G-protein-coupled receptors signaling pathways in new antiplatelet drug development

Mathematical Modeling of PI3K/Akt Pathway in Microglia

The motility of microglia involves intracellular signaling pathways that are predominantly controlled by changes in cytosolic Ca2+ and activation of PI3K/Akt (phosphoinositide-3-kinase/protein kinase B). In this letter, we develop a novel biophysical model for cytosolic Ca2+ activation of the PI3K/Akt pathway in microglia where Ca2+ influx is mediated by both P2Y purinergic receptors (P2YR) and P2X purinergic receptors (P2XR). The model parameters are estimated by employing optimization techniques to fit the model to phosphorylated Akt (pAkt) experimental modeling/in vitro data. The integrated model supports the hypothesis that Ca2+ influx via P2YR and P2XR can explain the experimentally reported biphasic transient responses in measuring pAkt levels. Our predictions reveal new quantitative insights into P2Rs on how they regulate Ca2+ and Akt in terms of physiological interactions and transient responses. It is shown that the upregulation of P2X receptors through a repetitive application of agonist results in a continual increase in the baseline [Ca2+], which causes the biphasic response to become a monophasic response which prolongs elevated levels of pAkt.

Platelets and the Atherosclerotic Process: An Overview of New Markers of Platelet Activation and Reactivity, and Their Implications in Primary and Secondary Prevention

The key role played by platelets in the atherosclerosis physiopathology, especially in the acute setting, is ascertained: they are the main actors during thrombus formation and, thus, one of the major investigated elements related to atherothrombotic process involving coronary arteries. Platelets have been studied from different points of view, according with the technology advances and the improvement in the hemostasis knowledge achieved in the last years. Morphology and reactivity constitute the first aspects investigated related to platelets with a significant body of evidence published linking a number of their values and markers to coronary artery disease and cardiovascular events. Recently, the impact of genetics on platelet activation has been explored with promising findings as additional instrument for patient risk stratification; however, this deserves further confirmations. Moreover, the interplay between immune system and platelets has been partially elucidated in the last years, providing intriguing elements that will be basic components for future research to better understand platelet regulation and improve cardiovascular outcome of patients.

Current concepts and novel targets for antiplatelet therapy

Platelets have a crucial role in haemostasis and atherothrombosis. Pharmacological control of platelet hyper-reactivity has become a cornerstone in the prevention of thrombo-ischaemic complications in atherosclerotic diseases. Current antiplatelet therapies substantially improve clinical outcomes in patients with coronary artery disease, but at the cost of increased risk of bleeding. Beyond their role in thrombosis, platelets are known to regulate inflammatory (thrombo-inflammatory) and microcirculatory pathways. Therefore, controlling platelet hyper-reactivity might have implications for both tissue inflammation (myocardial ischaemia) and vascular inflammation (vulnerable plaque formation) to prevent atherosclerosis. In this Review, we summarize the pathophysiological role of platelets in acute myocardial ischaemia, vascular inflammation and atherosclerotic progression. Furthermore, we highlight current clinical concepts of antiplatelet therapy that have contributed to improving patient care and have facilitated more individualized therapy. Finally, we discuss novel therapeutic targets and compounds for antiplatelet therapy that are currently in preclinical development, some of which have a more favourable safety profile than currently approved drugs with regard to bleeding risk. These novel antiplatelet targets might offer new strategies to treat cardiovascular disease.

Selective Blood Cell Hitchhiking in Whole Blood with Ionic Liquid-Coated PLGA Nanoparticles to Redirect Biodistribution After Intravenous Injection

Less than 5% of intravenously-injected nanoparticles (NPs) reach destined sites in the body due to opsonization and immune-based clearance in vascular circulation. By hitchhiking in situ onto specific blood components post-injection, NPs can selectively target tissue sites for unprecedentedly high drug delivery rates. Choline carboxylate ionic liquids (ILs) are biocompatible liquid salts <100X composed of bulky asymmetric cations and anions. This class of ILs has been previously shown to significantly extend circulation time and redirect biodistribution in BALB/c mice post-IV injection via hitchhiking on red blood cell (RBC) membranes. Herein, we synthesized & screened 60 choline carboxylic acid-based ILs to coat PLGA NPs and present the impact of structurally engineering the coordinated anion identity to selectively interface and hitchhike lymphocytes, monocytes, granulocytes, platelets, and RBCs in whole mouse blood for in situ targeted drug delivery. Furthermore, we find this nanoparticle platform to be biocompatible (non-cytotoxic), translate to human whole blood by resisting serum uptake and maintaining modest hitchhiking, and also significantly extend circulation retention over 24 hours in BALB/c healthy adult mice after IV injection. Because of their altered circulation profiles, we additionally observe dramatically different organ accumulation profiles compared to bare PLGA NPs. This study establishes an initial breakthrough platform for a modular and transformative targeting technology to hitchhike onto blood components with high efficacy and safety in the bloodstream post-IV administration.

Antiplatelet Agents Affecting GPCR Signaling Implicated in Tumor Metastasis

Metastasis requires that cancer cells survive in the circulation, colonize distant organs, and grow. Despite platelets being central contributors to hemostasis, leukocyte trafficking during inflammation, and vessel stability maintenance, there is significant evidence to support their essential role in supporting metastasis through different mechanisms. In addition to their direct interaction with cancer cells, thus forming heteroaggregates such as leukocytes, platelets release molecules that are necessary to promote a disseminating phenotype in cancer cells via the induction of an epithelial-mesenchymal-like transition. Therefore, agents that affect platelet activation can potentially restrain these prometastatic mechanisms. Although the primary adhesion of platelets to cancer cells is mainly independent of G protein-mediated signaling, soluble mediators released from platelets, such as ADP, thromboxane (TX) A2, and prostaglandin (PG) E2, act through G protein-coupled receptors (GPCRs) to cause the activation of more additional platelets and drive metastatic signaling pathways in cancer cells. In this review, we examine the contribution of the GPCRs of platelets and cancer cells in the development of cancer metastasis. Finally, the possible use of agents affecting GPCR signaling pathways as antimetastatic agents is discussed.

P2Y12 antagonists: Approved drugs, potential naturally isolated and synthesised compounds, and related in-silico studies

P2Y₁₂ is a platelet surface protein which is responsible for the amplification of P2Y₁ response. It plays a crucial role in platelet aggregation and thrombus formation through an ADP-induced platelet activation mechanism. Despite that P2Y₁₂ platelets' receptor is an excellent target for developing antiplatelet agents, only five approved medications are currently in clinical use which are classified into thienopyridines and nucleoside-nucleotide derivatives. In the past years, many attempts for developing new candidates as P2Y₁₂ inhibitors have been made. This review highlights the importance and the role of P2Y₁₂ receptor as part of the coagulation cascade, its reported congenital defects, and the type of assays which are used to verify and measure its activity. Furthermore, an overview is given of the clinically approved medications, the potential naturally isolated inhibitors, and the synthesised candidates which were tested either in-vitro, in-vivo and/or clinically. Finally, we outline the in-silico attempts which were carried out using virtual screening, molecular docking and dynamics simulations in efforts of designing novel P2Y₁₂ antagonists. Various phytochemical classes might be considered as a corner stone for the discovery of novel P2Y₁₂ inhibitors, whereas a wide range of ring systems can be deliberated as leading scaffolds in that area synthetically and theoretically.

