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Respiratory Medicine Jun 2013Pulse oximetry has revolutionized the ability to monitor oxygenation in a continuous, accurate, and non-invasive fashion. Despite its ubiquitous use, it is our... (Review)
Review
Pulse oximetry has revolutionized the ability to monitor oxygenation in a continuous, accurate, and non-invasive fashion. Despite its ubiquitous use, it is our impression and supported by studies that many providers do not know the basic principles behind its mechanism of function. This knowledge is important because it provides the conceptual basis of appreciating its limitations and recognizing when pulse oximeter readings may be erroneous. In this review, we discuss how pulse oximeters are able to distinguish oxygenated hemoglobin from deoxygenated hemoglobin and how they are able to recognize oxygen saturation only from the arterial compartment of blood. Based on these principles, we discuss the various conditions that can cause spurious readings and the mechanisms underlying them.
Topics: Diagnostic Errors; Fetal Hemoglobin; Hemoglobins, Abnormal; Humans; Oximetry; Oxygen; Oxyhemoglobins; Partial Pressure
PubMed: 23490227
DOI: 10.1016/j.rmed.2013.02.004 -
Medicine Nov 2021β-thalassemia is a hereditary hematological disease caused by over 350 mutations in the β-globin gene (HBB). Identifying the genetic variants affecting fetal... (Review)
Review
β-thalassemia is a hereditary hematological disease caused by over 350 mutations in the β-globin gene (HBB). Identifying the genetic variants affecting fetal hemoglobin (HbF) production combined with the α-globin genotype provides some prediction of disease severity for β-thalassemia. However, the generation of an additive composite genetic risk score predicts prognosis, and guide management requires a larger panel of genetic modifiers yet to be discovered.Presently, using data from prior clinical trials guides the design of further research and academic studies based on gene augmentation, while fundamental insights into globin switching and new technology developments have inspired the investigation of novel gene therapy approaches.Genetic studies have successfully characterized the causal variants and pathways involved in HbF regulation, providing novel therapeutic targets for HbF reactivation. In addition to these HBB mutation-independent strategies involving HbF synthesis de-repression, the expanding genome editing toolkit provides increased accuracy to HBB mutation-specific strategies encompassing adult hemoglobin restoration for personalized treatment of hemoglobinopathies. Allogeneic hematopoietic stem cell transplantation was, until very recently, the curative option available for patients with transfusion-dependent β-thalassemia. Gene therapy currently represents a novel therapeutic promise after many years of extensive preclinical research to optimize gene transfer protocols.We summarize the current state of developments in the molecular genetics of β-thalassemia over the last decade, including the mechanisms associated with ineffective erythropoiesis, which have also provided valid therapeutic targets, some of which have been shown as a proof-of-concept.
Topics: Fetal Hemoglobin; Gene Editing; Hemoglobinopathies; Humans; Molecular Biology; beta-Thalassemia
PubMed: 34766559
DOI: 10.1097/MD.0000000000027522 -
Blood Reviews Nov 2022Sickle cell disease is a very variable condition, with outcomes ranging from death in childhood to living relatively symptom free into the 8 decade. Much of this... (Review)
Review
Sickle cell disease is a very variable condition, with outcomes ranging from death in childhood to living relatively symptom free into the 8 decade. Much of this variability is unexplained. The co-inheritance of α thalassaemia and factors determining HbF levels significantly modify the phenotype, but few other significant genetic variants have been identified, despite extensive studies. Environmental factors are undoubtedly important, with socio-economics and access to basic medical care explaining the huge differences in outcomes between many low- and high-income countries. Exposure to cold and windy weather seems to precipitate acute complications in many people, although these effects are unpredictable and vary with geography. Many studies have tried to identify prognostic factors which can be used to predict outcomes, particularly when applied in infancy. Overall, low haemoglobin, low haemoglobin F percentage and high reticulocytes in childhood are associated with worse outcomes, although again these effects are fairly weak and inconsistent.
Topics: Humans; Fetal Hemoglobin; Anemia, Sickle Cell; Reticulocytes
PubMed: 35750558
DOI: 10.1016/j.blre.2022.100983 -
The New England Journal of Medicine Jan 2021Sickle cell disease is characterized by hemolytic anemia, pain, and progressive organ damage. A high level of erythrocyte fetal hemoglobin (HbF) comprising α- and... (Clinical Trial)
Clinical Trial
BACKGROUND
Sickle cell disease is characterized by hemolytic anemia, pain, and progressive organ damage. A high level of erythrocyte fetal hemoglobin (HbF) comprising α- and γ-globins may ameliorate these manifestations by mitigating sickle hemoglobin polymerization and erythrocyte sickling. is a repressor of γ-globin expression and HbF production in adult erythrocytes. Its down-regulation is a promising therapeutic strategy for induction of HbF.
