Reversal of HO-1 related cytoprotection with increased expression is due to reactive iron

Carbon Monoxide: Endogenous Production, Physiological Functions, and Pharmacological Applications

Over the last decade, studies have unraveled many aspects of endogenous production and physiological functions of carbon monoxide (CO). The majority of endogenous CO is produced in a reaction catalyzed by the enzyme heme oxygenase (HO). Inducible HO (HO-1) and constitutive HO (HO-2) are mostly recognized for their roles in the oxidation of heme and production of CO and biliverdin, whereas the biological function of the third HO isoform, HO-3, is still unclear. The tissue type-specific distribution of these HO isoforms is largely linked to the specific biological actions of CO on different systems. CO functions as a signaling molecule in the neuronal system, involving the regulation of neurotransmitters and neuropeptide release, learning and memory, and odor response adaptation and many other neuronal activities. The vasorelaxant property and cardiac protection effect of CO have been documented. A plethora of studies have also shown the importance of the roles of CO in the immune, respiratory, reproductive, gastrointestinal, kidney, and liver systems. Our understanding of the cellular and molecular mechanisms that regulate the production and mediate the physiological actions of CO has greatly advanced. Many diseases, including neurodegenerations, hypertension, heart failure, and inflammation, have been linked to the abnormality in CO metabolism and function. Enhancement of endogenous CO production and direct delivery of exogenous CO have found their applications in many health research fields and clinical settings. Future studies will further clarify the gasotransmitter role of CO, provide insight into the pathogenic mechanisms of many CO abnormality-related diseases, and pave the way for innovative preventive and therapeutic strategies based on the physiologic effects of CO.

Heme-oxygenase-1 promotes polychlorinated biphenyl mixture aroclor 1254-induced oxidative stress and dopaminergic cell injury

Dopaminergic (DAergic) systems have been identified as putative targets for polycholorinated biphenyl (PCB) actions. However, the precise mechanisms leading to neurotoxicity are unresolved. Reactive oxygen species (ROS) were recently shown to mediate injury in DAergic MN9D cells following exposure to Aroclor 1254 (A1254), a commercial PCB mixture. The oxidative stress response in DAergic cells included a persistent expression of heme oxygenase-1 (HO-1). This study tested the hypothesis that a sustained PCB-induced HO-1 response leads to abnormally high Fe levels, which generates ROS production and mediates death in the MN9D DAergic cell model. Accordingly, results indicated that A1254 augmented intracellular Fe levels in MN9D cells after 24 h. Fe chelation by desferoxamine or pharmacologic inhibition of HO activity with tin-protoporphyrin reduced Fe accumulation, ROS production, and cytotoxicity following A1254 exposure. HO-1 over-expression predisposed MN9D DAergic cells to enhanced ROS production and cell death in response to PCBs. Conversely, antisense inhibition of HO-1 expression prevented PCB-induced ROS production and cell death. These observations suggest that enhanced HO-1 catalytic activity and subsequent liberation of Fe participate in neurotoxic DAergic cell injury caused by A1254 exposure in vitro.

Heme regulation in traumatic brain injury: relevance to the adult and developing brain

Intracranial bleeding is one of the most prominent aspects in the clinical diagnosis and prognosis of traumatic brain injury (TBI). Substantial amounts of blood products, such as heme, are released because of traumatic subarachnoid hemorrhages, intraparenchymal contusions, and hematomas. Despite this, surprisingly few studies have directly addressed the role of blood products, in particular heme, in the setting of TBI. Heme is degraded by heme oxygenase (HO) into three highly bioactive products: iron, bilirubin, and carbon monoxide. The HO isozymes, in particular HO-1 and HO-2, exhibit significantly different expression patterns and appear to have specific roles after injury. Developmentally, differences between the adult and immature brain have implications for endogenous protection from oxidative stress. The aim of this paper is to review recent advances in the understanding of heme regulation and metabolism after brain injury and its specific relevance to the developing brain. These findings suggest novel clinical therapeutic options for further translational study.

Is there a causal relationship between the receipt of blood transfusions and the development of chronic lung disease of prematurity?

The number and total volume of blood transfusions received by premature babies is, after gestational age and birth weight a good predictor of the likelihood of developing chronic lung disease of prematurity (CLD) and retinopathy of prematurity (ROP). Oxidative damage, inflammation and pulmonary infections are also strongly associated with the development of CLD. It is currently not clear whether there is a causal relationship between the receipt of blood transfusions and oxidative damage, infection, inflammation and CLD in these babies. Strong arguments may be made both for and against a causal relationship. The babies who receive blood transfusions are usually smaller than those who do not, and are ventilated, often with high oxygen levels, for a longer period of time. The longer the baby is on a ventilator the more likely it is to develop pulmonary infection and inflammation. All these factors will promote free radical production and oxidative damage irrespective of the receipt of blood transfusion. This would argue against a causal relationship. On the other hand, an argument may be presented which is based on iron promoted free radical generation, infection and fibrosis consequent to the breakdown of haeme released from transfused erythrocytes. Haeme is broken down by haeme oxygenase (HO) to iron, CO and bilirubin. Under normal circumstances the products of HO activity are beneficial to the organism, but when HO activity is excessive, the products are potentially damaging. Free iron, (in the Fe2+ form) if not sequestered with protein or urate, will generate highly toxic free radicals via the Fenton and Heber-Wiess reactions, predispose the tissue to infection and promote fibrosis. The iron chelating ability of the premature baby appears to be limited so that it would be difficult to deal with any increase in free iron production. Free iron will in turn induce HO activity leading to a potentially serious positive feedback process. The lung is particularly sensitive to iron induced HO activity. In addition, HO activity may be enhanced by other events occurring in the premature lung such as the production of proinflammatory cytokines and the reduced level of glutathione. Thus, the possibility of a causal relationship clearly exists and needs to be examined. This can be attempted by measuring the products of HO activity in relation to the receipt of blood transfusions.

Expression of heme oxygenase-1 in human livers before transplantation correlates with graft injury and function after transplantation

Upregulation of heme oxygenase-1 (HO-1) has been proposed as an adaptive mechanism protecting against ischemia/reperfusion (I/R) injury. We investigated HO-1 expression in 38 human liver transplants and correlated this with I/R injury and graft function. Before transplantation, median HO-1 mRNA levels were 3.4-fold higher (range: 0.7-9.3) in donors than in normal controls. Based on the median value, livers were divided into two groups: low and high HO-1 expression. These groups had similar donor characteristics, donor serum transaminases, cold ischemia time, HSP-70 expression and the distribution of HO-1 promoter polymorphism. After reperfusion, HO-1 expression increased significantly further in the initial low HO-1 expression group, but not in the high HO-1 group. Postoperatively, serum transaminases were significantly lower and the bile salt secretion was higher in the initial low HO-1 group, compared to the high expression group. Immunofluorescence staining identified Kupffer cells as the main localization of HO-1. In conclusion, human livers with initial low HO-1 expression (<3.4 times controls) are able to induce HO-1 further during reperfusion and are associated with less injury and better function than initial high HO-1 expression (>3.4 times controls). These data suggest that an increase in HO-1 during transplantation is more protective than high HO-1 expression before transplantation.

Ischemic preconditioning procedure induces behavioral deficits in the absence of brain injury?

Preconditioning describes a phenomenon whereby a sub-injury inducing insult can protect against a later larger injury. Thus, short-term cerebral ischemia can protect against a prolonged ischemia (ischemic preconditioning). This study examines rats undergoing ischemic preconditioning to test whether preconditioning may cause changes in behavior even though they do not cause an identifiable brain lesion. Rats had a transient (15 minutes) middle cerebral artery occlusion or a sham occlusion. Forelimb placing and forelimb use asymmetry tests were used to assess behavioral deficits. Brain histology, microglia activation, heat shock protein and ferritin levels were also examined. Ischemic preconditioning did not cause brain infarction, but induced behavioral changes. There were no significant differences between ischemic preconditioning and sham rats in the two behavioral tests at day one. However, the ischemic preconditioning group showed impaired forelimb placing at days 3, 7 and 14 (p<0.05). That group also had a significant (p<0.05) behavioral deficit in the forelimb use asymmetry test at days 3 and 7 (but not 14). Our present study demonstrated that a behavioral deficit occurred in ischemic preconditioning. This raises the question of whether induction of protective mechanisms by preconditioning stimuli necessarily involves some form of brain injury, detectable by changes in behavior though not by a lesion. This would be consistent with data suggesting that brain injury can initiate mechanisms potentially favorable to neuroplasticity and neuroprotection.

