sGPVI Levels Research Articles

Association of primary and secondary hemostasis biomarkers with acute ischemic stroke outcome in patients undergoing thrombectomy, with or without thrombolytics: Post-hoc analysis of the MR CLEAN-NOIV randomized clinical trial

Intravenous thrombolysis (IVT) using recombinant tissue plasminogen activator (r-tPA) prior to endovascular thrombectomy (EVT) failed to improve treatment effect in acute ischemic stroke (AIS) patients compared to EVT alone. We investigated whether primary and secondary hemostasis biomarkers are associated with the effect of IV thrombolytics on clinical and radiological outcomes after EVT. In MR CLEAN-NOIV study, AIS patients were randomized to receive IVT plus EVT or EVT alone. We measured hemostatic biomarkers before and 24h post-reperfusion, to determine changes in biomarkers and to determine the association of the biomarkers with short-time stroke severity (National Institutes of Health Stroke Scale (NIHSS) score), long-term functional outcome (modified Rankin scale (mRS) score), post-EVT extended thrombolysis in cerebral infarction (eTICI) score, and final infarct size. This substudy included 214 of the 539 AIS patients who underwent IVT+EVT (N=108/266) or EVT alone (N=106/273). In the EVT group, low soluble glycoprotein VI (sGPVI) and high factor (F)VIII levels before treatment were associated with severe NIHSS-score at 24h and poor mRS-score at 90-day post-treatment, respectively. Also in this group, sGPVI levels 24h after treatment were negatively associated with final infarct size. In the IVT+EVT group, high fibrinogen before treatment was associated with good eTICI-score and low ADAMTS13 activity 24h post-treatment was associated with unfavorable mRS-score at 90-day. Our findings suggest that patients with high FVIII and fibrinogen and low sGPVI levels might be most suitable candidates for IVT+EVT, and that patients with low ADAMTS13 activity might be suitable for EVT alone.

Soluble Glycoprotein VI Levels Assessed Locally within the Extra- and Intracerebral Circulation in Hyper-Acute Thromboembolic Stroke: A Pilot Study.

Background: Severe acute ischemic stroke (AIS) is mainly caused by thromboembolism originating from symptomatic carotid artery (ICA) stenosis or in the heart due to atrial fibrillation. Glycoprotein VI (GPVI), a principal platelet receptor, facilitates platelet adherence and thrombus formation at sites of vascular injury such as symptomatic ICA stenosis. The shedding of GPVI from the platelet surface releases soluble GPVI (sGPVI) into the circulation. Here, we aimed to determine whether sGPVI can serve as a local biomarker to differentiate between local atherosclerotic and systemic cardiac thromboembolism in AIS. Methods: We conducted a cohort study involving 105 patients undergoing emergency endovascular thrombectomy (EVT) for anterior circulation stroke. First, sGPVI concentrations were measured in systemic arterial plasma samples collected at the ipsilateral ICA level, including groups with significantly (≥50%) stenotic and non-stenotic arteries. A second sample, taken from the intracerebral pial circulation, was used to assess GPVI shedding locally within the ischemic brain. Results: Our analysis revealed no significant increase in systemic sGPVI levels in patients with symptomatic ≥ 50% ICA stenosis (3.2 [95% CI 1.5-5.0] ng/mL; n = 33) compared with stroke patients without significant ICA stenosis (3.2 [95% CI 2.3-4.2] ng/mL; n = 72). Additionally, pial blood samples, reflecting intravascular molecular conditions during collateral flow, showed similar sGPVI levels when compared to the systemic ICA samples in both groups. Conclusions: Our findings indicate that GPVI is not locally cleaved and shed into the bloodstream in significant amounts during hyper-acute ischemic stroke, neither at the level of symptomatic ICA nor intracranially during collateral blood supply. Therefore, sGPVI does not appear to be suitable as a local stroke biomarker despite strong evidence of a major role for GPVI-signaling in stroke pathophysiology.

