Information on
the Ballot Initiative in Humboldt County to Ban Genetically Modified Organisms
Mark S. Wilson, Humboldt State University, Department of Biology
GMO Foods: Assessment of Safety Based on Human Health Risks
Lisa Kentfield
Humboldt State University
Abstract
A great deal of controversy has arisen with the advent of Genetically Modified Organisms (GMOs), especially surrounding the production, sale, and consumption of genetically modified foods. Many people are concerned, if not convinced, that the consumption of GMO foods by human beings may pose serious health risks. The concern is centered around the notion that there could potentially be various different unforeseen consequences due to the consumption of GMO foods. In addressing potential side effects and byproducts of the creation of transgenic foods, such as potential toxicity and allergenicity, it was found that the possibility and probability of these side effects are being regularly assessed and precautions are being taken to detect and avoid them. Horizontal Gene Transfer (HGT) was also taken into consideration and though it is indeed possible that gene transfer of the genetically modified (GM) gene into the DNA of mammalian cells could occur, it would not have any persistent or negative effect on the recipient. HGT into microorganisms might be a concern if antibiotic resistance was conveyed to the recipient but in light of this fact resistance to key antibiotics is not used in the creation of GMOs. Therefore, the overall potential of GM foods to have negative effects on human health due to the aforementioned phenomena is negligible.
Introduction
The commercial production and consumption of Genetically Modified (GM) foods is perceived by many to be a novel technology that has been poorly evaluated and could potentially be harmful to humans. Though these foods seem very new, the first regulatory approval of GM crops occurred in 1995 (A. Konig et al., 2004). It was in the mid-1980s that the Organization for Economic Co-operation and Development and the US Office of Science and Technology Policy were working to assess the safety and need for regulation of GM crops and any other foods produced using GM crops. That puts us back at least twenty years from today in our ongoing scrutiny of the safety of GM foods.
Every newly proposed GM crop must undergo regulatory review to assess its safety. A systematic approach has been developed in order to test the safety of GM crops. The basic concept employed when evaluating the safety of GM foods is the comparison of the transgenic food to the comparative food product whose equivalent it will be sold as. This could either be a whole food or any food derived from other genetically modified foods. The term Œassessment of substantial equivalence¹ describes this approach because the novel food is being compared to its parent food to ensure that it is as safe as that which humans have been consuming throughout history. The reason for saying Œas safe as¹ lies in the fact that many of the foods humans have been consuming throughout history contain natural toxins or anti-nutritional compounds. One
example of this is the presence of neurotoxic glycoalkaloids in potatoes, which evidently are toxins that are tolerated by human beings (A. Konig et al., 2004). Thus the phrase Œas safe as¹ frees GM crops from being implicated for the presence of toxins or other undesirables that were already present in the food and have been being consumed by humans for years.
Given this evaluation approach, GM foods must be individually assessed on a case-by-case basis. Parameters as to the composition of the traditionally bred crop or comparative Œsafe¹ food are established. This type of targeted approach has already been used and considered effective in identifying alterations in composition resulting from conventional plant breeding (ENTRANSFOOD, 2003). These parameters of the expected chemical composition include expected levels of macro-nutrients (fats, proteins, carbohydrates), micro-nutrients (vitamins and minerals), key toxins, and key anti-nutrients (substances that inhibit important metabolic pathways or impair digestion). This compositional profile of the GM food is then compared to that of the parent crop or equivalent food item to detect any significant difference between the two. A difference in chemical composition, other than what was specifically intended by the genetic modification, could potentially be indicative of a fundamental change in the food being evaluated. If such a difference is detected it must undergo further testing to ensure that it poses no threat to human health upon being consumed.
Toxicity
One concern about compositional alterations of GM crops is that an unintentional toxin will be produced by the modified crop and go on to have adverse effects on the consumer who ingests the foodstuff. The evaluation of potential toxins, like that of the GM food itself, is done on a case-by-case basis. The amino acid sequences and structure of unintentionally produced proteins can be compared to databases to determine if the compound is a known toxin or similar in composition to a known toxin. In doing this, producing food that contains known human toxins can be avoided and any compounds that resemble known toxins will be flagged for further toxicity testing programs. In the case that there is no known analog to a protein being produced by a genetically modified crop, the protein will become subject to rigorous testing procedures to determine if it is safe for human consumption. The guidelines for testing GM organisms that are imposed by the European Commission¹s Scientific Steering Committee require that ³in the case of novel proteins with insufficient database, and in particular if the available data suggest the existence of any cause for concern, a repeated dose study should be performed using laboratory animals² (European Commission, 2003). These studies test for chronic toxicity, carcinogenicity and long-term effects, where applicable. Both single and repeated doses are administered at comparative levels and in high multiples of equivalent human consumption to account for circumstantial variance in consumption and varying sensitivity among individuals in the population.