The deleterious or beneficial effects of different agents in intracerebral hemorrhage: think big, think small, or is hematoma size important?

BACKGROUND AND PURPOSE

Thrombin, heme oxygenase, complement, microglia activation, and leukocyte infiltration are all actively upregulated in intracerebral hemorrhage (ICH). Experimental evidence suggests that all these factors are involved in ICH-induced brain injury. This suggests a scenario whereby ICH actively (through gene and protein upregulation) induces pathways that result in brain injury.

SUMMARY OF REVIEW

In this comment, we suggest a potential answer to this conundrum. The upregulation of these factors may have been an evolutionary adaptation to limit brain injury during small hematomas (microbleeds). There is evidence that low levels of thrombin and heme oxygenase limit brain injury. In contrast, the excessive upregulation of these same factors may have a harmful effect after a large hematoma.

CONCLUSIONS

The mechanisms upregulated to limit brain injury after microbleeds may also induce injury after large hematomas. The effect of hematoma size on the mechanisms involved in ICH-induced brain injury and the implications of any such effect on clinical therapies merit further investigation.

The synthetic triterpenoids, CDDO and CDDO-imidazolide, are potent inducers of heme oxygenase-1 and Nrf2/ARE signaling

The synthetic triterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO) and its derivative 1-[2-cyano-3-,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole (CDDO-Im) are multifunctional molecules with potent antiproliferative, differentiating, and anti-inflammatory activities. At nanomolar concentrations, these agents rapidly increase the expression of the cytoprotective heme oxygenase-1 (HO-1) enzyme in vitro and in vivo. Transfection studies using a series of reporter constructs show that activation of the human HO-1 promoter by the triterpenoids requires an antioxidant response element (ARE), a cyclic AMP response element, and an E Box sequence. Inactivation of one of these response elements alone partially reduces HO-1 induction, but mutations in all three sequences entirely eliminate promoter activity in response to the triterpenoids. Treatment with CDDO-Im also elevates protein levels of Nrf2, a transcription factor previously shown to bind ARE sequences, and increases expression of a number of antioxidant and detoxification genes regulated by Nrf2. The triterpenoids also reduce the formation of reactive oxygen species in cells challenged with tert-butyl hydroperoxide, but this cytoprotective activity is absent in Nrf2 deficient cells. These studies are the first to investigate the induction of the HO-1 and Nrf2/ARE pathways by CDDO and CDDO-Im, and our results suggest that further in vivo studies are needed to explore the chemopreventive and chemotherapeutic potential of the triterpenoids.

Influence of heme-based solutions on stress protein expression and organ failure after hemorrhagic shock

OBJECTIVE

Hemoglobin-based oxygen carriers (e.g., diaspirin-cross-linked hemoglobin [DCLHb] and hemoglobin glutamer-200 [HbG]) may have potential in the treatment of hemorrhagic shock. The nitric oxide scavenging and direct vasoconstrictive side effects of free hemoglobin of currently available preparations may increase organ injury after shock in contrast to non-oxygen-carrying heme solutions (e.g., hemin arginate [HAR]). However, both classes of substances might induce the protective enzyme heme oxygenase (HO)-1, particularly in the liver. The aim of the study was to assess the role of pretreatment with DCLHb, HbG, or HAR on HO-1 expression and organ injury after hemorrhagic shock.

DESIGN

Prospective controlled laboratory study.

SETTING

Animal research laboratory at a university hospital.

SUBJECTS

Male Sprague-Dawley rats (200-300 g body weight, n = 5-12/group).

INTERVENTIONS

Twenty-four hours after different doses of DCLHb, HbG (each 1, 2, or 3 g/kg of body weight), or HAR (5, 25, or 75 mg/kg of body weight), the protein expression of HO-1 and heat shock protein-70 in liver, kidney, heart, lungs, and aorta was determined. Twenty-four hours after pretreatment with DCLHb, HbG, or HAR, rats were subjected to hemorrhage (mean arterial blood pressure, 35-40 mm Hg for 1 or 2 hrs)/resuscitation (5 or 4 hrs, respectively). Animals treated with Ringer's solution (30 mL/kg of body weight) served as controls. In additional experiments, HO activity was blocked with tin mesoporphyrin-IX.

MEASUREMENTS AND MAIN RESULTS

DCLHb, HbG, and HAR dose-dependently induced HO-1 protein but not heat shock protein-70. Pretreatment with DCLHb or HbG shortened the onset of decompensation in shock (DCLHb, 40 +/- 11 mins; HbG, 36 +/- 4 mins) compared with vehicle (68 +/- 4 mins, p < .05) and HAR pretreatment (81 +/- 7 mins, p < .05). High doses of DCLHb pretreatment increased mortality (2 hrs of shock, 80%; p < .05 vs. vehicle or HAR). Pretreatment with HAR led to higher shed blood volumes (p < .05) and higher hepatocellular ATP levels (2 hrs of shock, p < .05 vs. DCLHb and HbG). Blockade of HO activity by tin mesoporphyrin-IX abolished the protection mediated by HAR.

CONCLUSIONS

Although DCLHb, HbG, and HAR induce HO-1 in the absence of an unspecific stress response, only HAR pretreatment protects against shock-induced organ failure. Although the underlying mechanisms of positive HAR priming are not completely understood, the induction of HO-1 expression and the lack of nitric oxide scavenging through HAR may play an important role.

Increased serum HO-1 in hemophagocytic syndrome and adult-onset Still's disease: use in the differential diagnosis of hyperferritinemia

Heme oxygenase-1 (HO-1), an inducible heme-degrading enzyme, is expressed by macrophages and endothelial cells in response to various stresses. Because ferritin synthesis is stimulated by Fe²⁺, which is a product of heme degradation, we examined the relation between HO-1 and ferritin levels in the serum of patients with hemophagocytic syndrome (HPS), adult-onset Still's disease (ASD), and other diseases that may cause hyperferritinemia. Seven patients with HPS, 10 with ASD, 73 with other rheumatic diseases, 20 with liver diseases, 10 recipients of repeated blood transfusion because of hematological disorders, and 22 healthy volunteers were enrolled. Serum HO-1 and ferritin levels were determined by ELISA. Expression of HO-1 mRNA and protein by peripheral blood mononuclear cells (PBMCs) was determined by real-time PCR and immunocytochemical techniques, respectively. Serum levels of HO-1 were significantly higher in patients with active HPS and ASD than in the other groups (P < 0.01). HO-1 levels were not elevated in patients with other causes of hyperferritinemia but were moderately elevated in patients with dermatomyositis/polymyositis. Among patients with HPS and ASD, serum HO-1 levels correlated closely with serum ferritin levels, and the levels of both returned to normal after therapy had induced remission. Increased expression of HO-1 mRNA was confirmed in PBMCs from some patients with HPS and ASD. Hyperferritinemia correlated closely with increased serum HO-1 in patients with HPS and ASD but not other conditions, indicating that measurement of serum HO-1 and ferritin levels would be useful in the differential diagnosis of hyperferritinemia and perhaps also in monitoring disease activity in HPS and ASD.

Paradoxical enhancement of oxidative cell injury by overexpression of heme oxygenase-1 in an anchorage-dependent cell ECV304

There has been increasing evidence suggesting the potent anti-inflammatory roles of heme oxygenase-1 (HO-1) in protecting renal tubular epithelial cells, vascular endothelial cells, and circulating monocytes. Based on these findings, novel therapeutic interventions have been proposed to control the expression of endothelial HO-1 levels to ameliorate various vascular diseases. We evaluated the effect of HO-1 gene transfer into an anchorage-dependent cell, ECV304. Effect of HO-1 production on the cell injury induced by hydrogen peroxide was evaluated after hemin stimulation and after HO-1 gene transfection. Morphological changes and the induction of various anti-apoptotic proteins were examined at the same time. Levels of HO-1 expression were variable in different clones of HO-1-transfected ECV304 cells. Among these, the clones with moderate levels of HO-1 expression were significantly more resistant to oxidative stress. In contrast, those with the highest levels of HO-1 exhibited paradoxically enhanced susceptibility to oxidative injury. Interestingly, the cell survival after oxidative stress was in parallel with the levels of Bcl-2 expression and of fibronectin receptor, alpha5 integrin. It is suggested from these results, that excessive HO-1 not only leads to enhanced cell injury, but also prolongs the repair process of the injured endothelial tissue. However, HO-1 reduces the oxidative cell injury and protects the endothelial cells, if its expression is appropriately controlled.