Soluble glycoprotein VI predicts abdominal aortic aneurysm growth rate and is a novel therapeutic target

AbstractA common feature in patients with abdominal aortic aneurysms (AAAs) is the formation of a nonocclusive intraluminal thrombus (ILT) in regions of aortic dilation. Platelets are known to maintain hemostasis and propagate thrombosis through several redundant activation mechanisms, yet the role of platelet activation in the pathogenesis of AAA-associated ILT is still poorly understood. Thus, we sought to investigate how platelet activation affects the pathogenesis of AAA. Using RNA sequencing, we identified that the platelet-associated transcripts are significantly enriched in the ILT compared with the adjacent aneurysm wall and healthy control aortas. We found that the platelet-specific receptor glycoprotein VI (GPVI) is among the top enriched genes in AAA ILT and is increased on the platelet surface of patients with AAAs. Examination of a specific indicator of platelet activity, soluble GPVI (sGPVI), in 2 independent cohorts of patients with AAAs is highly predictive of an AAA diagnosis and associates more strongly with aneurysm growth rate than D-dimer in humans. Finally, intervention with the anti-GPVI antibody (JAQ1) in mice with established aneurysms blunted the progression of AAA in 2 independent mouse models. In conclusion, we show that the levels of sGPVI in humans can predict a diagnosis of AAA and AAA growth rate, which may be critical in the identification of high-risk patients. We also identify GPVI as a novel platelet-specific AAA therapeutic target, with minimal risk of adverse bleeding complications, for which none currently exists.

Plasma Soluble Glycoprotein VI, Platelet Function, Bleeding, and Ischemic Events in Patients Undergoing Elective Percutaneous Coronary Intervention.

Glycoprotein VI (GPVI) is the major platelet-specific collagen receptor. GPVI shedding with generation of soluble GPVI (sGPVI) is an endogenous feedback mechanism preventing platelet overstimulation. sGPVI has not been investigated in patients with chronic coronary syndrome (CCS) undergoing percutaneous coronary intervention (PCI), especially regarding its potential value as a predictor of ischemic and bleeding risk. Baseline plasma sGPVI levels were available in 318 patients with CCS undergoing PCI. Platelet function was assessed by measuring both adenosine diphosphate (ADP) and collagen-induced platelet aggregation. Co-primary endpoints were a composite of death or myocardial injury at 48 hours after PCI, and Bleeding Academic Research Consortium (BARC) type 1 to 5 bleeding at 30 days. There was no significant correlation between sGPVI and platelet function at baseline or at 48 hours after PCI and loading with antiplatelet drugs. Baseline plasma sGPVI levels were not associated with the ischemic risk: the incidence of the ischemic endpoint was 25.0% in the lower, 22.9% in the middle, and 26.7% in the upper sGPVI tertile (p = 0.82). There was a significant nonlinear relationship between sGPVI and the risk of bleeding: the incidence of the bleeding endpoint was 11.8% in the lower, 12.6% in the middle, and 26.4% in the upper sGPVI tertile (p = 0.006). In patients with CCS undergoing PCI, plasma levels of sGPVI did not correlate with ADP- or collagen-induced platelet aggregation. Patients with higher baseline levels of sGPVI may carry an increased risk of bleeding at 30 days after PCI but no excess risk of ischemic events.

O079 Predictive value for elevated platelet-derived SGPVI in venous in-stent stenosis in patients with post-thrombotic syndrome

Abstract Introduction In-stent stenosis following intervention for post-thrombotic syndrome (PTS) occurs in ∼30% of cases, despite therapeutic anticoagulation. Our aim was to investigate whether platelets are involved. Methods Blood was taken from case-matched patients before and after venous stenting. Flow-cytometry was used to assess platelet activation (P-selectin and/or phosphatidylserine exposure) while= functional activity was measured by plate-based aggregation and through a flow-cell model of thrombus formation. Soluble glycoprotein VI (sGPVI) was measured in plasma. Patients with in-stent stenosis requiring reintervention (>50% diameter reduction) were compared with those who did not. Results Forty-five patients were recruited (median age: 43yrs (33–55yrs); 65% female), and 19/45 (42%) required reintervention (median time: 3wks (1day-3mths)). There was no difference in platelet activation or reactivity after stenting, but P-selectin exposure pre-stent was significantly higher in patients who developed in-stent stenosis (2.7%±0.4 vs 1.7%±0.2; P<0.05). Pre-stent sGPVI levels were increased in patients who developed in-stent stenosis (18.9±3.6ng/mL vs. 7.4±0.9ng/mL; P<0.01). Platelet reactivity to collagen-related peptide, a GPVI-specific platelet agonist, was reduced in patients who developed in-stent stenosis (logEC50 = -6.5M±0.3 vs -7.2M±0.2; P<0.05; n=33). Pre-stent platelet accumulation (26.6AU±0.5 vs 19.0AU±8.1; P=0.04) was significantly increased in PTS patients compared with healthy controls. Conclusion Venous stenting does not activate platelets, but patients who developed in-stent stenosis exhibited greater levels of pre-stent platelet activation, greater loss of platelet surface GPVI in the form of sGPVI and reduction in reactivity to GPVI activation. sGPVI may have potential to risk stratify patients undergoing venous stenting and predict who requires closer surveillance. Take-home message Soluble GPVI may have potential to risk-stratify patients undergoing deep venous reconstruction and predict who requires closer surveillance.

