Increased Hemoglobin Oxygen Affinity With 5-Hydroxymethylfurfural Supports Cardiac Function During Severe Hypoxia

Effects of drugs on the oxygen dissociation curve-a scoping review

PURPOSE

The shape and position of the hemoglobin-oxygen dissociation curve (ODC) is of critical importance in medicine, as it determines the uptake of O2 in the lungs and the delivery of O2 to the tissues. Numerous reports have identified affinity-modulating effects of drugs in humans. Such effects may be relevant to conditions such as pulmonary diffusion disorders, peripheral vascular disease, or coronary artery disease. The aim of this scoping review was to assess and summarize the current evidence on these effects.

METHODS

The review was based on the PRISMA-ScR guidelines. We searched PubMed and the Cochrane Library and only included papers with free full-text access. The search covers all papers published before September 2024 and used the following keywords: "Oxygen affinity" or "oxygen dissociation curve" in combination with > 100 substance classes that should cover most drugs in clinical use.

RESULTS

The search returned 2447 hits of which 80 were selected for further full text review. In terms of discipline, cardiology accounted for the largest proportion, and in terms of effect quality, a right-ward shift resulting in improved tissue oxygenation was most common. For example, quantitative data show an increase in P50 of 6.1-12.4% and 25-53% for propranolol and RSR13, respectively.

CONCLUSION

Despite a substantial body of data, the effects of the vast majority of drugs on the ODC have not been studied or have not been studied in sufficient detail. The undeniable potential for medical interventions to alter the ODC calls for revival of this area of research.

Hemoglobin Variants as Targets for Stabilizing Drugs

Hemoglobin is an oxygen-transport protein in red blood cells that interacts with multiple ligands, e.g., oxygen, carbon dioxide, carbon monoxide, and nitric oxide. Genetic variations in hemoglobin chains, such as those underlying sickle cell disease and thalassemias, present substantial clinical challenges. Here, we review the progress in research, including the use of allosteric modulators, pharmacological chaperones, and antioxidant treatments, which has begun to improve hemoglobin stability and oxygen affinity. According to UniProt (as of 7 August 2024), 819 variants of the α-hemoglobin subunit and 771 variants of the β-hemoglobin subunit have been documented, with over 116 classified as unstable. These data demonstrate the urgent need to develop variant-specific stabilizing options. Beyond small-molecule drugs/binders, novel protein-based strategies-such as engineered hemoglobin-binding proteins (including falcilysin, llama-derived nanobodies, and α-hemoglobin-stabilizing proteins)-offer promising new options. As our understanding of hemoglobin's structural and functional diversity grows, so does the potential for genotype-driven approaches. Continued research into hemoglobin stabilization and ligand-binding modification may yield more precise, effective treatments and pave the way toward effective strategies for hemoglobinopathies.

Effect of Hb conformational changes on oxygen transport physiology

Red blood cells (RBCs) are the primary mediators of oxygen transport in the human body, and their function is mainly achieved through conformational changes of hemoglobin (Hb). Hb is a tetramer composed of four subunits, with HbA being the predominant Hb in healthy adults, existing in two forms: tense state (T state) and relaxed state (R state). Endogenous regulators of Hb conformation include 2,3-diphosphoglyceric acid, carbon dioxide, protons, and chloride ions, while exogenous regulators include inositol hexaphosphate, inositol tripyrophosphate, benzabate, urea derivative L35, and vanillin, each with different mechanisms of action. The application of Hb conformational regulators provides new insights into the study of hypoxia oxygen supply issues and the treatment of sickle cell disease.