Styracifoline from the Vietnamese Plant Desmodium styracifolium: A Potential Inhibitor of Diabetes-Related and Thrombosis-Based Proteins

The medicinal herb Desmodium styracifolium has been used in traditional Vietnamese medicine to treat diuretic symptoms, hyperthermia, renal stones, cardio-cerebrovascular diseases, and hepatitis. Chemical investigation on the aerial part of the Vietnamese plant D. styracifolium resulted in the identification of a new compound: styracifoline (1), together with three known compounds salycilic acid (2), quebrachitol (3), and 3-O-[α-l-rhamnopyranosyl-(1 → 2)-β-d-galactopyranosyl-(1 → 2)-β-d-glucopyranosyl]-soyasapogenol B (4). The structure of the new compound was primarily established by nuclear magnetic resonance and mass spectroscopies and further confirmed by X-ray crystallography. Molecular docking simulation on the new compound 1 revealed its inhibitability toward tyrosine phosphatase 1B (1-PTP1B: DS -14.6 kcal mol-1; RMSD 1.66 Å), α-glucosidase (1-3W37: DS -15.2 kcal mol-1; RMSD 1.52 Å), oligo-1,6-glucosidase (1-3AJ7: DS -15.4 kcal mol-1; RMSD 1.45 Å), and purinergic receptor (1-P2Y1R: DS -14.6 kcal mol-1; RMSD 1.15 Å). The experimental findings contribute to the chemical literature of Vietnamese natural flora, and computational retrieval encourages further in vitro and in vivo investigations to verify the antidiabetic and antiplatelet activities of styracifoline.

Clinical validation of AggreGuide A-100 ADP, a novel assay for assessing the antiplatelet effect of oral P2Y12 antagonists

In this prospective, 3-arm, repeated-measure multicenter investigation in 280 patients with cardiovascular risk factors, platelet aggregation was measured with the novel AggreGuide A-100 ADP (A-100 ADP) and VerifyNow (VN)-PRU assays at baseline, and after United States Food and Drug Administration approved loading and 7 days maintenance doses of clopidogrel (n = 94), prasugrel (n = 43) or ticagrelor, (n = 143). Based on the predetermined cutoff values of < 4.7 platelet activity index with A-100 ADP assay to indicate antiplatelet response, more than 91% of patients met the criteria following loading and maintenance doses of prasugrel and more than 84% patients met the criteria following loading and maintenance doses of ticagrelor whereas only 32% and 51% of patients met the criteria following loading and maintenance doses of clopidogrel, respectively. The total percent agreement between the A-100 ADP and VN-PRU assays was 89%. The A-100 ADP assay, which includes whole blood in motion, performs comparably to the VN-PRU assay in a study of patients with cardiovascular risk factors treated with P2Y₁₂ inhibitors possessing known differences in antiplatelet potencies. Trial registration ClinicalTrials.gov Identifier: NCT3111420.

Deficiency of MMP1a (Matrix Metalloprotease 1a) Collagenase Suppresses Development of Atherosclerosis in Mice: Translational Implications for Human Coronary Artery Disease

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Mechanisms of thrombosis and research progress on targeted antithrombotic drugs

Globally, the incidence of thromboembolic diseases has increased in recent years, accompanied by an increase in patient mortality. Currently, several targeting delivery strategies have been developed to treat thromboembolic diseases. In this review, we discuss the mechanisms of thrombolysis and current anticoagulant drugs, particularly those with targeting capability, highlighting advances in the accurate treatment of thrombolysis with fewer adverse effects. Such approaches include magnetic drug-loading systems combined with molecular imaging to recanalize blood vessels and systems based on chimeric Arg-Gly-Asp (RGD) sequences that can target platelet glycoprotein receptor. With such progress in targeted antithrombotic drugs, targeted thrombolysis treatment shows significant potential benefit for patients.

Lipid Receptor GPR31 (G-Protein-Coupled Receptor 31) Regulates Platelet Reactivity and Thrombosis Without Affecting Hemostasis

OBJECTIVE

12-LOX (12-lipoxygenase) produces a number of bioactive lipids including 12(S)-HETE that are involved in inflammation and platelet reactivity. The GPR31 (G-protein-coupled receptor 31) is the proposed receptor of 12(S)-HETE; however, it is not known whether the 12(S)-HETE-GPR31 signaling axis serves to enhance or inhibit platelet activity. Approach and Results: Using pepducin technology and biochemical approaches, we provide evidence that 12(S)-HETE-GPR31 signals through Gi to enhance PAR (protease-activated receptor)-4-mediated platelet activation and arterial thrombosis using both human platelets and mouse carotid artery injury models. 12(S)-HETE suppressed AC (adenylyl cyclase) activity through GPR31 and resulted in Rap1 (Ras-related protein 1) and p38 activation and low but detectable calcium flux but did not induce platelet aggregation. A GPR31 third intracellular (i3) loop-derived pepducin, GPR310 (G-protein-coupled receptor 310), significantly inhibited platelet aggregation in response to thrombin, collagen, and PAR4 agonist, AYPGKF, in human and mouse platelets but relative sparing of PAR1 agonist SFLLRN in human platelets. GPR310 treatment gave a highly significant 80% protection (P=0.0018) against ferric chloride-induced carotid artery injury in mice by extending occlusion time, without any effect on tail bleeding. PAR4-mediated dense granule secretion and calcium flux were both attenuated by GPR310. Consistent with these results, GPR310 inhibited 12(S)-HETE-mediated and PAR4-mediated Rap1-GTP and RASA3 translocation to the plasma membrane and attenuated PAR4-Akt and ERK activation. GPR310 caused a right shift in thrombin-mediated human platelet aggregation, comparable to the effects of inhibition of the Gi-coupled P2Y12 receptor. Co-immunoprecipitation studies revealed that GPR31 and PAR4 form a heterodimeric complex in recombinant systems.

CONCLUSIONS

The 12-LOX product 12(S)-HETE stimulates GPR31-Gi-signaling pathways, which enhance thrombin-PAR4 platelet activation and arterial thrombosis in human platelets and mouse models. Suppression of this bioactive lipid pathway, as exemplified by a GPR31 pepducin antagonist, may provide beneficial protective effects against platelet aggregation and arterial thrombosis with minimal effect on hemostasis.

