Hypoxia-mediated impaired erythrocyte Lands' Cycle is pathogenic for sickle cell disease

Complete absence of GLUT1 does not impair human terminal erythroid differentiation

ABSTRACT

The glucose transporter 1 (GLUT1) is 1 of the most abundant proteins within the erythrocyte membrane and is required for glucose and dehydroascorbic acid (vitamin C precursor) transport. It is widely recognized as a key protein for red cell structure, function, and metabolism. Previous reports highlighted the importance of GLUT1 activity within these uniquely glycolysis-dependent cells, in particular for increasing antioxidant capacity needed to avoid irreversible damage from oxidative stress in humans. However, studies of glucose transporter roles in erythroid cells are complicated by species-specific differences between humans and mice. Here, using CRISPR-mediated gene editing of immortalized erythroblasts and adult CD34+ hematopoietic progenitor cells, we generate committed human erythroid cells completely deficient in expression of GLUT1. We show that absence of GLUT1 does not impede human erythroblast proliferation, differentiation, or enucleation. This work demonstrates, to our knowledge, for the first time, generation of enucleated human reticulocytes lacking GLUT1. The GLUT1-deficient reticulocytes possess no tangible alterations to membrane composition or deformability in reticulocytes. Metabolomic analyses of GLUT1-deficient reticulocytes reveal hallmarks of reduced glucose import, downregulated metabolic processes and upregulated AMP-activated protein kinase signaling, alongside alterations in antioxidant metabolism, resulting in increased osmotic fragility and metabolic shifts indicative of higher oxidant stress. Despite detectable metabolic changes in GLUT1-deficient reticulocytes, the absence of developmental phenotype, detectable proteomic compensation, or impaired deformability comprehensively alters our understanding of the role of GLUT1 in red blood cell structure, function, and metabolism. It also provides cell biological evidence supporting clinical consensus that reduced GLUT1 expression does not cause anemia in GLUT1-deficiency syndrome.

Proteostasis and metabolic dysfunction in a distinct subset of storage-induced senescent erythrocytes targeted for clearance

Although refrigerated storage slows the metabolism of volunteer donor RBCs, cellular aging still occurs throughout this in vitro process, which is essential in transfusion medicine. Storage-induced microerythrocytes (SMEs) are morphologically-altered senescent RBCs that accumulate during storage and which are cleared from circulation following transfusion. However, the molecular and cellular alterations that trigger clearance of this RBC subset remain to be identified. Using a staining protocol that sorts long-stored SMEs (i.e., CFSE high ) and morphologically-normal RBCs (CFSE low ), these in vitro aged cells were characterized. Metabolomics analysis identified depletion of energy, lipid-repair, and antioxidant metabolites in CFSE high RBCs. By redox proteomics, irreversible protein oxidation primarily affected CFSE high RBCs. By proteomics, 96 proteins, mostly in the proteostasis family, had relocated to CFSE high RBC membranes. CFSE high RBCs exhibited decreased proteasome activity and deformability; increased phosphatidylserine exposure, osmotic fragility, and endothelial cell adherence; and were cleared from the circulation during human spleen ex vivo perfusion. Conversely, molecular, cellular, and circulatory properties of long-stored CFSE low RBCs resembled those of short-stored RBCs. CFSE high RBCs are morphologically and metabolically altered, have irreversibly oxidized and membrane-relocated proteins, and exhibit decreased proteasome activity. In vitro aging during storage selectively alters metabolism and proteostasis in SMEs, targeting these senescent cells for clearance.

Multiomics analysis reveals the potential of LPCAT1-PC axis as a therapeutic target for human intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a highly prevalent musculoskeletal disorder that is associated with considerable morbidity. However, there is currently no drug available that has a definitive therapeutic effect on IDD. In this study, we aimed to identify the molecular features and potential therapeutic targets of IDD through a comprehensive multiomics profiling approach. By integrating transcriptomics, proteomics, and ultrastructural analyses, we discovered dysfunctions in various organelles, including mitochondria, the endoplasmic reticulum, the Golgi apparatus, and lysosomes. Metabolomics analysis revealed a reduction in total phosphatidylcholine (PC) content in IDD. Through integration of multiple omics techniques with disease phenotypes, a pivotal pathway regulated by the lysophosphatidylcholine acyltransferase 1 (LPCAT1)-PC axis was identified. LPCAT1 exhibited low expression levels and exhibited a positive correlation with PC content in IDD. Suppression of LPCAT1 resulted in inhibition of PC synthesis in nucleus pulposus cells, leading to a notable increase in nucleus pulposus cell senescence and damage to cellular organelles. Consequently, PC exhibits potential as a therapeutic agent, as it facilitates the repair of the biomembrane system and alleviates senescence in nucleus pulposus cells via reversal of downregulation of the LPCAT1-PC axis.

Functional and multi-omics signatures of mitapivat efficacy upon activation of pyruvate kinase in red blood cells from patients with sickle cell disease

Mitapivat, a pyruvate kinase activator, shows great potential as a sickle cell disease (SCD)-modifying therapy. The safety and efficacy of mitapivat as a long-term maintenance therapy are currently being evaluated in two open-label studies. Here we applied a comprehensive multi-omics approach to investigate the impact of activating pyruvate kinase on red blood cells (RBC) from 15 SCD patients. HbSS patients were enrolled in one of the open-label, extended studies (NCT04610866). Leukodepleted RBC obtained from fresh whole blood at baseline, prior to drug initiation, and at longitudinal timepoints over the course of the study were processed for multi-omics through a stepwise extraction of metabolites, lipids and proteins. Mitapivat therapy had significant effects on the metabolome, lipidome and proteome of SCD RBC. Mitapivat decreased 2,3-diphosphoglycerate levels, increased adenosine triphosphate levels, and improved hematologic and sickling parameters in patients with SCD. Agreement between omics measurements and clinical measurements confirmed the specificity of mitapivat on targeting late glycolysis, with glycolytic metabolites ranking as the top correlates to parameters of hemoglobin S oxygen affinity (p50) and sickling kinetics (t50) during treatment. Mitapivat markedly reduced levels of proteins of mitochondrial origin within 2 weeks of initiation of treatment, with minimal changes in reticulocyte counts. In the first 6 months of treatment there were also transient elevations of lysophosphatidylcholines and oxylipins with depletion of free fatty acids, suggestive of an effect on membrane lipid remodeling. Multi-omics analysis of RBC identified benefits for glycolysis, as well as activation of the Lands cycle.

Genetic regulation of carnitine metabolism controls lipid damage repair and aging RBC hemolysis in vivo and in vitro

ABSTRACT

Recent large-scale multiomics studies suggest that genetic factors influence the chemical individuality of donated blood. To examine this concept, we performed metabolomics analyses of 643 blood units from volunteers who donated units of packed red blood cells (RBCs) on 2 separate occasions. These analyses identified carnitine metabolism as the most reproducible pathway across multiple donations from the same donor. We also measured l-carnitine and acyl-carnitines in 13 091 packed RBC units from donors in the Recipient Epidemiology and Donor Evaluation study. Genome-wide association studies against 879 000 polymorphisms identified critical genetic factors contributing to interdonor heterogeneity in end-of-storage carnitine levels, including common nonsynonymous polymorphisms in genes encoding carnitine transporters (SLC22A16, SLC22A5, and SLC16A9); carnitine synthesis (FLVCR1 and MTDH) and metabolism (CPT1A, CPT2, CRAT, and ACSS2), and carnitine-dependent repair of lipids oxidized by ALOX5. Significant associations between genetic polymorphisms on SLC22 transporters and carnitine pools in stored RBCs were validated in 525 Diversity Outbred mice. Donors carrying 2 alleles of the rs12210538 SLC22A16 single-nucleotide polymorphism exhibited the lowest l-carnitine levels, significant elevations of in vitro hemolysis, and the highest degree of vesiculation, accompanied by increases in lipid peroxidation markers. Separation of RBCs by age, via in vivo biotinylation in mice, and Percoll density gradients of human RBCs, showed age-dependent depletions of l-carnitine and acyl-carnitine pools, accompanied by progressive failure of the reacylation process after chemically induced membrane lipid damage. Supplementation of stored murine RBCs with l-carnitine boosted posttransfusion recovery, suggesting this could represent a viable strategy to improve RBC storage quality.