High-molecular-weight linear polymers improve microvascular perfusion after extracorporeal circulation

High-molecular-weight linear polymers (HMWLPs) have earned the name "drag-reducing polymers" because of their ability to reduce drag in turbulent flows. Recently, these polymers have become popular in bioengineering applications. This study investigated whether the addition of HMWLP in a venoarterial extracorporeal circulation (ECC) model could improve microvascular perfusion and oxygenation. Golden Syrian hamsters were instrumented with a dorsal skinfold window chamber and subjected to ECC using a circuit comprised of a peristaltic pump and a bubble trap. The circuit was primed with lactated Ringer solution (LR) containing either 5 ppm of polyethylene glycol (PEG) with a low molecular weight of 500 kDa (PEG500k) or 5 ppm of PEG with a high molecular weight of 3,500 kDa (PEG3500k). After 90 min of ECC at 15% of the animal's cardiac output, the results showed that the addition of PEG3500k to LR improved microvascular blood flow in arterioles and venules acutely (2 h after ECC), whereas functional capillary density showed improvement up to 24 h after ECC. Similarly, PEG3500k improved venular hemoglobin O2 saturation on the following day after ECC. The serum and various excised organs all displayed reduced inflammation with the addition of PEG3500k, and several of these organs also had a reduction in markers of damage with the HMWLPs compared to LR alone. These promising results suggest that the addition of small amounts of PEG3500k can help mitigate the loss of microcirculatory function and reduce the inflammatory response from ECC procedures.NEW & NOTEWORTHY High-molecular-weight linear polymers have gained traction in bioengineering applications. The addition of PEG3500k to lactated Ringer solution (LR) improved microvascular blood flow in arterioles and venules acutely after extracorporeal circulation (ECC) in a hamster model and improved functional capillary density up to 24 h after ECC. PEG3500k improved venular hemoglobin O2 saturation and oxygen delivery acutely after ECC and reduced inflammation in various organs compared to LR alone.

X-ray crystallography and sickle cell disease drug discovery-a tribute to Donald Abraham

X-ray crystallography and structure-based drug discovery have played a major role in the discovery of antisickling agents that target hemoglobin (Hb) for the treatment of sickle cell disease (SCD). Sickle cell disease, the most common inherited hematologic disorder, occurs as a result of a single point mutation of βGlu6 in normal human adult hemoglobin (HbA) to βVal6 in sickle hemoglobin (HbS). The disease is characterized by polymerization of HbS and sickling of red blood cells (RBCs), leading to several secondary pathophysiologies, including but not limited to vaso-occlusion, hemolytic anemia, oxidative stress, inflammation, stroke, pain crisis, and organ damage. Despite the fact that SCD was the first disease to have its molecular basis established, the development of therapies was for a very long time a challenge and took several decades to find therapeutic agents. The determination of the crystal structure of Hb by Max Perutz in the early 60s, and the pioneering X-ray crystallography research by Donald J. Abraham in the early 80s, which resulted in the first structures of Hb in complex with small molecule allosteric effectors of Hb, gave much hope that structure-based drug discovery (SBDD) could be used to accelerate development of antisickling drugs that target the primary pathophysiology of hypoxia-induced HbS polymerization to treat SCD. This article, which is dedicated to Donald J. Abraham, briefly reviews structural biology, X-ray crystallography and structure-based drug discovery from the perspective of Hb. The review also presents the impact of X-ray crystallography in SCD drug development using Hb as a target, emphasizing the major and important contributions by Don Abraham in this field.

Solid-Phase Polymerization Using Anion-Exchange Resin Can Almost Completely Crosslink Hemoglobin to Prepare Hemoglobin-Based Oxygen Carriers

Introduction

A limitation of hemoglobin-based oxygen carriers (HBOCs) as oxygen therapeutics is unpolymerized hemoglobin, which induces vasoconstriction leading to hypertension. The removal of unpolymerized hemoglobin from polymerized hemoglobin (PolyHb) is complex, expensive, and time-consuming.

Methods

Herein, we developed a method to completely polymerize hemoglobin almost without unpolymerized hemoglobin. Hemoglobin was adsorbed on the anion-exchange resin Q Sepharose Fast Flow or DEAE Sepharose Fast Flow, and acetal, a crosslinker prepared from glutaraldehyde and ethylene glycol, was employed to polymerize the hemoglobin. The polymerization conditions, including reaction time, pH, resin type, and molar ratios of glutaraldehyde to ethylene glycol and hemoglobin to acetal, were optimized. The blood pressure and blood gas of mice injected with PolyHb were monitored as well.

