No abstract

Although red blood cell (RBC) transfusions can be lifesaving, they are not without risk. In critically ill patients, RBC transfusions are associated with increased morbidity and mortality, which may increase with prolonged RBC storage before transfusion. The mechanisms responsible remain unknown. We hypothesized that acute clearance of a subset of damaged, stored RBCs delivers large amounts of iron to the monocyte/macrophage system, inducing inflammation. To test this in a well-controlled setting, we used a murine RBC storage and transfusion model to show that the transfusion of stored RBCs, or washed stored RBCs, increases plasma nontransferrin bound iron (NTBI), produces acute tissue iron deposition, and initiates inflammation. In contrast, the transfusion of fresh RBCs, or the infusion of stored RBC-derived supernatant, ghosts, or stroma-free lysate, does not produce these effects. Furthermore, the insult induced by transfusion of stored RBC synergizes with subclinical endotoxinemia producing clinically overt signs and symptoms. The increased plasma NTBI also enhances bacterial growth in vitro. Taken together, these results suggest that, in a mouse model, the cellular component of leukoreduced, stored RBC units contributes to the harmful effects of RBC transfusion that occur after prolonged storage. Nonetheless, these findings must be confirmed by prospective human studies.

Transfusions of RBCs stored for longer durations are associated with adverse effects in hospitalized patients. We prospectively studied 14 healthy human volunteers who donated standard leukoreduced, double RBC units. One unit was autologously transfused "fresh" (3-7 days of storage), and the other "older" unit was transfused after 40 to 42 days of storage. Of the routine laboratory parameters measured at defined times surrounding transfusion, significant differences between fresh and older transfusions were only observed in iron parameters and markers of extravascular hemolysis. IntroductionThe safety of transfusing RBCs after longer durations of refrigerated storage was recently identified as "the most critical issue facing transfusion medicine." 1 page 667 Concern was heightened when a large observational study of cardiac surgery patients found an increased risk of postoperative complications and reduced survival in those who received RBCs stored for more than 14 days. 2 Although still controversial, adverse clinical consequences have since been reported in most, [3][4][5] although not all, 6,7 epidemiologic studies of transfusions of RBCs stored for longer durations, but still within Food and Drug Administration (FDA) guidelines. The association between the duration of RBC storage and increased rates of serious infections, sepsis, and mortality is particularly strong in trauma patients. [7][8][9][10][11] Definitive determination of the potential risks associated with transfusion of RBCs stored for longer durations has been elusive, in part because the mechanisms responsible have not yet been identified.More than 14 million RBC units are transfused in the United States each year, with a mean storage interval of 18 days before transfusion. 12 During storage, RBCs undergo cumulative biochemical and biomechanical changes (the "storage lesion") that reduce their survival in vivo after transfusion. 13,14 In mouse models, 15 transfusion of RBCs stored for longer durations was followed by brisk extravascular clearance of a subpopulation of these cells, which were damaged during storage and removed by macrophages in the spleen and liver of recipient mice. The iron liberated by phagocytic digestion of these RBCs rapidly entered the systemic circulation in amounts that exceeded the transport capacity of plasma transferrin, the physiologic iron-binding protein; in this way, circulating non-transferrin-bound iron appeared and promoted the proliferation of pathogenic bacteria both in vitro 15 and in vivo. 16 We hypothesized that the infectious complications observed in human patients after transfusion of RBCs stored for longer durations were, at least in part, the result of the production of circulating non-transferrin-bound iron. Therefore, we prospectively examined healthy human volunteers to determine (1) if transfusion of autologous RBCs stored for longer durations was followed by the appearance of circulating non-transferrin-bound iron in vivo, and (2) if this increased circulating non-transferrinbound iron was assoc...

The SARS-CoV-2 beta coronavirus is the etiological driver of COVID-19 disease, which is primarily characterized by shortness of breath, persistent dry cough, and fever. Because they transport oxygen, red blood cells (RBCs) may play a role in the severity of hypoxemia in COVID-19 patients. The present study combines state-of-the-art metabolomics, proteomics, and lipidomics approaches to investigate the impact of COVID-19 on RBCs from 23 healthy subjects and 29 molecularly diagnosed COVID-19 patients. RBCs from COVID-19 patients had increased levels of glycolytic intermediates, accompanied by oxidation and fragmentation of ankyrin, spectrin beta, and the N-terminal cytosolic domain of band 3 (AE1). Significantly altered lipid metabolism was also observed, in particular, short- and medium-chain saturated fatty acids, acyl-carnitines, and sphingolipids. Nonetheless, there were no alterations of clinical hematological parameters, such as RBC count, hematocrit, or mean corpuscular hemoglobin concentration, with only minor increases in mean corpuscular volume. Taken together, these results suggest a significant impact of SARS-CoV-2 infection on RBC structural membrane homeostasis at the protein and lipid levels. Increases in RBC glycolytic metabolites are consistent with a theoretically improved capacity of hemoglobin to off-load oxygen as a function of allosteric modulation by high-energy phosphate compounds, perhaps to counteract COVID-19-induced hypoxia. Conversely, because the N-terminus of AE1 stabilizes deoxyhemoglobin and finely tunes oxygen off-loading and metabolic rewiring toward the hexose monophosphate shunt, RBCs from COVID-19 patients may be less capable of responding to environmental variations in hemoglobin oxygen saturation/oxidant stress when traveling from the lungs to peripheral capillaries and vice versa.

Hypoxanthine catabolism in vivo is potentially dangerous as it fuels production of urate and, most importantly, hydrogen peroxide. However, it is unclear whether accumulation of intracellular and supernatant hypoxanthine in stored red blood cell units is clinically relevant for transfused recipients. Leukoreduced red blood cells from glucose-6-phosphate dehydrogenase-normal or -deficient human volunteers were stored in AS-3 under normoxic, hyperoxic, or hypoxic conditions (with oxygen saturation ranging from <3% to >95%). Red blood cells from healthy human volunteers were also collected at sea level or after 1–7 days at high altitude (>5000 m). Finally, C57BL/6J mouse red blood cells were incubated in vitro with 13C1-aspartate or 13C5-adenosine under normoxic or hypoxic conditions, with or without deoxycoformycin, a purine deaminase inhibitor. Metabolomics analyses were performed on human and mouse red blood cells stored for up to 42 or 14 days, respectively, and correlated with 24 h post-transfusion red blood cell recovery. Hypoxanthine increased in stored red blood cell units as a function of oxygen levels. Stored red blood cells from human glucose-6-phosphate dehydrogenase-deficient donors had higher levels of deaminated purines. Hypoxia in vitro and in vivo decreased purine oxidation and enhanced purine salvage reactions in human and mouse red blood cells, which was partly explained by decreased adenosine monophosphate deaminase activity. In addition, hypoxanthine levels negatively correlated with post-transfusion red blood cell recovery in mice and – preliminarily albeit significantly - in humans. In conclusion, hypoxanthine is an in vitro metabolic marker of the red blood cell storage lesion that negatively correlates with post-transfusion recovery in vivo. Storage-dependent hypoxanthine accumulation is ameliorated by hypoxia-induced decreases in purine deamination reaction rates.