Red cell pyruvate kinase deficiency: molecular and clinical aspects

The search for pyruvate kinase-R activators; from a HTS screening hit via an impurity to the discovery of a lead series

Pyruvate kinase (PK) is an essential component of cellular metabolism, converting ADP and phosphoenolpyruvate (PEP) to pyruvate in the final step of glycolysis. Of the four unique isoforms of pyruvate kinase, R (PKR) is expressed exclusively in red blood cells and is a tetrameric enzyme that depends on fructose-1,6-bisphosphate (FBP) for activation. PKR deficiency leads to hemolysis of red blood cells resulting in anemia. Activation of PKR in both sickle cell disease and beta-thalassemia patients could lead to improved red blood cell fitness and survival. The discovery of a novel series of substituted urea PKR activators, via the serendipitous identification and diligent characterization of a minor impurity in an High Throughput Screening (HTS) hit will be discussed.

Multicenter, phase 1 study of etavopivat (FT-4202) treatment for up to 12 weeks in patients with sickle cell disease

ABSTRACT

Etavopivat is an investigational, once daily, oral, selective erythrocyte pyruvate kinase (PKR) activator. A multicenter, randomized, placebo-controlled, double-blind, 3-part, phase 1 study was conducted to characterize the safety and clinical activity of etavopivat. Thirty-six patients with sickle cell disease (SCD) were enrolled into 4 cohorts: 1 single-dose, 2 multiple ascending doses, and 1 open-label (OL). In the OL cohort, 15 patients (median age 33.0 years [range, 17-55]) received 400 mg etavopivat once daily for 12 weeks; 14 patients completed treatment. Consistent with the mechanism of PKR activation, increases in adenosine triphosphate and decreases in 2,3-diphosphoglycerate were observed and sustained over 12 weeks' treatment. This translated clinically to an increase in hemoglobin (Hb; mean maximal increase 1.6 g/dL [range, 0.8-2.8]), with >1 g/dL increase in 11 (73%) patients during treatment. In addition, the oxygen tension at which Hb is 50% saturated was reduced (P = .0007) with a concomitant shift in point of sickling (P = .0034) to lower oxygen tension in oxygen-gradient ektacytometry. Hemolysis markers (absolute reticulocyte count, indirect bilirubin, and lactate dehydrogenase) decreased from baseline, along with matrix metalloproteinase-9 and erythropoietin. In the OL cohort, adverse events (AEs) were mostly grade 1/2, consistent with underlying SCD; 5 patients had serious AEs. Vaso-occlusive pain episode was the most common treatment-emergent AE (n = 7) in the OL cohort. In this, to our knowledge, the first study of etavopivat in SCD, 400 mg once daily for 12 weeks was well tolerated, resulting in rapid and sustained increases in Hb, improved red blood cell physiology, and decreased hemolysis. This trial was registered at www.ClinicalTrials.gov as #NCT03815695.

Novel therapeutic approaches in thalassemias, sickle cell disease, and other red cell disorders

ABSTRACT

In this last decade, a deeper understanding of the pathophysiology of hereditary red cell disorders and the development of novel classes of pharmacologic agents have provided novel therapeutic approaches to thalassemias, sickle cell disease (SCD), and other red cell disorders. Here, we analyze and discuss the novel therapeutic options according to their targets, taking into consideration the complex process of erythroid differentiation, maturation, and survival of erythrocytes in the peripheral circulation. We focus on active clinical exploratory and confirmatory trials on thalassemias, SCD, and other red cell disorders. Beside β-thalassemia and SCD, we found that the development of new therapeutic strategies has allowed for the design of clinic studies for hereditary red cell disorders still lacking valuable therapeutic alternative such as α-thalassemias, congenital dyserythropoietic anemia, or Diamond-Blackfan anemia. In addition, reduction of heme synthesis, which can be achieved by the repurposed antipsychotic drug bitopertin, might affect not only hematological disorders but multiorgan diseases such as erythropoietic protoporphyria. Finally, our review highlights the current state of therapeutic scenarios, in which multiple indications targeting different red cell disorders are being considered for a single agent. This is a welcome change that will hopefully expand therapeutic option for patients affected by thalassemias, SCD, and other red cell disorders.

Red Cell Pyruvate Kinase Deficiency With Hypertriglyceridemia: A Case Report

Red cell pyruvate kinase (PK) deficiency is a genetic disorder affecting the enzyme PK in red blood cells. A deficiency in PK leads to hemolytic anemia. Hypertriglyceridemia means elevated levels of triglycerides in the blood. The hypertriglyceridemia disorder can be primary or secondary to an underlying disease. Hypertriglyceridemia with β-thalassemia major is a known association and is called hypertriglyceridemia-thalassemia syndrome. A four-month-old male child was found to have milky serum. On investigation, there was severe anemia, with triglycerides at 1197 mg/dL and high lactate dehydrogenase (LDH). The child had severe pallor, mild icterus, a dysmorphic face, and splenohepatomegaly. Ophthalmic examination showed lipemia retinitis. The child was treated with medium-chain fatty acid formula feed. Regular blood transfusions, folic acid supplements, and avoidance of salicylate group drugs were advised. The child improved and is doing well. Thus, early diagnosis and treatment can change the prognosis and help maintain a near-normal life for affected infants.

Mitapivat improves ineffective erythropoiesis and iron overload in adult patients with pyruvate kinase deficiency

ABSTRACT

Pyruvate kinase (PK) deficiency is a rare, hereditary disease characterized by chronic hemolytic anemia. Iron overload is a common complication regardless of age, genotype, or transfusion history. Mitapivat, an oral, allosteric PK activator, improves anemia and hemolysis in adult patients with PK deficiency. Mitapivat's impact on iron overload and ineffective erythropoiesis was evaluated in adults with PK deficiency who were not regularly transfused in the phase 3 ACTIVATE trial and long-term extension (LTE) (#NCT03548220/#NCT03853798). Patients in the LTE received mitapivat throughout ACTIVATE/LTE (baseline to week 96; mitapivat-to-mitapivat [M/M] arm) or switched from placebo (baseline to week 24) to mitapivat (week 24 to week 96; placebo-to-mitapivat [P/M] arm). Changes from baseline in markers of iron overload and erythropoiesis were assessed to week 96. Improvements in hepcidin (mean, 4770.0 ng/L; 95% confidence interval [CI], -1532.3 to 11 072.3), erythroferrone (mean, -9834.9 ng/L; 95% CI, -14 328.4 to -5341.3), soluble transferrin receptor (mean, -56.0 nmol/L; 95% CI, -84.8 to -27.2), and erythropoietin (mean, -32.85 IU/L; 95% CI, -54.65 to -11.06) were observed in the M/M arm (n = 40) from baseline to week 24, sustained to week 96. No improvements were observed in the P/M arm (n = 40) to week 24; however, upon transitioning to mitapivat, improvements similar to those observed in the M/M arm were seen. Mean changes from baseline in liver iron concentration by magnetic resonance imaging at week 96 in the M/M arm and the P/M arm were -2.0 mg Fe/g dry weight (dw; 95% CI, -4.8 to -0.8) and -1.8 mg Fe/g dw (95% CI, -4.4 to 0.80), respectively. Mitapivat is the first disease-modifying pharmacotherapy shown to have beneficial effects on iron overload and ineffective erythropoiesis in patients with PK deficiency. This trial was registered at www.ClinicalTrials.gov as #NCT03548220 (ACTIVATE) and #NCT03853798 (LTE).

