scholarly journals Beyond the Definitions of the Phenotypic Complications of Sickle Cell Disease: An Update on Management

2012 ◽  
Vol 2012 ◽  
pp. 1-55 ◽  
Author(s):  
Samir K. Ballas ◽  
Muge R. Kesen ◽  
Morton F. Goldberg ◽  
Gerard A. Lutty ◽  
Carlton Dampier ◽  
...  
Keyword(s):  
Sickle Cell Disease ◽  
Point Mutation ◽  
Sickle Cell ◽  
Globin Gene ◽  
Single Point ◽  
Acute Chest Syndrome ◽  
Single Point Mutation ◽  
Cell Disease ◽  
Exon 1 ◽  
Abnormal Hemoglobin

The sickle hemoglobin is an abnormal hemoglobin due to point mutation (GAG → GTG) in exon 1 of theβglobin gene resulting in the substitution of glutamic acid by valine at position 6 of theβglobin polypeptide chain. Although the molecular lesion is a single-point mutation, the sickle gene is pleiotropic in nature causing multiple phenotypic expressions that constitute the various complications of sickle cell disease in general and sickle cell anemia in particular. The disease itself is chronic in nature but many of its complications are acute such as the recurrent acute painful crises (its hallmark), acute chest syndrome, and priapism. These complications vary considerably among patients, in the same patient with time, among countries and with age and sex. To date, there is no well-established consensus among providers on the management of the complications of sickle cell disease due in part to lack of evidence and in part to differences in the experience of providers. It is the aim of this paper to review available current approaches to manage the major complications of sickle cell disease. We hope that this will establish another preliminary forum among providers that may eventually lead the way to better outcomes.

scholarly journals Selenium Deficiency in a Mouse Model of Sickle Cell Disease Resulted in Increased Oxygen Consumption and Aberrant Mitochondrial Retention (OR11-05-19)

2019 ◽  
Vol 3 (Supplement_1) ◽  
Author(s):  
Lenny Hong ◽  
Ramasamy Jagadeeswaran ◽  
Robert Molokie ◽  
Donald Lavelle ◽  
Angela Rivers ◽  
...  
Keyword(s):  
Oxygen Consumption ◽  
Sickle Cell Disease ◽  
Mouse Model ◽  
Sickle Cell ◽  
Globin Gene ◽  
Single Point ◽  
Selenium Deficiency ◽  
Single Point Mutation ◽  
Cell Disease ◽  
Deficient Diet

Abstract Objectives Sickle Cell Disease (SCD) is caused by a single point mutation in the β-globin gene, resulting in the polymerization of the altered hemoglobin βS in hypoxic conditions, affecting millions of people worldwide. Previous studies have shown that there are lower selenium levels and reduced activity of the antioxidant selenoprotein GPX1 in SCD patients. The objective of this study was to investigate the consequences of selenium deficiency in a SCD mouse model. Methods Humanized SCD (HbSS) mice (Townes model) and wild type (HbAA) mice were purchased from Jackson Laboratories (Bar Harbor, ME). Mice were fed either a selenium-deficient (<0.01 mg/kg) or a selenium adequate (0.1 mg/kg) diet for 4 weeks. Hematological testing was performed using the ADVIATM 120 analyzer (Bayer Corporation, NY). Mitochondrial retention and reactive oxygen species (ROS) were measured by flow cytometry with a BD LSRFortessaTM analyzer using Kaluza analysis software (Beckman Coulter, CA). The oxygen consumption rate (OCR) was measured from isolated red blood cells (RBCs) in real time using the Seahorse Extracellular Analyzer (Agilent, CA). Results RBCs normally eject their mitochondria before reaching maturity. However, a previous study demonstrated that there was increased RBC mitochondrial retention in SCD mice and patients when compared to controls. Feeding SCD mice a selenium deficient diet resulted in increased retention of mitochondria in RBCs (26% + 6.9%, 5% + 3.5%, n = 3, P < 0.01), decreased hemoglobin levels (5.7 + 0.17 g/dl, 7.0 + 0.83 g/dl, n = 3, P < 0.05), and an increased OCR of the RBCs (P < 0.01) in these animals when compared to SCD mice fed a selenium adequate diet. Conclusions Providing humanized SCD mice a selenium deficient diet resulted in increased mitochondrial retention in mature RBCs, decrease hemoglobin levels, and increased RBC oxygen consumption. RBC retention of mitochondria is associated with increased ROS and hemolysis, potentially contributing to the pain and vaso-occlusive crises that occur in the disease. These studies indicate that selenium deficiency may contribute to the severity of symptoms experienced by patients with SCD. Funding Sources This work is supported by a grant from the NIH.