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.

Sickle cell disease iPSC-derived sensory neurons exhibit increased excitability and sensitization to patient plasma

ABSTRACT

Individuals living with sickle cell disease (SCD) experience severe recurrent acute and chronic pain. Challenges to gaining mechanistic insight into pathogenic SCD pain processes include differential gene expression and function of sensory neurons between humans and mice with SCD, and extremely limited availability of neuronal tissues from patients with SCD. Here, we used induced pluripotent stem cells (iPSCs), derived from patients with SCD, differentiated into sensory neurons (SCD iSNs) to begin to overcome these challenges. We characterize key gene expression and function of SCD iSNs to establish a model to investigate intrinsic and extrinsic factors that may contribute to SCD pain. Despite similarities in receptor gene expression, SCD iSNs show pronounced excitability using patch clamp electrophysiology. Furthermore, we find that plasma taken from patients with SCD during acute pain associated with a vaso-occlusive event increases the calcium responses to the nociceptive stimulus capsaicin in SCD iSNs compared with those treated with paired plasma from patients with SCD at steady state baseline or healthy control plasma samples. We identified high levels of the polyamine spermine in baseline and acute pain states of plasma from patients with SCD, which sensitizes SCD iSNs to subthreshold concentrations of capsaicin. Together, these data identify potential intrinsic mechanisms within SCD iSNs that may extend beyond a blood-based pathology.

Simvastatin-Mediated Nrf2 Activation Induces Fetal Hemoglobin and Antioxidant Enzyme Expression to Ameliorate the Phenotype of Sickle Cell Disease

Sickle cell disease (SCD) is a pathophysiological condition of chronic hemolysis, oxidative stress, and elevated inflammation. The transcription factor Nrf2 is a master regulator of oxidative stress. Here, we report that the FDA-approved oral agent simvastatin, an inhibitor of hydroxymethyl-glutaryl coenzyme A reductase, significantly activates the expression of Nrf2 and antioxidant enzymes. Simvastatin also induces fetal hemoglobin expression in SCD patient primary erythroid progenitors and a transgenic mouse model. Simvastatin alleviates SCD symptoms by decreasing hemoglobin S sickling, oxidative stress, and inflammatory stress in erythroblasts. Particularly, simvastatin increases cellular levels of cystine, the precursor for the biosynthesis of the antioxidant reduced glutathione, and decreases the iron content in SCD mouse spleen and liver tissues. Mechanistic studies suggest that simvastatin suppresses the expression of the critical histone methyltransferase enhancer of zeste homolog 2 to reduce both global and gene-specific histone H3 lysine 27 trimethylation. These chromatin structural changes promote the assembly of transcription complexes to fetal γ-globin and antioxidant gene regulatory regions in an antioxidant response element-dependent manner. In summary, our findings suggest that simvastatin activates fetal hemoglobin and antioxidant protein expression, modulates iron and cystine/reduced glutathione levels to improve the phenotype of SCD, and represents a therapeutic strategy for further development.

Effect of leukoreduction on the metabolism of equine packed red blood cells during refrigerated storage

BACKGROUND

Understanding of the biochemical and morphological lesions associated with storage of equine blood is limited.

OBJECTIVE

To demonstrate the temporal sequences of lipid and metabolic profiles of equine fresh and stored (up to 42 days) and leukoreduced packed red blood cells (LR-pRBC) and non-leukoreduced packed RBC (nLR-pRBC).

ANIMALS

Packed RBC units were obtained from 6 healthy blood donor horses enrolled in 2 blood banks.

METHODS

Observational study. Whole blood was collected from each donor using transfusion bags with a LR filter. Leukoreduction pRBC and nLR-pRBC units were obtained and stored at 4°C for up 42 days. Sterile weekly sampling was performed from each unit for analyses.

RESULTS

Red blood cells and supernatants progressively accumulated lactate products while high-energy phosphate compounds (adenosine triphosphate and 2,3-Diphosphoglycerate) declined. Hypoxanthine, xanthine, and free fatty acids accumulated in stored RBC and supernatants. These lesions were exacerbated in non-LR-pRBC.

CONCLUSION AND CLINICAL IMPORTANCE

Leukoreduction has a beneficial effect on RBC energy and redox metabolism of equine pRBC and the onset and severity of the metabolic storage lesions RBC.

Erythrocyte metabolism

Our aim is to present an updated overview of the erythrocyte metabolism highlighting its richness and complexity. We have manually collected and connected the available biochemical pathways and integrated them into a functional metabolic map. The focus of this map is on the main biochemical pathways consisting of glycolysis, the pentose phosphate pathway, redox metabolism, oxygen metabolism, purine/nucleoside metabolism, and membrane transport. Other recently emerging pathways are also curated, like the methionine salvage pathway, the glyoxalase system, carnitine metabolism, and the lands cycle, as well as remnants of the carboxylic acid metabolism. An additional goal of this review is to present the dynamics of erythrocyte metabolism, providing key numbers used to perform basic quantitative analyses. By synthesizing experimental and computational data, we conclude that glycolysis, pentose phosphate pathway, and redox metabolism are the foundations of erythrocyte metabolism. Additionally, the erythrocyte can sense oxygen levels and oxidative stress adjusting its mechanics, metabolism, and function. In conclusion, fine-tuning of erythrocyte metabolism controls one of the most important biological processes, that is, oxygen loading, transport, and delivery.

Maternal nanoplastic ingestion induces an increase in offspring body weight through altered lipid species and microbiota

The rapidly increasing prevalence of obesity and overweight, especially in children and adolescents, has become a serious societal issue. Although various genetic and environmental risk factors for pediatric obesity and overweight have been identified, the problem has not been solved. In this study, we examined whether environmental nanoplastic (NP) pollutants can act as environmental obesogens using mouse models exposed to NPs derived from polystyrene and polypropylene, which are abundant in the environment. We found abnormal weight gain in the progeny until 6 weeks of age following the oral administration of NPs to the mother during gestation and lactation. Through a series of experiments involving multi-omic analyses, we have demonstrated that NP-induced weight gain is caused by alterations in the lipid composition (lysophosphatidylcholine/phosphatidylcholine ratio) of maternal breast milk and he gut microbiota distribution of the progeny. These data indicate that environmental NPs can act as obesogens in childhood.

