Inhibitory Effect of Epigallocatechin 3-O-Gallate on Vascular Smooth Muscle Cell Hypertrophy Induced by Angiotensin II

Mechanisms Underlying the Effects of the Green Tea Polyphenol EGCG in Sarcopenia Prevention and Management

Sarcopenia is prevalent among the older population and severely affects human health. Tea catechins may benefit for skeletal muscle performance and protect against secondary sarcopenia. However, the mechanisms underlying their antisarcopenic effect are still not fully understood. Despite initial successes in animal and early clinical trials regarding the safety and efficacy of (-)-epigallocatechin-3-gallate (EGCG), a major catechin of green tea, many challenges, problems, and unanswered questions remain. In this comprehensive review, we discuss the potential role and underlying mechanisms of EGCG in sarcopenia prevention and management. We thoroughly review the general biological activities and general effects of EGCG on skeletal muscle performance, EGCG's antisarcopenic mechanisms, and recent clinical evidence of the aforesaid effects and mechanisms. We also address safety issues and provide directions for future studies. The possible concerted actions of EGCG indicate the need for further studies on sarcopenia prevention and management in humans.

Serotonin receptor subtype-2B signaling is associated with interleukin-18-induced cardiomyoblast hypertrophy in vitro

Background

In patients with heart failure, interleukin-18 (IL-18) levels increase in the circulatory system and injured myocardial tissue. Serotonin (5-hydroxytryptamine) receptors subtype 2B (HTR2B) play an essential role in cardiac function and development, and their overexpression in rats leads to myocardial hypertrophy. Epigallocatechin gallate (EGCG) is cardioprotective in myocardial ischemia-reperfusion injury in rats and can prevent pressure overload-mediated cardiac hypertrophy in vivo. Mice deficient in peroxisome proliferator-activated receptor delta (PPARδ) can have cardiac dysfunction, myocardial hypertrophy, and heart failure. Matrix metalloproteinases (MMPs) are possibly involved in cardiac remodeling. However, the relationship between IL-18 signaling, cardiac hypertrophy, and the molecular mechanisms involved remain to be fully elucidated.

Objectives

To elucidate the relationship between HTR2B and IL-18-induced myocardial hypertrophy and examine the antihypertrophic effects of EGCG and PPARδ.

Methods

We induced H9c2 cardiomyoblast hypertrophy with IL-18 in vitro and investigated the downstream signaling by real-time polymerase chain reaction (PCR) and western blotting. Hypertrophy was assessed by flow cytometry. We determined the effects of EGCG and PPARδ on IL-18-induced hypertrophic signaling via HTR2B-dependent mechanisms.

Results

IL-18-induced H9c2 hypertrophy upregulated brain natriuretic peptide (BNP) protein and mRNA expression by inducing the expression of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and the hypertrophy was attenuated by pretreatment with EGCG (20 μM) and L-165,041 (2 μM), a PPARδ agonist. IL-18 upregulated the expression of HTR2B, which was inhibited by pretreatment with EGCG and L-165,041. SB215505 (0.1 μM), a HTR2B antagonist and siRNA for HTR2B, attenuated H9c2 hypertrophy significantly. Inhibition of HTR2B also downregulated the expression of MMP-3 and MMP-9.

Conclusions

IL-18 and HTR2B play critical roles in cardiomyoblast hypertrophy. EGCG and L-165,041 inhibit the expression of HTR2B and augment remodeling of H9c2 cardiomyoblasts, possibly mediated by MMP-3 and MMP-9.

Antihypertensive activity of a new c-Jun N-terminal kinase inhibitor in spontaneously hypertensive rats

c-Jun N-terminal kinases (JNKs) are involved in the myocardial and aortic remodeling, increased arterial tone, and arterial blood pressure elevation associated with hypertension. The aim of the present study was to investigate the antihypertensive effect of a new JNK inhibitor, 1H-indeno[1,2-b]quinoxalin-11-one oxime sodium salt (IQ-1S), on spontaneously hypertensive rats (SHRs). Experiments were performed using normotensive Wistar-Kyoto (WKY) rats and SHRs. Experimental groups of SHRs received IQ-1S intragastrically for 6 weeks in daily doses of 5 and 50 mg/kg; experimental groups of WKY rats received 50 mg/kg IQ-1S according to the same regimen. The IQ-1S administration regimen induced decreases in systolic blood pressure, mean arterial blood pressure, total peripheral resistance, blood viscosity, hematocrit, myocardial cell cross-sectional area, and aortic wall thickness in SHRs vs untreated SHRs. There were no significant differences in systolic blood pressure values between the control and experimental groups of WKY rats during the treatment period. A concentration-dependent decrease in the tone of carotid arterial rings isolated from SHRs was observed after JNK inhibitor application in vitro. Application of the JNK inhibitor diminished endothelin-1 secretion by human umbilical vein endothelial cells in vitro. The main mechanisms of the antihypertensive effect of IQ-1S included the attenuation of blood viscosity due to decreased hematocrit, a vasodilatory effect on arterial smooth muscle cells, and a decrease in endothelin-1 production by endothelial cells.

