Oxidative Stress Increases Erythrocyte Sensitivity to Shear-Mediated Damage

Erythrocyte deformability correlates with systemic inflammation

Recent evidence suggests that systemic conditions, particularly those associated with inflammation, can affect erythrocyte deformability in the absence of haematological conditions. In this exploratory study, we investigated the relationship between systemic inflammatory status and erythrocyte deformability (using osmotic gradient ektacytometry) in a heterogenous study population consisting of individuals with no medical concerns, chronic conditions, and acute illness, providing a wide range of systemic inflammation severity. 22 participants were included in a prospective observational study. Maximum Elongation Index (EImax) in ektacytometry served as the readout for erythrocyte deformability. Inflammatory status was assessed using C-reactive protein (CRP) and self-reported symptoms associated with inflammatory activation (Sickness Questionnaire Scores, SicknessQ). In a univariate linear regression, both CRP and SicknessQ scores significantly predicted EImax (CRP: F(1,20) = 7.751, p < 0.05 (0.011), R2 = 0.279; SicknessQ: F(1,18) = 4.831, p < 0.05 (0.041), R2 = 0.212). Sensitivity analyses with multivariable linear regression correcting for age showed concordant findings. Results suggest a linear relationship between erythrocyte deformability and biochemical and clinical markers of systemic inflammation. Replication of findings in a larger study, and mechanisms and clinical consequences need further in investigation.

Analysis of non-physiological shear stress-induced red blood cell trauma across different clinical support conditions of the blood pump

Systematic research into device-induced red blood cell (RBC) damage beyond hemolysis, including correlations between hemolysis and RBC-derived extracellular vesicles, remains limited. This study investigated non-physiological shear stress-induced RBC damage and changes in related biochemical indicators under two blood pump clinical support conditions. Pressure heads of 100 and 350 mmHg, numerical simulation methods, and two in vitro loops were utilized to analyze the shear stress and changes in RBC morphology, hemolysis, biochemistry, metabolism, and oxidative stress. The blood pump created higher shear stress in the 350-mmHg condition than in the 100-mmHg condition. With prolonged blood pump operation, plasma-free hemoglobin and cholesterol increased, whereas plasma glucose and nitric oxide decreased in both loops. Notably, plasma iron and triglyceride concentrations increased only in the 350-mmHg condition. The RBC count and morphology, plasma lactic dehydrogenase, and oxidative stress across loops did not differ significantly. Plasma extracellular vesicles, including RBC-derived microparticles, increased significantly at 600 min in both loops. Hemolysis correlated with plasma triglyceride, cholesterol, glucose, and nitric oxide levels. Shear stress, but not oxidative stress, was the main cause of RBC damage. Hemolysis alone inadequately reflects overall blood pump-induced RBC damage, suggesting the need for additional biomarkers for comprehensive assessments.

Accelerated Hemocompatibility Testing of Rotary Blood Pumps

Ex vivo hemocompatibility testing is a vital element of preclinical assessment for blood-contacting medical devices. Current approaches are resource intensive; thus, we investigated the feasibility of accelerating hemocompatibility testing by standardizing the number of pump exposures in loops of various sizes. Three identical blood loops were constructed, each with a custom-molded reservoir able to facilitate large-volume expansion. Using the HVAD rotary blood pump operating at 5 L·min -1 and 100 mmHg, three test volumes (80, 160, and 320 ml) were circulated for 4000 pump exposures. Blood sampling was performed at individualized intervals every one-sixth of total duration for the assessment of hemolysis and von Willebrand Factor (vWF) degradation. While steady increases in hemolysis (~24 mg·dl -1 ) were identified in all tests at completion, loop volume was not a primary discriminator. The normalized index of hemolysis did not vary significantly between loops (4.2-4.9 mg·100 L -1 ). vWF degradation progressively occurred with duration of testing to a similar extent under all conditions. These data support an accelerated approach to preclinical assessment of ex vivo blood damage. Adopting this approach enables: enhanced efficiency for rapid prototyping; reduced ex vivo blood aging, and; greater utility of blood, which is presently limited if 450 ml loops are desired.

