Toward Translational Impact of Low-Glucose Strategies on Red Blood Cell Storage Optimization.

Transfusion of stored red blood cells (RBCs) to patients is a critical component of human healthcare. Following purification from whole blood, RBCs are stored in one of many media known as additive solutions for up to 42 days. However, during the storage period, the RBCs undergo adverse chemical and physical changes that are often collectively known as the RBC storage lesion. Storage of RBCs in additive solutions modified to contain physiological levels of glucose, as opposed to hyperglycemic levels currently used in most cases, reduces certain markers of the storage lesion, although intermittent doses of glucose are required to maintain normoglycemic conditions. Here, we describe an electrically actuated valving system to dispense small volumes of glucose into 100 mL PVC storage bags containing packed RBCs from human donors. The RBCs were stored in a conventional additive solution (AS-1) or a normoglycemic version of AS-1 (AS-1N) and common markers of stored RBC health were measured at multiple time points throughout storage. The automated feeding device delivered precise and predictable volumes of concentrated glucose to maintain physiological glucose levels for up to 37 days. Hemolysis, lactate accumulation, and pH values of RBCs stored in AS-1N were statistically equivalent to values measured in AS-1, while significant reductions in osmotic fragility and intracellular sorbitol levels were measured in AS-1N. The reduction of osmotic fragility and oxidative stress markers in a closed system may lead to improved transfusion outcomes for an important procedure affecting millions of people each year.

A 3D-printed transfusion platform reveals beneficial effects of normoglycemic erythrocyte storage solutions and a novel rejuvenating solution.

A set of 3D-printed analytical devices were developed to investigate erythrocytes (ERYs) processed in conventional and modified storage solutions used in transfusion medicine. During storage, prior to transfusion into a patient recipient, ERYs undergo many chemical and physical changes that are not completely understood. However, these changes are thought to contribute to an increase in post-transfusion complications, and even an increase in mortality rates. Here, a reusable fluidic device (fabricated with additive manufacturing technologies) enabled the evaluation of ERYs prior to, and after, introduction into a stream of flowing fresh ERYs, thus representing components of an in vivo ERY transfusion on an in vitro platform. Specifically, ERYs stored in conventional and glucose-modified solutions were assayed by chemiluminescence for their ability to release flow-induced ATP. The ERY's deformability was also determined throughout the storage duration using a novel membrane transport approach housed in a 3D-printed scaffold. Results show that hyperglycemic conditions permanently alter ERY deformability, which may explain the reduced ATP release, as this phenomenon is related to cell deformability. Importantly, the reduced deformability and ATP release were reversible in an in vitro model of transfusion; specifically, when stored cells were introduced into a flowing stream of healthy cells, the ERY-derived release of ATP and cell deformability both returned to states similar to that of non-stored cells. However, after 1-2 weeks of storage, the deleterious effects of the storage were permanent. These results suggest that currently approved hyperglycemic storage solutions are having adverse effects on stored ERYs used in transfusion medicine and that normoglycemic storage may reduce the storage lesion, especially for cells stored for longer than 14 days.

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.

Pannexin 1 channels control the hemodynamic response to hypoxia by regulating O2-sensitive extracellular ATP in blood.

Pannexin 1 (Panx1) channels export ATP and may contribute to increased concentration of the vasodilator ATP in plasma during hypoxia in vivo. We hypothesized that Panx1 channels and associated ATP export contribute to hypoxic vasodilation, a mechanism that facilitates the matching of oxygen delivery to metabolic demand of tissue. Male and female mice devoid of Panx1 (Panx1-/-) and wild-type controls (WT) were anesthetized, mechanically ventilated, and instrumented with a carotid artery catheter or femoral artery flow transducer for hemodynamic and plasma ATP monitoring during inhalation of 21% (normoxia) or 10% oxygen (hypoxia). ATP export from WT vs. Panx1-/-erythrocytes (RBC) was determined ex vivo via tonometer experimentation across progressive deoxygenation. Mean arterial pressure (MAP) was similar in Panx1-/- (n = 6) and WT (n = 6) mice in normoxia, but the decrease in MAP in hypoxia seen in WT was attenuated in Panx1-/- mice (-16 ± 9% vs. -2 ± 8%; P < 0.05). Hindlimb blood flow (HBF) was significantly lower in Panx1-/- (n = 6) vs. WT (n = 6) basally, and increased in WT but not Panx1-/- mice during hypoxia (8 ± 6% vs. -10 ± 13%; P < 0.05). Estimation of hindlimb vascular conductance using data from the MAP and HBF experiments showed an average response of 28% for WT vs. -9% for Panx1-/- mice. Mean venous plasma ATP during hypoxia was 57% lower in Panx1-/- (n = 6) vs. WT mice (n = 6; P < 0.05). Mean hypoxia-induced ATP export from RBCs from Panx1-/- mice (n = 8) was 82% lower than that from WT (n = 8; P < 0.05). Panx1 channels participate in hemodynamic responses consistent with hypoxic vasodilation by regulating hypoxia-sensitive extracellular ATP levels in blood.NEW & NOTEWORTHY Export of vasodilator ATP from red blood cells requires pannexin 1. Blood plasma ATP elevations in response to hypoxia in mice require pannexin 1. Hemodynamic responses to hypoxia are accompanied by increased plasma ATP in mice in vivo and require pannexin 1.