Epigallocatechin-3-gallate regulates mitofusin 2 expression through the peroxisome proliferator-activated receptor-γ coactivator-1α and estrogen-related receptor-α pathway

Our previous study showed that epigallocatechin-3-gallate (EGCG) inhibition of human aortic smooth muscle cell (HASMC) proliferation might be mediated via upregulation of mitofusin 2 (Mfn-2). Studies on the mechanism of Mfn-2 inhibition of cell proliferation have mainly focused on downstream signaling. However, it is still not clear how upstream signaling molecules regulate Mfn-2. The promoter region of the Mfn-2 gene contains cis-acting elements of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) and estrogen-related receptor-α (ERR-α), suggesting a possible link between EGCG, Mfn-2, and PGC-1α/ERR-α. However, the effect of EGCG on PGC-1α/ERR-α remains unknown. In this study, we investigated the role of PGC-1α/ERR-α in the regulation of Mfn-2 induced by EGCG and assessed the underlying mechanisms. The effects of EGCG on cell proliferation of cultured HASMCs were observed by a cell counting kit-8 (CCK8) and 5-ethynyl-2-deoxyuridine (EdU) incorporation assay. Mfn-2, PGC-1α, and ERR-α gene and protein levels were determined by quantitative real-time polymerase chain reaction (PCR) and Western blot analysis. PGC-1α gene-silencing (PGC-1α small interfering RNA [siRNA]) was achieved by RNA interference and Mfn-2 promoter and peroxisome proliferator response element (PPRE) functional activity was achieved by a luciferase transfection assay. The results showed that the ERR-α-specific antagonist XCT-790 and PGC-1α siRNA decreased the expression of Mfn-2, thus antagonizing the inhibition of HASMC proliferation induced by EGCG. EGCG enhanced Mfn-2 promoter (-352 to 459) activity, while XCT-790 and PGC-1α siRNA abrogated this effect. PGC-1α stimulating Mfn-2 expression was dependent on intact ERR-α binding in the Mfn-2 promoter. The transcriptional effect of PGC-1α on the Mfn-2 promoter required the integrity of the -432 to 459 region and supported that Mfn-2 was a key target gene of PGC-1α. These results imply that PGC-1α/ERR-α played important physiological roles in inhibiting the proliferation of HASMCs by modulating Mfn-2 gene expression. Hence, EGCG regulated Mfn-2 expression likely through the PGC-1α/ERR-α pathway.

Regular consumption of green tea improves pulse pressure and induces regression of left ventricular hypertrophy in hypertensive patients

This study characterized the effects of regular green tea (GT) and hot water (HW) ingestion on systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse pressure (PP), and left ventricular hypertrophy (LVH) in two equal, sex- and age-matched groups; Grp1 and Grp2 (n = 100 each; age 53 ± 4 years) of hypertensive patients. Grp1 had regular GT treatment, followed by HW ingestion, whereas Grp2 had HW ingestion followed by GT treatment for periods of 4 months each. Electrocardiographic (ECG) and echocardiographic assessments of LVH were made before and at the end of both periods. SBP was lowered significantly by 6.6%; DBP by 5.1%, and PP by 9.1% by the end of month 4 of GT treatment in Grp1. Upon GT cessation and HW ingestion, SBP, DBP, and PP returned to pretreatment levels over 4 months. In Grp2, SBP, DBP, and PP were reduced insignificantly by 1.5%, 1.0%, and 2.3% by the end of the 4th month of HW ingestion. Conversely, over 4 months of GT treatment, SBP, DBP, and PP were significantly lowered by 5.4%, 4.1%, and 7.7% from the baseline values, respectively. ECG and echocardiographic evidence of LVH was shown in 20% of Grp1 and 24% of Grp2 patients before intervention. This was significantly lowered to 8% and 10% in Grp1 and Grp2 by GT treatment. However, this increased to 16% following HW ingestion in Grp1. HW ingestion did mot induce regression of LVH in Grp2. Thus, regular GT ingestion has cardiovascular protective effects.

Cardiovascular Effects of Flavonoids

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Cardiovascular Disease (CVD) is the major cause of death worldwide, especially in Western society. Flavonoids are a large group of polyphenolic compounds widely distributed in plants, present in a considerable amount in fruit and vegetable. Several epidemiological studies found an inverse association between flavonoids intake and mortality by CVD. The antioxidant effect of flavonoids was considered the main mechanism of action of flavonoids and other polyphenols. In recent years, the role of modulation of signaling pathways by direct interaction of flavonoids with multiple protein targets, namely kinases, has been increasingly recognized and involved in their cardiovascular protective effect. There are strong evidence, in in vitro and animal experimental models, that some flavonoids induce vasodilator effects, improve endothelial dysfunction and insulin resistance, exert platelet antiaggregant and atheroprotective effects, and reduce blood pressure. Despite interacting with multiple targets, flavonoids are surprisingly safe. This article reviews the recent evidence about cardiovascular effects that support a beneficial role of flavonoids on CVD and the potential molecular targets involved.

