Chemiluminescence-high-performance liquid chromatographic determination of tea catechin, (-)-epigallocatechin 3-gallate, at picomole levels in rat and human plasma

Distinct effects of tea catechins on 6-hydroxydopamine-induced apoptosis in PC12 cells

Green tea polyphenols have aroused considerable attention in recent years for preventing oxidative stress related diseases including cancer, cardiovascular disease, and degenerative disease. Neurodegenerative diseases are cellular redox status dysfunction related diseases. The present study investigated the different effects of the five main components of green tea polyphenols on 6-hydroxydopamine (6-OHDA)-induced apoptosis in PC12 cells, the in vitro model of Parkinson's disease (PD). When the cells were treated with five catechins respectively for 30 min before exposure to 6-OHDA, (-)-epigallocatechins gallate (EGCG) and (-)-epicatechin gallate (ECG) in 50-200 microM had obvious concentration-dependent protective effects on cell viability, while (-)-epicatechin (EC), (+)-catechin ((+)-C), and (-)-epigallocatechin (EGC) had almost no protective effects. The five catechins also showed the same pattern described above of the different effects against 6-OHDA-induced cell apoptotic characteristics as analyzed by cell viability, fluorescence microscopy, flow cytometry, and DNA fragment electrophoresis methods. The present results indicated that 200 microM EGCG or ECG led to significant inhibition against typical apoptotic characteristics of PC12 cells, while other catechins had little protective effect against 6-OHDA-induced cell death. Therefore, the classified protective effects of the five catechins were in the order ECG> or = EGCG>>EC> or = (+)-C>>EGC. The antiapoptotic activities appear to be structurally related to the 3-gallate group of green tea polyphenols. The present data indicate that EGCG and ECG might be potent neuroprotective agents for PD.

Capillary electrophoretic application of 1-alkyl-3-methylimidazolium-based ionic liquids

Ionic substances with melting points at or close to room temperature are referred to as ionic liquids. Interest in ionic liquids for their potential in different chemical processes is increasing, because they are environmentally benign and are good solvents for a wide range of both organic and inorganic materials. In this study, a capillary electrophoretic method for resolving phenolic compounds found in grape seed extracts is reported. The method, in which 1-alkyl-3-methylimidazolium-based ionic liquids are used as the running electrolytes, is simple and reproducible. The separation mechanism seems to involve association between the imidazolium cations and the polyphenols. The role of the alkyl substituents on the imidazolium cations was investigated and will be discussed.

Metabolic fate of (-)-[4-(3)H]epigallocatechin gallate in rats after oral administration

After oral administration of [4-(3)H]EGCg to rats, the radioactivity in blood, major tissues, urine, and feces was measured over time. The radioactivity in blood and most tissues remained low for 4 h postdose, began to increase after 8 h, peaked at 24 h, and then decreased. Major urinary excretion of radioactivity occurred in the 8-24 h period, and the cumulative radioactivity excreted by 72 h was 32.1% of the dose. The radioactivity in the feces was 35.2% of the dose within 72 h postdose. In the case of rats pretreated with antibiotics (antibiotic-pretreated rats), the radioactivity levels of the blood and urine were definitely lower than those in rats not pretreated with antibiotics (normal rats). The radioactivity recovered in the antibiotic-pretreated rat urine was estimated to be only (1)/(100) of that in the normal rat urine. These results clearly demonstrated that the radioactivity detected in the blood and urine of normal rats mostly originated from degradation products of EGCg produced by intestinal bacteria. Furthermore, a main metabolite in the normal rats was purified and identified as 5-(5'-hydroxyphenyl)-gamma-valerolactone 3'-O-beta-glucuronide (M-2). In feces of the normal rats, EGC (40.8% of the fecal radioactivity) and 5-(3',5'-dihydroxyphenyl)-gamma-valerolactone (M-1, 16.8%) were detected. These results suggested that M-1 was absorbed in the body after degradation of EGCg by intestinal bacteria, yielding M-1 with EGC as an intermediate. Furthermore, M-2 was thought to be formed from M-1 in the intestinal mucosa and/or liver, then to enter the systemic circulation, and finally to be excreted in the urine. Taking into account all of the above findings, a possible metabolic route of EGCg orally administered to rats is proposed.

