Impaired blood rheology plays a role in the chronic disorders associated with sickle cell-hemoglobin C disease

Iron restriction in sickle cell disease: When less is more

Primum non nocere! Can iron deficiency, an abnormality that causes anemia, benefit people with sickle cell disease (SCD) who already have an anemia? The published literature we review appears to answer this question in the affirmative: basic science considerations, animal model experiments, and noncontrolled clinical observations all suggest a therapeutic potential of iron restriction in SCD. This is because SCD's clinical manifestations are ultimately attributable to the polymerization of hemoglobin S (HbS), a process strongly influenced by intracellular HbS concentration. Even small decrements in HbS concentration greatly reduce polymerization, and iron deficiency lowers erythrocyte hemoglobin concentration. Thus, iron deficiency could improve SCD by changing its clinical features to those of a more benign anemia (i.e., a condition with fewer or no vaso-occlusive events). We propose that well-designed clinical studies be implemented to definitively determine whether iron restriction is a safe and effective option in SCD. These investigations are particularly timely now that pharmacologic agents are being developed, which may directly reduce red cell hemoglobin concentrations without the need for phlebotomies to deplete total body iron.

Thrombosis risk with haemoglobin C trait and haemoglobin C disease: A systematic review

The thrombotic risk with haemoglobin C trait (HbAC) or haemoglobin C disease (HbCC) is unclear. However, individuals with HbCC have demonstrated chronic haemolysis, higher blood viscosity and altered rheology when compared to individuals with wild-type haemoglobin (HbAA). These physiological alterations may theoretically translate to increased risk of thrombosis; therefore, a systematic literature review was performed to investigate the possible association between HbAC and/or HbCC and thrombosis. Twenty-two studies met inclusion criteria representing 782 individuals with HbAC (n = 694) or HbCC (n = 88). Fifteen studies described the presence/absence of venous thromboembolism (VTE) in patients with HbAC (n = 685) or HbCC (n = 79), while seven studies described patients with HbAC (n = 9) or HbCC (n = 9) and arterial thrombosis. Most (n = 20) studies were case reports or case series; however, two studies suggested a potential increased VTE risk with HbAC compared to HbAA in (i) all patients (OR 2.2, 95% CI: 0.9-5.5) and in (ii) pregnant individuals (RR 3.7, 95% CI 0.9-16). This review is the largest assessment of patients with HbC trait or disease and thrombosis to date; despite its limitations, the findings suggest HbC may be a predisposing risk factor to thrombosis. Prospective cohort studies are warranted to definitively elucidate the risk of thrombosis in this population.

Prospective identification of variables as outcomes for treatment (PIVOT): study protocol for a randomised, placebo-controlled trial of hydroxyurea for Ghanaian children and adults with haemoglobin SC disease

BACKGROUND

Haemoglobin SC (HbSC) is a common form of sickle cell disease (SCD), especially among individuals of West African ancestry. Persons with HbSC disease suffer from the same clinical complications and reduced quality of life that affect those with sickle cell anaemia (HbSS/Sβ0). Retrospective anecdotal data suggest short-term safety and benefits of hydroxyurea for treating HbSC, yet rigorous prospective data are lacking regarding optimal dosing, clinical and laboratory effects, long-term safety and benefits, and appropriate endpoints to monitor. Prospective Investigation of Variables as Outcomes for Treatment (PIVOT) was designed with three aims: (1) to measure the toxicities of hydroxyurea treatment on laboratory parameters, (2) to assess the effects of hydroxyurea treatment on sickle-related clinical and laboratory parameters, and (3) to identify study endpoints suitable for a future definitive phase III trial of hydroxyurea treatment of HbSC disease.

METHODS

PIVOT is a randomised, placebo-controlled, double blind clinical trial of hydroxyurea. Approximately 120 children and 120 adults ages 5-50 years with HbSC disease will be enrolled, screened for 2 months, and then randomised 1:1 to once-daily oral hydroxyurea or placebo. Study treatment will be prescribed initially at 20 ± 5 mg/kg/day with an opportunity to escalate the dose twice over the first 6 months. After 12 months of blinded study treatment, all participants will be offered open-label hydroxyurea for up to 4 years. Safety outcomes include treatment-related cytopenias, whole blood viscosity, and adverse events. Efficacy outcomes include a variety of laboratory and clinical parameters over the first 12 months of randomised treatment, including changes in haemoglobin and fetal haemoglobin, intracranial arterial velocities measured by transcranial Doppler ultrasound, cerebral oxygenation using near infrared spectrometry, spleen volume and kidney size by ultrasound, proteinuria, and retinal imaging. Exploratory outcomes include functional erythrocyte analyses with ektacytometry for red blood cell deformability and point-of-sickling, patient-reported outcomes using the PROMIS questionnaire, and 6-min walk test.

