Cryopreservation is the use of very low temperatures to preserve structurally intact living cells and tissues for a long period of time (suspended animation).
April 2002, on the 11th floor of the University of Minnesota, Joseph Sushil Rao, a transplant surgeon in training, is retrieving a kidney from a plastic box. The kidney had been plucked from a white lab rat, placed in a freezer at minus 150 degrees Celsius, and zapped by a powerful magnet. Now peering through a microscope, Sushil splices the kidneys artery and vein into the body of a different white lab rat using a thread half the thickness of a human hair. The kidney blushes pink when he finally removes the tiny clips pinching off the blood supply. A good sign. Forty-five minutes later a golden drop of urine from the ureter (that would normally feed the bladder from the kidney) emerges. Success.
This is just one of the many instances scientists have tried to "freeze time" by freezing entire organs. The possibility of freezing organs or tissues or even whole organisms is one that seemed fictional decades ago but new advances in technology and a couple many trials and errors have scientists edging ever closer. It is important to note that currently human organs can’t be frozen, they are just placed in cold storage. This is mainly for transplants and in other cases scientific reasons. Cryopreservation as it is called is a complicated and delicate procedure especially when dealing with living organs.
However, nature does not follow the same rules as human medicine. Up in the Arctic region and areas of North America lives the wood frog. This amphibian species can not only freeze its organs but its entire body. Generally, human organs such as the heart and lungs can only be stored for about 4 to 6 hours, the liver for about 8 to 12 hours and the kidney for up to 36 hours. The wood frog breaks all those records and by a far distance. The wood frog is able to freeze its body for weeks or months depending on how long winter temperatures persist. But before we dive into how these frogs are able to achieve this let’s explore why cryopreservation is complex.
Firstly, there is the problem of antifreeze chemicals being highly toxic. To keep cells from being damaged antifreeze chemicals have to be used otherwise the organ will not survive. However, placing organs in highly toxic antifreeze chemicals for long periods of time will eventually lead to cell damage.
Secondly, there is the problem of ice formation. If ice forms inside the cells, it will tear the cell up from the inside out. If ice forms outside the cell, it causes an osmotic differential. As the ice forms the salts outside the cell become concentrated creating the osmotic differential. Water then moves from inside the cell through the semipermeable membrane causing the cell to shrink resulting in damage.
Thirdly, heating the organ rapidly and evenly. If the organ warms too slowly ice crystals will form as it nears its freezing point resulting in osmotic differentials. If it warms unevenly stresses will cause the organ to crack (like an ice cube in water)
How is the wood frog able to counter this:
As winter approaches the wood frog's brain sends a message to the liver to produce glucose. Just this solves problems 1 and 2 (toxicity of antifreeze chemicals and cell damage). Since the glucose is produced by the frog’s liver in large amounts it is not toxic. In addition, glucose helps the cells retain water and counter osmotic differentials. The wood frog also contains a nucleating protein that ensures ice forms outside the cells and away from vital organs. During the freezing process, the frog also conserves its urine increasing its plasma urea which just like glucose acts as a cryoprotectant
Cryoprotectants protect the cells from damage during freezing
How then does the wood frog survive if all its organs are frozen?
During the early stages of freezing blood continues to deliver oxygen to the tissues. Later on, the blood itself stops flowing. The tissues then survive through a process called anaerobic glycolysis which is an energy-production pathway that does not require oxygen.
In the spring water flows back into cells, the heart restarts and blood flows again and lastly, the brain becomes active. The frog can then hop off.
We will crack the code…..maybe
Replicating this process in a lab is far from easy. Keep in mind that wood frogs' DNA has genes that allow for freezing and thawing something that we humans lack. We can’t start trying to sequence such genes from frogs to humans. That will be taking Dr. Frankenstein to a whole new level but we can borrow ideas and techniques to use. Numerous cryopreservation companies are forming to help crack the code. Many people are also choosing to have their bodies cryopreserved after death with the hope that one day they can be brought back to life. New techniques are being explored from developing less toxic cryoprotectants to new ways of warming frozen organs. So far we have only been able to freeze human eggs, sperm, stem cells, rat kidneys, fruit flies, and some species of coral.
The possibility we can successfully cryopreserve humans and bring them back to life has a fair way to go before it can be achieved. Drawing inspirations from the wood frog is one way of going about it.
The idea that we can play God and rely on science for resurrection doesn't sit right with many and their still many legal and ethical discussions that must be heard on the topic. Where you stand on the science is a personal choice but it can be used to save lives apart (through transplants) from just resurrecting the clinically dead.
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