Biomarker optimization to track the antithrombotic and hemostatic effects of clopidogrel in rats

A dry immersion model of microgravity modulates platelet phenotype, miRNA signature, and circulating plasma protein biomarker profile

Ground based research modalities of microgravity have been proposed as innovative methods to investigate the aetiology of chronic age-related conditions such as cardiovascular disease. Dry Immersion (DI), has been effectively used to interrogate the sequelae of physical inactivity (PI) and microgravity on multiple physiological systems. Herein we look at the causa et effectus of 3-day DI on platelet phenotype, and correlate with both miRomic and circulating biomarker expression. The miRomic profile of platelets is reflective of phenotype, which itself is sensitive and malleable to the exposome, undergoing responsive transitions in order to fulfil platelets role in thrombosis and haemostasis. Heterogeneous platelet subpopulations circulate at any given time, with varying degrees of sensitivity to activation. Employing a DI model, we investigate the effect of acute PI on platelet function in 12 healthy males. 3-day DI resulted in a significant increase in platelet count, plateletcrit, platelet adhesion, aggregation, and a modest elevation of platelet reactivity index (PRI). We identified 15 protein biomarkers and 22 miRNA whose expression levels were altered after DI. A 3-day DI model of microgravity/physical inactivity induced a prothrombotic platelet phenotype with an unique platelet miRNA signature, increased platelet count and plateletcrit. This correlated with a unique circulating protein biomarker signature. Taken together, these findings highlight platelets as sensitive adaptive sentinels and functional biomarkers of epigenetic drift within the cardiovascular compartment.

Hyperglycemia Potentiates Prothrombotic Effect of Aldosterone in a Rat Arterial Thrombosis Model

We investigated the role of aldosterone (ALDO) in the development of arterial thrombosis in streptozotocin-induced diabetic rats. To evaluate the effect of endogenous ALDO, the rats underwent adrenalectomy (ADX). ADX reduced the development of arterial thrombosis. A 1 h infusion of ALDO (30 μg/kg/h) enhanced thrombosis in adrenalectomized rats, while this effect was potentiated in diabetic rats. ALDO shortened bleeding time, increased plasma levels of tissue factor (TF) and plasminogen activator inhibitor, decreased plasma level of nitric oxide (NO) metabolites, and increased oxidative stress. Moreover, 2 h incubation of human umbilical vein endothelial cells (HUVECs) with ALDO (10^-7 M) disrupted hemostatic balance in endothelial cells in normoglycemia (glucose 5.5 mM), and this effect was more pronounced in hyperglycemia (glucose 30 mM). We demonstrated that the acute ALDO infusion enhances arterial thrombosis in rats and hyperglycemia potentiates this prothrombotic effect. The mechanism of ALDO action was partially mediated by mineralocorticoid (MR) and glucocorticoid (GR) receptors and related to impact of the hormone on primary hemostasis, TF-dependent coagulation cascade, fibrinolysis, NO bioavailability, and oxidative stress balance. Our in vitro study confirmed that ALDO induces prothrombotic phenotype in the endothelium, particularly under hyperglycemic conditions.

Twenty-four-hour time dependency of clopidogrel effects in patients with acute coronary syndromes: The CiCAD-Study

Long-term evidence shows an increased risk of cardiovascular events in the morning hours and recent studies in aspirin-treated patients have shown increased platelet reactivity at the end of the dosing interval. Similar pharmacodynamic analyses of adenosine-diphosphate (ADP) receptor inhibitors are scarce. We therefore investigated changes in clopidogrel-dependent platelet function and activation over 24 h and whether enhanced platelet turnover might explain diurnal variability of platelet function and activation. Twenty-one patients after acute coronary syndromes (ACS) on maintenance doses of clopidogrel (75 mg) and aspirin (100 mg) Once per day (OD) were included. Blood was collected at five time points in 24 h. Platelet function and activation was analyzed by vasodilator-stimulated phosphoprotein-phosphorylation (VASP-P), Verify Now, multiple electrode aggregometry (MEA), and platelet PAC-1 and P-selectin (P-sel) expression. Additionally, platelet count, mean platelet volume (MPV), and reticulated platelet fraction (RPF) were analyzed. There was significant diurnal variability of clopidogrel effects as documented with VASP-P, Verify Now, and PAC-1 and P-sel (all p < 0.05), whereas MEA did not differ over 24 h. Neither MPV nor RPF varied significantly over 24 h. In patients with high RPF, platelet function and activation was significantly higher in all assays, compared to patients with low RPF (all p < 0.05). However, the changes over time in low versus high RPF groups were similar. ADP-dependent platelet function and activation recovers significantly at the end of the 24-h dosing interval in patients with ACS on a maintenance dose of clopidogrel and aspirin. Although platelet function and activation is increased in patients with higher RPF, platelet turnover might not explain the observed diurnal variability.

