Hemoglobin-driven pathophysiology is an in vivo consequence of the red blood cell storage lesion that can be attenuated in guinea pigs by haptoglobin therapy

Navigating Hemolysis, Hemoglobin Toxicity, and Its Renal Implications in Cardiac Surgery

Cardiopulmonary bypass–induced hemolysis is linked to acute kidney injury in cardiac surgery. Emerging therapies targeting cell-free hemoglobin (CFHb), like haptoglobin, nitric oxide (NO), and antioxidants, show promise in reducing kidney injury, highlighting the need for further research.

Ultraviolet light and riboflavin accelerates red blood cell dysfunction in vitro and in a guinea pig transfusion model

BACKGROUND

Quality assessment of modified or processed red blood cell (RBC) components, such as pathogen-reduced RBCs, using only in vitro testing may not always be predictive of in vivo performance. Mouse or rat in vivo models are limited by a lack of applicability to certain aspects of human RBC biology. Here, we used a guinea pig model to study the effects of riboflavin combined with UV light on the integrity of RBCs in vitro and following transfusion in vivo.

MATERIALS AND METHODS

Guinea pig RBCs were collected from whole blood (WB) treated with varying UV doses (10, 20, 40 or 80 J/mL) in the presence of riboflavin (UVR-RBCs). In vitro tests for UVR-RBCs included hemolysis, osmotic fragility, and cellular morphology by scanning electron microscopy. Guinea pigs transfused with one-day post-treatment UVR-RBCs were evaluated for plasma hemoglobin (Hb), non-transferrin bound iron (NTBI), total iron and Perls-detectable hemosiderin deposition in the spleen and kidney, and renal uptake of Hb.

RESULTS

Acute RBC injury was dose dependently accelerated after treatment with UV light in the presence of riboflavin. Aberrant RBC morphology was evident at 20, 40, and 80 J/mL, and membrane lysis with Hb release was prominent at 80 J/mL. Guinea pigs transfused with 40 and 80 J/mL UVR-RBCs showed increased plasma Hb levels, and plasma NTBI was elevated in all UVR-RBC groups (10-80 J/mL). Total iron levels and Perls-hemosiderin staining in spleen and kidney as well as Hb uptake in renal proximal tubules were increased 8 hours post-transfusion with 40 and 80 J/mL UVR-RBCs.

DISCUSSION

UVR-RBCs administered to guinea pigs increased markers of intravascular and extravascular hemolysis in a UV dose-dependent manner. This model may allow for the discrimination of RBC injury during testing of extensively processed RBCs intended for transfusion.

Mechanisms of persistent hemolysis-induced middle kidney injury in grass carp (Ctenopharyngodon idella)

Infection-induced hemolysis results in intravascular hemolysis, which releases hemoglobin (Hb) into the tissues. Free Hb exhibits cytotoxic, oxidative, and pro-inflammatory effects, leading to systemic inflammation, vascular constriction dysfunction, thrombosis, and proliferative vascular lesions. Currently, the impact of intravascular hemolysis on the middle kidney in fish is unclear. Here, the injection of phenylhydrazine (PHZ) was used to establish a persistent hemolysis model in grass carp. The determination results revealed that the PHZ-induced hemolysis caused conspicuous tissue damage in the kidneys of grass carp, increased the levels of Cr in the serum and the expression indicators of kidney injury-related genes in the middle kidney. Prussian blue staining indicated that PHZ-induced hemolysis significantly increased the deposition of iron ions in the kidneys of grass carp, and activated the expression levels of iron metabolism-related genes. The results of oxidative damage-related experiments indicate that under PHZ treatment, the activity of middle kidney cells decreases, and the production of oxidative damage markers malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) increases, simultaneously inhibiting the activity of antioxidant enzymes and upregulating the transcription levels of antioxidant enzyme-related genes. Additionally, the analysis of inflammatory factors revealed a significant upregulation of genes associated with inflammation induced by PHZ-induced hemolysis. The transcriptome analysis was performed to further explore the molecular regulatory effects of hemolysis on tissues, the analysis revealed the treatment of PHZ activated various of programmed cell death (PCD) pathways, including ferroptosis, apoptosis, and autophagy. In summary, this study found that sustained hemolysis in fish results in Hb and iron ion deposition in middle kidney, promoting oxidative damage, ultimately inducing various forms of PCD.

Cardiac Surgery-Associated Acute Kidney Injury

AKI is a common and serious complication of cardiac surgery that has a significant impact on patient morbidity and mortality. The Kidney Disease Improving Global Outcomes definition of AKI is widely used to classify and identify AKI associated with cardiac surgery (cardiac surgery-associated AKI [CSA-AKI]) on the basis of changes in serum creatinine and/or urine output. There are various preoperative, intraoperative, and postoperative risk factors for the development of CSA-AKI which should be recognized and addressed as early as possible to expedite its diagnosis, reduce its occurrence, and prevent or ameliorate its devastating complications. Crucial issues are the inaccuracy of serum creatinine as a surrogate parameter of kidney function in the perioperative setting of cardiothoracic surgery and the necessity to discover more representative markers of the pathophysiology of AKI. However, except for the tissue inhibitor of metalloproteinase-2 and insulin-like growth factor binding protein 7 ratio, other diagnostic biomarkers with an acceptable sensitivity and specificity are still lacking. This article provides a comprehensive review of various aspects of CSA-AKI, including pathogenesis, risk factors, diagnosis, biomarkers, classification, prevention, and treatment management.

What is the role of complement in bystander hemolysis? Old concept, new insights

INTRODUCTION

Bystander hemolysis occurs when antigen-negative red blood cells (RBCs) are lysed by the complement system. Many clinical entities including passenger lymphocyte syndrome, hyperhemolysis following blood transfusion, and paroxysmal nocturnal hemoglobinuria are complicated by bystander hemolysis.

AREAS COVERED

The review provides data about the role of the complement system in the pathogenesis of bystander hemolysis. Moreover, future perspectives on the understanding and management of this syndrome are described.

EXPERT OPINION

Complement system can be activated via classical, alternative, and lectin pathways. Classical pathway activation is mediated by antigen-antibody (autoantibodies and alloantibodies against autologous RBCs, infectious agents) complexes. Alternative pathway initiation is triggered by heme, RBC microvesicles, and endothelial injury that is a result of intravascular hemolysis. Thus, C5b is formed, binds with C6-C9 compomers, and MAC (C5b-9) is formulated in bystander RBCs membranes, leading to cell lysis. Intravascular hemolysis, results in activation of the alternative pathway, establishing a vicious cycle between complement activation and bystander hemolysis. C5 inhibitors have been used effectively in patients with hyperhemolysis syndrome and other entities characterized by bystander hemolysis.

Cell-Free Hemoglobin in the Pathophysiology of Trauma: A Scoping Review

OBJECTIVES

Cell-free hemoglobin (CFH) is a potent mediator of endothelial dysfunction, organ injury, coagulopathy, and immunomodulation in hemolysis. These mechanisms have been demonstrated in patients with sepsis, hemoglobinopathies, and those receiving transfusions. However, less is known about the role of CFH in the pathophysiology of trauma, despite the release of equivalent levels of free hemoglobin.

DATA SOURCES

Ovid MEDLINE, Embase, Web of Science Core Collection, and BIOSIS Previews were searched up to January 21, 2023, using key terms related to free hemoglobin and trauma.

DATA EXTRACTION

Two independent reviewers selected studies focused on hemolysis in trauma patients, hemoglobin breakdown products, hemoglobin-mediated injury in trauma, transfusion, sepsis, or therapeutics.

DATA SYNTHESIS

Data from the selected studies and their references were synthesized into a narrative review.

CONCLUSIONS

Free hemoglobin likely plays a role in endothelial dysfunction, organ injury, coagulopathy, and immune dysfunction in polytrauma. This is a compelling area of investigation as multiple existing therapeutics effectively block these pathways.

Acute Kidney Injury after Cardiac Surgery: Prediction, Prevention, and Management

Acute kidney injury (AKI) is a common complication in cardiac surgery patients, with a reported incidence of 20 to 30%. The development of AKI is associated with worse short- and long-term mortality, and longer hospital length of stay. The pathogenesis of cardiac surgery-associated AKI is poorly understood but likely involves an interplay between preoperative comorbidities and perioperative stressors. AKI is commonly diagnosed by using increases in serum creatinine or decreased urine output and staged using a standardized definition such as the Kidney Disease Improving Global Outcomes classification. Novel biomarkers under investigation may provide earlier detection and better prediction of AKI, enabling mitigating therapies early in the perioperative period. Recent clinical trials of cardiac surgery patients have demonstrated the benefit of goal-directed oxygen delivery, avoidance of hyperthermic perfusion and specific fluid and medication strategies. This review article highlights both advances and limitations regarding the prevention, prediction, and treatment of cardiac surgery-associated AKI.

