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methods+for+the+Study+of+Irritation+and+Toxicity+of+Substances+Applied+Topically+to+the+Skin+and+Mucous+Membranes.">Methods for the Study of Irritation and Toxicity of Substances Applied Topically to the Skin and Mucous Membranes.</a> J Pharmacol Exp Ther November. 82, 377-390 (1944).</li><li>Adriaens, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Retrospective+analysis+of+the+Draize+test+for+serious+eye+damage/eye+irritation:+importance+of+understanding+the+in+vivo+endpoints+under+UN+GHS/EU+CLP+for+the+development+and+evaluation+of+in+vitro+test+methods.">Retrospective analysis of the Draize test for serious eye damage/eye irritation: importance of understanding the in vivo endpoints under UN GHS/EU CLP for the development and evaluation of in vitro test methods.</a> Arch tox. 88, 701-723 (2014).</li><li>Balls, M., Botham, P. A., Bruner, L. H., Spielmann, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+EC/HO+international+validation+study+on+alternatives+to+the+Draize+eye+irritation+test.">The EC/HO international validation study on alternatives to the Draize eye irritation test.</a> Toxicol in Vitro. 9, 871-929 (1995).</li><li>Curren, R. D., Harbell, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ocular+safety:+a+silent+(in+vitro)+success+story.">Ocular safety: a silent (in vitro) success story.</a> Altern Lab Anim. 30, 69-74 (2002).</li><li>Wilhelmus, K. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Draize+Eye+Test.">The Draize Eye Test.</a> Survey of Ophthalmology. 45, 493-515 (2001).</li><li>Curren, R. D., Harbell, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+alternatives+for+ocular+irritation.">In vitro alternatives for ocular irritation.</a> Environ health persp. 106, 485-492 (1998).</li><li>McCain, N. E., Binetti, R. R., Gettings, S. D., Jones, B. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+ocular+irritation+ranges+of+market-leading+cosmetic+and+personal-care+products+using+an+in+vitro+tissue+equivalent.">Assessment of ocular irritation ranges of market-leading cosmetic and personal-care products using an in vitro tissue equivalent.</a> Toxicologist. 66, 243 (2002).</li><li>Niranjan, P., Dang, A. H., January, B. G., Gomez, C., Harbell, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+the+EpiOcular+assay+for+preclinical+qualification+of+formulas+for+human+clinical+studies.">Use of the EpiOcular assay for preclinical qualification of formulas for human clinical studies.</a> Toxicologist. 96, 249 (2007).</li><li>Yin, X. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prediction+of+ocular+irritation+potential+of+surfactants-based+formulations+at+different+concentrations+using+the+EpiOcular+model.">Prediction of ocular irritation potential of surfactants-based formulations at different concentrations using the EpiOcular model.</a> Toxicologist. 108, 378 (2009).</li><li>Harbell, J., Curren, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+methods+for+the+prediction+of+ocular+and+dermal+toxicity.">In vitro methods for the prediction of ocular and dermal toxicity.</a> Handbook of Toxicology. , (2001).</li><li>Kaluzhny, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+the+EpiOcular(TM)+eye+irritation+test+for+hazard+identification+and+labelling+of+eye+irritating+chemicals+in+response+to+the+requirements+of+the+EU+cosmetics+directive+and+REACH+legislation.">Development of the EpiOcular(TM) eye irritation test for hazard identification and labelling of eye irritating chemicals in response to the requirements of the EU cosmetics directive and REACH legislation.</a> Altern Lab Anim. 39, 339-364 (2011).</li><li>Pfannenbecker, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cosmetics+Europe+Multi-Laboratory+Pre-Validation+of+the+EpiOcular+Reconstituted+Human+Tissue+Test+Method+for+the+Prediction+of+Eye+Irritation.">Cosmetics Europe Multi-Laboratory Pre-Validation of the EpiOcular Reconstituted Human Tissue Test Method for the Prediction of Eye Irritation.</a> Toxicol in vitro. , (2013).</li><li>MatTek Corporation. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> EpiOcular™ Eye Irritation Test (OCL-200-EIT) for the prediction of acute ocular irritation of chemicals for use with Reconstructed Human EpiOcular Model (OCL-200-EIT). Protocol#MK-24-007-0055. , (2014).</li><li>Kaluzhny, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=EpiOcular+Eye+Irritation+Test+(EIT)+for+Hazard+Identification+and+Labeling+of+Eye+Irritating+Chemicals:+Protocol+Optimization+for+Solid+Materials+and+Extended+Shipment+Times.">EpiOcular Eye Irritation Test (EIT) for Hazard Identification and Labeling of Eye Irritating Chemicals: Protocol Optimization for Solid Materials and Extended Shipment Times.</a> Altern Lab Anim. 43 (2), 101-127 (2015).</li><li>Kolle, S. N., Kandarova, H., Wareing, B., van Ravenzwaay, B., Landsiedel, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In-house+validation+of+the+EpiOcular(TM)+eye+irritation+test+and+its+combination+with+the+bovine+corneal+opacity+and+permeability+test+for+the+assessment+of+ocular+irritation.">In-house validation of the EpiOcular(TM) eye irritation test and its combination with the bovine corneal opacity and permeability test for the assessment of ocular irritation.</a> Altern Lab Anim. 39, 365-387 (2011).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reconstructed+Human+Cornea-like+Epithelium+(RhCE)+Test+Method+for+Identifying+Chemicals+Not+Requiring+Classification+and+Labelling+for+Eye+Irritation+or+Serious+Eye+Damage.+Draft+proposal+for+a+new+test+guideline..">Reconstructed Human Cornea-like Epithelium (RhCE) Test Method for Identifying Chemicals Not Requiring Classification and Labelling for Eye Irritation or Serious Eye Damage. Draft proposal for a new test guideline..</a> OECD Guideline for the Testing of Chemicals. , (2014).</li><li>Blazka, M. E., Harbell, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluating+the+ocular+irritation+potential+of+54+test+articles+using+the+EpiOcular+Human+tissue+Construct+Model.">Evaluating the ocular irritation potential of 54 test articles using the EpiOcular Human tissue Construct Model.</a> Toxicol. In Vitro. , (2003).</li><li>Kandarova, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+EpiDerm+Test+Protocol+for+the+Upcoming+ECVAM+Validation+Study+on+In+Vitro+Skin+Irritation+Tests+&#8212;+An+Assessment+of+the+Performance+of+the+Optimised+Test.">The EpiDerm Test Protocol for the Upcoming ECVAM Validation Study on In Vitro Skin Irritation Tests &#8212; An Assessment of the Performance of the Optimised Test.</a> Altern Lab Anim. 33, 351-367 (2005).</li></ol>

