THIS year marks the 50th anniversary of what many would consider to be the first serious, academic consideration of laboratory animal welfare.
Russell and Burch’s Principles of Humane Experimental Technique (1959) championed the now-famous three Rs (3Rs): the replacement (with non-animal models), reduction (of animal numbers), and refinement (to decrease animal suffering) of laboratory animal use.
Since 1959, these 3Rs have become almost universally accepted as fundamental to good laboratory animal practice, for both animal welfare reasons, and to increase research quality. Yet, have we made sufficient progress in advancing laboratory animal welfare in the last 50 years?
Surprisingly, the answer appears to be no. Within the UK, the largest annual increase in animal experiments since 1987 was recently reported by the Home Office (Home Office, 2009): 3,656,080 scientific procedures were conducted on animals in 2008 – 14% more than the previous year. Numbers have risen for seven consecutive years, and are now higher than any time since the mid 1980s.
Yet, as Russell and Burch stated, “Refinement is never enough, and we should always seek further reduction and if possible replacement … Replacement is always a satisfactory answer.”
Accordingly, the sizeable increase in animal experiments attracted criticism by BVA president Nicky Paull and others (Dudley, 2009). However, such condemnation was by no means universal. Some expressed the opinion that animal experiments have the potential to yield great societal benefits (Dudley, 2009; Henderson, 2009).
Others have similarly claimed that medical progress would be “severely maimed by prohibition or severe curtailing of animal experiments,” and that “catastrophic consequences would ensue” (Osswald, 1992).
Reviewing the evidence
The prevalence of such opinions among animal researchers may partially explain the seemingly inexorable rise in animal experiments. Yet, regardless of the passion with which such views are expressed, or the credentials of those expressing them, they remain firmly within the realm of opinion. They are not evidence.
In recent years, however, a considerable body of systematic reviews has been published, examining the human utility of large numbers of animal experiments, selected without bias, via randomisation, or similarly impartial and methodical means (Knight, 2008a). Of 20 reviews examining human clinical utility, animal models demonstrated significant potential to contribute toward the development of clinical interventions in only two cases, one of which was contentious.
Seven additional reviews failed to demonstrate utility in reliably predicting human toxicological outcomes such as carcinogenicity and teratogenicity. Results in animal models were frequently equivocal, or inconsistent with human outcomes.
Given that millions of animal experiments have been conducted to date, it is inevitable that links to human healthcare advancements will exist. However, what the evidence establishes with remarkable consistency is that such links are far too few.
Animal experiments constitute a very inefficient tool for developing new human clinical interventions, and are insufficiently reliable when predicting human toxicity. Within the US, for example, only 8% of all drugs progressing to human trials after demonstration of safety in animal studies gain licensing approval by the Food and Drug Administration (Pippin, 2008). In most cases concerns subsequently arise about human toxicity or efficacy.
Non-animal alternatives
Fortunately, a rapidly growing range of non-animal alternatives exists (Knight, 2008b). These include mechanisms to enhance the sharing and assessment of existing data prior to conducting further studies, and physicochemical evaluation and computerised modelling.
The latter include the use of structure-activity relationships (which predict biological activities such as toxicity, on the basis of molecular substructures or other chemical moieties), and expert systems. Such systems seek to mimic the judgment of expert toxicologists, by using known rules about factors affecting toxicity, in combination with physicochemical or other information about a specific compound. They make predictions about toxicity and related biological outcomes, such as metabolic fate.
Micro-organisms, higher plants, minimally-sentient animals from lower phylogenetic orders and early developmental vertebral stages are all sometimes used, although the “harvesting” and use of embryonic and foetal forms can pose substantial ethical problems in their own right.
A variety of tissue cultures, including immortalised cell lines (including neoplastic cell lines), embryonic and adult stem cells, and organotypic cultures, are also available. The ability of stem cells to differentiate into a wide variety of tissue types offers exciting potential for the future replacement of dysfunctional tissues. However, the harvesting of embryonic stem cells can be ethically contentious, and substantial regulatory restrictions exist in many regions.
In vitro assays utilising bacterial, yeast, protozoal, mammalian or human cell cultures exist for a wide range of toxic and other endpoints. These may be used individually, or combined within test batteries – which increases the sensitivity of the assay to toxins of different types.
The generation of toxic metabolites by the liver, the main metabolising organ, is a key cause of toxicity, and so human hepatocyte cultures and metabolic activation systems may be used to assess metabolite activity and organ-organ interaction.
Identification of genes that are upor down-regulated by cellular exposure (potentially in vitro) to toxins of a certain type, may allow toxin detection in a fraction of the time required for more traditional, invasive endpoints, such as those resulting in organ damage or death.
This developing field is termed “toxicogenomics”. Micro-array technology (“gene-chips”) allowing examination of the activity of hundreds of genes simultaneously are being developed to facilitate such genetic expression profiling.
Enhanced human clinical trials utilising microdosing, staggered dosing, and more representative study populations and durations, would all increase safety for volunteers, and predictivity for diverse patient populations.
Surrogate human tissues, advanced imaging modalities, and human epidemiological, sociological and psychological studies, may all increase understanding of illness aetiology and pathogenesis. Particularly when human tissues are used, non-animal models may generate faster, cheaper results, more reliably predictive for humans, whilst yielding greater insights into human biochemical processes.
Increasing 3Rs compliance
Ever-increasing numbers of animal experiments indicate the necessity for considerably greater awareness of, and compliance with, the 3Rs. More stringent compliance with animal welfare legislation requiring the consideration or use of alternatives could, and should, become a prerequisite of research funding, ethics committee approval, and publication of results (Knight, 2008b).
Increased compliance with the 3Rs would be likely to improve research quality and the robustness of results, result in reduced timeframes and resource consumption, and jointly benefit consumers, industry and laboratory animals.
Combinations of 3Rs strategies may also have synergistic effects, improving both scientific outcomes and animal welfare (De Boo and Knight, 2008).
References
De Boo, J. and Knight, A. (2008) Increasing the implementation of alternatives to laboratory animal use. AATEX 13 (3): 109- 117.
Dudley, J. (2009) Animal experiments reach highest level for 25 years. Vet Times 39 (31): 1-2.
Henderson, N. (2009) Attention all dissatisfied dogs – interesting new life beckons. Vet Times 39 (31): 22.
Home Office (2009) Statistics of Scientific Procedures on Living Animals: Great Britain 2008. London, UK: The Stationery Office.
www.homeoffice.gov.uk/rds/pdfs… mals08.pdf, accessed 11th Aug. 2009.
Knight, A. (2008a) Systematic reviews of animal experiments demonstrate poor contributions toward human healthcare. Rev Recent Clin Trials 3 (2): 89-96.
http://www.benthamdirect.org/p… /00000003/00000002/0002RRCT.sgm, accessed 11 Aug. 2009.
Knight, A. (2008b) Non-animal methodologies within biomedical research and toxicity testing. ALTEX 25 (3): 213- 231.
Osswald, W. (1992) Etica da investigacão no animal e aplicacão ao homem. [Ethics of animal research and application to humans]. Acta Medica Portuguesa 5 (4): 222-225.
Pippin, J. J. (2008) “MAP” for improving drug testing: Mandatory Alternatives Petition urges FDA to require use of replacements to animal testing. Genetic Engineering and Biotechnology News 28 (5).
http://www.genengnews.com/arti… m.aspx?aid=2384, accessed 23 Aug. 2009.
Russell, W. M. S. and Burch, R. L. (1959) The Principles of Humane Experimental Technique. London, UK: Methuen.
