epigallocatechin-3-O-gallate Research Articles

Comparison of (−)-Epigallocatechin-3-<i>O</i>-gallate (EGCG) and <i>O</i>-Methyl EGCG Bioavailability in Rats

(-)-Epigallocatechin-3-O-(3-O-methyl)gallate (EGCG3″Me) and (-)-epigallocatechin-3-O-(4-O-methyl)gallate (EGCG4″Me) are O-methyl derivatives of (-)-epigallocatechin-3-O-gallate (EGCG) present in tea cultivars such as Benifuuki. Although O-methyl EGCGs have various bioactivities, their bioavailabilities have not been determined. In this study, we compared the bioavailability of EGCG and O-methyl EGCGs in rats, and clarified the pharmacokinetics of O-methyl EGCGs. Following oral administration (100 mg/kg), the areas under the concentration-time curves (AUCs) for EGCG, EGCG3″Me, and EGCG4″Me were 39.6 ± 14.2 µg·h/L, 317.2 ± 43.7 µg·h/L, and 51.9 ± 11.0 µg·h/L, respectively. The AUC after intravenous administration (10 mg/kg) was 2772 ± 480 µg·h/L for EGCG, 8209 ± 549 µg·h/L for EGCG3″Me, and 2465 ± 262 µg·h/L for EGCG4″Me. The bioavailability of EGCG3″Me (0.38%) was the highest (EGCG: 0.14% and EGCG4″Me: 0.21%). The distribution volume of EGCG3″Me (0.26 ± 0.02 L/kg) was the lowest (EGCG: 0.94 ± 0.16 L/kg and EGCG4″Me: 0.93 ± 0.14 L/kg). These results suggested that the higher AUC of EGCG3″Me after oral administration was related to its high bioavailability and low distribution volume. These findings supported the stronger bioactivity of EGCG3″Me in vivo.

Hydroxylation of (−)-epigallocatechin-3-O-gallate at 3′′, but not 4′′, is essential for the PI3-kinase/Akt-dependent phosphorylation of endothelial NO synthase in endothelial cells and relaxation of coronary artery rings

(-)-Epigallocatechin-3-O-gallate (EGCg) has been shown to induce endothelium-dependent nitric oxide (NO)-mediated relaxation via the redox-sensitive Src/PI3-kinase/Akt-dependent phosphorylation of endothelial NO synthase (eNOS). Although the presence of 8 hydroxyl functions, mainly on B and D rings, is essential for the EGCg-induced activation of eNOS, the relative role of each individual hydroxyl function still remains unclear. This study examined the effect of selective replacement of hydroxyl functions by methoxy moieties on either the B or D ring on the EGCg-induced phosphorylation of Akt and eNOS, formation of reactive oxygen species (ROS) and NO in cultured coronary artery endothelial cells, and endothelium-dependent relaxation of coronary artery rings. Replacement of a single hydroxyl by the methoxy group on position 3', 4' or 4'' affected little the EGCg-induced phosphorylation of Akt and eNOS, formation of ROS and NO in endothelial cells, and induction of endothelium-dependent relaxations. In contrast, the single methylation at position 3'' and the double methylation at both positions 3' and 4' reduced markedly the phosphorylation of Akt and eNOS, the formation of ROS and NO in endothelial cells and the relaxation of artery rings. These findings suggest that the hydroxyl group at the 3'' position of the gallate ring is essential and, also, to some extent, the two hydroxyl groups at positions 3' and 4', for the EGCg-induced redox-sensitive activation of eNOS leading to the subsequent NO-mediated vascular relaxation.