Regulation of kynurenine metabolism by blood donor genetics and biology impacts red cell hemolysis in vitro and in vivo

ABSTRACT

In the field of transfusion medicine, the clinical relevance of the metabolic markers of the red blood cell (RBC) storage lesion is incompletely understood. Here, we performed metabolomics of RBC units from 643 donors enrolled in the Recipient Epidemiology and Donor Evaluation Study, REDS RBC Omics. These units were tested on storage days 10, 23, and 42 for a total of 1929 samples and also characterized for end-of-storage hemolytic propensity after oxidative and osmotic insults. Our results indicate that the metabolic markers of the storage lesion poorly correlated with hemolytic propensity. In contrast, kynurenine was not affected by storage duration and was identified as the top predictor of osmotic fragility. RBC kynurenine levels were affected by donor age and body mass index and were reproducible within the same donor across multiple donations from 2 to 12 months apart. To delve into the genetic underpinnings of kynurenine levels in stored RBCs, we thus tested kynurenine levels in stored RBCs on day 42 from 13 091 donors from the REDS RBC Omics study, a population that was also genotyped for 879 000 single nucleotide polymorphisms. Through a metabolite quantitative trait loci analysis, we identified polymorphisms in SLC7A5, ATXN2, and a series of rate-limiting enzymes (eg, kynurenine monooxygenase, indoleamine 2,3-dioxygenase, and tryptophan dioxygenase) in the kynurenine pathway as critical factors affecting RBC kynurenine levels. By interrogating a donor-recipient linkage vein-to-vein database, we then report that SLC7A5 polymorphisms are also associated with changes in hemoglobin and bilirubin levels, suggestive of in vivo hemolysis in 4470 individuals who were critically ill and receiving single-unit transfusions.

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.

Red Blood Cells from Individuals with Lesch-Nyhan Syndrome: Multi-Omics Insights into a Novel S162N Mutation Causing Hypoxanthine-Guanine Phosphoribosyltransferase Deficiency

Lesch-Nyhan syndrome (LN) is an is an X-linked recessive inborn error of metabolism that arises from a deficiency of purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). The disease manifests severely, causing intellectual deficits and other neural abnormalities, hypercoagulability, uncontrolled self-injury, and gout. While allopurinol is used to alleviate gout, other symptoms are less understood, impeding treatment. Herein, we present a high-throughput multi-omics analysis of red blood cells (RBCs) from three pediatric siblings carrying a novel S162N HPRT1 mutation. RBCs from both parents-the mother, a heterozygous carrier, and the father, a clinically healthy control-were also analyzed. Global metabolite analysis of LN RBCs shows accumulation of glycolytic intermediates upstream of pyruvate kinase, unsaturated fatty acids, and long chain acylcarnitines. Similarly, highly unsaturated phosphatidylcholines are also elevated in LN RBCs, while free choline is decreased. Intracellular iron, zinc, selenium, and potassium are also decreased in LN RBCs. Global proteomics documented changes in RBC membrane proteins, hemoglobin, redox homeostasis proteins, and the enrichment of coagulation proteins. These changes were accompanied by elevation in protein glutamine deamidation and methylation in the LN children and carrier mother. Treatment with allopurinol incompletely reversed the observed phenotypes in the two older siblings currently on this treatment. This unique data set provides novel opportunities for investigations aimed at potential therapies for LN-associated sequelae.

Peripheral transient receptor potential vanilloid type 4 hypersensitivity contributes to chronic sickle cell disease pain

ABSTRACT

Debilitating pain affects the lives of patients with sickle cell disease (SCD). Current pain treatment for patients with SCD fail to completely resolve acute or chronic SCD pain. Previous research indicates that the cation channel transient receptor potential vanilloid type 4 (TRPV4) mediates peripheral hypersensitivity in various inflammatory and neuropathic pain conditions that may share similar pathophysiology with SCD, but this channel's role in chronic SCD pain remains unknown. Thus, the current experiments examined whether TRPV4 regulates hyperalgesia in transgenic mouse models of SCD. Acute blockade of TRPV4 alleviated evoked behavioral hypersensitivity to punctate, but not dynamic, mechanical stimuli in mice with SCD. TRPV4 blockade also reduced the mechanical sensitivity of small, but not large, dorsal root ganglia neurons from mice with SCD. Furthermore, keratinocytes from mice with SCD showed sensitized TRPV4-dependent calcium responses. These results shed new light on the role of TRPV4 in SCD chronic pain and are the first to suggest a role for epidermal keratinocytes in the heightened sensitivity observed in SCD.

In vivo evaluation of the effect of sickle cell hemoglobin S, C and therapeutic transfusion on erythrocyte metabolism and cardiorenal dysfunction

Despite a wealth of exploratory plasma metabolomics studies in sickle cell disease (SCD), no study to date has evaluate a large and well phenotyped cohort to compare the primary erythrocyte metabolome of hemoglobin SS, SC and transfused AA red blood cells (RBCs) in vivo. The current study evaluates the RBC metabolome of 587 subjects with sickle cell sickle cell disease (SCD) from the WALK-PHaSST clinical cohort. The set includes hemoglobin SS, hemoglobin SC SCD patients, with variable levels of HbA related to RBC transfusion events. Here we explore the modulating effects of genotype, age, sex, severity of hemolysis, and transfusion therapy on sickle RBC metabolism. Results show that RBCs from patients with Hb SS genotypes-compared to AA RBCs from recent transfusion events or SC RBCs-are characterized by significant alterations of RBC acylcarnitines, pyruvate, sphingosine 1-phosphate, creatinine, kynurenine and urate metabolism. Surprisingly, the RBC metabolism of SC RBCs is dramatically different from SS, with all glycolytic intermediates significantly elevated in SS RBCs, with the exception of pyruvate. This result suggests a metabolic blockade at the ATP-generating phosphoenolpyruvate to pyruvate step of glycolysis, which is catalyzed by redox-sensitive pyruvate kinase. Metabolomics, clinical and hematological data were collated in a novel online portal. In conclusion, we identified metabolic signatures of HbS RBCs that correlate with the degree of steady state hemolytic anemia, cardiovascular and renal dysfunction and mortality.

Red Blood Cell Metabolism In Vivo and In Vitro

Red blood cells (RBC) are the most abundant cell in the human body, with a central role in oxygen transport and its delivery to tissues. However, omics technologies recently revealed the unanticipated complexity of the RBC proteome and metabolome, paving the way for a reinterpretation of the mechanisms by which RBC metabolism regulates systems biology beyond oxygen transport. The new data and analytical tools also informed the dissection of the changes that RBCs undergo during refrigerated storage under blood bank conditions, a logistic necessity that makes >100 million units available for life-saving transfusions every year worldwide. In this narrative review, we summarize the last decade of advances in the field of RBC metabolism in vivo and in the blood bank in vitro, a narrative largely influenced by the authors' own journeys in this field. We hope that this review will stimulate further research in this interesting and medically important area or, at least, serve as a testament to our fascination with this simple, yet complex, cell.

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.

In vivo evaluation of the effect of sickle cell hemoglobin S, C and therapeutic transfusion on erythrocyte metabolism and cardiorenal dysfunction

Despite a wealth of exploratory plasma metabolomics studies in sickle cell disease (SCD), no study to date has evaluate a large and well phenotyped cohort to compare the primary erythrocyte metabolome of hemoglobin SS, SC and transfused AA red blood cells (RBCs) in vivo . The current study evaluates the RBC metabolome of 587 subjects with sickle cell sickle cell disease (SCD) from the WALK-PHaSST clinical cohort. The set includes hemoglobin SS, hemoglobin SC SCD patients, with variable levels of HbA related to RBC transfusion events, and HbF related to hydroxyurea therapy. Here we explore the modulating effects of genotype, age, sex, severity of hemolysis, and hydroxyurea and transfusion therapy on sickle RBC metabolism. Data - collated in an online portal - show that the Hb SS genotype is associated with significant alterations of RBC acylcarnitines, pyruvate, sphingosine 1-phosphate, creatinine, kynurenine and urate metabolism. Surprisingly, the RBC metabolism of SC RBCs is dramatically different from SS, with all glycolytic intermediates significantly elevated in SS RBCs, with the exception of pyruvate. This result suggests a metabolic blockade at the ATP-generating phosphoenolpyruvate to pyruvate step of glycolysis, which is catalyzed by redox-sensitive pyruvate kinase. Increasing in vivo concentrations of HbA improved glycolytic flux and normalized the HbS erythrocyte metabolome. An unexpectedly limited metabolic effect of hydroxyurea and HbF was observed, possibly related to the modest induction of HbF in this cohort. The metabolic signature of HbS RBCs correlated with the degree of steady state hemolytic anemia, cardiovascular and renal dysfunction and mortality.