A critical assessment of some biomarker approaches linked with dietary intake

In this review many examples are given of the complexities involved in using some biomarkers in relation to assessing the effects of dietary exposure, when there is frequently a need to determine changes following long-term low level exposure to dietary components. These range from understanding why the biomarker might be valuable and how best it can be measured, to the pitfalls which can occur in the interpretation of data. Analytical technique is considered in relation to folate and selenium, and flavonoid and carotenoid species are used to illustrate how the metabolism of a compound may alter the validity or adequacy of a marker. Vitamin A is discussed in relation to the difficulties which can arise when there are several biomarkers that may be available to assess exposure to one nutrient. Vitamin B12 is discussed in relation to the dietary choices made by individuals. Possible interactions and the role of measuring total antioxidant capacity is considered in some detail. In contrast to most nutrients, there is a marked lack of biomarkers of either exposure or effect for most non-nutrients. The role of biological effect monitoring is considered for dietary contaminants, fumonisins and polyhalogenated aromatic hydrocarbons. Aflatoxins are discussed to exemplify food contaminants for which the biomarker approach has been extensively studied. Finally some compounds which are deliberately added to foods and some which appear as processing contaminants are each considered briefly in relation to the requirement for a biomarker of exposure to be developed.

Phase I trial of oral green tea extract in adult patients with solid tumors

PURPOSE

This trial was designed to determine the maximum-tolerated dose, toxicity, and pharmacology of oral green tea extract (GTE) once daily or three times daily.

PATIENTS AND METHODS

Cohorts of three or more adult cancer patients were administered oral GTE with water after meals one or three times daily for 4 weeks, to a maximum of 6 months, depending on disease response and patient tolerance. Pharmacokinetic analyses were encouraged but optional.

RESULTS

Dose levels of 0.5 to 5.05 g/m(2) qd and 1.0 to 2.2 g/m(2) tid were explored. A total of 49 patients were studied.

PATIENT CHARACTERISTICS

median age, 57 years (range, 27 to 77 years); 23 patients were women (47%); 98% had a Zubrod PS of 1%; 98% had PS of 1; and 21 had non-small-cell lung, 19 had head & neck cancer, three had mesothelioma, and six had other. Mild to moderate toxicities were seen at most dose levels and promptly reversed on discontinuation of GTE. Dose-limiting toxicities were caffeine related and included neurologic and gastrointestinal effects. The maximum-tolerated dose was 4.2 g/m(2) once daily or 1.0 g/m(2) three times daily. No major responses occurred; 10 patients with stable disease completed 6 months of GTE. Pharmacokinetic analyses found accumulation of caffeine levels that were dose dependent, whereas epigallocatechin gallate levels did not accumulate nor appear dose related.

CONCLUSION

A dose of 1.0 g/m(2) tid (equivalent to 7 to 8 Japanese cups [120 mL] of green tea three times daily) is recommended for future studies. The side effects of this preparation of GTE were caffeine related. Oral GTE at the doses studied can be taken safely for at least 6 months.

Synthesis of (-)-[4-3H]epigallocatechin gallate and its metabolic fate in rats after intravenous administration

Because a great deal of attention has been focused on the metabolism of (-)-epigallocatechin gallate (EGCg), quantitative analysis of this compound is required. For this purpose we developed a method of chemical synthesis of [4-(3)H]EGCg. Synthesized [4-(3)H]EGCg showed 99.5% radiochemical purity and a specific activity of 13 Ci/mmol. To clarify the excretion route of EGCg, the radioactivity levels of bile and urine were quantified after intravenous administration of [4-(3)H]EGCg to bile-duct-cannulated rats. Results showed that the radioactivity of the bile sample excreted within 48 h accounted for 77.0% of the dose, whereas only 2.0% of the dose was recovered in the urine. The excretion ratio of bile to urine was calculated to be about 97:3. These results clearly showed that bile was the major excretion route of EGCg. Time-course analysis of the radioactivity in blood was also performed to estimate the pharmacokinetic parameters following intravenous administration of [4-(3)H]EGCg. In addition, EGCg metabolites excreted in the bile within 4 h after the intravenous dose of [4-(3)H]EGCg were analyzed by HPLC. The results showed that 4',4"-di-O-methyl-EGCg was present in the conjugated form and made up about 14.7% of the administered radioactivity.