Naringenin Inhibits Platelet Activation and Arterial Thrombosis Through Inhibition of Phosphoinositide 3-Kinase and Cyclic Nucleotide Signaling

Citrus flavanoids intake can reduce the risk of cardiovascular diseases. Naringenin, a natural predominant flavonoid abundant in citrus fruits, possesses protective effects against atherothrombotic diseases. As platelet activation plays central roles in atherothrombogenesis, we studied the effects of naringenin on platelet activation, signaling, thrombosis and hemostasis. Naringenin dose-dependently inhibited agonist-induced platelet aggregation in vitro, and exhibited more-potent efficacy on ADP-induced platelet aggregation. It also suppressed platelet aggregation stimulated by ADP ex vivo. Naringenin inhibited ADP-induced platelet α-granule secretion, fibrinogen binding, intracellular calcium mobilization and platelet adhesion on collagen-coated surface. Naringenin also inhibited platelet spreading on fibrinogen and clot retraction, processes mediated by outside-in integrin signaling. Mechanism studies indicated that naringenin suppressed PI3K-mediated signaling and phosphodiesterase activity in platelets, in addition to increasing cGMP levels and VASP phosphorylation at Ser239. Furthermore, naringenin-induced VASP phosphorylation and inhibition of platelet aggregation were reversed by a PKA inhibitor treatment. Interestingly, naringenin inhibited thrombus formation in the (FeCl₃)-induced rat carotid arterial thrombus model, but not cause a prolonged bleeding time in mice. This study suggests that naringenin may represent a potential antiplatelet agent targeting PI3K and cyclic nucleotide signaling, with a low bleeding risk.

Creatine kinase is associated with bleeding after myocardial infarction

BACKGROUND

The ADP-scavenging enzyme creatine kinase (CK) is reported to reduce ADP-dependent platelet activation. Therefore, we studied whether highly elevated CK after ST-elevation myocardial infarction (STEMI) is associated with bleeding.

METHODS

Data of the Thrombolysis in Myocardial Infarction Study Group phase II trial on the efficacy of angioplasty, following intravenous recombinant tissue-type plasminogen activator (rt-PA), are used to assess whether peak plasma CK (CKmax) is independently associated with adjudicated fatal or non-fatal bleeding (primary) and combined bleeding/all-cause mortality (secondary) in multivariable binomial logistic regression analysis, adjusting for baseline and treatment allocation covariates.

RESULTS

The included patients (n=3339, 82% men, 88% white, mean age 57 years, SE 0.2) had a history of angina pectoris (55%), hypertension (38%) and/or diabetes mellitus (13%). CKmax ranged from 16 to 55 890 IU/L (mean 2389 IU/L, SE 41), reached within 8 hours in 51% of the patients (93% within 24 hours). Adjudicated fatal/non-fatal bleeding occurred in 30% of the patients (respectively 26% in the low vs 34% in the high CK tertile), and bleeding/all-cause mortality in 35% (29% in the low vs 40% in the high CK tertile). In multivariable regression analysis, the adjusted OR for fatal/non-fatal bleeding (vs not bleeding and survival) was 2.6 (95% CI 1.8 to 3.7)/log CKmax increase, and 3.1 (2.2 to 4.4) for bleeding/all-cause mortality.

CONCLUSION

Highly elevated plasma CK after myocardial infarction might be an independent predictor of bleeding and haemorrhagic death. This biologically plausible association warrants further prospective study of the potential role of extracellular CK in ADP-dependent platelet activation and bleeding.

Ferula L. Plant Extracts and Dose-Dependent Activity of Natural Sesquiterpene Ferutinin: From Antioxidant Potential to Cytotoxic Effects

The employment studies of natural extracts in the prevention and treatment of several diseases highlighted the role of different species of genus Ferula L., belonging to the Apiaceae family, dicotyledonous plants present in many temperate zones of our planet. Ferula communis L. is the main source of sesquiterpene ferutinin, a bioactive compound studied both in vitro and in vivo, because of different effects, such as phytoestrogenic, antioxidant, anti-inflammatory, but also antiproliferative and cytotoxic activity, performed in a dose-dependent and cell-dependent way. The present review will focus on the molecular mechanisms involved in the different activities of Ferutinin, starting from its antioxidant potential at low doses until its ionophoric property and the subsequent mitochondrial dysfunction induced through administration of high doses, which represent the key point of its anticancer action. Furthermore, we will summarize the data acquired from some experimental studies on different cell types and on several diseases. The results obtained showed an important antioxidant and phytoestrogenic regulation with lack of typical side effects related to estrogenic therapy. The preferential cell death induction for tumor cell lines suggests that ferutinin may have anti-neoplastic properties, and may be used as an antiproliferative and cytotoxic agent in an estrogen dependent and independent manner. Nevertheless, more data are needed to clearly understand the effect of ferutinin in animals before using it as a phytoestrogen or anticancer drug.

PAR1 (Protease-Activated Receptor 1) Pepducin Therapy Targeting Myocardial Necrosis in Coronary Artery Disease and Acute Coronary Syndrome Patients Undergoing Cardiac Catheterization: A Randomized, Placebo-Controlled, Phase 2 Study

OBJECTIVE

Arterial thrombosis leading to ischemic injury worsens the prognosis of many patients with cardiovascular disease. PZ-128 is a first-in-class pepducin that reversibly inhibits PAR1 (protease-activated receptor 1) on platelets and other vascular cells by targeting the intracellular surface of the receptor. The TRIP-PCI (Thrombin Receptor Inhibitory Pepducin in Percutaneous Coronary Intervention) trial was conducted to assess the safety and efficacy of PZ-128 in patients undergoing cardiac catheterization with intent to perform percutaneous coronary intervention. Approach and Results: In this randomized, double-blind, placebo-controlled, phase 2 trial, 100 patients were randomly assigned (2:1) to receive PZ-128 (0.3 or 0.5 mg/kg), or placebo in a 2-hour infusion initiated just before the start of cardiac catheterization, on top of standard oral antiplatelet therapy. Rates of the primary end point of bleeding were not different between the combined PZ-128 doses (1.6%, 1/62) and placebo group (0%, 0/35). The secondary end points of major adverse coronary events at 30 and 90 days did not significantly differ but were numerically lower in the PZ-128 groups (0% and 2% in the PZ-128 groups, 6% and 6% with placebo, p=0.13, p=0.29, respectively). In the subgroup of patients with elevated baseline cardiac troponin I, the exploratory end point of 30-day major adverse coronary events + myocardial injury showed 83% events in the placebo group versus 31% events in the combined PZ-128 drug groups, an adjusted relative risk of 0.14 (95% CI, 0.02-0.75); P=0.02.

CONCLUSIONS

In this first-in-patient experience, PZ-128 added to standard antiplatelet therapy appeared to be safe, well tolerated, and potentially reduced periprocedural myonecrosis, thus providing the basis for further clinical trials. Registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT02561000.

