Science of Storage Lesion
The storage lesion refers to the collection of changes that occur to red blood cells (RBCs) during storage. RBC experience progressive damage during storage that may affect their viability, impact the ability of the vessels to facilitate blood flow, decrease the red cell’s ability to delivery oxygen, and increase the generation of potentially harmful waste particles. The existence of the storage lesion process has been well established, and recent scientific work has increased the precision and depth with which the field understands these effects.
ATP is the source of energy within all living cells. It is produced within a cell by converting fuel molecules, then expended at other locations within the same cell for maintaining its vital functions. When ATP is lost, the red cell loses ability to maintain its characteristic shape as well as sustain its vital functions, resulting in removal from circulation. In RBC, ATP is produced by glycolysis (the breakdown of glucose) and converted into lactic acid without needing oxygen, in contrast to nearly all other cells in the human body. ATP in RBC also serves as a signaling molecule for regional vasodilation (widening of blood vessels) under oxygen-deprived conditions in tissue.
One of the most notable changes during RBC storage is the rapid fall of 2,3-DPG.2 This molecule influences hemoglobin (the oxygen carrier and main constituents of RBC giving its color) so that it releases oxygen to the tissues more easily. Without 2,3-DPG, oxygen would be more tightly bound to hemoglobin and thus less easily off-loaded to body tissues. Levels of 2,3-DPG have been shown to fall quickly during current methods of storage of RBC, becoming nearly undetectable within one to two weeks.
The physical shape of RBCs also goes through a progressive change during storage, affected by the oxidative damage to their membranes (skin) as well as the changes brought on by the depletion of ATP. These effects cause RBC to shed damaged membrane during storage thereby transforming RBC from a pliable biconcave disc that has the capacity to fold and deform into narrow capillaries, into an aspherical shape that cannot deform because, unlike a balloon, the RBC membrane is not stretchable. Alterations in the deformability of an RBC has substantial impact on its ability to traverse the microcirculation where capillary vessels may be as small as 3 to 8-µM in diameter, smaller than RBC’s 8.5µm diameter of the biconcave disc.
Loss of red cell integrity during storage results in hemolysis (destruction of red cells) during storage and after transfusion. The transfusion of a large volume of damaged non-viable cells results in the release of hemoglobin and iron contained within hemoglobin as the body attempts to clear the waste from its system. These byproducts of oxidative stress can have an inflammatory effect on recipients, as well as increase the risk of bacterial infection.
Microparticles, fragments of RBC formed during storage, will scavenge nitric oxide (NO) similarly to free hemoglobin released during hemolysis. NO plays a critical role in regulating vascular reactivity, allowing the blood vessels to dilate to facilitate blood flow to tissues in response to increased oxygen need. When NO availability is impaired, the “gates” do not open fully to allow oxygen delivery. Combined with the loss in RBC deformability, peripheral tissue oxygen delivery compromised.