Sickle cell disease: old discoveries, new concepts, and future promise

Natural antiband 3 antibodies in patients with sickle cell disease

Band 3 oligomers, precociously formed in the membrane of sickle red blood cells (SS RBC) as a result of oxidative damage, induce two significant changes: (1) contribution to the adhesive nature of these cells to endothelial cells; (2) production of recognition sites for natural antiband 3 antibodies (antiband 3 Nabs). The inhibition of the adhesion of SS RBC to endothelial cells by band 3 peptides suggests a participation of antiband 3 Nabs in the etiology and prevention of vaso-occlusive crises (VOC). To address this question, we measured the levels of antiband 3 Nabs in sickle cell anaemia (SCA) patients (45 in steady state, 35 in VOC) and in controls (27 sickle trait, 30 normal AA subjects). A significant decreased of antiband 3 Nabs in the VOC group was demonstrated as compared with the steady state group, the sickle trait and healthy controls. This study provides data suggesting that Antiband 3 Nabs are likely to play a role in the SCA VOC.

Adrenergic nerves govern circadian leukocyte recruitment to tissues

The multistep sequence leading to leukocyte migration is thought to be locally regulated at the inflammatory site. Here, we show that broad systemic programs involving long-range signals from the sympathetic nervous system (SNS) delivered by adrenergic nerves regulate rhythmic recruitment of leukocytes in tissues. Constitutive leukocyte adhesion and migration in murine bone marrow (BM) and skeletal-muscle microvasculature fluctuated with circadian peak values at night. Migratory oscillations, altered by experimental jet lag, were implemented by perivascular SNS fibers acting on β-adrenoreceptors expressed on nonhematopoietic cells and leading to tissue-specific, differential circadian oscillations in the expression of endothelial cell adhesion molecules and chemokines. We showed that these rhythms have physiological consequences through alteration of hematopoietic cell recruitment and overall survival in models of septic shock, sickle cell vaso-occlusion, and BM transplantation. These data provide unique insights in the leukocyte adhesion cascade and the potential for time-based therapeutics for transplantation and inflammatory diseases.

Hydroxyurea and a cGMP-amplifying agent have immediate benefits on acute vaso-occlusive events in sickle cell disease mice

Inhibition of leukocyte adhesion to the vascular endothelium represents a novel and important approach for decreasing sickle cell disease (SCD) vaso-occlusion. Using a humanized SCD-mouse-model of tumor necrosis factor-α-induced acute vaso-occlusion, we herein present data demonstrating that short-term administration of either hydroxyurea or the phosphodiesterase 9 (PDE9) inhibitor, BAY73-6691, significantly altered leukocyte recruitment to the microvasculature. Notably, the administration of both agents led to marked improvements in leukocyte rolling and adhesion and decreased heterotypic red blood cell-leukocyte interactions, coupled with prolonged animal survival. Mechanistically, these rheologic benefits were associated with decreased endothelial adhesion molecule expression, as well as diminished leukocyte Mac-1-integrin activation and cyclic guanosine monophosphate (cGMP)-signaling, leading to reduced leukocyte recruitment. Our findings indicate that hydroxyurea has immediate beneficial effects on the microvasculature in acute sickle-cell crises that are independent of the drug's fetal hemoglobin-elevating properties and probably involve the formation of intravascular nitric oxide. In addition, inhibition of PDE9, an enzyme highly expressed in hematopoietic cells, amplified the cGMP-elevating effects of hydroxyurea and may represent a promising and more tissue-specific adjuvant therapy for this disease.

Tissue factor promotes activation of coagulation and inflammation in a mouse model of sickle cell disease

Sickle cell disease (SCD) is associated with a complex vascular pathophysiology that includes activation of coagulation and inflammation. However, the crosstalk between these 2 systems in SCD has not been investigated. Here, we examined the role of tissue factor (TF) in the activation of coagulation and inflammation in 2 different mouse models of SCD (BERK and Townes). Leukocytes isolated from BERK mice expressed TF protein and had increased TF activity compared with control mice. We found that an inhibitory anti-TF antibody abrogated the activation of coagulation but had no effect on hemolysis or anemia. Importantly, inhibition of TF also attenuated inflammation and endothelial cell injury as demonstrated by reduced plasma levels of IL-6, serum amyloid P, and soluble vascular cell adhesion molecule-1. In addition, we found decreased levels of the chemokines MCP-1 and KC, as well as myeloperoxidase in the lungs of sickle cell mice treated with the anti-TF antibody. Finally, we found that endothelial cell-specific deletion of TF had no effect on coagulation but selectively attenuated plasma levels of IL-6. Our data indicate that different cellular sources of TF contribute to activation of coagulation, vascular inflammation, and endothelial cell injury. Furthermore, it appears that TF contributes to these processes without affecting intravascular hemolysis.

