New tricks for old dogs: nonthrombotic effects of thrombin in vessel wall biology

Systemic Delivery of Clopidogrel Inhibits Neointimal Formation in a Mouse Vein Graft Model

ABSTRACT

Clopidogrel inhibits platelet aggregation and has beneficial effects on patients undergoing coronary artery bypass grafting surgery, but it is unknown whether clopidogrel inhibits the neointima formation of grafted veins. In this study, we used a murine vein graft model to study the effect of clopidogrel on intima hyperplasia of the vein graft. Vein grafting was performed among C57BL/6J mice, immediately after surgery; 1 mg/kg clopidogrel and vehicle control were used to inject mice peritoneally daily for 2 weeks. As compared with the vehicle, clopidogrel significantly inhibited the neointima formation of vein grafts at 4 weeks after surgeries. The immunohistochemistry study showed that as compared with the vehicle, clopidogrel significantly decreased the rate of proliferating cell nuclear antigen-positive cells in the wall of vein grafts and significantly increased the expression of vascular smooth muscle cell (VSMC) contractile protein markers (α-smooth muscle actin, calponin, and SM22) within the neointima area of vein grafts. Clopidogrel significantly decreased the plasma interleukin 6 (IL-6) level at 1 week after surgery as compared with the vehicle. We isolated VSMCs from mouse aortic arteries. As compared with the vehicle, clopidogrel significantly inhibited thrombin-induced VSMC proliferation and migration, significantly decreased IL-6 mRNA expression and protein secretion, and increased intracellular cyclic adenosine monophosphate generation in a dose-dependent manner. In conclusion, systemic delivery of clopidogrel inhibits neointima formation of the mouse vein graft, the mechanisms of which are associated with its inhibitory effects on VSMC proliferation, migration, and the tendency to synthetic phenotype after vein graft surgery, reducing the expression of IL-6 and increasing the intracellular cyclic adenosine monophosphate level.

Expression/Activation of PAR-1 in Airway Epithelial Cells of COPD Patients: Ex Vivo/In Vitro Study

The role of PAR-1 expression and activation was described in epithelial cells from the central and distal airways of COPD patients using an ex vivo/in vitro model. PAR-1 immunoreactivity was studied in epithelial cells from surgical specimens of the central and distal airways of COPD patients and healthy control (HC). Furthermore, PAR-1 expression and activation were measured in both the human bronchial epithelial cell line (16HBE) and normal human bronchial epithelial cells (NHBEs) exposed to cigarette smoke extract (CSE) (10%) or thrombin. Finally, cell proliferation, apoptosis, and IL-8 release were detected in stimulated NHBEs. We identified higher levels of PAR-1 expression/activation in epithelial cells from the central airways of COPD patients than in HC. Active PAR-1 increased in epithelial cells from central and distal airways of COPD, with higher levels in COPD smokers (correlated with pack-years) than in COPD ex-smokers. 16HBE and NHBEs exposed to CSE or thrombin showed increased levels of active PAR-1 (localized in the cytoplasm) than baseline conditions, while NHBEs treated with thrombin or CSE showed increased levels of IL-8 proteins, with an additional effect when used in combination. Smoking habits generate the upregulation of PAR-1 expression/activation in airway epithelial cells, and promoting IL-8 release might affect the recruitment of infiltrating cells in the airways of COPD patients.

Thrombin-Induced Responses via Protease-Activated Receptor 1 Blocked by the Endothelium on Isolated Porcine Retinal Arterioles

PURPOSE

Thrombin, a serine protease, causes organ-specific responses to vessels. However, the mechanism by which thrombin affects the retinal microcirculation remains unclear. We examined the effects of thrombin on the retinal microvasculature and signaling mechanisms.

METHODS

Porcine retinal arterioles were isolated, cannulated, and pressurized (55 cmH₂O) without flow in this in vitro study. Videomicroscopy techniques recorded changes in diameter in the retinal arterioles in response to thrombin at concentrations ranging from 0.001 to 20 mU/ml.

RESULTS

Extraluminal administration of thrombin induced concentration-dependent vascular responses, that is, vasoconstriction at low concentrations less than 5 mU/ml and vasorelaxation with high concentrations greater than 5 mU/ml. However, intraluminal administration of thrombin (5 mU/m) did not constrict the retinal arterioles; in denuded vessels, intraluminal administration constricted the retinal arterioles. Thrombin-induced vasoconstriction was significantly (p < 0.01) suppressed by pretreatment with a protein kinase C (PKC) inhibitor and a protease-activated receptor (PAR)-1 inhibitor but not by PAR-2 and PAR-4 inhibitors or denudation. A rho kinase (ROCK) inhibitor also suppressed thrombin-induced vasoconstriction (5 mU/ml) compared with sodium nitroprusside. Endothelial denudation and pretreatment with an endothelial nitric oxide (NO) synthase inhibitor suppressed vasorelaxation caused by a high concentration of thrombin.

CONCLUSIONS

A low concentration of thrombin causes vasoconstriction of smooth muscles via PAR-1, PKC, and ROCK, and a high concentration of thrombin possibly causes vasorelaxation of the retinal arterioles via nitric oxide synthase activation in the endothelium. The vascular endothelium might block signaling of thrombin-induced vasoconstriction in the retinal arterioles when administered intraluminally.

Role for Thrombin Receptor Antagonism With Vorapaxar in Secondary Prevention of Atherothrombotic Events: From Bench to Bedside

In spite of treatment with the current standard of care antiplatelet regimens including dual antiplatelet therapy, recurrence rates of ischemic events remain elevated for high-risk patients with atherosclerotic disease. This may be in part attributed to the fact that other key platelet activation pathways remain uninhibited and can thus continue to trigger platelet activation and lead to thrombotic complications. Thrombin is a powerful inducer of platelet activation and mediates its effects directly on platelets through protease activator receptors (PARs), particularly the PAR-1 subtype, making PAR-1 inhibition an attractive approach for reducing atherothrombotic events. These observations have led to the development of several PAR-1 antagonists. Vorapaxar is a direct inhibitor of PAR-1 and the only agent of this class approved for the prevention of recurrent ischemic events in patients with prior myocardial infarction or peripheral artery disease. In the present manuscript, we present a review of the pathophysiologic role of thrombin on thrombotic complications, the impact of vorapaxar on outcomes, including the most recent updates deriving from clinical trials, as well as future perspectives in the field.

