Mechanisms of neuroprotection by hemopexin: modeling the control of heme and iron homeostasis in brain neurons in inflammatory states

Exploring the Changes in Mild Cognitive Impairment Blood-Based Biomarkers after Local Antibiotic Periodontal Treatment in Diabetic Patients: Secondary Analysis of Data from a Randomized Controlled Trial

OBJECTIVES

 This article investigates the changes in blood-based biomarkers associated with mild cognitive impairment (MCI) risk in type 2 diabetic patients following local antibiotic periodontal treatment.

MATERIALS AND METHODS

 A secondary analysis of data from a 24-week randomized controlled trial was conducted, involving 27 patients with type 2 diabetes mellitus and periodontitis. Participants received periodontal treatment biweekly from baseline until the 6th week of the study. Sixteen patients were assigned to an intervention group and received local antibiotic periodontal treatment (Periofol 2%). The outcomes were periodontal inflammation score, which was measured using periodontal inflamed surface area, the inflammation markers levels (tumor necrosis factor-α, C-reactive protein, and interleukin [IL]-6), and MCI risk score, which was assessed using protein plasma analysis through blood test. The evaluations were performed at baseline and week 24th in both groups. The changes in periodontal inflammation scores, inflammation parameters, and MCI risk in baseline and week 24th were analyzed.

STATISTICAL ANALYSIS

 The Wilcoxon signed-rank test was used for within-group analysis and the Mann-Whitney U test was utilized for between-group analysis.

RESULTS

 Periodontal parameters were improved in both groups (p < 0.05). IL-6, complement C3, and alpha-2-antiplasmin levels were significantly decreased in the intervention group (p < 0.05). In between-group comparisons, there was a significant difference between the control and intervention groups in apolipoprotein A1, apolipoprotein C1, and alpha-1-B glycoprotein levels in week 24th (p < 0.05).

CONCLUSION

 Even though the periodontal status showed significant improvement after being given local antibiotic periodontal treatment, the changes in MCI risk proteins plasma remained unclear.

The Neural Palette of Heme: Altered Heme Homeostasis Underlies Defective Neurotransmission, Increased Oxidative Stress, and Disease Pathogenesis

Heme, a complex iron-containing molecule, is traditionally recognized for its pivotal role in oxygen transport and cellular respiration. However, emerging research has illuminated its multifaceted functions in the nervous system, extending beyond its canonical roles. This review delves into the diverse roles of heme in the nervous system, highlighting its involvement in neural development, neurotransmission, and neuroprotection. We discuss the molecular mechanisms by which heme modulates neuronal activity and synaptic plasticity, emphasizing its influence on ion channels and neurotransmitter receptors. Additionally, the review explores the potential neuroprotective properties of heme, examining its role in mitigating oxidative stress, including mitochondrial oxidative stress, and its implications in neurodegenerative diseases. Furthermore, we address the pathological consequences of heme dysregulation, linking it to conditions such as Alzheimer's disease, Parkinson's disease, and traumatic brain injuries. By providing a comprehensive overview of heme's multifunctional roles in the nervous system, this review underscores its significance as a potential therapeutic target and diagnostic biomarker for various neurological disorders.

Extracellular Vesicles from hiPSC-derived NSCs Protect Human Neurons against Aβ-42 Oligomers Induced Neurodegeneration, Mitochondrial Dysfunction and Tau Phosphorylation

Background

One of the hallmarks of Alzheimer's disease (AD) is the buildup of amyloid beta-42 (Aβ-42) in the brain, which leads to various adverse effects. Therefore, therapeutic interventions proficient in reducing Aβ-42-induced toxicity in AD are of great interest. One promising approach is to use extracellular vesicles from human induced pluripotent stem cell-derived neural stem cells (hiPSC-NSC-EVs) because they carry multiple therapeutic miRNAs and proteins capable of protecting neurons against Aβ-42-induced pathological changes. Therefore, this in vitro study investigated the proficiency of hiPSC-NSC-EVs to protect human neurons derived from two distinct hiPSC lines from Aβ-42o-induced neurodegeneration.

Methods

We isolated hiPSC-NSC-EVs using chromatographic methods and characterized their size, ultrastructure, expression of EV-specific markers and proficiency in getting incorporated into mature human neurons. Next, mature human neurons differentiated from two different hiPSC lines were exposed to 1 µM Aβ-42 oligomers (Aβ-42o) alone or with varying concentrations of hiPSC-NSC-EVs. The protective effects of hiPSC-NSC-EVs against Aβ-42o-induced neurodegeneration, increased oxidative stress, mitochondrial dysfunction, impaired autophagy, and tau phosphorylation were ascertained using multiple measures and one-way ANOVA with Newman-Keuls multiple comparisons post hoc tests.

Results

Significant neurodegeneration was observed when human neurons were exposed to Aβ-42o alone. Notably, neurodegeneration was associated with elevated levels of oxidative stress markers malondialdehyde (MDA) and protein carbonyls (PCs), increased expression of proapoptotic Bax and Bad genes and proteins, reduced expression of the antiapoptotic gene and protein Bcl-2, increased expression of genes encoding mitochondrial complex proteins, decreased expression of autophagy-related proteins Beclin-1 and microtubule-associated protein 1 light chain 3B, and increased phosphorylation of tau. However, the addition of an optimal dose of hiPSC-NSC-EVs (6 x 10 9 EVs) to human neuronal cultures exposed to Aβ-42o significantly reduced the extent of neurodegeneration, along with diminished levels of MDA and PCs, normalized expressions of Bax, Bad, and Bcl-2, and genes linked to mitochondrial complex proteins, and reduced tau phosphorylation.

Conclusions

The findings demonstrate that an optimal dose of hiPSC-NSC-EVs could significantly decrease the degeneration of human neurons induced by Aβ-42o. The results also support further research into the effectiveness of hiPSC-NSC-EVs in AD, particularly their proficiency in preserving neurons and slowing disease progression.

Which neuroimaging and fluid biomarkers method is better in theranostic of Alzheimer's disease? An umbrella review

Biomarkers are measured to evaluate physiological and pathological processes as well as responses to a therapeutic intervention. Biomarkers can be classified as diagnostic, prognostic, predictor, clinical, and therapeutic. In Alzheimer's disease (AD), multiple biomarkers have been reported so far. Nevertheless, finding a specific biomarker in AD remains a major challenge. Three databases, including PubMed, Web of Science, and Scopus were selected with the keywords of Alzheimer's disease, neuroimaging, biomarker, and blood. The results were finalized with 49 potential CSF/blood and 35 neuroimaging biomarkers. To distinguish normal from AD patients, amyloid-beta42 (Aβ42), plasma glial fibrillary acidic protein (GFAP), and neurofilament light (NFL) as potential biomarkers in cerebrospinal fluid (CSF) as well as the serum could be detected. Nevertheless, most of the biomarkers fairly change in the CSF during AD, listed as kallikrein 6, virus-like particles (VLP-1), galectin-3 (Gal-3), and synaptotagmin-1 (Syt-1). From the neuroimaging aspect, atrophy is an accepted biomarker for the neuropathologic progression of AD. In addition, Magnetic resonance spectroscopy (MRS), diffusion weighted imaging (DWI), diffusion tensor imaging (DTI), tractography (DTT), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI), can be used to detect AD. Using neuroimaging and CSF/blood biomarkers, in combination with artificial intelligence, it is possible to obtain information on prognosis and follow-up on the different stages of AD. Hence physicians could select the suitable therapy to attenuate disease symptoms and follow up on the efficiency of the prescribed drug.

Metal dyshomeostasis in the substantia nigra of patients with Parkinson's disease or multiple sclerosis

Abnormal metal distribution in vulnerable brain regions is involved in the pathogenesis of most neurodegenerative diseases, suggesting common molecular mechanisms of metal dyshomeostasis. This study aimed to compare the intra- and extra-neuronal metal content and the expression of proteins related to metal homeostasis in the substantia nigra (SN) from patients with Parkinson's disease (PD), multiple sclerosis (MS), and control subjects. Metal quantification was performed via ion-beam micro-analysis in neuromelanin-positive neurons and the surrounding tissue. For proteomic analysis, SN tissue lysates were analyzed on a nanoflow chromatography system hyphenated to a hybrid triple-quadrupole time-of-flight mass spectrometer. We found increased amounts of iron in neuromelanin-positive neurons and surrounding tissue in patients with PD and MS compared to controls (4- to 5-fold higher) that, however, also showed large inter-individual variations. Copper content was systematically lower (-2.4-fold) in neuromelanin-positive neurons of PD patients compared with controls, whereas it remained unchanged in MS. Protein-protein interaction (PPI) network analyses revealed clusters related to Fe and Cu homeostasis among PD-deregulated proteins. An enrichment for the term "metal homeostasis" was observed for MS-deregulated proteins. Important deregulated hub proteins included hemopexin and transferrin in PD, and calreticulin and ferredoxin reductase in MS. Our findings show that PD and MS share commonalities in terms of iron accumulation in the SN. Concomitant proteomics experiments revealed PPI networks related to metal homeostasis, substantiating the results of metal quantification.

