Novel permeability characteristics of red blood cells from sickle cell patients heterozygous for HbS and HbC (HbSC genotype)

The association of sickle cell disorder with adverse outcomes in COVID-19 patients: A meta-analysis

The aim is to elucidate the relationship between sickle cell disorder and severe COVID-19. We systematically searched the required articles in three electronic databases, extracting and pooling effect sizes (ES) and 95% confidence interval (CI) from each eligible study to evaluate the effect of combined sickle cell disorder on adverse consequences in patients with COVID-19. This meta-analysis included 21 studies. Sickle cell disease (SCD) was a risk factor for mortality (pooled ES = 1.70, 95% CI: 1.00-2.92, p = 0.001), hospitalization (pooled ES = 6.21, 95% CI: 3.60-10.70, p = 0.000) and intensive care unit (ICU) admission (pooled ES = 2.29, 95% CI: 1.61-3.24, p = 0.099) in COVID-19 patients. Patients with SCD had an increased risk of respiratory failure/mechanical ventilation, but a statistical association was not found (pooled ES = 1.21, 95%CI: 0.74-1.98, p = 0.036). There was significant heterogeneity between SCD and death, hospitalization, and respiratory failure/mechanical ventilation. The results of meta-regression of SCD and hospitalization suggested that the tested variables including Area (p = 0.642), study design (p = 0.739), sample size (p = 0.397), proportion of males (p = 0.708), effect type (p = 0.723), whether confounding factors are adjusted (p = 0.606) might not be the source of heterogeneity. In addition, sickle cell trait (SCT) was significantly associated with the mortality (pooled ES = 1.54, 95% CI: 1.28-1.85, p = 0.771) and hospitalization (pooled ES = 1.20, 95% CI: 1.07-1.35，p = 0.519) in patients with COVID-19. But any increased risk of ICU admission/severe (pooled ES = 1.24, 95% CI: 0.95-1.62, p = 0.520) and mechanical ventilation (OR = 1.00, 95%CI:0.59-1.69) in COVID-19 patients with SCT was not observed. Sensitivity analysis demonstrated that the results were robust. The results of the funnel plot and Egger's test did not support the existence of publication bias. Current meta-analysis indicated that sickle cell disorder has a meaningful impact on COVID-19 progression to severe cases and associated deaths. However, further investigations and research to validate the current findings is indispensable.

Impact of a submaximal mono-articular exercise on the skeletal muscle function of patients with sickle cell disease

PURPOSE

Sickle cell disease (SCD) patients exhibit a limited exercise tolerance commonly attributed to anaemia, as well as hemorheological and cardio-respiratory abnormalities, but the functional status of skeletal muscle at exercise is unknown. Moreover, the effect of SCD genotype on exercise tolerance and skeletal muscle function has been poorly investigated. The aim of this study was to investigate skeletal muscle function and fatigue during a submaximal exercise in SCD patients.

METHODS

Nineteen healthy individuals (AA), 28 patients with sickle cell anaemia (SS) and 18 with sickle cell-haemoglobin C disease (SC) performed repeated knee extensions exercise (FAT). Maximal isometric torque (Tmax) was measured before and after the FAT to quantify muscle fatigability. Electromyographic activity and oxygenation by near-infrared spectroscopy of the Vastus Lateralis were recorded.

RESULTS

FAT caused a reduction in Tmax in SS (- 17.0 ± 12.1%, p < 0.001) and SC (- 21.5 ± 14.5%, p < 0.05) but not in AA (+ 0.58 ± 29.9%). Root-mean-squared value of EMG signal (RMS) decreased only in SS after FAT, while the median power frequency (MPF) was unchanged in all groups. Oxygenation kinetics were determined in SS and AA and were not different.

CONCLUSION

These results show skeletal muscle dysfunction during exercise in SCD patients, and suggest different fatigue aetiology between SS and SC. The changes in EMG signal and oxygenation kinetics during exercise suggest that the greater skeletal muscle fatigue occurring in SCD patients would be rather due to intramuscular alterations modifications than decreased tissue oxygenation. Moreover, SS patients exhibit greater muscle fatigability than SC.