Multiple electrode aggregometry and vasodilator stimulated phosphoprotein-phosphorylation assay in clinical routine for prediction of postprocedural major adverse cardiovascular events

Reduced antiplatelet effect of clopidogrel assessed with multiple electrode aggregometry (MEA) and vasodilator stimulated phosphoprotein-phosphorylation (VASP-P) assay has been proven to predict major adverse cardiovascular events (MACE) after coronary stenting. So far no consecutive registry has evaluated the usefulness of different adenosine diphosphate-based platelet function tests to predict outcome in unselected patients. Hence, our objective was to determine the feasibility of MEA and VASP-P for clinical routine and whether low-response to clopidogrel as determined by MEA and/or the VASP-P assays predicts MACE in a “real-life” population undergoing coronary stenting. Threehundred consecutive patients were included in this prospective registry. Blood was sampled 6–24 hours after stenting to measure MEA and VASP-P. The use of glycoprotein-IIb/IIIa-blockers limited MEA to 196 measurements. Concerning the VASP-P assay, 300 measurements were achieved. Receiver Operating Characteristics (ROC)-curves of sensitivity and specificity estimates for MACE were plotted for VASP-P assay. The area under the ROC-curve was 0.683 (p=0.014) for the platelet reactivity index (PRI) calculated from median fluorescence intensities (FI) with an optimal cut-off at 60.2% PRI. Patients above 60.2% had a significantly increased risk for MACE at six months follow-up (p=0.007). Estimating the cut-offs for the PRI from mean FI (52%) or from geometric mean FI (56.6%) led to clinically relevant differences. VASP-P assay is feasible for clinical routine to measure clopidogrel effects and to predict post-procedural MACE in unselected patients. With regard to differing cut-offs, exact standardisation of the VASP-P assay is mandatory. The use of GP-IIb/IIIa-blockers prevents MEA testing and limits its usability in unselected patients.

Drug-like Antagonists of P2Y Receptors-From Lead Identification to Drug Development

P2Y receptors are expressed in virtually all cells and tissue types and mediate an astonishing array of biological functions, including platelet aggregation, smooth muscle cell proliferation, and immune regulation. The P2Y receptors belong to the G protein-coupled receptor superfamily and are composed of eight members encoded by distinct genes that can be subdivided into two groups on the basis of their coupling to specific G-proteins. Extensive research has been undertaken to find modulators of P2Y receptors, although to date only a limited number of small-molecule P2Y receptor antagonists have been approved by drug/medicines agencies. This Perspective reviews the known P2Y receptor antagonists, highlighting oral drug-like receptor antagonists, and considers future opportunities for the development of small molecules for clinical evaluation.

Pretreatment with a combination of ligustrazine and berberine improves cardiac function in rats with coronary microembolization

AIM

We have shown that a combination of ligustrazine and berberine produces more effective inhibition on platelet activation and inflammatory reactions in rat acute myocardial infarction compared with either agent alone. In this study we evaluated the beneficial effects of a combination of ligustrazine and berberine in a rat model of coronary microembolization (CME).

METHODS

SD rats were treated with ligustrazine, berberine, ligustrazine+berberine, or clopidogrel for 2 weeks. When the treatment completed, CME was induced by injection of sodium laurate into the left ventricular, while obstructing the ascending aorta. All rats were intubated for hemodynamic measurements. Blood samples were collected for biochemical analyses, flow cytometry, and ELISAs. Heart tissues were isolated for histopathology and subsequent protein analyses.

RESULTS

Pretreatment with the combination of ligustrazine (27 mg·kg(-1)·d(-1)) and berberine (90 mg·kg(-1)·d(-1)) significantly improved cardiac function, and decreased myocardial necrosis, inflammatory cell infiltration, microthrombosis and serum CK-MB levels in CME rats. In addition, this combination significantly decreased plasma ET-1 levels and von Willebrand factor, inhibited ADP-induced platelet activation, and reduced TNFα, IL-1β, ICAM-1 and RANTES levels in serum and heart tissues. The protective effects of this combination were more prominent than those of ligustrazine or berberine alone, but comparable to those of a positive control clopidogrel (6.75 mg·kg(-1)·d(-1)).

CONCLUSION

The combination of ligustrazine and berberine significantly improved cardiac function in rat CME model via a mechanism involving antiplatelet and anti-inflammatory effects.

Platelet transfusion reverses bleeding evoked by triple anti-platelet therapy including vorapaxar, a novel platelet thrombin receptor antagonist

Vorapaxar is a novel protease-activated receptor-1 (PAR-1) antagonist recently approved for the reduction of thrombotic cardiovascular events in patients with a history of myocardial infarction or with peripheral arterial disease. Patients who received vorapaxar in addition to standard of care antiplatelet therapy had an increased incidence of major bleeding events compared with placebo. To assess whether platelet transfusion can restore hemostasis in primates on triple antiplatelet therapy, template bleeding times were assessed concurrently in the buccal mucosa, finger pad, and distolateral tail of anesthetized cynomolgus macaques to evaluate bleeding with vorapaxar as either monotherapy or in combination with aspirin or aspirin and clopidogrel. Aspirin (5mg/kg, IV) or vorapaxar (1mg/kg, PO) alone had no significant effect on bleeding times in the three vascular beds examined. A modest (<2-fold) increase in bleeding time was achieved in the three beds with the dual combination of aspirin and vorapaxar. Major increases in bleeding time were achieved in the three beds with the triple combination of aspirin (5mg/kg, IV), vorapaxar (1mg/kg, PO), and clopidogrel (1mg/kg, PO). Transfusion of fresh human platelet rich plasma, but not platelet poor plasma, reversed the increase in bleeding time in the triple therapy group. Transfusion of human platelets may be a viable approach in situations requiring a rapid reversal of platelet function in individuals treated with triple anti-platelet therapy that includes vorapaxar.

