Red blood cell proteomics update: is there more to discover?

Porphyrin overdrive rewires cancer cell metabolism

All cancer cells reprogram metabolism to support aberrant growth. Here, we report that cancer cells employ and depend on imbalanced and dynamic heme metabolic pathways, to accumulate heme intermediates, that is, porphyrins. We coined this essential metabolic rewiring "porphyrin overdrive" and determined that it is cancer-essential and cancer-specific. Among the major drivers are genes encoding mid-step enzymes governing the production of heme intermediates. CRISPR/Cas9 editing to engineer leukemia cell lines with impaired heme biosynthetic steps confirmed our whole-genome data analyses that porphyrin overdrive is linked to oncogenic states and cellular differentiation. Although porphyrin overdrive is absent in differentiated cells or somatic stem cells, it is present in patient-derived tumor progenitor cells, demonstrated by single-cell RNAseq, and in early embryogenesis. In conclusion, we identified a dependence of cancer cells on non-homeostatic heme metabolism, and we targeted this cancer metabolic vulnerability with a novel "bait-and-kill" strategy to eradicate malignant cells.

Metabolite and protein shifts in mature erythrocyte under hypoxia

As the only cell type responsible for oxygen delivery, erythrocytes play a crucial role in supplying oxygen to hypoxic tissues, ensuring their normal functions. Hypoxia commonly occurs under physiological or pathological conditions, and understanding how erythrocytes adapt to hypoxia is fundamental for exploring the mechanisms of hypoxic diseases. Additionally, investigating acute and chronic mountain sickness caused by plateaus, which are naturally hypoxic environments, will aid in the study of hypoxic diseases. In recent years, increasingly developed proteomics and metabolomics technologies have become powerful tools for studying mature enucleated erythrocytes, which has significantly contributed to clarifying how hypoxia affects erythrocytes. The aim of this article is to summarize the composition of the cytoskeleton and cytoplasmic proteins of hypoxia-altered erythrocytes and explore the impact of hypoxia on their essential functions. Furthermore, we discuss the role of microRNAs in the adaptation of erythrocytes to hypoxia, providing new perspectives on hypoxia-related diseases.

Multiomics Signatures of Coagulopathy in a Polytrauma Swine Model Contrasted with Severe Multisystem Injured Patients

Trauma-induced coagulopathy (TIC) is a leading contributor to preventable mortality in severely injured patients. Understanding the molecular drivers of TIC is an essential step in identifying novel therapeutics to reduce morbidity and mortality. This study investigated multiomics and viscoelastic responses to polytrauma using our novel swine model and compared these findings with severely injured patients. Molecular signatures of TIC were significantly associated with perturbed coagulation and inflammation systems as well as extensive hemolysis. These results were consistent with patterns observed in trauma patients who had multisystem injuries. Here, intervention using resuscitative endovascular balloon occlusion of the aorta following polytrauma in our swine model revealed distinct multiomics alterations as a function of placement location. Aortic balloon placement in zone-1 worsened ischemic damage and mitochondrial dysfunction, patterns that continued throughout the monitored time course. While placement in zone-III showed a beneficial effect on TIC, it showed an improvement in effective coagulation. Taken together, this study highlights the translational relevance of our polytrauma swine model for investigating therapeutic interventions to correct TIC in patients.

Erythrocyte metabolism

Our aim is to present an updated overview of the erythrocyte metabolism highlighting its richness and complexity. We have manually collected and connected the available biochemical pathways and integrated them into a functional metabolic map. The focus of this map is on the main biochemical pathways consisting of glycolysis, the pentose phosphate pathway, redox metabolism, oxygen metabolism, purine/nucleoside metabolism, and membrane transport. Other recently emerging pathways are also curated, like the methionine salvage pathway, the glyoxalase system, carnitine metabolism, and the lands cycle, as well as remnants of the carboxylic acid metabolism. An additional goal of this review is to present the dynamics of erythrocyte metabolism, providing key numbers used to perform basic quantitative analyses. By synthesizing experimental and computational data, we conclude that glycolysis, pentose phosphate pathway, and redox metabolism are the foundations of erythrocyte metabolism. Additionally, the erythrocyte can sense oxygen levels and oxidative stress adjusting its mechanics, metabolism, and function. In conclusion, fine-tuning of erythrocyte metabolism controls one of the most important biological processes, that is, oxygen loading, transport, and delivery.

Red Blood Cell Omics and Machine Learning in Transfusion Medicine: Singularity Is Near

Background

Blood transfusion is a life-saving intervention for millions of recipients worldwide. Over the last 15 years, the advent of high-throughput, affordable omics technologies - including genomics, proteomics, lipidomics, and metabolomics - has allowed transfusion medicine to revisit the biology of blood donors, stored blood products, and transfusion recipients.

Summary

Omics approaches have shed light on the genetic and non-genetic factors (environmental or other exposures) impacting the quality of stored blood products and efficacy of transfusion events, based on the current Food and Drug Administration guidelines (e.g., hemolysis and post-transfusion recovery for stored red blood cells). As a treasure trove of data accumulates, the implementation of machine learning approaches promises to revolutionize the field of transfusion medicine, not only by advancing basic science. Indeed, computational strategies have already been used to perform high-content screenings of red blood cell morphology in microfluidic devices, generate in silico models of erythrocyte membrane to predict deformability and bending rigidity, or design systems biology maps of the red blood cell metabolome to drive the development of novel storage additives.

Key Message

In the near future, high-throughput testing of donor genomes via precision transfusion medicine arrays and metabolomics of all donated products will be able to inform the development and implementation of machine learning strategies that match, from vein to vein, donors, optimal processing strategies (additives, shelf life), and recipients, realizing the promise of personalized transfusion medicine.