Recent developments in the use of pyruvate kinase activators as a new approach for treating sickle cell disease

ABSTRACT

Pyruvate kinase (PK) is a key enzyme in glycolysis, the sole source of adenosine triphosphate, which is essential for all energy-dependent activities of red blood cells. Activating PK shows great potential for treating a broad range of hemolytic anemias beyond PK deficiency, because they also enhance activity of wild-type PK. Motivated by observations of sickle-cell complications in sickle-trait individuals with concomitant PK deficiency, activating endogenous PK offers a novel and promising approach for treating patients with sickle-cell disease.

Pyruvate kinase activators for treatment of pyruvate kinase deficiency

Pyruvate kinase (PK) deficiency is a congenital hemolytic anemia with wide-ranging clinical symptoms and complications associated with significant morbidity and reduced health-related quality of life in both children and adults. The management of patients with PK deficiency has been historically challenging due to difficulties in the diagnostic evaluation, heterogeneity of clinical manifestations, and treatment options limited to supportive care with transfusions and splenectomy. An oral allosteric PK activator, mitapivat, is now a clinically available disease-modifying treatment for adults with PK deficiency. Phase 2 and 3 clinical trials of mitapivat have demonstrated sustained improvements in hemolytic anemia, hematopoiesis, and quality of life in many adults with PK deficiency and a generally reassuring safety profile with continued dosing. Additional long-term benefits include rapid and ongoing reduction in iron overload and potential stabilization of bone health. Clinical trials of treatment with mitapivat in children with PK deficiency are ongoing. In addition to disease-modifying treatment with PK activators, gene therapy is a potentially curative treatment currently under evaluation in clinical trials. With the availability of disease-targeted therapies, accurately diagnosing PK deficiency in patients with chronic hemolytic anemia is critical. PK activation and gene therapy have the potential to change the natural history of PK deficiency by improving clinical manifestations and patient quality of life and decreasing the risk of long-term complications.

Psychometric validation of the Pyruvate Kinase Deficiency Diary and Pyruvate Kinase Deficiency Impact Assessment in adults in the phase 3 ACTIVATE trial

BACKGROUND

Pyruvate kinase (PK) deficiency is a rare hereditary disorder characterized by chronic hemolytic anemia and serious sequalae which negatively affect patient quality of life. This study aimed to psychometrically validate the first disease-specific patient-reported outcome (PRO) instruments: the 7-item PK Deficiency Diary (PKDD) and 12-item PK Deficiency Impact Assessment (PKDIA), designed to assess signs, symptoms, and impacts of PK deficiency in patients enrolled in the ACTIVATE global phase 3 study of mitapivat versus placebo (NCT03548220).

METHODS

All validation analyses for the PKDD and PKDIA were performed on blinded data, with analyses on item integrity, scoring, reliability, and validity conducted on data from screening and baseline. Completion rates and baseline response distributions were characterized using descriptive statistics. Item response modelling was used to inform a weighted scoring system. Reliability was assessed by internal consistency and test-retest reliability; and validity by convergent and known-groups analyses.

RESULTS

Of the 80 adults enrolled, baseline data were available for 77 (96.3%) and 78 (97.5%) patients for the PKDD and PKDIA, respectively. Item responses skewed right, indicating that mean values exceeded median values, especially for items utilizing a 0-10 numeric scale, which were subsequently recoded to a 0-4 scale; 4 items were removed from the PKDIA due to redundancy or low relevance to the trial population. Both the PKDD and PKDIA demonstrated high internal consistency (McDonald's coefficient ω = 0.86 and 0.90, respectively), test-retest reliability (intra-class coefficients of 0.94 and 0.87, respectively), and convergent validity with other PROs (linear correlation coefficients [|r|] between 0.30-0.73 and 0.50-0.82, respectively).

CONCLUSIONS

The findings provide evidence of validity and reliability for the PKDD and PKDIA, the first disease-specific PRO measures for PK deficiency, and can therefore increase understanding of, and more accurately capture, the wider impact of PK deficiency on health-related quality of life. Trial registration ClinicalTrials.gov, NCT03548220. Registered June 07, 2018; https://www.

CLINICALTRIALS

gov/ct2/show/NCT03548220 .

Mitochondrial and Proteasome Dysfunction Occurs in the Hearts of Mice Treated with Triazine Herbicide Prometryn

Prometryn is a methylthio-s-triazine herbicide used to control the growth of annual broadleaf and grass weeds in many cultivated plants. Significant traces of prometryn are documented in the environment, mainly in waters, soil, and plants used for human and domestic consumption. Previous studies have shown that triazine herbicides have carcinogenic potential in humans. However, there is limited information about the effects of prometryn on the cardiac system in the literature, or the mechanisms and signaling pathways underlying any potential cytotoxic effects are not known. It is important to understand the possible effects of exogenous compounds such as prometryn on the heart. To determine the mechanisms and signaling pathways affected by prometryn (185 mg/kg every 48 h for seven days), we performed proteomic profiling of male mice heart with quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) using ten-plex tandem mass tag (TMT) labeling. The data suggest that several major pathways, including energy metabolism, protein degradation, fatty acid metabolism, calcium signaling, and antioxidant defense system were altered in the hearts of prometryn-treated mice. Proteasome and immunoproteasome activity assays and expression levels showed proteasome dysfunction in the hearts of prometryn-treated mice. The results suggest that prometryn induced changes in mitochondrial function and various signaling pathways within the heart, particularly affecting stress-related responses.

An innovative phase I study in healthy subjects to determine the mass balance, elimination, metabolism, and absolute bioavailability of mitapivat

Mitapivat, a first-in-class, oral, small-molecule, allosteric activator of the red blood cell-specific form of pyruvate kinase (PKR), was approved for the treatment of hemolytic anemia in adults with pyruvate kinase (PK) deficiency. In this phase I mass balance study in healthy males, we administered a single ~120 mg oral dose of [14 C]mitapivat and a concomitant intravenous ~0.1 mg microdose of [13 C6 ]mitapivat. We determined (1) the routes of total radioactivity excretion, including the mass balance of total radioactivity in urine and feces; (2) the pharmacokinetics of mitapivat and [13 C6 ]mitapivat in plasma and total radioactivity in whole blood and plasma; (3) the absolute oral bioavailability of mitapivat; and (4) the metabolite profiles in plasma and excreta. Mean recovery of the radioactive dose was 89.1% (49.6% in urine and 39.6% in feces). [14 C]Mitapivat was rapidly absorbed and extensively metabolized as <4% of the total radioactive dose was excreted unaltered in urine and feces. Mean absolute oral bioavailability was 72.7%. A total of 17 metabolites were identified. Mitapivat accounted for 57% and 34% of plasma radioactivity in AUC0-24 and AUC0-72 pooled samples, respectively. The remaining radioactivity was attributable to several metabolites, each representing <10% of the total radioactivity in pooled samples; none were disproportionate metabolites as defined by the US Food and Drug Administration and International Conference on Harmonisation M3 guidelines. Metabolite structures suggest that the primary metabolic pathways for [14 C]mitapivat in humans include N-dealkylation of the cyclopropylmethyl moiety, oxygenation of the quinoline-8-sulfonamide, oxidation/unsaturation, scission of the piperazine moiety, and amide hydrolysis.

