A systems biology consideration of the vasculopathy of sickle cell anemia: the need for multi-modality chemo-prophylaxsis

Sickle cell disease in children: an update of the evidence in low- and middle-income settings

Sickle cell disease (SCD), one of the most common monogenetic diseases in the world, is associated with multisystemic complications that begin in childhood. Most of the babies homozygous for the sickle haemoglobin gene are born in sub-Saharan Africa. Over the years, progress has been made with early diagnosis through newborn screening, penicillin prophylaxis, pneumococcal immunisation, transcranial Doppler (TCD) screening, hydroxyurea therapy and chronic blood transfusions with remarkably improved survival and quality of life of children with SCD. However, wide disparities in outcomes exist between high-income countries (HICs) where over 90% survive to adulthood, and low-income and middle-income countries (LMICs) where less than half achieve that milestone. Even in HICs, racial inequities pose barriers to accessing specialised care and receiving treatment for acute pain episodes. Better understanding of SCD pathophysiology is being exploited to develop new disease-modifying drugs and gene therapy approaches to further improve outcomes. Bone marrow transplantation is established as a curative treatment for SCD, but it is largely unavailable in LMICs. To bridge the disparity and inequity gaps, innovative approaches are needed in LMICs. Validated and more affordable, easy-to-use point-of-care tests offer opportunities to link early diagnosis with immunisation programmes and healthcare encounters. Widespread use of hydroxyurea therapy-a relatively affordable and effective disease-modifying drug-in LMICs would help improve survival and quality of life. Integration of SCD treatment into primary care linked to district level/provincial hospitals that are supported with evidence-based guidelines will help extend needed interventions to many more patients living in LMICs.

Functional foods: promising therapeutics for Nigerian Children with sickle cell diseases

Sickle cell disease (SCD), also known as sickle cell anemia (SCA) is one of the structural hemoglobinopathies that occurs due to a single nucleotide mutation from GAG to GTG, which changes the amino acid of a β-globin chain of hemoglobin (Hb) from glutamate to valine. This singular mutation results to disorderliness in red blood cells (RBCs) with advent of changes in RBC morphology and other pathological conditions. In the 1980s, intermittent red blood cell transfusions, opioids, and penicillin prophylaxis were the only available therapy for SCA and were commonly reserved for acute, life threatening complications. So far, the US Food and Drug Administration (FDA) has granted a total of four drugs approval for the prophylaxis and treatment of the clinical complications of SCD. Due to limitations (adherence, safety, adverse effects) of existing therapies in the prophylaxis and treatment of SCD complications in Nigerian children and their inaccessibility to approved drugs, the present study discusses the therapeutic effects of readily available functional food as one of the therapies or an adjunct therapy to tackle the sickle cell crisis in Nigerian Children.

Transfusional Approach in Multi-Ethnic Sickle Cell Patients: Real-World Practice Data From a Multicenter Survey in Italy

Sickle cell disease (SCD) is a worldwide distributed hereditary red cell disorder characterized by recurrent acute vaso-occlusive crises (VOCs and anemia). Gold standard treatments are hydroxycarbamide (HC) and/or different red blood cell (RBC) transfusion regimens to limit disease progression. Here, we report a retrospective study on 1,579 SCD patients (median age 23 years; 802 males/777 females), referring to 34 comprehensive Italian centers for hemoglobinopathies. Although we observed a similar proportion of Caucasian (47.9%) and African (48.7%) patients, Italian SCD patients clustered into two distinct overall groups: children of African descent and adults of Caucasian descent. We found a subset of SCD patients requiring more intensive therapy with a combination of HC plus chronic transfusion regimen, due to partial failure of HC treatment alone in preventing or reducing sickle cell-related acute manifestations. Notably, we observed a higher use of acute transfusion approaches for SCD patients of African descent when compared to Caucasian subjects. This might be related to (i) age of starting HC treatment; (ii) patients' low social status; (iii) patients' limited access to family practitioners; or (iv) discrimination. In our cohort, alloimmunization was documented in 135 patients (8.5%) and was more common in Caucasians (10.3%) than in Africans (6.6%). Alloimmunization was similar in male and female and more frequent in adults than in children. Our study reinforces the importance of donor-recipient exact matching for ABO, Rhesus, and Kell antigen systems for RBC compatibility as a winning strategy to avoid or limit alloimmunization events that negatively impact the clinical management of SCD-related severe complications.

Is there bacterial infection in the intact crowns of teeth with pulp necrosis of sickle cell anaemia patients? A case series study nested in a cohort

AIM

To evaluate the presence of bacteria in permanent teeth with intact crowns (without caries, periodontal disease or dental trauma) in patients with sickle cell anaemia (HbSS genotype) by analysing their clinical, imaging and microbiological parameters.

METHODOLOGY

This is a case series study nested in a cohort. In the first follow-up of this cohort study (Journal of Endodontics, 2013, 39, 177), 10 HbSS patients with at least one tooth with an intact crown and clinically diagnosed with pulp necrosis by pulse oximetry adapted for dentistry and a cold pulp sensitivity test (n = 27 teeth) were selected. Changes in the pulp chamber, root and periodontal ligament were identified in the tomographic analysis. Bacterial culture, staining for live and dead bacteria, and real-time polymerase chain reaction with 16S rRNA primers were used to identify the presence of bacteria. Culture sample collection was performed immediately after access to the pulp chamber. The microbiome was analysed with a MiSeq sequencer (Illumina, San Diego, CA).

RESULTS

The diagnosis of pulp necrosis was confirmed clinically in 82% (22/27) of the teeth. The amount of bacterial load identified was less than 100 copies μL^-1 in 23% (5/22) of the teeth with intact crowns and pulp necrosis. Thirteen bacterial species were identified that are commonly found in urinary tract infections, septicaemia and infective endocarditis. Only one of these species, Granulicatella adjacens, has also be found in primary endodontic infections.

CONCLUSION

Prospective clinical, imaging and microbiological analyses suggest that pulp necrosis of teeth with intact crowns in HbSS patients is not associated with the presence of bacteria.

Neutrophil extracellular trap regulators in sickle cell disease: Modulation of gene expression of PADI4, neutrophil elastase, and myeloperoxidase during vaso-occlusive crisis

BACKGROUND

Recent evidence suggests that generation of neutrophil extracellular traps (NETosis), one of the components of immunothrombosis, is associated with the pathogenesis of both venous thromboembolism and sickle cell disease (SCD). NETosis is a complex process regulated by several proteins such as peptidyl arginine deaminase 4 (PADI4), neutrophil elastase (ELANE), and myeloperoxidase (MPO). Among these regulators, PADI4 is responsible of histone citrullination, an essential step for NETosis. Accordingly, its inhibition has been recently cited as a promising therapeutic strategy for diseases such as SCD. Although attractive, this strategy requires supportive evidence of its role in the pathogenesis of SCD.

PATIENTS AND METHODS

Patients from two independent cohorts were enrolled in this study. Samples were obtained at steady state (53 patients) or during acute episodes of vaso-occlusive crisis (VOC; 28 patients) in patients from cohort 1. mRNA was extracted from granulocytes to analyze PADI4, ELANE, and MPO expression by qPCR. Furthermore, plasma activity of PADI4 was assessed from an independent cohort in 15 patients, within 24 hours from admission for VOC. Race-matched healthy individuals from the same geographic regions were used as controls for each cohort.

RESULTS AND CONCLUSIONS

Higher levels of gene expression of PADI4 and ELANE were observed during VOC. Furthermore, plasma activity of PADI4 was higher in acute VOC when compared to healthy individuals. These results demonstrate that NETosis regulators are modulated during acute VOC, and pave the way for studies of PADI4 inhibition as a therapeutic strategy for acute VOC in SCD.