Unlocking the binding and reaction mechanism of hydroxyurea substrates as biological nitric oxide donors

Hydroxyurea is the only FDA approved treatment of sickle cell disease. It is believed that the primary mechanism of action is associated with the pharmacological elevation of nitric oxide in the blood; however, the exact details of this are still unclear. In the current work, we investigate the atomic level details of this process using a combination of flexible-ligand/flexible-receptor virtual screening coupled with energetic analysis that decomposes interaction energies. Utilizing these methods, we were able to elucidate the previously unknown substrate binding modes of a series of hydroxyurea analogs to hemoglobin and the concomitant structural changes of the enzyme. We identify a backbone carbonyl that forms a hydrogen bond with bound substrates. Our results are consistent with kinetic and electron paramagnetic resonance (EPR) measurements of hydroxyurea-hemoglobin reactions, and a full mechanism is proposed that offers new insights into possibly improving substrate binding and/or reactivity.

Polarization holographic microscopy for extracting spatio-temporally resolved Jones matrix

We present a high-speed holographic microscopic technique for quantitative measurement of polarization light-field, referred to as polarization holographic microscopy (PHM). Employing the principle of common-path interferometry, PHM quantitatively measures the spatially resolved Jones matrix components of anisotropic samples with only two consecutive measurements of spatially modulated holograms. We demonstrate the features of PHM with imaging the dynamics of liquid crystal droplets at a video-rate.

Carbon-fiber microelectrode amperometry reveals sickle-cell-induced inflammation and chronic morphine effects on single mast cells

Sickle cell disease, caused by a mutation of hemoglobin, is characterized by a complex pathophysiology including an important inflammatory component. Mast cells are tissue-resident leukocytes known to influence a range of immune functions in a variety of different ways, largely through the secretion of biologically active mediators from preformed granules. However, it is not understood how mast cells influence the inflammatory environment in sickle cell disease. A notable consequence of sickle cell disease is severe pain. Therefore, morphine is often used to treat this disease. Because mast cells express opioid receptors, it is pertinent to understand how chronic morphine exposure influences mast cell function and inflammation in sickle cell disease. Herein, carbon-fiber microelectrode amperometry (CFMA) was used to monitor the secretion of immunoactive mediators from single mast cells. CFMA enabled the detection and quantification of discrete exocytotic events from single mast cells. Mast cells from two transgenic mouse models expressing human sickle hemoglobin (hBERK1 and BERK) and a control mouse expressing normal human hemoglobin (HbA-BERK) were monitored using CFMA to explore the impact of sickle-cell-induced inflammation and chronic morphine exposure on mast cell function. This work, utilizing the unique mechanistic perspective provided by CFMA, describes how mast cell function is significantly altered in hBERK1 and BERK mice, including decreased serotonin released compared to HbA-BERK controls. Furthermore, morphine was shown to significantly increase the serotonin released from HbA-BERK mast cells and demonstrated the capacity to reverse the observed sickle-cell-induced changes in mast cell function.

Intravenous immunoglobulins modulate neutrophil activation and vascular injury through FcγRIII and SHP-1

RATIONALE

Intravascular neutrophil recruitment and activation are key pathogenic factors that contribute to vascular injury. Intravenous immunoglobulin (IVIG) has been shown to have a beneficial effect in systemic inflammatory disorders; however, the mechanisms underlying IVIG's inhibitory effect on neutrophil recruitment and activation are not understood.

OBJECTIVE

We studied the mechanisms by which IVIG exerts protection from neutrophil-mediated acute vascular injury.

METHODS AND RESULTS

We examined neutrophil behavior in response to IVIG in vivo, using real-time intravital microscopy. We found that an antibody that blocks both FcγRIII and its inhibitory receptor counterpart, FcγRIIB, abrogated the inhibitory effect of IVIG on leukocyte recruitment and heterotypic red blood cell (RBC) interactions with adherent leukocytes in wild-type mice. In the context of sickle cell disease, the blockade of both FcγRIIB and III abrogated the protective effect of IVIG on acute vaso-occlusive crisis caused by neutrophil recruitment and activation. Analysis of FcγRIIB- and FcγRIII-deficient mice revealed the predominant expression of FcγRIII on circulating neutrophils. FcγRIII mediated IVIG-triggered inhibition of leukocyte recruitment, circulating RBC capture, and enhanced Mac-1 activity, whereas FcγRIIB was dispensable. In addition, FcγRIII-induced IVIG anti-inflammatory activity in neutrophils was mediated by recruitment of Src homology 2 (SH2)-containing tyrosine phosphatase-1 (SHP-1). Indeed, the protective effect of IVIG on leukocyte recruitment and activation was abrogated in SHP-1-mutant mice.

CONCLUSIONS

FcγRIII, a classic activating receptor, has an unexpected inhibitory role on neutrophil adhesion and activation via recruitment of SHP-1 in response to IVIG. Our results identify SHP-1 as a therapeutic target in neutrophil-mediated vascular injury.

Tissue factor and thrombin in sickle cell anemia

Sickle cell anemia is an inherited hematologic disorder associated with hemolytic and vaso-occlusive complications. An activation of coagulation is also a prominent feature of sickle cell anemia. Growing evidence indicates that coagulation may contribute to the inflammation and vascular injury in sickle cell anemia. This review focuses on tissue factor expression and its contribution to the activation of coagulation, thrombosis and vascular inflammation in sickle cell anemia.

