Blocking of Platelets or Intrinsic Coagulation Pathway–Driven Thrombosis Does Not Prevent Cerebral Infarctions Induced by Photothrombosis

Abstract

Background and Purpose-Models of photochemically-induced thrombosis are widely used in cerebrovascular research. Photothrombotic brain infarctions can be induced by systemic application of photosensitizing dyes followed by focal illumination of the cerebral cortex. Although the ensuing activation of platelets is well established, their contribution for thrombosis and tissue damage has not formally been proved. Methods-Infarction to the cerebral cortex was induced in mice by Rose Bengal and a cold light source. To assess the functional role of platelets, animals were platelet-depleted by anti-GPIb␣ antibodies or treated with GPIIb/IIIa-blocking F(ab) 2 fragments. The significance of the plasmatic coagulation cascade was determined by using blood coagulation factor XII (FXII)-deficient mice or heparin. Infarct development and infarct volumes were determined by serial MRI and conventional and electron microscopy. Results-There was no difference in development and final size of photothrombotic infarctions in mice with impaired platelet function. Moreover, deficiency of FXII, which initiates the intrinsic pathway of coagulation and is essential for thrombus formation, or blockade of FXa, the key protease during the waterfall cascade of plasmatic coagulation, by heparin likewise did not affect lesion development. Conclusions-Our data demonstrate that platelet activation, factor XII-driven thrombus formation, and plasmatic coagulation pathways downstream of FX are not a prerequisite for ensuing tissue damage in models of photothrombotic vessel injury indicating that other pathomechanisms are involved. We suggest that this widely used model does not depend on platelet-or plasmatic coagulation-derived thrombosis. (Stroke. 2008;39:1262-1268.)

Photothrombotic Ischemia: A Minimally Invasive and Reproducible Photochemical Cortical Lesion Model for Mouse Stroke Studies

“…Indeed it has been suggested that in peculiar conditions the platelet coagulation was not necessary to photothrombotic occlusion in which disruption of the endothelial integrity would induce edema and associated compression of the surrounding vessels. Moreover in the same study MRI analysis did not show modification of the infarct size after blockade of platelet function or depletion of platelets 17 .…”

“…MRI shows a simultaneous development of the ischemic infarction and vasogenic edema in large photothrombotic lesion whereas the development of the ischemic infarction prevails over vasogenic edema in human stroke 16 . Conversely, photothrombosis may not be adequate for the study of anti-thrombotic agent studies due to the fact that photothrombotic infarction occurs also after blocking of platelets or inhibition of intrinsic coagulation pathway 17 . Indeed it has been suggested that in peculiar conditions the platelet coagulation was not necessary to photothrombotic occlusion in which disruption of the endothelial integrity would induce edema and associated compression of the surrounding vessels.…”

Thrombotic distal middle cerebral artery occlusion produced by topical FeCl3 application: A novel model suitable for intravital microscopy and thrombolysis studies

“…However, occlusion induced by electrocoagulation (Backhauss et al, 1992;Tyson et al, 1984) or by placing a snare ligature or surgical clip around the MCA can injure the duramater and cortex, induce spreading depression, and poses a risk of subarachnoid hemorrhage. Photochemical MCA occlusion, which involves irradiation of several branches of the distal MCA with laser after intravenous administration of the photosensitizing dye Rose Bengal (Watson et al, 1985;Yao et al, 1996), is not depended on platelet-derived or plasmatic coagulation-derived thrombosis and can damage the microvascular bed irradiated (Kleinschnitz et al, 2008). Furthermore, it requires relatively expensive equipment.…”

Molecular mechanisms of thrombus formation in ischemic stroke: novel insights and targets for treatment

“…Cerebral photothrombosis has often been used as an alternative model to induce focal cerebral lesions, but recent studies have shown that the development of brain lesions after photothrombosis does not require intravascular thrombus formation. 50,51 Recently, a promising novel mouse model of thromboembolic stroke was reported based on microinjection of murine thrombin, 52 but, as with older similar clot models in mice, no data on the effect of antiplatelet treatment or anticoagulation are available yet. Moreover, embolic models are limited by variable infarct sizes, since it is difficult to anticipate which branch of the middle cerebral artery will finally be occluded by the inserted clot.…”