Heme oxygenase expression in human central nervous system disorders

In the normal mammalian CNS, heme oxygenase-2 (HO-2) is constitutively, abundantly, and fairly ubiquitously expressed, whereas heme oxygenase-1 (HO-1) mRNA and protein are confined to small populations of scattered neurons and neuroglia. Unlike ho-2, the ho-1 gene in neural (and many systemic) tissues is exquisitely sensitive to upregulation by a host of pro-oxidant and other noxious stimuli. In Alzheimer disease, HO-1 immunoreactivity is significantly augmented in neurons and astrocytes of the hippocampus and cerebral cortex relative to age-matched, nondemented controls and colocalizes to senile plaques, neurofibrillary tangles, and corpora amylacea. In Parkinson disease, HO-1 decorates Lewy bodies of affected dopaminergic neurons and is highly overexpressed in astrocytes residing within the substantia nigra. The ho-1 gene is also upregulated in glial cells within multiple sclerosis plaques; in the vicinity of human cerebral infarcts, hemorrhages, and contusions; and in various other degenerative and nondegenerative human CNS disorders. The products of the heme oxygenase reaction, free ferrous iron, carbon monoxide, and biliverdin/bilirubin, are all biologically active molecules that may profoundly influence tissue redox homeostasis under a wide range of pathophysiological conditions. Evidence adduced from whole animal and in vitro studies indicates that enhanced HO-1 activity may either ameliorate or exacerbate neural injury, effects likely contingent upon the specific model employed, the duration and intensity of HO-1 induction, and the chemistry of the local redox microenvironment. HO-1 hyperactivity also promotes mitochondrial sequestration of nontransferrin iron in oxidatively challenged astroglia and may thereby contribute to the pathological iron deposition and bioenergetic failure amply documented in aging and degenerating human neural tissues.

HO-1 induction restores c-AMP-dependent lung epithelial fluid transport following severe hemorrhage in rats

Inhibition of cAMP-dependent stimulation of the vectorial fluid transport across the lung epithelium following hemorrhagic shock is mediated by NO released within the airspaces of the lung. We tested here the hypothesis that prior induction of HO-1 would attenuate the release of NO in the airspaces, thus preventing the inhibition of the c-AMP stimulation of alveolar fluid clearance (ALC) in rats. Indeed, HO-1 induction restored the cAMP-mediated up-regulation of ALC after hemorrhage by decreasing NO released within the airspaces of the lung. In vitro studies demonstrated that HO-1 induction significantly reduced the iNOS-mediated release of NO by alveolar macrophages stimulated with endotoxin for 24 h. This effect is explained in part by a HO-1-dependent attenuation of the LPS-mediated nuclear translocation of NF-kappaB. In addition, HO-1 induction also significantly reduced the iNOS-mediated release of NO by MH-S cells that were stimulated with interferon-gamma by decreasing the phosphorylation of STAT 1, another transcription factor important for the activation of the iNOS promoter. In contrast, HO-1 induction did not affect the production of NO by rat alveolar epithelial type II cells that were stimulated with cytomix (a mixture of TNF-alpha, IL-1beta, and IFN-gamma) for 24 h. In summary, these results provide the first in vivo evidence that the induction of HO-1 in the lung restores a normal fluid transport capacity of the alveolar epithelium following hemorrhagic shock by inhibiting the iNOS-mediated release of NO by alveolar macrophages.

Adenoviral transfer of the heme oxygenase-1 gene protects striatal astrocytes from heme-mediated oxidative injury

Heme oxygenase-1 (HO-1) is induced in the CNS after hemorrhage, and may have an effect on injury to surrounding tissue. Hemin, the preferred substrate of HO, is a neurotoxin that is present in intracranial hematomas. In a prior study, we observed that HO inhibitors increased the vulnerability of cultured cortical astrocytes to heme-mediated oxidative injury. To investigate the effect of HO more specifically, we used an adenoviral vector encoding the human HO-1 gene to specifically increase HO-1 expression. Incubation with 100 MOI of the HO-1 adenovirus (Adv-HHO-1) for 24 h increased both HO-1 protein and HO activity; a control adenovirus lacking the HO-1 gene had no effect. Using a DNA probe that was specific for human HO-1, 80.5 +/- 7.2% of astrocytes were observed to be infected by in situ hybridization. The cell death produced by 30-60 microM hemin was significantly reduced by pretreatment with 100 MOI Adv-HHO-1, as assessed by LDH release, propidium iodide exclusion, and MTT reduction assay. The threefold increase in cell protein oxidation produced by hemin was also attenuated in cultures pretreated with Adv-HHO-1. These results support the hypothesis that HO-1 protects astrocytes from heme-mediated oxidative injury. Specifically increasing astrocytic HO-1 by gene transfer may have a beneficial effect on hemorrhagic CNS injury.

Complex role of heme oxygenase-1 in angiogenesis

Angiogenesis occurring during reparative or pathological processes is driven by various inflammatory mediators that influence the synthesis of growth factors. It has been recognized recently that reactive oxygen species (ROS) and nitric oxide (NO) are important modulators of the synthesis and activity of vascular endothelial growth factor (VEGF), a major angiogenic molecule. Moreover, heme oxygenase-1 (HO-1), a ubiquitous stress-inducible enzyme that is induced by ROS and NO, was recently discovered to be involved in angiogenesis. Genetic overexpression of HO-1 enhanced VEGF synthesis and augmented formation of vascular capillaries, improving the blood flow in ischemic tissues. In addition, by-products of HO-1 exert numerous effects that can also influence angiogenesis in both positive and negative ways. Therefore, the antiinflammatory effects of HO-1 can attenuate the excess formation of blood vessels in inflammatory angiogenesis. In this review, the recent data on the role of HO-1 in angiogenesis are critically discussed. It is suggested that further studies using potent and specific augmentation of HO-1 gene expression by viral vectors, as well as targeted, specific inhibition of HO-1 expression, are required to elucidate fully the complex role of this enzymatic pathway in angiogenesis.

Hypoxia-regulated therapeutic gene as a preemptive treatment strategy against ischemia/reperfusion tissue injury

Ischemia and reperfusion represent major mechanisms of tissue injury and organ failure. The timing of administration and the duration of action limit current treatment approaches using pharmacological agents. In this study, we have successfully developed a preemptive strategy for tissue protection using an adenoassociated vector system containing erythropoietin hypoxia response elements for ischemia-regulated expression of the therapeutic gene human heme-oxygenase-1 (hHO-1). We demonstrate that a single administration of this vector several weeks in advance of ischemia/reperfusion injury to multiple tissues such as heart, liver, and skeletal muscle yields rapid and timely induction of hHO-1 during ischemia that resulted in dramatic reduction in tissue damage. In addition, overexpression of therapeutic transgene prevented long-term pathological tissue remodeling and normalized tissue function. Application of this regulatable system using an endogenous physiological stimulus for expression of a therapeutic gene may be a feasible strategy for protecting tissues at risk of ischemia/reperfusion injury.