Soluble glycoprotein VI is a predictor of major bleeding in patients with suspected heparin-induced thrombocytopenia

AbstractWe have shown that patients with suspected heparin-induced thrombocytopenia (HIT) have a high incidence of major bleeding. Recent studies have implicated elevated soluble glycoprotein VI (sGPVI) levels as a potential risk factor for bleeding. We sought to determine if elevated sGPVI plasma levels are associated with major bleeding events in patients with suspected HIT. We used a cohort of 310 hospitalized adult patients with suspected HIT who had a blood sample collected at the time HIT was suspected. Plasma sGPVI levels were measured by using enzyme-linked immunosorbent assay. Patients were excluded who had received a platelet transfusion within 1 day of sample collection because of the high levels of sGPVI in platelet concentrates. We assessed the association of sGPVI (high vs low) with International Society on Thrombosis and Haemostasis major bleeding events by multivariable logistic regression, adjusting for other known risk factors for bleeding. Fifty-four patients were excluded due to recent platelet transfusion, leaving 256 patients for analysis. Eighty-nine (34.8%) patients had a major bleeding event. Median sGPVI levels were significantly elevated in patients with major bleeding events compared with those without major bleeding events (49.09 vs 31.93 ng/mL; P < .001). An sGPVI level >43 ng/mL was independently associated with major bleeding after adjustment for critical illness, sepsis, cardiopulmonary bypass surgery, and degree of thrombocytopenia (adjusted odds ratio, 2.81; 95% confidence interval, 1.51-5.23). Our findings suggest that sGPVI is associated with major bleeding in hospitalized patients with suspected HIT. sGPVI may be a novel biomarker to predict bleeding risk in patients with suspected HIT.

Shedding of soluble glycoprotein VI is neither affected by animal-derived antibeta-2-glycoprotein 1 antibodies nor IgG fractions from patients with systemic lupus erythematosus.

: Antibeta-2-glycoprotein 1 (antiβ2GP1) antibodies are associated with increased risk of thrombosis in patients with systemic lupus erythematosus (SLE). The specific effect(s) of antiβ2GP1 antibodies on platelets are unclear. Platelet activation in response to antiplatelet antibodies has been shown to induce shedding of the ectodomain of the platelet collagen receptor, glycoprotein VI (GPVI), releasing soluble GPVI (sGPVI). The aim of this study was to therefore determine whether antiβ2GP1 antibodies, and/or purified IgG fractions, from patients with SLE shed sGPVI from platelets. We determined sGPVI levels in platelet poor plasma from SLE patients with/without antiβ2GP1 antibodies (n = 37), as well as in platelet-rich plasma from healthy donors treated with either SLE-derived IgG fractions containing antiβ2GP1, animal-derived antiβ2GP1, or isotype control antibodies. Levels of sGPVI were higher in three SLE-derived platelet poor plasma with antiβ2GP1 antibodies (103.52 ± 12.32 ng/ml) compared with those without (28.11 ± 12.73 ng/ml). Neither SLE-derived IgG fractions containing antiβ2GP1 antibodies, nor animal-derived antiβ2GP1 antibodies induced significant shedding of sGPVI from healthy donor platelets compared with isotype controls. These results suggest that antiβ2GP1 antibodies do not affect shedding of sGPVI, and therefore collagen-mediated platelet signalling pathways. The shedding activity in SLE patients may be due to factors other than antiβ2GP1 antibodies, for example, metalloproteinases.