Recommendations for Pregnancy in Rare Inherited Anemias

Rare inherited anemias are a subset of anemias caused by a genetic defect along one of the several stages of erythropoiesis or in different cellular components that affect red blood cell integrity, and thus its lifespan. Due to their low prevalence, several complications on growth and development, and multi-organ system damage are not yet well defined. Moreover, during the last decade there has been a lack of proper understanding of the impact of rare anemias on maternal and fetal outcomes. In addition, there are no clear-cut guidelines outlining the pathophysiological trends and management options unique to this special population. Here, we present on behalf of the European Hematology Association, evidence- and consensus-based guidelines, established by an international group of experts in different fields, including hematologists, gynecologists, general practitioners, medical geneticists, and experts in rare inherited anemias from various European countries for standardized and appropriate choice of therapeutic interventions for the management of pregnancy in rare inherited anemias, including Diamond-Blackfan Anemia, Congenital Dyserythropoietic Anemias, Thalassemia, Sickle Cell Disease, Enzyme deficiency and Red cell membrane disorders.

Biochemical and therapeutic effects of Omega-3 fatty acids in sickle cell disease

Sickle cell disease (SCD) is a hematologic disorder with complex pathophysiology that includes chronic hemolysis, vaso-occlusion and inflammation. Increased leukocyte-erythrocyte-endothelial interactions, due to upregulated expression of adhesion molecules and activated endothelium, are thought to play a primary role in initiation and progression of SCD vaso-occlusive crisis and end-organ damage. Several new pathophysiology-based therapeutic options for SCD are being developed, chiefly targeting the inflammatory pathways. Omega-3 fatty acids are polyunsaturated fatty acids that are known to have effects on diverse physiological processes. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are the principal biologically active omega-3 fatty acids. The therapeutic effects of DHA and EPA on chronic inflammatory disorders and cardiovascular diseases are well recognized. The therapeutic effects of omega-3 fatty acids are attributed to their anti-inflammatory and anti-thrombotic eicosanoids, and the novel class of EPA and DHA derived lipid mediators: resolvins, protectins and maresins. Blood cell membranes of patients with SCD have abnormal fatty acids composition characterized by high ratio of pro-inflammatory arachidonic acid (AA) to anti-inflammatory DHA and EPA (high omega-6/omega-3 ratio). In addition, experimental and clinical studies provide evidence that treatment with DHA does confer improvement in rheological properties of sickle RBC, inflammation and hemolysis. The clinical studies have shown improvements in VOC rate, markers of inflammation, adhesion, and hemolysis. In toto, the results of studies on the therapeutic effects of omega-3 fatty acids in SCD provide good body of evidence that omega-3 fatty acids could be a safe and effective treatment for SCD.

Association between Endothelial Dysfunction, Biomarkers of Renal Function, and Disease Severity in Sickle Cell Disease

Background

Endothelial dysfunction (ED), as ascertained by brachial artery flow-mediated dilation (FMD), is a known feature of sickle cell disease (SCD), which is present both in crisis and in steady state. The assessment of FMD was introduced to examine the vasodilator function. Our objective was to establish the relationship between ED determined by FMD, biomarkers of renal dysfunction, and biomarkers of disease severity in SCD subjects asymptomatic of renal disease.

Methods

We enrolled 44 patients with homozygous SCD in steady state and 33 age- and sex-matched controls between 2013 and 2014 in a tropical tertiary hospital. Ultrasonographic FMD of the right brachial artery, renal arterial Doppler, complete blood count, creatinine, fetal hemoglobin, soluble P-selectin, and cystatin C (Cys-C) levels were determined. Using the median FMD value of the control group, the SCD subjects were further classified into two groups for comparison.

Results

The median FMD in SCD subjects of 3.44 (IQR, 0.00-7.08) was significantly lower than that of controls, which was 5.35 (IQR, 3.60-6.78; P=0.04). There was negative correlation between FMD and Cys-C levels (r=-0.372; P=0.01) along with renal artery resistivity index (RARI; r=-0.307; P=0.04) in SCD subjects. Additionally, Cys-C level was significantly higher in SCD subjects with FMD<5.35.

Conclusions

Brachial artery FMD was significantly lower in SCD subjects compared with a control group. Cys-C and RARI show a negative correlation with FMD, indicating that renal function is related to ED in SCD.

Emerging drugs in randomized controlled trials for sickle cell disease: are we on the brink of a new era in research and treatment?

Introduction: Sickle cell disease (SCD) is caused by a mutation in the HBB gene which is key for making a component of hemoglobin. The mutation leads to the formation of an abnormal hemoglobin molecule called sickle hemoglobin (HbS). SCD is a chronic, complex disease with a multiplicity of pathophysiological targets; it has high morbidity and mortality.Hydroxyurea has for many years been the only approved drug for SCD; hence, the development of new therapeutics is critical.Areas covered: This article offers an overview of the key studies of new therapeutic options for SCD. We searched the PubMed database and Cochrane Database of Systemic Reviews for agents in early phase clinic trials and preclinical development.Expert opinion: Although knowledge of SCD has progressed, patient survival and quality of life must be improved. Phase II and phase III clinical trials investigating pathophysiology-based novel agents show promising results in the clinical management of SCD acute events. The design of long-term clinical studies is necessary to fully understand the clinical impact of these new therapeutics on the natural history of the disease. Furthermore, the building of global collaborations will enhance the clinical management of SCD and the design of primary outcomes of future clinical trials.

Erythrocyte and plasma oxidative stress appears to be compensated in patients with sickle cell disease during a period of relative health, despite the presence of known oxidative agents

Sickle cell disease (SCD) is a monogenetic disease that results in the formation of hemoglobin S. Due to more rapid oxidation of hemoglobin S due to intracellular heme and adventitious iron in SCD, it has been thought that an inherent property of SCD red cells would be an imbalance in antioxidant defenses and oxidant production. Less deformable and fragile RBC in SCD results in intravascular hemolysis and release of free hemoglobin (PFHb) in the plasma, which might be expected to produce oxidative stress in the plasma. Thus, we aimed to characterize intracellular and vascular oxidative stress in whole blood and plasma samples from adult SCD patients and controls recruited into a large study of SCD at Children's Hospital of Los Angeles. We evaluated the cellular content of metHb and several components of the antioxidant system in RBC as well as oxidation of GSH and Prx-2 oxidation in RBC after challenge with hydroperoxides. Plasma markers included PFHb, low molecular weight protein bound heme (freed heme), hemopexin, isoprostanes, and protein carbonyls. While GSH was slightly lower in SCD RBC, protein carbonyls, NADH, NAD+ and total NADP+ + NADPH were not different. Furthermore, GSH or Prx-2 oxidation was not different after oxidative challenge in SCD vs. Control. Elevated freed heme and PFHb had a significant negative, non-linear association with hemopexin. There appeared to be a threshold effect for hemopexin (200 μg/ml), under which the freed heme rose acutely. Plasma F2-isoprostanes were not significantly elevated in SCD. Despite significant release of Hb and elevation of freed heme in SCD when hemopexin was apparently saturated, there was no clear indication of uncompensated vascular oxidative stress. This somewhat surprising result, suggests that oxidative stress is well compensated in RBCs and plasma during a period of relative health.

