animal experiment

/Tag:animal experiment

Animal Carcinogenicity Studies: 1. Poor Human Predictivity

Andrew Knight, Jarrod Bailey and Jonathan Balcombe

The regulation of human exposure to potentially carcinogenic chemicals constitutes society’s most important use of animal carcinogenicity data. Environmental contaminants of greatest concern within the USA are listed in the Environmental Protection Agency’s (EPA’s) Integrated Risk Information System (IRIS) chemicals database. However, of the 160 IRIS chemicals lacking even limited human exposure data but possessing animal data that had received a human carcinogenicity assessment by 1 January 2004, we found that in most cases (58.1%; 93/160), the EPA considered animal carcinogenicity data inadequate to support a classification of probable human carcinogen or non-carcinogen. For the 128 chemicals with human or animal data also assessed by the World Health Organisation’s International Agency for Research on Cancer (IARC), human carcinogenicity classifications were compatible with EPA classifications only for those 17 having at least limited human data (p = 0.5896). For those 111 primarily reliant on animal data, the EPA was much more likely than the IARC to assign carcinogenicity classifications indicative of greater human risk (p < 0.0001). The IARC is a leading international authority on carcinogenicity assessments, and its significantly different human carcinogenicity classifications of identical chemicals indicate that: 1) in the absence of significant human data, the EPA is over-reliant on animal carcinogenicity data; 2) as a result, the EPA tends to over-predict carcinogenic risk; and 3) the true predictivity for human carcinogenicity of animal data is even poorer than is indicated by EPA figures alone. The EPA policy of erroneously assuming that tumours in animals are indicative of human carcinogenicity is implicated as a primary cause of these errors.
You need to register (for free) to download this article. Please log in/register here.

Animal Carcinogenicity Studies: 2. Obstacles to Extrapolation of Data to Humans

Andrew Knight, Jarrod Bailey and Jonathan Balcombe

Due to limited human exposure data, risk classification and the consequent regulation of exposure to potential carcinogens has conventionally relied mainly upon animal tests. However, several investigations have revealed animal carcinogenicity data to be lacking in human predictivity. To investigate the reasons for this, we surveyed 160 chemicals possessing animal but not human exposure data within the US Environmental Protection Agency chemicals database, but which had received human carcinogenicity assessments by 1 January 2004. We discovered the use of a wide variety of species, with rodents predominating, and of a wide variety of routes of administration, and that there were effects on a particularly wide variety of organ systems. The likely causes of the poor human predictivity of rodent carcinogenicity bioassays include: 1) the profound discordance of bioassay results between rodent species, strains and genders, and further, between rodents and human beings; 2) the variable, yet substantial, stresses caused by handling and restraint, and the stressful routes of administration common to carcinogenicity bioassays, and their effects on hormonal regulation, immune status and predisposition to carcinogenesis; 3) differences in rates of absorption and transport mechanisms between test routes of administration and other important human routes of exposure; 4) the considerable variability of organ systems in response to carcinogenic insults, both between and within species; and 5) the predisposition of chronic high dose bioassays toward false positive results, due to the overwhelming of physiological defences, and the unnatural elevation of cell division rates during ad libitum feeding studies. Such factors render profoundly difficult any attempts to accurately extrapolate human carcinogenic hazards from animal data.
You need to register (for free) to download this article. Please log in/register here.