Fibrin exposure triggers αIIbβ3‐independent platelet aggregate formation, ADAM10 activity and glycoprotein VI shedding in a charge‐dependent manner

BackgroundCollagen and fibrin engagement and activation of glycoprotein (GP) VI induces proteolytic cleavage of the GPVI ectodomain generating shed soluble GPVI (sGPVI). Collagen‐mediated GPVI shedding requires intracellular signalling to release the sGPVI, mediated by A Disintegrin And Metalloproteinase 10 (ADAM10); however, the precise mechanism by which fibrin induces GPVI shedding remains elusive. Plasma sGPVI levels are elevated in patients with coagulopathies, sepsis, or inflammation and can predict onset of sepsis and sepsis‐related mortality; therefore, it is clinically important to understand the mechanisms of GPVI shedding under conditions of minimal collagen exposure. ObjectivesOur aim was to characterize mechanisms by which fibrin‐GPVI interactions trigger GPVI shedding. MethodsPlatelet aggregometry, sGPVI ELISA, and an ADAM10 fluorescence resonance energy transfer assay were used to measure fibrin‐mediated platelet responses. ResultsFibrin induced αIIbβ3‐independent washed platelet aggregate formation, GPVI shedding, and increased ADAM10 activity, all of which were insensitive to pre‐treatment with inhibitors of Src family kinases but were divalent cation‐ and metalloproteinase‐dependent. In contrast, treatment of washed platelets with other GPVI ligands, collagen, and collagen‐related peptide caused αIIbβ3‐dependent platelet aggregation and GPVI release but did not increase constitutive ADAM10 activity. ConclusionsFibrin engages GPVI in a manner that differs from other GPVI ligands. Inclusion of polyanionic molecules disrupted fibrin‐induced platelet aggregate formation and sGPVI release, suggesting that electrostatic charge may play a role in fibrin/GPVI engagement. It may be feasible to exploit this property and specifically disrupt GPVI/fibrin interactions whilst sparing GPVI/collagen engagement.Fibrin engages GPVI in a manner that differs from other GPVI ligands. Inclusion of polyanionic molecules disrupted fibrin‐induced platelet aggregate formation and sGPVI release, suggesting that electrostatic charge may play a role in fibrin/GPVI engagement. It may be feasible to exploit this property and specifically disrupt GPVI/fibrin interactions whilst sparing GPVI/collagen engagement.

Plasma levels of the soluble form of the FcγRIIa receptor vary with receptor polymorphisms and are elevated in rheumatoid arthritis

Soluble forms of the low-affinity immunoglobulin receptor FcγRIIa (sFcγRIIa) lacking the cytoplasmic tail have been reported in plasma however the mechanism and functional consequences are unknown. This study aimed to evaluate mechanisms of FcγRIIa release compared to GPVI release from platelets, and examine whether genetic polymorphisms at positions 27 and 131 within FcγRIIa correlate with platelet FcγRIIa stability and function. Enzyme-linked immunosorbent assays (ELISAs) were used to measure plasma sFcγRIIa and sGPVI levels. FcγRIIa genotype at positions 27 and 131 was evaluated. sFcγRIIa levels were not significantly different between non-131HH and 131HH but were significantly lower in 27W than non-27W. Treatment of platelets with aggregated immunoglobulin (Ig) G induced release of FcγRIIa and GPVI, but only sGPVI release was statistically significant, required functional FcγRIIa, and was blocked by inhibitors of signaling pathways and metalloproteinases. This indicated that sFcγRIIa was not released from platelets by metalloproteolysis. sFcγRIIa levels were not correlated with sGPVI levels in healthy individuals however levels of sFcγRIIa and sGPVI in plasma from patients with rheumatoid arthritis (RA) were significantly elevated above levels found in healthy individuals. Elevated level of sFcγRIIa in RA patients may reflect active immune-based arthritis and be predictive of active inflammation.

