Free heme toxicity and its detoxification systems in human

Analysis of clinical presentation, hematological factors, self-reported bed net usage, and malaria burden in sickle cell disease patients

BACKGROUND

Sickle cell anemia (SCA) is a severe monogenic disorder, caused by single nucleotide mutations in the hemoglobin (Hb) gene, that is prevalent in malaria endemic regions of the world. Sickle cell trait (SCT) individuals carry only one of the mutated alleles and were shown to be protected against malaria. However, defining the relative contribution of hematological, clinical, and environmental factors to the overall burden of malaria in individuals with hemoglobinopathies such as SCA has been challenging.

METHODS

We hypothesized that hematological differences, clinical presentations, and self-reported bed net usage among Plasmodium-infected and uninfected individuals may govern overall malaria burden in individuals with sickle cell disease (SCD). We conducted a cross-sectional study in Ghana from 2014 to 2019 and described clinical presentations, hematological characteristics, and bed net use based on a comprehensive questionnaire. Hematological characteristics were compared using a parametric or nonparametric ANOVA, pending if data passed D'Agostino & Pearson normality test. When comparing only two Hb genotypes hematological characteristics a Mann-Whitney U-test were used. Logistic regressions and Chi-squared tests were used to compare questionnaire responses between Hb genotypes. All statistical significance was set at p < 0.05.

FINDINGS

Multiple hematological parameters were significantly (p < 0.05) altered depending on sickle cell genotype and/or malaria status. When compared to other Hb genotypes, SCA individuals with or without malaria had significantly (p < 0.05) higher WBC and platelets counts and lower Hb levels. While the sickle cell genotype may affect malaria severity, SCT and SCA participants were found to significantly (p < 0.007) use bet nets more than HbAA participants.

INTERPRETATIONS

Our findings can be utilized to enhance national guidelines for reducing the incidence of malaria especially among individuals with SCD, SCT protection and health disparities among hemoglobinopathies.

FUNDING

This study was supported by the National Institute for Health.

Targetting ferroptosis for blood cell-related diseases

Ferroptosis is an iron-dependent cell death pathway and participates in various diseases. Current evidence suggests that ferroptosis can obviously affect the function of blood cells. This paper aims to elaborate the role of ferroptosis in blood cells and related diseases. First, abnormal ferroptosis damages the developing red blood cells by breaking systemic iron homeostasis, leading to erythropoiesis suppression and anaemia. Ferroptosis mediates neutrophils recruitment and neutrophil extracellular trap formation (NETosis). In T-cells, ferroptosis induces a novel point of synergy between immunotherapy and radiotherapy. Additionally, ferroptosis may mediate B cells differentiation, antibody responses and lymphoma. Nevertheless, increased ferroptosis can ameliorate acute myeloid leukaemia and T-cell leukaemia/lymphoma by inducing iron-dependent cancer cells death. Besides, ferroptosis activates platelets by increasing P-selectin, thus causing thromboembolism. Ferroptosis mediates virus infection and parasite infection by driving T-cell death and preventing T-cell immunity. Interestingly, ferroptosis is also considered as a critical player in COVID-19 infections, while targetting ferroptosis may also improve thromboembolism and prognosis in patients with COVID-19 infection. Overall, the crucial role of ferroptosis in blood cells will show a new therapeutic potential in blood cell-related diseases.HighlightsFerroptosis shows a new therapeutic potential for blood cell-related diseases.Ferroptosis damages erythropoiesis and thus induces anaemia.Ferroptosis induces platelet activation and leads to thromboembolism.Ferroptosis regulates T-cell and B-cell immunity, which participant in infectious diseases.Inversely, ferroptosis ameliorates acute myeloid leukaemia and T-cell leukaemia.

Novel Therapies for Parkinsonian Syndromes-Recent Progress and Future Perspectives

Background: Atypical parkinsonian syndromes are rare, fatal neurodegenerative diseases associated with abnormal protein accumulation in the brain. Examples of these syndromes include progressive supranuclear palsy, multiple system atrophy, and corticobasal degeneration. A common clinical feature in parkinsonism is a limited improvement with levodopa. So far, there are no disease-modifying treatments to address these conditions, and therapy is only limited to the alleviation of symptoms. Diagnosis is devastating for patients, as prognosis is extremely poor, and the disease tends to progress rapidly. Currently, potential causes and neuropathological mechanisms involved in these diseases are being widely investigated. Objectives: The goal of this review is to summarize recent advances and gather emerging disease-modifying therapies that could slow the progression of atypical parkinsonian syndromes. Methods: PubMed and Google Scholar databases were searched regarding novel perspectives for atypical parkinsonism treatment. The following medical subject headings were used: "atypical parkinsonian syndromes-therapy," "treatment of atypical parkinsonian syndromes," "atypical parkinsonian syndromes-clinical trial," "therapy of tauopathy," "alpha-synucleinopathy treatment," "PSP therapy/treatment," "CBD therapy/treatment," "MSA therapy/treatment," and "atypical parkinsonian syndromes-disease modifying." All search results were manually reviewed prior to inclusion in this review. Results: Neuroinflammation, mitochondrial dysfunction, microglia activation, proteasomal impairment, and oxidative stress play a role in the neurodegenerative process. Ongoing studies and clinical trials target these components in order to suppress toxic protein accumulation. Various approaches such as stem cell therapy, anti-aggregation/anti-phosphorylation agent administration, or usage of active and passive immunization appear to have promising results. Conclusion: Presently, disease-modifying strategies for atypical parkinsonian syndromes are being actively explored, with encouraging preliminary results. This leads to an assumption that developing accurate, safe, and progression-halting treatment is not far off. Nevertheless, the further investigation remains necessary.

SARS-CoV-2 Proteins Bind to Hemoglobin and Its Metabolites

(1) Background: coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been linked to hematological dysfunctions, but there are little experimental data that explain this. Spike (S) and Nucleoprotein (N) proteins have been putatively associated with these dysfunctions. In this work, we analyzed the recruitment of hemoglobin (Hb) and other metabolites (hemin and protoporphyrin IX-PpIX) by SARS-Cov2 proteins using different approaches. (2) Methods: shotgun proteomics (LC-MS/MS) after affinity column adsorption identified hemin-binding SARS-CoV-2 proteins. The parallel synthesis of the peptides technique was used to study the interaction of the receptor bind domain (RBD) and N-terminal domain (NTD) of the S protein with Hb and in silico analysis to identify the binding motifs of the N protein. The plaque assay was used to investigate the inhibitory effect of Hb and the metabolites hemin and PpIX on virus adsorption and replication in Vero cells. (3) Results: the proteomic analysis by LC-MS/MS identified the S, N, M, Nsp3, and Nsp7 as putative hemin-binding proteins. Six short sequences in the RBD and 11 in the NTD of the spike were identified by microarray of peptides to interact with Hb and tree motifs in the N protein by in silico analysis to bind with heme. An inhibitory effect in vitro of Hb, hemin, and PpIX at different levels was observed. Strikingly, free Hb at 1mM suppressed viral replication (99%), and its interaction with SARS-CoV-2 was localized into the RBD region of the spike protein. (4) Conclusions: in this study, we identified that (at least) five proteins (S, N, M, Nsp3, and Nsp7) of SARS-CoV-2 recruit Hb/metabolites. The motifs of the RDB of SARS-CoV-2 spike, which binds Hb, and the sites of the heme bind-N protein were disclosed. In addition, these compounds and PpIX block the virus's adsorption and replication. Furthermore, we also identified heme-binding motifs and interaction with hemin in N protein and other structural (S and M) and non-structural (Nsp3 and Nsp7) proteins.

