Program: Oral and Poster Abstracts
Type: Oral
Session: 302. Vascular Wall Biology, Endothelial Progenitor Cells and Platelet Adhesion
Methods: Two females with a history of prior episodes of TTP presented with acute TTP [ADAMTS13 < 10%, positive for ADAMTS13 inhibitors, platelet count ≤ 10,000/uL, lactate dehydrogenase (LDH) > 600 IU/L] and both were treated with NAC per IRB-approved protocol [150 mg/kg bolus over 1 hr and 150 mg/kg as continuous infusion until the next therapeutic plasma exchange (TPE)]. They received daily TPE until their platelet counts normalized, and intravenous NAC during days 2–5. Blood was collected daily for 8 days for research assays. ADAMTS13 concentrations in patient plasma were measured by ELISA. ADAMTS13 activity was measured using HRP-conjugated A2 peptide substrate (Wu J-J et al. J Thromb Haemost 2006, 4:129-136). Concentrations of NAC, total cysteine, and total free thiols (free thiol cysteine and free thiol NAC) in plasma were determined by mass spectrometry. Plasma VWF multimer patterns were analyzed by 1.5% agarose gel electrophoresis followed by western blotting with an HRP-conjugated polyclonal VWF antibody. Platelets in whole blood were labeled for platelet markers (CD41a or CD42b) together with one of the activation markers, P-selectin or phosphatidylserine (lactadherin). The labeled platelets were analyzed by flow cytometry.
Results: Platelet counts in both patients started to increase 1 day after NAC infusion and continued to increase after discontinuation of NAC and TPE. After NAC infusion, the free thiol concentration (NAC and cysteine) in plasma increased 4 and 59 fold in patients 1 and 2, respectively. This was accompanied by increasing ADAMTS13 specific activity (ADAMTS13 activity/ADAMTS13 antigen). In patient 1, the specific activity increased from 127% (prior to NAC infusion but after TPE) to 270% during NAC infusion; in patient 2, the specific activity increased from 56% to 86%. In patient 1, the VWF multimer size decreased during NAC treatment and the VWF multimers migrated slightly faster. NAC also appeared to inhibit platelet activation. Before NAC infusion, the platelets in both patients were positive for phosphatidylserine (PS, > 30%) and P-selectin (> 15%), compared to 2% and 5%, respectively, in a normal control. The percentages of PS- and P-selectin–positive platelets decreased to less than 18% and 10% respectively, during NAC treatment.
Summary: NAC treatment of two patients with TTP in conjunction with TPE was well tolerated and associated with recovery of platelet count and LDH, increased ADAMTS13 specific activity and total free thiol concentration in plasma, reduced platelet activation, and decreased VWF multimer size in one patient.
Disclosures: Konkle: CSL Behring: Consultancy ; Pfizer: Consultancy ; Baxalta: Consultancy , Research Funding ; Biogen: Consultancy , Research Funding ; Octapharma: Research Funding ; Novo Nordisk: Consultancy .
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