Studies on protective mechanisms of four components of green tea polyphenols against lipid peroxidation in synaptosomes

Mechanisms of action of green tea catechins, with a focus on ischemia-induced neurodegeneration

Catechins are dietary polyphenolic compounds associated with a wide variety of beneficial health effects in vitro, in vivo and clinically. These therapeutic properties have long been attributed to the catechins' antioxidant and free radical scavenging effects. Emerging evidence has shown that catechins and their metabolites have many additional mechanisms of action by affecting numerous sites, potentiating endogenous antioxidants and eliciting dual actions during oxidative stress, ischemia and inflammation. Catechins have proven to modulate apoptosis at various points in the sequence, including altering expression of anti- and proapoptotic genes. Their anti-inflammatory effects are activated through a variety of different mechanisms, including modulation of nitric oxide synthase isoforms. Catechins' actions of attenuating oxidative stress and the inflammatory response may, in part, account for their confirmed neuroprotective capabilities following cerebral ischemia. The versatility of the mechanisms of action of catechins increases their therapeutic potential as interventions for numerous clinical disorders. However, more epidemiological and clinical studies need to be undertaken for their efficacy to be fully elucidated.

Green tea polyphenol epigallocatechin-3-gallate differentially modulates oxidative stress in PC12 cell compartments

Tea polyphenols have been reported to be potent antioxidants and beneficial in oxidative stress related diseases. Prooxidant effects of tea polyphenols have also been reported in cell culture systems. In the present study, we have studied oxidative stress in the subcellular compartments of PC12 cells after treatment with different concentrations of the green tea polyphenol, epigallocatechin-3-gallate (EGCG). We have demonstrated that EGCG has differentially affected the production of reactive oxygen species (ROS), glutathione (GSH) metabolism and cytochrome P450 2E1 activity in the different subcellular compartments in PC12 cells. Our results have shown that although the cell survival was not inhibited by EGCG, there was, however, an increased DNA breakdown and activation of apoptotic markers, caspase 3 and poly- (ADP-ribose) polymerase (PARP) at higher concentrations of EGCG treatment. Our results suggest that the differential effects of EGCG might be related to the alterations in oxidative stress, GSH pools and CYP2E1 activity in different cellular compartments. These results may have implications in determining the chemopreventive therapeutic use of tea polyphenols in vivo.

Green tea polyphenols and dietary fibre protect against kidney damage in rats with diabetic nephropathy

In this study we examined the effect of green tea polyphenols (GTP) and partially hydrolysed guar gum (PHGG) as dietary fibre on diabetic nephropathy, using rats that had been subjected to subtotal nephrectomy and injection of streptozotocin. The subtotally nephrectomized rats were subjected to resection of three-quarters of the kidney. Rats with diabetic nephropathy were divided into four groups: untreated controls, and animals that received GTP (100 mg kg-1 body weight day-1), PHGG (100 mg kg-1 body weight day-1) and GTP plus PHGG (50 mg kg-1 body weight day-1 plus 50 mg kg-1 body weight day-1). After 50 days of administration, attenuation of urinary protein excretion and the morphological changes peculiar to diabetic nephropathy were observed in all three treated groups. Furthermore, the group treated with GTP plus PHGG showed an improvement of kidney weight and serum levels of urea nitrogen, creatinine and creatinine clearance. Hyperglycaemia, as assessed in terms of blood glucose and glycosylated protein levels, was also improved by administration of GTP plus PHGG. On the other hand, GTP administration increased the activity of superoxide dismutase in the kidney to a significant extent. A significant reduction in the total cholesterol concentration was also observed in the PHGG-treated group. These results suggest that GTP and PHGG could be beneficial as additional therapy in the management of diabetic nephropathy.

Green tea supplementation in rats of different ages mitigates ethanol-induced changes in brain antioxidant abilities

Oxidative stress induced by chronic ethanol consumption, particularly in aging subjects, has been implicated in the pathophysiology of many neurodegenerative diseases. Antioxidants with polyphenol structures, such as those contained in green tea, given alone for 5 weeks in liquid Lieber de Carli diet followed by administration with ethanol for 4 weeks with ethanol have been investigated as potential therapeutic antioxidant agents in the brain in rats of three ages (2, 12, and 24 months). Ethanol consumption caused age-dependent decreases in brain superoxide dismutase, glutathione peroxidase, glutathione reductase, and catalase activities. In addition, ethanol consumption caused age-dependent decreases in the levels of GSH, selenium, vitamins, E, A and C, and beta-carotene and increases in the levels of oxidized glutathione (GSSG). Changes in the brain's antioxidative ability were accompanied by enhanced oxidative modification of lipids (increases in lipid hydroperoxides, malondialdehyde, and 4-hydroxynonenal levels) and proteins (increases in carbonyl groups and bistyrosine). Reduced risk of oxidative stress and protection of the central nervous system, particularly in young and adult rats, after green tea supplementation were observed. Green tea partially prevented changes in antioxidant enzymatic as well as nonenzymatic parameters induced by ethanol and enhanced by aging. Administration of green tea significantly protects lipids and proteins against oxidative modifications in the brain tissue of young and adult rats. The beneficial effect of green tea can result from the inhibition of free radical chain reactions generated during ethanol-induced oxidative stress and/or from green tea-induced increases in antioxidative abilities made possible by increases in the activity/concentration of endogenous antioxidants.

Antioxidant properties of two gallotannins isolated from the leaves of Pistacia weinmannifolia

Pistacia weinmannifolia J. Poisson ex Franch (Anacardiaceae) is a shrub or arbor widely found in Yunnan province of China and its leaves are used as traditional Chinese medicine by herbalists. The leaves of P. weinmannifolia are rich in phenolic compounds, among which two novel gallotannins, Pistafolin A and Pistafolin B, are identified. In the present investigation, the antioxidant efficiency of Pistafolin A and Pistafolin B in preventing lipid, protein and DNA from reactive oxygen species-mediated damage was studied. Both Pistafolin A and Pistafolin B inhibited the peroxyl-radical induced lipid peroxidation of l-alpha-phosphatidylcholine liposomes dose-dependently and prevented the bovine serum albumin from peroxyl-induced oxidative damage. Pistafolin A and Pistafolin B also inhibited copper (II)-1,10-phenanthroline complex-induced DNA oxidative damage. Both Pistafolin A and Pistafolin B scavenged the hydrophilic 2,2'-azinobis(3-ethylbenzothiozoline-6-sulphonic acid) diammonium salt-free radicals and the hydrophobic 1,1-dipheny-2-picrylhydrazyl radicals effectively, suggesting they may act as hydrogen donating antioxidants. The protective effects of the two gallotannins against oxidative damage of biomacromolecules were due to their strong free radical scavenging ability. Pistafolin A with three galloyl moieties showed stronger antioxidant ability than Pistafolin B with two galloyl moieties.

Protective effect of green tea on erythrocyte membrane of different age rats intoxicated with ethanol

It is known that aging is characterized by changes in cell metabolism resulting in modification of the structure and function of cell membrane components which is mainly the consequence of reactive oxygen species action. These disturbances are also enhanced by different xenobiotics, e.g. ethanol. Therefore, the aim of this paper is to examine green tea influence on total antioxidant status (TAS) and on composition and electric charge of erythrocyte membrane phospholipids in ethanol intoxicated rats of various ages. Antioxidant abilities of erythrocytes were estimated by measuring TAS. Qualitative and quantitative composition of phospholipids in the membrane was determined by HPLC, while the extent of erythrocytes lipid peroxidation was estimated by HPLC measurement of malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) levels. Electrophoresis was used to determine the surface charge density of the rat erythrocyte membrane. It was shown that the process of aging was accompanied by a decrease in TAS and in the total amount of phospholipids as well as by enhancement of lipid peroxidation and increase in surface charge density of erythrocyte membrane. Ethanol administration caused, in term, decrease in TAS and increase in the level of all phospholipids and lipid peroxidation products. Ethanol as well significantly enhanced changes in surface charge density of erythrocyte membrane. The ingestion of green tea partially prevented decrease in erythrocyte antioxidant abilities observed during aging and ethanol intoxication. Moreover, long-term drinking of green tea protects the structure of the erythrocytes membrane disturbed during aging process and/or chronic ethanol intoxication.

