I am a post-doctoral researcher. I am also a Doctor of Veterinary Medicine which explains why I like to work on research projects involving animal models. This type of research continues to draw criticism and to generate debate. I hope that the following will shed some light on certain aspects of scientific research which uses animal models in academia.
A few models
Mice are often thought of as the research model of choice, but we shouldn’t forget invertebrates, such as the fruit fly or Drosophila, or the Caenorhabditis elegans (pronounced “Saynorabditis elegance”), a small roundworm better known in our field by its nickname, C. elegans. These models provide a number of benefits over vertebrates. To begin with, husbandry of these models under laboratory conditions is easy and inexpensive. Their life cycle is short and can also be genetically modified in numerous ways. And, unlike when vertebrates are involved, there are no ethical rules governing the use of the Drosophila or C. elegans.
Even if human beings and Drosophila or worms don’t seem to have much in common, it has been well established that most of the fundamental biological mechanisms as well as the pathways controlling development and survival are preserved throughout species evolution.
Thomas Hunt Morgan refined the theory of inheritance first put forward by Gregor Mendel thanks to his research on the Drosophila. He introduced the concept of the gene and showed that these genes were located on the chromosomes, which earned him the Nobel Prize in Physiology or Medicine in 1933.
C. elegans was the study model used by Robert Horvitz and Sydney Brenner, recipients of the 2002 Nobel Prize in Physiology or Medicine for the discovery of programmed cell death regulated by genes, also known as apoptosis.
These are but two historical examples which demonstrate the value of these models, still widely used today.
But let’s get back to mice. It is true that the mouse remains the model par excellence as far as vertebrates are concerned: 1.4 million mice were used in Canada in 2015 for research and teaching purposes, in tests or for production (of animals or biological products). Among the 3.5 million animals (vertebrates) used for research are fish (1.2 million), livestock (pigs, sheep, cows…), rats, birds, amphibians, dogs, cats and primates. Dogs, cats and primates add up, overall, to fewer than 1% of all animals used.
We share almost 90% of our genetic makeup, as well as considerable physiological similarities, with mice. The mouse is a model of choice to study the genetics of mammals and is a valuable tool when studying immune, nervous and cardiovascular systems and other complex systems common to all mammals. Illnesses such as cancer, atherosclerosis, hypertension or diabetes develop naturally in mice, as they do in human beings. Other illnesses which affect humans do not develop in mice but can be induced by manipulating either a genome or the mouse’s environment so as to make it a study model, in cases such as Alzheimer’s disease for instance.
Pure strains of mice were developed under different code names: C57Bl6, Balbc, C3H… In a group of pure-strain mice, the various individuals are genetically similar, which helps minimize biological variations. The mouse genome can be modified to remove a gene (the knock-out mouse), add a gene (the transgenic mouse) or replace a gene by its specifically altered version (the knock-in mouse). We can even decide in which organ to silence a gene or to overexpress it, or even to regulate its expression throughout the mouse’s life, which makes it a very powerful tool. Thousands of mouse lines have thus been created and many are commercially available.
For all these reasons, mice are a particularly attractive model for academic research, as do their relatively low husbandry costs as well as their ability to reproduce quickly. This model has led to countless discoveries and, in many cases, Nobel Prizes.
Compliance with regulations
The use of vertebrates or superior invertebrates (an octopus, for instance) in academic research is subject to Canadian Council on Animal Care (CCAC) regulations. It is the national organization responsible for setting, maintaining, and overseeing the implementation of high standards for animal ethics and care in science throughout Canada.
More specifically, in a public research centre, each protocol involving sentient animals must be submitted to a local ethics committee (the CDEA – Animal Experimentation Ethic Committee – at the Université de Montréal), which represents the CCAC, for approval. A committee of experts, which includes a veterinarian and a community representative, studies the project and its experimental procedures. For each protocol, the research team and the committee work towards the implementation of the Three Rs: Replacement, Reduction and Refinement. Replacement refers to methods used to avoid or replace the use of animals in fields where they are commonly used. Reduction refers to all the strategies that bring about a reduction of the number of animals used. The goal of these two Rs is to minimize the number of animals needed to reach scientific results. Refinement refers to the modification of husbandry or experimental procedures so as to keep pain and animal distress at a minimum. Refinement also provides the means to supplement the living environment of the animals by taking into consideration their psychological needs, by providing for instance nest material to species whose natural behaviour involves nest building.
The stress, pain and distress are measured and classified in 4 categories:
- None: experiments cause little or no discomfort or stress.
- Low: experiments cause a minimal level of stress or pain over a short period of time.
- Moderate: experiments cause moderate to severe levels of discomfort or distress.
- Severe: the procedures cause severe pain near or at the pain tolerance threshold of unanesthetized conscious animals.
Protocol classification is based on each animal. Thus, if a study involves administering animals with various doses of a compound, the protocol will be categorized according to the compound’s effects on the group of animals which received the highest dose.
In 2015, 31% of protocols were in the “none” category, 37% in the “low” category, 29% in the “moderate” category, and 2% were identified as “severe”. To receive approval, any protocol recognized as generating potential pain or distress will be reviewed to allow the inclusion of measures to reduce animal suffering and establish restrictive intervention criteria called endpoints.
Allow me to illustrate what this means. Take, for instance, a classic cancer research protocol which involves injecting tumoral cells under the skin of a mouse’s flanks so as to form a tumour. Scientists can manipulate the genes of these cells to better understand their effect within the cancer or test the chemical compounds which may cause the tumour’s regression. In this model, a maximum tumour volume is introduced; it has been ascertained that beyond this volume, it would interfere with the mouse’s normal behaviour and lead to some distress for the animal. An ulceration of the tumour mass is a second endpoint. These 2 criteria supplement other endpoints which signal the mouse’s distress such as, for instance, a more than 10% weight loss, signs of dehydration or an arched back. All these endpoints indicate when the experiment must come to an end to avoid all animal suffering.
These experimental protocols must be re-examined yearly to check on the project’s progression and assess if it can be improved through any additional Three R strategies. Furthermore, all employees dealing with the animals have received a special training regarding the use of research animals. This training covers ethical and technical (how to handle a mouse or give an injection for instance) aspects. Finally, facilities undergo a CCAC assessment so as to evaluate the program as well as the standards of care and use of the animals.
Compliance with these standards is especially important in academic research since all institutions using animals for research must hold a valid CCAC certificate in order to secure a grant at the federal level in Canada (through the Canadian Institutes of Health Research, or CIHR, and the Natural Sciences and Engineering Research Council of Canada, or NSERC).
Advances in medical science
We must keep in mind that the different models outlined here are only models. The perfect model does not exist. Human beings, for ethical reasons that everyone understands, cannot be considered as guinea pigs for research. We must have a proper understanding of the strengths and weaknesses of each model in order to choose the one best suited for each study. When reviewing the list of Nobel Prizes in Medicine and the contribution of animal models to studies related to the aforementioned prizes, there is little doubt that these tools are essential to academic research and that they too will lead to many more advances in the medical field.
Barbara H. Jennings, Drosophila – a versatile model in biology & medicine, Materials Today, 2011, 14(5), 190-195
2015 Animal Data Report: http://www.ccac.ca/Documents/AUD/2015-Animal-Data-Report.pdf
Mouse as a Model Organism: https://www.genome.gov/10005834/background-on-mouse-as-a-model-organism/
Three Rs Microsite: http://3rs.ccac.ca/en/about/
Animal models associated to Nobel Prizes: https://fbresearch.org/medical-advances/nobel-prizes/.
Sylvain Meloche laboratory