Comparing two extracellular additives to facilitate extended storage of red blood cells in a supercooled state

Background: Adenosine triphosphate (ATP) levels guide many aspects of the red blood cell (RBC) hypothermic storage lesions. As a result, efforts to improve the quality of hypothermic-stored red cell concentrates (RCCs) have largely centered around designing storage solutions to promote ATP retention. Considering reduced temperatures alone would diminish metabolism, and thereby enhance ATP retention, we evaluated: (a) whether the quality of stored blood is improved at -4°C relative to conventional 4°C storage, and (b) whether the addition of trehalose and PEG400 can enhance these improvements. Study Design and Methods: Ten CPD/SAGM leukoreduced RCCs were pooled, split, and resuspended in a next-generation storage solution (i.e., PAG3M) supplemented with 0-165 mM of trehalose or 0-165 mM of PEG400. In a separate subset of samples, mannitol was removed at equimolar concentrations to achieve a fixed osmolarity between the additive and non-additive groups. All samples were stored at both 4°C and -4°C under a layer of paraffin oil to prevent ice formation. Results: PEG400 reduced hemolysis and increased deformability in -4°C-stored samples when used at a concentration of 110 mM. Reduced temperatures did indeed enhance ATP retention; however, in the absence of an additive, the characteristic storage-dependent decline in deformability and increase in hemolysis was exacerbated. The addition of trehalose enhanced this decline in deformability and hemolysis at -4°C; although, this was marginally alleviated by the osmolarity-adjustments. In contrast, outcomes with PEG400 were worsened by these osmolarity adjustments, but at no concentration, in the absence of these adjustments, was damage greater than the control. Discussion: Supercooled temperatures can allow for improved ATP retention; however, this does not translate into improved storage success. Additional work is necessary to further elucidate the mechanism of injury that progresses at these temperatures such that storage solutions can be designed which allow RBCs to benefit from this diminished rate of metabolic deterioration. The present study suggests that PEG400 could be an ideal component in these solutions.

Potential of cell-free hemoglobin and haptoglobin as prognostic markers in patients with ARDS and treatment with veno-venous ECMO

BACKGROUND

Hemolysis is associated with increased mortality in patients with sepsis, ARDS, or therapy with extracorporeal membrane oxygenation (ECMO). To quantify a critical threshold of hemolysis in patients with ARDS and treatment with veno-venous ECMO, we aimed to identify cutoff values for cell-free hemoglobin (CFH) and haptoglobin (Hp) plasma concentrations associated with a significant increase in ICU mortality.

METHODS

Patients with ARDS admitted to a tertiary ARDS referral center between 01/2007 and 12/2018 and treatment with veno-venous ECMO were included. Cutoff values for mean CFH (mCFH) and mean Hp (mHp) plasma concentrations dividing the cohort into groups with significantly different ICU mortalities were calculated and patient characteristics were compared. A multiple logistic regression model with stepwise backward variable selection was included. In addition, cutoff values for vulnerable relative timespans for the respective CFH and Hp concentrations were calculated.

RESULTS

A quantitative cutoff value of 11 mg/dl for mCFH separated the cohort (n = 442) regarding ICU mortality (mCFH ≤ 11 mg/dl: 38%, [95%-CI: 32.22-43.93] (n = 277) vs. mCFH > 11 mg/dl: 70%, [61.99-76.47] (n = 165), p < 0.001). Analogously, a mHp cutoff value ≤ 0.39 g/l was associated with a significant increase in ICU mortality (mHp ≤ 0.39 g/l: 68.7%, [60.91-75.61] (n = 163) vs. mHp > 0.39 g/l: 38.7%, [33.01-44.72] (n = 279), p < 0.001). The independent association of ICU mortality with CFH and Hp cutoff values was confirmed by logistic regression adjusting for confounders (CFH Grouping: OR 3.77, [2.51-5.72], p < 0.001; Hp Grouping: OR 0.29, [0.19-0.43], p < 0.001). A significant increase in ICU mortality was observed when CFH plasma concentration exceeded the limit of 11 mg/dl on 13.3% of therapy days (≤ 13.3% of days with CFH > 11 mg/dl: 33%; [26.81-40.54] (n = 192) vs. > 13.3% of days with CFH > 11 mg/dl: 62%; [56.05-68.36] (n = 250), p < 0.001). Analogously, a mortality increase was detected when Hp plasma concentration remained ≤ 0.39 g/l for > 18.2% of therapy days (≤ 18.2% days with Hp ≤ 0.39 g/l: 27%; [19.80-35.14] (n = 138) vs. > 18.2% days with Hp ≤ 0.39 g/l: 60%; [54.43-65.70] (n = 304), p < 0.001).

CONCLUSIONS

Moderate hemolysis with mCFH-levels as low as 11 mg/dl impacts mortality in patients with ARDS and therapy with veno-venous ECMO. Furthermore, a cumulative dose effect should be considered indicated by the relative therapy days with CFH-concentrations > 11 mg/dl. In addition, also Hp plasma concentrations need consideration when the injurious effect of elevated CFH is evaluated.

Different-sized extracellular vesicles derived from stored red blood cells package diverse cargoes and cause distinct cellular effects

BACKGROUND

The formation of extracellular vesicles (EVs) occurs during cold storage of RBCs. Transfusion of EVs may contribute to adverse responses in recipients receiving RBCs. However, EVs are poorly characterized with limited data on whether distinct vesicles are formed, their composition, and potential biological effects.

STUDY DESIGN AND METHODS

Stored RBC-derived EVs were purified using protocols that separate larger microvesicle-like EVs (LEVs) from smaller exosome-like vesicles (SEVs). Vesicles were analyzed by electron microscopy, content of hemoglobin, heme, and proteins (by mass spectrometry), and the potential to mediate lipid peroxidation and endothelial cell permeability in vitro.

RESULTS

SEVs were characterized by having an electron-dense double membrane whereas LEVs had more uniform electron density across the particles. No differences in hemoglobin nor heme levels per particle were observed, however, due to smaller volumes, SEVs had higher concentrations of oxyHb and heme. Both particles contained antioxidant proteins peroxiredoxin-2 and copper/zinc superoxide dismutase, these were present in higher molecular weight fractions in SEVs suggesting either oxidized proteins are preferentially packaged into smaller vesicles and/or that the environment associated with SEVs is more pro-oxidative. Furthermore, total glutathione (GSH + GSSG) levels were lower in SEVs. Both EVs mediated oxidation of liposomes that were prevented by hemopexin, identifying heme as the pro-oxidant effector. Addition of SEVs, but not LEVs, induced endothelial permeability in a process also prevented by hemopexin.

CONCLUSION

These data show that distinct EVs are formed during cold storage of RBCs with smaller particles being more likely to mediate pro-oxidant and inflammatory effects associated with heme.

Oxidized hemoglobin triggers polyreactivity and autoreactivity of human IgG via transfer of heme

Intravascular hemolysis occurs in diverse pathological conditions. Extracellular hemoglobin and heme have strong pro-oxidative and pro-inflammatory potentials that can contribute to the pathology of hemolytic diseases. However, many of the effects of extracellular hemoglobin and heme in hemolytic diseases are still not well understood. Here we demonstrate that oxidized hemoglobin (methemoglobin) can modify the antigen-binding characteristics of human immunoglobulins. Thus, incubation of polyclonal or some monoclonal human IgG in the presence of methemoglobin results in an appearance of binding reactivities towards distinct unrelated self-proteins, including the protein constituent of hemoglobin i.e., globin. We demonstrate that a transfer of heme from methemoglobin to IgG is indispensable for this acquisition of antibody polyreactivity. Our data also show that only oxidized form of hemoglobin have the capacity to induce polyreactivity of antibodies. Site-directed mutagenesis of a heme-sensitive human monoclonal IgG1 reveals details about the mechanism of methemoglobin-induced antigen-binding polyreactivity. Further here we assess the kinetics and thermodynamics of interaction of a heme-induced polyreactive human antibody with hemoglobin and myoglobin. Taken together presented data contribute to a better understanding of the functions of extracellular hemoglobin in the context of hemolytic diseases.

