Protein C and free protein S in children with sickle cell anemia

Liver Disease and Sickle Cell Disease: Auto-Immune Hepatitis more than a Coincidence; A Systematic Review of the Literature

In patients with SCD, chronic liver damage is a common manifestation. More than 50% of SCD patients have elevated liver enzymes. Common underlying aetiologies include sickle cell hepatic crisis, viral hepatitis, sickle cell intrahepatic cholestasis and hepatic sequestration in the acute setting, and cholelithiasis and iron overload in the chronic setting. Autoimmune hepatitis (AIH) is a rare disease that appears to occur more commonly in the sickle cell disease (SCD) population than in the general population. There are many schools of thought as to why this is the case, including the phosphatidylserine hypothesis, the heme inflammatory hypothesis, the complement generation hypothesis, and the transfusion alloimmunization hypothesis. Due to the natural history of the two illnesses, SCD is almost always diagnosed first in cases of dual pathology. Symptoms such as jaundice, fatigue, and abdominal pain are common in SCD, as are abnormal liver function tests (LFTs). These abnormalities, attributed to the other more frequent liver involvements in SCD, can lead to delays in AIH diagnosis in this population. Corticosteroids, sometimes with other immunosuppressive agents, such as azathioprine, are the cornerstone of acute AIH treatment. However, corticosteroid use in the SCD population has been shown to carry an increased risk of vaso-occlusive crises, providing a treatment dilemma. The following is a review of AIH in the SCD population, where we explore the pathophysiology behind the association between the two disorders, discuss an approach to investigating abnormal LFTs in SCD, and examine treatment options in this population with co-existing diseases.

Sickle red blood cell-derived extracellular vesicles activate endothelial cells and enhance sickle red cell adhesion mediated by von Willebrand factor

Endothelial activation and sickle red blood cell (RBC) adhesion are central to the pathogenesis of sickle cell disease (SCD). Quantitatively, RBC-derived extracellular vesicles (REVs) are more abundant from SS RBCs compared with healthy RBCs (AA RBCs). Sickle RBC-derived REVs (SS REVs) are known to promote endothelial cell (EC) activation through cell signalling and transcriptional regulation at longer terms. However, the SS REV-mediated short-term non-transcriptional response of EC is unclear. Here, we examined the impact of SS REVs on acute microvascular EC activation and RBC adhesion at 2 h. Compared with AA REVs, SS REVs promoted human pulmonary microvascular ECs (HPMEC) activation indicated by increased von Willebrand factor (VWF) expression. Under microfluidic conditions, we found abnormal SS RBC adhesion to HPMECs exposed to SS REVs. This enhanced SS RBC adhesion was reduced by haeme binding protein haemopexin or VWF cleaving protease ADAMTS13 to a level similar to HPMECs treated with AA REVs. Consistent with these observations, haemin- or SS REV-induced microvascular stasis in SS mice with implanted dorsal skin-fold chambers that was inhibited by ADAMTS13. The adhesion induced by SS REVs was variable and was higher with SS RBCs from patients with increased markers of haemolysis (lactate dehydrogenase and reticulocyte count) or a concomitant clinical diagnosis of deep vein thrombosis. Our results emphasise the critical contribution made by REVs to the pathophysiology of SCD by triggering acute microvascular EC activation and abnormal RBC adhesion. These findings may help to better understand acute pathophysiological mechanism of SCD and thereby the development of new treatment strategies using VWF as a potential target.

Neuroimaging and Cognitive Function in Sickle Cell Disease: A Systematic Review

Sickle cell disease (SCD) is the most common inherited single-gene disease. Complications include chronic anaemia, reduced oxygen-carrying capability, and cerebral vasculopathy, resulting in silent cerebral infarction, stroke, and cognitive dysfunction with impairments in measures of executive function, attention, reasoning, language, memory, and IQ. This systematic review aims to investigate the association between neuroimaging findings and cognition in children with SCD. Searches of PubMed and Embase were conducted in March 2022. Studies were included if participants were <18 years, if original data were published in English between 1960 and 2022, if any genotype of SCD was included, and if the relationship between cognition and neuroimaging was examined. Exclusion criteria included case studies, editorials, and reviews. Quality was assessed using the Critical Appraisal Skills Programme Case Control Checklist. A total of 303 articles were retrieved; 33 met the eligibility criteria. The presence of overt or silent strokes, elevated blood flow velocities, abnormal functional connectivity, and decreased fMRI activation were associated with neuropsychological deficits in children with SCD when compared to controls. There is a critical need to address the disease manifestations of SCD early, as damage appears to begin at a young age. Most studies were cross-sectional, restricting the interpretation of the directionality of relationships. Future research employing longitudinal neuroimaging and neuropsychological assessments could improve our understanding of the cumulative consequences of SCD on the developing brain.