Contemporary Outcomes of Endovascular Intervention for Critical Limb Ischemia

Critical limb ischemia (CLI) remains a significant cause of morbidity and mortality in patients with peripheral arterial disease. Optimal treatment strategies for CLI remain controversial. The only randomized trial comparing surgical with endovascular revascularization suggests no significant difference in limb salvage between open surgical bypass and angioplasty. Although novel endovascular strategies are now available, their efficacies remain largely untested in a randomized fashion. This review provides an overview of the data surrounding contemporary outcomes of endovascular therapy with an emphasis on current knowledge gaps.

Vorapaxar: A Protease-Activated Receptor Antagonist for the Prevention of Thrombotic Events

Antiplatelet therapy reduces the risks for cardiovascular morbidity and mortality in patients with atherosclerotic disease, and it is also beneficial in managing peripheral arterial disease (PAD). These agents work through various therapeutic pathways to achieve antithrombotic effects. Although single- or two-drug regimens have been deployed to prevent vascular events, approximately 10% of the patients with acute coronary syndrome remain at risk for recurrent thrombotic events and may need a more aggressive preventative strategy. Vorapaxar offers a unique mechanism for platelet inhibition via the antagonism of protease-activated receptor-1. It is approved for the reduction of thrombotic cardiovascular events in patients with a history of myocardial infarction (MI) or PAD. This new drug approval was mainly based on the results from subgroup analyses from a large landmark trial (Thrombin Receptor Antagonist in Secondary Prevention of Atherothrombotic Ischemic Events-Thrombolysis in Myocardial Infarction 50), which found that vorapaxar reduces the rate of the combined end point of cardiovascular death, MI, stroke, and urgent coronary revascularization when used in addition to aspirin and/or clopidogrel in patients without a history of stroke. In this study, vorapaxar was discontinued in patients with a history of stroke due to excessive risk for intracranial hemorrhage after 2 years of therapy. As an adjunctive therapy to standard regimens, vorapaxar provides a greater net clinical benefit in MI patients who are at a lower risk for bleeding. In patients with PAD, it reduces the rates of recurrent acute limb ischemia with rehospitalization or peripheral revascularization. The most concerning adverse effect is bleeding. Vorapaxar should not be used in patients with a history of stroke, transient ischemic attack, intracranial hemorrhage, or active pathological bleeding. The risks and benefits of adding vorapaxar to intensify antiplatelet regimens should be assessed in individual patients to aim for additional therapeutic outcomes with minimal bleeding risks.

Emerging roles for vascular smooth muscle cell exosomes in calcification and coagulation

Vascular smooth muscle cell (VSMC) phenotypic conversion from a contractile to 'synthetic' state contributes to vascular pathologies including restenosis, atherosclerosis and vascular calcification. We have recently found that the secretion of exosomes is a feature of 'synthetic' VSMCs and that exosomes are novel players in vascular repair processes as well as pathological vascular thrombosis and calcification. Pro-inflammatory cytokines and growth factors as well as mineral imbalance stimulate exosome secretion by VSMCs, most likely by the activation of sphingomyelin phosphodiesterase 3 (SMPD3) and cytoskeletal remodelling. Calcium stress induces dramatic changes in VSMC exosome composition and accumulation of phosphatidylserine (PS), annexin A6 and matrix metalloproteinase-2, which converts exosomes into a nidus for calcification. In addition, by presenting PS, VSMC exosomes can also provide the catalytic surface for the activation of coagulation factors. Recent data showing that VSMC exosomes are loaded with proteins and miRNA regulating cell adhesion and migration highlight VSMC exosomes as potentially important communication messengers in vascular repair. Thus, the identification of signalling pathways regulating VSMC exosome secretion, including activation of SMPD3 and cytoskeletal rearrangements, opens up novel avenues for a deeper understanding of vascular remodelling processes.

G-protein Coupled Receptor Signaling in Pluripotent Stem Cell-derived Cardiovascular Cells: Implications for Disease Modeling

Human pluripotent stem cell derivatives show promise as an in vitro platform to study a range of human cardiovascular diseases. A better understanding of the biology of stem cells and their cardiovascular derivatives will help to understand the strengths and limitations of this new model system. G-protein coupled receptors (GPCRs) are key regulators of stem cell maintenance and differentiation and have an important role in cardiovascular cell signaling. In this review, we will therefore describe the state of knowledge concerning the regulatory role of GPCRs in both the generation and function of pluripotent stem cell derived-cardiomyocytes, -endothelial, and -vascular smooth muscle cells. We will consider how far the in vitro disease models recapitulate authentic GPCR signaling and provide a useful basis for discovery of disease mechanisms or design of therapeutic strategies.

New Insights into the Pros and Cons of the Clinical Use of Vitamin K Antagonists (VKAs) Versus Direct Oral Anticoagulants (DOACs)

Vitamin K-antagonists (VKA) are the most widely used anticoagulant drugs to treat patients at risk of arterial and venous thrombosis for the past 50 years. Due to unfavorable pharmacokinetics VKA have a small therapeutic window, require frequent monitoring, and are susceptible to drug and nutritional interactions. Additionally, the effect of VKA is not limited to coagulation, but affects all vitamin K-dependent proteins. As a consequence, VKA have detrimental side effects by enhancing medial and intimal calcification. These limitations stimulated the development of alternative anticoagulant drugs, resulting in direct oral anticoagulant (DOAC) drugs, which specifically target coagulation factor Xa and thrombin. DOACs also display non-hemostatic vascular effects via protease-activated receptors (PARs). As atherosclerosis is characterized by a hypercoagulable state indicating the involvement of activated coagulation factors in the genesis of atherosclerosis, anticoagulation could have beneficial effects on atherosclerosis. Additionally, accumulating evidence demonstrates vascular benefit from high vitamin K intake. This review gives an update on oral anticoagulant treatment on the vasculature with a special focus on calcification and vitamin K interaction.

