Heme is a potent inducer of inflammation in mice and is counteracted by heme oxygenase

Maternal social environment shapes yolk testosterone allocation and embryonic neural gene expression in tree swallows

Offspring from females breeding in competitive social environments are often exposed to more testosterone (T) during embryonic development, which can affect traits from growth to behavior in potentially adaptive ways. Despite the important role of maternally derived steroids in shaping offspring development, the molecular mechanisms driving these processes are currently unclear. Here, we use tree swallows (Tachycineta bicolor) to explore the effects of the maternal social environment on yolk T concentrations and genome-wide patterns of neural gene expression in embryos. We measured aggressive interactions among females breeding at variable densities and collected their eggs at two timepoints, including the day laid to measure yolk T concentrations and on embryonic day 11 to measure gene expression in whole brain samples. We found that females breeding in high-density sites experienced elevated rates of physical aggression and their eggs had higher yolk T concentrations. A differential gene expression and weighted gene co-expression network analysis indicated that embryos from high-density sites experienced an upregulation of genes involved in hormone, circulatory, and immune processes, and these gene expression patterns were correlated with yolk T levels and aggression. Genes implicated in neural development were additionally downregulated in embryos from high-density sites. These data highlight how early neurogenomic processes may be affected by the maternal social environment, giving rise to phenotypic plasticity in offspring.

Mild Systemic Inflammation Increases Erythrocyte Fragility

There is growing evidence that inflammation impairs erythrocyte structure and function. We assessed the impact of mild systemic inflammation on erythrocyte fragility in three different settings. In order to investigate causation, erythrocyte osmotic fragility was measured in mice challenged with a live attenuated bacterial strain to induce low-grade systemic inflammation; a significant increase in erythrocyte osmotic fragility was observed. To gather evidence that systemic inflammation is associated with erythrocyte fragility in humans, two observational studies were conducted. First, using a retrospective study design, the relationship between reticulocyte-based surrogate markers of haemolysis and high-sensitivity C-reactive protein was investigated in 9292 healthy participants of the UK Biobank project. Secondly, we prospectively assessed the relationship between systemic inflammation (measured by the urinary neopterin/creatinine ratio) and erythrocyte osmotic fragility in a mixed population (n = 54) of healthy volunteers and individuals with long-term medical conditions. Both human studies were in keeping with a relationship between inflammation and erythrocyte fragility. Taken together, we conclude that mild systemic inflammation increases erythrocyte fragility and may contribute to haemolysis. Further research is needed to assess the molecular underpinnings of this pathway and the clinical implications in inflammatory conditions.

Alpha1-antitrypsin improves survival in murine abdominal sepsis model by decreasing inflammation and sequestration of free heme

Background

Excessive inflammation, hemolysis, and accumulation of labile heme play an essential role in the pathophysiology of multi-organ dysfunction syndrome (MODS) in sepsis. Alpha1-antitrypsin (AAT), an acute phase protein with heme binding capacity, is one of the essential modulators of host responses to inflammation. In this study, we evaluate the putative protective effect of AAT against MODS and mortality in a mouse model of polymicrobial abdominal sepsis.

Methods

Polymicrobial abdominal sepsis was induced in C57BL/6N mice by cecal ligation and puncture (CLP). Immediately after CLP surgery, mice were treated intraperitoneally with three different forms of human AAT-plasma-derived native (nAAT), oxidized nAAT (oxAAT), or recombinant AAT (recAAT)-or were injected with vehicle. Sham-operated mice served as controls. Mouse survival, bacterial load, kidney and liver function, immune cell profiles, cytokines/chemokines, and free (labile) heme levels were assessed. In parallel, in vitro experiments were carried out with resident peritoneal macrophages (MPMΦ) and mouse peritoneal mesothelial cells (MPMC).

Results

All AAT preparations used reduced mortality in septic mice. Treatment with AAT significantly reduced plasma lactate dehydrogenase and s-creatinine levels, vascular leakage, and systemic inflammation. Specifically, AAT reduced intraperitoneal accumulation of free heme, production of cytokines/chemokines, and neutrophil infiltration into the peritoneal cavity compared to septic mice not treated with AAT. In vitro experiments performed using MPMC and primary MPMΦ confirmed that AAT not only significantly decreases lipopolysaccharide (LPS)-induced pro-inflammatory cell activation but also prevents the enhancement of cellular responses to LPS by free heme. In addition, AAT inhibits cell death caused by free heme in vitro.

Conclusion

Data from the septic CLP mouse model suggest that intraperitoneal AAT treatment alone is sufficient to improve sepsis-associated organ dysfunctions, preserve endothelial barrier function, and reduce mortality, likely by preventing hyper-inflammatory responses and by neutralizing free heme.

Immune-Mediated Hemolytic Anemia and Clinically Suspected Acute Pancreatitis in Dogs, a Pilot Study

Acute pancreatitis can be a complication of massive hemolysis, above all when intravascular in nature. Therefore, the aim of this study was to investigate the association between canine immune mediated hemolytic anemia (IMHA) and clinically suspected acute pancreatitis (CSAP) and the role of calculated free plasma hemoglobin (Hbfp) in CSAP occurrence/development. In this cohort study the records of 95 dogs with IMHA and 95 sick dogs with pathologies other than IMHA were compared for CSAP occurrence/development. At presentation, 12/95 dogs with IMHA met criteria for CSAP, while only 3/95 sick control dogs met these criteria (χ2 =1.58, P = .008). Within 7 days of hospitalization 9 additional dogs with IMHA had developed CSAP. The Hbfp was calculated and compared for dogs with IMHA that had/developed CSAP and for those without CSAP. In dogs with IMHA, a calculated Hbfp concentration ≥ 0.08 g/dL resulted in an increased relative risk (RR) of having/developing CSAP (RR = 2.54, 95% CI, 1.51-4.29; P = .003). No significant effect on short-term prognosis in dogs with IMHA was found between those having/developing CSAP and those without CSAP. This study showed that dogs with IMHA have an increased risk of having CSAP and Hbfp concentration may be involved in the pathogenesis of acute pancreatitis.

Management of Bleeding and Hemolysis During Percutaneous Microaxial Flow Pump Support: A Practical Approach

Percutaneous ventricular assist devices (pVADs) are increasingly being used because of improved experience and availability. The Impella (Abiomed), a percutaneous microaxial, continuous-flow, short-term ventricular assist device, requires meticulous postimplantation management to avoid the 2 most frequent complications, namely, bleeding and hemolysis. A standardized approach to the prevention, detection, and treatment of these complications is mandatory to improve outcomes. The risk for hemolysis is mostly influenced by pump instability, resulting from patient- or device-related factors. Upfront echocardiographic assessment, frequent monitoring, and prompt intervention are essential. The precarious hemostatic balance during pVAD support results from the combination of a procoagulant state, due to critical illness and contact pathway activation, together with a variety of factors aggravating bleeding risk. Preventive strategies and appropriate management, adapted to the impact of the bleeding, are crucial. This review offers a guide to physicians to tackle these device-related complications in this critically ill pVAD-supported patient population.

Safety and feasibility of the gene transfer of hemopexin for conditions with increased free heme

Heme is a fundamental molecule for several biological processes, but when released in the extracellular space such as in hemolytic diseases, it can be toxic to cells and tissues. Hemopexin (HPX) is a circulating protein responsible for removing free heme from the circulation, whose levels can be severely depleted in conditions such as sickle cell diseases. Accordingly, increasing HPX levels represents an attractive strategy to mitigate the deleterious effects of heme in these conditions. Gene transfer of liver-produced proteins with adeno-associated virus (AAV) has been shown to be an effective and safety strategy in animal and human studies mainly in hemophilia. Here, we report the feasibility of increasing HPX levels using an AAV8 vector expressing human HPX (hHPX). C57Bl mice were injected with escalating doses of our vector, and expression was assessed by enzyme immunoassay (ELISA), Western blot, and quantitative polymerase chain reaction (qPCR). In addition, the biological activity of transgenic hHPX was confirmed using two different models of heme challenge consisting of serial heme injections or phenylhydrazine-induced hemolysis. Sustained expression of hHPX was confirmed for up to 26 weeks in plasma. Expression was dose-dependent and not associated with clinical signs of toxicity. hHPX levels were significantly reduced by heme infusions and phenylhydrazine-induced hemolysis. No clinical toxicity or laboratory signs of liver damage were observed in preliminary short-term heme challenge studies. Our results confirm that long-term expression of hHPX is feasible and safe in mice, even in the presence of heme overload. Additional studies are needed to explore the effect of transgenic HPX protein in animal models of chronic hemolysis.