Flavanocoumarins from Guazuma ulmifolia bark and evaluation of their affinity for STAT1

From the bark of Guazuma ulmifolia, a plant used as anti-inflammatory remedy, the flavanocoumarin epiphyllocoumarin (1) along with epiphyllocoumarin-[4β→8]-(-)-epicatechin (2) and epiphyllocoumarin-[4β→8]-(-)-epicatechin-[4β→8]-(-)-epicatechin (3), never reported before, have been isolated. The structures of the proantocyanidins 2-3 have been elucidated by extensive NMR and ESI-MS analysis. On the basis of the flavane nature of the isolated compounds and considering the strong anti-STAT1 activity reported for epigallocatechin 3-O-gallate (EGCG), the affinity of compounds 1-3 for STAT1 has been evaluated by Surface Plasmon Resonance. Compounds 1-2 showed affinity for STAT1 comparable to that exerted by EGCG. In order to confirm this result, molecular docking studies to evaluate the interactions of compounds 1-3, phyllocoumarin (4), the reference compound EGCG (5), and its related compound (+)-gallocatechin 3-O-gallate (6) with STAT1 have been carried out. Furthermore the ability of compounds 1-3 to inhibit STAT1 activation has been evaluated using a nuclear extract obtained from the human monocytic leukemia cell line TPH-1. Flavanocoumarins 1-2 inhibited STAT1-DNA binding.

Transepithelial Transport of Theasinensins through Caco-2 Cell Monolayers and Their Absorption in Sprague–Dawley Rats after Oral Administration

The aim of this study is to illustrate the in vivo and in vitro absorption of theasinensins B and A that are (-)-epigallocatechin-3-O-gallate (EGCG)-(-)-epigallocatechin (EGC) dimer and EGCG dimer, respectively, and their transport pathway across the intestinal membrane. Our animal study by a single oral administration to rats demonstrated the intact absorption of theasinensins into the blood system, which was estimated to be a >10-fold lower absorption amount than EGCG. The in vitro absorption study indicated that theasinensins can be transported across Caco-2 cell monolayers, while their permeability coefficients were also >10-fold lower than those of EGCG and EGC. Transport experiments using cytochalasin D or quercetin as a tight junction (TJ) modulator and a non-saturable permeation revealed that theasinensins were transported across Caco-2 cells in a TJ paracellular diffusion route. In conclusion, the dimers of condensed catechins, theasinensins B and A, can be absorbed intact into rat blood and transported across Caco-2 cell monolayers probably through a TJ paracellular pathway.

Oxygen partial pressure modulates 67-kDa laminin receptor expression, leading to altered activity of the green tea polyphenol, EGCG

(−)-Epigallocatechin-3-O-gallate (EGCG) exhibits anti-tumor activity mediated via the 67-kDa laminin receptor (67LR). In this study, we found that 67LR protein levels are reduced by exposure to low O2 levels (5%), without affecting the expression of HIF-1α. We also found that EGCG-induced anti-cancer activity is abrogated under low O2 levels (5%) in various cancer cells. Notably, treatment with the proteasome inhibitor, prevented down-regulation of 67LR and restored sensitivity to EGCG under 5% O2. In summary, 67LR expression is highly sensitive to O2 partial pressure, and the activity of EGCG can be regulated in cancer cells by O2 partial pressure.

Therapeutic effects of epigallocatechin gallate on streptozotocin-induced diabetic nephropathy in mice.

Diabetic nephropathy is one of the most serious complications in diabetes mellitus and has been the most common cause of end-stage renal disease. Green tea extracts have antioxidant properties, and (-)-epigallocatechin 3-O-gallate (EGCG) is known to be the most abundant in green tea. Osteopontin (OPN) is a large phosphoglycoprotein adhesion molecule, and has emerged as a potentially key pathophysiologic contributor in diabetic nephropathy. We examined whether EGCG could amelliorate the development of diabetic nephropathy and its role of OPN. The mice ( n =28) were divided into 3 groups. Control group ( n =7) was intraperitoneal (IP) injected 0.9% saline, Streptozotocin (STZ) group ( n =7) was IP injected STZ 200 mg/Kg and induced diabetic nephropathy. After a 8weeks, EGCG groups ( n =7/each group) were received EGCG 50 mg/kg and 100 mg/kg body weight by subcutaneous injection. Serum glucose, blood urea nitrogen, serum creatinine, urine volume and urine protein amounts were measured. Western blot assay of OPN was compared for the different groups. Histopathologic examination and immunohistochemical staining of mice kidney were performed. Compared with control group, STZ-group showed an increase in blood glucose, blood urea nitrogen, creatinine levels and urine protein amounts, and a decrease in body weight. All the above parameters were significantly reversed with EGCG treatment. After STZ injection, there were an diabetic glomerulosclerosis with increased renal OPN accumulation and its protein expression in the kidney cortex. EGCG-treated mice kidney showed a reduced expression of above parameters and an reserved pathologic findings. These results suggest that EGCG ameliorates STZ-induced diabetic nephropathy by OPN suppression. The potential use of EGCG in the treatment of diabetic nephropathy should be further explored.

