In vivo regulation of von willebrand factor synthesis: von Willebrand factor production in endothelial cells after lung transplantation between normal pigs and von Willebrand factor-deficient pigs

Recombinant von Willebrand factor and tranexamic acid for heavy menstrual bleeding in patients with mild and moderate von Willebrand disease in the USA (VWDMin): a phase 3, open-label, randomised, crossover trial

BACKGROUND

Heavy menstrual bleeding occurs in 80% of women with von Willebrand disease and is associated with iron deficiency and poor response to current therapies. International guidelines indicate low certainty regarding effectiveness of hormonal therapy and tranexamic acid. Although von Willebrand factor (VWF) concentrate is approved for bleeds, no prospective trials guide its use in heavy menstrual bleeding. We aimed to compare recombinant VWF with tranexamic acid for reducing heavy menstrual bleeding in patients with von Willebrand disease.

METHODS

VWDMin, a phase 3, open-label, randomised crossover trial, was done in 13 haemophilia treatment centres in the USA. Female patients aged 13-45 years with mild or moderate von Willebrand disease, defined as VWF ristocetin cofactor less than 0·50 IU/mL, and heavy menstrual bleeding, defined as a pictorial blood assessment chart (PBAC) score more than 100 in one of the past two cycles were eligible for enrolment. Participants were randomly assigned (1:1) to two consecutive cycles each of intravenous recombinant VWF, 40 IU/kg over 5-10 min on day 1, and oral tranexamic acid 1300 mg three times daily on days 1-5, the order determined by randomisation. The primary outcome was a 40-point reduction in PBAC score by day 5 after two cycles of treatment. Efficacy and safety were analysed in all patients with any post-baseline PBAC scores. The trial was stopped early due to slow recruitment on Feb 15, 2022, by a data safety monitoring board request, and was registered at ClinicalTrials.gov, NCT02606045.

FINDINGS

Between Feb 12, 2019, and Nov 16, 2021, 39 patients were enrolled, 36 of whom completed the trial (17 received recombinant VWF then tranexamic acid and 19 received tranexamic acid then recombinant VWF). At the time of this unplanned interim analysis (data cutoff Jan 27, 2022), median follow-up was 23·97 weeks (IQR 21·81-28·14). The primary endpoint was not met, neither treatment corrected PBAC score to the normal range. Median PBAC score was significantly lower after two cycles with tranexamic acid than with recombinant VWF (146 [95% CI 117-199] vs 213 [152-298]; adjusted mean treatment difference 46 [95% CI 2-90]; p=0·039). There were no serious adverse events or treatment-related deaths and no grade 3-4 adverse events. The most common grade 1-2 adverse events were mucosal bleeding (four [6%] patients during tranexamic acid treatment vs zero during recombinant VWF treatment) and other bleeding (four [6%] vs two [3%]).

INTERPRETATION

These interim data suggest that recombinant VWF is not superior to tranexamic acid in reducing heavy menstrual bleeding in patients with mild or moderate von Willebrand disease. These findings support discussion of treatment options for heavy menstrual bleeding with patients based on their preferences and lived experience.

FUNDING

National Heart Lung Blood Institute (National Institutes of Health).

Quantification of von Willebrand factor and ADAMTS-13 after traumatic injury: a pilot study

BACKGROUND

Von Willebrand factor (VWF) is an acute phase reactant synthesized in the megakaryocytes and endothelial cells. VWF forms ultra-large multimers (ULVWF) which are cleaved by the metalloprotease ADAMTS-13, preventing spontaneous VWF-platelet interaction. After trauma, ULVWF is released into circulation as part of the acute phase reaction. We hypothesized that trauma patients would have increased levels of VWF and decreased levels of ADAMTS-13 and that these patients would have accelerated thrombin generation.

METHODS

We assessed plasma concentrations of VWF antigen and ADAMTS-13 antigen, the Rapid Enzyme Assays for Autoimmune Diseases (REAADS) activity of VWF, which measure exposure of the platelet-binding A1 domain, and thrombin generation kinetics in 50 samples from 30 trauma patients and an additional 21 samples from volunteers. Samples were analyzed at 0 to 2 hours and at 6 hours from the time of injury. Data are presented as median (IQR) and Kruskal-Wallis test was performed between trauma patients and volunteers at both time points.