Red cell haemolysis secondary to intraosseous (IO) blood transfusion in adult patients with major trauma: a systematic review

INTRODUCTION

Intraosseous (IO) administration of medications and blood products is accepted practice in major trauma when intravenous access is not immediately available. However, there is a concern that the high infusion pressures required for IO transfusion may increase the risk of red cell haemolysis and its associated complications. The aim of this systematic review is to synthesise the existing evidence describing the risks of red cell haemolysis in IO blood transfusion.

METHODS

We undertook a systematic search of MEDLINE, CINAHL and EMBASE using the search terms: "intraosseous transfusion" and "haemolysis". Two authors independently screened abstracts, and reviewed full-text articles against the inclusion criteria. Reference lists of included studies were reviewed and a grey literature search undertaken. Studies were assessed for risk of bias. Inclusion criteria were: all human and animal study types that reported novel data on IO-associated red cell haemolysis. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guideline was used.

RESULTS

Twenty-three abstracts were identified; n=9 full papers met the inclusion criteria. No further studies were identified from reference lists or grey literature. These papers included: seven large animal translational studies, a prospective and a retrospective human study. The overall risk of bias was high. One animal study with good translatability to adult patients with trauma demonstrated haemolysis. Other animal studies had methodological constraints that limit their human applicability. No haemolysis was observed in low-density flat bones (sternum), whereas haemolysis was reported in long bones (humerus, tibia). IO infusion using a three-way tap was associated with haemolysis. Conversely, pressure bag transfusion was not associated with haemolysis, but this method may result in insufficient flow rates for effective resuscitation.

CONCLUSIONS

There is a paucity of high-quality evidence surrounding the risks of red cell haemolysis in IO blood transfusion. However, evidence from one study suggests that the likelihood is increased by use of a three-way tap to administer blood transfusion to young adult male patients with trauma. Further research is needed to address this important clinical question.

PROSPERO REGISTRATION NUMBER

CRD42022318902.

Assessment of total and unbound cell-free heme in plasma of patients with sickle cell disease

Intravascular hemolysis results in the release of cell-free hemoglobin and heme in plasma. In sickle cell disease, the fragility of the sickle red blood cell leads to chronic hemolysis, which can contribute to oxidative damage and activation of inflammatory pathways. The scavenger proteins haptoglobin and hemopexin provide pathways to remove hemoglobin and heme, respectively, from the circulation. Heme also intercalates in membranes of blood cells and endothelial cells in the vasculature and associates with other plasma components such as albumin and lipoproteins. Hemopexin has a much higher affinity and can strip heme from the other pools and detoxify plasma from cell-free circulatory heme. However, due to chronic hemolysis, hemopexin is depleted in individuals with sickle cell disease. Thus, cell-free unbound heme is expected to accumulate in plasma. We developed a methodology for the accurate quantification of the fraction of heme, which is pathologically relevant in sickle cell disease, that does not appear to be sequestered to a plasma compartment. Our data show significant variation in the concentration of unbound heme, and rather unexpectedly, the size of the unbound fraction does not correlate to the degree of hemolysis, as measured by the concentration of bound heme. Very high heme concentrations (>150 µM) were obtained in some plasma with unbound concentrations that were several fold lower than in plasma with much lower hemolysis (<50 µM). These findings underscore the long-term effects of chronic hemolysis on the blood components and of the disruption of the essential equilibrium between release of hemoproteins/heme in the circulation and adaptative response of the scavenging/removal mechanisms. Understanding the clinical implications of this loss of response may provide insights into diagnostic and therapeutic targets in patients with sickle cell disease.

Alloimmunisation against red blood cells in sickle cell disease: transfusion challenges in high-income and low-income countries

Sickle cell disease is the most frequent inherited disorder in sub-Saharan Africa and in many high-income countries (HICs). Transfusion is a key element of treatment, but it results in high rates of alloimmunisation against red blood cell antigens and post-transfusion haemolysis, which can be life-threatening in severe cases. The prevention of alloimmunisation is, therefore, an important issue in both HICs and in low-income countries (LICs). In HICs, the main reason for high alloimmunisation rates is blood group disparity between blood donors, who are mostly of European descent, and the patients, who are mostly of African descent. However, alloimmunisation rates also remain high in sub-Saharan Africa despite the homogeneity of blood group antigen frequencies between donors and patients; this occurrence is probably due to matching strategies limited to ABO blood group and RhD. However, other possible underlying causes of alloimmunisation have also been suggested, with each cause affecting HICs and LICs in different ways-eg, the immunogenetic and inflammatory status of the patient and the characteristics of the red blood cell products. In this Viewpoint, we discuss the available data and hypotheses that potentially account for the association of sickle cell disease with high rates of alloimmunisation in both settings, HICs and LICs (focusing particularly on sub-Saharan Africa), and the challenges faced by HICs and LICs to improve prevention of alloimmunisation.

Hemoglobin increases leukocyte adhesion and initiates lung microvascular endothelial activation via Toll-like receptor 4 signaling

Cell-free hemoglobin is a pathophysiological driver of endothelial injury during sepsis and acute respiratory distress syndrome (ARDS), but the precise mechanisms are not fully understood. We hypothesized that hemoglobin (Hb) increases leukocyte adhesion and endothelial activation in human lung microvascular endothelial cells (HLMVEC). We stimulated primary HLMVEC, or leukocytes isolated from healthy human donors, with Hb (0.5 mg/mL) and found that leukocyte adhesion to lung endothelium in response to Hb is an endothelial-dependent process. Next, we stimulated HLMVEC with Hb over time (1, 3, 6, and 24 h) and found increased transcription and release of inflammatory cytokines (IL-1β, IL-8, and IL-6). In addition, Hb exposure variably upregulated transcription, total protein expression, and cell-surface localization of adhesion molecules E-selectin, P-selectin, intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1). Since VCAM-1 was most upregulated by Hb, we further tested mechanisms for Hb-mediated upregulation of VCAM-1 in HLMVEC. Although upregulation of VCAM-1 was not prevented by hemoglobin scavenger haptoglobin, heme scavenger hemopexin, or inhibition of nod-like receptor protein 3 (NLRP3) signaling, blocking Toll-like receptor 4 (TLR4) with small molecule inhibitor TAK-242 (1 µM) prevented upregulation of VCAM-1 in response to Hb. Consistently, Hb increased nuclear factor-κB (NF-κB) activation and intracellular reactive oxygen species (ROS), which were both prevented by TLR4 inhibition. Together, these data demonstrate that Hb increases leukocyte-endothelial adhesion and activates HLMVEC through TLR4 signaling, indicating a potential mechanism for Hb-mediated pulmonary vascular injury during inflammatory and hemolytic conditions.

Oxidized hemoglobin triggers polyreactivity and autoreactivity of human IgG via transfer of heme

Intravascular hemolysis occurs in diverse pathological conditions. Extracellular hemoglobin and heme have strong pro-oxidative and pro-inflammatory potentials that can contribute to the pathology of hemolytic diseases. However, many of the effects of extracellular hemoglobin and heme in hemolytic diseases are still not well understood. Here we demonstrate that oxidized hemoglobin (methemoglobin) can modify the antigen-binding characteristics of human immunoglobulins. Thus, incubation of polyclonal or some monoclonal human IgG in the presence of methemoglobin results in an appearance of binding reactivities towards distinct unrelated self-proteins, including the protein constituent of hemoglobin i.e., globin. We demonstrate that a transfer of heme from methemoglobin to IgG is indispensable for this acquisition of antibody polyreactivity. Our data also show that only oxidized form of hemoglobin have the capacity to induce polyreactivity of antibodies. Site-directed mutagenesis of a heme-sensitive human monoclonal IgG1 reveals details about the mechanism of methemoglobin-induced antigen-binding polyreactivity. Further here we assess the kinetics and thermodynamics of interaction of a heme-induced polyreactive human antibody with hemoglobin and myoglobin. Taken together presented data contribute to a better understanding of the functions of extracellular hemoglobin in the context of hemolytic diseases.

Hyperoxidized Species of Heme Have a Potent Capacity to Induce Autoreactivity of Human IgG Antibodies

The interaction of some human antibodies with heme results in posttranslational acquisition of binding to various self- and pathogen-derived antigens. The previous studies on this phenomenon were performed with oxidized heme (Fe³⁺). In the present study, we elucidated the effect of other pathologically relevant species of heme, i.e., species that were formed after contact of heme with oxidizing agents such as hydrogen peroxide, situations in which heme's iron could acquire higher oxidation states. Our data reveal that hyperoxidized species of heme have a superior capacity to heme (Fe³⁺) in triggering the autoreactivity of human IgG. Mechanistic studies demonstrated that oxidation status of iron was of critical importance for the heme's effect on antibodies. We also demonstrated that hyperoxidized heme species interacted at higher affinities with IgG and that this binding occurred through a different mechanism as compared to heme (Fe³⁺). Regardless of their profound functional impact on the antigen-binding properties of antibodies, hyperoxidized species of heme did not affect Fc-mediated functions of IgG, such as binding to the neonatal Fc receptor. The obtained data contribute to a better understanding of the pathophysiological mechanism of hemolytic diseases and of the origin of elevated antibody autoreactivity in patients with some hemolytic disorders.