Animal Carcinogenicity Studies: 3. Alternatives to the Bioassay

Andrew Knight, Jarrod Bailey and Jonathan Balcombe

Conventional animal carcinogenicity tests take around three years to design, conduct and interpret. Consequently, only a tiny fraction of the thousands of industrial chemicals currently in use have been tested for carcinogenicity. Despite the costs of hundreds of millions of dollars and millions of skilled personnel hours, as well as millions of animal lives, several investigations have revealed that animal carcinogenicity data lack human specificity (i.e. the ability to identify human non-carcinogens), which severely limits the human predictivity of the bioassay. This is due to the scientific inadequacies of many carcinogenicity bioassays, and numerous serious biological obstacles, which render profoundly difficult any attempts to accurately extrapolate animal data in order to predict carcinogenic hazards to humans. Proposed modifications to the conventional bioassays have included the elimination of mice as a second species, and the use of genetically-altered or neonatal mice, decreased study durations, initiation–promotion models, the greater incorporation of toxicokinetic and toxicodynamic assessments, structure-activity relationship (computerised) systems, in vitro assays, cDNA microarrays for detecting changes in gene expression, limited human clinical trials, and epidemiological research. The potential advantages of nonanimal assays when compared to bioassays include the superior human specificity of the results, substantially reduced time-frames, and greatly reduced demands on financial, personnel and animal resources. Inexplicably, however, the regulatory agencies have been frustratingly slow to adopt alternative protocols. In order to decrease the enormous cost of cancer to society, a substantial redirection of resources away from excessively slow and resource-intensive rodent bioassays, into the further development and implementation of non-animal assays, is both strongly justified and urgently required.
You need to register (for free) to download this article. Please log in/register here.

Animal Carcinogenicity Studies: Implications for the REACH System

Andrew Knight, Jarrod Bailey and Jonathan Balcombe

The 2001 European Commission proposal for the Registration, Evaluation and Authorisation of Chemicals (REACH) aims to improve public and environmental health by assessing the toxicity of, and restricting exposure to, potentially toxic chemicals. The greatest benefits are expected to accrue from decreased cancer incidences. Hence the accurate identification of chemical carcinogens must be a top priority for the REACH system. Due to a paucity of human clinical data, the identification of potential human carcinogens has conventionally relied on animal tests. However, our survey of the US Environmental Protection Agency’s (EPA’s) toxic chemicals database revealed that, for a majority of the chemicals of greatest public health concern (93/160, i.e. 58.1%), the EPA found animal carcinogenicity data to be inadequate to support classifications of probable human carcinogen or non-carcinogen. A wide variety of species were used, with rodents predominating; a wide variety of routes of administration were used; and a particularly wide variety of organ systems were affected. These factors raise serious biological obstacles that render accurate extrapolation to humans profoundly difficult. Furthermore, significantly different International Agency for Research on Cancer assessments of identical chemicals, indicate that the true human predictivity of animal carcinogenicity data is even poorer than is indicated by the EPA figures alone. Consequently, we propose the replacement of animal carcinogenicity bioassays with a tiered combination of non-animal assays, which can be expected to yield a weight-of-evidence characterisation of carcinogenic risk with superior human predictivity. Additional advantages include substantial savings of financial, human and animal resources, and potentially greater insights into mechanisms of carcinogenicity.
You need to register (for free) to download this article. Please log in/register here.

Systematic Reviews of Animal Experiments Demonstrate Poor Human Clinical and Toxicological Utility

Andrew Knight

The assumption that animal models are reasonably predictive of human outcomes provides the basis for their widespread use in toxicity testing and in biomedical research aimed at developing cures for human diseases. To investigate the validity of this assumption, the comprehensive Scopus biomedical bibliographic databases were searched for published systematic reviews of the human clinical or toxicological utility of animal experiments. In 20 reviews in which clinical utility was examined, the authors concluded that animal models were either significantly useful in contributing to the development of clinical interventions, or were substantially consistent with clinical outcomes, in only two cases, one of which was contentious. These included reviews of the clinical utility of experiments expected by ethics committees to lead to medical advances, of highly-cited experiments published in major journals, and of chimpanzee experiments — those involving the species considered most likely to be predictive of human outcomes. Seven additional reviews failed to clearly demonstrate utility in predicting human toxicological outcomes, such as carcinogenicity and teratogenicity. Consequently, animal data may not generally be assumed to be substantially useful for these purposes. Possible causes include interspecies differences, the distortion of outcomes arising from experimental environments and protocols, and the poor methodological quality of many animal experiments, which was evident in at least 11 reviews. No reviews existed in which the majority of animal experiments were of good methodological quality. Whilst the effects of some of these problems might be minimised with concerted effort (given their widespread prevalence), the limitations resulting from interspecies differences are likely to be technically and theoretically impossible to overcome. Non-animal models are generally required to pass formal scientific validation prior to their regulatory acceptance. In contrast, animal models are simply assumed to be predictive of human outcomes. These results demonstrate the invalidity of such assumptions. The consistent application of formal validation studies to all test models is clearly warranted, regardless of their animal, non-animal, historical, contemporary or possible future status. Likely benefits would include, the greater selection of models truly predictive of human outcomes, increased safety of people exposed to chemicals that have passed toxicity tests, increased efficiency during the development of human pharmaceuticals and other therapeutic interventions, and decreased wastage of animal, personnel and financial resources. The poor human clinical and toxicological utility of most animal models for which data exists, in conjunction with their generally substantial animal welfare and economic costs, justify a ban on animal models lacking scientific data clearly establishing their human predictivity or utility.
You need to register (for free) to download this article. Please log in/register here.