Polo-like kinase inhibitor BI2536 induces eryptosis

BI2536 is potent inhibitor of polo-like kinases PLK1, 2, and 3. The inhibition of PLKs in nucleated cells induces apoptosis by perturbing the cell cycle with consequent engagement of mitotic catastrophe. BI2536 is being tested as chemotherapy in various phase I/II/III clinical trials. Erythrocytes do not have a nucleus; however, they may undergo programmed suicide with characteristic hallmarks including cell shrinkage and phosphatidylserine translocation to the cell surface. This particular death is baptized eryptosis. Our study explored whether BI2536 induces eryptosis. We used flow cytometry to access death in red blood cells. We analyzed the cellular volume, the intracellular calcium concentration, the cell surface phosphatidylserine exposure, and the ceramide abundance. In addition, we analyzed the effect of BI2536 on hemolysis. Our investigation showed that after 48 h of incubation with PLK inhibitor BI2536, erythrocytes lost volume and were positive for annexin‑V without any effect on hemolysis. Cells also showed an abundance of ceramide and an increase of intracellular calcium. All these finding suggest that BI2536 provokes eryptosis in red blood cells, ostensibly in part due to Ca2+ entry and ceramide accumulation.

MicroRNAs as Quality Assessment Tool in Stored Packed Red Blood Cell in Blood Banks

Micro-ribonucleic acids are control gene expression in cells. They represent the changed cellular states that occur can be employed as biomarkers. Red blood cells alter biochemically and morphologically while they are being stored, which could be detrimental to transfusion. The effect of storage on the erythrocyte transcriptome is not mostly investigated. Because adult erythrocytes lack a nucleus, it has long been assumed that they lack deoxyribonucleic acid and ribonucleic acid. On the other hand, erythrocytes contain a diverse range of ribonucleic acids, of which micro-ribonucleic acids are key component. Changes in this micro-ribonucleic acid protect cells from death and adenine triphosphate depletion, and they are linked to specific storage lesions. As a result, changes in micro-ribonucleic acid in stored erythrocytes may be used as a marker to assess the quality and safety of stored erythrocytes. Therefore, this review ams to review the role of microRNA in stored packed red blood cells as quality indicator. Google Scholar, PubMed, Scopus, and Z-libraries are used for searching articles and books. The article included in this paper was written in the English language and had the full article. During long storage of RBCs, miR-16-2-3p, miR-1260a, miR-1260b, miR-4443, miR-4695-3p, miR-5100, let-7b, miR-16, miRNA-1246, MiR-31-5p, miR-203a, miR-654-3p, miR-769-3p, miR-4454, miR-451a and miR-125b- 5p are up regulated. However, miR-96, miR-150, miR-196a, miR-197, miR-381 and miR-1245a are down regulated after long storage of RBCs. The changes of this microRNAs are linked to red blood cell lesions. Therefore, micro-ribonucleic acids are the potential quality indicator in stored packed red blood cells in the blood bank. Particularly, micro-ribonucleic acid-96 is the most suitable biomarker for monitoring red blood cell quality in stored packed red blood units.

NCOA4 Regulates Iron Recycling and Responds to Hepcidin Activity and Lipopolysaccharide in Macrophages

Macrophages, via erythrophagocytosis, recycle iron from effete erythrocytes to newly developing red blood cells. Conversion of potentially cytotoxic levels of iron from its heme into nonheme form during iron recycling is safely accomplished via coordinated regulations of cellular iron transport and homeostasis. Herein, we demonstrate the roles and regulation of NCOA4 (nuclear receptor coactivator 4)-mediated ferritinophagy in macrophages after erythrophagocytosis using the mouse macrophage cell line J774 cells. Ferritin in J774 cells increased with the rise of nonheme iron by erythrocyte ingestion and declined when total cellular iron contents subsequently decreased. NCOA4, a selective autophagic cargo receptor for ferritin, was responsible for the control of cellular ferritin and total iron contents at the later stage of erythrophagocytosis. A hepcidin analog, which limits the flux of iron through iron-recycling by inhibiting iron export at the plasma membrane, repressed NCOA4 expression and led to accumulation of ferritin in the mouse macrophages. Transcriptome analyses revealed a functional association of immune response with NCOA4-dependent gene expressions, and we confirmed repression of Ncoa4 by lipopolysaccharide (LPS) in J774 cells and the spleen of mice. Collectively, our studies indicate that NCOA4 facilitates cellular ferritin turnover and the release of iron by macrophages after erythrophagocytosis and functions as a regulatory target for molecular signals of systemic iron overload and inflammation. These identify macrophage NCOA4 as a potential therapeutic target for disorders of systemic iron dysregulation, including anemia of inflammation and hemochromatosis.

COVID-19 metabolism: Mechanisms and therapeutic targets

Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) dysregulates antiviral signaling, immune response, and cell metabolism in human body. Viral genome and proteins hijack host metabolic network to support viral biogenesis and propagation. However, the regulatory mechanism of SARS‐CoV‐2‐induced metabolic dysfunction has not been elucidated until recently. Multiomic studies of coronavirus disease 2019 (COVID‐19) revealed an intensive interaction between host metabolic regulators and viral proteins. SARS‐CoV‐2 deregulated cellular metabolism in blood, intestine, liver, pancreas, fat, and immune cells. Host metabolism supported almost every stage of viral lifecycle. Strikingly, viral proteins were found to interact with metabolic enzymes in different cellular compartments. Biochemical and genetic assays also identified key regulatory nodes and metabolic dependencies of viral replication. Of note, cholesterol metabolism, lipid metabolism, and glucose metabolism are broadly involved in viral lifecycle. Here, we summarized the current understanding of the hallmarks of COVID‐19 metabolism. SARS‐CoV‐2 infection remodels host cell metabolism, which in turn modulates viral biogenesis and replication. Remodeling of host metabolism creates metabolic vulnerability of SARS‐CoV‐2 replication, which could be explored to uncover new therapeutic targets. The efficacy of metabolic inhibitors against COVID‐19 is under investigation in several clinical trials. Ultimately, the knowledge of SARS‐CoV‐2‐induced metabolic reprogramming would accelerate drug repurposing or screening to combat the COVID‐19 pandemic.

