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5 Humane Endpoints for Animals in Pain T his chapter presents an overview of the concept of humane endpoints and their application in studies that cause pain in research animals. It sets the stage with a review of pertinent guidance documents, focusing on the Organization for Economic Cooperation and Development (OECD) 2000 Guidance on Humane Endpoints for Experimental Animals Used in Safety Evaluation. It provides a discussion of the usefulness of pilot studies as a refinement and potential replacement tool. Further, it presents humane endpoints in relation to specific research fieldsâtoxicology, infec- tious diseases, vaccine safety, cancer, and pain. It concludes with a discus- sion of euthanasia. GUIDELINES AND REFERENCE DOCUMENTS Moral and ethical obligations are inherent in all aspects of research, testing, and teaching that use research subjects. The question of when a study using animal models should end or the study design be changed due to animal pain, distress, or welfare considerations has been the subject of many publications, symposia, guidance documents, and regulations. Defin- ing a humane endpoint can vary widely depending on a number of factors, of which study design and research objectives are but two. Consequently, attempting to provide specific endpoint criteria for all study designs and other factors cannot be adequately addressed in this one report (Morton 1999, 2000). Not only would such a list be inadequate, it could prove det- rimental to hitherto unknown study objectives. This report does not go into specifics but rather presents selected pertinent guidelines and documents. 11
120 RECOGNITION AND ALLEVIATION OF PAIN IN LABORATORY ANIMALS Investigators, study personnel, veterinary staff, and institutional animal care and use committees (IACUCs) are obligated to thoroughly research and incorporate humane endpoints in every study or use involving laboratory animals. National and International Guidelines A number of national and international guidelines are available to assist researchers in determining humane endpoints for research animals. The Office of Laboratory Animal Welfare (OLAW) defines these as â[c]riteria used to end experimental studies earlier in order to avoid or terminate unrelieved pain and/or distress are referred to as humane endpoints. An important feature of humane endpoints is that they should ensure that study objectives will still be met even though the study is ended at an earlier point. Ideally, humane endpoints are sought that can be used to end studies before the onset of pain and distressâ (OLAW/ARENA 2002, p. 103). The Canadian Council for Animal Care (CCAC) has published an excel- lent document with general recommendations on humane endpoints in animal studies. According to the CCAC guidelines, in âexperiments involv- ing animals, any actual or potential pain, distress, or discomfort should be minimized or alleviated by choosing the earliest endpoint that is compat- ible with the scientific objectives of the research. Selection of this endpoint by the investigator should involve consultation with the laboratory animal veterinarian and the animal care committeeâ (CCAC 1998, p. 5). In 1994, the OECD recognized that while ambiguous test guidelines may be necessary, such ambiguity fosters an overbroad interpretation of what constitutes a humane endpoint in toxicology studies. The organiza- tion therefore created a working group to develop a guidance document using clinical signs as humane endpoints in safety evaluation studies (OECD 2000; Box 5-1). The resulting document put forth criteria based on the principles of the 3Rs as well as descriptions of clinical signs to assist study personnel in determining when death may be imminent or when severe pain may be present after an animalâs exposure to a test substance. The criteria are broad enough to apply to a wide range of study types, test substances, species, and strains of animals. The reader is encouraged to examine this resource when developing internal guidance documents to assess humane endpoints. OECD invested considerable time and effort in addressing and defin- ing potential endpoints in safety assessment studies (see the Addendum at the end of this chapter for the OECD definition). The OECD Guidance Document defines humane endpoints âas the earliest indicator in an animal experiment of severe pain, severe distress, suffering, or impending death. The ultimate purpose of the application of humane endpoints to toxicol-
121 HUMANE ENDPOINTS FOR ANIMALS IN PAIN BOX 5-1 OECD Guidance Document on the Recognition, Assessment, and Use of Clinical Signs as Humane Endpoints for Experimental Animals Used in Safety Evaluation (OECD 2000) â¢ A humane endpoint can be defined as the earliest indicator in an animal ex- periment of severe pain, severe distress, suffering, or impending death. â¢ The ultimate purpose of the application of humane endpoints to toxicology studies is to be able to accurately predict severe pain, severe distress, suffer- ing, or impending death, before the animal experiences these effects. However, the science of toxicology is not yet to the point where such accurate predic- tions can be made prior to the onset of severe pain and distress. It is possible at this time to identify pain, distress, or suffering, very early after their onset by careful clinical examination of animals on test using well-defined endpoints and criteria. Humane endpoints for use in research and testing have been addressed in a number of publications. . . . These adverse conditions, once identified, should be minimized or eliminated, either by humanely killing the animal or, in long-term studies, by (temporary) termination of exposure, or by reduction of the test substance dose. â¢ Different animal species, and animals at different stages of development, may respond differently to test conditions, and exhibit different indications of distress. The clinical signs described here should be evaluated in consider- ation of these potential differences. If relevant humane endpoints have been identified, they should be described when an experiment is being planned, and incorporated into the experimental protocol and all related standard operating procedures (SOPs). ogy studies is to be able to accurately predict severe pain, severe distress, suffering, or impending death, before the animal experiences these effectsâ (OECD 2000, p. 10). While the OECD indicated that the science of toxi- cology cannot accurately predict pain prior to onset, careful observations can âidentify pain, distress, or suffering, very early after their onset . . . using well-defined endpoints and criteria.â The OECD further advises that suffering âshould be minimized or eliminated, either by humanely killing the animal or, in long-term studies, by (temporary) termination of exposure, or by reduction of the test substance dose. Different animal species, and animals at different stages of development, may respond differently to test conditions, and exhibit different indications of distressâ (ibid.). These guidance documents are consistent in their recommendations. Predictive parameters must be reliable, reproducible, and objective, and allow both the achievement of study objectives and goals and the use of appropriate methodologies at the earliest point to alleviate or avoid pain. As discussed below, pilot studies are an effective means to identify and validate