Characterization of Platelet Activation in Patients with Eisenmenger Syndrome

▪BackgroundEisenmenger Syndrome (ES) is an extremely rare and serious complication of congenital heart disease in which pulmonary vascular resistance overcomes that of the systemic circulation causing bidirectional or reversed flow across an intracardiac shunt. Patients with ES have an increased incidence of both thrombotic and bleeding complications which occur through poorly understood mechanisms. We have recently demonstrated a critical mechanistic role for platelets in supporting abnormal hypercoagulability in patients with ES using calibrated automated thrombography (Kevane & Ní Áinle et al., J Thromb Haemost 2018).AimsBased upon our published data, we further hypothesized that patients with ES would have higher plasma concentrations of platelet activation markers. Therefore, the aim of this study was to measure plamsa levels of soluble P-Selectin (sP-Selectin) and soluble glycoprotein VI (sGPVI) in patients with ES and in matched healthy controls.MethodsPatients over the age of 18 with Eisenmenger Syndrome and healthy controls were recruited from the cardiology service at a large tertiary referral centre (Mater Misericordiae University Hospital) incorporating the Irish national congenital heart disease service. Platelet poor plasma (PPP) was generated from participants' blood by centrifugation at 2000xg for 10 minutes at room temperature. Commercially available ELISA assays employing quantitative sandwich immunoassay techniques were performed according to manufacturer protocol to measure plasma sP-Selectin and sGPVI levels. All experiments were performed in duplicate with results expressed as mean +/- standard error of mean. Comparisons between groups were made utilising the Student's t-test with a p-value < 0.05 deemed to represent statistical significance.ResultsDuring the study period, >14,000 patients attended the MMUH cardiology service. Of these, 14 consecutive patients with a diagnosis of ES and 10 matched healthy controls were recruited. Patients with ES had significantly elevated plasma concentrations of both soluble P-Selectin [38.5 +/- 8.3 vs. 11.3 +/- 4.2 ng/ml (p < 0.05)] and soluble GPVI [10.5 +/- 2.4 vs. 1.5 +/- 1.4 ng/ml (p < 0.01)] compared to healthy controls.ConclusionBuilding upon our recently published data in this population, a large cohort given the extreme rarity of this condition, increased concentrations of markers of platelet activation in individuals with ES further suggest a mechanistic role for platelets in ES-mediated hypercoagulability. This phenotype may be a consequence of vascular pathology associated with pulmonary hypertension in these patients. As such, therapies targeted at underlying vascular pathologies may act to ameliorate prothrombotic tendencies and we aim to characterize response to therapy during this ongoing study. DisclosuresNi Ainle:Leo Pharma: Research Funding; Actelion: Research Funding; Bayer: Research Funding; Bayer: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees; Boehringer: Membership on an entity's Board of Directors or advisory committees.

Soluble GPVI is elevated in injured patients: shedding is mediated by fibrin activation of GPVI

AbstractSoluble glycoprotein VI (sGPVI) is shed from the platelet surface and is a marker of platelet activation in thrombotic conditions. We assessed sGPVI levels together with patient and clinical parameters in acute and chronic inflammatory conditions, including patients with thermal injury and inflammatory bowel disease and patients admitted to the intensive care unit (ICU) for elective cardiac surgery, trauma, acute brain injury, or prolonged ventilation. Plasma sGPVI was measured by enzyme-linked immunosorbent assay and was elevated on day 14 after thermal injury, and was higher in patients who developed sepsis. sGPVI levels were associated with sepsis, and the value for predicting sepsis was increased in combination with platelet count and Abbreviated Burn Severity Index. sGPVI levels positively correlated with levels of D-dimer (a fibrin degradation product) in ICU patients and patients with thermal injury. sGPVI levels in ICU patients at admission were significantly associated with 28- and 90-day mortality independent of platelet count. sGPVI levels in patients with thermal injury were associated with 28-day mortality at days 1, 14, and 21 when adjusting for platelet count. In both cohorts, sGPVI associations with mortality were stronger than D-dimer levels. Mechanistically, release of GPVI was triggered by exposure of platelets to polymerized fibrin, but not by engagement of G protein-coupled receptors by thrombin, adenosine 5′-diphosphate, or thromboxane mimetics. Enhanced fibrin production in these patients may therefore contribute to the observed elevated sGPVI levels. sGPVI is an important platelet-specific marker for platelet activation that predicts sepsis progression and mortality in injured patients.

Soluble glycoprotein VI, a specific marker of platelet activation is increased in the plasma of subjects with seropositive rheumatoid arthritis.

ObjectivesAnti-citrullinated protein antibodies (ACPA) have been shown to cause platelet activation in vitro, through the low-affinity immunoglobulin G (IgG) receptor (FcγRIIa) on platelets. Platelet activation via engagement of FcγRIIa results in proteolytic cleavage and shedding of platelet specific glycoprotein VI (GPVI) which can be detected in the plasma as soluble GPVI (sGPVI). We hypothesized that plasma levels of sGPVI would be increased among patients with seropositive RA as a consequence of antibody-induced platelet activation and GPVI shedding.MethodsSamples from 84 patients with RA (65 seropositive and 19 seronegative) and 67 healthy controls were collected prospectively and analysed for sGPVI using a standardised ELISA.ResultsPatients with seropositive RA had significantly higher levels of sGPVI compared to seronegative RA and controls. Median (IQR) sGPVI levels were 4.2 ng/ml (3.2, 8.0) in seropositve RA, 2.2 ng/ml (1.5, 3.5) in seronegative RA and 2.2 ng/ml (1.6, 3.4) in controls (p<0.0001). sGPVI levels correlated with ACPA titres (r = 0.32, p = 0.0026) and with RF titres (r = 0.48, p<0.0001).ConclusionPlasma sGPVI, a specific marker of platelet activation is increased among patients with seropositive RA.

