On pages 42-43 of Dr. Moalem's book Survival of the Sickest, biochemist Ken Storey's work related to cryptopreservation - the freezing of living tissue for preservation - and wood frogs is discussed. After years of research, Storey discovered that the species of wood frogs, Rana sylvatica, were able to survive temperatures near freezing by releasing large amounts of glucose and sugar alcohols. The secreted substances act almost as a sugary antifreeze by lowering the freezing point of the water in the frog's body. The concentration of sugar not only lowers the freezing point but prevents any drastic damage by forming smoother ice shapes that don't injure cells or capillaries.
This overall adaptation of wood frogs relates to Big Idea 2, in which biological systems utilize free energy and molecular building blocks to grow, reproduce, and to maintain dynamic homeostasis. The Rana sylvatica have adapted to successfully maintain their internal environments so that their organs aren't damaged from the external freezing temperatures. Wood frogs also have feedback mechanisms (such as their skin) that allow them to respond to changes in temperature and maintain homeostasis.
This knowledge could possible be useful in preserving human organs for transplanting. Currently, it's impossible for organs to be frozen and stored for later revivals and transplants because freezing increases the size and shape of water molecules, and damages the internal structure of organs. How could we apply the information gained from Storey's research to human organs? Would the sugary antifreeze mechanism that wood frogs have developed be a viable solution for successfully maintaining human organs?
And most importantly, why don't humans currently have this ability to utilize a sugary concentration? List and describe, if there are any, some other possible adaptations that might have allowed humans to survive in near-freezing temperature conditions in the past?
(Tony Chung, kchung4@students.d125.org)
All living organisms, shaped by countless selection pressures throughout the history of their existence, have undergone evolution and taken on a variety of remarkable adaptations that aid in survival and reproduction. Take natural freeze-tolerance, a defense mechanism that has proved to be crucial for the survival of numerous marine invertebrates and species of amphibians and reptiles in cold environments. The Rana sylvatica, or wood frog, is an example of such a creature with this ability. Although this critter of two inches long appears to be miniscule, it can achieve a grand feat- it freezes solid in the winter and comes back to life. What seems to be an unfeasible, “death-defying” task (Moalem 43) is merely just the workings of evolution at their finest!
ReplyDeleteIn Survival of the Sickest by Dr. Moalem, the studies of wood frogs conducted by biochemists Ken and Janet Storey is discussed on page 43. The Storeys discovered the mystery behind the wood frog’s freezing capabilities: The frog’s body detects severe temperatures and responds by moving water from the blood and organ cells into the abdomen. Simultaneously, the liver releases large amounts of glucose into the frog’s bloodstream, which combine with other various sugar alcohols to lower the freezing point of the blood. The removal of the liquid increases the concentration of sugar, and also prevents puncture damage to the cells from ice particles. When the frogs were dissected for examination, there was a big body of ice in the abdominal cavity formed around the organs- as if the frog’s body had simulated the process of freezing human organs before transplant. This relates to Big Idea 2 because it represents the frog’s ability to respond to their environments in order to maintain dynamic homeostasis, internal conditions suitable for life.
Such an astounding discovery sparked ideas regarding cryopreservation, the freezing of living tissue to preserve it, which is discussed on page 42. Experts had hoped to utilize these concepts of natural freeze-tolerance to increase the number of days organs could be frozen before transplant. This would be revolutionary to the medical field because it would increase the success rate of organ transplants by allowing more time to match donors and recipients. Currently, a kidney can only be stored for 2 days, and a heart for only several hours. Liquid nitrogen has helped keep organs at a very low temperature of -196 degrees Celsius at which molecular activity ceases and tissue decay slows. However, it is not entirely successful. Whole organs struggle to survive through these frigid temperatures; water leaks during freezing and forms ice crystals between cells, which punctures fragile ducts and blood vessels.
Due to the complexity of organ preservation, extending the “shelf-life” of entire human organs by utilizing a sugary antifreeze, similar to that of the wood frog, is not a viable solution. Cryobiologists have recently tried using a similar technique called vitrification, or “ice-free cryopreservation.” They have used various fluids that reduce the formation of rough icy crystals at lower temperatures, but have found that the substances themselves damaged the organs. A human organ would probably not be as healthy if it was filled with a sugary antifreeze composed of high levels of glucose. Cryobiologist David Pegg from the University of York (UK) says, “vitrification is very, very complicated.” That is why if it functions, it functions better on small-scale structures, such as 2-3 cm long rabbit organs or the minute organs of the wood frog, as opposed to large, complicated human organs. Humans do not have the ability to naturally produce a sugary antifreeze on their own either, because our livers do not release high levels of glucose upon temperature decrease. High levels of glucose are also very dangerous for humans. When frogs fill their blood with glucose, they practically go into a state of death with no heartbeat, no breathing, and no brain activity (Moalem 41). Human beings, being much larger, complicated organisms, cannot be revived from such a prolonged state of hibernation. Therefore it is not practical to use a sugary antifreeze with humans.
ReplyDeleteAlthough humans do not have as intriguing of adaptations as that of the wood frog, we have other defense mechanisms against cold, described on pages 35-40. One example is shivering, during which muscle activity increases and heat is generated. Next is numbing of the extremities. When the body detects cold, it forms a thin web of capillaries in the fingers and toes, and then arms and legs. The capillary walls constrict and blood is squeezed into the torso to keep the organs warm and safe. The “hunter’s response” is a variation of this adaptation in which individuals posses the ability to dilate capillaries and release blood back into the extremities periodically, which allows them to save these structures. Lastly, a method of survival is cold diuresis, which is the increase of urination in low temperatures. The removal of water from the system is not fully understood, but is related to the removal of water in organisms such as the wood frog to prevent freezing and damage from ice.
Sources:
• Survival of the Sickest by Dr. Sharon Moalem
• Storey, Kenneth B., and Janet M. Storey. "Natural Freezing Survival In Animals." Annual Review of Ecology and Systematics 27.1 (1996): 365-86. Print
• Kaiser, Jocelyn. "New Prospects for Putting Organs on Ice." Science (2002): n. pag. JSTOR. Web. 5 Apr. 2013.
(Michelle Liang, mliang4@students.d125.org)