Optimized TAL effector nucleases (TALENs) for use in treatment of sickle cell disease

TAL effector nucleases (TALENs) represent a new class of artificial nucleases capable of cleaving long, specific target DNA sequences in vivo and are powerful tools for genome editing with potential therapeutic applications. Here we report a pair of custom-designed TALENs for targeted genetic correction of the sickle cell disease mutation in human cells, which represents an example of engineered TALENs capable of recognizing and cleaving a human disease-associated gene. By using a yeast reporter system, a systematic study was carried out to optimize TALEN architecture for maximal in vivo cleavage efficiency. In contrast to the previous reports, the engineered TALENs were capable of recognizing and cleaving target binding sites preceded by A, C or G. More importantly, the optimized TALENs efficiently cleaved a target sequence within the human β-globin (HBB) gene associated with sickle cell disease and increased the efficiency of targeted gene repair by >1000-fold in human cells. In addition, these TALENs showed no detectable cytotoxicity. These results demonstrate the potential of optimized TALENs as a powerful genome editing tool for therapeutic applications.

Perioperative genomics

Since the completion of the Human Genome Project 10 years ago, the world has witnessed an incredible progress in human genetics and genomics.(1) This progress was largely driven by the availability of better, faster and cheaper sequencing technology.(2) While it took more than 10 years and more than 1 billion dollars to complete the Human Genome Project,(3-5) an individual in the year 2011 can have his whole genome sequenced within a week for less than $30,000. With cheaper and faster sequencing came a wealth of novel discoveries which makes it timely to review how these newly found insights into the human genome are relevant for perioperative medicine. This article summarises the basics of genetic inheritance, the human genome and modern sequencing methods, as well as genetic variation and how this knowledge may be applied to patient care and research in the perioperative setting.

The influence of hydroxyurea on oxidative stress in sickle cell anemia

OBJECTIVE

The oxidative stress in 20 sickle cell anemia patients taking hydroxyurea and 13 sickle cell anemia patients who did not take hydroxyurea was compared with a control group of 96 individuals without any hemoglobinopathy.

METHODS

Oxidative stress was assessed by thiobarbituric acid reactive species production, the Trolox-equivalent antioxidant capacity and plasma glutathione levels.

RESULTS

Thiobarbituric acid reactive species values were higher in patients without specific medication, followed by patients taking hydroxyurea and the Control Group (p < 0.0001). The antioxidant capacity was higher in patients taking hydroxyurea and lower in the Control Group (p = 0.0002 for Trolox-equivalent antioxidant capacity and p < 0.0292 for plasma glutathione). Thiobarbituric acid reactive species levels were correlated with higher hemoglobin S levels (r = 0.55; p = 0.0040) and lower hemoglobin F concentrations(r = -0.52; p = 0.0067). On the other hand, plasma glutathione levels were negatively correlated with hemoglobin S levels (r = -0.49; p = 0.0111) and positively associated with hemoglobin F values (r = 0.56; p = 0.0031).

CONCLUSION

Sickle cell anemia patients have high oxidative stress and, conversely, increased antioxidant activity. The increase in hemoglobin F levels provided by hydroxyurea and its antioxidant action may explain the reduction in lipid peroxidation and increased antioxidant defenses in these individuals.

Adhesion molecules and high-sensitivity C-reactive protein levels in patients with sickle cell beta-thalassaemia

BACKGROUND AND AIM

  The primary symptoms of sickle cell disease (SCD) arise from vaso-occlusive crises. The pathogenesis of these crises is complex phenomenon where endothelial activation and damage has a major role. Chronic inflammation also plays an important role in the pathophysiology of SCD. We aimed to investigate endothelial activation in Caucasian Greek patients with SCD by means of measuring adhesion molecules and markers of inflammation.

SUBJECTS AND METHODS

Twenty-eight patients with SCD aged 5-63 years were included in the study. Most of the patients (23/28) were double heterozygotes for sickle cell/beta-thalassaemia, while five patients (5/28) were sickle cell homozygotes. Patients were treated with one/or more of hydroxyurea, therapeutic phlebotomies, blood transfusion or splenectomy. Twenty apparently healthy individuals matched for age and sex formed the control group. Measurements of soluble intercellular adhesion molecule-1, (sICAM-1), soluble vascular cell adhesion molecule-1 (sVCAM-1), P-selectin, E-selectin, soluble thrombomodulin (sTM) and high-sensitivity C-reactive protein (hs-CRP) levels were performed using immunoassays in both patients and healthy individuals.

RESULTS

We found that all endothelial adhesion molecules and hs-CRP were significantly increased (P < 0·001) in patients with SCD compared with controls, while sTM levels did not differ significantly (P > 0·05) and this increase was not influenced by the treatment.

CONCLUSION

Our findings demonstrate the high degree of endothelial activation and damage seen in sickle cell patients even in steady-state condition, as well as the important chronic inflammation underlying the pathophysiology of this widespread disease.

