Comparative evaluation of five in vitro tests for assessing the eye irritation potential of hair-care products

In vitro reconstructed 3D corneal tissue models for ocular toxicology and ophthalmic drug development

Testing of all manufactured products and their ingredients for eye irritation is a regulatory requirement. In the last two decades, the development of alternatives to the in vivo Draize eye irritation test method has substantially advanced due to the improvements in primary cell isolation, cell culture techniques, and media, which have led to improved in vitro corneal tissue models and test methods. Most in vitro models for ocular toxicology attempt to reproduce the corneal epithelial tissue which consists of 4-5 layers of non-keratinized corneal epithelial cells that form tight junctions, thereby limiting the penetration of chemicals, xenobiotics, and pharmaceuticals. Also, significant efforts have been directed toward the development of more complex three-dimensional (3D) equivalents to study wound healing, drug permeation, and bioavailability. This review focuses on in vitro reconstructed 3D corneal tissue models and their utilization in ocular toxicology as well as their application to pharmacology and ophthalmic research. Current human 3D corneal epithelial cell culture models have replaced in vivo animal eye irritation tests for many applications, and substantial validation efforts are in progress to verify and approve alternative eye irritation tests for widespread use. The validation of drug absorption models and further development of models and test methods for many ophthalmic and ocular disease applications is required.

CON4EI: CONsortium for in vitro Eye Irritation testing strategy - EpiOcular™ time-to-toxicity (EpiOcular ET-50) protocols for hazard identification and labelling of eye irritating chemicals

Assessment of acute eye irritation potential is part of the international regulatory requirements for testing of chemicals. The objective of the CON4EI (CONsortium for in vitro Eye Irritation testing strategy) project was to develop tiered testing strategies for eye irritation assessment for all drivers of classification. A set of 80 reference chemicals (38 liquids and 42 solids) was tested with eight different alternative methods. Here, the results obtained with reconstructed human cornea-like epithelium (RhCE) EpiOcular™ in the EpiOcular time-to-toxicity Tests (Neat and Dilution ET-50 protocols) are presented. The primary aim of this study was to evaluate whether test methods can discriminate chemicals not requiring classification for serious eye damage/eye irritancy (No Category) from chemicals requiring classification and labelling for Category 1 and Category 2. In addition, the predictive capacity in terms of in vivo drivers of classification was investigated. The chemicals were tested in two independent runs by MatTek In Vitro Life Science Laboratories. Results of this study demonstrate very high specificity of both test protocols. With the existing prediction models described in the SOPs, the specificity of the Neat and Dilution method was 87% and 100%, respectively. The Dilution method was able to correctly predicting 66% of GHS Cat 2 chemicals, however, prediction of GHS Cat 1 chemicals was only 47%-55% using the current protocols. In order to achieve optimal prediction for all three classes, a testing strategy was developed which combines the most predictive time-points of both protocols and for tests liquids and solids separately. Using this new testing strategy, the sensitivity for predicting GHS Cat 1 and GHS Cat 2 chemicals was 73% and 64%, respectively and the very high specificity of 97% was maintained. None of the Cat 1 chemicals was underpredicted as GHS No Category. Further combination of the EpiOcular time-to-toxicity protocols with other validated in vitro systems evaluated in this project, should enable significant reduction and even possible replacement of the animal tests for the final assessment of the irritation potential in all of the GHS classes.

In vitro cell culture models to study the corneal drug absorption

INTRODUCTION

Many diseases of the anterior eye segment are treated using topically applied ophthalmic drugs. For these drugs, the cornea is the main barrier to reaching the interior of the eye. In vitro studies regarding transcorneal drug absorption are commonly performed using excised corneas from experimental animals. Due to several disadvantages and limitations of these animal experiments, establishing corneal cell culture models has been attempted as an alternative.

AREAS COVERED

This review summarizes the development of in vitro models based on corneal cell cultures for permeation studies during the last 20 years, starting with simple epithelial models and moving toward complex organotypical 3D corneal equivalents.

EXPERT OPINION

Current human 3D corneal cell culture models have the potential to replace excised animal corneas in drug absorption studies. However, for widespread use, the contemporary validation of existent systems is required.

