Hemopexin decreases spontaneous chemiluminescence of cold preserved liver after reperfusion

Hemopexin as an Inhibitor of Hemolysis-Induced Complement Activation

Hemopexin is the main plasmatic scavenger of cell-free heme, released in the context of intravascular hemolysis or major cell injury. Heme is indispensable for the oxygen transport by hemoglobin but when released outside of the erythrocytes it becomes a danger-associated molecular pattern, contributing to tissue injury. One of the mechanisms of pro-inflammatory action of heme is to activate the innate immune complement cascade. Therefore, we hypothesized that injection of hemopexin will prevent hemolysis-induced complement activation. Human plasma-derived hemopexin is compatible with the heme clearance machinery of the mice. 100 or 500 mg/kg of hemopexin was injected in C57Bl/6 mice before treatment with phenylhydrazine (inducer of erythrocytes lysis) or with PBS as a control. Blood was taken at different timepoints to determine the pharmacokinetic of injected hemopexin in presence and absence of hemolysis. Complement activation was determined in plasma, by the C3 cleavage (western blot) and in the kidneys (immunofluorescence). Kidney injury was evaluated by urea and creatinine in plasma and renal NGAL and HO-1 gene expression were measured. The pharmacokinetic properties of hemopexin (mass spectrometry) in the hemolytic mice were affected by the target-mediated drug disposition phenomenon due to the high affinity of binding of hemopexin to heme. Hemolysis induced complement overactivation and signs of mild renal dysfunction at 6 h, which were prevented by hemopexin, except for the NGAL upregulation. The heme-degrading capacity of the kidney, measured by the HO-1 expression, was not affected by the treatment. These results encourage further studies of hemopexin as a therapeutic agent in models of diseases with heme overload.

Heme scavenging reduces pulmonary endoplasmic reticulum stress, fibrosis, and emphysema

Pulmonary fibrosis and emphysema are irreversible chronic events after inhalation injury. However, the mechanism(s) involved in their development remain poorly understood. Higher levels of plasma and lung heme have been recorded in acute lung injury associated with several insults. Here, we provide the molecular basis for heme-induced chronic lung injury. We found elevated plasma heme in chronic obstructive pulmonary disease (COPD) (GOLD stage 4) patients and also in a ferret model of COPD secondary to chronic cigarette smoke inhalation. Next, we developed a rodent model of chronic lung injury, where we exposed C57BL/6 mice to the halogen gas, bromine (Br2) (400 ppm, 30 minutes), and returned them to room air resulting in combined airway fibrosis and emphysematous phenotype, as indicated by high collagen deposition in the peribronchial spaces, increased lung hydroxyproline concentrations, and alveolar septal damage. These mice also had elevated pulmonary endoplasmic reticulum (ER) stress as seen in COPD patients; the pharmacological or genetic diminution of ER stress in mice attenuated Br2-induced lung changes. Finally, treating mice with the heme-scavenging protein, hemopexin, reduced plasma heme, ER stress, airway fibrosis, and emphysema. This is the first study to our knowledge to report elevated heme in COPD patients and establishes heme scavenging as a potential therapy after inhalation injury.

Role of heme in bromine-induced lung injury

Bromine (Br2 ) gas inhalation poses an environmental and occupational hazard resulting in high morbidity and mortality. In this review, we underline the acute lung pathology (within 24 h of exposure) and potential therapeutic interventions that may be utilized to mitigate Br2 -induced human toxicity. We discuss our latest published data, which suggest that an increase in heme-dependent tissue injury underlies the pathogenesis of Br2 toxicity. Our study was based on previous findings that demonstrated that Br2 upregulates the heme-degrading enzyme heme oxygenase-1 (HO-1), which converts toxic heme into bilverdin. Interestingly, following Br2 inhalation, heme levels were indeed elevated in bronchoalveolar lavage fluid, plasma, and whole lung tissue in C57BL/6 mice. High heme levels correlated with increased lung oxidative stress, lung inflammation, respiratory acidosis, lung edema, higher airway resistance, and mortality. However, therapeutic reduction of heme levels, by either scavenging with hemopexin or degradation by HO-1, improved lung function and survival. Therefore, heme attenuation may prove a useful adjuvant therapy to treat patients after Br2 exposure.

Heme Attenuation Ameliorates Irritant Gas Inhalation-Induced Acute Lung Injury

AIMS

Exposure to irritant gases, such as bromine (Br2), poses an environmental and occupational hazard that results in severe lung and systemic injury. However, the mechanism(s) of Br2 toxicity and the therapeutic responses required to mitigate lung damage are not known. Previously, it was demonstrated that Br2 upregulates the heme degrading enzyme, heme oxygenase-1 (HO-1). Since heme is a major inducer of HO-1, we determined whether an increase in heme and heme-dependent oxidative injury underlies the pathogenesis of Br2 toxicity.