Erythrocyte plasma membrane-bound ERK1/2 activation promotes ICAM-4-mediated sickle red cell adhesion to endothelium

The core pathology of sickle cell disease (SCD) starts with the erythrocyte (RBC). Aberration in MAPK/ERK1/2 signaling, which can regulate cell adhesion, occurs in diverse pathologies. Because RBCs contain abundant ERK1/2, we predicted that ERK1/2 is functional in sickle (SS) RBCs and promotes adherence, a hallmark of SCD. ERK1/2 remained active in SS but not normal RBCs. β(2)-adrenergic receptor stimulation by epinephrine can enhance ERK1/2 activity only in SS RBCs via PKA- and tyrosine kinase p72(syk)-dependent pathways. ERK signaling is implicated in RBC ICAM-4 phosphorylation, promoting SS RBC adhesion to the endothelium. SS RBC adhesion and phosphorylation of both ERK and ICAM-4 all decreased with continued cell exposure to epinephrine, implying that activation of ICAM-4-mediated SS RBC adhesion is temporally associated with ERK1/2 activation. Furthermore, recombinant ERK2 phosphorylated α- and β-adducins and dematin at the ERK consensus motif. Cytoskeletal protein 4.1 also showed dynamic phosphorylation but not at the ERK consensus motif. These results demonstrate that ERK activation induces phosphorylation of cytoskeletal proteins and the adhesion molecule ICAM-4, promoting SS RBC adhesion to the endothelium. Thus, blocking RBC ERK1/2 activation, such as that promoted by catecholamine stress hormones, could ameliorate SCD pathophysiology.

Stress erythropoiesis: new signals and new stress progenitor cells

PURPOSE OF REVIEW

Acute anemic stress induces a physiological response that includes the rapid development of new erythrocytes. This process is referred to as stress erythropoiesis, which is distinct from steady state erythropoiesis. Much of what we know about stress erythropoiesis comes from the analysis of murine models. In this review, we will discuss our current understanding of the mechanisms that regulate stress erythropoiesis in mice and discuss outstanding questions in the field.

RECENT FINDINGS

Stress erythropoiesis occurs in the murine spleen, fetal liver and adult liver. The signals that regulate this process are Hedgehog, bone morphogenetic protein 4 (BMP4), stem cell factor and hypoxia. Recent findings show that stress erythropoiesis utilizes a population of erythroid-restricted self-renewing stress progenitors. Although the BMP4-dependent stress erythropoiesis pathway was first characterized during the recovery from acute anemia, analysis of a mouse model of chronic anemia demonstrated that activation of the BMP4-dependent stress erythropoiesis pathway provides compensatory erythropoiesis in response to chronic anemia as well.

SUMMARY

The BMP4-dependent stress erythropoiesis pathway plays a key role in the recovery from acute anemia and new data show that this pathway compensates for ineffective steady state erythropoiesis in a murine model of chronic anemia. The identification of a self-renewing population of stress erythroid progenitors in mice suggests that therapeutic manipulation of this pathway may be useful for the treatment of human anemia. However, the development of new therapies will await the characterization of an analogous pathway in humans.

Pathophysiological insights in sickle cell disease

The first coherent pathophysiological scheme for sickle cell disease (SCD) emerged in the sixties-seventies based on an extremely detailed description of the molecular mechanism by which HbS in its deoxy-form polymerises and forms long fibres within the red blood cell that deform it and make it fragile. This scheme explains the haemolytic anaemia, and the mechanistic aspects of the vaso-occlusive crises (VOCs), but, even though it constitutes the basic mechanism of the disease, it does not account for the processes that actually trigger VOCs. This paper reviews recent data which imply: red blood cell dehydration, its abnormal adhesion properties to the endothelium, the participation of inflammatory phenomenon and of a global activation of all the cells present in the vessel, and finally, abnormalities of the vascular tone and of nitric oxide metabolism. These data altogether have shed a new light on the pathophysiology of the first molecular disease i.e. sickle cell disease.

Biomarkers of inflammation, growth factor, and coagulation activation in patients with sickle cell disease

Acute painful crisis is a common sequela that can cause significant morbidity and negatively impact the quality of life of patients with sickle cell disease (SCD). Plasma levels of several chemokines and cytokines including tumor necrosis factor-α (TNF-α), interleukin 1β (IL-1β), IL-6, IL-8, monocyte chemoattractant protein 1 (MCP-1), macrophage inflammatory protein 1α (MIP-1α), and interferon γ (IFN-γ) in patients with SCD showed a distinct and statistically significant rise either during painful crisis or at steady state. Plasma levels of various growth factors, including human vascular endothelial growth factor (VEGF), human basic fibroblast growth factor (FGF), and human hepatocyte growth factor (HGF), showed a sustained 2- to 3-fold increase either during painful crisis or at steady state in patients with SCD. Furthermore, plasma levels of the biomarker d-Dimer, a marker of hypercoagulation, showed a 2- to 3-fold increase either during painful crisis or at steady state in patients with SCD as compared to that in healthy participants, suggesting an increased risk of thrombosis.

Minor antigens on transfused RBCs crossprime CD8 T cells but do not induce full effector function

HLA-matched bone marrow transplantation (BMT) is a cure for nonmalignant hematological disorders; however, rejection rates are high and correlate with the number of antecedent transfusions. Recently, using murine models, we reported that minor antigens (mHAs) in transfused leukoreduced red blood cell (RBC) or platelet units induce rejection of subsequent BMT. To study RBCs as an immunogen, we utilized transgenic donors that express a model mHA selectively on RBCs (HOD mouse). Transfusion of HOD blood did not induce BMT rejection of marrow that shared mHAs with the HOD RBCs. Similarly, no endogenous anti-HOD CD8(+) T-cell response was detected with antigen-specific tetramer reagents. Adoptively transferred OT-I T cells rapidly expanded after HOD blood transfusion; however, only a semi-effector phenotype was observed (tumor necrosis factor-α and interferon-γ secretion, but essentially no Granzyme B). After initial expansion, OT-I T cells contracted rapidly to very low levels. A similar trend was observed by in vivo CTL assay, with only transient lytic activity. Together, these data indicate that RBCs may not be the component of RBC units that induces BMT rejection, and suggest that contaminating platelets or leukocytes may be responsible.