Transpulmonary generation of cell-free hemoglobin contributes to vascular dysfunction in pulmonary arterial hypertension via dysregulated clearance mechanisms

Circulating cell-free hemoglobin (CFH) is elevated in pulmonary arterial hypertension (PAH) and associated with poor outcomes but the mechanisms are unknown. We hypothesized that CFH is generated from the pulmonary circulation and inadequately cleared in PAH. Transpulmonary CFH (difference between wedge and pulmonary artery positions) and lung hemoglobin α were analyzed in patients with PAH and healthy controls. Haptoglobin genotype and plasma hemoglobin processing proteins were analyzed in patients with PAH, unaffected bone morphogenetic protein receptor type II mutation carriers (UMCs), and control subjects. Transpulmonary CFH was increased in patients with PAH (p = 0.04) and correlated with pulmonary vascular resistanc (PVR) (r s = 0.75, p = 0.02) and mean pulmonary arterial pressure (mPAP) (r s = 0.78, p = 0.02). Pulmonary vascular hemoglobin α protein was increased in patients with PAH (p = 0.006), especially in occluded vessels (p = 0.04). Haptoglobin genotype did not differ between groups. Plasma haptoglobin was higher in UMCs compared with both control subjects (p = 0.03) and patients with HPAH (p < 0.0001); patients with IPAH had higher circulating haptoglobin levels than patients with HPAH (p = 0.006). Notably, circulating CFH to haptoglobin ratio was elevated in patients with HPAH compared to control subjects (p = 0.02) and UMCs (p = 0.006). Moreover, in patients with PAH, CFH: haptoglobin correlated with PVR (r s = 0.37, p = 0.0004) and mPAP (r s = 0.25, p = 0.02). Broad alterations in other plasma hemoglobin processing proteins (hemopexin, heme oxygenase-1, and sCD163) were observed. In conclusion, pulmonary vascular CFH is associated with increased PVR and mPAP in PAH and dysregulated CFH clearance may contribute to PAH pathology. Further study is needed to determine whether targeting CFH is a viable therapeutic for pulmonary vascular dysfunction in PAH.

TRAUMA INDUCES INTRAVASCULAR HEMOLYSIS, EXACERBATED BY RED BLOOD CELL TRANSFUSION AND ASSOCIATED WITH DISRUPTED ARGININE-NITRIC OXIDE METABOLISM

ABSTRACT

Background: Severe injury can provoke systemic processes that lead to organ dysfunction, and hemolysis of both native and transfused red blood cells (RBCs) may contribute. Hemolysis can release erythrocyte proteins, such as hemoglobin and arginase-1, the latter with the potential to disrupt arginine metabolism and limit physiologic NO production. We aimed to quantify hemolysis and arginine metabolism in trauma patients and measure association with injury severity, transfusions, and outcomes. Methods: Blood was collected from injured patients at a level I trauma center enrolled in the COMBAT (Control of Major Bleeding After Trauma) trial. Proteomics and metabolomics were performed on plasma fractions through liquid chromatography coupled with mass spectrometry. Abundances of erythrocyte proteins comprising a hemolytic profile as well as haptoglobin, l -arginine, ornithine, and l -citrulline (NO surrogate marker) were analyzed at different timepoints and correlated with transfusions and adverse outcomes. Results: More critically injured patients, nonsurvivors, and those with longer ventilator requirement had higher levels of hemolysis markers with reduced l -arginine and l -citrulline. In logistic regression, elevated hemolysis markers, reduced l -arginine, and reduced l -citrulline were significantly associated with these adverse outcomes. An increased number of blood transfusions were significantly associated with elevated hemolysis markers and reduced l -arginine and l -citrulline independently of New Injury Severity Score and arterial base excess. Conclusions: Severe injury induces intravascular hemolysis, which may mediate postinjury organ dysfunction. In addition to native RBCs, transfused RBCs can lyse and may exacerbate trauma-induced hemolysis. Arginase-1 released from RBCs may contribute to the depletion of l -arginine and the subsequent reduction in the NO necessary to maintain organ perfusion.

Determination of free heme in stored red blood cells with an apo-horseradish peroxidase-based assay

Transfusion effectiveness of red blood cells (RBCs) has been associated with duration of the storage period. Storage-dependent RBC alterations lead to hemolysis and release of toxic free heme, but the increase of free heme levels over time is largely unknown. In the current study, an apo-horseradish peroxidase (apoHRP)-based assay was applied to measure levels of free heme at regular intervals or periodically in supernatants of RBCs until a maximum storage period of 42 days. Free heme levels increased with linear time-dependent kinetics up to day 21 and accelerated disproportionally after day 28 until day 42, as determined with the apoHRP assay. Individual time courses of free heme in different RBC units exhibited high variability. Notably, levels of free hemoglobin, an established indicator of RBC damage, and those of total heme increased with continuous time-dependent linear kinetics over the entire 42 day storage period, respectively. Supernatants from RBC units with high levels of free heme led to inflammatory activation of human neutrophils. In conclusion, determining free heme in stored RBCs with the applied apoHRP assay may become feasible for testing of RBC storage quality in clinical transfusion medicine.

Cell-Free Hemoglobin in Acute Kidney Injury after Lung Transplantation and Experimental Renal Ischemia/Reperfusion

Cell-free hemoglobin (CFH), a pro-oxidant and cytotoxic compound that is released in hemolysis, has been associated with nephrotoxicity. Lung transplantation (LuTx) is a clinical condition with a high incidence of acute kidney injury (AKI). In this study, we investigated the plasma levels of CFH and haptoglobin, a CFH-binding serum protein, in prospectively enrolled LuTx patients (n = 20) with and without AKI. LuTx patients with postoperative AKI had higher CFH plasma levels at the end of surgery compared with no-AKI patients, and CFH correlated with serum creatinine at 48 h. Moreover, CFH levels inversely correlated with haptoglobin levels, which were significantly reduced at the end of surgery in LuTx patients with AKI. Because multiple other factors can contribute to AKI development in the complex clinical setting of LuTx, we next investigated the role of exogenous CFH administration in a mouse model of mild bilateral renal ischemia reperfusion injury (IRI). Exogenous administration of CFH after reperfusion caused overt AKI with creatinine increase, tubular injury, and enhanced markers of renal inflammation compared with vehicle-treated animals. In conclusion, CFH is a possible factor contributing to postoperative AKI after LuTx and promotes AKI in an experimental model of mild transient renal ischemia. Targeting CFH might be a therapeutic option to prevent AKI after LuTx.

Hemolysis, free hemoglobin toxicity, and scavenger protein therapeutics

During hemolysis, erythrophagocytes dispose damaged red blood cells. This prevents the extracellular release of hemoglobin, detoxifies heme, and recycles iron in a linked metabolic pathway. Complementary to this process, haptoglobin and hemopexin scavenge and shuttle the red blood cell toxins hemoglobin and heme to cellular clearance. Pathological hemolysis outpaces macrophage capacity and scavenger synthesis across a diversity of diseases. This imbalance leads to hemoglobin-driven disease progression. To meet a void in treatment options, scavenger protein-based therapeutics are in clinical development.

Peroxiredoxin-2 recycling is slower in denser and pediatric sickle cell red cells

Peroxiredoxin-2 (Prx-2) is a critical antioxidant protein in red blood cells (RBC). Prx-2 is oxidized to a disulfide covalently-bound dimer by H₂ O₂ , and then reduced back by the NADPH-dependent thioredoxin-thioredoxin reductase system. The reduction of oxidized Prx-2 is relatively slow in RBCs. Since Prx-2 is highly abundant, Prx-2s' peroxidase catalytic cycle is not considered to be limiting under normal conditions. However, whether Prx-2 recycling becomes limiting when RBCs are exposed to stress is not known. Using three different model systems characterized by increased oxidative damage to RBCs spanning the physiologic (endogenous RBCs of different ages), therapeutic (cold-stored RBCs in blood banks) and pathologic (RBCs from sickle cell disease (SCD) patients and humanized SCD mice) spectrum, basal levels of Prx-2 oxidation and Prx-2 recycling kinetics after addition of H₂ O₂ were determined. The reduction of oxidized Prx-2 was significantly slower in older versuin older versus younger RBCs, in RBCs stored for 4-5 weeks compared to 1 week, and in RBC from pediatric SCD patients compared to RBCs from control non-SCD patients. Similarly, the rate of Prx-2 recycling was slower in humanized SCD mice compared to WT mice. Treatment of RBC with carbon monoxide (CO) to limit heme-peroxidase activity had no effect on Prx-2 recycling kinetics. Treatment with glucose attenuated slowed Prx-2 recycling in older RBCs and SCD RBCs, but not stored RBCs. In conclusion, the reduction of oxidized Prx-2 can be further slowed in RBCs, which may limit the protection afforded by this antioxidant protein in settings associated with erythrocyte stress.

Anti-inflammatory cytokines in sickle cell disease

Sickle cell disease (SCD) is a well-studied monogenetic disease with an established chronic inflammatory component. The paradigm shift towards inflammation has made the pathophysiology of SCD even more complex. Studies have shown that an imbalance between the pro-inflammatory and anti-inflammatory cytokines in SCD exists; however, the reports are skewed toward the pro-inflammatory mediators. We enumerate recent in vitro and in vivo studies on anti-inflammatory cytokines in SCD patients, and discuss the biology of anti-inflammatory cytokines including the already reported IL-2, TGF-β, and IL-10 as well as the recently discovered IL-27, IL-35 and IL-37. This review will improve the understanding of the pathophysiology of SCD and aid in the search of new therapeutic options for patients with SCD.

The role of cell-free hemoglobin and haptoglobin in acute kidney injury in critically ill adults with ARDS and therapy with VV ECMO

Background

Increased plasma concentrations of circulating cell-free hemoglobin (CFH) are supposed to contribute to the multifactorial etiology of acute kidney injury (AKI) in critically ill patients while the CFH-scavenger haptoglobin might play a protective role. We evaluated the association of CFH and haptoglobin with AKI in patients with an acute respiratory distress syndrome (ARDS) requiring therapy with VV ECMO.