Effect Of Antioxidant To Progression Of Diabetic Nephropathy In Diabetic Rat

Reactive oxygen species play critical roles in the development and progression of diabetic nephropathy (DN). To evaluate the effect of antioxidant therapy on renal damage, we investigated the effect of green tea catechin on oxidative stress-induced renal cell damage in LLC-PK cells and DN induced by subtotal nephrectomy plus streptozotocin injection in rats, Antioxidant activities of 6 green tea catechins were evaluated by 1,1-diphenyl-2- picrylhydrazyl (DPPH) radical scavenging activity test. Protective effect of (-)-epigallocatechin 3-O-gallate (EGCG) as a representative tea catechin against oxidative renal cell damage was measured in LLC-PK cells. EGCG showed the strongest DPPH radical scavenging activity and protected renal epithelial LLC-PK cells from oxidative damage in the dose-dependent manner. Hyperglycemia, proteinuria and the elevated lipid peroxidation levels were reduced by EGCG administration. The renal protein expressions related to diabetic nephropathy such as iNOS, COX-2, NF-κB, phosphorylated IκB-α, TGF-β1 and fibronectin were significantly decreased after EGCG treatment. In conclusion, EGCG has beneficial effects on DN by suppressing hyperglycemia and related oxidative stress in kidney.

A chain reaction approach to modelling gene pathways.

A chain reaction approach to modelling gene pathways.

Green Tea Polyphenol EGCG Sensing Motif on the 67-kDa Laminin Receptor

BackgroundWe previously identified the 67-kDa laminin receptor (67LR) as the cell-surface receptor conferring the major green tea polyphenol (–)-epigallocatechin-3-O-gallate (EGCG) responsiveness to cancer cells. However, the underlying mechanism for interaction between EGCG and 67LR remains unclear. In this study, we investigated the possible role of EGCG-67LR interaction responsible for its bioactivities.Methodology/Principal FindingsWe synthesized various peptides deduced from the extracellular domain corresponding to the 102-295 region of human 67LR encoding a 295-amino acid. The neutralizing activity of these peptides toward EGCG cell-surface binding and inhibition of cancer cell growth were assayed. Both activities were inhibited by a peptide containing the 10-amino acid residues, IPCNNKGAHS, corresponding to residues 161-170. Furthermore, mass spectrometric analysis revealed the formation of a EGCG-LR161-170 peptide complex. A study of the amino acid deletion/replacement of the peptide LR161-170 indicated that the 10-amino acid length and two basic amino acids, K166 and H169, have a critical role in neutralizing EGCG’s activities. Moreover, neutralizing activity against the anti-proliferation action of EGCG was observed in a recombinant protein of the extracellular domain of 67LR, and this effect was abrogated by a deletion of residues 161-170. These findings support that the 10 amino-acid sequence, IPCNNKGAHS, might be the functional domain responsible for the anti-cancer activity of EGCG.Conclusions/SignificanceOverall, our results highlight the nature of the EGCG-67LR interaction and provide novel structural insights into the understanding of 67LR-mediated functions of EGCG, and could aid in the development of potential anti-cancer compounds for chemopreventive or therapeutic uses that can mimic EGCG-67LR interactions.