Red blood cell sublethal damage: haemocompatibility is not the absence of haemolysis

Blood is a complex fluid owing to its two-phase suspension of formed cellular elements within a protein-rich plasma. Vital to its role in distributing nutrients throughout the circulatory system, the mechanical properties of blood - and particularly red blood cells (RBC)-primarily determine bulk flow characteristics and microcirculatory flux. Various factors impair the physical properties of RBC, including cellular senescence, many diseases, and exposure to mechanical forces. Indeed, the latter is increasingly relevant following the advent of modern life support, such as mechanical circulatory support (MCS), which induce unique interactions between blood and artificial environments that leave blood cells with the signature of aging, albeit accelerated, and crucially underlie various serious complications, including death. Accumulating evidence indicates that these complications appear to be associated with mechanical shear forces present within MCS that are not extreme enough to overtly rupture cells, yet may still induce "sublethal" injury and "fatigue" to vital blood constituents. Impaired RBC physical properties following elevated shear exposure-a hallmark of sublethal injury to blood-are notable and may explain, at least in part, systemic complications and premature mortality associated with MCS. Design of optimal next-generation MCS devices thus requires consideration of biocompatibility and blood-device interactions to minimize potential blood complications and promote clinical success. Presented herein is a contemporary understanding of "blood damage," with emphasis on shear exposures that alter microrheological function but do not overtly destroy cells (ie, sublethal damage). Identification of key cellular factors perturbed by supraphysiological shear exposure are examined, offering potential pathways to enhance design of MCS and blood-contacting medical devices.

Vitamin C supplementation attenuates oxidative stress and improves erythrocyte deformability in cardiac surgery with cardiopulmonary bypass

Cardiopulmonary bypass (CPB) depletes endogenous Vitamin C and generates oxidative stress in cardiac surgery. This study aimed to clarify whether Vitamin C supplementation reduces oxidant production and improves erythrocyte deformability in cardiac surgery with CPB. In a randomized and controlled design, 30 eligible patients undergoing cardiac surgery with hypothermic CPB were equally assigned to the Vitamin C group and control group. Subjects of the Vitamin C group and control group received an intravenous infusion of Vitamin C 20 mg·kg^-1 and a placebo during rewarming period of CPB, respectively. We measured the plasma level of reactive oxygen species (ROS) and phosphorylation levels of non-muscle myosin IIA (NMIIA) in erythrocyte membrane, as an index of erythrocyte deformability, before and after CPB. Vitamin C supplementation attenuated the surge in plasma ROS after CPB, mean 1.661 ± standard deviation 0.801 folds in the Vitamin C group and 2.743 ± 1.802 in the control group. The tyrosine phosphorylation level of NMIIA after CPB was upregulated in the Vitamin C group compared to the control group, 2.159 ± 0.887 folds and 1.384 ± 0.445 (P = 0.0237). In addition, the phosphorylation of vasodilator-stimulated phosphoprotein (VASP) and focal adhesion kinase (FAK) in erythrocytes was concurrently enhanced in the Vitamin C group after CPB. The phosphorylation level of endothelial nitric oxide synthase in erythrocytes was significantly increased in the Vitamin C group (1.734 ± 0.371 folds) compared to control group (1.102 ± 0.249; P = 0.0061). Patients receiving Vitamin C had lower intraoperative blood loss and higher systemic vascular resistance after CPB compared to controls. Vitamin C supplementation attenuates oxidative stress and improves erythrocyte deformability via VASP/FAK signaling pathway in erythrocytes during CPB.

Reprogramming of red blood cell metabolism in Zika virus-infected donors

BACKGROUND

Diseases caused by arthropod-borne viruses remain a burden to global health; in particular, Zika virus (ZIKV) has been reported in 87 countries and territories. In healthy blood donors, ZIKV RNA can be detected in red blood cells (RBCs) months after infection, clearance of detectable nucleic acid in plasma, and seroconversion. However, little information is available on the impact of ZIKV infection to metabolism.

STUDY DESIGN AND METHODS

We applied mass spectrometry-based metabolomics and lipidomics approaches to investigate the impact of ZIKV infection on RBCs over the course of infection. ZIKV-infected blood donors (n = 25) were identified through molecular and serologic methods, which included nucleic acid amplification testing and real-time polymerase chain reaction (PCR) for detection of ZIKV RNA and enzyme-linked immunosorbent assay (ELISA) for detection of flavivirus-specific IgM and IgG.

RESULTS

In ZIKV RNA-positive donors, we observed lower glucose and lactate levels, and higher levels of ribose phosphate, suggestive of the activation of the pentose phosphate pathway. The top pathways altered in RBCs from ZIKV-IgM-positive donors include amino acid metabolism and biosynthesis, fatty acid metabolism and biosynthesis, linoleic acid and arachidonate metabolism and glutathione metabolism. RBCs from ZIKV-infected donors had increased levels of early glycolytic metabolites, and higher levels of metabolites of the pentose phosphate pathway. Alterations in acyl-carnitine and fatty acid metabolism are consistent with impaired membrane lipid homeostasis in RBCs from ZIKV IgM positive donors.

