Rapid measurement of hemoglobin-oxygen dissociation by leveraging Bohr effect and Soret band bathochromic shift.

Oxygen (O2) binds to hemoglobin (Hb) in the lungs and is then released (dissociated) in the tissues. The Bohr effect is a physiological mechanism that governs the affinity of Hb for O2 based on pH, where a lower pH results in a lower Hb-O2 affinity and higher Hb-O2 dissociation. Hb-O2 affinity and dissociation are crucial for maintaining aerobic metabolism in cells and tissues. Despite its vital role in human physiology, Hb-O2 dissociation measurement is underutilized in basic research and in clinical laboratories, primarily due to the technical complexity and limited throughput of existing methods. We present a rapid Hb-O2 dissociation measurement approach by leveraging the Bohr effect and detecting the optical shift in the Soret band that corresponds to the light absorption by the heme group in Hb. This new method reduces Hb-O2 dissociation measurement time from hours to minutes. We show that Hb deoxygenation can be accelerated chemically at the optimal pH of 6.9. We show that time and pH-controlled deoxygenation of Hb results in rapid and distinct conformational changes in its tertiary structure. These molecular conformational changes are manifested as significant, detectable shifts in Hb's optical absorption spectrum, particularly in the characteristic Soret band (414 nm). We extensively validated the method by testing human blood samples containing normal Hb and Hb variants. We show that rapid Hb-O2 dissociation can be used to screen for and detect Hb-O2 affinity disorders and to evaluate the function and efficacy of Hb-modifying therapies. The ubiquity of optical absorption spectrophotometers positions this approach as an accessible, rapid, and accurate Hb-O2 dissociation measurement method for basic research and clinical use. We anticipate this method's broad adoption will democratize the diagnosis and prognosis of Hb disorders, such as sickle cell disease. Further, this method has the potential to transform the research and development of new targeted and genome-editing-based therapies that aim to modify or improve Hb-O2 affinity.

Catch bonds in sickle cell disease: Shear-enhanced adhesion of red blood cells to laminin.

Could the phenomenon of catch bonding-force-strengthened cellular adhesion-play a role in sickle cell disease, where abnormal red blood cell (RBC) adhesion obstructs blood flow? Here, we investigate the dynamics of sickle RBCs adhering to a surface functionalized with the protein laminin (a component of the extracellular matrix around blood vessels) under physiologically relevant microscale flow. First, using total internal reflectance microscopy we characterize the spatial fluctuations of the RBC membrane above the laminin surface before detachment. The complex dynamics we observe suggest the possibility of catch bonding, where the mean detachment time of the cell from the surface initially increases to a maximum and then decreases as a function of shear force. We next conduct a series of shear-induced detachment experiments on blood samples from 25 sickle cell disease patients, quantifying the number and duration of adhered cells under both sudden force jumps and linear force ramps. The experiments reveal that a subset of patients does indeed exhibit catch bonding. By fitting the data to a theoretical model of the bond dynamics, we can extract the mean bond lifetime versus force for each patient. The results show a striking heterogeneity among patients, both in terms of the qualitative behavior (whether or not there is catch bonding) and in the magnitudes of the lifetimes. Patients with large bond lifetimes at physiological forces are more likely to have certain adverse clinical features, like a diagnosis of pulmonary arterial hypertension and intracardiac shunts. By introducing an in vitro platform for fully characterizing RBC-laminin adhesion dynamics, our approach could contribute to the development of patient-specific antiadhesive therapies for sickle cell disease. The experimental setup is also easily generalizable to studying adhesion dynamics in other cell types, for example, leukocytes or cancer cells, and can incorporate disease-relevant environmental conditions like oxygen deprivation.

Sickle red blood cell-derived extracellular vesicles activate endothelial cells and enhance sickle red cell adhesion mediated by von Willebrand factor.