A time-series analysis of blood-based biomarkers within a 25-year longitudinal dolphin cohort

Causal interactions and correlations between clinically-relevant biomarkers are important to understand, both for informing potential medical interventions as well as predicting the likely health trajectory of any individual as they age. These interactions and correlations can be hard to establish in humans, due to the difficulties of routine sampling and controlling for individual differences (e.g., diet, socio-economic status, medication). Because bottlenose dolphins are long-lived mammals that exhibit several age-related phenomena similar to humans, we analyzed data from a well controlled 25-year longitudinal cohort of 144 dolphins. The data from this study has been reported on earlier, and consists of 44 clinically relevant biomarkers. This time-series data exhibits three starkly different influences: (A) directed interactions between biomarkers, (B) sources of biological variation that can either correlate or decorrelate different biomarkers, and (C) random observation-noise which combines measurement error and very rapid fluctuations in the dolphin's biomarkers. Importantly, the sources of biological variation (type-B) are large in magnitude, often comparable to the observation errors (type-C) and larger than the effect of the directed interactions (type-A). Attempting to recover the type-A interactions without accounting for the type-B and type-C variation can result in an abundance of false-positives and false-negatives. Using a generalized regression which fits the longitudinal data with a linear model accounting for all three influences, we demonstrate that the dolphins exhibit many significant directed interactions (type-A), as well as strong correlated variation (type-B), between several pairs of biomarkers. Moreover, many of these interactions are associated with advanced age, suggesting that these interactions can be monitored and/or targeted to predict and potentially affect aging.

Genomic organization and gene evolution of two warm temperature acclimation proteins (Wap65s) of Micropterus salmoides and their responses to temperature and bacterial/viral infections

Warm temperature acclimation-related 65-kDa proteins (Wap65s) are fish plasma acute-phase glycoproteins homologous to hemopexin with high affinity and clearance for heme. The study characterized Mswap65-1 and Mswap65-2 genes in Micropterus salmoides. Structural analysis showed MsWap65s contained conserved heme-binding sites. MsWap65-1 had a chloride-binding site similar to hemopexin, while MsWap65-2 had an additional calcium-binding site. Phylogenetic and Ka/Ks analysis showed that fish Wap65s were evolutionarily conserved and underwent strong purifying selection. Functional divergence analysis indicated that fish Wap65-2 retained the putative function of ancestral Wap65, while Wap65-1 underwent neofunctional differentiation. QPCR showed Mswap65s were predominantly expressed in liver, but prolonged hyperthermy inhibited Mswap65-2 expression. Mswap65-2 expression was up-regulated in liver and spleen after Nocardia seriolae infection, while Mswap65-1 was down-regulated. MsWap65-2 may be associated with pathogenesis and play potential role in pathogen resistance. LMBV infection resulted in both significant downregulation of Mswap65s were both significantly down-regulated, with differences observed between sexes. We speculated the immune system might suppress expression after viral infection. Exogenous rMsWap65s were prepared, and injection of rMsWap65s alleviated phenylhydrazine-induced hemolysis and inhibited increases in heme, complement C3 and inflammatory symptoms. Our results contribute to an advanced understanding of the functions and mechanisms of MsWap65s in stress resistance.

Changes in Heme Levels During Acute Vaso-occlusive Crisis in Sickle Cell Anemia

OBJECTIVE/BACKGROUND

Sickle cell anemia (SCA) is associated with increased levels of extracellular heme, which is a key mediator of inflammation in this condition. Despite abundant evidence supporting this concept in cell and animal models, few studies addressed the association between heme levels and the development and severity of acute vasoocclusive crises (VOC) in humans.

METHODS

A cross-sectional study was conducted in patients with acute VOC. Total extracellular heme levels were measured in both plasma and serum at admission and after convalescence, and correlated with other clinical and laboratory markers of SCA severity.

RESULTS

A total of 28 episodes of VOC in 25 patients were included. Heme levels were similar between admission and convalescence, and correlated with the difference between pre and post hemoglobin, and SCA severity estimated by a composite score of clinical and laboratory markers. Heme levels were neither associated with VOC severity nor with markers of hemostasis activation, and were similar to those reported in an independent population of SCA patients at steady state.

DISCUSSION

Acute VOC are not characterized by significant increases in total extracellular heme levels. Studies measuring the fraction of free extracellular heme unbound to proteins are warranted to further refine our understanding of the role of heme in acute VOC.

Characterization of exercise-induced hemolysis in endurance horses

Exercise-induced hemolysis occurs as the result of intense physical exercise and is caused by metabolic and mechanical factors including repeated muscle contractions leading to capillary vessels compression, vasoconstriction of internal organs and foot strike among others. We hypothesized that exercise-induced hemolysis occurred in endurance racehorses and its severity was associated with the intensity of exercise. To provide further insight into the hemolysis of endurance horses, the aim of the study was to deployed a strategy for small molecules (metabolites) profiling, beyond standard molecular methods. The study included 47 Arabian endurance horses competing for either 80, 100, or 120 km distances. Blood plasma was collected before and after the competition and analyzed macroscopically, by ELISA and non-targeted metabolomics with liquid chromatography-mass spectrometry. A significant increase in all hemolysis parameters was observed after the race, and an association was found between the measured parameters, average speed, and distance completed. Levels of hemolysis markers were highest in horses eliminated for metabolic reasons in comparison to finishers and horses eliminated for lameness (gait abnormality), which may suggest a connection between the intensity of exercise, metabolic challenges, and hemolysis. Utilization of omics methods alongside conventional methods revealed a broader insight into the exercise-induced hemolysis process by displaying, apart from commonly measured hemoglobin and haptoglobin, levels of hemoglobin degradation metabolites. Obtained results emphasized the importance of respecting horse limitations in regard to speed and distance which, if underestimated, may lead to severe damages.

Low grade intravascular hemolysis associates with peripheral nerve injury in type 2 diabetes

Type 2 diabetes (T2D) induces hyperglycemia, alters hemoglobin (Hb), red blood cell (RBC) deformability and impairs hemorheology. The question remains whether RBC breakdown and intravascular hemolysis (IVH) occur in T2D patients. We characterized RBC-degradation products and vesiculation in a case-control study of 109 T2D patients and 65 control subjects. We quantified heme-related absorbance by spectrophotometry and circulating extracellular vesicles (EV) by flow cytometry and electron microscopy. Heme-related absorbance was increased in T2D vs. control plasma (+57%) and further elevated in obese T2D plasma (+27%). However, large CD235a+ EV were not increased in T2D plasma. EV from T2D plasma, or shed by isolated T2D RBC, were notably smaller in diameter (-27%) and carried heme-related absorbance. In T2D plasma, higher heme-related absorbance (+30%) was associated to peripheral sensory neuropathy, and no other vascular complication. In vitro, T2D RBC-derived EV triggered endothelial stress and thrombin activation in a phosphatidylserine- and heme-dependent fashion. We concluded that T2D was associated with low-grade IVH. Plasma absorbance may constitute a novel biomarker of peripheral neuropathy in T2D, while flow cytometry focusing on large EV may be maladapted to characterize RBC EV in T2D. Moreover, therapeutics limiting IVH or neutralizing RBC breakdown products might bolster vasculoprotection in T2D.

Glutathione-Hemin/Hematin Adduct Formation to Disintegrate Cytotoxic Oxidant Hemin/Hematin in Human K562 Cells and Red Blood Cells' Hemolysates: Impact of Glutathione on the Hemolytic Disorders and Homeostasis

Hemin, an oxidized form of heme, acts as potent oxidant to regulate glutathione (GSH) content in pro-erythroid K562 nucleated cells, via activation of the KEAP1/NRF2 defensive signaling pathway. Moreover, GSH, as an essential metabolite, is involved in the regulation of cell-redox homeostasis and proposed to scavenge cytotoxic free heme, which is released from hemoglobin of damaged red blood cells (RBCs) during different hemolytic disorders. In the present study, we aimed to uncover the molecular mechanism by which GSH inhibits hemin-induced cytotoxicity (HIC) by affecting hemin’s structural integrity in K562 cells and in RBC hemolysates. GSH, along with other thiols (cysteine, thioglycolic acid, and mercaptoethanol) altered the spectrum of hemin, while each of them co-added with hemin in cultures of K562 cells prevented HIC and growth arrest and markedly reduced the intracellular level of hemin. In addition, GSH endogenous levels served as a barrier to HIC in K562 cells, as shown by the depletion in GSH. LC-MS/MS analysis of the in vitro reaction between hemin and GSH revealed at least five different isomers of GSH–hemin adducts, as well as hydroxy derivatives as reaction products, which are characterized by unique mass spectra (MS). The latter allowed the detection of adducts in human RBC hemolysates. Based on these findings, we proposed a molecular mechanism via which GSH prevents HIC and structurally disintegrates heme. An analogous reaction was observed in RBC hemolysates via direct inter-reaction between hematin (ferric and hydroxide heme) released from hemoglobin and GSH. Overall, GSH–hematin adducts could be considered as novel entities of the human metabolome of RBCs in hemolytic disorders.