Key points

In vivo dysregulation of RBC metabolism by HbS is evaluated by metabolic profiling of 587 patients with variable HbA, HbC and HbF levels;RBC acyl-carnitines, urate, pyruvate metabolism, S1P, kynurenine relate to hemolysis and cardiorenal dysfunction, respond to transfusion.

Increased Susceptibility for Adverse Reactions to Ultrasound Enhancing Agents in Sickle Cell Disease

BACKGROUND

Pain-related adverse events (AEs) to ultrasound enhancing agents (UEAs) have been reported in patients with sickle cell disease (SCD). The aims of this study were to characterize the scope of these AEs in the SCD population and to investigate potential mechanisms on the basis of pathways involved in SCD vaso-occlusive crisis (VOC) and pain.

METHODS

The prevalence and classification of AEs were analyzed from two clinical trials in which high-dose Definity infusions were used in patients with SCD (n = 55) or matched control subjects (n = 43) to study muscle or myocardial microvascular perfusion. Because complement (C') activation can trigger VOC in SCD, C' activation and surface adhesion of C' proteins on lipid UEAs were studied in vitro. C'-mediated UEA attachment to bone marrow immune cells was assessed using flow cytometry in a murine SCD model (Townes mice). Blood from patients receiving Definity was obtained to measure specific lysophospholipid metabolites of lipids in Definity thought to mediate SCD pain.

RESULTS

Moderate or greater AEs, all of which were nociceptive (back or bone pain), occurred in one control subject and nine SCD subjects (2% vs 16%, P = .02). Patients with SCD who had AEs tended to have more severe manifestations of SCD. Three of the subjects with SCD had previously received Definity without complications. In patients with SCD, four AEs were classified as severe in intensity and as serious AEs on the basis of need for medical intervention. AEs were described to be similar to SCD-related pain, but there was no evidence for VOC, hemolysis, hypotension, or hypoxemia. At baseline, markers of C' activation were greater in patients with SCD than control subjects. However, after administration of lipid UEAs, SCD and control subjects were similar with regard to C' activation response, anaphylatoxin production, bone marrow microbubble retention, and production of lysophospholipids. There was a trend toward increased deposition of C3b and C3bi on lipid UEAs exposed to serum from patients with SCD.

CONCLUSIONS

Patients with SCD are particularly susceptible to nociceptive AEs when given Definity at high doses. The mechanism for these AEs remains unclear but most are not related to the triggering of classic VOC.

Sickle cell disease patient plasma sensitizes iPSC-derived sensory neurons from sickle cell disease patients

Individuals living with sickle cell disease (SCD) experience severe recurrent acute and chronic pain. In order to develop novel therapies, it is necessary to better understand the neurobiological mechanisms underlying SCD pain. There are many barriers to gaining mechanistic insight into pathogenic SCD pain processes, such as differential gene expression and function of sensory neurons between humans and mice with SCD, as well as the limited availability of patient samples. These can be overcome by utilizing SCD patient-derived induced pluripotent stem cells (iPSCs) differentiated into sensory neurons (SCD iSNs). Here, we characterize the key gene expression and function of SCD iSNs to establish a model for higher-throughput investigation of intrinsic and extrinsic factors that may contribute to increased SCD patient pain. Importantly, identified roles for C-C Motif Chemokine Ligand 2 (CCL2) and endothelin 1 (ET1) in SCD pain can be recapitulated in SCD iSNs. Further, we find that plasma taken from SCD patients during acute pain increases SCD iSN calcium response to the nociceptive stimulus capsaicin compared to those treated with paired SCD patient plasma at baseline or healthy control plasma samples. Together, these data provide the framework necessary to utilize iSNs as a powerful tool to investigate the neurobiology of SCD and identify potential intrinsic mechanisms of SCD pain which may extend beyond a blood-based pathology.

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).

Lipidomics Analysis Reveals a Protective Effect of Myriocin on Cerebral Ischemia/Reperfusion Model Rats

Ceramide accumulation has been associated with ischemic stroke. Myriocin is an effective serine palmitoyltransferase (SPT) inhibitor that reduces ceramide levels by inhibiting the de novo synthesis pathway. However, the role of myriocin in cerebral ischemia/reperfusion (I/R) injury and its underlying mechanism remain unknown. The present study established an experimental rat model of middle cerebral artery occlusion (MCAO). We employed ultra-performance liquid chromatograph quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS)-based lipidomic analysis to identify the disordered lipid metabolites and the effects of myriocin in cerebral cortical tissues of rats. In this study, we found 15 characterized lipid metabolites involved in sphingolipid and glycerophospholipid metabolism in cerebral I/R-injured rats, and these alterations were significantly alleviated by myriocin. Specifically, the mRNA expression of metabolism-related enzyme genes was detected by real-time quantitative polymerase chain reaction (RT-qPCR). We demonstrated that myriocin could regulate the mRNA expression of ASMase, NSMase, SGMS1, SGMS2, ASAH1, ACER2, and ACER3, which are involved in sphingolipid metabolism and PLA2, which is involved in glycerophospholipid metabolism. Moreover, TUNEL and Western blot assays showed that myriocin plays a key role in regulating neuronal cell apoptosis. In summary, the present work provides a new perspective for the systematic study of metabolic changes in ischemic stroke and the therapeutic applications of myriocin.

Reprogramming of red blood cell metabolism in Zika virus-infected donors

BACKGROUND

Diseases caused by arthropod-borne viruses remain a burden to global health; in particular, Zika virus (ZIKV) has been reported in 87 countries and territories. In healthy blood donors, ZIKV RNA can be detected in red blood cells (RBCs) months after infection, clearance of detectable nucleic acid in plasma, and seroconversion. However, little information is available on the impact of ZIKV infection to metabolism.

STUDY DESIGN AND METHODS

We applied mass spectrometry-based metabolomics and lipidomics approaches to investigate the impact of ZIKV infection on RBCs over the course of infection. ZIKV-infected blood donors (n = 25) were identified through molecular and serologic methods, which included nucleic acid amplification testing and real-time polymerase chain reaction (PCR) for detection of ZIKV RNA and enzyme-linked immunosorbent assay (ELISA) for detection of flavivirus-specific IgM and IgG.

RESULTS

In ZIKV RNA-positive donors, we observed lower glucose and lactate levels, and higher levels of ribose phosphate, suggestive of the activation of the pentose phosphate pathway. The top pathways altered in RBCs from ZIKV-IgM-positive donors include amino acid metabolism and biosynthesis, fatty acid metabolism and biosynthesis, linoleic acid and arachidonate metabolism and glutathione metabolism. RBCs from ZIKV-infected donors had increased levels of early glycolytic metabolites, and higher levels of metabolites of the pentose phosphate pathway. Alterations in acyl-carnitine and fatty acid metabolism are consistent with impaired membrane lipid homeostasis in RBCs from ZIKV IgM positive donors.

