Ex Vivo Evaluation of Red Blood Cell Adhesion and Whole Blood Thrombosis in Pyruvate Kinase Deficiency

Introduction

Pyruvate Kinase Deficiency (PKD) is an inherited glycolytic enzymopathy that is characterized by a life-long chronic hemolytic anemia with severe comorbidities. Hypercoagulability due to increased platelet activity caused by nitric oxide sequestration by cell free hemoglobin has been well-described not just in PKD, but in other hemolytic anemias as well, such as e.g., sickle cell disease (SCD). Hypercoagulability is often accompanied by a cascade of pathophysiological events leading to cell oxidative damage, endothelial activation, and changes in both cell stability and adhesive properties. Increased red blood cell (RBC) adhesion and hypercoagulability may impair microvascular blood flow. Despite these well-recognized rheological changes that are similar to those that occur in other hemolytic anemias, the relationship between baseline erythrocyte adhesion and thrombosis potential have not been well-studied in PKD.

Methods

10 PKD subjects and 5 healthy controls were recruited under the IRB-approved protocol from Wayne State University. Flow adhesion of whole blood to vascular cell adhesion molecule-1 (FA-WB-VCAM) was performed by flowing whole blood (1:1 dilution) through a microfluidic channel for 3 minutes (1 dyne/cm ² shear stress, 1.67Hz pulse frequency). Flow adhesion avidity of the whole blood sample to VCAM-1 (FAAv-WB-VCAM), representing the strength of the RBC-VCAM-1 adhesive interactions, was assessed by quantifying adhesion following sequential increase in shear (5, 10, 20 dyne/cm ²). Thrombin generation assay was conducted using platelet poor plasma with and without thrombomodulin and microparticles (MP) as previously published [1]. Clotting time - reported as lag time (LT), time to peak (ttPeak) and peak height (velocity and amount of net thrombin production), and endogenous thrombin potential (ETP), representing number of substrates potentially convertible by thrombin, were measured. Significance was at p < 0.05.

Results

FA-WB-VCAM at baseline sample hematocrit was significantly elevated (Figure 1) in PKD subjects (808±377 cells/mm², n=10) compared to healthy controls (6±4 cells/mm², n=4) and even to our previously reported steady state levels in sickle cell samples (290±50 cells/mm² [2]. Thrombin generation profiles were similar between PKD subjects and healthy controls with the exception of the thrombin generation index (PPP+TP/PPP)*100ETP that was significantly (p<<0.01) elevated in citrated plasma of PKD subjects (92.9±6.8) as compared to healthy controls (68.6±11.9). For PKD subjects, FA-WB-VCAM correlated significantly with platelet counts (R²=0.81, p<0.05), and FAAv-WB-VCAM was negatively correlated with platelet (P=0.03, R ²=0.5), but not with erythrocyte-derived microparticles (MP). Platelet-derived MP strongly correlated with thrombin generation (ETP, p<0.01, R ²=0.76) but not with LT or ttPeak of thrombin generation. Red blood cell MP were significantly (p=0.02) decreased in splenectomized patients (200±170, n=7) vs. non-splenectomized subjects (2090±1860, n=3). LT and ttPeak were significantly longer in PKD subjects with thrombosis history than without.

Conclusions

PKD subjects in this study had elevated RBC adhesive properties similar to that observed in SCD, confirming that pathologic RBC membrane damage resulting in increased adhesion is a common feature of hemolytic anemias. The hemoglobin level of 7.8±1.1 g/dL (mean±SD) for PKD patients was within 6 to 11 g/dl range of hemoglobin levels typical for SCD. There was no significant difference in any other measured parameters (thrombin generation, adhesion avidity, microparticles data). Thrombin generation in PKD subjects was not consistent with hypercoagulability. Based on these observations, pathologic RBC adhesion may be both a novel a mechanism driving hypercoagulability in individuals with PKD. Further studies to determine whether RBC-modifying therapies may decrease thrombosis risk in PKD are warranted.

1. Zia A, Callaghan MU, Callaghan JH, et al. Hypercoagulability in adolescent girls on oral contraceptives - global coagulation profile and estrogen receptor polymorphisms. Am J Hematol, 2015;90:725-31

2. Pittman DD, Hines PC, Beidler D, et al. Evaluation of Longitudinal Pain Study in Sickle Cell Disease (ELIPSIS) by patient-reported outcomes, actigraphy, and biomarkers. Blood. 2021;137(15):2010-20

Figure 1

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Figure 1

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