Endogenous n-3 PUFAs attenuated olfactory bulbectomy-induced behavioral and metabolomic abnormalities in Fat-1 mice

Depression is associated with abnormal lipid metabolism, and omega (n)-3 polyunsaturated fatty acids (PUFAs) can effectively treat depression. However, mechanism of lipid metabolism involved in the depressive attenuation remains poorly understood. Olfactory bulbectomy (OB)-induced changes in animal behavior and physiological functions are similar to those observed in depressed patients. Therefore, the present study used wild type (WT) and Fat-1 mice with or without OB to explore whether endogenous n-3 PUFA treatment of depression was through rectifying lipid metabolism, and to discover the possible lipid metabolic pathways. In WT mice, OB enhanced locomotor activity associated with up-regulation of lipid metabolites in the serum, such as phosphatidylcholines, L-a-glutamyl-L-Lysine and coproporphyrinogen III (Cop), which were involved in anti-inflammatory lipid metabolic pathways. OB also increased microglia activation marker CD11b and pro-inflammatory cytokines in the hippocampus. In one of the lipid pathways, increased Cop was significantly correlated with the hyper-activity of the OB mice. These OB-induced changes were markedly attenuated by endogenous n-3 PUFAs in Fat-1 mice. Additionally, increased expressions of anti-inflammatory lipid genes, such as fatty acid desaturase (Fads) and phospholipase A2 group VI (Pla2g6), were found in the hippocampus of Fat-1 mice compared with WT mice. Furthermore, Cop administration increased the production of pro-inflammatory cytokines and nitric oxide in a microglial cell line BV2. In conclusion, endogenous n-3 PUFAs in Fat-1 mice attenuated abnormal behavior in the depression model through restoration of lipid metabolism and suppression of inflammatory response.

Hemin, a major heme molecule, induced cellular and genetic alterations in normal colonic and colon cancer cells

Heme, a molecule abundant in red meat, is assumed to exert carcinogenic effects on normal colonic cells and tumour suppressive effects on cancer cells, though the hypothesis has not been explicitly proven yet. The present study aims to investigate hemin induced cytotoxic, genetic and biological alterations in both normal and cancerous colonic epithelial cells, which may imply its carcinogenic and anticarcinogenic properties. Normal colonic epithelial cells and colon carcinoma cells were treated with a 0-500 µM concentration of hemin for 1-4 days following which cytotoxicity and wound healing assays, western blot, rt-PCR and cell cycle analysis were performed. Interestingly, hemin was cytotoxic to normal colonic cells, but carcinoma cells were more resistant. Cell migration potential of both normal colonic cells and colon carcinoma cells was impeded by hemin. Hemin caused upregulation of both P53 and β-catenin gene and proteins expression in normal colonic cells with concomitant cell cycle arrest at G1(Gap 1) and G2/M (Gap 2/ Mitosis). G1 and G2 cell cycle arrests were also observed in colon carcinoma cells. In conclusion, the present study confirms that hemin, a main heme molecule present in red meat, facilitates behavioural, genetic and cell cycle kinetic alterations in both normal colonic epithelial and colon carcinoma cells.

Iron and nitrogen-co-doped carbon quantum dots for the sensitive and selective detection of hematin and ferric ions and cell imaging

Iron, nitrogen-co-doped carbon quantum dots (Fe,N-CDs) were prepared via a simple one-step hydrothermal method. The quantum yield of fluorescence reached about 27.6% and the blue-emissive Fe,N-CDs had a mean size of 3.76 nm. The as-prepared carbon quantum dots showed good solubility, a high quantum yield, good biocompatibility, low cytotoxicity, and high photostability. Interestingly, the as-prepared Fe,N-CDs exhibited good selectivity and sensitivity toward both hematin and ferric ions, and the limit of detection for hematin and ferric ions was calculated to be about 0.024 μM and 0.64 μM, respectively. At the same time, Fe,N-CDs were used for imaging HeLa cells and showed that most Fe,N-CDs were detained in the lysosome. Thus, this fluorescent probe has potential application in the quantitative detection of hematin or Fe3+ in a complex environment and for determining Fe3+ at the cellular level.

Plasmodium vivax Infection Alters Mitochondrial Metabolism in Human Monocytes

Monocytes play an important role in the host defense against Plasmodium vivax as the main source of inflammatory cytokines and mitochondrial reactive oxygen species (mROS). Here, we show that monocyte metabolism is altered during human P. vivax malaria, with mitochondria playing a major function in this switch. The process involves a reprograming in which the cells increase glucose uptake and produce ATP via glycolysis instead of oxidative phosphorylation. P. vivax infection results in dysregulated mitochondrial gene expression and in altered membrane potential leading to mROS increase rather than ATP production. When monocytes were incubated with P. vivax-infected reticulocytes, mitochondria colocalized with phagolysosomes containing parasites representing an important source mROS. Importantly, the mitochondrial enzyme superoxide dismutase 2 (SOD2) is simultaneously induced in monocytes from malaria patients. Taken together, the monocyte metabolic reprograming with an increased mROS production may contribute to protective responses against P. vivax while triggering immunomodulatory mechanisms to circumvent tissue damage. IMPORTANCE Plasmodium vivax is the most widely distributed causative agent of human malaria. To achieve parasite control, the human immune system develops a substantial inflammatory response that is also responsible for the symptoms of the disease. Among the cells involved in this response, monocytes play an important role. Here, we show that monocyte metabolism is altered during malaria, with its mitochondria playing a major function in this switch. This change involves a reprograming process in which the cells increase glucose uptake and produce ATP via glycolysis instead of oxidative phosphorylation. The resulting altered mitochondrial membrane potential leads to an increase in mitochondrial reactive oxygen species rather than ATP. These data suggest that agents that change metabolism should be investigated and used with caution during malaria.

Carbon Monoxide Therapy Using Hybrid Carbon Monoxide-Releasing/Nrf2-Inducing Molecules through a Neuroprotective Lens

Carbon monoxide (CO) has long been known for its toxicity. However, in recent decades, new applications for CO as a therapeutic compound have been proposed, and multiple forms of CO therapy have since been developed and studied. Previous research has found that CO has a role as a gasotransmitter and promotes anti-inflammatory and antioxidant effects, making it an avenue of interest for medicine. Such effects are possible because of the Nrf2/HO1 pathway, which has become a target for therapy development because its activation also leads to CO release. Currently, different forms of treatment involving CO include inhaled CO (iCO), carbon monoxide-releasing molecules (CORMs), and hybrid carbon monoxide-releasing molecules (HYCOs). In this article, we review the progression of CO studies to develop possible therapies, the possible mechanisms involved in the effects of CO, and the current forms of therapy using CO.

Molecular docking analysis of furfural and isoginkgetin with heme oxygenase I and PPARγ

It is of interest to document the molecular docking analysis based binding data of furfural and isoginkgetin with heme oxygenase I and PPARγ in the context of inflammation for further consideration in drug design and development.

Regulation of inflammation by the antioxidant haem oxygenase 1

Haem oxygenase 1 (HO-1), an inducible enzyme responsible for the breakdown of haem, is primarily considered an antioxidant, and has long been overlooked by immunologists. However, research over the past two decades in particular has demonstrated that HO-1 also exhibits numerous anti-inflammatory properties. These emerging immunomodulatory functions have made HO-1 an appealing target for treatment of diseases characterized by high levels of chronic inflammation. In this Review, we present an introduction to HO-1 for immunologists, including an overview of its roles in iron metabolism and antioxidant defence, and the factors which regulate its expression. We discuss the impact of HO-1 induction in specific immune cell populations and provide new insights into the immunomodulation that accompanies haem catabolism, including its relationship to immunometabolism. Furthermore, we highlight the therapeutic potential of HO-1 induction to treat chronic inflammatory and autoimmune diseases, and the issues faced when trying to translate such therapies to the clinic. Finally, we examine a number of alternative, safer strategies that are under investigation to harness the therapeutic potential of HO-1, including the use of phytochemicals, novel HO-1 inducers and carbon monoxide-based therapies.