Induction of enucleation in primary and immortalized erythroid cells

Enucleation is a crucial event during the erythropoiesis, implicating drastic morphologic and transcriptomic/proteomic changes. While many genes deletion lead to failed or impaired enucleation have been identified, directly triggering the erythroid maturation, particularly enucleation, is still challenging. Inducing enucleation at the desired timing is necessary to develop efficient methods to generate mature, fully functional red blood cells in vitro for future transfusion therapies. However, there are considerable differences between primary erythroid cells and cultured cell sources, particularly pluripotent stem cell-derived erythroid cells and immortalized erythroid cell lines. For instance, the difference in the proliferative status between those cell types could be a critical factor, as cell cycle exit is closely connected to the terminal maturation of primary. In this review, we will discuss previous findings on the enucleation machinery and current challengings to trigger the enucleation of infinite erythroid cell sources.

Inductively-Coupled Plasma Mass Spectrometry-Novel Insights From an Old Technology Into Stressed Red Blood Cell Physiology

BACKGROUND

Ion and metal homeostasis are critical to red blood cell physiology and Inductively Coupled Plasma (ICP) is a decades old approach to pursue elemental analysis. Recent evolution of ICP has resulted in its coupling to mass spectrometry (MS) instead of atomic absorption/emission.

METHODS

Here we performed Inductively-coupled plasma mass spectrometry (ICP-MS) measurements of intra- and extra-cellular Na, K, Ca, Mg, Fe, and Cu in red blood cells undergoing ionic, heat, or starvation stress. Results were correlated with Ca measurements from other common platforms (e.g., fluorescence-based approaches) and extensive measurements of red blood cell metabolism.

RESULTS

All stresses induced significant intra- and extracellular alterations of all measured elements. In particular, ionomycin treatment or hypertonic stress significantly impacted intracellular sodium and extracellular potassium and magnesium levels. Iron efflux was observed as a function of temperatures, with ionic and heat stress at 40°C causing the maximum decrease in intracellular iron pools and increases in the supernatants. Strong positive correlation was observed between calcium measurements via ICP-MS and fluorescence-based approaches. Correlation analyses with metabolomics data showed a strong positive association between extracellular calcium and intracellular sodium or magnesium levels and intracellular glycolysis. Extracellular potassium or iron were positively correlated with free fatty acids (especially mono-, poly-, and highly-unsaturated or odd-chain fatty acid products of lipid peroxidation). Intracellular iron was instead positively correlated with saturated fatty acids (palmitate, stearate) and negatively with methionine metabolism (methionine, S-adenosylmethionine), phosphatidylserine exposure and glycolysis.

CONCLUSION

In the era of omics approaches, ICP-MS affords a comprehensive characterization of intracellular elements that provide direct insights on red blood cell physiology and represent meaningful covariates for data generated via other omics platforms such as metabolomics.

Hematopoietic responses to SARS-CoV-2 infection

Under physiological conditions, hematopoietic stem and progenitor cells (HSPCs) in the bone marrow niches are responsible for the highly regulated and interconnected hematopoiesis process. At the same time, they must recognize potential threats and respond promptly to protect the host. A wide spectrum of microbial agents/products and the consequences of infection-induced mediators (e.g. cytokines, chemokines, and growth factors) can have prominent impact on HSPCs. While COVID-19 starts as a respiratory tract infection, it is considered a systemic disease which profoundly alters the hematopoietic system. Lymphopenia, neutrophilia, thrombocytopenia, and stress erythropoiesis are the hallmark of SARS-CoV-2 infection. Moreover, thrombocytopenia and blood hypercoagulability are common among COVID-19 patients with severe disease. Notably, the invasion of erythroid precursors and progenitors by SARS-CoV-2 is a cardinal feature of COVID-19 disease which may in part explain the mechanism underlying hypoxia. These pieces of evidence support the notion of skewed steady-state hematopoiesis to stress hematopoiesis following SARS-CoV-2 infection. The functional consequences of these alterations depend on the magnitude of the effect, which launches a unique hematopoietic response that is associated with increased myeloid at the expense of decreased lymphoid cells. This article reviews some of the key pathways including the infectious and inflammatory processes that control hematopoiesis, followed by a comprehensive review that summarizes the latest evidence and discusses how SARS-CoV-2 infection impacts hematopoiesis.

Protein-L-isoaspartate O-methyltransferase is required for <i>in vivo</i> control of oxidative damage in red blood cells

Red blood cells (RBC) have the special challenge of a large amount of reactive oxygen species (from their substantial iron load and Fenton reactions) combined with the inability to synthesize new gene products. Considerable progress has been made in elucidating the multiple pathways by which RBC neutralize reactive oxygen species via NADPH driven redox reactions. However, far less is known about how RBC repair the inevitable damage that does occur when reactive oxygen species break through anti-oxidant defenses. When structural and functional proteins become oxidized, the only remedy available to RBC is direct repair of the damaged molecules, as RBC cannot synthesize new proteins. Amongst the most common amino acid targets of oxidative damage is the conversion of asparagine and aspartate side chains into a succinimidyl group through deamidation or dehydration, respectively. RBC express an L-isoaspartyl methyltransferase (PIMT, gene name PCMT1) that can convert succinimidyl groups back to an aspartate. Herein, we report that deletion of PCMT1 significantly alters RBC metabolism in a healthy state, but does not impair the circulatory lifespan of RBC. Through a combination of genetic ablation, bone marrow transplantation and oxidant stimulation with phenylhydrazine in vivo or blood storage ex vivo, we use omics approaches to show that, when animals are exposed to oxidative stress, RBC from PCMT1 knockout undergo significant metabolic reprogramming and increased hemolysis. This is the first report of an essential role of PCMT1 for normal RBC circulation during oxidative stress.