Methods

Patients with CFH and haptoglobin measurements before initiation of ECMO therapy were identified from a cohort of 1044 ARDS patients and grouped into three CFH concentration groups using a risk stratification. The primary objective was to assess the association of CFH and haptoglobin with KDIGO stage 3 AKI. Further objectives included the identification of a target haptoglobin concentration to protect from CFH-associated AKI.

Measurements and main results

Two hundred seventy-three patients fulfilled the inclusion criteria. Of those, 154 patients (56.4%) had AKI at ECMO initiation. The incidence of AKI increased stepwise with increasing concentrations of CFH reaching a plateau at 15 mg/dl. Compared to patients with low [< 5 mg/dl] CFH concentrations, patients with moderate [5–14 mg/dl] and high [≥ 15 mg/dl] CFH concentrations had a three- and five-fold increased risk for AKI (adjusted odds ratio [OR] moderate vs. low, 2.69 [95% CI, 1.25–5.95], P = 0.012; and OR high vs. low, 5.47 [2.00–15.9], P = 0.001). Among patients with increased CFH concentrations, haptoglobin plasma levels were lower in patients with AKI compared to patients without AKI. A haptoglobin concentration greater than 2.7 g/l in the moderate and 2.4 g/l in the high CFH group was identified as clinical cutoff value to protect from CFH-associated AKI (sensitivity 89.5% [95% CI, 83–96] and 90.2% [80–97], respectively).

Conclusions

In critically ill patients with ARDS requiring therapy with VV ECMO, an increased plasma concentration of CFH was identified as independent risk factor for AKI. Among patients with increased CFH concentrations, higher plasma haptoglobin concentrations might protect from CFH-associated AKI and should be subject of future research.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-03894-5.

The Oxidative Injury of Extracellular Hemoglobin Is Associated With Reactive Oxygen Species Generation of Grass Carp (Ctenopharyngodon idella)

Intravascular hemolysis is a fundamental feature of hemorrhagic venereal infection or tissue and releases the endogenous damage-associated molecular pattern hemoglobin (Hb) into the plasma or tissues, which results in systemic inflammation, vasomotor dysfunction, thrombophilia, and proliferative vasculopathy. However, how the cytotoxic Hb affects the tissues of grass carp remains unclear. Here, we established a hemolysis model in grass carp by injecting phenylhydrazine (PHZ). The data revealed that the PHZ-induced hemolysis increased the content of Hb and activated the antioxidant system in plasma. The histopathology analysis data showed that the PHZ-induced hemolysis increased the accumulation of Hb and iron both in the head and middle kidney. The results of quantitative real-time PCR (qRT-PCR) detection suggested that the hemolysis upregulated the expressions of iron metabolism-related genes. In addition, the immunofluorescence and immunohistochemistry data revealed that the hemolysis caused an obvious deposition of collagen fiber, malondialdehyde (MDA), and 4-hydroxynonenal (4-HNE) accumulation and increased the content of oxidative-related enzymes such as β-galactosidase (β-GAL), lipid peroxide (LPO), and MDA in both the head and middle kidney. Furthermore, the PHZ-induced hemolysis significantly increased the production of reactive oxygen species (ROS), which resulted in apoptosis and modulated the expressions of cytokine-related genes. Taken together, excess of Hb released from hemolysis caused tissue oxidative damage, which may be associated with ROS and inflammation generation.

Effect of microaggregate filter passage on feline whole blood stored for 35 days

OBJECTIVES

The aim of this study was to compare the characteristics of fresh and stored feline red blood cells (RBCs) after passage through an 18 μm microaggregate filter.

METHODS

Nine cats were recruited for a single blood donation using an open collection system. A simulated transfusion using a syringe driver and microaggregate filter was performed over 2 h with half the blood on the day of donation and the other half after 35 days of storage. Differences in haematological parameters, haemolysis percentage and osmotic fragility (OF) were compared on the day of donation pre-filter passage (D0-) vs day of donation post-filter (D0+) or day 35 storage pre-filter (D35-) and post-filter (D35+). Blood was cultured at D0+ and D35+.

RESULTS

There were no statistically significant differences in the D0- vs D0+ comparisons. There were statistically significant (P <0.05) increases in haemolysis percentage, red cell distribution width (RDW) percentage and mean OF, and decreases in packed cell volume (PCV), RBC count, haemoglobin and haematocrit for D0- vs D35-. The same was found for D0- vs D35+ with the addition of a significant increase in mean cell haemoglobin (MCH). For D35- vs D35+ only MCH significantly increased. At day 35, 6/9 units had haemolysis percentages that exceeded 1%. This increased to 8/9 of stored units post-filter passage. All blood units cultured negative.

CONCLUSIONS AND RELEVANCE

Fresh RBCs exhibited no in vitro evidence of injury following passage through an 18 μm microaggregate filter. Increased MCH was observed in the stored blood and may represent haemolysis induced by the filter. All other changes can be explained by storage lesion rather than filter passage. The findings highlight the importance of blood banking quality controls and the need for further research to assess the effects of transfusion technique, specifically filter passage, on storage lesion-affected feline blood.

Age of Red Cells for Transfusion and Outcomes in Patients with ARDS

Packed red blood cells (PRBCs), stored for prolonged intervals, might contribute to adverse clinical outcomes in critically ill patients. In this study, short-term outcome after transfusion of PRBCs of two storage duration periods was analyzed in patients with Acute Respiratory Distress Syndrome (ARDS). Patients who received transfusions of PRBCs were identified from a cohort of 1044 ARDS patients. Patients were grouped according to the mean storage age of all transfused units. Patients transfused with PRBCs of a mean storage age ≤ 28 days were compared to patients transfused with PRBCs of a mean storage age > 28 days. The primary endpoint was 28-day mortality. Secondary endpoints included failure-free days composites. Two hundred and eighty-three patients were eligible for analysis. Patients in the short-term storage group had similar baseline characteristics and received a similar amount of PRBC units compared with patients in the long-term storage group (five units (IQR, 3-10) vs. four units (2-8), p = 0.14). The mean storage age in the short-term storage group was 20 (±5.4) days compared with 32 (±3.1) days in the long-term storage group (mean difference 12 days (95%-CI, 11-13)). There was no difference in 28-day mortality between the short-term storage group compared with the long-term storage group (hazard ratio, 1.36 (95%-CI, 0.84-2.21), p = 0.21). While there were no differences in ventilator-free, sedation-free, and vasopressor-free days composites, patients in the long-term storage group compared with patients in the short-term storage group had a 75% lower chance for successful weaning from renal replacement therapy (RRT) within 28 days after ARDS onset (subdistribution hazard ratio, 0.24 (95%-CI, 0.1-0.55), p < 0.001). Further analysis indicated that even a single PRBC unit stored for more than 28 days decreased the chance for successful weaning from RRT. Prolonged storage of PRBCs was not associated with a higher mortality in adults with ARDS. However, transfusion of long-term stored PRBCs was associated with prolonged dependence of RRT in critically ill patients with an ARDS.

ZOOMICS: Comparative Metabolomics of Red Blood Cells From Guinea Pigs, Humans, and Non-human Primates During Refrigerated Storage for Up to 42 Days

Unlike other rodents, guinea pigs (Cavia porcellus) have evolutionarily lost their capacity to synthesize vitamin C (ascorbate) de novo and, like several non-human primates and humans, rely on dietary intake and glutathione-dependent recycling to cope with oxidant stress. This is particularly relevant in red blood cell physiology, and especially when modeling blood storage, which exacerbates erythrocyte oxidant stress. Herein we provide a comprehensive metabolomics analysis of fresh and stored guinea pig red blood cell concentrates (n = 20), with weekly sampling from storage day 0 through 42. Results were compared to previously published ZOOMICS studies on red blood cells from three additional species with genetic loss of L-gulonolactone oxidase function, including humans (n = 21), olive baboons (n = 20), and rhesus macaques (n = 20). While metabolic trends were comparable across all species, guinea pig red blood cells demonstrated accelerated alterations of the metabolic markers of the storage lesion that are consistent with oxidative stress. Compared to the other species, guinea pig red blood cells showed aberrant glycolysis, pentose phosphate pathway end product metabolites, purine breakdown products, methylation, glutaminolysis, and markers of membrane lipid remodeling. Consistently, guinea pig red blood cells demonstrated higher end storage hemolysis, and scanning electron microscopy confirmed a higher degree of morphological alterations of their red blood cells, as compared to the other species. Despite a genetic inability to produce ascorbate that is common to the species evaluated, guinea pig red blood cells demonstrate accelerated oxidant stress under standard storage conditions. These data may offer relevant insights into the basal and cold storage metabolism of red blood cells from species that cannot synthesize endogenous ascorbate.

