Partial amino acid sequence of purified von Willebrand factor-cleaving protease

Novel mechanisms of action of emerging therapies of hereditary thrombotic thrombocytopenic purpura

INTRODUCTION

Hereditary thrombotic thrombocytopenic purpura (hTTP) is caused by deficiency of plasma ADAMTS13 activity, resulting from ADAMTS13 mutations. ADAMTS13 cleaves ultra large von Willebrand factor (VWF), thus reducing its multimer sizes. Hereditary deficiency of plasma ADAMTS13 activity leads to the formation of excessive platelet-VWF aggregates in small arterioles and capillaries, resulting in hTTP.

AREAS COVERED

PubMed search from 1956 to 2024 using thrombotic thrombocytopenic purpura and therapy identified 3,675 articles. Only the articles relevant to the topic were selected for discussion, which focuses on pathophysiology, clinical presentations, and mechanisms of action of emerging therapeutics for hTTP. Current therapies include infusion of plasma, or coagulation factor VIII, or recombinant ADAMTS13. Emerging therapies include anti-VWF A1 aptamers or nanobody and gene therapies with adeno-associated viral vector or self-inactivated lentiviral vector or a sleeping beauty transposon system for a long-term expression of a functional ADAMTS13 enzyme.

EXPERT OPINION

Frequent plasma infusion remains to be the standard of care in most parts of the world, while recombinant ADAMTS13 has become the treatment of choice for hTTP in some of the Western countries. The success of gene therapies in preclinical models may hold a promise for future development of these novel approaches for a cure of hTTP.

Association of ADAMTS13 activity with cerebral deep medullary vein: A community-based cross-sectional study

Objectives

This study aims to investigate whether circulating ADAMTS13 activity can offer insights into the mechanism of pathophysiological changes in deep medullary veins (DMVs).

Methods

This study was conducted on a community cohort of elderly individuals in Shanghai. Plasma von Willebrand factor (VWF) levels and ADAMTS13 activity were measured. A validated DMV score described the overall burden of DMV on the brain. Through ordinal regression models, we investigated the correlation between VWF levels, ADAMTS13 activity, and increasing severity of DMV score while adjusting for demographics and cardiovascular risk factors.

Results

The study enrolled 262 subjects according to the inclusion criteria. The mean VWF level (1.35 ± 0.25) was higher in the DMV group than in the group without DMV (1.25 ± 0.30) (p = 0.025), and ADAMTS13 activity (83.76 ± 7.96) was relatively lower. After adjusting for age, sex, alcohol consumption, smoking, hypertension, and diabetes, reduced ADAMTS13 activity [β = -7.78; 95 % CI (-10.21, -5.35) p < 0.01] was associated with DMV. Moreover, correlation analysis indicated that ADAMTS13 activity was negatively correlated with the DMV score (Kendall's tau-b = -0.53, p < 0.001).

Discussion

In summary, there was an inverse correlation observed between ADAMTS13 activity and the DMV score, which may provide some clinical clues for exploring the potential pathogenesis of DMV.

Thrombotic Thrombocytopenic Purpura: From 1972 to 2022 and Beyond

This review tells the story of my personal experience with thrombotic thrombocytopenic purpura (TTP). It begins with my first encounter with TTP 50 years ago when 2 sisters presented 2 years apart, both pregnant and both died. At that time, I knew nothing about hereditary TTP (hTTP), the risks of pregnancy, or effective treatments. In 1991, a year after I moved to Oklahoma, therapeutic plasma exchange (TPE) was established as an effective treatment. With the availability of effective treatment, the number of patients presenting with suspected TTP soared. The diagnosis of TTP was imprecise. I worked with the Oklahoma Blood Institute (OBI) to understand the management of TTP. Because the OBI provided all TPE procedures for most of Oklahoma, we saw all consecutive patients within a defined geographic area who were identified at a uniform time early in the course of their TTP, without selection or referral bias. It was an inception cohort; this became the Oklahoma TTP Registry. In 2001, we began a very successful collaboration with the University of Bern, Switzerland, to measure ADAMTS13 activity in all of our patients. From our patients, we learned that acquired, autoimmune TTP (iTTP) is a chronic disease with risks for cognitive impairment and depression. Recognition in 2012 of three sisters with hTTP was reminiscent of the beginning of my story. hTTP has risks for multiple severe morbidities, beginning at birth and especially during pregnancy. Future management of both iTTP and hTTP will be more effective and more convenient.

ADAMTS13 conformations and mechanism of inhibition in immune thrombotic thrombocytopenic purpura

ADAMTS13, a plasma metalloprotease that cleaves von Willebrand factor, is crucial for normal hemostasis. Acquired autoantibody-mediated deficiency of plasma ADAMTS13 results in a potentially fatal blood disorder, immune thrombotic thrombocytopenic purpura (iTTP). Plasma ADAMTS13 protease appears to exist in multiple conformations. Under physiological conditions, plasma ADAMTS13 exists predominantly in its "closed" conformation (or latent form), which may be activated by lowering pH, ligand binding, and binding of an antibody against the distal domains of ADAMTS13. In patients with iTTP, polyclonal antibodies target at various domains of ADAMTS13. However, nearly all inhibitory antibodies bind the spacer domain, whereas antibodies that bind the distal C-terminal domains may activate ADAMTS13 through removing its allosteric inhibition. Additionally, the anti-C-terminal antibodies may alter the potency of inhibitory antibodies towards ADAMTS13 activity. This review summarizes some of the most recent knowledge about the ADAMTS13 conformation and its mechanism of inhibition by its autoantibodies.

Contribution of ADAMTS13-independent VWF regulation in sickle cell disease

BACKGROUND

Von Willebrand factor (VWF) is elevated in sickle cell disease (SCD) and contributes to vaso-occlusion through its thrombogenic properties. VWF is regulated by ADAMTS13, a plasma protease that cleaves VWF into less bioactive multimers. Independent investigations have shown VWF to be elevated in SCD, whereas measurements of ADAMTS13 have been variable.

OBJECTIVES

We assessed ADAMTS13 activity using multiple activity assays and measured levels of alternative VWF-cleaving proteases in SCD.

METHODS/ PATIENTS

Plasma samples were collected from adult patients with SCD (n = 20) at a single institution when presenting for routine red cell exchange transfusion therapy. ADAMTS13 activity was measured by FRETS-VWF73, Technozym ADAMTS-13 Activity ELISA kit and a full-length VWF digestion reaction. Alternative VWF-cleaving proteases were identified by ELISA. A cell culture model was used to study the impact of SCD stimuli on endothelial ADAMTS13 and alternative VWF-cleaving proteases.

RESULTS

ADAMTS13 activity was found to be moderately deficient across the SCD cohort as assessed by activity assays using a VWF A2 domain peptide substrate. However, SCD plasma showed preserved ability to digest full-length VWF, suggesting assay-discrepant results. Neutrophil and endothelial-derived proteases were found to be elevated in SCD plasma. Matrix metalloproteinase 9 specifically showed preferential cleavage of full-length VWF. Upregulation of alternative VWF-cleaving proteases occurred in endothelial cells exposed to SCD stimuli such as heme and hypoxia.

CONCLUSIONS

This is the first demonstration of accessory plasma enzymes contributing to the regulation of VWF in a specific disease state and may have implications for assessing the VWF/ADAMTS13 axis in other settings.

