Up or out: polarity of VWF release

Effect of Supplemental Oxygen on von Willebrand Factor Activity and Ristocetin Cofactor Activity in Patients at Risk for Cardiovascular Complications Undergoing Moderate-to High-Risk Major Noncardiac Surgery-A Secondary Analysis of a Randomized Trial

Increased von Willebrand Factor (vWF) activity mediates platelet adhesion and might be a contributor to the development of thrombotic complications after surgery. Although in vitro studies have shown that hyperoxia induces endovascular damage, the effect of perioperative supplemental oxygen as a possible trigger for increased vWF activity has not been investigated yet. We tested our primary hypothesis that the perioperative administration of 80% oxygen concentration increases postoperative vWF activity as compared to 30% oxygen concentration in patients at risk of cardiovascular complications undergoing major noncardiac surgery. A total of 260 patients were randomly assigned to receive 80% versus 30% oxygen throughout surgery and for two hours postoperatively. We assessed vWF activity and Ristocetin cofactor activity in all patients shortly before the induction of anesthesia, within two hours after surgery and on the first and third postoperative day. Patient characteristics were similar in both groups. We found no significant difference in vWF activity in the overall perioperative time course between both randomization groups. We observed significantly increased vWF activity in the overall study population throughout the postoperative time course. Perioperative supplemental oxygen showed no significant effect on postoperative vWF and Ristocetin cofactor activity in cardiac risk patients undergoing major noncardiac surgery. In conclusion, we found no significant influence of supplemental oxygen in patients undergoing major non-cardiac surgery on postoperative vWF activity and Ristocetin cofactor activity.

Low temperature induces von-willebrand factor expression via increased early growth response 1 transcriptional activity in splenic sinusoidal endothelial cells

von Willebrand factor (vWF) is a large plasma glycoprotein that plays an important role in hemostasis by forming molecular bridges with platelets following vascular injury. Previously, we reported that hypothermia enhanced vWF production in the spleen, which resulted in the activation of the platelet pool in a hypothermia-induced murine model. However, the mechanisms that regulate vWF expression under hypothermic conditions remain unclear. In this study, we focused on vWF expression under hypothermic conditions in splenic endothelial cell culture. Human splenic endothelial cells (HSEC) were incubated at 20 °C for 1 h. Total RNA was extracted from the cells, and cDNA microarray gene expression analysis was performed. Genes that may be associated with vWF expression in low temperature culture conditions were then selected for further analysis. Gene expression analysis showed that low temperature conditions increased the expression of FOS and EGR1. We then hypothesized that these factors upregulate vWF mRNA expression in HSEC. The transcriptional inhibitors of EGR1 significantly inhibited vWF mRNA expression in HSEC cultured at a low temperature. Our analysis revealed that low temperatures enhance the gene expression of EGR1, which transcriptionally increases vWF expression. This acute-phase reaction may play an important role in platelet activation in the spleen during hypothermia.

Platelet biology and functions: new concepts and clinical perspectives

Platelets - blood cells continuously produced from megakaryocytes mainly in the bone marrow - are implicated not only in haemostasis and arterial thrombosis, but also in other physiological and pathophysiological processes. This Review describes current evidence for the heterogeneity in platelet structure, age, and activation properties, with consequences for a diversity of platelet functions. Signalling processes of platelet populations involved in thrombus formation with ongoing coagulation are well understood. Genetic approaches have provided information on multiple genes related to normal haemostasis, such as those encoding receptors and signalling or secretory proteins, that determine platelet count and/or responsiveness. As highly responsive and secretory cells, platelets can alter the environment through the release of growth factors, chemokines, coagulant factors, RNA species, and extracellular vesicles. Conversely, platelets will also adapt to their environment. In disease states, platelets can be positively primed to reach a pre-activated condition. At the inflamed vessel wall, platelets interact with leukocytes and the coagulation system, interactions mediating thromboinflammation. With current antiplatelet therapies invariably causing bleeding as an undesired adverse effect, novel therapies can be more beneficial if directed against specific platelet responses, populations, interactions, or priming conditions. On the basis of these novel concepts and processes, we discuss several initiatives to target platelets therapeutically.