Cynthia M. Pruss

The effect of exercise on von Willebrand factor and ADAMTS‐13 in individuals with type 1 and type 2B von Willebrand disease

Summary.  Background: The effect of exercise on von Willebrand factor (VWF) and ADAMTS‐13 levels in individuals with von Willebrand disease (VWD) has never been reported.

Pathologic mechanisms of type 1 VWD mutations R1205H and Y1584C through in vitro and in vivo mouse models

Type 1 VWD is the mild to moderate reduction of VWF levels. This study examined the mechanisms underlying 2 common type 1 VWD mutations, the severe R1205H and more moderate Y1584C. In vitro biosynthesis was reduced for both mutations in human and mouse VWF, with the effect being more severe in R1205H. VWF knockout mice received hydrodynamic injections of mouse Vwf cDNA. Lower VWF antigen levels were demonstrated in both homozygous and heterozygous forms for both type 1 mutations from days 14-42. Recombinant protein infusions and hydrodynamic-expressed VWF propeptide to antigen ratios demonstrate that R1205H mouse VWF has an increased clearance rate, while Y1584C is normal. Recombinant ADAMTS13 digestions of Y1584C demonstrated enhanced cleavage of both human and mouse VWF115 substrates. Hydrodynamic-expressed VWF shows a loss of high molecular weight multimers for Y1584C compared with wild-type and R1205H. At normal physiologic levels of VWF, Y1584C showed reduced thrombus formation in a ferric chloride injury model while R1205H demonstrated similar thrombogenic activity to wild-type VWF. This study has elucidated several novel mechanisms for these mutations and highlights that the type 1 VWD phenotype can be recapitulated in the VWF knockout hydrodynamic injection model.

Associations of epicardial fat with coronary calcification, insulin resistance, inflammation, and fibroblast growth factor-23 in stage 3-5 chronic kidney disease.

BackgroundEpicardial fat, quantified in a single multi-slice computed tomography (MSCT) slice, is a reliable estimate of total epicardial fat volume (EFV). We sought to determine risk factors for EFV detected in a single-slice MSCT measurement (ssEFV) in pre-dialysis chronic kidney disease (CKD) patients. Our primary objective was to determine the association between ssEFV and coronary artery calcification (CAC).Methods94 pre-dialysis stage 3–5 CKD patients underwent MSCT to measure ssEFV and CAC. ssEFV was quantified at the level of the left main coronary artery. Measures of inflammation, traditional and kidney-related cardiovascular disease risk factors were collected.ResultsMean age: 63.7 ± 14 years, 56% male, 39% had diabetes, and mean eGFR: 25.1 ± 11.9 mL/min/1.73 m2. Mean ssEFV was 5.03 ± 2.4 cm3. By univariate analysis, body mass index (BMI) (r = 0.53; P = <0.0001), abdominal obesity (r = 0.51; P < 0.0001), high density lipoprotein (HDL) cholesterol (r = − 0.39; P = <0.0001), insulin resistance (log homeostasis model assessment of insulin resistance (log HOMA-IR)) (r = 0.38, P = 0.001), log interleukin-6 (IL-6) (r = 0.34; P = 0.001), and log urinary albumin to creatinine ratio (UACR) (r = 0.30, P = 0.004) demonstrated the strongest associations with ssEFV. Log coronary artery calcification (log CAC score) (r = 0.28, P = 0.006), and log fibroblast growth factor-23 (log FGF-23) (r = 0.23, P = 0.03) were also correlated with ssEFV. By linear regression, log CAC score (beta =0.40; 95% confidence interval (CI), 0.01-0.80; P = 0.045), increasing levels of IL-6 (beta = 0.99; 95% CI, 0.38 – 1.61; P = 0.002), abdominal obesity (beta = 1.86; 95% CI, 0.94 - 2.8; P < 0.0001), lower HDL cholesterol (beta = −2.30; 95% CI, – 3.68 to −0.83; P = 0.002) and albuminuria (log UACR, beta = 0.81; 95% CI, 0.2 to 1.4; P = 0.01) were risk factors for increased ssEFV.ConclusionsIn stage 3–5 CKD, coronary calcification and IL-6 and were predictors of ssEFV. Further studies are needed to clarify the mechanism by which epicardial fat may contribute to the pathogenesis of coronary disease, particularly in the CKD population.

