Role of extracellular hemoglobin in thrombosis and vascular occlusion in patients with sickle cell anemia

A novel role of acellular hemoglobin in hemolytic thrombosis

BACKGROUND

Hemolytic thrombosis has been associated with acellular hemoglobin released from damaged red blood cells during hemolysis. However, the precise molecular mechanism underlying acellular hemoglobin-induced thrombosis remains arguable. In this study, we examined the interaction between hemoglobin and the A1 domain of von Willebrand factor (VWF), which is a critical mediator of platelet activation.

METHODS

Previous studies have suggested that the interaction between hemoglobin and the A1 domain of VWF enhances VWF's hemostatic activity. We employed a multidisciplinary investigation to re-examine this interaction, and identified significant differences in binding affinity between the active and inactive forms of A1.

RESULTS

We found that hemoglobin binds more strongly to the active A1 than the inactive form. Using hydrogen‑deuterium exchange mass spectrometry, we identified the specific residues involved in this interaction, which are located on the α1-β2 and β3-α2 loops that are typically covered by the "autoinhibitory module" in the inactive A1. This observation provides a structural explanation for the differential binding affinity between the active and inactive forms of A1. We demonstrated that the binding of hemoglobin to A1 blocks the interaction between GPIbα and VWF, and inhibits VWF-mediated thrombosis in vivo. Furthermore, we found that administration of hemoglobin led to similar levels of thrombocytopenia and microthrombosis in both wildtype and VWF-deficient mice, indicating that the mechanism underlying acellular hemoglobin-induced thrombosis is VWF-independent.

CONCLUSIONS

These findings challenge the previous theory that hemoglobin-induced thrombosis occurs solely through binding with VWF, and provide evidence supporting a novel role for hemoglobin in hemolytic thrombosis.

Hidden behind thromboinflammation: revealing the roles of von Willebrand factor in sickle cell disease pathophysiology

PURPOSE OF REVIEW

This review provides an update on the pathophysiology of sickle cell disease (SCD) with a particular focus on the dysregulation of the von Willebrand factor (VWF) - ADAMTS13 axis that contributes to its pathogenesis. In discussing recent developments, we hope to encourage new and ongoing discussions surrounding therapeutic targets for SCD.

RECENT FINDINGS

Within the last 5 years, the role of VWF in the pathophysiology of SCD has been further elucidated and is now a target of study in ongoing clinical trials.

SUMMARY

The pathophysiology of SCD is multifaceted, as it involves systemwide vascular activation, altered blood rheology, and the activation of immune responses and coagulative pathways. The presence of VWF in excess in SCD, particularly in its largest multimeric form, greatly contributes to its pathogenesis. Understanding the molecular mechanisms that underly the presence of large VWF multimers in SCD will provide further insight into the pathogenesis of SCD and provide specific targets for therapy.

Treatment with recombinant ADAMTS13, alleviates hypoxia/reoxygenation-induced pathologies in a mouse model of human sickle cell disease

BACKGROUND

Sickle cell disease (SCD) is an inherited red blood cell disorder with a causative substitution in the beta-globin gene that encodes beta-globin in hemoglobin. Furthermore, the ensuing vasculopathy in the microvasculature involves heightened endothelial cell adhesion, inflammation, and coagulopathy, all of which contribute to vaso-occlusive crisis (VOC) and the sequelae of SCD. In particular, dysregulation of the von Willebrand factor (VWF) and a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13 (ADAMTS13) axis has been implicated in human SCD pathology.

OBJECTIVES

To investigate the beneficial potential of treatment with recombinant ADAMTS13 (rADAMTS13) to alleviate VOC.

METHODS

Pharmacologic treatment with rADAMTS13 in vitro or in vivo was performed in a humanized mouse model of SCD that was exposed to hypoxia/reoxygenation stress as a model of VOC. Then, pharmacokinetic, pharmacodynamic, and behavioral analyses were performed.

RESULTS

Administration of rADAMTS13 to SCD mice dose-dependently increased plasma ADAMTS13 activity, reduced VWF activity/antigen ratios, and reduced baseline hemolysis (free hemoglobin and total bilirubin) within 24 hours. rADAMTS13 was administered in SCD mice, followed by hypoxia/reoxygenation stress, and reduced VWF activity/antigen ratios in parallel to significantly (p < .01) improved recovery during the reoxygenation phase. Consistent with the results in SCD mice, we demonstrate in a human in vitro system that treatment with rADAMTS13 counteracts the inhibitory activity of hemoglobin on the VWF/ADAMTS13-axis.