Publication fees for this article were paid by MatTek Corporation. The authors are employees of MatTek Corporation.

We have presented the Eye Irritation Test (Figure 1) that was developed for the EpiOcular tissue model. The EIT is able to separate ocular irritants and corrosives (GHS Categories 1 and 2 combined) from materials that do not require labeling (GHS No Category) with high degree of sensitivity and specificity17. The EIT as presented herein does not discriminate between GHS Category 1 from Category 2 chemicals. The EIT was validated for classification and labeling of ocular irritation potential of a wide range of chemicals, including cosmetic and pharmaceutical ingredients. In conjunction with other in vitro tests, the EIT will serve as a replacement for the in vivo rabbit eye irritation test.
The EIT uses two similar but distinct protocols for liquid and solid materials, which vary in the length of exposure and post-exposure incubation periods (Figure 1). The endpoint used in the EIT is tissue viability, determined by the MTT assay, which has been previously used in validated human epithelial tissue models20,21. To perform this assay, no special equipment besides standard cell culture equipment is needed. Due to the high level of tissue-to-tissue reproducibility, n = 2 tissues instead of the usually recommended n = 3 are used. The ability to use n= 2 tissues is a critical aspect of the protocol, since it allows an experienced operator to process two tissues simultaneously, thereby minimizing the variability of the assay that can arise due to the different handling of individual tissues14. Also, by using n = 2 tissues per test article, the irritancy of 10 test substances of the same physical state (liquid or solid), along with the positive and negative controls, can be evaluated using one kit (24 tissues).
Other key points that ensure reliable classification of materials are specifications for the positive control substance (tissue viability &#8804;50.0%), reproducibility between duplicate tissues (difference &#60;20.0%), and negative control OD readings (&#62;0.8 and &#60;2.5).
When performing the EIT test, it is important to adhere to the validated protocol and to the suggested dosing and rinsing schedules (Tables 3 and 4), since deviation from the protocol or changes in the incubation periods may result in altered outcome. Likewise, deviations from the 3 hr time for MTT incubation will result in different MTT readings and may affect assay result.
Occasionally, a test chemical may have optical or other properties which may interfere with MTT tissue viability assay or cause reduction of MTT. For instance, a test chemical may directly reduce MTT into blue-purple reaction product, or may be a colored substance that absorbs light in the same range as MTT formazan (~570 nm). However, these test chemicals will present a problem only, if at the time of the MTT assay, a sufficient amount of the material is still present on (or absorbed by) the tissue. To avoid this interference, extensive rinsing procedures are incorporated into the EIT protocol. If rinsing does not remove the TA and the TA interferes with MTT reduction, additional controls must be used to detect and correct for it. Briefly, if direct MTT reduction of the test chemical is suspected, 50 &#181;l (or 50 mg for solids) of the chemical in question is incubated for 3 hr with working MTT solution at SCC (NC, 50 &#181;l of sterile deionized water, should be run concurrently). If the MTT solution turns blue-purple, the test article is presumed to have reduced the MTT. In this case a functional check using freeze-killed tissue controls should be performed to evaluate whether the test material is binding to the tissue and leading to a false MTT reduction signal. If there is appreciable MTT reduction in the TA-exposed, killed tissue control (relative to the amount in the untreated viable tissue), the mean tissue viability of the test article must be corrected by subtracting the mean viability of the killed control.
The EIT errs on the side of safety, as demonstrated by the low incidence of false negative classifications14,15,18. Importantly, none of the GHS Category 1 chemicals, which are corrosive to the eye and which represent the most serious ocular hazard, were classified as non-irritating in this assay14,15,18,19. Finally, one of the major advantages of the RhCE in vitro test method is the possibility of testing neat liquid and solid materials (which is not possible with two-dimensional, submerged cell cultures).
The EIT will &#160;contribute significantly in determining the ocular irritation potential of a wide range of materials according to the UN GHS classification and labeling system. The replacement of animals to determine ocular toxicity has been a goal of toxicological research for many years. The EIT test method has completed a formal validation study supported by EURL ECVAM in 2014 and the EpiOcular EIT was implemented into the OECD test Guidelines as OECD TG 492&#160;in 2015.

