Proteomic analysis of extracellular vesicle cargoes mirror the cardioprotective effects of rivaroxaban in patients with venous thromboembolism.

BACKGROUND: Venous thromboembolism (VTE) remains a significant cause of morbidity and mortality worldwide. Rivaroxaban, a direct oral factor Xa inhibitor, mediates anti-inflammatory and cardiovascular-protective effects besides its well-established anticoagulant properties; yet, these remain poorly characterized. Extracellular vesicles (EVs) are considered proinflammatory messengers regulating a myriad of (patho)physiological processes and may be highly relevant to the pathophysiology of VTE. The effects of Rivaroxaban on circulating EVs in VTE patients remain unknown. We have established that differential EV biosignatures are found in patients with non-valvular atrial fibrillation anticoagulated with Rivaroxaban versus warfarin. Here, we investigated whether differential proteomic profiles of circulating EVs could also be found in patients with VTE. METHODS AND RESULTS: We performed comparative label-free quantitative proteomic profiling of enriched plasma EVs from VTE patients anticoagulated with either Rivaroxaban or warfarin using a tandem mass spectrometry approach. Of the 182 quantified proteins, six were found to be either exclusive to, or enriched in, Rivaroxaban-treated patients. Intriguingly, these proteins are involved in negative feedback regulation of inflammatory and coagulation pathways, suggesting that EV proteomic signatures may reflect both Rivaroxaban's anti-coagulatory and anti-inflammatory potential. CONCLUSIONS: These differences suggest Rivaroxaban may have pleiotropic effects, supporting the reports of its emerging anti-inflammatory and cardiovascular-protective characteristics relative to warfarin.

Nonvalvular atrial fibrillation patients anticoagulated with rivaroxaban compared with warfarin exhibit reduced circulating extracellular vesicles with attenuated pro-inflammatory protein signatures.

BACKGROUND: Rivaroxaban, a direct oral factor Xa inhibitor, mediates anti-inflammatory and cardiovascular-protective effects besides its well-established anticoagulant properties; however, these remain poorly characterized. Extracellular vesicles (EVs) are important circulating messengers regulating a myriad of biological and pathological processes and may be highly relevant to the pathophysiology of atrial fibrillation as they reflect alterations in platelet and endothelial biology. However, the effects of rivaroxaban on circulating pro-inflammatory EVs remain unknown. OBJECTIVES: We hypothesized that rivaroxaban's anti-inflammatory properties are reflected upon differential molecular profiles of circulating EVs. METHODS: Differences in circulating EV profiles were assessed using a combination of single vesicle analysis by Nanoparticle Tracking Analysis and flow cytometry, and proteomics. RESULTS: We demonstrate, for the first time, that rivaroxaban-treated non-valvular atrial fibrillation (NVAF) patients (n=8) exhibit attenuated inflammation compared with matched warfarin controls (n=15). Circulating EV profiles were fundamentally altered. Moreover, quantitative proteomic analysis of enriched plasma EVs from six pooled biological donors per treatment group revealed a profound decrease in highly pro-inflammatory protein expression and complement factors, together with increased expression of negative regulators of inflammatory pathways. Crucially, a reduction in circulating levels of soluble P-selectin was observed in rivaroxaban-treated patients (compared with warfarin controls), which negatively correlated with the patient's time on treatment. CONCLUSION: Collectively, these data demonstrate that NVAF patients anticoagulated with rivaroxaban (compared with warfarin) exhibit both a reduced pro-inflammatory state and evidence of reduced endothelial activation. These findings are of translational relevance toward characterizing the anti-inflammatory and cardiovascular-protective mechanisms associated with rivaroxaban therapy.

Alterations in fibrin formation and fibrinolysis in early onset-preeclampsia: Association with disease severity.

