Non allergenic wheat

[David Tribe <detribe@unimelb.edu.au>]

Ag Researchers In The United States Prepare To Harvest The World's
First Hypoallergenic Wheat

- Stephen Day, the Guardian 24-May-2001

If wondering why European consumers have taken to genetically
modified crops much like florists to turnips, biotech companies could
do worse than look at their product lists.

Amongst the many pest, disease and herbicide-resistant GM varieties
created for farmers, only stay-firm-for-longer tomatoes have been
offered to woo supermarket shoppers: once sold as puree here and
fresh in the US, even these are no longer available.

Now, however, something metaphorically closer to a rose than a root
vegetable is on the horizon - researchers in California are testing
what could be the world's first harvest of hypoallergenic wheat.  In
the west, 90% of food allergies are caused by just eight food types:
wheat, soybeans, peanuts, tree nuts, milk, eggs, shellfish and fish.
These foods have little in common except for containing relatively
indigestible proteins.  Many food allergies develop when fragments of
such proteins survive digestion for long enough to induce the
production of IgE antibodies, which trigger allergic reactions on
subsequent exposures to the culprit food.

The Californian researchers are hoping to exploit the flip side of
this process. As Bob Buchanan, a leading member of the group
explains: "In most cases, increased digestibility goes hand in hand
with reduced allergenicity."  Buchanan and his colleagues at the
University of California at Berkeley are aiming to produce more
digestible and therefore less-allergenic crops. Proteins that resist
digestion often do so because they are folded too tightly for
digestive enzymes to gain access.

The researchers aim to tackle this problem using thioredoxin, a
non-allergenic protein found in all living organisms that
specifically targets chemical bonds that help hold proteins in their
folded shapes. Breaking these bonds allows proteins to unravel and so
makes them easier to digest, and the researchers have shown that as a
consequence, adding thioredoxin to wheat protein makes it less
allergenic in animal tests.

Since thioredoxin occurs naturally in seeds, where it accelerates the
breakdown of proteins to provide amino acids for the growing
seedling, the team reasoned that increasing the thioredoxin content
of wheat grains should make them less allergenic. Collaborating with
Peggy Lemaux and Lee Frick - both also at the University of
California and specialists in the genetic modification of cereals and
in allergy, respectively - the researchers inserted additional copies
of the thioredoxin gene into wheat and so produced lines whose grains
contain several fold more thioredoxin than normal.  "We have the
grains and now we have grown them in the field," says Buchanan. "We
are still testing allergenicity and baking properties." Apart from
saying that they are "optimistic" , he can't yet give details of
their results.

Besides reducing wheat allergy, the thioredoxin-enriched grains could
have other benefits: in particular, they may help alleviate gluten
intolerance. Glutens are a large group of proteins that collectively
allow wheat flour to form dough.

Unfortunately, a class of gluten proteins called gliadins cause
intestinal damage in people with gluten intolerance, leading to
symptoms such as chronic diarrhoea, weight loss and anaemia.
"Thioredoxin targets the gliadins," says Buchanan, "and what we hope
is that they will be more digestible." The researchers are not yet
testing the effects of thioredoxin-enrichment on gluten intoler ance.
Since there is no animal model for the condition, such tests would
require gluten-intolerant volunteers.

Buchanan and his colleagues have other allergy targets, including soy
beans and peanuts. In a paper just published, for example, they have
shown that thioredoxin acts on two of the major allergenic proteins
in peanuts.  "I think that the thioredoxin take on the problem is a
very good one," says Gary Bannon, a specialist on peanut allergens at
the University of Arkansas medical school in Little Rock. As with
wheat, thioredoxin-enrichment should lead to more digestible peanuts
and so help to prevent allergy from developing in the first place.

However, Bannon warns that this approach will not be enough to
benefit existing sufferers of peanut allergy, for some of whom even
traces of peanut can cause potentially fatal allergic reactions.
Bannon himself is working on this side of the problem.  Using IgE
antibodies collected from allergy sufferers, Bannon and his
colleagues have identified exactly which parts of the main allergenic
peanut proteins represent IgE binding sites. For example, one
allergenic protein, called Ara h1, has 23 such sites. This has
allowed the researchers to produce modified genes that encode the
proteins in forms with far fewer IgE binding sites.

"We are not at the peanut stage yet," says Bannon. "We have produced
the proteins themselves [using bacteria] and we are right now in the
process of trying to reintroduce those modified genes into plants."
He stresses that even this will not make peanuts completely safe for
allergy sufferers. "If we can produce a hypoallergenic peanut, it
wouldn't allow allergy sufferers to eat ad libitum, but it could
prevent accidental exposure from being life threatening," he says.

Of course, the extent to which hypoallergenic crops will reduce food
allergies depends on how widely such crops are used. Ironically, in
this context, in the US public acceptance of GM crops has recently
been dented by fear of allergens.  Last September, traces of the GM
maize variety, StarLink, were found in processed food on sale in the
US. StarLink is engineered to produce a pest-killing protein but only
registered as an animal feed because the introduced protein digests
relatively slowly - making it a potential allergen.

The discovery caused a massive recall of contaminated products and
lawsuits against StarLink's producer, Aventis CropScience, brought by
people saying that they have suffered allergies to StarLink.  So
while the biotech industry holds its collective breath, the US Food
and Drug Administration is now testing blood from some of the 50 or
so people claiming such allergies. Meanwhile, allergies to
conventional foods cause about 2,500 emergency hospital admissions
and around 135 deaths in the US each year. When hypoallergenic GM
crops are available, how long before allergy sufferers sue companies
for using the conventional, allergenic varieties?