Evaluation of the mechanisms of heme-induced tissue factor activation: Contribution of innate immune pathways

Hemolytic diseases such as Sickle Cell Disease (SCD) are characterized by a natural propensity for both arterial and venous thrombosis. The ability of heme to induce tissue factor (TF) activation has been shown both in animal models of SCD, and in human endothelial cells and monocytes. Moreover, it was recently demonstrated that heme can induce coagulation activation in the whole blood of healthy volunteers in a TF-dependent fashion. Herein, we aim to further explore the cellular mechanisms by which heme induces TF-coagulation activation, using human mononuclear cells, which have been shown to be relevant to in vivo hemostasis. TF mRNA expression was evaluated by qPCR and TF procoagulant activity was evaluated using a 2-stage assay based on the generation of activated factor X (FXa). Heme was capable of inducing both TF expression and activation in a TLR4-dependent pathway. This activity was further amplified after TNF-α-priming. Our results provide additional details on the mechanisms by which heme is involved in the pathogenesis of hypercoagulability in hemolytic diseases.

The oral ferroportin inhibitor vamifeport improves hemodynamics in a mouse model of sickle cell disease

Sickle cell disease (SCD) is an inherited hemolytic anemia caused by a single point mutation in the β-globin gene of hemoglobin that leads to synthesis of sickle hemoglobin (HbS) in red blood cells (RBCs). HbS polymerizes in hypoxic conditions, leading to intravascular hemolysis, release of free hemoglobin and heme, and increased adhesion of blood cells to the endothelial vasculature, which causes painful vaso-occlusion and organ damage. HbS polymerization kinetics are strongly dependent on the intracellular HbS concentration; a relatively small reduction in cellular HbS concentration may prevent HbS polymerization and its sequelae. We hypothesized that iron restriction via blocking ferroportin, the unique iron transporter in mammals, might reduce HbS concentration in RBCs, thereby decreasing hemolysis, improving blood flow, and preventing vaso-occlusive events. Indeed, vamifeport (also known as VIT-2763), a clinical-stage oral ferroportin inhibitor, reduced hemolysis markers in the Townes model of SCD. The RBC indices of vamifeport-treated male and female Townes mice exhibited changes attributable to iron-restricted erythropoiesis: decreased corpuscular hemoglobin concentration mean and mean corpuscular volume, as well as increased hypochromic and microcytic RBC fractions. Furthermore, vamifeport reduced plasma soluble VCAM-1 concentrations, which suggests lowered vascular inflammation. Accordingly, intravital video microscopy of fluorescently labeled blood cells in the microvasculature of Townes mice treated with vamifeport revealed diminished adhesion to the endothelium and improved hemodynamics. These preclinical data provide a strong proof-of-concept for vamifeport in the Townes model of SCD and support further development of this compound as a potential novel therapy in SCD.

The role of the alternative pathway in paroxysmal nocturnal hemoglobinuria and emerging treatments

INTRODUCTION

Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by uncontrolled activation of the terminal complement pathway, leading to intravascular hemolysis (IVH) and a prothrombotic state. Treatment with terminal complement (C5) inhibitors, the current standard of care, suppresses IVH and reduces the risk of thrombosis and the associated morbidity and mortality. Opportunities exist to further improve care by alternative modes of administration and the reduction of clinically significant anemia and transfusion dependence caused by extravascular hemolysis in some patients.

AREAS COVERED

This review describes the pathophysiology of PNH, provides an overview of the current standard of care, and discusses potential avenues for enhancing patient care, with a focus on the literature describing new and emerging treatments that target the alternative pathway. Emerging treatments include biosimilars and novel C5 inhibitors as well as agents with novel mechanisms of action that target the proximal complement pathways (C3 inhibitors, factor B inhibitors, and factor D inhibitors).

EXPERT OPINION

Alternative complement pathway inhibitors may offer further benefit as long as terminal complement is completely inhibited to reduce IVH and disease activity. This may lead to improvements in adherence and health-related quality of life for patients with PNH.

The metabolic characteristic of decidual immune cells and their unique properties in pregnancy loss

Maternal tolerance to semi- or fully allograft conceptus is a prerequisite for the maintenance of pregnancy. Once this homeostasis is disrupted, it may result in pregnancy loss. As a potential approach to prevent pregnancy loss, targeting decidual immune cells (DICs) at the maternal-fetal interface has been suggested. Although the phenotypic features and functions of DIC have been extensively profiled, the regulatory pathways for this unique immunological adaption have yet to be elucidated. In recent years, a pivotal mechanism has been highlighted in the area of immunometabolism, by which the changes in intracellular metabolic pathways in DIC and interaction with the adjacent metabolites in the microenvironment can alter their phenotypes and function. More inspiringly, the manipulation of metabolic profiling in DIC provides a novel avenue for the prevention and treatment of pregnancy loss. Herein, this review highlights the major metabolic programs (specifically, glycolysis, ATP-adenosine metabolism, lysophosphatidic acid metabolism, and amino acid metabolism) in multiple immune cells (including decidual NK cells, macrophages, and T cells) and their integrations with the metabolic microenvironment in normal pregnancy. Importantly, this perspective may help to provide a potential therapeutic strategy for reducing pregnancy loss via targeting this interplay.

Relationship between creatine kinase and liver enzymes in war wounded with rhabdomyolysis

BACKGROUND

Rhabdomyolysis is a frequent complication in war wounded. Its complex pathophysiology suggests that it not only affects kidneys but also other organs such as the liver. The aim of this study was to evaluate the relationship between creatine kinase (CK) and liver enzymes in war wounded with rhabdomyolysis.

METHODS

War wounded admitted to the intensive care unit of Percy Military Hospital between 2009 and 2017 with a rhabdomyolysis (CK peak >1,000 U/L) were included. They were divided in two groups: mild (CK peak <10,000 U/L) and severe rhabdomyolysis (CK peak ≥10,000 U/L). Demographic characteristics, peaks in transaminases, alkaline phosphatase (ALP), bilirubin, and CK were recorded. Mann Whitney-U test and, Fisher's exact test were used as appropriate. A Pearson's correlation test was used to determine the correlation between CK and liver enzymes after a log-normal transformation of the data.

RESULTS

Fifty-one patients were included (31 in the mild and 20 in the severe rhabdomyolysis group). Patients in the severe rhabdomyolysis group were more likely victims of explosions (85% vs 39%, p = 0.003). The transaminases peak was significantly higher in the severe rhabdomyolysis group (median AST peak 398 (270-944) vs 91 (63-157) U/L, p <0.0001, and median ALT peak 106 (77-235) vs 45 (34-71) U/L, p<0.0001). Bilirubin and ALP were higher in the severe rhabdomyolysis group (39 (25-49) vs 14(11-23) U/L, p = 0.0031 and 84 (55-170) vs 52 (39-85) U/L, p = 0.0063, respectively). We found a significant positive linear correlation between CK and ALT (r = 0.73, p<0.0001), AST (r = 0.89, p<0.0001), ALP (r = 0.41, p = 0.0035), and bilirubin (r = 0.37, p = 0.0083).

CONCLUSION

We found a statistically significant positive correlation between CK and liver enzymes in rhabdomyolysis war wounded, indicating that hepatic damage occurs when rhabdomyolysis is severe and associated with elevated bilirubin and ALP. Further studies are needed to confirm this phenomenon and elucidate the pathophysiological mechanism.

LEVEL OF EVIDENCE

IV STUDY TYPE: Diagnostic.

