Modeling hemoglobin and hemoglobin:haptoglobin complex clearance in a non-rodent species-pharmacokinetic and therapeutic implications

Biophysical Analysis and Preclinical Pharmacokinetics-Pharmacodynamics of Tangential Flow Filtration Fractionated Polymerized Human Hemoglobin as a Red Blood Cell Substitute

Red blood cell (RBC) substitutes tested in late-phase clinical trials contained low-molecular-weight hemoglobin species (<500 kDa), resulting in vasoconstriction, hypertension, and oxidative tissue injury; therefore, contributing to poor clinical outcomes. This work aims to improve the safety profile of the RBC substitute, polymerized human hemoglobin (PolyhHb), via in vitro and in vivo screening of PolyhHb fractionated into four molecular weight brackets (50-300 kDa [PolyhHb-B1]; 100-500 kDa [PolyhHb-B2]; 500-750 kDa [PolyhHb-B3]; and 750 kDa to 0.2 μm [PolyhHb-B4]) using a two-stage tangential flow filtration purification process. Analysis showed that PolyhHb's oxygen affinity, and haptoglobin binding kinetics decreased with increasing bracket size. A 25% blood-for-PolyhHb exchange transfusion guinea pig model suggests that hypertension and tissue extravasation decreased with increasing bracket size. PolyhHb-B3 demonstrated extended circulatory pharmacokinetics, no renal tissue distribution, no aberrant blood pressure, or cardiac conduction effects, and may therefore be appropriate material for further evaluation.

Increases in serum carbonylated protein levels of dogs with hypercortisolism

Protein carbonylation is an irreversible and degenerative modification that can be used to evaluate oxidative stress caused by glucocorticoids. In this study, we focused on protein carbonylation in dogs with hypercortisolism (HC). Sera samples were collected from 14 dogs diagnosed with HC and treated with trilostane, 12 dogs with inflammatory diseases (disease control group), and eight clinically healthy dogs. When the carbonylated protein levels were detected by the immunoblot analysis, one band of approximately 40 kDa was predominantly increased in the dogs with HC. The band was identified as haptoglobin using the liquid chromatography tandem mass spectrometry method. Furthermore, haptoglobin immune reactivity was higher in the dogs with HC. Although the average protein carbonylation level of the HC group was not significantly different from that of the other groups, the carbonylation level was significantly higher for the poorly controlled HC cases than for the well-controlled HC group. Additionally, the primary culture of canine hepatocytes was used to clarify the direct effect of glucocorticoids on protein carbonylation in dog livers. Both the carbonylated protein and haptoglobin clearly increased after 72 h. These findings suggest that haptoglobin and its carbonylated form are increased with canine HC, and that the protein carbonylation ratio and/or haptoglobin level could be related to disease management. These factors could be useful as biomarkers for an oxidative stress reaction, at least in the liver, and for treatment monitoring of HC.

The Multiple Facets of Iron Recycling

The production of around 2.5 million red blood cells (RBCs) per second in erythropoiesis is one of the most intense activities in the body. It continuously consumes large amounts of iron, approximately 80% of which is recycled from aged erythrocytes. Therefore, similar to the “making”, the “breaking” of red blood cells is also very rapid and represents one of the key processes in mammalian physiology. Under steady-state conditions, this important task is accomplished by specialized macrophages, mostly liver Kupffer cells (KCs) and splenic red pulp macrophages (RPMs). It relies to a large extent on the engulfment of red blood cells via so-called erythrophagocytosis. Surprisingly, we still understand little about the mechanistic details of the removal and processing of red blood cells by these specialized macrophages. We have only started to uncover the signaling pathways that imprint their identity, control their functions and enable their plasticity. Recent findings also identify other myeloid cell types capable of red blood cell removal and establish reciprocal cross-talk between the intensity of erythrophagocytosis and other cellular activities. Here, we aimed to review the multiple and emerging facets of iron recycling to illustrate how this exciting field of study is currently expanding.

