Refinement and validation of an alternative bioassay for potency testing of therapeutic botulinum type A toxin

Alternative Methods for Testing Botulinum Toxin: Current Status and Future Perspectives

Botulinum toxins are neurotoxic modular proteins composed of a heavy chain and a light chain connected by a disulfide bond and are produced by Clostridium botulinum. Although lethally toxic, botulinum toxin in low doses is clinically effective in numerous medical conditions, including muscle spasticity, strabismus, hyperactive urinary bladder, excessive sweating, and migraine. Globally, several companies are now producing products containing botulinum toxin for medical and cosmetic purposes, including the reduction of facial wrinkles. To test the efficacy and toxicity of botulinum toxin, animal tests have been solely and widely used, resulting in the inevitable sacrifice of hundreds of animals. Hence, alternative methods are urgently required to replace animals in botulinum toxin testing. Here, the various alternative methods developed to test the toxicity and efficacy of botulinum toxins have been briefly reviewed and future perspectives have been detailed.

Progress in Applying the Three Rs to the Potency Testing of Botulinum Toxin Type A

Botulinum toxin type A (BTA) is being increasingly used for a range of therapeutic purposes and also for cosmetic reasons. For many years, the potency of BTA has been measured by using an LD50 assay in mice. This assay is a cause for concern due to its unpleasant nature and extreme severity, and the requirement for high numbers of mice to be used. Alternatives to this potency assay are presently reviewed with particular reference to the work at the National Institute for Biological Standards and Control (NIBSC), and to recent work by the UK manufacturer of the substance. An in vivo local paralysis assay with considerably less severity has been developed and is in use at the NIBSC. Alternative, ex vivo functional assays in use include the measurement of BTA-induced paralysis of neurally-stimulated rodent diaphragm or rat intercostal muscle. The latter method has the advantage of allowing more preparations to be derived from one animal. However, these ex vivo methods have not yet been fully validated and accepted by regulatory agencies as potency assays. Endopeptidase assays, although not measuring muscle paralysis directly, may provide a very useful consistency test for batch release and may replace the routine use of the LD50 test for that purpose. These assays measure the cleavage of the SNAP-25 protein (the final stage of BTA action), and have been validated for batch release by the National Control Laboratory (NIBSC), and are in regular use there. ELISA assays, used alongside the endopeptidase assay, also provide useful confirmatory information on the amounts of functional (and non-functional) BTA present. The UK manufacturer is further validating its endopeptidase assay, an ex vivo muscle assay and an ELISA. It is anticipated that their work will lead to a change in the product license, hopefully within the next two years, and will form a critical milestone towards the end of the LD50 potency test.

Zebrafish Sensitivity to Botulinum Neurotoxins

Botulinum neurotoxins (BoNT) are the most potent known toxins. The mouse LD₅₀ assay is the gold standard for testing BoNT potency, but is not sensitive enough to detect the extremely low levels of neurotoxin that may be present in the serum of sensitive animal species that are showing the effects of BoNT toxicity, such as channel catfish affected by visceral toxicosis of catfish. Since zebrafish are an important animal model for diverse biomedical and basic research, they are readily available and have defined genetic lines that facilitate reproducibility. This makes them attractive for use as an alternative bioassay organism. The utility of zebrafish as a bioassay model organism for BoNT was investigated. The 96 h median immobilizing doses of BoNT/A, BoNT/C, BoNT/E, and BoNT/F for adult male Tübingen strain zebrafish (0.32 g mean weight) at 25 °C were 16.31, 124.6, 4.7, and 0.61 picograms (pg)/fish, respectively. These findings support the use of the zebrafish-based bioassays for evaluating the presence of BoNT/A, BoNT/E, and BoNT/F. Evaluating the basis of the relatively high resistance of zebrafish to BoNT/C and the extreme sensitivity to BoNT/F may reveal unique functional patterns to the action of these neurotoxins.