Calorimetric Characterisation of the Binding Reaction Between Human Ferric Haemoglobins and Haptoglobin to Develop a Drug for Removal of Cell-Free Haemoglobin

High levels of cell-free haemoglobin (Hb) may occur in plasma as a consequence of e.g., pathological haemolysis or blood transfusion. These Hb molecules can be removed from blood circulation by forming a complex with the acute-phase protein haptoglobin (Hp) and thereby can also the intrinsic toxicity of free Hb be limited. In this study it is shown that ferric HbA, HbF, HbE and HbS, respectively, all bind firmly to Hp at 25 °C. By using isothermal titration calorimetry (ITC), it is demonstrated that ferric HbF has higher affinity to Hp (Ka = 2.79 ± 0.29 ×10⁹ M^-1) compared with HbA and HbS (1.91 ± 0.24 ×10⁹ M^-1) and 1.41 ± 0.34 ×10⁹ M^-1 for HbA and HbS, respectively. In addition, the affinity constant for HbE is slightly lower than the other haemoglobins (0.47 ± 0.40 ×10⁹ M^-1). Since Hp shows a general and high affinity to all Hb variants tested, it can be concluded that Hp may be useful as a therapeutic agent for several different haemolytic conditions by intravenous injection.

Promises and challenges of personalized medicine to guide ARDS therapy

Identifying new effective treatments for the acute respiratory distress syndrome (ARDS), including COVID-19 ARDS, remains a challenge. The field of ARDS investigation is moving increasingly toward innovative approaches such as the personalization of therapy to biological and clinical sub-phenotypes. Additionally, there is growing recognition of the importance of the global context to identify effective ARDS treatments. This review highlights emerging opportunities and continued challenges for personalizing therapy for ARDS, from identifying treatable traits to innovative clinical trial design and recognition of patient-level factors as the field of critical care investigation moves forward into the twenty-first century.

Kinetic mechanisms for O2 binding to myoglobins and hemoglobins

Antonini and Brunori's 1971 book "Hemoglobin and Myoglobin in Their Reactions with Ligands" was a truly remarkable publication that summarized almost 100 years of research on O₂ binding to these globins. Over the ensuing 50 years, ultra-fast laser photolysis techniques, high-resolution and time resolved X-ray crystallography, molecular dynamics simulations, and libraries of recombinant myoglobin (Mb) and hemoglobin (Hb) variants have provided structural interpretations of O₂ binding to these proteins. The resultant mechanisms provide quantitative descriptions of the stereochemical factors that govern overall affinity, including proximal and distal steric restrictions that affect iron reactivity and favorable positive electrostatic interactions that preferentially stabilize bound O₂. The pathway for O₂ uptake and release by Mb and subunits of Hb has been mapped by screening libraries of site-directed mutants in laser photolysis experiments. O₂ enters mammalian Mb and the α and β subunits of human HbA through a channel created by upward and outward rotation of the distal His at the E7 helical position, is non-covalently captured in the interior of the distal cavity, and then internally forms a bond with the heme Fe(II) atom. O₂ dissociation is governed by disruption of hydrogen bonding interactions with His (E7), breakage of the Fe(II)-O₂ bond, and then competition between rebinding and escape through the E7-gate. The structural features that govern the rates of both the individual steps and overall reactions have been determined and provide the framework for: (1) defining the physiological functions of specific globins and their evolution; (2) understanding the clinical features of hemoglobinopathies; and (3) designing safer and more efficient acellular hemoglobin-based oxygen carriers (HBOCs) for transfusion therapy, organ preservation, and other commercially relevant O₂ transport and storage processes.

Modular Platform for the Development of Recombinant Hemoglobin Scavenger Biotherapeutics

Cell-free hemoglobin (Hb) is a driver of disease progression in conditions with intravascular or localized hemolysis. Genetic and acquired anemias or emergency medical conditions such as aneurysmal subarachnoid hemorrhage involve tissue Hb exposure. Haptoglobin (Hp) captures Hb in an irreversible protein complex and prevents its pathophysiological contributions to vascular nitric oxide depletion and tissue oxidation. Preclinical proof-of-concept studies suggest that human plasma-derived Hp is a promising therapeutic candidate for several Hb-driven diseases. Optimizing the efficacy and safety of Hb-targeting biotherapeutics may require structural and functional modifications for specific indications. Improved Hp variants could be designed to achieve the desired tissue distribution, metabolism, and elimination to target hemolytic disease states effectively. However, it is critical to ensure that these modifications maintain the function of Hp. Using transient mammalian gene expression of Hp combined with co-transfection of the pro-haptoglobin processing protease C1r-LP, we established a platform for generating recombinant Hp-variants. We designed an Hpβ-scaffold, which was expressed in this system at high levels as a monomeric unit (mini-Hp) while maintaining the key protective functions of Hp. We then used this Hpβ-scaffold as the basis to develop an initial proof-of-concept Hp fusion protein using human serum albumin as the fusion partner. Next, a hemopexin-Hp fusion protein with bispecific heme and Hb detoxification capacity was generated. Further, we developed a Hb scavenger devoid of CD163 scavenger receptor binding. The functions of these proteins were then characterized for Hb and heme-binding, binding of the Hp-Hb complexes with the clearance receptor CD163, antioxidant properties, and vascular nitric oxide sparing capacity. Our platform is designed to support the generation of innovative Hb scavenger biotherapeutics with novel modes of action and potentially improved formulation characteristics, function, and pharmacokinetics.

Blood Transfusion and Acute Kidney Injury After Total Aortic Arch Replacement for Acute Stanford Type A Aortic Dissection

AIM

To evaluate the effect of packed red blood cells (pRBCs), fresh frozen plasma (FFP), and platelet concentrate (PC) transfusions on acute kidney injury (AKI) in patients with acute Stanford type A aortic dissection (ATAAD) with total arch replacement (TAR).

METHOD

From December 2015 to October 2017, 421 consecutive patients with ATAAD undergoing TAR were included in the study. The clinical data of the patients and the amount of pRBCs, FFP, and PC were collected. Acute kidney injury was defined using the Kidney Disease: Improving Global Outcomes (KDIGO) criteria. Logistic regression was used to identify whether pRBCs, FFP, and platelet transfusions were risk factors for KDIGO AKI, stage 3 AKI, and AKI requiring renal replacement therapy (RRT).

RESULTS

The mean ± standard deviation age of the patients was 47.67±10.82 years; 77.7% were men; and the median time from aortic dissection onset to operation was 1 day (range, 0-2 days). The median transfusion amount was 8 units (range, 4-14 units) for pRBCs, 400 mL (range, 0-800 mL) for FFP, and no units (range, 0-2 units) for PC. Forty-one (41; 9.7%) patients did not receive any blood products. The rates of pRBC, PC, and FFP transfusions were 86.9%, 49.2%, and 72.9%, respectively. The incidence of AKI was 54.2%. Considering AKI as the endpoint, multivariate logistic regression showed that pRBCs (odds ratio [OR], 1.11; p<0.001) and PC transfusions (OR, 1.28; p=0.007) were independent risk factors. Considering KDIGO stage 3 AKI as the endpoint, multivariate logistic regression showed that pRBC transfusion (OR, 1.15; p<0.001), PC transfusion (OR, 1.28; p<0.001), a duration of cardiopulmonary bypass (CPB) ≥293 minutes (OR, 2.95; p=0.04), and a creatinine clearance rate of ≤85 mL/minute (OR, 2.12; p=0.01) were independent risk factors. Considering RRT as the endpoint, multivariate logistic regression showed that pRBC transfusion (OR, 1.12; p<0.001), PC transfusion (OR, 1.33; p=0.001), a duration of CPB ≥293 minutes (OR, 3.79; p=0.02), and a creatinine clearance rate of ≤85 mL/minute (OR, 3.34; p<0.001) were independent risk factors.

CONCLUSIONS

Kidney Disease: Improving Global Outcomes-defined stage AKI was common after TAR for ATAAD. Transfusions of pRBCs and PC increased the incidence of AKI, stage 3 AKI, and RRT. Fresh frozen plasma transfusion was not a risk factor for AKI.

Toxic effects of cell-free hemoglobin on the microvascular endothelium: implications for pulmonary and nonpulmonary organ dysfunction

Levels of circulating cell-free hemoglobin are elevated during hemolytic and inflammatory diseases and contribute to organ dysfunction and severity of illness. Though several studies have investigated the contribution of hemoglobin to tissue injury, the precise signaling mechanisms of hemoglobin-mediated endothelial dysfunction in the lung and other organs are not yet completely understood. The purpose of this review is to highlight the knowledge gained thus far and the need for further investigation regarding hemoglobin-mediated endothelial inflammation and injury to develop novel therapeutic strategies targeting the damaging effects of cell-free hemoglobin.

