Activated monocytes capture platelets for heterotypic association in patients with severe carotid artery stenosis

Platelet Biomarkers in Patients with Atherosclerotic Extracranial Carotid Artery Stenosis: A Systematic Review

OBJECTIVE

The aim was to enhance understanding of the role of platelet biomarkers in the pathogenesis of vascular events and risk stratifying patients with asymptomatic or symptomatic atherosclerotic carotid stenosis.

DATA SOURCES

Systematic review conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement.

REVIEW METHODS

A systematic review collated data from 1975 to 2020 on ex vivo platelet activation and platelet function/reactivity in patients with atherosclerotic carotid stenosis.

RESULTS

Forty-three studies met the inclusion criteria; the majority included patients on antiplatelet therapy. Five studies showed increased platelet biomarkers in patients with ≥ 30% asymptomatic carotid stenosis (ACS) vs. controls, with one neutral study. Preliminary data from one study suggested that quantification of "coated platelets" in combination with stenosis severity may aid risk stratification in patients with ≥ 50% - 99% ACS. Platelets were excessively activated in patients with ≥ 30% symptomatic carotid stenosis (SCS) vs. controls (≥ 11 positive studies and one neutral study). Antiplatelet-High on Treatment Platelet Reactivity (HTPR), previously called "antiplatelet resistance", was observed in 23% - 57% of patients on aspirin, with clopidogrel-HTPR in 25% - 100% of patients with ≥ 50% - 99% ACS. Aspirin-HTPR was noted in 9.5% - 64% and clopidogrel-HTPR in 0 - 83% of patients with ≥ 50% SCS. However, the data do not currently support the use of ex vivo platelet function/reactivity testing to tailor antiplatelet therapy outside of a research setting. Platelets are excessively activated (n = 5), with increased platelet counts (n = 3) in recently symptomatic vs. asymptomatic patients, including those without micro-emboli on transcranial Doppler (TCD) monitoring (n = 2). Most available studies (n = 7) showed that platelets become more reactive or activated following carotid endarterectomy or stenting, either as an acute phase response to intervention or peri-procedural treatment.

CONCLUSION

Platelets are excessively activated in patients with carotid stenosis vs. controls, in recently symptomatic vs. asymptomatic patients, and may become activated/hyper-reactive following carotid interventions despite commonly prescribed antiplatelet regimens. Further prospective multicentre studies are required to determine whether models combining clinical, neurovascular imaging, and platelet biomarker data can facilitate optimised antiplatelet therapy in individual patients with carotid stenosis.

Age-Dependent Control of Collagen-Dependent Platelet Responses by Thrombospondin-1-Comparative Analysis of Platelets from Neonates, Children, Adolescents, and Adults

Platelet function is developmentally regulated. Healthy neonates do not spontaneously bleed, but their platelets are hypo-reactive to several agonists. The mechanisms underlying immature platelet function in neonates are incompletely understood. This critical issue remains challenging for the establishment of age-specific reference ranges. In this study, we evaluated platelet reactivity of five pediatric age categories, ranging from healthy full-term neonates up to adolescents (11–18 years) in comparison to healthy adults (>18 years) by flow cytometry. We confirmed that platelet hypo-reactivity detected by fibrinogen binding, P-selectin, and CD63 surface expression was most pronounced in neonates compared to other pediatric age groups. However, maturation of platelet responsiveness varied with age, agonist, and activation marker. In contrast to TRAP and ADP, collagen-induced platelet activation was nearly absent in neonates. Granule secretion markedly remained impaired at least up to 10 years of age compared to adults. We show for the first time that neonatal platelets are deficient in thrombospondin-1, and exogenous platelet-derived thrombospondin-1 allows platelet responsiveness to collagen. Platelets from all pediatric age groups normally responded to the C-terminal thrombospondin-1 peptide RFYVVMWK. Thus, thrombospondin-1 deficiency of neonatal platelets might contribute to the relatively impaired response to collagen, and platelet-derived thrombospondin-1 may control distinct collagen-induced platelet responses.

Plasmin-Induced Activation of Human Platelets Is Modulated by Thrombospondin-1, Bona Fide Misfolded Proteins and Thiol Isomerases