Circulating ADAMTS13 Levels Are Associated with an Increased Occurrence of Obstructive Sleep Apnea

Background and Aims. Obstructive sleep apnea (OSA) is strongly associated with obesity, metabolic diseases, coronary artery disease (CAD), stroke, hypertension, and other disorders. This study assessed the relationship between circulating a disintegrin and metalloprotease with a thrombospondin type 1 motif, member 13 (ADAMTS13) levels and the presence of OSA. Materials and Methods. This cross-sectional study included a total of 223 patients. We used a powerful high-throughput multiplexed immunobead-based assay to detect circulating levels of ADAMTS13. The associations between circulating ADAMTS13 levels and OSA were evaluated by multivariate logistic regression analysis. Results. Circulating ADAMTS13 levels were significantly elevated in patients with OSA compared with controls (0.8 vs. 2.7 μg/mL, respectively, $P<0.001$ ). After adjusting for confounding factors, circulating ADAMTS13 levels were significantly independently associated with the presence of OSA ( $\text{odds}\text{ratio}=9.96$ , 95% confidence interval (CI) =4.11–24.13, $P<0.001$ ). Furthermore, circulating ADAMTS13 levels showed discriminatory accuracy in assessing the presence of OSA (area under the curve: 0.87, 95% CI 0.81–0.93, $P<0.001$ ). Conclusion. Circulating ADAMTS13 levels were significantly correlated with the presence of OSA. ADAMTS13 may therefore function as a novel biomarker for monitoring the development and progression of OSA.

von Willebrand factor propeptide-to-antigen ratio in HIV-infected pregnancy: Evidence of endothelial activation

BACKGROUND

Endothelial activation has been proposed as a potential mechanism for the increased risk of venous thromboembolism (VTE) in human immunodeficiency virus (HIV)-infected pregnancy.

OBJECTIVES

To assess the state of endothelial activation in HIV-infected pregnancy by measuring the von Willebrand factor (VWF) propeptide-to-antigen ratio, as an index of acute endothelial activation.

METHODS

VWF antigen and VWF propeptide were measured in HIV-negative participants (n = 85), HIV-infected virologically suppressed participants, (n = 89) and HIV-infected participants with HIV viral load (VL) of >50 copies/ml (n = 63) in each trimester. Results were correlated with multimer patterns and a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS-13) antigen, activity, and antibody levels.

RESULTS

VWF propeptide-to-antigen ratio was increased, in the first, second, and third trimester, in the HIV-infected virologically suppressed group (1.7 ± 0.7, 1.7 ± 0.4, 1.6 ± 0.5) and the HIV-infected group with VL > 50 copies/ml (1.9 ± 0.9, 1.7 ± 0.9, 1.6 ± 1.1) compared to the HIV-negative group (1.4 ± 0.6, 1.3 ± 0.4, 1.2 ± 0.3, P < .05). Increased high molecular weight multimers were observed in the HIV-infected groups, despite only a mild reduction in ADAMTS-13 activity compared to the HIV-negative group (P < .001). No correlation was observed between VWF antigen or VWF propeptide and ADAMTS-13 activity.

CONCLUSION

HIV-infected virologically suppressed pregnant participants showed persistent endothelial activation. Future research should focus on whether endothelial activation contributes to the excess risk of pregnancy-related VTE.

The Relationship Between ADAMTS13 Activity and Overall Cerebral Small Vessel Disease Burden: A Cross-Sectional Study Based on CSVD

Objectives: This study aimed to investigate the association between plasma von Willebrand factor (VWF) level, ADAMTS13 activity, and neuroimaging features of cerebral small vessel disease (CSVD), including the CSVD neuroimaging markers and the overall CSVD burden.

Methods: CSVD patients admitted to our hospital from 2016 to 2020 were recruited. Plasma VWF level and ADAMTS13 activity were measured. The overall effect of CSVD on the brain was described as a validated CSVD score. We evaluated the association between VWF levels, ADAMTS13 activity, and the increasing severity of CSVD score by the logistic regression model.

Results: We enrolled 296 patients into this study. The mean age of the sample was 69.0 years (SD 7.0). The mean VWF level was 1.31 IU/mL, and the ADAMTS13 activity was 88.01 (SD 10.57). In multivariate regression analysis, lower ADAMTS13 activity and higher VWF level was related to white matter hyperintensity (WMH) [β = −7.31; 95% confidence interval (CI) (−9.40, −4.93); p<0.01; β = 0.17; 95% confidence interval (0.11, 0.23); p<0.01], subcortical infarction (SI) [(β = −9.22; 95% CI (−11.37, −7.06); p<0.01); β = 0.21; 95% confidence interval (0.15, 0.27); p<0.01] independently, but not cerebral microbleed (CMB) [(β = −2.3; 95% CI (−4.95, 0.05); p = 0.22); β = 0.02; 95% confidence interval (−0.05, 0.08); p = 0.63]. Furthermore, ADAMTS13 activity was independently negatively correlated with the overall CSVD burden (odd ratio = 21.33; 95% CI (17.46, 54.60); p < 0.01) after adjustment for age, history of hypertension, and current smoking.

Conclusions: Reducing ADAMTS13 activity change is related to white matter hyperintensity, subcortical infarction, but not with cerebral microhemorrhage. In addition, ADAMTS13 may have played an essential role in the progression of CSVD.

Conformational plasticity of ADAMTS13 in hemostasis and autoimmunity

A disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) is a multidomain metalloprotease for which until now only a single substrate has been identified. ADAMTS13 cleaves the polymeric force-sensor von Willebrand factor (VWF) that unfolds under shear stress and recruits platelets to sites of vascular injury. Shear force–dependent cleavage at a single Tyr–Met peptide bond in the unfolded VWF A2 domain serves to reduce the size of VWF polymers in circulation. In patients with immune-mediated thrombotic thrombocytopenic purpura (iTTP), a rare life-threatening disease, ADAMTS13 is targeted by autoantibodies that inhibit its activity or promote its clearance. In the absence of ADAMTS13, VWF polymers are not adequately processed, resulting in spontaneous adhesion of blood platelets, which presents as severe, life-threatening microvascular thrombosis. In healthy individuals, ADAMTS13–VWF interactions are guided by controlled conversion of ADAMTS13 from a closed, inactive to an open, active conformation through a series of interdomain contacts that are now beginning to be defined. Recently, it has been shown that ADAMTS13 adopts an open conformation in the acute phase and during subclinical disease in iTTP patients, making open ADAMTS13 a novel biomarker for iTTP. In this review, we summarize our current knowledge on ADAMTS13 conformation and speculate on potential triggers inducing conformational changes of ADAMTS13 and how these relate to the pathogenesis of iTTP.

Von Willebrand factor, ADAMTS13 and mortality in dialysis patients

BACKGROUND

Von Willebrand Factor (VWF) multimers are cleaved into smaller and less coagulant forms by the metalloprotease ADAMTS13. The aim of this study was to investigate the association between VWF and ADAMTS13 and mortality in dialysis patients.

METHODS

We prospectively followed 956 dialysis patients. VWF levels and ADAMTS13 activity were measured. Cox proportional hazard analyses were used to calculate hazard ratios (HRs) with 95 % confidence intervals (CIs) to investigate the association between quartiles of VWF levels and ADAMTS13 activity and all-cause mortality. HRs were adjusted for age, sex, body mass index, cardiovascular disease, dialysis modality, primary kidney disease, use of antithrombotic medication, systolic blood pressure, albumin, C-reactive protein and residual GFR.

RESULTS

Of the 956 dialysis patients, 288 dialysis patients died within three years (mortality rate 151 per 1000 person-years). The highest quartile of VWF as compared with lower levels of VWF was associated with a 1.4-fold (95 %CI 1.1-1.8) increased mortality risk after adjustment. The lowest quartile of ADAMTS13 activity as compared with other quartiles was associated with a 1.3-fold (95 %CI 1.0-1.7) increased mortality risk after adjustment. The combination of the highest VWF quartile and lowest ADAMTS13 quartile was associated with a 2.0-fold (95 %CI 1.3-3.0) increased mortality risk as compared with the combination of the lowest VWF quartile and highest ADAMTS13 quartile.

CONCLUSIONS

High VWF levels and low ADAMTS13 activity were associated with increased mortality risks in dialysis patients.

The interaction between the complement system and hemostatic factors

PURPOSE OF REVIEW

To discuss the crosstalk between the complement system and hemostatic factors (coagulation cascade, platelet, endothelium, and Von Willebrand Factor), and the consequences of this interaction under physiologic and pathologic conditions.