Inhibitory effects of fermented extract of Ophiopogon japonicas on thrombin-induced vascular smooth muscle cells

Ophiopogon japonicus is known to have various pharmacological effects. The present study investigated the effects of an extract of fermented Ophiopogon japonicas (FEOJ) on thrombin‑treated vascular smooth muscle cells (VSMCs). FEOJ treatment inhibited the proliferation of VSMCs treated with thrombin as indicated by an MTT assay. These inhibitory effects were associated with decreased phosphorylation of AKT, reduced expression of cyclin D1 and increased expression of p27KIP1 in thrombin‑induced VSMCs. In addition, FEOJ treatment suppressed the thrombin‑stimulated migration of VSMCs as demonstrated by a wound‑healing migration assay. Furthermore, zymographic analyses demonstrated that treatment of FEOJ with VSMCs suppressed the thrombin‑induced expression of matrix metalloproteinase (MMP)‑2, which was attributed to the reduction of nuclear factor (NF)‑κB binding activity. Collectively, these results demonstrated that FEOJ induced p27KIP1 expression, reduced cyclin D1 expression and AKT phosphorylation, and inhibited MMP‑2 expression mediated by downregulation of NF‑κB binding activity in thrombin‑treated VSMCs, which led to growth inhibition and repression of migration. These results supported the use of FEOJ for the prevention of vascular diseases and provided novel insight into the underlying mechanism of action.

Sodium tanshinone IIA sulfonate ameliorates experimental coronary no-reflow phenomenon through down-regulation of FGL2

AIMS

The effects of sodium tanshinone IIA sulfonate (STS) on coronary no-reflow (CNR) relevant to microvascular obstruction (MVO) remain unknown. Studies had shown that fibrinogen-like protein 2 (FGL2) expressed in microvascular endothelial cells (MECs) is a key mediator in MVO. Thus, we aimed to elucidate the roles of STS in CNR and relations between STS and FGL2.

MAIN METHODS

Myocardial ischemia/reperfusion was selected to represent CNR model. The no-reflow zone and infarct area were assessed using Thioflavin S and TTC staining, and cardiac functional parameters were detected using echocardiography. Western blot was used to detected FGL2 level, fibrin level, protease-activated receptor-1 (PAR-1) activation and inflammation cells infiltration. FGL2 and inflammation cells were also identified by IHC. Microthrombus was detected by Carstairs' and MSB staining. We also detected the roles of STS on FGL2 expression, thrombin generation, phospho-Akt and NF-κB levels in MECs.

KEY FINDINGS

Upon treatment with STS in CNR model, the no-reflow and infarct areas decreased significantly and cardiac function improved. The FGL2 expression was inhibited by STS in vivo as well as in vitro with thrombin generation inhibition. In addition, STS up-regulates Akt phosphorylation and suppressed NF-κB expression in activated MECs. Furthermore, fibrin deposition, PAR-1 activation and inflammatory response were inhibited with STS administration in CNR model.

SIGNIFICANCE

Our results displayed a novel pharmacological action of STS on CNR. STS is able to ameliorate CNR through inhibition of FGL2 expression mediated by Akt and NF-κB pathways as well as prevention of MVO by suppressing fibrin deposition and inflammation.

Regulation of Bim in Health and Disease

The BH3-only Bim protein is a major determinant for initiating the intrinsic apoptotic pathway under both physiological and pathophysiological conditions. Tight regulation of its expression and activity at the transcriptional, translational and post-translational levels together with the induction of alternatively spliced isoforms with different pro-apoptotic potential, ensure timely activation of Bim. Under physiological conditions, Bim is essential for shaping immune responses where its absence promotes autoimmunity, while too early Bim induction eliminates cytotoxic T cells prematurely, resulting in chronic inflammation and tumor progression. Enhanced Bim induction in neurons causes neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's diseases. Moreover, type I diabetes is promoted by genetically predisposed elevation of Bim in β-cells. On the contrary, cancer cells have developed mechanisms that suppress Bim expression necessary for tumor progression and metastasis. This review focuses on the intricate network regulating Bim activity and its involvement in physiological and pathophysiological processes.

Platelet thrombin receptor antagonism with vorapaxar: pharmacology and clinical trial development

Oral antiplatelet therapies for secondary prevention of ischemic recurrences in patients with atherosclerotic disease manifestations include aspirin and P2Y12 receptor antagonists. Despite the use of these therapies, patients remain at risk for recurrent ischemic events, which may be attributed to other platelet signaling pathways which continue to be activated. More intense antithrombotic strategies have been investigated, including identifying additional targets to modulate platelet activation. Among these, thrombin-mediated platelet activation through PAR-1 has been subject to broad clinical investigation. Vorapaxar is the only PAR-1 receptor antagonists that completed large-scale clinical investigations and is approved for clinical use. This manuscript provides an overview of the pharmacology and clinical trial development of vorapaxar as well as its role in clinical practice.

Role of the extracellular signal-regulated kinase 1/2 signaling pathway in the process of thrombin-promoting airway remodeling in ovalbumin-allergic rats

CONTEXT

Although it is recognized that thrombin plays a key role in airway remodeling during chronic asthma. In a previous study, we have proved that thrombin promotes airway remodeling via PAR-1 in OVA-allergic rats, but little is known about intracellular signaling pathway involved in the event.

OBJECTIVE

In this study, we intend to explore the impact of pERK1/2 signaling pathway on the process of thrombin-induced airway remodeling in OVA-allergic rats.

MATERIALS AND METHODS

A rat model of chronic asthma was set up by systemic sensitization and repeated challenge to OVA. The doses of thrombin, recombinant hirudin, PAR-1 inhibitor ER-112780-06, and pERK1/2 inhibitor PD98059 varied for different groups. The expression of pERK1/2 was analyzed by western blot and RT-PCR. Secretion of TGF-β1 and IL-6 was detected by ELISA.

RESULTS

The expression of pERK1/2 was higher in the airway of asthmatic rats than those of normal rats, and was significantly increased by thrombin treatment but decreased by thrombin-inhibitor treatment. Airway remodeling was enhanced by thrombin but weakened by pERK1/2 inhibitor. Expression of growth factors and IL-6 in asthmatic rats was significantly increased by thrombin treatment and decreased by thrombin-inhibitor treatment and pERK1/2 inhibitor treatment.

