INTRODUCTION: Investigations on the role of various antioxidants in fighting cancer have been a subject of interest among many scientific and medical researchers in recent years. The latest reports show that a British research group engineered a purple tomato with the antioxidant anthocyanin and found that their product may be effective as an anti-cancer in mice used as an experimental animal. In this article the role of antioxidants in prevention and treatment of cancer, the historical information, and the recent research work on the new engineered purple tomato will be studied and discussed.
ROLE OF ANTIOXIDANTS IN FIGHTING CANCER: Antioxidants are substances that may protect cells from the damage caused by unstable molecules known as free radicals. Free radical damage may lead to cancer. Antioxidants interact with and stabilize free radicals and may prevent some of the damage free radicals otherwise might cause. Examples of antioxidants include Vitamins A, C, and E, beta-Carotene (the precursor of Vitamin A), Lycopene (a bright red carotenoid pigment and phytochemical found in tomatoes and other red fruits), Anthocyanins (the water-soluble vacuolar pigments which belong to a class of molecules called flavonoids and they occur in all tissues of higher plants, including leaves, stems, roots, flowers, and fruits) and other substances.
Antioxidants are widely used as ingredients in dietary supplements in the hope of maintaining health and preventing diseases such as cancer and coronary heart disease. Although some studies have suggested antioxidant supplements have health benefits, other large clinical trials did not detect any benefit for the formulations tested, and excess supplementation may be harmful. Current recommendations by the US government and health organizations are to consume a varied diet with at least five servings of fruits and vegetables per day and 6-11 servings of grains per day, with at least three of those being whole grains.
HISTORICAL INFORMATION: This author and his colleague were among the first researchers who reported the possible role of antioxidant Vitamin E in fighting Avian Leukosis caused by Avian Leukosis Virus, an endogenous retrovirus that infects and can lead to cancer in chickens (Saadat Noori and Afnan, 1970).
Some large-scale clinical trials published in recent years reached differing conclusions about the effect of antioxidants on human cancer. Here are the summaries of those conclusions:
The first large randomized trial on antioxidants and cancer risk was the Chinese Cancer Prevention Study, published in 1993. This trial investigated the effect of a combination of beta-Carotene, vitamin E, and Selenium on cancer in healthy Chinese men and women at high risk for gastric cancer. The study showed a combination of beta-Carotene, vitamin E, and Selenium significantly reduced incidence of both gastric cancer and cancer overall (Blot et al, 1993).
A 1994 cancer prevention study entitled the alpha-Tocopherol (Vitamin E)/Beta-Carotene Cancer Prevention Study demonstrated that lung cancer rates of Finnish male smokers increased significantly with beta-carotene and were not affected by Vitamin E (Cancer Prevention Study Group, 1994).
The 1999 Women’s Health Study tested effects of vitamin E and beta-carotene in the prevention of cancer and cardiovascular disease among women age 45 years or older. Among apparently healthy women, there was no benefit or harm from beta-Carotene supplementation (Lee et al, 1999).
THE EFFECTS OF NEW ENGINEERED PURPLE TOMATO: A research note entitled as ‘Enrichment of tomato fruit with health-promoting anthocyanins by expression of select transcription factors’ authored by Eugenio Butelli and his colleagues was published online in Nature Biotechnology on 26 October 2008. The note indicates that, “Dietary consumption of anthocyanins 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. Expression of the two transgenes enhanced the hydrophilic antioxidant capacity of tomato fruit threefold and resulted in fruit with intense purple coloration in both peel and flesh. In a pilot test, cancer-susceptible mice fed a diet supplemented with the high-anthocyanin tomatoes showed a significant extension of life span”.
In short, mice genetically engineered to develop cancer lived an average of 182 days when they were fed the purple tomatoes, compared with 142 days for animals on the standard diet.
In his note, Michael Kahn quoted Lara Bennett who said that, “It is exciting to see new techniques that could potentially make healthy foods even better for us but it is too early to say whether anthocyanins obtained through diet could help to reduce the risk of cancer”. Lara Bennett is a science information officer at Cancer Research in the UK.
The researchers cautioned that trials in humans are a long way off and the next step is to investigate how the antioxidants actually affect the tumors to promote better health. But the findings do support the research works suggesting that people can significantly improve their health by making simple changes to their daily diet.
Manouchehr Saadat Noury, PhD
REFERENCES:
Blot, W. J. et al (1993): Nutrition intervention trials in Linxian, China: supplementation with specific vitamin/mineral combinations, cancer incidence, and disease-specific mortality in the general population, J. Natl. Cancer Inst. 85:1483.
Butelli, E. et al (2008): Online Note on ‘Enrichment of tomato fruit with health-promoting anthocyanins by expression of select transcription factors’.
Cancer Prevention Study Group (1994): The effects of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers, New Engl. J. Med., 330:1029.
IFIC Website (2008): Online Fact Sheet of the International Food Information Council on Antioxidants.
Kahn, M. (2008): Online Note on ‘Purple tomato fights cancer’.
Lee, I. M. et al (1999): Beta-carotene supplementation and incidence of cancer and cardiovascular disease, Women’s Health Study, J. Natl. Cancer Inst. 91:2102.
Saadat Noori, M. and Afnan, M. (1970): Depression of plasma alpha-tocopherol (Vitamin E) level in chicks infected with Avian Leukosis, Poultry Sci. 49: 1385.
Saadat Noury, M. (1976): Principles of Experimental Nutrition (in Persian), ed., Tehran University Publications, Tehran, Iran.
US National Cancer Institute Website (2004): Online Fact Sheet on Antioxidants and Cancer Prevention.
Wikipedia Encyclopedia (2008): Online Notes on ‘Antioxidants’, ‘Lycopene’, ‘Anthocyanins’ and ‘Avian Sarcoma and Leukosis Virus’.
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