Altered T-cell profile in sickle cell disease

Background: Impaired immune status due to altered T-cell response in sickle cell disease (SCD) might provide substantial insight into immune activity in SCD patients. Materials & methods: A total of 30 healthy control, 20 SCD patients in a crisis state and 38 SCD patients in a steady state were evaluated for T-cell subsets. Results: A significant decrease in CD8+ (p = 0.012) and CD8+45RA-197+ (p = 0.015) T-cells were observed among SCD patients. Naive T-cells (45RA+197+; p < 0.01) were elevated and effector (RA-197-) and central memory (RA-197+) T-cells were grossly reduced in the crisis state. Negative regression of naive T-cells with CD8+57+ affirmed immune inactivation. The predictor score reflected 100% sensitivity for predicting the crisis state (area under the curve = 0.851; p < 0.001). Conclusion: Monitoring naive T-cells with predictive scores can help assess the early shift from a steady state to a crisis state.

Autoimmune disease and sickle cell anaemia: 'Intersecting pathways and differential diagnosis'

Sickle cell disease (SCD) is an inherited disorder, which occurs due to a single gene mutation. It has multisystemic manifestations, affecting millions of people worldwide. The effect of SCD on joints and musculature can overlap with clinical features of autoimmune disease (AD). It is therefore difficult for clinical haematologists and physicians treating SCD patients to discriminate between these two conditions clinically. A delay in diagnosis leads to untreated symptoms and treatment differs considerably. An accurate knowledge of clinical findings and laboratory results of AD and SCD can help physicians avoid this. In the review that follows, we examine the existing literature on SCD and AD, and describe the features that may distinguish SCD and autoimmune disease such as systemic lupus erythematosus and rheumatoid arthritis. We aim to guide clinical haematologists and physicians towards a more rapid diagnosis of AD in sickle cell anaemia patients, by correct interpretation of the clinical assessment and commonly available diagnostics.

Use of infusion ports in patients with sickle cell disease: Indications and complications

BACKGROUND

Peripheral venous access in patients with sickle cell disease (SCD) can become difficult over time due to frequent access and scarring. Infusion ports provide reliable central venous access. Deep venous thrombosis (DVT) and infections are complications associated with SCD and infusion ports.

METHODS

We performed a 17.5-year single-institution retrospective chart review (January 2000 to July 2018) with literature review regarding use of infusion ports in patients with SCD.

RESULTS

We identified 32 patients with infusion ports placed for a total of 63 devices (48 for chronic transfusion [CT] and 15 for poor venous access [PVA], not on CT) for a total of 99,272 catheter days. The mean age at first insertion was 8 years (range 1-20 years). Complications included malfunction, infection, thrombosis, difficult access, and pain over infusion port site. The rate of infection was 0.2 per 1000 catheter days. Thrombosis was identified in three devices (5%) in three patients (9%), with a rate of 0.03 per 1000 catheter days. There was no difference in complications by site in either the left or right subclavian vein (p = 1). The rate of premature removal was 0.36 per 1000 catheter days, which was higher among patients with infusion ports solely for PVA (0.87 per 1000 catheter days) compared with those placed for CT (0.29 per 1000 catheter days).

CONCLUSION

Infusion ports in patients with SCD was associated with low rates of thrombosis, infection, and malfunction, and may be considered as an alternative to frequent intravenous access, especially in patients requiring CT.

Iron Chelation Reduces DNA Damage in Sickle Cell Anemia

Sickle cell anemia (SCA) is a blood condition that causes severe pain. One of the therapeutic agents used for the treatment of SCA is hydroxyurea, which reduces the episodes of pain but causes DNA damage to white blood cells. The aim of this study was to evaluate the efficacy of the combination of hydroxyurea and iron chelation therapy in relation to the extent of DNA-associated damage. Blood samples were collected from 120 subjects from five groups. Various hematological parameters of the obtained serum were analyzed. The amount of damage caused to their DNA was detected using the comet assay and fluorescent microscopy techniques. The percentage of DNA damage in the group that was subjected to the combination therapy (target group) was 1.32% ± 1.51%, which was significantly lower (P < .05) than that observed in the group treated with hydroxyurea alone (6.36% ± 2.36%). While the target group showed comparable levels of hemoglobin F and lactate dehydrogenase compared to the group that was treated with hydroxyurea alone, highly significant levels of transferrin receptors and ferritin were observed in the target group. The results of this study revealed that the administration of iron chelation drugs with hydroxyurea may help improve patients' health and prevent the DNA damage caused to white blood cells due to hydroxyurea. Further studies are needed to better understand the underlying mechanisms that are involved in this process.

