Metabolomic and molecular insights into sickle cell disease and innovative therapies

Metabolic blood profile and response to treatment with the pyruvate kinase activator mitapivat in patients with sickle cell disease

Mitapivat is an investigational, oral, small-molecule allosteric activator of pyruvate kinase (PK). PK is a regulatory glycolytic enzyme that is key in providing the red blood cell (RBC) with sufficient amounts of adenosine triphosphate (ATP). In sickle cell disease (SCD), decreased 2,3-DPG levels increase the oxygen affinity of hemoglobin, thereby preventing deoxygenation and polymerization of sickle hemoglobin. The PK activator mitapivat has been shown to decrease levels of 2,3-DPG and increase levels of ATP in RBCs in patients with SCD. In this phase 2, investigator-initiated, open-label study (https://www.clinicaltrialsregister.eu/ NL8517; EudraCT 2019-003438-18), untargeted metabolomics was used to explore the overall metabolic effects of 8-week treatment with mitapivat in the dose-finding period. In total, 1773 unique metabolites were identified in dried blood spots of whole blood from ten patients with SCD and 42 healthy controls (HCs). The metabolic phenotype of patients with SCD revealed alterations in 139/1773 (7.8%) metabolites at baseline when compared to HCs (false discovery rate-adjusted p < 0.05), including increases of (derivatives of) polyamines, purines, and acyl carnitines. Eight-week treatment with mitapivat in nine patients with SCD altered 85/1773 (4.8%) of the total metabolites and 18/139 (12.9%) of the previously identified altered metabolites in SCD (unadjusted p < 0.05). Effects were observed on a broad spectrum of metabolites and were not limited to glycolytic intermediates. Our results show the relevance of metabolic profiling in SCD, not only to unravel potential pathophysiological pathways and biomarkers in multisystem diseases but also to determine the effect of treatment.

Metabolic signatures of cardiorenal dysfunction in plasma from sickle cell patients as a function of therapeutic transfusion and hydroxyurea treatment

Metabolomics studies in sickle cell disease (SCD) have been so far limited to tens of samples, owing to technical and experimental limitations. To overcome these limitations, we performed plasma metabolomics analyses on 596 samples from patients with SCD enrolled in the WALK-PHaSST study (clinicaltrials gov. Identifier: NCT00492531). Clinical covariates informed the biological interpretation of metabolomics data, including genotypes (hemoglobin [Hb] SS, hemoglobin SC), history of recent transfusion (HbA%), response to hydroxyurea treatment (fetal Hb%). We investigated metabolic correlates to the degree of intravascular hemolysis, cardiorenal function, as determined by tricuspid regurgitation velocity (TRV), estimated glomerular filtration rate (eGFR), and overall hazard ratio (unadjusted or adjusted by age). Recent transfusion events or hydroxyurea treatment were associated with elevation in plasma-free fatty acids and decreases in acyl-carnitines, urate, kynurenine, indoles, carboxylic acids, and glycine- or taurine-conjugated bile acids. High levels of these metabolites, along with low levels of plasma S1P and L-arginine were identified as top markers of hemolysis, cardiorenal function (TRV, eGFR), and overall hazard ratio. We thus uploaded all omics and clinical data on a novel online portal that we used to identify a potential mechanism of dysregulated red cell S1P synthesis and export as a contributor to the more severe clinical manifestations in patients with the SS genotype compared to SC. In conclusion, plasma metabolic signatures - including low S1P, arginine and elevated kynurenine, acyl-carnitines and bile acids - are associated with clinical manifestation and therapeutic efficacy in SCD patients, suggesting new avenues for metabolic interventions in this patient population.

Nrf2 sensitizes ferroptosis through l-2-hydroxyglutarate-mediated chromatin modifications in sickle cell disease

Sickle cell disease (SCD) is a chronic hemolytic and systemic hypoxia condition with constant oxidative stress and significant metabolic alterations. However, little is known about the correlation between metabolic alterations and the pathophysiological symptoms. Here, we report that Nrf2, a master regulator of cellular antioxidant responses, regulates the production of the metabolite l-2-hydroxyglutarate (L2HG) to mediate epigenetic histone hypermethylation for gene expression involved in metabolic, oxidative, and ferroptotic stress responses in SCD. Mechanistically, Nrf2 was found to regulate the expression of L2HG dehydrogenase (L2hgdh) to mediate L2HG production under hypoxia. Gene expression profile analysis indicated that reactive oxygen species (ROS) and ferroptosis responses were the most significantly affected signaling pathways after Nrf2 ablation in SCD. Nrf2 silencing and L2HG supplementation sensitize human sickle erythroid cells to ROS and ferroptosis stress. The absence of Nrf2 and accumulation of L2HG significantly affect histone methylation for chromatin structure modification and reduce the assembly of transcription complexes on downstream target genes to regulate ROS and ferroptosis responses. Furthermore, pharmacological activation of Nrf2 was found to have protective effects against ROS and ferroptosis stress in SCD mice. Our data suggest a novel mechanism by which Nrf2 regulates L2HG levels to mediate SCD severity through ROS and ferroptosis stress responses, suggesting that targeting Nrf2 is a viable therapeutic strategy for ameliorating SCD symptoms.

