Relationship between markers of platelet activation and inflammation with disease activity in Wegener's granulomatosis

OBJECTIVE

There remains a need for biomarkers to guide therapy in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis. Our objective was to determine whether measures of platelet activation or inflammation are associated with disease activity in Wegener's granulomatosis (WG).

METHODS

Study subjects were participants in a clinical trial. Soluble CD40 ligand (sCD40L), C-reactive protein, interleukin 6 (IL-6), IL-8, monocyte chemoattractant protein 1 (MCP-1), P-selectin, vascular endothelial growth factor, and proteinase 3 (PR3)-specific ANCA were measured by ELISA using plasma samples obtained at baseline (active disease), at remission, and prior to, during, and after first flares. Disease activity was assessed by the Birmingham Vasculitis Activity Score for WG (BVAS/WG). Association of biomarkers with disease activity was determined with conditional logistic and linear regression.

RESULTS

Over a mean followup of 27 months, 180 subjects underwent 2044 visits; markers were measured in 563 samples. Longitudinally, all markers other than IL-6 were associated with disease activity. The strongest associations for active disease at baseline versus remission were observed for sCD40L (OR 4.72, 95% CI 2.47-9.03), P-selectin (OR 6.26, 95% CI 2.78-14.10), PR3-ANCA (OR 9.41, 4.03-21.99), and inversely for MCP-1 (OR 0.36, 95% CI 0.22-0.57). BVAS/WG increased by 0.80 (95% CI 0.44-1.16), 0.83 (95% CI 0.42-1.25), and 0.81 (95% CI 0.48-1.15) per unit-increase in PR3-ANCA, sCD40L, and P-selectin, respectively; and decreased by 1.54 (95% CI 0.96-2.12) per unit-increase in MCP-1.

CONCLUSION

Cytokines arising from within the circulation, including those of platelet activation, correlate with disease activity in WG.

The role of the blood transcriptome in innate inflammation and stroke

Cerebrovascular disease is a major cause of death and disability, with a poorer outcome in patients having select risk factors including diabetes and hypertension. Risk factors and the state of cerebral ischemia-reperfusion associated with cerebrovascular occlusion are known to cause inflammatory changes. These events and the inflammatory state are reflected by transcript changes in various components of the blood and can be specifically measured. By defining these changes, new insight into cerebrovascular disease and its therapeutics is being achieved.

M118, a novel low-molecular weight heparin with decreased polydispersity leads to enhanced anticoagulant activity and thrombotic occlusion in ApoE knockout mice

Heparin and low-molecular weight heparin (LMWH) are complex, heterogeneous polysaccharides used in the treatment of arterial and venous thrombosis. M118 is a novel LMWH with low polydispersity and pronounced anti-Xa and anti-thrombin (IIa) activity as compared to current LMWHs. To determine if M118 is effective in preventing thrombosis in the setting of a vascular plaque, apolipoprotein E knockout mice fed a high fat diet were injected with M118, enoxaparin, unfractionated heparin, or saline control and examined for arterial thrombosis using a rose bengal laser induced carotid artery injury model. M118 significantly increased the time to occlusion as compared to control and unfractionated heparin but not compared to enoxaparin although fewer M118 treated animals had any vascular occlusion present at the time of protocol completion. Platelet-neutrophil aggregates were studied by flow cytometry and were found to be decreased with M118 as compared to enoxaparin. This is the first published report examining M118, a novel LMWH designed to have low polydispersity and enhanced anticoagulant activity. In an animal model of vascular plaque, M118 is a potent inhibitor of arterial thrombosis and, despite lower in vivo anti-Xa and anti-IIa activity levels, M118 was superior to UFH in the prevention of arterial thrombosis.

Relation of platelet and leukocyte inflammatory transcripts to body mass index in the Framingham heart study

BACKGROUND

Although many genetic epidemiology and biomarker studies have been conducted to examine associations of genetic variants and circulating proteins with cardiovascular disease and risk factors, there has been little study of gene expression or transcriptomics. Quantitative differences in the abundance of transcripts has been demonstrated in malignancies, but gene expression from a large community-based cohort examining risk of cardiovascular disease has never been reported.