Effects of oxidant-induced injury on heme oxygenase and glutathione in cultured aortic endothelial cells from atherosclerosis-susceptible and -resistant Japanese quail

Recent studies on cultured aortic endothelial cells (AECs) from atherosclerosis-susceptible (SUS) and -resistant (RES) strains of Japanese quail suggest that differences in atherosclerosis susceptibility between RES and SUS may be due to differences in endothelial heme oxygenase (HO) and antioxidant components. We have now investigated the effects of oxidant-induced injury on HO and glutathione (GSH) in AECs from SUS and RES quail. We report that cultured AECs from SUS and RES birds differ in their response to oxidative stress. AECs from the SUS strain cells are more susceptible than those from the RES strain to oxidative stress induced by tert-butylhydroperoxide, as judged by lower HO activity, HO-1 expression, ferritin and GSH levels. Aortic endothelial cells from SUS birds also showed higher levels of catalytic iron, TBARS production and LDH release compared with RES cells, indicating that SUS AECs are more susceptible to oxidative stress than cells from the resistant strain. Furthermore, independently of genetic status, AECs from old birds have higher TBARS and lower levels of HSP70 induction than AECs from younger birds, suggesting that aging is associated with a decreased ability of AECs to respond to oxidative stress, and this may be relevant to the permissive effect of aging on the process of atherogenesis. Our results indicate that genetic factors and endogenous antioxidant systems in the blood vessel wall may be important in determining the susceptibility of vascular cells to oxidative stress and atherosclerotic plaque formation.

Differential induction of heme oxygenase and other stress proteins in cultured hippocampal astrocytes and neurons by inorganic lead

We examined the effects of exposure to inorganic lead (Pb2+) on the induction of stress proteins in cultured hippocampal neurons and astrocytes, with particular emphasis on the induction of heme oxygenase-1 (HO-1). In radiolabeled neuronal cultures, Pb2+ exposure had no significant effect on the synthesis of any protein at any concentration (up to 250 microM) or duration of exposure (up to 4 days). In radiolabeled astrocyte cultures, however, Pb2+ exposure (100 nM to 100 microM; 1-4 days) increased synthesis of proteins with approximate molecular weights of 23, 32, 45, 57, 72, and 90 kDa. Immunoblot experiments showed that Pb2+ exposure (100 nM to 10 microM, 1-14 days) induces HO-1 synthesis in astrocytes, but not in neurons; this is probably the 32-kDa protein. The other heme oxygenase isoform, HO-2, is present in both neurons and astrocytes, but is not inducible by Pb2+ at concentrations up to 100 microM. HO-1 can be induced by a variety of stimuli. We found that HO-1 induction in astrocytes is increased by combined exposure to Pb2+ and many other stresses, including heat, nitric oxide, H2O2, and superoxide. One of the stimuli that may induce HO-1 is oxidative stress. Lead exposure causes oxidative stress in many cell types, including astrocytes. Induction of HO-1 by Pb2+ is reduced by the hydroxyl radical scavengers dimethylthiourea (DMTU) and mannitol, but not by inhibitors of calmodulin, calmodulin-dependent protein kinases, protein kinase C, or extracellular signal-regulated kinases (ERK). Therefore, we conclude that oxidative stress is an important mechanism by which Pb2+ induces HO-1 synthesis in astrocytes.

Differential MnSOD and HO-1 expression in cerebral endothelial cells in response to sublethal oxidative stress

The two inducible enzymes, manganese superoxide dismutase (MnSOD) and heme-oxygenase-1 (HO-1) may participate in the cellular defense of brain endothelium against oxidative stress. The time-dependent expression of MnSOD and HO-1 mRNAs and proteins was investigated in vitro in rat cerebral endothelial cells (CEC) subjected to sublethal mild or moderate hydroxyl radical-induced oxidative stress. Mild oxidative stress induced increases in both MnSOD and HO-1 mRNA and protein expression. Moderate oxidative stress resulted in a significant reduction in HO-1 mRNA and protein expression, whereas MnSOD expression pattern was similar to that observed after mild oxidative stress. A profound protein loss of both MnSOD and HO-1 was detected 24 h after exposure of CEC to a moderate oxidative stress. The data indicate that cerebral endothelial cells respond by increasing the expression of antioxidant defense enzymes in a manner dependent on the oxidative stress intensity.

Heme oxygenase in experimental intracerebral hemorrhage: the benefit of tin-mesoporphyrin

The prognosis of intracerebral hemorrhage (ICH) is unfavorable. Beyond immediate mass effect and tissue destruction, ICHs cause additional neuronal loss in a "perifocal reactive zone." Heme in ICH induces heme oxygenase-1 (HO-1), and the action of this enzyme on heme yields ferrous iron, biliverdin, and carbon monoxide. Iron is ultimately converted to ferritin and hemosiderin. Free iron is tissue-toxic, and inhibition of HO-1 should provide protection against additional damage. Experimental ICHs were made in adult rabbits by the stereotaxic injection of autologous blood, and the induction of HO-1 and increase in ferritin were followed by confocal immunofluorescence microscopy. Heme diffused rapidly through perivascular spaces, and HO-1 reaction product first occurred in perivascular cells and microglia. At this stage, HO-1 and ferritin showed extensive colocalization. As ICH resolution progressed, HO-1 immunoreactivity faded while ferritin and hemosiderin continued to accumulate. This process was accompanied by a gradient of destruction of neuronal cell bodies and dendrites in the perifocal reactive zone. In an effort to inhibit HO-1, repeated intravenous injections of tin-mesoporphyrin IX (SnMP) were given to ICH-bearing rabbits. The ICH disrupted the blood-brain barrier sufficiently to allow SnMP to enter the brain in pharmacological amounts, and the metalloporphyrin provided significant protection against neuronal loss.

Heme-oxygenase-1 expression correlates with severity of acute cellular rejection in lung transplantation

BACKGROUND

Heme-oxygenase-1 (HO-1) has been shown to play an important role in oxidative stress, and recent studies indicate that it is a graft survival protein in cardiac and liver transplant models. Our laboratory previously found HO-1 to be increased in human lung allografts with acute cellular rejection (ACR) and in active obliterative bronchiolitis. To better understand the role of HO-1 in ACR we studied the relationship between HO-1 expression and ACR in a rodent model of lung transplantation.

STUDY DESIGN

Orthotopic left lung transplantation was performed from Lewis (donor) to Sprague-Dawley (recipient) rats, and ACR (Grade A0 to A4) was evaluated at days 3, 5, and 7. HO-1 expression was assessed by immunohistochemistry and Western analysis, and compared with the degree of ACR. Myeloperoxidase staining was evaluated as an indirect measure of oxidant stress. Donors and recipients were also treated with either an inhibitor of HO activity, tin protoporphyrin or an inducer, cobalt protoporphyrin, and the severity of ACR was compared with that in untreated allografts.

RESULTS

HO-1 expression was elevated in transplanted versus native lungs or isografts, and the degree of elevation was closely correlated with ACR grade (p < 0.001). Similarly, myeloperoxidase expression increased with time and severity of ACR. Administration of the metalloporphyrins, tin protoporphyrin and cobalt protoporphyrin, produced no significant difference in the degree of ACR, but did alter the severity of ischemia-reperfusion injury.

CONCLUSIONS

Similar to what occurs in human lung transplantation, HO-1 expression is increased in a rodent lung transplant model of ACR and correlates with the severity of rejection. Altering its expression does not appear to affect the degree of ACR.

Lung heme oxygenase-1 is elevated in acute respiratory distress syndrome

OBJECTIVE

We aimed to quantify concentrations of inducible heme oxygenase (HO)-1 in the lungs of patients with acute respiratory distress syndrome (ARDS) and to investigate its role as a source of ferrous iron and as a signaling agent for iron regulation. Control of such processes by heme oxygenase has implications for the onset, progression, and resolution of ARDS.

DESIGN

Retrospective analysis of archived samples.

SETTING

Adult intensive care unit of a postgraduate teaching hospital.

PATIENTS

Patients admitted to the adult intensive care unit who fulfilled the American-European Consensus Conference criteria for ARDS.

INTERVENTIONS

Biochemical and immunohistochemical studies using bronchoalveolar lavage fluid or lung tissue were performed in patients with established ARDS and in those undergoing lung resection (controls).

