Clinical usefulness of a functional assay for the von Willebrand factor cleaving protease (ADAMTS 13) and its inhibitor in a patient with thrombotic thrombocytopenic purpura

Is thrombotic microangiopathy a paraneoplastic phenomenon? Case report and review of the literature

It is currently recognized that the pathogenesis of malignancy-associated thrombotic microangiopathy (TMA) is distinct from thrombotic thrombocytopenic purpura. This carries important implications in its classification and its management. Here, we report a case of occult malignancy presenting initially as acute kidney injury secondary to TMA and highlight the importance of considering an underlying malignancy in patients not responding to conventional therapy for TMA.

The aptamer ARC1779 blocks von Willebrand factor-dependent platelet function in patients with thrombotic thrombocytopenic purpura ex vivo

BACKGROUND

In thrombotic thrombocytopenic purpura (TTP), ultralarge von Willebrand factor (VWF) multimers bind platelet (PLT) glycoprotein Ib and lead to the formation of disseminated fibrin-poor, VWF-rich PLT thrombi. The aptamer ARC1779 blocks binding of the VWF A1 domain to PLT glycoprotein Ib. We evaluated whether ARC1779 inhibits the excessive VWF activity and VWF-mediated PLT function in patients with TTP.

STUDY DESIGN AND METHODS

We studied the ex vivo concentration response curves for ARC1779 on PLT function analyzer (PFA-100, Dade Behring) and cone-and-plate analyzer (CPA, Impact-R) PLT function tests, agonist-induced PLT aggregation, and VWF activity of TTP patients (n = 11, three in acute phase and eight in remission) and healthy controls (n = 44).

RESULTS

VWF activity and VWF-dependent PLT plug formation were increased in TTP patients relative to healthy controls, but agonist-induced PLT aggregation was not. ARC1779 blocked collagen/adenosine 5'-diphosphate (ADP)-induced PLT plug formation as measured by PFA-100 with an inhibitory concentration (IC)(100) of approximately 1 microg/mL in citrate-anticoagulated samples and approximately 3 to 4 microg/mL in hirudin-anticoagulated samples. A similar concentration of ARC1779 was necessary to block shear-dependent PLT adhesion in both TTP patients and healthy controls using the CPA assay (IC(100) of approx. 1 microg/mL for both). ARC1779 blocked VWF activity with an IC(90) of approximately 3 to 4 microg/mL in all subjects, but did not inhibit PLT aggregation by ADP, collagen, or arachidonic acid even at concentrations much greater than those that fully inhibited VWF-dependent PLT function.

CONCLUSIONS

ARC1779 potently and specifically inhibits VWF activity and VWF-dependent PLT function. ARC1779 may be a promising novel therapeutic for the treatment of TTP.

Thrombotic thrombocytopenic purpura in systemic lupus erythematosus: risk factors and clinical outcome: a single centre study

The study was undertaken to investigate clinical characteristics of thrombotic thrombocytopenic purpura (TTP) in patients with SLE and to determine risk factors and clinical outcome of TTP in patients with SLE. Among the 1203 patients with SLE admitted to catholic medical centre of the catholic university of Korea from January 1990 to December 2006, 26 patients with SLE were found to admit with TTP. TTP was defined if microangiopathic haemolytic anaemia, thrombocytopenia and negative Coombs’ test were present and when at least one of the following signs was noted: renal impairment, neurologic deficit or fever. Eighty-seven patients with SLE who admitted with other manifestations, matched for age and sex, were included as disease controls. Data were retrospectively analysed based on medical records. There were no significant demographic characteristics between SLE patients with TTP and those with other manifestations. Multivariate analysis showed that independent risk factors for the development of TTP included high SLE disease activity index score (SLEDAI > 10, P = 0.006) and coexisting nephritis ( P = 0.004). Among the 26 SLE patients with TTP, 12 died during admission period (in-hospital mortality rate: 46.1%). SLE patients with infection or neurologic manifestations had higher mortality rates. Multivariate analysis showed that infection is the only independent risk factor for mortality in SLE patients with TTP ( P = 0.035). Patients with SLE who are in the active stage or who have renal involvement have the increased risk for TTP. Development of TTP in patients with SLE can be fatal. Therefore, intensive therapy will be needed especially in the presence of infection.