CONCLUSION

Collectively, our data provide evidence that relative ADAMTS13 insufficiency in SCD mice is corrected by pharmacologic treatment with rADAMTS13 and provides an effective disease-modifying approach in a human SCD mouse model.

Absence of exaggerated pharmacology by recombinant ADAMTS13 in the rat and monkey

Insufficiency of ADAMTS13 (a disintegrin and metalloprotease with thrombospondin motif repeats-13) is the cause of thrombotic thrombocytopenic purpura (TTP) and contributes in microangiopathy in sickle cell disease (SCD). Recombinant ADAMTS13 effectively cleaves prothrombotic ultra-large von Willebrand factor (VWF) multimers. It is being tested as replacement therapy for TTP, and at supra-physiologic concentrations, for moderating vaso-occlusive crisis in SCD. Deficiencies of VWF, or concomitant treatment with antithrombotic drugs, could pose risks for increased bleeds in these patient populations. The purpose of the experiments was to evaluate the potential of exaggerated pharmacology and temporary bleeding risks associated with rADAMTS13 administration. We utilized safety studies in monkey and tested the effects of administering maximum-feasible doses of rADAMTS13 on nonclinical safety and spontaneous or aggressive bleeds in the rat model. Evaluation of pharmacokinetics, toxicity profiles, and challenge in a tail-tip bleeding model show that treatment with rADAMTS13 did not increase bleeding tendency, either alone, or in combination with enoxaparin or acetylsalicylic-acid. These novel findings demonstrate absence of rADAMTS13 exaggerated pharmacology without spontaneous or aggravated bleeds even at supra-physiologic (>100-fold) plasma concentrations.

Thrombosis associated with mycoplasma pneumoniae infection (Review)

Mycoplasma pneumoniae is a common pathogen causing respiratory infections in children and adults. In addition to respiratory diseases, Mycoplasma pneumoniae is also involved in numerous extrapulmonary diseases. Thrombosis is an extrapulmonary manifestation associated with Mycoplasma pneumoniae infection. In recent years, an increasing number of case reports have been published identifying thrombosis secondary to Mycoplasma pneumoniae infection. In the present study, the available relevant literature in English available on PubMed, Medline and Web of Science was consulted. The results of the present study demonstrated that in patients with thrombosis caused by Mycoplasma pneumoniae infection, some of the factors causing thrombosis are transient and some are due to hereditary thrombophilia. Following timely treatment, the majority of patients recovered completely but some patients had a poor prognosis. The present review focuses on the pathogenesis, clinical features, treatment and prognosis of this crucial issue, which contributes toward the understanding of the disease.

Evaluation of the expression of red blood cell CD36, interleukin-6 and interleukin-8 in sickle cell anemia pediatric patients

Sickle cell anemia (SCA) is a complex multisystem disease characterized by acute and chronic inflammation, with alterations in inflammatory cytokines and adhesion molecules. This case-control study was carried out to assess the levels of CD36, immature reticulocytes, interleukin (IL)-6 and IL8 in SCA patients (in crisis and the steady state) and healthy controls. It included 90 children who were 2-18 years old; 60 with SCA and 30 healthy controls. Complete blood count, total reticulocyte count, reticulocyte subpopulations, immature reticulocyte fraction (IRF), percentage of CD36-positive red blood cells (RBCs), IL-6 and IL-8 levels were evaluated. The total white blood cell (WBC) and neutrophil counts, CD36-positive RBCs percentage, IRF, IL-6 and IL-8 levels were significantly higher in crises than in the steady state (P < 0.05). We also found that patients with SCA had significantly higher reticulocyte, WBC and neutrophil counts, fetal hemoglobin, CD36-positive RBCs percentage, IRF, and IL-6 and IL-8 levels than healthy children (P < 0.05). A significant positive linear correlation was reported between IL-6 and neutrophils during crises (Spearman correlation coefficient = 0.397, P = 0.03). These findings suggest that the levels of adhesion molecules and inflammatory markers and IRF, as evidenced by CD36-positive RBCs, IL-6 and IL-8, are elevated in SCA patients, both during steady state and crises, although these elevations are more marked during crises. Further knowledge about these cytokines and adhesion molecules will help in understanding the pathogenesis and improve therapy of SCA.