Protective effect of green tea polyphenols on the SH-SY5Y cells against 6-OHDA induced apoptosis through ROS-NO pathway

Green tea polyphenols (GTP) are thought to help prevent oxidative stress-related diseases, such as cancer, cardiovascular disease, neurodegenerative disease, and aging. We here investigate the protective mechanisms of GTP on SH-SY5Y cells against apoptosis induced by the pro-parkinsonian neurotoxin 6-hydroxydopamine (6-OHDA). GTP rescued the changes in condensed nuclear and apoptotic bodies, attenuated 6-OHDA-induced early apoptosis, prevented the decrease in mitochondrial membrane potential, and suppressed accumulation of reactive oxygen species (ROS) and of intracellular free Ca(2+). GTP also counteracted the 6-OHDA-induced nitric oxide increase and overexpression of nNOS and iNOS, and decreased the level of protein-bound 3-nitrotyrosine (3-NT). In addition, GTP inhibited the autooxidation of 6-OHDA and scavenged oxygen free radicals in a dose- and time-dependent manner. Our results show that the protective effects of GTP on SH-SY5Y cells are mediated, at least in part, by controlling the ROS-NO pathway.

Mechanism of neuroprotective action of the anti-Parkinson drug rasagiline and its derivatives

The mitochondria are directly involved in cell survival and death. Drugs that protect mitochondria viability and prevent apoptotic cascade mechanisms involved in mitochondrial permeability transition pore (MPTp) will be cytoprotective. Rasagiline (N-propargyl-1R-aminoindan) is a novel, highly potent irreversible monoamine oxidase (MAO) B inhibitor, anti-Parkinson drug. Unlike selegiline, rasagiline is not derived from amphetamine, is not metabolized to neurotoxic l-methamphetamine derivative, nor does it have sympathomimetic activity. Rasagiline is effective as monotherapy or adjunct to L-dopa for patients with early and late Parkinson's disease (PD), and adverse events do not occur with greater frequency in subjects receiving rasagiline than those on placebo. Controlled studies indicate that it might have a disease-modifying effect in PD that may be related to neuroprotection. Its S-isomer, TVP1022, is a relatively inactive MAO inhibitor. However, both drugs have similar neuroprotective activities in neuronal cell cultures in response to various neurotoxins and in vivo (global ischemia, neurotrauma, head injury, anoxia, etc.), indicating that MAO inhibition is not a pre-requisite for neuroprotection. Structure activity studies have shown that the neuroprotective activity is associated with the propargyl moiety of rasagiline which protects mitochondrial viability and MPTp by activating Bcl-2 and protein kinase C (PKC), and down regulating pro-apoptotic FAS and Bax. Rasagiline and its derivatives also process amyloid precursor protein (APP) to the neuroprotective-neurotrophic soluble APP alpha (sAPPalpha) by PKC and MAP kinase-dependent activation of alpha-secretase. The neuroprotective activity of propargylamine has led us to develop novel bifunctional neuroprotective iron-chelating MAO-inhibiting drugs possessing propargyl moiety for the treatment of other neurodegenerative diseases.

Multifunctional Activities of Green Tea Catechins in Neuroprotection

Many lines of evidence suggest that oxidative stress resulting in reactive oxygen species (ROS) generation and inflammation play a pivotal role in the age-associated cognitive decline and neuronal loss in neurodegenerative diseases including Alzheimer's (AD), Parkinson's (PD) and Huntington's diseases. One cardinal chemical pathology observed in these disorders is the accumulation of iron at sites where the neurons die. The buildup of an iron gradient in conjunction with ROS (superoxide, hydroxyl radical and nitric oxide) are thought to constitute a major trigger in neuronal toxicity and demise in all these diseases. Thus, promising future treatment of neurodegenerative diseases and aging depends on availability of effective brain permeable, iron-chelatable/radical scavenger neuroprotective drugs that would prevent the progression of neurodegeneration. Tea flavonoids (catechins) have been reported to possess potent iron-chelating, radical-scavenging and anti-inflammatory activities and to protect neuronal death in a wide array of cellular and animal models of neurological diseases. Recent studies have indicated that in addition to the known antioxidant activity of catechins, other mechanisms such as modulation of signal transduction pathways, cell survival/death genes and mitochondrial function, contribute significantly to the induction of cell viability. This review will focus on the multifunctional properties of green tea and its major component (-)-epigallocatechin-3-gallate (EGCG) and their ability to induce neuroprotection and neurorescue in vitro and in vivo. In particular, their transitional metal (iron and copper) chelating property and inhibition of oxidative stress.

The antioxidant effect of tannic acid on the in vitro copper-mediated formation of free radicals

Tannic acid (TA) has well-described antimutagenic and antioxidant activities. The antioxidant activity of TA has been previously attributed to its capacity to form a complex with iron ions, interfering with the Fenton reaction [Biochim. Biophys. Acta 1472, 1999, 142]. In this work, we observed that TA inhibits, in the micromolar range, in vitro Cu(II) plus ascorbate-mediated hydroxyl radical (*OH) formation (determined as 2-deoxyribose degradation) and oxygen uptake, as well as copper-mediated ascorbate oxidation and ascorbate radical formation (quantified in EPR studies). The effect of TA against 2-deoxyribose degradation was three orders of magnitude higher than classic *OH scavengers, but was similar to several other metal chelators. Moreover, the inhibitory effectiveness of TA, by the four techniques used herein, was inversely proportional to the Cu(II) concentration in the media. These results and the observation of copper-induced changes in the UV spectra of TA are indications that the antioxidant activity of TA relates to its copper chelating ability. Thus, copper ions complexed to TA are less capable of inducing ascorbate oxidation, inhibiting the sequence of reactions that lead to 2-deoxyribose degradation. On the other hand, the efficiency of TA against 2-deoxyribose degradation declined considerably with increasing concentrations of the *OH detector molecule, 2-deoxyribose, suggesting that the copper-TA complex also possesses an *OH trapping activity.

Effect of green tea decoction on long-term iron, zinc and selenium status of rats

AIMS

The objective was to examine the effect of green tea decoction given at two different concentrations on the long-term (6 weeks) iron, zinc and selenium status of rats.

METHODS

During the experimental period, the rats were given ad libitum a basic diet + ultra pure water (control group), a basic diet + green tea decoction prepared from 50 g/l (tea 50 group), or a basic diet + green tea decoction prepared from 100 g/l (tea 100 group). The zinc and iron status was evaluated by determining their concentrations in the serum, blood precipitate, liver, spleen, femur, heart and kidney. Selenium status was evaluated by the serum selenium concentration and whole blood glutathione peroxidase activity.

RESULTS

Green tea decoction significantly reduced serum iron by 26% in the tea groups (p < 0.01). The blood precipitate of iron was significantly decreased by 25 and 41% in the tea 50 and tea 100 groups (p < 0.01), respectively. The reserve of iron stored in the liver, spleen and femur was significantly reduced in the tea 100 group by 32% (p < 0.02), 20% (p < 0.04) and 35% (p < 0.005), respectively. Moreover, the two concentrations of green tea significantly decreased the reserve of iron stored in the kidney (p < 0.005) and heart (p < 0.02). In contrast with its effects on iron status, green tea decoction significantly increased the serum zinc in the tea 100 group by 24% (p < 0.001). It also increased the blood precipitate of zinc by 50 (p < 0.01) and 75% (p < 0.0001) in tea 50 and tea 100 groups, respectively. In the kidney, heart and femur, zinc significantly increased in the tea groups dependent on the tea dose. Similarly, the high concentration of green tea decoction significantly increased the serum selenium concentration by 16% (p < 0.004). In addition, both concentrations of green tea decoction significantly increased the whole blood glutathione peroxidase activity by 102 and 130% (p < 0.01).

CONCLUSION

Green tea decoction reduced the iron status and improved the zinc and selenium status of rats. These effects may constitute another beneficial effect of the green tea decoction which could play an important role in the antioxidant processes.