Consumer products such as cosmetics, detergents, and household cleaners include a variety of chemicals that may induce serious damage if they contact the eyes. Therefore, testing of these agents for eye irritation is required by the US and EU regulatory agencies to ensure consumer safety1. An assessment of the eye irritation potential of mixtures and formulations is also a requirement for complying with REACH (Registration, Evaluation, Authorization, and Restriction of Chemicals) legislation for the labeling of cosmetic ingredients under the EU Cosmetics Directive for transport of chemicals, and for the labeling of pesticides and household products2. Currently, regulatory agencies require ocular hazard assessment using the Globally Harmonized System of Classification and Labeling of Chemicals (GHS)3. GHS is mainly based on the Draize eye irritation test, the most widely used eye irritation assay in which foreign substances and mixtures are introduced directly into the conjunctival sac of the rabbit eye4. According to GHS classification, GHS Category 1 (ocular corrosives) refers to test chemicals that cause severe initial injury to the eye tissues or serious damage to the eye and vision which is not fully reversible within 21 days following exposure3,5. GHS Category 2 refers to test chemicals that produce significant changes in the eye that are fully reversible within 21 days of exposure. Test chemicals that are not corrosives or irritants are referred to as GHS No Category.
For more than 40 years, the Draize rabbit eye test has been criticized for its lack of reproducibility, overestimation of human responses, and the use of live animals5-8. These concerns have encouraged many proposals for refinement, reduction, and replacement of the in&#160;vivo&#160;test9. The need for validated non-animal alternatives was further strengthened by the adoption of the Seventh Amendment to the Cosmetics Directive, which banned the use of animals in the safety evaluation of cosmetic products (in 2005) and ingredients (in 2009)2.
Since 1996, the reconstructed cornea-like tissue model has been widely used by the cosmetic industry to evaluate the irritation potential of raw materials, surfactant-based formulations, and compounded mixtures that are designed for use in, or in the vicinity of, the eye10-13. Use of the RhCE tissue model allows direct topical application of the test material onto the tissue surface in its native, undiluted form. In this way, non-water soluble formulations can be tested without diluting them with solvents. In response to EURL ECVAM&#8217;s (European Union Reference Laboratory European Centre for the Validation of Alternative Methods) request for a widely applicable, straightforward, and economic method the Eye Irritation Test (EIT) which utilizes a single exposure time and is able to separate ocular irritants and corrosives from materials that do not require labeling was developed (Figure 1)14. Based on the results for 83 chemicals (44 liquids and 39 solids), the EIT achieved 95.5/68.2/ and 81.8% sensitivity/specificity and accuracy (SS&#38;A) for liquids, 100.0/68.4/ and 84.6% SS&#38;A for solids, and 97.6/68.3/ and 83.1% for overall SS&#38;A.
In 2007, a multi-laboratory pre-validation study sponsored by Cosmetics Europe (formerly Colipa) under the auspices of the EURL ECVAM assessed the relevance and reliability of the EIT with the goal of bringing it to formal validation15. In this study, 298 independent trials were performed in seven independent laboratories. Study results demonstrated 99.7% agreement in prediction with low coefficients of variation across all participating laboratories15. As a result, in 2010 the EIT protocol entered a formal EURL ECVAM validation program. The validation study utilized 104 coded test chemicals, including individual substances and chemical mixtures, for which in vivo reference data (Draize eye irritation data) were available. Based on the success of this work, an OECD draft test guideline was submitted in 2014. It is anticipated that the EIT will contribute significantly to classification of ocular irritation potential of a wide range of materials according to the UN GHS classification and labeling system.