Endothelial activation and sickle red blood cell (RBC) adhesion are central to the pathogenesis of sickle cell disease (SCD). Quantitatively, RBC-derived extracellular vesicles (REVs) are more abundant from SS RBCs compared with healthy RBCs (AA RBCs). Sickle RBC-derived REVs (SS REVs) are known to promote endothelial cell (EC) activation through cell signalling and transcriptional regulation at longer terms. However, the SS REV-mediated short-term non-transcriptional response of EC is unclear. Here, we examined the impact of SS REVs on acute microvascular EC activation and RBC adhesion at 2 h. Compared with AA REVs, SS REVs promoted human pulmonary microvascular ECs (HPMEC) activation indicated by increased von Willebrand factor (VWF) expression. Under microfluidic conditions, we found abnormal SS RBC adhesion to HPMECs exposed to SS REVs. This enhanced SS RBC adhesion was reduced by haeme binding protein haemopexin or VWF cleaving protease ADAMTS13 to a level similar to HPMECs treated with AA REVs. Consistent with these observations, haemin- or SS REV-induced microvascular stasis in SS mice with implanted dorsal skin-fold chambers that was inhibited by ADAMTS13. The adhesion induced by SS REVs was variable and was higher with SS RBCs from patients with increased markers of haemolysis (lactate dehydrogenase and reticulocyte count) or a concomitant clinical diagnosis of deep vein thrombosis. Our results emphasise the critical contribution made by REVs to the pathophysiology of SCD by triggering acute microvascular EC activation and abnormal RBC adhesion. These findings may help to better understand acute pathophysiological mechanism of SCD and thereby the development of new treatment strategies using VWF as a potential target.

Integrating deep learning with microfluidics for biophysical classification of sickle red blood cells adhered to laminin.

Sickle cell disease, a genetic disorder affecting a sizeable global demographic, manifests in sickle red blood cells (sRBCs) with altered shape and biomechanics. sRBCs show heightened adhesive interactions with inflamed endothelium, triggering painful vascular occlusion events. Numerous studies employ microfluidic-assay-based monitoring tools to quantify characteristics of adhered sRBCs from high resolution channel images. The current image analysis workflow relies on detailed morphological characterization and cell counting by a specially trained worker. This is time and labor intensive, and prone to user bias artifacts. Here we establish a morphology based classification scheme to identify two naturally arising sRBC subpopulations-deformable and non-deformable sRBCs-utilizing novel visual markers that link to underlying cell biomechanical properties and hold promise for clinically relevant insights. We then set up a standardized, reproducible, and fully automated image analysis workflow designed to carry out this classification. This relies on a two part deep neural network architecture that works in tandem for segmentation of channel images and classification of adhered cells into subtypes. Network training utilized an extensive data set of images generated by the SCD BioChip, a microfluidic assay which injects clinical whole blood samples into protein-functionalized microchannels, mimicking physiological conditions in the microvasculature. Here we carried out the assay with the sub-endothelial protein laminin. The machine learning approach segmented the resulting channel images with 99.1±0.3% mean IoU on the validation set across 5 k-folds, classified detected sRBCs with 96.0±0.3% mean accuracy on the validation set across 5 k-folds, and matched trained personnel in overall characterization of whole channel images with R2 = 0.992, 0.987 and 0.834 for total, deformable and non-deformable sRBC counts respectively. Average analysis time per channel image was also improved by two orders of magnitude (∼ 2 minutes vs ∼ 2-3 hours) over manual characterization. Finally, the network results show an order of magnitude less variance in counts on repeat trials than humans. This kind of standardization is a prerequisite for the viability of any diagnostic technology, making our system suitable for affordable and high throughput disease monitoring.

Leukocyte adhesion to P-selectin and the inhibitory role of Crizanlizumab in sickle cell disease: A standardized microfluidic assessment.

Upregulated expression of P-selectin on activated endothelium and platelets significantly contributes to the initiation and progression of vaso-occlusive crises (VOC), a major cause of morbidity in sickle cell disease (SCD). Crizanlizumab (ADAKVEO®), a humanized monoclonal antibody against P-selectin, primarily inhibits the interaction between leukocytes and P-selectin, and has been shown to decrease the frequency of VOCs in clinical trials. However, the lack of reliable in vitro assays that objectively measure leukocyte adhesion to P-selectin remains a critical barrier to evaluating and improving the therapeutic treatment in SCD. Here, we present a standardized microfluidic BioChip whole blood adhesion assay to assess leukocyte adhesion to P-selectin under physiologic flow conditions. Our results demonstrated heterogeneous adhesion by leukocytes to immobilized P-selectin, and dose-dependent inhibition of this adhesion following pre-exposure to Crizanlizumab. Importantly, treatment with Crizanlizumab following adhesion to P-selectin promoted detachment of rolling, but not of firmly adherent leukocytes. Taken together, our results suggest that the microfluidic BioChip system is a promising in vitro assay with which to screen patients, monitor treatment response, and guide current and emerging anti-adhesive therapies in SCD.