The role of antioxidants in models of inflammation: Emphasis on l-arginine and arachidonic acid metabolism

Inflammatory processes are made up of a multitude of complex cascades. Under physiological conditions these processes aid in tissue repair. However, under pathophysiological environments, such as wound healing and hypoxia-ischaemia (HI), inflammatory mediators become imbalanced, resulting in tissue destruction. This review addresses the changes in reactive oxygen species (ROS), L-arginine and arachidonic acid metabolism in wound healing and HI and subsequent treatments with promising anti-oxidants. Even though these models may appear divergent, anti-oxidant treatments are nevertheless still having favourable effects. On the basis of recent findings, it is apparent that protection with anti-oxidants is not solely attributed to scavenging of ROS. In addition, the actions of anti-oxidants must be considered in light of the inflammatory process being assessed. To this end, there does not appear to be any universally applicable single mechanism to explain the actions of anti-oxidants.

Evidence for alpha-tocopherol regeneration reaction of green tea polyphenols in SDS micelles

The synergistic antioxidant mechanism of alpha-tocopherol (vitamin E) with green tea polyphenols, i.e., (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin gallate (EGCG), and gallic acid (GA), was studied by assaying the kinetics of the reaction of alpha-tocopheroxyl radical with green tea polyphenols by stopped-flow electron paramagnetic resonance, the inhibition of linoleic acid peroxidation by these antioxidants, and the decay of alpha-tocopherol during the peroxidation. It was found that the green tea polyphenols could reduce alpha-tocopheroxyl radical to regenerate alpha-tocopherol with rate constants of 0.45, 1.11, 1.31, 1.91, and 0.43 x 10(2) M(-1) s(-1) for EC, EGC, ECG, EGCG, and GA, respectively, in sodium dodecyl sulfate micelles. In addition, these second-order rate constants exhibited a good linear correlation with their oxidation potentials, suggesting that electron transfer might play a role in the reaction.

Neuroprotective effects of (-)-epigallocatechin gallate following hypoxia-ischemia-induced brain damage: novel mechanisms of action

(-)-Epigallocatechin gallate (EGCG) is a potent antioxidant that is neuroprotective against ischemia-induced brain damage. However, the neuroprotective effects and possible mechanisms of action of EGCG after hypoxia-ischemia (HI) have not been investigated. Therefore, we used a modified "Levine" model of HI to determine the effects of EGCG. Wistar rats were treated with either 0.9% saline or 50 mg/kg EGCG daily for 1 day and 1 h before HI induction and for a further 2 days post-HI. At 26-days-old, both groups underwent permanent left common carotid artery occlusion and exposure to 8% oxygen/92% nitrogen atmosphere for 1 h. Histological assessment showed that EGCG significantly reduced infarct volume (38.0+/-16.4 mm(3)) in comparison to HI + saline (99.6+/-15.6 mm(3)). In addition, EGCG significantly reduced total (622.6+/-85.8 pmol L-[(3)H]citrulline/30 min/mg protein) and inducible nitric oxide synthase (iNOS) activity (143.2+/-77.3 pmol L-[(3)H]citrulline/30 min/mg protein) in comparison to HI+saline controls (996.6+/-113.6 and 329.7+/-59.6 pmol L-[(3)H]citrulline/30 min/mg protein for total NOS and iNOS activity, respectively). Western blot analysis demonstrated that iNOS protein expression was also reduced. In contrast, EGCG significantly increased endothelial and neuronal NOS protein expression compared with HI controls. EGCG also significantly preserved mitochondrial energetics (complex I-V) and citrate synthase activity. This study demonstrates that the neuroprotective effects of EGCG are, in part, due to modulation of NOS isoforms and preservation of mitochondrial complex activity and integrity. We therefore conclude that the in vivo neuroprotective effects of EGCG are not exclusively due to its antioxidant effects but involve more complex signal transduction mechanisms.

Protective effect of epigallocatechin gallate on brain damage after transient middle cerebral artery occlusion in rats

Epigallocatechin gallate (EGCG), a major constituent of green tea, is a potent free radical scavenger. The purpose of this study was to verify whether EGCG reduces focal ischemia/reperfusion-induced brain injury in a rat model. Male Sprague-Dawley rats were anesthetized with chloral hydrate (400 mg/kg, i.p.) and subjected to a middle cerebral artery 2 h occlusion and then a 24-h reperfusion. The EGCG (25 mg and 50 mg/kg, i.p.) or vehicle was administered immediately after reperfusion. Twenty-four hours after reperfusion, infarction size, levels of oxidative stress markers (malondialdehyde and oxidized/total glutathione ratio) in the brain and neurological deficits were evaluated. The dose of 50 mg/kg of EGCG significantly reduced the infarction volume (9.9+/-3.2%) as compared to those (45.6+/-5.3%, 34.5+/-7.8%) of the control group and the EGCG 25 mg/kg treated group (p<0.01). The dose of 50 mg/kg of EGCG significantly reduced the neurological deficit total score (5.2+/-1.7) as compared to those (9.5+/-1.2, 8.5+/-2.5) of the control group and the EGCG 25 mg/kg treated group (p<0.05). The dose of 50 mg/kg of EGCG significantly attenuated the level of malondialdehyde and the level of oxidized/total glutathione ratio (281+/-66 nmol/g and 0.48+/-0.03) as compared to the those (415+/-46 nmol/g and 0.64+/-0.05, 381+/-51 nmol/g and 0.61+/-0.06) of the control group and the EGCG 25 mg/kg treated group (p<0.05). These results demonstrate the anti-oxidant effects of EGCG (50 mg/kg) in a rat model of transient focal ischemia, which is a likely explanation for EGCG's neuroprotective effects.

Phosphatidylinositol-3 kinase/Akt and GSK-3 mediated cytoprotective effect of epigallocatechin gallate on oxidative stress-injured neuronal-differentiated N18D3 cells

Epigallocatechin gallate (EGCG) is one of most famous compounds of green tea. EGCG suppresses apoptosis induced by oxidative radical stress through several mechanisms. This study was designed to investigate whether EGCG plays a cytoprotective role by activating phosphatidylinositol-3 kinase (PI3K)/Akt-dependent anti-apoptotic pathway and inhibiting glycogen synthase kinase-3 (GSK-3) activity in oxidative stressed N18D3 neural cells. N18D3 cells, mouse neuroblastoma X dorsal root ganglion hybrid cell line, were pre-treated with EGCG or z-VAD-fmk, non-selective caspase inhibitor used as a control substance, for 2 h. The N18D3 cells were then exposed to low concentration of H(2)O(2) (100 microM) for 30 min, and further incubated for 24 h. MTT (3,[4,5-dimethylthiazol]-2-yl) assay and trypan blue staining were used to identify cell viability. Immunoreactivity (IR) of PI3K, Akt, and GSK-3 beta were measured by Western blotting. MTT assay and trypan blue staining showed that EGCG and z-VAD-fmk significantly increased cell viability, and IR of PI3K, phospho-Akt and phospho-GSK-3 beta was significantly increased in the cells treated with EGCG, but not in z-VAD-fmk treated. These results imply that EGCG has neuroprotective effect by increasing PI3K/Akt-dependent anti-apoptotic signals.

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Neurological mechanisms of green tea polyphenols in Alzheimer's and Parkinson's diseases

Tea consumption is varying its status from a mere ancient beverage and a lifestyle habit, to a nutrient endowed with possible prospective neurobiological-pharmacological actions beneficial to human health. Accumulating evidence suggest that oxidative stress resulting in reactive oxygen species generation and inflammation play a pivotal role in neurodegenerative diseases, supporting the implementation of radical scavengers, transition metal (e.g., iron and copper) chelators, and nonvitamin natural antioxidant polyphenols in the clinic. These observations are in line with the current view that polyphenolic dietary supplementation may have an impact on cognitive deficits in individuals of advanced age. As a consequence, green tea polyphenols are now being considered as therapeutic agents in well controlled epidemiological studies, aimed to alter brain aging processes and to serve as possible neuroprotective agents in progressive neurodegenerative disorders such as Parkinson's and Alzheimer's diseases. In particular, literature on the putative novel neuroprotective mechanism of the major green tea polyphenol, (-)-epigallocatechin-3-gallate, are examined and discussed in this review.