Development of rapid and simultaneous quantitative method for green tea catechins on the bioanalytical study using UPLC/ESI‐MS

A rapid and quantitative analytical method for the simultaneous determination of green tea catechins using ultra-performance liquid chromatography/electrospray ionization-mass spectrometry was developed. Total analytical run time was 3.5 min for the detection of (-)-epicatechin (EC), (-)-epicatechin-3-O-gallate (ECG), (-)-epigallocatechin (EGC), (-)-epigallocatechin-3-O-gallate (EGCG) and myricetin as the internal standard (IS) in rat plasma. The calibration curves were linear over the range of 10-5000 ng/mL for all the catechins. The inter- and intra-day precision (relative standard deviation) and accuracy (percentage deviation) of the method were both lower than 10%. The average extraction recoveries in plasma ranged from 68.5 to 86.5%, and the lower limits of quantification of EC, EGC, ECG and EGCG were 10 ng/mL with a signal-to-noise ratio of >10. The assay developed was successfully applied to a pharmacokinetic study of catechins following intravenous and intragastric administrations of green tea extract in rats. Plasma concentrations of four catechins were detected up to 5-24 h after administration, and the pharmacokinetic parameters of catechins were in agreement with previous studies. From these findings, taken together with the high productivity and precision, the developed method could be a reliable and reproducible tool for the evaluation of pharmacokinetic properties of catechins.

Transformation of tea catechins and flavonoid glycosides by treatment with Japanese post-fermented tea acetone powder

Japanese post-fermented teas are produced by a combination of aerobic and anaerobic microbial fermentation of the leaves of tea plant. Recently, it was revealed that tea products contain characteristic polyphenols identical to the tea catechin metabolites produced by mammalian intestinal bacteria, such as (2S)-1-(3′,4′,5′-trihydroxyphenyl)-3-(2″,4″,6″-trihydroxyphenyl)-propan-2-ol (EGC-M1). In the present study, degradation of epigallocatechin-3-O-gallate (EGCg) and epigallocatechin (EGC) with acetone powder prepared from Japanese post-fermented tea was examined. Under aerobic conditions, EGCg was hydrolysed to EGC and gallic acid, which were further converted to gallocatechin (GC) and pyrogallol, respectively. Under anaerobic conditions, EGCg was hydrolysed to EGC, which was further metabolised to GC, EGC-M1 and (4R)-5-(3,4,5-trihydroxyphenyl)-4-hydroxypentanoic acid (EGC-M2). Gallic acid was degraded to pyrogallol and then further decomposed. Anaerobic treatment of EGC with the acetone powder yielded EGC-M1, EGC-M2, (4R)-5-(3,4,5-trihydroxyphenyl)-γ-valerolactone, and (4R)-5-(3,4 -dihydroxyphenyl)-γ-valerolactone. Furthermore, similar anaerobic treatment of rutin and hesperidin yielded 3,4-dihydroxyphenylacetic acid and 3-(3,4-dihydroxyphenyl)propanoic acid, respectively.

Preventive effects of epigallocatechin-3-O-gallate against replicative senescence associated with p53 acetylation in human dermal fibroblasts.

Considering the various pharmacological activities of epigallocatechin-3-O-gallate (EGCG) including anticancer, and anti-inflammatory, antidiabetic, and so forth, relatively less attention has been paid to the antiaging effect of EGCG on primary cells. In this study, the preventive effects of EGCG against serial passage-induced senescence were investigated in primary cells including rat vascular smooth muscle cells (RVSMCs), human dermal fibroblasts (HDFs), and human articular chondrocytes (HACs). The involvement of Sirt1 and acetylated p53 was examined as an underlying mechanism for the senescence preventive activity of EGCG in HDFs. All cells were employed with the initial passage number (PN) between 3 and 7. For inducing senescence, the cells were serially passaged at the predetermined times and intervals in the absence or presence of EGCG (50 or 100 μM). Serial passage-induced senescence in RVSMCs and HACs was able to be significantly prevented at 50 μM EGCG, while in HDFs, 100 μM EGCG could significantly prevent senescence and recover their cell cycle progression close to the normal level. Furthermore, EGCG was found to prevent serial passage- and H2O2-induced senescence in HDFs by suppressing p53 acetylation, but the Sirt1 activity was unaffected. In addition, proliferating HDFs showed similar cellular uptake of FITC-conjugated EGCG into the cytoplasm with their senescent counterparts but different nuclear translocation of it from them, which would partly account for the differential responses to EGCG in proliferating versus senescent cells. Taking these results into consideration, it is suggested that EGCG may be exploited to craft strategies for the development of an antiaging or age-delaying agent.