RESULTS

C57BL/6 mice were exposed to Br2 gas (600 ppm, 30 min) and returned to room air. Thirty minutes postexposure, mice were injected intraperitoneally with a single dose of the heme scavenging protein, hemopexin (Hx) (3 μg/gm body weight), or saline. Twenty-four hours postexposure, saline-treated mice had elevated total heme in bronchoalveolar lavage fluid (BALF) and plasma and acute lung injury (ALI) culminating in 80% mortality after 10 days. Hx treatment significantly lowered heme, decreased evidence of ALI (lower protein and inflammatory cells in BALF, lower lung wet-to-dry weight ratios, and decreased airway hyperreactivity to methacholine), and reduced mortality. In addition, Br2 caused more severe ALI and mortality in mice with HO-1 gene deletion (HO-1-/-) compared to wild-type controls, while transgenic mice overexpressing the human HO-1 gene (hHO-1) showed significant protection.

INNOVATION

This is the first study delineating the role of heme in ALI caused by Br2.

CONCLUSION

The data suggest that attenuating heme may prove to be a useful adjuvant therapy to treat patients with ALI.

Expression of hemopexin in acute rejection of rat liver allograft identified by serum proteomic analysis

Acute rejection (AR) and acceptance of allograft after liver transplantation (LTx) remain critical issues that need addressing to improve prognosis. We therefore performed rat orthotopic LTx and proteomic analyses to screen for immune response-related biomarkers in sera. Markers identified were validated at the mRNA and/or protein levels, and the molecules of interest were functionally explored. Compared with syngeneic controls, signs of AR as well as spontaneous acceptance were observed in hematoxylin and eosin-stained sections of liver allografts. In accordance with the severity of AR, 30 protein spots displaying significant changes in abundance were identified using two-dimensional differential gel electrophoresis. Ultimately, 14 serum proteins were sequenced and five spots of interest were identified as hemopexin (HPX). Expression of HPX was significantly and inversely associated with the severity of AR at both the mRNA and protein levels. In vitro, Mt-1, Ho-1, Fth, Ifn-γ, and Il-17 transcripts were significantly upregulated in lysates of lymphocytes stimulated with HPX, whereas Il-10 markedly was remarkably downregulated. Interferon-γ, IL-10, and IL-17 proteins in the supernatant of HPX-stimulated lymphocytes were significantly altered in keeping with the mRNA level. Our data facilitated the generation of a proteomic profile to enhance the understanding of rat liver AR. In view of finding that the HPX serum level is negatively associated with the severity of AR of rat liver allograft, we propose that in vitro treatment with HPX regulates cytokine expression in rat lymphocytes.

Hemopexin induces neuroprotection in the rat subjected to focal cerebral ischemia

Background

The plasma protein hemopexin (HPX) exhibits the highest binding affinity to free heme. In vitro experiments and gene-knock out technique have suggested that HPX may have a neuroprotective effect. However, the expression of HPX in the brain was not well elucidated and its expression after cerebral ischemia-reperfusion injury was also poorly studied. Furthermore, no in vivo data were available on the effect of HPX given centrally on the prognosis of focal cerebral ischemia.

Results

In the present study, we systematically investigated expression of HPX in normal rat brain by immunofluorescent staining. The results showed that HPX was mainly expressed in vascular system and neurons, as well as in a small portion of astrocytes adjacent to the vessels in normal rat brain. Further, we determined the role of HPX in the process of focal cerebral ischemic injury and explored the effects of HPX treatment in a rat model of transient focal cerebral ischemia. After 2 h’ middle cerebral artery occlusion (MCAO) followed by 24 h’ reperfusion, the expression of HPX was increased in the neurons and astrocytes in the penumbra area, as demonstrated by immunohistochemistry and Western blot techniques. Intracerebroventricular injection of HPX at the onset of reperfusion dose-dependently reduced the infarct volumes and improved measurements of neurological function of the rat subjected to transient focal cerebral ischemia. The neuroprotective effects of HPX sustained for up to 7 days after experiments.

Conclusions

Our study provides a new insight into the potential neuroprotective role of HPX as a contributing factor of endogenous protective mechanisms against focal cerebral ischemia injury, and HPX might be developed as a potential agent for treatment of ischemic stroke.

