Factor In Thrombotic Thrombocytopenic Purpura Research Articles

Analysis of clinical and laboratory characteristics in 42 patients with thrombotic thrombocytopenic purpura from a single center in China

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening disease characterized by microvascular platelet deposition and thrombus formation with resulting microangiopathic hemolytic anemia. Deficiency of the von Willebrand factor cleavage protease, also known as ADAMTS 13, has been implicated as an important etiological factor in TTP. Little studies were obtained on Chinese patients with TTP until now. Our aim was to analyze the clinical features, outcome and laboratory characteristics of Chinese TTP patients, and determine whether plasma ADAMTS 13 activity is decreased in TTP and its diagnostic value for TTP. Forty-two TTP patients (29 females; 13 males) admitted to our hospital from 1998 to 2010 were analyzed. There were 34 patients (81%) with the triad of TTP, including hemolytic anemia, thrombocytopenia and neurologic abnormalities; 7 (16.7%) had the classical pentad of TTP. Major etiologic factors were acquired autoimmunological abnormalities (31%); no familial TTP was identified in this series. The schistocytes of peripheral blood smears were present in all cases with a mean frequency of 4.6% (range from 0.3% to 13.4%). Plasma ADAMTS 13 activity was determined in 22 patients with the FRET-vWF86 assay. Only 4 idiopathic TTP patients (18.2%) had severe ADAMTS 13 deficiency (activity<10%); 9 (40.9%) had moderate decrease of ADAMTS 13 activity (activity: 10-40%); another 9 (40.91%) had normal ADAMTS 13 activity (>40%). T lymphocyte subpopulation was measured in 23 TTP patients with FACS Calibur; 14 of the 23 (60.9%) had significantly decreased CD4 cells count and CD4/CD8 ratio, suggesting cellular immune dysfunction may be involved in the pathogenesis of TTP. In the studies, plasmapheresis is the main therapeutic method. 26 of 31 patients (83.9%) accepting plasmapheresis achieved complete remission; those patients who only underwent plasma infusion had low remission rate (18.2%) and high mortality (9/11; 81.8%). Four patients with packed RBC infusion manifested transient exacerbation of neurologic or psychiatric symptoms. In conclusion, the diagnosis of TTP in China is still based on clinical features including evidence of microangiopathic hemolysis. Severe ADAMTS 13 activity deficiency might be a valuable indicator for idiopathic TTP diagnosis. Further studies are needed to determine the real value of ADAMTS 13 activity for TTP diagnosis and whether T lymphocytes subset dysregulation plays important role in TTP pathogenesis.

Management of cancer‐associated thrombotic microangiopathy: What is the right approach?

A 49-year-old Caucasian woman presented with features suggestive of thrombotic microangiopathy (TMA). She did not respond to treatment with repeated plasma exchange and corticosteroids. A bone marrow biopsy revealed presence of metastatic carcinoma. A limited autopsy revealed presence of breast cancer with rib metastases. Though severe deficiency of von Willebrand factor-cleaving protease was initially proposed as a key pathogenetic factor for thrombotic thrombocytopenic purpura, subsequent studies involving patients with cancer-associated TMA did not find as severe a deficiency of von Willebrand factor-cleaving protease as is seen in idiopathic cases of thrombotic thrombocytopenic purpura. Here we address one approach of management of these patients with cancer-associated TMA.

The pathogenicity of von Willebrand factor in thrombotic thrombocytopenic purpura: reconsideration of treatment with cryopoor plasma

New developments in the understanding of thrombotic thrombocytopenic purpura (TTP) provide opportunities for improved patient care. A widely held historical model of TTP microvascular thrombosis implicated circulating ultra large von Willebrand factor (ULVWF) in causing spontaneous platelet (PLT) aggregation. From this pathogenic model, concerns about ULVWF in fresh-frozen plasma (FFP) used to treat patients led to widespread use of cryopoor plasma (CPP) as an alternative. There is scant evidence, however, that circulating ULVWF contributes to microvascular thrombosis in TTP. New evidence suggests that the formation of PLT aggregates in TTP may be mediated by VWF in the process of being released from endothelium. Moreover, clinical studies do not demonstrate superior efficacy of CPP compared to FFP in the treatment of TTP. Because CPP may have reduced concentrations of factors important in the treatment of TTP, including ADAMTS13 metalloprotease, a reappraisal of the use of CPP in the treatment of TTP is warranted.