RECENT FINDINGS

The complement and coagulation systems are comprised of serine proteases and are genetically related. In addition to the common ancestral genes, the complement system and hemostasis interact directly, through protein-protein interactions, and indirectly, on the surface of platelets and endothelial cells. The close interaction between the complement system and hemostatic factors is manifested both in physiologic and pathologic conditions, such as in the inflammatory response to thrombosis, thrombosis at the inflamed area, and thrombotic complications of complement disorders.

SUMMARY

The interaction between the complement system and hemostasis is vital for homeostasis and the protective response of the host to tissue injury, but also results in the pathogenesis of several thrombotic and inflammatory disorders.

Clinical significance of measuring ADAMTS-13, its inhibitor and von Willebrand factor in obstetric and gynecological practice

ADAMTS-13 is a crucial metalloproteinase involved in liberating fragments of von Willebrand factor (vWF) into the plasma as well as regulating its activity by cleaving "ultra-large" multimers into smaller and less active counterparts. Many pathological conditions, including those emerged during pregnancy are characterized by increased level of vWF and decreased ADAMTS-13 activity. In this regard, it is necessary to monitor the levels of vWF and ADAMTS-13 activity to prevent thrombotic thrombocytopenic purpura (Moschcowitz disease) as one of the most severe forms of thrombotic microangiopathy.

 

Thrombotic Thrombocytopenic Purpura: Pathophysiology, Diagnosis, and Management

Thrombotic thrombocytopenic purpura (TTP) is a rare thrombotic microangiopathy characterized by microangiopathic hemolytic anemia, severe thrombocytopenia, and ischemic end organ injury due to microvascular platelet-rich thrombi. TTP results from a severe deficiency of the specific von Willebrand factor (VWF)-cleaving protease, ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats, member 13). ADAMTS13 deficiency is most commonly acquired due to anti-ADAMTS13 autoantibodies. It can also be inherited in the congenital form as a result of biallelic mutations in the ADAMTS13 gene. In adults, the condition is most often immune-mediated (iTTP) whereas congenital TTP (cTTP) is often detected in childhood or during pregnancy. iTTP occurs more often in women and is potentially lethal without prompt recognition and treatment. Front-line therapy includes daily plasma exchange with fresh frozen plasma replacement and immunosuppression with corticosteroids. Immunosuppression targeting ADAMTS13 autoantibodies with the humanized anti-CD20 monoclonal antibody rituximab is frequently added to the initial therapy. If available, anti-VWF therapy with caplacizumab is also added to the front-line setting. While it is hypothesized that refractory TTP will be less common in the era of caplacizumab, in relapsed or refractory cases cyclosporine A, N-acetylcysteine, bortezomib, cyclophosphamide, vincristine, or splenectomy can be considered. Novel agents, such as recombinant ADAMTS13, are also currently under investigation and show promise for the treatment of TTP. Long-term follow-up after the acute episode is critical to monitor for relapse and to diagnose and manage chronic sequelae of this disease.

Atypical Presentation of Thrombotic Thrombocytopenic Purpura without Hematological Features

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening disease, usually diagnosed with high index of suspicion. The pathophysiology of TTP is due to severe deficiency of von Willebrand factor cleaving protease, known as ADAMTS 13. Early diagnosis is crucial as without treatment TTP is associated with high mortality rate. Plasma exchange is currently the mainstay of treatment. Nonetheless, the classical pentad of microangiopathic hemolytic anemia (MAHA), thrombocytopenia, neurological dysfunction, kidney dysfunction and fever are seen only in 40 percent of the patients. MAHA and thrombocytopenia are the common presenting features. Presentation with thrombotic complication without hematological features (MAHA and thrombocytopenia) is rare and makes the diagnosis difficult. Herein, we report an unusual presentation of a 53-year-old male, who was initially presented in 2014 with classical features of TTP, however had an atypical presentation of TTP in 2016 with only neurological features without hematological features.

Upshaw-Schulman syndrome-associated ADAMTS13 variants possess proteolytic activity at the surface of endothelial cells and in simulated circulation

ADAMTS13 regulates the hemostatic activity of von Willebrand factor (VWF). Determined by static assays, proteolytic activity <10IU/dL in patient plasma, in absence of ADAMTS13 autoantibodies, indicates Upshaw-Schulman syndrome (USS); the congenital form of Thrombotic Thrombocytopenic Purpura (TTP). We have recently functionally characterized sixteen USS-associated ADAMTS13 missense variants under static conditions. Here, we used two assays under shear flow conditions to analyze the activity of those seven mutants with sufficiently high residual secretion plus two newly identified variants. One assay determines cleavage of VWF strings bound to the surface of endothelial cells. The other, light transmission aggregometry-based assay, mimics degradation of VWF-platelet complexes, which are likely to be present in the circulation during TTP bouts. We found that 100 ng/ml of all variants were able to cleave about 80–90% of VWF strings even though 5 out of 9 exhibited activity ≤1% in the state-of-the-art static assay at the same concentration. These data indicate underestimation of ADAMTS13 activity by the used static assay. In simulated circulation, two variants, with missense mutations in the vicinity of the catalytic domain, exhibited only minor residual activity while all other variants were able to effectively break down VWF-platelet complexes. In both assays, significant proteolytic activity could be observed down to 100 ng/ml ADAMTS13. It is thus intriguing to postulate that most variants would have ample activity if secretion of 10% of normal plasma levels could be achieved.

Identification of cysteine thiol-based linkages in ADAMTS13 in support of a non-proteolytic regulation of von Willebrand factor

BACKGROUND

ADAMTS13, a plasma metalloprotease, cleaves von Willebrand factor (VWF) to regulate its function. Additionally, ADAMTS13 is thought to regulate lateral association of VWF multimers to form fibrillar structures through its free thiols.

OBJECTIVE

The purpose of the present study is to obtain direct evidence for ADAMTS13 to engage in thiol/disulfide exchange reactions.

METHODS

Covalent complexes between ADAMTS13 and VWF were determined by agarose gel electrophoresis under nonreducing conditions. Free thiols in ADAMST13 were identified by a reversed phase high-performance liquid chromatography electrospray ionization quadrupole time-of-flight mass spectrometry system.

RESULTS

We demonstrate formation of covalent linkage between ADAMTS13 and VWF, which is time, concentration, temperature, and shear dependent. This interaction is independent of proteolytic activity of ADAMTS13 but depends on the C-terminal domains comprising the fifth through eighth thrombospondin type 1 repeats and C1r/C1s, Uegf, Bmp1 (CUB) domains. The interaction can be blocked by thiol-reactive agents, indicating that association is accomplished through disulfide bridge formation. Several partially reduced free thiols are identified in ADAMTS13, with cysteines 1254 and 1275 being the most prominent, although a point mutation (C1275S) in ADAMTS13 does not alter its ability to form covalent linkages with VWF. This suggests functionally relevant disulfide plasticity in ADAMTS13. Interestingly, ADAMTS13 also forms homo-oligomers under the same conditions as required for the generation of hetero-oligomeric complexes of ADAMTS13 and VWF.

CONCLUSIONS

Our results suggest that a dynamic network of free thiols in ADAMTS13 undergoing intra- and inter-molecular redox reactions may add another layer of regulation to VWF function under various conditions.

Temporal map of the pig polytrauma plasma proteome with fluid resuscitation and intravenous vitamin C treatment

BACKGROUND

Fluid resuscitation plays a prominent role in stabilizing trauma patients with hemorrhagic shock yet there remains uncertainty with regard to optimal administration time, volume, and fluid composition (e.g., whole blood, component, colloids) leading to complications such as trauma-induced coagulopathies (TIC), acidosis, and poor oxygen transport. Synthetic fluids in combination with antioxidants (e.g., vitamin C) may resolve some of these problems.

OBJECTIVES

We applied quantitative mass spectrometry-based proteomics [liquid chromatography-mass spectrometry (LC-MS/MS)] to map the effects of fluid resuscitation and intravenous vitamin C (VitC) in a pig model of polytrauma (hemorrhagic shock, tissue injury, liver reperfusion, hypothermia, and comminuted bone fracture). The goal was to determine the effects of VitC on plasma protein expression, with respect to changes associated with coagulation and trauma-induced coagulopathy (TIC).

