Alternatives to animal experiments for eye irritation

1. Introduction

World-wide there is a strongly increased interest in the use of alternatives to animal experiments, in particular concerning safety assessments of cosmetics. Most resources have been used on the development and validation of alternative methods for evaluation of ocular irritation, where the existing animal experiments have been subject to intensive critizism based on scientific and ethical arguments.

A lot of in vitro tests have been introduced as possible alternatives to in vivo eye irritation tests. These methods comprise simple physico-chemical tests with plant proteins, methods with cultures of cells from humans and other mammals, systems with isolated eyes or ocular tissues and tests with the chorioallantoic membrane of hens eggs. A new type of in vitro tests with human tissues that have been reconstructed from cell cultures has also been introduced. Good correlations have been found between results obtained with reconstructed tissue models and results from animal experiments and human data in several toxicological areas. The present report is initiated with a section on reconstruction of tissue models with human cells, especially concerning tests for local irritancy.

The report deals also with experiments with a corneal tissue model, SKIN² ZK1200, which has been evaluated as a possible replacement of eye irritation tests using rabbits. 55 cosmetic ingredients and finished products were tested in a validation study organized by the European cosmetics industry (COLIPA), and 10 alternative methods were evaluated. The Institute of Food Safety and Toxicology participated in the validation study sponsored by the Danish Environmental Protection Agency as one of the two laboratories using the SKIN² ZK1200 model.

COLIPA is the European trade association of cosmetics industry. The organisation was established in 1962, and it represents 95% of the cosmetics industry in the EU member states with approximately 2000 companies. Additionally, COLIPA comprises 6 groups of companies from non-EU states and 21 large international companies.

The cosmetics industry is one of the major promoters of development and validation of alternatives to animal experiments, and COLIPA has been arranging several programs on the validation of alternative tests. In 1992, COLIPA established a Steering Commitee on Alternatives to Animal Testing (SCAAT), which coordinates the efforts of the cosmetics industry in the development of alternative methods. The members of SCAAT come from the companies Biersdorf, L'Oreal, Procter & Gamble, SmithKline Beecham, Unilever and Wella, but all of the international companies in COLIPA provide support and funding to SCAAT. Currently, there are four SCAAT task forces focusing on: eye irritation, photoirritation, human skin compatibility and percutaneous absorption.

The provisions for a potential ban on animal testing of cosmetics and their ingredients implied in the EU Cosmetics Directive (EU, 1993) have added additional impetus to the progress of the alternative methods. COLIPA is one of the major interest groups involved in the discussions of the progress of alternative methods arranged by the European Commission.

In the COLIPA eye irritation validation study, very good correlations were demonstrated between prediction of eye irritancy from data obtained with the tissue model SKIN² ZK1200 and acute ocular irritation observed with the Draize test. The method used with the tissue model was, however, not suited for prediction of the persistency of ocular irritation. In an independent preliminary study with 9 test substances, a method for the evaluation of recovery from acute ocular irritation using the SKIN² ZK1200 model was developed. In the present report, the new model for recovery for ocular irritation is described after the presentation of the COLIPA eye irritation validation study.

A discussion of the future prospects for replacement of animal experiments for ocular irritation is also included in the present report. Most of the alternative methods have a better reproducibibility than the Draize test. For this reason, an evaluation of the ability of the alternatives to predict the in vivo response should be given priority to evaluation of the intra- and interlaboratory reproducibility of the methods. The SKIN² ZK1200 model is the first in vitro method, which has shown a convincing potential as a model which may totally replace the Draize test. The production and sales of the tissue model has ceased, but it may be possible to use other commercial tissue models or to develop new, non-commercial tissue models to be used in ocular irritancy testing. Other types of alternative methods have not been shown to be suited for a general prediction of ocular irritancy, but several of the existing alternative tests may be suited for test of water soluble compounds, for example, surfactant based products.