Development of human-like scFv-Fc antibodies neutralizing Botulinum toxin serotype B

Botulinum neurotoxins (BoNTs) are responsible for human botulism, a life-threatening disease characterized by flaccid muscle paralysis that occurs naturally by food poisoning or colonization of the gastrointestinal tract by BoNT-producing clostridia. BoNTs have been classified as category A agents by the Centers for Disease Control and Prevention. To date, 7 subtypes of BoNT/B were identified showing that subtypes B1 (16 strains) and B2 (32 strains) constitute the vast majority of BoNT/B strains. Neutralizing antibodies are required for the development of anti-botulism drugs to deal with the potential risk. In this study, macaques (Macaca fascicularis) were immunized with recombinant light chain (LC) or heavy chain (HC) of BoNT/B2, followed by the construction of 2 hyper-immune phage display libraries. The best single-chain variable fragments (scFvs) isolated from each library were selected according to their affinities and cross reactivity with BoNT/B1 toxin subtype. These scFvs against LC and HC were further analyzed by assessing the inhibition of in vitro endopeptidase activity of BoNT/B1 and B2 and neutralization of BoNT/B1 and B2 toxin-induced paralysis in the mouse ex vivo phrenic nerve assay. The antibodies B2–7 (against HC) and BLC3 (against LC) were produced as scFv-Fc, and, when tested individually, neutralized BoNT/B1 and BoNT/B2 in a mouse ex vivo phrenic nerve assay. Whereas only scFv-Fc BLC3 alone protected mice against BoNT/B2-induced paralysis in vivo, when B2–7 and BLC3 were combined they exhibited potent synergistic protection. The present study provided an opportunity to assess the extent of antibody-mediated neutralization of BoNT/B1 and BoNT/B2 subtypes in ex vivo and in vitro assays, and to confirm the benefit of the synergistic effect of antibodies targeting the 2 distinct functional domains of the toxin in vivo. Notably, the framework regions of the most promising antibodies (B2–7 and BLC3) are close to the human germline sequences, which suggest that they may be well tolerated in potential clinical development.

Improved bioassays using a local effect, such as muscle paralysis, as an endpoint

Drug potency testing consumes many animals, botulinum neurotoxin (BoNT) testing being perhaps the most notorious example. To avoid 50% lethal dose determination, the so-called digital abduction score (DAS) and other BoNT induced local paralysis assays were developed. This paper reveals that a simple mathematical expression - the Bateman's equation used in many pharmacokinetic data analyses - can describe in full detail the time dependence of the BoNT induced local paralysis; the equation hence allows robust interpolation and extrapolation, as well as integral effect (AUC), and its dose dependence, evaluation. The equation is moreover a convenient tool for experimental planning and for extracting, from experimental data, the parameters that characterise BoNT potency. Most important, one can generally reduce the number of animals needed to gain reliable results at least 20-33% (and possibly 50% or even 75%) by analysing and modelling the time course of a local effect (such as muscle paralysis) with the equation, rather than just by averaging the maximum observed effect size at one point in time.

Establishment of alternative potency test for botulinum toxin type A using compound muscle action potential (CMAP) in rats

The biological activity of botulinum toxin type A has been evaluated using the mouse intraperitoneal (ip) LD50 test. This method requires a large number of mice to precisely determine toxin activity, and, as such, poses problems with regard to animal welfare. We previously developed a compound muscle action potential (CMAP) assay using rats as an alternative method to the mouse ip LD50 test. In this study, to evaluate this quantitative method of measuring toxin activity using CMAP, we assessed the parameters necessary for quantitative tests according to ICH Q2 (R1). This assay could be used to evaluate the activity of the toxin, even when inactive toxin was mixed with the sample. To reduce the number of animals needed, this assay was set to measure two samples per animal. Linearity was detected over a range of 0.1-12.8 U/mL, and the measurement range was set at 0.4-6.4 U/mL. The results for accuracy and precision showed low variability. The body weight was selected as a variable factor, but it showed no effect on the CMAP amplitude. In this study, potency tests using the rat CMAP assay of botulinum toxin type A demonstrated that it met the criteria for a quantitative analysis method.

Methods and difficulties in detection of Clostridium botulinum and its toxins

The aim of this work was to present selected data regarding traditional and modern methods for C. botulinum and its toxins detection. In this article, methods based on culturing techniques, mouse bioassay, immunological techniques, chromatography and PCR, PFGE, RFLP, AFLP are described. The mentioned techniques were evaluated considering their usefulness in the samples examination, genotyping of strains and the diagnostics of botulism.

Electrophysiological study for comparing the effect of biological activity between type A botulinum toxins in rat gastrocnemius muscle

Background:

New cosmetic applications and products based on the effects of botulinum toxin (BTX) treatment have stimulated demand for this class of natural compounds. This demand generates the need for appropriate standardized protocols to test and compare the effectiveness of new BTX preparations.

Objectives:

Based on the previously described electrophysiological methods, we measured and compared the inhibitory effects of two BTX type A (BTX-A) preparations on neuromuscular transmission through split-body test.