Identifying Clinical and Research Priorities in Sickle Cell Lung Disease. An Official American Thoracic Society Workshop Report

Background: Pulmonary complications of sickle cell disease (SCD) are diverse and encompass acute and chronic disease. The understanding of the natural history of pulmonary complications of SCD is limited, no specific therapies exist, and these complications are a primary cause of morbidity and mortality.Methods: We gathered a multidisciplinary group of pediatric and adult hematologists, pulmonologists, and emergency medicine physicians with expertise in SCD-related lung disease along with an SCD patient advocate for an American Thoracic Society-sponsored workshop to review the literature and identify key unanswered clinical and research questions. Participants were divided into four subcommittees on the basis of expertise: 1) acute chest syndrome, 2) lower airways disease and pulmonary function, 3) sleep-disordered breathing and hypoxia, and 4) pulmonary vascular complications of SCD. Before the workshop, a comprehensive literature review of each subtopic was conducted. Clinically important questions were developed after literature review and were finalized by group discussion and consensus.Results: Current knowledge is based on small, predominantly observational studies, few multicenter longitudinal studies, and even fewer high-quality interventional trials specifically targeting the pulmonary complications of SCD. Each subcommittee identified the three or four most important unanswered questions in their topic area for researchers to direct the next steps of clinical investigation.Conclusions: Important and clinically relevant questions regarding sickle cell lung disease remain unanswered. High-quality, multicenter, longitudinal studies and randomized clinical trials designed and implemented by teams of multidisciplinary clinician-investigators are needed to improve the care of individuals with SCD.

Insight into the complex pathophysiology of sickle cell anaemia and possible treatment

Sickle cell anaemia (SCA) is the consequence of abnormal haemoglobin production due to an inherited point mutation in the β-globin gene. The resulting haemoglobin tetramer is poorly soluble when deoxygenated, and when this is prolonged, intracellular gelation of sickle haemoglobin occurs, followed by haemoglobin polymerisation. If many cycles of sickling and unsickling occur, the red cell membrane will be disrupted leading to haemolysis and vaso-occlusive events. Recent studies have also shown that leucocyte adhesion molecules and nitric oxide (NO) depletion are involved in endothelial damage. New insights in SCA pathophysiology and vascular biology have shown that cell-derived microparticle (MP) generation is also involved in the vaso-occlusion. Endothelial damage is perpetuated by impaired production or increased consumption of protective modulators such as protein C, protein S and NO. New therapeutic interventions should address these aspects of SCA pathogenesis. To date, the only US-FDA-approved therapy to prevent painful vaso-occulsive episodes is hydroxyurea that reduces haemoglobin polymerisation in sickle cells by increasing the production of foetal haemoglobin and L-glutamine. However, several new drugs have been tested in the last years in randomised clinical trials. We here report an update on the current status of knowledge on SCA.

Prevalence and risk factors for venous thromboembolism in children with sickle cell disease: an administrative database study

A hypercoagulable state resulting in increased venous thromboembolism (VTE) has been described in adults with sickle cell disease (SCD), but similar data for children are lacking. The objective of this retrospective cohort study was to describe the rate of VTE and risk factors associated with VTE in children with SCD across tertiary-care children's hospitals in the United States between the years 2009 and 2015. We used the Pediatric Health Information System database to investigate all pediatric patients with SCD admitted to 1 of 48 participating institutions between 1 January 2009 and 30 September 2015. International Classification of Disease, Ninth Edition, Clinical Modification codes were used to identify index thromboembolic events and chronic medical conditions known to be associated with VTE. Billing codes were used to identify central venous line (CVL) placement and pharmaceutical billing codes to identify estrogen containing oral-contraceptive use. Logistic regression analysis was used to study the association among unique patient characteristics, VTE, and death. 10 454 eligible subjects with SCD were identified. Median age (±interquartile range) of study cohort was 10 (±11) years. 181 subjects (1.7%) developed an index venous thromboembolic event during the study period. Median age at VTE diagnosis was 15.9 (±7.4) years. On multivariable logistic regression analysis, CVL placement, chronic renal disease, history of stroke, female sex, length of hospitalization, intensive care unit utilization, and older age were associated with VTE. After adjusting for other variables, VTE was independently associated with death. In summary, VTE can occur in pediatric patients with SCD. CVL placement is a modifiable risk factor for VTE development.

