CO2 -dependent metabolic modulation in red blood cells stored under anaerobic conditions

Impact of production methods and storage conditions on extracellular vesicles in packed red blood cells and platelet concentrates

The use of blood and blood products can be life-saving, but there are also certain risks associated with their administration and use. Packed red blood cells (pRBCs) and platelet concentrates are the most commonly used blood products in transfusion medicine to treat anemia or acute and chronic bleeding disorders, respectively. During the production and storage of blood products, red blood cells and platelets release extracellular vesicles (EVs) as a result of the storage lesion, which may affect product quality. EVs are subcellular structures enclosed by a lipid bilayer and originate from the endosomal system or from the plasma membrane. They play a pivotal role in intercellular communication and are emerging as important regulators of inflammation and coagulation. Their cargo and their functional characteristics depend on the cell type from which they originate, as well as on their microenvironment, influencing their capacity to promote coagulation and inflammatory responses. Hence, the potential involvement of EVs in transfusion-related adverse events is increasingly recognized and studied. Here, we review the knowledge regarding the effect of production and storage conditions of pRBCs and platelet concentrates on the release of EVs. In this context, the mode of processing and anticoagulation, the influence of additive solutions and leukoreduction, as well as the storage duration will be addressed, and we discuss potential implications of EVs for the clinical outcome of transfusion.

Evaluating the effects of hypoxic storage on platelet function and health using a novel storage system

BACKGROUND

Thousands of units of whole blood (WB) and blood components are transfused daily to treat trauma patients. Improved methods for blood storage are critical to support trauma-related care. The Hemanext ONE® system offers a unique method for hypoxic storage of WB, with successfully demonstrated storage of clinically viable RBCs. This work evaluated the system for the storage of WB, focusing on platelet health and function.

STUDY DESIGN AND METHODS

WB was collected from healthy donors and processed through the Hemanext ONE® system. Hemoglobin oxygen saturation (HbSO2) levels of WB were depleted to 10%, 20%, or 30% of total HbSO2 and then stored in PVC bags sealed in oxygen-impermeable bags (except for normoxic control) with samples collected on days 1, 7, and 14 post-processing. Flow cytometry assessed the activation and apoptosis of platelets. Clot dynamics were assessed based on aggregometry and thromboelastography assays, as well as thrombin generation using a calibrated-automated thrombogram method.

RESULTS

Hypoxic storage conditions were maintained throughout the storage period. Hypoxia triggered increased lactate production, but pH changes were negligible compared to normoxic control. Storage at 10% HbSO2 had a significant impact on platelet function, resulting in increased activation and reduced clot formation and aggregation. These effects were less significant at 20% and 30% HbSO2.

DISCUSSION

This study indicates that platelets are sensitive to hypoxic storage and suffer significant metabolic and functional deterioration when stored at or below 10% HbSO2.

Red Blood Cell Storage with Xenon: Safe or Disruption?

Xenon, an inert gas commonly used in medicine, has been considered as a potential option for prolonged preservation of donor packed red blood cells (pRBCs) under hypoxic conditions. This study aimed to investigate how xenon affects erythrocyte parameters under prolonged storage. In vitro model experiments were performed using two methods to create hypoxic conditions. In the first method, xenon was introduced into bags of pRBCs which were then stored for 42 days, while in the second method, xenon was added to samples in glass tubes. The results of our experiment showed that the presence of xenon resulted in notable alterations in erythrocyte morphology, similar to those observed under standard storage conditions. For pRBC bags, hemolysis during storage with xenon exceeded the acceptable limit by a factor of six, whereas the closed-glass-tube experiment showed minimal hemolysis in samples exposed to xenon. Notably, the production of deoxyhemoglobin was specific to xenon exposure in both cell suspension and hemolysate. However, this study did not provide evidence for the purported protective properties of xenon.

Extracellular vesicles: effectors of transfusion-related acute lung injury

Respiratory transfusion reactions represent some of the most severe adverse reactions related to receiving blood products. Of those, transfusion-related acute lung injury (TRALI) is associated with elevated morbidity and mortality. TRALI is characterized by severe lung injury associated with inflammation, pulmonary neutrophil infiltration, lung barrier leak, and increased interstitial and airspace edema that cause respiratory failure. Presently, there are few means of detecting TRALI beyond clinical definitions based on physical examination and vital signs or preventing/treating TRALI beyond supportive care with oxygen and positive pressure ventilation. Mechanistically, TRALI is thought to be mediated by the culmination of two successive proinflammatory hits, which typically comprise a recipient factor (1st hit-e.g., systemic inflammatory conditions) and a donor factor (2nd hit-e.g., blood products containing pathogenic antibodies or bioactive lipids). An emerging concept in TRALI research is the contribution of extracellular vesicles (EVs) in mediating the first and/or second hit in TRALI. EVs are small, subcellular, membrane-bound vesicles that circulate in donor and recipient blood. Injurious EVs may be released by immune or vascular cells during inflammation, by infectious bacteria, or in blood products during storage, and can target the lung upon systemic dissemination. This review assesses emerging concepts such as how EVs: 1) mediate TRALI, 2) represent targets for therapeutic intervention to prevent or treat TRALI, and 3) serve as biochemical biomarkers facilitating TRALI diagnosis and detection in at-risk patients.

Atomic Force Microscopy and High-Resolution Spectrophotometry for Study of Anoxemia and Normoxemia in Model Experiment In Vitro

The oxygen content in the blood may decrease under the influence of various physicochemical factors and different diseases. The state of hypoxemia is especially dangerous for critically ill patients. In this paper, we describe and analyze the changes in the characteristics of red blood cells (RBCs) with decreasing levels of oxygen in the RBC suspension from normoxemia to hypoxemia/anoxemia in an in vitro model experiment. The RBCs were stored in hypoxemia/anoxemia and normoxemia conditions in closed and open tubes correspondingly. For the quantitative study of RBC parameter changes, we used atomic force microscopy, digital spectrophotometry, and nonlinear curve fitting of the optical spectra. In both closed and open tubes, at the end of the storage period by day 29, only 2% of discocytes remained, and mainly irreversible types, such as microspherocytes and ghosts, were observed. RBC hemolysis occurred at a level of 25-30%. Addition of the storage solution, depending on the concentration, changed the influence of hypoxemia on RBCs. The reversibility of the change in hemoglobin derivatives was checked. Based on the experimental data and model approach, we assume that there is an optimal level of hypoxemia at which the imbalance between the oxidative and antioxidant systems, the rate of formation of reactive oxygen species, and, accordingly, the disturbances in RBCs, will be minimal.

Red Blood Cell Metabolism In Vivo and In Vitro

Red blood cells (RBC) are the most abundant cell in the human body, with a central role in oxygen transport and its delivery to tissues. However, omics technologies recently revealed the unanticipated complexity of the RBC proteome and metabolome, paving the way for a reinterpretation of the mechanisms by which RBC metabolism regulates systems biology beyond oxygen transport. The new data and analytical tools also informed the dissection of the changes that RBCs undergo during refrigerated storage under blood bank conditions, a logistic necessity that makes >100 million units available for life-saving transfusions every year worldwide. In this narrative review, we summarize the last decade of advances in the field of RBC metabolism in vivo and in the blood bank in vitro, a narrative largely influenced by the authors' own journeys in this field. We hope that this review will stimulate further research in this interesting and medically important area or, at least, serve as a testament to our fascination with this simple, yet complex, cell.

Hypoxic storage of murine red blood cells improves energy metabolism and post-transfusion recoveries

BACKGROUND

The Red blood cell (RBC) storage lesion results in decreased circulation and function of transfused RBCs. Elevated oxidant stress and impaired energy metabolism are a hallmark of the storage lesion in both human and murine RBCs. Although human studies don't suffer concerns that findings may not translate, they do suffer from genetic and environmental variability amongst subjects. Murine models can control for genetics, environment, and much interventional experimentation can be carried out in mice that is neither technically feasible nor ethical in humans. However, murine models are only useful to the extent that they have similar biology to humans. Hypoxic storage has been shown to mitigate the storage lesion in human RBCs, but has not been investigated in mice.

MATERIALS AND METHODS

RBCs from a C57BL6/J mouse strain were stored under normoxic (untreated) or hypoxic conditions (SO2 ~ 26%) for 1h, 7 and 12 days. Samples were tested for metabolomics at steady state, tracing experiments with 1,2,3-¹³C₃-glucose, proteomics and end of storage post transfusion recovery.

