by Pat Howard
Few rules exist in the food engineering game
Since 1995, I have studied the scientific debates regarding the potential hazards of genetically modified plants, animals, and micro-organisms. The concerns expressed by ecologists, agronomists, microbiologists, veterinarians, physicians, toxicologists, and immunologists in the scientific literature are considerable. Coverage in the media, on the other hand, has been very inadequate.
The one study that received a brief flurry of media coverage was conducted by a research team in Scotland, led by Dr. Arpad Pusztai, an international expert on lectins, which are insecticidal molecules produced by plants. In 1995, Pusztai’s team received a $3.2 million research grant to investigate the safety of genetically engineered potatoes producing such an insecticidal molecule. Pusztai had already spent six years studying this lectin. He had fed it to rats in very large quantities without any deleterious effects. He did not expect to uncover any health hazards.
The rat-feeding study was meticulously designed to maximize the reliability of the findings. One group of rats ate the genetically modified potatoes, a control group consumed unmodified potatoes, and a third group ate unmodified potatoes laced with the lectin. To everyone’s surprise, the rats that ate the genetically modified potatoes suffered serious health effects. The study used young, growing rats.
After only 10 days, a significant number of the rats that ate the GM potatoes showed signs of arrested development of their livers, testicles, and brains. Some suffered damage to the thymus and spleen, which are both crucial to immune system function. The rats’ white blood cells also appeared to have been affected. The cells lining their stomachs and intestines had begun to proliferate and undergo structural change, an ominous sign of the possibility of an increased risk of cancer. The feeding continued for 110 days, the equivalent of the first 10 years of a child’s life.
To rule out any other causes, the researchers repeated the tests with boiled, baked, and raw potatoes and varied the amount of food and percentage of protein. The results were consistent; the GM potatoes alone damaged the young rats’ organs and immune systems. On October 16, 1999, The Lancet reported the study. Pusztai, however, went public with his findings before publication in this peer-reviewed journal. He appeared on television and expressed his concern for the public, which was already eating genetically modified potatoes, tomatoes, corn products, and soy. He was subsequently fired and his computer and research data confiscated. He and his colleague Stanley Ewen later obtained all the data and published their analysis in Britain’s most prestigious medical journal.
Since the lectin did not damage the rats’ organs and immune systems, what did? Is there something about the genetic modification process itself that makes the feed immunogenic, toxic, or carcinogenic? Feeding studies involving rats, mice, pigs, and cows, conducted in Mexico, Brazil, Cuba, Japan, Egypt, Slovenia, and Russia have produced comparable, negative health effects. In fact, a rat-feeding study of the first commercial GMO, the FlavorSavr tomato, also revealed lesions that caused FDA scientists to protest the agency’s approval of the product in 1994.
How do genetic engineers manage to get foreign DNA into the genome of a host plant and enable the plant to utilize it to produce proteins that confer the ability to tolerate a particular herbicide or antibiotic, or to kill insect pests? The fact is that they exploit the infectious capacities of viruses and bacteria. One commonly used vector is a soil bacterium, a plant pathogen that causes galls or tumours. Only the DNA coding for proteins involved in inducing tumours is used. It is taken from a plasmid; plasmids are small, free-floating circles of DNA that provide bacteria a greater capacity to deal with environmental changes than any other life form. They are able to exchange and share plasmids, which contain genes for adaptive capacities. This is how they spread antibiotic resistance. There is evidence that antibiotics may function as sex hormones stimulating gene transfer via the exchange of plasmids, among even different species of promiscuous bacteria.
Genetic engineers open up plasmids and insert a set of genes borrowed from other species. The ideal transformation would incorporate one copy of the foreign gene set into the genome of the host plant’s cells. However, this is rarely, if ever, what actually occurs. Most of the approved commercial varieties have either only a portion of the foreign DNA that was successfully transferred, or multiple copies of the desired transgenic DNA. Recent research, after regulatory approval, has revealed that unintended bits of bacterial DNA are frequently incorporated, which may result in deletions, multiplications, or movements of the host plant’s DNA.
The transformed configuration of DNA that characterizes the transgenic plant’s genome is called the transformation event. After a long struggle in Europe, regulators now require this information from applicants seeking approval for the sale and growth of transgenic varieties. Many of the varieties currently being analyzed by European scientists are turning out to be other than what they are supposed to be.
In 2003, government scientists in France reported on studies of five transgenic crops: Monsanto’s Round-up Ready
soybeans and four Bt insecticidal corn varieties. All five transgenic lines had inserted foreign DNA, whose structure was no longer the same as was originally reported by the company.