CONCLUSION

RBC from healthy blood donors who had been infected by ZIKV are characterized by long-lasting metabolic alterations even months after infection has resolved.

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.

p53-driven lipidome influences non-cell-autonomous lysophospholipids in pancreatic cancer

Adaptation of the lipid metabolism participates  in cancer pathogenesis, facilitating energy storage and influencing cell fate and control of molecular signalling. The tumour suppressor protein p53 is a molecular hub of cell metabolism, supporting antioxidant capabilities and counteracting oncogene-induced metabolic switch. Despite extensive work has described the p53-dependent metabolic pathways, a global profiling of p53 lipidome is still missing. By high-throughput untargeted lipidomic analysis of pancreatic ductal adenocarcinoma (PDAC) cells, we profile the p53-dependent lipidome, revealing intracellular and secreted lysophospholipids as one of the most affected class. Lysophospholipids are hydrolysed forms of phospholipids that results from phospholipase activity, which can function as signalling molecules, exerting non-cell-autonomous effects and instructing cancer microenvironment and immunity. Here, we reveal that p53 depletion reduces abundance of intracellular lysophosphatidyl-choline, -ethanolamine and -serine and their secretion in the extracellular environment. By integrating this with genomic and transcriptomic studies from in vitro models and human PDAC patients, we identified potential clinically relevant candidate p53-dependent phospholipases. In particular PLD3, PLCB4 and PLCD4 expression is regulated by p53 and chromatin immunoprecipitation followed by deep sequencing (ChIP-seq) indicates a direct transcriptional control on their chromatin accessible genomic loci. Consistently, PLD3, PLCB4 and PLCD4 expression correlates with p53 mutational status in PDAC patients, and these genes display prognostic significance. Overall, our data provide insights into lipidome rewiring driven by p53 loss and identify alterations of lysophospholipids as a potential molecular mechanism for p53-mediated non-cell-autonomous molecular signalling that instructs cancer microenvironment and immunity during PDAC pathogenesis.

Circulating primitive murine erythroblasts undergo complex proteomic and metabolomic changes during terminal maturation

Terminal maturation of primary murine primitive erythroid precursors is characterized by loss of organelles and anabolic components.

Metabolic reprogramming includes depression of mitochondrial metabolism and upregulation of the pentose phosphate pathway and redox metabolism.

Primitive erythropoiesis is a critical component of the fetal cardiovascular network and is essential for the growth and survival of the mammalian embryo. The need to rapidly establish a functional cardiovascular system is met, in part, by the intravascular circulation of primitive erythroid precursors that mature as a single semisynchronous cohort. To better understand the processes that regulate erythroid precursor maturation, we analyzed the proteome, metabolome, and lipidome of primitive erythroblasts isolated from embryonic day (E) 10.5 and E12.5 of mouse gestation, representing their transition from basophilic erythroblast to orthochromatic erythroblast (OrthoE) stages of maturation. Previous transcriptional and biomechanical characterizations of these precursors have highlighted a transition toward the expression of protein elements characteristic of mature red blood cell structure and function. Our analysis confirmed a loss of organelle-specific protein components involved in messenger RNA processing, proteostasis, and metabolism. In parallel, we observed metabolic rewiring toward the pentose phosphate pathway, glycolysis, and the Rapoport-Luebering shunt. Activation of the pentose phosphate pathway in particular may have stemmed from increased expression of hemoglobin chains and band 3, which together control oxygen-dependent metabolic modulation. Increased expression of several antioxidant enzymes also indicated modification to redox homeostasis. In addition, accumulation of oxylipins and cholesteryl esters in primitive OrthoE cells was paralleled by increased transcript levels of the p53-regulated cholesterol transporter (ABCA1) and decreased transcript levels of cholesterol synthetic enzymes. The present study characterizes the extensive metabolic rewiring that occurs in primary embryonic erythroid precursors as they prepare to enucleate and continue circulating without internal organelles.

Inductively-Coupled Plasma Mass Spectrometry-Novel Insights From an Old Technology Into Stressed Red Blood Cell Physiology

BACKGROUND

Ion and metal homeostasis are critical to red blood cell physiology and Inductively Coupled Plasma (ICP) is a decades old approach to pursue elemental analysis. Recent evolution of ICP has resulted in its coupling to mass spectrometry (MS) instead of atomic absorption/emission.

METHODS

Here we performed Inductively-coupled plasma mass spectrometry (ICP-MS) measurements of intra- and extra-cellular Na, K, Ca, Mg, Fe, and Cu in red blood cells undergoing ionic, heat, or starvation stress. Results were correlated with Ca measurements from other common platforms (e.g., fluorescence-based approaches) and extensive measurements of red blood cell metabolism.

RESULTS

All stresses induced significant intra- and extracellular alterations of all measured elements. In particular, ionomycin treatment or hypertonic stress significantly impacted intracellular sodium and extracellular potassium and magnesium levels. Iron efflux was observed as a function of temperatures, with ionic and heat stress at 40°C causing the maximum decrease in intracellular iron pools and increases in the supernatants. Strong positive correlation was observed between calcium measurements via ICP-MS and fluorescence-based approaches. Correlation analyses with metabolomics data showed a strong positive association between extracellular calcium and intracellular sodium or magnesium levels and intracellular glycolysis. Extracellular potassium or iron were positively correlated with free fatty acids (especially mono-, poly-, and highly-unsaturated or odd-chain fatty acid products of lipid peroxidation). Intracellular iron was instead positively correlated with saturated fatty acids (palmitate, stearate) and negatively with methionine metabolism (methionine, S-adenosylmethionine), phosphatidylserine exposure and glycolysis.

CONCLUSION

In the era of omics approaches, ICP-MS affords a comprehensive characterization of intracellular elements that provide direct insights on red blood cell physiology and represent meaningful covariates for data generated via other omics platforms such as metabolomics.

Irradiation Causes Alterations of Polyamine, Purine, and Sulfur Metabolism in Red Blood Cells and Multiple Organs

Investigating the metabolic effects of radiation is critical to understand the impact of radiotherapy, space travel, and exposure to environmental radiation. In patients undergoing hemopoietic stem cell transplantation, iron overload is a common risk factor for poor outcomes. However, no studies have interrogated the multiorgan effects of these treatments concurrently. Herein, we use a model that recapitulates transfusional iron overload, a condition often observed in chronically transfused patients. We applied an omics approach to investigate the impact of both the iron load and irradiation on the host metabolome. The results revealed dose-dependent effects of irradiation in the red blood cells, plasma, spleen, and liver energy and redox metabolism. Increases in polyamines and purine salvage metabolites were observed in organs with high oxygen consumption including the heart, kidneys, and brain. Irradiation also impacted the metabolism of the duodenum, colon, and stool, suggesting a potential effect on the microbiome. Iron infusion affected the response to radiation in the organs and blood, especially in erythrocyte polyamines and spleen antioxidant metabolism, and affected glucose, methionine, and glutathione systems and tryptophan metabolism in the liver, stool, and the brain. Together, the results suggest that radiation impacts metabolism on a multiorgan level with a significant interaction of the host iron status.

