The effects of epinephrine infusion in patients with von Willebrand's disease

Myosin IIa is critical for cAMP-mediated endothelial secretion of von Willebrand factor

Nonmuscle myosin II has been implicated in regulation of von Willebrand factor (VWF) release from endothelial Weibel-Palade bodies (WPBs), but the specific role of myosin IIa isoform is poorly defined. Here, we report that myosin IIa is expressed both in primary human endothelial cells and intact mouse vessels, essential for cyclic adenosine monophosphate (cAMP)-mediated endothelial VWF secretion. Downregulation of myosin IIa by shRNAs significantly suppressed both forskolin- and epinephrine-induced VWF secretion. Endothelium-specific myosin IIa knockout mice exhibited impaired epinephrine-stimulated VWF release, prolonged bleeding time, and thrombosis. Further study showed that in resting cells, myosin IIa deficiency disrupted the peripheral localization of Rab27-positive WPBs along stress fibers; on stimulation by cAMP agonists, myosin IIa in synergy with zyxin promotes the formation of a functional actin framework, which is derived from preexisting cortical actin filaments, around WPBs, facilitating fusion and subsequent exocytosis. In summary, our findings not only identify new functions of myosin IIa in regulation of WPB positioning and the interaction between preexisting cortical actin filaments and exocytosing vesicles before fusion but also reveal myosin IIa as a physiological regulator of endothelial VWF secretion in stress-induced hemostasis and thrombosis.

Zyxin regulates endothelial von Willebrand factor secretion by reorganizing actin filaments around exocytic granules

Endothelial exocytosis of Weibel-Palade body (WPB) is one of the first lines of defence against vascular injury. However, the mechanisms that control WPB exocytosis in the final stages (including the docking, priming and fusion of granules) are poorly understood. Here we show that the focal adhesion protein zyxin is crucial in this process. Zyxin downregulation inhibits the secretion of von Willebrand factor (VWF), the most abundant cargo in WPBs, from human primary endothelial cells (ECs) induced by cAMP agonists. Zyxin-deficient mice exhibit impaired epinephrine-stimulated VWF release, prolonged bleeding time and thrombosis, largely due to defective endothelial secretion of VWF. Using live-cell super-resolution microscopy, we visualize previously unappreciated reorganization of pre-existing actin filaments around WPBs before fusion, dependent on zyxin and an interaction with the actin crosslinker α-actinin. Our findings identify zyxin as a physiological regulator of endothelial exocytosis through reorganizing local actin network in the final stage of exocytosis.

VWF excess and ADAMTS13 deficiency: a unifying pathomechanism linking inflammation to thrombosis in DIC, malaria, and TTP

Absent or severely diminished activity of ADAMTS13 (A Disintegrin And Metalloprotease with a ThromboSpondin type 1 motif, member 13) resulting in the intravascular persistence and accumulation of highly thrombogenic ultra large von Willebrand factor (UL-VWF) multimers is the pathophysiological mechanism underlying thrombotic thrombocytopenic purpura. Reduced VWF-cleaving protease levels, however, are not uniquely restricted to primary thrombotic microangiopathy (TMA), e. g. thrombotic thrombocytopenic purpura, but also occur in other life-threatening thrombocytopenic conditions: severely decreased ADAMTS13 activity is seen in severe sepsis, disseminated intravascular coagulation (DIC) and complicated malarial infection. The clinical relevance of these secondary thrombotic microangiopathies is increasingly recognised, but its therapeutic implications have not yet been determined. The presence of a secondary TMA in certain diseases may define patient groups which possibly could benefit from ADAMTS13 replacement or a VWF-targeting therapy. This short-review focuses on the role of UL-VWF multimers in secondary TMA and discusses the potential of investigational therapies as candidates for the treatment of TTP. In conclusion, prospective clinical trials on the effectiveness of protease replacementin vivo seem reasonable. Carefully selected patients with secondary TMA may benefit from therapies primarily intended for the use in patients with TTP.

An update on type 2B von Willebrand disease

Type 2B von Willebrand disease (VWD) accounts for fewer than 5% of all VWD patients. In this disease, mutations in the A1 domain result in increased von Willebrand factor (VWF) binding to platelet GPIbα receptors, causing increased platelet clearance and preferential loss of high molecular weight VWF multimers. Diagnosis is complicated because of significant clinical variations even among patients with identical mutations. Platelet transfusion often provides suboptimal results since transfused platelets may be aggregated by the patients' abnormal VWF. Desmopressin may cause a transient decrease in platelet count that could lead to an increased risk of bleeding. Replacement therapy with factor VIII/VWF concentrates is the most effective approach to prevention and treatment of bleeding in type 2B VWD.

Endothelial Von Willebrand factor promotes blood-brain barrier flexibility and provides protection from hypoxia and seizures in mice

OBJECTIVE

Aberrant blood-brain barrier (BBB) permeability is a hallmark pathology of many central nervous system diseases. von Willebrand factor (VWF) is stored in endothelial Weibel-Palade bodies from where it is released on activation into plasma and basement membrane. The role of VWF in endothelial homeostasis is unclear. The goal of this study was to assess the role of VWF in disease models associated with increased BBB permeability.

APPROACH AND RESULTS

We did not find any differences in BBB permeability to Evans blue dye at baseline between wild-type and VWF(-/-) animals. We next used 2 models presenting with increased BBB permeability, hypoxia/reoxygenation and pilocarpine-induced status epilepticus, to assess the response of VWF(-/-) animals. In both models, VWF(-/-) mice maintained a tighter BBB than wild-type mice. VWF(-/-) mice fared worse in both conditions, with ≈ 100% of VWF(-/-) mice dying within 120 minutes after pilocarpine administration, whereas >80% of wild-type animals survived. Investigation into the status of tight junction proteins revealed that VWF(-/-) mice expressed more claudin-5 at baseline. In vitro work confirmed that the presence of subendothelial VWF is inhibitory to claudin-5 expression.