Interplay between ADAMTS13 and von Willebrand factor in inherited and acquired thrombotic microangiopathies

The presence of unusually large multimers of von Willebrand factor (VWF) is thought to be a major pathogenic factor for thrombotic thrombocytopenic purpura (TTP). ADAMTS13 is a protease that regulates the multimeric size and function of VWF by cleaving VWF. Hence, congenital or acquired deficiency of ADAMTS13 causes life-threatening illness of TTP. Mutations in the ADAMTS13 gene cause inherited TTP, and the development of autoantibodies that inhibit ADAMTS13 activity frequently are associated with acquired TTP. ADAMTS13 consists of 1,427 amino acid residues and is composed of multiple structural and functional domains, containing a signal peptide, a propeptide, a reprolysin-like metalloprotease domain, a disintegrin-like domain, a thrombospondin type-1 (Tsp1) motif, a cysteine-rich domain, a spacer domain, seven additional Tsp1 repeats, and two CUB domains. In particular, the cysteine-rich/spacer domains are essential for VWF cleavage and are the principal epitopes recognized by autoantibodies in patients with acquired TTP. Therefore, it is likely that these domains are involved in the recognition and binding of ADAMTS13 to VWF. ADAMTS13 circulates in the blood in an active state, and efficiently cleaves unfold form of VWF induced under shear stress caused by blood flow, preventing the accumulation of pathogenic unusually large VWF multimers (ULVWF). Thus, ADAMTS13 helps maintain vascular homeostasis by preventing the excess thrombus formation.

Thrombotic thrombocytopenic purpura: Proposal of a new pathogenic mechanism involving Helicobacter pylori infection

Thrombotic thrombocytopenic purpura (TTP) is a severe, occlusive, thrombotic microangiopathy characterized by a systemic platelet aggregation, organ ischemia, profound thrombocytopenia and erythrocyte fragmentation. Recent observations have documented that a deficiency of a von Willebrand factor (VWF)-cleaving protease, termed ADAMTS13, that normally cleaves hyper-reactive unusually large VWF multimers into smaller and less adhesive VWF forms, may be responsible for many cases of TTP. Multiple mutations of the ADAMTS13 gene can result in ADAMTS13 deficiency and cause congenital TTP, while autoantibodies neutralizing ADAMTS13 protease activity have been associated with acquired TTP. However, in spite of the recent progresses in the pathophysiology of TTP, many aspects of this disease remain still controversial. In this study, basing on the laboratory results of a group of eight patients with an acquired form of TTP, an alternative pathogenic mechanism for TTP involving Helicobacter pylori infection is proposed. In fact, Helicobacter pylori, which has been recently implied in the pathogenesis of idiopathic thrombocytopenic purpura (ITP), could function as a triggering factor in TTP by inducing platelet aggregation through an interaction with VWF.

The Clinical Spectrum of Thrombotic Thrombocytopenic Purpura

The clinical syndrome of fever, neurologic abnormalities, renal impairment with laboratory findings of thrombocytopenic and microangiopathic hemolytic anemia is seen in thrombotic thrombocytopenic purpura (TTP) and a variety of disorders associated with thrombotic microangiopathy (TMA). With improved understanding of the pathogenesis of the perturbed metabolic pathway of von Willebrand factor in TTP, the classic Moschcowitz syndrome, now more accurately referred to as idiopathic TTP, can be distinguished from other TMAs. The distinguishing features are useful not only in providing an accurate diagnosis but also help to determine the best therapeutic strategy.

