Rapid quantitative assay of ADAMTS13 activity on an automated coagulation analyzer: clinical applications and comparison with immunoblot method

Correlating S100B with disease course in a case of new onset, acquired thrombotic thrombocytopenic purpura (TTP): Could this be a new predictive biomarker in TTP?

Acute thrombotic thrombocytopenic purpura (TTP) is an aggressive thrombotic microangiopathy that if not treated, can have a 90% mortality rate. Clinical manifestations of this disease include profound thrombocytopenia, hemolytic anemia, and end-organ dysfunction. Neurologic symptoms can occur in 80% of patients and range from mild confusion to coma (Scully et al., Br J Haematol 142:819-826). Here, we present the clinical course of a patient diagnosed with new onset acquired TTP who presented with neurologic changes that waxed and waned during her disease course. In addition to usual clinical and laboratory markers for TTP severity and activity, we also collected and analyzed the protein S100B, an astroglial protein studied as a marker for central nervous system injury and impairment of the blood-brain barrier. Our hypothesis here is that because TTP involves endovascular damage, S100B could function as a biomarker for neurologic dysfunction and ultimately, predict disease activity. As illustrated in this case, our patient's S100B levels did appear to correlate with TTP disease activity and the trajectory of this protein seemed a better predictor of cognitive function. Furthermore, increased S100B velocity seemed to be the earliest indicator of a refractory TTP disease process requiring more intensive plasma exchange (TPE) therapy regimen. Therefore, we would suggest that S100B is a promising predictive biomarker of disease activity in guiding the intensity of TPE therapy for TTP as well as cognitive function.

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.

Successful treatment of intravenously abused oral Opana ER-induced thrombotic microangiopathy without plasma exchange

In January 2013, the Centers for Disease Control and Prevention reported an illness associated with intravenous (IV) abuse of oral Opana ER (oxymorphone) in Tennessee. The clinical presentation of this syndrome was reported to resemble that of thrombotic thrombocytopenic purpura in the 15 patients reported; 12 were treated with plasma exchange. We report a similar case series of 15 patients with 18 episodes of thrombotic microangiopathy associated with recent IV abuse of oral Opana ER. In our series, we demonstrate that therapeutic plasma exchange is unnecessary; supportive care and treatment of underlying infections and renal dysfunction (without use of plasma exchange) resulted in clinical improvement in all patients. Thus, it appears that plasma exchange with associated costs and risks can be safely omitted in patients with thrombotic microangiopathy resulting from IV abuse of oral Opana ER.

ADAMTS-13 assays in thrombotic thrombocytopenic purpura

ADAMTS-13, the thirteenth member of the ADAMTS (A Disintegrin And Metalloprotease with Thrombo-Spondin 1 repeats) family, is the plasma metalloprotease responsible for regulating the multimeric structure of VWF. In congenital or acquired deficiency it is actively involved in the pathophysiology of thrombotic thrombocytopenic purpura (TTP), a rare but life threatening disease characterized by microangiopathic haemolytic anaemia and consumptive thrombocytopenia leading to disseminated microvascular thrombosis and variable signs and symptoms of organ ischemia and damage. In the last few years, a number of in house and commercial laboratory assays for ADAMTS-13 and its autoantibodies have been developed. The features and clinical utility of ADAMTS-13 assays are summarized in this review.

A novel protease activity assay using a protease-responsive chaperone protein

Protease activity assays are important for elucidating protease function and for developing new therapeutic agents. In this study, a novel turbidimetric method for determining the protease activity using a protease-responsive chaperone protein is described. For this purpose, a recombinant small heat-shock protein (sHSP) with an introduced Factor Xa protease recognition site was synthesized in bacteria. This recombinant mutant, FXa-HSP, exhibited chaperone-like activity at high temperatures in cell lysates. However, the chaperone-like activity of FXa-HSP decreased dramatically following treatment with Factor Xa. Protein precipitation was subsequently observed in the cell lysates. The reaction was Factor Xa concentration-dependent and was quantitatively suppressed by a specific inhibitor for Factor Xa. Protein aggregation was detected by a simple method based on turbidimetry. The results clearly demonstrate that this assay is an effective, easy-to-use method for determining protease activities without the requirement of labeling procedures and the use of radioisotopes.

ADAMTS13 activity and inhibitor

Thrombotic thrombocytopenic purpura (TTP) is often associated with acquired or congenital deficiency of the von Willebrand factor-cleaving metalloprotease, ADMATS13 (Lammle B et al., J Thromb Haemost 2005;3:1663-1675; Schneppenheim et al., Blood 2003;101:1845-1850). Although undetectable levels of enzyme activity (<10%) are diagnostic of inherited or acquired TTP in the correct clinical setting (absence is specific), not all patients diagnosed with TTP have severe protease deficiency, and it is therefore not recommended as an initial test for diagnosis (Copelovitch and Kaplan, Pediatr Nephrol, in press). Many prospective and retrospective studies have demonstrated that patients with severe protease deficiency have a higher likelihood of relapse, making it helpful as an indicator of recurrence. The short-term prognostic usefulness of ADAMTS13 testing during acute TTP warrants further investigation because of limited prospective studies (Ferrari S et al., Blood 2007;109:2815-2822; Peyvandi et al., Haematologica 2008;93:232-239).