CONCLUSION

These results suggest that ERK1/2 signaling pathway may play an important role in the process of thrombin-promoting airway remodeling in OVA-allergic rats, and pERK1/2 inhibitor effectively inhibits the process.

Antithrombin nanoparticles improve kidney reperfusion and protect kidney function after ischemia-reperfusion injury

In the extension phase of acute kidney injury, microvascular thrombosis, inflammation, vasoconstriction, and vascular endothelial cell dysfunction promote progressive damage to renal parenchyma after reperfusion. In this study, we hypothesized that direct targeting and pharmaceutical knockdown of activated thrombin at the sites of injury with a selective nanoparticle (NP)-based thrombin inhibitor, PPACK (phenylalanine-proline-arginine-chloromethylketone), would improve kidney reperfusion and protect renal function after transient warm ischemia in rodent models. Saline- or plain NP-treated animals were employed as controls. In vivo 19F magnetic resonance imaging revealed that kidney nonreperfusion was evident within 3 h after global kidney reperfusion at 34 ± 13% area in the saline group and 43 ± 12% area in the plain NP group and substantially reduced to 17 ± 4% (∼50% decrease, P < 0.05) in the PPACK NP pretreatment group. PPACK NP pretreatment prevented an increase in serum creatinine concentration within 24 h after ischemia-reperfusion, reflecting preserved renal function. Histologic analysis illustrated substantially reduced intrarenal thrombin accumulation within 24 h after reperfusion for PPACK NP-treated kidneys (0.11% ± 0.06%) compared with saline-treated kidneys (0.58 ± 0.37%). These results suggest a direct role for thrombin in the pathophysiology of AKI and a nanomedicine-based preventative strategy for improving kidney reperfusion after transient warm ischemia.

Differential cellular effects of old and new oral anticoagulants: consequences to the genesis and progression of atherosclerosis

The main purpose of anticoagulants is to diminish fibrin formation, thereby decreasing the risk of venous or arterial thrombosis. Vitamin K antagonist have been used for many decades in order to achieve reduced thrombotic risk, despite major drawbacks of this class of drugs such as cumbersome dossing and monitoring of anticoagulant status. To overcome these drawbacks of VKA, new classes of anticoagulants have been developed including oral anticoagulants for direct inhibition of either thrombin or factor Xa, which can be administrated in a fixed dose without monitoring. Coagulation factors can activate cellular protease-activated receptors, thereby inducing cellular processes as inflammation, apoptosis, migration, and fibrosis. Therefore, inhibition of coagulation proteases not only attenuates fibrin formation, but may also influence pathophysiological processes like vascular calcification and atherosclerosis. Animal models revealed that VKA therapy induced both intima and media calcification and accelerated plaque vulnerability, whereas specific and direct inhibition of thrombin or factor Xa attenuated atherosclerosis. In this review we provide an overview of old and new oral anticoagulants, as well discuss potential pleiotropic effects with regard to calcification and atherosclerosis. Although translation from animal model to clinical patients seems difficult at first sight, effort should be made to fully understand the clinical implications of long-term oral anticoagulant therapy on vascular side effects.

Thrombin promotes airway remodeling via protease-activated receptor-1 and transforming growth factor-β1 in ovalbumin-allergic rats

BACKGROUND

Protease-activated receptor-1 (PAR-1) is widely distributed in platelets and involved in coagulation cascade activated by thrombin. In this study, we intend to explore the role of PAR-1 in the process of thrombin-inducing transforming growth factor-β1 (TGF-β1) to promote airway remodeling in ovalbumin (OVA)-allergic rats.

MATERIALS AND METHODS

A rat model of chronic asthma was set up by systemic sensitization and repeated challenge to OVA. The doses of thrombin, recombinant hirudin, PAR-1 inhibitor ER-112780-06 varied for different groups. We evaluated the bronchoalveolar lavage fluid (BALF) concentration of thrombin in these groups. The protein and gene expression of PAR-1 was assessed and the expression of TGF-β1 was also detected.

RESULTS

The PAR-1 mRNA level and the protein level were higher in the airway of asthmatic rats than those of normal rats, and were significantly increased by thrombin treatment but decreased by thrombin-inhibitor treatment. Airway remodeling was strengthened by thrombin but weakened by thrombin inhibitor and PAR-1 antagonist. Expression of TGF-β1 protein in asthmatic rats was significantly increased by thrombin treatment and decreased by thrombin-inhibitor treatment and PAR-1 antagonist treatment.

CONCLUSION

The expression of PAR-1 is regulated by thrombin that induces the expression of TGF-β1 to promote airway remodeling via PAR-1 in OVA-allergic rats.

Dichotomous effects of exposure to bivalirudin in patients undergoing percutaneous coronary intervention on protease-activated receptor-mediated platelet activation

Bivalirudin is a direct thrombin inhibitor that is increasingly used in percutaneous coronary intervention (PCI) and has been previously shown to lack inherent platelet activation. Thrombin works through activation of protease activated receptor-1 (PAR1) and PAR4 on human platelets to initiate signaling cascades leading to platelet aggregation. Despite the increasing usage of bivalirudin, the effects on platelet function have not been well defined. Bivalirudin exposure during PCI was therefore assessed for its potential short-term effects on washed platelet function through PAR1 and PAR4. Bivalirudin significantly inhibited low-dose thrombin-mediated platelet aggregation, dense granule secretion, integrin αIIbβ3 activation and Rap1 activation and high dose thrombin-mediated dense granule secretion and Rap1 activation. Exposure to bivalirudin did not alter PAR1 or 4 agonist peptide (PAR1-AP or PAR4-AP) induced aggregation, dense granule secretion, integrin glycoprotein IIbIIIa activation or Rap1 activation. However, exposure to bivalirudin significantly potentiated surface expression of P-selectin following stimulation with high dose thrombin and PAR1-AP, and both low and high dose PAR4-AP. Hence, our data are the first to show that exposure to bivalirudin increased P-selectin expression with certain conditions demonstrating that bivalirudin can increase inherent platelet activity.

Antithrombotic Strategies in Endovascular Interventions: Current Status and Future Directions

Despite increasing numbers of endovascular interventions to treat arterial and venous disease, scant level 1 evidence is available regarding the role of antithrombotic and antiplatelet therapy in patients undergoing these procedures. The current practice in this regard is heterogeneous and has mainly been driven by data from coronary artery disease and percutaneous coronary intervention. This article discusses the role of antithrombotic and antiplatelet agents for endovascular intervention.