HGT in the human and skin commensal Malassezia: A bacterially derived flavohemoglobin is required for NO resistance and host interaction.

The skin of humans and animals is colonized by commensal and pathogenic fungi and bacteria that share this ecological niche and have established microbial interactions. Malassezia are the most abundant fungal skin inhabitant of warm-blooded animals and have been implicated in skin diseases and systemic disorders, including Crohn's disease and pancreatic cancer. Flavohemoglobin is a key enzyme involved in microbial nitrosative stress resistance and nitric oxide degradation. Comparative genomics and phylogenetic analyses within the Malassezia genus revealed that flavohemoglobin-encoding genes were acquired through independent horizontal gene transfer events from different donor bacteria that are part of the mammalian microbiome. Through targeted gene deletion and functional complementation in Malassezia sympodialis, we demonstrated that bacterially derived flavohemoglobins are cytoplasmic proteins required for nitric oxide detoxification and nitrosative stress resistance under aerobic conditions. RNA-sequencing analysis revealed that endogenous accumulation of nitric oxide resulted in up-regulation of genes involved in stress response and down-regulation of the MalaS7 allergen-encoding genes. Solution of the high-resolution X-ray crystal structure of Malassezia flavohemoglobin revealed features conserved with both bacterial and fungal flavohemoglobins. In vivo pathogenesis is independent of Malassezia flavohemoglobin. Lastly, we identified an additional 30 genus- and species-specific horizontal gene transfer candidates that might have contributed to the evolution of this genus as the most common inhabitants of animal skin.

Red Blood Cell Deformability, Vasoactive Mediators, and Adhesion.

Healthy red blood cells (RBCs) deform readily in response to shear stress in the circulation, facilitating their efficient passage through capillaries. RBCs also export vasoactive mediators in response to deformation and other physiological and pathological stimuli. Deoxygenation of RBC hemoglobin leads to the export of vasodilator and antiadhesive S-nitrosothiols (SNOs) and adenosine triphosphate (ATP) in parallel with oxygen transport in the respiratory cycle. Together, these mediated responses to shear stress and oxygen offloading promote the efficient flow of blood cells and in turn optimize oxygen delivery. In diseases including sickle cell anemia and conditions including conventional blood banking, these adaptive functions may be compromised as a result, for example, of limited RBC deformability, impaired mediator formation, or dysfunctional mediator export. Ongoing work, including single cell approaches, is examining relevant mechanisms and remedies in health and disease.

Nitric oxide loading reduces sickle red cell adhesion and vaso-occlusion in vivo.