Pharmacological Assessment of the Antiprotozoal Activity, Cytotoxicity and Genotoxicity of Medicinal Plants Used in the Treatment of Malaria in the Greater Mpigi Region in Uganda

We investigated the potential antimalarial and toxicological effects of 16 medicinal plants frequently used by traditional healers to treat malaria, fever, and related disorders in the Greater Mpigi region in Uganda. Species studied were Albizia coriaria, Cassine buchananii, Combretum molle, Erythrina abyssinica, Ficus saussureana, Harungana madagascariensis, Leucas calostachys, Microgramma lycopodioides, Morella kandtiana, Plectranthus hadiensis, Securidaca longipedunculata, Sesamum calycinum subsp. angustifolium, Solanum aculeastrum, Toddalia asiatica, Warburgia ugandensis, and Zanthoxylum chalybeum. In addition, the traditional healers indicated that P. hadiensis is used as a ritual plant to boost fertility and prepare young women and teenagers for motherhood in some Ugandan communities where a high incidence of rapidly growing large breast masses in young female patients was observed (not necessarily breast cancer). We present results from various in vitro experiments performed with 56 different plant extracts, namely, 1) an initial assessment of the 16 species regarding their traditional use in the treatment of malaria by identifying promising plant extract candidates using a heme biocrystallization inhibition library screen; 2) follow-up investigations of antiprotozoal effects of the most bioactive crude extracts against chloroquine-resistant P. falciparum K1; 3) a cytotoxicity counterscreen against human MRC-5SV2 lung fibroblasts; 4) a genotoxicity evaluation of the extract library without and with metabolic bioactivation with human S9 liver fraction; and 5) an assessment of the mutagenicity of the ritual plant P. hadiensis. A total of seven extracts from five plant species were selected for antiplasmodial follow-up investigations based on their hemozoin formation inhibition activity in the heme biocrystallization assay. Among other extracts, an ethyl acetate extract of L. calostachys leaves exhibited antiplasmodial activity against P. falciparum K1 (IC50 value: 5.7 µg/ml), which was further characterized with a selectivity index of 2.6 (CC50 value: 14.7 µg/ml). The experiments for assessment of potential procarcinogenic properties of plant extracts via evaluation of in vitro mutagenicity and genotoxicity indicated that few extracts cause mutations. The species T. asiatica showed the most significant genotoxic effects on both bacterial test strains (without metabolic bioactivation at a concentration of 500 µg/plate). However, none of the mutagenic extracts from the experiments without metabolic bioactivation retained their genotoxic activity after metabolic bioactivation of the plant extract library through pre-incubation with human S9 liver fraction. While this study did not show that P. hadiensis has genotoxic properties, it did provide early stage support for the therapeutic use of the medicinal plants from the Greater Mpigi region.

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.

A Transcriptomic Approach to the Metabolism of Tetrapyrrolic Photosensitizers in a Marine Annelid

The past decade has seen growing interest in marine natural pigments for biotechnological applications. One of the most abundant classes of biological pigments is the tetrapyrroles, which are prized targets due their photodynamic properties; porphyrins are the best known examples of this group. Many animal porphyrinoids and other tetrapyrroles are produced through heme metabolic pathways, the best known of which are the bile pigments biliverdin and bilirubin. Eulalia is a marine Polychaeta characterized by its bright green coloration resulting from a remarkably wide range of greenish and yellowish tetrapyrroles, some of which have promising photodynamic properties. The present study combined metabolomics based on HPLC-DAD with RNA-seq transcriptomics to investigate the molecular pathways of porphyrinoid metabolism by comparing the worm’s proboscis and epidermis, which display distinct pigmentation patterns. The results showed that pigments are endogenous and seemingly heme-derived. The worm possesses homologs in both organs for genes encoding enzymes involved in heme metabolism such as ALAD, FECH, UROS, and PPOX. However, the findings also indicate that variants of the canonical enzymes of the heme biosynthesis pathway can be species- and organ-specific. These differences between molecular networks contribute to explain not only the differential pigmentation patterns between organs, but also the worm’s variety of novel endogenous tetrapyrrolic compounds.

A first principle study of heme molecule as an active adsorbent for halogenated hydrocarbons

Heme, a biomolecule with complex structure and unique properties and strong adsorption of oxygen, is utilized as an adsorbing material for haloalkene gas molecules. It has been systematically investigated employing density functional theory. Among the haloalkene gases chosen in the present study, the interaction energy is maximum for CDFM (-10.66 kcal/mol) and lowest for TFM (-5.02 kcal/mol). The calculated bond stabilization energy for heme-haloalkene complexes correlates with findings of interaction energy. The noncovalent interaction between heme and haloalkenes is confirmed from the topological analysis. The energy gap values decrease on adsorption of haloalkenes along with a decrease in reactivity of the complexes.

Ferryl Hemoglobin and Heme Induce A1-Microglobulin in Hemorrhaged Atherosclerotic Lesions with Inhibitory Function against Hemoglobin and Lipid Oxidation

Infiltration of red blood cells into atheromatous plaques and oxidation of hemoglobin (Hb) and lipoproteins are implicated in the pathogenesis of atherosclerosis. α₁-microglobulin (A1M) is a radical-scavenging and heme-binding protein. In this work, we examined the origin and role of A1M in human atherosclerotic lesions. Using immunohistochemistry, we observed a significant A1M immunoreactivity in atheromas and hemorrhaged plaques of carotid arteries in smooth muscle cells (SMCs) and macrophages. The most prominent expression was detected in macrophages of organized hemorrhage. To reveal a possible inducer of A1M expression in ruptured lesions, we exposed aortic endothelial cells (ECs), SMCs and macrophages to heme, Oxy- and FerrylHb. Both heme and FerrylHb, but not OxyHb, upregulated A1M mRNA expression in all cell types. Importantly, only FerrylHb induced A1M protein secretion in aortic ECs, SMCs and macrophages. To assess the possible function of A1M in ruptured lesions, we analyzed Hb oxidation and heme-catalyzed lipid peroxidation in the presence of A1M. We showed that recombinant A1M markedly inhibited Hb oxidation and heme-driven oxidative modification of low-density lipoproteins as well plaque lipids derived from atheromas. These results demonstrate the presence of A1M in atherosclerotic plaques and suggest its induction by heme and FerrylHb in the resident cells.

The Effectiveness of Potential Probiotics Lactobacillus rhamnosus Vahe and Lactobacillus delbrueckii IAHAHI in Irradiated Rats Depends on the Nutritional Stage of the Host

Several species of eukaryotic organisms living in the high mountain areas of Armenia with naturally occurring levels of radiation have high adaptive responses to radiation. We speculate on the role of the gastrointestinal microbiota in this protection against radiation. Therefore, seventeen microorganisms with high antagonistic activities against several multi-drug-resistant pathogens were isolated from the human and animal gut microbiota, as well as from traditional Armenian fermented products. These strains were tested in vivo on Wistar rats to determine their ability to protect the eukaryotic host against radiation damages. The efficiency of the probiotics' application and the dependence on pre- and post-radiation nutrition of rats were described. The effects of Lactobacillus rhamnosus Vahe, isolated from a healthy breastfed infant, and Lactobacillus delbrueckii IAHAHI, isolated from the fermented dairy product matsuni, on the survival of irradiated rats, and their blood leucocyte and glucose levels, were considered to be the most promising, based on this study's results.