Free heme induces neuroinflammation and cognitive impairment by microglial activation via the TLR4/MyD88/NF-κB signaling pathway

BACKGROUND

Red blood cells (RBCs) transfusion is related to perioperative neurocognitive disorders. The toxic effect of free heme has been identified in many pathologies. However, the underlying mechanisms of RBCs transfusion or free heme in cognitive impairment have not been clearly explored. Therefore, this research was conducted to determine the mechanism of free heme-induced neuroinflammation and cognitive impairment.

METHODS

Rats were received intraperitoneal injection of hemin alone or combined with intracerebroventricular injection of Hemopexin (HPX), and MWM test was conducted to measure cognitive function. The amount of heme-HPX complexes was evaluated by flow cytometry for CD91 + cells. The microglial inflammatory response in rat brain was observed by immunofluorescence staining of Iba-1, and the inflammatory factors of TNF-α, IL-1β and IL-6 in rat brain and BV2 cells were detected by ELISA analysis. Furthermore, neuronal apoptosis in HT22 cells alone and in HT22 + BV2 coculture system was detected by flow cytometry and immunofluorescence staining. Finally, western blot was conducted to detect TLR4/MyD88/NF-κB proteins in rat brain and BV2 cells treated with hemin or combined with pathway inhibitors. Additionally, the M1 surface marker CD86 was observed in BV2 cells to further confirm neuroinflammation.

RESULTS

Intraperitoneal injection of hemin induced cognitive impairment, increase of CD91 + cells, up-regulation of TNF-α and IL-1β, down-regulation of IL-6, activation of microglia, and activation of the TLR4/MyD88/NF-κB signaling pathway in rat brain. Significantly, intracerebroventricular injection of HPX reduced the above effects. Hemin induced boost of TNF-α, IL-1β and IL-6 in BV2 cells, as well as apoptosis in HT22 cells. Notably, when HT22 cells were cocultured with BV2 cells, apoptosis was significantly increased. Hemin also induced activation of the TLR4/MyD88/NF-κB signaling pathway and increased the M1 surface marker CD86 in BV2 cells, and inhibiting this pathway reduced the inflammatory responses.

CONCLUSIONS

Free heme induces cognitive impairment, and the underlying mechanism may involve neuronal apoptosis and microglial inflammation via the TLR4/MyD88/NF-κB signaling pathway. HPX may have potential therapeutic effects. Video Abstract.

Identification of Plasma Proteins as Biomarkers for Mild Cognitive Impairment and Alzheimer's Disease Using Liquid Chromatography-Tandem Mass Spectrometry

Blood proteins can be used for biomarkers to monitor the progression of cognitive decline, even in the early stages of disease. In this study, we developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based blood test to identify plasma proteins that can be used to detect mild cognitive impairment (MCI) and Alzheimer's disease (AD). Using this system, we quantified plasma proteins using isotope-labeled synthetic peptides. A total of 192 patients, including 63 with AD, 71 with MCI, and 58 non-demented controls (NDCs), were analyzed. Multinomial regression and receiver operating characteristic (ROC) analyses were performed to identify specific combinations of plasma protein panels that could differentiate among NDCs, those with MCI, and those with AD. We identified eight plasma protein biomarker candidates that can be used to distinguish between MCI and AD. These biomarkers were associated with coagulation pathways, innate immunity, lipid metabolism, and nutrition. The clinical potential to differentiate cognitive impairment from NDC was assessed using area under the curve values from ROC analysis, which yielded values of 0.83 for males and 0.71 for females. This LC-MS-based plasma protein panel allows the pathophysiology of AD to be followed through detection of cognitive decline and disease progression markers.

Age prediction from human blood plasma using proteomic and small RNA data: a comparative analysis

Aging clocks, built from comprehensive molecular data, have emerged as promising tools in medicine, forensics, and ecological research. However, few studies have compared the suitability of different molecular data types to predict age in the same cohort and whether combining them would improve predictions. Here, we explored this at the level of proteins and small RNAs in 103 human blood plasma samples. First, we used a two-step mass spectrometry approach measuring 612 proteins to select and quantify 21 proteins that changed in abundance with age. Notably, proteins increasing with age were enriched for components of the complement system. Next, we used small RNA sequencing to select and quantify a set of 315 small RNAs that changed in abundance with age. Most of these were microRNAs (miRNAs), downregulated with age, and predicted to target genes related to growth, cancer, and senescence. Finally, we used the collected data to build age-predictive models. Among the different types of molecules, proteins yielded the most accurate model (R² = 0.59 ± 0.02), followed by miRNAs as the best-performing class of small RNAs (R² = 0.54 ± 0.02). Interestingly, the use of protein and miRNA data together improved predictions (R2 = 0.70 ± 0.01). Future work using larger sample sizes and a validation dataset will be necessary to confirm these results. Nevertheless, our study suggests that combining proteomic and miRNA data yields superior age predictions, possibly by capturing a broader range of age-related physiological changes. It will be interesting to determine if combining different molecular data types works as a general strategy to improve future aging clocks.

CLEC-2 Supports Platelet Aggregation in Mouse but not Human Blood at Arterial Shear

C-type lectin-like receptor 2 (CLEC-2) is highly expressed on platelets and a subpopulation of myeloid cells, and is critical in lymphatic development. CLEC-2 has been shown to support thrombus formation at sites of inflammation, but to have a minor/negligible role in hemostasis. This identifies CLEC-2 as a promising therapeutic target in thromboinflammatory disorders, without hemostatic detriment. We utilized a GPIbα-Cre recombinase mouse for more restricted deletion of platelet-CLEC-2 than the previously used PF4-Cre mouse. clec1bfl/flGPIbα-Cre+ mice are born at a Mendelian ratio, with a mild reduction in platelet count, and present with reduced thrombus size post-FeCl3-induced thrombosis, compared to littermates. Antibody-mediated depletion of platelet count in C57BL/6 mice, to match clec1bfl/flGPIbα-Cre+ mice, revealed that the reduced thrombus size post-FeCl3-injury was due to the loss of CLEC-2, and not mild thrombocytopenia. Similarly, clec1bfl/flGPIbα-Cre+ mouse blood replenished with CLEC-2-deficient platelets ex vivo to match littermates had reduced aggregate formation when perfused over collagen at arterial flow rates. In contrast, platelet-rich thrombi formed following perfusion of human blood under flow conditions over collagen types I or III, atherosclerotic plaque, or inflammatory endothelial cells were unaltered in the presence of CLEC-2-blocking antibody, AYP1, or recombinant CLEC-2-Fc. The reduction in platelet aggregation observed in clec1bfl/flGPIbα-Cre+ mice during arterial thrombosis is mediated by the loss of CLEC-2 on mouse platelets. In contrast, CLEC-2 does not support thrombus generation on collagen, atherosclerotic plaque, or inflamed endothelial cells in human at arterial shear.

Regional heterogeneity in mitochondrial function underlies region specific vulnerability in human brain ageing: Implications for neurodegeneration

Selective neuronal vulnerability (SNV) of specific neuroanatomical regions such as frontal cortex (FC) and hippocampus (HC) is characteristic of age-associated neurodegenerative diseases (NDDs), although its pathogenetic basis remains unresolved. We hypothesized that physiological differences in mitochondrial function in neuroanatomical regions could contribute to SNV. To investigate this, we evaluated mitochondrial function in human brains (age range:1-90 y) in FC, striatum (ST), HC, cerebellum (CB) and medulla oblongata (MD), using enzyme assays and quantitative proteomics. Striking differences were noted in resistant regions- MD and CB compared to the vulnerable regions- FC, HC and ST. At younger age (25 ± 5 y), higher activity of electron transport chain enzymes and upregulation of metabolic and antioxidant proteins were noted in MD compared to FC and HC, that was sustained with increasing age (≥65 y). In contrast, the expression of synaptic proteins was higher in FC, HC and ST (vs. MD). In line with this, quantitative phospho-proteomics revealed activation of upstream regulators (ERS, PPARα) of mitochondrial metabolism and inhibition of synaptic pathways in MD. Microtubule Associated Protein Tau (MAPT) showed overexpression in FC, HC and ST both in young and older age (vs. MD). MAPT hyperphosphorylation and the activation of its kinases were noted in FC and HC with age. Our study demonstrates that regional heterogeneity in mitochondrial and other cellular functions contribute to SNV and protect regions such as MD, while rendering FC and HC vulnerable to NDDs. The findings also support the "last in, first out" hypothesis of ageing, wherein regions such as FC, that are the most recent to develop phylogenetically and ontogenetically, are the first to be affected in ageing and NDDs.