Haptoglobin: From hemoglobin scavenging to human health

Haptoglobin (Hp) belongs to the family of acute-phase plasma proteins and represents the most important plasma detoxifier of hemoglobin (Hb). The basic Hp molecule is a tetrameric protein built by two α/β dimers. Each Hp α/β dimer is encoded by a single gene and is synthesized as a single polypeptide. Following post-translational protease-dependent cleavage of the Hp polypeptide, the α and β chains are linked by disulfide bridge(s) to generate the mature Hp protein. As human Hp gene is characterized by two common Hp1 and Hp2 alleles, three major genotypes can result (i.e., Hp1-1, Hp2-1, and Hp2-2). Hp regulates Hb clearance from circulation by the macrophage-specific receptor CD163, thus preventing Hb-mediated severe consequences for health. Indeed, the antioxidant and Hb binding properties of Hp as well as its ability to stimulate cells of the monocyte/macrophage lineage and to modulate the helper T-cell type 1 and type 2 balance significantly associate with a variety of pathogenic disorders (e.g., infectious diseases, diabetes, cardiovascular diseases, and cancer). Alternative functions of the variants Hp1 and Hp2 have been reported, particularly in the susceptibility and protection against infectious (e.g., pulmonary tuberculosis, HIV, and malaria) and non-infectious (e.g., diabetes, cardiovascular diseases and obesity) diseases. Both high and low levels of Hp are indicative of clinical conditions: Hp plasma levels increase during infections, inflammation, and various malignant diseases, and decrease during malnutrition, hemolysis, hepatic disease, allergic reactions, and seizure disorders. Of note, the Hp:Hb complexes display heme-based reactivity; in fact, they bind several ferrous and ferric ligands, including O₂, CO, and NO, and display (pseudo-)enzymatic properties (e.g., NO and peroxynitrite detoxification). Here, genetic, biochemical, biomedical, and biotechnological aspects of Hp are reviewed.

Sample preparation of blood plasma enables baseline separation of iron metalloproteins by SEC-GFAAS

The analysis of human plasma for biomarkers holds promise to revolutionize disease diagnosis, but is hampered by the inherent complexity of the plasma proteome. One way to overcome this problem is to analyze plasma for a sub-proteome, such as the metalloproteome. Previous studies employing size-exclusion chromatography (SEC) coupled on-line to an inductively coupled plasma-atomic emission spectrometer (ICP-AES) have revealed that plasma contains ~12 copper, iron and zinc metalloproteins. This included the iron metalloproteins transferrin (Tf) and a recently identified haptoglobin-hemoglobin (Hp-Hb) complex, which is formed in plasma when red blood cells rupture. Since this SEC-ICP-AES method required a sample volume of 500 µL to generate diagnostically useful results, we sought to develop an alternative SEC-based hyphenated approach using a smaller SEC column (150 × 5 mm I.D.) and a graphite furnace atomic absorption spectrometer (GFAAS) as the iron-specific detector. A designed interface enabled the integration of the SEC system with the GFAAS. Baseline separation between the Hp-Hb complex and Tf was achieved by developing a sample preparation procedure which involved the chelating agent-based mobilization of Fe from Tf to a small molecular weight Fe complex. Spiking of human plasma (1.0 mL) with red blood cell lysate (1-2 µL) increased only the intensity of the Fe peak corresponding to the Hp-Hb complex, but not that of Tf. Since the developed SEC-GFAAS method requires only 50 µL of plasma for analysis, it can now be employed for the cost-effective quantification of the clinically relevant Hb-Hp complex in human plasma in <50 min.

Laboratory assessment of multiple myeloma

Laboratory testing plays an essential role in the diagnosis and management of patients with multiple myeloma. A variety of chemistry and molecular assays are routinely used to monitor patient progress, response to treatment and relapse. Here, we have reviewed current literature and core guidelines on the details of laboratory testing in myeloma-related investigations. This includes the use and value of protein electrophoresis, serum free light chain and cytogenetic testing. Furthermore, we discuss other traditional chemistry assays essential to myeloma investigation, and potential interferences that may arise due to the disease nature of myeloma, that is, the presence of a monoclonal immunoglobulin. Finally, we discuss the importance of communication in protein electrophoresis results, where laboratorians are required to relate clinically relevant myeloma-relevant information to the ordering physician on the background of a complex pattern of serum or urine proteins. Laboratory testing in myeloma-related investigation relies on several traditional chemistry assays. However, we anticipate new tests and technologies to become available in the future with improved analytical sensitivity, as well as improved clinical sensitivity in identifying patients who are at high risk of progression to multiple myeloma.

