Putting human tissue under glass.

Putting human tissue under glass

Human organs cannot survive long-term freezing--the ice crystals that inevitably form fatally impair their function. But Gregory M. Fahy, a researcher at the American Red Cross's Transplantation Laboratory in Bethesda, Md., thinks he has an alternative. Instead of turning the water within organs into ice, he supercools it into glass. He and a former co-worker have already "vitrified' mouse embryos; at the Red Cross's recent Annual Scientific Symposium in Washington, D.C., Fahy described modifications to the procedure that may allow it to be used on entire organs.

With cooling, kidneys can be banked for two to three days, and hearts and livers for six to eight hours. Transplantation experts estimate that as many as 20 percent of the organs donated and available for transplantation have to be discarded because a matched recipient can't be found before the organs spoil.

Fahy and William F. Rall, now at Rio Vista Laboratories in San Antonio, Tex., have succeeded in vitrifying mouse embryos, a process they initially described in the Feb. 14, 1985 NATURE. Since then, Rall has reimplanted the embryos, which then continued their development and grew into normal mice. Their offspring were normal as well, Rall says.

The vitrification process relies on the addition of several chemicals that prevent the crystallization of water within and outside the cells. With cooling, the molecules essentially are fixed in place, becoming what Fahy calls "a solid liquid.' This is unlike conventional freezing, in which the water molecules crystallize into an orderly structure.

Organs present what Rall terms "huge technical problems.' Among them are determining a way to use high enough levels of chemicals to induce vitrification without poisoning the cells, and getting the tissue to warm properly. Fahy reported at the symposium that doing the procedure at 1,000 atmospheres of pressure limits the concentration of chemicals needed.

The largest organ he has so far been able to vitrify has been a rabbit kidney. The result, which is stored at -125|C, looks something like a gruesome paperweight. The vitrified tissue itself appears normal from the outside, with no visible traces of ice. Fahy has not yet done microscopic studies of the tissue, but he says that because vitrified cell preparations retain their normal architecture and viability, and because the process of vitrification doesn't involve any sudden changes as does freezing, he expects that further investigation will show that the organ tissue is preserved.

While he can vitrify organs, the key is going to be in reversing the process. Thawing, Fahy says, is "the last barrier.' The problem is balancing the speed of heating, making it fast enough to prevent ice crystals from forming as the specimen "warms' from -125|C, but slow enough to avoid stress fractures of the sort that can crack a glass into which boiling water has been poured.

"We have a new direction, new possibilities and a lot of data,' says Fahy. "But we don't have proof it's going to work in [an intact] organ.'

Photo: Capillaries within the kidney show the disruption of freezing: Walls between the vessels in the upper left quadrant have broken down. Vitrification, Fahy says, will prevent this.