Green tea polyphenols prevent toxin-induced hepatotoxicity in mice by down-regulating inducible nitric oxide-derived prooxidants

BACKGROUND

Recently, considerable attention has been focused on dietary and medicinal phytochemicals that inhibit, reverse, or retard diseases caused by oxidative and inflammatory processes. Green tea polyphenols have both antioxidant and antiinflammatory properties.

OBJECTIVE

We examined the effects of green tea polyphenols in carbon tetrachloride-treated mice, a model of liver injury in which oxidant stress and cytokine production are intimately linked. We tested the effect of a pure form of epigallocatechin gallate (EGCG), the major polyphenol in green tea, in mice treated with carbon tetrachloride.

DESIGN

Eight-week-old ICR mice were administered 20 microL/CCl(4) kg dissolved in olive oil. Two different doses of EGCG, 50 and 75 mg/kg, were tested. Control mice were treated with saline and olive oil. We analyzed liver histopathology, lipid peroxidation, and messenger RNA and protein concentrations of inducible nitric oxide synthase. Additionally, nitric oxide-generated radicals were assessed by electron paramagnetic resonance spectroscopy, and protein concentrations were measured by immunohistochemistry and Western blot analysis.

RESULTS

Carbon tetrachloride administration caused an intense degree of liver necrosis associated with increases in lipid peroxidation, inducible nitric oxide synthase messenger RNA and protein, nitrotyrosine, and nitric oxide radicals. EGCG administration led to a dose-dependent decrease in all of the histologic and biochemical variables of liver injury observed in the carbon tetrachloride-treated mice.

CONCLUSIONS

Green tea polyphenols reduce the severity of liver injury in association with lower concentrations of lipid peroxidation and proinflammatory nitric oxide-generated mediators. Green tea polyphenols can be a useful supplement in the treatment of liver disease and should be considered for liver conditions in which proinflammatory and oxidant stress responses are dominant.

A gallic acid derivative and polysaccharides with antioxidative activity from rose (Rosa rugosa) flowers

In this study, the major antioxidant components of rose flower were identified. An aqueous extract of rose flowers was chromatographed on CM-cellulose in ammonium acetate buffer (10 mM, pH 4.5) to yield three un-adsorbed peaks F1, F2 and F3. Each of these peaks was subjected to gel filtration on Sephadex G75. F1 yielded two peaks, whereas both F2 and F3 gave rise to only a single peak. Spectroscopic studies using NMR and FTIR revealed that F3 is a gallic acid derivative. It exhibited the highest antioxidative potency. F1-a derived from F1 by gel filtration is mainly a polysaccharide-peptide complex with less potent antioxidative activity. F2 is a polysaccharide also with reduced antioxidant activity. This study demonstrates, for the first time, the presence of both gallic acid derivatives and polysaccharides as major antioxidant principles of the aqueous extract of rose flowers.

Strictinin as an efficient antioxidant in lipid peroxidation

The antioxidant effect of strictinin (SOH), which was extracted from green tea leaves, against the peroxidation of linoleic acid in sodium dodecyl sulfate (SDS) and cetyl trimethylammonium (CTAB) micelles, against the peroxidation of low-density lipoprotein (LDL) and against oxidative hemolysis of human red blood cells (RBCs), has been studied. The peroxidation of linoleic acid and LDL, and oxidative hemolysis of RBCs were initiated thermally by a water-soluble azo initiator 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH), and the reaction kinetics in micelles and LDL were monitored by uptake of oxygen. The synergistic antioxidant effect of SOH with alpha-tocopherol (Vitamin E) was also studied by following the decay kinetics of alpha-tocopherol. Kinetic analysis of the antioxidation process demonstrates that SOH, used either alone or in combination with alpha-tocopherol, is an effective antioxidant against lipid peroxidation, but its effects significantly depend on the reaction medium.

(-)-EPIGALLOCATECHIN GALLATE ATTENUATES GLUTAMATE-INDUCED CYTOTOXICITY VIA INTRACELLULAR CA2+ MODULATION IN PC12 CELLS

1. The effects of (-)-epigallocatechin gallate (EGCG), a green tea polyphenol, on glutamate-induced increases in intracellular Ca2+ concentrations ([Ca2+]i) and cytotoxicity in PC12 cells were investigated. 2. Changes in [Ca2+]i were measured using Fura-2/AM calcium indicator dye and cellular viabilities were determined by a viable cell count and a 3-(4,4-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay. 3. Glutamate increased [Ca2+]i in PC12 cells in a dose-dependent manner. (-)-Epigallocatechin gallate attenuated this glutamate (30 mmol/L)-induced [Ca2+]i increase and EGCG (50 micromol/L) increased the viability of PC12 cells against glutamate-induced cytotoxicity. The EGCG effect was also found to be independent of its general anti-oxidant mechanism. In contrast, EGCG directly suppressed both N-methyl-D-aspartate (50 mmol/L)- and kainate (20 mmol/L)-mediated Ca2+ influx, but not metabotropic receptor-mediated Ca2+ release. 4. These results suggest that EGCG reduces the glutamate-induced [Ca2+]i increase by attenuating ionotropic Ca2+ influx and that this promotes the viability of PC12 cells.

Catechin polyphenols: neurodegeneration and neuroprotection in neurodegenerative diseases

Neurodegeneration in Parkinson's, Alzheimer's, and other neurodegenerative diseases seems to be multifactorial, in that a complex set of toxic reactions including inflammation, glutamatergic neurotoxicity, increases in iron and nitric oxide, depletion of endogenous antioxidants, reduced expression of trophic factors, dysfunction of the ubiquitin-proteasome system, and expression of proapoptotic proteins leads to the demise of neurons. Thus, the fundamental objective in neurodegeneration and neuroprotection research is to determine which of these factors constitutes the primary event, the sequence in which these events occur, and whether they act in concurrence in the pathogenic process. This has led to the current notion that drugs directed against a single target will be ineffective and rather a single drug or cocktail of drugs with pluripharmacological properties may be more suitable. Green tea catechin polyphenols, formerly thought to be simple radical scavengers, are now considered to invoke a spectrum of cellular mechanisms of action related to their neuroprotective activity. These include pharmacological activities like iron chelation, scavenging of radicals, activation of survival genes and cell signaling pathways, and regulation of mitochondrial function and possibly of the ubiquitin-proteasome system. As a consequence these compounds are receiving significant attention as therapeutic cytoprotective agents for the treatment of neurodegenerative and other diseases.

Antioxidant properties and protective effects of a standardized extract of Hypericum perforatum on hydrogen peroxide-induced oxidative damage in PC12 cells

Free radical scavenging and antioxidant activities of a standardized extract of Hypericum perforatum (SHP) were examined for inhibition of lipid peroxidation, for hydroxyl radical scavenging activity and interaction with 1,1-diphenyl-2-picrylhydrazyl stable free radical (DPPH). Concentrations between 1 and 50 microg/ml of SHP effectively inhibited lipid peroxidation of rat brain cortex mitochondria induced by Fe2+/ascorbate or NADPH system. The results showed that SHP scavenged DPPH radical in a dose-dependent manner and also presented inhibitory effects on the activity of xanthine oxidase. In contrast, hydroxyl radical scavenging occurs at high doses. The protective effect of the standardized extract against H2O2-induced oxidative damage on the pheochromocytoma cell line PC 12 was investigated by measuring cell viability via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), lactate dehydrogenase (LDH) assays, caspase-3-enzyme activity and accumulation of reactive oxygen species [2',7'-dichlorofluorescin (DCF) assay]. Following 8-h cell exposure to H2O2 (300 microM), a marked reduction in cell survival was observed, which was significantly prevented by SHP (pre-incubated for 24 h) at 1-100 microg/ml. In a separate experiment, different concentrations of the standardized extract (0.1-100 microg/ml) also attenuated the increase in caspase-3 activity and suppressed the H2O2 -induced reactive oxygen species generation. Taken together, these results suggest that SHP shows relevant antioxidant activity both in vitro and in a cell system, by means of inhibiting free radical generation and lipid peroxidation.

