Animal models are non-human species that can be applied to reproduce the disease, diagnosis, and treatment progression that occurs in humans. Animal models are a fundamental tool in biomedical research and have many applications and advantages. However, many scientists are considering shifting to the newly developed three-dimensional technologies which allow the implementation of the 3R principle: Reducing, Refining, and Replacing animal experiments. Keeping in mind the ethical issues animal experiments have, many countries, including the Countries of the European Union, Israel, India, Brazil, South Korea, and Turkey have adopted a full or partial ban on animal testing in the context of cosmesis. This article summarizes the problems of animal models (1).
Animals are not small humans
Different animals have similarities in basic biological processes and anatomy but they show major differences as well. For instance, to study the effect of a certain chemical substance on an animal, chemical exposure is assessed based on how the chemical is Absorbed (A), Distributed (D), Metabolized (M), and Eliminated (E) from the body. The ADME process varies immensely from one species to another. For example, the skin of rats and mice absorbs chemicals much faster than the skin of humans (2).
Ethical problems with animal models
The use of animals in research is very controversial as they may suffer during experiments. Animals in laboratories are frequently treated as objects and little value is ascribed to their lives beyond the cost of their purchase. An appropriate justification is thus required, to prove that the results of the research outweigh the sufferings imposed on the animals. Many countries and industries are adopting new technologies to replace animal experiments (3).
Animal models can delay drug discovery
Drugs that fail to show efficacy in animal models are rarely tested in humans. It means that even the procedures and drugs that have the potential to be effective in humans may never be developed if they fail animal testing. For example, Pfizer’s drug Lipitor did not show promising results in early animal tests. However, when it was tested on a small group of human volunteers, Lipitor proved to be successful. It is now widely used to reduce the level of bad cholesterol and helps prevent heart problems (4).
References
1. Mukherjee, P., Roy, S., Ghosh, D. et al. Role of animal models in biomedical research: a review. Lab Anim Res 38, 18 (2022). https://doi.org/10.1186/s42826-022-00128-1
2. Bracken MB. Why animal studies are often poor predictors of human reactions to exposure. J R Soc Med. 2009 Mar;102(3):120-2. doi: 10.1258/jrsm.2008.08k033. PMID: 19297654; PMCID: PMC2746847.
3. Levy N. The use of animal as models: ethical considerations. Int J Stroke. 2012 Jul;7(5):440-2. doi: 10.1111/j.1747-4949.2012.00772.x. PMID: 22712743.
4. Pecoraro V, Moja L, Dall’Olmo L, Cappellini G, Garattini S. Most appropriate animal models to study the efficacy of statins: a systematic review. Eur J Clin Invest. 2014 Sep;44(9):848-71. doi: 10.1111/eci.12304. PMID: 25066257.