Methods:

The effectiveness was evaluated in terms of the compound muscle action potential (CMAP) and conduction velocity after BTX-A injection. We used a split-body method to compare two different BTX-As in the rat.

Results:

Based on the changes in the CMAP, the two different BTX-As induced paralytic effect on the rat tibialis anterior muscle. However, the two different BTX-A preparations did not differ significantly in effectiveness and did not induce a delay in conduction velocity.

Conclusions:

The new BTX-A preparation used in this electrophysiological study had similar effect compared with the previously marketed BTX-A.[AQ: Please approve the edits made to the sentence “The new BTX-A preparation…”) We propose that a split-body electrophysiological protocol will be useful in establishing the comparative effectiveness of new BTX products.

Botulinum neurotoxin serotype A specific cell-based potency assay to replace the mouse bioassay

Botulinum neurotoxin serotype A (BoNT/A), a potent therapeutic used to treat various disorders, inhibits vesicular neurotransmitter exocytosis by cleaving SNAP25. Development of cell-based potency assays (CBPAs) to assess the biological function of BoNT/A have been challenging because of its potency. CBPAs can evaluate the key steps of BoNT action: receptor binding, internalization-translocation, and catalytic activity; and therefore could replace the current mouse bioassay. Primary neurons possess appropriate sensitivity to develop potential replacement assays but those potency assays are difficult to perform and validate. This report describes a CBPA utilizing differentiated human neuroblastoma SiMa cells and a sandwich ELISA that measures BoNT/A-dependent intracellular increase of cleaved SNAP25. Assay sensitivity is similar to the mouse bioassay and measures neurotoxin biological activity in bulk drug substance and BOTOX® product (onabotulinumtoxinA). Validation of a version of this CBPA in a Quality Control laboratory has led to FDA, Health Canada, and European Union approval for potency testing of BOTOX®, BOTOX® Cosmetic, and Vistabel®. Moreover, we also developed and optimized a BoNT/A CBPA screening assay that can be used for the discovery of novel BoNT/A inhibitors to treat human disease.

Emerging opportunities for serotypes of botulinum neurotoxins

Background: Two decades ago, botulinum neurotoxin (BoNT) type A was introduced to the commercial market. Subsequently, the toxin was approved by the FDA to address several neurological syndromes, involving muscle, nerve, and gland hyperactivity. These syndromes have typically been associated with abnormalities in cholinergic transmission. Despite the multiplicity of botulinal serotypes (designated as types A through G), therapeutic preparations are currently only available for BoNT types A and B. However, other BoNT serotypes are under study for possible clinical use and new clinical indications; Objective: To review the current research on botulinum neurotoxin serotypes A-G, and to analyze potential applications within basic science and clinical settings; Conclusions: The increasing understanding of botulinal neurotoxin pathophysiology, including the neurotoxin’s effects on specific neuronal populations, will help us in tailoring treatments for specific diagnoses, symptoms and patients. Scientists and clinicians should be aware of the full range of available data involving neurotoxin subtypes A-G.

Bioassays for evaluation of medical products derived from bacterial toxins

Bioassays play central role in evaluation of biological products and those derived from bacterial toxins often rely exclusively on in vivo models for assurance of safety and potency. This chapter reviews existing regulatory approved methods designed to provide information on potency and safety of complex biological medicines with an insight into strategies considered for alternative procedures.

Sensing the deadliest toxin: technologies for botulinum neurotoxin detection

Sensitive and rapid detection of botulinum neurotoxins (BoNTs), the most poisonous substances known to date, is essential for studies of medical applications of BoNTs and detection of poisoned food, as well as for response to potential bioterrorist threats. Currently, the most common method of BoNT detection is the mouse bioassay. While this assay is sensitive, it is slow, quite expensive, has limited throughput and requires sacrificing animals. Herein, we discuss and compare recently developed alternative in vitro detection methods and assess their ability to supplement or replace the mouse bioassay in the analysis of complex matrix samples.

Sensing the deadliest toxin: technologies for botulinum neurotoxin detection

Sensitive and rapid detection of botulinum neurotoxins (BoNTs), the most poisonous substances known to date, is essential for studies of medical applications of BoNTs and detection of poisoned food, as well as for response to potential bioterrorist threats. Currently, the most common method of BoNT detection is the mouse bioassay. While this assay is sensitive, it is slow, quite expensive, has limited throughput and requires sacrificing animals. Herein, we discuss and compare recently developed alternative in vitro detection methods and assess their ability to supplement or replace the mouse bioassay in the analysis of complex matrix samples.