Eplerenone reduces arterial thrombosis in diabetic rats

INTRODUCTION

Clinical studies demonstrated the benefits of eplerenone (EPL) in reduction of cardiovascular events in diabetic patients. Since acute myocardial infarction (AMI) and stroke are related to acute intravascular thrombosis, we postulate that the beneficial effects of EPL may result from its antithrombotic action.

MATERIALS AND METHODS

Streptozotocin (STZ)-induced diabetic rats were treated with EPL (100 mg/kg/day) for 10 days. Thrombosis in the carotid artery was stimulated electrically.

RESULTS

Thrombosis development was enhanced in STZ-induced diabetic rats as compared to normoglycaemic controls. EPL caused prolongation of the time to artery occlusion, reduction in the incidence of occlusion and decrease in thrombus weight. Changes in the thrombi structure and the inhibition of hypertrophy of the tunica media in the artery wall were also observed. EPL caused reduction in tissue factor, plasminogen activator inhibitor type 1 and interleukin-1β plasma levels.

CONCLUSIONS

Our study demonstrated the antithrombotic effect of EPL manifested by a decrease in the dynamics of thrombus formation and changes in its structure. The changes in thrombosis process were accompanied by antihaemostatic, profibrinolytic and anti-inflammatory effects. The aldosterone blockade with EPL seems to be an additional pharmacological strategy for the prevention and treatment of thrombotic disorders in diabetes.

4-Benzothiazole-7-hydroxyindolinyl diaryl ureas are potent P2Y1 antagonists with favorable pharmacokinetics: low clearance and small volume of distribution

Current antithrombotic discovery efforts target compounds that are highly efficacious in thrombus reduction with less bleeding liability than the standard of care. Preclinical data suggest that P2Y1 antagonists may have lower bleeding liabilities than P2Y12 antagonists while providing similar antithrombotic efficacy. This article describes our continuous SAR efforts in a series of 7-hydroxyindolinyl diaryl ureas. When dosed orally, 4-trifluoromethyl-7-hydroxy-3,3-dimethylindolinyl analogue 4 was highly efficacious in a model of arterial thrombosis in rats with limited bleeding. The chemically labile CF3 group in 4 was then transformed to various groups via a novel one-step synthesis, yielding a series of potent P2Y1 antagonists. Among them, the 4-benzothiazole-substituted indolines had desirable PK properties in rats, specifically, low clearance and small volume of distribution. In addition, compound 40 had high i.v. exposure and modest bioavailability, giving it the best overall profile.

Central P2Y12 receptor blockade alleviates inflammatory and neuropathic pain and cytokine production in rodents

In this study the role of P2Y₁₂ receptors (P2Y₁₂R) was explored in rodent models of inflammatory and neuropathic pain and in acute thermal nociception. In correlation with their activity to block the recombinant human P2Y₁₂R, the majority of P2Y₁₂R antagonists alleviated mechanical hyperalgesia dose-dependently, following intraplantar CFA injection, and after partial ligation of the sciatic nerve in rats. They also caused an increase in thermal nociceptive threshold in the hot plate test. Among the six P2Y₁₂R antagonists evaluated in the pain studies, the selective P2Y₁₂ receptor antagonist PSB-0739 was most potent upon intrathecal application.

P2Y₁₂R mRNA and IL-1β protein were time-dependently overexpressed in the rat hind paw and lumbar spinal cord following intraplantar CFA injection. This was accompanied by the upregulation of TNF-α, IL-6 and IL-10 in the hind paw. PSB-0739 (0.3 mg/kg i.t.) attenuated CFA-induced expression of cytokines in the hind paw and of IL-1β in the spinal cord. Subdiaphragmatic vagotomy and the α7 nicotinic acetylcholine receptor antagonist MLA occluded the effect of PSB-0739 (i.t.) on pain behavior and peripheral cytokine induction. Denervation of sympathetic nerves by 6-OHDA pretreatment did not affect the action of PSB-0739. PSB-0739, in an analgesic dose, did not influence motor coordination and platelet aggregation. Genetic deletion of the P2Y₁₂R in mice reproduced the effect of P2Y₁₂R antagonists on mechanical hyperalgesia in inflammatory and neuropathic pain models, on acute thermal nociception and on the induction of spinal IL-1β.

