The role of antiplatelet therapy in the management of acute coronary syndromes

The effect of hormone therapy and tibolone on serum CD40L and ADAM-8 in healthy post-menopausal women

BACKGROUND/AIM

The role of neutrophils and platelets in atherothrombotic disease is well established. The aim of our study was to investigate the effect of HT and tibolone on the soluble markers of neutrophil and platelet activation, "a disentigrin and metalloproteinase domain" (ADAM-8) and CD40 ligand (CD40L) respectively, in healthy post-menopausal women.

SUBJECTS AND METHODS

One hundred and six healthy post-menopausal women were randomly allocated to: estradiol plus drospirenone (E₂/DSP), E₂ hemihydrate 1 mg plus norethisterone acetate (E₂/NETA) 0.5 mg, and tibolone 2.5 mg. Serum ADAM-8 and CD40L were measured at baseline and at 6 months.

RESULTS

Baseline values of ADAM-8 and CD40L were similar between groups. No significant correlation was revealed between ADAM-8 or CD40L and parameters related to cardiovascular risk factors in each group. No significant changes were observed between baseline values and values at 6 months (E₂/DSP group: ADAM-8: 267.4±71.3 pg/ml vs 270.7±42.8 pg/ml, p=0.86, CD40L: 6.43±3.13 vs 6.79±2.70 ng/ml, p=0.67), (E₂/NETA group: ADAM-8: 308.3±64.3 vs 294.7±57.7 pg/ml, p=0.40, CD40L: 9.68±2.81 vs 8.59±5.13 ng/ml, p=0.51), (tibolone group: ADAM-8: 307.5±87.5 vs 289±48.1 pg/ml, p=0.48, CD40L: 9.46±4.30 vs 9.26±4.60 ng/ml, p=0.99).

CONCLUSIONS

Our study has not revealed an association between estrogen plus progestin treatment or tibolone on serum ADAM-8 and CD40L levels in healthy post-menopausal women. Larger prospective studies are needed to further investigate the effect of low-dose HT or tibolone on serum markers of neutrophil and platelet activation.

Thrombin receptor (PAR-1) antagonists as novel antithrombotic agents

In addition to its central role in haemostasis and wound healing, thrombin activates platelets and smooth muscle cells by proteolytic activation of cell surface protease-activated receptor-1 (PAR-1), which is also known as the thrombin receptor. Thrombin is the most potent activator of human platelets and, as such, a thrombin receptor antagonist is likely to exert potent antithrombotic effect in platelet-rich arterial thrombosis. As thrombin receptor antagonism does not inhibit the ability of thrombin to generate fibrin, such an agent is likely to have less bleeding liability than conventional anticoagulants. The proof-of-concept of the antithrombotic effect of PAR-1 antagonists has been established in several non-human primate models. The current success of PAR-1 research is underscored by the advancement of two candidates into clinical trails for acute coronary syndrome by Schering-Plough and Eisai Company.

Developments in antiplatelet therapy for acute coronary syndromes and considerations for long-term management

OBJECTIVE

This article reviews the currently available antiplatelet therapies and emerging investigational drugs in the treatment of acutecoronary syndrome (ACS), and considerations for primary and secondary prevention in the long-term management of ACS patients undergoing percutaneous coronary intervention (PCI).

RESEARCH DESIGN AND METHODS

Primary studies and reviews in the peer-reviewed, English-language literature were identified through searches of MEDLINE (1966-2008) using the terms 'acute coronary syndrome', 'antiplatelet', 'aspirin', 'long-term management', 'P2Y(12) receptor', and 'thienopyridine'. Additional references were obtained by searching the reference lists of the identified articles. Articles were included if they were recently published and pertinent, patient-focused, and authors were recognized as leaders in the field. Current review is limited by literature search on single database.

RESULTS

Platelets play a major role in atherogenesis and the formation of thrombi, the main events in the pathogenesis of ACS. Although aspirin is an effective antiplatelet agent, efficacy and safety data from a number of randomized clinical trials on atherothrombotic disease support the use of dual antiplatelet therapies such as aspirin and thienopyridines over single antiplatelet therapy for ACS and up to 1 year following ACS. Antiplatelet agents reduce, but do not eliminate, ischemic events after ACS due, in part, to variable individual response (or resistance) in antiplatelet agents, non-compliance, progression of atherosclerosis, modest inhibition of platelet aggregation (IPA) levels and other factors. Several antiplatelet agents, including novel P2Y(12)-receptor antagonists and thrombin-receptor antagonists, are currently under investigation for ACS and primary and secondary prevention in the long-term management of patients undergoing PCI.

CONCLUSIONS

Current antiplatelet therapies have clinical benefits such as reducing immediate and long-term cardiovascular risk, but substantial residual risk remains indicating a need for new therapeutic agents. Additional large randomized trials are necessary to determine the most appropriate treatment regimens for ACS patients.

Heterotricyclic himbacine analogs as potent, orally active thrombin receptor (protease activated receptor-1) antagonists

Pursuing our earlier efforts in the himbacine-based thrombin receptor antagonist area, we have synthesized a series of compounds that incorporate heteroatoms in the C-ring of the tricyclic motif. This effort has resulted in the identification of several potent heterocyclic analogs with excellent affinity for the thrombin receptor. Several of these compounds demonstrated robust inhibition of platelet aggregation in an ex vivo model in cynomolgus monkeys following oral administration. A detailed profile of 28b, a benchmark compound in this series, with a Ki of 4.3 nM, is presented.