Epigallocatechin gallate increase the prostacyclin production of bovine aortic endothelial cells

Pomegranate Juice Supplementation Alters Utero-Placental Vascular Function and Fetal Growth in the eNOS-/- Mouse Model of Fetal Growth Restriction

The eNOS^−/− mouse provides a well-characterized model of fetal growth restriction (FGR) with altered uterine and umbilical artery function and reduced utero- and feto-placental blood flow. Pomegranate juice (PJ), which is rich in antioxidants and bioactive polyphenols, has been posited as a beneficial dietary supplement to promote cardiovascular health. We hypothesized that maternal supplementation with PJ will improve uterine and umbilical artery function and thereby enhance fetal growth in the eNOS^−/− mouse model of FGR. Wild type (WT, C57Bl/6J) and eNOS^−/− mice were supplemented from E12.5-18.5 with either PJ in their drinking water or water alone. At E18.5 uterine (UtA) and umbilical (UmbA) arteries were isolated for study of vascular function, fetuses and placentas were weighed and fetal biometric measurements taken. PJ supplementation significantly increased UtA basal tone (both genotypes) and enhanced phenylephrine-induced contraction in eNOS^−/− but not WT mice. Conversely PJ significantly reduced UtA relaxation in response to both acetylcholine (Ach) and sodium nitroprusside (SNP), endothelium dependent and independent vasodilators respectively from WT but not eNOS^−/− mice. UmbA sensitivity to U46619-mediated contraction was increased by PJ supplementation in WT mice; PJ enhanced contraction and relaxation of UmbA to Ach and SNP respectively in both genotypes. Contrary to our hypothesis, the changes in artery function induced by PJ were not associated with an increase in fetal weight. However, PJ supplementation reduced litter size and fetal abdominal and head circumference in both genotypes. Collectively the data do not support maternal PJ supplementation as a safe or effective treatment for FGR.

Acute vascular and metabolic actions of the green tea polyphenol epigallocatechin 3-gallate in rat skeletal muscle

Epidemiological studies show a dose-dependent relationship between green tea consumption and reduced risk for type 2 diabetes and cardiovascular disease. Bioactive compounds in green tea including the polyphenol epigallocatechin 3-gallate (EGCG) have insulin-mimetic actions on glucose metabolism and vascular function in isolated cell culture studies. The aim of this study is to explore acute vascular and metabolic actions of EGCG in skeletal muscle of Sprague-Dawley rats. Direct vascular and metabolic actions of EGCG were investigated using surgically isolated constant-flow perfused rat hindlimbs. EGCG infused at 0.1, 1, 10 and 100 μM in 15 min step-wise increments caused dose-dependent vasodilation in 5-hydroxytryptamine pre-constricted hindlimbs. This response was not impaired by the phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin or the AMP-kinase inhibitor Compound C. The nitric oxide synthase (NOS) inhibitor N^G-Nitro-l-Arginine Methyl Ester (L-NAME) completely blocked EGCG-mediated vasodilation at 0.1-10 μM, but not at 100 μM. EGCG at 10 μM did not alter muscle glucose uptake nor did it augment insulin-stimulated muscle glucose uptake. The acute metabolic and vascular actions of 10 μM EGCG in vivo were investigated in anaesthetised rats during a hyperinsulinemic-euglycemic clamp (10 mU min^-1 kg^-1 insulin). EGCG and insulin both stimulated comparable increases in muscle microvascular blood flow without an additive effect. EGCG-mediated microvascular action occurred without altering whole body or muscle glucose uptake. We concluded that EGCG has direct NOS-dependent vasodilator actions in skeletal muscle that do not acutely alter muscle glucose uptake or enhance the vascular and metabolic actions of insulin in healthy rats.

Endothelial NO Production Is Mandatory for Epigallocatechin-3-Gallate-induced Vasodilation: Results From eNOS Knockout (eNOS-/-) Mice

The underlying mechanisms for the vasodilating effects of the tea catechin epigallocatechin-3-gallate (EGCG) are still not fully understood. Besides nitric oxide (NO)-dependent effects, other modes of action are discussed. To elucidate whether the NO pathway is a prerequisite in mediating vasodilating effects, we investigated EGCG-induced vasorelaxation in isolated aortic rings of endothelial nitric oxide knockout (eNOS^−/−) mice. Vasodilation to acetylcholine was fully prevented in aortic rings of eNOS^−/− mice, confirming lack of vascular NO production. Vasodilation to the exogenous NO donor sodium nitroprusside was preserved in eNOS^−/− mice aortic rings. Low concentrations of EGCG (5–15 µM) resulted in strong vasorelaxation in aortic rings of wild type mice, whereas it was completely absent in eNOS^−/− mice. In corroboration, relaxation in response to green tea was significantly inhibited in aortic rings of eNOS^−/− mice. These results demonstrate that EGCG-induced vasodilation strongly relies on functional NO synthase in endothelial cells and subsequent stimulation of NO production in vessels.