CONCLUSION

RBC from healthy blood donors who had been infected by ZIKV are characterized by long-lasting metabolic alterations even months after infection has resolved.

COVID-19 and erythrocrine function: The roller coaster and danger

Erythrocrine function refers to erythrocytes' ability to synthesize and release active signaling molecules such as ATP and nitric oxide (NO). Erythrocyte NO regulates its deformability and increases its perfusion and circulation that prevent tissue hypoxia. Recently, there is a connotation between SARS-CoV-2 infection and erythrocrine function due to alteration in the release of NO and ATP from erythrocytes. SARS-CoV-2 binds erythrocyte band3 protein, which has a similar characteristic of ACE2, leading to alteration of erythrocyte physiology like oxygen transport with development of hypoxia. Similarly, SARS-CoV-2 infection activates erythrocyte protein kinase C alpha (PKC-α), causing significant changes in the erythrocyte functions. The erythrocytes can bind SARS-CoV-2 and its active particles with subsequent virus delivery to the liver and spleen macrophages. Thus, the erythrocytes act as elimination for SARS-CoV-2 in COVID-19. Moreover, the erythrocyte stored, release sphingosine-1 phosphate (S1P) improves endothelial and regulates lymphocyte functions. SARS-CoV-2 ORF8 protein binds the porphyrin part of hemoglobin heme at the β1 chain, causing hemolysis and dysfunctional hemoglobin to reduce oxygen-carrying capacity. In conclusion, SARS-CoV-2 infection and associated pro-inflammatory disorders lead to abnormal erythrocrine function with subsequent inflammatory complications and endothelial dysfunction due to deficiency of protective released molecules (NO, G1P, and ATP) from functional erythrocytes. In vitro, preclinical, and clinical studies are mandatory in this regard.

Erythrocyte morphological symmetry analysis to detect sublethal trauma in shear flow

The viscoelastic properties of red blood cells (RBC) facilitate flexible shape change in response to extrinsic forces. Their viscoelasticity is intrinsically linked to physical properties of the cytosol, cytoskeleton, and membrane-all of which are highly sensitive to supraphysiological shear exposure. Given the need to minimise blood trauma within artificial organs, we observed RBC in supraphysiological shear through direct visualisation to gain understanding of processes leading to blood damage. Using a custom-built counter-rotating shear generator fit to a microscope, healthy red blood cells (RBC) were directly visualised during exposure to different levels of shear (10-60 Pa). To investigate RBC morphology in shear flow, we developed an image analysis method to quantify (a)symmetry of deforming ellipsoidal cells-following RBC identification and centroid detection, cell radius was determined for each angle around the circumference of the cell, and the resultant bimodal distribution (and thus RBC) was symmetrically compared. While traditional indices of RBC deformability (elongation index) remained unaltered in all shear conditions, following ~100 s of exposure to 60 Pa, the frequency of asymmetrical ellipses and RBC fragments/extracellular vesicles significantly increased. These findings indicate RBC structure is sensitive to shear history, where asymmetrical morphology may indicate sublethal blood damage in real-time shear flow.

Impact of small fractions of abnormal erythrocytes on blood rheology

Red blood cell (RBC) populations are inherently heterogeneous, given mature RBC lack the transcriptional machinery to re-synthesize proteins affected during in vivo aging. Clearance of older, less functional cells thus aids in maintaining consistent hemorheological properties. Scenarios occur, however, where portions of mechanically impaired RBC are re-introduced into blood (e.g., damaged from circulatory support, blood transfusion) and may alter whole blood fluid behavior. Given such perturbations are associated with poor clinical outcomes, determining the tolerable level of abnormal RBC in blood is valuable. Thus, the current study aimed to define the critical threshold of blood fluid properties to re-infused physically-impaired RBC. Cell mechanics of RBC were impaired through membrane cross-linking (glutaraldehyde) or intracellular oxidation (phenazine methosulfate). Mechanically impaired RBC were progressively re-introduced into the native cell population. Negative alterations of cellular deformability and high shear blood viscosity were observed following additions of only 1-5% rigidified RBC. Low-shear blood viscosity was conversely decreased following addition of glutaraldehyde-treated cells; high-resolution microscopy of these mixed cell populations revealed decreased capacity to form reversible aggregates and decreased aggregate size. Mixed RBC populations, when exposed to supraphysiological shear, presented with compounded mechanical impairment. Collectively, key determinants of blood flow behavior are sensitive to mechanical perturbations in RBC, even when only 1-5% of the cell population is affected. Given this fraction is well-below the volume of rigidified RBC introduced during circulatory support or transfusion practice, it is plausible that some adverse events following surgery and/or transfusion may be related to impaired blood fluidity.