Inflammatory processes are triggered by the fibrinolytic enzyme plasmin. Tissue-type plasminogen activator, which cleaves plasminogen to plasmin, can be activated by the cross-β-structure of misfolded proteins. Misfolded protein aggregates also represent substrates for plasmin, promoting their degradation, and are potent platelet agonists. However, the regulation of plasmin-mediated platelet activation by misfolded proteins and vice versa is incompletely understood. In this study, we hypothesize that plasmin acts as potent agonist of human platelets in vitro after short-term incubation at room temperature, and that the response to thrombospondin-1 and the bona fide misfolded proteins Eap and SCN^--denatured IgG interfere with plasmin, thereby modulating platelet activation. Plasmin dose-dependently induced CD62P surface expression on, and binding of fibrinogen to, human platelets in the absence/presence of plasma and in citrated whole blood, as analyzed by flow cytometry. Thrombospondin-1 pre-incubated with plasmin enhanced these plasmin-induced platelet responses at low concentration and diminished them at higher dose. Platelet fibrinogen binding was dose-dependently induced by the C-terminal thrombospondin-1 peptide RFYVVMWK, Eap or NaSCN-treated IgG, but diminished in the presence of plasmin. Blocking enzymatically catalyzed thiol-isomerization decreased plasmin-induced platelet responses, suggesting that plasmin activates platelets in a thiol-dependent manner. Thrombospondin-1, depending on the concentration, may act as cofactor or inhibitor of plasmin-induced platelet activation, and plasmin blocks platelet activation induced by misfolded proteins and vice versa, which might be of clinical relevance.

Simultaneous assessment of plaque morphology, cerebral micro-embolic signal status and platelet biomarkers in patients with recently symptomatic and asymptomatic carotid stenosis

The relationship between plaque morphology, cerebral micro-embolic signals (MES) and platelet biomarkers in carotid stenosis patients warrants investigation.We combined data from two prospective, observational studies to assess carotid plaque morphology and relationship with cerebral MES and platelet biomarkers in patients with recently symptomatic (≤4 weeks of transient ischaemic attack (TIA)/ischaemic stroke) versus asymptomatic carotid stenosis. Plaque morphology on ultrasound was graded with Grey-Scale Median (GSM) and Gray-Weale (GW) scoring. Bilateral transcranial Doppler ultrasound classified patients as 'MES+ve' or 'MES-ve'. Full blood counts were analysed and flow cytometry quantified CD62P and CD63 expression, leucocyte-platelet complexes and reticulated platelets.Data from 42 recently symptomatic carotid stenosis patients were compared with those from 36 asymptomatic patients. There were no differences in median GSM scores between symptomatic and asymptomatic patients (25 vs. 30; P = 0.31) or between MES+ve vs. MES-ve symptomatic patients (36 vs. 25; P = 0.09). Symptomatic patients with GSM-echodense plaques (GSM ≥25) had higher platelet counts (228 vs. 191 × 10⁹/L), neutrophil-platelet (3.3 vs. 2.7%), monocyte-platelet (6.3 vs. 4.55%) and lymphocyte-platelet complexes (2.91 vs. 2.53%) than 'asymptomatic patients with GSM-echodense plaques' (P ≤ 0.03).Recently, symptomatic carotid stenosis patients with 'GSM-echodense plaques' have enhanced platelet production/secretion/activation compared with their asymptomatic counterparts. Simultaneous assessment with neurovascular imaging and platelet biomarkers may aid risk-stratification in carotid stenosis.

High on-clopidogrel platelet reactivity in ischaemic stroke or transient ischaemic attack: Systematic review and meta-analysis

OBJECTIVES

To assess the prevalence of high on-clopidogrel platelet reactivity (HCPR) in patients with ischaemic stroke or transient ischaemic attack (IS/TIA), their outcome and genetic basis of on-treatment response variability in IS/TIA patients.

METHODS

We conducted a comprehensive search of PubMed and EMBASE from their inceptions to March 9, 2019. Studies that reported absolute numbers/percentages of HCRP at any time point after IS/TIA onset evaluated with any type of platelet function tests, clinical outcomes and genotyping data were included.

RESULTS

Among 21 studies of 4312 IS/TIA patients treated with clopidogrel, the pooled prevalence of HCPR was 28% (95%CI: 24-32%; high heterogeneity: I² = 88.2%, p < 0.001). Heterogeneity degree diminished across groups defined by the HCPR testing method. Clopidogrel non-responder IS/TIA patients had poorer outcome compared to responders (RR = 2.09, 95%CI: 1.61-2.70; p = 0.036; low heterogeneity across studies: I² = 27.4%, p = 0.210). IS/TIA carriers of CYP2C19*2 or CYP2C19*3 loss of function alleles had a higher risk of HCPR compared to wild type (RR = 1.69, 95%CI: 1.47-1.95; p < 0.001; I² = 0.01%, p = 0.475).

CONCLUSIONS

This systematic review shows a high prevalence of clopidogrel resistance in IS/TIA and poor outcome in these patients. CYP2C19 polymorphisms may potentially influence clopidogrel resistance.

