By Staff Writers
Leeds UK (SPX) Jun 28, 2011
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| Cryoprotectants, such as glycerol, lower the freezing temperature of water to prevent crystallisation. Credit: Wikipedia, Benjah-bmm27 |
Researchers from the Universities of Leeds and Illinois, and Columbia University in New York, studied a particular type of cryoprotectants known as osmolytes. They found that small osmolyte molecules are better at protecting proteins than larger ones.
The findings, published in Proceedings of the National Academy of Sciences, could help scientists develop better storage techniques for a range of materials, including human reproductive tissue used in IVF.
Biological systems can usually only operate within a small range of temperatures. If they get too hot or too cold, the molecules within the system can become damaged (denatured), which affects their structure and stops them from functioning.
But certain species of fish, reptiles and amphibians can survive for months below freezing by entering into a kind of suspended animation. They are able to survive these extreme conditions thanks to osmolytes - small molecules within their blood that act like antifreeze -preventing damage to their vital organs.
These properties have made osmolytes attractive to scientists. They are used widely in the storage and testing of drugs and other pharmaceuticals; in food production; and to store human tissue like egg and sperm cells at very low temperatures (below -40 degrees C) for a long period of time.
"If you put something like human tissue straight in the freezer, ice crystals start to grow in the freezing water and solutes - solid particles dissolved in the water - get forced out into the remaining liquid.
This can result in unwanted high concentrations of solutes, such as salt, which can be very damaging to the tissue," said Dr Lorna Dougan from the University of Leeds, who led the study. "The addition of cryoprotectants, such as glycerol, lowers the freezing temperature of water and prevents crystallisation by producing a 'syrupy' semi-solid state. The challenge is to know which cryoprotectant molecule to use and how much of it is necessary.
"We want to get this right so that we recover as much of the biological material as possible after re-thawing. This has massive cost implications, particularly for the pharmaceutical industry because at present they lose a large proportion of their viable drug every time they freeze it."
Dr Dougan and her team tested a range of different osmolytes to find out which ones are most effective at protecting the 3D structure of a protein. They used an atomic force microscope to unravel a test protein in a range of different osmolyte environments to find out which ones were most protective. They discovered that smaller molecules, such as glycerol, are more effective than larger ones like sorbitol and sucrose.
Dr Dougan said: "We've been able to show that if you want to really stabilise a protein, it makes sense to use small protecting osmolytes. We hope to use this discovery and future research to develop a simple set of rules that will allow scientists and industry to use the best process parameters for their system and in doing so dramatically increase the amount of material they recover from the freeze-thaw cycle."
The research was funded by the UK Engineering and Physical Sciences Research Council, the US National Institutes of Health and the China National Basic Research Program.
Dr Dougan and her team at Leeds are also exploring what a 'syrupy mixture' of glycerol and water looks like using neutron diffraction experiments at the Rutherford Appleton Laboratories. Their latest findings have been published in Journal of Physical Chemistry B.
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Cryoprotectant (Swedish: cryoprotectant?)
A is a substance that is used to protect biological tissue from freezing damage (damage due to ice formation). Arctic and Antarctic insects, fish, amphibians and reptiles create cryoprotectants in their bodies to minimize freezing damage during cold winter periods. Insects most often use sugars as cryoprotectants. Arctic frogs use glucose, but Arctic salamanders create glycerol in their livers for use as cryoprotectant.
Conventional cryoprotectants are glycols (alcohols containing at least two hydroxyl groups), such as ethylene glycol, propylene glycol and glycerol. Ethylene glycol is commonly used as automobile antifreeze and propylene glycol has been used to reduce ice formation in ice cream. Dimethyl sulfoxide (DMSO) is also regarded as a conventional cryoprotectant. Glycerol and DMSO have been used for decades by cryobiologists to reduce ice formation in sperm and embryos that are cold-preserved in liquid nitrogen.
Mixtures of cryoprotectants have less toxicity and are more effective than single-agent cryoprotectants. A mixture of formamide with DMSO, propylene glycol and a colloid was for many years the most effective of all artificially created cryoprotectants. Cryoprotectant mixtures have been used for vitrification, i.e. solidification without any crystal ice formation. Vitrification has important application in preserving embryos, biological tissues and organs for transplant. Vitrification is also used in cryonics in an effort to eliminate freezing damage.
Some cryoprotectants function by lowering a solution's or a material's Glass transition temperature. In this way, the cryprotectants prevent actual freezing, and the solution maintains some flexibility in a glassy phase. Many cryoprotectants also function by forming hydrogen bonds with biological molecules as water molecules are displaced. Hydrogen bonding in aqueous solutions is important for proper protein and DNA function. Thus, as the cryoprotectant replaces the water molecules, the biological material retains its native physiological structure (and function), although they are no longer immersed in an aqueous environment. This preservation strategy is most often observed in anhydrobiosis.
Cryoprotectants are also used to preserve foods. These compounds are typically sugars that are inexpensive and do not pose any toxicity concerns. For example, many (raw) frozen chicken products contain a "solution" comprised of water, sucrose, and sodium phosphates.
Cryoprotectant = cryoprotectant ? Korrekt svenska (?): Glykol är en cryoprotectant (Min adress högst på sidan).