Moderate hypoxia induces metabolic divergence in circulating monocytes and tissue resident macrophages from Berkeley sickle cell anemia mice

Introduction

Human and murine sickle cell disease (SCD) associated pulmonary hypertension (PH) is defined by hemolysis, nitric oxide depletion, inflammation, and thrombosis. Further, hemoglobin (Hb), heme, and iron accumulation are consistently observed in pulmonary adventitial macrophages at autopsy and in hypoxia driven rodent models of SCD, which show distribution of ferric and ferrous Hb as well as HO-1 and ferritin heavy chain. The anatomic localization of these macrophages is consistent with areas of significant vascular remodeling. However, their contributions toward progressive disease may include unique, but also common mechanisms, that overlap with idiopathic and other forms of pulmonary hypertension. These processes likely extend to the vasculature of other organs that are consistently impaired in advanced SCD.

Methods

To date, limited information is available on the metabolism of macrophages or monocytes isolated from lung, spleen, and peripheral blood in humans or murine models of SCD.

Results

Here we hypothesize that metabolism of macrophages and monocytes isolated from this triad of tissue differs between Berkley SCD mice exposed for ten weeks to moderate hypobaric hypoxia (simulated 8,000 ft, 15.4% O2) or normoxia (Denver altitude, 5000 ft) with normoxia exposed wild type mice evaluated as controls.

Discussion

This study represents an initial set of data that describes the metabolism in monocytes and macrophages isolated from moderately hypoxic SCD mice peripheral lung, spleen, and blood mononuclear cells.

Self-Reported Medication Adherence Measured with Morisky Scales in Rare Disease Patients: A Systematic Review and Meta-Analysis

BACKGROUND

The visibility of Rare Diseases is a new challenge for society. These diseases are numerous, heterogeneous in nature and distribution, characterized by a high mortality rate but low prevalence, and usually presenting a severe evolution. Adherence to medication studies in rare diseases are uncommon, due to treatment scarcity.

OBJECTIVES

The main purpose of this study is to do a meta-analysis, evaluating the level of adherence to medication in the most prevalent rare diseases.

METHODS

This work is a systematic review, and meta-analysis was registered in the International Prospective Register of Systematic Reviews (PROSPERO) (Registration number: CRD42022372843) and conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Adherence to treatment in this systematic review and meta-analysis was collected from all studies included, based on the crude numerators and denominators reported, using either the Morisky Medication Adherence Scale 4 or -8.

RESULTS

A total of 54 records were identified through database searches, or after screening relevant manuscripts' references. Finally, 18 studies were included in this systematic review and meta-analysis. A total of 1559 participants (54.18% women) aged less than 84 years old were included. Twelve studies used the MMAS-8. In 8 of them, they established the level of adherence to treatment in three categories (low, medium, and high), with the mean prevalence in each of them being 41.4%, 30.4%, and 28.2%, respectively.

CONCLUSIONS

The results observed in adherence to treatment in patients with rare diseases show great variability, due to the different aspects involved in the greater or lesser applicability of the medication.

Evaluation of 2D and 3D Erythroid Differentiation Protocols Using Sickle Cell Disease and Healthy Donor Induced Pluripotent Stem Cells

BACKGROUND

Sickle cell disease (SCD) is a highly prevalent genetic disease caused by a point mutation in the HBB gene, which can lead to chronic hemolytic anemia and vaso-occlusive events. Patient-derived induced pluripotent stem cells (iPSCs) hold promise for the development of novel predictive methods for screening drugs with anti-sickling activity. In this study, we evaluated and compared the efficiency of 2D and 3D erythroid differentiation protocols using a healthy control and SCD-iPSCs.

METHODS

iPSCs were subjected to hematopoietic progenitor cell (HSPC) induction, erythroid progenitor cell induction, and terminal erythroid maturation. Differentiation efficiency was confirmed by flow cytometry analysis, colony-forming unit (CFU) assay, morphological analyses, and qPCR-based gene expression analyses of HBB and HBG2.

RESULTS

Both 2D and 3D differentiation protocols led to the induction of CD34⁺/CD43⁺ HSPCs. The 3D protocol showed good efficiency (>50%) and high productivity (45-fold) for HSPC induction and increased the frequency of BFU-E, CFU-E, CFU-GM, and CFU-GEMM colonies. We also produced CD71⁺/CD235a⁺ cells (>65%) with a 630-fold cell expansion relative to that at the beginning of the 3D protocol. After erythroid maturation, we observed 95% CD235a⁺/DRAQ5- enucleated cells, orthochromatic erythroblasts, and increased expression of fetal HBG2 compared to adult HBB.

CONCLUSION

A robust 3D protocol for erythroid differentiation was identified using SCD-iPSCs and comparative analyses; however, the maturation step remains challenging and requires further development.