Here we report the robust involvement of the P2Y₁₂R in inflammatory pain. The anti-hyperalgesic effect of P2Y₁₂R antagonism could be mediated by the inhibition of both central and peripheral cytokine production and involves α7-receptor mediated efferent pathways.

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Pharmacological blockade of P2Y₁₂ receptors alleviates inflammatory and neuropathic pain.

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Central inhibition of P2Y₁₂ receptors attenuates cytokine production in the spinal cord.

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Central P2Y₁₂ receptor inhibition attenuates cytokine production in the inflamed hind paw.

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α7-Receptors mediate the effect of P2Y₁₂ receptor blockade on hyperalgesia and cytokine level.

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Genetic deletion of P2Y₁₂ receptors alleviates inflammatory, neuropathic and acute pain.

Comparison of the effect of coagulation and platelet function impairments on various mouse bleeding models

Haemostatic impairments are studied in vivo using one of several murine bleeding models. However it is not known whether these models are equally appropriate for assessing coagulation or platelet function defects. It was our study objective to assess the performance of arterial, venous and combined arterial and venous murine bleeding models towards impaired coagulation or platelet function. Unfractionated heparin (UFH) or αIIbβ3inhibitory antibody (Leo.H4) were administered to mice, and their effects on bleeding in saphenous vein, artery, and tail tip transection models were quantified and correlated with their effects on plasma clotting and ADP-induced platelet aggregation, respectively. All models exhibited similar sensitivity with UFH (EC50 dose = 0.19, 0.13 and 0.07 U/g, respectively) (95% CI = 0.14 - 0.27, 0.08 - 0.20, and 0.03 - 0.16 U/g, respectively). Maximal inhibition of ex vivo plasma clotting could be achieved with UFH doses as low as 0.03 U/g. In contrast, the saphenous vein bleeding model was less sensitive to αIIbβ3 inhibition (EC50 = 6.9 μg/ml) than tail transection or saphenous artery bleeding models (EC50 = 0.12 and 0.37 μg/ml, respectively) (95% CI = 2.4 - 20, 0.05 - 0.33, and 0.06 - 2.2 μg/ml, respectively). The EC50 of Leo.H4 for ADP-induced platelet aggregation in vitro (8.0 μg/ml) was at least 20-fold higher than that of the tail and arterial, but not the venous bleeding model. In conclusion, venous, arterial and tail bleeding models are similarly affected by impaired coagulation, while platelet function defects have a greater influence in models incorporating arterial injury.

Identification of 1-{2-[4-chloro-1'-(2,2-dimethylpropyl)-7-hydroxy-1,2-dihydrospiro[indole-3,4'-piperidine]-1-yl]phenyl}-3-{5-chloro-[1,3]thiazolo[5,4-b]pyridin-2-yl}urea, a potent, efficacious and orally bioavailable P2Y(1) antagonist as an antiplatelet agent

Spiropiperidine indoline-substituted diaryl ureas had been identified as antagonists of the P2Y1 receptor. Enhancements in potency were realized through the introduction of a 7-hydroxyl substitution on the spiropiperidinylindoline chemotype. SAR studies were conducted to improve PK and potency, resulting in the identification of compound 3e, a potent, orally bioavailable P2Y1 antagonist with a suitable PK profile in preclinical species. Compound 3e demonstrated a robust antithrombotic effect in vivo and improved bleeding risk profile compared to the P2Y12 antagonist clopidogrel in rat efficacy/bleeding models.

Conformationally constrained ortho-anilino diaryl ureas: discovery of 1-(2-(1'-neopentylspiro[indoline-3,4'-piperidine]-1-yl)phenyl)-3-(4-(trifluoromethoxy)phenyl)urea, a potent, selective, and bioavailable P2Y1 antagonist

Preclinical antithrombotic efficacy and bleeding models have demonstrated that P2Y1 antagonists are efficacious as antiplatelet agents and may offer a safety advantage over P2Y12 antagonists in terms of reduced bleeding liabilities. In this article, we describe the structural modification of the tert-butyl phenoxy portion of lead compound 1 and the subsequent discovery of a novel series of conformationally constrained ortho-anilino diaryl ureas. In particular, spiropiperidine indoline-substituted diaryl ureas are described as potent, orally bioavailable small-molecule P2Y1 antagonists with improved activity in functional assays and improved oral bioavailability in rats. Homology modeling and rat PK/PD studies on benchmark compound 3l will also be presented. Compound 3l was our first P2Y1 antagonist to demonstrate a robust oral antithrombotic effect with mild bleeding liability in the rat thrombosis and hemostasis models.

Potent P2Y1 urea antagonists bearing various cyclic amine scaffolds

A number of new amine scaffolds with good inhibitory activity in the ADP-induced platelet aggregation assay have been found to be potent antagonists of the P2Y1 receptor. SAR optimization led to the identification of isoindoline 3c and piperidine 4a which showed good in vitro binding and functional activities, as well as improved aqueous solubility. Among them, the piperidine 4a showed the best overall profile with favorable PK parameters.