122 RECOGNITION AND ALLEVIATION OF PAIN IN LABORATORY ANIMALS humane endpoints, which can then be incorporated in research methods to minimize, alleviate, or avoid pain for the animal subjects (also see Morton 1999, 2000; Stokes 2002; NRC 2008, p. 61). Humane endpoints were the focus of a 1998 international confer- ence in Ziest, The Netherlands. The editors of the conference proceedings determined that humane endpoints are specific to individual studies or a particular testing paradigm (Hendriksen and Morton 1999, pp. v-vi), based on study design and intent, regulatory requirements, personnel connected to the study, and the animals themselves, whether as individuals or as a group. The conference participants concluded that the establishment of humane endpoints is, and should be, subject to adaptation as societal mores, atti- tudes, regulations, and technologies change. The conference report further stated that for ethical reasons, the formulation of endpoints to avoid or alleviate pain in laboratory animals must be a high ethical priority in every facility that conducts any form of animal experimentation (ibid.). Beyond Formal Guidelines Many of the articles and recommendations that address humane end- points focus on very specific study or research types that can cause pain to laboratory animals; for example, studies on the identification and use of humane endpoints in animal models of sepsis and shock provide an excel- lent overview of the methodologies to determine humane endpoints yet still achieve study objectives (Nemzek et al. 2004, 2008). More generally, the Institute for Laboratory Animal Research (ILAR) bases its reports on its mis- sion statement promoting âhigh-quality science and humane care and use of research animals based on the principles of refinement, replacement, and reduction (the 3Rs) and high ethical standardsâ (ILAR 2009). The Instituteâs Guidelines for the Care and Use of Mammals in Neuroscience and Beha- ioral Research (NRC 2003) provide criteria for evaluating levels of pain that help in the development of endpoints for studies in neuroscience and behavioral research. An ILAR Journal issue dedicated to Humane Endpoints for Animals Used in Biomedical Research and Testing (ILAR 2000) provides an overview of several research areas where pain is a potential outcome, including infectious disease and cancer research (Olfert and Godson 2000; Wallace 2000) and vaccine potency and and acute toxicity testing (Hen- driksen and Steen 2000; Sass 2000). ILAR also published the proceedings of a symposium on Regulatory Testing and Animal Welfare, detailing best practices for the humane conduct of animal testing for regulatory purposes (NRC 2004). While these references are extremely valuable, it is important to view them in accordance with their intent: they are guidance documents only
123 HUMANE ENDPOINTS FOR ANIMALS IN PAIN and as such have limitations. No single document could cover all poten- tially painful study types, all animal species used in research, or all clinical signs associated with all research projects. In the absence of comprehensive guidance, the scientific community has an ethical responsibility to develop a general humane endpoint policy at each institution to provide guidance and a basis for dialogue between scientists and IACUCs about individual protocols. Caution is advisable, however, in efforts to develop a policy on humane endpoints. While the ideal is to avoid pain, personnel also need to ensure that the study objectives are attained before a procedure or animal is termi- nated (OLAW/ARENA 2002, p. 103). If a full study, or aspect of a study, is ended before the objectives have been met, one can argue that the animals used have been wasted. Moreover, if the purpose of a study is to meet the requirements for the safety assessment of a substance, a regulatory agency may reject the submitted data as insufficient and require that the study be repeated. On the other hand, if researchers are reluctant to intervene, study animals may unnecessarily experience pain, distress, or severely diminished welfare. Further, without adequate guidance, death is likely to be selected as a convenient endpoint that is reproducible and objective. If regulatory guidelines do not specify an endpoint, as in vaccine potency studies (CFR Title 9, 2006), regulated entities can and will use lethality. For all these reasons identification of humane endpoints should take into account the following factors: the role of regulatory agencies in the overall process; the need for scientifically appropriate endpoints; and the reliability of clinical observations of the animals to ensure a proper outcome for both the animals and the study. As a corollary, it is worth emphasizing that investigators, technicians, and other staff responsible for the care of research animals should be well trained and able to make impartial judg- ments about an animalâs well-being. OLAW approached the subject of humane endpoints in its Institutional Animal Care and Use Committee Guidebook (OLAW/ARENA 2002, p. 103), advising internal oversight committees to review protocols to determine whether âdiscomfort to animals will be limited to that which is unavoidable for the conduct of scientifically valuable research, and [whether] unrelieved pain and distress will only continue for the duration necessary to accom- plish the scientific objectives.â The OLAW reference is careful to state that potential pain or distress should be relieved with appropriate medication or with euthanasia, although the study objectives should still be met. The intent is to end a study before the development of pain or distress, as is emphasized in the OECD document.