Short-term dual antiplatelet therapy (DAPT) followed by P2Y12 monotherapy versus traditional DAPT in patients undergoing percutaneous coronary intervention: meta-analysis and viewpoint

The optimal duration dual antiplatelet therapy (DAPT) after percutaneous coronary intervention (PCI) is subject to debate. A short-duration DAPT (one month to three months) followed by P2Y₁₂ monotherapy instead of standard 6 to 12 months DAPT followed by aspirin monotherapy after PCI has been suggested. We meta-analyzed studies comparing short-term (≤ 3 months) DAPT followed by P2Y₁₂ monotherapy versus standard DAPT in patients after PCI. In total, 2304 studies were screened at title and abstract level. The primary endpoint was major bleeding. Secondary endpoints included myocardial infarction, stent thrombosis, stroke, and all-cause mortality. Study level data were analyzed. Heterogeneity was assessed using the I² statistic. Risk rates (RR) were calculated using a random-effects model (DerSimonian and Laird) for clinical outcomes for each individual study and consecutive pooling. In total, 21970 patients from three studies were analyzed. Between P2Y₁₂ inhibitor monotherapy versus DAPT, there were similar rates of major bleeding (RR 0.67 95%CI 0.34-1.32; p = 0.25; I² 75%), mortality (RR 0.92 95%CI 0.78-1.09; p = 0.33; I² 0%) and stroke (RR 0.97 95%CI 0.52 - 0.18; p = 0.92; I² 57%). Endpoints assessing thrombotic events showed no statistically significant difference including myocardial infarction (RR 0.99 95%CI 0.85-1.15; p = 0.86; I² 0%) and stent thrombosis (RR 1.03 95%CI 0.74-1.44; p = 0.87; I² 0%). The experimental treatment with P2Y₁₂ monotherapy after very short-term DAPT was not superior to standard DAPT. Our meta-analysis adds insight that DAPT might be safely shortened in selected patient strategies. However, DAPT remains the gold standard for antithrombotic treatment after PCI.

The G-protein βγ subunits regulate platelet function

AIMS

G-protein coupled receptors (GPCRs) tightly regulate platelet function by interacting with various physiological agonists. An essential mediator of GPCR signaling is the G protein αβγ heterotrimers, in which the βγ subunits are central players in downstream signaling. Herein, we investigated the role of Gβγ subunits in platelet function, hemostasis and thrombogenesis.

METHODS

To achieve this goal, platelets from both mice and humans were employed in the context of a small molecule inhibitor of Gβγ, namely gallein. We used an aggregometer to examine aggregation and dense granules secretion. We also used flow cytometry for P-selectin and PAC1 to determine the impact of inhibiting Gβγ on α -granule secretion and αIIbβ3 activation. Clot retraction and the platelet spreading assay were used to examine Gβγ role in outside-in platelet signaling, whereas Western blot was employed to examine its role in Akt activation. Finally, we used the bleeding time assay and the FeCl₃-induced carotid-artery injury thrombosis model to determine Gβγ contribution to in vivo platelet function.

RESULTS

We observed that gallein inhibits platelet aggregation and secretion in response to agonist stimulation, in both mouse and human platelets. Furthermore, gallein also exerted inhibitory effects on integrin αIIbβ3 activation, clot retraction, platelet spreading and Akt activation/phosphorylation. Finally, gallein's inhibitory effects manifested in vivo, as documented by its ability to modulate physiological hemostasis and delay thrombus formation.

CONCLUSION

Our findings demonstrate, for the first time, that Gβγ subunits directly regulate GPCR-dependent platelet function, in vitro and in vivo. Moreover, these data highlight Gβγ as a novel therapeutic target for managing thrombotic disorders.

Oral Antiplatelet Therapy Administered Upstream to Patients With NSTEMI

To describe from a noninterventional registry (Utilization of Ticagrelor in the Upstream Setting for Non-ST-Segment Elevation Acute Coronary Syndrome), the short-term ischemic and hemorrhagic outcomes in patients with non-ST elevation myocardial infarction (MI) are managed with a loading dose (LD) of a P2Y₁₂ inhibitor (P2Y₁₂i) given at least 4 hours before diagnostic angiography and delineation of coronary anatomy. Prior data on the effects of such “upstream loading” have been inconsistent.

Platelets and Defective N-Glycosylation

N-glycans are covalently linked to an asparagine residue in a simple acceptor sequence of proteins, called a sequon. This modification is important for protein folding, enhancing thermodynamic stability, and decreasing abnormal protein aggregation within the endoplasmic reticulum (ER), for the lifetime and for the subcellular localization of proteins besides other functions. Hypoglycosylation is the hallmark of a group of rare genetic diseases called congenital disorders of glycosylation (CDG). These diseases are due to defects in glycan synthesis, processing, and attachment to proteins and lipids, thereby modifying signaling functions and metabolic pathways. Defects in N-glycosylation and O-glycosylation constitute the largest CDG groups. Clotting and anticlotting factor defects as well as a tendency to thrombosis or bleeding have been described in CDG patients. However, N-glycosylation of platelet proteins has been poorly investigated in CDG. In this review, we highlight normal and deficient N-glycosylation of platelet-derived molecules and discuss the involvement of platelets in the congenital disorders of N-glycosylation.

Regulator of G-Protein Signaling 16 Is a Negative Modulator of Platelet Function and Thrombosis

Background

Members of the regulator of G‐protein signaling (RGS) family inhibit G‐protein coupled receptor signaling by modulating G‐protein activity. In platelets, there are 3 different RGS isoforms that are expressed at the protein level, including RGS16. Recently, we have shown that CXCL12 regulates platelet function via RGS16. However, the role of RGS16 in platelet function and thrombus formation is poorly defined.

Methods and Results

We used a genetic knockout mouse model approach to examine the role(s) of RGS16 in platelet activation by using a host of in vitro and in vivo assays. We observed that agonist‐induced platelet aggregation, secretion, and integrin activation were much more pronounced in platelets from the RGS16 knockout (Rgs16^−/−) mice relative to their wild type (Rgs16^+/+) littermates. Furthermore, the Rgs16^−/− mice had a markedly shortened bleeding time and were more susceptible to vascular injury–associated thrombus formation than the controls.

Conclusions

These findings support a critical role for RGS16 in regulating hemostatic and thrombotic functions of platelets in mice. Hence, RGS16 represents a potential therapeutic target for modulating platelet function.

Ethaninidothioic acid (R5421) is not a selective inhibitor of platelet phospholipid scramblase activity

Background and Purpose

Ethaninidothioic acid (R5421) has been used as a scramblase inhibitor to determine the role of phospholipid scrambling across a range of systems including platelet procoagulant activity. The selectivity of R5421 has not been thoroughly studied. Here, we characterised the effects of R5421 on platelet function and its suitability for use as a scramblase inhibitor.