eye irritation test (eit) for hazard identification of eye irritating chemicals using reconstructed human cornea-like epithelial (rhce) tissue model

To comply with the Seventh Amendment to the EU Cosmetics Directive and EU REACH legislation, validated non-animal alternative methods for reliable and accurate assessment of ocular toxicity in man are needed. To address this need, we have developed an eye irritation test (EIT) which utilizes a three dimensional reconstructed human cornea-like epithelial (RhCE) tissue model that is based on normal human cells. The EIT is able to separate ocular&#160;irritants and corrosives (GHS Categories 1 and 2 combined) and those that do not require labeling (GHS No Category). The test utilizes two separate protocols, one designed for liquid chemicals and a second, similar protocol for solid test articles. The EIT prediction model uses a single exposure period (30 min for liquids, 6 hr for solids) and a single tissue viability cut-off (60.0% as determined by the MTT assay). Based on the results for 83 chemicals (44 liquids and 39 solids) EIT achieved 95.5/68.2/ and 81.8% sensitivity/specificity and accuracy (SS&#38;A) for liquids, 100.0/68.4/ and 84.6% SS&#38;A for solids, and 97.6/68.3/ and 83.1% for overall SS&#38;A. The EIT will contribute significantly to classifying the ocular irritation potential of a wide range of liquid and solid chemicals without the use of animals to meet regulatory testing requirements. The EpiOcular EIT method was implemented in 2015 into the OECD Test Guidelines as TG 492.

Watch this Scientific Journal Video about Eye Irritation Test EIT for Hazard Identification of Eye Irritating Chemicals using Reconstructed Human Cornea-like Epithelial RhCE Tissue Model at JoVE.com

Eye Irritation Test EIT for Hazard Identification of Eye Irritating Chemicals using Reconstructed Human Cornea-like Epithelial RhCE Tissue Model

We have developed an eye irritation test which utilizes a three dimensional reconstructed human cornea-like epithelial (RhCE) tissue model. The test is able to discriminate between ocular irritant and corrosive materials (GHS Categories 1 and 2 combined) and those that do not require labeling (GHS No Category).

Eye Irritation Test (EIT) for Hazard Identification of Eye Irritating Chemicals using Reconstructed Human Cornea-like Epithelial (RhCE) Tissue Model

To comply with the Seventh Amendment to the EU Cosmetics Directive and EU REACH legislation, validated non-animal alternative methods for reliable and ...

eye-irritation-test-eit-for-hazard-identification-eye-irritating

Research

JoVE Journal

Bioengineering

37.4K Views.  MatTek Corporation. We have developed an eye irritation test which utilizes a three dimensional reconstructed human cornea-like epithelial (RhCE) tissue model. The test is able to discriminate between ocular irritant and corrosive materials (GHS Categories 1 and 2 combined) and those that do not require labeling (GHS No Category).

Video: Eye Irritation Test EIT for Hazard Identification of Eye Irritating Chemicals using Reconstructed Human Cornea-like Epithelial RhCE Tissue Model

An In Vitro Skin Irritation Test (SIT) using the EpiDerm Reconstructed Human Epidermal (RHE) Model

