Reduce, replace, refine—Animal experiments

Abstract

In recent years, most of the manuscripts published as a regular paper in ACTA Physiologica are based on animal experiments. As the mouse is the workhorse of physiological research, most of the papers would not exist without animal experiments. All authors willing to submit manuscripts to ACTA Physiologica are expected to follow the 3R principle to reduce, refine and replace animal experiments.1 Most of the major research funding bodies in Europe require that the projects funded by them take full account of the 3Rs principle. It is a major issue for much of the public who are concerned about animal welfare and the need to avoid causing unnecessary or unjustified suffering. Applying the 3R strategy in physiological research is not without difficulties but it is possible. Physiology is the science of life. It deals with the functions and activities of life or of living matter, such as organs, tissues or cells. The potential for replacing animal experiments depends on the nature and aim of each experiment. Replacing animals in physiological research becomes increasingly difficult when it involves the analysis of physiological processes in organs or the interaction of several organs. Thinking about strategies to reduce, replace or refine animal experiments it is not only to meet ethical and social concerns or legal requirements. Planning experiments along the 3R principle might also be associated with practical and economic gains for the researcher. Therefore, it might be useful to think about experiments, which could be performed in advance of an animal experiment to reduce the number of animals. These experiments might be the use of isolated cells, tissues and whole organs.2 As scientists often have preferred ways of working, changing their approach requires persuasion, increased communication and training in the use of alternatives. However, it is important not to dismiss the concept of reduce, replace and refine animal experiments. The possibility of replacing animals should be a constant consideration throughout the design and conduct of a research program. Simple organisms, such as bacteria, are in most cases not a considerable replacement option to understand physiological processes in mammals. Using computers and mathematics to model biological processes and investigate the molecular dynamics might be helpful.3 Exploring new advanced technologies such as artificial intelligence, molecular techniques, tissue engineering and organ-on-chips should be considered.4, 5 The organ-on-chip technology has been used to model the human lung and to replace animal experiments. It can be utilized to study pulmonary oedema, a deadly condition in which the lungs fill with fluid and blood forms clots and to test potential new drugs.6 Physiology has a long tradition of ex-vivo experiments on whole organs, vessel or organ slices. These are still used in physiological research and deliver excellent research results.7-10 These technologies should be preserved for the future. Some techniques are performed in only one or two groups around the world and the knowledge and skills how they are performed might be forgotten in the near future. There is great scientific value in these techniques and they have a great potential to replace animal experiments. Some effort should be done to combine them with new innovative research techniques like human pluripotent stem cells, transduction with viral vectors, gene editing optogenetics or one of the omics. To reduce animal experiments there is always the option of not doing the experiment at all. Nevertheless, reduction is not `all or nothing`. Replacing parts of the research program, an individual experiment or one type of procedure might be worthwhile to consider. In many of the papers published in ACTA Physiologica this is already done as animal experiments are only one part of the research program. Still, in most cases they are necessary as a proof of principle. In some research fields animals like mice are not the best model for research on human physiology and disease, then replacing them by another model can result in a scientific gain. Animal models of intestinal disease can be poorly predictive of human disease. Recent 3D tissue models of human colonic epithelium have been developed which will improve the mechanistic understanding of human intestinal function.11 The possibility of obtaining the information required through ethical research on human subjects or human tissue should be considered. Humans are usually the best model for other humans. Access to human volunteers or their tissues may prove challenging. There are good examples that physiological research will benefit if one succeeds here. Pallubinky et al analysed the adaptation of the glucose metabolism in overweight humans after passive exposure to heat.12 When it comes to metabolism, the human species is quite unique. Therefore, data collected in studies based on humans have a high scientific value. In exercise research, using volunteers in a study has a long tradition.13 The process of ageing is another good example as it is different in humans compared to rodents. Karlsen et al investigated the influence of exercise on old humans with the interesting outcome that heavy resistance training did not result in muscle hypertrophy in very old individuals.14 These results are outstanding because of the fact that this study was done in humans. This is also underlined by several other studies published in ACTA Physiologica. Hansen et al analysed the effect of reactive oxygen species on hypoxic cerebral vasodilatation in healthy humans.15 A study in healthy volunteers by Haddock et al showed the renal response to furosemide.16 Additionally, studies in patients are useful to understand patho-physiological mechanism.17-19 Therefore, some effort should be made to establish collaborations with clinicians, designing safe experiments in human volunteers or obtain donated human tissue samples. Save imaging techniques like MRI and PET scanning are of great advantage here and these techniques also play an important role in refining animal experiments.20 Nevertheless, it is extremely difficult to eliminate all animal models from physiological research. By using animals for research, we gain knowledge on basic mechanism. Later we can prove these mechanisms in humans.21 Without animal research, these tests in humans would often be considered unsafe. When thinking about reduction or replacement of animal experiments it must be considered that knowledge gained in animal experiments is the basis to create test-systems like organ-on-chip, 3D cell culture or organoids. First, the physiological mechanism of an organ needs to be understood before an artificial organ can be developed, which behaves in a physiologic way. One day, when we have gained a substantial amount of knowledge, we probably do not need animal experiments anymore. Nevertheless, until that day it will be difficult to fully replace animals in physiological research. So far, the society needs to decide, if it allows the performance of animal experiments for the gain of knowledge. However, it is the responsibility of every physiologist to communicate how much knowledge we would miss and what we would lose when the society is not accepting animal experiments for physiological research anymore. There is no conflict of interest to declare.

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