Adenosine signaling inhibits erythropoiesis and promotes myeloid differentiation.

Intracellular uptake of adenosine is essential for optimal erythroid commitment and differentiation of hematopoietic progenitor cells. The role of adenosine signaling is well documented in the regulation of blood flow, cell proliferation, apoptosis, and stem cell regeneration. However, the role of adenosine signaling in hematopoiesis remains unclear. In this study, we show that adenosine signaling inhibits the proliferation of erythroid precursors by activating the p53 pathway and hampers the terminal erythroid maturation. Furthermore, we demonstrate that the activation of specific adenosine receptors promotes myelopoiesis. Overall, our findings indicate that extracellular adenosine could be a new player in the regulation of hematopoiesis.

Stroke without cerebral arteriopathy in sickle cell disease children: causes and treatment.

Cerebral arteriopathy (CA) in children with sickle cell disease (SCD) is classically described as chronic stenosis of arteries in the anterior brain circulation, leading to ischemic stroke. Some studies have, however, reported strokes in children with SCD but without CA. In order to better understand the etiology and risk factors of these strokes, we retrospectively analyzed ischemic strokes occurring in a large cohort of children over a 13-year period. Between 2007 and 2020, 25 of 1,500 children with SCD had an ischemic stroke in our center. Among them, 13 (52%) had CA, described as anatomical arterial stenosis, while 12 (48%) did not. Patients with stroke without CA were older than patients with stroke attributed to SCD-CA (9.0 years old vs. 3.6 years old; P=0.008), and more frequently had SC genotype (25% vs. 0%, respectively). Their strokes more frequently involved the posterior circulation, with cerebellar involvement in 42%. Retained stroke etiologies in patients without typical SCD-related CA were reversible cerebral vasoconstriction syndrome, cerebral fat embolism, arterial thrombosis or thromboembolism, hyperviscosity, vasculitis in a context of infectious meningo-encephalitis, and severe hemodynamic failure. No recurrence was observed in the 24 months following stroke, even though 67% of the patients in this group were no longer receiving exchange transfusions. In conclusion, in a cohort of pediatric SCD patients with an efficient stroke screening strategy, half of the ischemic strokes that occurred were related to causes other than CA. They affected a different population of SCD children and systematic long-term transfusion programs may not be necessary in these cases.

Case-control study of heart rate variability and sleep apnea in childhood sickle cell disease.

Obstructive sleep apnea (OSA) is common in sickle cell disease (SCD) despite the absence of overweight, suggesting a specific pathophysiology. We previously showed that otherwise healthy children with increased pharyngeal compliance, a main endotype of OSA, exhibited decreased sympathetic modulation. Our objective was to assess whether modifications of heart rate variability (HRV) and compliance are associated in SCD. Cases (children with SCD, African or Caribbean ethnicity) and controls (otherwise healthy children, same ethnicity), aged 4-18 years, were selected from our database of children referred for OSA and matched for sex, age, and obstructive apnea-hypopnoea index (OAHI) score. The children underwent polysomnography and acoustic pharyngometry (to compute compliance). HRV analyses were performed from 5 min ECG recordings in wakeful, NREM, and REM sleep states and from the whole night. Twenty-one pairs were analysed (median age 10.5 years, 24 girls). Children with SCD had lower BMI z-scores and more tonsil hypertrophy than control children. Children with SCD and OSA (OAHI ≥2/hour) were characterised by lower compliance than children with SCD without OSA. An inverse relationship between compliance and SD2 (HRV from whole night, inversely related to sympathetic modulation) was evidenced (negative relationship in SCD: R = -0.63, p = 0.002 vs. positive relationship in controls R = 0.59, p = 0.006). In conclusion, while the decrease in sympathetic modulation in control children may contribute to increasing pharyngeal compliance, its decrease seems protective in children with sickle cell disease, which underlines the specificity of OSAS pathophysiology in SCD that could be due to sickle cell disease related smooth muscle dystonia.

Comparative histological analysis of spleens in pediatric patients with hemolytic anemias: Insights into the pathophysiological mechanisms of spleen destruction in sickle cell anemia.