Tea catechins inhibit cholesterol oxidation accompanying oxidation of low density lipoprotein in vitro

Endogenous oxidized cholesterols are potent atherogenic agents. Therefore, the antioxidative effects of green tea catechins (GTC) against cholesterol oxidation were examined in an in vitro lipoprotein oxidation system. The antioxidative potency of GTC against copper catalyzed LDL oxidation was in the decreasing order (-)-epigalocatechin gallate (EGCG)=(-)-epicatechin gallate (ECG)>(-)-epicatechin (EC)=(+)-catechin (C)>(-)-epigallocatechin (EGC). Reflecting these activities, both EGCG (74%) and ECG (70%) inhibited the formation of oxidized cholesterol, as well as the decrease of linoleic and arachidonic acids, in copper catalyzed LDL oxidation. The formation of oxidized cholesterol in 2,2'-azobis(2-amidinopropane) hydrochloride (AAPH)-mediated oxidation of rat plasma was also inhibited when the rats were given diets containing 0.5% ECG or EGCG. In addition, EGCG and ECG highly inhibited oxygen consumption and formation of conjugated dienes in AAPH-mediated linoleic acid peroxidative reaction. These two species of catechin also markedly lowered the generation of hydroxyl radical and superoxide anion. Thus, GTC, especially ECG and EGCG, seem to inhibit cholesterol oxidation in LDL by combination of interference with PUFA oxidation, the reduction and scavenging of copper ion, hydroxyl radical generated from peroxidation of PUFA and superoxide anion.

Determination of catechins in human urine subsequent to tea ingestion by high-performance liquid chromatography with electrochemical detection

The title determination was conducted by HPLC with electrochemical detection using an ODS column and a mobile phase of acetonitrile: 0.1 M phosphate buffer (pH 2.5) (15:85, v/v). The eight catechins, gallocatechin (GC), epigallocatechin (EGC), catechin (C), epicatechin (EC), epigallocatechin gallate (EGCg), gallocatechin gallate (GCg), epicatechin gallate (ECg), and catechin gallate (Cg), were detected at 0.6 V vs Ag/AgCl. Good linear relationships between current and amount were noted for 0.5-250 pmol of each catechin, with a correlation coefficient of 0.999 in each case. The detection limit for any one was 0.5 pmol (signal to noise ratio, S/N = 3). After the ingestion of 340 ml canned green tea, GC, EGC, C, and EC, mostly in conjugated form, were determined in urine samples. Conjugated catechins were hydrolyzed by enzymes using sulfatase and beta-glucuronidase. The time courses of the above four catechins showed a maxima at 1-3 h after tea ingestion. (+), (-)-EC and (+), (-)-C were present in canned tea.

Flavonoids as antioxidants

Flavonoids are phenolic substances isolated from a wide range of vascular plants, with over 8000 individual compounds known. They act in plants as antioxidants, antimicrobials, photoreceptors, visual attractors, feeding repellants, and for light screening. Many studies have suggested that flavonoids exhibit biological activities, including antiallergenic, antiviral, antiinflammatory, and vasodilating actions. However, most interest has been devoted to the antioxidant activity of flavonoids, which is due to their ability to reduce free radical formation and to scavenge free radicals. The capacity of flavonoids to act as antioxidants in vitro has been the subject of several studies in the past years, and important structure-activity relationships of the antioxidant activity have been established. The antioxidant efficacy of flavonoids in vivo is less documented, presumably because of the limited knowledge on their uptake in humans. Most ingested flavonoids are extensively degraded to various phenolic acids, some of which still possess a radical-scavenging ability. Both the absorbed flavonoids and their metabolites may display an in vivo antioxidant activity, which is evidenced experimentally by the increase of the plasma antioxidant status, the sparing effect on vitamin E of erythrocyte membranes and low-density lipoproteins, and the preservation of erythrocyte membrane polyunsaturated fatty acids. This review presents the current knowledge on structural aspects and in vitro antioxidant capacity of most common flavonoids as well as in vivo antioxidant activity and effects on endogenous antioxidants.