RESULTS

Hypoxic storage improved post-transfusion recovery and energy metabolism, including increased steady state and ¹³C₃-labeled metabolites from glycolysis, high energy purines (adenosine triphosphate) and 2,3-diphospholgycerate. Hypoxic storage promoted glutaminolysis, increased glutathione pools, and was accompanied by elevation in the levels of free fatty acids and acyl-carnitines.

DISCUSSION

This study isolates hypoxia, as a single independent variable, and shows similar effects as seen in human studies. These findings also demonstrate the translatability of murine models for hypoxic RBC storage and provide a pre-clinical platform for ongoing study.

Hypoxic storage of donor red cells preserves deformability after exposure to plasma from adults with sickle cell disease

BACKGROUND

Red cell (RBC) transfusions are beneficial for patients with sickle cell disease (SCD), but ex vivo studies suggest that inflamed plasma from patients with SCD during crises may damage these RBCs, diminishing their potential efficacy. The hypoxic storage of RBCs may improve transfusion efficacy by minimizing the storage lesion. We tested the hypotheses that (1) The donor RBCs exposed to the plasma of patients in crisis would have lower deformability and higher hemolysis than those exposed to non-crisis plasma, and (2) hypoxic storage, compared to standard storage, of donor RBCs could preserve deformability and reduce hemolysis.

STUDY DESIGN AND METHODS

18 SCD plasma samples from patients who had severe acute-phase symptoms (A-plasma; n = 9) or were at a steady-state (S = plasma; n = 9) were incubated with 16 RBC samples from eight units that were stored either under conventional(CRBC) or hypoxic(HRBC) conditions. Hemolysis and microcapillary deformability assays of these RBCs were analyzed using linear mixed-effect models after each sample was incubated in patient plasma overnight at 37°C RESULTS: Relative deformability was 0.036 higher (p < 0.0001) in HRBC pairs compared to CRBC pairs regardless of plasma type. Mean donor RBC hemolysis was 0.33% higher after incubation with A-plasma compared to S-plasma either with HRBC or CRBC (p = 0.04). HRBCs incubated with steady-state patient plasma demonstrated the highest deformability and lowest hemolysis.

CONCLUSION

Hypoxic storage significantly influenced RBC deformability. Patient condition significantly influenced post-incubation hemolysis. Together, HRBCs in steady-state plasma maximized donor red cell ex vivo function and survival.

Intermittent scavenging of storage lesion from stored red blood cells by electrospun nanofibrous sheets enhances their quality and shelf-life

Transfusion of healthy red blood cells (RBCs) is a lifesaving process. However, upon storing RBCs, a wide range of damage-associate molecular patterns (DAMPs), such as cell-free DNA, nucleosomes, free-hemoglobin, and poly-unsaturated-fatty-acids are generated. DAMPs can further damage RBCs; thus, the quality of stored RBCs declines during the storage and limits their shelf-life. Since these DAMPs consist of either positive or negative charged species, we developed taurine and acridine containing electrospun-nanofibrous-sheets (Tau-AcrNFS), featuring anionic, cationic charges and an DNA intercalating group on their surfaces. We show that Tau-AcrNFS are efficient in scavenging DAMPs from stored human and mice RBCs ex vivo. We find that intermittent scavenging of DAMPs by Tau-AcrNFS during the storage reduces the loss of RBC membrane integrity and reduces discocytes-to-spheroechinocytes transformation in stored-old-RBCs. We perform RBC-transfusion studies in mice to reveal that intermittent removal of DAMPs enhances the quality of stored-old-RBCs equivalent to freshly collected RBCs, and increases their shelf-life by ~22%. Such prophylactic technology may lead to the development of novel blood bags or medical device, and may therefore impact healthcare by reducing transfusion-related adverse effects.

A deep 96-well plate RBC storage platform for high-throughput screening of novel storage solutions

Background: Red blood cell (RBC) storage solutions, also known as additive solutions (ASs), first developed in the 1970s, enable extended storage of RBCs. Unfortunately, the advancements in this field have been limited, due to labor intensive and time-consuming serial in vitro and in vivo testing, coupled with very high commercialization hurdles. This study examines the utility of deep 96-well plates for preliminary screenings of novel ASs through comparison of RBC storage with the standard PVC bags in terms of hemolysis and ATP levels, under both normoxic (N) and hypoxic/hypocapnic (H) storage conditions. The necessity for the presence of DEHP, normally provided by PVC bags, is also examined. Materials and methods: A pool of 2 ABO compatible RBC units was split between a bag and a plate. Each plate well contained either 1, 2 or 0 PVC strips cut from standard storage bags to supply DEHP. The H bags and plates were processed in an anaerobic glovebox and stored in O2 barrier bags. Hemolysis and ATP were measured bi-weekly using standard methods. Results: Final ATP and hemolysis values for the plate-stored RBCs were comparable to the typical values observed for 6-week storage of leukoreduced AS-3 RBCs in PVC bags under both N and H conditions. Hemolysis was below FDA and EU benchmarks of 1% and 0.8%, respectively, and excluding DEHP from plates during storage, resulted in an inconsequential increase when compared to bag samples. Discussion: In combination with high-throughput metabolomics workflow, this platform provides a highly efficient preliminary screening platform to accelerate the initial testing and consequent development of novel RBC ASs.

Metabolic reprogramming under hypoxic storage preserves faster oxygen unloading from stored red blood cells

Stored red blood cells (RBCs) incur biochemical and morphological changes, collectively termed the storage lesion. Functionally, the storage lesion manifests as slower oxygen unloading from RBCs, which may compromise the efficacy of transfusions where the clinical imperative is to rapidly boost oxygen delivery to tissues. Recent analysis of large real-world data linked longer storage with increased recipient mortality. Biochemical rejuvenation with a formulation of adenosine, inosine, and pyruvate can restore gas-handling properties, but its implementation is impractical for most clinical scenarios. We tested whether storage under hypoxia, previously shown to slow biochemical degradation, also preserves gas-handling properties of RBCs. A microfluidic chamber, designed to rapidly switch between oxygenated and anoxic superfusates, was used for single-cell oxygen saturation imaging on samples stored for up to 49 days. Aliquots were also analyzed flow-cytometrically for side-scatter (a proposed proxy of O2 unloading kinetics), metabolomics, lipidomics and redox proteomics. For benchmarking, units were biochemically rejuvenated at four weeks of standard storage. Hypoxic storage hastened O2 unloading in units stored to 35 days, an effect that correlated with side-scatter but was not linked to post-translational modifications of hemoglobin. Although hypoxic storage and rejuvenation produced distinct biochemical changes, a subset of metabolites including pyruvate, sedoheptulose 1-phosphate, and 2/3 phospho-D-glycerate, was a common signature that correlated with changes in O2 unloading. Correlations between gas-handling and lipidomic changes were modest. Thus, hypoxic storage of RBCs preserves key metabolic pathways and O2 exchange properties, thereby improving the functional quality of blood products and potentially influencing transfusion outcomes.

High-Throughput Metabolomics Platform for the Rapid Data-Driven Development of Novel Additive Solutions for Blood Storage

Red blood cell transfusion is a life-saving intervention, and storage is a logistic necessity to make ~110 million units available for transfusion every year worldwide. However, storage in the blood bank is associated with a progressive metabolic decline, which correlates with the accumulation of morphological lesions, increased intra- and extra-vascular hemolysis upon transfusion, and altered oxygen binding/off-loading kinetics. Prior to storage, red blood cells are suspended in nutrient formulations known as additive solutions to prolong cellular viability. Despite a thorough expansion of knowledge regarding red blood cell biology over the past few decades, only a single new additive solution has been approved by the Food and Drug Administration this century, owing in part to the limited capacity for development of novel formulations. As a proof of principle, we leveraged a novel high-throughput metabolomics technology as a platform for rapid data-driven development and screening of novel additive solutions for blood storage under both normoxic and hypoxic conditions. To this end, we obtained leukocyte-filtered red blood cells (RBCs) and stored them under normoxic or hypoxic conditions in 96 well plates (containing polyvinylchloride plasticized with diethylhexylphthalate to concentrations comparable to full size storage units) in the presence of an additive solution supplemented with six different compounds. To inform this data-driven strategy, we relied on previously identified metabolic markers of the RBC storage lesion that associates with measures of hemolysis and post-transfusion recovery, which are the FDA gold standards to predict stored blood quality, as well as and metabolic predictors of oxygen binding/off-loading parameters. Direct quantitation of these predictors of RBC storage quality were used here-along with detailed pathway analysis of central energy and redox metabolism-as a decision-making tool to screen novel additive formulations in a multiplexed fashion. Candidate supplements are shown here that boost-specific pathways. These metabolic effects are only in part dependent on the SO2 storage conditions. Through this platform, we anticipate testing thousands of novel additives and combinations thereof in the upcoming months.

