AT FACE value, Arpad Pusztai鈥檚 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鈥攑rimed to
distrust official assurances about food safety after their experience with
BSE鈥攁re up in arms.
Yet Pusztai鈥檚 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鈥攚hich were never
intended for human consumption鈥攔ather 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.
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Some of Pusztai鈥檚 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
鈥渃onstruct鈥濃�攖he 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
鈥減romoter鈥� 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鈥檚 a disturbing suggestion.
One of Pusztai鈥檚 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鈥檚 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 鈥淎natomy of a food scare鈥�).
Most of the researchers contacted by 快猫短视频 are unconvinced
by Pusztai鈥檚 data and sceptical of the theory that the construct is to blame.
One problem is that Pusztai鈥檚 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鈥� other
genes. This may have altered the plants鈥� 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鈥� meals.
If the altered potatoes鈥� 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鈥檛 approve such a plant. 鈥淲e would chuck it out straight away,鈥� says Mike
Gasson of the Institute of Food Research in Norwich, who sits on the British
government鈥檚 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鈥檚 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鈥檚 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. 鈥淲hat we need is a set of data from experiments
with the construct alone,鈥� says Ewen.