New azole antagonists with high affinity for the P2Y(1) receptor

Five-membered-ring heterocyclic urea mimics have been found to be potent and selective antagonists of the P2Y1 receptor. SAR of the various heterocyclic replacements is presented, as well as side-chain SAR of the more potent thiadiazole ring system which leads to thiadiazole 4c as a new antiplatelet agent.

Discovery of diarylurea P2Y(1) antagonists with improved aqueous solubility

Preclinical data suggests that P2Y1 antagonists, such as diarylurea compound 1, may provide antithrombotic efficacy similar to P2Y12 antagonists and may have the potential of providing reduced bleeding liabilities. This manuscript describes a series of diarylureas bearing solublizing amine side chains as potent P2Y1 antagonists. Among them, compounds 2l and 3h had improved aqueous solubility and maintained antiplatelet activity compared with compound 1. Compound 2l was moderately efficacious in both rat and rabbit thrombosis models and had a moderate prolongation of bleeding time in rats similar to that of compound 1.

Discovery of 2-(phenoxypyridine)-3-phenylureas as small molecule P2Y1 antagonists

Two distinct G protein-coupled purinergic receptors, P2Y1 and P2Y12, mediate ADP-driven platelet activation. The clinical effectiveness of P2Y12 blockade is well established. Recent preclinical data suggest that P2Y1 and P2Y12 inhibition provide equivalent antithrombotic efficacy, while targeting P2Y1 has the potential for reduced bleeding liability. In this account, the discovery of a 2-(phenoxypyridine)-3-phenylurea chemotype that inhibited ADP-mediated platelet aggregation in human blood samples is described. Optimization of this series led to the identification of compound 16, 1-(2-(2-tert-butylphenoxy)pyridin-3-yl)-3-4-(trifluoromethoxy)phenylurea, which demonstrated a 68 ± 7% thrombus weight reduction in an established rat arterial thrombosis model (10 mg/kg plus 10 mg/kg/h) while only prolonging cuticle and mesenteric bleeding times by 3.3- and 3.1-fold, respectively, in provoked rat bleeding time models. These results suggest that a P2Y1 antagonist could potentially provide a safe and efficacious antithrombotic profile.

A platelet target for venous thrombosis? P2Y1 deletion or antagonism protects mice from vena cava thrombosis

A role for platelets in the pathogenesis of venous thrombosis was suggested by clinical and preclinical studies. However, examination of the platelet receptor, P2Y1, in this area has been limited. The goal of the current study was to examine effects of P2Y1 deletion, or selective antagonism with MRS2500, in oxidative venous thrombosis in mice. The P2Y12 antagonist, clopidogrel, was included as a reference agent. Anesthetized C57BL/6 or genetically modified mice underwent 3.5 or 5 % FeCl(3)-induced vena cava thrombosis. Pharmacokinetic properties of MRS2500 were defined for dose selection. Platelet aggregation and renal or tail bleeding times (BT) were measured to put antithrombotic effects into perspective. P2Y1 deletion significantly reduced (p < 0.001) venous thrombus weight by 74 % in 3.5 % FeCl(3) injury compared to P2Y1(+/+) littermates. MRS2500 (2 mg/kg, i.v.) significantly decreased (p < 0.001) thrombus weight 64 % in C57BL/6 mice. In the more severe 5 % FeCl(3)-induced injury model, thrombus weight significantly (p < 0.001) decreased 68 % in P2Y1(-/-) mice versus P2Y1(+/+) mice, and MRS2500 (2 mg/kg) was also beneficial (54 % decrease, p < 0.01). Renal BT doubled in P2Y1(-/-) versus P2Y1(+/+) mice, and increased threefold with MRS2500 compared to vehicle. Tail BT was markedly prolonged in P2Y1(-/-) mice (7.9X) and in C57BL/6 mice given MRS2500. The current study demonstrates that P2Y1 deletion or antagonism significantly reduced venous thrombosis in mice, suggesting that P2Y1 receptors play a role in the pathogenesis of venous thrombosis, at least in this species. However as with many antithrombotic agents the benefit comes at the potential price of an increase in provoked bleeding times.

Modified clopidogrel loading dose according to platelet reactivity monitoring in patients carrying ABCB1 variant alleles in patients with clopidogrel resistance

OBJECTIVES

The aim of the present study was to investigate the impact of a adjusted clopidogrel loading dose (LD) according to platelet reactivity index in carriers of ABCB1 mutant allele undergoing percutaneous coronary intervention (PCI).

METHODS

All patients met the inclusion criteria were recruited in the present study. Platelet reactivity was measured using the vasodilator-stimulated phosphoprotein (VASP) index. High treatment platelet reactivity (HTPR) was determined by a cut-off value of >50%. The genetic polymorphism of ABCB1 was determined by allele-specific polymerase chain reaction (PCR). In patients carrying ABCB1 and HTPR after a first 300-mg LD of clopidogrel, dose adjustment was performed by using up to 3 additional 300-mg LDs to obtain a VASP index<50%. The rate of major adverse cardiovascular events (MACE) and major or minor bleeding in one month were recorded.