Epigallocatechin gallate protects against homocysteine-induced vascular smooth muscle cell proliferation

Epigallocatechin gallate (EGCG), a bioactive ingredient of green tea, plays a protective role in the cardiovascular system. Homocysteine (Hcy) is a major risk factor for chronic kidney disease and cardiovascular disease. The present study aimed to investigate the role of EGCG in Hcy-induced proliferation of vascular smooth muscle cells (VSMCs) and its underlying mechanism. We also explored the roles of rennin-angiotensin system (RAS), extracellular signal-regulated kinases (ERK1/2), and p38 mitogen-activated protein kinase (p38 MAPK) in this process. Human aortic smooth muscle cells (HASMCs) were treated with different drugs for different periods. The proliferation rate of HASMCs was detected using the CCK-8 and BrdU labeling assays. The Western blot assay was used to determine the expression levels of angiotensin II type 1 receptor (AT-1R), ERK1/2, and p38 MAPK. Compared with the control group, the HASMCs treated with Hcy at different doses (100, 200, 500, and 1000 µM) showed significantly increased proliferation. Hcy increased the expression of AT-1R, whereas EGCG decreased the protein expression of AT-1R. Furthermore, we found that Hcy-induced expression of p-ERK1/2 and p-p38MAPK was dependent on AT-1R. Compared with Hcy (500 µM)-treated cells, EGCG (20 µM)-treated cells showed decreased proliferation as well as expression of AT-1R, p-ERK1/2, and p-p38MAPK. In addition, HASMC proliferation was suppressed by the addition of an AT-1R blocker (olmesartan), an ERK1/2 inhibitor (PD98059), and a p38MAPK inhibitor (SB202190). EGCG can inhibit AT-1R and affect ERK1/2 and p38MAPK signaling pathways, resulting in the decrease of VSMC proliferation induced by Hcy.

Conditional expression of the type 2 angiotensin II receptor in mesenchymal stem cells inhibits neointimal formation after arterial injury

Percutaneous coronary interventions (PCIs) are an effective treatment for obstructive coronary artery diseases. However, the procedure's success is limited by remodeling and formation of neointima. In the present study, we engineered rat mesenchymal stem cells (MSCs) to express type 2 angiotensin II receptor (AT2R) using a tetracycline-regulated system that can strictly regulate AT2R expression. We tested the ability of the modified MSCs to reduce neointima formation following arterial injury. We subjected rats to balloon injury, and reverse transcriptase polymerase chain reaction (RT-PCR) indicated no significant AT2R expression in normal rat arteries. Low expression of AT2R was observed at 28 days after balloon-induced injury. Interestingly, MSCs alone were unable to reduce neointimal hyperplasia after balloon-induced injury; after transplantation of modified MSCs, doxycycline treatment significantly upregulated neointimal AT2R expression and inhibited osteopontin mRNA expression, as well as neointimal formation. Taken together, these results suggest that transplantation of MSCs conditionally expressing AT2R could effectively suppress neointimal hyperplasia following balloon-induced injury. Therefore, MSCs with a doxycycline-controlled gene induction system may be useful for the management of arterial injury after PCI.

Epigallocatechin-3-gallate inhibits proliferation of human aortic smooth muscle cells via up-regulating expression of mitofusin 2

Previous studies have shown that epigallocatechin-3-gallate (EGCG) inhibits the proliferation of vascular smooth muscle cells (VSMCs) via the extracellular-signal-regulated kinase (ERK1/2) and mitogen activated protein kinases (MAPKs) pathway. Mitofusin 2 (Mfn-2) also suppresses VSMC proliferation through Ras-Raf-ERK/MAPK, suggesting a possible link between EGCG, Mfn-2 and ERK/MAPK. However, the effect of EGCG on Mfn-2 remains unknown. In this study, we investigated the role of Mfn-2 in the regulation of VSMC proliferation by EGCG, and assessed the underlying mechanisms. The effects of EGCG on the proliferation of cultured human aortic smooth muscle cells (HASMCs) were observed by 5-ethynl-2-deoxyuridine (EdU) incorporation assay. Mfn-2 gene and protein levels, and Ras, p-c-Raf and p-ERK1/2 protein levels were determined by quantitative real-time polymerase chain reaction and western blotting, respectively. Mfn-2 gene silencing was achieved by RNA interference. EGCG 50 μmol/L profoundly inhibited the proliferation of HASMCs in culture, up-regulated Mfn-2, and down-regulated the expression of p-c-Raf and p-ERK1/2. Furthermore, RNA interference-mediated gene knockdown of Mfn-2 antagonized EGCG-induced anti-proliferation and down-regulation of Ras, p-c-Raf and p-ERK1/2. These results suggest that EGCG inhibits the proliferation of HASMCs in vitro largely via Mfn-2-mediated suppression of the Ras-Raf-ERK/MAPK signaling pathway.

