Vorapaxar in the secondary prevention of atherothrombosis

Crystal Structures of d-Lyxono-1,4-lactone and Its O-Tosyl Derivative

γ- and δ-lactones were formed by bromine oxidation of commercially available D-lyxose, as confirmed by IR analysis. The former was isolated, and its structure was confirmed by NMR spectra and X-ray analysis. In this structure, the presence of both intermolecular and intramolecular hydrogen bonds was found. Intermolecular interactions in the crystal were illustrated using the Hirshfeld surfaces. Due to steric reasons, 3,5-O-isopropylidene-d-lyxono-1,4-lactone was formed, which in a further step led to the formation of a 2-O-tosyl derivative. Its structure was confirmed by X-ray diffraction analysis. The additional ring of the O-isopropylidene derivative caused the lactone ring to change conformation to 3E. In the crystal structure of this compound, only C-H⸱⸱⸱O intermolecular interactions were present, as confirmed by the Hirshfeld surface analysis.

Antiplatelet strategies: past, present, and future

Antiplatelet therapy plays a critical role in the prevention and treatment of major cardiovascular diseases triggered by thrombosis. Since the 1900s, significant progress in reducing morbidity and death caused by cardiovascular diseases has been made. However, despite the development and approval of drugs that specifically target the platelet, including inhibitors for cycloxygenase-1, P2Y12 receptor, integrin αIIbβ3, phosphodiesterases, and protease-activated receptor 1, the risk of recurrent thrombotic events remains high, and the increased risk of bleeding is a major concern. Scientific advances in our understanding of the role of platelets in haemostasis and thrombosis have revealed novel targets, such as protease-activated receptor 4 (PAR4), glycoprotein Ib (GPIb)-V-IX complex, glycoprotein VI, and 12-lipoxygenase. The antithrombotic effects and safety of the pharmacologic inhibition of these targets are currently under investigation in clinical studies. This review provides an overview of drugs in early development to target the platelet and those in current use in clinical practice. Furthermore, it describes the emerging drug targets being developed and studied to reduce platelet activity and outlines potential novel therapeutic targets in the platelet.

Thrombin receptor PAR1 silencing in endothelial colony-forming cells modifies stemness and vasculogenic properties

BACKGROUND

The involvement of thrombin receptor PAR1 in blood vessel development has been largely demonstrated in knockout mice; however, its implication in adult mouse angiogenesis seems very moderate.

OBJECTIVES

We aimed to explore the potential relationships between PAR1, stemness, and angiogenic properties of human endothelial colony-forming cells (ECFCs).

METHODS AND RESULTS

PAR1 activation on ECFCs using the selective PAR1-activating peptide induced a significant decrease in CD133 expression (RTQ-PCR analysis). In line, silencing of PAR1 gene expression with siRNA increased CD133 mRNA as well as intracellular CD133 protein expression. To confirm the link between CD133 and PAR1, we explored the association between PAR1 and CD133 levels in fast and slow fibroblasts prone to reprogramming. An imbalance between PAR1 and CD133 levels was evidenced, with a decreased expression of PAR1 in fast reprogramming fibroblasts expressing a high CD133 level. Regarding in vitro ECFC angiogenic properties, PAR1 silencing with specific siRNA induced cell proliferation evidenced by the overexpression of Ki67. However, it did not impact migration properties nor ECFC adhesion on smooth muscle cells or human arterial endothelial cells. In a mouse model of hind-limb ischemia, PAR1 silencing in ECFCs significantly increased postischemic revascularization compared to siCtrl-ECFCs along with a significant increase in cutaneous blood flows (P < .0001), microvessel density (P = .02), myofiber regeneration (P < .0001), and human endothelial cell incorporation in muscle (P < .0001).

CONCLUSION

In conclusion, our work describes for the first time a link between PAR1, stemness, and vasculogenesis in human ECFCs.

