Pig Bladder Helps Replace Muscle Lost by Trauma Victims

A scaffold crafted from pig bladder and implanted in patients’ severely injured legs spurred stem cells to make muscle and improve limb function, a method that may change the standard of care.

The technique, which didn’t require adding stem cells developed in the laboratory, improved abilities in three of five patients by at least 25 percent over physical therapy alone, researchers from the University of Pittsburgh said. All five patients, some with battlefield injuries who had lost 58 percent to 90 percent of muscle, reported improvement in quality of life.

The results, described today in the journal Science Translational Medicine, show the approach may be an effective way to restore functioning in victims of accidents, blasts or other traumatic injuries with extensive muscle loss, researchers said. As a stem-cell technique, the method is less fraught with regulatory hurdles and would be less costly than those that involve delivering cells into the body, they said.

“The approach we’ve taken is intended to be type of approach that can be utilized anywhere good surgery is available,” Stephen Badylak, professor of surgery at the University of Pittsburgh and one of the study’s researchers, said during a conference call with reporters.

Muscle, which accounts for more than 40 percent of body mass, is unlike other tissues in that it has the ability to regenerate. Regeneration is difficult when a large volume of muscle is lost in an injury. Current therapies involve removing scar tissue to aid in regeneration or moving muscle tissue from one part of the body to the other.

Biologic Scaffold

In an initial study of rodents, reported today along with results from the five patients, researchers implanted a biologic scaffold, a structure to support new tissue formation. As the scaffold started to degrade, it acted as a homing device for stem cells that became muscle cells. That finding prompted testing the technique in humans.

“One of the specialized populations of cells we identified are called perivascular stem cells; we identified specifically this cell type as participating in remodeling the scaffold,” said Brian Sicari, research assistant professor with Badylak at the University of Pittsburgh’s McGowan Institute for Regenerative Medicine. “What’s unique about these cells is they’re found in all vascularized tissues of the body.”

In each patient, researchers removed scar tissue and inserted a scaffold made from pig bladder. The material was placed adjacent to the remaining healthy muscle so the new growth area would have a blood supply. Cells from the pig tissue’s surface had been cleared to reduce rejection, leaving collagen and structural molecules. Within 24 to 48 hours after the operation, patients were put into aggressive physical therapy.

New Muscle

As the scaffold material degrades, signaling chemicals involved in the process draw stem cells to the wound site, maturing into muscle cells and building healthy, new tissue, researchers said.

Intense physical therapy also proved crucial to the success of the technique, as stem cells come into the site seeking instructions on how to become a muscle cell, researchers said.

“They depend on local and environmental cues,” Badylak said. “One of them is the mechanical forces at the site.”

The study of five men, sponsored by the U.S. Department of Defense, included military and civilian patients. Before the surgery, patients underwent physical therapy until they reached a point where there was no further improvement.

In each case after surgery, muscle regrew and helped to restore normal appearance. Following five to 23 weeks of post-operative surgery, the patients were tested to see if their abilities -- such as walking, going up and down stairs, raising a leg, or getting out of a car -- improved at least 25 percent above their function before the operation.

“We recognize that this is a small number of patients we started with,” Badylak said. “But we are very confident in the results and the science behind it, and look forward to treating additional patients in the future.”

To contact the reporter on this story: Angela Zimm in Boston at azimm@bloomberg.net

To contact the editors responsible for this story: Reg Gale at rgale5@bloomberg.net Andrew Pollack, Bruce Rule

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