Dengue in hospitalized children with sickle cell disease: A retrospective cohort study in the French departments of America

BACKGROUND

To describe the characteristics of dengue in sickle cell children and try to identify risk factors of severity.

METHODS

In this retrospective study, we describe the evolution according to genotype (SS or SC and controls) and severity.

RESULTS AND CONCLUSIONS

From 2005 to 2013, 106 hospitalizations for dengue fever were recorded, 35 SS genotype, 35 SC and 36 without SCD or any other chronic disease. The clinical evolution was quite different. During hospitalization, SC patients were more likely to develop multiorgan failure (31.4% versus 25.7% for SS, and 0% for controls, p=0.001), or acute pulmonary complications than patients without SC sickle cell disease (14.3% versus 8.6% for SS, and 0% for controls, p=0.03). Level 3 analgesic treatment was more frequent in SC patients (22.9% versus 3% for SS, and 0% for controls, p<0.001). Patients with SC sickle cell disease had a higher proportion of severe forms of dengue (57.1% versus 37.1% for SS, and 0% for controls, p<0.001) than patients without SC sickle cell disease. Transfer in intensive care unit was required for most SC patients (22.9% versus 3% for SS, and 0% for controls, p=0.005).Fatal episodes were more frequent in SC patients than in patients without SC sickle cell disease (5 deaths versus 1 for SS and 0 for controls, p=0.02). Thirty-three patients (47.1%) were diagnosed as having severe dengue (13 SS and 20 SC). On univariate analysis, age >10 years, acute pulmonary complications, multiorgan failure, severe anemia requiring transfusion, use of antibiotic treatment, need for treatment with morphine, and longer hospital stay were statistically more frequent in severe dengue-associated cases. Multiple logistic regression analysis showed that HbSC genotype and acute pulmonary complications, were significantly associated with severe dengue. In the multivariate model, the area of the ROC curve was 0.831. Children with SC genotype, typically thought to have less severe disease, actually had a higher rate of severe dengue and death than those with SS genotype.

Clinical and hematological profile in a newborn cohort with hemoglobin SC

OBJECTIVES

Hemoglobin SC is the second most common variant of sickle-cell disease worldwide, after hemoglobin SS. The objectives of the study were to describe the clinical and laboratory characteristics of hemoglobin SC disease in children from a newborn screening program and treated at a blood center.

METHODOLOGY

This study assessed a cohort of 461 infants born between 01/01/1999 and 12/31/2012 and followed-up until 12/31/2014. Clinical events were expressed as rates for 100 patient-years, with 95% confidence intervals. Kaplan-Meier survival curves were created.

RESULTS

The median age of patients was 9.2 years; 47.5% were female. Mean values of blood tests were: hemoglobin, 10.5g/dL; reticulocytes, 3.4%; white blood cells, 11.24×10⁹/L; platelets, 337.1×10⁹/L; and fetal hemoglobin, 6.3%. Clinical events: acute splenic sequestration in 14.8%, blood transfusion 23.4%, overt stroke in 0.2%. The incidence of painful vaso-occlusive episodes was 51 (48.9-53.4) per 100 patient-years and that of infections, 62.2 episodes (59.8-64.8) per 100 patient-years. Transcranial Doppler ultrasonography (n=71) was normal given the current reference values for SS patients. Hydroxyurea was given to ten children, all of whom improvement of painful crises. Retinopathy was observed in 20.3% of 59 children who underwent ophthalmoscopy. Avascular necrosis was detected in seven of 12 patients evaluated, predominantly in the left femur. Echocardiogram compatible with pulmonary hypertension was recorded in 4.6% of 130 children, with an estimated average systolic pulmonary artery pressure of 33.5mmHg. The mortality rate from all causes was 4.3%.

CONCLUSIONS

Clinical severity is variable in SC hemoglobinopathy. Several children have severe manifestations similar to those with SS disease.