DISCUSSION

For children and adults with HbSC disease, PIVOT will determine the safety of hydroxyurea and identify measurable changes in laboratory and clinical parameters, suitable for future prospective testing in a definitive multi-centre phase III clinical trial.

TRIAL REGISTRATION

PACTR, PACTR202108893981080. Registered 24 August 2021, https://pactr.samrc.ac.za.

[The broad spectrum of sickle cell disease: HbSC in everyday clinical practice]

Sickle cell disease has come to Germany from the Mediterranean region, Africa and the Middle East since the 1950 s and initially mainly concerned paediatricians. Since the 1970 s, the life expectancy of those affected has risen significantly, and about 95 % now live to adulthood. Therefore, general practitioners and internists should be familiar with the different forms of sickle cell disease, especially HbSC disease (approx. 20 %).A precise diagnosis of sickle cell disease (exact phenotype) is essential; the term "sickle cell anaemia" must be avoided. In patients of African origin with microcytosis, slightly elevated reticulocytes and pain symptomatology, the possibility of HbSC disease should be considered - even with age-appropriate haemoglobin values. Annual retinoscopy is recommended for HbSC patients from the age of 7, and for all other sickle cell patients from the age of 10. If a hearing loss occurs in an HbSC patient, phlebotomy should be performed immediately. In all sickle cell patients with dizziness or pain and an Hb > 10 g/dl, phlebotomy is indicated.

Effects of Genotypes and Treatment on Oxygenscan Parameters in Sickle Cell Disease

(1) Background: The aim of the present study was to compare oxygen gradient ektacytometry parameters between sickle cell patients of different genotypes (SS, SC, and S/β⁺) or under different treatments (hydroxyurea or chronic red blood cell exchange). (2) Methods: Oxygen gradient ektacytometry was performed in 167 adults and children at steady state. In addition, five SS patients had oxygenscan measurements at steady state and during an acute complication requiring hospitalization. (3) Results: Red blood cell (RBC) deformability upon deoxygenation (EImin) and in normoxia (EImax) was increased, and the susceptibility of RBC to sickle upon deoxygenation was decreased in SC patients when compared to untreated SS patients older than 5 years old. SS patients under chronic red blood cell exchange had higher EImin and EImax and lower susceptibility of RBC to sickle upon deoxygenation compared to untreated SS patients, SS patients younger than 5 years old, and hydroxyurea-treated SS and SC patients. The susceptibility of RBC to sickle upon deoxygenation was increased in the five SS patients during acute complication compared to steady state, although the difference between steady state and acute complication was variable from one patient to another. (4) Conclusions: The present study demonstrates that oxygen gradient ektacytometry parameters are affected by sickle cell disease (SCD) genotype and treatment.

Oxidative stress, inflammation, blood rheology, and microcirculation in adults with sickle cell disease: Effects of hydroxyurea treatment and impact of sickle cell syndrome

Inflammation and oxidative stress play a key role in the pathophysiology of sickle cell disease (SCD). However, the potential influence of different sickle genotypes, or hydroxyurea (HU) treatment, on these factors remains poorly documented. The present study compared several plasma markers of inflammation and oxidative stress, as well as microvascular function, between patients with sickle SC disease (HbSC, n = 19) and patients with sickle cell anemia (HbSS) under hydroxyurea (HU) treatment (n = 16), or not (n = 13). Hemorheological parameters and levels of inflammatory (IL-6, IL-8, IFN-γ, MCP-1, MIP-1β, TNF-α) and oxidative stress (AOPP, MDA, MPO) markers were determined. Peripheral microcirculatory cutaneous blood flow and immediate microvascular response to local heat were evaluated using laser Doppler flowmetry. Oxidative stress and inflammation were lower in HbSC patients and HbSS patients under HU therapy compared to HbSS patients not treated with HU. Blood viscosity was higher in HbSC than in HbSS patients treated with or not with HU. Vasodilation response of the cutaneous microcirculation to heat stress was higher in HbSS patients receiving HU treatment. Our results clearly established that both sickle cell genotype and HU treatment modulate inflammation and oxidative stress.