METHODS
We enrolled patients with sickle cell disease in a single-center, open-label pilot study. The investigational therapy involved infusion of autologous CD34+ cells transduced with the BCH-BB694 lentiviral vector, which encodes a short hairpin RNA (shRNA) targeting mRNA embedded in a microRNA (shmiR), allowing erythroid lineage-specific knockdown. Patients were assessed for primary end points of engraftment and safety and for hematologic and clinical responses to treatment.
RESULTS
As of October 2020, six patients had been followed for at least 6 months after receiving BCH-BB694 gene therapy; median follow-up was 18 months (range, 7 to 29). All patients had engraftment, and adverse events were consistent with effects of the preparative chemotherapy. All the patients who could be fully evaluated achieved robust and stable HbF induction (percentage HbF/(F+S) at most recent follow-up, 20.4 to 41.3%), with HbF broadly distributed in red cells (F-cells 58.9 to 93.6% of untransfused red cells) and HbF per F-cell of 9.0 to 18.6 pg per cell. Clinical manifestations of sickle cell disease were reduced or absent during the follow-up period.
CONCLUSIONS
This study validates BCL11A inhibition as an effective target for HbF induction and provides preliminary evidence that shmiR-based gene knockdown offers a favorable risk-benefit profile in sickle cell disease. (Funded by the National Institutes of Health; ClinicalTrials.gov number, NCT03282656).
Topics: Adolescent; Adult; Anemia, Sickle Cell; Child; Down-Regulation; Female; Fetal Hemoglobin; Gene Knockdown Techniques; Genetic Therapy; Genetic Vectors; Humans; Male; Pilot Projects; RNA Interference; RNA, Small Interfering; Repressor Proteins; Transplantation, Autologous; Young Adult; gamma-Globins
PubMed: 33283990
DOI: 10.1056/NEJMoa2029392 -
Nature Genetics Jul 2023Inducing fetal hemoglobin (HbF) in red blood cells can alleviate β-thalassemia and sickle cell disease. We compared five strategies in CD34 hematopoietic stem and...
Inducing fetal hemoglobin (HbF) in red blood cells can alleviate β-thalassemia and sickle cell disease. We compared five strategies in CD34 hematopoietic stem and progenitor cells, using either Cas9 nuclease or adenine base editors. The most potent modification was adenine base editor generation of γ-globin -175A>G. Homozygous -175A>G edited erythroid colonies expressed 81 ± 7% HbF versus 17 ± 11% in unedited controls, whereas HbF levels were lower and more variable for two Cas9 strategies targeting a BCL11A binding motif in the γ-globin promoter or a BCL11A erythroid enhancer. The -175A>G base edit also induced HbF more potently than a Cas9 approach in red blood cells generated after transplantation of CD34 hematopoietic stem and progenitor cells into mice. Our data suggest a strategy for potent, uniform induction of HbF and provide insights into γ-globin gene regulation. More generally, we demonstrate that diverse indels generated by Cas9 can cause unexpected phenotypic variation that can be circumvented by base editing.
Topics: Mice; Animals; gamma-Globins; Gene Editing; Fetal Hemoglobin; Anemia, Sickle Cell; Antigens, CD34; beta-Thalassemia
PubMed: 37400614
DOI: 10.1038/s41588-023-01434-7 -
Nature Oct 2022Around birth, globin expression in human red blood cells (RBCs) shifts from γ-globin to β-globin, which results in fetal haemoglobin (HbF, αγ) being gradually...
