In a feat of biological alchemy, scientists have converted human fat into cells that make muscle, bone and cartilage, suggesting that people's least-favorite body part could become a rich source of repair cells for disease or injury.
The new fat stem cells "may take the use of fetal tissue or embryonic tissue off the table as a practical matter," said Dr. Marc H. Hedrick, a plastic surgery specialist at the University of California at Los Angeles School of Medicine. The Bush administration has said it supports the use of adult stem cells but not embryonic ones.
Working with fat from liposuction patients, the researchers isolated multipurpose "stem cells" that they said were previously unknown. In laboratory dishes, the stem cells spawned a variety of specialized cells and made more of their own kind.
The discovery is the latest in a series that indicates the adult human body contains reserves of versatile stem cells that scientists hope can be harnessed one day to repair everything from hearts to brains. Collecting these adult stem cells doesn't carry the ethical and political conflicts that come with using cells from human embryos or fetuses.
However, many scientists and some patient research groups argue that embryonic cells may prove to be better and more versatile. They can be obtained from frozen embryos created during in vitro fertilization but never implanted into a woman's uterus.
Hedrick said the fat stem cells could serve as a storehouse of repair cells for breast reconstruction or to replace bone or cartilage lost in injuries or, for example, cancer operations. "It's the sort of tissue we all hate and are trying to get rid of," he said.
A report on which Hedrick is the senior author was published Monday in the journal Tissue Engineering.
He and colleagues at UCLA and the University of Pittsburgh School of Medicine say that fatty tissue is more complex than had been thought. When they studied it, they found that fat contained some cells that spontaneously divided into more specialized cells, "but in small amounts."
To get a bigger yield, the scientists processed the fat and got rid of most elements except the adult stem cells. Then they exposed the cells in different batches to biochemicals previously known to prod stem cells into becoming different types of cells.
"When you give these cells a nice push from behind they show very dramatic changes in their behavior" and begin to form cells typical of muscle, bone, cartilage and fat, Hedrick said.
He cautioned that his team had not proved that the cells that developed into various types are "the real McCoy" - true stem cells that can spawn almost any kind of cell. They could be partially differentiated and therefore not "pluripotent" - able to develop into nearly all cell types.
"But it doesn't matter what you call them," Hedrick said. "If it's going to fix your bone defect or reconstruct a breast, who cares?"
Researchers who are testing the promise of embryonic cells aren't ready to capitulate and abandon them for adult stem cells.
"I think it's too easy for people to ascribe more plasticity" or versatility to adult cells than has been proved, said Dr. George Daley, an embryonic stem cell researcher at the Whitehead Institute in Cambridge, Mass.
"It's more convenient politically, but if you look very closely at what the adult cells are going to do, there are limitations," he said. Embryonic cells may be longer-lived when implanted in the body than adult stem cells would be, Daley said.
As adult stem cells have begun to look increasingly useful, groups opposed to abortion rights have used that prospect to intensify their attack on the use of embryonic stem cells. Some researchers fear that this trend will result in the Bush administration overturning National Institutes of Health guidelines giving approval for federal funding of embryonic stem cell research, providing that the cells are obtained from embryos by private-sector firms.