GBT440 improves red blood cell deformability and reduces viscosity of sickle cell blood under deoxygenated conditions

BACKGROUND

In sickle cell disease (SCD), polymerization of hemoglobin S (HbS) leads to the formation of rigid, non-deformable sickled RBCs. Loss of RBC deformability, sickling and irreversible membrane damage causes abnormal blood rheology, and increases viscosity which contributes to vasoocclusion and other SCD pathophysiology. GBT440 (generic name voxelotor) is a novel anti-polymerization and anti-sickling agent currently undergoing clinical evaluation for the treatment of SCD.

OBJECTIVE

The purpose of this study was to determine the effects of GBT440 on deformability of sickle RBCs (SS RBCs) and the hyperviscosity of sickle cell blood (SS blood).

METHODS

The mechanical and rheological properties of GBT440-treated SS RBCs were measured using micropipette and filtration techniques. The viscosity of sickle blood was measured using a Wells-Brookfield cone/plate viscometer.

RESULTS

GBT440 restored movement of deoxygenated SS RBCs through a gel filtration column and reduced the pressure required to pass SS RBCs through a polycarbonate filter. Moreover, GBT440 decreased the membrane shear elastic modulus of SS RBCs assessed via micropipette aspiration and reduced the hyperviscosity of SS blood under deoxygenated conditions.

CONCLUSIONS

GBT440 maintains SS RBC deformability and improves SS blood viscosity by inhibiting HbS polymerization under deoxygenated conditions. These results further support development of GBT440 as a disease-modifying agent in SCD patients.

Hydroxyurea therapy modulates sickle cell anemia red blood cell physiology: Impact on RBC deformability, oxidative stress, nitrite levels and nitric oxide synthase signalling pathway

Hydroxyurea (HU) has been suggested to act as a nitric oxide (NO) donor in sickle cell anemia (SCA). However, little is known about the HU NO-related effects on red blood cell (RBC) physiology and NO signalling pathway. Thirty-four patients with SCA (22 under HU treatment (HU+) and 12 without (HU-)) and 17 healthy subjects (AA) were included. RBC nitrite content, deformability and reactive oxygen species (ROS) levels were measured. RBC NO-synthase (RBC-NOS) signalling pathway was assessed by the measurement of RBC-NOS serine¹¹⁷⁷ and RBC-AKT serine⁴⁷³ phosphorylation. We also investigated the in vitro effects of Sodium Nitroprusside (SNP), a NO donor, on the same parameters in SCA RBC. RBC nitrite content was higher in HU+ than in HU- and AA. RBC deformability was decreased in SCA patients compared to AA but the decrease was more pronounced in HU-. RBC ROS level was increased in SCA compared to AA but the level was higher in HU- than in HU+. RBC-NOS serine¹¹⁷⁷ and RBC-AKT serine⁴⁷³ phosphorylation were decreased in HU+ compared to HU- and AA. SCA RBC treated with SNP showed increased deformability, reduced ROS content and a decrease in AKT and RBC-NOS phosphorylation. Our study suggests that HU, through its effects on foetal hemoglobin and possibly on NO delivery, would modulate RBC NO signalling pathway, RBC rheology and oxidative stress.

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.

Genetic modifiers of severity in sickle cell disease

Sickle cell disease (SCD) is one of the most common single disease disorders world-wide. It is remarkable for its clinical heterogeneity, even among individuals with identical genotypes. Some individuals experience morbidity and mortality in early childhood, while others have a relatively mild course, and normal or near normal life expectancy. Many clinical complications are associated with SCD; most notably frequent pain episodes, stroke, acute chest syndrome, avascular necrosis, nephropathy, retinopathy and pulmonary hypertension. While the effects of higher fetal hemoglobin (HbF) levels, UGTA1A polymorphisms, alpha-thalassemia and G6PD deficiency on SCD has been extensively studied, these variables do not explain all of the clinical heterogeneity of SCD. It is not known why some patients develop certain complications, and it is difficult to predict which complications a particular patient will experience. Much work has been done to identify genetic variants associated with these disease complications; many associations remain unvalidated. As the field continues to move beyond small sample collections and candidate gene approaches into whole genome sequencing and merging of samples from all over the world, we will identify more genetic variants associated with development of specific SCD related complications, and hopefully leverage this knowledge into targeted therapies.