Tumor Cell-Induced Platelet Aggregation as an Emerging Therapeutic Target for Cancer Therapy

Tumor cells have the ability to induce platelet activation and aggregation. This has been documented to be involved in tumor progression in several types of cancers, such as lung, colon, breast, pancreatic, ovarian, and brain. During the process, platelets protect circulating tumor cells from the deleterious effects of shear forces, shield tumor cells from the immune system, and provide growth factors, facilitating metastatic spread and tumor growth at the original site as well as at the site of metastasis. Herein, we present a wider view on the induction of platelet aggregation by specific factors primarily developed by cancer, including coagulation factors, adhesion receptors, growth factors, cysteine proteases, matrix metalloproteinases, glycoproteins, soluble mediators, and selectins. These factors may be presented on the surface of tumor cells as well as in their microenvironment, and some may trigger more than just one simple receptor-ligand mechanism. For a better understanding, we briefly discuss the physiological role of the factors in the platelet activation process, and subsequently, we provide scientific evidence and discuss their potential role in the progression of specific cancers. Targeting tumor cell-induced platelet aggregation (TCIPA) by antiplatelet drugs may open ways to develop new treatment modalities. On the one hand, it may affect patients' prognosis by enhancing known therapies in advanced-stage tumors. On the other hand, the use of drugs that are mostly easily accessible and widely used in general practice may be an opportunity to propose an unparalleled antitumor prophylaxis. In this review, we present the recent discoveries of mechanisms by which cancer cells activate platelets, and discuss new platelet-targeted therapeutic strategies.

Which proteinase-activated receptor-1 antagonist is better?: Evaluation of vorapaxar and parmodulin-2 effects on human left internal mammary artery endothelial function

OBJECTIVE

Endothelial dysfunction occurs as an early event in cardiovascular disease. Previously, vorapaxar, a proteinase-activated receptor-1 antagonist, was shown to cause endothelial damage in a cell culture study. Therefore, our study aimed to compare the effects of vorapaxar and parmodulin-2, proteinase-activated receptor-1 biased agonist, on human left internal mammary artery endothelial function in vitro.

METHOD

Isolated arteries were hung in the organ baths. Acetylcholine responses (10^-11-10^-6 M) were obtained in endothelium-intact tissues the following incubation with vorapaxar/parmodulin-2 (10^-6 M) to determine the effects of these molecules on the endothelium-dependent relaxation. Subsequently, endothelium-dependent relaxation responses of tissues were investigated in the presence of L-NAME (10^-4 M), L-arginine (10^-5 M), indomethacin (10^-5 M), and charybdotoxin-apamin (10^-7 M) in addition to vorapaxar/parmodulin-2 incubation. Besides, the effect of these molecules on endothelium-independent relaxation response was evaluated with sodium nitroprusside (10^-11-10^-6 M). Finally, the sections of human arteries were imaged using a transmission electron microscope, and the integrity of the endothelial layer was evaluated.

RESULTS

We found that vorapaxar caused significant endothelial dysfunction by disrupting nitric oxide and endothelium-derived hyperpolarizing factor-dependent relaxation mechanisms. Parmodulin-2 did not cause endothelial damage. Neither vorapaxar nor parmodulin-2 disrupted endothelium-independent relaxation responses. The effect of vorapaxar on the endothelial layer was supported by the transmission electron microscope images.

CONCLUSION

Parmodulin-2 may be a better option than vorapaxar in treating cardiovascular diseases since it can inhibit PAR-1 without caused endothelial dysfunction.

Net clinical benefit of antiplatelet therapy was affected by patient preferences: A personalized benefit-risk assessment

OBJECTIVE

To assess the effect of patient preferences on the net clinical benefit (NCB) of an antiplatelet therapy for the secondary prevention of cardiovascular complications.

STUDY DESIGN AND SETTING

Risk equations were developed to estimate the individual predicted risk of key outcomes of antiplatelet treatment in patients with a prior myocardial infarction using the Clinical Practice Research Datalink linked to the Hospital Episode Statistics and UK Office of National Statistics databases. Patient preferences for outcomes of antiplatelet therapies were elicited in a separate discrete choice experiment survey. Trial hazard ratios, relative to placebo, were used to calculate the per-patient NCB using equal or preference weighting of outcomes.

