Platelet von Willebrand factor: sweet resistance

Platelet morphology, ultrastructure and function changes in acute ischemic stroke patients based on structured illumination microscopy

Acute ischemic stroke (AIS) is the second leading cause of death worldwide. This study aims at assessing platelet morphology, ultrastructure and function changes of platelets in acute ischemic stroke (AIS) patients by the technique of Structured Illumination Microscopy (SIM). This assay collected platelet-rich plasma (PRP) from 11 AIS patients and 12 healthy controls. Each PRP sample was divided into 7 groups:1) rest group; 2) Thrombin-treated 5 min group; 3) Thrombin plus 2MeSAMP-treated 5 min group; 4) Thrombin plus Aspirin-treated 5 min group; 5) Thrombin-treated 1 h group; 6) Thrombin plus 2MeSAMP-treated 1 h group; 7) Thrombin plus Aspirin-treated 1 h group. SIM was applied to observe dense granules and α-granules morphology changes of platelet in AIS patients. FIJI was used to quantify the image data. We finally observed 1448 images of platelets within the 7 groups. In rest group, 7162 platelets were calculated platelet diameter, CD63 dots, average CD63-positive dots area, CD63-positive area per platelet, CD63-positive area Fov, VWF dots, average VWF-positive dots area, VWF-positive area per platelet and VWF-positive area Fov. ELISA was used to detect release of platelet factor 4 (PF4) of α-granules. The results showed that AIS patients had lower number and smaller area of platelet granules. Platelet α-granules of AIS patients concentrated to parenchymal-like fluorescent blocks in Thrombin-treated 1 h group. Antiplatelet drug treatment could reverse the concentration of platelets α-granules, and 2MeSAMP was more powerful than Aspirin in vitro. This study complemented detail information of platelet ultrastructure of AIS patients, provided a new perspective on the pathogenesis of AIS and the mechanism of antiplatelet drugs based on SIM and provided a reference for future related studies. SIM-based analysis of platelet ultrastructure may be useful for detecting antiplatelet drugs and AIS in the future.

The association of von willebrand factor and its cleaving protease (ADAMTS13) with health behaviours in young black and white adults: the African-PREDICT study

To reduce cardiovascular risks imposed by Von Willebrand factor (vWF) and ADAMTS13 from young ages, knowledge on health behaviours that may affect their concentrations is essential. We therefore determined whether circulating vWF antigen and ADAMTS13 associate with health behaviours. We included 1196 black and white healthy adults aged 20-30 years and used questionnaires for socio-economic, tobacco and alcohol use data. vWF:Ag was measured from citrated samples and ADAMTS13, cotinine and gamma-glutamyl transferase (GGT) from serum. Salt intake was estimated from 24-hour urine and body mass index (BMI) was calculated. Black adults had higher vWF:Ag and lower ADAMTS13 levels compared to whites (all p < 0.001). In multiple regression analyses in the total group, vWF:Ag associated positively with BMI (p = 0.037), while ADAMTS13 associated negatively with BMI (p = 0.016) and cotinine (p = 0.029); and positively with GGT (p = 0.002). When exploring within each ethnic group, vWF:Ag associated positively with estimated salt intake (p = 0.043) only in blacks. In whites, vWF:Ag associated positively with BMI (p = 0.023) while ADAMTS13 associated positively with GGT (p = 0.003) and negatively with cotinine (p = 0.041). Young black adults may have an increased thrombotic risk due to higher vWF and lower ADAMTS13. The ethnic-specific associations observed may have implications for public health initiatives to improve cardiovascular outcomes.