The Mystery of Red Blood Cells Extracellular Vesicles in Sleep Apnea with Metabolic Dysfunction

Sleep is very important for overall health and quality of life, while sleep disorder has been associated with several human diseases, namely cardiovascular, metabolic, cognitive, and cancer-related alterations. Obstructive sleep apnea (OSA) is the most common respiratory sleep-disordered breathing, which is caused by the recurrent collapse of the upper airway during sleep. OSA has emerged as a major public health problem and increasing evidence suggests that untreated OSA can lead to the development of various diseases including neurodegenerative diseases. In addition, OSA may lead to decreased blood oxygenation and fragmentation of the sleep cycle. The formation of free radicals or reactive oxygen species (ROS) can emerge and react with nitric oxide (NO) to produce peroxynitrite, thereby diminishing the bioavailability of NO. Hypoxia, the hallmark of OSA, refers to a decline of tissue oxygen saturation and affects several types of cells, playing cell-to-cell communication a vital role in the outcome of this interplay. Red blood cells (RBCs) are considered transporters of oxygen and nutrients to the tissues, and these RBCs are important interorgan communication systems with additional functions, including participation in the control of systemic NO metabolism, redox regulation, blood rheology, and viscosity. RBCs have been shown to induce endothelial dysfunction and increase cardiac injury. The mechanistic links between changes of RBC functional properties and cardiovascular are largely unknown. Extracellular vesicles (EVs) are secreted by most cell types and released in biological fluids both under physiological and pathological conditions. EVs are involved in intercellular communication by transferring complex cargoes including proteins, lipids, and nucleic acids from donor cells to recipient cells. Advancing our knowledge about mechanisms of RBC-EVs formation and their pathophysiological relevance may help to shed light on circulating EVs and to translate their application to clinical practice. We will focus on the potential use of RBC-EVs as valuable diagnostic and prognostic biomarkers and state-specific cargoes, and possibilities as therapeutic vehicles for drug and gene delivery. The use of RBC-EVs as a precision medicine for the diagnosis and treatment of the patient with sleep disorder will improve the prognosis and the quality of life in patients with cardiovascular disease (CVD).

Red blood cells from patients with pre-eclampsia induce endothelial dysfunction

RATIONALE

Pre-eclampsia is a multisystem disorder associated with systemic vascular dysfunction and decreased nitric oxide (NO) bioactivity. Arginase competes with NO synthase (NOS) for l-arginine, and its upregulation may reduce NOS-derived NO formation or induce production of reactive oxygen species (ROS) via uncoupling of NOS, resulting in endothelial dysfunction. Red blood cells (RBCs) have emerged as key players in NO homeostasis via their interactions with the endothelium. Studies have demonstrated that abnormal RBC arginase function in patients with diabetes contributes to oxidative stress and endothelial dysfunction.

AIM

The aim of the study was to investigate if reduced NO bioavailability and increased ROS in pre-eclampsia is mediated via RBC-dependent mechanisms.

METHODS

In this translational study, plasma and RBCs were isolated from gestationally matched pre-eclamptic and healthy pregnant women and co-incubated overnight with mouse aortas for vascular reactivity studies. NO bioactivity, that is, nitrate, nitrite and cGMP, was assessed in plasma. Arginase activity and expression were analysed in RBCs.

RESULTS

Plasma markers of NO homeostasis and signalling were decreased in pre-eclamptic women vs. healthy pregnant women. Co-incubation of aorta with pre-eclamptic RBCs, but not healthy pregnant RBCs, induced endothelial dysfunction, which was ameliorated by pharmacological inhibition of arginase, scavenging of ROS, and by nitrite treatment. This pathological vascular phenotype was not observed following incubation with pre-eclamptic plasma. Arginase expression and activity in RBCs were increased in pre-eclamptic vs. healthy pregnant women and was associated with pre-eclampsia severity. Pre-eclamptic RBC-induced endothelial dysfunction was not because of increased haemolysis/cell-free haemoglobin.

CONCLUSION

This study demonstrates a novel role of the RBC in mediating the endothelial dysfunction associated with pre-eclampsia through arginase-dependent and oxidative stress-dependent mechanisms. Targeting of RBC arginase may provide a novel treatment modality for pre-eclampsia.

Hemolysis transforms liver macrophages into antiinflammatory erythrophagocytes

During hemolysis, macrophages in the liver phagocytose damaged erythrocytes to prevent the toxic effects of cell-free hemoglobin and heme. It remains unclear how this homeostatic process modulates phagocyte functions in inflammatory diseases. Using a genetic mouse model of spherocytosis and single-cell RNA sequencing, we found that erythrophagocytosis skewed liver macrophages into an antiinflammatory phenotype that we defined as MarcohiHmoxhiMHC class IIlo erythrophagocytes. This phenotype transformation profoundly mitigated disease expression in a model of an anti-CD40-induced hyperinflammatory syndrome with necrotic hepatitis and in a nonalcoholic steatohepatitis model, representing 2 macrophage-driven sterile inflammatory diseases. We reproduced the antiinflammatory erythrophagocyte transformation in vitro by heme exposure of mouse and human macrophages, yielding a distinctive transcriptional signature that segregated heme-polarized from M1- and M2-polarized cells. Mapping transposase-accessible chromatin in single cells by sequencing defined the transcription factor NFE2L2/NRF2 as a critical driver of erythrophagocytes, and Nfe2l2/Nrf2 deficiency restored heme-suppressed inflammation. Our findings point to a pathway that regulates macrophage functions to link erythrocyte homeostasis with innate immunity.

Reduced lifespan of erythrocytes in Dahl/Salt sensitive rats is the cause of the renal proximal tubule damage

We studied the mechanisms of anemia and the influence of anemia on renal pathology in Dahl/Salt Sensitive (Dahl/SS) rat, a model of cardio-renal-anemia syndrome. Erythrocyte lifespan was shortened and associated with decreased hemoglobin level in the Dahl/SS rats given high-salt diet. Serum haptoglobin decreased, reticulocytes increased, and erythropoiesis in the bone marrow and extramedullary hematopoiesis in the spleen was markedly stimulated by increased serum erythropoietin in them. As a mechanism of hemolysis, we investigated the incidence of eryptosis, suicidal death of erythrocytes. Eryptosis was increased, and red blood cell-derived microparticles, small particle which are generated in hemolytic disease, were also increased in Dahl/SS rats fed with high-salt diet. Deposition of hemosiderin and mitochondrial morphologic abnormality, a sign of ferroptosis, in proximal renal tubules was associated with intravascular hemolysis. Treatment with deferasirox, an oral iron chelator, reduced the renal proximal tubular injury and the glomerular sclerosis in Dahl/SS rats fed with high-salt diet. In conclusion, reduced half-life of erythrocytes induced by hemolysis is the major cause of anemia in Dahl/SS rat. Iron accumulation induced by hemolysis causes renal proximal tubule injury and accelerates renal damage in this model.

In vitro iatrogenic hemolysis of canine packed red blood cells during various rapid transfusion techniques

OBJECTIVE

To evaluate which rapid blood administration technique causes the least iatrogenic hemolysis in canine packed red blood cells (pRBCs) as determined by plasma free hemoglobin (fHb) and percent hemolysis (% hemolysis).

DESIGN

Prospective in vitro randomized study.

SETTING

Private referral center.

ANIMALS

None.

INTERVENTIONS

Thirteen units of canine pRBCs were divided equally into 5 aliquots, resulting in 65 trials. The aliquots of each unit were subjected to the following administration techniques: gravity-driven (control), an infusion pump at maximal rate, application of a pressure bag, manual compression, and syringe bolus. Plasma fHb and % hemolysis were recorded before and after each trial. Rate of administration (mL/s) was calculated for each method.

MEASUREMENTS AND MAIN RESULTS

Compared to the control, there were no significant increases in % hemolysis or plasma fHb noted among any of the trial methods. The manual compression and syringe bolus methods resulted in the fastest transfusion rates, whereas the infusion pump was not faster than the gravity-driven method. Despite a storage time of ≤14 days, 15% of pRBC units had unsuitable (>0.8%) hemolysis before even being subjected to the trials.

CONCLUSIONS

Commonly used rapid infusion techniques in small animal transfusion medicine do not cause significant iatrogenic hemolysis of canine pRBCs in vitro, although a significant risk is present in stored blood. This suggests that if an expedited transfusion is needed, any method described in this study could be considered, although stored pRBCs should be tested for unsuitable levels of hemolysis prior to transfusion.

The relationship of membrane stiffness, cytoskeleton structure and storage time of pRBCs

BACKGROUND AND OBJECTIVES

In clinical practice, it has been shown that transfusion of packed red blood cells (pRBCs) with late shelf life increases the risk of post-transfusion complications.

OBJECTIVE

To study relationship of membrane stiffness, cytoskeleton structure and storage time of pRBCs.

MATERIALS AND METHODS

pRBCs were processed and stored according to blood bank procedure, for 42 days, at +4°C; pRBC samples were taken on days 3, 12, 19, 21, 24, 28, 35 and 42. Cytoskeleton images and membrane stiffness were studied using atomic force microscope.

