Carbon monoxide rescues ischemic lungs by interrupting MAPK-driven expression of early growth response 1 gene and its downstream target genes

Plasma biomarkers in carbon monoxide poisoning

OBJECTIVES

The severity of acute carbon monoxide (CO) poisoning is often based on non-specific clinical criteria because there are no reliable laboratory markers. We hypothesized that a pattern of plasma protein values might objectively discern CO poisoning severity. This was a pilot study to evaluate protein profiles in plasma samples collected from patients at the time of initial hospital evaluation. The goal was to assess whether any values differed from age- and sex-matched controls using a commercially available plasma screening package.

METHODS

Frozen samples from 63 suspected CO poisoning patients categorized based on clinical signs, symptoms, and blood carboxyhemoglobin level were analyzed along with 42 age- and sex-matched controls using Luminex-based technology to determine the concentration of 180 proteins.

RESULTS

Significant differences from control values were found for 99 proteins in at least one of five CO poisoning groups. A complex pattern of elevations in acute phase reactants and proteins associated with inflammatory responses including chemokines/cytokines and interleukins, growth factors, hormones, and an array of auto-antibodies was found. Fourteen protein values were significantly different from control in all CO groups, including patients with nominal carboxyhemoglobin elevations and relatively brief intervals of exposure.

CONCLUSIONS

The data demonstrate the complexity of CO pathophysiology and support a view that exposure causes acute inflammatory events in humans. This pilot study has insufficient power to discern reliable differences among patients who develop neurological sequelae but future trials are warranted to determine whether plasma profiles predict mortality and morbidity risks of CO poisoning.

Early growth response-1 worsens ventilator-induced lung injury by up-regulating prostanoid synthesis

RATIONALE

Ventilator-induced lung injury (VILI) is common and serious and may be mediated in part by prostanoids. We have demonstrated increased expression of the early growth response-1 (Egr1) gene by injurious ventilation, but whether-or how-such up-regulation contributes to injury is unknown.

OBJECTIVES

We sought to define the role of Egr1 in the pathogenesis of VILI.

METHODS

An in vivo murine model of VILI was used, and Egr1(+/+) (wild-type) and Egr1(-/-) mice were studied; the effects of prostaglandin E receptor subtype 1 (EP1) inhibition were assessed.

MEASUREMENTS AND MAIN RESULTS

Injurious ventilation caused lung injury in wild-type mice, but less so in Egr1(-/-) mice. The injury was associated with expression of EGR1 protein, which was localized to type II cells and macrophages and was concentrated in nuclear extracts. There was a concomitant increase in expression of phosphorylated p44/p42 mitogen-activated protein kinases. The prostaglandin E synthase (mPGES-1) gene has multiple EGR1 binding sites on its promoter, and induction of mPGES-1 mRNA (as well as the prostanoid product, PGE2) by injurious ventilation was highly dependent on the presence of the Egr1 gene. PGE2 mediates many lung effects via EP1 receptors, and EP1 blockade (with ONO-8713) lessened lung injury.

CONCLUSIONS

This is the first demonstration of a mechanism whereby expression of a novel gene (Egr1) can contribute to VILI via a prostanoid-mediated pathway.

Dissecting the factors involved in the locomotion mode of neuronal migration in the developing cerebral cortex

Neuronal migration is essential for proper cortical layer formation and brain function, because migration defects result in neurological disorders such as mental retardation and epilepsy. Neuronal migration is divided into several contiguous steps: early phase (multipolar mode), locomotion mode, and terminal translocation mode. The locomotion mode covers most of the migration route and thereby is the main contributor to cortical layer formation. However, analysis of the molecular mechanisms regulating this mode is difficult due to the secondary effects of defects at the early phase of migration. In this study, we established an ex vivo chemical inhibitor screening, allowing us to directly analyze the locomotion mode of migration. Roscovitine and PP2, inhibitors for Cdk5 and Src family kinases, respectively, suppressed the locomotion mode of migration. In line with this, a small percentage of Cdk5- or Src family kinase (Fyn)-knockdown cells exhibited locomoting morphology but retarded migration, although the majority of cells were stalled at the early phase of migration. We also showed that rottlerin, widely used as a specific inhibitor for protein kinase Cdelta (PKCdelta), suppressed the locomotion mode. Unexpectedly, however, the dominant-negative form as well as RNA interference for PKCdelta hardly affected the locomotion, whereas they may disturb terminal translocation. In addition, we found JNK to be a potential downstream target of rottlerin. Taken together, our novel chemical inhibitor screening provides evidence that Cdk5 and Src family kinases regulate the locomotion mode of neuronal migration. It also uncovered roles for Fyn and PKCdelta in the early and final phases of migration, respectively.

