The welfare problems associated with using transgenic mice to bioassay for bovine spongiform encephalopathy

Prion diseases are fatal neurodegenerative disorders, epitomized by the the recent bovine spongiform encephalopathy (BSE) epidemic in cattle and the emergence of a novel variant of Creutzfeldt-Jacob disease (vCJD) in humans. In prion disease, the agent of infection is believed to be composed of proteinaceous particles, termed prions, which are converted from a normal isoform into a pathogenic isoform during pathogenesis. A bioassay to detect pathogenic prions of BSE in bovine products consumed by humans was unattainable until the development of transgenic mice, due to the significantly lower susceptibility of wild-type mice to BSE. Transgenic mice have now been generated which express the bovine prion protein and are susceptible to BSE. Following an intracerebral injection with brain homogenate of BSE-infected cattle, transgenic mice develop numerous clinical signs of prion disease, including truncal ataxia (inability to coordinate the torso's muscular activity), increased tone of the tail, generalized tremor, and lack of a forelimb extensor response. In this study, the ethical score system devised by Porter (1992) was applied to the BSE bioassay as a tool for identifying welfare issues affecting animals used in the bioassay. We acknowledge that there are limitations to the use of the information arising from the application of the Porter scoring scheme for assessing the justification to proceed with any animal experiment; notwithstanding these problems, however, our application of the Porter model to the BSE bioassay enabled us to identify potential targets for refinement: pain involved, duration of distress and the duration of the experiment. This was despite lenient scoring for the duration of distress and pain experienced by the mice, and optimal scoring for the quality of animal care. The targets identified for refinement are discussed in relation to the method of inoculation, the duration of the bioassay, and the duration of the clinical phase, with the objective of exploring ways of reducing the severity of the bioassay.

Ethical investment--what is it, and what are the implications for industry funding of research into alternatives?

This paper is intended to be a critical appraisal of ethical investment with respect to animal experimentation. It is aimed at a wide readership, ranging from scientists in the field and laypersons interested in laboratory animal welfare, potential investors, to senior management in industries directly or indirectly involved in animal testing.

The use of structure-activity relationships and markers of cell toxicity to detect non-genotoxic carcinogens

In contrast to the situation for genotoxic carcinogens, few in vitro tests exist that can detect early markers of the events thought to be associated with non-genotoxic carcinogenesis. Also, comparatively little is known about the quantitative structure-activity relationships (Q)SARs of these agents. This review discusses published SAR studies conducted on non-genotoxic carcinogens, in relation to the use of several markers of in vitro cell toxicity (inhibition of gap-junctional intercellular communication, inhibition of tubulin polymerization, modulation of apoptosis and induction of cell proliferation), which are used as endpoints for screening this class of carcinogen. Much of the work has involved the identification of new biophores (substructural features of molecules associated with toxicity), as well as other structural features, which are thought to predispose the chemicals to ligand binding with specific target molecules acting as possible receptors (e.g. protein kinase C, the oestrogen, peroxisome-proliferator and tubulin protein receptors), implicated in the mechanism of toxicity involved. It is concluded that (a) there is an urgent need for more information on (Q)SARs for non-genotoxic carcinogens; (b) this information should be acquired by using several different approaches in a variety of laboratories; and (c) such research should proceed together with more studies on the mechanisms of cell toxicity caused by these chemicals, including the identification and characterisation of further specific receptors involved in mediating the various types of cell toxicity associated with this type of carcinogenesis.

Transgenic Models for Prion Disease: Have They Outlived Their Useful Purpose?

Prions are a recently identified class of proteinaceous pathological agents. Prion diseases are fatal neurological disorders, the importance of which is exemplified by the recent emergence of a novel variant of Creutzfeldt-Jacob disease (CJD) in humans. During pathogenesis, prion proteins undergo a conformational change, which converts the normal isoform to a pathogenic isoform. Several approaches are available for studying prion disease. The predominant approach has involved in vivo studies, especially involving transgenic mice. In vitro alternatives available for studying prion disease include a cell-free conversion assay, cell culture systems, and an immunoassay for the pathogenic form of the prion protein. Prion-like proteins have been identified in yeast, and therefore this constitutes another non-animal approach. Four main areas of prion research are discussed in this paper, to illustrate the potential applications and limitations of the in vivo and alternative systems. From this study, we conclude that, while current in vitro approaches can be used initially, in vivo studies are still needed to confirm data obtained in vitro. Priority should be given to the non-animal alternatives, as well as to developing new methods, and these should be given primary consideration at the outset of a project.