Metabolic signatures of cardiorenal dysfunction in plasma from sickle cell patients, as a function of therapeutic transfusion and hydroxyurea treatment

Metabolomics studies in sickle cell disease (SCD) have been so far limited to tens of samples, owing to technical and experimental limitations. To overcome these limitations, we performed plasma metabolomics analyses on 596 samples from patients with sickle cell sickle cell disease (SCD) enrolled in the WALK-PHaSST study. Clinical covariates informed the biological interpretation of metabolomics data, including genotypes (hemoglobin SS, hemoglobin SC), history of recent transfusion (HbA%), response to hydroxyurea treatment (HbF%). We investigated metabolic correlates to the degree of hemolysis, cardiorenal function, as determined by tricuspid regurgitation velocity (TRV), estimated glomerular filtration rate (eGFR), and overall hazard ratio (unadjusted or adjusted by age). Recent transfusion events or hydroxyurea treatment were associated with elevation in plasma free fatty acids and decreases in acyl-carnitines, urate, kynurenine, indoles, carboxylic acids, and glycine- or taurine-conjugated bile acids. High levels of these metabolites, along with low levels of plasma S1P and L-arginine were identified as top markers of hemolysis, cardiorenal function (TRV, eGFR), and overall hazard ratio. We thus uploaded all omics and clinical data on a novel online portal that we used to identify a potential mechanism of dysregulated red cell S1P synthesis and export as a contributor to the more severe clinical manifestations in patients with the SS genotype compared to SC. In conclusion, plasma metabolic signatures - including low S1P, arginine and elevated kynurenine, acyl-carnitines and bile acids - are associated with clinical manifestation and therapeutic efficacy in SCD patients, suggesting new avenues for metabolic interventions in this patient population.

Metabolic correlates to critical speed in murine models of sickle cell disease

Introduction: Exercise intolerance is a common clinical manifestation in patients with sickle cell disease (SCD), though the mechanisms are incompletely understood. Methods: Here we leverage a murine mouse model of sickle cell disease, the Berkeley mouse, to characterize response to exercise via determination of critical speed (CS), a functional measurement of mouse running speed upon exerting to exhaustion. Results: Upon observing a wide distribution in critical speed phenotypes, we systematically determined metabolic aberrations in plasma and organs-including heart, kidney, liver, lung, and spleen-from mice ranked based on critical speed performances (top vs. bottom 25%). Results indicated clear signatures of systemic and organ-specific alterations in carboxylic acids, sphingosine 1-phosphate and acylcarnitine metabolism. Metabolites in these pathways showed significant correlations with critical speed across all matrices. Findings from murine models were thus further validated in 433 sickle cell disease patients (SS genotype). Metabolomics analyses of plasma from 281 subjects in this cohort (with HbA < 10% to decrease confounding effects of recent transfusion events) were used to identify metabolic correlates to sub-maximal exercise test performances, as measure by 6 min walking test in this clinical cohort. Results confirmed strong correlation between test performances and dysregulated levels of circulating carboxylic acids (especially succinate) and sphingosine 1-phosphate. Discussion: We identified novel circulating metabolic markers of exercise intolerance in mouse models of sickle cell disease and sickle cell patients.

Hydroxyurea Decouples Persistent F-Cell Elevation and Induction of γ-Globin

Mechanisms that control the fetal-to-adult hemoglobin switch are attractive therapeutic targets in sickle cell disease. In this study, we investigated developmental γ-globin silencing in the Townes humanized knock-in mouse model, which harbors a construct containing the human γ-, β^A-, and β^S-globin genes, and examined the utility of this model in evaluation of pharmacologic induction of fetal hemoglobin (HbF). We studied mouse pups on the day of delivery (P0) to 28 days after birth (P28). Regardless of the hemoglobin genotype (SS, AS, or AA), the proportion of F cells in peripheral blood was 100% at P0, declined sharply to 20% at P2, and was virtually undetectable at P14. Developmental γ-globin silencing in Townes mice was complete at P4 in association with significantly increased BCL11A expression in the primary erythropoietic organs of the mouse. Hydroxyurea given at P2 significantly sustained elevated percentages of F cells in mice at P14. However, the percentage of F cells declined at P14 for treatment begun at P4. A lack of augmentation of γ-globin mRNA in erythroid tissues suggests that the apparent increase in HbF in red cells caused by hydroxyurea was not due to sustained or re-activation of γ-globin transcription, but was instead a function of erythropoiesis suppression. Thus, we provide new details of the hemoglobin switch in the Townes murine model that recapitulates postnatal γ- to β-globin switch in humans and identify the myelosuppressive toxicity of hydroxyurea as a superseding factor in interpreting pharmacologic induction of HbF.