Real-time imaging of nanobubble ultrasound contrast agent flow, extravasation, and diffusion through an extracellular matrix using a microfluidic model.

Lipid shell-stabilized nanoparticles with a perfluorocarbon gas-core, or nanobubbles, have recently attracted attention as a new contrast agent for molecular ultrasound imaging and image-guided therapy. Due to their small size (∼275 nm diameter) and flexible shell, nanobubbles have been shown to extravasate through hyperpermeable vasculature (e.g., in tumors). However, little is known about the dynamics and depth of extravasation of intact, acoustically active nanobubbles. Accordingly, in this work, we developed a microfluidic chip with a lumen and extracellular matrix (ECM) and imaging method that allows real-time imaging and characterization of the extravasation process with high-frequency ultrasound. The microfluidic device has a lumen and is surrounded by an extracellular matrix with tunable porosity. The combination of ultrasound imaging and the microfluidic chip advantageously produces real-time images of the entire length and depth of the matrix. This captures the matrix heterogeneity, offering advantages over other imaging techniques with smaller fields of view. Results from this study show that nanobubbles diffuse through a 1.3 µm pore size (2 mg mL-1) collagen I matrix 25× faster with a penetration depth that was 0.19 mm deeper than a 3.7 µm (4 mg mL-1) matrix. In the 3.7 µm pore size matrix, nanobubbles diffused 92× faster than large nanobubbles (∼875 nm diameter). Decorrelation time analysis was successfully used to differentiate flowing and extra-luminally diffusing nanobubbles. In this work, we show for the first time that combination of an ultrasound-capable microfluidic chip and real-time imaging provided valuable insight into spatiotemporal nanoparticle movement through a heterogeneous extracellular matrix. This work could help accurately predict parameters (e.g., injection dosage) that improve translation of nanoparticles from in vitro to in vivo environments.

Motion Blur Microscopy.

Imaging and characterizing the dynamics of cellular adhesion in blood samples is of fundamental importance in understanding biological function. In vitro microscopy methods are widely used for this task, but typically require diluting the blood with a buffer to allow for transmission of light. However whole blood provides crucial mechanical and chemical signaling cues that influence adhesion dynamics, which means that conventional approaches lack the full physiological complexity of living microvasculature. We propose to overcome this challenge by a new in vitro imaging method which we call motion blur microscopy (MBM). By decreasing the source light intensity and increasing the integration time during imaging, flowing cells are blurred, allowing us to identify adhered cells. Combined with an automated analysis using machine learning, we can for the first time reliably image cell interactions in microfluidic channels during whole blood flow. MBM provides a low cost, easy to implement alternative to intravital microscopy, the in vivo approach for studying how the whole blood environment shapes adhesion dynamics. We demonstrate the method's reproducibility and accuracy in two example systems where understanding cell interactions, adhesion, and motility is crucial-sickle red blood cells adhering to laminin, and CAR-T cells adhering to E-selectin. We illustrate the wide range of data types that can be extracted from this approach, including distributions of cell size and eccentricity, adhesion times, trajectories and velocities of adhered cells moving on a functionalized surface, as well as correlations among these different features at the single cell level. In all cases MBM allows for rapid collection and processing of large data sets, ranging from thousands to hundreds of thousands of individual adhesion events. The method is generalizable to study adhesion mechanisms in a variety of diseases, including cancer, blood disorders, thrombosis, inflammatory and autoimmune diseases, as well as providing rich datasets for theoretical modeling of adhesion dynamics.

A microfluidic device for assessment of E-selectin-mediated neutrophil recruitment to inflamed endothelium and prediction of therapeutic response in sickle cell disease.