Cellular Reprogramming toward the Erythroid Lineage

Haemoglobinopathies such as thalassaemia and sickle cell disease present a major health burden. Currently, the main forms of treatment for these diseases are packed red blood cell transfusions and the administration of drugs which act to nonspecifically reactivate the production of foetal haemoglobin. These treatments are ongoing throughout the life of the patient and are associated with a number of risks, such as limitations in available blood for transfusion, infections, iron overload, immune rejection, and side effects associated with the drug treatments. The field of cellular reprogramming has advanced significantly in the last few years and has recently culminated in the successful production of erythrocytes in culture. This paper will discuss cellular reprogramming and its potential relevance to the treatment of haemoglobinopathies.

Lensfree On-Chip Microscopy and Tomography for Bio-Medical Applications

Lensfree on-chip holographic microscopy is an emerging technique that offers imaging of biological specimens over a large field-of-view without using any lenses or bulky optical components. Lending itself to a compact, cost-effective and mechanically robust architecture, lensfree on-chip holographic microscopy can offer an alternative toolset addressing some of the emerging needs of microscopic analysis and diagnostics in low-resource settings, especially for telemedicine applications. In this review, we summarize the latest achievements in lensfree optical microscopy based on partially coherent on-chip holography, including portable telemedicine microscopy, cell-phone based microscopy and field-portable optical tomographic microscopy. We also discuss some of the future directions for telemedicine microscopy and its prospects to help combat various global health challenges.

Induction of human fetal hemoglobin via the NRF2 antioxidant response signaling pathway

Although hematopoietic stem cell transplantation and gene therapy have the potential to cure β-thalassemia and sickle cell disease, they are not currently available to most people with these diseases. In the near term, pharmacologic induction of fetal hemoglobin (HbF) may offer the best possibility for safe, effective, and widely available therapy. In an effort to define new pathways for targeted drug development for HbF induction, we evaluated the nuclear factor erythroid 2-related factor 2 (NRF2) antioxidant response element signaling pathway. We found that 3 well-known activators of this pathway increased γ-globin mRNA at nontoxic doses in K562 cells. Tert-butylhydroquinone (tBHQ), the most active of these compounds, increased cellular levels and nuclear translocation of NRF2 and binding of NRF2 to the γ-globin promoter. siRNA knockdown of NRF2 inhibited γ-globin induction by tBHQ. When tested in human primary erythroid cells, tBHQ induced NRF2 binding to the γ-globin promoter, increased γ-globin mRNA and HbF, and suppressed β-globin mRNA and HbA, resulting in a > 3-fold increase in the percentage of HbF. These results suggest that drugs that activate the NRF2/antioxidant response element signaling pathway have the potential to induce therapeutic levels of HbF in people with β-hemoglobinopathies.

Membrane stability of sickle erythrocytes incubated in extracts of three medicinal plants: Anacardium occidentale, Psidium guajava, and Terminalia catappa

BACKGROUND

Many reports showed that medicinal plant extracts cause alterations on the shape and physiology of erythrocytes.

OBJECTIVE

The present study seeks to ascertain the osmotic stability of sickle erythrocytes incubated in aqueous extracts of Anacardium occidentale, Psidium guajava, and Terminalia catappa.

MATERIALS AND METHODS

The fraction of erythrocytes lysed when suspended in saline solution of varying concentrations was investigated by spectrophotometric method. The percentage hemolysis of erythrocytes in the control and test samples showed a sigmoidal relationship with increasing concentrations of saline solution. Membrane stability was ascertained as mean corpuscular fragility (MCF) index of erythrocytes incubated in 400 and 800 mg/dL aqueous concentrations of the three plant extracts.

RESULTS

The two experimental concentrations of P. guajava and T. catappa protected the erythrocytes against osmotic stress, as evidenced by decreases in the values of MCF compared with the control sample (P < 0.05). However, 800 mg/dL of A. occidentale promoted significant (P < 0.05) distabilization of sickle erythrocytes.

CONCLUSION

Whereas the two experimental concentrations of aqueous extracts of P. guajava and T. catappa stabilized erythrocyte membrane, higher concentration (800 mg/dL) of A. occidentale exhibited no membrane protective effect.

