X-Message-Number: 10012
Date: Wed, 8 Jul 1998 03:10:09 -0700 (PDT)
From: Doug Skrecky <>
Subject: Is Erythritol a Superior Cryoprotectant?

    Using glycerol to preserve entire organs has certain drawbacks.
 Glycerol is actively metabolised to formaldehyde, and in addition at high
 enough concentrations it can destroy cell membranes. Erythritol appears
 not to suffer from any of these side effects. Unlike glycerol, erythritol
 is not actively metabolised. (1) Like sorbitol, erthyritol appears to
 stabilise membranes. Adding 5% erthyritol to bacteria cultures, which are
 freeze-dried preserves them well at 22 C for one month, whereas 5%
 glycerol is harmful. (2)
    Unfortuately, unlike glycerol very little work has been done with
 testing erythritol as a cryoprotectant. However in one test it proved to
 be superior to glycerol. Survival of rat embryos exposed to 0.3 M
 glycerol was 16%, while with 0.3 M erythritol it was 56%. At 1.0 M
 survival with glycerol 52%, and with erythritol it was 79%. (3)
    In addition to being less toxic, and yielding better results in at
 least one test, erythritol also offers the possibility of eliminating
 liquid nitrogen as a storage medium and replacing this with less
 expensive dry ice. Excellent stability of slowly cooled cryoprotectant
 solutions is known to occur at temperatures below the annealed glass
 transition temperature (Tg'), where the unfrozen phase of a solution
 hardens to a glass. This is known to correlate with the melting
 temperature of the cryoprotectant. The melting point of erythritol at 122
 C is actually higher than for sorbitol, and since the Tg' of sorbitol is
 above dry ice temperatures, then one can predict that this would also
 probably be the case for erythritol.
    All of these advantages would be of little avail if erythritol did not
 penetrate tissue. Fortunately the membrane permeability in bull
 spermatozoa of erythritol is about 40 times that of sorbitol, so this
 would not appear to be a serious problem. (4) This is still slower than
 for glycerol, but in the case of erythritol the results may make it well
 worth the wait.

 (1) "Erythritol: A Review of Biological and Toxicological Studies"
     Regulatory Toxicology and Pharmacology 24: S191-S197 1996
 (2) "Effect of Carbohydrates and Related Compounds on the
      Long-Term Preservation of Freeze-dried Bacteria"
     Cryobiology 11: 73-79 1974
 (3) "Cryoprotective Effect of Polyols on Rat Embryos During
      Two-Step Freezing"
     Cryobiology 29: 332-341 1992
 (4) "Permeability Coefficients of Bull Spermatozoa for Water
      and Polyhydric Alcohols"
     Experimental Cell Research 69: 212-216 1971

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