Hypoxic Storage of Red Blood Cells: Assessment of Adhesion Properties Using a Standardized Endothelium-on-a-Chip Microfluidic Platform

Background: Blood transfusions are routine medical procedures in which stored blood or blood products (i.e., red blood cells, RBCs) are given to the patient to prevent adverse health outcomes due to acute or chronic anemia. The current regulations require RBCs to be stored at 4 ºC not more than 42 days before a transfusion. However, RBCs undergo extensive rheological changes during storage and may contribute to complications associated with transfusion. Hemanext has recently introduced an innovative storage system to ameliorate such storage lesions, in which RBCs are stored in a hypoxic environment, and thus they are exposed to much lower oxidative stress during storage. In this study, we report the changes in adhesion properties of stored RBCs to human endothelial cells following a 42-day storage in normoxia vs hypoxia, using a standardized endothelialized microfluidic platform: Endothelium-on-a-chip.

Methods: Two units of 1-day old blood type O positive leukocyte reduced RBCs in additive solution were pooled and divided into equal aliquots (300mL each) A and B. Unit A was stored under conventional normoxic storage condition at 4°C for 42 days. Unit B was deoxygenated so that the percent oxygen saturation of the hemoglobin was less than 20%. The deoxygenated RBCs were stored in an oxygen impermeable storage bag for 42 days at 4°C. Adhesion levels were tested at the beginning (baseline, Week 1) and the end of the storage period (Week 6). To conduct the adhesion experiments, human umbilical vein endothelial cells (HUVECs) were first cultured within microfluidic channels under flow for at least 48 hours. Next, the HUVECs were treated with 40 µM heme for 4 hours at 37 ºC [1]. RBCs were centrifuged to remove the storage buffer and resuspended in basal cell culture medium (EGM, Lonza, Morristown, USA) supplemented with 10 mM HEPES at a hematocrit of 40%. A 15 µl of RBC solution was then injected over heme-activated HUVECs at a shear stress of 1 dyne/cm ² followed by a 10-minute rinse with fresh basal culture medium to remove non-adherent RBCs. At the end of the experiment, adherent erythrocytes were manually quantified. Control experiments were conducted with non-activated HUVECs.

Results: We found that RBCs that were stored under conventional normoxic condition displayed higher adhesion to heme-activated HUVECs than hypoxic condition as illustrated in Figure 1A and 1B. The baseline adhesion levels (Week 1) to non-activated HUVECs (control) were negligible (Fig. 1C, normoxia: 13±6; hypoxia: 18±10, p>0.05) while both cell populations had considerable adhesion levels to heme-activated HUVECs at baseline (Fig. 1C, normoxia: 372±59; hypoxia: 335±37). Following a 6-week storage, adhesion of RBCs stored in normoxia to heme-activated HUVECs was higher compared to those stored in hypoxic conditions while the p-value was not significant, which was likely due to the limited sample size (Fig. 1C, 1782±519 vs 594±55, p=0.08, N=3). These results suggest that storage-mediated RBC adhesion to heme-activated HUVECs may be ameliorated by the novel hypoxic-storage condition.

Discussion: This study showed a decrease in the adhesion of hypoxic RBCs to heme-activated HUVECs when compared to conventionally stored RBCs for transfusion. This result suggests that hypoxic RBCs may reduce the risk of developing vaso-occlusion (VOC) after RBC transfusion in patients such as in sickle cell disease where adhesion to heme-activated HUVECs has been implicated in the pathogenesis of VOC [1].

Acknowledgements: This work was funded by Hemanext. The authors would like to thank the Ohio Third Frontier Technology Validation and Start-up Fund (TVSF) and National Science Foundation Phase-I Small Business Technology Transfer (STTR) award, which supported this work in part. Stored RBCs were donated by Hemanext.

Reference:

1. Kucukal, E., et al., American Journal of Hematology, 2018. 93(8): p.1050-1060

Figure 1

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Figure 1

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