Tag Archives: 35S Promoter

“Are GMO’s Good or Bad?” and Why That’s a Stupid Question

 

“Are GMO’s good or bad?” and Why That’s a Stupid Question

All over the internet, you can hear people arguing about whether or not GMO’s or GM crops are safe. Are GMO’s good, or are they bad? It’s a pretty stupid question, honestly. Saying you have a philosophical stance that they’re inherently good or inherently bad is basically admitting up-front that you’re foregoing the use of logic in favor of dogma. The genetic code of an organism can be modified in an infinite number of ways. It would be quite an amazing coincidence if those infinite possible modifications just happened to be all harmful, or all beneficial.

Whether or not a GM crop is good or bad depends entirely on how it has been modified.  Therefore, this post will not attempt to prove that genetic modification itself is inherently right or wrong. Instead, it will focus on whether or not specific GM crops in circulation today can be shown to be harmful. The question shall be rephrased as “Are any existing GMO’s bad?”  My post will also explore the differences between genetic modification and artificial selection.

Roundup

One of the first anti-GMO claims I heard had to do with “roundup-ready” crops.  These crops tolerate  the herbicide Roundup, particularly its active ingredient glyphosate. It is worth noting that the metabolic pathway that is targeted by glyphosate, the Shikimic Acid pathway, is not used by animals. (1) We ingest our aromatic acids directly, instead of synthesizing them.  It just goes to show you that the term “poison” is relative. Many poisons do affect multiple types of life, but there are also major differences in toxicities between kingdoms of life. That doesn’t mean that glyphosate is automatically safe in all quantities, but neither can we simply assume that weed-killer is automatically animal-killer.

Many images used by anti-GMO  activists  feature people spraying crops down with glyphosate while wearing hazard suits. To be sure, a freshly-sprayed field of roundup-ready crops is not something you would want to frolic around in. It produces eye and skin irritation. More extreme symptoms, such as vomiting and diarrhea, are thought to be due to the surfactants that are mixed in with the glyphosate to increase its dispersal and penetration ability. (2)

Many sources seem to point to these surfactants being more toxic than glyphosate itself. However, some studies take surfactants into account, particularly POEA (Polyethoxylated Tallow Amine) which is the primary surfactant used.  They conclude that under current consumption levels, neither is a danger to the human population.(3)

For glyphosate, very high doses above 3,125 mg/kg body weight per day do seem to be associated with adverse effects in mice, such as weight loss, decreased sperm count, growth retardation,and hepatocyte hypertrophy. However, some animal studies show no ill effects from doses as high as 20,000 mg/kg. (4) For comparison, the lethal dose for caffeine is around 100 mg/kg. (5) Many of us regularly ingest over 1% of a lethal dose of caffeine.

For research on GMO crops, one source of misinformation is Gilles-Éric Séralini. He is most famous for a study in which he fed glyphosate-resistant corn to 10 rats of each sex over the span of two years. Those fed glyphosate-ready corn developed more tumors, and died earlier. However, considering the frequency with which these rats develop cancer (>70%), and the long duration of the study, tumors would be expected to be very common. In fact, it wouldn’t be hugely surprising if all of them had developed tumors in that time frame. With these factors taken into account, the experiment should have included at least 65 of each sex in order to be statistically sound.  (6) The paper has since been retracted by the Journal of Food and Chemical Toxicology. (7)

A joint statement has been released by the French National Scientific Academies, denouncing work by the same author.(8) This is compelling, considering that GMO’s have been largely banned throughout Europe for political reasons. Clearly, the anti-GMO activists in Europe have a lot more political power than agricultural biotech companies like Monsanto. Yet even in these countries, scientists agree that Seralini is unreliable.  It’s clear that Seralini is not a respectable source.

