Genetically modified tomatoes to fight cancer?
Despite advertising campaigns, we don't eat the five fruits and vegetables we're supposed to do to protect us from obesity and many diseases. This is why European researchers have decided to genetically modify one of the plants we still often eat, the tomato. And the high anthocyanins content purple tomatoes they've produced are apparently able to extend lifespan in cancer-prone mice. (Annthocyanins are part of a category of antioxidants belonging to the class of flavonoids). Experiments on mice look promising, with the ones eating these purple tomatoes having an average lifespan of 182 days in comparison to the 142 recorded for mice fed with standard diet. But the scientists are cautious, adding that these are very preliminary results. I guess we'll not see purple tomatoes before a while. But read more...
You can see above two kinds of tomatoes: purple, high anthocyanin tomatoes (left) and red wild-type tomatoes (right). (Credit: John Innes Centre, UK; link to the original version)
This research has been done for the EU-funded Flora project which wants to set a strategy of improving health through diet. One of the institutions involved is the Norwich BioScience Institutes at the John Innes Centre, UK. And one of Flora's subprojects is the Moli-sani project of the Università Cattolica del Sacro Cuore, Italy.
This Norwich BioScience Institutes news release, Fried purple tomatoes, gives more details about the process. "Scientists have expressed genes from snapdragon in tomatoes to grow purple tomatoes high in health-protecting anthocyanins. Anthocyanins are naturally occurring pigments found at particularly high levels in berries such as blackberry, cranberry and chokeberry. Scientists are investigating ways to increase the levels of health-promoting compounds in more commonly eaten fruits and vegetables."
The researchers add that "anthocyanins offer protection against certain cancers, cardiovascular disease and age-related degenerative diseases. There is evidence that anthocyanins also have anti-inflammatory activity, promote visual acuity and hinder obesity and diabetes." So how did the scientists do? For 'this study the scientists expressed two genes from snapdragon that induce the production of anthocyanins in snapdragon flowers. The genes were turned on in tomato fruit. Anthocyanins accumulated in tomatoes at higher levels than anything previously reported for metabolic engineering in both the peel and flesh of the fruit. The fruit are an intense purple colour."
Now, let's return to the Università Cattolica del Sacro Cuore news release mentioned in the introduction to see if these genetically modified tomatoes are good for the mice. "Mice used in the experiment have been divided into three groups, fed three different diets: the first one has received a standard diet, while the second group was fed diet supplemented with 10% powder from freeze-dried red tomatoes and the last one with 10% powder from purple tomatoes. 'We have not recorded significant differences between the first two groups,' argues Marco Giorgio from the European Institute of Oncology who followed the experimental phase on mice. 'But mice fed with purple tomatoes showed a significant increase of lifespan.' The last group has reported an average lifespan of 182 days in comparison to the 142 recorded for mice fed standard diet."
Even with such results, Giorgio is still very cautious. "Although mice's lifespan has significantly increased once fed on purple tomatoes we still don't know how it works. It is not likely everything can be explained on antioxidants basis alone. Moreover, we have to consider that in this study we have not taken into account any possible toxicity so I shall say we're far from considering a human trial. Next step is to investigate the effect of purple tomatoes on different kinds of tumor models and define the mechanism of action."
For more information, this research work has been published in Nature Biotechnology as an advance online publication under the title "Enrichment of tomato fruit with health-promoting anthocyanins by expression of select transcription factors" (October 26, 2008). Here is the comment from Nature Biotechnology about this paper. "Fruit-specific overexpression of a pair of snapdragon transcription factors produces tomatoes that uniformly accumulate anthocyanins at levels unprecedented for metabolic engineering. When included as a dietary supplement, the purple tomatoes increase the life spans of tumorigenic p53 knockout mice."
And here is the beginning of the abstract. "Dietary consumption of anthocyanins, a class of pigments produced by higher plants, has been associated with protection against a broad range of human diseases. However, anthocyanin levels in the most commonly eaten fruits and vegetables may be inadequate to confer optimal benefits. When we expressed two transcription factors from snapdragon in tomato, the fruit of the plants accumulated anthocyanins at levels substantially higher than previously reported for efforts to engineer anthocyanin accumulation in tomato and at concentrations comparable to the anthocyanin levels found in blackberries and blueberries."
If you see purple tomatoes in a future visit to your market, don't hesitate to buy them. They might be good for you. But if you don't like the idea of genetically modified tomatoes to avoid future cancers, drop me a note.
Sources: Università Cattolica del Sacro Cuore news release, October 26, 2008; Norwich BioScience Institutes news release, October 26, 2008; and various websites
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