Erythrocyte transglutaminase-2 combats hypoxia and chronic kidney disease by promoting oxygen delivery and carnitine homeostasis

Due to lack of nuclei and de novo protein synthesis, post-translational modification (PTM) is imperative for erythrocytes to regulate oxygen (O₂) delivery and combat tissue hypoxia. Here, we report that erythrocyte transglutminase-2 (eTG2)-mediated PTM is essential to trigger O₂ delivery by promoting bisphosphoglycerate mutase proteostasis and the Rapoport-Luebering glycolytic shunt for adaptation to hypoxia, in healthy humans ascending to high altitude and in two distinct murine models of hypoxia. In a pathological hypoxia model with chronic kidney disease (CKD), eTG2 is critical to combat renal hypoxia-induced reduction of Slc22a5 transcription and OCNT2 protein levels via HIF-1α-PPARα signaling to maintain carnitine homeostasis. Carnitine supplementation is an effective and safe therapeutic approach to counteract hypertension and progression of CKD by enhancing erythrocyte O₂ delivery. Altogether, we reveal eTG2 as an erythrocyte protein stabilizer orchestrating O₂ delivery and tissue adaptive metabolic reprogramming and identify carnitine-based therapy to mitigate hypoxia and CKD progression.

Deuterated Linoleic Acid Attenuates the RBC Storage Lesion in a Mouse Model of Poor RBC Storage

Background: Long-chain polyunsaturated fatty acids (PUFAs) are important modulators of red blood cell (RBC) rheology. Dietary PUFAs are readily incorporated into the RBC membrane, improving RBC deformability, fluidity, and hydration. However, enriching the lipid membrane with PUFAs increases the potential for peroxidation in oxidative environments (e.g., refrigerated storage), resulting in membrane damage. Substitution of bis-allylic hydrogens with deuterium ions in PUFAs decreases hydrogen abstraction, thereby inhibiting peroxidation. If lipid peroxidation is a causal factor in the RBC storage lesion, incorporation of deuterated linoleic acid (DLA) into the RBC membrane should decrease lipid peroxidation, thereby improving RBC lifespan, deformability, filterability, and post-transfusion recovery (PTR) after cold storage. Study Design and Methods: Mice associated with good (C57BL/6J) and poor (FVB) RBC storage quality received diets containing 11,11-D2-LA Ethyl Ester (1.0 g/100 g diet; deuterated linoleic acid) or non-deuterated LA Ethyl Ester (control) for 8 weeks. Deformability, filterability, lipidomics, and lipid peroxidation markers were evaluated in fresh and stored RBCs. Results: DLA was incorporated into RBC membranes in both mouse strains. DLA diet decreased lipid peroxidation (malondialdehyde) by 25.4 and 31% percent in C57 mice and 12.9 and 79.9% in FVB mice before and after cold storage, respectively. In FVB, but not C57 mice, deformability filterability, and post-transfusion recovery were significantly improved. Discussion: In a mouse model of poor RBC storage, with elevated reactive oxygen species production, DLA attenuated lipid peroxidation and significantly improved RBC storage quality.

Red Blood Cell Metabolism in Pyruvate Kinase Deficient Patients

Background: Pyruvate kinase deficiency (PKD) is the most frequent congenital enzymatic defect of glycolysis, and one of the most common causes of hereditary non spherocytic hemolytic anemia. Therapeutic interventions are limited, in part because of the incomplete understanding of the molecular mechanisms that compensate for the metabolic defect.

Methods: Mass spectrometry-based metabolomics analyses were performed on red blood cells (RBCs) from healthy controls (n=10) and PKD patients (n=5).

Results: In PKD patients, decreases in late glycolysis were accompanied by accumulation of pentose phosphate pathway (PPP) metabolites, as a function of oxidant stress to purines (increased breakdown and deamination). Markers of oxidant stress included increased levels of sulfur-containing compounds (methionine and taurine), polyamines (spermidine and spermine). Markers of hypoxia such as succinate, sphingosine 1-phosphate (S1P), and hypoxanthine were all elevated in PKD subjects. Membrane lipid oxidation and remodeling was observed in RBCs from PKD patients, as determined by increases in the levels of free (poly-/highly-unsaturated) fatty acids and acyl-carnitines.

Conclusion: In conclusion, in the present study, we provide the first overview of RBC metabolism in patients with PKD. Though limited in scope, the study addresses the need for basic science to investigate pathologies targeting underrepresented minorities (Amish population in this study), with the ultimate goal to target treatments to health disparities.

Transient receptor potential canonical 5 mediates inflammatory mechanical and spontaneous pain in mice

Tactile and spontaneous pains are poorly managed symptoms of inflammatory and neuropathic injury. Here, we found that transient receptor potential canonical 5 (TRPC5) is a chief contributor to both of these sensations in multiple rodent pain models. Use of TRPC5 knockout mice and inhibitors revealed that TRPC5 selectively contributes to the mechanical hypersensitivity associated with CFA injection, skin incision, chemotherapy induced peripheral neuropathy, sickle cell disease, and migraine, all of which were characterized by elevated concentrations of lysophosphatidylcholine (LPC). Accordingly, exogenous application of LPC induced TRPC5-dependent behavioral mechanical allodynia, neuronal mechanical hypersensitivity, and spontaneous pain in naïve mice. Lastly, we found that 75% of human sensory neurons express TRPC5, the activity of which is directly modulated by LPC. On the basis of these results, TRPC5 inhibitors might effectively treat spontaneous and tactile pain in conditions characterized by elevated LPC.

Fatty acid desaturase activity in mature red blood cells and implications for blood storage quality

BACKGROUND

Increases in the red blood cell (RBC) degree of fatty acid desaturation are reported in response to exercise, aging, or diseases associated with systemic oxidant stress. However, no studies have focused on the presence and activity of fatty acid desaturases (FADS) in the mature RBC.

STUDY DESIGN AND METHODS

Steady state metabolomics and isotope-labeled tracing experiments, immunofluorescence approaches, and pharmacological interventions were used to determine the degree of fatty acid unsaturation, FADS activity as a function of storage, oxidant stress, and G6PD deficiency in human and mouse RBCs.

RESULTS

In 250 blood units from the REDS III RBC Omics recalled donor population, we report a storage-dependent accumulation of free mono-, poly-(PUFAs), and highly unsaturated fatty acids (HUFAs), which occur at a faster rate than saturated fatty acid accumulation. Through a combination of immunofluorescence, pharmacological inhibition, tracing experiments with stable isotope-labeled fatty acids, and oxidant challenge with hydrogen peroxide, we demonstrate the presence and redox-sensitive activity of FADS2, FADS1, and FADS5 in the mature RBC. Increases in PUFAs and HUFAs in human and mouse RBCs correlate negatively with storage hemolysis and positively with posttransfusion recovery. Inhibition of these enzymes decreases accumulation of free PUFAs and HUFAs in stored RBCs, concomitant to increases in pyruvate/lactate ratios. Alterations of this ratio in G6PD deficient patients or units supplemented with pyruvate-rich rejuvenation solutions corresponded to decreased PUFA and HUFA accumulation.

CONCLUSION

Fatty acid desaturases are present and active in mature RBCs. Their activity is sensitive to oxidant stress, storage duration, and alterations of the pyruvate/lactate ratio.

Blood donor obesity is associated with changes in red blood cell metabolism and susceptibility to hemolysis in cold storage and in response to osmotic and oxidative stress

BACKGROUND

Obesity is a global pandemic characterized by multiple comorbidities, including cardiovascular and metabolic diseases. The aim of this study was to define the associations between blood donor body mass index (BMI) and RBC measurements of metabolic stress and hemolysis.

STUDY DESIGN AND METHODS

The associations between donor BMI (<25 kg/m2 , normal weight; 25-29.9 kg/m2 , overweight; and ≥30 kg/m2 , obese) and hemolysis (storage, osmotic, and oxidative; n = 18 donors) or posttransfusion recovery (n = 14 donors) in immunodeficient mice were determined in stored leukocyte-reduced RBC units. Further evaluations were conducted using the National Heart, Lung, and Blood Institute RBC-Omics blood donor databases of hemolysis (n = 13 317) and metabolomics (n = 203).