RESULTS

REAADS activity was greater in trauma patients than volunteers both at 0 to 2 hours (190.0 (132.0-264.0) vs. 92.0 (71.0-114.0), p<0.002) and at 6 hours (167.5 (108.0-312.5.0) vs. 92.0 (71.0-114.0), p<0.001). ADAMTS-13 antigen levels were also decreased in trauma patients both at 0 to 2 hours (0.84 (0.51-0.94) vs. 1.00 (0.89-1.09), p=0.010) and at 6 hours (0.653 (0.531-0.821) vs. 1.00 (0.89-1.09), p<0.001). Trauma patients had accelerated thrombin generation kinetics, with greater peak height and shorter time to peak than healthy volunteers at both time points.

DISCUSSION

Trauma patients have increased exposure of the VWF A1 domain and decreased levels of ADAMTS-13 compared with healthy volunteers. This suggests that the VWF burst after trauma may exceed the proteolytic capacity of ADAMTS-13, allowing circulating ULVWF multimers to bind platelets, potentially contributing to trauma-induced coagulopathy.

LEVEL OF EVIDENCE

Prospective case cohort study.

Conformation-dependent blockage of activated VWF improves outcomes of traumatic brain injury in mice

Traumatic brain injury-induced coagulopathy (TBI-IC) causes life-threatening secondary intracranial bleeding. Its pathogenesis differs mechanistically from that of coagulopathy arising from extracranial injuries and hemorrhagic shock, but it remains poorly understood. We report results of a study designed to test the hypothesis that von Willebrand factor (VWF) released during acute TBI is intrinsically hyperadhesive because its platelet-binding A1-domain is exposed and contributes to TBI-induced vascular leakage and consumptive coagulopathy. This hyperadhesive VWF can be selectively blocked by a VWF A2-domain protein to prevent TBI-IC and to improve neurological function with a minimal risk of bleeding. We demonstrated that A2 given through intraperitoneal injection or IV infusion reduced TBI-induced death by >50% and significantly improved the neurological function of C57BL/6J male mice subjected to severe lateral fluid percussion injury. A2 protected the endothelium from extracellular vesicle-induced injury, reducing TBI-induced platelet activation and microvesiculation, and preventing a TBI-induced hypercoagulable state. A2 achieved this therapeutic efficacy by specifically blocking the A1 domain exposed on the hyperadhesive VWF released during acute TBI. These results suggest that VWF plays a causal role in the development of TBI-IC and is a therapeutic target for this life-threatening complication of TBI.

A 12.3-kb Duplication Within the VWF Gene in Pigs Affected by Von Willebrand Disease Type 3

Von Willebrand Disease (VWD) type 3 is a serious and sometimes fatal hereditary bleeding disorder. In pigs, the disease has been known for decades, and affected animals are used as models for the human disease. Due to the recessive mode of inheritance of VWD type 3, severe bleeding is typically seen in homozygous individuals. We sequenced the complete porcine VWF (Von Willebrand Factor) complementary DNA (cDNA) and detected a tandem duplication of exons 17 and 18, causing a frameshift and a premature termination codon (p.Val814LeufsTer3) in the affected pig. Subsequent next generation sequencing on genomic DNA proved the existence of a 12.3-kb tandem duplication associated with VWD. This duplication putatively originates from porcine Short Interspersed Nuclear Elements (SINEs) located within VWF introns 16 and 18 with high identity. The premature termination truncates the VWF open reading frame by a large part, resulting in an almost entire loss of the mature peptide. It is therefore supposed to account for the severe VWD type 3. Our results further indicate the presence of strong, nonsense-mediated decay in VWF messenger RNA (mRNA) containing the duplication, which was supported by the almost complete absence of the complete VWF protein in immunohistochemistry analysis of the VWD-affected pig. In the past, differentiation of wild-type and heterozygous pigs in this VWD colony had to rely on clinical examinations and additional laboratory methods. The present study provides the basis to distinguish both genotypes by performing a rapid and simple genetic analysis.