124 RECOGNITION AND ALLEVIATION OF PAIN IN LABORATORY ANIMALS PILOT STUDIES An effective way to reduce negative impacts on laboratory animals is the use of a pilot study, which can be critical to the success of a larger study (DeHaven 2002; Morton et al. 1990; NRC 2003, p. 14; NRC 2008, pp. 61- 62; OECD 2000, p. 14). The premise behind this concept is to conduct the proposed study on a small number of animals rather than the full comple- ment necessary for a statistically valid study and thus prevent unnecessary pain for a larger number of animals. Pilot studies are advantageous because they help researchers to identify: â¢ potential interactions between proposed analgesic and anesthetic treatments and specific research goals, â¢ potentially useful means of assessing pain in a specific research model, and â¢ humane endpoint criteria specific to an individual project. Problems that occur in the pilot study can inform the discussion and development of strategies to address an animalâs deteriorating condition. Such strategies may include (but certainly not be limited to) the adjustment of dose levels, changes in sample size, identification of adverse effects, incorporation of refinements (e.g., use of analgesics, procedural changes), or alteration to the duration of exposure to minimize negative impacts on the animals. Caution is essential in the design and conduct of pilot studies as the risk of causing significant pain to the animals in such studies can be high. This risk necessitates close oversight by the IACUC and careful monitoring of the animals by study personnel and veterinary staff. Good communication among all involved can ensure both the collection of the maximum amount of useful data and appropriate interventions on behalf of the animals (NRC 2003, p. 14). INTERNATIONAL REGULATIONS AND GUIDELINES FOR SAFETY ASSESSMENT Regulatory bodies in most countries have developed standards and guidelines to ensure the conduct of appropriate safety assessments on test substances (Hicks 1997; Merrill 2001; USEPA 2008). For example, after the use of thalidomide by pregnant women in the 1960s caused severe birth defects in the long bones of the fetuses, US legislation required adequate testing of drugs in animals before human exposure (Gallo 2001; Nies 2001).
12 HUMANE ENDPOINTS FOR ANIMALS IN PAIN Similar legislative actions followed environmental disasters like the Love Canal contamination (Merrill 2001). The purpose of testing requirements for pharmaceutical, consumer, and industrial products is to ensure the safety of the environment and of the human and animal populations. However, these requirements have tended to focus on the safety of the user and do not necessarily consider humane endpoints for the animals used in the safety assessment, although such consideration is becoming a more prominent component of some newer regulatory requirements. In June 2007, the European Commission established a regulation to evaluate the hazards and risks of chemicals (Regulation (EC) No. 1907/2006 of the European Parliament and of the Council of 18 December 2006); the mission of REACH (Registration, Evaluation, and Authorization of Chemi- cals) is to improve the assessment of chemicals in order to better protect human health and the environment. Because the range of chemicals cov- ered by REACH is enormous, there is great potential for increased use of animals in corresponding toxicity and safety testing. But the regulation ensures the authorization of animal testing only when necessitated by iden- tification of data gaps (ECHA 2008). Furthermore, the regulation requires industry to share data on similar chemicals to avoid duplicative animal testing; allows for the submission of data using nonanimal tests; strongly encourages the use of Quantitative Structure-Activity Relationship (QSAR) or other computer-generated information; and invites the grouping of sub- mitted data for similar chemicals that may result in similar hazards and risks (the so-called âread-acrossâ principle). While these efforts do not define humane endpoints, the authors of the regulation are commended for the consideration of responsible animal use in safety assessment. Also useful in the toxicology regulatory arena is a February 2008 Mem- orandum of Understanding (MOU) that lays the foundation and framework for the US Environmental Protection Agency (EPA) and two NIH agencies to collaborate in sharing data, resources, and expertise in efforts to replace ani- mal testing for chemical toxicity assessment (Collins et al. 2008; NIH/USEPA 2008; NIH 2008). The MOU calls for the evaluation of in vitro assays, such as those used for identification of toxicity pathways and high-throughput screening (as described in NRC 2007), to better predict potential health and environmental hazards from chemicals. The ambitious goals of the MOU are the development of more accurate assays and changes in regulatory guidelines, both of which are likely to be a long-term process. Similar goals should be encouraged on a global scale to effect change in regulatory agen- cies and eliminate potentially painful animal testing. Although harmonization of regulatory guidelines has significantly reduced discrepancies between cooperating countries, efforts for the global