MEASUREMENTS AND MAIN RESULTS

Concentrations of heme oxygenase protein were significantly elevated in lung tissue (193.7 +/- 13.27 vs. 81.0 +/- 16.0%, p < .01) and in bronchoalveolar lavage fluid (2.4 x 10(5) vs. 1.4 x 10(5) densitometric units, p = .047) taken from patients with ARDS compared with controls. Concentrations of heme oxygenase protein in bronchoalveolar lavage fluid from patients with ARDS correlated positively and significantly with changes in the concentrations of ferritin (r = .697, p = .02) and the iron saturation of transferrin (r = .8, p = .014) but correlated negatively and significantly with concentrations of bleomycin-detectable (redox-active) iron (r = -.73, p = .031). Significantly elevated (p < .05) concentrations of heme oxygenase staining in cell types expressing this protein were detected in patients with ARDS, compared with concentrations in the same cells taken from controls undergoing lung resection.

CONCLUSIONS

Heme oxygenase protein is elevated in the lungs of patients with ARDS and may contribute to the changes in iron mobilization, signaling, and regulation seen in this condition.

Reduction of circulating redox-active iron by apotransferrin protects against renal ischemia-reperfusion injury

BACKGROUND

Warm ischemia-reperfusion (I/R) injury plays an important role in posttransplant organ failure. In particular, organs from marginal donors suffer I/R injury. Although iron has been implicated in the pathophysiology of renal I/R injury, the mechanism of iron-mediated injury remains to be established. The authors therefore investigated the role of circulating redox-active iron in an experimental model for renal I/R injury.

METHODS

Male Swiss mice were subjected to unilateral renal ischemia for 45 min, followed by contralateral nephrectomy and reperfusion. To investigate the role of circulating iron, mice were treated with apotransferrin, an endogenous iron-binding protein, or iron-saturated apotransferrin (holotransferrin).

RESULTS

Renal ischemia induced a significant increase in circulating redox-active iron levels during reperfusion. Apotransferrin, in contrast to holotransferrin, reduced the amount of circulating redox-active iron and abrogated renal superoxide formation. Apotransferrin treatment did not affect I/R-induced renal apoptosis, whereas holotransferrin aggravated apoptotic cell death. Apotransferrin, in contrast to holotransferrin, inhibited the influx of neutrophils. Both apo- and holotransferrin reduced I/R-induced complement deposition, indicating that the effects of transferrin are differentially mediated by its iron and protein moiety. Finally, apotransferrin, in contrast to holotransferrin, dose-dependently inhibited the loss of renal function induced by ischemia.

CONCLUSIONS

Redox-active iron is released into the circulation in the course of renal I/R. Reducing the amount of circulating redox-active iron by treatment with apotransferrin protects against renal I/R injury, inhibiting oxidative stress, inflammation, and loss of function. Apotransferrin could be used in the treatment of acute renal failure, as seen after transplantation of ischemically damaged organs.

Attenuation of bleomycin induced pulmonary fibrosis in mice using the heme oxygenase inhibitor Zn-deuteroporphyrin IX-2,4-bisethylene glycol

BACKGROUND

Pulmonary fibrosis is associated with a poor prognosis. The pathogenesis of fibrotic lung disorders remains unclear, but the extent of tissue damage due to the persistent presence of oxidants or proteases is believed to be important. The heme degrading enzyme heme oxygenase (HO) has been found to be expressed in experimental fibrosis, and generation of free iron and carbon monoxide (CO) by HO has been implicated in oxidant induced lung damage. A study was undertaken to examine the effects of the HO inhibitor Zn-deuteroporphyrin-IX-2,4-bisethylene glycol (Zndtp) on the development of pulmonary fibrosis in the bleomycin model of lung injury and repair.

METHODS

Zndtp (10 micro mol/kg) was administered subcutaneously twice daily to mice 1 week following the intratracheal instillation of 0.025 U bleomycin. Animals were killed 10 or 21 days after bleomycin instillation and indices of lung damage and fibrosis were evaluated.

RESULTS

Bleomycin treatment induced pulmonary cytotoxicity, increased levels of active transforming growth factor beta (TGF-beta), enhanced lung collagen accumulation, and decreased glutathione content. Zndtp administration significantly attenuated these indices.

CONCLUSIONS

Administration of Zndtp in the bleomycin model resulted in appreciable alveolar cytoprotection and amelioration of pulmonary fibrosis. This molecule and its analogues may warrant further consideration in the treatment of acute lung injury and fibrotic lung disorders.

The story so far: Molecular regulation of the heme oxygenase-1 gene in renal injury

Heme oxygenases (HOs) catalyze the rate-limiting step in heme degradation, resulting in the formation of iron, carbon monoxide, and biliverdin, the latter of which is subsequently converted to bilirubin by biliverdin reductase. Recent attention has focused on the biological effects of product(s) of this enzymatic reaction, which have important antioxidant, anti-inflammatory, and cytoprotective functions. Two major isoforms of the HO enzyme have been described: an inducible isoform, HO-1, and a constitutively expressed isoform, HO-2. A third isoform, HO-3, closely related to HO-2, has also been described. Several stimuli implicated in the pathogenesis of renal injury, such as heme, nitric oxide, growth factors, angiotensin II, cytokines, and nephrotoxins, induce HO-1. Induction of HO-1 occurs as an adaptive and beneficial response to these stimuli, as demonstrated by studies in renal and non-renal disease states. This review will focus on the molecular regulation of the HO-1 gene in renal injury and will highlight the interspecies differences, predominantly between the rodent and human HO-1 genes.

Heme Oxygenase-1: Transducer of Pathological Brain Iron Sequestration under Oxidative Stress

Mechanisms responsible for the pathological deposition of redox-active brain iron in human neurological disorders remain incompletely understood. Heme oxygenase-1 (HO-1) is a 32-kDa stress protein that degrades heme to biliverdin, free iron, and carbon monoxide. In this chapter, we review evidence that (1) HO-1 is overexpressed in CNS tissues affected by Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), and other degenerative and nondegenerative CNS diseases; (2) the pro-oxidant effects of dopamine, hydrogen peroxide, beta-amyloid, and proinflammatory cytokines stimulate HO-1 expression in some of these conditions; and (3) upregulation of HO-1 in astrocytes exacerbates intracellular oxidative stress and promotes sequestration of nontransferrin-derived iron by the mitochondrial compartment. A model is presented implicating glial HO-1 induction as a "final common pathway" leading to pathological iron sequestration and mitochondrial insufficiency in a host of human CNS disorders.

Protease inhibitors modulate apoptosis in mesangial cells derived from a mouse model of HIVAN11See Editorial by Foster, p. 1105

BACKGROUND

Oxidative stress as well as opiate addiction has been shown to play a role in the development of complications associated with human immunodeficiency virus (HIV) infection.

METHODS

We studied the occurrence of apoptosis in mesangial cells derived from control (NTrMC) mice and mice transgenic for HIV-1 genes (HTrMC) under basal and morphine-stimulated states (MSS). We evaluated the effect of free radical scavengers and antioxidants on HTrMC apoptosis and production of superoxide under basal and MSS. In addition, we examined the effect of protease inhibitors (PI) on apoptosis of NTrMCs/HTrMCs as well as morphine-induced superoxide dismutase (SOD) and nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH) oxidase activation.

RESULTS

HTrMCs showed greater apoptosis when compared with NTrMCs. Morphine triggered (P < 0.001) apoptosis of both NTrMCs and HTrMCs. Both antioxidants and free radical scavengers inhibited apoptosis of NTrMCs and HTrMCs under both basal and MSS. Morphine stimulated the production of superoxide by NTrMCs as well as by HTrMCs. Nevertheless, HTrMCs produced a greater (P < 0.001) amount of superoxide when compared with NTrMCs both under basal and MSS. PIs such as saquinavir and Indinavir inhibited HTrMC apoptosis in a dose-dependent manner. Saquinavir also protected HTrMCs against the proapoptotic effect of morphine. Moreover, saquinavir inhibited the production of superoxide by HTrMCs under both basal and MSS. Saquinavir also attenuated the morphine-induced expression of SOD and NADPH oxidase (Gp91phox) by HTrMCs. Interestingly, hemin exacerbated morphine-triggered HTrMC apoptosis.

CONCLUSION

Oxidative stress seems to play a role in the accelerated rate of HTrMC apoptosis both under basal and MSS. Saquinavir may be inhibiting HTrMC apoptosis by mitigating oxidative stress.