Activation of pyruvate kinase as therapeutic option for rare hemolytic anemias: Shedding new light on an old enzyme

Novel developments in therapies for various hereditary hemolytic anemias reflect the pivotal role of pyruvate kinase (PK), a key enzyme of glycolysis, in red blood cell (RBC) health. Without PK catalyzing one of the final steps of the Embden-Meyerhof pathway, there is no net yield of adenosine triphosphate (ATP) during glycolysis, the sole source of energy production required for proper RBC function and survival. In hereditary hemolytic anemias, RBC health is compromised and therefore lifespan is shortened. Although our knowledge on glycolysis in general and PK function in particular is solid, recent advances in genetic, molecular, biochemical, and metabolic aspects of hereditary anemias have improved our understanding of these diseases. These advances provide a rationale for targeting PK as therapeutic option in hereditary hemolytic anemias other than PK deficiency. This review summarizes the knowledge, rationale, (pre)clinical trials, and future advances of PK activators for this important group of rare diseases.

An Overall View of the Functional and Structural Characterization of Glucose-6-Phosphate Dehydrogenase Variants in the Mexican Population

Glucose-6-phosphate dehydrogenase (G6PD) deficiency, affecting an estimated 500 million people worldwide, is a genetic disorder that causes human enzymopathies. Biochemical and genetic studies have identified several variants that produce different ranges of phenotypes; thus, depending on its severity, this enzymopathy is classified from the mildest (Class IV) to the most severe (Class I). Therefore, understanding the correlation between the mutation sites of G6PD and the resulting phenotype greatly enhances the current knowledge of enzymopathies' phenotypic and genotypic heterogeneity, which will assist both clinical diagnoses and personalized treatments for patients with G6PD deficiency. In this review, we analyzed and compared the structural and functional data from 21 characterized G6PD variants found in the Mexican population that we previously characterized. In order to contribute to the knowledge regarding the function and structure of the variants associated with G6PD deficiency, this review aimed to determine the molecular basis of G6PD and identify how these mutations could impact the structure, stability, and function of the enzyme and its relation with the clinical manifestations of this disease.

Association of PKLR gene copy number, expression levels and enzyme activity with 2,3,7,8-TCDD exposure in individuals exposed to Agent Orange/Dioxin in Vietnam

2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) is the most toxic congener of dioxin and has serious long-term effects on the environment and human health. Pyruvate Kinase L/R (PKLR) gene expression levels and gene variants are associated with pyruvate kinase enzyme deficiency, which has been identified as the cause of several diseases linked to dioxin exposure. In this study, we estimated PKLR gene copy number and gene expression levels using real-time quantitative PCR (RT-qPCR) assays, genotyped PKLR SNP rs3020781 by Sanger sequencing, and quantified plasma pyruvate kinase enzyme activity in 100 individuals exposed to Agent Orange/Dioxin near Bien Hoa and Da Nang airfields in Vietnam and 100 healthy controls. The means of PKLR copy numbers and PKLR gene expression levels were significantly higher, while pyruvate kinase enzyme activity was significantly decreased in Agent Orange/Dioxin-exposed individuals compared to healthy controls (P < 0.0001). Positive correlations of PKLR gene copy number and gene expression with 2,3,7,8-TCDD concentrations were observed (r = 0.2, P = 0.045 and r = 0.54, P < 0.0001, respectively). In contrast, pyruvate kinase enzyme activity was inversely correlated with 2,3,7,8-TCDD concentrations (r = -0.52, P < 0.0001). PKLR gene copy number and gene expression levels were also inversely correlated with pyruvate kinase enzyme activity. Additionally, PKLR SNP rs3020781 was found to be associated with 2,3,7,8-TCDD concentrations and PKLR gene expression. In conclusion, PKLR copy number, gene expression levels, and pyruvate kinase enzyme activity are associated with 2,3,7,8-TCDD exposure in individuals living in Agent Orange/Dioxin-contaminated areas.

Biphosphoglycerate Mutase: A Novel Therapeutic Target for Malaria?

Biphosphoglycerate mutase (BPGM) is a tri-functional enzyme expressed exclusively in erythroid cells and tissues that is responsible for the production of 2,3-biphosphoglycerate (2,3-BPG) through the Rapoport-Luebering shunt. The 2,3-BPG is required for efficient glycolysis and ATP production under anaerobic conditions, but is also a critical allosteric regulator of hemoglobin (Hb), acting to regulate oxygen release in peripheral tissues. In humans, BPGM deficiency is very rare, and is associated with reduced levels of erythrocytic 2,3-BPG and ATP, left shifted Hb-O2 dissociation curve, low P50, elevated Hb and constitutive erythrocytosis. BPGM deficiency in mice recapitulates the erythroid defects seen in human patients. A recent report has shown that BPGM deficiency in mice affords striking protection against both severe malaria anemia and cerebral malaria. These findings are reminiscent of studies of another erythrocyte specific glycolytic enzyme, Pyruvate Kinase (PKLR), which mutational inactivation protects humans and mice against malaria through impairment of glycolysis and ATP production in erythrocytes. BPGM, and PKLR join glucose-6-phosphate dehydrogenase (G6PD) and other erythrocyte variants as modulating response to malaria. Recent studies reviewed suggest glycolysis in general, and BPGM in particular, as a novel pharmacological target for therapeutic intervention in malaria.

PYK-SubstitutionOME: an integrated database containing allosteric coupling, ligand affinity and mutational, structural, pathological, bioinformatic and computational information about pyruvate kinase isozymes

Interpreting changes in patient genomes, understanding how viruses evolve and engineering novel protein function all depend on accurately predicting the functional outcomes that arise from amino acid substitutions. To that end, the development of first-generation prediction algorithms was guided by historic experimental datasets. However, these datasets were heavily biased toward substitutions at positions that have not changed much throughout evolution (i.e. conserved). Although newer datasets include substitutions at positions that span a range of evolutionary conservation scores, these data are largely derived from assays that agglomerate multiple aspects of function. To facilitate predictions from the foundational chemical properties of proteins, large substitution databases with biochemical characterizations of function are needed. We report here a database derived from mutational, biochemical, bioinformatic, structural, pathological and computational studies of a highly studied protein family-pyruvate kinase (PYK). A centerpiece of this database is the biochemical characterization-including quantitative evaluation of allosteric regulation-of the changes that accompany substitutions at positions that sample the full conservation range observed in the PYK family. We have used these data to facilitate critical advances in the foundational studies of allosteric regulation and protein evolution and as rigorous benchmarks for testing protein predictions. We trust that the collected dataset will be useful for the broader scientific community in the further development of prediction algorithms. Database URL https://github.com/djparente/PYK-DB.

Erythrocyte pyruvate kinase activation in red cell disorders

PURPOSE OF REVIEW

In red cells, pyruvate kinase is a key enzyme in the final step of glycolytic degradative process, which generates a constant energy supply via ATP production. This commentary discusses recent findings on pyruvate kinase activators as new therapeutic option in hereditary red cell disorders such as thalassemic syndromes or sickle cell disease (SCD).

RECENT FINDINGS

Mitapivat and etavopivat are two oral pyruvate kinase activators. Studies in a mouse model for β thalassemia have shown beneficial effects of mitapivat on both red cell survival and ineffective erythropoiesis, with an amelioration of iron homeostasis. This was confirmed in a proof-of-concept study in patients with nontransfusion-dependent thalassemias. Both mitapivat and etavopivat have been evaluated in mouse models for SCD, showing an increased 2-3DPG/ATP ratio and a reduction in haemolysis as well as in sickling. These data were confirmed in proof-of-concept clinical studies with both molecules carried in patients with SCD.

SUMMARY

Preclinical and clinical evidence indicate that pyruvate kinase activators represent new therapeutic option in hemoglobinopathies or SCD. Other red cell disorders such as hereditary spherocytosis or hereditary anaemias characterized by defective erythropoiesis might represent additional areas to investigate the therapeutic impact of pyruvate kinase activators.