126 RECOGNITION AND ALLEVIATION OF PAIN IN LABORATORY ANIMALS harmonization of safety guidelines are neither consistent nor well coordi- nated. As a result, tests must comply with all the requirements of each coun- try where a product is to be marketed for a particular use. For example, the regulatory agency of one country may require an additional group of ani- mals to assess recovery from exposure, while other countries may not have this requirement or may even reject the study depending on their review process. Or one countryâs regulatory agency may accept an alternative that has been validated as scientifically reliable and relevant (NIH 1997), such as the local lymph node assay in mice, whereas agencies in other countries may not accept the data in lieu of the guinea pig dermal sensitization test. While a comparison of all safety assessment guidelines is well beyond the scope of this report, differences in regulatory-driven studies can have a negative impact on the prevention and alleviation of pain in laboratory animals. An example of a safety assessment test that may cause pain is the acute eye irritation study, the purpose of which is to evaluate the potential hazards of ocular exposure to a substance. Although requirements for this procedure are generally in agreement across international regulatory bod- ies and national agencies (JMAFF 2000; OECD 1987, #405; USEPA OPPTS 1998, #870.2400), the same is not true for the reversibility of ocular lesions, an additional requirement of this test in order to more fully assess the risk of human exposure. The procedures for this component of the toxicity evalua- tion vary considerably with respect to animal welfare. The OECD guidelines recommend a step-wise evaluation paradigm that starts with assessment of structurally related substances and other in vitro tests prior to any ani- mal use. The guidelines also identify ocular lesions that are considered irreversible and thereby meet OECD criteria for terminating the study and euthanizing the animal. But while guidelines in various countries reference the OECD guidance document for humane endpoints and recommend the use of local anesthetics in cases of extreme pain, they do not recognize the OECD criterion for early termination of the study (identification of irrevers- ible lesions). HUMANE ENDPOINTS IN TOXICOLOGY STUDIES In recognition of the pain and distress inflicted on animals in many safety and toxicology studies, regulatory guidelines have begun to address the concept of humane endpoints, although sometimes in vague terms. The EPA Health Effects Test Guidelines for Acute Oral Toxicity (USEPA OPPTS 2002) provide instruction for following the OECD Guidance Document (OECD 2000) to reduce the suffering of animals in toxicity studies. Eutha- nasia of animals that are either moribund or in severe pain is also encour- aged. Regrettably, vague statements such as âanimals showing severe and enduring signs of distress and pain may need to be humanely killed,â which
12 HUMANE ENDPOINTS FOR ANIMALS IN PAIN are common in regulatory guidelines (USEPA OPPTS 1998), may promote a reluctance to terminate a study or an animalâs exposure to the testing substance because a regulatory body may consider the action premature and mandate a repeat study. This is not a good situation for researchers, laboratories, or animals. Not all test substances cause ocular (or other) pain or injury, but the potential exists. As pointed out by Durham and colleagues (1992), there is a gap in the data for analgesia appropriate for use in ocular toxicity tests and that gap persists, as evidenced in a US Federal Register notice (Federal Register 2007) requesting data on analgesic use in ocular irritancy tests to alleviate pain without affecting test results. Current guidelines include neither justification for withholding analgesic agents nor guidance for the use of analgesic agents to alleviate ongoing pain. As a result, testing entities may be reluctant to provide analgesia beyond initial local anesthetics, to avoid the possibility of interference with the test substance (Stokes 2005). Yet numerous published studies demonstrate that the use of analgesics to alleviate pain from ocular irritancy tests does not interfere with the scien- tific objectives of this safety test (Patrone et al. 1999; Peyman et al. 1994; Stiles et al. 2003). Such evidence can be used to avoid or alleviate pain as well as to provide scientific rationale for the use of analgesics in ocular irritancy tests. Chronic toxicity and carcinogenicity testing are currently required to assess effects after long-term, repeated exposure to a test substance (JMAFF 2000; OECD 1987, #405; USEPA OPPTS 1998, #870.2400). The incidence of tumor burden, geriatric changes, and premature death can be signifi- cant near the scheduled termination of these studies. Guidelines generally specify the survival rates necessary to provide meaningful interpretation of a chronic study, but the OECD document is the only one to discuss humane endpoints and provide guidance for the early termination of a study if survival rates fall below a specified percentage. In order to achieve the required survival rate at the end of the mandated study, animals often are not euthanized until very close to death, an outcome that may entail needless pain for the animals. True harmonization of guideline safety assess- ment tests and global adoption of the OECD humane endpoints document would be an important step toward the alleviation and avoidance of pain in laboratory animals. The NRC report Toxicity Testing in the Twenty-first Century: A Vision and a Strategy (NRC 2007) evaluated current toxicity testing schemes and developed a long-term strategy for the direction of safety assessments based on state-of-the-art sciences (e.g., genomics, proteomics, and pharmacoki- netics) and emerging technologies (e.g., bioinformatics). Although the report acknowledges that implementation of the strategy will require much effort on the part of scientists, regulators, and law makers to develop workable