Erythroid precursors and progenitors suppress adaptive immunity and get invaded by SARS-CoV-2

SARS-CoV-2 infection is associated with lower blood oxygen levels, even in patients without hypoxia requiring hospitalization. This discordance illustrates the need for a more unifying explanation as to whether SARS-CoV-2 directly or indirectly affects erythropoiesis. Here, we show significantly enriched CD71⁺ erythroid precursors/progenitors in the blood circulation of COVID-19 patients. We found that these cells have distinctive immunosuppressive properties. In agreement, we observed a strong negative correlation between the frequency of these cells with T and B cell proportions in COVID-19 patients. The expansion of these CD71⁺ erythroid precursors/progenitors was negatively correlated with the hemoglobin levels. A subpopulation of abundant erythroid cells, CD45⁺ CD71⁺ cells, co-express ACE2, TMPRSS2, CD147, and CD26, and these can be infected with SARS-CoV-2. In turn, pre-treatment of erythroid cells with dexamethasone significantly diminished ACE2/TMPRSS2 expression and subsequently reduced their infectivity with SARS-CoV-2. This provides a novel insight into the impact of SARS-CoV-2 on erythropoiesis and hypoxia seen in COVID-19 patients.

Fatty acid desaturase activity in mature red blood cells and implications for blood storage quality

BACKGROUND

Increases in the red blood cell (RBC) degree of fatty acid desaturation are reported in response to exercise, aging, or diseases associated with systemic oxidant stress. However, no studies have focused on the presence and activity of fatty acid desaturases (FADS) in the mature RBC.

STUDY DESIGN AND METHODS

Steady state metabolomics and isotope-labeled tracing experiments, immunofluorescence approaches, and pharmacological interventions were used to determine the degree of fatty acid unsaturation, FADS activity as a function of storage, oxidant stress, and G6PD deficiency in human and mouse RBCs.

RESULTS

In 250 blood units from the REDS III RBC Omics recalled donor population, we report a storage-dependent accumulation of free mono-, poly-(PUFAs), and highly unsaturated fatty acids (HUFAs), which occur at a faster rate than saturated fatty acid accumulation. Through a combination of immunofluorescence, pharmacological inhibition, tracing experiments with stable isotope-labeled fatty acids, and oxidant challenge with hydrogen peroxide, we demonstrate the presence and redox-sensitive activity of FADS2, FADS1, and FADS5 in the mature RBC. Increases in PUFAs and HUFAs in human and mouse RBCs correlate negatively with storage hemolysis and positively with posttransfusion recovery. Inhibition of these enzymes decreases accumulation of free PUFAs and HUFAs in stored RBCs, concomitant to increases in pyruvate/lactate ratios. Alterations of this ratio in G6PD deficient patients or units supplemented with pyruvate-rich rejuvenation solutions corresponded to decreased PUFA and HUFA accumulation.

CONCLUSION

Fatty acid desaturases are present and active in mature RBCs. Their activity is sensitive to oxidant stress, storage duration, and alterations of the pyruvate/lactate ratio.

Single-Cell Native Mass Spectrometry of Human Erythrocytes

Native mass spectrometry (MS) enables the determination of the molecular mass of protein complexes. Generally, samples for native MS are isolated, purified, and prepared in volatile solutions. However, to understand the function of proteins in living cells, it is essential to characterize the protein complex as is, without isolation/purification of the protein, using the smallest possible amount of the sample. In the present study, we modified the "live single-cell MS" method, which has mainly been used in metabolomics, and applied it to observe hemoglobin directly sampled from human erythrocytes. By optimizing the experimental methods and conditions, we obtained native mass spectra of hemoglobin using only a single erythrocyte, which was directly sampled into a nanoelectrospray ionization emitter using a micromanipulator and microinjector system. That is, our method enables the analysis of ∼0.45 fmol of hemoglobin directly sampled from an erythrocyte. To our knowledge, this is the first report of native MS for endogenous proteins using a single intact human cell.

Blood donor exposome and impact of common drugs on red blood cell metabolism

Computational models based on recent maps of the RBC proteome suggest that mature erythrocytes may harbor targets for common drugs. This prediction is relevant to RBC storage in the blood bank, in which the impact of small molecule drugs or other xenometabolites deriving from dietary, iatrogenic, or environmental exposures (“exposome”) may alter erythrocyte energy and redox metabolism and, in so doing, affect red cell storage quality and posttransfusion efficacy. To test this prediction, here we provide a comprehensive characterization of the blood donor exposome, including the detection of common prescription and over-the-counter drugs in blood units donated by 250 healthy volunteers in the Recipient Epidemiology and Donor Evaluation Study III Red Blood Cell–Omics (REDS-III RBC-Omics) Study. Based on high-throughput drug screenings of 1366 FDA-approved drugs, we report that approximately 65% of the tested drugs had an impact on erythrocyte metabolism. Machine learning models built using metabolites as predictors were able to accurately predict drugs for several drug classes/targets (bisphosphonates, anticholinergics, calcium channel blockers, adrenergics, proton pump inhibitors, antimetabolites, selective serotonin reuptake inhibitors, and mTOR), suggesting that these drugs have a direct, conserved, and substantial impact on erythrocyte metabolism. As a proof of principle, here we show that the antacid ranitidine — though rarely detected in the blood donor population — has a strong effect on RBC markers of storage quality in vitro. We thus show that supplementation of blood units stored in bags with ranitidine could — through mechanisms involving sphingosine 1–phosphate–dependent modulation of erythrocyte glycolysis and/or direct binding to hemoglobin — improve erythrocyte metabolism and storage quality.