Around birth, globin expression in human red blood cells (RBCs) shifts from γ-globin to β-globin, which results in fetal haemoglobin (HbF, αγ) being gradually replaced by adult haemoglobin (HbA, αβ). This process has motivated the development of innovative approaches to treat sickle cell disease and β-thalassaemia by increasing HbF levels in postnatal RBCs. Here we provide therapeutically relevant insights into globin gene switching obtained through a CRISPR-Cas9 screen for ubiquitin-proteasome components that regulate HbF expression. In RBC precursors, depletion of the von Hippel-Lindau (VHL) E3 ubiquitin ligase stabilized its ubiquitination target, hypoxia-inducible factor 1α (HIF1α), to induce γ-globin gene transcription. Mechanistically, HIF1α-HIF1β heterodimers bound cognate DNA elements in BGLT3, a long noncoding RNA gene located 2.7 kb downstream of the tandem γ-globin genes HBG1 and HBG2. This was followed by the recruitment of transcriptional activators, chromatin opening and increased long-range interactions between the γ-globin genes and their upstream enhancer. Similar induction of HbF occurred with hypoxia or with inhibition of prolyl hydroxylase domain enzymes that target HIF1α for ubiquitination by the VHL E3 ubiquitin ligase. Our findings link globin gene regulation with canonical hypoxia adaptation, provide a mechanism for HbF induction during stress erythropoiesis and suggest a new therapeutic approach for β-haemoglobinopathies.
Topics: Humans; Chromatin; Fetal Hemoglobin; gamma-Globins; Hypoxia; Prolyl Hydroxylases; Proteasome Endopeptidase Complex; RNA, Long Noncoding; Ubiquitin; Ubiquitin-Protein Ligases; Erythropoiesis
PubMed: 36224385
DOI: 10.1038/s41586-022-05312-w -
Blood Advances Dec 2022The fetal-to-adult hemoglobin transition is clinically relevant because reactivation of fetal hemoglobin (HbF) significantly reduces morbidity and mortality associated...
The fetal-to-adult hemoglobin transition is clinically relevant because reactivation of fetal hemoglobin (HbF) significantly reduces morbidity and mortality associated with sickle cell disease (SCD) and β-thalassemia. Most studies on the developmental regulation of the globin genes, including genome-wide genetics screens, have focused on DNA binding proteins, including BCL11A and ZBTB7A/LRF and their cofactors. Our understanding of RNA binding proteins (RBPs) in this process is much more limited. Two RBPs, LIN28B and IGF2BP1, are known posttranscriptional regulators of HbF production, but a global view of RBPs is still lacking. Here, we carried out a CRISPR/Cas9-based screen targeting RBPs harboring RNA methyltransferase and/or RNA recognition motif (RRM) domains and identified RNA binding motif 12 (RBM12) as a novel HbF suppressor. Depletion of RBM12 induced HbF expression and attenuated cell sickling in erythroid cells derived from patients with SCD with minimal detrimental effects on cell maturation. Transcriptome and proteome profiling revealed that RBM12 functions independently of major known HbF regulators. Enhanced cross-linking and immunoprecipitation followed by high-throughput sequencing revealed strong preferential binding of RBM12 to 5' untranslated regions of transcripts, narrowing down the mechanism of RBM12 action. Notably, we pinpointed the first of 5 RRM domains as essential, and, in conjunction with a linker domain, sufficient for RBM12-mediated HbF regulation. Our characterization of RBM12 as a negative regulator of HbF points to an additional regulatory layer of the fetal-to-adult hemoglobin switch and broadens the pool of potential therapeutic targets for SCD and β-thalassemia.
Topics: Adult; Humans; Fetal Hemoglobin; beta-Thalassemia; Cell Line, Tumor; DNA-Binding Proteins; Transcription Factors; Anemia, Sickle Cell; RNA-Binding Proteins
PubMed: 35622975
DOI: 10.1182/bloodadvances.2022007904 -
Neonatology 2022Concentration of fetal hemoglobin (HbFc) in human neonates determines oxygen-carrying capacity of blood and the position of oxyhemoglobin dissociation curve....
INTRODUCTION
Concentration of fetal hemoglobin (HbFc) in human neonates determines oxygen-carrying capacity of blood and the position of oxyhemoglobin dissociation curve. Near-infrared spectroscopy enables the measurement of regional cerebral tissue oxygen saturation (rScO2) and in combination with measurements of pulsatile arterial oxygen saturation (SpO2), the calculation of cerebral fractional tissue oxygen extraction (cFTOE).
METHODS
We aimed to investigate the impact of HbFc on rScO2, cFTOE, and SpO2 in preterm and term neonates during the first 15 min after birth. Blood analyses provided total blood hemoglobin (Hb) and HbFc measurements. Correlations between HbFc, Hb and rScO2, cFTOE, and SpO2 in each minute were analyzed.