Heme: a determinant of life and death in renal tubular epithelial cells

Heme oxygenase-1 (HO-1) and p21 influence cell fate, and genetic HO-1 overexpression upregulates p21 and confers resistance to apoptosis. The present study examined the effects of heme, a metabolite incriminated in renal injury, on sensitivity to apoptosis and cell growth in conjunction with cellular expression of HO-1 and p21. Immortalized rat proximal tubular epithelial cells (IRPTCs) were exposed to hemin (10 microM) in serum-deplete media (0.1% FBS) and in standard cell culture media (5.0% FBS). In the presence of 0.1% FBS media, hemin induced p21 through an HO-dependent, p53-independent mechanism; certain products of HO activity (iron and carbon monoxide), but not others (ferritin, apoferritin, bilirubin), recapitulated these inductive effects on p21 expression. Along with this inductive effect on HO-1 and p21, hemin worsened apoptosis, the latter exacerbated by the inhibition of HO activity and loss of p21 expression. In IRPTCs maintained in 5% FBS, hemin induced HO-dependent p21 expression, provoked cell cycle arrest, and inhibited cell growth without inducing apoptosis; this inhibitory effect of hemin on cell growth was blocked by the concomitant inhibition of HO activity and loss of p21 expression. We conclude that hemin is a potent HO-dependent inducer of p21 and that hemin increases the sensitivity to apoptosis in serum-deplete conditions and decreases cell growth in serum-replete conditions; inhibiting HO activity and concomitantly ablating p21 expression exacerbate apoptosis and reverse the growth-inhibitory actions of hemin. We suggest that these effects of heme may influence the nature of, and recovery from, ischemic and nephrotoxic insults to the kidney.

Protective effect of SnCl2 on K2Cr2O7-induced nephrotoxicity in rats: the indispensability of HO-1 preinduction and lack of association with some antioxidant enzymes

We have shown that the ameliorative effect of stannous chloride (SnCl2) pretreatment on potassium dichromate (K2Cr2O7)-induced renal damage 24 h after K2Cr2O7 injection was associated with the induction of heme oxygenase-1 (HO-1). In this work we evaluated: (a) if the protective effect of SnCl2 (given 12 h before K2Cr2O7) is associated with changes in the renal activity of HO-1, superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), and catalase (CAT) 24 and 48 h after K2Cr2O7 injection, and (b) if HO-1 induction is indispensable before K2Cr2O7 injection. It was found that the protective effect of SnCl2 on renal function was observed both at 24 and 48 h reaching its maximum at 24 h when HO-1 expression was higher. Cu,Zn-SOD, Mn-SOD, and GR activities remained unchanged whereas GPx and CAT activities decreased at 48 h in K2Cr2O7-treated rats. The activity of Cu,Zn-SOD, Mn-SOD, GPx, CAT, and GR was unchanged in the SnCl2-treated rats. To fulfill the objective (b) groups of rats treated with K2Cr2O7 and SnCl2 (given at the same time or 12 h after K2Cr2O7) were studied 24 h after K2Cr2O7-injection. The simultaneous injections of SnCl2 and K2Cr2O7 had no protective effect whereas the injection of SnCl2 12 h after K2Cr2O7 exacerbated renal damage. In conclusion, the protective effect of SnCl2 on K2Cr2O7-induced nephrotoxicity is associated with HO-1 induction and not with other antioxidant enzymes (Cu,Zn-SOD, Mn-SOD, GPx, GR, and CAT) and SnCl2 has a preventive and not a therapeutic effect on renal damage induced by K2Cr2O7.

Heme oxygenase-2 knockout neurons are less vulnerable to hemoglobin toxicity

When cortical neurons are exposed to hemoglobin, they undergo oxidative stress that ultimately results in iron-dependent cell death. Heme oxygenase (HO)-2 is constitutively expressed in neurons and catalyzes heme breakdown. Its role in the cellular response to hemoglobin is unclear. We tested the hypothesis that HO-2 attenuates hemoglobin neurotoxicity by comparing reactive oxygen species (ROS) formation and cell death in wild-type and HO-2 knockout cortical cultures. Consistent with prior observations, hemoglobin increased ROS generation, detected by fluorescence intensity after dihydrorhodamine 123 or dichlorofluorescin-diacetate loading, in wild-type neurons. This fluorescence was significantly attenuated in cultures prepared from HO-2 knockout mice, and cell death as determined by propidium iodide staining was decreased. In other experiments, hemoglobin exposure was continued for 19 h; cell death as quantified by LDH release was decreased in knockout cultures, and was further diminished by treatment with the HO inhibitor tin protoporphyrin IX. In contrast, HO-2 knockout neurons were more vulnerable than wild-type neurons to inorganic iron. HO-1, ferritin, and superoxide dismutase expression in HO-2 -/- cultures did not differ significantly from that observed in HO-2 +/+ cultures; cellular glutathione levels were slightly higher in knockout cultures. These results suggest that heme breakdown by heme oxygenase accelerates the oxidative neurotoxicity of hemoglobin, and may contribute to neuronal injury after CNS hemorrhage.

Interaction between heme oxygenase-1 and -2 proteins

The three isoforms of heme oxygenase (HO), the rate-limiting enzyme in heme degradation, are the products of different genes that show marked differences in regulation and expression. Why is there redundancy in the heme degradation pathway, and why are there differences in tissue expression of HO isoenzymes are unanswered questions? An interaction between HO-1 and HO-2 is suspected by the co-localization of these enzymes in the lung and regions of the brain. Using multiple models and assays, we demonstrated an interaction between HO-1 and HO-2 at amino acids 0-45 of HO-2 and amino acids 58-80 of HO-1. The latter corresponds to a highly conserved, hydrophilic, and exposed region of the protein. Furthermore, the observed activity of the HO-1.HO-2 complex was lower than that expected from the sum of HO-1- and HO-2-derived activities, suggesting that this interaction serves to limit HO enzymatic activity. We speculate that this HO-1.HO-2 protein interaction may promote non-enzymatic functions of HO.

Different faces of the heme-heme oxygenase system in inflammation

The heme-heme oxygenase system has recently been recognized to possess important regulatory properties. It is tightly involved in both physiological as well as pathophysiological processes, such as cytoprotection, apoptosis, and inflammation. Heme functions as a double-edged sword. In moderate quantities and bound to protein, it forms an essential element for various biological processes, but when unleashed in large amounts, it can become toxic by mediating oxidative stress and inflammation. The effect of this free heme on the vascular system is determined by extracellular factors, such as hemoglobin/heme-binding proteins, haptoglobin, albumin, and hemopexin, and intracellular factors, including heme oxygenases and ferritin. Heme oxygenase (HO) enzyme activity results in the degradation of heme and the production of iron, carbon monoxide, and biliverdin. All these heme-degradation products are potentially toxic, but may also provide strong cytoprotection, depending on the generated amounts and the microenvironment. Pre-induction of HO activity has been demonstrated to ameliorate inflammation and mediate potent resistance to oxidative injury. A better understanding of the complex heme-heme

Characteristics of CD59 up-regulation induced in porcine endothelial cells by alphaGal ligation and its association with protection from complement

BACKGROUND

Activation of endothelial cells may result in proinflammatory and procoagulant changes, or in changes that protect the endothelial cells (EC) from injurious insults. Stimulation of porcine EC with human anti-porcine antibodies, or lectins from Bandeiraea simplicifolia that bind terminal Galalpha(1-3)Gal (abbreviated alphaGal), can induce EC protection from cytotoxicity by human complement. These EC also exhibit up-regulation of CD59 protein and mRNA expression. Porcine CD59 has been reported to protect porcine cells from human complement. Therefore we investigated the specificity requirements and other characteristics of the induced CD59 up-regulation, as well as the role of up-regulated CD59 in lectin-induced protection of EC from human complement.

METHODS

Aortic EC were incubated in vitro with alphaGal-binding lectins B. simplicifolia lectin I isolectin B4 (IB4) and B. simplicifolia lectin I (BS-I) and CD59 expression was assessed by flow cytometry and enzyme linked immunosorbent assay (ELISA). Binding requirement was studied using disaccharides containing either alphagalactosyl or betagalactosyl moieties to inhibit CD59 up-regulation. Protection from complement killing was assessed after incubation of EC with human serum as a source of anti-porcine antibodies and complement. The role of CD59 in lectin-induced protection was studied in the presence of an anti-pig CD59 antibody and after removal of CD59 using phosphatidylinositol (PI)-specific phospholipase C (PI-PLC).