Vascular Instability and Neurological Morbidity in Sickle Cell Disease: An Integrative Framework

It is well-established that patients with sickle cell disease (SCD) are at substantial risk of neurological complications, including overt and silent stroke, microstructural injury, and cognitive difficulties. Yet the underlying mechanisms remain poorly understood, partly because findings have largely been considered in isolation. Here, we review mechanistic pathways for which there is accumulating evidence and propose an integrative systems-biology framework for understanding neurological risk. Drawing upon work from other vascular beds in SCD, as well as the wider stroke literature, we propose that macro-circulatory hyper-perfusion, regions of relative micro-circulatory hypo-perfusion, and an exhaustion of cerebral reserve mechanisms, together lead to a state of cerebral vascular instability. We suggest that in this state, tissue oxygen supply is fragile and easily perturbed by changes in clinical condition, with the potential for stroke and/or microstructural injury if metabolic demand exceeds tissue oxygenation. This framework brings together recent developments in the field, highlights outstanding questions, and offers a first step toward a linking pathophysiological explanation of neurological risk that may help inform future screening and treatment strategies.

Receptor for Advanced Glycation End Products Antagonism Blunts Kidney Damage in Transgenic Townes Sickle Mice

A large proportion of adult patients with sickle cell disease (SCD) develops kidney disease and is at a high risk of mortality. The contribution of advanced glycation end products and their receptor (AGE/RAGE) axis has been established in the pathogenesis of multiple kidney diseases. The aim of the present study was to determine the implication of RAGE in the development of SCD-related kidney complications in a mouse model of SCD, as this has never been investigated. 8-week-old AA (normal) and SS (homozygous SCD) Townes mice were treated with a specific RAGE antagonist (RAP) or vehicle (NaCl). After 3 weeks of treatment, red blood cell count, hematocrit, and hemoglobin levels were significantly higher in RAP-treated SS mice. Reticulocyte count and sickle cell count were reduced in RAP-SS compared to their NaCl-treated littermates. The lower NADPH oxidase activity in the kidney of RAP-treated mice compared to NaCl-treated mice suggests limited ROS production. RAP-treated SS mice had decreased NF-κB protein expression and activation as well as reduced TNF-α mRNA expression in the kidney. Glomerular area, interstitial fibrosis, tubular iron deposits, and KIM-1 protein expression were significantly reduced after RAP treatment. In conclusion, this study provides evidence supporting the pathogenic role of RAGE in kidney injuries in sickle cell mice.

Sickle cell disease: Reducing the global disease burden

Sickle cell disease has been largely an invisible global health issue, especially in regions of high incidence mainly due to lack of awareness among both the local health policy makers and the public. Public health interventions, such as screening of newborns, provision of prophylaxis against bacterial infections, and immunizations against pneumococcal infections can have the greatest impact. Family education on assessment of spleen size and subsequent detection of splenic sequestration and promptness to seek medical attention for a febrile child is also important in the control of the morbidity and mortality of children with SCD living in resource-poor countries. In addition to these affordable interventions, hydroxyurea therapy is necessary to decrease both the acute and chronic complications of sickle cell anemia. Sickle cell disease has been recognized to have global health significance by key institutions including the World Health Organization in 2006 and the United Nation is 2008. In 2010, the WHO released national health care management goals and set targets to be achieved by the countries in sub-Saharan Africa for the control and management of SCD. These are yet to be translated into action. To do, this would require active and sustainable public-private partnerships for sustainable program development in these regions. Effective interventions should be integrated into existing health systems, the best examples linking primary healthcare facilities to specialized sickle cell disease centers in regional and tertiary healthcare institutions.

Muscle dysfunction is associated with poorer health-related quality of life in adults with sickle cell anaemia

BACKGROUND

It is known that episodes of microvascular obstruction and oxidative stress in sickle cell anaemia (SCA) can damage muscle tissue. As a consequence, deterioration in muscle function may potentially contribute to poor health-related quality of life (HRQoL) in subjects with SCA, particularly those who do not use long-term treatment.

OBJECTIVES

To evaluate muscle function in adults with SCA, to study the correlations between muscle function and HRQoL and to analyse the impact of hydroxyurea treatment.

METHODS

Twenty-two adults with SCA and 20 matched controls were subjected to Short Form-36 (SF-36), respiratory muscle strength measurement, isometric hand grip strength (iHGS) measurement and knee isokinetic dynamometry.

RESULTS

In relation to their healthy peers, adults with SCA had lower SF-36 scores, respiratory muscle strength and iHGS. Regarding the isokinetic test, adults with SCA showed lower values, especially in the variables measured in flexion and with an angular velocity of 240∘/s. There was a significant correlation between the peak torque (PT) at 240∘/s and the physical component summary (SF-36PCS) in both extension (r= 0.77; p< 0.001) and flexion (r= 0.82; p< 0.001). Significant correlations were also observed between the agonist/antagonist ratio at 240∘/s and the SF-36PCS (r= 0.50; p< 0.001). The use of hydroxyurea led to higher scores on the SF-36 and higher values in knee isokinetic dynamometry.

CONCLUSIONS

Adults with SCA have muscle dysfunction, especially with regard to endurance of the knee flexor muscles. In these patients, there is a significant association between muscle function and HRQoL. Moreover, the use of hydroxyurea is associated with better HRQoL and less muscle dysfunction.

Therapeutic strategies for sickle cell disease: towards a multi-agent approach

For over 100 years, clinicians and scientists have been unravelling the consequences of the A to T substitution in the β-globin gene that produces haemoglobin S, which leads to the systemic manifestations of sickle cell disease (SCD), including vaso-occlusion, anaemia, haemolysis, organ injury and pain. However, despite growing understanding of the mechanisms of haemoglobin S polymerization and its effects on red blood cells, only two therapies for SCD - hydroxyurea and L-glutamine - are approved by the US Food and Drug Administration. Moreover, these treatment options do not fully address the manifestations of SCD, which arise from a complex network of interdependent pathophysiological processes. In this article, we review efforts to develop new drugs targeting these processes, including agents that reactivate fetal haemoglobin, anti-sickling agents, anti-adhesion agents, modulators of ischaemia-reperfusion and oxidative stress, agents that counteract free haemoglobin and haem, anti-inflammatory agents, anti-thrombotic agents and anti-platelet agents. We also discuss gene therapy, which holds promise of a cure, although its widespread application is currently limited by technical challenges and the expense of treatment. We thus propose that developing systems-oriented multi-agent strategies on the basis of SCD pathophysiology is needed to improve the quality of life and survival of people with SCD.

New Therapeutic Options for the Treatment of Sickle Cell Disease

Sickle cell disease (SCD; ORPHA232; OMIM # 603903) is a chronic and invalidating disorder distributed worldwide, with high morbidity and mortality. Given the disease complexity and the multiplicity of pathophysiological targets, development of new therapeutic options is critical, despite the positive effects of hydroxyurea (HU), for many years the only approved drug for SCD. New therapeutic strategies might be divided into (1) pathophysiology-related novel therapies and (2) innovations in curative therapeutic options such as hematopoietic stem cell transplantation and gene therapy. The pathophysiology related novel therapies are: a) Agents which reduce sickling or prevent sickle red cell dehydration; b) Agents targeting SCD vasculopathy and sickle cell-endothelial adhesive events; c) Anti-oxidant agents. This review highlights new therapeutic strategies in SCD and discusses future developments, research implications, and possible innovative clinical trials.

