Essentials
Conformational changes in ADAMTS‐13 are part of its mode‐of‐action.
The murine anti‐ADAMTS‐13 antibody 1C4 discriminates between folded and open ADAMTS‐13.
ADAMTS‐13 conformation is open ...in acute acquired thrombotic thrombocytopenic purpura (TTP).
Our study forms an important basis to fully elucidate the pathophysiology of TTP.
Summary
Background
Acquired thrombotic thrombocytopenic purpura (aTTP) is an autoimmune disorder characterized by absent ADAMTS‐13 activity and the presence of anti‐ADAMTS‐13 autoantibodies. Recently, it was shown that ADAMTS‐13 adopts a folded or an open conformation.
Objectives
As conformational changes in self‐antigens play a role in the pathophysiology of different autoimmune diseases, we hypothesized that the conformation of ADAMTS‐13 changes during acute aTTP.
Methods
Antibodies recognizing cryptic epitopes in the spacer domain were generated. Next, the conformation of ADAMTS‐13 in 40 healthy donors (HDs), 99 aTTP patients (63 in the acute phase versus 36 in remission), 12 hemolytic–uremic syndrome (HUS) patients and 63 sepsis patients was determined with ELISA.
Results
The antibody 1C4 recognizes a cryptic epitope in ADAMTS‐13. Therefore, we were able to discriminate between a folded and an open ADAMTS‐13 conformation. We showed that ADAMTS‐13 in HDs does not bind to 1C4, indicating that ADAMTS‐13 circulates in a folded conformation. Similar results were obtained for HUS and sepsis patients. In contrast, ADAMTS‐13 of acute aTTP patients bound to 1C4 in 92% of the cases, whereas, in most cases, this binding was abolished during remission, showing that the conformation of ADAMTS‐13 is open during an acute aTTP episode.
Conclusions
Our study shows that, besides absent ADAMTS‐13 activity and the presence of anti‐ADAMTS‐13 autoantibodies, an open ADAMTS‐13 conformation is also a hallmark of acute aTTP. Demonstrating this altered ADAMTS‐13 conformation in acute aTTP will help to further unravel the pathophysiology of aTTP and lead to improved therapy and diagnosis.
Essentials
An international collaboration provides a consensus for clinical definitions.
This concerns thrombotic microangiopathies and thrombotic thrombocytopenic purpura (TTP).
The consensus ...defines diagnosis, disease monitoring and response to treatment.
Requirements for ADAMTS‐13 are given.
Summary
Background
Thrombotic thrombocytopenic purpura (TTP) and hemolytic–uremic syndrome (HUS) are two important acute conditions to diagnose. Thrombotic microangiopathy (TMA) is a broad pathophysiologic process that leads to microangiopathic hemolytic anemia and thrombocytopenia, and involves capillary and small‐vessel platelet aggregates. The most common cause is disseminated intravascular coagulation, which may be differentiated by abnormal coagulation. Clinically, a number of conditions present with microangiopathic hemolytic anemia and thrombocytopenia, including cancer, infection, transplantation, drug use, autoimmune disease, and pre‐eclampsia and hemolysis, elevated liver enzymes and low platelet count syndrome in pregnancy. Despite overlapping clinical presentations, TTP and HUS have distinct pathophysiologies and treatment pathways.
Objectives
To present a consensus document from an International Working Group on TTP and associated thrombotic microangiopathies (TMAs).
Methods
The International Working Group has proposed definitions and terminology based on published information and consensus‐based recommendations.
Conclusion
The consensus aims to aid clinical decisions, but also future studies and trials, utilizing standardized definitions. It presents a classification of the causes of TMA, and criteria for clinical response, remission and relapse of congenital and immune‐mediated TTP.
Background: ADAMTS13‐neutralizing IgG autoantibodies are the major cause of acquired thrombotic thrombocytopenic purpura (TTP). Objective: To analyze the IgG subclass distribution of anti‐ADAMTS13 ...antibodies and a potential relationship between subclass distribution and disease prognosis. Methodology: An enzyme‐linked immunosorbent assay‐based method was used to quantify the relative amounts of IgG subclasses of anti‐ADAMTS13 antibodies in acquired TTP plasma. Results: IgG4 (52/58, 90%) was the most prevalent IgG subclass in patients with acquired TTP, followed by IgG1 (52%), IgG2 (50%), and IgG3 (33%). IgG4 was found either alone (17/52) or with other IgG subclasses (35/52). IgG4 was not detected in 10% of the patients. There was an inverse correlation between the frequency and abundance of IgG4 and IgG1 antibodies (P < 0.01). Patients with high IgG4 levels and undetectable IgG1 are more prone to relapse than patients with low IgG4 levels and detectable IgG1. Conclusions: All IgG subclasses of anti‐ADAMTS13 antibodies were detected in patients with acquired TTP, with IgG4, followed by IgG1, antibodies dominating the anti‐ADAMTS13 immune response. Levels of IgG4 could be useful for the identification of patients at risk of disease recurrence.