Quantitative determination of biological activity of botulinum toxins utilizing compound muscle action potentials (CMAP), and comparison of neuromuscular transmission blockage and muscle flaccidity among toxins

The biological activity of various types of botulinum toxin has been evaluated using the mouse intraperitoneal LD(50) test (ip LD(50)). This method requires a large number of mice to precisely determine toxin activity, and so has posed a problem with regard to animal welfare. We have used a direct measure of neuromuscular transmission, the compound muscle action potential (CMAP), to evaluate the effect of different types of botulinum neurotoxin (NTX), and we compared the effects of these toxins to evaluate muscle relaxation by employing the digit abduction scoring (DAS) assay. This method can be used to measure a broad range of toxin activities the day after administration. Types A, C, C/D, and E NTX reduced the CMAP amplitude one day after administration at below 1 ip LD(50), an effect that cannot be detected using the mouse ip LD(50) assay. The method is useful not only for measuring toxin activity, but also for evaluating the characteristics of different types of NTX. The rat CMAP test is straightforward, highly reproducible, and can directly determine the efficacy of toxin preparations through their inhibition of neuromuscular transmission. Thus, this method may be suitable for pharmacology studies and the quality control of toxin preparations.

Measurement of botulinum types A, B and E neurotoxicity using the phrenic nerve-hemidiaphragm: improved precision with in-bred mice

Botulinum neurotoxins induce a prolonged muscle paralysis by specifically blocking the release of neuronal transmitters from peripheral nerve junctions. The current method for assessing the potency of botulinum toxin and antitoxins is the mouse LD50 assay. The mouse phrenic nerve-diaphragm assay is an in vitro assay that closely mimics in vivo respiratory paralysis. In this study, we have further improved the assay by using gelatin as a non-frothing alternative to albumin and investigated the effects of botulinum toxin serotypes A, B and E on phrenic nerve-hemidiaphragms from out-bred MF1 and in-bred Balb/c mice. Improved reproducibility was found with in-bred mice. Balb/c mice were also found to be much less sensitive to type B toxin perhaps indicating differences in the expression of receptor components. Hemidiaphragm preparations from Balb/c mice were approximately 7 times more sensitive to type A toxin and 7-12 times more sensitive to type E toxin relative to type B toxin. These findings indicate that when fully optimised the mouse nerve-diaphragm preparation can provide a functional in vitro model for accurate and reproducible assessment of toxin activity.

Planning for Reduction

Reduction is one of the Three Rs which can be readily achieved in practice. This can be done by careful consideration of the experimental strategy and the implementation of good experimental design. Moreover, strategic planning leads to ‘best’ scientific practice and can have a positive impact on both refinement and replacement. The FRAME Reduction Steering Committee has developed a flow chart for an overall strategy for planning and conducting biomedical research. This, and important planning considerations for each of the steps proposed, are discussed. The strategy involves taking an initial overview and undertaking related background research, then planning a sequence of experiments expected to give satisfactory results with the least animal use and minimal severity, choosing an efficient design for each experiment in the sequence, reviewing the results of one experiment before progressing to the next, and conducting an overall analysis at the end of the programme. This approach should minimise animal use and maximise the quality of the resultant scientific output.

The in vivo rat muscle force model is a reliable and clinically relevant test of consistency among botulinum toxin preparations

To ensure safety and predictable clinical efficacy, the biological activity of type A botulinum toxin (BoNT-A) preparations must remain consistent. Several methods have been employed to assess consistency but lack clinical applicability and/or are associated with animal welfare concerns. Here, we describe a novel in vivo rat muscle force model for evaluating the biological activity of formulated BoNT-A product (Dysport) prepared from bulk toxin batches manufactured at different facilities. Toxin activity was assessed by measuring muscle force generation over time in the triceps surae muscles in the rat hind leg. Animals received 0.1 ml gelatine phosphate buffer (negative vehicle control) or 0.1 or 1.0 LD50 units of BoNT-A in phosphate buffer. Batch equivalence and consistency were confirmed by the lack of significant differences in muscle force generation and duration of effect between each test batch and the reference preparation tested in the same series of experiments. The reduction in muscle force generation was dose-related and reproducible for all active treatment groups. At appropriate dose levels, the rat muscle force model is a reliable tool for measuring biological activity in bulk toxin batches used to formulate clinical product and demonstrates the consistency of batches manufactured over many years.