Role of G protein-coupled receptors in inflammation

G protein-coupled receptors (GPCRs) play important roles in inflammation. Inflammatory cells such as polymorphonuclear leukocytes (PMN), monocytes and macrophages express a large number of GPCRs for classic chemoattractants and chemokines. These receptors are critical to the migration of phagocytes and their accumulation at sites of inflammation, where these cells can exacerbate inflammation but also contribute to its resolution. Besides chemoattractant GPCRs, protease activated receptors (PARs) such as PAR1 are involved in the regulation of vascular endothelial permeability. Prostaglandin receptors play different roles in inflammatory cell activation, and can mediate both proinflammatory and anti-inflammatory functions. Many GPCRs present in inflammatory cells also mediate transcription factor activation, resulting in the synthesis and secretion of inflammatory factors and, in some cases, molecules that suppress inflammation. An understanding of the signaling paradigms of GPCRs in inflammatory cells is likely to facilitate translational research and development of improved anti-inflammatory therapies.

Modifiers of symptomatic embolic risk in infective endocarditis

OBJECTIVE

To ascertain the impact of prior antiplatelet and statin therapy on symptomatic embolic events in [corrected] infective endocarditis (IE).

PATIENTS AND METHODS

We studied a retrospective cohort of adult patients with a diagnosis of IE who presented to Mayo Clinic (Rochester, MN) from January 1, 2003, to December 31, 2006. Patients were grouped into those who received treatment before infection or controls who did not receive treatment for both antiplatelet therapy and, separately, statin therapy. Because of the retrospective study design and thus the nonrandomized treatment groups, a propensity score approach was used to account for the confounding factors that may have influenced treatment allocation. Antiplatelet therapy included aspirin, dipyridamole, clopidogrel, ticlopidine or any combination of these agents. Statin therapy included atorvastatin, simvastatin, pravastatin, lovastatin, rosuvastatin, or fluvastatin. The primary end point was a symptomatic embolic event that occurred before or during hospitalization. Multivariable logistic regression was used to assess the propensity-adjusted effects of continuous daily therapy with antiplatelet and statin agents on risk of symptomatic emboli. Likewise, Cox proportional hazards regression was used to test for an independent association with 6-month mortality for each of the treatments.

RESULTS

The study cohort comprised 283 patients with [corrected] IE. Twenty-eight patients (24.1%) who received prior continuous antiplatelet therapy developed a symptomatic embolic event compared with 66 (39.5%) who did not receive such treatment. After adjusting for propensity to treat, the effect of antiplatelet therapy on embolic risk was not statistically significant (odds ratio, 0.71; 95% confidence interval [CI], 0.37-1.36; P=.30). Only 14 patients (18.2%) who received prior continuous statin therapy developed a symptomatic embolic event compared with 80 (39.4%) of the 203 patients who did not. After adjusting for propensity to treat with statin therapy, the benefit attributable to statins was significant (odds ratio, 0.30; 95% CI, 0.14-0.62; P=.001). The 6-month mortality rate of the entire cohort was 28% (95% CI, 23%-34%). No significant difference was found in the propensity-adjusted rate of 6-month mortality between patients who had and had not undergone prior antiplatelet therapy (P=.91) or those who had and had not undergone prior statin therapy (P=.87).

CONCLUSION

The rate of symptomatic emboli associated with IE was reduced in patients who received continuous daily statin therapy before onset of IE. Despite fewer embolic events observed in patients who received antiplatelet agents, a significant association was not found after adjusting for propensity factors. A continued evaluation of these drugs and their potential impact on subsequent embolism among IE patients is warranted.

Effects of antithrombin III treatment in vascular injury model of mice

BACKGROUND

Balloon angioplasty has recently been adopted as an acceptable form of treatment for stenotic vessel lesions of congenital heart diseases. However, precise mechanisms of restenosis and thrombosis, which are the most common complications after these procedures, are unknown.

METHODS

We examined the effects of antithrombin III (ATIII) on inflammation, thrombus formation, and remodeling of vascular wall after guidewire-induced injury in the femoral artery of mice. ATIII or saline was administered as a bolus intravenous infusion before injury.

RESULTS

Seventy-two hours after injury, approximately half of the saline-treated vessels showed macroscopic thrombus formation. In contrast, no thrombi were seen in the arteries pretreated with ATIII. Significantly higher levels of inflammation were induced in the injured vessels than in the sham-operated controls, as determined by CD11b-positive cell density in the adventitial area. ATIII treatment resulted in marked reduction of inflammatory cell infiltration. Twenty-eight days after injury, similar levels of neointimal proliferation were found in the injured arteries in both groups.

CONCLUSIONS

Our results suggested that a high dose of ATIII may influence the sequelae of arterial injury by reducing mural thrombus formation and limiting the inflammatory reaction of the vessel wall without altering the process of vascular remodeling.

Clinical use of topical thrombin as a surgical hemostat

When surgical ligation of bleeding fails, or is not possible, surgeons rely on a number of hemostatic aids, including thrombin. This review discusses the history, pharmacology and clinical application of thrombin as a surgical hemostat. The initial thrombin was bovine in origin, but its use has been complicated by the formation of antibodies that cross react with human coagulation factors. This has been associated with life threatening bleeding and in some circumstances anaphylaxis and death. Human thrombin, isolated from pooled plasma of donors, has been developed in an effort to minimize these risks, but its downside is the potential of transmitting blood-borne pathogens and limited availability. Recently a recombinant thrombin has been developed and approved for use by the FDA. It has the advantage of being minimally antigenic and devoid of the risk if viral transmission. Thrombin is often used in conjunction with other hemostatic aids, including absorbable agents (like gelfoam, collagen, and cellulose), and with fibrinogen in fibrin glues. The last part of this review will discuss these agents in detail, and review their clinical applications.