New Insights into Hemopexin-Binding to Hemin and Hemoglobin

Hemopexin (Hx) is a plasma glycoprotein that scavenges heme (Fe(III) protoporphyrin IX). Hx has important implications in hemolytic disorders and hemorrhagic conditions because releasing hemoglobin increases the labile heme, which is potentially toxic, thus producing oxidative stress. Therefore, Hx has been considered for therapeutic use and diagnostics. In this work, we analyzed and mapped the interaction sequences of Hx with hemin and hemoglobin. The spot-synthesis technique was used to map human hemopexin (P02790) binding to hemin and human hemoglobin. A library of 15 amino acid peptides with a 10-amino acid overlap was designed to represent the entire coding region (aa 1-462) of hemopexin and synthesized onto cellulose membranes. An in silico approach was taken to analyze the amino acid frequency in the identified interaction regions, and molecular docking was applied to assess the protein-protein interaction. Seven linear peptide sequences in Hx were identified to bind hemin (H1-H7), and five were described for Hb (Hb1-Hb5) interaction, with just two sequences shared between hemin and Hb. The amino acid composition of the identified sequences demonstrated that histidine residues are relevant for heme binding. H105, H293, H373, H400, H429, and H462 were distributed in the H1-H7 peptide sequences, but other residues may also play an important role. Molecular docking analysis demonstrated Hx's association with the β-chain of Hb, with several hotspot amino acids that coordinated the interaction. This study provides new insights into Hx-hemin binding motifs and protein-protein interactions with Hb. The identified binding sequences and specific peptides can be used for therapeutic purposes and diagnostics as hemopexin is under investigation to treat different diseases and there is an urgent need for diagnostics using labile heme when monitoring hemolysis.

Heme Oxygenase 1 in Vertebrates: Friend and Foe

HO-1 is the inducible form of the enzyme heme-oxygenase. HO-1 catalyzes heme breakdown, reducing the levels of this important oxidant molecule and generating antioxidant, anti-inflammatory, and anti-apoptotic byproducts. Thus, HO-1 has been described as an important stress response mechanism during both physiologic and pathological processes. Interestingly, some findings are demonstrating that uncontrolled levels of HO-1 byproducts can be associated with cell death and tissue destruction as well. Furthermore, HO-1 can be located in the nucleus, influencing gene transcription, cellular proliferation, and DNA repair. Here, we will discuss several studies that approach HO-1 effects as a protective or detrimental mechanism in different pathological conditions. In this sense, as the major organs of vertebrates will deal specifically with distinct types of stresses, we discuss the HO-1 role in each of them, exposing the contradictions associated with HO-1 expression after different insults and circumstances.

Oxidative-Signaling in Neural Stem Cell-Mediated Plasticity: Implications for Neurodegenerative Diseases

The adult mammalian brain is capable of generating new neurons from existing neural stem cells (NSCs) in a process called adult neurogenesis. This process, which is critical for sustaining cognition and mental health in the mature brain, can be severely hampered with ageing and different neurological disorders. Recently, it is believed that the beneficial effects of NSCs in the injured brain relies not only on their potential to differentiate and integrate into the preexisting network, but also on their secreted molecules. In fact, further insight into adult NSC function is being gained, pointing to these cells as powerful endogenous "factories" that produce and secrete a large range of bioactive molecules with therapeutic properties. Beyond anti-inflammatory, neurogenic and neurotrophic effects, NSC-derived secretome has antioxidant proprieties that prevent mitochondrial dysfunction and rescue recipient cells from oxidative damage. This is particularly important in neurodegenerative contexts, where oxidative stress and mitochondrial dysfunction play a significant role. In this review, we discuss the current knowledge and the therapeutic opportunities of NSC secretome for neurodegenerative diseases with a particular focus on mitochondria and its oxidative state.

Critical Role of Hemopexin Mediated Cytoprotection in the Pathophysiology of Sickle Cell Disease

Circulating hemopexin is the primary protein responsible for the clearance of heme; therefore, it is a systemic combatant against deleterious inflammation and oxidative stress induced by the presence of free heme. This role of hemopexin is critical in hemolytic pathophysiology. In this review, we outline the current research regarding how the dynamic activity of hemopexin is implicated in sickle cell disease, which is characterized by a pathological aggregation of red blood cells and excessive hemolysis. This pathophysiology leads to symptoms such as acute kidney injury, vaso-occlusion, ischemic stroke, pain crises, and pulmonary hypertension exacerbated by the presence of free heme and hemoglobin. This review includes in vivo studies in mouse, rat, and guinea pig models of sickle cell disease, as well as studies in human samples. In summary, the current research indicates that hemopexin is likely protective against these symptoms and that rectifying depleted hemopexin in patients with sickle cell disease could improve or prevent the symptoms. The data compiled in this review suggest that further preclinical and clinical research should be conducted to uncover pathways of hemopexin in pathological states to evaluate its potential clinical function as both a biomarker and therapy for sickle cell disease and related hemoglobinopathies.

Pharmacological Activities and Mechanisms of Hirudin and Its Derivatives - A Review

Hirudin, an acidic polypeptide secreted by the salivary glands of Hirudo medicinalis (also known as "Shuizhi" in traditional Chinese medicine), is the strongest natural specific inhibitor of thrombin found so far. Hirudin has been demonstrated to possess potent anti-thrombotic effect in previous studies. Recently, increasing researches have focused on the anti-thrombotic activity of the derivatives of hirudin, mainly because these derivatives have stronger antithrombotic activity and lower bleeding risk. Additionally, various bioactivities of hirudin have been reported as well, including wound repair effect, anti-fibrosis effect, effect on diabetic complications, anti-tumor effect, anti-hyperuricemia effect, effect on cerebral hemorrhage, and others. Therefore, by collecting and summarizing publications from the recent two decades, the pharmacological activities, pharmacokinetics, novel preparations and derivatives, as well as toxicity of hirudin were systematically reviewed in this paper. In addition, the clinical application, the underlying mechanisms of pharmacological effects, the dose-effect relationship, and the development potential in new drug research of hirudin were discussed on the purpose of providing new ideas for application of hirudin in treating related diseases.

HEME: a neglected player in nociception?

Despite increasing progress in the understanding of the pathophysiology of pain, current management of pain syndromes is still unsatisfactory. The recent discovery of novel pathways associated with pain insensitivity in humans represents a unique opportunity to improve our knowledge on the pathophysiology of pain. Heme metabolism recently emerged as a crucial regulator of nociception. Of note, alteration of heme metabolism has been associated with pain insensitivity as well as with acute and chronic pain in porphyric neuropathy and hemolytic diseases. However, the molecular mechanisms linking heme to the pain pathways still remain unclear. The review focuses on the major heme-regulated processes relevant for sensory neurons' maintenance, peripheral and central sensitization as well as for pain comorbidities, like anxiety and depression. By discussing the body of knowledge on the topic, we provide a novel perspective on the molecular mechanisms linking heme to nociception.

Human Plasma and Recombinant Hemopexins: Heme Binding Revisited

Plasma hemopexin (HPX) is the key antioxidant protein of the endogenous clearance pathway that limits the deleterious effects of heme released from hemoglobin and myoglobin (the term “heme” is used in this article to denote both the ferrous and ferric forms). During intra-vascular hemolysis, heme partitioning to protein and lipid increases as the plasma concentration of HPX declines. Therefore, the development of HPX as a replacement therapy during high heme stress could be a relevant intervention for hemolytic disorders. A logical approach to enhance HPX yield involves recombinant production strategies from human cell lines. The present study focuses on a biophysical assessment of heme binding to recombinant human HPX (rhHPX) produced in the Expi293F^TM (HEK293) cell system. In this report, we examine rhHPX in comparison with plasma HPX using a systematic analysis of protein structural and functional characteristics related to heme binding. Analysis of rhHPX by UV/Vis absorption spectroscopy, circular dichroism (CD), size-exclusion chromatography (SEC)-HPLC, and catalase-like activity demonstrated a similarity to HPX fractionated from plasma. In particular, the titration of HPX apo-protein(s) with heme was performed for the first time using a wide range of heme concentrations to model HPX–heme interactions to approximate physiological conditions (from extremely low to more than two-fold heme molar excess over the protein). The CD titration data showed an induced bisignate CD Soret band pattern typical for plasma and rhHPX versions at low heme-to-protein molar ratios and demonstrated that further titration is dependent on the amount of protein-bound heme to the extent that the arising opposite CD couplet results in a complete inversion of the observed CD pattern. The data generated in this study suggest more than one binding site in both plasma and rhHPX. Furthermore, our study provides a useful analytical platform for the detailed characterization of HPX–heme interactions and potentially novel HPX fusion constructs.