Neutrophil recruitment to the inflamed endothelium is a multistep process and is of utmost importance in the development of the hallmark vaso-occlusive crisis in sickle cell disease (SCD). However, there lacks a standardized, clinically feasible approach for assessing neutrophil recruitment to the inflamed endothelium for individualized risk stratification and therapeutic response prediction in SCD. Here, we describe a microfluidic device functionalized with E-selectin, a critical endothelial receptor for the neutrophil recruitment process, as a strategy to assess neutrophil binding under physiologic flow in normoxia and clinically relevant hypoxia in SCD. We show that hypoxia significantly enhances neutrophil binding to E-selectin and promotes the formation of neutrophil-platelet aggregates. Moreover, we identified two distinct patient populations: a more severe clinical phenotype with elevated lactate dehydrogenase levels and absolute reticulocyte counts but lowered fetal hemoglobin levels associated with constitutively less neutrophil binding to E-selectin. Mechanistically, we demonstrate that the extent of neutrophil activation correlates with membrane L-selectin shedding, resulting in the loss of ligand interaction sites with E-selectin. We also show that inhibition of E-selectin significantly reduces leukocyte recruitment to activated endothelial cells. Our findings add mechanistic insight into neutrophil-endothelial interactions under hypoxia and provide a clinically feasible means for assessing neutrophil binding to E-selectin using clinical whole blood samples, which can help guide therapeutic decisions for SCD patients.

Kindlin-3 deficiency leads to impaired erythropoiesis and erythrocyte cytoskeleton.

Kindlin-3 (K3) is critical for the activation of integrin adhesion receptors in hematopoietic cells. In humans and mice, K3 deficiency is associated with impaired immunity and bone development, bleeding, and aberrant erythrocyte shape. To delineate how K3 deficiency (K3KO) contributes to anemia and misshaped erythrocytes, mice deficient in erythroid (K3KO∖EpoR-cre) or myeloid cell K3 (K3KO∖Lyz2cre), knockin mice expressing mutant K3 (Q597W598 to AA) with reduced integrin-activation function (K3KI), and control wild-type (WT) K3 mice were studied. Both K3-deficient strains and K3KI mice showed anemia at baseline, reduced response to erythropoietin stimulation, and compromised recovery after phenylhydrazine (PHZ)-induced hemolytic anemia as compared with K3WT. Erythroid K3KO and K3 (Q597W598 to AA) showed arrested erythroid differentiation at proerythroblast stage, whereas macrophage K3KO showed decreased erythroblast numbers at all developmental stages of terminal erythroid differentiation because of reduced erythroblastic island (EBI) formation attributable to decreased expression and activation of erythroblast integrin α4ß1 and macrophage αVß3. Peripheral blood smears of K3KO∖EpoR-cre mice, but not of the other mouse strains, showed numerous aberrant tear drop-shaped erythrocytes. K3 deficiency in these erythrocytes led to disorganized actin cytoskeleton, reduced deformability, and increased osmotic fragility. Mechanistically, K3 directly interacted with F-actin through an actin-binding site K3-LK48. Taken together, these findings document that erythroid and macrophage K3 are critical contributors to erythropoiesis in an integrin-dependent manner, whereas F-actin binding to K3 maintains the membrane cytoskeletal integrity and erythrocyte biconcave shape. The dual function of K3 in erythrocytes and in EBIs establish an important functional role for K3 in normal erythroid function.

Membrane bending and sphingomyelinase-associated, sulfatide-dependent hypoxic adhesion of sickle mature erythrocytes.