Mitogenesis of vascular smooth muscle cell stimulated by platelet-derived growth factor-bb is inhibited by blocking of intracellular signaling by epigallocatechin-3-O-gallate

Epigallocatechin gallate (EGCG) is known to exhibit antioxidant, antiproliferative, and antithrombogenic effects and reduce the risk of cardiovascular diseases. Key events in the development of cardiovascular disease are hypertrophy and hyperplasia according to vascular smooth muscle cell proliferation. In this study, we investigated whether EGCG can interfere with PDGF-bb stimulated proliferation, cell cycle distribution, and the gelatinolytic activity of MMP and signal transduction pathways on RAOSMC when it was treated in two different ways-cotreatment with PDGF-bb and pretreatment of EGCG before addition of PDGF-bb. Both cotreated and pretreated EGCG significantly inhibited PDGF-bb induced proliferation, cell cycle progression of the G0/G1 phase, and the gelatinolytic activity of MMP-2/9 on RAOSMC. Also, EGCG blocked PDGF receptor-β (PDGFR-β) phosphorylation on PDGF-bb stimulated RAOSMC under pretreatment with cells as well as cotreatment with PDGF-bb. The downstream signal transduction pathways of PDGFR-β, including p42/44 MAPK, p38 MAPK, and Akt phosphorylation, were also inhibited by EGCG in a pattern similar to PDGFR-β phosphorylation. These findings suggest that EGCG can inhibit PDGF-bb stimulated mitogenesis by indirectly and directly interrupting PDGF-bb signals and blocking the signaling pathway via PDGFR-β phosphorylation. Furthermore, EGCG may be used for treatment and prevention of cardiovascular disease through blocking of PDGF-bb signaling.

Epigallocatechin-3-gallate is a potent phytochemical inhibitor of intimal hyperplasia in the wire-injured carotid artery

OBJECTIVE

Epigallocatechin-3-gallate (EGCG), a catechin gallate ester, is the major component of green tea and has been demonstrated to inhibit tumor growth as well as inhibit smooth muscle cell migration. We evaluated the effect of the phytochemicals resveratrol, allicin, sulforaphane (SFN), and EGCG on intimal hyperplasia in the carotid artery injury model.

METHODS

Intimal hyperplasia was induced in carotid arteries of adult Sprague-Dawley rats with a wire injury. Experimental animals received intraperitoneal injections of one of the four phytochemicals daily beginning 1 day prior to surgery and continued for up to 4 weeks. Control animals were administered saline. Carotid specimens were harvested at 2 weeks and subjected to quantitative image analysis. In addition, EGCG specimens were analyzed for cell proliferation, immunohistochemistry, and Western blot analysis.

RESULTS

Quantitative image analysis showed significant phytochemical suppression of intimal hyperplasia at 2 and 4 weeks postoperatively with EGCG (62% decrease in intimal area). Significant decreases were also noted at 2 weeks for SFN (56%) and resveratrol (44%), whereas the decrease with allicin (24%) was not significant. Quantification of intimal hyperplasia by intima:media ratio showed similar results. Cell proliferation assay of specimens demonstrated suppression by EGCG. Immunohistochemical staining of EGCG-treated specimens showed extracellular signal-regulated kinase (ERK) suppression but not of the c-jun N-terminal kinase or p38 pathways. Western blot analysis confirmed reduced ERK activation in arteries treated with EGCG.

CONCLUSIONS

Intraperitoneal injection of the phytochemicals EGCG, SFN, resveratrol, and allicin have suppressive effects on the development of intimal hyperplasia in the carotid artery injury model, with maximal effect due to EGCG. The mechanism of EGCG action may be due to inhibition of ERK activation. EGCG may affect a common pathway underlying either neoplastic cellular growth or vascular smooth muscle cellular proliferation.

EGCG inhibits CTGF expression via blocking NF-κB activation in cardiac fibroblast

Connective tissue growth factor (CTGF) has been reported to play an important role in tissue fibrosis and presents a promising therapeutic target for fibrotic diseases. In heart, inappropriate increase in level of CTGF promotes fibroblast proliferation and extracellular matrix (ECM) accumulation, thereby exacerbating cardiac hypertrophy and subsequent failure. Epigallocatechin-3-gallate (EGCG), the major polyphenol found in green tea, possesses multiple protective effects on the cardiovascular system including cardiac fibrosis. However, the molecular mechanism by which EGCG exerts its anti-fibrotic effects has not been well investigated. In this study, we found that EGCG could significantly reduce collagen synthesis, fibronectin (FN) expression and cell proliferation in rat cardiac fibroblasts stimulated with angiotensinII (AngII). It also ameliorated cardiac fibrosis in rats submitted to abdominal aortic constriction (AAC). Moreover, EGCG attenuated the excessive expression of CTGF induced by AAC or AngII, and reduced the nuclear translocation of NF-κB p65 subunit and degradation of IκB-α. Subsequently, we demonstrated that in cardiac fibroblasts NF-κB inhibition could suppress AngII-induced CTGF expression. Taken together, these findings provide the first evidence that the effect of EGCG against cardiac fibrosis may be attributed to its inhibition on NF-κB activation and subsequent CTGF overexpression, suggesting the therapeutic potential of EGCG on the prevention of cardiac remodeling in patients with pressure overload hypertrophy.

