Difference between revisions of "Polyphenol antioxidant"

Latest revision as of 20:29, 21 September 2010

A polyphenol antioxidant is a type of antioxidant containing a polyphenolic substructure. Numbering over 4,000 distinct species, these compounds have antioxidant activity in vitro but are unlikely to have antioxidant roles in vivo.^[1][2] Rather, they may affect cell-to-cell signaling, receptor sensitivity, inflammatory enzyme activity or gene regulation.^[2][3]

Sources of polyphenol antioxidants

The main source of polyphenols is dietary, since they are found in a wide array of phytochemical-bearing foods. For example, most legumes; fruits such as apples, blackberries, blueberries, cantaloupe, cherries, cranberries, grapes, pears, plums, raspberries, and strawberries; and vegetables such as broccoli, cabbage, celery, onion and parsley and honey are rich in polyphenols. Red wine^[4], chocolate, green tea, olive oil, argan oil,bee pollen and many grains are sources. Ingestion of polyphenols occurs by consuming a wide array of plant foods; correspondingly, the role of dietary supplements as a method of realizing these health benefits is the subject of considerable discussion.

Biochemical theory

The regulation theory considers a polyphenol antioxidant’s ability to scavenge free radicals and up-regulate certain metal chelation reactions. Various reactive oxygen species, such as singlet oxygen, peroxynitrite and hydrogen peroxide, must be continually removed from cells to maintain healthy metabolic function. Diminishing the concentrations of reactive oxygen species can have several benefits possibly associated with ion transport systems and so may affect redox signaling.

Potential biological consequences

Consuming dietary polyphenols may be associated with beneficial effects in higher animal species:

• Reduction in inflammatory effects such as coronary artery disease^[5][6] including specific medical research into the pathways of improved endothelial health via downregulation of oxidative LDL.^[7]

• More generally, the tea polyphenol antioxidant epigallocatechin gallate (EGCG) has been shown to reduce reactive oxygen species levels in vitro.^[8]

• Some polyphenols, such as resveratrol, inhibit occurrence and/or growth of experimental tumors.^[9]

• Other beneficial health effects may result from consumption of foods rich in polyphenols, but are not yet proved scientifically in humans so are not allowed as health statements by regulatory authorities like the FDA. Among these potential effects are anti-aging consequences such as slowing the process of skin wrinkling.^[10] For some of the side-benefits (such as prevention of peripheral artery disease), further research is continuing to clarify the role polyphenol antioxidants may have.^[11][12]

• Although initial studies suggested that antioxidant supplements might promote health, later large clinical trials did not detect any benefit and suggested instead that excess supplementation may be harmful.^[13]

Difficulty in analyzing effects of specific chemicals

It is difficult to evaluate the physiological effects of specific polyphenolic antioxidants, since such a large number of individual compounds may occur even in a single food and their fate in vivo cannot be measured. For example, over sixty different chemically distinct flavonoids are known to occur in a given red wine. Wine, although nonessential, has a high polyphenol content of up to 2-3 grams per liter in red wines analyzed by traditional maceration techniques.^{[citation needed]} The polyphenol content of wines is usually evaluated by the Folin-Ciocalteu reagent which correlates well with alternative chemical and biological procedures for determining antioxidant potential.^[14]

Other more detailed chemical research has elucidated the difficulty of isolating individual polyphenolic antioxidants. Significant variation in polyphenol content occurs among various brands of tea may underlie^[15] inconsistencies of epidemiological studies implying beneficial health effects of polyphenol antioxidants of green tea blends. The Oxygen Radical Absorbance Capacity (ORAC) test is a laboratory indicator of antioxidant potential in foods and dietary supplements. However, as ORAC is only a test tube measure unconfirmed to be physiologically applicable, it likely bears no relevance to antioxidant activity in the human body.^[2]

Practical aspects of dietary polyphenol antioxidants

There is debate regarding the total body absorption of dietary intake of polyphenolic compounds. While some indicate potential health effects of certain specific polyphenols, most studies demonstrate low bioavailability and rapid excretion of polyphenols, indicating their potential roles only in small concentrations in vivo.^[1][2][3] More research is needed to understand the interactions between a variety of these chemicals acting in concert within the human body. In particular there is evidence that some combinations of foods may inhibit efficient intestinal transfer of certain polyphenol antioxidants; refined sugars, for example, have been shown to impede this uptake under certain circumstances.^[16] Furthermore caution should be exercised in attempting diets depending largely on dietary supplements as opposed to a broad array of food sources, since the quality and concentrations of beneficial chemicals in some commercial products is subject to question.

Topical application of polyphenol antioxidants

There is some data that reactive oxygen species play a role in the process of aging. The skin is exposed to various exogenous sources of oxidative stress, including ultraviolet radiation. These spectral components are generally viewed as responsible for the extrinsic type of skin aging, sometimes termed photo-aging. It has been shown not only that increased levels of protective low molecular weight antioxidants through a diet rich in phytochemicals, but also by direct topical dermal application^[17] of low molecular weight antioxidants, notably vitamins C and E, as well as lipoic acid, may confer protective effects against oxidative stress. However, controlled long-term studies on the efficacy of low molecular weight antioxidants in the prevention or treatment of skin aging in humans are lacking.

References

See also

Other articles

• Asymmetric dimethylarginine
• Coronary artery disease
• List of grape varieties
• Low density lipoprotein
• Nitric oxide
• Resveratrol

External links

• Félicien Breton (2008). "Polyphenol antioxidants in red wine". zh:多酚抗氧化劑