Updates and advances in pyruvate kinase deficiency

Mutations in the PKLR gene lead to pyruvate kinase (PK) deficiency, causing chronic hemolytic anemia secondary to reduced red cell energy, which is crucial for maintenance of the red cell membrane and function. Heterogeneous clinical manifestations can result in significant morbidity and reduced health-related quality of life. Treatment options have historically been limited to supportive care, including red cell transfusions and splenectomy. Current disease-modifying treatment considerations include an oral allosteric PK activator, mitapivat, which was recently approved for adults with PK deficiency, and gene therapy, which is currently undergoing clinical trials. Studies evaluating the role of PK activators in other congenital hemolytic anemias are ongoing. The long-term effect of treatment with disease-modifying therapy in PK deficiency will require continued evaluation.

Roadmap to Pyruvate Kinase M2 Modulation - A Computational Chronicle

Pyruvate kinase M2 (PKM2) has surfaced as a potential target for anti-cancer therapy. PKM2 is known to be overexpressed in the tumor cells and is a critical metabolic conduit in supplying the augmented bioenergetic demands of the recalcitrant cancer cells. The presence of PKM2 in structurally diverse tetrameric as well as dimeric forms has opened new avenues to design novel modulators. It is also a truism to state that drug discovery has advanced significantly from various computational techniques like molecular docking, virtual screening, molecular dynamics, and pharmacophore mapping. The present review focuses on the role of computational tools in exploring novel modulators of PKM2. The structural features of various isoforms of PKM2 have been discussed along with reported modulators. An extensive analysis of the structure-based and ligand- based in silico methods aimed at PKM2 modulation has been conducted with an in-depth review of the literature. The role of advanced tools like QSAR and quantum mechanics has been established with a brief discussion of future perspectives.

Pyruvate Kinase Deficiency: Current Challenges and Future Prospects

Pyruvate kinase deficiency (PKD) is a rare autosomal recessive disease marked by chronic hemolytic anemia of various severity and frequent complications including gallstones, splenomegaly, iron overload, and others. Disease phenotype is highly heterogeneous and changes over time with children, adolescents and adult patients displaying different transfusion requirement and rates of complications. The diagnosis relies on the initial clinical suspicion in a patient with chronic hemolysis and exclusion of other more common congenital forms of hemolytic anemias; it is supported by the demonstration of reduced PK enzyme activity, and further confirmed by the detection of (homozygous or compound heterozygous) mutations of PKLR gene. Therapy is mainly supportive, with vitamin supplementation and transfusions (based on symptoms and patient growth rather than on fixed Hb thresholds). Splenectomy is widely performed, although it is less effective than in membrane defects and carries thrombotic and infectious risk. In the last decade, the allosteric PK enzyme activator mitapivat showed dramatic clinical benefit in clinical trials and gene therapy is also being studied to substitute the defective enzyme. In this review, we provide an insight in the current challenges of PKD diagnosis and management and discuss the future application of novel drugs and gene therapy, including a focus on quality of life.

Haematological profile of malaria patients with G6PD and PKLR variants (erythrocytic enzymopathies): a cross-sectional study in Thailand

Background

Glucose 6-phosphate dehydrogenase (G6PD) and pyruvate kinase (PKLR) deficiencies are common causes of erythrocyte haemolysis in the presence of antimalarial drugs such as primaquine and tafenoquine. The present study aimed to elucidate such an association by thoroughly investigating the haematological indices in malaria patients with G6PD and PKLR^R41Q variants.

Methods

Blood samples from 255 malaria patients from Thailand, Myanmar, Laos, and Cambodia were collected to determine haematological profile, G6PD enzyme activity and G6PD deficiency variants. The multivariate analysis was performed to investigate the association between anaemia and G6PD Mahidol^G487A, the most common mutation in this study.

Results

The prevalence of G6PD deficiency was 11.1% (27/244) in males and 9.1% (1/11) in female. The MAFs of the G6PD Mahidol^G487A and PKLR^R41Q variants were 7.1% and 2.6%, respectively. Compared with patients with wildtype G6PD after controlling for haemoglobinopathies, G6PD-deficient patients with hemizygous and homozygous G6PD Mahidol^G487A exhibited anaemia with low levels of haemoglobin (11.16 ± 2.65 g/dl, p = 0.041). These patients also exhibited high levels of reticulocytes (3.60%). The median value of G6PD activity before treatment (Day 0) was significantly lower than that of after treatment (Day 28) (5.51 ± 2.54 U/g Hb vs. 6.68 ± 2.45 U/g Hb; p < 0.001). Reticulocyte levels on Day 28 were significantly increased compared to that of on Day 0 (2.14 ± 0.92% vs 1.57 ± 1.06%; p < 0.001). PKLR^R41Q had no correlation with anaemia in malaria patients. The risk of anaemia inpatients with G6PDMahidol^G487A was higher than wildtype patients (OR = 3.48, CI% 1.24–9.75, p = 0.018). Univariate and multivariate analyses confirmed that G6PDMahidol^G487A independently associated with anaemia (< 11 g/dl) after adjusted by age, gender, Plasmodium species, parasite density, PKLR^R41Q, and haemoglobinopathies (p < 0.001).

Conclusions

This study revealed that malaria patients with G6PD Mahidol^G487A, but not with PKLR^R41Q, had anaemia during infection. As a compensatory response to haemolytic anaemia after malaria infection, these patients generated more reticulocytes. The findings emphasize the effect of host genetic background on haemolytic anaemia and the importance of screening patients for erythrocyte enzymopathies and related mutations prior to anti-malarial therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-022-04267-7.

Diagnosis, monitoring, and management of pyruvate kinase deficiency in children

Pyruvate kinase (PK) deficiency is a rare, congenital red blood cell disorder caused by a single gene defect. The spectrum of genotypes, variants, and phenotypes are broad, commonly requiring a multimodal approach including enzyme and genetic testing for accurate and reliable diagnosis. Similarly, management of primary and secondary sequelae of PK deficiency varies, mainly including supportive care with transfusions and surgical interventions to improve symptoms and quality of life. Given the risk of acute and long-term complications of PK deficiency and its treatment, regular monitoring and management of iron burden and organ dysfunction is critical. Therefore, all children and adolescents with PK deficiency should receive regular hematology care with visits at least every 6 months regardless of transfusion status. We continue to learn more about the spectrum of symptoms and complications of PK deficiency and best practice for monitoring and management through registry efforts (NCT03481738). The treatment of PK deficiency has made strides over the last few years with newer disease-modifying therapies being developed and studied, with the potential to change the course of disease in childhood and beyond.

Efficient and Fast Generation of Relevant Disease Mouse Models by In Vitro and In Vivo Gene Editing of Zygotes

Knockout mice for human disease-causing genes provide valuable models in which new therapeutic approaches can be tested. Electroporation of genome editing tools into zygotes, in vitro or within oviducts, allows for the generation of targeted mutations in a shorter time. We have generated mouse models deficient in genes involved in metabolic rare diseases (Primary Hyperoxaluria Type 1 Pyruvate Kinase Deficiency) or in a tumor suppressor gene (Rasa1). Pairs of guide RNAs were designed to generate controlled deletions that led to the absence of protein. In vitro or in vivo ribonucleoprotein (RNP) electroporation rendered more than 90% and 30% edited newborn animals, respectively. Mice lines with edited alleles were established and disease hallmarks have been verified in the three models that showed a high consistency of results and validating RNP electroporation into zygotes as an efficient technique for disease modeling without the need to outsource to external facilities.

