3.3. Eye Irritation

Toxic External Exposure Leading to Ocular Surface Injury

The surface of the eye is directly exposed to the external environment, protected only by a thin tear film, and may therefore be damaged by contact with ambient particulate matter, liquids, aerosols, or vapors. In the workplace or home, the eye is subject to accidental or incidental exposure to cleaning products and pesticides. Organic matter may enter the eye and cause infection. Ocular surface damage can trigger a range of symptoms such as itch, discharge, hyperemia, photophobia, blurred vision, and foreign body sensation. Toxin exposure can be assessed clinically in multiple ways, including via measurement of tear production, slit-lamp examination, corneal staining, and conjunctival staining. At the cellular level, environmental toxins can cause oxidative damage, apoptosis of corneal and conjunctival cells, cell senescence, and impaired motility. Outcomes range from transient and reversible with complete healing to severe and sight-compromising structural changes. Classically, evaluation of tolerance and safety was carried out using live animal testing; however, new in vitro and computer-based, in silico modes are superseding the gold standard Draize test. This review examines how environmental features such as pollutants, temperature, and seasonality affect the ocular surface. Chemical burns to the eye are considered, and approaches to protect the ocular surface are detailed.

Mucoadhesive PLGA Nanospheres and Nanocapsules for Lactoferrin Controlled Ocular Delivery

Background: the present work describes the preparation, characterization and optimization of eight types of PLGA-based nanosystems (nanospheres and nanocapsules) as innovative mucoadhesive drug delivery systems of lactoferrin, in order to achieve a preclinical consistent base as an alternative pharmacological treatment to different ocular syndromes and diseases. Methods: All different nanoparticles were prepared via two modified nanoprecipitation techniques, using a three-component mixture of drug/polymer/surfactant (Lf/PLGA/Poloxamer), as a way to overcome the inherent limitations of conventional PLGA NPs. These modified polymeric nanocarriers, intended for topical ophthalmic administration, were subjected to in vitro characterization, surface modification and in vitro and in vivo assessments. Results: An appropriate size range, uniform size distribution and negative ζ potential values were obtained for all types of formulations. Lactoferrin could be effectively included into all types of nanoparticles with appropriate encapsulation efficiency and loading capacity values. A greater, extended, and controlled delivery of Lf from the polymeric matrix was observed through the in vitro release studies. No instability or cytotoxicity was proved for all the formulations by means of organotypic models. Additionally, mucoadhesive in vitro and in vivo experiments show a significant increase in the residence time of the nanoparticles in the eye surface. Conclusions: all types of prepared PLGA nanoparticles might be a potential alternative for the topical ophthalmic administration of lactoferrin.

Synthesis and potential vasorelaxant effect of a novel ruthenium-based nitro complex

This study aimed to investigate the synthesis and potential vasodilator effect of a novel ruthenium complex, cis-[Ru(bpy)₂(2-MIM)(NO₂)]PF₆ (bpy = 2,2'-bipyridine and 2-MIM = 2-methylimidazole) (FOR711A), containing an imidazole derivative via an in silico molecular docking model using β1 H-NOX (Heme-nitric oxide/oxygen binding) domain proteins of reduced and oxidized soluble guanylate cyclase (sGC). In addition, pharmacokinetic properties in the human organism were predicted through computational simulations and the potential for acute irritation of FOR711A was also investigated in vitro using the hen's egg chorioallantoic membrane (HET-CAM). FOR711A interacted with sites of the β1 H-NOX domain of reduced and oxidized sGC, demonstrating shorter bond distances to several residues and negative values of total energy. The predictive study revealed molar refractivity (RM): 127.65; Log Po/w = 1.29; topological polar surface area (TPSA): 86.26 Å²; molar mass (MM) = 541.55 g/mol; low solubility, high unsaturation index, high gastrointestinal absorption; toxicity class 4; failure to cross the blood-brain barrier and to react with cytochrome P450 (CYP) enzymes CYP1A2, CYP2C19, CYP2C9, CYP2D6 and CYP3A4. After the HET-CAM assay, the FOR711A complex was classified as non-irritant (N.I.) and its vasodilator effect was confirmed through greater evidence of blood vessels after the administration and ending of the observation period of 5 min. These results suggest that FOR711A presented a potential stimulator/activator effect of sGC via NO/sGC/cGMP. However, results indicate it needs a vehicle for oral administration.