OBJECTIVE: ; Early-onset preeclampsia is a rare pregnancy-specific disorder associated with significantly increased maternal and fetal morbidity and mortality. Whilst it is known that even normotensive pregnancies are associated with changes in clot formation and dissolution, the nature of how these changes differ in those with early onset preeclampsia has not been well established. We sought to evaluate parameters of fibrin formation and fibrinolysis in individuals with early onset preeclampsia in comparison to both pregnant and non-pregnant controls. Furthermore, such parameters were correlated with markers of disease severity in this patient cohort, including the presence of multiorgan involvement, the rate of disease progression and the extent of the anti-angiogenic state in this condition. STUDY DESIGN: ; Patients with early onset preeclampsia (N = 20) and both pregnant (N = 16) and non -pregnant (N = 16) controls were recruited from the cohort at a large urban maternity hospital which saw over 15,000 deliveries during the study period. Platelet poor plasma was prepared from collected whole blood and analysed for parameters of fibrin formation and fibrinolysis (lagtime to and rate of fibrin formation; PAI-1; PAI-2; D-dimer; plasmin-antiplasmin; tPA) in addition to markers of angiogenesis (sFLT-1; Endoglin) using commercially available specific immunoassays. RESULTS: ; The maximum rate of fibrin formation as well as PAI-1, PAI-2 and D-dimer levels were all significantly increased in those with early onset preeclampsia and pregnant controls when compared to non-pregnant controls without significant differences between the 2 former groups. Plasmin-antiplasmin levels were significantly reduced in a similar manner. tPA levels were significantly elevated in EOP compared to both pregnant and non-pregnant controls. EOP was associated with significantly increased anti-angiogenic factors (sFLT-1; Endoglin) when compared to both pregnant and non-pregnant controls. CONCLUSION: ; Markers of fibrin formation and fibrinolysis are significantly alerted in early onset preeclampsia; furthermore, certain markers correlate with disease severity in this patient cohort.

Liver stiffness and thrombin generation in compensated cirrhosis.

BACKGROUND: Decompensated cirrhosis is associated with coagulation abnormalities that can increase the risk of thrombosis and bleeding. It is unclear precisely when these abnormalities arise and whether they are exacerbated as compensated cirrhosis progresses. Transient elastography using FibroScan generates liver stiffness measurements (LSM) that associate with portal hypertension, clinical outcomes and provides prognostic information at an earlier stage than traditional liver function scores eg, MELD score. OBJECTIVE: To characterize thrombin generation in patients with compensated cirrhosis and to determine whether parameters of coagulation change throughout compensated cirrhosis, staged using LSM. PATIENTS/METHODS: Blood samples were collected from well-compensated cirrhotic patients n = 61, All Child Pugh A stage) attending the Mater Misericordiae University Hospital, Ireland. Comprehensive clinical staging of liver disease, including LSM, was performed. Tissue Factor-stimulated thrombin generation was measured by calibrated automated thrombography. RESULTS: Using LSM to stage well-compensated cirrhotic patients, we demonstrate a significant decrease in the rate of propagation, the rate of attenuation, and total thrombin generation as LSM increase. LSM correlated with endogenous thrombin potential, peak thrombin generation, the rate of propagation, and the rate of attenuation. This association between thrombin generation and LSM was still evident in sub-analyses excluding patients with ongoing alcohol use, active HCV infection, or a history of decompensation. In contrast, there was no significant correlation between thrombin generation, prothrombin times, Child-Pugh scores, or MELD scores. CONCLUSION: Liver stiffness measurements identify differences in parameters of thrombin generation within a cohort of compensated cirrhotic patients before changes in clotting times occur.

The Platelet Releasate is Altered in Human Pregnancy.

PURPOSE: Healthy pregnancy is characterized by an increase in platelet activation and a decrease in the number of circulating platelets with gestation. Despite this recognized importance, proteomic studies investigating platelets in healthy pregnancy have not been performed. As platelet cargo can be altered in different conditions, it is hypothesized that platelets may store a relevant and bespoke collection of molecules during pregnancy. EXPERIMENTAL DESIGN: Comparative label-free quantitative proteomic profiling of platelet releasates (PRs) is performed from 18 healthy pregnant and 13 non-pregnant women using an MS/MS approach. RESULTS: Of the 723 proteins identified, 69 PR proteins are found to be differentially released from platelets in pregnancy, including proteins only expressed during pregnancy such as pregnancy-specific glycoproteins and human placental lactogen. Moreover, the population of exosomal vesicles present in the PR is also modified in pregnancy. Receiver operating characteristic analysis shows the predictive ability of 11 PR proteins to distinctly classify pregnant and nonpregnant women with an area under the curve of 0.876, a sensitivity of 88.9%, and a specificity of 84.6%. CONCLUSIONS AND CLINICAL RELEVANCE: Taken together this demonstrates that platelets and their released cargo are 'educated' in physiologic stressful conditions such as pregnancy and may represent a promising platform to study pregnancy complications.