Von Willebrand Factor in Thrombotic Thrombocytopenic Purpura

IntroductionThrombotic thrombocytopenic purpura (TTP), a disseminated form of thrombotic microangiopathy, was initially described by Moschcowitz in 1924.1 TTP is defined by a pentad of findings, including severe thrombocytopenia, intravascular hemolysis with erythrocyte fragmentation, neurologic deficit, renal dysfunction, and fever.2–4 The thrombocytopenia occurs in the presence of normal or even increased numbers of megakaryocytes in the bone marrow, suggesting increased consumption. Platelet aggregates, found in the microcirculation, contain little if any fibrin polymers, indicating that activation of coagulation and fibrin formation may be secondary and limited in extent.About one-third of patients experience recurrent acute episodes at irregular and unpredictable intervals, whereas the majority of patients who recover from an acute TTP event experience no relapse and no persistent organ failure. TTP is usually classified as relapsing if complete remissions occurred between acute events and as chronic if complete recovery did not occur between bouts.Genetic predisposition to TTP has been shown in several siblings suffering from recurrent TTP.5 Thus, cases of TTP can be further divided according to whether the disease has a familial or genetic component or is not heritable. Acute episodes of TTP may be triggered by viral or bacterial infection, autoimmune disorders, bone marrow transplantation, drug therapy, cancer, chemotherapy, and pregnancy.3,4 The incidence of TTP is estimated to be two to eight cases per million people per year.3,6 Until four decades ago, the mortality rate was virtually 100% but has since decreased to less than 20% after introduction of plasma therapy. Still, there were more than 4,500 TTP-associated deaths recorded in the United States between 1968 and 1991.6

Acute pancreatitis as a triggering factor for thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) constitutes a poorly understood multisystemic disease of vascular origin that may involve any organ by thrombotic occlusions of the small vessels. Treatment with plasmapheresis is the best therapeutic option at this present moment. Involvement of the pancreas is a well established feature of this disease, which has generally been interpreted as a consequence of pancreatic vascular compromise. However, there are a few cases in the literature in which the clinical signs of TTP developed well after the clinical and laboratory demonstration of acute pancreatitis (AP). Therefore, the possibility of pancreatic inflammation as a triggering factor of TTP may need to be considered. This cause–effect relationship between AP and TTP remains unclear. We report a patient with chronic pancreatitis presenting with two episodes of TTP, triggered by acute relapses of pancreatitis. TTP may, thus, constitute a hematological complication of AP. We discuss the pathophysiological aspects of this association, along with therapeutical options.

Activated platelet aggregates in thrombotic thromboctyopenic purpura: decrease with plasma infusions and normalization in remission.

Circulating activated platelet aggregates (aPA) were assayed by flow cytometry employing mAb alpha-CD62p in eight patients with thrombotic thrombocytopenic purpura (TTP). Elevation of aPA was observed in all patients in active stages of TTP; aPA normalized in remission. Plasma infusions with plasmapheresis decreased aPA in responding patients. The rise and fall of aPA preceded relapses and improvements, respectively. These changes were seen prior to the traditional indicators, LDH, haematocrit, and platelet count. Incubation of plasma from TTP patients with normal whole blood induced formation of aPA; this effect was significantly greater than that of plasmas from ITP patient controls (P < 0.01), suggesting the presence of an aPA-promoting factor in TTP plasma. Parallel experiments using a platelet aggregometer failed to detect effect of TTP plasma on normal blood. In summary, aPA appear to be a marker of disease activity, rising with relapse, falling with plasma therapy, and normalizing in remission. The flow cytometric assay of aPA is more sensitive than aggregometry in detecting the putative aPA-promoting factor in TTP.