Sickle cell disease, sickle trait and the risk for venous thromboembolism: a systematic review and meta-analysis

Background

Globally, sickle cell disease (SCD) is one of the most common haemoglobinopathy. Considered a public health problem, it leads to vessel occlusion, blood stasis and chronic activation of the coagulation system responsible for vaso-occlussive crises and venous thromboembolism (VTE) which may be fatal. Although contemporary observational studies suggest a relationship between SCD or sickle trait (SCT) and VTE, there is lack of a summary or meta-analysis data on this possible correlation. Hence, we propose to summarize the available evidence on the association between SCD, SCT and VTE including deep vein thrombosis (DVT) and pulmonary embolism (PE).

Methods

We searched PubMed and Scopus to identify all cross-sectional, cohort and case-control studies reporting on the association between SCD or SCT and VTE, DVT or PE in adults or children from inception to April 25, 2017. For measuring association between SCD or SCT and VTE, DVT, or PE, a meta-analysis using the random-effects method was performed to pool weighted odds ratios (OR) of risk estimates.

Results

From 313 records initially identified from bibliographic databases, 10 studies were eligible and therefore included the meta-analysis. SCD patients had significantly higher risk for VTE (pooled OR 4.4, 95%CI 2.6–7.5, p < 0.001), DVT (OR 1.1, 95% CI 1.1–1.2, p < 0.001) and PE (pooled OR 3.7, 95% CI 3.6–3.8, p < 0.001) as compared to non SCD-adults. A higher risk of VTE (OR 33.2, 95% CI 9.7–113.4, p < 0.001) and DVT (OR 30.7, 95% CI 1.6–578.2, p = 0.02) was found in pregnant or postpartum women with SCD as compared to their counterparts without SCD. Compared to adults with SCT, the risk of VTE was higher in adults with SCD (pooled OR 3.1, 95% CI 1.8–5.3, p < 0.001), and specifically in SCD pregnant or postpartum women (OR 20.3, 95% CI 4.1–102, p = 0.0003). The risk of PE was also higher in adults with SCD (OR 3.1, 95% CCI 1.7–5.9, p = 0.0004) as compared to those with SCT. The risk of VTE was higher in individuals with SCT compared to controls (pooled OR 1.7, 95% CI 1.3–2.2, p < 0.0001), but not in pregnant or postpartum women (OR 0.9, 95% CI 0.3–2.9, p = 0.863). Compared to controls, SCT was associated with a higher risk of PE (pooled OR 2.1, 95% CI 1.2–3.8, p = 0.012) but not of DVT (pooled OR 1.2, 95% CI 0.9–1.7, p = 0.157).

Conclusion

Individuals with SCD, especially pregnant or postpartum women, might have a higher risk of VTE compared to the general population. SCT might also increases the risk of VTE. However, currently available data are not sufficient to allow a definite conclusion. Further larger studies are needed to provide a definitive conclusion on the association between SCD, SCT and VTE.

Electronic supplementary material

The online version of this article (10.1186/s12959-018-0179-z) contains supplementary material, which is available to authorized users.

Venous Thromboembolism in Children with Sickle Cell Disease: A Retrospective Cohort Study

OBJECTIVES

To describe the cumulative incidence of venous thromboembolism (VTE) in children with sickle cell disease (SCD) followed at a single institution and report on the risk factors associated with VTE development.

STUDY DESIGN

Charts for all patients with SCD, aged 0-21 years, followed at Nationwide Children's Hospital over a 6-year period (January 1, 2009, to January 31, 2015) were reviewed. Data on VTE diagnosis, sex, body mass index/weight-for-length, SCD genotype, SCD clinical complications, central venous catheter (CVC) placement, and thrombophilia testing were collected.