Heme Detoxification in the Malaria Parasite: A Target for Antimalarial Drug Development

Over the last century, malaria deaths have decreased by more than 85%. Nonetheless, there were 405 000 deaths in 2018, mostly resulting from Plasmodium falciparum infection. In the 21st century, much of the advance has arisen from the deployment of insecticide-treated bed nets and artemisinin combination therapy. However, over the past few decades parasites with a delayed artemisinin clearance phenotype have appeared in Southeast Asia, threatening further gains. The effort to find new drugs is thus urgent. A prominent process in blood stage malaria parasites, which we contend remains a viable drug target, is hemozoin formation. This crystalline material consisting of heme can be readily seen when parasites are viewed microscopically. The process of its formation in the parasite, however, is still not fully understood.In early work, we recognized hemozoin formation as a biomineralization process. We have subsequently investigated the kinetics of synthetic hemozoin (β-hematin) crystallization catalyzed at lipid-aqueous interfaces under biomimetic conditions. This led us to the use of neutral detergent-based high-throughput screening (HTS) for inhibitors of β-hematin formation. A good hit rate against malaria parasites was obtained. Simultaneously, we developed a pyridine-based assay which proved successful in measuring the concentrations of hematin not converted to β-hematin.The pyridine assay was adapted to determine the effects of chloroquine and other clinical antimalarials on hemozoin formation in the cell. This permitted the determination of the dose-dependent amounts of exchangeable heme and hemozoin in P. falciparum for the first time. These studies have shown that hemozoin inhibitors cause a dose-dependent increase in exchangeable heme, correlated with decreased parasite survival. Electron spectroscopic imaging (ESI) showed a relocation of heme iron into the parasite cytoplasm, while electron microscopy provided evidence of the disruption of hemozoin crystals. This cellular assay was subsequently extended to top-ranked hits from a wide range of scaffolds found by HTS. Intriguingly, the amounts of exchangeable heme at the parasite growth IC₅₀ values of these scaffolds showed substantial variation. The amount of exchangeable heme was found to be correlated with the amount of inhibitor accumulated in the parasitized red blood cell. This suggests that heme-inhibitor complexes, rather than free heme, lead to parasite death. This was supported by ESI using a Br-containing compound which showed the colocalization of Fe and Br as well as by confocal Raman microscopy which confirmed the presence of a complex in the parasite. Current evidence indicates that inhibitors block hemozoin formation by surface adsorption. Indeed, we have successfully introduced molecular docking with hemozoin to find new inhibitors. It follows that the resulting increase in free heme leads to the formation of the parasiticidal heme-inhibitor complex. We have reported crystal structures of heme-drug complexes for several aryl methanol antimalarials in nonaqueous media. These form coordination complexes but most other inhibitors interact noncovalently, and the determination of their structures remains a major challenge.It is our view that key future developments will include improved assays to measure cellular heme levels, better in silico approaches for predicting β-hematin inhibition, and a concerted effort to determine the structure and properties of heme-inhibitor complexes.

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.

Toxic effects of cell-free hemoglobin on the microvascular endothelium: implications for pulmonary and nonpulmonary organ dysfunction

Levels of circulating cell-free hemoglobin are elevated during hemolytic and inflammatory diseases and contribute to organ dysfunction and severity of illness. Though several studies have investigated the contribution of hemoglobin to tissue injury, the precise signaling mechanisms of hemoglobin-mediated endothelial dysfunction in the lung and other organs are not yet completely understood. The purpose of this review is to highlight the knowledge gained thus far and the need for further investigation regarding hemoglobin-mediated endothelial inflammation and injury to develop novel therapeutic strategies targeting the damaging effects of cell-free hemoglobin.

Heme supplementation ameliorates lupus nephritis through rectifying the disorder of splenocytes and alleviating renal inflammation and oxidative damage

Heme is an important iron-containing porphyrin molecule expressed ubiquitously in organisms. Recently, this endogenous molecule has been widely reported to be involved in the pathogenesis of numerous diseases such as sepsis, atherosclerosis and inflammatory bowel disease. However, the role of heme during systemic lupus erythematosus (SLE) pathogenesis has not been previously evaluated. Herein, we have measured the levels of heme in lupus-prone mice and explored the influence of heme on the pathogenesis of lupus. We revealed that heme levels in serum, kidney and spleen lymphocytes are all negatively associated with the levels of proteinuria in lupus-prone mice. Heme supplementation at 15 mg/kg could significantly ameliorate the syndromes of lupus in MRL/lpr mice, extending lifespan, reducing the level of proteinuria and alleviating splenomegaly and lymphadenopathy. Further study demonstrated that heme replenishment corrected the abnormal compartment of T cell subsets, plasma cells and macrophages in the spleen and alleviates inflammation and oxidative damage in kidney of MRL/lpr mice. Our study well defined heme as a relevant endogenous molecule in the etiology of SLE, as well as a potential therapeutic target for treating this autoimmune disease. Meanwhile, heme replenishment might be a new choice to therapeutically modulate immune homeostasis and prevent SLE.

Effect of hemopexin treatment on outcome after intracerebral hemorrhage in mice

Heme release from hemoglobin may contribute to secondary injury after intracerebral hemorrhage (ICH). The primary endogenous defense against heme toxicity is hemopexin, a 57 kDa glycoprotein that is depleted in the CNS after hemorrhagic stroke. We hypothesized that systemic administration of exogenous hemopexin would reduce perihematomal injury and improve outcome after experimental ICH. Intraperitoneal treatment with purified human plasma hemopexin beginning 2 h after striatal ICH induction and repeated daily for the following two days reduced blood-brain barrier disruption and cell death at 3 days. However, it had no effect on neurological deficits at 4 or 7 days or striatal cell viability at 8 days. Continuous daily hemopexin administration had no effect on striatal heme content at 3 or 7 days, and did not attenuate neurological deficits, inflammatory cell infiltration, or perihematomal cell viability at 8 days. These results suggest that systemic hemopexin treatment reduces early injury after ICH, but this effect is not sustained, perhaps due to an imbalance between striatal tissue heme and hemopexin content at later time points. Future studies should investigate its effect when administered by methods that more efficiently target CNS delivery.

Heme-binding protein CYB5D1 is a radial spoke component required for coordinated ciliary beating

Coordinated beating is crucial for the function of multiple cilia. However, the molecular mechanism is poorly understood. Here, we characterize a conserved ciliary protein CYB5D1 with a heme-binding domain and a cordon-bleu ubiquitin-like domain. Mutation or knockdown of Cyb5d1 in zebrafish impaired coordinated ciliary beating in the otic vesicle and olfactory epithelium. Similarly, the two flagella of an insertional mutant of the CYB5D1 ortholog in Chlamydomonas (Crcyb5d1) showed an uncoordinated pattern due to a defect in the cis-flagellum. Biochemical analyses revealed that CrCYB5D1 is a radial spoke stalk protein that binds heme only under oxidizing conditions. Lack of CrCYB5D1 resulted in a reductive shift in flagellar redox state and slowing down of the phototactic response. Treatment of Crcyb5d1 with oxidants restored coordinated flagellar beating. Taken together, these data suggest that CrCYB5D1 may integrate environmental and intraciliary signals and regulate the redox state of cilia, which is crucial for the coordinated beating of multiple cilia.

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.