Role of thrombospondin‑1 and thrombospondin‑2 in cardiovascular diseases (Review)

Thrombospondin (TSP)-1 and TSP-2 are matricellular proteins in the extracellular matrix (ECM), which serve a significant role in the pathological processes of various cardiovascular diseases (CVDs). The multiple effects of TSP-1 and TSP-2 are due to their ability to interact with various ligands, such as structural components of the ECM, cytokines, cellular receptors, growth factors, proteases and other stromal cell proteins. TSP-1 and TSP-2 regulate the structure and activity of the aforementioned ligands by interacting directly or indirectly with them, thereby regulating the activity of different types of cells in response to environmental stimuli. The pathological processes of numerous CVDs are associated with the degradation and remodeling of ECM components, and with cell migration, dysfunction and apoptosis, which may be regulated by TSP-1 and TSP-2 through different mechanisms. Therefore, investigating the role of TSP-1 and TSP-2 in different CVDs and the potential signaling pathways they are associated with may provide a new perspective on potential therapies for the treatment of CVDs. In the present review, the current understanding of the roles TSP-1 and TSP-2 serve in various CVDs were summarized. In addition, the interacting ligands and the potential pathways associated with these thrombospondins in CVDs are also discussed.

Relationship between 'on-treatment platelet reactivity', shear stress, and micro-embolic signals in asymptomatic and symptomatic carotid stenosis

BACKGROUND

Assessment of 'high on-treatment platelet reactivity (HTPR)' could enhance understanding of the pathophysiology of first or recurrent vascular events in carotid stenosis patients on antiplatelet therapy.

METHODS

This prospective, multi-centre study assessed antiplatelet-HTPR status and its relationship with micro-emboli signals (MES) in asymptomatic vs. symptomatic ≥ 50-99% carotid stenosis. Platelet function/reactivity was assessed under 'moderately high shear stress' with the PFA-100^® and 'low shear stress' with VerifyNow^® and Multiplate^® analysers. Bilateral 1-h transcranial Doppler ultrasound of the middle cerebral arteries classified patients as MES + ve or MES - ve.

RESULTS

Data from 34 asymptomatic patients were compared with 43 symptomatic patients in the 'early phase' (≤ 4 weeks) and 37 patients in the 'late phase' (≥ 3 months) after TIA/ischaemic stroke. Median daily aspirin doses were higher in early symptomatic (225 mg; P < 0.001), but not late symptomatic (75 mg; P = 0.62) vs. asymptomatic patients (75 mg). There was a lower prevalence of aspirin-HTPR in early (28.6%; P = 0.028), but not late symptomatic (38.9%; P = 0.22) compared with asymptomatic patients (56.7%) on the PFA-100^®, but not on the VerifyNow^® or Multiplate^® (P ≤ 0.53). Early symptomatic patients had a higher prevalence of aspirin-HTPR on the PFA-100^® (28.6%) vs. VerifyNow^® (9.5%; P = 0.049), but not Multiplate^® assays (11.9%, P = 0.10). There was no difference in aspirin-HTPR prevalence between any symptomatic vs. asymptomatic MES + ve or MES - ve subgroup.

DISCUSSION

Recently symptomatic moderate-severe carotid stenosis patients had a lower prevalence of aspirin-HTPR than their asymptomatic counterparts on the PFA-100^®, likely related to higher aspirin doses. The prevalence of antiplatelet-HTPR was positively influenced by higher shear stress levels, but not MES status.

Review of serum biomarkers in carotid atherosclerosis

BACKGROUND

Carotid artery atherosclerotic stenosis is a preventable major cause of stroke, but there is still a need for definition of high-risk plaque in asymptomatic patients who might benefit from interventional therapies. Several image markers are recommended to characterize unstable plaques. The measurement of serum biomarkers is a promising method to assist in decision making, but the lack of robust evidence in the carotid environment burdens their potential as a standard of care. The goal of this review was to offer an updated state-of-the-art study of available serum biomarkers with clinical implications, with focus on those that may predict carotid symptom development.

METHODS

The Cochrane Library and MEDLINE databases were searched (all until September 2018) for studies on carotid plaque and serum biomarkers of atherosclerosis. Nonhuman, basic science, and histology studies were excluded, focusing on clinical studies. Selected abstracts were screened to include the most relevant articles on atherosclerotic plaque presence, progression, instability or symptom development.

RESULTS

Some well-established biomarkers for coronary disease are not relevant to carotid atherosclerosis and other inflammatory biomarkers, lipids, interleukins, homocysteine, and adipokines may be useful in quantifying carotid disease-related risk. Some serum biomarkers combined with image features may assist vascular specialists in selecting patients at high risk for stroke and in need of intervention.

CONCLUSIONS

Prospective studies applying a combination of biomarkers are essential to prove clinical usefulness.

Increased platelet count and reticulated platelets in recently symptomatic versus asymptomatic carotid artery stenosis and in cerebral microembolic signal-negative patient subgroups: results from the HaEmostasis In carotid STenosis (HEIST) study

BACKGROUND

The pathophysiological mechanisms responsible for the disparity in stroke risk between asymptomatic and symptomatic carotid stenosis patients are not fully understood. The functionally important reticulated platelet fraction and reticulocytes could play a role.