Blood rheological abnormalities in sickle cell anemia

This review focuses on the contribution of abnormal blood rheology in the pathophysiology of sickle cell anemia (SCA). SCA is characterized by a reduction of red blood cell (RBC) deformability but this reduction is very heterogeneous among patients. Recent works have shown that patients with the lowest RBC deformability (measured by ektacytometry) have enhanced hemolysis and would be more prone to develop several complications such as priapism, leg ulcers and glomerulopathy. In contrast, patients with the highest deformability, and not under hydroxyurea therapy, seem to develop more frequently vaso-occlusive like events. Although less studied, RBC aggregation properties are very different between SCA and healthy individuals and it was demonstrated that increased RBC aggregates strength could be involved in some complications. Finally, several studies have established that the vascular system of SCA patients could not fully compensate any increase in blood viscosity because of the loss of vascular reactivity, which may result in vaso-occlusive crises.

Blood hyperviscosity identification with reflective spectroscopy of tongue tip based on principal component analysis combining artificial neural network

Background

With spectral methods, noninvasive determination of blood hyperviscosity in vivo is very potential and meaningful in clinical diagnosis. In this study, 67 male subjects (41 health, and 26 hyperviscosity according to blood sample analysis results) participate.

Methods

Reflectance spectra of subjects’ tongue tips is measured, and a classification method bases on principal component analysis combined with artificial neural network model is built to identify hyperviscosity. Hold-out and Leave-one-out methods are used to avoid significant bias and lessen overfitting problem, which are widely accepted in the model validation.

Results

To measure the performance of the classification, sensitivity, specificity, accuracy and F-measure are calculated, respectively. The accuracies with 100 times Hold-out method and 67 times Leave-one-out method are 88.05% and 97.01%, respectively.

Conclusions

Experimental results indicate that the built classification model has certain practical value and proves the feasibility of using spectroscopy to identify hyperviscosity by noninvasive determination.

Otological burdens of Nigerian children with sickle cell disease

INTRODUCTION/OBJECTIVE

Sickle cell disease (SCD) is associated with episodic illnesses, multi-systemic affectations and end-organs damages. Otolaryngological related complications are not unexpected. Studies on the overall Otolaryngological pathologies in children with SCD relative to their non-SCD counterparts are scanty in Nigeria. We hypothesized that children with SCD are likely to have more otological burdens than their non-SCD counterparts. Thus, we embarked on this study to describe and compare the overall ear diseases burdens seen in children with sickle cell disease relative to their non-SCD counterparts.

METHODOLOGY

A cross-sectional study of otologic diseases among children with SCD and their non-SCD counterparts attending the paediatrics and otolaryngological clinics of a Nigerian tertiary institution was conducted.

RESULTS

Overall, 80 (47.62%) of the 168 ears of SCD patients compared to 37 (22.02%) of the 168 ears of their non-SCD counterparts were affected by diseases (p < 0.0001). The diseases were Wax, Otitis Media with Effusion, Suppurative Otitis Media, Otosclerosis and Sensorineural Hearing Loss (SNHL). There was a significant difference in the prevalence of SNHL and solitary otosclerosis between the SCD patients and their non-SCD counterparts (P < 0.05) respectively. Both the Haemoglobin concentration and HbF did not discriminate between the SCD participants with or without SNHL (P > 0.05).

CONCLUSION

This study showed that otological burdens are more prevalent in children with SCD than the non-SCD population. The microbiological peculiarity of suppurative otitis media (SOM) among participants stresses the need for concerted efforts at preventing SOM in SCD children. There is need for special Otolaryngological care for SCD children.

Lipid profiles in French West Indies sickle cell disease cohorts, and their general population

BACKGROUND

The pathophysiology of sickle cell disease (SCD) and the variability of its clinical expression remain not fully understood, whether within or between different SCD genotypes. Recent studies have reported associations between lipid levels and several SCD complications. If lipid levels have been previously described as low in sickle cell anemia (SCA), few data have been provided for sickle cell SC disease (SCC). We designed our epidemiological study to isolate lipid levels and profiles by genotype in Guadeloupian cohorts of SCA and SCC adult patients, at steady state. We compared SCD lipid levels with those of the Guadeloupian general population (GGP), and analyzed potential associations between lipid levels and SCD complications (vaso-occlusive crises, acute chest syndrome and osteonecrosis).