A previously unknown way of heme detoxification in the digestive tract of cats

Free heme is a highly toxic molecule for a living organism and its detoxification is a very important process, especially for carnivorous animals. Here we report the discovery of a previously unknown process for neutralizing free heme in the digestive tract of domestic cats. The cornerstone of this process is the encapsulation of heme into carbonated hydroxyapatite nanoparticles, followed by their excretion with faeces. This way of heme neutralization resembles the formation of insoluble heme-containing particles in the digestive tracts of other hematophagous species (for example, the formation of insoluble hemozoin crystals in malaria-causing Plasmodium parasites). Our findings suggest that the encapsulation of heme molecules into a hydroxyapatite matrix occurs during the transition from the acidic gastric juice to the small intestine with neutral conditions. The formation of these particles and their efficiency to include heme depends on the bone content in a cat's diet. In vitro experiments with heme-hydroxyapatite nanoparticles confirm the proposed scenario.

Acute Phase Responses Vary Between Children of HbAS and HbAA Genotypes During Plasmodium falciparum Infection

Purpose

Haemoglobin genotype S is known to offer protection against Plasmodium falciparum infections but the mechanism underlying this protection is not completely understood. Associated changes in acute phase proteins (APPs) during Plasmodium falciparum infections between Haemoglobin AA (HbAA) and Haemoglobin AS (HbAS) individuals also remain unclear. This study aimed to evaluate changes in three APPs and full blood count (FBC) indices of HbAA and HbAS children during Plasmodium falciparum infection.

Methods

Venous blood was collected from three hundred and twenty children (6 months to 15 years) in Begoro in Fanteakwa District of Ghana during a cross-sectional study. Full blood count (FBC) indices were measured and levels of previously investigated APPs in malaria patients; C-reactive protein (CRP), ferritin and transferrin measured using Enzyme-Linked Immunosorbent Assays.

Results

Among the HbAA and HbAS children, levels of CRP and ferritin were higher in malaria positive children as compared to those who did not have malaria. The mean CRP levels were significantly higher among HbAA children (p=0.2e-08) as compared to the HbAS children (p=0.43). Levels of transferrin reduced in both HbAA and HbAS children with malaria, but the difference was only significant among HbAA children (p=0.0038), as compared to the HbAS children. No significant differences were observed in ferritin levels between HbAA and HbAS children in both malaria negative (p=0.76) and positive (p=0.26) children. Of the full blood count indices measured, red blood cell count (p=0.044) and haemoglobin (Hb) levels (p=0.017) differed between HbAA and HbAS in those without malaria, with higher RBC counts and lower Hb levels found in HbAS children. In contrast, during malaria, lymphocyte and platelet counts were elevated, whilst granulocytes and Mean Cell Haematocrit counts were reduced among children of the HbAS genotypes.

Conclusion

Significant changes in APPs were found in HbAA children during malaria as compared to HbAS children, possibly due to differences in malaria-induced inflammation levels. This suggests that the HbAS genotype is associated with better control of P. falciparum infection-induced inflammatory response than HbAA genotype.

Electronic structure and reactivity of heme bound insulin

Insulin resistance as well as insulin deficiency are said to be principal to the development of type 2 diabetes mellitus (T2Dm). Heme has also been suggested to play an important role in the disease etiology since many of the heme deficiency symptoms constitute the common pathological features of T2Dm. Besides, iron overload, higher heme iron intake and transfusion requiring diseases are associated with a higher risk of T2Dm development. In this study the interaction between these two key components i.e. heme and insulin has been studied spectroscopically under different conditions which include the effect of excess peptide as well as increasing pH. The resultant heme-insulin complexes in their reduced state are found to produce very little partially reduced oxygen species (PROS) on getting oxidized by molecular oxygen. The interaction between insulin and previously reported T2Dm relevant heme-amylin complex were also examined using absorption and resonance Raman spectroscopy. The corresponding data suggest that insulin sequesters heme from heme-amylin to form the much less cytotoxic heme-insulin.

Hemeprotein Tpx1 interacts with cell-surface heme transporter Str3 in Schizosaccharomyces pombe

Str3 is a transmembrane protein that mediates low-affinity heme uptake in Schizosaccharomyces pombe. Under iron-limiting conditions, Str3 remains at the cell surface in the presence of increasing hemin concentrations. Using a proximity-dependent biotinylation approach coupled to mass spectrometry and coimmunoprecipitation assays, we report that the peroxiredoxin Tpx1 is a binding partner of Str3. Under microaerobic conditions, cells deficient in heme biosynthesis and lacking the heme receptor Shu1 exhibit poor hemin-dependent growth in the absence of Tpx1. Analysis of membrane protein preparations from iron-starved hem1Δ shu1Δ str3Δ tpx1Δ cells coexpressing Str3-GFP and TAP-Tpx1 showed that TAP-Tpx1 is enriched in membrane protein fractions in response to hemin. Bimolecular fluorescence complementation assays brought additional evidence that an interaction between Tpx1 and Str3 occurs at the plasma membrane. Results showed that Tpx1 exhibits an equilibrium constant value of 0.26 μM for hemin. The association of Tpx1 with hemin protects hemin from degradation by H2 O2 . The peroxidase activity of hemin is lowered when it is bound to Tpx1. Taken together, these results revealed that Tpx1 is a novel interacting partner of Str3. Our data are the first example of an interaction between a cytoplasmic heme-binding protein and a cell-surface heme transporter.

Skeletal muscle heme oxygenase-1 activity regulates aerobic capacity

Physical exercise has profound effects on quality of life and susceptibility to chronic disease; however, the regulation of skeletal muscle function at the molecular level after exercise remains unclear. We tested the hypothesis that the benefits of exercise on muscle function are linked partly to microtraumatic events that result in accumulation of circulating heme. Effective metabolism of heme is controlled by Heme Oxygenase-1 (HO-1, Hmox1), and we find that mouse skeletal muscle-specific HO-1 deletion (Tam-Cre-HSA-Hmox1^fl/fl) shifts the proportion of muscle fibers from type IIA to type IIB concomitant with a disruption in mitochondrial content and function. In addition to a significant impairment in running performance and response to exercise training, Tam-Cre-HSA-Hmox1^fl/fl mice show remarkable muscle atrophy compared to Hmox1^fl/fl controls. Collectively, these data define a role for heme and HO-1 as central regulators in the physiologic response of skeletal muscle to exercise.

Hypoxia-Induced Alpha-Globin Expression in Syncytiotrophoblasts Mimics the Pattern Observed in Preeclamptic Placentas

Preeclampsia (PE) is a pregnancy disorder associated with placental dysfunction and elevated fetal hemoglobin (HbF). Early in pregnancy the placenta harbors hematopoietic stem and progenitor cells (HSPCs) and is an extramedullary source of erythropoiesis. However, globin expression is not unique to erythroid cells and can be triggered by hypoxia. To investigate the role of the placenta in increasing globin levels previously reported in PE, flow cytometry, histological and immunostaining and in situ analyses were used on placenta samples and ex vivo explant cultures. Our results indicated that in PE pregnancies, placental HSPC homing and erythropoiesis were not affected. Non-erythroid alpha-globin mRNA and protein, but not gamma-globin, were detected in syncytiotrophoblasts and stroma of PE placenta samples. Similarly, alpha-globin protein and mRNA were upregulated in normal placenta explants cultured in hypoxia. The upregulation was independent of HIF1 and NRF2, the two main candidates of globin transcription in non-erythroid cells. Our study is the first to demonstrate alpha-globin mRNA expression in syncytiotrophoblasts in PE, induced by hypoxia. However, gamma-globin was only expressed in erythrocytes. We conclude that alpha-globin, but not HbF, is expressed in placental syncytiotrophoblasts in PE and may contribute to the pathology of the disease.

