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Phenolic phytochemicals are widely distributed in the plant kingdom. In terms of protective effects on organisms, the group of polyphenols is the most important. In various experiments, it has been shown that selected polyphenols, mainly flavonoids, confer protective effects on the cardiovascular system and have anti-cancer, antiviral and antiallergic properties. In coronary artery disease, the protective effects are due mainly to antithrombic, antioxidant, anti-ischemic and vasorelaxant properties of flavonoids. Flavonoids are low molecular weight compounds composed of a three-ring structure with various substitutions, which appear to be responsible for the antioxidant and antiproliferative properties. It has been hypothesized that the low incidence of coronary artery disease in the French population may be partially related to the pharmacological properties of polyphenolic compounds present in red wine. Many epidemiological studies have shown that regular flavonoid intake is associated with reduced risk of cardiovascular diseases.
Consumption of diets high in saturated fat and cholesterol is usually associated with increased risk of cardiovascular disease. However, epidemiological evidence has shown that cardiovascular disease is less prevalent in the French population than expected in light of their saturated fat intake and serum cholesterol concentrations. This paradoxical finding has been attributed to regular consumption of fresh vegetables, fruit and red wine (1,2).
Law and Wald (3), however, predicted that it would be only a matter of time before the ‘French paradox’ resolved itself as the only recently comparable pattern of risk factors (animal fat consumption, serum cholesterol concentrations and blood pressure) between France and Britain would be translated into similar death rates from coronary disease. Although red wine consumption remains higher in France than in Britain, the authors rejected this as a possible explanation because they consider that wine intake greater than one unit a day confers no greater benefit (3). The protective effect of moderate consumption (two to three units) of red wine on the risk of cardiovascular disease morbidity and mortality, however, has been consistently shown in many epidemiological studies (reviewed in 2). Phenolic compounds and especially a group of flavonoids seem to be responsible for the majority of protective effects of red wine. A major activity of plant polyphenols is their antioxidant properties, which may explain many of their beneficial effects on cardiovascular function (4–6). Polyphenols also act on other targets involved in the metabolism of mammalian cells, including nitric oxide (NO), which regulates hemostasis (6,7), thrombus development (8) and vascular tone (9,10). The beneficial properties of NO may therefore explain in part the anti-ischemic activities of plant polyphenols.
This minireview describes the protective effects of red wine polyphenolic compounds on cardiovascular disease, particularly their antithrombic, antioxidant, anti-ischemic, vasorelaxant and antihypertensive properties.
From the chemical point of view, natural polyphenols are derivatives of chromane. A wide range of polyphenols have desirable biological properties for humans. Among them are flavonoids, phenolic acids, 3,4-trihydroxystilbens and leucocyanidols (11).
Because of their beneficial effects on the cardiovascular system, the flavonoid group has been studied the most. Over 4000 naturally existing flavonoids are widespread among plants and plant products (6). Flavonoids are the derivatives of phenylchroman. Depending on the structural features, they can be divided into the following subgroups: flavanes, flavanones, flavones, flavonoles, chalcones and anthocyanidins (Figure 1). The basic structure comprises two benzene rings linked by a central heterocyclic pyran or pyrone ring. Flavonoids and tocopherols (vitamin E) share a common structure, the chromane ring (12). Flavonoids differ from one another in the orientation of hydroxylation or methylation, in the position of benzoid substituent and in the degree of unsaturation. They usually occur in the form of glycosides. The characteristics of flavonoids appear also to be required especially for their antioxidant and antiproliferative activity (6,12,13).
Polyphenols have been shown to be able to modulate the process of thrombosis in several systems. Fuster et al (14) reported that a reduced rate of development of atherosclerosis and coronary artery disease caused by daily intake of flavonoids was based mainly on the possibility of flavonoids to inhibit acute thrombus formation.
In both platelets and leukocytes, interference with arachidonic acid metabolism has been shown, resulting in inhibition of platelet aggregation and reduction of prothrombic and proinflammatory mediator synthesis in humans (15,16) and in experimental models (17,18). In humans, Pace-Asciak et al (15) showed that polyphenolic compounds from red wine, especially quercetin, catechin and resveratrol, inhibited the synthesis of thromboxane in platelets and of leukotriene in neutrophils. In their experiments, resveratrol and quercetin exhibited a dose-dependent inhibition of thromboxane-induced and ADP-induced platelet aggregation, while epicatechin, alpha-tocopherol and butylated hydroxytoluene were inactive. Trans-resveratrol also inhibited synthesis of thromboxane B2 and hydroxyheptadecatrienoate, and slightly inhibited synthesis of 12-hydroxyeicosatetraenoate (12-HETE). Alcohol-free red wine inhibited the synthesis of thromboxane B2 but not of 12-HETE. Other investigators studying platelet aggregation and lipid concentrations in humans who consumed red or white wine found an increase in high density lipoprotein concentrations in both groups and a decrease in ADP-induced platelet aggregation in humans who consumed red wine (19).