RESULTS

Risk equations were estimated using 31,941 adults in the Clinical Practice Research Datalink population, of which 22,125 were included in the benefit-risk assessment. The mean NCB was lower in the preference-weighted than in the equal-weighted analysis (0.040 vs 0.057; p < 0.0001), but the direction of effect was unchanged by the weighting. In analyses stratified by the presence of bleeding risk factors, including preference weighting altered the ranking of subgroups by NCB.

CONCLUSION

Patient preference weighting may have a significant effect on NCB and should be included in personalized benefit-risk assessments.

A Review of the Pharmacological Activities and Recent Synthetic Advances of γ-Butyrolactones

γ-Butyrolactone, a five-membered lactone moiety, is one of the privileged structures of diverse natural products and biologically active small molecules. Because of their broad spectrum of biological and pharmacological activities, synthetic methods for γ-butyrolactones have received significant attention from synthetic and medicinal chemists for decades. Recently, new developments and improvements in traditional methods have been reported by considering synthetic efficiency, feasibility, and green chemistry. In this review, the pharmacological activities of natural and synthetic γ-butyrolactones are described, including their structures and bioassay methods. Mainly, we summarize recent advances, occurring during the past decade, in the construction of γ-butyrolactone classified based on the bond formation in γ-butyrolactone between (i) C5-O1 bond, (ii) C4-C5 and C2-O1 bonds, (iii) C3-C4 and C2-O1 bonds, (iv) C3-C4 and C5-O1 bonds, (v) C2-C3 and C2-O1 bonds, (vi) C3-C4 bond, and (vii) C2-O1 bond. In addition, the application to the total synthesis of natural products bearing γ-butyrolactone scaffolds is described.

Effects of vorapaxar on clot characteristics, coagulation, inflammation, and platelet and endothelial function in patients treated with mono- and dual-antiplatelet therapy

BACKGROUND

Vorapaxar is indicated with standard antiplatelet therapy (APT) in patients with a history of myocardial infarction (MI) or peripheral arterial disease (PAD).

OBJECTIVES

To evaluate the comparative effects of vorapaxar on platelet-fibrin clot characteristics (PFCC), coagulation, inflammation, and platelet and endothelial function during treatment with daily 81 mg aspirin (A), 75 mg clopidogrel (C), both (C + A), or neither.

METHODS

Thrombelastography, conventional platelet aggregation (PA), ex vivo endothelial function by ENDOPAT, coagulation, platelet activation/inflammation marked by urinary 11-dehydrothromboxane B2 (UTxB2 ) and safety were determined in patients who were APT naïve (n = 21), on C (n = 8), on A (n = 29), and on A + C (n = 23) during 1 month of vorapaxar therapy and 1 month of offset.

RESULTS

Vorapaxar had no effect on PFCC, ADP- or collagen-induced PA, thrombin time, fibrinogen, PT, PTT, von Willebrand factor (vWF), D-dimer, or endothelial function (P > .05 in all groups). Inhibition of SFLLRN (PAR-1 activating peptide)-stimulated PA by vorapaxar was accelerated by A + C at 2 hours (P < .05 versus other groups) with nearly complete inhibition by 30 days that persisted through 30 days after discontinuation in all groups (P < .001). SFLLRN-induced PA during offset was lower in APT patients versus APT-naïve patients (P < .05). Inhibition of UTxB2 was observed in APT-naive patients treated with vorapaxar (P < .05). Minor bleeding was only observed in C-treated patients.

CONCLUSION

Vorapaxar had no influence on PFCC measured by thrombelastography, coagulation, or endothelial function irrespective of APT. Inhibition of protease activated receptor (PAR)-1 mediated platelet aggregation by vorapaxar was accelerated by A + C and offset was prolonged by concomitant APT. Vorapaxar-induced anti-inflammatory effects were observed in non-aspirin-treated patients.