Effect of Pneumatic Tubing System Transport on Platelet Apheresis Units

Platelet apheresis units are transfused into patients to mitigate or prevent bleeding. In a hospital, platelet apheresis units are transported from the transfusion service to the healthcare teams via two methods: a pneumatic tubing system (PTS) or ambulatory transport. Whether PTS transport affects the activity and utility of platelet apheresis units is unclear. We quantified the gravitational forces and transport time associated with PTS and ambulatory transport within our hospital. Washed platelets and supernatants were prepared from platelet apheresis units prior to transport as well as following ambulatory or PTS transport. For each group, we compared resting and agonist-induced platelet activity and platelet aggregate formation on collagen or von Willebrand factor (VWF) under shear, platelet VWF-receptor expression and VWF multimer levels. Subjection of platelet apheresis units to rapid acceleration/deceleration forces during PTS transport did not pre-activate platelets or their ability to activate in response to platelet agonists as compared to ambulatory transport. Platelets within platelet apheresis units transported via PTS retained their ability to adhere to surfaces of VWF and collagen under shear, although platelet aggregation on collagen and VWF was diminished as compared to ambulatory transport. VWF multimer levels and platelet GPIb receptor expression was unaffected by PTS transport as compared to ambulatory transport. Subjection of platelet apheresis units to PTS transport did not significantly affect the baseline or agonist-induced levels of platelet activation as compared to ambulatory transport. Our case study suggests that PTS transport may not significantly affect the hemostatic potential of platelets within platelet apheresis units.

Potential Mechanisms of Vascular Thrombosis after Microwave Ablation in an in Vivo Liver

PURPOSE

To evaluate potential biologic and thermal mechanisms of the observed differences in thrombosis rates between hepatic vessels during microwave (MW) ablation procedures.

MATERIALS AND METHODS

MW ablation antennae were placed in single liver lobes of 2 in vivo porcine liver models (n = 3 in each animal; N = 6 total) in the proximity of a large (> 5 mm) portal vein (PV) and hepatic veins (HVs). Each ablation was performed with 100 W for 5 minutes. Conventional ultrasound imaging and intravascular temperature probes were used to evaluate vessel patency and temperature changes during the ablation procedure. Vascular endothelium was harvested 1 hour after ablation and used to characterize genes and proteins associated with thrombosis in PVs and HVs.

RESULTS

Targeted PVs within the MW ablation zone exhibited thrombosis at a significantly higher rate than HVs (54.5% vs 0.0%; P = .0046). There was a negligible change in intravascular temperature in PVs and HVs during the ablation procedure (0.2°C ± 0.4 vs 0.6°C ± 0.9; P = .46). PVs exhibited significantly higher gene expression than HVs in terms of fold differences in thrombomodulin (2.9 ± 2.0; P = .0001), von Willebrand factor (vWF; 7.6 ± 1.5; P = .0001), endothelial protein C receptor (3.50 ± 0.49; P = .0011), and plasminogen activator inhibitor (1.46 ± 0.05; P = .0014). Western blot analysis showed significantly higher expression of vWF (2.32 ± 0.92; P = .031) in PVs compared with HVs.

CONCLUSIONS

Large PVs exhibit thrombosis more frequently than HVs during MW ablation procedures. Biologic differences in thrombogenicity, rather than heat transfer, between PVs and HVs may contribute to their different rates of thrombosis.

Platelet-derived VWF is not essential for normal thrombosis and hemostasis but fosters ischemic stroke injury in mice

Von Willebrand factor (VWF) is a key hemostatic protein synthesized in both endothelial cells and megakaryocytes. Megakaryocyte-derived VWF is stored in α-granules of platelets and is enriched in hyperactive "ultra-large" VWF multimers. To elucidate the specific contribution of platelet VWF in hemostasis and thrombosis, we performed crossed bone marrow transplantations between C57BL/6J and Vwf(-/-) mice to generate chimeric mice. Chimeric mice specifically lacking platelet VWF showed normal tail bleeding and carotid artery thrombosis, similar to wild-type mice. Chimeric mice with VWF present only in platelets were not able to support normal thrombosis and hemostasis. However, using a mouse model of transient middle cerebral artery occlusion, we observed that cerebral infarct sizes and fibrin(ogen) deposition in chimeric mice with only platelet VWF were significantly increased compared with Vwf(-/-) mice (P < .01). Blocking of the platelet VWF-glycoprotein (GP)Ib interaction abrogated this platelet VWF-mediated injury. These data suggest that whereas platelet-derived VWF does not play a crucial role in hemostasis and arterial thrombosis, it aggravates thrombo-inflammatory diseases such as stroke via a GPIb-dependent mechanism.