Antibacterial and Antifungal Activities of New Acylated Derivatives of Epigallocatechin Gallate

(−)-Epigallocatechin-3-O-gallate (EGCG) has useful antiviral, antimicrobial, antitoxin, and antitumor properties. Previously, Mori et al. (2008) found that addition of long acyl chains (C16–18) to EGCG enhanced its anti-influenza virus activity up to 44-fold. The chemical stability of EGCG against oxidative degradation was also enhanced by acylation. We further evaluated the in vitro activity spectrum of the EGCG derivatives against a wide range of bacteria and fungi. A series of EGCG O-acyl derivatives were synthesized by lipase-catalyzed transesterification. These derivatives exhibited several-fold higher activities than EGCG, particularly against Gram-positive organisms. Antifungal MICs of the derivatives were also two to fourfold lower than those of EGCG. The activities of the EGCG derivatives against Gram-negative bacteria were not distinguishable from those of EGCG. Among the derivatives evaluated, MICs of dioctanoate and palmitate (C16) for 17 Staphylococcus aureus strains were 4–32 μg/ml, although MIC of EGCG for these 17 strains was ≥128 μg/ml. C16 demonstrated rapid bactericidal activity against methicillin-resistant S. aureus (MRSA) ATCC43300 at ≥16 μg/ml. The enhanced activity of C16 against S. aureus was supported by its increased membrane-permeabilizing activity determined by increased SYTOX Green uptake. The EGCG derivatives were exported in Escherichia coli using the efflux pump AcrAB–TolC. The tolC deletion mutant exhibited higher sensitivity to EGCG and the derivatives than wild-type. Addition of long alkyl chains to EGCG significantly enhanced its activities against several bacteria and fungi, particularly against S. aureus including MRSA. C16 might potentially become under specified circumstances an alternative or supplement to antibiotics and disinfectants in the future.

Abstract B74: EGCG inhibits cancer invasion by regulating tumor-stromal crosstalk in oral squamous cell carcinoma

Abstract Introduction: Epigallocatechin-3-O-gallate (EGCG), a major constituent polyphenol of green tea, has been shown to have suppressive effects on the invasion of various cancer cells, whereas the exact mechanisms have not yet been fully elucidated. In this study, the effects of EGCG on the invasion of oral squamous cell carcinoma (OSCC) were investigated where the new perspective focused on tumor-stromal crosstalk was emphasized, unlikely other previous studies focused on cancer cell mainly. Materials and Methods: OSCC were cultured with or without carcinoma-associated fibroblasts (CAF) in the dose dependent treatment of EGCG. In order to investigate the invasiveness, invasion assay and zymography were examined. Based on our previous study found that several cytokines are concerned with tumor-stromal crosstalk in invasion of OSCC, RT-PCR and ELISA assay were employed to examine the influence of EGCG on the expression levels of cytokines. Results: The invasiveness of OSCC was reduced by EGCG treatment, and the 50% reduction was demonstrated at the half concentration of EGCG (25 μM) in co-cultured group with CAF, compared to OSCC mono-cultured (50 μM). Zymography showed that EGCG treatment reduced MMP-9 expression in co-cultured condition. In addition, EGCG resulted in a noticeable decrease in the expression of cytokines, especially GRO-α/CXCL1, concerned with tumor-stromal crosstalk in invasion of OSCC. Conclusions: In this study, inhibitory effect of EGCG on cancer invasion was found at which its concentration is lower than previously known. Taking these results into consideration, EGCG may play an effective role in preventing invasion of OSCC by regulating tumor-stromal crosstalk. Acknowledgement: This work was supported by Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010–0029702). Citation Information: Cancer Prev Res 2011;4(10 Suppl):B74.

