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PubMed2001

von Willebrand factor-cleaving protease in childhood diarrhoea-associated haemolytic uraemic syndrome.

A deficiency of von Willebrand factor (vWF)-cleaving protease, either due to a congenital deficiency or to the presence of a protease inhibitor of vWF-cleaving protease has been associated with thrombotic thrombocytopenic purpura (TTP). We have studied vWF-cleaving protease in diarrhoea-associated haemolytic uraemic syndrome (D+ HUS), which shares clinical features with TTP. 29 children with acute D+ HUS and 13 control children were studied. vWF-cleaving protease activity was normal (range 50-150%) in 39 of 42 plasma samples. Levels of protease activity between 25 and 50% were noted in plasma from two D+ HUS patients. One D+HUS patient, who had clinical features of TTP, had a vWF-cleaving protease inhibitor producing a severe deficiency of vWF-cleaving protease. Thus a deficiency of vWF-cleaving protease appears to be atypical in D+HUS. The detection of a vWF-cleaving protease inhibitor in one patient suggests it may be associated with infection such as E. coli O157.

ADAM Proteins↗
PubMed2001

Inhibitors of von Willebrand factor-cleaving protease in thrombotic thrombocytopenic purpura.

Thrombotic thrombocytopenic purpura (TTP), characterized by platelet thrombi in the arterioles and capillaries, is associated with antibodies that inhibit the activity of von Willebrand factor (vWF)-cleaving protease. Using a modified Bethesda method, we studied the inhibitor titers in patients who participated in the trial conducted by the Canadian Apheresis Group. Among the 41 patients investigated, the inhibitor titers at presentation were 1.4 +/- 1.7 U/mL (range -0.2-6.2 U/mL). Thirty-one patients (76%) had a titer > or = 0.2 U/mL, 8 patients (20%) had a titer > or = 2.0 U/mL but none had a titer > or = 10 U/mL. Among the 33 patients with an inhibitor titer < 2.0 U/mL (low titer group) and the 8 patients with an inhibitor titer > or = 2 U/mL (high titer group), 20 (61%) and 8 (100%) respectively had a platelet count < 25x10(9)/L (P = 0.04). Neurological abnormalities were among the presenting problems in 19 (58%) of the low titer and 6 (75%) of the high titer groups. Among the 23 patients who were randomized to plasma exchange, 5 patients had an inhibitor titer > or = 2 U/mL and none responded at the end of the first treatment cycle, while 8 of the 18 patients (44%) with a titer < 2 U/mL responded. This study shows that inhibitors of vWF-cleaving protease are of low titers in most cases of acquired TTP. A higher inhibitor titer is associated with a more advanced stage of the disease and may delay the response to plasma exchange.

ADAM Proteins↗
PubMed2002

[Hemolytic uremic syndrome and thrombotic thrombocytopenic purpura].

Hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP) are thrombotic microangiopathies (TMA). Both familial and sporadic forms exist: anaemia, thrombopaenia, renal failure and neurologic disorders are common clinical features. The differential diagnosis depends on plasma levels of von Willebrand factor-cleaving protease: there is a deficiency of this protease in patients with TTP whereas its rate is normal in HUS. We remind pathophysiology, etiologies and treatment of these TMA.

ADAM Proteins↗
PubMed2002

[Von Willebrand factor-cleaving protease activity in patients of collagen disease with antiphospholipid antibodies].

Acquired thrombotic thrombocytopenic purpura (TTP), characterized by widespread thrombus formation in the microcirculation, is a ponderous complication of antiphospholipid syndrome. Recently, von Willebrand factor-cleaving protease (VWF-CPase) activity has been reported as a possible determinant for the occurrence of TTP. To clarify the role of VWF-CPase in the thrombus formation associated with antiphospholipid syndrome, we investigated plasma VWF-CPase activity in patients of collagen diseases with lupus anticoagulant (LA). Decreased plasma VWF-CPase activity less than 50% of the normal activity was observed in 25.7% (n = 18) in 70 patients with collagen diseases and 7 (10%) cases of them showed more lower VWF-CPase activity less than 25%. The IgG fractions obtained from 2 patients with the low VWF-CPase activity strongly inhibited the proteolytic reaction of normal VWF-CPase. There was no significant relationship between LA and plasma VWF-CPase activity. Thrombotic episodes, especially arterial thrombosis, were more frequently observed in LA-positive patients with low VWF-CPase activity. These results suggest that decreased activity of VWF-CPase, partly due to IgG type inhibitor to the enzyme activity may be an additional risk factor for arterial thrombosis in collagen disease patients with antiphospholipid antibodies.

ADAM Proteins↗
PubMed2002

Complete defect in vWF-cleaving protease activity associated with increased shear-induced platelet aggregation in thrombotic microangiopathy.

