Effects of N-Acetylcysteine Infusion in Patients with Sickle Cell Disease during Vaso-Occlusive Crises

Background: Our earlier studies showed that patients with sickle cell disease (SCD) have a high von Willebrand factor (VWF) activity index, which correlates with the extent of the hemolysis they experience [Chen et al Blood 2011; 117:3680‐3]. We are evaluating whether N-acetylcysteine (NAC), which dissociates VWF multimers, has a therapeutic role in SCD. Previously, we studied stable outpatients with SCD [Özpolat et al Blood Dec 2016, 128 (22) 1299]. In that study, we found that NAC infusion was safe and decreased red blood cell (RBC) fragments, dense cells, the size of VWF multimers, platelet activation, and the percentage of platelet-monocyte complexes. In addition, NAC infusion increased the total and free-thiol concentrations of cysteine and glutathione in blood, relieving oxidative stress in the patients at disease baseline. Given these findings, we have begun a pilot study of NAC in SCD patients admitted as inpatients with vaso-occlusive crisis (VOC) (NCT01800526) to examine the safety of NAC infusion and its effects on laboratory markers in that setting.

Protocol and patients: Patients are approached for the study in the outpatient setting and consent is re-affirmed when they are admitted in VOC. We plan to enroll enough patients to treat 20 VOCs with NAC infusion, with each patient being treated up to two times in the study. Inclusion criteria: SCD patients with history of VOC requiring narcotics treatment. Exclusion criteria: SCD patients on chronic RBC exchange, expected to be treated by simple or exchange transfusion, inpatient with VOC in the previous 30 days, already had NAC infusion twice in our trial during VOC, and/or had oral NAC in the past 7 days. NAC (75 mg/kg/hr) is infused over 1 hr every 6 hr, for a total daily dose of 300 mg/kg. All patients also receive standard care. Blood is collected immediately before NAC infusion on the first day of admission, daily during admission, and at medical follow-ups during the first week after discharge. To date, we have completed NAC infusion in two patients with VOC under this protocol. Patient 1 is a 26-year-old male with Sβ⁰ thalassemia, a history of recurrent VOC and avascular necrosis (AVN) of both hips and the left shoulder, on hydroxyurea and oral narcotics. Patient 2 is a 58-year-old female with SS genotype, recurrent VOC and history of bilateral AVN of the hips and knees, pulmonary embolism, on hydroxyurea, oral narcotics, and rivaroxaban. We analyzed patient samples for dense cells, sickle cells (by imaging flow cytometry), VWF antigen and multimer distribution, ADAMTS13 activity and antigen. In addition, we will analyze the concentrations of NAC, cysteine and glutathione and their oxidized and mixed disulfide forms by mass spectrometry.

Results: NAC infusions in the two SCD patients with VOC were safe and well tolerated. After NAC treatment, the number of dense cells were reduced (before vs after NAC treatment: patient 1; 1826/µl vs 46/µl, patient 2: 667/µl vs 36/µl), The VWF multimers migrated slightly faster during NAC infusion, indicating possible reduction of intra-chain disulfide bonds by NAC within VWF monomers [Chen J et al. JCI 2011, 121: 593]. The VWF concentrations were increased at the end of both NAC treatments. For patient 1, the ADAMTS13 activity was decreased during the NAC treatment, but the antigen remained unchanged. For patient 2, both the ADAMTS13 activity and antigen were increased with NAC treatment. For patient 1, phosphatidylserine positive microparticles (MP) and MP generated from RBCs and platelets were decreased with NAC treatment but there was no apparent trend for patient 2.

Summary: In the first two SCD patients treated, NAC infusion during VOC was safe and well tolerated. NAC infusion decreased dense cells, and reduced intra-chain disulfide bonds in VWF. The full study should determine if NAC is useful therapy for SCD patients during VOC, acting through diverse mechanisms by improving RBC parameters and reducing adhesive activity of VWF.