However, Seralini may not be incorrect in principle, even if his methodology sucks. The comparison of Roundup to caffeine may not be a valid one. One concern regarding roundup is that it may be an endocrine disruptor. The endocrine system includes a number of glands that  release hormones, like testosterone, estrogen, and thyroxine. These can cause physiological changes at incredibly low concentrations, sometimes below the picomolar range. So a compound that disrupts the endocrine system could also potentially be harmful at very low concentrations. Additionally, the usual linear dose-dependent assumptions that hold true for many toxins may not hold true for roundup if it is shown to be an endocrine disruptor, because endocrine disruptors often demonstrate non-linear relationships between dose and effect.  In fact, some endocrine disruptors may have non-monotonic dose response curves (NMDRC’s) ,  in which lower doses are sometimes more harmful than higher doses.(9)

How can this be? As I wrote in my last post, one of the Bradford criteria for demonstrating epidemiological correlation is supposed to be dose-effect response. However, this should not be interpreted as an assumption of a linear relationship. If a mechanism for non-linearity exists, it should not be rejected outright. There are a number of potential causes for NMDRC’s. For one, an endocrine disruptor may cause cancer cells to proliferate at low doses, but kill them at higher doses. There may also be a negative feedback mechanism, like when the abundance of a hormone inhibits its own production. Other mechanisms are more complex. One demonstrated in prostate cell lines, can involve two different populations of cells with different types of receptors on their surfaces. One population may rapidly multiply at low doses, and the other population divides more slowly at higher doses. At intermediate doses, the proliferation of one population compensated for the slower proliferation of the other. However, at low doses and at high doses, only one type of cell is affected, so no balancing occurs.

It seems there are many dangers to assuming linearity for dose-effect from endocrine disruptors. One study shows it can cause a certain type of breast cancer cell (T47D cells) to grow more quickly, although the other type of breast cancer cell tested did not. Others have found similar evidence of roundup interacting with estrogen receptors, and altering estrogen production. This could translate into an increased risk of reproductive problems, such as miscarriage and premature birth. Higher levels of estrogen production are also associated with increased breast cancer growth.  This actually seems to be a credible risk. (10)(11) Through the same mechanism, roundup also seems to cause reduced testosterone production in rats. (12) As with many of the issues with roundup, it seems that much of, if not most of the negative effects are not due to glyphosate alone, but involve the numerous other additives in the mix.

One study found that when treated with the full roundup mix, cells produced 40% more estrogen, followed by an eventual decline in estrogen production. However, as  Dorothy Bonn (13) admits, it is uncertain how the results of cell culture tests translate into effects on cells in the human body. She says serum proteins can help cleanse the body of such chemicals. This, coupled with the lack of strong evidence for ill effects in most animal/human tests may suggest that these effects are mitigated in vivo (in the body) versus in vitro. Even so, it seems that whatever the effect is, it may not be negligible, as has been widely assumed. Previous research does seem to have underestimated two things; 1) the toxicity of the entire roundup formulation vs just the active ingredient (glyphosate) alone, and 2) The extremely low dose at which an endocrine disruptor can alter cell signaling.  To date, studies monitoring testosterone levels in men over their life-span have tentatively identified a gradual decline that may be associated with endocrine disruptors. (14) However, more research on the subject is required. At least one review (already cited [3]) does take these things into account, and still concludes that roundup is safe. It calls into question whether or not the concentrations of roundup used to demonstrate endocrine disruption reflect the low doses human consumers are exposed to. Not to mention, a cell culture is not a human being.

Where possible, I think it’s clear exposure to these things should be minimized. However, even as we acknowledge the danger, we must remember not to panic before we quantify it.  After all, we are  sometimes exposed to natural endocrine disruptors, like phytoestrogens in soy .  Some have argued that even these are harmful, with others contending that they can actually have health benefits. (15) So does roundup have a greater effect on the endocrine system than phytoestrogens? I don’t believe the answer to that question is clear at this time.