The Effect of Use of Individualized Pain Plans in Sickle Cell Patients Presenting to the Emergency Department

STUDY OBJECTIVE

Sickle cell disease (SCD) is an inherited hematologic disorder that affects approximately 100,000 US individuals and results in greater than 200,000 emergency department (ED) visits annually in the United States, with pain being the most common complaint. The objective of this retrospective study is to determine the effect of implementing individualized pain plans in the treatment of patients with SCD in the ED on time to first opioid, length of stay, and disposition.

METHODS

At The Ohio State University Wexner Medical Center, a multidisciplinary group including hematologists and ED physicians was formed and enacted a protocol for using individualized pain plans, with the goal of decreasing time to treatment for patients with SCD who presented to the ED with chief complaint of pain. In this retrospective study, data from the year before through the year of implementation were gathered. Generalized linear models were fit to compare time to first opioid, length of stay, and disposition before and after protocol implementation.

RESULTS

Data showed a 48% decrease in time to first opioid and a 22% decrease in length of ED stay after protocol implementation. No significant change was found in disposition or length of inpatient admission before and after protocol initiation.

CONCLUSION

The use of individualized pain plans in the treatment of patients with SCD in the ED is a useful method of not only ensuring rapid and adequate treatment but also decreasing use of health care resources.

The vaso-occlusive pain crisis in sickle cell disease: Definition, pathophysiology, and management

Early diagnosis, treatment, and prevention of a vaso-occlusive crisis (VOC) are critical to the management of patients with sickle cell disease. It is essential to differentiate between VOC-associated pain and chronic pain, hyperalgesia, neuropathy, and neuropathic pain. The pathophysiology of VOCs includes polymerization of abnormal sickle hemoglobin, inflammation, and adhesion. Hydroxyurea, L-glutamine, crizanlizumab, and voxelotor have been approved by the US Food and Drug Administration for reducing the frequency of VOCs; the European Medicines Agency has approved only hydroxyurea. Other novel treatments are in late-stage clinical development in both the United States and the European Union. The development of agents for prevention and treatment of VOCs should be driven by our understanding of its pathophysiology.

Mimicking the Endothelium: Dual Action Heparinized Nitric Oxide Releasing Surface

The management of thrombosis and bacterial infection is critical to ensure the functionality of medical devices. While administration of anticoagulants is the current antithrombotic clinical practice, a variety of complications, such as uncontrolled hemorrhages or heparin-induced thrombocytopenia, can occur. Additionally, infection rates remain a costly and deadly complication associated with use of these medical devices. It has been hypothesized that if a synthetic surface could mimic the biochemical mechanisms of the endothelium of blood vessels, thrombosis could be reduced, anticoagulant use could be avoided, and infection could be prevented. Herein, the interfacial biochemical effects of the endothelium were mimicked by altering the surface of medical grade silicone rubber (SR). Surface modification was accomplished via heparin surface immobilization (Hep) and the inclusion of a nitric oxide (NO) donor into the SR polymeric matrix to achieve synergistic effects (Hep-NO-SR). An in vitro bacteria adhesion study revealed that Hep-NO-SR exhibited a 99.46 ± 0.17% reduction in viable bacteria adhesion compared to SR. An in vitro platelet study revealed Hep-NO-SR reduced platelet adhesion by 84.12 ± 6.19% compared to SR, while not generating a cytotoxic response against fibroblast cells. In a 4 h extracorporeal circuit model without systemic anticoagulation, all Hep-NO-SR samples were able to maintain baseline platelet count and device patency; whereas 66% of SR samples clotted within the first 2 h of study. Results indicate that Hep-NO-SR creates a more hemocompatible and antibacterial surface by mimicking two key biochemical functions of the native endothelium.

On artherogenic index of plasma in sickle cell anaemia patients

INTRODUCTION

Sickle cell anaemia (SCA) is an inherited abnormality of haemoglobin associated with reduced life expectancy. Patients' complications include dyslipideamia. This study was aimed at determining the artherogenic index of plasma (AIP) in sickle cell anaemia patients and compares the value to HbAA controls value. A high AIP is strongly predictive of elevated cardiovascular risk.