Extracorporeal Membrane Oxygenation for Acute Toxic Inhalations: Case Reports and Literature Review

Previous studies have shown that poisoning is a major threat to human health. Inhalation of acute toxic gas has been linked to serious health consequences. Among the antidotes for poisoning currently used, supportive care is the most common intervention in clinical practice. Severe acute respiratory distress syndrome (ARDS) and/or refractory cardiogenic shock or cardiac arrest caused by toxins are associated with high mortality and are difficult to treat. Extracorporeal membrane oxygenation (ECMO) is an aggressive supportive measure used to manage severely poisoned patients. This study presents two cases of acute toxic gases inhalation, severe ARDS and circulatory instability induced by bromine inhalation, and ARDS induced by nitric acid inhalation which were successfully treated with ECMO. The ECMO techniques used in the animal models and in human cases to treat severe poisoning are described as well as the indications, contraindications, complications, and weaning of ECMO.

The Role of RBC Oxidative Stress in Sickle Cell Disease: From the Molecular Basis to Pathologic Implications

Sickle cell disease (SCD) is an inherited monogenic disorder and the most common severe hemoglobinopathy in the world. SCD is characterized by a point mutation in the β-globin gene, which results in hemoglobin (Hb) S production, leading to a variety of mechanistic and phenotypic changes within the sickle red blood cell (RBC). In SCD, the sickle RBCs are the root cause of the disease and they are a primary source of oxidative stress since sickle RBC redox state is compromised due to an imbalance between prooxidants and antioxidants. This imbalance in redox state is a result of a continuous production of reactive oxygen species (ROS) within the sickle RBC caused by the constant endogenous Hb autoxidation and NADPH oxidase activation, as well as by a deficiency in the antioxidant defense system. Accumulation of non-neutralized ROS within the sickle RBCs affects RBC membrane structure and function, leading to membrane integrity deficiency, low deformability, phosphatidylserine exposure, and release of micro-vesicles. These oxidative stress-associated RBC phenotypic modifications consequently evoke a myriad of physiological changes involved in multi-system manifestations. Thus, RBC oxidative stress in SCD can ultimately instigate major processes involved in organ damage. The critical role of the sickle RBC ROS production and its regulation in SCD pathophysiology are discussed here.

New Insights into the Pivotal Role of Iron/Heme Metabolism in TLR4/NF-κB Signaling-Mediated Inflammatory Responses in Human Monocytes

Iron metabolism and heme biosynthesis are essential processes in cells during the energy cycle. Alteration in these processes could create an inflammatory condition, which results in tumorigenesis. Studies are conducted on the exact role of iron/heme metabolism in induced inflammatory conditions. This study used lipopolysaccharide (LPS)- or high-glucose-induced inflammation conditions in THP-1 cells to study how iron/heme metabolism participates in inflammatory responses. Here, we used iron and heme assays for measuring total iron and heme. We also used flow cytometry and Western blotting to analyze molecular responses. Our results demonstrated that adding LPS or high-glucose induced iron formation and heme synthesis and elevated the expression levels of proteins responsible for iron metabolism and heme synthesis. We then found that further addition of heme or 5-aminolevulinic acid (ALA) increased heme biosynthesis and promoted inflammatory responses by upregulating TLR4/NF-κB and inflammatory cytokine expressions. We also demonstrated the inhibition of heme synthesis using succinylacetone (SA). Moreover, N-MMP inhibited LPS- or high-glucose-induced inflammatory responses by inhibiting TLR4/NF-κB signaling. Hence, iron/heme metabolism checkpoints could be considered a target for treating inflammatory conditions.

Heme Burden and Ensuing Mechanisms That Protect the Kidney: Insights from Bench and Bedside

With iron at its core, the tetrapyrrole heme ring is a cardinal prosthetic group made up of many proteins that participate in a wide array of cellular functions and metabolism. Once released, due to its pro-oxidant properties, free heme in sufficient amounts can result in injurious effects to the kidney and other organs. Heme oxygenase-1 (HO-1) has evolved to promptly attend to such injurious potential by facilitating degradation of heme into equimolar amounts of carbon monoxide, iron, and biliverdin. HO-1 induction is a beneficial response to tissue injury in diverse animal models of diseases, including those that affect the kidney. These protective attributes are mainly due to: (i) prompt degradation of heme leading to restraining potential hazardous effects of free heme, and (ii) generation of byproducts that along with induction of ferritin have proven beneficial in a number of pathological conditions. This review will focus on describing clinical aspects of some of the conditions with the unifying end-result of increased heme burden and will discuss the molecular mechanisms that ensue to protect the kidneys.

Arsenic Trioxide Combining Leflunomide Activates Nrf2-ARE-HO-1 Signaling Pathway and Protects Heart Xenografts

OBJECTIVE

To investigate the molecular mechanisms underlying the effects of arsenic trioxide (As₂O₃) in combination with leflunomide on the hamster-to-rat heart xenotransplant.

METHODS

Transplantation of LVG hamster hearts to Lewis rats was performed by anastomosis of vessels in the neck using end-to-end anastomosis with a non-suture cuff technique. Four groups of recipient rats (n=6 in each) were treated with normal saline (control), As₂O₃ [5 mg/(kg·day) intraperitoneally], leflunomide [5 mg/(kg·d) orally], or leflunomide [5 mg/(kg·d)+As₂O₃ [5 mg/(kg·d)] in combination. Donor hearts and/or rat spleens were harvested and analyzed 4 days after transplantation. Quantitative reverse-transcription polymerase chain reaction and Western blot analysis were performed to detect the expression of the nuclear factor erythroid-derived factor 2-related factor (Nrf2) and its target gene heme oxygenase-1 (HO-1), Treg cell marker fork-head Box P3 (FOXP3), apoptosis-associated proteins Bcl-2, Bax, and cleaved caspase-3. Immunohistochemical staining was used to detect the levels of inflammatory natural killer cell and macrophage infiltration, intercellular cell adhesion molecule-1 (ICAM-1) and complement C3.

RESULTS

Expression of Nrf2-ARE-HO-1 signaling pathway was upregulated in heart xenografts in rats treated with As₂O₃ plus leflunomide compared with control rats or rats treated with either drug alone (P<0.01), and this was accompanied by an increased Treg cells in the recipient rat spleen (P<0.01). In contrast, the expressions of Bax, cleaved caspase-3, ICAM-1, and complement C3, and infiltration of inflammatory cells in the xenografts were inhibited by As₂O₃ plus leflunomide treatment (P<0.01).

CONCLUSION

Combination treatment with As₂O₃ and leflunomide protected hamster heart-xenografts in recipient rats.

Alpha1-antitrypsin counteracts heme-induced endothelial cell inflammatory activation, autophagy dysfunction and death

Free heme toxicity in the vascular endothelium is critical for the pathogenesis of hemolytic disorders including sickle cell disease. In the current study, it is demonstrated that human alpha1-antitrypsin (A1AT), a serine protease inhibitor with high binding-affinity for heme, rescues endothelial cell (EC) injury caused by free heme. A1AT provided endothelial protection against free heme toxicity via a pathway that differs from human serum albumin and hemopexin, two prototypical heme-binding proteins. A1AT inhibited heme-mediated pro-inflammatory activation and death of ECs, but did not affect the increase in intracellular heme levels and up-regulation of the heme-inducible enzyme heme oxygenase-1. Moreover, A1AT reduced heme-mediated generation of mitochondrial reactive oxygen species. Extracellular free heme led to an increased up-take of A1AT by ECs, which was detected in lysosomes and was found to reduce heme-dependent alkalization of these organelles. Finally, A1AT was able to restore heme-dependent dysfunctional autophagy in ECs. Taken together, our findings show that A1AT rescues ECs from free heme-mediated pro-inflammatory activation, cell death and dysfunctional autophagy. Hence, A1AT therapy may be useful in the treatment of hemolytic disorders such as sickle cell disease.

Heme induces significant neutrophil adhesion in vitro via an NFκB and reactive oxygen species-dependent pathway

Intravascular hemolysis, a major manifestation of sickle cell disease (SCD) and other diseases, incurs the release of hemoglobin and heme from red blood cells, in turn triggering inflammatory processes. This study investigated the in vitro effects of heme, a major inflammatory DAMP, on the adhesive properties of isolated human neutrophils. Heme (20 and 50 µM) significantly increased the adhesion of neutrophils to fibronectin and to recombinant ICAM-1, under static conditions, even more efficiently than the potent pro-inflammatory cytokine, tumor necrosis factor-α (TNF); a microfluidic assay confirmed that heme stimulated neutrophil adhesion under conditions of shear stress. Heme-induced neutrophil adhesion was associated with the increased activities, but not expressions, of the Mac-1 and LFA-1 integrin subunits, CD11b and CD11a, on the cell surface. Notably, heme (50 µM) significantly induced NFκB translocation in neutrophils, and inhibition of NFκB activity with the BAY11-7082 molecule abolished heme-induced cell adhesion to fibronectin and significantly decreased CD11a activity. Flow cytometric analysis demonstrated major reactive oxygen species (ROS) generation in neutrophils following heme stimulation that could be inhibited by the antioxidant, α-tocopherol, and by BAY11-7082. Furthermore, co-incubation with α-tocopherol abrogated both heme-stimulated neutrophil adhesion and CD11a/CD11b activation. Thus, our data indicate that heme, at clinically relevant concentrations, is a potent activator of neutrophil adhesion, increasing the ligand affinity of the β2 integrins via a mechanism that may be partially mediated by an NFkB-dependent pathway and the generation of ROS. Given the fundamental role that the adhesion of neutrophils to the vascular wall plays in SCD vaso-occlusion and other vascular inflammatory processes, our findings provide further evidence that cell-free heme is a major therapeutic target in the hemolytic diseases.

