X-Message-Number: 13333
From: "James J. Hughes" <>
Subject: Glassy vitrification
Date: Tue, 29 Feb 2000 18:35:34 -0500

http://helix.nature.com/nsu/000302/000302-6.html

medicine : Bypass of glass

HENRY GEE

Transplantation surgery is all too often a matter of matching supply
with demand. A key ingredient of the process is a reliable way of
storing organs for transplant, so that organs not used immediately can
be held 'on ice' for some later date.

It is estimated that 30% of patients in need of arterial bypass
surgery do not have suitable veins of their own that might be
used. Frozen, donated blood vessels provide an alternative
source. Between 1985 and 1992, approximately 3,000 frozen vein
segments were used for arterial bypass.

But conventional freezing has its problems. The formation of jagged
ice crystals in an organ during the cooling process can damage organs
or tissue. And thawed, damaged transplants do not last as long as
fresh. So researchers are increasingly looking at ways to cool tissues
and organs without ice forming.

One option is 'vitrification': solidification in a kind of glassy
state, in which ice crystals do not form. By perfusing a tissue with a
cocktail of chemicals as it is carefully cooled, medical specimens can
be kept unfrozen even at temperatures approaching minus 80 degrees
Centigrade. In the latest Nature Biotechnology (March 2000) Michael
J. Taylor and colleagues of Organ Recovery Systems Inc., Charleston,
South Carolina, show how vitrified blood vessels perform much better
in transplants than conventionally frozen vessels.

The researchers tested their procedures on rabbit jugular veins.  They
looked at how these veins responded to various drugs and tests when
fresh, vitrified or conventionally frozen. The headline figures are
impressive: smooth-muscle contraction in the walls of vitrified
vessels was more than 80% that of fresh, unfrozen vessels. Frozen
vessels never reached 30%.  Relaxation in response to natural and
artificial muscle relaxants showed a similar pattern, with vitrified
vessels outstripping frozen ones.

The feasibility of ice-free cryopreservation by vitrification has been
established for some biological systems, such as certain white blood
cells, egg cells, the 'islet' cells of the pancreas that secrete
insulin, and very early embryos. But in these cases, vitrification is
probably no better than freezing because all these systems essentially
consist of single cells, and most damage is done by ice forming in
water in spaces outside cells.

However, when applied to multicellular tissues -- such as a blood
vessel -- in which viability depends on all component parts working
together smoothly, vitrification offers dramatic improvements over
freezing, as this new research demonstrates for the first time.

Macmillan Magazines Ltd 2000 - NATURE NEWS SERVICE 

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-----------------------
J. Hughes                          "On Saturday, my teachers, me, and all 
Changesurfer Radio            my friends went to Never Never Land. 
www.changesurfer.com               It was a short trip."
        Tristan Bock-Hughes, 3

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