Carbon monoxide blocks lipopolysaccharide-induced gene expression by interfering with proximal TLR4 to NF-kappaB signal transduction in human monocytes

Carbon monoxide (CO) is an endogenous messenger that suppresses inflammation, modulates apoptosis and promotes vascular remodeling. Here, microarrays were employed to globally characterize the CO (250 ppm) suppression of early (1 h) LPS-induced inflammation in human monocytic THP-1 cells. CO suppressed 79 of 101 immediate-early genes induced by LPS; 19% (15/79) were transcription factors and most others were cytokines, chemokines and immune response genes. The prototypic effects of CO on transcription and protein production occurred early but decreased rapidly. CO activated p38 MAPK, ERK1/2 and Akt and caused an early and transitory delay in LPS-induced JNK activation. However, selective inhibitors of these kinases failed to block CO suppression of LPS-induced IL-1β, an inflammation marker. Of CO-suppressed genes, 81% (64/79) were found to have promoters with putative NF-κB binding sites. CO was subsequently shown to block LPS-induced phosphorylation and degradation of IκBα in human monocytes, thereby inhibiting NF-κB signal transduction. CO broadly suppresses the initial inflammatory response of human monocytes to LPS by reshaping proximal events in TLR4 signal transduction such as stress kinase responses and early NF-κB activation. These rapid, but transient effects of CO may have therapeutic applications in acute pulmonary and vascular injury.

Role of alveolar epithelial early growth response-1 (Egr-1) in CD8+ T cell-mediated lung injury

Influenza infection of the distal airways results in severe lung injury, a considerable portion of which is immunopathologic and attributable to the host responses. We have used a mouse model to specifically investigate the role of antiviral CD8(+) T cells in this injury, and have found that the critical effector molecule is TNF-alpha expressed by the T cells upon antigen recognition. Interestingly, the immunopathology which ensues is characterized by significant accumulation of host inflammatory cells, recruited by chemokines expressed by the target alveolar epithelial cells. In this study we analyzed the mechanisms involved in the induction of epithelial chemokine expression triggered by antigen-specific CD8(+) T cell recognition, and demonstrate that the early growth response-1 (Egr-1) transcription factor is rapidly induced in epithelial cells, both in vitro and ex vivo, and that this is a critical regulator of a host of inflammatory chemokines. Genetic deficiency of Egr-1 significantly abrogates both the chemokine expression and the immunopathologic injury associated with T cell recognition, and it directly regulates transcriptional activity of a model CXC chemokine, MIP-2. We further demonstrate that Egr-1 induction is triggered by TNF-alpha-dependent ERK activation, and inhibition of this pathway ablates Egr-1 expression. These findings suggest that Egr-1 may represent an important target in mitigating the immunopathology of severe influenza infection.

Bench-to-bedside review: Carbon monoxide--from mitochondrial poisoning to therapeutic use

Carbon monoxide (CO) is generated during incomplete combustion of carbon-containing compounds and leads to acute and chronic toxicity in animals and humans depending on the concentration and exposure time. In addition to exogenous sources, CO is also produced endogenously by the activity of heme oxygenases (HOs) and the physiological significance of HO-derived CO has only recently emerged. CO exerts vasoactive, anti-proliferative, anti-oxidant, anti-inflammatory and anti-apoptotic effects and contributes substantially to the important role of the inducible isoform HO-1 as a mediator of tissue protection and host defense. Exogenous application of low doses of gaseous CO might provide a powerful tool to protect organs and tissues under various stress conditions. Experimental evidence strongly suggests a beneficial effect under pathophysiological conditions such as organ transplantation, ischemia/reperfusion, inflammation, sepsis, or shock states. The cellular and molecular mechanisms mediating CO effects are only partially characterized. So far, only a few studies in humans are available, which, however, do not support the promising results observed in experimental studies. The protective effects of exogenous CO may strongly depend on the pathological condition, the mode, time point and duration of application, the administered concentration, and on the target tissue and cell. Differences in bioavailability of endogenous CO production and exogenous CO supplementation might also provide an explanation for the lack of protective effects observed in some experimental and clinical studies. Further randomized, controlled clinical studies are needed to clarify whether exogenous application of CO may turn into a safe and effective preventive and therapeutic strategy to treat pathophysiological conditions associated with inflammatory or oxidative stress.

Therapeutic applications of the gaseous mediators carbon monoxide and hydrogen sulfide

BACKGROUND

Hydrogen sulfide (H(2)S) and carbon monoxide (CO) are endogenously produced gaseous autacoids that regulate a number of physiological processes, including the inflammatory response, cell death and proliferation, neural transmission and smooth muscle tone.

OBJECTIVE/METHODS

The current review aims to provide a comprehensive overview of all recent patent applications that address the potential therapeutic applications of CO and H(2)S.

RESULTS/CONCLUSION

Beyond the direct administration of CO and H(2)S, this review highlights the therapeutic applications of a variety of gas-releasing molecules that are being developed to deliver CO and H(2)S to diseased tissues at therapeutic doses. The term autacoid, which, in addition to its pharmacological use to describe a locally-acting hormone, literally translates from Greek as 'self-drug', seems to particularly well describe the current approach to capture the potential therapeutic use of these two gasotransmitters. In summary, we can conclude that there is a markedly growing interest in harnessing the tissue-protective actions of CO and H(2)S.

