Alternatives to Laboratory Animals

Most in vitro models are only used to assess the short-term effects of test compounds. However, as demonstrated here, hippocampal slice cultures can be used for long-term studies. The test compound used was the metabotropic glutamate receptor antagonist, L(+)-2-amino-3-phosphonopropionic acid (L-AP3), which is known to be toxic in vivo after subchronic, but not acute, administration. Degenerative effects were monitored by measuring the cellular uptake of propidium iodide (PI; continuously present in the medium) and lactate dehydrogenase (LDH) leakage, and by using a panel of histological stains. Hippocampal slices, derived from 2–3 day old rats and grown for 3 weeks, were subsequently exposed for the next 3 weeks to 0, 10 or 100μM L-AP3, with PI (2μM) in the culture medium. Exposure to 100μM L-AP3 induced severe toxicity after 4–6 days, as shown by massive PI uptake, LDH leakage, and changes in MAP2 and GFAP immunostaining and in Nissl and Timm staining. In contrast, 10μM L-AP3 did not induce detectable neuronal degeneration. Treatment with the NMDA receptor antagonist, MK-801, or the AMPA/KA receptor antagonist, NBQX, together with 100μM L-AP3, reduced neurodegeneration to close to control values. It is concluded that the continuous incubation of hippocampal slice cultures with PI is technically feasible for use in studies on inducible neuronal degeneration over time.

The introduction of in vitro assays in pharmacological research has led to a reduction in the number of experimental animals used. But what has been the degree of this reduction, and when did it really start? This report describes the events in a medium-sized pharmaceutical company. Analysis of data collected over the last 12 years shows a five-fold reduction in the number of experimental animals used per compound synthesised. Compounds from compound libraries (large collections of randomly-synthesised molecules) that are being assessed for potential bioactivity in ‘high-throughput screening’ were not included in this analysis. Over the years, the (average) degree of discomfort for the animals in the experiments did not vary much; with variation generally observed from 1.5 to 2.0 (on a scale from 1–6). There was a peak in the discomfort score of experimental mice in 1997, which could be explained by the initiation of arthritis models that were subsequently refined, resulting in a lower degree of suffering. It might be concluded that the introduction of in vitro assays has indeed brought about a significant reduction in the number of experimental animals required to select a good compound (i.e. one that could progress to the preclinical toxicology phase). However, this development appears to have been neutralised by the low survival rate of new chemical entities in clinical studies, leading to a lower number of compounds per annum that actually reach the market place. Put in this ‘productivity perspective’, the number of experimental animals required to select a marketable drug has not much changed in the last decade.

An express (3-minute) test for acute toxicity determination by using the oligochaete annelid, Tubifex tubifex, is described. The EC50(Tubifex tubifex) [EC50(Tt)] for movement inhibition was calculated by using a concentration–response dependence. The reproducibility of the test was checked over several years and by several workers. Its applicability is limited to compounds which are soluble in water. The calculated EC50(Tt) indices correlate with LC50 values determined by using the fish, Pimephales promelas (96hour assay), and with ICG50 values determined by using the ciliate, Tetrahymena pyriformis (48-hour assay) with high statistical significance (r = 0.822, n = 35, and r = 0.927, n = 80, respectively). The correlation between the EC50(Tt) indices and rat oral LD50 values (48-hour assay) was r = 0.519 (n = 67). The correlation within organic compounds was closer (r = 0.635, n = 60) than with the heterogeneous series of chemicals. A similar trend was noticed for the correlation with mouse oral LD50 values (r = 0.479, n = 56) with the heterogeneous series of chemicals, as compared that with the series without inorganic salts (r = 0.605, n = 42), and similarly with mouse intraperitoneal LD50 values, where r = 0.543 (n = 50) with the heterogeneous series of chemicals and r = 0.893 (n = 33) with the series of organic chemicals.

The final EU REACH legislation has recently been adopted. This article considers the progress that has been made toward reducing the numbers of animals likely to be required to fulfil the testing requirements, and also considers the benefits to animal welfare and science that have arisen since the original REACH system proposals were published in 2003. Several positive changes have been made, including: the use of exposure-based testing; the requirement for scientific justification of any proposed animal testing; mandatory data sharing; and the fact that the EU is to take responsibility for the development and validation of alternative methods. While these changes are to be commended, there is still much room for improvement, particularly with respect to the adoption of integrated testing strategies that make maximum use of non-animal approaches to expedite the risk assessment process of existing chemicals, with the use of refined and updated animal tests only as a last resort.

Liverpool John Moores University and FRAME recently conducted a research project sponsored by Defra, on the status of alternatives to animal testing with regard to the European Union REACH (Registration, Evaluation and Authorisation of Chemicals) system for the safety testing and risk assessment of chemicals. The project covered all the main toxicity endpoints associated with the REACH system. This paper focuses on the prospects for using alternative methods (both in vitro and in silico) for mutagenicity (genotoxicity) and carcinogenicity testing — two toxicity endpoints, which, together with reproductive toxicity, are of pivotal importance for the REACH system. The manuscript critically discusses well-established testing approaches, and in particular, the requirement for short-term in vivo tests for confirming positive mutagenicity, and the need for the rodent bioassay for detecting non-genotoxic carcinogens. Recently-proposed testing strategies focusing on non-animal approaches are also considered, and our own testing scheme is presented and supported with background information. This scheme makes maximum use of pre-existing data, computer (in silico) and in vitro methods, with weight-of-evidence assessments at each major stage. The need for the improvement of in vitro methods, to reduce the generation of false-positive results, is also discussed. Lastly, ways in which reduction and refinement measures can be used are also considered, and some recommendations are made for future research to facilitate the implementation of the proposed testing scheme.

The final text of the REACH legislation, that has recently been published by the European Parliament, and which will come into force in the middle of 2007, implies that results obtained from so-called ‘suitable’ in vitro methods could be used for testing. It is also stated that a ‘suitable’ test is one that has been deemed to be ready to enter a validation study — for example, according to criteria specified by ECVAM. It is argued that, because the wording of the legal text is too vague and imprecise, it is totally unsatisfactory, mainly because it seems to endorse the application of non-validated methods for regulatory risk assessment. While their use might be suitable for providing information for classification in a weight-of-evidence approach, setting safe dose levels should only ever be based on the use of data from a properly validated test method. This concern, and other problems raised by the final legislation, is discussed, and recommendations are made which could avoid the premature use of potentially unsuitable methods for risk assessment, whilst ensuring that potentially suitable tests can be used for this purpose, once they have been formally validated.