Sickle red blood cells (SSRBCs) are adherent to the endothelium, activate leukocyte adhesion, and are deficient in bioactive nitric oxide (NO) adducts such as S-nitrosothiols (SNOs), with reduced ability to induce vasodilation in response to hypoxia. All these pathophysiologic characteristics promote vascular occlusion, the hallmark of sickle cell disease (SCD). Loading hypoxic SSRBCs in vitro with NO followed by reoxygenation significantly decreased epinephrine-activated SSRBC adhesion to the endothelium, the ability of activated SSRBCs to mediate leukocyte adhesion in vitro, and vessel obstruction in vivo. Because transfusion is frequently used in SCD, we also determined the effects of banked (SNO-depleted) red blood cells (RBCs) on vaso-occlusion in vivo. Fresh or 14-day-old normal RBCs (AARBCs) reduced epinephrine-activated SSRBC adhesion to the vascular endothelium and prevented vaso-occlusion. In contrast, AARBCs stored for 30 days failed to decrease activated SSRBC adhesivity or vaso-occlusion, unless these RBCs were loaded with NO. Furthermore, NO loading of SSRBCs increased S-nitrosohemoglobin and modulated epinephrine's effect by upregulating phosphorylation of membrane proteins, including pyruvate kinase, E3 ubiquitin ligase, and the cytoskeletal protein 4.1. Thus, abnormal SSRBC NO/SNO content both contributes to the vaso-occlusive pathophysiology of SCD, potentially by affecting at least protein phosphorylation, and is potentially amenable to correction by (S)NO repletion or by RBC transfusion.

Red blood cell phenotype fidelity following glycerol cryopreservation optimized for research purposes.

Intact red blood cells (RBCs) are required for phenotypic analyses. In order to allow separation (time and location) between subject encounter and sample analysis, we developed a research-specific RBC cryopreservation protocol and assessed its impact on data fidelity for key biochemical and physiological assays. RBCs drawn from healthy volunteers were aliquotted for immediate analysis or following glycerol-based cryopreservation, thawing, and deglycerolization. RBC phenotype was assessed by (1) scanning electron microscopy (SEM) imaging and standard morphometric RBC indices, (2) osmotic fragility, (3) deformability, (4) endothelial adhesion, (5) oxygen (O2) affinity, (6) ability to regulate hypoxic vasodilation, (7) nitric oxide (NO) content, (8) metabolomic phenotyping (at steady state, tracing with [1,2,3-13C3]glucose ± oxidative challenge with superoxide thermal source; SOTS-1), as well as in vivo quantification (following human to mouse RBC xenotransfusion) of (9) blood oxygenation content mapping and flow dynamics (velocity and adhesion). Our revised glycerolization protocol (40% v/v final) resulted in >98.5% RBC recovery following freezing (-80°C) and thawing (37°C), with no difference compared to the standard reported method (40% w/v final). Full deglycerolization (>99.9% glycerol removal) of 40% v/v final samples resulted in total cumulative lysis of ~8%, compared to ~12-15% with the standard method. The post cryopreservation/deglycerolization RBC phenotype was indistinguishable from that for fresh RBCs with regard to physical RBC parameters (morphology, volume, and density), osmotic fragility, deformability, endothelial adhesivity, O2 affinity, vasoregulation, metabolomics, and flow dynamics. These results indicate that RBC cryopreservation/deglycerolization in 40% v/v glycerol final does not significantly impact RBC phenotype (compared to fresh cells).

Drebrin regulates angiotensin II-induced aortic remodelling.

Aims: The actin-binding protein Drebrin is up-regulated in response to arterial injury and reduces smooth muscle cell (SMC) migration and proliferation through its interaction with the actin cytoskeleton. We, therefore, tested the hypothesis that SMC Drebrin inhibits angiotensin II-induced remodelling of the proximal aorta. Methods and results: Angiotensin II was administered via osmotic minipumps at 1000 ng/kg/min continuously for 28 days in SM22-Cre+/Dbnflox/flox (SMC-Dbn-/-) and control mice. Blood pressure responses to angiotensin II were assessed by telemetry. After angiotensin II infusion, we assessed remodelling in the proximal ascending aorta by echocardiography and planimetry of histological cross sections. Although the degree of hypertension was equivalent in SMC-Dbn-/- and control mice, SMC-Dbn-/- mice nonetheless exhibited 60% more proximal aortic medial thickening and two-fold more outward aortic remodelling than control mice in response to angiotensin II. Proximal aortas demonstrated greater cellular proliferation and matrix deposition in SMC-Dbn-/- mice than in control mice, as evidenced by a higher prevalence of proliferating cell nuclear antigen-positive nuclei and higher levels of collagen I. Compared with control mouse aortas, SMC-Dbn-/- aortas demonstrated greater angiotensin II-induced NADPH oxidase activation and inflammation, evidenced by higher levels of Ser-536-phosphorylated NFκB p65 subunits and higher levels of vascular cell adhesion molecule-1, matrix metalloproteinase-9, and adventitial macrophages. Conclusions: We conclude that SMC Drebrin deficiency augments angiotensin II-induced inflammation and adverse aortic remodelling.