OBJECTIVES

We performed a prospective, multi-centre, observational analytical study comparing full blood count parameters and platelet production/turnover/activation markers in patients with asymptomatic versus recently symptomatic moderate (≥ 50-69%) or severe (≥ 70-99%) carotid stenosis.

PATIENTS/METHODS

Data from 34 asymptomatic patients were compared with 43 symptomatic patients in the 'early phase' (≤ 4 weeks) and 37 of these patients in the 'late phase' (≥ 3 months) after TIA/ischaemic stroke. Reticulated platelets were quantified by whole blood flow cytometry and reticulated platelets and red cell reticulocytes by 'automated assays' (Sysmex XE-2100™). Bilateral simultaneous transcranial Doppler ultrasound monitoring classified patients as micro-embolic signal (MES)+ve or MES-ve.

RESULTS

Mean platelet count was higher in early (216 × 10⁹/L; P = 0.04) and late symptomatic (219 × 10⁹/L; P = 0.044) than asymptomatic patients (194 × 10⁹/L). Mean platelet volume was higher in early symptomatic than asymptomatic patients (10.8 vs. 10.45 fl; P = 0.045). Automated assays revealed higher % reticulated platelet fractions in early (5.78%; P < 0.001) and late symptomatic (5.11%; P = 0.01) than asymptomatic patients (3.48%). Red cell reticulocyte counts were lower in early (0.92%; P = 0.035) and late symptomatic (0.93%; P = 0.036) than asymptomatic patients (1.07%). The automated % reticulated platelet fraction was also higher in early symptomatic than asymptomatic MES-ve patients (5.7 vs. 3.55%; P = 0.001).

DISCUSSION

The combination of increased platelet counts and a shift towards production of an increased population of larger, young, reticulated platelets could contribute to a higher risk of first or recurrent cerebrovascular events in recently symptomatic versus asymptomatic carotid stenosis, including those who are MES-ve.

Platelet-localized FXI promotes a vascular coagulation-inflammatory circuit in arterial hypertension

Multicellular interactions of platelets, leukocytes, and the blood vessel wall support coagulation and precipitate arterial and venous thrombosis. High levels of angiotensin II cause arterial hypertension by a complex vascular inflammatory pathway that requires leukocyte recruitment and reactive oxygen species production and is followed by vascular dysfunction. We delineate a previously undescribed, proinflammatory coagulation-vascular circuit that is a major regulator of vascular tone, blood pressure, and endothelial function. In mice with angiotensin II-induced hypertension, tissue factor was up-regulated, as was thrombin-dependent endothelial cell vascular cellular adhesion molecule 1 expression and integrin α_Mβ₂- and platelet-dependent leukocyte adhesion to arterial vessels. The resulting vascular inflammation and dysfunction was mediated by activation of thrombin-driven factor XI (FXI) feedback, independent of factor XII. The FXI receptor glycoprotein Ibα on platelets was required for this thrombin feedback activation in angiotensin II-infused mice. Inhibition of FXI synthesis with an antisense oligonucleotide was sufficient to prevent thrombin propagation on platelets, vascular leukocyte infiltration, angiotensin II-induced endothelial dysfunction, and arterial hypertension in mice and rats. Antisense oligonucleotide against FXI also reduced the increased blood pressure and attenuated vascular and kidney dysfunction in rats with established arterial hypertension. Further, platelet-localized thrombin generation was amplified in an FXI-dependent manner in patients with uncontrolled arterial hypertension, suggesting that platelet-localized thrombin generation may serve as an inflammatory marker of high blood pressure. Our results outline a coagulation-inflammation circuit that promotes vascular dysfunction, and highlight the possible utility of FXI-targeted anticoagulants in treating hypertension, beyond their application as antithrombotic agents in cardiovascular disease.

Measurement of residual platelet thrombogenicity under arterial shear conditions in cerebrovascular disease patients receiving antiplatelet therapy

Essentials A consensus methodology for assessing the effects of antiplatelet agents has not been established. Measuring platelet thrombus formation (PTF) for evaluating antiplatelet effects was assessed. PTF differentially reflected antiplatelet effects compared to other tests. PTF may be associated with the severity of carotid or intracranial arterial stenosis. Click to hear a presentation on platelet function testing in the clinic by Gresele and colleagues

