-Caveat Lector-
from New Scientist,
http://www.newscientist.com/cgi-bin/pageserver.cgi?/ns/19990220/newsstory1.html
Frankenfears
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, 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
� Copyright New Scientist, RBI Limited 1999
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