Pigs Lacking the Scavenger Receptor Cysteine-Rich Domain 5 of CD163 Are Resistant to Porcine Reproductive and Respiratory Syndrome Virus 1 Infection

Porcine reproductive and respiratory syndrome virus (PRRSV) has a narrow host cell tropism, limited to cells of the monocyte/macrophage lineage. CD163 protein is expressed at high levels on the surface of specific macrophage types, and a soluble form is circulating in blood. CD163 has been described as a fusion receptor for PRRSV, with the scavenger receptor cysteine-rich domain 5 (SRCR5) region having been shown to be the interaction site for the virus. As reported previously, we have generated pigs in which exon 7 of the CD163 gene has been deleted using CRISPR/Cas9 editing in pig zygotes. These pigs express CD163 protein lacking SRCR5 (ΔSRCR5 CD163) and show no adverse effects when maintained under standard husbandry conditions. Not only was ΔSRCR5 CD163 detected on the surface of macrophage subsets, but the secreted, soluble protein can also be detected in the serum of the edited pigs, as shown here by a porcine soluble CD163-specific enzyme-linked immunosorbent assay (ELISA). Previous results showed that primary macrophage cells from ΔSRCR5 CD163 animals are resistant to PRRSV-1 subtype 1, 2, and 3 as well as PRRSV-2 infection in vitro Here, ΔSRCR5 pigs were challenged with a highly virulent PRRSV-1 subtype 2 strain. In contrast to the wild-type control group, ΔSRCR5 pigs showed no signs of infection and no viremia or antibody response indicative of a productive infection. Histopathological analysis of lung and lymph node tissue showed no presence of virus-replicating cells in either tissue. This shows that ΔSRCR5 pigs are fully resistant to infection by the virus.IMPORTANCE Porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) is the etiological agent of PRRS, causing late-term abortions, stillbirths, and respiratory disease in pigs, incurring major economic losses to the worldwide pig industry. The virus is highly mutagenic and can be divided into two species, PRRSV-1 and PRRSV-2, each containing several subtypes. Current control strategies mainly involve biosecurity measures, depopulation, and vaccination. Vaccines are at best only partially protective against infection with heterologous subtypes and sublineages, and modified live vaccines have frequently been reported to revert to virulence. Here, we demonstrate that a genetic-control approach results in complete resistance to PRRSV infection in vivo CD163 is edited so as to remove the viral interaction domain while maintaining protein expression and biological function, averting any potential adverse effect associated with protein knockout. This research demonstrates a genetic-control approach with potential benefits in animal welfare as well as to the pork industry.

Haptoglobin Preserves Vascular Nitric Oxide Signaling during Hemolysis

RATIONALE

Hemolysis occurs not only in conditions such as sickle cell disease and malaria but also during transfusion of stored blood, extracorporeal circulation, and sepsis. Cell-free Hb depletes nitric oxide (NO) in the vasculature, causing vasoconstriction and eventually cardiovascular complications. We hypothesize that Hb-binding proteins may preserve vascular NO signaling during hemolysis.

OBJECTIVES

Characterization of an archetypical function by which Hb scavenger proteins could preserve NO signaling during hemolysis.

METHODS

We investigated NO reaction kinetics, effects on arterial NO signaling, and tissue distribution of cell-free Hb and its scavenger protein complexes.

MEASUREMENTS AND MAIN RESULTS

Extravascular translocation of cell-free Hb into interstitial spaces, including the vascular smooth muscle cell layer of rat and pig coronary arteries, promotes vascular NO resistance. This critical disease process is blocked by haptoglobin. Haptoglobin does not change NO dioxygenation rates of Hb; rather, the large size of the Hb:haptoglobin complex prevents Hb extravasation, which uncouples NO/Hb interaction and vasoconstriction. Size-selective compartmentalization of Hb functions as a substitute for red blood cells after hemolysis and preserves NO signaling in the vasculature. We found that evolutionarily and structurally unrelated Hb-binding proteins, such as PIT54 found in avian species, functionally converged with haptoglobin to protect NO signaling by sequestering cell-free Hb in large protein complexes.