SUMMARY

Background A consensus methodology for assessing the effects of antiplatelet agents has not been established. Objective We investigated the usefulness of directly measuring platelet thrombus formation (PTF) using a microchip-based flow chamber system for evaluating antiplatelet therapy. Patients/Methods Platelet thrombus formation in the whole blood of 94 patients with ischemic cerebrovascular disease treated with clopidogrel and/or aspirin was measured in a flow chamber system at a shear rate of 1500 s(-1) and was compared with the results of assays for agonist-induced platelet aggregability, phosphorylation of vasodilator-stimulated phosphoprotein, platelet p-selectin expression (PS), and platelet-monocyte complexes. Results In all patients tested, area under the flow pressure curve (AUC10), which represents platelet thrombogenicity, showed weak correlation with platelet aggregation induced by either adenosine diphosphate or collagen. In addition, AUC10 was lower in patients treated with dual antiplatelet therapy (median 79.4) compared with patients treated with aspirin or clopidogrel alone (217.7 and 301.0, respectively), whereas the parameters evaluated by the other assays did not reflect the combined treatment efficacy. In clopidogrel monotherapy patients, AUC10 was associated with the severity of arterial stenosis (R(2) = 0.127, β = 1.25), and AUC10 and PS were higher in patients with severe carotid or intracranial arterial stenosis than in those with mild stenosis. Conclusions Platelet thrombus formation measurement using a flow-chamber system was useful for evaluating the efficacy of treatment with aspirin and clopidogrel, both alone and in combination. The present findings indicate that high residual platelet thrombogenicity in patients treated with clopidogrel may be associated with the severity of carotid or intracranial arterial stenosis.

Atrial fibrillation is associated with high levels of monocyte-platelet-aggregates and increased CD11b expression in patients with aortic stenosis

A growing body of evidence suggests a pivotal role of inflammatory processes in AF in a bidirectional manner. Infiltrating leukocytes seem to promote both structural and electrical remodelling processes in patients with AF. Monocyte-platelets-aggregates (MPAs) are sensitive markers of both platelets and monocyte activation. So far it is not clear whether the content of MPAs is affected by AF. The present study examined the content of MPAs and the activation of monocytes in elderly patients with an aortic stenosis in dependence of AF. These patients are known to have a high prevalence of AF. Flow-cytometric quantification analysis demonstrated that patients with AF have an increased content of MPAs (207 ± 13 cells/µl vs 307 ± 21 cells/µl, p< 0.001), and enhanced expression of CD11b on monocytes (p< 0.001), compared to patients in stable sinus rhythm (SR). The number of CD14+/CD16+ monocytes were only slightly elevated in patients with AF. These findings were seen in patients with permanent AF. But also patients with paroxysmal AF, even when presenting in SR, the MPAs were increased by 50 % (p< 0.05) as well as the CD11b expression, which was twice as high (p< 0.05) compared to stable SR. These results demonstrate for the first time a dependency of MPAs and CD11b expression on monocytes in the presence of AF and support the notion of a close relationship between AF, thrombogenesis and inflammation. The content of MPAs and the extent of activation on monocytes appear promising as biomarkers for paroxysmal AF and as possible future targets for developing novel pharmacological therapeutic strategies.

Kindlin 3 (FERMT3) is associated with unstable atherosclerotic plaques, anti-inflammatory type II macrophages and upregulation of beta-2 integrins in all major arterial beds

BACKGROUND

Kindlins (FERMT) are cytoplasmic proteins required for integrin (ITG) activation, leukocyte transmigration, platelet aggregation and thrombosis. Characterization of kindlins and their association with atherosclerotic plaques in human(s) is lacking.

METHODS AND RESULTS

Exploratory microarray (MA) was first performed followed by selective quantitative validation of robustly expressed genes with qRT-PCR low-density array (LDA). In LDA, ITGA1 (1.30-fold, p = 0.041) and ITGB3 (1.37-fold, p = 0.036) were upregulated in whole blood samples of patients with coronary artery disease (CAD) compared to healthy controls. In arterial plaques, both robustly expressed transcript variants of FERMT3 (MA: 5.90- and 3.4-fold; LDA: 3.99-fold, p < 0.0001 for all) and ITGB2 (MA: 4.81- and 4.92-fold; LDA: 5.29-fold, p < 0.0001 for all) were upregulated while FERMT2 was downregulated (MA: -1.61-fold; LDA: -2.88-fold, p < 0.0001 for both). The other integrins (ITGA1, ITGAV, ITGB3, ITGB5) were downregulated. All these results were replicated in at least one arterial bed. The latter FERMT3 transcript variant associated with unstable plaques (p = 0.0004). FERMT3 correlated with M2 macrophage markers and in hierarchical cluster analysis clustered with inflammatory and macrophage markers, while FERMT2 correlated with SMC-rich plaque markers and clustered with SMC markers. In confocal immunofluorescence analysis, FERMT3 protein colocalized with abundant CD68-positive cells of monocytic origin in the atherosclerotic plaques, while co-localization of FERMT3 with HHF35 indicative of smooth muscle cells was low.

CONCLUSIONS

Kindlin-3 (FERMT3) is upregulated in atherosclerotic, especially unstable plaques, mainly in cells of monocytic origin and of M2 type. Simultaneous upregulation of ITGB2 suggests a synergistic effect on leukocyte adherence and transmigration into the vessel wall.

