The hemostatic system as a modulator of atherosclerosis

Synergistic effect of thrombin and CD40 ligand on endothelial matrix metalloproteinase-10 expression and microparticle generation in vitro and in vivo

OBJECTIVE

Thrombin induces CD40 ligand (CD40L) and matrix metalloproteinases (MMPs) under inflammatory/prothrombotic conditions. Thrombin and CD40L could modulate endothelial MMP-10 expression in vitro and in vivo.

METHODS AND RESULTS

Human endothelial cells were stimulated with thrombin (0.1-10 U/mL), CD40L (0.25-1 μg/mL), or their combination (thrombin/CD40L) to assess MMP-10 expression and microparticle generation. Thrombin/CD40L elicited higher MMP-10 mRNA (5-fold; P<0.001) and protein levels (4.5-fold; P<0.001) than either stimulus alone. This effect was mimicked by a protease-activated receptor-1 agonist and antagonized by hirudin, a-protease-activated receptor-1, α-CD40L, and α-CD40 antibodies. The synergistic effect was dependent on p38 mitogen-activated protein kinase and c-Jun N-terminal kinase-1 pathways. Thrombin also upregulated the expression of CD40 in endothelial cell surface increasing its availability, thereby favoring its synergistic effects with CD40L. In mice, thrombin/CD40L further increased the aortic MMP-10 expression. Septic patients with systemic inflammation and enhanced thrombin generation (n=60) exhibited increased MMP-10 and soluble CD40L levels associated with adverse clinical outcome. Endothelial and systemic activation by thrombin/CD40L and lipopolysaccharide also increased microparticles harboring MMP-10 and CD40L.

CONCLUSIONS

Thrombin/CD40L elicited a strong synergistic effect on endothelial MMP-10 expression and microparticles containing MMP-10 in vitro and in vivo, which may represent a new link between inflammation/thrombosis with prognostic implications.

Statins but not aspirin reduce thrombotic risk assessed by thrombin generation in diabetic patients without cardiovascular events: the RATIONAL trial

BACKGROUND

The systematic use of aspirin and statins in patients with diabetes and no previous cardiovascular events is controversial. We sought to assess the effects of aspirin and statins on the thrombotic risk assessed by thrombin generation (TG) among patients with type II diabetes mellitus and no previous cardiovascular events.

METHODOLOGY/PRINCIPAL FINDINGS

Prospective, randomized, open, blinded to events evaluation, controlled, 2×2 factorial clinical trial including 30 patients randomly allocated to aspirin 100 mg/d, atorvastatin 40 mg/d, both or none. Outcome measurements included changes in TG levels after treatment (8 to 10 weeks), assessed by a calibrated automated thrombogram. At baseline all groups had similar clinical and biochemical profiles, including TG levels. There was no interaction between aspirin and atorvastatin. Atorvastatin significantly reduced TG measured as peak TG with saline (85.09±55.34 nmol vs 153.26±75.55 nmol for atorvastatin and control groups, respectively; p = 0.018). On the other hand, aspirin had no effect on TG (121.51±81.83 nmol vs 116.85±67.66 nmol, for aspirin and control groups, respectively; p = 0.716). The effects of treatments on measurements of TG using other agonists were consistent.

CONCLUSIONS/SIGNIFICANCE

While waiting for data from ongoing large clinical randomized trials to definitively outline the role of aspirin in primary prevention, our study shows that among diabetic patients without previous vascular events, statins but not aspirin reduce thrombotic risk assessed by TG.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00793754.

Infections and inflammatory diseases as risk factors for venous thrombosis. A systematic review

Inflammation and venous thrombosis are intertwined. Only in the recent 15 years clinical epidemiological studies have focussed on inflammatory or infectious diseases as risk factors for venous thrombosis. Although a few reviews and many case reports or studies on these topic has been written, a review reporting relative or absolute risks for venous thrombosis has not been published yet. We performed a systematic review using Medline, Pubmed and Embase and found 31 eligible articles. Inflammatory bowel disease, ANCA-associated vasculitis, infections in general and more specifically, human immunodeficiency virus, pneumonia and urinary tract infections are associated with an increased risk of venous thrombosis.

Tissue factor-driven thrombin generation and inflammation in atherosclerosis

The transmembrane receptor tissue factor is a prominent protein expressed at macrophages and smooth muscle cells within human atherosclerotic lesions. While many coagulation proteins are detectable in atherosclerosis, a locally active thrombin and fibrin generating molecular machinery may be instrumental in manipulating cellular functions involved in atherogenesis. These include inflammation, angiogenesis and cell proliferation. Indeed, many experimental studies in mice show a correlation between hypercoagulability and increased atherosclerosis. In mice, the amount of atherosclerosis and/or the plaque phenotype, appear to be modifiable by specific anticoagulant interventions. While attempts to vary tissue factor level in the vasculature does not directly reduce plaque burden, the overexpression of tissue factor pathway inhibitor attenuates thrombogenicity and neo intima formation in mice. Moreover, inhibition of factor Xa or thrombin with novel selective agents, including rivaroxaban and dabigatran, inhibits inflammation associated with atherosclerosis in apoE(-/-) mice. The potential to modify a complex chronic disease like atherosclerosis with novel selective anticoagulants merits further clinical study.