Gαq-protein carboxyl terminus imitation polypeptide GCIP-27 attenuates proliferation of vascular smooth muscle cells and vascular remodeling in spontaneously hypertensive rats

Gq-protein is located at the convergent point in signal transduction pathways leading to vascular remodeling. The carboxyl terminus of Gα-subunit plays a vital role in G-protein-receptor interaction. The present study was designed to explore the effects of a synthetic Gαq carboxyl terminus imitation peptide, namely GCIP-27, on vascular smooth muscle cells (VSMC) in vitro and vascular remodeling in spontaneous hypertensive rats (SHR). Hyperplasia and hypertrophy of VSMC wre determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, [(3)H]-thymidine and [(3)H]-leucine incorporation, and [Ca(2+)](i) was measured with Fluo-3/AM staining. Systolic blood pressure (SBP), the ratio of media thickness to lumen diameter (MT/LD) of aorta, collagen content, and phospholipase C activity in aorta were measured in SHR. GCIP-27 (3-100 µg/l) significantly decreased proliferation activity, protein content, incorporation of [(3)H]-thymidine and [(3)H]-leucine, and [Ca(2+)](i) level in VSMC. SBP, MT/LD, collagen content, and phospholipase C activity in aorta of SHR were decreased significantly in GCIP-27 (7, 20, 60 µg/kg)-treated groups and losartan (6 mg/kg) group compared with vehicle group. In conclusion, GCIP-27 could inhibit vascular remodeling effectively in vitro and in vivo.

(-)-Epigallocatechin gallate suppresses proliferation of vascular smooth muscle cells induced by high glucose by inhibition of PKC and ERK1/2 signalings

Proliferation of vascular smooth muscle cells (VSMCs) plays an important role in the development and progression of diabetes-related vascular complications. (-)-Epigallocatechin gallate (EGCG), the major catechin derived from green tea, is able to exert antidiabetes effects in animal models. However, it is not known whether or not EGCG inhibits VSMC proliferation induced by high glucose. This study tested the hypothesis that EGCG might have an inhibitory effect on VSMC proliferation induced by high glucose. VSMC proliferation was determined by [(3)H]-thymidine incorporation and uptake of 3-(4,5-dimethylthiazol-2-yl)-diphenyltetrazolium bromide (MTT). Extracellular signal-regulated kinase (ERK) 1/2 phosphorylation was determined by immunoblotting, and ERK 1/2 activity was detected by measuring the ability to phosphorylate its substrate Elk-1. Glucose increased VSMC proliferation in a concentration-dependent manner, which was reduced in the presence of EGCG. VSMC proliferation mediated by high glucose (30 mM) was involved in protein kinase C (PKC) and ERK1/2 signalings, because its effect was blocked by PKC inhibitor (PKC inhibitor 19-31) and ERK1/2 inhibitor (PD98059). Pretreatment of VSMCs with EGCG significantly inhibited the stimulatory effect of high glucose on PKC and ERK1/2 activation, followed by attenuation of its downstream transcription factor Elk-1 phosphorylation. Taken together, these results suggest that EGCG could suppress VSMC proliferation induced by high glucose by inhibition of PKC and ERK1/2 signalings in VSMCs, which indicates that EGCG might be a possible medicine to reduce vascular complications in diabetes.

Antihypertensive and cardiovascular effects of catechin-rich oil palm (Elaeis guineensis) leaf extract in nitric oxide-deficient rats

Oil palm (Elaeis guineensis) leaf extract (OPLE) possesses good ex vivo vasodilation and antioxidant properties. This study evaluated the catechin-rich OPLE antioxidant, antihypertensive, and cardiovascular effects in normal and nitric oxide (NO)-deficient hypertensive rats. OPLE was administered orally (500 mg/kg of body weight/day) to normotensive Wistar rats and N(ω)-nitro-L-arginine methyl ester (L-NAME)-induced NO-deficient hypertensive rats. OPLE significantly (P<.05) attenuated blood pressure increases, increased serum NO, reduced lipid peroxidation, and showed antioxidant effects in NO-deficient hypertensive rats. OPLE decreased the coronary arteriole wall-to-lumen ratio to near normal values under NO deficiency. Although OPLE showed good antihypertensive and antioxidant effects under NO deficiency, it was not hypotensive to normal rats and produced no chronic cardiovascular toxicity in any of the rats throughout the 12-week study. This is the first report on the in vivo antihypertensive properties of green tea catechins extracted from an alternative source, namely, oil palm leaf, for use as a medicinal food for hypertension and cardiovascular ailments.