Oral administration of the thrombin receptor antagonist E5555 (atopaxar) attenuates intimal thickening following balloon injury in rats

Thrombin is a powerful agonist for a variety of cellular responses including platelet aggregation and vascular smooth muscle cell (SMC) proliferation. These actions are mediated by a thrombin receptor known as protease-activated receptor-1 (PAR-1). Recently we discovered that 1-(3-tert-butyl-4-methoxy-5-morpholinophenyl)-2-(5,6-diethoxy-7-fluoro-1-imino-1,3-dihydro-2H-isoindol-2-yl)ethanone hydrobromide (E5555, atopaxar) is a potent and selective thrombin receptor antagonist. This study characterized the pharmacological effects of E5555 on SMC proliferation in vitro and in a rat model of intimal thickening after balloon injury in vivo. E5555 selectively inhibited rat aortic SMC proliferation induced by thrombin and thrombin receptor-activating peptide (TRAP) with half maximal inhibitory concentration (IC(50)) values of 0.16 and 0.038 μM, respectively. E5555 did not inhibit rat SMC proliferation induced by basic fibroblast growth factor (bFGF) and platelet-derived growth factor (PDGF) at concentrations up to 1μM. In addition, E5555 inhibited human aortic SMC proliferation induced by thrombin at concentrations of 0.3 and 3units/ml with IC(50) values of 0.028 and 0.079 μM, respectively, whereas it did not affect bFGF-induced proliferation at concentrations up to 1μM. Repeated oral administration of 30 mg/kg E5555 (once daily for 16 days) significantly reduced neointimal formation in the balloon-injured rat arterial model. These results suggested that a PAR-1 antagonist could be effective for treating restenosis following vascular intervention in addition to preventing thrombus formation. E5555 could thus have therapeutic potential for restenosis and chronic atherothrombotic disease.

Blood coagulation factor Xa as an emerging drug target

INTRODUCTION

Factor (F)Xa is well-known as an important player in the coagulation cascade responsible for thrombin generation. More recently, FXa emerged as an essential player in cell biology via activation of protease-activated receptors (PAR)-1 and -2. This pleiotropic role of FXa forms the basis for its potential contribution to the pathogenesis of several diseases.

AREAS COVERED

The role of FXa in pathophysiology is reviewed with special emphasis on its signal transduction properties. To this end, we first discuss the important role of FXa in the coagulation cascade, we continue with recent data on FXa induced signaling in pathophysiology with special emphasis on tissue remodeling and fibrosis and discuss the potential of FXa as an emerging drug target.

EXPERT OPINION

FXa is more than a passive intermediate in the coagulation cascade and FXa may in fact orchestrate fundamental processes during pathophysiology. Targeting FXa may be an exciting new therapeutic strategy in the treatment of (fibro)proliferative diseases for which current treatment options are limited.

cAMP-Response-element-binding-protein-binding protein silencing inhibits thrombin-induced endothelial progenitor cell migration via downregulation of CXCR4 expression

Previous studies have demonstrated that activation of thrombin receptor could promote endothelial progenitor cell (EPC) migration. As cAMP-response-element-binding-protein-binding protein (CBP) is involved in many cellular biological processes, we hypothesized that CBP mediates thrombin-induced EPC migration. In this study, we examined whether CBP silencing would affect EPC migration induced by thrombin using small interference RNA approach. EPC isolated from the bone marrow of femurs and tibias of Sprague-Dawley rats were cultured and identified, and then were treated by thrombin alone or combined with CBP-shRNA lentivirus. Transwell chamber assay was performed to measure EPC migration. Quantitative real-time polymerase chain reaction and Western blot were carried out to detect the expression of CBP and CXCR4. Thrombin induced CBP expression in a time- and dose-dependent manner. Small interference RNA for CBP downregulated thrombin-induced CBP expression. Thrombin-induced EPC migration was also attenuated by CBP downregulation. Western blot indicated that CXCR4 expression on EPC is upregulated by thrombin and this effect was blocked by CBP silencing. In conclusion, thrombin-induced EPC migration was inhibited by CBP silencing via downregulation of CXCR4 expression, indicating that CBP plays an important role in thrombin-induced EPC migration.

Activation of protease-activated receptors 3 and 4 accelerates tissue factor-induced thrombin generation on the surface of vascular smooth muscle cells

OBJECTIVE

To determine factors regulating human aortic smooth muscle cells (HASMC) supported tissue factor-induced thrombin generation.

METHODS AND RESULTS

The addition of nonlipidated tissue factor and Ca(2+) to HASMCs maintained in reptilase-treated platelet-poor plasma resulted in the robust formation of thrombin after a lag phase of approximately 6 minutes. Pretreatment with low concentrations of α-thrombin before the addition of tissue factor and Ca(2+) accelerated the rate of thrombin generation (time to reach half of peak thrombin was reduced by [mean ± SD] 42.0 ± 2.2%; P<0.05) but had no effect on the amount of peak thrombin generated. Protease-activated receptor (PAR) 3 activating peptides (APs) or PAR-4 APs accelerated thrombin generation without affecting peak thrombin levels (time to half of peak thrombin decreased by 17.4 ± 5.6% and 21.7 ± 3.5%; P<0.05 with PAR-3 AP and PAR-4 AP, respectively). The addition of PAR-3 AP and PAR-4 AP together had an additive effect, with a reduction in time to half of peak thrombin of 43.9 ± 4.0%. PAR-3 AP or PAR-4 AP enhanced tissue factor-induced factor Xa production and phosphatidylserine exposure on the surface of HASMCs. PAR-1 activation had no effect on thrombin generation, factor Xa production, or phosphatidylserine exposure.

CONCLUSIONS

Low concentrations of α-thrombin accelerate tissue factor-induced thrombin generation on the surface of HASMCs, and this effect is mediated by PAR-3 and PAR-4.

SCH 530348: a novel oral thrombin receptor antagonist

SCH 530348, a synthetic tricyclic 3-phenylpyridine, is an orally active fourth generation himbacine-based antagonist of the protease-activated receptor (PAR)-1, the primary receptor for thrombin on platelets in humans. SCH 530348 is the first in a new class of compounds that inhibit thrombin-mediated platelet aggregation without affecting the enzymatic activity of thrombin on fibrinogen. Preclinical and initial clinical studies have demonstrated this compound to be a highly potent inhibitor of thrombin-induced platelet activation, to have excellent oral bioavailability and to have a favorable safety profile. These data suggest that this compound has the potential to reduce the risk of ischemic events without significantly increasing the rate of bleeding. Two large Phase III clinical outcome trials are currently underway to evaluate the safety and efficacy of SCH 530348 for the management of acute coronary syndromes and the secondary prevention of atherothrombotic events.