It remains to be seen if roundup is any more toxic than the alternative herbicides it has displaced. Studies have found Reglone and Stomp to be more genotoxic than Roundup. (16) From what I can tell, there is literature finding health issues with pretty any much herbicide out there, and yet this may not justify an abandonment of herbicides. In the early 2000’s, the most commonly used, most abundant herbicide in the U.S. water supply was atrazine, which is also an endocrine disruptor, with at least equal evidence of toxicity. (17) (18) Yet atrazine is not particularly associated with GMO’s.  Since the spread of GMO’s, atrazine  has been largely displaced by roundup.  Clearly, agrochemicals can be just as harmful on conventional crops as on GMO’s. This makes me wonder if the problem is really specific to GMO’s, or with our current standards for agrochemicals in general.

So Roundup is suspect, at least. Yet this is a potential problem with an agrochemical, not with any genetic modifications themselves. Roundup ready maze is genetically altered to tolerate roundup, but there are equally harmful herbicides that are not associated with GMO’s. More to the point though, it is not the altered genome of the plant that is harmful. Even if we do discover extreme toxicity issues with roundup, it is still a dubious argument against genetic modification.

Bt Toxin

GMO corn does seem to get singled out a lot by activists. When they’re not complaining against glyphosate-ready corn, they’re usually complaining about Bt corn. There are a variety of Bt crystal (Cry) toxins  normally produced by the soil bacterium, Bacillus thuringiensis, during sporulation.  Different Bt toxin genes are used in genetic modification, to target different insects. These crystallized proteins are ingested by insects, where they encounter a very different environment from the human gut. The human gut is highly acidic, with a pH of 2, whereas many insects have an incredibly basic digestive system, with a pH of around 10, or even 11. (19)(20) . Even subtle changes in pH can change the distribution of charges throughout the length of a protein molecule, causing it to denature, or rearrange its three-dimensional structure. So the Bt Cry toxin behaves drastically different in the stomach of an insect than it would in that of a human.  In fact, you would be hard-pressed to find any protein that was functional at both a pH of 2 and 11. In addition to denaturing the Bt toxin, the higher acidity of the human stomach also rapidly breaks it down. (21) That’s just one of many differences between insects and humans.

The Bt Cry toxin acts by binding to cell receptors on insect gut epithelial cells, and forming pores in the cell surface that allow water and harmful ions to flood the cell. (22) So even supposing t Bt Cry proteins survived  vertebrate stomach acid, our epithelial cells would need to have receptors that are recognized by the Bt Cry protein. This seems unlikely, considering that many Bt Cry toxins target only a few species of insect.  Tests on Bt toxin have shown a lack of toxicity against mammal lymphocytes, erythrocytes, bacteria, yeast, or brine shrimp- strongly supporting a narrow range of target organisms for Bt toxin. (23) Unsurprisingly, animal studies on Bt toxin demonstrate its safety repeatedly. (24) (25) (26)

It is a curious rallying point for the anti-GMO movement anyway, considering that the use of Bt toxin as a pesticide predates genetic engineering. As early as the 1920’s, it was used as a pesticide spray, without any protest. Only later were plants genetically engineered to produce it.(27) It seems the activists care more about the means of introducing a pesticide than they do about the pesticide itself.

In fact, it’s very difficult to find a pesticide with less evidence of toxicity to humans than Bt Toxin. Unlike many pesticides, it also breaks down easily in soil, sparing the environment of the sort of contamination commonly caused by pesticides. (28)

Unlike roundup, this is a direct result of genetic modification. On the internet, you see it argued back and forth over whether or not GMO’s increase the amount of chemicals used, or decrease them. On the one hand, you have roundup ready crops, but on the other, there are crops that have been engineered to require fewer chemical pesticides. In reality, both are possible outcomes of genetic modification.  If we just stuck with Bt toxin crops, we would be reducing pesticides, but the roundup ready crops unfortunately erase these gains by driving up herbicide use. (29) The fact remains; some genetic modifications can and do reduce chemical use. For example, it is estimated that Bt cotton has reduced pesticide use in cotton by about 19.4%. (30)

