Heme oxygenase-1 affords protection against noncerebral forms of severe malaria

Immunoregulatory properties of heme oxygenase-1

Heme oxygenase-1 (HO-1) is one of the three isoforms of the heme oxygenase enzyme that catabolyzes the degradation of heme into biliverdin with the production of free iron and CO. HO-1 is induced by its substrate and by other stimuli, including agents involved in oxidative stress and proinflammatory cytokines as well as several anti-inflammatory stimuli. A growing body of evidence points toward the capacity of this molecule to inhibit immune reactions and the pivotal role of HO-1 in inflammatory diseases. We will first review the physiological role of HO-1 as determined by the analysis of HO-1-deficient individuals. This will be followed by an examination of the effect of HO-1 within immunopathological contexts such as immune disorders (autoimmunity and allergy) or infections. A section will be devoted to the use of an HO-1 inducer as an immunosuppressive molecule in transplantation. Finally, we will review the molecular basis of HO-1 actions on different immune cells.

Heme oxygenase system in hepatic ischemia-reperfusion injury

Hepatic ischemia-reperfusion injury (IRI) limits access to transplantation. Heme oxygenase-1 (HO-1) is a powerful antioxidant enzyme which degrades free heme into biliverdin, free iron and carbon monoxide. HO-1 and its metabolites have the ability to modulate a wide variety of inflammatory disorders including hepatic IRI. Mechanisms of this protective effect include reduction of oxygen free radicals, alteration of macrophage and T cell phenotype. Further work is required to understand the physiological importance of the many actions of HO-1 identified experimentally, and to harness the protective effect of HO-1 for therapeutic potential.

Apoptosis induced by parasitic diseases

Fatalities caused by parasitic infections often occur as a result of tissue injury that results from a form of host-cell death known as apoptosis. However, instead of being pathogenic, parasite-induced apoptosis may facilitate host survival. Consequently, it is of utmost importance to decipher and understand the process and the role of apoptosis induced or controlled by parasites in humans. Despite this, few studies provide definitive knowledge of parasite-induced host-cell apoptosis. Here, the focus is on a consideration of host-cell apoptosis as either a pathogenic feature or as a factor enabling parasite survival and development.

Cell death by apoptotic-like mechanisms could be described as a ride to death with a return ticket, as initiation of the pathway may be reversed, with the potential that it could be manipulated for therapeutic purposes. The management of host-cell apoptosis could thus be an adjunctive factor for parasitic disease treatment. Evidence that the apoptotic process could be reversed by anti-apoptotic drugs has recently been obtained, leading to the possibility of host-cell rescue after injury. An important issue will be to predict the beneficial or deleterious effects of controlling human cell death by apoptotic-like mechanisms during parasitic diseases.

The redox activity of hemoglobins: from physiologic functions to pathologic mechanisms

Pentacoordinate respiratory hemoproteins such as hemoglobin and myoglobin have evolved to supply cells with oxygen. However, these respiratory heme proteins are also known to function as redox enzymes, reacting with compounds such as nitric oxide and peroxides. The recent discoveries of hexacoordinate hemoglobins in vertebrates and nonsymbiotic plants suggest that the redox activity of globins is inherent to the molecule. The uncontrolled formation of radical species resulting from such redox chemistry on respiratory hemoproteins can lead to oxidative damage and cellular toxicity. In this review, we examine the functions of various globins and the mechanisms by which these globins act as redox enzymes under physiologic conditions. Evidence that redox reactions also occur under disease conditions, leading to pathologic complications, also is examined, focusing on recent discoveries showing that the ferryl oxidation state of these hemoproteins is present in these disease states in vivo. In addition, we review the latest advances in the understanding of globin redox mechanisms and how they might affect cellular signaling pathways and how they might be controlled therapeutically or, in the case of hemoglobin-based blood substitutes, through rational design.

Robust erythrophagocytosis leads to macrophage apoptosis via a hemin-mediated redox imbalance: role in hemolytic disorders

MP from the RES are responsible for the clearance of senescent RBC. Although the frequency of senescent RBC is low under steady-state conditions, it increases dramatically during hemolytic disorders, resulting in enhanced erythrophagocytosis. As erythrophagocytosis has been involved in MP dysfunction and as certain hemolytic disorders associate to MP apoptosis, a possible link between erythrophagocytosis and the viability of phagocytes was investigated herein. To mimic hemolytic disorders, two distinct in vitro models, artificially oxidized RBC and DSRBC, were chosen to study the erythrophagocytosis impact on the viability of J774A.1 MP. Although CRBC were weakly phagocytosed and did not affect MP viability significantly, erythrophagocytosis of oxidized RBC and DSRBC was robust and resulted in a sharp decrease of MP viability via apoptosis. Under these conditions, Hb-derived HE was shown to be involved in the induction of apoptosis. Moreover, oxidized RBC, DSRBC, and HE generated ROS species, which were responsible for the apoptosis of MP. Furthermore, HO-1, strongly induced in response to treatment with oxidized RBC, DSRBC, or HE, was shown to protect MP partially against apoptosis, suggesting that robust erythro-phagocytosis may exceed the detoxification capabilities of MP. Taken together, these results suggest that enhanced erythrophagocytosis associated to hemolytic disorders leads to MP apoptosis in vitro and may have critical implications for the control of malaria infection and for the exacerbated susceptibility to bacterial infections during hemolytic disorders.