Mitapivat versus Placebo for Pyruvate Kinase Deficiency

BACKGROUND

Pyruvate kinase deficiency is a rare, hereditary, chronic condition that is associated with hemolytic anemia. In a phase 2 study, mitapivat, an oral, first-in-class activator of erythrocyte pyruvate kinase, increased the hemoglobin level in patients with pyruvate kinase deficiency.

METHODS

In this global, phase 3, randomized, placebo-controlled trial, we evaluated the efficacy and safety of mitapivat in adults with pyruvate kinase deficiency who were not receiving regular red-cell transfusions. The patients were assigned to receive either mitapivat (5 mg twice daily, with potential escalation to 20 or 50 mg twice daily) or placebo for 24 weeks. The primary end point was a hemoglobin response (an increase from baseline of ≥1.5 g per deciliter in the hemoglobin level) that was sustained at two or more scheduled assessments at weeks 16, 20, and 24. Secondary efficacy end points were the average change from baseline in the hemoglobin level, markers of hemolysis and hematopoiesis, and the change from baseline at week 24 in two pyruvate kinase deficiency-specific patient-reported outcome measures.

RESULTS

Sixteen of the 40 patients (40%) in the mitapivat group had a hemoglobin response, as compared with none of the 40 patients in the placebo group (adjusted difference, 39.3 percentage points; 95% confidence interval, 24.1 to 54.6; two-sided P<0.001). Patients who received mitapivat had a greater response than those who received placebo with respect to each secondary end point, including the average change from baseline in the hemoglobin level. The most common adverse events were nausea (in 7 patients [18%] in the mitapivat group and 9 patients [23%] in the placebo group) and headache (in 6 patients [15%] and 13 patients [33%], respectively). Adverse events of grade 3 or higher occurred in 10 patients (25%) who received mitapivat and 5 patients (13%) who received placebo.

CONCLUSIONS

In patients with pyruvate kinase deficiency, mitapivat significantly increased the hemoglobin level, decreased hemolysis, and improved patient-reported outcomes. No new safety signals were identified in the patients who received mitapivat. (Funded by Agios Pharmaceuticals; ACTIVATE ClinicalTrials.gov number, NCT03548220.).

Etavopivat, a Pyruvate Kinase Activator in Red Blood Cells, for the Treatment of Sickle Cell Disease

Etavopivat is an investigational, oral, small molecule activator of erythrocyte pyruvate kinase (PKR) in development for the treatment of sickle cell disease (SCD) and other hemoglobinopathies. PKR activation is proposed to ameliorate the sickling of SCD red blood cells (RBC) through multiple mechanisms, including reduction of 2,3-diphosphoglycerate (2,3-DPG), which consequently increases hemoglobin (Hb)-oxygen affinity; increased binding of oxygen reduces HbS polymerization and sickling. In addition, PKR activation increases adenosine triphosphate (ATP) produced via glycolytic flux, which helps preserve membrane integrity and RBC deformability. We evaluated the pharmacodynamic response to etavopivat in non-human primates (NHP) and in healthy human subjects, and the effects in RBC from patients with SCD after ex vivo treatment with etavopivat. A single dose of etavopivat decreased 2,3-DPG in NHP and healthy subjects. Hb-oxygen affinity was significantly increased in healthy subjects after 24 hours. Following daily dosing of etavopivat over 5 consecutive days in NHP, ATP was increased by 38% from baseline. Etavopivat increased Hb-oxygen affinity and reduced sickling in RBC collected from SCD patients with either HbSS or HbSC disease. Collectively, these results demonstrate the ability of etavopivat to decrease 2,3-DPG and increase ATP, resulting in increased Hb-oxygen affinity and improved sickle RBC function. Etavopivat is currently being evaluated in clinical trials for the treatment of SCD. ClinicalTrials.gov identifier: NCT03815695 Significance Statement Etavopivat-a small molecule activator of the glycolytic enzyme erythrocyte pyruvate kinase -decreased 2,3-diphosphoglycerate in red blood cells (RBC) from non-human primates and healthy subjects and significantly increased hemoglobin (Hb)-oxygen affinity in healthy subjects. Using ex vivo RBC from donors with sickle cell disease (SCD) (HbSS or HbSC genotype), etavopivat increased Hb-oxygen affinity and reduced sickling under deoxygenation. Etavopivat shows promise as a treatment for SCD, that potentially might reduce vaso-occlusion and improve anemia.

Safety, Pharmacokinetics, and Pharmacodynamics of Etavopivat (FT-4202), an Allosteric Activator of Pyruvate Kinase-R, in Healthy Adults: A Randomized, Placebo-Controlled, Double-Blind, First-in-Human Phase 1 Trial

Etavopivat (FT‐4202) is an orally administered, small‐molecule allosteric activator of erythrocyte pyruvate kinase‐R (PKR) in clinical development for the treatment of sickle cell disease and other hemoglobin disorders. This randomized, placebo‐controlled, double‐blind, first‐in‐human combination single‐ascending dose and multiple‐ascending dose phase 1 trial (NCT03815695) evaluated the safety and pharmacokinetics/pharmacodynamics of etavopivat in 90 healthy adult subjects. In 4 single‐ascending dose cohorts, 8 participants were randomized 3:1 to a single oral dose of either etavopivat (n = 6) or placebo (n = 2). In four 14‐day multiple‐ascending dose cohorts, 12 participants were randomized 3:1 to 14 days of etavopivat (n = 9) or placebo (n = 3). In these studies, most treatment‐emergent adverse events were of mild severity (grade 1) and none led to study discontinuation. Etavopivat exhibited a linear and time‐independent pharmacokinetic profile (at doses ≤400 mg) and elicited the expected pharmacodynamic effects of PKR activation (decreased 2,3‐diphosphoglycerate and increased adenosine triphosphate) and evidence of improved hemoglobin‐oxygen affinity. In addition, pharmacodynamic responses were durable with effects continuing for 48 to 72 hours after the last dose, thereby supporting once‐daily dosing. Food appeared to have no clinically meaningful effects on etavopivat exposure, thus facilitating administration with or without food. In conclusion, the evaluation of etavopivat in healthy subjects demonstrated proof of mechanism (PKR activation) without significant adverse events. This study also allowed for the selection of dose levels, projected to have an acceptable safety profile and provide therapeutic benefit, for evaluation in future trials in patients with sickle cell disease.

Case report: Compound heterozygosity in PKLR gene with a large exon deletion and a novel rare p.Gly536Asp variant as a cause of severe pyruvate kinase deficiency

Red cell pyruvate kinase (PK) deficiency is the most common cause of hereditary nonspherocytic hemolytic anemia and the most frequent enzyme abnormality of the glycolytic pathway. To the best of our knowledge, this is the first Korean PK deficiency study that analyzes copy number variation (CNV) using next-generation sequencing (NGS). A 7-year-old girl with jaundice was admitted for evaluation of a persistent hemolytic anemia. The proband appeared chronically ill, showing a yellowish skin color, icteric sclera, hepatomegaly, and splenomegaly on physical examination. Sequence variants and CNV generated from NGS data were estimated to determine if there was a potential genetic cause. As a result, compound heterozygosity in the PKLR gene for a large exon deletion between exon 3 and exon 9 accompanied with a novel rare p.Gly536Asp variant located on exon 10 was identified as a cause of severe PK deficiency in the proband. The PK activity of the proband had been measured at the time of day 1, 21, and 28 after receiving transfusion to indirectly assume the effect of the transfused blood, and the results were 100.9%, 73.0%, and 48.5%, compared with average of normal controls, respectively. Our report emphasizes the need to perform complete CNV analysis of NGS data and gene dosage assays such as multiplex ligation-dependent probe amplification to evaluate large deletions or duplications/insertions of the PKLR gene in patients with suspected PK deficiency.

