Antioxidant

An antioxidant is a chemicalthat prevents the oxidationof other chemicals. These compounds, despite their name, do not prevent oxidation. Instead, they oxidize first, preventing the oxidizing agent from oxidizing compounds that are more important to proper functioning of a system, as in a cell.

Antioxidants in biology

In biological systems, the normal processes of oxidation (plus a minor contribution from ionizing radiation) produce highly reactive free radicals. These can readily react with and damage other molecules. In some cases the body uses free radicals to destroy foreign or unwanted objects, such as in an infection. However, in the wrong place, the body's own cellsmay become damaged. Should the damage occur to DNA, the result could be cancer. Antioxidants decrease the damage done to cells by reducingoxidants before they can damage the cell.

Virtually all studies of mammals have concluded that a restricted calorie dietextends the lifespan of mammals by as much as 100%. This remarkable finding suggests that food is actually more damaging than smoking. As food produces free radicals (oxidants) when metabolized, antioxidant-rich diets are thought to stave off the effects of aging significantly better than diets lacking in antioxidants. The reduced levels of free radicals, resulting from a reduction in their production by metabolism, is thought to be a major cause of the success of caloric restriction in increasing life span.

Free radical damage in the mitochondriaof living cells is a byproduct of oxidative phosphorylation. Superoxideradicals are generated, which can damage mitochodrial and mitochondrial membranes. Unlike DNA in the cell nucleus, mitochondrial DNA has only a few DNA-repair enzymes and the DNA is not protected by histones.

Many antioxidants, however (including vitamin C and vitamin E) can't get into mitochondria for various reasons (e.g. because they are too hydrophilic to cross mitochondrial membranes or too hydrophobic to cross the cytoplasm). A group of scientists in Russia (led by V. Skulachev) have created a custom antioxidant (a Skulachev ionforms the point of the molecule and penetrates the mitochondrial membrane; the antioxidising part is attached behind it) that can enter the mitochondria and stays there due to the membrane potentialgradient; preventing damage to DNA.

Although there is little doubt that antioxidants are a necessary component for good health, there is considerable doubt as to the most beneficial antioxidant(s) and as to the optimal amount for results. A study of lung cancer patients found that those given antioxidant supplements had worse prognoses. This is believed to be due to antioxidant interference with the body's normal use of localised free radicals e.g. Nitric oxidefor cell signalling. Due to the complex nature of the interactions of antioxidants with the body, it is difficult to interpret the results of many experiments designed to test such things. In vitro testing (outside the body) has shown many natural antioxidants, in specific concentration, can halt the growth of or even kill cancerous cells.

For example, recent studies are suggesting that at high levels, synthetic antioxidant vitamins such as A, E and C may prove to have pro-oxidant effects: increasing the formation of free radicals. The fact that natural antioxidants are always ingested together with a wide variety of flavonoidsand other phytochemicalsalso likely plays a part. Many supplement manufacturers supply more expensive tablets containing these. Newer liquid nutritional supplements using plant ionic compounds are believed to be more readily absorbed in the human body.

The benefits of antioxidants were examined during the Age-Related Eye Disease Study.

Nutritional antioxidants

The following substances have shown positive antioxidant effects:

• Vitamin A(Retinol, also synthesized by the body from beta-carotene) protects dark green, yellow and orange vegetables and fruits from solar radiation damage, and is thought to play a similar role in the human body. Carrots, squash, broccoli, sweet potatoes, tomatoes (which gain their color from the compound lycopene), kale, collards, cantaloupe, peaches and apricots are particularly rich sources of beta-carotene.

• Vitamin C(Ascorbic acid) is a water-solublecompound that fulfills several roles in living systems. Important sources include citrus fruits (such as oranges, sweet lime, etc.), green peppers, broccoli, green leafy vegetables, strawberries, raw cabbage and tomatoes. Linus Paulingwas a major advocate for its use.

• Vitamin E, including Tocotrienoland Tocopherol, is fat soluble and protects lipids. Sources include wheat germ, nuts, seeds, whole grains, green leafy vegetables, vegetable oil, and fish-liver oil. Recent studies showed that some tocotrienol isomers have significant anti-oxidant properties.

