Histopathological effects of different therapy strategies in experimental sinus thrombosis.

The optimal treatment for cerebral venous thrombosis is still under debate. The histological consequences of different treatments have not been systematically studied and may be of value in this debate. Thrombosis of the superior sagittal sinus was induced in rats by topical application of ferric chloride. Animals were treated 6 h after operation with subcutaneous injection of 450 IU/kg enoxaparin twice daily (n = 10), with 10 mg recombinant tissue plasminogen activator (rt-PA)/kg (n = 12), and with 6 mg abciximab/kg (n = 10). Eleven animals were treated with saline (controls), and four animals were sham-operated without thrombosis induction. Animals were killed on day 7. Coronal brain slices were stained with hematoxylin-eosin (HE) and against glial fibrillary acidic protein (GFAP), and factor VIII. Histology was quantified in parasagittal and temporal regions of interest. Compared with controls, counts of pyknotic neurons on HE stain were significantly lower in the enoxaparin group. Counts for GFAP-expressing astrocytes were highest in the enoxaparin (p < 0.001) and rt-PA (p < 0.05)-treated groups. Angiogenesis defined as factor VIII-expressing vessels was significantly (p < 0.01) higher in the enoxaparin and significantly lower (p < 0.01) in the rt-PA group compared with controls. In this animal model, we found histological differences related to the different treatments, which cannot be explained by recanalization and its speed alone.

Extracellular RNA mediates endothelial-cell permeability via vascular endothelial growth factor.

Cell injury leads to exposure of intracellular material and is associated with increased permeability of vessels in the vicinity of the damage. Here, we demonstrate that natural extracellular RNA as well as artificial RNA (poly-I:C), or single-stranded RNA but not DNA, significantly increased the permeability across brain microvascular endothelial cells in vitro and in vivo. RNA-induced hyperpermeability of tight monolayers of endothelial cells correlated with disintegration of tight junctions and was mediated through vascular endothelial growth factor (VEGF), reminiscent of heparin's activities. Antisense oligonucleotides against VEGF-receptor 2 (VEGF-R2) prevented the permeability-inducing activity of extracellular RNA and heparin completely. Hence, these polyanionic substances can lead to mobilization/stabilization of VEGF with the subsequent activation of VEGF-R2. In accordance with these functional data, strong binding of VEGF as well as other growth factors to RNA was demonstrable. In in vivo rat models of FeCl(3)-induced sinus sagittal is superior thrombosis and stroke/brain edema, pretreatment of animals with RNase (but not DNase) resulted in a significant reduction of vessel occlusion, infarct volume, and prevention of brain edema formation. Together, these results identify extracellular RNA as a novel natural permeability factor, upstream of VEGF, whereas counteracting RNase treatment may serve as new vessel-protective modality.