Heme oxygenase-1, a critical arbitrator of cell death pathways in lung injury and disease

Increases in cell death by programmed (i.e., apoptosis, autophagy) or nonprogrammed mechanisms (i.e., necrosis) occur during tissue injury and may contribute to the etiology of several pulmonary or vascular disease states. The low-molecular-weight stress protein heme oxygenase-1 (HO-1) confers cytoprotection against cell death in various models of lung and vascular injury by inhibiting apoptosis, inflammation, and cell proliferation. HO-1 serves a vital metabolic function as the rate-limiting step in the heme degradation pathway and in the maintenance of iron homeostasis. The transcriptional induction of HO-1 occurs in response to multiple forms of chemical and physical cellular stress. The cytoprotective functions of HO-1 may be attributed to heme turnover, as well as to beneficial properties of its enzymatic reaction products: biliverdin-IXalpha, iron, and carbon monoxide (CO). Recent studies have demonstrated that HO-1 or CO inhibits stress-induced extrinsic and intrinsic apoptotic pathways in vitro. A variety of signaling molecules have been implicated in the cytoprotection conferred by HO-1/CO, including autophagic proteins, p38 mitogen-activated protein kinase, signal transducer and activator of transcription proteins, nuclear factor-kappaB, phosphatidylinositol 3-kinase/Akt, and others. Enhanced HO-1 expression or the pharmacological application of HO end-products affords protection in preclinical models of tissue injury, including experimental and transplant-associated ischemia/reperfusion injury, promising potential future therapeutic applications.

Low-dose carbon monoxide inhibits progressive chronic allograft nephropathy and restores renal allograft function

Chronic allograft nephropathy (CAN) represents progressive deterioration of renal allograft function with fibroinflammatory changes. CAN, recently reclassified as interstitial fibrosis (IF) and tubular atrophy (TA) with no known specific etiology, is a major cause of late renal allograft loss and remains a significant deleterious factor of successful renal transplantation. Carbon monoxide (CO), an effector byproduct of heme oxygenase pathway, is known to have potent anti-inflammatory and antifibrotic functions. We hypothesized that inhaled CO would inhibit fibroinflammatory process of CAN and restore renal allograft function, even when the treatment was initiated after CAN was established. Lewis rat kidney grafts were orthotopically transplanted into binephrectomized allogenic Brown Norway rats under brief tacrolimus (0.5 mg/kg im, days 0-6). At day 60, CO (20 ppm) inhalation was initiated to recipients and continued until day 150 or animal death. Development of CAN was confirmed at day 60 with decreased creatinine clearance (CCr), significant proteinuria, and histopathological findings of TA, IF, and intimal arteritis. Air-treated control recipients continued to deteriorate with further declines of CCr and increases of urinary protein excretion and died with a median survival of 82 days. In contrast, progression of CAN was decelerated when recipients received CO on days 60-150, showing markedly improved graft histopathology, restored renal function, and improved recipient survival to a median of >150 days. CO significantly reduced intragraft mRNA levels for IFN-gamma and TNF-alpha at day 90. Expression of profibrotic TGF-beta/Smad was significantly suppressed with CO, together with downregulation of ERK-MAPK pathways. Continuous CO (20 ppm) treatment for days 0-30, days 30-60, or days 0-90, or daily 1-h CO (250 ppm) treatment for days 0-90, also showed efficacy in inhibiting CAN. The study demonstrates that CO is able to inhibit progression of fibroinflammatory process of CAN, restore renal allograft function, and improve survival even when the treatment is started after CAN is diagnosed.

Carbon monoxide modulates alpha-smooth muscle actin and small proline rich-1a expression in fibrosis

Carbon monoxide (CO) is a biologically active molecule produced in the body by the stress-inducible enzyme, heme oxygenase. We have previously shown that CO suppresses fibrosis in a murine bleomycin model. To investigate the mechanisms by which CO opposes fibrogenesis, we performed gene expression profiling of fibroblasts treated with transforming growth factor-beta(1) and CO. The most highly differentially expressed categories of genes included those related to muscular system development and the small proline-rich family of proteins. We confirmed in vitro, and in an in vivo bleomycin model of lung fibrosis, that CO suppresses alpha-smooth muscle actin expression and enhances small proline-rich protein-1a expression. We further show that these effects of CO depend upon signaling via the extracellular signal-regulated kinase pathway. Our results demonstrate novel transcriptional targets for CO and further elucidate the mechanism by which CO suppresses fibrosis.

Proinflammatory role of leukocyte-derived Egr-1 in the development of murine postoperative ileus

BACKGROUND & AIMS

Early growth response gene-1 (Egr-1) is an important inflammatory transcription factor. We hypothesize that leukocyte-derived Egr-1 plays a key inflammatory role in causing postoperative ileus.

METHODS

Wild-type, Egr-1 knockout, and chimera mice (constructed by irradiation followed by injection with Egr-1(+/+) or Egr-1(-/-) bone marrow) were subjected to surgical manipulation of the gastrointestinal tract to induce ileus. Reverse-transcription polymerase chain reaction, Western blot, and immunohistochemistry quantified and localized Egr-1. Lumenal transit of nonabsorbable fluorescein isothiocyanate-labeled dextran and in vitro organ bath techniques measured functional gastrointestinal motility. Inflammatory mediator expressions were measured by Griess reaction, enzyme-linked immunosorbent assay, and multiplex Luminex assay.