Von Willebrand factor (vWF) cleaving metalloprotease activity represents an important factor in understanding the pathophysiology of thrombotic microangiopathies (TMA). Thrombotic events, leading to dramatic complications, occur preferentially in the microvasculature. Our aim was to determine the ability of TMA plasma with a complete deficiency of protease activity to promote shear-induced platelet aggregation (SIPA) at high shear rates using a coaxial cylinder shearing device. We have demonstrated the ability of four out of seven TMA plasma to aggregate normal washed platelets at 4,000 s(-1). In these four TMA plasma, significant SIPA was obtained, whereas control plasma did not induce more SIPA than buffer. The % of unusually large (UL) multimers in TMA plasma varied from 1 to 18%. Surprisingly, the extent of SIPA in TMA plasma appeared independent of the percentage of UL multimers. Interestingly, anti-GPIb antibody 6D1 could block completely this pathological aggregation, opening new therapeutic possibilities. In contrast, none of eight other TMA patients' plasma with a normal protease activity, exhibited any increase of SIPA compared with control plasma. These results strongly suggest that the deficiency of vWF-cleaving protease appears to be necessary, but not sufficient for elevated SIPA. In contrast, the % of UL is not associated with increased SIPA.

ADAM Proteins↗
PubMed2002

[Pathophysiology of thrombotic microangiopathies: current understanding].

Thrombotic microangiopathies (TMA) encompass various severe diseases characterized by microangiopathic hemolytic anemia and peripheral thrombocytopenia, associated with fever, neurological signs and renal involvement. Microvascular thrombosis is the typical lesion, and results in tissue ischemia. Thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS) are the two most classical forms. These two entities are clinically and histopathologically closely related. There is a body of evidence suggesting that endothelial cell injury is the initial event in TTP and HUS, and that it may be related to a large number of triggering factors, such as infection, connective tissue disease, drugs, cancer and chemotherapy, transplantation, and pregnancy. Endothelial cell injury enhances the release of ultra large forms of von Willebrand factor (ULvWF) multimers and other prothrombotic agents, such as plasminogen activator inhibitor and platelet activating factor, whereas it decreases the release of prostaglandin-I2, a strong inhibitor of platelet aggregation. Recently however, it has been shown that TTP and HUS were pathophysiologically distinct. Actually, TTP is associated with a deficiency in von Willebrand factor-cleaving protease, an enzyme involved in cleavage of ULvWF into circulating 200 kDa and 350 kDa fragments. This deficiency may be either congenital or acquired, and then related to an IgG inhibitory autoantibody. This protease deficiency may account for the high amounts of plasmatic ULvWF in TTP patients. In HUS, vWF-cleaving protease activity is found normal. HUS encompasses two distinct entities. Epidemic, or diarrhea-associated HUS, is associated with verotoxin or Shiga toxin-associated enterobacteriaceae. These toxins are directly responsible for endothelial cell injury. Sporadic HUS (also termed atypical HUS in children) is closely related to TTP, and shares the same triggering factors. Familial HUS has been associated in some cases with hypocomplementemia and factor H dysfunction, the pathophysiological role of which remains unclear. The study of the different triggering factors and predisposing factors may be useful to define different subsets of TMA, that may be characterized by their course and prognosis.

ADAM Proteins↗
PubMed2002

Clinical use of a rapid collagen binding assay for von Willebrand factor cleaving protease in patients with thrombotic thrombocytopenic purpura.

A simple collagen binding assay (CBA) for measuring activity of the von Willebrand factor cleaving protease in clinical samples is described, and results of fifty masked plasmapheresis samples rom patients with TTP/HUS and other diseases are presented. There was 97.5% concordance between the CBA and a multimer gel assay. The CBA identified low protease activity in 78% of patients who had a clinical syndrome consistent with TTP/HUS and in 2 of 10 sick controls, giving it a positive predictive value of 0.94. The heterogeneity regarding the presence or absence of vWF protease activity in patients with TTP/HUS was confirmed by finding a low negative predictive value of 0.50 with the CBA. The CBA detected inhibitors of the protease in 26 of 29 patients (90%) with TTP/HUS and low protease activity levels. The CBA is a useful clinical assay for examining von Willebrand factor protease activity and detecting inhibitors against the protease.

ADAM Proteins↗
PubMed2002

[Thrombotic microangiopathy: thrombocytopenia and hemolytic anemia].

Thrombotic microangiopathy is an acute and severe syndrome characterised by a combination of thrombocytopenia, haemolytic anaemia with a negative direct antiglobulin test, and fragmentocytes in the blood smear. The condition can be idiopathic but can also be caused by various underlying diseases. The main causes are thrombotic thrombocytopenic purpura and haemolytic uraemic syndrome. By measuring the von Willebrand factor cleaving protease activity, it now appears possible to distinguish between the different causes of thrombotic microangiopathy, although the sensitivity and specificity of this measurement still need to be clarified. In patients with haemolytic uraemic syndrome without preceding diarrhoea, one should search for infectious foci outside the gastrointestinal tract, using a polymerase-chain reaction to detect the two different verotoxin genes where necessary. Plasmapheresis treatment has reduced the fatality rate amongst patients with thrombotic thrombocytopenic purpura from 90% to 10-25%. Since patients benefit most from rapid institution of treatment, yet the diagnostics currently take several days, the recommendation in case of doubt regarding the original diagnosis is to apply initial plasma exchange therapy to all patients with thrombotic microangiopathy.