METHODS

Lipids, apolipoproteins, biological variables and anthropometric evaluation, were collected at steady state from medical files for 62 SCC and 97 SCA adult patients. Clinical SCD complications were collected from the clinical files. Analysis was conducted by genotype for all variables.

RESULTS

Different SCC and SCA lipid profiles, both distinct from their GGP's, were identified. Compared to SCC and GGP, higher triglyceride (TG) levels were observed in SCA patients, independent of hydroxyurea, hemolysis, gender, age, body mass index (BMI), abdominal obesity and clinical nutritional status. Our survey highlights also subsequent anthropometrical phenotypes, with an over-representation of abdominal obesity with normal BMI in SCA patients, and affecting almost exclusively females in both genotypes. Moreover, more frequent positive history of acute chest syndrome (ACS) was observed in SCA patients with TG level higher than 1.50 g/l, and of osteonecrosis in SCC patients having non high-density lipoprotein-cholesterol level (Non HDL-C) higher than 1.30 g/l.

CONCLUSIONS

This study reveals that SCA and SCC patients exhibit distinct lipid profiles and suggests that high TG and Non HDL-C levels are associated with past histories of ACS and osteonecrosis in SCA and SCC patients, respectively.

Association between oxidative stress and vascular reactivity in children with sickle cell anaemia and sickle haemoglobin C disease

Oxidative stress and haemolysis-associated nitric oxide (NO) depletion plays a crucial role in the development of vasculopathy in sickle cell anaemia (SS). However it remains unknown whether oxidative stress and haemolysis levels influence vascular function in patients with sickle haemoglobin C disease (SC). Microvascular response to heat (using Laser Doppler flowmetry on finger), oxidative stress biomarkers, NO metabolites, endothelin-1 and haematological parameters were compared between patients with SS and SC. Vascular function, oxidative and nitrosative markers were also measured in healthy (AA) children. SS and SC had increased plasma advanced oxidation protein products (AOPP), malondialdehyde, plasma antioxidant activities and NO end products, compared to AA. SC had lower catalase activity compared to AA and SS. Haemolytic rate, glutathione peroxidase and nitrotyrosine concentrations were significantly increased in children with SS compared to SC and AA. SS and SC had impaired microvascular reactivity compared to AA. In SS, the plateau phase of the response to local thermal heating was negatively associated with nitrotyrosine and AOPP. No association between vascular function parameters and oxidative stress markers was observed in SC. Mild haemolysis in SC, compared to SS, may limit oxidative and nitrosative stress and could explain the better preserved microvascular function in this group.

Cerebral and muscle microvascular oxygenation in children with sickle cell disease: Influence of hematology, hemorheology and vasomotion

The present study investigated cerebral and muscle hemoglobin oxygen saturation (tissue oxygen index, TOI) in children with sickle cell anemia (SS), sickle cell hemoglobin C disease (SC) and healthy children (AA). TOI was measured by near-infrared spectroscopy (NIRS) and spectral analysis of the TOI variability was used to assess flowmotion and vasomotion. Arterial oxyhemoglobin saturation (SpO₂), hemorheological and hematological parameters were also measured in SS and SC children. Both TOI were lower in SS compared to both AA and SC children, with SC exhibiting lower values than AA children. Cerebral vasomotion expressed in absolute values was enhanced in SS compared to AA and SC children. Muscle vasomotion did not differ between the three groups. Hematocrit, SpO₂ and red blood cell deformability were positively associated with cerebral TOI in SS children. We demonstrated that 1) cerebral and muscle TOI were markedly decreased in SS children while the decrease of TOI was milder in SC children, 2) cerebral TOI level was associated with several biological markers in SS children only and 3) cerebral vasomotion was enhanced in SS, possibly to counterbalance the effects of chronic cerebral hypoxia.