RESULTS

In the course of the pRBC storage, the cytoskeleton network configuration underwent structural changes. Simultaneously, pRBC membrane stiffness was increasing, with the correlation coefficient 0·88. Until 19 days, the stiffness grew slowly, in 19-24 days there occurred a transition period, after which its growth rate was three times higher than the initial. A chain of pathological processes developed in pRBC during long storage: pH reduction (linked to increased oxidative stress), then cytoskeletal destruction and an associated increase in pRBC membrane stiffness.

CONCLUSION

During prolonged storage of pRBCs and their acidification, there is a progression of pRBC cytoskeletal changes and associated increase of membrane stiffness, observed to increase in rate after days 19-24. Mutual measurements of cytoskeletal integrity and membrane stiffness may be useful quality assessment tool to study the molecular mechanisms of RBC structural degradation during storage.

Ovine red cell concentrates for transfusion research - is the storage lesion comparable to human red cell concentrates?

BACKGROUND AND OBJECTIVES

Sheep are increasingly being used as a large in vivo animal model of blood transfusion because they provide several advantages over small animals. Understanding the effects of storage duration on ovine (ov) red cell concentrates (RCCs) and how these changes compare with stored human (hu) RCCs is necessary to facilitate clinical translation of research findings.

MATERIALS AND METHODS

OvRCCs (n = 5) collected and processed in standard human blood collection packs, and equivalent huRCCs provided by Australian Red Cross Lifeblood (n = 5), were stored at 2-6°C for 42 days, with samples collected weekly. Haemolysis index was determined by measuring supernatant haemoglobin concentration. Biochemical parameters were evaluated using a blood gas analyser. Energy metabolites and biologically active lipids were measured using commercial assays. Osmotic fragility was determined by lysis in various saline concentrations. Extracellular vesicles were characterized by nanoparticle tracking analysis.

RESULTS

Ovine red blood cells (RBCs) are double in number, smaller in size and more fragile than human RBCs. Haematological values were unchanged throughout storage. In contrast, biochemical and metabolic values, and haemolysis index in three of the five ovRCCs exceeded huRCCs licensing criteria by day 42. Accumulation of extracellular vesicles and biologically active lipids was comparable between huRCCs and ovRCCs.

CONCLUSION

This study documents similarities and differences in the storage lesion of ovRCCs and huRCCs. This new information will guide the design of ovine transfusion models to enhance translation of findings to human transfusion settings.

Kinetic inequivalence between α and β subunits of ligand dissociation from ferrous nitrosylated human haptoglobin:hemoglobin complexes. A comparison with O2 and CO dissociation

Haptoglobin (Hp) counterbalances the adverse effects of extra-erythrocytic hemoglobin (Hb) by trapping the αβ dimers of Hb in the bloodstream. In turn, the Hp:Hb complexes display Hb-like reactivity. Here, the kinetics of NO dissociation from ferrous nitrosylated Hp:Hb complexes (i.e., Hp1-1:Hb(II)-NO and Hp2-2:Hb(II)-NO, respectively) are reported at pH 7.0 and 20.0 °C. NO dissociation from Hp:Hb(II)-NO complexes has been followed by replacing NO with CO. Denitrosylation kinetics of Hp1-1:Hb(II)-NO and Hp2-2:Hb(II)-NO are biphasic, the relative amplitude of the fast and slow phase being 0.495 ± 0.015 and 0.485 ± 0.025, respectively. Values of k_off(NO)1 and k_off(NO)2 (i.e., (6.4 ± 0.8) × 10^-5 s^-1 and (3.6 ± 0.6) × 10^-5 s^-1 for Hp1-1:Hb(II)-NO and (5.8 ± 0.8) × 10^-5 s^-1 and (3.1 ± 0.6) × 10^-5 s^-1 for Hp2-2:Hb(II)-NO) are unaffected by allosteric effectors and correspond to those reported for the α and β subunits of tetrameric Hb(II)-NO and isolated α(II)-NO and β(II)-NO chains, respectively. This highlights the view that the conformation of the Hb α₁β₁ and α₂β₂ dimers matches that of the Hb high affinity conformation. Moreover, the observed functional heterogeneity reflects the variation of energy barriers for the ligand detachment and exit pathway(s) associated to the different structural arrangement of the two subunits in the nitrosylated R-state. Noteworthy, the extent of the inequivalence of α and β chains is closely similar for the O₂, NO and CO dissociation in the R-state, suggesting that it is solely determined by the structural difference between the two subunits.

Red Blood Cells and Hemoglobin in Human Atherosclerosis and Related Arterial Diseases

As the main particulate component of the circulating blood, RBCs play major roles in physiological hemodynamics and impact all arterial wall pathologies. RBCs are the main determinant of blood viscosity, defining the frictional forces exerted by the blood on the arterial wall. This function is used in phylogeny and ontogeny of the cardiovascular (CV) system, allowing the acquisition of vasomotricity adapted to local metabolic demands, and systemic arterial pressure after birth. In pathology, RBCs collide with the arterial wall, inducing both local retention of their membranous lipids and local hemolysis, releasing heme-Fe⁺⁺ with a high toxicity for arterial cells: endothelial and smooth muscle cells (SMCs) cardiomyocytes, neurons, etc. Specifically, overloading of cells by Fe⁺⁺ promotes cell death. This local hemolysis is an event associated with early and advanced stages of human atherosclerosis. Similarly, the permanent renewal of mural RBC clotting is the major support of oxidation in abdominal aortic aneurysm. In parallel, calcifications promote intramural hemorrhages, and hemorrhages promote an osteoblastic phenotypic shift of arterial wall cells. Different plasma or tissue systems are able, at least in part, to limit this injury by acting at the different levels of this system.

Dynamics of shape recovery by stored red blood cells during washing at the single cell level

BACKGROUND

Hypothermic storage transforms red blood cells (RBC) from smooth biconcave discocytes into increasingly spherical spiculated echinocytes and, ultimately, fragile spherocytes (S). Individual cells undergo this transformation at different rates, producing a heterogeneous mixture of RBCs at all stages of echinocytosis in each unit of stored blood. Here we investigated how washing (known to positively affect RBC properties) changes morphology of individual RBCs at the single-cell level.

STUDY DESIGN AND METHODS

We tracked the change in shape of individual RBCs (n = 2870; drawn from six 4- to 6-week-old RBC units) that were confined in an array of microfluidic wells during washing in saline (n = 1095), 1% human serum albumin (1% HSA) solution (n = 999), and the autologous storage supernatant (control, n = 776).

RESULTS

Shape recovery proceeded through the disappearance of spicules followed by the progressive smoothening of the RBC contour, with the majority of changes occurring within the initial 10 minutes of being exposed to the washing solution. Approximately 57% of all echinocytes recovered by at least one morphologic class when washed in 1% HSA (36% for normal saline), with 3% of cells in late-stage echinocytosis restoring their discoid shape completely. Approximately one-third of all spherocytic cells were lysed in either washing solution. Cells washed in their autologous storage supernatant continued to deteriorate during washing.

CONCLUSION

Our findings suggest that the replacement of storage supernatant with a washing solution during washing induces actual shape recovery for RBCs in all stages of echinocytosis, except for S that undergo lysis instead.

Hemopexin as an Inhibitor of Hemolysis-Induced Complement Activation

Hemopexin is the main plasmatic scavenger of cell-free heme, released in the context of intravascular hemolysis or major cell injury. Heme is indispensable for the oxygen transport by hemoglobin but when released outside of the erythrocytes it becomes a danger-associated molecular pattern, contributing to tissue injury. One of the mechanisms of pro-inflammatory action of heme is to activate the innate immune complement cascade. Therefore, we hypothesized that injection of hemopexin will prevent hemolysis-induced complement activation. Human plasma-derived hemopexin is compatible with the heme clearance machinery of the mice. 100 or 500 mg/kg of hemopexin was injected in C57Bl/6 mice before treatment with phenylhydrazine (inducer of erythrocytes lysis) or with PBS as a control. Blood was taken at different timepoints to determine the pharmacokinetic of injected hemopexin in presence and absence of hemolysis. Complement activation was determined in plasma, by the C3 cleavage (western blot) and in the kidneys (immunofluorescence). Kidney injury was evaluated by urea and creatinine in plasma and renal NGAL and HO-1 gene expression were measured. The pharmacokinetic properties of hemopexin (mass spectrometry) in the hemolytic mice were affected by the target-mediated drug disposition phenomenon due to the high affinity of binding of hemopexin to heme. Hemolysis induced complement overactivation and signs of mild renal dysfunction at 6 h, which were prevented by hemopexin, except for the NGAL upregulation. The heme-degrading capacity of the kidney, measured by the HO-1 expression, was not affected by the treatment. These results encourage further studies of hemopexin as a therapeutic agent in models of diseases with heme overload.