Design, Optimization, and Characterization of Lactoferrin-Loaded Chitosan/TPP and Chitosan/Sulfobutylether-β-cyclodextrin Nanoparticles as a Pharmacological Alternative for Keratoconus Treatment

This research study describes the design, optimization, and characterization of two different types of chitosan-based nanoparticles as novel drug delivery systems of a protein drug, lactoferrin. A preclinical consistent base was obtained for both nanosystems, being considered as the first pharmacological treatment for keratoconus as an alternative to current invasive clinical methods. Both types of nanoparticles were obtained via the ionotropic gelation technique. The size and morphology of the nanoparticles were studied as a function of the preparation conditions. A mean size of 180.73 ± 40.67 nm, a size distribution [polydispersity index (PDI)] of 0.170 ± 0.067, and positive ζ-potential values, ranging from 17.13 to 19.89 mV, were achieved. Lactoferrin was successfully incorporated into both types of nanocarriers. In vitro release profiles showed a lactoferrin enhanced, prolonged, and controlled delivery from the polymeric matrix. These formulations also demonstrated no stability or cytotoxicity problems, as well as appropriate mucoadhesive properties, with a high permanence time in the ocular surface. Thus, both types of nanoparticles may be considered as nanocarriers for the controlled release of lactoferrin as novel topical ophthalmic drug delivery systems.

Strategy Combining Nonanimal Methods for Ocular Toxicity Evaluation

Historically, the ocular toxicity of manufactured consumer materials has been evaluated using the rabbit in vivo Draize rabbit eye test. The animal data obtained were used by the United Nations Globally Harmonized System of Classification and Labelling of Chemicals (UN GHS) to define the classification and labelling (C&L) for eye damage/irritation endpoint. However, the Draize test, a method which was never formally validated, has been widely criticized because of its technical limitations. In addition, ethical and economic issues and advances in scientific knowledge, and political and public pressures have made animal experimentation unsustainable. This scenario has consequently led to the development of nonanimal testing and protocols/approaches with considerable predictive value and relevance for humans. It is widely accepted that one single nonanimal method cannot cover all the criteria of damage/inflammation assessed by regulatory adopted in vivo animal testing. Thus, integrated testing strategies (ITS) have been proposed, including a tiered testing approach combining different nonanimal testing with different endpoints, which have been used for regulatory purposes, on a case-by-case basis and within integrated approaches to testing and assessment (IATA), to identify materials according to their ability to trigger eye damage. In particular, the top-down and bottom-up approaches have been recommended for the C&L of materials, which cause serious eye damage or eye irritation, respectively. This chapter describes detailed protocols for eye irritation testing based on cells (Short Time Exposure-STE, OECD No. 491/2017), a vascularized membrane (the Hen's Egg Test-Chorioallantoic Membrane-HET-CAM) and corneal tissue (Bovine Corneal Opacity and Permeability-BCOP, OECD No. 437/2017), which can be applied using top-down or bottom-up approaches. In addition, it suggests making a corneal histomorphometric evaluation as an additional parameter in the BCOP method to differentiate materials that cause serious eye tissue damage (UN GHS Cat. 1) from materials that have reversible eye irritation effects (UN GHS Cat. 2).