ADAM Proteins↗
PubMed2003

Patients with localized and disseminated tumors have reduced but measurable levels of ADAMTS-13 (von Willebrand factor cleaving protease).

BACKGROUND AND OBJECTIVES: Patients with disseminated malignancies have been noted to have a deficiency of von Willebrand factor (VWF) cleaving protease, ADAMTS-13. The very low or undetectable plasma levels of this protease are said to be similar to those found in patients with thrombotic thrombocytopenic purpura (TTP). This observation, which challenges the paradigm that severe ADAMTS-13 deficiency is a specific diagnostic marker for TTP, remains so far unconfirmed. DESIGN AND METHODS: We measured the protease and VWF antigen (VWF:Ag) in parallel in 49 Iranian patients with solid tumors, which in 29 cases were localized (stages I and II) and in 20 disseminated (stage IV). Forty-nine healthy individuals matched with cases for sex, age and smoking habits were taken as controls. RESULTS: Patients with disseminated tumors had lower mean plasma levels of ADAMTS-13 than those with localized tumors, but these differences did not reach the level of statistical significance (p=0.059). However, in no patient was the level of ADAMTS-13 below 18% of normal, at variance with previous findings of lower or unmeasurable levels (<15%). The level of ADAMTS-13 was significantly lower in patients with localized tumors than in controls ( p = 0.0003 ), but higher than in patients with disseminated disease (p=0.0001 vs controls). INTERPRETATION AND CONCLUSIONS: Malignancy, whether localized or disseminated, is another condition associated with low ADAMTS-13 levels not accompanied by signs and symptoms of TTP and other thrombotic microangiopathies.

ADAM Proteins↗
PubMed2003

Von Willebrand factor cleaving protease activity in the physiopathology of microangiopathic disorders.

The von Willebrand factor cleaving protease (VWFCP) modulates the von Willebrand factor (VWF) multimeric size in normal plasma. VWFCP activity levels are decreased in different physiological and pathologic situations. Different techniques have been developed to unfold the purified VWF (perfusion at high shear rate, dialysis against urea in nitrocellulose filters), to detect the VWFCP activity on it (multimeric analysis of VWF, collagen binding to VWF assay) and to use the patient plasma both as the source of the enzyme and substrate. In this paper we compared the above mentioned methods with new ones: normal plasma dialyzed on membranes instead of purified VWF, dialysis of the samples against urea in tubing instead of nitrocellulose filters, and sonicated plasma to remove the endogenous VWF. The perfusion assay and detection by multimeric analysis showed a limit of detection (25%) of VWFCP activity. Dialysis against urea in both supports and detection by multimeric analysis, showed a better limit of detection (3%), but the recovery of the samples was not as efficient in nitrocellulose filters as it was in tubing. The detection by collagen binding to VWF has more advantages because it allows to analyze more samples than the multimeric analysis does in the same assay. The dialysis of plasma by membranes to obtain the source of exogenous VWF requires no complex equipment. The method, which uses patient plasma as the source of the enzyme and substrate, was inapplicable in our experience because the values could not be interpolated in the reference curve.

ADAM Proteins↗
PubMedDate not supplied

[A case of Duchenne muscular dystrophy complicated by thrombotic thrombocytopenic purpura].

We experienced a patient with Duchenne muscular dystrophy (DMD) complicated by thrombotic thrombocytopenic purpura (TTP). This patient exhibited abrupt high fever, renal dysfunction and thrombocytopenia from February 2, 2002. Hemolysis was also indicated by indirect dominant hyperbilirubinemia, although hemoglobin was only slightly decreased. No central nervous system signs and symptoms were detected. TTP was suggested by these findings and confirmed by decreased activity (21%) of von Willebrand factor cleaving protease activity. Plasma exchange was performed for 4 days from February 5, and enabled recovery. Thrombosis, such as cerebral and lung infarction, has occasionally been seen in DMD. Recently, several findings associating muscle degeneration with hypercoagulation have been reported, for example, a strong correlation between serum CK level and FDP. In seven cases of DMD with pulmonary infarction, transient elevation of serum CK was detected prior to LDH elevation. However, there have been no reports of TTP in DMD patients. Since serum CK was not elevated during our patient's clinical course, it is unlikely that muscle degeneration played a role in TTP in this patient. It should be noted that endothelial abnormalities have been reported in DMD, since endothelial injury is considered a fundamental factor in TTP.

ADAM Proteins↗