RESULTS

Cumulative incidence of VTE in children with SCD followed at a single tertiary care institution was found to be 2.9% (12/414). Nine of the 12 VTE were CVC-associated. On univariate analysis, hemoglobin SS genotype (OR 10.7, 95% CI 1.4-83.5), CVC presence (OR 34.4, 95% CI 8.9-134.6), central nervous system vasculopathy (OR 19.4, 95% CI 5.6-63.4), chronic transfusion therapy (OR 30.6, 95% CI 8.9-122.2), and older age (P = .03) were associated with VTE. However, presence of CVC was the only independent risk factor identified on multivariable logistic regression analysis (OR 33.8, 95% CI 8.7-130.9).

CONCLUSION

In our institution, nearly 3% of children with SCD had a history of VTE. CVC is an independent predictor of VTE in children with SCD.

Lethal End of Spectrum of Clots-Thrombotic Storm

Thrombotic storm (TS) is a rare, acute, hypercoagulable state characterized by multiple thromboembolic events affecting at least two different areas of the vascular system/organs over a short period of time. Typical triggers include inflammation, infections, minor trauma, surgery, pregnancy, and the puerperium. A single thrombotic event can set off a number of thromboembolic events, often including unusual locations like hepatic, portal, or renal veins, skin (purpura fulminans), adrenal glands, and cerebral sinus venous thrombosis. Usually, younger female patients are affected; in some patients, there is an association with an autoimmune disorder like lupus erythematosus, and they show evidence of antiphospholipid antibodies or other phenotypic expressions of anticoagulation disorders. The majority of patients have no previous history of thromboembolism. As the diagnosis of thrombotic storm relies solely on clinical symptoms with a lack of specific diagnostic tests, this can result in a delay of diagnosis. The treatment consists of uninterrupted lifelong anticoagulation. Sometimes immunomodulatory therapies have been used. The distinction between extensive thrombotic events like Heparin Induced Thrombosis (HIT), Thrombotic Thrombocytopenic Purpura (TTP), Antiphospholipids Syndrome (APS), and TS can sometimes be difficult, and the etiology of TS remains uncertain.

Vascular disease

The child presenting with possible sentinel transient ischemic event or stroke requires prompt diagnosis so that strategies to limit injury and prevent recurrent stroke can be instituted. Cerebral arteriopathy is a potent risk factor for arterial ischemic stroke in childhood. Though acute imaging study in the setting of possible stroke is often a head computed tomography, when possible magnetic resonance imaging (MRI) is recommended as the first-line study as confirmation and imaging evaluation of ischemic stroke will typically require MRI. The MRI scanning approach should include diffusion-weighted imaging (DWI) early in the sequence order, since normal DWI excludes acute infarct with rare exception. In most cases, arterial imaging with time-of-flight (TOF) magnetic resonance angiography (MRA) is warranted. Dedicated MRA may not be possible in the acute setting, but should be pursued as promptly as possible, particularly in the child with findings and history suggestive of arteriopathy, given the high risk of recurrent stroke in these children. MRA can overestimate the degree of arterial compromise due to complex/turbulent flow, and be insensitive to subtle vessel irregularity due to resolution and complex flow. In cases with high imaging suspicion for dissection despite normal MRA findings, catheter angiogram is indicated. A thoughtful, stepwise approach to arterial neuroimaging is critical to optimize diagnosis, treatment, and primary and secondary prevention of childhood stroke.

Adherence to hydroxyurea medication by children with sickle cell disease (SCD) using an electronic device: a feasibility study

Adherence to hydroxyurea (HU) is a significant modifying factor in sickle cell vaso-occlusive pain. We conducted a study using an electronic medication container-monitor-reminder device (GlowCap™) to track adherence and determine whether use of this device affected rates of HU adherence. Subjects were regular attendees to our clinic. They were given a 37-item questionnaire and were asked to use a GlowCap containing HU. When the device cap is opened, it makes a remote "medication taken" record. The device also provides usage reminder in the form of lights and alarm sounds if the cap opening is delayed. Nineteen subjects participated in the survey, and 17 in the intervention phase. Of the 17, 12 had reliable adherence data. Seventeen caregivers of patients and two patients completed the survey. Two most common barriers to adherence identified were lack of reminders and absence of medicine home delivery. The intervention component of this study, which used both the electronic (GlowCap) method and medication possession ratio showed that the median adherence rate for the 12 patients evaluated was 85 %. The GlowCap device accurately kept a record of adherence rates. This device may be an effective tool for increasing HU medication adherence.

