Evaluation and clinical application of a new method for detecting ADAMTS13 activity.
BACKGROUND
A severe deficiency of ADAMTS13 activity contributes to the pathogenesis of thrombotic thrombocytopenic purpura (TTP). Measuring the activity of ADAMTS13 is helpful for the diagnosis of TTP and the prognostic monitor in TTP patients. Most available assays are cumbersome and costly, so not easily adapted to routine laboratories. ADAMTS13 cleaves von Willebrand factor (VWF) within the domain A2, located between domains A1 and A3. Therefore, specific assays for ADAMTS13 activity could be based on the different structures of VWF before and after the cleavage. Using this hypothesis we try to establish a new and simple method to determine ADAMTS13 activity.


METHODS
First, plasma samples were exposed in denaturing condition to allow cleavage of VWF by ADAMTS13. Then, the ADAMTS13 activity was measured with two novel monoclonal antibodies, SZ-129 and SZ-125, which specifically recognize the VWF A1 and A3 domains by using a two-site sandwich ELISA. Compared with a residual-collagen binding assay (R-CBA), plasma ADAMTS13 activities in 161 samples were assessed, and the inhibitory activities of ADAMTS13 autoantibody in 24 TTP patients were determined. The relationship of these two assays was analyzed by linear correlation, and the sensitivity and specificity of the new assay was also evaluated.


RESULTS
Plasma ADAMTS13 activities in normal people and TTP, acute myocardial infarction (AMI), and idiopathic thrombocytopenic purpura (ITP) patients determined by the new assay were (89.75 +/- 7.93)%, (17.63 +/- 18.71)%, (68.55 +/- 18.08)%, (85.83 +/- 9.84)%, respectively. Results were consistent with those of R-CBA, the squared correlation factor was 0.9183 of the two assays. The new assay can easily discriminate a TTP plasma sample from a non-TTP plasma sample (P < 0.01), and the coefficient of variation for the new assay was 6.17%. In 23 idiopathic TTP patients, the inhibitor activity of ADAMTS13 autoantibody ranged from 12% to 100%, while no inhibitory activity was detected in one hereditary TTP patient.


CONCLUSIONS
This new and simple assay for ADAMTS13 activity could be used routinely in the clinic to determine the activity of ADAMTS13.
Wang
An-You
AY
Key Laboratory of Thrombosis and Hemostasis of Ministry of Health, Jiangsu Institute of Hematology, First Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215006, China.
Dong
Ning-Zheng
NZ
Ma
Zhen-Ni
ZN
Zhang
Jing-Yu
JY
Su
Jian
J
Ruan
Chang-Geng
CG
D051722:ADAM Proteins / Q000378:metabolism*; D000071120:ADAMTS13 Protein; D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011697:Purpura, Thrombotic Thrombocytopenic / Q000378:metabolism; D055815:Young Adult; D014841:von Willebrand Factor / Q000378:metabolism
D014841:von Willebrand Factor; D051722:ADAM Proteins; D000071120:ADAMTS13 Protein; C099604:ADAMTS13 protein, human