Preparing for the safety issues surrounding genetically modified animals that are to be used for producing foods

Genetically modified (GM) crops that are used for producing human food and animal feed are grown on a continuously increasing scale around the globe. Their worldwide acreage reached 134 million hectares in 2009, most of which was located in North and South America, China, India and South Africa, and growth is likely to continue1. Before these crops are allowed onto the market, they have to receive regulatory approval from the national authorities in many countries. Part of the procedure for obtaining approval usually is an assessment of the safety of the pertinent GM crops.

According to the regulations, the same applies to other GM organisms, such as micro-organisms and animals. Whereas food-producing GM animals have not reached the market yet, there are indications that, in nations outside the EU, this may become a reality in the near future. It is therefore important that the regulatory authorities prepare themselves for reviewing the safety of these GM animals. Below, the potential issues with regard to the food safety of GM animals are reviewed.

foodproducing animals that are in an advanced stage of development include, for example, a GM salmon with increased growth rate, to be used in aquaculture, i.e. ‘salmon farming’. This GM salmon has been genetically modified with a ‘foreign’ gene coding for the production of salmon growth hormone. This gene is under the control of a promoter from another fish species, the ocean pout, which probably leads to continuous expression of the growth hormone, contrary to the expression of the naturally occurring growth hormone, which is triggered by neuro-endocrine factors. It has previously been observed that providing salmon with additional growth hormone, either orally or via implants, can stimulate growth. The use of genetic modification to introduce growth hormone is being considered as an alternative to these practices. The GM salmon shows enhanced growth rates as compared to its conventional counterpart, as well as increased feed conversion2.

The adult marketable size of the GM salmon is reportedly the same as that of conventional salmon. The GM salmon’s enhanced growth rate allows fish farms to grow the salmon to a marketable size of four kilograms within a shorter period than conventional salmon, i.e. within approximately two years instead of three-anda- half years, as has recently been observed in a commercial market test performed by the company that developed the salmon. It is also reported that the company is in the final stage of the regulatory review of its submission for marketing the salmon. The submission has been made to the United States Food and Drug Administration (US FDA), which also considers the GM salmon as a ‘veterinary drug’ given the impact of the genetic modification on the animal’s physiology3.

Another example of an experimental foodproducing GM animal that is in an advanced stage of development is a GM pig producing the phytase enzyme in its salivary glands. Phytase degrades phytic acid, an anti-nutrient that is present in a number of animal feeds of plant origin, including cereal grains and soybeans. Phytic acid is a carbohydrate with covalently bound phosphate groups, which are not bio-available to the pig during digestion, leading to a higher release of phosphate into the environment via the pig’s excrement. Environmental phosphate loads are known to contribute to eutrophication of surface waters, with an impact on marine and freshwater wildlife. Moreover, phytic acid also acts as an anti-nutrient by binding essential minerals with its phosphate groups. Phytase produced by moulds is therefore commonly added to animal feeds for non-ruminants as a technological aid to remove phytic acid and to raise the digestible phosphate content.

The GM pig, which has been developed by researchers at a Canadian university, has been genetically modified with a gene coding for the production of a phytase from the bacterium Escherichia coli. Within the DNA construct that was used for the genetic modification, this gene has been put under the control of a promoter that is specifically active in salivary glands, enabling the continuous expression of the phytase in salivary glands of the GM pigs. The E. coli phytase is stable and active in the animal stomach. Feeding trials in which with GM pigs were compared to their non-GM counterparts thus showed that the digestibility of dietary phosphorus from diets with a high level of soybean meal, in which most of the phosphorus occurs in the form of phytic acid, approached nearly 100 per cent, leading to reductions in excreted phosphorus by 56 per cent or more in the GM animals4.