Effects of catechin-rich oil palm leaf extract on normal and hypertensive rats' kidney and liver

Catechin-rich oil palm (Elaeis guineensis) leaf extract (OPLE) possesses good ex vivo vasodilation, antioxidant and cardiovascular properties. This study evaluated the beneficial or toxic effects of OPLE on the liver and kidneys of normal and hypertensive rats. The OPLE (500mg/kg body weight) were administered orally to normal Wistar Kyoto rats, spontaneously hypertensive rats (SHR) and N-ω-nitro-l-arginine methyl ester (l-NAME)-induced NO-deficient hypertensive rats. The OPLE reduced hypertension in NO-deficient rats, but not in SHR. Hepatocytes or glomeruli injury and oxidative markers were high in hypertensive rats compared to normal rats, and they were reduced (p<0.05) by OPLE supplementation, even when there was no blood pressure reduction. Unlike the hypertensive drug captopril, the OPLE showed no toxicity to normal rats. The dose reported is equivalent 0.5g of catechins/day for humans or 2.5cups of tea. The catechins are from an abundant alternative source for potential use as functional food.

(-)-epigallocatechin gallate inhibits endothelin-1-induced C-reactive protein production in vascular smooth muscle cells

Numerous studies have shown that C-reactive protein (CRP), a pro-inflammation cytokine, makes a direct contribution to atherosclerosis, and that (-)-epigallocatechin gallate (EGCG) is able to exert an anti-atherosclerotic effect by anti-oxidative and anti-inflammatory activities. Based on our previous study, the effect of EGCG on endothelin-1 (ET-1)-induced CRP production in rat vascular smooth muscle cells (VSMCs) and the possible mechanism were observed. The in vitro experiments showed that EGCG concentration-dependently inhibited ET-1-stimulated expression of CRP both in protein and mRNA levels in VSMCs as determined by the immunocytochemical staining, the enzyme-linked immunosorbent assay and the real-time quantitative polymerase chain reaction (RT-qPCR). The in vivo investigation with the double-labelled immunofluorescence staining and RT-qPCR displayed that EGCG also prevented ET-1-induced CRP expression in protein and mRNA levels in the aortic VSMCs of rats receiving the subchronic infusion of ET-1. In addition, EGCG suppressed reactive oxygen species (ROS) generation evoked by ET-1 in VSMCs as observed by the fluorescence probe. These demonstrate that EGCG may inhibit ET-1-stimulated generation of CRP in VSMCs so to relieve the inflammatory response and oxidative stress via blocking ROS signal, which provides new evidence for an anti-atherosclerotic effect of EGCG.

Epigallocatechin-3-gallate relaxes the isolated bovine ophthalmic artery: involvement of phosphoinositide 3-kinase-Akt-nitric oxide/cGMP signalling pathway

The present study investigates the direct action and the underlying mechanism(s) of epigallocatechin-3-gallate (EGCG) vasomotor effects on the bovine isolated ophthalmic artery. Adjacent rings were cut from each artery and mounted in a wire miograph system for isometric recording. Concentration-response curves for EGCG were constructed by adding cumulative concentrations of the drug to arterial rings pre-contracted with 5-HT (1 microM). Effects of mechanical endothelial cell removal and of selective blockers of the nitric oxide (NO)/cGMP pathways were investigated on the EGCG relaxant responses. EGCG relaxed ophthalmic arteries and maximum relaxation was 78.4+/-2.64%. Mechanical removal of endothelium, blockade of soluble guanylyl cyclase by 1H-1,2,4-oxadiazolo [4,3-a]quinoxalin-1-one (ODQ, 1 and 5 microM) or inhibition of nitric oxide (NO) synthase by N(G)-nitro-L-arginine (L-NAME, 50 and 100 microM) reduced significantly the relaxant response to catechin; moreover, the NO donor S-nitroso-N-acetylpenicillamine (SNAP, 100 microM) significantly increased the vasorelaxant responses to EGCG. Relaxation to EGCG was inhibited by iberiotoxin (200 nM), a blocker of big-conductance Ca(2+)-activated K(+) (BK(Ca)) channel, whereas the blockade of K(ATP) channel by glibenclamide (5 microM) and of small-conductance Ca(2+)-activated K(+) (SK(Ca)) channel by apamin (100 nM) elicited no effect. Interestingly, also inhibition of phosphoinositide-3-kinase (PI3K) by wortmannin (100 nM) and of Akt by SH6 (1 microM) markedly decreased the EGCG-evoked vasorelaxation. These data suggest that EGCG induced vasorelaxation in ophthalmic arteries with endothelium-intact via the activation of the NO/cGMP signalling pathway and defined an intriguing role for PI3K and Akt as upstream mediators for activation of NO-mediated relaxant responses.