Proceedings of the Food and Drug Administration's public workshop on new red blood cell product regulatory science 2016.

The US Food and Drug Administration (FDA) held a workshop on red blood cell (RBC) product regulatory science on October 6 and 7, 2016, at the Natcher Conference Center on the National Institutes of Health (NIH) Campus in Bethesda, Maryland. The workshop was supported by the National Heart, Lung, and Blood Institute, NIH; the Department of Defense; the Office of the Assistant Secretary for Health, Department of Health and Human Services; and the Center for Biologics Evaluation and Research, FDA. The workshop reviewed the status and scientific basis of the current regulatory framework and the available scientific tools to expand it to evaluate innovative and future RBC transfusion products. A full record of the proceedings is available on the FDA website (http://www.fda.gov/BiologicsBloodVaccines/NewsEvents/WorkshopsMeetingsConferences/ucm507890.htm). The contents of the summary are the authors' opinions and do not represent agency policy.

Biomarkers in Pulmonary Vascular Disease: Gauging Response to Therapy.

Biomarkers are increasingly being investigated in the treatment of pulmonary vascular disease. In particular, the signaling pathways targeted by therapies for pulmonary arterial hypertension provide biomarkers that potentially can be used to guide therapy and to assess clinical response as an alternative to invasive procedures such as right-sided cardiac catheterization. Moreover, the growing use of combination therapy for both the initial and subsequent treatment of pulmonary arterial hypertension highlights the need for biomarkers in this treatment approach. Currently approved therapies for pulmonary arterial hypertension target 3 major signaling pathways: the nitric oxide-soluble guanylate cyclase-cyclic guanosine monophosphate pathway, the endothelin pathway, and the prostacyclin pathway. Although the main biomarker used in practice and evaluated in clinical trials is N-terminal pro-brain natriuretic peptide, other putative biomarkers include the endogenous nitric oxide (NO) synthase inhibitor asymmetric dimethylarginine, NO metabolites including S-nitrosothiols and nitrite, exhaled NO, endothelins, cyclic guanosine monophosphate, cyclic adenosine monophosphate, and atrial natriuretic peptide. This review describes accessible biomarkers, related to the actual molecules targeted by current therapies, for measuring and predicting response to the individual pulmonary arterial hypertension treatment classes as well as combination therapy.

Antagonists of the system L neutral amino acid transporter (LAT) promote endothelial adhesivity of human red blood cells.

The system L neutral amino acid transporter (LAT; LAT1, LAT2, LAT3, or LAT4) has multiple functions in human biology, including the cellular import of S-nitrosothiols (SNOs), biologically active derivatives of nitric oxide (NO). SNO formation by haemoglobin within red blood cells (RBC) has been studied, but the conduit whereby a SNO leaves the RBC remains unidentified. Here we hypothesised that SNO export by RBCs may also depend on LAT activity, and investigated the role of RBC LAT in modulating SNO-sensitive RBC-endothelial cell (EC) adhesion. We used multiple pharmacologic inhibitors of LAT in vitro and in vivo to test the role of LAT in SNO export from RBCs and in thereby modulating RBC-EC adhesion. Inhibition of human RBC LAT by type-1-specific or nonspecific LAT antagonists increased RBC-endothelial adhesivity in vitro, and LAT inhibitors tended to increase post-transfusion RBC sequestration in the lung and decreased oxygenation in vivo. A LAT1-specific inhibitor attenuated SNO export from RBCs, and we demonstrated LAT1 in RBC membranes and LAT1 mRNA in reticulocytes. The proadhesive effects of inhibiting LAT1 could be overcome by supplemental L-CSNO (S-nitroso-L-cysteine), but not D-CSNO or L-Cys, and suggest a basal anti-adhesive role for stereospecific intercellular SNO transport. This study reveals for the first time a novel role of LAT1 in the export of SNOs from RBCs to prevent their adhesion to ECs. The findings have implications for the mechanisms of intercellular SNO signalling, and for thrombosis, sickle cell disease, and post-storage RBC transfusion, when RBC adhesivity is increased.

S-Nitrosylated fetal hemoglobin in neonatal human blood.