Summary
Background
Cardiac involvement is a major cause of mortality in patients with thrombotic thrombocytopenic purpura (TTP). However, diagnosis remains underestimated and delayed, owing to ...subclinical injuries. Cardiac troponin‐I measurement (cTnI) on admission could improve the early diagnosis of cardiac involvement and have prognostic value.
Objectives
To assess the predictive value of cTnI in patients with TTP for death or refractoriness.
Patients/Methods
The study involved a prospective cohort of adult TTP patients with acquired severe ADAMTS‐13 deficiency (< 10%) and included in the registry of the French Reference Center for Thrombotic Microangiopathies. Centralized cTnI measurements were performed on frozen serum on admission.
Results
Between January 2003 and December 2011, 133 patients with TTP (mean age, 48 ± 17 years) had available cTnI measurements on admission. Thirty‐two patients (24%) had clinical and/or electrocardiogram features. Nineteen (14.3%) had cardiac symptoms, mainly congestive heart failure and myocardial infarction. Electrocardiogram changes, mainly repolarization disorders, were present in 13 cases. An increased cTnI level (> 0.1 μg L−1) was present in 78 patients (59%), of whom 46 (59%) had no clinical cardiac involvement. The main outcomes were death (25%) and refractoriness (17%). Age (P = 0.02) and cTnI level (P = 0.002) showed the greatest impact on survival. A cTnI level of > 0.25 μg L−1 was the only independent factor in predicting death (odds ratio OR 2.87; 95% confidence interval CI 1.13–7.22; P = 0.024) and/or refractoriness (OR 3.03; 95% CI 1.27–7.3; P = 0.01).
Conclusions
A CTnI level of > 0.25 μg L−1 at presentation in patients with TTP appears to be an independent factor associated with a three‐fold increase in the risk of death or refractoriness. Therefore, cTnI level should be considered as a prognostic indicator in patients diagnosed with TTP.
Essentials
Cancer patients are at high risk of venous thromboembolism (VTE).
In this study, cases and controls were cancer patients who did or did not develop VTE.
von Willebrand factor (VWF) levels ...were higher if compared with controls and correlated with cancer stage.
VWF and ADAMTS‐13 are associated with the occurrence of VTE in cancer.
Summary
Background
Patients with cancer are at high risk of venous thromboembolism (VTE). ADAMTS‐13 regulates von Willebrand factor (VWF) activity, which plays a role in the development of cancer and in VTE.
Objectives
The aim of this study was to search for an association between the levels of VWF and ADAMTS‐13 and VTE in patients with cancer and to compare current scoring systems for prediction of VTE before and after addition of these parameters.
Patients/Methods
In a case–control study, in which patients with recently diagnosed cancer were followed‐up for 6 months, we compared 20 patients who developed VTE (cases) and 140 patients with cancer without VTE (controls), matched for sex, age, and type and stage of cancer. We measured VWF, ADAMTS‐13 (activity and antigen), P‐selectin, D‐dimer and F1 + 2 levels at baseline, and calculated both the Khorana score and the Khorana score expanded after addition of P‐selectin and D‐dimer levels.
Results
VWF levels were significantly higher in cases when compared with controls (326 ± 185% vs. 242 ± 158%) and correlated with advanced stage of cancer: localized, 185 142; 222; locally advanced, 240 146; 257; metastatic, 267 153; 324 (mean interquartile range). The addition of two biomarkers, ADAMTS‐13 activity and F1 + 2 levels, to the Khorana score improved receiver operating curves.
Conclusions
von Willebrand factor and ADAMTS‐13 are associated with the occurrence of VTE in patients with cancer. Moreover, addition of ADAMTS‐13 and F1 + 2 levels to the Khorana score considerably increases the predictive value for VTE.
Summary
Background
Among patients with thrombotic microangiopathies, acute kidney injury (AKI) is the hallmark of hemolytic uremic syndrome (HUS) and is largely underestimated in patients with ...thrombotic thrombocytopenic purpura (TTP).
Objective
We sought to report AKI features and outcomes in patients with TTP.
Methods
We conducted a retrospective study of 92 patients with TTP assessed by low ADAMTS13 activity (< 10%) between 2001 and 2013. A logistic regression identified variables independently associated with AKI.