In vitro assay for single-cell characterization of impaired deformability in red blood cells under recurrent episodes of hypoxia

Red blood cells (RBCs) are subjected to recurrent changes in shear stress and oxygen tension during blood circulation. The cyclic shear stress has been identified as an important factor that alone can weaken cell mechanical deformability. The effects of cyclic hypoxia on cellular biomechanics have yet to be fully investigated. As the oxygen affinity of hemoglobin plays a key role in the biological function and mechanical performance of RBCs, the repeated transitions of hemoglobin between its R (high oxygen tension) and T (low oxygen tension) states may impact their mechanical behavior. The present study focuses on developing a novel microfluidic-based assay for characterization of the effects of cyclic hypoxia on cell biomechanics. The capability of this assay is demonstrated by a longitudinal study of individual RBCs in health and sickle cell disease subjected to cyclic hypoxia conditions of various durations and levels of low oxygen tension. The viscoelastic properties of cell membranes are extracted from tensile stretching and relaxation processes of RBCs induced by the electrodeformation technique. Results demonstrate that cyclic hypoxia alone can significantly reduce cell deformability, similar to the fatigue damage accumulated through cyclic mechanical loading. RBCs affected by sickle cell disease are less deformable (significantly higher membrane shear modulus and viscosity) than normal RBCs. The fatigue resistance of sickle RBCs to the cyclic hypoxia challenge is significantly inferior to that of normal RBCs, and this trend is more significant in mature erythrocytes of sickle cells. When the oxygen affinity of sickle hemoglobin is enhanced by anti-sickling drug treatment of 5-hydroxymethyl-2-furfural (5-HMF), sickle RBCs show ameliorated resistance to fatigue damage induced by cyclic hypoxia. These results indicate an important biophysical mechanism underlying RBC senescence in which the cyclic hypoxia challenge alone can lead to mechanical degradation of the RBC membrane. We envision that the application of this assay can be further extended to RBCs in other blood diseases and other cell types.

A Novel Fragmentation Sensitivity Index Determines the Susceptibility of Red Blood Cells to Mechanical Trauma

Supraphysiological shear stresses (SSs) induce irreversible impairments of red blood cell (RBC) deformability, overstretching of RBC membrane, or fragmentation of RBCs that causes free hemoglobin to be released into plasma, which may lead to anemia. The magnitude and exposure tisme of the SSs are two critical parameters that determine the hemolytic threshold of a healthy RBC. However, impairments in the membrane stability of damaged cells reduce the hemolytic threshold and increase the susceptibility of the cell membrane to supraphysiological SSs, leading to cell fragmentation. The severity of the RBC fragmentation as a response to the mechanical damage and the critical SS levels causing fragmentation are not previously defined. In this study, we investigated the RBC mechanical damage in oxidative stress (OS) and metabolic depletion (MD) models by applying supraphysiological SSs up to 100 Pa by an ektacytometer (LORRCA MaxSis) and then assessed RBC deformability. Next, we examined hemolysis and measured RBC volume and count by Multisizer 3 Coulter Counter to evaluate RBC fragmentation. RBC deformability was significantly impaired in the range of 20-50 Pa in OS compared with healthy controls (p < 0.05). Hemolysis was detected at 90-100 Pa SS levels in MD and all applied SS levels in OS. Supraphysiological SSs increased RBC volume in both the damage models and the control group. The number of fragmented cells increased at 100 Pa SS in the control and MD and at all SS levels in OS, which was accompanied by hemolysis. Fragmentation sensitivity index increased at 50-100 Pa SS in the control, 100 Pa SS in MD, and at all SS levels in OS. Therefore, we propose RBC fragmentation as a novel sensitivity index for damaged RBCs experiencing a mechanical trauma before they undergo fragmentation. Our approach for the assessment of mechanical risk sensitivity by RBC fragmentation could facilitate the close monitoring of shear-mediated RBC response and provide an effective and accurate method for detecting RBC damage in mechanical circulatory assist devices used in routine clinical procedures.