The EpiDerm Skin Irritation test (EpiDerm SIT) was developed (1,2,3) and validated (4,5) for in vitro skin irritation testing of chemicals, including cosmetic and pharmaceutical ingredients. The EpiDerm SIT utilizes the 3D in vitro reconstructed human epidermal (RHE) model EpiDerm. The procedure described in this protocol allows for discrimination between irritants of GHS category 2 and non-irritants (6). The test is performed over the course of a 4 day time period, consisting of pre-incubation, 60 minute exposure, 42 hour post-incubation and MTT viability assay. After tissue receipt and overnight pre-incubation (Day 0), tissues are topically exposed to the test chemicals (Day 1), which can be liquid, semi-solids, solid or wax. Three tissues are used for each test chemical, as well as for the positive control (5% aq. SDS solution), and a negative control (DPBS). Chemical exposure lasts for 60 minutes, 35 min of which the tissues are kept in an incubator at 37&deg;C. The test substances are then removed from the tissue surface by an extensive washing procedure. The tissue inserts are blotted and transferred to fresh medium. After a 24 hr incubation period (Day 2), the medium is exchanged. The medium can be saved for further analysis of cytokines or other endpoints of interest. After the medium exchange, tissues are incubated for an additional 18 hours. At the end of the entire 42h post-incubation (day 3), the tissues are transferred into yellow MTT solution and incubated for 3 hours. The resultant purple-blue formazan salt, formed mainly by mitochondrial metabolism, is extracted for 2 hours using isopropanol. The optical density of the extracted formazan is determined using a spectrophotometer. A chemical is classified as an irritant if the tissue viability relative to the negative control treated tissues is reduced below 50%. This procedure can be used as full replacement of the in vivo rabbit skin irritation test for hazard identification and labeling of chemicals in line with EU regulations (7).

An In Vitro Skin Irritation Test SIT using the EpiDerm Reconstructed Human Epidermal RHE Model

In this video, we demonstrate the EpiDerm Skin Irritation test (EpiDerm SIT) developed and validated for in vitro skin irritation testing of chemicals, including cosmetic and pharmaceutical ingredients.

The EpiDerm Skin Irritation test (EpiDerm SIT) was developed (1,2,3) and validated (4,5) for in vitro skin irritation testing of chemicals, including ...

Biology

Development of an In Vitro Ocular Platform to Test Contact Lenses

Currently, in vitro evaluations of contact lenses (CLs) for drug delivery are typically performed in large volume vials,1-6 which fail to mimic physiological tear volumes.7 The traditional model also lacks the natural tear flow component and the blinking reflex, both of which are defining factors of the ocular environment. The development of a novel model is described in this study, which consists of a unique 2-piece design, eyeball and eyelid piece, capable of mimicking physiological tear volume. The models are created from 3-D printed molds (Polytetrafluoroethylene or Teflon molds), which can be used to generate eye models from various polymers, such as polydimethylsiloxane (PDMS) and agar. Further modifications to the eye pieces, such as the integration of an explanted human or animal cornea or human corneal construct, will permit for more complex in vitro ocular studies. A commercial microfluidic syringe pump is integrated with the platform to emulate physiological tear secretion. Air exposure and mechanical wear are achieved using two mechanical actuators, of which one moves the eyelid piece laterally, and the other moves the eyeballeyepiece circularly. The model has been used to evaluate CLs for drug delivery and deposition of tear components on CLs.

Development of an In Vitro Ocular Platform to Test Contact Lenses

Current in vitro models for evaluating contact lenses (CLs) and other eye-related applications are severely limited. The presented ocular platform simulates physiological tear flow, tear volume, air exposure and mechanical wear. This system is highly versatile and can be applied to various in vitro analyses with CLs.

Currently, in vitro evaluations of contact lenses (CLs) for drug delivery are typically performed in large volume vials,1-6 which fail to mimic ...

Cultivating a Three-dimensional Reconstructed Human Epidermis at a Large Scale

A three-dimensional human epidermis model reconstructed from neonatal primary keratinocytes is presented. Herein, a protocol for the cultivation process and the characterization of the model is described. Neonatal primary keratinocytes are grown submerged on permeable polycarbonate inserts and lifted to the air-liquid interface three days after seeding. After fourteen days of stimulation with defined growth factors and ascorbic acid in high calcium culture medium, the model is fully differentiated. Histological analysis revealed a completely stratified epidermis, mimicking the morphology of native human skin. To characterize the model and its barrier functions, protein levels and localization specific for early-stage keratinocyte differentiation (i.e., keratin 10), late-stage differentiation (i.e., involucrin, loricrin, and filaggrin) and tissue adhesion (i.e., desmoglein 1), were assessed by immunofluorescence. The tissue barrier integrity was further evaluated by measuring transepithelial electrical resistance. Reconstructed human epidermis was responsive to proinflammatory stimuli (i.e., lipopolysaccharide and tumor necrosis factor alpha), leading to increased cytokine release (i.e., interleukin 1 alpha and interleukin 8). This protocol represents a straightforward and reproducible in vitro method to cultivate reconstructed human epidermis as a tool to assess environmental effects and a broad range of skin-related studies.

This protocol describes a straightforward method to cultivate three-dimensional reconstituted human epidermis in a reproducible and robust manner. Additionally, it characterizes the structure-function relationship of the epidermal barrier model. The biological responses of the reconstituted human epidermis upon proinflammatory stimuli are also presented.

