X-Message-Number: 7686
From:  (Brian Wowk)
Newsgroups: sci.cryonics
Subject: Re: Hextend as cryoprotectant?
Date: 12 Feb 97 19:45:29 GMT
Message-ID: <>
References: <01bc18af$ee2cfb40$>

In <01bc18af$ee2cfb40$> "JDY" <> 

>I came across a news item at http://www.businesswire.com/cnn/btim.htm,
>dated may 96. It's probably old news to most readers here, but it was new
>to me. BioTime researchers were presented results at a meeting, and the
>text mentioned experimental results which pointed to the possibility for
>long term preservation of organs. My question is, would the solution
>(hextend?) be useable as a cryoprotectant? Are any of the cryonics
>organizations considering using it? Why or why not?

	Hextend (tm) is not a cryoprotectant per se, but a plasma
volume expander (blood substitute) whose key ingredient is HES
(hydroxyehtyl starch).  HES is a very large molecule that does not
penetrate cells, and whose cryoprotective effects are therefore
confined to the extracellular and especially intravascular spaces.

	HES has been used as "nonpenetrating" cryoprotectant by
organ cryopreservationists for at least 15 years.  It has been used
as a perfusate ingredient by most cryonics organizations for the
past ten years ever since the pioneering work of Jerry Leaf and
Mike Darwin who demonstrated that HES inhibits edema during 
blood washout with great effectiveness.  Paul Segal and associates
have since formed a remarkably successful company (Biotime)
oriented around the development of commercial blood substitutes
using HES as a colloid.

>    Additional research on the use of Hextend supplemented with
>cold-protective agents was presented by Dr. Hal Sternberg, BioTime's
>research vice president.  He described experiments in which hamsters
>were completely blood substituted at hypothermic temperatures with
>BioTime solutions, and then placed in sub-zero freezing baths for
>periods of up to 2 hours.  These animals reached deep body
>temperatures as low as -4 C, and then were revived to consciousness
>and reactivity.

	These experiments are similar to the work of Audrey Smith
40 years ago, who demonstrated that hamsters could be recovered 
after partial freezing near 0'C.  Hextend is being used essentially
as a carrier solution in Dr. Sternberg's experiments to introduce
"supplementary cold-protective agents" such as glycerol, which are
the real cryoprotectants that penetrate and protect intracellularly.
At last report to CryoNet, I believe Dr. Sternberg gave the opinion
that more than 3% glycerol was fatal to whole hamsters.  This is
a factor of 20 short of the concentration required for recovery
from deep sub-zero temperatures, so this work still has as a long
way to go.

 Brian Wowk          CryoCare Foundation               1-800-TOP-CARE
 President           Human Cryopreservation Services   

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