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Predicting Human Drug Toxicity and Safety via Animal Tests: Can Any One Species Predict Drug Toxicity in Any Other, and Do Monkeys Help?

Jarrod Bailey, Michelle Thew and Michael Balls

Animals are still widely used in drug development and safety tests, despite evidence for their lack of predictive value. In this regard, we recently showed, by producing Likelihood Ratios (LRs) for an extensive data set of over 3,000 drugs with both animal and human data, that the absence of toxicity in animals provides little or virtually no evidential weight that adverse drug reactions will also be absent in humans. While our analyses suggest that the presence of toxicity in one species may sometimes add evidential weight for risk of toxicity in another, the LRs are extremely inconsistent, varying substantially for different classes of drugs. Here, we present further data from analyses of other species pairs, including nonhuman primates (NHPs), which support our previous conclusions, and also show in particular that test results inferring an absence of toxicity in one species provide no evidential weight with regard to toxicity in any other species, even when data from NHPs and humans are compared. Our results for species including humans, NHPs, dogs, mice, rabbits, and rats, have major implications for the value of animal tests in predicting human toxicity, and demand that human-focused alternative methods are adopted in their place as a matter of urgency.
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An Analysis of the Use of Animal Models in Predicting Human Toxicology and Drug Safety

Jarrod Bailey, Michelle Thew and Michael Balls

Animal use continues to be central to preclinical drug development, in spite of a lack of its demonstrable validity. The current nadir of new drug approvals and the drying-up of pipelines may be a direct consequence of this. To estimate the evidential weight given by animal data to the probability that a new drug may be toxic to humans, we have calculated Likelihood Ratios (LRs) for an extensive data set of 2,366 drugs, for which both animal and human data are available, including tissue-level effects and MedDRA Level 1–4 biomedical observations. This was done for three preclinical species (rat, mouse and rabbit), to augment our previously-published analysis of canine data. In common with our dog analysis, the resulting LRs show: a) that the absence of toxicity in the animal provides little or virtually no evidential weight that adverse drug reactions (ADRs) will also be absent in humans; and b) that, while the presence of toxicity in these species can add considerable evidential weight for human risk, the LRs are extremely inconsistent, varying by over two orders of magnitude for different classes of compounds and their effects. Therefore, our results for these additional preclinical species have important implications for their use in predicting human toxicity, and suggest that alternative methods are urgently required.

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Lack of Effect of Medium Supplementation With Pyruvate and Hormones on Cytochrome P450-mediated Activity of Rat Hepatocytes in Primary Culture

Porntip Wirachwong and Jeffrey R. Fry

The loss of cytochrome P450 (CYP)-dependent activity continues to be a problem in the use of cultured hepatocytes in xenobiotic toxicity studies. It has been reported that the inclusion of pyruvate and various hormones in the culture medium improves the maintenance of various hepatic functions, including that of CYP2C11 mRNA expression. We have studied this further, by investigating the effects of the addition of pyruvate and hormones on various CYP-dependent enzyme activities and on the CYP-dependent toxicity of precocene II in rat hepatocyte cultures. No beneficial effects of this medium supplementation could be demonstrated.
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Is it Possible to Replace Stimulus Animals by Scent-filled Cups in the Social Discrimination Test?

Ruud van den Bos, Klaske J. van der Horst, Annemarie M. Baars and Berry M. Spruijt

A study in which the rat social discrimination test was refined is described. This test measures social memory by using, in general, juvenile rats as stimulus animals. Rats are offered a first juvenile to investigate (learning trial), and after a specified interval, the rats are offered the same rat and a second juvenile rat to investigate again (retrieval trial). When the rats sniff the second juvenile in the retrieval trial more than the first, social memory for the first juvenile is said to be present. This test is mainly based on scents from the juvenile. Attempts were made to refine the test to reduce the number of animals used, to enhance the scope of the test, and to improve its validity. Firstly, the stimulus animals were replaced by the scent of juveniles, in the form of cups filled with sawdust taken from cages of juvenile rats. Similar results to those in the original test were obtained when using these scents. Furthermore, male and female scents were tested, and showed the same results as for the juvenile scents. Secondly, rats were also given two cups (one scent-filled and one filled with plain sawdust) in the learning trial, to determine which allowed a more-precise delineation of motivational, discriminatory and memory components. Overall, it is possible to replace stimulus animals by scent-filled cups in the social discrimination test, to enhance the scope of the test, and to draw more-valid conclusions with respect to social memory.
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Anaesthesia and Post-operative Analgesia Following Experimental Surgery in Laboratory Rodents: Are We Making Progress?

Claire A. Richardson and Paul A. Flecknell

Current attitudes to the use of animals in biomedical research require that any pain or distress should be minimised. This can often be achieved by the use of appropriate anaesthetic and analgesic regimens. There, is however, little information on the peri-operative regimens used. A literature review was conducted to estimate how commonly analgesics are administered to laboratory rodents, the most widely used species of laboratory animals, and to assess the anaesthetic regimens employed. Studies describing potentially painful experimental procedures involving rodents were identified from peer-reviewed journals published from 1990 to 1992 and from 2000 to 2002. In papers published between 2000 and 2002, if analgesic administration was not specified, the institutional veterinary surgeons or authors of the papers were contacted by e-mail to obtain additional information on analgesic use. From 1992 to 2002, there was an
increase in the reported prevalence of analgesic administration to laboratory rodents from 2.7% to 19.8%. Although the use of analgesics has increased over the past ten years, the overall level of post-operative pain relief for laboratory rodents is still low. Anaesthetic methodology changed markedly between the two timeperiods sampled. Notably, there was an increase in the use of isoflurane and of injectable anaesthetic combinations such as ketamine/xylazine, whereas the use of ether and methoxyflurane decreased.
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Detection of Electrophysiological Indicators of Neurotoxicity in Human and Rat Brain Slices by a Three-Dimensional Microelectrode Array