Effect of Hypoxic Blood Infusion on Pulmonary Physiology

The ability to store red blood cells (RBCs) and other components for extended periods of time has expanded the availability and use of transfusion as a life-saving therapy. However, conventional RBC storage has a limited window of effective preservation and is accompanied by the progressive accumulation of a series of biochemical and morphological modifications, collectively referred to as “storage lesions.” These lesions have been associated with negative clinical outcomes (i.e., postoperative complications as well as reduced short-term and long-term survival) in patients transfused with conventionally stored blood with older and deteriorated transfused red cells. Hence, there is an increased unmet need for improved RBC storage. Hypoxic storage of blood entails the removal of large amounts of oxygen to low levels prior to refrigeration and maintenance of hypoxic levels through the entirety of storage. As opposed to conventionally stored blood, hypoxic storage can lead to a reduction of oxidative damage to slow storage lesion development and create a storage condition expected to result in enhanced efficacy of stored RBCs without an effect on oxygen exchange in the lung. Hypoxic blood transfusions appear to offer minimal safety concerns, even in patients with hypoxemia. This review describes the physiology of hypoxically stored blood, how it differs from conventionally stored blood, and its use in potential clinical application, such as massively transfused and critically ill patients with oxygenation/ventilation impairments.

Generation and Export of Red Blood Cell ATP in Health and Disease

Metabolic homeostasis in animals depends critically on evolved mechanisms by which red blood cell (RBC) hemoglobin (Hb) senses oxygen (O₂) need and responds accordingly. The entwined regulation of ATP production and antioxidant systems within the RBC also exploits Hb-based O₂-sensitivity to respond to various physiologic and pathophysiologic stresses. O₂ offloading, for example, promotes glycolysis in order to generate both 2,3-DPG (a negative allosteric effector of Hb O₂ binding) and ATP. Alternatively, generation of the nicotinamide adenine dinucleotide phosphate (NADPH) critical for reducing systems is favored under the oxidizing conditions of O₂ abundance. Dynamic control of ATP not only ensures the functional activity of ion pumps and cellular flexibility, but also contributes to the availability of vasoregulatory ATP that can be exported when necessary, for example in hypoxia or upon RBC deformation in microvessels. RBC ATP export in response to hypoxia or deformation dilates blood vessels in order to promote efficient O₂ delivery. The ability of RBCs to adapt to the metabolic environment via differential control of these metabolites is impaired in the face of enzymopathies [pyruvate kinase deficiency; glucose-6-phosphate dehydrogenase (G6PD) deficiency], blood banking, diabetes mellitus, COVID-19 or sepsis, and sickle cell disease. The emerging availability of therapies capable of augmenting RBC ATP, including newly established uses of allosteric effectors and metabolite-specific additive solutions for RBC transfusates, raises the prospect of clinical interventions to optimize or correct RBC function via these metabolite delivery mechanisms.

Effects of hypoxic storage on the efficacy of gamma irradiation in abrogating lymphocyte proliferation and on the quality of gamma-irradiated red blood cells in additive solution 3

BACKGROUND

Gamma irradiation of blood products is used to prevent transfusion-associated graft-versus-host disease by inhibiting the proliferation of lymphocytes that are implicated in the disease. Gamma irradiation also damages the red blood cells (RBCs). It is unknown whether hypoxia reduces the efficacy of gamma irradiation in inhibiting lymphocyte proliferation (LP). The objectives of the study were to investigate the effects of hypoxia on gamma irradiation-induced inhibition of LP and on the in vitro properties of RBCs.

MATERIALS AND METHODS

Forty-four units (300-340 ml each) of less than 8-h-old ABO-matched leukocyte reduced red cell concentrates (LR-RCC) in additive solution 3 were pooled in pairs. Peripheral blood mononuclear cells were isolated from non-leukocyte reduced RCCs and added back to the pool at a final concentration of 2 × 10⁵ /ml. The pool was divided equally into a conventional storage bag A and a hypoxic processing and storage bag B. The units were gamma-irradiated at 25Gy on day 7 for the LP experiment and on either day 7 or 14 for the RBC quality experiments. LP was measured using a limiting dilution assay, and several in vitro metrics of RBCs were measured.

RESULTS

Gamma irradiation inhibited T-lymphocyte proliferation by 4.7 × 10⁴ -fold reduction in both hypoxic and conventional storage. The in vitro metrics of RBC quality were better preserved in hypoxic storage.

DISCUSSION

T lymphocytes present in hypoxic RBC are equally susceptible to gamma irradiation as conventional storage. Hypoxic storage also reduces the deleterious effects of gamma irradiation on RBCs.

Use of antioxidant nanoparticles to reduce oxidative stress in blood storage

Oxidative damage by free radicals has a negative effect on blood quality during storage. Antioxidant nanoparticles can prevent oxidative stress. We use SOD-CAT-Alb-PEG-PLGA- nanoparticles to reduce the effects of oxidative stress in blood storage. Electrospray was employed to prepare nanoparticles. Nanoparticles entered the test bags and were kept for 35 days from the time of donation under standard conditions. On target days, experiments were performed on the samples taken. The examination included blood smear, red blood cells count, hemoglobin, hematocrit, K, Fe, glutathione peroxidase, glutathion reductase, glucose-6-phosphate dehydrogenase, prooxidant-antioxidant balance, malondialdehyde, and flow cytometric assay for phosphatidylserine. The repeated measures analysis was performed on samples every week. Morphological changes were less in the test group compared to the control. The quantitative hemolysis profile test showed significant changes in the test and control groups (p < 0.05) in consecutive weeks except for K and Fe. Oxidative stress parameters too showed a significant change during the target days of the examination (p < 0.05). Also, the phosphatidylserine expression was increased in control groups more than test in consecutive weeks (p < 0.05). It seems that the use of antioxidant nanoparticles improves the quality of stored red blood cells and can prevent posttransfusion complications and blood loss by reducing oxidative stress.

Transfusion of Anaerobically or Conventionally Stored Blood After Hemorrhagic Shock

Background:

Resuscitation from hemorrhagic shock (HS) by blood transfusion restores oxygen (O₂) delivery and provides hemodynamic stability. Current regulations allow red blood cells (RBCs) to be stored and used for up to 42 days. During storage, RBCs undergo many structural and functional changes. These storage lesions have been associated with adverse events and increased mortality after transfusion, increasing the need for improved RBC storage protocols. This study evaluates the efficacy of anaerobically stored RBCs to resuscitate rats from severe HS compared with conventionally stored RBCs.

Methods and results:

Rat RBCs were stored under anaerobic, anaerobic/hypercapnic, or conventional conditions for a period of 3 weeks. Hemorrhage was induced by controlled bleeding, shock was maintained for 30 min, and RBCs were transfused to restore and maintain blood pressure near the prhemorrhage level. All storage conditions met current regulatory 24-h posttransfusion recovery requirements. Transfusion of anaerobically stored RBCs required significantly less RBC volume to restore and maintain hemodynamics. Anaerobic or anaerobic/hypercapnic RBCs restored hemodynamics better than conventionally stored RBCs. Resuscitation with conventionally stored RBCs impaired indices of left ventricular cardiac function, increased hypoxic tissue staining and inflammatory markers, and affected organ function compared with anaerobically stored RBCs.

Conclusions:

Resuscitation from HS via transfusion of anaerobically stored RBCs recovered cardiac function, restored hemodynamic stability, and improved outcomes.