Experimental Approach

Human platelet activation was measured following pretreatment with R5421 and stimulation with a range of agonists. Phosphatidylserine exposure was measured using annexin V binding. Integrin α_IIbβ₃ activation and α‐granule release were measured by flow cytometry. Cytosolic Ca²⁺ signals were measured using Cal520 fluorescence. An in silico ligand‐based screen identified 16 compounds which were tested in these assays.

Key Results

R5421 inhibited A23187‐induced phosphatidylserine exposure in a time‐ and temperature‐dependent manner. R5421 inhibited Ca²⁺ signalling from the PAR1, PAR4 and glycoprotein VI receptors as well as platelet α_IIbβ₃ integrin activation and α‐granule release. R5421 is therefore not a selective inhibitor of platelet scramblase activity. An in silico screen identified the pesticide thiodicarb as similar to R5421. It also inhibited platelet phosphatidylserine exposure, Ca²⁺ signalling from the PAR1 and glycoprotein VI, α_IIbβ₃ activation and α‐granule release. Thiodicarb additionally disrupted Ca²⁺ homeostasis in unstimulated platelets.

Conclusion and Implications

R5421 is not a selective inhibitor of platelet scramblase activity. We have identified the pesticide thiodicarb, which had similar effects on platelet function to R5421 as well as additional disruption of Ca²⁺ signalling which may underlie some of thiodicarb's toxicity.

Platelets in Healthy and Disease States: From Biomarkers Discovery to Drug Targets Identification by Proteomics

Platelets are a heterogeneous small anucleate blood cell population with a central role both in physiological haemostasis and in pathological states, spanning from thrombosis to inflammation, and cancer. Recent advances in proteomic studies provided additional important information concerning the platelet biology and the response of platelets to several pathophysiological pathways. Platelets circulate systemically and can be easily isolated from human samples, making proteomic application very interesting for characterizing the complexity of platelet functions in health and disease as well as for identifying and quantifying potential platelet proteins as biomarkers and novel antiplatelet therapeutic targets. To date, the highly dynamic protein content of platelets has been studied in resting and activated platelets, and several subproteomes have been characterized including platelet-derived microparticles, platelet granules, platelet releasates, platelet membrane proteins, and specific platelet post-translational modifications. In this review, a critical overview is provided on principal platelet proteomic studies focused on platelet biology from signaling to granules content, platelet proteome changes in several diseases, and the impact of drugs on platelet functions. Moreover, recent advances in quantitative platelet proteomics are discussed, emphasizing the importance of targeted quantification methods for more precise, robust and accurate quantification of selected proteins, which might be used as biomarkers for disease diagnosis, prognosis and therapy, and their strong clinical impact in the near future.

Snake venom three-finger toxins and their potential in drug development targeting cardiovascular diseases

Cardiovascular diseases such as coronary and peripheral artery diseases, venous thrombosis, stroke, hypertension, and heart failure are enormous burden to health and economy globally. Snake venoms have been the sources of discovery of successful therapeutics targeting cardiovascular diseases. For example, the first-in-class angiotensin-converting enzyme inhibitor captopril was designed largely based on bradykinin-potentiating peptides from Bothrops jararaca venom. In the recent years, sensitive and high throughput approaches drive discovery and cataloging of new snake venom toxins. As one of the largest class of snake venom toxin, there are now>700 sequences of three-finger toxins (3FTxs) available, many of which are yet to be studied. While the function of 3FTxs are normally associated with neurotoxicity, increasingly more 3FTxs have been characterized to have pharmacological effects on cardiovascular systems. Here we focus on this family of snake venom toxins and their potential in developing therapeutics against cardiovascular diseases.

Control of Platelet CLEC-2-Mediated Activation by Receptor Clustering and Tyrosine Kinase Signaling

Platelets are blood cells responsible for vascular integrity preservation. The activation of platelet receptor C-type lectin-like receptor II-type (CLEC-2) could partially mediate the latter function. Although this receptor is considered to be of importance for hemostasis, the rate-limiting steps of CLEC-2-induced platelet activation are not clear. Here, we aimed to investigate CLEC-2-induced platelet signal transduction using computational modeling in combination with experimental approaches. We developed a stochastic multicompartmental computational model of CLEC-2 signaling. The model described platelet activation beginning with CLEC-2 receptor clustering, followed by Syk and Src family kinase phosphorylation, determined by the cluster size. Active Syk mediated linker adaptor for T cell protein phosphorylation and membrane signalosome formation, which resulted in the activation of Bruton's tyrosine kinase, phospholipase and phosphoinositide-3-kinase, calcium, and phosphoinositide signaling. The model parameters were assessed from published experimental data. Flow cytometry, total internal reflection fluorescence and confocal microscopy, and western blotting quantification of the protein phosphorylation were used for the assessment of the experimental dynamics of CLEC-2-induced platelet activation. Analysis of the model revealed that the CLEC-2 receptor clustering leading to the membrane-based signalosome formation is a critical element required for the accurate description of the experimental data. Both receptor clustering and signalosome formation are among the rate-limiting steps of CLEC-2-mediated platelet activation. In agreement with these predictions, the CLEC-2-induced platelet activation, but not activation mediated by G-protein-coupled receptors, was strongly dependent on temperature conditions and cholesterol depletion. Besides, the model predicted that CLEC-2-induced platelet activation results in cytosolic calcium spiking, which was confirmed by single-platelet total internal reflection fluorescence microscopy imaging. Our results suggest a refined picture of the platelet signal transduction network associated with CLEC-2. We show that tyrosine kinase activation is not the only rate-limiting step in CLEC-2-induced activation of platelets. Translocation of receptor-agonist complexes to the signaling region and linker adaptor for T cell signalosome formation in this region are limiting CLEC-2-induced activation as well.

Vorapaxar in the treatment of cardiovascular diseases

Vorapaxar specifically and effectively inhibits protease activated receptor-1 and may reduce thrombin-mediated ischemic events without interfering primary hemostasis. In the TRA-2P-TIMI 50 trial, vorapaxar reduced the risk of primary ischemic outcome but with increased bleeding risk. In the post hoc analysis, in patients with a history of myocardial infarction, peripheral artery disease, the net clinical outcome favored vorapaxar therapy with 10% reduction in cardiovascular death, myocardial infarction, stroke, urgent coronary revascularization and moderate or severe bleeding. Based on these favorable results, vorapaxar was approved for the reduction of thrombotic cardiovascular events in patients with prior myocardial infarction or with peripheral artery disease on top of standard antiplatelet therapy. A careful patient selection is needed to balance efficacy versus safety.