While sickle cell anemia (SCA) and hereditary spherocytosis (HS) share common features of increased spleen erythrophagocytosis due to increased red blood cell (RBC) turnover, SCA is specifically characterized by susceptibility to infections. In this study, histological lesions in the spleens of pediatric patients with SCA were analyzed, in close correlation with past clinical history and comparatively to HS, healthy and transfused ß-thalassemia patients (TDT). An evaluation of red pulp elementary lesions (red pulp fibrosis, iron deposition, number of Gandy-Gamna, and RBC trapping) combined into a severity score was established, as well as B-cell follicles analysis. Quantification on digitalized slides of iron deposition, RBC trapping, and red pulp fibrosis was additionally performed. Spleens from 22 children with SCA, eight with HS, eight with TDT, and three healthy controls (HC) were analyzed. Median age at splenectomy was not different between SCA and HS patients, 6.05 years (range: 4.5-16.0) versus 4.75 (range: 2.2-9.5). Marked heterogeneity was found in SCA spleens in contrast to other conditions. Contrary to previous reports, B-cell follicles were generally preserved in SCA. While RBC trapping was significantly increased in both SCA and HS (compared to TDT and HC), quantitative fibrosis and overall red pulp severity score were significantly increased in SCA spleens compared to other conditions. Moreover, there was an inverse correlation between quantitative fibrosis and number of B-cell follicles, linking these two compartments as well as spleen fibrosis to infectious susceptibility in SCA, potentially through impaired red pulp macrophage scavenging and B-cell subpopulations defects.

Erythrocyte type 1 equilibrative nucleoside transporter expression in sickle cell disease and sickle cell trait.

Hypoxia-mediated red blood cell (RBC) sickling is central to the pathophysiology of sickle cell disease (SCD). The signalling nucleoside adenosine is thought to play a significant role in this process. This study investigated expression of the erythrocyte type 1 equilibrative nucleoside transporter (ENT1), a key regulator of plasma adenosine, in adult patients with SCD and carriers of sickle cell trait (SCT). Relative quantitative expression analysis of erythrocyte ENT1 was carried out by Western blot and flow cytometry. Patients with SCD with steady state conditions, either with SS or SC genotype, untreated or under hydroxycarbamide (HC) treatment, exhibited a relatively high variability of erythrocyte ENT1, but with levels not significantly different from normal controls. Most strikingly, expression of erythrocyte ENT1 was found to be significantly decreased in patients with SCD undergoing painful vaso-occlusive episode and, unexpectedly, also in healthy SCT carriers. Promoting hypoxia-induced adenosine signalling, the reduced expression of erythrocyte ENT1 might contribute to the pathophysiology of SCD and to the susceptibility of SCT individuals to altitude hypoxia or exercise to exhaustion.

Delayed haemolytic transfusion reaction in paediatric patients with sickle cell disease: A retrospective study in a French national reference centre.

Delayed haemolytic transfusion reaction (DHTR) is a life-threatening haemolytic anaemia following red blood cell transfusion in patients with sickle cell disease, with only scarce data in children. We retrospectively analysed 41 cases of DHTR in children treated between 2006 and 2020 in a French university hospital. DHTR manifested at a median age of 10.5 years, symptoms occurred a median of 8 days after transfusion performed for an acute event (63%), before surgery (20%) or in a chronic transfusion programme (17%). In all, 93% of patients had painful crisis. Profound anaemia (median 49 g/L), low reticulocyte count (median 140 ×109 /L) and increased lactate dehydrogenase (median 2239 IU/L) were observed. Antibody screening was positive in 51% of patients, and more frequent when there was a history of alloimmunisation. Although no deaths were reported, significant complications occurred in 51% of patients: acute chest syndrome (12 patients), cholestasis (five patients), stroke (two patients) and kidney failure (two patients). A further transfusion was required in 23 patients and corticosteroids were used in 21 to reduce the risk of additional haemolysis. In all, 13 patients subsequently received further transfusions with recurrence of DHTR in only two. The study affords a better overview of DHTR and highlights the need to establish guidelines for its management in children.

Inherited glycosylphosphatidylinositol defects cause the rare Emm-negative blood phenotype and developmental disorders.

Glycosylphosphatidylinositol (GPI) is a glycolipid that anchors >150 proteins to the cell surface. Pathogenic variants in several genes that participate in GPI biosynthesis cause inherited GPI deficiency disorders. Here, we reported that homozygous null alleles of PIGG, a gene involved in GPI modification, are responsible for the rare Emm-negative blood phenotype. Using a panel of K562 cells defective in both the GPI-transamidase and GPI remodeling pathways, we show that the Emm antigen, whose molecular basis has remained unknown for decades, is carried only by free GPI and that its epitope is composed of the second and third ethanolamine of the GPI backbone. Importantly, we show that the decrease in Emm expression in several inherited GPI deficiency patients is indicative of GPI defects. Overall, our findings establish Emm as a novel blood group system, and they have important implications for understanding the biological function of human free GPI.