One ring to bring them all and in the darkness bind them: The trafficking of heme without deliverers

Heme, as a hydrophobic iron-containing organic ring, is lipid soluble and can interact with biological membranes. The very same properties of heme that nature exploits to support life also renders heme potentially cytotoxic. In order to utilize heme, while also mitigating its toxicity, cells are challenged to tightly control the concentration and bioavailability of heme. On the bright side, it is reasonable to envision that, analogous to other transition metals, a combination of membrane-bound transporters, soluble carriers, and chaperones coordinate heme trafficking to subcellular compartments. However, given the dual properties exhibited by heme as a transition metal and lipid, it is compelling to consider the dark side: the potential role of non-proteinaceous biomolecules including lipids and nucleic acids that bind, sequester, and control heme trafficking and bioavailability. The emergence of inter-organellar membrane contact sites, as well as intracellular vesicles derived from various organelles, have raised the prospect that heme can be trafficked through hydrophobic channels. In this review, we aim to focus on heme delivery without deliverers - an alternate paradigm for the regulation of heme homeostasis through chaperone-less pathways for heme trafficking.

Testosterone replacement therapy in blood donors modulates erythrocyte metabolism and susceptibility to hemolysis in cold storage

BACKGROUND

Red blood cells (RBCs) derived from patients who receive testosterone replacement therapy (TRT) may be considered eligible for component production and transfusion. The aim of this study was to identify testosterone-dependent changes in RBC metabolism and to evaluate its impact on susceptibility to hemolysis during cold storage.

STUDY DESIGN AND METHODS

We characterized stored RBCs from two cohorts of TRT patients who were matched with control donors (no TRT) based upon sex, age, and ethnicity. We further evaluated the impact of testosterone deficiency (orchiectomy) on RBC metabolism in FVB/NJ mice. RBC metabolites were quantified by ultra-high-pressure liquid chromatography-mass spectrometry. RBC storage stability was determined in RBC units from TRT and controls by quantifying storage, osmotic, and oxidative hemolysis.

RESULTS

Orchiectomy in mice was associated with significant (P < 0.05) changes in RBC metabolism as compared with intact males including increased levels of acyl-carnitines, long-chain fatty acids (eg, docosapentaenoic acids), arginine, and dopamine. Stored RBCs from TRT patients exhibited higher levels of pentose phosphate pathway metabolites, glutathione, and oxidized purines (eg, hypoxanthine), suggestive of increased activation of antioxidant pathways in this group. Further analyses indicated significant changes in free fatty acids and acyl-carnitines in response to testosterone therapies. With regard to hemolysis, TRT was associated with enhanced susceptibility to osmotic hemolysis. Correlation analyses identified acyl-carnitines as significant modifiers of RBC predisposition to osmotic and oxidative hemolysis.

CONCLUSIONS

These observations provide new insights into testosterone-mediated changes in RBC metabolome and biology that may impact the storage capacity and posttransfusion efficacy of RBCs from TRT donors.

Evidence of Structural Protein Damage and Membrane Lipid Remodeling in Red Blood Cells from COVID-19 Patients

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.

Modeling the activation of the alternative complement pathway and its effects on hemolysis in health and disease

The complement system is a powerful mechanism of innate immunity poised to eliminate foreign cells and pathogens. It is an intricate network of >35 proteins, which, once activated, leads to the tagging of the surface to be eliminated, produces potent chemoattractants to recruit immune cells, and inserts cytotoxic pores into nearby lipid surfaces. Although it can be triggered via different pathways, its net output is largely based on the direct or indirect activation of the alternative pathway. Complement dysregulation or deficiencies may cause severe pathologies, such as paroxysmal nocturnal hemoglobinuria (PNH), where a lack of complement control proteins leads to hemolysis and life-threatening anemia. The complexity of the system poses a challenge for the interpretation of experimental data and the design of effective pharmacological therapies. To address this issue, we developed a mathematical model of the alternative complement pathway building on previous modelling efforts. The model links complement activation to the hemolytic activity of the terminal alternative pathway, providing an accurate description of pathway activity as observed in vitro and in vivo, in health and disease. Through adjustment of the parameters describing experimental conditions, the model was capable of reproducing the results of an array of standard assays used in complement research. To demonstrate its clinical applicability, we compared model predictions with clinical observations of the recovery of hematological biomarkers in PNH patients treated with the complement inhibiting anti-C5 antibody eculizumab. In conclusion, the model can enhance the understanding of complement biology and its role in disease pathogenesis, help identifying promising targets for pharmacological intervention, and predict the outcome of complement-targeting pharmacological interventions.

Red blood cell metabolism in Rhesus macaques and humans: comparative biology of blood storage

Macaques are emerging as a critical animal model in transfusion medicine, because of their evolutionary similarity to humans and perceived utility in discovery and translational science. However, little is known about the metabolism of Rhesus macaque red blood cells (RBC) and how this compares to human RBC metabolism under standard blood banking conditions. Metabolomic and lipidomic analyses, and tracing experiments with [1,2,3-¹³C₃]glucose, were performed using fresh and stored RBC (sampled weekly until storage day 42) obtained from Rhesus macaques (n=20) and healthy human volunteers (n=21). These results were further validated with targeted quantification against stable isotope-labeled internal standards. Metabolomic analyses demonstrated inter-species differences in RBC metabolism independent of refrigerated storage. Although similar trends were observed throughout storage for several metabolic pathways, species- and sex-specific differences were also observed. The most notable differences were in glutathione and sulfur metabolites, purine and lipid oxidation metabolites, acylcarnitines, fatty acyl composition of several classes of lipids (including phosphatidylserines), glyoxylate pathway intermediates, and arginine and carboxylic acid metabolites. Species-specific dietary and environmental compounds were also detected. Overall, the results suggest an increased basal and refrigerator-storage-induced propensity for oxidant stress and lipid remodeling in Rhesus macaque RBC cells, as compared to human red cells. The overlap between Rhesus macaque and human RBC metabolic phenotypes suggests the potential utility of a translational model for simple RBC transfusions, although inter-species storage-dependent differences need to be considered when modeling complex disease states, such as transfusion in trauma/hemorrhagic shock models.