CONCLUSIONS

VWF deficiency confers partial preservation of BBB integrity after hypoxia/reoxygenation and seizures. Surprisingly, this decrease in BBB permeability did not result in protection of animals because they demonstrated more severe pathology in both models compared with wild-type animals. These data suggest that a rigid BBB is detrimental (to the organism) during certain disease states and that VWF release may provide desired flexibility under stress.

The Epac-Rap1 signaling pathway controls cAMP-mediated exocytosis of Weibel-Palade bodies in endothelial cells

Endothelial cells contain specialized storage organelles called Weibel-Palade bodies (WPBs) that release their content into the vascular lumen in response to specific agonists that raise intracellular Ca(2+) or cAMP. We have previously shown that cAMP-mediated WPB release is dependent on protein kinase A (PKA) and involves activation of the small GTPase RalA. Here, we have investigated a possible role for another PKA-independent cAMP-mediated signaling pathway in the regulation of WPB exocytosis, namely the guanine nucleotide exchange factor Epac1 and its substrate, the small GTPase Rap1. Epinephrine stimulation of endothelial cells leads to Rap1 activation in a PKA-independent fashion. siRNA-mediated knockdown of Epac1 abolished epinephrine-induced activation of Rap1 and resulted in decreased epinephrine-induced WPB exocytosis. Down-regulation of Rap1 expression and prevention of Rap1 activation through overexpression of Rap1GAP effectively reduced epinephrine- but not thrombin-induced WPB exocytosis. Taken together, these data uncover a new Epac-Rap1-dependent pathway by which endothelial cells can regulate WPB exocytosis in response to agonists that signal through cAMP.

Targeting von Willebrand factor and platelet glycoprotein Ib receptor

Atherothrombotic events, such as acute coronary syndrome or stroke, are the result of platelet activation. Von Willebrand factor (vWF), a multimeric glycoprotein, plays a key role in aggregation of platelets, especially under high-shear conditions. Acting as bridging element or ligand between damaged endothelial sites and the glycoprotein Ib (GPIb) receptor on platelets, vWF is responsible for platelet adhesion and aggregation. This vWF activation and further platelet aggregation mainly occurs under high shear stress present in small arterioles or during deficiency of the vWF-cleaving protease ADAMTS13. There are several substances targeting vWF itself or its binding receptor GPIb on platelets. Two antibodies are directed against vWF: AJW200, an IgG4 humanized monoclonal antibody, and 82D6A3, a monoclonal antibody of the collagen-binding A-3 domain of vWF. ALX-0081 and ALX-0681 are bivalent humanized nanobodies targeting the GPIb binding site of vWF. Aptamers are oligonucleotides with drug-like properties that share some of the attributes of monoclonal antibodies. ARC1779 is a second-generation, nuclease-resistant aptamer, binding to the activated vWF A1 domain and ARC15105 is a chemically advanced follower with an assumed higher affinity to vWF. Antibodies targeting GPIbα are h6B4-Fab, a murine monoclonal antibody; GPG-290, a recombinant, chimeric protein containing the amino-terminal 290 amino acids of GPIbα linked to human IgG1 Fc; and the monoclonal antibody SZ2. There are a number of promising preclinical results and development of some agents (AJW 200, ARC1779 and ALX-0081) has already reached Phase II trials.

Functional architecture of Weibel-Palade bodies

Weibel-Palade bodies (WPBs) are elongated secretory organelles specific to endothelial cells that contain von Willebrand factor (VWF) and a variety of other proteins that contribute to inflammation, angiogenesis, and tissue repair. The remarkable architecture of WPBs is because of the unique properties of their major constituent VWF. VWF is stored inside WPBs as tubules, but on its release, forms strikingly long strings that arrest bleeding by recruiting blood platelets to sites of vascular injury. In recent years considerable progress has been made regarding the molecular events that underlie the packaging of VWF multimers into tubules and the processes leading to the formation of elongated WPBs. Mechanisms directing the conversion of tightly packaged VWF tubules into VWF strings on the surface of endothelial cells are starting to be unraveled. Several modes of exocytosis have now been described for WPBs, emphasizing the plasticity of these organelles. WPB exocytosis plays a role in the pathophysiology and treatment of von Willebrand disease and may have impact on common hematologic and cardiovascular disorders. This review summarizes the major advances made on the biogenesis and exocytosis of WPBs and places these recent discoveries in the context of von Willebrand disease.

Local anesthetic use in the pregnant and postpartum patient

The use of systemically absorbed drugs in the gravid and in the lactating patient is of concern to the dentist. This article reviews concerns for the health and safety of the mother, developing fetus, and neonate involving local anesthetics. The available literature on the use of local anesthetics for dentistry in the pregnant and postpartum patient is also reviewed. In addition, the physiology of the pregnant and postpartum woman is discussed because this is essential to understanding potential interplay with local anesthesia and the stress of a dental appointment.

Targeting FVIII expression to endothelial cells regenerates a releasable pool of FVIII and restores hemostasis in a mouse model of hemophilia A

The natural cell type(s) that synthesize and release factor VIII (FVIII) into the circulation are still not known with certainty. In vitro studies indicate that artificial expression of FVIII in endothelial cells produces an intracellular pool of FVIII that can be mobilized together with its carrier protein, von Willebrand factor (VWF), by agonists. Here, we show that expression of human B-domain deleted FVIII (hFVIII) in the vascular endothelium of otherwise FVIII-deficient mice results in costorage of FVIII and VWF in endothelial Weibel-Palade bodies and restores normal levels and activity of FVIII in plasma. Stored FVIII was mobilized into the circulation by subcutaneous administration of epinephrine. Human FVIII activity in plasma was strictly dependent on the presence of VWF. Endothelial-specific expression of hFVIII rescued the bleeding diathesis of hemophilic mice lacking endogenous FVIII. This hemostatic function of endothelial cell-derived hFVIII was suppressed in the presence of anti-FVIII inhibitory antibodies. These results suggest that targeting FVIII expression to endothelial cells may establish a releasable pool of FVIII and normalize plasma FVIII level and activity in hemophilia A, but does not prevent the inhibitory effect of anti-FVIII antibodies on the hemostatic function of transgene-derived hFVIII as is seen with platelet-derived FVIII expression.