Pfaffia paniculata extract improves red blood cell deformability in sickle cell patients

The aim of the present study was to test the effects of Pfaffia paniculata (PP) extract on the red blood cell (RBC) rheological properties of patients with sickle cell disease (SCD) and healthy (AA) individuals. Blood from 7 SCD and 4 AA individuals were collected in EDTA tubes. Washed RBCs were incubated with various concentration of PP extract: 0.0, 0.2 or 0.5 mg/ml of PP solution for 5 hrs at 37°C. RBC deformability was measured by ektacytometry at 9 shear stresses ranging from 0.3 to 30 Pa, and RBC aggregation properties were determined by laser-backscattered techniques. Because RBCs from SCD patients are fragile, a stability test was also performed to test for the fragility of RBC exposed to a constant shear stress (70 Pa) for 10 min. While RBC deformability was not improved by the use of PP extract in AA, we noted an improvement of this parameter in patients with SCD between the 0.0 and 0.5 mg/ml conditions. In contrast to AA RBCs, the fragility of SCD RBCs was not affected by PP extract. In conclusion, this study demonstrates the beneficial effects, in-vitro, of PP extract on the RBC deformability of SCD patients, notably at high shear stress (a shear stress condition usually found in capillaries).

Rheology of red blood cells in patients with HbC disease

Patients with hemoglobin C disease (CC) usually do not develop severe complications in comparison with individuals with sickle cell anemia (SS) or with sickle cell hemoglobin C disease (SC). The present study compared the hematological, biochemical, hemorheological and clinical characteristics of CC patients to those of SS, SC and healthy individuals (AA). Blood viscosity was measured at 225 s(-1) with a cone plate viscometer. The hematocrit-to-blood viscosity ratio (HVR), i.e. an index of red blood cell (RBC) oxygen transport effectiveness, was calculated. RBC deformability was determined at 30 Pa by ektacytometry, and RBC aggregation properties by syllectometry. CC and SC had higher blood viscosity and lower HVR than AA. Nevertheless, HVR was higher in CC compared to SS and tended to be higher than in SC. The CC group exhibited very rigid hyperchromic RBC compared to the three other groups. RBC aggregation abnormalities were observed in CC: low RBC aggregation index and high RBC aggregates strength. Despite these hemorheological abnormalities, CC never had hospitalized painful vaso-occlusive crisis or acute chest syndrome. In contrast, all of them had splenomegaly. Of note, 2 out of 7 CC developed retinopathy or otologic disorders. Whether the blood hyperviscosity and decreased RBC deformability are responsible for these complications is unknown. The higher oxygen transport effectiveness (i.e., HVR) of CC compared to SS is probably at the origin of the very low risk of medical complication in this population.

Knowledge insufficient: the management of haemoglobin SC disease

Although haemoglobin SC (HbSC) accounts for 30% of sickle cell disease (SCD) in the United States and United Kingdom, evidence-based guidelines for genotype specific management are lacking. The unique pathology of HbSC disease is complex, characterized by erythrocyte dehydration, intracellular sickling and increased blood viscosity. The evaluation and treatment of patients with HbSC is largely inferred from studies of SCD consisting mostly of haemoglobin SS (HbSS) patients. These studies are underpowered to allow definitive conclusions about HbSC. We review the pathophysiology of HbSC disease, including known and potential differences between HbSS and HbSC, and highlight knowledge gaps in HbSC disease management. Clinical and translational research is needed to develop targeted treatments and to validate management recommendations for efficacy, safety and impact on quality of life for people with HbSC.

Effect of Age on Blood Rheology in Sickle Cell Anaemia and Sickle Cell Haemoglobin C Disease: A Cross-Sectional Study

OBJECTIVES

Blood rheology plays a key role in the pathophysiology of sickle cell anaemia (SS) and sickle cell haemoglobin C disease (SC), but its evolution over the lifespan is unknown.

MATERIALS AND METHODS

Blood viscosity, red blood cell (RBC) deformability and aggregation, foetal haemoglobin (HbF) and haematocrit were measured in 114 healthy individuals (AA), 267 SS (161 children + 106 adults) and 138 SC (74 children + 64 adults) patients.

RESULTS

Our results showed that 1) RBC deformability is at its maximal value during the early years of life in SS and SC populations, mainly because HbF level is also at its peak, 2) during childhood and adulthood, hydroxycarbamide treatment, HbF level and gender modulated RBC deformability in SS patients, independently of age, 3) blood viscosity is higher in older SS and SC patients compared to younger ones and 4) haematocrit decreases as SS patients age.

