Polyphenol , activation

One main line of future research could be in the inhibitory/activating effect on key enzymes involved in the pathogenesis of arteriosclerosis. In particular, enzymes regulating signal transduction involved in phosphorylation of proteins, such as PKC and tyrosine protein kinase, seems to be somehow modulated by different polyphenols and may represent a possible target for polyphenol activity. 

Antioxidant activity of silica nanocomposites with immobilized vitamin C was tested using the polyphenolic activity index.8 After adsorption of ascorbic acid on the silica surface and centrifugation, the excess solution was removed to obtain the suspension of a fixed volume (2 ml). Distilled water, sodium carbonate solution, and Folin-Ciocalteu s phenol reagent were subsequently added to suspensions and to the reference Vitamin C solution. The suspensions were then stored for 30 min, and the optical density of supernatant was measured at X = 750 nm. The reference solution of ascorbic acid was used to compare antioxidant activity of vitamin-containing nanocomposites with the activity of dissolved vitamin C. 

So, as we are the first to show, humic acids, being natural polyphenols, actively dissolve the biogenic silica of siliceous rocks, and we used the scheme of obtaining the ammonium salt of the tricatechol ether of monosilicic acid in order to understand the methods of synthesis of biogeochemically active SOC, formed from natural amorphous silica and polyphenols in natural systems. 

Enzyme treatment of fruit pulp before pressing improves the yield and the colour. Pectin in soft fmits forms a gel-like mass which is very difficult to press. Treatment with pectinase leads to a thin, free rurming liquid and good pressable pulp. Since some of the pectinase are inhibited by polyphenols, activation of polyphenoloxidase which is present in fmits, is an important aspect of pulp treatment and can be achieved by aeration of the pulp. 

The potential health benefits of plant polyphenols, such as the flavonoids, have been addressed over the years in the framework of the oxidative stress concept. Oxidative stress, as initially formulated by Sies (1985), refers to an imbalance in the dynamic equilibrium between oxidants and antioxidants that favors the formers, potentially leading to damage. As several diseases are supposed to mechanistically involve oxidative stress, such as atherosclerosis, ischemia-reperfusion injury, cancer, and neurodegenerative disorders (Halliwell Gutteridge, 1999), an impressive number of studies on the in vitro antioxidant activity of polyphenols have spotted these compounds as putatively useful to counteract the deleterious oxidant imbalance associated with disease. However, as will be discussed later, because of limited bioavailability and recent updated concept of oxidative stress, the putative activity of polyphenols as global antioxidants is a limited and simplistic view of polyphenol activity in vivo that can be scarcely supported by experimental data. 

Another line of investigation is bridging polyphenol activity with NO bioavailability via the chemical reduction of nitrite to NO (Takahama et al, 2002 Peri et al, 2005 Gago et al, 2007). The redox properties that have been proposed to confer polyphenols with antioxidant activity by quenching oxidizing radicals may, alternately, endow the phenolic compounds with the capacity to promote the formation of NO from nitrite, particularly in the gastrointestinal tract, a location where both nitrite and polyphenols achieve high concentrations. 

Chemical Antioxidant Systems. The antioxidant activity of tea extracts and tea polyphenols have been determined using in vitro model systems which are based on hydroxyl-, peroxyl-, superoxide-, hydrogen peroxide-, and oxygen-induced oxidation reactions (109—113). The effectiveness of purified tea polyphenols and cmde tea extracts as antioxidants against the autoxidation of fats has been studied using the standard Rancimat system, an assay based on air oxidation of fats or oils. A direct correlation between the antioxidant index of a tea extract and the concentration of epigallocatechin gallate in the extract was found (107). 

The total antioxidant activity of teas and tea polyphenols in aqueous phase oxidation reactions has been deterrnined using an assay based on oxidation of 2,2 -azinobis-(3-ethylbenzothiazoline-sulfonate) (ABTS) by peroxyl radicals (114—117). Black and green tea extracts (2500 ppm) were found to be 8—12 times more effective antioxidants than a 1-mAf solution of the water-soluble form of vitamin E, Trolox. The most potent antioxidants of the tea flavonoids were found to be epicatechin gallate and epigallocatechin gallate. A 1-mAf solution of these flavanols were found respectively to be 4.9 and 4.8 times more potent than a 1-mAf solution of Trolox in scavenging an ABT radical cation. 

Biological activity (BA) was chosen as such parameter. The BA determined using a system and a technique for a class of natural polyphenolic bonds nicotinamide adenine dinucleotide restored (NAD H ) - ferricyanide (KjFe(CN)g) in a phosphates buffer solution. 

Tissue and Bacteria Electrodes The limited stability of isolated enzymes, and the fact that some enzymes are expensive or even unavailable in the pure state, has prompted the use of cellular materials (plant tissues, bacterial cells, etc.) as a source for enzymatic activity (35). For example, banana tissue (which is rich with polyphenol oxidase) can be incorporated by mixing within the carbon paste... 

Polyphenols and flavanoids in rat liver microsomal fractions have been demonstrated to inhibit glucuronidation of estrone and estradiol in vitro (Zhu et al, 1998). In addition, flavonoids have also been found to induce phase I and II enzymes in rats including UDP-glucuronosyl transferase (Seiss et al, 1996). However, the effects of phytoestrogens have not been evaluated for either their inhibition or induction of glucuronosyl transferase activity. 

YAMAGUCHI M and MA z J (2001) Effect of polyphenols on calcium content and alkaline phosphatase activity in rat femoral tissues in vitro. Biol Pharm Bull 24, 1437-9. 

Diabetic patients have reduced antioxidant defences and suffer from an increased risk of free radical-mediated diseases such as coronary heart disease. EC has a pronounced insulin-like effect on erythrocyte membrane-bound acetylcholinesterase in type II diabetic patients (Rizvi and Zaid, 2001). Tea polyphenols were shown to possess anti-diabetic activity and to be effective both in the prevention and treatment of diabetes (Choi et al, 1998 Yang et al, 1999). The main mechanism by which tea polyphenols appear to lower serum glucose levels is via the inhibition of the activity of the starch digesting enzyme, amylase. Tea inhibits both salivary and intestinal amylase, so that starch is broken down more slowly and the rise in serum glucose is thus reduced. In addition, tea may affect the intestinal absorption of glucose. 

Green tea consists of a wealth of simple phenolics (monomers), whereas black tea provides more complex polyphenols (dimers and polymers). It was found that with lipids the simple compounds were more effective antioxidants, while under aqueous conditions, polymers tended to have more activity. Weisburger (2001) suggested that polymers formed from a 2-5 unit polymerisation state seemed to be optimal, probably because the monomer is metabolised and excreted too rapidly, whereas the higher 6-10 unit polymers may suffer from difficulty in penetrating cellular membranes and be poorly absorbed. 

ISHIGAMI T (1991) Antibacterial activity of tea polyphenols against foodbome, cariogenic and phytopathogenic bacteria , in Proc of Intern Symp on Tea Sci, 26-29 August, 1991, Shizuoka, Japan, 248-52. 

UNTEN L, KOKETSU M and KIM M (1997) Antidiscoloring activity of green tea polyphenols on beta-carotene , JAgric Food Chem, 45, 2009-12. 

WANG s M and zhao j f (1997) Antioxidant activities of tea polyphenol on edible oils . Western Cereal and Oil Technology, 11, 44-6. 

---