Vascular and metabolic actions of the green tea polyphenol epigallocatechin gallate

Epidemiological studies demonstrate robust correlations between green tea consumption and reduced risk of type 2 diabetes and its cardiovascular complications. However, underlying molecular, cellular, and physiological mechanisms remain incompletely understood. Health promoting actions of green tea are often attributed to epigallocatechin gallate (EGCG), the most abundant polyphenol in green tea. Insulin resistance and endothelial dysfunction play key roles in the pathogenesis of type 2 diabetes and its cardiovascular complications. Metabolic insulin resistance results from impaired insulin-mediated glucose disposal in skeletal muscle and adipose tissue, and blunted insulin-mediated suppression of hepatic glucose output that is often associated with endothelial/vascular dysfunction. This endothelial dysfunction is itself caused, in part, by impaired insulin signaling in vascular endothelium resulting in reduced insulin-stimulated production of NO in arteries, and arterioles that regulate nutritive capillaries. In this review, we discuss the considerable body of literature supporting insulin-mimetic actions of EGCG that oppose endothelial dysfunction and ameliorate metabolic insulin resistance in skeletal muscle and liver. We conclude that EGCG is a promising therapeutic to combat cardiovascular complications associated with the metabolic diseases characterized by reciprocal relationships between insulin resistance and endothelial dysfunction that include obesity, metabolic syndrome and type 2 diabetes. There is a strong rationale for well-powered randomized placebo controlled intervention trials to be carried out in insulin resistant and diabetic populations.

Dietary polyphenols regulate endothelial function and prevent cardiovascular disease

Vascular endothelial cell (EC) dysfunction strongly induces development of cardiovascular and cerebrovascular diseases. Epidemiologic studies demonstrated a preventative effect of dietary polyphenols toward cardiovascular disease. In studies using cultured vascular ECs, polyphenols were recognized to regulate nitric oxide and endothelin-1 (ET-1) production. Furthermore, epigallocatechin-3-gallate inhibited the expression of adhesion molecules by a signaling pathway that is similar to that of high-density lipoprotein and involves induction of Ca(2+)/calmodulin-dependent kinase II, liver kinase B, and phosphatidylinositol 3-kinase expression. The effects of polyphenols on ECs include antioxidant activity and enhancement of the expression of several protective proteins, including endothelial nitric oxide synthase and paraoxonase 1. However, the observed effects of dietary polyphenols in vitro do not always translate to an in vivo setting. As such, there are many questions concerning their physiological mode of action. In this review, we discuss research on the effect of dietary polyphenols on cardiovascular disease and their protective effect on EC dysfunction.

Effects of selected bioactive natural products on the vascular endothelium

The endothelium, a highly active structure, regulates vascular homeostasis through the release of numerous vasoactive factors that control vascular tone and vascular smooth cell proliferation. A larger number of medicinal plants and their isolated chemical constituents have been shown to beneficially affect the endothelium. For example, flavonoids in black tea, green tea, and concord grape cause a vasodilation possibly through their antioxidant properties. Allicin, a by-product of the enzyme alliinase, has been proposed to be the main active metabolite and responsible for most of the biological activities of garlic, including a dose-dependent dilation on the isolated coronaries. Thymoquinone, the principal phytochemical compound found in the volatile oil of the black seed, and the hawthorn extract have also been shown to improve aging-related impairment of endothelium-dependent relaxations in animal models. In this review, the effect of some of the natural products, including Camellia sinensis (black tea and green tea), Vitis labrusca (concord grape), Allium sativum (garlic), and Nigella sativa (black seed) and Crataegus ssp (hawthorn extract), is explored. The molecular mechanisms behind these potential therapeutic effects are also discussed.

The impact of the catechol-O-methyltransferase genotype on vascular function and blood pressure after acute green tea ingestion

SCOPE

Evidence for the benefits of green tea catechins on vascular function is inconsistent, with genotype potentially contributing to the heterogeneity in response. Here, the impact of the catechol-O-methyltransferase (COMT) genotype on vascular function and blood pressure (BP) after green tea extract ingestion are reported.

METHODS AND RESULTS

Fifty subjects (n = 25 of the proposed low-activity [AA] and of the high-activity [GG] COMT rs4680 genotype), completed a randomized, double-blind, crossover study. Peripheral arterial tonometry, digital volume pulse (DVP), and BP were assessed at baseline and 90 min after 1.06 g of green tea extract or placebo. A 5.5 h and subsequent 18.5 h urine collection was performed to assess green tea catechin excretion. A genotype × treatment interaction was observed for DVP reflection index (p = 0.014), with green tea extract in the AA COMT group attenuating the increase observed with placebo. A tendency for a greater increase in diastolic BP was evident at 90 min after the green tea extract compared to placebo (p = 0.07). A genotypic effect was observed for urinary methylated epigallocatechin during the first 5.5 h, with the GG COMT group demonstrating a greater concentration (p = 0.049).