Von Willebrand factor, red cell fragmentation, and disease activity in systemic lupus erythematosus

This study sought to determine whether the plasma levels of Von Willebrand factor (vWf) and the degree of red blood cell (RBC) fragmentation on peripheral smear correlate with disease activity in systemic lupus erythematosus (SLE). Forty consecutive patients who fulfilled the criteria for SLE were studied prospectively for 1 year. Patients were categorized according to the SLE Disease Activity Index (SLEDAI) as either active (>2) or inactive disease and followed up monthly (active) or quarterly (inactive). At each visit, patients were examined fully and had complete blood count, tests on antibodies to double-stranded DNA, C3, and C4 levels, and urinalysis. Citrated plasma was analyzed for vWf antigen by standard enzyme-linked immunosorbent assay. A Wright's stained blood smear was obtained and schistocytes were quantitated on blood smear. The number of schistocytes per 500 RBCs was determined and a schistocyte index (SI) was calculated. At baseline, vWf correlated with SLEDAI (r = 0.64, p < 0.01), SI correlated with SLEDAI (r = 0.62, p < 0.01), and vWf and SI correlated with each other (r = 0.41, p = 0.01). There was an inverse correlation between baseline C3 levels and vWf (r = 0.49, p = 0.0013) and C3 levels and SI (r = 0.40, p = 0.01). Over time, there was also a correlation of SLEDAI with vWf (r = 0.53, p = 0.002) and SI (r = 0.57;p = 0.002). The relation of vWf with SI approached but did not reach statistical significance (r = 0.37, p = 0.06). We found that the plasma levels of vWf and the degree of RBC fragmentation correlate with lupus disease activity over time. Therefore, inflammation in SLE may be associated with endothelial injury.

Von Willebrand factor, ADAMTS13, and thrombotic thrombocytopenic purpura

Discoveries during the past decade have revolutionized our understanding of idiopathic thrombotic thrombocytopenic purpura (TTP). Most cases in adults are caused by acquired autoantibodies that inhibit ADAMTS13, a metalloprotease that cleaves von Willebrand factor within nascent platelet-rich thrombi to prevent hemolysis, thrombocytopenia, and tissue infarction. Although approximately 80% of patients respond to plasma exchange, which removes autoantibody and replenishes ADAMTS13, one third to one half of survivors develop refractory or relapsing disease. Intensive immunosuppressive therapy with rituximab appears to be effective as salvage therapy, and ongoing clinical trials should determine whether adjuvant rituximab with plasma exchange also is beneficial at first diagnosis. A major unanswered question is whether plasma exchange is effective for the subset of patients with idiopathic TTP who do not have severe ADAMTS13 deficiency.

ADAMTS-13 levels in fresh, stored, and solvent detergent treated plasma

BACKGROUND

ADAMTS-13 is implicated in the pathophysiology of thrombotic thrombocytopenic purpura (TTP). Plasma exchange is thought to be effective through removal of a harmful substance or provision of a required material such as ADAMTS-13. As various methods are used to prepare plasma we determined the effects of storage and solvent detergent treatment on the ADAMTS-13 levels in plasma.

METHODS

Samples from fresh plasma and fresh frozen plasma (FFP) were stored at 22 degrees C and ADAMTS-13 levels were measured at 0, 12, 24, 48 and 72 h. Samples were also taken from solvent detergent treated plasma (SDP) and cryosupernatant plasma (CSP). Total protein, albumin, fibrinogen and immunoglobulins were also measured.