von Willebrand factor in cardiovascular disease: focus on acute coronary syndromes

von Willebrand factor (VWF) plays a pivotal role in platelet adhesion and aggregation at sites of high shear rates (eg, in coronary arteries that have stenotic or ruptured atherosclerotic plaque lesions). Numerous studies have investigated the relationship between VWF plasma levels and thromboembolic cardiovascular events. In contrast to the rather weak association in the general population, in patients with preexisting vascular disease, VWF is significantly predictive for adverse cardiac events, including death. Likewise, VWF typically rises during the course of acute coronary syndrome, and the extent of this VWF release is an independent predictor of adverse clinical outcome in these patients. Various lines of evidence indicate that VWF is not only a marker but also actually an important effector in the pathogenesis of myocardial infarction. This central role of VWF in thrombogenesis has made it a promising target for research into new antiplatelet therapies that specifically inhibit VWF. This review focuses on the role of VWF in acute coronary syndrome and further outlines the relevance of therapeutic interventions targeting VWF for acute coronary syndrome patients.

Fluvastatin inhibits regulated secretion of endothelial cell von Willebrand factor in response to diverse secretagogues

Regulated secretion of EC (endothelial cell) vWF (von Willebrand factor) is part of the haemostatic response. It occurs in response to secretagogues that raise intracellular calcium or cAMP. Statins are cholesterol-lowering drugs used for the treatment of cardiovascular disease. We studied the effect of fluvastatin on regulated secretion of vWF from HUVEC (human umbilical-vein ECs). Secretion in response to thrombin, a protease-activated receptor-1 agonist peptide, histamine, forskolin and adrenaline (epinephrine) was inhibited. This inhibition was reversed by mevalonate or geranylgeranyl pyrophosphate, and mimicked by a geranylgeranyl transferase inhibitor, demonstrating that the inhibitory mechanism includes inhibition of protein geranylgeranylation. To investigate this mechanism further, calcium handling and NO (nitric oxide) regulation were studied in fluvastatin-treated HUVEC. Intracellular calcium mobilization did not correlate with vWF secretion. Fluvastatin increased eNOS [endothelial NOS (NO synthase)] expression, but NOS inhibitors failed to reverse the effect of fluvastatin on vWF secretion. Exogenous NO did not inhibit thrombin-induced vWF secretion. Many small GTPases are geranylgeranylated and some are activated by secretagogues. We overexpressed DN (dominant negative) Rho GTPases, RhoA, Rac1 and Cdc42 (cell division cycle 42), in HUVEC. DNCdc42 conferred inhibition of thrombin- and forskolin-induced vWF secretion. We conclude that, via inhibition of protein geranylgeranylation, fluvastatin is a broadspectrum inhibitor of regulated vWF secretion. Geranylgeranylated small GTPases with functional roles in regulated secretion, such as Cdc42, are potential targets for the inhibitory activity of fluvastatin.

A practical approach to genetic testing for von Willebrand disease

von Willebrand disease (vWD) is the most commonly diagnosed congenital bleeding disorder. The laboratory diagnosis of type 2 variants and type 3 vWD is reasonably well defined, and characterization of the von Willebrand factor (vWF) gene has facilitated definition of their molecular basis. However, for type 1 vWD, the laboratory diagnosis poses a diagnostic dilemma, and knowledge of its molecular basis is evolving. Characterization of the vWF gene and refinement of genetic techniques have led to an evolving repertoire of genetic tests. Genetic testing is costly, and thus judicious use will be increasingly important for appropriate genetic-counseling of patients with vWD and their family members. This article provides a practical approach to utilization of genetic testing in vWD.

Dynamics and plasticity of Weibel-Palade bodies in endothelial cells

Agonist-induced release of endothelial cell specific storage granules, designated Weibel-Palade bodies (WPBs), provides the endothelium with the ability to rapidly respond to changes in its micro-environment. Originally being defined as an intracellular storage pool for von Willebrand factor (VWF), it has recently been shown that an increasing number of other components, including P-selectin, interleukin (IL)-8, eotaxin-3, endothelin-1, and angiopoietin-2, is present within this subcellular organelle, implicating a role for WPB exocytosis in inflammation, hemostasis, regulation of vascular tone and angiogenesis. Recent studies emphasize that WPBs provide a dynamic storage compartment whose contents can be regulated depending on the presence of inflammatory mediators in the vascular micro-environment. Additionally, release of WPBs is tightly regulated and feedback mechanisms have been identified that prevent excessive release of bioactive components from this subcellular organelle. The ability to regulate both contents and exocytosis of WPBs endows these endothelial cell specific organelles with a remarkable plasticity. This is most likely needed to allow for controlled delivery of bioactive components into the circulation on vascular perturbation.

