Increasing interest in the health benefits of tea has led to the inclusion of tea extracts in dietary supplements and functional foods. However, epidemiologic evidence regarding the effects of tea consumption on cancer and cardiovascular disease risk is conflicting. While tea contains a number of bioactive chemicals, it is particularly rich in catechins, of which epigallocatechin gallate (EGCG) is the most abundant. Catechins and their derivatives are thought to contribute to the beneficial effects ascribed to tea. Tea catechins and polyphenols are effective scavengers of reactive oxygen species in vitro and may also function indirectly as antioxidants through their effects on transcription factors and enzyme activities. The fact that catechins are rapidly and extensively metabolized emphasizes the importance of demonstrating their antioxidant activity in vivo. In humans, modest transient increases in plasma antioxidant capacity have been demonstrated following the consumption of tea and green tea catechins. The effects of tea and green tea catechins on biomarkers of oxidative stress, especially oxidative DNA damage, appear very promising in animal models, but data on biomarkers of in vivo oxidative stress in humans are limited. Larger human studies examining the effects of tea and tea catechin intake on biomarkers of oxidative damage to lipids, proteins, and DNA are needed.

Tea catechins and polyphenols: health effects, metabolism, and antioxidant functions.

In this review, primary attention is given to the antioxidant (and prooxidant) activity of polyphenols arising from their interactions with iron both in vitro and in vivo. In addition, an overview of oxidative stress and the Fenton reaction is provided, as well as a discussion of the chemistry of iron binding by catecholate, gallate, and semiquinone ligands along with their stability constants, UV–vis spectra, stoichiometries in solution as a function of pH, rates of iron oxidation by O2 upon polyphenol binding, and the published crystal structures for iron–polyphenol complexes. Radical scavenging mechanisms of polyphenols unrelated to iron binding, their interactions with copper, and the prooxidant activity of iron–polyphenol complexes are briefly discussed.

/pdf/a-review-of-the-antioxidant-mechanisms-of-polyphenol-24tylaz1o3.pdf

A Review of the Antioxidant Mechanisms of Polyphenol Compounds Related to Iron Binding

The neurodegenerative diseases, Alzheimer's disease (AD) and Parkinson's disease (PD), are age-related disorders characterized by the deposition of abnormal forms of specific proteins in the brain. AD is characterized by the presence of extracellular amyloid plaques and intraneuronal neurofibrillary tangles in the brain. Biochemical analysis of amyloid plaques revealed that the main constituent is fibrillar aggregates of a 39-42 residue peptide referred to as the amyloid-β protein (Aβ). PD is associated with the degeneration of dopaminergic neurons in the substantia nigra pars compacta. One of the pathological hallmarks of PD is the presence of intracellular inclusions called Lewy bodies that consist of aggregates of the presynaptic soluble protein called α-synuclein. There are various factors influencing the pathological depositions, and in general, the cause of neuronal death in neurological disorders appears to be multifactorial. However, it is clear, that the underlying factor in the neurological disorders is increased oxidative stress substantiated by the findings that the protein side-chains are modified either directly by reactive oxygen species (ROS) or reactive nitrogen species (RNS), or indirectly, by the products of lipid peroxidation. The increased level of oxidative stress in AD brain is reflected by the increased brain content of iron (Fe) and copper (Cu) both capable of stimulating free radical formation (e.g. hydroxyl radicals via Fenton reaction), increased protein and DNA oxidation in the AD brain, enhanced lipid peroxidation, decreased level of cytochrome c oxidase and advanced glycation end products (AGEs), carbonyls, malondialdehyde (MDA), peroxynitrite, and heme oxygenase-1 (HO-1). AGEs, mainly through their interaction with receptors for advanced glycation end products (RAGEs), further activate signaling pathways, inducing formation of proinflammatory cytokines such as interleukin-6 (IL-6). The conjugated aromatic ring of tyrosine residues is a target for free-radical attack, and accumulation of dityrosine and 3-nitrotyrosine has also been reported in AD brain. The oxidative stress linked with PD is supported by both postmortem studies and by studies showing the increased level of oxidative stress in the substantia nigra pars compacta, demonstrating thus the capacity of oxidative stress to induce nigral cell degeneration. Markers of lipid peroxidation include 4-hydroxy-trans-2-nonenal (HNE), 4-oxo-trans-2-nonenal (4-ONE), acrolein, and 4-oxo-trans-2-hexenal, all of which are well recognized neurotoxic agents. In addition, other important factors, involving inflammation, toxic action of nitric oxide (NO·), defects in protein clearance, and mitochondrial dysfunction all contribute to the etiology of PD. It has been suggested that several individual antioxidants or their combinations can be neuroprotective and decrease the risk of AD or slow its progression. The aim of this review is to discuss the role of redox metals Fe and Cu and non-redox metal zinc (Zn) in oxidative stress-related etiology of AD and PD. Attention is focused on the metal-induced formation of free radicals and the protective role of antioxidants [glutathione (GSH), vitamin C (ascorbic acid)], vitamin E (α-Tocopherol), lipoic acid, flavonoids [catechins, epigallocatechin gallate (EGCG)], and curcumin. An alternate hypothesis topic in AD is also discussed.

