For the first time, researchers have succeeded in growing thyroid mini-organs in the laboratory.
A study published March 11 in Stem Cell Reports describes how the team used a patient's own healthy tissue to recreate thyroid glands and then transplant them into mice. It provides evidence that the re-engineered thyroid gland mini-organs can effectively grow in a mouse and treat an underactive thyroid gland, or hypothyroidism, potentially paving the way for new treatment routes for this common condition and several others.
The findings also coincide with mounting evidence on the existence of thyroid stem cells in adult mice and humans. A specific thyroid stem cell marker has yet to be discovered, which is partly what signaled an opportunity for the team to fill in the gap in stem cell research. A transplant of a thyroid gland can resemble that of a kidney. There are two thyroid lobes.
However, pointing to small belt-like regions, this study notes the discovery that a thyroid stem cell marker, the tight-junction marker known as ZO-1, was expressed in both mouse and human organoids, "indicating that these organoids are able to maintain and/or redevelop thyroid epithelium integrity." This was reportedly the first tight-junction protein to be cloned and has been implicated as an important scaffold protein.
Study author Rob Coppes, a professor of radiotherapy with a focus on the radiation biology of tissue at the Netherlands' University Medical Center Groningen, told The Academic Times that this new study, "where you actually grow organs in a different place in the body and not in the same situation where it normally is, is a first-of-its-kind."
The idea to use patient tissue and build mini-thyroids to transplant in living mice speaks to similar work in stem cell research that examined other organs in other living animals such as rats and ferrets in recent years. Previously, researchers replaced a piece of gut tissue and also experimented with the salivary gland. But work on re-engineering such organs in the lab using patient tissue is scarce, with the liver and pancreas being exceptions.
"We have to improve it," Coppes acknowledged of the transplant method. "It still has to be optimized, and you have to make it safe for patients, but it's a nice proof of principle that this could be possible in the future."
The team additionally looked to fill in a gap in hypothyroidism research, as the condition is increasingly prevalent worldwide and poses a range of treatment issues. Besides costly medications with sometimes severe side effects, there are no treatments for hypothyroidism, let alone organ transplantations. Potential therapies that could emerge thanks to the new findings range from hypothyroidism and hyperthyroidism to thyroid cancer and thyroidectomy.
A healthy thyroid gland secretes hormones essential for developing tissues in the body, including the brain, skeletal muscles and bones. These hormones are needed for processes related to metabolism, regulating tissue maintenance and heat production.
For their study, the researchers digested the thyroid glands from three mice and then they digested healthy human thyroid gland tissue, with the dispersed cells directly seeded into Matrigel, a gelatinous protein mixture resembling the complex extracellular environment. The team mechanically and enzymatically digested mouse, or murine, and human thyroid gland tissue, then did immunostaining using paraffin-embedded sections. For transplantation, 600,000 organoid cells were dispersed underneath the kidney capsule, the sheath covering the kidney's outer surface, of a hypothyroid mouse.
The gland's major cell type — thyroid follicular cells, otherwise known as thyroid epithelial cells or thyrocytes — produces and secretes the thyroid hormones thyroxine, or T4, and triiodothyronine, T3. Mouse embryonic stem cells, and mouse and human-induced pluripotent stem cells, can differentiate themselves into T4-producing thyrocyte-like cells in vitro and in vivo.
The murine and human thyroid organoids described in the study contained cells with growing potential of self-renewal and differentiation, which form functional hormone-producing thyroid follicles when transplanted into hypothyroid mice. This resulted in the proof of principle that thyroid organoid-derived cells can form functional T4-producing follicles.
Regenerating a thyroid gland derived from embryonic stem cells and induced pluripotent stem cells is "hampered by ethical and practical difficulties," the authors note, adding that stem cells derived from autologous adult tissue "could circumvent these issues."
Hypothyroidism, where underactive thyroids do not secrete enough of certain essential hormones, is a common condition that affects about one in 300 Americans. Globally, it is among the most common diseases and becomes more prevalent with age. Gender and genetic predisposition are driving factors of the condition, which increases the risk of cardiovascular, metabolic, depressive and anxiety disorders.
The condition requires varying dosages of a thyroid hormone replacement therapy consisting of levothyroxine, which was the fourth-most prescribed drug in the nation in August 2020, according to GoodRx, with Lipitor for high cholesterol, Lisinopril for high blood pressure and Albuterol for a potentially life-threatening airway construction called bronchospasm topping the list.