128 RECOGNITION AND ALLEVIATION OF PAIN IN LABORATORY ANIMALS testing schemes, the concepts envisioned could significantly improve the science of toxicology, assessment of risk to human safety, alleviation of pain in laboratory animals, and reduction or replacement of animals in toxicity testing (ibid.). One of the sources reviewed for the NRC report was the approach developed by the Health and Environmental Sciences Institute (HESI) of the International Life Sciences Institute (ILSI). In 2000, this organization convened an Agricultural Chemical Safety Assessment (ACSA) committee to redesign safety testing schemes for agricultural chemicals. The resulting multifaceted approach redesigns traditional toxicology tests to integrate sev- eral sciences, such as metabolism/kinetics and life stages, in a single study to eliminate the requirement for separate studies to evaluate each parameter and reduce the number of animals used (Carmichael et al. 2006; Cooper et al. 2006; Doe et al. 2006; ILSI-HESI 2008). Further, the metabolism/kinet- ics component of the strategy is particularly relevant to the alleviation of pain in laboratory animals: based on the metabolism of a test substance in the animal model, a saturation point can be determined and used as the high dose level in subsequent studies because it is considered more relevant to actual human exposure levels. This approach, based on step-wise, or tiered, testing, is expected to reduce animal numbers, minimize potential pain to laboratory animals by avoiding exposure levels that produce clinical signs of toxicity, and improve the quality of data for assessments of risk to humans (Carmichael et al. 2006). HUMANE ENDPOINTS IN INFECTIOUS DISEASE RESEARCH There has been an increase in infectious disease research as a result of bioterrorism threats and anthrax attacks since September 11, 2001 (Copps 2005; Jaax 2005). Whether the disease agent is of interest for bioterrorism or for human or animal welfare, the study of a targeted disease typically involves exposing healthy research animals to a disease agent that culmi- nates in clinical disease and death. The animals may experience significant pain during these experiments, but identification and validation of earlier endpoints to safeguard animal welfare can be difficult, as an inappropriate endpoint may not adequately identify the full course of a disease or the efficacy of a potential medication (Olfert and Godson 2000). It is impera- tive, therefore, to examine and validate endpoints within a solid scientific framework that includes, among others, immunological parameters, bio- chemical and endocrine changes, and other pathophysiologic changes (e.g., decreased body temperature). Moreover, eliminating death as the endpoint for infectious disease research can benefit not only the laboratory animals but the research itself because pathological changes are easier to identify in
12 HUMANE ENDPOINTS FOR ANIMALS IN PAIN fresh tissues as opposed to autolyzed tissues from animals that have been allowed to die (Copps 2005). HUMANE ENDPOINTS IN VACCINE SAFETY AND POTENCY TESTING Another area of research that frequently results in the death of study animals is vaccine testing for regulatory agencies. Because vaccines are biological products and one batch may not be as potent as the next or may contain harmful byproducts, it is important to test both their efficacy and safety (Castle 1999; Cussler et al. 1999; Hendriksen 2002). To ensure qual- ity control and the safety of each batch, regulatory agencies such as the US Food and Drug Administration (FDA), the US Department of Agriculture (USDA), the European Pharmacopoeia, and the World Health Organiza- tion (WHO) require potency testing during which animals are vaccinated and then exposed to the virulent disease agent. However, the endpoint for each potency test is not consistent across disease agents. In some instances, regulations require that a certain percentage of control animals die before a test is considered valid, while other tests are based on the survival of the vaccinated animals. For example, the FDA-administered safety test for general biological products requires vaccination of healthy guinea pigs and mice with a small dose of the final product from each vaccine lot (CFR 2008, 610.11). A safety test is considered unsatisfactory if the animals do not survive the 7-day test period, in which case additional safety tests over a larger test population are required. The USDA-mandated potency testing for Leptospira pomona bacterin (CFR 2006, 113.101) requires that at least eight of ten unvaccinated control animals die in order to validate the test. Other potency testing may require a comparison of death rates in the vac- cinated versus control animals, as, for example, in the USDA safety test for Marekâs disease vaccine (CFR 2006, 113.330). For this type of testing a more humane endpoint would be the onset of clinical signs in unvac- cinated controls; thus for example the potency test for tetanus antitoxin is met when unvaccinated control guinea pigs are unable to stand within 24 hours postchallenge, at which point the animals may be euthanized (CFR 2006, 113.451). Regulations may also encourage the use of in vitro methods. The USDA canine distemper killed virus vaccine potency test (CFR 2006, 113.201) accepts serum titer levels in vaccinated animals for potency data; if, how- ever, the tests are inconclusive, a viral challenge test is required, using both vaccinated and unvaccinated controls. The agency identifies the survival of all vaccinated animals and the death of all controls as a satisfactory indica- tor of both the safety and efficacy of a canine distemper vaccine batch. While lethality may be the easier endpoint because of its objectivity and simplicity (Cussler et al. 1999), it is always worthwhile to identify reliable