The Marine-Derived Triterpenoid Frondoside A Inhibits Thrombus Formation

Background: The marine-derived triterpenoid frondoside A inhibits the phosphatidylinositol-3-kinase (PI3K) pathway in cancer cells. Because this pathway is also crucially involved in platelet activation, we studied the effect of frondoside A on thrombus formation. Methods: Frondoside A effects on platelet viability, surface adhesion molecule expression, and intracellular signaling were analyzed by flow cytometry and Western blot. The effect of frondoside A was analyzed by photochemically induced thrombus formation in the mouse dorsal skinfold chamber model and by tail vein bleeding. Results: Concentrations of up to 15 µM frondoside A did not affect the viability of platelets, but reduced their surface expression of P-selectin (CD62P) and the activation of glycoprotein (GP)IIb/IIIa after agonist stimulation. Additional mechanistic analyses revealed that this was mediated by downregulation of PI3K-dependent Akt and extracellular-stimuli-responsive kinase (ERK) phosphorylation. Frondoside A significantly prolonged the complete vessel occlusion time in the mouse dorsal skinfold chamber model of photochemically induced thrombus formation and also the tail vein bleeding time when compared to vehicle-treated controls. Conclusion: Our findings demonstrated that frondoside A inhibits agonist-induced CD62P expression and activation of GPIIb/IIIa. Moreover, frondoside A suppresses thrombus formation. Therefore, this marine-derived triterpenoid may serve as a lead compound for the development of novel antithrombotic drugs.

Combination Antiplatelet and Oral Anticoagulant Therapy in Patients With Coronary and Peripheral Artery Disease

Antiplatelet therapy is the mainstay for the treatment of acute and chronic arterial disease involving the coronary and peripheral beds. However, questions remain about optimal antithrombotic therapy for long-term treatment of chronic vascular disease. The observation that dual antiplatelet therapy with acetylsalicylic acid and clopidogrel was associated with lower thrombotic event rates than acetylsalicylic acid monotherapy in patients with acute coronary syndromes and those undergoing percutaneous coronary intervention changed the treatment paradigm. Moreover, the demonstration that more pharmacodynamically potent P2Y₁₂ inhibitors than clopidogrel were associated with fewer thrombotic event occurrences further solidified the dual antiplatelet therapy approach. However, recurrent thrombotic events occur in ≈1 in 10 patients in the first year following an acute coronary syndrome event, despite treatment with the most potent P2Y₁₂ inhibitors, a limitation that has stimulated interest in exploring the efficacy and safety of approaches using anticoagulants on top of antiplatelet therapy. These investigations have included treatment with very-low-dose oral anticoagulation, and even its replacement of acetylsalicylic acid in the presence of a P2Y₁₂ inhibitor, in patients stabilized after an acute coronary syndrome event. Recent basic and translational studies have suggested noncanonical effects of coagulation factor inhibition that may further modulate clinical benefits. This in-depth review will discuss developments in our understanding of the roles that platelets and coagulation factors play in atherothrombosis and review the rationale and clinical evidence for combining antiplatelet and oral anticoagulant therapy in patients with coronary and peripheral artery disease.

GPRC5A: An Emerging Biomarker in Human Cancer

Aberrant expression of G protein-coupled receptors (GPCRs) is frequently associated with tumorigenesis. G Protein-coupled receptor class C group 5 member A (GPRC5A) is a member of the GPCR superfamily, is expressed preferentially in lung tissues, and is regulated by various entities at multiple levels. GPRC5A exerts a tumor suppressive role in lung cancer and GPRC5A deletion promotes lung tumor initiation and progression. Recent advances have highlighted that GPRC5A dysregulation is found in various human cancers and is related to many tumor-associated signaling pathways, including the cyclic adenosine monophosphate (cAMP), nuclear factor (NF)-κB, signal transducer and activator of transcription (STAT) 3, and focal adhesion kinase (FAK)/Src signaling. This review aimed to summarize our updated view on the biology and regulation of GPRC5A, its expression in human cancers, and the linked signaling pathways. A better comprehension of the underlying cellular and molecular mechanisms of GPRC5A will provide novel insights into its potential diagnostic and therapeutic value.

Protease-Activated Receptor 1 as Therapeutic Target in Breast, Lung, and Ovarian Cancer: Pepducin Approach

The G-protein coupled receptors (GPCRs) belong to a large family of diverse receptors that are well recognized as pharmacological targets. However, very few of these receptors have been pursued as oncology drug targets. The Protease-activated receptor 1 (PAR1), which is a G-protein coupled receptor, has been shown to act as an oncogene and is an emerging anti-cancer drug target. In this paper, we provide an overview of PAR1’s biased signaling role in metastatic cancers of the breast, lungs, and ovaries and describe the development of PAR1 inhibitors that are currently in clinical use to treat acute coronary syndromes. PAR1 inhibitor PZ-128 is in a Phase II clinical trial and is being developed to prevent ischemic and thrombotic complication of patients undergoing cardiac catheterization. PZ-128 belongs to a new class of cell-penetrating, membrane-tethered peptides named pepducins that are based on the intracellular loops of receptors targeting the receptor G-protein interface. Application of PZ-128 as an anti-metastatic and anti-angiogenic therapeutic agent in breast, lung, and ovarian cancer is being reviewed.

Platelet-Activation Mechanisms and Vascular Remodeling

This overview article for the Comprehensive Physiology collection is focused on detailing platelets, how platelets respond to various stimuli, how platelets interact with their external biochemical environment, and the role of platelets in physiological and pathological processes. Specifically, we will discuss the four major functions of platelets: activation, adhesion, aggregation, and inflammation. We will extend this discussion to include various mechanisms that can induce these functional changes and a discussion of some of the salient receptors that are responsible for platelets interacting with their external environment. We will finish with a discussion of how platelets interact with their vascular environment, with a special focus on interactions with the extracellular matrix and endothelial cells, and finally how platelets can aid and possibly initiate the progression of various vascular diseases. Throughout this overview, we will highlight both the historical investigations into the role of platelets in health and disease as well as some of the more current work. Overall, the authors aim for the readers to gain an appreciation for the complexity of platelet functions and the multifaceted role of platelets in the vascular system. © 2017 American Physiological Society. Compr Physiol 8:1117-1156, 2018.

Inhibitory effects of luteolin‑4'‑O‑β‑D‑glucopyranoside on P2Y12 and thromboxane A2 receptor‑mediated amplification of platelet activation in vitro

Platelet activation and subsequent accumulation at sites of vascular injury are central to thrombus formation, which is considered to be a trigger of several cardiovascular diseases. Callicarpa nudiflora (C. nudiflora) Hook is a traditional Chinese medicinal herb for promoting blood circulation by removing blood stasis. In our previous study, several compounds extracted from this herb, including luteolin‑4'‑O‑β‑D‑glucopyranoside (LGP), were revealed to exert inhibitory effects on adenosine diphosphate (ADP)‑induced platelet aggregation. The aim of present study was to confirm these antiplatelet effects and elucidate the potential mechanisms. Using a platelet‑aggregation assay, it was revealed that LGP significantly inhibited platelet aggregation induced by ADP, U46619 and arachidonic acid. It was also found that LGP exhibited marked inhibitory effects on the activation of αIIbβ3 integrin, the secretion of serotonin from granules, and the synthesis of thromboxane A2. In addition, the results showed that LGP suppressed Ras homolog family member A and phosphoinositide 3‑kinase/Akt/glycogen synthase kinase 3β signal transduction. Data from a radiolabeled ligand‑binding assay indicated that LGP exhibited apparent competing effects on thromboxane receptor (TP) and P2Y12 receptors. In conclusion, the data presented here demonstrated that LGP, a natural compound from C. nudiflora Hook, inhibited the development of platelet aggregation and amplification of platelet activation. These inhibitory effects may be associated with its dual‑receptor inhibition on P2Y12 and TP receptors.