RESULTS

536 patients were included in the present study. One hundred seventy-two patients (32%) carried ABCB1 mutant allele (11 homozygotes [2%] and 161 heterozygotes [30%]). The VASP index in these patients was significantly higher than in homozygotic patients for the wild allele (65.5±13.8% vs. 47.6±21.8%; p<0.001). Of the 172 ABCB1 mutant allele carriers, 130 were considered to have HTPR. After a second clopidogrel LD, the VASP index was significantly decreased in these patients (66.9±12.8% vs.50.2±18.3%; <0.001). Finally, dose adjustment according to platelet reactivity monitoring enabled 88% of ABCB1 mutant allele carriers and 91% of wild allele carriers exhibiting HTPR to reach a VASP index<50%. The rate of MACE and major or minor bleeding in one-month follow-up between the wild allele carriers and the mutant allele carriers didn't differentiate significantly.

CONCLUSIONS

Increased and adjusted clopidogrel loading dose according to platelet reactivity monitoring attenuated clopidogrel resistance in carriers of ABCB1 mutant allele.

Effect of clopidogrel besylate on platelet reactivity in patients with acute coronary syndromes. Comparison with clopidogrel hydrogen sulfate

OBJECTIVE

The efficacy of clopidogrel therapy in patients with an acute coronary syndrome (ACS) has been established using the clopidogrel hydrogen sulfate (CHS) formulation. In this study we compared the antiplatelet effectiveness of a generic clopidogrel salt, clopidogrel besylate (CB), with the original CHS in patients with an ACS.

RESEARCH DESIGN AND METHODS

Ninety-six ACS patients were randomized to receive a 600-mg loading dose of either CHS (n = 45) or CB (n = 51), followed by 75 mg/day. Sixty-eight patients underwent a percutaneous coronary intervention (PCI), whereas 28 were treated conservatively. Platelet aggregatory response, vasodilator-stimulated phosphoprotein (VASP) phosphorylation, P-selectin expression and platelet-leucocyte conjugates were determined before clopidogrel loading (baseline), as well as at 5 days and at 1 month afterwards.

RESULTS

No difference in the clopidogrel response variability was observed between patients receiving CHS or CB either at 5 days or at 1 month of follow-up. Similarly, no difference in the inhibition of platelet aggregation, P-selectin expression or in the platelet-leucocyte conjugates was observed between CHS and CB group during the follow-up.

CONCLUSIONS

There is no overall significant difference in the antiplatelet efficacy between CB and CHS during their administration in ACS patients for up to 1 month after the episode.

The platelet hyporesponsiveness to clopidogrel in acute coronary syndrome patients treated with 75 mg/day clopidogrel may be overcome within 1 month of treatment

Platelets are involved in thrombus formation and inflammation following vascular injury, while clopidogrel exerts antithrombotic and anti-inflammatory actions. We investigated various platelet-derived prothrombotic and proinflammatory mediators as well as the platelet aggregatory response in patients with acute coronary syndromes (ACS) receiving clopidogrel, as a function of the patient responsiveness to drug treatment. Blood samples were obtained from 40 patients with recent (<24 h) ACS before clopidogrel loading 600 mg (followed by a maintenance dose of 75 mg/day) as well as 5-days and 30-days afterwards. Twelve patients exhibited platelet reactivity index (PRI) values higher than 50% evaluated by the Vasodilator Stimulated Phosphoprotein (VASP) test at 5 days and were characterized as nonresponders. The platelet response to adenosine diphosphate (ADP) and thrombin receptor agonist peptide-14 (TRAP) was studied by flow cytometry and light transmission aggregometry. A maximum reduction of ADP- or TRAP-induced platelet aggregation in 28 clopidogrel responding patients was observed at 5 days postclopidogrel loading, whereas in nonresponders, it was achieved at 30-days along with a significant decrease in the PRI values. Similar results were obtained for the membrane expression of CD40L and the production of platelet-derived microparticles. By contrast, the maximum inhibition of P-selectin expression and platelet-leukocyte conjugate formation was observed at 30-days in both patient groups. A maintenance dose of 75 mg clopidogrel differentially affects the platelet aggregation and platelet-derived prothrombotic and proinflammatory mediators in ACS patients within the first month of the treatment, a phenomenon that is highly influenced by the drug response variability. Since these factors may be involved in the major adverse cardiovascular events in ACS patients, especially in those undergoing percutaneous coronary intervention, the above findings may be clinically important.

Modifying clopidogrel maintenance doses according to vasodilator-stimulated phosphoprotein phosphorylation index improves clinical outcome in patients with clopidogrel resistance

BACKGROUND

Despite dual antiplatelet therapy, the rate of major adverse cardiovascular events (MACE) after percutaneous coronary intervention (PCI) remains high. Ex vivo tests of clopidogrel resistance can predict MACE after PCI. The purpose of this study is to evaluate the clinical impact of adjusting phosphorylation analysis in patients with clopidogrel resistance undergoing PCI.