Downregulated Recycling Process but Not De Novo Synthesis of Glutathione Limits Antioxidant Capacity of Erythrocytes in Hypoxia

Red blood cells (RBCs) are susceptible to sustained free radical damage during circulation, while the changes of antioxidant capacity and regulatory mechanism of RBCs under different oxygen gradients remain unclear. Here, we investigated the changes of oxidative damage and antioxidant capacity of RBCs in different oxygen gradients and identified the underlying mechanisms using an in vitro model of the hypoxanthine/xanthine oxidase (HX/XO) system. In the present study, we reported that the hypoxic RBCs showed much higher oxidative stress injury and lower antioxidant capacity compared with normoxic RBCs. In addition, we found that the disturbance of the recycling process, but not de novo synthesis of glutathione (GSH), accounted for the significantly decreased antioxidant capacity of hypoxic RBCs compared to normoxic RBCs. We further elucidated the underlying molecular mechanism by which oxidative phosphorylation of Band 3 blocked the hexose monophosphate pathway (HMP) and decreased NADPH production aggravating the dysfunction of GSH synthesis in hypoxic RBCs under oxidative conditions.

Impact of taurine on red blood cell metabolism and implications for blood storage

BACKGROUND

Taurine is an antioxidant that is abundant in some common energy drinks. Here we hypothesized that the antioxidant activity of taurine in red blood cells (RBCs) could be leveraged to counteract storage-induced oxidant stress.

STUDY DESIGN AND METHODS

Metabolomics analyses were performed on plasma and RBCs from healthy volunteers (n = 4) at baseline and after consumption of a whole can of a common, taurine-rich (1000 mg/serving) energy drink. Reductionistic studies were also performed by incubating human RBCs with taurine ex vivo (unlabeled or ¹³ C¹⁵ N-labeled) at increasing doses (0, 100, 500, and 1000 μmol/L) at 37°C for up to 16 hours, with and without oxidant stress challenge with hydrogen peroxide (0.1% or 0.5%). Finally, we stored human and murine RBCs under blood bank conditions in additives supplemented with 500 μmol/L taurine, before metabolomics and posttransfusion recovery studies.

RESULTS

Consumption of energy drinks increased plasma and RBC levels of taurine, which was paralleled by increases in glycolysis and glutathione (GSH) metabolism in the RBC. These observations were recapitulated ex vivo after incubation with taurine and hydrogen peroxide. Taurine levels in the RBCs from the REDS-III RBC-Omics donor biobank were directly proportional to the total levels of GSH and glutathionylated metabolites and inversely correlated to oxidative hemolysis measurements. Storage of human RBCs in the presence of taurine improved energy and redox markers of storage quality and increased posttransfusion recoveries in FVB mice.

CONCLUSION

Taurine modulates RBC antioxidant metabolism in vivo and ex vivo, an observation of potential relevance to transfusion medicine.

Hypoxic storage of red blood cells improves metabolism and post-transfusion recovery

BACKGROUND

Blood transfusion is a lifesaving intervention for millions of recipients worldwide every year. Storing blood makes this possible but also promotes a series of alterations to the metabolism of the stored erythrocyte. It is unclear whether the metabolic storage lesion is correlated with clinically relevant outcomes and whether strategies aimed at improving the metabolic quality of stored units, such as hypoxic storage, ultimately improve performance in the transfused recipient.

STUDY DESIGN AND METHODS

Twelve healthy donor volunteers were recruited in a two-arm cross-sectional study, in which each subject donated 2 units to be stored under standard (normoxic) or hypoxic conditions (Hemanext technology). End-of-storage measurements of hemolysis and autologous posttransfusion recovery (PTR) were correlated to metabolomics measurements at Days 0, 21, and 42.

RESULTS

Hypoxic red blood cells (RBCs) showed superior PTR and comparable hemolysis to donor-paired standard units. Hypoxic storage improved energy and redox metabolism (glycolysis and 2,3-diphosphoglycerate), improved glutathione and methionine homeostasis, decreased purine oxidation and membrane lipid remodeling (free fatty acid levels, unsaturation and hydroxylation, acyl-carnitines). Intra- and extracellular metabolites in these pathways (including some dietary purines) showed significant correlations with PTR and hemolysis, though the degree of correlation was influenced by sulfur dioxide (SO₂ ) levels.

CONCLUSION

Hypoxic storage improves energy and redox metabolism of stored RBCs, which results in improved posttransfusion recoveries in healthy autologous recipients-a Food and Drug Administration gold standard of stored blood quality. In addition, we identified candidate metabolic predictors of PTR for RBCs stored under standard and hypoxic conditions.

Effects of aged stored autologous red blood cells on human plasma metabolome

Cold storage of blood for 5 to 6 weeks has been shown to impair endothelial function after transfusion and has been associated with measures of end-organ dysfunction. Although the products of hemolysis, such as cell-free plasma hemoglobin, arginase, heme, and iron, in part mediate these effects, a complete analysis of transfused metabolites that may affect organ function has not been evaluated to date. Blood stored for either 5 or 42 days was collected from 18 healthy autologous volunteers, prior to and after autologous transfusion into the forearm circulation, followed by metabolomics analyses. Significant metabolic changes were observed in the plasma levels of hemolytic markers, oxidized purines, plasticizers, and oxidized lipids in recipients of blood stored for 42 days, compared with 5 days. Notably, transfusion of day 42 red blood cells (RBCs) increased circulating levels of plasticizers (diethylhexyl phthalate and derivatives) by up to 18-fold. Similarly, transfusion of day 42 blood significantly increased circulating levels of proinflammatory oxylipins, including prostaglandins, hydroxyeicosatrienoic acids (HETEs), and dihydroxyoctadecenoic acids. Oxylipins were the most significantly increasing metabolites (for 9-HETE: up to ∼41-fold, P = 3.7e-06) in day 42 supernatants. Measurements of arginine metabolism confirmed an increase in arginase activity at the expense of nitric oxide synthesis capacity in the bloodstream of recipients of day 42 blood, which correlated with measurements of hemodynamics. Metabolic changes in stored RBC supernatants impact the plasma metabolome of healthy transfusion recipients, with observed increases in plasticizers, as well as vasoactive, pro-oxidative, proinflammatory, and immunomodulatory metabolites after 42 days of storage.

Transition to 37°C reveals importance of NADPH in mitigating oxidative stress in stored RBCs

The RBC storage lesion is a multiparametric response that occurs during storage at 4°C, but its impact on transfused patients remains unclear. In studies of the RBC storage lesion, the temperature transition from cold storage to normal body temperature that occurs during transfusion has received limited attention. We hypothesized that multiple deleterious events might occur in this period of increasing temperature. We show dramatic alterations in several properties of therapeutic blood units stored at 4°C after warming them to normal body temperature (37°C), as well as febrile temperature (40°C). In particular, the intracellular content and redox state of NADP(H) were directly affected by post-storage incubation at 37°C, as well as by pro-oxidant storage conditions. Modulation of the NADPH-producing pentose phosphate pathway, but not the prevention of hemoglobin autoxidation by conversion of oxyhemoglobin to carboxyhemoglobin, provided protection against storage-induced alterations in RBCs, demonstrating the central role of NADPH in mitigating increased susceptibility of stored RBCs to oxidative stress. We propose that assessing RBC oxidative status after restoration of body temperature constitutes a sensitive method for detecting storage-related alterations that has the potential to improve the quality of stored RBCs for transfusion.

Improved flowing behaviour and gas exchange of stored red blood cells by a compound porous structure

Storage lesions in red blood cells (RBCs) hinder efficient circulation and tissue oxygenation. The absence of flow mechanics and gas exchange may contribute to this problem. To test if in vitro compensation of flow mechanics and gas exchange helps RBC recovery, three-dimensional polydimethylsiloxane (PDMS) porous structures were fabricated with a sugar mould, simulating lung alveoli. RBC suspensions were passed through the porous structure cyclically, simulating in vivo blood circulation. Acid-base indices, partial gas pressures, ions, glucose and RBC indices were analyzed. An atomic force microscope was used to investigate local mechanical properties of intact RBCs. RBCs suspensions that passed through the porous structures had a higher pH and oxygen partial pressure, and a lower potassium concentration and carbon dioxide partial pressure. Meantime they had better biochemical properties relative to static samples, namely, they exhibited a more homogenous distribution of Young's Modulus. RBCs that passed through a PDMS porous structure were healthier than static ones, giving hints to prevent RBC storage lesions.