Comparative analysis of tea catechins and theaflavins by high-performance liquid chromatography and capillary electrophoresis

This paper describes the simultaneous determination of catechins and theaflavins in green and black teas, using reversed-phase high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE). The tea polyphenols analyzed included (+)-catechin, catechin gallate, (-)-epicatechin, epicatechin-3-gallate, epigallocatechin, epigallocatechin-3-gallate, theaflavin, theaflavin-3-monogallate, theaflavin-3'-monogallate and theaflavin-3,3'-gallate. These polyphenols together with six other tea ingredients such as caffeine, adenine, theophylline, quercetin, gallic acid and caffeic acid were separated within 27 min by HPLC and in less than 10 min by CE. The optimal analytical conditions of both chromatographic methods were investigated for the convenience and reliability for routine analysis. Both HPLC and CE were found to be reliable and compatible. The reproducibility of the within-day assay using both methods was generally >90%. The day-to-day variation of retention time was <5% for HPLC, while the variation of migration time for CE was <2%. The analysis time of CE was three-times faster, however it is five-times less sensitive than HPLC, which has detection limits of 0.05 microg/ml and 0.5 microg/ml for catechins and theaflavins, respectively.

Analysis of tea components by high-performance liquid chromatography and high-performance capillary electrophoresis

Tea is one of the most popular beverages in the world. The number of reports on the analysis of tea components, especially for catechins, has recently been increasing. We review the recent reports on the analysis of tea components using the analytical methods of high-performance liquid chromatography and high-performance capillary electrophoresis.

An improved method for the determination of green and black tea polyphenols in biomatrices by high-performance liquid chromatography with coulometric array detection

Tea polyphenols are strong antioxidants and are believed to have beneficial health effects. However, the blood and tissue levels of these compounds are not well characterized because of a lack of suitable analytical methods for the biological resolution of these compounds. Previously, we developed methods for the analysis of three green tea catechins. Now we report an improved method for the measurement of the levels of the different catechins and theaflavins in biological fluids and tissues. The method includes digestion of the plasma, urine, or tissue samples with beta-d-glucuronidase and sulfatase, followed by extraction with ethyl acetate and subsequent separation by reversed-phase high-performance liquid chromatography (HPLC). The polyphenols are identified on the basis of their retention times, spectral analysis, and electrochemical behavior across an array of electrodes. In a single HPLC run, it is possible to determine the major catechins and theaflavins as well as some of the catechin metabolites. The detection limits for catechins and theaflavins are from 5 to 10 ng/ml of saliva, plasma, or urine.

Green tea polyphenols induce apoptosis in vitro in peripheral blood T lymphocytes of adult T-cell leukemia patients

Green tea polyphenols (TEA) are known to exhibit antioxidative activity as well as tumor-suppressing activity. In order to examine the tumor-suppressing activity of TEA against adult T-cell leukemia (ATL), we cultivated peripheral blood T lymphocytes of ATL patients (ATL PBLs), an HTLV-I-infected T-cell line (KODV) and healthy controls (normal PBLs) for 3 days in the presence of TEA and its main constituent, epigallocatechin-3-gallate (EGCg), to measure cell proliferation and apoptosis, and to quantitate mRNAs of HTLV-I pX and beta-actin genes of the cultured cells. Growth of ATL PBLs was significantly inhibited by 9-27 microg/ml of TEA and EGCg, in contrast to minimal growth inhibition of T cells of normal PBLs. Inhibition of KODV was intermediate between ATL PBLs and normal PBLs. The ATL PBLs and KODV treated with 27 microg/ml of either TEA or EGCg induced apoptotic DNA fragmentation, producing terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL)-positive cells, while the normal PBLs treated with the same concentration of TEA or EGCg produced a negligibly small number of TUNEL-positive cells, in which apoptotic DNA fragmentation was not detectable. Expression of HTLV-I pX mRNA was suppressed more than 90% in ATL PBLs by treatment with 3-27 microg/ml of either TEA or EGCg, while expression of beta-actin mRNA was much less suppressed by treatment with the same concentration of TEA or EGCg. These results indicate that TEA and EGCg inhibit growth of ATL PBLs, as well as HTLV-I-infected T-cells, by suppressing HTLV-I pX gene expression and inducing apoptotic cell death.

Absorption, metabolism and antioxidative effects of tea catechin in humans

Green tea is consumed as a popular beverage in Japan and throughout the world. During the past decade, epidemiological studies have shown that tea catechin intake is associated with lower risk of cardiovascular disease. In vitro biochemical studies have reported that catechins, particularly epigallocatechin-3-gallate (EGCg), help to prevent oxidation of plasma low-density lipoprotein (LDL). LDL oxidation has been recognized to be an important step in the formation of atherosclerotic plaques and subsequent cardiovascular disease. Metabolic studies have shown that EGCg supplement is incorporated into human plasma at a maximum concentration of 4400 pmol/mL. Such concentrations would be enough to exert antioxidative activity in the blood stream. The potent antioxidant property of tea catechin may be beneficial in preventing the oxidation of LDL. It is of interest to examine the effect of green tea catechin supplementation on antioxidant capacity of plasma in humans by measuring plasma phosphatidylcholine hydroperoxide (PCOOH) as a marker of oxidized lipoproteins.

