Not simply misshapen red cells: multimolecular and cellular events in sickle vaso-occlusion

The many faces of sickle cell disease in children: complications in the appendicular skeleton

Sickle cell disease (SCD) is a hereditary red cell disorder with clinical manifestations secondary to sickling or crescent-shaped distortion of the red blood cells. Musculoskeletal complications of SCD are often the main causes for acute and chronic morbidities in children with manifestations including osteomyelitis, osteoporosis and osteonecrosis. This article aims to familiarise the paediatric radiologist with appendicular skeletal complications of SCD in the paediatric population and their imaging appearance.

Process and procedural adjustments to improve CD34+ collection efficiency of hematopoietic progenitor cell collections in sickle cell disease

BACKGROUND

Adequate CD34+ collection efficiency (CE) is critical to achieve target CD34+ cell doses in hematopoietic progenitor cell (HPC) collections. Autologous HPC collection in sickle cell disease (SCD) is associated with unstable collection interfaces and low CD34+ CEs. We hypothesized that variables specific to SCD, activation of blood cells and elevated viscosity, might contribute to these issues and made adjustments to the collection process and procedure to address our hypothesis.

STUDY DESIGN AND METHODS

In two patients with SCD undergoing autologous HPC collection on our clinical trial (NCT02193191), we therefore implemented adjustments to the process and procedure in the following areas: proximity of RBC exchange to HPC collection, the type of anticoagulation, and the packing factor setting.

RESULTS

There was no collection interface instability. Our CD34+ CE1s were high at 70% and 51%, and granulocyte CE, platelet CE, and product granulocyte % were remarkably low. Product hematocrits were not as high as previously reported to be required to obtain adequate CEs. Interestingly, one HPC product showed a hemoglobin S (HbS) of 91% at the same time that the peripheral blood (PB) showed a HbS of 22%.

DISCUSSION

Adjustments to the HPC collection process and procedure were associated with adequate CD34+ CEs and low granulocyte and platelet contamination in HPC products from SCD patients. Given the discrepancy in the percentage of sickle RBCs in the product versus the PB, we hypothesize that CD34+ cells and RBCs may aggregate. Our interventions and hypothesis should be further investigated in larger studies.

Hemopexin as an Inhibitor of Hemolysis-Induced Complement Activation

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

Inflammation in sickle cell disease

The primary β-globin gene mutation that causes sickle cell disease (SCD) has significant pathophysiological consequences that result in hemolytic events and the induction of the inflammatory processes that ultimately lead to vaso-occlusion. In addition to their role in the initiation of the acute painful vaso-occlusive episodes that are characteristic of SCD, inflammatory processes are also key components of many of the complications of the disease including autosplenectomy, acute chest syndrome, pulmonary hypertension, leg ulcers, nephropathy and stroke. We, herein, discuss the events that trigger inflammation in the disease, as well as the mechanisms, inflammatory molecules and cells that propagate these inflammatory processes. Given the central role that inflammation plays in SCD pathophysiology, many of the therapeutic approaches currently under pre-clinical and clinical development for the treatment of SCD endeavor to counter aspects or specific molecules of these inflammatory processes and it is possible that, in the future, we will see anti-inflammatory drugs being used either together with, or in place of, hydroxyurea in those SCD patients for whom hematopoietic stem cell transplants and evolving gene therapies are not a viable option.

Microvasculature-on-a-chip for the long-term study of endothelial barrier dysfunction and microvascular obstruction in disease

Alterations in the mechanical properties of erythrocytes occurring in inflammatory and hematologic disorders such as sickle cell disease (SCD) and malaria often lead to increased endothelial permeability, haemolysis, and microvascular obstruction. However, the associations among these pathological phenomena remain unknown. Here, we report a perfusable, endothelialized microvasculature-on-a-chip featuring an interpenetrating-polymer-network hydrogel that recapitulates the stiffness of blood-vessel intima, basement membrane self-deposition and self-healing endothelial barrier function for longer than 1 month. The microsystem enables the real-time visualization, with high spatiotemporal resolution, of microvascular obstruction and endothelial permeability under physiological flow conditions. We found how extracellular heme, a hemolytic byproduct, induces delayed but reversible endothelial permeability in a dose-dependent manner, and demonstrate that endothelial interactions with SCD or malaria-infected erythrocytes cause reversible microchannel occlusion and increased in situ endothelial permeability. The microvasculature-on-a-chip enables mechanistic insight into the endothelial barrier dysfunction associated with SCD, malaria and other inflammatory and haematological diseases.