Type I interferon is induced by hemolysis and drives antibody-mediated erythrophagocytosis in sickle cell disease

Patients with sickle cell disease (SCD) suffer from intravascular hemolysis associated vascular injury and tissue damage. Classical monocytes (CMo), which are the most abundant of circulating monocytes, are activated in SCD, but the cause and consequences of activation remain incompletely understood. We found a positive correlation between total plasma heme levels and circulating IFN-α in patients with SCD along with upregulation of the type I Interferon (IFN-I) inducible genes in sort-purified SCD patients' CMo by transcriptome analysis. We demonstrated that hemolysis led to IFN-I expression, predominantly by mouse liver monocyte and macrophages (Mϕ), primarily through Tank kinase binding 1 (TBK1)/IκB kinase-ε (IKKε) but not TLR4. In response to hemolysis-induced IFN-I, mouse CMo migrated to the liver and differentiated into monocyte derived Mϕ, increasing their numbers by 6-fold with acute hemin treatment. Hemolysis-driven IFN-I activity also led to the induction of Fc receptor CD64 expression on monocyte and Mϕ populations, enhancing alloantibody-mediated erythrophagocytosis in SCD both in vivo in mice and in in vitro human cultures. Altogether, these data demonstrate IFN-I response to hemolysis as a novel activation pathway in monocytes and Mϕ in SCD, opening the possibility for development of IFN-I-based diagnostics and therapeutics against alloantibody-mediated erythrophagocytosis.

Significance of Heme and Heme Degradation in the Pathogenesis of Acute Lung and Inflammatory Disorders

The heme molecule serves as an essential prosthetic group for oxygen transport and storage proteins, as well for cellular metabolic enzyme activities, including those involved in mitochondrial respiration, xenobiotic metabolism, and antioxidant responses. Dysfunction in both heme synthesis and degradation pathways can promote human disease. Heme is a pro-oxidant via iron catalysis that can induce cytotoxicity and injury to the vascular endothelium. Additionally, heme can modulate inflammatory and immune system functions. Thus, the synthesis, utilization and turnover of heme are by necessity tightly regulated. The microsomal heme oxygenase (HO) system degrades heme to carbon monoxide (CO), iron, and biliverdin-IXα, that latter which is converted to bilirubin-IXα by biliverdin reductase. Heme degradation by heme oxygenase-1 (HO-1) is linked to cytoprotection via heme removal, as well as by activity-dependent end-product generation (i.e., bile pigments and CO), and other potential mechanisms. Therapeutic strategies targeting the heme/HO-1 pathway, including therapeutic modulation of heme levels, elevation (or inhibition) of HO-1 protein and activity, and application of CO donor compounds or gas show potential in inflammatory conditions including sepsis and pulmonary diseases.

Molecular and Cellular Mechanisms of Metformin in Cervical Cancer

Simple Summary

The potential effects of metformin in terms of cancer prevention and therapy have been widely studied, and a number of studies have indicated its potential role in cancer treatment. Metformin exerts anticancer effects, alone or in combination with other agents, on cervical cancer in vitro and in vivo. Metformin might thus serve as an adjunct therapeutic agent for cervical cancer.

Abstract

Cervical cancer is one of the major gynecologic malignancies worldwide. Treatment options include chemotherapy, surgical resection, radiotherapy, or a combination of these treatments; however, relapse and recurrence may occur, and the outcome may not be favorable. Metformin is an established, safe, well-tolerated drug used in the treatment of type 2 diabetes; it can be safely combined with other antidiabetic agents. Diabetes, possibly associated with an increased site-specific cancer risk, may relate to the progression or initiation of specific types of cancer. The potential effects of metformin in terms of cancer prevention and therapy have been widely studied, and a number of studies have indicated its potential role in cancer treatment. The most frequently proposed mechanism underlying the diabetes–cancer association is insulin resistance, which leads to secondary hyperinsulinemia; furthermore, insulin may exert mitogenic effects through the insulin-like growth factor 1 (IGF-1) receptor, and hyperglycemia may worsen carcinogenesis through the induction of oxidative stress. Evidence has suggested clinical benefits of metformin in the treatment of gynecologic cancers. Combining current anticancer drugs with metformin may increase their efficacy and diminish adverse drug reactions. Accumulating evidence is indicating that metformin exerts anticancer effects alone or in combination with other agents in cervical cancer in vitro and in vivo. Metformin might thus serve as an adjunct therapeutic agent for cervical cancer. Here, we reviewed the potential anticancer effects of metformin against cervical cancer and discussed possible underlying mechanisms.

Chronic intestinal inflammation drives colorectal tumor formation triggered by dietary heme iron in vivo

The consumption of red meat is associated with an increased risk for colorectal cancer (CRC). Multiple lines of evidence suggest that heme iron as abundant constituent of red meat is responsible for its carcinogenic potential. However, the underlying mechanisms are not fully understood and particularly the role of intestinal inflammation has not been investigated. To address this important issue, we analyzed the impact of heme iron (0.25 µmol/g diet) on the intestinal microbiota, gut inflammation and colorectal tumor formation in mice. An iron-balanced diet with ferric citrate (0.25 µmol/g diet) was used as reference. 16S rRNA sequencing revealed that dietary heme reduced α-diversity and caused a persistent intestinal dysbiosis, with a continuous increase in gram-negative Proteobacteria. This was linked to chronic gut inflammation and hyperproliferation of the intestinal epithelium as attested by mini-endoscopy, histopathology and immunohistochemistry. Dietary heme triggered the infiltration of myeloid cells into colorectal mucosa with an increased level of COX-2 positive cells. Furthermore, flow cytometry-based phenotyping demonstrated an increased number of T cells and B cells in the lamina propria following heme intake, while γδ-T cells were reduced in the intraepithelial compartment. Dietary heme iron catalyzed formation of fecal N-nitroso compounds and was genotoxic in intestinal epithelial cells, yet suppressed intestinal apoptosis as evidenced by confocal microscopy and western blot analysis. Finally, a chemically induced CRC mouse model showed persistent intestinal dysbiosis, chronic gut inflammation and increased colorectal tumorigenesis following heme iron intake. Altogether, this study unveiled intestinal inflammation as important driver in heme iron-associated colorectal carcinogenesis.

Mn porphyrins as a novel treatment targeting sickle cell NOXs to reverse and prevent acute vaso-occlusion in vivo

In sickle cell disease (SCD), adhesion of sickle red blood cells (SSRBCs) and activated leukocytes in inflamed venules affects blood rheology, causing vaso-occlusive manifestations and vital reduction in microvascular blood flow. Recently, we found that NADPH oxidases (NOXs) create a vicious feedback loop within SSRBCs. This positive feedback loop mediates SSRBC adhesion to the endothelium. We show for the first time the therapeutic effectiveness of the redox-active manganese (Mn) porphyrins MnTnBuOE-2-PyP5+ (MnBuOE; BMX-001) and MnTE-2-PyP5+ (MnE; BMX-010, AEOL10113) to treat established vaso-occlusion in a humanized sickle mouse model of an acute vaso-occlusive crisis using intravital microscopy. These Mn porphyrins can suppress SSRBC NOX activity. Subcutaneous administration of only 1 dose of MnBuOE or MnE at 0.1 to 2 mg/kg after the inflammatory trigger of vaso-occlusion, or simultaneously, reversed and reduced leukocyte and SSRBC adhesion, diminished leukocyte rolling, restored blood flow, and increased survival rate. Furthermore, MnBuOE and MnE administered to sickle mice subcutaneously at 0.1 to 1 mg/kg for 28 days (except on weekends) did not exacerbate anemia, which seemed to be due to downregulation of both SSRBC reactive oxygen species production and exposure of the eryptotic marker phosphatidylserine. In addition, Mn porphyrins ameliorated leukocytosis, venous blood gases, endothelial activation, and organ oxidative damage. Our data suggest that Mn porphyrins, likely by repressing NOX-mediated adhesive function of SSRBCs and activated leukocytes, could represent a novel, safe therapeutic intervention to treat or prevent the establishment of acute pain crises. These NOX-targeted antioxidants merit further assessment in SCD clinical trials.