scholarly journals Sickle Cell Anemia: A review on the most severe form of Sickle Cell Disease

Bionatura ◽  
2019 ◽  
Vol 02 (Bionatura Conference Serie) ◽  
Author(s):  
María Belén Paredes ◽  
María Eugenia Sulen
Keyword(s):  
Sickle Cell Disease ◽  
Sickle Cell ◽  
Sickle Cell Anemia ◽  
Globin Gene ◽  
Single Point ◽  
Clinical Manifestations ◽  
Severe Form ◽  
Single Point Mutation ◽  
Cell Disease ◽  
Hemoglobin S

Sickle cell disease (SCD) is a group of hereditary disorders caused by a single point mutation in the β-globin gene. This mutation results in the formation of a mutated hemoglobin S (HbS) and the consequent sickle phenotype of erythrocytes. SCD is common in regions of malaria endemicity. However, changes in population dynamics enabled the movement of the mutated gene to other areas such as North America and Europe. Sickle cell anemia (SCA) is the most severe form of SCD and affects millions of people around the globe. The clinical manifestations of SCA arise primarily from the polymerization of deoxygenated hemoglobin S (deoxyHbS) leading to vascular occlusion and hemolytic anemia. Clinical complications of the disease are derived from deoxyHbS polymerization, but there are several therapeutic strategies to reduce the severity of the symptoms. Gene therapy has arisen as a new therapeutic approach aimed to cure rather than to treat the symptomatology of SCA by targeting the altered β-globin gene for gene correction.

scholarly journals Heme oxygenase-1 gene promoter polymorphism is associated with reduced incidence of acute chest syndrome among children with sickle cell disease

Blood ◽  
2012 ◽  
Vol 120 (18) ◽  
pp. 3822-3828 ◽  
Author(s):  
Christopher J. Bean ◽  
Sheree L. Boulet ◽  
Dorothy Ellingsen ◽  
Meredith E. Pyle ◽  
Emily A. Barron-Casella ◽  
...  
Keyword(s):  
Sickle Cell Disease ◽  
Heme Oxygenase ◽  
Sickle Cell ◽  
Globin Gene ◽  
Fetal Hemoglobin ◽  
Promoter Polymorphism ◽  
Adverse Outcomes ◽  
Acute Chest Syndrome ◽  
Heme Oxygenase 1 ◽  
Cell Disease

Abstract Sickle cell disease is a common hemolytic disorder with a broad range of complications, including vaso-occlusive episodes, acute chest syndrome (ACS), pain, and stroke. Heme oxygenase-1 (gene HMOX1; protein HO-1) is the inducible, rate-limiting enzyme in the catabolism of heme and might attenuate the severity of outcomes from vaso-occlusive and hemolytic crises. A (GT)n dinucleotide repeat located in the promoter region of the HMOX1 gene is highly polymorphic, with long repeat lengths linked to decreased activity and inducibility. We examined this polymorphism to test the hypothesis that short alleles are associated with a decreased risk of adverse outcomes (hospitalization for pain or ACS) among a cohort of 942 children with sickle cell disease. Allele lengths varied from 13 to 45 repeats and showed a trimodal distribution. Compared with children with longer allele lengths, children with 2 shorter alleles (4%; ≤ 25 repeats) had lower rates of hospitalization for ACS (incidence rate ratio 0.28, 95% confidence interval, 0.10-0.81), after adjusting for sex, age, asthma, percentage of fetal hemoglobin, and α-globin gene deletion. No relationship was identified between allele lengths and pain rate. We provide evidence that genetic variation in HMOX1 is associated with decreased rates of hospitalization for ACS, but not pain. This study is registered at www.clinicaltrials.gov as #NCT00072761.