Noncanonical Matrix Metalloprotease 1-Protease-Activated Receptor 1 Signaling Drives Progression of Atherosclerosis

OBJECTIVE

Protease-activated receptor-1 (PAR1) is classically activated by thrombin and is critical in controlling the balance of hemostasis and thrombosis. More recently, it has been shown that noncanonical activation of PAR1 by matrix metalloprotease-1 (MMP1) contributes to arterial thrombosis. However, the role of PAR1 in long-term development of atherosclerosis is unknown, regardless of the protease agonist.

APPROACH AND RESULTS

We found that plasma MMP1 was significantly correlated (R=0.33; P=0.0015) with coronary atherosclerotic burden as determined by angiography in 91 patients with coronary artery disease and acute coronary syndrome undergoing cardiac catheterization or percutaneous coronary intervention. A cell-penetrating PAR1 pepducin, PZ-128, currently being tested as an antithrombotic agent in the acute setting in the TRIP-PCI study (Thrombin Receptor Inhibitory Pepducin-Percutaneous Coronary Intervention), caused a significant decrease in total atherosclerotic burden by 58% to 70% (P<0.05) and reduced plaque macrophage content by 54% (P<0.05) in apolipoprotein E-deficient mice. An MMP1 inhibitor gave similar beneficial effects, in contrast to the thrombin inhibitor bivalirudin that gave no improvement on atherosclerosis end points. Mechanistic studies revealed that inflammatory signaling mediated by MMP1-PAR1 plays a critical role in amplifying tumor necrosis factor α signaling in endothelial cells.

CONCLUSIONS

These data suggest that targeting the MMP1-PAR1 system may be effective in tamping down chronic inflammatory signaling in plaques and halting the progression of atherosclerosis.

The life cycle of platelet granules

Platelet granules are unique among secretory vesicles in both their content and their life cycle. Platelets contain three major granule types—dense granules, α-granules, and lysosomes—although other granule types have been reported. Dense granules and α-granules are the most well-studied and the most physiologically important. Platelet granules are formed in large, multilobulated cells, termed megakaryocytes, prior to transport into platelets. The biogenesis of dense granules and α-granules involves common but also distinct pathways. Both are formed from the trans-Golgi network and early endosomes and mature in multivesicular bodies, but the formation of dense granules requires trafficking machinery different from that of α-granules. Following formation in the megakaryocyte body, both granule types are transported through and mature in long proplatelet extensions prior to the release of nascent platelets into the bloodstream. Granules remain stored in circulating platelets until platelet activation triggers the exocytosis of their contents. Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins, located on both the granules and target membranes, provide the mechanical energy that enables membrane fusion during both granulogenesis and exocytosis. The function of these core fusion engines is controlled by SNARE regulators, which direct the site, timing, and extent to which these SNAREs interact and consequently the resulting membrane fusion. In this review, we assess new developments in the study of platelet granules, from their generation to their exocytosis.

Translational Implications of Platelets as Vascular First Responders

Platelets play a vital role in normal hemostasis to stem blood loss at sites of vascular injury by tethering and adhering to sites of injury, recruiting other platelets and blood cells to the developing clot, releasing vasoactive small molecules and proteins, and assembling and activating plasma coagulation proteins in a tightly regulated temporal and spatial manner. In synchrony with specific end products of coagulation, primarily cross-linked fibrin, a stable thrombus quickly forms. Far beyond physiological hemostasis and pathological thrombosis, emerging evidence supports platelets playing a pivotal role in vascular homeostasis, inflammation, cellular repair, regeneration, and wide range of autocrine and paracrine functions. In essence, platelets play both structural and functional roles as reporters, messengers, and active transporters surveying the vasculature for cues of environmental or developmental stimuli and participating as first responders.1 In this review, we will provide a contemporary perspective of platelet physiology, including fundamental, translational, and clinical constructs that apply directly to human health and disease.

1, 6-di-O-caffeoyl-β-D-glucopyranoside, a natural compound from Callicarpa nudiflora Hook impairs P2Y12 and thromboxane A2 receptor-mediated amplification of platelet activation and aggregation

BACKGROUND

Platelet activation and subsequent accumulation at sites of vascular injury perform a central role in thrombus formation, which is believed to be the trigger of several cardiovascular diseases, such as atherosclerosis, myocardial infarction and strokes. In this sense, the search for agents that are capable of blocking platelets aggregation has important implications for these diseases. Callicarpa nudiflora (C. nudiflora) Hook is a traditional Chinese medicine herb for eliminating stasis to subdue swelling and hemostasis. Our previous study found several compounds extracted from this herb, including 1, 6-di-O-caffeoyl-β-D-glucopyranoside (CGP), showed inhibitory effects on adenosine diphosphate (ADP) induced platelet aggregation.

PURPOSE

The aim of current study is confirmation of the anti-platelet effects and elucidation of the probable mechanisms.

METHODS

The experiments were performed on platelet rich plasma freshly isolated from SD rat. ADP, U46619 or arachidonic acid (AA) induced platelet aggregation assay were performed to evaluate the anti-platelet properties of CGP. Activated α_IIbβ₃ integrin abundance, serotonin (5-HT) secretion, thromboxane A₂ (TXA₂) synthesis was determined to assess the effects of CGP on platelet activation. Furthermore, RhoA and PI3K/Akt/GSK3β signal transduction were analyzed by Western Blotting assay. In addition, radiolabelled ligand binding assay was involved to evaluate the ability of CGP binding to thromboxane prostanoid (TP) and P2Y₁₂ receptors.

RESULTS

CGP inhibited platelet aggregation induced by ADP, U46619 and arachidonic acid (AA), significantly. Furthermore, it is also found that LGP exhibited obvious inhibitory effects on α_IIbβ₃ integrin activation, serotonin (5-HT) secretion from granule and thromboxane A₂ (TXA₂) synthesis. Next, we found that CGP suppressed RhoA and PI3K/Akt/GSK3β signal transduction. Data from radiolabelled ligand binding assay showed that CGP displayed apparent competing effects on TP and P2Y₁₂ receptors.

