X-Message-Number: 7473
From: Brian Wowk <>
Date: Fri, 10 Jan 1997 00:05:46 -0600
Subject: Frogs and Mummification

Henry R. Hirsch <> writes on CryoNet:

>1.      Has glucose been studied as a cryoprotectant in humans or
>        other mammals?

	Yes, although typically as a component in solutions
containing more penetrating cryoprotectants.  Its utility as
monoagent is limited. 

>
>Background:  Glucose serves as the major cryoprotectant in the
>freeze-tolerant frog R. Sylvatica (1).  If effective, advantages to its 
>use in human cryonics patients would include: (a) Apart from glycosylation
>reactions, it is nontoxic.  (b)  It crosses the blood-brain barrier.

	Unfortunately it doesn't penetrate cells very well (compared
to other cryoprotectants), so it has osmotic toxicity at high
concentrations.  Like all solutes, it also has direct biochemical
toxicities at high concentrations.  Whenever you replace water
molecules with other molecules, you will inevitably denature
macromolecules beyond some threshold concentration.  (Tip: Anyone who
finds the magic formula for an unfreezable liquid that proteins can't
distinguish from water will win Nobel Prizes for both chemistry and
medicine.) 

	The problem with extending strategies employed by
overwintering amphibians like Rana Slyvatica to human organ
crypreservation is that you have to replace much more water with
cryoprotectant to survive cooling to -130'C than you do to
survive cooling to -20'C.  Amphibian organs have also evolved
to survive quantities of ice and concentrations of
cryoprotectant that are lethal to humans. 


>2.      Has glucose been studied as a "dryoprotectant", i. e. a
>substance which stabilizes cell membranes against dehydration?

	Suffice it to say that while numerous mammalian tissues
and even some organs can survive cryopreservation, NONE have
ever been shown to survive dessication and rehydration.  (Organisms
that survive complete dehydration have no doubt evolved proteins 
uniquely suited to the trick.)  So mummification is not currently
currently pursued as a promising approach to suspended animation.

	A good way to get up to speed on the cryobiology most
relevant to suspended animation is to read the vitrification
review article on the Prometheus Project Web site:

http://www.prometheus-project.org/prometheus

and look up some of the references at the end.  Perusing back issues
of the journal Cryobiology is also a useful for getting an
impression of the field.

***************************************************************************
Brian Wowk          CryoCare Foundation               1-800-TOP-CARE
President           Human Cryopreservation Services   
   http://www.cryocare.org/cryocare/

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