Platelet Releasate Proteome Profiling Reveals a Core Set of Proteins with Low Variance between Healthy Adults.

Upon activation, platelets release a powerful cocktail of soluble and vesicular signals, collectively termed the "platelet releasate" (PR). Although several studies have used qualitative/quantitative proteomic approaches to characterize PR; with debated content and significant inter-individual variability reported, confident, and reliable insights have been hindered. Using label-free quantitative (LFQ)-proteomics analysis, a reproducible, quantifiable investigation of the 1U mL-1 thrombin-induced PR from 32 healthy adults was conducted. MS proteomics data are available via ProteomeXchange, identifier PXD009310. Of the 894 proteins identified, 277 proteins were quantified across all donors and form a "core" PR. Bioinformatics and further LFQ-proteomic analysis revealed that the majority (84%) of "core" PR proteins overlapped with the protein composition of human platelet-derived exosomes. Vesicles in the exosomal-size range were confirmed in healthy-human PR and reduced numbers of similar-sized vesicles were observed in the PR of a mouse model of gray platelet syndrome, known to be deficient in platelet alpha-granules. Lastly, the variability of proteins in the PR was assessed, and reproducible secretion levels were found across all 32 healthy donors. Taken together, the PR contains valuable soluble and vesicular cargo and has low-population variance among healthy adults, rendering it a potentially useful platform for diagnostic fingerprinting of platelet-related disease.

Early onset preeclampsia is associated with an elevated mean platelet volume (MPV) and a greater rise in MPV from time of booking compared with pregnant controls: results of the CAPE study.

OBJECTIVE: To characterise Mean platelet volume (MPV) in patients with early onset preeclampsia (EOPE) and unaffected controls from time of first antenatal visit until the postpartum. MATERIALS AND METHODS: Retrospective secondary analysis of an observational study in an Irish tertiary referral centre with 9000 deliveries annually. The MPV of 27 women with EOPE was compared to 19 unaffected controls. The inclusion criteria for the disease state was the development of EOPE defined by the National Institute for Health and Care Excellence (NICE) guideline, as new onset hypertension presenting after 20 weeks and prior to 34 weeks with significant proteinuria. Between October 2013 and July 2015 we recruited 27 women with EOPE and 19 pregnant controls. Statistical analysis was performed using paired T-test of Mann-Whitney test where appropriate and a P-value <0.05 was deemed significant. RESULTS: At time of diagnosis and late in the third trimester MPV was significantly increased to 9.0 (±0.3) fL in cases of EOPE in comparison to 8.5 (±0.6) fL in normotensive controls (P<0.05). There was no significant difference during the first trimester or postpartum when comparing the MPV in EOPE to controls. CONCLUSION: Despite an increased MPV at time of diagnosis of EOPE this study did not demonstrate a potential use for increased MPV as a first trimester screening tool.

Elevated plasma TFPI activity causes attenuated TF-dependent thrombin generation in early onset preeclampsia.

Early onset preeclampsia (EOP) is a pregnancy-specific proinflammatory disorder that is characterised by competing thrombotic and bleeding risks. It was the aim of this study to characterise thrombin generation, a major determinant of thrombotic and bleeding risk, in order to better understand the haemostatic balance in patients with EOP. Patients with EOP were recruited at the Rotunda Hospital, Dublin. Twenty-six cases of EOP were recruited over a 21-month period, out of 15,299 deliveries at the Rotunda. Blood samples were collected into sodium citrate plus corn trypsin inhibitor anticoagulated vacutainers, platelet-poor plasma was prepared, and calibrated automated thrombography was used to assess thrombin generation. Results were compared to age and sex-matched non-pregnant controls (n=13) and age- and gestation-matched pregnant controls (n=20). The rate and extent of thrombin generation triggered by low-dose tissue factor (TF) was significantly reduced in patients with EOP compared to pregnant controls, most significantly in cases of severe EOP. EOP patients displayed a trend towards an increased response to endogenous activated protein C and thrombomodulin relative to pregnant controls. Plasma tissue factor pathway inhibitor (TFPI) activity was increased in EOP patients. Inhibition of TFPI abolished the attenuation of thrombin generation stimulated by low-dose TF. In conclusion, patients with EOP are characterised by an attenuated coagulation response characterised by reduced thrombin generation stimulated by low-dose TF and elevated plasma TFPI activity. These changes in coagulation may modulate thrombotic risk and bleeding risk in patients with EOP.