Bleeding manifestations in males with von Willebrand disease

von Willebrand disease (vWD) is the most common congenital bleeding disorder in the USA, affecting 1-3% of the population. Previously characterizing the bleeding symptoms in females with type 1 vWD, we evaluated 42 males with type 1 vWD, mean age 16 years (1-64), of whom 24 (57%) presented with bleeding symptoms. The most common initial symptom was postoperative bleeding (26%). The most common bleeding symptoms ever were epistaxis (53%), bruising (50%), postoperative bleeding (47%), haematomas (29%) and oral bleeding (29%). Of postoperative bleeding, ear/nose/throat (44%), dental (17%) and circumcision bleeding (22%) occurred at a median 10 years of age, despite a previous bleeding or family history in 89%. Complications included anaemia in five (12%), neurological sequelae after subdural haematoma and tonsillectomy in two (5%), transfusion-associated hepatitis C in two (5%) and degenerative joint disease after traumatic haemarthroses in one (2%). The bleeding time (BT) was prolonged in 83%, and the ristocetin cofactor (vW:RCoF) and factor VIII (FVIII:C) decreased in 64% and 43%, respectively. Haemarthroses and haematoma formation were associated with a longer activated partial thromboplastin time (APTT) (P < 0.05), and anaemia with a lower FVIII:C (P < 0.05). In 81%, a haemostatic response occurred with 1-8 deamino-d-arginine vasopressin (DDAVP), although, in 13%, surgical intervention was also required to achieve haemostasis. Postoperative bleeding could have been avoided in 89%, if a preoperative past bleeding history or family history had been obtained, and, in at least 94%, if a preoperative BT and APTT had also been performed. The failure to avoid postoperative bleeding and related complications in patients with vWD by taking a personal and family bleeding history constitutes a major public health problem.

Cellular mechanisms of the hemostatic effects of desmopressin (DDAVP)

The synthetic analog of vasopressin desmopressin (DDAVP) is widely used for the treatment of patients with von Willebrand disease (VWD), hemophilia A, several platelet disorders, and uremic bleeding. DDAVP induces an increase in plasma levels of von Willebrand factor (VWF), coagulation factor VIII (FVIII), and tissue plasminogen activator (t-PA). It also has a vasodilatory action. In spite of its extensive clinical use, its cellular mechanism of action remains incompletely understood. Its effect on VWF and t-PA as well as its vasodilatory effect are likely explained by a direct action on the endothelium, via activation of endothelial vasopressin V2R receptor and cAMP-mediated signaling. This leads to exocytosis from Weibel Palade bodies where both VWF and t-PA are stored, as well as to nitric oxide (NO) production via activation of endothelial NO synthase. The mechanism of action of DDAVP on FVIII plasma levels remains to be elucidated. The hemostatic effect of DDAVP likely involves additional cellular effects that remain to be discovered.

Plasma concentrations of von Willebrand factor and intracellular adhesion molecule-1 for prediction of outcome after successful cardiopulmonary resuscitation

OBJECTIVE

Ischemia/reoxygenation following cardiopulmonary resuscitation might cause endothelial injury/activation that could contribute to an adverse outcome after cardiopulmonary resuscitation. We studied plasma concentrations of von Willebrand factor (vWF) antigen and soluble intracellular adhesion molecule (sICAM)-1 as markers of a generalized endothelial injury/activation in relation to outcome after cardiopulmonary resuscitation.

DESIGN

Retrospective study on stored plasma samples.

SETTING

Intensive care unit at a university hospital.

PATIENTS

Thirty-five patients who survived >24 hrs after in- or out-of-hospital cardiopulmonary resuscitation and 15 noncritically ill control patients.I NTERVENTIONS: Blood sampling.

MEASUREMENTS AND MAIN RESULTS

Plasma concentrations of vWF antigen and sICAM-1 on day 2 after cardiopulmonary resuscitation were higher in patients than in controls (p < .001 and p = .001, respectively). In-hospital cardiopulmonary resuscitation, cardiopulmonary resuscitation duration > or = 15 mins, severe cardiovascular failure, and renal dysfunction/failure at the time of blood sampling were associated with significant elevations in vWF antigen and sICAM-1 concentrations. Patients with an unfavorable outcome after cardiopulmonary resuscitation (cerebral performance category > or = 3) exhibited higher vWF antigen and sICAM-1 concentrations than patients with good outcome (cerebral performance category 1-2; p < .001 and p = .097, respectively). Renal dysfunction/failure, severe cardiovascular failure, systemic inflammatory response syndrome, and cardiopulmonary resuscitation duration > or = 15 mins were also associated with higher adverse outcome rates. Combination of these four variables into a cardiac arrest risk score (levels 0-4) showed adverse outcome rates of 100, 56, and 0% in patients with arrest scores of 4, 2-3, and 0-1, respectively. A vWF antigen concentration >166% was an independent predictor of outcome after cardiopulmonary resuscitation (p = .002) and was associated with increased adverse outcome rates in patients with cardiac arrest risk scores of 2-3. Furthermore, both vWF antigen concentrations >166% and sICAM-1 concentrations >500 ng/mL had 100% specificity for an adverse outcome in patients after out-of-hospital cardiopulmonary resuscitation but were less predictive in patients after in-hospital cardiopulmonary resuscitation.

CONCLUSIONS

vWF antigen and sICAM-1 might be useful adjunctive variables for early determination of outcome in patients after successful out-of-hospital cardiopulmonary resuscitation.

The molecular biology of von Willebrand disease

von Willebrand disease (VWD) is a common autosomally inherited bleeding disorder associated with mucosal or trauma-related bleeding in affected individuals. VWD results from either a quantitative or qualitative deficiency of von Willebrand factor (VWF)--a glycoprotein with essential roles in primary haemostasis and as a carrier of coagulation factor VIII (FVIII) in the circulation. In recent years the identification of mutations in the VWF gene in patients with VWD has improved our understanding of the structure and function of the VWF protein, and has illustrated the importance of specific regions of VWF for its interaction with other components of the vasculature. The underlying genetic lesions and associated molecular pathology have been identified in many cases of type 2A, type 2B, type 2M, type 2N and type 3 VWD. However in the most common variant, type 1 VWD, the causative molecular defect is unknown in the large majority of cases. In the absence of an understanding of the molecular pathology underlying type 1 VWD, precise diagnosis and classification of this common disorder remains problematic.