• Seleniumhas been shown as early as the 1950's to have a beneficial effect in reducing the occurrence of male prostatecancer, and a recent study done by the National Health System of China have verified previous results. However, the substance must be taken in measured amounts because large doses of the element can be toxic. Good food sources include fish, shellfish, red meat, grains, eggs, sunflower seeds, chicken, garlic, and brazil nuts. Vegetables can also be a good source if they are grown in selenium-rich soils, and some nutritional supplements contain a supply of selenium.

• Bio-flavonoidsare present in many dark berries such as pomegranate, noni, blueberries, and blackberries, as well as in certain types of teaand coffee, especially green tea. Coffee is often depleted of antioxidants due to the high-temperature roasting process. Applied Food Sciences has introduced Healthy Roast, a product that remove antioxidants from the green coffee beans before roasting and then adds them back when beans are quenched. The FDAmay have recently suggested that the average person should consume up to 7000 ORACunits daily, in order to reduce the risk of cancer. As this is nearly 12 servings of high-ORAC-value fruit, the use of nutritional supplements containing bio-flavonoids is likely necessary to reach this target.

• Several food additives, including pectin, ascorbic acid (vitamin C) and tocopherol-derived compounds are used as antioxidants to help guard against food deterioration.

• A wide variety of antioxidants occur naturally in the body; many of these are enzymessuch as glutathione peroxidase, superoxide dismutaseand catalase. Bilirubin, a breakdown product of blood, has been identified [1]as a possibly significant antioxidant.

In addition, Omega 3fatty acids prevent the formation of atherosclerosiswhen they are taken in conjunction with antioxidants. The antioxidants prevent the acids from being oxidised.

Many nutraceuticaland health food companies have, in light of scientific studies, produced products that supplement the diet with antioxidants. Large companies such as the Nutraceutical Corporationand Natrolhave products that are explicitly composed of derivatives that contain antioxidants, like resveratrolin grape seeds. Other companies, such as Canprev, Vemmaand Natural Health, produce supplements that contain a combination of antioxidants, like their Immunotality formula.

Specialty herbs such as green teaand jiaogulan, with makers like Japanese Green Tea and Arizona (for iced) have benefitted tremendously from recent articles on antioxidants in green tea delaying onset of age-related macular degeneration.

Antioxidants in fuels

Some antioxidants are added to liquid industrial chemicals, most often fuelsand lubricantsto prevent oxidation, and in gasolines to prevent polymerization leading to gumming. Some examples are:

• AO-22(N,N'-di-2-butyl-1,4-phenylenediamine), for turbine oils, transformer oils, hydraulic fluids, waxes, and greases
• AO-24(mostly N,N'-di-2-butyl-1,4-phenylenediamine), blended for low-temperature handling)
• AO-29(2,6-di-tert-butyl-4-methylphenol), for turbine oils, transformer oils, hydraulic fluids, waxes, greases, and gasolines
• AO-30(alkylated phenols, mostly 2,4-dimethyl-6-tert-butylphenol(>97%)), for jet fuelsand gasolines, including aviation gasolines
• AO-31(alkylated phenols, mostly 2,4-dimethyl-6-tert-butylphenol(>72%)), for jet fuels and gasolines, including aviation gasolines
• AO-32(alkylated phenols, mostly 2,4-dimethyl-6-tert-butylphenol(>55%), and 2,6-di-tert-butyl-4-methylphenol(>15%)), for jet fuels and gasolines, including aviation gasolines
• AO-36(alkylated phenols), for gasolines
• AO-37(alkylated phenols, mostly 2,6-di-tert-butylphenol), for jet fuels and gasolines, widely approved for aviation fuels

Antioxidants are frequently used together with metal deactivatorsand corrosion inhibitors.

References

• Halliwell B. 1999. Antioxidant defense mechanisms: from the beginning to the end (of the beginning). Free Radical Research 31:261-72.

• Rhodes C.J. Book: Toxicology of the Human Environment - the critical role of free radicals, Taylor and Francis, London (2000).

External links

• Antioxidants: Introduction, Biochemistry & Classification
• Damage-Based Theories of AgingIncludes a description of the free radical theory of aging and a discussion of the role of antioxidants in aging.
• Foods that are rich in antioxidants
• General Anti-Oxidant Actions
• Natural Herbal Antioxidant
• Supplements (Antioxidant) Forum
• Organic Herbal Antioxidantcs:Antioxidant

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It uses material from the http://en.wikipedia.org/wiki/Antioxidant Wikipedia article Antioxidant.