Soluble Platelet Glycoprotein V Is a Marker of Thrombosis in Patients With Ischemic Stroke
Background and Purpose— The diagnosis and management of patients with acute ischemic stroke still lack an informative biochemical test. Soluble glycoprotein V (sGPV) is a new plasmatic marker of thrombosis released from the platelet surface by thrombin. The objective of this prospective study was to compare the levels of sGPV in stroke and control patients.
Methods— Consecutive patients with acute ischemic stroke (n=159) and controls (n=70) were recruited for sGPV measurement.
Results— Plasmatic levels of sGPV were significantly increased in ischemic stroke compared with control patients (median [interquartile range] 39.4 [31.8 to 52.9] versus 28.1 [24.0 to 37.9] ng/mL; P<0.0001). In multivariate analysis, ischemic stroke was the major determinant of the sGPV increase (odds ratio [95% CI], 5.87 [2.62 to 13.12]; P<0.0001).
Conclusions— sGPV is a new marker of arterial thrombosis and represents a tool to study the mechanisms involved in ischemic stroke. The increase in plasmatic sGPV observed in stroke patients supports a role of platelets and thrombin in the events leading to ischemic stroke.
Platelet activation and thrombin generation play a key role in vascular occlusion during ischemic stroke.1 The generation of thrombin and its action on platelets can now be monitored by measuring plasmatic levels of soluble glycoprotein V (sGPV). A 69-kDa fragment is the predominant sGPV form released from the platelet surface by thrombin cleavage.2 Increased plasma levels of sGPV have been documented with an ELISA in clinical thrombotic disorders such as atherosclerosis3 or atrial fibrillation.4 Interestingly, sGPV is significantly elevated after acute myocardial infarction.5
On the hypothesis that similar mechanisms mediate thrombin generation and subsequent platelet activation after ischemic stroke, the aim of this prospective study was to measure the release of sGPV in stroke patients. Results were compared with those obtained using classical markers of platelet activation (platelet factor 4 [PF4]), coagulation (thrombin-antithrombin complexes [TAT]), and fibrinolysis (d-dimers).
Consecutive patients with acute ischemic stroke (median delay from the onset of symptoms 1 day), confirmed by a computed tomography scan or MRI within 1 day of admission, were recruited between December 2000 and July 2002 on admission to the Neurology Department of Strasbourg or Dijon University Hospital. Controls were consecutive patients without antithrombotic treatment hospitalized during the same period in the same neurology departments for a chronic nonvascular neurological disorder (epilepsy 21%; Parkinson’s disease 19%; neuropathy 19%; multiple sclerosis 13%; and other 28%).
Blood was drawn within 1 day of admission into a Diatube H (Becton-Dickinson) for measurement of sGPV (Asserachrom Soluble GPV; Stago), PF4 (Asserachrom PF4; Stago), TAT (Enzygnost TAT; Dade Behring), d-dimers (immunoturbidimetric method), activated partial thromboplastin time (aPTT), and international normalized ratio (INR) in an STA-R automat (Stago). All tests were performed at the Etablissement Français du Sang (EFS) in Strasbourg. Ineffective and effective anticoagulation were defined by an aPTT ratio or INR <2 and between 2 and 3, respectively. The study was approved by the ethics committees of both hospitals, and informed consent to participate was obtained from all patients.
Results are expressed as median and interquartile (25th to 75th percentile) range. For univariate analysis, qualitative data were analyzed using bilateral Fisher exact test. Continuous variables were tested for normality using the Shapiro–Wilk test. When this hypothesis was rejected, nonparametrical tests were used to compare continuous values between groups (Mann–Whitney or Kruskall–Wallis tests, depending on the number of groups). Continuous variables were further dichotomized (median as cut-off value) for subsequent logistic regression to predict a high or a low value of sGPV, on the basis of disease status and potential confounding factors. After univariate screening, an ascending stepwise procedure for multivariate analysis was used with an entry P level of 0.20. All significance levels were set at 0.05. Correlations between the levels of sGPV and the other thrombosis markers were calculated using the Spearman nonparametric correlation coefficient. Computations have been run with SPSS 11.5 (SPSS Inc).
Plasmatic levels of sGPV were significantly increased in the 159 ischemic stroke patients compared with the 70 controls (39.4 [31.8 to 52.9] versus 28.1 [24.0 to 37.9] ng/mL; P<0.0001; Table 1). Levels of PF4, TAT, and d-dimers were also significantly elevated in ischemic stroke. sGPV levels were not influenced by the stroke subtype (large-artery atherosclerosis 42.7 [33.8 to 53.7]; cardioembolism 39.0 [28.1 to 54.2]; small vessel occlusion 41.9 [33.1 to 51.1]; other etiologies 38.6 [28.3 to 45.9] ng/mL) or by antithrombotic therapy (Figure).
Using multivariate analysis, sGPV was significantly correlated with stroke and with platelet and leukocyte counts, whereas cardiovascular risk factors did not significantly influence sGPV levels (Table 2).
Paired correlations between sGPV and other thrombosis markers were analyzed in the untreated ischemic stroke group (n=77) to eliminate possible confounding effects of antithrombotic therapy. This analysis showed sGPV levels to be significantly correlated with PF4 levels (r=0.46; P<0.0001) but not with TAT (r=0.12; P=0.31) or d-dimers (r=0.06; P=0.60).
This study revealed that sGPV is significantly increased in acute ischemic stroke. Given the known mechanism of GPV cleavage and the predominant role of thrombin,2,8 these results support an important participation of platelets and thrombin in the events leading to ischemic stroke.
Increased levels of PF4, TAT, and d-dimers were also found in the stroke group, in agreement with previous reports.6,7 However, sGPV was significantly correlated with PF4 but not with TAT or d-dimers, suggesting that thrombin was not the sole factor responsible for sGPV release in stroke. Minor cleavage of GPV by leukocyte elastase and endogenous platelet calpain has been reported,8 and the correlation between sGPV levels and platelet and leukocyte counts would support the occurrence of both modes of cleavage in stroke. An association between leukocyte counts and ischemic events has been described previously.9 These additional cleavages could also explain the fact that efficient anticoagulation did not lower sGPV levels with respect to untreated patients. New tests will be needed to discriminate between cleavage by thrombin and other proteases and to study the role of leukocytes and inflammation in stroke.
In conclusion, this study has demonstrated that sGPV represents a new marker of arterial thrombosis in stroke and a new tool to study the mechanisms involved in its occurrence. However, overlapping sGPV levels between patients and controls might limit its use as a diagnostic tool. Further work will be needed to evaluate the relevance of sGPV as a prognostic factor in ischemic stroke.
This work was supported by ARMESA, the EFS-Alsace, the Fondation de France, and by the Contrat d’Interface INSERM-Hôpitaux Universitaires de Strasbourg (F.L.). The authors would like to thank Juliette Mulvihill for reviewing the English of the manuscript, and Fabienne Dutrillaux and Christian Gachet for their important technical and intellectual participation throughout the study. This work is dedicated to Professor Jean-Marie Warter, who died September 17, 2003.
- Received September 6, 2004.
- Revision received November 15, 2004.
- Accepted November 30, 2004.
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