Abnormal erythrocyte adhesion owing to polymerization of sickle hemoglobin is central to the pathophysiology of sickle cell disease (SCD). Mature erythrocytes constitute >80% of all erythrocytes in SCD; however, the relative contributions of erythrocytes to acute and chronic vasculopathy in SCD are not well understood. Here, we showed that bending stress exerted on the erythrocyte plasma membrane by polymerization of sickle hemoglobin under hypoxia, enhances sulfatide-mediated abnormal mature erythrocyte adhesion. We hypothesized that sphingomyelinase (SMase) activity, which is upregulated by accumulated bending energy, leads to elevated membrane sulfatide availability, and thus, hypoxic mature erythrocyte adhesion. We found that mature erythrocyte adhesion to laminin in controlled microfluidic experiments is significantly greater under hypoxia than under normoxia (1856 ± 481 vs 78 ± 23, mean ± SEM), whereas sickle reticulocyte (early erythrocyte) adhesion, high to begin with, does not change (1281 ± 299 vs 1258 ± 328, mean ± SEM). We showed that greater mean accumulated bending energy of adhered mature erythrocytes was associated with higher acid SMase activity and increased mature erythrocyte adhesion (P = .022, for acid SMase activity and P = .002 for the increase in mature erythrocyte adhesion with hypoxia, N = 5). In addition, hypoxia results in sulfatide exposure of the erythrocyte membrane, and an increase in SMase, whereas anti-sulfatide inhibits enhanced adhesion of erythrocytes. These results suggest that the lipid components of the plasma membrane contribute to SCD complications. Therefore, sulfatide and the components of its upregulation pathway, particularly SMase, should be further explored as potential therapeutic targets for inhibiting sickle erythrocyte adhesion.

Size and density measurements of single sickle red blood cells using microfluidic magnetic levitation.

Single cells have unique biophysical signatures that can rapidly change during various disease states. For instance, cellular density is an inherent property differing between cell types. Characterizing changes in fundamental density properties down to the single-cell level can reveal sub-populations in pathological states. Here, we have developed a microfluidic, magnetic levitation-based assay (MagDense) that detects minute density differences of individual red blood cells (RBCs) down to 0.0001 g mL-1 resolution. This assay fractionates RBCs based on their density profiles in a non-ionic paramagnetic medium flowing in a capillary microchannel placed between magnets with same poles facing each other. Based on precisely measured levitation height and density of individual RBCs at their specific equilibrium state, we demonstrated that MagDense can accurately analyze the density of sickle hemoglobin (HbS)-containing RBCs and normal hemoglobin (HbA)-containing RBCs. In addition, the precise density and cell size measurements at the single cell level showed three different sub-populations of RBCs in blood samples from individuals with homozygous sickle cell disease receiving blood transfusions; where less dense, HbA-containing RBCs levitated higher, while the denser, HbS-containing RBCs levitated lower. We compared the mean RBC densities of sickle cell disease subjects with healthy controls and found distinctly separated bands of RBC density for each group denoting the likely range of cell densities seen in the blood samples. The high resolution of our method enabled measurement of deviation from the mean RBC density. Moreover, we introduced a new term as a measure of density dispersion, "RBC levitational density width, RLDW". Mean RBC density in sickle cell disease associated with hemoglobin from complete blood count (p = 0.032, linear regression) and RLDW associated with absolute reticulocyte count (ARC) and RBC distribution width (RDW) from complete blood count (p = 0.002 for ARC and p = 003 for RDW, linear regression). Our magnetic levitation-based assay enables rapid, accurate, density-based imaging, profiling and label-free monitoring of single RBCs. Our approach can be broadly applicable to investigate blood cell disorders and the effects of emerging pharmacological and curative therapies in patient outcomes.

OcclusionChip: A functional microcapillary occlusion assay complementary to ektacytometry for detection of small-fraction red blood cells with abnormal deformability.

Red blood cell (RBC) deformability is a valuable hemorheological biomarker that can be used to assess the clinical status and response to therapy of individuals with sickle cell disease (SCD). RBC deformability has been measured by ektacytometry for decades, which uses shear or osmolar stress. However, ektacytometry is a population based measurement that does not detect small-fractions of abnormal RBCs. A single cell-based, functional RBC deformability assay would complement ektacytometry and provide additional information. Here, we tested the relative merits of the OcclusionChip, which measures RBC deformability by microcapillary occlusion, and ektacytometry. We tested samples containing glutaraldehyde-stiffened RBCs for up to 1% volume fraction; ektacytometry detected no significant change in Elongation Index (EI), while the OcclusionChip showed significant differences in Occlusion Index (OI). OcclusionChip detected a significant increase in OI in RBCs from an individual with sickle cell trait (SCT) and from a subject with SCD who received allogeneic hematopoietic stem cell transplant (HSCT), as the sample was taken from normoxic (pO2:159 mmHg) to physiologic hypoxic (pO2:45 mmHg) conditions. Oxygen gradient ektacytometry detected no difference in EI for SCT or HSCT. These results suggest that the single cell-based OcclusionChip enables detection of sickle hemoglobin (HbS)-related RBC abnormalities in SCT and SCD, particularly when the HbS level is low. We conclude that the OcclusionChip is complementary to the population based ektacytometry assays, and providing additional sensitivity and capacity to detect modest abnormalities in red cell function or small populations of abnormal red cells.