RESULTS

We found that induction of CD59 up-regulation required specific binding of the lectin to terminal alphaGal and was not induced either by soluble factors that may be released from EC by stimulation with the lectin or by TNF-alpha, IFN-gamma, or IL-1alpha. Unstimulated or BS-I-treated EC showed little or no expression of decay accelerator factor (DAF). Removal of membrane-associated CD59 (and other proteins that are associated with the membrane through PI linkage) with PI-PLC from EC that had been exposed to lectin restored their complement sensitivity to various degrees, depending on the extent of lectin-induced protection. Cytotoxicity was completely restored in cells that exhibited partial protection induced with lectin at low doses or for a short period of time. However, EC that were fully resistant to complement did not regain sensitivity to complement after removal of CD59. Changes in CD59 expression did not modify the degree of C9 binding.

CONCLUSIONS

Induction of CD59 expression required specific binding of the lectin to terminal alphaGal and was not induced by soluble factors that may be released from EC by lectin stimulation. Increased CD59 expression may contribute to this form of protection from complement; however, mechanisms other than CD59 up-regulation appear to be essential for the development of full protection.

Heme oxygenase-1 in SJL mice with experimental allergic encephalomyelitis

The expression of heme oxygenase-1 (HO-1) is increased in the CNS of mice and rats with experimental allergic encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). To investigate the role of HO-1 in EAE, a putative inhibitor [tin-protoporphyrin IX (Sn-PP IX)] of HO-1 was administered to SJL mice during active disease. Sn-PP IX (200 micromol/kg) attenuated clinical scores, weight loss, and some signs of pathology in comparison to vehicle treatment. Glutathione levels were greater in treated EAE mice than in those receiving vehicle, indicating lower oxidative stress in the former group. These data suggest that inhibition of HO-1 attenuated disease and suppressed free radical production. In the SJL model of EAE, extravasated blood is present in the CNS, and iron released by HO-1 from this heme source may not be adequately sequestered by ferritin, allowing for iron-mediated tissue damage. Thus, HO-1 may act to amplify the disease process in this model.

Gestational pattern of heme oxygenase expression in the rat

Fetal growth is influenced by many intrinsic and extrinsic factors. Our objective was to determine the pattern of heme oxygenase (HO) expression in the pregnant rat and to study its association with fetal growth and growth factors. Uterine tissues were obtained from nonpregnant and from time-mated rats at 7, 13, 16, 19, and 21 d of pregnancy. Placental tissue was obtained on d 13, 16, 19 and 21 of pregnancy. Tissues were evaluated for HO activity, HO-1, HO-2, leptin and vascular endothelial growth factor protein, and HO-1 and HO-2 mRNA. HO activity in both the uterus and placenta peaked on d 21 of pregnancy. In the uterus, HO-1 and HO-2 protein and total mRNA levels peaked on d 16 of pregnancy, whereas, in the placenta, HO-1 and HO-2 protein levels peaked on d 19. Additionally, placental HO-1 mRNA peaked on d 16, but placental HO-2 mRNA declined toward the end of pregnancy. Placental leptin and vascular endothelial growth factor protein levels followed a similar pattern to placental HO-1 and peaked on d 16. We conclude that there is a clear uterine and placental gestational pattern of HO expression in the rat. This pattern is comparable to that of vascular endothelial growth factor and leptin.

Heme oxygenase-1 in growth control and its clinical application to vascular disease

Heme oxygenase-1 (HO-1) catalyzes the degradation of heme to carbon monoxide (CO), iron, and biliverdin. Biliverdin is subsequently metabolized to bilirubin by the enzyme biliverdin reductase. Although interest in HO-1 originally centered on its heme-degrading function, recent findings indicate that HO-1 exerts other biologically important actions. Emerging evidence suggests that HO-1 plays a critical role in growth regulation. Deletion of the HO-1 gene or inhibition of HO-1 activity results in growth retardation and impaired fetal development, whereas HO-1 overexpression increases body size. Although the mechanisms responsible for the growth promoting properties of HO-1 are not well established, HO-1 can indirectly influence growth by regulating the synthesis of growth factors and by modulating the delivery of oxygen or nutrients to specific target tissues. In addition, HO-1 exerts important effects on critical determinants of tissue size, including cell proliferation, apoptosis, and hypertrophy. However, the actions of HO-1 are highly variable and may reflect a role for HO-1 in maintaining tissue homeostasis. Considerable evidence supports a crucial role for HO-1 in blocking the growth of vascular smooth muscle cells (SMCs). This antiproliferative effect of HO-1 is mediated primarily via the release of CO, which inhibits vascular SMC growth via multiple pathways. Pharmacologic or genetic approaches targeting HO-1 or CO to the blood vessel wall may represent a promising, novel therapeutic approach in treating vascular proliferative disorders.

Heme and iron metabolism: role in cerebral hemorrhage

Heme and iron metabolism are of considerable interest and importance in normal brain function as well as in neurodegeneration and neuropathologically following traumatic injury and hemorrhagic stroke. After a cerebral hemorrhage, large numbers of hemoglobin-containing red blood cells are released into the brain's parenchyma and/or subarachnoid space. After hemolysis and the subsequent release of heme from hemoglobin, several pathways are employed to transport and metabolize this heme and its iron moiety to protect the brain from potential oxidative stress. Required for these processes are various extracellular and intracellular transporters and storage proteins, the heme oxygenase isozymes and metabolic proteins with differing localizations in the various brain-cell types. In the past several years, additional new genes and proteins have been discovered that are involved in the transport and metabolism of heme and iron in brain and other tissues. These discoveries may provide new insights into neurodegenerative diseases like Alzheimer's, Parkinson's, and Friedrich's ataxia that are associated with accumulation of iron in specific brain regions or in specific organelles. The present review will examine the uptake and metabolism of heme and iron in the brain and will relate these processes to blood removal and to the potential mechanisms underlying brain injury following cerebral hemorrhage.

HO-1 induction attenuates renal damage and oxidative stress induced by K2Cr2O7

Heme oxygenase (HO) is the rate-limiting enzyme in the degradation of heme; its inducible isozyme HO-1 protects against some types of acute tissue injury. The expression and functional role of HO-1 in rats with renal injury induced by potassium dichromate (K(2)Cr(2)O(7)) was investigated in this work. Rats were studied 24 h after a single injection of K(2)Cr(2)O(7). To address the possible protective effect of HO-1 in this experimental model, this enzyme was induced by an injection of stannous chloride (SnCl(2)) 12 h before K(2)Cr(2)O(7) administration. The functional role of HO-1 in K(2)Cr(2)O(7) + SnCl(2)-treated animals was tested by inhibiting HO activity with an injection of zinc (II) protoporphyrin IX (ZnPP) 18 h before K(2)Cr(2)O(7). In K(2)Cr(2)O(7)-treated rats: (i) renal HO-1 content, measured by Western blot, increased 2.6-fold; and, (ii) renal nitrotyrosine and protein carbonyl content, markers of oxidative stress, increased 3.5- and 1.36-fold, respectively. Renal damage and oxidative stress were ameliorated and HO-1 content was increased in the K(2)Cr(2)O(7) + SnCl(2) group. The attenuation of renal injury and oxidative stress was lost by the inhibition of HO activity in K(2)Cr(2)O(7) + SnCl(2) + ZnPP-treated animals. Our data suggest that HO-1 overexpression induced by SnCl(2) is responsible for the attenuation of renal damage and oxidative stress induced by K(2)Cr(2)O(7).

Antioxidant effects of selenium in rat brain and the stimulating role of nitric oxide

OBJECTIVE

To evaluate the antioxidant effect of selenium on Na+, K(+)-ATPase in rat brain in the presence of nitric oxide.

METHODS

Male Wistar rats (70 g) were treated as follows: group 1 received 1 microg of i.p. sodium nitroprus-side per kg (SNP), group 2 received 5 microg sodium selenite during 20 days, group 3 received sodium selenite 5 microg + SNP 1 microg and the control group received vehicle 50 microl (0.9% NaCl), same period and route. At the end of treatment, animals were sacrificed and their brain dissected into cortex, hemispheres, cerebellum and brain stem in order to determine lipid peroxidation (TBARS), Na+, K+ ATPase and total ATPase in each section. Blood hemoglobin concentration (Hb) and prostate weight were also assessed.