Epigallocatechin-3-gallate induces cytokine production in mast cells by stimulating an extracellular superoxide-mediated calcium influx

The green tea polyphenol (−)-epigallocatechin-3-O-gallate (EGCG) has various biological activities, including anti-inflammatory, anti-neoplastic, anti- and pro-apoptotic, and neuroprotective effects. Although these are often associated with increased intracellular reactive oxygen species (ROS) and Ca2+ levels, their involvement in biological effects is poorly understood. Here we report that EGCG induces cytokine production in mast cells via Ca2+ influx and ROS generation. EGCG at concentrations of ≥50μM induced interleukin-13 and tumor necrosis factor-α production in RBL-2H3 and bone marrow-derived mast cells. The effects were dependent on extracellular Ca2+, and EGCG induced Ca2+ release from intracellular stores and Ca2+ influx. Ca2+ influx was suppressed by 2-aminoethoxydiphenyl borate, an inhibitor of store-operated Ca2+ (SOC) channels, including Ca2+ release-activated Ca2+ channels and transient receptor potential canonical channels. EGCG failed to induce Ca2+ influx through SOC channels. EGCG-activated Ca2+ channels were genetically and pharmacologically distinct from Cav1.2 L-type Ca2+ channels, another route of Ca2+ influx into mast cells. EGCG evoked release of superoxide (O2−) into the extracellular space. Exogenous superoxide dismutase, but not catalase, inhibited EGCG-evoked Ca2+ influx and cytokine production, indicating that extracellular O2− regulates these events. EGCG can serve as a powerful tool for studying O2−-regulated Ca2+ channels, which may be selectively involved in the regulation of cytokine production but have yet to be elucidated.

(–)-Epigallocatechin-3-O-Gallate Augments Pentobarbital-Induced Sleeping Behaviors Through Cl− Channel Activation

This experiment investigated whether (-)-epigallocatechin-3-O-gallate (EGCG) (5-20 mg/kg, p.o.) has hypnotic effects and/or enhances pentobarbital-induced sleeping behaviors and whether these effects are mediated by γ-aminobutyric acid (GABA) receptors. EGCG prolonged sleeping time induced by pentobarbital (42 mg/kg, i.p.) and reduced sleeping latency induced by pentobarbital similarly to muscimol (0.2 mg/kg, i.p.), a GABA(A) receptor agonist in mice. EGCG also increased sleeping rate and sleeping time when co-administered with pentobarbital (28 mg/kg, i.p.) at a subhypnotic dosage. In addition, EGCG and pentobarbital increased chloride (Cl(-)) influx in primary cultured cerebellar cells. EGCG and pentobarbital decreased GABA(A) receptors α-subunit expression and had no effect on the expression of β- and γ-subunits and of glutamic acid decarboxylase in the hippocampus of rats. In conclusion, the EGCG enhancement of Cl(-) influx may play an important role in pentobarbital-induced sleeping behaviors.

In vitro anti-uveal melanoma activity of phenolic compounds from the Egyptian medicinal plant Acacia nilotica

Anti-uveal melanoma activity-guided fractionation of the MeOH extract of Acacia nilotica pods resulted in the isolation of the new compound gallocatechin 5-O-gallate (5) in addition to methyl gallate (1), gallic acid (2), catechin (3), catechin 5-O-gallate (4), 1-O-galloyl-β-D-glucose (6), 1,6-di-O-galloyl-β-D-glucose (7) and digallic acid (8). The structures of the isolated compounds were elucidated on the basis of HRESIMS, NMR spectroscopy and CD data. In addition to uveal melanoma, the antiproliferative activities of the isolated compounds and the related compound epigallocatechin 3-O-gallate (EGCG) were evaluated against cutaneous melanoma, ovarian cancer, glioblastoma and normal retinal pigmented cells.