An integrative review of factors that influence reproductive decisions in women with sickle cell disease

Sickle cell disease is one of the most prevalent genetic diseases in the world. Improvements in care have enabled those affected to experience an improved quality of life, with many affected persons now reaching reproductive age. However, pregnancy poses significant risks for women with the disease and this may affect their reproductive decisions. We conducted an integrative review of the published relevant scientific evidence to ascertain the factors that may influence these women with their reproductive decisions. The electronic databases MEDLINE, CINAHL, and PsychInfo and relevant journals were searched for peer-reviewed papers published between 2005 and 2015. Of the 440 papers identified, six papers satisfied the inclusion criteria and were assessed for quality. Results were analysed and synthesised using a thematic approach to produce a narrative report of the findings. Two main themes were identified: (1) factors influencing reproductive decision-making and (2) experiences during pregnancy. Education regarding disease knowledge and genetic implications may improve participation into screening programmes, facilitate the effective treatment needed to create trust in healthcare services, and promote better self-management. Educating professionals involved in family planning will facilitate women with this condition to make informed decisions regarding pregnancy. However, further research is required to explore the understanding of the risks involved with sickle cell disease, the best methods to educate people with sickle cell disease, and the influence that partners and families may have on women's reproductive decisions.

Blood rheology in children with the S/β+-thalassemia syndrome

The aim of the present study was to compare blood rheological parameters between children with homozygous sickle cell disease (SS), sickle cell SC disease or S/β+-thalassemia syndrome, and healthy children (AA) and to test the associations between blood rheology and the clinical severity in S/β+-thalassemia. Sixty-two SS, 14 SC, 11 S/β+-thalassemia and 12 healthy children participated in this study. Blood viscosity was measured with a cone-plate viscometer at 225 s-1. Red blood cell (RBC) deformability was measured by ektacytometry and RBC aggregation, by syllectometry. Nitric oxide and nitrotyrosine levels were determined for each child. While most of the hematological parameters were not different between SC and S/β+-thalassemia children, we demonstrated that SC patients had lower RBC deformability and aggregation than S/β+ individuals. Nitrotyrosine level, which indicates peroxynitrite production, was similar and lower in both healthy and S/β+ compared to SS children. However, S/β+-thalassemia children who experienced vaso-occlusive crises (VOC) in the 2 previous years had lower NOx and higher nitrotyrosine levels than those who never had VOC within the same period. These findings suggest that vascular function could be impaired in the most severe S/β+-thalassemia children compared to the less severe one.

Sickle cell dehydration: Pathophysiology and therapeutic applications

Cell dehydration is a distinguishing characteristic of sickle cell disease and an important contributor to disease pathophysiology. Due to the unique dependence of Hb S polymerization on cellular Hb S concentration, cell dehydration promotes polymerization and sickling. In double heterozygosis for Hb S and C (SC disease) dehydration is the determining factor in disease pathophysiology. Three major ion transport pathways are involved in sickle cell dehydration: the K-Cl cotransport (KCC), the Gardos channel (KCNN4) and Psickle, the polymerization induced membrane permeability, most likely mediated by the mechano-sensitive ion channel PIEZO1. Each of these pathways exhibit unique characteristics in regulation by oxygen tension, intracellular and extracellular environment, and functional expression in reticulocytes and mature red cells. The unique dependence of K-Cl cotransport on intracellular Mg and the abnormal reduction of erythrocyte Mg content in SS and SC cells had led to clinical studies assessing the effect of oral Mg supplementation. Inhibition of Gardos channel by clotrimazole and senicapoc has led to Phase 1,2,3 trials in patients with sickle cell disease. While none of these studies has resulted in the approval of a novel therapy for SS disease, they have highlighted the key role played by these pathways in disease pathophysiology.

Cohort study of adult patients with haemoglobin SC disease: clinical characteristics and predictors of mortality

Haemoglobin (Hb) SC disease is the second most common subtype of sickle cell disease and is potentially fatal. This study aimed to determine the clinical characteristics, outcome and predictors of mortality in HbSC disease patients, and to compare these findings with patients followed-up in different centres. Clinical, laboratory and outcome data were collected from a cohort of adult patients with HbSC disease followed between 1991 and 2103. Cox regression multivariate analysis was used to determine predictors of mortality. One hundred and fifty-five patients were followed-up over 20 years: 9% died and 70·8% had at least one complication. The most common complications were: painful crises (38·3%), retinopathy (33·8%), cholelithiasis (30·3%), osteonecrosis (24·8%) and sensorineural hearing disorders (9·7%). Frequency of chronic complications was similar in most studies. In multivariate analysis, hearing disorders remained an independent predictor of mortality (Odds Ratio 9·26, 95% confidence interval 1·1-74·8; P = 0·03). It was concluded that patients with HbSC disease receive a late diagnosis and there is remarkable similarity between the studies conducted in different centres around the world. Sensorineural hearing disorders were an independent predictor of mortality, suggesting that it may be useful to implement routine diagnostic screening.