MicroRNAs in the regulation of immune cell functions--implications for atherosclerotic vascular disease

Regarded as a chronic inflammatory disease of the vessel wall, the development of atherosclerotic lesions is shaped by immune responses and their regulation. Macrophages and dendritic cells are positioned at the crossroad of innate and adaptive immune responses by sensing atherogenic danger signals and by taking up and presenting antigens. T helper cells and auto-antibodies produced by B cells, together with their cytokine responses in turn modulate atheroprogression. In addition, platelets contribute to atherosclerosis by multiple pathways. microRNAs (miRNAs) that post-transcriptionally regulate gene expression may thus critically control immune cell differentiation and functions during plaque evolution. This review summarises the role of miRNAs in regulating lipid uptake and expression of inflammatory mediators in monocytes/macrophages and dendritic cells, in lymphocyte functions with a focus on T helper cell responses, as well as in platelet biology, and the implications of altering these functions in vascular pathology and atherosclerosis. T systematically survey miRNA functions in controlling molecular mechanisms and immune responses in atherosclerosis holds potential for the development of novel miRNA-based strategies for therapies targeting inflammation and immunity in atherosclerosis.

Effect of the factor Xa inhibitor rivaroxaban on arterial thrombosis in wild-type and apolipoprotein E-deficient mice

Rivaroxaban is a potent and specific direct inhibitor of coagulation factor Xa. Recent studies have highlighted its effectiveness in the prevention of venous thrombosis and embolic stroke due to atrial fibrillation. To evaluate the antithrombotic effects of rivaroxaban in an in vivo model of arterial thrombosis, photochemical vascular injury was induced in wild-type mice by intravenous rose bengal (50 mg/kg body weight [BW]) followed by illumination of the left common carotid artery using a 543 nm helium-neon laser beam. Rivaroxaban, injected concomitantly with rose bengal at doses of 1.0, 1.5, 2.0, or 3.0 mg/kg BW, dose-dependently prolonged the times to first thrombotic occlusion and stable thrombosis. Quantitative analysis of carotid flow curves revealed higher blood volumes passing through the injured artery with increasing rivaroxaban doses (P<0.01 and P<0.001 vs. vehicle for 2.0 and 3.0 mg/kg , respectively), suggesting a dose-dependent effect on vascular patency. Consistently, a significantly higher proportion of mice that received 2.0 and 3.0 mg/kg rivaroxaban exhibited patent carotid arteries at the end of the flow monitoring period compared to vehicle alone (P<0.05 and P<0.001, respectively). Histological analysis showed complete thrombotic arterial occlusion in vehicle-treated mice compared to less thrombotic material in mice injected with 3.0 mg/kg rivaroxaban (P<0.05). Rivaroxaban also prolonged the time to cessation of tail bleeding in a dose-dependent manner, starting at 1.5 mg/kg. Similar findings were obtained in apolipoprotein E-knockout mice. Rivaroxaban may exert beneficial effects by preventing arterial thrombosis and vascular occlusion after endothelial injury.

Factor VIII deficiency does not protect against atherosclerosis

BACKGROUND

Hemophilia A patients have a lower cardiovascular mortality rate than the general population. Whether this protection is caused by hypocoagulability or decreased atherogenesis is unclear.

OBJECTIVES

To evaluate atherosclerosis and endothelial function in hemophilia A patients with and without obesity as well as in matched, unaffected controls.

METHODS

Fifty-one obese (body mass index [BMI] ≥ 30 kg m(-2)) and 47 non-obese (BMI ≤ 25 kg m(-2)) hemophilia A patients, and 42 obese and 50 matched non-obese male controls were included. Carotid and femoral intima–media thickness [IMT] and brachial flow-mediated dilatation (FMD) were measured as markers of atherogenesis and endothelial function.

