Platelet function and coronary artery disease

Antioxidative properties of hydrogen sulfide may involve in its antiadhesive action on blood platelets

BACKGROUND

Hydrogen sulfide (H(2)S) is a signaling molecule in different systems, including the cardiovascular system. However, mechanisms involved in the relationship between the action of H(2)S and hemostasis process are still unclear.

OBJECTIVE AND METHODS

The present work was designed to study the effects of hydrogen sulfide on adhesion of blood platelets in vitro. Platelet suspensions were preincubated (5-30 min) with NaHS as a hydrogen sulfide donor at the final concentrations of 0.00001-10 mM. Then, for platelet activation thrombin (0.1 U/mL) or TRAP, peptide with the sequence Ser-Phe-Leu-Leu-Arg-Asn (SFLLRN; 20 μM) was used. We also measured the effects of H(2)S on superoxide anion radicals (O(2)(-•)) production in blood platelets.

RESULTS

We observed that adhesion to collagen and to fibrinogen of resting platelets preincubated with NaHS was changed, and this process was statistically significant (for 0.00001-5mM NaHS, p<0.05; 10 mM, p<0.01). The inhibitory effect of NaHS on adhesion of thrombin - or TRAP - stimulated platelets to collagen was found (for 0.00001 and 0.0001 mM NaHS, p<0.05; 0.001-1 mM NaHS, p<0.01; 5 and 10 mM NaHS, p<0.001). Hydrogen sulfide reduced also the thrombin- or TRAP-induced platelet adhesion to fibrinogen (for 0.00001 and 0.0001 mM NaHS, p<0.05; 0.001-1 mM NaHS, p<0.01; 5 and 10 mM NaHS, p<0.001). Moreover, H(2)S caused a dose-dependent reduction of O(2)(-•) produced in platelets (p<0.05).

CONCLUSION

The results obtained that the antioxidative activity of H(2)S may involve in its antiadhesive properties on blood platelets.

Resveratrol, a phenolic antioxidant with effects on blood platelet functions

The main purpose of this article is to provide an overview of the currently available evidence of antiplatelet properties of resveratrol (3,4('),5-trihydroxystilbene). Resveratrol, a phenolic compound found naturally in fruits, nuts, flowers, seeds and bark of different plants is integral part of human diet. It exhibits a wide range of biological effects, including antiplatelet, anti-inflammatory, anticancer, antimutagenic and antifungal properties. It is also a potent antioxidant, reactive oxygen species scavenger and metal chelators. Resveratrol reduces lipid peroxidation, oxidation and nitration of platelet and plasma proteins. This review article describes the chemical structure of resveratrol, its biological activity, the effects on blood platelet functions and the mechanisms involved in its action on blood platelets, the cells which play an important role not only in the haemostatic process, but also in pathogenesis of cardiovascular diseases.

d-glucaro 1,4-lactone and resveratrol as antioxidants in blood platelets

The aim of our work was to study the anti-aggregatory and antioxidative effects of natural dietary products, D-glucaro 1,4-lactone (1,4-GL) in combination with phenolic compound resveratrol (trans-3,4',5-trihydroxystilbene). Our results in vitro showed that 1,4-GL alone slightly inhibits platelet aggregation induced by thrombin. The combination of resveratrol (0.1 microM) with 0.5 mM of 1,4-GL caused a significant decrease of thrombin-induced platelet aggregation; however separately, neither of studied compound at used concentrations was not effective. When platelets were treated with 1,4-GL (at the concentration of 0.1 mM and higher) and resveratrol (0.1 microM), similar synergistic action of both tested compound on markers of oxidative stress formation was observed. We measured the levels of different specific markers of oxidative stress, e.g., superoxide anion radicals O(2)(-)*, thiobarbituric acid-reactive substances and carbonyl group formation. Both tested compounds inhibited also the generation of O(2)(-)* and malondialdehyde that represents enzymatical peroxidation of arachidonic acid leading to thromboxane A(2) (TXA(2)) formation in platelets after thrombin stimulation. The obtained in vitro results demonstrate that anti-platelet and antioxidative properties of resveratrol may be significantly augmented by another dietary agent such as 1,4-GL, but mechanism synergistic action of these compounds is not yet known.

Inhibition of blood platelet adhesion and secretion by different phenolics from Yucca schidigera Roezl. bark

OBJECTIVE

Yucca schidigera is a plant that grows in Mexico, and it has a very high level of saponins and phenolic compounds with antioxidant action. The products of Y. schidigera are used as food additives and have a generally recognized as safe label. This study investigated the antiplatelet mechanisms of four phenolic compounds.

METHODS

We investigated antiplatelet mechanisms of the phenolic compounds trans-3,4',5-trihydroxystilbene (trans-resveratrol), trans-3,3',5,5'-tetrahydroxy-4'-methoxystilbene, and yuccaols A and C that had been isolated from the bark of Y. schidigera by studying their effects on the first step of platelet activation, i.e., platelet adhesion to collagen and fibrinogen. The effects of these compounds on the release of adenine nucleotides, proteins, and beta-N-acetyl-glycosaminidase (a marker of lysosomal secretion) from blood platelets activated by thrombin were also studied.

RESULTS

These different phenolic compounds (1 to 25 microg/mL) and their extracts decreased platelet adhesion and secretion.

CONCLUSIONS

Resveratrol and yucca extract were more reactive in decreasing these processes than were other tested phenolic compounds.

Glycoprotein IIb/IIIa inhibition attenuates platelet-activating factor-induced platelet activation by reducing protein kinase C activity

Glycoprotein (GP)IIb/IIIa inhibition may abolish activated leukocyte-induced platelet activation, in which leukocyte-released platelet-activating factor (PAF) is a major mediator. The present study thus investigated if and how GPIIb/IIIa inhibitors interfere with PAF-induced platelet activation. Platelet and leukocyte activation were monitored by flow cytometry and immunoblotting. GPIIb/IIIa inhibitors (c7E3, non-peptide SR121566, and MAb RFGP56) attenuated PAF-induced, but not adenosine diphosphate (ADP)- or thrombin receptor activating peptide (TRAP)-induced platelet P-selectin expression in whole blood. GPIIb/IIIa blockade enhanced ADP- or TRAP-induced leukocyte CD11b expression, but not the response to PAF. GPIIb/IIIa blockade attenuated PAF-induced, but enhanced ADP- or TRAP-induced platelet-leukocyte aggregation. Under the present experimental conditions, thromboxane A2 receptor antagonism did not significantly influence PAF-induced platelet activation, and GPIIb/IIIa inhibition did not interfere with calcium mobilization/influx in platelets. Protein kinase C (PKC) blockade inhibited PAF-induced platelet P-selectin expression, and PAF-induced PKC activity was reduced by GPIIb/IIIa inhibition. PAF (=1 micro m) did not induce MEK 1/2 or ERK 1/2 phosphorylation, whilst thrombin induced marked responses, which were enhanced by GPIIb/IIIa blockade. Thus, GPIIb/IIIa inhibition attenuates PAF-induced platelet activation via inhibiting PKC activity. GPIIb/IIIa blockade enhances thrombin-induced platelet MEK 1/2 and ERK 1/2 activation, and augments ADP- and TRAP-induced leukocyte activation by enhancing platelet-leukocyte aggregation.