The Icy World of Organ Freezing

Abstract

Scientists have been curious about the effects of cold on life for several centuries. But serious scientific investigations into the biological effects of cold are essentially a 20th-century phenomenon. Efforts to freeze and revive organs, in fact, are quite recent, and have been spurred on by organ transplants of the past decade. If whole organs could be frozen and stored, particularly ones immunologically suitable for recipients, surgeons would be able to perform far more transplants and have better prospects of success. For all their efforts, though, cryobiologists (biologists who study the effects of cold on life) have not been very successful with organ freezing. In the area of heart freezing, for example, G. L. Rapatz of the Cryobiology Research Institute at Madison, Wis., has managed to freeze and revive a frog heart. But the frog heart is considerably less complex than the mammalian heart, where nutrients and oxygen are transported through coronary blood vessels. Some mammalian embryonic hearts have been frozen and revived. A number of mammalian cardiac muscle fibers have been frozen and reactivated. Some investigators have managed to cool adult mammalian hearts to minus 20 degrees C. (minus 196 degrees or lower, would be the ideal storage temperature) and revive them. But in nearly all of these instances the hearts were not kept cold for more than 20 minutes. One exception, is when F. G. J. Offerijns of the Central Laboratory of the Netherlands Red Cross Blood Transfusion Service cooled them for six hours. In any event, nobody to date has cooled whole mammalian hearts any lower or longer and revived them. Organs would have to survive freezing temperatures if they were stored for any length of time. Harold Meryman of the American National Red Cross Blood Research Laboratory in Bethesda, Md., and a cryobiologist who has probably been in the red-blood-freezing business as long as anybody, sheds some light on why mammalian organ freezing hasn't been more successful. A quarter century ago, biologists accidentally discovered that the chemical glycerol can safeguard bull sperm from the harmful effects of freezing. Then optimal freezing and thawing rates for the sperm were found. Glycerol was subsequently found to also protect human red blood cells and human sperm, and optimal freezing and thawing rates for these cells were also determined. It was possible to set up banks for the longterm preservation of animal and human sperm and of human red blood cells. stage appeared to be set for tissue and organ freezing. The pot of gold appeared to be just around the corner, Meryman recalls. 'It was a kind of race. We were all guilty. I certainly was. But cryobiologists were fooled. Freezing and reviving mammalian tissues and organs have not panned out by sheer trial and error experiments-trying to find the right cryoprotective agents and the right freezing and thawing temperatures. Consequently some cryobiologists decided the only way they will ever be able to freeze human organs for long periods and revive them is to first understand the effects of freezing and thawing on various cells and tissues in various organs. Although probing the basics is, understandably, tedious, cryobiologists are making progress. Some of their latest efforts and results were reported in Washington at the recent annual meeting of the Society for Cryobiology. Particularly interesting is work reported by Rapatz and Offerijns, not just because they have good track records in organ freezing, but because they are focusing on one of the most vital organs-the heart. During the past two or three years, both cryobiologists have been largely dealing with pacemaker cells of the heart-those cells that beat and contract even -when removed from the heart. Rapatz has managed to cool these cells to minus 80 degrees C. and revive them. Offerijns has actually frozen them, using a cryoprotectant agent called dimethyl sulfoxide (DMSO), and revived 80 percent of them successfully. But both scientists have noted