Mechanisms of Toxicity and Modulation of Hemoglobin-based Oxygen Carriers

Several adverse events have been associated with the infusion of hemoglobin-based oxygen carriers (HBOCs), including transient hypertension, gastrointestinal, pancreatic/liver enzyme elevation, and cardiac/renal injury in humans. Although several mechanisms have been suggested, the basis of HBOC toxicity is still poorly understood. Scavenging of vascular endothelial nitric oxide (NO) and heme-mediated oxidative side reactions are thought to be the major causes of toxicity. However, based on more recent preclinical studies, oxidative pathways (driven by the heme prosthetic group) seem to play a more prominent role in the overall toxicity of free Hb or HBOCs. HBOCs display a diversity of physicochemical properties, including molecular size/cross-linking characteristics leading to differences in oxygen affinity, allosteric, redox properties, and even oxidative inactivation by protein/heme clearing mechanisms. These diverse characteristics can therefore be manipulated independently, leaving open the possibility of engineering a safe and effective HBOC. To date, several antioxidative strategies have been proposed to counteract the redox side reactions of current generation HBOCs.

Current Challenges in the Development of Acellular Hemoglobin Oxygen Carriers by Protein Engineering

This article reviews the key biochemical mechanisms that govern O2 transport, NO scavenging, and oxidative degradation of acellular hemoglobin (Hb) and how these ideas have been used to try to develop strategies to engineer safer and more effective hemoglobin-based oxygen carriers (HBOCs). Significant toxicities due to acellular Hb have been observed after the administration of HBOCs or after the lysis of red cells, and include rapid clearance and kidney damage due to dissociation into dimers, haptoglobin binding, and macrophage activation; early O2 release leading to decreased tissue perfusion in capillary beds; interference with endothelial and smooth muscle signaling due to nitric oxide (NO) scavenging; autooxidization of heme iron followed by production of reactive oxygen species; and iron overload symptoms due to hemin loss, globin denaturation, iron accumulation, and further inflammation. Protein engineering can be used to mitigate some of these side effects, but requires an in-depth mechanistic understanding of the biochemical and biophysical features of Hb that regulate quaternary structure, O2 affinity, NO dioxygenation, and resistance to oxidation, hemin loss, and unfolding.

Haptoglobin: From hemoglobin scavenging to human health

Haptoglobin (Hp) belongs to the family of acute-phase plasma proteins and represents the most important plasma detoxifier of hemoglobin (Hb). The basic Hp molecule is a tetrameric protein built by two α/β dimers. Each Hp α/β dimer is encoded by a single gene and is synthesized as a single polypeptide. Following post-translational protease-dependent cleavage of the Hp polypeptide, the α and β chains are linked by disulfide bridge(s) to generate the mature Hp protein. As human Hp gene is characterized by two common Hp1 and Hp2 alleles, three major genotypes can result (i.e., Hp1-1, Hp2-1, and Hp2-2). Hp regulates Hb clearance from circulation by the macrophage-specific receptor CD163, thus preventing Hb-mediated severe consequences for health. Indeed, the antioxidant and Hb binding properties of Hp as well as its ability to stimulate cells of the monocyte/macrophage lineage and to modulate the helper T-cell type 1 and type 2 balance significantly associate with a variety of pathogenic disorders (e.g., infectious diseases, diabetes, cardiovascular diseases, and cancer). Alternative functions of the variants Hp1 and Hp2 have been reported, particularly in the susceptibility and protection against infectious (e.g., pulmonary tuberculosis, HIV, and malaria) and non-infectious (e.g., diabetes, cardiovascular diseases and obesity) diseases. Both high and low levels of Hp are indicative of clinical conditions: Hp plasma levels increase during infections, inflammation, and various malignant diseases, and decrease during malnutrition, hemolysis, hepatic disease, allergic reactions, and seizure disorders. Of note, the Hp:Hb complexes display heme-based reactivity; in fact, they bind several ferrous and ferric ligands, including O₂, CO, and NO, and display (pseudo-)enzymatic properties (e.g., NO and peroxynitrite detoxification). Here, genetic, biochemical, biomedical, and biotechnological aspects of Hp are reviewed.

Haptoglobin administration into the subarachnoid space prevents hemoglobin-induced cerebral vasospasm

Delayed ischemic neurological deficit (DIND) is a major driver of adverse outcomes in patients with aneurysmal subarachnoid hemorrhage (aSAH), defining an unmet need for therapeutic development. Cell-free hemoglobin that is released from erythrocytes into the cerebrospinal fluid (CSF) is suggested to cause vasoconstriction and neuronal toxicity, and correlates with the occurrence of DIND. Cell-free hemoglobin in the CSF of patients with aSAH disrupted dilatory NO signaling ex vivo in cerebral arteries, which shifted vascular tone balance from dilation to constriction. We found that selective removal of hemoglobin from patient CSF with a haptoglobin-affinity column or its sequestration in a soluble hemoglobin-haptoglobin complex was sufficient to restore physiological vascular responses. In a sheep model, administration of haptoglobin into the CSF inhibited hemoglobin-induced cerebral vasospasm and preserved vascular NO signaling. We identified 2 pathways of hemoglobin delocalization from CSF into the brain parenchyma and into the NO-sensitive compartment of small cerebral arteries. Both pathways were critical for hemoglobin toxicity and were interrupted by the large hemoglobin-haptoglobin complex that inhibited spatial requirements for hemoglobin reactions with NO in tissues. Collectively, our data show that compartmentalization of hemoglobin by haptoglobin provides a novel framework for innovation aimed at reducing hemoglobin-driven neurological damage after subarachnoid bleeding.

Tangential flow filtration of haptoglobin

Haptoglobin (Hp) is a plasma glycoprotein that scavenges cell-free hemoglobin (Hb). Hp has various potential therapeutic applications, but it has been mainly studied for treatment of acute hemolytic conditions that can arise from situations such as massive blood transfusion, infusion of stored red blood cells, severe burns, trauma, sepsis, radiation injury, and others. Therefore, Hp may also be beneficial during chronic hemolytic disease states such as hereditary spherocytosis, nocturnal hemoglobinuria, sickle-cell anemia, and malaria. Various methods have been developed to purify Hp from plasma or plasma fractions. However, none of these methods have exploited the large molecular weight (MW) range distribution of Hp polymers to easily isolate Hp from other plasma proteins. The present study used tangential flow filtration (TFF) to isolate polymeric Hp from plasma proteins using human Fraction IV (FIV) as the starting material. After removal of insoluble material from a suspension of FIV paste, the protein mixture was clarified on a 0.2 μm hollow fiber (HF) TFF filter. The clarified protein solution was then bracketed based on protein MW using HF filters with MW cut-offs (MWCOs) of 750, 500, and 100 kDa. Using untreated FIV, the Hp purity of the main bracket was ~75% with a total Hb binding capacity (HbBC) yield of 1.2 g starting from 500 g of FIV paste. However, pretreatment of FIV with fumed silica to remove lipoproteins increased Hp purity to >95% with a HbBC yield of 1.7 g per 500 g of FIV. Taken together this study provides a novel and scalable method to purify Hp from plasma or plasma fractions.

Graphene Oxide Nanosheets for Localized Hyperthermia-Physicochemical Characterization, Biocompatibility, and Induction of Tumor Cell Death

Background: The main goals of cancer treatment are not only to eradicate the tumor itself but also to elicit a specific immune response that overcomes the resistance of tumor cells against chemo- and radiotherapies. Hyperthermia was demonstrated to chemo- and radio-sensitize cancerous cells. Many reports have confirmed the immunostimulatory effect of such multi-modal routines. Methods: We evaluated the interaction of graphene oxide (GO) nanosheets; its derivatives reduced GO and PEGylated rGO, with components of peripheral blood and evaluated its thermal conductivity to induce cell death by localized hyperthermia. Results: We confirmed the sterility and biocompatibility of the graphene nanomaterials and demonstrated that hyperthermia applied alone or in the combination with radiotherapy induced much more cell death in tumor cells than irradiation alone. Cell death was confirmed by the release of lactate dehydrogenase from dead and dying tumor cells. Conclusion: Biocompatible GO and its derivatives can be successfully used in graphene-induced hyperthermia to elicit tumor cell death.

Haptoglobin Therapeutics and Compartmentalization of Cell-Free Hemoglobin Toxicity

Hemolysis and accumulation of cell-free hemoglobin (Hb) in the circulation or in confined tissue compartments such as the subarachnoid space is an important driver of disease. Haptoglobin is the Hb binding and clearance protein in human plasma and an efficient antagonist of Hb toxicity resulting from physiological red blood cell turnover. However, endogenous concentrations of haptoglobin are insufficient to provide protection against Hb-driven disease processes in conditions such as sickle cell anemia, sepsis, transfusion reactions, medical-device associated hemolysis, or after a subarachnoid hemorrhage. As a result, there is increasing interest in developing haptoglobin therapeutics to target 'toxic' cell-free Hb exposures. Here, we discuss key concepts of Hb toxicity and provide a perspective on the use of haptoglobin as a therapeutic protein.