Not only were the inserted genes rearranged, but the plants’ own genomes had also been scrambled around the insertion site. Belgian scientists also conducted similar studies that turned up comparable evidence of DNA scrambling. This signifies that the precise varieties evolving in fields in Canada, the US, China, Argentina, Australia, the Philippines, and elsewhere have not been tested for potential
allergenic or toxic effects on the humans and animals that consume them. If the lines are unstable, no amount of testing can guarantee their safety in the future, or when they are subjected to different
Genetic engineers have no control over where their foreign DNA constructs will be inserted into the host cell’s DNA. Research has revealed that the insertions often occur inside or near genes, which can be turned on or off by the invading foreign DNA. This can have serious consequences.
Of particular concern are fragments of foreign DNA that appear in virtually all genetically modified crops: the cauliflower mosaic virus (CaMV) promoter is used to ensure that the foreign genes continue to express their proteins at a high level. This viral gene switch, or promoter, is able to stimulate the expression of genes, not only in plant cells, but also in the cells of mammals, including humans. This promoter is in all the cells of transgenic plants. Thus, the question of whether it is broken down by digestion processes, or ends up in cows milk, or in the muscles and blood of animals fed GM feeds, or in the milk of breast-feeding mothers, becomes a really important issue.
When critical scientists have raised these concerns, proponents have responded that we have been eating cauliflower, which is sometimes infected with this virus, for a very long time with no apparent consequences. However, the cauliflower mosaic virus promoter used in genetic engineering is, in its naked form, unlike the natural wild-type virus that has a protective protein coat. The naked forms of viruses are more infectious because their viral coats generally determine host specificity. CaMV promoter is particularly prone to integrate into host cell genomes because it has a recombination hotspot, meaning it is prone to breaking and joining with other DNA at that spot. This increases the likelihood that the promoter, and any other genes linked to it, will be integrated into the genomes of cells they manage to enter. Cancer could be one of the outcomes in cells in which genes are turned on and kept on by this particularly strong promoter.
Throughout all GM crops, another hazard of this viral promoter is its potential to reactivate dormant viruses, which exist in the genomes of all higher organisms, including plants and animals. There is also a danger of the creation of new viruses by recombination. Yet another concern is the use of antibiotic resistance marker genes that could conceivably transfer resistance to bacteria in the mouths and guts of people and animals that ingest GM food and feed. It could also be transferred to bacteria in soil that surrounds the roots of transgenic plants, or soil that contains decomposing GM crop residues. Soil containing such bacteria could be dangerous for farmers and children, who might end up passing the resistance to bacteria resident in their own bodies. If pathogenic bacteria later infect them, antibiotics may prove useless because of transfer of the resistance gene from their resident bacteria to the pathogenic invader.
Concern about this possibility prompted the British Medical Association to call for a moratorium on field trials or commercialization of GM crops containing these genes. The European Food Safety Authority has also recommended that no crops containing antibiotic resistance marker genes be approved anywhere in Europe. Many of the crops growing in Canada carry these antibiotic resistance genes in every cell of the plant.
Safety assessments are necessary to determine whether these genes are present in soil bacteria, or in bacteria in the mouths, stomachs, and intestines of people who have been eating genetically modified foods. One major problem we face is the underdeveloped state of safety assessment science. We can only culture less than one percent of bacterial species found in soil, and in our own bodies. Is there any evidence of lesions in our digestive organs, especially in those of babies and young children? What about their immune systems and their livers and brains? If the foods are not even labelled, how can we know whether what we are eating and feeding our infants and children is harmful?
In 2004, people living near a field of Bt corn in the Philippines developed respiratory and gastric illness when the corn flowered. Tests of their blood revealed antibodies to the Bt toxin in the corn pollen, which suggested that it might have caused the illnesses. In Germany, between 2001 and 2002, 12 cows, illegally fed a steady diet of Bt corn, mysteriously died. Milk from the herd was tested and found to contain the genes for the bacterial Bt toxin. Neither Canada nor the US conducts tests on milk from cows fed GM feed for the presence of bacterial toxin or viral promoter DNA. How can we know if GM plants are producing dangerous allergens or toxic metabolites as a result of disruptions of plant genomes caused by the insertion of foreign DNA? We are part of one enormous feeding experiment in which none of us have given informed consent.
Pat Howard is associate professor of communication at Simon Fraser University. She teaches courses on scientific controversies and government regulation related to genetic engineering.