Cryoprotectant

Source: Wikipedia, the free encyclopedia.

A cryoprotectant is a substance used to protect

biological tissue from freezing damage (i.e. that due to ice formation). Arctic and Antarctic insects, fish and amphibians create cryoprotectants (antifreeze compounds and antifreeze proteins
) in their bodies to minimize freezing damage during cold winter periods. Cryoprotectants are also used to preserve living materials in the study of biology and to preserve food products.

For years,

Twenty-First Century Medicine has vitrified a rabbit kidney to -135 °C with their proprietary vitrification cocktail. Upon rewarming, the kidney was successfully transplanted into a rabbit, with complete functionality and viability, able to sustain the rabbit indefinitely as the sole functioning kidney.[1]

Mechanism

Cryoprotectants operate by increasing the solute concentration in cells. However, in order to be biologically viable they must easily penetrate and must not be toxic to cells.

Glass transition temperature

Some cryoprotectants function by lowering the

glass transition temperature of a solution or of a material. In this way, the cryoprotectant prevents 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 utilized in anhydrobiosis
.

Toxicity

Mixtures of cryoprotectants have less

transplant. Vitrification is also used in cryonics
, in an effort to eliminate freezing damage.

Conventional

Conventional cryoprotectants are glycols (alcohols containing at least two hydroxyl groups), such as ethylene glycol [citation needed], propylene glycol and glycerol. Ethylene glycol is commonly used as automobile antifreeze; while 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,[3] oocytes,[4] and embryos that are cold-preserved in liquid nitrogen. Cryoconservation of animal genetic resources is a practice that involves conventional cryoprotectants to store genetic material with the intention of future revival. Trehalose is non-reducing sugar produced by yeasts and insects in copious amounts. Its use as a cryoprotectant in commercial systems has been patented widely.

Examples in nature

Arctic fish use antifreeze proteins, sometimes appended with sugars, as cryoprotectants.

Insects

Further information: Antifreeze protein and Threitol

Insects most often use sugars or polyols as cryoprotectants. One species that uses cryoprotectant is Polistes exclamans (a wasp). In this species, the different levels of cryoprotectant can be used to distinguish between morphologies.[5]

Amphibians

Cold-adapted arctic frogs, such as wood frogs, and some other ectotherms in polar and subpolar regions naturally produce glucose,[6] but southern brown tree frogs and Arctic salamanders create glycerol in their livers to reduce ice formation.

When glucose is used as a cryoprotectant by arctic frogs, massive amounts of glucose are released at low temperature and a special form of insulin allows for this extra glucose to enter the cells. When the frog rewarms during spring, the extra glucose must be rapidly eliminated, but stored.

Food preservation

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 sucrose and sodium phosphates solution in water.

Common

See also

References

  1. PMID 20046680
    .
  2. PMID 25826677
    .
  3. PMID 23168056
    .
  4. PMID 24246951
    .
  5. S2CID 39394207
    .
  6. PMID 24737762
    .

7. Urmatskikh A.V. "Method of cryopreservation of cells, organs, tissues and organisms." RU 2804972 C2, 04.05.2022.

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