A three-dimensional human epidermis model reconstructed from neonatal primary keratinocytes is presented. Herein, a protocol for the cultivation process ...

Corneal Epithelial Abrasion with Ocular Burr As a Model for Cornea Wound Healing

The murine cornea provides an excellent model to study wound healing. The cornea is the outermost layer of the eye, and thus is the first defense to injury. In fact, the most common type of eye injury found in clinic is a corneal abrasion. Here, we utilize an ocular burr to induce an abrasion resulting in removal of the corneal epithelium in vivo on anesthetized mice. This method allows for targeted and reproducible epithelial disruption, leaving other areas intact. In addition, we describe the visualization of the abraded epithelium with fluorescein staining and provide concrete advice on how to visualize the abraded cornea. Then, we follow the timeline of wound healing 0, 18, and 72 h after abrasion, until the wound is re-epithelialized. The epithelial abrasion model of corneal injury is ideal for studies on epithelial cell proliferation, migration and re-epithelialization of the corneal layers. However, this method is not optimal to study stromal activation during wound healing, because the ocular burr does not penetrate to the stromal cell layers. This method is also suitable for clinical applications, for example, pre-clinical test of drug effectiveness.

This protocol describes a method to inflict an abrasion to the ocular surface of the mouse, and to follow the wound healing process thereafter. The protocol takes advantage of an ocular burr to partially remove the surface epithelium of the eye in anaesthetized mice.

The murine cornea provides an excellent model to study wound healing. The cornea is the outermost layer of the eye, and thus is the first defense to ...

Medicine

Effect of Artificial Tear Formulations on the Metabolic Activity of Human Corneal Epithelial Cells after Exposure to Desiccation

Artificial lipid-containing tear formulations are developed to reduce tear evaporation by the restoration of a deficient tear lipid layer. Artificial tear formulations that prevent cell desiccation will result in ocular surface protection and the maintenance of cell metabolic activity. During dehydration, cells undergo the process of loss of metabolic activity and subsequently cell death. This work describes a method for assessing the efficacy of artificial tear formulations. The metabolic dye (i.e., alamarBlue) changes from a low fluorescent molecule resazurin to a fluorescent molecule resorufin in viable cells. The biological performance of an artificial tear formulation is measured as the ability of the formulation to (a) maintain cell viability and (b) provide cell protection from desiccation. Growth media and saline are used as controls for the cell viability/desiccation tests. Cells are incubated with test solutions for 30 min and then desiccated for 0 or 5 min at 37 &#176;C and 45% relative humidity. Cell metabolic activity after initial exposure and after cell desiccation is then determined. The results show the comparative effects of eye drop formulations on cell metabolic activity and desiccation protection. This method can be used to test dry eye formulations that are designed to treat individuals with evaporative dry eye.

The purpose of this protocol is to evaluate if different artificial tear formulations can protect human corneal epithelial cells from desiccation using an in vitro model. After exposure to artificial tear formulations and desiccation, human corneal epithelial cells are assessed for metabolic activity.

Artificial lipid-containing tear formulations are developed to reduce tear evaporation by the restoration of a deficient tear lipid layer. Artificial tear ...

Ex Vivo and In Vivo Animal Models for Mechanical and Chemical Injuries of Corneal Epithelium

Corneal injury to the ocular surface, including chemical burn and trauma, may cause severe scarring, symblepharon, corneal limbal stem cells deficiency, and result in a large, persistent corneal epithelial defect. Epithelial defect with the following corneal opacity and peripheral neovascularization result in irreversible visual impairment and hinder future management, especially keratoplasty. Since the animal model can be used as an effective drug development platform, models of corneal injury to the mouse and alkali burn to rabbit corneal epithelium are developed here. New Zealand white rabbit is used in the alkali burn model. Different concentrations of sodium hydroxide can be applied onto the central circular area of the cornea for 30 s under intramuscular and topical anesthesia. After copious isotonic normal saline irrigation, residual loose corneal epithelium was removed with corneal burr deep down to the Bowman's layer within this circular area. Wound healing was documented by fluorescein staining under Cobalt blue light. C57BL/6 mice were used in the traumatic model of murine corneal epithelium. The murine central cornea was marked using a skin punch, 2 mm in diameter, and then debrided by a corneal rust ring remover with a 0.5 mm burr under a stereomicroscope. These models can be prospectively used to validate the therapeutic effect of eye drops or mixed agents such as stem cells, which potentially facilitate corneal epithelial regeneration. By observing corneal opacity, peripheral neovascularization, and conjunctival congestion with stereomicroscope and imaging software, therapeutic effects in these animal models can be monitored.