Pig Liver Xenotransplantation: A Review of Progress Toward the Clinic

Experience with clinical liver xenotransplantation has largely involved the transplantation of livers from nonhuman primates. Experience with pig livers has been scarce. This brief review will be restricted to assessing the potential therapeutic impact of pig liver xenotransplantation in acute liver failure and the remaining barriers that currently do not justify clinical trials. A relatively new surgical technique of heterotopic pig liver xenotransplantation is described that might play a role in bridging a patient with acute liver failure until either the native liver recovers or a suitable liver allograft is obtained. Other topics discussed include the possible mechanisms for the development of the thrombocytopenis that rapidly occurs after pig liver xenotransplantation in a primate, the impact of pig complement on graft injury, the potential infectious risks, and potential physiologic incompatibilities between pig and human. There is cautious optimism that all of these problems can be overcome by judicious genetic manipulation of the pig. If liver graft survival could be achieved in the absence of thrombocytopenia or rejection for a period of even a few days, there may be a role for pig liver transplantation as a bridge to allotransplantation in carefully selected patients.

Acquired von Willebrand syndrome associated with left ventricular assist device. Blood. 2016;127:3133-3141. [PMID: 27143258 DOI: 10.1182/blood-2015-10-636480]

Left ventricular assist devices (LVAD) provide cardiac support for patients with end-stage heart disease as either bridge or destination therapy, and have significantly improved the survival of these patients. Whereas earlier models were designed to mimic the human heart by producing a pulsatile flow in parallel with the patient's heart, newer devices, which are smaller and more durable, provide continuous blood flow along an axial path using an internal rotor in the blood. However, device-related hemostatic complications remain common and have negatively affected patients' recovery and quality of life. In most patients, the von Willebrand factor (VWF) rapidly loses large multimers and binds poorly to platelets and subendothelial collagen upon LVAD implantation, leading to the term acquired von Willebrand syndrome (AVWS). These changes in VWF structure and adhesive activity recover quickly upon LVAD explantation and are not observed in patients with heart transplant. The VWF defects are believed to be caused by excessive cleavage of large VWF multimers by the metalloprotease ADAMTS-13 in an LVAD-driven circulation. However, evidence that this mechanism could be the primary cause for the loss of large VWF multimers and LVAD-associated bleeding remains circumstantial. This review discusses changes in VWF reactivity found in patients on LVAD support. It specifically focuses on impacts of LVAD-related mechanical stress on VWF structural stability and adhesive reactivity in exploring multiple causes of AVWS and LVAD-associated hemostatic complications.

Von Willebrand Factor Deficiency Corrected by Lung Transplantation

BACKGROUND

In experimental models with von Willebrand disease pigs, plasma von Willebrand factor (vWF) was significantly increased after lung transplantation because lung endothelial cells strongly express vWF. However, these findings have not been confirmed in human beings.

METHODS

A 26-year-old man with mild vWF deficiency (FvW:antigen 39 IU/dL; FvW:ristocetin cofactor activity 44 IU/dL; factor VIII 99%; normal multimeric plasma vWF pattern) was referred to our institution and underwent bilateral lung transplantation for cystic fibrosis. The patient received factor VIII/vWF concentrate both during and after surgery without any relevant bleeding events. At hospital discharge, he was taking immunosuppression with oral tacrolimus, prednisone, and mycophenolate mofetil, which has continued until the present day (22 months after the procedure).

RESULTS

Plasma vWF level increased during the postoperative days, presumably due to endothelial injuries and the infusion of vWF concentrate. Laboratory tests at 5, 11, 14, and 22 months after lung transplantation demonstrated sustained normalization of all parameters.

CONCLUSIONS

To our knowledge, this is the first reported case of von Willebrand deficiency corrected through lung transplantation.

Coagulopathy associated with traumatic brain injury

Coagulopathy is often observed after traumatic brain injury (TBI), but the pathogenic mechanisms of this phenomenon remain elusive. Brain injury is the leading cause of trauma deaths, and the development of coagulopathy after TBI is associated with increased morbidity and mortality in these patients. The coagulopathy after TBI comprises a hypocoagulable and a hypercoagulable state with hemorrhagic and thrombotic phenotypes that are both associated with worse outcome. Some theories of its pathogenesis include massive release of tissue factor, altered protein C homeostasis, microparticle upregulation, and platelet hyperactivity. This article aims to examine the coagulopathy associated with blunt head injury, to review its effect on progression of hemorrhagic injury, and to discuss the possible relevant pathophysiological mechanisms.