RESULTS

Intestinal manipulation rapidly and significantly induced Egr-1 messenger RNA and protein within the inflamed muscularis externa. Egr-1 was colocalized early to smooth muscle and enteric neurons and later in extravasated monocytes after surgery when postoperative ileus was functionally prominent. The functional severity of postoperative ileus was significantly ameliorated in mice deficient in Egr-1(-/-) and chimera wild-type mice transplanted with Egr-1(-/-) bone marrow, whereas knockout mice with Egr-1(+/+) bone marrow again displayed significant ileus. Motility was mechanistically associated in Egr-1(-/-) gene deficiency with a down-regulation in the release of nitric oxide, prostanoids, monocyte chemoattractant protein-1, macrophage inflammatory protein-1alpha, interleukin-6, interleukin-1, and granulocyte colony-stimulating factor, as well as a decrease in the recruitment of leukocytes into the manipulated muscle wall of the intestine compared with wild-type mice.

CONCLUSIONS

Leukocyte-derived Egr-1 plays an early critical inflammatory role in the initiation of the postoperative inflammatory response, which leads to a prolonged decreased in gastrointestinal motility after intestinal surgery.

Gastric pentadecapeptide BPC 157 as an effective therapy for muscle crush injury in the rat

PURPOSE

Stable gastric pentadecapeptide BPC 157 accelerates the healing of a transected Achilles tendon and a transected quadriceps muscle. It may also be of clinical relevance as a systemic and local peptide treatment for crush injury of a major muscle, such as gastrocnemius muscle complex. BPC 157 is effective without a carrier, and it is presently undergoing trials for inflammatory bowel disease, and no toxicity has so far been reported.

METHODS

In crushed rats (force delivered 0.727 Ns/cm2), BPC 157 was applied either intraperitoneally or locally, as a thin cream layer, immediately after injury (sacrifice at 2 h), and once a day for 14 days.

RESULTS

BPC 157 improved muscle healing, macroscopically (less hematoma and edema, no post-injury leg contracture), microscopically, functionally, and also based on enzyme activity (creatine kinase, lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase).

CONCLUSION

BPC 157, at all investigated intervals, given locally or intraperitoneally, accelerated post-injury muscle healing and also helped to restore the full function.

Carbon monoxide protects against ventilator-induced lung injury via PPAR-gamma and inhibition of Egr-1

RATIONALE

Ventilator-induced lung injury (VILI) leads to an unacceptably high mortality. In this regard, the antiinflammatory properties of inhaled carbon monoxide (CO) may provide a therapeutic option.

OBJECTIVES

This study explores the mechanisms of CO-dependent protection in a mouse model of VILI.

METHODS

Mice were ventilated (12 ml/kg, 1-8 h) with air in the absence or presence of CO (250 ppm). Airway pressures, blood pressure, and blood gases were monitored. Lung tissue was analyzed for inflammation, injury, and gene expression. Bronchoalveolar lavage fluid was analyzed for protein, cell and neutrophil counts, and cytokines.

MEASUREMENTS AND MAIN RESULTS

Mechanical ventilation caused significant lung injury reflected by increases in protein concentration, total cell and neutrophil counts in the bronchoalveolar lavage fluid, as well as the induction of heme oxygenase-1 and heat shock protein-70 in lung tissue. In contrast, CO application prevented lung injury during ventilation, inhibited stress-gene up-regulation, and decreased lung neutrophil infiltration. These effects were preceded by the inhibition of ventilation-induced cytokine and chemokine production. Furthermore, CO prevented the early ventilation-dependent up-regulation of early growth response-1 (Egr-1). Egr-1-deficient mice did not sustain lung injury after ventilation, relative to wild-type mice, suggesting that Egr-1 acts as a key proinflammatory regulator in VILI. Moreover, inhibition of peroxysome proliferator-activated receptor (PPAR)-gamma, an antiinflammatory nuclear regulator, by GW9662 abolished the protective effects of CO.

CONCLUSIONS

Mechanical ventilation causes profound lung injury and inflammatory responses. CO treatment conferred protection in this model dependent on PPAR-gamma and inhibition of Egr-1.

Does activation of the blood coagulation cascade have a role in malaria pathogenesis?

Plasmodium falciparum infection is often associated with a procoagulant state. Recent identification of tissue factor in the brain endothelium of patients who have died from cerebral malaria casts new light on our understanding of the coagulation disorder found in P. falciparum infection. It has also been revealed that parasitized red blood cells support the assembly of multimolecular coagulation complexes. Tissue factor expression by the endothelium and amplification of the coagulation cascade by parasitized red blood cells and/or activated platelets (particularly at sequestration sites) have crucial roles in mounting and sustaining a coagulation-inflammation cycle which contributes to organ dysfunction and coma in falciparum malaria.