Epigallocatechin-3-O-gallate inhibits the production of thymic stromal lymphopoietin by the blockade of caspase-1/NF-κB pathway in mast cells

The cytokine thymic stromal lymphopoietin (TSLP) has been implicated in the development and progression of allergic diseases such as atopic dermatitis, asthma, and chronic obstructive pulmonary disease. However, it has not yet been clarified the effect of epigallocatechin-3-O-gallate (EGCG) on the production of TSLP. Thus, we investigated how EGCG inhibits the production of TSLP in the human mast cell line (HMC-1) cells. Enzyme-linked immunosorbent assay, reverse transcription-polymerase chain reaction, luciferase assay, and Western blot analysis were used to investigate the effects of EGCG. EGCG inhibited the production and mRNA expression of TSLP in HMC-1 cells. EGCG also inhibited the nuclear factor-κB luciferase activity induced by phorbol myristate acetate plus A23187. Furthermore, EGCG inhibited the activation of caspase-1 in HMC-1 cells. These results provide evidence that EGCG can help us to treat inflammatory and atopic diseases through the inhibition of TSLP.

Increases in Blood Pressure and Heart Rate Induced by Caffeine are Inhibited by (-)-Epigallocatechin-3-O-gallate: Involvement of Catecholamines

In a previous experiment, (-)-epigallocatechin-3-O-gallate (EGCG) reduced caffeine-induced locomotor activity and stereotyped behaviors and inhibited caffeine-induced neuronal stimulant activity. This research was performed to give additional evidence that EGCG counteracts caffeine-induced stimulant effects in animals. EGCG inhibited caffeine-induced cardiovascular activation measures, such as arterial pressure and heart rate. In addition, the increases in the levels of adrenaline and noradrenaline in the blood induced by caffeine was reduced by EGCG. We suggest that EGCG may reduce caffeine-induced increases in blood pressure and heart rate and may decrease the levels of catecholamines in the blood. Therefore, EGCG counteracts caffeine-induced cardiovascular activity. The stimulant effects of caffeine should be reduced by the amount of EGCG in green tea.

Epigallocatechin-3-O-gallate (EGCG) attenuates FFAs-induced peripheral insulin resistance through AMPK pathway and insulin signaling pathway in vivo

We aimed to investigate the effects and possible mechanisms of Epigallocatechin-3-O-gallate (EGCG) on free fatty acids (FFAs)-induced peripheral insulin resistance in vivo. Overnight-fasted Wistar rats were subjected to 48-h intravenous infusion of either saline or Intralipid plus heparin (IH) with or without different doses of EGCG co-injection. Hyperinsulinemic–euglycemic clamp was performed in awake rats to assess peripheral insulin sensitivity. Co-injection with EGCG significantly prevented FFAs-induced peripheral insulin resistance, decreased plasma markers of oxidative stress: malondialdehyde (MDA) and 8-isoprostaglandin, and increased antioxidant enzymes: superoxide dismutases (SOD) and Glutathione peroxidase (GPx). Furthermore, EGCG treatment reversed IH-induced: (1) decrease in Thr172 phosphorylation of AMP activated protein kinase (AMPK); (2) increase in protein kinase Cθ(PKCθ) membrane translocation and Ser307 phosphorylation of insulin receptor substrate-1 (IRS-1); (3) decrease in Ser473 phosphorylation of Akt and Glucose transporter 4 (GLUT4) translocation in skeletal muscle and adipose tissue. Our data suggest that EGCG treatment ameliorated FFAs-induced peripheral insulin resistance in vivo, and this might be through decreasing oxidative stress and PKCθ membrane translocation, activating the AMPK pathway and improving insulin signaling pathway in vivo. This study suggests the therapeutic value of EGCG in protecting from insulin resistance caused by elevated FFAs.