Plasma Levels of Acyl-Carnitines and Carboxylic Acids Correlate With Cardiovascular and Kidney Function in Subjects With Sickle Cell Trait

Subjects with sickle cell trait (SCT) carry one copy of mutated β-globin gene at position E6V at the origin of the production of sickle hemoglobin (HbS). Indeed, individuals with SCT have both normal hemoglobin and HbS, in contrast to patients with sickle cell disease who inherited of two copies of the mutated gene. Although SCT is generally benign/asymptomatic, carriers may develop certain adverse outcomes such as renal complications, venous thromboembolism, exercise-induced rhabdomyolysis … However, little is known about whether similar metabolic pathways are affected in individuals with SCT and whether these metabolic derangements, if present, correlate to clinically relevant parameters. In this study, we performed metabolomics analysis of plasma from individuals with sickle cell trait (n = 34) compared to healthy controls (n = 30). Results indicated a significant increase in basal circulating levels of hemolysis markers, mono- (pyruvate, lactate), di- and tri-carboxylates (including all Krebs cycle intermediates), suggestive of systems-wide mitochondrial dysfunction in individuals with SCT. Elevated levels of kynurenines and indoles were observed in SCT samples, along with increases in the levels of oxidative stress markers (advanced glycation and protein-oxidation end-products, malondialdehyde, oxylipins, eicosanoids). Increases in circulating levels of acyl-carnitines and fatty acids were observed, consistent with increased membrane lipid damage in individuals with sickle cell trait. Finally, correlation analyses to clinical co-variates showed that alterations in the aforementioned pathways strongly correlated with clinical measurements of blood viscosity, renal (glomerular filtration rate, microalbuminuria, uremia) and cardiovascular function (carotid-femoral pulse wave velocity, blood pressure).

p97 dysfunction underlies a loss of quality control of damaged membrane proteins and promotes oxidative stress and sickling in sickle cell disease

Sickling is the central pathogenic process of sickle cell disease (SCD), one of the most prevalent inherited hemolytic disorders. Having no easy access to antioxidants in the cytosol, elevated levels of reactive oxygen species (ROS) residing at the plasma membrane in sickle red blood cells (sRBCs) easily oxidize membrane proteins and thus contribute to sickling. Although the ubiquitin-proteasome system (UPS) is essential to rapidly clear ROS-damaged membrane proteins and maintain cellular homeostasis, the function and regulatory mechanism of the UPS for their clearance in sRBCs remains unidentified. Elevated levels of polyubiquitinated membrane-associated proteins in human sRBCs are reported here. High throughput and untargeted proteomic analyses of membrane proteins immunoprecipitated by ubiquitin antibodies detected elevated levels of ubiquitination of a series of proteins including cytoskeletal proteins, transporters, ROS-related proteins, and UPS machinery components in sRBCs. Polyubiquitination of membrane-associated catalase was increased in sRBCs, associated with decreased catalase activity and elevated ROS. Surprisingly, shuttling of p97 (ATP-dependent valosin-containing chaperone protein), a key component of the UPS to shuttle polyubiquitinated proteins from the membrane to cytosol for proteasomal degradation, was significantly impaired, resulting in significant accumulation of p97 along with polyubiquitinated proteins in the membrane of human sRBCs. Functionally, inhibition of p97 directly promoted accumulation of polyubiquitinated membrane-associated proteins, excessive ROS levels, and sickling in response to hypoxia. Overall, we revealed that p97 dysfunction underlies impaired UPS and contributes to oxidative stress in sRBCs.

Purinergic signaling is essential for full Psickle activation by hypoxia and by normoxic acid pH in mature human sickle red cells and in vitro-differentiated cultured human sickle reticulocytes

Paracrine ATP release by erythrocytes has been shown to regulate endothelial cell function via purinergic signaling, and this erythoid-endothelial signaling network is pathologically dysregulated in sickle cell disease. We tested the role of extracellular ATP-mediated purinergic signaling in the activation of Psickle, the mechanosensitive Ca²⁺-permeable cation channel of human sickle erythrocytes (SS RBC). Psickle activation increases intracellular [Ca²⁺] to stimulate activity of the RBC Gardos channel, KCNN4/KCa3.1, leading to cell shrinkage and accelerated deoxygenation-activated sickling.We found that hypoxic activation of Psickle recorded by cell-attached patch clamp in SS RBC is inhibited by extracellular apyrase, which hydrolyzes extracellular ATP. Hypoxic activation of Psickle was also inhibited by the pannexin-1 inhibitor, probenecid, and by the P2 antagonist, suramin. A Psickle-like activity was also activated in normoxic SS RBC (but not in control red cells) by bath pH 6.0. Acid-activated Psickle-like activity was similarly blocked by apyrase, probenecid, and suramin, as well as by the Psickle inhibitor, Grammastola spatulata mechanotoxin-4 (GsMTx-4).In vitro-differentiated cultured human sickle reticulocytes (SS cRBC), but not control cultured reticulocytes, also exhibited hypoxia-activated Psickle activity that was abrogated by GsMTx-4. Psickle-like activity in SS cRBC was similarly elicited by normoxic exposure to acid pH, and this acid-stimulated activity was nearly completely blocked by apyrase, probenecid, and suramin, as well as by GsMTx-4.Thus, hypoxia-activated and normoxic acid-activated cation channel activities are expressed in both SS RBC and SS cRBC, and both types of activation appear to be mediated or greatly amplified by autocrine or paracrine purinergic signaling.