Chronic Pulmonary Complications of Sickle Cell Disease

Sickle cell disease (SCD), the most common genetic hemolytic anemia worldwide, affects 250,000 births annually. In the United States, SCD affects approximately 100,000 individuals, most of African descent. Hemoglobin S (HbS) results from a glutamate-to-valine mutation of the sixth codon of the β-hemoglobin allele; the homozygous genotype (HbSS) is associated with the most prevalent and severe form of the disease. Other SCD genotypes include HbSC, composed of one HbS allele and one HbC (glutamate-to-lysine mutation) allele; and HbS-β-thalassemia(0) or HbS-β-thalassemia(+), composed of one HbS allele and one β-thalassemia allele with absent or reduced β-chain production, respectively. Despite advances in care, median survival remains in the fifth decade, due in large part to chronic complications of the disease. Chronic pulmonary complications in SCD are major contributors to this early mortality. Although our understanding of these conditions has improved much over the past 10 to 15 years, there remains no specific treatment for pulmonary complications of SCD. It is unclear whether conventional treatment regimens directed at non-SCD populations have equivalent efficacy in patients with SCD. This represents a critical research need. In this review, the authors review the state-of-the-art understanding of the following pulmonary complications of SCD: (1) pulmonary hypertension; (2) venous thromboembolic disease; (3) sleep-disordered breathing; (4) asthma and recurrent wheezing; and (5) pulmonary function abnormalities. This review highlights the advances as well as the knowledge gaps in this field to update clinicians and other health care providers and to garner research interest from the medical community.

Circulating microparticles, protein C, free protein S and endothelial vascular markers in children with sickle cell anaemia

INTRODUCTION

Circulating microparticles (MP) have been described in sickle cell anaemia (SCA); however, their interaction with endothelial markers remains unclear. We investigated the relationship between MP, protein C (PC), free protein S (PS), nitric oxide (NO), endothelin-1 (ET-1) and adrenomedullin (ADM) in a large cohort of paediatric patients.

METHOD

A total of 111 children of African ethnicity with SCA: 51 in steady state; 15 in crises; 30 on hydroxyurea (HU) therapy; 15 on transfusion; 17 controls (HbAA) of similar age/ethnicity. MP were analysed by flow cytometry using: Annexin V (AV), CD61, CD42a, CD62P, CD235a, CD14, CD142 (tissue factor), CD201 (endothelial PC receptor), CD62E, CD36 (TSP-1), CD47 (TSP-1 receptor), CD31 (PECAM), CD144 (VE-cadherin). Protein C, free PS, NO, pro-ADM and C-terminal ET-1 were also measured.

RESULTS

Total MP AV was lower in crisis (1.26×10(6) ml(-1); 0.56-2.44×10(6)) and steady state (1.35×10(6) ml(-1); 0.71-3.0×10(6)) compared to transfusion (4.33×10(6) ml(-1); 1.6-9.2×10(6), p<0.01). Protein C levels were significantly lower in crisis (median 0.52 IU ml(-1); interquartile range 0.43-0.62) compared with all other groups: HbAA (0.72 IU ml(-1); 0.66-0.82, p<0.001); HU (0.67 IU ml(-1); 0.58-0.77, p<0.001); steady state (0.63 IU ml(-1); 0.54-0.70, p<0.05) and transfusion (0.60 IU ml(-1); 0.54-0.70, p<0.05). In addition, levels were significantly reduced in steady state (0.63 IU ml(-1); 0.54-0.70) compared with HbAA (0.72 IU ml(-1); 0.66-0.80, p<0.01). PS levels were significantly higher in HbAA (0.85 IU ml(-1); 0.72-0.97) compared with crisis (0.49 IU ml(-1); 0.42-0.64, p<0.001), HU (0.65 IU ml(-1); 0.56-0.74, p<0.01) and transfusion (0.59 IU ml(-1); 0.47-0.71, p<0.01). There was also a significant difference in crisis patients compared with steady state (0.49 IU ml(-1); 0.42-0.64 vs. 0.68 IU ml(-1); 0.58-0.79, p<0.05). There was high correlation (R>0.9, p<0.05) between total numbers of AV-positive MP (MP AV) and platelet MP expressing non-activation platelet markers. There was a lower correlation between MP AV and MP CD62P (R=0.73, p<0.05) (platelet activation marker), and also a lower correlation between percentage of MP expressing CD201 (%MP CD201) and %MP CD14 (R=0.627, p<0.001). %MP CD201 was higher in crisis (11.6%) compared with HbAA (3.2%, p<0.05); %MP CD144 was higher in crisis (7.6%) compared with transfusion (2.1%, p<0.05); %CD14 (0.77%) was higher in crisis compared with transfusion (0.0%, p<0.05) and steady state (0.0%, p<0.01); MP CD14 was detectable in a higher number of samples (92%) in crisis compared with the rest (40%); %MP CD235a was higher in crisis (17.9%) compared with transfusion (8.9%), HU (8.7%) and steady state (9.9%, p<0.05); %CD62E did not differ significantly across the groups and CD142 was undetectable. Pro-ADM levels were raised in chest crisis: 0.38 nmol L(-1) (0.31-0.49) versus steady state: 0.27 nmol L(-1) (0.25-0.32; p<0.01) and control: 0.28 nmol L(-1) (0.27-0.31; p<0.01). CT-proET-1 levels were reduced in patients on HU therapy: 43.6 pmol L(-1) (12.6-49.6) versus control: 55.1 pmol L(-1) (45.2-63.9; p<0.05). NO levels were significantly lower in chest crisis (19.3 mmol L(-1) plasma; 10.7-19.9) compared with HU (22.2 mmol L(-1) plasma; 18.3-28.4; p<0.05), and HbSC (30.6 mmol L(-1) plasma; 20.8-39.5; p<0.05) and approach significance when compared with steady state (22.5mmol L(-1) plasma; 16.9-28.2; p=0.07).