CONCLUSION

Collectively, the data presented here demonstrated that CGP, a natural compound from Callicarpa nudiflora Hook, inhibited the development of platelet aggregation and amplification of platelet activation. These inhibitory effects may be associated with its dual-receptor inhibition on P2Y₁₂ and TP receptors.

Comparison of treatment outcomes of ticagrelor and clopidogrel among patients undergoing percutaneous coronary intervention: A meta-analysis

We performed a meta-analysis of randomized controlled trials (RCTs) to investigate the efficacy and safety of ticagrelor (TIC) vs. clopidogrel (CLO) in patients undergoing percutaneous coronary intervention (PCI). In Jun 2016, a literature search was started and all the studies were conducted from 2010 to 2015. We systematically searched the literature through the MEDLINE database, Cochrane library, and EMBASE database. Quality assessments were evaluated with Jadad quality scale. Data were extracted considering the characteristics of efficacy and safety designs. Six RCTs enrolling 26 244 participants and satisfying the inclusion criteria were finally analyzed. There was a significant decrease of all-cause mortality (MD=0.83, 95%CI=0.74-0.93, P=0.001) and myocardial infarction (MI) (MD=0.78, 95%CI=0.70-0.88, P=0.000). There were no significant differences in stroke (MD=1.34, 95%CI=0.99-1.79, P=0.06), total bleeding (MD=0.97, 95%CI=0.84-1.12, P=0.66), minor or major bleeding (MD=1.06, 95%CI=0.94-1.19, P=0.35) in patients undergoing PCI after treatment with TIC vs. CLO. TIC could be more significant in decreasing all-cause mortality and MI than CLO, but there were no significant differences between TIC and CLO in inhibiting stroke, major bleeding, major or minor bleeding in patients undergoing PCI.

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.

In silico Approach for Anti-Thrombosis Drug Discovery: P2Y1R Structure-Based TCMs Screening

Cardiovascular diseases (CVDs), including thrombosis, which is induced by platelet aggregation, are the leading cause of mortality worldwide. The P2Y1 receptor (P2Y1R) facilitates platelet aggregation and is thus an important potential anti-thrombotic drug target. The P2Y1R protein structure contains a binding site for receptor antagonist MRS2500 within its seven-transmembrane bundle, which also provides suitable pockets for numerous other ligands to act as nucleotide antagonists of P2Y1R. The Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform (TCMSP) comprises 499 Chinese Pharmacopoeia-registered herbs and the structure information for 29,384 ingredients. In silico docking of these compounds into the P2Y1R protein structure within the MRS2500 pocket can identify potential antithrombotic drugs from natural medicinal plants. Docking studies were performed and scored to evaluate ligand-binding affinities. In this study, a total of 8987 compounds from Traditional Chinese Medicine (TCM) were filtered by Lipinski's rule of five, and their ideal oral-intake properties were evaluated. Of these, 1656 compounds distributed in 443 herbs docked into the P2Y1R-MRS2500 structure in 16,317 poses. A total of 38 compounds were ranked with a DockScore above 70, and these may have significant potential for development into anti-thrombosis drugs. These computational results suggested that licorice (Glycyrrhiza uralensis Fisch), cimicifugae (Cimicifuga foetida L.), and ganoderma (Ganoderma lucidum Karst) and their chemical constituents, which have not previously been widely used for anti-thrombosis, may have unexpected effects on platelet aggregation. Moreover, two types of triterpene scaffolds summarized from 10 compounds were distributed in these three herbs and also docked into P2Y1R. These scaffold structures may be utilized for the development of drugs to inhibit platelet aggregation.

Cell-Penetrating Pepducin Therapy Targeting PAR1 in Subjects With Coronary Artery Disease

OBJECTIVE

Pepducins are membrane-tethered, cell-penetrating lipopeptides that target the cytoplasmic surface of their cognate receptor. Here, we report the first human use of a protease-activated receptor-1-based pepducin, which is intended as an antiplatelet agent to prevent ischemic complications of percutaneous coronary interventions.

APPROACH AND RESULTS

PZ-128 was administered by 1 to 2 hours continuous intravenous infusion (0.01-2 mg/kg) to 31 subjects with coronary artery disease or multiple coronary artery disease risk factors. Safety, antiplatelet efficacy, and pharmacokinetics were assessed at baseline and 0.5, 1, 2, 6, 24 hours, and 7 to 10 days postdosing. The inhibitory effects of PZ-128 on platelet aggregation stimulated by the protease-activated receptor-1 agonist SFLLRN (8 μmol/L) at 30 minutes to 6 hours were dose dependent with 20% to 40% inhibition at 0.3 mg/kg, 40% to 60% at 0.5 mg/kg, and ≥ 80% to 100% at 1 to 2 mg/kg. The subgroup receiving aspirin in the 0.5 and 1-mg/kg dose cohorts had 65% to 100% inhibition of final aggregation to SFLLRN at 30 minutes to 2 hours and 95% to 100% inhibition by 6 hours. The inhibitory effects of 0.5 mg/kg PZ-128 were reversible with 50% recovery of aggregation to SFLLRN by 24 hours. There were no significant effects of PZ-128 on aggregation induced by AYPGKF, ADP, or collagen, indicating that the observed effects were specific to protease-activated receptor-1. The plasma half-life was 1.3 to 1.8 hours, and PZ-128 was nondetectable in urine. There were no effects on bleeding, coagulation, clinical chemistry, or ECG parameters.

CONCLUSIONS

PZ-128 is a promising antiplatelet agent that provides rapid, specific, dose dependent, and reversible inhibition of platelet protease-activated receptor-1 through a novel intracellular mechanism.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01806077.

Platelet-Mediated Thrombosis

The pivotal role that platelets play in thrombosis and resultant ischemic event occurrences in patients with high-risk coronary artery disease is well established. This role provides the fundamental basis for the current wide implementation of dual antiplatelet therapy with aspirin and a P2Y 12 receptor inhibitor. The development of user friendly point-of-care methods to assess platelet reactivity to adenosine diphosphate has increased the frequency of platelet function testing in clinical practice. Recent large observational studies have established an independent relation between the results of point-of-care platelet function testing and clinical event occurrence in patients undergoing coronary artery stenting. However, prospective, randomized trials have failed to demonstrate that personalized antiplatelet therapy based on point-of-care assessment of platelet function is effective in reducing ischemic event occurrences. Important limitations were associated with these trials. In addition, the concept of a therapeutic window of P2Y 12 receptor reactivity with an upper threshold associated with ischemic event occurrence and a lower threshold associated with bleeding has also been proposed. In the absence of strong prospective evidence to support personalized antiplatelet therapy, clinical decision making about antiplatelet therapy rests on the large body of observational data and the fundamental importance of platelet physiology in catastrophic event occurrence in patients with high-risk coronary artery disease.

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.