Von Willebrand Disease and Pregnancy

A 26-year-old woman (gravida 1) was seen when she was 33½ weeks pregnant. She was healthy except for easy bruising, which had been a problem since childhood. The patient did not have nosebleeds or prolonged bleeding after toothbrushing, flossing, or minor cuts. Menarche had occurred at age 13, with a 28-day cycle. Her heavy menstrual periods usually lasted 7 to 10 days. She underwent tonsillectomy and adenoidectorny at age 7 and bilateral bunionectomy at age 20; hemorrhage did not occur after the operations. The patient did not smoke or abuse drugs or alcohol. She took no medications except for prenatal vitamins. Mild von Willebrand disease (vWD) had recently been diagnosed in her mother. Her father had anemia of unknown cause; his family history included thalassemia, and his father had Hodgkin disease that was diagnosed when he was 30 years old. Her 23-year-old brother was healthy and had no bleeding disorders. The patient appeared well-nourished and was in no distress. Vital signs were stable, and site was afebrile. Heart sounds were normal; lungs were clear. Her abdomen was soft and rumtender. There was no spine tenderness, mucosal bleeding, ocular hemorrhage, or skin bruising. Because of the patient's history of easy bruising and heavy menstrual bleeding and her mother's recently diagnosed vWD, testing for the disorder was ordered. Laboratory results revealed von Willebrand factor (vWF) antigen activity of 75 U/dL, activated partial thromboplastin time (aPTT) of 32 seconds, factor VIII activity of 100%, and bleeding time of 9 minutes. (Normal values are vWF antigen level, 50 to 200 U/dL; aPTT) 20 to 32 seconds; factor VIII activity, 60% to 150%; and bleeding time, 5.5 minutes.) A ristocetin-induced platelet aggregation test did not show aggregation at tow concentrations of ristocetin, and vWF multimers showed a normal distribution. These laboratory data suggested that the patient had type 1 vWD. She was closely monitored during the rest of her pregnancy. At full term, the patient went into labor. About 1 to 2 hours before the delivery, she was given intravenous desmopressin at a dosage of 0.3 μg/kg in 50 mL of saline over 30 minutes. When vaginal bleeding (approximately 150 mL) occurred on postpartum day 3, the patient was given nasal desmopressin and advised to limit her physical activity. No excessive bleeding occurred thereafter.

Vasopressin-induced von Willebrand factor secretion from endothelial cells involves V2 receptors and cAMP

Vasopressin and its analogue 1-deamino-8-D-arginine vasopressin (DDAVP) are known to raise plasma von Willebrand factor (vWF) levels. DDAVP is used as a hemostatic agent for the treatment of von Willebrand's disease. However, its cellular mechanisms of action have not been elucidated. DDAVP, a specific agonist for the vasopressin V2 receptor (V2R), exerts its antidiuretic effect via a rise in cAMP in kidney collecting ducts. We tested the hypothesis that DDAVP induces vWF secretion by binding to V2R and activating cAMP-mediated signaling in endothelial cells. vWF secretion from human umbilical vein endothelial cells (HUVECs) can be mediated by cAMP, but DDAVP is ineffective, presumably due to the absence of V2R. We report that DDAVP stimulates vWF secretion in a cAMP-dependent manner in HUVECs after transfection of the V2R. In addition, vasopressin and DDAVP induce vWF secretion in human lung microvascular endothelial cells (HMVEC-L). These cells (but not HUVECs) express endogenous V2R, as shown by RT-PCR. Vasopressin-induced vWF secretion is mimicked by DDAVP and inhibited by the selective V2R antagonist SR121463B. It is mediated by cAMP, since it is inhibited by the protein kinase A inhibitor Rp-8CPT-cAMPS. These results indicate that vasopressin induces cAMP-mediated vWF secretion by a direct effect on endothelial cells. They also demonstrate functional expression of V2R in endothelial cells, and provide a cellular mechanism for the hemostatic effects of DDAVP.

Regulated von Willebrand factor secretion is associated with agonist-specific patterns of cytoskeletal remodeling in cultured endothelial cells

von Willebrand factor (vWF), an adhesive glycoprotein involved in primary hemostasis, is stored and released from endothelial secretory granules called Weibel-Palade bodies. Regulated secretion occurs in reaction either to [Ca(2+)](i)-raising agents (histamine or thrombin) or to cAMP-raising agents (epinephrine, adenosine, or forskolin). We investigated the pattern of release and the cytoskeletal requirements for secretion in response to these 2 classes of agonists. Secretion induced by [Ca(2+)](i)-raising agents involves peripheral and central granules and is inhibited by colchicine-induced microtubule disruption. It is accompanied by Rho-dependent stress fiber formation and cell retraction. Secretion and remodeling occur in the same individual cells. However, secretion is potentiated by cytochalasin E and C3 toxin, indicating that stress fiber formation antagonizes vWF secretion. In contrast, vWF secretion induced by cAMP-raising agents involves the release of only peripheral granules (implying less vWF release on a per cell basis) and is not inhibited by microtubule disruption. cAMP-mediated secretion is accompanied by disruption of stress fibers, strengthening of the cortical actin rim, and preservation of cell-cell contacts. It is unaffected by cytochalasins or C3 toxin. In contrast to [Ca(2+)](i)-raising agents, cAMP-raising agents induce secretion without cell retraction/intercellular gap formation. Thus, they are likely to play a physiological role in the regulation of endothelial vWF secretion and, therefore, of plasma vWF levels.

von Willebrand disease and bleeding in women

Menorrhagia is a common health problem in women, particularly those with bleeding disorders. Little is known about the course of menorrhagia or other bleeding symptoms in women with the most common congenital bleeding disorder, von Willebrand disease (vWD). We determined the prevalence of menorrhagia, bleeding symptoms and coagulation abnormalities associated with vWD, including factor VIII activity, von Willebrand factor (vWF) antigen, ristocetin cofactor and bleeding time (BT), on a cohort of 38 females with type 1 vWD referred for diagnosis and medical care. Menorrhagia was the most common bleeding symptom in females with vWD, occurring in 93.1% of adult women. Menorrhagia was also the most common initial bleeding symptom, occurring in 53.1% of adult women in all of whom it began at menarche, median 14 years of age. There was a delay from initial bleeding symptoms, at median age 12 years, to diagnosis, at median age 16 years, P=0.0049. Although 94% undergoing surgery had previous bleeding, a vWD diagnosis was known preoperatively in only 6.2%, resulting in potentially preventable bleeding. In summary, menorrhagia is the most common bleeding symptom in females with vWD and begins at menarche. Obtaining a personal and family bleeding history promotes early diagnosis, potentially prevents postoperative bleeding, and improves the health of women with vWD.