Thrombin use in surgery: an evidence-based review of its clinical use

When surgical ligation of bleeding fails, or is not possible, surgeons rely on a number of hemostatic aids, including thrombin. This review discusses the history, pharmacology and clinical application of thrombin as a surgical hemostat. The initial thrombin was bovine in origin, but its use has been complicated by the formation of antibodies that cross-react with human coagulation factors. This has been associated with life-threatening bleeding and in some circumstances anaphylaxis and death. Human thrombin, isolated from pooled plasma of donors, was developed in an effort to minimize these risks, but its downsides are its limited availability and the potential for transmitting blood-borne pathogens. Recently a recombinant thrombin has been developed, and approved for use by the FDA. It has the advantage of being minimally antigenic and devoid of the risk of viral transmission. Thrombin is often used in conjunction with other hemostatic aids, including absorbable agents such as Gelfoam, and with fibrinogen in fibrin glues. The last part of this review will discuss these agents in detail, and review their clinical applications.

Vascular PAR-1: activity and antagonism

Despite major advances in antiplatelet therapies, recurrent cardiovascular events remain high after acute coronary syndrome. Furthermore, incremental benefits achieved in the reduction of atherothrombotic events have almost always been at the expense of hemorrhagic side effects. Thrombin is the most potent platelet activating factor known and it makes important interactions with the endothelium and vascular smooth muscle with proinflammatory, proatherogenic effects. Distinct from its activity within the coagulation cascade, thrombin mediates these effects via protease-activated receptor type 1 (PAR-1) in man. This review discusses the role of PAR-1 in the vasculature and the development of novel PAR-1 antagonists. These drugs may provide important antiatherothrombotic effects without attendant bleeding complications and could represent a major breakthrough for the treatment of cardiovascular diseases.

Haemostatic and fibrinolytic factors in men with a small abdominal aortic aneurysm

BACKGROUND

: The presence of an abdominal aortic aneurysm (AAA) independently predicts cardiovascular disease (CVD) and its complications. Levels of plasma markers of fibrin turnover are raised in men with a large AAA (at least 5.5 cm) and predict CVD risk in healthy subjects. This study examined fibrin turnover in men with a small AAA.

METHODS

: Seventy-five men with a small AAA (30-55 mm) were compared with 90 controls matched for age, sex and race. Haemostatic and fibrinolytic parameters were assessed.

RESULTS

: Men with a small AAA had higher mean levels of fibrinogen (2.92 versus 2.59 g/l; P = 0.019), thrombin-antithrombin (TAT) complex (4.57 versus 1.89 ng/ml; P < 0.001), prothrombin F1 + 2 (1.13 versus 0.82 ng/ml; P = 0.004) and D-dimer (346.7 versus 120.2 ng/ml; P < 0.001). All markers correlated with maximum aortic diameter determined by ultrasonography. On multivariable regression the association between presence of an AAA and fibrinogen, TAT complex, prothrombin F1 + 2 and D-dimer levels remained significant after adjustment for confounding influences.

CONCLUSION

: Fibrin turnover was increased in these men with a small AAA, independently of concomitant CVD, conventional risk factors and inflammatory markers. Enhanced fibrin turnover may contribute to the risk of cardiac complications in this group.

Inhibition of neointimal hyperplasia by a specific thrombin inhibitor

OBJECTIVE

Restenosis secondary to neointimal hyperplasia remains the major limiting factor after vascular interventions. Thrombin generated in high concentrations at the site of vascular injury plays a central role in thrombosis and hemostasis. Thrombin has also been implicated as a mitogen for smooth muscle cell proliferation that contributes to restenosis. This study was designed to determine the effects of a specific thrombin inhibitor on neointimal hyperplasia after balloon injury in a rat carotid artery model.

DESIGN

A total of 47 male Sprague-Dawley rats were divided into five groups. All groups underwent balloon injury of the left carotid artery. A specific thrombin inhibitor, inogatran, was given in four different regimens: low and high dose injections, short-term infusion for 3 h, and long-term infusion for 1 week. After 2 weeks the animals were killed and the carotid neointima/media area ratio and the luminal narrowing were calculated.

RESULTS

All treatments significantly reduced the neointimal hyperplasia. Inogatran given as a long-term infusion for 1 week had the lowest neointima/media ratio compared with the other groups. The percentage of lumen narrowing was also significantly lower in all treatment groups compared with the control group.

CONCLUSION

A specific direct thrombin inhibitor, inogatran, reduces neointimal hyperplasia after arterial injury in rats. A more prolonged administration of the thrombin inhibitor gave a further reduction of the neointimal hyperplasia. It seems that inhibition of thrombin activity is not only important early after injury, but also later. This could have clinical implications in the treatment of restenosis and needs to be further evaluated.

Percutaneous transluminal angioplasty of lower limb arteries causes a systemic inflammatory response

BACKGROUND

Percutaneous transluminal angioplasty (PTA) of a lower limb arterial segment is a well-established treatment for suitable lesions for critical or noncritical lower limb ischemia. Our aim was to define the inflammatory response after PTA by measuring inflammatory markers.

METHODS

Twenty-five patients having PTA were compared with 20 patients having angiography alone. Interleukin-6 (IL-6), IL-8, IL-10, and tumor necrosis factor-alpha (TNF-alpha) were measured sequentially. The difference between postprocedure and preprocedure baseline levels were compared statistically between angiography alone and PTA. Patients were followed up to 1 year after the procedure, and the failure rate of PTA was noted.

RESULTS

IL-6 and TNF-alpha were significantly higher in PTA patients at 1 hr after PTA (p < 0.05), and the IL-6 level only was significantly higher at 24 hr post-PTA (p < 0.05) compared to angiography alone (Mann-Whitney test). IL-8 and IL-10 levels did not differ significantly in the PTA group. At 1 year after the procedure, 45% of PTAs had failed. There was no statistically significant correlation between failed PTA and inflammatory response.