130 RECOGNITION AND ALLEVIATION OF PAIN IN LABORATORY ANIMALS markers of predictive or impending mortality to serve as alternative and more humane endpoints. No purpose is served when the administration of a vaccine results in harm rather than protection but, as with all research stud- ies and testing guidelines, there must be a balance between effective safety evaluation and humane endpoints for the sake of the laboratory animal. HUMANE ENDPOINTS IN CANCER RESEARCH Identification of humane endpoints in cancer research can be chal- lenging. Although the wide range of tumor types and scientific objectives associated with this research prohibits standardization of humane endpoints (Wallace 1999, 2000), the United Kingdom Coordinating Committee on Cancer Research (UKCCCR) has developed a document to guide researchers working with animal models (UKCCCR 1988). Investigators should evalu- ate tumor size, tumor appearance, and animal condition to identify reliable indicators that may permit earlier termination of a study, and establish and validate endpoints that retain scientific objectives and avoid, minimize, or alleviate potential pain in the laboratory animals. Avoiding death or exces- sive tumor burden, particularly when coupled with clinical signs of pain or distress, should be a desirable goal in cancer research studies. HUMANE ENDPOINTS IN PAIN RESEARCH Of critical importance to this report, as well as to improvements in qual- ity of life for both humans and animals, is research on pain itself, including the mechanisms of pain and methods of pain alleviation. Complicating the ethical issues inherent in producing pain in research subjects is the ability to accurately predict and measure pain responses in animals (Le Bars et al. 2001; Meyerson and Linderoth 2006; Walker et al. 1999). It is imperative for pain investigators to establish endpoints in each study design to minimize the duration and intensity of the pain and to validate those endpoints for the integrity, objectivity, and reproducibility of the study. Productive dialogue between the IACUC and researcher is critical for ensuring the best outcome for both the animalsâ welfare and the study objectives in these research programs (Mench 1999). EUTHANASIA Euthanasia, the act of inducing death without pain, is an acceptable method for relieving or alleviating pain that cannot be controlled by other means (NRC 1992, pp. 102-104). The humane death of an animal is one in which the animal is first rendered unconscious, and thus insensitive to pain, as rapidly as possible and with a minimum of fear and anxiety. A
131 HUMANE ENDPOINTS FOR ANIMALS IN PAIN humane death, or endpoint, is a fundamental tenet of the US Principles for the Utilization and Care of Vertebrate Animals Used in Testing, Research, and Training (IRAC 2001), as Principle VI states that â[a]nimals that would otherwise suffer severe or chronic pain that cannot be relieved should be painlessly killed at the end of the procedure or, if appropriate, during the procedure.â There is no rigidly defined point at which euthanasia should be per- formed for humane reasons, as it is not possible to apply a single set of euthanasia criteria across all study designs, animal models, and experimen- tal goals. The decision should involve a team approach among veterinarians, study directors, and animal care personnel using all available information about the affected animal(s). Body condition scores, as described in Chap- ter 3, can be used to determine when to consider euthanasia for humane reasons. The earliest possible indicators for euthanasia should be clearly identified so as to avoid pain and yet still achieve study objectives. Methods of euthanasia have recently been updated by the American Veterinary Medical Association (AVMA 2007), although objective informa- tion on laboratory animals is sparse, particularly concerning the evaluation of potential pain and distress that may be caused by a particular euthanasia technique. The controversy that may result from this lack of data is evi- dent in the recent discussions about the use of carbon dioxide on rodents (ACLAM 2005; AVMA 2007; Conlee et al. 2005; Hawkins et al. 2006; Kirkden et al. 2008; Niel et al. 2008; NRC 2003; Stephens et al. 2002). As conversations on this subject will likely continue, the reader is encouraged to follow the published literature for the most up-to-date information. For all these reasons, well-designed objective studies of euthanasia across all laboratory animal species and age groups are needed and rec- ommended. The assessment tools and measures to consider for such stud- ies include electroencephalograms, electrocardiograms, electromyograms, arterial blood pressure, respiration and heart rates, serum biochemical parameters, pupil diameter, and behavioral changes. In particular, there is an urgent need for studies that provide measures of nociception, pain, distress, and the relation of these to loss of consciousness. CONCLUSIONS AND RECOMMENDATIONS Avoiding or minimizing pain in animal research is a fundamental obli- gation of all researchers for moral and ethical reasons. The criteria for early termination of a research project or alteration to a study design for the purpose of alleviating or avoiding pain in an animal are defined as humane endpoints. Identification and validation of humane endpoints should be considered for studies involving pain, but this is neither an easy nor a simple process.
