Effect of polyphenolic flavonoid compounds on platelets

Differential effects of grape ( Vitis vinifera ) skin polyphenolics on human platelet aggregation and low-density lipoprotein oxidation

Antioxidant and antiplatelet properties of grape products are thought to be responsible for observed antiatherosclerotic effects. Diverse classes of phenolics are derived from the seed and skin (GSK) of grapes. The relative contributions of the classes of phenolics to observed properties of grape products are unknown. In this paper, GSK fractions were used to examine effects on platelet aggregation, low-density lipoprotein (LDL) oxidation in vitro, and relative binding of phenolics to LDL. GSK was separated into six fractions (fractions 1-6), and primary phenolics were characterized using high-performance liquid chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Fractions 4, 5, and 6, enriched in polygalloyl polyflavan-3-ols (PGPFs) with 3-6, 4-8, and 6-15 degrees of polymerization, respectively, inhibited platelet aggregation. Fractions 1-3, containing various amounts of oligosaccharides, hydroxycinnamic acids, anthocyanins, flavanols, and low molecular weight PGPFs, significantly increased platelet aggregation. Fractions 4-6 were most effective in binding LDL and inhibiting LDL oxidation. Fractions 5 and 6 exhibited the greatest inhibition of platelet aggregation and LDL oxidation, suggesting that polymeric PGPFs are responsible for the beneficial effects of grape products. Conversely, phenolics in fractions 1-3 may reduce the net biological potency of the grape products and have undesirable effects on cardiovascular disease risk factors.

Antiplasmin activity of natural occurring polyphenols

The equilibrium between proteolytic enzymes and their cognate inhibitors is crucial in a number of physiological as well as pathological processes, including cancer, inflammatory processes and thrombosis. Therefore, both synthetic and natural small molecule inhibitors are object of extensive studies as drugs in the treatment of these pathologies. Two natural occurring polyphenolic compounds, representative of glycosylated and unglycosylated flavonoid structures, namely quercetin and rutin, were thereby tested as potential ligands of plasmin(ogen), a serine (pro)protease, whose role in tumor cell invasion and migration has been reported. Quercetin showed a ten folds higher affinity with plasmin with respect to rutin in terms of equilibrium dissociation constant, both compounds acting as in vitro moderate reversible inhibitors; additionally, quercetin and rutin prevented plasmin-incubated BB1 cells from releasing E-cadherin fragment to a different extent, respectively. Furthermore, a feasible mechanism of interaction was analyzed and discussed using a molecular modeling approach.

Flavonoids inhibit the amidolytic activity of human thrombin

The effect of a group of natural flavonoids on human thrombin amidolytic activity was investigated using a spectrophotometric inhibition assay while information on the kinetics and thermodynamics was obtained using optical biosensor techniques. All the flavonoids tested acted as reversible inhibitors, and the quercetin-thrombin complex was found to be most stable at pH=7.5. Docking analysis indicated that quercetin's inhibitory behavior could be related to its planar structure and low steric hindrance, and to its ability to form a critical H-bond with thrombin His57.

Antithrombotic Properties of the Thromboxane A2/Prostaglandin H2 Receptor Antagonist S18886 on Prevention of Platelet-Dependent Cyclic Flow Reductions in Dogs

A potent thromboxane A2/PGH2 (TP)-receptor antagonist, S18886, was evaluated for its antithrombotic property in a dog model of acute periodic platelet-mediated thrombosis in stenosed coronary arteries with endothelial damage. After thrombosis had been obtained in 11 dogs, S18886 (300 microg/kg bolus) was administered IV. Heart rate, systemic blood pressure, and coronary blood flow were continuously recorded. Ex vivo whole blood platelet aggregation (PA), blood pH, hematocrit, platelet count, PO2, PCO2, and bleeding times were measured before and 30 minutes after administration of S18886. S18886 completely inhibited thrombosis in all dogs in approximately 5-10 minutes. No change in heart rate, blood pressure, pH, PO2, PCO2, platelet count, or bleeding time and a slight but significant elevation in hematocrit occurred. Infusion of epinephrine IV after complete inhibition of thrombosis by S18886 partially restored thrombosis in 3 of the 11 dogs. PA induced by collagen (4 microg/mL), collagen (0.25 microg/mL) plus epinephrine (1 microg/mL), collagen (1 microg/mL) plus epinephrine (1 microg/mL), ADP (40 microM) plus epinephrine (1 microg/mL), and phorbol 12-myristate 13-acetate (0.5 nM) were attenuated by 90 +/- 8% (P < 0.005), 98 +/- 2% (P < 0.05), 78 +/- 6% (P < 0.005), 70 +/- 10% (P < 0.005), and 28 +/- 8% (P < 0.05), respectively. In conclusion, S18886 is a potent platelet inhibitor that attenuates in vivo platelet-dependent thrombosis in the experimental dog model and reduces ex vivo platelet aggregation.