Sub-Fractions of Red Blood Cells Respond Differently to Shear Exposure Following Superoxide Treatment

Simple Summary

Deformation of red blood cells (RBCs) is essential in order to pass through the smallest blood vessels. This cell function is impaired in the presence of high levels of free radicals and shear stress that highly exceeds the physiological range. In contrast, shear stress within the physiological range positively affects RBC function. RBCs are a heterogeneous cell population in terms of RBC age with different RBC deformability described for young and old RBCs, but whether these different sub-populations tolerate mechanical and oxidative stress to the same extent remains unknown. The results of the present investigation revealed lower RBC deformability of old RBCs compared to young RBCs and comparable reductions in RBC deformability of the sub-populations caused by free radicals. Physiological shear stress did not further affect free radical content within the RBCs and reversed the deleterious effects of free radicals on RBC deformability of old RBCs only by improving RBC deformability. The changes were aimed to be explained by changes in the formation of nitric oxide (NO), but outputs of NO generation appeared dependent on cell age. These novel findings highlight a yet less-described complex relation between shear stress, free radicals, and RBC mechanics.

Abstract

Red blood cell (RBC) deformability is an essential component of microcirculatory function that appears to be enhanced by physiological shear stress, while being negatively affected by supraphysiological shears and/or free radical exposure. Given that blood contains RBCs with non-uniform physical properties, whether all cells equivalently tolerate mechanical and oxidative stresses remains poorly understood. We thus partitioned blood into old and young RBCs which were exposed to phenazine methosulfate (PMS) that generates intracellular superoxide and/or specific mechanical stress. Measured RBC deformability was lower in old compared to young RBCs. PMS increased total free radicals in both sub-populations, and RBC deformability decreased accordingly. Shear exposure did not affect reactive species in the sub-populations but reduced RBC nitric oxide synthase (NOS) activation and intriguingly increased RBC deformability in old RBCs. The co-application of PMS and shear exposure also improved cellular deformability in older cells previously exposed to reactive oxygen species (ROS), but not in younger cells. Outputs of NO generation appeared dependent on cell age; in general, stressors applied to younger RBCs tended to induce S-nitrosylation of RBC cytoskeletal proteins, while older RBCs tended to reflect markers of nitrosative stress. We thus present novel findings pertaining to the interplay of mechanical stress and redox metabolism in circulating RBC sub-populations.

Hemochromatosis alters the sensitivity of red blood cells to mechanical stress

BACKGROUND

Hemochromatosis (HH) is characterized by chronic iron accumulation, leading to deleterious effects to various organ systems. A common approach to managing iron load involves large-volume venesection. Some countries authorize HH venesections to be used in the development of transfusable blood products, although concerns remain regarding suitability. Due to the high oxidative load associated with hyperferritinemia, it has been proposed that HH blood products may be susceptible to mechanical damage. This is particularly relevant given that typical blood product destinations (eg, transfusion, cardiopulmonary bypass) expose blood to supraphysiologic levels of mechanical stress. We sought to explore the mechanical tolerance of red blood cells (RBC) derived from HH venesections to varied magnitudes and durations of sublethal shear stress.

STUDY DESIGN AND METHODS

Initially, 110 individuals with HH were recruited; to eliminate the effects of comorbidities, only those who were untreated and uncomplicated were included for comparisons with age-matched healthy controls (Con). RBC were exposed to 25 discrete magnitudes (1-64 Pa) and durations (1-64 seconds) of shear stress. Cellular deformability was assessed before, and immediately after, each shear exposure.

RESULTS

In the absence of prior shear exposure, RBC deformability of HH was significantly decreased by 11.5%, compared with Con. For both HH and Con, supraphysiologic shear exposure significantly impaired RBC deformability, although the rate and magnitude of deterioration were elevated for HH.

CONCLUSION

Given that blood products are commonly exposed to high-shear environments (eg, during high-volume transfusion), venesections from asymptomatic and untreated individuals with HH appear suboptimal for the development of therapeutic RBCs.

Mechanical sensitivity of red blood cells improves in individuals with hemochromatosis following venesection therapy

BACKGROUND

Individuals with hereditary hemochromatosis (HH) receive frequent blood withdrawals (ie, venesections) as part of their primary treatment to assist in normalizing blood iron levels. It remains unclear whether this source of blood is suitable for use in blood product development, as current data indicate that red blood cell (RBC) deformability, both before and after shear stress exposure, is impaired in individuals with HH, relative to healthy controls. Given that venesection therapy is known to significantly reduce circulating iron levels in individuals with HH, the current study examined whether venesection therapy is effective at improving RBC mechanical properties, both before and after shear stress exposure, in individuals with HH.

STUDY DESIGN AND METHODS

Blood samples were initially collected from untreated HH patients (age, 61 ± 9 years; 14% female) undergoing their first venesection, and then again during their second (approx. 9 weeks later) and third (approx. 16 weeks later) venesections. RBC deformability was measured at each time point with a commercial ektacytometer. Moreover, to determine cell responses to mechanical stimuli, the mechanical sensitivity of blood samples was determined at each time point.