Results
Among the 92 patients, 54 (58.7%) presented with AKI, including 25 (46.3%) with stage 3 AKI. Fourteen (27.4%) patients had a nephrotic‐range proteinuria and 21 (45.6%) had hemoglobinuria. Hematuria and leucocyturia were detected in 19 (41.3%) and 16 patients (36.4%), respectively. Renal replacement therapy (RRT) was required in 14 patients (25.9%). Six months after TTP remission, RRT‐free patients had median (IQR) MDRD (Modification of Diet in Renal Disease formula estimating the glomerular filtration rate) of 93 mL min−1 per 1.73 m2 (68.8–110) and three patients required long‐term dialysis. Mild or moderate chronic renal disease occurred in 23/54 (42.6%) AKI patients. By multivariate analysis, serum level of complement component 3 at admission was the only factor independently associated with AKI (OR per 0.25 unit decrease of C3, 0.85; CI, 1.82–8.33; P = 0.001).
Conclusions
In patients with TTP, AKI is present in more than half the patients, and half of those will have lasting renal effects. Further studies to better understand the pathophysiology of renal involvement in patients with TTP and to identify a subset of patients with TTP syndrome overlapping HUS are warranted.
Thrombotic thrombocytopenic purpura (TTP) is a devastating disease characterized by disseminated microvascular thrombosis. Despite pro-thrombotic predisposing conditions, the prevalence of ...macrovascular venous thrombosis event (VTE) in immune-mediated TTP (iTTP) has rarely been assessed.
We reviewed data of all iTTP patients of the French reference Center for thrombotic microangiopathies registry prospectively enrolled through a 10-year period, between 2008 and 2018. Venous thrombosis included either thrombosis of central venous catheter, symptomatic deep venous thrombosis of the limbs or pulmonary embolism.
Forty-eight (12.7%) VTE were diagnosed. VTE was diagnosed after a median time of 7 IQR, 3-16 days following the first therapeutic plasma exchange (TPE) and consisted mainly in catheter-related thrombosis (73%), and to a lesser extend symptomatic deep venous thrombosis (16%), proximal pulmonary embolism (8%) and splanchnic vein thrombosis (2%). Cases with VTE (VTE+ cases), required more TPE to achieve remission (P < 0.01), and the total volume of plasma required to achieve remission was larger (P < 0.01) than for VTE- cases. There was also a trend for more rituximab use in the VTE+ cases as compared to the VTE- cases (47% vs 33%; respectively; P = 0.07). Curative anticoagulation was started in 38 cases (79%), while 6 VTE cases did not receive any antithrombotic agents, and catheter was systematically removed when catheter-related thrombosis was diagnosed. VTE+ cases had a higher number of inserted central venous catheters than VTE- cases (P < 0.05).
VTE is a frequent condition occurring during iTTP management and is observed when patients require a prolonged treatment with daily TPE and multiple catheter insertions. Therapeutic strategies aimed at reducing the duration of TPE treatment in iTTP should substantially reduce this complication.
Essentials
Plasmin is able to proteolyse von Willebrand factor.
It was unclear if plasmin influences acute thrombotic thrombocytopenic purpura (TTP).
Plasmin levels are increased during acute TTP ...though suppressed via plasmin(ogen) inhibitors.
Allowing amplified endogenous plasmin activity in mice results in resolution of TTP signs.
Summary
Background
Thrombotic thrombocytopenic purpura (TTP) is an acute life‐threatening pathology, caused by occlusive von Willebrand factor (VWF)‐rich microthrombi that accumulate in the absence of ADAMTS‐13. We previously demonstrated that plasmin can cleave VWF and that plasmin is generated in patients during acute TTP. However, the exact role of plasmin in TTP remains unclear.
Objectives
Investigate if endogenous plasmin‐mediated proteolysis of VWF can influence acute TTP episodes.
Results
In mice with an acquired ADAMTS‐13 deficiency, plasmin is generated during TTP as reflected by increased plasmin‐α2‐antiplasmin (PAP)‐complex levels. However, mice still developed TTP, suggesting that this increase is not sufficient to control the pathology. As mice with TTP also had increased plasminogen activator inhibitor 1 (PAI‐1) levels, we investigated whether blocking the plasmin(ogen) inhibitors would result in the generation of sufficient plasmin to influence TTP outcome in mice. Interestingly, when amplified plasmin activity was allowed (α2‐antiplasmin−/− mice with inhibited PAI‐1) in mice with an acquired ADAMTS‐13 deficiency, a resolution of TTP signs was observed as a result of an increased proteolysis of VWF. In line with this, in patients with acute TTP, increased PAP‐complex and PAI‐1 levels were also observed. However, neither PAP‐complex levels nor PAI‐1 levels were related to TTP signs and outcome.
Conclusions
In conclusion, endogenous plasmin levels are increased during acute TTP, although limited via suppression through α2‐antiplasmin and PAI‐1. Only when amplified plasmin activity is allowed, plasmin can function as a back‐up for ADAMTS‐13 in mice and resolve TTP signs as a result of an increased proteolysis of VWF.
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