The molecular basis of von Willebrand disease

von Willebrand disease (VWD) is a clinically heterogeneous bleeding disorder that reflects a wide array of defects. Quantitative subtypes of the disorder, including types 1 and 3 VWD, result in bleeding due to reduced levels of circulating von Willebrand factor (VWF) protein. Qualitative subtypes, defined as type 2 VWD, act through altered VWF function. A range of molecular defects are responsible for many of these subtypes, including missense, nonsense, splicing, insertion, and deletion mutations, resulting in either dominant or recessive inheritance. While many mutations correspond to selected variants, the basis for variation in expression and the imperfect correlations between genotype and phenotype remain to be understood.

Autocrine regulation of endothelial exocytosis: von Willebrand factor release is induced by prostacyclin in cultured endothelial cells

Vascular endothelial cells respond to external stimuli by altering the secretion of several bioactive molecules, including von Willebrand factor (vWf), prostacyclin (PGI2) and nitric oxide (NO). The release of all three molecules is regulated by a rise in cytosolic calcium ([Ca2+]i). In the present study we investigated whether cAMP-dependent signaling provides differential regulation of these effector systems by modulating the effect of [Ca2+]i in cultured human endothelial cells. The stable PGI2 analog iloprost, like other cAMP-raising agents (forskolin and adenosine), caused an acute dose-dependent increase in vWf release and potentiated the secretory response to thrombin. In contrast, iloprost, forskolin and adenosine failed to induce PGI2 release and inhibit thrombin-induced release. Our findings indicate cAMP-raising agents have opposite effects on [Ca2+]i-mediated vWf secretion and PGI2 release. PGI2 may potentiate vWf release and inhibit its own release in an autocrine manner.

von Willebrand disease

Considerable progress has been made in characterizing the specific molecular defects responsible for the heterogeneous disorder known as von Willebrand disease (VWD). A large number of molecular defects have been identified and precise characterization may now be possible in the majority of type 2A, type 2B, type 2N, and potentially also type 3 VWD cases. However, the most common variant, type 1 VWD, still remains a major challenge. Continued progress in this area will improve our understanding of the pathogenesis of VWD and lead to more rapid and precise diagnosis and classification for this common disorder. The problems of incomplete VWD penetrance and poor diagnostic sensitivity and accuracy for the currently available clinical laboratory tests provide strong incentives for the development of DNA-based diagnostics. In addition, prenatal diagnosis is now possible either at the level of single point mutations (for some subtypes) or by RFLP analysis (assuming linkage to the von Willebrand factor [VWF] gene) and will probably be applied with increasing frequency for VWD type 3 (17, 133, 175). Understanding the molecular basis of VWD also has important implications for VWF structure and function and is helping to define critical binding domains within the VWF molecule. Insights gained from these studies may eventually lead to improved therapeutic approaches not only for VWD, but also for a variety of other genetic and acquired hemorrhagic and thrombotic disorders.

A novel modifier gene for plasma von Willebrand factor level maps to distal mouse chromosome 11

Type 1 von Willebrand disease (VWD), characterized by reduced levels of plasma von Willebrand factor (VWF), is the most common inherited bleeding disorder in humans. Penetrance of VWD is incomplete, and expression of the bleeding phenotype is highly variable. In addition, plasma VWF levels vary widely among normal individuals. To identify genes that influence VWF level, we analyzed a genetic cross between RIIIS/J and CASA/Rk, two strains of mice that exhibit a 20-fold difference in plasma VWF level. DNA samples from F2 progeny demonstrating either extremely high or extremely low plasma VWF levels were pooled and genotyped for 41 markers spanning the autosomal genome. A novel locus accounting for 63% of the total variance in VWF level was mapped to distal mouse chromosome 11, which is distinct from the murine Vwf locus on chromosome 6. We designated this locus Mvwf for "modifier of VWF." Additional genotyping of as many as 2407 meioses established a high resolution genetic map with gene order Cola1-Itg3a-Ngfr-Mvwf/Gip-Hoxb9-Hoxb1++ +-Cbx'rs2-Cox5a-Gfap. The Mvwf candidate interval between Ngfr and Hoxb9 is approximately 0.5 centimorgan (cM). These results demonstrate that a single dominant gene accounts for the low VWF phenotype of RIIIS/J mice in crosses with several other strains. The pattern of inheritance suggests a gain-of-function mutation in a unique component of VWF biosynthesis or processing. Characterization of the human homologue for Mvwf may have relevance for a subset of type 1 VWD cases and may define an important genetic factor modifying penetrance and expression of mutations at the VWF locus.

Diagnosis and management of von Willebrand's syndrome

von Willebrand's disease is the most common of the inherited bleeding disorders. It is caused by quantitative and/or qualitative abnormalities of von Willebrand factor, and it usually presents with bleeding from mucosal surfaces. The diagnosis is confirmed by measuring von Willebrand factor activity and antigen levels, factor VIII activity, and performing a multimer analysis of von Willebrand factor. Treatment may require plasma-derived concentrates, but can often be accomplished with DDAVP, a vasopressin analogue that causes transient release of von Willebrand factor from body storage sites.