Intima-media thickness of the common femoral artery as a marker of leg ulceration in sickle cell disease patients

Leg ulceration is a debilitating chronic complication of sickle cell disease (SCD) the pathogenesis of which is yet to be fully elucidated. We hypothesized that SCD patients with histories of previous leg ulcers would have intima hyperplasia of the common femoral artery (CFA). We enrolled 44 SCD patients and 33 age-matched and sex-matched controls with hemoglobin AA. Anthropometric measurements, biochemical parameters, and sonographic intima-media thickness (IMT) of the CFA were determined. The median CFA IMT in SCD limbs with history of leg ulcers (SWLU) was 1.0 mm, whereas it was 0.7 mm in SCD limbs with no history of leg ulcer (SNLU) and 0.60 mm in controls (P < .001). Among the SNLU, 70.3% had CFA IMT <0.9 mm, whereas only 29.7% had CFA IMT ≥0.9 mm. Conversely, only 20.8% of SWLU had CFA IMT <0.9 mm, whereas the remaining 79.2% had CFA IMT ≥0.9 mm. All the controls had CFA IMT <0.9 mm. Binary logistic regression to determine the odds of having leg ulcer among SCD limbs with CFA IMT of ≥0.9 mm yielded an odds ratio of 9, indicating that SCD limbs with CFA IMT ≥0.9 mm had a 9 times greater risk of having leg ulcer compared with those with CFA IMT <0.9 mm. There is a significant increase in the CFA IMT of SCD limbs with ulcer compared with controls and SCD limbs without ulcer, suggesting that arterial vasculopathy plays a major role in the formation of these ulcers.

Coagulation profile of Sudanese children with homozygous sickle cell disease and the effect of treatment with omega-3 fatty acid on the coagulation parameters

Background

It has been reported that patients with SCD do have an abnormal coagulation profile. Coagulopathy is thought to be one of the key factors that contribute to the vaso-occlusive crisis that characterises sickle cell disease (SCD). In this study, we investigated whether Sudanese sickle cell patients have an abnormal coagulation profile. In addition, the effect of treatment with either omega-3 fatty acids or hydroxyurea on coagulation profile was assessed.

Methods

Homozygous SCD patients untreated (n = 52), omega-3 treated (n = 44), hydroxyurea (HU) treated (n = 8) and healthy (HbAA) controls (n = 52) matched for age (4–20 years), gender and socioeconomic status were enrolled. Patients on omega-3 fatty acids, according to age, received one to four capsules containing 277.8 mg DHA and 39.0 mg eicosapentnoic. Patients on Hydroxyurea were in on dosage more than 20 mg/kg/day. The steady state levels of the coagulation parameters and the effect of the treatments with either HU or omega-3 fatty acids on markers of coagulation were investigated.

Results

Compared to the healthy controls, treated and untreated HbSS patients had lower hemoglobin, plasma Protein C, proteins S and higher white blood cell count (WBC), platelets count (PLTs) and plasma D-dimer levels,(p < 0.05). In comparison to untreated HbSS, treatment with neither omega-3 nor HU had effect on the WBC, plasma proteins C and S, (p > 0.05). HU treated group had a lower PLTs count compared to HbSS untreated group (p < 0.5). The prothrombin and activated partial thromboplastin times and international normalized ratio (INR) of untreated patients are significantly higher than n-3 treated, HU-treated patients and health controls, (p < 0.05). Patients treated with omega-3 had lowered D-dimer levels in comparison to HU-treated and untreated HbSS patients, (p < 0.001).

Conclusion

This study provides evidence that Sudanes patients have abnormal coagulation profile and treatment with either HU or omega-3 fatty acids might partially ameliorate SCD-associated chronic coagulopathic state.

Exosomes contribute to endothelial integrity and acute chest syndrome risk: Preliminary findings

BACKGROUND

Acute Chest Syndrome (ACS) is one of the leading causes of death among children with Sickle Cell Disease (SCD). Disruption of microvascular integrity is critical to the pathophysiology of ACS, but the factors governing its phenotypic variability are incompletely understood. Because circulating exosomes have been implicated in vascular dysfunction in various diseases, we hypothesized that exosomes induce endothelial dysfunction in patients who experience ACS.

PROCEDURE

Cross-sectional cohort study including 33 outpatients with SCD (without new health-related complaints or recent transfusions) and a cohort of control patients. Exosomes were isolated from platelet-free plasma.

RESULTS

ImageStream showed that exosome counts were greatly increased in patients with SCD compared with controls, but there were few differences in the concentrations of exosomes between patients who had experienced ACS (ACS(+)) and those who had not (ACS(-)). Exosomes were added to human microvascular endothelial cells, and the exosomal effects on monolayer integrity was determined using Electric Cell-substrate Impedance Sensing (ECIS). Exosomes from SCD patients without ACS differed minimally from control patients; however, exosomes from ACS(+) decreased endothelial cell resistance compared to ACS(-), (Relative resistance: ACS(+): 0.981 ± 0.055 vs ACS(-): 1.124 ± 0.042; P = 0.006). Treatment of endothelial cultures with exosomes from ACS(-) patients increased endothelial Nitric Oxide Synthase (eNOS) mRNA expression, while ACS(+)-derived exosomes were not able to increase eNOS expression above that of controls.

CONCLUSIONS

These findings demonstrate that patients with SCD have circulating exosomes that produce differential effects that may contribute to the pathophysiology of ACS and may serve as risk-related biomarkers.

Imaging of musculoskeletal manifestations in sickle cell disease patients

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. Major clinical manifestations of SCD include haemolytic anaemia and vaso-occlusive phenomena resulting in ischaemic tissue injury and organ damage. Chronic sequelae of the anaemia and vaso-occlusive processes involving the musculoskeletal system include complications related to extramedullary haematopoiesis, osteonecrosis, myonecrosis and osteomyelitis. Sickle cell bone disease is one of the commonest clinical presentations. Awareness and knowledge of the imaging features related to these complications are essential for early diagnosis and prompt management. In this article, the pathophysiology and key imaging findings related to these complications are reviewed.

Albuminuria Is Associated with Endothelial Dysfunction and Elevated Plasma Endothelin-1 in Sickle Cell Anemia

Background

The pathogenesis of albuminuria in SCD remains incompletely understood. We evaluated the association of albuminuria with measures of endothelial function, and explored associations of both albuminuria and measures of endothelial function with selected biological variables (vascular endothelial growth factor [VEGF], endothelin-1 [ET-1], soluble fms-like tyrosine kinase-1 [sFLT-1], soluble vascular cell adhesion molecule-1 [soluble VCAM-1] and plasma hemoglobin).

Methods

Spot urine measurements for albumin-creatinine ratio (UACR) and 24-hour urine protein were obtained. Endothelial function was assessed using brachial artery ultrasound with measurements of flow-mediated dilation (FMD), nitroglycerin-mediated dilation (NTMD) and hyperemic velocity.

Results

Twenty three subjects with varying degrees of albuminuria were evaluated. UACR was significantly correlated with FMD (ρ = -0.45, p = 0.031). In univariate analysis, UACR was correlated with VEGF (ρ = -0.49; 95% CI: -0.75 –-0.1, p = 0.015), plasma hemoglobin (ρ = 0.50; 95% CI: 0.11–0.75, p = 0.013) and ET-1 (ρ = 0.40; 95% CI: -0.03–0.69, p = 0.06). Multivariable analysis showed significant associations of ET-1 (estimate: 455.1 [SE: 198.3], p = 0.02), VEGF (estimate: -1.1 [SE: 0.53], p = 0.04) and sFLT-1 (estimate: -1.14 [SE: 0.49], p = 0.02) with UACR. Only ET-1 (estimate: -8.03 [SE: 3.87], p = 0.04) was significantly associated with FMD in multivariable analyses. Finally, UACR was correlated with both 24-hour urine protein (ρ = 0.90, p < 0.0001) and urine aliquots for albumin-creatinine ratio obtained from the 24-hour urine collection (ρ = 0.97, p < 0.0001).

Conclusion

This study provides more definitive evidence for the association of albuminuria with endothelial dysfunction in SCD. Elevated circulating levels of ET-1 may contribute to SCD-related glomerulopathy by mediating endothelial dysfunction.