Hypoxic storage of erythrocytes slows down storage lesions and prolongs shelf-life

Conventional storage conditions of erythrocytes cause storage lesions. We propose that hypoxic storage conditions, involving removal of oxygen and replacement with helium, the changes in stored erythrocytes under hypoxic condition were observed and assessed. Erythrocytes were divided into two equal parts, then stored in conventional and hypoxic conditions, separately. Blood gas analysis, hemorheology, and hemolysis were performed once a week. Energy metabolism and membrane damage were monitored by enzyme-linked immunosorbent assay. Phosphatidylserine exposure was measured by flow cytometry. P₅₀ was measured and the oxygen dissociation curve (ODC) plotted accordingly. Erythrocyte morphology was observed microscopically. In the 9th week of storage, the hemolysis of the hypoxia group was 0.7%; lower (p < .05) than that of the control group and still below the threshold of quality requirements. The dissolved oxygen and pO₂ were only 1/4 of that in the control group (p < .01); the adenosine triphosphate, glucose, and lactic acid levels were decreased (p < .05), while the 2,3-diphosphoglycerate levels were increased relative to that in the control group (p < .01). There were no statistically significant differences in membrane damage, deformability, and aggregation between the two groups. In addition, the ODC of the two groups was shifted to the left but this difference was not statistically different. Basically similar to the effect of completely anaerobic conditions. Erythrocytes stored under hypoxic conditions could maintain a relatively stable state with a significant decrease in hemolysis, reduction of storage lesions, and an increase in shelf-life.

Reexamination of the chromium-51-labeled posttransfusion red blood cell recovery method

BACKGROUND

The chromium-51-labeled posttransfusion recovery (PTR) study has been the gold-standard test for assessing red blood cell (RBC) quality. Despite guiding RBC storage development for decades, it has several potential sources for error.

METHODS

Four healthy adult volunteers each donated an autologous, leukoreduced RBC unit, aliquots were radiolabeled with technetium-99m after 1 and 6 weeks of storage, and then infused. Subjects were imaged by single-photon-emission computed tomography immediately and 4 hours after infusion. Additionally, from subjects described in a previously published study, adenosine triphosphate levels in transfusates infused into 52 healthy volunteers randomized to a single autologous, leukoreduced, RBC transfusion after 1, 2, 3, 4, 5, or 6 weeks of storage were correlated with PTR and laboratory parameters of hemolysis.

RESULTS

Evidence from one subject imaged after infusion of technetium-99m-labeled RBCs suggests that, in some individuals, RBCs may be temporarily sequestered in the liver and spleen immediately following transfusion and then subsequently released back into circulation; this could be one source of error leading to PTR results that may not accurately predict the true quantity of RBCs cleared by intra- and/or extravascular hemolysis. Indeed, adenosine triphosphate levels in the transfusates correlated more robustly with measures of extravascular hemolysis in vivo (e.g., serum iron, indirect bilirubin, non-transferrin-bound iron) than with PTR results or measures of intravascular hemolysis (e.g., plasma free hemoglobin).

CONCLUSIONS

Sources of measurement error are inherent in the chromium-51 PTR method. Transfusion of an entire unlabeled RBC unit, followed by quantifying extravascular hemolysis markers, may more accurately measure true posttransfusion RBC recovery.

From omics technologies to personalized transfusion medicine

INTRODUCTION

Blood transfusion is the single most frequent in-hospital medical procedure, a life-saving intervention for millions of recipients worldwide every year. Storage in the blood bank is an enabling strategy for this critical procedure, as it logistically solves the issue of making ~110 million units available for transfusion every year. Unfortunately, storage in the blood bank promotes a series of biochemical and morphological changes to the red blood cell that compromise the integrity and functionality of the erythrocyte in vitro and in animal models, and could negatively impact transfusion outcomes in the recipient. Areas covered: While commenting on the clinical relevance of the storage lesion is beyond the scope of this manuscript, here we will review recent advancements in our understanding of the storage lesion as gleaned through omics technologies. We will focus on how the omics-scale appreciation of the biological variability at the donor and recipient level is impacting our understanding of red blood cell storage biology. Expert commentary: Omics technologies are paving the way for personalized transfusion medicine, a discipline that promises to revolutionize a critical field in medical practice. The era of recipient-tailored additives, processing, and storage strategies may not be too far distant in the future.

Red blood cell storage lesion: causes and potential clinical consequences

Red blood cells (RBCs) are a specialised organ that enabled the evolution of multicellular organisms by supplying a sufficient quantity of oxygen to cells that cannot obtain oxygen directly from ambient air via diffusion, thereby fueling oxidative phosphorylation for highly efficient energy production. RBCs have evolved to optimally serve this purpose by packing high concentrations of haemoglobin in their cytosol and shedding nuclei and other organelles. During their circulatory lifetimes in humans of approximately 120 days, RBCs are poised to transport oxygen by metabolic/redox enzymes until they accumulate damage and are promptly removed by the reticuloendothelial system. These elaborate evolutionary adaptions, however, are no longer effective when RBCs are removed from the circulation and stored hypothermically in blood banks, where they develop storage-induced damages ("storage lesions") that accumulate over the shelf life of stored RBCs. This review attempts to provide a comprehensive view of the literature on the subject of RBC storage lesions and their purported clinical consequences by incorporating the recent exponential growth in available data obtained from "omics" technologies in addition to that published in more traditional literature. To summarise this vast amount of information, the subject is organised in figures with four panels: i) root causes; ii) RBC storage lesions; iii) physiological effects; and iv) reported outcomes. The driving forces for the development of the storage lesions can be roughly classified into two root causes: i) metabolite accumulation/depletion, the target of various interventions (additive solutions) developed since the inception of blood banking; and ii) oxidative damages, which have been reported for decades but not addressed systemically until recently. Downstream physiological consequences of these storage lesions, derived mainly by in vitro studies, are described, and further potential links to clinical consequences are discussed. Interventions to postpone the onset and mitigate the extent of the storage lesion development are briefly reviewed. In addition, we briefly discuss the results from recent randomised controlled trials on the age of stored blood and clinical outcomes of transfusion.

Heterogeneity of blood processing and storage additives in different centers impacts stored red blood cell metabolism as much as storage time: lessons from REDS-III-Omics

BACKGROUND

Biological and technical variability has been increasingly appreciated as a key factor impacting red blood cell (RBC) storability and, potentially, transfusion outcomes. Here, we performed metabolomics analyses to investigate the impact of factors other than storage duration on the metabolic phenotypes of stored RBC in a multicenter study.

STUDY DESIGN AND METHODS

Within the framework of the REDS-III (Recipient Epidemiology and Donor Evaluation Study-III) RBC-Omics study, 13,403 donors were enrolled from four blood centers across the United States and tested for the propensity of their RBCs to hemolyze after 42 days of storage. Extreme hemolyzers were recalled and donated a second unit of blood. Units were stored for 10, 23, and 42 days prior to sample acquisition for metabolomics analyses.

RESULTS

Unsupervised analyses of metabolomics data from 599 selected samples revealed a strong impact (14.2% of variance) of storage duration on metabolic phenotypes of RBCs. The blood center collecting and processing the units explained an additional 12.2% of the total variance, a difference primarily attributable to the storage additive (additive solution 1 vs. additive solution 3) used in the different hubs. Samples stored in mannitol-free/citrate-loaded AS-3 were characterized by elevated levels of high-energy compounds, improved glycolysis, and glutathione homeostasis. Increased methionine metabolism and activation of the transsulfuration pathway was noted in samples processed in the center using additive solution 1.

CONCLUSION

Blood processing impacts the metabolic heterogeneity of stored RBCs from the largest multicenter metabolomics study in transfusion medicine to date. Studies are needed to understand if these metabolic differences influenced by processing/storage strategies impact the effectiveness of transfusions clinically.

Metabolomics evaluation of early-storage red blood cell rejuvenation at 4°C and 37°C

BACKGROUND

Refrigerated red blood cell (RBC) storage results in the progressive accumulation of biochemical and morphological alterations collectively referred to as the storage lesion. Storage-induced metabolic alterations can be in part reversed by rejuvenation practices. However, rejuvenation requires an incubation step of RBCs for 1 hour at 37°C, limiting the practicality of providing "on-demand," rejuvenated RBCs. We tested the hypothesis that the addition of rejuvenation solution early in storage as an adjunct additive solution would prevent-in a time window consistent with the average age of units transfused to sickle cell recipients at Duke (15 days)-many of the adverse biochemical changes that can be reversed via standard rejuvenation, while obviating the incubation step.

STUDY DESIGN AND METHODS

Metabolomics analyses were performed on cells and supernatants from AS-1 RBC units (n = 4), stored for 15 days. Units were split into pediatric bag aliquots and stored at 4°C. These were untreated controls, washed with or without rejuvenation, performed under either standard (37°C) or cold (4°C) conditions.