Effect of platelet-derived ß-thromboglobulins on coagulation.

BACKGROUND: ß-thromboglobulins are derived from the cleavage of the CXC chemokine platelet basic protein and are released in high concentrations by activated platelets. Platelet-derived ß-thromboglobulins (ßTG) share 70% homology with platelet factor 4 (PF4), another CXC chemokine released by activated platelets. PF4 modulates coagulation by inhibiting heparin-antithrombin interactions, promoting protein C activation, and attenuating the activity of activated protein C. In contrast, the effect of ßTG on coagulation is unknown. AIM/METHODS: Clotting times, thrombin generation, chromogenic clotting factor assays, and surface plasmon resonance (SPR) were used to assess the effect of purified ßTG on coagulation. RESULTS: In normal pooled plasma, ßTG shortened the lagtime and time to peak thrombin generation of tissue factor (TF)-dependent and TF-independent thrombin generation. In factor VIII and factor IX-deficient plasmas, ßTG induced thrombin generation in the absence of a TF stimulus and in the presence of anti-TF and factor VIIa inhibitory antibodies. The procoagulant effect was not observed when thrombin generation was independent of factor X activation (supplementation of factor X-deficient plasma with factor Xa). Cleavage of a factor Xa-specific chromogenic substrate was observed when ßTG was incubated with factor X, suggesting a direct interaction between ßTG and factor X. Using SPR, ßTG were found to bind to immobilised factor X in a dose dependent manner. CONCLUSION: ßTG modulate coagulation in vitro via an interaction with factor X.

Comparative proteomic analysis of trophoblast cell models reveals their differential phenotypes, potential uses, and limitations.

Trophoblastic cell lines are widely used in in vitro studies of placental function as a surrogate for primary trophoblasts. To date, no reference proteomics dataset exists to directly compare the shared and unique characteristics of these cells. Here, we performed comparative proteomic profiling of the BeWo and HTR8/SVneo cell lines using label-free quantitative MS. A total of 1557 proteins were identified, which included 338 uniquely attributed to BeWo cells, and a further 304 specifically identified in HTR8/SVneo cells. Raw data are available via ProteomeXchange, identifier PDX005045. Of the 915 proteins expressed by both cell lines, 105 were of higher abundance in BeWo cells, while 199 proteins had a significantly higher expression in HTR8/SVneo cells. Comparative GO of unique and upregulated proteins revealed principal differences in cell junction/adhesion, catenin complex, spindle and microtubule associated complex, as well as cell differentiation. Our data indicate that BeWo cells express an epithelial proteome more characteristic of villous trophoblasts, whereas HTR8/SVneo cells embrace a mesenchymal phenotype, more characteristic of extravillous trophoblasts. This novel comparative proteomic profiling of these trophoblastic cell lines provides a useful platform for future investigations of placental function.

Increased soluble GPVI levels in cirrhosis: evidence for early in vivo platelet activation.

