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Antioxidants
What are antioxidants?
An antioxidant is a molecule capable of slowing or preventing the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons from a substance to an oxidizing agent. Oxidation reactions can produce free radicals, which start chain reactions that damage cells. Antioxidants terminate these chain reactions by removing free radical intermediates, and inhibit other oxidation reactions by being oxidized themselves. As a result, antioxidants are often reducing agents such as thiols or polyphenols.
Although oxidation reactions are crucial for life, they can also be damaging; hence, plants and animals maintain complex systems of multiple types of antioxidants, such as glutathione, vitamin C, and vitamin E as well as enzymes such as glutathione, catalase, superoxide dismutase and various peroxidases. Low levels of antioxidants, or inhibition of the antioxidant enzymes, causes oxidative stress and may damage or kill cells.
Oxidative Stress
As oxidative stress might be an important part of many human diseases, the use of antioxidants in pharmacology is intensively studied, particularly as treatments for stroke and neurodegenerative diseases. However, it is unknown whether oxidative stress is the cause or the consequence of disease. Antioxidants are also 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. This is mainly the case with synthetic supplements, as the recent JAMA study clearly showed!
FREE RADICALS AND THE THEORY OF AGING
Presse Med. 2002 Jul 27;31(25):1174-84.Links
Bonnefoy M, Drai J, Kostka T.
Service de médecine gériatrique, Pavillon Michel Perret. CH. Lyon-Sud, 69495 Pierre-Bénite. marc.bonnefoy@chulyon.fr
Severe oxidative stress progressively leads to cell dysfunction and ultimately cell death. Oxidative stress is defined as an imbalance between pro-oxidants and/or free radicals on the one hand, and anti-oxidizing systems on the other. The oxygen required for living may indirectly be responsible for negative effects; these deleterious effects are due to the production of free radicals, which are toxic for the cells (superoxide anions, hydroxyl radicals, peroxyl radicals, hydrogen peroxide, hydroperoxides and peroxinitrite anions). Free radical attacks are responsible for cell damage and the targeted cells are represented by the cell membranes, which are particularly rich in unsaturated fatty acids, sensitive to oxidation reactions; DNA is also the target of severe attacks by these reactive oxygen species (ROS).
THE DEFENCE SYSTEMS: These are represented by the enzymes and free radical captors. The latter are readily oxidizable composites. The free radical captor or neutralization systems of these ROS use a collection of mechanisms, vitamins (E and C), enzymes [superoxide dismutase (SOD), glutathion peroxidase (GPx) and others], and glutathion reductase (GSH), capable of neutralizing peroxinitrite. The efficacy of this system is dependent on the genome for the enzymatic defence systems, and on nutrition for the vitamins. Some strategies aimed at reducing oxidative stress-related alterations have been performed in animals. However, only a few can be used and are efficient in humans, such as avoidance of unfavourable environmental conditions (radiation, dietary carcinogens, smoking...) and antioxidant dietary supplementation.
DIETARY SUPPLEMENTATION: Epidemiological data suggest that antioxidants may have a beneficial effect on many age-related diseases: atherosclerosis, cancer, some neurodegenerative and ocular diseases. However, the widespread use of supplements is hampered by several factors: the lack of prospective and controlled studies; insufficient knowledge on the pro-oxidant, oxidant and antioxidant properties of the various supplements; growing evidence that free radicals are not only by-products, but also play an important role in cell signal transduction, apoptosis and infection control.
RECOMMENDATIONS: Although current data indicate that antioxidants cannot prolong maximal life span, the beneficial impact of antioxidants on various age-related degenerative diseases may forecast an improvement in life span and enhance quality of life. The current lack of sufficient data does not permit the systematic recommendation of anti-oxidants. Nevertheless, antioxidant-rich diets with fruit and vegetables should be recommended.
Lipophilic antioxidants in human sebum and aging.
Passi S, De Pità O, Puddu P, Littarru GP.
IDI-IRCCS, Rome, Italy. Free Radic Res. 2002 Apr;36(4):471-7.
Skin surface lipids (SSL), a very complex mixture of sebum mixed to small amounts of epidermal lipids, mantle the human epidermis, thus representing the outermost protection of the body against exogenous oxidative insults. The present work is a systematic and quantitative analysis of upper-chest SSL and their content in antioxidants in 100 healthy volunteers, divided into five age groups using TLC, HPLC, and GC-MS methods. Further, the effect of exposing SSL in vitro to increasing doses of UV irradiation was examined.
Straight monounsaturated and diunsaturated as well as branched monounsaturated fatty acids of triglycerides and pooled fractions were found to be higher at maturity than in childhood and in advancing age. Diunsaturated fatty acids were below 3% of the total and constituted exclusively of C18:2delta5,8, C20:2delta7,10, C18:2delta9,12. Squalene, vitamin E (vit. E) and Coenzyme Q10 (CoQ10) were found to increase from childhood to maturity to decrease again significantly in old age. Vitamin E and CoQ10 were the only known lipophilic antioxidants present in SSL. In spite of their low levels they were found to synergically inhibit the UV induced depletion of squalene, cholesterol and of unsaturated fatty acids of SSL. In fact, exposure of SSL to increasing amounts of UV irradiation led preferentially to lowering of the levels of vit. E and CoQ10. Four minimal erythema dose (MED) (5.6J/cm2) were able to deplete 84% vit. E and 70% ubiquinone, and only 13% squalene. Diunsaturated and monounsaturated fatty acids as well as cholesterol were unaffected even following 10 MED UV exposures, which produced a 26% loss of squalene. The same UV dose when applied in the absence of vit. E and CoQ10 produced a 90% decrease of squalene.
Studies:
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