The clinical significance of K-Cl cotransport activity in red cells of patients with HbSC disease

HbSC disease is the second commonest form of sickle cell disease, with poorly understood pathophysiology and few treatments. We studied the role of K-Cl cotransport activity in determining clinical and laboratory features, and investigated its potential role as a biomarker. Samples were collected from 110 patients with HbSC disease and 41 with sickle cell anemia (HbSS). K-Cl cotransport activity was measured in the oxygenated (K-Cl cotransport(100)) and deoxygenated (K-Cl cotransport(0)) states, using radioactive tracer studies. K-Cl cotransport activity was high in HbSC and decreased significantly on deoxygenation. K-Cl cotransport activity correlated significantly and positively with the formation of sickle cells. On multiple regression analysis, K-Cl cotransport increased significantly and independently with increasing reticulocyte count and age. K-Cl cotransport activity was increased in patients who attended hospital with acute pain in 2011 compared to those who did not (K-Cl cotransport(100): mean 3.87 versus 3.20, P=0.009, independent samples T-test; K-Cl cotransport(0): mean 0.96 versus 0.68, P=0.037). On logistic regression only K-Cl cotransport was associated with hospital attendance. Increased K-Cl cotransport activity was associated with the presence of retinopathy, but this effect was confounded by age. This study links variability in a fundamental aspect of cellular pathology with a clinical outcome, suggesting that K-Cl cotransport is central to the pathology of HbSC disease. Increased K-Cl cotransport activity is associated with increasing age, which may be of pathophysiological significance. Effective inhibition of K-Cl cotransport activity is likely to be of therapeutic benefit.

Identification of the Ca²⁺ entry pathway involved in deoxygenation-induced phosphatidylserine exposure in red blood cells from patients with sickle cell disease

Phosphatidylserine (PS) exposure in red blood cells (RBCs) from sickle cell disease (SCD) patients is increased compared to levels in normal individuals and may participate in the anaemic and ischaemic complications of SCD. Exposure is increased by deoxygenation and occurs with elevation of intracellular Ca²⁺ to low micromolar levels. The Ca²⁺ entry step has not been defined but a role for the deoxygenation-induced pathway, P_sickle, is postulated. Partial P_sickle inhibitors 4-acetamido-4′-isothiocyanostilbene-2,2′-disulphonic acid (SITS), 4,4′-dithiocyano-2,2′-stilbene-disulphonic acid (DIDS) and dipyridamole inhibited deoxygenation-induced PS exposure (DIDS IC₅₀, 118 nM). Inhibitors and activators of other pathways (including these stimulated by depolarisation, benzodiazepines, glutamate and stretch) were without effect. Zn²⁺ and Gd³⁺ stimulated PS exposure to high levels. In the case of Zn²⁺, this effect was independent of oxygen (and hence HbS polymerisation and RBC sickling) but required extracellular Ca²⁺. The effect was completely abolished when Zn²⁺ (100 μM) was added to RBCs suspended in autologous plasma, implying a requirement of high levels of free Zn²⁺.