Polyphenols from Camellia sinenesis prevent primary graft failure after transplantation of ethanol-induced fatty livers from rats

Fatty liver caused by ethanol decreases survival after liver transplantation in rats. This study investigated if antioxidant polyphenols from Camellia sinenesis (green tea) prevent failure of fatty grafts from ethanol-treated rats. Donor rats were given ethanol intragastrically (6 g/kg). After 20 h, livers were explanted and stored in University of Wisconsin solution for 24 h. Prior to implantation, the explanted grafts were rinsed with lactated Ringer's solution containing 0 to 60 microg/ml polyphenols. Alanine aminotransferase (ALT) release after liver transplantation was 4.5-fold higher in recipients receiving ethanol-induced fatty grafts than in those receiving normal grafts. Liver grafts from ethanol-treated donors also developed severe focal necrosis. Graft survival was 11% in the ethanol group versus 88% for normal grafts. Polyphenol treatment at 60 microg/ml blunted ALT release by 66%, decreased necrotic areas by 84%, and increased survival to 75%. Ethanol increased alpha-(4-pyridyl-1-oxide)-N-tert.-butylnitrone free radical adducts in bile by 2.5-fold, as measured by electron spin resonance spectroscopy, and caused accumulation of 4-hydroxynonenal in liver sections, effects blunted by polyphenols. Epicatechin gallate, a major polyphenol from C. sinenesis, also decreased enzyme release, minimized pathological changes, and decreased free radical adduct formation. In conclusion, polyphenols scavenged free radicals in ethanol-induced fatty livers and decreased injury after liver transplantation.

Cell signaling pathways in the neuroprotective actions of the green tea polyphenol (-)-epigallocatechin-3-gallate: implications for neurodegenerative diseases

Accumulating evidence supports the hypothesis that brain iron misregulation and oxidative stress (OS), resulting in reactive oxygen species (ROS) generation from H2O2 and inflammatory processes, trigger a cascade of events leading to apoptotic/necrotic cell death in neurodegenerative disorders, such as Parkinson's (PD), Alzheimer's (AD) and Huntington's diseases, and amyotrophic lateral sclerosis (ALS). Thus, novel therapeutic approaches aimed at neutralization of OS-induced neurotoxicity, support the application of ROS scavengers, transition metals (e.g. iron and copper) chelators and non-vitamin natural antioxidant polyphenols, in monotherapy, or as part of antioxidant cocktail formulation for these diseases. Both experimental and epidemiological evidence demonstrate that flavonoid polyphenols, particularly from green tea and blueberries, improve age-related cognitive decline and are neuroprotective in models of PD, AD and cerebral ischemia/reperfusion injuries. However, recent studies indicate that the radical scavenger property of green tea polyphenols is unlikely to be the sole explanation for their neuroprotective capacity and in fact, a wide spectrum of cellular signaling events may well account for their biological actions. In this article, the currently established mechanisms involved in the beneficial health action and emerging studies concerning the putative novel molecular neuroprotective activity of green tea and its major polyphenol (-)-epigallocatechin-3-gallate (EGCG), will be reviewed and discussed.

Green tea protection against age-dependent ethanol-induced oxidative stress

Ethanol intoxication leads to oxidative stress, which may be additionally enhanced by aging. The aim of this study was to investigate the influence of green tea as a source of water-soluble antioxidants on the ability to prevent oxidative stress in aged rats sub-chronically intoxicated with ethanol. Two-, 12-, and 24-mo-old male Wistar rats were divided into 4 experimental groups: (1) control, (2) green tea, (3) ethanol, and (4) ethanol and green tea. Ethanol intoxication produced age-dependent decrease in the activity of serum superoxide dismutase, glutathione peroxidase, and reductase and in levels of glutathione (GSH), vitamins C, E, and A, and beta-carotene. Changes in the serum antioxidative ability were accompanied by enhanced oxidative modification of lipid (increase in lipid hydroperoxides, malondiadehyde, and 4-hydroxynonenal levels) and protein (rise in carbonyl group levels). Green tea partially protected against changes in antioxidant enzymatic as well as nonenzymatic parameters produced by ethanol and enhanced by aging. Administration of green tea significantly protects cellular components such as lipids and proteins against oxidative modification. Results indicate that green tea effectively protects blood serum against oxidative stress produced by ethanol as well as aging.

Epigallocatechin gallate protects nerve growth factor differentiated PC12 cells from oxidative-radical-stress-induced apoptosis through its effect on phosphoinositide 3-kinase/Akt and glycogen synthase kinase-3

The effects of epigallocatechin gallate (EGCG) on the phosphoinositide 3-kinase (PI3K)/Akt and glycogen synthase kinase-3 (GSK-3) pathway during oxidative-stress-induced injury were studied using H2O2-treated PC12 cells, which were differentiated by nerve growth factor (NGF). Following 100 microM H2O2 exposure, the viability of differentiated PC12 cells (EGCG or z-VAD-fmk pretreated vs. not pretreated) was evaluated the number of viable cell with Trypan blue and 3,4,5-dimethylthiazol-2-yl (MTT). Additionally, expression of cytochrome c, caspase-3, poly(ADP-ribose) polymerase (PARP), PI3K/Akt and GSK-3 was examined using Western blot analyses. EGCG or z-VAD-fmk-pretreated PC12 cells showed an increase of viability compared to untreated PC12 cells, and pretreatment of PC12 cells with either agent induced a dose-dependent inhibition of caspase-3 activation and PARP cleavage. However, inhibition of cytochrome c release was only detected in EGCG-pretreated cells. Upon examination of the PI3K/Akt and GSK-3 upstream pathway, Western blots of EGCG pretreated cells showed decreased immunoreactivity (IR) of Akt and GSK-3 and increased IR of p85a PI3K, phosphorylated Akt and phosphorylated GSK-3. In contrast, no changes were seen in z-VAD-fmk-pretreated cells. These results show that EGCG affects the PI3K/Akt, GSK-3 pathway as well as downstream signaling, including the cytochrome c and caspase-3 pathways. Therefore, it is suggested that EGCG-mediated activation of PI3K/Akt and inhibition of GSK-3 could be a new potential therapeutic strategy for neurodegenerative diseases associated with oxidative injury.

Green tea polyphenol (−)-epigallocatechin gallate attenuates the neuronal NADPH-d/nNOS expression in the nodose ganglion of acute hypoxic rats

Recent studies have shown that (-)-epigallocatechin gallate (EGCG), one of the green tea polyphenols, has a potent antioxidant property. Nitric oxide (NO) plays an important role in the neuropathogenesis induced by brain ischemia/reperfusion and hypoxia. This study aimed to explore the potential neuroprotective effect of EGCG on the ganglionic neurons of the nodose ganglion (NG) in acute hypoxic rats. Thus, the young adult rats were pretreated with EGCG (10, 25, or 50 mg/kg, i.p.) 30 min before they were exposed to the altitude chamber at 10,000 m with the partial pressure of oxygen set at the level of 0.27 atm (pO2=43 Torr) for 4 h. All the animals examined were allowed to survive for 3, 7, and 14 successive days, respectively, except for those animals sacrificed immediately following hypoxic exposure. Nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry and neuronal nitric oxide synthase (nNOS) immunohistochemistry were carried out to detect the neuronal NADPH-d/nNOS expression in the NG. The present results show a significant increase in the expression of NADPH-d/nNOS reactivity in neurons of the NG at various time intervals following hypoxia. However, the hypoxia-induced increase in NADPH-d/nNOS expression was significantly depressed only in the hypoxic rats treated with high dosages of EGCG (25 or 50 mg/kg). These data suggest that EGCG may attenuate the oxidative stress following acute hypoxia.