35S CamV Promoter

Another of the first GMO-scares I was exposed to involved the claim that a virus had been discovered in GMO cauliflower. This sounded pretty fishy from the start, and upon research, it doesn’t get much more credible.  I was unsurprised to find that a scientific paper had been misrepresented, as they so often are. The paper cited actually suggests that a fragment of a single viral protein may get translated in the cauliflower plant. (31)

In short, scientists add the 35S promoter from the virus genome to a DNA sequence that they want to be very strongly expressed. This sequence subverts the plant’s own DNA transcription mechanisms, causing it to produce mRNA for the gene attached to 35s promoter. It is used by the virus to trick the host into transcribing the viral genome, but that means we can also use it to subvert the plant’s RNA polymerase for our own purposes. The concern stems from the fact that the promoter overlaps with a particular viral gene (gene VI) coding for Protein P6. The concern is that the gene fragment might cause the plant to produce a fragment of the protein P6.

More specifically, under the scenario supported by the authors, the fragment might be incorporated into a plant protein, creating a sort of chimeric or hybrid protein, particularly with domain 1 of the P6 protein.  While you would expect a chimeric protein to be pretty non-functional, the fact that P6 has so many different functions makes it difficult to ascertain whether or not  domain 1 can do anything on its own. Evidently, the P6 protein allows viral clusters to transport themselves along microfilaments throughout a plant cell. It also counteracts RNA silencing, which involves halting viral RNA in its tracks before it can be copied or translated. Finally, it interferes with cell signaling. With so many diverse functions, it’s understandable why people might be concerned about a fragment having negative effects on plant health.

However, there is strong evidence that a partial P6 protein would have limited impact on a plant, much less a human. The DNA coding for the N-terminus of P6 protein is not included in any GMO crop. Any chimeric protein would exclude it. It has been demonstrated that without this segment, interference with RNA silencing and sialic-acid cell-signaling (via PR1a) is eliminated.  So even if such a protein was abundant in GMO’s, which has yet to be proven, we would expect its function to be badly impaired. For a detailed, fragment-by-fragment look at the P6 protein, there’s a good paper on pubmed. (32)

Viruses require multiple complete proteins working in concert, and most of those proteins don’t work too well unless the virus can first gain entry into a cell, much less while immersed in stomach acid.  Viruses are highly specific in which type of organism they infect. After all, they have to trick their host’s system into copying them, so they usually are specifically tailored to a host, or a group of similar hosts. Of course, viruses are very adaptive, and host-switching does happen. However, it seems that switching to a distantly related host is a rare event, even for a virus. Only three families of virus are known to include both animal and plant pathogens. This proves that at some point in the evolutionary history of those virus families, a transmission between plant and animal did in fact occur. Plant viruses often use animals as transmission vectors, particularly insects. However, actual entry of a plant virus into an animal cell appears to be an extremely rare event, even on the long evolutionary timescale. No plant pathogen is currently known to cause us any harm. One exception may be the Pepper mild mottle virus (PMMoV) from chili peppers. Some evidence suggests it can cause abdominal pain and fever in humans, although that might just be from the chili peppers themselves. (33)

One big issue with the idea of P6 protein toxicity to humans is that viruses are part of nature. Even if you eat organic, home-grown plants, those plants will contain viral genetic material, and viral proteins. If those plants include cauliflower, turnips, or even potatoes, then you may very well be ingesting complete P6 CamV proteins, not just fragments. Naturally infected plants can have as many as 10^5 copies of 35S promoter per cell, whereas a genetically modified plant will generally contain only a few copies per cell. So if this CamV promoter region really is dangerous, you would be exposed to far more danger from plants naturally infected with the virus than from any GMO. Despite frequent human exposure to CamV, and other pararetroviruses in plants, no evidence of danger to humans has been found. (34) In fact, of the tens of thousands of viruses isolated from the human gut in one study, the majority appeared to be plant viruses, largely ingested from crops. (35) So it seems very disproportionate to worry about a function-impaired fragment of a viral protein when we’re all constantly ingesting plants that are chock-full of natural virus. Yum!