Isolation and characterization of cysteine proteinase in thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is an uncommon disorder characterized by thrombocytopenia, schistocytic haemolytic anaemia, fever, neurologic lesions, and renal failure. A platelet aggregating factor has been postulated to be responsible for this disorder, but its precise identity remains debated. Two different groups of investigators have provided evidence that the platelet aggregating factor is a cysteine proteinase. We have suggested that it was calpain, whereas others have suggested that it was calpain, whereas others have suggested that it was cathepsin L. To help resolve this issue, we have studied the platelet activating activity found in the acute serum samples from 10 different TTP patients as well as purified calpain and cathepsin L. The TTP activity was measured functionally (platelet serotonin release assay and casein lysis assay) and antigenically (immunodepletion using anti-calpain and anti-cathepsin L antibodies and antigenic analysis using SDS PAGE). The TTP serum paralleled the activity of the purified calpain and had optimal pH activity of 7.5. The purified cathepsin L activity had optimal activity at low pH (5.5) and activity was no longer measurable at pH 7.5. Similarly, a specific cathepsin L inhibitor (Z-Phe-Phe-CHN2) had no effect on the activity of the TTP samples nor on purified calpain, but it did abolish the activity activity of purified cathepsin L. The platelet activating of the TTP samples was detectable in the microparticle pellet following ultracentrifugation of TTP serum, and could be immunodepleted using antibodies to calpain but not to cathepsin L. These studies indicate that the microparticle-associated platelet activating factor in TTP corresponds to calpain.

Early plasmapheresis in patients with thrombotic thrombocytopenic purpura

To investigate the relationship of thrombotic thrombocytopenic purpura to adult respiratory distress syndrome (ARDS) and study the responses of thrombotic thrombocytopenic purpura patients to early plasmapheresis. Case series. ICU of a university hospital. Twenty-four consecutive patients with thrombotic thrombocytopenic purpura, with various periods of time (1 to 18 days) having elapsed since the onset of this condition. Patients ranged in age from 17 to 66 yrs. Plasmapheresis, using intermittent flow separators, was instituted soon after the patients' ICU admission. The retinoscopic findings on admission and the relationship of Pao2 to platelet counts before and after plasmapheresis therapy were recorded. Antiplatelet agents were given to the survivors to prevent relapses. Eighteen patients survived and six died. Plasmapheresis was administered for a range of 1 to 5 days (mean 3) and 3 to 18 days (mean 9.8) in survivors and nonsurvivors, respectively (p less than .001). Four patients with confluent fundus hemorrhages died and seven without these fundoscopic findings had easily controlled disease. Increases in Pao2 paralleled increases in platelet counts after plasmapheresis (p less than .001) in this small series of patients. Three of 18 discharged survivors relapsed over a period of 3 to 56 months of follow-up. Early introduction of plasmapheresis in thrombotic thrombocytopenic purpura seems to increase the survival rate and to halt the development of ARDS. Fundus findings may be a prognostic factor in thrombotic thrombocytopenic purpura. The antiplatelet agents seem to be efficacious in the prevention of relapses.

Enhanced proteolysis of plasma von Willebrand factor in thrombotic thrombocytopenic purpura and the hemolytic uremic syndrome

To examine whether enhanced in vivo proteolysis of von Willebrand factor (vWF) would account for the reported loss of larger multimers in acute thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS), we studied eight patients with acute TTP/HUS whose blood samples were collected into an anticoagulant containing a cocktail of protease inhibitors to impede in vitro proteolysis. In all, enhanced proteolytic degradation of vWF was expressed as a relative decrease in the intact 225-Kd subunit of vWF and a relative increase in the 176-Kd fragment. However, instead of the loss of larger forms of normal multimers reported by other investigators, the plasma of all but one of our patients (whether they had TTP or HUS) contained a set of larger than normal (supranormal) multimers. Hence, although proteolytic fragmentation of vWF was enhanced during acute TTP/HUS, this phenomenon was not associated with the loss of larger multimers. In the five patients who survived the acute disease and underwent plasma exchange (three with HUS and two with chronic relapsing TTP), subunits and fragments returned to normal values, and supranormal multimers were no longer detected in plasma. In conclusion, even though vWF proteolysis is enhanced in acute TTP/HUS, it does not lead to loss of larger multimers.