Green tea polyphenol epigallocatechin-3-gallate protects HepG2 cells against CYP2E1-dependent toxicity

Chronic ethanol consumption causes oxidative damage in the liver, and induction of cytochrome P450 2E1 (CYP2E1) is one pathway involved in oxidative stress produced by ethanol. The hepatic accumulation of iron and polyunsaturated fatty acids significantly contributes to ethanol hepatotoxicity in the intragastric infusion model of ethanol treatment. The objective of this study was to analyze the effect of the green tea flavanol epigallocatechin-3-gallate (EGCG), which has been shown to prevent alcohol-induced liver damage, on CYP2E1-mediated toxicity in HepG2 cells overexpressing CYP2E1 (E47 cells). Treatment of E47 cells with arachidonic acid plus iron (AA + Fe) was previously reported to produce synergistic toxicity in E47 cells by a mechanism dependent on CYP2E1 activity and involving oxidative stress and lipid peroxidation. EGCG protected E47 cells against toxicity and loss of viability induced by AA+Fe; EGCG had no effect on CYP2E1 activity. Prevention of this toxicity was associated with a reduction in oxidative damage as reflected by decreased generation of reactive oxygen species, a decrease in lipid peroxidation, and maintenance of intracellular glutathione in cells challenged by AA+Fe in the presence of EGCG. AA+Fe treatment caused a decline in the mitochondrial membrane potential, which was also blocked by EGCG. In conclusion, EGCG exerts a protective action on CYP2E1-dependent oxidative stress and toxicity that may contribute to preventing alcohol-induced liver injury, and may be useful in preventing toxicity by various hepatotoxins activated by CYP2E1 to reactive intermediates.

Potential therapeutic properties of green tea polyphenols in Parkinson's disease

Tea is one of the most frequently consumed beverages in the world. It is rich in polyphenols, a group of compounds that exhibit numerous biochemical activities. Green tea is not fermented and contains more catechins than black tea or oolong tea. Although clinical evidence is still limited, the circumstantial data from several recent studies suggest that green tea polyphenols may promote health and reduce disease occurrence, and possibly protect against Parkinson's disease and other neurodegenerative diseases. Green tea polyphenols have demonstrated neuroprotectant activity in cell cultures and animal models, such as the prevention of neurotoxin-induced cell injury. The biological properties of green tea polyphenols reported in the literature include antioxidant actions, free radical scavenging, iron-chelating properties, (3)H-dopamine and (3)H-methyl-4-phenylpyridine uptake inhibition, catechol-O-methyltransferase activity reduction, protein kinase C or extracellular signal-regulated kinases signal pathway activation, and cell survival/cell cycle gene modulation. All of these biological effects may benefit patients with Parkinson's disease. Despite numerous studies in recent years, the understanding of the biological activities and health benefits of green tea polyphenols is still very limited. Further in-depth studies are needed to investigate the safety and efficacy of green tea in humans and to determine the different mechanisms of green tea in neuroprotection.

Protective effect of green tea polyphenol EGCG against neuronal damage and brain edema after unilateral cerebral ischemia in gerbils

Previous studies have demonstrated that a green tea polyphenol, (-)-epigallocatechine gallate (EGCG), has a potent free radical scavenging and antioxidant effect. Glutamate leads to excitotoxicity and oxidative stress, which are important pathophysiologic responses to cerebral ischemia resulting in brain edema and neuronal damage. We investigated the effect of EGCG on excitotoxic neuronal damage in a culture system and the effect on brain edema formation and lesion after unilateral cerebral ischemia in gerbils. In vitro, excitotoxicity was induced by 24-hr incubation with N-methyl-D-aspartate (NMDA; 10 microM), AMPA (10 microM), or kainate (20 microM). EGCG (5 microM) was added to the culture media alone or with excitotoxins. We examined malondialdehyde (MDA) level and neuronal viability to evaluate the effect of EGCG. In vivo, unilateral cerebral ischemia was induced by occlusion of the right common carotid artery for 30, 60, or 90 min and followed by reperfusion of 24 hr. Brain edema, MDA, and infarction were examined to evaluate the protective effect of EGCG. EGCG (25 or 50 mg/kg, intraperitoneally) was administered twice, at 30 min before and immediately after ischemia. EGCG reduced excitotoxin-induced MDA production and neuronal damage in the culture system. In the in vivo study, treatment of gerbils with the lower EGCG dose failed to show neuroprotective effects; however, the higher EGCG dose attenuated the increase in MDA level caused by cerebral ischemia. EGCG also reduced the formation of postischemic brain edema and infarct volume. These results demonstrate EGCG may have future possibilities as a neuroprotective agent against excitotoxicity-related neurologic disorders such as brain ischemia.

Green tea protects against ethanol-induced lipid peroxidation in rat organs

Ethanol metabolism is accompanied by generation of free radicals, which stimulates lipid peroxidation. Natural antioxidants are particularly useful in such a situation. The current study was designed to investigate the efficacy of green tea, as a source of water-soluble antioxidants (catechins), on lipid peroxidation in liver, brain, and blood induced by chronic (4 weeks) ethanol intoxication in rats. Feeding of ethanol led to a significant increase in lipid peroxidation, as measured by increased concentrations of lipid hydroperoxides, 4-hydroxynonenal, and malondialdehyde. Feeding of ethanol also changed the glutathione-dependent lipid hydroperoxide decomposition system, resulting in a decrease in both reduced glutathione concentration and activity of glutathione peroxidase. Observed changes were statistically significant in all examined tissues. Enhancement in lipid peroxidation was associated with disruption of hepatocyte cell membranes, as observed through electron microscopic evaluation. Green tea protects phospholipids from enhanced peroxidation and prevents changes in biochemical parameters and morphologic changes observed after ethanol consumption. These results support the suggestion that green tea protects membranes from peroxidation of lipids associated with ethanol consumption.

Effects of Oolong Tea on Plasma Antioxidative Capacity in Mice Loaded with Restraint Stress Assessed Using the Oxygen Radical Absorbance Capacity (ORAC) Assay

In the present study, we investigated the antioxidative effect of oolong tea in vitro and in vivo using the oxygen radical absorbance capacity (ORAC) assay. An oolong tea extract, catechin and related compounds suppressed the oxidation of fluorescence induced by AAPH in a dose-dependent manner, that is, they prolonged the antioxidant time in vitro. Oral administration of the oolong tea extract to mice treated with restraint stress increased ORAC activity in plasma as compared with a stress control group. The extract also increased plasma vitamin C levels, and there was a good relationship between ORAC activity and the vitamin C level in plasma. The elevation of plasma ORAC and vitamin C level may have been related to the stress-relieving effect of oolong tea. These effects are probably due to the antioxidative properties of the tea. Thus, these findings suggested that oolong tea has beneficial effects on health related to its antioxidative action.

Neuroprotective strategies in Parkinson's disease : an update on progress

In spite of the extensive studies performed on postmortem substantia nigra from Parkinson's disease patients, the aetiology of the disease has not yet been established. Nevertheless, these studies have demonstrated that, at the time of death, a cascade of events had been initiated that may contribute to the demise of the melanin-containing nigro-striatal dopamine neurons. These events include increased levels of iron and monoamine oxidase (MAO)-B activity, oxidative stress, inflammatory processes, glutamatergic excitotoxicity, nitric oxide synthesis, abnormal protein folding and aggregation, reduced expression of trophic factors, depletion of endogenous antioxidants such as reduced glutathione, and altered calcium homeostasis. To a large extent, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 6-hydroxydopamine (6-OHDA) animal models of Parkinson's disease confirm these findings. Furthermore, neuroprotection can be afforded in these models with iron chelators, radical scavenger antioxidants, MAO-B inhibitors, glutamate antagonists, nitric oxide synthase inhibitors, calcium channel antagonists and trophic factors. Despite the success obtained with animal models, clinical neuroprotection is much more difficult to accomplish. Although the negative studies obtained with the MAO-B inhibitor selegiline (deprenyl) and the antioxidant tocopherol (vitamin E) may have resulted from an inappropriate choice of drug (selegiline) or an inadequate dose (tocopherol), the niggling problem that still remains is why these drugs, and others, do work in animals while they fail in the clinic. One reason for this may be related to the fact that in normal human brains the number of dopaminergic neurons falls by around 3-5% every decade, while in Parkinson's disease this decline is greater. Brain autopsy studies have shown that by the time the disease is identified, some 70-75% of the dopamine-containing neurons have been lost. More sensitive reliable methods and clinical correlative markers are required to discern between confoundable symptomatic effects versus a possible neuroprotective action of drugs, namely, the ability to delay or forestall disease progression by protecting or rescuing the remaining dopamine neurons or even restoring those that have been lost.A number of other possibilities for the clinical failure of potential neuroprotectants also exist. First, the animal models of Parkinson's disease may not be totally reflective of the disease and, therefore, the chemical pathologies established in the animal models may not cause, or contribute to, the progression of the disease clinically. Second, because of the series of events occurring in neurodegeneration and our ignorance about which of these factors constitutes the primary event in the pathogenic process, a single drug may not be adequate to induce neuroprotection and, as a consequence, use of a cocktail of drugs may be more appropriate. The latter concept receives support from recent complementary DNA (cDNA) microarray gene expression studies, which show the existence of a gene cascade of events occurring in the nigrostriatal pathway of MPTP, 6-OHDA and methamphetamine animal models of Parkinson's disease. Even with the advent of powerful new tools such as genomics, proteomics, brain imaging, gene replacement therapy and knockout animal models, the desired end result of neuroprotection is still beyond our current capability.