Increased platelet reactivity as measured by plasma glycoprotein VI in gout

Patients with gout have an increased risk of cardiovascular events. The glycoprotein VI (GPVI) receptor is found exclusively on platelets and megakaryocytes, is proteolytically cleaved upon platelet activation, and detectable in plasma as soluble GPVI (sGPVI). Therefore, elevated sGPVI is a marker of platelet activation and a risk marker for cardiovascular events. The aim of this study was to assess platelet activation, as measured by plasma sGPVI level in gout.Blood samples were taken from patients with gout or osteoarthritis, and from healthy volunteers. Demographic and clinical data were collected for all participants. Blood samples were processed as double-spun platelet-poor plasma. Plasma sGPVI levels were measured using enzyme-linked immunosorbent assay. Mann–Whitney U test was used to compare groups.In total, 91 patients were included, 27 during gout flare, 41 with intercritical gout, 23 with osteoarthritis, and 53 healthy controls. Median (interquartile range) sGPVI levels were 6.51 ng/mL (4.52, 8.41) in gout flare, 3.58 ng/mL (2.11, 5.55) in intercritical gout, 2.73 ng/mL (2.17, 3.72) in osteoarthritis, and 2.19 ng/mL (1.72, 3.31) in healthy controls. Plasma sGPVI levels in both gout groups were significantly increased compared to healthy controls (p < 0.005 for each), in gout flare compared to osteoarthritis (p < 0.005), and in gout flare compared to intercritical gout (p = 0.001). There was no significant difference in sGPVI levels in gout patients with and without tophi or in those prescribed colchicine.We conclude that patients with gout exhibit platelet hyperactivity as demonstrated by elevated sGPVI levels. Platelet activation is exacerbated in gout, especially during gout flares.

Decreased levels of platelet-derived soluble glycoprotein VI detected prior to the first diagnosis of coronary artery disease in HIV-positive individuals

ABSTRACTHIV-positive patients are at increased risk for coronary artery disease (CAD); changes in platelet activation may play a role. This study was performed to determine if levels of soluble glycoprotein VI (sGPVI), a platelet-specific marker of activation, were different in HIV-positive patients compared with HIV-negative controls and further if levels were predictive of CAD in HIV. Twenty-four HIV-positive individuals (HIV cases) with CAD were compared with 46 age- and sex-matched HIV-positive controls without CAD and 41 HIV-negative controls (healthy controls). Platelet activation (represented by sGPVI level) was compared 12 months and 1 month prior to CAD diagnosis. sGPVI was quantified by ELISA. sGPVI levels were higher in HIV-positive subjects (combined) than healthy controls (122.5 ng/mL [interquartile ranges (IQR) 90.3–160.5] versus 84.7 ng/mL [IQR 48.6–119.5], p <0.001). Twelve months before the event, there was no difference in sGPVI between HIV cases and HIV controls (113.4 ng/mL [IQR 85.6–141.65] versus 128.0 ng/mL [IQR 96.6–179.4], p = 0.369). One month prior to the event, sGPVI was significantly lower in HIV cases compared with HIV controls (109.0 ng/mL [IQR 79.4–123.4] versus 133.9 ng/mL [IQR 112.7–171.9], p = 0.010). These results remained significant following adjustment for possible confounders. This work demonstrates that HIV infection is associated with higher sGPVI levels. A fall in sGPVI immediately prior to first coronary artery event may reflect a loss of negative-feedback mechanism and be an important pathological step in the development of symptomatic CAD, but further work is needed to confirm these findings and determine their clinical impact.

Elevated Soluble Platelet Glycoprotein VI Levels in Patients After Living Donor Liver Transplantation.