Investigation of Cyanide Ligand as an Active Site Probe of Human Heme Oxygenase

Human heme oxygenase (hHO-1) is a physiologically important enzyme responsible for free heme catabolism. The enzyme's high regiospecificity is controlled by the distal site hydrogen bond network that involves water molecules and the D140 amino acid residue. In this work, we probe the active site environment of the wild-type (WT) hHO-1 and its D140 mutants using resonance Raman (rR) spectroscopy. Cyanide ligands are more stable than dioxygen adducts and are an effective probe of active site environment of heme proteins. The inherently linear geometry of the Fe-C-N fragment can be altered by the steric, electrostatic, and H-bonding interactions imposed by the amino acid residues present in the heme distal site, resulting in a tilted or bent configuration. The WT hHO-1 and its D140A, D140N, and D140E mutants were studied in the presence of natural abundance CN^- and its isotopic analogues (¹³CN^-, C¹⁵N^-, and ¹³C¹⁵N^-). Deconvolution of spectral data revealed that the ν(Fe-CN) stretching and δ(Fe-CN) bending modes are present at 454 and 376 cm^-1, respectively. The rR spectral patterns of the CN^- adducts of WT revealed that the Fe-C-N fragment adopts a tilted conformation, with a larger bending contribution for the D140A, D140N, and D140E mutants. These studies suggest that the FeCN fragment in hHO-1 is tilted more strongly toward the porphyrin macrocycle compared to other histidine-ligated proteins, reflecting the propensity of the exogenous hHO-l ligands to position toward the α-meso-carbon, which is crucial for the HO reactivity and essential for regioselectivity.

Interaction of clinical-stage antibodies with heme predicts their physiochemical and binding qualities

Immunoglobulin repertoires contain a fraction of antibodies that recognize low molecular weight compounds, including some enzymes' cofactors, such as heme. Here, by using a set of 113 samples with variable region sequences matching clinical-stage antibodies, we demonstrated that a considerable number of these antibodies interact with heme. Antibodies that interact with heme possess specific sequence traits of their antigen-binding regions. Moreover they manifest particular physicochemical and functional qualities i.e. increased hydrophobicity, higher propensity of self-binding, higher intrinsic polyreactivity and reduced expression yields. Thus, interaction with heme is a strong predictor of different molecular and functional qualities of antibodies. Notably, these qualities are of high importance for therapeutic antibodies, as their presence was associated with failure of drug candidates to reach clinic. Our study reveled an important facet of information about relationship sequence-function in antibodies. It also offers a convenient tool for detection of liabilities of therapeutic antibodies.

Endometriosis Is Associated with Functional Polymorphism in the Promoter of Heme Oxygenase 1 (HMOX1) Gene

Endometriosis is a common gynecological disorder characterized by the ectopic growth of endometrial-like tissue outside the uterine cavity. Etiopathogenesis of endometriosis is poorly understood; it is plausible, however, that the disease may be associated with oxidative stress related to local heme and iron metabolism. Therefore, the aim of the study was to reveal a possible association of endometriosis with a stress-inducible heme oxygenase 1 (HMOX1). For this purpose, 228 patients with clinically confirmed endometriosis and 415 control parous women from general Polish population were examined for functional -413A>T (rs2071746) single-nucleotide polymorphism (SNP) and (GT)_n dinucleotide repeat length polymorphism in the promoter of HMOX1 gene. In addition, -413A>T SNP was assessed by the specific TaqMan^® SNP Genotyping Assay, and (GT)_n polymorphism was determined by PCR product size analysis. We found that endometriosis is associated with an increased frequency of -413A(GT)_31,32 haplotype (OR (95%CI) = 1.27 (1.01-1.60), p = 0.0381) and -413A(GT)_31,32 homozygous genotype [OR (95%CI) = 1.51 (1.06-2.17), p = 0.0238]. These data suggest that endometriosis is associated with functional polymorphism of HMOX1 gene, and this gene may play a part in the pathogenesis of this disorder.

Vascular and Macrophage Heme Oxygenase-1 in Hypertension: A Mini-Review

Hypertension is one predictive factor for stroke and heart ischemic disease. Nowadays, it is considered an inflammatory disease with elevated cytokine levels, oxidative stress, and infiltration of immune cells in several organs including heart, kidney, and vessels, which contribute to the hypertension-associated cardiovascular damage. Macrophages, the most abundant immune cells in tissues, have a high degree of plasticity that is manifested by polarization in different phenotypes, with the most well-known being M1 (proinflammatory) and M2 (anti-inflammatory). In hypertension, M1 phenotype predominates, producing inflammatory cytokines and oxidative stress, and mediating many mechanisms involved in the pathogenesis of this disease. The increase in the renin-angiotensin system and sympathetic activity contributes to the macrophage mobilization and to its polarization to the pro-inflammatory phenotype. Heme oxygenase-1 (HO-1), a phase II detoxification enzyme responsible for heme catabolism, is induced by oxidative stress, among others. HO-1 has been shown to protect against oxidative and inflammatory insults in hypertension, reducing end organ damage and blood pressure, not only by its expression at the vascular level, but also by shifting macrophages toward the anti-inflammatory phenotype. The regulatory role of heme availability for the synthesis of enzymes involved in hypertension development, such as cyclooxygenase or nitric oxide synthase, seems to be responsible for many of the beneficial HO-1 effects; additionally, the antioxidant, anti-inflammatory, antiapoptotic, and antiproliferative effects of the end products of its reaction, carbon monoxide, biliverdin/bilirubin, and Fe²⁺, would also contribute. In this review, we analyze the role of HO-1 in hypertensive pathology, focusing on its expression in macrophages.

Iron intake with the risk of breast cancer among Chinese women: a case-control study

OBJECTIVE

The current study evaluated the associations between different forms and sources of Fe and breast cancer risk in Southern Chinese women.

DESIGN

Case-control study. We collected data on the consumption of Fe from different forms and food sources by using a validated FFQ. Multivariable logistic regression and restricted cubic spline (RCS) analysis was used to reveal potential associations between Fe intake and breast cancer risk.

SETTING

A case-control study of women at three major hospitals in Guangzhou, China.

PARTICIPANTS

From June 2007 to March 2019, 1591 breast cancer cases and 1622 age-matched controls were recruited.

RESULTS

In quartile analyses, Fe from plants and Fe from white meat intake were inversely associated with breast cancer risk, with OR of 0·65 (95 % CI 0·47, 0·89, Ptrend = 0·006) and 0·76 (95 % CI 0·61, 0·96, Ptrend = 0·014), respectively, comparing the highest with the lowest quartile. No associations were observed between total dietary Fe, heme or non-heme Fe, Fe from meat or red meat and breast cancer risk. RCS analysis demonstrated J-shaped associations between total dietary Fe, non-heme Fe and breast cancer, and reverse L-shaped associations between heme Fe, Fe from meat and Fe from red meat and breast cancer.

CONCLUSION

Fe from plants and white meat were inversely associated with breast cancer risk. Significant non-linear J-shaped associations were found between total dietary Fe, non-heme Fe and breast cancer risk, and reverse L-shaped associations were found between heme Fe, Fe from meat or red meat and breast cancer risk.

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.