Expansion of the applicability domain for highly volatile substances on the Short Time Exposure test method and the predictive performance in assessing eye irritation potential

The Short Time Exposure (STE) test method is an in vitro method for assessing the eye irritation potential of chemicals and is used to classify the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) Category 1 and No Category (NC). The method has been adopted by the Organisation for Economic Co-operation and Development (OECD) as test guideline (TG) 491 since 2015. While this method can be used to classify GHS NC, it is not suitable for testing highly volatile substances and solids other than surfactants. Here we evaluated highly volatile substances to expand the applicability domain. According to TG 491, acetone, ethanol, iso-propanol, and methyl acetate as highly volatile substances resulted in false negatives. Saline was selected as a solvent of these false negatives. In this study, mineral oil was used as the solvent, because these false negatives were amphiphilic. Based on this change, four highly volatile substances were correctly evaluated. The predictive performance for classifying GHS NC was then verified using a substance dataset constructed in reference to the Draize eye test Reference Database and STE Summary Review Document. The accuracy and false-negative rate were 86.6% (194/224) and 3.8% (3/80), respectively. Collectively, the applicability domain was expanded by changing the solvent to mineral oil for highly volatile substances, and the predictive performance for the new applicability domain including highly volatile substances was excellent. The STE test method is suitable to classify GHS NC, indicating its applicability as a test method in a bottom-up approach.

Ophthalmic gels: Past, present and future

Aqueous gels formulated using hydrophilic polymers (hydrogels) along with those based on stimuli responsive polymers (in situ gelling or gel forming systems) continue to attract increasing interest for various eye health-related applications. They allow the incorporation of a variety of ophthalmic pharmaceuticals to achieve therapeutic levels of drugs and bioactives at target ocular sites. The integration of sophisticated drug delivery technologies such as nanotechnology-based ones with intelligent and environment responsive systems can extend current treatment duration to provide more clinically relevant time courses (weeks and months instead of hours and days) which will inevitably reduce dose frequency, increase patient compliance and improve clinical outcomes. Novel applications and design of contact lenses and intracanalicular delivery devices along with the move towards integrating gels into various drug delivery devices like intraocular pumps, injections and implants has the potential to reduce comorbidities caused by glaucoma, corneal keratopathy, cataract, diabetic retinopathies and age-related macular degeneration. This review describes ophthalmic gelling systems with emphasis on mechanism of gel formation and application in ophthalmology. It provides a critical appraisal of the techniques and methods used in the characterization of ophthalmic preformed gels and in situ gelling systems along with a thorough insight into the safety and biocompatibility of these systems. Newly developed ophthalmic gels, hydrogels, preformed gels and in situ gelling systems including the latest in the area of stimuli responsive gels, molecularly imprinted gels, nanogels, 3D printed hydrogels; 3D printed devices comprising ophthalmic gels are covered. Finally, new applications of gels in the production of artificial corneas, corneal wound healing and hydrogel contact lenses are described.

Poly[acrylonitrile-co-(N-vinyl pyrrolidone)] nanoparticles - Composition-dependent skin penetration enhancement of a dye probe and biocompatibility

Nanoparticles can improve topical drug delivery: size, surface properties and flexibility of polymer nanoparticles are defining its interaction with the skin. Only few studies have explored skin penetration for one series of structurally related polymer particles with systematic alteration of material composition. Here, a series of rigid poly[acrylonitrile-co-(N-vinyl pyrrolidone)] model nanoparticles stably loaded with Nile Red or Rhodamin B, respectively, was comprehensively studied for biocompatibility and functionality. Surface properties were altered by varying the molar content of hydrophilic NVP from 0 to 24.1% and particle size ranged from 35 to 244nm. Whereas irritancy and genotoxicity were not revealed, lipophilic and hydrophilic nanoparticles taken up by keratinocytes affected cell viability. Skin absorption of the particles into viable skin ex vivo was studied using Nile Red as fluorescent probe. Whilst an intact stratum corneum efficiently prevented penetration, almost complete removal of the horny layer allowed nanoparticles of smaller size and hydrophilic particles to penetrate into viable epidermis and dermis. Hence, systematic variations of nanoparticle properties allows gaining insights into critical criteria for biocompatibility and functionality of novel nanocarriers for topical drug delivery and risks associated with environmental exposure.

In Vitro Cell Models for Ophthalmic Drug Development Applications

Tissue engineering is a rapidly expanding field that aims to establish feasible techniques to fabricate biologically equivalent replacements for diseased and damaged tissues/organs. Emerging from this prospect is the development of in vitro representations of organs for drug toxicity assessment. Due to the ever-increasing interest in ocular drug delivery as a route for administration as well as the rise of new ophthalmic therapeutics, there is a demand for physiologically accurate in vitro models of the eye to assess drug delivery and safety of new ocular medicines. This review summarizes current existing ocular models and highlights the important factors and limitations that need to be considered during their use.

