Frankenfears
New Scientist Planet Science
20 February, 1999
Andy Coghlan, David Concar, Debora MacKenzie
Hostility to genetically modified food has exploded
in Britain amid claims that it is being rammed down
the public's throat without proper safety testing. At
the centre of the storm is a researcher who argues
that GM foods could create unforeseen hazards. New
Scientist looks at the science behind the accusations.
Just how worried should we be?
At face value, Arpad Pusztai's findings cast a pall
over the entire GM food industry. His results,
obtained at the Rowett Research Institute in
Aberdeen, suggest that procedures routinely used in
genetic engineering can make plants harmful. No
wonder, then, that the British public and
media--primed to distrust official assurances about
food safety after their experience with BSE--are up in
arms.
Yet Pusztai's data remain mired in confusion. His
claim that rats are harmed by eating a particular kind
of genetically engineered potato has yet to be
confirmed. And even if the potatoes are harmful, this
may not have any relevance to GM crops approved
for sale. Any ill effects could have been caused by
something specific to the transgenic potatoes he
used--which were never intended for human
consumption--rather than the process of genetic
engineering itself.
Pusztai was trying to discover if a protein taken from
snowdrops could harm rats when fed to them in
potatoes. Several labs are investigating whether the
gene for this protein, which is of a type known as a
lectin, could be added to crops such as rice to make
them resistant to sap-sucking insects. So data on its
safety are important.
Some of Pusztai's rats were fed ordinary potatoes
laced with the lectin. Others ate potatoes genetically
engineered to make the lectin themselves. A control
group of rats ate ordinary potatoes.
Pusztai found differences in the size of several organs
in young rats eating the transgenic potatoes (see
Figure), and evidence of damage to their immune
systems. Rats eating the lectin-spiked potatoes
showed no such effects, he claims, suggesting that
something other than the lectin caused the damage.
One suggestion is that the problem lies with what
genetic engineers call the "construct"--the package of
DNA introduced along with the foreign gene.
This DNA includes a gene that makes the potato
resistant to the antibiotic kanamycin and another that
makes a substance which stains blue. These extra
genes give researchers a convenient way to identify
plants that have incorporated the lectin gene into their
DNA. The construct also includes a "promoter"
sequence from a cauliflower mosaic virus, which
boosts the production of the lectin protein.
The idea that such a construct is a health risk flies in
face of the conventional biological wisdom. But given
that similar constructs are found in other GM plants,
it's a disturbing suggestion.
One of Pusztai's supporters, Stanley Ewen, a
pathologist at the University of Aberdeen, has made
further observations that add to the controversy.
When Ewen examined samples of gut lining from rats
which had eaten the transgenic potatoes, he saw
abnormalities such as increased production of cells in
intestinal crypts, the clefts between the finger-like villi
that line the wall of the small intestine.
Pusztai's own report on his experiments, which he
sent to Rowett director Philip James in October, was
released last week by the environmental group
Friends of the Earth at a press conference attended by
scientists sympathetic to Pusztai. They are angry with
the institute for disciplining Pusztai after he spoke out
on television (see "Anatomy of a food scare").
Most of the researchers contacted by New Scientist
are unconvinced by Pusztai's data and sceptical of the
theory that the construct is to blame. One problem is
that Pusztai's report does not include key raw data on
the spiked potatoes needed to verify his claim that the
genetic manipulation was the source of the problems.
The most likely explanation, says Willy Peumans,
whose team at the Catholic University of Leuven in
Belgium has supplied Pusztai with lectins to feed to
rats, is that the process of inserting the lectin gene into
potato cells and their growth in tissue culture
disrupted the behaviour of the potatoes' other genes.
This may have altered the plants' biochemistry and
made them produce high levels of other toxic
substances, such as alkaloids. This theory is
strengthened by the fact that the protein, starch and
glucose levels of the transgenic potatoes all differed
markedly from those of the natural plant. They
contained 20 per cent less protein than normal, for
example, and Pusztai had to add protein supplements
to the rats' meals.
If the altered potatoes' strange biochemistry, rather
than the inserted DNA, lies behind their toxic effects,
the implications for food safety are less serious. Crop
engineers already test for altered biochemistry, and
regulators won't approve such a plant. "We would
chuck it out straight away," says Mike Gasson of the
Institute of Food Research in Norwich, who sits on
the British government's Advisory Committee on
Novel Foods and Processes.
Companies that produce GM crops claim that their
own toxicity tests would have identified similar
problems. James Astwood, head of product safety at
Monsanto's headquarters in St Louis, Missouri, says
the company routinely carries out feeding trials on
mice in which internal organs are closely examined
and weighed. Novartis of Basel, Switzerland, which
makes maize with a gene for an insecticidal toxin,
says that mice were unharmed when they ate the
maize.
On one thing, however, everyone agrees. Answering
all the questions raised by Pusztai's preliminary
findings will require tests on plants engineered to
contain DNA constructs, but lacking genes for lectin
or the other genes added in commercially grown GM
crops. "What we need is a set of data from
experiments with the construct alone," says Ewen.
From New Scientist, 20 February 1999
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