Sickle Cells Abolish Melanoma Tumorigenesis in Hemoglobin SS Knockin Mice and Augment the Tumoricidal Effect of Oncolytic Virus In Vivo

Insights from the study of cancer resistance in animals have led to the discovery of novel anticancer pathways and opened new venues for cancer prevention and treatment. Sickle cells (SSRBCs) from subjects with homozygous sickle cell anemia (SCA) have been shown to target hypoxic tumor niches, induce diffuse vaso-occlusion, and potentiate a tumoricidal response in a heme- and oxidant-dependent manner. These findings spawned the hypothesis that SSRBCs and the vasculopathic microenvironment of subjects with SCA might be inimical to tumor outgrowth and thereby constitute a natural antitumor defense. We therefore implanted the B16F10 melanoma into humanized hemoglobin SS knockin mice which exhibit the hematologic and vasculopathic sequelae of human SCA. Over the 31-day observation period, hemoglobin SS mice showed no significant melanoma outgrowth. By contrast, 68-100% of melanomas implanted in background and hemoglobin AA knockin control mice reached the tumor growth end point (p < 0.0001). SS knockin mice also exhibited established markers of underlying vasculopathy, e.g., chronic hemolysis (anemia, reticulocytosis) and vascular inflammation (leukocytosis) that differed significantly from all control groups. Genetic differences or normal AA gene knockin do not explain the impaired tumor outgrowth in SS knockin mice. These data point instead to the chronic pro-oxidative vasculopathic network in these mice as the predominant cause. In related studies, we demonstrate the ability of the sickle cell component of this system to function as a therapeutic vehicle in potentiating the oncolytic/vasculopathic effect of RNA reovirus. Sickle cells were shown to efficiently adsorb and transfer the virus to melanoma cells where it induced apoptosis even in the presence of anti-reovirus neutralizing antibodies. In vivo, SSRBCs along with their viral cargo rapidly targeted the tumor and initiated a tumoricidal response exceeding that of free virus and similarly loaded normal RBCs without toxicity. Collectively, these data unveil two hitherto unrecognized findings: hemoglobin SS knockin mice appear to present a natural barrier to melanoma tumorigenesis while SSRBCs demonstrate therapeutic function as a vehicle for enhancing the oncolytic effect of free reovirus against established melanoma.

Red cell DAMPs and inflammation

Intravascular hemolysis, or the destruction of red blood cells in the circulation, can occur in numerous diseases, including the acquired hemolytic anemias, sickle cell disease and β-thalassemia, as well as during some transfusion reactions, preeclampsia and infections, such as those caused by malaria or Clostridium perfringens. Hemolysis results in the release of large quantities of red cell damage-associated molecular patterns (DAMPs) into the circulation, which, if not neutralized by innate protective mechanisms, have the potential to activate multiple inflammatory pathways. One of the major red cell DAMPs, heme, is able to activate converging inflammatory pathways, such as toll-like receptor signaling, neutrophil extracellular trap formation and inflammasome formation, suggesting that this DAMP both activates and amplifies inflammation. Other potent DAMPs that may be released by the erythrocytes upon their rupture include heat shock proteins (Hsp), such as Hsp70, interleukin-33 and Adenosine 5' triphosphate. As such, hemolysis represents a major inflammatory mechanism that potentially contributes to the clinical manifestations that have been associated with the hemolytic diseases, such as pulmonary hypertension and leg ulcers, and likely plays a role in specific complications of sickle cell disease such as endothelial activation, vaso-occlusive processes and tissue injury.

Extracellular microvesicle microRNAs in children with sickle cell anaemia with divergent clinical phenotypes

Sickle cell anaemia (SCA) is the most frequent genetic haemoglobinopathy, which exhibits a highly variable clinical course characterized by hyper-coagulable and pro-inflammatory states, as well as endothelial dysfunction. Extracellular microvesicles are released into biological fluids and play a role in modifying the functional phenotype of target cells. We hypothesized that potential differences in plasma-derived extracellular microvesicles (EV) function and cargo from SCA patients may underlie divergent clinical trajectories. Plasma EV from SCA patients with mild, intermediate and severe clinical disease course were isolated, and primary endothelial cell cultures were exposed. Endothelial cell activation, monocyte adhesion, barrier disruption and exosome cargo (microRNA microarrays) were assessed. EV disrupted the endothelial barrier and induced expression of adhesion molecules and monocyte adhesion in a SCA severity-dependent manner compared to healthy children. Microarray approaches identified a restricted signature of exosomal microRNAs that readily distinguished severe from mild SCA, as well as from healthy children. The microRNA candidates were further validated using quantitative real time polymerase chain reaction assays, and revealed putative gene targets. Circulating exosomal microRNAs may play important roles in predicting the clinical course of SCA, and in delineation of individually tailored, mechanistically-based clinical treatment approaches of SCA patients in the near future.

Supplementation with l-arginine stabilizes plasma arginine and nitric oxide metabolites, suppresses elevated liver enzymes and peroxidation in sickle cell anaemia

The effect of l-arginine on liver function in SCD has received little or no attention. The effect of a chronic, oral, low-dose supplementation with l-arginine (1gm/day for 6 weeks) on some liver enzymes, lipid peroxidation and nitric oxide metabolites was studied in 20 normal (non-sickle cell anaemia; NSCA) subjects and 20 sickle cell anaemia (SCA) subjects. Ten milliliters of blood was withdrawn from an ante-cubital vein for the estimation of plasma arginine concentration ([R]), alanine aminotransaminase (ALT), aspartate aminotransaminase (AST) and alkaline phosphatase (ALP), plasma total bilirubin concentration [TB], malondialdehyde concentration [MDA] and nitric oxide metabolites concentration [NOx]. Before supplementation, ALT, AST, ALP (p<0.05 respectively) and TB (p<0.001) were higher in SCA subjects than in NSCA subjects. [R] and [NOx] were higher in NSCA subjects (p<0.001 and p<0.05 respectively). Supplementation caused greater percent increases in [R], and [NOX] in SCA than in NSCA subjects (p<0.001 in each case). l-Arginine caused greater percent reductions in ALT and AST in SCA subjects but greater percent reduction in ALP in NSCA subjects (p<0.001 in each case). Changes in [MDA] and [TB] in the two groups were similar. Study shows that chronic, oral, low-dose supplementation with l-arginine improved liver function, oxidative stress, plasma arginine concentration and nitric oxide metabolites levels in NSCA and SCA subjects. Responses in SCA subjects to l-arginine were more sensitive than in NSCA subjects.

Role of innate immunity-triggered pathways in the pathogenesis of Sickle Cell Disease: a meta-analysis of gene expression studies

Despite the detailed characterization of the inflammatory and endothelial changes observed in Sickle Cell Disease (SCD), the hierarchical relationship between elements involved in the pathogenesis of this complex disease is yet to be described. Meta-analyses of gene expression studies from public repositories represent a novel strategy, capable to identify key mediators in complex diseases. We performed several meta-analyses of gene expression studies involving SCD, including studies with patient samples, as well as in-vitro models of the disease. Meta-analyses were performed with the Inmex bioinformatics tool, based on the RankProd package, using raw gene expression data. Functional gene set analysis was performed using more than 60 gene-set libraries. Our results demonstrate that the well-characterized association between innate immunity, hemostasis, angiogenesis and heme metabolism with SCD is also consistently observed at the transcriptomic level, across independent studies. The enrichment of genes and pathways associated with innate immunity and damage repair-associated pathways supports the model of erythroid danger-associated molecular patterns (DAMPs) as key mediators of the pathogenesis of SCD. Our study also generated a novel database of candidate genes, pathways and transcription factors not previously associated with the pathogenesis of SCD that warrant further investigation in models and patients of SCD.