RESULTS

All three treatments removed most metabolic storage by-products from RBC supernatants. However, only standard and cold rejuvenation provided significant metabolic benefits as judged by the reactivation of glycolysis and regeneration of adenosine triphosphate and 2,3-diphosphoglycerate. Improvements in energy metabolism also translated into increased capacity to restore the total glutathione pool and regenerate oxidized vitamin C in its reduced (ascorbate) form.

CONCLUSION

Cold and standard rejuvenation of 15-day-old RBCs primes energy and redox metabolism of stored RBCs, while providing a logistic advantage for routine blood bank processing workflows.

Nitric oxide in red blood cell adaptation to hypoxia

Nitric oxide (NO) appears to be involved in virtually every aspect of cardiovascular biology. Most attention has been focused on the role of endothelial-derived NO in basal blood flow regulation by relaxing vascular smooth muscle; however, it is now known that NO derived from red blood cells (RBCs) plays a fundamental role in vascular homeostasis by enhancing oxygen (O2) release at the cellular and physiological level. Hypoxia is an often seen problem in diverse conditions; systemic adaptations to hypoxia permit people to adjust to the hypoxic environment at high altitudes and to disease processes. In addition to the cardiopulmonary and hematologic adaptations that support systemic O2 delivery in hypoxia, RBCs assist through newly described NO-based mechanisms, in line with their vital role in O2 transport and delivery. Furthermore, to increase the local blood flow in proportion to metabolic demand, NO regulates membrane mechanical properties thereby modulating RBC deformability and O2 carrying-releasing function. In this review article, we focus on the effect of NO bioactivity on RBC-based mechanisms that regulate blood flow and RBC deformability. RBC adaptations to hypoxia are summarized, with particular attention to NO-dependent S-nitrosylation of membrane proteins and hemoglobin (S-nitrosohemoglobin). The NO/S-nitrosylation/RBC vasoregulatory cascade contributes fundamentally to the molecular understanding of the role of NO in human adaptation to hypoxia and may inform novel therapeutic strategies.

Metabolic effect of alkaline additives and guanosine/gluconate in storage solutions for red blood cells

BACKGROUND

Over a century of advancements in the field of additive solutions for red blood cell (RBC) storage has made transfusion therapy a safe and effective practice for millions of recipients worldwide. Still, storage in the blood bank results in the progressive accumulation of metabolic alterations, a phenomenon that is mitigated by storage in novel storage additives, such as alkaline additive solutions. While novel alkaline additive formulations have been proposed, no metabolomics characterization has been performed to date.

STUDY DESIGN AND METHODS

We performed UHPLC-MS metabolomics analyses of red blood cells stored in SAGM (standard additive in Europe), (PAGGSM), or alkaline additives SOLX, E-SOL 5 and PAG3M for either 1, 21, 35 (end of shelf-life in the Netherlands), or 56 days.

RESULTS

Alkaline additives (especially PAG3M) better preserved 2,3-diphosphoglycerate and adenosine triphosphate (ATP). Deaminated purines such as hypoxanthine were predictive of hemolysis and morphological alterations. Guanosine supplementation in PAGGSM and PAG3M fueled ATP generation by feeding into the nonoxidative pentose phosphate pathway via phosphoribolysis. Decreased urate to hypoxanthine ratios were observed in alkaline additives, suggestive of decreased generation of urate and hydrogen peroxide. Despite the many benefits observed in purine and redox metabolism, alkaline additives did not prevent accumulation of free fatty acids and oxidized byproducts, opening a window for future alkaline formulations including (lipophilic) antioxidants.

CONCLUSION

Alkalinization via different strategies (replacement of chloride anions with either high bicarbonate, high citrate/phosphate, or membrane impermeant gluconate) results in different metabolic outcomes, which are superior to current canonical additives in all cases.

Blood storage alters mechanical stress responses of erythrocytes

BACKGROUND: Erythrocytes undergo irreversible morphological and biochemical changes during storage. Reduced levels of deformability have been reported for stored erythrocytes. Erythrocyte deformability is essential for healthy microcirculation.

OBJECTIVE: The aim of this study is to evaluate shear stress (SS) induced improvements of erythrocyte deformability in stored blood.

METHODS: Deformability changes were evaluated by applying physiological levels of SS (5 and 10 Pa) in metabolically depleted blood for 48 hours and stored blood for 35 days with citrate phosphate dextrose adenine-1 (CPDA-1). Laser diffractometry was used to measure erythrocyte deformability before and after application of SS.

RESULTS: Erythrocyte deformability, as a response to continuous SS, was significantly improved in metabolically depleted blood, whereas it was significantly impaired in the blood stored for 35 days with CPDA-1 (p≤0.05). The SS-induced improvements of deformability were deteriorated due to storage and relatively impaired according to the storage time. However, deformability of stored blood after exposure to mechanical stress tends to increase at low levels of shear while decreasing at high SS levels.

CONCLUSION: Impairment of erythrocyte deformability after storage may contribute to impairments in the recipient’s microcirculation after blood transfusion. The period of the storage should be considered to prevent microcirculatory problems and insufficient oxygen delivery to the tissues.

Metabolism of Citrate and Other Carboxylic Acids in Erythrocytes As a Function of Oxygen Saturation and Refrigerated Storage

State-of-the-art proteomics technologies have recently helped to elucidate the unanticipated complexity of red blood cell metabolism. One recent example is citrate metabolism, which is catalyzed by cytosolic isoforms of Krebs cycle enzymes that are present and active in mature erythrocytes and was determined using quantitative metabolic flux analysis. In previous studies, we reported significant increases in glycolytic fluxes in red blood cells exposed to hypoxia in vitro or in vivo, an observation relevant to transfusion medicine owing to the potential benefits associated with hypoxic storage of packed red blood cells. Here, using a combination of steady state and quantitative tracing metabolomics experiments with ¹³C_1,2,3-glucose, ¹³C₆-citrate, ¹³C₅¹⁵N₂-glutamine, and ¹³C₁-aspartate via ultra-high performance liquid chromatography coupled on line with mass spectrometry, we observed that hypoxia in vivo and in vitro promotes consumption of citrate and other carboxylates. These metabolic reactions are theoretically explained by the activity of cytosolic malate dehydrogenase 1 and isocitrate dehydrogenase 1 (abundantly represented in the red blood cell proteome), though moonlighting functions of additional enzymes cannot be ruled out. These observations enhance understanding of red blood cell metabolic responses to hypoxia, which could be relevant to understand systemic physiological and pathological responses to high altitude, ischemia, hemorrhage, sepsis, pulmonary hypertension, or hemoglobinopathies. Results from this study will also inform the design and testing of novel additive solutions that optimize red blood cell storage under oxygen-controlled conditions.

Red blood cells in hemorrhagic shock: a critical role for glutaminolysis in fueling alanine transamination in rats

Red blood cells (RBCs) are the most abundant host cell in the human body and play a critical role in oxygen transport and systemic metabolic homeostasis. Hypoxic metabolic reprogramming of RBCs in response to high-altitude hypoxia or anaerobic storage in the blood bank has been extensively described. However, little is known about the RBC metabolism following hemorrhagic shock (HS), the most common preventable cause of death in trauma, the global leading cause of total life-years lost. Metabolomics analyses were performed through ultra-high pressure liquid chromatography-mass spectrometry on RBCs from Sprague-Dawley rats undergoing HS (mean arterial pressure [MAP], <30 mm Hg) in comparison with sham rats (MAP, >80 mm Hg). Steady-state measurements were accompanied by metabolic flux analysis upon tracing of in vivo-injected ¹³C¹⁵N-glutamine or inhibition of glutaminolysis using the anticancer drug CB-839. RBC metabolic phenotypes recapitulated the systemic metabolic reprogramming observed in plasma from the same rodent model. Results indicate that shock RBCs rely on glutamine to fuel glutathione (GSH) synthesis and pyruvate transamination, whereas abrogation of glutaminolysis conferred early mortality and exacerbated lactic acidosis and systemic accumulation of succinate, a predictor of mortality in the military and civilian critically ill populations. Glutamine is here identified as an essential amine group donor in HS RBCs, plasma, liver, and lungs, providing additional rationale for the central role glutaminolysis plays in metabolic reprogramming and survival following severe hemorrhage.