ADAMTS13 cleavage efficiency is altered by mutagenic and, to a lesser extent, polymorphic sequence changes in the A1 and A2 domains of von Willebrand factor.

The multimeric plasma protein von Willebrand factor (VWF) is regulated in size by its protease, ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13). Y1605‐M1606 cleavage site mutations and single nucleotide polymorphisms (SNPs) in the VWF A1 and A2 domains were examined for alteration in ADAMTS13‐mediated cleavage of VWF. Recombinant human full‐length VWF (rVWF) was digested with recombinant human ADAMTS13 (rADAMTS13) using a dialysis membrane method with 1·5 mol/l urea, and analyzed via multimer migration distance. The glutathione‐S‐transferase (GST) and histidine‐tagged construct, E1554‐R1668 of VWF (VWF115) was assayed via enzyme‐linked immunosorbent assay: VWF115 was bound to anti‐GST coated plates, digested with rADAMTS13, and intact VWF115 detected via horseradish peroxidase‐labelled anti‐histidine tag antibody. All alterations examined in the Y1605‐M1606 cleavage site greatly reduced the cleavability of VWF by ADAMTS13 in the rVWF assay. Greatest cleavage resistance in both assays was observed in Y1605A/M1606A. In contrast, Y1605H and M1606L show a loss of cleavability only in the rVWF assay, suggesting that an aromatic ring at 1605 is critical for ADAMTS13 recognition. Additionally, under our rVWF assay conditions, the G1643S polymorphism showed increased cleavage, suggesting a Type 2A VWD phenotype, while D1472H, Q1571H and P1601T showed slightly decreased ADAMTS13 cleavage. Our two complementary assay conditions show that A‐domain changes in VWF alter ADAMTS13‐mediated proteolysis.

Use of a mouse model to elucidate the phenotypic effects of the von Willebrand factor cleavage mutants, Y1605A/M1606A and R1597W

Background: von Willebrand Factor (VWF) is tightly regulated by the metalloproteinase ADAMTS13, which cleaves VWF to reduce VWF multimer size and binding affinity for collagen and platelets.

Analysis of the role of von Willebrand factor, platelet glycoprotein VI-, and α2β1-mediated collagen binding in thrombus formation.

Rare missense mutations in the von Willebrand factor (VWF) A3 domain that disrupt collagen binding have been found in patients with a mild bleeding phenotype. However, the analysis of these aberrant VWF-collagen interactions has been limited. Here, we have developed mouse models of collagen-binding mutants and analyzed the function of the A3 domain using comprehensive in vitro and in vivo approaches. Five loss-of-function (p.S1731T, p.W1745C, p.S1783A, p.H1786D, A3 deletion) and 1 gain-of-function (p.L1757A) variants were generated in the mouse VWF complementary DNA. The results of these various assays were consistent, although the magnitude of the effects were different: the gain-of-function (p.L1757A) variant showed consistent enhanced collagen binding whereas the loss-of-function mutants showed variable degrees of functional deficit. We further analyzed the impact of direct platelet-collagen binding by blocking glycoprotein VI (GPVI) and integrin α2β1 in our ferric chloride murine thrombosis model. The inhibition of GPVI demonstrated a comparable functional defect in thrombosis formation to the VWF(-/-) mice whereas α2β1 inhibition demonstrated a milder bleeding phenotype. Furthermore, a delayed and markedly reduced thrombogenic response was still evident in VWF(-/-), GPVI, and α2β1 blocked animals, suggesting that alternative primary hemostatic mechanisms can partially rescue the bleeding phenotype associated with these defects.

Calcification of the Internal Pudendal Artery and Development of Erectile Dysfunction in Adenine‐Induced Chronic Kidney Disease: A Sentinel of Systemic Vascular Changes