A review of WHO International Standards for botulinum antitoxins

Clostridium botulinum produces the most potent known toxins, with seven distinct serotypes currently defined (A-G). These toxins can cause a life threatening systemic toxicity whether through natural causes such as food poisoning, infant botulism, wound botulism, or through use as bio-terror agents (e.g. inhalational botulism). It was realised early on that standard reference botulinum antitoxins were required to reduce the variation between assays and ensure a consistent potency of therapeutic antitoxins and vaccines, and to define the serotype. This led to the International Unit being defined by the World Health Organisation (WHO) in the 1960s with the establishment of the first International Standards (IS) for serotypes A-F. Since then botulinum antitoxin ISs have been used world wide as the 'yard stick' to measure the neutralising potency of antitoxins. These primary WHO ISs are used to calibrate in house working reagents that are more extensively utilised. A definition of the International Unit for serotype G antitoxin has yet to be defined or accepted by the WHO and urgently needs addressing. However, before September 11th 2001 there was very little interest in botulinum antitoxin IS and as a result stocks of most of the original preparations are now completely exhausted or depleted and replacements long overdue. We have reviewed the extensive history and availability of the primary WHO ISs and interim materials. All type A and B antitoxin materials were recently assayed and their relative activities confirmed against the original IS preparations. The recent increase in demand for these materials has further exacerbated the shortage. We describe here the production and characterization of stable freeze dried potential candidate replacements along with a new prospective first IS for type G antitoxin. Available toxin A reference preparations are also briefly reviewed.

Immunomagnetic beads assay for the detection of botulinum neurotoxin types C and D

An immunomagnetic beads assay for the simultaneous quantification of botulinum neurotoxin types C and D was developed. Specific monoclonal antibodies against the heavy chain of the toxin and affinity-purified biotinylated polyclonal antibodies (pAbs) were used. The antibodies were preincubated with the sample. The complex being formed was then captured by magnetic beads coated with antimouse IgG. Streptavidin-poly-horseradish peroxidase, a signal amplifier, bound to the biotinylated pAb. A maximum sensitivity of approximately 0.3 minimal lethal doses for mice per milliliter was achieved with culture supernatants of both toxin types.

Botulinum type A toxin neutralisation by specific IgG and its fragments: a comparison of mouse systemic toxicity and local flaccid paralysis assays

In this study, we have compared two in vivo assay methods to measure the type A botulinum toxin neutralising activity of specific immunoglobulin G (IgG) and its fragments (F(ab')(2), Fab', Fab) purified from pentavalent botulinum antisera raised in goats. Each assay method was repeated on three separate occasions in mice and relative potencies calculated with respect to a type A equine reference antitoxin. The conventional assay, which measures the number of mice surviving typically after 72 or 96 h following the intraperitoneal administration of a mixture of toxin and antitoxin, gave the following order of potency IgG>F(ab')(2)>Fab'>Fab (6.8>4.7>3.5>2.6 IU/mg). Differences in potency are likely to be due to differences in the pharmacokinetics of the antitoxins, which are related to their molecular weight. The alternative local flaccid paralysis assay, where toxin and antitoxin are injected subcutaneously into the left inguinocrural region, gave results with a narrower range of activities: IgG>Fab'>F(ab')(2)>Fab (6.0>5.9>5.5>4.6 IU/mg). Comparison of the two assay methods showed no significant differences for IgG, F(ab')(2) or Fab', although the Fab fragment was significantly more potent in the non-lethal assay probably because of the reduced influence of antitoxin pharmacokinetics in this localised assay. These findings show that a local flaccid paralysis assay provides a less time consuming and more humane alternative to the lethal assay for the potency testing of botulinum IgG and F(ab')(2) antitoxins.

Laboratory diagnostics of botulism

Botulism is a potentially lethal paralytic disease caused by botulinum neurotoxin. Human pathogenic neurotoxins of types A, B, E, and F are produced by a diverse group of anaerobic spore-forming bacteria, including Clostridium botulinum groups I and II, Clostridium butyricum, and Clostridium baratii. The routine laboratory diagnostics of botulism is based on the detection of botulinum neurotoxin in the patient. Detection of toxin-producing clostridia in the patient and/or the vehicle confirms the diagnosis. The neurotoxin detection is based on the mouse lethality assay. Sensitive and rapid in vitro assays have been developed, but they have not yet been appropriately validated on clinical and food matrices. Culture methods for C. botulinum are poorly developed, and efficient isolation and identification tools are lacking. Molecular techniques targeted to the neurotoxin genes are ideal for the detection and identification of C. botulinum, but they do not detect biologically active neurotoxin and should not be used alone. Apart from rapid diagnosis, the laboratory diagnostics of botulism should aim at increasing our understanding of the epidemiology and prevention of the disease. Therefore, the toxin-producing organisms should be routinely isolated from the patient and the vehicle. The physiological group and genetic traits of the isolates should be determined.