Heme amplifies the innate immune response to microbial molecules through spleen tyrosine kinase (Syk)-dependent reactive oxygen species generation

Infectious diseases that cause hemolysis are among the most threatening human diseases, because of severity and/or global distribution. In these conditions, hemeproteins and heme are released, but whether heme affects the inflammatory response to microorganism molecules remains to be characterized. Here, we show that heme increased the lethality and cytokine secretion induced by LPS in vivo and enhanced the secretion of cytokines by macrophages stimulated with various agonists of innate immune receptors. Activation of nuclear factor κB (NF-κB) and MAPKs and the generation of reactive oxygen species were essential to the increase in cytokine production induced by heme plus LPS. This synergistic effect of heme and LPS was blocked by a selective inhibitor of spleen tyrosine kinase (Syk) and was abrogated in dendritic cells deficient in Syk. Moreover, inhibition of Syk and the downstream molecules PKC and PI3K reduced the reactive oxygen species generation by heme. Our results highlight a mechanism by which heme amplifies the secretion of cytokines triggered by microbial molecule activation and indicates possible pathways for therapeutic intervention during hemolytic infectious diseases.

Bryonolic acid: a large-scale isolation and evaluation of heme oxygenase 1 expression in activated macrophages

Bryonolic acid (BA) is a triterpenoid found in the Cucurbitaceae family of plants. Our interests in the immunomodulatory effects of this class of natural products led us to discover that BA induces a marked increase in the expression of a phase 2 response enzyme, heme oxygenase 1 (HO-1), in a dose-dependent manner. This phenotype has translational implications in malarial disease progression, and consequently we developed a large-scale isolation method for BA that will enable future in vitro and in vivo analyses. We have determined ideal growth conditions and time scale for maximizing BA content in the roots of Cucurbita pepo and analyzed BA production by HPLC. Large-scale extraction yielded 1.34% BA based on dry weight, allowing for the isolation of BA on a multigram scale.

Heme impairs prostaglandin E2 and TGF-beta production by human mononuclear cells via Cu/Zn superoxide dismutase: insight into the pathogenesis of severe malaria

In many hemolytic disorders, such as malaria, the release of free heme has been involved in the triggering of oxidative stress and tissue damage. Patients presenting with severe forms of malaria commonly have impaired regulatory responses. Although intriguing, there is scarce data about the involvement of heme on the regulation of immune responses. In this study, we investigated the relation of free heme and the suppression of anti-inflammatory mediators such as PGE(2) and TGF-beta in human vivax malaria. Patients with severe disease presented higher hemolysis and higher plasma concentrations of Cu/Zn superoxide dismutase (SOD-1) and lower concentrations of PGE(2) and TGF-beta than those with mild disease. In addition, there was a positive correlation between SOD-1 concentrations and plasma levels of TNF-alpha. During antimalaria treatment, the concentrations of plasma SOD-1 reduced whereas PGE(2) and TGF-beta increased in the individuals severely ill. Using an in vitro model with human mononuclear cells, we demonstrated that the heme effect on the impairment of the production of PGE(2) and TGF-beta partially involves heme binding to CD14 and depends on the production of SOD-1. Aside from furthering the current knowledge about the pathogenesis of vivax malaria, the present results may represent a general mechanism for hemolytic diseases and could be useful for future studies of therapeutic approaches.

Heme Oxygenase-1 expression in M-CSF-polarized M2 macrophages contributes to LPS-induced IL-10 release

The shift between pro-inflammatory (M1) and anti-inflammatory (M2) states of macrophage polarization allows the resolution of inflammatory processes as well as the maintenance of a basal anti-inflammatory environment in tissues continuously exposed to harmless antigens (e.g., lung and gut). To identify markers for the anti-inflammatory state of macrophages, expression profiling was performed on human macrophages polarized by either GM-CSF or M-CSF, which lead to the generation of TNF-alpha and IL-12p40-producing pro-inflammatory macrophages [M1 (GM-CSF)] or IL-10-producing anti-inflammatory macrophages [M2 (M-CSF)] upon exposure to LPS, respectively. A different iron metabolism gene signature was detected in both macrophage types, with the heme regulatory molecules CD163 and Heme Oxygenase-1 (HO-1) being preferentially expressed by M2 (M-CSF) macrophages. M1-polarizing cytokines (GM-CSF, IFNgamma) inhibited, while IL-4 enhanced, the M-CSF-driven HO-1 expression. In agreement with this in vitro data, HO-1 expression in metastatic melanoma was primarily detected in CD163(+) tumor-associated macrophages, which are known to exhibit an M2-skewed polarization phenotype. In contrast to the HO-1 inhibitor tin protoporphyrin (SnPP), the administration of cobalt protoporphyrin (CoPP), a potent inducer of HO-1 resulted in increased LPS-triggered IL-10 release from M2 (M-CSF) macrophages. The data suggests that HO-1 is important for the anti-inflammatory activities of M-CSF-polarized M2 macrophages. Moreover, since M2 (M-CSF) macrophages also express higher levels of the CD163 scavenger receptor, the CD163/HO-1/IL-10 axis appears to contribute to the generation of an immunosuppressive environment within the tumor stroma.

