University researchers have taken a major step toward what some consider to be the next frontier in medical advancements: regenerative medicine or the repair and replacement of diseased or otherwise troubled tissues and organs.
This time, using embryonic stem cells, scientists have come closer to being able to create functional parathyroid cells as the basis for future parathyroid gland transplants.
Located in the neck next to the thyroid are four pea-sized parathyroid glands, which are important to the regulation of calcium levels within bones. For some patients, these glands may be inadvertently damaged during the course of a thyroid surgery, resulting in long-term bone weakening or loss.
Dr. Gerard Doherty, chief of endocrine surgery and the lead researcher for the project, said that he and his team used stem cells to form differentiated cells. These cells are capable of producing an important chemical messenger — parathyroid hormone or PTH — that directs other cells called osteoclasts to break down and remodel bones.
Decreased PTH levels in the body can lead to a condition where bones soften, resulting in muscle weakness and bone frailty, referred to as osteomalacia.
“By using molecular markers to change the way treatment is done, we have come up with a way to take undifferentiated embryonic stem cells and make them develop into parathyroid-like cells,” Doherty said.
Doherty said the results of the study hold promise for the foreseeable future — not just for parathyroid replacement but for regenerative medicine as a whole.
Using biological parts over prosthetic ones in medical practice, he said, has the advantage of minimizing patient rejection of transplants.
“If we can get to the long-term goal of making replacement parts for people, then regenerative medicine will be the next frontier in medical practice,” Doherty said.
The development comes within a year of two major legal milestones for researchers working with stem cells.
In November 2008, Michigan voters passed a constitutional amendment allowing researchers to develop their own stem cell lines.
Then, last March, President Barack Obama reversed an executive order signed by President George W. Bush in 2001 that limited federal funding for stem cell research.
Doherty’s team relied on one of the 60 embryonic stem cell lines approved by the Bush administration.
The next step in the project, he said, would be to circumvent the use of embryonic stem cells altogether and use each patient’s own cells.
Doherty, a Norman W. Thompson Professor of endocrine surgery at the University’s Medical School, said that differentiated cells within the thymus — an organ critical to the immune system — are an attractive option to cultivate parathyroid cells for transplants.
“We like to start with cells which are as close to the end point as we can, so we can do as few steps in the Petri dish as possible,” he said. “Some cells within the thymus express markers similar to parathyroid cells.”
Clinical application of this laboratory success may not be too far away, Doherty said.
Transplantation of parathyroid cells from their normal position in the neck to other places in the body has been successful in the past. The function of the parathyroid glands, he said, is preserved within each of its cells, reducing the number of challenges of complete organ replacement.
“I would anticipate that, over the next couple of years, we could potentially make this work in animals,” said Doherty. “For people, it’s five to 10 years away.”