Impact of structural differences in hyperbranched polyglycerol–polyethylene glycol nanoparticles on dermal drug delivery and biocompatibility

Polyglycerol scaffolds and nanoparticles emerged as prominent material for various biomedical applications including topical drug delivery. The impact of slight structural modifications on the nanoparticles' properties, drug delivery potential, and biocompatibility, however, is still not fully understood.Hence, we explored the influence of structural modifications of five structurally related polyglycerol-based nanoparticles (PG-PEG, SK1-SK5) on dermal drug delivery efficiency and biocompatibility. The PG-PEG particles were synthesized via randomly and controlled alkylated chemo-enzymatic approaches resulting in significantly varying particle sizes and interactions with guest molecules. Furthermore, weobserved considerably improved dermal drug delivery with the smallest particles SK4 and SK5 (11 nm and 14 nm) which also correlated with well-defined surface properties achieved by the controlled alkylated synthesis approach. The consistently good biocompatibility for all PG-PEG particles was mainly attributed to the neutral surface charge. No irritation potential, major cytotoxicity or genotoxicity was observed. Nevertheless, slightly better biocompatibility was again seen for the particles characterized by alkyl chain substitution in the core and not on the particle surface.Despite the high structural similarity of the PG-PEG particles, the synthesis and the functionalization significantly influenced particle properties, biocompatibility, and most significantly the drug delivery efficiency.

Determining the Depth of Injury in Bioengineered Tissue Models of Cornea and Conjunctiva for the Prediction of All Three Ocular GHS Categories

The depth of injury (DOI) is a mechanistic correlate to the ocular irritation response. Attempts to quantitatively determine the DOI in alternative tests have been limited to exvivo animal eyes by fluorescent staining for biomarkers of cell death and viability in histological cross sections. It was the purpose of this study to assess whether DOI could also be measured by means of cell viability detected by the MTT assay using 3-dimensional (3D) reconstructed models of cornea and conjunctiva. The formazan-free area of metabolically inactive cells in the tissue after topical substance application is used as the visible correlate of the DOI. Areas of metabolically active or inactive cells are quantitatively analyzed on cryosection images with ImageJ software analysis tools. By incorporating the total tissue thickness, the relative MTT-DOI (rMTT-DOI) was calculated. Using the rMTT-DOI and human reconstructed cornea equivalents, we developed a prediction model based on suitable viability cut-off values. We tested 25 chemicals that cover the whole range of eye irritation potential based on the globally harmonized system of classification and labelling of chemicals (GHS). Principally, the MTT-DOI test method allows distinguishing between the cytotoxic effects of the different chemicals in accordance with all 3 GHS categories for eye irritation. Although the prediction model is slightly over-predictive with respect to non-irritants, it promises to be highly valuable to discriminate between severe irritants (Cat. 1), and mild to moderate irritants (Cat. 2). We also tested 3D conjunctiva models with the aim to specifically address conjunctiva-damaging substances. Using the MTT-DOI method in this model delivers comparable results as the cornea model, but does not add additional information. However, the MTT-DOI method using reconstructed cornea models already provided good predictability that was superior to the already existing established invitro/exvivo methods.

Estimation of the chemical-induced eye injury using a weight-of-evidence (WoE) battery of 21 artificial neural network (ANN) c-QSAR models (QSAR-21): part I: irritation potential