Sickle Cell Disease: Advances in Treatment

BACKGROUND

Sickle cell disease causes significant morbidity and mortality and affects the economic and healthcare status of many countries. Yet historically, the disease has not had commensurate outlays of funds that have been aimed at research and development of drugs and treatment procedures for other diseases.

METHODS

This review examines several treatment modalities and new drugs developed since the late 1990s that have been used to improve outcomes for patients with sickle cell disease.

RESULTS

Targeted therapies based upon the pathophysiologic mechanisms of sickle cell disease that result in organ dysfunction and painful episodes include hydroxyurea, L-glutamine, crizanlizumab, and other drugs that are currently on the market or are on the verge of becoming available. These agents have the potential to improve survival and quality of life for individuals with sickle cell disease. Also discussed is stem cell transplantation that, to date, is the only curative approach for this disease, as well as the current status of gene therapy.

CONCLUSION

These examples demonstrate how the current knowledge of sickle cell disease pathophysiology and treatment approaches intersect. Although interest in sickle cell research has blossomed, many more clinical trials need to be initiated and subjected to more strenuous examination and analysis than have been used in the past.

Dimethyl fumarate increases fetal hemoglobin, provides heme detoxification, and corrects anemia in sickle cell disease

Sickle cell disease (SCD) results from a point mutation in the β-globin gene forming hemoglobin S (HbS), which polymerizes in deoxygenated erythrocytes, triggering recurrent painful vaso-occlusive crises and chronic hemolytic anemia. Reactivation of fetal Hb (HbF) expression ameliorates these symptoms of SCD. Nuclear factor (erythroid derived-2)-like 2 (Nrf2) is a transcription factor that triggers cytoprotective and antioxidant pathways to limit oxidative damage and inflammation and increases HbF synthesis in CD34+ stem cell-derived erythroid progenitors. We investigated the ability of dimethyl fumarate (DMF), a small-molecule Nrf2 agonist, to activate γ-globin transcription and enhance HbF in tissue culture and in murine and primate models. DMF recruited Nrf2 to the γ-globin promoters and the locus control region of the β-globin locus in erythroleukemia cells, elevated HbF in SCD donor-derived erythroid progenitors, and reduced hypoxia-induced sickling. Chronic DMF administration in SCD mice induced HbF and increased Nrf2-dependent genes to detoxify heme and limit inflammation. This improved hematological parameters, reduced plasma-free Hb, and attenuated inflammatory markers. Chronic DMF administration to nonanemic primates increased γ-globin mRNA in BM and HbF protein in rbc. DMF represents a potential therapy for SCD to induce HbF and augment vasoprotection and heme detoxification.

Vitamin D Deficiency and Its Association with Inflammatory Markers, Lipid Profile and Regulatory T-cells in Pediatric Sickle Cell Disease Patients

