Matrix metalloproteinase-10 effectively reduces infarct size in experimental stroke by enhancing fibrinolysis via a thrombin-activatable fibrinolysis inhibitor-mediated mechanism.

BACKGROUND: The fibrinolytic and matrix metalloproteinase (MMP) systems cooperate in thrombus dissolution and extracellular matrix proteolysis. The plasminogen/plasmin system activates MMPs, and some MMPs have been involved in the dissolution of fibrin by targeting fibrin(ogen) directly or by collaborating with plasmin. MMP-10 has been implicated in inflammatory/thrombotic processes and vascular integrity, but whether MMP-10 could have a profibrinolytic effect and represent a promising thrombolytic agent is unknown. METHODS AND RESULTS: The effect of MMP-10 on fibrinolysis was studied in vitro and in vivo, in MMP-10-null mice (Mmp10(-/-)), with the use of 2 different murine models of arterial thrombosis: laser-induced carotid injury and ischemic stroke. In vitro, we showed that MMP-10 was capable of enhancing tissue plasminogen activator-induced fibrinolysis via a thrombin-activatable fibrinolysis inhibitor inactivation-mediated mechanism. In vivo, delayed fibrinolysis observed after photochemical carotid injury in Mmp10(-/-) mice was reversed by active recombinant human MMP-10. In a thrombin-induced stroke model, the reperfusion and the infarct size in sham or tissue plasminogen activator-treated animals were severely impaired in Mmp10(-/-) mice. In this model, administration of active MMP-10 to wild-type animals significantly reduced blood reperfusion time and infarct size to the same extent as tissue plasminogen activator and was associated with shorter bleeding time and no intracranial hemorrhage. This effect was not observed in thrombin-activatable fibrinolysis inhibitor-deficient mice, suggesting thrombin-activatable fibrinolysis inhibitor inactivation as one of the mechanisms involved in the MMP-10 profibrinolytic effect. CONCLUSIONS: A novel profibrinolytic role for MMP-10 in experimental ischemic stroke is described, opening new pathways for innovative fibrinolytic strategies in arterial thrombosis.

Lack of secondary microthrombosis after thrombin-induced stroke in mice and non-human primates.

BACKGROUND: Secondary microthrombosis is a major pathophysiologic mechanism leading to brain damage following transient mechanical vascular occlusion (TMVO), the most widely used experimental stroke model. Whether secondary microthrombosis also occurs in non-TMVO stroke models represents an important issue for clinical translation of antimicrothrombosis therapeutic strategies. OBJECTIVES: To assess the occurrence and the pathogenic role of secondary microthrombosis in two thrombin-induced stroke models in mice and non-human primates (Macaca mulatta). METHODS: Stroke was induced in mice and non-human primates by intra-arterial administration of recombinant thrombin. This method induces the formation of a fibrin-rich thrombus, which is spontaneously dissolved in the following hours by the endogenous fibrinolytic system. Perfusion-weighted imaging and fluorescent-lectin microangiography were performed after recanalization to detect secondary microthrombosis. Moreover, to investigate its pathogenic role, thrombin-induced stroke was induced in bradykinin receptor B1 (B1R) knockout mice, which are protected from the thromboinflammation responsible for secondary microthrombosis in TMVO models. RESULTS: Reperfusion was stable and complete in all mice and non-human primates tested, revealing no secondary decrease in cerebral blood flow. No evidence of secondary microthrombosis was found in the two models. Accordingly, deficiency in B1R did not protect the mice from brain damage after thrombin-induced stroke. CONCLUSIONS: Our data demonstrate that secondary microthrombosis does not occur after thrombin-induced stroke. In view of this, the pathophysiologic roles of hematologic players promoting or protecting against secondary microthrombosis (such as factor XII, von Willebrand factor, and T cells) deserve to be re-evaluated in non-TMVO stroke models.

Tissue factor expressed by microparticles is associated with mortality but not with thrombosis in cancer patients.

A prothrombotic state is one of the hallmarks of malignancy and a major contributor to morbidity and mortality in cancer patients.Tissue factor (TF) is often overexpressed in malignancy and is a prime candidate in predicting the hypercoagulable state. Moreover, increased number of TF-exposing microparticles (MPs) in cancer patients may contribute to venous thromboembolism (VTE). We have conducted a prospective cohort study to determine whether elevated TF antigen, TF activity and TF associated to MPs (MPs-TF) are predictive of VTE and mortality in cancer patients. The studied population consisted of 252 cancer patients and 36 healthy controls. TF antigen and activity and MPs-TF were determined by ELISA and chromogenic assays. During a median follow-up of 10 months, 40 thrombotic events were recorded in 34 patients (13.5%), and 73 patients (28.9%) died. TF antigen and activity were significantly higher in patients than in controls (p<0.01) mainly in patients with advanced stages, whereas no differences were observed for TF activity of isolated MPs. We did not find a statistically significant association of TF variables with the risk of VTE. Multivariate analysis adjusting for age, sex, type of cancer and other confounding variables showed that TF activity (p<0.01) and MPs-TF activity (p<0.05) were independently associated with mortality. In conclusion, while TF variables were not associated with future VTE in cancer patients, we found a strong association of TF and MPs-TF activity with mortality, thus suggesting they might be good prognostic markers in cancer patients.