Antioxidants are chemical or biochemical compounds that neutralise free radicals. As our cells release the energy locked up in food molecules, small amounts of highly reactive entities called free radicals are produced. These can damage the cell if they are not neutralised immediately. Free radicals are mostly produced by structures in the cell called mitochondria. It is within the mitochondria, which are known as the ‘power houses’ of the cell, that most of the energy produced from food is generated.
It is widely believed that polyphenolic compounds present in the fruit and vegetables we eat have an antioxidant effect within the body. Recent research, conducted by scientists from Plant & Food Research in collaboration with overseas scientists, has revealed that this effect has been overstated. More complicated mechanisms that directly affect the mitochondria seem to be involved.
Plant & Food Research’s Dr David Stevenson is a lead researcher in this field. He is conducting a series of experiments to find out which polyphenols can gain access to the cell or its mitochondria and what effect they have on the production of the mitochondria’s own antioxidants such as SOD (superoxide dismutase).
For many years, the antioxidant capacity of polyphenolic phytochemicals was measured using a simple chemical test. This worked well to predict which compounds found in foods would help preserve their nutritional qualities from oxidation before they were eaten. We now know that this test cannot predict which compounds are beneficial to health because the situation in living cells is very much more complex than in a food.
A new approach using mouse muscle cells in culture is being trialled. Although it has some limitations because it is not a perfect simulation of the environment the cells experience in the body, it is much easier to measure what happens when the cells are treated with a polyphenol. Muscle cells contain a lot of mitochondria, and if the polyphenol under study gains access to the mitochondria, any beneficial effects it has in enhancing the production of natural antioxidants will be easier to measure.
One of the tests applied is to impregnate the cells with a fluorescent stain and then incubate them with a test compound. The stain only fluoresces in the presence of the free radical superoxide, and this can be easily measured.
Results to date seem to indicate that, if the compound is active, it places the mitochondria under an oxidative stress resulting in the release of superoxide free radicals. This stimulates the mitochondria to quickly produce their own highly efficient antioxidant enzymes to neutralise these free radicals.
With regular exposure to active polyphenolic compounds, scientists now think that the mitochondria develop an enhanced response to oxidative stress that quickly reduces the damaging effects of free radicals.
It is also now thought that polyphenolic antioxidants have a similar effect to exercise.
If a given polyphenol is found to have a beneficial effect, by carefully studying the genome of the plant it came from, a breeding programme could lead to the development of cultivars with enhanced levels of the active polyphenol. Eating plants rich in this phytochemical could help to regulate the body’s own antioxidant production system.
Nature of science
Because science is a feedback process that learns from its own mistakes, explanations previously accepted on the basis of evidence current at the time often need to be changed or modified in the light of new evidence. The recent Plant & Food Research findings of how phytochemical antioxidants work in the body is a good example of this.