We investigated vitamin D deficiency in pediatric sickle cell disease patients and its association with selected bone, lipid and inflammatory parameters. The study included 64 patients (33 SS and 31 SB) and 21 carriers (AS). Blood was obtained to assess levels of vitamin D, WBC, CRP, Ca, P, ALP, PTH, triglyceride, total cholesterol, LDL, VLDL, HDL, IL-2, IL-12, TNF-α, IL-4, IL-6, IL-10 and regulatory T cells. The patients were grouped according to their genotype (SS, SB) and vitamin D status (low or normal). Carriers were also grouped as low or normal vitamin D. Laboratory findings were similar between low and normal Vit D groups in SS, SB and AS genotypes except a lower IL-12 in SB-low vitamin D compared SB-normal vitamin D group. Acute chest syndrome was more frequent in SS-low Vit D (63%) compared to SS-normal Vit D (25%), SB-low Vit D (21%) and SB-normal Vit D (33%) (P = 0.045). Both SS and SB with low vitamin D had higher VLDL (P = 0.006 and P = 0.022), TNF-α (P = 0.001) and regulatory T cells (P = 0.000) compared to AS-low vitamin D. Both SS and SB with normal vitamin D had higher levels of regulatory T cells (P = 0.000) compared to AS-normal vitamin D. Vit D was not a modifier of selected inflammation, bone and lipid parameters in sickle cell disease. Acute chest syndrome was comparably more frequent in SS-low vitamin D. Increase of regulatory T cells in the patients was a result of chronic inflammation in sickle cell disease.

Low-dose methotrexate in sickle-cell disease: a pilot study with rationale borrowed from rheumatoid arthritis

Background

Inflammation is a major feature of sickle cell disease (SCD). Low-dose methotrexate (MTX) has long been used in chronic inflammatory diseases. This pilot study examined the MTX effect on acute vaso-occlusive pain crises (VOC) in SCD patients.

Methods

Fourteen adults on hydroxyurea with severe and refractory VOC received one intramuscular injection of 10 mg of MTX per week for 12 weeks. A single weekly dose of 5 mg of leucovorin was administered orally 48 h after each MTX injection. The primary outcome was reduction in number/intensity of acute pain episodes. The secondary outcomes were improvement of quality of life (QOL) and reduction of the inflammatory status.

Results

MTX did not significantly change the median VOC frequency (12 before vs 10.5 during treatment, P = 0.6240) or the median McGill pain index (45 at week 0 vs 39.5 at week 12, P = 0.9311). However, there was a decrease of ≥50% in chronic pain resulting from avascular osteonecrosis (AVN) in 5 out of 7 patients with radiologic evidence of AVN, with the perception of longer pain-free periods. There was a 44.4% median gain in physical function in the SF-36 QOL questionnaire (P = 0.0198). MTX treatment up-regulated two C-X-C motif chemokines (CXCL), CXCL10 (P = 0.0463) and CXCL12 (P < 0.0001), without significant effect on 14 additional plasma inflammatory markers. Adverse events: One individual had fever of unknown origin. Respiratory tract infections were recorded in five patients. Among the latter, one also had dengue fever and another had a central venous line infection and died of pneumonia and septic shock. Three patients with previous history of hydroxyurea-induced hematological toxicity developed low blood platelet counts while receiving simultaneously MTX and hydroxyurea.

Conclusions

Although MTX did not reduce acute VOC frequency/intensity, it decreased chronic pain and led to QOL improvement.

Trial registrationhttp://www.who.int/ictrp/en/ and http://www.ensaiosclinicos.gov.br, RBR-2s9xvn, 19 December 2016, retrospectively registered

Electronic supplementary material

The online version of this article (doi:10.1186/s40164-017-0078-1) contains supplementary material, which is available to authorized users.

Markers of endothelial dysfunction and leucocyte activation in Saudi and non-Saudi haplotypes of sickle cell disease