CONCLUSION

Differences in small vessel tone according to COMT genotype were evident after acute green tea extract.

Dietary flavan-3-ols intake and metabolic syndrome risk in Korean adults

Flavan-3-ols are a subclass of flavonoids found in a variety of foods including teas. The effects of flavan-3-ols on the risk of metabolic syndrome (MetS) have been investigated, generally focusing on tea catechins or individual flavan-3-ol rich foods, but there is little information on dietary flavan-3-ols intake and risk of MetS in population-based studies. In this cross-sectional study, we examined the association between dietary flavan-3-ols intake and the risk of MetS in Korean adults. Subjects comprised 1,827 men and 2,918 women aged 20-69 years whose data was included in the 2008 Korean National Health and Nutrition Examination Survey. This survey was conducted between January 2008 and December 2008. Total flavan-3-ols intakes were calculated from 24-hour dietary recalls using a flavonoids database. Thirty percent of the male subjects and 24% of the female subjects were reported as having MetS. In the female subjects, flavan3-ols intake was inversely associated with the risk of MetS after adjusting for potential confounders (5th vs. 1st quintile, OR = 0.64, 95% CI = 0.45-0.91, P for trend = 0.384). The main food source of flavan-3-ols was green tea followed by apples and grapes. Among MetS components, flavan3-ols intake was inversely associated with the risk of high blood pressure after adjusting for potential confounders (5th vs. 1st quintile, OR = 0.64, 95% CI = 0.45-0.90, P for trend = 0.005). No significant association between flavan-3-ols intake and risk of MetS was found in the male subjects. After stratified analysis by obesity (BMI ≥ 25 or BMI < 25), however, flavan3-ols intake was inversely related to the risk of hypertension in non-obese men. These results suggest that dietary flavan-3-ols intake may have beneficial effects on MetS risk by reducing the risk of hypertension. The effects of flavan-3-ols intake dependent on obesity need further investigation.

Green tea (Camellia sinensis) catechins and vascular function

The health benefits of green tea (Camellia sinensis) catechins are becoming increasingly recognised. Amongst the proposed benefits are the maintenance of endothelial function and vascular homeostasis and an associated reduction in atherogenesis and CVD risk. The mounting evidence for the influential effect of green tea catechins on vascular function from epidemiological, human intervention and animal studies is subject to review together with exploration of the potential mechanistic pathways involved. Epigallocatechin-3-gallate, one of the most abundant and widely studied catechin found in green tea, will be prominent in the present review. Since there is a substantial inconsistency in the published data with regards to the impact of green tea catechins on vascular function, evaluation and interpretation of the inter- and intra-study variability is included. In conclusion, a positive effect of green tea catechins on vascular function is becoming apparent. Further studies in animal and cell models using physiological concentrations of catechins and their metabolites are warranted in order to gain some insight into the physiology and molecular basis of the observed beneficial effects.

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.

Effects of inhibitors of the arachidonic acid cascade on primary muscle culture from a Duchenne muscular dystrophy patient

The aim of this study was to elucidate the mechanisms of action for potential targets of therapeutic intervention related to the arachidonic acid cascade in muscular dystrophy. Primary cultures from a Duchenne patient were used to study the expression of dystrophin-1, utrophin, desmin, neonatal myosin heavy chain (MHCn) and Bcl-2 during inhibition of phospholipase A2 (PLA2), cyclooxygenase (COX) and lipoxygenase (LOX). Hypo-osmotic treatment was applied in order to trigger Ca2+ influx and PLA2 activity. Inhibition of PLA2 and LOX with prednisolone and nordihydroguaiaretic acid (NDGA) caused a semi-quantitative increase of utrophin and Bcl-2-, and a dose-dependent, quantitative increase of desmin expression, an effect that was augmented by hypo-osmotic treatment. Our results indicate that LOX inhibitors, similarly to corticosteroids, can be beneficial in the treatment of muscular dystrophies.

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.

