By RONDA WENDLER
Texas Medical Center News
Texas Heart Institute physicians are poised to become the first to use magnets to deliver stem cells to human hearts, pending approval from the Food and Drug Administration.
For nine years, heart institute researchers have been conducting clinical trials during which they inject patients’ failing hearts with stem cells taken from the patients’ own bone marrow. Serving as a sort of repair system for the body, stem cells can develop into the types of cells that surround them, so when placed in the heart stem cells become heart cells. They then divide without limit to replenish other cells in the area that have been damaged.
Thanks to a $1 million grant from the National Institutes of Health, the way these stem cells are delivered, tracked, and held in place in the hearts of Texas Heart Institute patients is about to get safer and more precise.
In a soon-to-commence clinical trial, heart institute physicians will use a catheter guided by magnets to deliver stem cells to patients’ hearts. The Gentle Touch Magnetic Navigation System, as it is called, was developed by Stereotaxis Inc., and has been used for other heart procedures – but never to deliver stem cells.
"We’re very optimistic that this work may allow us to steer stem cells to a desired position and retain them in the heart with an external magnet," said James Willerson, M.D., Texas Heart Institute president and a partner in the stem-cell research. "That would be a major milestone."
Here’s how it works:
The patient lies on a table in the procedure room. Two giant magnets, one on each side of the patient, are mounted on pivoting arms.
The cardiologist inserts a catheter – a long, thin tube tipped with metal and loaded with stem cells, into an artery in the patient’s groin, then snakes the catheter up through the arteries to the heart.
Once the catheter reaches the heart, the cardiologist takes a seat in a control room next to the procedure room. On a computer screen and using special software, the cardiologist maps out each move the catheter will make inside the heart as it delivers stem cells to damaged areas. Using a joystick, the cardiologist executes the mapped-out moves on the computer, and the computer relays the commands to the two magnets on either side of the patient, which twist and pivot in response to the commands.
As the magnets move up, down, and around, the magnetic field changes, pulling the catheter by its metal tip to the damaged areas of the heart with millimeter accuracy. The catheter then deposits a load of stem cells at each destination.
"Instead of controlling the catheter by hand, you control it by computer," said Emerson Perin, M.D., medical director of Texas Heart Institute’s Stem Cell Center and principal investigator on the NIH grant. "This system makes a skilled cardiologist even better."
Prior to the invention of the magnet-guided system, physicians manually manipulated catheters in patients’ hearts. In many hospitals, this is still considered the standard method. The physician stands over a patient and guides the catheter by hand, gently pushing, pulling, twisting and turning.
The standard, manually manipulated catheter is stiff but flexible, and physicians must be ultra-careful to avoid damaging the delicate heart muscle. In rare cases, a stiff catheter can puncture a hole in the heart. While the hole almost always heals by itself, the cardiologist must end the procedure. And in a small minority of such cases, surgery is required to repair the hole.
By contrast, the magnetically guided catheter is soft and flexible, "sort of like a wet noodle," Perin says, "so it’s gentler on the heart."
Furthermore, the magnetically guided catheter can go places the manually guided catheter can’t, navigating into the most remote areas of the heart that before were difficult or even impossible to reach.
"Magnetic navigation is much more precise than manual navigation," Perin said. "It’s all about precision."
40 TIMES MORE EFFECTIVE
But here’s where the story gets even better, thanks to Rice University.
The stem cells slated for delivery to the heart will be covered in nanotubes – tiny carbon tubes that are hollow on the inside, like straws.
Each nanotube will be stuffed with a toxic metal called gadolinium, which today is the most common contrast agent used by radiologists to read MRI images.
"When you have an MRI done and they inject you with dye before your MRI – that’s gadolinium," said Rice chemistry professor Lon Wilson, Ph.D.
It was in Wilson’s lab that the idea was hatched to pack gadolinium inside nanotubes. The nanotubes act like little sealed suitcases, allowing the gadolinium to be delivered in higher concentrations in the patient’s body while protecting the patient from the gadolinium’s toxicity.
The nanotubes packed with gadolinium, dubbed "gadonanotubes," are 40 times more effective than traditional gadolinium contrast agents.
"That means MRI images are 40 times clearer, brighter and easier to read than before," Wilson said.
Gadonanotubes will be attached to the stem cells implanted in the heart in the Texas Heart Institute study, which will cause the stem cells to glow and signal to scientists their location.
"Until now, there hasn’t been an effective way to track the cells within the body after they’re delivered to the heart, and to test their effectiveness while they’re in the heart," said Wilson.
Furthermore, the gadonanotubes make the stem cells highly magnetic, allowing their location to be controlled by an external magnetic field.
"This may help keep the stem cells in a desired place for the several weeks it takes them to differentiate into heart muscle cells and start healing the heart," Perin said.
For information, call 1-866-924-STEM (7836) or visit the institute’s Web site at www.texasheart.org