FRAME Recommendations for the Application of the Three Rs to the Regulatory Toxicity Testing of Food Additives

Direct food additives are tested for genotoxicity, acute and subchronic toxicity, carcinogenicity and teratogenicity. International guidelines differ in the types of tests required, the duration of the tests, the species of animals to be used, the number of animals recommended and the method of housing experimental animals. This lack of harmonisation is wasteful in terms of animal use and creates additional and, perhaps, unnecessary work for the food industry. In addition, unlike other chemicals, food additives pose a special problem for toxicity testing due to repeated low-dose, life-time human exposure, which is difficult to model in animal studies. In an assessment of the extent to which the Three Rs (reduction, refinement and replacement) can be applied to food additive toxicity testing, it was concluded that differences in regulatory requirements and testing protocols can be improved in both the short term and longer term. Suggestions for improvements to existing alternative approaches for food toxicity testing are made.

The use of L5178Y mouse lymphoma cells to assess the mutagenic, clastogenic and aneugenic properties of chemicals

Guidelines have been proposed to assess the potential of chemicals to affect human health. Written into these guidelines is the requirement that information be submitted on mutagenic activity. Although regulatory agencies accept mutagenicity data from both the hprt and tk loci in mammalian cells, many studies suggest that the L5178Y mouse lymphoma assay at the thymidine kinase locus is likely to detect a greater spectrum of mutagenic lesions. Thus, there is increasing emphasis being placed on this assay in many proposed and published guidelines. The L5178Y mouse lymphoma suspension protocol produces both small and large colonies which are the products of mutants growing at different rates. There is a reduction in the proportion of slowly growing mutants with respect to the total population of cells when expression is carried out in suspension. This potentially leads to quantitatively inaccurate assessments of the mutagenic activity of chemicals. Therefore an in situ procedure was developed that more accurately assesses the mutagenic activity of chemicals by maximizing the detection of small colonies. Many guidelines recommend tests that assess the clastogenic activity of chemicals. Some regulatory agencies accept data from the mouse lymphoma mutation assay to detect clastogens if the protocol is optimized for the detection of small colonies or if colony sizing data are submitted. The conventional suspension assay protocol is not sufficiently validated for this purpose. The in situ protocol has greater potential to meet these requirements.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulatory Genotoxicity Testing: A Critical Appraisal

This review considers current approaches to regulatory genotoxicity testing, focusing on how the use of animals can be further replaced, reduced and refined. The complementary roles of in vitro and in vivo testing, and the justification for using animals, are discussed in detail. Recommendations are made for improvements and further work, in the light of the considerable current controversy surrounding the composition and deployment of testing strategies, and the interpretation of the data generated, particularly for carcinogenicity prediction. The major problems are the oversensitivity of in vitro tests and the insensitivity of in vivo assays. On the basis of an analysis of some published databases, it is concluded that there is insufficient support for using in vivo genotoxicity assays for screening. Also, it is questionable whether the scientific benefits of using such assays always outweigh the costs to the animals involved. The considerable efforts being made to harmonise in vivo protocols and to develop improved methods for detecting genotoxicity are discussed. It is recommended that more emphasis be placed on characterising genotoxins in vitro, especially for mechanisms of activity, to optimise the benefits of any confirmatory animal tests.. Also, regulatory agencies are urged to require better-designed and more-scientifically sound protocols, in which animal numbers are minimised and data interpretation, particularly that of negative results, is facilitated. Lastly, in the development and validation of transgenic rodent systems, emphasis should be placed on developing protocols in which other acute toxicity and metabolism endpoints can be measured simultaneously with in vivo mutagenesis, while minimising animal numbers.

Interaction of cimetidine with cytochrome P450 and effect on mixed-function oxidase activities of liver microsomes

The histamine H2-receptor antagonist drug, cimetidine (CM), was investigated to determine its effect on the metabolism of 'model' alkoxyphenoxazone substrates ethoxyresorufin (ER) and pentoxyresorufin (PR). The investigation was carried out under different conditions in rat liver microsomes from rodents pretreated with various classical cytochrome P450 inducers. CM exerted a dual effect on uninduced and PB-induced liver microsomal ethoxyresorufin-O-de-ethylase (EROD) activities; it was initially stimulatory but became inhibitory. However, when 3-MC-induced preparations were used. CM only exerted an inhibitory effect on EROD activity over the whole concentration range (0.01 microM-20 mM). Pre-incubating PB-induced and uninduced liver microsomes with NADPH before the addition of ER and CM decreased the stimulatory effect of CM and increased the inhibitory effect in the concentration range (5-20 mM). With 3-MC-induced preparations, the inhibition of EROD was only marginally potentiated. Overall conclusions for the diphasic effects of CM on biological activities were due to CM binding with differing affinities to different P450s. Subsequent decreases and increases in stimulation and inhibition, respectively, on pre-incubation with NADPH were thought to be due to an increased affinity of CM for reduced cytochrome P450.