Plasma-soluble platelet glycoprotein VI (sGPVI) levels were examined in patients undergoing living donor liver transplantation (LDLT), and the relationship between platelet activation and thrombocytopenia was evaluated to understand the mechanism of thrombocytopenia in LDLT. Platelet counts were significantly higher in the donors compared to the recipient, and the plasma sGPVI levels increased in both groups after the operation. Regarding the relationship between the platelet counts and the sGPVI levels, the slope varied on different days, and it became negative on day 3, suggesting that the plasma sGPVI levels are related to platelet activation in LDLT. The frequency of complications was high in the nonsurvivors. The platelet counts were higher in the survivors than in the nonsurvivors on days 14 and 28. Although the plasma levels of sGPVI in the survivors increased after the operation, those in the nonsurvivors were high only on day 3. Although the ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 domain, member 13) levels were markedly reduced, von Willebrand factor (VWF) and VWF propeptide (VWFpp) were markedly elevated during LDLT. The antithrombin activity was significantly lower (day 14) and VWFpp (day 28) was significantly higher in the nonsurvivors than in the survivors. These findings suggest that platelet activation first occurs after LDLT, and it is high in the nonsurvivors on day 3. Thereafter, the hemostatic abnormality and vascular endothelial cell injuries may appear on days 14 and 28.

Increased Soluble GPVI Levels in Cirrhosis: Evidence for Collagen Induced Platelet Activation In Vivo

BackgroundCirrhosis is a consequence of prolonged inflammation arising from chronic liver disease of different aetiologies. It is characterised by tissue fibrosis, the deposition of collagen-rich extracellular matrix tissue within the liver. Glycoprotein VI (GPVI) is platelet-specific collagen receptor that is shed from the platelet surface in a metalloproteinase-dependent manner in response to GPVI ligation. The shed extracellular region of GPVI can be detected in plasma and used as a measure of GPVI-dependent platelet activation in vivo. Several lines of evidence suggest that GPVI-dependent platelet activation occurs in cirrhosis. Platelets have been shown to accumulate at sites of collagen-rich fibrotic tissue. Circulating levels of collagen are increased in cirrhosis. Collagen-induced platelet aggregation responses are reduced in vitro with cirrhosis. Based on these results, we hypothesised that soluble GPVI (sGPVI) levels are increased in patients with cirrhosis. As such, the aim of this study was to quantify sGPVI levels in patients with cirrhosis and compare to healthy controls.MethodsCompensated cirrhotic patients were recruited at the Mater Misericordiae University Hospital, Dublin, Ireland. The diagnosis of cirrhosis was based on clinical examination, blood tests, and radiological examination (nodular surface, larger right lobe, coarse echotexture). Exclusion criteria were decompensated cirrhosis, recent thrombotic events, and antiplatelet and/or anticoagulant therapies. Healthy controls were recruited at the Royal College of Surgeons in Ireland and Beaumont Hospital, Dublin, Ireland. Blood samples were collected into vacutainers containing 3.2 % sodium citrate as anticoagulant. sGPVI levels in platelet poor plasma were measured using an in house custom ELISA.Results57 patients with mixed aetiology cirrhosis and 55 healthy controls were recruited. In the patient group, 42% of patients had alcoholic liver disease (ALD), 30% had hepatitis C (HCV), 7% had non alcoholic fatty liver disease (NAFLD), 5% had Hepatitis B (HBV), 5% had autoimmune hepatitis (AIH), 5% had cryptogenic liver disease, 4% had hereditary haemochromatosis (HH), and 2% had primary biliary cholangitis (PBC). sGPVI levels were significantly increased in patients with cirrhosis (5.8 ± 0.6 ng/ml, n = 57) compared to healthy controls (3.2 ± 0.4 ng/ml, n = 55, p < 0.0001). There was no significant difference between sGPVI levels in AIH (4 ± 1 ng/ml, n = 3), ALD (5.6 ± 1 ng/ml, n = 24), cryptogenic (12 ± 5 ng/ml, n = 3), HBV (3.1 ± 1 ng/ml, n = 3), HCV (5 ± 0.6 ng/ml), or NAFLD (5.3 ± 1.1 ng/ml, n = 4). sGPVI levels did not correlate with platelet count (r = 0.12, p = 0.3) or parameters of liver cell function (albumin, bilirubin, prothrombin time, and liver stiffness measurements).ConclusionsGPVI levels are significantly increased in patients with mixed aetiology cirrhosis. This indicates collagen induced platelet activation is occurring in vivo and suggests the presence of an underlying coagulopathy in patients with cirrhosis. DisclosuresNí Áinle:Actelion Pharma: Research Funding; Leo Pharma: Research Funding; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees; Boehringer Ingelheim: Membership on an entity's Board of Directors or advisory committees.

Increased Thrombopoiesis and Platelet Activation in Hantavirus-Infected Patients.