Results

The optimal polymerization condition of PolyHb was when the molar ratio of glutaraldehyde to ethylene glycol was 1:20, and the molar ratio of 10 mg/mL hemoglobin adsorbed on anion-exchange resin to glutaraldehyde was 1:300 for 60 min. Under optimized reactive conditions, hemoglobin was almost completely polymerized, with <1% hemoglobin remaining unpolymerized, and the molecular weight of PolyHb was more centrally distributed. Furthermore, hypertension was not induced in mice by PolyHb, and there were also no pathological changes observed in arterial oxygen, blood gas, electrolytes, and some metabolic indicators.

Conclusion

The findings of this study indicate that the use of solid-phase polymerization and acetal is a highly effective and innovative approach to HBOCs, resulting in the almost completely polymerized hemoglobin. These results offer promising implications for the development of new methods for preparing HBOCs.

The oxygen dissociation curve of blood in COVID-19-An update

An impressive effect of the infection with SARS-Co-19 is the impairment of oxygen uptake due to lung injury. The reduced oxygen diffusion may potentially be counteracted by an increase in oxygen affinity of hemoglobin. However, hypoxia and anemia associated with COVID-19 usually decrease oxygen affinity due to a rise in [2,3-bisphosphoglycerate]. As such, COVID-19 related changes in the oxygen dissociation curve may be critical for oxygen uptake and supply, but are hard to predict. A Pubmed search lists 14 publications on oxygen affinity in COVID-19. While some investigations show no changes, three large studies found an increased affinity that was related to a good prognosis. Exact causes remain unknown. The cause of the associated anemia in COVID-19 is under discussion. Erythrocytes with structural alterations of membrane and cytoskeleton have been observed, and virus binding to Band 3 and also to ACE2 receptors in erythroblasts has been proposed. COVID-19 presentation is moderate in many subjects suffering from sickle cell disease. A possible explanation is that COVID-19 counteracts the unfavorable large right shift of the oxygen dissociation curve in these patients. Under discussion for therapy are mainly affinity-increasing drugs.

Influence of cigarettes on myocardial injury in healthy population after exposure to high altitude over 5000 m

BACKGROUND

Myocardial injury (MI) is a severe complication once subjected to hypoxic condition at high altitude. Little evidence exists about the association of cigarettes and MI at high altitude, especially over 5000 m. In the present study, we intend to explore the influence of cigarettes on MI in healthy population after travelling to this extreme environment.

METHODS

Physical examination was performed in population at Pamirs plateau during November and December 2020. All participants were divided into cigarette group or control group. MI was diagnosed based on lactate dehydrogenase (LDH), creatine kinase (CK), creatine kinase isoenzymes (CK-MB) and aspartate amino transferase (AST).

RESULTS

311 people were included, 58 of whom developed MI, accounting for 18.6 %. Participants in cigarette group were all male, and younger than those in control group. There was longer exposure time in cigarette group. Compared with control group, red blood cell counting, hemoglobin (HGB) and hematocrit in cigarette group were significantly increased, while heart rate was significantly decreased. Cigarettes were found to significantly upregulate the level of CK-MB and LDH. After adjustment with age, sex, body mass index, altitude and exposure time as covariables, 108 male participants remained in each group, showing that none of clinical indexes had significant difference between the two groups. Logistic regression analysis revealed that female sex and oxygen saturation (SO₂) were independent risk factors for MI in non-smokers while HGB was independent risk factor in smokers. By using Spearman correlation analysis, four myocardial enzymes were not relevant with the level of SO₂ in non-smokers. For smokers, HGB was found to be in significant positive correlation with LDH.

CONCLUSION

Our study suggested that exposure to high altitude over 5000 m could abrogate the impact of cigarettes on MI in healthy population. The independent factors affecting the occurrence of MI were distinctive depending on current smoking status.