Sickle Cell Disease: Role of Oxidative Stress and Antioxidant Therapy

Sickle cell disease (SCD) is the most common hereditary disorder of hemoglobin (Hb), which affects approximately a million people worldwide. It is characterized by a single nucleotide substitution in the β-globin gene, leading to the production of abnormal sickle hemoglobin (HbS) with multi-system consequences. HbS polymerization is the primary event in SCD. Repeated polymerization and depolymerization of Hb causes oxidative stress that plays a key role in the pathophysiology of hemolysis, vessel occlusion and the following organ damage in sickle cell patients. For this reason, reactive oxidizing species and the (end)-products of their oxidative reactions have been proposed as markers of both tissue pro-oxidant status and disease severity. Although more studies are needed to clarify their role, antioxidant agents have been shown to be effective in reducing pathological consequences of the disease by preventing oxidative damage in SCD, i.e., by decreasing the oxidant formation or repairing the induced damage. An improved understanding of oxidative stress will lead to targeted antioxidant therapies that should prevent or delay the development of organ complications in this patient population.

Cell-free oxidized hemoglobin drives reactive oxygen species production and pro-inflammation in an immature primary rat mixed glial cell culture

Background

Germinal matrix intraventricular hemorrhage (GM-IVH) is associated with deposition of redox active cell-free hemoglobin (Hb), derived from hemorrhagic cerebrospinal fluid (CSF), in the cerebrum and cerebellum. In a recent study, using a preterm rabbit pup model of IVH, intraventricularly administered haptoglobin (Hp), a cell-free Hb scavenger, partially reversed the damaging effects observed following IVH. Together, this suggests that cell-free Hb is central in the pathophysiology of the injury to the immature brain following GM-IVH. An increased understanding of the causal pathways and metabolites involved in eliciting the damaging response following hemorrhage is essential for the continued development and implementation of neuroprotective treatments of GM-IVH in preterm infant.

Methods

We exposed immature primary rat mixed glial cells to hemorrhagic CSF obtained from preterm human infants with IVH (containing a mixture of Hb-metabolites) or to a range of pure Hb-metabolites, incl. oxidized Hb (mainly metHb with iron in Fe³⁺), oxyHb (mainly Fe²⁺), or low equivalents of heme, with or without co-administration with human Hp (a mixture of isotype 2-2/2-1). Following exposure, cellular response, reactive oxygen species (ROS) generation, secretion and expression of pro-inflammatory cytokines and oxidative markers were evaluated.

Results

Exposure of the glial cells to hemorrhagic CSF as well as oxidized Hb, but not oxyHb, resulted in a significantly increased rate of ROS production that positively correlated with the rate of production of pro-inflammatory and oxidative markers. Congruently, exposure to oxidized Hb caused a disintegration of the polygonal cytoskeletal structure of the glial cells in addition to upregulation of F-actin proteins in microglial cells. Co-administration of Hp partially reversed the damaging response of hemorrhagic CSF and oxidized Hb.

Conclusion

Exposure of mixed glial cells to oxidized Hb initiates a pro-inflammatory and oxidative response with cytoskeletal disintegration. Early administration of Hp, aiming to minimize the spontaneous autoxidation of cell-free oxyHb and liberation of heme, may provide a therapeutic benefit in preterm infant with GM-IVH.

Carbonyl Stress in Red Blood Cells and Hemoglobin

The paper overviews the peculiarities of carbonyl stress in nucleus-free mammal red blood cells (RBCs). Some functional features of RBCs make them exceptionally susceptible to reactive carbonyl compounds (RCC) from both blood plasma and the intracellular environment. In the first case, these compounds arise from the increased concentrations of glucose or ketone bodies in blood plasma, and in the second-from a misbalance in the glycolysis regulation. RBCs are normally exposed to RCC-methylglyoxal (MG), triglycerides-in blood plasma of diabetes patients. MG modifies lipoproteins and membrane proteins of RBCs and endothelial cells both on its own and with reactive oxygen species (ROS). Together, these phenomena may lead to arterial hypertension, atherosclerosis, hemolytic anemia, vascular occlusion, local ischemia, and hypercoagulation phenotype formation. ROS, reactive nitrogen species (RNS), and RCC might also damage hemoglobin (Hb), the most common protein in the RBC cytoplasm. It was Hb with which non-enzymatic glycation was first shown in living systems under physiological conditions. Glycated HbA1c is used as a very reliable and useful diagnostic marker. Studying the impacts of MG, ROS, and RNS on the physiological state of RBCs and Hb is of undisputed importance for basic and applied science.

A Novel Enterococcus faecalis Heme Transport Regulator (FhtR) Senses Host Heme To Control Its Intracellular Homeostasis

Enterococcus faecalis, a normal and harmless colonizer of the human intestinal flora can cause severe infectious diseases in immunocompromised patients, particularly those that have been heavily treated with antibiotics. Therefore, it is important to understand the factors that promote its resistance and its virulence. E. faecalis, which cannot synthesize heme, an essential but toxic metabolite, needs to scavenge this molecule from the host to respire and fight stress generated by oxidants.

Enterococcus faecalis is a commensal Gram-positive pathogen found in the intestines of mammals and is also a leading cause of severe infections occurring mainly among antibiotic-treated dysbiotic hospitalized patients. Like most intestinal bacteria, E. faecalis does not synthesize heme (in this report, heme refers to iron protoporphyrin IX regardless of the iron redox state). Nevertheless, environmental heme can improve E. faecalis fitness by activating respiration metabolism and a catalase that limits hydrogen peroxide stress. Since free heme also generates toxicity, its intracellular levels need to be strictly controlled. Here, we describe a unique transcriptional regulator, FhtR (named FhtR for faecalis heme transport regulator), which manages heme homeostasis by controlling an HrtBA-like efflux pump (named HrtBA_Ef for the HrtBA from E. faecalis). We show that FhtR, by managing intracellular heme concentration, regulates the functional expression of the heme-dependent catalase A (KatA), thus participating in heme detoxification. The biochemical features of FhtR binding to DNA, and its interaction with heme that induces efflux, are characterized. The FhtR-HrtBA_Ef system is shown to be relevant in a mouse intestinal model. We further show that FhtR senses heme from blood and hemoglobin but also from crossfeeding by Escherichia coli. These findings bring to light the central role of heme sensing by FhtR in response to heme fluctuations within the gastrointestinal tract, which allow this pathogen to limit heme toxicity while ensuring expression of an oxidative defense system.

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.

Generation of a Bovine Serum Albumin-Diligand Complex for the Protection of Bioactive Quercetin and Suppression of Heme Toxicity

As an abundant protein in milk and blood serum, bovine serum albumin (BSA) contains various sites to bind a lot of bioactive components, generating BSA-monoligand complex. Demonstration of the interaction between BSA and bioactive components (such as heme, flavonoids) is important to develop effective carrier for the protection of bioactive ligands and to reduce cytotoxicity of heme. Herein, the bindings of BSA to quercetin and/or heme were investigated by multispectroscopic and molecular docking methods. The fluorescence of protein was significantly quenched by both quercetin and heme in a static mode (i.e., generation of BSA-ligand complex). Although quercetin had lower affinity to protein than heme, the interactions of both compounds with protein did locate in site I (i.e., subdomain IIA). BSA-diligand complex was successfully generated after the coaddition of quercetin and heme. The cytotoxicity of free heme to endothelial cells was reduced in the BSA-diligand complex relative to that of heme or BSA-monoligand complex, while the stability of bioactive quercetin was promoted in the complex relative to free flavonoid. The complex provided a better inhibition on the cytotoxicity of heme than BSA-monoligand complex, in which the copresence of quercetin played a vital role.