Markers of inflammation associated with plaque progression and instability in patients with carotid atherosclerosis

Atherosclerosis is the focal expression of a systemic disease affecting medium- and large-sized arteries, in which traditional cardiovascular risk factor and immune factors play a key role. It is well accepted that circulating biomarkers, including C-reactive protein and interleukin-6, reliably predict major cardiovascular events, including myocardial infarction or death. However, the relevance of biomarkers of systemic inflammation to atherosclerosis progression in the carotid artery is less established. The large majority of clinical studies focused on the association between biomarkers and subclinical atherosclerosis, that is, carotid intima-media thickening (cIMT), which represents an earlier stage of the disease. The aim of this work is to review inflammatory biomarkers that were associated with a higher atherosclerotic burden, a faster disease progression, and features of plaque instability, such as inflammation or neovascularization, in patients with carotid atherosclerotic plaque, which represents an advanced stage of disease compared with cIMT. The association of biomarkers with the occurrence of cerebrovascular events, secondary to carotid plaque rupture, will also be presented. Currently, the degree of carotid artery stenosis is used to predict the risk of future cerebrovascular events in patients affected by carotid atherosclerosis. However, this strategy appears suboptimal. The identification of suitable biomarkers could provide a useful adjunctive criterion to ensure better risk stratification and optimize management.

In vitro and in vivo characterization of a new organic nitrate hybrid drug covalently bound to pioglitazone

BACKGROUND/AIMS

Organic nitrates represent a group of nitrovasodilators that are clinically used for the treatment of ischemic heart disease. The new compound CLC-3000 is an aminoethyl nitrate (AEN) derivative of pioglitazone, a thiazolidinedione antidiabetic agent combining the peroxisome proliferator-activated receptor γ agonist activity of pioglitazone with the NO-donating activity of the nitrate moiety.

METHODS

In vitro and in vivo characterization was performed by isometric tension recording, platelet function, bleeding time and detection of oxidative stress.

RESULTS

In vitro, CLC-3000 displayed more potent vasodilation than pioglitazone alone or classical nitrates. In vitro, some effects on oxidative stress parameters were observed. Authentic AEN or the AEN-containing linker CLC-1275 displayed antiaggregatory effects. In vivo treatment with CLC-3000 for 7 days did neither induce endothelial dysfunction nor nitrate tolerance nor oxidative stress. Acute or chronic administration of AEN increased the tail vein bleeding time in mice.

CONCLUSION

In summary, the results of these studies demonstrate that CLC-3000 contains a vasodilative and antithrombotic activity that is not evident with pioglitazone alone, and that 7 days of exposure in vivo showed no typical signs of nitrate tolerance, endothelial dysfunction or other safety concerns in Wistar rats.

Thrombospondin-1 and CD47 regulation of cardiac, pulmonary and vascular responses in health and disease

Cardiovascular homeostasis and health is maintained through the balanced interactions of cardiac generated blood flow and cross-talk between the cellular components that comprise blood vessels. Central to this cross-talk is endothelial generated nitric oxide (NO) that stimulates relaxation of the contractile vascular smooth muscle (VSMC) layer of blood vessels. In cardiovascular disease this balanced interaction is disrupted and NO signaling is lost. Work over the last several years indicates that regulation of NO is much more complex than previously believed. It is now apparent that the secreted protein thrombospondin-1 (TSP1), that is upregulated in cardiovascular disease and animal models of the same, on activating cell surface receptor CD47, redundantly inhibits NO production and NO signaling. This inhibitory event has implications for baseline and disease-related responses mediated by NO. Further work has identified that TSP1-CD47 signaling stimulates enzymatic reactive oxygen species (ROS) production to further limit blood flow and promote vascular disease. Herein consideration is given to the most recent discoveries in this regard which identify the TSP1-CD47 axis as a major proximate governor of cardiovascular health.

Increased platelet activation in early symptomatic vs. asymptomatic carotid stenosis and relationship with microembolic status: results from the Platelets and Carotid Stenosis Study

BACKGROUND

Cerebral microembolic signals (MES) may predict increased stroke risk in carotid stenosis. However, the relationship between platelet counts or platelet activation status and MES in symptomatic vs. asymptomatic carotid stenosis has not been comprehensively assessed.

SETTING

University teaching hospitals.

METHODS

This prospective, pilot observational study assessed platelet counts and platelet activation status, and the relationship between platelet activation and MES in asymptomatic vs. early (≤ 4 weeks after TIA/stroke) and late phase (≥ 3 months) symptomatic moderate or severe (≥ 50%) carotid stenosis patients. Full blood count measurements were performed, and whole blood flow cytometry was used to quantify platelet surface activation marker expression (CD62P and CD63) and circulating leucocyte-platelet complexes. Bilateral simultaneous transcranial Doppler ultrasound monitoring of the middle cerebral arteries was performed for 1 h to classify patients as MES positive or MES negative.