RESULTS

The overall population age was 50 ± 13 years. Carotid IMT was increased in obese subjects (0.77 ± 0.22 mm) as compared with non-obese subjects (0.69 ± 0.16 mm) [mean difference 0.07 mm (95% confidence interval [CI] 0.02–0.13, P = 0.008)]. No differences in mean carotid and femoral IMT between obese hemophilic patients and obese controls were found (mean difference of 0.02 mm [95% CI ) 0.07–0.11, P = 0.67], and mean difference of 0.06 mm [95% CI ) 0.13–0.25, P = 0.55], respectively). Thirty-five per cent of the obese hemophilic patients and 29% of the obese controls had an atherosclerotic plaque (P = 0.49), irrespective of the severity of hemophilia. Brachial FMD was comparable between obese hemophilic patients and obese controls (4.84% ± 3.24% and 5.32% ± 2.37%, P = 0.45).

CONCLUSION

Hemophilia A patients with obesity develop atherosclerosis to a similar extent as the general male population. Detection and treatment of cardiovascular risk factors in hemophilic patients is equally necessary.

Strategies for asymptomatic carotid artery stenosis

The treatment of asymptomatic carotid artery stenosis (ACAS) has continued to evolve for the past 3 decades. With rapidly advancing technology, the results of old trials have become obsolete. While there has been little change in the efficacy of carotid endarterectomy, there have been vast improvements in both medical management and carotid angioplasty with stenting. Finding the best therapy for a given patient can therefore be difficult. In this article, the authors review the current literature regarding treatment options for ACAS and the methods available for stratifying patients who would benefit from surgical versus medical treatment.

Characterization of the in vivo antiplatelet activity of the antihypertensive agent losartan

OBJECTIVE

The purpose of this study is to investigate the potential in vivo antiplatelet and thromboprotective properties of the antihypertensive drug losartan in mice.

METHODS

Aggregometry studies were performed on platelets obtained from mice administered losartan for 5 days, via tail vein to examine the ex vivo effects (dose dependence) of this agent and to select an appropriate dose for the in vivo studies. Next, the tail bleeding time test and the time for occlusion in a carotid artery injury thrombosis model (ferric chloride) were also performed to assess the in vivo effects of losartan treatment.

RESULTS

These data indicate that the antihypertensive agent losartan exerts dose-dependent inhibition of the thromboxane receptor-mediated (U46619/agonist)-induced platelet aggregation (ex vivo), whereas it produced no detectable effects on aggregation triggered by adenosine diphosphate or the thrombin receptor activating peptide 4. Findings from the in vivo analysis revealed that tail bleeding time of losartan-treated mice was not different from vehicle-treated mice. On the other hand, in the carotid artery injury thrombosis model, it was found that the losartan-treated mice had significantly longer time for occlusion in comparison with those treated with vehicle control.

CONCLUSIONS

These findings provide evidence that administration of the antihypertensive drug losartan into live mice produces thromboxane A(2) receptor-specific antiplatelet effects. Furthermore, interestingly, this antiplatelet activity appears to translate into thromboprotective properties, without resulting in a bleeding phenotype. Consequently, aside from its potential use as an antithrombotic agent, losartan's chemistry may provide a "blueprint" for designing or repurposing novel derivatives which may have the potential to serve as an antiplatelet and thromboprotective agents but are deprived of the usually concomitant bleeding adverse effects.

Thrombin generation in clinical conditions

Commercial assays for determining thrombin generation in plasma are being tested in clinical conditions associated with thrombosis or bleeding. While pre-analytical conditions remain a source of inter laboratory variation, demanding for further standardization, clinical research proceeds. In patients at risk of venous thrombosis thrombin generation (TG) analysis may be utilized to detect underlying thrombophilia and this has been achieved both with addition of thrombomodulin or activated protein C, to test the contribution of the protein C system. In patients with documented venous thromboembolism, increased TG values are seen in those patients at greatest risk for recurrence, although the data are not consistent yet. In patients with arterial vascular disease, effects on TG patterns are seen that both reflect atherosclerosis (and its risk factors) and link to risk of recurrent atherothrombosis (coronary or stroke), but the data are limited. In patients with a bleeding diathesis, like hemophilia, the main importance of TG assays lies in the application for monitoring replacement therapy, either with factor concentrate or rFVIIa. An interesting application is in conjunction with thromboelastography, for monitoring peri-operative transfusion policy. Finally, TG analysis may contribute to monitoring anticoagulant drug treatment, but these and other applications would greatly benefit from whole blood, point of care applications of TG testing.

Mean platelet volume predicting carotid atherosclerosis in atherothrombotic ischemic stroke

BACKGROUND

Platelets are involved in atherosclerosis. Mean platelet volume (MPV) could be a marker of platelet activation. We aim to determine whether MPV levels were correlated with the presence of atherosclerotic disease in carotid arteries of patients with stroke.

METHODS

We recruited 215 patients with atherothrombotic stroke. All the participants underwent ultrasonographic evaluation of their extracranial carotid arteries. MPV was measured in automated hematology analysis system. The subjects were divided according to plaques and severity of carotid stenosis. Univariate and multivariate statistical analyses and a ROC curve to predict carotid stenosis were performed.