132 RECOGNITION AND ALLEVIATION OF PAIN IN LABORATORY ANIMALS 1. It is important to ensure that endpoints are validated and based on sound science. Pilot studies are invaluable for the determination of earlier and more humane endpoints. 2. Given the wide scope of procedures and goals of animal research, no single reference can document every humane endpoint for every research protocol. Therefore, more effort must be made to identify appropriate humane endpoints for each. Good communication between researchers, veterinary staff, animal care staff, and the IACUC is crucial. 3. Productive strides have been made in the harmonization of safety assessment guidelines between countries but global harmonization is not yet complete. For global acceptance of humane endpoints in safety assessment test guidelines, dialogue should continue between all countries and agencies responsible for animal welfare, the environment, and human safety. 4. Efforts should continue in the development and validation of alter- native procedures for incorporation in research projects and safety assessment tests to avoid or alleviate pain in laboratory animals. Hendriksen and Morton (1999) observed that the goal of developing humane endpoints in animal experiments is constantly shifting. All scien- tists, managers, technicians, oversight committees, and regulators involved with animal experimentation where pain is a potential component should participate in regular communication and creative problem solving. The criteria for determining the humane end to a study should be frequently reevaluated and revised as new information becomes available. The sus- tained pursuit of these directed efforts can, and will, result in more humane animal use.
133 HUMANE ENDPOINTS FOR ANIMALS IN PAIN ADDENDUM As stated in this chapter, the establishment of surrogate or humane endpoints as part of the experimental protocol and before experiments com- mence is one of the ways to minimize and alleviate pain and safeguard the well-being and welfare of laboratory animals. In support of this goal, two sample resources are provided for adaptation and use. The first is a score sheet to assess animals in cancer studies based on a behavioral and tumor scoring system (Table 5A-1). The recorded symptomatology will determine the diagnosis and measures for alleviation. The sheet can be adapted to any protocol or animal care facility system as long as the behavioral definitions are uniform across the same facility. The second resource is a model for developing guidelines for humane endpoints that may be suitable for any protocol within a facility (Box 5A-1).
TABLE 5A-1 Sample Tumor Scoring Sheet 134 Calendar days SECTION A LESION/TUMOR CHARACTERISTICS Score MOUSE ID Study No. Group No. Dr y scab/crust forming coherent covering with skin 0 Acute burst releasing fluid/pus OR acute split at border 1 Chronically wet/weeping scab/crust OR solid yellow matter exposed 2 Bleeding or raw tissue exposed or white basal layer exposed 3 BEHAVIORAL CHANGES 0 No changes (i.e., normal) Repeated grooming (tumor may not be easily visible or quite small) 1 Abnormal gait (tumor may not be easily visible or quite small) 1 Locomotion impeded (tumor is pronounced) 2 Recurrent scratching/biting of tumor 3 Nociception (struggling/sqeaking) on touching tumor 3 IF YOU HAVE SCORED ANY 3s IN SECTION A, CULL TODAY. IF YOU HAVE SCORED ANY 2s IN SECTION A, REFER TO SECTION B, ELSE GO TO SECTION C. # D1/D2** SECTION B SIZE/PROGRESSION OF LESION (expressed in orthogonal diameters**) 0 Shrinking 1 Static 2 2-3 mm growing 3 3-5 mm growing 4 5+ mm growing SIZE/PROGRESSION OF TUMOR 0 Shrinking 1 Static 2 10-12 mm growing 4 12-14 mm growing 6 14+ mm growing (mean D1/D2 or D1 or either > 17 mm) TOTAL FOR SECTION A + SECTION B **# D1 and D2 are or thogonal diameters IF THE TOTAL FOR SECTIONS A + B IS 6, CULL WITHIN 1 DAY. IF 4-5 MONITOR DAILY, CULL WITHIN 1 WEEK IF NO IMPROVEMENT. ELSE GO TO SECTION C SECTION C KEEP MONITORING AS REQUIRED (DAILY) Date Adapted with permission from a scoring sheet developed by Fraser Darling, The Institute of Cancer Research, London, UK.