The therapeutic use of botulinum toxin

Since Alan Scott's research, botulinum toxin (BoNT) has been used in several diseases or conditions characterised by muscular overactivity. BoNT acts on either neuromuscular or autonomic cholinergic junctions. Seven different serotypes are known, with antigenic specificity and different therapeutic profiles. BoNT is made up of a heavy chain, involved in binding and membrane translocation, and a light chain, involved in blocking neuroexcytosis. Each serotype shares a specific acceptor on the presynaptic membrane of a cholinergic junction. The available BoNT preparations differ in toxicity, purity and stability. Injection of the neurotoxin produces several modifications at a neuromuscular junction. Axonal sprouting, muscular fibre atrophy, and new end-plates are the most evident histological events after BoNT treatment. They appear to be reversible in untreated muscles. Diffusion can occur at first by haematogeneous or local BoNT spread. Several factors, such as dose, volume, site of injection, muscle size, and muscular fascia, can influence the amount of diffusion and possible side-effects. After prolonged BoNT treatment patients can become unresponsive. Antibodies directed against BoNT have been observed with ELISA or mouse bioassay. Different serotypes have been used to treat non-responder patients. Novel toxins with lower immunogenicity and prolonged clinical efficacy are required for more effective treatment.

Role for standards in assays of botulinum toxins: international collaborative study of three preparations of botulinum type A toxin

The biological activity of therapeutic preparations of botulinum type A toxin is currently expressed in units defined on the basis of the median lethal intraperitoneal dose of that preparation in mice at 72 h, the LD50 dose. In this study we describe the comparison, by ten laboratories in five countries, of three different formulations of botulinum type A toxin using the mouse lethality test, and also using the relative activities of the preparations. The results of this study show that use of a standard preparation and expression of relative potency gives substantially greater consistency between and within laboratories than when mouse LD50 unit is used to define activity of botulinum toxin.

Detection of antibodies against botulinum toxins

After immunisation with botulinum vaccine, antibodies to multiple epitopes are produced. Only some of these will have the capacity to neutralise the toxin activity. In fact, the ability of toxoid vaccine to induce toxin neutralising antibodies has provided the basis for the use of therapeutic antitoxins and immunoglobulins for the prophylaxis and treatment of diseases caused by bacterial toxins. Increasing indications for the chronic use of botulinum toxin for therapy have inevitably resulted in concern for patients becoming unresponsive because of the presence of circulating toxin-specific antibodies. Highly sensitive and relevant assays to detect only clinically relevant toxin neutralising antibodies are essential. Although immunoassays often provide the sensitivity, their relevance and specificity is often questioned. The mouse protection LD(50) bioassay is considered most relevant but can often only detect 10 mIU/ml of antitoxin. This sensitivity, although sufficient for confirming protective immunity, is inadequate for patients undergoing toxin therapy. An intramuscular paralysis assay improves the sensitivity to ca. 1 mIU/ml, and a mouse ex vivo diaphragm assay, with sensitivity of < 0.5 mIU/ml, is the most sensitive functional assay to date for this purpose. Alternative approaches for the detection of antibodies to botulinum toxin have included in vitro endopeptidase activity neutralisation. Unlike any other functional assay, this approach is not reliant on serotype-specific antibodies for specificity. Most recent promising developments are focused on cellular assays utilising primary rat embryonic cord cells or more conveniently in vitro differentiated established cell lines such as human neuroblastoma cells.