RESULTS

The salient findings indicate that venesection therapy used for managing plasma ferritin concentration significantly improves the cellular deformability of RBC in individuals with HH. Further, the sensitivity of RBC to supraphysiological mechanical stress is decreased (ie, improved) in a dose-response fashion with routine venesection.

CONCLUSION

While cellular mechanics of RBC from individuals with HH are impaired when untreated, venesection therapy significantly improves cellular properties of RBC, supporting the use of venesections in blood product development from individuals with well-managed HH.

Haemolysis induced by mechanical circulatory support devices: unsolved problems

Since the use of continuous flow blood pumps as ventricular assist devices is standard, the problems with haemolysis have increased. It is mainly induced by shear stress affecting the erythrocyte membrane. There are many investigations about haemolysis in laminar and turbulent blood flow. The results defined as threshold levels for the damage of erythrocytes depend on the exposure time of the shear stress, but they are very different, depending on the used experimental methods or the calculation strategy. Here, the results are resumed and shown in curves. Different models for the calculation of the strengths of erythrocytes are discussed. There are few results reported about tests of haemolysis in blood pumps, but some theoretical approaches for the design of continuous flow blood pumps according to low haemolysis have been investigated within the last years.

The Red Blood Cell-Inflammation Vicious Circle in Sickle Cell Disease

Sickle cell disease (SCD) is a genetic disease caused by a single mutation in the β-globin gene, leading to the production of an abnormal hemoglobin called hemoglobin S (HbS), which polymerizes under deoxygenation, and induces the sickling of red blood cells (RBCs). Sickled RBCs are very fragile and rigid, and patients consequently become anemic and develop frequent and recurrent vaso-occlusive crises. However, it is now evident that SCD is not only a RBC rheological disease. Accumulating evidence shows that SCD is also characterized by the presence of chronic inflammation and oxidative stress, participating in the development of chronic vasculopathy and several chronic complications. The accumulation of hemoglobin and heme in the plasma, as a consequence of enhanced intravascular hemolysis, decreases nitric oxide bioavailability and enhances the production of reactive oxygen species (ROS). Heme and hemoglobin also represent erythrocytic danger-associated molecular pattern molecules (eDAMPs), which may activate endothelial inflammation through TLR-4 signaling and promote the development of complications, such as acute chest syndrome. It is also suspected that heme may activate the innate immune complement system and stimulate neutrophils to release neutrophil extracellular traps. A large amount of microparticles (MPs) from various cellular origins (platelets, RBCs, white blood cells, endothelial cells) is also released into the plasma of SCD patients and participate in the inflammation and oxidative stress in SCD. In turn, this pro-inflammatory and oxidative stress environment further alters the RBC properties. Increased pro-inflammatory cytokine concentrations promote the activation of RBC NADPH oxidase and, thus, raise the production of intra-erythrocyte ROS. Such enhanced oxidative stress causes deleterious damage to the RBC membrane and further alters the deformability of the cells, modifying their aggregation properties. These RBC rheological alterations have been shown to be associated to specific SCD complications, such as leg ulcers, priapism, and glomerulopathy. Moreover, RBCs positive for the Duffy antigen receptor for chemokines may be very sensitive to various inflammatory molecules that promote RBC dehydration and increase RBC adhesiveness to the vascular wall. In summary, SCD is characterized by a vicious circle between abnormal RBC rheology and inflammation, which modulates the clinical severity of patients.

The effects of stenting on hemorheological parameters: An in vitro investigation under various blood flow conditions

 Despite their wide clinical usage, stent functionality may be compromised by complications at the site of implantation, including early/late stent thrombosis and occlusion. Although several studies have described the effect of fluid-structure interaction on local haemodynamics, there is yet limited information on the effect of the stent presence on specific hemorheological parameters. The current work investigates the red blood cell (RBC) mechanical behavior and physiological changes as a result of flow through stented vessels. Blood samples from healthy volunteers were prepared as RBC suspensions in plasma and in phosphate buffer saline at 45% haematocrit. Self-expanding nitinol stents were inserted in clear perfluoroalkoxy alkane tubing which was connected to a syringe, and integrated in a syringe pump. The samples were tested at flow rates of 17.5, 35 and 70 ml/min, and control tests were performed in non-stented vessels. For each flow rate, the sample viscosity, RBC aggregation and deformability, and RBC lysis were estimated. The results indicate that the presence of a stent in a vessel has an influence on the hemorheological characteristics of blood. The viscosity of all samples increases slightly with the increase of the flow rate and exposure. RBC aggregation and elongation index (EI) decrease as the flow rate and exposure increases. RBC lysis for the extreme cases is evident. The results indicate that the stresses developed in the stent area for the extreme conditions could be sufficiently high to influence the integrity of the RBC membrane.