RESULTS

Data from 31 asymptomatic patients were compared with 46 symptomatic patients in the early phase, and 35 of these patients were followed up to the late phase after symptom onset. The median platelet count (211 vs. 200 × 10(9)  L(-1) ; P = 0.03) and the median percentage of lymphocyte-platelet complexes was higher in early symptomatic than asymptomatic patients (2.8 vs. 2.4%; P = 0.001). The percentage of lymphocyte-platelet complexes was higher in early symptomatic than in asymptomatic patients with ≥ 70% carotid stenosis (P = 0.0005) and symptomatic patients recruited within 7 days of symptom onset (P = 0.028). Complete TCD data were available in 25 asymptomatic, 31 early phase symptomatic and 27 late phase symptomatic patients. Twelve per cent of asymptomatic vs. 32% of early phase symptomatic (P = 0.02) and 19% of late phase symptomatic patients (P = 0.2) were MES positive. Early symptomatic MES-negative patients had a higher percentage of lymphocyte-platelet complexes than asymptomatic MES-negative patients (2.8 vs. 2.3%; P = 0.0085).

DISCUSSION

Recently, symptomatic carotid stenosis patients have had higher platelet counts (potentially reflecting increased platelet production, mobilization or reduced clearance) and platelet activation status than asymptomatic patients. MES were more frequently detected in early symptomatic than asymptomatic patients, but the differences between late symptomatic and asymptomatic groups were not significant. Increased lymphocyte-platelet complex formation in recently symptomatic vs. asymptomatic MES-negative patients indicates enhanced platelet activation in this early symptomatic subgroup. Platelet biomarkers, in combination with TCD, have the potential to aid risk-stratification in asymptomatic and symptomatic carotid stenosis patients.

State of the art in platelet function testing

Platelets perform many functions in hemostasis but also in other areas of physiology and pathology. Therefore, it is obvious that many different function tests have been developed, each one conceived and standardized for a special purpose. This review will summarize the different fields in which platelet function testing is currently in use; diagnostics of patients with bleeding disorders, monitoring patients' response to anti-platelet therapy, monitoring in transfusion medicine (blood donors, platelet concentrates, and after transfusion), and monitoring in perioperative medicine to predict bleeding tendency. The second part of the review outlines different methods for platelet function testing, spanning bleeding time, and platelet counting as well as determining platelet adhesion, platelet secretion, platelet aggregation, platelet morphology, platelet signal transduction, platelet procoagulant activity, platelet apoptosis, platelet proteomics, and molecular biology.

Platelet-leukocyte crosstalk: Linking proinflammatory responses to procoagulant state

Platelet activation is known to be associated with the release of a vast array of chemokines and proinflammatory lipids which induce pleiotropic effects on a wide variety of tissues and cells, including leukocytes. During thrombosis, the recruitment of leukocytes to activated platelets is considered an important step which not only links thrombosis to inflammatory responses but may also enhance procoagulant state. This phenomenon is highly regulated and influenced by precise mutual interactions between the cells at site of vascular injury and thrombi formation. Platelet-leukocyte interaction involves a variety of mediators including adhesion molecules, chemokines and chemoattractant molecules, shed proteins, various proinflammatory lipids and other materials. The current review addresses the detailed mechanisms underlying platelet-leukocyte crosstalk. This includes their adhesive interactions, transcellular metabolisms, induced tissue factor activity and neutrophil extracellular traps formation as well as the impacts of these phenomena in modulation of the proinflammatory and procoagulant functions in a reciprocal manner that enhances the physiological responses.

A contemporary viewpoint on 'aspirin resistance'

Aspirin is an irreversible inhibitor of platelet prostaglandin synthase activity, and is the most widely prescribed drug for the secondary prevention of cardiovascular disease. In recent years, clinical and laboratory evidence has shown significant individual variability in the response to aspirin and its link to clinical outcome. The term 'aspirin resistance' has been introduced to describe situations when clinical or ex-vivo effects of aspirin are less than expected. The accumulating evidence of increased risk of major adverse clinical events (MACE) associated with 'aspirin resistance' in the settings of acute coronary syndrome (ACS), stroke, and peripheral arterial disease has stimulated the search for ways of overcoming aspirin resistance. Existence of the link between high on-treatment platelet reactivity and atherothrombotic events suggests the common mechanisms for atherosclerosis progression and thrombotic complications with the platelets, being a key cellular interface between coagulation and inflammation. This review article provides a contemporary view on 'aspirin resistance' and discusses its definition, clinical importance, and possible mechanisms in light of recent data on the role of platelets in atherothrombosis.