RESULTS

Univariate analysis showed a positive relationship between MPV and the degree of carotid atherosclerosis (p < 0.00007), and with carotid intima to media thickness (p < 0.00002). In ROC curve, a MPV cut-off of 11.25 fl was obtained for a sensibility of 70% and a specificity of 71% (p < 0.02). Multivariate analysis showed significant correlation with severity of carotid stenosis, when MPV was higher than 11.25 fl (OR: 2.9, p < 0.00007).

CONCLUSIONS

Our results indicate that an elevated MPV could be an easily measurable marker of severity of carotid stenosis in patients with atherothrombotic stroke.

Biological characteristics of foam cell formation in smooth muscle cells derived from bone marrow stem cells

Bone marrow mesenchymal stem cells (BMSC) can differentiate into diverse cell types, including adipogenic, osteogenic, chondrogenic and myogenic lineages. There are lots of BMSC accumulated in atherosclerosis vessels and differentiate into VSMC. However, it is unclear whether VSMC originated from BMSC (BMSC-SMC) could remodel the vessel in new tunica intima or promote the pathogenesis of atherosclerosis. In this study, BMSC were differentiated into VSMC in response to the transforming growth factor β (TGF-β) and shown to express a number of VSMC markers, such as α-smooth muscle actin (α-SMA) and smooth muscle myosin heavy chain1 (SM-MHC1). BMSC-SMC became foam cells after treatment with 80 mg/L ox-LDL for 72 hours. Ox-LDL could upregulate scavenger receptor class A (SR-A) but downregulate the ATP-binding cassette transporter A1 (ABCA1) and caveolin-1 protein expression, suggesting that modulating relative protein activity contributes to smooth muscle foam cell formation in BMSC-SMC. Furthermore, we found that BMSC-SMC have some biological characteristics that are similar to VSMC, such as the ability of proliferation and secretion of extracellular matrix, but, at the same time, retain some biological characteristics of BMSC, such as a high level of migration. These results suggest that BMSC-SMC could be induced to foam cells and be involved in the development of atherosclerosis.

Role of vitamin K-dependent proteins in the arterial vessel wall

Vitamin K was discovered early last century at the same time as the vitamin K-antagonists. For many years the role of vitamin K was solely ascribed to coagulation and coagulation was thought to be involved only at the venous blood side. This view has dramatically changed with the discovery of vitamin K-dependent proteins outside the coagulation cascade and the role of coagulation factors at the arterial side. Vitamin K-dependent proteins are involved in the regulation of vascular smooth muscle cell migration, apoptosis, and calcification. Vascular calcification has become an important independent predictor of cardiovascular disease. Vitamin K-antagonists induce inactivity of inhibitors of vascular calcification, leading to accelerated calcification. The involvement of vitamin K-dependent proteins such as MGP in vascular calcification make that calcification is amendable for intervention with high intake of vitamin K. This review focuses on the effect of vitamin K-dependent proteins in vascular disease.

The role of platelets in atherothrombosis

Platelets have evolved highly specialized adhesion mechanisms that enable cell-matrix and cell-cell interactions throughout the entire vasculature irrespective of the prevailing hemodynamic conditions. This unique property of platelets is critical for their ability to arrest bleeding and promote vessel repair. Platelet adhesion under conditions of high shear stress, as occurs in stenotic atherosclerotic arteries, is central to the development of arterial thrombosis; therefore, precise control of platelet adhesion must occur to maintain blood fluidity and to prevent thrombotic or hemorrhagic complications. Whereas the central role of platelets in hemostasis and thrombosis has long been recognized and well defined, there is now a major body of evidence supporting an important proinflammatory function for platelets that is linked to host defense and a variety of autoimmune and inflammatory diseases. In the context of the vasculature, experimental evidence indicates that the proinflammatory function of platelets can regulate various aspects of the atherosclerotic process, including its initiation and propagation. The mechanisms underlying the proatherogenic function of platelets are increasingly well defined and involve specific adhesive interactions between platelets and endothelial cells at atherosclerotic-prone sites, leading to the enhanced recruitment and activation of leukocytes. Through the release of chemokines, proinflammatory molecules, and other biological response modulators, the interaction among platelets, endothelial cells, and leukocytes establishes a localized inflammatory response that accelerates atherosclerosis. These inflammatory processes typically occur in regions of the vasculature experiencing low shear and perturbed blood flow, a permissive environment for leukocyte-platelet and leukocyte-endothelial interactions. Therefore, the concept has emerged that platelets are a central element of the atherothrombotic process and that future therapeutic strategies to combat this disease need to take into consideration both the prothrombotic and proinflammatory function of platelets.