Effect of exercise, DDAVP, and epinephrine on the factor VIII:C/von Willebrand factor complex in normal dogs and von Willebrand factor deficient Doberman pinscher dogs

Endothelial cells in biopsied blood vessels from von Willebrand factor (vWf)-deficient Doberman pinscher dogs contain immunologically detectable vWf. These dogs and normal dogs were treated with DDAVP (0.6 microgram/kg) and epinephrine (0.5 microgram/kg/min for 30 minutes) and were exercised, using 5 different exercise protocols, (3-4 m/s for 5-40 minutes at 0-5% grade) to determine if treatments reported to increase plasma factor VIII:C/vWf complex in humans would elevate canine plasma vWf. Following the two most strenuous exercise conditions--30 and 40 minutes--plasma von Willebrand factor antigen (vWf:Ag) increased in normal dogs by 30% and 70%, respectively. Factor VIII:C was increased 47% by the most strenuous exercise conditions. The vWf-deficient dogs would not exercise beyond 30 minutes and neither vWf:Ag nor factor VIII:C activity increased. Following DDAVP, plasma vWf:Ag increased in the normal dogs by 47% and factor VIII:C activity was increased by 48%. Factor VIII:C activity increased by 30% in the vWf-deficient dogs, but there was only a slight change in vWf:Ag. Bleeding time decreased in 5 of 6 vWf-deficient dogs. In the normal dogs vWf:Ag increased by 14% after epinephrine infusion, but factor VIII:C activity did not change; neither parameter was altered in the vWf-deficient dogs. While the factor VIII:C/vWf:Ag complex was increased in the normal dog by exercise and DDAVP, the increase is not as pronounced as has been reported for humans. It is not known whether the poor response of the vWf-deficient dog is due to low levels of vWf in their endothelium or to a release defect.

Effects of growth hormone on the factor VIII complex in patients with growth hormone deficiency

Factor VIII activity (VIII C), factor VIII coagulant antigen (VIII C:Ag), factor VIII-related antigen (VIII R:Ag), Ristocetin cofactor (R:Cof), and growth hormone were studied in eight children with growth hormone deficiency prior to, and 60, 120, and 180 minutes after administration of human growth hormone (Crescormone, Kabi), 4 U/m2. Growth hormone has been administered for 1.0 to 6.8 years but was stopped one week prior to this investigation. Basal levels of VIII C, VIII C:Ag, VIII R:Ag, and R:Cof were within the normal limits. After administration of human growth hormone, VIII C, VIII C:Ag, VIII R:Ag, and R:Cof showed a significant rise. Our study shows that growth hormone is not necessary to maintain the basal levels of the factor VIII complex within the normal limits. However, out data suggest that growth hormone has some influences on the levels of the factor VIII complex. The mechanisms for the rise of the factor VIII complex--whether this is a direct effect of growth hormone or not--are not clear at this point.

Changes in coagulation parameters with exercise in patients with classic hemophilia

Vigorous exercise is known to increase VIII:C and VIIIR:Ag levels transiently in normal individuals. Although exercise programs are frequently advocated in the management of hemophilia, the effects of exercise on coagulation parameters in these patients have not been well studied. Eleven hemophiliacs were exercised on a bicycle ergometer to maximum voluntary effort as evidenced by an increase in pulse, blood pressure, and plasma catecholamine (norepinephrine and epinephrine) levels. The effects of this exercise on coagulation parameters, including functional and antigenic components of the factor VIII molecule, were determined. The entire group demonstrated a decrease in mean prothrombin time (11.7 to 11.2 sec). Four mild hemophiliacs demonstrated an increase in mean VIII:C (14.5% to 17.3%), and VIII:CAg (12% to 17.8%). Changes in VIII:C and VIII:CAg were not noted in the seven severe hemophiliacs. Both severe and mild patients demonstrated significant changes in fibrinogen, factor II, and factor VII after exercise. This study indicates that submaximal exercise modifies coagulation parameters in patients with hemophilia.

Platelet-vessel-wall interactions: experiences with von Willebrand platelets

Adhesion of platelets from 15 patients with von Willebrand's disease was tested in an ex vivo human umbilical vein model. Experiments employed umbilical veins still in their umbilical cords taken from patients undergoing cesarean section and platelets (fetal, adult and vW) either apyrase-washed or used as platelet-rich plasma or whole blood. F VIII R:Ag, F VIII:Rcof, and F VIII:C were measured in initial fresh plasma and in effluents from the umbilical vein segments. F VIII:Rcof increased in most perfusates. Binding of latex-linked specific antihuman F VIII R:Ag demonstrated that F VIII R:Ag existed on subendothelium and on injured endothelial cells. Scanning electron microscopy three-dimensionally displayed vW platelet--vessel-wall interactions. Although vW platelets adhered to injured vein, both qualitative and quantitative differences existed in comparison with adhesion of normal platelets. The differences correlated best with the plasma F VIII:Rcof level. The best adhesion shown by vW platelets was only 51 percent of the adhesion of control fetal or adult platelets. vW platelets had less surface activity, fewer pseudopods, and little ability to spread and pave the exposed subendothelium. Pretreatment of the vein with F VIII R:Ag antibody partly blocked adhesion. Coperfusion of cryoprecipitate with vW platelets improved their adhesivity, state of activation on subendothelium, and ability to form aggregates. ABO differences in blood cell types of fetal material and platelet donors seemed without effect, which further establishes this model's validity for studies of platelet dysfunction and platelet or endothelial reactive agents.