RESULTS

Evaluations in 18 donors revealed that BMI was significantly (P < 0.05) and positively associated with storage and osmotic hemolysis. A BMI of 30 kg/m2 or greater was also associated with lower posttransfusion recovery in mice 10 minutes after transfusion (P = 0.026). Multivariable linear regression analyses in RBC-Omics revealed that BMI was a significant modifier for all hemolysis measurements, explaining 4.5%, 4.2%, and 0.2% of the variance in osmotic, oxidative, and storage hemolysis, respectively. In this cohort, obesity was positively associated (P < 0.001) with plasma ferritin (inflammation marker). Metabolomic analyses on RBCs from obese donors (44.1 ± 5.1 kg/m2 ) had altered membrane lipid composition, dysregulation of antioxidant pathways (eg, increased oxidized lipids, methionine sulfoxide, and xanthine), and dysregulation of nitric oxide metabolism, as compared to RBCs from nonobese (20.5 ± 1.0 kg/m2 ) donors.

CONCLUSIONS

Obesity is associated with significant changes in RBC metabolism and increased susceptibility to hemolysis under routine storage of RBC units. The impact on transfusion efficacy warrants further evaluation.

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.

Acute Cycling Exercise Induces Changes in Red Blood Cell Deformability and Membrane Lipid Remodeling

Here we describe the effects of a controlled, 30 min, high-intensity cycling test on blood rheology and the metabolic profiles of red blood cells (RBCs) and plasma from well-trained males. RBCs demonstrated decreased deformability and trended toward increased generation of microparticles after the test. Meanwhile, metabolomics and lipidomics highlighted oxidative stress and activation of membrane lipid remodeling mechanisms in order to cope with altered properties of circulation resulting from physical exertion during the cycling test. Of note, intermediates from coenzyme A (CoA) synthesis for conjugation to fatty acyl chains, in parallel with reversible conversion of carnitine and acylcarnitines, emerged as metabolites that significantly correlate with RBC deformability and the generation of microparticles during exercise. Taken together, we propose that RBC membrane remodeling and repair plays an active role in the physiologic response to exercise by altering RBC properties.

Testosterone replacement therapy in blood donors modulates erythrocyte metabolism and susceptibility to hemolysis in cold storage

BACKGROUND

Red blood cells (RBCs) derived from patients who receive testosterone replacement therapy (TRT) may be considered eligible for component production and transfusion. The aim of this study was to identify testosterone-dependent changes in RBC metabolism and to evaluate its impact on susceptibility to hemolysis during cold storage.

STUDY DESIGN AND METHODS

We characterized stored RBCs from two cohorts of TRT patients who were matched with control donors (no TRT) based upon sex, age, and ethnicity. We further evaluated the impact of testosterone deficiency (orchiectomy) on RBC metabolism in FVB/NJ mice. RBC metabolites were quantified by ultra-high-pressure liquid chromatography-mass spectrometry. RBC storage stability was determined in RBC units from TRT and controls by quantifying storage, osmotic, and oxidative hemolysis.

RESULTS

Orchiectomy in mice was associated with significant (P < 0.05) changes in RBC metabolism as compared with intact males including increased levels of acyl-carnitines, long-chain fatty acids (eg, docosapentaenoic acids), arginine, and dopamine. Stored RBCs from TRT patients exhibited higher levels of pentose phosphate pathway metabolites, glutathione, and oxidized purines (eg, hypoxanthine), suggestive of increased activation of antioxidant pathways in this group. Further analyses indicated significant changes in free fatty acids and acyl-carnitines in response to testosterone therapies. With regard to hemolysis, TRT was associated with enhanced susceptibility to osmotic hemolysis. Correlation analyses identified acyl-carnitines as significant modifiers of RBC predisposition to osmotic and oxidative hemolysis.

CONCLUSIONS

These observations provide new insights into testosterone-mediated changes in RBC metabolome and biology that may impact the storage capacity and posttransfusion efficacy of RBCs from TRT donors.

Immune and Metabolic Interactions of Human Erythrocytes: A Molecular Perspective

Apart from their main function as oxygen carriers in vertebrates, erythrocytes are also involved in immune regulation. By circulating throughout the body, the erythrocytes are exposed and interact with tissues that are damaged as a result of a disease. In this study, we summarize the literature regarding the contribution of erythrocytes to immune regulation and metabolism. Under the circumstances of a disease state, the erythrocytes may lose their antioxidant capacity and release Damage Associated Molecular Patterns, resulting in the regulation of innate and adaptive immunity. In addition, the erythrocytes scavenge and affect the levels of chemokines, circulating cell-free mtDNA, and C3b attached immune complexes. Furthermore, through surface molecules, erythrocytes control the function of T lymphocytes, macrophages, and dendritic cells. Through an array of enzymes, red blood cells contribute to the pool of blood's bioactive lipids. Finally, the erythrocytes contribute to reverse cholesterol transport through various mechanisms. Our study is highlighting overlooked molecular interactions between erythrocytes and immunity and metabolism, which could lead to the discovery of potent therapeutic targets for immunometabolic diseases.

Evidence of Structural Protein Damage and Membrane Lipid Remodeling in Red Blood Cells from COVID-19 Patients

The SARS-CoV-2 beta coronavirus is the etiological driver of COVID-19 disease, which is primarily characterized by shortness of breath, persistent dry cough, and fever. Because they transport oxygen, red blood cells (RBCs) may play a role in the severity of hypoxemia in COVID-19 patients. The present study combines state-of-the-art metabolomics, proteomics, and lipidomics approaches to investigate the impact of COVID-19 on RBCs from 23 healthy subjects and 29 molecularly diagnosed COVID-19 patients. RBCs from COVID-19 patients had increased levels of glycolytic intermediates, accompanied by oxidation and fragmentation of ankyrin, spectrin beta, and the N-terminal cytosolic domain of band 3 (AE1). Significantly altered lipid metabolism was also observed, in particular, short- and medium-chain saturated fatty acids, acyl-carnitines, and sphingolipids. Nonetheless, there were no alterations of clinical hematological parameters, such as RBC count, hematocrit, or mean corpuscular hemoglobin concentration, with only minor increases in mean corpuscular volume. Taken together, these results suggest a significant impact of SARS-CoV-2 infection on RBC structural membrane homeostasis at the protein and lipid levels. Increases in RBC glycolytic metabolites are consistent with a theoretically improved capacity of hemoglobin to off-load oxygen as a function of allosteric modulation by high-energy phosphate compounds, perhaps to counteract COVID-19-induced hypoxia. Conversely, because the N-terminus of AE1 stabilizes deoxyhemoglobin and finely tunes oxygen off-loading and metabolic rewiring toward the hexose monophosphate shunt, RBCs from COVID-19 patients may be less capable of responding to environmental variations in hemoglobin oxygen saturation/oxidant stress when traveling from the lungs to peripheral capillaries and vice versa.

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.