Thrombocytopenia is a common finding during viral hemorrhagic fever, which includes hemorrhagic fever with renal syndrome (HFRS). The 2 main causes for thrombocytopenia are impaired thrombopoiesis and/or increased peripheral destruction of platelets. In addition, there is an increased intravascular coagulation risk during HFRS, which could be due to platelet activation. Thrombopoiesis was determined by quantification of platelet counts, thrombopoietin, immature platelet fraction, and mean platelet volume during HFRS. The in vivo platelet activation was determined by quantification of soluble P-selectin (sP-selectin) and glycoprotein VI (sGPVI). The function of circulating platelets was determined by ex vivo stimulation followed by flow cytometry analysis of platelet surface-bound fibrinogen and P-selectin exposure. Intravascular coagulation during disease was determined by scoring for disseminated intravascular coagulation (DIC) and recording thromboembolic complications. The levels of thrombopoietin, immature platelet fraction, and mean platelet volume all indicate increased thrombopoiesis during HFRS. Circulating platelets had reduced ex vivo function during disease compared to follow-up. Most interestingly, we observed significantly increased in vivo platelet activation in HFRS patients with intravascular coagulation (DIC and thromboembolic complications) as shown by sP-selectin and sGPVI levels. HFRS patients have increased thrombopoiesis and platelet activation, which contributes to intravascular coagulation.

Properties of soluble glycoprotein VI, a potential platelet activation biomarker

Glycoprotein VI (GPVI) plays a critical role in the platelet response to collagen. Clinical studies suggest that the plasma level of soluble GPVI (sGPVI) is a highly specific and useful platelet activation marker. However, many properties of sGPVI have not been fully characterized, such as its sensitivity in detecting platelet activation and its elimination rate from the blood. In this study we established a sandwich enzyme-linked immunosorbent assay for human sGPVI, which cross-reacts to cynomolgus monkey sGPVI, and evaluated the time course of sGPVI production in a cynomolgus monkey model of lipopolysaccharide (LPS)-induced thrombocytopenia. The sGPVI levels in this model were dramatically elevated and returned to baseline by 24 hours after LPS injection, the change was more pronounced than the existing platelet activation biomarker, soluble P-selectin (sP-selectin) levels. The elimination half-life of recombinant human sGPVI was about 2.5 hours following intravenous administration to monkeys. These results suggest that plasma sGPVI closely reflects platelet activation in the bloodstream and has a short half-life. sGPVI would be a useful biomarker for disorders marked by platelet activation and for monitoring anti-platelet therapy.

Elevated soluble platelet glycoprotein VI is a useful marker for DVT in postoperative patients treated with edoxaban.

Prevention of deep vein thrombosis (DVT) is important in patients undergoing major orthopedic surgery. Although the detection of an elevated D-dimer level is useful for predicting DVT, it is not efficacious in postoperative patients being treated with anti-Xa agents. The soluble platelet glycoprotein VI (sGPVI) level is a marker of activated platelets, but not bleeding. Therefore, sGPVI levels are usually examined as a predictor of DVT in such patients. In the present study, 83 orthopedic patients were treated with 30mg of edoxaban for prophylaxis of DVT. Fourteen patients developed DVT and 17 patients discontinued the prophylaxis due to decreased hemoglobin levels. Plasma levels of sGPVI in the patients were significantly higher after surgery than before surgery. On day 1, the sGPVI levels increased, while the platelet counts decreased. There were no significant differences in D-dimer, soluble fibrin, or FDP levels in orthopedic patients with and without DVT before surgery and on days 1, 4, and 8. Plasma sGPVI levels were significantly higher in the patients with DVT than in those without DVT on days 1 and 4. Plasma levels of D-dimer were significantly higher in patients with withdrawal than in those without. However, there were no significant differences in sGPVI levels between those with and without withdrawal. As D-dimer levels are known to increase in patients with withdrawal, this parameter is not useful for evaluating the risk of DVT in these patients. In contrast, the sGPVI level is not increased in those with withdrawal and may therefore be useful for evaluating the risk of DVT in postoperative patients treated with an anticoagulant.

The Relationship Between Platelet Collagen Receptor Glycoprotein VI and No-Reflow Phenomenon in Patients With Acute ST-Segment Elevation Myocardial Infarction

ObjectivesThe purpose of this study was to determine whether admission soluble glycoprotein VI (sGP-VI) level is associated with no-reflow phenomenon (NRP) after primary percutaneous coronary intervention (P-PCI) in patients with...