Animal experimentation in snake venom research and in vitro alternatives

Current experimental techniques used in snake venom research (with and without the use of animals) are reviewed. The emphasis is on the reduction of the use of animals in the development of antivenoms for the clinical treatment of snakebite. Diagnostic and research techniques for the major pathologies of envenoming are described and those using animals are contrasted with non-sentient methods where possible. In particular, LD50 and ED50 assays using animals (in vivo) and fertilised eggs (in vivo, non-sentient) are compared as well as in vitro procedures (ELISA and haemolytic test) for ED50 estimations. The social context of antivenom production, supply and demand is outlined together with the consequent tension between the benefits derived and the increase in opposition to experiments on animals. Stringent regulations governing the use of animals, limited research funds and public pressure all focus the need for progress towards non-animal, or non-sentient, research methods. Some achievements are noted but success is hampered by lack of detailed knowledge of the many constituents of venom which have to be assessed as a whole rather than individually. The only way to evaluate the net pathological effect of venom is to use a living system, usually a rodent, and similarly, the efficacy of antivenoms is also measured in vivo. The pre-clinical testing of antivenoms in animals is therefore a legal requirement in many countries and is strictly monitored by government authorities. New technologies applied to the characterisation of individual venom proteins should enable novel in vitro assays to be designed thus reducing the number of animals required. In the meantime, the principles of Reduce, Refine and Replace relating to animals in research are increasingly endorsed by those working in the field and the many agencies regulating ethical and research policy.

Growing Old Disgracefully: The Cosmetic Use of Botulinum Toxin

The explosive growth in the use of botulinum toxin for cosmetic purposes has undoubtedly had an impact on the number of animals used in the potency testing of this product. The test used is a classical LD50, a severe procedure during which animals experience increasing paralysis until the occurrence of death. The enthusiastic adoption by the general public of the use of botulinum toxin as an anti-wrinkle treatment has, at least in Europe, paradoxically taken place against a background of moves to stop animal testing of cosmetics and cosmetic ingredients. There appears to be a dearth of information aimed at the public concerning botulinum toxin testing. Botulinum toxin does have important medical applications; however, the question arises whether a blanket licence for the testing can be justified, when a large proportion of the product is being used cosmetically. A further question is why death continues to be the endpoint of the potency test, when a more-humane endpoint has been proposed. In addition, a number of alternative methods have been developed, which could have the potential to replace the lethal potency test altogether. These methods are discussed in this paper, and the importance of establishing a strategy for their validation is emphasised, a need that has become even more urgent in the light of the recently published draft monograph on botulinum toxin by the European Pharmacopoeia Commission.

Role of ancillary variables in the design, analysis, and interpretation of animal experiments

During the course of an experiment using animals, many variables (e.g., age, body weight at several times, food and water consumption, hematology, and clinical biochemistry) and other characteristics are often recorded in addition to the primary response variable(s) specified by the experimenter. These additional variables have an important role in the design and interpretation of the experiment. They may be formally incorporated into the design and/or analysis and thus increase precision and power. However, even if these variables are not incorporated into the primary statistical design or into the formal analysis of the experiment, they may nevertheless be used in an ancillary or exploratory way to provide valuable information about the experiment, as shown by various examples. Used in this way, ancillary variables may improve analysis and interpretation by providing an assessment of the randomization process and an approach to the identification of outliers, lead to the generation of new hypotheses, and increase generality of results or account for differences in results when compared across different experiments. Thus, appropriate use of additional variables may lead to reduction in the number of animals required to achieve the aims of the experiment and may provide additional scientific information as an extra benefit. Unfortunately, this type of information is sometimes effectively discarded because its potential value is not recognized. Guidelines for use of animals include, in addition to the obligation to follow humane procedures, the obligation to use no more animals than necessary. Ethical experimental practice thus requires that all information be properly used and reported.

Animal usage in vaccine development and production: maximising results while minimizing use

The Third International Symposium on Advancing Science and Elimination of the Use of Laboratory Animals for Development and Control of Vaccines and Hormones, organized by the National Institute of Public Health and the Environment (RIVM, The Netherlands) under the auspices of the International Association for Biologicals (IABS), was held in Utrecht, The Netherlands, 12-14 November 2001.

A comparison of the safety margins of botulinum neurotoxin serotypes A, B, and F in mice

