Search

Background: Protein S (PS) is a natural anticoagulant acting as a cofactor for activated protein C (APC) for the inactivation of activated factors V and VIII(1). We identified an anti-PS single-domain antibody (PS003biv) that surprisingly enhanced the APC-cofactor activity of PS and exerted an in vivo antithrombotic effect(2). A moderate decrease in PS plasma levels is frequently observed in sickle cell disease (SCD) patients, with a further reduction during vaso-occlusive crises (VOC) (3). We hypothesized that PS003biv might limit VOC in SCD. Methods: HbSS-Townes mice were intravenously injected with 10 mg/kg PS003biv or vehicle (control). Mice were placed in a hypoxic atmosphere chamber (8% O2) for 3 h, after which they were returned to room air. Spleen, liver and plasma were collected. The intensity of vaso-occlusion was quantified by Ter-119 immunofluorecence staining of red blood cells (RBC) clogging the vessels in the liver and spleen. Bilirubin, free heme, and thrombin-antithrombin complexes were measured in plasma. Results: Quantifying Ter-119 staining density in liver and spleen showed that PS003biv decreased RBC accumulation and VOC (liver control 13.57 ± 1.46 × 106 versus PS003biv 7.28 ± 0.38 × 106 AU; and spleen control 5.64 ± 0.21 × 107 vs PS003biv 5.03 ± 0.03 × 107 AU, p < 0.05). Biomarkers for hemolysis were lower in PS003biv-treated mice: bilirubin control 6.87 ± 0.21 vs PS003biv 4.88 ± 0.60 mg/dl; and free heme control 133.0 ± 10.4 vs PS003biv 77.5 ± 5.3 μM. PS003biv decreased thrombin-antithrombin complexes (control: 10.14 ± 0.72 vs PS003biv 7.47 ± 0.33 ng/mL, p < 0.05). Conclusions: PS003biv showed beneficial properties in the context of a hypoxia/reoxygenation murine model of SCD, with reduced vasoocclusion, hemolysis, and coagulation activation. The mechanism of action of PS003biv needs to be determined. [ABSTRACT FROM AUTHOR]