ProCarcinogenic Action of Beta Carotene Homer S Black
Pro-Carcinogenic Action of Beta. Carotene Homer S. Black Department of Dermatology Baylor College of Medicine Houston, Texas, USA
Dietary Recommendations* (to reduce cancer risk) 1. Caloric reduction, i. e. , lowering the level of free-radical reactions arising in the course of normal metabolism 2. Minimize dietary components, e. g. , polyunsaturated fats, that tend to increase the level of free-radical reactions 3. Supplement the diet with one or more freeradical reaction inhibitors, i. e. , antioxidants *Harman D. The free radical theory of aging. In: Pryor WA, ed. Free Radicals in Biology V. New York: Academic Press, 1982.
Butylated Hydroxytoluene (BHT) Control BHT
Carotenoids Lycopene Zeaxanthin Canthaxanthin -Carotene
“Human cancer risks are inversely correlated with (a) blood retinol and (b) dietary ß-carotene” Peto, R, Doll, R, Buckley, JD. And Sporn, MB. Can dietary beta-carotene materially reduce human cancer rates” Nature 290: 201 -208, 1981.
β-Carotene Photoprotection • Mathews-Roth MM. Antitumor activity of βcarotene, canthaxanthin, and phytoene. Oncology, 1982; 38: 33 -37. • Mathews-Roth MM, Krinsky NI. Carotenoid dose level and protection against UV-Binduced skin tumors. Photochem Photobiol 1985; 42: 33 -38.
Influence of β-Carotene on Tumor Incidence
Influence of Diet on β-Carotene Modulated UVR-Carcinogenic Expression DIET Med. Tumor Time, wk Tumors/Animal Closed Formula Control 20. 6 0. 52 0. 07% β-car 20. 0 0. 60 Control 19. 5 0. 60 0. 07% β-car 17. 2 (p<0. 002) 1. 63 (p<0. 03) Semi-Defined
Proposed Mechanism by which -Carotene Interacts with Vitamins E and C to Quench Radical Reactions -Electron Transfer Scheme- Edge R, Land EJ, Mc. Garvey D, Mulroy L, Truscott TG, Relative One Electron Reduction Potentials of Carotenoid Radical Cations…. . J Amer Chem Soc 120, 4987, 1998.
Repair of the Carotene Cation Radical by Ascorbic Acid CAR + Asc. H CAR + Asc + H+
Tumor Incidence: -carotene, vit C
What Repairs the β-Carotene Radical Cation? CAR●+ + ? CAR + H● + ?
Tumor Incidence: Beta-carotene, low Vit E; No Vit C
Influence of Varying Levels of Vitamins E and C on β-Carotene Modulated Tumor Multiplicity Control (-βC) + βC – Vit C, low E 1. 05 3. 2 3. 45 5. 9
“Until further insight is gained, ß-carotene should not be recommended for use in cancer prevention in the general population and it should not be assumed that ß-carotene is responsible for the cancer protecting effects of diets rich in carotenoid containing fruits and vegetables” IARC Working Group on the Evaluation of Cancer Preventive Agents. IARC Handbooks of Cancer Prevention, “Carotenoids”, Vol. 2, Lyon, 1998. “A general recommendation to consume supplements for cancer prevention might have unexpected adverse effects” and thus “Dietary supplements are not recommended for cancer prevention” World Cancer Research Fund/American Institute for Cancer Research, Food, Nutrition, Physical Activity, and the Prevention of Cancer: A Global Perspective. Washington, D. C: AICR, 2007.
Recommendation • The best recommendation for maintaining a strong defensive antioxidant system may be the consumption of a balanced diet containing adequate green leafy and yellow vegetables that are known to be rich in a broad range of antioxidants and from which the original observations of reduced cancer risks were based.
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