RESULTS

A significant increase of Hb in blood and of proteins in cortex and hemisphere was detected, but TBARS values fell due to the effect of sodium selenite in all examined regions, except for cerebellum. ATPase activity declined in all groups and regions with and without NTP. We conclude that diet supplementary selenium to inhibit NO generation can be a useful treatment in chronic inflammatory diseases.

Deregulation of iron homeostasis and cold-preservation injury to rat liver stored in University of Wisconsin solution

Very little is known about iron metabolism and the mediators of iron metabolism in liver subjected to cold storage before transplantation. Therefore, in this study, we investigated the effect of cold storage on iron homeostasis in the rat liver. When livers were stored at 4 degrees C in University of Wisconsin solution for up to 6 and 24 hours, significant increases occurred in the labile iron pool, ferritin protein, and heme oxygenase activity. Significant decreases in heme content and iron regulatory protein 1 and 2 binding activities occurred by 24 hours. Liver injury indicated by significant increases in University of Wisconsin solution transaminase activity and liver lipid hydroperoxide levels occurred by 6 and 24 hours. Taken together, these results suggest that during pretransplantation cold storage of the liver, an aberrant iron homeostasis develops that contributes to preservation injury, and predisposes the liver to reperfusion injury by iron-dependent reactive oxygen species/Fenton reaction.

Preconditioning with tin-protoporphyrin IX attenuates ischemia/reperfusion injury in the rat kidney

BACKGROUND

Heme oxygenase (HO)-1 is induced as a unique stress response and leads to a transient resistance against oxidative damage, including ischemia and reperfusion (I/R) injury. In the present study, we examined whether HO-1 induction may confer a protection against I/R injury in the rat kidney.

METHODS

Lewis rats were divided into four groups as follows: (1) vehicle group; (2) group treated with ferri-protoporphyrin IX (hemin), an inducer of HO; (3) group treated with low-dose tin-protoporphyrin IX (SnPP), an inhibitor of HO; and (4) group treated with high-dose SnPP. Renal warm ischemia for 60 minutes was performed 24 hours after each treatment.

RESULTS

At 24 hours after treatment, hemin induced a significant increase in renal HO activity, but failed to induce HO-1 protein synthesis. Although both low- and high-dose SnPP reduced HO activity, a marked HO-1 expression was observed only in the high-dose SnPP-treated kidney. Hemin exacerbated the renal function after reperfusion, while high-dose SnPP significantly suppressed the intercellular adhesion molecule (ICAM)-1 expression, the infiltration of ED-1-positive macrophages and the expression of activated caspase-3, which resulted in attenuation of apoptotic cell death and ameliorated I/R injury.

CONCLUSION

These results suggest that prior induction of HO-1 protein by high-dose SnPP may lead to anti-inflammatory and antiapoptotic effects on warm renal I/R injury independently of its enzyme activity, and that HO enzyme activation may not always act as an antioxidant, especially under I/R-induced oxidative stress.

Antiapoptotic effect of haem oxygenase-1 induced by nitric oxide in experimental solid tumour

Induction of haem oxygenase-1 (HO-1) may provide an important protective effect for cells against oxidative stress. Here, we investigated the mechanism of cytoprotection of HO-1 in solid tumour with a focus on the antiapoptotic activity of HO-1. Treatment of rat hepatoma AH136B cells with the HO inhibitor zinc protoporphyrin IX (ZnPP IX) or tin protoporphyrin IX resulted in extensive apoptotic changes of tumour cells both in vivo and in vitro. Caspase-3 activity of the ZnPP IX-treated hepatoma cells increased significantly. Moreover, ZnPP IX-induced apoptosis was completely inhibited by simultaneous incubation with a specific caspase-3 inhibitor and was partially abrogated by bilirubin, a reaction product of HO. In vivo ZnPP IX treatment did not affect nitric oxide (NO) production and tumour blood flow. Western blot analyses showed that HO-1 expression in AH136B cells was strongly upregulated by NO donors, for example, S-nitroso-N-acetyl penicillamine and propylamine NONOate in vitro; conversely, it was remarkably reduced in vivo by pharmacological blockade of NOS. We conclude that HO-1 may function in antiapoptotic defense of the tumour, and thus it may have important protective and beneficial effects for tumour cells against oxidative stress induced by NO, which is produced in excess during solid tumour growth in vivo.

Comparison of the heme-free and -bound crystal structures of human heme oxygenase-1

Heme oxygenase (HO) catalyzes the degradation of heme to biliverdin. The crystal structure of human HO-1 in complex with heme reveals a novel helical structure with conserved glycines in the distal helix, providing flexibility to accommodate substrate binding and product release (Schuller, D. J., Wilks, A., Ortiz de Montellano, P. R., and Poulos, T. L. (1999) Nat. Struct. Biol. 6, 860-867). To structurally understand the HO catalytic pathway in more detail, we have determined the crystal structure of human apo-HO-1 at 2.1 A and a higher resolution structure of human HO-1 in complex with heme at 1.5 A. Although the 1.5-A heme.HO-1 model confirms our initial analysis based on the 2.08-A model, the higher resolution structure has revealed important new details such as a solvent H-bonded network in the active site that may be important for catalysis. Because of the absence of the heme, the distal and proximal helices that bracket the heme plane in the holo structure move farther apart in the apo structure, thus increasing the size of the active-site pocket. Nevertheless, the relative positioning and conformation of critical catalytic residues remain unchanged in the apo structure compared with the holo structure, but an important solvent H-bonded network is missing in the apoenzyme. It thus appears that the binding of heme and a tightening of the structure around the heme stabilize the solvent H-bonded network required for proper catalysis.

Ischemia-reperfusion-induced lung injury

Ischemia-reperfusion-induced lung injury is characterized by nonspecific alveolar damage, lung edema, and hypoxemia occurring within 72 hours after lung transplantation. The most severe form may lead to primary graft failure and remains a significant cause of morbidity and mortality after lung transplantation. Over the past decade, better understanding of the mechanisms of ischemia-reperfusion injury, improvements in the technique of lung preservation, and the development of a new preservation solution specifically for the lung have been associated with a reduction in the incidence of primary graft failure from approximately 30 to 15% or less. Several strategies have also been introduced into clinical practice for the prevention and treatment of ischemia-reperfusion-induced lung injury with various degrees of success. However, only three randomized, double-blinded, placebo-controlled trials on ischemia-reperfusion-induced lung injury have been reported in the literature. In the future, the development of new agents and their application in prospective clinical trials are to be expected to prevent the occurrence of this potentially devastating complication and to further improve the success of lung transplantation.

Heme oxygenase/carbon monoxide signaling pathways: regulation and functional significance

Carbon monoxide (CO), a gaseous second messenger, arises in biological systems during the oxidative catabolism of heme by the heme oxygenase (HO) enzymes. HO exists as constitutive (HO-2, HO-3) and inducible isoforms (HO-1), the latter which responds to regulation by multiple stress-stimuli. HO-1 confers protection in vitro and in vivo against oxidative cellular stress. Although the redox active compounds that are generated from HO activity (i.e. iron, biliverdin-IXα, and bilirubin-IXα) potentially modulate oxidative stress resistance, increasing evidence points to cytoprotective roles for CO. Though not reactive, CO regulates vascular processes such as vessel tone, smooth muscle proliferation, and platelet aggregation, and possibly functions as a neurotransmitter. The latter effects of CO depend on the activation of guanylate cyclase activity by direct binding to the heme moiety of the enzyme, stimulating the production of cyclic 3′:5′-guanosine monophosphate. CO potentially interacts with other intracellular hemoprotein targets, though little is known about the functional significance of such interactions. Recent progress indicates that CO exerts novel anti-inflammatory and anti-apoptotic effects dependent on the modulation of the p38 mitogen activated protein kinase (MAPK)-signaling pathway. By virtue of these effects, CO confers protection in oxidative lung injury models, and likely plays a role in HO-1 mediated tissue protection.