Hypoxia-reperfusion affects osteogenic lineage and promotes sickle cell bone disease

Sickle cell disease (SCD) is a worldwide distributed hereditary red cell disorder, characterized by severe organ complication. Sickle bone disease (SBD) affects a large part of the SCD patient population, and its pathogenesis has been only partially investigated. Here, we studied bone homeostasis in a humanized mouse model for SCD. Under normoxia, SCD mice display bone loss and bone impairment, with increased osteoclast and reduced osteoblast activity. Hypoxia/reperfusion (H/R) stress, mimicking acute vaso-occlusive crises (VOCs), increased bone turnover, osteoclast activity (RankL), and osteoclast recruitment (Rank) with upregulation of IL-6 as proresorptive cytokine. This was associated with further suppression of osteogenic lineage (Runx2, Sparc). To interfere with the development of SBD, zoledronic acid (Zol), a potent inhibitor of osteoclast activity/osteoclastogenesis and promoter of osteogenic lineage, was used in H/R-exposed mice. Zol markedly inhibited osteoclast activity and recruitment, promoting osteogenic lineage. The recurrent H/R stress further worsened bone structure, increased bone turnover, depressed osteoblastogenesis (Runx2, Sparc), and increased both osteoclast activity (RankL, Cathepsin k) and osteoclast recruitment (Rank) in SCD mice compared with either normoxic or single-H/R-episode SCD mice. Zol used before recurrent VOCs prevented bone impairment and promoted osteogenic lineage. Our findings support the view that SBD is related to osteoblast impairment, and increased osteoclast activity resulted from local hypoxia, oxidative stress, and the release of proresorptive cytokine such as IL-6. Zol might act on both the osteoclast and osteoblast compartments as multimodal therapy to prevent SBD.

Mechanism of testosterone deficiency in the transgenic sickle cell mouse

Testosterone deficiency is associated with sickle cell disease (SCD), but its underlying mechanism is not known. We investigated the possible occurrence and mechanism of testosterone deficiency in a mouse model of human SCD. Transgenic sickle male mice (Sickle) exhibited decreased serum and intratesticular testosterone and increased luteinizing hormone (LH) levels compared with wild type (WT) mice, indicating primary hypogonadism in Sickle mice. LH-, dbcAMP-, and pregnenolone- (but not 22-hydroxycholesterol)- stimulated testosterone production by Leydig cells isolated from the Sickle mouse testis was decreased compared to that of WT mice, implying defective Leydig cell steroidogenesis. There also was reduced protein expression of steroidogenic acute regulatory protein (STAR), but not cholesterol side-chain cleavage enzyme (P450scc), in the Sickle mouse testis. These data suggest that the capacity of P450scc to support testosterone production may be limited by the supply of cholesterol to the mitochondria in Sickle mice. The sickle mouse testis exhibited upregulated NADPH oxidase subunit gp91phox and increased oxidative stress, measured as 4-hydroxy-2-nonenal, and unchanged protein expression of an antioxidant glutathione peroxidase-1. Mice heterozygous for the human sickle globin (Hemi) exhibited intermediate hypogonadal changes between those of WT and Sickle mice. These results demonstrate that testosterone deficiency occurs in Sickle mice, mimicking the human condition. The defects in the Leydig cell steroidogenic pathway in Sickle mice, mainly due to reduced availability of cholesterol for testosterone production, may be related to NADPH oxidase-derived oxidative stress. Our findings suggest that targeting testicular oxidative stress or steroidogenesis mechanisms in SCD offers a potential treatment for improving phenotypic changes associated with testosterone deficiency in this disease.

Dietary ω-3 fatty acids protect against vasculopathy in a transgenic mouse model of sickle cell disease

The anemia of sickle cell disease is associated with a severe inflammatory vasculopathy and endothelial dysfunction, which leads to painful and life-threatening clinical complications. Growing evidence supports the anti-inflammatory properties of ω-3 fatty acids in clinical models of endothelial dysfunction. Promising but limited studies show potential therapeutic effects of ω-3 fatty acid supplementation in sickle cell disease. Here, we treated humanized healthy and sickle cell mice for 6 weeks with ω-3 fatty acid diet (fish-oil diet). We found that a ω-3 fatty acid diet: (i) normalizes red cell membrane ω-6/ω-3 ratio; (ii) reduces neutrophil count; (iii) decreases endothelial activation by targeting endothelin-1 and (iv) improves left ventricular outflow tract dimensions. In a hypoxia-reoxygenation model of acute vaso-occlusive crisis, a ω-3 fatty acid diet reduced systemic and local inflammation and protected against sickle cell-related end-organ injury. Using isolated aortas from sickle cell mice exposed to hypoxia-reoxygenation, we demonstrated a direct impact of a ω-3 fatty acid diet on vascular activation, inflammation, and anti-oxidant systems. Our data provide the rationale for ω-3 dietary supplementation as a therapeutic intervention to reduce vascular dysfunction in sickle cell disease.

Key endothelial cell angiogenic mechanisms are stimulated by the circulating milieu in sickle cell disease and attenuated by hydroxyurea

As hypoxia-induced inflammatory angiogenesis may contribute to the manifestations of sickle cell disease, we compared the angiogenic molecular profiles of plasma from sickle cell disease individuals and correlated these with in vitro endothelial cell-mediated angiogenesis-stimulating activity and in vivo neovascularization. Bioplex demonstrated that plasma from patients with steady-state sickle cell anemia contained elevated concentrations of pro-angiogenic factors (angiopoietin-1, basic fibroblast growth factor, vascular endothelial growth factor, vascular endothelial growth factor-D and placental growth factor) and displayed potent pro-angiogenic activity, significantly increasing endothelial cell proliferation, migration and capillary-like structure formation. In vivo neovascularization of Matrigel plugs was significantly greater in sickle cell disease mice than in non-sickle cell disease mice, consistent with an up-regulation of angiogenesis in the disease. In plasma from patients with hemoglobin SC disease without proliferative retinopathy, anti-angiogenic endostatin and thrombospondin-2 were significantly elevated. In contrast, plasma from hemoglobin SC individuals with proliferative retinopathy had a pro-angiogenic profile and more significant effects on endothelial cell proliferation and capillary formation than plasma from patients without retinopathy. Hydroxyurea therapy was associated with significant reductions in plasma angiogenic factors and inhibition of endothelial cell-mediated angiogenic mechanisms and neovascularization. Thus, individuals with sickle cell anemia or hemoglobin SC disease with retinopathy present a highly angiogenic circulating milieu, capable of stimulating key endothelial cell-mediated angiogenic mechanisms. Combination anti-angiogenic therapy to prevent the progression of unregulated neovascularization and associated manifestations in sickle cell disease, such as pulmonary hypertension, may be indicated; furthermore, the benefits and drawbacks of the potent anti-angiogenic effects of hydroxyurea should be clarified.