RESULTS

In fresh plasma, the levels of both the 175 and 140 Kd subunits of von Willebrand factor were consistent at 1.38 and 1.35 OD units from 0 to 48 h indicating normal ADAMTS-13 activity. The Vitex SDP produced slightly more of the 140 Kd subunit than did Octapharma SDP which gave equivalent fragments. Cryosupernatant plasma was the same as normal plasma. None of these values changed over 48 h. There was a 28% decrease in FVIII in fresh plasma over 24 h. Fibrinogen and albumin were unchanged.

CONCLUSION

ADAMTS-13 levels are not significantly decreased by storage of plasma at room temperature for up to 48 h. Both CSP and SDP also contained essentially normal levels of ADAMTS-13 and therefore could be used for treatment of patients with TTP.

Thrombotic thrombocytopenic purpura associated with systemic lupus erythematosus

Thrombotic thrombocytopenic purpura (TTP) occurring in patients with systemic lupus erythematosus (SLE) is rare and can be difficult to diagnose because of overlapping features of the two disorders. The aim of this study is to further characterize this uncommon association in terms of presenting features, diagnostic difficulties and treatment outcome. This is the largest series from a single centre with 6 patients diagnosed over a 6-year period. Two thirds of the patients had a simultaneous diagnosis of TTP and SLE. Half of the patients had a positive Coombs test along with clear features of TTP. Five patients received plasmapheresis as initial treatment while 1 patient received plasma infusions only. Four out of 5 patients responded to plasmapheresis and only 1 patient required cytotoxic therapy. TTP in association with SLE appears to be underdiagnosed and a positive Coombs test is not against the diagnosis of TTP in this setting. Most of the patients respond well to plasmapheresis. In case of a poor response, cytotoxic drugs should be considered early.

A case of thrombotic thrombocytopenic purpura with systemic lupus erythematosus

We described a case of thrombotic thrombocytopenic purpura (TTP) with systemic lupus erythematosus (SLE). A-60-year old woman was admitted to our hospital because of fever, disconsciousness, and general fatigue. 32 years ago, she was diagnosed as SLE with Raynaud's phenomenon, rash, photosensitivity, arthritis, lymphocytopenia, and ANA. Her SLE was well controlled with 10 mg predonisolone as a maintance dose until several weeks ago. On admission, severe thrombocytopenia (0.7x10(4)/microl) and other laboratory data revealed microangiopathic hemolytic anemia and renal dysfunction, Immediately after diagnosed as TTP, plasma exchange and corticosteroid therapy started. In spite of the treatment, disconsciousness progressed and systemic convulsion occurred and died 4 days after admission. Autopsied examination revealed diffuse microvascular hyalinized thrombi in heart, kidney, liver, spleen, and pancreas. Some microvascular thrombi were detected in lymph nodes, bone marrow, intestine. Pathological diagnosis of TTP was made on microvascular hyalinized platelet thrombi in organs. Von Willebrand factor-cleaving protease (VWF-CP) activity in plasma on set is less than 0.5 percent of normal and inhibitor for VWF-CP was detected. We here report a valuable case for analysis of pathogenesis in SLE-TTP.

Thrombotic thrombocytopenic purpura: a moving target

Almost 80 years after Eli Moschcowitz published the first description of the disease, most patients with idiopathic thrombotic thrombocytopenic purpura (TTP) were found to have acquired autoantibody inhibitors of the ADAMTS13 metalloprotease. Plasma ADAMTS13 normally cleaves von Willebrand factor within nascent platelet-rich thrombi, and ADAMTS13 deficiency allows unchecked thrombus growth to cause microangiopathic hemolysis, thrombocytopenia, and tissue infarction. At present, ADAMTS13 deficiency with a high-titer inhibitor level appears to be associated with an increased risk of early death and subsequent relapse. Thus, acquired ADAMTS13 deficiency identifies a specific mechanism of TTP and is a potential biomarker of disease activity or risk. At present, two major clinical questions in the field may be summarized as follows. First, by emphasizing TTP caused by ADAMTS13 deficiency, are we in danger of neglecting other causes that should be treated with plasma exchange? Second, should we treat asymptomatic patients who have severe ADAMTS13 deficiency to prevent future disease, and if so, how?