METHODS

Longitudinal blood samples were drawn from nine male Sinclair pigs at baseline, 2 h post trauma, and 0.25, 2, and 4 h post fluid resuscitation with 500 mL hydroxyethyl starch. Pigs were treated intravenously (N = 3/treatment group) with saline, 50 mg VitC/kg (Lo-VitC), or 200 mg VitC/kg (Hi-VitC) during fluid resuscitation.

RESULTS

A total of 436 plasma proteins were quantified of which 136 changed following trauma and resuscitation; 34 were associated with coagulation, complement cascade, and glycolysis. Unexpectedly, Lo-VitC and Hi-VitC treatments stabilized ADAMTS13 levels by ~4-fold (P = .056) relative to saline and enhanced ADAMTS13/von Willebrand factor (VWF) cleavage efficiency based on LC-MS/MS evidence for the semitryptic VWF cleavage product (VWF1275-1286 ).

CONCLUSIONS

This study provides the first comprehensive map of trauma-induced changes to the plasma proteome, especially with respect to proteins driving the development of TIC.

Synergistic effects of ADAMTS13 deficiency and complement activation in pathogenesis of thrombotic microangiopathy

Severe deficiency of plasma ADAMTS13 activity is the primary cause of thrombotic thrombocytopenic purpura (TTP) whereas overwhelming activation of complement via an alternative pathway results in atypical hemolytic uremic syndrome (aHUS), the prototypes of thrombotic microangiopathy (TMA). However, clinical and pathogenic distinctions between TTP and aHUS are often quite challenging. Clinical reports have suggested that complement activation may play a role in the development of TTP, which is caused by severe deficiency of plasma ADAMTS13 activity. However, the experimental evidence to support this hypothesis is still lacking. Here, we show that mice with either Adamts13 -/- or a heterozygous mutation of complement factor H (cfh) at amino acid residue of 1206 (ie, cfh W/R ) alone remain asymptomatic despite the presence of occasional microvascular thrombi in various organ tissues. However, mice carrying both Adamts13 -/- and cfh W/R exhibit thrombocytopenia, low haptoglobin, increased fragmentation of erythrocytes in peripheral blood smear, increased plasma levels of lactate dehydrogenase activity, blood urea nitrogen, and creatinine, as well as an increased mortality rate, consistent with the development of TMA. Moreover, mice with a homozygous mutation of cfh (ie, cfh R/R ) with or without Adamts13 -/- developed severe TMA. The mortality rate in mice with Adamts13 -/- cfh R/R was significantly higher than that in mice with cfh R/R alone. Histological and immunohistochemical analyses demonstrated the presence of disseminated platelet-rich thrombi in terminal arterioles and capillaries of major organ tissues in these mice that were either euthanized or died. Together, our results support a synergistic effect of severe ADAMTS13 deficiency and complement activation in pathogenesis of TMA in mice.

Temperature-dependent irreversible conformational change of recombinant ADAMTS13 upon metal ion chelation

BACKGROUND

The catalytic domain of ADAMTS13 possesses one Zn2+ and up to three putative Ca2+ binding sites and can be inactivated by chelating agents. Although replenishment with an appropriate metallic cation is thought to restore the enzyme's proteolytic activity fully, ADAMTS13 stability in a metal ion-depleting environment has not been explored.

OBJECTIVES

To address the stability of ADAMTS13 in citrated human plasma.

METHODS

ADAMTS13 activity was measured using the FRETS-VWF73 fluorogenic assay. The molar ratio of metals bound to ADAMTS13 was determined by size exclusion chromatography inductively coupled plasma mass spectrometry (SEC-ICP-MS). Higher-order structural changes were analyzed using Fourier-transformed infrared spectroscopy and dynamic light scattering.

RESULTS

ADAMTS13 was stable at room temperature for up to 24 hours irrespective of the presence of citrate (0.38%). However, at 37°C, citrate caused a time-dependent activity decrease. No ADAMTS13 activity decrease was seen in heparinized plasma, but the addition of citrate again caused ADAMTS13 instability at 37°C. Scavenging of citrate by the addition of Ca2+ or Zn2+ prior to but not postincubation prevented the activity decrease of the enzyme. The SEC-ICP-MS analyses showed that ADAMTS13 only bound Zn2+ and that its reduced activity correlated with a gradual loss of bound Zn2+ . Concomitant higher-order structural analyses demonstrated structural changes in ADAMTS13 that are typical of less-ordered protein structures.

CONCLUSIONS

Zn2+ is required to stabilize ADAMTS13 structure at physiologic temperature, thereby preventing irreversible loss of enzyme activity. This finding is particularly important to consider when using citrated human plasma as a source of ADAMTS13 in clinical settings.

von Willebrand factor/ADAMTS-13 interactions at birth: implications for thrombosis in the neonatal period

von Willebrand factor (VWF) and its cleaving protease ADAMTS-13 (A Disintegrin and Metalloproteinase with Thrombospondin type 1 motif, member 13) are essential components to hemostasis. These plasma proteins have also been implicated in a number of disease states, including those affecting children. The best described abnormality is the congenital form of thrombotic thrombocytopenic purpura (TTP) resulting from germline mutations in the ADAMTS-13 gene. The VWF/ADAMTS-13 interaction has more recently emerged as a causative risk factor in the pathogenesis of pediatric stroke and secondary microangiopathies. There is now increasing interest and need to measure these coagulation factors during the neonatal period and throughout childhood. Methods adopted from a multitude of technically diverging studies have been used to understand their role during this period. To date, studies of VWF/ADAMTS-13 in this group of patients have reported conflicting results, which makes interpreting values in the clinical setting especially challenging. In this review we describe the historical evolution of the methodology used to measure VWF/ADAMTS-13 and how it may influence the results obtained during the first days of life. We review the individual assays used to analyze VWF/ADAMTS-13 as well as published reference values. Finally, we bring attention to the potential pathophysiologic role of VWF/ADAMTS-13 in neonatal thrombosis. This has significant implications because the pathologic processes that explain thrombosis in neonates remain poorly characterized and thromboembolism remains a significant source of morbidity and mortality, particularly in sick children.

Pediatric thrombotic thrombocytopenic purpura

Child-onset thrombotic thrombocytopenic purpura (TTP) is a rare entity of thrombotic microangiopathy (TMA). The pathophysiology of the disease is based on a severe functional deficiency of ADAMTS13 (activity <10%), the specific von Willebrand factor (VWF)-cleavage protease. This deficiency may be either acquired (associated anti-ADAMTS13 autoantibodies) or congenital (resulting from biallelic mutations of ADAMTS13 gene). ADAMTS13 deficiency is responsible for the accumulation of high molecular weight multimers of VWF and the formation of platelet thrombi in the microcirculation. Consequently, microangiopathic hemolytic anemia and consumption thrombocytopenia are associated with organ ischemia. The differential diagnosis with other TMAs, autoimmune cytopenias or hematological malignancies may be challenging. The exploration of ADAMTS13 (activity, antibodies, antigen, ADAMTS13 gene) supports the diagnosis of TTP. The first-line treatment of the acute phase of TTP is based on plasmatherapy. In congenital TTP, patients with a chronic disease benefit from a prophylactic plasmatherapy. In autoimmune TTP, steroids and B-cells depleting therapies increasingly are used together with plasma exchange. Long-term follow-up including the monitoring of ADAMTS13 activity is mandatory. A severe decrease in ADAMTS13 activity (<10%) may predict relapses and preemptive B-cell depletion with rituximab can be used to prevent relapses.

ADAMTS-13 and von Willebrand factor: a dynamic duo

von Willebrand factor (VWF) is a key player in hemostasis, acting as a carrier for factor VIII and capturing platelets at sites of vascular damage. To capture platelets, it must undergo conformational changes, both within its A1 domain and at the macromolecular level through A2 domain unfolding. Its size and this function are regulated by the metalloproteinase ADAMTS-13. Recently, it has been shown that ADAMTS-13 undergoes a conformational change upon interaction with VWF, and that this enhances its activity towards its substrate. This review summarizes recent work on these conformational transitions, describing how they are controlled. It points to their importance in hemostasis, bleeding disorders, and the developing field of therapeutic application of ADAMTS-13 as an antithrombotic agent in obstructive microvascular thrombosis and in cardiovascular disease.