CONCLUSION

PTA appears to cause a significant inflammatory response compared to angiography alone. This demonstrates a systemic manifestation of localized ischemia/reperfusion injury. Further investigation of the inflammatory response due to ischemia/reperfusion injury and its correlation with restenosis is recommended.

Regulation of protease-activated receptor-1 by vasodilatory prostaglandins via NFAT

AIMS

We recently reported that prostacyclin suppresses protease-activated receptor-1 (PAR-1) in human vascular smooth muscle cells (VSMC) via cyclic AMP and protein kinase A. This study examines the downstream mechanisms, particularly the role of nuclear factor of activated T-cells (NFAT).

METHODS AND RESULTS

Human saphenous vein VSMC were exposed to phorbol 12-myristate 13-acetate (PMA) to induce endogenous cyclooxygenase-2-dependent prostaglandin generation. This was found to attenuate PAR-1 expression; similar suppression was seen with the EP2-prostaglandin receptor agonist butaprost. Stimulation of the 'exchange protein directly activated by cyclic AMP' (EPAC) was without effect. The NFAT inhibitor cyclosporin A (CsA) or NFAT2 siRNA both reduced PAR-1 mRNA and protein expression and prevented the stimulatory effects of thrombin or PAR-1 activating peptide (TFLLRN) on ERK1/2 phosphorylation and interleukin-6 expression. CsA or mutation of the NFAT binding motif in the PAR-1 promoter also blunted PAR-1 promoter activity (luciferase reporter assay). These inhibitory actions of CsA were comparable to those of the prostacyclin-mimetic iloprost, and both CsA and iloprost similarly attenuated nuclear NFAT2 localization and binding to the PAR-1 promoter (chromatin immunoprecipitation assay).

CONCLUSIONS

This study provides the first evidence that NFAT2 contributes to the transcriptional control of PAR-1 in human VSMC and that PKA-dependent NFAT2 inhibition represents a mechanism by which vasodilatory prostaglandins regulate the vascular actions of thrombin.

Association of aortic valve sclerosis with thrombin generation in hypertensive patients

Aortic valve sclerosis (AVS) may predispose to a prothrombotic state, as AVS is predictor of cardiovascular events in hypertensive populations. Thrombin exerts non-thrombotic effects such as vessel tone regulation, progression of atherosclerosis and stimulation of atrial natriuretic peptide (ANP) secretion. We hypothesized that hypertensive patients with AVS may have a persistently activated thrombin generation. We studied 234 asymptomatic never-treated hypertensive patients (73 of them with AVS). Prothrombin F1+2 (F1+2), as a marker of thrombin generation and fibrin D-dimer, as a marker of thrombus formation, ANP and brain natriuretic peptide (BNP) were measured. Presence of AVS, aortic jet velocity and left ventricular diameter at diastole were determined by echocardiography. Glomerular filtration rate was estimated using the Modification of Diet in Renal Disease formula. F1+2 (median and interquartile range (IQR) = 1.05, 0.87-1.38 nM vs. 0.93, 0.72-1.16) and ANP (22, 14-37 pg ml(-1) vs. 17, 11-25) levels were greater, and glomerular filtration rate values (65+/-9 ml min(-1)/1.73 m2 vs. 68+/-11) were lower in hypertensive patients with AVS than in those without AVS. F1+2 (odds ratio, 95% CI = 2.94, 1.07-8.6) was independently associated with AVS after being adjusted for age, gender and the variables of cardiorenal functions measured. After 6 months of treatment using valsartan, F1+2 levels remained elevated in hypertensive patients with AVS (1.14, 0.83-1.42 nM vs. 1.07, 0.84-1.5, n=19), but decreased in those without AVS (1.01, 0.85-1.31 vs. 0.8, 0.84-1.78, n=27). Thrombin generation was associated with AVS in untreated hypertensive patients, and this association was persistent after blood-pressure-lowering treatment using valsartan.

Role of the endothelium in the vascular effects of the thrombin receptor (protease-activated receptor type 1) in humans

OBJECTIVES

The purpose of this study was to determine the role of the endothelium in the vascular actions of protease-activated receptor type 1 (PAR-1) activation in vivo in man.

BACKGROUND

Thrombin is central to the pathophysiology of atherothrombosis. Its cellular actions are mediated via PAR-1. Protease-activated receptor type 1 activation causes arterial vasodilation, venoconstriction, platelet activation, and tissue-type plasminogen activator release in man.

METHODS

Dorsal hand vein diameter was measured in 6 healthy volunteers before and after endothelial denudation. Forearm arterial blood flow, plasma fibrinolytic factors, and platelet activation were measured in 24 healthy volunteers during venous occlusion plethysmography. The effects of inhibition of prostacyclin, nitric oxide (NO), and endothelium-derived hyperpolarizing factor on PAR-1 responses were assessed during coadministration of aspirin, the "NO clamp" (L-N(G)-monomethyl arginine and sodium nitroprusside), and tetraethylammonium ion, respectively.

RESULTS

Endothelial denudation did not affect PAR-1-evoked venoconstriction (SFLLRN; 0.05 to 15 nmol/min). Although aspirin had no effect, SFLLRN-induced vasodilation (5 to 50 nmol/min) was attenuated by the NO clamp (p < 0.0001) and tetraethylammonium ion (p < 0.05) and abolished by their combination (p < 0.01). The NO clamp augmented SFLLRN-induced tissue-type plasminogen activator and plasminogen activator inhibitor type 1 antigen (p < 0.0001) release, but tetraethylammonium ion and aspirin had no effect. SFLLRN-induced platelet activation was unaffected by NO or prostacyclin inhibition.

CONCLUSIONS

Acting via PAR-1, thrombin causes contrasting effects in the human vasculature and has a major interaction with the endothelium. This highlights the critical importance of endothelial function during acute arterial injury and intravascular thrombosis, as occurs in cardiovascular events including myocardial infarction and stroke.

Direct thrombin inhibitors: alternatives to heparin

After more than 70 years of effective clinical use, heparin remains the most common anticoagulant in use and one of the most commonly prescribed drugs to hospitalized patients. However, the biologic variability and immunogenicity limit its utility. With increasing volumes of vascular intervention and an aging population, an increase in the need for anticoagulation can be anticipated. This article reviews current viable options and barriers to the use of heparin.