Metals, oxidative stress and neurodegenerative disorders

Green tea and its polyphenolic catechins: medicinal uses in cancer and noncancer applications.

The flavonoids are plant polyphenols found frequently in fruits, vegetables, and grains. Divided into several subclasses, they include the anthocyanidins, pigments chiefly responsible for the red and blue colors in fruits, fruit juices, wines, and flowers; the catechins, concentrated in tea; the flavanones and flavanone glycosides, found in citrus and honey; and the flavones, flavonols, and flavonol glycosides, found in tea, fruits, vegetables, and honey. Known for their hydrogen-donating antioxidant activity as well as their ability to complex divalent transition metal cations, flavonoids are propitious to human health. Computer-controlled high-performance liquid chromatography (HPLC) has become the analytical method of choice. Many systems have been developed for the detection and quantification of flavonoids across one, two, or three subclasses. A summary of the various HPLC and sample preparation methods that have been employed to quantify individual flavonoids within a subclass or across several subclasses are tabulated in this review.

Measurement of food flavonoids by high-performance liquid chromatography: A review.

The Effects of pH on antioxidative activities of catechol, pyrogallol, and four catechins, and effects of metal ions (Al3+,Ca2+,Cd2+,Co2+,Cr3+,Cu2+,Fe2+,Fe3+,K3,Mg2+,Mn2+,Na+, and Zn2+) on antioxidative activities of (−)-epigallocatechin gallate (EGCG) were studied by an oxygen electrode method. The antioxidative activities of catechins were high and constant at pH 6-12, but decreased in acidic and strong alkaline solutions. Copper(II) ion the most strongly increased the antioxidative activity of EGCG among these metal ions examined, but iron(II) ion largely inhibited the antioxidative activity of EGCG. These effects are discussed considering the formation of metal complexes with catechins and the change in oxidation potentials.

Effects of pH and Metal Ions on Antioxidative Activities of Catechins

The structure of acetonitrile−water mixtures has been investigated by X-ray diffraction with an imaging plate detector and IR spectroscopy over a wide range of acetonitrile mole fractions (0.0 ≤ XAN ≤ 1.0). Reichardt ETN and Sone-Fukuda DII,I values were also measured for the mixtures. It has been found from the X-ray data that in pure acetonitrile an acetonitrile molecule interacts with two nearest neighbors by antiparallel dipole−dipole interaction together with a small shift of the two molecular centers and that two acetonitrile molecules in the second-neighbor shell interact with a central molecule through parallel dipole−dipole interaction. Thus, acetonitrile molecules are alternately aligned to form a zigzag cluster. On addition of water into pure acetonitrile, water molecules interact with acetonitrile molecules through a dipole−dipole interaction in an antiparallel orientation. The IR spectra of O−D and C⋮N stretching vibrations, observed for mixtures of acetonitrile AN and water containing 20% D2...