Use of carbon monoxide as a therapeutic agent: promises and challenges

As a by-product of heme catabolism by the heme oxygenase system, carbon monoxide (CO) has been neglected for many years, and only recently has its role as an essential signaling molecule been appreciated. In the past decade, the use of CO gas in pre-clinical experimental models of disease has produced some remarkable data indicating that its therapeutic delivery to mammals could alleviate inflammatory processes and cardiovascular disorders. However, the inherent toxic nature of CO cannot be ignored, knowing that inhalation of uncontrolled amounts of this gas can ultimately lead to serious systemic complications and neuronal derangements. From a clinical perspective, a key question is whether a safe and therapeutically effective threshold of CO can be reached locally in organs and tissues without delivering potentially toxic amounts through the lung. The advent of CO-releasing molecules (CO-RMs), a group of compounds capable of carrying and liberating controlled quantities of CO in cellular systems, appears a plausible alternative in the attempt to overcome the limitations of CO gas. Although in its infancy and far from being used for clinical applications, the CO-RMs technology is supported by very encouraging biological results and reflected by the chemical versatility of these compounds and their endless potential to be transformed into CO-based pharmaceuticals.

HIF activation protects from acute kidney injury

The contribution of hypoxia to cisplatin-induced renal tubular injury is controversial. Because the hypoxia-inducible factor (HIF) pathway is a master regulator of adaptation to hypoxia, we measured the effects of cisplatin on HIF accumulation in vitro and in vivo, and tested whether hypoxic preconditioning is protective against cisplatin-induced injury. We found that cisplatin did not stabilize HIF-1alpha protein in vitro or in vivo under normoxic conditions. However, hypoxic preconditioning of cisplatin-treated proximal tubular cells in culture reduced apoptosis in an HIF-1alpha-dependent fashion and increased cell proliferation as measured by BrdU incorporation. In vivo, rats preconditioned with carbon monoxide before cisplatin administration had significantly better renal function than rats kept in normoxic conditions throughout. Moreover, the histomorphological extent of renal damage and tubular apoptosis was reduced by the preconditional treatment. Therefore, development of pharmacologic agents to induce renal HIF might provide a new approach to ameliorate cisplatin-induced nephrotoxicity.

Exhaled carbon monoxide as a biomarker of inflammatory lung disease

Carbon monoxide (CO) can be detected on the exhaled breath of humans. Exhaled CO (E-CO) originates from the inspiration of ambient CO and from endogenous metabolic sources that include heme metabolism catalyzed by heme oxygenase (HO) enzymes. HO occurs in both constitutive (HO-2) and inducible (HO-1) forms; the latter responds to pro-inflammatory or pro-oxidative stimuli. E-CO may arise in the airways from inducible HO-1 activity in the bronchial epithelium, alveolar macrophages and other lung cell types, as a consequence of local inflammation, and from the alveolae in equilibrium with carboxyhemoglobin (Hb-CO) in the pulmonary circulation. Elevations in Hb-CO in turn may reflect increases in ambient CO, as well as increased HO activity in systemic tissues. E-CO increases dramatically in active smokers and can be used to monitor the smoking habit. Elevations in E-CO have been observed in critically ill or post-surgical patients and those with various pulmonary diseases associated with inflammation, including chronic obstructive pulmonary disease (COPD), asthma, cystic fibrosis and infections. Despite improvements in the standardization and sensitivity of methods to detect E-CO, the predictive value of this measurement as a diagnostic tool remains unclear.

Protective functions of heme oxygenase-1 and carbon monoxide in the respiratory system

The respiratory system, including the lung and upper airways, succumbs to injury and disease through acute or chronic exposures to adverse environmental agents, in particular, those that promote increased oxidative or inflammatory processes. Cigarette smoke and other forms of particulate or gaseous air pollution, allergens, microorganisms infections, and changes in inspired oxygen may contribute to lung injury. Among the intrinsic defenses of the lung, the stress protein heme oxygenase-1 constitutes an inducible defense mechanism that can protect the lung and its constituent cells against such insults. Heme oxygenases degrade heme to biliverdin-IXalpha, carbon monoxide, and iron, each with candidate roles in cytoprotection. At low concentrations, carbon monoxide can confer similar cyto and tissue-protective effects as endogenous heme oxygenase-1 expression, involving antioxidative, antiinflammatory, antiproliferative, and antiapoptotic effects. Lung protection by heme oxygenase-1 or its enzymatic reaction products has been demonstrated in vitro and in vivo in a number of pulmonary disease models, including acute lung injury, cigarette smoke-induced lung injury/chronic obstructive pulmonary disease, interstitial lung diseases, ischemia/reperfusion injury, and asthma/airway inflammation. This review summarizes recent findings on the functions of heme oxygenase-1 in the respiratory system, with an emphasis on possible roles in disease progression and therapies.

