(374d) Magnetic Separation of Apoptotic Red Blood Cells for Better Blood Transfusion Practices

Authors: 
Kim, J., Ohio State University
Chalmers, J. J., The Ohio State University
Weigand, M., The Ohio State University
In 1936, Pauling and Coryell observed that human RBCs in different chemical state express different magnetic moment due to the number of unpaired electrons between the hemoglobin and the stored iron. This difference in magnetic moment has led many researchers to explore the possibility of magnetically separating the RBCs. In 2017, Chalmers et al. has found that RBCs lose an average of 17% of their hemoglobin during ex vivo storage using magnetic characterization method. This finding has brought many attentions around the blood community for the need of better blood transfusion practices. In this study, we focus on attempting to find the relationship between the loss of hemoglobin in RBCs and the translocation of phosphatidylserine (PS, a phospholipid commonly used for detecting apoptosis of animal cells) and investigate the feasibility of magnetically separating the apoptotic RBCs from the fresh, healthy RBCs for blood transfusion.
Five expired human RBC units were obtained and were oxidized with sodium nitrate solution into paramagnetic RBCs. After labelling the RBCs with Annexin-V FLUOS (a fluorescent marker that would bind to translocated PS), the sample was sorted into four population based on the intensity of the marker expression using flow cytometer. The sorted samples were then magnetically characterized using the cell tracking velocimetry system (CTV), an analysis system that uses scientific camera and magnetic microfluidic channel to measure/quantify the magnetic susceptibility of cells. Then, the magnetic deposition microscopy (MDM), which is a microfluidic magnetic separation system, has been numerically modelled using a combination of commercial computational fluid dynamics software (ANSYS-Fluent) and custom algorithm that uses the magnetic characterization data from CTV. This numerical simulation method was used to calculate the theoretical separation site of the paramagnetic RBCs.
The magnetic data of the sorted RBCs were converted into pgHb/cell, a common unit measure used in the clinic to detect low iron deficiency anemia, and high PS expressing sub-population was shown to be low in hemoglobin concentration compared to the other sub-populations. The numerical model of the MDM system has also shown that different magnetic moment of entities can lead to different location of the deposition location, implying that the different magnetic moment of high PS-expressing (damaged) RBCs and PS-negative (healthy) RBCs could be used to magnetically separate healthy and damaged RBCs.
Annually, an average of 21 million units of human blood components are transfused in the US for various medical purposes. However, the blood transfusion efficiency (the rate of transfused RBCs’ survival rate in a human recipient after 24 hours) is known to be about 75%, which can lead to serious clinical effects such as impaired oxygen delivery, iron overload, and many more. With the improvement in transfusion practices through these findings in research, more effective blood transfusion will be possible.