13 HUMANE ENDPOINTS FOR ANIMALS IN PAIN BOX 5A-1 Guidelines for Humane Endpoints in Animal Studiesa PURPOSE: To assure compliance with the Animal Welfare Act (AWA), the Guide for the Care and Use of Laboratory Animals (the âGuideâ) and (institutionally relevant) policies, as well as to promote good research. This policy describes the responsibilities and procedures that investigators and veterinary staff must follow when determining appropriate, humane endpoints. PRINCIPLES: It is the responsibility of the Principal Investigator/Study Director (PI/SD) to define humane endpoints and to explore alternatives to death as an endpoint. If no alternative exists, the PI/SD must scientifically justify the use of death as an endpoint, and outline procedures that will be taken to minimize pain and distress to the animal. Efforts must be made to minimize pain and distress experienced by animals used in research. This policy letter is to provide investigators with guidelines for deter- mining humane endpoints in compliance with the XXXXXX policy. To this end, the use of death as an endpoint to experimental studies, rather than performing eutha- nasia to humanely terminate an animal, is discouraged and must be justified. Each Animal Use Protocol (AUP), especially those that are anticipated to result in severe or chronic pain, should describe endpoint(s) and specify a plan and criteria for removal/euthanasia of animals from the study, or the disposition of animals at the termination of the study. For many studies, the endpoint will be euthanasia upon study completion, euthanasia at certain time points, or the return of animals to stock. For studies where moderate to severe clinical signs can be anticipated, the endpoint description in the AUP shall include identification of personnel re- sponsible for decision making, specific criteria (body weight, mass size, appetite, etc.) that will be monitored at prescribed frequencies (daily, weekly, etc), and a disposition (treatment, euthanasia, early removal from study, etc.) once those criteria have been met or exceeded. SCOPE: This policy covers any animal used for research. POLICY STATEMENT: Animal studies may involve procedures that cause severe clinical signs or morbidity, and investigators must consider the selection of the most appropriate endpoint(s) for their study. This requires careful consideration of the scientific objectives of the study, the expected and possible adverse effects the research animals may experience, the most likely time course and progression of those adverse effects, and the earliest most predictive indicators of present or impending adverse effects. Prior to the initiation of the study, the PI/SD should determine the criteria that would lead to termination of the study for any animal, when appropriate, and the method of euthanasia to be employed. A clear chain of command for the decision-making process should be documented, including contingency plans if said individuals are unavailable for consultation. Optimally, studies are terminated when animals begin to exhibit severe clinical signs if this endpoint is compatible with meeting the research objectives. Such endpoints are preferable to death or moribundity (defined by the IACUC as imminent death) as endpoints since they minimize pain and distress.
136 RECOGNITION AND ALLEVIATION OF PAIN IN LABORATORY ANIMALS There must be scientific justification in the AUP for allowing an animal to die without intervention if the goals of a study can be accomplished by euthanizing animals before they become moribund. Animals involved in experiments that may lead to moribundity or death must be monitored daily (including weekends) by personnel experienced in recognizing signs of morbidity. Once severe clinical signs develop, more frequent observation (2-3 times daily) may be required. The following conditions usually necessitate euthanasia. The PI/SD must provide scientific justification for exemptions: Rapid weight loss of â¥20% of body weight. â¢ â¢ Extended period of weight loss, progressing to emaciated state. â¢ Surgical complications unresponsive to medical intervention. â¢ Combination of the following: poor physical appearance (very rough hair coat, abnormal posture, grunting on exhalation); abnormal behavior (reduced mobil- ity/unconsciousness, unsolicited vocalizations, self-mutilation); severe depres- sion or abnormal/exaggerated responses to external stimuli. â¢ Severe respiratory distress, which is unresponsive to treatment. â¢ Occurrence of a serious injury or trauma from which recovery is unlikely. â¢ Neurological signs (e.g., persistent convulsions, persistent circling, paresis/ paralysis) that interfere with eating and drinking and from which recovery is unlikely. â¢ Frank bleeding from any orifice, which is unresponsive to treatment. â¢ One or more skin ulcers that do not heal, depending upon the species and severity of the ulcers. â¢ Mass size or location that interferes with normal function or ulcerates with no evidence of healing. â¢ A mass that is greater than 15% of normal body weight. For chronic toxicology studies (e.g., 2-year carcinogenicity studies), it is necessary to rely on experi- ence and good judgment when deciding when to euthanize an animal as a result of one or more masses. Many of these masses grow slowly and do not compromise the animal. RESPONSIBILITY: The PI/SD is responsible for ensuring that this IACUC policy is followed. Exceptions to this policy must be scientifically justified and approved by the IACUC before they can be implemented. The IACUC has the authority, mandated by law (7 U.S. Code Section 2131 et seq.), to act on behalf of the head of the institution to investigate and if neces- sary suspend any activity which violates applicable laws, regulations, standards, guidelines, policies and procedures. REFERENCES Montgomery CA. 1990. Oncologic and toxicologic research: Alleviation and control of pain and distress in laboratory animals. Canc Bull 42(4):230-237. Stokes WS. 2002. Humane endpoints for laboratory animals used in regulatory testing. ILAR J 43(Suppl):S31-S38. aExample of an IACUC Humane Endpoints Policy Letter, developed by Maryfrances Lutz, Cecilia Pate, and Gaye Ruble, sanofi-aventis US.
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