CONCLUSION

Protein C and free PS are reduced in crisis with lower numbers of platelet MP and higher percentage of markers of endothelial damage and of red cell origin. During chest crisis, ADM and ET-1 were elevated suggesting a role for therapy inhibiting ET-1 in chest crisis.

Erythrocyte-derived microparticles supporting activated protein C-mediated regulation of blood coagulation

Elevated levels of erythrocyte-derived microparticles are present in the circulation in medical conditions affecting the red blood cells. Erythrocyte-derived microparticles expose phosphatidylserine thus providing a suitable surface for procoagulant reactions leading to thrombin formation via the tenase and prothrombinase complexes. Patients with elevated levels of circulating erythrocyte-derived microparticles have increased thrombin generation in vivo. The aim of the present study was to investigate whether erythrocyte-derived microparticles are able to support the anticoagulant reactions of the protein C system. Erythrocyte-derived microparticles were isolated using ultracentrifugation after incubation of freshly prepared erythrocytes with the ionophore A23187 or from outdated erythrocyte concentrates, the different microparticles preparations yielding similar results. According to flow cytometry analysis, the microparticles exposed phoshatidylserine and bound lactadherin, annexin V, and protein S, which is a cofactor to activated protein C. The microparticles were able to assemble the tenase and prothrombinase complexes and to stimulate the formation of thrombin in plasma-based thrombin generation assay both in presence and absence of added tissue factor. The addition of activated protein C in the thrombin generation assay inhibited thrombin generation in a dose-dependent fashion. The anticoagulant effect of activated protein C in the thrombin generation assay was inhibited by a monoclonal antibody that prevents binding of protein S to microparticles and also attenuated by anti-TFPI antibodies. In the presence of erythrocyte-derived microparticles, activated protein C inhibited tenase and prothrombinase by degrading the cofactors FVIIIa and FVa, respectively. Protein S stimulated the Arg306-cleavage in FVa, whereas efficient inhibition of FVIIIa depended on the synergistic cofactor activity of protein S and FV. In summary, the erythrocyte-derived microparticle surface is suitable for the anticoagulant reactions of the protein C system, which may be important to balance the initiation and propagation of coagulation in vivo.

Sickle cell disease and venous thromboembolism: what the anticoagulation expert needs to know

Venous thromboembolism (VTE) is common in patients with sickle cell disease (SCD). The etiology of increased risk of VTE in SCD patients is multifactorial and is related to both traditional factors and SCD-specific factors. Traditional risk factors such as central venous catheters, frequent hospitalization, orthopedic surgeries for avascular necrosis, and pregnancy may lead to increased incidence of VTE in the SCD population. In addition, SCD itself appears to be a hypercoagulable state, and many SCD-specific factors such as thrombophilic defects, genotype and splenectomy may modify the risk of VTE. SCD complications such as acute chest syndrome and pulmonary hypertension may also be related to VTE. Anticoagulation experts should be aware of these factors to help inform prophylaxis and treatment decisions.