Muscle oxygenation during normoxic and hypoxic cycling exercise in humans with high affinity haemoglobin

NEW FINDINGS

What is the central question of this study? Do humans with high affinity haemoglobin (HAH) demonstrate attenuated skeletal muscle deoxygenation during normoxic and hypoxic exercise? What is the main finding and its importance? Examination of NIRS-derived muscle oxygenation profiles suggests that fractional oxygen extraction is blunted during hypoxic exercise in humans with HAH compared to controls. However, muscle tissue oxygen saturation levels were higher in humans with HAH during exercise in normoxia compared to controls. These alterations in fractional oxygen extraction in humans with HAH may influence blood flow regulation and exercise capacity during hypoxia.

ABSTRACT

Recently, our lab has shown that humans with genetic mutations resulting in high affinity haemoglobin (HAH) demonstrate better maintained aerobic capacity and peak power output during hypoxic exercise versus normoxic exercise compared to humans with normal affinity haemoglobin. However, the influence of HAH on tissue oxygenation within exercising muscle during normoxia and hypoxia is unknown. Therefore, we examined near-infrared spectroscopy (NIRS)-derived oxygenation profiles of the vastus lateralis during graded cycling exercise in normoxia and hypoxia among humans with HAH (n = 5) and controls with normal affinity haemoglobin (n = 12). The HAH group elicited a blunted increase of deoxygenated haemoglobin+myoglobin during hypoxic exercise compared to the control group (P = 0.03), suggesting reduced fractional oxygen extraction in the HAH group. In addition, the HAH group maintained a higher level of muscle tissue oxygen saturation during normoxic exercise (HAH, 75 ± 4% vs. controls, 65 ± 3%, P = 0.049) and there were no differences between groups in muscle tissue oxygen saturation during hypoxic exercise (HAH, 68 ± 3% vs. controls, 68 ± 2%, P = 0.943). Overall, our results suggest that humans with HAH may demonstrate divergent patterns of fractional oxygen extraction during hypoxic exercise and elevated muscle tissue oxygenation during normoxic exercise compared to controls. This article is protected by copyright. All rights reserved.

Comprehensive Metabolomics and Network Pharmacology to Explore the Mechanism of 5-Hydroxymethyl Furfural in the Treatment of Blood Deficiency Syndrome

Radix Rehmanniae (RR, from Radix Rehmanniae (Gaertn.) DC.) is a natural medicine used in traditional Chinese medicine (TCM) since ancient times for the treatment of blood disorders. RR is steamed to get Rehmanniae Radix Praeparata (RP), which has a tonic effect on blood; the content of 5-hydromethylfurfural (5-HMF) increases more than four times after steaming. Studies have shown that 5-HMF has positive pharmacological effects on cardiovascular and hematological disorders. This study aimed to explore and verify the impact of 5-HMF on rats with chemotherapy-induced blood deficiency syndrome (BDS). Rats were given cyclophosphamide (CP) and acetophenhydrazine (APH) to induce BDS, the coefficients of some organs (liver, spleen, and kidney) were measured, and a routine blood test examined the coefficients of several peripheral blood cells. Metabolomics and network pharmacology were combined to find important biomarkers, targets, and pathways. Western blot was used to detect the expression of CYP17A1 and HSD3B1 proteins in the spleen. All these findings suggested that the 5-HMF significantly increased the number of peripheral blood cells and reversed splenomegaly in rats. In addition, 5-HMF upregulated CYP17A1 and HSD3B1 protein expression in splenic tissues. Also, 5-HMF ameliorated chemotherapy-induced BDS in rats, and its therapeutic mechanism might depend on steroid hormone biosynthesis and other pathways. It acts on blood deficiency via multiple targets and pathways, which is unique to Chinese medicine.