Inflammation/oxidation in chronic rejection: apolipoprotein a-i mimetic peptide reduces chronic rejection of transplanted hearts

BACKGROUND

Chronic rejection in transplanted hearts or cardiac allograft vasculopathy (CAV) is the leading cause of late death among heart transplant recipients. Strategies to control CAV traditionally have focused on lymphocyte functions. We hypothesized that D-4F, an apoA-I mimetic peptide with potent anti-inflammatory/antioxidant properties, will attenuate CAV.

METHODS

We used a previously characterized murine model of CAV. B6.C-H2 hearts were heterotopically transplanted into C57BL/6 mice. Recipient mice were treated with either 20 microg of D-4F or carrier daily. Donor hearts were harvested on day 24 after transplantation.

RESULTS

Treatment of recipients with D-4F reduced the severity of intimal lesions (62.5+/-3.4% vs. 31.1+/-8.7%, P<0.009). Treatment also resulted in a decrease in the number of graft-infiltrating CD4 and CD8 lymphocytes and CXCR3+ T-lymphocyte subsets. Heme oxygenase-1 (HO-1) gene transcript in the donor hearts was up-regulated with D-4F treatment, and HO-1 blockade partially reversed the beneficial effects of D-4F. In vitro studies showed that D-4F reduced allogeneic T-lymphocyte proliferation and effector cytokine production. These processes were HO-1 independent.

CONCLUSION

This study suggests that D-4F, a prototypical apoA-I mimetic peptide, is effective in controlling CAV via induction of HO-1 in the graft and a direct effect on T-lymphocyte function. This class of peptides with anti-inflammatory/antioxidant properties provides a novel strategy in the treatment of CAV.

Cytoprotective Gene HO-1 and Chronic Rejection in Heart Transplantation

Chronic rejection in transplanted hearts or cardiac allograft vasculopathy (CAV) is the leading cause of late death among heart transplant recipients. We hypothesized that induction of HO-1 by D4-F, an apoA-I mimetic peptide with potent antiinflammatory/antioxidant properties, attenuated CAV. We utilized a previously characterized murine model of CAV. B6.C-H2(bml2) hearts were heterotopically transplanted into C57BL/6 mice. In the control group, recipient mice were treated with 20 microg of saline daily. In experimental group I, mice were treated daily with 20 microg of D4-F. In experimental group II, mice were treated daily with 20 microg of D4-F daily, plus CuPP, which does not have any effect on HO-1 activity. In experimental group III, recipient mice were treated with 20 mug of D4-F daily, plus SnPP, which is a competitive inhibitor of HO-1. Donor hearts were harvested on day 24 after transplantation. The donor hearts in the control group developed severe intimal lesions. In experimental group I, treatment with D4-F was associated with upregulation of HO-1 and a marked reduction in intimal lesions, which was consistent in experimental group II. In experimental group III, inhibition of HO-1 was associated with partial restoration of intimal lesions. Induction of HO-1 by an apoA-1 mimetic peptide was effective to control CAV. This class of antiinflammatory peptides, which show an ability to induce HO-1, provides a novel strategy for the treatment of CAV.

Variation in gene expression in response to stress in two populations of Fundulus heteroclitus

We used differential display PCR to identify hepatic genes responsive to handling stress and genes that differ in expression between populations of a fish, Fundulus heteroclitus, from different thermal environments. Despite substantial inter-individual variation, we cloned 20 putatively stress-regulated bands from Northern fish, 10 of which had high similarity to genes of known function. We selected five of these genes for further analysis based on their known roles in the stress response. Three of these genes (glucokinase, serine-threonine kinase 10 and cRAF) were confirmed as stress-responsive using real-time PCR. These genes increased in expression in response to a 7-day chronic stress protocol in fish from the Southern population of F. heteroclitus, but did not change significantly in fish from the Northern population. These three genes also differed in expression between populations in control fish, suggesting a link between the response to chronic stress and inter-population differences in gene expression in unstressed laboratory-acclimated fish. Two genes that did not respond to stress (glycogen synthase kinase and warm acclimation-related protein (WAP)) also differed between populations. Expression of WAP was eight-fold higher in Southern than in Northern fish, consistent with a previously suggested role for this gene in thermal acclimation or adaptation in fish.

