Polyphenols biological effects

Collins, A.R., Assays for oxidative stress and antioxidant status applications to research into the biological effectiveness of polyphenols. Am. J. Clin. Nutr., 81, 261S, 2005. 

Plant polyphenols have been of interest for long time owing to their role in plant pigmentation, reproduction and protection against predators and pathogens. Recently, interest in the biological effects of plant polyphenols (particularly flavonoids) has increased, because of the the potential health benefits associated with some dietary polyphenols. This... 

Finally, binding studies revealed the existence, at the level of the cell plasma membrane, of specific polyphenol binding sites in the rat brain. Structure-activity data support the hypothesis that these specific binding sites may mediate numerous biological effects of these polyphenols, including their neuroprotective abilities. 

Ellagitannins—a class of bitter-tasting polyphenols comprising ellagic acid and tannin under research for various biological effects... 

Most studies on the biological properties of polyphenols have been carried out on flavonoids in their native form. However, many of their biological effects observed in animal or clinical studies may be equally explained by their microbial metabolites. 

The biological effects of polyphenols, and in particular of flavonoids, are thought to result from their most widely studied property, their antioxidant activity. Littie is known about their ability to bind to proteins. Interaction between small moleeules sueh as phenolic acids and polyphenols and... 

The plant polyphenol trani-resveratrol (3, 5, 4 -trihydroxystilbene), mainly found in grape, peanut, and other few plants, displays a wide range of biological effects. Numerous in vitro studies have described various biological effects of resveratrol. In order to provide more information regarding absorption, metabolism, and bioavailability of resveratrol, different research approaches... 

Fig. 71.1 Multitargeted cellular, molecular, and biological effect of polyphenols relevant to cancer prevention and therapy...

Details about structure, biosynthesis, and classification of phenolics are described in the other chapters in this handbook. Plant phenolics have a distinctive ability to form non-covalent, intermolecular complexes with each other and with both large and small molecules. Recognition of the antioxidant activities of many polyphenols has established correlation with the health benefits by such compounds [34]. This leads to the development of commercial products containing free-radical-scavenging phytochemical mixtures, for example, Pycnogenol (procyanidin extracted from Pinus maritima). Table 82.2 represents a list of polyphenolic compounds used in nutraceuticals and their biologic effects on human health. 

Table 82.2 Polyphenolic compounds used in nutraceuticals and their biologic effects ...

Active polyphenolic compound Source Biologic effect References... 

The redox potential of interest to understand the biological effects of flavan-3-ols is the one related to phenoxyl radical-phenate couple, as this potential is roughly 1 V lower than the potential of the phenoxyl radical-phenol couple, which furthermore may transiently involve the oxidation of the aromatic atoms. Standard potential can be measured by electrochemistry [49] or pulse radiolysis [40 4]. However, determining the redox potential of polyphenolic compounds is a real challenge since for these methods the measurement must be faster than the subsequent reactions induced by the oxidation of the phenol group in order to obtain the thermodynamic value. By using ultramicroelectrodes (electrodes with a micrometer diameter), it has been shown that a very high scan rate, up to 1 milUon... 

Fig. 5.1 Chemical structures reporting examples of natural compounds with different biological effects, a a-Linolenic acid, an essential omega-3 fatty acid. Omega-3 is known to decrease the risk of cardiovascular diseases b a-amantine is a deadly natural compound found in the Amanita phalloides mushrooms c resveratrol, a polyphenolic stilbenoid produced in plants with several reported pharmacological actions...

Biological Antioxidant Models. Tea extracts, tea polyphenol fractions, and purified catechins have all been shown to be effective antioxidants in biologically-based model systems. A balance between oxidants and antioxidants is critical for maintenance of homeostasis. Imbalances between free radicals and antioxidants may be caused by an increased production of free radicals or decreased effectiveness of the antioxidants within the reaction system. These imbalances can be caused by the radicals overwhelming the antioxidants within the system, or by an excess of antioxidants leading to a prooxidant functionaHty (105—118). When antioxidant defense systems are consistently overwhelmed by oxidative reactions, significant damage can... 

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