Author: Kaitlin Weskamp
Editors: Brittany Dixon, Zuleirys Santana Rodriguez, Scott Barolo
Zebrafish may not look impressive, but they can do something that no human can: regenerate large portions of organs that are damaged or lost. These fish, each about as long as your pinky finger, are able to regrow amputated fins, repair lesioned brains, and mend damaged eyes, spinal cords, and hearts. This remarkable ability to heal has fascinated scientists for some time, and in recent years, large strides have been made towards translating this regenerative ability to humans.
This field, termed regenerative medicine, holds tremendous potential to treat diseases that cannot be cured through medication or surgical intervention. Both the general public and the scientific community are hopeful that this field will provide a solution to currently incurable diseases. However, this excitement has led to exaggerated reports by the media and others who are not familiar with the current limitations of these therapies. In this article, we will first explore the science behind regenerative medicine, and then determine how soon we can expect to heal ourselves like the humble zebrafish.
The key to regeneration, both in zebrafish and humans, is stem cells. The human body is made up of many different types of cells: fibroblasts in your skin, hepatocytes in your liver, and so on. Stem cells, however, have the ability to produce multiple different cell types. Scientists are currently establishing ways to coax these stem cells to reliably become specific cell types, which can then be used to replace lost or damaged tissue.
Stem cell therapies currently break down into two groups: rejuvenation, which uses stem cells to stimulate existing tissue to repair itself, and regeneration, which uses stem cells to rebuild lost or damaged tissue. The vast majority of current stem cell therapies employ the former approach, in which stem cells are harvested from the bone marrow of either the patient or a donor and then reintroduced at the site of injury. These cells do not settle at the injured area and build new tissue; rather, they are thought to secrete chemicals that encourage the damaged tissue to repair itself.
Every drug or therapy intended for human use must undergo rigorous testing to determine if it is both safe and effective, and there are many ongoing clinical trials to determine if stem cells are safe in the treatment of stroke, neurodegenerative disease, diabetes, heart disease, and more. A handful of studies have shown that stem cell therapy is both safe and results in a modest improvement in outcome, but these results are often transient and are largely thought to be a result of the stem cells influencing local inflammation or immune response. There are currently several studies that suggest that the stem cells are truly stimulating regeneration in animal models, but this phenomenon has not been observed in human studies. A great deal more research is needed to determine exactly how these stem cell transplants act in the human body, and how to most effectively use them to treat disease.
While the use of stem cells to treat most diseases remains highly experimental, stem cells are approved to treat a few conditions. Patients with leukemia, a cancer of the blood and bone marrow, often receive chemotherapy or radiation to destroy the uncontrollably dividing cancer cells. Unfortunately, this also severely damages the remaining normal blood-forming cells in the bone marrow. To combat this, patients are often given a stem cell transplant to repopulate the bone marrow with stem cells that were either collected from the patient prior to chemotherapy or from a donor. Additionally, in cases where damage to the skin or cornea is treated by grafting or implanting tissue from a donor, stem cells are frequently used to assist in the healing process. Scientists are working to expand this short list of stem cell applications to other diseases.
Though regenerative medicine is progressing at a rapid rate, it is vitally important to maintain a realistic sense of what it can currently accomplish. Too often, the media presents modest results from clinical trials in a sensational manner, extolling stem cell therapies as a panacea or cure-all. Recently, for-profit clinics cropping up in China, Mexico, and the United States have capitalized on these misleading reports by exploiting seriously sick or injured patients. These clinics charge large sums of money for stem cell transplants, often making unsubstantiated claims about their efficacy and relying on customer testimonials in place of scientific studies. Normally, new drugs and therapeutics must undergo rigorous testing and a series of clinical trials supervised by the Food and Drug Administration (FDA) before they are deemed safe and effective for the human use. These for-profit clinics argue that stem cells harvested from patients do not qualify as a drug, and therefore do not require the approval or oversight of the FDA. As a result, they are providing a service that is ineffective at best, and at worst puts the patient in danger of further physical harm. While not technically illegal, these dubious practices are allowed to operate due to a lack of FDA action in recent years that has created a gray zone in which hundreds of clinics are now operating. New legislation may eventually bring these practices under tighter supervision, but in the meantime it’s essential that patients understand the risks associated with these clinics and be able to distinguish them from science-based therapies.
About the author
Kaitlin is a doctoral student in the Neuroscience Graduate Program at the University of Michigan. Her research focuses on how hyperactive neurons play a role in amyotrophic lateral sclerosis, a neurodegenerative disease that affects the function of nerves and muscles. She holds a degree in biochemistry and molecular biology from Nebraska Wesleyan University, where she also studied mathematics and studio art. Kate spends her free time painting, hiking, cooking, and walking dogs at the local animal shelter.
Zebrafish – By Azul. Own work, Copyrighted free use, https://commons.wikimedia.org/w/index.php?curid=260841