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.

Low Cerebrospinal Fluid Levels of Hemopexin Are Associated With Increased Alzheimer's Pathology, Hippocampal Hypometabolism, and Cognitive Decline

Brain iron dyshomeostasis is a feature of Alzheimer's disease. Conventionally, research has focused on non-heme iron although degradation of heme from hemoglobin subunits can generate iron to augment the redox-active iron pool. Hemopexin both detoxifies heme to maintain iron homeostasis and bolsters antioxidant capacity via catabolic products, biliverdin and carbon monoxide to combat iron-mediated lipid peroxidation. The aim of the present study was to examine the association of cerebrospinal fluid levels (CSF) hemopexin and hemoglobin subunits (α and β) to Alzheimer's pathological proteins (amyloid and tau), hippocampal volume and metabolism, and cognitive performance. We analyzed baseline CSF heme/iron proteins (multiplexed mass spectrometry-based assay), amyloid and tau (Luminex platform), baseline/longitudinal neuroimaging (MRI, FDG-PET) and cognitive outcomes in 86 cognitively normal, 135 mild-cognitive impairment and 66 Alzheimer's participants from the Alzheimer's Disease Neuroimaging Initiative-1 (ADNI-1) cohort. Multivariate regression analysis was performed to delineate differences in CSF proteins between diagnosis groups and evaluated their association to amyloid and tau, neuroimaging and cognition. A p-value ≤ 0.05 was considered significant. Higher hemopexin was associated with higher CSF amyloid (implying decreased brain amyloid deposition), improved hippocampal metabolism and cognitive performance. Meanwhile, hemoglobin subunits were associated with increased CSF tau (implying increased brain tau deposition). When dichotomizing individuals with mild-cognitive impairment into stable and converters to Alzheimer's disease, significantly higher baseline hemoglobin subunits were observed in the converters compared to non-converters. Heme/iron dyshomeostasis is an early and crucial event in AD pathophysiology, which warrants further investigation as a potential therapeutic target.

Automated Capillary Isoelectric Focusing-Tandem Mass Spectrometry for Qualitative and Quantitative Top-Down Proteomics

Top-down proteomics (TDP) aims to delineate proteomes in a proteoform-specific manner, which is vital for accurately understanding protein function in cellular processes. It requires high-capacity separation of proteoforms before mass spectrometry (MS) and tandem MS (MS/MS). Capillary isoelectric focusing (cIEF)-MS has been recognized as a useful tool for TDP in the 1990s because cIEF is capable of high-resolution separation of proteoforms. Previous cIEF-MS studies concentrated on measuring the protein's mass without MS/MS, impeding the confident proteoform identification in complex samples and the accurate localization of post-translational modifications on proteoforms. Herein, for the first time, we present automated cIEF-MS/MS-based TDP for large-scale delineation of proteoforms in complex proteomes. Single-shot cIEF-MS/MS identified 711 proteoforms from an Escherichia coli (E. coli) proteome consuming only nanograms of proteins. Coupling two-dimensional size-exclusion chromatography (SEC)-cIEF to ESI-MS/MS enabled the identification of nearly 2000 proteoforms from the E. coli proteome. Label-free quantitative TDP of zebrafish male and female brains using SEC-cIEF-MS/MS quantified thousands of proteoforms and revealed sex-dependent proteoform profiles in brains. Particularly, we discovered several proteolytic proteoforms of pro-opiomelanocortin and prodynorphin with significantly higher abundance in male zebrafish brains as potential endogenous hormone proteoforms. Multilevel quantitative proteomics (TDP and bottom-up proteomics) of the brains revealed that the majority of proteoforms having statistically significant difference in abundance between genders showed no abundance difference at the protein group level. This work represents the first multilevel quantitative proteomics study of sexual dimorphism of the brain.

Characterization of carp seminal plasma Wap65-2 and its participation in the testicular immune response and temperature acclimation

Two functionally distinct isoforms of warm-temperature acclimation related 65-kDa protein (Wap65-1 and Wap65-2) with a role in the immune response are present in fish. To our knowledge, contrary to Wap65-1, Wap65-2 has neither been isolated nor functionally characterized in carp especially in reproductive system. The aim of this study was to characterize Wap65-2 and ascertain its functions in immune response and temperature acclimation within reproductive system. Wap65-2 corresponded to one of the most abundant proteins in carp seminal plasma, with a high immunologic similarity to their counterparts in seminal plasma of other fish species and a wide tissue distribution, with predominant expression in the liver. The immunohistochemical localization of Wap65-2 to spermatogonia, Leydig cells, and the epithelium of blood vessels within the testis suggests its role in iron metabolism during spermatogenesis and maintenance of blood-testis barrier integrity. Wap65-2 secretion by the epithelial cells of the spermatic duct and its presence around spermatozoa suggests its involvement in the protection of spermatozoa against damage caused by heme released from erythrocytes following hemorrhage and inflammation. Our results revealed an isoform-specific response of Wap65 to temperature acclimation and Aeromonas salmonicida infection which alters blood-testis barrier integrity. Wap65-2 seems to be related to the immune response against bacteria, while Wap65-1 seems to be involved in temperature acclimation. This study expands the understanding of the mechanism of carp testicular immunity against bacterial challenge and temperature changes, in which Wap65-2 seems to be involved and highlights their potential usefulness as biomarkers of inflammation and temperature acclimation.

Extracellular vesicles from human iPSC-derived neural stem cells: miRNA and protein signatures, and anti-inflammatory and neurogenic properties

Grafting of neural stem cells (NSCs) derived from human induced pluripotent stem cells (hiPSCs) has shown promise for brain repair after injury or disease, but safety issues have hindered their clinical application. Employing nano-sized extracellular vesicles (EVs) derived from hiPSC-NSCs appears to be a safer alternative because they likely have similar neuroreparative properties as NSCs and are amenable for non-invasive administration as an autologous or allogeneic off-the-shelf product. However, reliable methods for isolation, characterization and testing the biological properties of EVs are critically needed for translation. We investigated signatures of miRNAs and proteins and the biological activity of EVs, isolated from hiPSC-NSCs through a combination of anion-exchange chromatography (AEC) and size-exclusion chromatography (SEC). AEC and SEC facilitated the isolation of EVs with intact ultrastructure and expressing CD9, CD63, CD81, ALIX and TSG 101. Small RNA sequencing, proteomic analysis, pathway analysis and validation of select miRNAs and proteins revealed that EVs were enriched with miRNAs and proteins involved in neuroprotective, anti-apoptotic, antioxidant, anti-inflammatory, blood-brain barrier repairing, neurogenic and Aβ reducing activities. Besides, EVs comprised miRNAs and/or proteins capable of promoting synaptogenesis, synaptic plasticity and better cognitive function. Investigations using an in vitro macrophage assay and a mouse model of status epilepticus confirmed the anti-inflammatory activity of EVs. Furthermore, the intranasal administration of EVs resulted in the incorporation of EVs by neurons, microglia and astrocytes in virtually all adult rat and mouse brain regions, and enhancement of hippocampal neurogenesis. Thus, biologically active EVs containing miRNAs and proteins relevant to brain repair could be isolated from hiPSC-NSC cultures, making them a suitable biologic for treating neurodegenerative disorders.

Iron-responsive-like elements and neurodegenerative ferroptosis

A set of common-acting iron-responsive 5′untranslated region (5′UTR) motifs can fold into RNA stem loops that appear significant to the biology of cognitive declines of Parkinson's disease dementia (PDD), Lewy body dementia (LDD), and Alzheimer's disease (AD). Neurodegenerative diseases exhibit perturbations of iron homeostasis in defined brain subregions over characteristic time intervals of progression. While misfolding of Aβ from the amyloid-precursor-protein (APP), alpha-synuclein, prion protein (PrP) each cause neuropathic protein inclusions in the brain subregions, iron-responsive-like element (IRE-like) RNA stem–loops reside in their transcripts. APP and αsyn have a role in iron transport while gene duplications elevate the expression of their products to cause rare familial cases of AD and PDD. Of note, IRE-like sequences are responsive to excesses of brain iron in a potential feedback loop to accelerate neuronal ferroptosis and cognitive declines as well as amyloidosis. This pathogenic feedback is consistent with the translational control of the iron storage protein ferritin. We discuss how the IRE-like RNA motifs in the 5′UTRs of APP, alpha-synuclein and PrP mRNAs represent uniquely folded drug targets for therapies to prevent perturbed iron homeostasis that accelerates AD, PD, PD dementia (PDD) and Lewy body dementia, thus preventing cognitive deficits. Inhibition of alpha-synuclein translation is an option to block manganese toxicity associated with early childhood cognitive problems and manganism while Pb toxicity is epigenetically associated with attention deficit and later-stage AD. Pathologies of heavy metal toxicity centered on an embargo of iron export may be treated with activators of APP and ferritin and inhibitors of alpha-synuclein translation.