Effects of Formyl Peptide Receptor Agonists Ac9-12 and WKYMV in In Vivo and In Vitro Acute Inflammatory Experimental Models

Formyl peptide receptors (Fprs) are a G-protein-coupled receptor family mainly expressed on leukocytes. The activation of Fpr1 and Fpr2 triggers a cascade of signaling events, leading to leukocyte migration, cytokine release, and increased phagocytosis. In this study, we evaluate the effects of the Fpr1 and Fpr2 agonists Ac_9-12 and WKYMV, respectively, in carrageenan-induced acute peritonitis and LPS-stimulated macrophages. Peritonitis was induced in male C57BL/6 mice through the intraperitoneal injection of 1 mL of 3% carrageenan solution or saline (control). Pre-treatments with Ac_9-12 and WKYMV reduced leukocyte influx to the peritoneal cavity, particularly neutrophils and monocytes, and the release of IL-1β. The addition of the Fpr2 antagonist WRW4 reversed only the anti-inflammatory actions of WKYMV. In vitro, the administration of Boc2 and WRW4 reversed the effects of Ac_9-12 and WKYMV, respectively, in the production of IL-6 by LPS-stimulated macrophages. These biological effects of peptides were differently regulated by ERK and p38 signaling pathways. Lipidomic analysis evidenced that Ac_9-12 and WKYMV altered the intracellular lipid profile of LPS-stimulated macrophages, revealing an increased concentration of several glycerophospholipids, suggesting regulation of inflammatory pathways triggered by LPS. Overall, our data indicate the therapeutic potential of Ac_9-12 and WKYMV via Fpr1 or Fpr2-activation in the inflammatory response and macrophage activation.

Murine bone marrow mesenchymal stromal cells have reduced hematopoietic maintenance ability in sickle cell disease

Sickle cell disease (SCD) is characterized by hemolytic anemia, which can trigger oxidative stress, inflammation, and tissue injury that contribute to disease complications. Bone marrow mesenchymal stromal cells (MSCs) tightly regulate hematopoietic stem cell (HSC) homeostasis in health and disease, but their functionality in SCD remains unclear. We identified for the first time that murine SCD MSCs have altered gene signatures, reduced stem cell properties, and increased oxidative stress, due in part to hemolysis. Murine SCD MSCs had lower HSC maintenance ability in vitro and in vivo, as manifested by increased HSC mobilization and decreased HSC engraftment after transplant. Activation of Toll-like receptor-4 through p65 in MSCs further contributed to MSC dysfunction. Transfusions led to an improved MSC and HSC oxidative state in SCD mice. Improving the regulation between MSCs and HSCs has vital implications for enhancing clinical HSC transplantation and gene therapy outcomes and for identification of new molecular targets for alleviating SCD complications.

Amniotic fluid metabolomic and lipidomic alterations associated with hemoglobin Bart's diseases

INTRODUCTION

α-Thalassemia is the most common inherited disease in southern China. The severest form is hemoglobin (Hb) Bart's disease, in which the affected fetuses almost always die in utero or shortly after birth, and the mothers are at high risk for severe morbidity.

OBJECTIVE

To investigate the changes in all metabolites in fetuses with Hb Bart's disease and to characterize the metabolomic and lipidomic biomarkers in the development of Hb Bart's fetuses.

METHODS

Amniotic fluid (AF) specimens were selected from 34 pregnant women who underwent interventional prenatal diagnosis from June 2017 to June 2018. Gap-PCR analysis was used to diagnose Hb Bart's disease, and untargeted metabolomic and lipidomic analyses were performed.

RESULTS

By analyzing AF samples, 935 differential metabolites were selected between Hb Bart's and control fetuses. The metabolites with significant changes mainly involved D-glutamine and D-glutamate metabolism, histidine metabolism, arginine metabolism, beta-alanine metabolism and alanine, aspartate and glutamate metabolism. Further lipidomics analysis revealed 132 differential lipids, mainly involved phosphatidylcholine and triglyceride metabolism. Through the characterized metabolites in AF, a schematic model of Hb Bart's disease was established.

CONCLUSION

Glutamate and glutathione metabolism, aspartate metabolism, urea metabolism and triglyceride metabolism were significantly changed in the Hb Bart's group compared to the control group. The characterized biomarkers were mainly involved in oxidative stress reaction, iron overload and liver dysfunction. This finding may help improve the treatment options for α-thalassemia as well as diagnosing phenotype of patients.

Priapism and Sickle Cell Disease: Special Considerations in Etiology, Management, and Prevention

Sickle cell disease (SCD) is an inherited medical condition where sickled red blood cells cause vaso-occlusive crisis. One major complication of SCD is priapism, defined as an erection of the penis lasting over four hours beyond sexual stimulation or orgasm. SCD priapism is caused by sickled erythrocytes obstructing venous outflow and can lead to permanent erectile dysfunction. This article reviews the pathology, physiology, and management of SCD priapism, including potential novel therapeutic agents.