Changes in plasma von Willebrand factor and von Willebrand factor cleaving protease in thrombotic thrombocytopenic purpura: A case report

The present case report described a patient with thrombotic thrombocytopenic purpura (TTP), who presented to the China-Japan Union Hospital of Jilin University (Changchun, China), and the changes in plasma von Willebrand factor (vWF) and vWF cleaving protease (vWF-cp) observed during treatment. Computed tomography and diffusion-weighted magnetic resonance (MR) imaging of the brain, cerebral MR angiography and other experimental tests were performed and the patient was subsequently diagnosed with TTP. The patient underwent treatment with plasma exchange, glucocorticoids and supportive care. Hematologic and biochemical parameters began to gradually improve over the 12 days after admission; platelet count, serum creatinine and serum lactate dehydrogenase concentrations returned to their normal ranges, plasma vWF concentration decreased to normal levels over the 30 days after admission, and vWF-cp activity increased compared with the levels detected in healthy volunteers. Monthly rituximab treatment was administered 4 times following patient discharge to prevent relapse, and no recurrence was detected at the 20-month follow-up. Plasma exchange therapy is effective in patients with TTP. After low-dose rituximab treatment, recurrent TTP has not been detected found till now. In the present case, vWF concentration and vWF-cp activity were measured at 8, 10, 23 and 32 days after admission; compared with the control group, patient's vWF concentration gradually decreased and vWF-cp activity slowly increased, suggesting that the patient had a favorable prognosis and a low risk of recurrence.

Regulation der primären Hämostase durch von-Willebrand-Faktor und ADAMTS13

Von Willebrand factor (VWF) is an adhesive, multi-functional huge multimerized protein with multiple domains harboring binding sites for collagen, platelet glycoprotein receptors and coagulation factor VIII (FVIII). The functional domains enable VWF to bind to the injured vessel wall, to recruit platelets to the site of injury by adhesion and aggregation and to bind and protect FVIII, an important cofactor of the coagulation cascade. VWF function in primary haemostasis is located in particular in the arterial and micro-circulation. This environment is exposed to high shear forces with hydrodynamic shear rates ranging over several orders of magnitude from 10–1 to 105 s-1 and requires particular mechanisms to enable platelet adhesion and aggregation under these variable conditions. The respective VWF function is strictly correlating with its multimer size. Lack or reduction of large VWF multimers is seen in patients with von Willebrand disease (VWD) type 2A which correlates with reduction of both VWF:platelet GPIb-binding and VWF:collagen binding and a bleeding phenotype. To prevent unlimited platelet adhesion and aggregation which is the cause of the microangiopathic disorder thrombotic thrombocytopenic purpura (TTP), VWF function is regulated by its specific protease ADAMTS13. Whereas a particular susceptibility of VWF to ADAMTS13 proteolysis is the cause of a frequent VWD type 2A phenotype, lack or dysfunction of ADAMTS13, either acquired by ADAMTS13 antibodies or by inherited ADAMTS13 deficiency (Upshaw-Schulman Syndrome), causes TTP. Therefore VWD and TTP represent the opposite manifestations of VWF related disorders, tightly linked to each other.

Elevated preoperative von Willebrand factor is associated with perioperative thrombosis in infants and neonates with congenital heart disease

Essentials Perioperative thrombosis is a major cause of morbidity and mortality in congenital heart disease. Neonates and infants undergoing repair of congenital heart lesions were prospectively followed. Elevated von Willebrand factor (VWF) to ADAMTS-13 activity ratios typified the postoperative period. Thrombosis was associated with preoperative VWF activity and cryoprecipitate transfusion SUMMARY: Background The surgical repair of congenital heart malformations is frequently complicated by perioperative thrombosis of unclear etiology. An imbalance between von Willebrand factor (VWF) and ADAMTS-13 is an emerging variable in thrombosis. Objectives To describe perioperative changes to VWF, ADAMTS-13 and NETosis, and evaluate clinical and biochemical associations with postoperative thrombosis. Methods Neonates and infants undergoing palliation or definitive surgical repair of congenital heart malformations were recruited (n = 133). Preoperative and postoperative plasma levels of VWF, ADAMTS-13 and markers of NETosis were determined. Patients were followed for up to 30 days for the occurrence of thrombosis. Univariate and multivariate logistic regression analyses were conducted to identify variables associated with thrombosis. Results We identified significant postoperative increases in VWF activity, VWF level, DNA-histone complexes and cell-free DNA with an overall decrease in ADAMTS-13 activity. Patients experiencing postoperative thrombotic events (9%) were characterized by surgery performed at a lower intraoperative temperature, higher preoperative lactic acid levels, and higher preoperative VWF activity and level. A multivariate logistic regression model identified preoperative VWF activity (odds ratio (OR) 8.39 per IU mL-1 , 95% confidence interval [CI] 1.73-40.55) and transfusion of cryoprecipitate (OR 1.10 per mL kg-1 , 95% CI 1.03-1.17) as being associated with thrombosis. Conclusions Pediatric patients undergoing surgical repair of congenital heart malformations are exposed to high levels of VWF with diminished or minimal change to ADAMTS-13 in the immediate postoperative period. Elevated preoperative VWF activity is associated with postoperative thrombosis in pediatric congenital heart disease.

Thrombotic thrombocytopenic purpura: pathogenesis, diagnosis and potential novel therapeutics

Thrombotic thrombocytopenic purpura (TTP), a potentially fatal clinical syndrome, is primarily caused by autoantibodies against the von Willebrand factor (VWF)-cleaving metalloprotease ADAMTS-13. In general, severe deficiency of plasma ADAMTS-13 activity (< 10 IU dL-1 ) with or without detectable inhibitory autoantibodies against ADAMTS-13 supports the diagnosis of TTP. A patient usually presents with thrombocytopenia and microangiopathic hemolytic anemia (i.e. schistocytes, elevated serum lactate dehydrogenase, decreased hemoglobin and haptoglobin) without other known etiologies that cause thrombotic microangiopathy (TMA). Normal to moderately reduced plasma ADAMTS-13 activity (> 10 IU dL-1 ) in a similar clinical context supports an alternative diagnosis such as atypical hemolytic uremic syndrome (aHUS) or other types of TMA. Prompt differentiation of TTP from other causes of TMA is crucial for the initiation of an appropriate therapy to reduce morbidity and mortality. Although plasma infusion is often sufficient for prophylaxis or treatment of hereditary TTP due to ADAMTS-13 mutations, daily therapeutic plasma exchange remains the initial treatment of choice for acquired TTP with demonstrable autoantibodies. Immunomodulatory therapies, including corticosteroids, rituximab, vincristine, cyclosporine, cyclophosphamide and splenectomy, etc., should be considered to eliminate autoantibodies for a sustained remission. Other emerging therapeutic modalities, including recombinant ADAMTS-13, adeno-associated virus (AAV) 8-mediated gene therapy, platelet-delivered ADAMTS-13, and antagonists targeting the interaction between platelet glycoprotein 1b and VWF are under investigation. This review highlights the recent progress in our understanding of the pathogenesis and diagnosis of, and current and potential novel therapies for, hereditary and acquired TTP.