Plasma transferrin and hemopexin are associated with altered Aβ uptake and cognitive decline in Alzheimer's disease pathology

Background

Heme and iron homeostasis is perturbed in Alzheimer’s disease (AD); therefore, the aim of the study was to examine the levels and association of heme with iron-binding plasma proteins in cognitively normal (CN), mild cognitive impairment (MCI), and AD individuals from the Australian Imaging, Biomarker and Lifestyle Flagship Study of Ageing (AIBL) and Kerr Anglican Retirement Village Initiative in Ageing Health (KARVIAH) cohorts.

Methods

Non-targeted proteomic analysis by high-resolution mass spectrometry was performed to quantify relative protein abundances in plasma samples from 144 CN individuals from the AIBL and 94 CN from KARVIAH cohorts and 21 MCI and 25 AD from AIBL cohort. ANCOVA models were utilized to assess the differences in plasma proteins implicated in heme/iron metabolism, while multiple regression modeling (and partial correlation) was performed to examine the association between heme and iron proteins, structural neuroimaging, and cognitive measures.

Results

Of the plasma proteins implicated in iron and heme metabolism, hemoglobin subunit β (p = 0.001) was significantly increased in AD compared to CN individuals. Multiple regression modeling adjusted for age, sex, APOEε4 genotype, and disease status in the AIBL cohort revealed lower levels of transferrin but higher levels of hemopexin associated with augmented brain amyloid deposition. Meanwhile, transferrin was positively associated with hippocampal volume and MMSE performance, and hemopexin was negatively associated with CDR scores. Partial correlation analysis revealed lack of significant associations between heme/iron proteins in the CN individuals progressing to cognitive impairment.

Conclusions

In conclusion, heme and iron dyshomeostasis appears to be a feature of AD. The causal relationship between heme/iron metabolism and AD warrants further investigation.

Blood-Related Toxicity after Traumatic Brain Injury: Potential Targets for Neuroprotection

Emergency visits, hospitalizations, and deaths due to traumatic brain injury (TBI) have increased significantly over the past few decades. While the primary early brain trauma is highly deleterious to the brain, the secondary injury post-TBI is postulated to significantly impact mortality. The presence of blood, particularly hemoglobin, and its breakdown products and key binding proteins and receptors modulating their clearance may contribute significantly to toxicity. Heme, hemin, and iron, for example, cause membrane lipid peroxidation, generate reactive oxygen species, and sensitize cells to noxious stimuli resulting in edema, cell death, and increased morbidity and mortality. A wide range of other mechanisms such as the immune system play pivotal roles in mediating secondary injury. Effective scavenging of all of these pro-oxidant and pro-inflammatory metabolites as well as controlling maladaptive immune responses is essential for limiting toxicity and secondary injury. Hemoglobin metabolism is mediated by key molecules such as haptoglobin, heme oxygenase, hemopexin, and ferritin. Genetic variability and dysfunction affecting these pathways (e.g., haptoglobin and heme oxygenase expression) have been implicated in the difference in susceptibility of individual patients to toxicity and may be target pathways for potential therapeutic interventions in TBI. Ongoing collaborative efforts are required to decipher the complexities of blood-related toxicity in TBI with an overarching goal of providing effective treatment options to all patients with TBI.

The role of haptoglobin and hemopexin in the prevention of delayed cerebral ischaemia after aneurysmal subarachnoid haemorrhage: a review of current literature

Delayed cerebral ischaemia (DCI) after aneurysmal subarachnoid haemorrhage (aSAH) is a major cause of mortality and morbidity. The pathophysiology of DCI after aSAH is thought to involve toxic mediators released from lysis of red blood cells within the subarachnoid space, including free haemoglobin and haem. Haptoglobin and hemopexin are endogenously produced acute phase proteins that are involved in the clearance of these toxic mediators. The aim of this review is to investigate the pathophysiological mechanisms involved in DCI and the role of both endogenous as well as exogenously administered haptoglobin and hemopexin in the prevention of DCI.

Deferoxamine therapy reduces brain hemin accumulation after intracerebral hemorrhage in piglets

Hemopexin (Hpx) is critical for hemin scavenging after the erythrocyte lysis that occurs following intracerebral hemorrhage (ICH). Low-density lipoprotein receptor-related protein-1 (LRP1, also called CD91) is an important receptor through which the hemin-Hpx complex can undergo endocytosis. This study investigated changes in the hemin-Hpx-CD91 axis in both hematoma and perihematomal tissue in a large animal ICH model. The effect of deferoxamine (DFX) on hemin-Hpx-CD91 was also examined. The study consisted of two parts. First, piglets had an injection of autologous blood into the right frontal lobe of brain and were euthanized from day 1 to day 7. Hematoma and perihematomal tissue of brains were used for hemin assay, immunohistochemistry, and immunofluorescence. Second, piglets with ICH were treated with deferoxamine or vehicle, and were euthanized for hemin measurement and Hpx and CD91 immunohistochemistry. We found that there was an increase of hemin levels within the hematoma and perihematomal brain tissue after ICH. Hpx and CD91-positive cells were present in the clot and perihematomal tissue from day 1. Hpx and CD91 positive cells were Iba1 positive. After DFX therapy, hemin dropped markedly in the hematoma and perihematomal brain tissue. Furthermore, DFX treatment decreased the number of Hpx and CD91 positive cells in and around the hematoma. In conclusion, hemin accumulation occurs in and around the hematoma. Increases in Hpx and CD91 may be important in scavenging that hemin. DFX treatment decreased hemin release from the hematoma and reduced the expression of Hpx and CD91.

Safe coordinated trafficking of heme and iron with copper maintain cell homeostasis: modules from the hemopexin system

Studies with patients, animal models of human disease and hemopexin null mice have shown that the heme-binding protein hemopexin is vital for the protection of a variety of cell types and tissues against heme toxicity. The presence of hemopexin in all biological fluids examined to date indicates wide roles in abrogating heme toxicity in human tissues; and, thus, is clinically relevant. Heme-hemopexin endocytosis leads to coordinated trafficking of heme, iron and copper as heme traffics from endosomes to heme oxygenases (HOs) in the smooth endoplasmic reticulum and to the nucleus. This is safe redox-metal trafficking, without oxidative stress, as iron released from heme catabolism by HOs as well as copper taken up with heme-hemopexin move through the cell. To our knowledge, this coordinated metal trafficking has been described only for the hemopexin system and differs from the cell's response to non-protein bound heme, which can be toxic. We propose that defining how cells respond to heme-hemopexin endocytosis, a natural cytoprotective system, will aid our understanding of how cells adapt as they safely respond to increases in heme, Fe(II) and copper. This is relevant for many genetic hemolytic diseases and conditions, stroke and hemorrhage as well as neurodegeneration. Such analyses will help to define a pattern of events that can be utilized to characterize how dysfunctional redox and transition metal handling is linked to the development of pathology in disease states such as Alzheimer's disease when metal homeostasis is not restored; and potentially provide novel targets and approaches to improve therapies.

Targeting the Iron-Response Elements of the mRNAs for the Alzheimer's Amyloid Precursor Protein and Ferritin to Treat Acute Lead and Manganese Neurotoxicity

The therapeutic value of inhibiting translation of the amyloid precursor protein (APP) offers the possibility to reduce neurotoxic amyloid formation, particularly in cases of familial Alzheimer’s disease (AD) caused by APP gene duplications (Dup–APP) and in aging Down syndrome individuals. APP mRNA translation inhibitors such as the anticholinesterase phenserine, and high throughput screened molecules, selectively inhibited the uniquely folded iron-response element (IRE) sequences in the 5’untranslated region (5’UTR) of APP mRNA and this class of drug continues to be tested in a clinical trial as an anti-amyloid treatment for AD. By contrast, in younger age groups, APP expression is not associated with amyloidosis, instead it acts solely as a neuroprotectant while facilitating cellular ferroportin-dependent iron efflux. We have reported that the environmental metallotoxins Lead (Pb) and manganese (Mn) cause neuronal death by interfering with IRE dependent translation of APP and ferritin. The loss of these iron homeostatic neuroprotectants thereby caused an embargo of iron (Fe) export from neurons as associated with excess unstored intracellular iron and the formation of toxic reactive oxidative species (ROS). We propose that APP 5’UTR directed translation activators can be employed therapeutically to protect neurons exposed to high acute Pb and/or Mn exposure. Certainly, high potency APP translation activators, exemplified by the Food and Drug Administration (FDA) pre-approved M1 muscarinic agonist AF102B and high throughput-screened APP 5’UTR translation activators, are available for drug development to treat acute toxicity caused by Pb/Mn exposure to neurons. We conclude that APP translation activators can be predicted to prevent acute metal toxicity to neurons by a mechanism related to the 5’UTR specific yohimbine which binds and targets the canonical IRE RNA stem loop as an H-ferritin translation activator.