One ring to bring them all and in the darkness bind them: The trafficking of heme without deliverers

Heme, as a hydrophobic iron-containing organic ring, is lipid soluble and can interact with biological membranes. The very same properties of heme that nature exploits to support life also renders heme potentially cytotoxic. In order to utilize heme, while also mitigating its toxicity, cells are challenged to tightly control the concentration and bioavailability of heme. On the bright side, it is reasonable to envision that, analogous to other transition metals, a combination of membrane-bound transporters, soluble carriers, and chaperones coordinate heme trafficking to subcellular compartments. However, given the dual properties exhibited by heme as a transition metal and lipid, it is compelling to consider the dark side: the potential role of non-proteinaceous biomolecules including lipids and nucleic acids that bind, sequester, and control heme trafficking and bioavailability. The emergence of inter-organellar membrane contact sites, as well as intracellular vesicles derived from various organelles, have raised the prospect that heme can be trafficked through hydrophobic channels. In this review, we aim to focus on heme delivery without deliverers - an alternate paradigm for the regulation of heme homeostasis through chaperone-less pathways for heme trafficking.

A Multiple-Hit Hypothesis Involving Reactive Oxygen Species and Myeloperoxidase Explains Clinical Deterioration and Fatality in COVID-19

Multi-system involvement and rapid clinical deterioration are hallmarks of coronavirus disease 2019 (COVID-19) related mortality. The unique clinical phenomena in severe COVID-19 can be perplexing, and they include disproportionately severe hypoxemia relative to lung alveolar-parenchymal pathology and rapid clinical deterioration, with poor response to O2 supplementation, despite preserved lung mechanics. Factors such as microvascular injury, thromboembolism, pulmonary hypertension, and alteration in hemoglobin structure and function could play important roles. Overwhelming immune response associated with "cytokine storms" could activate reactive oxygen species (ROS), which may result in consumption of nitric oxide (NO), a critical vasodilation regulator. In other inflammatory infections, activated neutrophils are known to release myeloperoxidase (MPO) in a natural immune response, which contributes to production of hypochlorous acid (HOCl). However, during overwhelming inflammation, HOCl competes with O2 at heme binding sites, decreasing O2 saturation. Moreover, HOCl contributes to several oxidative reactions, including hemoglobin-heme iron oxidation, heme destruction, and subsequent release of free iron, which mediates toxic tissue injury through additional generation of ROS and NO consumption. Connecting these reactions in a multi-hit model can explain generalized tissue damage, vasoconstriction, severe hypoxia, and precipitous clinical deterioration in critically ill COVID-19 patients. Understanding these mechanisms is critical to develop therapeutic strategies to combat COVID-19.

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.

The receptor for advanced glycation end products is a sensor for cell-free heme

Heme's interaction with Toll-like receptor 4 (TLR4) does not fully explain the proinflammatory properties of this hemoglobin-derived molecule during intravascular hemolysis. The receptor for advanced glycation end products (RAGE) shares many features with TLR4 such as common ligands and proinflammatory, prothrombotic, and pro-oxidative signaling pathways, prompting us to study its involvement as a heme sensor. Stable RAGE-heme complexes with micromolar affinity were detected as heme-mediated RAGE oligomerization. The heme-binding site was located in the V domain of RAGE. This interaction was Fe³⁺ -dependent and competitive with carboxymethyllysine, another RAGE ligand. We confirmed a strong basal gene expression of RAGE in mouse lungs. After intraperitoneal heme injection, pulmonary TNF-α, IL1β, and tissue factor gene expression levels increased in WT mice but were significantly lower in their RAGE^-/- littermates. This may be related to the lower activation of ERK1/2 and Akt observed in the lungs of heme-treated, RAGE^-/- mice. Overall, heme binds to RAGE with micromolar affinity and could promote proinflammatory and prothrombotic signaling in vivo, suggesting that this interaction could be implicated in heme-overload conditions.

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.

Haem oxygenases play a pivotal role in placental physiology and pathology

BACKGROUND

Haem oxygenases (HO) catabolise haem, which is the prosthetic group of numerous haemoproteins. Thus, multiple primary cellular pathways and functions rely on haem availability. HO exists in two isoforms, both expressed in the placenta, namely HO-1 and HO-2, the first being inducible. Haem oxygenases, particularly HO-1, have garnered specific interest in the field of physiological and pathological placental function. These enzymes mediate haem degradation by cleaving the alpha methene bridge to produce biliverdin, which is subsequently converted to bilirubin, carbon monoxide and iron. HO-1 has anti-inflammatory and antioxidant activities.

SEARCH METHODS

An initial literature analysis was performed using PubMed on 3 October 2018 using key terms such as 'haem oxygenase and pregnancy', 'haem oxygenase and placenta', 'HO-1 and pregnancy', 'HO-1 and placenta', 'HO and placenta', 'HO and pregnancy', 'genetic variant and HO', 'CO and pregnancy', 'CO and placenta', 'Bilirubin and pregnancy', 'Iron and pregnancy' and 'PPAR and Haem', selecting consensus conferences, recommendations, meta-analyses, practical recommendations and reviews. A second literature analysis was performed, including notable miscarriages, foetal loss and diabetes mellitus, on 20 December 2019. The three authors studied the publications independently to decipher whether they should be included in the manuscript.

OBJECTIVE AND RATIONALE

This review aimed to summarise current pieces of knowledge of haem oxygenase location, function and regulation in the placenta, either in healthy pregnancies or those associated with miscarriages and foetal loss, pre-eclampsia, foetal growth restriction and diabetes mellitus.

OUTCOMES

HO-1 exerts some protective effects on the placentation, probably by a combination of factors, including its interrelation with the PGC-1α/PPAR pathway and the sFlt1/PlGF balance, and through its primary metabolites, notably carbon monoxide and bilirubin. Its protective role has been highlighted in numerous pregnancy conditions, including pre-eclampsia, foetal growth restriction, gestational diabetes mellitus and miscarriages.

WIDER IMPLICATIONS

HO-1 is a crucial enzyme in physiological and pathological placentation. This protective enzyme is currently considered a potential therapeutic target in various pregnancy diseases.

Heme Degradation in Pathophysiology of and Countermeasures to Inflammation-Associated Disease

The class of tetrapyrrol "coordination complexes" called hemes are prosthetic group components of metalloproteins including hemoglobin, which provide functionality to these physiologically essential macromolecules by reversibly binding diatomic gasses, notably O₂, which complexes to ferrous (reduced/Fe(II)) iron within the heme porphyrin ring of hemoglobin in a pH- and PCO₂-dependent manner-thus allowing their transport and delivery to anatomic sites of their function. Here, pathologies associated with aberrant heme degradation are explored in the context of their underlying mechanisms and emerging medical countermeasures developed using heme oxygenase (HO), its major degradative enzyme and bioactive metabolites produced by HO activity. Tissue deposits of heme accumulate as a result of the removal of senescent or damaged erythrocytes from circulation by splenic macrophages, which destroy the cells and internal proteins, including hemoglobin, leaving free heme to accumulate, posing a significant toxicogenic challenge. In humans, HO uses NADPH as a reducing agent, along with molecular oxygen, to degrade heme into carbon monoxide (CO), free ferrous iron (FeII), which is sequestered by ferritin protein, and biliverdin, subsequently metabolized to bilirubin, a potent inhibitor of oxidative stress-mediated tissue damage. CO acts as a cellular messenger and augments vasodilation. Nevertheless, disease- or trauma-associated oxidative stressors sufficiently intense to overwhelm HO may trigger or exacerbate a wide range of diseases, including cardiovascular and neurologic syndromes. Here, strategies are described for counteracting the effects of aberrant heme degradation, with a particular focus on "bioflavonoids" as HO inducers, shown to cause amelioration of severe inflammatory diseases.