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.

[Consensus document for the diagnosis and treatment of pyruvate kinase deficiency]

Pyruvate kinase (PK) deficiency is the second most frequent enzymopathy and the most common cause of chronic hereditary non-spherocytic haemolytic anaemia. Its global prevalence is underestimated due to low clinical suspicion of mild cases, associated with difficulties in the performance and interpretation of PK enzymatic activity assays. With the advent of next generation sequencing techniques, a better diagnostic approach is achieved. Treatment remains based on red blood cell transfusions and splenectomy, with special attention to iron overload, not only in transfusion-dependent patients. Nowadays, allogeneic hematopoietic stem cell transplantation is the only curative treatment, recommended only in selected cases of severely affected patients with an HLA-identical donor. Novel pharmacological and gene therapies are in clinical trials, with promising results. In this article, the Spanish Erythropathology Group reviews the current situation of PK deficiency, paying special attention to the usefulness of different diagnostic techniques and to actual and emerging treatments.

Preclinical studies of efficacy thresholds and tolerability of a clinically ready lentiviral vector for pyruvate kinase deficiency treatment

Pyruvate kinase deficiency (PKD) is a rare autosomal recessive disorder caused by mutations in the PKLR gene. PKD is characterized by non-spherocytic hemolytic anemia of variable severity and may be fatal in some cases during early childhood. Although not considered the standard of care, allogeneic stem cell transplantation has been shown as a potentially curative treatment, limited by donor availability, toxicity, and incomplete engraftment. Preclinical studies were conducted to define conditions to enable consistent therapeutic reversal, which were based on our previous data on lentiviral gene therapy for PKD. Improvement of erythroid parameters was identified by the presence of 20%–30% healthy donor cells. A minimum vector copy number (VCN) of 0.2−0.3 was required to correct PKD when corrected cells were transplanted in a mouse model for PKD. Biodistribution and pharmacokinetics studies, with the aim of conducting a global gene therapy clinical trial for PKD patients (RP-L301-0119), demonstrated that genetically corrected cells do not confer additional side effects. Moreover, a clinically compatible transduction protocol with mobilized peripheral blood CD34⁺ cells was optimized, thus facilitating the efficient transduction on human cells capable of repopulating the hematopoiesis of immunodeficient mice. We established conditions for a curative lentiviral vector gene therapy protocol for PKD.

Health-Related Quality of Life and Fatigue in Children and Adults with Pyruvate Kinase Deficiency

The impact of PKD on HRQoL and fatigue is described in 254 children and adults using 6 validated instruments.

Severe anemia, regular transfusion, iron chelation, and nonmissense mutations are associated with worse patient-reported outcomes.

Pyruvate kinase deficiency (PKD) is the most common cause of congenital nonspherocytic hemolytic anemia. Although recognition of the disease spectrum has recently expanded, data describing its impact on health-related quality of life (HRQoL) are limited. In this prospective international cohort of 254 patients (131 adults and 123 children) with PKD, we used validated measures to assess the impact of disease on HRQoL (EuroQol 5-Dimension Questionnaire, Pediatric Quality of Life Inventory Generic Core Scale version 4.0, and Functional Assessment of Cancer Therapy-Anemia) and fatigue (Patient Reported Outcomes Measurement Information System Fatigue and Pediatric Functional Assessment of Chronic Illness Therapy-Fatigue). Significant variability in HRQoL and fatigue was reported for adults and children, although individual scores were stable over a 2-year interval. Although adults who were regularly transfused reported worse HRQoL and fatigue compared with those who were not (EuroQol-visual analog scale, 58 vs 80; P = .01), this difference was not seen in children. Regularly transfused adults reported lower physical, emotional, and functional well-being and more anemia symptoms. HRQoL and fatigue significantly differed in children by genotype, with the worst scores in those with 2 severe PKLR mutations; this difference was not seen in adults. However, iron chelation was associated with significantly worse HRQoL scores in children and adults. Pulmonary hypertension was also associated with significantly worse HRQoL. Additionally, 59% of adults and 35% of children reported that their jaundice upset them, identifying this as an important symptom for consideration. Although current treatments for PKD are limited to supportive care, new therapies are in clinical trials. Understanding the impact of PKD on HRQoL is important to assess the utility of these treatments. This trial was registered at www.clinicaltrials.gov as #NCT02053480.

A Sri Lankan girl with a new genetic variant in the PKLR gene causing pyruvate kinase deficiency: a case report

Background

Erythrocyte pyruvate kinase is expressed under the control of the PKLR gene located on chromosome 1q21. Pyruvate kinase catalyzes the final steps of the glycolytic pathway and creates 50% of the red cell total adenosine triphosphate. Pyruvate kinase deficiency is the commonest glycolytic defect causing congenital non-spherocytic hemolytic anemia inherited in an autosomal recessive trait in which homozygotes and compound heterozygotes are common. Over 200 mutations have been described in patients with pyruvate kinase deficiency. This case report identifies a new pathogenic variant in PKLR gene detected in a patient with severe pyruvate kinase deficiency.

Case presentation

A Sri Lankan Sinhalese girl who developed neonatal anemia and jaundice within 24 hours of birth with mild hepatomegaly. She was from a nonconsanguineous marriage and had two siblings who had no hematological disorders. She had repeated admissions due to similar illnesses and at the age of 8 years was found to have pyruvate kinase deficiency associated with a novel homozygous pathogenic variant c.507+1delG in the PKLR gene.

Conclusions

A novel genetic variant in PKLR gene, consistent with pyruvate kinase deficiency, was detected in a Sri Lankan girl. This genetic variant may be specific to the Asian population and requires further studies.

Successful Liver Transplantation for Adolescent Patient With Pyruvate Kinase Deficiency-induced Cirrhosis

We present the case of a successful liver transplant in a young adult patient with cholestasis and cirrhosis secondary to severe pyruvate kinase (PK) deficiency. Liver transplant resulted in resolution of liver dysfunction, decreased need for blood transfusions and eligibility for bone marrow transplantation. This case represents the third reported patient in the literature with severe PK deficiency who successfully underwent liver transplant as a result of profound cholestasis and liver failure. Explant pathology demonstrated a lack of significant iron deposition indicating that PK deficiency predisposes the liver to injury independent of transfusion-related iron overload.

Development of an Automated Enzymatic Method to Quantify Pyruvate Kinase in Red Blood Cells

BACKGROUND

Pyruvate kinase (PK) deficiency is the most common cause of nonspherocytic hemolytic anemia owing to defective glycolysis. This study developed and validated an automated method to measure PK activity in red blood cells (RBCs).

METHODS

PK catalyzes the reaction of phosphoenolpyruvate with ADP to form pyruvate and ATP. The pyruvate is reduced in the presence of lactate dehydrogenase and NADH to produce lactate and NAD+. The rate of absorbance decrease at 340 nm is proportional to PK activity. PK and hemoglobin (Hb) measurements were performed on a Roche cobas c501 analyzer. After establishing a k-factor, accuracy, linearity, imprecision, sensitivity, and stability were validated and the reference interval was verified.