CONCLUSION

The hemorheological changes detected in older patients could play a role in the progressive development of several chronic disorders in sickle cell disease, whose prevalence increases with age. Retarding these age-related haemorheological impairments, by using suitable drugs, may minimize the risks of vaso-occlusive events and chronic disorders.

Sickle Cell Trait Worsens Oxidative Stress, Abnormal Blood Rheology, and Vascular Dysfunction in Type 2 Diabetes

OBJECTIVE

It is predicted that Africa will have the greatest increase in the number of patients with type 2 diabetes mellitus (T2DM) within the next decade. T2DM patients are at risk for cardiovascular disorders. In Sub-Saharan African countries, sickle cell trait (SCT) is frequent. Despite the presence of modest abnormalities in hemorheology and oxidative stress, SCT is generally considered a benign condition. Little is known about vascular function in SCT, although recent studies demonstrated an increased risk of cardiovascular disorders, including venous thromboembolism, stroke, and chronic kidney disease. We hypothesized that SCT could accentuate the vascular dysfunction observed in T2DM.

RESEARCH DESIGN AND METHODS

The current study, conducted in Senegal, compared vascular function, hemorheological profile, and biomarkers of oxidative stress, inflammation, and nitric oxide metabolism in healthy individuals (CONT), subjects with T2DM or SCT, and patients with both T2DM and SCT (T2DM-SCT).

RESULTS

Flow-mediated dilation was blunted in individuals with T2DM, SCT, and T2DM-SCT compared with CONT, with vascular dysfunction being most pronounced in the latter group. Carotid-femoral pulse wave velocity measurements demonstrated increased arterial stiffness in T2DM-SCT. Oxidative stress, advanced glycation end products, and inflammation (interleukin-1β) were greater in patients with T2DM-SCT compared with the other groups. Blood viscosity was higher in individuals with TD2M, SCT carriers, and individuals with T2DM-SCT, and the values were further increased in the latter group.

CONCLUSIONS

Our results demonstrate severe biological abnormalities and marked vascular dysfunction in patients with both T2DM and SCT. SCT should be viewed as a risk factor for further cardiovascular disorders in individuals with T2DM.

The role of blood rheology in sickle cell disease

Studies performed in the last decades have highlighted the need to better understand the contribution of the endothelium, vascular function, oxidative stress, inflammation, coagulation, hemolysis and vascular adhesion mechanisms to the pathophysiology of acute vaso-occlusive like events and chronic organ damages in sickle cell disease (SCD). Although SCD is a hemorheological disease, a few works focused on the contribution of blood viscosity, plasma viscosity, red blood cell deformability and aggregation in the pathophysiology of SCD. After a brief description of basic hemorheology, the present review focuses on the role of the hemorheological abnormalities in the causation of several SCD complications, mainly in sickle cell anemia and hemoglobin (Hb) SC disease. Several genetic and cellular modulators of blood rheology in SCD are discussed, as well as unresolved questions and perspectives.

Red cell exchange transfusion halts progressive proliferative sickle cell retinopathy in a teenaged patient with hemoglobin SC disease

A male with sickle SC disease presented at age 8 years with proliferative sickle cell retinopathy (PSCR) and bilateral vitreous hemorrhage which spontaneously resolved, then recurred at 13 years of age. Despite conventional therapy with repeated pan-retinal photocoagulation and pars plana vitrectomy, he developed progressive PSCR and recurrent vitreous hemorrhage over the next 30 months. We describe the successful use of chronic red cell exchange transfusion (RCE) to preserve his vision and stabilize the retinopathy.

Deafness and sickle cell disease: three case reports and review of the literature

The otological complications of sickle cell disease (SCD) in general and the audiological complications in particular are not well documented and studied. Because the general management of patients with SCD has improved after the advent of newborn screening, antibiotic prophylaxis, safer blood transfusion and hydroxyurea therapy, patients with SCD are doing better in general and living longer than before. With longer longevity, the incidence of new complications of SCD became apparent and previously milder complications became more severe and more common. The dental and otological complications of SCD are examples of these changes that have become more common than before. Unfortunately with this increase, there are no guidelines or recommendations based on evidence on how to manage and treat these complications. The aim of this study was to describe three patients with SCD and deafness due to three different causes that were not adequately treated and to review the literature of deafness in SCD. We hope this may initiate more controlled trials on the incidence, prevalence and management of these complications.