scholarly journals Development of β-globin gene correction in human hematopoietic stem cells as a potential durable treatment for sickle cell disease

2021 ◽  
Vol 13 (598) ◽  
pp. eabf2444
Author(s):  
Annalisa Lattanzi ◽  
Joab Camarena ◽  
Premanjali Lahiri ◽  
Helen Segal ◽  
Waracharee Srifa ◽  
...  
Keyword(s):  
Sickle Cell Disease ◽  
Sickle Cell ◽  
Drug Product ◽  
Globin Gene ◽  
Monogenic Disease ◽  
Single Point Mutation ◽  
Cell Disease ◽  
Gene Correction ◽  
Hematopoietic Stem ◽  
Virus Serotype

Sickle cell disease (SCD) is the most common serious monogenic disease with 300,000 births annually worldwide. SCD is an autosomal recessive disease resulting from a single point mutation in codon six of the β-globin gene (HBB). Ex vivo β-globin gene correction in autologous patient-derived hematopoietic stem and progenitor cells (HSPCs) may potentially provide a curative treatment for SCD. We previously developed a CRISPR-Cas9 gene targeting strategy that uses high-fidelity Cas9 precomplexed with chemically modified guide RNAs to induce recombinant adeno-associated virus serotype 6 (rAAV6)–mediated HBB gene correction of the SCD-causing mutation in HSPCs. Here, we demonstrate the preclinical feasibility, efficacy, and toxicology of HBB gene correction in plerixafor-mobilized CD34+ cells from healthy and SCD patient donors (gcHBB-SCD). We achieved up to 60% HBB allelic correction in clinical-scale gcHBB-SCD manufacturing. After transplant into immunodeficient NSG mice, 20% gene correction was achieved with multilineage engraftment. The long-term safety, tumorigenicity, and toxicology study demonstrated no evidence of abnormal hematopoiesis, genotoxicity, or tumorigenicity from the engrafted gcHBB-SCD drug product. Together, these preclinical data support the safety, efficacy, and reproducibility of this gene correction strategy for initiation of a phase 1/2 clinical trial in patients with SCD.

scholarly journals Presentation, Management and Outcomes of COVID-19 Patients with Sickle Cell Disease

Blood ◽  
2020 ◽  
Vol 136 (Supplement 1) ◽  
pp. 29-30
Author(s):  
Nwabundo Anusim ◽  
Ruby Gupta ◽  
Hycienth O Ahaneku ◽  
Candace Franklin ◽  
Savitha Balaraman ◽  
...  
Keyword(s):  
Sickle Cell Disease ◽  
Sickle Cell ◽  
Respiratory Symptoms ◽  
Bone Pain ◽  
Globin Gene ◽  
Morbidity And Mortality ◽  
Polymerase Chain Reaction Test ◽  
Acute Chest Syndrome ◽  
Shortness Of Breath ◽  
Cell Disease