Red blood cell storage time and transfusion: current practice, concerns and future perspectives

Red blood cells (RBCs) units are the most requested transfusion product worldwide. Indications for transfusion include symptomatic anaemia, acute sickle cell crisis, and acute blood loss of more than 30% of the blood volume, with the aim of restoring tissue oxygen delivery. However, stored RBCs from donors are not a qualitative equal product, and, in many ways, this is a matter of concern in the transfusion practice. Besides donor-to-donor variation, the storage time influences the RBC unit at the qualitative level, as RBCs age in the storage bag and are exposed to the so-called storage lesion. Several studies have shown that the storage lesion leads to post-transfusion enhanced clearance, plasma transferrin saturation, nitric oxide scavenging and/or immunomodulation with potential unwanted transfusion-related clinical outcomes, such as acute lung injury or higher mortality rate. While, to date, several studies have claimed the risk or deleterious effects of "old" vs "young" RBC transfusion regimes, it is still a matter of debate, and consideration should be taken of the clinical context. Transfusion-dependent patients may benefit from transfusion with "young" RBC units, as it assures longer inter-transfusion periods, while transfusion with "old" RBC units is not itself harmful. Unbiased Omics approaches are being applied to the characterisation of RBC through storage, to better understand the (patho)physiological role of microparticles (MPs) that are found naturally, and also on stored RBC units. Perhaps RBC storage time is not an accurate surrogate for RBC quality and there is a need to establish which parameters do indeed reflect optimal efficacy and safety. A better Omics characterisation of components of "young" and "old" RBC units, including MPs, donor and recipient, might lead to the development of new therapies, including the use of engineered RBCs or MPs as cell-based drug delivering tools, or cost-effective personalised transfusion strategies.

Purinergic control of red blood cell metabolism: novel strategies to improve red cell storage quality

Transfusion of stored blood is regarded as one of the great advances in modern medicine. However, during storage in the blood bank, red blood cells (RBCs) undergo a series of biochemical and biomechanical changes that affect cell morphology and physiology and potentially impair transfusion safety and efficacy. Despite reassuring evidence from clinical trials, it is universally accepted that the storage lesion(s) results in the altered physiology of long-stored RBCs and helps explain the rapid clearance of up to one-fourth of long-stored RBCs from the recipient's bloodstream at 24 hours after administration. These considerations explain the importance of understanding and mitigating the storage lesion. With the emergence of new technologies that have enabled large-scale and in-depth screening of the RBC metabolome and proteome, recent studies have provided novel insights into the molecule-level metabolic changes underpinning the accumulation of storage lesions to RBCs in the blood bank and alternative storage strategies to mitigate such lesion(s). These approaches borrow from recent insights on the biochemistry of RBC adaptation to high altitude hypoxia. We recently conducted investigations in genetically modified mice and revealed novel insights into the role of adenosine signalling in response to hypoxia as a previously unrecognised cascade regulating RBC glucose metabolism and increasing O₂ release, while decreasing inflammation and tissue injuries in animal models. Here, we will discuss the molecular mechanisms underlying the role of purinergic molecules, including adenosine and adenosine triphosphate in manipulating RBCs and blood vessels in response to hypoxia. We will also speculate about new therapeutic possibilities to improve the quality of stored RBCs and the prognosis after transfusion.

Effects of Storage Time on Glycolysis in Donated Human Blood Units

Background: Donated blood is typically stored before transfusions. During storage, the metabolism of red blood cells changes, possibly causing storage lesions. The changes are storage time dependent and exhibit donor-specific variations. It is necessary to uncover and characterize the responsible molecular mechanisms accounting for such biochemical changes, qualitatively and quantitatively; Study Design and Methods: Based on the integration of metabolic time series data, kinetic models, and a stoichiometric model of the glycolytic pathway, a customized inference method was developed and used to quantify the dynamic changes in glycolytic fluxes during the storage of donated blood units. The method provides a proof of principle for the feasibility of inferences regarding flux characteristics from metabolomics data; Results: Several glycolytic reaction steps change substantially during storage time and vary among different fluxes and donors. The quantification of these storage time effects, which are possibly irreversible, allows for predictions of the transfusion outcome of individual blood units; Conclusion: The improved mechanistic understanding of blood storage, obtained from this computational study, may aid the identification of blood units that age quickly or more slowly during storage, and may ultimately improve transfusion management in clinics.

Hitchhiker's guide to the red cell storage galaxy: Omics technologies and the quality issue

Red blood cell storage in the blood bank makes millions of units of available for transfusion to civilian and military recipients every year. From glass bottles to plastic bags, from anticoagulants to complex additives, from whole blood to leukocyte filtered packed red blood cells: huge strides have been made in the field of blood component processing and storage in the blood bank during the last century. Still, refrigerated preservation of packed red blood cells under blood bank conditions results in the progressive accumulation of a wide series of biochemical and morphological changes to the stored erythrocytes, collectively referred to as the storage lesion(s). Approximately ten years ago, retrospective clinical evidence had suggested that such lesion(s) may be clinically relevant and mediate some of the untoward transfusion-related effects observed especially in some categories of recipients at risk (e.g. massively or chronically transfused recipients). Since then, randomized clinical trials have failed to prospectively detect any signal related to red cell storage duration and increased morbidity and mortality in several categories of recipients, at the limits of the statistical power of these studies. While a good part of the transfusion community has immediately adopted the take-home message "if it isn't broken, don't fix it" (i.e. no change to the standard of practice should be pursued), decision makers have been further questioning whether there may be room for further improvements in this field. Provocatively, we argue that consensus has yet to be unanimously reached on what makes a good quality marker of the red cell storage lesion and transfusion safety/efficacy. In other words, if it is true that "you can't manage what you can't measure", then future advancements in the field of transfusion medicine will necessarily rely on state of the art analytical omics technologies of well-defined quality parameters. Heavily borrowing from Douglas Adam's imaginary repertoire from the world famous "Hitchhiker's guide to the galaxy", we briefly summarize how some of the principles for intergalactic hitchhikers may indeed apply to inform navigation through the complex universe of red cell storage quality, safety and efficacy.

Omics markers of the red cell storage lesion and metabolic linkage

The introduction of omics technologies in the field of Transfusion Medicine has significantly advanced our understanding of the red cell storage lesion. While the clinical relevance of such a lesion is still a matter of debate, quantitative and redox proteomics approaches, as well quantitative metabolic flux analysis and metabolic tracing experiments promise to revolutionise our understanding of the role of blood processing strategies, inform the design and testing of novel additives or technologies (such as pathogen reduction), and evaluate the clinical relevance of donor and recipient biological variability with respect to red cell storability and transfusion outcomes. By reviewing existing literature in this rapidly expanding research endeavour, we highlight for the first time a correlation between metabolic markers of the red cell storage age and protein markers of haemolysis. Finally, we introduce the concept of metabolic linkage, i.e. the appreciation of a network of highly correlated small molecule metabolites which results from biochemical constraints of erythrocyte metabolic enzyme activities. For the foreseeable future, red cell studies will advance Transfusion Medicine and haematology by addressing the alteration of metabolic linkage phenotypes in response to stimuli, including, but not limited to, storage additives, enzymopathies (e.g. glucose 6-phosphate dehydrogenase deficiency), hypoxia, sepsis or haemorrhage.

Proteomic analysis of red blood cells and the potential for the clinic: what have we learned so far?

INTRODUCTION

Red blood cells (RBC) are the most abundant host cells in the human body. Mature erythrocytes are devoid of nuclei and organelles and have always been regarded as circulating 'bags of hemoglobin'. The advent of proteomics has challenged this assumption, revealing unanticipated complexity and novel roles for RBCs not just in gas transport, but also in systemic metabolic homeostasis in health and disease. Areas covered: In this review we will summarize the main advancements in the field of discovery mode and redox/quantitative proteomics with respect to RBC biology. We thus focus on translational/clinical applications, such as transfusion medicine, hematology (e.g. hemoglobinopathies) and personalized medicine. Synergy of omics technologies - especially proteomics and metabolomics - are highlighted as a hallmark of clinical metabolomics applications for the foreseeable future. Expert commentary: The introduction of advanced proteomics technologies, especially quantitative and redox proteomics, and the integration of proteomics data with omics information gathered through orthogonal technologies (especially metabolomics) promise to revolutionize many biomedical areas, from hematology and transfusion medicine to personalized medicine and clinical biochemistry.