INTRODUCTION Chronic kidney disease (CKD), erectile dysfunction (ED), and cardiovascular disease share common vascular etiologies and risk factors. AIM Using a rat model, this is the first study to characterize the consequences of CKD in the onset and development of ED associated with differential regional vascular calcification and circulatory changes. METHODS Stable CKD was generated at 3 weeks in male Sprague-Dawley rats given dietary adenine and progressed until 7 weeks. Mineral content and morphometry were assessed in the internal pudendal arteries (IPAs), thoracic aorta, and carotid artery. Endothelial function was determined via changes in serum von Willebrand factor (VWF) and endothelium-dependent relaxation of the thoracic aorta. RESULTS In severe CKD rats, calcium and phosphate content in all arteries increased, and pulse wave velocity was elevated. Distal IPA segments, in particular, were the first to calcify, but penile tissue per se did not. CKD rats had endothelial dysfunction, as indicated by a decrease in acetylcholine-mediated relaxation (∼40%) and an increase in serum VWF (∼40%), as well as increased lumen diameter (20%) of the distal IPA. Erectile function, assessed using a centrally acting dopaminergic agent, was significantly impaired by 7 weeks (∼40%). CONCLUSIONS In CKD, the distal IPA appears to be more susceptible to vascular dysfunction and calcification. Additionally, the onset of ED may be an important sentinel of impending systemic vascular disease. To confirm this concept, future experimental and clinical studies will need to examine a range of vessel types and the use of supplementary methods to assess erectile function.

Quantitative and qualitative changes of von Willebrand factor and their impact on mortality in patients with end-stage kidney disease.

von Willebrand factor (vWF) antigen levels are elevated in patients with end-stage kidney disease (ESKD). We determined the quantitative and qualitative abnormalities of vWF and factors influencing vWF proteolysis in participants with ESKD compared with age-matched controls and determined the association between abnormalities in vWF and mortality over 4 years of follow-up. vWF : Ag and von Willebrand factor propeptide (vWFpp) levels, vWF functional activity (vWF :RCo), vWF multimer profiles, ADAMTS-13, thrombospondin 1 (TSP-1), and interleukin 6 (IL-6) were evaluated before and after a single hemodialysis treatment in 55 individuals with vascular disease and an age-matched group of controls (n = 21). vWF : Ag and vWF activity were significantly higher in the ESKD patients and levels increased further following the dialysis procedure. The percentage of high molecular weight multimers (%HMWMs) was significantly elevated in the ESKD patients compared with controls. TSP-1 was lower and IL-6 was higher providing possible explanation for the increase in %HMWM in ESKD. The %HMWM dropped significantly in the postdialysis sample. Mortality at 4 years was significantly associated with vWF : Ag. There are higher plasma vWF : Ag levels and a small increase in HMWMs in the ESKD milieu. The acute drop in the %HMWM of vWF postdialysis appears to be due to shear forces encountered during the dialysis procedure. The contribution of these abnormalities to either a pro-thrombotic and/or pro-bleeding phenotype in this population requires further study.

1074 DISCORDANCE IN CIRCULATING VON WILLEBRAND FACTOR AND SEXUAL DYSFUNCTION BETWEEN MEN AND WOMEN WHO ARE OVERWEIGHT/OBESE

Introduction: There is an established link between sexual dysfunction (SD) and CVD in men, sharing similar etiologies including endothelial dysfunction. This association has not been well characterized in women. Our study evaluated circulating Von Willebrand Factor (VWF), a biomarker of endothelial function and its association with SD in men and women. Methods: A cross-sectional analysis of overweight and obese men (N = 19, 34-67yrs) and women (N = 29, 35-64yrs) was performed. Male sexual function was determined via IIEF questionnaires (scores ⩽25 reflect SD). Females received FSFI questionnaires (scores ⩽26 reflect SD). BMI, waist circumference and circulating osteoprotegerin (OPG), C reactive protein (CRP), VWF propeptide (VWFpp) and VWF antigen (VWF:Ag) were measured. Results: Biometrics were similar between SD and normal individuals. In males with SD there was a significant increase in VWF:Ag and VWFpp. In contrast, in women with SD the levels of VWFpp were significantly lower. There were no differences in other biomarkers. Table. No title available. Mean ± SD Conclusions: Increased circulating VWF, but not OPG or CRP, is associated with SD in overweight/obese men. Whether endothelial dysfunction precedes inflammatory changes associated with SD in men remains to be determined. Conversely, in women with SD the levels of VWFpp were decreased. Although the concept has been contentious, these findings suggest that vascular mechanisms may not be as important in the etiology of SD in women. (Funds:H&SC, CIHR, MTM:CIHR-DRA CP:Queens Dept.Med-PDF)