Comparative study of the antioxidant effect of ardisin and epigallocatechin gallate in rat hepatocytes exposed to benomyl and 1-nitropyrene

The objective of this study was to compare the antioxidant effect of ardisin and epigallocatechin 3-O-gallate (EGCG) in hepatocytes exposed to either benomyl or 1-nitropyrene (1-NP). Rat hepatocytes were incubated in a serum-free medium with non-cytotoxic concentrations of either ardisin (0.27 microg/ml) or EGCG (3 microg/ml), and with either benomyl (35 microg/ml) or 1-NP (0.25 microg/ml). The level of malondialdehyde (MDA) as a marker of lipid peroxidation was determined, as well as the content of glutathione (GSH) and the activities of glutathione peroxidase (GPx) and glutathione reductase (GR). In comparison to the control, the concentration of GSH improved 282% (P<0.05) and 260% (P<0.05) after the cells were pre-incubated with ardisin or EGCG and then exposed to benomyl, respectively. The activity of GPx decreased 55% with ardisin (P<0.05) and 51% with EGCG (P<0.05), and MDA decreased 7% and 23% (P<0.05) with the same treatments. The concentration of GSH also improved when the cells were incubated with either EGCG (49%, P<0.05) or ardisin (83%, P<0.05) simultaneously with 1-NP, relative to 1-NP alone. Moreover, ardisin decreased MDA formation by 65% (p<0.05), and enhanced the activity of GR by 137% (P<0.05). These results suggest that ardisin is a better suppressor of lipid peroxidation induced by benomyl and 1-NP than EGCG. It is concluded that ardisin and EGCG are potent antioxidants that can afford protection against free radical mediated diseases.

Protective effects of green tea polyphenols on human HepG2 cells against oxidative damage of fenofibrate

The aim of this work was to investigate the protective effects of green tea polyphenols on the cytotoxic effects of hypolipidemic agent fenofibrate (FF), a peroxisome proliferator (PP), in human HepG2 cells. The results showed that high concentrations of FF induced human HepG2 cell death through a mechanism involving an increase of reactive oxygen species (ROS) and intracellular reduced glutathione (GSH) depletion. These effects were partially prevented by antioxidant green tea polyphenols. The elevated expression of PP-activated receptors alpha (PPARalpha) in HepG2 cells induced by FF was also decreased by treatment with green tea polyphenols. In conclusion, this result demonstrates that oxidative stress and PPARalpha are involved in FF cytotoxicity and green tea polyphenols have a protective effect against FF-induced cellular injury. It may be beneficial for the hyperlipidemic patients who were administered the hypolipidemic drug fenofibrate to drink tea or use green tea polyphenols synchronously during their treatment.

Green tea polyphenols enhance sodium nitroprusside-induced neurotoxicity in human neuroblastoma SH-SY5Y cells

Oxidative stress is a main mediator in nitric oxide (NO) -induced neurotoxicity and has been implicated in the pathogenesis of many neurodegenerative disorders. Green tea polyphenols are usually expected as potent chemo-preventive agents due to their ability of scavenging free radicals and chelating metal ions. However, not all the actions of green tea polyphenols are necessarily beneficial. In the present study, we demonstrated that higher-concentration green tea ployphenols significantly enhanced the neurotoxicity by treatment of sodium nitroprusside (SNP), a nitric oxide donor. SNP induced apoptosis in human neuroblastoma SH-SY5Y cells in a concentration and time-dependent manner, as estimated by cell viability assessment, FACScan analysis and DNA fragmentation assay, whereas treatment with green tea polyphenols alone had no effect on cell viability. Pre-treatment with lower-dose green tea polyphenols (50 and 100 microm) had only a slightly deleterious effect in the presence of SNP, while higher-dose green tea polyphenols (200 and 500 microm) synergistically damaged the cells severely. Further research showed that co-incubation of green tea polyphenols and SNP caused loss of mitochondrial membrane potential, depletion of intracellular GSH and accumulation of reactive oxygen species, and exacerbated NO-induced neuronal apoptosis via a Bcl-2 sensitive pathway.

Effects of delayed administration of (-)-epigallocatechin gallate, a green tea polyphenol on the changes in polyamine levels and neuronal damage after transient forebrain ischemia in gerbils

(-)-Epigallocatechin gallate has a potent antioxidant property and can reduce free radical-induced lipid peroxidation as a green tea polyphenol. In previous study, systemic administration of (-)-epigallocatechin gallate immediately after ischemia has been shown to inhibit the hippocampal neuronal damage in the gerbil model of global ischemia. Polyamines are thought to be important in the generation of brain edema and neuronal cell damage associated with various types of excitatory neurotoxicity. We examined the effects of delayed administration of (-)-epigallocatechin gallate on the changes in polyamine levels and neuronal damage after transient global ischemia in gerbils. To produce transient global ischemia, both common carotid arteries were occluded for 3 min with micro-clips. The gerbils were treated with (-)-epigallocatechin gallate (50 mg/kg, i.p.) at 1 or 3 h after ischemia. The polyamines; putrescine, spermidine, and spermine levels were examined using high performance liquid chromatography in the cerebral cortex and hippocampus 24 h after ischemia. Putrescine levels in the cerebral cortex and hippocampus were increased significantly after ischemia and the delayed administrations of (-)-epigallocatechin gallate (1 or 3 h after ischemia) attenuated the increases. Only minor changes were noted in the spermidine and spermine levels after ischemia. In histology, neuronal injuries in the hippocampal CA1 regions were evaluated quantitatively 5 days after ischemia. (-)-Epigallocatechin gallate administered 1 h or 3 after ischemia significantly reduced hippocampal neuronal damage. The present results show that the delayed administrations of (-)-epigallocatechin gallate inhibit the transient global ischemia-induced increase of putrescine levels in the cerebral cortex and hippocampus. (-)-Epigallocatechin gallate is neuroprotective against neuronal damage even when administered up to 3 h after global ischemia. These findings suggest that (-)-epigallocatechin gallate may be promising in the acute treatment of stroke.

Epigallocatechin-3-gallate binding to MMP-2 inhibits gelatinolytic activity without influencing the attachment to extracellular matrix proteins but enhances MMP-2 binding to TIMP-2

Although epigallocatechin-3-gallate (EGCg), a dominant component of green tea catechins, has been demonstrated to have anti-gelatinase properties, the molecular mechanisms by which EGCg blocks gelatinolytic activities remain unknown. We investigated whether EGCg may affect matrix metalloproteinase-2 (MMP-2) binding to native and denatured-type I collagen, and binding to the tissue inhibitor of metalloproteinase-2 (TIMP-2). Here, we report that EGCg forms a reversible complex with MMP-2, resulting in the inhibition of gelatinolytic activity of MMP-2. EGCg had no effect on the MMP-2 binding to immobilized native and denatured-type I collagen, but significantly enhanced pro- and activated MMP-2 binding to TIMP-2, as assessed by immunoprecipitation. These findings provide a new understanding of the molecular mechanisms underlying the inhibitory effect of EGCg on the gelatinolytic activity of MMP-2.

Malondialdehyde production in Jurkat T cells subjected to oxidative stress

OBJECTIVE

We investigated the relation between membrane lipid peroxidation, as evaluated by malondialdehyde (MDA), and oxidative stimuli in the Jurkat T-cell line and designed a cellular model to assess the antioxidant potential of compounds.

METHODS

Jurkat T cells were subjected to different concentrations of Fe(2+) ions (from 25 to 150 micromol/L) or H(2)O(2) (from 0.1 to 5 mmol/L), and MDA was determined after separation in high-performance liquid chromatography of the adduct with thiobarbituric acid. MDA production also was investigated in cells supplemented with epigallocatechin gallate and genistein and subjected to Fe(2+) oxidative treatment.