So the viral DNA in some GMO crops faces three hurdles to being harmful to humans. One is the barrier between plants and humans, which are very different hosts. Additionally, simply on an evolutionary basis, we can assume that our bodies are equipped in such a way to withstand the many plant viruses we and our ancestors have always ingested in our food. The final hurdle is the fragmentary nature of the genetic material, which is only a small part of the total virus. Unsurprisingly, the main concern of the authors who initially warned of a chimeric P6 protein was that it might be allergenic, not that it might somehow mimic a viral infection in humans.  However, they found little evidence of allergenicity. Even if they eventually do, potential allergenicity is hardly a deal-breaker where food is concerned. Just look at peanuts and shellfish.

 

Benefits and Comparisons to Conventional Crops

A lot of this talk of GMO-danger overshadows the question of potential benefits. After all, every decision in society is just a question of cost-benefit analysis.  These benefits are particularly compelling for impoverished nations. Rice plays a crucial role in feeding about half of the world’s population, and in many nations, farmers devote a large proportion of their land to rice. Studies on GM rice have revealed immense potential benefits. The reduction in pesticides associated with insect-resistant rice is associated with measurably improved health in Chinese farmers. (36)

The beta-carotene producing GMO strain of golden rice can help with the worldwide problem of vitamin A deficiency. In India alone, it has the potential to prevent 40,000 child deaths a year, not to mention health problems such as blindness. (37)  In addition to vitamin A, plants have been produced with elevated levels of vitamin C and vitamin E. (38) There are of course vegetables with plenty of these vitamins already present. However, in a world where many people subsist mainly off of a single starchy crop, such as rice, wheat, potatoes, or corn, it seems more beneficial to try and increase the nutrition of such crops. People don’t want to swap rice for carrots when they’re hungry, and just want calories, but vitamin-A enriched rice may be an easier sell.

Obviously, we have been genetically altering our food for some time, through selective breeding. To some GMO activists, this is an outrageous comparison. They seem to assume that artificial selection is somehow more natural, or inherently safer. This is just a vague gut feeling on their part, though not an established fact. Artificial selection does rely on alleles already present naturally in a population, so it could be considered more natural in that sense. However, many of the alleles it selects for would never persist in nature. Additionally, since artificial selection doesn’t knowingly target any specific genes, the way genetic modification does, you generally alter the plant in far more ways than you are even aware of. Artificial selection has been used to drastically alter the entire genome of some plants, far beyond the level of change that has been attempted with GMO’s. The source of these changes is from the natural gene pool of that species, but there are far more of them. Just for one example, the wild plant Brassica oleracea  has been manipulated to create kale, collard greens, broccoli, brussel sprouts, cauliflower, and cabbage. (39) Whenever you have genetic manipulation on that level, there is potential for unpredictability.

As for being inherently safer, many of the same potential issues with GMO’s can be found in artificially selected crops. The recent rise in celiac disease has been linked, not to GMO wheat, but to hybridized wheat. (40) This wheat was produced just as all of our crops were produced; by selecting strains with desirable traits over multiple generations.  Yet despite this “natural” approach to genetic modification, the result has been an increase in celiac disease epitopes in modern wheat gluten.  (41)

An epitope is sort of like a bar-code for the immune system. In just the past hundred years, our wheat has become more prone to triggering an immune response, leading to celiac disease. This is reminiscent of the concerns over the P35 protein being allergenic, yet with more evidence. Absurdly, some GMO activists actually confuse the issue, and argue that the rise in celiac disease is caused by GMO wheat- something that does not even exist! Yet somehow I doubt they would turn against artificial selection with the same fervor, if it were possible to correct them.