Calcium-dependent cysteine protease activity in the sera of patients with thrombotic thrombocytopenic purpura

Plasma and serum from patients with thrombotic thrombocytopenic purpura (TTP) can cause activation and aggregation of normal human platelets in vitro. It is possible that this platelet-activating factor contributes to the disease. In this report we describe studies designed to identify the platelet-activating factor in TTP. Platelet activation by sera from 15 patients with TTP was inhibited by leupeptin, iodoacetamide, and antipain but not by phenylmethylsulphonylfluoride, epsilon-aminocaproic acid, soybean trypsin inhibitor, aprotinin, and D-phenylanyl-1-prolyl-1- arginine chloromethyl ketone. These studies suggested that the platelet- activating factor in TTP serum was a cysteine protease. We confirmed that a calcium-dependent cysteine protease (CDP) was present in the sera of each of the 15 patients when we used an assay based on the ability of CDP to proteolyse platelet membrane glycoprotein 1b (GP1b) and hence to abolish the ability of CDP-treated normal platelets to agglutinate in the presence of ristocetin and von Willebrand factor. This proteolytic activity was inhibited by EDTA, leupeptin, antipain, iodoacetamide, and by N-ethyl-maleamide (NEM) but not by the serine protease inhibitors. Activity was detected in 15 of 15 patients with TTP tested before therapy was begun. In contrast, no activity was detected in the serum of any of five of the TTP patients tested in remission or in any of the sera from 36 patients with thrombocytopenia and 423 nonthrombocytopenic controls. To look for in vivo CDP activity in patients with TTP, we studied platelets from two patients with acute TTP (drawn into acid-citrate-dextrose, NEM, and leupeptin). These platelets showed a loss of GP1b from the platelet surface. Both patients were also studied in remission: GP1b on the platelet surface had returned to normal. These studies provide evidence that CDP is present in the sera of patients with TTP, that it is specific to this disease, and that is is active in vivo as well as in vitro. We postulate that a disorder of CDP homeostasis plays a major role in the pathophysiology of TTP.

Calcium-Dependent Cysteine Protease Activity in the Sera of Patients With Thrombotic Thrombocytopenic Purpura

Plasma and serum from patients with thrombotic thrombocytopenic purpura (TTP) can cause activation and aggregation of normal human platelets in vitro. It is possible that this platelet-activating factor contributes to the disease. In this report we describe studies designed to identify the platelet-activating factor in TTP. Platelet activation by sera from 15 patients with TTP was inhibited by leupeptin, iodoacetamide, and antipain but not by phenylmethylsulphonylfluoride, epsilon-aminocaproic acid, soybean trypsin inhibitor, aprotinin, and D-phenylanyl-1-prolyl-1-arginine chloromethyl ketone. These studies suggested that the platelet-activating factor in TTP serum was a cysteine protease. We confirmed that a calcium-dependent cysteine protease (CDP) was present in the sera of each of the 15 patients when we used an assay based on the ability of CDP to proteolyse platelet membrane glycoprotein 1b (GP1b) and hence to abolish the ability of CDP-treated normal platelets to agglutinate in the presence of ristocetin and von Willebrand factor. This proteolytic activity was inhibited by EDTA, leupeptin, antipain, iodoacetamide, and by N-ethyl-maleamide (NEM) but not by the serine protease inhibitors. Activity was detected in 15 of 15 patients with TTP tested before therapy was begun. In contrast, no activity was detected in the serum of any of five of the TTP patients tested in remission or in any of the sera from 36 patients with thrombocytopenia and 423 nonthrombocytopenic controls. To look for in vivo CDP activity in patients with TTP, we studied platelets from two patients with acute TTP (drawn into acid-citrate-dextrose, NEM, and leupeptin). These platelets showed a loss of GP1b from the platelet surface. Both patients were also studied in remission: GP1b on the platelet surface had returned to normal. These studies provide evidence that CDP is present in the sera of patients with TTP, that it is specific to this disease, and that is is active in vivo as well as in vitro. We postulate that a disorder of CDP homeostasis plays a major role in the pathophysiology of TTP.

Relationship between platelet aggregating factor and von Willebrand factor in thrombotic thrombocytopenic purpura.

