Background and Purpose To provide the first correlative study of the hyperdense MCA sign (HMCAS) and gradient-echo (GRE) MRI blooming artifact (BA) with pathology of retrieved thrombi in acute ischemic stroke. Methods Noncontrast CT and GRE MRI studies prior to mechanical thrombectomy in 50 consecutive cases of acute MCA ischemic stroke were reviewed, blinded to clinical and pathology data. Occlusions retrieved by thrombectomy underwent histopathologic analysis, including automated quantitative and qualitative rating of proportion composed of red blood cells (RBC), white blood cells (WBC), and fibrin on microscopy of sectioned thrombi. Results Among 50 patients, mean age was 66 years and 48% were female. Mean (SD) proportion was 61% (±21) fibrin, 34% (±21) RBC, and 4% (±2) WBC. Of retrieved clots, 22 (44%) were fibrin-dominant, 13 (26%) RBC-dominant and 15 (30%) mixed. HMCAS was identified in 10/20 MCA stroke cases with CT, with mean Hounsfield Unit (HU) density of 61 (SD±8). BA occurred in 17/32 with GRE MRI. HMCAS was more commonly seen with RBC-dominant and mixed than fibrin-dominant clots (100% vs. 67% vs. 20%, p=0.016). Mean percent RBC composition was higher in clots associated with HMCAS (47% vs. 22%, p=0.016). BA was more common in RBC-dominant and mixed clots compared to fibrin-dominant clots (100% vs. 63% vs. 25%, p=0.002). Mean percent RBC was greater with BA (42% vs. 23%, p=0.011). Conclusions CT HMCAS and GRE MRI BA reflect pathology of occlusive thrombus. RBC content determines appearance of HMCAS and BA, whereas absence of HMCAS or BA may indicate fibrin-predominant occlusive thrombi.

Immunofluorescence staining of cultured human umbilical vein endothelial cells has shown the presence of von Willebrand protein in the perinuclear region, in small rodlike structures through the cytoplasm, and on filaments of the extracellular matrix. Nonendothelial cells showed no staining with anti-von Willebrand protein antiserum. At the light microscope level, immunoperoxidase treatment of endothelial cells revealed the same pattern and antibody specificity as the fluorescence staining. Thin sections of the peroxidase-stained cells showed decorated filaments close to the substratum and also specific deposits in the endoplasmic reticulum and WeibeI-Palade bodies. Control antisera against other selected proteins in endothelial cells failed to stain the WeibeI-Palade bodies. These data suggest that the WeibeI-Palade bodies of endothelial cells are storage and/or processing organelles for von Willebrand protein.Von Willebrand protein is a large glycoprotein of complex multimeric structure (1, 2) that mediates attachment ofplatelets to the subendothelium after vascular injury (3). It is synthesized by megakaryocytes (4), which assure its presence in platelets in granulelike storage compartments (5, 6). After activation, platelets bind both von Willebrand protein released from internal storage sites and protein recruited from plasma to their surface membrane (7). Endothelial cells also synthesize von Willebrand protein (8) and the low concentration present in plasma and the subendothelium is probably derived from this source. We studied the distribution of von Willebrand protein in endothelial cells, in an attempt to detect and identify a storage compartment which would allow rapid release of this protein upon appropriate stimulus or physiologic demand. Using indirect immunofluorescence and immunoelectron microscopy, we determined that von Willebrand protein is concentrated in Weibel-Palade bodies. These are membrane-bound, elongate vesicles of 0.1 x 2-3 #In size that contain regularly spaced tubular structures aligned parallel to the longitudinal axis (9). Our data suggest that Weibel-Palade bodies serve as storage and/or processing vesicles for this protein and provide the first demonstration of unique function for these endothelial cell-specific organelles. MATERIALS AND METHODS Cells and Culture ConditionsEndothelial cells were obtained from human umbilical vein using a modification of the method described by Gimbrone et al.(10). Mild proteolytic digestion was carried out with 5 mg/ml of pronase (Calbiochem-Behring,

These results suggest that inflammation as well as parts of the coagulation pathway may contribute to the association between particulate air pollution and coronary events.

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Despite the widespread use of intraarterial thrombolytic therapy for peripheral arterial occlusive disease, a randomized study comparing its efficacy with that of operative intervention has never• been performed. This study evaluates the potential of intraarterial urokinase infusion to provide clinical benefits in patients with acute peripheral arterial occlusion. Methods: Patients with limb-threatening ischemia of less than 7 days' duration were randomly assigned to intraarterial catheter-directed urokinase therapy or operative intervention. Anatomic lesions unmasked by thrombolysis were treated with balloon dilation or operation. The primary end points of the study were limb salvage and survival.Results: A total of 57 patients were randomized to the thrombolytic therapy group, and 57 patients were randomized to the operative therapy group. Thrombolytic therapy resulted in dissolution of the occluding thrombus in 40 (70%) patients. Although the cumulative limb salvage rate was similar in the two treatment groups (82% at 12 months), the cumulative survival rate was significandy improved in patients randomized to the thrombolysis group (84% vs 58% at 12 months, p = 0.01). The mortality differences seemed to be primarily attributable to an increased frequency of in-hospital cardiopulmonary complications in the operative treatment group (49% vs 16%, P = 0.001). The benefits of thrombolysis were achieved without significant differences in the duration of hospitalization (median 11 days) and with only modest increases in hospital cost in the thrombolytic treatment arm (median $15,672 vs $12,253, P = 0.02).Conclusions: Intraarterial thrombolytic therapy was associated with a reduction in the incidence of in-hospital cardiopulmonary complications and a corresponding increase in patient survival rates. These benefits were achieved without an appreciable increase in the duration of hospitalization and with only modest increases in hospital cost, suggesting that thrombolytic therapy may offer a safe and effective alternative to operation in the initial treatment of patients diagnosed with acute limb-threatening peripheral arterial occlusion.