Ideally, the two approaches should not be seen as mutually exclusive. Breeding can be equal or even superior to genetic modification in some areas. Current attempts to produce better drought-resistant strains of wheat have fared best where selective-breeding is involved. It seems unlikely that artificial selection will ever be rendered useless, because artificial selection allows you to select traits with mechanisms far beyond your understanding, whereas genetic modification is limited to constructing mechanisms we understand reasonably well. However, what if you breed multiple plant species with multiple drought-resistant mechanisms? What if the plants are not inter-fertile? Genetic modification would allow you to import adaptations across species, or even combine them all into one. After the genes were inserted, you could later smooth things out with a bit more selective breeding, possibly breeding around any fitness problems caused by the new gene/s. So it seems likely that both techniques together can be superior to either one alone.

As with many controversial issues in science, it’s risky to unequivocally endorse either side as being 100% correct. Even a broken clock is right twice a day.  There are potential risks with engineering crops to be more resistant to agrochemicals, but there are also potential benefits in terms of yield, nutrition, and chemical use. Even though the anti-GMO camp has some interesting arguments, it seems that the pro-GMO camp is more correct overall based on current knowledge.

1) http://www.annualreviews.org/doi/abs/10.1146/annurev.arplant.50.1.473

2) http://npic.orst.edu/factsheets/glyphotech.html#references

3) http://www.ncbi.nlm.nih.gov/pubmed/10854122

4) http://www.inchem.org/documents/ehc/ehc/ehc159.htm#SectionNumber:7.6

5) http://onlinelibrary.wiley.com/doi/10.1002/j.1552-4604.1967.tb00034.x/abstract;jsessionid=56520B78D423AC385FEB4F3D208B8267.f04t03

6) http://www.nature.com/news/hyped-gm-maize-study-faces-growing-scrutiny-1.11566

7) http://www.sciencedirect.com/science/article/pii/S0278691512005637

8) http://www.academie-sciences.fr/presse/communique/avis_1012.pdf

9) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3365860/

10) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1257596/

11) http://www.sciencedirect.com/science/article/pii/S0278691513003633

12) http://www.ncbi.nlm.nih.gov/pubmed/20012598

13) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1257636/

14) http://www.ncbi.nlm.nih.gov/pubmed/19396984

15) http://www.ncbi.nlm.nih.gov/pubmed/21175082

16) http://mutage.oxfordjournals.org/content/21/6/375.full

17) http://pubs.usgs.gov/circ/circ1225/pdf/

18) http://www.ncbi.nlm.nih.gov/pubmed/16967834

19) http://jeb.biologists.org/content/172/1/355.short

20) http://www.ncbi.nlm.nih.gov/pubmed/11171351

21) http://www.ask-force.org/web/Bt/Herman-Rapid-Digestion-2003.pdf

22) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1899880/

23) http://www.hindawi.com/journals/bmri/2014/810490/

24) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3678139/

25) http://www.ncbi.nlm.nih.gov/pubmed/17050059

26) http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0036141

27) http://www.annualreviews.org/doi/abs/10.1146/annurev.arplant.58.032806.103840

28) http://www.ncbi.nlm.nih.gov/pubmed/19295059

29) http://www.enveurope.com/content/24/1/24

30) http://afrsweb.usda.gov/sp2userfiles/person/4056/naranjoetal.btbook2008.pdf

31) http://www.landesbioscience.com/journals/gmcrops/2012GMC0020R.pdf

32) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3836500/

33) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3550769/

34) http://www.microbecolhealthdis.net/index.php/mehd/article/viewFile/8034/9373

35) http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.0040015

36) http://www.ncbi.nlm.nih.gov/pubmed/15860626

37) http://www.ncbi.nlm.nih.gov/pubmed/20643233

38) http://www.ncbi.nlm.nih.gov/pubmed/12940549

39) https://botanistinthekitchen.wordpress.com/2012/11/05/the-extraordinary-diversity-of-brassica-oleracea/

40) http://celiacdisease.about.com/od/celiacdiseasefaqs/f/Genetically-Modified-Wheat.htm

41) http://www.ncbi.nlm.nih.gov/pubmed/20664999