BACKGROUND: Nitric oxide (NO) and its derivatives play important roles in the cardiopulmonary transition upon birth and in other oxygen-sensitive developmental milestones. One mechanism for the coupling of oxygen sensing and signaling by NO species is via the formation of an S-nitrosothiol (SNO) moiety on hemoglobin (Hb, forming SNO-Hb) and its release from the red blood cell in hypoxia. Although SNO-Hb formed on adult-type Hb (HbA, forming SNO-HbA) has been documented in physiological and pathophysiological human states, the fetal variant, SNO-HbF, has thus far not been isolated or characterized in human blood. METHODS AND RESULTS: We developed a technique capable of separating Hbs A and F under conditions that preserve SNO. We then measured SNO-HbF in the blood of healthy and premature or otherwise ill neonates using the gold standard for SNO measurement, mercury-coupled photolysis-chemiluminescence. SNO-HbF levels were in the range of those previously reported for HbA in adults. We found that SNO-HbF was more abundant at earlier gestational age (<30 weeks), even when accounting for the absolute HbF level. CONCLUSIONS: The ability to monitor SNO-HbF could provide new insights into fetal development and the perinatal transition, and has potential as a biomarker relevant to the management of neonatal diseases.

Contact Lens Use in Patients With Boston Keratoprosthesis Type 1: Fitting, Management, and Complications.

The Boston type 1 keratoprosthesis (KPro) is the most commonly used artificial cornea worldwide. Long-term bandage contact lenses are the standard of care for patients with these devices. The goal of bandage contact lenses is to maintain hydration and to protect the corneal tissue that surrounds the anterior plate of the keratoprosthesis which is vulnerable to desiccation, epithelial breakdown, dellen formation, and corneal melt. Contact lenses can also improve comfort, correct refractive errors, and improve the cosmesis of patients with artificial corneas. However, the continuous use of contact lenses places these patients at risk for complications such as lens loss, lens deposits, chronic conjunctivitis, and infection. In addition, obtaining an adequate fit in a patient with a compromised ocular surface and history of multiple surgeries including glaucoma drainage devices can present a challenge. This review discusses the types of contact lenses used, special fitting considerations, and common complications in patients with previous KPro surgery.

Restoration of intracellular ATP production in banked red blood cells improves inducible ATP export and suppresses RBC-endothelial adhesion.

Transfusion of banked red blood cells (RBCs) has been associated with poor cardiovascular outcomes. Storage-induced alterations in RBC glycolytic flux, attenuated ATP export, and microvascular adhesion of transfused RBCs in vivo could contribute, but the underlying mechanisms have not been tested. We tested the novel hypothesis that improving deoxygenation-induced metabolic flux and the associated intracellular ATP generation in stored RBCs (sRBCs) results in an increased extracellular ATP export and suppresses microvascular adhesion of RBCs to endothelium in vivo following transfusion. We show deficient intracellular ATP production and ATP export by human sRBCs during deoxygenation (impairments ~42% and 49%, respectively). sRBC pretreatment with a solution containing glycolytic intermediate/purine/phosphate precursors (i.e., "PIPA") restored deoxygenation-induced intracellular ATP production and promoted extracellular ATP export (improvement ~120% and 50%, respectively). In a nude mouse model of transfusion, adhesion of human RBCs to the microvasculature in vivo was examined. Only 2% of fresh RBCs (fRBCs) transfused adhered to the vascular wall, compared with 16% of sRBCs transfused. PIPA pretreatment of sRBCs significantly reduced adhesion to just 5%. In hypoxia, adhesion of sRBCs transfused was significantly augmented (up to 21%), but not following transfusion of fRBCs or PIPA-treated sRBCs (3.5% or 6%). Enhancing the capacity for deoxygenation-induced glycolytic flux within sRBCs increases their ability to generate intracellular ATP, improves the inducible export of extracellular anti-adhesive ATP, and consequently suppresses adhesion of stored, transfused RBCs to the vascular wall in vivo.

Randomized study of washing 40- to 42-day-stored red blood cells.