Background Sickle cell disease (SCD) is an inherited disorder of red blood cell (RBC) caused by a mutation in the beta-globin gene resulting in abnormal hemoglobin known as hemoglobin S (HbS) or the sickle hemoglobin. Several clinical variants of SCD have been elucidated, all driven by two fundamental pathophysiologic processes: RBC hemolysis and intermittent vaso-occlusive vasculopathy resulting in tissue ischemia/infarction. These two processes underscore the many complications and eventual multi-organ damage that may develop in patients with the most severe types of SCD. Cardiopulmonary complications including heart failure, pulmonary hypertension and acute chest syndrome (ACS) are major drivers of morbidity and mortality among patients with SCD. With regards to ACS, patients often present with fever, cough and shortness of breath caused by vaso-occlusive crisis affecting the lungs. This is particular concerning in view of its similar features to symptomatic COVID-19 infection. Methods We retrospectively identified SCD patients with COVID-19 infection admitted to Beaumont hospitals in Michigan between March 1st 2020 and July 1st 2020. Data was abstracted using the ICD 10 code of U07. 1 for COVID-19, ICD 9 and 10 codes of 282.60 and D57 for sickle cell disease. We excluded patients with sickle cell trait. Data regarding the demographics, presentation, management and outcomes were abstracted. Results A total of eleven patients with sickle cell disease were identified as having a positive SARS-Cov19 polymerase chain reaction test (Table I). All were African American and predominantly female (64%) with a mean age of 44 (22-60) years and mean BMI of 30.2 kg/m2. Genotypes identified were HbSS in 5 (45%) patients, HbSC in 4 (36%), HbS/beta-thalassemia in 1 (9%) and HbS/alpha-thalassemia in 1 (9%). All of the patients had seen a haematologist since their diagnosis but none of the patients were on hydroxyurea, voxeloter, L-glutamine or crizanlizumab at admission. The predominant clinical presentation was fever, chest pain, chills, exertional shortness of breath and cough but this was not consistent across all patients. All the patients were managed with intravenous hydration, pain management as well as hydroxychloroquine/azithromycin per institutional guideline at that time. Three patients (cases 1-3) had recurrent visits to the hospital for similar symptoms and new bone pain crises. Case 1 had a pulmonary embolus which was evident on re-admission. Two patients (cases 3 and 10) succumbed to COVID-19. Two patients (cases 5 and 7) presented with bone pain crisis and no respiratory symptoms, but chest imaging was suggestive of COVID-19 infection necessitating treatment with antibiotics, possibly indicating that the virus can trigger vaso-occlusive crises without respiratory symptoms. Case 8 had a high Charlson comorbidity index and age over 60, had the lengthiest hospital stay complicated by renal failure and polyneuropathy, and was discharged to a long-term acute care facility: an outcome which is consistent with current data showing that the elderly and unfit patients are more likely to have a higher morbidity and mortality with COVID-19. Conclusion To date, there no compelling evidence to provide guidelines for the management of SCD patients with COVID-19. However, following existing recommendations in managing acute chest syndrome and those for COVID-19 symptomatic infection, is a good place to start. We continue to seek to improve management of these patients as new evidence of successful treatment emerges, and also encourage patients to participate in clinical trials. Disclosures No relevant conflicts of interest to declare.

scholarly journals Thromboinflammatory mechanisms in sickle cell disease - challenging the hemostatic balance

Haematologica ◽  
2020 ◽  
Vol 105 (10) ◽  
pp. 2380-2390 ◽  
Author(s):  
Nicola Conran ◽  
Erich V. De Paula
Keyword(s):  
Sickle Cell Disease ◽  
Sickle Cell ◽  
Ischemia Reperfusion ◽  
Organ Damage ◽  
Acute Chest Syndrome ◽  
Cellular Interactions ◽  
Innate Immune Responses ◽  
Cell Disease ◽  
Inflammatory Processes ◽  
Abnormal Hemoglobin

Sickle cell disease (SCD) is an inherited hemoglobinopathy that is caused by the presence of abnormal hemoglobin S (HbS) in red blood cells, leading to alterations in red cell properties and shape, as the result of HbS dexoygenation and subsequent polymerization. SCD pathophysiology is characterized by chronic inflammatory processes, triggered by hemolytic and vaso-occlusive events, which lead to the varied complications, organ damage and elevated mortality seen in individuals with the disease. In association with activation of the endothelium and leukocytes, hemostatic alterations and thrombotic events are well-documented in SCD. Here we discuss the role for inflammatory pathways in modulating coagulation and inducing platelet activation in SCD, due to tissue factor activation, adhesion molecule expression, inflammatory mediator production and the induction of innate immune responses, amongst other mechanisms. Thromboinflammatory pathways may play a significant role in some of the major complications of SCD, such as stroke, venous thromboembolism and possibly acute chest syndrome, besides exacerbating the chronic inflammation and cellular interactions that trigger vaso-occlusion, ischemia-reperfusion processes, and eventually organ damage.