With the aim to study the platelet inhibitory effects of different compounds including wine, Folt’s coronary thrombosis model of platelet aggregation and thrombus formation based on measurement of cyclic reductions in coronary flow (CFRs) in mechanically stenosed coronary artery was used (17). The authors showed that CFRs were eliminated by red wine and grape juice when given intravenously or intragastrically; however, a 2.5-fold greater amount of grape juice than red wine was needed for the elimination of CFRs. In the case of white wine, the elimination of CFRs was not significant. These results suggest that there are antiaggregative compounds present in red wine and grape juice that are absent from white wine. Quercetin and rutine were also found to eliminate CFRs in the same model. Measurement of quercetin, rutin and resveratrol content of red wine, white wine and grape juice indicated that flavonoid content was severalfold higher in red wine and grape juice than in white wine (8,17). Red wine polyphenols reduced the level of thromboxane A2 similarly to acetylsalicylic acid. Polyphenols, in contrast to acetylsalicylic acid, had a shorter term effect on coronary blood flow but interfered with glycoprotein receptors on endothelial cells. As a result of this interference, platelets were not able to adhere to the vessel wall and therefore thrombus formation was inhibited (20). Several polyphenols have been also shown to interfere with several enzyme systems critically involved in cellular responses, such as tyrosine and serine-threonine protein kinases, phospholipases and cyclo-oxygenases (12). Recent evidence indicates that some polyphenols modulate specific pathways regulating the expression and activation of genes involved in the control of the cardiovascular system (21).
Ruf (18) reported that, except for decreasing prostanoid synthesis from arachidonate, wine polyphenols reduced platelet activity by NO mediation. In agreement with this study, Wollny et al (8) found that red wine supplementation, after either 10-day or acute administration in rats, markedly prolonged bleeding time and inhibited platelet adhesion to fibrillar collagen by NO-dependent mechanism. In all cases, NG-nitro-l-arginine methyl ester (L-NAME), an inhibitor of NO formation, prevented the effects of red wine. The possibility of reverting the effect of L-NAME by l-arginine, the substrate for NO synthase, but not by its stereoisomer d-arginine, strengthens the role of NO in red wine-induced effects. Regarding the mechanisms of NO increase, it is possible that red wine polyphenols decrease degradation of basal levels of NO, preventing its destruction by superoxides, or stimulate NO synthase in endothelial cells. It is conceivable that both mechanisms are active in vivo (8,10). Adhesion of platelets to the subendothelial matrix, after vessel damage, is a triggering mechanism of thrombus formation, and thus platelet inhibition by red wine may partially explain the prevention of thrombus growth.
An increase in reactive oxygen species in the organism leads to oxidative stress with subsequent damage of many biological molecules. Proteins, DNA and cell membrane lipids are significant targets of cellular injury (22). Lipid peroxidation in vivo involves a radical chain reaction leading to lipid hydroperoxides, which can stimulate vascular cells to produce monocyte-chemotactic and macrophage-stimulating factors, resulting in formation of so-called foam cells and atherosclerotic plaques (22,23). Oxidized low density lipoproteins (LDLs) also play a part in thrombus development because they stimulate procoagulant activities in endothelial cells and monocytes, and inhibit vasodilation by decreasing expression of endothelial NO synthase. In the prevention of cardiovascular disease, many of the observed effects of polyphenols can therefore be attributed to their recognized antioxidant and radical scavenging properties, which may delay the onset of atherogenesis by reducing chemically and enzymatically mediated peroxidative reactions (24). According to the work of Rice-Evans and Miller (25) – which contributed to the understanding of the structure-activity relation of the antioxidant effects of flavonoids – quercetin, the common red wine flavonoid, appears to be an extremely efficient radical scavenger. Indeed, reduced progression of atherosclerosis in apolipoprotein E-deficient mice was shown after consumption of quercetin or red wine. Reduction in atherosclerosis progression was associated with decreased susceptibility of LDL to oxidation and aggregation (26). The studies of De Whally et al (27) and Miyagi et al (28) showed that red wine significantly inhibited Cu2+-catalized LDL oxidation, yet white wine and beer failed to do so. Similarly to red wine, grape juice, with a large amount of flavonoids, also significantly inhibited oxidation of LDL. However, in the experiment on 20 volunteers, the antioxidant activity was not significantly increased after ingestion of grape juice, suggesting that flavonoids in red wine can be absorbed from the intestine more easily than those in grape juice. It was concluded that the antioxidant properties of flavonoids concerning LDL oxidation were associated with absorption of flavonoids from the intestine into the circulation (5). Recently, Nigdikar et al (29) confirmed the finding of De Whally et al (27) and Miyagi et al (28), showing that two-week consumption of red wine, but not white wine, enhanced antioxidant capacity as measured by decreased plasma lipid peroxides, conjugated dienes and Cu2+-catalized peroxidation of LDL. Serafini et al (30) showed that the total radical-trapping antioxidant capacity of red wine was at least 20 times stronger than that of white wine. Frankel et al (4) reported that quercetin and trans-resveratrol were more effective than alpha-tocopherol in inhibiting the oxidation of human LDL. Moreover, flavonoids may protect alpha-tocopherol from oxidation by being themselves oxidized by free radicals or by regenerating active alpha-tocopherol (12). The antioxidant activities of flavonoids and their glycosides were even higher than those of vitamins C and E (31). Red wine consumption was also found to increase plasma high density lipoprotein concentrations characterized by their antiatherogenic effects (32).
