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Scientist Warns of Dangers of Genetically Engineered Food
The Risks of GM Food
Professor David Schubert
Cellular Neurobiology Lab, Salk Institute for Biological Studies,
San Diego, USA
July 2002
As a cell biologist
I am very much discouraged by the content of the ongoing debate
about introducing genetically modified (GM) plants into the marketplace.
While the voiced concerns usually center around irrational emotional
arguments on the one hand, and the erroneous concept that genetic
engineering is just like plant breeding on the other, I believe
that the three issues which should be of most concern on the basis
of established science receive little or no discussion.
These are:
1. that introducing the same gene into 2 different types of cells
can produce two very distinct protein molecules;
2. the recent observations
that the introduction of any gene, be it from a different or the
same species, always significantly changes overall gene expression
and therefore the phenotype of the recipient cell; and
3. the possibility that
enzymatic pathways introduced to synthesize small molecules such
as vitamins can interact with endogenous pathways to produce novel
molecules. The potential consequence of all of these perturbations
could be the production of biomolecules that are either toxic or
carcinogenic, and there is no a priori way of predicting the outcome.
I will give a few examples
and then argue why GM food is not a safe alternative.
In addition to their
primary sequence of amino acids, the structure and biological activity
of proteins can be modified by the addition of molecules such as
phosphate, sulfate, sugars or lipids. The nature of these secondary
modifications is totally dependent upon the cell type in which they
are expressed. For example, if a protein involved in the cause of
Alzheimer's disease, the beta amyloid precursor protein, is expressed
in liver cells it contains covalently attached chondroitin sulfate
carbohydrate, while the identical gene expressed in brain nerve
cells contains a much simpler sugar. This is because each cell type
expresses a unique repertoire of enzymes capable of modifying proteins
after they are synthesized. Once modified, the biological activity
of the molecule may be changed. In the case of the _ amyloid precursor
protein, the adhesive properties of the cells are changed, but there
is, at our current state of knowledge, no way of knowing the biological
effects of these modifications.
The second concern is
the potential for inducing the synthesis of poisonous or toxic compounds
following the introduction of a foreign gene. These observations
are clearly at odds with the individuals who imply that everything
is fine because they are simply introducing one gene. In fact, the
introduction of a single gene invariably alters the gene expression
pattern of the whole cell and each cell of the individual or plant
responds differently. One recently published example is the transfection
of a receptor gene into human cells. In this case, the gene was
a closely related isoform of an endogenously expressed gene. The
pattern of gene expression was monitored using gene chip technology,
and the mRNA levels of 5% of the genes was significantly upregulated
or downregulated. Similarly, the simple introduction of a bacterial
enzyme used for growth selection of transfected cells changes the
expression of 3% of the genes. While these types of unpredicted
changes in gene expression are very real, they have not received
much attention outside the community of the DNA chip users. Furthermore,
they are not unexpected. The maintenance of a specific cell phenotype
is a very precise balancing act of gene regulation, and any perturbation
is going to change the overall patterns of gene expression. The
problem, like that of secondary modifications, is that there is
currently no way to predict the resultant changes in protein synthesis.
Third, the introduction
of genes for a new enzymatic pathway into plants could lead to the
synthesis of totally novel or unexpected products via the interaction
with endogenous pathways. Some of the products could be toxic. For
example, retinoic acid (vitamin A) and derivatives of retinoic acid
are used in many signaling events that control mammalian development.
Since these compounds are soluble and work at ultralow concentrations,
a GM plant making vitamin A may also produce retinoic acid derivatives
which act as agonists or antagonists in these pathways, resulting
in abnormal embryonic development.
Given the fact that
genetically modified plants are going to make proteins in different
amounts and perhaps totally new proteins than their parental species,
what are the potential outcomes? A worst case scenario could be
that an introduced bacterial toxin is modified to make it toxic
to humans. Direct toxicity may be rapidly detected once the product
enters the marketplace, but carcinogenic activity or toxicity caused
by interaction with other foods would take decades to detect, if
ever. The same outcomes would be predicted for the production of
toxins or carcinogens via indirect changes in gene expression.
Finally, if the above
problems are real, what can be done to address these concerns? The
issue of secondary modification could be addressed by continual
monitoring of the introduced gene product by mass spectroscopy.
The problem is that some secondary modifications, like phosphorylation
or sulfation can be lost during purification. However, the best,
and to me the only reasonable solution, is to require all genetically
engineered plant products for human consumption be tested for toxicity
and carcinogenicity before they are marketed. These safety criteria
are required for many chemicals and all drugs, and the magnitude
of harm caused by a widely consumed toxic food would be much greater
than that of any single drug.
Professor David Schubert
Cellular Neurobiology Lab
The Salk Institute for Biological Studies
P.O. Box 85800
San Diego, CA 92186-5800
USA
Phone: (001) (858) 453-4100
Email: schubert@salk.edu
Source: http://www.organicconsumers.org/gefood/GMFoodRisks0702.cfm
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