Sickle cell vaso-occlusion: The dialectic between red cells and white cells

The pathophysiology of sickle cell anemia, a hereditary hemoglobinopathy, has fascinated clinicians and scientists alike since its description over 100 years ago. A single gene mutation in the HBB gene results in the production of abnormal hemoglobin (Hb) S, whose polymerization when deoxygenated alters the physiochemical properties of red blood cells, in turn triggering pan-cellular activation and pathological mechanisms that include hemolysis, vaso-occlusion, and ischemia-reperfusion to result in the varied and severe complications of the disease. Now widely regarded as an inflammatory disease, in recent years attention has included the role of leukocytes in vaso-occlusive processes in view of the part that these cells play in innate immune processes, their inherent ability to adhere to the endothelium when activated, and their sheer physical and potentially obstructive size. Here, we consider the role of sickle red blood cell populations in elucidating the importance of adhesion vis-a-vis polymerization in vaso-occlusion, review the direct adhesion of sickle red cells to the endothelium in vaso-occlusive processes, and discuss how red cell- and leukocyte-centered mechanisms are not mutually exclusive. Given the initial clinical success of crizanlizumab, a specific anti-P selectin therapy, we suggest that it is appropriate to take a holistic approach to understanding and exploring the complexity of vaso-occlusive mechanisms and the adhesive roles of the varied cell types, including endothelial cells, platelets, leukocytes, and red blood cells.

Management of Sickle Cell Disease Complications Beyond Acute Chest Syndrome

Sickle cell disease results in numerous complications that can lead to significant morbidity and mortality. Amongst them, acute chest syndrome is the leading cause of mortality. As a result, most providers are in tune with this complication and well versed with management. As sickle cell patients now live longer, they face a multitude of other complications that if left unattended, can lead to significant morbidity and mortality as well. It is critical to look beyond acute chest syndrome and adopt a more comprehensive approach to the management of the sickle cell patient.

Blood plasma metabolomics of children and adolescents with sickle cell anaemia treated with hydroxycarbamide: a new tool for uncovering biochemical alterations

Sickle cell anaemia (SCA) is a debilitating genetic haemoglobinopathy predominantly affecting the disenfranchised strata of society in Africa and the Americas. The most common pharmacological treatment for this disease is the administration of hydroxycarbamide (HC) for which questions remain regarding its mechanism of action, efficacy and long-term toxicity specifically in paediatric individuals. A multiplatform metabolomics approach was used to assess the metabolome of plasma samples from a population of children and adolescents with SCA with and without HC treatment along with non-SCA individuals. Fifty-three metabolites were identified by ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS) and ¹ H nuclear magnetic resonance (NMR) with a predominance of membrane lipids, amino acids and organic acids. The partial least-squares discriminant analysis (PLS-DA) analysis allowed a clear discrimination between the different studied groups, revealing clear effects of the HC treatment in the patients' metabolome including rescue of specific metabolites to control levels. Increased creatine/creatinine levels under HC treatment suggests a possible increase in the arginine pool and increased NO synthesis, supporting existing models for HC action in SCA. The metabolomics results extend the current knowledge on the models for SCA pathophysiology including impairment of Lands' cycle and increased synthesis of sphingosine 1-phosphate. Putative novel biomarkers are suggested.

Adenosine A2B receptor: A pathogenic factor and a therapeutic target for sensorineural hearing loss

Over 466 million people worldwide are diagnosed with hearing loss (HL). About 90% of HL cases are sensorineural HL (SNHL) with treatments limited to hearing aids and cochlear implants with no FDA-approved drugs. Intriguingly, ADA-deficient patients have been reported to have bilateral SNHL, however, its underlying cellular and molecular basis remain unknown. We report that Ada^-/- mice, phenocopying ADA-deficient humans, displayed SNHL. Ada^-/- mice cochlea with elevated adenosine caused substantial nerve fiber demyelination and mild hair cell loss. ADA enzyme therapy in these mice normalized cochlear adenosine levels, attenuated SNHL, and prevented demyelination. Additionally, ADA enzyme therapy rescued SNHL by restoring nerve fiber structure in Ada^-/- mice post two-week drug withdrawal. Moreover, elevated cochlear adenosine in untreated mice was associated with enhanced Adora2b gene expression. Preclinically, ADORA2B-specific antagonist treatment in Ada^-/- mice significantly improved HL, nerve fiber density, and myelin compaction. We also provided genetic evidence that ADORA2B is detrimental for age-related SNHL by impairing cochlear myelination in WT aged mice. Overall, understanding purinergic molecular signaling in SNHL in Ada^-/- mice allows us to further discover that ADORA2B is also a pathogenic factor underlying aged-related SNHL by impairing cochlear myelination and lowering cochlear adenosine levels or blocking ADORA2B signaling are effective therapies for SNHL.