All the mechanisms by which red wine polyphenols exert their antiatherogenic effect appear to be crucial in the prevention and treatment of cardiovascular disease.
The protective role of flavonoids in cardiac ischemia may be related mainly to their ability to scavenge oxygen free radicals (33), to maintain NO concentration (10,34) and to inhibit mast cell secretion (35).
Sato et al (33) found that an ethanol-free red wine extract as well as trans-resveratrol protected the hearts from detrimental effects of ischemia-reperfusion injury, as seen by improved postischemic ventricular function and reduced myocardial infarction.
Both the red wine extracts and trans-resveratrol reduced oxidative stress in the heart, as indicated by decreasing malondyaldehyde formation. These compounds were also found to be highly effective in direct scavenging of peroxyl radicals. Direct perfusion of ethanol into the hearts may, however, cause development of oxidative stress resulting in completely different effects on the heart (33). A reduction effect of several flavonoids on acute regional myocardial ischemia in isolated rabbit hearts was also reported (36). Ning et al (37) showed that flavone administration improved functional recovery in the reperfused heart after a bout of global ischemia. The effect of flavone on postischemic recovery was proposed to be caused by its stimulation of the cytochrome P450 system. It has been suggested that flavone may act as an allosteric effector of cytochrome P450 reductase, which improves catalytic efficiency, thereby diminishing production of free radicals. Quercetin was reported to exert a protective effect by preventing the decrease in the xanthine dehydrogenase to oxidase ratio observed during ischemia-reperfusion in rats (38). Inhibition of xanthine oxidase by flavonoids was also described (39). In addition, flavonoids were found to possess positive chronotropic and antiarrhythmic effects and to minimize mitochondrial ischemia-reperfusion injury (40).
Because changes in NO concentration were found during ischemia-reperfusion in rats (34), the effects of red wine polyphenols on NO stability and generation are crucial in prevention against ischemia. Recent studies reported an increase in NO synthase activity due to treatment with red wine polyphenolic compounds in the heart (41) and aorta (41,42).
The protective effects of flavonoids in cardiac ischemia are also associated with their ability to inhibit mast cell secretion, which may be involved in cardiovascular inflammation, at present considered one of the key factors in coronary artery disease (35). Quercetin and some other flavonoids were found to inhibit the release of rat mast cell histamine in a concentration-dependent manner (43,44).
The idea that phenolic compounds in grape juice, red wine and some other beverages have a protective effect on cardiovascular disease led investigators to think about the effect of these compounds on vascular functions. Polyphenolic compounds have the ability to relax precontracted smooth muscle of aortic rings with intact endothelium; moreover, some of them are able to relax endothelium-denuded arteries (9,10).
Fitzpatrick et al (9) reported that in aortic rings with endothelium, skin extracts from red grapes caused relaxation. On the contrary, in endothelium-denuded aortic rings, relaxation was not observed. However, Andriambeloson et al (10) reported relaxation induced by leucocyanidol and catechin in aortic rings both with and without endothelium. However, a 1000-fold greater amount of the substances was needed for relaxation in endothelium-denuded arteries. NG-mono-methyl-l-arginine and NG-nitro-l-arginine, inhibitors of NO synthesis, reversed the relaxation induced by grape skin extracts. By using electron paramagnetic resonance, acute administration of red wine polyphenolic compounds was found to elevate NO synthesis in the endothelium (45). However, the mechanism of NO synthase activation by red wine polyphenolic compounds is not satisfactorily understood. Recently, Andriambeloson et al (42) observed that red wine polyphenolic compounds produced NO-induced Ca2+-dependent vasorelaxation of rat aorta. Martin et al (46) suggested that the rise in intercellular Ca2+ involves both Ca2+ release and Ca2+ entry, the latter being an essential step for NO production in endothelial cells. However, the mechanisms of Ca2+ handling among different polyphenolic compounds may differ with regard to the type of intracellular Ca2+ stores mobilized and the nature of G proteins implicated. It has been suggested that phospholipase C and tyrosine kinase pathways are involved in Ca2+ signalling (46).