Allergenicity
Another big concern surrounding unintended products of GM Foods is their potential as human allergens. Food allergy is a pertinent health issue and there do exist plant proteins that are known to be allergens. Allergic reactions occur in an individual who has been exposed to a given amount of a protein that they were susceptible to which triggered an immune response. Subsequent exposure to the offensive protein will produce a larger and potentially adverse response, as is the nature of the immune system.
To envision the probability of this effect being produced by extraneous proteins of genetically modified foods, there are a few key considerations. One is whether the recombinant protein is derived from an allergenic source or a known allergen. Another is whether or not the protein reacts with antibodies for other commonly known allergens. When the genes inserted into the transgenic crop are not derived from an allergenic source there is still a systematic method to assess the potential allergenicity of any newly produced proteins. The primary amino acid sequence of the protein is compared to that of known allergens to determine if there is any similarity. There is some debate about whether six or eight contiguous amino acids should be considered sufficient similarity to know allergens. Some experts say that six will result in too many false positive correlations whereas others believe that eight could result in a false negative correlation between a protein and a corresponding allergen. Either way, it is evident that extensive efforts are being made to evaluate allergenicity even where it isn¹t a conspicuous issue.
To put it all in perspective, one must keep in mind that more than 90% of food allergies are triggered by specific proteins in only eight different foods: peanuts, tree nuts, milk, eggs, soybeans, shellfish, fish and wheat. Due to the evidence of the potential problem these proteins could cause were they inserted into other foods, steps have been taken by the FDA to prevent that from happening (Allred, 2000).
Horizontal Gene Transfer
Horizontal Gene Transfer (HGT) is probably the Œscariest¹ potential threat GM foods appear to pose to the consumer because many people have little or no understanding of the likelihood, mechanism, or possible effects of such an event. HGT would entail the transfer of parts of a genome, potentially a functional gene, from the DNA of one organism to another. There is evidence of inter-domain HGT in nature throughout evolution and in the natural world today. One example is the well known life cycle of the Agrobacterium spp., which transfer genetic material via plasmids into the genome of the plants they associate with.
The pertinent question regarding GM foods and humans is if the genes inserted in the food will be taken up by human cells during digestion and go on to cause adverse effects. Cells of animal guts are constantly exposed to fragments of DNA from food. It has even been shown that cattle and chicken have taken chloroplast DNA up into various tissues after being fed maize (Einspanier et al., 2001). Despite this seemingly alarming evidence, there are a few key points to keep in mind when absorbing this information.
One is that all sorts of foreign DNA sequences have already made their way into human food and animal feed throughout history so it is likely that any given transgenic sequence will have already been processed through the human gut before (F.Cellini et al. 2004).
Also, it is much more probable that DNA would be taken into gut cells or cells of the immune system, both of which have an extremely high turnover rate, and would simply exit the body via the feces.
The one potentially real threat that could come from HGT of a GM food would be if antibiotic resistance were to be conferred to the bacterial flora that inhabit the human intestinal tract. The inserted DNA of the GM crop is more likely to transfer to bacterial because they make share sequence homology with the insert, which is often derived from a bacterial species. The resident bacteria of the human body reside primarily in the colon. This is the last stretch of a long journey through the gastrointestinal tract, which degrades the DNA. Only a small percentage of the DNA will actually reach the colon, which would make HGT of any genes to the resident bacteria a rare event. Despite the rarity of such an event, certain antibiotic resistance markers, such as those commonly prescribed by medical professionals, are being carefully avoided.
Conclusion
When addressing all the possible unintended effects of GM food it should be kept in mind that the act of genetically modifying an organism is really done with much precision. Specific genes are inserted that produce very specific functional protein products. Unless specifically inserted, it is unlikely that toxic or allergenic substances should make their way into foods that were previously devoid of them. The
tests and precautions mentioned are a safeguard against unforeseen outcomes of genetic modification and not indicative of widespread production of myriad novel substances resulting from genetic modification that must be tirelessly sorted through to determine possible adverse effects. There is no reason to fear that one¹s health will be at all negatively affected by the consumption of GM foods. Concerns about toxicity and allergenicity are being addressing by way of avoidance and regular testing. HGT does not have any lasting effect on human tissues and medicinally utile antibiotic markers are avoided to ensure that resistance is not conferred to bacteria residing in the human gut.
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