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University of Newcastle Research on the
Transfer of DNA from GM Food Into
Bacteria in the Human Gut

Soil Association (UK) v.2 1jul2005

 

Summary

In July 2002, the Food Standards Agency (FSA) put the results of new research on its website which showed that genetically modified DNA material moves out of GM food and into human gut bacteria. These were the result of the first known human trial of GM food, carried out by the University of Newcastle and they disproved claims by the biotechnology industry. Although the findings were surprising and some scientists expressed concerns, the FSA denied that the study was significant. The research was published in Nature Biotechnology in January 2004.

We believe that in the absence of research showing otherwise, this means that the safety of GM food is in doubt; the approval procedures for GMOs are inadequate; and that the FSA is not taking a precautionary, science-based approach to the safety of GM foods or adequately informing the public or Government of the uncertainties.

1. Background

Some GM soya and maize has been allowed in UK food for several years. However, no human safety trial had ever been officially carried out and the approval procedures have not required data on the rate and effects of “horizontal gene transfer” compared to non-GM food. Horizontal gene transfer is when genetic material moves from one organism to another, usually of a different species, in a way that is different to the transfer of genetic material to another generation through reproductive processes; it occurs most commonly between micro-organisms.

In genetic engineering, the insertion process and the genetic material inserted in GMOs are designed to be particularly mobile and active to overcome the various cellular defense mechanisms that constitute the natural ‘species barrier’ against DNA transfer between different species. Some scientists are concerned that this means GMOs may have an artificially high potential for horizontal gene transfer compared to non-GMOs and that many or all GM characteristics, such as antibiotic resistance or toxin production, could possibly transfer from GMOs into other organisms.

The most immediate concern is over gene transfer from GM food or pollen into bacteria in humans, livestock and soil. Potential negative health effects include: undermining the medical use of antibiotics for controlling infections, causing bacteria or cells in our body to produce Bt toxin, or the creation of new viral diseases.

For years, the biotechnology companies have either denied that transgenes could transfer to gut bacteria or, more recently, asserted the opposite - that gene transfer has always occurred between micro-organisms and so there is no cause for concern with GMOs. Worryingly, the UK Government’s GM science review in 2003 also assumed that transgenic DNA is no different from other DNA and concluded that the transfer of GM DNA from GM crops to bacteria "is unlikely to occur because of a series of well established barriers", (www.gmsciencedebate.org/ uk/report/pdf/gmsci-report1-full.pdf). However, there is no body of scientific evidence or even serious rationale to support this view. GMOs have different features to non-GMOs and these are specifically designed to cross species barriers. So, in the view of those concerned about GMOs, that there is a real concern that the rates and negative effects of horizontal gene transfer could be higher than non-GMOs. We are greatly concerned that the FSA and European authorities publicly state that they are taking a precautionary science-based approach but, in this and other respects, are approving GMOs for use in food and feed on the basis of assumption alone.

Evidence that horizontal gene transfer from GMOs happens in animals has existed for a few years. In May 2000, German researchers at the University of Jena found that a herbicide resistance gene transferred from GM oilseed rape pollen to micro-organisms in the gut of bees. Researchers at the University of Leeds showed that the transgene for kanamycin resistance transfers to E.coli bacteria after being exposed to saliva in a sheep’s mouth (Duggan et al., British Journal of Nutrition, 2003, "Fate of genetically modified maize DNA in the oral cavity and rumen of sheep"). Until this study, gene transfer from GM food in humans had not been investigated.

2. University of Newcastle Study

In response to concerns, the FSA commissioned five studies into the fate of transgenic DNA. It was particularly interested in whether antibiotic resistance genes could transfer into the bacteria in the human gut. These are inserted into GM plants during the engineering process as ‘markers’, to enable successfully modified cells to be identified. This briefing covers one of the studies, “Assessing the survival of transgenic plant DNA in the human gastrointestinal tract”, Netherwood et al, 2004, which was the world’s first known trial of GM food on humans.

Part I – persistance of transgenic DNA in the gut

Nineteen volunteers were used, of which seven had had their lower intestine removed and used colostomy bags, enabling bowel samples to be taken from the small intestine. They were all given a meal containing GM soya. This comprised 190g of a deep fried burger made of 150g soya protein (plus eggs and water) and 264g of a milkshake made up of 600ml of soya milk and 100g of soya protein supplement, all purchased from retail outlets. (The soya meal was the brand El Corte Ingles and the protein supplement and soya milk were from Holland and Barrett.) Each meal contained an estimated 3000 billion copies of the epsps transgene (length 2,266 base pairs) which codes for resistance to the herbicide glyphosate. This transgene is originally of bacterial origin, but had been modified for greater expression in plants. The GM construct also included the Cauliflower mosaic virus 35S promoter.

The researchers collected their stools every 30 minutes for up to 6 hours after eating. The samples were freeze dried, ground and heated to 58C for three hours, and then tested for the presence of a specific portion of the transgene. From all seven of those without a lower intestine, they found "to their surprise" that "a relatively large portion" of GM DNA passed through the small intestine, ranging from 100,000 copies of the targeted portion of the transgene, up to 111 billion copies or 3.7% of the total. In six of the seven volunteers, the entire length of the transgene was identified in the samples. The levels of the epsps transgene in the samples was similar to the levels of a gene native to soya, for lectin, indicating that the transgene was being degraded at similar rates to the rest of the soya DNA. No transgenic DNA was found in the faeces from those with a complete intestine.