Effects of ethanol and other constituents of alcoholic beverages on coronary heart disease: a review

Moderate consumption of alcoholic beverages has been shown to reduce the incidence of coronary artery disease (CAD) compared to abstinence and heavy drinking. Epidemiologic studies suggest that any form of alcoholic beverage offers this protection. However, several studies have shown that the polyphenolic compounds found in many alcoholic beverages are more effective than pure alcohol for improving specific biologic factors known to contribute to atherosclerotic development. The alcoholic beverage polyphenols improve endothelial function, protect LDL from oxidation, inhibit platelet activity, inhibit vascular smooth muscle cell (VSMC) proliferation and migration, and reduce the activation of monocytes in the post-prandial period. Not only does pure alcohol not provide these benefits, but it has also been shown to act as a pro-oxidant, impair endothelial function, and possibly be proinflammatory. In studies comparing red wine, white wine, beer, and liquor, the red wine and dark-colored beer seem to provide more protection than liquor, even though the alcohol contents (per serving) are similar. The results suggest that the type of alcoholic beverage consumed does make a difference because pure alcohol cannot fully account for the beneficial effects.

Complex effects of different green tea catechins on human platelets

Epigallocatechin gallate (EGCG), a major component of green tea, has been previously shown to inhibit platelet aggregation. The effects of other green tea catechins on platelet function are not known. Pre-incubation with EGCG concentration-dependently inhibited thrombin-induced aggregation and phosphorylation of p38 mitogen-activated protein kinase and extracellular signal-regulated kinases-1/2. In contrast EGCG stimulated tyrosine phosphorylation of platelet proteins, including Syk and SLP-76 but inhibited phosphorylation of focal adhesion kinase. Other catechins did not inhibit platelet aggregation. Interestingly, when EGCG was added to stirred platelets, a tyrosine kinase-dependent stimulation of platelet aggregation was observed. The two other catechins containing a galloyl group in the 3' position (catechin gallate, epicatechin gallate) also stimulated platelet aggregation, while catechins without a galloyl group (catechin, epicatechin) or the catechin with a galloyl group in the 2' position (epigallocatechin) did not.

Grape seed and grape skin extracts elicit a greater antiplatelet effect when used in combination than when used individually in dogs and humans

Grape products, rich in polyphenolics, inhibit platelet aggregation (PA), a risk factor for coronary artery disease. We postulated that combining extracts of grape seed (GSD) and grape skin (GSK), primary sources of grape polyphenolics, individually shown to inhibit PA, might enhance their individual antiplatelet effects. This hypothesis was examined in vitro (human platelets) and ex vivo (dog platelets) by studying the effects of the extracts on collagen-induced whole blood PA. In vitro, threshold concentration of only GSD, individually incubated with blood, significantly inhibited PA; PA was inhibited by 12.7 +/- 3.5% (P < or = 0.01). No significant changes in Pa were observed with threshold concentrations of GSK, used individually. In two dose combinations, GSD and GSK inhibited PA 40.5 +/- 10.1% (P < or = 0.005) and 96.5 +/- 3.1% (P < or = 0.001). In the ex vivo study, seven dogs were fed threshold doses of GSD or GSK individually, in combination or in combination with a proprietary enzyme blend (EB; thought to enhance bioavailability) for 8 d. PA was measured before and after each treatment. PA measurements were also repeated 24 h after the final dose of GSD + GSK + EB. Feeding the extracts individually did not affect PA, whereas feeding them in combination inhibited PA by 31.9 +/- 7.1% (P < or = 0.05). Feeding EB in addition to GSD + GSK inhibited PA by 56.2 +/- 8.1% (P < or = 0.005); 24 h later, PA was still inhibited by 31.5 +/- 10.5% (P < or = 0.05), suggesting a residual antiplatelet effect from the administration of the final dose. The results suggest that the components of GSD and GSK, when present in combination as in red wine, grape juice or in a commercial preparation containing both extracts, exhibit a greater antiplatelet effect than when present individually.