ZOOMICS: Comparative Metabolomics of Red Blood Cells From Old World Monkeys and Humans

As part of the ZOOMICS project, we set out to investigate common and diverging metabolic traits in the blood metabolome across various species by taking advantage of recent developments in high-throughput metabolomics. Here we provide the first comparative metabolomics analysis of fresh and stored human (n = 21, 10 males, 11 females), olive baboon (n = 20), and rhesus macaque (n = 20) red blood cells at baseline and upon 42 days of storage under blood bank conditions. The results indicated similarities and differences across species, which ultimately resulted in a differential propensity to undergo morphological alterations and lyse as a function of the duration of refrigerated storage. Focusing on purine oxidation, carboxylic acid, fatty acid, and arginine metabolism further highlighted species-specific metabolic wiring. For example, through a combination of steady state measurements and ¹³C₆¹⁵N₄-arginine tracing experiments, we report an increase in arginine catabolism into ornithine in humans, suggestive of species-specific arginase 1 activity and nitric oxide synthesis—an observation that may impact the translatability of cardiovascular disease studies carried out in non-human primates (NHPs). Finally, we correlated metabolic measurements to storage-induced morphological alterations via scanning electron microscopy and hemolysis, which were significantly lower in human red cells compared to both NHPs.

A Comprehensive Functional Characterization of Escherichia coli Lipid Genes

Lipid membranes are the border between living cells and their environments. The membrane's lipid composition defines fluidity, thickness, and protein activity and is controlled by the intricate actions of lipid gene-encoded enzymes. However, a comprehensive analysis of each protein's contribution to the lipidome is lacking. Here, we present such a comprehensive and functional overview of lipid genes in Escherichia coli by individual overexpression or deletion of these genes. We developed a high-throughput lipidomic platform, combining growth analysis, one-step lipid extraction, rapid LC-MS, and bioinformatic analysis into one streamlined procedure. This allowed the processing of more than 300 samples per day and revealed interesting functions of known enzymes and distinct effects of individual proteins on the phospholipidome. Our data demonstrate the plasticity of the phospholipidome and unexpected relations between lipid classes and cell growth. Modeling of lipidomic responses to short-chain alcohols provides a rationale for targeted membrane engineering.

Evidence for structural protein damage and membrane lipid remodeling in red blood cells from COVID-19 patients

The SARS-CoV-2 beta coronavirus is the etiological driver of COVID-19 disease, which is primarily characterized by shortness of breath, persistent dry cough, and fever. Because they transport oxygen, red blood cells (RBCs) may play a role in the severity of hypoxemia in COVID-19 patients. The present study combines state-of-the-art metabolomics, proteomics, and lipidomics approaches to investigate the impact of COVID-19 on RBCs from 23 healthy subjects and 29 molecularly-diagnosed COVID-19 patients. RBCs from COVID-19 patients had increased levels of glycolytic intermediates, accompanied by oxidation and fragmentation of ankyrin, spectrin beta, and the N-terminal cytosolic domain of band 3 (AE1). Significantly altered lipid metabolism was also observed, especially short and medium chain saturated fatty acids, acyl-carnitines, and sphingolipids. Nonetheless, there were no alterations of clinical hematological parameters, such as RBC count, hematocrit, and mean corpuscular hemoglobin concentration, with only minor increases in mean corpuscular volume. Taken together, these results suggest a significant impact of SARS-CoV-2 infection on RBC structural membrane homeostasis at the protein and lipid levels. Increases in RBC glycolytic metabolites are consistent with a theoretically improved capacity of hemoglobin to off-load oxygen as a function of allosteric modulation by high-energy phosphate compounds, perhaps to counteract COVID-19-induced hypoxia. Conversely, because the N-terminus of AE1 stabilizes deoxyhemoglobin and finely tunes oxygen off-loading, RBCs from COVID-19 patients may be incapable of responding to environmental variations in hemoglobin oxygen saturation when traveling from the lungs to peripheral capillaries and, as such, may have a compromised capacity to transport and deliver oxygen.

Metabolomic and molecular insights into sickle cell disease and innovative therapies

Sickle cell disease (SCD) is an autosomal-recessive hemolytic disorder with high morbidity and mortality. The pathophysiology of SCD is characterized by the polymerization of deoxygenated intracellular sickle hemoglobin, which causes the sickling of erythrocytes. The recent development of metabolomics, the newest member of the "omics" family, has provided a powerful new research strategy to accurately measure functional phenotypes that are the net result of genomic, transcriptomic, and proteomic changes. Metabolomics changes respond faster to external stimuli than any other "ome" and are especially appropriate for surveilling the metabolic profile of erythrocytes. In this review, we summarize recent pioneering research that exploited cutting-edge metabolomics and state-of-the-art isotopically labeled nutrient flux analysis to monitor and trace intracellular metabolism in SCD mice and humans. Genetic, structural, biochemical, and molecular studies in mice and humans demonstrate unrecognized intracellular signaling pathways, including purinergic and sphingolipid signaling networks that promote hypoxic metabolic reprogramming by channeling glucose metabolism to glycolysis via the pentose phosphate pathway. In turn, this hypoxic metabolic reprogramming induces 2,3-bisphosphoglycerate production, deoxygenation of sickle hemoglobin, polymerization, and sickling. Additionally, we review the detrimental role of an impaired Lands' cycle, which contributes to sickling, inflammation, and disease progression. Thus, metabolomic profiling allows us to identify the pathological role of adenosine signaling and S1P-mediated erythrocyte hypoxic metabolic reprogramming and hypoxia-induced impaired Lands' cycle in SCD. These findings further reveal that the inhibition of adenosine and S1P signaling cascade and the restoration of an imbalanced Lands' cycle have potent preclinical efficacy in counteracting sickling, inflammation, and disease progression.

Erythrocyte adaptive metabolic reprogramming under physiological and pathological hypoxia

PURPOSE OF REVIEW

The erythrocyte is the most abundant cell type in our body, acting as both a carrier/deliverer and sensor of oxygen (O2). Erythrocyte O2 delivery capacity is finely regulated by sophisticated metabolic control. In recent years, unbiased and robust human metabolomics screening and mouse genetic studies have advanced erythroid research revealing the differential role of erythrocyte hypoxic metabolic reprogramming in normal individuals at high altitudes and patients facing hypoxia, such as sickle cell disease (SCD) and chronic kidney disease (CKD). Here we summarize recent progress and highlight potential therapeutic possibilities.

RECENT FINDINGS

Initial studies showed that elevated soluble CD73 (sCD73, converts AMP to adenosine) results in increased circulating adenosine that activates the A2B adenosine receptor (ADORA2B). Signaling through this axis is co-operatively strengthened by erythrocyte-specific synthesis of sphingosine-1-phosphate (S1P). Ultimately, these mechanisms promote the generation of 2,3-bisphosphoglycerate (2,3-BPG), an erythrocyte-specific allosteric modulator that decreases haemoglobin--O2-binding affinity, and thus, induces deoxygenated sickle Hb (deoxyHbS), deoxyHbS polymerization, sickling, chronic inflammation and tissue damage in SCD. Similar to SCD, plasma adenosine and erythrocyte S1P are elevated in humans ascending to high altitude. At high altitude, these two metabolites are beneficial to induce erythrocyte metabolic reprogramming and the synthesis of 2,3-BPG, and thus, increase O2 delivery to counteract hypoxic tissue damage. Follow-up studies showed that erythrocyte equilibrative nucleoside transporter 1 (eENT1) is a key purinergic cellular component controlling plasma adenosine in humans at high altitude and mice under hypoxia and underlies the quicker and higher elevation of plasma adenosine upon re-ascent because of prior hypoxia-induced degradation of eENT1. More recent studies demonstrated the beneficial role of erythrocyte ADORA2B-mediated 2,3-BPG production in CKD.

SUMMARY

Taken together, these findings revealed the differential role of erythrocyte hypoxic metabolic reprogramming in normal humans at high altitude and patients with CKD vs. SCD patients and immediately suggest differential and precision therapies to counteract hypoxia among these groups.

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.