A team of scientists from the UK and other European countries has created a genetically modified (GM) purple tomato that in a pilot test significantly extended the life span of cancer-susceptible mice that were fed the new tomatoes compared to mice that were fed normal tomatoes.
The study was the work of Professor Cathie Martin from the John Innes Centre in Norwich and colleagues from research centres in Italy, Germany and The Netherlands, and was published online in the journal Nature Biotechnology on 26 October.
Martin and colleagues took genes from the snapdragon plant (Antirrhinum), inserted them into tomato plants and grew purple tomatoes high in anthocyanins, pigments that occur naturally at high levels in berry fruits such as the blackberry, cranberry and blueberry. There is evidence that anthocyanins protect against some cancers, cardiovascular disease, age-related degenerative diseases, diabetes, obesity and other illnesses.
The researchers already knew about the health protective properties of anthocyanins that occur in high levels in some edible plants, but were of the opinion that the levels found in many commonly eaten fruits and vegetables were not high enough to give the best health benefits.
As Martin explained:
"Most people do not eat 5 portions of fruits and vegetables a day, but they can get more benefit from those they do eat if common fruit and veg can be developed that are higher in bioactive compounds."
Why tomatoes? Because they are an everyday food that already contain high levels of another important bioactive compound, the antioxidant lycopene. Highly processed tomatoes are the best source of lycopene. Tomatoes cooked in a little oil are as well, because this process helps to release lycopene from inside the cells of the fruit.
Another beneficial antioxidant found in tomatoes and other food plants is flavonoids. These can be water soluble (hydrophilic) and fat soluble and eating foods with both types is thought to offer the best protection against disease.
By expressing two transcription factors from snapdragon in the tomato plant, Martin and colleagues were able to produce tomato fruits that had accumulated anthocyanins at levels considerably higher than attained in other studies that had attempted to engineer anthocyanins in tomatoes and were much closes to the levels found in blackberries and blueberries.
Another effect of expressing the two transgenes in the tomato plants, apart from the fact they produced fruit of purple peel and flesh, was a threefold boost in the hydrophilic antioxidant capacity of the fruits.
In a pilot test on mice genetically bred to be susceptible to cancer (their gene for tumour protein p53 was turned off), the group that whose diet contained high anthocyanin tomatoes showed a significant extension of life span (182 days) compared to the group whose diet contained normal tomatoes (142 days).
Martin said this study was:
"One of the first examples of metabolic engineering that offers the potential to promote health through diet by reducing the impact of chronic disease."
"And certainly the first example of a GMO with a trait that really offers a potential benefit for all consumers. The next step will be to take the preclinical data forward to human studies with volunteers to see if we can promote health through dietary preventive medicine strategies," she added.
Reactions to the study have been cautiously optimistic, with some saying because this works in mice it doesn’t mean it will work in humans.
The current position of many cancer research establishments is that eating a healthy balanced diet rich in fibre, fruit and vegetables and low in processed and red meat is the best way to reduce your all round cancer risk.
A representative from the charity Cancer Research UK, Dr Lara Bennett told the BBC that while it was exciting to see new techniques being developed that could make food even healthier, it was too early to tell whether "anthocyanins obtained through diet could help to reduce the risk of cancer".
In a comment reported by the Independent, Martin said she accepted that it was unlikely that the purple GM tomato would go on sale in Britain in the near future because of considerable public opposition to GM foods.
(Source: Nature Biotechnology: John Innes Centre: October 2008)