Restoration of Physiological Levels of Uric Acid and Ascorbic Acid Reroutes the Metabolism of Stored Red Blood Cells

After blood donation, the red blood cells (RBCs) for transfusion are generally isolated by centrifugation and then filtrated and supplemented with additive solution. The consecutive changes of the extracellular environment participate to the occurrence of storage lesions. In this study, the hypothesis is that restoring physiological levels of uric and ascorbic acids (major plasmatic antioxidants) might correct metabolism defects and protect RBCs from the very beginning of the storage period, to maintain their quality. Leukoreduced CPD-SAGM RBC concentrates were supplemented with 416 µM uric acid and 114 µM ascorbic acid and stored during six weeks at 4 °C. Different markers, i.e., haematological parameters, metabolism, sensitivity to oxidative stress, morphology and haemolysis were analyzed. Quantitative metabolomic analysis of targeted intracellular metabolites demonstrated a direct modification of several metabolite levels following antioxidant supplementation. No significant differences were observed for the other markers. In conclusion, the results obtained show that uric and ascorbic acids supplementation partially prevented the metabolic shift triggered by plasma depletion that occurs during the RBC concentrate preparation. The treatment directly and indirectly sustains the antioxidant protective system of the stored RBCs.

Sedimentation rate of erythrocyte from physics prospective

An erythrocytes sedimentation rate (ESR) measures how fast a blood sample sediments along a test tube in one hour in a clinical laboratory. Since elevated level of ESR is associated with inflammatory diseases, ESR is one of the routine hematology test in a clinical laboratory. In this paper, the physics of erythrocyte (RBC) sedimentation rate as well as the dynamics of the RBC is explored by modeling the dynamics of the cells as the motion of Brownian particle moving in a viscous medium. The viscous friction of blood γ is considered to decrease as the temperature of the medium increases. The results obtained in this work show that the ESR increases as the number of red blood cells (that bind together in the sedimentation process) steps up. The room temperature also affects the sedimentation rate. As the room temperature rises up, the ESR steps up. Furthermore the dynamics of the RBC along a Westergren pipet that is held in an upright position is explored. The exact analytic result depicts that the velocity of cells increases as the number of cells that form rouleaux steps up. Since our study is performed by considering physiological parameters, the results obtained in this work not only can be justified experimentally but also helps to understand most hematological experiments that are conducted in vitro.

Experimental design and numerical investigation of a photoacoustic sensor for a low-power, continuous-wave, laser-based frequency-domain photoacoustic microscopy

We have developed a photoacoustic (PA) sensor using a low-power, continuous- wave laser and a kHz-range microphone. The sensor is simple, flexible, cost-effective, and compatible with commercial optical microscopes. The sensor enables noncontact PA measurements through air, whereas most current existing PA techniques require an acoustic coupling liquid for detection. The PA sensor has three main components: one is the chamber that holds the sample, the second is a resonator column used to amplify the weak PA signals generated within the sample chamber, and the third is a microphone at the end of the resonator column to detect the amplified signals. The chamber size was designed to be 8  mm  ×  3  mm as the thermal diffusion length and viscous-thermal damping of air at room pressure and temperature are 2 and 1 mm, respectively. We numerically and experimentally examined the effect of the resonator column size on the frequency response of the PA sensor. The quality factor decreased significantly when the sample chamber size was reduced from 4  mm  ×  3  mm to 2  mm  ×  3  mm due to thermos-viscous damping of the air. The quality factor decreased by 27%, demonstrating the need for optimal design for the sample chamber and resonator column size. The system exhibited noise equivalent molecular sensitivity (NEM) per unit bandwidth (NEM  /  √  Δf) of ∼19,966  Hz ^−1/2 or 33  ×  10^−21  mol or 33 zeptomol, which is an improvement of 2.2 times compared to the previous system design. This PA sensor has the potential for noncontact high-resolution PA imaging of materials without the need for coupling fluids.

Metabolic impact of red blood cell exchange with rejuvenated red blood cells in sickle cell patients

BACKGROUND

Red blood cell exchange (RCE) transfusions are a mainstay in the treatment of sickle cell anemia (SCA), and allow a temporary restoration of physiological parameters with respect to erythrocyte oxygen carrying capacity and systems metabolism. Recently, we noted that 1) RCE significantly impacts recipients' metabolism in SCA; 2) fresh and end-of-storage red blood cell (RBC) units differently impact systems of metabolism in healthy autologous recipients; and 3) phosphate/inosine/pyruvate/adenine (PIPA) solution reverses the metabolic age of stored RBCs. Therefore, we hypothesized that RCE with PIPA-treated RBC units could further increase the metabolic benefits of RCE in SCA patients.

STUDY DESIGN AND METHODS

Circulating plasma and erythrocytes were collected from patients with SCA before and after RCE, with either conventional or PIPA-treated RBC units, prior to metabolomics analyses.

RESULTS

Consistent with prior work, RCE significantly decreased circulating levels of markers of systemic hypoxemia (lactate, succinate) and decreased plasma levels of acyl-carnitines and amino acids. However, PIPA-treated exchanges were superior to untreated RCEs, with a higher energy state and an increased capacity to activate the pentose phosphate pathway and glutamine metabolism. In addition, RBCs and plasma from recipients of PIPA-treated RBC units resulted in significantly decreased levels of post-transfusion plasticizers, though at the expense of higher circulating levels of oxidized purines (hypoxanthine, xanthine, and the antioxidant urate).

CONCLUSION

Transfusion of PIPA-treated RBCs further increases the metabolic benefits of RCE to patients with SCA, significantly reducing the levels of post-transfusion plasticizers.