Sickle cell disease: renal manifestations and mechanisms

Sickle cell disease (SCD) substantially alters renal structure and function, and causes various renal syndromes and diseases. Such diverse renal outcomes reflect the uniquely complex vascular pathobiology of SCD and the propensity of red blood cells to sickle in the renal medulla because of its hypoxic, acidotic, and hyperosmolar conditions. Renal complications and involvement in sickle cell nephropathy (SCN) include altered haemodynamics, hypertrophy, assorted glomerulopathies, chronic kidney disease, acute kidney injury, impaired urinary concentrating ability, distal nephron dysfunction, haematuria, and increased risks of urinary tract infections and renal medullary carcinoma. SCN largely reflects an underlying vasculopathy characterized by cortical hyperperfusion, medullary hypoperfusion, and an increased, stress-induced vasoconstrictive response. Renal involvement is usually more severe in homozygous disease (sickle cell anaemia, HbSS) than in compound heterozygous types of SCD (for example HbSC and HbSβ(+)-thalassaemia), and is typically mild, albeit prevalent, in the heterozygous state (sickle cell trait, HbAS). Renal involvement contributes substantially to the diminished life expectancy of patients with SCD, accounting for 16-18% of mortality. As improved clinical care promotes survival into adulthood, SCN imposes a growing burden on both individual health and health system costs. This Review addresses the renal manifestations of SCD and focuses on their underlying mechanisms.

Ischemia-reperfusion injury in sickle cell anemia: relationship to acute chest syndrome, endothelial dysfunction, arterial vasculopathy, and inflammatory pain

Ischemia-reperfusion (I/R) physiology, also called reperfusion injury, instigates vascular and tissue injury in human disease states. This review describes why sickle cell anemia should be conceptualized in this fashion and how I/R physiology explains the genesis of characteristic aspects of vascular pathobiology and clinical disease in sickle cell anemia. The nature of I/R and its relevance to sickle cell anemia are discussed, with an emphasis on the acute chest syndrome, endothelial dysfunction with aberrant vasoregulation, circle of Willis vasculopathy, and inflammatory pain. Viewing sickle disease from this perspective elucidates defining pathophysiology and identifies a host of novel potential therapeutic targets.

Increased circulating PEDF and low sICAM-1 are associated with sickle cell retinopathy

Sickle cell retinopathy (SCR) develops in up to 30% of sickle cell disease patients (SCD) during the second decade of life. Treatment for this affection remains palliative, so studies on its pathophysiology may contribute to the future development of novel therapies. SCR is more frequently observed in hemoglobin SC disease and derives from vaso-occlusion in the microvasculature of the retina leading to neovascularization and, eventually, to blindness. Circulating inflammatory cytokines, angiogenic factors, and their interaction may contribute to the pathophysiology of this complication. Angiopoietin (Ang)-1, Ang-2, soluble vascular cell adhesion molecule-1, intercellular adhesion molecule (ICAM)-1, E-selectin, P-selectin, IL1-β, TNF-α, pigment epithelium derived factor (PEDF) and vascular endothelial growth factor plasmatic levels were determined in 37 SCD patients with retinopathy, 34 without retinopathy, and healthy controls. We observed that sICAM-1 is significantly decreased, whereas PEDF is elevated in HbSC patients with retinopathy (P=0.012 and P=0.031, respectively). Ang-1, Ang-2 and IL1-β levels were elevated in SCD patients (P=0.001, P<0.001 and P=0.001, respectively), compared to controls, and HbSS patients presented higher levels of Ang-2 compared to HbSC (P<0.001). Our study supports the possible influence of sICAM-1 and PEDF on the pathophysiology of retinal neovascularization in SCD patients.

H-ferritin ferroxidase induces cytoprotective pathways and inhibits microvascular stasis in transgenic sickle mice

Hemolysis, oxidative stress, inflammation, vaso-occlusion, and organ infarction are hallmarks of sickle cell disease (SCD). We have previously shown that increases in heme oxygenase-1 (HO-1) activity detoxify heme and inhibit vaso-occlusion in transgenic mouse models of SCD. HO-1 releases Fe(2+) from heme, and the ferritin heavy chain (FHC) ferroxidase oxidizes Fe(2+) to catalytically inactive Fe(3+) inside ferritin. FHC overexpression has been shown to be cytoprotective. In this study, we hypothesized that overexpression of FHC and its ferroxidase activity will inhibit inflammation and microvascular stasis in transgenic SCD mice in response to plasma hemoglobin. We utilized a Sleeping Beauty (SB) transposase plasmid to deliver a human wild-type-ferritin heavy chain (wt-hFHC) transposable element by hydrodynamic tail vein injections into NY1DD SCD mice. Control SCD mice were infused with the same volume of lactated Ringer's solution (LRS) or a human triple missense FHC (ms-hFHC) plasmid with no ferroxidase activity. 8 weeks later, LRS-injected mice had ~40% microvascular stasis (% non-flowing venules) 1 h after infusion of stroma-free hemoglobin, while mice overexpressing wt-hFHC had only 5% stasis (p < 0.05), and ms-hFHC mice had 33% stasis suggesting vascular protection by ferroxidase active wt-hFHC. The wt-hFHC SCD mice had marked increases in splenic hFHC mRNA and hepatic hFHC protein, ferritin light chain (FLC), 5-aminolevulinic acid synthase (ALAS), heme content, ferroportin, nuclear factor erythroid 2-related factor 2 (Nrf2), and HO-1 activity and protein. There was also a decrease in hepatic activated nuclear factor-kappa B (NF-κB) phospho-p65 and vascular cell adhesion molecule-1 (VCAM-1). Inhibition of HO-1 activity with tin protoporphyrin demonstrated HO-1 was not essential for the protection by wt-hFHC. We conclude that wt-hFHC ferroxidase activity enhances cytoprotective Nrf2-regulated proteins including HO-1, thereby resulting in decreased NF-κB-activation, adhesion molecules, and microvascular stasis in transgenic SCD mice.

Cellular adhesion and the endothelium: P-selectin

P-selectin on endothelial cell surfaces is central to impaired microvascular blood flow in sickle cell disease (SCD). Restoration of blood flow is expected to provide therapeutic benefit for SCD patients, whatever the mechanism of action of the treatment. Long-term oral administration of a P-selectin-blocking agent potentially improves blood flow and averts acute painful vaso-occlusive crises in patients with SCD. This review focuses on the pathophysiology of the impairment of microvascular blood flow in SCD with an emphasis on the role of P-selectin and summarizes the status of development of antiselectin therapies as a means of improving microvascular flow.

Treating pain in sickle cell disease with opioids: clinical advances, ethical pitfalls

This article explores the ethical principles of prescribing in Sickle Cell Disease. The first two sections of the article provide detailed scientific justification for the last section of the manuscript, which explores and discusses the ethical principles.

[Cardiopulmonary complications in sickle cell anemia]

Sickle cell anemia, considered the most prevalent genetic disease among African Americans, is a disease with autosomal recessive inheritance pattern, characterized by the production of hemoglobin S. This abnormal protein polymerizes and facilitates the formation of fibrillar aggregates that alters the erythrocyte morphology. The stiffness of the red blood cells hinders the adequate transit across microcirculation, leading to hemolysis and increased blood viscosity, which ease thrombogenesis and vascular occlusion, resulting in tissue ischemia and microinfarcts. This disease has a high rate of morbidity and mortality, especially in the first three years of life, when a rapid diagnosis and appropriate treatment are essential. Cardiovascular complications such as heart failure and pulmonary hypertension may develop independently, and each one contributes to increased mortality, being the combination of both risk factors, an important aggravating factor for prognosis and a determinant indicator of mortality.

Management of sickle cell disease from childhood through adulthood

Sickle cell disease (SCD) is a genetic disorder characterised by anaemia and "sickling" of red blood cells, leading to chronic haemolytic anaemia, vascular injury, and organ dysfunction. Although children and adults experience many similar symptoms and problems, complications increase with age, leading to early mortality. Hydroxyurea (hydroxycarbamide), the only US Food and Drug Administration-approved treatment, continues to be under-utilised and other treatments available to children are often inaccessible for adults. Haematopoietic stem-cell transplantation is a curative option, but is limited by a lack of donors and concerns for transplant-related toxicities. Although comprehensive programs exist in paediatrics, affected adults may not have access to preventative and comprehensive healthcare because of a lack of providers or care coordination. They are often forced to rely on urgent care, leading to increased healthcare utilisation costs and inappropriate treatment. This problem highlights the importance of primary care during the transition from paediatrics to adulthood.