Heme oxygenase-1 system in organ transplantation

The heme oxygenase-1 (HO-1) system, the rate-limiting step in the conversion of heme, is among the most critical of cytoprotective mechanisms activated during cellular stress. The cytoprotection may result from the elimination of heme and the function of HO-1 downstream mediators, that is, biliverdin, carbon monoxide, and free iron. HO-1 overexpression exerts beneficial effects in a number of transplantation models, including antigen-independent ischemia/reperfusion injury, acute and chronic allograft rejection, and xenotransplantation. The HO-1 system is thought to exert four major functions: (1) antioxidant function; (2) maintenance of microcirculation; (3) modulatory function upon the cell cycle; and (4) anti-inflammatory function. The antioxidant function depends on heme degradation, oxygen consumption, biliverdin, and production of ferritin via iron accumulation. The production of carbon monoxide, which has vasodilation and antiplatelet aggregation properties, maintains tissue microcirculation and may be instrumental in antiapoptotic and cell arrest mechanisms. Heme catabolism and HO-1 overexpression exert profound direct and indirect inhibitory effects on the cascade of host inflammatory responses mediated by neutrophils, macrophages, and lymphocytes. These anti-inflammatory properties result in cytoprotection in a broad spectrum of graft injury experimental models, including ischemia/reperfusion, acute and chronic allograft, and xenotransplant rejection. Further, the multifaceted targets of HO-1-mediated cytoprotection may simultaneously benefit both local graft function and host systemic immune responses. Thus, the HO-1 system serves as a novel therapeutic concept in organ transplantation.

A novel strategy against ischemia and reperfusion injury: cytoprotection with heme oxygenase system

Much interest has recently been focused on the physiological/pathological role of the heme oxygenase (HO) system, the rate-limiting step in the conversion of heme, in inflammatory events. The HO system may be instrumental in mediating a number of cytoprotective effects, because of its end products, biliverdin, carbon monoxide (CO) and ferrous free iron (Fe2+). As each of the byproducts acts dependently and/or co-operatively with each other, their in vivo effects are complex. In general, the HO system is thought to exert three major functions in ischemia/reperfusion injury: (1) anti-oxidant effects; (2) maintenance of microcirculation; and (3) modulatory effects upon the cell cycle. The anti-oxidant functions depend on heme degradation, oxygen consumption and the production of biliverdin/ferritin via iron accumulation. On the other hand, the production of CO, which has vasodilatory and anti-platelet aggregative properties, can maintain tissue microcirculation. Strikingly, CO may also be instrumental in anti-apoptotic and cell arrest mechanisms. The HO system prevents early injury in the re-perfused organ, and inhibits the function of immune reactive cells, such as neutrophils, macrophages and lymphocytes. The role of the HO system as a novel strategy to mitigate an antigen-independent ischemia/reperfusion injury has been documented in a number of transplantation models.

Hemopexin: structure, function, and regulation

Hemopexin (HPX) is the plasma protein with the highest binding affinity to heme among known proteins. It is mainly expressed in liver, and belongs to acute phase reactants, the synthesis of which is induced after inflammation. Heme is potentially highly toxic because of its ability to intercalate into lipid membrane and to produce hydroxyl radicals. The binding strength between heme and HPX, and the presence of a specific heme-HPX receptor able to catabolize the complex and to induce intracellular antioxidant activities, suggest that hemopexin is the major vehicle for the transportation of heme in the plasma, thus preventing heme-mediated oxidative stress and heme-bound iron loss. In this review, we discuss the experimental data that support this view and show that the most important physiological role of HPX is to act as an antioxidant after blood heme overload, rather than to participate in iron metabolism. Particular attention is also put on the structure of the protein and on its regulation during the acute phase reaction.

Hemopexin: a review of biological aspects and the role in laboratory medicine

BACKGROUND

Hemopexin is a heme-binding plasma glycoprotein which, after haptoglobin, forms the second line of defense against hemoglobin-mediated oxidative damage during intravascular hemolysis. A decrease in plasma hemopexin concentration reflects a recent release of heme compounds in the extracellular compartment. Heme-hemopexin complexes are delivered to hepatocytes by receptor-mediated endocytosis after which hemopexin is recycled to the circulation.

METHODS OF ANALYSIS

Immunonephelometric and -turbidimetric hemopexin assays are available as more precise and rapid alternatives to the radial immunodiffusion technique.

INTERPRETATIONS

Hemopexin determinations are not subject to interference by in vitro hemolysis. Altered serum or plasma concentrations of hemopexin are found not only in hemolytic anemias but also in other conditions such as chronic neuromuscular diseases and acute intermittent porphyria. In laboratory medicine, while hemopexin determination in tandem with haptoglobin has potential applications in the assessment of intravascular hemolysis and allows for the monitoring of the severity of hemolysis after depletion of haptoglobin, its diagnostic utility is less clear in other pathological conditions. Further studies are necessary to fully establish the clinical significance of hemopexin determination.