Part II – uptake of transgenic DNA by gut bacteria

To see if horizontal gene transfer was occurring, they tested the bacteria in the stools of the seven using colostomy bags before and six hours after the GM meal for the presence of the transgene. The wet bowel samples contained c.1 million bacteria per gram.

They could not detect any transgenes in the gut bacteria using normal PCR methods. However, after multiplying the bacteria in a broth to make detection more sensitive, they found that, in three of the seven volunteers, they had taken up a fragment of the transgenic epsps gene (conventional culture techniques cannot recover more than a tiny minority of the microbes in the gastrointestinal tract). The frequency of the transfer was low: 1-3 copies of the transgene fragment per million bacteria. None contained the entire transgene. The researchers say that the levels of transgene in the bacteria were similar in the samples before and after the GM meal (though no data for the latter is given). Sequence analysis confirmed that the transgenic material was identical to the GM plant transgene, rather than the bacterial one, confirming that the source was GM. Interestingly, they could not detect any transfer of one of the native genes in soya, that for lectin. None of the bacteria sampled from the stools of subjects with complete intestinal tracts contained the transgene.

Part III – uptake of transgenic DNA by human gut cells

To test if there had been horizontal gene transfer into the cells lining the gut (the enterocytes of the intestinal epithelium), they genetically modified Lactobacillus bacteria (which lives on the surface of the gut) and Salmonella bacteria (an intra-cellular pathogen). No gene transfer was detected.

3. Conclusions

The first part of the study shows that a proportion of GM DNA consumed is only fully degraded once it reaches the large intestine, where remaining naked DNA is hydrolysed by DNAases. The researchers considered it “surprising that even a fraction of GM soya DNA survives passage through the small bowel.” Nevertheless, this is consistent with the findings of the Duggan et al study on GM DNA in sheep, as the microbial system in the human colon is considered similar to that of the rumen.

The second part shows that during passage in the small intestine, horizontal gene transfer occurs with some of the GM DNA moving out of GM food and into the human gut bacteria. The fact that the transgene was detected after the population was amplified “indicates that that the DNA was stably maintained in the bacteria [over generations] and thus had integrated” into the bacterial DNA (as opposed to being present simply because the bacteria has eaten the GM material, as suggested some).

The levels of transfer were similar before and after the GM meal, suggesting “that gene transfer did not occur during the feeding experiment“ and “that these subjects had consumed the transgene before enrolling in our study”. As they could not detect transfer of the entire transgene, the researchers concluded, “it is unlikely that the gene transfer events seen in this study would alter gastrointestinal function or pose a risk to human health. Nevertheless, the observed survival of transgenic DNA from a GM plant during passage through the small intestine should be considered in future safety assessments of GM foods.”

We consider these findings to be very worrying as there are only small amounts of GM material in the UK diet because of the non-GM policies of most major food manufacturers and retailers. While this study indicates that a single meal may not have an immediately significant effect, it shows that the current small amounts of GMOs in the diet, present as contamination or from the use of GMOs in a small number of foods, are resulting in transformed bacteria in the human gut in the UK and these are persisting. Moreover, that the native lectin gene did not transfer is consistent with the concern that GMOs may have special characteristics that promote horizontal gene transfer. This raises serious health issues for GMOs.

On the results of the third part, the researchers say that any conclusion “that gene transfer from bacterial cells to enterocytes is unlikely must be treated with caution” as the complex environment of the intestine surface cannot be simulated perfectly.

4. The response of the media, scientists and FSA

Unfortunately, only the results of the first part of the research were widely publicised. The Guardian was the only newspaper to cover the key evidence of gene transfer. On 17 July 2002, it reported that “British researchers have demonstrated for the first time that genetically modified DNA material from crops is finding its way into human gut bacteria, raising potentially serious health questions”.

Michael Antoniou, senior lecturer in molecular genetics at King’s College Medical School, London, said, “To my knowledge they have demonstrated clearly that you can get GM plant material in the gut bacteria. ... it suggests that you can get antibiotic resistance marker genes spreading around the stomach which would compromise antibiotic resistance.” (The Guardian, 17.7. 2002).

In an article in Nature Biotechnology in February 2004 (Vol 22, no. 2, pp 170-172), John Heritage of the University of Leeds and one of the researchers in the Duggan et al study said “on balance, the data presented in the paper support the conclusion that gene flow from transgenic plants to the gut microflora does occur. Furthermore, because transfer events seem to have occurred in three of the seven subjects examined, it may be that transgenic gene transfers are not as rare as suggested by the UK GM Science Review Panel”. He said that the risks of horizontal gene transfer should be assessed in the approval process for GMOs.

The FSA, however, which advises on the safety of GMOs and is responsible for the approval of GM foods in the UK, mostly ignored the significance to human health. In its public statement in 2002, it chose to focus on the first part of the study saying that it “showed in real-life conditions with human volunteers, no GM material survived the passage through the entire human digestive tract.” However, whether GM material survives to leave the digestive tract is an environmental issue; it is what happens before it is degraded that is important for health.

On the evidence of gene transfer, the FSA said “the research concluded that the likelihood of functioning DNA being taken up by bacteria in the human or animal gut is extremely low”. This is a major generalisation and downplaying of the findings as persistant DNA uptake by human gut bacteria was found in nearly half the subjects apparently from general exposure to GMOs, despite the low level of GM material in the UK food chain, and scientists have said that the issue should be addressed in future safety assessments.

source: http://www.soilassociation.org/web/sa/saweb.nsf/0/cc6cdacf049756b980257006003ad8ad?OpenDocument 3jul2005

 

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