CONCLUSIONS

Sequential compartmentalization of Hb by erythrocytes and scavenger protein complexes is an archetypical mechanism, which may have supported coevolution of hemolysis and normal vascular function. Therapeutic supplementation of Hb scavengers may restore vascular NO signaling and attenuate disease complications in patients with hemolysis.

Haptoglobin

Haptoglobin (Hp) is an abundant human plasma protein that tightly captures hemoglobin (Hb) during hemolysis. The Hb-Hp complex formation reduces the oxidative properties of heme/Hb and promotes recognition by the macrophage scavenger receptor CD163. This leads to Hb-Hp breakdown and heme catabolism by heme oxygenase and biliverdin reductase. Gene duplications of a part of or the entire Hp gene in the primate evolution have led to variant Hp gene products that collectively may be designated "the haptoglobins (Hps)" as they all bind Hb. These variant products include the human-specific multimeric Hp phenotypes in individuals, which are hetero- or homozygous for an Hp² gene allele. The Hp-related protein (Hpr) is another Hp duplication product in humans and other primates. Alternative functions of the variant Hps are indicated by numerous reports on association between Hp phenotypes and disease as well as the elucidation of a specific role of Hpr in the innate immune defense. Recent Advances: Recent functional and structural information on Hp and receptor systems for Hb removal now provides insight on how Hp carries out essential functions such as the Hb detoxification/removal, and how Hpr, by acting as an Hp-lookalike, can sneak a lethal toxin into trypanosome parasites that cause mammalian sleeping sickness. Critical Issues and Future Directions: The new structural insight may facilitate ongoing attempts of developing Hp derivatives for prevention of Hb toxicity in hemolytic diseases such as sickle cell disease and other hemoglobinopathies. Furthermore, the new structural knowledge may help identifying yet unknown functions based on other disease-relevant biological interactions involving Hps. Antioxid. Redox Signal. 26, 814-831.

Haptoglobin and Free Haemoglobin during Cardiac Surgery—is there a Link to Acute Kidney Injury?

Acute kidney injury (AKI) is frequently observed after cardiac surgery (CS) with cardiopulmonary bypass (CPB). Multiple mechanisms underlie this phenomenon, including CPB-dependent haemolysis. Haemoglobin is released during haemolysis, and free haemoglobin (frHb) causes tubular cell injury after exceeding the binding capacity of haptoglobin (Hp). The objective of this study was to investigate the influence of perioperative changes in frHb and Hp levels on the incidence of CS-associated (CSA) AKI. After receiving local ethics committee approval and obtaining informed consent from our patients, we analysed the data pertaining to 154 patients undergoing CPB surgery. We recorded frHb and Hp concentrations pre-, intra- and postoperatively and defined AKI using the Kidney Disease Improving Global Outcomes (KDIGO) classification. We observed that frHb levels increased significantly during surgery and then decreased at ten hours thereafter and that Hp levels decreased during surgery and remained at low levels until the first postoperative day. We noted a moderate negative correlation between frHb and Hp levels. AKI was identified in 45.5% of patients; however, there was no significant difference in frHb or Hp levels between patients with and without AKI. We did not observe a relationship between frHb or Hp levels and CSA AKI and thus could not confirm the hypothesis that patients with higher baseline Hp concentrations experience a lower incidence of AKI than patients with lower baseline Hp concentrations.