Levothyroxine, brand name Synthroid, must be ingested every day while fasting for a patient's entire life. Issues with this treatment range from the dosage potentially being incorrect to various side effects, including sleep and memory problems, changes in appetite and hair loss. More severe side effects can include heart problems, chest pains and a decreased bone mineral density, which in turn causes decreases in height and bones that can easily fracture.
"For the patients suffering from severe side effects, there is an unmet need for the development of a stem cell-based therapy considering the large number of patients affected by hypothyroidism," the authors wrote. But obstacles remain, including "a persistent autoimmunity, the period of thyroid hormone-suppressive therapy in the first phase of cancer treatment and the security of organoids that harbor occult cancer cells."
Organ transplantation procedures are known to be more expensive than per-supply costs, but long-term cost savings associated with potential thyroid gland transplants are evident.
With continuing debate around the effectiveness of levothyroxine and Synthroid, there is medical consensus that patients cannot freely switch between the generic and brand name versions. Yet GoodRx reported Synthroid as one of the most expensive drugs in the U.S., following a 2017 analysis by the American health care company on why it was the most prescribed drug in the U.S. in 2016.
Synthroid can leave a dent in a person's pocket, costing upward of $100 for a 90-day supply, meaning each patient must pay around $500 yearly for this life-sustaining medication to supplement the body's T4 hormone.
"Moreover, in the past few years, the number of [levothyroxine] prescriptions has been increasing, with a growth of 23 million additional prescriptions in the United States, and 10 million in the United Kingdom, between 2007 and 2014," the authors wrote. "It is obvious that children need perfect dose delivery to support neurological development and growth, but 10% to 15% of the adult patients undergoing thyroid hormone replacement therapy also suffer from persistent complaints related to their treatment."
The many symptoms of hypothyroidism, such as feeling perpetually cold and an increased risk of infection, come back and sometimes even worsen with additional symptoms such as protruding eyes and debilitating weight loss, if and when patients skip their daily prescribed dose of Synthroid. But the jury is out on whether the hormone replacement therapy is sufficient for treating the condition. Some have advocated for leveraging the medication while managing psychosocial factors, also.
Last year, the Endocrine Society reported a 60% year-over-year spike in the risk of death in adults who used levothyroxine compared with those who had not.
Noting that, "A form of regenerative medicine to restore normal thyroid function might be an attractive alternative to drug treatment," the study's main finding confirms that growing an organ using a patient's own tissue works, in principle. To reach it, the researchers obtained a piece of tissue from the medical center's operation chamber.
"We collected it almost immediately after an operation and then ran to the lab and dissected the whole tissue into a single cell or a couple of cells," Coppes explained. "Then we grew the cells in a 3D matrix."
The team created an extracellular matrix, which in biology refers to a 3D network consisting of macromolecules and minerals such as collagen, enzymes and others, that are situated outside the cells but provide structural and biochemical support to the surrounding cells.
The team's argument for using the study as evidence for further exploring the potential of reengineered thyroid glands is twofold. First, the study shows that thyroid-lineage-specific cells can form organoids that are capable of self-renewal and differentiation into functional thyroid tissue. Second, miniature gland formation was possible in subsequent transplantation of the mini-organoids into mice.
"We grew that [thyroid gland] similar to how this grows in humans, but in mice," Coppes noted. "You see a tiny thyroid gland forming there, and it actually secretes some of the thyroid hormones."
"That was very surprising," he continued, adding that the gland's secretion of human hormones "looks very promising."
Coppes would like to see the methods used for transplanting the re-engineered mini-thyroid organoids move forward to the clinical setting, noting that they first need to be refined.
"That's something that we also have to do, and that may take some time. But we already have some experience with salivary glands, and that helps," Coppes said. "So we hope to speed up that process a little bit."
He pointed to a clinical trial already underway on the salivary gland demonstrating the same procedure, noting that similar findings will be unveiled in the upcoming weeks: "With this knowledge, we can probably proceed a bit quicker with the thyroid gland."
The study, "Generation and Differentiation of Adult Tissue-Derived Human Thyroid Organoids," published March 11 in Stem Cell Reports, was authored by Vivian Ogundipe, Andries Groen, Nynke Hosper, Peter Nagle, Julia Hess, Hette Faber, Anne Jellema, Mirjam Baanstra, Thera Links, Kristian Unger, John Plukker and Rob Coppes, University of Groningen.