Effects of three-month streptozotocin-induced diabetes in mice on blood platelet reactivity, COX-1 expression and adhesion potential

Diabetes is associated with an increased risk of cardiovascular disease. This is partially attributed to an altered activation status of blood platelets in this disease. Previously, alterations have been shown in COX-1 and protease activated receptor (PAR)-3 receptor expression in platelets in two animal models of diabetes, there have not been studies which address expression of these proteins in mice with long-term streptozotocin (STZ)-induced diabetes. We have also addressed the effect of diabetes on platelet adhesion under flow conditions. With the use of flow cytometry, we have shown that certain markers of platelet basal activation, such as active form of α_{II b} β₃ and of CD40L were increased in STZ-induced diabetic mice. Platelets from STZ-induced diabetic mice were also more reactive when stimulated with PAR-4 activating peptide as revealed by higher expression of active form of α_{II b} β₃ , membrane-bound on vWillebrand Factor and binding of exogenous fluorescein isothyanate-labelled fibrinogen. Expression of COX-1 and production of thromboxane A₂ in platelets of STZ-induced diabetic mice were higher than in control animals. We observed no effect of diabetes on ability of platelets to form stable adhesions with fibrinogen in flow conditions. We conclude that although certain similarities exist between patterns of activation of platelets in animal models of diabetes, the differences should also be taken into account.

Platelet receptors as therapeutic targets: Past, present and future

Anti-platelet drugs reduce arterial thrombosis after plaque rupture and erosion, prevent stent thrombosis and are used to prevent and treat myocardial infarction and ischaemic stroke. Some of them may also be helpful in treating less frequent diseases such as thrombotic thrombocytopenic purpura. The present concise review aims to cover current and future developments of anti-platelet drugs interfering with the interaction of von Willebrand factor (VWF) with glycoprotein (GP) Ibα, and directed against GPVI, GPIIb/IIIa (integrin αIIbβ3), the thrombin receptor PAR-1, and the ADP receptor P2Y12. The high expectations of having novel antiplatelet drugs which selectively inhibit arterial thrombosis without interfering with normal haemostasis could possibly be met in the near future.

Pharmacokinetic drug evaluation of vorapaxar for secondary prevention after acute coronary syndrome

INTRODUCTION

Vorapaxar is the first protease-activated receptor-1 inhibitor approved for clinical use. Its main indication is the reduction in thrombotic cardiovascular events in patients with previous myocardial infarction or symptomatic peripheral artery disease. Areas covered: This article reviews the pharmacokinetics of vorapaxar and its potential use in secondary prevention after an acute coronary syndrome. Expert opinion: Vorapaxar inhibits platelet aggregation mediated by thrombin. This effect is carried out without affecting to coagulation parameters and bleeding times. This drug has showed a significant reduction of cardiovascular events in patients with chronic atherosclerosis but not during the admission for an acute coronary syndrome. The rate of major bleeding found in patients treated with vorapaxar in randomized trials was consistently higher than placebo in most of the analyzed subgroups. For this reason, cautious evaluation of risk-benefit profiles should be required before prescribing this drug.

State of the art: Oral antiplatelet therapy

Platelet adhesion, activation, and aggregation are central to the propagation of coronary thrombosis following rupture, fissure, or erosion of an atherosclerotic plaque. This chain of deleterious events underlies the pathophysiological process leading to an acute coronary syndrome. Therefore, oral antiplatelet therapy has become the cornerstone of therapy for the management of acute coronary syndrome and the prevention of ischemic complications associated with percutaneous coronary intervention. Landmark trials have established aspirin, and the addition of clopidogrel to aspirin, as key therapeutic agents in the context of acute coronary syndrome and percutaneous coronary intervention. Dual antiplatelet therapy has been the guideline-mandated standard of care in acute coronary syndrome and percutaneous coronary intervention. Despite the proven efficacy of dual antiplatelet therapy, adverse ischemic events continue to occur and this has stimulated the development of novel, more potent antiplatelet agents. We focus this state-of-the-art review on the most recent advances in oral antiplatelet therapy, treading the tightrope of potency versus bleeding risk, the quest to determine the optimal duration of dual antiplatelet therapy and future of personalized antiplatelet therapy.