Cirrhosis is a consequence of prolonged liver injury and is characterised by extensive tissue fibrosis: the deposition of collagen-rich extracellular matrix. The haemostatic balance is disordered in cirrhosis and coagulation activation appears to promote fibrosis. In spite of recent studies demonstrating a role for anticoagulant therapy in preventing cirrhosis progression, there has not been a change in clinical practice, suggesting that physicians are reluctant to anticoagulate patients with cirrhosis due to bleeding risks. Platelets play an important role in facilitating coagulation. Glycoprotein VI (GPVI) is a platelet-specific collagen receptor that is shed from the platelet surface in a metalloproteinase-dependent manner in response to GPVI ligation and coagulation activation. Our aim was to use soluble GPVI levels to determine whether there was evidence for collagen and coagulation-induced platelet activation in early, well-compensated cirrhosis. Plasma soluble GPVI levels were quantified in 46 patients with mixed aetiology cirrhosis and 55 healthy controls using an immunoassay. In the cirrhosis group, soluble GPVI levels were significantly increased (5.8 ± 4.4 ng/ml, n = 46) compared to healthy controls (3.3 ± 3.4 ng/ml, n = 55, p < 0.05). This increase in soluble GPVI levels was still evident when levels were adjusted for platelet count (Healthy controls; 0.015 ± 0.018 ng/106 platelets/ml vs. cirrhosis; 0.048 ± 0.04 ng/106 platelets/ml, p < 0.0001). This study provides evidence for early platelet activation in patients with well-compensated cirrhosis. This may have translational implications for prognosis, treatment, and risk stratification.

Endothelial barrier protective properties of low molecular weight heparin: A novel potential tool in the prevention of cancer metastasis?

BACKGROUND: One of the key events in the progression of cancer metastasis is the trans-endothelial migration of circulating tumor cells. Moreover, inhibition of tumor-induced vascular permeability has been shown to inhibit metastasis in vivo. Low molecular weight heparin (LMWH) appears to confer a survival benefit in cancer but the underlying mechanisms are poorly understood. OBJECTIVE: To characterise LMWH-mediated endothelial barrier protection and to explore strategies to limit the LMWH-associated haemorrhagic risk in this setting. METHODS: Endothelial barrier function was assessed using in vitro assays of endothelial permeability and tumor cell trans-endothelial migration. Thrombin-mediated activation of PAR-1 signalling was assessed by flow cytometry and western blotting. LMWH anticoagulant activity was assessed by calibrated automated thrombography and plasma anti-factor Xa activity assay. RESULTS: LMWH tinzaparin enhanced endothelial barrier function and reduced tumor cell trans-endothelial migration (73.9±5.7% of baseline; P<.05). Tinzaparin-mediated attenuation of thrombin-induced permeability was not mediated through an inhibition of thrombin proteolytic activity. In addition, fractions of LMWH with diminished anticoagulant activity retained endothelial barrier protective properties and a marked synergistic effect on barrier function was observed using combinations of sub-anticoagulant concentrations of tinzaparin with simvastatin (which exhibits endothelial barrier protective properties in vitro), with almost complete protection against agonist-induced endothelial barrier permeability achieved (7.9±0.2% of baseline; P<.05). CONCLUSION: Collectively, these results suggest that LMWH supports endothelial barrier function in a manner which does not appear to be dependent on its anticoagulant activity. If replicated in vivo, these findings could represent a novel therapeutic approach to the suppression of metastasis.

Thrombin generation correlates with disease duration in multiple sclerosis (MS): Novel insights into the MS-associated prothrombotic state.

BACKGROUND: Thrombin is well recognised for its role in the coagulation cascade but it also plays a role in inflammation, with enhanced thrombin generation observed in several inflammatory disorders. Although patients with multiple sclerosis (MS) have a higher incidence of thrombotic disease, thrombin generation has not been studied to date. OBJECTIVES: The aim of this study was to characterise calibrated automated thrombography parameters in patients with relapsing-remitting MS (RRMS) and primary progressive MS (PPMS) in comparison to healthy controls (HCs). METHODS: Calibrated automated thrombography was performed on platelet poor plasma from 15 patients with RRMS, 15 with PPMS and 19 HCs. RESULTS: We found that patients with RRMS generate thrombin at a significantly faster rate than the less inflammatory subtype, PPMS or HCs. In addition, the speed of thrombin generation was significantly correlated with time from clinical diagnosis in both subtypes. However, in RRMS the rate of thrombin generation was increased with increased time from clinical diagnosis, while in PPMS the rate of thrombin generation decreased with increased time from clinical diagnosis. CONCLUSIONS: These data likely reflect the differential active proinflammatory states in each MS subtype and provide novel mechanistic insights into the clinically relevant prothrombotic state observed in these patients.