Evaluation of potential chemical-induced eye injury through irritation and corrosion is required to ensure occupational and consumer safety for industrial, household and cosmetic ingredient chemicals. The historical method for evaluating eye irritant and corrosion potential of chemicals is the rabbit Draize test. However, the Draize test is controversial and its use is diminishing - the EU 7th Amendment to the Cosmetic Directive (76/768/EEC) and recast Regulation now bans marketing of new cosmetics having animal testing of their ingredients and requires non-animal alternative tests for safety assessments. Thus, in silico and/or in vitro tests are advocated. QSAR models for eye irritation have been reported for several small (congeneric) data sets; however, large global models have not been described. This report describes FDA/CFSAN's development of 21 ANN c-QSAR models (QSAR-21) to predict eye irritation using the ADMET Predictor program and a diverse training data set of 2928 chemicals. The 21 models had external (20% test set) and internal validation and average training/verification/test set statistics were: 88/88/85(%) sensitivity and 82/82/82(%) specificity, respectively. The new method utilized multiple artificial neural network (ANN) molecular descriptor selection functionalities to maximize the applicability domain of the battery. The eye irritation models will be used to provide information to fill the critical data gaps for the safety assessment of cosmetic ingredient chemicals.

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).

ECVAM and new technologies for toxicity testing

The development of alternative empirical (testing) and non-empirical (non-testing) methods to traditional toxicological tests for complex human health effects is a tremendous task. Toxicants may potentially interfere with a vast number of physiological mechanisms thereby causing disturbances on various levels of complexity of human physiology. Only a limited number of mechanisms relevant for toxicity ('pathways' of toxicity) have been identified with certainty so far and, presumably, many more mechanisms by which toxicants cause adverse effects remain to be identified. Recapitulating in empirical model systems (i.e., in vitro test systems) all those relevant physiological mechanisms prone to be disturbed by toxicants and relevant for causing the toxicity effect in question poses an enormous challenge. First, the mechanism(s) of action of toxicants in relation to the most relevant adverse effects of a specific human health endpoint need to be identified. Subsequently, these mechanisms need to be modeled in reductionist test systems that allow assessing whether an unknown substance may operate via a specific (array of) mechanism(s). Ideally, such test systems should be relevant for the species of interest, i.e., based on human cells or modeling mechanisms present in humans. Since much of our understanding about toxicity mechanisms is based on studies using animal model systems (i.e., experimental animals or animal-derived cells), designing test systems that model mechanisms relevant for the human situation may be limited by the lack of relevant information from basic research. New technologies from molecular biology and cell biology, as well as progress in tissue engineering, imaging techniques and automated testing platforms hold the promise to alleviate some of the traditional difficulties associated with improving toxicity testing for complex endpoints. Such new technologies are expected (1) to accelerate the identification of toxicity pathways with human relevance that need to be modeled in test methods for toxicity testing (2) to enable the reconstruction of reductionist test systems modeling at a reduced level of complexity the target system/organ of interest (e.g., through tissue engineering, use of human-derived cell lines and stem cells etc.), (3) to allow the measurement of specific mechanisms relevant for a given health endpoint in such test methods (e.g., through gene and protein expression, changes in metabolites, receptor activation, changes in neural activity etc.), (4) to allow to measure toxicity mechanisms at higher throughput rates through the use of automated testing. In this chapter, we discuss the potential impact of new technologies on the development, optimization and use of empirical testing methods, grouped according to important toxicological endpoints. We highlight, from an ECVAM perspective, the areas of topical toxicity, skin absorption, reproductive and developmental toxicity, carcinogenicity/genotoxicity, sensitization, hematopoeisis and toxicokinetics and discuss strategic developments including ECVAM's database service on alternative methods. Neither the areas of toxicity discussed nor the highlighted new technologies represent comprehensive listings which would be an impossible endeavor in the context of a book chapter. However, we feel that these areas are of utmost importance and we predict that new technologies are likely to contribute significantly to test development in these fields. We summarize which new technologies are expected to contribute to the development of new alternative testing methods over the next few years and point out current and planned ECVAM projects for each of these areas.

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.

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.