Red blood cell tolerance to shear stress above and below the subhemolytic threshold

Mechanical circulatory support device (MCS) design has improved over the years and yet blood damage (e.g., hemolysis) remains a problem. Accumulating evidence indicates a subhemolytic threshold for red blood cells (RBC)-a threshold at which RBC deformability is impaired prior to hemolysis. The current study aimed to assess the deformability of RBC exposed to supra-physiological shear stresses that are typical of MCS devices and assess whether a method used to estimate an individualized subhemolytic threshold, accurately demarcates whether future application of shear stress was damaging. Suspensions of RBC were "conditioned" with discrete magnitudes of shear stress (5-100 Pa) for specific durations (1-16 s). Cellular deformability was subsequently measured via ektacytometry and a mechanical sensitivity (MS) index was calculated to identify the subhemolytic threshold. Thereafter, fresh RBC suspensions were exposed to a magnitude of shear stress 10 Pa above, 10 Pa below, or matched to a donor's previously estimated subhemolytic threshold for a given duration (1, 4, 16 s) to ascertain the sensitivity of the subhemolytic threshold. The MS index of RBC was significantly impaired following exposure to 10 Pa above the subhemolytic threshold (p < 0.0001), and significantly enhanced following exposure to 10 Pa below the subhemolytic threshold (p < 0.01). For all shear conditions, there was no significant increase in free hemoglobin. Functional assessments of RBC may be useful when conducting biocompatibility testing of MCS devices, to detect trauma to blood prior to overt cell rupture being induced.

Artificial Organs 2018: A Year in Review

In this Editor's Review, articles published in 2018 are organized by category and summarized. We provide a brief reflection of the research and progress in artificial organs intended to advance and better human life while providing insight for continued application of these technologies and methods. Artificial Organs continues in the original mission of its founders "to foster communications in the field of artificial organs on an international level." Artificial Organs continues to publish developments and clinical applications of artificial organ technologies in this broad and expanding field of organ Replacement, Recovery, and Regeneration from all over the world. Peer-reviewed special issues this year included contributions from the 13th International Conference on Pediatric Mechanical Circulatory Support Systems and Pediatric Cardiopulmonary Perfusion edited by Dr. Akif Undar, and the 25th Congress of the International Society for Mechanical Circulatory Support edited by Dr. Marvin Slepian. Additionally, many editorials highlighted the worldwide survival differences in hemodialysis and perspectives on mechanical circulatory support and stem cell therapies for cardiac support. We take this time also to express our gratitude to our authors for offering their work to this journal. We offer our very special thanks to our reviewers who give so generously of time and expertise to review, critique, and especially provide meaningful suggestions to the author's work whether eventually accepted or rejected. Without these excellent and dedicated reviewers the quality expected from such a journal could not be possible. We also express our special thanks to our Publisher, John Wiley & Sons for their expert attention and support in the production and marketing of Artificial Organs. We look forward to reporting further advances in the coming years.

Red blood cell mechanical sensitivity improves in patients with sickle cell disease undergoing chronic transfusion after prolonged, subhemolytic shear exposure

BACKGROUND

Sickle cell disease (SCD) is a genetically inherited hemoglobinopathy in which deoxygenated hemoglobin S polymerizes, leading to stiff red blood cells (RBCs) and inefficient microcirculatory blood flow. Transfusion therapy acts as primary and secondary prevention of ischemic stroke in SCD. Whether blood transfusion alters the mechanical sensitivity (MS) of RBCs to prolonged subhemolytic shear stress (shear) is unknown. We hypothesized that individuals with SCD undergoing chronic blood transfusion would have improved sensitivity to shear, compared with patients not undergoing transfusion therapy.

STUDY DESIGN AND METHODS

Blood suspensions from individuals with SCD not receiving (n = 15) and receiving (n = 15) chronic simple transfusion were conditioned to shear (1, 4, 16, 32, and 64 Pa) for various durations (1, 4, 16, 32, and 64 sec), and then deformability of RBCs was immediately measured. Healthy young controls (n = 15) were included for reference. A surface mesh was interpolated using the data to determine the effect of blood transfusion on MS of RBCs.