Phase II prospective open-label trial of recombinant interleukin-11 in desmopressin-unresponsive von Willebrand disease and mild or moderate haemophilia A

Desmopressin (DDAVP) is the treatment of choice in those with mild von Willebrand disease (VWD), yet 20% are unresponsive to DDAVP, and among the 80% who respond, the response is transient, as endothelial stores are depleted after three days. We, therefore, conducted a single-center Phase II clinical trial to determine safety and biologic efficacy of recombinant interleukin-11 (rhIL-11, Neumega®) in patients with VWD unresponsive or allergic to DDAVP, or mild or moderate haemophilia A (HA). Increases in VWF:RCo wer e observed by 48 hours after rhIL-11, with a 1.54-fold increase by Day 4, 1.30-fold in VWD and 1.73-fold in HA. Similarly, by 48 hours, increases in VIII:C were observed, with a 1.65-fold increase by Day 4, 1.86-fold in VWD and 1.48-fold in HA. Platelet VWFmRNA expression by qPCR increased 0.81-fold but did not correlate with plasma VWF:Ag responses. rhIL-11 was well tolerated, with grade 1 or less fluid retention, flushing, conjunctival erythema, except for transient grade 3 hyponatraemia in one subject after excess fluid intake for diabetic hyperglycaemia, which resolved with fluid restriction. In summary, rhIL-11 increases VWF levels in two of four DDAVP-unresponsive or allergic VWD and F.VIII levels in four of five mild or moderate haemophilia A subjects, suggesting its potential use in treatment of these disorders.

Traumatic brain injury-associated coagulopathy

Traumatic injury is a common cause of coagulopathy, primarily due to blood loss and hemodilution secondary to fluid resuscitation. Traumatic injury-associated coagulopathy often follows a course of transition from hyper- to hypocoagulable state exemplified in disseminated intravascular coagulation. The incidence of coagulopathy is significantly higher in patients with traumatic brain injury (TBI), especially those with penetrating trauma compared to injury to the trunk and limbs. This occurs despite the fact that patients with isolated TBI bleed less and receive restricted volume load of fluids. TBI-associated coagulopathy is extensively documented to associate with poor clinical outcomes, but its pathophysiology remains poorly understood. Studies in the past have shown that brain tissue is highly enriched in key procoagulant molecules. This review focuses on the biochemical and cellular characteristics of these molecules and pathways that could make brain uniquely procoagulant and prone to coagulopathy. Understanding this unique procoagulant environment will help to identify new therapeutic targets that could reverse a state of coagulopathy with minimal impacts on hemostasis, a critical requirement for neurosurgical treatments of TBI.

Phase II prospective open-label trial of recombinant interleukin-11 in women with mild von Willebrand disease and refractory menorrhagia

Lack of effective treatment for menorrhagia is the greatest unmet healthcare need in women with von Willebrand disease (VWD). We conducted a single-centre phase II clinical trial to determine efficacy and safety of recombinant IL-11 (rhIL-11, Neumega®) given subcutaneously for up to seven days during six consecutive menstrual cycles each in seven women with mild VWD and menorrhagia refractory to haemostatic or hormonal agents. rhIL-11 reduced menstrual bleeding severity as measured by pictorial blood assessment chart (PBAC) ≥ 50% (to <100) in 71% of subjects, cycle severity ≥ 50% in 71%, and bleeding duration ≥ 2 days in 85%, all p ≤ 0.01. After rhIL-11, plasma VWF:RCo increased 1.1-fold, but did not correlate with PBAC, r=0.116, bleeding duration, r=0.318, or cycle severity, r=-0.295, or hsCRP, r=-0.003, all p>0.05. Platelet VWF mRNA expression by quantitative PCR increased mean four-fold (1.0-13.5). rhIL-11 was well tolerated with grade 1 or less fluid retention, flushing, conjunctival erythema, and local bruising. In summary, rhIL-11 reduces menorrhagia safely and warrants further study.

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.

