When we think of scientists, we frequently picture them donning white lab coats, handling test tubes, and experimenting on mice. Why mice specifically? Even though animal testing remains an ethically contentious practice, mice fill a crucial role in medical research and the study of human biology. However, mice are not the only non-human organisms that we study extensively to understand biological processes.
What is the value of studying animals instead of humans then? People have been using animals since the Neolithic period (10,000-4,500 BC) to learn more about human anatomy and surgical techniques. We may learn about how these animals work, but how would we make that information useful when they are so different from humans? For various reasons, it is easier to acquire and experiment on certain non-human organisms to study human biological phenomena.
These animals have come to be collectively termed as model organisms. Model organisms such as mice are susceptible to human health problems such as cancer, organ failure and diabetes. Thus, studying how they can be treated can help promote the safety and efficacy of human treatments. However, imprecision, risk of bias, and unregulated ethics can potentially harm humans and expose patients to risks. Let us look briefly at why certain species are selected as model organisms.
Model organisms are usually chosen because they are easy to maintain, manipulate and breed in large numbers. Therefore, they are readily available specimens which are affordable to research. The specimens that are used most are mice, fruit flies, zebrafish, frogs, roundworms and yeast. Because their genetics, physiology, behaviour and developmental patterns resemble ours, findings from studying model organisms can be applied to human beings.
Due to their shorter life cycles, it is easier and faster to study phenomena related to ageing, reproduction, and development in specimens such as mice and fruit flies. The standardised protocol for researching model organisms has made research materials and findings accessible to many scientists. Many significant breakthroughs in medicine are achieved through studying these organisms. Some examples include the development of pregnancy tests, the use of insulin for the treatment of diabetes and the establishment of the link between cholesterol levels and heart disease. Model organisms help scientists understand the mechanisms and pathways underlying diseases, facilitate rare disease diagnoses and the development of drugs and therapeutics.
While model organisms were irreplaceable gateways to biological and clinical research, they are imperfect in predicting certain side effects of some drugs. There are still significant physiological differences between humans and model organisms that we cannot account for even with the best models. For example, mouse physiology doesn’t equal human physiology. Part of their biological systems are different and hence everything discovered based on mice specimens should always be taken with precautions.
Additionally, replicating certain human conditions can raise ethical concerns in terms of animal welfare. For example, scientists may implant the specimens with tumours or induce them with cancer in order to study the genetic basis of cancer progression and tumour development. Such studies can be invasive and could cause pain and distress to the animal subjects. Even though model organisms can imitate certain human conditions, they are often unable to accurately mimic more complex interactions or behaviours due to their physiological differences. Successfully curing cancer in mice doesn’t mean much when the findings do not remotely translate to curing cancer in humans.
As useful as model organisms have been in answering certain questions about our biological processes, certain flaws in the experimentation process can harm us. Imprecise results from such studies may cause biologically faulty or harmful substances to make their way into clinical trials and expose patients to unnecessary risks. In certain drug trials, such as for stroke, hormone replacement therapy and TGN1412, human volunteers and patients have been seriously harmed even though the new drugs were deemed safe and effective in animal trials.
The complexities of the female hormonal cycle and its effects on the body have been cited as the main reasons why female specimens are not ideal subjects for medical studies and clinical trials. In other words, the cyclic and hormonal effects of pre-menstruation, menstruation, and menopause on the female body often complicate medical research. In the same vein, this made female mice undesirable specimens and difficult to work with compared to their male counterparts. Excluding female specimen in research can affect human patients since drug and treatment efficacies are only tested on male bodies. Many drugs and therapeutics developed using model organisms are based on the male specimen become the basis of procedures and treatments which can work against women’s wellness.
Undeniably, the study of model organisms has contributed greatly to our body of knowledge in clinical and biological research. However, the use of model organisms cannot perfectly replicate the human condition and has harmed human patients due their failure to indicate certain side effects in drugs. This begs the question — will model organisms continue to be viable modes of discovery in the future? It seems that the need for model organisms will only decline after most of the fundamental mechanisms of biology have been understood. We do not have enough knowledge to rely on human tissue cultures and in silico methods for drug discovery. Thus, model organisms will likely remain an indispensable tool for researchers to answer the immeasurable number of unresolved questions in biology. It seems like scientists will continue to be associated with white mice for the foreseeable future.
Written by Liaw Jia Xuan
Model Organisms [https://biology.uiowa.edu/model-organisms]
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In Silico Models [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7149665/]
Zebrafish Models of Cancer—New Insights on Modeling Human Cancer in a Non-Mammalian Vertebrate [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6896156/]
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Cholesterol lowering attenuates pressure overload-induced heart failure in mice with mild hypercholesterolemia [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6756886/]