RESULTS

There was impaired RBC deformability to prolonged supraphysiologic shear in both SCD groups; however, MS improved in transfused patients when exposed to prolonged physiologic shear. Furthermore, in the transfused patients with SCD, the threshold above which subhemolytic damage occurs was similar to controls.

CONCLUSION

We found that chronic transfusion therapy normalizes the MS threshold above which RBC subhemolytic damage occurs after prolonged shear exposure in SCD. An important and novel finding in transfused patients with SCD was the improvement in RBC deformability in response to prolonged shear exposure over the physiologic range.

Susceptibility of density-fractionated erythrocytes to subhaemolytic mechanical shear stress

INTRODUCTION:

Accumulating evidence demonstrates that subhaemolytic mechanical stresses, typical of circulatory support, induce physical and biochemical changes to red blood cells. It remains unclear, however, whether cell age affects susceptibility to these mechanical forces. This study thus examined the sensitivity of density-fractionated red blood cells to sublethal mechanical stresses.

METHODS:

Red blood cells were isolated and washed twice, with the least and most dense fractions being obtained following centrifugation (1500 g × 5 min). Red blood cell deformability was determined across an osmotic gradient and a range of shear stresses (0.3-50 Pa). Cell deformability was also quantified before and after 300 s exposure to shear stresses known to decrease (64 Pa) or increase (10 Pa) red blood cell deformability. The time course of accumulated sublethal damage that occurred during exposure to 64 Pa was also examined.

RESULTS:

Dense red blood cells exhibited decreased capacity to deform when compared with less dense cells. Cellular response to mechanical stimuli was similar in trend for all red blood cells, independent of density; however, the magnitude of impairment in cell deformability was exacerbated in dense cells. Moreover, the rate of impairment in cellular deformability, induced by 64 Pa, was more rapid for dense cells. Relative improvement in red blood cell deformability, due to low-shear conditioning (10 Pa), was consistent for both cell populations.

CONCLUSION:

Red blood cell populations respond differently to mechanical stimuli: older (more dense) cells are highly susceptible to sublethal mechanical trauma, while cell age (density) does not appear to alter the magnitude of improved cell deformability following low-shear conditioning.

Effects and influencing factors on hemorheological variables taken into consideration in surgical pathophysiology research

In surgical pathophysiology ischemia-reperfusion, inflammatory processes, sepsis, vascular interventions, tissue trauma, shock, all mean conditions in which hemorheological parameters show alterations. Despite of numerous clinical and experimental studies, the in vivo hemorheology is not completely understood yet, and several fundamental questions still need to be answered. Investigating these issues, experimental surgical models are important, in point of view of the translational research as well. In this paper we aimed to make an attempt on summarizing the possible factors and conditions that might have an effect on hemorheological results in experimental surgical studies. Hemorheological parameters show alterations in surgical pathophysiological processes in a complex way. However, the changes are dominantly non-specific. Standardized experimental conditions, related to the experimental animal (species, animal welfare) anesthesia-medications, operation, sampling and, if applicable, conditions of the postoperative period, are inevitable for a safe assessment of valuable (hemorheological) results. Parallel investigations - such as microcirculatory monitoring, imaging techniques, other laboratory methods, histomorphology- have great importance, together with individual analysis of changes, for a better understanding of the changes and for comparability with clinical results.

Experimental measurement and numerical modelling of dye washout for investigation of blood residence time in ventricular assist devices

Ventricular assist devices have become the standard therapy for end-stage heart failure. However, their use is still associated with severe adverse events related to the damage done to the blood by fluid dynamic stresses. This damage relates to both the stress magnitude and the length of time the blood is exposed to that stress. We created a dye washout technique which combines experimental and numerical approaches to measure the washout times of ventricular assist devices. The technique was used to investigate washout characteristics of three commercially available and clinically used ventricular assist devices: the CentriMag, HVAD and HeartMate II. The time taken to reach 5% dye concentration at the outlet (T05) was used as an indicator of the total residence time. At a typical level of cardiac support, 5 L/min and 100 mmHg, T05 was 0.93, 0.28 and 0.16 s for CentriMag, HVAD and HeartMate II, respectively, and increased to 5.06, 1.64 and 0.96 s for reduced cardiac support of 1 L/min. Regional variations in washout characteristics are described in this article. While the volume of the flow domain plays a large role in the differences in T05 between the ventricular assist devices, after standardising for ventricular assist device volume, the secondary flow path was found to increase T05 by 35%. The results explain quantitatively, for the first time, why the CentriMag, which exerts low shear stress magnitude, has still been found to cause acquired von Willebrand Syndrome in patients.