Natural RNA, Transgenic DNA, and What They Actually Mean for Our Food

By Veronique Greenwood | January 13, 2012 2:33 pm

rice

Earlier this week, food columnist Ari LeVaux set off a storm of media reaction with a piece with this premise: tiny plant RNAs, recently discovered to survive digestion and alter host gene expression, are a major reason why genetically modified foods should be considered dangerous. For anyone familiar with the paper he referred to, or with molecular biology in general, the article was full of conflation and sloppy logic, and even as it became the most-emailed story on TheAtlantic.com, where it was published, biology bloggers and science writers were pointing out its significant flaws. To his credit, LeVaux revised the article to fix many (though not all) of the errors concerning genetics; the new version appeared yesterday at AlterNet and today replaced his original piece at The Atlantic.

So what did LeVaux get so wrong, and, once all of the wheat was sorted from the chaff, was there anything to what he was trying to say?

At the heart of the fracas is LeVaux’s claim that a class of molecules called miRNA is a reason to fear GMOs specifically, more than any other food plant or animal. miRNA, which is short for microRNA, is a class of molecules that perform various tasks in plants and animals. They were first discovered about twenty years ago, in nematode worms, and they regulate gene expression by binding the messenger RNA involved in translating a gene into a protein. The messenger RNA carries the “message” of the DNA’s sequence to a group of enzymes that translate it into the amino acid sequence of a protein. But if a miRNA binds to a messenger RNA, the message is destroyed, and the protein is never made. Thus, miRNA can be a powerful tool for preventing the expression of genes. In fact, that is what’s made it such an important lab tool in recent years: it allows researchers to knock down the expression of genes without physically removing them from an organism’s genome.

In the paper that LeVaux pegged his article on, Nanjing University researchers found that miRNAs usually seen in rice were circulating in the blood of humans, and that mice fed rice had the miRNA in their blood as well. That particular miRNA, in its native context, regulates plant development. When the researchers added it to human cells, it appeared to bind to the messenger RNA of a gene involved in removing cholesterol from the blood. Previous papers had found that plants have plenty of miRNA floating around in them [pdf] (as does just about everything we eat, since plants and animals make them by the thousands), but having them show up whole and unmolested in blood, apparently after digestion, was a new and very intriguing discovery.

Here is where the trouble starts. LeVaux leapt immediately from “miRNA from plants can affect gene expression in humans” to “Genetically modified organisms will have miRNAs that could be dangerous to us” (paraphrasing here). It is reasonable to wonder whether miRNA that survives digestion might represent a new way that plants can have an effect on our health, a way that may not be accounted for in current safety regulation. In fact, that’s not a bad topic for a thoughtful essay. But in his (original) Atlantic article, LeVaux skipped a number of logical steps, and did not present this as an interesting possibility that could relate to any kinds of plants and animals we eat. Instead, he leaped to pin GMOs, and in so doing, missed the point that we don’t know right now whether the miRNA of any food affects human health. We have just one interesting finding at the moment, and other scientists and science writers are curious as to whether the miRNA really does come directly from food, since, as biologists can attest, RNA is pretty fragile stuff that can be destroyed by marauding enzymes even in tidy labs. How the heck it makes it through digestion will be hugely fascinating, if it indeed does. For more information on how LeVaux’s description of genetic modification is flawed, check out this post from Christie Wilcox at Scientific American.

As it turns out, what LeVaux was actually hoping to write about, judging from the updated piece, is the idea of “substantial equivalence,” which allows companies producing genetically modified foods to have their products considered by the FDA to be basically the same as unmodified versions. Ah, now that’s a topic with some meat on it.

Substantial equivalence is a concept developed in 1991 by the OECD, a group of nations that deals with international economic issues. It states that if a genetically modified food has biochemistry that falls within the range of the normal version of the food—same amount of certain proteins, same amount of nutrients, same basic nutritional profile—it shouldn’t require any safety testing before being deployed. (The principle also applies to new medical devices, if they are substantially equivalent to what already exists.) In the two decades since this approach was devised, millions of people have been eating genetically modified foods (primarily corn, soy, and canola), and there have been no credible reports of it causing health problems.

But it wouldn’t hurt to examine the way we regulate genetically modified foods with an eye toward making it more transparent. There is great interest on the part of the companies involved to make the regulatory process quicker, and the FDA, unfortunately, is notoriously overworked. Moreover, it’s surprisingly difficult for the interested consumer to find clear, recent information about how substantial equivalence is applied in practice. The FDA has an easy-to-find, thorough primer on how drugs are regulated; it would be nice if they provided similar information on what are still, at this point, relatively new foods.

Image courtesy of  AMagill / flickr

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