Early splenectomy in a large cohort of children with sickle cell anemia: risks and consequences.

In children with sickle cell anemia (SCA), early splenic complications can require splenectomy, but the benefit-to-risk ratio and the age at which splenectomy may be safely performed remain unclear. To address this question, we analyzed the rate of post-splenectomy events in children with SCA splenectomized between 2000-2018 at the Robert Debré University Hospital, Paris, France. A total of 188 children underwent splenectomy, including 101 (11.9%) from our newborn cohort and 87 referred to our center. Median (Q1-Q3) age at splenectomy was 4.1 years (range 2.5-7.3 years), with 123 (65.4%) and 65 (34.6%) children splenectomized at ≥3 years of age or <3 years of age, respectively. Median postsplenectomy follow-up was 5.9 years (range 2.7-9.2 years) yielding 1192.6 patient-years (PY) of observation. Indications for splenectomy were mainly acute splenic sequestration (101 [53.7%]) and hypersplenism (75 [39.9%]). All patients received penicillin prophylaxis; 98.3% received 23-valent polysaccharic pneumococcal (PPV-23) vaccination, and 91.9% a median number of 4 (range 3-4) pneumococcal conjugate vaccine shots prior to splenectomy. Overall incidence of invasive bacterial infection and thrombo-embolic events were 0.005 / PY (no pneumococcal infections) and 0.003 / PY, respectively, regardless of age at splenectomy. There was an increased proportion of children with cerebral vasculopathy in children splenectomized <3 years of age (0.037 / PY vs. 0.011 / PY; P<0.01). A significantly greater proportion of splenectomized than non-splenectomized children were treated with hydroxycarbamide (77.2% vs. 50.1%; P<0.01), suggesting a more severe phenotype in children who present spleen complications. If indicated, splenectomy should not be delayed in children, provided recommended pneumococcal prophylaxis is available. Spleen complications in childhood may serve as a marker of severity.

Resolution of sickle cell disease-associated inflammation and tissue damage with 17R-resolvin D1.

Resolvins (Rvs), endogenous lipid mediators, play a key role in the resolution of inflammation. Sickle cell disease (SCD), a genetic disorder of hemoglobin, is characterized by inflammatory and vaso-occlusive pathologies. We document altered proresolving events following hypoxia/reperfusion in humanized SCD mice. We demonstrate novel protective actions of 17R-resolvin D1 (17R-RvD1; 7S, 8R, 17R-trihydroxy-4Z, 9E, 11E, 13Z, 15E, 19Z-docosahexaenoic acid) in reducing ex vivo human SCD blood leukocyte recruitment by microvascular endothelial cells and in vivo neutrophil adhesion and transmigration. In SCD mice exposed to hypoxia/reoxygenation, oral administration of 17R -RvD1 reduces systemic/local inflammation and vascular dysfunction in lung and kidney. The mechanism of action of 17R-RvD1 involves (1) enhancement of SCD erythrocytes and polymorphonuclear leukocyte efferocytosis, (2) blunting of NF-κB activation, and (3) a reduction in inflammatory cytokines, vascular activation markers, and E-selectin expression. Thus, 17R-RvD1 might represent a new therapeutic strategy for the inflammatory vasculopathy of SCD.

Preventing Post-Lumbar Puncture Headache.

Post-lumbar puncture headache is the main adverse event from lumbar puncture and occurs in 3.5% to 33% of patients, causing functional and socio-professional disability. We searched the post-lumbar puncture headache literature and, based on this review and personal expertise, identified and addressed 19 frequently asked questions regarding post-lumbar puncture headache risk factors and prevention. Among the nonmodifiable factors, older age is associated with a lower incidence of post-lumbar puncture headache, while female sex, lower body mass index, and history of headache might be associated with increased risk. The use of atraumatic, noncutting needles is the most effective intervention for post-lumbar puncture headache prevention. These needles are not more difficult to use than cutting needles. Other commonly recommended measures (eg, fluid supplementation, caffeine) appear unhelpful, and some (eg, bed rest) may worsen post-lumbar puncture headache.