Genetic determinants of plasma von Willebrand factor antigen levels: a target gene SNP and haplotype analysis of ARIC cohort

von Willebrand factor (VWF) is an essential component of hemostasis and has been implicated in thrombosis. Multimer size and the amount of circulating VWF are known to impact hemostatic function. We associated 78 VWF single nucleotide polymorphisms (SNPs) and haplotypes constructed from those SNPs with VWF antigen level in 7856 subjects of European descent. Among the nongenomic factors, age and body mass index contributed 4.8% and 1.6% of VWF variation, respectively. The SNP rs514659 (tags O blood type) contributed 15.4% of the variance. Among the VWF SNPs, we identified 18 SNPs that are associated with levels of VWF. The correlative SNPs are either intronic (89%) or silent exonic (11%). Although SNPs examined are distributed throughout the entire VWF gene without apparent cluster, all the positive SNPs are located in a 50-kb region. Exons in this region encode for VWF D2, D', and D3 domains that are known to regulate VWF multimerization and storage. Mutations in the D3 domain are also associated with von Willebrand disease. Fifteen of these 18 correlative SNPs are in 2 distinct haplotype blocks. In summary, we identified a cluster of intronic VWF SNPs that associate with plasma levels of VWF, individually or additively, in a large cohort of healthy subjects.

Porcine and canine von Willebrand factor and von Willebrand disease: hemostasis, thrombosis, and atherosclerosis studies

Use of animal models of inherited and induced von Willebrand factor (VWF) deficiency continues to advance the knowledge of VWF-related diseases: von Willebrand disease (VWD), thrombotic thrombocytopenic purpura (TTP), and coronary artery thrombosis. First, in humans, pigs, and dogs, VWF is essential for normal hemostasis; without VWF bleeding events are severe and can be fatal. Second, the ADAMTS13 cleavage site is preserved in all three species suggesting all use this mechanism for normal VWF multimer processing and that all are susceptible to TTP when ADAMTS13 function is reduced. Third, while the role of VWF in atherogenesis is debated, arterial thrombosis complicating atherosclerosis appears to be VWF-dependent. The differences in the VWF gene and protein between humans, pigs, and dogs are relatively few but important to consider in the design of VWF-focused experiments. These homologies and differences are reviewed in detail and their implications for research projects are discussed. The current status of porcine and canine VWD are also reviewed as well as their potential role in future studies of VWF-related disorders of hemostasis and thrombosis.

Disulfide bond reduction of von Willebrand factor by ADAMTS-13

BACKGROUND

von Willebrand factor (VWF) released from endothelial cells is rich in ultra-large (UL) multimers that are intrinsically active in binding platelets, whereas plasma-type VWF multimers require shear stress to be activated. This functional difference may be attributed to thiols exposed on the surface of plasma-type VWF multimers, but not on ULVWF multimers. Shear stress induces the exposed thiols to form disulfide bonds between laterally apposed plasma-type VWF multimers, leading to enhanced VWF binding to platelets.

OBJECTIVES

We tested a hypothesis that ADAMTS-13 has a disulfide bond reducing activity that regulates shear-induced thiol-disulfide exchange of VWF.

METHODS

Thiol blocking agents and active thiol bead capturing were used to identify and locate this activity, along with truncated ADAMTS-13 mutants.

RESULTS

ADAMTS-13 contains a disulfide bond reducing activity that primarily targets disulfide bonds in plasma-type VWF multimers induced by high shear stress or formed with thiol beads, but not disulfide bonds in native multimeric structures. Cysteine thiols targeted by this activity are in the VWF C-domain and are known to participate in shear-induced thiol-disulfide exchange. ADAMTS-13 contains cysteine thiols that remain exposed after being subjected to hydrodynamic forces. Blocking these active thiols eliminates this reducing activity and moderately decreases ADAMTS-13 activity in cleaving ULVWF strings anchored to endothelial cells under flow conditions, but not under static conditions. This activity is located in this C-terminal region of ADAMTS-13.

CONCLUSIONS

This novel disulfide-bond-reducing activity of ADAMTS-13 may prevent covalent lateral association and increased platelet adherence of plasma-type VWF multimers induced by high fluid shear stress.

A phase II prospective open-label escalating dose trial of recombinant interleukin-11 in mild von Willebrand disease