Interplay between coagulation and vascular inflammation in sickle cell disease

Sickle cell disease is the most common inherited haematological disorder that leads to the irreversible damage of multiple organs. Although sickling of red blood cells and vaso-occlusion are central to the pathophysiology of sickle cell disease, the importance of haemolytic anaemia and vasculopathy has been recently recognized. A hypercoagulable state is another prominent feature of sickle cell disease and is mediated by activation of both intrinsic and extrinsic coagulation pathways. Growing evidence demonstrates that coagulation may not only contribute to the thrombotic complications, but also to vascular inflammation associated with this disease. This article summarizes the role of vascular inflammation and coagulation activation, discusses potential mechanisms responsible for activation of coagulation and reviews recent data demonstrating the crosstalk between coagulation and vascular inflammation in sickle cell disease.

Potential role for statins in sickle cell disease

The complex pathophysiology of sickle cell disease (SCD) is remarkably similar to that observed in other chronic vascular diseases and involves multiple biologic pathways triggered by ischemia reperfusion injury, coagulation activation, and inflammation. Statins are potent lipid-lowering agents commonly used to reduce the risk of cardiovascular disease. Independent of their lipid lowering effect, statins have been shown to down-regulate inflammatory mediators and endothelial adhesion molecules, reduce tissue factor expression and restore nitric oxide bioavailability. The pleiotropic effects of statins make these agents attractive therapeutic candidates for SCD. This article reviews available evidence for the potential role of statins in SCD.

Biologic complexity in sickle cell disease: implications for developing targeted therapeutics

Current therapy for sickle cell disease (SCD) is limited to supportive treatment of complications, red blood cell transfusions, hydroxyurea, and stem cell transplantation. Difficulty in the translation of mechanistically based therapies may be the result of a reductionist approach focused on individual pathways, without having demonstrated their relative contribution to SCD complications. Many pathophysiologic processes in SCD are likely to interact simultaneously to contribute to acute vaso-occlusion or chronic vasculopathy. Applying concepts of systems biology and network medicine, models were developed to show relationships between the primary defect of sickle hemoglobin (Hb S) polymerization and the outcomes of acute pain and chronic vasculopathy. Pathophysiologic processes such as inflammation and oxidative stress are downstream by-products of Hb S polymerization, transduced through secondary pathways of hemolysis and vaso-occlusion. Pain, a common clinical trials endpoint, is also complex and may be influenced by factors outside of sickle cell polymerization and vascular occlusion. Future sickle cell research needs to better address the biologic complexity of both sickle cell disease and pain. The relevance of individual pathways to important sickle cell outcomes needs to be demonstrated in vivo before investing in expensive and labor-intensive clinical trials.

Hemopexin therapy improves cardiovascular function by preventing heme-induced endothelial toxicity in mouse models of hemolytic diseases

BACKGROUND

Hemolytic diseases are characterized by enhanced intravascular hemolysis resulting in heme-catalyzed reactive oxygen species generation, which leads to endothelial dysfunction and oxidative damage. Hemopexin (Hx) is a plasma heme scavenger able to prevent endothelial damage and tissue congestion in a model of heme overload. Here, we tested whether Hx could be used as a therapeutic tool to counteract heme toxic effects on the cardiovascular system in hemolytic diseases.

METHODS AND RESULTS

By using a model of heme overload in Hx-null mice, we demonstrated that heme excess in plasma, if not bound to Hx, promoted the production of reactive oxygen species and the induction of adhesion molecules and caused the reduction of nitric oxide availability. Then, we used β-thalassemia and sickle cell disease mice as models of hemolytic diseases to evaluate the efficacy of an Hx-based therapy in the treatment of vascular dysfunction related to heme overload. Our data demonstrated that Hx prevented heme-iron loading in the cardiovascular system, thus limiting the production of reactive oxygen species, the induction of adhesion molecules, and the oxidative inactivation of nitric oxide synthase/nitric oxide, and promoted heme recovery and detoxification by the liver mainly through the induction of heme oxygenase activity. Moreover, we showed that in sickle cell disease mice, endothelial activation and oxidation were associated with increased blood pressure and altered cardiac function, and the administration of exogenous Hx was found to almost completely normalize these parameters.

CONCLUSIONS

Hemopexin treatment is a promising novel therapy to protect against heme-induced cardiovascular dysfunction in hemolytic disorders.

Erythrocyte NADPH oxidase activity modulated by Rac GTPases, PKC, and plasma cytokines contributes to oxidative stress in sickle cell disease

Chronic inflammation has emerged as an important pathogenic mechanism in sickle cell disease (SCD). One component of this inflammatory response is oxidant stress mediated by reactive oxygen species (ROS) generated by leukocytes, endothelial cells, plasma enzymes, and sickle red blood cells (RBC). Sickle RBC ROS generation has been attributed to sickle hemoglobin auto-oxidation and Fenton chemistry reactions catalyzed by denatured heme moieties bound to the RBC membrane. In this study, we demonstrate that a significant part of ROS production in sickle cells is mediated enzymatically by NADPH oxidase, which is regulated by protein kinase C, Rac GTPase, and intracellular Ca(2+) signaling within the sickle RBC. Moreover, plasma from patients with SCD and isolated cytokines, such as transforming growth factor β1 and endothelin-1, enhance RBC NADPH oxidase activity and increase ROS generation. ROS-mediated damage to RBC membrane components is known to contribute to erythrocyte rigidity and fragility in SCD. Erythrocyte ROS generation, hemolysis, vaso-occlusion, and the inflammatory response to tissue damage may therefore act in a positive-feedback loop to drive the pathophysiology of sickle cell disease. These findings suggest a novel pathogenic mechanism in SCD and may offer new therapeutic targets to counteract inflammation and RBC rigidity and fragility in SCD.

Systems biology of HBOC-induced vasoconstriction

Vasoconstriction is a major adverse effect of HBOCs. The use of a single drug for attenuating HBOC-induced vasoconstriction has been tried with limited success. Since HBOC causes disruptions at multiple levels of organization in the vascular system, a systems approach is helpful to explore avenues to counteract the effects of HBOC at multiple levels by targeting multiple sites in the system. A multi-target approach is especially appropriate for HBOC-induced vasoconstriction, because HBOC disrupts the cascade of amplification by NO-cGMP signaling and protein phosphorylation, ultimately resulting in vasoconstriction. Targeting multiple steps in the cascade may alter the overall gain of amplification, thereby limiting the propagation of disruptive effects through the cascade. As a result, targeting multiple sites may accomplish a relatively high overall efficacy at submaximal drug doses. Identifying targets and doses for developing a multi-target combination HBOC regimen for oxygen therapeutics requires a detailed understanding of the systems biology and phenotypic heterogeneity of the vascular system at multiple layers of organization, which can be accomplished by successive iterations between experimental studies and mathematical modeling at multiple levels of vascular systems and organ systems. Towards this goal, this article addresses the following topics: a) NO-scavenging by HBOC, b) HBOC autoxidation-induced reactive oxygen species generation and endothelial barrier dysfunction, c) NO- cGMP signaling in vascular smooth muscle cells, d) NO and cGMP-dependent regulation of contractile filaments in vascular smooth muscle cells, e) phenotypic heterogeneity of vascular systems, f) systems biology as an approach to developing a multi-target HBOC regimen.