A non-electrolyte haemolysis assay for diagnosis and prognosis of sickle cell disease

Red blood cells (RBCs) from patients with sickle cell disease (SCD) lyse in deoxygenated isosmotic non-electrolyte solutions. Haemolysis has features which suggest that it is linked to activation of the pathway termed P_sickle. This pathway is usually described as a non-specific cationic conductance activated by deoxygenation, HbS polymerisation and RBC sickling. The current work addresses the hypothesis that this haemolysis will provide a novel diagnostic and prognostic test for SCD, dependent on the altered properties of the RBC membrane resulting from HbS polymerisation. A simple test represented by this haemolysis assay would be useful especially in less affluent deprived areas of the world where SCD is most prevalent. RBCs from HbSS and most HbSC individuals showed progressive lysis in deoxygenated isosmotic sucrose solution at pH 7.4 to a level greater than that observed with RBCs from HbAS or HbAA individuals. Cytochalasin B prevented haemolysis. Haemolysis was temperature- and pH-dependent. It required near physiological temperatures to occur in deoxygenated sucrose solutions at pH 7.4. At pH 6, haemolysis occurred even in oxygenated samples. Haemolysis was reduced in patients on long-term (>5 months) hydroxyurea treatment. Several manoeuvres which stabilise soluble HbS (aromatic aldehydes o-vanillin or 5-hydroxymethyl, and urea) reduced haemolysis, an effect not due to increased oxygen affinity. Conditions designed to elicit HbS polymerisation in cells from sickle trait patients (deoxygenated hyperosmotic sucrose solutions at pH 6) supported their haemolysis. These findings are consistent with haemolysis requiring HbS polymerisation and support the hypothesis that this may be used as a test for SCD.

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

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

The conductance of red blood cells from sickle cell patients: ion selectivity and inhibitors

The abnormally high cation permeability in red blood cells (RBCs) from patients with sickle cell disease (SCD) occupies a central role in pathogenesis. Sickle RBC properties are notably heterogeneous, however, thus limiting conventional flux techniques that necessarily average out the behaviour of millions of cells. Here we use the whole-cell patch configuration to characterise the permeability of single RBCs from patients with SCD in more detail. A non-specific cation conductance was reversibly induced upon deoxygenation and was permeable to both univalent (Na+, K+, Rb+) and also divalent (Ca2+, Mg2+) cations. It was sensitive to the tarantula spider toxin GsMTx-4. Mn2+ caused partial, reversible inhibition. The aromatic aldehyde o-vanillin also irreversibly inhibited the deoxygenation-induced conductance, partially at 1mM and almost completely at 5mM. Nifedipine, amiloride and ethylisopropylamiloride were ineffective. In oxygenated RBCs, the current was pH sensitive showing a marked increase as pH fell from 7.4 to 6, with no change apparent when pH was raised from 7.4 to 8. The effects of acidification and deoxygenation together were not additive. Many features of this deoxygenation-induced conductance (non-specificity for cations, permeability toCa2+ andMg2+, pH sensitivity, reversibility, partial inhibition by DIDS and Mn2+) are shared with the flux pathway sometimes referred to as Psickle. Sensitivity to GsMTx-4 indicates its possible identity as a stretch-activated channel. Sensitivity to o-vanillin implies that activation requires HbS polymerisation but since the conductance was observed in whole-cell patches, results suggest that bulk intracellular Hb is not involved; rather a membrane-bound subfraction is responsible for channel activation. The ability to record P(sickle)-like activity in single RBCs will facilitate further studies and eventual molecular identification of the pathway involved.

The Properties of Red Blood Cells from Patients Heterozygous for HbS and HbC (HbSC Genotype)

Sickle cell disease (SCD) is one of the commonest severe inherited disorders, but specific treatments are lacking and the pathophysiology remains unclear. Affected individuals account for well over 250,000 births yearly, mostly in the Tropics, the USA, and the Caribbean, also in Northern Europe as well. Incidence in the UK amounts to around 12-15,000 individuals and is increasing, with approximately 300 SCD babies born each year as well as with arrival of new immigrants. About two thirds of SCD patients are homozygous HbSS individuals. Patients heterozygous for HbS and HbC (HbSC) constitute about a third of SCD cases, making this the second most common form of SCD, with approximately 80,000 births per year worldwide. Disease in these patients shows differences from that in homozygous HbSS individuals. Their red blood cells (RBCs), containing approximately equal amounts of HbS and HbC, are also likely to show differences in properties which may contribute to disease outcome. Nevertheless, little is known about the behaviour of RBCs from HbSC heterozygotes. This paper reviews what is known about SCD in HbSC individuals and will compare the properties of their RBCs with those from homozygous HbSS patients. Important areas of similarity and potential differences will be emphasised.