SC411 treatment can enhance survival in a mouse model of sickle cell disease

Sickle cell disease (SCD) is one of the most common inherited blood disorder among African Americans affecting 70,000-100,000 individuals in the United States. It is characterized by abnormal hemoglobin (HbS) which develops into severe hemolytic anemia and vaso-occlusive crisis. Therefore, patients with SCD suffer from a chronic state of inflammation, which is responsible for multiple organ damage, ischemic attacks, and premature death. Another major hallmark of SCD patients is the abnormally low levels of omega-3 fatty acids, especially docosahexaenoic acid (DHA) in their red blood cell membranes. Treatment with DHA can reduce red blood cell adhesion and enhance cerebral blood flow, thus, our main goal is to investigate the effect of SC411, which is a novel, highly purified DHA ethyl ester formulation with a proprietary delivery platform in SCD. Utilizing a transgenic mouse model of SCD (HbSS-Townes) and recurrent hypoxic challenges (10%O₂, 0.5% CO₂ and balance N₂ for 3 h) to mimic ischemic-like conditions, our data suggest that SC411 can elevate blood DHA and eicosapentaenoic acid (EPA) levels after 8 weeks of treatment. SC411 can also decrease arachidonic acid (AA) and sickling of red blood cells. In addition, SC411-treated SCD mice showed presented with cerebral blood flow, alleviated neuroinflammation, and revived working memory which ultimately enhanced overall survival. In summary, this study suggests that treatment with SC411 improves cellular and functional outcomes in SCD mice. This finding may provide novel therapeutic opportunities in the treatment against ischemic injury elicited by SCD.

Current Status of Metabolomic Biomarker Discovery: Impact of Study Design and Demographic Characteristics

Widespread application of omic technologies is evolving our understanding of population health and holds promise in providing precise guidance for selection of therapeutic interventions based on patient biology. The opportunity to use hundreds of analytes for diagnostic assessment of human health compared to the current use of 10–20 analytes will provide greater accuracy in deconstructing the complexity of human biology in disease states. Conventional biochemical measurements like cholesterol, creatinine, and urea nitrogen are currently used to assess health status; however, metabolomics captures a comprehensive set of analytes characterizing the human phenotype and its complex metabolic processes in real-time. Unlike conventional clinical analytes, metabolomic profiles are dramatically influenced by demographic and environmental factors that affect the range of normal values and increase the risk of false biomarker discovery. This review addresses the challenges and opportunities created by the evolving field of clinical metabolomics and highlights features of study design and bioinformatics necessary to maximize the utility of metabolomics data across demographic groups.

Metabolomic Profiling of Plasma and Erythrocytes in Sickle Mice Points to Altered Nociceptive Pathways

Few data-driven metabolomic approaches have been reported in sickle cell disease (SCD) to date. We performed a metabo-lipidomic study on the plasma and red blood cells of a steady-state mouse model carrying the homozygous human hemoglobin SS, compared with AS and AA genotypes. Among the 188 metabolites analyzed by a targeted quantitative metabolomic approach, 153 and 129 metabolites were accurately measured in the plasma and red blood cells, respectively. Unsupervised PCAs (principal component analyses) gave good spontaneous discrimination between HbSS and controls, and supervised OPLS-DAs (orthogonal partial least squares-discriminant analyses) provided highly discriminant models. These models confirmed the well-known deregulation of nitric oxide synthesis in the HbSS genotype, involving arginine deficiency and increased levels of dimethylarginines, ornithine, and polyamines. Other discriminant metabolites were newly evidenced, such as hexoses, alpha-aminoadipate, serotonin, kynurenine, and amino acids, pointing to a glycolytic shift and to the alteration of metabolites known to be involved in nociceptive pathways. Sharp remodeling of lysophosphatidylcholines, phosphatidylcholines, and sphingomyelins was evidenced in red blood cells. Our metabolomic study provides an overview of the metabolic remodeling induced by the sickle genotype in the plasma and red blood cells, revealing a biological fingerprint of altered nitric oxide, bioenergetics and nociceptive pathways.

Metabolomics and lipidomics study unveils the impact of polybrominated diphenyl ether-47 on breast cancer mice

Polybrominated diphenyl ether-47 (BDE-47) is a congener of polybrominated diphenyl ethers (PBDEs) and relates to different health risks. However, in vivo study of the association between BDE-47 and breast cancer was scarce. In this study, we performed in vivo exposure of BDE-47 to breast cancer nude mice and conducted mass spectrometry-based metabolomics and lipidomics analysis to investigate the metabolic changes in mice. Results showed that the tumor sizes were positively associated with the dosage of BDE-47. Metabolomics and lipidomics profiling analysis indicated that BDE-47 induced significant alterations of metabolic pathways in livers, including glutathione metabolism, ascorbate and aldarate metabolism, and lipids metabolism, etc. The upregulations of phosphatidylcholines (PCs) and phosphatidylethanolamines (PEs) suggested the membrane remodeling, and the downregulations of Lyso-PCs and Lyso-PEs might be associated with the tumor growth. Targeted metabolomics analysis revealed that BDE-47 inhibited fatty acid β-oxidation (FAO) and induced incomplete FAO. The inhibition of FAO and downregulation of PPARγ would contribute to inflammation, which could promote tumor growth. In addition, BDE-47 elevated the expression of the cytokines TNFRSF12A, TNF-α, IL-1β and IL-6, and lowered the cytokines SOCS3 and the nuclear receptor PPARα. The changes of cytokines and receptor may contribute to the tumor growth of mice.

