Beating the Big Freeze
How Natural Cryoprotectants Work
|
Media Release - School of Physics
The University of New South Wales
Monday 19th October 1998
|
Transplant surgeons would love to be
able to freeze hearts and kidneys for later use, but today only
a few human tissues (such as blood and sperm) can successfully be
frozen for future use. The process of cryopreservation usually involves
adding chemicals, called cryoprotectants, which are usually toxic.
Many plant and animal tissues can survive
freezing using natural cryoprotectants which are clearly not toxic.
Biophysicists from the University of New South Wales and the Queensland
University of Technology have recently announced results which explain
how some of these cryoprotectants can limit the huge mechanical
stresses which are produced by freezing.
"When tissues are frozen, there is usually
a loss of water from the cells by osmosis" explained Associate Professor
Joe Wolfe of UNSW. "This can produce very large mechanical stresses
in cellular components. These stresses, which can be tens or even
hundreds of atmospheres, are one of the causes of freezing damage.
Organisms that can withstand severe freezing - or other causes of
cellular dehydration - often produce high concentrations of natural
cryoprotectants, including sugars. We set out to discover how different
cryoprotectants, both natural and artificial, reduced the mechanical
stresses." Professor Jim Pope of QUT suggested using nuclear magnetic
resonance. "It is an ideal tool for this study because it can tell
us how much of water is frozen, how the cryoprotectants are distributed
and how the water is affected by its cellular environment."
This technique was applied to cryobiology
by Yong Hyeon Yoon, a student at UNSW, in a project with Wolfe and
Pope. The team's results, recently published in Biophysical Journal,
show that all of the cryoprotectants studied have an osmotic effect
that reduces the mechanical stress. Two of the sugars studied, however,
have an extra effect that further reduces the stress by changing
the way water interacts with membranes. This can reduce the mechanical
stresses by a factor of up to three times, in addition to the osmotic
effect.
So can we survive freezing by eating
enough of the right type of sugar? "No", says Wolfe. "The cryoprotectant
has to be inside the cells, and it's difficult to get it there.
The species that use natural cryoprotectants are able to produce
them inside their cells. Humans cannot do that. Knowing the molecular
details of how cryoprotectants work does, however, give us some
ideas for where to look for new techniques."
|
Further Information
|
|