Alternatives to Aroclor 1254-induced S9 in in vitro genotoxicity assays

A working party was set up by the UK Environmental Mutagen Society to consider alternatives to Aroclor 1254 (Aroclor)-induced S9 in in vitro genotoxicity assays, with the aims of considering whether a replacement for Aroclor in its role in general screening assays could be readily identified. The working party concluded that there was sufficient support in the literature to justify the use of an appropriate phenobarbital/beta-naphthoflavone regime as an acceptable alternative to Aroclor.

Inhibition of dinitropyrene mutagenicity in vitro and in vivo using Salmonella typhimurium and the intrasanguinous host-mediated assay

Dinitropyrenes (DNP), present in polluted air, are potent direct-acting mutagens in Salmonella typhimurium TA98. This mutagenicity is markedly reduced in the presence of rat-liver S9 or microsomes. This has now been confirmed using mouse hepatic fractions. Since most in vitro test systems do not adequately simulate conditions encountered in the intact animal, we have investigated dinitropyrene mutagenicity to Salmonella in the host-mediated assay. 1,8-Dinitropyrene (1,8-DNP) given p.o. to BALB/c mice induced a weak mutagenic effect in S. typhimurium TA98 recovered from the liver 1 h after i.v. administration (optimum time). Over the entire dose range tested no toxicity to bacterial cells was detected. Mutation induction in vivo was dose-related with maximum response at 1 mg DNP/kg body weight. This optimum dose, however, was non-mutagenic to strains TA98/1,8-DNP6 (O-transacetylase-deficient) or TA98NR/1,8-DNP6 (nitroreductase- and O-transacetylase-deficient). 1,3-Dinitropyrene and 1,6-dinitropyrene were weakly mutagenic to TA98 at doses similar to 1,8-DNP. Studies with [14C]1,8-DNP showed that 1 h after oral dosing (1 mg/kg), over 100 ng of 1,8-DNP equivalents were present in the liver (= 0.73% dose). However, only about 5.5 ng were present in the bacterial pellet, suggesting that hepatic components in vivo, as in vitro, bind to DNP, thus interfering with its interaction with Salmonella.

Interaction with microsomal lipid as a major factor responsible for S9-mediated inhibition of 1,8-dinitropyrene mutagenicity

1,8-Dinitropyrene (1,8-DNP), present in polluted air, is a rodent carcinogen and a potent, direct-acting mutagen in salmonella typhimurium TA98. This mutagenicity is markedly reduced in the presence of mammalian hepatic S9 or microsomes. We demonstrate that at least a substantial part of this effect is attributable to non-enzymatic processes. The microsomal-dependent inhibition was unaffected by omission of an NADPH-generating system or when the cytochrome P-450 inhibitor, SKF-525A, or the cytochrome P-448 inhibitor, ellipticine, was incorporated in the metabolic activation system, suggesting that mixed function oxidases are not involved. Heat inactivation partially decreased the ability of induced S9 to reduce DNP mutagenicity. Substitution of S9 with a similar concentration of bovine serum albumin did not affect DNP activity. Thus non-specific binding to microsomal protein is not involved. However, when lipids, derived from uninduced microsomes, were added to incubations of DNP and S. typhimurium TA98, mutagenicity was decreased. Furthermore, substitution of microsomal lipids with a suspension of phosphatidylcholine (PC), a major lipid constituent of microsomes, affected DNP mutagenicity similarly. An increase in PC concentration resulted in a greater inhibitory effect. The reduction in DNP mutagenicity observed with microsomal lipids or with PC was less than that detected with uninduced S9, whilst the mutagenicity of 2-nitrofluorene was reduced to an approximately equal extent by lipids and S9. This phenomenon may be responsible for the S9-mediated detoxification of other mutagenic nitroaromatic compounds and may have important implications for mutagenicity testing.