HYPOTHESIS

We hypothesized that VASP-guided clopidogrel maintenance doses, compared to fixed doses, improved clinical outcome.

METHODS

This monocentric, prospective, randomized study was performed on 306 patients undergoing PCI. Patients were randomized to a control group (n = 156) and to a vasodilator-stimulated phosphoprotein (VASP)-guided group (n = 150). In the VASP-guided group, patients received adjusted maintenance doses of clopidogrel to obtain platelet reactivity index (PRI) of <50% during 1 year after PCI. The primary endpoint was the rate of MACE. The secondary endpoints were major and minor bleeding.

RESULTS

All patients completed the PCI procedure and 298 patients completed follow-up. The control and VASP-guided groups had similar demographic, clinical, and angiographic characteristics. In the VASP-guided group, PRI was significantly decreased (from 72.1% ± 11.4% to 27.7% ± 8.4%; P = 0.001) in 128 patients (87.1% of all participants). During the 1-year follow-up, 14 MACEs were recorded in the VASP-guided group and 30 MACEs were recorded in the control group (9.3% vs 20.4%, respectively; P = 0.008). There was no difference in the rate of major and minor bleeding in the VASP-guided group compared with the control group (12.9% vs 16.6%; P = 0.06).

CONCLUSIONS

Modifying clopidogrel maintenance doses according to platelet reactivity monitoring decreases the rate of MACE after PCI without increasing bleeding in patients with clopidogrel resistance during 1-year follow-up.

Investigation of the potential effects of metformin on atherothrombotic risk factors in hyperlipidemic rats

The increased mortality rate due to atherothrombotic events and related complications has necessitated the search for new pharmacological agents. Hyperlipidemia, thrombosis and oxidative stress are the primary underlying concerns in the pathogenesis of atherosclerosis. Metformin, although proved to be beneficial in micro and macrovascular complications of diabetes mellitus, its effects on pure cardiovascular subjects are still debatable. Hence, the aim of the present study was to investigate the effects of metformin on atherothrombotic risk factors in experimental hyperlipidemic rats. Hyperlipidemia was induced by an intra-peritoneal injection of criton X-100 (25 mg/kg). Assessment of the effects of metformin (300 mg/kg/day, 400 mg/kg/day and 500 mg/kg/day) on lipid profile, coagulation time (activated partial thromboplastin time and prothrombin time), fibrinogen level, thrombosis, lipid peroxidation, antioxidant enzymes level, plasma fluorescent oxidation products and aortic nitrite level revealed an overall improvement in the lipid profile at the dose of 400 mg/kg along with a significant reduction in oxidative stress as compared to criton X-100 treated control. Activated partial thromboplastin and prothrombin times were prolonged at all doses, while plasma fibrinogen level remained unaffected. Metformin pre-treatment also reduced endothelial cell damage in ferrous chloride induced thrombosis in carotid arteries. Thus, the results indicate a potential protective effect of metformin on atherothrombotic risk factors, as evident from an improvement in lipid profile, reduction in oxidative stress and thrombotic events.

Effect of the direct factor Xa inhibitor apixaban in rat models of thrombosis and hemostasis

Apixaban is an oral, direct, and highly selective factor Xa inhibitor in late-stage clinical development for the prevention and treatment of thromboembolic diseases. Apixaban was evaluated in rat thrombosis and hemostasis models. Thrombosis was produced in the carotid artery by FeCl2 application, in the vena cava by either FeCl2 application or tissue factor injection, and in an arterial-venous shunt. Hemostasis was assessed using cuticle, renal cortex, and mesenteric artery bleeding times. Intravenous apixaban infusions of 0.1, 0.3, 1, and 3 mg/kg per hour increased the ex vivo prothrombin time to 1.24, 1.93, 2.75, and 3.98 times control, respectively. The 0.3, 1, and 3-mg/kg per hour doses inhibited thrombosis in all models. Concentrations for 50% thrombus reduction ranged from 1.84 to 7.57 microM. The 3-mg/kg per hour dose increased cuticle, renal, and mesenteric bleeding times to 1.92, 2.13, and 2.98 times control, respectively. Lower doses had variable (1 mg/kg per hour) or no effect (0.1, 0.3 mg/kg per hour) on hemostasis. Heparin's prolongation of renal and cuticle bleeding time was twice that of apixaban when administered at a dose that approximated apixaban (3 mg/kg per hour) efficacy in arterial thrombosis. In summary, apixaban was effective in a broad range of thrombosis models at doses producing modest increases in multiple bleeding time models.

Hepatic stellate cells promote hepatocyte engraftment in rat liver after prostaglandin-endoperoxide synthase inhibition

BACKGROUND & AIMS

Hepatic inflammation occurs immediately after cells are transplanted to the liver, but the mechanisms that underlie this process are not fully defined. We examined cyclooxygenase pathways that mediate hepatic inflammation through synthesis of prostaglandins, prostacyclins, thromboxanes, and other prostanoids following transplantation of hepatocytes.