Rüdiger Köhling, Raffaella Melani, Uwe Koch, Erwin-Josef Speckmann, Milena Koudelka-Hep, Pierre Thiébaud and Maurizio Balestrino

Electrophysiological techniques for the assessment of in vitro neurotoxicology have several advantages over other currently-used methods (for example, morphological techniques), including the ability to detect damage at a very early stage. Novel recording techniques based on microelectrode arrays are available, and could improve recording power. In this study, we investigated how a three-dimensional microelectrode array detects the electrophysiological endpoints of neurotoxicity. We conclude that electrophysiology sensitively reveals neurotoxic actions, and that three-dimensional microelectrode arrays could be proposed for use in neurotoxicology as recording tools that allow easy and sensitive multisite recording, from both rodent and human brain tissue.
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The Tubifex tubifex Assay for the Determination of Acute Toxicity

Milonv Tichý, Marián Rucki, Iveta Hanzlíková and Zdenevk Roth

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 (96- hour 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.
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Development of an Innervated Model of Human Skin

Nancy Khammo, Jane Ogilvie and Richard H. Clothier

Neuronal cell responses and interactions with the epithelial and fibroblastic cells of the skin are a key factor in the production in vivo of the irritation/inflammatory response. Currently, few in vitromodels are available that contain dermal, epidermal and the relevant neuronal components. The primary objective of this study was to produce and maintain a 3-D in vitro model of human skin containing these elements. The relevant neuronal component was supplied by adding sensory neurons derived from the dorsal root ganglion (DRG). Since adult neuronal cells do not grow significantly in vivo or in vitro, and since it is very difficult to obtain such cells from humans, it was necessary to employ embryonic rat DRG cells. The ultimate purpose of this model is to improve prediction of the in vivo skin irritancy potential of chemicals and formulations, without the need to use animal models. In addition, this approach has also been applied to the in vitro human eye and bronchial 3-D models being developed in the FRAME Alternatives Laboratory.
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The Intercostal NMJ Assay — A New Alternative to the Conventional LD50 Assay for the Determination of the Therapeutic Potency of Botulinum Toxin Preparations

Alexander Huber, Richard M. France, Lisa Riccalton-Banks, Jane McLaren, Helen Cox, Robin A. Quirk, Kevin M. Shakesheff, David Thompson, Naveed Panjwani, Sarah Shipley and Andy Pickett

Therapeutic botulinum neurotoxin type A preparations have found an increasing number of clinical uses for a large variety of neuromuscular disorders and dermatological conditions. The accurate determination of potency in the clinical application of botulinum toxins is critical to ensuring clinical efficacy and safety, and is currently achieved by using a lethal dose (LD50) assay in mice. Ethical concerns and operational constraints associated with this assay have prompted the development of alternative assay systems that could potentially lead to its replacement. As one such alternative, we describe the development and evaluation of a novel ex vivo assay (the Intercostal Neuromuscular Junction [NMJ] Assay), which uses substantially fewer animals and addresses ethical concerns associated with the LD50 assay. The assay records the decay of force from electrically-stimulated muscle tissue sections in response to the toxin, and thus combines the important mechanisms of receptor binding, translocation, and the enzymatic action of the toxin molecule. Toxin application leads to a time-related and dose-related reduction in contractile force. A regression model describing the relationship between the applied dose and force decay was determined statistically, and was successfully tested as able to correctly predict the potency of an unknown sample. The tissue sections used were found to be highly reproducible, as determined through the innervation pattern and the localisation of NMJs in situ. Furthermore, the efficacy of the assay protocol to successfully deliver the test sample to the cellular target sites, was critically assessed by using molecular tracer molecules.
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Strategies for the Reduction of Live Animal Use in Microsurgical Training and Education

Harald Schöffl, Stefan M. Froschauer, Karin M. Dunst, Dietmar Hager, Oskar Kwasny and Georg M. Huemer

Education and training in microsurgical techniques have historically relied on the use of live animal models. Due to an increase in the numbers of microsurgical operations in recent times, the number of trainees in this highly-specialised surgical field has continued to grow. However, strict legislation, greater public awareness, and an increasing sensitivity toward the ethical aspects of scientific research and medical education, emphatically demand a significant reduction in the numbers of animals used in surgical and academic education. Hence, a growing number of articles are reporting on the use of alternatives to live animals in microsurgical education and training. In this review, we report on the current trends in the development and use of microsurgical training models, and on their potential to reduce the number of live animals used for this purpose. We also share our experiences in this field, resulting from our performance of numerous microsurgical courses each year, over more than ten years. The porcine heart, in microvascular surgery training, and the fresh chicken leg, in microneurosurgical and microvascular surgery training, are excellent models for the teaching of basic techniques to the microsurgical novice. Depending on the selected level of expertise of the trainee, these alternative models are capable of reducing the numbers of live animals used by 80–100%. For an even more enhanced, “closer-to-real-life” scenario, these non-animated vessels can be perfused by a pulsatile pump. Thus, it is currently possible to provide excellent and in-depth training in microsurgical techniques, even when the number of live animals used is reduced to a minimum. With these new and innovative techniques, trainees are able to learn and prepare themselves for the clinical situation, with the sacrifice of considerably fewer laboratory animals than would have occurred previously.
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