Effects of the selective inhibition of platelet thromboxane synthesis on the platelet-subendothelium interaction

Cardiovascular Risk Reduction: A Pharmacotherapeutic Update for Antiplatelet Medications

This update presents evidence for new antiplatelet therapies including modified P2Y₁₂ inhibitors and a new class of thromboxane antagonists. Discussed are emerging data on established antihyperlipidemic medications that support an additional antiplatelet effect. Current information about the effectiveness of several bleeding reversal agents is discussed, and the concept of personalized antiplatelet therapy, wherein selection of an antiplatelet therapy is based on genetic factors or laboratory testing that predict response to therapy and risk of adverse effects. Finally, future drug targets are introduced and drug interactions that can be leveraged to design more effective and safe antiplatelet therapies are described.

Markers of endothelial dysfunction

Endothelial dysfunction is considered as a universal non-specific link in the pathogenesis of many diseases, primarily the cardiovascular system. This review is devoted to the discussion of the main functions of the endothelium and mechanisms for their implementation. One of the most striking features of endothelial cells is their morphological heterogeneity, which allows us to identify several typical forms of endothelial dysfunction (vasomotor, hemostatic, adhesion and angiogenous). Also, the review presents the most promising predictors of cardiovascular diseases and their complications among endothelial damage markers.

Licochalcones extracted from Glycyrrhiza inflata inhibit platelet aggregation accompanied by inhibition of COX-1 activity

Licochalcones extracted from Glycyrrhiza inflata are known to have a variety of biological properties such as anti-inflammatory, anti-bacterial, and anti-tumor activities, but their action on platelet aggregation has not yet been reported. Therefore, in this study we investigated the effects of licochalcones on platelet aggregation. Collagen and U46619, a thromboxane A₂ receptor agonist, caused rabbit platelet aggregation, which was reversed by pretreatment with licochalcones A, C and D in concentration-dependent manners. Among these compounds, licochalcone A caused the most potent inhibitory effect on collagen-induced platelet aggregation. However, the licochalcones showed marginal inhibitory effects on thrombin or ADP-induced platelet aggregation. In addition to rabbit platelets, licochalcone A attenuated collagen-induced aggregation in human platelets. Because licochalcone A also inhibited arachidonic acid-induced platelet aggregation and production of thromboxane A₂ induced by collagen in intact platelets, we further examined the direct interaction of licochalcone A with cyclooxygenase (COX)-1. As expected, licochalcone A caused an inhibitory effect on both COX-1 and COX-2 in vitro. Regarding the effect of licochalcone A on COX-1 enzyme reaction kinetics, although licochalcone A showed a stronger inhibition of prostaglandin E₂ synthesis induced by lower concentrations of arachidonic acid, Vmax values in the presence or absence of licochalcone A were comparable, suggesting that it competes with arachidonic acid at the same binding site on COX-1. These results suggest that licochalcones inhibit collagen-induced platelet aggregation accompanied by inhibition of COX-1 activity.

15,16-dihydrotanshinone I, a major component from Salvia miltiorrhiza Bunge (Dansham), inhibits rabbit platelet aggregation by suppressing intracellular calcium mobilization

Radix Salviae miltiorrhiza (RSM, 'Dansham' in Korea, 'Danshen' in Chinese), the root of Salviae miltiorrhiza Bunge (Labiate) has been used as Chinese fork medicine for the treatment of cardiovascular diseases such as angina pectoris, coronary heart disease, myocardial infarction, and hypertension. In the present study, we evaluated the inhibitory effects of 15,16-Dihydrotanshinone I, one of the major ingredients of Salvia miltiorrhiza Bunge, on platelet aggregation, with elucidation of its mechanisms of action. 15,16-Dihydrotanshinone I concentration-dependently inhibited collagen-induced aggregation of rabbit washed platelets with IC50 of 8.7+/-5.6 microM, the potency being about seven-fold greater than EGCG, an active Green tea catechin component (IC50: 56.6+/-48.7 microM). 15,16-Dihydrotanshinone I significantly inhibited the intracellular calcium ([Ca2+]i) mobilization in a concentration-dependent manner. 15,16-dihdydrotanshinone I also significantly suppressed collagen (50 microg/mL)-induced liberation of [3H]Arachidonic acid from [3H]Arachidonic acid-incorporated rabbit platelet. In addition, 15,16-Dihydrotanshinone I at 50 microM slightly but significantly inhibited collagen-induced production of thromboxane B2. These results indicate that 15,16-Dihydrotanshinone I exert potent anti-platelet activity via suppression of [Ca2+]i mobilization and arachidonic acid liberation.