Heme oxygenase and carbon monoxide initiate homeostatic signaling

Carbon monoxide (CO), a gaseous second messenger, arises in biological systems during the oxidative catabolism of heme by the heme oxygenase (HO) enzymes. Many biological functions of HO, such as regulation of vessel tone, smooth muscle cell proliferation, neurotransmission, and platelet aggregation, and anti-inflammatory and antiapoptotic effects have been attributed to its enzymatic product, CO. How can such diverse actions be achieved by a simple diatomic gas; can its protective effects be explained via regulation of a common signaling pathway? A number of the known signaling effects of CO depend on stimulation of soluble guanylate cyclase and/or activation of mitogen-activated protein kinases. The consequences of this activation remain unknown but appear to differ depending on cell type and circumstances. The majority of studies reporting a protective role of CO focus on pathways initiated by the pathological stimulus (e.g., lipopolysaccharide, hypoxia, balloon injury, tumor necrosis factor alpha, etc.) and its consequential modulation by CO. What has been less studied is the manner in which CO exposure alone modulates the molecular machinery of the cell so that a subsequent stress stimulus will elicit a homeostatic response as opposed to one that is chaotic and disordered. CO potentially interacts with other intracellular hemoprotein targets, although little is known about the functional significance of such interactions other then the known targets including mitochondrial oxidases, oxygen sensors, and nitric oxide synthases. The earliest response of a cell exposed to low concentrations of CO is clearly an increase in reactive oxygen species formation that we define as oxidative conditioning. This has important consequences for inflammation, proliferation, mitochondria biogenesis, and apoptosis. Within this review, we will highlight recent research on the molecular events underlying the physiologic effects of CO-which lead to cytoprotective conditioning.

Heme Oxygenase-1 Deficiency Accelerates Formation of Arterial Thrombosis Through Oxidative Damage to the Endothelium, Which Is Rescued by Inhaled Carbon Monoxide

Heme oxygenase (HO)-1 (encoded by Hmox1 ) catalyzes the oxidative degradation of heme to biliverdin and carbon monoxide. HO-1 is induced during inflammation and oxidative stress to protect tissues from oxidative damage. Because intravascular thrombosis forms at sites of tissue inflammation, we hypothesized that HO-1 protects against arterial thrombosis during oxidant stress. To investigate the direct function of HO-1 on thrombosis, we used photochemical-induced vascular injury in Hmox1 −/− and Hmox1 +/+ mice. Hmox1 −/− mice developed accelerated, occlusive arterial thrombus compared with Hmox1 +/+ mice, and we detected several mechanisms accounting for this antithrombotic effect. First, endothelial cells in Hmox1 −/− arteries were more susceptible to apoptosis and denudation, leading to platelet-rich microthrombi in the subendothelium. Second, tissue factor, von Willebrand Factor, and reactive oxygen species were significantly elevated in Hmox1 −/− mice, consistent with endothelial cell damage and loss. Third, following transplantation of Hmox1 −/− donor bone marrow into Hmox1 +/+ recipients and subsequent vascular injury, we observed rapid arterial thrombosis compared with Hmox1 +/+ mice receiving Hmox1 +/+ bone marrow. Fourth, inhaled carbon monoxide and biliverdin administration rescued the prothrombotic phenotype in Hmox1 −/− mice. Fifth, using a transcriptional analysis of arterial tissue, we found that HO-1 determined a transcriptional response to injury, with specific effects on cell cycle regulation, coagulation, thrombosis, and redox homeostasis. These data provide direct genetic evidence for a protective role of HO-1 against thrombosis and reactive oxygen species during vascular damage. Induction of HO-1 may be beneficial in the prevention of thrombosis associated with vascular oxidant stress and inflammation.

Hemin upregulates Egr-1 expression in vascular smooth muscle cells via reactive oxygen species ERK-1/2-Elk-1 and NF-kappaB

Reactive oxygen species (ROS) and oxidant stress are important mediators of cardiovascular pathologies including atherosclerosis. One source of ROS in the vasculature is free heme released from hemoglobin. Because Egr-1, the regulator of cell proliferation and apoptosis, is also induced by oxidant stress and is likewise implicated in atherosclerosis, we examined the regulation of Egr-1 by heme in vascular smooth muscle cells (SMCs). Hemin increased Egr-1 expression (mRNA, protein) within 30 minutes and ERK-1/2 phosphorylation and nuclear translocation within 5 minutes. Inhibiting hemin-induced ERK-1/2 activation by U0126 (MAPK-inhibitor), the antioxidant N-acetyl cysteine, the NADPH oxidase inhibitors apocynin and diphenyleneiodonium chloride, the superoxide scavenger tiron, or tricarbonyldichlororuthenium(II)-dimer (carbon-monoxide donor; CORM-2) blocked hemin-induced Egr-1 expression. Hemin activated Elk-1, SRF, and NF-kappaB and promoted their interaction with the Egr-1 promoter. Downregulating Elk-1 (via siRNA) or blocking NF-kappaB activation (via BAY-11-7082) abolished hemin induction of Egr-1. Finally, hemin-induced Egr-1 bound the promoters of tissue factor (TF), Plasminogen Activator Inhibitor (PAI)-1, and NGF-1A Binding (NAB)-2, upregulating their expression, and increased the biochemical activity of TF and PAI-1. Upregulation of Egr-1 and its target genes by heme-induced oxidant stress may be an important event in the initiation and progression of inflammatory vascular diseases such as atherosclerosis.