Mass spectrometry-based analysis of cerebrospinal fluid from arthritis patients-immune-related candidate proteins affected by TNF blocking treatment

Background

Signs of inflammation in cerebrospinal fluid (CSF) of rheumatoid arthritis patients correlate positively with fatigue, a central nervous system (CNS)-related symptom that can be partially suppressed by TNF blockade. This suggests a possible role for CNS inflammation in arthritis that may be affected by TNF blockade. We therefore investigated the effects of TNF blockade on the arthritis CSF proteome and how candidate proteins related to clinical measures of disease activity and inflammation.

Methods

Mass spectrometry-based quantitative proteomic analysis was performed on CSF from seven polyarthritis patients before and during infliximab treatment. Treatment-associated proteins were identified using univariate (Wilcoxon signed rank test) and multivariate (partial least squares discriminant analysis (PLS-DA)) strategies. Relations between selected candidate proteins and clinical measures were investigated using the Spearman correlations. Additionally, selected proteins were cross-referenced to other studies investigating human CSF in a thorough literature search to ensure feasibility of our results.

Results

Univariate analysis of arthritis CSF proteome revealed a decrease of 35 proteins, predominantly involved in inflammatory processes, following TNF blockade. Seven candidate proteins, Contactin-1 (CNTN1), fibrinogen gamma chain (FGG), hemopexin (HPX), cell adhesion molecule-3 (CADM3), alpha-1B-glycoprotein (A1BG), complement factor B (CFB), and beta-2-microglobulin (B2M), were selected for further studies based on identification by both univariate and multivariate analyses and reported detection in human CSF and known associations to arthritis. Decreased levels of FGG and CFB in CSF after treatment showed strong correlations with both erythrocyte sedimentation rate and disability scores, while CNTN1 and CADM3 were associated with pain.

Conclusion

Several immune-related proteins in the CSF of arthritis patients decreased during TNF blockade, including FGG and CFB that both correlated strongly with systemic inflammation. Our findings stress that also intrathecal inflammatory pathways are related to arthritis symptoms and may be affected by TNF blockade.

Electronic supplementary material

The online version of this article (10.1186/s13075-019-1846-6) contains supplementary material, which is available to authorized users.

Unraveling the Role of Heme in Neurodegeneration

Heme (iron-protoporphyrin IX) is an essential co-factor involved in several biological processes, including neuronal survival and differentiation. Nevertheless, an excess of free-heme promotes oxidative stress and lipid peroxidation, thus leading to cell death. The toxic properties of heme in the brain have been extensively studied during intracerebral or subarachnoid hemorrhages. Recently, a growing number of neurodegenerative disorders have been associated to alterations of heme metabolism. Hence, the etiology of such diseases remains undefined. The aim of this review is to highlight the neuropathological role of heme and to discuss the major heme-regulated pathways that might be crucial for the survival of neuronal cells. The understanding of the molecular mechanisms linking heme to neurodegeneration will be important for therapeutic purposes.

Mitochondrial Targeting in Neurodegeneration: A Heme Perspective

Mitochondrial dysfunction has achieved an increasing interest in the field of neurodegeneration as a pathological hallmark for different disorders. The impact of mitochondria is related to a variety of mechanisms and several of them can co-exist in the same disease. The central role of mitochondria in neurodegenerative disorders has stimulated studies intended to implement therapeutic protocols based on the targeting of the distinct mitochondrial processes. The review summarizes the most relevant mechanisms by which mitochondria contribute to neurodegeneration, encompassing therapeutic approaches. Moreover, a new perspective is proposed based on the heme impact on neurodegeneration. The heme metabolism plays a central role in mitochondrial functions, and several evidences indicate that alterations of the heme metabolism are associated with neurodegenerative disorders. By reporting the body of knowledge on this topic, the review intends to stimulate future studies on the role of heme metabolism in neurodegeneration, envisioning innovative strategies in the struggle against neurodegenerative diseases.

Identification of plasma biomarkers for diffuse axonal injury in rats by iTRAQ-coupled LC-MS/MS and bioinformatics analysis

DAI is a serious and complex brain injury associated with significant morbidity and mortality. The lack of reliable objective diagnostic modalities for DAI delays administration of therapeutic interventions. Hence, identifying reliable biomarkers is urgently needed to enable early DAI diagnosis in the clinic. Herein, we established a rat model of DAI and applied an isobaric tags for a relative and absolute quantification (iTRAQ) coupled with nano-liquid chromatography-tandem mass spectrometry (nano-LC-MS/MS) proteomics approach to screen differentially expressed plasma proteins associated with DAI. A total of 58 proteins were found to be significantly modulated in blood plasma samples of the injury group in at least one time point compared to controls. Bioinformatics analysis of the differentially expressed proteins revealed that the pathogenesis of axonal injury underlying DAI is multi-stage biological process involved. Two significantly changed proteins, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and hemopexin (Hpx), were identified as potential diagnostic biomarkers for DAI, and were successfully confirmed by further western blot analysis. This proteomic profiling study not only identified novel plasma biomarkers that may facilitate the development of clinically diagnostic for DAI, but also provided enhanced understanding of the molecular mechanisms underlying DAI.

Increased brain hemopexin levels improve outcomes after intracerebral hemorrhage

Following intracerebral hemorrhage (ICH), extracellular heme precipitates secondary brain injury, which results in irreversible brain damage and enduring neurological deficits. Hemopexin (Hpx) is an endogenous protein responsible for scavenging heme, thereby modulating its intrinsic proxidant/proinflammatory properties. Although Hpx is present in the brain, the endogenous levels are insufficient to combat the massive heme overload following ICH. We hypothesized that increasing brain Hpx levels would improve ICH outcomes. Unique recombinant adeno-associated viral vectors were designed to specifically overexpress Hpx within the mouse brain. Western blotting, ELISA, and immunohistochemistry of brain homogenates/sections, CSF, and serum were performed. As compared to controls, Hpx mice have increased Hpx protein levels in all three types of biospecimens evaluated, which results in 45.6 ± 6.9% smaller lesions and improved functional recovery after ICH (n=14-19/group, p < 0.05). Local mechanistic analyses show significantly less tissue injury, trends toward smaller hematoma volumes, unchanged heme oxygenase 1 and iron levels, and significantly increased microgliosis and decreased astrogliosis and lipid peroxidation. Peripheral levels of heme-related markers indicate a positive modulation of iron-binding capacity. These findings reveal that high local Hpx levels improve ICH outcomes, likely through both central and peripheral clearance mechanisms, and establish the potential for therapeutically administering clinical-grade Hpx for ICH.

The Aging of Iron Man

Brain iron is tightly regulated by a multitude of proteins to ensure homeostasis. Iron dyshomeostasis has become a molecular signature associated with aging which is accompanied by progressive decline in cognitive processes. A common theme in neurodegenerative diseases where age is the major risk factor, iron dyshomeostasis coincides with neuroinflammation, abnormal protein aggregation, neurodegeneration, and neurobehavioral deficits. There is a great need to determine the mechanisms governing perturbations in iron metabolism, in particular to distinguish between physiological and pathological aging to generate fruitful therapeutic targets for neurodegenerative diseases. The aim of the present review is to focus on the age-related alterations in brain iron metabolism from a cellular and molecular biology perspective, alongside genetics, and neuroimaging aspects in man and rodent models, with respect to normal aging and neurodegeneration. In particular, the relationship between iron dyshomeostasis and neuroinflammation will be evaluated, as well as the effects of systemic iron overload on the brain. Based on the evidence discussed here, we suggest a synergistic use of iron-chelators and anti-inflammatories as putative anti-brain aging therapies to counteract pathological aging in neurodegenerative diseases.

Hemopexin is required for adult neurogenesis in the subventricular zone/olfactory bulb pathway

The neural stem cells (NSCs) of the subventricular zone (SVZ) reside within a specialized niche critical for neurogenesis. Hemopexin, a plasma glycoprotein, has been extensively studied as a heme scavenger at the systemic level. However, little is known about its function in the central nervous system, especially in neurogenesis. In the present study, we demonstrate that deletion of hemopexin leads to neurogenic abnormalities in the SVZ/olfactory bulb (OB) pathway. The lateral ventricle is enlarged in hemopexin-deficient mice, and more apoptosis was observed in Dcx+ cells. Lineage differentiation of NSCs was also inhibited in the SVZ of hemopexin-deficient mice, with more stem cells stayed in an undifferentiated, GFAP+ radial glia-like cell stage. Moreover, hemopexin deletion resulted in impaired neuroblast migration in the rostral migratory stream. Furthermore, exogenous hemopexin protein inhibited apoptosis and promoted the migration and differentiation of cultured NSCs. Finally, immunohistochemical analysis demonstrated that deletion of hemopexin reduced the number of interneurons in the OB. Together, these results suggest a new molecular mechanism for the NSC niche that regulates adult neurogenesis in the SVZ/OB pathway. Our findings may benefit the understanding for olfactory system development.

