Organs outside the body do not survive for long because of inevitable decay after death. Research is being done to extend their shelf life.
In every medical drama, there is at least one episode where the doctors race against time to secure an organ for someone in desperate need of a transplant. They jump into helicopters or jets, hitch rides from strangers, or heroically run to deliver a precious life-saving organ to the patient in the nick of time. But why the rush? Do organs outside the body have a shelf life?
How much time does an organ have outside the body?
An organ outside the body doesn’t have much time. Decomposition starts just a few minutes after death through a process called auto-digestion.
Programmed cell death
When a human dies, the heart stops beating and blood flow to the organs ceases. Cells receive no more oxygen and become acidic due to the build-up of toxic byproducts from metabolic reactions. Cells primarily need oxygen to stay alive and perform their fundamental metabolic functions.
This lack of oxygen, change in pH and buildup of toxic byproducts activates certain proteins and enzymes. These proteins and enzymes are responsible for degrading the cells. They break down the other proteins, DNA, carbohydrates and fats, leaving the cell broken and non-functional. This process is called programmed cell death. These enzymes leak out of the cells and can begin to affect neighboring cells.
The rate of this self-digestion differs depending on the organ. The brain is usually the first to undergo cellular decay, often within minutes of death (Source). Within a few hours, other organs—usually led by the liver, as it has comparatively more digestive enzymes—begin the decomposition process. Skin and bone cells last significantly longer.
Due to differences in the cellular composition of different organs, their shelf lives also differ. The kidneys, for example, can be kept viable for up to 24 hours, but organs like the heart and lungs can only be kept viable for a mere 3 to 6 hours (Source) . This causes many organs that are viable for donation to go to waste, as there is no time to get that organ to a recipient. The method of preserving an organ also affects the duration that it is viable.
Increasing the shelf life of an organ: Preservation methods
Preventing cellular decay before irrevocable damage to the organ is the most important goal. The best way to do this is by decreasing the temperature. A cell’s metabolic activity decreases at low temperatures, making the cell-degrading machinery lethargic, effectively buying more time. At low temperatures, the kinetic energy of the system decreases, which does two things. For an enzyme to catalyze a reaction, the molecules must collide with enough energy for the reaction to occur (activation). At cold temperatures, these collisions do not occur with enough energy, nor do they occur frequently enough. This slows down cellular activity, and for the purposes of organ transplantation, successfully delays decay.
Keeping the organ in static cold conditions of temperatures near 4-8 °C in an electrolyte solution is the current gold standard (Source). However, the low temperatures can lead to injury to the cells, while rewarming and re-oxygenating the organ can cause ischemia-reperfusion injury (injury to the cells when oxygen is reintroduced to the organ).
The best way to preserve an organ would be to freeze it, as this would stop all cellular activity and you would not have to worry about decay. However, freezing organs at such low temperatures causes the formation of ice crystals, which can damage the cell, its membrane and molecules, while the subsequent thawing can cause even more injury, often leaving the organ inviable.
One way to achieve the temperatures necessary for freezing without actually freezing the organ is cryopreservation. Cryopreservation allows medical practitioners to side-step the formation of ice crystals and achieve low enough temperatures to preserve the organ for weeks, months or even years. That being said, the technique is far from being perfected. Researchers from the Hebrew University in Jerusalem and Queens University in Canada are studying antifreeze proteins that prevent the formation of ice crystals. Research is being done to bioengineer molecules that can allow for cryopreservation and not interfere with transplantation.
Another technique that takes a different approach is machine perfusion. In ex vivo (outside the living organism) perfusion, the organ is maintained at near body temperatures, with blood being pumped to keep the organ viable. This is a relatively new technique, but it shows promise. The shelf life of kidneys has been shown to increase from 8 hours to 21 hours. An advantage of using ex vivo perfusion is that it can allow the organ to adjust to the recipient’s physiology, such as body temperature and blood pressure.
20 people die every day waiting for a transplant in the United States. Having more time is crucial, as it allows doctors and scientists to find out how compatible an organ is with its recipient. Without determining compatibility, transplanting an incompatible organ can potentially cause more damage in the receiving patient than save their life. The window in which an organ remains viable is small, so work must be done to widen it!