METHODS AND RESULTS

On the basis of preliminary microarray data and previously suggested genes from the literature, we measured expression of 48 genes by high-throughput quantitative reverse-transcriptase polymerase chain reaction in 1846 participants of the Framingham Offspring cohort from RNA derived from isolated platelets and leukocytes. A multivariable stepwise regression model was used to assess clinical correlates of quantitative RNA expression. For specific inflammatory platelet-derived transcripts, including ICAM1, IFNG, IL1R1, IL6, MPO, COX2, TNF, TLR2, and TLR4, there were significant associations with higher body mass index (BMI). Compared with platelets, fewer leukocyte-derived transcripts were associated with BMI or other cardiovascular risk factors. Select transcripts were found to be highly heritable, including GPIBA and COX1. Almost uniformly, heritable transcripts were not those associated with BMI.

CONCLUSIONS

Inflammatory transcripts derived from platelets, particularly those part of the nuclear factor kappa B pathway, are associated with BMI, whereas others are heritable. This is the first study, using a large community-based cohort, to demonstrate clinical correlates of gene expression and is consistent with the hypothesis that specific peripheral-blood transcripts play a role in the pathogenesis of coronary heart disease and its risk factors.

The role of CD40L and VEGF in the modulation of angiogenesis and inflammation

Recently, there has been growing interest in deciphering the role of angiogenesis in the progression of atherogenesis. Importantly, CD40-CD40L interactions are of significant relevance because of their involvement in both angiogenesis and atherosclerotic development. Previously, we have shown that recombinant soluble CD40 ligand (rsCD40L) stimulates auto-inflammatory CD40L synthesis and reactive oxygen species (ROS) generation in vascular cells. In the current study, we demonstrate that redox-mediated CD40-CD40L interaction can enhance vascular endothelial growth factor (VEGF)-induced angiogenesis, endothelial migration, and actin polymerization processes. Interestingly, the addition of exogenous VEGF leads to cleavage of de novo CD40L produced in endothelial cells following rsCD40L treatment. Using inhibitor and silencing RNA-based experiments, it was observed that VEGF-induced protease, calpain 2, was responsible for the cleavage of de novo CD40L. While our in vivo experiments using a matrigel plug assay indicate a VEGF and CD40L induced enhancement of angiogenesis, our studies also identify a novel mechanism by which VEGF can abrogate CD40L-mediated inflammation. Together, these studies reveal a new pathway by which VEGF-CD40L interactions can regulate the angiogenic and inflammatory process depending on the specific environment.

A new role for the A2b adenosine receptor in regulating platelet function

BACKGROUND

Activation of platelets is a critical component of atherothrombosis and plays a central role in the progression of unstable cardiovascular syndromes. Adenosine, acting through adenosine receptors, increases intracellular cAMP levels and inhibits platelet aggregation. The A2a adenosine receptor has already been recognized as a mediator of adenosine-dependent effects on platelet aggregation, and here we present a new role for the A2b adenosine receptor (A2bAR) in this process.

METHODS AND RESULTS

As compared with platelets from wild-type controls, platelets derived from A2bAR knockout mice have significantly greater ADP receptor activation-induced aggregation. Although mouse megakaryocytes and platelets express low levels of the A2bAR transcript, this gene is highly upregulated following injury and systemic inflammation in vivo. Under these conditions, A2bAR-mediated inhibition of platelet aggregation significantly increases. Our studies also identify a novel mechanism by which the A2bAR could regulate platelet aggregation; namely, ablation of the A2bAR leads to upregulated expression of the P2Y1 ADP receptor, whereas A2bAR-mediated or direct elevation of cAMP has the opposite effect. Thus, the A2bAR regulates platelet function beyond mediating the immediate effect of adenosine on aggregation.

CONCLUSIONS

Taken together, these investigations show for the first time that the platelet A2bAR is upregulated under stress in vivo, plays a significant role in regulating ADP receptor expression, and inhibits agonist-induced platelet aggregation.