Quantifying the influences of radiation therapy on deformability of human red blood cells by dual-beam optical tweezers.

Radiation therapy is widely used as a treatment tool for malignancies. However, radiation-related complications are still unavoidable risks for off-target cells. Little is known about radiation therapy's possible effects on mechanical features of the off-target cells such as human red blood cells (RBCs). RBCs are nucleus-free circulating cells that can deform without losing functionality in healthy conditions. Thus, to evaluate in vitro effects of radiation therapy on the healthy plasma membrane of cells, RBCs were selected as a primary test model. RBCs were exposed to clinically prescribed radiotherapy doses of 2 Gy, 12 Gy and, 25 Gy, and each radiotherapy dose group was compared to a non-irradiated group. Cells were characterized by stretching using dual-beam optical tweezers and compared using the resulting deformability index. The group receiving the highest radiation dose was found statistically distinguishable from the control group (DI0Gy = 0.33 ± 0.08), and revealed the highest deformability index (DI25Gy = 0.38 ± 0.11, p = 0.0068), while no significant differences were found for 2 Gy (DI2Gy = 0.33 ± 0.08, p = 0.9) and 12 Gy (DI12Gy = 0.31 ± 0.09, p = 0.2) dose groups. Based on these findings, we conclude that radiotherapy exposure may alter the deformability of red blood cells depending on the dose amount, and measurement of deformability index by dual-beam optical tweezers can serve as a sensitive biomarker to probe responses of cells to the radiotherapy.

Point-of-care microchip electrophoresis for integrated anemia and hemoglobin variant testing.

Anemia affects over 25% of the world's population with the heaviest burden borne by women and children. Genetic hemoglobin (Hb) variants, such as sickle cell disease, are among the major causes of anemia. Anemia and Hb variant are pathologically interrelated and have an overlapping geographical distribution. We present the first point-of-care (POC) platform to perform both anemia detection and Hb variant identification, using a single paper-based electrophoresis test. Feasibility of this new integrated diagnostic approach is demonstrated via testing individuals with anemia and/or sickle cell disease. Hemoglobin level determination is performed by an artificial neural network (ANN) based machine learning algorithm, which achieves a mean absolute error of 0.55 g dL-1 and a bias of -0.10 g dL-1 against the gold standard (95% limits of agreement: 1.5 g dL-1) from Bland-Altman analysis on the test set. Resultant anemia detection is achieved with 100% sensitivity and 92.3% specificity. With the same tests, subjects with sickle cell disease were identified with 100% sensitivity and specificity. Overall, the presented platform enabled, for the first time, integrated anemia detection and hemoglobin variant identification using a single point-of-care test.

Emerging point-of-care technologies for anemia detection.

Anemia, characterized by low blood hemoglobin level, affects about 25% of the world's population with the heaviest burden borne by women and children. Anemia leads to impaired cognitive development in children, as well as high morbidity and early mortality among sufferers. Anemia can be caused by nutritional deficiencies, oncologic treatments and diseases, and infections such as malaria, as well as inherited hemoglobin or red cell disorders. Effective treatments are available for anemia upon early detection and the treatment method is highly dependent on the cause of anemia. There is a need for point-of-care (POC) screening, early diagnosis, and monitoring of anemia, which is currently not widely accessible due to technical challenges and cost, especially in low- and middle-income countries where anemia is most prevalent. This review first introduces the evolution of anemia detection methods followed by their implementation in current commercially available POC anemia diagnostic devices. Then, emerging POC anemia detection technologies leveraging new methods are reviewed. Finally, we highlight the future trends of integrating anemia detection with the diagnosis of relevant underlying disorders to accurately identify specific root causes and to facilitate personalized treatment and care.