Characterization of methylation site of monomethylflavan-3-ols by liquid chromatography/electrospray ionization tandem mass spectrometry

Liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) was used for the structural characterization and differentiation of four isomeric O-monomethylated catechins (on phenolic positions) by the analysis of the fragmentation behaviour of catechin. The catechin fragmentation routes were rationalized and it is shown that several diagnostic ions such as (1,3)A(+), (1,2)B(+), and (1,4)B(+) allow the unambiguous identification of the methylated ring. The precise position of the methyl group on each ring is determined by the difference in the relative intensities of the diagnostic ions. Isomeric O-methylepicatechins were also differentiated using this methodology.

Tea catechin supplementation increases antioxidant capacity and prevents phospholipid hydroperoxidation in plasma of humans

The effect of green tea catechin supplementation on antioxidant capacity of human plasma was investigated. Eighteen healthy male volunteers who orally ingested green tea extract (254 mg of total catechins/subject) showed 267 pmol of epigallocatechin-3-gallate (EGCg) per milliliter of plasma at 60 min after administration. The plasma phosphatidylcholine hydroperoxide (PCOOH) levels attenuated from 73.7 pmol/mL in the control to 44.6 pmol/mL in catechin-treated subjects, being correlated inversely with the increase in plasma EGCg level. The results suggested that drinking green tea contributes to prevent cardiovascular disease by increasing plasma antioxidant capacity in humans.

Analysis of (+)-catechin, (-)-epicatechin and their 3'- and 4'-O-methylated analogs. A comparison of sensitive methods

(+)-Catechin and (-)-epicatechin are found in many foods and may have important effects on human health. These compounds, like many other catechols, are thought to be converted to methylated metabolites after ingestion. This paper describes the synthesis of the 3'- and 4'-methyl ethers and their unambiguous identification. These products, along with catechin, epicatechin and an internal standard, (+)-taxifolin, were separated using RP-HPLC with ultraviolet, electrochemical and fluorescence detection. The trimethylsilylated derivatives of the seven compounds were also separated by GC with mass spectrometric detection. The limits of detection and selectivity of the analytical methods were compared with respect to their application in complex matrices such as human plasma.

Direct intestinal absorption of red fruit anthocyanins, cyanidin-3-glucoside and cyanidin-3,5-diglucoside, into rats and humans

We determined red fruit anthocyanins, cyanidin-3-glucoside (Cy-g) and cyanidin-3,5-diglucoside (Cy-dg), incorporated into plasma and liver of rats and human plasma by UV-HPLC. Fifteen minutes after an oral supplementation of a mixture of 320 mg of Cy-g and 40 mg of Cy-dg/kg of body weight, rats showed an increase to a maximum of 1563 microg (3490 nmol) of Cy-g/L and 195 microg (320 nmol) of Cy-dg/L in plasma and 0.067 microg (0.15 nmol) of Cy-g/g and a trace of Cy-dg together with methylated metabolites such as peonidin-3-glucoside in liver. In human plasma, 30 min after intake (2.7 mg of Cy-g and 0.25 mg of Cy-dg/kg of body weight), an average of 11 microg (24 nmol) of Cy-g/L and a trace of Cy-dg were found. Cyanidin as aglycone of Cy-g and Cy-dg was not found in such plasma samples, neither were conjugated and methylated anthocyanins. The results indicated that anthocyanins are incorporated keeping structurally intact glycoside forms, from the digestive tract into the blood circulation system in mammals.

Flavonoids in foods as in vitro and in vivo antioxidants

The polyphenol antioxidants in foods and beverages are shown to be powerful in vitro antioxidants. The polyphenols in foods and beverages enrich low density lipoproteins and decrease their oxidizability ex vivo after spiking and in vivo after absorption of the polyphenols following ingestion of beverages. These studies provide mechanisms to explain the epidemiological study which shows that consumption of fruits, vegetables and beverages reduce the risk of cardiovascular and cerebrovascular disease.