Potential role of ferric hemoglobin in MS pathogenesis: Effects of oxidative stress and extracellular methemoglobin or its degradation products on myelin components

There is a well-documented relationship between cerebral vasculature and multiple sclerosis (MS) lesions: abnormal accumulations of iron have been found in the walls of the dilated veins in cerebral MS plaques. The source of this iron is unknown, but could be related to the recognized phenomenon of capillary and venous hemorrhages leading to blood extravasation. In turn, hemorrhaging leading to hemolysis results in extracellular release of hemoglobin, a reactive molecule that could induce local oxidative stress, inflammation, and tissue damage. Our previous studies with a reduced form of hemoglobin (oxyHb) have demonstrated its ability to cause extensive lipid and protein oxidation in vitro, which would result in membrane destabilization. Here, we investigated in further detail the mechanism by which the more abundant oxidized form of extracellular hemoglobin (metHb), and dissociated hemin, cause direct oxidative damage to myelin components, specifically membrane-mimetic lipid vesicles and myelin basic protein (MBP), a highly-abundant protein in the CNS. Oxidation of lipids was assessed by the formation of conjugated diene/triene and malondialdehyde, and oxidation of MBP was demonstrated by the bityrosine formation and by the change in protein mass. Our results show that metHb causes oxidative damage to MBP and myelin lipids, partly by transferring its hemin moiety to protein and lipid, but mostly as an intact protein possibly via formation of a ferryl radical. These results elucidating the mechanism of extracellular hemoglobin-induced oxidative damage to myelin components support the need for further research into vascular pathology in MS pathogenesis, to gain insight into the role of iron deposits and/or in stimulation of different comorbidities associated with the disease.

Identification of oxidative modifications of hemopexin and their predicted physiological relevance

Hemopexin protects against heme toxicity in hemolytic diseases and conditions, sepsis, and sickle cell disease. This protection is sustained by heme-hemopexin complexes in biological fluids that resist oxidative damage during heme-driven inflammation. However, apo-hemopexin is vulnerable to inactivation by reactive nitrogen (RNS) and oxygen species (ROS) that covalently modify amino acids. The resultant nitration of amino acids is considered a specific effect reflecting biological events. Using LC-MS, we discovered low endogenous levels of tyrosine nitration in the peptide YYCFQGNQFLR in the heme-binding site of human hemopexin, which was similarly nitrated in rabbit and rat hemopexins. Immunoblotting and selective reaction monitoring were used to quantify tyrosine nitration of in vivo samples and when hemopexin was incubated in vitro with nitrating nitrite/myeloperoxidase/glucose oxidase. Significantly, heme binding by hemopexin declined as tyrosine nitration proceeded in vitro Three nitrated tyrosines reside in the heme-binding site of hemopexin, and we found that one, Tyr-199, interacts directly with the heme ring D propionate. Investigating the oxidative modifications of amino acids after incubation with tert-butyl hydroperoxide and hypochlorous acid in vitro, we identified additional covalent oxidative modifications on four tyrosine residues and one tryptophan residue of hemopexin. Importantly, three of the four modified tyrosines, some of which have more than one modification, cluster in the heme-binding site, supporting a hierarchy of vulnerable amino acids. We propose that during inflammation, apo-hemopexin is nitrated and oxidated in niches of the body containing activated RNS- and ROS-generating immune and endothelial cells, potentially impairing hemopexin's protective extracellular antioxidant function.

Blood Proteomic Profiling in Inherited (ATTRm) and Acquired (ATTRwt) Forms of Transthyretin-Associated Cardiac Amyloidosis

Transthyretin-associated forms of cardiac amyloidosis are fatal protein misfolding diseases that can be inherited (ATTRm) or acquired (ATTRwt). An accurate diagnosis of ATTR amyloidosis can be challenging as biopsy evidence, usually from the affected organ, is required. Precise biomarkers for ATTR disease identification and monitoring are undiscovered, disease-specific therapeutic options are needed, and the current understanding of ATTR molecular pathogenesis is limited. The aim of this study was to investigate and compare the serum proteomes in ATTRm and ATTRwt cardiac amyloidosis to identify differentially expressed blood proteins that were disease-specific. Using multiple-reaction monitoring mass spectrometry (MRM-MS), the concentrations of 160 proteins were analyzed in serum samples from ATTRm and ATTRwt patients, and a healthy control group. Patient and control sera were matched to age (≥60 years), gender (male), and race (Caucasian). The circulating concentrations of 123/160 proteins were significantly different in patient vs control sera; TTR and retinol-binding protein (RBP4) levels were significantly decreased (p < 0.03) in ATTRm compared to controls. In ATTRm, 14/123 proteins were identified as unique to that group and found generally to be lower than controls; moreover, the concentrations of RBP4 and 6 other proteins in this group were significantly different (p < 0.04) compared to ATTRwt. Predicted interactions among the 14 proteins unique to ATTRm were categorized as reaction and binding associations. Alternatively, 27 proteins were found to be unique to ATTRwt with associated interactions defined as activation, catalysis, and inhibition, in addition to reaction and binding. This study demonstrates significant proteomic differences between ATTR patient and control sera, and disease-associated variations in circulating levels of several proteins including TTR and RBP4. The identification of serum proteins unique to ATTRm and ATTRwt cardiac amyloidosis may have diagnostic and prognostic utility, and may provide important clues about disease mechanisms.

Copper induced spin state change of heme–Aβ associated with Alzheimer's disease

Binding of Cu(ii) not only drives the conversion of the benign bis-His bound low spin heme(iii)–Aβ complex to the detrimental mono-His high spin form, even in the presence of excess Aβ, but it also forms the most toxic heme(iii)–Cu(ii)–Aβ species.

Brain iron overload following intracranial haemorrhage

Intracranial haemorrhages, including intracerebral haemorrhage (ICH), intraventricular haemorrhage (IVH) and subarachnoid haemorrhage (SAH), are leading causes of morbidity and mortality worldwide. In addition, haemorrhage contributes to tissue damage in traumatic brain injury (TBI). To date, efforts to treat the long-term consequences of cerebral haemorrhage have been unsatisfactory. Incident rates and mortality have not showed significant improvement in recent years. In terms of secondary damage following haemorrhage, it is becoming increasingly apparent that blood components are of integral importance, with haemoglobin-derived iron playing a major role. However, the damage caused by iron is complex and varied, and therefore, increased investigation into the mechanisms by which iron causes brain injury is required. As ICH, IVH, SAH and TBI are related, this review will discuss the role of iron in each, so that similarities in injury pathologies can be more easily identified. It summarises important components of normal brain iron homeostasis and analyses the existing evidence on iron-related brain injury mechanisms. It further discusses treatment options of particular promise.

Alterations in Systemic Extracellular Heme and Hemopexin Are Associated With Adverse Clinical Outcomes in Ugandan Children With Severe Malaria

Background. Malaria remains a major cause of global mortality. Extracellular heme, released during malaria-induced hemolysis, mediates a number of pathogenic processes associated with vascular and organ injury. Hemopexin (hpx) facilitates the degradation of extracellular heme. In this study, we explore the hypothesis that dysregulation of the heme-hpx axis is associated with disease severity, acute kidney injury (AKI), and outcome.

Methods. Plasma levels of hemin and hpx (at admission, day 3, and day 14) were assessed in children with severe malaria in Jinja, Uganda.

Results. The ratio of heme to hpx was higher at admission and decreased with recovery (median, 0.043 [interquartile range {IQR}, 0.007–0.239] on day 1, 0.024 [IQR, 0.005–0.126] on day 3, and 0.008 [IQR, 0.002–0.022] on day 14; P < .001). Ratios of heme to hpx at admission were higher in children with as compared to those without severe anemia (median, 0.124 [IQR, 0.024–0.431] vs 0.016 [IQR, 0.003–0.073]; P < .0001), children with as compared to those without respiratory distress (median, 0.063 [IQR, 0.017–0.413] vs 0.020 [IQR, 0.004–0.124]; P < .01), and children with as opposed to those without stage 3 AKI (median, 0.354 [IQR, 0.123–2.481] vs 0.037 [IQR, 0.005–0.172], P < .01). The heme to hpx ratio at admission was associated with 6-month mortality (median, 0.148 [IQR, 0.042–0.500] vs 0.039 [IQR, 0.007–0.172]; P = .012).