Ex Vivo and In Vivo Animal Models for Mechanical and Chemical Injuries of Corneal Epithelium

Here, animal models based on mouse and rabbit are developed for mechanical and chemical injury of corneal epithelium to screen new therapeutics and the underlying mechanism.

Corneal injury to the ocular surface, including chemical burn and trauma, may cause severe scarring, symblepharon, corneal limbal stem cells deficiency, ...

High Throughput SiRNA Screening for Chloropicrin and Hydrogen Fluoride-Induced Cornea Epithelial Cell Injury

Toxicant-induced ocular injury is a true ocular emergency because chemicals have the potential to rapidly inflict significant tissue damage. Treatments for toxicant-induced corneal injury are generally supportive as no specific therapeutics exist to treat these injuries. In the efforts to develop treatments and therapeutics to care for exposure, it can be important to understand the molecular and cellular mechanisms of these injuries. We propose that utilization of high throughput small inhibitory RNA (siRNA) screening can be an important tool that could help to more rapidly elucidate the molecular mechanisms of chemical cornea epithelial injury. siRNA are double stranded RNA molecules that are 19-25 nucleotides long and utilize the post-transcriptional gene silencing pathway to degrade mRNA which have homology to the siRNA. The resulting reduction of expression of the specific gene can then be studied in toxicant exposed cells to ascertain the function of that gene in the cellular response to the toxicant. The development and validation of in vitro exposure models and methods for the high throughput screening (HTS) of hydrogen fluoride- (HF) and chloropicrin- (CP) induced ocular injury are presented in this article. Although we selected these two toxicants, our methods are applicable to the study of other toxicants with minor modifications to the toxicant exposure protocol. The SV40 large T antigen immortalized human corneal epithelial cell line SV40-HCEC was selected for study. Cell viability and IL-8 production were selected as endpoints in the screening protocol. Several challenges associated with the development of toxicant exposure and cell culture methods suitable for HTS studies are presented. The establishment of HTS models for these toxicants allows for further studies to better understand the mechanism of injury and to screen for potential therapeutics for chemical ocular injury.

High throughput small inhibitory RNA screening is an important tool that could help to more rapidly elucidate the molecular mechanisms of chemical cornea epithelial injury. Herein, we present the development and validation of exposure models and methods for the high throughput screening of hydrogen fluoride- and chloropicrin-induced cornea epithelial injury.

Toxicant-induced ocular injury is a true ocular emergency because chemicals have the potential to rapidly inflict significant tissue damage. Treatments ...

A Modified Biopsy Punch Method for Precise Alkali Burns in Mice

Corneal and Limbal Alkali Injury Induction Using a Punch-Trephine Technique in a Mouse Model

The cornea is critical for vision, and corneal healing after trauma is fundamental in maintaining its transparency and function. Through the study of corneal injury models, researchers aim to enhance their understanding of how the cornea heals and develop strategies to prevent and manage corneal opacities. Chemical injury is one of the most popular injury models that has extensively been studied on mice. Most previous investigators have used a flat paper soaked in sodium hydroxide to induce corneal injury. However, inducing corneal and limbal injury using flat filter paper is unreliable, since the mouse cornea is highly curved. Here, we present a new instrument, a modified biopsy punch, that enables the researchers to create a well-circumscribed, localized, and evenly distributed alkali injury to the murine cornea and limbus. This punch-trephine method enables researchers to induce an accurate and reproducible chemical burn to the entire murine cornea and limbus while leaving other structures, such as the eyelids, unaffected by the chemical. Moreover, this study introduces an enucleation technique that preserves the medial caruncle as a landmark for identifying the nasal side of the globe. The bulbar and palpebral conjunctiva, and lacrimal gland are also kept intact using this technique. Ophthalmologic examinations were performed via slit lamp biomicroscope and fluorescein staining on days 0, 1, 2, 6, 8, and 14 post-injury. Clinical, histological, and immunohistochemical findings confirmed limbal stem cell deficiency and ocular surface regeneration failure in all experimental mice. The presented alkali corneal injury model is ideal for studying limbal stem cell deficiency, corneal inflammation, and fibrosis. This method is also suitable for investigating pre-clinical and clinical efficacies of topical ophthalmologic medications on the murine corneal surface.

Author Spotlight: Advancing Research in Corneal Opacity Treatment and Regeneration 

This protocol describes a method to induce an accurate and reproducible corneal and limbal alkali injury in a mouse model. The protocol is advantageous as it allows for an evenly distributed injury to the highly curved mouse cornea and limbus.