The pathophysiology of the platelet thrombotic disorder, thrombotic thrombocytopenic purpura (TTP), is not well understood. Two apparently unrelated laboratory abnormalities have recently been described in patients with TTP: a platelet aggregating factor and abnormalities in von Willebrand factor (vWF). Although an interaction between these two abnormalities has been postulated to participate in the disease, this has not been proved. In this report we describe studies on a patient with relapsing TTP. These studies demonstrate that a consistent relationship exists between the platelet aggregating factor present in the patient's serum and vWF. The patient had chronic low-grade thrombocytopenic and schistocytic haemolytic anaemia that could be temporarily cured by infusions of plasma and certain other blood products. During acute exacerbations of the illness, a platelet aggregating factor was detectable in the patient's serum and this was associated with the loss of the larger multimers of vWF. During remissions of the illness, abnormally large multimers of vWF were present. The results of this study support the concept that a platelet aggregating factor plus large multimers of vWF participate in the acute platelet thrombi that characterize TTP.

A platelet aggregating factor in thrombotic thrombocytopenic purpura: initial activity, fluctuations, and removal by plasma exchange

A factor capable of aggregating normal platelets was found in the plasma of six consecutive patients with thrombotic thrombocytopenic purpura (TTP). The activity of the aggregating factor in whole plasma, the cold protein fraction from plasma and the residual supernatant was monitored during each patient's course of therapeutic plasma exchange. Although two patients demonstrated the highest level of aggregating activity at the time of diagnosis, the level fluctuated in five of six patients. Increasing levels of activity were usually accompanied by signs of clinical deteroration. Activity repeatedly within the normal range was not seen until remission of the syndrome. Neutralization of the aggregating activity in vivo through removal of patient plasma and replacement with fresh frozen plasma (plasma exchange) was accomplished less readily and less predictably than by mixing patient plasma and normal plasma in vitro. Use of the aggregating factor level in evaluating the need of plasma exchange is discussed.

Von Willebrand factor in thrombotic thrombocytopenic purpura [letter

von Willebrand factor in thrombotic thrombocytopenic purpura [letter

Investigation of the role of von Willebrand factor in thrombotic thrombocytopenic purpura

AbstractVon Willebrand factor (vWF) has been implicated to function as a cofactor in platelet aggregation induced by thrombotic thrombocytopenic purpura (TTP) plasma. To investigate further this role of vWF, we have used rabbit monospecific anti-FVIII/vWF antibodies and a monoclonal antibody to platelet glycoprotein Ib (GP Ib) that blocks the ristocetin- induced platelet aggregation. The monoclonal anti-platelet GP Ib antibody inhibited the platelet aggregation induced by ristocetin in the presence of normal plasma, but not that by any of the five TTP plasma samples. The TTP plasma samples from five patients were incubated with the monospecific antibodies to FVIII/vWF. In all of the samples, the FVIII/vWF:Ag was drastically reduced; however, there was almost no effect on the platelet-aggregating activity. Therefore, it is concluded that vWF is unlikely to play a major role in platelet aggregation induced by majority of TTP plasmas and that the site of platelet GP Ib, to which vWF binds in the presence of ristocetin, is not involved in TTP plasma-induced aggregation.

Investigation of the role of von Willebrand factor in thrombotic thrombocytopenic purpura

Von Willebrand factor (vWF) has been implicated to function as a cofactor in platelet aggregation induced by thrombotic thrombocytopenic purpura (TTP) plasma. To investigate further this role of vWF, we have used rabbit monospecific anti-FVIII/vWF antibodies and a monoclonal antibody to platelet glycoprotein Ib (GP Ib) that blocks the ristocetin- induced platelet aggregation. The monoclonal anti-platelet GP Ib antibody inhibited the platelet aggregation induced by ristocetin in the presence of normal plasma, but not that by any of the five TTP plasma samples. The TTP plasma samples from five patients were incubated with the monospecific antibodies to FVIII/vWF. In all of the samples, the FVIII/vWF:Ag was drastically reduced; however, there was almost no effect on the platelet-aggregating activity. Therefore, it is concluded that vWF is unlikely to play a major role in platelet aggregation induced by majority of TTP plasmas and that the site of platelet GP Ib, to which vWF binds in the presence of ristocetin, is not involved in TTP plasma-induced aggregation.