Conclusions. The ratio of heme to hpx is associated with disease severity and adverse clinical outcomes in Ugandan children, and dysregulation of the heme axis may contribute to malaria pathogenesis.

A role for amyloid precursor protein translation to restore iron homeostasis and ameliorate lead (Pb) neurotoxicity

Iron supplementation ameliorates the neurotoxicity of the environmental contaminant lead (Pb); however, the mechanism remains undefined. Iron is an essential nutrient but high levels are toxic due to the catalytic generation of destructive hydroxyl radicals. Using human neuroblastoma SH-SY5Y cells to model human neurons, we investigated the effect of Pb on proteins of iron homeostasis: the Alzheimer's amyloid precursor protein (APP), which stabilizes the iron exporter ferroportin 1; and, the heavy subunit of the iron-storage protein, ferritin (FTH). Lead (Pb(II) and Pb(IV) inhibited APP translation and raised cytosolic iron(II). Lead also increased iron regulatory protein-1 binding to the cognate 5'untranslated region-specific iron-responsive element (IRE) of APP and FTH mRNAs. Concurrent iron treatment rescued cells from Pb toxicity by specifically restoring APP synthesis, i.e. levels of the APP-related protein, APLP-2, were unchanged. Significantly, iron/IRE-independent over-expression of APP695  protected SH-SY5Y cells from Pb toxicity, demonstrating that APP plays a key role in maintaining safe levels of intracellular iron. Overall, our data support a model of neurotoxicity where Pb enhances iron regulatory protein/IRE-mediated repression of APP and FTH translation. We propose novel treatment options for Pb poisoning to include chelators and the use of small molecules to maintain APP and FTH translation. We propose the following cascade for Lead (Pb) toxicity to neurons; by targeting the interaction between Iron regulatory protein-1 and Iron-responsive elements, Pb caused translational repression of proteins that control intracellular iron homeostasis, including the Alzheimer's amyloid precursor protein (APP) that stabilizes the iron exporter ferroportin, and the ferroxidase heavy subunit of the iron-storage protein, ferritin. When unregulated, IRE-independent over-expression of APP695 protected SH-SY5Y neurons from Pb toxicity. There is a novel and key role for APP in maintaining safe levels of intracellular iron pertinent to lead toxicity.

Deferoxamine inhibits microglial activation, attenuates blood-brain barrier disruption, rescues dendritic damage, and improves spatial memory in a mouse model of microhemorrhages

Cerebral microbleeds are strongly linked to cognitive dysfunction in the elderly. Iron accumulation plays an important role in the pathogenesis of intracranial hemorrhage. Deferoxamine (DFX), a metal chelator, removes iron overload and protects against brain damage in intracranial hemorrhage. In this study, the protective effects of DFX against microhemorrhage were examined in mice. C57BL6 and Thy-1 green fluorescent protein transgenic mice were subjected to perforating artery microhemorrhages on the right posterior parietal cortex using two-photon laser irradiation. DFX (100 mg/kg) was administered 6 h after microhemorrhage induction, followed by every 12 h for three consecutive days. The water maze task was conducted 7 days after induction of microhemorrhages, followed by measurement of blood-brain barrier permeability, iron deposition, microglial activation, and dendritic damage. Laser-induced multiple microbleeds in the right parietal cortex clearly led to spatial memory disruption, iron deposits, microglial activation, and dendritic damage, which were significantly attenuated by DFX, supporting the targeting of iron overload as a therapeutic option and the significant potential of DFX in microhemorrhage treatment. Irons accumulation after intracranial hemorrhage induced a serious secondary damage to the brain. We proposed that irons accumulation after parietal microhemorrhages impaired spatial cognition. After parietal multiple microhemorrhages, increased irons and ferritin contents induced blood-brain barrier disruption, microglial activation, and further induced dendrites loss, eventually impaired the water maze, deferoxamine treatment protected from these damages.

Deciphering glycomics and neuroproteomic alterations in experimental traumatic brain injury: Comparative analysis of aspirin and clopidogrel treatment

As populations age, the number of patients sustaining traumatic brain injury (TBI) and concomitantly receiving preinjury antiplatelet therapy such as aspirin (ASA) and clopidogrel (CLOP) is rising. These drugs have been linked with unfavorable clinical outcomes following TBI, where the exact mechanism(s) involved are still unknown. In this novel work, we aimed to identify and compare the altered proteome profile imposed by ASA and CLOP when administered alone or in combination, prior to experimental TBI. Furthermore, we assessed differential glycosylation PTM patterns following experimental controlled cortical impact model of TBI, ASA, CLOP, and ASA + CLOP. Ipsilateral cortical brain tissues were harvested 48 h postinjury and were analyzed using an advanced neuroproteomics LC-MS/MS platform to assess proteomic and glycoproteins alterations. Of interest, differential proteins pertaining to each group (22 in TBI, 41 in TBI + ASA, 44 in TBI + CLOP, and 34 in TBI + ASA + CLOP) were revealed. Advanced bioinformatics/systems biology and clustering analyses were performed to evaluate biological networks and protein interaction maps illustrating molecular pathways involved in the experimental conditions. Results have indicated that proteins involved in neuroprotective cellular pathways were upregulated in the ASA and CLOP groups when given separately. However, ASA + CLOP administration revealed enrichment in biological pathways relevant to inflammation and proinjury mechanisms. Moreover, results showed differential upregulation of glycoproteins levels in the sialylated N-glycans PTMs that can be implicated in pathological changes. Omics data obtained have provided molecular insights of the underlying mechanisms that can be translated into clinical bedside settings.

Heme-Hemopexin Scavenging Is Active in the Brain and Associates With Outcome After Subarachnoid Hemorrhage

BACKGROUND AND PURPOSE

Long-term outcome after subarachnoid hemorrhage (SAH) is potentially linked to cytotoxic heme. Free heme is bound by hemopexin and rapidly scavenged by CD91. We hypothesized that heme scavenging in the brain would be associated with outcome after hemorrhage.

METHODS

Using cerebrospinal fluid and tissue from patients with SAH and control individuals, the activity of the intracranial CD91-hemopexin system was examined using ELISA, ultrahigh performance liquid chromatography, and immunohistochemistry.

RESULTS

In control individuals, cerebrospinal fluid hemopexin was mainly synthesized intrathecally. After SAH, cerebrospinal fluid hemopexin was high in one third of cases, and these patients had a higher probability of delayed cerebral ischemia and poorer neurological outcome. The intracranial CD91-hemopexin system was active after SAH because CD91 positively correlated with iron deposition in brain tissue. Heme-hemopexin uptake saturated rapidly after SAH because bound heme accumulated early in the cerebrospinal fluid. When the blood-brain barrier was compromised after SAH, serum hemopexin level was lower, suggesting heme transfer to the circulation for peripheral CD91 scavenging.

CONCLUSIONS

The CD91-heme-hemopexin scavenging system is important after SAH and merits further study as a potential prognostic marker and therapeutic target.

Molecular, Cellular and Clinical Aspects of Intracerebral Hemorrhage: Are the Enemies Within?

Hemorrhagic stroke is a disease with high incidence and mortality rates. In addition to the mass lesions that result from hemorrhagic stroke, substances such as the blood-derived products (BDP) (hemoglobin (Hb), heme and iron) induce a potent inflammatory response and exert direct toxic effects on neurons, astrocytes, and microglia. In the present review, we discuss the mechanisms of brain injury secondary to hemorrhagic stroke, focusing on the involvement of BDP as major players of cellular redox imbalance, inflammation, and glutamate excitotoxicity. Potential natural mechanisms of protection against free Hb and heme such as haptoglobin and hemopexin, respectively, are highlighted. We finally discuss the experimental and clinical trials targeting free iron and heme scavenging as well as inflammation, as potential new therapies to minimize the devastating effects of hemorrhagic stroke on brain structure and function.

Oxidative Stress in Intracerebral Hemorrhage: Sources, Mechanisms, and Therapeutic Targets

Intracerebral hemorrhage (ICH) is associated with the highest mortality and morbidity despite only constituting approximately 10–15% of all strokes. Complex underlying mechanisms consisting of cytotoxic, excitotoxic, and inflammatory effects of intraparenchymal blood are responsible for its highly damaging effects. Oxidative stress (OS) also plays an important role in brain injury after ICH but attracts less attention than other factors. Increasing evidence has demonstrated that the metabolite axis of hemoglobin-heme-iron is the key contributor to oxidative brain damage after ICH, although other factors, such as neuroinflammation and prooxidases, are involved. This review will discuss the sources, possible molecular mechanisms, and potential therapeutic targets of OS in ICH.