Cryoprotective agents, effect

In preparation for bone marrow transplantation, autologous hemopoietic stem cells are normally frozen in liquid nitrogen after harvesting. However, a cryoprotective agent is required, and dimethylsulfoxide is normally used. During and immediately after stem cell infusion, many adverse effects, which may be severe or life-threatening, have been reported. They include hypotension and hjrpertension, anaphylactic reactions, and cardiac and respiratory failure, all possibly due to dimethylsulfoxide, hemolysis induced by cryopreservation and thawing, and fluid overload. 

The protective effect of the surfactant can be compromised by lyophilization [48], It has been found that, to prevent an increase in particle size, the lipid content of the SLN dispersion should not exceed 5%. Direct contact of lipid particles is decreased in diluted samples. Furthermore, diluted SLN dispersions will also have higher sublimation velocities and a higher specific surface area [49], The addition of cryoprotectors will be necessary to decrease SLN aggregation and to obtain a better redispersion of the dry product. Typical cryoprotective agents are sorbitol, mannose, trehalose, glucose, and polyvinylpyrrolidone. 

MSG is also an effective cryoprotective agent for myosin, HMM, LMM, and actin that have been isolated from carp muscle (63,64). Collectively, these results suggest that the cryoprotective effect of MSG extends to each constituent protein and each subunit of the myofibrils. 

Controlling freeze denaturation, which appeared very difficult only a short time ago, is now within reach as far as minced muscle is concerned. MSG has proved to be an especially effective cryoprotective agent. Still to be accomplished is the control of protein denaturation in intact fish muscle. 

Cryo- and Lyoprotectants and Bulking Agents Various mechanisms are proposed to explain why excipients serve as cryo- or lyoprotectants. The most widely accepted mechanism to explain the action of cryoprotection is the preferential exclusion mechanism [177]. Excipients that will stabilize proteins against the effects of freezing do so by not associating with the surface of the protein. Such excipients actually increase the surface tension of water and induce preferential hydration of the protein. Examples of solutes that serve as cryoprotectants by this mechanism include amino acids, polyols, sugars, and polyethylene glycol. 

What then is the effect of adding a macromolecular cryoprotectant to this system Such agents are effective at doses nearly stoichiometric with the catalase concentration and we interpret their effect as similar to that of increasing the enzyme concentration or to adding albumin to enzyme solutions, as is commonly done in biochemistry, to improve stability. The generic effect is to increase macromolecular interactions which retard solvent-solute inactivation. 

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