Plasma Thrombin Generation and Sensitivity to Activated Protein C Among Patients With Myeloma and Monoclonal Gammopathy of Undetermined Significance.

The etiology of the prothrombotic state in myeloma has yet to be definitively characterized. Similarly, while recent evidence suggests that patients with monoclonal gammopathy of undetermined significance (MGUS) may also be at increased risk of thrombosis, the magnitude and the etiology of this risk have also yet to be defined. The present study aims to characterize patterns of plasma thrombin generation and sensitivity to the anticoagulant activity of activated protein C (APC) at the time of initial diagnosis of myeloma and in response to therapy in comparison to that observed among patients with MGUS and matched, healthy volunteers. Patients presenting with newly diagnosed/newly relapsed myeloma (n = 8), MGUS (n = 8), and matched healthy volunteers (n = 8) were recruited. Plasma thrombin generation was determined by calibrated automated thrombography. Peak thrombin generation was significantly higher in patients with myeloma (383.4 ± 33.4 nmol/L) and MGUS (353.4 ± 16.5 nmol/L) compared to healthy volunteers (276.7 ± 20.8 nmol/L; P < .05). In the presence of APC, endogenous thrombin potential was significantly lower in control plasma (228.6 ± 44.5 nmol/L × min) than in either myeloma (866.2 ± 241.3 nmol/L × min, P = .01) or MGUS plasma (627 ± 91.5 nmol/L × min, P = .003). Within the myeloma cohort, peak thrombin generation was significantly higher at diagnosis (353.2 ± 15.9 nmol/L) than following completion of the third cycle of therapy (282.1 ± 15.2 nmol/L; P < .005). Moreover, sensitivity to APC increased progressively with each cycle of chemotherapy. Further study of the etiology and evolving patterns of hypercoagulability among patients with these conditions is warranted and may have future implications for thromboprophylaxis strategies.

Platelet aggregation in response to ADP is highly variable in normal donors and patients on anti-platelet medication.

BACKGROUND: P2Y12 inhibitors are indicated in patients following percutaneous coronary intervention. Several studies have demonstrated that high on treatment platelet reactivity is correlated with outcomes yet prospective studies of guided therapy have failed to show benefit. There is a paucity of studies on the platelet aggregation response to ADP before P2Y12 therapy is started. The aim of this study was to characterize platelet responses to 20 µM ADP by light transmission aggregometry (LTA) in a homogenous population. METHODS: Platelet aggregation was assessed in 201 patients on dual antiplatelet therapy, 98 patients on aspirin alone and 47 normal, healthy volunteers free from anti-platelet medication. RESULTS: Consensus guidelines suggest that a platelet aggregation response in response to the agonist ADP of <57% is an adequate therapeutic response to P2Y12 inhibition. Seven healthy donors and 38 patients taking aspirin only had aggregation responses below 57%. CONCLUSIONS: The results of our study demonstrate that 15% of normal donors and 38% of patients taking aspirin only would be classified as having a therapeutic response to P2Y12 inhibition using current guidelines.

Elevated venous thromboembolism risk in preeclampsia: molecular mechanisms and clinical impact.

Venous thromboembolism (VTE) remains a leading cause of maternal death and morbidity in the developed world. Strategies for prevention of VTE in pregnancy have been the subject of recent guidelines and consensus statements. These guidelines recommend thrombosis prevention in women who have risk factors associated with an elevated VTE risk. Preeclampsia is characterized by maternal hypertension and proteinuria developing after 20 weeks gestation, complicating up to 7% of pregnancies and is associated with a massive annual morbidity and mortality burden. Women with preeclampsia have been shown to be at increased risk of VTE with studies to date suggesting that this risk may be up to 5-fold greater than the risk of pregnancy-associated VTE in the general population. Despite the fact that preeclampsia is so common and potentially devastating, our understanding of its pathogenesis and potential therapeutic strategies remain poor. In addition, the mechanisms underlying the prothrombotic phenotype in preeclampsia are also poorly characterized although a number of potential mechanisms have been postulated. Derangements of platelet and endothelial activation and impairment of endogenous anti-coagulant pathways have been reported and may contribute to the observed VTE risk. Recently, evidence for the role of neutrophil extracellular traps (NETs) and cell-free DNA in the pathogenesis of VTE has emerged and some evidence exists to suggest that this may be of relevance in preeclampsia. Future studies aimed at understanding the diagnostic and potential therapeutic relevance of this procoagulant state are likely to be of enormous clinical benefit for pregnant women affected with this potentially devastating condition.