Kinetics of plasma von Willebrand factor in acute myocardial infarction patients: a meta-analysis

Previous studies have shown a variation in plasma level of von Willebrand factor (vWF) in acute myocardial infarction (AMI) patients but with contentious results. In this study, we performed a meta-analysis to evaluate the kinetics of plasma vWF after AMI. A total of 11 qualified studies were obtained through systematical search in PubMed, Web of science, Cochrane Library database and CNKI, followed by search of reference lists, involving 519 AMI patients and 466 non-AMI controls. The standard mean difference (SMD) and 95% confidence intervals (95% CI) were calculated using random-effects model. Results indicated that the plasma vWF was significantly increased in the first several hours after onset of AMI (SMD = 1.94, 95% CI = 1.39-2.48, P < 0.001) and stayed at high level until 24 h (SMD = 1.17, 95% CI = 0.45-1.89, P = 0.001). Elevated level of vWF appeared to persist for one week and reduced to normal until the fourteenth day after AMI (SMD = 0.44, 95% CI = -0.14-1.02, P = 0.14). Subgroup analysis revealed that the high level of vWF lasted just for 1 day in patients with a symptom duration ≤ 6 h before admission. For patients with a symptom duration > 6 h, elevated vWF was found in all 7 days except day 1. Our findings determined the kinetics of plasma vWF after AMI, and might provide a new insight in monitoring AMI progression.

Clinical features and outcomes in patients with thrombotic microangiopathy not associated with severe ADAMTS13 deficiency

BACKGROUND

The a disintegrin and metalloprotease with thrombospondin type 1 motifs, member 13 (ADAMTS13) activity assay has become important in distinguishing autoimmune thrombotic thrombocytopenic purpura from other forms of thrombotic microangiopathy (TMA). Although the significance of severe deficiency in ADAMTS13 (activity levels 10% or less) has been well defined, little data are available on the clinical importance of mild to moderate deficiency (activity levels 11%-70%) among patients with TMA.

STUDY DESIGN AND METHODS

We conducted a retrospective study using the Harvard TMA Research Collaborative Registry. Among 254 patients who met the inclusion criteria for TMA, 186 patients with ADAMTS13 activity levels greater than 10% were divided into moderate-deficiency (11%-40%), mild-deficiency (41%-70%), and no-deficiency (greater than 70%).

RESULTS

Compared with mild or no deficiency, moderate ADAMTS13 deficiency correlated with older age; higher bilirubin and international normalized ratio; and increased frequency of sepsis, shock, or multiorgan failure. Platelet counts, lactate dehydrogenase levels, and the presence of renal or neurologic dysfunction did not vary across the three patient cohorts. While moderate ADAMTS13 deficiency was associated with increased 90-day mortality in univariate analysis, this association was no longer significant in multivariate analysis. Variables that independetly predicted 90-day mortality in this cohort of patients included Charlson comorbidity index, alanine aminotransferase level, platelet count, creatinine, and the presence of sepsis, shock, or multiorgan failure.

CONCLUSION

Moderately deficient ADAMTS13 activity identifies a cohort of patients with TMA who are at increased risk for 90-day mortality. The ADAMTS13 activity level in this group is not an independent predictor of poor outcomes but instead appears to be a marker of disease acuity.

siRNA-knockdown of ADAMTS-13 modulates endothelial cell angiogenesis

ADAMTS-13, a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13, is a zinc-containing metalloprotease that cleaves von Willebrand factor (vWf). Previous publications by our laboratory have shown that ADAMTS-13 may also be involved in angiogenesis. For this study, we report the successful transient knockdown of endogenous ADAMTS-13 in human umbilical vein endothelial cells (HUVEC) via siRNA and the effects of reduced endogenous ADAMTS-13 on HUVEC angiogenesis functions. 15nM of ADAMTS-13 siRNA reduced HUVEC ADAMTS-13 protein levels by 90% after 24h incubation, whereas control siRNA did not affect endogenous ADAMTS-13 levels. Furthermore, this transfection did not affect the HUVEC endogenous protein level of ADAMTS-1, a related family member of ADAMTS-13 indicating the specificity of the siRNA. Transfection of HUVEC with 15nM of ADAMTS-13 siRNA resulted in a 21% decrease in proliferation after 24h incubation. The effects of ADAMTS-13 knockdown on migration of HUVEC across a scratch wound were also evaluated. 24h after transfection with control siRNA, there was increased cell migration across the scratch wound. This dramatic migration did not occur with ADAMTS-13 knockdown cells. Decreased protein levels of endogenous ADAMTS-13 also affected angiogenesis as measured by endothelial cell tube formation using a Matrigel matrix method. The tube lengths, sizes and junction numbers of the ADAMTS-13 knockdown cells were all significantly lower compared to control cells by about 40%. The protein level of vascular endothelial growth factor (VEGF), a well-known regulator of angiogenesis, was significantly decreased by 45% upon knockdown of ADAMTS-13. Moreover, activity of the AKT pathway, one of the VEGF angiogenesis downstream signaling pathways was down-regulated by ADAMTS-13 siRNA. These data indicate that in cultured endothelial cells, one role of endogenous ADAMTS-13 is regulation of angiogenesis, mediated through VEGF and AKT signaling pathway. Overall, our data suggest an additional model of endogenous ADAMTS-13 functionality, beyond that of cleaving von Willebrand factor.

Thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP; also known as Moschcowitz disease) is characterized by the concomitant occurrence of often severe thrombocytopenia, microangiopathic haemolytic anaemia and a variable degree of ischaemic organ damage, particularly affecting the brain, heart and kidneys. Acute TTP was almost universally fatal until the introduction of plasma therapy, which improved survival from <10% to 80-90%. However, patients who survive an acute episode are at high risk of relapse and of long-term morbidity. A timely diagnosis is vital but challenging, as TTP shares symptoms and clinical presentation with numerous conditions, including, for example, haemolytic uraemic syndrome and other thrombotic microangiopathies. The underlying pathophysiology is a severe deficiency of the activity of a disintegrin and metalloproteinase with thrombospondin motifs 13 (ADAMTS13), the protease that cleaves von Willebrand factor (vWF) multimeric strings. Ultra-large vWF strings remain uncleaved after endothelial cell secretion and anchorage, bind to platelets and form microthrombi, leading to the clinical manifestations of TTP. Congenital TTP (Upshaw-Schulman syndrome) is the result of homozygous or compound heterozygous mutations in ADAMTS13, whereas acquired TTP is an autoimmune disorder caused by circulating anti-ADAMTS13 autoantibodies, which inhibit the enzyme or increase its clearance. Consequently, immunosuppressive drugs, such as corticosteroids and often rituximab, supplement plasma exchange therapy in patients with acquired TTP.

A mechanistic investigation of thrombotic microangiopathy associated with IV abuse of Opana ER

Since 2012, a number of case reports have described the occurrence of thrombotic microangiopathy (TMA) following IV abuse of extended-release oxymorphone hydrochloride (Opana ER), an oral opioid for long-term treatment of chronic pain. Here, we present unique clinical features of 3 patients and investigate IV exposure to the tablet's inert ingredients as a possible causal mechanism. Guinea pigs were used as an animal model to understand the hematopathologic and nephrotoxic potential of the inert ingredient mixture (termed here as PEO+) which primarily contains high-molecular-weight polyethylene oxide (HMW PEO). Microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury were found in a group of 3 patients following recent injection of adulterated extended-release oxymorphone tablets. Varying degrees of cardiac involvement and retinal ischemia occurred, with TMA evident on kidney biopsy. A TMA-like state also developed in guinea pigs IV administered PEO+. Acute tubular and glomerular renal injury was accompanied by nonheme iron deposition and hypoxia-inducible factor-1α upregulation in the renal cortex. Similar outcomes were observed following dosing with HMW PEO alone. IV exposure to the inert ingredients in reformulated extended-release oxymorphone can elicit TMA. Although prescription opioid abuse shows geographic variation, all physicians should be highly inquisitive of IV drug abuse when presented with cases of TMA.

ADAMTS13 activity as a novel risk factor for incident type 2 diabetes mellitus: a population-based cohort study

AIMS/HYPOTHESIS

ADAMTS13 is a protease that breaks down von Willebrand factor (VWF) multimers into smaller, less active particles. VWF has been associated with an increased risk of incident type 2 diabetes mellitus. Here, we determine whether ADAMTS13 activity and VWF antigen are associated with incident diabetes.

METHODS

This study included 5176 participants from the Rotterdam Study, a prospective population-based cohort study. Participants were free of diabetes at baseline and followed up for more than 20 years. Cox proportional hazards models were used to examine the association of ADAMTS13 activity and VWF antigen with incident diabetes.