RESULTS

The k-factor was -9477. Accuracy was evaluated by method comparison (n = 56). Linear regression yielded y = 1.0x - 0.57, and R2 of 0.93. Linearity was determined by combining a high sample with hemolyzing solution in 6 different ratios. Linear regression analysis yielded y = 1.02x - 2.68, and R2 of 1.0. The assay was linear to 87 U/dL. Precision was evaluated by testing hemolysates in 3 replicates/day for 10 days. Within-run imprecision was 1.9% and 2.5% and total imprecision was 4.0% and 5.6% at 14.0 and 8.1 U/g Hb, respectively. The limit of blank was 0.0, and the limit of detection was 1.0 U/dL. Stability was determined in 4 sample types at 3 different temperatures; the changes were all <10% when compared with t0. The current PK reference interval of 4.6 to 11.2 U/g Hb was verified.

CONCLUSIONS

This automated assay for quantifying PK in RBCs has acceptable performance characteristics and is fit for intended use.

Management of pyruvate kinase deficiency in children and adults

Pyruvate kinase deficiency (PKD) is an autosomal-recessive enzyme defect of the glycolytic pathway that causes congenital nonspherocytic hemolytic anemia. The diagnosis and management of patients with PKD can be challenging due to difficulties in the diagnostic evaluation and the heterogeneity of clinical manifestations, ranging from fetal hydrops and symptomatic anemia requiring lifelong transfusions to fully compensated hemolysis. Current treatment approaches are supportive and include transfusions, splenectomy, and chelation. Complications, including iron overload, bilirubin gallstones, extramedullary hematopoiesis, pulmonary hypertension, and thrombosis, are related to the chronic hemolytic anemia and its current management and can occur at any age. Disease-modifying therapies in clinical development may decrease symptoms and findings associated with chronic hemolysis and avoid the complications associated with current treatment approaches. As these disease-directed therapies are approved for clinical use, clinicians will need to define the types of symptoms and findings that determine the optimal patients and timing for initiating these therapies. In this article, we highlight disease manifestations, monitoring approaches, strategies for managing complications, and novel therapies in development.

The variable manifestations of disease in pyruvate kinase deficiency and their management

Pyruvate kinase deficiency (PKD) is the most common cause of chronic hereditary non-spherocytic hemolytic anemia and results in a broad spectrum of disease. The diagnosis of PKD requires a high index of suspicion and judicious use of laboratory tests that may not always be informative, including pyruvate kinase enzyme assay and genetic analysis of the PKLR gene. A significant minority of patients with PKD have occult mutations in non-coding regions of PKLR which are missed on standard genetic tests. The biochemical consequences of PKD result in hemolytic anemia due to red cell pyruvate and ATP deficiency while simultaneously causing increased red cell 2,3-diphosphoglycerate, which facilitates oxygen unloading. This phenomenon, in addition to numerous other factors such as genetic background and differences in splenic function result in a poor correlation between symptoms and degree of anemia from patient to patient. Red cell transfusions should, therefore, be symptom-directed and not based on a hemoglobin threshold. Patients may experience specific complications, such as paravertebral extramedullary hematopoiesis and chronic debilitating icterus, which require personalized treatment. The decision to perform splenectomy or hematopoietic stem cell transplantation is nuanced and depends on disease burden and long-term outlook given that targeted therapeutics are in development. In recognition of the complicated nature of the disease and its management and the limitations of the PKD literature, an international working group of ten PKD experts convened to better define the disease burden and manifestations. This article summarizes the conclusions of this working group and is a guide for clinicians and investigators caring for patients with PKD.

Niche-Selective Inhibition of Pathogenic Th17 Cells by Targeting Metabolic Redundancy

Targeting glycolysis has been considered therapeutically intractable owing to its essential housekeeping role. However, the context-dependent requirement for individual glycolytic steps has not been fully explored. We show that CRISPR-mediated targeting of glycolysis in T cells in mice results in global loss of Th17 cells, whereas deficiency of the glycolytic enzyme glucose phosphate isomerase (Gpi1) selectively eliminates inflammatory encephalitogenic and colitogenic Th17 cells, without substantially affecting homeostatic microbiota-specific Th17 cells. In homeostatic Th17 cells, partial blockade of glycolysis upon Gpi1 inactivation was compensated by pentose phosphate pathway flux and increased mitochondrial respiration. In contrast, inflammatory Th17 cells experience a hypoxic microenvironment known to limit mitochondrial respiration, which is incompatible with loss of Gpi1. Our study suggests that inhibiting glycolysis by targeting Gpi1 could be an effective therapeutic strategy with minimum toxicity for Th17-mediated autoimmune diseases, and, more generally, that metabolic redundancies can be exploited for selective targeting of disease processes.

Congenital Hemolytic Anemias: Is There a Role for the Immune System?

Congenital hemolytic anemias (CHAs) are a heterogeneous group of rare hereditary conditions including defects of erythrocyte membrane proteins, red cell enzymes, and disorders due to defective erythropoiesis. They are characterized by variable degree of anemia, chronic extravascular hemolysis, reduced erythrocyte life span, splenomegaly, jaundice, biliary lithiasis, and iron overload. Although few data are reported on the role of the immune system in CHAs, several immune-mediated mechanisms may be involved in the pathogenesis of these rare diseases. We reported in ~60% of patients with hereditary spherocytosis (HS), the presence of naturally-occurring autoantibodies (NAbs) directed against different membrane proteins (α- and β-spectrin, band 3, and dematin). Positive HS subjects showed a more hemolytic pattern and NAbs were more evident in aged erythrocytes. The latter is in line with the function of NAbs in the opsonization of damaged/senescent erythrocytes and their consequent removal in the spleen. Splenectomy, usually performed to reduce erythrocyte catheresis and improve Hb levels, has different efficacy in various CHAs. Median Hb increase is 3 g/dL in HS, 1.6–1.8 g/dL in pyruvate kinase deficiency (PKD), and 1 g/dL in congenital dyserythropoietic anemias (CDA) type II. Consistently with clinical severity, splenectomy is performed in 20% of HS, 45% of CDAII, and in 60% of PKD patients. Importantly, sepsis and thrombotic events have been registered, particularly in PKD with a frequency of ~7% for both. Furthermore, we analyzed the role of pro-inflammatory cytokines and found that interleukin 10 and interferon γ, and to a lesser extent interleukin 6, were increased in all CHAs compared with controls. Moreover, CDAII and enzymatic defects showed increased tumor necrosis factor-α and reduced interleukin 17. Finally, we reported that iron overload occurred in 31% of patients with membrane defects, in ~60% of CDAII cases, and in up to 82% of PKD patients (defined by MRI liver iron concentration >4 mg Fe/gdw). Hepcidin was slightly increased in CHAs compared with controls and positively correlated with ferritin and with the inflammatory cytokines interleukin 6 and interferon γ. Overall the results suggest the existence of a vicious circle between chronic hemolysis, inflammatory response, bone marrow dyserythropoiesis, and iron overload.

Targeted repression of Plasmodium apicortin by host microRNA impairs malaria parasite growth and invasion

Mature human erythrocytes contain a rich pool of microRNAs (miRNAs), which result from differentiation of the erythrocytes during the course of haematopoiesis. Recent studies have described the effect of erythrocytic miRNAs on the invasion and growth of the malaria parasite Plasmodium falciparum during the asexual blood stage of its life cycle. In this work, we have identified two erythrocytic miRNAs, miR-150-3p and miR-197-5p, that show favourable in silico hybridization with Plasmodium apicortin, a protein with putative microtubule-stabilizing properties. Co-expression of P. falciparum apicortin and these two miRNAs in a cell line model resulted in downregulation of apicortin at both the RNA and protein level. To create a disease model of erythrocytes containing miRNAs, chemically synthesized mimics of miR-150-3p and miR-197-5p were loaded into erythrocytes and subsequently used for invasion by the parasite. Growth of the parasite was hindered in miRNA-loaded erythrocytes, followed by impaired invasion; micronemal secretion was also reduced, especially in the case of miR-197-5p. Apicortin expression was found to be reduced in miRNA-loaded erythrocytes. To interpret the effect of downregulation of apicortin on parasite invasion to host erythrocytes, we investigated the secretion of the invasion-related microneme protein apical membrane antigen 1 (AMA1). AMA1 secretion was found to be reduced in miRNA-treated parasites. Overall, this study identifies apicortin as a novel target within the malaria parasite and establishes miR-197-5p as its miRNA inhibitor. This miRNA represents an unconventional nucleotide-based therapeutic and provides a new host factor-inspired strategy for the design of antimalarial molecular medicine.