CXCL1 and its receptor, CXCR2, mediate murine sickle cell vaso-occlusion during hemolytic transfusion reactions

Hemolytic transfusion reactions (HTRs) can produce serious and potentially life-threatening complications in sickle cell disease (SCD) patients; however, the mechanisms underlying these complications remain undetermined. We established a model of alloimmune, IgG-mediated HTRs in a well-characterized humanized murine model of SCD. HTRs induced acute vaso-occlusive crisis (VOC), resulting in shortened survival of SCD mice. Acute VOC was associated with elevated circulating inflammatory chemokine levels, including striking elevation of the levels of the neutrophil chemoattractant CXCL1. Recombinant CXCL1 administration was sufficient to induce acute VOC in SCD mice, characterized by leukocyte recruitment in venules, capture of circulating red blood cells, reduction of venular flow, and shortened survival. In contrast, blockade of the CXCL1 receptor, CXCR2, prevented HTR-elicited acute VOC and prolonged survival in SCD mice. These results indicate that CXCL1 is a key inflammatory mediator of acute VOC in SCD mice. Targeted inhibition of CXCL1 and/or CXCR2 may therefore represent a new therapeutic approach for acute VOC in SCD patients.

Mechanisms of enhanced thrombus formation in cerebral microvessels of mice expressing hemoglobin-S

The microvasculature assumes an inflammatory and procoagulant state in a variety of different diseases, including sickle cell disease (SCD), which may contribute to the high incidence of ischemic stroke in these patients. This study provides evidence for accelerated thrombus formation in arterioles and venules in the cerebral vasculature of mice that express hemoglobin-S (β(s) mice). Enhanced microvascular thrombosis in β(s) mice was blunted by immunologic or genetic interventions that target tissue factor, endothelial protein C receptor, activated protein C, or thrombin. Platelets from β(s) mice also exhibited enhanced aggregation velocity after stimulation with thrombin but not ADP. Neutropenia also protected against the enhanced thrombosis response in β(s) mice. These results indicate that the cerebral microvasculature is rendered vulnerable to thrombus formation in β(s) mice via a neutrophil-dependent mechanism that is associated with an increased formation of and enhanced platelet sensitivity to thrombin.

Understanding Growth Failure in Children With Homozygous Sickle-Cell Disease

Sickle-cell disease is the most prevalent genetic hematologic condition in the United States. Numerous studies have demonstrated poor growth and delayed maturation in children with homozygous sickle-cell disease; however, the pathophysiology remains inadequately understood. Affected children have normal weight and length at birth, and then around 6 months of age their growth patterns begin to diverge from the norm. The growth deficits experienced by these children remain a problem with clinical significance and intangible consequences. A review of literature has provided insight into the multifactorial basis of the growth failure experienced by this population. It is important that nurses and health care providers are familiar with the growth patterns unique to sickle-cell disease and recognize their role in clinical practice.

Sickle cell biomechanics

As the predominant cell type in blood, red blood cells (RBCs) and their biomechanical properties largely determine the rheological and hemodynamic behavior of blood in normal and disease states. In sickle cell disease (SCD), mechanically fragile, poorly deformable RBCs contribute to impaired blood flow and other pathophysiological aspects of the disease. The major underlying cause of this altered blood rheology and hemodynamics is hemoglobin S (HbS) polymerization and RBC sickling under deoxygenated conditions. This review discusses the characterization of the biomechanical properties of sickle RBCs and sickle blood as well as their implications toward a better understanding of the pathophysiology of the disease.

Specific binding of red blood cells to endothelial cells is regulated by nonadsorbing macromolecules

Abnormal adhesion of red blood cells to the endothelium has been linked to the pathophysiology of several diseases associated with vascular disorders. Various biochemical changes, including phosphatidylserine exposure on the outer membrane of red blood cells as well as plasma protein levels, have been identified as being likely to play a key role, but the detailed interplay between plasma factors and cellular factors remains unknown. It has been proposed that the adhesion-promoting effect of plasma proteins originates from ligand interaction, but evidence substantiating this assumption is often missing. In this work, we identified an alternative pathway by demonstrating that nonadsorbing macromolecules can also have a marked impact on the adhesion efficiency of red blood cells with enhanced phosphatidylserine exposure to endothelial cells. It is concluded that this adhesion-promoting effect originates from macromolecular depletion interaction and thereby presents an alternative mechanism by which plasma proteins could regulate cell-cell interactions. These findings should thus be of potential value for a detailed understanding of the pathophysiology of diseases associated with vascular complications and might be applicable to a wide range of cell-cell interactions in plasma or plasma-like media.

GMI-1070, a novel pan-selectin antagonist, reverses acute vascular occlusions in sickle cell mice

Leukocyte adhesion in the microvasculature influences blood rheology and plays a key role in vaso-occlusive manifestations of sickle cell disease. Notably, polymorphonuclear neutrophils (PMNs) can capture circulating sickle red blood cells (sRBCs) in inflamed venules, leading to critical reduction in blood flow and vaso-occlusion. Recent studies have suggested that E-selectin expression by endothelial cells plays a key role by sending activating signals that lead to the activation of Mac-1 at the leading edge of PMNs, thereby allowing RBC capture. Thus, the inhibition of E-selectin may represent a valuable target in this disease. Here, we have tested the biologic properties of a novel synthetic pan-selectin inhibitor, GMI-1070, with in vitro assays and in a humanized model of sickle cell vaso-occlusion analyzed by intravital microscopy. We have found that GMI-1070 predominantly inhibited E-selectin-mediated adhesion and dramatically inhibited sRBC-leukocyte interactions, leading to improved microcirculatory blood flow and improved survival. These results suggest that GMI-1070 may represent a valuable novel therapeutic intervention for acute sickle cell crises that should be further evaluated in a clinical trial.