Extracorporeal circulation impairs microcirculation perfusion and organ function

Extracorporeal membrane oxygenation (ECMO) is a procedure used to aid respiratory function in critical patients, involving extracorporeal circulation (ECC) of blood. There is a limited number of studies quantifying the hemodynamic effects of ECC procedures on the microcirculation. We sought to mimic veno-arterial-ECMO flow conditions by use of a scaled-down circuit primed with either lactate Ringer (LR) or 5% human serum albumin (HSA). The circuit was first tested using benchtop runs with blood, and subsequently used for in vivo experiments in Golden Syrian hamsters instrumented with a dorsal window chamber to allow for quantification of microvascular hemodynamics and functional capillary density (FCD). Results showed significant impairment in FCD, and a reduction of arteriolar and venular blood flow, with HSA providing significant higher blood flows and FCD compared with LR. Changes in hematocrit and RBC labeling after ECC reflected a shift in plasma volume, which may stem from a loss in intravascular oncotic pressure due to priming fluids. The distribution of hemoglobin oxygen saturation in the microvasculature showed a significant decrease in venules after ECC. In addition, major organs such as the kidney and heart showed increases in both inflammatory and damage markers. These results suggest that ECC impairs microvasculature function and promotes ischemia and hypoxia in the tissues, which can be vital to understanding comorbid clinical outcomes from ECC procedures such as acute kidney injury and multiorgan dysfunction.NEW & NOTEWORTHY ECC reduces microvascular perfusion, with no full recovery 24 h after ECC. HSA performed better as compared with LR in terms of FCD and venule flow, as well as venule oxygen saturation. Increases in inflammatory and damage markers in key organs were observed within all organs analyzed.

A Lignocellulolytic Colletotrichum sp. OH with Broad-Spectrum Tolerance to Lignocellulosic Pretreatment Compounds and Derivatives and the Efficiency to Produce Hydrogen Peroxide and 5-Hydroxymethylfurfural Tolerant Cellulases

Fungal endophytes are an emerging source of novel traits and biomolecules suitable for lignocellulosic biomass treatment. This work documents the toxicity tolerance of Colletotrichum sp. OH toward various lignocellulosic pretreatment-derived inhibitors. The effects of aldehydes (vanillin, p-hydroxybenzaldehyde, furfural, 5-hydroxymethylfurfural; HMF), acids (gallic, formic, levulinic, and p-hydroxybenzoic acid), phenolics (hydroquinone, p-coumaric acid), and two pretreatment chemicals (hydrogen peroxide and ionic liquid), on the mycelium growth, biomass accumulation, and lignocellulolytic enzyme activities, were tested. The reported Colletotrichum sp. OH was naturally tolerant to high concentrations of single inhibitors like HMF (IC50; 17.5 mM), levulinic acid (IC50; 29.7 mM), hydroquinone (IC50; 10.76 mM), and H2O2 (IC50; 50 mM). The lignocellulolytic enzymes displayed a wide range of single and mixed inhibitor tolerance profiles. The enzymes β-glucosidase and endoglucanase showed H2O2- and HMF-dependent activity enhancements. The enzyme β-glucosidase activity was 34% higher in 75 mM and retained 20% activity in 125 mM H2O2. Further, β-glucosidase activity increased to 24 and 32% in the presence of 17.76 and 8.8 mM HMF. This research suggests that the Colletotrichum sp. OH, or its enzymes, can be used to pretreat plant biomass, hydrolyze it, and remove inhibitory by-products.

High-throughput determination of oxygen dissociation curves in a microplate reader-A novel, quantitative approach

In vitro determination of the hemoglobin oxygen dissociation curve (ODC) requires highly elaborate, specialized, and costly technical equipment. In addition, there is a lack of methods that combine reliable ODC recordings with high throughput in small blood samples for routine analysis. We here introduce a modified, commercial 96-well plate with an integrated unidirectional gas flow system specifically adapted for use in fluorescence microplate readers. Up to 92 samples of whole or hemolyzed, buffered or unbuffered blood, including appropriate controls or internal standard hemoglobin solutions, can be analyzed within ~25 min. Oxygen saturation is measured in each well with dual wavelength spectroscopy, and oxygen partial pressure using fluorescence lifetime of commercial oxygen sensors at the in- and outlet ports of the gas-flow system. Precision and accuracy of this method have been determined and were compared with those of a standard method. We further present two applications that exemplarily highlight the usefulness and impact of this novel approach for clinical diagnostics or basic research.