Sickle cell disease (SCD) is an autosomal recessive inherited hemoglobinopathy, characterized by chronic hemolysis and recurrent vaso-occlusive crisis (VOC). This study investigates changes in leucocyte subsets and the relationship between cell adhesion molecule expression and disease manifestations in patients during steady state and acute VOC. We compared soluble E-selectin and P-selectin levels in 84 SCD patients, in steady state and during VOC to 84 healthy controls. Using immunophenotyping, we also compared lymphocyte subsets in these three groups. Further, we compared E-selectin and P-selectin levels in patients of Saudi ethnicity to non-Saudi patients, in all three groups. Lymphocyte subsets showed high percentages of total T lymphocytes, T helper and suppressor lymphocytes, B lymphocytes as well as NK cells in patients with SCD during steady state, while B lymphocytes and NK cells were significantly higher during acute VOC crisis. High levels of both soluble E-selectin (sE-selectin) and soluble P-selectin (sP-selectin) markers were demonstrated in the serum of patients with SCD during both steady state and acute VOC. Levels of selectins were significantly higher in acute VOC. The immunophenotypic expression of L-selectin, on leucocytes, was high in SCD both during steady state and during acute VOC in comparison to normal control subjects. There was no significant difference in all three study groups between Saudi and non-Saudi patients. These findings suggest that patients with SCD have increased expression of adhesion molecules: E-selectin and P-selectin, which play an important role in the pathogenesis of VOC. Despite the distinct phenotype of Saudi patients with SCD, there was no significant difference in levels of soluble E-selectin and soluble P-selectin between Saudi and non-Saudi patients in all three groups. While sickle cell disease is a well-recognized state of chronic inflammation, the role of specific adhesion molecules is steadily unraveling. Studies are underway to investigate the potential role of selectin antagonists, for prevention and reversal of acute vascular occlusions in SCD patients.

Inflammatory targets of therapy in sickle cell disease

Sickle cell disease (SCD) is a monogenic globin disorder characterized by the production of a structurally abnormal hemoglobin (Hb) variant Hb S, which causes severe hemolytic anemia, episodic painful vaso-occlusion, and ultimately end-organ damage. The primary disease pathophysiology is intracellular Hb S polymerization and consequent sickling of erythrocytes. It has become evident for more than several decades that a more complex disease process contributes to the myriad of clinical complications seen in patients with SCD with inflammation playing a central role. Drugs targeting specific inflammatory pathways therefore offer an attractive therapeutic strategy to ameliorate many of the clinical events in SCD. In addition, they are useful tools to dissect the molecular and cellular mechanisms that promote individual clinical events and for developing improved therapeutics to address more challenging clinical dilemmas such as refractoriness to opioids or hyperalgesia. Here, we discuss the prospect of targeting multiple inflammatory pathways implicated in the pathogenesis of SCD with a focus on new therapeutics, striving to link the actions of the anti-inflammatory agents to a defined pathobiology, and specific clinical manifestations of SCD. We also review the anti-inflammatory attributes and the cognate inflammatory targets of hydroxyurea, the only Food and Drug Administration-approved drug for SCD.

2015 Clinical trials update in sickle cell anemia

Polymerization of HbS and cell sickling are the prime pathophysiological events in sickle cell disease (SCD). Over the last 30 years, a substantial understanding at the molecular level has been acquired on how a single amino acid change in the structure of the beta chain of hemoglobin leads to the explosive growth of the HbS polymer and the associated changes in red cell morphology. O2 tension and intracellular HbS concentration are the primary molecular drivers of this process, and are obvious targets for developing new therapies. However, polymerization and sickling are driving a complex network of associated cellular changes inside and outside of the erythrocyte, which become essential components of the inflammatory vasculopathy and result in a large range of potential acute and chronic organ damages. In these areas, a multitude of new targets for therapeutic developments have emerged, with several ongoing or planned new therapeutic interventions. This review outlines the key points of SCD pathophysiology as they relate to the development of new therapies, both at the pre-clinical and clinical levels.

Updated Mechanisms of Sickle Cell Disease-Associated Chronic pain

Sickle cell disease (SCD), a hemoglobinopathy, causes sickling of red blood cells, resulting in vessel blockage, stroke, anemia, inflammation, and extreme pain. A vast majority of SCD patients experience pain on a chronic basis, and many turn to opioids to provide limited relief. The side effects that come with chronic opioid use push for research into understanding the specific mechanisms of SCD-associated chronic pain. Current advances in SCD-associated pain have focused on alterations in the pain pathway including nociceptor sensitization and endogenous pain inducers. This article reviews the underlying pathophysiology of SCD, potential pain mechanisms, current treatments and their mechanism of action, and future directions of SCD-associated pain management. The information provided could help propel research in SCD-associated chronic pain and uncover novel treatment options for clinicians.