Parabiosis Incompletely Reverses Aging-Induced Metabolic Changes and Oxidant Stress in Mouse Red Blood Cells

Mature red blood cells (RBCs) not only account for ~83% of the total host cells in the human body, but they are also exposed to all body tissues during their circulation in the bloodstream. In addition, RBCs are devoid of de novo protein synthesis capacity and, as such, they represent a perfect model to investigate system-wide alterations of cellular metabolism in the context of aging and age-related oxidant stress without the confounding factor of gene expression. In the present study, we employed ultra-high-pressure liquid chromatography coupled with mass spectrometry (UHPLC–MS)-based metabolomics and proteomics to investigate RBC metabolism across age in male mice (6, 15, and 25 months old). We report that RBCs from aging mice face a progressive decline in the capacity to cope with oxidant stress through the glutathione/NADPH-dependent antioxidant systems. Oxidant stress to tryptophan and purines was accompanied by declines in late glycolysis and methyl-group donors, a potential compensatory mechanism to repair oxidatively damaged proteins. Moreover, heterochronic parabiosis experiments demonstrated that the young environment only partially rescued the alterations in one-carbon metabolism in old mice, although it had minimal to no impact on glutathione homeostasis, the pentose phosphate pathway, and oxidation of purines and tryptophan, which were instead aggravated in old heterochronic parabionts.

Protect, repair, destroy or sacrifice: a role of oxidative stress biology in inter-donor variability of blood storage?

Red blood cells (RBCs) have been historically regarded as a critical model to investigate cellular and oxidant stress biology. First of all, they are constantly exposed to oxidant stress, as their main function is to transport and deliver oxygen to tissues. Second, they are devoid of de novo protein synthesis capacity, which prevents RBCs from replacing irreversibly oxidised proteins with newly synthesised ones. As such, RBCs have evolved to (i) protect themselves from oxidant stress, in order to prevent oxidant damage from reactive species; (ii) repair oxidatively damaged proteins, through mechanisms that involve glutathione and one-carbon metabolism; (iii) destroy irreversibly oxidised proteins through proteasomal or protease-dependent degradation; and (iv) sacrifice membrane portions through mechanism of vesiculation. In this brief review we will summarize these processes and their relevance to RBC redox biology (within the context of blood storage), with a focus on how polymorphisms in RBC antioxidant responses could contribute to explaining the heterogeneity in the progression and severity of the RBC storage lesion that can be observed across the healthy donor population.

Red Blood Cell Metabolic Responses to Torpor and Arousal in the Hibernator Arctic Ground Squirrel

Arctic ground squirrels provide a unique model to investigate metabolic responses to hibernation in mammals. During winter months these rodents are exposed to severe hypothermia, prolonged fasting, and hypoxemia. In the light of their role in oxygen transport/off-loading and owing to the absence of nuclei and organelles (and thus de novo protein synthesis capacity), mature red blood cells have evolved metabolic programs to counteract physiological or pathological hypoxemia. However, red blood cell metabolism in hibernation has not yet been investigated. Here we employed targeted and untargeted metabolomics approaches to investigate erythrocyte metabolism during entrance to torpor to arousal, with a high resolution of the intermediate time points. We report that torpor and arousal promote metabolism through glycolysis and pentose phosphate pathway, respectively, consistent with previous models of oxygen-dependent metabolic modulation in mature erythrocytes. Erythrocytes from hibernating squirrels showed up to 100-fold lower levels of biomarkers of reperfusion injury, such as the pro-inflammatory dicarboxylate succinate. Altered tryptophan metabolism during torpor was here correlated to the accumulation of potentially neurotoxic catabolites kynurenine, quinolinate, and picolinate. Arousal was accompanied by alterations of sulfur metabolism, including sudden spikes in a metabolite putatively identified as thiorphan (level 1 confidence)-a potent inhibitor of several metalloproteases that play a crucial role in nociception and inflammatory complication to reperfusion secondary to ischemia or hemorrhage. Preliminary studies in rats showed that intravenous injection of thiorphan prior to resuscitation mitigates metabolic and cytokine markers of reperfusion injury, etiological contributors to inflammatory complications after shock.

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.

Proteomics study of human cord blood reticulocyte-derived exosomes

Reticulocyte-derived exosomes (Rex), extracellular vesicles of endocytic origin, were initially discovered as a cargo-disposal mechanism of obsolete proteins in the maturation of reticulocytes into erythrocytes. In this work, we present the first mass spectrometry-based proteomics of human Rex (HuRex). HuRex were isolated from cultures of human reticulocyte-enriched cord blood using different culture conditions and exosome isolation methods. The newly described proteome consists of 367 proteins, most of them related to exosomes as revealed by gene ontology over-representation analysis and include multiple transporters as well as proteins involved in exosome biogenesis and erythrocytic disorders. Immunoelectron microscopy validated the presence of the transferrin receptor. Moreover, functional assays demonstrated active capture of HuRex by mature dendritic cells. As only seven proteins have been previously associated with HuRex, this resource will facilitate studies on the role of human reticulocyte-derived exosomes in normal and pathological conditions affecting erythropoiesis.

Biliverdin Reductase B Dynamics Are Coupled to Coenzyme Binding

Biliverdin reductase B (BLVRB) is a newly identified cellular redox regulator that catalyzes the NADPH-dependent reduction of multiple substrates. Through mass spectrometry analysis, we identified high levels of BLVRB in mature red blood cells, highlighting the importance of BLVRB in redox regulation. The BLVRB conformational changes that occur during conezyme/substrate binding and the role of dynamics in BLVRB function, however, remain unknown. Through a combination of NMR, kinetics, and isothermal titration calorimetry studies, we determined that BLVRB binds its coenzyme 500-fold more tightly than its substrate. While the active site of apo BLVRB is highly dynamic on multiple timescales, active site dynamics are largely quenched within holo BLVRB, in which dynamics are redistributed to other regions of the enzyme. We show that a single point mutation of Arg78➔Ala leads to both an increase in active site micro-millisecond motions and an increase in the microscopic rate constants of coenzyme binding. This demonstrates that altering BLVRB active site dynamics can directly cause a change in functional characteristics. Our studies thus address the solution behavior of apo and holo BLVRB and identify a role of enzyme dynamics in coenzyme binding.