Factor VII and fibrinolytic response to deamino-8-D-argenine vasopressin in normal subjects and dissociate response in some patients with haemophilia and von Willebrand's disease

Deamino-8-D-argenine vasopressin (DDAVP) was given by intravenous infusion to normal subjects, haemophiliacs and patients with von Willebrand's disease (vWd) and the factor VIII and plasminogen activator response was studied. In normal subjects and most patients with mild haemophilia and mild (intermediate) von Willebrand's disease there was an increase in plasminogen activator and all factor VIII related activities. In patients with mild vWd the prolonged bleeding time was shortened by DDAVP despite only a modest rise in factor VIII related Ristocetin cofactor activity (VIIIR:RiCoF). Sub-groups of patients have been characterized in whom atypical responses was observed. In two brothers with clinically severe haemophilia, but with 5--6 u/dl procoagulant factor VIII (VIIIC), there was an increase in VIIIC but no rise of the corresponding antigen, suggesting increased release of an antigenically abnormal poorly functioning molecule. A patient with intermediate vWd was studied in whom neither DDAVP, adrenaline infusion, nor venous occlusion resulted in an increase in either plasminogen activator or factor VIII related antigen (VIIRAg), although there was a significant increase in VIIIC. In a further patient with severe vWd, DDAVP failed to elicit any plasminogen activator or VIII response. The results obtained from these two patients suggested that in some individuals the presumed endothelial cell abnormality in vWd may be more extensive than a defect in VIIIRAg synthesis. Sub-groups of patients have been identified for whom treatment with factor VIII concentrates would be more appropriate than DDAVP prior to minor surgery.

Specificity in the factor VIII response to vasopressin infusion in man

Structural requirements of the systemic factor VIII response to intravenous vasopressin in man has been investigated using vasopressin analogues. With the analogues available the receptor specificity of this phenomenon could not be distinguished from those associated with the previously described plasminogen activator release or antidiuretic effects of this hormone. Further studies using 1-desamino-[8-D-arginine]vasopressin showed a dose-related release of both procoagulant and antigenic components of the factor VIII complex. The newly released factor VIII could not be distinguished from circulating factor VIII on the basis of molecular size, electrophoretic mobility or in vitro stability despite apparent differences in the duration of response of the procoagulant and antigenic components in vivo.

The properties of immune complexes formed by human antibodies to factor VIII

Although human antibodies to Factor VIII inactivate its procoagulant activity, they do not form immunoprecipitates when tested with this antigen. To understand this observation, we have examined the interaction of normal human Factor VIII with four high-titer human anti-Factor VIII, two from transfused hemophiliacs and two "spontaneous" antibodies from nonhemophilic individuals. An estimate of the size of complexes formed by these antibodies has been obtained by agarose gel filtration of mixtures of anti-Factor VIII with cryoprecipitate. Complexed anti-Factor VIII was detected by the method of Allain and Frommel: acid dissociation of complexes at pH 3.5. Complexed anti-Factor VIII was detected in column fractions eluting between the void volume and those which correspond to the elution volume of human IgG. In contrast, Factor VIII procoagulant activity was restricted to void volume fractions when separations were carried out in antigen excess, and free anti-Factor VIII was limited to late-eluting fractions when separations were carried out in antibody excess. A small proportion of the complexed anti-Factor VIII was present in void volume fractions; the quantity was directly related to the ratio of antibody to antigen.Thus, although some complexed anti-Factor VIII is detected in void volume fractions, as would be expected for complexes formed with a very large plasma protein, most immune complexes elute in fractions that indicate interaction with a smaller antigen. These findings suggest that human anti-Factor VIII inactivates procoagulant activity by forming a complex with a small, apparently univalent, component of Factor VIII. This property may prevent immunoprecipitate formation.

Stabilization of factor VIII in plasma by the von Willebrand factor. Studies on posttransfusion and dissociated factor VIII and in patients with von Willebrand's disease

In normal plasma, the ratio of the procoagulant activity of factor VIII (VIII(AHF)) to that of the von Willebrand factor activity (ristocetin cofactor, VIII(VWF)) or factor VIII antigen (VIII(AGN)) is approximately 1, but ratios > 1 (e.g., VIII(AHF) > VIII(VWF) or VIII(AGN)) may be observed in some patients with von Willebrand's disease and in the "late" posttransfusion plasmas of patients with this disorder. The lability of VIII(AHF) was studied by incubating plasma, diluted 1:10 in imidazole buffer pH 7.1, for 6 h at 37 degrees C. With normal plasmas, 77+/-12% (SD) of the original VIII(AHF) activity remained after incubation. VIII(AHF) was labile (e.g., 35-55% residual activity) in the "late" posttransfusion plasmas (VIII(AHF) >> VIII(VWF)) of a patient with von Willebrand's disease, but not in the "early" posttransfusion plasmas (VIII(AHF) approximately VIII(VWF)). VIII(AHF) was also labile in the (base-line) plasmas of three patients with von Willebrand's disease in whom the ratios of VIII(AHF) to VIII(VWF) were 4.4 to 8.1, but not in the plasmas of four other patients in whom the ratio was approximately 1. The electrophoretic mobility of factor VIII antigen was increased in two of the three patients with labile VIII(AHF). In both of these patients, and in the late posttransfusion plasmas, labile VIII(AHF) activity could be stabilized by the addition of purified von Willebrand factor (lacking VIII(AHF) activity) or by hemophilic plasma, but not by plasmas of patients with severe von Willebrand's disease. Thus, VIII(VWF) may serve to stabilize VIII(AHF) and this might explain the posttransfusion findings in von Willebrand's disease.

Absence of VIII AHF response to adrenalin in hemophilia A

Proportionate twofold or greater increases in both Factor VIII procoagulant activity (VIII AHF) and Factor VIII-like antigen (VIII AGN) have been observed to follow the administration of adrenalin in normal individuals. Levels of factor VIII procoagulant or clot-promoting activity (VIII AHF) and VIII AGN were measured immediately before and one hour after the subcutaneous injection of adrenalin (0.35 ml) in ten adults with hemophilia A documented by low VIII AHF levels (ranging from 0.01-0.25 units/ml, normal VIII AGN levels, and normal VIII VWF levels as measured by the washed-platelet ristocetin assay). Eighteen normal adults served as controls. Results were analyzed by the paired test. It was shown that VIII AGN increased significantly, while VIII AHF did not change, in hemophiliacs after adrenalin stimulation, regardless of the base line level. This fixed rate of VII AHF production, release, or activation may help to explain the constancy of VII AHF levels in individual hemophiliacs and their affected family members.