PUTTING your eggs on ice to prevent them being damaged by ageing or medical
treatments is looking more feasible.
One group has successfully transplanted entire ovaries back into rats after
freezing them, while another has shown that adding a little sugar to ripe human
eggs greatly increases their chances of surviving a spell in the deep
freeze.
A team at McGill University in Montreal slowly froze eight fresh rat ovaries
after bathing them in a solution containing the cryoprotectants fructose and
dimethylsulphoxide. All eight survived defrosting and transplantation back into
other rats, though the level of hormone production fell (Nature, vol
415, p 385).
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The technique might not work for other organs, admits team member Roger
Gosden, now at Eastern Virginia Medical School in Norfolk, Virginia. 鈥淭he ovary
may be one of the easier organs to do this with.鈥�
Nevertheless, the work holds out hope for cancer patients who often have to
resign themselves to infertility after treatment that destroys the ovaries.
Attempts to restore fertility by saving and re-implanting small pieces of ovary
have so far failed.
Another possibility is simply to freeze mature human eggs. You can extract
such eggs in a relatively minor procedure, whereas removing ovaries or parts of
them involves full surgery and can leave a woman with menopausal symptoms.
Yet while freezing sperm and embryos is a routine procedure, large mature
human eggs are much more delicate. Few survive freezing, though some children
have been born this way.
Cells usually become dehydrated as they freeze. So Thomas Toth鈥檚 team at
Harvard Medical School in Boston has tried using trehalose, a sugar found in
animals such as arctic frogs that can survive severe dehydration. Over half the
eggs injected with the sugar survived freezing, the researchers found (
Fertility and Sterility, vol 77, p 152).
Toth says his group is cautiously optimistic, but he doesn鈥檛 want to raise
people鈥檚 hopes too soon. 鈥淚t鈥檚 premature even to think about clinical
applications,鈥� he cautions. His institution has already applied for a patent,
however.
Other teams have got similar results. Last year Rafaella Fabbri鈥檚 group at
the University of Bologna, Italy, greatly increased the survival rate of eggs by
bathing them in a sucrose solution.
Gosden says Toth鈥檚 work is something he contemplated looking into himself.
鈥淭he reason I didn鈥檛 go ahead with it,鈥� he says, 鈥渋s that I couldn鈥檛 figure out
how to get the trehalose out of the cell.鈥� Toth is hoping it will simply be
metabolised or discharged.