Epigallocatechin-3 gallate prevents cardiac hypertrophy induced by pressure overload in rats

Pressure overload diseases, such as valvular stenosis and systemic hypertension, manifest morphologically in patients as cardiac concentric hypertrophy. Prevention of cardiac remodeling due to increased pressure overload is important to reduce morbidity and mortality. Epigallocatechin-3 gallate (EGCG) is a major bioactive polyphenol present in green tea which has been found to be a nitric oxide-mediated vasorelaxant and to be cardioprotective in myocardial ischemia-reperfusion injury. Therefore, we investigated whether EGCG supplementation could reduce in vivo pressure overload-mediated cardiac hypertrophy. Cardiac hypertrophy was induced by suprarenal transverse abdominal aortic constriction (AC) in rats. Three weeks after AC surgery, heart to body weight ratio increased in the AC group by 34% compared to the sham group. EGCG administration suppressed the load-induced increase in heart weight by 69%. Attenuation of cardiac hypertrophy by EGCG was associated with attenuation of the increase in myocyte cell size and fibrosis induced by aortic constriction. Despite abolition of hypertrophy by EGCG, transstenotic pressure gradients did not change. Echocardiogram revealed that increased left ventricular systolic dimensions and deteriorated systolic function were relieved by EGCG. These results suggest that EGCG prevents the development of left ventricular concentric hypertrophy by pressure overload and may be a useful therapeutic modality to prevent cardiac remodeling in patients with pressure overload myocardial diseases.

Hibernation, reversible cell growth inhibition by epigallocatechin-3-O-gallate

Epigallocatechin-3-O-gallate (EGCg) and related polyphenolic compounds found in tea are known to have antioxidative activities. However, they also have pro-oxidative activities such as generation of hydrogen peroxide. In this report, we investigated the effect on cells and showed the potential usage of EGCg in cell preservation. H(2)O(2) was generated from EGCg at concentrations of more than 300 microg/mL for 6 h at 37 degrees C, and high cytotoxicity for L929 cells were shown. In contrast, in the presence of 1 microg/mL catalase, the amount of generated H(2)O(2) was significantly low and cytotoxicity decreased markedly. This indicates that catalase eliminated H(2)O(2) generated by degradation of EGCg. Although H(2)O(2) generation was prevented, L929 cell proliferation was slightly inhibited in proportion to the concentrations of EGCg. L929 was exposed able to be 300 microg/mL to EGCg and 1 microg/mL catalase for maximum 18 days. EGCg inhibited the growth of L929 cells, and cell proliferation was restarted immediately after medium change for removing EGCg. We concluded that EGCg had a reversible growth inhibition when H(2)O(2) was eliminated from cell cultures.

Study of the mechanisms involved in the vasorelaxation induced by (-)-epigallocatechin-3-gallate in rat aorta

This study investigated several mechanisms involved in the vasorelaxant effects of (-)-epigallocatechin-3-gallate (EGCG). EGCG (1 microM-1 mM) concentration dependently relaxed, after a transient increase in tension, contractions induced by noradrenaline (NA, 1 microM), high extracellular KCl (60 mM), or phorbol 12-myristate 13-acetate (PMA, 1 microM) in intact rat aortic rings. In a Ca2+ -free solution, EGCG (1 microM-1 mM) relaxed 1 microM PMA-induced contractions, without previous transient contraction. However, EGCG (1 microM-1 mM) did not affect the 1 microM okadaic acid-induced contractions. Removal of endothelium and/or pretreatment with glibenclamide (10 microM), tetraethylammonium (2 mM) or charybdotoxin (100 nM) plus apamin (500 nM) did not modify the vasorelaxant effects of EGCG. In addition, EGCG noncompetitively antagonized the contractions induced by NA (in 1.5 mM Ca2+ -containing solution) and Ca2+ (in depolarizing Ca2+ -free high KCl 60 mM solution). In rat aortic smooth muscle cells (RASMC), EGCG (100 microM) reduced increases in cytosolic free Ca2+ concentration ([Ca2+]i) induced by angiotensin II (ANG II, 100 nM) and KCl (60 mM) in 1.5 mM CaCl2 -containing solution and by ANG II (100 nM) in the absence of extracellular Ca2+. In RASMC, EGCG (100 microM) did not modify basal generation of cAMP or cGMP, but significantly reversed the inhibitory effects of NA (1 microM) and high KCl (60 mM) on cAMP and cGMP production. EGCG inhibited the enzymatic activity of all the cyclic nucleotide PDE isoenzymes present in vascular tissue, being more effective on PDE2 (IC50 approximately 17) and on PDE1 (IC50 approximately 25). Our results suggest that the vasorelaxant effects of EGCG in rat aorta are mediated, at least in part, by an inhibition of PDE activity, and the subsequent increase in cyclic nucleotide levels in RASMC, which, in turn, can reduce agonist- or high KCl concentration-induced increases in [Ca2+]i.