A few additional examples of experimental GM animals producing foods, which are not further elaborated here, include mastitisresistant GM cattle producing the antibacterial protein lysostaphin through their milk glands (Figure 1, page 30)5, GM cows producing milk with increased content of the casein proteins, GM tilapia and river carp with enhanced growth rates and influenza-resistant GM chicken. Contrary to food producing GM animals, which have not reached the market yet, anti-thrombin that is produced as a medicine in the milk of GM goats kept in containment on a special farm in the US has received regulatory authorisation from the US FDA and the European Medicines Agency. A number of other non-food applications for GM domestic animals are still under development, such as goats producing antiwarfare- agents and spider-silk-like protein as a biopolymer (e.g. for medical applications), through their milk, in Northern America.

As mentioned above, GM animals and other organisms which are to be marketed need to receive regulatory approval in many countries’ legislations. Part of the regulatory procedure is a pre-market safety assessment carried out by experts advising the authorities. Similar to what has previously been described for GM crops6, the principles of the safety assessment of GM animals have been internationally harmonised. The Codex Alimentarius Commission, which is a joint collaboration between the Food and Agriculture Organisation and World Health Organisation establishing standards, protocols and guidelines for food safety, published its guidelines for the safety assessment of foods derived from GM animals in 20087.

Central to the safety assessment is the comparative approach, which comprises a comparison of the foods produced by the GM animal with those produced by conventional counterparts with a history of safe use and preferably also with matching genetics, housing conditions, life stage, and other parameters. The requirement for the counterpart to have a history of safe use is because, as the Codex Alimentarius’ guidelines explain, conventional food-producing animals usually have not been subject to rigorous safety tests such as toxicity experiments in animals but are considered suitable for human consumption based on experience gained from a history of use as food. The assessment therefore focuses on the differences between the GM animal and its counterpart, i.e. the changes, both intended and unintended, that have been caused by the genetic modification7.

Data that have to be provided by the company or institution wishing to introduce a food produced from a GM animal include data on the following items: (1) molecular characteristics of the modification (2) comparative analysis of the GM animals versus its counterpart (3) food safety of the genetic modification and (4) nutritional aspects.

With regard to molecular characterisation, information should be furnished on:

1. The origin, sequence, structure and function of the DNA that has been used for the genetic modification
2. The method that has been used for genetic modification, such as the use of viruses carrying the DNA to be transferred
3. Information on the recipient organism, i.e. the animal that is genetically modified, including its history of food use, husbandry conditions, breeding history and how it is further handled to eventually obtain foodproducing animals
4. Characterisation of the DNA that has been introduced into the animal’s DNA, including the inserted elements, their potential for mobilisation or recombination, the number of insertion sites, the organisation of the inserted DNA at each insertion site

For the comparative analysis of GM versus non-GM animals, the levels of key components present within the food products derived from these animals are measured and compared with each other. The animals should preferably be reared under the same husbandry conditions and be at the same developmental or physio – logical state, although it can be envisaged that the new trait introduced by the genetic modification may also have an impact on these conditions. Differences that are found between the GM animal and its counterpart in this comparative analysis do not constitute hazards per se but should, for example, be interpreted within the context of natural background variation of the parameter showing a difference, which reflects the product variability to which consumers are commonly exposed. Contrary to GM plants, the number of animals that can be used for such experiments may be limited, such as for experiments involving large domestic animals7.

In addition to compositional parameters, also the health and welfare status of the GM animal as compared to non-GM animals can provide useful indications on the potential health and welfare effects of the genetic modification. Generally spoken, effects observed in animals can also provide indirect evidence and thus have a sentinel function for physiological effects of the products derived from these animals in human consumers7.

The comparative analysis of compositional and health parameters can help with identifying both intended and unintended effects of the genetic modification. In many cases, the genetic modification will give rise to the expression of new proteins that are encoded by the introduced genes. These substances that do not occur naturally – or whose levels have been altered beyond the background ranges – in foods derived from the GM animal should then be further considered for their safety7.

During the safety assessment of GM foods, a number of items are commonly addressed in a way that is similar to what has previously been described in more detail elsewhere8. The toxicity and allergenicity of the newly expressed proteins is tested, for example, using various techniques including data on the toxicity or allergenicity of the gene donor; the similarity of the sequence of the new protein to the sequences of known protein toxins and allergens; the susceptibility of the newly expressed protein to proteolytic enzymes that are also present in the gastrointestinal tract; and, if needed, its toxicity in laboratory animals6,7.