Carbon monoxide protects rat lung transplants from ischemia-reperfusion injury via a mechanism involving p38 MAPK pathway

Carbon monoxide (CO) provides protection against oxidative stress via anti-inflammatory and cytoprotective actions. In this study, we tested the hypothesis that a low concentration of exogenous (inhaled) CO would protect transplanted lung grafts from cold ischemia-reperfusion injury via a mechanism involving the mitogen-activated protein kinase (MAPK) signaling pathway. Lewis rats underwent orthotopic syngeneic or allogeneic left lung transplantation with 6 h of cold static preservation. Exposure of donors and recipients (1 h before and then continuously post-transplant) to 250 ppm CO resulted in significant improvement in gas exchange, reduced leukocyte sequestration, preservation of parenchymal and endothelial cell ultrastructure and reduced inflammation compared to animals exposed to air. The beneficial effects of CO were associated with p38 MAPK phosphorylation and were significantly prevented by treatment with a p38 MAPK inhibitor, suggesting that CO's efficacy is at least partially mediated by activation of p38 MAPK. Furthermore, CO markedly suppressed inflammatory events in the contralateral naïve lung. This study demonstrates that perioperative exposure of donors and recipients to CO at a low concentration can impart potent anti-inflammatory and cytoprotective effects in a clinically relevant model of lung transplantation and support further evaluation for potential clinical use.

Low-concentration carbon monoxide protects against lipopolysaccharide-induced rat small intestine injury

AIM: To observe the effects of the inhalation or intraperitoneal infusion of a low concentration of carbon monoxide (CO) on lipopolysaccharide (LPS)-induced rat small intestine injury, and to identify the roles of the p38 mitogen-activated protein kinase (p38 MAPK) pathway in these effects.

METHODS: Sprague-Dawley rats with small intestine injury induced by a 5 mg/kg LPS intravenous injection or an equal volume of NS were divided into six groups: A, control group (inhalation of room air); B, CO group (inhalation of 2.5 × 10^-4V/V CO ); C, CO intraperitoneal infusion group (intraperitoneal infusion of 2.5 × 10^-4V/V CO); D, LPS group (inhalation of room air); E, LPS + CO group (inhalation of 2.5 × 10^-4V/V CO); and F, LPS + CO intraperitoneal infusion group (intraperitoneal infusion of 2.5 × 10^-4V/V CO). Rats were sacrificed by exsanguination and small intestinal tissues were homogenized for testing. The levels of platelet activator factor (PAF) and intercellular adhesion molecule-1 (ICAM-1) were determined by enzyme-linked immunosorbent assay. Maleic dialdehyde (MDA) content and myeloperoxidase (MPO) activity were determined by chemical methods. The extent of cell apoptosis was determined by flow cytometry. The expression level of the heme oxygenase-1 (HO-1) gene was analyzed by semi-quantitative reverse transcription-polymerase chain reaction and the level of phosphorylated p38 mitogen-activated protein kinase (MAPK) activity was determined by Western blot. Pathology was determined by light microscopy.

RESULTS: The levels of PAF, ICAM -1, MDA and MPO (P < 0.05), and the rates of apoptosis, were lower in groups E (0.87 ± 0.18 ng/g, 2.96 ± 0.39 ng/g, 1.74 ± 0.17 mmol/g, 35.34 ± 14.67 μkat/g, 30.56% ± 6.33%) and F (0.82 ± 0.16 ng/g, 2.69 ± 0.23 ng/g, 1.71 ± 0.24 mmol/g, 33.01 ± 12.84 μkat/g, 34.45% ± 5.77%) than in group D (1.15 ± 0.21 ng/g, 3.48 ± 0.36 ng/g, 2.75 ± 0.76 mmol/g, 68.01 ± 18.67 μkat/g, 41.52% ± 3.36%, P < 0.05). The levels of HO-1 mRNA and phosphorylated p38 MAPK were higher in groups E (6.29 ± 1.56, 14 219 ± 1724) and F (7.21 ± 1.78, 13 774 ± 1886) than in group D (3.97 ± 1.16, 10 227 ± 1312; P < 0.05). In contrast to group D rats, the small intestine injury in rats in groups E and F was ameliorated. There were no significant differences between groups E and F.

CONCLUSION: Low-concentration CO inhalation and intraperitoneal infusion exert similar protection against LPS-induced rat small intestine injury via anti-oxidant, anti-inflammatory and anti-apoptotic mechanisms, as well as through the up-regulation of HO-1 expression. This may involve the p38 MAPK pathway.

Early growth response 1 mediates the systemic and hepatic inflammatory response initiated by hemorrhagic shock