Immune versus thrombotic stimulation of platelets differentially regulates signalling pathways, intracellular protein-protein interactions, and alpha-granule release

In addition to haemostasis, platelets mediate inflammation and clearance of bacteria from the bloodstream. As with platelet-platelet interactions, platelet-bacteria interactions involve cytoskeletal rearrangements and release of granular content. Stimulation of the immune Toll-like receptor 2 (TLR2) on the platelet surface, activates phosphoinositide-3-kinase (PI3K) and causes platelet activation and platelet-dependent thrombosis. It remains unknown if platelet activation by immune versus thrombotic pathways leads to the differential regulation of signal transduction, protein-protein interactions, and alpha-granule release, and the physiological relevance of these potential differences. We investigated these processes after immune versus thrombotic platelet stimulation. We examined selected signalling pathways and found that phosphorylation kinetics of Akt, ERK1/2 and p38 differed dramatically between agonists. Next, we investigated platelet protein-protein interactions by mass spectrometry (MS)-based proteomics specifically targeting cytosolic factor XIIIa (FXIIIa) because of its function as a cytoskeleton-crosslinking protein whose binding partners have limited characterisation. Four FXIIIa-binding proteins were identified, two of which are novel interactions: FXIIIa-focal adhesion kinase (FAK) and FXIIIa-gelsolin. The binding of FAK to FXIIIa was found to be altered differentially by immune versus thrombotic stimulation. Lastly, we studied the effect of thrombin versus Pam(3)CSK(4) stimulation on alpha-granule release and observed differential release patterns for selected granule proteins and decreased fibrin clot formation compared with thrombin. The inhibition of PI3K caused a decrease in protein release after Pam(3)CSK(4)- but not after thrombin-stimulation. In summary, stimulation of platelets by either thrombotic or immune receptors leads to markedly different signalling responses and granular protein release consistent with differential contribution to coagulation and thrombosis.

Innate immunity and toll-like receptor antagonists: a potential role in the treatment of cardiovascular diseases

Toll-like receptors (TLRs) are germline-encoded receptors that recognize various pathogen-associated molecular patterns (PAMPs). They are key components of the innate immunity which are activated in response to pathogens as well as non-pathogenic components of damaged tissues. TLR agonists have been developed to treat allergies, cancers, and chronic infections by upregulating the innate immune system. TLR antagonists may be used to treat a number of inflammatory conditions, such as rheumatoid arthritis and systemic lupus erythematosus. Recent research also has shown that TLRs are involved in the pathogenesis of atherosclerosis, thrombosis, myocardial remodeling, ischemic/reperfusion injury, and valvular disease. This article reviews the current experimental and clinical evidence for the role of TLRs in the cardiovascular system, and examines the mechanisms by which TLR antagonists could potentially be used in targeted therapy.

Facts and controversies of aspirin and clopidogrel therapy

Because of the central role of platelets in mediating ischemic events, antiplatelet agents are critical components of atherothrombosis prevention. Given their robust safety and efficacy profiles, aspirin and clopidogrel are consistently recommended by evidence-based treatment guidelines. Despite these recommendations, controversies surrounding the appropriate application of aspirin and clopidogrel remain. Questions of appropriate dosing, length of therapy, and use of combination therapy are most pressing, and considerable debate exists regarding the variability of response to antiplatelet therapy, including the definition, measurement, and clinical relevance of responsiveness. This review discusses the facts and controversies surrounding the use of aspirin and clopidogrel. Overall, despite the existing controversies, antiplatelet therapy with aspirin and/or clopidogrel remains a proven and essential therapeutic tool for safe and effective management of atherothrombotic risk in specific clinical settings.

Stimulation of Toll-like receptor 2 in human platelets induces a thromboinflammatory response through activation of phosphoinositide 3-kinase