scholarly journals Cardiovascular complications in patients with sickle cell disease

Hematology ◽  
2017 ◽  
Vol 2017 (1) ◽  
pp. 423-430 ◽  
Author(s):  
Mark T. Gladwin
Keyword(s):  
Sickle Cell Disease ◽  
Hemolytic Anemia ◽  
Sickle Cell ◽  
Single Point ◽  
Systolic Pressure ◽  
Cardiovascular Complications ◽  
Left Ventricular ◽  
Pulmonary Artery Systolic Pressure ◽  
Single Point Mutation ◽  
Cell Disease

Abstract Sickle cell disease (SCD) is an autosomal recessive disease in which homozygosity for a single point mutation in the gene encoding the β-globin chain produces hemoglobin S molecules that polymerize within the erythrocyte during deoxygenation; the result is sustained hemolytic anemia and vaso-occlusive events. As patients live to adulthood, the chronic impact of sustained hemolytic anemia and episodic vaso-occlusive episodes leads to progressive end-organ complications. This scenario culminates in the development of 1 or more major cardiovascular complications of SCD for which there are no approved or consensus therapies. These complications include elevated pulmonary artery systolic pressure, pulmonary hypertension, left ventricular diastolic heart disease, dysrhythmia, sudden death, and chronic kidney disease with associated proteinuria, microalbuminuria, and hemoglobinuria. In patients with advancing age, cardiopulmonary organ dysfunction and chronic kidney injury have significant effects on morbidity and premature mortality. Over the last 15 years, a number of tests have been validated in multiple replicate cohort studies that identify patients with SCD at the highest risk of experiencing pulmonary and systemic vasculopathy and death, providing for screening strategies tied to targeted, more aggressive diagnostic and therapeutic interventions.

Fetal Hemoglobin In Sickle Cell Anemia: A Glass Half Full?

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 4691-4691
Author(s):  
Martin H. Steinberg ◽  
David H.K. Chui ◽  
George J. Dover ◽  
Paola Sebastiani ◽  
Abdulrahman Alsultan
Keyword(s):  
Sickle Cell Disease ◽  
Sickle Cell ◽  
Sickle Cell Anemia ◽  
Conflicts Of Interest ◽  
Globin Gene ◽  
Single Agent ◽  
Acute Chest Syndrome ◽  
Cell Disease ◽  
Sickle Erythrocytes ◽  
F Cells