Epigallocathechin-3 gallate inhibits cardiac hypertrophy through blocking reactive oxidative species-dependent and -independent signal pathways

Cardiac hypertrophy is a major cause of morbidity and mortality worldwide. Recent in vitro and in vivo studies have suggested that reactive oxygen species (ROS) may play an important role in cardiac hypertrophy. It was therefore thought to be of particular value to examine the effects of antioxidants on cardiac hypertrophy. Epigallocatechin-3-gallate (EGCG) is a major bioactive polyphenol present in green tea and a potent antioxidant. The current study was designed to test the hypothesis that EGCG inhibits cardiac hypertrophy in vitro and in vivo. In this study, we investigated the effects of EGCG on angiotensin II- (Ang II) and pressure-overload-induced cardiac hypertrophy. Our results showed that EGCG attenuated Ang II- and pressure-overload-mediated cardiac hypertrophy. Both reactive oxygen species generation and NADPH oxidase expressions induced by Ang II and pressure overload were suppressed by EGCG. The increased hypertension by pressure overload was almost completely blocked after EGCG treatment. Further studies showed that EGCG inhibited Ang II-induced NF-kappaB and AP-1 activation. Inhibition of the activity of NF-kappaB was through blocking ROS-dependent p38 and JNK signaling pathways, whereas inhibition of AP-1 activation was via blocking EGFR transactivation and its downstream events ERKs/PI3K/Akt/mTOR/p70(S6K). The combination of these actions resulted in repressing the reactivation of ANP and BNP, and ultimately preventing the progress of cardiac hypertrophy. These findings indicated that EGCG prevents the development of cardiac hypertrophy through ROS-dependent and -independent mechanisms involving inhibition of different intracellular signaling transductional pathways.

The role of tea and tea flavonoids in cardiovascular health

Consumption of green or black tea has been inversely associated with the development and progression of cardiovascular diseases. In this review, the current knowledge about protective effects of tea and tea constituents, particularly flavonoids, on the cardiovascular system is summarized. Underlying mechanisms for the beneficial effects of tea include vasculoprotective, antioxidative, antithrombogenic, anti-inflammatory, and lipid-lowering properties of tea flavonoids. Although promising experimental data on beneficial effects of tea in various cardiovascular diseases are available, results of clinical studies in humans are not uniform. A number of factors are discussed which may contribute to inconsistent data in humans. Overall, tea represents a promising tool for the prevention and treatment of cardiovascular disorders.

Trapping of growth factors by catechins: a possible therapeutical target for prevention of proliferative diseases

The prevention of cancer through dietary intervention is currently receiving considerable attention. Several epidemiological studies substantiate that green tea has a protective effect against a variety of malignant proliferative disorders such as lung cancer, breast cancer and prostate cancer. This preventive potential of green tea against cancer is attributed to the biologically active flavonoids called catechins. Epigallocatechin 3-o-gallate, the major catechin found in green tea, mediates diverse physiological and pharmacological actions in bringing about the regression of the tumors and also lowers the risk of nonmalignant cardiovascular proliferative diseases. Much of the current research is being focused on how these catechins specifically bring about the regression of the experimentally induced tumors both in vitro and in vivo. These catechins exert diverse physiological effects against proliferative diseases by several mechanisms, most of which are not completely characterized. This review summarizes the mechanisms by which these catechins play an essential role in regulating the process of carcinogenesis, with a special emphasis on how these catechins antagonize the growth factor-induced proliferative disorders.

Leptin induces hypertrophy via p38 mitogen-activated protein kinase in rat vascular smooth muscle cells

The hypertrophy of vascular smooth muscle cells (VSMCs) is critical in vascular remodeling associated with hypertension, atherosclerosis, and restenosis. Recently, leptin has appeared to play a pivotal role in vascular remodeling. However, the mechanism by which leptin induces hypertrophy in vascular smooth muscle cells is still unknown. We studied the role of leptin as a potential hypertrophic factor in rat VSMCs. In the present study, leptin significantly increased [(3)H]leucine incorporation and the total protein/DNA ratio in VSMCs. The maximal hypertrophic effect was at 100ng/ml of leptin. Leptin induced phosphorylation and activation of p38 mitogen-activated protein (p38 MAP) kinase and of signal transducers and activators of transcription 3 in a concentration- and time-dependent manner. A p38 MAP kinase inhibitor SB203580 significantly inhibited leptin-induced hypertrophy, AG490 (a JAK2 inhibitor) partially inhibited it, and other MAP kinase inhibitors, PD98059 (an ERK inhibitor) and SP600125 (a JNK inhibitor), had no effect. These results indicate that leptin directly stimulates cellular hypertrophy via p38 MAP kinase in rat VSMCs.