Inflammation 2010: new adventures of an old flame

Inflammation is an essential immune response that enables survival during infection or injury and maintains tissue homeostasis under a variety of noxious conditions. Inflammation comes at the cost of a transient decline in tissue function, which can in turn contribute to the pathogenesis of diseases of altered homeostasis.

Up- and down-modulation of liver cytochrome P450 activities and associated events in two murine malaria models

Background

The mechanisms by which malaria up and down-regulates CYP activities are not understood yet. It is also unclear whether CYP activities are modulated during non-lethal malaria infections. This study was undertaken to evaluate the time course of CYP alterations in lethal (Plasmodium berghei ANKA) and non-lethal (Plasmodium chabaudi chabaudi) murine malaria. Additionally, hypotheses on the association of CYP depression with enhanced nitric oxide (NO) production, and of CYP2a5 induction with endoplasmic reticulum dysfunction, enhanced haem metabolism and oxidative stress were examined as well.

Methods

Female DBA-2 and C57BL/6 mice were infected with P.berghei ANKA or P. chabaudi and killed at different post-infection days. Infection was monitored by parasitaemia rates and clinical signs. NO levels were measured in the serum. Activities of CYP1a (ethoxyresorufin-O-deethylase), 2b (benzyloxyresorufin-O-debenzylase), 2a5 (coumarin-7-hydroxylase) and uridine-diphosphoglucuronyl-transferase (UGT) were determined in liver microsomes. Glutathione-S-transferase (GST) activity and concentrations of gluthatione (GSH) and thiobarbituric acid-reactive substances (TBARS) were determined in the liver. Levels of glucose-regulated protein 78 (GRP78) were evaluated by immunoblotting, while mRNAs of haemoxygenase-1 (HO-1) and inducible nitric oxide synthase (iNOS) were determined by quantitative RT-PCR.

Results

Plasmodium berghei depressed CYP1a and 2b and induced 2a5 in DBA-2 mice. In P.berghei-infected C57BL/6 mice CYP activities remained unaltered. In both strains, GST and UGT were not affected by P.berghei. Plasmodium c. chabaudi depressed CYP1a and 2b and induced 2a5 activities on the day of peak parasitaemia or near this day. CYP2a5 induction was associated with over-expression of HO-1 and enhanced oxidative stress, but it was not associated with GRP78 induction, a marker of endoplasmic reticulum stress. Plasmodium chabaudi increased serum NO on days near the parasitaemia peak in both strains. Although not elevating serum NO, P.berghei enhanced iNOS mRNA expression in the liver.

Conclusion

Down-regulation of CYP1a and 2b and induction of 2a5 occurred in lethal and non-lethal infections when parasitaemia rates were high. A contribution of NO for depression of CYP2b cannot be ruled out. Results were consistent with the view that CYP2a5 and HO-1 are concurrently up-regulated and suggested that CYP2a5 induction may occur in the absence of enhanced endoplasmic reticulum stress.

Mechanisms of cell protection by heme oxygenase-1

Heme oxygenases (HO) catabolize free heme, that is, iron (Fe) protoporphyrin (IX), into equimolar amounts of Fe(2+), carbon monoxide (CO), and biliverdin. The stress-responsive HO-1 isoenzyme affords protection against programmed cell death. The mechanism underlying this cytoprotective effect relies on the ability of HO-1 to catabolize free heme and prevent it from sensitizing cells to undergo programmed cell death. This cytoprotective effect inhibits the pathogenesis of a variety of immune-mediated inflammatory diseases.

Is Ozone Really a “Wonder Drug”?

Even if the reader has only browsed through the previous chapters, he ought to have received my feeling that ozone has an enormous therapeutic potential that, so far, has been either disregarded, if not obstructed by world medical authorities. Reasons for delaying the use of ozone are multiple: while quacks and inexpert ozonetherapists are at fault for poor work, other aspects such as commercial and pharmaceutical interests, prejudice, lack of knowledge and a myopic medical vision have done their best to block a substantial and rapid progress.