Hemorrhagic shock (HS) is a major cause of morbidity and mortality in trauma patients. The early growth response 1 (Egr-1) transcription factor is induced by a variety of cellular stresses, including hypoxia, and may function as a master switch to trigger the expression of numerous key inflammatory mediators. We hypothesized that HS would induce hepatic expression of Egr-1 and that Egr-1 upregulates the inflammatory response after HS. The Egr-1 mice and wild-type (WT) controls (n>or=5 for all groups) were subjected to HS alone or HS followed by resuscitation (HS/R). Other mice were subjected to a sham procedure which included general anesthesia and vessel cannulation but no shock (sham). After the HS, HS/R, or sham procedures, mice were euthanized for determination of serum concentrations of interleukin (IL) 6, IL-10, and alanine aminotransferase. Northern blot analysis was performed to evaluate Egr-1 messenger RNA (mRNA) expression. Liver whole cell lysates were evaluated for Egr-1 protein expression by Western blot analysis. Hepatic expression of IL-6, granulocyte colony-stimulating factor, and intracellular adhesion molecule 1 mRNA was determined by semiquantitative reverse transcriptase-polymerase chain reaction. The Egr-1 DNA binding was assessed using the electrophoretic mobility shift assay. Hemorrhagic shock results in a rapid and transient hepatic expression of Egr-1 mRNA in WT mice by 1 h, whereas protein and DNA binding activity was evident by 2.5 h. The Egr-1 mRNA expression diminished after 4 h of resuscitation, whereas Egr-1 protein expression and DNA binding activity persisted through resuscitation. The Egr-1 mice exhibited decreased levels of hepatic inflammatory mediators compared with WT controls with a decrease in hepatic mRNA levels of IL-6 by 42%, granulocyte colony-stimulating factor by 39%, and intracellular adhesion molecule 1 by 43%. Similarly, Egr-1 mice demonstrated a decreased systemic inflammatory response and hepatic injury after HS/R compared with their WT counterparts. Early growth response 1 is rapidly upregulated in the liver during and after resuscitation from HS. Our results showing a blunted inflammatory response in Egr-1 mice provides evidence that Egr-1 functions as a proximal signal transduction mechanism responding to shock by amplifying the systemic inflammatory response.

Early growth response gene-1 promotes airway allograft rejection

Chronic airway rejection, characterized by lymphocytic bronchitis, epithelial cell damage, and obliterative bronchiolitis (OB), limits long-term survival after lung transplantation. The transcription factor early growth response gene-1 (Egr-1) induces diverse inflammatory mediators, some involved in OB pathogenesis. An orthotopic mouse tracheal transplant model was used to determine whether Egr-1 promotes development of airway allograft rejection. Significantly higher Egr-1 mRNA levels were seen in allografts (3.2-fold increase vs. isografts, P = 0.012). Allografts revealed thickening of epithelial and subepithelial airway layers (51 +/- 4% luminal encroachment for allografts vs. 20 +/- 3% for isografts, P < 0.0001) marked by significant lymphocytic infiltration. Absence of the Egr-1 gene in donor (but not recipient) tissue resulted in significant reduction in luminal narrowing (34 +/- 4%, P = 0.0001) with corresponding diminution of T cell infiltration. Egr-1 null allografts exhibited a striking reduction in inducible nitric oxide synthase (iNOS) expression. Effector cytokines previously implicated in OB pathogenesis with known Egr-1 promoter motifs (IL-1beta and JE/monocyte chemoattractant protein-1) were reduced in Egr-1 null allografts. These data suggest a paradigm wherein local induction of Egr-1 in tracheal allografts drives expression of inflammatory mediators responsible for lymphocyte recruitment and tissue destruction characteristic of airway rejection.

Hypoxia-inducible factor 1alpha stabilization by carbon monoxide results in cytoprotective preconditioning

The most salient feature of carbon monoxide (CO)-mediated cytoprotection is the suppression of inflammation and cell death. One of the important cellular targets of CO is the macrophage (mphi). Many studies have shown that exposure of mphi to CO results in the generation of an antiinflammatory phenotype; however, these reports have ignored the effect of CO alone on the cell before stimulation. Most investigations have focused on the actions of CO in modulating the response to noxious stimuli. We demonstrate here that exposure of mphi to CO results in a significant and transient burst of reactive oxygen species (ROS) arising from the mitochondria (mitochondria-deficient mphi do not respond to CO to produce ROS). The ROS promote rapid activation and stabilization of the transcription factor hypoxia-inducible factor 1alpha (HIF-1alpha), which regulates expression of genes involved in inflammation, metabolism, and cell survival. The increase in HIF-1alpha expression induced by CO results in regulated expression of TGF-beta, a potent antiinflammatory cytokine. CO-induced HIF-1alpha and TGF-beta expression are necessary to prevent anoxia/reoxygenation-induced apoptosis in mphi. Furthermore, blockade of HIF-1alpha using RNA interference and HIF-1alpha-cre-lox mphi resulted in a loss of TGF-beta expression and CO-induced protection. A similar mechanism of CO-induced protection was operational in vivo to protect against lung ischemia-reperfusion injury. Taken together, we conclude that CO conditions the mphi via a HIF-1alpha and TGF-beta-dependent mechanism and we elucidate the earliest events in mphi signaling that lead to and preserve cellular homeostasis at the site of injury.

CO–metal interaction: vital signaling from a lethal gas

The past few years have witnessed intense research into the biological significance of carbon monoxide (CO) as an essential signaling mediator in cells and tissues. To transduce the signal properly, CO must react selectively with functional and structural proteins containing moieties that show preferred reactivity towards this gaseous molecule. This selectivity is exemplified by the interaction of CO with iron- and heme-dependent proteins, although systems containing other transition metals can potentially become a preferential target for CO. Notably, transition metal carbonyls, which carry and liberate CO, are also emerging as a pharmacological tool to mimic the bioactivity of endogenously generated CO. Thus, exploring how CO binding to metal complexes is translated into a cytoprotective function is a challenging task and might open up opportunities for therapeutic applications based on CO delivery.