Review: Management of Painful Vaso-Occlusive Crisis of Sickle-Cell Anemia: Consensus Opinion

Sickle-cell disease (SCD) is a wide-spread inherited hemolytic anemia that is due to a point mutation, leading to the substitution of valine for glutamic acid, causing a spectrum of clinical manifestations in addition to hemolysis and anemia. Acute painful crisis is a common sequela that can cause significant morbidity and negatively impact the patient’s quality of life. Remarkable improvements in the understanding of the pathogenesis of this clinical syndrome and the role of cell adhesion, inflammation, and coagulation in acute painful crisis have led to changes in the management of pain. Due to the endemic nature of SCD in various parts of the Middle East, a group of physicians and scientists from the United States and Middle East recently met to draw up a set of suggested guidelines for the management of acute painful crisis that are reflective of local and international experience. This review brings together a detailed etiology, the pathophysiology, and clinical presentation of SCD, including the differential diagnoses of pain associated with the disease, with evidence-based recommendations for pain management and the potential impact of low-molecular-weight heparin (LMWH), from the perspective of physicians and scientists with long-term experience in the management of a large number of patients with SCD.

Sickle cell disease in the United States: looking back and forward at 100 years of progress in management and survival

The past 100 years since James Herrick's first description of sickle cell disease in the United States have been characterized by the gradual development of management strategies. We review the progress in sickle cell disease management in the United States over the past 100 years, with emphasis on the diverse forces surrounding advances in disease management. Mortality and survival data are presented chronologically, with an attempt to highlight improvements in survival associated with specific advancements for pediatric and adult care. Finally, the future course for sickle cell disease management is explored, given the continued work in advancing the field.

Pulmonary hypertension and nitric oxide depletion in sickle cell disease

During the past decade a large body of experimental and clinical studies has focused on the hypothesis that nitric oxide (NO) depletion by plasma hemoglobin in the microcirculation plays a central role in the pathogenesis of many manifestations of sickle cell disease (SCD), particularly pulmonary hypertension. We have carefully examined those studies and believe that the conclusions drawn from them are not adequately supported by the data. We agree that NO depletion may well play a role in the pathophysiology of other hemolytic states such as paroxysmal nocturnal hemoglobinuria, in which plasma hemoglobin concentrations are often at least an order of magnitude greater than in SCD. Accordingly, we conclude that clinical trials in SCD designed to increase the bioavailability of NO or association studies in which SCD clinical manifestations are related to plasma hemoglobin via its surrogates should be viewed with caution.

The use of partial exchange blood transfusion and anaesthesia in the management of sickle cell disease in a perioperative setting: two case reports

INTRODUCTION

Homozygous sickle cell carriers have an increased perioperative mortality. Some indications may justify an exchange blood transfusion to reduce the proportion of haemoglobin S. The advantages of general blood transfusion in a perioperative setting have not been proven and thus remain controversial. It is not clear whether reducing the proportion of haemoglobin S minimizes perioperative complications or whether patients with sickle cell disease in a stable clinical condition benefit from an exchange blood transfusion in a perioperative setting.

CASE PRESENTATION

We report the case of two Angolan children aged 10 and 11 respectively, of African origin with sickle cell anaemia who underwent surgery to treat chronic necrosis, fistula of the bones and bone destruction. This presentation describes the perioperative course, including general anaesthesia. A partial exchange blood transfusion decreased S-haemoglobin levels from 81% to 21% and simultaneously treated the anaemia.

CONCLUSION

There is a consensus that imbalances in homoeostasis, including operative procedures, can cause a critical exacerbation of sickle cell disease. The case presented here illustrates a strategy for successfully managing sickle cell disease in the perioperative period to minimize its complications. It is important for the anaesthesiologist to carefully manage pulmonary gas exchange and to ensure sufficient tissue perfusion, balanced fluid resuscitation and normothermia, while keeping in mind the level of organ impairment in order to prevent an acute exacerbation of sickle cell disease.We performed a partial exchange blood transfusion due to the following factors: high haemoglobin S-fraction, anaemia, operating procedure at several sites, and difficult management of body temperature. Esmarch ischemia is an established tool for preventing uncontrolled blood loss. There is no known contraindication for this, but attention must be paid to prevent uncontrolled tissue ischemia and acidosis. The use of regional anaesthesia should be considered for postoperative pain management.

Neutrophil microdomains: linking heterocellular interactions with vascular injury

PURPOSE OF REVIEW

Neutrophil infiltration is an important feature in inflammatory scenarios. Before these cells infiltrate tissues, however, they contribute to crucial intravascular events in which neutrophil microdomains mediate heterotypic interactions with endothelial cells, red blood cells and/or platelets. In vascular diseases, this can result in exacerbated neutrophil activation, subsequent vascular injury and obstruction of microcirculatory blood flow. This review discusses recent advances in elucidating these neutrophil domains and their associated functions in cell adhesion.

RECENT FINDINGS

Neutrophil recruitment is mediated by sequential interactions with the endothelium, termed rolling, adhesion and extravasation. Evidence points to novel signaling pathways induced during the rolling phase resulting in the transition to leukocyte adhesion, which appear to contribute to chemokine mediated activation. In addition, specific neutrophil microdomains are important for interactions with other hematopoietic cells inducing reductions in microvascular flow and injury.