Liquid Structure of Acetonitrile−Water Mixtures by X-ray Diffraction and Infrared Spectroscopy

Fourteen water-miscible polar solvents were investigated for the separation from their aqueous solutions by salting-out using sodium chloride (4mol dm-3). The following solvents showed the phase separation: acetone, acetonitrile, 1, 4- dioxane, tetrahydrofuran, 1-propanol, and 2-propanol. The chemical properties of the separated organic solvents were determined by measuring ET(30)(=1.196×105/λ (kJmol 1)) and DII.I(=1.196×105(λII-1-λI-1)(kJ mol-1))values from the spectral change of 2, 6-Biphenyl-4-(2, 4, 6-triphenylpyridinio)phenolate (DTP) and bis(1, 3-propanediolato)vanadium(IV) (VO(acac)2), where λ, λI, and λII denote the absorption maximum wavelengths (nm) of DTP and VO(acac)2. Solvent properties of acetone, acetonitrile, 1, 4-dioxane, and tetrahydrofuran were dramatically altered by the salting- out. Acceptability of the phase-separated solvents increased due to the dissolution of water molecules having large acceptor numbers. The ion-pair complex of tris(1, 10-phenanthroline)iron(II) chloride was easily extracted into the phase-separated acetonitrile by the salting-out. Some metal chelates of 1-(2-pyridylazo)-2-naphthol (Hpan) and 8- quinolinol (Hox), 5, 10, 15, 20-tetraphenylporphyrin (H2tpp), and ionic species (H2ox+, ox-, and H4tpp2+) were also extracted into 1, 4-dioxane. The raised donor and acceptor abilities of the phase-separated solvents allowed application to solvent extraction.

Chemical Properties of Water-Miscible Solvents Separated by Salting-out and Their Application to Solvent Extraction

Equilibrium study of ion-pair extraction of a cationic water-soluble porphyrin [5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin, H2tmpyp4+] and its metalloporphyrins (MP) into the acetonitrile layer, separated by addition of sodium chloride (4.00 mol dm-3) to a 1:1 (v/v) acetonitrile−water mixed solvent, was carried out to develop a new and useful method for the determination of a subnanogram amount of copper(II). M denotes Zn2+, Cu2+, Co3+, Fe3+, and Mn3+, and P2- is porphyrinate ion. The extraction and dissociation constants of the ion-pair complexes, defined by Kex = [MP(ClO4)4]org[MP4+]aq-1[ClO4-]aq-4, Kdis,1 = [MP(ClO4)3+]org[ClO4-]org[MP(ClO4)4]org-1, and Kdis,2 = [MP(ClO4)22+]org[ClO4-]org[MP(ClO4)3+]org-1, were determined by taking into account the partition constant of sodium perchlorate (KD = 1.82 ± 0.01). The equilibrium constants were found to be KexKdis,1 = (7.2 ± 1.3) × 104, (6.4 ± 0.9) × 104, (1.35 ± 0.13) × 105, (4.8 ± 0.6) × 103, (1.23 ± 0.05) × 104, and (1.42 ± 0.07) × 103 at 25 °C...

Ion-Pair Extraction of Metalloporphyrins into Acetonitrile for Determination of Copper(II).

Phase separation of acetonitrile−water mixtures by addition of NaCl has been studied on the molecular level by large-angle X-ray scattering (LAXS) and small-angle neutron scattering (SANS) methods. A phase diagram of acetonitrile−water−NaCl mixtures at 298 K has shown that phase separation occurs over a wide range of acetonitrile mole fraction (xAN) of ∼0.1 < xAN ≤ ∼0.7, where the microheterogeneity of the mixtures occurs. The radial distribution functions obtained by the LAXS measurements have revealed that before phase separation the amounts of preferentially hydrated Na+ and Cl- gradually increase with increasing NaCl concentration and that the number of linear hydrogen bonds among water molecules increases when the concentration of NaCl increases. After phase separation of the acetonitrile−water−NaCl mixtures the structures of the acetonitrile-rich phase are very similar to those of the acetonitrile−water binary mixtures at the corresponding acetonitrile mole fractions. The water-rich phase which cont...

Midori Kumamoto

Papers

Effects of pH and Metal Ions on Antioxidative Activities of Catechins

Liquid Structure of Acetonitrile−Water Mixtures by X-ray Diffraction and Infrared Spectroscopy

Chemical Properties of Water-Miscible Solvents Separated by Salting-out and Their Application to Solvent Extraction

Ion-Pair Extraction of Metalloporphyrins into Acetonitrile for Determination of Copper(II).

Large-Angle X-ray Scattering and Small-Angle Neutron Scattering Study on Phase Separation of Acetonitrile−Water Mixtures by Addition of NaCl