Platelet activation, function, and reactivity in atherosclerotic carotid artery stenosis: a systematic review of the literature

An important proportion of transient ischemic attack or ischemic stroke is attributable to moderate or severe (50-99%) atherosclerotic carotid stenosis or occlusion. Platelet biomarkers have the potential to improve our understanding of the pathogenesis of vascular events in this patient population. A detailed systematic review was performed to collate all available data on ex vivo platelet activation and platelet function/reactivity in patients with carotid stenosis. Two hundred thirteen potentially relevant articles were initially identified; 26 manuscripts met criteria for inclusion in this systematic review. There was no consistent evidence of clinically informative data from urinary or soluble blood markers of platelet activation in patients with symptomatic moderate or severe carotid stenosis who might be considered suitable for carotid intervention. Data from flow cytometry studies revealed evidence of excessive platelet activation in patients in the early, sub-acute, or late phases after transient ischemic attack or stroke in association with moderate or severe carotid stenosis and in asymptomatic moderate or severe carotid stenosis compared with controls. Furthermore, pilot data suggest that platelet activation may be increased in recently symptomatic than in asymptomatic severe carotid stenosis. Excessive platelet activation and platelet hyperreactivity may play a role in the pathogenesis of first or subsequent transient ischemic attack or stroke in patients with moderate or severe carotid stenosis. Larger longitudinal studies assessing platelet activation status with flow cytometry and platelet function/reactivity in symptomatic vs. asymptomatic carotid stenosis are warranted to improve our understanding of the mechanisms responsible for transient ischemic attack or stroke.

Chronic hyper-reactivity of platelets resulting in enhanced monocyte recruitment in patients after ischaemic stroke

Although the platelet activation profile after stroke is a well-known issue, the platelet reactivity assessed prospectively after ischaemic stroke still remains equivocal. The aim of this study was to evaluate the reactivity of platelets in response to stimulation with thrombin receptor-activating peptide (TRAP) at 1, 10 and 90 days after ischaemic stroke and to compare it with results obtained in control groups. We determined the increment in surface expression of CD62P, CD40L and monocyte- and granulocyte-platelet aggregate formation using five-colour flow cytometry in 86 subjects after an ischaemic event, in 62 disease controls, and in 38 healthy volunteers. We assessed the plasma levels of CD62P and CD40L soluble forms. In patients after stroke a significantly lower increment in CD62P surface expression (p < 0.01) and higher increments in both CD40L platelet surface expression (p < 0.01) and monocyte-platelet aggregate percentage (p < 0.01) were found at every studied time point, as compared with the control groups. Plasma levels of soluble CD62P (sCD62P) and soluble CD40L (sCD40L) were increased in stroke subjects in both the acute and the subacute phase of the stroke and they dropped to levels observed in controls at day 90 after the ischaemic incident. In all studied groups a positive correlation was noted between plasma levels of sCD62P and sCD40L. In conclusion, while at 3-month follow-up the levels of soluble forms normalize in stroke patients, the profile of platelet reactivity in response to activation with TRAP differs from that observed in the controls despite the secondary stroke prevention.

[Pathophysiology and biochemistry of platelets]

Although their central role is to control bleeding and to induce thrombosis, platelets are important inflammatory and immune cells as well as modulators of angiogenesis. This review focuses on the different roles of platelets in hemostasis, thrombosis, inflammation, arteriosclerosis, angiogenesis, antimicrobial host defense and hematogenous tumor metastasis. Platelets are the central regulators of hemostasis. On their surface the important thrombin burst takes place. Platelets cause atherothrombotic vascular occlusions. However, they are probably involved in early stages of arteriosclerosis, e.g. extravasation of leukocytes at sites of vascular injury, formation of foam cells and proliferation of smooth muscle cells. These processes are triggered by secretion of proinflammatory substances and growth factors as well as by platelet-cell interactions via specific adhesive axes. During infections platelets kill pathogens through secretion of antimicrobial substances and extracellular traps or nets. Platelets facilitate the revascularisation of ischemic tissue and therefore even promote tumor growth.

Platelet - leukocyte interactions: multiple links between inflammation, blood coagulation and vascular risk

The aim of this review is to summarize the contribution of platelets and leukocytes and their interactions in inflammation and blood coagulation and its possible relevance in the pathogenesis of thrombosis. There is some evidence of an association between infection/inflammation and thrombosis. This is likely a bidirectional relationship. The presence of a thrombus may serve as a nidus of infection. Vascular injury indeed promotes platelet and leukocyte activation and thrombus formation and the thrombus and its components facilitate adherence of bacteria to the vessel wall. Alternatively, an infection and the associated inflammation can trigger platelet and leukocyte activation and thrombus formation. In either case platelets and leukocytes co-localize and interact in the area of vascular injury, at sites of inflammation and/or at sites of thrombosis. Following vascular injury, the subendothelial tissue, a thrombogenic surface, becomes available for interaction with these blood cells. Tissue factor, found not only in media and adventitia of the vascular wall, but also on activated platelets and leukocytes, triggers blood coagulation. Vascular-blood cell interactions, mediated by the release of preformed components of the endothelium, is modulated by both cell adhesion and production of soluble stimulatory or inhibitory molecules that alter cell function: adhesion molecules regulate cell-cell contact and facilitate the modulation of biochemical pathways relevant to inflammatory and/or thrombotic processes.