A Coumarin-Porphyrin FRET Break-Apart Probe for Heme Oxygenase-1

Heme oxygenase-1 (HO-1) is a vital enzyme in humans that primarily regulates free heme concentrations. The overexpression of HO-1 is commonly associated with cardiovascular and neurodegenerative diseases including atherosclerosis and ischemic stroke. Currently, there are no known chemical probes to detect HO-1 activity, limiting its potential as an early diagnostic/prognostic marker in these serious diseases. Reported here are the design, synthesis, and photophysical and biological characterization of a coumarin-porphyrin FRET break-apart probe to detect HO-1 activity, Fe-L1. We designed Fe-L1 to "break-apart" upon HO-1-catalyzed porphyrin degradation, perturbing the efficient FRET mechanism from a coumarin donor to a porphyrin acceptor fluorophore. Analysis of HO-1 activity using Escherichia coli lysates overexpressing hHO-1 found that a 6-fold increase in emission intensity at 383 nm was observed following incubation with NADPH. The identities of the degradation products following catabolism were confirmed by MALDI-MS and LC-MS, showing that porphyrin catabolism was regioselective at the α-position. Finally, through the analysis of Fe-L2, we have shown that close structural analogues of heme are required to maintain HO-1 activity. It is anticipated that this work will act as a foundation to design and develop new probes for HO-1 activity in the future, moving toward applications of live fluorescent imaging.

Dual role of heme iron in cancer; promotor of carcinogenesis and an inducer of tumour suppression

PURPOSE

Heme is a crucial compound for cell survival but is also equipped with the potential to be toxic and carcinogenic to cells. However, with the recent advancement of knowledge regarding ferroptosis, the iron mediated cell death, heme can be postulated to induce tumour suppression through ferroptosis. This review summarizes the literature on the carcinogenic and anticarcinogenic properties of heme with specific emphasis on the alterations observed on heme synthesis, metabolism and transport in tumour cells.

METHODS

Literature search was performed in PubMed data base using the MeSH terms 'heme iron or heme', 'cancer or carcinogenesis' and 'tumour suppression' or 'anticarcinogenic properties. Out of 189 results, 166 were relevant to the current review.

RESULTS

Heme supports carcinogenesis via modulation of immune cell function, promoting inflammation and gut dysbiosis, impeding tumour suppressive potential of P53 gene, promoting cellular cytotoxicity and reactive oxygen species generation and modulating Nfr2 /HO-1 axis. The carcinogenic and anticarcinogenic properties of heme are both dose and oxygen concentration dependant. At low doses, heme is harmless and even helpful in maintaining the much-needed redox balance within the cell. However, when heme exceeds physiological concentrations, it could initiate and propagate carcinogenesis, due to its ability to produce reactive oxygen species (ROS). The same phenomenon of heme mediated ROS generation could be manipulated to initiate tumour suppression via ferroptosis, but the therapeutic doses are yet to be determined.

CONCLUSION

Heme iron possesses powerful carcinogenic and anticarcinogenic properties which are dosage and oxygen availability dependant.

Neuroprotection of Heme Oxygenase-2 in Mice AfterIntracerebral Hemorrhage

There are few effective preventive or therapeutic strategies to mitigate the effects of catastrophic intracerebral hemorrhage (ICH) in humans. Heme oxygenase is the rate-limiting enzyme in heme metabolism; heme oxygenase-2 (HO-2) is a constitutively expressed heme oxygenase. We explored the involvement of HO-2 in a collagenase-induced mouse model of ICH in C57BL/6 wild-type and HO-2 knockout mice. We assessed oxidative stress injury, blood-brain barrier permeability, neuronal damage, late-stage angiogenesis, and hematoma clearance using immunofluorescence, Western blot, MRI, and special staining methods. Our results show that HO-2 reduces brain injury volume and brain edema, alleviates cytotoxic injury, affects vascular function in the early stage of ICH, and improves hematoma absorbance and angiogenesis in the late stage of ICH in this model. Thus, we found that HO-2 has a protective effect on brain injury after ICH.

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

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

Vasculopathy in Sickle Cell Disease: From Red Blood Cell Sickling to Vascular Dysfunction

Sickle cell disease (SCD) is a hereditary disorder that leads to the production of an abnormal hemoglobin, hemoglobin S (HbS). HbS polymerizes in deoxygenated conditions, which can prompt red blood cell (RBC) sickling and leaves the RBCs more rigid, fragile, and prone to hemolysis. SCD patients suffer from a plethora of complications, ranging from acute complications, such as characteristic, frequent, and debilitating vaso-occlusive episodes to chronic organ damage. While RBC sickling is the primary event at the origin of vaso-occlusive processes, other factors that can further increase RBC transit times in the microcirculation may also be required to precipitate vaso-occlusive processes. The adhesion of RBC and leukocytes to activated endothelium and the formation of heterocellular aggregates, as well as increased blood viscosity, are among the mechanisms involved in slowing the progress of RBCs in deoxygenated vascular areas, favoring RBC sickling and promoting vascular occlusion. Chronic inflammatory processes and oxidative stress, which are perpetuated by hemolytic events and ischemia-reperfusion injury, result in this pan cellular activation and some acute events, such as stroke and acute chest syndrome, as well as chronic end-organ damage. Furthermore, impaired vasodilation and vasomotor hyperresponsiveness in SCD also contribute to vaso-occlusive processes. Treating SCD as a vascular disease in addition to its hematological perspective, the present article looks at the interplay between abnormal RBC physiology/integrity, vascular dysfunction and clinical severity in SCD, and discusses existing therapies and novel drugs in development that may ameliorate vascular complications in the disease. © 2021 American Physiological Society. Compr Physiol 11:1785-1803, 2021.

Noncanonical Roles of Caspase-4 and Caspase-5 in Heme-Driven IL-1β Release and Cell Death

Excessive release of heme from RBCs is a key pathophysiological feature of several disease states, including bacterial sepsis, malaria, and sickle cell disease. This hemolysis results in an increased level of free heme that has been implicated in the inflammatory activation of monocytes, macrophages, and the endothelium. In this study, we show that extracellular heme engages the human inflammatory caspases, caspase-1, caspase-4, and caspase-5, resulting in the release of IL-1β. Heme-induced IL-1β release was further increased in macrophages from patients with sickle cell disease. In human primary macrophages, heme activated caspase-1 in an inflammasome-dependent manner, but heme-induced activation of caspase-4 and caspase-5 was independent of canonical inflammasomes. Furthermore, we show that both caspase-4 and caspase-5 are essential for heme-induced IL-1β release, whereas caspase-4 is the primary contributor to heme-induced cell death. Together, we have identified that extracellular heme is a damage-associated molecular pattern that can engage canonical and noncanonical inflammasome activation as a key mediator of inflammation in macrophages.

Chinese Herbs and Repurposing Old Drugs as Therapeutic Agents in the Regulation of Oxidative Stress and Inflammation in Pulmonary Diseases

Several pro-inflammatory factors and proteins have been characterized that are involved in the pathogenesis of inflammatory diseases, including acute respiratory distress syndrome, chronic obstructive pulmonary disease, and asthma, induced by oxidative stress, cytokines, bacterial toxins, and viruses. Reactive oxygen species (ROS) act as secondary messengers and are products of normal cellular metabolism. Under physiological conditions, ROS protect cells against oxidative stress through the maintenance of cellular redox homeostasis, which is important for proliferation, viability, cell activation, and organ function. However, overproduction of ROS is most frequently due to excessive stimulation of either the mitochondrial electron transport chain and xanthine oxidase or reduced nicotinamide adenine dinucleotide phosphate (NADPH) by pro-inflammatory cytokines, such as interleukin-1β and tumor necrosis factor α. NADPH oxidase activation and ROS overproduction could further induce numerous inflammatory target proteins that are potentially mediated via Nox/ROS-related transcription factors triggered by various intracellular signaling pathways. Thus, oxidative stress is considered important in pulmonary inflammatory processes. Previous studies have demonstrated that redox signals can induce pulmonary inflammatory diseases. Thus, therapeutic strategies directly targeting oxidative stress may be effective for pulmonary inflammatory diseases. Therefore, drugs with anti-inflammatory and anti-oxidative properties may be beneficial to these diseases. Recent studies have suggested that traditional Chinese medicines, statins, and peroxisome proliferation-activated receptor agonists could modulate inflammation-related signaling processes and may be beneficial for pulmonary inflammatory diseases. In particular, several herbal medicines have attracted attention for the management of pulmonary inflammatory diseases. Therefore, we reviewed the pharmacological effects of these drugs to dissect how they induce host defense mechanisms against oxidative injury to combat pulmonary inflammation. Moreover, the cytotoxicity of oxidative stress and apoptotic cell death can be protected via the induction of HO-1 by these drugs. The main objective of this review is to focus on Chinese herbs and old drugs to develop anti-inflammatory drugs able to induce HO-1 expression for the management of pulmonary inflammatory diseases.