The cornea is critical for vision, and corneal healing after trauma is fundamental in maintaining its transparency and function. Through the study of ...

Determining the Toxicity of UV Radiation and Chemicals on Primary and Immortalized Human Corneal Epithelial Cells

This article describes the methods of measuring the toxicity of ultraviolet (UV) radiation and ocular toxins on primary (pHCEC) and immortalized (iHCEC) human corneal epithelial cell cultures. Cells were exposed to UV radiation and toxic doses of benzalkonium chloride (BAK), hydrogen peroxide (H2O2), and sodium dodecyl sulfate (SDS). Metabolic activity was measured using a metabolic assay. The release of inflammatory cytokines was measured using a multi-plex interleukin (IL)-1&#946;, IL-6, IL-8, and tumor necrosis factor-alpha (TNF-&#945;) assay, and cells were evaluated for viability using fluorescent dyes. 
The damaging effects of UV on cell metabolic activity and cytokine release occurred at 5 min of UV exposure for iHCEC and 20 min for pHCEC. Similar percent drops in metabolic activity of the iHCEC and pHCEC occurred after exposure to BAK, H2O2, or SDS, and the most significant changes in cytokine release occurred for IL-6 and IL-8. Microscopy of fluorescently stained iHCEC and pHCEC BAK-exposed cells showed cell death at 0.005% BAK exposure, although the degree of ethidium staining was greater in the iHCECs than pHCECs. Utilizing multiple methods of assessing toxic effects using microscopy, assessments of metabolic activity, and cytokine production, the toxicity of UV radiation and chemical toxins could be determined for both primary and immortalized cell lines.

This article describes the procedures used to evaluate the toxicity of UV radiation and chemical toxins on a primary and immortalized cell line.

This article describes the methods of measuring the toxicity of ultraviolet (UV) radiation and ocular toxins on primary (pHCEC) and immortalized (iHCEC) ...

Ex Vivo Porcine Corneal Culture System for Toxicity Testing and Wound Healing

Evaluating Therapeutic and Chemical Toxicity Using Organ-Cultured Porcine Corneas and Epithelial Wound Healing

Due to its anatomical and physiological similarities to the human eye, the porcine eye serves as a robust model for biomedical research and ocular toxicity assessment. An air/liquid corneal culture system using porcine eyes was developed, and ex vivo epithelial wound healing was utilized as a critical parameter for these studies. Fresh pig corneas were processed for organ culture, with or without epithelial wounding. The corneas were cultured in a humidified 5% CO2 incubator at 37 &#176;C in MEM, with or without testing agents. Corneal permeability and wound healing rates were measured, and epithelial cells and/or whole corneas can be processed for immunohistochemistry, western blotting, and qPCR for molecular and cellular analyses. This study describes a detailed protocol and presents two studies using this ex vivo system. The data show that porcine corneal organ culture, combined with epithelial wound healing, is a suitable ex vivo model for chemical toxicity testing, studying diabetic keratopathy, and identifying potential therapies.

Author Spotlight: Exploring Corneal Innate Immunity and Delayed Wound Healing in Diabetic Patients

Porcine corneal ex vivo organ culture and epithelial wound healing provide an economical, ethical, reproducible, and quantitative means for testing the ocular toxicity of chemicals. They also aid in elucidating mechanisms underlying the regulation of epithelialization and tissue repair, and in evaluating therapeutics for treating diabetic keratopathy and delayed wound healing.

Eye Irritation Test (EIT) for Hazard Identification of Eye Irritating Chemicals using Reconstructed Human Cornea-like Epithelial (RhCE) Tissue Model

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Development of an In Vitro Ocular Platform to Test Contact Lenses

Cultivating a Three-dimensional Reconstructed Human Epidermis at a Large Scale

Corneal Epithelial Abrasion with Ocular Burr As a Model for Cornea Wound Healing

Effect of Artificial Tear Formulations on the Metabolic Activity of Human Corneal Epithelial Cells after Exposure to Desiccation

Ex Vivo and In Vivo Animal Models for Mechanical and Chemical Injuries of Corneal Epithelium

High Throughput SiRNA Screening for Chloropicrin and Hydrogen Fluoride-Induced Cornea Epithelial Cell Injury

Corneal and Limbal Alkali Injury Induction Using a Punch-Trephine Technique in a Mouse Model

Determining the Toxicity of UV Radiation and Chemicals on Primary and Immortalized Human Corneal Epithelial Cells

Evaluating Therapeutic and Chemical Toxicity Using Organ-Cultured Porcine Corneas and Epithelial Wound Healing