Evaluation of Gallium as a Tracer of Exogenous Hemoglobin-Haptoglobin Complexes for Targeted Drug Delivery Applications

Haptoglobin (Hp) is a plasma glycoprotein that generates significant interest in the drug delivery community because of its potential for delivery of antiretroviral medicines with high selectivity to macrophages and monocytes, the latent reservoirs of human immunodeficiency virus. As is the case with other therapies that exploit transport networks for targeted drug delivery, the success of the design and optimization of Hp-based therapies will critically depend on the ability to accurately localize and quantitate Hp-drug conjugates on the varying and unpredictable background of endogenous proteins having identical structure. In this work, we introduce a new strategy for detecting and quantitating exogenous Hp and Hp-based drugs with high sensitivity in complex biological samples using gallium as a tracer of this protein and inductively coupled plasma mass spectrometry (ICP MS) as a method of detection. Metal label is introduced by reconstituting hemoglobin (Hb) with gallium(III)-protoporphyrin IX followed by its complexation with Hp. Formation of the Hp/Hb assembly and its stability are evaluated with native electrospray ionization mass spectrometry. Both stable isotopes of Ga give rise to an abundant signal in ICP MS of a human plasma sample spiked with the metal-labeled Hp/Hb complex. The metal label signal exceeds the spectral interferences' contributions by more than an order of magnitude even with the concentration of the exogenous protein below 10 nM, the level that is more than adequate for the planned pharmacokinetic studies of Hp-based therapeutics. Graphical Abstract ᅟ.

The Staphylococcus aureus Protein IsdH Inhibits Host Hemoglobin Scavenging to Promote Heme Acquisition by the Pathogen

Hemolysis is a complication in septic infections with Staphylococcus aureus, which utilizes the released Hb as an iron source. S. aureus can acquire heme in vitro from hemoglobin (Hb) by a heme-sequestering mechanism that involves proteins from the S. aureus iron-regulated surface determinant (Isd) system. However, the host has its own mechanism to recapture the free Hb via haptoglobin (Hp) binding and uptake of Hb-Hp by the CD163 receptor in macrophages. It has so far remained unclear how the Isd system competes with this host iron recycling system in situ to obtain the important nutrient. By binding and uptake studies, we now show that the IsdH protein, which serves as an Hb receptor in the Isd system, directly interferes with the CD163-mediated clearance by binding the Hb-Hp complex and inhibiting CD163 recognition. Analysis of truncated IsdH variants including one or more of three near iron transporter domains, IsdH^N1, IsdH^N2, and IsdH^N3, revealed that Hb binding of IsdH^N1 and IsdH^N2 accounted for the high affinity for Hb-Hp complexes. The third near iron transporter domain, IsdH^N3, exhibited redox-dependent heme extraction, when Hb in the Hb-Hp complex was in the oxidized met form but not in the reduced oxy form. IsdB, the other S. aureus Hb receptor, failed to extract heme from Hb-Hp, and it was a poor competitor for Hb-Hp binding to CD163. This indicates that Hb recognition by IsdH, but not by IsdB, sterically inhibits the receptor recognition of Hb-Hp. This function of IsdH may have an overall stimulatory effect on S. aureus heme acquisition and growth.

Hemoglobinuria-related acute kidney injury is driven by intrarenal oxidative reactions triggering a heme toxicity response

Intravascular hemolysis can result in hemoglobinuria with acute kidney injury. In this study we systematically explored two in vivo animal models and a related cell culture system to identify hemoglobinuria-triggered damage pathways. In models of stored blood transfusion and hemoglobin (Hb) exposure in guinea pigs and beagle dogs we found that hemoglobinuria led to intrarenal conversion of ferrous Hb(Fe²⁺) to ferric Hb(Fe³⁺), accumulation of free heme and Hb-cross-linking products, enhanced 4-hydroxynonenal reactivity in renal tissue, and acute tubule injury. These changes were associated in guinea pigs with activation of a renal cortex gene expression signature indicative of oxidative stress and activation of the unfolded protein response (UPR). Tubule cells of hemolytic animals demonstrated enhanced protein expression of heme oxygenase and heat shock protein and enhanced expression of acute kidney injury-related neutrophil gelatinase-associated lipocalin. These adverse changes were completely prevented by haptoglobin treatment. The in vivo findings were extrapolated to a MS-based proteome analysis of SILAC-labeled renal epithelial cells that were exposed to free heme within a concentration range estimate of renal tubule heme exposure. These experiments confirmed that free heme is a likely trigger of tubule barrier deregulation and oxidative cell damage and reinforced the hypothesis that uncontrolled free heme could trigger the UPR as an important pathway of renal injury during hemoglobinuria.