RESULTS

ADAMTS13 activity was associated with an increased risk of incident diabetes (HR 1.17 [95% CI 1.08, 1.27]) after adjustment for known risk factors and VWF antigen levels. Although ADAMTS13 activity was positively associated with fasting glucose and insulin, the association with incident diabetes did not change when we adjusted for these covariates. ADAMTS13 activity was also associated with incident prediabetes (defined on the basis of both fasting and non-fasting blood glucose) after adjustment for known risk factors (HR 1.11 [95% CI 1.03, 1.19]), while the VWF antigen level was not. VWF antigen was associated with incident diabetes, but this association was attenuated after adjustment for known risk factors.

CONCLUSIONS/INTERPRETATION

ADAMTS13 activity appears to be an independent risk factor for incident prediabetes and type 2 diabetes. As the association between ADAMTS13 and diabetes did not appear to be explained by its cleavage of VWF, ADAMTS13 may have an independent role in the development of diabetes.

Von Willebrand factor processing

Von Willebrand factor (VWF) is a multimeric glycoprotein essential for primary haemostasis that is produced only in endothelial cells and megakaryocytes. Key to VWF's function in recruitment of platelets to the site of vascular injury is its multimeric structure. The individual steps of VWF multimer biosynthesis rely on distinct posttranslational modifications at specific pH conditions, which are realized by spatial separation of the involved processes to different cell organelles. Production of multimers starts with translocation and modification of the VWF prepropolypeptide in the endoplasmic reticulum to produce dimers primed for glycosylation. In the Golgi apparatus they are further processed to multimers that carry more than 300 complex glycan structures functionalized by sialylation, sulfation and blood group determinants. Of special importance is the sequential formation of disulfide bonds with different functions in structural support of VWF multimers, which are packaged, stored and further processed after secretion. Here, all these processes are being reviewed in detail including background information on the occurring biochemical reactions.

Blood biomarkers associated with neurological deterioration in patients with acute penetrating artery territory infarction: A multicenter prospective observational study

Background and purpose

Neurological deterioration in acute penetrating artery territory infarction is unpredictable and associated with unfavorable clinical outcomes. The aim of this prospective study was to clarify the cause of neurological worsening and predict clinical outcomes using blood biomarkers.

Methods

Eight Japanese stroke centers participated. Blood samples were obtained within 24 h (the first sampling) and on day 7 in hospital (the second sampling) in patients with penetrating artery territory infarction, arriving within two days of stroke onset. Symptomatic worsening was defined as a minimum increase of one point on the National Institutes of Health Stroke Scale. Poor outcome was defined as a modified Rankin Scale score of ≥3 at 90 days after ictus.

Results

Of the 89 patients, 25 (28%) had symptomatic worsening, and 25 (28%) had a poor outcome. Although tumor necrosis factor-alpha, high-sensitivity C-reactive protein levels were significantly increased in both groups at the second sampling, soluble lectin-like oxidized low-density lipoprotein receptor-1, CD40 ligand, and pro-adrenomedullin levels were significantly increased and ADAMTS13 activity was decreased in symptomatic worsening patients ( p < 0.05 for all). After multivariate adjustment, a low number of CD34+ cells at the first sampling was an independent predictor of poor outcome (odds ratio, 0.20; 95% confidence interval, 0.04–0.74, p = 0.011, per 1 cell/µl increase).

Conclusions

Blood biomarkers associated with atherosclerotic processes seem to be an indication for symptomatic worsening, and the number of CD34+ cells may help to predict three-month functional outcome in patients with penetrating artery territory infarction.

Low ADAMTS-13 activity and the risk of coronary heart disease - a prospective cohort study: the Rotterdam Study

Essentials An association between ADAMTS-13 and coronary heart disease (CHD) has been suggested. 5688 participants ≥ 55 years from the Rotterdam Study without a history of CHD were included. Over a median follow-up time of 9.7 years, 456 individuals suffered from CHD. Low ADAMTS-13 activity was associated with an increased CHD risk.

SUMMARY

Background The metalloprotease ADAMTS-13 cleaves high-molecular-weight von Willebrand factor multimers into smaller, less procoagulant forms. Low ADAMTS-13 activity is associated with an increased risk of ischemic stroke but its pathogenic role in coronary heart disease (CHD) is unclear. Objectives We aimed to determine the association between ADAMTS-13 activity and the risk of CHD in a large prospective population-based cohort study. Methods A total of 5688 participants of the Rotterdam Study, a population-based cohort study involving individuals aged ≥ 55 years without a history of CHD, were included. ADAMTS-13 activity was measured by the FRETS-VWF73 assay and VWF:Ag levels by ELISA. We assessed the association between ADAMTS-13 activity, VWF:Ag levels and CHD using Cox proportional hazard regression analysis, adjusting for cardiovascular risk factors. Results Over a median follow-up time of 9.7 years, 456 individuals suffered from CHD. A low ADAMTS-13 activity (quartile 1) was associated with an increased CHD risk (HR 1.42, 95% CI 1.07-1.89) compared with the reference highest quartile. Conclusions Low ADAMTS-13 activity is associated with an increased risk of CHD in the elderly, independently of VWF and established cardiovascular risk factors.

Microangiopathic haemolytic anaemia secondary to lupus nephritis: an important differential diagnosis of thrombotic thrombocytopenic purpura

Systemic lupus erythematosus (SLE) has been described as a cause of microangiopathic haemolytic anaemia (MAHA), however there is little literature to support this assertion. We report on three patients presenting with SLE and MAHA with a clinical picture indistinguishable from thrombotic thrombocytopenic purpura (TTP), who had underlying lupus nephritis. They all had significant proteinuria and normal Von Willebrand Factor cleaving protease (vWF-CP) levels. Their MAHA fitted better for haemolytic syndrome (HUS) and their cerebral signs were explained either by malignant hypertension or cerebral lupus. Their MAHA only improved when the appropriate treatment for lupus nephritis was given.

We propose that the previously described association between SLE and MAHA, in actuality relates to the underlying presence of lupus nephritis causing haemolytic uraemic syndrome, not TTP. Significant proteinuria was present in all cases of MAHA due to lupus nephritis, so may be a useful discriminatory sign. Furthermore the demonstration of a normal vWF-CP assay aided in the distinction between TTP and MAHA due to lupus nephritis. All our patients responded to mycophenolate mofetil suggesting this may be useful in other cases of lupus nephritis causing HUS. Lupus (2007) 16, 358—362.

Plasma ADAMTS13, von Willebrand Factor (VWF), and VWF Propeptide Profiles in Patients With Connective Tissue Diseases and Antiphospholipid Syndrome

Thrombotic thrombocytopenic purpura (TTP) frequently develops in patients with connective tissue diseases (CTDs). ADAMTS13 and von Willebrand factor (VWF) are closely related to the onset of TTP. We investigated the roles of ADAMTS13 and VWF in thrombotic events of patients with CTD. ADAMTS13 activity and VWF and VWF propeptide (VWFpp) levels in CTD, primary antiphospholipid antibody syndrome (pAPS), and controls were measured to examine their relationship with thrombosis. ADAMTS13 activity levels were significantly low in the patients with CTD but not in the patients with pAPS. No significant difference in the ADAMTS13 activity levels among the various CTD subgroups was found. The levels of VWF and VWFpp were significantly elevated in the patients with pAPS and CTD compared with that of control groups. Eleven patients with CTD developed TTP, and their ADAMTS13 activity levels were significantly lower than patients having CTD without TTP. However, the ADAMTS13 activity levels showed no difference between the patients having CTD with and without thrombotic events. The VWF antigen levels were significantly high in the patients having CTD with TTP. There were no significant differences in the VWF levels of the patients having CTD with TTP and thrombosis. The VWFpp levels were significantly high in the patients having CTD with TTP and thrombosis. The VWF and VWFpp levels were significantly high in the patients with pAPS. Decreased ADAMTS13 activity and elevated VWF and VWFpp levels were observed in patients with CTD. These abnormalities in patients with CTD may represent the increased risk of thrombosis in CTD.

