Quantification of changes in oxygen release from red blood cells as a function of age based on magnetic susceptibility measurements

This study extends the in vitro understanding of the RBC storage lesion by serially analyzing the RBC's magneophoretic mobility, a property dependent on the content and oxygenation or oxidation state of hemoglobin (Hb) iron, during storage. Four prestorage leukoreduced, AS-5 preserved RBC units were stored between 1 and 6 degrees C for 42 days. Weekly starting on storage day 7, each unit was sampled, divided into 3 aliquots, each subjected to different reactions: one aliquot was exposed to room air to produce oxyhemoglobin (oxyHb), another aliquot was mixed with sodium nitrite to produce methemoglobin (metHb), while the third aliquot was desaturated of oxygen (deoxyhemoglobin, deoxyHb) using nitrogen gas. These aliquots were placed into a cell tracking velocimetry (CTV) apparatus which measured both the settling velocity (u(s)) of the RBCs as well as their magnetically induced velocity (u(m)). The u(m)/u(s) ratio depends on the oxygenation state of the hemoglobin and the quantity of iron within the RBC. The RBC density was measured by percoll centrifugation. There was a significant reduction in the u(m)/u(s) ratio for the deoxyHb RBC aliquot as storage time elapsed, with a smaller but still significant reduction in the u(m)/u(s) ratio for the metHb aliquot. The average RBC density decreased very slightly during storage, as determined by the percoll centrifugation technique, although the average settling velocity (another measure of cell density) seemed to fluctuate during storage. The decrease in magnetophoretic mobility of the deoxyHb portion is explicable either by Hb's increased affinity for oxygen during storage, or else a loss of iron from the cells.