2015 Clinical trials update in sickle cell anemia

Polymerization of HbS and cell sickling are the prime pathophysiological events in sickle cell disease (SCD). Over the last 30 years, a substantial understanding at the molecular level has been acquired on how a single amino acid change in the structure of the beta chain of hemoglobin leads to the explosive growth of the HbS polymer and the associated changes in red cell morphology. O2 tension and intracellular HbS concentration are the primary molecular drivers of this process, and are obvious targets for developing new therapies. However, polymerization and sickling are driving a complex network of associated cellular changes inside and outside of the erythrocyte, which become essential components of the inflammatory vasculopathy and result in a large range of potential acute and chronic organ damages. In these areas, a multitude of new targets for therapeutic developments have emerged, with several ongoing or planned new therapeutic interventions. This review outlines the key points of SCD pathophysiology as they relate to the development of new therapies, both at the pre-clinical and clinical levels.

Pharmacokinetics and mechanisms of plasma removal of hemoglobin-based oxygen carriers

The circulatory persistence, distribution, and metabolism of hemoglobin-based oxygen carriers (HBOCs) is a major determinant of their safety and efficacy. In this communication, published data on the pharmacokinetics and routes of plasma elimination of HBOCs are summarized and evaluated. The circulating half-life of HBOCs is dose-dependent in both animals and humans. Half-life also increases with molecular weight in animals, at least up to the MDa range. The functional half-life of HBOCs is diminished by as much as 40% due to oxidation of the heme group relative to the overall rate of removal of hemoglobin (Hb) from plasma. Kidney excretion of HBOCs is greatly diminished compared to that of unmodified Hb, but the liver remains a primary site of catabolism. Both hepatocytes and Kupffer cells have been implicated in receptor-mediated HBOC uptake. Removal also occurs in the spleen and/or bone marrow and probably at dispersed sites in the endothelium as well. HBOCs extravasate into the lymph at a rate inversely proportional to their molecular weight and are taken up by monocyte/macrophage CD163 receptors, both as free Hb and in complexes with haptoglobin (Hp). The interactions with both Hp and the CD163 receptor are altered by Hb modification. However, monocyte/macrophage uptake may not be a quantitatively important route for the removal of clinically relevant doses of HBOCs. The relative contributions of different removal pathways have yet to be comprehensively determined, particularly in humans.

Haptoglobin, hemopexin, and related defense pathways-basic science, clinical perspectives, and drug development

Hemolysis, which occurs in many disease states, can trigger a diverse pathophysiologic cascade that is related to the specific biochemical activities of free Hb and its porphyrin component heme. Normal erythropoiesis and concomitant removal of senescent red blood cells (RBC) from the circulation occurs at rates of approximately 2 × 10⁶ RBCs/second. Within this physiologic range of RBC turnover, a small fraction of hemoglobin (Hb) is released into plasma as free extracellular Hb. In humans, there is an efficient multicomponent system of Hb sequestration, oxidative neutralization and clearance. Haptoglobin (Hp) is the primary Hb-binding protein in human plasma, which attenuates the adverse biochemical and physiologic effects of extracellular Hb. The cellular receptor target of Hp is the monocyte/macrophage scavenger receptor, CD163. Following Hb-Hp binding to CD163, cellular internalization of the complex leads to globin and heme metabolism, which is followed by adaptive changes in antioxidant and iron metabolism pathways and macrophage phenotype polarization. When Hb is released from RBCs within the physiologic range of Hp, the potential deleterious effects of Hb are prevented. However, during hyper-hemolytic conditions or with chronic hemolysis, Hp is depleted and Hb readily distributes to tissues where it might be exposed to oxidative conditions. In such conditions, heme can be released from ferric Hb. The free heme can then accelerate tissue damage by promoting peroxidative reactions and activation of inflammatory cascades. Hemopexin (Hx) is another plasma glycoprotein able to bind heme with high affinity. Hx sequesters heme in an inert, non-toxic form and transports it to the liver for catabolism and excretion. In the present review we discuss the components of physiologic Hb/heme detoxification and their potential therapeutic application in a wide range of hemolytic conditions.