Free radical theory

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The free-radical theory of aging , including free radical theory ( Engl. Free Radical Theory of Aging called FRTA) is an explanatory model for the aging of all organisms .

description

The theory of free radicals is based on the fact that so-called free radicals are formed in cells as a result of the metabolic processes from molecular oxygen . These short-lived molecular fragments, such as the hydroxyl radical • OH, play an important role in a number of cell biological processes and can be detected using various analytical methods. In 1956, the American biogerontologist Denham Harman proposed that these free radicals are the cause of the aging process. When they are released, the free radicals damage molecules that are important for the functioning of the cell, such as DNA , RNA and a large number of proteins and lipids . According to the thesis, this leads to a steadily growing accumulation of damaged cell components, which in turn causes the complex aging process. The cells themselves are able to produce substances that can render free radicals harmless by reacting with them or by catalytically breaking them down. These include, for example, urates or the enzyme catalase . Antioxidants such as ascorbic acid , β-carotene , polyphenols or flavonoids , which can react in the cells with the free radicals, can also be ingested through food . Nevertheless, degradation products can be detected in urine, for example, which arise as a result of damage to DNA or lipids.

reception

At the beginning, the theory of free radicals was rejected by many gerontologists and sometimes viewed as para-scientific . In the following years, however, some scientific findings could be explained with this theory. It also serves as an explanatory model for the development of a number of diseases such as cancer , arteriosclerosis , diabetes mellitus and Alzheimer's .

Less food intake means less oxidative stress on the cells, which in turn leads to a lower amount of free radicals and thus less damage within the cell. In fact, a calorie restriction in a wide variety of model organisms causes a significant increase in life expectancy . The supplementation of antioxidants leads to an increase in the average survival time of a number of species if these substances are administered very early. In contrast, the maximum service life could not be increased.

A number of other experiments produce conflicting results on the theory of free radicals. The working group led by the German internist Michael Ristow was able to show that free radicals are necessary to set mitohormesis in motion, whereby the cell achieves an increased defense capacity against free radicals. Antioxidants, on the other hand, prevent mitohormesis.

From the theory of free radicals the theory of mitochondrial aging was developed.

The United States Department of Agriculture (USDA) stated in 2012 that there was no evidence of the theory of free radicals and that measuring the antioxidant effects did not allow any conclusions to be drawn about the benefits of polyphenols.

further reading

Individual evidence

  1. ^ D. Harman: Aging: a theory based on free radical and radiation chemistry. In: Journal of Gerontology 11, 1956, pp. 298-300, PMID 13332224
  2. ^ D. Harman: The free radical theory of aging. In: Antioxid Redox Signal 5, 2003, pp. 557-561, PMID 14580310 .
  3. ^ D. Harman: Free radical theory of aging. In: Mutat Res 275, 1992, pp. 257-266, PMID 1383768 .
  4. ↑ HC Schröder: Superoxide radicals, gene expression and aging: Repairable damage at the level of DNA and irreparable damage at the level of mRNA maturation. In: Successful aging , MM Baltes, M. Kohli and K. Sames (eds.), Verlag Huber, 1989, ISBN 3-456-81841-6 , pp. 259-269.
  5. ^ GG Duthie et al. a .: Oxidants, antioxidants and cardiovascular disease. In: Nut Res Rev 2, 1989, pp. 51-62, PMID 19094346 .
  6. ↑ T. Schmidt et al. a .: Physiological potentials of longevity and health in an evolutionary and cultural context - basic requirements for a productive life. ( Memento from January 12, 2012 in the Internet Archive ) In: Productive life in old age M. Baltes and L. Montada (eds.), Campus-Verlag, 1996, ISBN 3-593-35456-X , pp. 69–130.
  7. ↑ BN Ames u. a .: Oxidants, antioxidants, and the degenerative diseases of aging. In: PNAS 90, 1993, pp. 7915-7922, PMID 8367443 , PMC 47258 (free full text).
  8. ↑ G. Bjelakovic et al. a .: Mortality in Randomized Trials of Antioxidant Supplements for Primary and Secondary Prevention. In: JAMA 297, 2007, pp. 842-857.
  9. ↑ TJ Schulz u. a .: Glucose Restriction Extends Caenorhabditis elegans Life Span by Inducing Mitochondrial Respiration and Increasing Oxidative Stress. In: Cell Metabolism 6, 2007, pp. 280-293, doi: 10.1016 / j.cmet.2007.08.011 .
  10. ↑ KB Beckman, BN Ames: Mitochondrial aging: open questions. In: Ann NY Acad Sci 854, 1998, pp. 118-127, PMID 9928425
  11. ↑ Withdrawn: Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2 (2010) . United States Department of Agriculture, Agricultural Research Service. May 16, 2012. Retrieved June 13, 2012.