Proteomics of Stored Red Blood Cell Membrane and Storage-Induced Microvesicles Reveals the Association of Flotillin-2 With Band 3 Complexes

The storage of erythrocyte concentrates (ECs) induces lesions that notably affect metabolism, protein activity, deformability of red blood cells (RBCs), as well as the release of oxygen. Band 3 is one of the proteins affected during the ex vivo aging of RBCs. This membrane protein is an anion transporter, an anchor site for the cytoskeleton and other membrane proteins as well as a binding site for glycolytic enzymes and bears blood group antigens. In the present study, band 3 complexes were isolated from RBCs stored for 7 and 42 days in average (n = 3), as well as from microvesicles (n = 3). After extraction of membrane proteins with a deoxycholate containing buffer, band 3 complexes were co-immunoprecipitated on magnetic beads coated with two anti-band 3 antibodies. Both total membrane protein extracts and eluates (containing band 3 complexes) were separated on SDS-PAGE and analyzed by bottom-up proteomics. It revealed that three proteins were present or absent in band 3 complexes stemming from long-stored or short-stored ECs, respectively, whereas the membrane protein contents remained equivalent. These potential markers for storage-induced RBC aging are adenylosuccinate lyase (ADSL), α-adducin and flotillin-2, and were further analyzed using western blots. ADSL abundance tended to increase during storage in both total membrane protein and band 3 complexes, whereas α-adducin mainly tended to stay onto the membrane extract. Interestingly, flotillin-2 was equivalently present in total membrane proteins whereas it clearly co-immunoprecipitated with band 3 complexes during storage (1.6-fold-change, p = 0.0024). Moreover, flotillin-2 was enriched (almost threefold) in RBCs compared to microvesicles (MVs) (p < 0.001) and the amount found in MVs was associated to band 3 complexes. Different types of band 3 complexes are known to exist in RBCs and further studies will be required to better understand involvement of this protein in microvesiculation during the storage of RBCs.

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.

Investigation of the effects of storage and freezing on mixes of heavy-labeled metabolite and amino acid standards

RATIONALE

High-throughput metabolomics has now made it possible for small/medium-sized laboratories to analyze thousands of samples/year from the most diverse biological matrices including biofluids, cell and tissue extracts. In large-scale metabolomics studies, stable-isotope-labeled standards are increasingly used to normalize for matrix effects and control for technical reproducibility (e.g. extraction efficiency, chromatographic retention times and mass spectrometry signal stability). However, it is currently unknown how stable mixes of commercially available standards are following repeated freeze/thaw cycles or prolonged storage of aliquots.

METHODS

Standard mixes for 13 C, 15 N or deuterated isotopologues of amino acids and key metabolites from the central carbon and nitrogen pathways (e.g. glycolysis, Krebs cycle, redox homeostasis, purines) were either repeatedly frozen/thawed for up to 10 cycles or diluted into aliquots prior to frozen storage for up to 42 days. Samples were characterized by ultra-high-pressure liquid chromatography/mass spectrometry to determine the stability of the aliquoted standards upon freezing/thawing or prolonged storage.

RESULTS

Metabolite standards were stable over up to 10 freeze/thaw cycles, with the exception of adenosine and glutathione, showing technical variability across aliquots in a freeze/thaw-cycle-independent fashion. Storage for up to 42 days of mixes of commercially available standards did not significantly affect the stability of amino acid or metabolite standards for the first 2 weeks, while progressive degradation (statistically significant for fumarate) was observed after 3 weeks.

CONCLUSIONS

Refrigerated or frozen preservation for at least 2 weeks of aliquoted heavy-labeled standard mixes for metabolomics analysis is a feasible and time-/resource-saving strategy for standard metabolomics laboratories.

Hypoxia modulates the purine salvage pathway and decreases red blood cell and supernatant levels of hypoxanthine during refrigerated storage

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.

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.

Hupresin Retains Binding Capacity for Butyrylcholinesterase and Acetylcholinesterase after Sanitation with Sodium Hydroxide

Hupresin is a new affinity resin that binds butyrylcholinesterase (BChE) in human plasma and acetylcholinesterase (AChE) solubilized from red blood cells (RBC). Hupresin is available from the CHEMFORASE company. BChE in human plasma binds to Hupresin and is released with 0.1 M trimethylammonium bromide (TMA) with full activity and 10-15% purity. BChE immunopurified from plasma by binding to immobilized monoclonal beads has fewer contaminating proteins than the one-step Hupresin-purified BChE. However, when affinity chromatography on Hupresin follows ion exchange chromatography at pH 4.5, BChE is 99% pure. The membrane bound AChE, solubilized from human RBC with 0.6% Triton X-100, binds to Hupresin and remains bound during washing with sodium chloride. Human AChE is not released in significant quantities with non-denaturing solvents, but is recovered in 1% trifluoroacetic acid. The denatured, partially purified AChE is useful for detecting exposure to nerve agents by mass spectrometry. Our goal was to determine whether Hupresin retains binding capacity for BChE and AChE after Hupresin is washed with 0.1 M NaOH. A 2 mL column of Hupresin equilibrated in 20 mM TrisCl pH 7.5 was used in seven consecutive trials to measure binding and recovery of BChE from 100 mL human plasma. Between each trial the Hupresin was washed with 10 column volumes of 0.1 M sodium hydroxide. A similar trial was conducted with red blood cell AChE in 0.6% Triton X-100. It was found that the binding capacity for BChE and AChE was unaffected by washing Hupresin with 0.1 M sodium hydroxide. Hupresin could be washed with sodium hydroxide at least seven times without losing binding capacity.

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.