HbF modulates the phenotype of sickle cell anemia by inhibiting deoxyHbS polymerization. HbF is confined to erythrocytes called F-cells that can be detected by FACS when these cells contain sufficient HbF. Measuring the amount of HbF/F-cell is difficult and not clinically available. African-Americans with sickle cell anemia have 2-80% F-cells with an average HbF/F-cell of 6.4±1.6 pg. The distribution of HbF/F-cell is highly individual regardless of HbF level. People with HbS-gene deletion hereditary persistence of HbF (HPFH) have a mean HbF of 30%, and HbF is evenly distributed among their erythrocytes. Polymer is not present in these cells either experimentally or after calculating the HbS polymer fraction at 70% O2 saturation. Therefore, each cell contains about 10 pg. of HbF. DeoxyHbS polymerization is prevented at physiologic venous and capillary O2 saturations of 40-70% when HbF/F-cell is 9-12 pgs. We call this the “protective” level of HbF. F-cells need not contain “protective” levels of HbF. Some β-globin gene cluster haplotypes are associated with high HbF. Carriers of these haplotypes can have milder disease. Nevertheless, even patients with high HbF can have frequent painful episodes, acute chest syndrome and osteonecrosis. Patients with HbS-δβ thalassemia have 15 to 25% HbF but are anemic and have vasoocclusive complications, albeit less often than in sickle cell anemia. Hydroxyurea reduces the morbidity and mortality of sickle cell anemia, an effect likely to be mediated by its induction of HbF. Patients treated with hydroxyurea are better and probably live longer, but adults are anemic and rarely asymptomatic. In all these patient groups, HbF is unevenly distributed among erythrocytes. In contrast, people with HbS-HPFH are nearly asymptomatic and not anemic. The failure of HbF to modulate uniformly all complications of sickle cell disease might be related to the heterogeneous concentration of HbF in sickle erythrocytes. HbF is associated with protection from the development of certain disease subphenotypes but has limited prognostic value in individuals. In many cross-sectional studies, high HbF was associated with a reduced rate of acute painful episodes, fewer leg ulcers, less osteonecrosis, less frequent acute chest syndromes and reduced disease severity. HbF had a weak or no clear association with priapism, urine albumin excretion, stroke and silent cerebral infarction, systemic blood pressure and tricuspid regurgitant velocity. Perhaps this is because intravascular hemolysis of cells with little or no HbF causes nitric oxide scavenging, or because these complications are less dependent on HbS polymerization. No study provides information on the concentration of HbF/F-cell other than providing the relatively meaningless calculated mean value. Rather than the total number of F-cells or the concentration of HbF in the hemolysate, HbF/F-cell and the proportion of F-cells that have “protective” HbF is the most critical predictor of the likelihood of some disease subphenotypes. Hypothetical distributions of HbF-cells with different levels of HbF/F-cell can be plotted for different concentrations of HbF. With mean HbF levels of 5%, 10% and 20%, and HbF content per cell of 1.5, 3 and 6 pg., assuming a fixed mean, the variance was changed to show how the distribution of HbF per cell can greatly vary, even if the mean is constant. For example, with 20% HbF, as few as 1% and as many as 24% of cells have “protective” HbF. When HbF is lower, few or no “protected” cells can be present. Due to the heterogeneous concentrations of HbF, HbS can polymerize in some F-cells that have sub-polymer inhibiting concentrations of HbF. Inducing high levels of HbF is one approach to treating sickle cell disease. Inactivating BCL11A, a repressor of γ-globin gene expression, abrogates sickle cell disease in transgenic sickle mice. Their HbF was distributed homogeneously, and their phenotype mimicked HbS-HPFH. If it becomes possible in humans to target BCL11A or its pathway with agents that affect gene transcription, will it result in pancellular HbF? Broadening the distribution of HbF amongst sickle erythrocytes with drugs like hydroxyurea that effect the kinetics of erythropoiesis, coupled with an agent whose primary mechanism of action is to increase the transcription of the γ-globin genes, might be the most fruitful approach to HbF induction therapy and more efficacious than single agent treatment. Disclosures: No relevant conflicts of interest to declare.

Sickle Cell Disease

2015 ◽  
Author(s):  
Caroline Freiermuth ◽  
Idan Cudykier
Keyword(s):  
Sickle Cell Disease ◽  
Sickle Cell ◽  
Blood Cells ◽  
Genetic Basis ◽  
Globin Gene ◽  
The United States ◽  
Acute Chest Syndrome ◽  
Cell Disease ◽  
The Past ◽  
Pain Medications

Sickle cell disease affects between 70,000 and 90,000 individuals in the United States, the majority of whom are of African-American descent. The genetic basis of the disease is an abnormality in the β-globin gene, which causes the red blood cells to change to a “sickle” shape due to low oxygenation. The life span of patients with this disease has improved over the past few decades, although morbidity remains high. This review covers the pathophysiology of sickle cell disease and the stabilization and assessment, diagnosis and treatment, maintenance and preventive therapies, and cure of patients with sickle cell disease. Figures show hemoglobin electrophoresis; age at death for individuals with sickle cell disease in the years 1979, 1989, 1999, and 2006; sickled cells blocking blood flow; acute chest syndrome; dactylitis; and avascular necrosis. Tables list important trials, topics in need of further research, common complications, most common intravenous pain medications, and indications for transfusion. This review contains 6 highly rendered figures, 5 tables, 97 references, and a list of educational resources.