Sickle cell disease as a vascular disorder

INTRODUCTION

In sickle cell disease (SCD), hemoglobin S (HbS) red blood cells (RBCs) are characteristically deformed and inflexible. Often breaking down in the circulation, they exhibit increased adhesive properties with the endothelium and activated neutrophils and platelets, increasing the risk of occlusion of the microcirculation. SCD is categorized into two sub-phenotypes: hyperhemolytic, associated with priapism, leg ulcers, pulmonary hypertension, and stroke, and high hemoglobin/viscosity, which may promote vaso-occlusion-associated pain, acute chest syndrome, and osteonecrosis.

AREAS COVERED

The sub-phenotypes are not completely distinct. Hemolysis may trigger vaso-occlusion, contributing to vascular complications. Targeting P-selectin, a key mediator of cross-talk between hyperhemolysis and vaso-occlusion, may be beneficial for vascular and vaso-occlusion-associated complications. English-language articles from PubMed on the topic of SCD and vaso-occlusive crises (VOCs) were reviewed from 1 January 2000 to 1 January 2019 using the search terms 'sickle cell disease,' 'vaso-occlusive crises,' and 'selectin.'

EXPERT OPINION

Besides targeting P-selectin, other strategies to counter VOCs and RBC sickling are being pursued. These include platelet inhibition to counter aggregation, intercellular adhesion, and thrombosis during VOCs; gene therapy to correct the homozygous missense mutation in the β-globin gene, causing polymerization of HbS; L-glutamine, possibly reducing oxidative stress in sickled RBCs; and fetal hemoglobin inducers.

Sickle Cell Disease: Metabolomic Profiles of Vaso-Occlusive Crisis in Plasma and Erythrocytes

The metabolomic profile of vaso-occlusive crisis, compared to the basal state of sickle cell disease, has never been reported to our knowledge. Using a standardized targeted metabolomic approach, performed on plasma and erythrocyte fractions, we compared these two states of the disease in the same group of 40 patients. Among the 188 metabolites analyzed, 153 were accurately measured in plasma and 143 in red blood cells. Supervised paired partial least squares discriminant analysis (pPLS-DA) showed good predictive performance for test sets with median area under the receiver operating characteristic (AUROC) curves of 99% and mean p-values of 0.0005 and 0.0002 in plasma and erythrocytes, respectively. A total of 63 metabolites allowed discrimination between the two groups in the plasma, whereas 61 allowed discrimination in the erythrocytes. Overall, this signature points to altered arginine and nitric oxide metabolism, pain pathophysiology, hypoxia and energetic crisis, and membrane remodeling of red blood cells. It also revealed the alteration of metabolite concentrations that had not been previously associated with sickle cell disease. Our results demonstrate that the vaso-occlusive crisis has a specific metabolomic signature, distinct from that observed at steady state, which may be potentially helpful for finding predictive biomarkers for this acute life-threatening episode.

In silico study of peculiarities of metabolism of erythrocytes with glucosephosphate isomerase deficiency

Glucose phosphate isomerase (GPI) deficiency, the third most common cause of hereditary nonspherocytic hemolytic anemia, is associated with the mutation of the GPI gene. The results of the GPI deficiency are premature aging of erythrocytes, macrocytosis, reticulocytosis, minor splenomegaly, hyperbilirubinemia and hyperferritinemia, and hemolytic crisis under the influence of exogenous oxidants such as infections or drugs. Regarding the the lack of GPI correction drugs, the theoretical substantiation of supportive therapy based on system biology approaches that would allow the analysis of the relationships between numerical metabolic processes in a cell would be beneficial. The stoichiometric model of erythrocytes’ steady state metabolism, including the pathways of Embden-Meyerhof and pentose phosphate (PPP), purine metabolism cycles and glutathione synthesis, has been developed. To predict the redistribution of metabolic flows in erythrocytes under conditions of GPI deficiency, we used the flux balance analysis (FBA). In this approach, calculations of the elementary flux modes (EFMs) and the control-effective flux (CEF) have been performed. Using the CEF evaluation approach, effective profiles of enzymatic reactions depending on the degree of enzyme deficiency were obtained. It has been shown that these relationships can be the basis for future experimental studies. Analysis of the profiles of enzymatic reactions of metabolic networks suggests that erythrocytes are capable of metabolizing other substrates that contribute to overcoming the effects of energy stress in the case of enzymopathies. So, it is shown that erythrocytes can effectively use SAM and adenosine as alternative energy sources. It has been established that the GPI enzymopathy results in a decrease in the flow through the glycolysis and pentose phosphate pathway, resulting in a decrease in the content of such reducing agents as NADPH and GSH, ATP. The processes of the GSH synthesis from amino acids in the cell are shown to be suppressed. Decreased content of NADPH and GSH cause the premature aging of erythrocytes. The target therapeutic approaches that influence the behaviour of the metabolic network of erythrocytes are discussed.