SUMMARY

Neutrophils integrate signals received from the endothelium to act as linkers between the vessel wall and a variety of vascular components (i.e. endothelial cells, platelets, red blood cells) in acute and chronic inflammatory conditions to mediate interactions that can result in vascular injury and vasoocclusion.

Diagnosis and management of sickle cell disorders

Sickle cell disease (SCD) is a wide-spread inherited hemolytic anemia that is due to a point mutation leading to a valine/glutamic acid substitution in the beta-globin chain, causing a spectrum of clinical manifestations in addition to hemolysis and anemia. Acute painful crisis is a common sequela that can cause significant morbidity and negatively impact the patient's quality of life. Remarkable improvements in our understanding of the pathogenesis of this clinical syndrome and the role of cell adhesion, inflammation, and coagulation in acute painful crisis have led to changes in the management of pain. Due to the endemic nature of SCD in various parts of the Middle East, a group of physicians and scientists from the United States and Middle East recently met to draw up a set of suggested guidelines for the management of acute painful crisis that are reflective of local and international experience. This chapter brings together a detailed etiology, pathophysiology, and clinical presentation of SCD, including the differential diagnoses of pain associated with the disease, with evidence-based recommendations for pain management and the potential impact of low-molecular weight heparin (LMWH), from the perspective of physicians and scientists with long-term experience in the management of a large number of SCD patients.

Increased levels of the inflammatory biomarker C-reactive protein at baseline are associated with childhood sickle cell vasocclusive crises

Several lines of evidence suggest that sickle cell disease (SCD) is associated with a chronic inflammatory state. In this study of 70 children with SCD at steady state evaluated by a broad panel of biomarkers representing previously examined mechanisms of pathogenicity in SCD, high sensitivity C-reactive protein (hs-CRP), a marker of low-grade, systemic inflammation, emerged as the most significant laboratory correlate of hospitalizations for pain or vaso-occlusive (VOC) events. While markers of increased haemolytic status, endothelial activation and coagulation activation all correlated positively with VOC events by univariate analysis, baseline hs-CRP levels provided the most significant contribution to the association in multiple regression models (22%), and, hs-CRP, along with age, provided the best fit in negative binomial models. These data highlight the clinical relevance of the role of inflammation in paediatric VOC, providing both a rationale for future therapeutic strategies targeting inflammation in microvessel occlusive complications of SCD, and the potential clinical use of hs-CRP as a biomarker in childhood SCD.

Genetics and the general physician: insights, applications and future challenges

Scientific and technological advances in our understanding of the nature and consequences of human genetic variation are now allowing genetic determinants of susceptibility to common multifactorial diseases to be defined, as well as our individual response to therapy. I review how genome-wide association studies are robustly identifying new disease susceptibility loci, providing insights into disease pathogenesis and potential targets for drug therapy. Some of the remarkable advances being made using current genetic approaches in Crohn's disease, coronary artery disease and atrial fibrillation are described, together with examples from malaria, HIV/AIDS, asthma, prostate cancer and venous thrombosis which illustrate important principles underpinning this field of research. The limitations of current approaches are also noted, highlighting how much of the genetic risk remains unexplained and resolving specific functional variants difficult. There is a need to more clearly understand the significance of rare variants and structural genomic variation in common disease, as well as epigenetic mechanisms. Specific examples from pharmacogenomics are described including warfarin dosage and prediction of abacavir hypersensitivity that illustrate how in some cases such knowledge is already impacting on clinical practice, while in others prospective evaluation of clinical utility and cost-effectiveness is required to define opportunities for personalized medicine. There is also a need for a broader debate about the ethical implications of current advances in genetics for medicine and society.

Minor histocompatibility antigens on transfused leukoreduced units of red blood cells induce bone marrow transplant rejection in a mouse model

When successful, human leukocyte antigen (HLA)-matched bone marrow transplantation with reduced-intensity conditioning is a cure for several nonmalignant hematologic disorders that require chronic transfusion, such as sickle cell disease and aplastic anemia. However, there are unusually high bone marrow transplant (BMT) rejection rates in these patients. Rejection correlates with the number of transfusions before bone marrow transplantation, and it has been hypothesized that preimmunization to antigens on transfused blood may prime BMT rejection. Using a novel mouse model of red blood cell (RBC) transfusion and major histocompatibility complex-matched bone marrow transplantation, we report that transfusion of RBC products induced BMT rejection across minor histocompatibility antigen (mHA) barriers. It has been proposed that contaminating leukocytes are responsible for transfusion-induced BMT rejection; however, filter leukoreduction did not prevent rejection in the current studies. Moreover, we generated a novel transgenic mouse with RBC-specific expression of a model mHA and demonstrated that transfusion of RBCs induced a CD8(+) T-cell response. Together, these data suggest that mHAs on RBCs themselves are capable of inducing BMT rejection. Cellular immunization to mHAs is neither monitored nor managed by current transfusion medicine practice; however, the current data suggest that mHAs on RBCs may represent an unappreciated and significant consequence of RBC transfusion.