Background and Purpose-Information regarding the histological structure of thromboemboli that cause acute stroke provides insight into pathogenesis and clinical management. Methods-This report describes the histological analysis of thromboemboli retrieved by endovascular mechanical extraction from the middle cerebral artery (MCA) and intracranial carotid artery (ICA) of 25 patients with acute ischemic stroke. Results-The large majority (75%) of thromboemboli shared architectural features of random fibrin:platelet deposits interspersed with linear collections of nucleated cells (monocytes and neutrophils) and confined erythrocyte-rich regions. This histology was prevalent with both cardioembolic and atherosclerotic sources of embolism. "Red" clots composed uniquely of erythrocytes were uncommon and observed only with incomplete extractions, and cholesterol crystals were notably absent. The histology of thromboemboli that could not be retrieved from 29 concurrent patients may be different. No thrombus Ͼ3 mm wide caused stroke limited to the MCA, and no thrombus Ͼ5 mm wide was removed from the ICA. A mycotic embolus was successfully removed in 1 case, and a small atheroma and attached intima were removed without clinical consequence from another. Conclusions-Thromboemboli retrieved from the MCA or intracranial ICA of patients with acute ischemic stroke have similar histological components, whether derived from cardiac or arterial sources. Embolus size determines ultimate destination, those Ͼ5 mm wide likely bypassing the cerebral vessels entirely. The fibrin:platelet pattern that dominates thromboembolic structure provides a foundation for both antiplatelet and anticoagulant treatment strategies in stroke prevention.

The possibility that bacteria may have evolved strategies to overcome host cell apoptosis was explored by using Rickettsia rickettsii, an obligate intracellular Gram-negative bacteria that is the etiologic agent of Rocky Mountain spotted fever. The vascular endothelial cell, the primary target cell during in vivo infection, exhibits no evidence of apoptosis during natural infection and is maintained for a sufficient time to allow replication and cell-to-cell spread prior to eventual death due to necrotic damage. Prior work in our laboratory demonstrated that R. rickettsii infection activates the transcription factor NF-B and alters expression of several genes under its control. However, when R. rickettsiiinduced activation of NF-B was inhibited, apoptosis of infected but not uninfected endothelial cells rapidly ensued. In addition, human embryonic fibroblasts stably transfected with a superrepressor mutant inhibitory subunit IB that rendered NF-B inactivatable also underwent apoptosis when infected, whereas infected wild-type human embryonic fibroblasts survived. R. rickettsii, therefore, appeared to inhibit host cell apoptosis via a mechanism dependent on NF-B activation. Apoptotic nuclear changes correlated with presence of intracellular organisms and thus this previously unrecognized proapoptotic signal, masked by concomitant NF-B activation, likely required intracellular infection. Our studies demonstrate that a bacterial organism can exert an antiapoptotic effect, thus modulating the host cell's apoptotic response to its own advantage by potentially allowing the host cell to remain as a site of infection.

Biosynthesis of von Willebrand protein by human umbilical vein endothelial cells involved distinct processing steps marked by the presence of several intermediate molecular species. Examination of endoglycosidase H sensitivity of these intracellular intermediates indicated that the processing steps occurred in at least two separate cellular compartments. In the pre-Golgi apparatus (most probably the endoplasmic reticulum), the high mannose carbohydrates were added onto the precursor monomer chains and the 260,000-mol-wt monomers dimerized by interchain disulfide bond formation. The other processing steps have been localized to the Golgi apparatus and later compartments (e.g., WeibeI-Palade bodies). High mannose carbohydrate was converted to the complex type, leading to the appearance of a larger precursor subunit of 275,000 mol wt. The 275,000-mol-wt species was not formed if carbohydrate processing was inhibited by the ionophore monensin. From the large pool of dimers of precursor subunits, the high molecular weight multimers were built. These dimer molecules appeared to have free sulfhydryls which might have been involved in the interdimer disulfide bond formation. Simultaneously with multimerization, the precursor subunits were cleaved to the 220,000-mol-wt form. The cleavage of the pro-sequence was not likely to be an absolute requirement for von Willebrand protein multimerization or secretion, as the 275,000-mol-wt precursor subunit was present in secreted high molecular weight multimers of the protein.von Willebrand (vW) ~ protein is a large glycoprotein of complex multimeric structure held together by disulfide bonds (1, 2). Absence of or molecular defects in the protein may cause a bleeding disorder owing to inadequate binding of platelets at sites of injury (1, 3, 4). vW protein is synthesized by megakaryocytes (5) and by endothelial cells that are likely to be responsible for the presence of vW protein in blood and subendothelium. In the endothelial cells, vW protein is concentrated in organelles called Weibel-Palade bodies (6). Endothelial cells synthesize vW protein subunits first as large precursors of 260,000-mol-wt (7,8), which undergo several processing steps including carbohydrate addition, polymerization by disulfide bond formation, and proteolytic cleavage to a mature subunit form of 220,000-mol-wt. Although the ~Abbreviations used in this paper. DTNB, 5,5'-dithiobis(2-nitrobenzoic acid); HMW, high molecular weight; vW, von Willebrand. presence of high molecular weight (HMW) polymers of vW protein in cell lysates of trypsin-treated cells indicates that they form within the cells (7), the intracellular locations of the processing steps are not known. Pulse-chase experiments on human umbilical vein endothelial cells have demonstrated that cleavage of the intracellular precursor to the mature subunit is very slow. It is first observed 2 h after the onset of labeling and even after several hours of chase some uncleaved precursor protein is still present. This slow processing explains the ...