Reviewing Existing Knowledge Prior to Conducting Animal Studies

Andrew Knight

Highly polarised viewpoints about animal experimentation have often prevented agreement. However, important common ground between advocates and opponents was demonstrated within a discussion forum hosted at www.research-methodology.org.uk in July–August 2008, by the independent charity, SABRE Research UK. Agreement existed that many animal studies have methodological flaws — such as inappropriate sample sizes, lack of randomised treatments, and unblinded outcome assessments — that may introduce bias and limit statistical validity. There was also agreement that systematic reviews of the human utility of animal models yield the highest quality of evidence, as their reliance on methodical and impartial methods to select significant numbers of animal studies for review, serves to minimise bias. Unfortunately, disagreement remained that animal experimental licence applications should reference systematic reviews of existing studies, before approval. The UK Medical Research Council requires that researchers planning human clinical trials must reference such reviews of related previous work. Existing knowledge is thereby fully and appropriately utilised, and redundant experimentation is avoided. However, objections were raised that a similar requirement would interfere with animal experimental licensing, because, to date, there have been very few systematic reviews of animal studies. In fact, the relative dearth of such reviews is a matter of considerable concern, and may partially explain the very poor human success rates of drugs that appear safe and/or efficacious in animal trials. Nevertheless, the disturbing number of human trials which have proceeded concurrently with, or prior to, animal studies, or have continued despite equivocal evidence of efficacy in animals, clearly demonstrate that many researchers fail to conduct adequate prior reviews of existing evidence. Where neither sufficient primary studies, nor systematic reviews of such studies, exist, for citation within a licence application, researchers should be able to provide evidence of this shortcoming, and, concurrently, demonstrate that the available literature and evidence have been adequately reviewed. This should also enable them to clearly demonstrate the need and scientific appropriateness of their proposed study, the validity of its design, and — importantly — that the benefits are reasonably likely to exceed the animal welfare, bioethical and financial costs. Invasive animal studies should never be permitted solely on the basis of less probable,speculative or intangible human benefits, or the mere satisfaction of scientific curiosity.
You need to register (for free) to download this article. Please log in/register here.

More is Less: Reducing Animal Use by Raising Awareness of the Principles of Efficient Study Design and Analysis

Bryan Howard, Michelle Hudson and Richard Preziosi

Good experimental design and the appropriate use of statistical tests form the corner stone of high-quality scientific research. This is especially important when the experiments involve the use of laboratory animals, to ensure that their use is appropriate and that the minimum number of animals will be used that will provide data which are sufficiently statistically-sound to meet the objectives of the study. One way to raise awareness of the importance of efficient study design and analysis is to provide training courses. This paper reports the views of participants at two such training schools, with reference to why they felt that attendance was necessary and how effective they felt the experience had been. The implications of the responses are discussed, and considerations for future training events are noted.
You need to register (for free) to download this article. Please log in/register here.