Headlines about Prof Cathie Martin's GMO purple "anti-cancer" tomato bear little relation to reality.
The GM tomatoes are being grown in Canada and will be used to generate 2000 litres of juice.
The plan is to feed the juice to UK heart patients in trials.
However, these GM tomatoes have never been tested for toxicity in animal feeding trials.
Martin said she chose to grow the tomatoes in Canada because the regulatory system there is "very enlightened", in comparison to the "restrictions" placed on GMOs by the European system.
Our main response to the hype around this tomato is here:
Cathie Martin's GM purple tomato study is here:
Here are some more uncomfortable facts about the GM purple tomato.
1. A general point about anthocyanins. There are over 200 types and they constitute the main red/purple pigment class found in common fruit and veg, e.g. red cabbage, red onions, berries, etc. (Note: the purple of beetroot is not an anthocyanin but another nonetheless valuable antioxidant.) Thus one can have a diet rich in anthocyanins without resorting to GM purple tomatoes. What Cathie Martin and her colleagues have produced is totally unnecessary given the abundance of anthocyanins already in food plants.
2. The Ti-plasmid transgene cassette contains a kanamycin (antibiotic) resistance gene, which would have been used in the initial selection of the GM transformants. They don’t mention the use of kanamycin selection in the methods section of their paper but there is no other way they could have conveniently selected for transformants. It is conspicuous they avoid mentioning this, perhaps in order to avoid attracting attention to it, in light of the fact that the EU has asked for antibiotic resistance genes not to be present in the final GM plant.
3. The transgenes involved are two from snapdragons and are a class of proteins known as “transcription factors”; ie proteins that control the expression of many other genes. Thus there is no way that these two transcription factor genes would have just turned on the target genes for anthocyanin synthesis and not interfered with the function of others. The data they present looking at gene expression profiles is inconclusive in this respect using a somewhat outdated, crude method compared to what can be done now. The tomato genome sequence has now been determined and so state-of-the-art methods such as gene-chip microarrays or better still total mRNA (transcriptome) analysis by high throughput sequencing can now be used to properly assess what the GM process has actually resulted in.
4. These tomatoes CANNOT be called substantially equivalent to the non-GM parent as they have a substantially different chemistry and composition compared to the non-GM parent.
5. No generic toxicity testing, either short- or long-term, of these tomatoes has been published and we must assume it has not been done. The only additional work published with these GM purple tomatoes is to show that high anthocyanin in the skin extends shelf life. No work has been done to see if nutrient content is preserved during the time of extended shelf life. If the nutrient content is not preserved, then it’s a rip-off in terms of what the consumer is getting.
6. If regulators in the EU allow human trials before animal testing, this may violate EU regulations for GMOs and at worst would border on a criminal act, given that it is possible that an adverse reaction might take place.
7. The whole idea of GM “nutritionally enhanced” foods starts with two major conceptual flaws; (i) there is something wrong with the diversity of foods we have already and (ii) that high levels of a single nutrient is going to result in significantly improved health status - in this case, warding off cancer. This is nonsense on both counts.
8. Very likely antioxidants do have benefits, but we really do not know a huge amount about their effects on the body beyond the typical reductionist, targeted testing that has occurred for them. It's probable that they have effects beyond those that are typically focused on in tests. Maybe all of those effects are good, maybe some are not. Maybe (likely) they depend on the total dietary context of nutrients that likely can modify each others' effects. And maybe where typical or moderate amounts of one of these compounds has generally positive effects, very high amounts may have some negative effects. This is true of vitamins like vitamin A.
So in allowing these GM tomatoes to be grown on their territory, the Canadian authorities, rather than being more “enlightened”, as Martin claims, appear to have been “endarkened” by pro-GM propaganda.
For those who are fixated on a purple tomato-related answer to cancer, a peer-reviewed study found that extracts of the fruit of non-GM anthocyanin-rich tomatoes inhibited two human cancer cell lines in a dose dependent manner. See below.
Novel phenotypes related to the breeding of purple-fruited tomatoes and effect of peel extracts on human cancer cell proliferation.
Mazzucato A, Willems D, Bernini R, Picarella ME, Santangelo E, Ruiu F,
Tilesi F, Soressi GP. Plant Physiol Biochem. 2013 Nov;72:125-33. doi:10.1016/j.plaphy.2013.05.012.
The production of anthocyanins in the tomato (Solanum lycopersicum L.) fruit is normally absent or poor, but a number of mutants or introgression lines are known to increase anthocyanin levels in vegetative and reproductive tissues. Through conventional breeding, a genetic combination was obtained with the remarkable phenotype of a deep purple fruit pigmentation, due to an accumulation of anthocyanins on the peel. Such a genotype was named Sun Black (SB) as a consequence of its sensitivity to light induction. When characterized for morpho-agronomic traits, SB plants showed increased fertility. Purple fruits displayed an arrangement of the epicarp cells different from normal tomatoes, a feature that could account for different mechanical properties and shelf-life potential. The SB genotype and, to a lesser extent, its single mutant parents showed the capacity to accumulate anthocyanins in the seedling root when grown under light. This phenotype, which was greatly improved by the addition of sucrose to the germination medium, proved to be useful as selection index and gave new insights for in vitro production of anthocyanin extracts. To assess the nutraceutical potential of purple tomatoes, we tested the activity of SB skin extracts on the proliferation of two human cancer cells lines. Cell proliferation was significantly inhibited by SB extract in a dose-dependent manner. When the bioactivity of SB extracts was compared with that of other anthocyanin-containing fruits or vegetables, a significant "Extract*Line" interaction was evidenced, suggesting a crucial role for the extract composition in terms of anthocyanidins and other eventual cell growth-inhibiting compounds.