Increased hemoglobin affinity for oxygen with GBT1118 improves hypoxia tolerance in sickle cell mice

Therapeutic agents that increase the Hb affinity for oxygen (O₂) could, in theory, lead to decreased O₂ release from Hb and impose a hypoxic risk to tissues. In this study, GBT1118, an allosteric modifier of Hb affinity for O₂, was used to assess the impact of increasing Hb affinity for O₂ on brain tissue oxygenation, blood pressure, heart rate, O₂ delivery, and tolerance to hypoxia in Townes transgenic sickle cell disease (SCD) mice. Brain oxygenation and O₂ delivery were studied during normoxia and severe hypoxic challenges. Chronic treatment with GBT1118 increased Hb affinity for O₂, reducing the Po₂ for 50% HbO₂ saturation (P50) in SCD mice from 31 mmHg to 18 mmHg. This treatment significantly reduced anemia, increasing hematocrit by 33%, improved cardiac output (CO), and O₂ delivery and extraction. Chronically increasing Hb affinity for O₂ with GBT1118 preserved cortical O₂ tension during normoxia, improved cortical O₂ tension during hypoxia, and increased tolerance to severe hypoxia in SCD mice. Independent of hematological changes induced by chronic treatment, a single dose of GBT1118 significantly improved tolerance to hypoxia, highlighting the benefits of increasing Hb affinity for O₂ and consequently reducing sickling of RBCs in blood during hypoxia in SCD.NEW & NOTEWORTHY Chronic pharmacologically increased hemoglobin affinity for oxygen in sickle cell disease mice alleviated hematological consequences of sickle cell disease, increasing RBC half-life, hematocrit, and hemoglobin concentration, while also decreasing reticulocyte count. Additionally, chronically increased hemoglobin affinity for oxygen significantly improved survival as well as cortical tissue oxygenation in sickle cell disease mice during hypoxia, suggesting that oxygen delivery and utilization is improved by increased hemoglobin affinity for oxygen.

Safety profile of high molecular weight polymerized hemoglobins

BACKGROUND

Hemoglobin (Hb)-based oxygen (O₂ ) carriers (HBOCs) are being developed as alternatives to red blood cells and blood when these products are unavailable. Clinical trials of previous HBOC generations revealed side effects, including hypertension and vasoconstriction, that were not observed in preclinical studies. Large molecular weight (MW) polymerized bovine Hb (PolybHb) represents a new class of HBOC with promising results. We evaluated the safety profile of PolybHb after an exchange transfusion (ET) in guinea pigs (GPs). This study compares changes in indices of cardiac, inflammatory, and organ function after ET with high (R-state) and low (T-state) O₂ affinity PolybHb with high MW.

STUDY DESIGN AND METHODS

Guinea pigs underwent a 20% ET with PolybHb. To assess the implication of PolybHb ET on the microcirculation, hamsters instrumented with a dorsal window chamber were subjected to a similar volume ET.

RESULTS

T and R-state PolybHb did not induce significant alterations in cardiac function. T-state PolybHb induced mild vasoconstriction shortly after transfusion, while R-state did not have acute effects on microvascular tone.

CONCLUSION

Large MW PolybHbs were found to be safe and efficacious in increasing O₂ carrying capacity and the O₂ affinity of the PolybHb did not affect O₂ delivery or extraction by tissues in relevant preclinical models. In conclusion, these results suggest that both T-state and R-state PolybHb are safe and do not impair O₂ delivery. The results are encouraging and support further evaluation of high MW PolybHbs and their future feasibility compared to allogenic blood in a trauma model.