The Proteome of the Red Blood Cell: An Auspicious Source of New Insights into Membrane-Centered Regulation of Homeostasis

During the past decade, the hand-in-hand development of biotechnology and bioinformatics has enabled a view of the function of the red blood cell that surpasses the supply of oxygen and removal of carbon dioxide. Comparative proteomic inventories have yielded new clues to the processes that regulate membrane-cytoskeleton interactions in health and disease, and to the ways by which red blood cells communicate with their environment. In addition, proteomic data have revealed the possibility that many, hitherto unsuspected, metabolic processes are active in the red blood cell cytoplasm. Recent metabolomic studies have confirmed and expanded this notion. Taken together, the presently available data point towards the red blood cell membrane as the hub at which all regulatory processes come together. Thus, alterations in the association of regulatory proteins with the cell membrane may be a sine qua non for the functional relevance of any postulated molecular mechanism. From this perspective, comparative proteomics centered on the red blood cell membrane constitute a powerful tool for the identification and elucidation of the physiologically and pathologically relevant pathways that regulate red blood cell homeostasis. Additionally, this perspective provides a focus for the interpretation of metabolomic studies, especially in the development of biomarkers in the blood.

Citrate metabolism in red blood cells stored in additive solution-3

BACKGROUND

Red blood cells (RBCs) are thought to have a relatively simple metabolic network compared to other human cell types. Recent proteomics reports challenge the notion that RBCs are mere hemoglobin carriers with limited metabolic activity. Expanding our understanding of RBC metabolism has key implications in many biomedical areas, including transfusion medicine.

STUDY DESIGN AND METHODS

In-gel digestion coupled with mass spectrometric analysis proteomics approaches were combined with state-of-the-art tracing experiments by incubating leukofiltered RBCs in additive solution-3 for up to 42 days under blood bank conditions, in presence of ¹³ C_1,2,3 -glucose, 2,2,4,4-d-citrate, and ¹³ C,¹⁵ N-glutamine.

RESULTS

Results indicate that the pentose phosphate pathway/glycolysis ratio increases during storage in additive solution-3. While the majority of supernatant glucose is consumed to fuel glycolysis, incorporation of glucose-derived pentose phosphate moieties was observed in nucleoside monophosphates. Incubation with deuterated citrate indicated that citrate uptake and metabolism contribute to explain the origin of up to approximately 20% to 30% lactate that could not be explained by glucose oxidation and 2,3-diphosphoglycerate consumption alone. Incubation with ¹³ C,¹⁵ N-glutamine showed that glutaminolysis fuels transamination reactions and accumulation of millimolar levels of 5-oxoproline, while de novo glutathione synthesis was not significantly active during refrigerated storage.

CONCLUSION

Quantitative tracing metabolic experiments revealed that mature RBCs can metabolize other substrates than glucose, such as citrate, an observation relevant to transfusion medicine (i.e., formulation of novel additives), and other research endeavors where metabolic modulation of RBCs opens potential avenues for therapeutic interventions, such as in sickle cell disease.

[Innovative technology and blood safety]

If technological innovations are not enough alone to improve blood safety, their contributions for several decades in blood transfusion are major. The improvement of blood donation (new apheresis devices, RFID) or blood components (additive solutions, pathogen reduction technology, automated processing of platelets concentrates) or manufacturing process of these products (by automated processing of whole blood), all these steps where technological innovations were implemented, lead us to better traceability, more efficient processes, quality improvement of blood products and therefore increased blood safety for blood donors and patients. If we are on the threshold of a great change with the progress of pathogen reduction technology (for whole blood and red blood cells), we hope to see production of ex vivo red blood cells or platelets who are real and who open new conceptual paths on blood safety.

Metabolic fate of adenine in red blood cells during storage in SAGM solution

BACKGROUND

Red blood cells (RBCs) are routinely stored and transfused worldwide. Recently, metabolomics have shown that RBCs experience a three-phase metabolic decay process during storage, resulting in the definition of three distinct metabolic phenotypes, occurring between Days 1 and 10, 11 and 17, and 18 and 46. Here we use metabolomics and stable isotope labeling analysis to study adenine metabolism in RBCs.

STUDY DESIGN AND METHODS

A total of 6 units were prepared in SAGM or modified additive solutions (ASs) containing ¹⁵ N₅ -adenine. Three of them were spiked with ¹⁵ N₅ -adenine on Days 10, 14, and 17 during storage. Each unit was sampled 10 times spanning Day 1 to Day 32. At each time point metabolic profiling was performed.

RESULTS

We increased adenine concentration in the AS and we pulsed the adenine concentration during storage and found that in both cases the RBCs' main metabolic pathways were not affected. Our data clearly show that RBCs cannot consume adenine after 18 days of storage, even if it is still present in the storage solution. However, increased levels of adenine influenced S-adenosylmethionine metabolism.

CONCLUSION

In this work, we have studied in detail the metabolic fate of adenine during RBC storage in SAGM. Adenine is one of the main substrates used by RBCs, but the metabolic shift observed during storage is not caused by an absence of adenine later in storage. The rate of adenine consumption strongly correlated with duration of storage but not with the amount of adenine present in the AS.

Small-Scale Perfusion Bioreactor of Red Blood Cells for Dynamic Studies of Cellular Pathways: Proof-of-Concept

To date, the development of bioreactors for the study of red blood cells (RBCs, daily transfused in the case of disease or hemorrhage) has focused on hematopoietic stem cells. Despite the fact that mature RBCs are enucleated and do not expand, they possess complex cellular and metabolic pathways, as well as post-translation modification signaling and gas-exchange regulation. In order to dynamically study the behavior of RBCs and their signaling pathways under various conditions, a small-scale perfusion bioreactor has been developed. The most advanced design developed here consists of a fluidized bed of 7.6 mL containing 3·10⁹ cells and perfused at 8.5 μL/min. Mimicking RBC storage conditions in transfusion medicine, as a proof-of-concept, we investigated the ex vivo aging of RBCs under both aerobic and anaerobic conditions. Hence, RBCs stored in saline-adenine-glucose-mannitol (SAGM) were injected in parallel into two bioreactors and perfused with a modified SAGM solution over 14 days at room temperature under air or argon. The formation of a fluidized bed enabled easy sampling of the extracellular medium over the storage period used for the quantitation of glucose consumption and lactate production. Hemolysis and microvesiculation increased during aging and were reduced under anaerobic (argon) conditions, which is consistent with previously reported findings. Glucose and lactate levels showed expected trends, i.e., decreased and increased during the 2-week period, respectively; whereas extracellular glucose consumption was higher under aerobic conditions. Metabolomics showed depletion of glycolsis and pentose phosphate pathway metabolites, and an accumulation of purine metabolite end-products. This novel approach, which takes advantage of a fluidized bed of cells in comparison to traditional closed bags or tubes, does not require agitation and limit shear stress, and constantly segragates extracellular medium from RBCs. It thus gives access to several difficult-to-obtain on- and off-line parameters in the extracellular medium. This dynamic bioreactor system does not only allow us to probe the behavior of RBCs under different storage conditions, but it also could be a powerful tool to study physiological or pathological RBCs exposed to various conditions and stimuli.

Metabolomics in transfusion medicine

Biochemical investigations on the regulatory mechanisms of red blood cell (RBC) and platelet (PLT) metabolism have fostered a century of advances in the field of transfusion medicine. Owing to these advances, storage of RBCs and PLT concentrates has become a lifesaving practice in clinical and military settings. There, however, remains room for improvement, especially with regard to the introduction of novel storage and/or rejuvenation solutions, alternative cell processing strategies (e.g., pathogen inactivation technologies), and quality testing (e.g., evaluation of novel containers with alternative plasticizers). Recent advancements in mass spectrometry-based metabolomics and systems biology, the bioinformatics integration of omics data, promise to speed up the design and testing of innovative storage strategies developed to improve the quality, safety, and effectiveness of blood products. Here we review the currently available metabolomics technologies and briefly describe the routine workflow for transfusion medicine-relevant studies. The goal is to provide transfusion medicine experts with adequate tools to navigate through the otherwise overwhelming amount of metabolomics data burgeoning in the field during the past few years. Descriptive metabolomics data have represented the first step omics researchers have taken into the field of transfusion medicine. However, to up the ante, clinical and omics experts will need to merge their expertise to investigate correlative and mechanistic relationships among metabolic variables and transfusion-relevant variables, such as 24-hour in vivo recovery for transfused RBCs. Integration with systems biology models will potentially allow for in silico prediction of metabolic phenotypes, thus streamlining the design and testing of alternative storage strategies and/or solutions.