Usefulness of whole blood aggregometry and its comparison with thromboxane generation assay in monitoring acetylsalicylic acid effectiveness--a multiparametric study in rats

BACKGROUND

There is a need for consensus concerning universal methodological criteria for detection of suboptimal response to acetylsalicylic acid (ASA) therapy. Therefore, animal models to test for ASA effectiveness remain of interest. Our objective was to verify the usefulness of multiparametric whole-blood impedance aggregometry and thromboxane A(2) generation, which are the most popular techniques used for monitoring of ASA treatment effectiveness.

METHODS

Using multiparametric analysis of whole-blood impedance aggregometry, we examined which parameters of platelet aggregation or disaggregation allow for the best discrimination between ASA-treated (4 or 40 mg/kg for 60 days) and non-treated male rats. The effectiveness of ASA-mediated inhibition of platelet cyclooxygenase-1 was verified by determination of plasma thromboxane B(2) and urine 11-dehydro-thromboxane B(2), accepted as reference assays for monitoring of ASA-mediated platelet cyclooxygenase-1 inhibition.

RESULTS

Two of the platelet agonists used, collagen (1 mg/L) and arachidonic acid (0.5 mmol/L), allowed discrimination of control and ASA-treated animals, whereas adenosine diphosphate (5 micromol/L) was not effective. It is noteworthy that only ASA-mediated changes in duration of the rising phase for platelet aggregation and the area under the curve for collagen-induced aggregation allowed significant discrimination between low and high ASA dose and remained correlated with the reference parameter, plasma thromboxane B(2).

CONCLUSIONS

Analysis of aggregation curves, routinely based only on the amplitude and rate of platelet aggregation, may not be enough discriminative to distinguish between varying ASA doses and treatment schedules.

Antiplatelet Agents: Current Drugs and Future Trends

Antiplatelet drugs in clinical use are discussed in terms of their mechanisms of action and the relevancy of that to the physiology of platelets and the pathophysiology of arterial thrombosis. Current clinical usage is outlined in detail for each drug. Experimental antiplatelet drugs also are discussed.

Increased platelet deposition on extracellular matrix under flow conditions in patients with antiphospholipid syndrome who experience thrombotic events

OBJECTIVE

To assess platelet function under defined flow conditions in patients with antiphospholipid syndrome (APS) and to correlate the results with thrombotic complications and the presence of subsets of antiphospholipid antibodies (aPL), lupus anticoagulant (LAC), and/or anticardiolipin antibodies (aCL).

METHODS

We studied 88 randomized APS patients with or without a history of thrombosis. Seventeen patients with other thrombosis (no APS) and 26 healthy subjects served as controls. Platelet adhesion and aggregation on the extracellular matrix were measured with a cone-and-plate(let) analyzer (CPA) by examining the percentage of total area covered with platelets (surface coverage [SC]) and the mean size of surface-bound objects (average size [AS]) and were compared with platelet responses to different ADP concentrations by conventional aggregometry.

RESULTS

Under defined flow conditions, SC and AS were significantly higher for venous thrombosis and arterial thrombosis in APS patients compared with no thrombosis, other thrombosis, and healthy control groups. The increased platelet adhesion and aggregation in APS patients with thrombotic events was associated with higher levels of von Willebrand factor (vWF) antigen (mean +/- SD 230.6 +/- 51.2%) and ristocetin cofactor activity (181.0 +/- 36.0%). No change in CPA and vWF parameters was found in APS patients with positive results for aPL who did not undergo thrombotic events or in patients with other thrombosis. The CPA parameters were neither associated with the high response of platelets to ADP nor associated with the presence of LAC, aCL, or both. The CPA parameters were similarly increased irrespective of aspirin use. The results suggest that the increased adhesion properties of platelets in APS patients could be mediated by high levels and activity of vWF. This complements the known ability of APS antibodies to enhance platelet response to agonists in conventional aggregometry.

CONCLUSION

The CPA test was found to be valuable in differentiating APS patients with and without thrombotic complications.