Vascular protection by dietary polyphenols

Consumption of polyphenol-rich foods, such as fruits and vegetables, and beverages derived from plants, such as cocoa, red wine and tea, may represent a beneficial diet in terms of cardiovascular protection. Indeed, epidemiological studies demonstrate a significant inverse correlation between polyphenol consumption and cardiovascular risk. Among the numerous plausible mechanisms by which polyphenols may confer cardiovascular protection, improvement of the endothelial function and inhibition of angiogenesis and cell migration and proliferation in blood vessels have been the focus of recent studies. These studies have indicated that, in addition to and independently from their antioxidant effects, plant polyphenols (1) enhance the production of vasodilating factors [nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF) and prostacyclin] and inhibit the synthesis of vasoconstrictor endothelin-1 in endothelial cells; and (2) inhibit the expression of two major pro-angiogenic factors, vascular endothelial growth factor (VEGF) and matrix metalloproteinase-2 (MMP-2) in smooth muscle cells. The mechanisms of these effects involve: (1) in endothelial cells, increased Ca(2+) level and redox-sensitive activation of the phosphoinositide 3 (PI3)-kinase/Akt pathway (leading to rapid and sustained activation of nitric oxide synthase and formation of EDHF) and enhanced expression of nitric oxide synthase; and (2) in smooth muscle cells, both redox-sensitive inhibition of the p38 mitogen-activated protein kinase (p38 MAPK) pathway activation (leading to inhibition of platelet-derived growth factor (PDGF)-induced VEGF gene expression) and redox-insensitive mechanisms (leading to inhibition of thrombin-induced MMP-2 formation). The current evidence suggests that all these mechanisms are triggered by polyphenols with specific structures, although the structural requirements may be different from one effect to the other, and that they all contribute to the vasoprotective, anti-angiogenic, anti-atherogenic, vasorelaxant and anti-hypertensive effects of acute or chronic administration of plant polyphenols found in vivo in animals and in patients.

Effects of Flavonoid-Rich Beverages on Prostacyclin Synthesis in Humans and Human Aortic Endothelial Cells: Association withEx VivoPlatelet Function

Diets rich in flavonoids have been associated with reduced risk for cardiovascular disease. This may be due, in part, to flavonoid-induced alterations in eicosanoid synthesis. Our objective was to identify plant-derived beverages that alter synthesis of prostacyclin in cultured human aortic endothelial cells (HAEC), and to determine if these beverages could alter in vivo 6-keto-prostaglandin F(1alpha) (a stable metabolite of prostacyclin) synthesis and platelet function. HAEC were treated with nine commonly consumed beverages to determine their effects on prostacyclin synthesis under acute and chronic treatment regimens. Orange, purple grape, and pomegranate juices and coffee (6-9 mL/kg) were then provided to 28 fasted, healthy adult subjects (eight men and 20 women) on five separate days. Plasma samples were collected immediately following juice consumption (baseline), and at 2 and 6 hours post-consumption. On an acute basis, administration of HAEC with pomegranate juice increased media prostacyclin. Chronic exposure to purple grape and pomegranate juice increased aortic endothelial cell prostacyclin synthesis (38% and 61%, respectively; P <.05). The consumption of purple grape, pomegranate, and orange juice prolonged epinephrine/collagen-induced clotting time (P <.05). Purple grape juice increased plasma 6-keto-prostaglandin F(1alpha) (20%; P <.05) at 2 hours; pomegranate and orange juice did not significantly influence plasma prostacyclin concentrations. Consistent with the in vitro data, coffee consumption did not influence clotting time or plasma prostacyclin concentrations. These results indicate that the HAEC model system can provide a qualitative means to screen food and food-derived products for biologic activity related to cardiovascular health.

Green tea catechins inhibit the cultured smooth muscle cell invasion through the basement barrier

Epidemiological studies suggest that green tea consumption is associated with a reduced risk of cardiovascular disease. Antioxidative properties of green tea flavonoids, catechins, have been believed to be involved in the antiatherogenic effect of green tea, since catechins inhibit low density lipoprotein oxidation. The migration of vascular smooth muscle cells (SMCs) from the tunica media to the subendothelial region is a key event in the development and progression of atherosclerosis and post-angioplasty vascular remodeling. Matrix metalloproteinases (MMPs) play a key role in these processes of SMC migration. In the present study, we investigated the effect of catechins on the gelatinolytic activity of MMP-2 that was derived from cultured bovine aortic SMCs. We also investigated the effect of catechins on the SMC invasion through the reconstituted basement membrane barrier. A major constituent of green tea catechins, (-)-epigallocatechin gallate (EGCG), inhibited the gelatinolytic activity of MMP-2 and concanavalin A (ConA)-induced pro-MMP-2 activation without the influence of membrane-type MMP expression in SMCs. EGCG also inhibited the SMC invasion through the basement membrane barrier in a concentration-dependent manner without any influence of SMC migration across the basement membrane protein thin-coated filter. The antagonistic effects of other catechins, namely (-)-epigallocatechin (EGC) and (-)-epicatechin gallate (ECG), on gelatinolytic activity of MMP-2, ConA-induced pro-MMP-2 activation, or PDGF-BB-directed SMC invasion were much less pronounced than those of EGCG. Also, (+)-catechin and (-)-epicatechin failed to show any effect. These findings may suggest that the anti-invasive and anti-metalloproteinase activities involve at least part of the anti-atherogenic action of catechin in accordance with the antioxidant properties of catechin.