Because red wine polyphenols consist of hydroxycinnamic acid, proanthocyanidins, anthocyanins, flavanes and flavonols, the question of which substance(s) may be responsible for increased NO synthesis had to be addressed. From anthocyanin-enriched wine extracts, aglycone-, monoglycoside- and diglycoside-enriched fractions induced endothelium-dependent vasorelaxation, similar to that elicited by the original red wine polyphenolic extract. Of the anthocyanins, delphinidin, but not cyanidin or malvidin, mimicked the effect of the original extract (47). The representative derivatives of phenolic acid (benzoic, vanillic and gallic acid), hydroxycinnamic acid (p-coumaric and caffeic acid), flavanols (catechine and epicatechine) and the higher polymerenriched fraction of condensed tannins failed to induce endothelium-dependent vasorelaxation (47,48).
Mechanisms implicated in the vasorelaxant effects of flavonoids may also include inhibition of cyclic nucleotide phosphodiesterases (49) and activation of Ca2+- activated K+ channels (50); both pathways are linked to the effects of flavonoids on smooth muscle cells rather than the endothelium. Ferrell et al (51) proposed that the flavonoid inhibitory activity on phosphodiesterases may be ascribed to the structural mimicry of the purine ring in cyclic AMP and cyclic GMP, and the pyranone ring of active flavonoids. Both an increase in NO synthase activity and a decrease in phosphodiesterase activity may lead to increased cyclic GMP concentration, resulting in vasorelaxation and inhibition of platelet aggregation.
The ability of polyphenolic compounds to activate the NO-cyclic GMP system seems to be associated also with their antihypertensive effect. The effects of the red wine extract provinol were tested on the experimental model of L-NAME-induced hypertension, which was developed by long term inhibition of NO synthase activity. Provinol partially prevented an increase in blood pressure when given simultaneously with the NO synthase inhibitor L-NAME (41). In rats with developed hypertension, provinol treatment resulted in more decreased blood pressure and greater NO synthase activity in the heart and aorta than in rats with spontaneous recovery (52). Similarly, Mizutani et al (53) reported that in vivo administration of an extract of polyphenolic compounds from wine attenuated elevated blood pressure in spontaneously hypertensive rats, and Hara (54) found that in vivo administration of an extract of polyphenolic compounds from tea reduced blood pressure and decreased risk of stroke in susceptible rats. Improved biomechanical properties of aorta, lowering of cholesterol concentrations and inhibition of LDL oxidation were suggested as the mechanisms responsible for blood pressure reduction (53,54). Recently Diebolt et al (55) found that short term oral administration of red wine polyphenolic compounds produced a decrease in blood pressure in normotensive rats. This hemodynamic effect of red wine polyphenolic compounds was associated with augmented endothelium-dependent relaxation and a modest induction of gene expression of inducible NO synthase and cyclo-oxygenase 2 within the arterial wall, which together maintained unchanged agonist-induced contractility (55).
The effects of decaffeinated green tea were studied on mice exposed to various intensities of social stress associated with hypertension. In mice given decaffeinated green tea, blood pressure fell from 150 mmHg to 133 mmHg. It is speculated that the sympathetic adrenal medullary system may be involved in the mechanisms of blood pressure reduction in this model because the heart rate was also affected (56). The mechanisms by which red wine polyphenols exert their antihypertensive effect appear to be important in the prevention and treatment of cardiovascular disease.
It is evident that polyphenolic compounds possess antithrombic, antioxidant, anti-ischemic, vasorelaxant and anti-hypertensive properties. All these effects may improve cardiovascular functions and potentially result in decreased morbidity and mortality due to coronary artery diseases. Red wine, as opposed to other sources of polyphenols, is unique in a number of selected dietary polyphenols as well as in their ingestion and bioavailability. Various procedures involved in the production of red wine enrich its polyphenol content. Additionally, the low alcohol content allows better solubilization of the polyphenols, resulting in greater bioavailability. And finally, red wine contains trans-resveratrol and some other polyphenols that are absent from commonly consumed fresh fruits and vegetables. Taken together, red wine is a rich source of natural polyphenols with beneficial effects on human health.
This work was supported by The Slovak Grant Agency for Science, grants No. 2/7165/20, 2/7240/20 and 2/7156/20.