Nov 05, 2002
By ED SUSMAN, UPI Science News
United Press International
Scientists have achieved success in manipulating primitive cells to become nervous system cells, which, in some cases, restored leg function to laboratory animals with spinal cord injuries, they reported Tuesday.
However, they cautioned, translating the promising animal work to people could take years.
"These things are not impossible," said Dr. Mark Tuszynski, associate professor of neuroscience at the University of California, San Diego. "But we are looking at a time frame of several years, if everything goes well -- which it rarely does."
In a series of presentations at the annual meeting of the Society for Neuroscience -- the world's largest organization of researchers and clinicians who study the brain and nervous system -- doctors described how they employed a variety of stem cells therapies to treat laboratory rats with experimental injuries.
Dr. Evan Snyder, assistant professor of neurology at Harvard Medical School in Cambridge, Mass., said when embryonic stem cells were inserted into the injury site, some animals were able to recover from their paralyzing injuries.
"They could support their weight and there was some coordinated movement," Snyder said at the meeting, which attracted about 26,000 scientists. He said the cells would engraft -- become integrated into the anatomy of the rats -- and then migrate from the site of the injury. This allowed new nervous system connections to become established and the embryonic stem cells would change form to become different types of nervous system cells necessary for normal function.
The scientists also determined that neurons required for transmitting nerve signals appeared to emerge at the injury site, and those neurons would extend fibers above the injury in the region of the brain where movement is coordinated.
"We would see evidence of signaling between the brain and the region affected in response to sensation, not perfectly as would be seen in a normal animal, but certainly better you would see without an intervention," Snyder said. "And coincident with that, the animals seemed to have a improved behavior."
Of his work, Tuszynski said, "Our results highlight some of the potential and some of the limitations of stem cell therapy particularly when applied to a situation as complex as spinal cord injury."
He noted after a spinal cord injury the primary loss of function is related to the interruption of more than a million axons or "wires" in the rat spinal cord that are necessary for normal function.
"In an attempt to find a bridge for those injured axons or 'wires' to reconnect to their disconnected targets, we took cells from the bone marrow -- bone marrow stromal cells -- and implanted them into sites of spinal cord injury. The stromal cells help generate the bone marrow's own stem cells and support the function of those cells," he said.
Tuszynski also used the bone marrow to carry genetically engineered cells in the injured area. These cells were designed to produce nerve growth factors to additionally stimulate regeneration of the fibers.
He said the axons grew extensively in the area but did not complete the connections, so the animals in his work failed to regain lost motor function. He suggested future experiments, in which genetically modified cells are implanted both above and below the injury, might result in improved function. These manipulated cells showed greater growth of axons, he said.
"Bone marrow stem cells are a promising source for reconstituting bridges across these injury sites," he said, "but in its present formulation has not shown functional recovery."
In another study involving bone marrow cells, researchers at Jefferson Medical College in Philadelphia determined that when mixed in a growth factor cocktail they changed into dopamine-producing cells.
Hoa Jin, a research assistant at the college, said the work may hold promise for using the cells in treating people with Parkinson's disease.
"The obvious extension of these results is to take these predifferentiated
human dopamine neurons and transplant them into Parkinson's disease model
systems," said principal investigator and study co-author Lorraine Iacovitti,
professor of neurology at the college.
Copyright 2002 by United Press International