Living in shear: platelets protect cancer cells from shear induced damage.

Pharmacologically and genetically induced thrombocytopenia is associated with decreased metastasis, highlighting the importance of platelets in the bloodborne dissemination of cancer cells. It is frequently suggested that platelets support metastasis, in part, by protecting cancer cells from shear stress, a biomechanical force generated by blood flow. However, there is currently no evidence to support this hypothesis. To address this, we investigated the effect of shear stress on A2780 ovarian cancer cells in the presence and absence of platelets. Using a cone and plate viscometer, suspensions of A2780 cells with and without platelets were exposed to shear rates representing venous (200 s(-1)) and arterial (1,500 s(-1)) blood flow. Lactate dehydrogenase (LDH) release was used to quantify shear induced membrane damage. Both venous and arterial shear rates induced the release of LDH from A2780 cells, demonstrating their susceptibility to shear forces. In contrast, platelets released minimal levels of LDH in response to similar conditions. In the presence of platelets, there was a significant decrease in LDH release by A2780 cells under shear conditions, suggesting that platelets can confer protection against shear induced damage. The disruption of platelet-cancer cell interactions could increase the shear stress induced destruction of cancer cells in vivo.

Increased platelet reactivity in patients with late-stage metastatic cancer.

Platelet hyperreactivity is associated with an increased risk of thrombosis. Cancer patients are at an increased risk of thrombosis, a risk that increases with disease progression. While cancer patients show evidence of platelet activation in vivo, few studies have extensively assessed whether these patients display platelet hyperreactivity. We hypothesized that patients with metastatic cancer would display platelet hyperreactivity, reflecting their associated high risk of thrombosis. In a cohort of patients with metastatic cancer (n = 13), we assessed platelet function using well-established assays of platelet reactivity (agonist-induced platelet aggregation, spontaneous platelet aggregation, and agonist-induced P-selectin expression). In comparison with healthy controls (n = 10), patients with metastatic cancer displayed global platelet hyperreactivity. Agonist-induced platelet aggregation responses to ADP (adenosine diphosphate), epinephrine, collagen, arachidonic acid, and PAR-1 (protease-activated receptor-1) activating peptide, as well as spontaneous platelet aggregation, were significantly increased in patients with metastatic cancer. Furthermore, agonist-induced platelet P-selectin expression was also significantly increased within the patient cohort. We demonstrate that patients with metastatic cancer are characterized by global platelet hyperreactivity, a factor that may contribute to their increased risk of thrombosis.

Individual platelet adhesion assay: measuring platelet function and antiplatelet therapies in whole blood via digital quantification of cell adhesion.

Widespread monitoring of platelet function and the effect of antiplatelet drugs will improve outcomes in cardiovascular patients, but platelet function testing is not routine in clinical practice. We report a rapid, accurate methodology to quantify platelet-protein interactions: a microarray of contact-printed 6-µm fibrinogen dots on a transparent substrate binds platelets from whole blood, one platelet per dot. The fractional occupancy of an array of fibrinogen dots after a predefined incubation time quantitatively assays platelet adhesion to the protein matrix. We demonstrate this technique by measurement of platelet adhesion to fibrinogen as a means to quantify the effect of the P2Y12 and αIIbß3 receptor inhibitors cangrelor and abciximab, respectively, both in vitro--by incubating the drug with a freshly drawn blood sample--and in blood from patients treated with antiplatelet agents. The effects of single- and dual-antiplatelet therapy are also assessed. Results from this platelet-binding assay are well correlated with standard techniques including flow cytometry and light transmission aggregometry. This assay technology, readily integrated with microfluidic platforms, is generally applicable to the assay of cell-protein interactions and promises more effective, rapid assay of drug effects in cardiovascular disease patients.