This article has an associated First Person interview with the first author of the paper.

Summary: The role of host erythrocyte microRNA in the downregulation of malaria parasite gene expression is investigated. Two microRNAs are identified, miR-197-5p and miR-150-3p, which affect parasite growth and invasion when enriched in erythrocytes.

Genotype-phenotype correlation and molecular heterogeneity in pyruvate kinase deficiency

Pyruvate kinase (PK) deficiency is a rare recessive congenital hemolytic anemia caused by mutations in the PKLR gene. This study reports the molecular features of 257 patients enrolled in the PKD Natural History Study. Of the 127 different pathogenic variants detected, 84 were missense and 43 non-missense, including 20 stop-gain, 11 affecting splicing, five large deletions, four in-frame indels, and three promoter variants. Within the 177 unrelated patients, 35 were homozygous and 142 compound heterozygous (77 for two missense, 48 for one missense and one non-missense, and 17 for two non-missense variants); the two most frequent mutations were p.R510Q in 23% and p.R486W in 9% of mutated alleles. Fifty-five (21%) patients were found to have at least one previously unreported variant with 45 newly described mutations. Patients with two non-missense mutations had lower hemoglobin levels, higher numbers of lifetime transfusions, and higher rates of complications including iron overload, extramedullary hematopoiesis, and pulmonary hypertension. Rare severe complications, including lower extremity ulcerations and hepatic failure, were seen more frequently in patients with non-missense mutations or with missense mutations characterized by severe protein instability. The PKLR genotype did not correlate with the frequency of complications in utero or in the newborn period. With ICCs ranging from 0.4 to 0.61, about the same degree of clinical similarity exists within siblings as it does between siblings, in terms of hemoglobin, total bilirubin, splenectomy status, and cholecystectomy status. Pregnancy outcomes were similar across genotypes in PK deficient women. This report confirms the wide genetic heterogeneity of PK deficiency.

Pyruvate kinase variant of fission yeast tunes carbon metabolism, cell regulation, growth and stress resistance

Cells balance glycolysis with respiration to support their metabolic needs in different environmental or physiological contexts. With abundant glucose, many cells prefer to grow by aerobic glycolysis or fermentation. Using 161 natural isolates of fission yeast, we investigated the genetic basis and phenotypic effects of the fermentation-respiration balance. The laboratory and a few other strains depended more on respiration. This trait was associated with a single nucleotide polymorphism in a conserved region of Pyk1, the sole pyruvate kinase in fission yeast. This variant reduced Pyk1 activity and glycolytic flux. Replacing the "low-activity" pyk1 allele in the laboratory strain with the "high-activity" allele was sufficient to increase fermentation and decrease respiration. This metabolic rebalancing triggered systems-level adjustments in the transcriptome and proteome and in cellular traits, including increased growth and chronological lifespan but decreased resistance to oxidative stress. Thus, low Pyk1 activity does not lead to a growth advantage but to stress tolerance. The genetic tuning of glycolytic flux may reflect an adaptive trade-off in a species lacking pyruvate kinase isoforms.

Gender-specific changes in energy metabolism and protein degradation as major pathways affected in livers of mice treated with ibuprofen

Ibuprofen, an inhibitor of prostanoid biosynthesis, is a common pharmacological agent used for the management of pain, inflammation and fever. However, the chronic use of ibuprofen at high doses is associated with increased risk for cardiovascular, renal, gastrointestinal and liver injuries. The underlying mechanisms of ibuprofen-mediated effects on liver remain unclear. To determine the mechanisms and signaling pathways affected by ibuprofen (100 mg/kg/day for seven days), we performed proteomic profiling of male mice liver with quantitative liquid chromatography tandem mass spectrometry (LC-MS/MS) using ten-plex tandem mass tag (TMT) labeling. More than 300 proteins were significantly altered between the control and ibuprofen-treated groups. The data suggests that several major pathways including (1) energy metabolism, (2) protein degradation, (3) fatty acid metabolism and (4) antioxidant system are altered in livers from ibuprofen treated mice. Independent validation of protein changes in energy metabolism and the antioxidant system was carried out by Western blotting and showed sex-related differences. Proteasome and immunoproteasome activity/expression assays showed ibuprofen induced gender-specific proteasome and immunoproteasome dysfunction in liver. The study observed multifactorial gender-specific ibuprofen-mediated effects on mice liver and suggests that males and females are affected differently by ibuprofen.

Laboratory Approach to Hemolytic Anemia

Hemolytic anemias are a group of disorders with varied clinical and molecular heterogeneity. They are characterized by decreased levels of circulating erythrocytes in blood. The pathognomic finding is a reduced red cell life span with severe anemia or, compensated hemolysis accompanied by reticulocytosis. The diagnostic workup or laboratory approach for hemolytic anemias is based on methodical step-wise testing which includes red blood cell morphology, hematological indices with increased reticulocyte count along with clinical features of hemolytic anemias. If conventional laboratory tests are unable to detect the underlying cause of hemolysis, genetic testing is recommended. Sanger sequencing along with conventional testing is the most efficient way to diagnose the underlying genetic causes, especially in thalassemias/hemoglobinopathies, if required. However, hemolytic anemias being highly heterogeneous disorders, next-generation sequencing-based screening is rapidly becoming an efficient way to decipher the etiologies where common causes have been excluded.

Pyruvate kinase genes in grass carp Ctenopharyngodon idella: molecular characterization, expression patterns, and effects of dietary carbohydrate levels

To explore features of carbohydrate metabolism and evolution of carbohydrate metabolism-associated genes in herbivorous fishes, the open reading frames (ORF) of PKL, PKMa, and PKMb genes of grass carp (Ctenopharyngodon idella) were obtained, encoding 538, 528, and 532 amino acids, respectively. Comparative genomic analysis showed that adjacent PK genes were highly conserved between fish and mammals. Gene expression profiles were quite different between the three PK genes in tissues and at developmental stages. PKL, PKMa, and PKMb had the highest expression levels in the liver, heart, and muscle, respectively. During embryogenesis, high expression levels of PKMa and PKMb were detected in unfertilized and fertilized eggs. Following a non-expression period, PKMa and PKMb exhibited high expressions again after the hatching stage. In contrast, PKL transcripts could not be detected in early developmental stages, and expression levels continued to increase from the hatching stage to 144 h post hatching. After the 8-week feeding trial with 18%, 30%, and 42% dietary carbohydrate levels, the concentrations of glucose and insulin in serum, pyruvate kinase enzymes, and gene expression levels in brain, muscle, and liver tissues all increased with the increase in carbohydrate levels in the diets. Furthermore, high carbohydrate levels (30% and 42% carbohydrate diets) had a greater effect on grass carp growth. This indicated that PKL, PKMa, and PKMb genes were not only very important in catalytic enzymes, which can be up-regulated by high carbohydrate dietary conditions, but also exhibited a complex and detailed division of labor in different tissues and developmental stages.