RESULTS
Ninety term and 19 preterm neonates without medical support were included. HbFc was significantly higher in preterm neonates, whereas there were no significant differences in Hb between the groups. In preterm neonates, we found positive correlations of both HbFc and Hb with rScO2 and negative correlations of HbFc and Hb with cFTOE in the first minutes after birth. In contrast, there were no significant correlations between the same parameters in term neonates. Correlations between HbFc or Hb and SpO2 were either insignificant, negligible, or very low in both groups.
DISCUSSION/CONCLUSION
In preterm neonates, higher HbFc was associated with higher rScO2 and lower cFTOE in the first minutes after birth. This phenomenon could not be confirmed in term neonates and might reflect immature autoregulation of oxygen delivery to the brain or lower oxygen consumption in preterm neonates in the first minutes of immediate postnatal transition.
Topics: Brain; Cerebrovascular Circulation; Fetal Hemoglobin; Humans; Infant, Newborn; Infant, Premature; Oximetry; Oxygen; Oxyhemoglobins
PubMed: 35882188
DOI: 10.1159/000525847 -
Nature Genetics Jun 2022The mechanisms by which the fetal-type β-globin-like genes HBG1 and HBG2 are silenced in adult erythroid precursor cells remain a fundamental question in human biology...
The mechanisms by which the fetal-type β-globin-like genes HBG1 and HBG2 are silenced in adult erythroid precursor cells remain a fundamental question in human biology and have therapeutic relevance to sickle cell disease and β-thalassemia. Here, we identify via a CRISPR-Cas9 genetic screen two members of the NFI transcription factor family-NFIA and NFIX-as HBG1/2 repressors. NFIA and NFIX are expressed at elevated levels in adult erythroid cells compared with fetal cells, and function cooperatively to repress HBG1/2 in cultured cells and in human-to-mouse xenotransplants. Genomic profiling, genome editing and DNA binding assays demonstrate that the potent concerted activity of NFIA and NFIX is explained in part by their ability to stimulate the expression of BCL11A, a known silencer of the HBG1/2 genes, and in part by directly repressing the HBG1/2 genes. Thus, NFI factors emerge as versatile regulators of the fetal-to-adult switch in β-globin production.
Topics: Animals; Carrier Proteins; Erythroid Cells; Fetal Hemoglobin; Gene Editing; Mice; NFI Transcription Factors; Transcription Factors; beta-Globins; gamma-Globins
PubMed: 35618846
DOI: 10.1038/s41588-022-01076-1 -
Seminars in Hematology Apr 2018Fetal hemoglobin (HbF) inhibits the root cause of sickle pathophysiology, sickle hemoglobin polymerization. Individuals who naturally express high levels of HbF beyond... (Review)
Review
Fetal hemoglobin (HbF) inhibits the root cause of sickle pathophysiology, sickle hemoglobin polymerization. Individuals who naturally express high levels of HbF beyond infancy thus receive some protection from sickle complications. To mimic this natural genetic experiment using drugs, one guiding observation was that HbF is increased during recovery of bone marrow from extreme stress. This led to evaluation and approval of the cytotoxic (cell killing) drug hydroxyurea to treat sickle cell disease. Cytotoxic approaches are limited in potency and sustainability, however, since they require hematopoietic reserves sufficient to repeatedly mount recoveries from stress that destroys their counterparts, and such reserves are finite. HbF induction even by stress ultimately involves chromatin remodeling of the gene for HbF (HBG), therefore, a logical alternative approach is to directly inhibit epigenetic enzymes that repress HBG-implicated enzymes include DNA methyltransferase 1, histone deacetylases, lysine demethylase 1, protein arginine methyltransferase 5, euchromatic histone lysine methyltransferase 2 and chromodomain helicase DNA-binding protein 4. Clinical proof-of-principle that this alternative, noncytotoxic approach can generate substantial HbF and total hemoglobin increases has already been generated. Thus, with continued careful attention to fundamental biological and pharmacologic considerations (reviewed herein), there is potential that rational, molecular-targeted, safe and highly potent disease-modifying therapy can be realized for patients with sickle cell disease, with the accessibility and cost-effective properties needed for world-wide effect.
Topics: Antineoplastic Agents; Epigenomics; Fetal Hemoglobin; Humans; Hydroxyurea; Transcription Factors
PubMed: 29958562
DOI: 10.1053/j.seminhematol.2018.04.008