Revisiting the interaction of heme with hemopexin

In hemolytic disorders, erythrocyte lysis results in massive release of hemoglobin and, subsequently, toxic heme. Hemopexin is the major protective factor against heme toxicity in human blood and currently considered for therapeutic use. It has been widely accepted that hemopexin binds heme with extraordinarily high affinity of <1 pM in a 1:1 ratio. However, several lines of evidence point to a higher stoichiometry and lower affinity than determined 50 years ago. Here, we re-analyzed these data. SPR and UV/Vis spectroscopy were used to monitor the interaction of heme with the human protein. The heme-binding sites of hemopexin were characterized using hemopexin-derived peptide models and competitive displacement assays. We obtained a K _D value of 0.32 ± 0.04 nM and the ratio for the interaction was determined to be 1:1 at low heme concentrations and at least 2:1 (heme:hemopexin) at high concentrations. We were able to identify two yet unknown potential heme-binding sites on hemopexin. Furthermore, molecular modelling with a newly created homology model of human hemopexin suggested a possible recruiting mechanism by which heme could consecutively bind several histidine residues on its way into the binding pocket. Our findings have direct implications for the potential administration of hemopexin in hemolytic disorders.

Linking Labile Heme with Thrombosis

Thrombosis is one of the leading causes of death worldwide. As such, it also occurs as one of the major complications in hemolytic diseases, like hemolytic uremic syndrome, hemorrhage and sickle cell disease. Under these conditions, red blood cell lysis finally leads to the release of large amounts of labile heme into the vascular compartment. This, in turn, can trigger oxidative stress and proinflammatory reactions. Moreover, the heme-induced activation of the blood coagulation system was suggested as a mechanism for the initiation of thrombotic events under hemolytic conditions. Studies of heme infusion and subsequent thrombotic reactions support this assumption. Furthermore, several direct effects of heme on different cellular and protein components of the blood coagulation system were reported. However, these effects are controversially discussed or not yet fully understood. This review summarizes the existing reports on heme and its interference in coagulation processes, emphasizing the relevance of considering heme in the context of the treatment of thrombosis in patients with hemolytic disorders.

Human radical scavenger α1-microglobulin protects against hemolysis in vitro and α1-microglobulin knockout mice exhibit a macrocytic anemia phenotype

During red blood cell (RBC) lysis hemoglobin and heme leak out of the cells and cause damage to the endothelium and nearby tissue. Protective mechanisms exist; however, these systems are not sufficient in diseases with increased extravascular hemolysis e.g. hemolytic anemia. α₁-microglobulin (A1M) is a ubiquitous reductase and radical- and heme-binding protein with antioxidation properties. Although present in the circulation in micromolar concentrations, its function in blood is unclear. Here, we show that A1M provides RBC stability. A1M^-/- mice display abnormal RBC morphology, reminiscent of macrocytic anemia conditions, i.e. fewer, larger and more heterogeneous cells. Recombinant human A1M (rA1M) reduced in vitro hemolysis of murine RBC against spontaneous, osmotic and heme-induced stress. Moreover, A1M is taken up by human RBCs both in vitro and in vivo. Similarly, rA1M also protected human RBCs against in vitro spontaneous, osmotic, heme- and radical-induced hemolysis as shown by significantly reduced leakage of hemoglobin and LDH. Addition of rA1M resulted in decreased hemolysis compared to addition of the heme-binding protein hemopexin and the radical-scavenging and reducing agents ascorbic acid and Trolox (vitamin E). Furthermore, rA1M significantly reduced spontaneous and heme-induced fetal RBC cell death. Addition of A1M to human whole blood resulted in a significant reduction of hemolysis, whereas removal of A1M from whole blood resulted in increased hemolysis. We conclude that A1M has a protective function in reducing hemolysis which is neither specific to the origin of hemolytic insult, nor species specific.

Methods for Assessment of Interactions of Proteins with Heme: Application for Complement Proteins and Immunoglobulins

Heme (Fe protoporphyrin IX) serves as a prosthetic group of numerous proteins implicated in oxidative metabolism. This molecule is abundantly present in the red blood cells where it serves as a cofactor of hemoglobin. As consequence of various pathological conditions, the membrane of red blood cells can be damaged and therefore large quantities of hemoglobin and subsequently heme released in the extracellular space. Since heme is a highly reactive compound, when released extracelluarly it can influence the functional activity of different plasma components. Thus, previous investigations have demonstrated that heme can interact with components of complement system and immunoglobulins, profoundly affecting their functions. Here we propose two basic protocols that can be used for characterization of interaction of free heme with complement proteins and immunoglobulins. The first technique is based on UV-Vis absorbance spectroscopy. It allows general characterization of the heme binding to the protein and estimation of the number of heme binding sites. The second protocol consists in the use of biosensor assay based on surface plasmon resonance. This protocol would be useful for evaluation of heme binding kinetics and equilibrium affinity. Besides for complement components and immunoglobulins, the presented protocols can be utilized for characterization of the interaction of heme with other proteins.

Heme as Possible Contributing Factor in the Evolvement of Shiga-Toxin Escherichia coli Induced Hemolytic-Uremic Syndrome

Shiga-toxin (Stx)-producing Escherichia coli hemolytic-uremic syndrome (STEC-HUS) is one of the most common causes of acute kidney injury in children. Stx-mediated endothelial injury initiates the cascade leading to thrombotic microangiopathy (TMA), still the exact pathogenesis remains elusive. Interestingly, there is wide variability in clinical presentation and outcome. One explanation for this could be the enhancement of TMA through other factors. We hypothesize that heme, as released during extensive hemolysis, contributes to the etiology of TMA. Plasma levels of heme and its scavenger hemopexin and degrading enzyme heme-oxygenase-1 (HO-1) were measured in 48 STEC-HUS patients. Subsequently, the effect of these disease-specific heme concentrations, in combination with Stx, was assessed on primary human glomerular microvascular endothelial cells (HGMVECs). Significantly elevated plasma heme levels up to 21.2 µM were found in STEC-HUS patients compared to controls and were inversely correlated with low or depleted plasma hemopexin levels (R² −0.74). Plasma levels of HO-1 are significantly elevated compared to controls. Interestingly, especially patients with high heme levels (n = 12, heme levels above 75 quartile range) had high plasma HO-1 levels with median of 332.5 (86–720) ng/ml (p = 0.008). Furthermore, heme is internalized leading to a significant increase in reactive oxygen species production and stimulated both nuclear translocation of NF-κB and increased levels of its target gene (tissue factor). In conclusion, we are the first to show elevated heme levels in patients with STEC-HUS. These increased heme levels mediate endothelial injury by promoting oxidative stress and a pro-inflammatory and pro-thrombotic state. Hence, heme may be a contributing and driving factor in the pathogenesis of STEC-HUS and could potentially amplify the cascade leading to TMA.

Reduced lifespan of erythrocytes in Dahl/Salt sensitive rats is the cause of the renal proximal tubule damage

We studied the mechanisms of anemia and the influence of anemia on renal pathology in Dahl/Salt Sensitive (Dahl/SS) rat, a model of cardio-renal-anemia syndrome. Erythrocyte lifespan was shortened and associated with decreased hemoglobin level in the Dahl/SS rats given high-salt diet. Serum haptoglobin decreased, reticulocytes increased, and erythropoiesis in the bone marrow and extramedullary hematopoiesis in the spleen was markedly stimulated by increased serum erythropoietin in them. As a mechanism of hemolysis, we investigated the incidence of eryptosis, suicidal death of erythrocytes. Eryptosis was increased, and red blood cell-derived microparticles, small particle which are generated in hemolytic disease, were also increased in Dahl/SS rats fed with high-salt diet. Deposition of hemosiderin and mitochondrial morphologic abnormality, a sign of ferroptosis, in proximal renal tubules was associated with intravascular hemolysis. Treatment with deferasirox, an oral iron chelator, reduced the renal proximal tubular injury and the glomerular sclerosis in Dahl/SS rats fed with high-salt diet. In conclusion, reduced half-life of erythrocytes induced by hemolysis is the major cause of anemia in Dahl/SS rat. Iron accumulation induced by hemolysis causes renal proximal tubule injury and accelerates renal damage in this model.