RESULTS

MDA production increased with the concentration of Fe(2+), whereas H(2)O(2) had no effect at any concentration. Oxidative stress for 15 min or 2 h produced similar MDA levels. The supplementation of epigallocatechin gallate partly prevented MDA production (about 40%, P < 0.05), whereas genistein exerted no preventive effect on lipid peroxidation.

CONCLUSION

We propose this cellular model, consisting of Jurkat T cells subjected to 100 micromol/L of Fe(2+) for 15 min, to study the protective effect of antioxidant supplementation against membrane lipid peroxidation.

Neuroprotection and neurorescue against Abeta toxicity and PKC-dependent release of nonamyloidogenic soluble precursor protein by green tea polyphenol (-)-epigallocatechin-3-gallate

Green tea extract and its main polyphenol constituent (-)-epigallocatechin-3-gallate (EGCG) possess potent neuroprotective activity in cell culture and mice model of Parkinson's disease. The central hypothesis guiding this study is that EGCG may play an important role in amyloid precursor protein (APP) secretion and protection against toxicity induced by beta-amyloid (Abeta). The present study shows that EGCG enhances (approximately 6-fold) the release of the non-amyloidogenic soluble form of the amyloid precursor protein (sAPPalpha) into the conditioned media of human SH-SY5Y neuroblastoma and rat pheochromocytoma PC12 cells. sAPPalpha release was blocked by the hydroxamic acid-based metalloprotease inhibitor Ro31-9790, which indicated mediation via alpha-secretase activity. Inhibition of protein kinase C (PKC) with the inhibitor GF109203X, or by down-regulation of PKC, blocked the EGCG-induced sAPPalpha secretion, suggesting the involvement of PKC. Indeed, EGCG induced the phosphorylation of PKC, thus identifying a novel PKC-dependent mechanism of EGCG action by activation of the non-amyloidogenic pathway. EGCG is not only able to protect, but it can rescue PC12 cells against the beta-amyloid (Abeta) toxicity in a dose-dependent manner. In addition, administration of EGCG (2 mg/kg) to mice for 7 or 14 days significantly decreased membrane-bound holoprotein APP levels, with a concomitant increase in sAPPalpha levels in the hippocampus. Consistently, EGCG markedly increased PKCalpha and PKC in the membrane and the cytosolic fractions of mice hippocampus. Thus, EGCG has protective effects against Abeta-induced neurotoxicity and regulates secretory processing of non-amyloidogenic APP via PKC pathway.

Epicatechin-copper 9II) complexes: Damage of small intestinal epithelium

Four epicatechins [(−)-epicatechin (EC), (−)-epicatechin gallate (ECg), (−)-epigallocatechin (EGC), (−)-epigallocatechin gallate (EGCg)] and their corresponding copper complexes were compared with regard to their effect on the viability of Caco-2 colon cancer cells in vitro, measured by 3-(4,5-dimethylthyazol-2-yl) 2,5-diphenyltetrazolium bromide (MTT) assay. The viability of Caco-2 cells exposed to EC (1 mM), ECg (1 mM) or EGC (1mM) respectively, for 30 min, was comparable to that of the saline control group, while EGCg (1 mM) apparently enhanced cellular activity. in contrast, the cells treated with epicatechin-copper complexes were killed. Bivalent copper 91 mM), in similar conditions, did not affect the cells. No cell leakage or other histological differences were observed, implying a rapid cell death. The suggested mechanism of killing is by OH radical attack, produced in the presence of epicatechin-copper complexes, but not in the presence of either of the epicatechins or copper alone. The reaction sites are discussed.

Antioxidants in grasshoppers: higher levels defend the midgut tissues of a polyphagous species than a graminivorous species

Polyphagous grasshoppers consume plants that contain markedly greater amounts of potentially prooxidant allelochemicals than the grasses eaten by graminivorous grasshoppers. Therefore, levels of antioxidant defenses maintained by these herbivores might be expected to differ in accordance with host plant ranges. Antioxidant levels were compared in midgut tissues and gut fluids of a polyphagous grasshopper. Melanoplus sanguinipes, and a graminivorous grasshopper, Aulocara ellioti. Glutathione concentrations in midgut tissues of M. sanguinipes (10.6 mM) are among the highest measured in animal tissues and are twice as high as those in A. ellioti. Alpha-tocopherol levels are 126% higher in midgut tissues of M. sanguinipes than in those of A. ellioti, and remain at high levels when M. sanguinipes is reared on plants containing a wide range of alpha-tocopherol concentrations. Ascorbate levels in M. sanguinipes midgut tissues are 27% higher than in those of A. ellioti, but vary depending on the host plant on which they are reared. Midgut fluids of both species contain elevated levels of glutathione, as well as large (millimolar) amounts of undetermined antioxidants that are produced in the insects. The consumption of tannic acid decreases ascorbate concentrations in midgut tisssues and gut fluids of A. ellioti but has no effect on ascorbate levels in M. sanguinipes. The results of this study provide the first measurements of antioxidants in grasshoppers and suggest that the maintenance of high levels of antioxidants in the midgut tissues of polyphagous grasshoppers might effectively protect them from oxidative stress.

Protective effect of green tea polyphenol (-)-epigallocatechin gallate and other antioxidants on lipid peroxidation in gerbil brain homogenates

The aim of this study was to compare the protective effects of green tea polyphenol (-)-epigallocatechin gallate (EGCG) and other well-known antioxidants on the lipid peroxidation in gerbil brain homogenates. Oxidative stress was induced by H2O2 (10 mM) or ferrous ammonium sulfate (5 microM) and lipid peroxidation was studied. Hydrogen peroxide and ferrous ions are capable of oxidizing a wide range of substrates and causing biological damage. The reaction, referred to as the Fenton process, is complex and can generate both hydroxyl radicals and higher oxidation states of the iron. Thiobarbituric acid-reactive substances (TBA-RS) were used as a marker of lipid peroxidation. EGCG, trolox, lipoic acid, and melatonin reduced H2O2- or ferrous ion-induced lipid peroxidation in a concentration-dependent manner. In reducing the H2O2-induced lipid peroxidation, IC50 values of antioxidants were as follows: EGCG (0.66 microM), trolox (37.08 microM), lipoic acid (7.88 mM), and melatonin (19.11 mM). In reducing the ferrous ion-induced lipid peroxidation, IC50 values of antioxidants were as follows: EGCG (3.32 microM), trolox (75.65 microM), lipoic acid (7.63 mM), and melatonin (15.48 mM). Under the in vitro conditions of this experiment, EGCG was the most potent antioxidant in inhibiting H2O2 or ferrous ion-induced lipid peroxidation in the gerbil brain homogenates.

Protective effects of green tea polyphenols and their major component, (-)-epigallocatechin-3-gallate (EGCG), on 6-hydroxydopamine-induced apoptosis in PC12 cells

Green tea polyphenols exert a wide range of biochemical and pharmacological effects, and have been shown to possess antimutagenic and anticarcinogenic properties. Oxidative stress is involved in the pathogenesis of Parkinson's disease. However, although green tea polyphenols may be expected to inhibit the progression of Parkinson's disease on the basis of their known antioxidant activity, this has not previously been established. In the present study, we evaluated the neuroprotective effects of green tea polyphenols in the Parkinson's disease pathological cell model. The results show that the natural antioxidants have significant inhibitory effects against apoptosis induced by oxidative stress. 6-Hydroxydopamine (6-OHDA)-induced apoptosis in catecholaminergic PC12 cells was chosen as the in vitro model of Parkinson's disease in our study. Apoptotic characteristics of PC12 cells were assessed by MTT assay, flow cytometry, fluorescence microscopy and DNA fragmentation. Green tea polyphenols and their major component, EGCG at a concentration of 200 microM, exert significant protective effects against 6-OHDA-induced PC12 cell apoptosis. EGCG is more effective than the mixture of green tea polyphenols. The antioxidant function of green tea polyphenols may account for this neuroprotective effect. The present study supports the notion that green tea polyphenols have the potential to be effective as neuropreventive agents for the treatment of neurodegenerative diseases.