von Willebrand factor (VWF) is a multimeric glycoprotein that mediates platelet adhesion and is decreased in von Willebrand disease (VWD). 1-8 deamino-d-arginine vasopressin (DDAVP), the most common treatment for VWD, is limited by tachyphylaxis and inconvenience, and in 20% of the patients, unresponsiveness. Recombinant human interleukin-11 (rhIL-11), a gp-130 signalling cytokine with haematopoietic and anti-inflammatory activity, increases VWF antigen and its activity in heterozygous VWF(+/-) mice and dogs. To determine the biological efficacy and safety of rhIL-11 in non-bleeding human subjects with mild VWD, we conducted a phase II prospective open-label trial of rhIL-11 at 10, 25 and 50 mug kg(-1) subcutaneously (s.c.), given daily for 7 days in nine subjects with mild VWD. VWF and factor VIII (FVIII) levels increased gradually and progressively after s.c. rhIL-11, which was sustained through 7 days of dosing to 1.5- to 3-fold over baseline. Following intravenous DDAVP, 0.3 mug kg(-1), on day 7 there was a further boost in VWF and FVIII levels, suggesting that the mechanism of rhIL-11 differs from that of DDAVP. Platelet VWF mRNA expression measured by quantitative PCR increased from two- to eightfold over baseline, suggesting that the mechanism of rhIL-11 effect may be upregulation of VWF mRNA. VWF and FVIII levels returned to baseline by day 14. rhIL-11 was well tolerated with less than grade-1 hypertension, hypokalaemia and fluid retention. Recombinant IL-11 increases VWF levels in humans with mild VWD, justifying future clinical trials to determine its potential in preventing or reducing bleeding in this patient population.

Covalent regulation of ULVWF string formation and elongation on endothelial cells under flow conditions

BACKGROUND AND OBJECTIVES

The adhesion ligand von Willebrand factor (VWF) is a multimeric glycoprotein that mediates platelet adhesion to exposed subendothelium. On endothelial cells, freshly released ultra-large (UL) VWF multimers form long string-like structures to which platelets adhere.

METHODS

The formation and elongation of ULVWF strings were studied in the presence of the thiol-blocking N-ethylmaleimide (NEM). The presence of thiols in ULVWF and plasma VWF multimers was determined by maleimide-PEO(2)-Biotin labeling and thiol-chromatography. Finally, covalent re-multimerization of ULVWF was examined in a cell- and enzyme-free system.

RESULTS

We found that purified plasma VWF multimers adhere to and elongate ULVWF strings under flow conditions. The formation and propagation of ULVWF strings were dose-dependently reduced by blocking thiols on VWF with NEM, indicating that ULVWF strings are formed by the covalent association of perfused VWF to ULVWF anchored to endothelial cells. The association is made possible by the presence of free thiols in VWF multimers and by the ability of (UL) VWF to covalently re-multimerize.

CONCLUSION

The data provide a mechanism by which the thrombogenic ULVWF strings are formed and elongated on endothelial cells. This mechanism suggests that the thiol-disulfide state of ULVWF regulates the adhesion properties of strings on endothelial cells.

Shear-induced disulfide bond formation regulates adhesion activity of von Willebrand factor

von Willebrand factor (VWF) is the largest multimeric adhesion ligand circulating in blood. Its adhesion activity is related to multimer size, with the ultra-large forms freshly released from the activated endothelial cells being most active, capable of spontaneously binding to platelets. In comparison, smaller plasma forms circulating in blood bind platelets only under high fluid shear stress or induced by modulators. The structure-function relationships that distinguish the two types of VWF multimers are not known. In this study, we demonstrate that some of the plasma VWF multimers contain surface-exposed free thiols. Physiological and pathological levels of shear stresses (50 and 100 dynes/cm(2)) promote the formation of disulfide bonds utilizing these free thiols. The shear-induced thiol-disulfide exchange increases VWF binding to platelets. The thiol-disulfide exchange involves some or all of nine cysteine residues (Cys(889), Cys(898), Cys(2448), Cys(2451), Cys(2490), Cys(2491), Cys(2453), Cys(2528), and Cys(2533)) in the D3 and C domains as determined by mass spectrometry of the tryptic VWF peptides. These results suggest that the thiol-disulfide state may serve as an important structural determinant of VWF adhesion activity and can be modified by fluid shear stress.

Lung transplantation: opportunities for research and clinical advancement

Lung transplantation is the only definitive therapy for many forms of end-stage lung diseases. However, the success of lung transplantation is limited by many factors: (1) Too few lungs available for transplantation due to limited donors or injury to the donor lung; (2) current methods of preservation of excised lungs do not allow extended periods of time between procurement and implantation; (3) acute graft failure is more common with lungs than other solid organs, thus contributing to poorer short-term survival after lung transplant compared with that for recipients of other organs; (4) lung transplant recipients are particularly vulnerable to pulmonary infections; and (5) chronic allograft dysfunction, manifest by bronchiolitis obliterans syndrome, is frequent and limits long-term survival. Scientific advances may provide significant improvements in the outcome of lung transplantation. The National Heart, Lung, and Blood Institute convened a working group of investigators on June 14-15, 2004, in Bethesda, Maryland, to identify opportunities for scientific advancement in lung transplantation, including basic and clinical research. This workshop provides a framework to identify critical issues related to clinical lung transplantation, and to delineate important areas for productive scientific investigation.