Integrated risk assessment of a hydroxyapatite-protein-composite for use in oral care products: a weight-of-evidence case study

Risk assessment of cosmetic ingredients represents a regulatory standard requirement in Europe and other regions. An integrated approach was designed to assess the safety of HPC, a particulate composite of hydroxyapatite and protein (gelatin) for use in oral care products, employing a weight-of-evidence assessment and considering specific physico-chemical properties and exposure conditions. An initial evaluation of the constituents suggested that their chemical nature does not represent a particular health hazard per se. Hydroxyapatite is the main component of teeth and bones in mammals; gelatin is used in food and assumed to be safe once a BSE/TSE risk has been excluded. In vitro screening tests were chosen to further evaluate the biocompatibility: Hen's egg test-chorioallantoic membrane (HET-CAM) to assess irritating effects towards mucous membranes; MTT cytotoxicity test with 3T3 fibroblasts; human corneal epithelial models to investigate inflammatory mediators and cytotoxicity; macrophage assays to measure cytotoxicity, inflammatory mediators and oxidative stress. Together with results from clinical studies, exposure estimates and analyses of kinetic properties, the presented information provides sound evidence to support the safe use of HPC. This is an example of a risk assessment for cosmetic use of small particles without the need for additional animal studies.

Can mutagenicity information be useful in an Integrated Testing Strategy (ITS) for skin sensitization?

Our previous work has investigated the utility of mutagenicity data in the development and application of Integrated Testing Strategies (ITS) for skin sensitization by focusing on the chemical mechanisms at play and substantiating these with experimental data where available. The hybrid expert system TIMES (Tissue Metabolism Simulator) was applied in the identification of the chemical mechanisms since it encodes a comprehensive set of established structure-activity relationships for both skin sensitization and mutagenicity. Based on the evaluation, the experimental determination of mutagenicity was thought to be potentially helpful in the evaluation of skin sensitization potential. This study has evaluated the dataset reported by Wolfreys and Basketter (Cutan. Ocul. Toxicol. 23 (2004), pp. 197-205). Upon an update of the experimental data, the original reported concordance of 68% was found to increase to 88%. There were several compounds that were 'outliers' in the two experimental evaluations which are discussed from a mechanistic basis. The discrepancies were found to be mainly associated with the differences between skin and liver metabolism. Mutagenicity information can play a significant role in evaluating sensitization potential as part of an ITS though careful attention needs to be made to ensure that any information is interpreted in the appropriate context.

Validating and troubleshooting ocular in vitro toxicology tests

In vitro organotypic models for testing ocular irritants have warranted sufficient interest as methods to replace in vivo ocular testing. The in vitro organotypic models claim to maintain short-term normal physiological and biochemical functions of the mammalian cornea in an isolated system. In these test methods, damage by the test substance is assessed by quantitative measurements of changes in corneal opacity and permeability using opacitometry and spectrophotometry, respectively. Both measurements are used quantitatively for irritancy classification for prediction of the in vivo ocular irritation potential of a test substance. Examples of organotypic models that incorporate these criteria include: the bovine corneal opacity and permeability (BCOP) assay, the isolated chicken eye (ICE) test method and the isolated rabbit eye (IRE) assay. A fourth method, the hen's egg test-chorioallantoic membrane (HET-CAM) assay, differs in the evaluation criteria but is also normally included among this class of in vitro protocols. Each of these protocols is discussed in detail as representative candidate in vitro methods for assessing ocular irritation and corrosion. The methodologies, protocol details, applications, and their validation status are discussed. A brief historical perspective of the development of original in vitro ocular testing models is also mentioned. More importantly, improving and troubleshooting the current techniques, in order to present the models as stand-alone in vitro tools for ocular toxicity assessment, is emphasized.

Occludin gene expression as an early in vitro sign for mild eye irritation assessment

PURPOSE

To test a new multiple endpoint analysis (MEA) including occludin gene expression for screening the ocular irritation potential of tear substitutes on human corneal epithelium (HCE), an in vitro model proposed to limit the use of animal testing in pre-clinical studies.

METHODS

Four chemically-preserved and two non chemically-preserved tear substitutes were tested after acute (24h, 24h+24h post incubation) and repeated applications (for 72h) and compared to the positive control, benzalkonium chloride (BAK) at 0.1% and 0.01%, by assessing complementary parameters. Cellular viability was evaluated using MTT, histomorphologic analysis was performed on H&E stained vertical sections, IL-8 release was measured by ELISA, and occludin gene expression was quantified using qRT-PCR.