Low ADAMTS13 activity is associated with an increased risk of ischemic stroke

ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin motif repeats 13) has antithrombotic properties because it cleaves von Willebrand factor (VWF) in smaller, less active multimers. The aim of our study was to investigate prospectively the association between ADAMTS13 activity and ischemic stroke. We included 5941 individuals ≥55 years without a history of stroke or transient ischemic attack (TIA) of the Rotterdam Study, a population-based cohort study. ADAMTS13 activity was measured at inclusion with the FRETS-VWF73 assay and VWF antigen (VWF:Ag) levels by enzyme-linked immunosorbent assay. We assessed the association among ADAMTS13 activity, VWF:Ag levels, and ischemic stroke by Cox proportional hazard analysis. The added value of ADAMTS13 activity above the traditional risk factors for ischemic stroke risk prediction was examined by the C-statistic and the net reclassification improvement index (NRI). All individuals were followed for incident stroke or TIA. Over a median follow-up time of 10.7 years (56,403 total person-years), 461 participants had a stroke, 306 of which were ischemic. After adjustment for cardiovascular risk factors, individuals with ADAMTS13 activity in the lowest quartile had a higher risk of ischemic stroke (absolute risk, 7.3%) than did those in the reference highest quartile (absolute risk, 3.8%; hazard ratio, 1.65; 95% confidence interval [CI], 1.16-2.32). Adding ADAMTS13 to the model in prediction of ischemic stroke, increased the C-statistic by 0.013 (P = .003) and provided 0.058 (95% CI, -0.002 to 0.119) NRI. Low ADAMTS13 activity is associated with the risk of ischemic stroke and improves the accuracy of risk predictions for ischemic stroke beyond traditional risk factors.

ADAMTS13 and von Willebrand factor in thrombotic thrombocytopenic purpura

Pathogenesis of thrombotic thrombocytopenic purpura (TTP) was a mystery for over half a century until the discovery of ADAMTS13. ADAMTS13 is primarily synthesized in the liver, and its main function is to cleave von Willebrand factor (VWF) anchored on the endothelial surface, in circulation, and at the sites of vascular injury. Deficiency of plasma ADAMTS13 activity (<10%) resulting from mutations of the ADAMTS13 gene or autoantibodies against ADAMTS13 causes hereditary or acquired (idiopathic) TTP. ADAMTS13 activity is usually normal or modestly reduced (>20%) in other forms of thrombotic microangiopathy secondary to hematopoietic progenitor cell transplantation, infection, and disseminated malignancy or in hemolytic uremic syndrome. Plasma infusion or exchange remains the initial treatment of choice to date, but novel therapeutics such as recombinant ADAMTS13 and gene therapy are under development. Moreover, ADAMTS13 deficiency has been shown to be a risk factor for the development of myocardial infarction, stroke, cerebral malaria, and preeclampsia.

Genetic variants in the ADAMTS13 and SUPT3H genes are associated with ADAMTS13 activity

We identify rs41314453 as the strongest genetic predictor of ADAMTS13 activity, associated with a decrease of >20%. We present evidence of further independent associations with a common variant in SUPT3H, as well as 5 variants at the ADAMTS13 locus.

Nxf1 natural variant E610G is a semi-dominant suppressor of IAP-induced RNA processing defects

Endogenous retroviruses and retrotransposons contribute functional genetic variation in animal genomes. In mice, Intracisternal A Particles (IAPs) are a frequent source of both new mutations and polymorphism across laboratory strains. Intronic IAPs can induce alternative RNA processing choices, including alternative splicing. We previously showed IAP I∆1 subfamily insertional mutations are suppressed by a wild-derived allele of the major mRNA export factor, Nxf1. Here we show that a wider diversity of IAP insertions present in the mouse reference sequence induce insertion-dependent alternative processing that is suppressed by Nxf1CAST alleles. These insertions typically show more modest gene expression changes than de novo mutations, suggesting selection or attenuation. Genome-wide splicing-sensitive microarrays and gene-focused assays confirm specificity of Nxf1 genetic modifier activity for IAP insertion alleles. Strikingly, CRISPR/Cas9-mediated genome editing demonstrates that a single amino acid substitution in Nxf1, E610G, is sufficient to recreate a quantitative genetic modifier in a co-isogenic background.

ADAMTS proteases and cancer

ADAMTSs (A disintegrin and metalloprotease domains with thrombospondins motifs) are complex extracellular proteases that have been related to both oncogenic and tumor-protective functions. These enzymes can be secreted by cancer and stromal cells and may contribute to modify the tumor microenvironment by multiple mechanisms. Thus, ADAMTSs can cleave or interact with a wide range of extracellular matrix components or regulatory factors, and therefore affect cell adhesion, migration, proliferation and angiogenesis. The balance of protumor versus antitumor effects of ADAMTSs may depend on the nature of their substrates or interacting-partners upon secretion from the cell. Moreover, different ADAMTS genes have been found overexpressed, mutated or epigenetically silenced in tumors from different origins, suggesting the direct impact of these metalloproteases in cancer development. However, despite the important advances on the tumor biology of ADAMTSs in recent years, more mechanistic and functional studies are necessary to fully understand how these proteases can influence tumor microenvironment to potentiate cancer growth or to induce tumor regression. This review outlines current and emerging connections between ADAMTSs and cancer.

Allosteric activation of ADAMTS13 by von Willebrand factor

The metalloprotease ADAMTS13 cleaves von Willebrand factor (VWF) within endovascular platelet aggregates, and ADAMTS13 deficiency causes fatal microvascular thrombosis. The proximal metalloprotease (M), disintegrin-like (D), thrombospondin-1 (T), Cys-rich (C), and spacer (S) domains of ADAMTS13 recognize a cryptic site in VWF that is exposed by tensile force. Another seven T and two complement C1r/C1s, sea urchin epidermal growth factor, and bone morphogenetic protein (CUB) domains of uncertain function are C-terminal to the MDTCS domains. We find that the distal T8-CUB2 domains markedly inhibit substrate cleavage, and binding of VWF or monoclonal antibodies to distal ADAMTS13 domains relieves this autoinhibition. Small angle X-ray scattering data indicate that distal T-CUB domains interact with proximal MDTCS domains. Thus, ADAMTS13 is regulated by substrate-induced allosteric activation, which may optimize VWF cleavage under fluid shear stress in vivo. Distal domains of other ADAMTS proteases may have similar allosteric properties.

ADAMTS-13 in the Diagnosis and Management of Thrombotic Microangiopathies

Thrombotic microangiopathies (TMAs) comprise a group of distinct disorders characterized by microangiopathic hemolytic anemia, thrombocytopenia, and microvascular thrombosis. For many years distinction between these TMAs, especially between thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS), remained purely clinical and hard to make. Recent discoveries shed light on different pathogenesis of TTP and HUS. Ultra-large von Willebrand factor (UL-VWF) platelet thrombi, resulting from the deficiency of cleavage protease which is now known as ADAMTS-13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), were found to cause TTP pathology, while Shiga toxins or abnormalities in regulation of the complement system cause microangiopathy and thrombosis in HUS. TMAs may appear in various conditions such as pregnancy, inflammation, malignancy, or exposure to drugs. These conditions might cause acquired TTP, HUS, or other TMAs, or might be a trigger in individuals with genetic predisposition to ADAMTS-13 or complement factor H deficiency. Differentiation between these TMAs is highly important for urgent initiation of appropriate therapy. Measurement of ADAMTS-13 activity and anti-ADAMTS-13 antibody levels may advance this differentiation resulting in accurate diagnosis. Additionally, assessment of ADAMTS-13 levels can be a tool for monitoring treatment efficacy and relapse risk, allowing consideration of therapy addition or change. In the past few years, great improvements in ADAMTS-13 assays have been made, and tests with increased sensitivity, specificity, reproducibility, and shorter turnaround time are now available. These new assays enable ADAMTS-13 measurement in routine clinical diagnostic laboratories, which may ultimately result in improvement of TMA management.