METHODS

We transplanted F344 rat hepatocytes into syngeneic dipeptidyl peptidase IV-deficient F344 rats. Changes in cyclooxygenase pathways were analyzed, and specific pathways were blocked pharmacologically; the effects on cell engraftment and native liver cells were determined.

RESULTS

Transplantation of hepatocytes induced hepatic expression of prostaglandin-endoperoxide synthases 1 and 2, which catalyze production of prostaglandin H2, as well as the downstream factor thromboxane synthase, which produces thromboxane A2 (a regulator of vascular and platelet responses in inflammation). Transplanted hepatocytes were in proximity with liver cells that expressed prostaglandin-endoperoxide synthases. The number of engrafted hepatocytes increased in rats given naproxen or celecoxib before transplantation but not in rats given furegrelate (an inhibitor of thromboxane synthase) or clopodigrel (an antiplatelet drug). Naproxen and celecoxib did not prevent hepatic ischemia or activation of neutrophils, Kupffer cells, or inflammatory cytokines, but they did induce hepatic stellate cells to express cytoprotective genes, vascular endothelial growth factor and hepatocyte growth factor, and matrix-type metalloproteinases and tissue inhibitor of metalloproteinase-1, which regulate hepatic remodeling.

CONCLUSIONS

Activation of cyclooxygenase pathways interferes with engraftment of transplanted hepatocytes in the liver. Pharmacologic blockade of prostaglandin-endoperoxide synthases stimulated hepatic stellate cells and improved cell engraftment.

Prediction of the therapeutic index of marketed anti-coagulants and anti-platelet agents by guinea pig models of thrombosis and hemostasis

INTRODUCTION

Animal models of thrombosis and hemostasis are critical for target validation in pharmaceutical research. Guinea pig haemostatic mechanisms, such as the platelet thrombin receptor repertoire, resemble those of humans. Measuring the performance characteristics of marketed antithrombotic drugs in guinea pig models is a key to predicting therapeutic indices of new agents. The goal of the current study was to benchmark representative marketed drugs in thrombosis and hemostasis models in guinea pigs.

METHODS

Effects of the cyclooxygenase inhibitor, aspirin, the P2Y(12) antagonist, clopidogrel, the glycoprotein IIb/IIIa inhibitor, tirofiban, and the direct thrombin inhibitors, argatroban and hirudin, were evaluated in this study. Antithrombotic agents were tested in FeCl(3)-induced carotid artery thrombosis and arterio-venous shunt thrombosis models. Haemostatic effects of drugs were evaluated in cuticle and renal bleeding models. Ex vivo measurements of platelet function and coagulation inhibition were performed to benchmark preclinical doses of each agent to those used clinically.

RESULTS

The overall rank-order of potency in thrombosis models based on per cent of vessels occluded, average carotid blood flow, and thrombus weight was aspirin=argatroban=tirofiban<hirudin=clopidogrel. In bleeding models, the rank order was: aspirin<clopidogrel=argatroban=tirofiban<hirudin.

CONCLUSION

This characterization of representative drugs from two important classes of anti-coagulant and anti-platelet agents in efficacy and bleeding models in guinea pigs provides a reference point for evaluation of new antithrombotic agents.

Adjusted clopidogrel loading doses according to vasodilator-stimulated phosphoprotein phosphorylation index decrease rate of major adverse cardiovascular events in patients with clopidogrel resistance: a multicenter randomized prospective study

OBJECTIVES

This study evaluates the clinical impact of adjusting the loading dose of clopidogrel according to vasodilator-stimulated phosphoprotein (VASP) index in patients with clopidogrel resistance undergoing percutaneous coronary intervention (PCI).

BACKGROUND

Clopidogrel resistance plays a key role in ischemic recurrence after PCI. In vitro tests of clopidogrel resistance can accurately predict major adverse cardiac events after PCI.

METHODS

In this prospective, randomized, multicenter study, clopidogrel resistance was defined as a VASP index of more than 50% after a 600-mg loading dose. Patients with clopidogrel resistance undergoing coronary stenting were randomized to a control group or to the VASP-guided group, in which patients received additional bolus clopidogrel to decrease the VASP index below 50%.

RESULTS

A total of 162 patients were included. The control (n = 84) and VASP-guided groups (n = 78) had similar demographic, clinical, and biological characteristics. In the VASP-guided group, dose adjustment was efficient in 67 patients (86%) and VASP index was significantly decreased (from 69.3 +/- 10 to 37.6 +/- 13.8; p < 0.001). Eight major adverse cardiac events (5%) were recorded during the 1-month follow-up, with a significantly lower rate in the VASP-guided group compared with the control group (0% vs. 10%; p = 0.007). There was no difference in the rate of major and minor bleeding (5% vs. 4%; p = 1).

CONCLUSIONS

This is the first study to suggest that adjusting the clopidogrel loading dose according to platelet monitoring using the VASP index is safe and may significantly improve the clinical outcome after PCI in patients with clopidogrel resistance despite a first 600-mg loading dose.