scholarly journals Neutrophil-Platelet Micro-Emboli Enable Vaso-Occlusion in Sickle Cell Disease

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 2695-2695
Author(s):  
Prithu Sundd ◽  
Maritza Jimenez ◽  
Enrico M Novelli ◽  
Mark T Gladwin
Keyword(s):  
Endothelial Cells ◽  
Sickle Cell Disease ◽  
Sickle Cell ◽  
Globin Gene ◽  
Cellular Adhesion ◽  
Epifluorescence Microscopy ◽  
Single Point Mutation ◽  
Cellular Interactions ◽  
Cell Disease ◽  
Cellular Adhesion Molecule

Abstract Introduction: Sickle Cell Disease (SCD) is an autosomal-recessive-hemolytic disorder caused by a single point mutation in the β-globin gene that leads to sickling of RBCs under deoxygenated condition. Sickle RBCs (sRBCs) are not only rigid but also express adhesion molecules, which are not normally expressed on RBCs. The sticky and rigid sRBCs are believed to get trapped in blood vessels along with leukocytes to cause vaso-occlusion, which is the predominant pathophysiology underlying acute pain crisis in SCD patients. The process of sickling and vaso-occlusion leads to sRBC hemolysis, which releases hemoglobin, ADP and other RBC contents into the blood giving rise to a pro-inflammatory and pro-coagulant state, characterized by activated leukocytes, platelets, endothelial cells (ECs), tissue factor (TF) and enhanced adhesion of these cells to each other. Leukocyte–endothelium adhesion starts with leukocyte rolling mediated by P-selectin-glycoprotein-ligand (PSGL)-1 on leukocytes binding to P-selectin on endothelium. Rolling is followed by firm arrest, which is mediated by activated β­2-integrins (LFA-1 and Mac-1) on the leukocytes binding to inter-cellular-adhesion-molecule (ICAM)-1 on endothelium. Although neutrophils have been shown to play a role in the onset of vaso-occlusion by interacting with sRBCs and platelets in cremaster venules of SCD mice; the cellular, molecular and biophysical mechanisms that enable vaso-occlusion in SCD patients are not known. Materials and Methods: Freshly collected heparinized blood from SCD patients and race matched control subjects was perfused through a polydimethylsiloxane (PDMS) based microfluidic flow chamber with a glass bottom coated with either human micro-vascular endothelial cells or a cocktail of recombinant human P-selection, ICAM-1 and IL-8 at a venular/arteriolar wall shear stress. Fluorochrome conjugated Abs against CD16, CD235a and CD49b were added to the blood to stain neutrophils, sRBCs and platelets, respectively, and cellular interactions were recorded using multi-color Quantitative Dynamic Footprinting (qDF; Sundd et al Nature Methods 2010) or epifluorescence microscopy. Specificity of cellular interactions was tested using function blocking Abs against human Mac-1, LFA-1, P-selectin and PSGL-1. Results: SCD patients had much higher number of circulating neutrophils than control patients. Neutrophils rolled, arrested and then captured free flowing platelets in both SCD and control blood. However, significantly larger number of neutrophils rolled and arrested in SCD blood than control blood. As a result, much higher number of platelets was captured by arrested neutrophils in SCD blood than control blood, which led to the formation of neutrophil-platelet micro-emboli. The micro-emboli formation was mediated by a unique biophysical mechanism, which involved PSGL-1 and Mac-1 on neutrophils binding to P-selectin and GPIbα on platelets, respectively. Conclusion: Vaso-occlusion involves a cascade of adhesive events. First, neutrophils roll and arrest at the site of vaso-occlusion. Second, arrested neutrophils capture free flowing platelets and RBCs to form micro-emboli. Third, eventually these micro-emboli give rise to micro-thrombi, which cause stasis of blood flow. Acknowledgments: This study is supported by 11SDG7340005 from the American Heart Association (P.S.), VMI start-up funds (P.S.) and CBTP-T32 fellowship HL076124 (M.J). Disclosures No relevant conflicts of interest to declare.

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