Cells of the innate immune system use Toll-like receptors (TLRs) to initiate the proinflammatory response to microbial infection. Recent studies have shown acute infections are associated with a transient increase in the risk of vascular thrombotic events. Although platelets play a central role in acute thrombosis and accumulating evidence demonstrates their role in inflammation and innate immunity, investigations into the expression and functionality of platelet TLRs have been limited. In the present study, we demonstrate that human platelets express TLR2, TLR1, and TLR6. Incubation of isolated platelets with Pam(3)CSK4, a synthetic TLR2/TLR1 agonist, directly induced platelet aggregation and adhesion to collagen. These functional responses were inhibited in TLR2-deficient mice and, in human platelets, by pretreatment with TLR2-blocking antibody. Stimulation of platelet TLR2 also increased P-selectin surface expression, activation of integrin alpha(IIb)beta(3), generation of reactive oxygen species, and, in human whole blood, formation of platelet-neutrophil heterotypic aggregates. TLR2 stimulation also activated the phosphoinositide 3-kinase (PI3-K)/Akt signaling pathway in platelets, and inhibition of PI3-K significantly reduced Pam(3)CSK4-induced platelet responses. In vivo challenge with live Porphyromonas gingivalis, a Gram-negative pathogenic bacterium that uses TLR2 for innate immune signaling, also induced significant formation of platelet-neutrophil aggregates in wild-type but not TLR2-deficient mice. Together, these data provide the first demonstration that human platelets express functional TLR2 capable of recognizing bacterial components and activating the platelet thrombotic and/or inflammatory pathways. This work substantiates the role of platelets in the immune and inflammatory response and suggests a mechanism by which bacteria could directly activate platelets.

Clinical correlates, heritability, and genetic linkage of circulating CD40 ligand in the Framingham Offspring Study

BACKGROUND

The CD40 receptor and its ligand (CD40L) are known to modulate both inflammation and thrombosis-2 processes important for the development and clinical expression of atherosclerosis. Circulating soluble CD40L (sCD40L) concentration predicts cardiovascular risk in selected patient samples. The purpose of this study was to determine the predictors of sCD40L in a large, community-based sample.

METHODS

We determined both serum and plasma sCD40L concentration in 3,259 participants (54% women) from the Framingham Offspring Study.

RESULTS

In multivariable models, advancing age was the only consistent (inverse) correlate of both serum and plasma sCD40L concentration. Overall, the variability explained by clinical covariates was very low for both measurements of sCD40L; with values of only 1.4% and 2.7% for serum and plasma, respectively. We observed that genetic factors accounted for a modest (12% serum; 14% plasma) amount of the adjusted variability in sCD40L.

CONCLUSIONS

Circulating sCD40L concentration was poorly associated with known cardiovascular disease (CVD) risk factors and was modestly heritable. Determining if either serum or plasma sCD40L are predictive of CVD risk in the community will require longitudinal follow-up.

CD40-CD40 ligand interactions in oxidative stress, inflammation and vascular disease

CD40 ligand (CD40L) and its receptor CD40 participate in numerous inflammatory pathways that contribute to multiple pathophysiological processes. A role for CD40-CD40L interactions has been identified in atherosclerosis, and such interactions are known to destabilize atherosclerotic plaques by inducing the expression of cytokines, chemokines, growth factors, matrix metalloproteinases and pro-coagulant factors. The CD40-CD40L interaction has also been implicated in immune system disorders. Recent studies have suggested that CD40-CD40L interactions regulate oxidative stress and affect various signaling pathways in both the immunological and cardiovascular systems. Here, we discuss the emerging role of CD40-CD40L-mediated processes in oxidative stress, inflammatory pathways and vascular diseases. Understanding the roles and regulation of CD40-CD40L-mediated oxidative signaling in immune and non-immune cells could facilitate the development of therapeutics targeting diverse inflammatory diseases.

Aspirin resistance in atherosclerosis

Clinically, aspirin resistance is defined as the failure of aspirin therapy to prevent an acute vascular thrombotic event despite regular intake of appropriate doses. In the laboratory, aspirin resistance encompasses the drug's failure to attain a particular level of platelet inhibition. From a clinical standpoint, the inability of aspirin to prevent a thrombotic event, despite appropriate cyclooxygenase-1 inhibition, implies the involvement of other factors. Evidence is emerging that aspirin resistance, as defined by residual platelet activity, merely reflects an individual's enhanced basal platelet function and suggests a hereditary component. Due to the multifactorial nature of cardiovascular disease, it is likely that a single therapy like aspirin cannot fully treat and prevent all thrombotic complications in the setting of atherosclerosis.