Predictors of the rise in vWF after ST elevation myocardial infarction: implications for treatment strategies and clinical outcome

AIMS

Prior studies suggest that acute coronary syndromes (ACSs) are associated with endothelial activation and that this is of prognostic significance. We hypothesized that endothelial activation, as measured by a rise in von Willebrand Factor (DeltavWF), was influenced by the thrombolysis in myocardial infarction flow grade (TFG), the corrected TIMI frame count (CTFC) and the choice of anticoagulant therapy after fibrinolysis in ST elevation myocardial infarction (STEMI).

METHODS AND RESULTS

Data were drawn from the enoxaparin and tenecteplase tissue plasminogen activator (TNK-tpa) with or without GPIIb/IIIa inhibitor as the reperfusion strategy in the STEMI trial (ENTIRE-TIMI 23). Three hundred and fourteen patients had serial measurements of vWF (baseline and 48-72 h) and angiographic data available. TFG<3 (P=0.0042) or CTFC>/=40 at 60 min (P=0.0035) were associated with a higher DeltavWF. DeltavWF >/=75th percentile was associated with a higher incidence of death or myocardial infarction (MI) at 30 days, compared with <75th percentile (11.2 vs. 4.1%, P=0.027). Enoxaparin independently reduced the DeltavWF (P=0.019) and also the composite of death or MI (OR 0.33, 95% CI 0.12-0.91, P=0.03) compared with unfractionated heparin.

CONCLUSION

In STEMI treated by fibrinolysis, coronary flow at 60 min and choice of adjunctive anticoagulant appear to be independent determinants of DeltavWF. Enoxaparin is independently associated with a reduction in DeltavWF and a reduction in death or MI. The clinical benefits of enoxaparin as an adjunctive treatment in STEMI may be mediated in part by a reduction in vWF release.

Non-heart-beating donors in thoracic transplantation

Access to lung transplantation is severely limited by a scarcity of suitable donors, resulting in increasing numbers of deaths on the heart and lung transplant waiting lists, and strict selection criteria for recipients. Unlike some other solid organs, the lung may be ideally suited to retrieval for transplant following substantial intervals after circulatory arrest. This may be because lung parenchymal cells do not rely on perfusion for cellular respiration. This review outlines the relevant published experimental data that addresses the concept that lungs might be suitable for transplant even if retrieved from non-heart-beating donors (NHBDs), and the small published clinical experience with NHBDs as lung donors. Aspects of reperfusion injury in this setting are reviewed. The prospect of heart transplant from NHBDs is addressed. The impact of the routine use of NHBDs on lung transplantation is discussed.

The role of antibodies and von Willebrand factor in discordant pulmonary xenotransplantation

Pulmonary xenotransplantation is one potential solution to the paucity of donors but is currently limited by rapid failure of the graft. Unlike cardiac and renal xenotransplants, pulmonary xenografts release large quantities of swine von Willebrand factor (vWF). Swine vWF binds xenoreactive antibodies and is capable of activating primate platelets. The contribution of swine vWF to lung xenograft dysfunction is not entirely clear. To probe the role vWF plays in xenograft dysfunction, we traced the fate of xenoantibodies in vWF+ and von Willebrand factor-deficient (vWFD) swine lungs. These studies showed that the vast majority of xenoantibodies bind the vWF released from the vWF+ swine lung, and thus do not remain bound on lung endothelium. The vWF complexed to xenoantibody remained capable of aggregating primate platelets. With this information, we performed swine-to-baboon lung transplants using vWF+ and vWFD donors. Without vWF present to complex xenoantibodies, a picture of hyperacute rejection more typical of heart and kidney xenografts, with antibody deposition along the graft endothelium, interstitial hemorrhage, and edema occurred. These findings suggest that porcine vWF plays a major role in the pathogenesis of pulmonary xenograft dysfunction, and suggests promising strategies to treat lung xenograft dysfunction.