The following is a brief overview of some new test methods that should be used in the EU chemical-testing programme to reduce or eliminate animal use:

Acute (short-term) toxicity can be studied using cell culture (in vitro) systems, since the actions of toxic chemicals are often focused at the cellular level. For example, a series of four cell culture tests can predict toxicity in humans with nearly 85 per cent accuracy (compared to 65 per cent in acute toxicity studies using animals). This method should, within several years, be able to replace the horrendously cruel use of animals in acute lethal poisoning testing.

Skin irritation testing can be carried out without any animal use, with the aid of human volunteers who agree to participate in brief and non-invasive ‘skin patch’ tests. Testing for irreversible skin irritation (corrosion) can also be carried out using such widely accepted non-animal methods as CORROSITEX™, EPIDERM™ and the EPISKIN™ reconstituted human skin test. The rate of chemical absorption through the skin can also be modelled in cell culture using human skin from cadavers. The above methods are all largely accepted by government regulators internationally and should be used as total replacements for skin irritation, corrosion and absorption testing in animals.

Eye irritation testing is almost identical to skin irritation testing, i.e., a chemical that is a skin irritant will also be an eye irritant. Therefore, eye irritation testing in animals should be discontinued immediately. Government regulators should instead use the results of non-animal skin irritation or corrosion tests to predict potential eye irritancy.

Skin sensitisation cannot, as yet, be studied using strictly non-animal methods. However, a less-invasive test method that also reduces the number of animals used (called the Local Lymph Node Assay) has been developed and should be used in place of the current Guinea Pig Maximisation Test.

Repeated dose toxicity can be studied using cells cultured from different body tissues to estimate the effects of a chemical on different organ systems. For example, human liver cells in culture could be exposed to repeated low doses of a chemical in order to study how the substance is broken down (metabolised) by the body and to identify any toxic byproducts (metabolites) that may be produced in the process. Stable human cell cultures have been produced for kidney, nervous, immune, reproductive and other essential organ systems. A ‘tiered’ testing strategy that combines several of these tissues in culture with the use of computer and mathematical modelling has the potential to do away with animal use in repeated-dose toxicity studies.

Genetic toxicity (mutagenicity) can be studied entirely without the use of animals. Three methods in particular (the Bacterial Reverse Mutation Test, In Vitro Cell Gene Mutation Test and the In Vitro Chromosomal Aberration Test) have been accepted by government regulators worldwide as valid alternatives to using animals. Therefore, genetic toxicity testing in animals should be discontinued immediately.

Reproductive toxicity and certain aspects of male and female reproductive function can be modelled to some extent in vitro, and several cellular components of reproductive organs can be maintained in cell cultures. Although no test method has yet been used or validated for routine use in reproductive toxicity studies, it is possible that a battery of such systems may in the future be able to model a large proportion of the male and female reproductive cycles, thereby reducing or replacing animal use in reproductive toxicity testing.

Developmental toxicity (teratogenicity) can be studied in cell cultures using an embryonic stem cell test, which is currently being validated as a screen for birth defects. Preliminary reports indicate that the in vitro embryonic stem cell test can predict toxicity in humans with greater than 80 per cent accuracy. It is hoped that within several years, this method will be able to eliminate animal use in developmental toxicity testing.

More generally, the following computer-based modelling approaches have shown great promise in contributing to the replacement of animals in toxicity testing:

Structure-activity relationship (SAR) analyses use computers to predict biological responses to chemicals based on their molecular structure, weight and electronic charge. SAR data can be used to estimate whether a specific chemical produces effects such as toxicity without the use of animals. SAR’s have been found to predict effects such as skin sensitisation, developmental toxicity and carcinogenicity for related groups of chemicals with 85 to 97 per cent accuracy. Although SAR models have proven to be extremely useful in the screening of chemicals, they are not stand-alone replacements. Therefore, they must be used in combination with other non-animal methods, such as cell-culture systems.

Computer-based mathematical modelling involves the use of computers to model living biological systems, such as the human circulatory and respiratory systems. For example, physiologically based biokinetic models (PBBK’s) use computers to study the absorption, distribution, metabolism and excretion of a chemical by the body. They can also be used to determine the relationship between the dose of a chemical and a particular metabolic effect. One such model, the ED01, studies tumour production in response to chemical exposure. It can detect increased tumour activity of 1 per cent at exposure levels much lower than those used in rodent toxicity studies.