METHODS

A comparative study was conducted among SCA patients attending the haematology clinic, Lagos State University Teaching Hospital (LASUTH) and HbAA Phenotype controls. A total of 304 participants were recruited consisting of equal numbers of SCA and HbAA controls. Single lipid profiles were done; logarithms of triglycerides/high density lipoprotein were calculated to obtain AIP and lipid profile ratios established for all participants.

RESULTS

There were lower mean values of Total Cholesterol (TC), High Density Lipoprotein(HDL) and Low Density Lipoprotein (LDL) amongst SCD participants than controls and higher mean values of triglycerides (TG) and Very Low Density Lipoprotein (VLDL) in SCD p < 0.05. The AIP in SCD ranges from -0.62 to 1.32 while that of controls ranges from -0.56 to 0.61.The mean AIP were 0.14 ± 0.29 and -0.009 ± 0.26 in SCD and controls respectively. P value = 0.002.

CONCLUSION

AIP value is higher in sickle cell anaemia than controls, the former have lower mean values of TC, HDL and LDL and higher mean values of TG and VLDL.

Massive Ovarian Edema in a Girl with Hemoglobin SC Disease

Massive ovarian edema is a benign tumor like lesion of the ovary. The widely accepted mechanism is disruption of vascular drainage resulting in accumulation of fluid within the stroma and enlargement of the ovary. We report a case of massive ovarian edema in a teenage girl with hemoglobin SC disease. A 16-year-old female with hemoglobin SC disease was admitted with right lower quadrant pain. An ultrasound and CT scan showed a large, heterogeneous solid, and cystic pelvic mass. Due to the size and the possibility of malignancy, the patient underwent a salpingo-oophorectomy. The mass was an 8.3 cm hemorrhagic cyst with some solid areas. Histologic exam showed diffuse edema with scattered entrapped follicles and a narrow rim of normal appearing ovarian stroma. Dilated and occluded capillaries were seen along with hemorrhage and sickled red blood cells but no necrosis was identified. These histologic features were consistent with massive ovarian edema. Massive ovarian edema is thought to be caused by disturbance of the vascular outflow resulting in fluid buildup in the stroma. It is most often attributed to intermittent ovarian torsion that disrupts capillary and venous flow, but arterial flow is maintained. Rare cases of massive ovarian edema caused by tumor emboli or external compression by tumors have been reported, but this is the first case of a patient with hemoglobin SC disease developing vasoocclusions resulting in this lesion.

Molecular mechanisms of bio-catalysis of heme extraction from hemoglobin

Red blood cell hemolysis in sickle cell disease (SCD) releases free hemoglobin. Extracellular hemoglobin and its degradation products, free heme and iron, are highly toxic due to oxidative stress induction and decrease in nitric oxide availability. We propose an approach that helps to eliminate extracellular hemoglobin toxicity in SCD by employing a bacterial protein system that evolved to extract heme from extracellular hemoglobin. NEAr heme Transporter (NEAT) domains from iron-regulated surface determinant proteins from Staphylococcus aureus specifically bind free heme as well as facilitate its extraction from hemoglobin. We demonstrate that a purified NEAT domain fused with human haptoglobin β-chain is able to remove heme from hemoglobin and reduce heme content and peroxidase activity of hemoglobin. We further use molecular dynamics (MD) simulations to resolve molecular pathway of heme transfer from hemoglobin to NEAT, and to elucidate molecular mechanism of such heme transferring process. Our study is the first of its kind, in which simulations are employed to characterize the process of heme leaving hemoglobin and subsequent rebinding with a NEAT domain. Our MD results highlight important amino acid residues that facilitate heme transfer and will guide further studies for the selection of best NEAT candidate to attenuate free hemoglobin toxicity.

Sustained treatment of sickle cell mice with haptoglobin increases HO-1 and H-ferritin expression and decreases iron deposition in the kidney without improvement in kidney function

There is growing evidence that extracellular haemoglobin and haem mediate inflammatory and oxidative damage in sickle cell disease. Haptoglobin (Hp), the scavenger for free haemoglobin, is depleted in most patients with sickle cell disease due to chronic haemolysis. Although single infusions of Hp can ameliorate vaso-occlusion in mouse models of sickle cell disease, prior studies have not examined the therapeutic benefits of more chronic Hp dosing on sickle cell disease manifestations. In the present study, we explored the effect of Hp treatment over a 3-month period in sickle mice at two dosing regimens: the first at a moderate dose of 200 mg/kg thrice weekly and the second at a higher dose of 400 mg/kg thrice weekly. We found that only the higher dosing regimen resulted in increased haem-oxygenase-1 and heavy chain ferritin (H-ferritin) expression and decreased iron deposition in the kidney. Despite the decreased kidney iron deposition following Hp treatment, there was no significant improvement in kidney function. However, there was a nearly significant trend towards decreased liver infarction.