This study compared the respective intramuscular (IM) safety margins of two preparations of botulinum toxin (BTX) serotype A and one preparation each of BTX serotypes B and F in mice. Mice received an IM injection (0-200 U kg(-1) body weight) of BTX-A (BOTOX or DYSPORT), an experimental preparation of BTX-B (WAKO Chemicals, Inc.), or an experimental preparation of BTX-F (WAKO). An observer who was masked to treatment scored muscle weakness using the Digit Abduction Scoring (DAS) assay. Peak DAS responses were plotted and IM ED(50) values calculated. The safety margin for each BTX preparation was calculated as a ratio of the IM median lethal dose after hind limb injection to the median effective dose in the DAS assay (IM LD(50)/IM ED(50)). Experiments were repeated 4-6-times for each preparation (10 mice/dose). Mean safety margin values were highest for BTX-F (WAKO; 16.7+/-3.9) and one of the BTX-A preparations (BOTOX; 13.9+/-1.7). Mean safety margins values for the other BTX-A preparation (DYSPORT) and BTX-B (WAKO) were significantly lower (7.6+/-0.9 and 4.8+/-1.1, respectively). Thus, the BTX preparations exhibited different safety margins in mice. These results support the hypothesis that the preparations are unique therapeutics and are not interchangeable based on a simple dose ratio.

Recombinant SNAP-25 is an effective substrate for Clostridium botulinum type A toxin endopeptidase activity in vitro

Bacterial neurotoxins are now being used routinely for the treatment of neuromuscular conditions. Alternative assays to replace or to complement in vivo bioassay methods for assessment of the safety and potency of these botulinum neurotoxin-based therapeutic products are urgently needed. Advances made in understanding the mode of action of clostridial neurotoxins have provided the basis for the development of alternative mechanism-based assay methods. Thus, the identification of SNAP-25 (synaptosomal-associated protein of molecular mass 25 kDa) as the intracellular protein target which is selectively cleaved during poisoning by botulinum neurotoxin type A (BoNT/A) has enabled the development of a functional in vitro assay for this toxin. Using recombinant DNA methods, a segment of SNAP-25 (aa residues 134-206) spanning the toxin cleavage site was prepared as a fusion protein to the maltose-binding protein in Escherichia coli. The fusion protein was purified by affinity chromatography and the fragment isolated after cleavage with Factor Xa. Targeted antibodies specific for the N and C termini of SNAP-25, as well as the toxin cleavage site, were prepared and used in an immunoassay to demonstrate BoNT/A endopeptidase activity towards recombinant SNAP-25 substrates. The reaction required low concentrations of reducing agents which were inhibitory at higher concentrations as were metal chelators and some inhibitors of metallopeptidases. The endopeptidase assay has proved to be more sensitive than the mouse bioassay for detection of toxin in therapeutic preparations. A good correlation with results obtained in the in vivo bioassay (r = 0.95, n = 23) was demonstrated. The endopeptidase assay described here may provide a suitable replacement assay for the estimation of the potency of type A toxin in therapeutic preparations.

Pharmacologic characterization of botulinum toxin for basic science and medicine

The use of Botulinum neurotoxin (BoNT) is increasing in both clinical and basic science. Clinically, intramuscular injection of nanogram quantities of BoNT is fast becoming the treatment of choice for a spectrum of disorders including movement disorders such as torticollis, blepharospasm, Meige Disease, and hemifacial spasm (Borodic et al., 1991, 1994a; Jankovic and Brin, 1991; Clarke, 1992). Neuroscientists are using BoNTs as tools to develop a better understanding of the mechanisms underlying the neurotransmitter release process. Consequently, our ability to accurately and reliably quantify the biologic activity of botulinum toxin has become more important than ever. The accurate measurement of the pharmacologic activity of BoNTs has become somewhat problematic with the most significant problems occurring with the clinical use of the toxins. The biologic activity of BoNTs has been measured using a variety of techniques including assessment of whole animal responses to in vitro effects on neurotransmitter release. The purpose of this review is to examine the approaches employed to characterize, quantify and investigate the actions of the BoNTs and to provide a guide to aid investigators in determining which of these methods is most appropriate for their particular application or use.

Therapeutic botulinum type A toxin: factors affecting potency

The type A neurotoxin produced by Clostridium botulinum is a potent neuromuscular blocking agent which causes paralysis by preventing the release of neurotransmitter from motor neurons. This property has resulted in the use of the toxin in the treatment of a number of neuromuscular diseases involving muscle spasms. At present, the only recognised assay to estimate accurately the potency of botulinum toxin in clinical preparations is bioassay, in which lethality is used as the endpoint. Such bioassay is inherently variable and large interlaboratory variability has been reported, highlighting problems for standardisation of activity in the absence of any commonly used reference preparation. In the present study, we have confirmed that many different assay conditions can affect potency estimates of clinical formulations of type A botulinum toxin. Further, our studies indicate that different preparations, because of their unique formulation and stability, are differentially affected by some of these assay conditions and that these differences might well contribute to the differences observed in their clinical use.