If the modification targets the nutritional properties of the food produced by the GM animal, then the comparative compositional analysis can provide useful indications of the changes in the nutritional value of the product. If needed, such as in the case of sizable changes in the levels or bioavailability of nutrients, further comparisons with other foods with similar contents of the pertinent nutrient or animal feeding tests with the whole food may have to be considered7.

It can be envisaged that not only safety but also other considerations, such as ethical and socio-economic considerations will impact on the decisions of policy makers to allow GManimal- derived foods onto the market or not. The current discussion on the permissibility of the food use of cloned animals already highlights the importance of ethical and welfare aspects in this regard. Currently, the EU-funded PEGASUS project (www.projectpegasus.eu) is exploring the advantages and disadvantages of the technology, taking stock of the social, economic, technical, ethical and policy-related issues surrounding the technology with the aim of providing an overview and recommendations to the European policy makers.

Acknowledgement

The author thanks Dr E.J. Kok for her valuable comments to the manuscript of this article. Financial support from the Dutch Ministry of Agriculture, Nature, and Food Quality is gratefully acknowledged (project number 7229601).

References

1. James, C. (2009) ISAAA Brief 41-2009: Executive Summary, Global Status of Commercialized Biotech/GM Crops 2009. International Service for the Acquisition of Agri-Biotech Applications, Ithaca NY. http://www.isaaa.org/resources/publications/briefs/41/executivesu mmary/default.asp
2. Cook, J.T., McNiven, M.A., Richardson, G.F., Sutterlin, A.M. (2000) Growth rate, body composition and feed digestibility/conversion of growth-enhanced transgenic Atlantic salmon (Salmo salar). Aquaculture, 188(1-2), 15-32.
3. Aquabounty (2010) Preliminary Results for the Year ended 31 December 2009. AquaBounty Technologies, Waltham MA. http://www.aquabounty.com/documents/press/2010/2010%2005. 14%20-%20Preliminary%20Results%20for%202009.pdf
4. Golovan, S.P., Meidinger, R.G., Ajakaiye, A., Cottrill, M., Wiederkehr, M.Z., Barney, D.J., Plante, C., Pollard, J.W., Fan, M.Z., Hayes, M.A., Laursen, J., Hjorth, J.P., Hacker, R.R., Phillips, J.P., Forsberg, C.W. (2001) Pigs expressing salivary phytase produce low-phosphorus manure. Nature Biotechnology, 19(8), 741-745 [erratum in 19(10), 979]
5. Wall, R.J., Powell, A.M., Paape, M.J., Kerr, D.E., Bannerman, D.D., Pursel, V.G., Wells, K.D., Talbot, N., Hawk, H.W. (2005) Genetically enhanced cows resist intramammary Staphylococcus aureus infection. Nature Biotechnology, 23(4), 445-451.
6. Kleter, G.A. (2009) Assessing the safety of genetically modified crops used for food and feed purposes. New Food, (1), 53-55.
7. Codex alimentarius (2008) Guideline for the Conduct of Food Safety Assessment of Foods derived from Recombinant-DNA Animals. Joint FAO/WHO Food Standards Program, Codex alimentarius Commission, Rome. http://www.codexalimentarius.net/ download/ standards/11023/CXG_068e.pdf
8. Kleter, G.A., Kuiper, H.A. (2002) Considerations for the assessment of the safety of genetically modified animals used for human food or animal feed. Livestock Production Science, 74(3), 275-285.

About the author

Dr Gijs A. Kleter

Dr Gijs Kleter is a natural scientist specialised in risk assessment of foods and animal feeds, in particular the safety of biotechnologyderived products and emerging risks. He is with RIKILT – Institute of Food Safety (www.rikilt.nl), which is part of Wageningen University and Research Center in Wageningen, The Netherlands.