Venous thromboembolism in adults with sickle cell disease: a serious and under-recognized complication

BACKGROUND

Sickle cell disease is recognized as a hypercoagulable state; however, the frequency and characteristics of venous thromboembolism in sickle cell patients have not been well defined. The purpose of this study was to establish the prevalence and risk factors for venous thromboembolism in a large cohort of patients with sickle cell disease and determine the relationship between venous thromboembolism and mortality.

METHODS

We performed a cross-sectional study of 404 sickle cell disease patients cared for at the Sickle Cell Center for Adults at Johns Hopkins. Demographic, sickle cell disease-specific comorbidity, and venous thromboembolism data were collected on all patients.

RESULTS

One hundred one patients (25%) had a history of venous thromboembolism with a median age at diagnosis of 29.9 years. A history of non-catheter-related venous thromboembolism was found in 18.8% of patients. Sickle variant genotypes conferred a higher risk of non-catheter-related venous thromboembolism compared with sickle cell anemia genotypes (SS/Sβ(0)) (relative risk [RR] 1.77; 95% confidence interval [CI], 1.18-2.66). Tricuspid regurgitant jet velocity ≥2.5 m/s also was associated with non-catheter-related venous thromboembolism (RR 1.65; 95% CI, 1.12-2.45). Thirty patients (7.4%) died during the study period. Adjusting for all variables, non-catheter-related venous thromboembolism was independently correlated with death (RR 3.63; 95% CI, 1.66-7.92).

CONCLUSION

Venous thromboembolism is common in adults with sickle cell disease. Sickle variant genotypes and tricuspid regurgitant jet velocity ≥2.5 m/s are associated with non-catheter-related venous thromboembolism. In addition, non-catheter-related venous thromboembolism appears to be an independent risk factor for death in our cohort. These results suggest that disease-specific prophylaxis and treatment strategies for venous thromboembolism should be investigated in sickle cell disease patients.

The effect of hemolysis on plasma oxidation and nitration in patients with sickle cell disease

This study aimed to determine the effect of haemolysis on plasma oxidation and nitration in sickle cell disease (SCD) patients. Blood was collected from haemoglobin (Hb)A volunteers and homozygous HbSS patients who had not received blood transfusions in the last 3 months. Haemolysis was characterised by low levels of haemoglobin and haptoglobin and high levels of reticulocyte, mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), plasma cell-free haemoglobin, bilirubin, total lactate dehydrogenase (LDH) and dominance of LDH-1 isoenzyme. Plasma 8-isoprostane, protein carbonyl and nitrotyrosine levels were measured to evaluate oxidised lipids, oxidised and nitrated proteins, respectively. Plasma nitrite-nitrate levels were also determined to assess nitric oxide (NO) production in both SCD patients and controls. Markers of haemolysis were significantly evident in SCD patients compared to controls. Plasma 8-isoprostane, protein carbonyl and nitrotyrosine levels were markedly elevated in SCD patients compared to controls. Linear regression analysis revealed a significant inverse correlation between haemoglobin and reticulocyte counts and a significant positive correlation of plasma cell-free haemoglobin with protein carbonyl and nitrotyrosine levels. The obtained data shows that increased haemolysis in SCD increases plasma protein oxidation and nitration.

Pulmonary complications of sickle cell disease

Sickle cell disease (SCD) is a common monogenetic disorder with high associated morbidity and mortality. The pulmonary complications of SCD are of particular importance, as acute chest syndrome and pulmonary hypertension have the highest associated mortality rates within this population. This article reviews the pathophysiology, diagnosis, and treatment of clinically significant pulmonary manifestations of SCD, including acute chest syndrome, asthma, and pulmonary hypertension in adult and pediatric patients. Clinicians should be vigilant in screening and treating such comorbidities to improve patient outcomes.