BACKGROUND: Pretransfusion washing of red blood cells (RBCs) stored for a longer duration may have theoretical advantages but few data exist to support this practice. In many hospital settings, use of a point-of-care cell washer could conceivably be used to quickly wash allogeneic RBCs before transfusion. The purpose of this preliminary study was to compare a point-of-care device with a common blood bank device for washing longer-stored RBCs. STUDY DESIGN AND METHODS: Forty RBC units stored for 40 to 42 days were randomized to washing with the COBE 2991 device (Terumo BCT; FDA-cleared for washing stored RBCs) or the Cell Saver Elite (Haemonetics; FDA-cleared point-of-care device for processing and washing fresh autologous shed whole blood). Supernatant and unit RBCs from unwashed (baseline) and washed blood were assayed for potassium, lactate, intracellular ATP, percentage of RBC recovery, cell-free hemoglobin, RBC microparticles, and RBCs were examined for susceptibility to hemolysis by physical stress. RESULTS: Both devices recovered a high percentage of RBCs and efficiently removed extracelluar potassium. Washing with the Elite resulted in significant increases in cell-free Hb, percent hemolysis, and RBC microparticle production, whereas washing with the COBE 2991 did not (fold Δ = 2.1 vs. 1.0, 4.6 vs. 1.2, 2.0 vs. 1.1, respectively; p < 0.05). Hemolysis induced by physical stress was not altered by washing. CONCLUSION: Although point-of-care washing of longer-stored RBCs is appealing, these preliminary data suggest that transfusion of washed, longer-stored units could result in potentially greater exposure to plasma free Hb. More data are needed before this practice can be routinely recommended.

Proteomic analysis of the NOS2 interactome in human airway epithelial cells.

The cytokine-inducible isoform of nitric oxide synthase (NOS2) is constitutively expressed in human respiratory epithelia and is upregulated in inflammatory lung disease. Here, we sought to better define the protein interactions that may be important for NOS2 activity and stability, as well as to identify potential targets of NOS2-derived NO, in the respiratory epithelium. We overexpressed Flag-tagged, catalytically-inactive NOS2 in A549 cells and used mass spectrometry to qualitatively identify NOS2 co-immunoprecipitating proteins. Stable isotope labeling of amino acids in cell culture (SILAC) was used to quantify the coordinate effects of cytokine stimulation on NOS2-protein interactions. Multi-protein networks dominated the NOS2 interactome, and cytokine-inducible interactions with allosteric activators and with the ubiquitin-proteasome system were correlated with cytokine-dependent increases in NO metabolites and in NOS2 ubiquitination. The ubiquitin ligase scaffolding protein, FBXO45, was identified as a novel, direct NOS2 interactor. Similar to the SPRY domain-containing SOCS box (SPSB) proteins, FBXO45 requires Asn27 in the (23)DINNN(27) motif of NOS2 for its interaction. However, FBXO45 is unique from the SPSBs in that it recruits a distinct E3 ligase complex containing MYCBP2 and SKP1. Collectively, these findings demonstrate the general utility of interaction proteomics for defining new aspects of NOS2 physiology.

Impact of transfusion of autologous 7- versus 42-day-old AS-3 red blood cells on tissue oxygenation and the microcirculation in healthy volunteers.

BACKGROUND: Stored red blood cells (RBCs) accumulate biochemical and biophysical changes. Maximum storage duration is based on acceptable in vitro characteristics and 24-hour survival, but not RBC function. Relatively little is known about the impact of RBC storage duration on oxygenation and the microcirculation. STUDY DESIGN AND METHODS: Eight healthy subjects donated a double RBC apheresis, which were prestorage leukoreduced and processed in AS-3. Subjects were transfused 1 unit of RBCs at 7 and 42 days after blood collection. Measurements of percentage of tissue oxygenation in the thenar eminence muscle (StO2) and brain (SctO2) were recorded with Food and Drug Administration-cleared noninvasive devices. Sublingual microvascular blood flow (microcirculatory flow index [MFI]) was quantified before and after RBC transfusion using a video microscope. Raw electronic data for all measurements were analyzed by a blinded observer at a core laboratory. RESULTS: The only pre- versus posttransfusion change observed in measurements of SctO2, StO2, or MFI was a very small increase in SctO2, from 70.4 to 71.8 (means, p=0.032) at 7 days. There was no significant difference in the amount of pre-post change at 7 days versus 42 days for any of the measures. CONCLUSION: Transfusion of 1 unit of 42-day-stored RBCs to healthy subjects has no overt detrimental effect on tissue oxygenation or the microcirculation assessed by clinically available monitors.