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Food RNA gets into blood and so does DNA

We have alerted readers to research showing how tiny RNA molecules in food eaten can circulate in the bloodstream and turn genes off in the body [1], raising concerns over the safety of genetically modified organisms (GMOs), which introduce many novel and synthetic nucleic acids into the human food chain ([2] How Food Affects Genes, SiS 53). New research shows that pieces of DNA large enough to code for complete genes can also escape degradation in the gut and enter the human circulatory system, and the presence of circulating RNA from food is much more extensive and widespread.

DNA known to resist digestion and may form part of circulating cell free DNA

A study led by Sándor Spisák who holds a joint appointment at Hungarian Academy of Sciences in Budapest and Harvard Medical School Boston, Massachusetts in the USA analysed over 1 000 human adult samples from four independent studies, and found DNA fragments derived from food in all plasma samples, some large enough to code for complete genes [3].

Previous animal feeding studies have demonstrated that a minor proportion of fragmented dietary DNA may resist digestion [4], but the degradation of long chains of DNA and the possible uptake and transport into the bloodstream are not at all understood. Circulating cell free DNA (cfDNA) in the human bloodstream, first described in 1948, are mostly double-stranded molecules with a wide range of fragment sizes from 180 – 21 k bp.

Most people think cfDNA are from apoptotic cells (resulting from programmed cell-death), and in different diseases such as inflammation, autoimmune, trauma and cancer, necrotic cells (from non-programmed cell death) may increase the amount. In fact, both DNA and RNA are found circulating in the bloodstream, and there is good evidence that they are actively secreted from living cells as a nucleic acid intercommunication system (see [5] Intercommunication via Circulating Nucleic Acids, SiS 42).

Apart from the individual’s own cells, DNA of the foetus can be detected in maternal plasma. Viral DNA, bacterial DNA may also be found in various disease states. DNA from consumed food is not usually considered, although there are animal studies suggesting that small fragments of nucleic acids may pass into the bloodstream and even into various tissues. For example, foreign DNA fragments were detected by PCR in the digestive tract and leukocytes of rainbow trout [6] fed GM soybean, and other similar findings were reported in goats [7]., pigs [8, 9] and mice [4].

These recent discoveries were possible thanks to huge advances in nucleic acid sequencing technology, in particular, next generation deep sequencing (NGS) (see Box).