RESULTS

Cellular viability was moderately reduced by Perborate and Polyquad-preserved tear substitutes and dramatically reduced by BAK and by Thiomersal and Oxyd preserved tear substitutes. Thiomersal also increased IL-8 release. Occludin expression profiles were modified by the four chemically-preserved tear substitutes and by the mechanically-preserved Comod, but not by the mechanically-preserved Abak. The behavior of BAK and tear substitutes led us to propose a prediction model for the classification of different levels of irritants, mainly based on the occludin transcriptional study.

CONCLUSION

The versatility and sensitivity of the HCE model allowed the modeling of cumulative effects that may approach conditions obtained after long term application of tear substitutes. Thus, the modified MEA proposed in this study represents a valuable tool for in vitro eye irritation assessment with the power to detect mild irritants and subclinical eye irritant potential.

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.

Development of the short time exposure (STE) test: an in vitro eye irritation test using SIRC cells

Using SIRC (rabbit corneal cell line) cells, we developed an alternative eye irritation test: the short time exposure (STE) test. This STE test is a cytotoxicity test using physiological saline or mineral oil as the test solvent. Evaluation exposure time is short (5 min), which is similar to actual exposure situations, and uses the cell viability (CV) at a constant concentration as the endpoint for irritation potential. First, in order to confirm the usefulness of this STE test in assessing eye irritation potential of chemicals, 51 raw materials were tested and the correlation between CV in the STE test and the eye irritation score in the Draize test was examined. For the undiluted raw materials tested in the Draize test, the 5% test concentration in the STE test gave irritation classes that correlated well with the irritation classes from the Draize test (accuracy: 89.6%). For those materials tested as a 10% solution in the Draize test, STE irritation classes with 0.05% test concentration corresponded well with the Draize irritation classes (accuracy: 80.0%). Next, using the cell viabilities at these two concentrations, the STE prediction model (PM) was developed. A score of 1 or 2 was given for the results from each tested concentration in the STE test and Draize test. The scores from each test were then summed to yield a 3-level (Rank 1: minimally irritant, Rank 2: moderate irritant, Rank 3: severe irritant) eye irritation potential classification. Rank classification in the STE test showed a good correlation mostly to that in the Draize test (irritation class correspondence rate: 70.2%, but after exclusion of data of alcoholic materials, the rate was 91.7%). In most cytotoxicity test, the cytotoxicity of acids and amines is generally underestimated due the use of medium as the solvent. This is the result of the buffering capacity of the media. On the other hand, the STE test could predict the eye irritation potential by evaluating the chemical with a 5% test concentration. Eleven water insoluble materials such as toluene, octanol, and hexanol could be evaluated by using mineral oil as test solvent in the STE test. The STE test demonstrated itself to be simple, promising, have great potential, be of value, and to be an easily standardized alternative eye irritation test.

Simple stochastic fingerprints towards mathematical modeling in biology and medicine. 3. ocular irritability classification model

MARCH-INSIDE methodology and a statistical classification method--linear discriminant analysis (LDA)--is proposed as an alternative method to the Draize eye irritation test. This methodology has been successfully applied to a set of 46 neutral organic chemicals, which have been defined as ocular irritant or nonirritant. The model allow to categorize correctly 37 out of 46 compounds, showing an accuracy of 80.46%. Specifically, this model demonstrates the existence of a good categorization average of 91.67 and 76.47% for irritant and nonirritant compounds, respectively. Validation of the model was carried out using two cross-validation tools: Leave-one-out (LOO) and leave-group-out (LGO), showing a global predictability of the model of 71.7 and 70%, respectively. The average of coincidence of the predictions between leave-one-out/leave-group-out studies and train set were 91.3% (42 out of 46 cases)/89.1% (41 out of 46 cases) proving the robustness of the model obtained. Ocular irritancy distribution diagram is carried out in order to determine the intervals of the property where the probability of finding an irritant compound is maximal relating to the choice of find a false nonirritant one. It seems that, until today, the present model may be the first predictive linear discriminant equation able to discriminate between eye irritant and nonirritant chemicals.