Comparative study of the ocular irritation potential of various alkyl polyglucoside surfactants

In the present work, we assessed the relationship between alkyl carbon chain length and ocular irritation potentials using the hen's egg test-chorioallantoic membrane (HET-CAM) and bovine corneal opacity and permeability (BCOP) assays using 5 commercial alkyl polyglucoside surfactants with different compositions of alkyl chain lengths (C(6)-C(16)). With HET-CAM, there was a good correlation between the proportion of C(10) alkyl polyglucoside and the eye irritation potential Q score (r(2) = 0.912, p = .011). There were no significant differences between the proportion of C(10) alkyl polyglucoside and corneal opacity in BCOP assays; however, there was a relatively high positive correlation between the proportion of C(10) alkyl carbon chain lengths and corneal permeability (r(2) = 0.736, p = .063).

Cell culture models of the human cornea - a comparative evaluation of their usefulness to determine ocular drug absorption in-vitro

Cell culture models of the cornea are continually developed to replace the isolated animal cornea for transcorneal drug absorption studies. The aim of this study was to determine and compare epithelial tightness and permeability of currently available corneal cell culture models to avoid interlaboratory variability and to assess their usefulness for in-vitro permeation studies. Pure epithelial cell culture models (CEPI, SIRC and HCE-T cell lines), primary cultures of human corneal epithelium (HCEpiC) and the two commercially available models (RHC and Epiocular), as well as organotypic human cornea constructs (HCC, HCC-HCE-T), were investigated and data were compared with those obtained from the excised bovine cornea. Barrier properties were assessed by measurements of transepithelial electrical resistance (TEER) and permeability of three passively absorbed substances (mannitol, testosterone and timolol maleate) with different physico-chemical properties. TEER experiments revealed weak barrier functions for all of the investigated epithelial models (<or=100-200 Omega cm2), except the HCE-T cell line. Transport studies confirmed TEER results insofar that models showing low TEER values also had higher permeation rates in comparison with the excised bovine cornea. However, models based on HCE-T cells demonstrated similar barrier properties to isolated corneal tissue. The corneal models investigated in our laboratory show clear differences in epithelial barrier function. In-vitro systems comprising the HCE-T cell line seem to be most appropriate to replace excised animal cornea for assessing corneal permeability.

Alternative Methods for Eye and Skin Irritation Tests: An Overview

The evaluation of eye and skin irritation potential is essential to ensuring the safety of individuals in contact with a wide variety of substances designed for industrial, pharmaceutical or cosmetic use. The Draize rabbit eye and skin irritancy tests have been used for 60 years to attempt to predict the human ocular and dermal irritation of such products. The Draize test has been the standard for ocular and dermal safety assessments for decades. However, several aspects of the test have been criticised. These include: the subjectivity of the method; the overestimation of human responses; and the method's cruelty. The inadequacies of the Draize test have led to several laboratories over the last 20 years making efforts to develop in vitro assays to replace it. Protocols that use different types of cell cultures and other methods have been devised to study eye and skin irritation. Different commercial kits have also been developed to study eye and skin irritation, based on the action of chemicals on these tissues. This article presents a review of the main alternatives developed to replace the use of animals in the study of chemical irritation. Particular attention is paid to the reproducibility of each method.

In vitro alternatives to the use of animals in ocular toxicology testing

Chemical substances, including household products, industrial chemicals, and cosmetics, must be tested for ocular toxicity or irritancy so that the public can be assured of their safety or warned of dangers associated with their use. The in vivo Draize test is the standard method used to meet this requirement; however, this test is coming under increasing criticism on scientific and ethical grounds. This has led to the development of a large number of proposed in vitro tests, some of which are routinely used to screen chemicals in toxicology laboratories. This review addresses regulations governing ocular irritancy testing and the current status of the movement toward use of alternative methods. Such methods include the use of cultured cells, hen's eggs, isolated animal eyes and corneas, human corneal epithelial cell lines, and the recently developed in vitro corneal equivalent models. The protocols for these methods are outlined, and their endpoints are described with respect to prediction of in vivo responses. The tests are evaluated in the context of the outcomes of validation studies and acceptance by regulatory agencies. While several of these tests yield useful information concerning ocular irritancy, to date, no in vitro alternative test has been validated as a replacement for the Draize test. If the goal of replacing the in vivo test while protecting the public from chemical eye injury is to be achieved, further development and improvement of alternative tests, as well as establishment of a human ocular toxicity data base, are required.